Defect and Diffusion Forum Vols. 297-301

Abstract: Volume-fraction weighted and Reynolds averaged momentum transport equations are solved in an Euler/Euler approach to simulate numerically the turbulent, dispersed two- phase °ow in a two-dimensional channel and a three-dimensional conic di®user °ow. Particular attention is given to the modelling of turbulent di®usion and particle wall interaction, assuming local equilibrium but introducing individual terms for particle/°uid drag interaction, particle collisions and trajectory crossings. These in°uences have been quanti¯ed in terms of partial viscosities, a restitution power and a turbulence structure parameter. Boussinesq approxima- tions have been used for each phase and their interaction, whose formulation was provided in the framework of the eddy-viscosity modelling concept.

Abstract: It is a common point for the current fuel cell research to correlate the composition of the feedstream to the output of a Solid Oxide Fuel Cell (SOFC). In this direction, the detailed steady-state transport processes (i.e. the flow regime, the heat transfer, the mass and the charge transport) are mathematically described here. A new mesoscopic mathematical model has been developed through the relative differential equations along with the appropriate boundary conditions, which have been numerically integrated by using the commercially available software CFD-ACE+, in order to calculate the electricity produced by the fuel cell. It is found that the produced current density increases with CH4 percentage in the feeding mixture.

Abstract: In this paper, two different technologies for preparation of the composite are presented: vacuum diffusion bonding and gas pressure infiltration. Samples contained different volume fractions of tungsten fibres (10%, 50% and 78%) that were arranged in unidirectional, cross-ply and circular architecture. The coefficient of thermal expansion (CTE) of Cu/W MMC samples was measured in the longitudinal and transverse direction to the fibre orientation and it strongly depended on arrangement of reinforcing phase and direction of measurement. For the unidirectional material the CTE was 4 - 6 ppm.K-1 and 11-12 ppm.K-1 in directions parallel and transverse to the fibre orientation, respectively. Samples in a shape of a ring contained reinforcement that was wounded around the sample centre (circumferential winding) or was cut-out from the Cu/W MMC plate. In the second case, the reinforced fibres had the woven arrangement. The CTE of ring measured in radial direction showed values from 5 ppm.K-1 to 20 ppm.K-1 for composites containing 72 and 10 vol. % of W-fibres, respectively.

Abstract: High resolution X-ray photoelectron spectroscopy (XPS) is used to investigate the spectra of nanolayered films. Amorphous gallium oxide (Ga2O3)-silicon dioxide (SiO2) nanolayered thin films are grown using ultrahigh vacuum radio frequency (rf) magnetron sputtering on sapphire substrates at room temperature. Films are layered with 15-angstrom Ga2O3 oxide and 75-angstrom SiO2 for a total of 10 layers. Referring to atomic core levels, atomic contribution to valence band density of states is experimentally nominated. This analytical technique has particular applicability to the evaluation of the density of states with atomic contributions.

Abstract: The relation of the microstructure and hydrogenation property of a hypoeutectic Mg-6.7 mol%Ni alloy consisted of primary Mg crystal and Mg2Ni phase has been investigated. In the case that the specimen has a very fine structure, hydrogen is hardly absorbed into the specimen. The growth of both the primary Mg crystal and Mg2Ni phase allow easy hydrogen penetration, but the growth of the primary Mg crystal is more effective. The highest hydrogenation rate and absorption amount of 5 mass% are obtained when the Mg2Ni phase has a rounded shape.

Abstract: Cr in Fe-Cr alloys often forms some different phase of oxides during annealing at high temperatures. The phases of Cr oxides are determined depending on the annealing condition such as temperature and oxygen partial pressure. In this study, depth-resolved X-ray fluorescence analysis (XRF) of Fe and Cr were carried out using a two-dimensional pixel array detector with geometrical arrangement of the grazing exit in detection of fluorescence X-ray emitted from the sample surface, in order to characterize the depth-directional distribution of the elements in the surface layers of Fe-Cr alloys annealed under low oxygen partial pressure. In addition, depth-resolved X-ray absorption spectra will also be able to be obtained by measuring the incident X-ray energetic dependencies of the fluorescence intensity. These techniques facilitate non-destructive measurement of the elemental distribution and the phase of metal or oxides in depth direction. The experiments were performed at the BL01B1 of SPring-8 synchrotron radiation facility. The results showed that Cr was enriched and covered on the surface of the alloys during annealing and formed as Cr2O3 or FeCr2O4. The phase and thickness of formed oxides depended on the alloy composition and the annealing conditions.

