Carbothermal reactions of quartz and kaolinite with coal char

Reactions of quartz and kaolinite separately with coal char were examined a t temperatures up:to 1600 degrees C in argon and nitrogen atmospheres, by u sing thermogravimetric analysis combined with off-gas analysis. X-ray diffr action analysis was utilized to identify the reaction products. The carboth ermal reactions of quartz and kaolinite began, respectively, at temperature s as low as 1200 and 1150 degrees C, with the evolution of CO. The formatio n of reaction products was quite dependent on heating conditions. Under Ar, the main product(s) were beta-SiC for quartz, and beta-SIC and alpha-Al2O3 for kaolinite. Above 1550 degrees C, Al2O3 gradually formed Al4C3. Under N -2, the carbothermic nitridation occurred for both quartz and kaolinite in company with the formation of SiC. For quartz, the products were SiC and he xagonal beta-Si3N4 at 1600 degrees C; however, no crystalline nitrides were distinctly observed at 1400 degrees C. For the case of kaolinite, beta-Si3 N4 was appreciably formed at 1400 degrees C and it disappeared at 1600 degr ees C; above 1500 degrees C, AlN was formed from Al2O3. Similar changes of crystalline mineral phases were examined on heating three coals in the same manner. Silicon carbide (SiC) and aluminum nitride (AlN) were the major pr oducts in the coals treated under nitrogen at 1600 degrees C for 10 min. Th e formation of these compounds could be attributed primarily to the carboth ermal reactions of kaolinite and quartz inherent in coal.