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  • Articles  (64,029)
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  • 1995-1999  (39,407)
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  • 1
    Electronic Resource
    Electronic Resource
    Hospital Reimbursement Incentives: An Empirical Analysis (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: Reimbursement systems for health-care providers are very complex, like the production systems that they regulate. This complexity has led to some important misperceptions about the incentive consequences of major reimbursement reforms. One example is the prospective payment system (PPS), developed to provide “high-powered” incentives through fixed prices for hospital admissions for the US elderly. In fact, various features of the DRG system allow reimbursement to vary with actual treatment decisions during an admission, and so are not prospective. This paper develops a general method for measuring actual reimbursement incentives in complex regulated price systems. The method uses regression techniques with variance decompositions to quantify the effects of particular features of the payment system on prospective and retrospective cost sharing, as well as overall generosity of payments. I apply this method to microdata on 20 percent of Medicare hospital admissions in 1987 and 1990 to summarize the incentives created by PPS in practice, and how the incentives are evolving over time. I show that PPS involves limited and decreasing cost sharing with hospitals, most of which is not prospective. The reimbursement incentives vary substantially across diagnoses, demographic groups, and types of intensive treatments, possibly with important implications for hospital behavior and medical expenditure growth. The techniques developed here can be used to analyze a broad range of provider reimbursement mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00091.x
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  • 2
    Electronic Resource
    Electronic Resource
    Buyer Alliances and Managed Competition (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: In a health insurance market, a large employer or an organized “buyer alliance” is in a position to influence the design of plans offered to its members. We study how the sponsors of buyer alliances manage competition among insurance firms by focusing on their choices of the format of competition, the number of firms allowed to compete, and the quality of care offered by the firms. We find deviations from optimality in all three dimensions. Specifically, we find a tendency toward too many firms and too much quality, and a bias toward a format involving the prescreening of insurance plans by the sponsor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00175.x
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  • 3
    Electronic Resource
    Electronic Resource
    Firm Characteristics and the Speed of FDA Approval (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper empirically examines the effect of firm-specific characteristics on the length of time required by the Food and Drug Administration (FDA) to review and approve new-drug applications between 1990 and 1992. The approach treats regulatory decisions as endogenous and explains the variation in regulatory behavior as a function of differences that exist between firms and drugs. Results show that, controlling for drug-specific characteristics, regulators respond to firm-specific characteristics when evaluating new drug applications. For instance, firms that are less diversified and more R&D-inten-sive receive shorter review times for their new-drug applications than more diversified and less R&D-intensive firms. The reason is that most firm characteristics signal information to reviewers about either firm reputation or application quality. This information reduces reviewers' uncertainty about approving a dangerous or ineffective drug and leads to faster review times. The results suggest that regulators respond to the heterogeneities among firms in the pharmaceutical market in systematic ways.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00377.x
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  • 4
    Electronic Resource
    Electronic Resource
    Entry and Predation: British Shipping Cartels 1879–1929 (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: I examine the outcomes of cases of entry by merchant shipping lines into established markets around the turn of the century. These established markets are completely dominated by an incumbent cartel composed of several member shipping lines. The cartel makes the decision whether or not to begin a price war against the entrant; some entrants are formally admitted to the cartel without any conflict. I use characteristics of the entrant to predict whether or not the entrant will encounter a price war conditional on entering. I find that weaker entrants are fought, where “weaker” means having fewer financial resources, less experience, smaller size, or poor trade conditions. The empirical results provide most support for the long-purse theory of predation. Due to the small number of observations available, 47, I discuss qualitative evidence (such as predatory intent expressed in correspondence between cartel members) that supports the empirical results. The results are also found to be robust to misclassification of the dependent variable, which is a particular concern when dealing with historical data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00679.x
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  • 5
    Electronic Resource
    Electronic Resource
    Tender Offers, Proxy Contests, and Large-Shareholder Activism (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: The paper analyzes tender offers and proxy contests as alternative means of resolving corporate governance conflicts between dissidents and incumbent management. We show that when a dissident shareholder is sufficiently confident about the potential benefits from changing corporate policy, he will seek majority control by making a tender offer rather than initiating a proxy contest. When the dissident is relatively uninformed, however, he may opt for a proxy contest, thereby utilizing the information of other shareholders to implement the better policy. Consistent with empirical evidence, the model predicts that announcements of tender offers will tend to be associated with larger positive stockprice reactions than announcements of proxy contests. The model is easily extended to allow for promanagement bias in proxy voting by institutional investors. Empirical observations that have been viewed as evidence of such promanagement bias are shown to be quite consistent with the absence of such bias. Policy issues are discussed as well. An interesting result is that even policies targeted at reducing the costs of conducting proxy contests may have ambiguous social consequences, given the possibility of substitution between tender offers and proxy contests.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00787.x
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  • 6
    Electronic Resource
    Electronic Resource
    The Regulation of Predatory Firms (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This article investigates the issue ofpredation by a regulated firm. Since it has private information, a regulated firm obtains higher rents in case of successful predation: the fewer the competitors, the higher the marginal social value of the regulated firm's effort and the higher the informational rents. Both principals (the investor of a “target” firm and the regulator) have to provide some incentives to prevent predation: the investor has to reduce the sensitivity of refinancing to predation; the regulator has to lower the gain of successful predation. It is shown that there is a trade-off between the power of the regulatory incentive scheme and the regulated firm's incentives to prey. In addition, as deterring predation is costly, the investor and the regulator compete when offering contracts: each wants to free-ride on the other. Hence, predation may occur in equilibrium although it makes both principals worse off.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00849.x
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  • 7
    Electronic Resource
    Electronic Resource
    Limited Liability and Bonus Contracts (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper studies the nature of incentive contracts between a risk-neutral principal and a risk-neutral agent under the constraint that the agent's liability is limited. A necessary and sufficient condition is derived for the existence of a first-best contract under this constraint, and a bonus-based contract is shown to be the most efficient contractual form. Implications of bonus contracts are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00899.x
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  • 8
    Electronic Resource
    Electronic Resource
    The Interaction between a Most-Favored-Customer Clause and Price Dispersion: An Empirical Examination of the Medicaid Rebate Rules of 1990 (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper examines the effect of the MFC rules adopted by Medicaid on both price dispersion and price levels in the wholesale pharmaceutical market. Theory suggests that the regulations should reduce price dispersion and increase the average price for those products with a high initial level of price dispersion. Using data which can only measure some dimensions of price discrimination, I find that discrimination falls for products sold to hospitals, but not drugstores. Branded drugs facing generic competition have the most dispersion ex ante. Prices of these brands rise with dispersion at the implementation of the new rules. The last two results are consistent with Scott Morton (1997), where I look only at price changes due to the law. The results of this paper confirm that part of the mechanism of action for the price increase is the high level of price dispersion for some products combined with the MFC.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00151.x
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  • 9
    Electronic Resource
    Electronic Resource
    Division of Labor in Teams (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper examines the incentive effects of division of labor on worker effort, in the absence of the scale effects studied by Adam Smith. The game-theoretic model gives two results. (1) Suppose workers are identical and risk-neutral, and there is stochastic observation of group output by the firm offering compensations subject to some worker-participation constraint. Then the firm can arrive at the same first-best outcome with or without division of labor. However, if workers are risk-averse, division of labor can give the firm strictly greater profit. (2) A deepening division of labor magnifies this positive incentive effect; but if workers are heterogeneous, or if there are certain informational imperfections in the production process, this incentive advantage of division of labor could be impaired or even reversed. The first result may help explain the emergence of division of labor in the early stages of industrialization without relying on the Smithian advantages, which are also present in some labor deployment schemes without division of labor. The second result throws light on some recent anecdotal evidence of a shallowing division of labor in some areas of modern manufacturing. These factors affecting the efficiency of division of labor are then further discussed in the light of recent empirical findings on division of labor and team work, such as those in Katzenbach and Smith (1993).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00403.x
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  • 10
    Electronic Resource
    Electronic Resource
    Capacity Commitment versus Flexibility (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We show how technological flexibility choices and equilibrium configurations (both simultaneous and sequential duopoly) depend on six industry characteristics. Low market volatility combined with intermediate market size favors inflexible technologies; large values of either volatility or size favor flexible technologies; low or intermediate values of both favor the coexistence of flexible and inflexible technologies. The possibility of a flexibility trap exists in industries of low volatility and intermediate size. Entry prevention can sometimes be achieved by inflexible technologies or flexible technologies, depending on the industry characteristics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00347.x
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  • 11
    Electronic Resource
    Electronic Resource
    Nonlinear Supply Contracts, Exclusive Dealing, and Equilibrium Market Foreclosure (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We examine how the feasibility of both nonlinear pricing and exclusive dealing arrangements affect incentives for market foreclosure when two manufacturers contract with a retail monopolist. Surprisingly, we find that although market foreclosure equilibria exist, they are Pareto-dominated (from each manufacturer's perspective) by all nonforeclosure equilibria. If one believes that Pareto-dominated equilibria are unlikely to arise, then the difference between our results and those of Mathewson and Winter (1987), who do not allow for nonlinear pricing, suggests an ironic twist on the notion that quantity discounts and other kinds of nonlinear pricing can provide an additional way for a manufacturer to foreclose a rival. By providing a manufacturer with increased flexibility (beyond linear pricing) to extract a retailer's surplus, nonlinear pricing may instead have the effect of reducing the incidence of observed market foreclosure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00755.x
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  • 12
    Electronic Resource
    Electronic Resource
    Option Contracts and Vertical Foreclosure (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: A model of vertical integration is studied. Upstream firms sell differentiated inputs; downstream firms bundle them to make final products. Downstream products are sold as option contracts, which allow consumers to choose from a set of commodities at predetermined prices. The model is illustrated by examples in telecommunication and health markets. Equilibria of the integration game must result in upstream input foreclosure and downstream monopolization. Consumers may or may not benefit from integration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00725.x
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  • 13
    Electronic Resource
    Electronic Resource
    Regulation of Duopoly: Managed Competition vs Regulated Monopolies (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper discusses the regulation of oligopolistic differentiated-product industries. The regulator can control prices and impose quantity restrictions, but cannot control the quality choices of the firms. We inquire about the optimal choice of regulatory regime—whether and under what conditions managed competition or segmentation of the market between regulated monopolies achieves better results. In the spatial duopoly model analyzed here, unhindered competition generally results in an inefficient allocation. When the regulator knows the technologies, optimal managed competition results in distortions of the quality choice, but an optimal regulated-monopolies regime achieves the first best outcome. When the regulator is uncertain about the technologies, neither of these methods yields the first-best outcome. The regulated-monopolies regime still tends to produce better quality choices, but managed competition tends to be more effective at extracting rents from the firms. The overall comparison depends on some finer details of the environment.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00821.x
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  • 14
