Experimental study of the phase equilibria in the crystallization region of the chalkopyrite solid solution

Abstract

Citation: Kravchenko, T.A. (2011), Experimental study of the phase equilibria in the crystallization region of the cнalkopyrite solid solution, Vestn. Otd. nauk Zemle, 3, NZ6056, doi:10.2205/2011NZ000186. The Chalcopyrite (or intermediate) solid solution has been experimentally established in the center section of the Cu–Fe–S system at 300–800 °C [Merwin and Lombard, 1937; Yund and Kullerud, 1966; Cabri, 1973; Barton, 1973; Lihachev, 1973; Sugaki, et. al., 1975; Vaughan and Craig, 1978; 1997; Tsujmura and Kitakaze, 2004]. The phase equilibria concepts of the chalcopyrite solid solution crystallization products at low temperatures are not clear and contradictory, since they are based on the results of investigating the natural phase associations and the extrapolation of the separate experimental data to the low temperatures region [Vaughan and Craig, 1978; 1997]. The phase associations of the center section of the system Cu–Fe–S: 50 at.% S, Cu/Fe = 1.22–0.25, 47 at.% S, Cu/Fe = 1.12–0.63 and 45 at.% S, Cu/Fe = 1.44–0.69 have been synthesized to determine the phase equilibria in the crystallization region of the chalcopyrite solid solution. The scheme of the phase relations in the central Сu–Fe–S system (marked with the dashed lines in the figure below) considering the results of the most complete experimental study of phases from the region of the chalcopyrite solid solution [Cabri, 1973] has been used as the basis for the selection of the initial compositions of the synthesized samples. The synthesis has been carried out in the vacuum quartz ampoules using the melt cooling method from 1150– 1100 °C to the room temperature and the following annealing at 600 and 800 °C. The synthesized samples have been studied using the optical microscope and the X-ray diffraction methods. The obtained results are represented in the figure and in the table below. Talnakhitе Cu9Fe8S16 has been synthesized in samples 1 and 8: 50 at.% S, Cu/Fe = 1.22 and 47 at.% S, Cu/Fe = 1.12 in the association with chalcopyrite and bornite, whereas in sample 5а: 50 ат.% S, Cu/Fe = 0.54 it has been synthesized in the association with cubanite. Cubanite CuFe2S (cubic fcc) has been synthesized in samples 3–7, which original compositions are located on the chalcopyrite-cubanite-pyrrhotite line (fig.). In samples 3–5a: 50 at.% S, Cu/Fe = 0.82–0.54 cubanite has been synthesized in the association with the tetragonal chalcopyrite, in sample 6: 50 at.% S, Cu/Fe = 0.43 — in the association with pyrrhotite and haycockite, and in sample 7: 50 at.% S, Cu/Fe = 0.25 — in the association with pyrrhotite. It has been established that cubanite CuFe2S3 enriched by iron (Cu/Fe  0.5), is crystallized in the associations with haycockite and pyrrhotite, while being enriched by copper (Cu/Fe  0.5) it is crystallized in the associations with talnakhitе or chalcopyrite (samples 5 and 5a), depending on the cooling regime. Mooihoekite Cu9Fe9S16 has been synthesized in samples 9 and 12: 47 at.% S, Cu /Fe = 0.93 and 45 at.% S, Cu/Fe = 1.44 in the association with bornite, regardless of the synthesis regime. As opposed to cubanite and talnakhitе, which are crystallized in the form of the exsolution texture with chalcopyrite, mooihoekite is the easily diagnosed homogeneous phase. Haycockite Cu4Fe5S8 (phase of the haycockite composition with the cubic pc structure) has been synthesized in sample 10: 47 at.% S, Cu/Fe = 0.77 and 13: 45 at.% S, Cu/Fe = 1.20 in the association with bornite, in sample 11: 47 at.% S Of cu/Fe = 0.63 and 14–15: 45 at.% S, Cu/Fe = 1–0.83 in the association with bornite and pyrrhotine, and also in the above sample 6 in the association with pyrrhotite and cubanite enriched by iron. Same as mooihoekite, haycockite is diagnosed easily.