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- ItemModelling the effect of ventilation on the concentration and distribution of radon in closed environments(University of Zululand, 2023) Mngonyama, Sifiso; Ntshangase S.S. and Lindsay R.Epidemiological studies show that radon (222Rn and 220Rn) is the second most important cause of lung cancer after smoking. Prolonged exposure to high levels of this radioactive gas in various indoor environments is linked to multiple lung cancer-related deaths around the world. It was classified as a human carcinogen by The International Agency for Research on Cancer. One of the most effective techniques used to mitigate radon is adequate ventilation, which can be natural (e.g., natural winds) or mechanical (e.g., fans). Recently, Computational Fluid Dynamics (CFD) has become an efficient and powerful tool for studying radon concentration and distribution in ventilated environments. This is mainly because these codes are time and cost-effective. The current work aimed to study the effects of natural ventilation in the Huguenot second tunnel and mechanical ventilation in the Steenkampskraal monazite mine on the concentration and distribution of radon using a CFD package called ANSYS FLUENT based on realistic values for the radon exhalation and ventilation rates. The radon measurements were conducted at three points along the tunnel and two points in the mine using a combination of the RAD7, Airthings, and Electret Ion Chambers (EICs). The exhalation rates in the tunnel were measured with EIC flux monitors, and in the mine, it was measured using the accumulator method. Additionally, the wind speed and direction in both environments were measured with an anemometer and wind vane. These measurements were conducted in the tunnel in July 2021 (winter) and November 2021 (spring). In the mine, measurements were collected in August 2021. During the CFD analyses, two setups (or cases) were considered for each geometry (mine or tunnel). Additionally, for the tunnel in each case, two sets of simulations were conducted, one for July and one for November, each based on measurements of these respective months. For tunnel Case 1, the exhalation distribution in the walls was based on an average, and in Case 2, it was based on the tunnel geology. Whereas for the mine, Case 1 had no ventilation, and Case 2 had ventilation. Various approximations were made to simplify these models (e.g., simplified geometry and constant wind directions). The tunnel simulation for both Cases and months showed that the 222Rn concentration increases in the flow direction and that the levels depend on the exhalation rate, tunnel geometry (e.g., length), and natural wind velocity (or wind speed and magnitude). This behaviour was further supported by the measurements, which agreed with the simulations, with some relative deviation as low as 4%. This suggested that the tunnel model can be used in future works with only minor improvements. On the other hand, the simulation for the mine with no ventilation showed that the 220Rn concentration decreases exponentially from the source wall's normal direction towards the centre, a behaviour noted in the literature. This highlighted the importance of monitoring points for representative values when studying 220Rn. When there was mechanical ventilation, 220Rn was moderately mitigated. This was because the 220Rn distribution field changed from being inhomogeneous when there was no ventilation to being mostly homogenous when there was ventilation, which reduced the 220Rn by about half in some of the near-wall regions. This overall 220Rn behaviour was in line with the measured general behaviour and existing literature. However, there was a disagreement between the simulated and measured concentration at the monitoring points in the current work. This suggested that the mine model still needs further improvement (e.g., improved geometry).
