THE SOLUBILITY OF AMORPHOUS SILICA IN WATER
THE SOLUBILITY OF AMORPHOUS SILICA IN WATER
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DOI：
10.1021/j150516a002
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发表时间：
1954-01-01
影响因子：
--
通讯作者：
ILER, RK
中科院分区：
文献类型：
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作者：
ALEXANDER, GB;HESTON, WM;ILER, RK
无定形二氧化硅在25 ℃时在水中的溶解度表明，固相和溶液中二氧化硅的单体形式（可能是Si（OH）4）之间存在平衡。相同的溶解度（0.01至0. 012%）。显示pH 8以上的总溶解二氧化硅的增加是由于溶液中除了Si（OH）4之外还存在[H3 SiO 4]离子。与固相平衡的Si（OH）4的浓度显然不受pH值的影响。关于二氧化硅在水中的溶解度的许多研究已被证实1 -7（图1），但在大多数情况下，溶解度平衡是否真的建立起来并不清楚。也没有确定表观溶液中的二氧化硅是以单油酸、多油酸还是胶体二氧化硅颗粒的形式存在。本研究的目的是澄清这些问题。为了确保达到平衡，我们从不饱和状态开始，用无定形二氧化硅的胶体颗粒在水中的悬浮液，从过饱和状态开始，用低分子量的可溶性柠檬酸，使其变成胶体状态，从而接近25 ℃时溶解度的真实值。为了确定溶液中的二氧化硅是单体还是聚合物，我们采用了先前描述的方法的修改，包括硅多酸的形成。8-11通过这种方法，可以在其他形式的二氧化硅存在下测量单辛酸的浓度，因为单体与钼酸反应非常迅速;多辛酸反应较慢，胶体形式的二氧化硅几乎不存在。已知一元酸由硅胶的溶解产生12，并且在溶液中已显示为SiO2，13的水合形式，推测为Si（OH）4。溶解度已经被证明在pH 9.14以上增加。我们研究的另一个目的是解释这种行为。众所周知，无定形二氧化硅比结晶二氧化硅（石英）更易溶解，但尚未证明不同形式的无定形二氧化硅，如细粉、湿硅胶和溶胶形式的胶体颗粒的溶解程度相同。因此，在本研究中采用了这些不同形式的二氧化硅。事实上，我们发现这些不同的溶解度-
The solubility of amorphous silica in water at 25 is shown toinvolve an equilibrium between the solid phase and a mono-meric form of silica in solution, presumably Si (OH) 4. The same solubility (0.01 to0. 012%) was found using a suspension of finely divided amorphous silica powder and sols of colloidal particles of silica. The increase in total dissolved silica above pH 8 is shown to be due to the presence of [H3Si04] ion in addition to Si (OH) 4 in solution. The concentration of Si (OH) 4 in equilibrium with the solid phase apparently is not affectedby pH.Introduction.—Numerous studies of the solu-bility of silica in water have been reported1-7 (Fig. 1) but it was not clear in most cases whether solubilityequilibrium was actually established. Also it was not determined whether the silica in apparentsolu-tion was present as monosilicic acid, polysilicic acid or colloidal silica particles. It is the purpose of this investigation to clarify these points. In orderto ensure that equilibrium was reached, we have approached the true value of the solubility at 25 from the unsaturatedstate bystarting with suspensions of colloidal particles of amorphous silica in water, and from the supersaturated condition by starting with soluble silicic acid of low molecular weight, letting it polymerize to the colloidal state. In order to determinewhether the silica in solution is monomeric or polymeric, we have employed a modification of previously described methods involving the formation of silicomolybic acid. 8-11 By this method it is possible to measure the concen-tration of monosilicic acid in the presence of other forms of silica, since the monomer reacts with mo lybdic acid very rapidly; polysilicic acids react more slowly and colloidal forms of silica scarcely at all. Monosilicic acid is known to result from the dissolution of silica gel12 and in solution has been shown to be a hydrated form of S1O2, 13 presumably Si (OH) 4. The solubility has already been shown to increase above pH 9.14 It was another objective of our investigation to explain this behavior. It is well known that amorphous silica is more soluble than crystalline silica (quartz) but it has not been demonstrated that the different forms of amor-phous silica such as finely divided powder, wet silica gel andcolloidal particles in the form of a sol, are soluble to the same extent. Accordingly, these different forms of silica were employed in this study. The fact that we find the solubilities of these dif-