Characterization of complex die-pressed Al2O3 green compact using liquid immersion,X-ray tomography,and numerical simulations

This study examined the compaction behavior of a green ceramic component with a complex shape formed by die pressing at 50 MPa using spray-dried alumina. Compared to a simple cylindrical sample, the sample with a complex shape revealed a higher degree of microstructural inhomogeneity and crack formation. Granule deformation and pore distribution at different sample locations were observed by optical microscopy after infiltrating liquid into the voids of a green compact. The refractive index of the immersion liquid should be different slightly from that of alumina for better observations. X-ray micro-computed tomography was also used to visualize the pore distribution and crack shape. Numerical simulations based on the Drucker-Prager/Cap model were performed to distinguish the stress and displacement distribution within the compact. The significant stress gradient at the crack initiation point could explain crack formation, whereas the application of a higher pressure resulted in a further increase in stress gradient.     

Quantitative study on area fraction of precipitated carbides of HP40Nb steel as a function of service period

Journal of Mechanical Science and Technology - Life assessment predictions of reformer tubes of HP40Nb grade steel used in the petrochemical industry were investigated by quantitative...     

Benign enzymatic synthesis of multiwalled carbon nanotube composites uniformly coated with polypyrrole for supercapacitors

BACKGROUND: Recently, various composites of carbon nanomaterials and conducting polymers have been actively investigated as potential electrode materials for supercapacitors which can store and deliver large amounts of electrical energy promptly. Harsh chemical or complex electrodeposition methods have been studied to prepare such composites. In this report, the mild and simple enzymatic catalysis of horseradish peroxidase (EC 1.11.1.7) in aqueous solutions (pH 4.0) was utilized for the first time to prepare composites of multiwalled carbon nanotubes and polypyrrole. RESULTS: Electron micrographs show that in situ enzymatic reaction by horseradish peroxidase enables the uniform coating of multiwalled carbon nanotubes with polypyrrole without containing the polymer aggregates. The specific capacitance of the composites (46.2 F g^?1) measured with a two‐electrode cell containing an electrolyte of 1 mol L^?1 NaNO₃ increased more than four‐fold compared with that obtained with bare multiwalled carbon nanotubes (10.8 F g^?1). CONCLUSIONS: Horseradish peroxidase‐catalyzed in situ synthesis of the composites of multiwalled carbon nanotubes and polypyrrole requires neither the derivatization of multiwalled carbon nanotubes and/or pyrrole monomers nor the post‐doping of the synthesized composites to enhance the capacitance of the composites. © 2012 Society of Chemical Industry     

Improvement of ink and heavy metal removal from old corrugated container stock by alkali kneading

One of the possible ways to strengthen competitiveness of Kraft paper industry is to replace the expensive virgin unbleached kraft pulp (UKP) with old corrugated container (OCC), a cheaper and lower grade raw material. When OCC is utilized to produce kraft paper, the main problems are the impaired appearance of the products, and heavy metals and hazardous materials in the products caused by the printed ink and other contaminants. In order to improve the removal efficiency of ink and heavy metals from old corrugated container stock, the effect of adding alkali during kneading of OCC stock was investigated. It was found that adding NaOH and sodium silicate during kneading could improve detachment of ink from fiber surface and removal of it from stock and hence improve heavy metal removal from OCC stock. Since alkali addition improves ink detachment, effective residual ink concentration (ERIC) of pulp was decreased and brightness was increased. Tensile strength and tensile energy absorption (TEA) were increased with addition of alkali.     

Mechanical Abrasion by Bi-layered Pad Micro-Asperity in Chemical Mechanical Polishing

Pad asperities in chemical-mechanical polishing (CMP) provide necessary forces for mechanical abrasion. This article investigates the abrasive behaviour of polishing pads at the asperity contact scale. A contact mechanics model predicts that compliant and soft asperities or rigid and hard asperities may solely achieve either large contact area or high indentation depth respectively, whereas bi-layered asperities can enable both the enlarged contact and deep abrasion. Hemispherical pad micro-asperities with precise dimensions, including the new bi-layered design, were fabricated using thermal reflow and micro-replica molding techniques and their polishing behaviours were experimentally compared using a pin-on-disk polishing setup.     

Crystallography and Morphology of Carbides in a Low-Cycle Fatigued 1Cr-1Mo-0.25V Steel

The carbide precipitation in 1Cr-1Mo-0.25V steel subjected to low-cycle fatigue (LCF) deformation at room and elevated temperatures was investigated by means of transmission electron microscopy. Based on the electron diffraction analyses, three types of carbides, M₃C-type cementite, M₂C, and MC, were identified in normalized and subsequently tempered specimen. The cyclic deformation at high temperature led to the following changes in morphology and composition of carbides: the spheroidization of cementite, the enhanced precipitation of H-carbide, the formation of M₂C and M₂₃C₆ at lath or prior-austenite grain boundaries, and the enrichment of Mo in most of carbides. Particular attention has been paid to the crystallographic orientation relationship (OR) between the cementite and the ferrite (α) matrix. The combined analyses based on the simulation of diffraction patterns and the trace analyses of habit plane on stereographic projection have shown that most cementite was related to the α matrix in accordance with Bagaryatskii OR, but in some cases, the Isaichev OR also was observed in the lath interior after LCF deformation at elevated temperature. In addition, M₂C obeyed the Burgers–Jack OR, and MC was related to the α by the Baker–Nutting OR.     

Effect of interface affinity on the performance of a composite of microcrystalline cellulose and polypropylene/polylactide blends

The effects of compatibilizer and fillers on the mechanical properties and dispersion state of droplets of polypropylene (PP)/polylactide (PLA) blends were investigated. Two blended composite systems, i.e. PP‐rich (80/20) containing microcrystalline cellulose (MCC) modified with silane (m‐MCC) and PLA‐rich (20/80) containing MCC were prepared by melt compounding using a twin‐screw extruder. The structural differences between MCC and m‐MCC were confirmed using Fourier transform infrared spectra. Universal testing machine results revealed that the tensile strength and Young's modulus increased with the addition of compatibilizer and filler, respectively. These results were supported by the reduction of domain size observed by scanning electron microscopy. Differential scanning calorimetric analysis showed a change of the melting and crystallization behavior of blends according to the presence of compatibilizer or filler. An increase of the dynamic storage modulus and a decrease in tan δ with addition of compatibilizer indicated that the interfacial adhesion between PP and PLA improved. © 2019 Society of Chemical Industry     

Room-temperature multiferroicity in NiFe2O4 and its magnetoelectric coupling intensified through defect engineering

The well-known ferromagnetic oxide, NiFe₂O₄, was studied as a potential candidate for room-temperature Type II magnetoelectrics. A spin canting as one of the essential requirements for Type II multiferroics was induced by breaking the stoichiometry, that is, intentionally subtracting Fe ions. We observed that Fe ions were first subtracted exclusively from the tetrahedral sites, leading to an increase in the magnetoelectric coupling owing to an increasing degree of spin canting. The enhancement in the magnetoelectric coupling culminated beyond the subtraction level of ~30 at.%, at which Fe ions started to be removed from the octahedral sites. Alongside, we observed that the subtraction of Fe ions gives rise to a ferroelectricity due to the formation of defect complexes that establish an internal bias field.