Showing papers by "Defence Metallurgical Research Laboratory published in 2014"

Adsorption, photodegradation and antibacterial study of graphene???Fe3O4 nanocomposite for multipurpose water purification application

Abstract: Graphene–Fe3O4 (G–Fe3O4) composite was prepared from graphene oxide (GO) and FeCl3·6H2O by a one-step solvothermal route. The as-prepared composite was characterized by field-emission scanning electron microscopy, transmission electron microscopy, dynamic light scattering and X-ray powder diffraction. SEM analysis shows the presence of Fe3O4 spheres with size ranging between 200 and 250 nm, which are distributed and firmly anchored onto the wrinkled graphene layers with a high density. The resulting G–Fe3O4 composite shows extraordinary adsorption capacity and fast adsorption rates for the removal of Pb metal ions and organic dyes from aqueous solution. The adsorption isotherm and thermodynamics were investigated in detail, and the results show that the adsorption data was best fitted with the Langmuir adsorption isotherm model. From the thermodynamics investigation, it was found that the adsorption process is spontaneous and endothermic in nature. Thus, the as-prepared composite can be effectively utilized for the removal of various heavy metal ions and organic dyes. Simultaneously, the photodegradation of methylene blue was studied, and the recycling degradation capacity of dye by G–Fe3O4 was analyzed up to 5 cycles, which remained consistent up to ∼97% degradation of the methylene blue dye. Although iron oxide has an affinity towards bacterial cells, its composite with graphene still show antibacterial property. Almost 99.56% cells were viable when treated with Fe3O4 nanoparticle, whereas with the composite barely 3% cells survived. Later, the release of ROS was also investigated by membrane and oxidative stress assay. Total protein degradation was analyzed to confirm the effect of the G–Fe3O4 composite on E. coli cells.

Enhanced Room-Temperature Ferromagnetism on Co-Doped CeO2 Nanoparticles: Mechanism and Electronic and Optical Properties

Abstract: The present study reports the effect of Co doping on the structural, optical, magnetic, and electronic properties of CeO2 nanoparticles (NPs) synthesized by a simple low-temperature co-precipitation method. Co doping was introduced by adding CoCl3 with different mole percentages (0%, 2%, 4%, and 6%) to cerium nitrate, which resulted in room-temperature ferromagnetism (RTFM). TEM and XRD analysis showed that the Co-doped CeO2 NPs are monodispersed with face centered cubic structure. The 6% Co-doped CeO2 NPs showed a coercivity value of 155 Oe and saturation magnetization of 0.028 emu/g at room temperature. The electronic structures of the as-prepared CeO2 and Co-doped CeO2 NPs were investigated by X-ray absorption near-edge structure (XANES) spectroscopy. The XANES spectra at Ce M- and L-edges clearly indicated a decrease in the valency state of Ce ions from Ce4+ to Ce3+ upon Co doping. This causes redistribution of oxygen ions and Co–Co bonding. The XANES study revealed that Co doping plays a prominent ro...

Genotoxicity assessment of cerium oxide nanoparticles in female Wistar rats after acute oral exposure

Abstract: Cerium oxide nanoparticles (CeO2 NPs; nanoceria) have demonstrated excellent potential for commercial use in various arenas, such as in biomedical industry in cosmetics and as a fuel additive. However, limited knowledge exists regarding their potential toxicity. In this study, acute oral toxicity of CeO2 NPs and their microparticles (MPs; bulk) was carried out in female albino Wistar rats. The CeO2 NPs and CeO2 MPs were characterized utilizing transmission electron microscopy (TEM), dynamic light scattering (DLS) and laser Doppler velocimetry (LDV) for the size, distribution and surface charge respectively. The genotoxicity studies were conducted using micronucleus test (MNT), comet and chromosomal aberration (CA) assays. Results revealed that at high dose (1000mg/kg bw) CeO2 NPs induced significant DNA damage in peripheral blood leukocytes (PBL) and liver cells, micronucleus formation in bone marrow and blood cells and total cytogenetic changes in bone marrow. However, significant genotoxicity was not observed at 500 and 100mg/kg bw of CeO2 NPs. The findings from biochemical assays depicted significant alterations in ALP and LDH activity in serum and GSH content in liver, kidneys and brain only at the high dose of CeO2 NPs. Tissue biodistribution of both particles was analyzed by inductively coupled plasma optical emission spectrometer (ICP-OES). Bioaccumulation of nanoceria in all tissues was significant and dose-, time- and organ-dependent. Moreover, CeO2 NPs exhibited higher tissue distribution along with greater clearance in large fractions through urine and feces than CeO2 bulk, whereas, maximum amount of micro-sized CeO2 got excreted in feces. The histopathological examination documented alterations in the liver due to exposure with CeO2 NPs only. Hence, the results suggest that bioaccumulation of CeO2 NPs may induce genotoxic effects. However, further research on long term fate and adverse effects of CeO2 NPs is warranted.

