Tribochemistry in contact recording

Even though the flying height is approaching molecular dimensions, it is expected to decrease as the areal recording density is increased. This study employs a new low-velocity test to obtain ultralow flying height with sustained intermittent asperity contacts and random seek accessing in a region near the middle diameter of the disk. Sensitive surface analytical tools are employed to follow tribochemical changes. Profiles are periodically measured across the disk surface using Fourier transform infrared spectroscopy for lubricant thickness and scanning-imaging micro-ellipsometry. Zdol lubricant is removed from the tested region through evaporation of low molecular weight scission fragments. The removal rate increased with increasing chemisorbed fraction and decreasing relative humidity. The increased removal rate is attributed to increases in the Zdol relaxation time. A longer relaxation time allows more time for bond dissociation following asperity contacts. Chemisorption sites in the tested region were occupied by chemisorbed scission fragments with a carboxylic acid end group. Amine and sodium salts of the carboxylic acid were detected on the tested regions of Zdol lubricated, and unlubricated, overcoats. The presence of tribochemically generated carboxylic acid groups on Zdol and overcoat carbon explain the increased water adsorption measured on the tested regions.     

含磷抗磨,极压添加剂在铝—钢摩擦副中摩擦学特性的研究

利用Ｏｐｔｉｍｏｌ ＳＲＶ试验机考察了边界润滑条件下四种含磷添加剂在铝－钢摩擦副中的摩擦，磨损特性，研究了添加剂的摩擦化学反应，结果表明：含磷添加剂在铝－钢摩擦融 中不仅没有起到抗磨作用，相反会增加基础油润滑对铝的磨损，尤以亚磷酸酯为甚。磷酸酯与亚磷酸酯之间抗磨作用的差别在于其与铝之间的反应活性不同，在试验条件下化学腐蚀磨损可能是主要的磨损形式。     

含氮、氧改性菜籽油润滑添加剂对钢-钢摩擦副和钢-铝摩擦副摩擦学性能的影响

对菜籽油进行化学改性制备了一类氮氧型改性菜籽油添加剂（NOR），并利用红外光谱对其主要官能团进行鉴定。分别通过四球和SRV摩擦磨损试验机考察了以菜籽油为基础油，以NOR为添加剂时对钢-钢摩擦副和钢-铝摩擦副抗磨减摩性能的影响，用扫描电子显微镜观察分析钢球磨斑表面的形貌，同时通过对铝合金磨痕进行X射线光电子能谱分析，探讨了氮氧型改性菜籽油润滑添加剂的抗磨减摩机理。结果表明：以氮氧型改性菜籽油为添加剂，以菜籽油为基础油时，钢-钢摩擦副和钢-铝摩擦副均表现出良好的抗磨减摩作用，其润滑作用机理是由于长链菜籽油分子的载体作用、氮的高反应活性以及二者的协同作用在金属摩擦表面形成了含氮、氧及碳等元素的表面保护膜。     

Importance of the triboemission process for tribochemical reaction

Chemical reactions under boundary lubrication conditions are distinct from those of thermochemical ones. Flash temperature is very short and holding in esteem the mechanically triggered chemistry and thermally triggered chemistry at the contact of asperities caused by the flash temperature effect, the following question arises. ‘Can this reaction initiation process be considered in terms of overcoming the activation energy by heat or by another form of energy’? The purpose of this paper is to discuss that question in terms of the hypothesis: The common denominator of tribochemical reactions is that they might be initiated by low-energy electrons. This is consistent with the negative-ion-radical action mechanism (NIRAM) approach assuming that tribochemical reactions are initiated by electrons in the energy-range of 1–4 eV. The hypothesis is also relevant to the next author's hypothesis saying that the intermediate reactive species of both tribochemical reactions and some heterogeneous catalytic reactions are produced by the same mechanism, governed by the NIRAM approach. The catalyst effect on a chemical reaction is to increase its rate. The reaction rate is further increased when the catalyst is under friction (tribocatysis). The primary objective of this work is to better understand mechanisms of tribochemical reactions and catalytic processes. To initiate thermochemical reactions, heat should be supplied. The same is due to heterogeneous catalytic reactions, however, the catalyst lowers the reaction activation energy. Even a very high calculated flash temperature is short lived, thus, it rather cannot initiate tribochemical reactions by heat. The present author assumes that flash temperature can be expressed in the form of the thermionic emission. Bearing this in mind, it is possible to hypothesize that heterogeneous catalytic reactions are also initiated by thermal electrons. Accordingly, the tribocatalytic process might be initiated and/or enhanced by triboelectrons. Important objective of this work is to better understand both tribochemical reactions and catalytic/tribocatalytic processes. Tribochemistry of simple environment friendly lubricant compounds and examples of water synthesis catalytic and tribocatalytic processes are presented and discussed.     

