硫铋银矿(AgBiS_2)、Ag_2Bi_4S_7稳定性及在Ag_2S-Bi_2S_3体系中相关系

THE STABILITY OF MATILDITE(AgBiS_2) AND Ag_2Bi_4S_7 AND PHASE RELATJONS IN THE SYSTEM Ag_2S-Bi_2S_3

对Ag_2S-Bi_2S_3体系相图重新测定发现,硫铋银矿温度稳定范围是从室温直到其熔点773±5℃。在二元体系Ag_2S-Bi_2S_3内,硫铋银矿有一狭窄的固溶体区,在600℃时其组分变化范围是50.0+—54mol%Bi_2S_3,500℃时是50.0+—53.5mol%Bi_2S_3,400℃时是50.0+—52.5mol%Bi_2S_3。与此同时,α-AgBiS_2是在高于195±5℃富Ag_2S条件下稳定,低于此温度,转变为硫铋银矿。α-AgBiS_2在600℃时,其组分变化范围为46.5—50.0mol%Bi_2S_3,500℃时为47.0—50.0mol%Bi_2S_3,400℃时为48.0—50.0mol%Bi_2S_3。铜银铅铋矿纯银端元Ag_2Bi_4S_7最高稳定温度是697±5℃。高于此温度,转变为硫铋银矿和液相。块硫铋银矿(AgBi_3S_5)为同成分熔化,其熔点为745±5℃。

The phase diagram of the system Ag_2S-Bi_2S_3 has been re-determlned by vacuum silica technique. Matildite, which has a narrow solid solution range in the binary system, is present till its melting point, 773±5℃, but only has a composition of more than 50 mol% Bi_2S_3. Experiments show that variations in matildite composition are 50.0±54.0 mol% Bi_2S_3 at 600℃, 50.0±53.5 mol% at 500℃, and 50.0±52.5 mol% at 400℃. On the contrary, the compositional extent of the phase α-AgBiS_2 in the binary system is 46.5—50.0 mol% Bi_2S_3 at 600℃, 47.0—50.0 mol% at 500℃, and 48.0—50.0 mol% at 400℃. α-AgBiS_2 is stable only at the temperature higher than 195±5℃. Below this matildite is a stable phase.The upper temperature limit of the phase Ag_2Bi_4S_7 stability is 6974±5℃. Beyond that, it will be converted to matildite and liquid phase. Pavonite (AgBi_3S_5) congruently melts at 745±5℃. No solid solutions have been found for both phases in the binary system.