A new approach to the synthesis of nanosized powder CaO and its application as precursor for the synthesis of calcium borates

Abstract

A procedure for the synthesis of calcium oxide has been developed, which consists in heat treatment of an aqueous solution of calcium acetate and d-glucose at 350 and then at 700 °C. The process parameters have been determined. It has been shown that when d-glucose is used and the reaction mixture is heat treated at 700 °C, highly dispersed calcium oxide with an average particle size of 77 nm is formed. CaO formed has been used as a precursor for the synthesis of priceite (Ca2(B5O7)(OH)5 · H2O) during hydrothermal treatment of CaO in an aqueous solution of boric acid. It has been found that the optimal conditions for the synthesis of monophase priceite under hydrothermal conditions include the temperature range of 170–200 °C and the heating time of 12 h. When heating priceite at 800 °C in air for 1 h, highly dispersed powder calcium bis(borate) Ca(BO2)2 has been isolated as the final product. It is shown that the use of synthesized powder CaO leads to the formation of fine-crystalline powders of calcium borates. Samples obtained at each stage of the proposed synthesis of highly dispersed calcium oxide and calcium borates, using the example of priceite and calcium bis(borate), have been studied by powder X-ray diffraction, SEM, TEM, BET, IR spectroscopy, and DTA.