Journal Articles

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2D numerical model for heat transfer on a laser deposited high entropy alloy baseplate using Comsol Multiphysics
(2021-12) Dada, A; Popoola, P; Mathe, Ntombizodwa R; Adeosun, S; Aramide, O
In an optimization study, cracks were observed in the microstructures of laser-deposited HEAs on a steel baseplate from residual stresses, thus, the optimization of crack-free microstructures was achieved by the optimization of the laser parameters by baseplate preheating attributed to the lowering of the thermal gradients of the deposition process. This study reports the finite element analysis on the temperature distribution by the moving laser modelled to achieve process optimization with the necessary boundary conditions. Simulation has been reported as a facilitating tool in predicting the behaviour of materials during process optimization. Comsol Multiphysics 4.4, was used to create a 2D transient heat transfer time-dependent model to simulate the temperature distribution and the laser heating of the A301 steel baseplate surface and determine the effect of temperature on the optimization process of the alloys. Gaussian profiles were used as the heat source distributed per time. The results are presented in terms of thermal fields and Gaussian temperature profiles. Which show the temperature distribution that occurred in the steel baseplate during fabrication and the high cooling rate of the laser additive manufacturing technique restricted thermal stresses, improving adhesion and facilitating the optimization process.
3D printed microfluidic chip design for diagnostic studies
(2024-12) Sekhwama, Masindi; Mpofu, Kelvin T; Mcoyi, Michael P; Sivarasu, S
In this study, additive manufacturing (3D printing) is utilised to fabricate lateral flow microfluidic chips (LFMC). Our chips were designed using Autodesk design software and printed using a Formlabs 3D printer. They are printed using Formlabs V4 resin polymer. In this work, the design process is highlighted in detail and shows an LFMC design that is made for potential applications in diagnostics studies. Our study also tested the performance of one of the chip designs in actual diagnostics experiment on an optical transmittance setup with a peristaltic pump. The LFMC was integrated onto a custom-built transmittance optical biosensor to measure the transmission intensity. A real-time kinetic study was conducted using an HIV-1 oligonucleotide probe. The study involved performing real-time transmittance analysis by pumping the HIV-1 oligonucleotide probe at different flow rates, ranging from 9. 5 μm/min to 13 μm/min with intervals of 0.5 μm/min. During the experiment, transmission intensity or transmitted light was measured in real time as the oligonucleotide HIV probe bound to neutravidin immobilised on the Au metal surface. These measurements were recorded using a USB400 spectrometer, with a broad- band UV light source that emits wavelengths ranging from 400 to 800 nm. The study underscored the significance of microfluidic chips as devices capable of enhancing the performance of biosensors as well as the use of 3D printing in the design and manufacture of these microfluidic chips.
A comparison of weldability and mechanical properties of additive manufactured and bulk Ti6Al4V alloy
(2024-11) Akinlabi, ET; Omoniyi, PO; Mahamood, RM; Arthur, Nana KK; Pityana, Sisa L; Skhosane, Besabakhe S; Okamoto, Y; Shinonaga, T; Maina, MR; Akinlabi, SA; Jen, TC
Titanium and its alloys, especially the Ti6Al4V, have tremendous use in the aerospace and biomedical industries. Since conceptualizing additive manufacturing techniques, it has been one of the most popular manufacturing techniques used on Titanium and its alloys. However, building large parts of the Ti6Al4V through additive manufacturing can be cumbersome due to the multiphysics involved in the heating and cooling of the material and the limited building space. This article examines the weldability of additive manufactured Ti6Al4V, manufactured through laser metal deposition (LMD) technique, and bulk sheet metal of Ti6Al4V manufactured through the rolling process. The welds were characterized using hardness, tensile, X-ray diffraction (XRD), and the evolving microstructure. Results show martensitic microstructure within the fusion zone, resulting in high hardness within the zone, which is confirmed in the XRD results. Failure occurred at the LMD heat-affected zone side of the sample due to the martensitic microstructure within the zone. The research further affirms the feasibility of joining Ti6Al4V manufactured through different routes through laser welding.
