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  • 1
    ISSN: 1433-075X
    Keywords: Key words Yttrium oxide ; Silicon carbide ; Nanocomposites ; Mechanical properties
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Y2O3-based nanocomposites were fabriacted by hot-press and the microstructures and mechanical properties were investigated. Transmission-electron-microscope observations revealed that the SiC particles were distributed both within Y2O3 matrix grains and at the grain boundaries. Significant mechanical properties improvements were identified particularly at high temperatures above 1000 ºC both in air and inert atmospheres.
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  • 2
    ISSN: 1433-075X
    Keywords: Key words Microwave ; Synthesis ; Processing ; WC ; BaTiO3 ; Hydrothermal
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The innovations in microwave processing of ceramics have been dominated to date by serendipitous discovery, because the interaction between such radiation as delivered via available tools and the materials of widely varying properties, sizes, and shapes is so complex that it has defied quantitative analysis. For over 10 years a wide variety of inorganic ceramic and semiconducting materials have been synthesized, sintered, and reacted in our own labs, including microwave hydrothermal synthesis of metals, ferrites, and electroceramic phases. These local results are summarized and used as the reference point for reporting on two different new advances: sintering of WC-Co composite tool bits and other similar objects in under 15 min, while retaining extremely fine microstructures, without any grain growth inhibitors; using reduced TiO2 or Ta2O5 for the synthesis of phases such as BaTiO3, Ba3MgTa2O9, and Pb(Zr.Ti)O3 in a few minutes in a 2.45 GHz field at the astonishing temperatures of 300–700 ºC.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1433-075X
    Keywords: Key words Transmission electron microscopy ; Defects ; Wire drawing ; Failure ; ”Copper rain” ; Solidification phenomena
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Utilizing transmission electron microscopy (TEM), we have discovered a defect, which we call a void-lobed defect, in copper precursor rod and in sections of failed copper magnet wire. This defect is the origin of, or basis for, stringers or stringer defects in copper rod and wire, and consists of a contaminated, solidified copper microdroplet which is entrained in the solidifying rod, and is disconnected at its ends in the rod drawing direction, forming voids and elongated void lobes at the ends of the copper inclusion. Utilizing a novel technique to build up fine wires by copper electroplating, we have followed their progress in the magnet-wire drawing process using TEM. Detailed examination of wire failures showed that these defects are forced to the wire axis by successive drawing stages forming coalesced void/debris channels which provide a mechanism for failure. There was no evidence for copper oxides either as stringer components or in connection with debris channels in failed wires. These defects and therefore stringers in precursor rod are created as contaminated or reacted ”copper rain” prior to the solidification stage, and entrained in the rod. The process is usually intermittent and may be reduced or eliminated by properly adjusting the equilibrium chemistry through hydrogen control for oxygen reduction and steam formation; thereby producing high-quality rod for magnet wire produciton. This is an extraordinary example of TEM application in the solution of a contemporary industrial problem which has been otherwise intractable.
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  • 4
    ISSN: 1433-075X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Materials research innovations 1 (1997), S. 71-76 
    ISSN: 1433-075X
    Keywords: Keywords Chemical hardness ; Hardness ; Chemical reactivity ; Elastic stiffness ; Polarizability ; Dislocation mobility ; Structural stability ; Band gap ; Molecular stability
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  A common theme links chemical, mechanical, and optical hardnesses. It is the gap in the bonding energy spectra of materials. This gap determines molecular stability, and therefore ”chemical hardness”. Chemists call it the LUMO-HOMO gap between anti-bonding and bonding molecular orbitals. Physicists call it the band-gap between the conduction and valence energy bands. It forms a basis of various properties; including: chemical reactivity, elastic stiffnesses, plastic flow resistance (dislocation mobility), crystal structure stability, and optical polarizability (refractive indices). These unifying relationships are the subject here. Manipulation of these gaps and their cross-connections plays a critical role in current technology and has led to recent new devices.
