Phase-Field simulation of phase decomposition in Fe−Cr−Co alloy under an external magnetic field

Phase decomposition during isothermal aging of a Fe−Cr−Co ternary alloy under an external magnetic field is simulated based on the phase-field method. In this simulation, since the Gibbs energy available from the thermodynamic CALPHAD database of the equilibrium phase diagram is employed as a chemical free energy, the present calculation provides the quantitative microstructure changes directly linked to the phase diagram. The simulated microstructure evolution demonstrates that the lamella like microstructure elongated along the external magnetic field is evolved with the progress of aging. The morphological and temporal developments of the simulated microstructures are in good agreement with experimental results that have been obtained for this alloy system.     

Unsteady-State Absorption of Co 2 Into W/O Type Emulsion with Aqueous Amine Liquid Droplets

Unsteady-state absorption of CO 2 into W/O type emulsion was studied by both experimental measurements and prediction from mathematical modeling. Absorption experiments were carried out using a stirred vessel with a flat gas-liquid interface under 0.101 MPa and 25°C. Continuous phase was benzene, which has larger solubility than water. Dispersed phase was an aqueous solution of MEA, DEA, TEA, and AMP. The effects of reactant concentration, size of aqueous droplets, volume fraction of continuous phase, and stirring speed on the absorption rate of CO 2 were investigated. In the mathematical model, the mechanism of CO 2 absorption into the continuous phase through a gas-liquid interface was described on the basis of the penetration model, while the subsequent absorption/reaction in dispersed droplets was modeled on the basis of the film model.     

Transport phenomena in gas permeation through glassy polymer membranes with concentration-dependent sorption and diffusion parameters

The modified dual-mode mobility model for permeation of a gas in glassy polymer membranes was combined with the extended dual-mode sorption model to take account of the plasticization effect of sorbed gas molecules on both sorption and diffusion processes. The combined model was further simplified by the introduction of a concentration of the mobile gas species. However, the observed pressure dependence of mean permeability coefficients of carbon dioxide in methylmethacrylate-n-butyl acrylate copolymer and polymethylmethacrylate films at 30°c and also that of oxygen in a polycarbonate film at 50°C and 60°C showed that a plasticization action of sorbed gas species has an influence on the diffusion process rather than on the sorption process, that is, were simulated by the modified dual-mode mobility model combined with the conventional dual-mode sorption model.     

Dyeing of Nylon Fabrics with an Acid Dye in a Rotating-disc Contactor

The kinetics of dyeing a nylon fabric with an acid dye (C. I. Acid Blue 182) were investigated using a rotating-disc contactor, and were analysed in terms of intrapolymer diffusion with trimodal (one Nernst-type and two Langmuir-types) adsorption. The resistance of mass transfer from liquor to film in film dyeing was found to be negligible relative to resistance inside the film. The effective interfilament diffusion coefficient in the fabric was found to be dependent on the rotational speed of the disc. It appears that the process of dyeing nylon fabric with an acid dye might be governed by interfilament diffusion of dye in the fabric rather than mass transfer from liquor to fabric and intrafilament diffusion.     

CHARACTERISTICS OF MICROMETER AND SUBMICROMETER SIZE O/W EMULSIONS PRODUCED BY RAMOND SUPERMIXER®

A novel motionless mixer named the Ramond Supermixer® (RSM®) was employed to produce O/W emulsions composed of micrometer and submicrometer-size droplets. Liquid paraffin as dispersed phase, aqueous sucrose solution as continuous phase, and anionic sodium dodecyl sulfate as emulsifying agent were used as the model emulsification system. Pressure drop, droplet size distribution, Sauter mean diameter (d₃₂), and geometric standard deviation of the droplet size distribution (σ_g) were investigated under the various combinations of process variables; superficial liquid velocity, number of mixing units, number of passages through RSM®, dispersed phase viscosity (η_d), continuous phase viscosity (η_c), and dispersed phase volume fraction. Different modes of droplet size variations with process variables were obtained, with respect to micrometer- and submicrometer-size ranges, and theoretical explanations are forwarded. For the micrometer-size range, maximum droplet diameter (d_max) was proportional to d₃₂. For the submicrometer-size range, d_max varied with d₃₂ in the range of 1.53-2.19-fold, and a correlation is proposed with K (=η_d/η_c); d₃₂ and σ_g were well correlated with the process variables. Furthermore, a semi-empirical mechanistic model was developed for the formation of droplets obtained under inertial sub-range to interpret the effect of process variables.     

