Defect and Diffusion Forum Vols. 312-315

Abstract: U-Mo has thus far proven to be one of the most feasible metallic fuel alloys for use in research and test reactors due to its high density and stability during irradiation. However, an adverse diffusional interaction can occur between the fuel alloy and the Al based matrix. This forms an interaction layer (IL) that has undesirable thermal properties and irradiation behavior leading to accelerated swelling and reduced fuel efficiency. This study focused on the effects of ternary alloying additions on the formation of IL between U based alloys and Al. Diffusion couples of U-8Mo-3Nb, U-7Mo-6Zr, and U-10Nb-4Zr (wt.%) vs. pure Al were assembled and annealed at 600°C for 10 hours. Both thickness and phase constituent analyses were performed via electron microscopy. The major phase constituent of the IL was determined to be the UAl3 intermetallic compound. The Nb and Zr alloying additions did not reduce growth rate of IL (1.3~1.4 m/sec1/2) as compared to couples made between binary U-Mo and Al (0.9~1.8 m/sec1/2).

Abstract: Liquid transportation through pipelines for very long distances is one of the most power consuming sectors in the industry. Synthetic polymers were used as flow improvers for many years to solve the power dissipation problem. These polymers are toxic and expensive. An environmentally friendly and more natural product that can replace the usage of polymers as flow improvers is needed. The present study focused on a new, cheap, natural and environmentally friendly flow improver that was extracted from the cocoa husk wastes. Mucilage was prepared from the cocoa husk waste and tested in aqueous media at concentrations between 100 ppm and 400 ppm using pipes with an internal diameter of 0.0125, 0.0254 and 0.0381 m and five different fluid velocities represented by the corresponding Reynolds Numbers (Re). It was found that the cocoa husk mucilage was an effective drag reducing agent. A maximum drag reduction percentage of 44% could be achieved by adding as little as 400 ppm of mucilage. Drag reduction was found to increase by increasing Reynolds Numbers, additive concentrations and pipe lengths. It also increased with decreasing pipe diameters.

Abstract: This work reports on research being carried out in the area of functional knitted fabrics with a special structure incorporating hydrophobic fibres near to the skin and suction channels of hydrophilic fibres to suck moisture from the skin on the hydrophilic layer away from the skin; in this way, comfort is maximised in active wear as the fabric does not feel wet near to the skin.

Abstract: Porous materials have gained wide use in high level engineering structures due to their high stiffness/weight ratio, good energy absorption properties, etc. Frequently, thermal behavior is also an issue of concern and optimized multifunctional thermo-mechanical responses are sought for. This paper presents the application of a hybrid two-stage method for achieving an optimized layout of periodic truss-like structures in order to obtain a good compromise between thermal and mechanical elastic properties. The first stage employs a derivative free optimization method, which explores the design space, not getting trapped by local minima. The second stage uses a derivative based optimization algorithm to perform a refinement of the solution obtained in the first stage.

Abstract: A two-phase model is proposed for describing the dynamics of a fluidized bed reactor used for polypropylene production. In the proposed model, the fluidized bed is divided into an emulsion phase and bubble phase where the bubble phase flow pattern is assumed to be plug flow and the emulsion phase is considered to be perfectly mixed. Similar previous models consider the reaction in the emulsion phase only. In this work the contribution of reaction in the bubble phase is considered and its effect on the overall polypropylene production is investigated. The kinetic model combined with hydrodynamic model in order to develop a comprehensive model for gas-phase propylene copolymerization reactor. Simulation profiles of the proposed model were compared with those of well mixed model for the emulsion phase temperature. The simulated temperature profile showed a lower rate of change compared to the previously reported models due to lower polymerization rate. Model simulation showed that about 13% of the produced polymer comes from the bubble phase and this considerable amount of polymerization in the bubbles should not be neglected in any modeling attempt.

Abstract: On the basis of advanced computer simulations a relationship between the structure and the phase behaviour of Li-intercalated titanates is established. The relationship is based on the charge transfer occurring upon intercalation and strong coupling between electronic and structural degree of freedom. Furthermore, a model inferring phase behaviour of lithiated titanates on consideration of the properties of the parent phase is proposed. As an example, the model is used here for screening of prospective morphologies that would exhibit considerable enhancement of Li-uptake on the nanoscale.

Abstract: DNA molecules can be transported through microchannels with help of electrophoresis and flow. Confinement of DNA molecules leads to elongation of their unconstrained equilibrium configuration when passing the microchannel. Application of electrical fields reduces the mobility and entails DNA trapping because of high gradients of the field due to a decrease in the channels’ magnitude. Microfluidic channels in polydimethylsiloxane (PDMS) were formed by soft replica molding technology combining micro- and nanofluidic features. The applicability of the hybrid micro- and nanofluidic PDMS structures for single molecule observation and manipulation was demonstrated by introducing single molecules of λ-DNA into the channels using optimized conditions for the applied potential and flow.

Abstract: Three studies on the oxidation behaviour of austenitic stainless steels were described in the present paper. (1) High temperature oxidation behaviour and its mechanism in austenitic stainless steels with high silicon: Sulfur contained as impurity in steel showed a harmful influence to the oxidation resistance of 19Cr-13Ni-3.5Si stainless steels. It was found that the abnormal oxidation was caused from the surroundings of MnS inclusions. (2) Effect of a small addition of yttrium on high temperature oxidation resistance of Si-containing austenitic stain less steels: The oxidation resistance of 19Cr-10Ni-1.5Si steels was improved remarkably even with only 0.01%Y addition, which is the same concentration as added for de-oxygenation. Y was enriched at the grain boundary of oxide scale and metal-oxide interface. It was suggested that Y-containing steels shoed good oxidation resistance, because the enriched Y at the grain boundary and metal-oxide interface prevented the diffusion of iron and oxygen ions through the oxide scale. (3) Effect of grain size on the oxidation behaviour of austenitic stainless steels: Type 304, 316 and 310 steels with finer grain size showed better oxidation resistance than those with coarser grain size at 850°C. The oxide scale of steels with coarser grain size easily spalled during the cooling process.

Abstract: The equilibrium concentration of vacancies in metals is invariably enhanced in the presence of interstitial hydrogen atoms – a phenomenon called superabundant vacancy (SAV) formation. It has been recognized that the SAV formation occurs in electrodeposition, as M-, H-atoms and M-atom vacancies are deposited by atom-by-atom process. Effects of SAV formation are described for electrodeposited Ni, Ni-Fe alloys, Fe-C alloys and Cu. Possible implication of SAV formation for corrosion in Al and steels is also briefly described.

Abstract: Recent models of grain-boundary diffusion are briefly reviewed. Models of diffusion along equilibrium boundaries of recrystallization origin in coarse-grained materials and along non-equilibrium boundaries in nanocrystalline materials obtained by gas condensation and compacting or by severe plastic deformation are considered separately.