Pearlescent BiOCl Pitment:Synthesis And Characterization

Bismuth oxychloride（BiOCl）is the first synthetic,non-toxic pearlescent pigment which has excellent physico-chemical properties and wide application.With the expansion of the market for BiOCl,the requirement for higher quality BiOCl increases correspondingly in recent years.The present synthetic methods of BiOCl have the disadvantages of small particle size,poor dispersity,irregular morphology and so on.The hydrolysis of bismuth oxychloride was investigated systematically.The studied was carried out in detail from the aspects of solubility,reaction kinetics,process optimization and performance testing.The solubility of BiOCl in hydrochloric acid solution was experimentally determined by the equilibrium method at the temperatures range from 303.15 to 363.15K.The experimental data was correlated by Apelblat equation、Empirical equation and λh equation.The results show that the solubility of BiOCl increases with the increase of the temperature and the concentration of hydrochloric acid solution.Moreover,the concentration of hydrochloric acid solution has greater effect on the solubility of BiOCl than the temperature.The solubility data is well correlated by the three models for BiCl₃-HCl-H₂O system,among which Apelblat equation is the best form.The reaction crystallization kinetics of BiOCl was investigated.The effects of suspension density and supersaturation on the crystallization were discussed.The dynamic model of the crystallization process was established using moment transformation method and the kinetic parameters were obtained using least square method for the multivariate linear regression.The nucleation and growth rate equations of BiOCl were determined by the least square method.The reaction crystallization kinetics provides a good foundation for further technical research and industrial scale up.Based on the studies of the solubility and the reaction crystallization kinetics,single factor experiments and Response Surface Methodology were applied to optimize the reaction process.The optimal process parameters are found as the reaction temperature of 83℃ BiCl3 solution concentration of 0.33 mol·L^-1,the deionized water dropping speed of 765ml·min^-1,the reaction time of 1 h,and the stirring rate of 100 r·min^-1.Pearlescent BiOCl of large size about 28 μm is obtained successfully.The glossiness of BiOCl was detected and the effects of the dispersity and particle size on the glossiness of BiOCl were also investigated.The results show that the glossiness of BiOCl is severely affected by the particle size and dispersity.Mono-disperse bismuth oxychloride with large size shows excellent pearlescent performance.The results of this research can provide effective guidance for further production.