ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2012, Vol. 57, No. 8, pp. 1158–1162. © Pleiades Publishing, Ltd., 2012.
Original Russian Text © Z.T. Gasanova, Z.S. Aliev, Yu.A. Yusibov, M.B. Babanly, 2012, published in Zhurnal Neorganicheskoi Khimii, 2012, Vol. 57, No. 8, pp. 1238–1242.
PHYSICOCHEMICAL ANALYSIS
OF INORGANIC SYSTEMS
Phase Equilibria in the Cu–Cu S–As System
2
Z. T. Gasanova, Z. S. Aliev, Yu. A. Yusibov, and M. B. Babanly
Baku State University, Baku, Azerbaijan
eꢀmail: Babanly_mb@rambler.ru
Received January 20, 2011
Abstract—Phase equilibria in the Cu–Cu S–Assystem have been studied by DTA and Xꢀray powder diffracꢀ
2
tion. Cu0.667S0.333–As, Cu0.667S0.333–Cu0.735As0.265, and Cu S –As polythermal sections, an isothermal
0.8
0.2
section at 300 K, and the liquidus projection have been constructed. Our data differ from reported data in the
extents of primary crystallization phase fields and the coordinates of some invariant equilibrium points.
DOI: 10.1134/S0036023612050075
The Cu–As–S system has long kept the attention reaction Cu As → α
+
β
(where
α
and
β
are solid soluꢀ
8
of researches for the following two reasons. First, tions based on copper and Cu As, respectively). The
3
almost all of the hitherto known ternary compounds of
this system are naturally occurring as minerals [1, 2]:
Сu AsS (enargite and luzonite), Cu As S or
other two copper arsenides are phases of variable comꢀ
position with homogeneity ranges of 25.6–27.4 at %
3
4
12
4 31
As (
melts congruently at 1100 K (the dystectic point has
the composition 26.5 at % As). The phase is stable
β
phase) and 30.31 at % As
γ
phase). The
β
phase
Cu AsS (tennantite), Cu As S (sinnerite), CuAsS
3
4
6
4 9
(
lautite), and Cu As S (pearceite), and they are of
3 2 4
γ
great interest for the geochemistry of the Earth.
within a range of 573–982 K. At 573 K, it decomposes
by the solidꢀphase reaction γ → β + As, and at 982 K,
Second, ternary compounds and vitreous alloys of
this system are valuable functional materials, which
have semiconductor, photoelectric, and other imporꢀ
tant properties [3–5].
T, K
Numerous reported data on phase equilibria in the
Cu–As–S system and the properties of its ternary
phases are compiled in the survey [5]. However, an
inspection of these data shows that, although some
polythermal sections have been studied, there is yet no
comprehensive idea of phase equilibria in the system.
The schematic liquidusꢀsurface projection conꢀ
structed in [5] using data taken from [6–9] suffers
from serious drawbacks: because of the insufficiency
of experimental data, primary crystallization fields for
most phases are demarcated only conventionally, isoꢀ
therms are not shown on them, nor are exact coordiꢀ
nates of invariant equilibrium points, and so on. The
schematic and controversial character of this diagram
was also mentioned by Müller and Blachnik [10, 11].
1
400
L
1200
L +
85
α'''
L + As
e4
9
1
000
α
'''
α
''' + As
800
705
(
6
00
00
Cu S) + As
2
II
In the context of the foregoing, we have undertaken
a new, detailed study of phase equilibria in the Cu–
As–S system. Here, we report on the Cu–Cu S–As
2
375
4
subsystem.
The boundary constituents and binary phases of the
(
Cu S) + As
2
I
Cu–Cu S–As subsystem have been studied in a
2
detailed way.
Cu0.667S0.333 20
40
60
80
As
The Cu–As system [12,13] is characterized by the
formation of three intermediate phases: Cu As, Cu As
at %
,
8
3
and Cu As2. The first phase is stable below 653 K, a temꢀ
perature at which it decomposes by the peritectoid
5
Fig. 1. Cu
S –As quasiꢀbinary system.
0.677 0.333
1158