Department of Metallurgical & Materials Engineering

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IIT Jodhpur

Efficient water splitting requires highly active, earth-abundant, and robust catalysts. Monometallic phosphides such as Ni2P have been shown to be active toward water splitting. Our theoretical analysis has suggested that their performance can be further enhanced by substitution with extrinsic metals, though very little work has been conducted in this area. Here we present for the first time a novel PH3 plasma-assisted approach to convert NiCo hydroxides into ternary NiCoP. The obtained NiCoP nanostructure supported on Ni foam shows superior catalytic activity toward the hydrogen evolution reaction (HER) with a low overpotential of 32 mV at 10 mA cm-2 in alkaline media. Moreover, it is also capable of catalyzing the oxygen evolution reaction (OER) with high efficiency though the real active sites are surface oxides in situ formed during the catalysis. Specifically, a current density of 10 mA cm-2 is achieved at overpotential of 280 mV. These overpotentials are among the best reported values for non-noble metal catalysts. Most importantly, when used as both the cathode and anode for overall water splitting, a current density of 10 mA cm-2 is achieved at a cell voltage as low as 1.58 V, making NiCoP among the most efficient earth-abundant catalysts for water splitting. Moreover, our new synthetic approach can serve as a versatile route to synthesize various bimetallic or even more complex phosphides for various applications. © 2016 American Chemical Society.

World University root node

Nano Letters

Plasma-Assisted Synthesis of NiCoP for Efficient Overall Water Splitting

Cytocompatibility and biodegradation behaviour were investigated for a newly developed ultralight Mg-4Li-1Ca (LX41) alloy with different starting microstructures. This established the important role of microstructure in determining the pH variation, H2 evolution and amount of ions (Mg, Li, Ca) released during degradation. Thus, different thermomechanical treatments were utilised to alter the microstructure of the alloy and to evaluate its bio-response. The as-cast and two step rolled+annealed (TA30) materials showed stronger X-ray diffraction peaks for Mg- and Li-containing hydroxyapatite (HA) than the two step rolled (TSR) and the equal channel angular pressed (ECAP) materials. It was also found that the as-cast and TA30 variants of LX41 showed good cell viability of more than 100% with preferential attachment and healthier cell morphology than the TSR material. This is associated with greater content of Mg and Li ions released during alloy degradation. These act as mediators to establish contact between the cells and the substrate, and thereby promote cell attachment and proliferation. These findings suggest the existence of a strong microstructure-cytocompatibility relation for the present LX41 alloy, which can be used as an important tool for further magnesium alloy development for biological applications. © 2016 Walter de Gruyter GmbH, Berlin/Boston.

Fulltext

BioNanoMaterials

Towards microstructure-cytocompatibility relationship in ultralight Mg-4Li-1Ca (LX41) alloy for degradable implant applications

The development of ferrite-martensite dual-phase microstructures by cold-rolling and intercritical annealing of 0.06 wt pct carbon steel was systematically studied using a dilatometer for two different heating rates (1 and 10 K/s). A step quenching treatment has been designed to develop dual-phase structures having a similar martensite fraction for two different heating rates. An increase in heating rate seemed to refine the ferrite grain size, but it increased the size and spacing of the martensitic regions. As a result, the strength of the steel increased with heating rate; however, the formability was affected. It has been concluded that the distribution of C during the annealing treatment of cold-rolled steel determines the size, distribution, and morphology of martensite, which ultimately influences the mechanical properties. Experimental detection of carbon distribution in austenite is difficult during annealing of the cold-rolled steel as the phase transformation occurs at a high temperature and C is an interstitial solute, which diffuses fast at that temperature. Therefore, a cellular automata (CA)-based phase transformation model is proposed in the present study for the prediction of C distribution in austenite during annealing of steel as the function of C content and heating rate. The CA model predicts that the carbon distribution in austenite becomes more inhomogeneous when the heating rate increases. In the CA model, the extent of carbon inhomogeneity is measured using a kernel averaging method for different orders of neighbors, which accounts for the different physical space during calculation. The obtained results reveal that the 10th order (covering 10-µm physical spaces around the cell of interest) is showing the maximum inhomogeneity of carbon and the same effect has been investigated and confirmed using auger electron spectroscopy (AES) for 0.06 wt pct carbon steel. Furthermore, the optimization of carbon homogeneity with respect to heating rate has been performed using a bi-objective genetic programming (BioGP) strategy for the steel composition varying from 0.06 to 0.12 wt pct carbon along with other parameters like average austenite grain size and time of heating as the input variables. The analysis of the results obtained from BioGP suggests that the homogeneity of carbon increases with the increasing carbon concentration of steel. This is corroborated by analyzing the AES results obtained for 0.28 wt pct carbon steel using the same technique as that used for 0.06 wt pct carbon steel. © 2016, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A

