Abstract

Research on the effects of applied electrical potential on friction and wear, a topic sometimes termed “Triboelectrochemistry”, has been reviewed. Historically, most such research has focussed on aqueous lubricants, whose relatively high electrical conductivities enable use of three-electrode electrochemical kinetic techniques, in which the electrode potential at a single electrode | fluid interface is controlled relative to a suitable reference electrode. This has led to identification of several different mechanisms by which applied electrode potentials can influence friction and wear. Of these, the most practically important are: (i) promotion of adsorption/desorption of polar additives on tribological surfaces by controlling the latters’ surface charges; (ii) stimulation or suppression of redox reactions involving either oxygen or lubricant additives at tribological surfaces. In recent years, there has been growing interest in the effects of applied electrical potentials on rubbing contacts lubricated by non-aqueous lubricants, such as ester- and hydrocarbon-based oils. Two different approaches have been used to study this. In one, a DC potential difference in the mV to V range is applied directly across a thin film, lubricated contact to form a pair of electrode | fluid interfaces. This has been found to promote some additive reactions and to influence friction and wear. However, little systematic exploration has been reported of the underlying processes and generally the electrode potentials at the interfaces have not been well defined. The second approach is to increase the conductivity of non-aqueous lubricants by adding secondary electrolytes and/or using micro/nanoscale electrodes, to enable the use of three-electrode electrochemical methods at single metal | fluid interfaces, with reference and counter electrodes. A recent development has been the introduction of ionic liquids as both base fluids and lubricant additives. These have relatively high electrical conductivities, allowing control of applied electrode potentials of individual metal | fluid interfaces, again with reference and counter electrodes. The broadening use of “green”, aqueous-based lubricants also enlarges the possible future scope of applied electrode potentials in tribology. From research to date, there would appear to be considerable opportunities for using applied electrical potentials both to promote desirable and to supress unwanted lubricant interactions with rubbing surfaces, thereby improving the tribological performance of lubricated machine components.

Graphical Abstract

中文翻译：

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摩擦电化学：施加的电势对润滑触点的摩擦和磨损的影响

摘要

已经审查了有关施加电势对摩擦和磨损的影响的研究，该主题有时被称为“摩擦电化学”。历史上，大多数这样的研究已集中在水性润滑剂，其相对高的电导率能够使用的三电极电化学动力学技术，其中在一个单一的电极的电极电位|相对于合适的参比电极控制流体界面。这导致确定了几种不同的机制，通过这些机制，施加的电极电势会影响摩擦和磨损。其中，最重要的是：（i）通过控制摩擦添加剂的表面电荷来促进极性添加剂在摩擦表面上的吸附/解吸；（ii）刺激或抑制涉及摩擦表面的氧气或润滑剂添加剂的氧化还原反应。近年来，人们越来越关注施加电势对由非水基润滑剂（例如酯基和烃基油）润滑的摩擦触点的影响。已经使用两种不同的方法来对此进行研究。一种是将mV到V范围内的DC电势差直接施加到薄膜上，| 流体接口。已经发现这会促进一些加成反应并影响摩擦和磨损。然而，关于基础过程的报道很少，而且界面上的电极电位还没有得到很好的定义。第二种方法是通过添加二次电解质和/或使用微米/纳米级电极来增加非水润滑剂的电导率，从而能够在单金属|上使用三电极电化学方法。流体界面，带有参比电极和对电极。最近的发展是引入离子液体作为基础流体和润滑剂添加剂。这些具有较高的电导率，可以控制单个金属的施加电极电位| 流体接口，同样与参比电极和对电极。“绿色”水基润滑剂的广泛使用也扩大了摩擦学中未来施加的电极电位的可能范围。从研究至今，使用施加的电势似乎有很大的机会，既可以促进理想的摩擦，也可以抑制不需要的润滑剂与摩擦表面的相互作用，从而改善润滑的机械部件的摩擦性能。

图形概要