Ceramic flake formation in the aluminosilicate system by plasma spraying

Abstract

Alumina and aluminosilicate flakes with compositions Al2O3, 3Al(2)O(3) center dot 2SiO(2) and Al2O3 center dot 2SiO(2) have been produced from commercial raw materials using a direct current plasma spray process in air. The microstructure and phase constitution of the as-sprayed flakes were examined with optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Changes in phase constitution of the flakes with heat-treatment were examined using differential thermal analysis (DTA) and XRD of heat-treated samples. The as-sprayed Al2O3 flakes consisted of alpha-Al2O3 phase plus a minor gamma- Al2O3 phase. The. - phase could be removed by heat treating the flakes at 1300 degrees C for 2 h. The aluminosilicate flakes consisted of 3Al(2)O(3): 2SiO(2) ( mullite) and an amorphous phase which crystallised to 3Al(2)O(3): 2SiO(2) ( mullite) after heat treatment at 1100 degrees C for 2 h. These flakes may find applications as high temperature thermal insulation materials. (C) 2005 Springer Science + Business Media, Inc.