Anjan Sil

Cost effective urea combustion derived mesoporous-Li2MnSiO4 as a novel material for supercapacitors

Mesoporous-Li2MnSiO4 (LMS) having a surface area of 35 (±2) m2 g−1 is produced using a very simple, fast and cost effective urea combustion method for the first time and characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy and surface area analysis. Li2MnSiO4 is crystallized in the orthorhombic phase with space group – Pmn21. The lattice parameters: a = 6.317(10) A, b = 5.385(9) A, c = 4.988(8) A are calculated by the Rietveld method. The urea combustion derived LMS is found to be thermally stable till 600 °C in air and thereafter disintegrates into Li2SiO3 (orthorhombic) and MnO2 (cubic). The presence of a homogeneous mesoporous (<20 nm) framework with a high surface area shows orthorhombic Li2MnSiO4 to be promising as a novel supercapacitor electrode as it delivers a specific capacitance of 175 (±5) F g−1 at 3 mV s−1 in 2 M KOH solution. The supercapacitive performance was further examined by galvanostatic charge–discharge cycling and complimented by electrochemical impedance spectroscopy.

Estimation of dispenser cathode surface temperature of a practical potted heater cathode assembly

The heat transfer through the porous and/or infiltrated potted heater-cathode structure is simulated by a numerical model. The model includes heat conduction through a porous potting having isometric pore shape and uniform size (310 mu m in alumina potting and 20 mu m in tungsten cathode pellet), imperfect interface heat transfer effect and radiative boundaries. In addition to the transient study, a steady-state analysis, using the numerical model has also been done for a commercial Spectra-Mat cathode. The predicted results have been compared with the experimental measurements and are found to be in good agreement. >

Phase Stability and Charge Capacity of Cubic Spinel in Li1 + δ Mn2 − δ O4 and Consequence of Magnesium Doping

The X-ray diffraction analysis of Li 1+δ Mn 2-δ O 4 having 8 = 0.00, 0.03, 0.06, 0.12, 0.18, 0.24, 0.33, 0.42, and 0.50 powders, synthesized by a sol-gel process, shows that a single-phase cubic spinel structure is stable only when δ ≤ 0.24. When lithium content increases to 8 > 0.24, the percentage of monoclinic Li 2 MnO 3 increases until 8 = 0.42 and saturates thereafter. On magnesium doping, the range of stability of cubic spinel Li 1+δ Mn 2-δ-0.1 Mg 0.1 O 4 decreases to δ ≤ 0.18, and monoclinic Li 2 MnO 3 starts to appear when 8 > 0.18. In magnesium-doped Li 1+δ Mn 1.9-δ-0.1 Mg 0.1 O 4 , the ion Mg 2+ goes to octahedral sites and decreases the population of Mn 3+ in the 16d octahedral sites, and so the lattice parameter of the magnesium-doped cubic spinel for the same 8 is lower than that for undoped Li 1+δ Mn 2-δ O 4 , However, at higher 8, the population of Mn 3+ may get totally exhausted and the charge balance may be maintained by the creation of defects. The voltage step appearing in the discharge curve has been attributed to a transition from two cubic phases to one cubic phase. With increasing 8, the size of the step decreases and becomes broader. However, this voltage step does not appear to be affected by magnesium doping.

Imperfect boundaries: thermal response of the cathode surface of a potted heater-cathode assembly

Abstract This paper extends the thermal analysis of the potted heater-cathode assembly described in our earlier paper [1] to show the effect of non-ideal interfaces formed during fabrication of the potted structure. The present analysis also accounts for the variable thermo-physical properties of the various materials used. The results of steady- and transient-state analyses are presented for some typical values of the interface heat transfer coefficient. Our results reaffirm the superiority of the pancake heater performance when considered for thermal response to the cathode surface but in the case where uniformity of surface temperature is desired, a helical heater is still preferred even in the situation of nonideal interfaces. Co-axial heat shield calculation with reference to the Spectra-Mat 600 ion source design has also been modified by taking into account the possible imperfections at the respective interfaces.

Thermal analysis of a cathode: temperature distribution and warm-up time

Abstract This paper gives a theoretical estimate of the cathode temperature distribution at the surface and the warm-up time. Several cases of practical interest have been studied from the thermodynamic considerations using the software specially developed for this application. The software is in two parts, viz., the steady-state analysis which gives the cathode surface temperatures and the transient analysis which yields the warm-up time. Temperature-dependent thermal conductivity, specific heat, density, and emissivity have been used in the transient analysis which improves the accuracy. Scaling laws for the determination of cathode surface temperature have been devised to cater for various sizes of cathodes used in industry. Not reported so far, our results show that a pancake-heater configuration has a better thermal response but a non-uniform cathode surface temperature profile whereas the conventional helical-heater configuration has a relatively poor thermal response but a more uniform temperature profile on the cathode. This aspect gets amplified and is very revealing at larger cathode dimensions.