Addition of Chromium and its effect on the microstructure and mechanical properties of laser- coated high carbon ferrochrome alloy on mild steel
(2021-08) Aramide, BP; Popoola, P; Sadiku, R; Jamiru, T; Pityana, Sisa L
Laser cladding is an additive manufacturing technology that can be utilized in surface strengthening, modification, and repair of components that are subjected to adverse working conditions. This can be accomplished by the addition of functionally graded material with a remarkable limit to enhancing an engaged credited property of monolithic material that is superior and better than its monolithic counterparts. Chromium addition to the microstructure of components has been found to increase the electrochemical stability, high-temperature strength and corrosion resistance of laser additive manufactured components. The current study investigates the effect of the extra addition of chromium on the hardness and microstructure of laser coated high carbon ferrochrome FeCrV15 on steel baseplate.
The adsorption of halogen molecules on Ti (110) surface
(2021-01) Tshwane, David M; Modiba, Rosinah; Govender, Gonasagren; Ngoepe, PE; Chauke, R
Adsorption of halogen on the metal surface has received much attention due to its technological applications and major relevance for material surface processing, corrosion protection and etching. In this work, first-principle approach was used to investigate the interaction of halogen molecules on Ti (110) surface. The present results revealed that adsorption of the halogen molecule is exothermic and occurs by dissociation bonding. The HF molecule was found to be more thermodynamically stable than the HI molecule. In addition, our results revealed that the adsorption of halogen ions on Ti (110) surface is energetically favourable than the adsorption of halogen molecule. The possible adsorption sites were tested, and the top site position was found to be the most favourable followed by the hollow and bridging site for both halogens. Furthermore, the results showed the linear relationship between adsorption energy strength and charge transfer. Also, the density of states and charge density difference was studied to investigate the electronic interaction. The charge redistribution showed an electron depletion on Ti atom and charge accumulation on the halogen region.
Adsorption of NH3 and NO2 molecules on sn-doped and undoped ZnO (101) surfaces using density functional theory
(2022) Dima, Ratshilumela S; Tshwane, David M; Shingange, Katekani; Modiba, Rosinah; Maluta, NE; Maphanga, Rapela R
The adsorption and interaction mechanisms of gaseous molecules on ZnO surfaces have received considerable attention because of their technological applications in gas sensing. The adsorption behavior of NH3 and NO2 molecules on undoped and Sn-doped ZnO (101) surfaces was investigated using density functional theory. The current findings revealed that both molecules adsorb via chemisorption rather than physisorption, with all the adsorption energy values found to be negative. The calculated adsorption energy revealed that the adsorption of the NH3 molecule on the bare ZnO surface is more energetically favorable than the adsorption of the NO2 molecule. However, a stable adsorption configuration was discovered for the NO2 molecule on the surface of the Sn-doped ZnO surface. Furthermore, the adsorption on the undoped surface increased the work function, while the adsorption on the doped surface decreased. The charge density redistribution showed charge accumulation and depletion on both adsorbent and adsorbate. In addition, the density of states and band structures were studied to investigate the electronic behavior of NH3 and NO2 molecules adsorbed on undoped and Sn-doped ZnO (101) surfaces.
Adsorption-desorption of F2 diatomic molecule on Ti (100) surface at different coverages
(2021-12) Tshwane, David M; Modiba, Rosinah; Govender, Gonasagren; Ngoepe, PE; Chauke, HR
Fluorine molecules and ions are used as an etchant for metal surface processing. The presence of fluorine significantly influences the electrochemical behaviour on a metal surface, which has major relevance for etching, corrosion, electro-catalysis and galvanic deposition processes. Although the fluorine ions play an important role in metal surface etching, the studies remain limited and unclear, especially at the atomistic scale. In this work, density functional theory is used to investigate the structural and electronic properties of F2 diatomic molecule adsorption on Ti (100) surface at different coverages. Results revealed a dissociative adsorption mechanism of F2 on the Ti (100) surface. Adsorption energy analysis of F2 on Ti (100) surface denotes an exothermic process. Moreover, increasing F2 coverage resulted in the formation of TiF4 and Ti2F6 molecules on the surface. In addition, the calculated heat of formation for TiF4 was found to be more favourable than Ti2F6 species. Calculated desorption energies for TiF4 and Ti2F6 is 11.73 eV/atom and 9.04 eV/atom, suggesting non-spontaneous.
