硅酸聚合中盐效应的机理

在广泛pH范围内研究了硅酸聚合中盐效应的机理。实验结果表明:外加盐的阳离子既可与水配位形成水合金属阳离子,又可与硅酸负离子形成配合物。因此外加盐的阳离子同时以静电效应和化学反应两种机理来影响硅酸的聚合速度,这种影响随溶液pH增大而加强。在强酸性溶液中,外加盐被酸化成的酸和硅酸或硅酸阳离子反应,以化学反应机理来改变硅酸的聚合速度。这一作用随溶液pH增大而减小。根据上述机理,提出了一个表示硅酸聚合速度与包括盐效应在内的各种因素的关系式,由此求得的计算值与实验值基本符合。

MECHANISM OF SALT EFFECT ON POLY-MERIZATION OF SILICIC ACID

We have studied the mechanism of the polymerization of silicic acid in wide pH range. Experimental results showed that the cation of the added salts combined either with water forming aquo-metal ions or with the anion of silicic acid forming coordination complexes and thus giving rise to two different effects on the rate cf polymerization of silicic acid: electrostatic and chemical reaction.The relative degree of these two effects depends on the pH of the solution and the total cationic effect of salts increased with the increase of pH of the solution. In strongly acidic solution, the added salt will be acidified to form an acid which reacts with silicic acid or its cation and variates the rate of polymerization reaction. This effect decreases with increase of pH of the solution. On the basis of the above findings, an equation has been derived to express the relationship of the rate of polymerization of silicic acid and various factors with salt effect included. The equation gives calculated values in fairly good agreement with experimental results.