摘要: Spinel zinc ferrite (ZnFe2O4) nanoparticles have engrossed immense attention due to its unusual amalgamation of its properties especially the magnetic properties and these properties are catered as fitting candidates in the field of electronics. Nanostructured spinel zinc ferrite particles were synthesized using scalable co-precipitation technique. The morphology, particle size and reaction pace of the nanoparticles (NPs) were fine tuned by eco-friendly technique. These NPs were characterized by UV-Visible spectroscopy (UV-Vis), photoluminescence (PL), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and Transmission electron microscopy (TEM), vibrating sample magnetometer ((VSM) and Dielectric studies. The required profiles were confirmed by XRD and FTIR spectra, UV-Vis, PL spectral studies. Further these measurements divulge the significance of optical properties and the spectral parameters are used to appraise the optical constants required for fabrication. Transmission electron microscopy eventually discloses the morphological analysis of the synthesized ZnFe2O4 nanoparticle as 15 nm within the scaling limitations. Using, VSM, the magnetic behaviour of the material have been determined as a function of magnetic field at ambient temperature; the magnetic measurements well-establishes the magnetic property and disclosed to have weak ferromagnetic behaviour as the crystallite size decreases. The A.C. conductivity measurements and dielectric studies were done as a functional dependence of frequency and temperature on synthesized nanoparticles.
摘要: Phase change material (PCM) based thermal energy storage systems (TES) are mandatoryto utilize solar energy efficiently and effectively. Paraffin is widely used phase change material and the only disadvantage with paraffin is that its poor thermal conductivity. The objective of the study is to increase the thermal conductivity of the PCM based TES. The thermal conductivity of the paraffin PCM blended with Al2O3 nanoparticle with different proportions was determined both experimentally and analytically for solid and liquid states. The different volume concentrations of Al2O3 nanoparticle blended with paraffin are 0.01, 0.02, 0.03, 0.04, 0.05 and 0.1. The charging and discharging characteristics of the thermal energy storage system was also determined for the above mentioned different volumetric concentrations of nanoparticles blended with paraffin using an experimental set up fabricated. It was found that, Al2O3 nanoparticle can be blended to maximum of 0.1% volume concentration with n-tricosane paraffin without any agglomeration. The significant improvement in thermal conductivity, charging & discharging characteristics of the thermal energy storage system was observed corresponding to this proportion of blending.
摘要: Zinc antimonate (ZnSb2O6) nanoparticles were prepared by an inexpensive chemical precipitation method and its structural properties were studied using X-ray diffraction (XRD). Further in electrochemical analysis, Nafion, a per-fluorinated sulfonic acid polymer solution that serves as a binder, wherein the hydrophilic sulfonic acid group provides proton-exchange between electrolyte and active electrode material thereby, it is beneficial in the improvement of the capacitance, chemical and mechanical stability of a material. Considering this key point, the significance of the nafion on the electrochemical characteristics of zinc antimonate nanoparticles were studied through cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis in 1 M H2SO4 electrolyte. The significant changes in the capacitance, electrochemical behavior and electrochemical stability of the nanostructure with and without the binder were investigated.
摘要: Analysis of major heat transfer mechanisms in nanofluids specifically, thermophoresis and diffusiophoresis under pool boiling condition is attempted in this paper. Basic approach of the study tries to correlate thermophoresis in nanofluids to the behavior of rigid particles in gases. Ultimate objective of the study is to elucidate the thermophoresis/diffusiophoresis mechanism in nanofluids using thermophoretic velocity and viscosity of nanofluids. Thermophoretic velocity of water-alumina nanofluid analyzed in this study is assumed to be inversely proportional to fluid viscosity. Experiments and Computational Fluid Dynamics (CFD) tool are used for analyzing the effects of thermophoresis and diffusiophoresis on the heat transfer enhancement process. The numerical model considered for the study is a (2-D) rectangular container with the dimensions of the experimental set-up and a stainless steel heater inside it. Energy equation constituent of ANSYS Fluent is solved using a pressure based implicit solver and appropriate boundary conditions to obtain the temperature distribution pattern of the model. SIMPLE is used as the pressure correction method with Gauss-Siedel iterative method. Numerical simulation results for temperature distribution are validated using experimental readings. Thermophoretic velocity outputs derived from numerical simulation show significant movement of nanoparticles very close to realistic values. However, numerical results of viscosity, specific heat and diffusion coefficient of nanofluids were found to deviate from the results of the experiments. The dependency effect of these parameters needs further attention.