An optical gas imaging technique based on strobed illumination
(2024-12) Chirindo, Mathews; Cox, Ettienne; Duness, Kahesh
Gas leakage from equipment poses undesirable safety, environmental and operational impacts. Many optimal gas imaging techniques exist which detect and visualize gas plumes. However, most of these techniques struggle to produce clear images when the temperature gradient between the scene background and the gas plume is small. This paper presents an optical gas imaging technique that is based on strobed illumination, wherein the strobing frequency of the illuminating device is associated with the camera frame rate. Experimental test results are presented to show the improved detection of volatile organic compound gases during strobed illumination under dark room laboratory conditions where the percentage contrast value of the illuminated gas relative to its background varies by 50.8% The test results for the detection of sulphur hexafluoride gas and liquid petroleum gas under an outside environment are also presented.
Analysis of dry sliding wear performance of tribaloy T-800/Tungsten carbide coating deposited via laser cladding assisted with preheating
(2022-10) Nyadongo, ST; Olakanmi, EO; Pityana, Sisa L
Shafts, gears, axles and crankshafts, which are exposed to severe sliding wear environment, are made from wear resistant EN8 medium carbon steel. The wear resistance of EN8 can be enhanced by depositing it with laser cladding assisted with preheat (LCAP) fabricated T-800/WC composite coating. A systematic study via accurate, reproducible ball on disk tests which explores how extreme sliding force and velocity influence wear resistance and mechanism of the coating and the uncoated EN8 is carried out. It was revealed that EN8 substrate has up to six (6) times more special specific wear rate (SSWR) relative to T-800/WC coating. An increase in sliding force increased the SSWR whilst an increase in sliding velocity reduced the SSWR for the LCAP coating. Alumina (Al2O3) counter wear body exhibited the highest SSWR compared to silicon carbide (SiC) and silicon nitride (Si3N4) counter wear body on both T-800/WC and EN8. Oxidative and abrasive wear mechanisms were evident on the coating. A wear mechanism for the T-800/WC was deduced which showed abrasive wear, oxide layer formation, breaking of the formed oxide layer and back to abrasive wear during dry sliding wear.
Analysis of failure characteristics of screen plates of ring hammer crusher used in coal handling applications
(2024-08) Kyekyere, E; Olakanmi, EO; Prasad, RVS; Matshediso, B; Motimedi, T; Botes, A; Pityana, Sisa L
The screen plate, a critical component within a ring hammer crusher (also known as a ring granulator or rolling ring crusher), plays a vital role in the secondary crushing of coal. Functioning both as a platform for coal crushing and as a sieve to achieve the desired coal size, it is essential to understand and examine its failure characteristics to enhance its mechanical and wear resistance properties in coal handling applications. This study thoroughly explored the failure modes, mechanisms, and underlying causes of screen plate failures. Microscopic techniques such as optical microscopy (OM), scanning electron microscopy (SEM), Vickers microhardness test and spectrochemical analysis were utilised to identify the failure mechanism. Failure modes identified from the macroscopic analysis were discharged hole widening, hole wall break-off, plate edge crack, plate fracture, one-sided edge slimming, and general surface wear of the screen plate. The fractographic and wear track analysis identified the principal failure mechanisms of three-body abrasive wear, two-body sliding abrasion wear, shear-induced fatigue fracture and brittle shear fracture. The root causes of the failures are the rotor’s direct impact, defects in the parent material, the presence of hard materials in the coal and the use of unsuitable steel grade in the screen plate manufacturing. The service life of the screen plate can be improved through proper material selection, uniform crusher feeding, surface modification of the surface of the “as purchase” screen plate with appropriate wear-resistant materials, and adherence to good maintenance practices.
