Silica gel from water glass: a SAXS study of the formation and ageing of fractal aggregates

Abstract

The influence of pH, cations, F− and temperature on the aggregation, gelation and ageing of aqueous silica gels has been investigated using small‐angle X‐ray scattering (SAXS). At both low and intermediate pH (pH = 4 and 6–8, respectively), fractal aggregates are formed during gelation from silicic monomers or small oligomers. The fractal dimensionality is 2.20 (5), to be expected for reaction‐limited cluster–cluster aggregates. During ageing silicic ions dissolve from the more soluble peripheral primary particles and condense in the crevices of the core of the aggregates. This process results in an increase in the size of the scattering primary particles and in a decrease in the fractal dimensionality of the silica aggregates from D = 2.25 to D = 2.0 or D = 1.85. The ageing processes are strongly enhanced by a slight increase in the pH of the solution, addition of fluorine anions and a rise in temperature. The aged silica gel is constructed of an ensemble of densified aggregates of which the density variation within the aggregates is larger than that of the freshly prepared aggregates. The primary particles of which the aggregates are built grow during ageing from molecular size to dense particles in the nanometer range, the ultimate radius depending on the type and duration of the ageing process.

Morphology and viscoelasticity of PP/TiO2 nanocomposites prepared by in situ sol–gel method

“…We relate this scattering behavior with the fractal morphology of aggregates of TiO 2 particle. Accordingly, the scattering intensity in SAXS is given by the power law:40 …”

Impact of coal composition and pore structure on gas adsorption: a study based on a synchrotron radiation facility

“…For synchrotron radiation SAXS, the SAXS intensity of fractal objects can be expressed by the power law in the fractal region, where α is a value between 0 and 4, when the slope of the linear region in the curve is d , . When , the scattering system is mass fractal or pore fractal, with the fractal dimension being .…”

Synthesis of High Purity Nano-Silica Using Water Glass

“…[1][2][3][4][5][6] 이러한 나노실리카 분말의 제조 방법으로는 광물 의 분쇄, 염화실리카를 이용한 기상반응 7) , TEOS(Tetraethylorthosilicate)나 물유리(sodium silicate)를 이용한 졸 -겔(Sol-Gel) 공정이 있다. …”