Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions.
Silica/alkali ratio dependence of the microscopic structure of sodium silicate solutions.
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DOI：
10.1016/j.jcis.2013.01.048
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发表时间：
2013-05
影响因子：
9.9
通讯作者：
Jonas Nordström;Andreas Sundblom;G. Jensen;J. S. Pedersen;A. Palmqvist;A. Matic
中科院分区：
文献类型：
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作者：
Jonas Nordström;Andreas Sundblom;G. Jensen;J. S. Pedersen;A. Palmqvist;A. Matic
已知SiO2：Na 2 O摩尔比在4-10范围内的碱性硅酸钠溶液是胶体不稳定的，表现为相分离或凝胶化。对这种不稳定性的机械理解通常很差。为了改善这种情况的微观结构的一系列解决方案的比例在3.3-8.9的范围内，其特征在于使用小角X射线散射，动态光散射，傅立叶变换红外光谱，和29硅核磁共振光谱，以涵盖相关的长度尺度相关的二氧化硅集群，聚集体，和颗粒存在。在比率为3.3的起始溶液中，二氧化硅存在于三个级分中。主要部分是以半径为0.7nm的小二氧化硅簇存在。还存在显著部分的单体/小低聚二氧化硅物质以及微量的较大胶体二氧化硅颗粒。在较高的SiO2：Na 2 O比下，高于约4，由于缩合反应形成较小的球形胶体颗粒。然而，由于过高的离子强度，悬浮液不稳定，并且颗粒聚集成分形结构，其尺寸取决于比率和老化时间。当SiO_2：Na_2O比最高时，由于离子强度较低，不形成分形，较小的胶体颗粒在溶液中稳定。通过小心地向高比率溶液中加入少量NaCl，可以诱导溶液的凝胶化，证实了不稳定区域是由于在那些条件下存在的二氧化硅物质的电解质浓度过高的假设。
Alkaline sodium silicate solutions with SiO2:Na2O molar ratios in the range 4–10 are known to be colloidally unstable manifested in phase separation or gelation. The mechanistic understanding of this instability is generally poor. To improve this situation the microscopic structure of a series of solutions with ratios in the range 3.3–8.9 has been characterised using small-angle X-ray scattering, Dynamic light scattering, Fourier transformed infrared spectroscopy, and29Si Nuclear magnetic resonance spectroscopy to cover the relevant length scales related to silica clusters, aggregates, and particles present. In the starting solution, with ratio 3.3, there are silica present in three fractions. The main part is present as small silica clusters with a radius of 0.7nm. There are also a significant portion of monomers/small oligomeric silica species as well as a minute amount of larger colloidal silica particles. At a higher SiO2:Na2O ratio, above approximately 4, smaller spherical colloidal particles are formed due to condensation reactions. However, as a result of a too high ionic strength the suspension is not stable and the particles aggregate to fractal structures with a size that depends on ratio and ageing time. At the highest SiO2:Na2O ratio, fractals are not formed because of the lower ionic strength and the smaller colloidal particles are stable in the solution. By carefully adding small amounts of NaCl to the high ratio solution it is possible to induce gelation of the solution confirming the hypothesis that the instability region is due to too high electrolyte concentration for the silica species present under those conditions.