Thermodiffusion and Vaporization of Metal from Levitated Droplet V. Determination of Condensation Rate and Thermodiffusion Parameters of Mn, Fe, and Ni Vapours

In the present paper the experimental data of vaporization from levitated droplet for Mn, Co, Ni in the flow of argon obtained from the bibliography were evaluated by means of the new method published in the previous work [Czech. J. Phys. 50 (2000) 737]. The rate constants of condensation, thermodiffusion ratios, thermodiffusion coefficients and the corresponding temperature dependencies were determined together with other physical quantities for Mn vapour at the temperature 2000 K and for Fe, Ni at 2200 K. The rate constant of condensation and the thermodiffusion ratio are higher for Ni than for Fe. The value of thermodiffusion coefficient determined for Mn is rather high and the rate constant of condensation is higher than for Ni. The increase of vaporization resulting from condensation and thermodiffusion for Mn was only 2.7-times and for Fe and Ni (5.5-5.65)-times. The process of vaporization from a levitated droplet includes molecular diffusion and convective diffusion, molecular thermodiffusion with vapour condensation and condensation without thermodiffusion. The proportions of these processes were for Mn in the range (37-29) condensation dominated and its share was over 70 accurate experimental data and this is the reason why the evaluation of the Co vaporization was unsuccessful. The work also presents some proposals of experimental procedures leading to the data accuracy improvement.     

Thermodiffusion and vaporization of metal from levitated droplet III. Vaporization rate at molecular diffusion and total vaporization rate

In the present paper the problem of the molecular diffusion in the proximity of the levitated droplet surface respecting the metal vapour condensation influence and temperature dependences of basic physical quantities was solved. The molecular diffusion flow density was derived and the final relation for the mean total thermodiffusion flow density from the droplet surface, i.e. the vaporization rate, was presented. The results are completed by some numerical values and the accuracy of some calculations performed in the linear approximations was analyzed. Theory. Numerical calculations.     

Thermodiffusion and vaporization of metal from levitated droplet II. Vaporization rate at convective diffusion

In the present paper the problem of convective thermodiffusion from a levitated droplet is solved respecting the temperature dependence of the diffusion coefficient and including the metal vapour condensation in the proximity of the droplet surface and the thermodiffusion. The relation for the mean density of the convective diffusion flow from the surface was derived. This relation describes the rate of metal evaporation in which the case of diffusion without convections is not included. The derivation was performed in the first approximation. Theory. Numerical calculations.     

Thermodiffusion and vaporization of metal from levitated droplet I. Calculation of temperature field

In the present paper the initial partial differential equations resulting from the thermodynamics of irreversible processes and Onsager theory are presented and transformed in a way describing convective thermodiffusion in the proximity of a levitated droplet in forced laminar flow. To solve the temperature field the procedure used by Levich for describing diffusion to the falling particle was applied. This procedure was generalized for the temperature dependence of the temperature conductivity coefficient. The results of this solution were compared with the case when the mean constant value of this coefficient is used and an acceptable agreement of the results was stated. The derived theory will be used as the basis for calculation of the vaporization rate of metal from the levitated droplet taking into account metal vapour condensation in the temperature and diffusion boundary layer.P. Kubíek — theory, L. Mrázek — numerical calculations.     

Finite element simulation of pulsed laser ablation of titanium carbide

In the present paper, a 2D finite element model based on the heat-conduction equation and on the Hertz-Knudsen equation for vaporization was developed and used to simulate the ablation of TiC by Nd:YAG and KrF pulsed laser radiation. The calculations were performed for fluences of 8 and 10 J/cm², which according to experimental results obtained previously, correspond to large increases of the ablation rate. The calculated maximum surface temperature of the target for both lasers is higher than the estimated value of TiC critical temperature, corroborating the hypothesis that the increase of the ablation rate is explained by the explosive boiling mechanism.     

