Vol 57, No 2 (2019)

Different morphologies of nanostructured TiO₂ materials can be tailor-made as a function of growth time varied from 1 to 7 h with a step of 2 h. TiO₂ nanostructures were prepared on titanium foil by a facile water-assisted chemical vapor deposition method at 850°C. Scanning electron microscopy examination of the samples reveled that, under the treatment time of 7 h, the morphology of nanostructures transformed from cubic nanostructure-like to agglomerated nanorod-like and nanoplate shape. The X-ray diffraction through synthesized TiO₂ nanostructures exhibited the crystalline structure of rutile TiO₂ formed during the synthesis process. X-ray diffraction analysis showed that at deposition time of 7 h the intensity peak of [110] plane strongly decreased and seems that the [210] plane peak is the preferred orientation at this condition. Present paper deals with studies of the antibacterial activity of different synthesized samples after 24 h in the presence of Escherichia coli and Staphylococcus aureus cells. It is found that the growth time has an essential role in the morphology and antibacterial properties of TiO₂ nanostructures.

The results of an experimental study of the total hemispherical and spectral normal emittances powers of siliconized silicon carbide in the temperature range of 1400–2200 K are presented for the first time.

An analytical method that takes into account axial thermal conductivity was proposed for the calculation of eigenvalues and eigenfunction in a problem of heat exchange for laminar liquid flow in a cylindrical channel. The method was based on the use of the special hypergeomertic confluent function. With this function, it is possible to find the precise fudical values of eigenvalues and eigenfunctions at specific relations of the Bio and Peclet numbers. Moreover, the recommended approach makes it possible to carry out the necessary mathematical calculation operation with an arbitrary combination of the named similarity numbers with a sufficient degree of accuracy. This creates the corresponding dimensionless complex α. Such an approach makes it possible to considerably limit (reduce) the number of weighty members of an infinite series of the applicable hypergeometric function. With the use of the named functions, the derived strict and approximate analytical solutions can be applied in the theoretical analysis of a wide class of thermal physics problems, including nonlinear problems.

The method of water purification from admixture molecules via air bubbles is presented. These bubbles are formed at the vessel bottom and floating up to the surface, are captured by admixture molecules and transported them to the surface of the contaminated water flow. The surface electric discharge then removes admixture molecules from the surface or destroy them. Theoretical and experimental analyses demonstrate the reality of such a water purification method. This method is not suitable for large-scale water purification because of a large number of air molecules needed to remove a single admixture molecule. However, it is suitable for water purification of carcinogenic or biologically dangerous admixtures.

Experimental findings suggest that a strongly ionized, arc He plasma of atmospheric pressure does not exist in the state of the local thermodynamic equilibrium (LTE) expected for a plasma with an electron concentration above 10¹⁶ cm^–3. This is found to be caused by transverse plasma nonuniformity and density effects. The plasma quasistatic microfield destroys the upper electron levels of He atoms, and the radial ambipolar diffusion flow transports the charged particles from the narrow (1–2 mm) plasma channel on the chamber wall. In the distribution of atoms and the ions over the excited levels, strong ionization nonequilibrium and a large gap of the ground state are observed; these factors cause substantial difficulties in the spectral diagnostics of the plasma parameters due to the inapplicability of the relations taking into account the equilibrium conditions. A method is proposed to measure the concentration of double-charged ions He⁺⁺ (α particle), which is inaccessible by direct spectral registration, as well as a simple kinetic model of strongly ionized He plasma with the use of a modified diffusion approximation; the model adequately describes the plasma parameters.

Under the conditions of a nonstationary pulsating longitudinal-transverse discharge produced in a supersonic cold (T = 175 K) air flow, the combustion of a propane–air mixture has been stabilized. It has been shown that the completeness of propane combustion after stabilization under the conditions of low-temperature plasma amounts to about 95%. The combustion occurs at a flame temperature of 1800–2000 K. A propulsion thrust of about 55 N has been obtained the course of an experiment with plasma-assisted combustion of propane in an expanding channel with a length of 50 cm and a ratio of the inlet and outlet cross sections of S₂/S₁ = 12.7 at mass flow rates of 105 and 4.9 g/s for air and propane, respectively. This shows good agreement with the value of 60 N calculated under the conditions of complete propane burning.