- ItemComparative study of rare- earth based ferrites for flammable and volatile organic compound gas sensors(University of Zululand, 2023) Mkwae, Prince S’busisoThe monitoring of flammables and VOCs is still a challenge. In addition, acetone (CH3CH3CO) is a one of the toxic and harmful volatile organic compounds (VOCs) commonly used as a solvent in various laboratories and industries. Its high level of inhalation and ingestion can cause low, acute and chronic poisoning. Another commonly used highly flammable gas is liquefied petroleum gas (LPG), commonly known as a cooking gas, which is widely available in almost all communities and working environments to create fires for various uses. This gas causes many fatalities due to its nature of complexities in detection and can easily ignite. This, therefore, suggests that it is one of the main air pollutants that require constant detection and monitoring. Most studies in the chemical gas sensing community focus on just the normal sensing of these gases. In an attempt to solve the long existing problem, we have undertaken this study, where MgCexFe2-xO4 (0 ≤ x ≤ 0.4) nanoparticles have been produced by the glyco-thermal technique and characterised by X-ray diffraction, electron microscopy, X-ray photoelectron spectroscopy, Mössbauer spectroscopy and gas sensing analyses. The X-ray diffraction results indicated that a pure cubic spinel phase was formed for samples having a low concentration of Ce, but the high Ce doping (x ≥ 0.2) of magnesium ferrite resulted in the formation of secondary phases. The crystallite size of the compounds ranged from 2.2 nm to 15.3 nm. The 57Fe Mössbauer spectra showed transformation from an ordered to a paramagnetic spin state with an increase in Ce concentration. Gas sensors fabricated from the spinel ferrites were tested towards various organic compound vapours (acetone, methanol, p-xylene, ethylbenzene, toluene, and benzene) and flammable gases (LPG, Methane, Propane, Butane and Ammonia) at an operating temperature of 225 °C. The MgCe0.2Fe1.8O4 nano-ferrites proved to possess quality sensor characteristics of high sensitivity and selectivity to acetone vapour, with a response of over 500@100 ppm concentration as well as reproducibility, reversibility, and stability of over 120 days. This sensor not only displayed high responses, but could also maintain them over 1, 3, 5, 10, 20, and 30 min of acetone exposure time. On flammable gases, the addition of cerium to magnesium ferrites proved to kill the sensing. The best performing sensor was found to be the undoped Magnesium ferrite on LPG gas. It was resilient and sensitive to an oxygen reduced, inert ambient environment. Under relative humidity, the response was reduced, but stable, due to physisorbed water molecules. In addition, this SMO sensor was tested at 200 ˚C on vegetables and fruit to evaluate their off-shelf freshness during the ripening process. These plants show a dramatic increase in the respiration rate over their maturation or ripening process over time. OKUHUNYUSHWE NGOLIMI LWESIZULU IMFINGQO Ukuqapha izinto ezivuthayo kanye nama-VOC kuseyinselelo. Ngaphezu kwalokho, i-acetone (CH3CH3CO) ingenye yezinhlanganisela eziphilayo ezinobuthi neziyingozi (VOCs) ezivame ukusetshenziswa njengesinyibilikisi kumalabhorethri nezimboni ezihlukahlukene. Izinga layo eliphezulu lokuhogela kanye nokumunca lingabangela ubuthi obuphansi, obunamandla futhi obungapheli. Enye igesi evame ukuvutha esetshenziswa kakhulu i-liquefied petroleum gas (LPG), eyaziwa ngokuthi igesi yokupheka, etholakala cishe kuyo yonke imiphakathi nasezindaweni zokusebenza ukuze kubase imililo esetshenziselwa ukusetshenziswa okuhlukahlukene. Le gesi idala ukufa kwabantu abaningi ngenxa yemvelo yayo yobunzima ekubonweni futhi ingavutha kalula. Ngakho-ke, lokhu kuphakamisa ukuthi ingenye yezinto ezingcolisa umoya ezidinga ukubonwa nokuqapha njalo. Ucwaningo oluningi emphakathini ozwa igesi yamakhemikhali lugxile ekuzwaneni nje okujwayelekile kwala magesi. Emzamweni wokuxazulula inkinga ende ekhona, senze lolu cwaningo, lapho i-MgCexFe2-xO4 (0 ≤ x ≤ 0.4) nanoparticles ikhiqizwe indlela ye-glyco-thermal futhi ibonakala nge-X-ray diffraction, i-electron microscopy, i-X-ray photoelectron