Effect of carbon distribution during the microstructure evolution of dual-phase steels studied using cellular automata, genetic algorithms and experimental strategies

Epitaxial thin films of ferromagnetic La0.7Sr0.3MnO3 (LSMO) and charge-ordered, antiferromagnetic Y0.5Ca0.5MnO3 (YCMO) were deposited on SrTiO3 (100) substrates by pulsed laser deposition (PLD). The heterostructure undergoes tetragonal distortion due to strong biaxial tensile strain imposed by the substrate. The LSMO–YCMO bilayers exhibit significant exchange bias (EB) across the interface even in a very small remnant magnetic field (∼5 Oe) present in the superconductor magnet. The unidirectional exchange anisotropy at the interface can be switched by reversing the polarity of the remnant magnetic field. (Figure presented.) Significant asymmetry in the M (H) loop is exhibited by the heterostructure interface under cooling in the presence of small remnant magnetic field (Hr ∼ 5 Oe). (© 2016 WILEY-VCH Verlag GmbH &amp;Co. KGaA, Weinheim). © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

physica status solidi (RRL)–Rapid Research Letters

Exchange bias at low fields exhibited by the interface between epitaxial layers of ferromagnetic and charge‐ordered rare‐earth manganites

Pilgering is a complex incremental manufacturing process for seamless tubes. In this work, a miniature physical simulator for pilgering was designed and fabricated. This miniature simulator employs a grooved roll-die and a mandrel and can impose controlled reductions in both tube diameter and wall thickness. Pilgering deformation over a range of ratios of reductions in wall thickness and in tube diameter, known as the Q-factor, was imposed on hemi-cylindrical zirconium alloy specimens. The influence of the Q-factor on the microstructure and deformation texture of the deformed specimens was quantified. A polycrystal plasticity calculation based on the binary tree model was used to simulate texture evolution during the simulated pilgering process. The computer model quantitatively captured the variation with Q of the Kearns factors, as measured in the physically simulated specimen. The small differences noticed between the predicted and experimental final textures point to unaccounted transverse components of the flow field. These observations suggest that physical and/or computer simulations can form the basis of a rapid methodology for tool selection to realize prescribed post-pilgering textures. © 2016 Elsevier B.V.

Journal of Materials Processing Technology

A miniature physical simulator for pilgering

Traditionally thermodynamically bistable ferroic materials are used for nonvolatile operations based on logic gates (e.g., in the form of field effect transistors). But, this inherent bistability in these class of materials limits their applicability for adaptive operations. Emulating biological synapses in real materials necessitates gradual tuning of resistance in a nonvolatile manner. Even though in recent years few observations have been made of adaptive devices using a ferroelectric, the principal question as to how to make a ferroelectric adaptive has remained elusive in the literature. Here, it is shown that by locally controlling the nucleation energy distribution at the ferroelectric–electrode interface multiple-addressable states in a ferroelectric can be created, which is necessary for adaptive/synaptic applications. This is realized by depositing a layer of nonswitchable ZnO on top of thin film ferroelectric PbZr x Ti(1– x )O3. This methodology of interface-engineered ferroelectric should enable realising brain-like adaptive/synaptic memory in complementary metal-oxide-semiconductor (CMOS) devices. Furthermore, the temporally stable multistability in ferroelectrics should enable the designing of multistate memory and logic devices. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Advanced Functional Materials

