Effect of Concentration and Type of Liquid Crystal Additive on Tribological Characteristics of Industrial Oils

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ct of Concentration and Type of Liquid Crystal Additive on Tribological Characteristics of Industrial Oils S. V. Voronina, *, V. A. Stefanova, D. V. Onopreichuka, I. Yu. Safoniuka, and N. N. Anoshkinaa aUkrainian

State University of Railway Transport, Kharkiv, 61050 Ukraine *e-mail: [email protected]

Received February 5, 2020; revised May 6, 2020; accepted May 6, 2020

Abstract—This paper considers the mechanism of formation and structure of boundary lubricating films on the metal surface in the presence of different types of additives, namely fatty acids and cholesteric-type mesogens, whose molecules have a phenanthrene skeleton. The results of laboratory studies of the tribological properties of industrial oil I-30A supplemented with the indicated types of additives in various concentrations are presented. The studies were carried out on a four-ball friction machine according to the standard method, and the main indicators of the lubricating ability of oil samples with additives, such as the diameter of the wear spot, critical load, scoring index, and welding load, were determined. According to the obtained results, it was found that the greatest positive effect on the lubricating ability of industrial oils is exerted by a liquid crystal additive, when compared to fatty acid, and the maximum anti-wear effect is observed at concentrations lying within the studied range. These data indicate the presence of a region of rational concentration of the liquid crystal additive in industrial oil. Keywords: liquid crystal, additive, friction, industrial oil, wear, tribological properties, lubricity DOI: 10.3103/S1068366620040133

INTRODUCTION The search for new solutions in the field of tribology very often involves the search for analogies between technical systems and living organisms. Such an analogy can be drawn between the joints of living beings and the friction nodes of technical systems [1], where the former successfully use liquid crystals as lubricants, and the latter require improvement through the use of liquid crystal lubricants. In [1–7], it was experimentally proved that liquid crystal compounds form surface-oriented layers on friction surfaces. This determines the effectiveness of antifriction, antiwear, and antiscoring properties of such additives. Three types of liquid crystals are distinguished as cholesterics, nematics, and smectics. All these are different types of substances of different nature, with different forms of molecules, and their way of ordering [3]. Analysis of publications [4–7] showed that most of the works relate to the study of smectic lubricant layers. In such layers, molecules form boundary films, orienting themselves perpendicular to the friction surface, but under higher loads the polymolecular layers are destroyed, becoming monomolecular. Papers [1, 8] showed that the lubricating layers of the cholesteric structure should not have such a disadvantage. This is due to the specific features of their structure, namely, that they consist of multiple spirally twisted

layers, and th

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