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Manikandan D.,University of Concepcion | Mangalaraja R.V.,University of Concepcion | Siddheswaran R.,University of Concepcion | Avila R.E.,Personal Dosimetry Section | Ananthakumar S.,Indian National Institute for Interdisciplinary Science and Technology
Applied Surface Science | Year: 2012

Growth of multiwalled carbon nanotube (CNT) assemblies by chemical vapour decomposition (CVD) technique was achieved through decomposition of acetylene using iron impregnated montmorillonite (MM) catalysts. Various amounts of iron loaded montmorillonite catalysts were prepared by wet impregnation method and calcined at 450°C. The catalysts were subjected to X-ray diffraction (XRD) and surface area analyses. Acetylene decomposition at a feed ratio of N 2:H 2:C 2H 2 = 1:1:0.18 was conducted in the presence of iron impregnated montmorillonite catalysts in the CVD reactor for the growth of CNT structures. The role of Fe-activated clay catalyst on the formation of CNT structures has been systematically examined at various temperatures and correlated with the morphological features of CNTs. Catalyst assisted acetylene decomposition results the formation of different carbon nanostructures such as nanotubes, nanofibres and nanoflakes. These clay-CNT products were characterised for their morphological, thermal, qualitative and quantitative analyses. The morphological variations of CNT assemblies reveal Fe-montmorillonite catalysts have high selectivity at given reaction conditions. Thermogravimetric and Raman spectral analyses prove that the CNTs contain a good crystallanity and less structural defects. © 2011 Elsevier B.V. All rights reserved.

Siddheswaran R.,University of Concepcion | Mangalaraja R.V.,University of Concepcion | Avila R.E.,Personal Dosimetry Section | Gomez M.E.,University of Valle | And 4 more authors.
Journal of Ceramic Processing Research | Year: 2012

Transparent polycrystalline ZnO and Co,Al co-doped ZnO [Zn1-x-yCoxAlyO; x = 0.03; y = 0.02] thin films were fabricated using sol-gel spin coating on glass substrates and subsequently annealed at 500 °C for 2 h in an ambient atmosphere. The decomposition of the precursors and formation of the metal oxide during annealing was explained by thermal analysis. X-ray crystal diffraction analysis on the co-doped ZnO thin films confirmed the formation of the hexagonal wurtzite structure. Microstructural studies revealed that the films were filled with particulates of sizes ranging between 40-50 nm and with a uniform film thickness of about 700 nm after annealing at 500 °C. Atomic force microscopy (AFM) images demonstrated a fine and smooth surface of the thin films. The spin coated films have also been shown to possess polycrystalline grains with a compact and void-free morphology. The energy dispersive X-ray spectroscopic (EDS) analysis confirmed the presence of Co, Al, Zn and O. The room temperature (300 K) ferromagnetic behavior of Co, Al co-doped ZnO thin films is also discussed.

Siddheswaran R.,University of Concepcion | Mangalaraja R.V.,University of Concepcion | Gomez M.E.,University of Valle | Avila R.E.,Personal Dosimetry Section | And 2 more authors.
Journal of Alloys and Compounds | Year: 2013

Pure and Co, Al co-doped ZnO(Zn1-x-PCoxAlyO; x = 0.04, 0.03, 0.02; y = 0.01, 0.02, 0.03) nanoparticles were synthesized by wet chemical combustion method at 500 °C for various doping levels using zinc, cobalt and aluminium nitrates as precursors. The synthesized powders were calcined at 600 °C and sintered at 1000 °C after uni-axial compaction. Structure, morphology and the presence of magnetism in combusted and sintered materials of pure and doped ZnO were examined. At room temperature, both the calcined nanoparticles and sintered compacts of pure ZnO exhibited paramagnetism. But, ferromagnetism was observed for Co and Al co-doped ZnO (diluted magnetic semiconductor) nanoparticles calcined at 600 °C. Also, it was found that the ferromagnetism increased correspondingly for the calcined particles with Co concentration. Whereas, a strong paramagnetic behavior was observed for the sintered compacts of various concentrations of Co and Al dopants due to grain growth. © 2013 Elsevier B.V. All rights reserved.

Siddheswaran R.,University of Concepcion | Mangalaraja R.V.,University of Concepcion | Tijerina E.P.,Autonomous University of Nuevo Leon | Menchaca J.-L.,Autonomous University of Nuevo Leon | And 4 more authors.
Spectrochimica Acta - Part A: Molecular and Biomolecular Spectroscopy | Year: 2013

Effect of transition metal oxides (TM = Co and Ni) co-doping on the crystallinity, surface morphology, grain growth and magnetic properties of nanostructure Al:ZnO thin films has been studied for diluted magnetic semiconductor applications. Al:ZnO thin films were fabricated by sol-gel spin coating on p-type Si (100) substrates. Fabrication of hexagonal wurtzite TM co-doped Al:ZnO thin films having thickness 2 μm was successfully achieved. The Raman spectra of the TM co-doped Al:ZnO thin films showed a broad vibrational mode in the range 520-540 cm-1 due to crystal defects created co-doping elements in the ZnO host lattice. Scanning electron microscopy (SEM) revealed that the films are composed of uniform size, polycrystalline dense ZnO particles with defect free, smooth surfaces. The surface roughness was further verified with atomic force microscopy (AFM). The energy dispersive X-ray spectroscopic analysis (EDX) confirmed the stoichiometric compositions of the TM co-doped Al:ZnO films. The magnetic measurements exhibited that the Co, Al:ZnO and Ni, Al:ZnO thin films were ferromagnetic at room temperature. © 2013 Elsevier B.V. All rights reserved.

Siddheswaran R.,University of Concepcion | Mangalaraja R.V.,University of Concepcion | Avila R.E.,Personal Dosimetry Section | Manikandan D.,University of Concepcion | And 2 more authors.
Materials Science and Engineering A | Year: 2012

Combustion synthesized nanocrystalline Co and Al co-doped ZnO powders [(Zn 1-x-yCo xAl yO; x=0.04, 0.03, 0.02; y=0.01, 0.02, 0.03)] were fabricated into cylindrical discs by uni-axial pressing and sintered intentionally at 1000°C for 2h to assess the mechanical performance. The crystallinity of the pure and doped ZnO was confirmed by X-ray diffraction analysis. The microstructures of the sintered samples were investigated by scanning electron microscopy (SEM) to examine the density, porosity, grain size and its distribution. Grains of 0.5-3μm were observed for the samples sintered at 1000°C. The mechanical properties such as micro-hardness, fracture toughness and strain hardening co-efficient were investigated by the Vickers indentation method. It was found that the crack mode observed during the indentation on the samples belongs to median cracks under a load of 19.6N. Also, the hardness was enhanced with increasing mol% of Co, while the trend was reversed with the increase of Al content. In addition, the strain hardening coefficient and fracture toughness were calculated using the indentation data. © 2012 Elsevier B.V.

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