Effect of Formation Rate of Silicon Gel on Compact Silicon Coating of Titanium Pigment
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摘要: 对钛白粉致密包硅进行机理研究。通过对硅酸水溶液体系的热力学分析,绘出硅胶水解产生的H5SiO4+、H4SiO4、H3SiO4-及H2SiO42-的优势存在区,计算表明:随着硅酸根总浓度的增加,上述硅酸根离子优势存在区均向高pH值方向平移。凝胶形成试验及结合热力学分析表明凝胶形成速率是由H4SiO4浓度和优势存在硅酸根离子的浓度共同决定的,在一定硅酸根总浓度下,凝胶形成速度最快为H4SiO4和H3SiO4+分布系数相等时,二者浓度乘积最大。凝胶形成速率随硅酸根总浓度增加而加快,凝胶形成速率过快,将形成絮状凝聚硅酸,影响包膜致密性。在温度为80℃及硅酸钠浓度分别为0.2、0.3、0.4 mol/L的条件下包硅,应控制体系的pH值分别大于9、9.5、10。Abstract: A study on mechanism of compact silicon coating of titanium pigment was carried out.Through thermodynamic analysis of silicic acid aqueous solution system,the advantage existing zones of H5SiO4+, H4SiO4,H3SiO4- and H2SiO42- produced by hydrolysis of silica gel were drawn.With the addition of silicate concentration,the advantage existences tend to move to higher pH.It can be concluded from the experiment of gel formation and thermodynamic analysis that the gel formation rate is determined by the concentration of both H4SiO4 and other silicate ions.When the distrabution coefficient of H4SiO4 and H3SiO4- are equal,the product of their concentration is the largest at certain total concentration of silicate ions.With the increase of silicate ions' total concentration,the gel formation rate speeds up.If the rate is out of control,flocculent silicate would form,which affects the coating compactness.With the temperature of 80℃ and silicate ion' concentration of 0.2 mol/L,0.3 mol/L and 0.4 mol/L,the pH value of the system should be greater than 9,9.5 and 10 respectively.
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Key words:
- titanium dioxide /
- coating /
- silicic acid /
- gel /
- thermodynamics
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