Fired Porcelain Microstructures Revisited

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 (2Al 2 O 3 :1SiO 2 ) mullite crystals in aluminosilicate glass and feldspar relicts of acicular (>1 µm long) secondary (3Al 2 O 3 :2SiO 2 ) 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 Al 2 O 3 ‐rich glass) were detected adjacent to these corundum grains.