Giridhar Mishra

Study of Copper/Palladium Nanoclusters Using Acoustic Particle Sizer

Department of Physics, University of Allahabad, Allahabad-211002, India In the present study polyvinylpyrrolidone (PVP) stabilised copper/palladium bimetallic nanoclusters were synthesised through chemical routes. The prepared Cu/Pd bimetallic nanoparticles were characterised by ultraviolet-visible (UV-vis) spectroscopy, X-ray diffraction (XRD) and transmission electron microscopy (TEM). The UV-vis absorbance band confi rmed the formation of complex metal ions triggered by the complexing agent trisodium citrate. The XRD pattern indicated the formation of bimetallic nanoparticles. The TEM images of the synthesised bimetallic Cu/Pd nanoparticles showed that the size distribution of the particles was in the range 5–15 nm. An acoustic particle sizer was then used to analyse the size distribution. The results obtained by the acoustic particle sizer were consistent with the XRD and TEM analyses. These results demonstrate the potential usefulness of the acoustic particle sizer for quick and easy characterisation of nanoparticles in various catalytic, sensor and fuel cell applications.

Temperature Dependent Heat Transfer Performance of Multi-walled Carbon Nanotube-based Aqueous Nanofluids at Very Low Particle Loadings

Aqueous suspensions of multi-walled carbon nanotubes (MWCNTs + deionised water) have been synthesised. Carbon nanotubes (CNTs) were derived by chemical vapour deposition (CVD). Transmission electron microscopy (TEM) measurements show the formation of MWCNTs. Three samples of CNT-based aqueous nanofluids having MWCNT concentrations of 0.01 vol%, 0.03 vol% and 0.05 vol% were prepared with the help of ultrasonic irradiation. A very small amount of sodium dodecyl sulfate (SDS) was used as a surfactant to minimise the agglomeration of the MWCNTs. An effective enhancement in thermal conductivity was observed at different temperatures. The obtained results are explained with percolation theory.

Temperature Dependence of Elastic and Ultrasonic Properties of Sodium Borohydride

We present the temperature dependent elastic and ultrasonic properties of sodium borohydride. The second and third order elastic constants of NaBH4 have been computed in the temperature range 0-300K using Coulomb and Born-Mayer potentials. The sodium borohydride crystallizes into NaCl-type structure. The computed values of second order elastic constants have been applied to evaluate the temperature dependent mechanical properties such as bulk modulus, shear modulus, tetragonal modulus, Poisson’s ratio and Zener anisotropy factor and ultrasonic velocity to predict futuristic information about sodium borohydride. The fracture to toughness ratio (bulk modulus/shear modulus) in sodium borohydride varied from 1.91 to 1.62, which shows its behavioral change from ductile to brittle on increasing the temperature. Then, ultrasonic Grüneisen parameters have been computed with the use of elastic constants in the temperature regime 100300K. The obtained results have been discussed in correlation with available experimental and theoretical results.