    Electronic Resource
    Electronic Resource
    Paying Customers to Switch (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper studies the business practice of offering discounts to new customers in markets with switching costs. In a two-period homogeneous-good duopoly model, it is shown that the equilibrium amount of discounts increases continuously in the expected switching costs of a typical consumer. In equilibrium, firms offer the same prices and discounts in a mature market even if they have different market shares, and the demands faced by these firms in a new market become more elastic. Firms are worse off engaging in the discriminatory pricing, while consumers need not necessarily benefit from it. There is costly equilibrium switching of consumers, which creates a dead-weight loss to the society.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00877.x
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  • 15
    Electronic Resource
    Electronic Resource
    Introduction (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00425.x
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  • 16
    Electronic Resource
    Electronic Resource
    The FCC Spectrum Auctions: An Early Assessment (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper analyzes six spectrum auctions conducted by the Federal Communications Commission from July 1994 to May 1996. These auctions were simultaneous multiple-round auctions in which collections of licenses were auctioned simultaneously. This auction form proved remarkably successful. Similar items sold for similar prices, and bidders successfully formed efficient aggregations of licenses. Bidding behavior differed substantially in the auctions. The extent of bidder competition and price uncertainty played an important role in determining behavior. Bidding credits and installment payments also played a major role in several of the auctions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00431.x
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  • 17
    Electronic Resource
    Electronic Resource
    Synergies in Wireless Telephony: Evidence from the Broadband PCS Auctions (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We examine bid data from the first two broadband PCS spectrum auctions for evidence of value synergies. First, we estimate a benchmark regression for the determinants of final auction prices. Then, we include variables reflecting the extent to which bidders ultimately won or already owned the adjacent wireless properties. Consistent with geographic synergies in an ascending-bid auction, prices were higher when the highest losing bidder had adjacent licenses. The footprints of winning bidders suggest that they were often successful in realizing these synergies.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00497.x
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  • 18
    Electronic Resource
    Electronic Resource
    Making More from Less: Strategic Demand Reduction in the FCC Spectrum Auctions (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: When multiple items are sold through the use of simultaneous ascending-bid auctions, bidders can find it in their mutual interests to reduce their aggregate demand for the items while prices are still low relative to the bidders' valuations. The FCC's first broadband PCS auction provides examples of how such mutual reductions might be arranged even when the bidders are not allowed to communicate with one another outside of the auction arena.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00529.x
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  • 19
    Electronic Resource
    Electronic Resource
    Up in the Air: GTE's Experience in the MTA Auction for Personal Communication Services Licenses (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: In late 1994, GTE, one of the largest telecommunications firms in the world, entered an auction for the rights to provide personal communications services (PCS) using the electromagnetic spectrum. The administering agency, the Federal Communications Commission, adopted a novel multiple-round format for the PCS auction. The format presented GTE with a complex bidding problem. This article describes how the GTE bidding team answered the following question: Given its budget and valuations and the information available about rival bidders, how should GTE bid to achieve the best attainable outcome?
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00549.x
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  • 20
    Electronic Resource
    Electronic Resource
    Laboratory Experimental Testbeds: Application to the PCS Auction (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: The paper reviews the uses of laboratory experimental economics methods in the background research and implementation of the Personal Communication Systems auctions held by the Federal Communications Commission. The applications began during the rule making process with the testing of broad rules that might be implemented. Data from experiments were systematically used. The methods were used again in the software development process where several important contributions were made. Finally, experiences gained from the study of experimental auction processes were used in the actual management of the first auctions and in interpreting auction performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00605.x
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  • 21
    Electronic Resource
    Electronic Resource
    Second-Price Auctions with Asymmetric Payoffs: An Experimental Investigation (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: A series of two-player, second-price common-value auctions are reported. In symmetric auctions, bidders suffer from a winner's curse. In asymmetric auctions in which one bidder has a private value advantage, the effect on bids and prices is proportional rather than explosive (the prediction of Nash equilibrium bidding theory). Although advantaged bidders are close to making best responses to disadvantaged bidders, the latter bid much more aggressively than in equilibrium, thereby earning negative average profits. Experienced bidders consistently bid closer to the Nash equilibrium than inexperienced bidders, although these adjustments towards equilibrium are small and at times uneven.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00573.x
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  • 22
    Electronic Resource
    Electronic Resource
    Experiments Testing Multiobject Allocation Mechanisms (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
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    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper reports the results of over 130 auctions conducted under controlled conditions to examine the robustness of several auction mechanisms to allocate multiple objects. The simultaneous discrete auction process used by the Federal Communications Commission to allocate Personal Communications licenses was contrasted with a sequential auction and a combinatorial auction over a variety of demand conditions. In test environments created to check only the minimum competency of the procedures, the simultaneous discrete auction process produces highly efficient allocations, approaching levels similar to those found with a continuous form of the auction, and it outperforms a sequential auction. However, in environments created to stress test the procedures, a combinatorial auction outperforms the simultaneous discrete auction.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00639.x
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  • 23
    Electronic Resource
    Electronic Resource
    The Firm as a Multicontract Organization (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: The firm is often considered as a nexus of contracts linking the management and its different stakeholders: claim-holders, workers, unions, customers, suppliers, and the state, among others. This paper surveys recent work in contract theory, the multiprincipal incentive theory, and the theory of side contracts, which provides some insights into the structure of those contracts and therefore into the structure of the firm. First, we discuss the incomplete contracting assumptions underlying these variations of the usual grand contract approach. Second, we explain how the theoretical lessons learned from this work—the distribution of contracting rights, the power of incentive schemes within organizations, and the design of communication channels—apply to the theory of the firm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00201.x
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  • 24
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    Electronic Resource
    Introduction (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00001.x
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  • 25
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    Electronic Resource
    Dynamic Equilibrium in the Hospital Industry (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We present a dynamic model of the hospital industry in which nonprofit and for-profit hospitals coexist and compete and are differentiated by their objective functions, investment technologies, and taxation rates. In our model, patients differ by income and type of insurance coverage, and choose admission to their preferred hospital, while hospitals choose investment, entry, exit, and pricing strategies. We estimate the parameters of the model with aggregate data and a GMM procedure. We then use the model to examine the effects of changes in the Medicare reimbursement system, universal health-care coverage, and taxation of nonprofits.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00045.x
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  • 26
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    Exclusionary Equilibria in Health-Care Markets (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We have demonstrated that when providers of health insurance are perceived to be differentiated by consumers, circumstances may arise under which they find it advantageous to restrict the set of health-care providers that they approve to their customers. Even if all health-care providers are equally qualified and efficient, payers may choose to contract with a selected subset of them in order to secure more favorable contract terms. Moreover, in a concentrated health-care market that consists of two health insurance companies (payers) and two health-care providers (hospitals), both payers may choose to contract with only one of the hospitals while excluding the other completely from the market. When consumers' valuation of an extended choice of providers is small in comparison with the extent of differentiation that exists between the payers, such an exclusionary outcome is the unique equilibrium of the game.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00005.x
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    Generic Entry and the Pricing of Pharmaceuticals (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: During the 1980s the share of prescriptions sold by retail pharmacies that was accounted for by generic products roughly doubled. The price response to generic entry of brand-name products has been a source of controversy. In this paper we estimate models of price responses to generic entry in the market for brand-name and generic drugs. We study a sample of 32 drugs that lost patent protection during the early to mid-1980s. Our results provide evidence that brand-name prices increase after generic entry and are accompanied by large decreases in the price of generic drugs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00075.x
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    Competition among Health Maintenance Organizations (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: We develop a model of competition among health maintenance organizations (HMOs) to analyze the effects of market power, scale economies, and asymmetric knowledge of health risk on market outcomes. We find that competition among HMOs may, but need not, ensure socially preferred outcomes. Market power or scale economies can sometimes admit socially preferred outcomes when they would otherwise not arise. Asymmetric knowledge of health risk may or may not be constraining. When it is constraining, a variety of patterns of incomplete health insurance can arise, along with excessive or insufficient treatment and preventive care for either high-risk or low-risk individuals.
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    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00129.x
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    Multiprincipal Agency Relationships as Implied by Product Market Competition (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper surveys recent work in contract theory that relates to the allocation of tasks among agents within an organization as well as to the effect of product market competition upon optimal contracting and agency costs.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00235.x
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    Contract Complexity, Incentives, and the Value of Delegation (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: In settings where the revelation principle applies, delegation arrangements are frequently inferior to centralized decision making, and at best achieve the same level of performance. This paper studies the value of delegation when organizations are constrained by a bound on the number of contingencies in any contract. For a principal-agent setting with asymmetric information, we compare centralized mechanisms where the principal retains sole responsibility for contracting and coordinating production, with delegation mechanisms where one agent (a manager) is delegated authority to contract with other agents and coordinate production. Relative to centralization, delegation entails a control loss, but allows decisions to be more sensitive to the manager's private information. We identify circumstances under which the flexibility gain outweighs the control loss, so that delegation emerges superior to centralized contracting.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00257.x
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    Integrated Strategy and International Trade Disputes: The Kodak-Fujifilm Case (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This paper examines the integration of market and nonmarket strategies in a setting involving market competition and international trade policy where governments serve as bargaining agents for firms. In the case modeled, the Eastman Kodak Company (Kodak) filed a Section 301 petition under US trade law against practices of Fuji Photo Film Company (Fujifilm) in the Japanese distribution system that Kodak alleges constitute trade barriers. The model has four components. The market model characterizes the competition between Fujifilm and Kodak, incorporating characteristics descriptive of the demand and market structure in Japan. Enforcement of an international trade agreement focusing on practices in a distribution system are problematic, so the second model characterizes the sustainability of concessions obtained through a trade agreement using a repeated game extension of the market model. The third model characterizes the bargaining between the US and Japanese governments using the preferences induced by the market model and the limits on sustainable concessions characterized in the second model. Using a common-agency framework, the fourth model represents the nonmarket competition between the two firms as they work to influence the bargaining positions of the governments. The result is a model in which market and nonmarket strategies are integrated in a formal theory of the resolution of trade disputes and the subsequent effects on market competition. The equilibrium characterized allows a comparative statics analysis of the synergies between market and nonmarket strategies.
