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New source of biogenic silicon from sugarcane bagasse
(Springer Nature, 2024-11) Seroka, Ntalane S; Khotseng, L
This paper describes the generation of biogenic silicon from sugarcane bagasse ash (SCBA). Furthermore, silica was recovered from sugarcane waste using a modified thermochemical approach, that is, tetrapropylammonium hydroxide, and then reacted with magnesium in the magnesiothermic reduction process to produce biogenic silicon. The physicochemical properties of the produced nanocrystalline silicon were examined using Powder XRD (P’XRD), Raman spectroscopy, FTIR, TEM, and SEM. X-ray diffraction spectroscopy revealed a peak at 2θ of 28 corresponding to a 30 nm crystallite size. The Raman analysis revealed a pronounced peak at 510 cm−1, indicating highly ordered silicon. The surface analysis revealed two distinct bands at 445 cm−1 and 1046 cm−1, representing the Si-O rocking and Si-O-Si stretching behavior. Nanotechnology as an enabler has proved that SCBA as a sustainable and renewable resource can be used for the production of biogenic silicon.
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The numerical comparison of various hole-set design methodologies for a micro gas turbine combustor
(2024-09) Meyers, Bronwyn C; Grobler, Jan-Hendrik
A combustor design programme was initiated to design a combustor for a 200N microgas turbine. The method is that of a phased approach in order to gain better insight into the effect of various aspects of the combustor geometry as well as the combustor boundary conditions. The preliminary combustor design was performed using the NREC design method resulting in multiple designs to consider. This first phase focused on the Annuli mass flow splits and ensuring an improved Primary zone by devising a configuration conducive to a Recirculation zone approaching that shown in the theory. In order to make design selections, and later evaluate the effects of boundary conditions and design methods, a scoring and ranking method was devised to effectively evaluate the cold flow CFD simulation results. The second phase involved the evaluation of the effect of inlet swirling flow on the designs selected in phase one. This study, constituting phase three, is focused on the design of the Secondary and Dilution zone hole-sets using multiple methods available in literature, namely Lefebvre, Lefebvre and Ballal, and Mattingly et al. The purpose of this design phase is to improve the Secondary and Dilution zone holes. The resultant hole-sets were evaluated for practicality and manufacturability and adjustments were made to the number and size of the holes while maintaining a constant Total hole-set area (Aht) and attempting to maintain a constant Jet Diameter - Momentum flux ratio (djJ0.5). In addition to the design improvements, the aim is to compare four additional design methods and identify the preferred hole-set design method as well as to evaluate whether the applied adjustments maintain the penetration depths as was indicated should be the case in the literature. It was found that although the Lefebvre method produced some improved designs, it also produced many designs that were not improvements, thus it can not be said that the particular method is a better one. In addition, there weren’t highly evident trends that emerged with the systematic changes, thus a change in the combustor design approach could be beneficial which involves design through the optimisation of a complete parameter space to determine a better design per application or engine.
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Electrochemical and tribological performance of Ti–Al with xNb addition synthesized via laser In situ alloying
(2024-01) Kanyane, LR; Raji, SA; Tlotleng, Monnamme
Additive manufacturing is a growing technique of producing 3D parts directly using metal powders or wires melted with a high-powered intensity beam or laser. It is still a challenging process as to how laser processing parameters such as gas flow rate and powder flow rate can profitably be adopted to significantly produce Ti–Al-based materials from elemental powders to synthesize alloys that are defect-free and have good mechanical properties. The density of titanium aluminide (Ti–Al) intermetallic alloys makes it gain lots of interests due to its potential ability to substitute nickel-based superalloys in gas turbine engines. This work aims to investigate the effects of Niobium (Nb) additions on Ti–Al–xNb ternary alloys created via the use of 3D printing technology, specifically looking at microstructural evolution, microhardness, electrochemical behavior, and tribological properties. Ti–Al–Nb alloy was synthesized at scan speed of 26 in/min and laser power of 450 W. The structural morphology of the alloys produced was investigated using scanning electron microscopy equipped with energy dispersive spectroscopy and the electrochemical studies of the in situ alloyed Ti–Al–xNb were studied using potentiodynamic techniques. Using an Emco microhardness tester, the microhardness characteristics of the produced TiAl–xNb alloys were examined. From the results obtained, it was observed that the microstructure showed not much substantial cracking or crack initiation. The micrographs are evident of refined microstructure associated to increase in Nb feed rate with α-Ti3Al, γ-TiAl and precipitates of β-TiAl phases as the distinctively identified in the microstructure. The highest recorded microhardness value of 679.1  HV0.5 was achieved at Nb feed of 0.5 rpm and gas carrier of 2 L/min. The fabricated Ti–Al–Nb alloys showed good corrosion resistance behavior in HCl and appreciable wear characteristics with coefficient of friction of 0.412, 0.401, and 0.414 µ at B1, B3, and B5, respectively.
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Experimental and Computational Thermal Analysis of Ti-Based Alloy Produced by Laser Metal Deposition Technique
(2024-02) Kanyane, LR; Malatji, N; Popoola, AP; Raji, SA; Pityana, Sisa L; Shongwe, MB; Tlotleng, Monnamme
A Ti-Fe-Si-Cr-Nb alloy was fabricated using laser metal deposition (LMD) technique. The laser power and scanning speed were varied during fabrication to optimize the processing parameters. The thermal behavior during LMD processing was modeled and simulated by means of COMSOL Multiphysics 6.0 software. The samples produced were characterized using an optical microscope, X-ray diffractometer, and scanning electron microscope coupled with energy dispersive spectroscopy. The microhardness and wear behavior of the alloy were tested using a diamond indenter and ball-on-disk wear machine. The results obtained showed that the alloys exhibited similar dendritic microstructure for all processing parameters. The formation of cracks and pores were evident mainly in samples that were produced at high scanning speed and low laser power. A decrease in microhardness was noticed when the laser power was increased, while an increase in scanning speed yielded samples with high microhardness values. The alloy showed good tribological behavior, but no clear relationship between the wear resistance of the alloy and the variation of the laser processing parameters could be established.
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Validation of CSIR wind tunnel calibration data under different barometric conditions using comparisons with a reference laboratory
(2024-09) Dikgale, Moyahabo S
This paper presents the validation of the calibration data of the Council of Scientific and Industrial Research (CSIR) Calibration Wind Tunnel by evaluating its accuracy under different barometric conditions. Using a reference laboratory with established calibration standards as a benchmark, we compared the CSIR wind tunnel's measurements against those from the reference facility across a range of wind speeds. Our methodology involved a series of controlled calibration designed to assess the consistency and reliability of the wind tunnel's calibration data in different atmospheric conditions. The results demonstrated that the CSIR wind tunnel maintains a high degree of accuracy and reliability, with deviations falling within acceptable limits relative to the reference laboratory's data. This validation highlights the robustness of the CSIR wind tunnel calibration process and its capability to deliver precise wind speed measurements’ calibration across different environmental conditions.