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  • 6
    ISSN: 1433-075X
    Keywords: Keywords Microwave processing ; Microwave effect ; Ponderomotive force ; Ionic transport ; Nonthermal ; Sintering
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Numerous observations have been reported in the literature of enhanced mass transport and solid-state reaction rates during microwave heating or processing of a variety of ceramic, glass, and polymer materials. These empirical observations of microwave enhancements have been broadly called the ”microwave effect”. In the past, these claims have been the source of significant controversy, due in part to the lack of a credible and verifiable theoretical explanation. Moreover, certain notable microwave heating experiments have failed to observe any resolvable reaction or transport rate enhancements. This paper describes a series of recent experimental and numerical investigations that have established the fact that strong microwave electric fields induce a (previously unknown) nonlinear driving force for (ionic) mass transport near surfaces and structural interfaces (e.g., grain boundaries) in ceramic materials. This driving force can influence reaction kinetics by enhancing mass transport rates in heterogeneous solid-state reactions. Most of the previously reported observations regarding ”microwave effects” (both for and against) are consistent with the characteristics of this newly identified microwave-induced driving force.
    Type of Medium: Electronic Resource
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  • 7
    ISSN: 1433-075X
    Keywords: Keywords Microwave heating ; Microwave processing ; Microwave susceptor ; Casket ; Microwave cavity ; Single-mode cavity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  This study demonstrates experimentally that for a fixed microwave input power, the steady-state temperature for microwave ”caskets” (specimen enclosures) can vary significantly as the casket geometry changes. Also, the steady-state casket temperatures are very similar for caskets with and without an included specimen, as long as the specimen’s volume and mass are small compared to the casket’s volume and mass. In addition to the experimental work, a simple model is presented that describes the variation in steady-state temperature as a function of casket geometry. The model also describes how the steady-state casket temperature scales with microwave input power level. For the single-mode microwave cavity operated at 2.45 GHz that is used in this study, the steady-state casket temperature at 600 Watts of input power ranged from 1112°C to 1519°C as the casket geometry changed for caskets composed of porous zirconia cylinders with aluminosilicate end pla tes.
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 1433-075X
    Keywords: Key words Wood ; Composites ; Ceramics ; Carbon/carbon ; Carbon/epoxy ; Porous carbons ; Lignocellulosics ; Processing ; Net-shape
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  This research demonstrated for the first time a method for producing net shape polymer, ceramic and carbon composites using wood as a precursor. The conversion of wood to carbon has been practiced for centuries but the controlled thermal decomposition to form a monolithic carbon to be used as a template for composites as demonstrated by this research is a unique discovery. This was accomplished by thermal decomposition of wood under controlled conditions to produce a crack-free porous carbon monolith which was readily shaped by conventional methods. The shaped carbons have converted to carbon/polymer composites, carbon/carbon composites, ceramics, and ceramic composites without significant changes in dimensions. This research has demonstrated that composites derived from wood can eliminate several expensive processing steps. Specifically, no fiber lay-up or powder consolidation is required, and final grinding and polishing steps are minimized.
    Type of Medium: Electronic Resource
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  • 9
    ISSN: 1433-075X
    Keywords: Key words Standard free energy ; Unit volume ; Selective oxidation ; Metal oxide ; Metal sulphide ; Metal carbide ; Metal nitride
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  The present paper introduces a thermodynamic parameter, the standard free energy changes of formation of oxide, sulphide, carbide and nitride per unit volume, as a criterion for comparing the formation tendency of these compounds. The diagrams for the standard free energy change of formation of common oxides, sulphides, carbides and nitrides per unit volume vs temperature have been calculated and established based on the available thermodynamic data. It is believed that these diagrams can provide better explanations to some oxidation phenomena including the effects of reactive elements on the selective oxidation of Cr2O3 and Al2O3.
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 1433-075X
    Keywords: Keywords Composites ; Metal composites ; Microtomy ; Sample preparation ; TEM samples ; Ultra-microtomy
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract  Two variations of a new method of TEM metal sample preparation are proposed, hereby labeled RUM1 and RUM2, for ”reverse ultra-microtomy” 1 and 2, respectively. With these techniques, the TEM samples are formed from bulk specimens by successively slicing off layers, with an ultra-microtome, until the remnant is partially thinned to electron transparency. This requires the sample to be embedded with excellent adhesion in a mounting material whose mechanical properties resemble that of the sample. While these methods are by far slower than ordinary microtomy wherein the individual slices are used as samples, preparation times are comparable to those for creating TEM samples by standard techniques. Furthermore, the methods (i) can be used where electropolishing fails, (ii) can be favorably applied to finely layered materials and composites, (iii) permit studies of near-surface structure gradients, and (iv) permit the simultaneous observation of an original surface and the underlying material. The methods have been successfully demonstrated through comparisons between samples created through RUM1 and 2 and standard TEM samples. Artifacts caused by the new method of reverse microtoming are shown to be very much reduced compared to direct microtoming.
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