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- ItemEffects of particles’ size and composition on magnetic properties of substituted ferrite nanoparticles(University of Zululand, 2024) Majozi, Prince Phathizwe; Msomi, J. Z. and Jili, T. P.This project presents the effects of particle size and composition on the magnetic properties of ferrites investigated by magnetization and electron spin resonance (ESR) spectroscopy. CuxMn1−xFe2O4, (Zn, Cd)Fe1.2Al0.8O4, NixCo1−xFe2O4 and Cu0.5Ni0.5Fe2O4 nanoferrites were produced by glycol-thermal reaction under a low reaction temperature of 200 ◦C. Structural properties were analysed by transmission electron microscopy (TEM) and X-ray diffraction (XRD). For CuxMn1−xFe2O4, the majority of the XRD peaks were indexed to the cubic spinel phase. However, a small impurity peak at 2θ ≈ 52◦ attributed to α-Fe2O3 and Mn2O3 phases for samples 0.4≤ x ≤ 0.8 was observed. The particle sizes varied between 8 nm and 16 nm. The particle size for the sample x = 0.3 (Cu0.3Mn0.7O4), which did not show any impurity phases was about 8 nm. The reduction of lattice parameters as a function of increasing Cu content is attributed to the smaller Cu replacing Mn ions. Magnetization data revealed superparamagnetic Cu0.3Mn0.7Fe2O4 fine particles and spin-glass behaviour. Enhanced magnetization and coercive fields at 10 K were explained by the core-shell model and spin freezing. An attempt to produce (Zn, Cd)Fe1.2Al0.8O4 was made. The XRD spectrum of the Cd-based sample showed impurity phases. XRD analysis showed clean ZnFe1.2Al0.8O4 with a particle size of about 6 nm. TEM images revealed nearly spherical particles with a reasonably narrow distribution of particle size which compared well with the value estimated from XRD data. ESR measurements showed a single-line signal indicative of dominant superexchange interactions. A small peak at very low magnetic field (about -500 ≤ H ≤ 500 G) was observed for the Zn- based oxide annealed at 1000 ◦C. This anomalous peak may be due to the low field microwave absorption(LFMA) phenomenon that is not fully understood in magnetic materials. NixCo1−xFe2O4 were successfully indexed to the cubic spinel. An additional peak associated with α-Fe2O3 was observed for samples with 0.7 ≤ x ≤ 0.9. XRD spectra revealed crystallite sizes ranging from 8 nm to 13 nm. There was no significant change in lattice parameters with increasing Ni concentration due to the small difference in their atomic radii. The ESR results showed single-line signals. Additional resonances were observed at low fields which need further measurements. We suspect these additional resonance peaks to be due to LFMA. The Land´e g-values varied between 1.98 and 3.6. Nanosized Cu0.5Ni0.5Fe2O4 fine particles with particle sizes of about 12 nm were produced. XRD did not show any impurity phases. The as-prepared oxide was annealed from 500 ◦C to 1100 ◦C to investigate particle size effects. Grain growth to about 46 nm was observed after annealing at 900 ◦C. ESR data revealed enhanced magnetization on the sample annealed at 900 ◦C due to the large ferromagnetic domains.
- 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.