羽状氮化碳水润滑剂对环氧树脂-不锈钢配副摩擦学性能的影响

随着人们环保意识的逐渐增强，对可能存在污染或破坏环境且造成资源浪费的生产活动以及设备的更新升级提出了新的更高的要求. 对于介质润滑领域，尤其是应用广泛且节能环保的水润滑领域，相比传统的润滑油，水作为润滑剂除了安全性高和具有冷却作用外，最大特点就是绿色环保、节约资源且成本低廉. 但是，纯水本身具有一些不足之处，比如黏度低、耐极压能力差、承载和润滑性能差等，导致纯水不适合直接作为润滑剂，这在很大程度上限制了涉及水润滑相关产业的发展. 基于此，在本文中以柠檬酸和尿素为原料，采用一步水热法合成了羽状氮化碳材料. 此方法的特点在于可将氮化碳原位分散于水中，制成水基润滑剂，既实现了溶质的均匀分散和有效抑制团聚，同时可以制备微米级分布的水溶性氮化碳材料. 将其作为水润滑剂，利用环-块摩擦磨损试验机，以逐滴滴加的方式考察了不同质量分数羽状氮化碳对环氧树脂-不锈钢配副在苛刻边界润滑条件下的摩擦学性能. 材料的微观形貌表征结果表明：体相氮化碳在水热条件下直接发生了层间剥离，生成了层间结构蓬松的羽状结构材料. 由于水热条件下的高温和高压环境，导致其层间结合强度显著降低. 同时，蓬松的层间结构有利于氮化碳材料在摩擦过程中向界面转移，在界面形成薄而连续的转移膜. 界面转移物质的拉曼分析结果表明：相较于单纯去离子水，以羽状氮化碳为水润滑剂时，金属对偶表面转移的含碳物质的有序化程度显著提高，而且有序化程度随着水润滑剂中氮化碳含量的增加而逐步提高，间接表明氮化碳材料在界面形成了结构有序的转移膜. 而且氮化碳基转移膜的承载能力和润滑性能俱佳，它可有效保护环氧树脂(EP)-不锈钢配副，避免单纯去离子水润滑时因其承载和润滑性能差导致EP严重磨损的发生. 纯去离子水作为润滑剂时，配副的摩擦系数和EP磨损量分别为0.56和2.92×10−4 mm3/(N·m). 而逐滴添加质量分数20%的羽状氮化碳水润滑剂，上述配副的摩擦系数和EP磨损量分别下降了71.4%和78.1%. 原位水基羽状氮化碳作为一种新型绿色环保水润滑剂，在聚合物-金属配副的润滑设计和使用寿命延长方面具有一定的研究价值和应用潜力.

As public awareness of environmental protection continues to grow, new and higher requirements have been put forward for the upgrading of production activities and equipment that may cause environmental pollution, damage or resource waste. In the field of medium lubrication, especially the widely used, energy-saving and environmentally friendly water lubrication, compared with traditional lubricating oils, water as a lubricant boasts high safety and cooling effects, with its most prominent features being environmental friendliness, resource conservation and low cost. However, pure water has several inherent drawbacks, including low viscosity, poor extreme pressure resistance, inadequate load-bearing and lubricating properties, etc., which make it unsuitable for direct use as a lubricant, largely restricting the development of industries related to water lubrication. In view of this, this paper synthesizes feather-like carbon nitride materials via one-step hydrothermal method using citric acid and urea as raw materials. This method features in-situ dispersion of carbon nitride in water to prepare water-based lubricants, which not only achieves uniform dispersion of solutes and effectively inhibits agglomeration, but also prepares water-soluble carbon nitride materials with micron-scale distribution. Using a ring-on-block friction and wear tester, the tribological properties of epoxy resin-stainless steel pairs under severe boundary lubrication conditions were investigated by dropping feather-like carbon nitride with different mass fractions as water lubricants. Results of microscopic morphology characterization show that bulk carbon nitride undergoes direct interlayer exfoliation under hydrothermal conditions, forming feather-like structural materials with loose interlayer structures. The high-temperature and high-pressure environment during hydrothermal treatment significantly reduces the interlayer bonding strength. Meanwhile, the loose interlayer structure facilitates the transfer of carbon nitride materials to the friction interface during the sliding process, forming a thin and continuous transfer film at the interface. Raman analysis of the interface transfer substances shows that compared with pure deionized water, the degree of ordering of carbon-containing substances transferred to the metal counterface is significantly improved when using feather-like carbon nitride as the water lubricant, and the degree of ordering gradually increases with the increase of carbon nitride content in the water lubricant, indirectly indicating that carbon nitride materials form structurally ordered transfer films at the interface. Moreover, the carbon nitride-based transfer film has excellent load-bearing capacity and lubricating performance, which effectively protects the epoxy resin (EP)-stainless steel pair and prevents severe EP wear caused by the poor load-bearing and lubricating properties of pure deionized water lubrication. When pure deionized water was used as the lubricant, the friction coefficient and EP wear volume of the pair were 0.56 and 2.92×10−4 mm3/(N·m), respectively. When using the feather-like carbon nitride water-based lubricant with a mass fraction of 20% added dropwise, the friction coefficient and EP wear volume of the above pair decreased by 71.4% and 78.1%, respectively. As a novel environmentally friendly water-based lubricant, in-situ prepared water-based feather-like carbon nitride has certain research value and application potential in the lubrication design and service life extension of polymer-metal pairs.