A Simulation study of the cooling of an isolated metal sphere in aqueous media (quenching)

A quantitative study is carried of a metal cooling process in aqueous and water-polymer cooling liquids. In the study, an original spherical hot probe with a heat-insulated stem is used to simulate the cooling conditions of the operating part of the probe and to correspond to the cooling conditions of an isolated sphere. It has been shown that in this case the process consists of distinct consecutive stages, each of which can be studied separately in a quantitative way. The cooling process in all stages is described with a simple exponential relationship containing two parameters. One of these is the effective temperature of the cooling medium; the other is a time constant of the cooling process uniquely related to the heat dissipation coefficient. In the film boiling stage the effective temperature can be much lower than the nominal temperature; moreover, for cooling in cold water it is found to be lower than the absolute temperature, which indicates the dominant contribution of convection to the heat dissipation. The effective temperature of the medium is a monotonously increasing function of the nominal temperature and rises with rising liquid viscosity. Dependence of the cooling process time constant on the liquid temperature is influenced by two competing processes affecting convection, namely, by variations with temperature of the density and viscosity of a liquid. The effect of diminishing density becomes prevalent at temperatures of the liquid above ≈80°C.     

A new method for separation of 97Ru from irradiated by α-particles molybdenum for nuclear medicine

Russian Chemical Bulletin - A new method for separation of 97Ru radionuclide from irradiated by a-particles molybdenum, which potentially could be applied in nuclear medicine, is proposed....     

Elastic properties of two-dimensional two-phase composites with isotropic phases

Formal series of powers of Fourier coefficients for the effective elastic constants of a heterogeneous material (Herring’s series) are considered. It is demonstrated that, on their basis, all the known exact solutions of an elastic problem for a two-dimensional two-phase composite can be found. It is also shown how a full renormalization of the series for the inverse bulk modulus can be carried out. A general expression for Young’s modulus is deduced, leading to considerable simplifications in some special cases. All results have been obtained without any restrictions on the Fourier coefficients of local parameters of the composite.     

On the solution of the kinetic equation for a heat flux between concentric spheres

The problem of calculating a heat flux in a spherical layer is considered. The results are obtained in terms of the Bhatnagar-Gross-Krook model and the Boltzmann collision integral. A general (independent of the form of the kinetic equation and the solution method) expression for the heat flux as a function of the energy accommodation coefficient is derived. The results are compared with the experiment and the analytical results obtained previously.     

Kinetic resistance of borofluoride complexes of dipyrrolylmethenes to acids

The trends of kinetic resistance of borofluoride complexes of alkyl- and sulfo-substituted dipyrrolylmethene (Bodipy) to protolytic and solvoprotolytic dissociation in organic solvents and aqueous solutions are studied. It is established that among dipyrrolylmethene complexes with d elements, Bodipy is notable for its superresistance to acids. The rate of the dissociation reaction increases with increasing acidity of protonating mixtures or decreasing effective charge of the coordinating nitrogen atoms of the ligand. Dissociation of the complexes occurs in accordance with a second-order rate equation. A kinetic model of the process is proposed; its kinetic and activation parameters are determined. The energy profiles of the initial stages of protolytic dissociation reactions are calculated using quantum-chemical methods for two suggested variants of the transient state; the energetically preferable pathway is recognized.     

Protolytic dissociation of copper(II) and nickel(II) dipyrrolylmethenates in benzene solutions of acetic acid

Protolytic dissociation of copper(II) and nickel(II) dipyrrolylmethenates in benzene solutions of acetic acid has been studied. The results have completed the knowledge of kinetics of dipyrrolylmethene complexes dissociation in acidic medium. The effect of the nature of complex forming atom, ligand, and other factors on the complexes kinetic stability has been analyzed.     

Solid-phase fluorometric determination of Al(III), Be(II), and Ga(III) using dynamic preconcentration on reagent cellulose matrix

A fluorimeter is developed, which provides sample pretreatment, preconcentration of analytes from natural waters on the surface of indicator cellulose matrices, and the simultaneous measurement of their fluorescence. The device employs a L-711UVC ultraviolet light diode and a Digital color sensor S9706 photodiode, which registers simultaneously in the red (615 nm), green (540 nm), and blue (465 nm) spectrum regions. The opportunities of the application of this fluorimeter have been shown by an example of determination of 1–100 μg/L Al(III) and 0.1–10 μg/L Be(II) and Ga(III).     

Silver and palladium nanoparticles-containing products of the low-temperature wave conversion of an energetic material: Catalytic activity in piperylene hydrogenation

The hydrogenation of 1,3-pentadiene into pentenes over the commercial 0.5% Pd/Al₂O₃ catalyst and over a new catalyst containing 1.0% Pd and 3.7% Ag (μ-catalyst) has been investigated. The new catalyst has been prepared via the flameless wave conversion of cyclotrimethylenetrinitramine in a porous composite. The catalytic properties of the new composite in the hydrogenation reaction depend on the hydrogen/1,3-pentadiene ratio and on the catalyst activation temperature. The reaction conditions for selective 1,3-pentadiene hydrogenation have been optimized. The pentenes yield as a function of temperature passes through a maximum at any H₂/C₅H₈ ratio between 1 and 2. The 2-pentene/1-pentene ratio in the reaction products increases as the temperature is raised.     

High-rate combustion of cellulose nitrate in filled polymer systems

It was found that, at a certain external pressure, the conventional slow flameless combustion of nitrocellulose in filled compositions can go over into a high-rate low-temperature mode, with a burning velocity increasing by more than 40-fold. It was shown that the critical external pressure at which the changeover of the combustion modes occurs decreases with the sample porosity. It was assumed that the high-rate combustion of nitrocellulose in filled systems proceeds by the well-known mechanism of convective combustion of energetic condensed systems with some specific features.