Nitride Intermediates in the Preparation of Columbium, Vanadium, and Tantalum Metals (In Two Parts). 1. Nitride Preparation.
The federal Bureau of Mines has studied the reaction of oxides of columbium, vanadium, and tantalum with ammonia in vertical, gas- solids reactors at temperatures ranging from 300 deg to 1,300 deg c with the goal of preparing nitride intermediates for subsequent preparation of the metals by a thermal-decomposition step. The best nitride conversions were obtained in nonmetal reactors. With cb2o5, v2o3, and v2o5, low-temperature maxima in reaction rates occurred at 800 deg, 800 deg, and 450 deg c, respectively, during oxynitride formation (in al2o3) in 1 atm of pure ammonia. Conversion of the oxynitride, in a second step, to the mononitride was optimum at 1,200 deg c for columbium and 1,050 deg c for vanadium. In the case of ta2o5, the rate of reaction to form ta3n5 (in a single step) was highest at 900 deg c, where the presence of up to 5 percent methane was found to be beneficial; improved results were obtained by conducting the nitriding in a rotary kiln. Optimum space velocities (in the vertical al2o3 reactor) ranged from 5,280 hr-1 for cb2o5 to 7,950 hr-1 for v2o3. Oxide particle size had little effect upon reaction rates. Under fully optimized conditions, products containing less than 1 percent oxygen were readily obtained in under 6 hours.