Fired Porcelain Microstructures Revisited

Abstract

The microstructure of standard commercial porcelain consists of alpha‐quartz grains held in a complex matrix. Quartz grains are surrounded by amorphous silica‐rich solution rims while the matrix contains clay relicts of small (~200 nm × 40 nm × 40 nm) primary (2Al2O3:1SiO2) mullite crystals in aluminosilicate glass and feldspar relicts of acicular (>1 µm long) secondary (3Al2O3:2SiO2) mullite in potassium aluminosilicate glass. A continuous increase in mullite crystal size from the clay‐feldspar relict interface to the feldspar relict center and their compositions indicate a transformation from primary to secondary mullite. In aluminous porcelain, corundum grains are observed in addition to alpha‐quartz and regions of clay and feldspar relicts. Small (~50 nm × 10 nm × 10 nm) tertiary mullite crystals (formed by precipitation from Al2O3‐rich glass) were detected adjacent to these corundum grains.