Abstract
<jats:p>Relevance. Calcium dialuminate CaAl4O7 is of interest to both the construction industry and the production of LEDs and decorative coatings due to its excellent luminescent properties when doped with rare-earth and transition metal ions. Solid-phase synthesis in Ca(OH)2/CaCO3-Al2O3 systems with the addition of an H3BO3-based flux has become widely used for synthesizing aluminates. The transition from Al2O3 to metallic Al in such systems increases the reaction rate due to additional heating of the system during Al oxidation. Nanosized Al powders also increase the reactivity of the system due to their large specific surface area. However, the addition of a flux to such systems can have both a positive (liquid-phase synthesis) and a negative (hindrance to Al oxidation) effect. Therefore, assessing the effect of a flux on aluminate synthesis in systems with metallic aluminum powder requires separate study. Aim. To study H3BO3 (flux) effect on phase formation of calcium aluminate in the Ca(OH)2–Alnp system. Methods. Investigation in situ X-ray phase analysis using synchrotron radiation. Heating of powder compositions was carried out in an air atmosphere using a platinum heater in the temperature range of 25–1350°C at a rate of 30 °C/min. Results and conclusions. Boric acid acts as an inhibitor of calcium carbonate (CaCO3) formation in the temperature range of 25–900°C. The flux also helps to reduce the formation temperature of calcium monoaluminate (CaAl2O4) from 1149 to 1110°C and calcium dialuminate (CaAl4O7) from 1330 to 1245–1260°C. It was established that the intermediate phase Ca3B2O6 in the boron-containing system is formed at 680–900°C. This phase disappears upon completion of the synthesis. The authors proposed mechanism of action of the flux, suggesting improved contact between the solid phases in the liquid melt B2O3 and better diffusion of oxygen in the intermediate phase Ca3B2O6. The obtained results are of practical importance for optimizing the synthesis of luminescent materials based on calcium aluminates and calculating the initial composition of components using the solid-phase synthesis method. For citation: Tokarev D.S., Mostovshchikov A.V., Sharafutdinov M.R., Syrtanov M.S., Kargin A.E. Boric acid effect on phase formation in a calcium hydroxide – aluminum nanopowder system in situ. Bulletin of the Tomsk Polytechnic University. Geo Assets Engineering, 2026, vol. 337, no. 4, pp.115-126.</jats:p>