Calculating the low temperature vapour line by Monte Carlo

A combination of canonical and grand-canonical ensemble Monte Carlo calculations, together with the virial expansion, have been used to calculate the thermodynamic properties of the liquid/vapour co-existence curve of the (6 : 12) Lennard-Jones fluid for reduced temperatures, [Ttilde] ? 1·1. The results for the liquid density and energy and the latent heat of vaporization are believed to be precise, with the exception of the point at [Ttilde]=1·1 which may lie outside the range of the function fitting the liquid phase Monte Carlo data. The liquid density and the saturated vapour pressure are in very good agreement with the results of perturbation theory. The latent heat of vaporization does not agree well with the experimental data for argon though the fit to liquid density and internal energy is good.     

Temperature dependence of the conductivity of a silicon inversion layer at low temperatures

The temperature dependence of the conductivity of a high-mobility silicon MOSFET is reported for temperatures from 0.2 to 23 K and electron densities from 1 to 20 × 10¹¹cm⁻². The results show a strong increase in conductivity with decreasing temperature. However, this rate of increase was observed to rapidly diminish outside of a restricted range of temperature for a given density. The decreasing temperature dependence at the lower temperatures is attributed to the saturation of screening as the effects of broadening become comparable to thermal effects. The diminishing temperature dependence at the higher temperatures puts limits on the applicability of recent calculations for the conductivity.     

Estimation of the ultracold neutron production by a source designed for the WWR-M reactor

The results of calculations related to designing an ultracold neutron source with superfluid helium for the WWR-M reactor have been presented. The ultracold neutron production rate has been estimated for different types of premoderator chamber filling. The dependence of this rate on the temperature of helium has been determined. If the premoderator chamber is filled with liquid orthodeuterium, the ultracold neutron production rate remains almost constant in the range of helium temperatures of 1.0–1.5 K and is as high as 3.1 × 10³ cm^–3 s^–1.     

Migration of Mn<Superscript>2+</Superscript> excitations in Cd<Subscript>0.5</Subscript>Mn<Subscript>0.5</Subscript>Te crystal

The experimentally obtained intensity decay curves for the 2-eV intracenter luminescence band of Mn²⁺ ions in Cd_0.5Mn_0.5Te semiconductor solid solution at a temperature of 77 K have been simulated by the Monte Carlo method. The calculations show that the initial nonexponential behavior of the intensity decay curves at the band wings, as well as the time dependence of the band peak energy, are determined by the fast migration of excitations through the Mn²⁺ ion subsystem. There are more than 200 jumps per each emitted photon, and the migration rate increases by almost two orders of magnitude in comparison with the rate at 4 K. The analysis of the simulation results and the calculation based on the experimental data show the interaction between ions to be resonant. The estimate derived from the Anderson criterion suggests that the excited state is not delocalized. An increase in the migration rate with an increase in temperature significantly reduces the inhomogeneous broadening dispersion.     

Nanosecond laser ablation for pulsed laser deposition of yttria

A thermal model to describe high-power nanosecond pulsed laser ablation of yttria (Y₂O₃) has been developed. This model simulates ablation of material occurring primarily through vaporization and also accounts for attenuation of the incident laser beam in the evolving vapor plume. Theoretical estimates of process features such as time evolution of target temperature distribution, melt depth and ablation rate and their dependence on laser parameters particularly for laser fluences in the range of 6 to 30 J/cm² are investigated. Calculated maximum surface temperatures when compared with the estimated critical temperature for yttria indicate absence of explosive boiling at typical laser fluxes of 10 to 30 J/cm². Material ejection in large fragments associated with explosive boiling of the target needs to be avoided when depositing thin films via the pulsed laser deposition (PLD) technique as it leads to coatings with high residual porosity and poor compaction restricting the protective quality of such corrosion-resistant yttria coatings. Our model calculations facilitate proper selection of laser parameters to be employed for deposition of PLD yttria corrosion-resistive coatings. Such coatings have been found to be highly effective in handling and containment of liquid uranium.     