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    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.00291.x
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    The Regulation of Predatory Firms (1997)
    Oxford, UK : Blackwell Publishing Ltd.
    Journal of economics & management strategy 6 (1997), S. 0 
    Details
    ISSN: 1530-9134
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Economics
    Notes: This article investigates the issue of predation by a regulated firm. Since it has private information, a regulated firm obtains higher rents in case of successful predation: the fewer the competitors, the higher the marginal social value of the regulated firm's effort and the higher the informational rents. Both principals (the investor of a “target” firm and the regulator) have to provide some incentives to prevent predation: the investor has to reduce the sensitivity of refinancing to predation; the regulator has to lower the gain of successful predation. It is shown that there is a trade-off between the power of the regulatory incentive scheme and the regulated firm's incentives to prey. In addition, as deterring predation is costly, the investor and the regulator compete when offering contracts: each wants to free-ride on the other. Hence, predation may occur in equilibrium although it makes both principals worse off.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1430-9134.1997.jems0697_425.x
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    Mechanical Damping Arising from Dislocation Motion in Sapphire and Ruby Crystals (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Internal friction was measured up to the melting point (i.e., Tm≈ 2050°C) in sapphire and two ruby single crystals (chromium content of 0.1 and 0.5 wt%), as a function of strain amplitude, temperature, and composition. The frequency range of the measurements was 6.7–17 Hz. Static (torsional creep) experiments also were performed up to very high temperatures, to provide further phenomenological insight about the mechanism of crystal deformation. Results of dynamic and static experiments were analyzed and discussed in terms of dislocation motion along the basal (0001) plane, perpendicular to which the torsion axes of the crystals were oriented. Particular emphasis was placed on isolating the role of chromium concentration, in regard to impeding dislocation motion and multiplication. An equivalent spring-dashpot model, which attempts to represent the damping results quantitatively, also has been given.
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    Tensile Creep of Alumina-Silicon Carbide “Nanocomposites” (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The tensile creep behavior of an (Al2O3-SiC) nanocomposite that contains 5 vol% of 0.15 μm SiC particles is examined in air under constant-load conditions. For a stress level of 100 MPa and in the temperature range of 1200°–1300°C, the SiC reduces the creep rate of Al2O3 by 2–3 orders of magnitude. In contrast to Al2O3, the nanocomposite exhibits no primary or secondary stages, with only tertiary creep being observed. Microstructural examination reveals extensive cavitation that is associated with SiC particles that are located at the Al2O3 grain boundaries. Failure of the nanocomposite occurs via growth of subcritical cracks that are nucleated preferentially at the gauge corners. A modified test procedure enables creep lifetimes to be estimated and compared with creep rupture data. Several possible roles of the SiC particles are considered, including (i) chemical alteration of the Al2O3 grain boundaries, (ii) retarded diffusion along the Al2O3-SiC interface, and (iii) inhibition of the accommodation process (either grain-boundary sliding or grain-boundary migration).
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03111.x
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    Microstructure Refinement of Sintered Alumina by a Two-Step Sintering Technique (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: For a few oxide ceramics, the use of an initial precoarsening step prior to densification (referred to as two-step sintering) has been observed to produce an improvement in the microstructural homogeneity during subsequent sintering. In the present work, the effect of a precoarsening step (50 h at 800°C) on the subsequent densification and microstructural evolution of high-quality alumina (Al2O3) powder compacts during constant-heating-rate sintering (4°C/min to 1450°C) was characterized in detail. The data were compared with those for similar compacts that were sintered conventionally (without the heat treatment step) and used to explore the mechanism of microstructural improvement during two-step sintering. After the precoarsening step, the average pore size was larger, but the distribution in pore sizes was narrower, than those for similar compacts that were sintered conventionally to 800°C. In subsequent sintering, the microstructure of the precoarsened compact evolved in a more homogeneous manner and, at the same density, the amount of closed porosity was lower for the compacts that were sintered by the two-step technique, in comparison to the conventional heating schedule. Furthermore, a measurably higher final density, a smaller average grain size, and a narrower distribution in grain sizes were achieved with the two-step technique. The microstructural refinement that was produced by the two-step sintering technique is explained in terms of a reduction in the effects of differential densification and the resulting delay of the pore channel pinch-off to higher density.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03117.x
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    Colloidal Processing of Silicon Nitride with Poly(acrylic acid): I, Adsorption and Electrostatic Interactions (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The role of poly(acrylic acid) (PAA) in the dispersion of silicon nitride suspensions was investigated experimentally. The effects of concentration, relative molecular mass, and suspension pH were evaluated. The ionization of PAA was characterized by potentiometric titration and indicated a pH-dependent conformational transition. The isoelectric point for silicon nitride decreased from pH 6.3 to pH 3 as the PAA concentration increased, roughly independent of relative molecular mass. A broadening of the stability region for silicon nitride was attributed to this effect. Redispersion in alkaline media, subsequent to destabilization by surface-charge neutralization, improved following preadsorption of PAA in acidic media. This effect was attributed to formation of a protective polymer adlayer on the surface, which prevented primary minimum aggregation; an electrosteric contribution also may be present. The influence of free polymer on the suspension properties also is discussed.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03122.x
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    Preparation of Crystallized Sr1−XCaXMoO4 Solid-Solution Films by an Electrochemical Method at Room Temperature and Their Luminescence (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A complete series of well-crystallized solid-solution Sr1–X-CaXMoO4 films has been prepared on molybdenum substrates in an electrolytic solution containing Sr2+ and Ca2+ ions by an electrochemical method at room temperature (25°C). The peak positions of excitation and emission of the Sr1–XCaXMoO4 solid-solution films were independent of the Ca content: 285 ± 2 nm for excitation and 536 ± 2 nm for emission at liquid-nitrogen temperature (−196°C).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03146.x
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    Electrical-Impulse-Induced Fracture of Zinc Oxide Varistor Ceramics (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: When varistors are subject to very short (˜1 μ s), high-current pulses, they occasionally fracture. We attribute the occurrence of fracture to stress waves, created by inertial forces in response to the rapid Joule heating, causing the propagation of preexisting microstructural flaws. The amplitude of the stress oscillation is shown to be proportional to the second derivative of temperature with respect to time which, in turn, is directly related to the rate of increase of power. An upper limit for the magnitude of the peak stress is derived in terms of material parameters, varistor geometry, and the maximum electrical power. From the magnitude of the peak stress, a critical defect size is estimated which will cause fracture under given pulse conditions. Conclusions for the design and testing of varistors are drawn.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03092.x
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    Thermal Conductivity of Packed Beds of Refractory Particles: Experimental Results (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Experimental data on thermal conductivity of packed beds composed from various refractory particles (corundum, silica, magnesia, baddeleyite, yttrium oxide, spinel) obtained in the temperature range 400-2000 K in various gases are presented. It is found that thermal conductivity of a bed composed from crushed refractory particles may change after the first and subsequent heatings. This occurs as a result of smoothing of particle surfaces and decreasing of contact heat barrier resistances between the granules. The influence of smoothing is most significant for beds composed from particles with sizes below 2 mm. In polydisperse beds, containing micrometer-size particles, sintering processes were found to occur at temperatures above 1600 K. This led to a sharp increase of the bed thermal conductivity. In regimes where sintering did not take place, decreasing of particle size resulted in a decrease of the effective thermal conductivity. This is attributed to the increased number of contacts between the particles and the scattering of thermal radiation.
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    Evidence for a Phase Transition of β-Gallium Oxide at Very Low Oxygen Pressures (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Depending on the operating temperature, gas sensors that are based on n-type-semiconductor, polycrystalline gallium oxide (Ga2O3) thin films are used to detect oxygen (at temperatures, T, of 850°C) or reducing gases (T 900°C). At high temperatures (T 900°C), beta-Ga2O3has an oxygen deficiency in the crystal lattice that is in dynamic equilibrium with the oxygen in the surrounding atmosphere. Variations in the conductivity of the sensor are caused by variations of the concentration of ionized oxygen vacancies. Therefore, a reduction in the proportion of oxygen or an increase in the concentration of reducing gases in the atmosphere in which the sensor is located leads to an increasing number of conducting electrons and, hence, an increasing conductivity. During a research project to investigate the long-term stability of thin beta-Ga2O3 films in a variety of strongly reducing atmospheres at T 〉 600°C, a previously unknown phenomenon has been observed when measurements on low oxygen partial pressures (pO210-10 Pa (10-15bar)) have been made. A sharp decrease in sensor conductivity, by several orders of magnitude, is observed each time when pO2 is reduced to a value of 〈10-15bar at temperatures in the range of ˜750°-1000°C. The reason for this may be a phase transition in the β-Ga2O3 layer. However, attempts to freeze the new state with subsequent identification by X-ray diffractometry have not succeeded in identifying the new phase.
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    Tensile Stress Rupture of SiCf/SiCmMinicomposites with Carbon and Boron Nitride Interphases at Elevated Temperatures in Air (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The stress-rupture properties of precracked minicomposites were determined in air at temperatures in the range of 700°-1200°C. The minicomposite systems consisted of a single tow of Nicalon or Hi-Nicalon fibers with carbon or boron nitride (BN) interphases and a chemical-vapor-infiltrated silicon carbide (CVI-SiC) matrix. The stress-rupture results were compared to single-fiber stress-rupture data and composite data in the literature. Severe embrittlement occurred for carbon interphase minicomposites. However, BN interphase minicomposites showed only mild degradation in the rupture properties. This was true even though the BN interphase reacted and vaporized because of water vapor in the atmosphere at intermediate temperatures (700°-950°C) and glass formation occurred at higher temperatures (950°-1200°C). The severe degradation in rupture properties that occurred for carbon interphase composites at intermediate temperatures was due to degradation of the Nicalon-fiber properties from the environment. The rupture properties of the BN-interphase minicomposites were controlled by the fiber rupture properties at temperatures of less than ˜900°C and greater than ~1100°C. In the range of ˜900°-1100°C, most fibers fused to the matrix because of a glass layer that formed between the fiber and matrix, resulting in fiber stress concentrations that led to the mild embrittlement of the BN-interphase minicomposites.
