A. V. Lazarev

Quantum effects under free expansion of monatomic gas mixtures into a vacuum

Abstract The influence of quantum effects during the elastic scattering of atoms on the velocity slip in the jets of some binary mixtures of inert gases is investigated. The kinetic model used is based on a set of momentum transfer equations for the components, with collisional terms being calculated using the quantum first-order effective cross sections of elastic scattering. It is shown that in this approach the quantum correction factor depends only on a quantity which is connected with the temperature and the Knudsen number in the source. The quantum effects are shown to be considerable in mixtures containing helium, with the shape of the potential function playing an essential part. The range of applicability of the kinetic model used is estimated.

Formation of microcapsules containing titanium dioxide nanoparticles by pulse expansion of a supercritical solution into a background gas

The formation of microcapsules with a core of TiO2 nanoparticles in a shell of polyethylene glycol by pulse expansion (pulse duration of 400 µs) of a supersonic jet of TiO2-suspension in a supercritical solution of polyethylene glycol (PEG 8000) in CO2 into a background gas (He) is studied. It is shown that the size of capsules and the content of TiO2 in them depend on the pressure of the background gas in the inlet chamber in the range from 0.125 to 3 atm. The upper (1.5 atm) and the lower (0.25 atm) limits of the pressure range, in which microcapsules with a relatively high content of titanium dioxide are formed, are determined.

Kinetic description of the expansion of a supersonic pulsed jet to vacuum: II. Mixtures of monoatomic gases

A model for the expansion of a pulsed jet of a mixture of monoatomic gases was advanced on the basis of the Boltzmann kinetic equation. The Grad method was used to solve the Boltzmann equation. The set of moment equations was analyzed by matching asymptotic expansions. The behavior of the velocity slip and temperature difference was analyzed as a function of the conditions in the source and the component-gas concentrations in the mixture. A functional relationship between these quantities and the form of the interaction potential has been established.

Determination of the dispersion constant of the interaction potential of SF6-SF6 and SF6-Ne at low energies from experiments with supersonic pulse jets

A determination method for the parameters of the potentials of interatomic distances based on the expansion model of a supersonic pulse jet in a vacuum was used for the determination of C6 dispersion constants of interactions of SF6-SF6 and SF6-Ne. The measured value is the value of the position of the maximum of the TOF spectrum. It has been shown that the obtained C6 values satisfactorily coincide with the available data.

Nonequilibrium effects in a steady supersonic jet of a mixture of monatomic gases

On the basis of the moment equation system for parameters of a steady supersonic jet of a mixture of monatomic gases, the analysis of nonequilibrium effects as a velocity slip and temperature difference of components was carried out in hypersonic and spherically symmetric approximations. The limiting values of velocity slips and kinetic temperatures of mixture components depending on the source jet conditions and interaction potential were obtained.

Equations for translational relaxation in a steady supersonic jet of a mixture of monoatomic gases

On the basis of the Boltzmann kinetic equation with the use of the ellipsoidal distribution function a system of equations that takes the two-dimensional flow near a nozzle into account was derived for the parameters of a supersonic steady jet expanding into a vacuum.

Kinetic description of the expansion of a supersonic pulsed jet into a vacuum: III. Determination of the parameters of the atomic interaction potential at low temperatures

A new method based on the kinetic description of a supersonic pulsed jet is proposed for the determination of the parameters of the atomic interaction potential. Analytical relationships are established between the peak position of the observed time-of-flight spectrum, on the one hand, and the source conditions and interaction potential parameters, on the other.

Simulation of scattering in molecular beams

Abstract In the single-collision approximation, the boundary-value problem for the Boltzmann equation has been solved, simulating molecular-beam scattering. The relationship connecting the experimentally measured intensity of scattered particles, the velocity distribution functions in the initial beams, and differential cross sections of the corresponding processes is obtained. It is shown that the ordinary relationship which corresponds to a uniform scattering pattern in the reaction zone is valid only in the case of precisely collimated beams.

Long-range dispersion C6 coefficient for SF6 dimer: Experimental and theoretical study

The long-range dispersion C6 coefficient for the SF6 dimer is experimentally measured using a technique that uses the expansion of a supersonic pulse jet into a vacuum. A dynamic model of the jet enables us to correlate the position of the maximal peak in the time-of-flight spectrum with the initial conditions of the experiment and the parameters of the intermolecular interaction potential. Due to the low temperature of the jet target, the C6 coefficient can be extracted directly from the experimental results. Theoretical calculation of the C6 dispersion coefficient is also performed by using linearly approximated explicitly correlated coupled-cluster singles and doubles (CCSD(F12)) method with the subsequent utilization of the Casimir-Polder formula. Good agreement of experimental and theoretical results confirms the reliability of results.

Aerodynamic acceleration of heavy particles in a supersonic jet of a binary mixture of gases with disparate-mass components

The method of moments for the ellipsoidal distribution function was used for solving the Boltzmann equation describing binary gas mixtures with large mass disparity and highly diluted heavy component. Analysis of the system of moment equations results in a simple analytic expression for the terminal slip velocities of components that depends on the conditions in the source of jet, composition of mixture, and C6 constant of the attractive branch of the interaction potential. The results are in good agreement with experimental data including low pressure conditions when the Miller-Andres correlation is unsatisfactory.