α-wollastonite crystallization at low temperature

Abstract

The phase of crystalline α-wollastonite (α-CaSiO3) powders was prepared at low temperature via sol gel method. The formation mechanisms of α-wollastonite (α-CaSiO3) using different calcium salts were examined. The synthesis was carried out in absence of organic solvents, using as starting materials silicic acid and inorganic salts (CaCl2.H2O and Ca(NO3)2.4H2O). The samples were analyzed by Fourier Transform Infrared Spectroscopy (FT-IR), Thermogravimetry/Differential Scanning Calorimetry (TGA-DSC), X-Ray Diffraction (XRD) and Field Emission Gun-Scanning Electron Microscopy (FEG-SEM). The experimental results demonstrate that the calcium source strongly influences the characteristics of the resultant powders, as phase purity and morphology of the wollastonite particles. XRD analysis showed that, using CaCl2.H2O on the synthesis, α-wollastonite started to crystallize as majority phase at 700 °C. The complete crystallization of α-wollastonite was observed after the calcination at 1000 °C for 5 h, while samples prepared with Ca(NO3)2.4H2O, only crystallized α-wollastonite at 1200 °C. This difference in crystallization temperature is probably related to the higher homogeneity and the elevated number of Si–O–Ca bonds present in samples prepared with CaCl2.H2O.