牙膏磨擦剂二氧化硅制备条件的优化

以硅酸钠和硫酸为原料，采用硫酸沉淀法，合成适用于牙膏以及透明牙膏的SiO2。首先考察了釜底液硅酸钠浓度、温度以及陈化时间对SiO2性能的影响。结果表明：当釜底液中硅酸钠浓度为0.13mol/L、合成温度为65℃以及陈化时间为30min的条件下，合成SiO2的透光率可以达到89%。随后，以提高透光率为目标研究了在釜底液中添加Na2SO4、NaCl两种电解质对SiO2性能的影响。结果表明：在合成温度为65℃的条件下，添加浓度为0.04～0.12mol/L的Na2SO4、NaCl对合成SiO2的透光率基本上没有影响；而在合成温度为85℃的条件下，添加浓度为0.08mol/L的Na2SO4合成SiO2的透光率可以达到97%，添加浓度为0.12mol/L的NaCl合成SiO2的透光率可以达到96%。造成这种现象的可能原因是：在相对高的合成温度下，电解质能够更加有效的参与到硅酸的聚合中，使得SiO2的透光率得到一定的改善。按照QB/T 2346—2007对所合成的物质的牙膏磨擦剂特性进行测定，达到了标准要求。

Preparation of silica for toothpaste as abrasive

Using sodium silicate and sulphuric acid as raw materials，the silica suitable for using in transparent toothpaste has been synthesized by precipitation process. Effects of the reaction conditions on the properties of silica have been investigated，such as the concentration of sodium silicate in the reactor，reaction temperature and aging time. It was found that optimal reaction condition was determined as sodium silicate in the reactor 0.13mol/L，65 degree C and ageing time 30 min. Under the condition，the light transmittance of silica was 89%. On this basis，it was focused on the influence of the concentration of Na2SO4 and NaCl adding in reaction liquid to improve light transmittance. It turned out that the light transmittance of silica synthesized at 65 degree C has negligible influence on the concentration of Na2SO4 or NaCl adding in the reaction liquid 0.04～0.12mol/L. But at 85 degree C，the light transmittance of silica synthesized under Na2SO4 0.08mol/L was 97% and the light transmittance of silica synthesized under NaCl 0.12mol/L was 96%. The possible reason for this phenomenon could be that the electrolytes participate in the polymerization of silicic acid more effectively at a relatively high temperature，improving the transmittance of SiO2. The properties of the synthesized substance have met the standard of QB/T 2346—2007.