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硅酸溶液有自聚作用,即从低聚硅酸→中聚硅酸→高聚硅酸→硅凝胶。将硅酸溶液的胶凝时间对溶液的 pH 作图,曲线呈“N”形,曲线的位置随酸化剂种类等不同而改变。“N”曲线最高点位置用强酸(Hcl、H_2SO_4、HNO_3)皆在 pH1.5—2.0;用中强酸(H_3PO_4)在2.5左右;用弱酸(CH_3COOH)在2.5—4.0之间。并且曲线最低点位置也随酸化剂不同而明显不同。由于在所试酸化剂中,醋酸的差别最大,多年来一直引
Silicic acid solution has a self-polymerization, that is, from the oligomeric silicic acid → polysilicic acid → high polysilicic acid → silica gel. The gelling time of the silicic acid solution is plotted against the pH of the solution. The curve shows “N” shape, and the position of the curve changes with the type of acidifier. Strong acid (Hcl, H_2SO_4, HNO_3) is at pH 1.5-2.0 at the highest point of “N” curve, about 2.5 at medium strong acid (H_3PO_4), and 2.5-4.0 at weak acid (CH_3COOH). And the location of the lowest point of the curve is also significantly different with the acidifier. As the acidifier in the test, the largest difference between acetic acid, has been cited for many years