Multistability in Bistable Ferroelectric Materials toward Adaptive Applications

Cu-1 wt%Al2O3 composite powder, prepared by mechanical milling and consolidated by spark plasma sintering to have about 98-99% of theoretical density, were characterized by scanning electron microscope, focused ion beam microscope, X-ray diffraction, nanoindentation and transmission electron microscope. The mechanically milled powders, upon consolidation, exhibited a finer grain size of 2 μm. Tensile deformation behavior of this composite, at ambient temperature but over the strain rates of 10-4 s-1 to 5 × 10-2 s-1, exhibited typical manifestations of dynamic strain ageing in the form of serrations and negative strain rate dependence of flow stress. The yield and ultimate tensile strengths, and so also the elongation decrease gradually with increase in strain rate. Such variation was also shown by nanoindentation hardness as a function of loading rate over 1-100 mN/s. The observed results are explained by the dislocation structure evolved from its interaction with Al2O3 dispersoids and impurity atoms like Fe, C and O coming from the powder processing. © 2015 Elsevier B.V. All rights reserved.

Journal of Alloys and Compounds

Dynamic strain ageing in fine grained Cu-1 wt%Al2O3 composite processed by two step ball milling and spark plasma sintering

In the present study, Fe-10 vol pct Al2O3in situ nanocomposite has been derived by high-energy ball milling of Fe2O3-Fe-Al powder mixture followed by the consolidation using spark plasma sintering (SPS). The consolidated nanocomposite has bimodal-grained structure consisting of nanometer- and submicron-sized Fe grains along with nanometer-sized Al2O3, and Fe3O4 particles. The mechanical property analysis reveals that compressive yield strength of Fe-10 vol pct Al2O3 nanocomposite is 2100 MPa which is nearly two times higher than that of monolithic Fe processed by Mechanical Milling and SPS. The strengthening contributions obtained from matrix, grain size, and particles in the synthesized nanocomposite have been calculated theoretically, and are found to be matching well with the experimental strength levels. © 2016, The Minerals, Metals & Materials Society and ASM International.

Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science

Structure–Property Correlation in Fe-Al2O3 In Situ Nanocomposite Synthesized by High-Energy Ball Milling and Spark Plasma Sintering

A new modified technique of synthesizing tin oxide nanoparticles with crystallite size of 2?nm to 6?nm has been developed. Surface area of the nanoparticle has been increased as we approached towards the Debye length. Such a techniques for approaching the Debye length is expected to bring remarkable changes in the properties of resistive based gas sensors. The technique used here is less toxic, economical and has high yield. Phase purity, size, shape and composition has been investigated using x-ray diffraction, micro Raman, scanning electron microscopy and energy dispersive x ray spectroscopy. While surface area has been calculated through Brunaur-Emmett-Teller (BET). © 2016 Author(s).

AIP Conference Proceedings

Solvent free tin oxide nanoparticle for gas sensing application

Closed end burst tests, using room temperature water as pressurizing medium, were performed on a number of industrially produced zirconium (Zr) clads. A total of 31 samples were selected based on observed differences in burst ductility. The latter was represented as total circumferential elongation or TCE. The selected samples, with a range of TCE values (5 to 35 pct), did not show any correlation with mechanical properties along axial direction, microstructural parameters, crystallographic textures, and outer tube-surface normal (σ11) and shear (τ13) components of the residual stress matrix. TCEs, however, had a clear correlation with hydrostatic residual stress (Ph), as estimated from tri-axial stress analysis on the outer tube surface. Estimated Ph also scaled with measured normal stress (σ33) at the tube cross section. An elastic–plastic finite element model with ductile damage failure criterion was developed to understand the burst mechanism of zirconium clads. Experimentally measured Ph gradients were imposed on a solid element continuum finite element (FE) simulation to mimic the residual stresses present prior to pressurization. Trends in experimental TCEs were also brought out with computationally efficient shell element-based FE simulations imposing the outer tube-surface Ph values. Suitable components of the residual stress matrix thus determined the burst performance of the Zr clads. © 2016, The Minerals, Metals & Materials Society and ASM International.