Crystal growth, structure and thermal properties of anhydrous zinc carbonate (ZnCO3)

Carbonate materials have been increasingly favoured in terms of the development of flame retardants because of the eternal subject of inorganic carbon sequestration. In this regard, anhydrous zinc carbonate (ZnCO3) has been deemed as suitable candidate thanks to its excellent flame retardancy compared to traditional hydroxid flame retardant. However, the single crystals growth, accurate characterizations of structural and thermal properties are still not entirely clear from previous studies. With this in mind, ZnCO3 single crystals were synthesized under high-pressure-temperature conditions (high P-T; 3 GPa and 973 K). The crystal structure of impurity-free ZnCO3 was determined by means of single crystal X-ray diffraction (XRD). The symmetry was identified as R3¯c, while the unit cell parameters were a= 4.6463(3) Å and c= 15.0015(11) Å with a final R value of 0.0229. The quantitative analyses of Raman spectrum and infrared absorption indicate that the as-synthesized ZnCO3 is anhydrous phase. Using Thermogravimetric (TG) / Differential Scanning Calorimeter (DSC) measurements, ZnCO3 was decomposed in the temperature range of 593–773 K, whereas the heat capacity and the endothermic peak were determined. According to the single crystal XRD from 150 K to 383 K, the thermal expansion coefficients were quantified as αa= 7.90 × 10−6 K−1 and αc= 22.8 × 10–6 K−1, as well as αVunit cell= 38.8 × 10–6 K−1. These findings provide a precise characterisation and obtain important thermal parameters for the evaluation of its flame retardant properties.