R. Tewari

Induction heating studies of Fe3O4 magnetic nanoparticles capped with oleic acid and polyethylene glycol for hyperthermia

Fe3O4 magnetic nanoparticles (Fe3O4-MN) capped with either oleic acid (Fe3O4-OA-MN) or polyethylene glycol (Fe3O4-PEG-MN) were prepared by a co-precipitation method. From X-ray diffraction studies, the average crystallite sizes of Fe3O4-MN, Fe3O4-OA-MN and Fe3O4-PEG-MN were found to be 12, 6 and 8 nm, respectively. A reduction in the agglomeration of particles was observed when the magnetic nanoparticles (MN) were capped with oleic acid (OA) and polyethylene glycol (PEG), as confirmed by a transmission electron microscopy study. Magnetization of these MN was almost zero at room temperature in the absence of an applied magnetic field, indicating their superparamagnetic behavior. Magnetization was lower and the superparamagnetic fraction was higher for Fe3O4-OA-MN and Fe3O4-PEG-MN compared to Fe3O4-MN studied using a Mossbauer spectrometer. Compared to the control, an increased killing (35%) was observed in human breast cancer cells (MCF7) after Fe3O4-OA-MN treatment, which was further enhanced (65%) under induction heating conditions. However, MCF7 cells treated with Fe3O4-MN or Fe3O4-PEG-MN showed 5–10% killing after induction heating. These results showed the characterization of MN with different lipophilicity and suggests their suitability for hyperthermia applications in cancer therapy.

Luminescence, lifetime, and quantum yield studies of redispersible Eu3+-doped GdPO4 crystalline nanoneedles: Core-shell and concentration effects

Crystalline nanoneedles of Eu3+-doped GdPO4 and Eu3+-doped GdPO4 covered with GdPO4 shell (core shell) have been prepared at relatively low temperature of 150 °C in ethylene glycol medium. From luminescence study, asymmetric ratio of Eu3+ emission at 612 nm (electric dipole transition) to 592 nm (magnetic dipole transition) is found to be less than one. Maximum luminescence was observed from the nanoparticles with Eu3+ concentration of 5 at. %. For a fixed concentration of Eu3+ doping, there is an improvement in emission intensity for core-shell nanoparticles compared to that for core. This has been attributed to effective removal of surface inhomogeneities around Eu3+ ions present on the surface of core as well as the passivation of inevitable surface states, defects or capping ligand (ethylene glycol) of core nanoparticles by bonding to the shell. Lifetime for D50 level of Eu3+ was found to increase three times for core-shell nanoparticles compared to that for core confirming the more Eu3+ ions with sym...

Observation of intermediate bands in Eu3+ doped YPO4 host: Li+ ion effect and blue to pink light emitter

This article explores the tuning of blue to pink colour generation from Li+ ion co-doped YPO4:5Eu nanoparticles prepared by polyol method at ∼100-120 °C with ethylene glycol (EG) as a capping agent. Interaction of EG molecules capped on the surface of the nanoparticles and/or created oxygen vacancies induces formation of intermediate/mid gap bands in the host structure, which is supported by UV-Visible absorption data. Strong blue and pink colors can be observed in the cases of as-prepared and 500 °C annealed samples, respectively. Co-doping of Li+ enhances the emission intensities of intermediate band as well as Eu3+. On annealing as-prepared sample to 500 °C, the intermediate band emission intensity decreases, whereas Eu3+ emission intensity increases suggesting increase of extent of energy transfer from the intermediate band to Eu3+ on annealing. Emission intensity ratio of electric to magnetic dipole transitions of Eu3+ can be varied by changing excitation wavelength. The X-ray photoelectron spectrosc...

Luminescence study of Eu3+ doped GdVO4 nanoparticles: Concentration, particle size, and core/shell effects

Nanoparticles of GdVO4 doped with Eu3+ and core/shell of GdVO4:Eu3+/GdVO4 are prepared by urea hydrolysis method using ethylene glycol as capping agent as well as reaction medium at 130 °C. Unit cell volume increases when GdVO4 is doped with Eu3+ indicating the substitution of Gd3+ lattice sites by Eu3+. From luminescence study, it is confirmed that there is no particle size effect on emission positions of Eu3+. Optimum luminescence intensity is found to be in 5–10 at. % Eu3+. Above these concentrations, luminescence intensity decreases due to concentration quenching effect. There is an enhancement in luminescence intensity of core/shell nanoparticles. This has been attributed to the reduction in surface inhomogenities of Eu3+ surroundings by bonding to GdVO4 shell. The lifetime for D50 level increases with annealing and core/shell formation.

Explaining absence of texture development in cold rolled two-phase Zr–2.5 wt% Nb alloy

Abstract In the present study, two distinct starting microstructures of Zr–2.5 wt% Nb have been used: (1) single-phase α hcp martensitic structure; and (2) two-phase, 10% bcc β and rest hcp α, Widmanstatten structure. In the second case, two types of α were present—near grain boundary predominantly single-phase α (about 5% of the total α) and α plates in an apparently continuous β matrix. Both (1) and (2) had similar starting crystallographic texture of the hcp α phase and were deformed by unidirectional and cross rolling. In the two-phase structure the changes in the bulk texture on cold rolling was found to be insignificant, while in the single-phase material noticeable textural changes were observed. Taylor type deformation texture models predicted textural changes in single-phase structure but failed to predict the observed lack of textural development in the two-phase material. Microtexture observations showed that α plates remained approximately single crystalline after cold rolling, while the β matrix underwent significant orientational changes. Relative hardening, estimated by X-ray peak broadening, was observed mainly in β phase; while aspect ratio of α plates remained unchanged with cold rolling—indicating absence of effective macroscopic strain in the hcp α plates. Based on microstructural and microtextural observations, a simple model is proposed in which the plastic flow is mainly confined to the β matrix within which the α plates are subjected to ‘in-plane rigid body rotation’. The model explains the observed lack of textural developments in the two-phase structure.

