ALBERT — All Library Books, journals and Electronic Records Telegrafenberg

1

Electronic Resource

Feedback-Controlled Firing of Reaction-Bonded Aluminum Oxide (2005)

Watson, Matthew J. ; Chan, Helen M. ; Harmer, Martin P. ; [et al.]

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

add to mindlist on the mindlist

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-bonded aluminum oxide (RBAO) process utilizes the oxidation of intensely milled aluminum/alumina powder compacts that are heat treated in air to make alumina-based ceramics. RBAO samples are typically oxidized in a furnace which is heated at 1°C/min to 1100°C. Heat-treating samples with a characteristic dimension 〉1 mm, without adjusting the furnace temperature program, usually results in a cracked ceramic. Cracking is caused by the excessive thermal and chemical stresses that result from steep temperature gradients (〉30°C/mm) and compositional gradients (〉5000 mol·(m3·mm)−1), which develop under the deleterious ignition and shrinking core reaction regimes. While adjustments to the furnace temperature program based on continuum models have had some success, the use of feedback-controlled firing is investigated as a means to avoid the furnace temperature program design step and to decrease the firing time. Feedback-controlled firing is shown to improve yields and significantly reduce the time required to completely oxidize the aluminum. For example, a 16 g sample with a characteristic dimension of 7.56 mm, which previously took 〉100 h to oxidize completely, was successfully oxidized crack free in 18.3 h using feedback control. Using the typical heat-treatment cycle, a 1 mm sample was fired in 18 h. With feedback-controlled firing, the same sized sample was fired in only 5 h.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00639.x

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

2

Electronic Resource

Effect of Alumina Additions on Microstructural Aspects of the β to α Transformation in Tantalum (V) Oxide (2005)

Wu, Suxing ; Chan, Helen M. ; Harmer, Martin P.

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

add to mindlist on the mindlist

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: Tantalum (V) oxide (Ta2O5) has potential applications as part of an environmental barrier coating system for Si3N4-based turbine components. However, at elevated temperatures, Ta2O5 undergoes a phase transformation from the orthorhombic (β) phase to the tetragonal phase (α), which is undesirable because of the associated volume change. The purpose of the present work was to study the effect of alumina additions (0–5 wt%) on the β to α transformation temperature, and associated modifications to the Ta2O5 microstructure. Sintered microstructures were characterized using SEM (scanning electron microscopy), and XRD (X-ray diffraction) was used to identify the phases present at room temperature. It was found that for undoped Ta2O5, transformation of the low-temperature β-phase begins at ∼1300°C, and leads to extensive microcracking of the sintered sample. For samples containing alumina, an increase in the transformation temperature was observed. The solubility limit of alumina in Ta2O5 was between 1 and 3 wt%; for samples in which this was exceeded, the AlTaO4 second and phase particles were seen to be highly effective at inhibiting grain growth.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00450.x

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

3

Electronic Resource

Processing and Properties of ZrO2-Containing Reaction-Bonded Aluminum Oxide with High Initial Aluminum Contents (2005)

Sheedy, Paul M. ; Caram, Hugo S. ; Chan, Helen M. ; [et al.]

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

add to mindlist on the mindlist

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-bonded aluminum oxide (RBAO) process relies upon the oxidation of Al/Al2O3 powder compacts, and many of its associated advantages stem from the presence of the aluminum in the green powder. Higher aluminum contents in the starting powders allow for higher green strengths, densities, and lower overall shrinkage, all while producing a fine-grained, high-strength sintered material. However, it is evident that the reaction and sintering of ZrO2-containing RBAO with higher aluminum contents are more challenging. Therefore, in this study, the effects of aluminum content on the processing, structure, and properties of RBAO ceramics were comprehensively characterized. It was found that RBAO samples with high aluminum contents were more prone to cracking during reaction and even when successfully fired were not able to be sintered to full density. Despite these characteristics, RBAO samples with increasing aluminum contents showed no significant degradation in mechanical properties.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00392.x

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

4

Electronic Resource

Effects of Aluminum and Zirconia Contents on the Sintering of Reaction-Bonded Aluminum Oxide Ceramics (2005)

Sheedy, Paul M. ; Caram, Hugo S. ; Chan, Helen M. ; [et al.]

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

add to mindlist on the mindlist

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-bonded aluminum oxide (RBAO) process is an attractive alternative to the conventional processing of Al2O3-based ceramics. The most attractive features of the process are the high strengths, densities, and easy machinability of the green powder compacts, and the low shrinkage and high strengths of the sintered ceramics. These advantages result from the presence of aluminum in the green bodies and are enhanced further with increasing aluminum contents. However, it is apparent that ZrO2-containing RBAO powders with higher aluminum contents (〉45 vol%) are increasingly more difficult to densify, as the start of densification is delayed (shifted to higher temperatures) and the densification rates are decreased. Ultimately, this results in a decrease in the limiting density to which the RBAO ceramic may be sintered. In this study, the cooperative effects of ZrO2 and aluminum contents on the sintering of RBAO ceramics are discussed in terms of densification behavior and microstructural analysis.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00393.x

Permalink

	Location	Call Number	Expected	Availability

Others were also interested in ...

Paper (German National Licenses)

Fulltext

5

Electronic Resource

Effect of AC-Powered Water Electrolysis on the Structural and Optical Properties of Indium Tin Oxide Thin Films (2005)

Wang, Yu ; Chen, Wan Ping ; Cheng, K. C. ; [et al.]

Oxford, UK : Blackwell Science Inc

Journal of the American Ceramic Society 88 (2005), S. 0

add to mindlist on the mindlist

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 changes in the structure and optical properties of indium tin oxide (ITO) thin films that were subjected to water electrolysis using an alternating current power source were investigated. X-ray diffraction indicated that the film was reduced to metallic indium after the treatment. Scanning electron microscopy revealed that the film became porous after the treatment. These structural changes had led to a dramatic degradation in the optical properties of ITO. The electrochemical mechanism responsible for the changes was discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1111/j.1551-2916.2005.00191.x

Permalink