spectroscopy, i-Mössbauer spectroscopy kanye nokuhlaziywa kokuzwa kwegesi. Imiphumela ye-X-ray diffraction ibonise ukuthi isigaba se-cubic spinel esihlanzekile sakhiwe amasampula ane-concentration ephansi ye-Ce, kodwa i-Ce doping ephezulu (x ≥ 0.2) ye-magnesium ferrite ibangele ukwakheka kwezigaba zesibili. Ubukhulu be-crystallite bezinhlanganisela busukela ku-2.2 nm kuya ku-15.3 nm. I-spectra ye-57Fe Mössbauer ibonise ukuguqulwa ukusuka ku-oda ukuya esimweni sokujikeleza kwe-paramagnetic kanye nokwenyuka kokugxila kwe-Ce. Izinzwa zegesi ezakhiwe ngama-spinel ferrites zahlolelwa ukushunqa inhlabathi ehlukahlukene (i-acetone, i-methanol, i-p-xylene, i-ethylbenzene, i-toluene, ne-benzene) namagesi avuthayo (LPG, Methane, Propane, Butane kanye ne-ammonia) ezingeni lokushisa elingu-225°C. I-MgCe0.2Fe1.8O4 nanoferrites ibonakale inezici zezinzwa zekhwalithi zokuzwela okuphezulu nokukhetha kumhwamuko we-acetone, nempendulo yokugxila okungaphezu kuka-500@100 ppm kanye nokuphindaphindeka, ukuhlehla, nokuzinza kwezinsuku ezingaphezu kweziyi-120. Le nzwa ayizange ibonise ukusabela okuphezulu kuphela, kodwa futhi ibikwazi ukuzigcina ngaphezu kwe-1, 3, 5, 10, 20, kanye nemizuzu engama-30 yesikhathi sokuchayeka kwe-acetone. Kumagesi avuthayo, ukungezwa kwe-cerium kuma-magnesium ferrites kufakazele ukubulala inzwa. Inzwa esebenza kahle kakhulu itholwe iyi-Magnesium ferrite engafakwanga i cerium kugesi ye-LPG. Yayikwazi ukumelana nezimo futhi izwela umoya-mpilo oncishisiwe, indawo ezungezile engenzi lutho. Ngaphansi komswakama ohlobene, impendulo yancishiswa, kodwa yazinza, ngenxa yama-molecule amanzi afakwe i-physisorbed. Ukwengeza, le nzwa ye-SMO ihlolwe ku-200 ˚C ezitshalweni nasezithelweni ukuze kuhlolwe ubusha bazo obungekho eshalofini ngesikhathi sokuvuthwa. Lezi zitshalo zibonisa ukwanda okumangalisayo kwezinga lokuphefumula phezu kokuvuthwa kwazo noma inqubo yokuvuthwa ngokuhamba kwesikhathi.
- ItemPalladium (pd) decorated zinc oxide (ZnO) nanoparticles for gas sensing applications: meat spoilage gases(University of Zululand, 2024) Manqele, K.B.The detection of odours emitted by meat products when they start to spoil remains a challenge. In response to this, materials of ZnO decorated with palladium nanoparticles were synthesised using the hydrothermal method for the purpose of testing their gas sensing properties. After the synthesis of these nanoparticles, various characterization techniques for the investigation of both physical and chemical properties were employed. Different percentages of Palladium ranging between 0.2% and 0.7% from a PdCl2 precursor with 99.9% purity were used during the synthesis. A gas sensor was fabricated through the drop casting method on a gold grid. These gas sensor samples were exposed to both reducing and oxidizing gases. Sensing was performed at a temperature from 25°C to 225°C. The best result was obtained at 150°C using 0.2%Pd-ZnO sensor for NO2 gas sensing. A sensitivity of 3.8 was recorded, with both response time and recovery time of 3.5 minutes. The 0.5%Pd-ZnO sensor performs well at room temperature for CO2, SO2, and ethanol gases. OKUHUNYUSHWE NGOLIMI LWESIZULU Ukutholakala kwephunga elikhishwa yinyama lapho isiqala ukubola kuseyinselelo. Ukuphendula lokhu, izinto ze-ZnO ezihlotshiswe nge-palladium (Pd) nanoparticles zahlanganiswa kusetshenziswa indlela ye-hydrothermal ngenhloso yokuhlola izakhiwo zabo zokuzwa igesi. Ngemva kokuhlanganiswa kwalawa ma-nanoparticles, kwasetshenziswa amasu ahlukahlukene kucutshungulwa izakhiwo ezingokomzimba nezamakhemikhali. Amaphesenti ahlukene e-Palladium aphakathi kuka-0.2% no-0.7% kusukela ku- PdCl2 eyandulelayo enobumsulwa obungu-99.9% asetshenziswe ngesikhathi sokuhlanganiswa. Inzwa yegesi yakhiwe ngendlela yokulahla phansi kugridi yegolide. Lawa masampula enzwa yegesi avezwe kukho kokubili amagesi anciphisa nawoku-oxidizing. Ukuzwa kwenziwa ezingeni lokushisa elisuka ku-25°C kuya ku-225°C. Umphumela omuhle kakhulu utholwe ku-150°C kusetshenziswa inzwa engu-0.2% Pd-ZnO yenzwa yegesi engu- NO2. Ukuzwela kwe-3.8 kwarekhodwa, nakho kokubili isikhathi sokuphendula nesikhathi sokuthola kabusha semizuzu ye-3.5. Inzwa engu-0.5% Pd-ZnO isebenza kahle ekamelweni lokushisa le- CO2, SO2, kanye negesi ye-ethanol.
