Defect and Diffusion Forum Vols. 319-320

Abstract: Copper-based microcomposites fabricated by powder metallurgy with subsequent plastic deformation have received increasing attention over recent years. These microcomposites possess good electrical conductivity in combination with high mechanical properties. The present study aims to explore potential technical merits in developing a prealloyed powder metallurgy copper based composites with silica sand nanoparticles reinforcement. Relevant mechanical properties and electrical conductivity improvements are the main targets. A copper based composite with 5, 10, 15 and 20 wt.% of silica sand nanoparticles were developed through the powder metallurgy process. It was observed that by addition of silica sand nanoparticles with 20% increased the hardness up to 143HV. Optimum electrical conductivity of the composites was achieved in the 15 wt.% silica sand nanoparticles. Advanced particle rearrangement mechanism due to homogeneous and fine distribution of silica sand nanoparticles into pore sites of the composites was also observed. The silica sand nanoparticles composites properties that are much more surface-related seen to be improved convincingly compared with the bulk controlled.

Abstract: The diffusion processes taking place in heterogeneous catalytic systems have been discussed. Various diffusion mechanisms such as Knudsen diffusion, molecular diffusion, configurational diffusion and surface diffusion sensitivity in catalytic systems were investigated. The concentration gradients inside the catalyst pellet were obtained for various Thiele modulus. The Knudsen number was calculated and discussed for large and small pores. The transitional diffusion coefficient was determined for diethylbenzene. The experimental pore size distribution carves for an industrial and synthesized catalyst was obtained and the effect of pore size distribution on diffusion coefficient was discussed.

Abstract: An attempt has been made in this paper to findout the trainsent temperature distribution on the welded plates through analytical as well as numerical method considering double elliptic paraboloid moving heat source volume.It has been assumed that heat is distributed through gaussian manner on the welded plates and modes of heat transfer for welded plates are conduction as well as convection.With the help of these solutions dimnesions of weld bead geometry,HAZ width and thermal stress have been predicted and validated with the experimental data.

Abstract: The determination of the temperature distribution of submerged arc-welded plates is essential when designing submerged arc-welded joints. The key role for the change of weld-bead geometry dimension, thermal stress, residual stress, tensile stress, hardness, etc., is heat input. Heat input is the function of temperature distribution of submerged arc welded plates. An attempt is made in this paper to find the analytical solution for a moving heat-source of egg-shape in a semi-infinite body. The considered modes of heat transfer for this study are conduction and convection. The solution has been obtained by integrating the instantaneous point heat source throughout the heat source volume. Very good agreement between the predicted and measured transient temperatures at various points on submerged arc-welded plates has been obtained. The predicted yield parameters are also in good agreement with the measured values.

Abstract: Positron annihilation techniques (PAT) have recently been successfully employed for the characterization of phase transitions in metals and compounds. In the present study, positron annihilation lifetime (PAL) measurements have been carried out on a nanocrystalline titania (TiO2) in the form of powders that had been heat-treated at temperatures ranging from 300 to 1273K. The PAL spectra were analyzed into two lifetime components. The shorter lifetime τ1 (185-300 ps) is attributed to positron annihilation in vacancies and the longer lifetime τ1 (400-580 ps) to positrons in microviods at interfaces. The rutile phase of TiO2 powders was utilized as a reference in order to compare their behavior with the commercially supplied and widely available anatase phase (Degussa P25). The influence of the heat-treatment upon the nanostructure during the transition of the anatase to rutile phase were also investigated by X-ray diffraction (XRD), TEM and BET surface area methods. Understanding of this effect is expected to enhance our knowledge of the morphology and nanocrystallite size of TiO2 powders and their T-dependence, and hence their physical properties.

Abstract: BSCCO 2212 superconducting samples, doped Tellurium, with the chemical formula Bi2-xTexSr2CaCu2O8, were prepared by the conventional solid state reaction technique. The prepared samples were studied utilizing XRD, DC-electrical conductivity and SEM. XRD spectra indicated that 2212 with tetragonal structure is the major phase, whereas Bi-2201 and CaTeO4 are minor phases. At higher Te-additions x, traces from some other semi conducting phases were detected. The critical transition temperature Tcoffset was found to decrease non-linearly with x, which attributed to the hole filling caused by the liberated electrons of Te4+ ions. For x–values in the range 0.1 ≤ x ≤ 0.4, the steepness of (ρ vs T) relationship increases abruptly around 150 K; this was attributed to change in the oxygen vacancy feature (phase-like transition). SEM photographs revealed that as Te-content increases the compactness of the surface and the connectivity of the grains decreases, while pores and voids increase as a result of decreasing the amount of Bi and presence of multiple-phases in the sample.

Abstract: Self-diffusion, both cationic and anionic diffusion, in ZnS nanoparticles is studied here following reaction coordinate theory. The jump frequencies, at various temperatures are computed. The isotope effect reveals the self-diffusion in nano ZnS is mainly through interstitial migration.

Abstract: A detailed analysis on the depth profiles of 30 keV H+ ion implanted n-GaAs for various doses from 1014 to 1017 cm-2 was carried by using Secondary ion mass spectrometry (SIMS), to identify the buried amorphous layer. The results are correlated with Raman and XRD strain parameter studies. Various thermal parameters are computed for the 30 keV H+ ion implanted n-GaAs and SIMS study reported for the first time.

Abstract: Silver telluride (Ag2Te), I-VI semiconductor compound with potential applications in various advanced fields. Ag2Te nano films of thickness between 16 nm and 145 nm prepared by thermal evaporation technique at high vacuum better than 2x105 mbar. These films are found to exhibit polycrystalline nature with monoclinic structure from their XRD studies. The average particle size of these films are found to be around 24 nm using the Debye-Scherrer’s formula From AFM measurements, the average particle size is around 24 nm. The emission spectra of these films were recorded and analysed to determine its optical band gap. Optical band gap of Ag2Te varies from 1.6 eV to 1.8 eV with respect to their corresponding thicknesses of films.