| Nano-molybdenum disulfide（nano-Mo S2）has potential application value in the field of engine oil lubrication modification additives due to its excellent lubrication performance.Soot particles produced by diesel combustion will enter the engine oil,thus necessitating a systematic investigation of the interaction between nano-Mo S2 and soot.Figuring out the interaction mechanism and related tribochemical behavior of two particles,base oil and friction pair surface are the prerequisite for promoting the application of nano-Mo S2 in the field of engine oil additives.In this paper,the interaction between nano-Mo S2 and soot particles was deeply investigated,and the relevant lubrication mechanism was revealed,which has a certain innovation and application value in the development of nano-lubricating additives and lubricating materials.The research results provide a theoretical basis and data support for promoting the application of nano-Mo S2 in the field of engine lubrication.Spherical nano-molybdenum disulfide（s-Mo S2）was prepared by precursor method using thioacetamide and sodium molybdate as sulfur and molybdenum sources,respectively.Soot particles（DCS）obtained from incomplete combustion of diesel fuel were employed to simulate engine soot.The s-Mo S2 and DCS were characterized by scanning electron microscopy（SEM）,high-resolution transmission electron microscopy and X-ray diffraction.Subsequently,the tribological properties of s-Mo S2,DCS and s-Mo S2/DCS compound in dioctyl sebacate（DOS）and poly alpha olefin（PAO）,respectively,were tested using a high-frequency reciprocating ball-on-disk tribometer,and the effect of ZDDP on the above lubrication system also was investigated.Finally,the wear surface was characterized and analyzed by X-ray photoelectron spectroscopy,Raman spectroscopy,3D laser scanning microscope and SEM,and the relevant antagonistic or interaction mechanisms were revealed.The main research results are as follows:In DOS base oil,the addition of s-Mo S2 can significantly improve the lubrication performance of DOS base oil under selected test conditions.The DOS with 0.50 wt%s-Mo S2 presents the best lubrication performance,compared with that of pure DOS,the friction coefficient and total wear rate were reduced by～22%and～54%,respectively.When 0.50 wt%DCS was added into the DOS base oil,the wear on the surface of the friction pair was aggravated,compared with that of pure DOS,the friction coefficient was increased by about 37%,and the total wear rate was increased by about 50%.As0.50 wt%s-Mo S2 and 0.50 wt%DCS were simultaneously added into the DOS base oil,the lubrication modification effect of s-Mo S2 disappeared completely and even compared with DOS of 0.50 wt%DCS,the total wear rate and friction coefficient increased by about 9%.This result shows that DCS not only reduces the lubrication performance of DOS,but also inhibits the lubrication modification of s-Mo S2,showing the lubrication antagonism between the two particles.After adding 2.0 wt%ZDDP T203 into the lubricating system consisting of 0.50 wt%s-Mo S2 and 0.50 wt%DCS,the friction coefficient did not change significantly,while the wear rate basically recovered to a level close to that of the DOS with 0.50 wt%s-Mo S2.The results show that ZDDP T203 could weaken the antagonistic effect between s-Mo S2 and DCS.In PAO base oil,the addition of an appropriate amount of s-Mo S2 or DCS can improve its lubrication performance.Among the testing samples,the addition of 0.50 wt%s-Mo S2could reduce the friction coefficient and total wear rate of PAO by 48%and 75%,respectively.Similar to the lubricating function of s-Mo S2,the addition of 0.50 wt%DCS could reduce the friction coefficient by 16%and the total wear rate by 25%.However,when 0.50 wt%s-Mo S2 and 0.50 wt%DCS were simultaneously added to the PAO,the friction coefficient and total wear of the resulting lubrication system were lower than those of pure PAO,yet the two additives did not exhibit the lubrication synergies.Compared with the 0.50 wt%s-Mo S2 modified PAO,the total wear rate and friction coefficient increased by 181%and 69%respectively.The results show that the lubrication effect of s-Mo S2 was inhibited,and the inhibition was gradually serious with the increase of DCS amount.However,after adding 1.0 wt%ZDDP T202 was added into the lubricating system consisting of 0.50 wt%s-Mo S2 and 0.50 wt%DCS,the friction coefficient of the oil sample decreased by 24%and the total wear rate decreased by 69%.The lubrication effect was similar to that of 0.50 wt%s-Mo S2,indicating that ZDDP T202 could weaken the inhibitory effect of DCS on s-Mo S2.From the characterization results of the wear surface,it can be seen that no s-Mo S2lubricating film was generated on the friction surface when the DOS with s-Mo S2 and DCS acts as a lubricating medium,indicating that the antagonistic mechanism between DCS and s-Mo S2 was that the presence of DCS inhibited the formation of s-Mo S2lubricating film on the friction surface.Additionally,under the action of friction heat,DCS reacts with s-Mo S2 in DOS to also form the cemented molybdenum carbide on the friction surface,thus aggravating the abrasive wear on the friction pair surface,which is another reason for the lubrication antagonism between DCS and s-Mo S2.Interestingly,the Mo S2 lubrication film was reformed when ZDDP was added into the DOS with s-Mo S2/DCS compound.This phenomenon proves that the anti-antagonistic mechanism of ZDDP should be to promote s-Mo S2 to form Mo S2 composite lubrication film at the friction interface,thus showing a synergistic effect between the two particles.In PAO base oil,DCS also significantly inhibits s-Mo S2 film formation on friction surfaces,and the synergistic effect of ZDDP and s-Mo S2 could weaken the inhibitory effect of DCS. |
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