A. P. Krasnov

Effect of particle size and composition of powdered nanocrystalline molybdenum disulfide on its tribological behavior

The tribological behavior of two types of nanocrystalline molybdenum disulfide produced from natural molybdenum disulfide by monolayer dispersion in the presence of water (nano-MoS2(H2O)) and acetonitrile (nano-MoS2(CH3CN)) is studied. The study of the friction of these materials against polished and ground steels, as well as XPS examinations, show the advantage of the more thermally stable nano-MoS2(CH3CN), which is primarily due to the origin of low-molecular products adsorbed on the surfaces of nanoparticles.

Synthesis and characteristics of the composites based on poly(caproamide) and multiwalled carbon nanotubes

Polycaproamide composites are synthesized by the anionic activated bulk polymerization of ɛ-caprolactam in the presence of 0.1–5.0 wt % of multiwalled carbon nanotubes and using low-molecularmass monofunctional (N-acetyl-ɛ-caprolactam) and macromolecular polyfunctional (aromatic polyimides) activating agents. The effect of nanotubes on the polymerization of ɛ-caprolactam is studied, and this effect is shown to become more pronounced as the concentration of nanotubes is increased. The effect of nanotubes on the microstructure, phase composition, water sorption, thermophysical, mechanical, and friction characteristics of poly(caproamide) is analyzed.

Friction of self-lubricating polymer composites reinforced by heat-resistant fabrics

The effect of a phenolformaldehyde binder and the nature of reinforcing fibers, i.e., polyoxadiazol and carbon fabrics, on the specific features of the friction of polymer composite materials (PCMs) and the formation of their self-lubricating properties is shown. The friction of these PCMs is experimentally studied and an analysis of specific features of this process is carried out based on the first formulated general principle of the structure of a friction surface of these PCMs that implies the rigid fixation of fibers in the structure of a fabric. The effect of properties of the fibers and binder on this process is established.

Properties and microstructure of composites derived from polycaproamide and multiwall carbon nanotubes

Composites were synthesized by anionic in situ polymerisation of ɛ-caprolactam in the presence of 0.1–5.0% of multiwall carbon nanotubes. It is found that nanotube filling increases rigidity and improves the friction characteristics of polycaproamide. The friction coefficient decrease is especially significant at a nanotube concentration of 0.1%. It is shown that nanotubes affect the composite film microstructure.

Tribological studies for developing friction modifiers in the wheel–rail system

In this work, friction modifiers in a wheel–rail system and their operation mechanism are considered. Three stages of a complex tribological study and tribological tests are applied within the development of friction modifiers and estimation of their tribological properties. The first stage (Institute of Element and Organic Compounds, Russian Academy of Sciences) is to elaborate hydroalcoholic soluble compounds and polymeric binders, as well as of methods of applying them to steel surfaces, and to study their tribological characteristics using an I-47 friction machine. The second stage (Institute of Mechanics Problems, Russian Academy of Sciences) is devoted to probing of tribological characteristics and durability of the elaborated composites on a tribometer, which allows to implement a cylinder–plate contact interaction under full slip conditions. The third stage (JSC “Railway Research Institute”) is aimed at studying the tribological parameters of the developed modifier composites at rolling-sliding conditions under real contact pressure of 1200 MPa.

Role of nanofiller in friction of polymers based on polycaproamide: Indirect effect

The effect of nanofillers (multiwalled carbon nanotubes) on the tribological behavior of polycaproamide is studied when introduced into the polymer by polymerization filling. The introduction of insignificant quantities (∼0.1 wt %) of nanotubes provides their homogeneous distribution in the polymer and contributes to reducing the wear and friction coefficient. This is mainly due to the role of nanotubes as nucleators of the fine spherulitic polycaproamide structure. Such an indirect effect of the nanofiller on the polymer’s tribological behavior is seen when nanotubes are added to the melt in the course of granulation of polycaproamide compositions reinforced by carbon fibers, the effect of nanotubes being reduced with increasing amount of the reinforcing filler.

A comprehensive study of ultra-high molecular weight polyethylene modified by α-tocopherol after exposure to extremely high temperatures

The processes occurring in friction of samples of ultra-high molecular weight polyethylene (UHMWPE) obtained by pressing at 190 °C from discrete UHMWPE particles modified by α-tocopherol (α-T) were studied using X-ray photoelectron spectroscopy, thermogravimetry, thermomechanical analysis, investigation of the oxygen uptake kinetics, and determination of the inhibitory activity. Pressing results in the isolation of α-T on the sample surface, its oxidative destruction, and inhibition of UHMWPE oxidation. After tribological tests, the atomic content of oxygen in the surface layer of the modified sample remains at the initial level, while that in the non-modified UHMWPE sample increases by 50%.

Effect of the Molecular Weight of Polyarylene Ether Ketones on the Tribological Properties

The effect of the molecular weights of amorphous polyarylene ether ketone (PAEK) synthesized by the reaction of 4,4-difluorobenzophenone with 2,2-bis (4-hydroxyphenyl) propane (bisphenol A) potassium diphenolate on its tribological characteristics has been studied. In the case of the friction of a sample with Mw < 200 × 103 Da, its high wear resistance and the coefficient of friction decreased to 0.4, even at high pressures of up to 10 MPa. These properties of high-molecular-weight PAEK are due to the high contribution of the weak dispersion forces into the intermolecular interaction energy of the polymer. Low wear determines the nature of tribodestruction, which, during the process of self-organization, leads to the appearance of a positive gradient in the physicomechanical properties in the surface layers. The XPS study shows that, during PAEK pressing at 260°C, the intensive oxidation of a thin surface layer occurs.

Effect of the Chemical Structure of Heat-Resistant Thermoplastics on the Friction on Steel

A general approach to understanding the complex nature of the friction of friction-resistant heatresistant thermoplastics has been developed. This approach made it possible to idenify two main factors determining the basic character of the friction of these polymers on steel: the dispersion component of the intermolecular interaction energy and the molecular weight. Specific properties of some polymers can be used to refine the friction behavior.

Tribochemical processes in epoxyorganic textolite–steel friction pair

The role of a phenol formaldehyde oligomer additive to the epoxy binder in friction of organic textolite is studied. It is shown that, in the course of friction, the polymer surface becomes enriched in the tribochemically stable phenolic component, while new C=O and O–C–O bonds appear that result from the oxidation of the aliphatic epoxy groups of macromolecules. During friction, the aliphatic component of the polymer specimen is predominantly involved in reactions with the counterbody; this selective wear makes the outer surface of the polymer specimen less hydrophilic. Comparative tribological and thermofrictional tests have shown that, unlike the phenol structure, the use of an epoxy-phenolic structure in the materials reinforced by polyoxadiazole fabrics is more efficient at low temperatures, while phenol formaldehyde binder exhibits better stability at high temperatures.