Mohammed Shahabuddin

CNTs grown on nanoporous carbon from zeolitic imidazolate frameworks for supercapacitors.

Carbon nanotubes (CNT) grown on nanoporous carbon (NPC), which yields coexisting amorphous and graphitic nanoarchitectures, have been prepared on a large scale from zeolitic imidazolate framework (ZIF) by introducing bimetallic ions (Co2+ and Zn2+). Interestingly, the hybrid Co/Zn-ZIF-derived NPC showed rich graphitic CNTs on the surface. This NPC was utilized for a coin-type supercapacitor cell with an aqueous electrolyte, which showed enhanced retention at high current density and good stability over 10 000 cycles.

Enhanced magnetization of sol-gel synthesized Pb-doped strontium hexaferrites nanocrystallites at low temperature

Effect of Pb doping on the structural and low temperature magnetic properties of SrPbxFe12-xO19 (x = 0, 0.1, 0.2, 0.3, and 0.4), synthesized by sol-gel autocombustion technique, has been investigated. The powder samples were sintered at 800°C for 2 h in order to develop the stable hexagonal phase, characteristic of the SrFe12O19 structure. The consequences of Pb substitution (at iron sites) on various structural parameters like lattice constants, unit cell volume, crystallite size, and porosity have been discussed. Fourier transform infrared frequency bands were utilized to determine the formation of tetrahedral and octahedral clusters of M-type ferrites. Hexagonal texture of the grains, a characteristic of the hexagonal crystal structure of SrFe12O19, was refined by Pb substitution. The magnetic properties, determined using a vibrating sample magnetometer, revealed that saturation magnetization decreased, while coercivity was increased with the increase of Pb contents. However, the increased squareness ratio and hence the energy product motivate the utilization of these ferrite compositions where hard magnetic characteristics are required.The increased values of saturation magnetization were observed at reduced temperature of 200 K, attributable to the better spin alignments of individual magnetic moments at low temperature.

The effect of nano-alumina on structural and magnetic properties of MgB2 superconductors

Nano-Al2O3 doped Mg1?xAlxB2 with 0?x?6% were synthesized by solid state reaction at 750??C in Fe tube encapsulation under a vacuum of 10?5?Torr. Resistance measurement shows that the Tc decreases with x and zero resistivity for x = 0 and 6% are obtained at 38 and 35?K, respectively. XRD measurement shows that the lattice parameter and cell volume also decrease monotonically with increasing doping levels. From this we infer that the Al has been substituted in the lattice of MgB2 at Mg sites. Resistivity measurement shows a systematic decrease in Tc with doping which also confirms the substitution of Al. Magnetization studies in the temperature range from 4 to 35?K and in the magnetic field up to 9?T shows a significant increase in the irreversibility field (Hirr), critical current density (Jc) and remanent magnetization (MR) with increasing concentration of the Al2O3 nanoparticle. At low fields we have observed large vortex instabilities (known as a vortex avalanche) associated with all doped samples. The vortex-avalanche effect is reduced with increasing temperature and vanishes near 20?K. The results are discussed in terms of local-vortex instabilities caused by doping of Al2O3 nanoparticles.

Strategic synthesis of mesoporous Pt-on-Pd bimetallic spheres templated from a polymeric micelle assembly

Core–shell–corona type triblock copolymer poly(styrene-b-2-vinylpyridine-b-ethylene oxide) (PS-b-P2VP-b-PEO) micelles have been selected here to direct the synthesis of mesoporous Pt-on-Pd spheres, consisting of a Pd concentrated core and a Pt shell, as established by elemental mapping. It is important to note that the size of the PS core determines the resultant size of the mesopores. A self-evaporation method has been developed to prepare swollen micelles, so as to further enlarge the pore size (∼40 nm). Compared with commercially available catalysts (e.g., Pt black or Pt, 20 wt% on carbon black), good oxygen reduction reaction performance on the mesoporous Pt-on-Pd spheres is observed, due to the exposure of the most active Pt (111) planes and the synergistic effects from Pt and Pd in the pseudo core–shell structure.

Evaluation of persistent-mode operation in a superconducting MgB2 coil in solid nitrogen

We report the fabrication of a magnesium diboride (MgB2) coil and evaluate its persistent-mode operation in a system cooled by a cryocooler with solid nitrogen (SN2) as a cooling medium. The main purpose of SN2 was to increase enthalpy of the cold mass. For this work, an in situ processed carbon-doped MgB2 wire was used. The coil was wound on a stainless steel former in a single layer (22 turns), with an inner diameter of 109 mm and height of 20 mm without any insulation. The two ends of the coil were then joined to make a persistent-current switch to obtain the persistent-current mode. After a heat treatment, the whole coil was installed in the SN2 chamber. During operation, the resultant total circuit resistance was estimated to be <7.4 × 10−14 Ω at 19.5 K ± 1.5 K, which meets the technical requirement for magnetic resonance imaging application.