Faraday effect in Tb3Ga5O12 in a rapidly increasing ultrastrong magnetic field

The Faraday effect is measured in paramagnetic terbium gallate garnet Tb₃Ga₅O₁₂ at a wavelength λ=0.63 μm at 6 K in pulsed magnetic fields up to 75 T increasing at a rate of 10⁷ T/s for field orientation along the crystallographic direction 〈110〉. The experimental data are compared with the results of theoretical calculations taking into account the crystal fields acting on the Tb³⁺ ion and various contributions to the Faraday rotation. Since the measurements in pulsed fields are carried out in the adiabatic regime, the dependence of the sample temperature on the magnetic field acting during a current pulse is obtained from the comparison of the experimental dependence of Faraday rotation with the theoretically calculated dependences of the Faraday effect under isothermal conditions at various temperatures. __________ Translated from Fizika Tverdogo Tela, Vol. 44, No. 11, 2002, pp. 2013–2017. Original Russian Text Copyright ? 2002 by Levitin, Zvezdin, Ortenberg, Platonov, Plis, Popov, Puhlmann, Tatsenko.     

Experimental Investigation of Heat Transfer at Downflow Condensation of Refrigerant R-21 in Assemblage of Minichannels

Presented are results of experimental investigation of heat transfer at downflow condensation of refrigerant R-21 in a vertical assemblage of minichannels in a plate-fin heat exchanger with plane fins. Selection of refrigerant was caused by the fact that its physical properties at room temperature are similar to those of cryogenic liquids at low temperatures. A pattern of vapor-liquid downflow in the heat exchanger channels was plotted using the working section with a transparent wall. For the mass velocity in the range of 30 to 50 kg/m²s and the wall subcooling below ?2?C, the dependence of the heat transfer coefficient on the mass vapor content is determined and a method is proposed to calculate the heat transfer coefficient that is in good agreement with the experimental data.     

On the Temperature Dependence of Radiationless Electron Transitions. I. The Morse Oscillator Model in case of a Small Value of the Parameter Z

A number of experimental results have been recently made available on the temperature dependence of lifetimes of excited states of polyatomic molecules in condenced^1–6 and gaseous phases. The dependence was shown to be quite substantial in experiments with both fluorescence^5,6 and phosphorescence^1–4 temperature quenching. The decay-rate constant of electronic excitation is 1/τ′ = β + 1/τ, where b is determined by radiative processes and is but slightly temperature-dependent^5,6. As for the rate constant 1/τ of radiationless electronic transitions, it might be the very parameter that governs the temperature dependence of 1/τ.     

Cross sections for scattering of deuterium mesic atoms on deuterium nuclei

Cross sections have been calculated for elastic scattering of deuterium mesic atoms in ortho and para states on deuterium nuclei in the 0–50 eV energy range; cross sections for spin-flip have also been calculated. The calculations have been performed in the adiabatic representation where the initial problem of slow collisions in a three-body system is reduced to the multichannel scattering problem. The temperature dependence of the ortho-para transition rate λ_hf(T) for dμ atoms is obtained for a deuterium target. The calculated rate 37.2×10⁶ s^-1 (at 30 K) is in good agreement with the recent experimental value, λ_exp(30 K) = (37.0±0.74)×10⁶ s^-1 (Vienna-SIN group, 1983).     

Gas-liquid phase transition and singularities

A new model for the space of undercritical states of a gas-liquid system is proposed. Simple, physically motivated mathematical hypotheses among which stsbility plays an essential role, determine differential types of germs of pressure and temperature at the critical point. They are connected with the class D⁺₄ of Arnold's classification. The general configuration of vaporization and condensation curves is examined. As a result, Guggenheim's one-third law is obtained.     

Homogeneous and unimolecular gas‐phase thermal decomposition kinetics of methyl benzoylformate: experimental and theoretical study

The kinetics of the gas‐phase thermal decomposition of the α‐ketoester methyl benzoylformate was carried out in a static system with reaction vessel deactivated with allyl bromide, and in the presence of the free radical inhibitor propene. The rate coefficients were determined over the temperature range of 440–481 °C and pressures from 32 to 80 Torr. The reaction was found to be homogenous, unimolecular and obey a first‐order rate law. The products are methyl benzoate and CO. The temperature dependence of the rate coefficient gives the following Arrhenius parameters: log₁₀ k (s^?1) = 13.56 ± 0.31 and E_a (kJ mol^?1) = 232.6 ± 4.4. Theoretical calculations of the kinetic and thermodynamic parameters are in good agreement with the experimental values using PBE1PBE/6‐311++g(d,p). A theoretical Arrhenius plot was constructed at this level of theory, and the good agreement with the experimental Arrhenius plot suggests that this model of transition state may describe reasonably the elimination process. These results suggest a concerted non‐synchronous semi‐polar three‐membered cyclic transition state type of mechanism. The most advanced coordinate is the bond breaking C^δ+‐‐‐^δ‐OCH₃ with an evolution of 66.7%, implying this as the limiting factor of the elimination process. Copyright © 2014 John Wiley & Sons, Ltd.     

