Synthesis of Calcium Hexaboride Powder via Boro/Carbothermal Reduction with a Gel Precursor

Abstract

In this study, the synthesis of calcium hexaboride powder via boro/carbothermal reduction (BCTR) using a single-step-processed gel product prepared from commercial boric acid, readily available and low-cost D(-)-Mannitol and calcium carbonate was investigated. The gel product was characterized by means of Fourier Transform Infrared Spectroscopy (FTIR) and Simultaneous Thermal Analysis (STA). The effect of the boro/carbothermal reduction temperature and dwell time on the phase formation were examined with x-ray diffractometry and scanning electron microscopy. CaB6 synthesis was performed with the gel product without additional heat treatment in air to obtain the appropriate C amount in the gel precursor. Ca3B2O6, B4C and Ca2B6O11 were formed as a transitional phase to create CaB6 particles. To understand the formation and consuming mechanism of the transitional phases, thermodynamic calculations were performed based on reactions that probably occurred in the system. The optimum synthesis conditions for the formation of calcium hexaboride were determined as 1400 degrees C for 12 h in an argon flow.