INFLUENCE OF FLUORIDES ON POLYMORPHOUS TRANSFORMATION OF ALPHA-AL2O3 FORMATION

Results of investigation into the influence of added fluorides (AIF(3) , CaF2, MgF2, LiF, NaF and Na(3)A1F(6), up to 10%) at the temperature of the polymorphous transformation gamma-Al2O3 double right arrow alph a-Al2O3 are presented. It was determined that, at a heating rate of 10 degrees C min(-1), addition of 2% fluoride decreases the transformati on temperature by 400 degrees C for AIF(3), by 220 degrees C for MgF2, and by 130 degrees C for CaF2. The other fluorides have no effect. Th e mechanism of the influence is determined, and it can be explained by the formation of fluorine bridges between fluoride cations and alumin ium on the gamma-Al2O3 surface.