Preparation Of Hydrotalcite‐like Anti‐friction Materials And Investigation On Its Antifriction Mechanism

As a kind of environmental friendly double layered minerals, hydrotalcite has been used widely. Our previous studies have shown that it has excellent antifriction and antiwear performances. However, as a new additive for lubricating oil, the study on it is less. Most works focus on the simple evaluation of its tribological properties, there is no more details on the analysis of tribofilms or the antifriction mechanism. So, in this paper, the micro-nano size of hydrotalcite was prepared, intercalated with organic anions and processed heat treatment. Then the tribological performance was investigated. Many surface analysis techniques were used to study the morphologies and chemistry of tribofilms. The paper also reported the interaction of hydrotalcite with rubbed surfaces and other additives. The mechanism of antifriction, antiwear, and tribofilms formation was investigated. The crystal structure of hydrotalcite under friction was also studied. All these works would provide theoretical and technical support for the industrialization of hydrotalcite in lubricating oil.In this study, Ni-Al, Mg-Al and Co-Al hydrotalcite were prepared and modified by organic surfactant. The optimization of preparation and modification conditions was obtained. The tribological performance of lubricating oil with hydrotalcite was investigated by four-ball, high frequency fretting and gear friction test machines. The atomic force microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray near edge spectroscopy were used to characterize the tribofilms. From the result of the surface analysis and the friction experiment, the antifriction and antiwear mechanism of hydrotalcite in base oil has obtained.The study has shown that the addition of Ni-Al, Mg-Al and Co-Al hydrotalcite all can effectively improve the antifriction and antiwear properties of base oil. The heat treatment of Mg-Al hydrotalcite could improve the antifriction performance origin powder. The friction coefficient of base oil and wear scar diameter could be reduced by 19%-22.3% and 33% respectively with addition of Co-Al hydrotalcite. The surface analysis has shown that the hydrotalcite particle can be absorbed on the rubbed surfaces during friction, which could prevent the direct contact of rubbed surfaces. Then the friction coefficient, wear rate, surface roughness, grinding depth and density would be reduced. The addition of hydrotalcite also could prevent the oxidation of base oil and eliminate the sulfate corrosion of steel surface. The structure of hydrotalcite was distorted under friction and some of Al in octahedral coordination was transferred to tetrahedron ones. That can be ascribed to the friction coefficient reduction of base oil with hydrotalcite. There is competition between hydrotalcite and zinc dialkyl dithiophosphates(ZDDP) when the mixture of them used as additive. The appearance of hydrotalcite would reduce the chain length of polyphosphate in ZDDP tribofilms and the sulfide near the tribofilms was oxidized to sulfate. That is why the friction coefficient increased when the mixture of hydrotalcite and ZDDP was used. After long time friction the appearance of hydrotalcite lead the formation Fe S in the ZDDP tribofilms, which could improve the extreme pressure properties of ZDDP.