Papers by Keyword: Concentration Profile

Abstract: Diffusion couple technique is an efficient tool for the estimating the chemical diffusion coefficients. Typical experimental uncertainties of the composition profile measurements complicate a correct determination of the interdiffusion coefficients via the standard Boltzmann-Matano, Sauer-Freise or the den Broeder methods, especially for systems with a strong compositional dependence of the interdiffusion coefficient. A new approach for reliable fitting of the experimental profiles with an improved behavior at both ends of the diffusion couple is proposed and tested against the experimental data on chemical diffusion in the system Fe-Ga. An extension of the approach for reliable description of the up-hill diffusion phenomenon in multicomponent systems is presented.

Abstract: An analytical approach to the determination of a varying salt diffusion coefficient is discussed. It is argued that the approach is fast and reliable and can be very convenient in various civil engineering applications dealing with the transport of salts in porous building materials. The advection-diffusion model of Bear and Bachmat is used to describe the salt transport, and the Bolztmann-Matano inverse analysis is applied to calculate the salt diffusion coefficient. Possible extensions to other models of transport are pointed out. The results are applied to a sandstone from the Msene quarry, Czech Republic.

Abstract: A new generation of gun propellant, named Modified Single Base Propellant (MSBP), was successfully studied recently. The MSBP was prepared from single base propellant grain by impregnation with blasting oil, followed by deterring with deterrent in water medium. The function components in this propellant were nitroglycerine (NG) and polymer ester (NA). The concentration profiles of them were studied by Fourier Transform Infrared (FTIR) Microspectroscopy. The combustion performance of this propellant was investigated by means of closed-bomb tests and interior ballistic tests. It is found that the concentration profile of the function component is the key factor in MSBP. The static combustion performance and the characteristic of the interior ballistic are dependent on the concentration profile of function component.

Abstract: In order to study evolution of the concentration profiles and markers velocities in various time and space scales quasi-one-dimensional model of interdiffusion in a polycrystalline alloy is proposed considering non-equilibrium vacancies and the Kirkendall effect. Sinks/sources of vacancies are assumed to be concentrated mainly at the moving grain boundaries. This model simultaneously takes into account the movement of grains and changes of grain sizes.

Abstract: A new method for studying multilayer structure using angle resolved XAFS measurements is proposed. The integral equation describing the relation between the fluorescence intensity for selective spectrum, the incident beam energy, the incident angle and a selective concentration profile, depth-dependent EXAFS has been derived. This integral Fredholm equation of the first kind belongs to the class of ill-posed problems and for the solution it needs special methods. We use the regularization Tikhonov method. The effectiveness of the proposed method was tested using the numerical simulations for trilayer system Cr-Fe-Cr. Some first experimental results for the thin films of pure Cr are also presented.

Abstract: The present work describes the mass transfer process between a moving fluid and a slightly soluble flat surface buried in a packed bed of small inert particles with uniform voidage, by both advection and diffusion. Numerical solutions of the differential equation describing solute mass conservation were undertaken to obtain the concentration profiles, for each concentration level, the width and downstream length of the corresponding contour surface and the mass transfer flux was integrated to give the Sherwood number as a function of Peclet number. A mathematical expression that relates the dependence with the Peclet number is proposed to describe the approximate size of the diffusion wake downstream of the reactive solid mass.

Abstract: The electrostatic precipitator (ESP) is usually employed by industries for the removal of aerosol particles from gaseous streams. The behavior of the particles inside the collection duct is of great interest as a tool for optimizing precipitator design and performance. In this work, a laboratory scale ESP (0.6m long, 0.3m high and 0.2m wide) was tested with electric fields of 250, 350 and 450 kV/m at a gas velocity of 1.0 m/s. The discharge electrode was located at 0.30 m from the beginning of the collector plate. The test aerosol was constituted of a phosphatic concentrate dispersed in air. Particles were sampled isokinetically in situ in the duct, at five different longitudinal positions. The experimental results for the aerosol studied show that concentration profile of particles are affected by the electrical field at considerable upstream distances from the charging electrode. The particle collection starts well before the charging electrode, characterizing a strong entrance effect, often disregarded in the existing correlations for predicting ESP performance.

Abstract: Initiated by the need of industry for gas carburizing process control and optimization, this paper focuses on understanding the effect of the time, temperature and carbon potential on the mass transfer coefficient and carbon diffusivity in Austenite. A method for direct flux integration has previously been proposed to calculate these kinetic parameters from the experimental carbon concentration profiles. AISI 8620 steel discs were gas carburized at different levels of atmosphere carburizing potential for selected austenizing temperatures. Analyses of the carburized parts included experimental measurement of weight gain, surface carbon concentration and carbon concentration profiles. The time-dependent weight gain and surface carbon content measurements allowed calculation of the time average mass transfer coefficient, while carbon concentration profiles were used to calculate the concentration dependent carbon diffusivity for selected process parameters. Excellent agreement was found between the calculated mass transfer coefficient and carbon diffusivity values and those reported in the literature. The calculated values served as input in the previously developed carburizing model validating the predicted results by comparison with the experimental concentration profiles.