Anomaly detection monitoring system for healthcare
(2021-01) Boloka, Tlou J; Crafford, Gerhardus J; Mokuwe, Mamuku W; Van Eden, Beatrice
Most developing countries suffer from inadequate health care facilities and a lack of medical practitioners as most of them emigrate to developed countries. The outbreak of the COVID-19 pandemic has left these countries more vulnerable to facing the worse outcome of the pandemic. This necessitates the need for a system that continuously monitors patient status and detects how their physiological variables will change over time. As a result, it will reduce the rate of mortality and mitigate the need for medical practitioners to monitor patients continuously. In this work, we show how an autoencoder and extreme gradient boosting can be merged to forecast physiological variables of a patient and detect anomalies and their level of divergence. An accurate detection of current and future anomalies will enable remedial action to be taken by medical practitioners at the right time and possibly save lives.
Applications of microfluidics in biosensing
(2024) Sekhwama, Masindi; Mpofu, Kelvin T; Sivarasu, S; Mthunzi-Kufa, Patience
Microfluidic devices have become a vastly popular technology, particularly because of the advantages they offer over their traditional counterparts. They have such a wide range of uses and can make complex tasks quite efficient. One area of research or work that has benefited greatly from the use of microfluidics is biosensing, where microfluidic chips are integrated into biosensor setups. There are growing numbers of applications of microfluidics in this area as researchers look for efficient ways to tackle disease diagnostics and drug discovery, which are critical in this era of recurring pandemics. In this work, the authors review the integration of microfluidic chips with biosensors, as well as microfluidic applications in biosensing, food security, molecular biology, cell diagnostics, and disease diagnostics, and look at some of the most recent research work in these areas. The work covers a wide range of applications including cellular diagnostics, life science research, agro-food processing, immunological diagnostics, molecular diagnostics, and veterinarian diagnostics. Microfluidics is a field which combines fundamental laws of physics and chemistry to solve miniaturization problems involving fluids at the nanoscale and microscale, and as such, the authors also examine some fundamental mathematical concepts in microfluidics and their applications to biosensing. Microfluidics has relatively new technologies with great potential in terms of applications.
Challenges in machining of advanced materials
(CRC Press, 2022-05) Mathabathe, Maria N; Bolokang, Amogelang S; Gajrani, KK; Prasad, A; Kumar, A
Contemporary ways of employing and combining existing materials are a requisite for meeting tomorrow’s engineering applications. This is upscaled by the potent attributes of remaining competitive by keeping costs effective while advancing the fabrication of new material technologies. Thus, moderation of the tool condition and machining process, for example, is becoming successively critical to achieving more eminent yields, exceptional machine automation, better product quality, and reduced labor-intensive costs. Owing to the intricate nature of advanced materials, such as ceramic matrix composites, their brittle and heterogeneous structure and their anisotropic mechanical and thermal behavior render a variety of material removal mechanisms that result in surface defects. Therefore, this chapter’s objective is to focally evaluate how dissimilar machining techniques influence the machined surfaces of advanced materials. Furthermore, the study aims to pioneer the fundamental technologies and trendsetting development for machining process monitoring, namely, contemporary industrial practice inclusive of general workpiece surface integrity parameters, fluid consignment systems, wheel preparation options, and machine tool design/alignments. Similarly, academic research on the conventional and nonconventional machinability of advanced materials in the aerospace industry is deeply investigated. This is achieved by assessing new, various material characterization methods to identify and quantify the mechanical and thermal surface/subsurface damages and highlight their governing removal/grinding-process mechanisms.
