State Key Laboratory of Tribology, Tsinghua University , Beijing 100084, China.
ACS Appl Mater Interfaces. 2017 Sep 13;9(36):30891-30899. doi: 10.1021/acsami.7b10515. Epub 2017 Sep 1.
Layered double hydroxides (LDHs) are a class of naturally occurring inorganic minerals that are composed of divalent and trivalent metal cations. In this study, three different sized NiAl-LDH nanoplatelets were synthesized by varying crystallization time during the microemulsification process. The layered structure and three-dimensional size of nanoplatelets were confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM). As lubricant additives, their tribological properties in base oil were evaluated by use of a ball-on-disk reciprocating tribometer under three different loads: 50, 100, and 150 N (which created peak Hertz pressures of 1.74, 2.16, and 2.47 GPa). Under contact pressures of up 2.16 GPa, not only did the coefficient of friction (COF) decrease by about 10% after nano-LDHs were added but also the wear performance improved substantially. These improvements resulted from a protective tribolayer formation on the contact interface, as revealed by detailed surface and structure analytical studies. In particular, cross-sectional TEM images revealed that the larger size nanoplatelets (NiAl-24h), rather than the smaller ones (NiAl-6h) showed the best and most stable tribological performance. This was mainly because of their higher degree of crystallinity, which in turn resulted in the formation of a tribofilm with far superior mechanical properties during sliding. Owing to the simple synthetic method and superior tribological properties as oil-based additives, nano-LDHs hold great potential for use in demanding industrial applications in the future.
层状双氢氧化物（LDHs）是一类天然无机矿物，由二价和三价金属阳离子组成。在这项研究中，通过在微乳液过程中改变结晶时间，合成了三种不同尺寸的 NiAl-LDH 纳米片。通过透射电子显微镜（TEM）和原子力显微镜（AFM）确认了纳米片的层状结构和三维尺寸。作为润滑剂添加剂，在三个不同载荷（50、100 和 150 N，产生的峰值赫兹压力分别为 1.74、2.16 和 2.47 GPa）下，使用球盘往复式摩擦磨损试验机在基础油中评估了它们的摩擦学性能。在接触压力高达 2.16 GPa 的情况下，纳米-LDH 添加后摩擦系数（COF）不仅降低了约 10%，而且磨损性能也得到了显著改善。这些改进是由于在接触界面上形成了保护性的摩擦层，通过详细的表面和结构分析研究得到了证实。特别是，横截面 TEM 图像表明，较大尺寸的纳米片（NiAl-24h）而不是较小尺寸的纳米片（NiAl-6h）表现出最佳和最稳定的摩擦学性能。这主要是因为它们具有更高的结晶度，从而在滑动过程中形成了具有优异机械性能的摩擦膜。由于其作为油基添加剂具有简单的合成方法和优异的摩擦学性能，纳米-LDH 在未来具有很大的潜力应用于苛刻的工业应用中。
