The so-called synthesis method is the destruction of molybdenum in molybdenite concentrate structure and composition, re-assembled, generate artificial lattice crystal of molybdenum disulfide.
Obviously, the molybdenum in the synthesis process undergoes two redox reactions of Mo 4 + →Mo 6+ →Mo 4+ , and is converted into molybdenum ore to form ammonium molybdate or high-purity molybdenum trioxide to molybdenum trisulfide. The product is finally reconverted into a series of phase transformations of synthetic molybdenite (Figure 1, Figure 2). The process is based on molybdenum ore, which is converted from the phase of molybdenum to remove impurities. Common production practices are as follows:
Figure 1 Synthesis method (1) Production process
Figure 2 full process (two) production process
1. Wet vulcanization process
The process produces high-purity molybdenum disulfide by using ammonium molybdate and molybdenum trisulfide intermediate products and using H 2 S as a vulcanization agent of ammonium molybdate.
There are many processes for producing ammonium molybdate, and any method can be used as long as a high-purity ammonium molybdate solution is obtained.
This production process, the purification process has been made of ammonium described in Section II, purified ammonium molybdate solution was not crystallized, precipitated, hydrogen sulfide gas directly into the body is vulcanized. With a large amount of H 2 S introduced, the following reactions will occur in the solution:
(NH 4 ) 2 MoO 4 +3H 2 S=MoS 3 ↓+2NH 3 ↑+4H 2 O
According to exp.B. Hexacos, the reaction mechanism is: First, a series of intermediate reactions in which sulfur is replaced by oxygen one by one after the ammonium molybdate solution is introduced into H 2 S:
(NH 4 ) 2 Mo | +H 2 S | (NH 4 ) 4 MoSO 3 | +H 2 S | (NH 4 ) 2 MoS 3 O | ||||
→ | → | |||||||
+H 2 S | (NH 4 )MoS 3 O | → | (NH 4 ) 2 MoS 4 | |||||
→ | +H 2 S | |||||||
[next]
This series of ammonium thiomolybdate can be dissolved in water and cannot be precipitated. After the reaction, the solution is acidified, and the following reaction occurs to form a precipitate:
(NH 4 ) 2 MoS 4 +2H + | → | 2NH + 4 + | H 2 MoS 4 | ||||
Acid decomposition | |||||||
MoS 3 ↓H 2 S↑ | |||||||
A dark brown precipitate of MoS 3 is finally produced. Pyrolysis of MoS 3 can produce MoS 2 :
MoS 3 | △ | MoS 2 +S↑ |
= |
In industrial practice, care should be taken to isolate the air, especially oxygen. Otherwise, even if a very small amount of oxygen is entered, the following reaction will occur:
2MoS 3 +9O 2 =2MoO 3 +6SO 2 ↑
In industrial practice, it should also be noted that the roasting process should maximize the sublimation of S. Otherwise, the mixing of free sulfur and molybdenum trioxide into molybdenum disulfide will greatly increase the acid value of the product and hinder its application.
2. Fire method (baking) vulcanization process
The process is made from molybdenum concentrate as raw material, firstly made of high-purity molybdenum trioxide, high-purity molybdenum trioxide and calcium sulfide are reacted in roasting, and vulcanization is a feature of the process. The process of producing high purity molybdenum trioxide has also been described in Section IV. MoO 3 reacts with CaS as follows:
MoO 3 +3CaS | â–³ | MoS 3 +3CaO |
= |
At the same time as this displacement reaction occurs, MoS 3 also produces an auto-oxidation reduction reaction. After the completion of the calcination, CaO may be separated by water dissolution, alkali-soluble or acid-soluble to remove the residual MoO 3 or CaS which is not sufficiently reacted. However, the requirements for MoS 3 due to the self-oxidation reduction reaction are the same.
In summary, the synthesis method can remove impurities to the utmost in the phase transformation process of molybdenum, and produce a product with high purity of MoS 2 . However, it also has the following shortcomings:
(1) The process is lengthy, the molybdenum recovery rate is low, the processing cost is high, and the cost is high.
(2) After auto-oxidation reduction of molybdenum trisulfide, the product tends to have free sulfur and molybdenum trioxide. These substances are the main impurities of molybdenum disulfide and have a great influence on the application.
(3) It is generally believed that the artificial lattice of molybdenum disulfide is not as good as the natural lattice molybdenum disulfide.
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