CaltechAUTHORS
  A Caltech Library Service

Palladium oxide equilibration and the thermodynamic properties of MgAl_2O_4 spinel

Chamberlin, Laurinda and Beckett, John R. and Stolper, Edward (1995) Palladium oxide equilibration and the thermodynamic properties of MgAl_2O_4 spinel. American Mineralogist, 80 (3-4). pp. 285-296. ISSN 0003-004X. http://resolver.caltech.edu/CaltechAUTHORS:20120823-160732559

Full text is not posted in this repository. Consult Related URLs below.

Use this Persistent URL to link to this item: http://resolver.caltech.edu/CaltechAUTHORS:20120823-160732559

Abstract

The technique of palladium oxide equilibration was used to measure activities of MgO and A1_2O_3 in stoichiometric MgAl_2O_4 spinel at 1150-1400 °C. Activities of MgO range from 0.63 ± 0.03 to 1.00 ± 0.07, and activities of Al_2O_3 range from 0.09 ± 0.01 to 0.05 ± 0.01 (1σ). The activities yield free energies of formation of spinel from the oxides ΔG^0_f,ranging from -31 kJ/mol at 1150 °C to -39 kJ/mol at 1400 °C, with a precision of 2-19% (1σ). The derived values of ΔG^0_f are consistent with the equilibrium amount of disorder present in the spinel under experimental conditions because the measured activities reflect equilibration at high temperature. Calorimetric heat contents were corrected for the state of order using a Landau formulation for the equilibrium amount of disorder in spinel as a function of temperature. The corrected heat contents, together with the measured ΔG^0_f, were used to produce a new, self-consistent C_p function that can account for available experimental data. The modeling results are consistent with previous suggestions that short-range ordering may be important in spinel.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://www.minsocam.org/MSA/AmMin/TOC/1995/MA95.htmlPublisherUNSPECIFIED
Additional Information:© 1995 Mineralogical Society of America. Manuscript received December 7, 1993; Manuscript accepted November 21, 1994. We thank G.S. Mattioli for generously providing samples of synthetic spinel and sharing his expertise on spinel. M. Carpenter, R.L. Millard, and R. Sack kindly provided data in advance of publication. J.T. Armstrong and P. Carpenter provided invaluable assistance with the electron microprobe analysis of dilute Pd alloys. Discussions with S. Kim were also helpful. M. Hirschmann and G. Mattioli reviewed an earlier version of this manuscript. The final version was improved by the reviews of W. Carlson, R. Sack, and an anonymous reviewer. This work was supported by NASA grants NAG 9-105 and NAGW 3533. L.C. would also like to acknowledge the support of NASA GSRP NGT-50672. Division of Geological and Planetary Sciences Contribution no. 5279.
Funders:
Funding AgencyGrant Number
NASANAG 9-105
NASANAGW 3533
NASAGSRP NGT-50672
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Division of Geological and Planetary Sciences5279
Record Number:CaltechAUTHORS:20120823-160732559
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120823-160732559
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33495
Collection:CaltechAUTHORS
Deposited By: Aucoeur Ngo
Deposited On:24 Aug 2012 14:29
Last Modified:24 Aug 2012 14:29

Repository Staff Only: item control page