Abstract: Alloying elements added to steel for improving surface properties such as corrosion resistance are often enriched to the surface of the alloys during annealing at high temperatures. Their behavior depends on difference in their chemical characters and the condition of annealing. In this study, nondestructive depth-resolved analysis of amount distribution and chemical state of alloying element by using X-ray fluorescence analysis (XRF) technique in combination with X-ray absorption spectroscopy (XAS) in order to characterize the enrichment and oxidation of manganese on the surface layers of an Fe-Mn alloy annealed under low oxygen partial pressure. The experiments were carried out using a two-dimensional detector with geometrical arrangement of grazing exit in detection of fluorescence X-ray emitted from sample surface. The results showed that manganese was enriched to surface layers of the Fe-Mn alloys during annealing at high temperatures and formed as manganese oxide. The preferential oxidation of manganese by annealing under low oxygen partial pressure is considered the driving force for their enrichment on the alloy surface.

Abstract: The glass molding process provides great potential for mass production of precise glass optical components at low cost. The key issue for achieving a low production cost is to extend the service life of the expensive mold inserts. The precious metal based alloy is one of the coating materials for the molds which provides excellent glass anti-sticking results. However, the inter-diffusion between the WC/Co mold materials and precious metal coatings will deteriorate the coatings which needs to be resolved. It is essentially to deposit an interlayer as the diffusion barrier to improve the inter-diffusion problem. A thin layer of TaN was deposited on the WC/Co substrate as the diffusion barrier using a magnetron sputtering system, and followed by the deposition of Pt-Ir layer as the protective layer. Low Tg Glass gobs (L-BAL 42) were placed on the coated substrate to investigate inter-diffusion between the substrate and coating at high temperature. The surface interaction between the glass gobs and protective coatings was also examined. The obtained TaN and Pt-Ir multilayer had a dense nano-crystalline structure. High temperature wetting tests showed that the TaN film could effectively resist the cobalt and tungsten diffusion into the precious metal protective layer and, as a result, minimized the possibility of oxidation and interaction between glass and protective coating. The coated substrates retained a good surface finish and the glass gobs stayed fully transparent after 6 hours reaction test at 700°C.

Abstract: There are growing varieties of glasses available on the market for the manufacture of molded optical lenses. A glass with a low transition temperature (Tg) has the advantage of extending the service life of molding dies. However, most of the low Tg glasses have a high content of alkali metal oxides and tend to induce severe glass sticking problems. This has made the molding process of these kinds of glasses very difficult indeed. The low Tg glasses normally demonstrate poor chemical durability and scratch resistance. As a result, the yields of fabricating the glass-preforms are frequently rather low. This research tried depositing a very thin layer of aluminum oxide on various glass-preforms by a water based sol-gel process. A high temperature glass wetting experiment was carried out to investigate the high temperature interfacial reaction between the coated glass gobs and stainless steel substrate. It was found that when the uncoated glass-preforms were brought into contact with stainless steel, the contact angle decreased with increasing heating temperature and duration. Owing to the severe interfacial chemical reaction, the originally transparent glass gradually turned translucent. In the case of Al2O3 coated glass-preforms, the variation of the contact angles was very limited, which presented no sticking and no wetting behavior. No reaction products could be detected on the contact area after the wetting test. The optical transmission of those lenses molded from the coated glass-preforms exhibited no or very little changes after the molding process.

Abstract: Diffusion and partition coefficients are two key parameters of importance for the characterization of building materials as sources and sinks of air pollutants indoors. The number of coefficients for each pair ‘chemical compound – material surface’ available in the literature are still scarce and with a high discrepancy in the results obtained by different methods, even for the same method [1]. The objectives of this study were (1) to develop a simple and rapid experimental method for directly measuring the diffusion coefficient (D), and (2) to perform determinations with both the new and the cup method comparing the results obtained. The new method is based on two existent methodologies, the passive sampling on Tenax TA and the dry cup method, proposed by Haghighat et al. [1] and also developed by this research team [2]. The experiments were carried for three different building materials (cork based material, gypsum board and PVC) and three different compounds (cyclohexane, n-octane and m-xylene). The discussion of the results obtained for D by the two methods is presented in this paper. Observed differences were not of the same order of magnitude for the pairs compound/material studied, varying from the order of 101 in the case of PVC to 102 in the gypsum and in the cork. However some facts were the same: the gypsum board presents the higher values of D and PVC the lower values of D for the three compounds studied in both methods. One of the causes of these marked differences could be high difference of the concentration of the compound in the air between the methods, saturation value in cup method (dozens g/m3) and low values typical from indoor environments (few mg/m3) in the proposed method.