Fired porcelain microstructures revisited

The microstructure of standard commercial porcelain consists of alpha-quart z grains held in a complex matrix. Quartz grains are surrounded by amorphou s silica-rich solution rims while the matrix contains clay relicts of small (similar to 200 nm x 40 nm x 40 nm) primary (2Al(2)O(3):1SiO(2)) mullite c rystals in aluminosilicate glass and feldspar relicts of acicular (>1 mu m long) secondary (3Al(2)O(3):2SiO(2)) mullite in potassium aluminosilicate g lass. A continuous increase in mullite crystal size from the clay-feldspar relict interface to the feldspar relict center and their compositions indic ate a transformation from primary to secondary mullite. In aluminous porcel ain, corundum grains are observed in addition to alpha-quartz and regions o f clay and feldspar relicts. Small (similar to 50 mm x 10 nm x 10 nm) terti ary mullite crystals (formed by precipitation from Al2O3-rich glass) were d etected adjacent to these corundum grains.