Grain Boundary Segregation Behavior of Boron in Low-Alloy Steel

The boron concentration profiles around prior austenite grain boundaries in Fe-0.05C-0.5Mo-0.001B (mass pct) are examined using aberration-corrected STEM-EELS. In order to obtain the precise distribution of boron around the boundaries, tilt series measurements with thin specimens (<30 nm) are performed and the EEL spectra are analyzed by principal component analysis (PCA) and multivariate curve resolution (MCR). The boron concentration profile changes with the cooling rate from the solid solution temperature. The concentration at grain boundaries is maximized at a medium rate (30 °C/s), where the concentration reaches 8 at. pct, and it decreases at a larger (250 °C/s) or smaller (5 °C/s) rate. On the other hand, the boron distribution becomes wider as the cooling rate becomes smaller. The current results suggest that the boron segregation in the alloy is formed by the “non-equilibrium segregation mechanism.”     

The structure solution of the F-type i-ZnMgHf from the X-ray diffraction

ABSTRACT

We report a successful growth of the ZnMgHf F-type icosahedral quasicrystal in the form of faceted single grains. By varying the heat treatment parameters we were able to obtain single crystals with a quality suitable for a single crystal X-ray diffraction which was conducted in a synchrotron facility. Ab initio structure solution by a charge flipping algorithm manifests the existence of two types of Bergman clusters. Clusters are differentiated by the preferential occupation of the high-symmetry positions by hafnium in a rhombic triacontahedron, being the outer shell of the atomic cluster.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Preparation of pectin‐inorganic composite material as accumulative material of metal ions

Pectin is one of the biopolymers in the cell walls of all plant tissues, but the pectin‐containing materials have been discarded as industrial waste in food‐processing factories. We prepared a water‐insoluble pectin‐inorganic composite material by mixing pectin and a silane coupling reagent, bis(3‐trimethoxysilylpropyl)amine. The mechanical strength of the pectin‐inorganic composite material was higher than that of the pectin material without the addition of an inorganic component. In addition, the thermal stability of the composite material increased with the addition of the inorganic component. Furthermore, when the pectin‐inorganic composite materials were incubated in an aqueous solution of Cu(II), Zn(II), or In(III), these composite materials effectively accumulated not only the heavy metal ions, but also rare‐earth metal ions. Additionally, based on the infrared (IR) measurements, the metal ion accumulative mechanism into the composite material is described. As a result, the IR spectra suggested an electrostatic interaction between the metal ion and carboxy group in the pectin. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42056.     

Strong Surface‐Termination Effect on Electroresistance in Ferroelectric Tunnel Junctions

Tunnel electroresistance in ferroelectric tunnel junctions (FTJs) has attracted considerable interest, because of a promising application to nonvolatile memories. Development of ferroelectric thin‐film devices requires atomic‐scale band‐structure engineering based on depolarization‐field effects at interfaces. By using FTJs consisting of ultrathin layers of the prototypical ferroelectric BaTiO₃, it is demonstrated that the surface termination of the ferroelectric in contact with a simple‐metal electrode critically affects properties of electroresistance. BaTiO₃ barrier‐layers with TiO₂ or BaO terminations show opposing relationships between the polarization direction and the resistance state. The resistance‐switching ratio in the junctions can be remarkably enhanced up to 10⁵% at room temperature, by artificially controlling the fraction of BaO termination. These results are explained in terms of the termination dependence of the depolarization field that is generated by a dead layer and imperfect charge screening. The findings on the mechanism of tunnel electroresistance should lead to performance improvements in the devices based on nanoscale ferroelectrics.     

Analytical and Experimental Evaluation of Dispersive Mixing Performance of Special Rotor Segments in a Corotating Twin-Screw Extruder

An intermeshing corotating twin-screw extruder is often used for producing polymer composites. In this study, we discussed mixing performance of special rotor segments in molten zone. These rotor segments have several tip clearances for achievement of self-cleaning and effective mixing, and these are named various clearance mixing technology. We studied about dispersive mixing performance of configuration, which consists of various clearance mixing technologys (various clearance mixing technology configuration) using numerical analyses and experiments. For the analytical evaluation of mixing performance, we have adopted a particle tracking method. As evaluation indices of dispersive mixing performance, we focused on following three values (1) maximum value in a history of first principal stress of each particle, (2) time-integrated shear rate of each particle, and (3) time-integrated first principal stress of each particle. And we made the probability distributions of the indices. We adopted weighted probability as approximation of volume probability in each region. The results were compared with those of kneading disk segments configuration (kneading disk configuration). Furthermore, we validated the accuracy of the analytical evaluation by performing experiments under same conditions as those of numerical analyses. For the experimental evaluation of mixing performance, we used twin-screw extruder. Polypropylene was selected as suspending media. And CaCO₃ was selected as filler. To compare just the mixing performance of various clearance mixing technology configuration with that of kneading disk configuration, side feeding and screw configuration which had third mixing segments zone were adopted. From the experimental result, it is found that various clearance mixing technology configuration dispersed better than kneading disk configuration. And from the comparison between the experimental evaluation and the analytical evaluation, it is found that the first principal stress is more appropriate for evaluation index of dispersive mixing. Finally, it can be mentioned that various clearance mixing technology configuration has better mixing performance than kneading disk configuration, and large stress is important for dispersive mixing.     

Use of polyethylene films photografted with 2‐(dimethylamino)ethyl methacrylate as a potential adsorbent for removal of chromium (VI) from aqueous medium

A new polymeric adsorbent material based on polyethylene (PE) was prepared by photografting of 2‐(dimethylamino)ethyl methacrylate (DMAEMA) as a positively chargeable monomer to a PE film. The effects of the experimental parameters, such as the pH value, temperature, and grafted amount on adsorption of chromium(VI) (Cr(VI)) ions were investigated for the DMAEMA‐grafted PE (PE‐g‐PDAMEMA) films. The maximum adsorption capacity was obtained at the initial pH value of 3.0 for a PE‐g‐PDMAEMA film with 1.8 mmol/g and the maximum adsorption capacity obtained was higher than or compatible to those of many of the other polymeric adsorbents prepared for Cr(VI) ions. The adsorption kinetics obeyed the mechanism of the pseudo‐second order kinetic model and adsorption of Cr(VI) ions on PE‐g‐PDMAEMA films was well expressed by the Langmuir isotherm model. A high Langmuir adsorption constant suggests that the adsorption of Cr(VI) ions occurs between protonated dimethylamino groups and ions mainly through the electrostatic interaction. Cr(VI) ions adsorbed were successfully desorbed from a PE‐g‐PDMAEMA film in solutions of NaCl, NH₄Cl, NH₄Cl containing NaOH, and NaOH and a PE‐g‐PDMAEMA film was regenerated and repeatedly used for adsorption of Cr(VI) ions without appreciable loss in the adsorption capacity. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43360.