Tribochemical Effects on Tribological Properties of Self-Mated Zirconia Ceramic in HFC-134a Gas

Tribochemical effects on the tribological properties of self-mated zirconia ceramic in CF₃CH₂F (HFC-134a) were investigated using a ball-on-disk type environmental tribometer. The friction chamber of the tribometer was attached to a micro-spot X-ray Photoelectron Spectrometer (XPS) for ensuring that surface analysis be conducted without exposuring the frictional surfaces to air. It was found that HFC-134a gas was an effective lubricant for zirconia ceramic, especially at a pressure higher than 10³ Pa. The products of tribochemical reactions between zirconia and HFC-134a molecules were detected. The amount and chemical state of the tribochemical products seemed to control the tribological behaviors. Thus, the role of tribochemical products on the tribological properties of zirconia in HFC-134a gas at 10⁴ Pa was studied in detail under applied loads of 0.6–5.0 N and sliding speed of 0.04–0.35 m/s. It was found that severe tribochemical reactions occurred at low speeds and high loads. The formation of ZrF₄ accelerated the chemical wear of zirconia, and raised the friction. Zirconia ceramic is suitable for use at moderate load and sliding speed under a reactive environment.     

含纳米碳酸钙、稀土粒子润滑油的摩擦学性能

采用透射电子显微镜（TEM）观察、测定了纳米碳酸钙、稀土（RE）粒子形貌和粒径；制备了含不同浓度与比例的纳米碳酸钙、稀土复合粒子的润滑油，并在四球摩擦磨损试验机上考察了其摩擦学性能；采用扫描电子显微镜与X射线光电子能谱仪分析了磨损钢球表面的形貌、化学组成。研究结果表明，纳米碳酸钙、稀土粒子的最佳的添加量为0.6%，最佳配比为w（CaC03）：w（RE）=1：1；该润滑油具有优良的抗磨、减摩性能；其抗磨、减摩机理与纳米粒子存在形态以及摩擦化学作用有关。     

Effect of amide type modified rapeseed oil as lubricating additive on friction and wear behavior of steel-steel and steel-aluminum alloy systems

A new type of environmentally friendly lube additive-amide type modified rapeseed oil was synthesized and characterized by infrared spectrum. Its effect on the friction and wear behavior of steel-steel and steel-aluminum alloy systems were investigated with a four-ball machine and an Optimol SRV friction and wear tester respectively.The morphographies of the worn surfaces were analyzed by means of scanning electron microscopy(SEM). The worn surfaces of the 2024Al alloy block were analyzed by means of X-ray photoelectron spectroscopy(XPS). The results show that the modified rapeseed oil as additives can obviously decrease the wear rate and friction coefficient of steel pair and steel-aluminum frictional pair. Its lubrication mechanism is inferred that a high strength complex protection films form on the worn surface of the Al alloy due to the adsorption or tribochemistry reaction of a long chain additive molecule and high reaction activity of N element.     

Study of interaction of EP and AW additives with dispersants using XANES

The chemical interaction of two kinds of dispersants (bis-succinimide dispersant and borated bis-succinimide dispersant) with four kinds of antiwear (AW) and extreme pressure (EP) additives (zinc dialkyldithiophosphate, dialkyldithiophosphate ester, diphenylphosphate ester and dialkyldithiocarbamate) has been investigated under different contact pressures. The chemical compositions of the tribofilms have been studied by B, N, P and S X-ray absorption near edge structure (XANES) spectroscopy. The N K-edge XANES analysis has been used to follow the reaction pathway of amine and imide functional groups in the dispersants and their interactions with EP and AW additives. It has been found that AW additives react with amine to form amine phosphate at low load. However, at high load, there is a good evidence for the formation of a nitrate phase in the tribofilms, the first direct observation of oxidative dispersant loss in the rubbing contact. On the other hand, EP additives behave differently and in general are less reactive. The B K-edge XANES has been employed to follow the interaction of borated dispersant with the EP and AW additive. In general, boron originally in the trigonal coordination, is converted to a tetrahedral coordination form in the process of tribofilm formation.     

A Combinatorial Approach to Elucidating Tribochemical Mechanisms

A new type of combinatorial tribological experiment is presented, which explores a series of tribological conditions, such as load and relative velocity, spatially separated as a library on one single sample. As an example, a library displaying the results of tribological testing of an additive under a series of different loads has been prepared and analyzed. The tribological information acquired during the testing has been correlated with spectroscopic information from the tribologically stressed surface. The use of imaging and small-area X-ray photoelectron spectroscopy has allowed the identification of the different tribologically stressed areas and the acquisition of detailed spectroscopic information. The composition and the thickness of the tribofilm were found to be dependent on the applied load. The use of the combinatorial approach shows the potential to greatly facilitate rapid characterization of new lubricant additives.     

羟基改性菜子油润滑添加剂的摩擦学性能

通过四球试验杌考察了羟基化改性菜子油润滑添加剂的抗磨性能与极压性能,用扫描电子显微镜观察分析磨斑表面的形貌,同时进行X射线光电子能谱分析,探讨了羟基化改性菜子油润滑添加剂的极压抗磨作用机理,结果表明：羟基化改性菜子油添加剂能明显改善菜子油的抗磨和减摩性能,其润滑作用机理是由于长链菜子油分子在摩擦面上吸附或发生摩擦化学反应形成了摩擦聚酯膜、氧化铁膜或铁皂共同组成的起抗磨作用的润滑膜。