GAS-METAL EQUILIBRIUM AND THE NIOBIUM-NITROGEN TERMINAL SOLID SOLUTION
The idealized behavior of a hypothetical gas-metal binary system is discussed in terms of a three dimensional phase diagram in which the variables are pressure, temperature, and composition. The phase diagram is then applied to the niobium--nitrogen system, and comparisons are made with the hypothetical ideally-behaving system. Various assumptions of ideality are made as follows: Henry's Law and Sievert's Law are both obeyed in the solid solution range; the activity of the solid solution is that of the pure metal; the composition of the second solid phase which forms is constant; and the gas obeys the ideal gas laws at all pressures and temperatures involved. It was found that when the variables are plotted with pressure and composition on logarithmic scales and temperature on a reciprocal scale, the surfaces are simplified so that they become planes and cylindrical surfaces. Analytical treatment of the equations for the various surfaces was found to substantiate the additivity of the heats involved in the various gas-metal reactions. Experimentally the Nb-N system was studied in order to determine to what extent a real system follows the idealized one. For the solid solution, Slevert's Law was found to be obeyed and the partial molar heat of solution of the gas in the metal was determined to be constant within the experimental error. it has a value-46 kcal per g-atom. Nb/sub 2/N was found to be the nitride in equilibrium with the solid solution in the temperature range from 300 to 2230 deg C; it has a heat of formation of --67 kcal per g-atom of nitrogen. The terminal solubility of nitrogen in niobium metal was found to obey the van't Hoff relation from 1150 to 2230 deg C, and the possible low temperature deviations are discussed. Comparison of the Nb--N results with those for an idealized system indicate that above 1150 deg C nitrogen reacts with niobium so that the idealized hypothetical phase diagram is a good approximation. The equations for the plane surfaces of the diagram are given, and the entropies for the various reactions were found to be in agreement both with theory and with the results obtained for comparable systems. It was concluded that the nitrogen atoms are a comfortable fit in the niobium lattice and that there is very little interaction between adjacent nitrogen atoms as they exist in solution.
- Research Organization:
- Univ. of Illinois, Urbana
- NSA Number:
- NSA-16-033492
- OSTI ID:
- 4804309
- Journal Information:
- Dissertation Abstr., Vol. Vol: 23; Other Information: Orig. Receipt Date: 31-DEC-62
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ATOMS
CHEMICAL REACTIONS
CYLINDERS
ENTROPY
EQUATIONS
ERRORS
GASES
HENRY LAW
HIGH TEMPERATURE
LATTICES
LIQUIDS
METALS
NIOBIUM
NIOBIUM NITRIDES
NITROGEN
PHASE DIAGRAMS
PRESSURE
QUANTITY RATIO
REACTION KINETICS
SOLID SOLUTIONS
SOLUTION HEAT
SOLUTIONS
SURFACES
TEMPERATURE
TESTING
THERMODYNAMICS
VARIATIONS