tailieunhanh - Handbook of Lubrication Episode 1 Part 12

Tham khảo tài liệu 'handbook of lubrication episode 1 part 12', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 272 CRC Handbook of Lubrication Table 3 PROPERTIES REQUIRED BY SOLID LUBRICANTS To Provide Low-Friction and Wear Thin films Self-lubricating materials Good film-forming ability powders Ductility Good adhesion to substrate Film continuity Ability to form transfer films Low-moderate elastic modulus Adequate strength for required load capacity Low-Shear Strength General High thermal oxidative hydrolytic stabilities High softening melting points Chemically inert High-thermal conducltvity diffusivity Corrosion protection of substrate Appropriate electrical conductivity No abrasive impurities Low toxicity environmental compatibility Low-thermal expansion electrical contacts it is being increasingly supplanted by MoS2 for three reasons. First is the wide variability in graphites from different sources MoS2 quality is more rigidly controlled by specifications. Second the low friction of MoS2 does not depend on adsorbed vapors and is in general lower in vacuum than in air. Finally the load-carrying capacity of MoS2 is generally superior. MoS2 has a lamellar structure but with interlamellar bonding being between adjacent layers of S atoms. The bonding is relatively weak via Van der Waals forces only and MoS2 is therefore an intrinsic solid lubricant. Adsorbed vapors usually increase friction but the effects are comparatively small. The thermal stability of MoS2 in nonoxidizing environments is of the order of 1100 C but in air oxidation begins to become significant at around 350 to 400 C. The normal air-oxidation product is MoO3 once believed to be abrasive but now known to be virtually A major concern with MoS2 is the presence of abrasive The reasons for concern are twofold. First and foremost chemical analyses provide no information about the form of the impurity abrasion by hard particles such as SiO2 depends greatly on their shape and size. Second other factors in addition to impurities can play a role in abrasiveness . crystallite .