R.R. Yadav

Growth morphologies, phase formation, optical & biological responses of nanostructures of CuO and their application as cooling fluid in high energy density devices

Different nanoscale objects of CuO have been synthesized by a simple chemical route where the Cu(OH)2 nanostructures were first synthesized by the alkaline hydrolysis of Cu(NO3)2·3H2O using NaOH as a base and the synthesized precipitate was subsequently annealed at a temperature of 130 °C. The alkaline content (pH) of the solutions during the hydrolysis process was varied to tailor the morphologies and dimensions of the nanostructures, consequently a series of fascinatingly shaped nanostructures, e.g. seeds, ellipsoidal, rods and leaves were obtained. Topographical characteristics along with the mechanism behind the structural variation have been rationalized by XRD, FTIR, SEM and HRTEM investigations. Optical performance of these samples provided simultaneous emission in the visible bands of blue, green, yellow and red, which were correlated to the size, shape and structural defects of these nano-scaled objects. The toxicity of these nanostructured materials were also put into perspective and it was found that the leaf shaped particles were the most toxic among the various shapes of nano-CuO. Finally the synthesized particles, when applied as nanofluids (water medium) showed their ability to enhance the thermal conductivity of water to a noticeable degree (above 40%) at high temperatures, even at very small concentrations, bespeaking their applicability in cooling fluids.

Ultrasonic properties of nanoparticles-liquid suspensions ☆

A polymer colloidal solution having dispersed nanoparticles of Cu and Au metals have been developed using a novel chemical method. Average size of the nanoparticles could be varied in the 4-10 nm range by conducting the reaction at an elevated temperature of 50-70 degrees C. Colloidal solutions of representative concentrations of 0.1-2.0 wt% Cu/Au contents in the primary solutions are used to study the modified ultrasonic attenuation and ultrasonic velocity in PVA polymer molecules on incorporating the Cu/Au particles. A characteristic behaviour of the ultrasonic velocity and the attenuation are observed at the particular temperature/particle concentration. The results demonstrate that the primary reaction during the nanoparticles-PVA colloidal formation occurs in divided groups in small micelles. The results are analyzed predicting the enhanced thermal conductivity of the samples.

NiO-based nanostructures with efficient optical and electrochemical properties for high-performance nanofluids

NiO nanostructures were synthesized via a simple wet chemical solution method with varying calcination temperatures. The synthesized nanostructures were characterized by XRD, TG/DSC, FT-IR and high-resolution electron microscopy techniques. The nanostructures revealed dependence of particle size, stoichiometry, optical band gap and luminescence intensity on calcination temperatures. The materials exhibited efficient electrochemical properties with decent capacitance values. Ethylene-glycol-based nanofluids of these nanoparticles registered excellent thermal conductivity enhancement of 59-69% in the room temperature region and 125% enhancement at higher temperatures (80 ° C), establishing NiO to be a top-draw contender for high-performance heat transfer fluids.

Elastic and Acoustic Properties of Heavy Rare-Earth Metals

In this paper, ultrasonic properties like ultrasonic attenuation, sound velocities, acoustic coupling constants and thermal relaxation time have been studied in hexagonal structured metals Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er) and Thulium (Tm) along unique axis at room temperature. For the evaluations of ultrasonic properties, secondand thirdorder elastic constants have been computed also. The peculiar behavior of these metals is found at 55° due their least thermal relaxation time and highest Debye average velocity. Dy is more ductile, stable, perfect metal in comparison to other chosen metals due to its lowest value of attenuation. So we predict that Dy is most suitable lanthanide metals for material science and engineering.

Ultrasonic Attenuation in Lanthanum Monochalcogenides

Ultrasonic attenuation due to phonon-phonon interaction and thermoelastic relaxation are studied in Lanthanum Monochalcogenides in direction at different higher temperatures. For evaluation of ultrasonic absorption coefficients the second and third order elastic constants (SOEC) and (TOEC) are also calculated. Shear wave attenuation shows maximum along propagation direction with polarized along and the attenuation increases at higher temperatures. Thermo-elastic loss is very small compared to phonon-viscosity loss. Behavior of temperature dependence of the absorption is the same as in case of pure metals and dielectric crystals.

An ultrasonic characterization of ferrofluid.

Nanoparticles of Cr(2)O(3) are prepared through hydrothermal synthesis process using CrO(3)/PVA in aqueous solution using sucrose as a reducing agent. The calcination temperature is taken 300 and 350 degrees C. XRD and SEM of the powdered Cr(2)O(3) particles are done for the characterization. The average particle size is found 30-80 nm. It is found that average particle size increases with calcination temperature. The UV-visible absorption spectra are taken for the study of photo-physical properties of ferrofluids. Ultrasonic velocity and absorption measurements are performed in Cr(2)O(3) ferrofluid using variable path interferometer and pulse-echo techniques, respectively. The achieved results are discussed in correlation with the magnetic and other physical properties of Cr(2)O(3).

Effect of thermal conductivity on ultrasonic attenuation in praseodymium monochalcogenides

The ultrasonic attenuation in intermetallic praseodymium monochalcogenides are evaluated in the temperature interval 100–500 K along the crystallographic directions 〈100〉, 〈110〉, and 〈111〉 for longitudinal and shear waves. A comparison has been made with lanthanum monochalcogenides and other similar materials. Ultrasonic attenuation at different temperatures is mainly affected by the lattice thermal conductivity values of the materials at these temperatures. Thermoelastic loss is very small in comparison to the attenuation due to phonon-phonon interaction mechanism at higher temperatures.

Behaviour of ultrasonic attenuation in intermetallics

Abstract Ultrasonic absorption due to electron-phonon interaction has been calculated in the intermetallic compounds in low temperature region between 2 K and 80 K. The resistivity of the substances is very large as compared to metals. Ultrasonic attenuation due to electron-phonon interaction is very small as compared to metals and the temperature dependence of attenuation is of the same nature as in common metals, except for some anomalous kinks.

CuO nanoellipsoids for superior physicochemical response of biodegradable PVA

PVA nanocomposites comprising of nanoparticles of CuO were prepared and their various physicochemical properties were evaluated. CuO with its impressive array of mechanical, optical, dielectric and hydrophilic properties as well as environmental friendliness is expected to augment the properties of the PVA matrix. The strong interaction between the polymer matrix and the nanofillers was confirmed via XRD and FT-IR investigations. The thermal stability and the mechanical strength of the polymer membranes indeed showed notable improvements in the composites. Thermal conductivity also increased to an extent beyond the theoretical prediction. The dielectric constant of the nanocomposite film was about 2 times higher than that of the pure PVA membrane. The high optical transparency of the PVA membrane also was not compromised with the inclusion of nanosized CuO particles.

A study of ZnO nanoparticles and ZnO-EG nanofluid

This study deals with the synthesis and characterisation of ZnO nanoparticles and suspension of ZnO-ethylene glycol (EG) nanofluid. Crystalline ZnO nanoparticles are synthesised using the chemical method. The nanofluids were synthesised by the dispersion of ZnO nanoparticles in EG solution using an ultrasonicator. The prepared ZnO nanoparticles are characterised by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and UV-Vis absorption spectrum. The particle size distribution and ultrasonic parameters of the synthesised nanofluid are measured with the help of acoustic particle sizer (APS-100) and ultrasonic interferometer. The observed features of ZnO nanoparticles and ZnO-EG nanofluids are discussed in correlation with known properties of other nanofluids.