Study On Preparation Of Silica Colloid By Silicon Powder Oxidation And Its Application Characteristics

Silica colloid (SiO2 colloid) has been widely used in the industries of coating, chemical mechanical polishing and catalyst carrier. In this paper, preparation of SiO2 colloid by silicon powder oxidation and its properties of viscosity and stability were studied, and then its application on color inkjet printing paper was also studied.The technological conditions of preparation of SiO2 colloid by silicon powder oxidation have been studied. The influence factors on performance of product were investigated. The optimum condition of SiO2 colloid preparation was obtained by orthogonal test. Stable silica colloid of high concentration(about 30%), low viscosity(3-5mPa.s) and particle size 10-13nm can be obtained under the reaction conditions:7 hours,80℃, the mass ratio of sodium silicate, water and silicon powder was 1:20:3. Influence factor and growth mechanism in particle size growth technology were investigated based on the preparation of SiO2 colloid. High concentration SiO2 colloid was prepared by the method of vacuum distillation with different types of surfactant. Function of different types of surfactant was discussed, in terms of the relationship between particle size or viscosity and mass concentration of SiO2 colloid during the process of preparing high concentration SiO2 colloid. The research results indicate that the stable and high concentration SiO2 colloid can be obtained under conditions as follows:70℃, vacuum degree of 0.095MPa and dispersant of anionic surfactant.The properties of viscosity and stability have been systematically studied. Effects of concentration, temperature, particle size, colloid type, surfactant on the viscosity were investigated. The special gel layer structure of SiO2 colloid surface and the mechanism of viscosity reduction by anionic surfactant sodium dodecyl benzene sulfonate (SDBS) were discussed. It shows that direct addition of three kinds of surfactant resulted in reduction of viscosity, SDBS is effective than OP-10 and sodium dodecyl sulfonate (SDS). It was speculated that the mechanism of viscosity reduction was relied on the covering process of SDBS on the colloid particle. The effect of concentration of SDBS on the viscosity reduction behaved as critical concentration is about 4.6×10-3mol/L. In terms of stability test, effects of pH, particle size, concentration, temperature, organic solvent, surfactant on the SiO2 colloid stability were investigated. The different influence mechanisms of above factors on the stability were discussed. The research results of different types of surfactant show that the stability could be increased by addition of anionic and non-ionic surfactants, but reduced by cationic surfactant. The stability function of SDBS involved in its amounts, the optimum extremum is about 1.43×10-3mol/L.The enclosed mode of SiO2 colloid inserted with SDBS has been constructed by comparing the viscosity reduction and stability function of SDBS for SiO2 colloid. Adsorption of anionic surfactant on the negative charge colloid particle was different from cationic and nonionic surfactants. It shows a inserting-enclosed model. The non-polar group tail of anionic surfactant inserted into the gel layer of SiO2 colloid particle, the polar group was toward outer edge. So the formation of dimolecular adsorption layer was difficult for the sake of repulsion of two like electric charges. This model provides a theory foundation for explaining the viscosity reduction and stability function.High concentration SiO2 colloid, gas silica, normal SiO2 colloid were applied on the preparation of color inkjet printing paper, the performance of printing paper was determined. The same performance can be achieved using high concentration SiO2 colloid and gas silica as pigment, but the high concentration SiO2 colloid is priced and easily prepared of high content coating(above 40%), so the high concentration SiO2 colloid is more suitable for the preparation of color inkjet printing paper pigment.