Synthesis of ReB2-Al2O3 composite powders and chemical resistance of the products to moisture

Synthesis of composite material from the ReO2 + Al2O3 + Al + B2O3 mixture was carried out. Mixtures were annealed at 1150 °C for 1 h or in two-steps process at 1050 °C and 1150 °C for 4 h, in argon. Different B2O3/ReO2 molar ratios were adopted: 1.0; 1.3; 1.5; 1.8; 2.0; 2.3, 2.5; 2.8; 3.0. The TG/DTA analysis was performed for the synthesis of mixtures of different molar ratios. Produced materials were tested by XRD phase composition studies. In every mixtures, products consisted mainly of ReB2, Al2O3, Re7B3 and aluminum borides. The research was aimed at reducing the share of the Re7B3 phase. Increase of the B2O3/ReO2 molar ratio in the syntheses results in the formation of boromullite phases such as Al5BO9, Al18B4O33, Al4B2O9. XRD and XPS investigations were carried out after prolonged exposure to humidity. Materials produced at a molar ratio B2O3/ReO2 = 1 are characterized by greater resistance to water from moisture compared to other tested mixtures. •Metallothermal synthesis of materials from the ReO2 + Al2O3 + Al + B2O3 were carried out.•For every mixture the synthesis products are composed mainly of ReB2, Al2O3 and Re7B3.•The molar ratios of B2O3/ReO2 affects formation of various types of aluminum borides.•Despite the Al2O3 presence in material, ReB2 and Re7B3 reacts with O2 and H2O.•The intensity of the reaction with water depends on the composition of the initial mixture.