摘要: Concrete is a very important composite for making different building structures to absorb different levels of radiation. Nuclear power plants, nuclear research reactors, particle accelerators and linear accelerator in medical institution use concrete in building construction. Nanoparticles or nanocrystals have different properties than their bulk counterparts. The gamma radiation absorption characteristics and beta back scattering by nanoparticles is also different than their counterparts. In this paper, carbon nanoparticles are mixed in the concrete composite during its preparation. The concrete composite with carbon nanoparticles as admixture were analyzed to provide radiation protection. The gamma radiation absorption characteristics and beta back scattering in ordinary and carbon nanoparticles contained concretes have been studied by GM counter. The results show that using carbon nanoparticles as an admixture in the concrete is one of the solutions for gamma ray shielding and beta back scattering. Therefore, it is good to use carbon nanoparticles as admixtures in concrete composites for beta and gamma radiation scattering and absorption respectively.
摘要: Yttrium iron garnet (YIG) powdered ceramic powders were synthesized as bulk quantity by traditional solid state synthesis method by the use of yttrium oxide and iron oxide powders. Finely grinded powders were then calcinated for various temperatures such as 900, 1200 oC for 3 hours and 1400oC for 6 hours respectively after making multiple grindings to obtain homogeneity. The calcinated powders were then subjected to phase purity by the use of powder X-ray analysis. As it is clear evident from the samples that the powdered samples were of single phase in nature and that it is clear evident from the nature of the sample which transforms to green in colour from the traditional red iron based oxides. The bonding nature was further ascertained by the used of Fourier transform infrared spectrometer (FTIR) analysis. Thermal stability and phase formation was confirmed through thermal analysis. The thermo-magnetization curve reveals the curie temperature of the sample which is in good agreemement with that of the reported values. Magnetization versus magnetic field curve was obtained which showed increase in magnetization due to the pure phase formation. These preliminary results suggest that the YIG powders could be made in to ceramic pellets for the use of tunable filters in the areas of microwave oscillators.
摘要: Heat transfer mechanisms and migration characteristics of volatile nanoparticles in a boiling fluid are complex phenomenon to understand. Boiling heat transfer mechanisms of the nanofluid (Al2O3/n-pentane) and migration characteristics of volatile Al2O3 nanoparticle are studied in this paper. Experiments were carried out using a sealed glass beaker partially filled with the nanofluid. Heat flux conditions and mass fractions of nanoparticles were varied to study the heat transfer mechanisms and migration characteristics of particles. Accuracy of experiments was checked using heat transfer correlations and repeated iterations. Also, in the present research, the solidification rate of pure water and water suspended with alumina nanoparticles is investigated to understand the freezing characteristics of nanofluids.
摘要: In view of the increase in demand of atomic energy and also dynamic increase in the number of space flights in our country, the limitation shown by developed countries on supply of hafnium metal for strategic applications has made our country to develop indigenously for its sustainability. The technology for the setting up of the hafnium pilot plant has been initiated by C-MET Hyderabad in collaboration with VSSC (ISRO) in order to compete with rest of the world. India has a good reserve of hafnium containing zircon sand where the hafnium containing zirconium is in the range of 1:50. A good quantity of zircon sand is available in mineral rich beach sands of India. Nuclear Fuel Complex, Hyderabad has commercial plant to produce nuclear grade zirconium for producing atomic energy. Zirconium scrub raffinate solution a by-product of NFC, Hyderabad containing decent amount of hafnium and zirconium is the raw material used for developing NIOBHAT 101 alloy such as niobium and hafnium for space grade applications and nuclear reactor control rods as the hafnium is having high neutron absorbing capacity. The major steps involved are separation of zirconium and purification of hafnium by solvent extraction, preparation of hafnium oxide, feed preparation and chlorination, reduction of hafnium chloride and separation of magnesium by vacuum distillation and sponge handling. In this regard Briquetting and Carbo-Chlorination processes are very vital because the reactivity of oxides depends on the calcination and coking conditions keeping a side precipitation conditions. The phase purity and chemical purity of hafnium chloride has immense influence on the following process namely, Kroll’s Reduction. This paper enumerates the experiments conducted in obtaining phase pure hafnium chloride. The data leading to optimised process parameters for the production of phase pure material has been presented.
摘要: Among several bimetallic nanoclusters, the compounds formed between Cu-Au have gained immense importance due to its remarkable optical, mechanical, electronic and catalytic behaviors. Density Functional Theory (DFT) is one of the most successful and popular approaches of quantum mechanics to explore electronic properties of materials. Conceptual DFT based descriptors have become indispensable tools for analyzing and correlating the experimental properties of compounds. In this venture, we have successfully investigated the physico-chemical properties of Au doped Cu nanoclusters invoking DFT methodology. Our results reveal that computed HOMO-LUMO gap of CunAu (n=1-7) nanoalloy clusters show pronounced even-odd alternation behavior. A close agreement between experimental and our computed data is observed.