The present paper reports the growth and branching mechanism of W18O49 nanowires grown on nanocrystalline tungsten (W) surfaces. Nanocrystalline W powder was prepared using high energy ball milling. The nanopowder was non-isothermally heat-treated up to 1400 °C in argon atmosphere. The nanowires of 30-50 nm diameter were observed on nanopowder surfaces after the heat-treatment. A model based on crystallographic shear phase formation to accommodate the oxygen deficiency during the reduction of WO3 is discussed to explain the growth and branching mechanism of these nanowires which correlates well with the observed angle for the branching. © 2016 Elsevier B.V.

Budaraju Srinivasa Murty

Department of Metallurgical and Materials Engineering

Ball milling

Mechanical Alloying

Milling (machining)

Nanostructured materials

Nanowires

Tungsten

Argon atmospheres

BRANCHING MECHANISM

CRYSTALLOGRAPHIC SHEARS

HIGH-ENERGY BALL MILLING

MECHANICAL MILLING

Nanocrystallines

OXYGEN DEFICIENCY

Phase formations

Nanocrystals

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Scripta Materialia

In this work, nanocrystalline tungsten oxide (WO3) powder was obtained by high energy ball milling (HEBM) followed by heat treatment of tungsten (W) powder. HEBM significantly influenced the oxidation behavior by reducing the crystallite size and inducing lattice strain in W powder. The resultant nanocrystalline WO3 shows variation in the optical bandgap with respect to the bulk counterparts. The alteration in the bandgap of WO3 is ascribed to the changes in crystallite size and the unit cell volume. In the end, a thorough correlation between fundamental interactions of these changes was succinctly highlighted. © 2019 Acta Materialia Inc.

Crystallite size induced bandgap tuning in WO3 derived from nanocrystalline tungsten

The present work reports the role of different atomic mobility induced localized pore evolution on densification during spark plasma sintering of nanocrystalline W-Mo alloy powder. The shrinkage (or expansion) behavior of cold compacted milled powders was studied using dilatometry during non-isothermal sintering up to 1600 °C. Subsequently, the milled powders were densified to ~95% relative density using spark plasma sintering up to 1600 °C. The enhanced localized Joule heating due to dynamically evolved porous structure could be attributed for the densification during spark plasma sintering. © 2018 Elsevier Ltd

Fulltext

Localized pore evolution assisted densification during spark plasma sintering of nanocrystalline W-5wt.%Mo alloy

AlSb is a low-cost, high-band-gap semiconducting material, yet largely limited in its potential due to difficulty in the synthesis of single-phase AlSb. The present work compares different processing routes in their potency to produce bulk and nanocrystalline AlSb. Vacuum arc melting has been successfully employed, for the first time, to synthesize single-phase bulk AlSb. Owing to high vapor pressure of Sb, an optimum amount of excess Sb (3%) needs to be added to achieve single-phase line compound AlSb. Two methods, viz. mechanical alloying of elemental powders and mechanical milling of cast alloy, have been used to synthesize nanocrystalline AlSb. Nanocrystalline AlSb could be produced after ball milling the cast alloy; however, prolonged milling results in the appearance of Sb along with a non-stoichiometric Al-Sb-O oxide. Mechanical alloying of Al and Sb does not lead to appearance of single-phase AlSb, and the mixture largely consists of starting material and amorphous products. Therefore, the effectiveness of a synthesis route in producing single-phase AlSb is governed by the tendency of oxygen pickup during the processing. © 2018, ASM International.

Journal of Materials Engineering and Performance

Comparison of Different Processing Routes for the Synthesis of Semiconducting AlSb

Nanocrystalline B2 aluminide (FeAl and NiAl) powders were synthesized using high energy ball milling and were consolidated using three different sintering methods: conventional pressureless sintering, microwave sintering and spark plasma sintering. The particle-particle contacts after sintering were found to have compositional gradient from interior to surface leading to formation of an Al-O rich phase. This Al-O rich phase formation is primarily attributed to oxygen pick-up during handling of powders and during sintering, leading to formation of amorphous alumina. The formation of amorphous phase is explained by examining the defect concentrations and their interactions. The composite developed with amorphous alumina as a second phase in an ordered B2 matrix can be of great interest for potential structural applications. © 2016 Elsevier Inc.

Materials Characterization

Formation of amorphous alumina during sintering of nanocrystalline B2 aluminides

The grain size dependency of lattice parameter during high-energy ball milling of W has been investigated. The lattice parameter varies non-monotonically with grain size during milling with a lattice contraction initially followed by an expansion. The lattice parameters were calculated in view of the non-equilibrium grain boundary structure that evolved during milling using excess free volume and the interfacial stresses at the grain boundaries. The calculated lattice parameters closely match the experimentally observed values. © 2014 Acta Materialia Inc.

Grain-size-dependent non-monotonic lattice parameter variation in nanocrystalline W: The role of non-equilibrium grain boundary structure

The present paper reports a study on the microstructural evolution during mechanical alloying of W-20wt%Mo using XRD line profile analysis. The W-20wt%Mo powder blends were ball milled using Fritsch Pulverisette P-5 high energy ball mill for varying milling time (0, 5, 10, 15, 20 h) at 300 rpm with 10:1 and 2:1 ball to powder weight ratio. The crystallite size and lattice strain were calculated using Langford method ('average' Williamson-Hall Plot). The precision lattice parameter calculation was done using Nelson-Riley method. The effect of milling on alloying behaviour has been investigated using change in relative integrated intensity ratios (I Mo /I W/W(Mo)) of (211) XRD peak. There was complete alloying in case of 10:1 ball to powder weight ratio, whereas half of the Mo (~10 % Mo) was alloyed with 2:1 ball to powder weight ratio. The paper also discusses the applicability of the criteria based on lattice parameter change (peak shift) for alloying behaviour during mechanical milling. © 2013 Indian Institute of Metals.

Transactions of the Indian Institute of Metals

XRD characterization of microstructural evolution during mechanical alloying of W-20 wt%Mo

Chemical Society Reviews

Flexible electronics based on inorganic nanowires

Advanced Functional Materials

Gram-Scale Synthesis of Ultrathin Tungsten Oxide Nanowires and their Aspect Ratio-Dependent Photocatalytic Activity

Nanoscale

W18O49nanowire alignments with a BiOCl shell as an efficient photocatalyst

Crystallographic-shear-phase-driven W18O49 nanowires growth on nanocrystalline W surfaces

Journal	Data powered by TypesetScripta Materialia
Publisher	Data powered by TypesetElsevier Ltd
ISSN	13596462
Open Access	No