锂基脂静态热氧化老化行为的红外吸收光谱定量分析

Fourier Transform Infrared Quantitative Analysis of Static Thermal Oxidation Aging Behavior of Lithium-Based Grease

为探讨锂基润滑脂在高温使用工况下的热老化行为,以不同矿物油、合成油PAO为基础油,以12-羟基硬脂酸锂为稠化剂制备润滑脂样品。使用自行设计的红外光谱定量分析设备,采用静态热老化方式模拟并系统研究了不同老化温度、不同基础油种类的锂基润滑脂老化过程。探索了该老化过程中的润滑脂中关键组分分子结构变化及其规律,并分析建立了可用于有效评定润滑脂热老化程度的综合性能指标E。结果表明:锂基润滑脂的热老化过程中,首先基础油发生氧化、硝化、硫化等反应,随着老化程度的加剧,稠化剂发生降解;对于140℃下静态热老化的1#锂基脂样品,E值上升至新脂的1~23倍时为初级氧化阶段,上升至23~38倍时为氧化的平台阶段,结合其他理化指标,前2个阶段为影响润滑脂寿命的主要部分,随老化时间增加,E值继续上升,润滑脂结构开始降解失效。另外,润滑脂老化程度随温度的升高而加速。基础油种类对老化速率有一定影响,聚α烯烃规整的长链烷烃结构在老化过程后期能够保持稠化剂结构的稳定,制备的润滑脂样品具有更好的高温性能。

To discuss the thermal aging behavior of lithium-based grease under high-temperature working conditions,the lubricating grease samples were prepared using different mineral oils and PAO as the base oil and lithium 12-hydroxystearate as the thickener.Based on the use of self-designed infrared spectrum quantitative analysis equipment,the static thermal aging method were applied to simulate and systematically study the thermal aging process of lithium-based grease of different base oil types under different aging temperatures.This aimed to explore the structural change and its rule of key component molecules in lubricating grease during aging process,and through analysis,set up the comprehensive performance index E that can effectively evaluate the thermal aging degree of lubricating grease.The results show that the oxidation,nitrification and sulfurization of the base oil occur firstly in the thermal aging process of lithium-based grease,and the degradation of the thickener occurs as the aging degree increases.For the 1#lithium-based grease sample under static thermal aging at 140℃,when the E value rises to 1—23 and 23—38 times as compared with the new grease,it is in the primary oxidation stage and on-platform oxidation stage,respectively.Based on other physical and chemical indicators,the first two stages are the main factors that affect the service life of lubricating grease.With the increase of aging time,E values continues to rise and then the structure of lubricating grease fails to be degraded.Besides,the aging degree of lubricating grease is accelerated with increasing temperature.The base oil type has certain influence on the aging rate.The regular long-chain alkane structure of polyalphaolefin can maintain the stability of thickener structure in the late aging process,and the prepared grease samples have better high temperature performance.