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January 5th, 2012

Previews from the Intl. Journal of Applied Ceramic Technology

Published on January 5th, 2012 | By: Eileen De Guire

New papers that have been accepted for publication in the International Journal of Applied Ceramic Technology are posted to “Early View” on the Wiley website and can be read even before the issue is printed. Below are summaries of selected papers currently available via Early View.

All members of The American Ceramic Society receive free online access to ACT. To access any of the ACerS journals, or to become a member, visit www.ceramics.org.

Joining of Sintered Silicon Carbide Ceramics Using Sodium Borosilicate Glass as the Solder
Zhaohua Luo, Dongliang Jiang, Jingxian Zhang, Qingling Lin, Zhongming Chen and Zhengren Huang

This team of researchers from the Shanghai Institute of Ceramics developed a sodium borosilicate glass powder (Si:B:Na molar ratio of 53:44:6) as a solder to join sintered SiC ceramics. The team reports that the coefficient of thermal expansion of the glass matches the SiC substrate well at low temperature and that the wettability of the solder on SiC substrate is excellent above 1150°C. The team also reports that good adhesion between the SiC substrate and solder layer was achieved.

Image: Interface between the interlayer (right side) and SiC substrate (left side). Credit: ACT; Wiley.

A Thermoanalytical Study of the Conversion of Amorphous Si-Ti-C-O Fibers to SiC
Nathan S. Jacobson and Sara E. Kline

Jacobson and Kline, NASA Glenn Research Center, studied the conversion of polytitanocarbosilane fibers to SiC from 1400°C to 1600°C using thermogravimetry, X-ray diffractometry and scanning electron microscopy. Their study suggests that a chemical reaction step is rate-limiting, there is conversion of an amorphous phase to crystalline SiC and there is development of internal porosity and large grains on the fiber surface.

Image: Cross-section of LoxM fiber heat-treated at 1600 °C for 4h. The white dashed line delineates an inner core region with more porosity. Credit: ACT; Wiley.

Tailoring the Relative Si3N4 and SiC Contents in Si3N4/SiC Nanopowders through Carbothermic Reduction and Nitridation of Silica Fume
Jyothi Suri, Leon L. Shaw and Mahmoud F. Zawrah

This team of researchers from the United States and Egypt reports that it has, for the first time, synthesized nanostructured Si3N4/SiC composite powders from waste silica fume using an integrated mechanical and thermal activation process. They conclude that the carbothermic reduction and nitridation temperature as well as the graphite concentration in the starting SiO2 + C mixture are the important parameters to obtain the nanopowders and control their crystal sizes (as small as 17 nanometers for SiC and 42 nanometers for Si3N4).

Image: SEM images of graphite: (a) before and (b) after ball milling alone for 6 h. Credit: ACT; Wiley.

Synthesis of Ceramic Bonded Carbon Using SiC-Coated Carbon Particles and Spark Plasma Sintering
Masaharu Nakamura, Tetsuro Tojo, Makio Naito and Yoshinari Miyamoto

These Japanese researchers used SiO powders and a chemical vapor reaction method to form a dense SiC coating on carbon particles by controlling atmosphere, temperature, time and SiO/C weight ratio. They used spark plasma sintering to sinter the SiC-coated carbon particles. They report that the product—called ceramic bonded carbon—can be easily joined to SiC ceramics using spark plasma sintering.

Image: Photo of a SiC/CBC nut machined with an internal thread of 6 mm diameter and 0.75 mm pitch. Credit: ACT; Wiley.

Effects and Control of Polymer-Converted Carbon Impurity in Synthesizing Continuous Boron Nitride Nanofibers by Electrospinning
Yejun Qiu, Jie Yu, Jing Yin and Xiaosong Zhou

This team of researchers from China reports that it introduced oxygen and ammonia gases simultaneously to effectively control and remove—by varying O2/NH3 ratio, temperature, time and gas flow rate—the carbon impurity that results from using a polymer as a thickener in the precursor solution method of preparing boron nitride nanofibers by electrospinning.

Image: SEM images of as-spun B2O3/PVB (polyvinylbutyral) composite fibers prepared using different PVB concentrations. Credit: ACT; Wiley.

Benefits of the LTCC Substrate Configuration with an Air-Gap for Realization of RF Inductor with High Q-Factor and SRF
Goran J. Radosavljević, Andrea M. Marić, Walter Smetana and Ljiljana D. Živanov

This research term from Austria and Serbia placed low-temperature cofired ceramic meander-type-structured inductors on various substrates with the placement of an air-gap beneath the inductor. The team reported that it achieved greater than 30-percent increase in quality factor and greater than 55-percent increase of operating frequency range width compared with inductors on standard substrate configurations.

Image: (a) Measurement of set-up and calibration and (b) moment of measurement. Credit: ACT; Wiley.

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