Архив

Electrochemical formation of transparent semiconductive oxide (TSO) coatings based on zincite is an attractive, versatile and easily scalable method,which is promising for optoelectronics and chemical sensors. The complexity of the formation of zinc oxide and doped compounds such as ZnO(Al) coatings by electrochemical co-precipitation of zinc and aluminum compounds in aqueous media is connected with both different redox potentials of two metals and the formation of galvanic precipitates of significantly hydrated zinc and aluminum oxides. Application of non-aqueous media for zinc electrolytes can form a bimetallic deposit for the following gently oxidation to oxide (AZO). In the present study, dimethylsulfoxide (DMSO) is applied as a solvent. It is shown that the specifics of nucleation of zincite phase in DMSO electrolytes results in more porous coatings in comparison to the processes in aqueous plating solutions. Here, compositions of non-aqueous electrolytes and corresponding deposition potentials in potentiostatic mode have been optimized. The correlations of microstructure and elemental composition of the coatings with parameters of galvanic process have been studied. The presence aluminum at the surface of the samples in two different valent states have been shown using X-ray photoelectron spectroscopy. This is the result of the deficiency of wurtzite structure and the presence of γ-Al2O3 phases, most likely, resulted from segregation. It is shown that the developed synthesis method is promising for direct synthesis of porous coatings of zincite with a variable deficiency of the structure.

In the present study, we report the calculated value of surface energy for liquid-phase exfoliated few-layer graphene platelets based on experimental data for contact angles of graphene-based films. Free mixing energies were calculated via direct technique from data on surface tensions and their temperature coefficients, as well as using Hansen solubility parametersto obtain Flory-Huggins constants. Although the values obtained for different methods vary, qualitatively it was shown that colloidal systems based on few-layered graphene platelets are lyophobic, and freeenergies for ethylene glycol, diethylene glycol and N-methylpyrrolidone are all close and far lower than that for water. For ethylene glycol-based suspension assessment of the structure via transmission electron microscopy and Raman spectroscopy was performed. Polyols were shown to be very promising media for dispersion and exfoliation of natural graphite to manufacture graphene of high structural quality, effective wetting and stabilization of the free surface at low free energy of mixing values. Calculated values of thermodynamic functions can be used in developing new graphene manufacturing technologies based on direct exfoliation and subsequent stabilization of the newly formed free surface.

The kinetics of the TiO2 crystalline phase formation in the powdered samples of protonated potassium polytitanate (PPPT) having an amorphous layered structure was studied by differential scanning calorimetry (DSC). The theoretical analysis was carried out using the THINKS free software, based on the methods of Kissinger, Friedman and Vyazovkin, as well as the method of combined kinetic analysis, and the methods of linear and non-linear regression. The obtained results have shown that the formation of the crystalline TiO2 (anatase) in the investigated system occurs in two stages. The theoretical results were analyzed taking into account their correspondence to the kinetic models of crystallization process including: two independent flexible one-step stages; two sequentially flowing flexible single-step stages; two parallel flowing (competing) flexible single-step stages. The main kinetic parameters of the crystallization process are determined using the best satisfaction to the Bayesian fit criterion (BIC). Based on the results obtained, the mechanism of two sequentially flowing stages is proposed. The first stage of crystallization, involves the diffusion of surface-active components (H2O, H3O+, K+) in the interlayer space to the surface of PPT particles and following desorption of water and transformation of the layered amorphous PPPT structural polyanions into the distorted crystalline anatase-like structure. At the second stage of the process, the distorted anatase structure is transformed into the traditional crystalline form, and, finally, the process of crystallization of protonated PPT is completed by the formation of small crystals of potassium hexatitanate onto the surface of particles with the participation of potassium ions previously diffused from the bulk.

The paper shows the relevance of research in the development of activated carbon materials with a high specific surface area and porosity, which can be used as materials for the separation or storage of various liquid and gaseous media. A plurality of approaches to the implementation of the activation process, characterized mainly by the accumulation of experimental data and laboratory studies, is noted. The possibility of realizing the process of carbonizate activation in two variants has been established: the first is high-temperature alkaline activation, the second is high-temperature alkaline activation with an additional activator in the form of water vapor. The most rational temperature regimes for the implementation of this activation process are determined, which are 750 °C for the first variant, and 600 °C for the second, as well as their key features are defined. The characteristics of the carbon material obtained as a result of two variants of activation – specific surface area and porosity –are analyzed, and their dependence on the temperature of this process is established. The possibility of industrial implementation of the considered activation options is substantiated, taking into account the peculiarities of their implementation to obtain an activated highly porous carbon material with a specific surface area of more than 2700 m2⋅g–1 and a porosity in the micro- and mesosize range of more than 1.3 cm3⋅g–1.

The efficiency of the separation process of impurity particles with different densities in a rapid gravity flow of monodisperse granular material has been studied. The study was carried out by mathematical modeling of particle concentration distribution dynamics on a rough chute using a mathematical model that takes into account the kinetics of convection, mixing, segregation and quasi-diffusion separation effects. During the research process, the relative density of impurity particles in the range of 0.2–4.0 was varied with respect to the base component particle density, and this confirms the defining role of the quasi-diffusive separation effect. It was found that the concentration distribution profiles of lowand high-density particles have a shape similar to the shape of the profiles of the volume fractions of voids and solids, respectively. With the same degree of difference between the light and heavy impurity particles from the base component particles, the light particles have a higher tendency to separate. The tendency to separation with increasing degree of difference between the density of the impurity particles and the density of the base component particles increases more intensively for the impurity particles with low density. It is found that with decreasing concentration of impurity particles in the flow, the intensity of their separation increases for particles with low density and decreases for particles with high density. A binary mixture of homogeneous particles with the minimum volume content of low density particles is characterized by the highest tendency to particle density separation.

In this work, using a technologically simple and low-cost method, as an alternative to the known layered inorganic ion exchangers of manganese and titanate type, protonated potassium polytitanate (K0.8H1.2Ti4.3O8.5) was obtained and studied to extract lithium from secondary natural resources. X-ray diffraction analysis confirmed the retention of the original X-ray amorphous structure of potassium polytitanate after the protonation process, which ensures good ion-exchange and adsorption capacity of the material. Functional groups of protonated potassium polytitanate, which are potential active sites for interaction with Li+ ions, were analyzed by FTIR spectroscopy. When lithium was extracted from an aqueous solution with a concentration of 0.01 mol⋅L–1, protonated potassium polytitanate demonstrated an equilibrium adsorption capacity of 0.52 mmol⋅g–1. In this case, the experimental data are in good agreement with the pseudosecond order kinetic model (R2 = 0.999). The adsorption process is described by the Freundlich isotherm and is characterized by the constant KF = 0.0013 (L)1/n(mmol)1–1/ng–1. The good selectivity of protonated potassium polytitanate with respect to Li+ ions in the presence of Na+, K+, Mg2+, and Ca2+ ions is shown, while the adsorption capacity is maintained at the level of 0.50–0.52 mmol⋅g–1.The results obtained indicate that protonated potassium polytitanate is a promising and competitive material for the extraction of Li+ ions from low concentration aqueous solutions.

The formation of an ultrafine-grained (UFG) structure of a mixed type in the EK61 superalloy provides the manifestation of the low-temperature superplasticity effect. It can be successfully implemented in an innovative process of pressure welding (PW) to obtain solid-state joints (SSJ) in a combination of EK61 and EP975 superalloys characterized by different types of hardening phases. According to the energy-dispersive analysis resultsin the process of PW in vacuum under low-temperature and rate superplasticity conditions (Т = 850 °С, ε