Characterisation of High-Density Polyethylene (DiaPow HDPE HXR)Powder for Use in Additive Manufacturing
(2024-08) Mwania, FW; Van der Walt, J; Wu, Lorinda; Koen, Wayne S; Maringa, M
High-density polyethylene (HDPE) is largely processed using conventional manufacturing techniques. However, there is a need to investigate its processability when fabricated using additive manufacturing (AM) in an efort to use this polymer for high-end applications, such as the fabrication of human implants. In this regard, the current study investigated the intrinsic and extrinsic properties of HDPE powders (DiaPow HDPE HX R) from Diamond Plastics GmbH, to determine its feasibility of use in powder bed fusion (PBF). Powder characterisation was undertaken using a scanning electron microscope (SEM), melt fow index (MFI) testing, tapped density testing, diferential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Fourier-transform infrared (FTIR) spectroscopy, and hot-stage microscopy. Te analysis revealed that this high-density polyethylene powder is suitable for processing using PBF based on the particle size distribution (PSD) (65–92μm), fowability (Hausner ratio �1.22±0.02), melting point range (125.7–135.2 degrees Celsius), enthalpy of melting (170.51J/g), and thermal stability (the materials starts to degrade at 350.0 degrees Celsius and completely degrades at 500.0 degrees Celsius). It also showed good coalescence behaviour. However, the narrow sintering window (7.9 degrees Celsius) of the material indicates possible challenges of shrinkage and curling during printing. Te material was also found to have poor absorptive properties of infrared radiation at 10.6 μm, which might make sintering using CO2 lasers challenging.
Chemical sensor nanotechnology in pharmaceutical drug research
(2022-08) Thobakgale, Setumo L; Ombinda-Lemboumba, Saturnin; Mthunzi-Kufa, Patience
The increase in demand for pharmaceutical treatments due to pandemic-related illnesses has created a need for improved quality control in drug manufacturing. Understanding the physical, biological, and chemical properties of APIs is an important area of health-related research. As such, research into enhanced chemical sensing and analysis of pharmaceutical ingredients (APIs) for drug development, delivery and monitoring has become immensely popular in the nanotechnology space. Nanomaterial-based chemical sensors have been used to detect and analyze APIs related to the treatment of various illnesses pre and post administration. Furthermore, electrical and optical techniques are often coupled with nano-chemical sensors to produce data for various applications which relate to the efficiencies of the APIs. In this review, we focus on the latest nanotechnology applied to probing the chemical and biochemical properties of pharmaceutical drugs, placing specific interest on several types of nanomaterial-based chemical sensors, their characteristics, detection methods, and applications. This study offers insight into the progress in drug development and monitoring research for designing improved quality control methods for pharmaceutical and healthrelated research.
The combination of low level laser therapy and efavirenz drastically reduces HIV infection in TZM-bl cells
(2020-06) Lugongolo, Masixole Y; Manoto, Sello L; Ombinda-Lemboumba, Saturnin; Maaza, M; Mthunzi-Kufa, Patience
Human immunodeficiency virus (HIV) infection remains a global health challenge despite the use of antiretroviral therapy, which has led to a significant decline in the mortality rates. Owing to the unavailability of an effective treatment to completely eradicate the virus, researchers continue to explore new methods. Low level laser therapy (LLLT) has been widely used to treat different medical conditions and involves the exposure of cells or tissues to low levels of red and near infrared light. The study aimed to determine the effect of combining two unrelated therapies on HIV infection in TZM-bl cells.
Comparative investigation and optimization of cutting tools performance during milling machining of titanium alloy (Ti6Al4V) using response surface methodology
(2024-02) Phokobye, SN; Desai, DA; Tlhabadira, I; Sadiku, ER; Mutombo, Kalenda
The purpose of this paper is to study the optimization of the cutting performance of three different cutting inserts, during the machining operation of titanium alloy (Ti6Al4V) by making use of the response surface methodology (RSM) on a computer numerical control (CNC) milling. The cutting tools employed for the optimisation of the cutting performance during machining operation are silicon, aluminium, oxygen, nitrogen (SiAlON), cubic-boron nitride and carbide cutting inserts. Scanning electron microscope (SEM) was used for the determination of the tool wear for the cutting inserts being compared during machining of Ti6Al4V, and the cutting parameters, which are cutting speed (Vc), feed per tooth (fz) and depth-of-cut that were evaluated from the cutting tools as per the manufacturer’s design specifications. The determination of the tool wear on the cutting inserts was achieved by using the SEM, while the machining operation for the experimental trails was performed from the CNC milling machine, where face milling operation was executed. The optimization process showed that carbide cutting inserts yielded the best performing results and were considered the most significant choice of cutting insert in machining Ti6Al4V when compared to SiAlON and CBN cutting inserts. This choice was from the cutting tool life obtained where a cutting tool life of 29 min was obtained from a use of carbide cutting inserts; 28 min resulted from a use SiAlON cutting inserts and 26 min from a use of CBN cutting inserts. This work finds appropriate value in assisting the machinists in the selection of the best most performing and cost-effective cutting tool.
