| Popis: |
The isothermal hot corrosion behavior of reaction -sintered Si 3 N 4 was evaluated at 1173 to 1293 K for 1.8 to 36 ks. Measurement of mass change, X-ray diffraction, surface observation and EPMA analysis were conducted during and after corrosion experiment. At temperatures above 1223 K mass of specimen slightly increased initially and then decreased rapidly with time. This decrease in mass was due to dissolution of Si 3 N 4 in molten Na 2 SO 4 evolving acidic and reductive gas. Below 1173 K mass-loss was not observed. Corrosion rate increased with increasing temperature. And the rate in argon was faster than that in oxygen. A glassy phase was formed on corroding specimen, and many small holes were observed on the phase. No corrosion product was identified by X-ray diffraction. Based in the above-mentioned experimental results, reaction mechanism was discussed. |
