Natural As-Sb Alloys: Texture Types, Thermal Behaviour and Mechanism of Formation

G. P. Bernardini1, C. Cipriani2, F. Corsini1, G. G. T. Guarini3, G. Mazzetti2 and L. Poggi1
1 Department of Earth Sciences, University of Florence, 1-50121 Florence, Italy
2 Mineralogical Museum, University of Florence, 1-50121 Florence, Italy
3 Department of Chemistry of the University of Florence, 1-50121 Florence, Italy

Abstract: The thermal behaviour and mechanism of formation of different texture types of intergrown As-Sb alloys have been studied by DTA and annealing experiments performed on natural samples. The constant composition of the As-rich component and of the stibarsen in the intergrowths, and the large compositional range of the homogeneous solid solution obtained after heating in the DTA cycle, have been established using the linear relationship between cell volume and composition. The high-temperature features detected in the DTA studies of the natural samples confirm previously published phase relations for the synthetic As-Sb system. The low-temperature features can be correlated with the homogenization reaction which leads to the formation of a complete solid solution. Study of TTT plots based on the annealing experiments clearly shows that a diffusion mechanism is involved in the homogenization reaction. This has been further substantiated by fitting the experimental data to kinetic equations for diffusion-controlled processes. The kinetic parameters evaluated from the ending time for the 520, 480, and 420 °C annealing experiments, using both the Arrhenius and the transition state theory formalisms, suggests a rather rigid activated complex for the rate-determining step of the process.

Keywords: arsenic • antimony • alloys • thermal analysis

Mineralogical Magazine; June 1987 v. 51; no. 360; p. 295-304; DOI: 10.1180/minmag.1987.051.360.12
© 1987, The Mineralogical Society
Mineralogical Society (