Synthesis of Nitrides via Magnesiothermic Reduction of Tantalum and Niobium Oxide Compounds

Resumo

We have studied the feasibility of preparing tantalum and niobium nitrides by reducing Та₂O₅, Nb₂O₅, Mg₄Та₂O₉, and Mg₄Nb₂O₉ with magnesium vapor. The process was run in two steps: (1) reduction of the oxides at a temperature of 820°C and a residual argon pressure of 5 kPa in the reactor for 4 h and (2) nitridation of the reduction products in a nitrogen atmosphere at 820 and 900°C for 1–12 h. The phase composition of the powders after leaching out the magnesium oxide was determined on DRF-2 and DRON-4 X‑ray diffractometers. The specific surface area was determined by BET adsorption measurements on a Micromeritics TriStar II 3020 analyzer. When Ta₂O₅ was used as precursor, the nitridation product contained θ-TaN, ε-TaN, and Ta₂N. The use of Nb₂O₅ as a precursor led to the formation of face-centered cubic NbN, hexagonal close-packed NbN, Nb₂N, and Nb₄N₃. The Mg₄Ta₂O₉ and Mg₄Nb₂O₉ reduction products did not absorb nitrogen. The results obtained are discussed in detail.