Preparation of low melting temperature, lead-free glaze by the sol–gel method

The sol–gel method was used to prepare low melting temperature, lead-free glaze based on the Na2O–K2O–CaO–ZnO–B2O3–Al2O3–SiO2 system. Tetraethoxysilane and aluminium sec-butoxide were used to replace silica and alumina, high melting constituents of the raw materials. A homogeneous gel was obtained through sequential hydrolysis by using 5 mol of water per mol of alkoxides, a mixture of ethanol and 2-butanol as solvent, and HCl as catalyst (pH ∼ 3). The remainder of the raw materials was processed to be coated by the gel. Gel as the coating layer was observed to be amorphous and homogeneously bonded around the raw materials particles and was very effective in lowering the melting temperature of the glaze by 30–130°C. This, however, depends on the amount of metal alkoxides used for replacement. TEM, SEM and porosimeter were used to characterize the glaze samples.