Role of hydroboron intermediates in the mechanism of chemical vapor generation in strongly acidic media

Unknown and controversial aspects related to the mechanisms of hydrolysis of borane complexes and to the mechanisms of chemical vapor generation for trace element determination in strongly acidic media (0.01-10 M HCl) have been investigated and clarified. The overall hydrolysis rates of borane complexes (BH(4)(-), H(3)N-BH(3)) in the acidity range of 0.2-10 M HCl were several orders of magnitude lower than those predicted by kinetics laws and obtained in the pH range of 3.8-14. The decomposition of the borane complexes takes place stepwise and proceeds through the formation of hydroboron intermediates, L(x)()BH(4)(-)(x)()(n)() (x = 1, 2, 3), where L could be one or more species among the donor groups H(2)O, NH(3), OH(-), and Cl(-) and n is the charge of the hydroboron species (n = 0, +1, -1, depending on L). Some intermediates present surprisingly long lifetimes at elevated acidities and play a key role in determining both the overall hydrolysis rates of borane complexes and the reactivity of Hg(II), As(III), Sb(III), Bi(III), Se(IV), Te(IV), and Sn(IV) in chemical vapor generation for trace element determination. Atomic absorption experiments demonstrated that almost all trihydroboron species (LBH(3)(n)()), dihydroboron species (L(2)BH(2)(n)()), and monohydroboron species (L(3)BH(n)()) play an active role in the generation of elemental mercury and stibine. Some of these intermediates are inactive or play a marginal role in the generation of arsine, bismuthine, and hydrogen selenide. Hydrogen telluride is preferentially formed by those hydroboron species, which are stable in strongly acidic conditions, while the same species are unreactive in the generation of stannane. The collected experimental evidence is in agreement with the general reactivity of the elements in chemical vapor generation techniques and, together with other literature data, definitely rule out the hypothesis of "nascent hydrogen" as a possible mechanism of chemical vapor generation by borane complex derivatization.     

Nonisothermal dissipative flow of viscous liquid in a porous channel

Stationary nonisothermal flow of viscous Newtonian liquid in a flat channel filled with porous material is studied. The Brinkman equation is used as a motion equation. It is assumed that viscosity depends on temperature. The energy equation is denoted using a single-temperature model. Dissipative heat emissions are accounted. The problem is solved for temperature first-order boundary conditions.     

Laminar vapor flow in a heat pipe

Laminar vapor flow in the evaporation, adiabatic, and condensation sections of a heat pipe is considered. The problem is solved by using a parametric method. The solution resulted in a graphoanalytical method of determining the vapor-pressure loss in all sections of the pipe.     

集散化系统的耗散结构

耗散结构理论在当代社会各诸多系统中的应用探索     

Analysis of the motion of a subsonic vapor flow in a quasi-closed volume

The motion of a vapor is described for the case in which the influence of geometry is isolated. The parameters are determined for a subsonic vapor flow on the outer boundary of a gas-kinetic layer near a surface of vaporization. Profiles of the gas-dynamic variables as a function of the dimensionless coordinate are calculated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 25, No. 3, pp. 460–466, September, 1973.     

A possible mechanism of triggering a vapor explosion

Relations are derived which enable one to assess the size of fragments of a liquid-metal droplet after its fragmentation formed in the case of instantaneous contact between a hot metal surface and a coolant. The obtained experimental data demonstrate that the amplitude of pressure pulses generated during vapor film collapse (second boiling crisis) is several times lower than the values required for triggering a spontaneous vapor explosion. The assumption is validated according to which progress in studying the process of triggering a spontaneous vapor explosion is associated primarily with advances in understanding the mechanism of fragmentation of individual droplet.     

The mechanism of vapor condensation from humid air in narrow channels and the hydrodynamics of a two-phase flow during droplet condensation

A study has been made concerning the effect of the condensation mode in a forced stream of humid air on the processes of heat and mass transfer in narrow channels.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 24, No. 2, pp. 240–244, February, 1973.     

