Sajan D, George; Rajesh, K; Warrier, K G K; Radhakrishnan, P; Nampoori, V P N; Vallabhan, C P G(October 29, 2011)
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Abstract:
The laser induced non-destructive photoacoustic technique has been employed
to measure the thermal diffusivity of lanthanum phosphate ceramics prepared
by the sol–gel route. The thermal diffusivity value was evaluated by knowing
the transition frequency between the thermally thin to thermally thick region
from the log–log plot of photoacoustic amplitude versus chopping frequency.
Analysis of the data was carried out on the basis of the one-dimensional
model of Rosencwaig and Gersho. The present investigation reveals that the
sintering temperature has great influence on the propagation of heat carriers
and hence on the thermal diffusivity value. The results were interpreted
in terms of variations in porosity with sintering temperature as well as with
changes in grain size.
The catalytic activity of some of the ABO3 (A = La, Pr
and Sm, B= Cr, Mn, Fe, Co and Ni) perovskite-type oxides
for the liquid phase reduction of ketone and oxidation of
alcohol in 2-propanol medium has been studied. The data
have been correlated with the surface electron donor
properties of these oxides. The surface electron donor
properties have been determined from the adsorption of
electron acceptors of varying electron affinities on the
oxide surface.
Geetha K, Varier; Harilal, S S; Bindhu, C V; Riju C, Issac; Nampoori, V P N; Vallabhan, C P G(December 3, 2011)
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Abstract:
Irradiation of a Polymethyl methacrylate target using a pulsed Nd-YAG laser causes plasma formation in the vicinity of the target. The refractive index gradient due to the presence of the plasma is probed using phase-shift detection technique. The phase-shift technique is a simple but sensitive technique for the determination of laser ablation threshold of solids. The number density of laser generated plasma above the ablation threshold from Polymethyl methacrylate is calculated as a function of laser fluence. The number density varies from 2×1016 cm-3 to 2×1017 cm-3 in the fluence interval 2.8-13 J · cm-2.