ALKALI CORROSION RESISTANT COATINGS FOR SI3N4 CERAMICS

摘要

The use of ceramic oxide coatings on silicon nitride is one method to improve its alkali corrosion resistance. Four oxide coatings, including (Ca-0.6, Mg-0.4) Zr-4(PO4)(6) (CMZP), zirconia, mullite and alumina, were examined. These coatings were applied on Si3N4 using both sol-gel and dip coating techniques. The coated and uncoated samples were exposed to sodium molten-salt and sodium-containing atmospheres at 1000 degrees C for 50 h. The weight loss of all the coated samples was less than that of the uncoated Si3N4 with CMZP-coated samples exhibiting the smallest weight loss. There was no decrease in the flexural strength of Si3N4 after coating with zirconia and CMZP, and a decrease in strength after coating with either mullite or alumina. After alkali exposure, the strength of the CMZP and zirconia coated samples were significantly higher than those of the mullite-coated, alumina-coated, and uncoated Si3N4. The observed behaviour is explained in terms of the microstructure and protection mechanisms. [References: 24]