The comparative study of the microstructural and corrosion behaviour of laser-deposited high entropy alloys
(2021-06) Dada, M; Popoola, P; Mathe, Ntombizodwa R; Pityana, Sisa L; Adeosun, S; Aramide, O
Corrosion is a conservational occurrence that has a large economic impact on most metals and its alloys because it destroys and deteriorates most materials by an electrochemical process through the reaction of these materials with the environment. High Entropy Alloys in aerospace applications react with the environment in applications such as jet engines, especially at elevated temperatures. Thus, the capacity of high entropy alloys to resist corrosion must be investigated to expand the application of this advanced material in the aerospace industry. In this comparative study, AlCoCrFeNiCu and AlCoCrFeNiTi High Entropy Alloy samples were fabricated by Laser Additive Manufacturing, particularly direct energy deposition and the corrosion behaviour of both alloys were examined and compared. The influence of the laser processing parameters on the microstructure and corrosion responses of the high entropy alloys in 3.5 wt% NaCl solution was also investigated. The microstructural morphologies were examined using an X-ray diffraction system (XRD) and Scanning electron microscope (SEM) equipped with Energy Dispersion Spectroscopy (EDS). The results showed that the Scan speed had the most influence on the microstructure and corrosion behaviour of the alloys. There was a strong relationship between the phase structure of the alloys and their susceptibility to localized corrosion. Therefore, it has been proposed in this study that the phase distribution within the alloys also influences the corrosion behaviour of laser deposited high entropy alloys.
Comparison study on the effect of oxygen, nitrogen and hydrogen absorption on phase transformation and mechanical properties of quenched CP Ti and Ti6Al4V alloy
(2024-11) Mguni, N; Mathabathe, Maria N; Shongwe, MB; Bolokang, Amogelang S
Microstructures and mechanical properties of commercial pure Ti and Ti6Al4V metal were studied after water quenching. The nitrogen (N), oxygen (O) and hydrogen (H) analysis was conducted on the quenched samples to establish the effect of impurities on phase transformation and mechanical properties. It was found that despite some negligible increment on the impurities, they could not be attributed to structural change but rather stabilization of the metastable FCC induced by rapid cooling. The formation of the metastable FCC phases was attributed to stresses induced by high cooling rates upon water quenching. Quenching from high temperatures has a significant effect on the crystal structure, microstructure and mechanical properties.
Conceptual design framework for setting up aluminum alloy powder production system for Selective Laser Melting (SLM) process
(2019-05) Matsagopane, G; Olakanmi, EO; Botes, Annelize; Kutua, S
Documentation on the correct process and component requirements for setting up efficient aluminum powder production systems capable of manufacturing powder that meets the requirements for the selective laser melting (SLM) process is not available due to its proprietary nature. This hinders powder metallurgy (PM) trainees in acquiring knowledge and skills needed in setting up such metal powder production systems. To address this challenge, powder requirements for the SLM process and powder production techniques for manufacturing powder that meets SLM requirements were identified and defined via literature review. User-value analysis and cost–benefit analysis techniques were applied as evaluation tools to identify the best components and process parameters for an aluminum powder production system. A conceptual design framework for setting up an aluminum powder gas atomizing system which meets SLM requirements is developed. This review improves the delivery of PM education in developing countries as trainees gain knowledge and skills for setting up powder production systems.

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