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Doctor of Philosophy




Experiments have been performed to help elucidate the high temperature phase diagram features and thermodynamic properties of the zirconium-aluminum system. The principal methods used were combinations of high temperature Knudsen effusion, heat treatment, and X-ray powder diffraction experiments performed with zirconium-aluminum samples in the composition range 0 < X(,Al) < 0.75. The results of these experiments confirmed in some respects the phase diagram features of Potschke and Schubert,('1) two previous investigators. In particular, X-ray powder diffraction experiments performed on samples in the composition range 0.50 < X(,Al) < 0.60 quenched from 800-1400(DEGREES)C indicate that ZrAl is stable below 1250(DEGREES)C, Zr(,4)Al(,3) below 1000(DEGREES)C, and Zr(,5)Al(,4) above about 1100(DEGREES)C;Aluminum vapor pressures were measured over compositions corresponding to mixtures of two solid phases between the com- positions ZrAl(,3) and Zr(,5)Al(,3), and as a function of composition over the solid solution of aluminum in bcc zirconium using a combined mass-loss-mass-spectrometric Knudsen effusion technique. In order to successfully measure the low aluminum pressures (less than (TURN)10('-8) atm) over the more zirconium-rich samples it was necessary to use a small computer to signal average the mass-spectrometer signal. Data collected over 7 two-phase regions and the solid solutions were used to calculate enthalpies of formation at 298 K of seven zirconium-aluminum compounds. The heat of formation values (kcal/mole) obtained were: ZrAl(,3) = -38.96, ZrAl(,2) = -32.86, Zr(,2)Al(,3) = -56.12, ZrAl = -21.36, Zr(,5)Al(,4) = -93.76, Zr(,3)Al(,2) = -48.78, and Zr(,5)Al(,3) = -74.57;A nonrelativistic, nonself-consistent band structure calculation for the compound Zr(,2)Al was performed in an attempt to provide insight;into the type of chemical bonding occurring in zirconium-aluminum compounds; *DOE Report IS-T-1148. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Oil, Gas, and Energy;('1)Potschke, M; Schubert, K. Z. Metallkde 1962, 53, 548.



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Robert Joseph Kematick



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137 pages