The Preparation Of Anatase TiO₂ Crystalline Glaze And Its Photocatalytic Properties

Anatase-type titanium dioxide is a widely used photocatalytic material.However,anatase is unstable at high temperatures,which constrains its practical application in ceramics.Currently,photocatalytic ceramics are commonly prepared by coating TiO₂ films and post heat treating at relatively low temperatures.Nevertheless,the coating prepared by this method has poor wear resistance and poor cohesion with the ceramic substrates,reducing product lifetime of the ceramics.In this research,we report a method for the preparation of anatase glass-ceramic glaze by crystallization.After a one-step sintering process of high-temperature sintering and low-temperature soaking,the glass-ceramic glaze with nanosized anatase were prepared.SEM results shows that there are many anatase grains with a mean size of 42.9±8.9 nm distributing in the glaze layer uniformly.Crystallization process of the glaze was studied by TG-DSC,XRD,hot-stage microscope and so on.It shows that the frit precipitates at first at the heating stage and then it is fired to glass melt at high temperature.At last the melt precipitates again at the cooling and soaking stage.The crystal forms and quantity precipitated in glaze are dependent on thermal schedule at the cooling and soaking stage.When the soaking temperature was higher than 740°C,TiO₂-B and anatase precipitates in the glaze;when the soaking temperature was at 700⁷20°C,much anatase and traces of rutile precipitate in the glaze;When the soaking temperature was at 610⁶80°C,only anatase precipitates in the glaze.The crystallization activation energies of anatase and rutile were calculated by the Kissinger and Ozawa methods:for anatase,131.3 kJ/mol and 133.3 kJ/mol,respectively;for rutile,173.2 kJ/mol and 176.6 kJ/mol,respectively.The average avrami index n for anatase and rutile deduced from Augis-Bennett equation are 1.74±0.30 and1.09±0.27,respectively,indicating that the growth of anatase is diffusion-controlled in a three-dimension way and that the growth of anatase transforming into rutile is diffusion-controlled in a two-dimension way.The crystallization mechanism of two crystals are both volume crystallization.The viscosity curve determined by VFT equation indicates that the presence of the nano-sized anatase in glaze is attributed to high viscosity of the glaze melt at crystallization temperature and locally higher viscosity due to the precipitation of TiO₂.The research used the crystalline glaze soaked at 720°C for 30min to evaluate its photocatalytic property,microhardness and cleanliness.With HF etching,the grains n?mber and surface area of anatase exposed on glaze surface are different,resulting in the difference of photocatalytic property.When etched with 2 vol%HF solution for 45 s,the crystalline glaze has the optimal photocatalytic performance under UV light.After 35 h,the methyl orange is largely degraded,and its reaction rate index is 0.081 h^-1.The cleanability of the glaze is superior to the floor-glaze tiles and door wall tiles,comparable to the commercially available external tiles.Its microhardness is 6.3±0.2 GPa,equivalent to the traditional household porcelain and architectural and sanitary porcelain.Results shows there is no obvious change for the cleanability and mirohardness before and after HF etching.Finally,the effects of F,P₂O₅,TiO₂ nucleating agents and Al₂O₃ component on the crystallization of glaze were studied.The results shows the addition of TiO₂ component will increase the content of anatase in glaze.The addition of Al₂O₃ component has no obvious effect on crystalline of the glaze,but it can adjust sintering temperature of the glaze.By changing the addition content of Al₂O₃,the firing temperature of glaze can vary between1180°C to 1220°C,adoptable to the sintering schedule of ceramic tiles and sanitary wares in Guangdong province.