Phase transformations during the dissolution-precipitation synthesis of magnesium whitlockite nanopowders from gypsum

Abstract

In the present work, magnesium whitlockite (Mg-WH) powders were synthesized via a low-temperature dissolution-precipitation process using gypsum as a starting material. The suggested synthetic approach is cost-effective and environmentally friendly solution, promoting sustainable manufacturing practises. The phase evolution and formation of Mg-WH in an aqueous medium in the presence of magnesium and phosphate ions under static and rotating conditions were investigated. Powder XRD patterns, FTIR spectra and SEM images were obtained for samples synthesized for different times to monitor the gradual phase transformation. It was found that single-phase Mg-WH can be obtained using both synthetic approaches, however, the reaction under rotating conditions favors faster formation of Mg-WH crystals. Samples obtained under static conditions had larger crystallite size and higher crystallinity, while those prepared under rotating conditions had smaller crystallites and lower crystallinity. The Rietveld refinement confirmed the structural parameters of the synthesized samples, indicating a slight change in the lattice parameters and magnesium occupancy with an extended synthesis time. We state that the phase composition, crystallite size, crystallinity, and powder morphology can be facilely controlled by regulating the synthesis time and selecting the synthesis setup.