Advanced Materials Research Vol. 67

Abstract: Large area arrays of highly oriented sulfur (S2-) doped ZnO nanorods are grown on silica glass substrate by wet chemical decomposition of zinc-thiourea precursor in an aqueous medium. A series of five samples were synthesized by varying the concentrtaions of sulfur ions in solution. The synthesized materials were studied by using XRD, SEM, AFM, UV-ViS spectroscopy and photoluminescence techniques. Microscopy studies reveal the formation of conical nanorods having length ~3.0μm with tip size ~ 50nm. XRD studies of these nanorods show formation of hexagonal phase of pure ZnO with c-axis preferred orientation. Reduction in band gap energy from 3.2 to 2.9 eV was observed from optical absorption studies when different mole concentrations of thourea was varied in the precursor solution. The photoluminiscence efficiency of the materials was found to decrease with increase in the concentartion of sulfur ions in ZnO nanorods.

Abstract: Pure and two different concentration of Iron (Fe) doped Zinc Oxide (ZnO) nanoparticles (Zn(1-x)FexO) with x = 0.03 and 0.05 were synthesized by chemical co-precipitation method. The structural characterizations of the samples were done by X-ray powder Diffraction (XRD) and Scanning Electron Microscopy (SEM). XRD data indicate that the replacement of Zn2+ ion by Fe3+ ion does not influence the wurtzite structure of ZnO samples. With increase in annealing temperature the intensity of the Zn(1-x)FexO (0 0 2) diffraction peak increases, indicating that the crystallinity quality of the particle improves. Using Scherrer equation the average particle sizes of Zn(1-x)FexO are calculated. The strain-induced broadening at Full Width Half Maximum (FWHM) of the XRD profile of Zn(1-x)FexO were estimated from Williamson Hall (W-H) plot. The results of SEM apparently show that the sample comprises of highly agglomerated particles with no definite shape. Optical absorption Ultraviolet-visible (UV-vis) and Photo Luminescence (PL) properties have been characterized and the effect of Fe addition on optical properties of ZnO has been discussed.

Abstract: Nanocrystalline PbTe particles of controlled size and shape are synthesized via chemical route at different growth temperatures. The size of the nanoparticles is in the range ~ 20 to 35 nm. The size and shape of the particles have been controlled by controlling temperature, using proper surfactant and maintaining the atomic ratio between Pb and Te. The intrinsic properties of surface energy of different crystallographic planes involve in growth process are studied. The crystallinity and phase of PbTe nanocrystals are analyzed by X-ray diffraction (XRD). The shape and size of the nanocrystals have been characterized by transmission electron microscopy (TEM). The optical band gap of nanocrystals is determined by FTIR photo-absorption spectra.

Abstract: Nanoparticles of chromic oxide (Cr2O3) are widely used in many fields serving as catalysts, wear resistance materials, and advanced colorants. By the reaction system of CrO3 and PVA in aqueous solution, Cr2O3 nanoparticles were prepared via hydrothermal synthesis. We have taken sucrose as reducing agent. The products were loosely agglomerated Cr2O3 particles of 30-80 nm in average particle size calculated from Scherrer’s formula, whose microstructure and the precursor were investigated by SEM. The findings showed that the higher calcination temperatures result in the larger average particle size. Ultrasonic velocity measurements in Cr2O3 nanoparticles suspended in PVA solution were made at different thermal conditions. In the sample Cr2O3+PVA the ultrasonic velocity increases up to 500C and then remains constant. The effort has been made to correlate the ultrasonic velocity/absorption behavior with the magnetic property.

Abstract: Zinc ferrite (ZnFe2O4) is a commercially important material and has wide applications. We report the synthesis of nanostructured ZnFe2O4 and Fe-doped ZnO nanorods via a low cost, open to atmosphere self catalyzed Chemical Vapor Deposition(CVD) method which uses the Vapor-Liquid-Solid (VLS) Mechanism for growth. A mixture of Zinc Oxide, Graphite and Zinc powder, along with the substrates were put at the closed end of a quartz tube and placed in a preheated furnace. The parameters varied were 1.)molar ratios 2.)types of substrates and 3.)the furnace temperature. The characterization was done using FE-SEM, TEM,and XRD. The growth morphology varies along the temperature gradient in the tube, resulting in the formation of ZnFe2O4 nanoribbons (800-750 0C), nanoellipsoids (700 0C) and nanowires (650 0C). Fe- doped ZnO nanorods have also formed as scattered bundles along with the zinc ferrite nanoribbons. This is the first reported synthesis of nanoribbon morphology of ZnFe2O4 . The effective diameter:width ratio of the morphology and the Zn atomic percentage decreases along the temperature gradient. Optimized parameters were:1.)mild steel substrates, 2.)furnace temperature 800 0C and 3.)1:1:0.05 molar ratio of ZnO:C:Zn in the reaction mixture. When stainless steel and gold sputtered steels were used as substrates there was no growth. This proves that iron from the substrate takes an active part in the reaction and is critical for the growth. The simplicity of the setup, control over growth morphology and cheap reagents used give the method potential commercial applications.

