1. Cobalt sulfide
Cobalt- sulfur state The following sulfides are present in Figure 1:
Figure 1 Co-S system state diagram
CoS theoretically contains Co64.76% and S35.24%. The most common cobalt-sulfur compound is classified into CoS 1+x and is a hexagonal system. When H 2 S passes through a slightly acidic or ammoniacal aqueous cobalt salt solution, a normal black CoS precipitate is formed. CoS has two kinds of α-CoS with a solubility product of 5×10 -22 and β-CoS of 1.9×10 -27 . CoS is a very stable compound that begins to dissociate near the melting point (1160 ° C). Water vapor can decompose CoS at about 650 °C.
Co 4 S 3 : It is obtained by a melt method at a temperature higher than 830 ° C or by reducing solid CoS with hydrogen at 300 to 400 ° C. Co 4 S 3 lattice same spot copper ore, body-centered cubic type products. ΔG°=-61900+23.21T for the formation of Co 4 S 3 per mole of sulfur.
Co 3 S 4 contains Co 5.455% and S 42.05%, which is a face-centered cubic crystal form. At a temperature of 400 ~ 450 ℃, cobalt sulfide in the treated stream of hydrogen sulfide gas for 10 hours to prepare. Above 480 ° C, the precipitation of sulfur begins. At 630 ° C, Co 3 S 4 is decomposed into CoS and CoS 2 .
CoS 2: having a crystalline pyrite, or by a CoS CoO with an excess of sulfur was prepared by prolonged heating. Co 3 S 4 are generated by the solid S 2 and CoS △ G 2 gas at a solid ° 600 ~ K-50160 + 50.41T ( cal / mol molecular sulfur).
In addition, it has been found that there are sulfides such as Co 2 S 3 , Co 6 S 5 , and Co 9 S 8 .
Second, cobalt arsenide
The cobalt and arsenic state diagram is shown in Figure 2.
Figure 2 Co-As system state diagram
Cobalt can form four stable compounds with arsenic: Co 5 As 2 , Co 2 As, Co 3 As 2 , CoAs. The synthesized CoAs were non-magnetic and had a melting point of 1180 °C. When the temperature rises, the CoAs dissociate into low arsenic compounds. Co 5 As 2 is the main component of the yellow slag.
The ignition point of cobalt arsenic compounds is related to the arsenic content. The lower the arsenic content, the higher the ignition point. For example, the arsenic ignition temperature of -200 mesh: CoAs 700 ~ 750 ° C, Co 5 As 2 ≥ 800 ° C.
When CoAs is heated, the reaction with concentrated hydrochloric acid and sulfuric acid is weak, but it can generate extremely toxic arsine. CoAs dissolve well in nitric acid and aqua regia.
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