Browsing by Author "Kirabira, J.B."

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    Adhesion And Composite Micro-Hardness Of DLC And Si-DLC Films Deposited On Nitrile Rubber
    (Surface and Coatings Technology, 2012) Lubwama, M.; Corcoran, B.; Sayers, K.; Kirabira, J.B.; Sebbit, A.; McDonnell, K.A.; Dowling, D.
    Thin films of hydrogenated diamond-like carbon (DLC) and silicon (Si) doped diamond-like carbon (Si-DLC) have been deposited on acrylonitrile butadiene rubber (NBR) using a closed field unbalanced magnetron sputtering ion plating system. A sputter cleaning process was integrated into the deposition process so as to reduce the likelihood of re-contamination between the cleaning and deposition stages. The deposited coatings showed excellent adherence with an adhesion rating of 4 A for films with a Si-C interlayer. The composite micro-hardness was highest for DLC films at 15.5 GPa for indentation load of 147.1 mN using a Vickers microhardness tester. Tribological tests undertaken under normal load of 5 N using a pin-on-disc tribometer for all of the samples of DLC and Si-DLC films, with and without Si-C interlayer, show a friction increase between 0.25 and 0.4 to between 0.45 and 0.6. This friction increase has been related to the micro-hardness of the films.
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    Characteristics and tribological performance of DLC and Si-DLC films deposited on nitrile rubber
    (Surface and Coatings Technology, 2012) Lubwama, M.; McDonnell, K.A.; Kirabira, J.B.; Sebbit, A.; Sayers, K.; Dowling, D.; Corcora, B.
    The characteristics and tribological performance of DLC and Si-DLC films with and without Si–C interlayers were studied in this paper. The films were deposited on nitrile rubber using a closed field unbalanced magnetron sputtering ion plating system. The film properties and characteristics were determined by scanning electron microscopy (SEM), hydrophobicity studies, Raman spectroscopy and tribological investigations. Tribological performance of these films was investigated using a pin-on-disc tribometer under applied loads of 1 N and 5 N under conditions of dry and wet sliding. The effect of immersing the films in water on tribological performance was also examined. The results show that the morphology of the films had a crack-like network. At a substrate bias of −30 V, the coatings were characterised by a very dense noncolumnar microstructure. The highest value of the ratio of intensities of the D and G peaks (ID/IG) was 1.2 for Si-DLC film with Si–C interlayer. The lowest value of 0.7 was observed for DLC film. The contact angle (CA) of water droplets showed that the films were hydrophobic. These results are interpreted in terms of hybridisation of carbon in these coatings. The tribological investigation showed a dependence on both the tribological condition under investigation and the atomic percentage of Si in the films. At 5 N normal load the lowest wear depth was observed for DLC films.
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    Characterization And Pre-Leaching Effect On The Peels Of Predominant Cassava Varieties In Uganda For Production Of Activated Carbon
    (Current Research in Green and Sustainable Chemistry, 2021) Kayiwa, R.; Kasedde, H.; Lubwama, M.; Kirabira, J.B.
    Activated Carbon (AC) remains a key material for both industrial and domestic applications. The aim of this work was to characterize the peels of predominant cassava varieties grown in Uganda for production of AC. The selected varieties were; NASE 1, NASE 3, NASE 14, NASE 19, NAROCAS 1, and NAROCAS 2 due to more guaranteed raw material availability and potential for sustainability for AC production. The peels were characterized through proximate and ultimate analysis, bulk density, water-binding capacity, and lignocellulosic composition. Pre-leaching was done using NaOH of 1–4% w/v concentrations on two representative peel varieties. The dry basis (db) values of ash content, volatile matter and fixed carbon percentages of the peel varieties ranged from 1.93 to 4.36%, 77.93–81.93% and 13.78–15.34%, respectively. The ash content values were below 5% and hence may not necessitate pre-leaching to remove any ash forming agents. The dry basis char yield from the peels at 400 ​°C is in the range of 27.76–31.09%, qualifying them for AC production. The lignin, cellulose and hemicellulose compositions are in the ranges 9.0–16.0%, 5.5–15.0%, and 41.0–65.0%, respectively. The varieties with higher cellulosic content may be more suitable for highly porous AC production. Pre-leaching showed no remarkable reduction in the ash content but increased the volatile matte and char yield at low NaOH concentrations. Predominant Ugandan cassava peel varieties have potential for production of AC with alkaline pretreatment required in applications where high char yields are required.
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    Raman analysis of DLC and Si-DLC films deposited on nitrile rubber
    (Surface and Coatings Technology, 2013) Lubwama, M.; Corcoran, B.; Rajani, K.V.; Wong, C.S.; Kirabira, J.B.; Sebbit, A.; McDonnell, K.A.; Dowling, D.; Sayers, K.
    In this study a hybrid diamond-like carbon (DLC) and silicon doped diamond-like carbon (Si-DLC), with and without Si–C interlayers, were deposited onto nitrile rubber substrates. The deposition was done in a closed field unbalanced magnetron sputtering ion plating (CFUBMSIP) rig in Ar/C4H10 plasma. A combination of visible (488nm) and ultra-violet (UV; 325nm) Raman analysis was used to determine the G-peak dispersion of the films. Raman analysis was also used to estimate the hydrogen concentration and residual stress in the films. Calculated hydrogen values for all of the films were between 26 and 31%. The residual stress estimates of the films indicated that the inclusion of Si dopant and Si–C interlayers reduced compressive stress in these films. Raman analysis of the wear tracks indicated an increase in the G-peak position which could indicate that graphitization occurred during pin-on-disc experiments.
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    Weldability of Recycled Steel Bars in Uganda
    (International Journal of Engineering and Technology, 2012) Senfuka, C.; Kirabira, J.B.; Byauhanga, J.K.
    The metallurgical reliability of welded recycled steel made in Uganda has been studied through the examination of manual metal arc weldments of steel samples of 0.27%C and less using the dye penetrant flaw detection method, micro-hardness plots and spark spectromentry. This method was selected to ensure reproducibility by taking repeated readings on the same sample since it is largely non-destructive. About thirteen percent of the samples exhibited post-weld cracks. Of these, 3% of the samples yielded hot cracks while the other 10% showed typical hydrogen assisted cracks. The cracking sensitivity has been attributed to the presence of large numbers and quantities of residual elements rather than high carbon content in particular. This resulted from the predominantly recycled production mode in the country. The use of more elaborate refining methods and the exploitation of virgin iron resources have been recommended. Pre- and post-heating techniques have been advised whenever weld cracking threatens.