Advanced Materials Research Vol. 545

Abstract: Resistance to wear is an important factor in design and selection of structural components in relative motion against a mating surface. The present work deals with studies on the wear behavior of metal matrix composites manufactured using powder metallurgy technique of ball milled mixing in a high energy attritor and using a blend-press-sinter methodology. Matrix of pre–mechanical alloyed Al-4.5 %wt Cu was used to which different weight percents of nano-sized TiC reinforcement were added. Microstructural characterization of the materials revealed reasonably uniform distribution of TiC reinforcement and presence of minimal porosity. Wear tests were performed using a pin on disk apparatus. The MMCs were rubbed against a carbon steel pin under loads of 10 and 20 N at a sliding velocity of 0.1 ms⁻¹; the environmental humidity lower than 30% and a track length of 1500 m. The degree of improvement in dry sliding wear resistance and hardness brought about by reinforcement is strongly dependent on the weight percent of reinforcement and the wear behavior was determined through the precise measurement of weight loss of the samples. Worn surfaces were analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).

Abstract: The present work deals with the synthesis of cobalt monometallic and bimetallic Co/Fe nanocatalysts supported on alumina. The nanocatalysts were prepared by a wet impregnation method. The samples were characterized in terms of reducibility, dispersion, metal particle size, textural characteristics and crystallinity. These characteristics were revealed using hydrogen temperature-programmed reduction (TPR), CO-chemisorption, transmission electron microscopy (TEM), X-ray diffraction (XRD) and nitrogen adsorption analysis. H₂-TPR analysis of Co/Al₂O₃ indicated three temperature regions at 507 ^◦C (low temperature), 650 ^◦C (medium temperature) and 731 ^◦C (high temperature) while characteristic peaks of Fe/ Al₂O₃ appeared at 454 ^◦C, 635 ^◦C and 716 ^◦C, respectively. Bimetallic nanocatalysts exhibited different physicochemical properties than those of the monometallic nanocatalysts. The incorporation of iron into cobalt nanocatalysts up to 50% of the total metal loaded enhanced the reducibility, increased the CO and H₂ chemisorbed and degree of reduction (DRT) while surface area decreased, further increase in the iron content resulted in a decrease in the crystallinity, increase in the average metal particle size and shift in the reduction towards higher temperatures.

Abstract: A sol-gel method was used to synthesize a highly stable form of MgO from magnesium oxalate dihydrate. The sol-gel products were characterized using simultaneous thermogravimetric analysis (STA), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and UV-Visible light spectroscopy (UV-Vis). From the XRD analysis, all the MgO samples showed a single face-centered cubic phase. FESEM micrographs showed a crystallite size ranging from 10 nm to 59 nm. The size of the MgO crystallites increased with increasing temperatures. The crystallite size of the MgO is still relatively small, that is, below 100 nm even when the precursor was calcined at a higher temperature of 950 °C and a longer time of 36 h. Such results indicated that the growth of the crystallites is slow for this route of synthesis. The morphologies of the MgO samples are varied from the all spherical of the lower temperature to the more cubic shape with less agglomeration of the higher calcined samples. The band gap energy of the MgO samples also increased with temperature.

Abstract: Titanium dioxide powders were synthesized via a sol-gel method using titanium nitride as the precursor. The structure and morphology of the synthesized powders were investigated and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD results indicate that pure single phase titanium dioxide of rutile structure had been obtained. It was also revealed that annealing temperature plays an important role in the formation of single phase titanium dioxide powders. Increasing heat treatments also modified the shape and surface morphology from chunks and rock-like morphology to a mixture of flaky aggregates. Conductivity studies using a.c. impedance technique was used. The conductivity of the sample annealed at 400 °C is 89 % higher than that annealed at 800 °C and attributed to the phase and morphology of the samples.

