Study on the Effect of Temperature on the Crystal Transformation of Microporous Calcium Silicate Synthesized of Extraction Silicon Solution from Fly Ash

In this study, microporous calcium silicate was synthesized from a silicon solution of fly ash extracted by soaking in strong alkali as a silicon source. By means of XRD, TEM, FTIR, and thermodynamic calculations, the crystal evolution and growth process of microporous calcium silicate were studied under the synthesis temperature of 295~365 K. The results show that calcium silicate is a single-chain structure of the Si-O tetrahedron: Q1 type Si-O tetrahedron is located at both ends of the chain, and the middle is the [SiO44-] tetrahedron connected by [O2-] coplanar, and Ca2+ is embedded in the interlayer structure of calcium silicate. The formation rate and crystallization degree of calcium silicate hydrate were positively correlated with temperature. When the synthesis temperature was 295 K, its particle size was about 8 μm, and when the synthesis temperature was 330 K, a large number of amorphous microporous calcium silicate with a particle size of about 14 μm will be generated. When the temperature was above 350 K, the average particle size was about 17 μm. The microporous calcium silicate showed obvious crystalline characteristics, which indicate that the crystallization degree and particle size of microporous calcium silicate could be controlled by a reasonable synthesis temperature adjustment.