In this paper, the process of spheroidization of natural graphite powders on an original impact-reflecting mill with internal separation of particles was investigated. It was established that the process of spheroidization of natural graphite by impact depends both on the intensity and duration of mechanical activation. For the type of mill used, the critical linear velocity of the impact elements of the mill rotor, at which the graphite particles can be spheroidized, is 45 m/s. An increase in the linear rotational speed of the mill (intensity of impact) leads to a decrease in the average particle size, an increase in particle roundness, but significantly increases product losses. In the process of mechanical activation by impact, it is possible to increase the coefficient of roundness of the graphite particles to an average value of 0.8-0.9, which leads to compaction of graphite powders. The presence of ash impurities has a negative effect on the ability of natural graphite powders to compact. A mechanism is proposed for the process of spheroidization of graphite particles in a shock-reflecting mill. According to the proposed mechanism, at first, small-sized graphite plates are detached and deformed due to impact. As the free energy accumulates, agglomeration of deformed particles into spheres takes place. With increasing processing time, the surface of the particles is smoothed due to their friction with each other and against the wall of the mill. Powders of spherical graphite obtained by the proposed method have shown the possibility of their use as an anode material of lithium-ion batteries. The type of equipment investigated has made it possible to reduce the required number of pieces of equipment from 20 to 12 impact mills per line in comparison with foreign analogues. For citation: Yudina T.F., Blinichev V.N., Bratkov I.V., Gushchina Т.V., Melnikov A.G. Investigation of process of natural graphite spheroidization. Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol. 2018. V. 61. N 9-10. P. 48-52

In this work, the effect of addition of colloidal solutions of electrochemical exfoliated graphene (EEG) to the Watts bath on the process of obtaining composite coatings based on a nickel matrix was studied. It was found that the introduction of nanoparticle additives has a significant effect on the value of cathodic overvoltage during electro reduction of Ni2+. The strongest inhibition of the cathode process takes place with the introduction of 0.2 g/l of additives investigated. Further increase in the concentration of nanoparticles in the bath reduces the effect. The inhibition of the cathodic reduction of Ni2+ is associated with the adsorption of graphene nanoparticles on the active faces of growing nickel crystallites and the blocking of the accessible surface for Ni2+ reduction. Due to the increase in cathodic polarization during the deposition of the composite coating, the crystallites of the deposited nickel decrease in size and the texture of the crystal structure of the coating changes. According to energy dispersive spectroscopy data, carbon has been included in the composite coating. The carbon content in the coating increases with increasing concentration of nanoparticles in the working electrolyte. The inclusion of negatively charged nanoparticles of electrochemically dispersed graphene in the resulting precipitate becomes possible due to adsorption of Ni2+ and recharging of graphene nanoparticles. It was found that the optimal concentration of electrochemically dispersed graphene in the working electrolyte is 0.1-0.2 g/l. At a given nanoparticle content in the working bath, the porosity and roughness of the coatings decreases. The Tafel polarization curves for composite coating samples obtained in a 0.5M NaCl solution showed that the inclusion of graphene nanoparticles in the resulting coating leads to a shift of the corrosion potential to the negative area. With an increase in the carbon content in the coating, the shift in corrosion potentials increases, and the value of corrosion currents increases. For samples of composite coatings obtained at an EEG additive concentration of 0.1 g/l, a slight improvement in the protective properties is noted, which is associated with a decrease in the porosity of the coatings.

In this work, the processes occurring during the electrochemical dispersion of graphite in a solution of sulfuric acid are investigated. The possibility of obtaining colloidal graphene solutions by combining electrochemical and ultrasonic graphite dispersion is shown. It is established that an increase in the operating voltage on the cell leads to the formation of a larger number of surface oxygen-containing groups. This allows increasing the yield of nanoscale particles. Ultrasonic treatment leads to an additional splitting of graphene plates and separation of nanosized particles from insufficiently oxidized particles of graphite. The thickness of graphite particles at each stage of obtaining nanoparticles was studied by X-ray diffraction analysis. It is established that as a result of electrochemical stratification a mixture of large undecomposed graphite particles and nano-sized graphite plates is formed. By ultrasonic dispersion with the subsequent classification of particles, it is possible to obtain colloidal solutions of low-layer graphene with a plate thickness of the order of 1 nm. At a working voltage of the cell equals to 10 V, the yield of nanoparticles is 10%, the change in the operating voltage does not significantly affect the concentration of the resulting colloid. The effect of adding nonionic and anionic surfactants to ultrasonic treatment of electrochemically dispersed graphite on the yield of a nanosized phase and the concentration of the resulting colloid is studied. The use of a nonionic surfactant (OP-10) negatively affects both the yield of nanoparticles and the concentration of the resulting colloid. The use of sodium dodecyl sulfonate in the stage of ultrasonic dispersion makes it possible to increase the yield of nanoparticles to 22% and the concentration of graphene particles in the colloid to 2.7 g/l. The obtained colloidal solutions are stable for more than a year. During this time there was no precipitation observed.