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    Glycothermal Reaction of Rare-Earth Acetate and Iron Acetylacetonate: Formation of Hexagonal ReFeO3 (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The reaction of a mixture of iron acetylacetonate and rare-earth (Tm-Lu) acetate in 1,4-butanediol at 300°C yielded a novel phase of ReFeO3 having a hexagonal crystal system (a0 = 6.06, c0= 11.74 A) together with small amounts of Fe3O4and/or the garnet phase. The particle size of the product distributed in a narrow range and selected area electron diffraction from a particle having apparent polycrystalline outlines suggested that each particle was actually a single crystal grown from one nucleus. On calcination, the hexagonal phase irreversibly transformed into the perovskite phase at around 980°C. The use of ethylene glycol in place of 1,4-butanediol of the present procedure afforded Fe3O4, while hydrothermal reaction of the same starting materials yielded a mixture of Fe2O3and an amorphous rare-earth phase.
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    Fabrication and Mechanical Properties of Continuously Graded MoSi2–ZrO2(2Y) Materials Using Wet-Molding (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Continuously graded MoSi2-ZrO2(2Y) materials with high density (97.5% of theoretical) have been fabricated by uniaxial wet-molding, followed by hot pressing (1000°C/1 h/30 MPa) and hot isostatic pressing (1400°C/2 h/196 MPa). Their composition profiles are greatly influenced by the viscosity of mixed solutions of glycerin and ethanol used as a dispersion medium; a linear compositional gradient from MoSi2/ZrO2(2Y) 70/30 to 20/80 mol% is obtained from the solution (50/50 vol%) with a viscosity of 20 mPa s. Vickers hardness (Hv) and fracture toughness (KIC) increase from 9.7 to 12.4 GPa and from 5.1 to 12.5 MPa m1/2, respectively, with increasing ZrO2(2Y) composition.
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    Computer Simulations of Diffraction Effects due to Stacking Faults in β-SiC: I, Simulation Results (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: X-ray diffraction (XRD) patterns from nominally β-SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β-SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1-D Ising model with a Boltzmann-type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.
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    Atomic Structure of a 36.8 (210) Tilt Grain Boundary in TiO2 (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An understanding of the atomic structure at internal interfaces is of crucial importance for the electronic and structural properties of most advanced materials. Here, we present a detailed study of the atomic structure at a [001] tilt grain boundary of σ5(210) in Tio2 (rutile). Z-contrast imaging is used to obtain a 2-D atomic map of the cation positions at the interface. Details of the charge state of cations and atomic structure around anion sites are then provided using electron energy loss spectroscopy. In particular, the spectroscopic data for oxygen is interpreted using multiple scattering theory to give 3-D structural information. These combined techniques allow a unique grain boundary structure to be defined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02857.x
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    Strain Tolerant Porous Silicon Nitride (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An approach to material strain tolerance, which basically makes it possible to lower the elastic modulus while retaining strength, was experimentally confirmed using as an example a porous silicon nitride composed of oriented anisotropic grains and pores. The porous structure consisting of tightly tangled rodlike grains and anisotropic pores was obtained by using β-Si3N4 whiskers. This material exhibited a low Youngs modulus while retaining a relatively high fracture stress, even though it contained 14.4% porosity. Consequently, the strain to failure of silicon nitride was appreciably increased.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02856.x
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    High-Temperature Bridging in a Vitreous Bonded Alumina (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The load supported by crack wake bridges was studied in glassy alumina at 1240°C using short double cantilever beam specimens with a rear notch wedge. Direct observation of fracture surfaces revealed the sizes and shapes of the high-temperature bridges. The bridged area was stochastic in nature but there was a clear trend toward decreased area bridged with increasing crack opening displacement consistent with existing models. Fracture surface observations on specimens without a rear notch were compared to bridge distributions in wedged specimens. Because of the complex bridge morphology the load supported by the bridges cannot be modeled as viscous uniaxial columns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02860.x
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    In Situ Synthesis of TiCp/Ni3Al Composites under High Pressure (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: In this paper, TiCp/Ni3Al composites are synthesized in situ at near theoretical density under high-pressure (1.56.5 GPa), high-temperature (1073–1473 K) conditions. The grain size of TiC-reinforced particles is nanometer scale, which influences the Vickers microhardness of the composites. The effect of pressure on the grain size of TiC is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02863.x
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  • 49
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    Acid–Base Reactions of Transition Metal Oxides in the Solid State (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Subsolidus compatibility data exist for a number of ternary oxide systems containing a transition metal oxide. Ternary diagrams, suitable for the present purpose, are limited mainly to those that include FeO, Fe2O3, ZnO, or Cr2O3, and these are examined in the context of Lewis acid–base interaction by considering the electron densities borne by the oxygen atoms or ions. These electron densities can be expressed on the optical basicity scale, and a significant acid–base difference exists between the reactants when they differ markedly in optical basicity. For many reactions the optical basicity difference between the products is much less, suggesting that acid–base neutralization is a major driving force. This principle has been found previously for nontransition metal oxide ternary systems. However, there are notable exceptions, especially in reactions where FeO or ZnO is the end product. This exceptional behavior is examined.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02999.x
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    High-Thermal-Conductivity Aluminum Nitride Ceramics: The Effect of Thermodynamic, Kinetic, and Microstructural Factors (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Improvement in the thermal conductivity of aluminum nitride (AlN) can be realized by additives that have a high thermodynamic affinity toward alumina (Al2O3), as is clearly demonstrated in the aluminum nitride-yttria (AlN-Y2O3) system. A wide variety of lanthanide dopants are compared at equimolar lanthanide oxide:alumina (Ln2O3: Al2O3, where Ln is a lanthanide element) ratios, with samaria (Sm2O3) and lutetia (Lu2O3) being the dopants that give the highest- and lowest-thermal-conductivity AlN composites, respectively. The choice of the sintering aid and the dopant level is much more important than the microstructure that evolves during sintering. A contiguous AlN phase provides rapid heat conduction paths, even at short sintering times. AlN contiguity decreases slightly as the annealing times increase in the range of 1–1000 min at 1850°C. However, a substantial increase in thermal conductivity results, because of purification of AlN grains by dissolution-reprecipitation and bulk diffusion. Removal of grain-boundary phases, with a concurrent increase in AlN contiguity, occurs at high annealing temperatures or at long times and is a natural consequence of high dihedral angles (poor wetting) in liquidphase-sintered AlN ceramics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03000.x
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    Preceramic Polymer Route to Amorphous and Crystalline Potassium Aluminosilicate Powders and Their Electrorheological Properties (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxide one-pot synthesis (OOPS) process was used to synthesize a polymer precursor to potassium aluminosilicate, KAlSiO4 (KASp). A KAlSiO4 gel (KASg) also was produced via a solgel route using the same precursor. The two routes to KAlSiO4 were explored to compare the effects of the two processing methods on powder properties. The KASp and KASg powders both transformed on heating (.500°C) to amorphous, high-surface-area powders with narrow pore-size distributions (4–24 nm). These anhydrous, amorphous powders were intrinsic electrorheological (ER) materials. Both materials crystallized at } 1070°C, and thermogravimetric analysis, differential thermal analysis, and X-ray diffractometry suggested that they were identical. Diffuse reflectance infrared Fourier transform spectroscopy and scanning electron microscopy proved that the KASp powders were homogeneous, whereas the KASg powders were heterogeneous and segregated. The KASg powders exhibited better ER properties that were associated with the segregated phases.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03001.x
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    Effect of Tetravalent Dopants on Raman Spectra of Tetragonal Zirconia (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Tetragonal zirconia solid solutions were prepared by the additions of ceria, titania, germania, and cassiterite into 2-mol%-Y2O3-stabilized t-ZrO2 (2Y-TZP), and the effect of the dopant size on the changes in the Raman spectra of t-ZrO2 was investigated. The frequencies of the Raman modes that were associated with Zr-O bond stretching decreased as doping with the oversized cation (Ce4+) increased and increased linearly as doping with the undersized dopants (Ti4+, Ge4+, Sn4+) increased within the solubility limits of the dopants in 2Y-TZP. The frequency of the 640 cm−1 Raman band decreased as the square root of the unit-cell volume increased, suggesting that the ionic size of dopants governs the Raman mode that is related to the short ZrO bond between two ZrO bonds in t-ZrO2 solid solutions. Although there was no consistent relationship between the change in the tetragonality of t-ZrO2 solid solutions and the tetravalent cation size, the intensity ratio of the Raman modes at 609 and 640 cm−1 (I609/I640) decreased as the ionic size decreased.
