Preparation and Application of Apatite–TiO[sub.2] Composite Opacifier: Preventing Titanium Glaze Yellowing through Pre-Combination

In order to enhance the degree of binding reaction of TiO[sub.2] in titanium-containing ceramic glazes and prevent the reaction of its transformation into rutile to eliminate the yellowing phenomenon of the glaze surface, an apatite–TiO[sub.2] composite opacifier (ATO) was prepared through the mechanical grinding of hydroxyapatite and anatase TiO[sub.2]. The properties, opacification mechanism, and yellowing inhibition of the prepared ceramic glazes were studied. The results show that the ATO is characterized by a uniform coating of TiO[sub.2] on the surface of the apatite and the formation of close chemical bonding between the apatite and TiO[sub.2]. The ceramic glaze surface when using an ATO has a white appearance and excellent opacification performance. When an ATO was used, the L*, a*, and b* values of the glaze were 89.99, −0.85, and 3.37, respectively, which were comparable to those of a ZrSiO[sub.4] glaze (L*, a*, and b[sup.*] were 88.24, −0.02, and 2.29, respectively). The opacification of the glaze was slightly lower than that of the TiO[sub.2] glaze (L* value was 92.13), but the appearance changed from yellow to the white of the TiO[sub.2] glaze (b* value was 9.18). The ceramic glaze layer when using an ATO mainly consists of titanite, glass phase, and a small amount of quartz, and the opacification mechanism is the crystallization of the generated titanite. ATOs can play an active role in solving the critical problem that arises when TiO[sub.2] replaces ZrSiO[sub.4] as an opacifier.