Preparation of TiO2–SiO2–CaCO3 composite opacifier by hydrophobic agglomeration and mechanism of inhibiting glaze yellowing.

This study investigates the preparation of TiO 2 –SiO 2 –CaCO 3 composite opacifier (Ti–Si–Ca) and its application in sanitary ceramic glazes. This approach involved hydrophobic agglomeration through surface-induced hydrophobic modification of TiO 2 , SiO 2 and CaCO 3 particles, along with the interactions between the hydrophobic carbon chains of modifiers. The Ti–Si–Ca formed a uniform coating with well-dispersed TiO 2 and SiO 2 particles on the CaCO 3 surface and strong bonds formed among TiO 2 , SiO 2 and CaCO 3 through interpenetration of the organic carbon chains on the surface. The Ti–Si–Ca was added to the basic glazes of sanitary ceramics at a proportion of 15.5 % and fired at 1125 °C for 4 h. The resulting white ceramic glazes had chromaticity values of L*, a*, and b* at 93.76, −0.73, and 3.89, respectively, demonstrating superior glaze opacity and whiteness compared to glazes made with a ZrSiO 4 opacifier (L* 90.30, b* 4.50). Glass and titanite phase make up the majority of the Ti–Si–Ca ceramic glazing layer of, with titanite serving as the opacified phase. Elimination of organic groups in Ti–Si–Ca during glaze firing formed interfacial chemical bonds among TiO 2 , SiO 2 and CaCO 3 , which facilitated the synthesis of titanite from the three components at high temperatures. The Ti–Si–Ca was a highly opaque glaze without yellowing because the organic groups of Ti–Si–Ca were removed and interfacial chemical bonds formed among the TiO 2 , SiO 2 and CaCO 3 in the low-temperature stage of glaze firing. This transformed the three phases into titanite at high temperature and eliminated free TiO 2. The formation of rutile TiO 2 , which has a yellow hue, at high temperatures was inhibited. This study provides a novel approach for low-energy preparation of TiO 2 –SiO 2 –CaCO 3 composite opacifiers and addresses the challenge of replacing ZrSiO 4 with TiO 2 in ceramic opacifiers. [ABSTRACT FROM AUTHOR]