Abstract:

Existing hydraulic transmission media of water, oil and other anhydrously synthesized materials have problems such as poor stability at high temperature and large temperature-dependent viscosity change. In contrast, In-Bi-Sn alloy has low melting point, good fluidity, and stable high-temperature properties, making it an ideal base fluid for hydraulic transmission media at extreme high temperature. In this work, In-Bi-Sn-based Si₃N₄/GNFs hybrid nano-fluids with volume fractions of 0, 5%, 10%, 20% and 30% were prepared by a two-step method. The morphology, dispersion, and thermal stability of the samples were characterized by TEM, SEM+EDS and TGA. The rheological properties and lubricity of the samples were studied by high-temperature rotary rheometer and friction wear testing machine. The differences in thermal stability, rheology, and lubricity between samples and existing high-temperature hydraulic media were compared. The results showed that Si₃N₄ was embedded in GNFs plates and dispersed in In-Bi-Sn matrix in the form of aggregates, and the aggregate size of 10% sample was smaller than that of 20% sample. The viscosity of the samples increased with the increase of the volume fraction of the hybrid nanoparticles, and the effects of the static time of the liquid and the number of phase transformation on the viscosity of the sample <30% were not obvious. Under the influence of Brownian motion of nanoparticles, the higher the volume fraction of nanoparticles was, the more significant its temperature-dependent viscosity change was. The 20% sample showed obvious thinning characteristics, due to the change of particle size. Adding Si₃N₄/GNFs hybrid nanoparticles could significantly improve the lubrication characteristics. Compared with the existing high-temperature hydraulic medium, the In-Bi-Sn-based Si₃N₄/GNFs hybrid nanofluid had excellent thermal stability, less temperature dependence in viscosity and good high-temperature lubrication.

Key words: liquid metal, nanoparticles, nanofluid, rheological properties, lubricity, thermal stability

摘要：

现有水基、油基及其他无水合成类液压传动介质存在高温稳定性差、温-黏变化大等问题。In-Bi-Sn合金熔点低、流动性好、高温性质稳定，是极端高温液压传动介质的理想基础液。本文采用两步法制备体积分数为0、5%、10%、20%、30%的In-Bi-Sn基Si₃N₄/GNFs混合纳米流体。利用TEM、SEM+EDS、热重分析等手段表征样品形貌、分散性和热稳定性，通过高温旋转流变仪和摩擦磨损试验机研究样品的流变性和润滑性，对比分析样品与现有高温液压介质在热稳定性、流变性、润滑性上的性能差异。结果表明：Si₃N₄嵌于GNFs片层之间，以团聚体形式分散于In-Bi-Sn基质，10%样品中的混合纳米颗粒团聚体尺寸小于20%样品；样品黏度随混合纳米颗粒体积分数增加而增大，液态静置时间和相变次数对<30%样品黏度的影响不明显；受纳米颗粒布朗运动影响，分散相体积分数越高，样品的温-黏变化越显著；因剪切改变了纳米颗粒团聚体的粒度，20%样品显示出明显的剪切致稀特征；添加Si₃N₄/GNFs混合纳米颗粒能够显著改善润滑特性；相较于现有高温液压介质，In-Bi-Sn基Si₃N₄/GNFs混合纳米流体热稳定性优异、温-黏变化更小、高温润滑性能佳。

关键词: 液态金属, 纳米粒子, 纳米流体, 流变性, 润滑性, 热稳定性