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    Analysis of Size Dependence of Ceramic Fiber and Whisker Strength (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The strengths of ceramic fibers and whiskers have been observed to increase with decreasing fiber diameter and length. Typically, both surface flaws and volume flaws exist in ceramic fibers and whiskers, which makes it impossible to characterize the strength dependence of both the diameter and the length with a single-modal Weibull distribution function. Our data also show that the single-modal Weibull distribution is inadequate to characterize the strength of fibers with varying diameters even in the case of a constant fiber length. In addition, experimental data also show that, for sapphire whiskers whose surface flaws were removed by chemical polishing, the whisker strength has a much stronger size dependence on diameter than predicted by the single-modal Weibull function, which indicates that factors other than those characterized by the Weibull function also play a role in the strength of sapphire whiskers. In this paper, the factors affecting the strengths of ceramic fibers and whiskers are analyzed in terms of Weibull statistics, fracture mechanics, and flaw size density variation with varying fiber diameters. A three-parameter modified Weibull distribution, which combines the above strength-affecting factors, is proposed to characterize both the diameter and the length dependence for ceramic fibers and whiskers with or without surface flaws. Characterization of the strength data of sapphire whiskers and Nicalon SiC fibers with varying diameters shows the validity of the modified Weibull distribution function.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03002.x
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    Nucleation and Crystallization of a Lithium Aluminosilicate Glass (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An aluminosilicate glass of composition 61SiO26Al2O310MgO6ZnO·12Li2O·5TiO2 (mol%) has been prepared by a melting process and investigated as far as crystallization is concerned. Glass-ceramic is easily obtained because glass shows a high tendency to crystallize starting from 700°C. The crystalline phases evolve with temperature, showing the aluminosilicates to be the main phase up to 1050°C, followed by metasilicates and silicates, some of which have lower melting points. The titanates of Mg and Zn develop from the phase-separated glass, soon after Tg, and grow to form nucleation centers for the other crystalline phases. The evolution from phase-separated glass to glass-ceramic has been followed by many thermal, diffractometric, spectroscopic, and microscopic techniques.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03235.x
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    An Analysis of Nucleation-Rate Type of Curves in Glass as Determined by Differential Thermal Analysis (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The nucleation rate (I) versus temperature type of curves for a Na2O2·CaO·3SiO2 (NC2S3) glass doped with 0.1 wt% platinum, 0.5 wt% Ag2O, and 2.0 wt% P2O5 were determined using a previously developed differential thermal analysis (DTA) technique. In this DTA technique, a constant amount of glass sample was nucleated at selected temperatures for a specific time, followed by a DTA scan at a fixed heating rate. The functional dependence of the maximum intensity of the exothermic DTA crystallization peak ((deltaT)p) or the inverse temperature at the DTA peak maximum (Tp−1) on the nucleation temperature (Tn) was used to determine the nucleation rate versus temperature type of curves. Calculations for qualitatively assessing the dependence of (deltaT)p on Tn were performed using I and crystal growth rate (U) curves for a hypothetical system. Values of (deltaT)p calculated for different degrees of overlap between the I and U curves were compared with those measured experimentally. The (deltaT)p vs Tn curves depended strongly on the overlap of I and U, whereas the Tp−1 vs Tn curves were unaffected by the overlap.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03238.x
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    Application of the Carreau Model to Tape-Casting Fluid Mechanics (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Tape-casting experiments were conducted with 30 different aqueous suspensions whose viscosities were functions of strain rate. Tape thickness measurements of the resulting casts varied from 180 to 310 μ m. The three-parameter Carreau model accurately conformed to the rheological data of the suspensions between 0.46 and 581 s−1. With this model, the zero-shear-rate viscosities of the various suspensions ranged from 20 to 2 × 105 mPa·s. Within the framework of the Carreau model, the equations of motion for the flow of the suspension through the doctor blade were solved numerically. Calculated thicknesses were in very good agreement with experimental measurements.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03244.x
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    Effect of Substrate Orientation, Roughness, and Film Deposition Mode on the Tensile Strength and Toughness of Niobium–Sapphire Interfaces (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The strength and toughness of interfaces between sputter-deposited polycrystalline niobium films and sapphire substrates with basal and prismatic orientations were measured. The effect of deposition parameters and substrate roughness on these interface properties also was investigated. Substrates of polycrystalline alumina with two different surface morphologies were chosen for studying the effect of interface roughness. The interface strength was measured using a previously developed laser spallation experiment in which a laser-generated compressive stress pulse in the substrate, upon reflection into a tensile stress pulse from the coating's free surface, pulls the interface apart. The interface toughness was obtained using a controlled delamination technique, in which a residually stressed loading layer was used to buckle the underlying test layer from its substrate. The energy balance in the prebuckeled and postbuckled states provided a direct measure of the interface toughness. These values were independently obtained by another experiment in which well-characterized, artificially generated, interfacial flaws were loaded using a stress pulse in the laser spallation assembly. The coating's free surface velocity upon crack initiation was related to the critical energy release rate via a numerical simulation. The results of the two toughness experiments conformed to each other and related fairly well to the independently obtained strength measurements.
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    Effect of Heat Treatment on Rapidly Quenched AgI-Based Silver Orthoborate Glasses Containing Large Amounts of AgI (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of heat treatment on the twin-roller rapidly quenched 75AgI·18.7Ag2O6.3B2O3 glass was investigated by differential scanning calorimetry (DSC), high-temperature X-ray diffraction (XRD), and field-emission-type scanning electron microscopy. The glass had an inhomogeneous microstructure with dispersed particles 40-60 nm in diameter at room temperature. On the other hand, island regions of several hundred nanometers with fine dispersed particles about 20-30 nm in diameter were observed in the glass after heating to 120°C. DSC and high-temperature XRD measurements revealed that crystallization occurred at around 120°C, which is lower than the α-β phase transformation temperature (147°C), to form α-AgI in the glass. The crystallization of α-AgI from the glass below the α-ß phase transformation temperature strongly supports the possibility of the existence of α-AgI nuclei in AgI-based silver orthoborate glasses. Validating the existence of AgI microcrystals supports the microdomain model for superionic AgI-based glasses.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03252.x
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    Characterization and Sintering of Reactive Cerium(IV) Oxide Powders Prepared by the Hydrazine Method (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Nanocrystalline cerium(IV) oxide (CeO2) powders have been prepared by adding hydrazine monohydrate to an aqueous solution of hydrous cerium nitrate (Ce(NO3)3·6H2O), followed by washing and drying. The lattice parameter of the as-prepared powder is a= 0.5415 nm. The powder characteristics and sinterability of reactive CeO2 have been studied. The surface areas of powders that have been heated at low temperatures are high, and these surface areas do not decrease to 10 m2/g until the temperature is 〉1200°C. Crystallite size and particle size are strongly dependent on the heating temperature. Optimum sintered densities are obtained by calcining in the temperature range of 700°–800°C. Ceramics with almost-full density can be fabricated at a temperature as low as 1150°C.
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    Phase Stability of Graphitelike BC4N up to 2100 K and 7 GPa (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Thermal phase stability of graphitelike BC4N (g-BC4N) has been studied up to 7 GPa and 2100 K using in-situ powder diffraction of synchrotron radiation. It has been shown that the process of g-BC4N decomposition at ambient pressure starts at 2050 K and occurs to form highly ordered hexagonal graphitelike boron nitride (hBN) and disordered graphite. As the pressure increases up to 6.6 GPa, the temperature of the decomposition onset decreases to 1070 K. At this pressure in the 1070-1400 K temperature range (decomposition degree of less than or equal to 0.1), the decomposition products remain the same, whereas at higher temperatures, the decomposition of g-BC4N is accompanied by the formation of cubic boron nitride (cBN) and disordered graphite. Measurement of 298 K equation of state of g-BC4N results in a zero-pressure bulk modulus of 18.1 ± 0.2 GPa and its pressure derivative of 6.6 ± 0.1. Thermodynamic analysis has shown that the g-BC4N decomposition is a nonequilibrium process and the phase itself is metastable.
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    Heavy-Water (D2O) Take-Up-Induced Lattice Expansion in the High-Temperature Proton Conductor Ba3Ca1.18Nb1.82O9−δ (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Dimensional changes of the high-temperature proton conductor Ba3Ca1.18Nb1.82O9−δ, when exposed to D2O vapor, were investigated using length-change and precision density measurements. Such information is essential for possible applications of proton conductors in solid oxide fuel cells and humidity and hydrogen sensors. A linear increase of the sample lengths with increases in the deuterium content was observed. Comparison of the present D2O data with those that were previously obtained for H2O showed that there was a small isotope effect in the lattice expansion. The fact that the length-change-versus-hydrogen-isotope-concentration curves were almost isotope independent supported the validity of the take-up reaction H2O(g) + VOö+ OxO is an ⇄ 2OHO. In regard to the latter equation, it was found that small islands of silver, palladium, nickel, and platinum act as catalytic promoters of the reaction and lead, for given heavy-water-steam exposure conditions, to an increase of water absorption of up to 100%, when compared with samples without the catalytic surface layers.
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    Fatigue and Static Crack Propagation in Yttria-Stabilized Tetragonal Zirconia Polycrystals: Crack Growth Micromechanisms and Precracking Effects (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The influence of precracking techniques in the crack growth behavior of yttria-stabilized tetragonal zirconia polycrystals (Y-TZP) is investigated. Load-bridge and cyclic-compression precracking enhance subsequent tensile crack growth rates, in comparison to results that are found with precracks that are extended under four-point bending prior to testing. The actual influence of these precracking techniques in the near-threshold crack growth regime is remarkably different. Although load-bridge precracking produces a pattern of crack growth fluctuations for stress intensity factors, K, lower than the effective crack-growth threshold of the material, compression-fatigue precracks start to propagate under far-field tensile loads at very fast growth rates and for K values that are slightly higher than the effective threshold. Crack-tip shielding by tetragonal-to-monoclinic transformation develops gradually, influencing the crack growth behavior in Y-TZP. Proposed fatigue crack growth micromechanisms involve damage accumulation at the crack-tip region. For Kmax 〉 3 MPa·m1/2, fatigue crack growth rates are strongly affected by environmental interactions at the crack tip, and postulated fatigue micromechanisms include the cyclic degradation of crack-tip shielding.
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    Hydroxyapatite/Hydroxyapatite-Whisker Composites without Sintering Additives: Mechanical Properties and Microstructural Evolution (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Hydroxyapatite/0%-30% hydroxyapatite-whisker (HAp/0%-30%HAp(w)) composites have been fabricated by pressureless sintering, hot pressing, and hot isostatic pressing (HIP). Composites that were HIPed at 1000°-1100°C (2 h, 190 MPa) exhibited the best properties: relative densities of 97.0-99.5%, fracture toughness of 1.4-2.0 MPa·m1/2 (as compared with 1.0 MPam1/2 for the nonreinforced HAp matrix). Compressive pre-stressing and crack deflection contributed mostly to the increase of fracture toughness. Depending on processing conditions, grain growth in the HAp matrix and/or Rayleigh instability of the HAp whiskers were probably responsible for microstructural changes in the composites. The HAp/HAp(w) composites exhibited improved toughness, attaining the lower fracture-toughness limit of bone without a decrease of bioactivity and biocompatibility.
