ISSN:
1573-4803
Source:
Springer Online Journal Archives 1860-2000
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Abstract Impurities in raw Si3N4 powders remain in intergranular glassy phases in Si3N4 and Si2N2O ceramics and degrade their high-temperature properties. Fluorine is one of the typical impurities in the raw powders. The oxidation rate of Si2N2O ceramics doped with Gd2O3 greatly varied with a difference in impurity contents (especially F) of the raw Si3N4 powders used. When a high concentration of impurity existed in the intergranular glassy phase, the rate of oxidation was controlled by O2− diffusion through the glassy phase in the partly oxidized scale and unoxidized body; outward diffusion of Gd3+ occurred concurrently. On the other hand, when the impurity contents in the intergranular glassy phase was very low, the diffusion rate of ions (Gd3+, O2−, etc.) in the glassy phase became very low (substantially zero in the oxidation at 1300°C). Only cristobalite (SiO2) was formed on the surface. The rate of oxidation was controlled by O2 diffusion through the cristobalite layer, and was very low.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1023/A:1004866726930
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