Study On The Preparation And Crystallization Kinetics Of Zinc Silicate Crystalline Glaze

Zn₂SiO₄ materials have attracted great interests in recently times owing to their potentially wide applications including glaze,coating material,paints and optical hosts.They are widely known to possess excellent phy-chemical properties like good environmental adaptability,humidity resistance and chemical stability.Among them,Zn₂SiO₄ crystalline glaze is widely used in ceramic decoration.Zinc silicate crystalline glaze,mixed with various colorants,shows more outstanding artistic value,making it better for art appreciation and decoration.Zn₂SiO₄ crystalline glaze was prepared using quartz,albite,kaolin,limestone and calcinated zinc oxide as raw materials by controlling the sintering temperature in this paper.With the increasing ZnO contents in the glaze,the size of zinc silicate crystals in fired glaze firstly increases and then decreases,reaching the maximum value when the adding content of ZnO is about 24 wt %.Opacifying effect appears with the decreasing silica-to-alumina mole ratio in the glaze.Great silica-to-alumina mole ratio will inhibit the crystallization process.With the decreasing silicon to calcium mole ratio,matt glaze will appear in the fired glaze.Based on silicate crystalline glaze,the calcinated zinc oxide are passed through40⁶0 mesh and employed as crystal nucleus.Under the firing system of 1140 ? for 120 min,crystallization degree reaches the maximum.With longer ball-milling time,the number of crystal flowers in the fired crystalline glaze increases,but the size for single crystal becomes smaller.With longer holding time in the crystallization process,the crystallization becomes greater.During the cooling process from sintering temperature to holing temperature,crystallization becomes greater with decreased cooling rate.The temperature,corresponding to obvious crystallization peak in the curves of thermogravimetric analysis?DTA?conducted with different heating rate,can be fitted into Kissinger law for the calculation of activation energy E.Using three different kinds of colorants MnO₂,Fe₂O₃,CuO,too much colorants contents will inhibit the growth of crystal flower in the glaze.Using colorimetric analysis,glaze colors are observed to gradually become deep dark and gloss also decreases to a certain degree.Chromaticity nearly remains unchangable for both crystallization area and non-crystallization area.On the analysis of the microscopic morphology and EDS contents,morphology for the doped zinc silicate crystalline glaze shows the continuous fibrous arrangement and Fe,Cu ions prefentially enter glass phase.With longer ball-milling time,the color arrangement for the doped samples becomes more uniform.Rapid cooling rate will prevent the crystallization of liquid,crystal growth and also cause the non-uniformality of crystallization process.Therefore rational cooling system will help promote the growth of crystalline.On the basis of MnO₂ doped zinc silicate crystalline glaze,great efforts are made to investigate the impact of firing system on crystallization process.Results show that Zn₂SiO₄ crystals become gradually bigger in size with longer holding time and crystallization degree reaches the maximum under the firing temperature 1140? for170 min.Through the simulation of dynamic analysis,Avrami pre-exponents for MnO₂ doped Zn₂SiO₄ crystals with different holding temperature,are n1110?=0.92,n1140?=1.38 and n1170?=1.27,respectively,indicating the transformation from diffusion mechanism to nucleation mechanism for Zn₂SiO₄ crystals.Through the thermal-dynamic analysis,the temperature,corresponding to obvious crystallization peak in the curves of thermogravimetric analysis?DTA?conducted with different heating rate,can be fitted into Kissinger law for the calculation of activation energy E,which is calculated to be210.7 kJ/mol for the MnO₂ doped Zn₂SiO₄ samples.