Determination of parameters of Cu surface mass transport on sapphire from morphological changes of beaded films caused by evaporation

s , the surface diffusion coefficient, D_s ^′, and the surface reaction rate coefficient, β_s ^′, of Cu on alumina are determined in the temperature range 1048–1198 K. Measuring simultaneously the time dependence of the effective thickness, H_eff(t), the lateral shift of the boundary, y(t) of beaded films (BF) and using vapour pressure data we concluded that the process is controlled by surface reaction at the perimeters of beads. Supposing Arrhenius-type temperature dependence for D_s ^′, β_s ^′ and λ_s the activation energies and preexponential factors have been calculated. Received: 2 October 1996/Accepted: 27 November 1996     

N2-, O2-, and air-broadened half-widths, their temperature dependence, and line shifts for the rotation band of H2O

Complex Robert–Bonamy (CRB) calculations of the half-width, its temperature dependence, and the line shift have been made for the rotation band transitions of H₂¹⁶O for N₂ or O₂, as the bath molecule. First the atom–atom component of the intermolecular potential was adjusted to reproduce the half-widths of the 22 and 183 GHz transition determined by Payne et al. (IEEE Trans. Geosci. Remote Sensing 46 (2007) 3601–3617). Then the line shape parameters were determined at seven temperatures (200, 225, 275, 296, 350, 500, and 700 K) for the H₂O–N₂ and H₂O–O₂ systems. The air-broadened values were determined at each temperature by the standard method. The half-widths, their temperature dependence, and the line shifts were studied as a function of the rotational quantum numbers. Estimating line shape parameters by scaling from one perturbing gas to another was investigated. The calculations were compared with measurement.     

Thermodiffusion of interstitials in a film

A general expression is obtained for the thermodiffusion coefficientD _T of a film, also for its dependence on temperature, film thickness and type of concentration distribution of the interstitials, according to its profile. In neglecting interaction of interstitials with each other in a model of a film with single-plane boundaries with the vacuum and the substrate, it is shown thatD _T>D _T ^(∞) is possible, whereD _T ^(∞) is the thermodiffusion coefficient of a bulk specimen. Ural State Technical University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 43–46, September, 1996.     

High-temperature mid-IR absorption spectra and reaction kinetics of 1,3-dioxolane

Cyclic saturated ethers are proposed as alternative fuels for future sustainability. In particular, dioxolanes have been identified as promising biofuel candidates. However, pyrolysis and oxidation of dioxolanes are not well understood. In this work, we measured the temperature-dependent absorption cross-section of 1,3-dioxolane (13DO) in the mid-IR region over 8.4 – 10.5 μm (950 –1190 cm⁻¹). We applied the spectroscopic knowledge to investigate the temperature and pressure dependence of the rate coefficients of the unimolecular decomposition of 13DO over the temperature range of 1000–1400 K and pressures near 0.7 and 2.4 bar. We employed a rapidly tuning MIRcat-QT™ laser in conjugation with a shock tube to carry out high-temperature spectroscopic and pyrolysis measurements. Measured IR spectra of 13DO exhibited a strong temperature dependence. For the kinetic study, we employed the vibrational feature of 13DO near 1120.5 cm⁻¹ to monitor the decay of 13DO quantitatively. The measured rate coefficients did not show any discernible pressure dependence. This indicates that the rate coefficients of the unimolecular decomposition of 13DO are close to the high-pressure limit under the present experimental conditions. In addition, we rationalized the temperature and pressure dependence of the reaction by employing electronic structure/RRKM-ME calculations. Our theoretical model accurately captured the experimental trends of the rate coefficients of the unimolecular decomposition of 13DO.