Relating Tribological Performance and Tribofilm Formation to the Adsorption Strength of Surface-Active Precursors
Relating Tribological Performance and Tribofilm Formation to the Adsorption Strength of Surface-Active Precursors
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DOI：
10.1007/s11249-019-1249-5
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发表时间：
2019-11
影响因子：
3.2
通讯作者：
A. Khan;Hongxing Wu;Q. Ma;Y. Chung;Q. Wang
中科院分区：
文献类型：
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作者：
A. Khan;Hongxing Wu;Q. Ma;Y. Chung;Q. Wang
由外力诱导的机械力化学反应为原位合成碳摩擦膜提供了一种独特的途径，可以改善摩擦磨损性能。在这项工作中，我们研究了摩擦膜的形成和摩擦学性能可能与三种添加剂在聚α烯烃（PAO 4）作为基础油中的吸附强度有关，即，环丙烷羧酸（CPCa）、环丙烷甲醇（CPMA）和1-环丙基乙醇（CPEA），其特征在于两个不同的表面活性基团-COOH和-OH。摩擦学试验结果表明，添加2.5wt%的CPCa的PAO 4得到最低的摩擦系数和磨损体积。FTIR和拉曼分析表明，尽管所有三种添加剂都含有相同的亚稳环丙烷环，但仅在使用CPCa而不是CPMA或CPEA作为油添加剂的情况下才形成大量摩擦膜。热重分析和分子动力学模拟表明，与CPMA和CPEA相比，CPCa在氧化铁表面的吸附更强。后一种分子的弱吸附导致它们在有机会参与摩擦膜形成所需的机械化学反应之前由于摩擦测试期间的闪速加热而从表面解吸。CPCa与钢表面的较强结合是这种类型的表面机械化学的必要条件，并且在我们的摩擦测试条件下对含碳摩擦膜的有效形成至关重要。
Mechanochemical reactions induced by external stress provide a unique approach for in situ synthesis of carbon tribofilms that can improve friction and wear performance. In this work, we studied how tribofilm formation and tribological performance might be related to the adsorption strength of three additives in polyalphaolefin (PAO4) as base oil, viz., cyclopropanecarboxylic acid (CPCa), cyclopropanemethanol (CPMA), and 1-cyclopropylethanol (CPEA) as characterized by two different surface-active groups –COOH and –OH. Tribo-testing results reveal that addition of 2.5 wt% CPCa to PAO4 gave the lowest friction coefficient and wear volume. FTIR and Raman analysis demonstrate substantial tribofilm formation only in the case when CPCa was used as the oil additive, not CPMA or CPEA, in spite of the fact that all three additives contain the same metastable cyclopropane ring. Thermogravimetric analysis and molecular dynamics simulations indicate the stronger adsorption of CPCa on the iron oxide surface compared with CPMA and CPEA. Weak adsorption of the latter molecules results in their desorption from the surface due to flash heating during tribotesting before they have the chance to participate in mechanochemical reactions required for tribofilm formation. The stronger binding of CPCa to the steel surface is a necessary condition for this type of surface mechanochemistry and appears critical to the efficient formation of carbon-containing tribofilms under our tribo-testing conditions.