Crystallization of aragonite particles from solution under microwave irradiation

The effect of intense electromagnetic fields, generated inside a multimode microwave applicators, on the crystallization of calcium carbonate polymorphs starting from calcium bicarbonate solutions has been investigated. The identification and quantitative analysis of the calcium carbonate polymorphs has been made by X-ray diffraction using Rietveld-Reference Intensity Ratio (RIR) method. Scanning Electron Microscopy analysis has also been performed to study the morphology of calcium carbonate samples. Crystallization tests have been conducted at atmospheric pressure while adjusting microwave power to maintain solution temperature between 80 °C and 90 °C. For the sake of comparison, calcium carbonate powders have also been prepared using conventional heating either in a oven or on a hot plate with a magnetic stirrer. The experiments conducted using microwave radiation gave in a high percentage yield of aragonite (99%) which has been favoured by increasing microwave exposure times. Low microwave exposure times, on the other hand, favours vaterite formation which crystallized in an unusual flower-like morphology.