Growth Rate of SiO2 Nanoclusters at Different Water : TEOS Molar Ratios in the Presence of an Alkaline Catalyst

Autor: I. I. Yurasova, N. K. Galkin, A. V. Sinyagin, V. A. Tetyanchuk, A. I. Plokhikh, N. I. Yurasov
Rok vydání: 2021
Předmět:
Zdroj: Russian Journal of Physical Chemistry A. 95:1207-1211
ISSN: 1531-863X
0036-0244
DOI: 10.1134/s0036024421060297
Popis: Real-time thermal analysis is used for the synthesis of silica globules. The rate of the reaction of sol synthesis is determined. The reaction order is found, depending on the concentration of water, and the kinetic and diffusion regions are identified. Dried (not annealed) samples are studied via DSC. The dynamics of ethanol and water evolution from the samples is studied in analyzing the heating and cooling curves. Structural phase transformations of the formation of β-cristobalite and its transition to the α-form are observed. The dependence of the amorphousness of the sample on the amount of water in the solid phase is determined. It is found that when the water–TEOS molar ratio is less than fifty, the process proceeds slowly and hydrolysis is incomplete. An explanation of this pattern is proposed. A reaction equation for the kinetic region is determined for the case when the indicated molar ratio is more than 100. A general chemical formula for the main structure of a globule’s core is proposed, with allowance for the presence of cristobalite fragments in all samples. Based on an analysis of this formula, a condition is found for the case when the hexagonal ring cannot be the basis of the structure, and the amount of chemically retained water can be determined. A stoichiometric formula for the product that forms in the diffusion region is obtained.
Databáze: OpenAIRE
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