Transparent glaze containing high-alumina glass frit: Batch-to-melt conversion

•High alumina frits is of technological interest in the field of transparent glazes.•The crystallization and melting behavior of a high alumina frit is investigated•A transparent glaze with improved hardness was obtained by using a high alumina frit. The use of high alumina (HA) glass frits in the production of transparent glazes is of potential technological interest due to their excellent mechanical properties. However, their strong tendency to crystallize limits their practical application. A transparent glaze was obtained by adding 30% by weight of the HA frit to a low-melting glaze fired at 1453 K for 30 min with a hardness between 5.92 GPa and 6.46 GPa. The crystallization and melting behavior of an HA frit mixed with a low-melting glaze model batch is investigated by studying the interaction between a compacted raw low-melting glaze placed on the polished surface of bulk HA glass. With increasing temperature, the low-melting glaze batch melts while CaAl2Si2O8 and MgAl2O4 crystallize in the HA frit. The melt surrounding the HA frit decreases the number of active nucleation sites weakening surface crystallization. In addition, the alkali cations in the melt tend to diffuse into the crystallized HA frit, reducing the viscosity of the layer surrounding the crystals, which accelerates their dissolution. The results provide information on the batch-to-melt conversion mechanism of high alumina content transparent glazes.