Physical and chemical aspects of the study of clusters, nanostructures and nanomaterials
Founded at 2009

Editor’s column

The effect of the nanodisperse phase of magnetic oils on their lubricating properties

Abstract: The work is devoted to the study of processes occurring in the boundary lubricant layer, in which nanodisperse magnetic particles play a decisive or significant role. The friction between metal surfaces with lubricated oils of different concentrations of the magnetic nanodisperse phase was studied. The dispersion medium of magnetic oils consisted of liquids with various physico-chemical properties: dioctylsebacinate, triethanolamine, polyethylsiloxane. It has been shown that the wear intensity of surfaces with a hardness higher than that of nanoparticles monotonically increases with increasing the particle concentration, and wear is abrasive in nature. The wear rate of softer materials passes through a minimum at a particle concentration of about 2 vol.%. Magnetic separation of large agglomerates in oil allows for some time to reduce the abrasive wear until they are formed again under friction conditions. It was not possible to identify the regularities of the influence of nanodispersed particles on the friction force, it is probably insignificant. Several examples of the indirect effect of nanodispersed particles on the boundary friction are considered. In all the examples, the determining role plays huge area of the active surface of particles per unit volume of oil. For example, under conditions of friction, atomic hydrogen can be actively formed during the chemical interaction of fatty acids with the surface. Atomic hydrogen accumulates in the subsurface pores and is crystallized there. The increased pressure in the pores created by hydrogen molecules leads to an increase in wear by the peeling mechanism. The established regularities of the influence of nanodispersed particles on the rate of formation of the boundary lubricant layer and the corrosion wear of surfaces caused by surface-active additives in magnetic oil are of scientific interest.

Viscometric studies in the process of synthesis of magnetic lubricant nano-oils

Abstract: In the field of tribology, magnetic lubricating oils are promising, in which polymers are used to increase their colloidal stability, but their use is limited by the low magnetization of the colloid. It is possible to increase the magnetization of nanooils by synthesizing polymer shells directly on the surface of magnetic particles in the process of obtaining nanooils. The features of the technology for the synthesis of magnetic lubricating nanooils with polymeric solvation shells on particles, which protect them from coagulation, are described. Polymerization of hydroxy acid molecules proceeds by the mechanism of polycondensation on the solid surface of magnetite. The viscosity of the magnetic colloid increases due to the increase in the thickness of the solvate shell. Proceeding from this, a differential equation is proposed, which shows the dependence of the growth rate of the colloid viscosity on the rate of the polycondensation reaction. An experimental verification of the equation showed that it is fulfilled with an accuracy up to 8%. The resulting equation makes it possible to determine an important thermodynamic characteristic – the activation energy of the process of synthesis of polymer shells on the surface of dispersed particles. For calculations, it is necessary to know the rate of change in the viscosity of a colloid with a dispersion medium without a monomer (hydroacid). Therefore, in the process of the polymer synthesis, samples of the intermediate magnetic colloid of a small volume are taken, which are used to determine the viscosity of the colloid and dispersion medium containing monomers. Then the viscosity of the colloid with a pure dispersion medium is found, which is necessary for calculating the activation energy of the polycondensation reaction. According to estimates, the error in determining the activation energy does not exceed 11%. In practice, using the values of the activation energy of polymerization, it is possible to carry out a purposeful choice of the optimal temperature-time regime for stabilizing the magnetic colloid in order to obtain a magnetic nanooil with the required viscosity and aggregative stability characteristics. Experimental studies were carried out on specially designed instruments for assessing the colloidal stability and dynamic viscosity of magnetic colloids.

General phenomenological approach for the description of adsorption and absorption equilibria

Abstract: Up to the present time, the construction of a general theory of the equilibrium adsorption is a very urgent task. In the present paper, a general phenomenological approach is developed to describe both adsorption and absorption equilibria. It was shown that under certain assumptions, the resulting equation transforms into the well-known classical Henry, Langmuir, Brunauer-Emmett-Teller equations with constants having a clear physical meaning. Thus, the constant in the Henry equation is determined by the temperature, the specific surface of the adsorbent, the size of the adsorbate molecules, the molar mass of the adsorbate and the isosteric heat of adsorption (the energy of interaction of the adsorbate molecules with the surface of the adsorbent). In the derived Brunauer-Emmett-Teller partial equation, in contrast to the classical version, a clear dependence of the equation constant on the specific physical characteristics of the adsorption system is indicated for the first time. It is determined by the concentration of adsorbate molecules in the liquid phase at the temperature under consideration, the concentration of adsorbate molecules during the formation of a dense monolayer on the surface of the adsorbent, the energy of interaction of adsorbate molecules with the surface of the adsorbent and the heat of condensation. The presented approach can serve as a basis for modeling a variety of adsorption and absorption phenomena, including adsorption on microporous adsorbents.