Evolution of ordered ω phases in (Zr3Al)–Nb alloys

Abstract Microstructural investigations on rapidly solidified Zr3Al based alloys (binary Zr3Al and ternary Zr3Al–3Nb and Zr3Al–10Nb) have revealed some unusual phase transformation sequences. The Zr5Al3 phase (D88 structure) has been found to occur in both the rapidly solidified ternary alloys unlike in the rapidly solidified stoichiometric Zr3Al alloy in which the Zr2Al phase (B82 structure) has been found to be present. The evolution of the D88 phase, which could be regarded as one of the ordered derivatives of the ω phase, could be described in terms of a superimposition of replacive and displacive ordering waves in the β phase. The orientation relationship between the β and the D88 phases has been established. The microstructural changes occurring in the rapidly solidified Zr3Al–Nb alloys during aging have been examined. It has been found that on aging the D88 phase gets transformed into the B82 phase which, on continued aging, transforms to other metastable and equilibrium phases, depending upon the aging temperature. The observed sequence of phase transformations involving different structurally related phases has been along the direction of progressively close packed structures. The symmetry changes associated with the sequence of ω related transformations have been summarized in the form of a symmetry tree.

Metastability of the β-phase in Zr-rich Zr-Nb alloys

Abstract The decomposition of the β-phase in Zr-rich Zr-Nb alloys by three processes viz., ω formation, α-formation and hydride precipitation has been examined. In the Zr-20Nb alloy, ω-formation has been examined after thermal treatment as well as after electron irradiation and a comparison has been made between the kinetics of ω-phase formation under these two conditions. The morphology of the α-precipitates and their internal structures has been found to depend upon the type of thermal treatment with step quenching from the β-phase field leading to an allotriomorphic morphology and quenching and aging leading to internally twinned Widmanstatten α. The different morphologies obtained due to change in thermal treatment and composition of the Zr Nb alloys has been rationalized. Hydride formation has been examined in α-Zr, β-Zr and in α + β microstructures. A comparison has been made between the mechanism of formation of hydride phase in these three types of microstructures and their morphology and internal structures have been explained.

Synthesis of uniform gold nanoparticles using non-pathogenic bio-control agent: Evolution of morphology from nano-spheres to triangular nanoprisms

Green synthesis of gold nanospheres with uniform diameter and triangular nanoprisms with optically flat surface was carried out using a non-pathogenic bio-control agent Trichoderma asperellum for reduction of HAuCl(4). Kinetics of the reaction was monitored by UV-Vis absorption spectroscopy. No additional capping/complexing agent was used for stabilizing the gold nanoparticles. Evolution of morphology from pseudospherical nanoparticles to triangular nanoprisms was studied by transmission electron microscopy (TEM). It revealed that three or more pseudospheres fused to form nanoprisms of different shapes and sizes. Slow rate of reduction of HAuCl(4) by constituents of cell-free fungal extract was instrumental in producing such exotic morphologies. Isolation of gold nanotriangles from the reacting masses was achieved by differential centrifugation.

Surface chemistry of surfactant AOT-stabilized SnO2 nanoparticles and effect of temperature

SnO(2).xH(2)O nanoparticles were prepared at room temperature by the microemulsion route. Sodium bis(2-ethylhexyl) sulfosuccinate (AOT) was used as a surfactant to stabilize the nanoparticles. These nanoparticles show green luminescence at 510nm, which has been assigned to oxygen vacancies. Infrared spectra of samples heated in the temperature range 500-900 degrees C show bond formation between SnO(2) nanoparticles and SO(4)(2-), which arises from oxidation of SO(3)(-) present in AOT. This was further supported by X-ray diffraction. Shape transformations of the particles from triangular to spherical and then to rectangular was observed as the heat-treatment temperature was increased, and this is related to the surface energy of particles. An enhancement in emission intensity of Eu(3+) was observed when Eu(3+) ions were doped into the SnO(2) nanoparticles due to significant energy transfer from SnO(2) (or Eu-O) to Eu(3+) through surface-mediated energy transfer as compared to direct excitation of Eu(3+) at 397nm. Interestingly, these nanoparticles are dispersible in water, and can be incorporated into polymer-based materials such as polyvinyl alcohol to give homogeneous films, giving rise to blue and red emissions.

Glass formation in binary and ternary Zr based Fe and Ni bearing alloys

Rapid solidification of the Zr76Fe24−xNix alloys (x = 8, 12, 16, 20 and 24) by melt spinning under different conditions has yielded fully amorphous as well as partially crystalline ribbons. The partially crystalline ribbons have been found to contain crystal aggregates comprising a core of the β-Zr phase surrounded by peripheral crystals of the Zr3(Fe,Ni) phase in alloys with x < 12. In alloys containing larger amount of Ni (x ⩾ 12), both Zr2Ni and Zr3(Fe,Ni) crystals have been found to be present in the periphery. The nucleation of the core crystals and the peripheral crystals in the undercooled melt has been examined by considering transient and steady state homogeneous and heterogeneous nucleation. The transient nucleation time and the steady state nucleation rate of crystals have been evaluated. For this purpose, use has been made of molar free energy difference ΔGc between the liquid and the crystalline phases determined from experimentally evaluated quantities. The growth of the crystals in the undercooled melt has been examined taking into account recalescence and heat removal during melt spinning. The glass forming ability of the alloys has been evaluated on the basis of the avoidance of crystallization approach. A comparison has been made between the microstructures of the splat cooled and the melt spun alloys in order to understand the process of solidification and the nature of phase transformation during post solidification cooling.