TO THE LOW-TEMPERATURE SYNTHESIS OF TITANIUM DIBORIDE

The PURPOSE of the paper is to determine the temperature ranges of dehydration and phase transformation of the initial components of the mixture of TiО₂-B₂О₃-C - sucrose, hydrated titanium and boron oxides under different conditions of titanium diboride synthesis. METHODS. The method used in the study is thermal analysis of the reaction mixture on the STA 429CD (NETZSCH) synchronous thermal analysis unit using a platinum-platinum-rhodium holder for “TG + DSC” type samples in helium, argon, vacuum and air atmospheres. RESULTS AND THEIR DISCUSSION. Boric acid is transformed in three stages at the temperature range of 73 ÷ 450°C: at the first stage the removal of 1 mole of water causes the transformation of the orthoboric acid H₂TiO₃ into the metaboric HBO₂ , which is transformed into boric anhydride В₂О₃ with further evaporation of moisture. The third stage features complete removal of moisture under the melting of boron oxide in the temperature range of 300 ÷ 600°C. The fluorine-doped titanium oxide TiO(OH)_2-xF_x loses moisture in the temperature range of 65-130°C, but its amorphous form TiO_2-xF_x undergoes its first phase transition to the crystal anatase modification of а-TiO₂ only after heating above 700°C. The greatest transformation and reduction depth of titanium oxide occur when the reaction mixture is heated in the air atmosphere. Pyrolysis of sucrose C₁₂H₂₂O₁₁ to complete removal of moisture and release of active carbon is a predominating process in a wide temperature range of 350÷740°C. CONCLUSIONS. Based on the thermal analysis results of the samples of the initial reaction composition under different atmospheric conditions the temperature ranges of the dehydration and transformation processes of mixture components have been determined. Found regularities must be accounted and applied under the low-temperature synthesis of titanium diboride TiB₂

anatase-rutile transformation, carbothermic reduction, low-temperature synthesis, titanium diboride, dynamic vacuum, controlled atmosphere

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