Dyeing Kinetics of an Acid Dye in a Nylon Film

The dyeing kinetics of an acid dye (C. I. Acid Blue 182) in a nylon 6 substrate was investigated using partition–cell and film–roil methods. The concentration dependence of the diffusion coefficient of acid dye in the nylon film was derived from both methods and compared with a prediction based on diffusion together with adsorption equilibrium established instantaneously between mobile and immobilised dye molecules in pores. These two sets of experimental results were found to be incompatible with each other. It was deduced that two kinds of region exist in the nylon, one being a region available for rapid penetration and the other, connected to it and formed by slow relaxation, a region of poor penetration.     

Spark-Plasma-Sintering Condition Optimization for Producing Transparent MgAl2O4 Spinel Polycrystal

By controlling the heating rate at <10°C/min during spark-plasma-sintering (SPS) processing, transparent polycrystalline spinel with an in-line transmission of 50% and 70% in the visible- and infrared-wavelengths, respectively, can be successfully fabricated for only a 20-min soak at 1300°C. The high transmission can be attained by reducing the residual porosity and pore size, which was achieved by the low-heating rate. At high heating rates, many closed pores are formed due to the high densification rate during the heating process and remain as large pores around grain junctions. At temperatures >1300°C, the coalescence of the residual pores and the precipitation of second phases, which are caused by rapid grain growth, degrade the transparency. The present study demonstrates that although the high heating rates have been regarded as a primary advantage for the SPS processing, the low heating rate is highly effective in attaining a high transparency in the spinel even at low temperatures and for short sintering times.     

Solute atmosphere around an edge dislocation in Al-based ternary alloys

We evaluated the solute atmosphere around a moving dislocation and the dragging stress due to the atmosphere in binary and ternary Al-based alloys in terms of a chemical potential gradient by modifying the method proposed by Yoshinaga et al. In ternary alloys, we analyzed formation of the complex solute atmosphere around a straight edge dislocation and the dragging stress in terms of a misfit parameter of a solute element (positive or negative) and an interaction parameter between solute elements (attractive or repulsive).     

LIQUID-PHASE PHOTOCATALYTIC REACTION ON TiO22 THIN FILM

The photocatalytic decomposition process on TiO₂ thin films, was modeled by taking the decay of illumination intensity via Lambert-Beer law into account. For the sake of experimental verification of the proposed model, Ti02 thin films were prepared on a glass substrate by a dip-coating method combined with a sol-gel process and the photocatalyuc activity of the thin films was evaluated by the decomposition of 2-propanol (IPA) in an aqueous solution under illumination of UV light source. The film thickness up to 1.4 μm increased with the withdrawal speed raised to the power 0.6 and was proportional to the number of application (i.e., repetition of dip-coating process). The TiO₂ gel films prepared by a dip-coating technique, were subject to firing at 500°C. The photocatalytic decomposition rate could be expressed apparently as first-order with respect to IPA concentration. The observed relationship between apparent first-order rate constant of decomposition and the film thickness could satisfactorily be explained by the proposed model.     

Hydrogen-induced phase transformation

Hydrogen-induced amorphization (HIA) of intermetallic compounds was simulated by the molecular dynamics (MD) method using pairwise potentials. The microscopic mechanism of HIA in AB₂ C15 Laves phase compound is discussed. The hydrogenation causes elastic softening in the bulk modulus and induces elastic instability. A phase transformation by elastic instability follows paths with minimal activation barriers, and nonequilibrium transformations including amorphization can be realized. The HIA can be considered as a case. The key to induce HIA is the expansion of the B atoms in a Laves phase; it facilitates the instability of the sublattice of B atoms. If the amount of hydrogen exceeds a critical value, HIA occurs. The HIA is a potential-driven phase transformation, and the resultant amorphous structure is potentially favored over the hydrogenated crystal. We also report the fracture process by isotropic loading and compare it to HIA.