Abstract
Abstract A complete thermodynamic analysis of chemical transformations in a BaO–B2O3–C system is performed in a temperature range of 1400–3000 K using the Terra software. Even before starting a reduction processes, the products of the reactions of boron and barium oxides are ortho-Ba3B2O6 and barium metaborate BaB2O4 with crystallization temperatures of 1656 and 1378 K, respectively. The reduction with carbon of a mixture of the oxides with high (90BaO + 10B2O3) and low (35BaO + 65B2O3) contents of barium oxide is studied. In all cases, the reaction products can be carbide BaC2, barium hexaboride BaB6, and boron carbide B4C. Barium carbide BaC2 prevails in the smelting products of the processed mixture rich in barium oxide, whereas barium hexaboride predominates in the processed mixture rich in boron oxide. The formation of barium borates impedes reduction because of the decreased reactivity of BaO and B2O3. Being strong basic (BaO) and acidic (B2O3) oxides, they form stable compounds. The temperature of the onset of barium reduction to BaC2 from BaO is 1500 K, and that from Ba3B2O6 is 2200 K. The combined reduction of barium and boron occurs from barium borates to form BaB6. For both mixtures, the formation of barium hexafluoride in the smelting products is detected at 2300 K. The presence of BaB6 in the condensed phase indicates that a complex ferroalloy simultaneously containing boron and barium, which are known as efficient alloying and modifying elements, can be produced. The method of mathematical experiment planning is applied to a numerical simulation of the technology. Equations are derived for the dependences of the amounts of the formed phases on the BaO and B2O3 consumptions and temperature. The entire oxide composition range is studied in accord with the phase diagram of the BaO–B2O3 system. The equations make it possible to select the temperature and charge smelting conditions to achieve the required compositions of the condensed phases. The results of numerical experiments can be applied to the production of boron–barium alloys and the synthesis of high-temperature materials based on BaB6, BaC2, and B4C.