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    Monolayer-Mediated Deposition of Tantalum(V) Oxide Thin Film Structures from Solution Precursors (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Integration of oxide thin films with semiconductor substrates is a critical technology for a variety of microelectronic memory and circuit applications. Patterned oxide thin film devices are typically formed by uniform deposition followed by postdeposition ion-beam or chemical etching in a controlled environment. This paper reports details of an ambient atmosphere technique which allows selective deposition of dielectric oxide thin layers without postdeposition etching. In this method, substrate surfaces are selectively functionalized with hydrophobic self-assembled monolayers of octadecyltrichlorosilane by microcontact printing (μ-CP). Sol-gel deposition of ceramic oxides on these functionalized substrates, followed by mild, nonabrasive polishing, yields high-quality, patterned oxide thin layers only on the unfunctionalized regions. A variety of micrometer-scale dielectric oxide devices have been fabricated by this process, with lateral resolutions as fine as 4 μm. In this paper, we describe the solution chemistry, evolution of microstructure, and electrical properties of Ta2O5 thin films, as well as the stress-related mechanism which enables selective de-adhesion and resultant patterning. Selectively deposited, 80-120 nm thick Ta2O5 thin film capacitors were crystallized on platinized silicon at 700-800°C, and had dielectric constants of 18-25 depending upon the processing conditions, with 1 V leakage current densities as low as 2 × 10−8 A/cm2. The ability to selectively deposit Ta2O5 and other electrical ceramics (such as LiNbO3 and PbTiO3) on a variety of technologically important substrate materials suggests broad potential for integrated circuit and hybrid microelectronics applications.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03199.x
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    Properties and Microstructure of Molybdenum Disilicide–β′;-SiAlON Particulate Ceramic Composites (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Particulate ceramic composites that were composed of a combustion-synthesized β′;-SiAlON matrix and dispersed MoSi2 particles were hot pressed at 1600°C in a nitrogen atmosphere. The physical and mechanical properties of the composites that contained 15, 30, and 45 vol% MoSi2 were evaluated. The average four-point bend strength, fracture toughness, and Vickers hardness of the composites were in the ranges of 500-600 MPa, 3-4 MP·am1/2, and 11-13 GPa, respectively. The measured mechanical strength and hardness were very similar to the values that were predicted from the rule of mixtures. The fracture toughness of the combustion-synthesized β′;-SiAlON (2.5 MPa·m1/2) was apparently enhanced by the MoSi2 particles that were added. The increase in the fracture toughness was predominately attributed to the residual thermal stress that was induced by the thermal expansion mismatch between the MoSi2 particles and the β′;-SiAlON matrix. The composites showed improved electrical conductivity and oxidation resistance over monolithic β′;-SiAlON. High-resolution transmission electron microscopy examination of the composites indicated that the MoSi2 was chemically well compatible with the β′;-SiAlON.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03201.x
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    Sintering Behavior of Cadmium-Doped Pb(Ni1/3Nb2/3)O3–PbZrO3–PbTiO3 Ceramics (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Substituting Cd2+ ions into the A and B sites in a Pb(Ni1/3Nb2/3)O3PbZrO3PbTiO3 (PNNPZPT) ternary perovskite material made it possible to determine the effects of the Cd2+ ion substitution site on sintering behavior. The substitution site of the Cd2+ ion was identified by using X-ray photoelectron spectroscopy spectra. Although Cd2+ ions were substituted into the A and B sites in PNNPZPT, the Cd2+ ions preferred the A site over the B site. When Cd2+ ions replaced Pb2+ ions, a weight gain was observed during sintering. On the other hand, replacing Ni2 ions with Cd2+ ions promoted weight loss. Those weight changes indicated that Cd2+ ions change the bonding strength between the B-site cations and the oxygen of the octahedron in a perovskite structure. Density was influenced by the Cd2+ ion substitution site, and the A-site-doped compositions had higher densities than the B-site-doped compositions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03012.x
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  • 67
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    Effect of Oxide Devitrification on Oxidation Kinetics of SiC (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of oxide crystallinity on the oxidation rate of silicon carbide was investigated. CVD SiC coupons were oxidized in a clean TGA reactor system at 1300°C initially in flowing oxygen, immediately annealed in argon, and then reoxidized, all in situ and without cooling (so as to preserve oxide integrity). The parabolic rate constants determined for the preoxidation regime (of mainly amorphous oxide film) and reoxidation regime (of devitrified oxide) were compared. The oxidation rate decreased by a factor of }30 following full oxide crystallization induced by the anneal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03014.x
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  • 68
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    Application of Weakest-Link Fracture Statistics to Fiber-Reinforced Ceramic-Matrix Composites (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The strength and reliability of fiber-reinforced ceramic-matrix composites (CMCs) are dependent on whether conditions of local or global load sharing prevail. Global load sharing is promoted by a low interfacial sliding stress and is manifested in a zero-tangent modulus at the point of tensile failure along with random fiber failures and extensive fiber pullout. In this paper, it is demonstrated that conditions of global load sharing are not present in two commonly studied CMCs, despite the fibrous appearance of their fracture surfaces. This behavior is manifested in a volume-dependent strength, as evidenced by strength differences measured in tension and flexure (accounting for the nonlinear stress distribution in flexure). Methods of weakest-link statistics are used to relate the strengths measured in the two test configurations. Estimates for the Weibull moduli of the two systems are obtained from the experiments and compared with values obtained through Monte Carlo simulations based on a three-dimensional-lattice Greens function method. The implications of these results on the strength of large components and of small regions of high stress concentration are discussed briefly.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03013.x
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  • 69
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    Mullite Transformation Kinetics in P2O5-, TiO2-, and B2O3-Doped Aluminosilicate Gels (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Mullite transformation kinetics of sol-gel-derived diphasic mullite gels doped with P2O5, TiO2, and B2O3 were studied using quantitative X-ray diffraction and differential thermal analysis (DTA). The mullite transformation temperature initially increased with P2O5 doping because of phase separation and formation of α-alumina and cristobalite. In TiO2-doped samples, the mullite transformation temperature decreased with TiO2 doping, and the transformation rate increased with decreasing TiO2 particle size. Kinetic studies showed that titania reduced the activation energy for both nucleation and growth relative to pure diphasic mullite gels by lowering the glass viscosity and/or enhancing the solid-state mass transport through lattice defects. B2O3 doping decreased the mullite transformation temperature and lowered the activation energy for both nucleation and growth but especially affected the mullite nucleation process, as indicated by the much smaller grain size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03015.x
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  • 70
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    Thermal Evolution and Sintering Behavior of a 2:1 Mullite Gel (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The thermal evolution of a mullite gel of composition 2Al2O3·SiO2 has been investigated. The gel crystallized at 1300°C into an alumina-rich mullite and corundum, instead of single-phase 2Al2O3·SiO2 mullite. The amount of Al2O3 that dissolved in the mullite structure has been determined in the 1300–1780°C temperature range by measuring the mullite lattice parameters. A maximum limit for the amount of Al2O3 in solid solution has been observed. Densification of the gel powders has been analyzed up to temperatures of 1780°C. The microstructure of dense materials always showed the presence of residual Al2O3 particles.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03018.x
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  • 71
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    Detection of Minor Crystalline Phases in Alumina Ceramics Using Synchrotron Radiation Diffraction (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The use of synchrotron radiation diffraction (SRD) in con-junction with conventional laboratory X-ray diffraction (XRD) for analyzing the phase assemblage of selected alu-mina-based ceramics is described. This paper outlines the benefits of synchrotron powder diffraction in resolving mi-norand impurity phases in various alumina ceramics. Laboratory XRD is shown to provide only cursory details of minor crystalline phases which are strikingly evident and clearly defined from application of SRD analysis. The po-tential of SRD techniques to characterize low-level crystal-line phases and as a check for “phase purity” in ceramic systems is considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03216.x
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  • 72
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    Comment on “Mesostructure of Calcium Silicate Hydrate (C-S-H) Gels in Portland Cement Paste: Short-Range Ordering, Nanocrystallinity, and Local Compositional Order” (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03220.x
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  • 73
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    Effect of Hydrogen Fluoride Gas Treatment on High-Strength Fluoride-Fiber Fabrication (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effect of treating a ZrF4-based fluoride-glass surface with hydrogen fluoride gas is investigated using secondary-ion mass spectroscopy. The analysis reveals that this treatment is effective in reducing the oxygen concentration at the surface. A strong fiber with a mean tensile strength of 550 MPa and maximum strength of 600 MPa is successfully fabricated by using this technique.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03150.x
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  • 74
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    Fibrous Monolithic Ceramics (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fibrous monolithic ceramics are an example of a laminate in which a controlled, three-dimensional structure has been introduced on a submillimeter scale. This unique structure allows this all-ceramic material to fail in a nonbrittle manner. Materials have been fabricated and tested with a variety of architectures. The influence on mechanical properties at room temperature and at high temperature of the structure of the constituent phases and the architecture in which they are arranged are discussed. The elastic properties of these materials can be effectively predicted using existing models. These models also can be extended to predict the strength of fibrous monoliths with an arbitrary orientation and architecture. However, the mechanisms that govern the energy absorption capacity of fibrous monoliths are unique, and experimental results do not follow existing models. Energy dissipation occurs through two dominant mechanisms—delamination of the weak interphases and then frictional sliding after cracking occurs. The properties of the constituent phases that maximize energy absorption are discussed.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03148.x
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  • 75
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    PbTiO3–PbO–SiO2 Glass-Ceramic Thin Film by a Sol–Gel Process (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: PbTiO3(PT)-PbO-SiO2 glass-ceramic thin films were pro-duced by a sol-gel process. The crystallization of PT oc-curred at ∼700°C and was higher than that in PT-PbO-B2 O3 sol-gel glass-ceramics. A pinhole-free thin film was obtained by a rapid thermal annealing process when the designed glass-forming phase content in the thin film was 〉24 vol%. The measured dielectric constants of the films fairly agreed with the predicted values, based on a parallel mixing model. The dielectric constant was 219 and the di-electric loss was 0.04 in the 0.6PT-0.4(PbO-SiO2) film that was fired at 700°C.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03152.x
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  • 76
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    Synthesis, Densification, and Conductivity Characteristics of BICUVOX Oxygen-Ion-Conducting Ceramics (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Copper-substituted bismuth vanadate (Bi2V0.9Cu0.1O5.35), known as BICUVOX, possesses high oxygen ion conductivities at low temperatures. The ionic conductivity of this material at 300°C (∼1 × 10−3 S/cm) is 50 to 100 times greater than any other solid electrolyte in this temperature range. In this paper we report the preparation of sinterable BICUVOX powders by solid-state reaction and conventional ceramic powder processing techniques. Densification studies indicate that optimum densities (〉95% theoretical) can be obtained after 10-20 h sintering at 800°C. Ionic conductivity characteristics were evaluated with respect to temperature, sample density, and prolonged isothermal heating.
