Surface segregation of Pd–Cu alloy in various gas atmospheres

Pd–Cu alloys have been investigated as promising candidates for hydrogen separation membranes. Surface segregation influences the long-term performance of these membranes since their catalytic effect is mainly controlled by the surface composition. In the present research, surface segregation of Pd-40 at.% Cu alloy in vacuum and various gas atmospheres (H₂, CO and CO₂) was investigated with both XPS and LEISS probing different depths below the surface. Adsorption of H₂ and CO on the surface has a significant impact and the surface segregation trend can be reversed as compared to segregation in vacuum, however, CO₂ has almost no influence on the segregation behaviour. A thermodynamic model is also presented to explain these phenomena and to understand surface segregation behaviour of binary alloys in various gas atmospheres. The results can be considered as basic guidelines to design novel alloys for hydrogen separation membranes and predict their long-term performance under actual working conditions.     

硼向奥氏晶界的扩散机制

通过解变温扩散方程 ,导出了硼在非平衡晶界偏聚的理论公式 ,建立了晶界贫硼区宽度与淬火加热温度、冷却速度以及非平衡晶界偏聚扩散激活能与扩散常数之间的关系 ,理论预言与实验结果能较好地吻合 .     

Segregation and intermixing in polydisperse liquid–solid fluidized beds: A multifluid model validation study

Multifluid model (MFM) simulations have been carried out on liquid–solid fluidized beds (LSFB) consisting of binary and higher-order polydisperse particle mixtures. The role of particle–particle interactions was found to be as crucial as the drag force under laminar and homogenous LSFB flow regimes. The commonly used particle–particle closure models are designed for turbulent and heterogeneous gas–solid flow regimes and thus exhibit limited to no success when implemented for LSFB operating under laminar and homogenous conditions. A need is perceived to carry out direct numerical simulations of liquid–solid flows and extract data from them to develop rational closure terms to account for the physics of LSFB. Finally, a recommendation flow regime map signifying the performance of the MFM has been proposed. This map will act as a potential guideline to identify whether or not the bed expansion characteristics of a given polydisperse LSFB can be correctly simulated using MFM closures tested.     

Investigations on air induced segregation of pharmaceutical powders and effect of material flow functions

For the pharmaceutical industry, powder segregation can occur in many processes such as blending and compression solid dose unit operations. Yet it is important that the high quality standards of drug product manufacture are maintained throughout the whole processes. Powder segregation has been identified by the pharmaceutical industry as a potential issue, and in some cases it may cause variability in tablet assay and uniformity throughout a compression run. Early studies suggested for certain Direct Compression (DC) products, the separation of Active Pharmaceutical Ingredient (API) from excipients could arise due to air-induced segregation of the powders discharging from an Intermediate Bulk Container (IBC) to the tablet press via a vertical chute.Segregation tests were carried out on trial powder blend materials supplied by GlaxoSmithKline (GSK), using a laboratory-scale air elutriation test facility at The Wolfson Centre. Particle size analysis of the virgin and segregated sub-samples clearly indicated that powder segregation occurred as a result of aerodynamic effects. Subsequent chemical assay results concurred with the particle size results. Flowability testing of the powder blends indicated them to be free-flowing materials; this in addition to the presence of large particle size differentials within the powder blends is the likely cause of the susceptibility to air-induced segregation.     

Development of novel surface modified phase inversion membranes having hydrophobic surface-modifying macromolecule (nSMM) for vacuum membrane distillation

Eleven PES membranes, into which newly synthesized surface-modifying macromolecule (nSMM) was incorporated, were prepared by using the ‘phase inversion technique’ with different preparation conditions to find the effects of membrane casting parameters on the characteristics and performances of the surface modified PES membranes. The membranes so prepared were characterized by solute separation data from ultrafiltration experiments. The results showed that the mean pore size as well as the surface hydrophobicity increased with an increase in evaporation time for the casting solution blended with nSMM (without PVP). When PVP was added into the casting solution, the mean pore size as well as the contact angle decreased while the pure water permeation flux increased. The surface hydrophobicity decreased with an increase in gelation bath temperature.Four membranes were further prepared and subjected to vacuum membrane distillation (VMD). They were characterized by different analytical instruments and pure water permeation test before being used to VMD. The results showed that a distinctive surface layer was formed in nSMM blended PES membranes. It was also found that nSMM blended PES membranes were sufficiently hydrophobic and porous to be used for the separation of an ethanol/water mixture.     

Catalytic performance and characterization of Pt-Ni bimetallic catalysts for oxidative steam reforming of methane

Effects of methane oxygen mixture addition to steam reforming of methane and subsequent removal of the methane oxygen mixture from the oxidative steam reforming of methane on catalytic performance were investigated using monometallic Ni and Pt catalysts and two Pt-Ni bimetallic catalysts. Hysteresis with respect to the addition and removal of the methane oxygen mixture was observed clearly on a Pt-Ni bimetallic catalyst prepared by co-impregnation method and the Ni catalyst. In contrast, no hysteresis was observed for a Pt-Ni catalyst that was prepared by sequential impregnation method. Combined with characterization results obtained using EXAFS analysis and FTIR of CO adsorption, Pt-Ni catalyst was prepared by sequential impregnation is formed Pt-Ni alloy particles, where Pt atoms are segregated on the surface, enhances the reducibility of Ni drastically and this is related to the behavior without hysteresis.     

Soft-and hard-segment phase segregation of polyester-based polyurethane

Polyester based polyurethanes were synthesized from 4,4′-methylene bis(phenyl isocyanate) (MDI) with butanediol as a chain extender and low molecular weight polyester-diol as a soft segment. Three polyesters were used in the synthesis of polyurethanes. Two of the polyesters, with molecular weight M_n = 2,660 and 2,155, were synthesized from adipic acid and 1,6-hexanediol, which had an even number of carbon atoms (polyester-6-6-1 and polyester-6-6-2). The other polyester with M_n = 2,770 was synthesized from pimelic acid and 1,5-pentanediol, which had an odd number of carbon atoms (polyester-7-5). Polyester-6-6-1 and polyester-6-6-2 consisting of even carbon monomers, had a higher degree of crystallinity at room temperature than polyester-7-5, which consists of an odd number of carbon monomers. The effect of polyester molecular weight and soft and hard-segmental geometric structure on the soft-and hard-segmental phase segregation was studied using differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and small angle X-ray scattering (SAXS).