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

-We have studied the feasibility of preparing tantalum and niobium nitrides by reducing ?a(2)O(5), Nb2O5, Mg-4?a(2)O(9), and Mg4Nb2O9 with magnesium vapor. The process was run in two steps: (1) reduction of the oxides at a temperature of 820 degrees 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 degrees 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 theta -TaN, epsilon -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.