Defect and Diffusion Forum Vols. 312-315

Abstract: In the paper the thermo-mechanical phenomena which occur in thermal shocked thermolabile porous ceramic material were described. Such materials are applied in foundry industry for mould making and they are characterized the low thermal stability losing its strength above 400°C. In [3] the usefulness of Hot Distortion Plus® to estimate the thermo-physical parameters (apparent thermal conductivity, heat capacity) was discussed. These parameters are necessary in data base of simulation codes which permit to simulate the phenomena in casting-mould system. The aim of these tests is to predict the mould material phenomena influence on castings quality. Parameters applied in these thermo-mechanical models (Young's modulus, Poisson's ratio, Yield stress) and their variations with temperature are not really known for thermal unstable mould material. There is no adapted method in literature and description of such total investigations of both parameters groups: thermo-physical and thermo-mechanical. The author's method called Hot Distortion Plus® consists in acquisition of temperature curves of heated sample of material and correlation with curves of their dilatation. Following the simulation using inverse solution method to reproduce the measured parameters with experiment was applied. The tests were carried out for the new quartz sand bonded by resin (approx. 1%). The specimens (dimensions 114 × 25 × 6mm) from binder-sand mixture were made using special core-box.

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: Co-doping of nanosilver, carbon and nitrogen is done on titania to get improved photodegradation of pollutants when compared to single doping. Anion doping extends the absorption of TiO2 to the visible region; whereas noble metal NP doping prevents the recombination of photoinduced electrons and holes. Doped TiO2 prepared using sol gel method allows efficient dispersion of nano silver and thus enhances the photodegradability. X-ray Diffraction analysis shows the efficient dispersion of incorporated nano silver over anatase TiO2. The visible light absorption is confirmed from UV-Vis Diffuse Reflectance spectral studies. Photocatalytic activity is investigated by the degradation of methyl orange as a model pollutant. Efficient degradation in visible light shows the synergetic effect of carbon and nitrogen doping as well as nano silver loading on the performance of TiO2.

Abstract: In this paper, we draw attention to the importance of the lateral convection heat transfer effect on the operation of thermoelements with variable cross-sectional area. The significance of lateral heat convection arises from a new application, in which thermoelements form the walls of a MEMS-based convergent-divergent micronozzle in order to pump heat from the divergent part of the micronozzle to the convergent part to enhance overall performance. To assess the effect of thermoelement, we develop a quasi-one-dimensional model for thermoelements, in which, the physical phenomena of Peltier effect, Joule heating, Seebeck effect, longitudinal heat conduction, and lateral heat convection are considered. The general energy equation of the thermoelement with variable material properties is formulated with heat convection modeled as a lateral heat source. We used the model to study thermoelements with rectangular cross section and uniform thickness, but variable width. The width of the element is maximum at the location forming the micronozzle throat. Several geometries have been investigated; a piece-wise linear, parabolic and piece-wise sine wave. Two parameters which play important role in the thermal performance of thermoelement are identified. These are the thermal resistance ratio; ratio of longitudinal conduction resistance to lateral convection resistance, and heating ratio; ratio of Joule heating to Fourier conducted heat. The effects of varying these two parameters as well as thermoelement geometry have been investigated thoroughly and the results are presented in the form of charts to assist the design and material selection of the thermoelement.

Abstract: Diffusion boride layer has been produced on the surface of a hot work tool steel. The microstructure and elemental spectra as well as depth profiles of the elements in the boride layer have been studied by scanning electron microscopy, X-ray diffraction analysis and energy dispersive X-ray spectrometry. Micro-hardness measurement was carried out using the Vickers micro-hardness test. The results showed that the boride layer is formed by boron compound Fe2B. Additionally, boron carbide B4C has been revealed embedded in the bulk of the boride layer.

Abstract: For mass transfer applications, CFD codes need the turbulent Schmidt number . The aim of our study is the analysis of some theoretical closure results and analytical formulations for . We will investigate different formulations of from the basic conservation equations for sediment-water mixtures in turbulent open-channel flows based on a two-fluid description and a kinetic model. The kinetic model for turbulent two-phase flows provides which depends on particle Stokes number. Our study show that the two approaches provide that depends on turbulent kinetic energy (TKE), eddy viscosity and particles settling velocity. For the analysis, accurate analytical formulations for TKE and eddy viscosity calibrated by DNS data are presented.

Abstract: We present an experimental study of the Ni+2/Ni(OH)2/NH3 reaction-diffusion system in a gel (agar). The system, which consists of a gel containing an inner electrolyte Ni+2 and a diffusing outer electrolyte (NH3/OH-), exhibits pulse propagation due to the concomitant precipitation reaction between Ni+2 and hydroxide ions and re-dissolution due to ammonia. During the propagation of the pulse, a transition to Liesegang banding is shown to take place. The bands are characterized by IR and XRD and are shown to consist of the polymorph -Ni(OH)2 whereas the pulse contains the other polymorph -Ni(OH)2. SEM measurements also reveal a morphological change accompanying the polymorphic transition between the pulse and the bands and uncovering an Ostwald ripening mechanism.

Abstract: In the field of the ANR-PROD’HYGE project an original coaxial architecture for a High Temperature Electrolyser (French Atomic Energy Commission Patented) is studied which makes use of low-cost spring-like interconnects to cope with thermal dilatation. Components and materials used for this application must ensure high long-term chemical and mechanical stability which are investigated here. Oxidation resistance of EN1.4509 and CroFer22APUI iron based alloy as well as Haynes 230 nickel based alloy is investigated with thermogravimetric analysis (TGA) in humid conditions, with or without mixing with hydrogen. Experiments reveal that oxidation kinetics is increased by 30% volume of hydrogen in moisture. Oxide layer composition and morphology are then investigated using Energy Dispersive Spectroscopy (EDS), and Auger Electron Spectroscopy (AES). Preliminary tensile tests are performed at room temperature showing embrittlement due to rough oxide layer, and CroFer22APU softening due to grain growth at elevated temperature.

Abstract: A glass wool media is commonly classified as a medium made up of many capillaries. They might, however, be considered analogous to a network of tubes as a bundle of capillaries. The capillary pressure of such a medium would be dependent on the amount of fluid held within the bundles. But, this very simple picture of porous media does not capture all the characteristics of this imbibition. We have determined capillaries radii by using Washburn and Laplace relations. Laplace radius can also be obtained by 3 approaches: using White’s relation and using Jurin’s law with visualized height and with weight. We have observed a single value of capillary radius cannot be used to determine the infiltration height as a function of time. This mechanism of capillary infiltration can be controlled by pores of more than one size and pores are interconnected.

Abstract: This paper aims to provide a better understanding of the gypsum hydric behavior used as coating during imbibition in liquid water. Firstly, we want to describe hydric transfer by determining sorptivity and hydraulic diffusivity of coating gypsum. Secondly, we evaluate the impact of the hemp fibers addition on hydric parameters. Experimentally, hydraulic diffusivity will be obtained by an overall measure of the moisture content (mc) in a defined sample volume, and the sorptivity describes capacity absorption. Through numerical simulation, hydraulic diffusivity will be determined by a local measure of the mc.