Growth of Mullite Whiskers on Alumina Particle by Thermal Decomposition of Clay Minerals

Abstract

Whisker formation on alumina particles was attempted through growth of a number of fine mullite whiskers by the thermal decomposition of clay for porcelain at 1400 to 1600°C. After firing, the excess silica phase was hydrothermally dissolved in 2N NaOH solution at 180°C. The effect of firing temperature, and compositions of alumina and clay on the formation of mullite whiskers on alumina particles was investigated. In case of 18.8mass% alumina and 81.2mass% calcined clay, the growth of whiskers enhanced by the decomposition of clay was promoted, and alumina particles were coated with a number of mullite whiskers 50 to 200μm in length and 1 to 3μm in diameter just like sea urchin. Furthermore, alumina particles reacted with the excess amorphous silica in the fired clay to form small pillarlike mullite crystals in an alumina particle. But growth of whiskers was inhibited with increasing amount of alumina.