The carbonate location in mixed calcium and strontium carbonated apatites

Mixed calcium/strontium carbonated apatites were obtained by aqueous addition of mixtures of calcium and strontium nitrate to NH4H2PO4 and Na2CO3 in the presence of both low and high sodium concentrations. The calcium: strontium ratios in the products were obtained by xrf and carbonate percentages by combustion analysis. Peak-fitting of the asymmetric carbonate region of the IR spectra, using the procedures developed previously, showed that an increase in the percentage of strontium in the apatite led to an enhancement in the percentage of A-type carbonate. Because of the larger size of Sr2+ relative to Ca2+, this result can be attributed to an expansion of the channel, which leads to an increased stability of carbonate in the channel. The cogwheel- like control of channel carbonate can be utilized to prepare apatites appropriate for various applications. (C) 2020 Elsevier Ltd. All rights reserved.