蒙脱石/二烷基二硫代磷酸钼复合润滑油添加剂的摩擦学性能

Tribological Properties of Montmorillonite/Molybdenum Dialkyl Dithiophosphate Composite Lubricant Additives

添加剂是改善润滑油性能的重要手段,对蒙脱石(MMT)和有机钼复合润滑油添加剂的减摩抗磨性能进行了研究,期望取得较单一添加剂更优异的润滑效果,提高机械设备在恶劣工况下的运行稳定性和安全性。研究结果表明:有机钼中的二烷基二硫代磷酸钼(MoDDP)和MMT作为单一润滑油添加剂均表现出较好的润滑性能,随着MMT和MoDDP添加质量分数的增加,摩擦系数和磨斑直径呈现先降低后升高的趋势,MMT和MoDDP的最佳添加质量分数分别为3.0%和1.5%。与基础油相比,1.5%MoDDP可分别降低41.0%的摩擦系数和48.9%的磨斑直径,3.0%MMT可分别降低40.6%的摩擦系数和48.2%的磨斑直径。与单一添加剂MMT、MoDDP相比,3.0%MMT/1.5%MoDDP复合添加剂可进一步改善润滑油的减摩抗磨性能,相较于基础油,可分别降低56.3%的摩擦系数和52.3%的磨斑直径。MMT和MoDDP具有优良的润滑性能和协同作用,润滑过程中能生成MoS_(2)、MoO_(2)、FeS_(2)、Fe_(2)O_(3)化学反应膜和SiO_(2)物理吸附膜,能够有效地降低摩擦、减少磨损。

Introduction Machinery and equipment are prone to equipment failure and even safety accidents caused by insufficient lubrication under severe working conditions.Adding additives with some superior performance in lubricant is an effective approach to improve the lubricant performance,reduce the friction and wear,and extend the service life of machinery.Lubricants are widely used in machinery and equipment as an important method of anti-wear and friction reduction.Silicate minerals are harmless to the environment and the humanbeing.A low roughness,high hardness friction reaction film can be formed by silicate minerals as lubricant additives during the lubrication process,which can effectively reduce wear.Organic molybdenum as a commonly used lubricant additive has superior antioxidant properties,and can decompose when pressure,temperature and other conditions meet the requirements,and then lead to a chemical reaction and form the protective film containing molybdenum elements,thus preventing the surface oxidation reactions to improve the tribological properties of the lubricant.In this paper,the friction and wear reduction properties of composite lubricant additives of montmorillonite(MMT)and organomolybdenum were investigated to obtain superior lubrication,thereby improving the operational stability and safety of machinery and equipment under severe operating conditions.Methods The lubrication performance of three molybdenum-based lubricants,i.e.,Mo DDP(C_(28)H_(60)O_(4)P_(2)S_(4)Mo),MoDTC(C_(34)H_(72)Mo_(2)N_(2)O_(2)S_6)and RS-568,was evaluated by a four-ball friction and wear tester to determine the organic molybdenum type and the optimal mass fraction of organic molybdenum in the composite lubricant additives.Tribological tests were then carried out on lubricant samples at different concentrations of MMT to determine the optimal mass fraction of MMT in the composite additives.After the preparation of the composite additive,the lubricating properties of the MMT/MoDDP composite additives were examined,and the friction reduction and anti-wear mechanism of the composite additive was investigated by energy dispersive spectroscopy,X-ray photoelectron spectroscopyand Raman spectroscopy.Results and discussion The results show that among the organic molybdenum additives,molybdenum dialkyldithiophosphate(Mo DDP)exhibits the optimum lubricant properties.The friction coefficient and wear spot diameter firstly decrease and then increase with the increase in the mass fraction of MMT and MoDDP in the oil,and the optimal mass fractions of MMT and MoDDP are 3.0%and 1.5%,respectively.Compared with the base oil,the friction coefficient is reduced by 41.0%and the wear spot diameteris decreased by 48.9%for oil sample at 1.5%MoDDP,and the friction coefficient is reduced by 40.6%and the wear spot diameter is decreased by 48.2%for the oil sample at 3.0%MMT.Compared with the oil samples at 3.0%MMT,the friction coefficient and the wear spot diameter was reduced by 26.3%and7.9%,respectively,for the oil sample with the composite additives.Compared with the oil samples at 1.5%MoDDP,the friction coefficient and the wear spot diameter are reduced by 26.6%and 6.6%,respectively,for the oil sample with the composite additives.The 3.0%MMT/1.5%MoDDP composite lubricant additives can further improve the friction reduction and anti-wear performance of the lubricant.Compared with the base oil,the friction coefficient and wear spot diameter are reduced by 56.3%and 52.3%,respectively,for the oil sample with the composite additives.During the friction process,a SiO_(2) physical adsorption film was deposited on the friction surface due to the adsorption property of MMT additives.Under the action of shear force,the layered MMT particles are subjected to shear,resulting in an interlayer slip,which can reduce the friction between the contact surfaces.The fractured MMT particles are mechanically filled in the surface wear area to improve the carrying capacity of the oil film.Moreover,a layered MoS_(2) film with a low shear strength and a high melting point can be generated due to the chemical reaction of the MoDDP additive.Also,the MoO_(2),FeS_(2),Fe_(2)O_(3) metal compound reaction film can be generated to prevent the direct contact of the friction interfaces.Although the single additive has a great lubrication effect,the MMT and MoDDP composite additives show a better lubrication performance and synergistic effects in the friction process.The composite metal compound layer and the physical adsorption film can be generated during friction to form the high load-bearing capacity of the lubricant film,thus increasing the strength and stability of the lubricant film,and it was able to continuously and effectively reduce friction and wear.The friction tests also verify that MoDDP and MMT have a positive synergistic effect in the friction process.During the lubrication process,chemical reaction films with MoS_(2),MoO_(2),FeS_(2),and Fe_(2)O_(3) and SiO_(2) physical adsorption films were generated,thus effectively reducing thefriction and wear.Conclusions The 3.0%(in mass fraction)MMT/1.5%(in mass fraction)Mo DDP composite additives exhibited the better lubricating properties,compared with a single additive.It was indicated that the MMT/MoDDP composite lubricant underwent a chemical reaction during the friction process,which produced molybdenum sulfides and oxides containing molybdenum(MoS_(2),Mo O_(2))and iron sulfides and oxides containing FeS_(2),Fe_(2)O_(3),as well as physically adsorbent films containing SiO_(2).The compound lubrication film could effectively reduce the friction of the interface.