(Digital Presentation) Investigation of the Influence of Parameters of Contact Nonequilibrium Plasma on the Structure of Copper Oxides

Abstract

Recently, the interest of researchers in nanodispersed oxides of monovalent and bivalent copper, ferrum, cobalt, nickel, and chromium has significantly increased. At the same time, interest in their micro- and nanosized particles is due, first of all, to a wide range of possibilities for their practical application. Today it is possible to use Cu2O, CuO in the creation of new catalysts for various industrial processes, as a filler for varnishes and paints, antiseptics. Cu2O is used in the production of galvanic cells, other fields of technology, etc. [1]. At the same time, the characteristics and variants of their practical application largely depend on the method of preparation, which usually determines their structure, dimensions, physical and chemical properties, etc. [2].Among the methods for obtaining micro- and nanoparticles, large groups form the methods of chemical, electrochemical, electropulse, and plasma-chemical synthesis, based on the processes of reduction or oxidation of metal ions in solutions, depending on the conditions.Each of these groups has its advantages and disadvantages, but the use of the plasma-electrochemical method (using the treatment of aqueous media with contact low-temperature non-equilibrium plasma (CNP) of reduced pressure) makes it possible to use the advantages of each of the groups [3-5]. However, in this case, it becomes necessary to establish the relationship between the synthesis parameters and the phase composition and morphology of the resulting particles.At the first stage, Pourbaix diagrams were constructed corresponding to the conditions of synthesis in a plasma reactor, and voltammograms were obtained, which made it possible to evaluate the effect of pH synthesis on the composition of products. The morphology of the particles was also studied depending on the current strength of the process at the same initial concentration of Сu2+ in an aqueous solution. The use of X-ray phase analysis and electron microscopy made it possible to evaluate the composition and dimensional characteristics of dry sediments. Thus, at the process current I=200-250 mA, particles were obtained, consisting of intergrowths of crystals, the size of which did not exceed 30 μm, at I=140-200 mA crystals up to 15 μm were obtained, at I=80-140 mA the average crystal size did not exceed 5 µm.The structure of the particles was also established: the largest particles were represented mainly by intergrowths of smaller crystals. It is obvious that the formation of numerous crystallization centers with the simultaneous intense evolution of hydrogen contributes to the fact that the rate of crystal growth at the cathode decreases. At higher current strength parameters, the growth of individual crystals is observed (mainly in the form of octahedrons and cuboctahedrons, the size of which reaches 10-15 μm. A decrease in the current strength leads to a decrease in the particle size - both individual crystals and their intergrowths, which in this case are predominantly octahedral structures, the largest of which are 1–2 µm, and the smaller ones are 100–200 nm.The results of X-ray diffraction analysis show that under the given conditions for the formation of a deposit, the surface of the formed particles consists mainly of Cu2O.On the basis of the conducted studies, it can be noted that the size of the precipitate particles obtained can vary within a fairly wide range. In this case, a change in the process parameters, especially a decrease in the process current, leads to a decrease in the size of the formed particles and an increase in the deposit uniformity, which is confirmed by the results of electron microscopic studies of the synthesized cathode deposits. This makes it possible to control the particle synthesis process by adjusting the parameters of the plasma-chemical processing process, which, due to its simple design, does not cause difficulties and, along with the possibility of using highly diluted solutions, is an advantage of this method.