The article presents a discussion on the use of hexagonal boron nitride as an additive to lubricants. Based on the analysis of the research, factors determining its application were identified. These include particle size distribution, their morphology, specific surface area, and porosity. Next, the research identifying these properties for the four types of h-BN was described. Based on the results, the possible mechanisms of the influence of individual h-BN types were described. It was also found that the use of h-BN nanoparticles as lubricants seems to be promising.

This paper presents the results of tribological tests of lubricating compositions containing SN150 mineral oilas a base, an additive of solid lubricant in the form of hexagonal boron nitrides (h-BN) of various particlesizes (nano- and micro-) and surfactants: succinic acid imide and sodium di-2-ethylhexyl sulphosuccinate.Particular attention was paid to analysing the properties of hexagonal boron nitrides in the context of theireffect on the tribological properties of the friction node under study. The effects of h-BN particle size, shape,specific surface area and porosity were considered. In addition, tests were carried out to check the surfactants'effect on the tested oil's hexagonal boron nitride sedimentation process. These tests confirmed the positiveeffect of succinic acid imide on maintaining a stable dispersion of h-BN particles in SN-150 mineral oil.Tribological tests were performed on a T-02 tribotester based on the PN-EN ISO 20623:2018-02 standard.The positive effect of hexagonal boron nitride on the lubricating properties of mixtures with SN150 mineraloil was established. In addition, hexagonal boron nitride, with a smaller particle size and a more developedporous structure, had a more favourable effect on improving the lubricity properties evaluated on the T-02tribotester.

The article presents historical review of the Polish standards for testing the extreme-pressure and anti-wear properties of lubricants on a four-ball apparatus, commonly used in the world for this type of test-ing. The current standards, approved by PKN for use in Poland, are also discussed. Withdrawn standards were compared and their updates, showing the direction of development of research into the lubricating properties of plastic oils and greases. As a result, the research scope of lubricating properties was arranged on the basis of the standards currently in force in Poland. Keywords: tribology, lubricity, four-ball apparatus, standardization

The article presents the results of tests on the lubricity properties of SN150 base oil containing hexagonal boron nitride (h-BN) of different granulation. The boron nitride with a particle size below 100 nm and the second one with a particle size below 25 μm were used. The lubricity tests were carried out on a four-ball apparatus. The methodology of these tests was determined on the basis of the normative document PN-EN ISO 20623: 2018-02, which contains the following parameters characterising the lubricity: initial seizure load ISL [N], weld load WL [N], load-wear index LWI [N], mean wear scar diameter MWSD [mm] obtained in a long duration wear test under a specified load; wear-load curve, i.e., the dependence of the mean wear scar diameter on the load, was also performed. Tests were also carried out to check the influence of selected surfactants on the sedimentation process of hexagonal boron nitride in the SN150 mineral base oil. Based on the conducted research and their analysis, it was found that hexagonal boron nitride has a positive effect on the lubricating properties of the base oil; better results were obtained for the boron nano-nitride with a particle size below 100 nm. It was also found that the problem of sedimentation of the solid particles of hexagonal boron nitride was solved by the addition of succinimide dispersant. Keywords: tribology, lubricity, boron nitride, surfactants, sedimentation