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| Comparison between Molybdenum Disulfide (MoS2) & Tungsten Disulfide (WS2): |
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Tungsten Disulfide (WS2) is one of the most lubricious materials known to science. With Coefficient of Friction at 0.03, it offers excellent dry lubricity unmatched to any other substance. It can also be used in high temperature and high pressure applications. It offers temperature resistance from -450º F (-270º C) to 1200º F (650º C) in normal atmosphere and from -305º F (-188º C) to 2400º F (1316º C) in Vacuum. Load bearing property of coated film is extremely high at 300,000 psi.
Tungsten Disulfide (WS2) can be used instead of Molybdenum Disulfide (MoS2)and Graphite in almost all applications, and even more. Molybdenum and Tungsten are from same chemical family. Tungsten is heavier and more stable. Molybdenum Disulfide (Also known as Moly Disulfide) till now has been extremely popular due to cheaper price, easier availability and strong and innovative marketing. Tungsten Disulfide is not new chemical and has been around as long as Moly, and is used extensively by NASA, military, aerospace and automotive industry.
Till few years ago, price was Tungsten Disulfide was almost 10 times that of Molybdenum Disulfide. But since then price of Molybdenum Disulfide has doubled every six months. Now the prices of both chemicals are within comparable range. Now, it makes more economic sense to use superior dry lubricant (Tungsten Disulfide) and improve the quality and competitiveness of final product.
Tungsten Disulfide offers excellent lubrication under extreme conditions of Load, Vacuum and Temperature. The properties below show that Tungsten Disulfide offers excellent thermal stability and oxidation resistance at higher temperatures. WS2 has thermal stability advantage of 93ºC (200ºF) over MoS2. Coefficient of Friction of WS2 actually reduces at higher loads.
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| Physical and Technical Properties |
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| Propoerties |
Tungsten Disulfide (WS2)
CAS No 12138-09-9 |
Molybdenum Disulfide (MoS2)
CAS No 1317-33-5 |
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| Colour |
Silver Gray |
Blue-Silver Gray |
| Appearance |
Crystalline Solid |
Crystalline Solid |
| Melting Point (º C) |
1250º C, 1260º C (decomposes) |
1185º C (decomposes) |
| Boiling Point |
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450º C |
| Density |
7500Kg.m-3 |
5060 Kg.m-3 |
| Molecular Weight |
248 |
160.08 |
| Coefficient of Friction |
0.03 Dynamic; 0.07 Static |
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| Thermal Stability in Air |
COF <0.1 till 1100ºF (594ºC) |
COF <0.1 @600ºF (316ºC) increases to 0.5 @1100ºF (594ºC) |
| Thermal Stability in Argon |
COF <0.1 till 1500ºF (815ºC) |
COF increases rapidly starting @800ºF (426ºC)
COF >0.1 @900ºF (482ºC) |
| Load Bearing Ability |
300,000 psi for coated film
COF:0.044 @ 20,000 psi
COF reduces to 0.024 between 200,000 to 400,000 psi |
250,000 psi |
| Lubrication Temperature Range |
Ambient: from -273ºC to 650ºC Vacuum(10-14 Torr): from -188ºC to 1316ºC |
Ambient: from -185ºC to 350ºC Vacuum: from -185ºC to 1100ºC |
| Chemical Durability |
Inert Substance, Non-Toxic |
Inert Substance, Non-Toxic |
| Magnetism |
Non-Magnetic |
Non-Magnetic |
| Electrical Properties |
Has Semiconductor properties |
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| Rockwell Hardness |
30HRc |
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| Coating Film Thickness |
0.5 micron |
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| Corrosion Stability |
Can slow down the corrosion rate, but can not fully prevent substrate corrosion |
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| Coatable Substrates |
Iron, Steel, Aluminum, Copper, other Metals, Plastics and Manmade Solids |
Iron, Steel, Aluminum, Copper, other Metals, Plastics and Manmade Solids |
| Compatibility |
Oil, Solvent, Paint, Fuel |
Oil, Solvent, Paint, Fuel |
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Tungsten Disulfide