【作者】 解国新；

【导师】 雒建斌；

【作者基本信息】 清华大学 ， 机械工程， 2010， 博士

【摘要】 电场作用下薄膜润滑性能研究不仅是润滑理论发展的一个前沿领域,而且在带电机械润滑系统、微/纳机电器件等方面有重要的学术和工程价值。本论文主要以外加电场对纳米级润滑膜性能影响为主题,从成膜特性和润滑膜内部产生微汽泡现象两个方面进行讨论和分析。(1)探讨了油基、乳液和水基等润滑剂在外加电场作用下的成膜特性:提出了阳离子对电场的响应特性不同是决定具有不同侧链长度的离子液体在电场作用下成膜能力存在差异的直接原因;考察了水包油乳液在外加电场下的成膜能力与电场强度、乳化剂浓度以及油相浓度的关系,通过构造楔形入口区油滴失稳模型从理论上分析了电场作用下油滴的变形和破裂能力对成膜性能的影响;对比考察了带正、负电头基以及不同浓度的表面活性剂水溶液在电场下的成膜性能,详细分析了表面活性剂分子与带电固体表面的相互作用对成膜性能的影响。实验发现润滑接触区纳米级润滑膜的流动性在外加电场强度达到一个临界值后会出现减弱甚至消失的现象。提出了靠近固体壁面的润滑液体分子类固化转变在电场作用下的大幅度增强是导致接触区润滑膜流动性出现减弱的重要原因。(2)深入地考察了外加电场作用下不同润滑膜内部产生微汽泡的现象,发现在其它实验条件相同情况下,电极表面有介电层存在时润滑膜中微汽泡产生更为剧烈的现象;提出产生的微汽泡是局部热效应和电化学反应共同作用的结果,其中局部热效应占主导作用;建立了描述纳米级润滑膜中微汽泡生长和运动特性的理论模型,并用该模型验证了微汽泡生长、运动特性与液体基本物化性质之间关系的实验结果。搭建了电致轴承破坏试验台,考察了轴承润滑表面在较小回路电流下(~1 mA)的损伤特性,提出了微汽泡的产生及其溃灭是润滑表面形成凹坑的主要原因。更多还原

【Abstract】 The study on thin film lubrication under an external electric field (EEF) is a frontier field of the lubrication research, and it is of considerable academic and engineering values to charged lubrication systems and micro/nano electromechanical devices, etc. This dissertation focuses on the properties of nanoscale lubricant films under an EEF in terms of the film forming properties and the microbubble emergence behavior in thin lubricant films. The following conclusions are drawn:Firstly, the film forming properties of oil based lubricants, emulsion and water based lubricants under EEFs are investigated. It is proposed that the difference in the response of cations to EEFs determines the discrepancy of the film forming properties among ionic liquids with various side chain lengths. The relationships between the film forming properties of oil-in-water emulsions and the EEF strength, the emulsifier concentration and the oil phase concentration are studied. Moreover, an oil destabilization model in the inlet region is constructed to analyze the effects of the deformation and breakup of oil droplets under EEFs on the film forming properties theoretically. Furthermore, the film forming properties of surfactant solutions with positive and negative charged head-groups and various surfactant concentrations are compared, and the effect of the interaction between surfactant molecules and charged solid surfaces on the film forming properties is also analyzed.Secondly, an interesting phenomenon is found that the fluidity of nanoconfined lubricants in the contact region becomes very weak and disappears eventually when an EEF of larger than the threshold intensity is applied. It is proposed that the solid-like transition of liquid molecules near charged confined solid surfaces is greatly intensified by the EEF, resulting in the reduction in the fluidity of lubricant films in the contact region.Thirdly, another interesting phenomenon that many microbubbles emerge in thin lubricant films under EEFs is studied. It is found that microbubbles emerge more intensively after a dielectric layer is coated onto the electrode while other experimental conditions remain unchanged. The relationships between the electric current, interfacial damage on the contact pairs and the emergence of microbubbles are discussed. It is proposed that overheating and electrochemical reactions contribute collectively to the occurrence of microbubbles in thin lubricant films under EEFs, and overheating plays a predominant role. A theoretical model describing the microbubble growth and motion characteristics in thin lubricant films is constructed, and the experimental relationships between the growth, motion characteristics of microbubbles and lubricant physicochemical properties can be well predicted with the proposed model.Finally, a bearing electrocorrosion tester is constructed to investigate the electrodamage behavior on the lubricated surfaces in bearings under the action of weak electrical currents as low as ~ 1 mA. It is demonstrated that the collapse of microbubbles contributes to the formation of craters on lubricated surfaces.更多还原