| Silica is widely used as good and important inorganic filler in national production such as rubber, cosmetics, petrochemicals, catalysts, coatings and so on. It can be made via many different ways, and sulfuric acid precipitation method with many advantages of easily obtained materials and simple production technology is usually used by the most of manufacturers of silica in our country. However the scope of the final products'size distribution is too wide, because of the uneven mixture of sulfuric acid with sodium silicate. Hypergravity sulfuric acid precipitation method is the combination of traditional sulfuric acid precipitation and hypergravity technology, and it can solve the problem of uneven mixing of sulfuric acid with sodium silicate.There are many hydroxyl groups (-OH) on the silica surface, which easily absorb moisture and as a result generally silica is hydrophilic. And the Si-OH is the main reason to limits the application of silica. To improve the performance of silica, surface modification is necessary to weaken the polar property and improve the ability of combining with organic groups.In this paper, silica was prepared via hypergravity sulfuric acid precipitation method, and surface modification was studied with SiO2 wet cake as the raw materials in the post-processing stage.The research of this paper focus on the following:1. Single factor experiments and orthogonal experiments were designed to investigate the main influence of experimental conditions on properties of silica powder. The results proved that:the main factor which has the most significant influence on BET is the reaction temperature. Rotational speed, flocculant dosage, and the flow of sodium silicate are followed. The amount of flocculants sodium sulfate is the most influential factor to DBP oil absorption value, followed by the reaction temperature, the flow of sodium and the rotating speed. The most optimal scheme was got after the assessment of weighted:the reaction temperature is 80℃, the rotating speed is 1100r/min, the flow of sodium silicate is 290L/h, the dosage of sodium sulfate is 130g.2. The water in pore of wet cake was exchange by ethanol solvent. It has been found that ethanol washing can effectually control the "hard" polymerization in the process of drying wet cake, and some of the pore structure of low strength can be retained. The performance of the final product is superior to ordinary dry products, BET surface area and DBP oil absorption value are larger, pore volume and the average pore diameter are increases. Meanwhile, the original size of silica and the surface groups (mainly Si-OH) are not changed due to the different drying methods.3. Silica wet cake as raw material was modified in different solvent. By comparing the dispersion in kerosene of different samples, we select hexane and ethanol as the modified system and KH-570 as the modifier. IR, BET, particle size distribution and hydroxyl number on surface of silica are used to investigate the samples after modification. The results show that the organic functional groups are grafted on the surface of silica. And the surface of product has a certain degree of hydrophobic and products'performances are significantly improved.Influences of the dosage of modifier and reaction time were investigated. Finally the results show that the number of Si-OH on surface of silica was lest when the reaction time was 4h, the dosage of modifier was 10%of SiO2.
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