alpha-wollastonite crystallization at low temperature

The phase of crystalline alpha-wollastonite (alpha-CaSiO3) powders was prepared at low temperature via sol gel method. The formation mechanisms of alpha-wollastonite (alpha-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 center dot H2O and Ca(NO3)(2)center dot 4H(2)O). 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 center dot H2O on the synthesis, a-wollastonite started to crystallize as majority phase at 700 degrees C. The complete crystallization of alpha-wollastonite was observed after the calcination at 1000 degrees C for 5 h, while samples prepared with Ca(NO3)(2)center dot 4H(2)O, only crystallized alpha-wollastonite at 1200 degrees 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 center dot H2O. (AU)