Phase relations in the system Ag 2 S-Cu 2 S-PbS-Bi 2 S 3

Abstract

The formation of sulfbismuthides and the extents of solid solutions in the system Ag 2 S-Cu 2 S-PbS-Bi 2 S 3 were studied at 500 degrees C using sealed and evacuated capsule methods. Liquid is present in the Cu 2 S-rich region of both the systems Ag 2 S-Cu 2 S-PbS and Cu 2 S-PbS-Bi 2 S 3 . In the system Ag 2 S-Cu 2 S-Bi 2 S 3 two new phases, Ag 2 Bi 4 S 7 and AgCu 5 Bi 6 S 12 , were found. Ag 2 Bi 4 S 7 was identified to be a benjaminite-type phase.Nine solid solutions were recognized in the system Ag 2 S-Cu 2 S-PbS-Bi 2 S 3 . Among the four extensive series, the pavonite solid solution can be expressed as Ag (sub 1-(x+y)) Cu (sub y+(n+1)z) Pb (sub 2x (super -) ) Bi (sub 3-(x+z) ) S 5 with 0 < x < 0.36, 0 < y < 0.36, 0 < z < 0.53 and n [asymp] 2, the benjaminite solid solution as Ag (sub 3.43-(x+y)) Cu (sub y+(n+1)z) Pb 2x Bi (sub 6.85-(x+z)) S 12 with 0 < x < 1.53, 0 < y < 0.55, 0 < z < 1.41, and n [asymp] 2, the Cu 3 Bi 5 S 9 solid solution as Ag y Cu (sub 3-(x+y)+(n+1)z) Pb 2x Bi (sub 5-(x+z)) S 9 with 0 < x < 0.56, 0 < y < 0.70, -0.21 < z < 0.16, and n [asymp] 2, and the CuBi 3 S 5 solid solution as Ag y Cu (sub 1-(x+y)+(n+1)z) Pb 2x Bi (sub 3-(x+z)) S 5 with 0 < x < 0.09, 0 < y < 0.12, 0 < z < 0.08, and n [asymp] 2. In each of the formulas, x, y, z, and n represent substitutions between Ag (or Cu) + Bi and 2Pb, Ag and Cu, and Bi and Cu, and interstitial addition of Cu, respectively. The lillianite solid solution extends from Pb (sub 2.8) Bi (sub 2.1) S 6 to Ag (sub 0.68) Cu (sub 0.20) Pb (sub 1.56) Bi (sub 2.67) S 6 , whereas the range of the heyrovskyite solid solution is limited to the range between Pb (sub 5.4) Bi (sub 2.4) S 9 and Ag (sub 0.76) Cu (sub 1.31) Pb (sub 3.18) Bi (sub 3.18) S 9 . In the AgBiS 2 solid solution, the amount of Cu varies inversely with the amount of Pb and the solid solution decreases in range with increasing PbS content. The wittichenite solid solution has a range from Cu 3 BiS 3 to Cu (sub 2.5) Ag (sub 0.5) BiS 3 and does not accommodate any detectable amount of PbS. The bismuthinite-aikinite solid solution is restricted to the system Cu 2 S-PbS-Bi 2 S 3 .