Browsing by Author "Lubwama, M."

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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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    Mesoporous activated carbon yielded from pre‑leached cassava peels
    (Bioresources and Bioprocessing, 2021) Kayiwa, R.; Kasedde, H.; Lubwama, M.; Kirabira, J. B.
    The search for alternatives to fossil-based commercial activated carbon (AC) continues to reveal new eco-friendly potential precursors, among which is agricultural waste. The key research aspect in all these endeavors is empirical ascertainment of the core properties of the resultant AC to suit a particular purpose. These properties include: yield, surface area, pore volume, and the active surface groups. It is therefore pertinent to have process conditions controlled and tailored towards these properties for the required resultant AC. Pre-leaching cassava peels with NaOH followed by KOH activation and carbonization at holding temperatures (780 °C) above the melting point of K (760 °C) yielded mesoporous activated carbon with the highest surface area ever reported for cassava peel-based AC. The carbonization temperatures were between 480 and 780 °C in an activation–carbonization stepwise process using KOH as the activator at a KOH:peel ratio of 5:2 (mass basis). A 42% maximum yield of AC was realized along with a total pore volume of 0.756 cm3g− 1 and BET surface area of 1684 m2g− 1. The AC was dominantly microporous for carbonization temperatures below 780 °C, but a remarkable increase in mesopore volume (0.471 cm3g− 1) relative to the micropore volume (0.281 cm3g− 1) was observed at 780 °C. The Fourier transform infrared (FTIR) spectroscopy for the pre-treated cassava peels showed distortion in the C–H bonding depicting possible elaboration of more lignin from cellulose disruption by NaOH. A carboxylate stretch was also observed owing to the reaction of Na+ ions with the carboxyl group in the raw peels. FTIR showed possible absorption bands for the AC between 1425 and 1712 cm− 1 wave numbers. Besides the botanical qualities of the cassava peel genotype used, pre-leaching the peels and also increasing holding activation temperature above the boiling point of potassium enabled the modified process of producing highly porous AC from cassava peel. The scanning electron microscope (SEM) and transmission electron microscope (TEM) imaging showed well-developed hexagonal pores in the resultant AC and intercalated K profile in the carbon matrices, respectively.
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    Occurrence and toxicological assessment of selected active pharmaceutical ingredients in effluents of pharmaceutical manufacturing plants and wastewater treatment plants in Kampala, Uganda
    (Water Practice & Technology, 2022) Kayiwa, R.; Kasedde, H.; Lubwama, M.; Kirabira, J. B.; Kayondo, Timothy
    There is an increasing eco-toxicological risk associated with pharmaceuticals globally. The prevalence of six active pharmaceutical ingredients (APIs) was studied in effluents of three pharmaceutical manufacturing plants (PMPs) and two wastewater treatment plants (WWTPs) in Kampala, Uganda to ascertain the removal potentials for APIs. The APIs include atenolol, losartan, carbamazepine, sulfamethoxazole, clarithromycin, and diclofenac. The APIs were extracted using solid-phase extraction cartridges and concentrations were analyzed using a liquid chromatography-mass spectrometer system. The concentration ranges of the APIs were
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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.