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    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03158.x
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  • 77
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    Structure and Properties of Silica Derived from Silicon Alkoxide Reacted with Tartaric Acid (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The effects of tartaric acid that was used in sol–gel processing on specific surface area, pore-size distribution, and gel structure of sol–gel-derived silica gels were investigated. The specific surface area of silicas that were calcined at 450°C increased from ∼600 m2/g to ∼1200 m2/g as the amount of tartaric acid that was used increased. The pore-size distribution changed as the surface area increased, and only the gels that had a surface area of 930-990 m2/g showed a very sharp pore-size distribution in the mesopore range. The difference in gel structure and properties was explained in terms of the acidity of tartaric acid and the inhibition of condensation among primary particles through the coordination or adsorption of tartaric acid on the particle surface. From the thermal behavior of the gels with different features, it was concluded that gel properties are determined not only by the structure of the precursor gel but also by the surface activity. The gel with uniform mesopores gave a high surface area over a wide range of calcination temperatures.
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  • 78
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    Microstructure and Phase Stability of Yttria-Doped Tetragonal Zirconia Polycrystals Heat Treated in Nitrogen Atmosphere (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The low-temperature degradation of zirconia (ZrO2) that was doped with 3 mol% yttria (Y2O3) (3Y-TZP) was prevented by the heat treatment of sintered specimens in nitrogen. The heat treatment of sintered specimens resulted in a surface layer that was stabilized by nitrogen ions, whereas the interior was only slightly affected by the heat treatment. X-ray diffractometry and transmission electron microscopy analyses revealed that the stabilized surface layer consisted of cubic grains with tetragonal precipitates. Although the presence of the surface layer decreased the strength of the sintered 3Y-TZP, the strength of nitrified specimens was maintained when low-temperature annealing was applied.
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  • 79
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    Particle Growth during Calcination of Polycation Oxides Synthesized by the Polymeric Precursors Method (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The particle-growth kinetics of sodium niobate and zirconium titanate powders that were processed by the polymeric precursors method were studied. The growth kinetics that were studied for the particle, in the final stage of crystallization, showed that the growth process occurs in two different stages. For temperatures 〈800°C, the particle-growth mechanism is associated with surface diffusion, with an activation energy in the range of 40-80 kJ/mol. For temperatures 〉800°C, particle growth is controlled by densification of the nanometric particle clusters and by a neck-size-controlled particle-growth mechanism. The results suggest that this behavior was typical of the synthesis method, because two different polycation oxides presented the same behavior.
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  • 80
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    Optical Spectra of Synthetic Spinels in the System MgAl2O4–MgCr2O4 (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Unpolarized optical spectra were measured in the wavelength range 322–1666 nm by the diffuse reflection technique from spinel powders synthesized in the system MgAl2O4–MgCr2O4. The spectra were interpreted by the crystal-field theory on the basis of trigonally distorted spinel octahedra with D3d symmetry. For chromium-rich solid solutions, including the MgCr2O4 end-member, results after peak fittings showed octahedral D3d local symmetry around Cr3+ ions, identical to the crystallographic site symmetry. For chromium-poor solid solutions, however, octahedral C3v local symmetry was suggested around Cr3+ ions, different from the D3d crystallographically expected.
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  • 81
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    Thermodynamic Analysis of the Cubic–Tetragonal Phase Equilibria in the System ZrO2–YO1.5 (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The cubic-tetragonal (c-t) phase equilibria in the system ZrO2-YO1.5 are thermodynamically analyzed from Landau's phenomenological theory. The calculated c-t two-phase field is depicted as a miscibility gap with a sharp maximum and the spinodal region as originally predicted by Hillert and Sakuma. However, the observed c-t two-phase field and the spinodal region are better described by the present model. In addition, this model can be used to discuss the nature of the c-t diffusionless transformation from the order parameter in contrast with the original model. The predicted change in the tetragonality of t-ZrO2 with YO1.5 content is slightly different from that in the c/a axial ratio estimated from X-ray diffraction analysis. The displacement of cations and anions may not take place simultaneously during the c-t transformation.
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  • 82
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    Preparation and Faraday Effect of Fluoroaluminate Glasses Containing Divalent Europium Ions (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Fluoroaluminate glasses containing various concentrations of Eu2+ were prepared under a reducing atmosphere for the present study, and the wavelength dependence of the Faraday rotation angle was examined. The magnitude of the Verdet constant (Vc) increased as the concentration of Eu2+ increased. In addition, the Verdet constant of glasses containing 5 cat.% Eu2+ was larger than that of fluoroaluminate glasses containing the same concentration of Tb3+ in the wavelength region from 400 to 600 nm. The effective transition wavelength, λt, for glasses containing Eu2+ as well as those containing Tb3+ was evaluated based on the Van Vleck and Hebb theory. Factors dominating the Verdet constant of those glasses are discussed in this report.
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  • 83
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    A Processable Mullite Precursor Prepared by Reacting Silica and Aluminum Hydroxide with Triethanolamine in Ethylene Glycol: Structural Evolution on Pyrolysis (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A simple, processable precursor to mullite can be synthesized in quantities of 100 g in a few hours by direct reaction of silica, aluminum hydroxide, and triethanolamine in ethylene glycol. To delineate a processing window whereby precursor shapes can be transformed into mullite, the chemical and phase microstructural evolution of this precursor on pyrolysis to selected temperatures in air is followed by thermal gravimetric analysis, differential thermal analysis, diffuse reflectance infrared Fourier transform spectroscopy, solid-state 27Al and 29Si nuclear magnetic resonance, X-ray diffractometry, and Brunauer-Emmett-Teller analytical methods. The precursor behaves as a single-phase, atomically mixed material that initially transforms to a porous, amorphous aluminosilicate when heated to temperatures as high as 950°C. Above 950°C, the precursor first transforms to tetragonal mullite, based on comparison with the literature, and, on continued heating above 1200°C, to orthorhombic mullite with coincident loss of porosity.
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    Oriented Lead Titanate Film Growth at Lower Temperatures by the Sol-Gel Method on Particle-Seeded Substrates (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: An approach to fabricate lead titanate (PbTiO3) films with preferred orientation on arbitrary substrates by a sol-gel method was developed. To ensure a preferred crystallographic orientation on the substrates with different crystal structure, well-defined platelet PbTiO3 particles were used as seeds. Because the basal plane of the platelet-shaped particles was the (001) plane, the particles aligned with the c-axis perpendicular to the substrates. During crystallization of the sol-gel PbTiO3 films on the particle-seeded substrate, preferential nucleation occurred on seeded particles with the same crystallographic orientation as the particles at a much lower temperature. In the current study, (100) and (001) textured PbTiO3 films have been produced on various substrate materials such as silicon, silicate glass, indium tin oxide (ITO) glass, and titanium metal at temperatures as low as 275°C. The microstructure of the films was examined by scanning electron microscopy and atomic force microscopy. Limited ferroelectric properties also were determined, to underscore the preferred orientation that was produced in these materials.
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    Thermodynamic Assessment of the Bismuth–Strontium–Oxygen Oxide System (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The experimental data on the oxide portion of the Bi–Sr–O system have been reviewed, and an optimized thermodynamic description is presented. There are at least seven stable ternary oxide phases, two of which show considerable solid-solution ranges. At least two phases—δ-Bi2O3 and the rhombohedral β-phase—are good oxygen-ion conductors. Most of the phases are confined to the Bi2O3-SrO line at ambient oxygen partial pressure; however, in the SrO-rich portion, there are at least two phases with oxygen in excess, i.e., with bismuth in the oxidation state Bi5+ instead of the usual Bi3+. There are rather large differences between different experimental data sets; nevertheless, a reasonably consistent set of data can be chosen for the optimization.
