Preparation And UV Shielding Of Nano-TiO₂/talc Compound Powder

Nano-structured TiO₂ has been widely used in coating, plastics, cosmetic and other industry as representative of inorganic ultraviolet shielding agents. However, nano-structured TiO₂ will not show nano-property well because of agglomeration during application. In this paper, nano-structured TiO₂ coating on talc substrate was prepared by homogeneous precipitation method using industrial grade TiOSO4 and talc powder as raw materials and urea as precipitant. The TiO₂/ talc compound powder which was dispersed in alkyd varnish showed excellent ultraviolet shielding quality.Process conditions of preparing TiO₂/ talc compound powder were studied, and the results indicated that nano-structured TiO₂ would be deposited on talc substrate under optimal conditions. The main experimental parameters were as follows: concentration of TiOSO4 was 0.02⁰.10 mol/L; concentration ratio of urea and TiOSO4 was 10¹5:1; initial pH should be kept around 1.0; drop speed of solution was 1²ml/min; reaction time was 3h. The compound powder was filtered off, washed with deionized water and dried at 80°C. Finally, the compound powder was calcined at 800°C for 1h. Besides, hydrolysis and precipitation mechanism of TiOSO4 was analyzed by theory of electrostatic adsorption and polynuclear titanium ions growth in talc-water suspension system. In this paper, heterogeneous nucleation and sediment morphology of hydrated TiO₂ coating on talc was also explored from thermodynamics viewpoint. Growth model of TiO₂ coating on talc was brought forward, which was based on island growth model accompanied by layer growth model.It was also studied that the technology of nano-TiO₂/talc dispersing in alkyd varnish (modified varnish) and preparation of modified varnish paint film. Glass slides should be pretreated at 300°C for 0.5h, and the addition amount of coupling agent was about 50wt% of compound powder. Spreading of paint film on glass slides was improved by multi-times painting. The paint film showed excellent ultraviolet shielding and visible light transmission properties when addition amount of TiO₂/talc compound powder was 3wt% of varnish (Ti4+=0.06mol/L, [Urea]: [Ti4+] =1:15). Ultraviolet shielding mechanism of the compound powder was analyzed which was interaction of absorption, scattering and reflection.