Role of the carrier gas flow rate in monolayer MoS2 growth by modified chemical vapor deposition

Monolayer molybdenum disulfide (MoS2) has attracted much attention because of the variety of potential applications.However,its controlled growth is still a great challenge.Here,we report a modified chemical vapor deposition method to grow monolayer MoS2.We observed that the quality of the MoS2 crystals could be greatly improved by tuning the carrier gas flow rate during the heating stage.This subtle modification prevents the uncontrollable reaction between the precursors,a critical factor for the growth of high-quality monolayer MoS2.Based on an optimized gas flow rate,the MoS2 coverage and flake size can be controlled by adjusting the growth time.     

Convective dissipative heat exchange in generalized couette flow of a nonlinearly viscoplastic liquid

Dissipative heat exchange in generalized Couette flow of a nonlinearly viscoplastic liquid between two parallel plates is investigated theoretically.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 37, No. 7, pp. 50–58, July, 1979.     

Problem of considering the effect of superheating of vapor on intense condensation process of vapor flow on a plate

The effect of superheating of vapor on the intense condensation process of vapor flow on a plate is analyzed.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 30, No. 4, pp. 598–600, April, 1976.     

Condensation coarsening of aerosol particles in a cooling vapor—gas flow

A system of equations is obtained to describe the motion of a vapor-gas flow with aerosol particles in a channel of variable cross-sectional area in the presence of external heat transfer. The system is solved analytically for a quasiequilibrium process.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 49, No. 2, pp. 194–201, August, 1985.     

The use of neutral Cs vapor flow in a negative-ion sputter source

Neutral Cs vapor flowing onto the sputter target in an inverted negative ion Cs sputter source has been used to enhance the intensity of the negative ion beam.     

Measurement of turbulent pressure and velocity fluctuations in a vapor flow by the condensation method

The inertial characteristics of the thermal processes underlying a new method of measuring turbulent pressure and velocity fluctuations are analyzed.     

Calculation of shock waves in a flow of moist vapor at low pressure

A method is given for calculating oblique shocks in a region of moist vapor, when conditions of phase equilibrium are satisfied in the shock process.     

Mass transfer in condensation of vapor from a flow of fog-containing vapor-gas mixture

Results are presented for the experimental settling of fog on the internal wall of a channel from a vapor-air mixture moving along it. Variation of fog concentration was determined by measurement of the intensity of scattered light. Experiment and theory are compared.     

Self-deflection of dissipative holographic screening-photovoltaic solitons in a biased dissipative photovoltaic-photorefractive crystal

The self-deflection of dissipative holographic screening-photovoltaic (DHSP) solitons has been investigated in the dissipative system, which consists of a biased dissipative photovoltaic-photorefractive (PV-PR) crystal and two coherently coupled beams; the signal beam (self-trapping beam) gets the energy gain from the pump beam via the two-beam coupling process. The analytical results are in good agreement with the numerical ones. Both predict that the centre of the solitary beam moves on a parabolic trajectory. Moreover, the central spatial-frequency component shifts linearly with the propagation distance. The DHSP soliton has the fixed self-deflection that is completely determined by the system parameters, its self-deflection is slight under small-signal condition, which will bring little influence on the formation of DHSP solitons. Furthermore, the relevant properties on the behaviour of bright DHSP soliton are discussed in detail.     

Heterogeneous nucleation mechanism in the flow of a superheated cryogenic liquid

A hypothesis on heterogeneous nucleation in a liquid volume is used as a basis for obtaining a relation to close a system of equations which describes non equilibrium discharge.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 46, No. 3, pp. 371–375, March, 1984.     

Water vapor sorption mechanism of furfurylated wood

Journal of Materials Science - Furfurylation could have a significant influence on wood hygroscopicity. However, moisture sorption and its mechanism of furfurylated wood are not fully understood....