Stoichiometric densification

In-pile self-diffusion of uranium in stoichiometric UO2 and UC has been measured by Hoh and Matzke 3J6). The diffusion coefficients obtained at a nominal irradiation temperature of 900°C and a fission rate of 1 x 10 //cm indicated that radiation-enhanced diffusion was higher by a factor of 10 to lO than determined by extrapolation of thermal diffusion coefficients. They suggested that the data are of immediate relevance to the understanding and the prediction of such quantities as in-pile sintering and densification, diffusion-controlled creep, and fission gas behavior in the outer zones of the fuel. 

Comparison of densification kinetics of polycrystalline and amorphous cordierite. The crystalline material is stoichiometric and has mean particle size of 8.6/tm the amorphous material is melted and crushed glass with some BjOj and P2O5 and slight excess of SiOj and MgO relative to stoichiometric cordierite and has a mean size of 10urn. From Ewsuk era/[109). 

The ZrBj-ZrC-SiC ceramic was synthesizedby reactive hot-pressing with amixture of Zr, B C and Si powders. The reaction of Zr-B C-Si powders commenced at 800 °C and non-stoichiometric formed preferentially a solution of B elements in Zr particles formed, which subsequently transformed to ZrB at approximately 900° C. The SiC phase was formed from the intermediate ZrC phase, and the residual B C and Si were formed at approximately 1100 °C. The final phases containing ZrBj, ZrC and SiC form when the temperature exceeded 1500 °C to a maximum temperature of 1700 °C. A fully dense ZrB -ZrC-SiC ceramic was obtained with a slow heating rate and significant holding time at a low temperature, and subsequently sintered for 60 min at 1900 °C with a pressure of 30 MPa for densification. The achievement of fully dense ZrB -ZrC-SiC ceramic resulted in a maximum Vickers... 

The objective of the experimental work described herein is to study the effect of oxygen contamination on the dispersion and subsequent densification behavior of ultra-high purity, laser-derived Si N powders. In particular, stoichiometric, amorphous powders approximately 17 nm in size, both exposed and unexposed to the ambient environment, were dispersed in a non-aqueous solution in an attempt to form high green density, uniformly packed green bodies with little or no O2 contamination. 

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