Heats of Formation of Niobium Nitride, Tantalum Nitride and Zirconium Nitride from

Heats of Formation of Niobium Nitride, Tantalum Nitride and Zirconium Nitride from

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July 20, 1936 HEATS OF FORMATION OF NIOBIUM NITRIDE 32G1 [CONTRIBUTIOX FROM THE MINERALS THERMODYNAMICS EXPERIMENT STATION, REGION 11, BUREAU OF MINES, UNITED STATES DEPARTMENT OF THE INTERIOR] Heats of Formation of Niobium Nitride, Tantalum Nitride and Zirconium Nitride from Combustion Calorimetry BY ALLA D. MAH AND NORMA L. GELLERT RECEIVED MARCH 1, 1956 The energies of combustion of niobium nitride (NbN), tantalum nitride (TaN) and zirconium nitride (ZrN) were deter- mined with a bomb calorimeter at 30 atm. pressure of oxygen and 303.15'K. as 1592.8,943.0 and 1652.6 cal./g., respectively. These results, in conjunction with the heats of formation of the corresponding oxides, lead to the following values of the heats of formation of the nitrides (kcal./mole) at 298.15"K.: -56.8 f 0.4 for NbN, -60.0 & 0.6 for TaN and -87.3 f 0.4 for ZrN. Previous papers from this Laboratory have re- ported heats of formation of titanium nitride' and hafnium nitride.2 Similar studies of other refrac- tory nitrides are being conducted whenever suit- able samples become available. The present paper describes measurements of the energies of combustion of niobium, tantalum and zirconium nitrides (containing 50 atomic % nitrogen), leading to the derivation of heats of formation of these nitrides from the elements. Materials.-The nitrides were prepared by treating the metals with purified nitrogen at high temperatures.8 Nitro- gen was purified by passing it through concentrated sulfuric acid, over copper at 375" and then over magnesium per- chlorate. The nitriding apparatus consisted of two concen- trically mounted porcelain tubes heated by a tube furnace. Nitrogen was passed between the walls of the two tubes, as well as through the inner tube which contained the metal to be nitrided. The metal was held in an alundum boat and was protected by finely divided titanium which was placed upstream from the boat to act as a "getter." The niobium metal was a Johnson, Matthey and Co. prod- uct containing 0.01c70 copper, 0.01% nickel and 0.017, sili- con as the only significant metallic impurities. The metal, as received in powder form, was treated with nitrogen for about 35 hr. at 1200-1400", the last several hours being at 1300". Account was kept of the mass increase during nitrid- ing and also portions of the product were tested to determine the mass increase upon conversion to niobium pentoxide. The results indicated the presence of 13.10% nitrogen, which fortuitously is virtually the theoretical amount for the com- position NbN. The X-ray diffraction pattern agreed with that of Brauer and Jande~-.~ The preparation and testing of tantalum nitride gave con- siderable difficulty. Three batches were prepared, two from Fansteel Metallurgical Co., tantalum in bar form, and one from metal powder obtained from Johnson, Matthey and co. The Fansteel tantalum contained 0.01% iron, 0.087, nio- bium, O.OIYo silicon, 0.005~0 titanium and no chromium, cobalt, molybdenum, nickel, tungsten or vanadium, accord- ing to spectrographic analysis. Lathe cuttings (0.002 in.), taken with a Carboloy tool, were treated with nitrogen for 20 hr. at 1200-1375'. The increase in mass during nitriding
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Heats of Formation of Niobium Nitride, Tantalum Nitride and Zirconium Nitride from

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