Improved electrochemical performance of Li4Ti5O12 by reducing rutile TiO2 phase impurity and particle size

Pure lithium titanate (Li4Ti5O12) powder having particle size of 100 (±38) nm has been prepared by solid-state synthesis method, using planetary ball milling at lower speed of 900 rpm as compared to high energy ball milling (3000 rpm) and characterized by X-ray diffractometer, field emission scanning electron microscopy and thermogravimetric analysis. Electrochemical performance of Li-ion battery cells is determined by charging–discharging and cyclic voltammetry tests. The material has shown very high discharge capacity of 171 and 108 mAhg−1 measured at current rates of 0.1C and 5C, respectively, as compared to 160 and 71 mAhg−1 for impure Li4Ti5O12 material (containing rutile phase of TiO2) having particle size 213 (±45) nm. Capacity retention of pure Li4Ti5O12 was 91% after 100 cycles, whereas the impure Li4Ti5O12 has shown the retention ability of 85%.

Wear of Plasma Sprayed Conventional and Nanostructured Al2O3 and Cr2O3, Based Coatings

An ever increasing demand for high-performance ceramic coatings has made it inevitable for developing techniques with precise control over the process parameters to enable the fabrication of coatings with the desired microstructure and improved structural properties. The literature on plasma sprayed nanostructured ceramic coatings such as of Al2O3, Cr2O3, and their composites obtained using reconstituted nano sized ceramic powders has been reviewed in this study. Ceramic coatings due to their enhanced properties are on the verge of replacing conventional ceramic coatings used for various applications like automotive systems, boiler components, power generation equipment, chemical process equipment, aircraft engines, pulp and paper processing equipment, land-based and marine engine components, turbine blades etc. In such cases, the advantage is greater longevity and reliability for realizing the improved performance of ceramic coatings. It has been observed that the plasma sprayed nanostructured ceramic coatings show improvement in resistance to wear, erosion, corrosion, and mechanical properties as compared to their conventional counterparts. This article reviews various aspects concerning the plasma sprayed ceramic coatings such as (i) the present understanding of formation of plasma-spray coatings and factors affecting them, (ii) wear performance of nanostructured Al2O3, Cr2O3 and their composite ceramic coatings in comparison to their conventional counterparts, and (iii) mechanisms of wear observed for these coatings under various conditions of testing.

Characterization of Plasticized PMMA-LiClO4 Solid Polymer Electrolytes

In the present work, the effect of Li salt i.e. LiClO4 contained in composite plasticizer (PC+DEC) with three different concentrations on ionic transport and other electrochemical properties of PMMA based gel polymer electrolytes synthesized has been investigated. The electrolytes have been synthesized by solution casting technique by varying the wt (%) of salt and plasticizer. The formation of polymer-salt complexes and their structural characterization have been carried out by FTIR spectroscopic and XRD analyses. The room temperature ionic conductivity of the electrolyte composition 0.6PMMA-0.125(PC+DEC)-0.15LiClO4 (wt %) has been found to be maximum whose magnitude is 0.40×10-5 S/cm as determined by ac impedance analysis. The temperature dependent ionic conductivity of electrolyte sample0.6PMMA-0.125(PC+DEC)-0.15LiClO4 has further been investigated. Thermal analyses of electrolyte samples of all three compositions have also been done.

Chemical nature of catalysts of oxide nanoparticles in environment prevailing during growth of carbon nanostructures by CCVD

Carbon nanostructures (CNS) are often grown using oxide nanoparticles as catalyst in chemical vapour deposition and these oxides are not expected to survive as such during growth. In the present study, the catalysts of cobalt- and nickel oxide-based nanoparticles of sizes varying over a range have been reduced at 575°C under environment resulting from the introduction of C2H2 + NH3 during growth of CNS as well as under introduction of C2H2 and NH3 separately. The structure of the reduced nanoparticles is often different from the equilibrium structure of the bulk. Nanoparticles of cobalt oxide with and without doping by copper oxide are reduced to cobalt alloy or cobalt nanoparticles having fcc structure, but the rate of reduction is relatively less in NH3 environment. However, reduced nickel oxide nanoparticles with and without doping shows a mix of fcc and hcp phases. The presence of hydrogen and nitrogen in the environment appears to discourage the formation of hcp nickel as inferred from the results in NH3 environment. Cobalt carbide forms when the 10 wt.% or less doped cobalt oxide is reduced in C2H2 + NH3 environment. At higher level of doping of 20 wt.%, separate metallic phase of copper appears and carbide formation gets suppressed.

Synthesis and Characterization of LiMn2O4 Nanoparticles Using Citric Acid as Chelating Agent

Nanocrystalline LiMn2O4 powder was synthesized by sol-gel method using citric acid as a chelating agent. The powders were characterized by X-ray diffraction (XRD), Field emission scanning electron microscopy (FESEM), Differential scanning calorimetry (DSC), Differential thermal analysis (DTA), Impedance spectroscopy (IS) and Electrochemical measurements. The powder particles having slight agglomeration characteristics were found to have prismatic morphology and a wider size distribution from 50 nm to 200 nm, which provides good packing density of the material. The electrical conductivity of the powder at room temperature is in the order of ~10-5 S/cm. The structural stability of LiMn2O4 cubic spinel over the temperature range of battery operation was assessed. Electrochemical performance of the material shows a discharge capacity of ~130 mAh/gm.