The effect of B2O3 addition on the crystallization of amorphous TiO2–ZrO2 mixed oxide

The effect of B2O3 addition on the crystallization of amorphous TiO2–ZrO2 mixed oxide was investigated by X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG/DTA). TiO2–ZrO2 mixed oxide was prepared by co-precipitation method with aqueous ammonia as the precipitation reagent. Boric acid was used as a source of boria, and boria contents varied from 2 to 20 wt%. The results indicate that the addition of small amount of boria (<8 wt%) hinders the crystallization of amorphous TiO2–ZrO2 into a crystalline ZrTiO4 compound, while a larger amount of boria (⩾8 wt%) promotes the crystallization process. FT-IR spectroscopy and 11B MAS NMR results show that tetrahedral borate species predominate at low boria loading, and trigonal borate species increase with increasing boria loading. Thus it is concluded that highly dispersed tetrahedral BO4 units delay, while a build-up of trigonal BO3 promote, the crystallization of amorphous TiO2–ZrO2 to form ZrTiO4 crystals.