WAXS- and SAXS-investigations of structure formation in alcoholic SiO2 solutions
WAXS- and SAXS-investigations of structure formation in alcoholic SiO2 solutions
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SiO2 醇溶液中结构形成的 WAXS 和 SAXS 研究
DOI：
10.1016/0022-3093(90)90234-d
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发表时间：
1990
期刊：
影响因子：
--
通讯作者：
H. Bürger
中科院分区：
文献类型：
--
作者：
B. Himmel;T. Gerber;H. Bürger
小角和广角X射线散射（SAXS和WAXS，分别）被用来检查原位形成和演变的SiO2-结构的四烷氧基硅烷（TAOS）的醇溶液中作为化学条件的函数。在H_2O与TAOS的摩尔比为1.51的酸催化反应中，总是发现直径为1.1nm的初级粒子，这些粒子聚集形成次级团簇。由此产生的聚集团簇可以通过分形概念来描述，扩散限制或化学限制的团簇-团簇聚集是主要的形成机制。当使用低于化学计量的水含量（rw= 1）时，观察到形成直径小于0.5nm的较小初级颗粒;这些颗粒优选聚集以形成线性颗粒链。在碱催化的反应中，SiO2-颗粒的生长超出了测量的视野（rmax= 20 nm），并且具有几乎光滑的表面。作为WAXS检查的结果，发现凝聚物的内部结构的特征在于明确定义的拓扑结构（多面体）。液体环境对SiO2颗粒施加力，多面体尺寸随溶液的组成而变化。
Small- and wide-angle X-ray scattering (SAXS and WAXS, respectively) were used to examine in situ formation and evolution of SiO2-structures in alcoholic solutions of tetra-alkoxysilanes (TAOS) as a function of chemical conditions. In acid-catalyzed reactions with a molar ratio of ⩽rw⩽ 51 forH2O against TAOS primary particles with a diameter of ∼ 1 nm were always found. These particles aggregated to form secondary clusters. The resulting aggregated clusters can be described by means of the fractal concept, diffusion-limited or chemical-limited cluster-cluster aggregations being the dominant mechanisms of formation. When using an under-stoichiometric water content (rw= 1) the formation of smaller primary particles with a diameter of ∼ 0.5 nm is observed; these particles preferably aggregated to form linear particle chains. In alkaline-catalyzed reactions the SiO2-particles grew beyond the visual field of the measurement (rmax= 20 nm) and featured nearly smooth surfaces. As a result of WAXS examinations, it was found that the internal structure of the condensates is characterized by a well-defined topology (polyhedrons). The liquid environment exerts a force on the SiO2-particles and the polyhedron size varies with the composition of the solution.