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Thermal expansion of troilite and pyrrhotite determined by in situ cooling (873 to 373 K) neutron powder diffraction measurements

Published online by Cambridge University Press:  05 July 2018

C. Tenailleau ,
B. Etschmann ,
H. Wang ,
A. Pring ,
B. A. Grguric  and
A. Studer
C. Tenailleau
Affiliation:
Mineralogy Department, South Australian Museum, North Terrace, Adelaide, S.A. 5000, Australia
B. Etschmann
Affiliation:
Mineralogy Department, South Australian Museum, North Terrace, Adelaide, S.A. 5000, Australia
H. Wang
Affiliation:
Mineralogy Department, South Australian Museum, North Terrace, Adelaide, S.A. 5000, Australia
A. Pring*
Affiliation:
Mineralogy Department, South Australian Museum, North Terrace, Adelaide, S.A. 5000, Australia Department of Geology and Geophysics, University of Adelaide, North Terrace, Adelaide, S.A. 5005, Australia
B. A. Grguric
Affiliation:
Exploration Group, WMC Resources Ltd, P.O. Box 91, Belmont, W.A. 6984, Australia
A. Studer
Affiliation:
Physics Division, ANSTO, PMB 1 Menai, N.S.W. 2234, Australia
*
E-mail: [email protected]
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Abstract

The thermal expansion coefficients for natural troilite, FeS, Ni-rich pyrrhotite, Fe0.84Ni0.11S, and Ni-poor pyrrhotite, Fe0.87Ni0.02S, were measured during cooling by in situ neutron powder diffraction over the temperature range 873–373 K. Between 873 and 573 K, the mean thermal expansion coefficients for the three compositions are 7.4(3)×10−5 {FeS}, 8.0(4)×10−5 {Fe0.84Ni0.11S} and 8.5(4)×10−5 K−1 {Fe0.87Ni0.02S}. Below 573 down to 373 K, the first two increase considerably to 14.1(7)×10−5 {FeS} and 9.3(5)×10−5 {Fe0.84Ni0.11S} while the latter sample shows no significant variation, 8.4(5)×10−5 K−1. Below 573 K, the thermal expansion is highly anisotropic, with Δa/100 K−1 ranging from 0.89(9)% {FeS} to 0.48(12)% {Fe0.87Ni0.02S} while Δc/100 K−1 ranges from −0.39(11)% {FeS} to −0.13(2)% {Fe0.87Ni0.02S}.

Upon cooling through 573 K, troilite and pyrrhotite undergo a transition where the FeS6 octahedra distort and in the case of pyrrhotite, cation-vacancy clustering occurs. The thermal expansion coefficients are bigger for low cation-vacancy concentrations and decrease as the pyrrhotites become less stoichiometric. This indicates that the thermal expansion in these minerals is damped by vacancy ordering or clustering. The thermal expansion coefficients for troilite and pyrrhotite are amongst the largest reported for sulphide minerals and their role in the formation of ore textures is discussed briefly.

Keywords

thermal expansiontroilitepyrrhotiteα and β transitionsneutron powder diffraction
Type
Research Article
Information
Mineralogical Magazine , Volume 69 , Issue 2 , April 2005 , pp. 205 - 216
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2005

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