Abstract: One of the aspects most intensively researched in the continuing improvisation of lithium battery is the search for high capacity, high energy density and high performance cathode materials. Substitution of the electroactive elements with heteroatoms is one of the promising methods. In this study, a potential cathode material with a layered structure was successfully synthesized via a sol-gel method. As a comparison, the well-known LiMn_1/3Co_1/3Ni_1/3O₂ (LiMn_0.333Co_0.333Ni_0.333O₂) was also synthesized using exactly the same method and conditions. Both materials were characterized using simultaneous thermogravimetric analysis (STA), X-ray powder diffraction (XRD), field-emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The stoichiometries of the compounds were also confirmed through energy-dispersive X-ray spectroscopy (EDX) measurement. XRD results show that both compounds are single phase and impurity-free with well-ordered hexagonal layered structure characteristics of R-3m space group. Both compounds also show similar morphologies with well-formed crystals and clean surfaces as depicted by the SEM images. XPS measurement reveals that the introduction of chromium into LiMn_1/3Co_1/3Ni_1/3O₂ results in a considerable change in the chemical environment as observed by significant changes in the binding energies (BE) of manganese, cobalt and nickel respectively.

Abstract: Magnesium oxide (MgO) is a metal oxide which has many applications in industry and can be synthesized by many different synthesis methods. In this study, MgO was synthesized by using two different methods which were sol-gel and solid-state reaction methods. Both samples were annealed at 800 oC for 24 hours and characterized by using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The band gap energies for both samples were determined by using UV-Vis NIR Spectroscopy. The band gap values of the samples are evaluated from the data. It was found that the band gap energies of the MgO using different synthesis route were not the same.

Abstract: In this work, the band gap energies of magnesium oxide (MgO) were investigated to see if calcination time affects the band gap energies of the MgO. MgO nanomaterials have been prepared by a sol-gel method. MgO precursors produced were calcined at a temperature of 600 °C for 24 hours and 48 hours. The structural characterization of samples is achieved using X-Ray Diffraction (XRD) and the morphology as well as particle size of MgO were examined by Field Emission Scanning Electron Microscopy (FESEM). UV-Vis NIR spectroscopy was used to determine the band gap energies of the materials. From the results, the band gap energy of the MgO with a longer heating time exhibited a higher value.

Abstract: ZnO is known as an inorganic material that has a variety of morphologies. The morphologies of the ZnO are much influenced by the synthesis route. In this work, two ZnO nanomaterials were prepared by the sol-gel route and the effect of detergent on the morphology and optical band gap of ZnO materials were investigated. The synthesized ZnO materials were characterized using Simultaneous Thermogravimetric Analyzer (STA), X-ray Diffraction (XRD) and Field Emission Scanning Electron Microscope (FESEM). The UV-Vis spectrophotometer is used to determine the optical band gap. The results show that the presence of detergent affected the morphology of the ZnO from nanorods to nano-flakes. The band gap energy of the ZnO were also reduced from 3.14 ev to 2.98 eV from the nanorod to the nanoflakes.

Abstract: Zinc oxide nanostructures were prepared by sol-gel method without using any chelating agents. The structural and optical properties of the nanostructures were studied. The precursors were annealed at 400 °C and 800 °C for 24 hours and characterized using X-Ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The band gap energies were analyzed by using a UV-Vis spectrophotometer. Based on the XRD results, all materials were single phase with the hexagonal structure without any impurities presents. Based on the FESEM results, it was found that the morphology for the materials annealed at 400 °C has nanorod shape while for the materials annealed at 800 °C, they have spherical shape. It was found that the band gap energies of the ZnO nanomaterials were dependent on the morphology of the nanostructures.

Abstract: Aluminium oxide is one of the metal oxides that can exist in many phases such as α, θ, η etc. All the phases obtained are affected by annealing temperature and synthesis route. In this research the Al₂O₃ powders were synthesized by the combustion method using triethanolamine as fuels. A pure η phase as well as a mixed α and η phases were obtained. The size and morphology of Al₂O₃ particles were studied using scanning electron microscopy (SEM).