Ni–P alloys containing phosphorus from 15 to 23 at %, which is close to the eutectic concentration, are studied with differential scanning calorimetry. The heat capacity C_P is calculated at a constant pressure for the melts from the obtained data. The C_P values of the alloys at temperatures above their melting points at 50°C are 0.53–0.59 J/(g K) and are in good agreement with the literature heat capacity values for liquid nickel and Ni₃P. The C_P of all of the melts linearly increases from the Т_L liquidus temperature to 1400°С. There is a maximum on the concentration dependence of C_P at the eutectic concentration.

The thermal diffusivity, thermal conductivity, and specific heat of solid solutions of Bi_1–xNd_xFe_{1 –x}Mn_xO₃ (x = 0.03, 0.09) multiferroics have been studied in a wide temperature range (above room temperature). It is established that substitutions Nd³⁺ → Bi³⁺ and Mn³⁺ → Fe³⁺ in BiFeO₃ lead to a decrease in the thermal diffusivity and thermal conductivity of Bi_1–xNd_xFe_1–xMn_xO₃ solid solutions and reduce the temperatures of antiferromagnetic and ferroelectric orderings. The temperature dependence of the phonon mean free path is found. The factors limiting the phonon transfer in samples are determined.

The temperature dependence of the electrical resistance of graphene oxide upon continuous heating and cooling under argon in the temperature range of 300–550 K and the Raman scattering spectra are studied. In the range 300–370 K, the resistance is constant during the cooling process and is thermostable under subsequent heating. The temperature dependence of the resistance in the 370–550 K range varies according to the activation law. The decrease in resistance with increasing temperature is associated with the removal of functional oxygen-containing groups, which is confirmed by the Raman spectra.

A method is proposed for the two-dimensional inverse heat conduction problem via reconstruction of the spatial and temporal density of a boundary heat flux. It is based on the optimal control theory for objects with distributed parameters. The method limits the set of desired solutions to the class of physically realized functions, which makes it possible to represent the desired-effect structure as a product of two one-variable functions. The problem of semi-infinite optimization, which minimizes temperature residuals in the uniform estimation metric, is formulated based on the parameterization of the desired characteristic (considered a control action). Analytical solution of the problem with the alternance properties of the desired optimal temperature deviations makes it possible to obtain the optimal values of the parameter vector.

The results of previous studies of the water droplet dynamics on a horizontal surface blown by air are briefly reviewed. The experiments were carried out on rectangular wing model profile as an example. The inclined plane method was used to measure the limiting hysteresis of the contact angle with respect to the surface properties. The values of the flow velocity at which the drop begins to move are found. The dependence of the drop velocity on its characteristic size and air velocity is obtained. A theoretical description of the drop dynamics is given, and a semiempirical expression for its velocity is proposed. The developed experimental-theoretical algorithm can be used for a wider range of control parameters (surface tension coefficient of the fluid, contact angle, gas flow velocity, droplet size).

The development of the initial stage of instability of a contact boundary of colliding metal plates has been numerically simulated. The mathematical model is based on the Euler system of equations for a medium obeying the two-term equation of state. The parameters of the equation of state are calibrated proceeding from the calculated and experimental data based on real wide-range equations of state for metals. The computational algorithm is based on the Harten–Lax–van Leer scheme. The initial sinusoidal perturbation of the contact boundary between the plates after the propagation of rarefaction waves from the free plate boundaries becomes crater-shaped, which qualitatively corresponds to natural experiments.

Mathematical and computer models of the behavior of thermal protection systems composed of highly extended elastomers are formulated based on the analysis and generalization of the results of theoretical and experimental research. The results of numerical studies show satisfactory agreement with the experimental data.

The influence of the parameters of monodisperse and polydisperse, one-component and multicomponent bubble media on the conditions of the initiation, structure, propagation speed, and pressure of detonation waves is experimentally studied. It is established that the variation in the parameters of the bubble medium, e.g., of the initial pressure, is an efficient way to control the characteristics of the detonation waves.