Synthesis and Cytotoxicity of Dendritic Platinum Nanoparticles with HEK‐293 Cells

Dendritic platinum nanoparticles (DPNs) have been synthesized from l-ascorbic acid and an amphiphilic non-ionic surfactant (Brij-58) via a sonochemical method. The particle size and shape of the DPNs could be tuned by changing the reduction temperature, resulting in a uniform DPN with a size of 23 nm or 60 nm. The facets of DPNs have been studied by high-resolution transmission electron microscopy. The cytotoxicity of DPNs has been investigated using human embryonic kidney cells (HEK-293), and the biological adaptability exhibited by DPNs has opened a pathway to biomedical applications such as drug-delivery systems, photothermal treatment, and biosensors.

Giant energy harvesting potential in (100)-oriented 0.68PbMg1/3Nb2/3O3–0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer and (001)-oriented 0.67PbMg1/3Nb2/3O3–0.33PbTiO3 thin films

This work emphasis on the competence of (100)-oriented PMN–PT buffer layered (0.68PbMg1/3Nb2/3O3–0.32PbTiO3 with Pb(Zr0.3Ti0.7)O3/PbOx buffer layer) and (001)-oriented PMN–PT (0.67PbMg1/3Nb2/3O3–0.33PbTiO3) for low grade thermal energy harvesting using Olsen cycle. Our analysis (based on well-reported experiments in literature) reveals that these films show colossal energy harnessing possibility. Both the films are found to have maximum harnessable energy densities (PMN–PT buffer layered: 8 MJ/m3; PMN–PT: 6.5 MJ/m3) in identical ambient conditions of 30–150°C and 0–600 kV/cm. This energy harnessing plausibility is found to be nearly five times higher than the previously reported values to date.

Microstructural and crystallographic imperfections of MgB2 superconducting wire and their correlation with the critical current density

A comprehensive study of the effects of structural imperfections in MgB2 superconducting wire has been conducted. As the sintering temperature becomes lower, the structural imperfections of the MgB2 material are increased, as reflected by detailed X-ray refinement and the normal state resistivity. The crystalline imperfections, caused by lattice disorder, directly affect the impurity scattering between the π and σ bands of MgB2, resulting in a larger upper critical field. In addition, low sintering temperature keeps the grain size small, which leads to a strong enhancement of pinning, and thereby, enhanced critical current density. Owing to both the impurity scattering and the grain boundary pinning, the critical current density, irreversibility field, and upper critical field are enhanced. Residual voids or porosities obviously remain in the MgB2, however, even at low sintering temperature, and thus block current transport paths.

A new approach to a superconducting joining process for carbon-doped MgB2 conductor

We report a new approach to a superconducting joining process for unreacted in situ carbon (C)-doped magnesium diboride (MgB2) wires. To operate a magnetic resonance imaging (MRI) magnet in the persistent mode, the superconducting joints between two conductors are as critical as the other key components. In addition, a stable and reliable joining process enables the superconducting magnet to operate without an external power supply. However, joint results using unreacted in situ C-doped MgB2 wires, which are used for high-field operation, have been limited, and only very poor performance has been obtained. By controlling the pressure inside a joint part, in this study, we successfully obtained current carrying retention in the joint of up to 72% compared to wire without a joint. The closed-circuit resistance of our closed-loop coil was less than 1.8 × 10−13 Ω at 16.7 ± 4.7 K, as measured by the field-decay measurement method. These results indicate that MgB2 has a promising future in MRI application.

Application Oriented Selection of Optimal Sintering Temperature from User Perspective: A Study on K0.5Na0.5NbO3 Ceramics

This work presents a novel user oriented approach that can relate materials science with technological applications in a more transparent, systematic and efficient manner. We have made an attempt to figure out the optimal (corresponding to best combination of material properties) sintering temperature of K0.5Na0.5NbO3 (KNN) for transducer and electrical energy storage applications. The weights and priority of vital physical properties for applications understudy are calculated using the quality function deployment (QFD) method. Losses (tanδ), charge storage properties (ϵr, Pr and EC) and elastic compliance (sE12 and sE11) are found to have negative priority for transducer application while in the other case d31, tanδ, sE12 and sE11 are spotted to have negative priority. Priority order for transducer and energy storage application is d31>kp>QM>Tc>tanδ>ϵr>Pr=EC=sE12=sE11>ρ and ϵr>d31=tanδ>sE12=sE11>Tc>Pr>EC>kp>ρ>QM, respectively. Finally, 1080°C (transducer) and 1120°C (capacitor) are the found to be the most appropriate solutions among the alternatives under using modified analytic hierarchy process (AHP).