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Lubricating properties
Molybdenum disulfide - natural or synthetic molybdenum ore, which is unmatched by lubricating grease and other solid lubricants, is widely used as the "king of solid lubrication".
Two conditions are necessary as a lubricant, that is, the material has a good slip surface inside, and the material has strong adhesion to the substrate.
The molybdenum disulfide is superposed by a sandwich interlayer of S—Mo—S. In the layer, S-Mo is closely connected by a polarity bond. Between the layers, S-S is connected by molecular bonds. The bonding force of Van der Waals-London force is too weak, and when it is subjected to a small shear stress, it can be broken and slip. And such a slip surface has one between every two sandwich layers. That is, there are 399 good slip surfaces in a thin layer of 1 μM thick molybdenum disulfide.
Molybdenum disulfide strongly adheres to the substrate, which is also unmatched by other lubricants such as graphite .
In addition, it has many good lubrication properties.
(1) Wide temperature adaptation range: high temperature aviation silicone oil can withstand high temperatures of 250 ° C, and refrigeration oil is resistant to -45 ° C low temperature, which is already a leader in lubricating grease. The molybdenum disulfide is used in air, and can be used for a long time at 349 ° C, or short-term use at 399 ° C; in vacuum, molybdenum disulfide can work at 1093 ° C; in an inert gas such as argon, molybdenum disulfide can be Working at 1427 ° C. In addition to being able to work at high temperatures, molybdenum disulfide can also work at temperatures up to -184 ° C or lower.
(2) Heavy-duty load: Under heavy load, the grease lubricating film will be ineffective due to thinning or even disappearance. However, the molybdenum disulfide lubricating film having a thickness of only 2.5 μm has good lubricating performance at a heavy load of 2800 MPa and 40 m/s at a high speed. Even if the load is increased to more than 3200MPa yield strength steel, molybdenum disulfide lubricating efficacy still exist. This is difficult to achieve with any other liquid and solid lubricants. Thus, molybdenum disulfide produced by most of the world are treated as "polar additive" in combination with fat, such as the common market lithium grease molybdenum disulfide, molybdenum disulfide, calcium based grease, molybdenum disulfide various gear Film-forming paste and so on.
(3) Vacuum resistance: The spacecraft flies at a height of more than 500km, and the vacuum in space has reached 1.3×10 -2 μPa or more: at this time, the evaporation of the grease lubricant has exceeded its limit evaporation rate. This will not only invalidate the lubrication, but also volatilize the gas and pollute the instrument and the environment. The lubrication performance of the graphite lubricant in the vacuum will also be greatly reduced, while the lubrication performance of molybdenum disulfide under vacuum is better than that in the air. Performance is better. At a vacuum of 1.3 × 10 -2 μPa, the friction coefficient of the molybdenum disulfide wipe film was reduced to 0.0016, which was much lower than 0.1 in air. The molybdenum disulfide sputter film bearing operating under the conditions of 1.3μPa vacuum, 8000r/min and 0.2MPa has a working life of more than 1500h.
(4) Radiation resistance: Oils and fats will fail due to molecular crosslinking under radioactive irradiation. The molybdenum disulfide film was almost unaffected by the 7×10 8 Roenten radiation before the irradiation. Before the irradiation, the molybdenum disulfide has a static friction coefficient of 0.13~0.14, a dynamic friction coefficient of 0.11~0.12, a wear of 306.1×10 -3 cm 3 , and an irradiation of 0.13, 0.11 and 382.3×10 -3 cm respectively. 3 . This is the main reason why molybdenum disulfide is widely used in the atomic industry.
(5) Corrosion resistance: The stable chemical properties of molybdenum disulfide make it have the advantages of acid resistance, alkali resistance and corrosion resistance, which creates conditions for the combination of molybdenum disulfide and other lubricants. [next]
(6) Wide range of speed adaptation: Molybdenum disulfide has good lubrication performance at very low or very high speeds. Grease lubricants will exhibit "stick-slip" or "cold welding" at low speeds; at high speeds, they will fail due to cracking of the lubricating film.
In view of the good lubricating properties of molybdenum disulfide, it has been developing rapidly since its application in 1940. Research in the United States and the former Soviet Union started early and was widely used; and Japan has seven companies that produce and market molybdenum disulfide. China's research on molybdenum disulfide started late, and began research in 1958. In 1963, Shanghai Jinggangshan Chemical Plant began production. As of 1986, China produced 150 tons of molybdenum disulfide powder per year, and the annual demand has reached 400 tons. Northwest Nonferrous Metal Research Institute to identify the "molybdenum disulfide lubricant preparation of new technology" in 1987 by the China Nonferrous Metals Industry Corporation has presided over, pressing process in 1987, and in Luanchuan Molybdenum Company 1992 The Northwest Nonferrous Metal Research Institute has newly built a production line with an annual production capacity of l00t, which has been officially put into production, which will alleviate the shortage of molybdenum disulfide in China. The criteria are shown in the table below.
Table 2: Molybdenum sulfide (lubricating grade) quality standard
Manufacturer
grade
Main ingredient content (%)
MoS 2
≥
Acid insoluble matter
Fe
≤
MoS 3
≤
water
≤
oil
≤
C
≤
acidity
Chinese professional standards
ZBG12022-90
First grade
98
1.50 1
0.30
0.50
5
Qualified product
96
2.50 1
0.70
0.50
5
Northwest Nonferrous Metal Research Institute Enterprise Standard
0 #
99
0.10 2
0.10
0.10
0.2
1 #
98
0.20 2
0.15
0.10
0.2
International trade standard
Non-micronized
98.0
0.40 1
0.13
0.05
micro-
0.03
1.10
0.5
Micropowder
98.0
0.40 1
0.13
0.20
0.15
0.20
1.10
3.0
Climax Chemical Product Standard
CC-3D72 years
Non-micronized
product
98.2
0.35 1
0.15
0.01
0.0
0.03
1.00
0.01
standard
98.2
0.50 1
0.20
0.05
0.05
0.05
1.50
0.05
Micropowder
product
98.0
0.35 1
0.15
0.03
0.0
0.25
1.20
0.55
standard
98.0
0.50 1
0.20
0.05
0.05
0.40
1.50
0.59
Shanghai Q/HG11-85-82
0 #
98
1 #
97
2 #
96
Liao Q240/80
0 #
99
0.02 1
0.06
1 #
99
0.02 1
0.04
2 #
98
0.05 1
0.1
Yanchuan Molybdenum Company Enterprise Standard
0 #
99
0.10
0.20
0.05
0.20
1.00
0.2
1 #
98
0.20
0.30
0.1
0.45
1.00
0.5
2 #
97
0.40
0.40
0.1
0.50
1.50
1.0
3 #
96
0.50
0.40
0.1
0.50
1.50
1.0
1 insoluble matter; 2 SiO 2 .
Molybdenum disulfide is not only the "king of solid lubrication" but also a good desulfurization Catalyst in the refining process of petroleum products.
Regardless of the lubricant or catalyst, the MoS 2 purity requirements of the product are high.
The molybdenum concentrate containing low purity of MoS 2 is produced into high-purity molybdenum disulfide powder. The production process is numerous, and each factory has its own characteristics, which are different, and the research classification is not uniform. The author summarizes them into two broad categories: synthesis and natural methods.