Effect of processing parameters on the morphology of hydrothermally synthesized calcium borate powders

Abstract

The present study aimed to examine the effect of pH and time on the final morphology of calcium borate powders. Primarily, aqueous solutions that mainly consisted of borax and calcium chloride were prepared with five different pH values varying between 2 and 15. Hydrothermal synthesis temperature was determined as 200°C, and four different times from 30 min to 24 h were selected. Phase formation and powder morphology were examined via an X‐ray diffractometer and scanning electron microscopy. Fourier transform infrared spectroscopy was used to identify the type of borate groups. Results revealed that pH directly determines the growth mechanism of calcium borate crystals. Lower pH induced nonclassical growth by forming self‐assembled nano‐plates. Individual, rodlike particles were observed for alkali solution. At weak basic conditions, priceite (4CaO·5B2O3·7H2O) and alkali condition parasibirskite (2CaO·B2O3·H2O) phases were obtained.