Yu. F. Migal

Study of friction and wear in the wheel-rail system by X-ray electron and auger-electron spectroscopy and quantum chemistry

The article presents the results of joint application of modern experimental and theoretical methods to analyze interatomic interactions on friction surfaces and in subsurface layers. The wear resistance of the wheel-rail system is shown to experience the effect of grain-boundary segregation, and the methods of suppressing its negative consequences are discussed. Adsorption on the iron surface of heteropolyphosphates of alkali metals, representing a new type of additive to lubricants, is studied.

Adsorption of heteropolyphosphates of alkaline metals on iron surface

The physical and chemical properties of heteropolyphosphates of alkaline metals are studied as promising antiwear and antiscoring additives to plastic lubricating materials. Quantum-chemical analysis of the interaction of the heteropolyphosphates with iron surfaces provides insight into the processes that evolve in these compounds during friction. The mechanism of opening of the heteropolyphosphatic cycles and their transition into linear structures is studied.

Quantum-chemical investigation of the effect of grain-boundary segregation on wear resistance of steel

Quantum-chemical calculations of polyatomic clusters modeling the grain boundaries in the surface layer of steel are presented. Along with iron atoms, the clusters contain atoms of doping and impurity elements yielded to the boundary due to grain-boundary segregation. The effect of the chemical composition of segregants on the bond strength between the grains and, ultimately, on the wear resistance of steel is investigated. It is shown that the bond strength of segregated atoms with iron atoms in the surface layer of a metal is a substantial factor affecting the wear resistance.

Properties of Puma and Buksol lubricants modified by inorganic additives of binary polyphosphates

Results of investigations of tribotechnical and physicochemical properties of plastic lubricants, which are based on Puma and Buksol and used in heavy duty friction units of railway equipment, are presented. The search for new multipurpose polymeric additives of the inorganic nature was carried out based on physicochemical studies of phase diagrams of multicomponent systems. The influence of Puma and Buksol with the synthesized additives on characteristics of the process of friction is studied. Judgments about the mechanism of antifrictional and antiwear effect during work with these greases are stated. The base of this mechanism is the interaction of flexible links of anions of polyphosphate chains with a surface of metal. As a result, the layer of secondary structures is formed on the surface that protects the metal from wear.

Compatibility of chemical elements on grain boundaries in steel and its influence on wear resistance of steel

A quantum-chemical analysis of the interaction of atoms of alloying and impurity elements with grain surfaces in steel has been performed. The cluster model and the two-periodic slab model have been used. The compatibility of various elements with iron on grain boundaries in steel has been estimated. The results are in agreement with the known experimental data and correspond to Mendeleev’s law. The obtained dependences can be used for predicting strength characteristics of polycrystalline materials with various alloying additives.

Compatibility of chemical elements at grain boundaries in steel

A quantum-chemical study was performed to analyze the interaction of atoms of impurity and alloying elements with the surface of grains in steel. Atoms of elements in the first five periods of the periodic table (from hydrogen to xenon) were considered. A cluster model and a two-period slab model were used. Estimates of the compatibility of elements with iron at grain boundaries in steel were made, which agree with the known experimental data and fit the periodic low. The results of this study can be used for predicting the strength properties of polycrystalline materials into which various alloying elements are added.

Interaction of silicate additives and iron surface

A quantum-chemical analysis of the interaction of the basic structural element of silicates (silicate group SiO4) and iron surface has been carried out. The cluster model and slab model were used. The adhesion energy and influence of the silicate group on the local atomic structure of a surface was estimated. It has been shown that a strong covalent bond is formed between this group and the surface, which occurs upon the adsorption of the group. Intensive force action causes the destruction of an adsorptive complex accompanied by tearing out the Fe atoms.

Determination of the local structure and parameters of the one-electron potential from XANES data (inverse problem of XANES theory)

A method of obtaining complex information on the structure of polyatomic systems using experimental data for one-electron quasistationary state (shape resonance) is developed. The method involves the equation for S-matrix poles in the muffintin (MT) approximation. The parameters of the model (intemuclear distances, valence angles, and potential characteristics) are fitted in such a way that the S-matrix poles in a complex energy plane be maximally close to {E-iГ/2}, where E and Fare the energies and widths of the XANES maxima of one-electron origin. Testing the method on a number of objects shows that it determines internuclear distances with an accuracy of 1% and valence angles with an accuracy of 3%. Among the potentials of this type, the empirical potentials obtained are the best for describing shape resonances. The suggested scheme is applicable in determining the microstructure and in the cases where the diffraction methods of structural analysis do not work (unordered systems, molecular adsorption on the surface of solids, etc.).

Formation of adhesive bonds under contact rotaprint lubrication

The mechanism of the formation of adhesive bonds of a friction modifier (a lubricant based on bitumen) with a wheel of railway transport is considered. Calculations performed using quantum chemical methods allow us to draw a conclusion on the existence of the physical adsorption of this lubricant on a wheel surface. The lubrication’s effectiveness can be improved using fatty acids whose introduction into the lubricating material leads to the formation of chemical bonds in the system; this is experimentally confirmed for the contact rotaprint lubrication technology.

Determining the lattice parameter and the single-electron model potential of the compound CdS by means of the soft x-ray absorption spectra

The method of determining the structure parameters of multiatomic systems, using the spectra of soft x rays (XANES) proposed earlier, is extended to the case of nonmetallic crystal bodies. This method is used to determine the lattice parameter and the empirical muffin-tin potential from the positions of maxima of single-electron origin in the sulfur K spectrum in the compound CdS.