Papers by Keyword: Diffusivity

Abstract: The carbon diffusion in steel, where the carbon diffusivity varies with the carbon content, was solved with the integral methods under the third boundary condition. The variation of carbon diffusivity in steel with the carbon content was described with two different functions, linear dependence and exponential dependence. The integral approximation for both cases was improved with the numerical computation to more accurately predict the carbon profiles. The integral solution is more accurate than the formulation based on the assumption of a constant diffusivity or those based on the assumption of a constant diffusivity and/or constant carbon content at part surface. It is also more easily used in practice than the numerical method to describe the carburising process and predict the carbon content at steel surface and carbon profiles in treated layer.

Abstract: The regenerative medicine uses gel and porous solid matrices as scaffolds for the growth of the stem cells in 3D structures. The structural and fluid dynamic properties of the matrices have been recognized to highly affect the behaviour and functions of the cells. The procedures of production and the clinical use of the matrices need a reliable and reproducible characterization of their properties, this means that the concepts of metrology must be applied to the measurement and definition of all the relevant properties. This paper deals with the calculation of uncertainty for diffusivity measurement in solids and the role of uncertainty in designing the measurement. Diffusion of a solute in spherical solid particles dispersed in a limited liquid volume where considered as measurement method for a Ca-alginate polymer. The model sensitivity to the concentration measurements, the model parameters and the fitting procedures have been discussed.

Abstract: To understand the structure of SiC–oxide interface more in detail, we propose a profiling theory of Si and C emission into SiC layer during oxidation. Simulations of the depth profiles of Si and C interstitials results in the structures analogous with those observed from a spectroscopic ellipsometry. To determine the diffusivities of Si and C interstitials, we performed capacitance–voltage measurements for examining the re-distribution profiles of nitrogen after oxidation and compared between observed and calculated profile. The calculated nitrogen profiles showed good fits to the observed ones in the case of self-diffusivity of C interstitials magnified by several 10 times for literature value. Finally, we discuss the validity of the proposed theory.

Abstract: A universal transit heat transport equation was represented and all parameters for applying such a formula to drying of Radiata pine were modeled, incorporating reasonable physical conditions. In previous empirical models, the influence of drying temperature on the conviction heat transfer was ignored, though it is parentally not negligible. In this study, a multivariate regression model was developed from previous experimental data, in which both air velocity and drying temperature were taken into consideration. In addition, the models of heat diffusion properties in axial, tangential and radial directions were presented in which drying conditions and wood properties were taken into account. With those models, scenario computer simulation may be conducted to explore the drying phenomena of Radiata pine board.

Abstract: The measurements of stress induced dichroism on oxygen absorption band near 1107 cm-1 in Si1-xGex compounds and subsequent kinetics of the dichroism recovery upon isothermal annealing have been carried out. It has been found that the magnitude of introduced by uniaxial stress dichroism decreases with increasing Ge content. Two components in the dichroism annealing kinetics have been found. On the basis of studying absorption spectra of samples under investigations it was assumed that two components in relaxation correspond to the diffusion of oxygen being in a different nearest environment: the one component corresponds to oxygen surrounded by silicon atoms and the second one to the oxygen the neighbour of which is Ge atom. Diffusivity for each of the components has been determined. It has been shown that the diffusivity of oxygen that is in both of these configurations decreases with increasing Ge content.

Abstract: Hydrogen diffusivity was estimated in three different eutectoid rail steels (C-Mn, Cu-Mo and Ni-Cu-Cr) at ambient temperatures using the technique of sub-surface microhardness profiling after cathodic hydrogen charging in 0.5mol/l sulphuric acid at a current density of 0.1A/cm2 for 24 hours. The increase in the concentration of hydrogen at a certain depth below the surface was related to the microhardness increase at this location as compared to the bulk value. The procedure used to obtain the diffusion coefficient of hydrogen from the microhardness profiles is discussed. The hydrogen diffusivity values in all of the rail steels were found to be similar (of the order of 10-13m2/sec). The estimated hydrogen diffusivity in the rail steel was lower than in pure iron (10-8m2/sec). Possible reasons for the difference are discussed.

Abstract: Contamination control has become a high-centered issue for the fabrication yield, performance and reliability of leading-edge ULSI devices. With the progress of sizing down dimensions in higher-density devices, complicated device structures and various novel electronic materials have been introduced, particularly in the latest devices such as CMOS and nonvolatile memory LSIs (Table I). On the other hand, high productivity is a necessity when you consider QTAT (quick turnaround time) and cost-effective flexible ULSI manufacturing lines. Therefore, effective contamination control coupled with adequate protocol has become essential in such production lines. The point of the protocol is minimization of damage caused by impurity metals diffused from these novel electronic materials [1-5].

Abstract: Fractography was used in order to investigate the effects of Ta addition on the diffusion behavior of carbon in molybdenum. Mo-1.5mass%Ta alloy was carburized by the solid-state carburization process at a temperature between 1073 and 1473 K. Fracture surface of the specimen was observed before and after the carburization process and carbon diffusion distance was estimated from the change in fracture mode as a function of distance from the specimen surface. Results are as follows. (1) Ta addition slightly decreased the carbon diffusion distance. (2) Ta addition had almost no effect on the activation energy for diffusion. (3) These results suggest preferential combination between carbon atoms and Ta atoms is only minor.