Effect of B2O3 on thermal reaction of kaolinite and MgO below 900 degrees C

Thermal reactions of mixtures of kaolinite and magnesium compounds in the m ole ratio of MgO :Al2O3: SiO2=1: 1:2 were investigated to obtain uniform am orphous materials containing magnesia below 900 degrees C. B2O3-added mixtu res of kaolinite and ultrafine particles of synthesized magnesium hydroxide with an average width of about 0.1 mu m resulted in the amorphous state at about 800-850 degrees C after decomposition of the starting materials. Add ition of B2O3 promoted the crystallization of mu-cordierite from amorphous state and then the crystallization of alpha-cordierite. Addition of B2O3 mo re than 1 mass% appeared to accelerate the direct crystallization of alpha- cordierite from the amorphous state, The complete transformation to alpha-c ordierite was obtained by firing at 900 degrees C for Ih. On the other hand , uniform amorphous materials were not obtained from mixtures of kaolinite and reagent-grade magnesium compounds with an average particle size of abou t 1 mu m by firing at 900 degrees C, because of insufficient diffusion reac tion of mixtures.