Processing-microstructure-yield strength correlation in a near β Ti alloy, Ti–5Al–5Mo–5V–3Cr

Abstract: A combined set of thermo-mechanical steps recommended for high strength beta Ti alloy are homogenization, deformation, recrystallization, annealing and ageing steps in sequence. Recrystallization carried out above or below beta transus temperature generates either beta annealed (lath type morphology of alpha) or bimodal (lath+globular morphology of alpha) microstructure. Through variations in heat treatment parameters at these processing steps, wide ranges of length scales of features have been generated in both types of microstructures in a near beta Ti alloy, Ti-5Al-5Mo-5V-3Cr (Ti-5553). 0.2% Yield strength (YS) has been correlated to various microstructural features and associated heat treatment parameters. Relative importance of microstructural features in influencing YS has been identified. Process parameters at different steps have been identified and recommended for attaining different levels of YS for this near beta Ti alloy. (C) 2014 Elsevier B.V. All rights reserved.

Ce-doped bismuth ferrite thin films with improved electrical and functional properties

Abstract: Bi1−xCexFeO3 (BCFO) thin film capacitors (x = 0 to 0.2) are fabricated on indium tin oxide coated corning glass substrate by chemical solution deposition method. X-ray diffraction results show a partial phase transition from rhombohedral to tetragonal structure induced in BCFO thin film having preferred (110) orientation with increase in Ce dopant concentration. Current density–field (J–E) characteristics indicate that the leakage current density reduces by several orders of magnitude in Ce-doped BFO thin films resulting from smaller grain sizes and smoother surfaces. Space-charge-limited current and Fowler–Nordheim tunneling are identified as dominating leakage behavior in BCFO thin film capacitors at moderate and high field regions, respectively. Enhanced ferroelectric response with well-saturated (P–E) hysteresis loop is observed for Bi0.88Ce0.12FeO3 thin film having high remnant polarization (P r—127 µC/cm2) at an applied field of 1080 kV/cm. Bi0.88Ce0.12FeO3 thin film exhibiting well-defined capacitance–field (C–E) butterfly loop with dielectric loss (tan δ—0.03) measured at 10 kHz suggested good ferroelectric properties with high tunability of about 88 %.

Ferroelectric and magnetic properties of magnetoelectric (Na0.5Bi0.5)TiO3–BiFeO3 synthesized by acetic acid assisted sol–gel method

Abstract: The perovskite solid solution system resulting from the combination of Na 0.5 Bi 0.5 TiO 3 (NBT) and BiFeO 3 (BFO) has been studied for its magnetoelectric properties in BFO-rich phases of the series, using magnetometry and piezoresponse force microscopy (PFM). Raman spectroscopy results confirmed the successful formation of solid solutions having spectral features that are combination of two parent compounds. The solid solutions displayed a variable bandgap in the range 2.12–2.39 eV with composition. The results of PFM suggest an improved spontaneous polarization with the progressive replacement of (Na,Bi) 2+ and Ti 4+ ions at A- and B-sites of BFO lattice. At the same time room temperature weak ferromagnetic response was seen in mixed compositions. A systematic shift in magnetic transition temperatures from 650 K to 410 K was observed with the increase of NBT content. Magnetoelectric (ME) coefficient of 9 mV/cm-Oe was obtained for 40NBT–60BFO composition. Our studies indicate that NBT–BFO solid solution system is a potentially useful candidate for lead-free single phase ME applications.

Thermo-mechanical processing, microstructure and tensile properties of a tungsten heavy alloy

Abstract: The effect of heat treatment and swaging on microstructure and mechanical properties of a tungsten heavy alloy (WHA) of composition 90.5W–7.1Ni–1.65Fe–0.5Co–0.25Mo (wt%) has been examined in this study. The volume fraction and the contiguity of W-grains in the sintered microstructure decrease from 80% to 75% and 0.7 to 0.3, respectively, following an intermediate heat treatment comprising annealing at 1373 K followed by oil quenching. The average aspect ratio of W-grain increases with the increase in swaging deformation. While the bulk hardness of the alloy increases with increase in swaging deformation, a minor drop in hardness is observed following intermediate heat treatment. Peak broadening is observed in the X-ray diffractograms following thermo-mechanical processing with full width at half maxima (FWHM) of W 110 peak exhibiting a similar trend as that of hardness. The as-sintered alloy exhibits low yield strength, tensile strength and very low elongation to failure. Subsequent thermo-mechanical treatment results in substantial improvement of both strength and elongation. A strength value of 1427 MPa with elongation of 5–6% has been achieved following 40% swaging. Work hardening behavior of the alloy in heat treated condition has been studied and the results are correlated with slip lines and dislocation behavior of the alloy.

Tensile and impact properties of microwave sintered tungsten heavy alloys

Abstract: The present study investigates the interrelationship between microstructure, tensile and impact properties of microwave sintered tungsten heavy alloys. Alloys of two different compositions were microwave sintered and conventionally liquid phase sintered using similar heating rate, followed by microstructure and mechanical property evaluation. The tensile properties of microwave sintered alloys were significantly superior to those of liquid phase sintered alloys in both the compositions. Excellent impact properties were obtained in microwave sintered alloys, without any subsequent heat treatment or processing. In order to understand the reasons for the improvement, a detailed comparative study of microstructural features in both microwave and conventionally sintered alloys was carried out and it was observed that both tensile and impact properties of these alloys were largely influenced by tungsten–tungsten contiguity; the weakest link in the microstructure. Microwave sintered alloys were found to exhibit substantially lower contiguity as compared to the conventionally sintered alloys and consequently their properties were found to be superior as compared to the conventionally sintered alloys.

