Browsing by Author "Maaza, M."

Now showing 1 - 4 of 4
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    Carbon, magnesium implantation and proton irradiation on pulsed laser deposited thermochromic thin film of VO2
    (University of Western Cape, 2020) Mabakachaba, Boitumelo Mafalo; Maaza, M.; Arendse, Christopher
    When the spacecrafts orbit in space, it is subjected to significant thermal cycling variation. Thermal regulation of the spacecraft temperature is required to ensure a good operation of the small crafts such as CubeSats and the on-board equipment while minimizing the weight. Three methods employed for the Smart Radiator Devices (SRD) are (i) mechanical louvers, (ii) electrochromic coatings and (iii) thermochromic coatings (which is of interest in this study). Based on the characteristics of the thermochromic coatings, the passive smart radiator device is by far the most efficient option since there are no mechanical moving components and also no electric energy needed for the craft to operate.
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    Irradiation induced effects on 6h-SIC
    (University of the Western Cape, 2012) Sibuyi, Praise; Maaza, M.
    The framework agreement in the year 2000 by the international community to launch Generation IV program with 10 nations, to develop safe and reliable nuclear reactors gave rise to the increased interest in the studies of SiC and the effect of different irradiations on solids. Silicon carbide is a preferred candidate used in harsh environments due to its excellent properties such as high chemical stability and strong mechanical strength. The PBMR technology promises to be the safest of all nuclear technology that have been developed before. SiC has been considered one candidate material being used in the fabrication of pebble bed fuel cell. Its outstanding physical and chemical properties even at high temperatures render it a material of choice for the future nuclear industry as whole and PBMR in particular. Due to the hostile environment created during the normal reactor operation, some of these excellent properties are compromised. In order to use this material in such conditions, it should have at least a near perfect crystal lattice to prevent defects that could compromise its strength and performance. A proper knowledge of the behavior of radiation-induced defects in SiC is vital. During irradiation, a disordered crystal lattice occurs, resulting in the production of defects in the lattice. These defects lead to the degradation of these excellent properties of a particular material. This thesis investigates the effects of various radiation effects to 6H-SiC. We have investigated the effects of radiation induced damages to SiC, with a description of the beds and the importance of the stability of the SiC-C interface upon the effects of radiations (y-rays, hot neutrons). The irradiated samples of 6H-SiC have been studied with various spectroscopic and structural characterization methods. The surface sensitive techniques such as Raman spectroscopy, UV-Vis, Photoluminescence and Atomic Force Microscopy will be employed in several complimentary ways to probe the effect of irradiation on SiC. The obtained results are discussed in details.
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    Nonlinear optical properties of natural dyes based on optical resonance
    (University of the Western Cape, 2012) Zongo, Sidiki; Maaza, M.
    Recent research shows that the study of optical properties of organic material natural dyes has gained much consideration. The specific functional groups in several natural dyes remain essential for the large nonlinear absorption expressed in terms of nonlinear optical susceptibilities or other mechanism of absorption such as two photon absorption (TPA), reverse saturable absorption (RSA) or intensitydependent refractive index characteristic. In this thesis we highlight the optical limiting responses of selected natural dyes as nonlinear response in the femtosecond regime. This technique refers to the decrease of the transmittance of the material with the increased incident light intensity.Three dyes derived from beetroot, flame flower and mimosa flower dyes were investigated. The results showed a limiting behaviour around 795 mW for the beetroot and the flame dye while there is total transmission in the flame dye sample. The performance of the nonlinearity i.e. the optical limiting is related to the existence of alternating single and double bonds(i.e. C-C and C=C bonds) in the molecules that provides the material with the electron delocalization, but also it is related to the light intensity.Beside nonlinearity study, crystallographic investigation was carried out for more possible applicability of the selected dyes and this concerned only the mimosa and flame flower dye thin film samples since the beetroot thin film was very sensitive to strong irradiation (i.e. immediately destroyed when exposed to light with high intensity). For more stability,dye solutions were encapsulated in gels for further measurements.
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    Synthesis of zinc oxide nanoparticles by a green process and the investigation of their physical properties
    (University of the Western Cape, 2017) Nethavhanani, Takalani; Maaza, M.; Madjoe, R.
    Zinc oxide (ZnO) is a wide and direct semiconductor with a wurtzite crystal structure. Its multifunctionality as the ideal candidate in applications such as blue-UV light emitting diodes, transparent conducting oxide, selective gas sensor and efficient catalyst support among others, has attracted a significant interest worldwide. Nano-scaled ZnO has been synthesized in a plethora of shapes. A rich variety of physical and chemical methodologies have been used in the synthesis of undoped or doped ZnO. However, such methods either necessitate relatively high vacuum infrastructures, elevated temperatures, or the use of toxic reagents. The "green chemistry" synthesis of metal oxide nanoparticles which is based on using natural plant extract as an effective 'reducing agent' of metal precursor, has been reported to be a cleaner and environment-friendly alternative to the physical and chemical methods. The thesis is based on the synthesis and the main physical properties of pure ZnO nanoparticles synthesized by a completely green chemistry process using the natural extract of Aspalathus Linearis to bio-reduce the zinc acetate precursor. The obtained ZnO nanopowdered samples were annealed at different temperatures from 300 °C to 600 °C. The samples were characterized using Scanning Electron Microscopy, Energy Dispersive Spectroscopy, Transmission Electron Microscopy, X-ray Diffraction, Differential Scanning Calorimetry, Thermogravimetric Analysis and Fourier Transform Infrared. Highly pure quasi-spherical ZnO nanoparticles with an average crystallite size of 24.6 nm (at 300 °C), 27.2 nm (at 400 °C), 27.6 nm (at 500 °C), and 28.5 nm (at 600 °C) were found. The results also showed that the average crystallite size increased with an increase in annealing temperature. It was successfully demonstrated that the natural plant extract of Aspalathus Linearis can be used in the bio-reduction of zinc acetate dihydrate to prepare highly pure ZnO nanoparticles.