Abstract: Precursor powder of calcia-stabilized zirconia (CSZ) with 4, 7 and 15 wt % was synthesized by mechanical alloying (MA) in cryogenic conditions. The phase evolution of the precursor powders over 100 hours of MA was analyzed by powder X-ray diffraction technique. Cylindrical shaped sensor elements of the calcined powders were fabricated in a uniaxial press followed by sintering at 15000C for 3 hours. Scanning electron microscopy (SEM) was used to analyze the microstructure of the sintered pellets. The co-relation between material compositions, microstructure of the sinter pellets and the electrical properties of the sensors are discussed.

Abstract: ZnO nanostructures of different morphologies were grown in a controlled manner by a novel sonication assisted sol gel process. Variation in the alcoholic medium resulted in nanorods and flower like ZnO nanostructures. Flower like ZnO nanostructures with a root size of 1m and a tip of 150nm were synthesized using ethanol as solvent, while ZnO nanorods with diameter less than 60 nm and length greater than 1m were synthesized using methanol as solvent. The samples were characterized by X-ray diffraction and Scanning Electron Microscopy. The XRD results show the formation of highly crystalline ZnO with no detectable level of impurity. In this paper, a possible mechanism for the variation of morphology with the change in solvent has been discussed. The effect of solvent vapour pressure on the sonication process has been explained. The solvent vapour pressure has an effect on the intensity of sonication which affects various chemical reactions taking place during the formation of ZnO. The effect of ethylenediamine on the chemical reactions leading to formation of ZnO nanostructures has also been analyzed.

Abstract: The reported work is on Ti-48Al-12Nb-1Cr (at %) system synthesized in a high-energy planetary ball mill with optimized milling parameters. The synthesized powders are characterized by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), X-Ray Diffraction (XRD) and Differential Thermal Analysis (DTA) in order to understand the structural and phase transformation. The results obtained from the above said studies show the particles refinement, formation of non-equilibrium structures, etc. High-energy ball milling results super saturation of Al and Nb in titanium matrix at 15 hrs of milling, nanocrystalline nature at 20 hrs and amorphous phase formation at 50 hrs of milling. Differential Thermal Analysis (DTA) and XRD scans of MA powder thermally treated at 750°C for 1 hr show the formation of TiAl and TiAl3 intermetallic compounds.

Abstract: Polylactic acid (PLA) based biocomposite films, reinforced with different loadings of organoclay, were prepared by solution casting method. Four different loadings of clay was done, 2, 5, 10 and 15 weight% with respect to the matrix. These biocomposite films were characterized by mechanical characterization, scanning electron microscopy (SEM) moisture diffusivity property at 93% RH. Both the mechanical and the visco-elastic property of these films were measured by nano indentation technique. Mechanical property by nano indentation analysis revealed an idea about the extent of clay dispersion in the matrix. The amount of clay loading and its dispersion significantly affected the mechanical as well as the Visco-elastic behavior of the biocomposite films. The morphology of the films were observed with the help of SEM.

Abstract: In modern nanotechnology one of the most exciting area of research is the formation of nanoparticles through the biological interventions. Microbes and plants have inherent capacity to reduce metal through their specific metabolic pathway. In the present study Brassica juncea have been used to produce silver nanoparticles. Seedlings of B. juncea prepared in vitro and 14-days old plants were transferred into nutrient solution augmented with silver nitrate (25-2000 μM) allow the plants to grow in hydroponic culture for seven days. Then, the plants are harvested and analyzed through UV-VIS spectrophotometer and by Transmission Electron Microscopy (TEM) that confirms the nanoscale silver nanoparticles. We have found absorption peak in visible range (420-430 nm) of spectrum that is chiefly due to the silver nanoparticles. These biological synthesis methods considered as environmentally safe because of no toxic byproducts. Moreover, size of the nanoparticles can also be controlled by altering some conditions like pH, concentration of AgNO3 and temperature. Silver nanoparticles have large number of applications in non-linear optics, spectrally selective coating for solar energy absorption, biolabelling intercalation materials for electrical batteries, as optical receptors, catalyst in chemical reactions and as antibacterial capacities. So if these nanoparticles are synthesized by the biological methods, this would be more eco-friendly than the other common methods.