Mamookho Makhatha - Academia.edu (original) (raw)

Papers by Mamookho Makhatha

Arsenic - Analytical and Toxicological Studies, 2018

The work represents the bio-adsorption of arsenic(III) from standard solutions and real water sam... more The work represents the bio-adsorption of arsenic(III) from standard solutions and real water samples using a powdered avocado seed as a bio-adsorbent. The adsorbent was synthesized, demineralized, and characterized by X-ray diffraction (XRD), scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS), Fourier transformation infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) theory. Batch adsorption studies were carried out by using avocado seed, and As III was analyzed by using inductively coupled plasma optical emission spectroscopy (ICPOES) after optimizing the following parameters: pH 6, analyte concentration 2 mg L À1 , bio-adsorbent dosage 0.8 g, contact time 120 min between analyte and adsorbent, and temperature from 22 to 40 C. The adsorption capacity of 93.75 mg/g was obtained, and the Langmuir isotherm was adopted by the adsorbent due to the chemisorption that occurs on the surface between the functional groups of the bio-adsorbent and As III .

International Journal of Corrosion and Scale Inhibition, Mar 26, 2021

One of the ways to protect aluminum metal from corrosion in polymer electrolyte membrane (PEM) hy... more One of the ways to protect aluminum metal from corrosion in polymer electrolyte membrane (PEM) hydrogen fuel cells is through the use of the chemical inhibition method. In this work, we present unsubstituted (NiPc) and tetrasubstituted nickel phthalocyanines (TNNiPc) as corrosion inhibitors for aluminum (Al) metal in 1 mol•L-1 hydrochloric acid (HCl) solution. The synthesized inhibitors were characterized using several techniques. The XRD patterns demonstrated that NiPc was more crystalline than TNNiPc (a nitro group at a peripheral position). The FTIR spectra for all the inhibitors showed a similar vibration band at around 730 cm-1 , which was due to C-H deformations. The TNNiPc inhibitor showed additional asymmetric and symmetric NO2 vibrations around 1336 and 1525 cm-1 , respectively. The UVvis spectrum of NiPc showed an intense Q-band at around 774 nm in 1 mol•L-1 H2SO4, whereas TNNiPc resulted in a blue shift of the Q-band due to the electron-withdrawing properties of the NO2 group. The TGA supported the presence of NO2 by the degradation step as indicative of decomposition of NO2 group in the TNNiPc inhibitor. Electrochemical studies showed that the inhibitors prevent Al metal sheet corrosion by adsorbing on Al surface to form a pseudocapacitive interface. The inhibitive effect of NiPc and TNNiPc inhibitors increased with increasing concentration. Furthermore, potentiodynamic polarization measurements revealed that the dyes are mixed-type corrosion inhibitors.

The International Journal of Advanced Manufacturing Technology

β-type titanium alloys are acquiring research interest in orthopaedic applications because of the... more β-type titanium alloys are acquiring research interest in orthopaedic applications because of their exceptional properties such as moderate strength, good biocompatibility and corrosion resistance, high ductility and low elastic modulus. The study aims at designing a series of binary Ti-Mo alloys (Ti-8.71 Mo, Ti-10.02 Mo, Ti-11.78 Mo and Ti-15.05 Mo (wt%)) using the cluster plus glue atom model to design the compositions. The prediction methods such as the molybdenum equivalence, the average electron ratio and the d-electron methods were used to predict the stability of the β phase. Microstructural evolution and phases of the designed alloys were characterized using the optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffractometry (EBSD) and X-ray diffractometry (XRD), while the microhardness and tensile properties were measured using the Vickers hardness tester and tensile testing machine. The microstructure of the cast Ti-Mo alloys comprised primarily the β phase and secondary orthorhombic martensitic α″ and athermal omega (ω) phases. Their elastic moduli (96.8–70.5 GPa) decreased with the amount of Ti in the glue side and were found to be lower than the commercially available 316 L stainless steel, Co-Cr and Ti6Al4V alloys. The microhardness values of the as-cast Ti-Mo alloys decreased as the amount of Ti in the glue side decreased in the cluster formula. The tensile strength of the as-cast alloys ranges from 796.76 to 593.48 MPa with Ti-8.71 wt% Mo alloy showing the highest tensile strength owing to the amount of Ti in the glue side. The yield strength of all the designed alloys decreased as the amount of Ti atoms placed in the glue side decreased. The elongation at fracture ranged between 0.28 and 0.71%, indicating that all the designed alloys fractured in a brittle manner. The elastic admissible strain of the designed alloys (Ti-15.05 wt% Mo) was significantly higher than the conventional orthopaedic implant materials (CP-Ti, Ti6Al4V) indicating that this study is promising for the development of excellent biomedical materials.

Minerals

Mining of minerals such as gold, copper, and platinum has been one of several activities sustaini... more Mining of minerals such as gold, copper, and platinum has been one of several activities sustaining the economy of South Africa. However, the mining sector has contributed significantly to environmental contamination through the improper disposal of mine tailings which covers vast areas of land. Therefore, this study utilised a vitrification process to manufacture glass from gold mine tailings. X-ray fluorescence was used to determine the chemical composition of the tailings while X-ray diffraction was adopted for the mineralogy. The tailings were of granitic composition enriched in potentially toxic elements such as copper, cadmium, zinc, lead, arsenic, and chromium. A representative sample of gold mine wastes of sandy grain size was used in making the glass. Based on composition, the glass was formulated by adding an average 10.0 mass% of CaCO3 and 5.0 mass% of Na2CO3 to 35.0 mass% of SiO2, which resulted in the production of a green-coloured glass.

