Degree Type

Dissertation

Date of Award

1984

Degree Name

Doctor of Philosophy

Department

Chemistry

Abstract

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.

DOI

https://doi.org/10.31274/rtd-180813-12535

Publisher

Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/

Copyright Owner

Robert Joseph Kematick

Language

en

Proquest ID

AAI8505833

File Format

application/pdf

File Size

137 pages

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