Structure and phase analysis of calcium carbonate powder prepared by a simple solution method

Abstract

This paper focused on the analysis of the crystal structure and phase transformation of CaCO₃ synthesized by simple solution method from 0.5 M Ca(NO₃)₂ precursor and 0.5 M Na₂CO₃ precipitant at ambient temperature (300 K). The pH of the sample solution at various reaction times of 5, 10, 15, and 30 min were measured and correlated with the supersaturating condition in the presence of the Na₂CO₃ which is responsible for vaterite phase formation. The formation of the polymorph structure of obtained CaCO₃ powders was characterized using powder X-ray diffraction patterns and their crystal structure and phase transformation were evaluated using the Rietveld refinement method. Moreover, the qualitative analysis of the CaCO₃ powders phase was conducted by Fourier Transform Infrared (FTIR) spectroscopy to evaluate the effect of reaction time correlated with their crystal formation. The XRD analysis showed that the vaterite formation was 89 % at a reaction time of 15 min and confirmed also by FTIR that the amount of vaterite increased due to the effect of increasing reaction time. The crystallite size of vaterite was stable at 36 nm at the reaction time of 15 and 30 min. The morphology of the CaCO₃ powders obtained from Scanning Electron Microscope (SEM) was spherical with sizes of 2-5 μm. It was highlighted that the supersaturating condition started occurred at a reaction time of 15 min at pH 7.88 which was responsible for vaterite formation took place. It was concluded that the amount of precipitant (Na₂CO₃) and reaction times play an important role to determine the saturation of carbonate source to allow vaterite phase formation of CaCO₃ powders to occur.

Keywords: Ca(NO3)2; calcium carbonate; simple solution method; vaterite.