Role of borate frit as co-flux in tile bodies

Abstract

Borate frit was added to a ceramic composition in proportions between 3 and 100% (equivalent to 1-2%B₂O₃) as a partial substitute for feldspar. Fuming silica, soda feldspar, and local beneficiated clay from the Red Sea were the other components of the mix. Mixes were fast fired at temperatures between 1100 and 1250 °C. The addition of borate frit hindered the rate of dissolution of feldspar at temperatures up to 1175 °C, entering the structure of the mullite to form a borate-mullite solid solution at 1200 °C. This phase occurs in ‘swamps’ of very fine acicular networks which raise the modulus of rupture of the investigated mixes. Addition of 5% frit (equivalent to 1-1 1%B₂O₃) improved the modulus of rupture without affecting other properties. Higher additions shortened the maturing range.