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    Dielectric Measurements on High-Q Ceramics in the Microwave Region (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
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    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The postresonator method proposed by Hakki and Coleman for the measurement of dielectric properties of solids in the microwave region is reexamined. Based on the experiments performed around 10 GHz, the limitations of the method in loss determination for materials with tan δ, 5 × 10−4 are outlined. Alternative techniques for studying high-Q materials are described. Loss measurements performed on well-prepared ceramics have been used to draw comparisons among these techniques. Some of the experimental findings are new and are reported for the first time.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02951.x
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  • 87
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    Time–Temperature–Transformation Diagrams for Borosilicate Glasses and Preparation of Chemically Durable Porous Glasses (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: To clarify the effects of glass composition and heat-treatment conditions on phase separation and crystallization, time–temperature–transformation (TTT) diagrams for the system (65 −x)SiO2·25B2O3·(10 −y)Na2O·yCaO·xZrO2, which is used for fabricating alkali-durable porous glasses, were determined. The microstructures and properties, such as resistance to alkaline attack as a function of ZrO2 content, of the porous glasses fabricated on the basis of the developed TTT diagrams were examined. CaO and ZrO2 additions were shown to affect the locations of the noses in the TTT curves for phase separation and crystallization. The substituting of CaO for Na2O was effective for retaining ZrO2 in the skeleton of the porous glasses. The alkali resistance of ZrO2-containing porous glasses was 8–10 times superior to that of the porous glass without ZrO2. The results demonstrate that TTT diagrams can be used as guides for heat-treatment scheduling in processing or predicting of glass-forming ability and the onset of phase separation and crystallization in glass-forming systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02952.x
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  • 88
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    Fabrication and Microstructures of MoSi2 Reinforced–Si3N4 Matrix Composites (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Details of the fabrication and microstructures of hot-pressed MoSi2 reinforced–Si3N4 matrix composites were investigated as a function of MoSi2 phase size and volume fraction, and amount of MgO densification aid. No reactions were observed between MoSi2 and Si3N4 at the fabrication temperature of 1750°C. Composite microstructures varied from particle–matrix to cermet morphologies with increasing MoSi2 phase content. The MgO densification aid was present only in the Si3N4 phase. An amorphous glassy phase was observed at the MoSi2–Si3N4 phase boundaries, the extent of which decreased with decreased MgO level. No general microcracking was observed in the MoSi2–Si3N4 composites, despite the presence of a substantial thermal expansion mismatch between the MoSi2 and Si3N4 phases. The critical MoSi2 particle diameter for microcracking was calculated to be 3 μm. MoSi2 particles as large as 20 μm resulted in no composite microcracking; this indicated that significant stress relief occurred in these composites, probably because of plastic deformation of the MoSi2 phase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02953.x
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  • 89
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    Strength vs Stressing Rate and Indentation Crack Growth Behavior of Indium(III) Phosphide (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Susceptibility of InP to environmentally enhanced crack growth behavior was investigated in water and in 50% relative humidity by strength vs stressing rate and indentation crack length measurements. Statistical analysis indicated that, at the 95% confidence level, no environmentally enhanced fracture was detected for InP in liquid or gaseous water.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03177.x
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  • 90
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    Effect of Porosity and Microstructure on the Strength of Si3N4: Designed Microstructure for High Strength, High Thermal Shock Resistance, and Facile Machining (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The flexural strength of porous Si3N4 ceramics with a variety of microstructures and porosities were evaluated, and the effect of microstructure on the flexural strength was investigated to obtain machinable Si3N4 ceramics having both high strength and high thermal shock resistance. Porous Si3N4 having three types of microstructure, consisting of (1) only spherical grains, (2) combinations of spherical and columnar grains, and (3) only columnar β-grains connected randomly in three dimensions, were readied as specimens. Their mean pore diameters and porosities were 0.2 to 0.3 μm and 8% to 59%, respectively. The flexural strength of the porous Si3N4 (3) was much larger than that of the porous Si3N4 having the other microstructures, and the maximum flexural strength was 455 MPa at a porosity of 38.3%. The thermal shock resistance (ΔT), which was determined by a water quench test, of porous Si3N4 with such microstructure and a porosity of 50% was 980 K. All of the porous Si3N4 (3) was easily machined with cemented carbide drills.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03179.x
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  • 91
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    Paralinear Oxidation of CVD SiC in Water Vapor (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The oxidation kinetics of CVDSiC were monitored by thermogravimetric analysis (TGA) in a 50% H2O/50% O2 gas mixture flowing at 1.4 cm/s for temperatures between 1200” and 1400°C. Paralinear weight change kinetics were observed as the water vapor oxidized the SiC and simultaneously volatilized the silica scale. The long-term degradation rate of SiC is determined by the volatility of the silica scale. Rapid SiC surface recession rates were estimated from these data for actual aircraft engine combustor conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02810.x
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  • 92
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    Forming Textured Microstructures via the Gelcasting Technique (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Crystallographically textured samples of iron titanate were produced by gelcasting in the presence of a strong magnetic field. Texture was assessed by measuring X-ray pole figures on samples that were cast in different orientations relative to the applied field. Specimens in this study exhibit fiber-type texture, with the b-axes aligned parallel to the applied field. Peak texture strengths were on the order of 3 and 48 multiples of a random distribution (MRD) when processed in a 3.2 and 8.4 T magnetic field, respectively. This study shows that a combination of gelcasting with magnetic-field-assisted processing provides a convenient method for fabricating samples which can be used to study the role of crystallographic texture on the physical properties of polycrystalline ceramics, e.g., their elastic or fracture behavior.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03184.x
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  • 93
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    Microstructural Evolution of Gas-Pressure-Sintered Si3N4 with Yb2O3 as a Sintering Aid (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microstructural evolution of gas-pressure-sintered Si3N4 with Yb2O3 as a sintering aid was observed. Microstructures typical for in situ toughened Si3N4, i.e., large elongated grains randomly distributed in a fine matrix, were observed. However, the size of the elongated grains near the surface was much larger than that at the center, resulting in two distinct regions: an inner region and an outer region. The smaller the amount of Yb2O3 added, the larger the difference in the size of the elongated grains between the outer and inner regions. The difference between microstructures was diminished when 16 wt% Yb2O3 was added. The microstructural change with Yb2O3 content was attributed to the evaporation of Yb-containing liquid phase from the surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb03187.x
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  • 94
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    Abnormal Grain Growth of Alumina (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Abnormal grain growth (AGG) is not one of the intrinsic properties of alumina but rather is an extrinsic property that is controlled by certain impurities that are introduced during powder synthesis, processing, or sintering. When small amounts of glass-forming impurities are introduced, some portion beyond their solubility limits will accumulate at grain boundaries at the final stage of densification, form thin intergranular glass films of thermodynamically stable thickness, and induce the sudden appearance of abnormal grains by increasing the rate of grain-boundary migration abruptly. The proposition has been tested experimentally with small, but varying, amounts of silica in ultrapure alumina (99.999%) that has been sintered in a contamination-free condition. Average grain sizes for the appearance of AGG are inversely related to the doping concentration of silica. The thickness of intergranular silicate glass films at the onset of AGG in alumina is constant and estimated to be }3.7 nm.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02957.x
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  • 95
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    Structural Analysis of Inclusions in β-Silicon Carbide Whiskers Grown from Rice Hulls (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Microcrystalline inclusions in the core of β-SiC whiskers derived from the pyrolysis of rice hulls have been studied by transmission electron microscopy using conventional brightfield and dark-field imaging. The electron diffraction patterns from the whiskers show extra reflections arising from these inclusions. Dark-field images from these reflections are consistent with the presence of three different variants of inclusions, all of which are oriented with their [001] axes parallel to the heavily faulted [111] growth axis of the whiskers. A structural model for these inclusions is proposed which accounts satisfactorily for the extra reflections in the electron diffraction patterns.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02959.x
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  • 96
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    Internal Oxidation of Ce3+-BaTiO3 Solid Solutions (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: The reoxidation process in highly Ce3+-doped BaTiO3 ceramics was studied using TEM. Samples of two different types of solid solutions, Ba1−XCe3+XTi1−X/4(VTi)X/4O3 and Ba1−XCe3+XTi4+1−XTi3+XO3, were prepared by sintering oxide mixtures in air and in a reducing atmosphere, respectively. The solid solutions were reoxidized by annealing in air at high temperatures (1000°—1100°C). As a result of internal oxidation of Ce3+ and Ti3+, fluorite CeO2 and monoclinic Ba6Ti17O40 phases were precipitated in the perovskite matrix. In Ba1−XCe3+XTi1−X/4(VTi)X/4O3 solid solution precipitates nucleate heterogeneously at grain boundaries and at extended defects inside the grains, whereas in Ba1−XCe3+XTi4+1−XTi3+XO3 solid solution precipitates are nucleated mainly homogeneously inside reoxidized perovskite grains. The form of the precipitates and their orientational relationship with the matrix, as well as the mechanism of internal oxidation, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02789.x
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  • 97
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    Coprecipitation and Hydrothermal Synthesis of Ultrafine 5.5 mol% CeO2-2 mol% YO1.5ZrO2 Powders (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: Ultrafine 5.5 mol% CeO2—2 mol% YO1.5ZrO2 powders with controllable crystallite size were synthesized by two kinds of coprecipitation methods and subsequent crystallization treatment. The amorphous gel produced by ammonia coprecipitation and hydrothermal treatment at 200°C for 3.5 h results in an ultrafine powder with a surface area of 206 m2/g and a crystallite size of 4.8 nm. The powder produced by urea hydrolysis and calcination exhibits a purely tetragonal phase. In addition, the powders crystallized by hydrothermal treatment exhibit high packing density and can be sintered at lower temperature (,1400°C) with nearly 100% tetragonal phase achieved.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02795.x
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  • 98
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    Laminated C-SiC Matrix Composites Produced by CVI (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A new type of composite, which consists of a reinforcement phase plus a matrix composed of many alternate thin layers of two different materials, has been prepared. CVI appears to be an appropriate process for the fabrication of this class of materials. We have successfully fabricated such a composite using the forced flow—thermal gradient CVI process. A carbon fibrous preform was infiltrated with alternate layers of C and SiC having thicknesses of 0.01 to 0.5μm. For a fixed cycle time, layer thicknesses increased with distance from the fiber surface. Crack deflection patterns indicate that the laminated matrix may contribute to mechanical toughness.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02798.x
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  • 99
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    Low-Temperature Chemical Synthesis of Lanthanum Monoaluminate (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: One of the promising candidates for ferroelectric substrate materials, lanthanum monoaluminate (LaAlO3), was successfully synthesized by two separate chemical powder preparation techniques: (i) homogeneous precipitation from aqueous solutions containing urea (CH4N2O) in the presence of nitrate salts, and (ii) self-propagating combustion synthesis from aqueous solutions containing CH4N2O and the respective nitrate salts of lanthanum and aluminum. The submicrometer, spherical-like particles of the precursors were completely converted to pure LaAlO3 at 850C in the homogeneous precipitation route, and the same conversion temperature was observed to be 750C, which becomes the lowest temperature ever reported for the powder synthesis of a pure LaAlO3 phase. The materials were characterized by powder X-ray diffractometry, simultaneous thermogravimetric/differential thermal analysis, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. Structural refinements by Rietveld analysis showed that LaAlO3 was isostructural with BaTbO3 and had the space group R-3c, in contrast to the previously assumed space group of R-3m for this phase. The atomic positions in the structure of LaAlO3 were refined and presented for the first time, with respect to the present space group.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02801.x
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  • 100
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    Improvement of Cutting Performance of Silicon Nitride Tool by Adherent Coating of Thick Diamond Film (1997)
    Westerville, Ohio : American Ceramics Society
    Journal of the American Ceramic Society 80 (1997), S. 0 
    Details
    ISSN: 1551-2916
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics
    Notes: A thick diamond film was coated using two-stage microwave plasma CVD in the COH, system on a pretreated silicon nitride substrate for a cutting tool. The effects of acid treatment and microflawing treatment of the substrate on adherence of the film and cutting performance were investigated as well as the effects of two-stage CVD conditions. The combination of substrate pretreatment in a hot, strong acid solution of HF and HNO3 and subsequent ultrasonic microflawing pretreatment with diamond grains resulted in the anchored deposition of CVD diamond into the micropores in the silicon nitride substrate. An excellent adherence of the diamond film to the substrate was attained by the two-stage CVD, which consists of a first CVD of fine diamond grains into the micropores and a second higher rate CVD of thick diamond film (thickness 〉30 pm). A dense layer composed of diamond-like carbon and silicon nitride was formed deep in the boundary region of the substrate during long CVD treatment. Long tool life of the silicon nitride chip coated with a thick diamond film was verified by a milling test using Al-20 wt% Si alloy as the work material.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1151-2916.1997.tb02809.x
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