Development and High Resistance in Severe Environment of β-Sialon Composites Materials with Controlled Microstructure

点击翻译按钮获取中文摘要

(1)F-doped sialons (β-, o-, and α/β-types) of a single phase were successfully synthesized using AIFィイD23ィエD2 or topaz as a reagent of fluorine at 1500-1780℃ by HIPing method. Fluorine was found to exist in grassy phase of all the sintered pellets of the sailons by TEM-EDX. The F-doped β-sialon showed much better corrosion resistance in NaCl vapors at 1300℃ than the pure β-silaon.(2) The wet oxidation of the α-SiィイD23ィエD2NィイD24ィエD2 and theβ-sialon (SiィイD26-zィエD2AlィイD2zィエD2OィイD2zィエD2NィイD28-zィエD2, z = 1, 2 and 3) powders at temperatures of 1000℃ to 13000℃ in 0〜20 kPa water vapor was followed by XRD, ィイD129ィエD1Si and ィイD117ィエD1O MAS NMR, transmission electron microscope (TEM), and thermogravimetric analysis. A considerable difference was not found in the oxide products and microstructure of the samples obtained by the wet and dry oxidation; the oxide phase was composed of very fine acicular mullite grains and amorphous SiOィイD22ィエD2. The oxidation was described by the linear kinetics in two successive early stages at reacted fractions of 0-20%, followed by the parabolic kinetics represented by the Ginstling-Brounshtein equation at fractions of 20〜80%. The wet oxidation rates in the diffusion process were 1.5〜10 times greater than in the dry oxidation, with the activation energies of 440, 350, 330 and 240 kJ molィイD1-1ィエD1 for the α-SiィイD23ィエD2NィイD24ィエD2, and the z = 1, 2 and 3 sialons, respectively. The dependency of the rate on water vapor pressure (0〜20 kPa) in the diffusion process was parabolic, indicative of the diffusion of OHィイD1-ィエD1. ィイD117ィエD1O atoms from HィイD22ィエD2ィイD117ィエD1O water vapor were detected in the oxide product, SiOィイD22ィエD2 and mullite by ィイD117ィエD1O MAS NMR when the sialon was oxidized in Ar/HィイD22ィエD2ィイD117ィエD1O and Ar/OィイD22ィエD2/HィイD22ィエD2ィイD117ィエD1O, indicating that oxygen atoms from water vapor make an nearly equal amount of mullite and SiOィイD22ィエD2.