Precursors of the zeolite ZSM-5 imaged by Cryo-TEM and analyzed by SAXS

The microstructural evolution in the nucleation stage of a synthesis reaction of ZSM-5 zeolite was studied, with particular emphasis on the role of the organic cation, TPA⁺ (tetrapropylammonium). Direct observation of the microstructure was achieved by cryo-transmission electron microscopy (cryo-TEM). The quantitative evaluation of the structural units was obtained by small-angle X-ray scattering (SAXS) measurements. In the presence of the organic cation TPA⁺, we found globular structural units 5 nm in diameter that aggregate to elongated bodies 44 nm long. The globular structural units were found in reaction mixtures with or without the organic template TPA-OH, as long as the pH of the initial solution was kept above 11.6. Without TPA⁺, aggregation to cylindrical particles was not observed after 2 h of heating, and no ZSM-5 crystallinity was attained at the end of the reaction (after 8 d). These results suggest that the zeolite ZSM-5 building blocks are globular structural units, 5 nm in diameter, containing silica, alumina, organic cation, and water, which fuse together to produce elongated aggregates that may compose the final unit cell. It is concluded that the globular structural unit is a cluster of tetrapods similar to those found in the final ZSM-5 crystals.     

Improved Scatter Search Algorithm for Multi-skilled Personnel Scheduling of Ship Block Painting

This paper focuses on the optimization method for multi-skilled painting personnel scheduling.The budget working time analysis is carried out considering the influence of operating area,difficulty of spraying area,multi-skilled workers,and worker’s efficiency,then a mathematical model is established to minimize the completion time. The constraints of task priority,paint preparation,pump management,and neighbor avoidance in the ship block painting production are considered. Based on this model,an...     

Hydrogen sorption-desorption characteristics of mixed and composite NiTiN nanoparticles

Mixed and composite NiTiN nanoparticles were prepared by an active plasma-metal reaction method. Homogeneous distribution of spherical Ni and cubical TiN nanoparticles is observed for the mixed NiTiN nanoparticles. Dumbbell-like morphology is seen for the composite NiTiN nanoparticles. Good thermal stability of both nanoparticles is confirmed. Hydrogen sorption-desorption characteristics of the nanoparticles were examined by temperature-programmed desorption measurements. Hydrogen desorption at 620–680 K is observed for the composite NiTiN nanoparticles, that is considered to be due to the spillover hydrogen. Effect of CO coadsorption on the hydrogen desorption is also examined and new adsorption states are suggested.     

Quantitative assessment of retained austenite in quenching and partitioning treated multiphase steel

For multiphase steel, an efficient and accurate quantitative analysis of constituent phases is critical in understanding the mechanical mechanism and optimising its properties. A method based on image digitisation and the concept of categorised linear interception has been proposed to study the amount of retained austenite (RA) residing in different phases in quenching and partitioning treated multiphase steel. It was found that RA at different locations transformed in different strain stages due to considerable influence from the surrounding phases, and the stability of each type of RA was estimated according to the above mentioned method. The proposed multistage transformation was proved to be more accurate than a single stage stability model.     

介绍国外最新几种船底防污涂料

介绍了日本和美国几种节能、环保型船底防污涂料,包括无毒防污剂。     

Modeling of transport phenomena in hybrid laser-MIG keyhole welding

Mathematical models and associated numerical techniques have been developed to investigate the complicated transport phenomena in spot hybrid laser-MIG keyhole welding. A continuum formulation is used to handle solid phase, liquid phase, and the mushy zone during the melting and solidification processes. The volume of fluid (VOF) method is employed to handle free surfaces, and the enthalpy method is used for latent heat. Dynamics of weld pool fluid flow, energy transfer in keyhole plasma and weld pool, and interactions between droplets and weld pool are calculated as a function of time. The effect of droplet size on mixing and solidification is investigated. It is found that weld pool dynamics, cooling rate, and final weld bead geometry are strongly affected by the impingement process of the droplets in hybrid laser-MIG welding. Also, compositional homogeneity of the weld pool is determined by the competition between the rate of mixing and the rate of solidification.     

A Review of two-phase flow dynamic instabilities in tube boiling systems

The earliest research in the field of two-phase flow was conducted by Lorentz (1909). The studies on the analysis of two-phase flow instabilities by Ledinegg (1938) created considerable interest concerning the phenomenon of thermally induced flow instability in two-phase flow systems. The objective of this review is to sum up the experimental and theoretical work carried out by various investigators over a period of several years, demonstrating and explaining three main instability modes of two-phase flow dynamic instabilities, namely, density-wave type, pressure-drop type and thermal oscillations, encountered in various boiling flow channel systems. The typical experimental investigations of these instabilities in tube boiling systems are indicated and the most popular models to predict the two-phase flow dynamic instabilities, namely the homogenous flow model and the drift-flux models are clarified with the solution examples and the validation of the model results with experimental findings are also provided.     

The effect of cooling rate on the morphology of primary Al3Sc intermetallic particles in Al–Sc alloys

The precipitation of Al₃Sc primary particles in aluminium alloy melts is of considerable technological significance due to their strong grain refining effect on cast structures. The nucleation behaviour and growth morphology of the Al₃Sc primary particles formed in a slightly hypereutectic Al–0.7Sc alloy have been studied for a range of cooling rates in a FEG-SEM, using extracted particles, and in the TEM. It has been found that the Al₃Sc particles nucleate heterogeneously on oxides within the melt. At slow cooling rates (∼1 K s⁻¹), the particles exhibit faceted growth, forming {100} faceted cubic shaped particles and larger particles comprised of several attached cubes. At higher cooling rates (100–1000 K s⁻¹), the particles' interface becomes unstable along the cube edges and corners, forming growth perturbations. This leads to the formation of particles, which still adhere to an overall cubic morphology, but have cellular–dendritic sub-structures.     

Advanced dual reciprocity method based on polynomial source and its application to eigenvalue problem for nonuniform media

A new dual reciprocity boundary element method has been developed to solve the modified Helmholtz-type equation, which has a space-dependent source term described by a polynomial. The domain integral related to the polynomial source is transformed into an infinite series of boundary integrals, by repeated application of particular solutions for the Poisson equation. This scheme is expanded to solve iteratively the Helmholtz-type eigenvalue problem for a “nonuniform” media. The results of BEM test calculations for solving the Schrödinger equation as well as the neutron diffusion equation show good agreement with those obtained from finite difference computations in which the nonuniformity was approximated by a large number of material subregions.