A Study on the Preparation of Alumina Powders from Bauxite by Wet Acid Process and Their Utilization (II) : Mullitization of Pyrophyllite-Aluminum Hydrate Gel Mixture

Bauxite로부터 습식산처리법에 의한 알루미나 분체의 제조 및 그 이용에 관한 연구(II) : 납석-Aluminum Hydrate Gel 혼합물의 Mullite화 거동

Pyrophyllite, which has low impurities, was used in the synthesis of mullite to decrease the glass phase, which can be formed from impurities such as alkali and alkali earth elemetns present in raw materials. But, as pyrophyllite has less alumina content than other aluminosilicate materials such as kaolin, more alumina sources were needed in the synthesis of mullite. In other to investigate the effect of particle size of alumina sources on the mullitization of pyrophyllite, aluminum hydrate gel and activated alumina were used. When activated alumina, which has large particle size, was added to pyrophyllite, mullitization was not fully accomplished regardless of temprature. In the case of aluminum hydrate gel, which has small particle size, the maximum yield of mullite was about 90.3% at 1700$^{\circ}C$, and grain size of mullite was larter than the case of activated alumina was added.