Friction welding of a nickel free high nitrogen steel: influence of forge force on microstructure, mechanical properties and pitting corrosion resistance

Abstract: a b s t r a c t In the present work, nickel free high nitrogen austenitic stainless steel specimens were joined by continuous drive friction welding process by varying the amount of forge (upsetting) force and keeping other friction welding parameters such as friction force, burn-off, upset time and speed of rotation as constant at appropriate levels. The joint characterization studies include microstructural examination and evaluation of mechanical (micro-hardness, impact toughness and tensile) and pitting corrosion behaviour. The integrity of the joint, as determined by the optical microscopy was very high and no crack and area of incomplete bonding were observed. Welds exhibited poor Charpy impact toughness than the parent material. Toughness for friction weld specimens decreased with increase in forge force. The tensile properties of all the welds were almost the same (irrespective of the value of the applied forge force) and inferior to those of the parent material. The joints failed in the weld region for all the weld specimens. Weldments exhibited lower pitting corrosion resistance than the parent material and the corrosion resistance of the weld specimens was found to decrease with increase in forge force.

Correlation between microstructural features and creep strain in a near-α titanium alloy processed in the α+β regime

Abstract: High temperature creep is an important property of titanium alloys used in aeroengines. Creep resistance of titanium alloys generally varies with heat treatment, temperature and cooling rate. Both the parameters affect the morphology and topology of the α (HCP) and β (BCC) phase present in the material. Various theories have been proposed in the literature to explain (i) the increase in creep strain with decreasing solution treatment temperature and (ii) the U-shaped variation of creep strain with cooling rate. Some of these theories are quite contradictory. An attempt is made here to systematically (a) evaluate and establish a direct microstructure–mechanical property correlation and (b) to explain the observed variation in the creep behaviour of a near-α titanium alloy IMI 834. The results obtained indicate that the observed U-shaped variation of creep curve is due to the counter acting nature of various microstructural features present in the material.

Microstructure and Precipitate Characteristics of Aluminum–Lithium Alloys

Abstract: This chapter reviews the precipitation and precipitate phases that occur during heat treatments in multi-component Al-Li based alloys. It describes aspects related to nucleation, growth, morphology and orientation relationships of the strengthening precipitates δ’ and T1, the toughening precipitate S’ and the recrystallisation-inhibiting precipitate β’. Equilibrium precipitate phases such as T2, which are deleterious to the mechanical and corrosion properties of the alloys, are also described. It is shown that careful alloy chemistry control, two-step homogenization and controlled stretching prior to ageing can be employed to improve the volume fraction and distribution of the precipitate phases. All these processing aspects are necessary to achieve optimum combinations of properties for the alloys.

Mechanical Properties Anisotropy of Cold-Rolled and Solution-Annealed Ni-Based Hastelloy C-276 Alloy

Abstract: This work describes a correlation among texture, in-plane anisotropy in tensile properties, and yield locus in Ni-based Hastelloy C-276 alloy. The alloy exhibits moderate values of in-plane anisotropy and anisotropy index, which has been attributed to the presence of moderate overall intensity of texture. The alloy displays two slopes in true plastic stress–strain curve and follows a Ludwigson relation. At low plastic strains, the sample displays the presence of annealing twins and less strain localization at grain boundaries, while the formation of deformation twins and high strain localization within the deformation twins and at the grain boundaries are observed in a high-strained region. The 45-deg and 67.5-deg orientation samples show relatively low ductility and low work-hardening exponent. This has been explained based on dislocation storage capacity and dynamic recovery coefficient using Kock–Mecking–Estrin analysis.

An in vitro analysis of H1N1 viral inhibition using polymer coated superparamagnetic Fe3O4 nanoparticles

Abstract: Monodispersed Fe3O4 nanoparticles were prepared by a polyol assisted solvothermal method and their activity against H1N1 influenza A virus was studied. The present study also elucidates the influence of size, shape and surface properties of the pristine, as well as polymer coated, magnetite nanoparticles. X-ray diffraction and Fourier transform infrared spectroscopic observations confirm the high crystallinity and the polymer attachment with the magnetite nanoparticles. Transmission electron microscopy (TEM) images confirm the monodispersed nanoprisms and flower like morphologies of the magnetite nanoparticles. The superparamagnetic behavior and other magnetic properties were also studied by measuring the hysteresis loop using a vibrating sample magnetometer. The cell viability studies of the magnetite nanoparticles using a standard MTT assay confirm the non-toxic nature of the samples. Reverse transcription polymerase chain reaction (RT-PCR) analysis confirms the Fe3O4 nanoparticles inhibit influenza viral RNA synthesis in MDCK cells.