Crystallographic characterization of naturally occurring aragonite and calcite phase: Rietveld refinement

Abstract

This research has comprehended the crystallographic characterization of two naturally occurring calcium carbonates phases e.g. aragonite and calcite in Pila globosa (P. globosa) and eggshells respectively. The tools employed to confirm the phases of aragonite and calcite were X-ray diffractoion (XRD) and Fourier Transform Infrared (FT-IR) spectroscopy. Several important crystallographic parameters like crystallite size, lattice parameters, dislocation density, crystallinity index, microstrain, volume of the unit cell, relative intensity of a certain plane, preference growth, and specific surface area were taken into account while assessing the desired aragonite and calcite phases. A number of well-known models e.g. Straight-line model of the Scherrer model, the Monshi-Scherrer model, the Williamson-Hall model, the Sahadat-Scherrer model, and the three-peak model aided the estimation of crystallite size. In all the cases, the observed crystallite size of calcite was larger than that of aragonite. The percentage of calcite and aragonite in eggshell and P. globosa were assessed by Rietveld refinement method. Observed results revealed that 97.4% calcite and 2.6% aragonite phases are present in eggshell while in P. globosa these percentages exist inversely, i.e. 93.2% aragonite and 6.8% calcite phases.

Keywords

• X-ray diffraction
• Phase analysis
• Eggshells
• Pila globosa