Papers by Keyword: Diffusion Constant

Abstract: Our research group is currently investigating a new kind of thermal desorption experiment (TDE), which uses a hydrogen isotope by loading-unloading process yielding transport parameters. Safety issues are limiting the hydrogen loading content to 3 % at 10⁵ Pa, while former experiments are using pure hydrogen for the loading process at nearly same pressure e. g. [1]. Especially the thermal elongation coefficient (TDE operating conditions 300° to 500 °C compatibility to stainless steel) forces to think about an alternative material of boron silicate glass for specimen containment, in this paper copper will be discussed. The analysis of TDE concerns the amount of hydrogen stored in the specimen, stored in the time variable gas phase as well as stored in the containment material. These three phases are coupled by phase equilibrium. The here developed analysis procedure can currently only be performed numerically for a two dimensional geometry. However a two dimensional analytical solution regarding the same boundary condition is currently under investigation. One part of the solution results of this problem can be compared to an additional analytical solution with simpler boundary conditions, e.g. a vanishing hydrogen amount inside the specimen containment observed in steady state. The numerical results will be used to check the suitability of several experimental scenarios, for example the usability of a copper based specimen containment. The approach currently practiced in many experiments is to simply subtract the zero rate of hydrogen without considering the phase equilibrium between the three mentioned phases. The main goal of this analysis procedure consists in the solution of the inverse problem, namely the extraction of the transport parameters like Sieverts ́-and diffusion-constant from a measured time dependent desorption pressure increase.

Abstract: Currently available diffusion constant and Sieverts constant experimental results are based on time dependent permeation experiments. The common principle is an analysis which is expecting that the permeating hydrogen is “transported” from the retentate chamber to the permeate chamber through the connecting membrane, with a vanishing hydrogen partial pressure on the permeate side. But reality shows a different behaviour caused by the fact that a nonzero hydrogen partial pressure in the permeate chamber is necessary for detection purposes. This nonzero pressure is mostly not considered by analysis. This issue is solved (approximatively) numerically by the procedure as described in this paper. This work is rooted in the field of fusion research, where so called purge gas with low partial pressure of tritium is contacting the structural materials (300-550°C) of the fusion reactor (blanket) and of process equipment, where the tritium losses are of interest. The developed algorithms are intended for the evaluation of an experiment termed “Q-PETE” (Q for any hydrogen isotope, PEermeation Transport Experiment), which abstracts the hydrogen transport conditions of the fusion blanket, and where the effect of nonzero hydrogen concentration on the permeate side is relevant. The algorithms are useful for all experiments, where the ratio of hydrogen pressures between retentate and peremeate side are far from infinite.

Abstract: We investigate the carrier lifetimes in very thick 4H-SiC epilayers (~250 μm) by means of time-resolved photoluminescence and microwave photoconductive decay. Both the minority carrier lifetime and the high injection lifetime are found to reach 18.5 μs by applying the carbon implantation/annealing method to the as-grown epilayers. We also study the epilayer thickness dependence of the carrier lifetime by successive experiments involving lifetime measurement and polishing. Based on the relationships between epilayer thickness and carrier lifetime, the bulk carrier lifetime and the hole diffusion constant are discussed.

Abstract: In this paper, the diffusion quantity of different temperatures and unit time have been investigated basing on experimental results and theoretical analysis. The diffusing parameters of molten tin in the reaction process is investigated according to diffusing formula. The results within the range of 260～350°C indicates that the diffusing activation energy is increased with the time until the reaction ceases and it is decreased with the increasing of the temperature and substrate vacancy, but the average diffusing constant of tin increased with the temperature.