HIGH-TEMPERATURE CORROSION OF AIN-BASED COMPOSITE CERAMIC IN AIR AND IN COMBUSTION PRODUCTS OF COMMERCIAL FUEL. I. CORROSION OF CERAMIC COMPOSITES IN THE A1N - SIC SYSTEM IN AIR AND IN COMBUSTION PRODUCTS OF KEROSENE AND DIESEL FUEL

摘要

We have established that scale formed upon oxidation of ceramic composites in the AIN - SiC system in air at temperatures up to 1550 deg C contains mullite 3Al_2O_3-2SiO_2 as the major phase of the outer layer, which provides its high protective properties. The inner layer of the scale contains beta-SiO_2, alpha-Al_2O_3, and a fairly small amount of the oxynitride Al_10NgO_2,. In dry air, even at 1500 deg C with a long holding time (50 h), material of 50 mass percent AIN -50 mass percent SiC retains extremely high corrosion resistance. We have shown that upon prolonged (up to 240 h) oxidation of the indicated ceramic in the combustion atmosphere of S- and Na-containing fuels (kerosene and marine diesel fuel) at 1200-1300°C, along with mullite in the scale we see formation (due to reaction of beta -cristobalite with Al_2O_3, and gaseous Na_2O and NaOH) of low-viscosity silicate glass Na_2SiO_3 and NaAlSiO_4. Together with impurity Fe_2O_3 and gaseous Na_2SO_4, it partially destroys the protective mullite layer and leads to degradation of the protective properties of the scale.