- ItemComparative of Flammable and Toxic Gas Sensing behavior for Rare-Earth Elements Substituted Cobalt based Spinel Ferrites(University of Zululand, 2021) Shozi, Euphemia Nolwazi NontobekoThere is a considerable need to design and develop a Liquid petroleum gas sensor due to its use in households and high flammability to protect human safety. Therefore, in this research work, we present a variety of cobalt-based spinel ferrites doped with 4f electron rare-earth ions to be used as flammable gas sensors. These spinel ferrites were fabricated following a glycol hydrothermal chemical-process. Due to their electronic configuration and charge dynamics, they are very sensitive and selective to integrative liquefied petroleum gases (LPG). A high response of over 730 was recorded towards 1 vol% (or 10 000 ppm) of LPG at 225 °C. The CoSm0.1Fe1.9O4 nano-ferrite meets the criteria of a potential sensor of being highly sensitive and selective with repeatability and stability that maintained a high response of 241 over 63 days. The rare-earth elements doped cobalt based ferrites were classified according to two categories in terms of overall performance. The first category were the ferrites doped with the low 4f electrons and the second category belonged to the high 4f electrons. The first category composed of solid and compact nanoparticles and proved to be better in the LPG performance while giving low photoluminescence emission intensities. This latter category had the highest combined percentages of oxygen vacancies and adsorbed oxygen. A temperature dependent tunable carrier-type transition was observed. The ferrite has p-type characteristics at 225 °C and above, otherwise n-type below this operating temperature to room temperature.
- ItemInvestigating the Feasibility of Using the Neutron Activation Analysis (NAA) Technique to Measure Industrial Pollution in Soil and Water in the Richards Bay Area(University of Zululand, 2020) Mhlongo, Sizwe SceloThe Neutron Activation Analysis (NAA) technique is one of the reliable and most sensitive analytical techniques for analyzing materials. The technique has unique capabilities that are not found in other analytical techniques. For instance, it is relatively faster as it does not require much sample preparation, if the instrumental approach is to be used, and can analyze bulk samples. In this study, the feasibility of using NAA to measure industrial pollution in the environmental samples (soil and water) was investigated, with Richards Bay being the area of interest. Although chemical elements are naturally present in the environment as major and trace elements, their content can increase due to anthropogenic activities. This leads to various issues that negatively affect the environment. Richards Bay is one of the towns that consist of various industries, among which are heavy industries. Thus, there is a need for routine pollution measurement, more especially in the sediments and water bodies of the area. Since the NAA technique has never been employed to measure pollution in this area, this study is aimed at investigating its sensitivity to Aluminum (Al), Chromium (Cr), Zinc (Zn), Manganese (Mn), Iron (Fe), Nickel (Ni), Cadmium (Cd) and Strontium (Sr), which are some of the typical pollutants from the various industries present in the area. The experiments were conducted at the University of Cape Town (UCT), where two neutron sources - the Deuterium-Tritium (D-T) neutron generator and the Americium-Beryllium (AmBe) source - and a γ-ray spectrometer are available. The soil and water samples collected from the study area were irradiated and their spectra were measured using the High-purity germanium (HPGe) detector system. In addition, CRMs were also irradiated, with only the water CRM being irradiated using both sources. To complement the experiments, predictions of dominant reactions and those of interest were made using Monte Carlo method, FLUKA. The simulation results showed that NAA is more sensitive to elements in the soil than in water, thus leading to the conclusion that elements need to be present in concentrations higher than those in the water CRM. This was also observed in the experimental results