Environmental effects on superlubricity of hydrogenated diamond-like carbon: Understanding tribochemical kinetics in O2 and H2O environments
Environmental effects on superlubricity of hydrogenated diamond-like carbon: Understanding tribochemical kinetics in O2 and H2O environments
复制标题
DOI：
10.1016/j.apsusc.2021.152299
复制
发表时间：
2022-04-01
影响因子：
6.7
通讯作者：
Kim, Seong H.
中科院分区：
文献类型：
--
作者：
Jang, Seokhoon;Chen, Zhe;Kim, Seong H.
氢化类金刚石(H-DLC)在惰性条件下表现出超润滑性，是机器防护涂层的理想材料，但在潮湿的空气中往往会失去超润滑性。了解这种氧化过程的反应机理将是将环境耐受性纳入H-DLC化学以在环境空气中获得超润滑性的先决条件。但是，在样品转移到异地分析过程中，摩擦测试的H-DLC表面的空气氧化阻碍了对机理的理解。作为一种替代方法，本研究推导了一个朗缪尔型动力学模型来分析氧化环境中H-DLC表面发生的摩擦化学过程。该模型揭示了O-2和H2O对H-DLC摩擦化学的环境效应。O-2氧化的氢-类金刚石表面在磨合期后仍保持较低的摩擦力(µ约为0.057)，但易发生摩擦磨损(磨损率约为32µm(3)/(N.mm))。相反，H2O氧化表面对水的吸附很敏感，水的吸附起到了边界润滑层的作用，保护表面免受磨损(类似于3.4µm(3)/(N.mm))，但在磨合期后具有相对较高的摩擦力(u约为0.22)。H-DLC被O-2或H2O氧化的几率(与10(-4)Torr(-1)S(-1)相似)与烃类在催化活性金属上的反应几率(与10(-3)Torr(-1)S(-1)相似)。
Hydrogenated diamond-like carbon (H-DLC) exhibits superlubricity in inert conditions, making it ideal for protective coating in machines, but its superlubricity is often lost in humid air. Knowing reaction mechanisms of such oxidation processes would be a prerequisite to incorporate environment tolerance into the H-DLC chemistry for superlubricious performance in ambient air. But mechanistic understanding has been hampered by air-oxidation of the tribo-tested H-DLC surface during the sample transfer for ex-situ analyses. As an alternative approach, this study derived a Langmuir-type kinetics model to analyze tribochemical processes occurring at the H-DLC surface in oxidative environments. The model unveiled very distinct environmental effects of O-2 and H2O on tribochemistry of H-DLC. The O-2-oxidized H-DLC surface retains low friction after the run-in period (mu approximate to 0.057) but is susceptible to frictional wear (wear rate approximate to 32 mu m(3)/(N.mm)). In contrast, the H2O-oxidized surface is susceptible to the adsorption of water which acts like boundary lubricant layers protecting the surface from wear (similar to 3.4 mu m(3)/(N.mm)) but with relatively high friction after the run-in period (mu approximate to 0.22). The oxidation probability of H-DLC by O-2 or H2O (similar to 10(-4) Torr(-1) s(-1)) is found to be comparable to the reaction probability of hydrocarbons on catalytically-active metals (similar to 10(-3) Torr(-1) s(-1)).