Study On Surface Modification Of Ultrafine Silica

Ultrafine SiO2 powder, the common name of white carbon black, is a kind of important inorganic powder materials. It is widely used in many industrial fields such as rubber, plastics, paints, ceramic glass and paper. There are hydroxyl groups in the surface of SiO2, which are in existence of chemical adsorption activity. If there are water molecules, hydroxyl groups will form hydrogen bonds, which is leading the dispersed difficulty of SiO2 powder in organic media. In addition, the precipitation method of SiO2 gel contains large amounts of water. It is very easy to form large capillary pressure in the dry removal process, make pore structure collapsed and cause hard agglomerates. To improve their application performance, we must carry on researching the surface modification, develop an effective drying process and improve the compatibility between powders and organic substrate.In view of the present study for modified SiO2 powders, it affects modification effect and increases the heat consumption of drying process. It is an innovation point of this passage that SiO2 gel is as the raw material which is prepared with supergravity continuous equipment. Respectively SiO2 gel is disposed of butanol azeotropic distillation and cthanol solvent replacement, after that it is directly dispersed in organic solvents for wet modification. This process is simple and the product has good hydrophobic effect.In this paper, we research modified conditions of ultrafine SiO2 gels and improve the traditional production process, which increases efficiency and reduces costs. The main contents of this paper include the following:1. Developing the special products of high market. For the domestic market demand hotspot of silica, several varieties must be concentrated, such as silicone rubber, silicone adhesives, dimethyldichlorosilane (DMDCS), hexamethyl disilazane (HMDS) and modified silica.2. Azeotropic distillation of n-butyl alcohol is used to dry the wet gel. We find that azeotropic distillation can greatly short the time of solvent exchange, control well the hard aggregation in the process of silica dehydration, protect the native structure of wet gel and improve product performance, such as BET surface area, BJH pore volume and oil absorption.3. Designing single factor experiments. After the azeotropic drying of SiO2 wet gel, DMDCS and HMDS are respectively used to modify SiO2 The results show that the different modified solvents significantly affect the modification effect. With the reaction time and the modifier amount increasing, the number of surface hydroxyl groups is in a decreasing trend. The samples with the filter cake modification have a loose appearance. The value of oil absorption is more than 3, the contact angle of water in the SiO2 surface is greater than 130°, and two modifiers have access to excellent hydrophobic properties.4. The ethanol is used to replace the water in the wet gel, and then silane coupling agent(A-151) is used to modify SiO2. The dispersion condition has greatly improved, optimal process conditions were followed by modifier solvent used ethanol, modifier content of 7.5% of the weight of silica, modification time of 2.5h.