Materials Today: Proceedings

Abstract Shea nut shell (SNS) is an agrowaste obtained from Vitellaria paradoxa tree and discarde... more Abstract Shea nut shell (SNS) is an agrowaste obtained from Vitellaria paradoxa tree and discarded by burning. The extraction of nanocellulose from this agrowaste is expected to be a value addition to Shea farming and processing. However, the isolation of quality nanocellulose begins with optimal pretreatment of the agrowaste material. In this work, the mercerization of SNS collected from local processing centers was carried out by varying the treatment conditions such as temperature, time, liquor ratio (LR) and concentration of the alkali solution. The resulting samples were characterized using FTIR, TGA and DTGA. From the results obtained, the minimum treatment conditions required to isolate cellulose from SNS was obtained as 100 °C for treatment temperature, 2 h for treatment time, 1:20 for LR and 20% for alkali solution concentration. The isolated cellulose was also found to be of good thermal properties when compared to cellulose from other agrowaste. However, these conditions can be varied to give desired properties for specific application.

Transactions of the Indian Institute of Metals

The environmental consciousness and consumer pressure have forced manufacturing industries to use... more The environmental consciousness and consumer pressure have forced manufacturing industries to use natural fibres as a substitute for conventional non-renewable reinforcing materials. In the present investigation, the effect of rate of loading on jute fibre-reinforced polymer composite was studied. The mechanical properties (in three-point bend test) like interlaminar shear strength, yield strength and energy at break were examined as a function of strain rate. It was observed that the untreated fibre-reinforced composites were not very sensitive to the rate of loading; however, loading rate sensitivity was observed in alkali-treated fibre-reinforced composites. It has been proposed that fibre pull-out dominates over mechanism of composite failure in alkali-treated condition, and the interlaminar shear strength/yield strength was increased due to the increase in stiffness of the composite with rate of loading (in initial stage); however, at higher strain rate, matrix became susceptible to brittleness as there was lesser time available for crack-blunting to take place. All the microstructures were generated using a scanning electron microscope, and mechanical testing was done using tensile testing machine Instron 1195.

International Journal of Environmental Research and Public Health

The problem of environmental pollution is a global concern as it affects the entire ecosystem. Th... more The problem of environmental pollution is a global concern as it affects the entire ecosystem. There is a cyclic revolution of pollutants from industrial waste or anthropogenic sources into the environment, farmlands, plants, livestock and subsequently humans through the food chain. Most of the toxic metal cases in Africa and other developing nations are a result of industrialization coupled with poor effluent disposal and management. Due to widespread mining activities in South Africa, pollution is a common site with devastating consequences on the health of animals and humans likewise. In recent years, talks on toxic metal pollution had taken center stage in most scientific symposiums as a serious health concern. Very high levels of toxic metals have been reported in most parts of South African soils, plants, animals and water bodies due to pollution. Toxic metals such as Zinc (Zn), Lead (Pb), Aluminium (Al), Cadmium (Cd), Nickel (Ni), Iron (Fe), Manganese (Mn) and Arsenic (As) ar...

Transactions of the Indian Institute of Metals

In the present study, microstructural analysis of post-deformation annealed sample has been carri... more In the present study, microstructural analysis of post-deformation annealed sample has been carried out for 23Cr–6Ni–3Mo duplex stainless steel. It was observed that the restoration mechanism and substructural characteristics were different for austenite and ferrite during post-deformation annealing. In the initial stage of post-deformation annealing, the restoration mechanism of austenite envisaged meta-dynamic recrystallization (MDRX), while the dominating mechanism of softer ferrite showed static recovery (SRV) with a minimal of static recrystallization (SRX). In the intermediate stage, the austenite showed SRX followed by coarsening of meta-dynamically recrystallized grains, and ferrite revealed mostly SRV. The last stage of post-deformation annealing showed the disintegration of substructures in both austenite and ferrite. The microstructure after 20 min of post-deformation annealing displayed coarse subgrains. Finer austenite subgrains were observed as compared to ferrite subgrains after the post-deformation annealing of 20 min. High-resolution EBSD was used to study substructural characteristics of microstructure, and post-processing of microstructural results was made by HKL Channel 5 software. Misorientation angle distribution, subgrain size as well as restoration mechanism corresponding to both austenite and ferrite were determined over intensive sample area.

Transactions of the Indian Institute of Metals

In the present investigation, the effect of substructures on hardness and conductivity during par... more In the present investigation, the effect of substructures on hardness and conductivity during partial annealing of cold-rolled copper was studied. Substructures were observed after annealing at lower temperature; however, the annealed sample (at higher temperature) was mostly free from substructures. Therefore, it is proposed that the restoration mechanism at lower temperature envisages recovery in copper; however, it is partial recrystallization at higher temperature. There was an increase in hardness observed at lower temperature due to higher fraction of substructures, while an increase in conductivity was observed at higher temperature due to partial recrystallization. It was confirmed that the twin boundaries produced during cold rolling provided dislocations pinning, leading to greater tensile strength.

Transactions of the Indian Institute of Metals

The pipes are subjected to different load conditions such as internal stress, compression, tensio... more The pipes are subjected to different load conditions such as internal stress, compression, tension, bending and/or any combination thereof. These various types of load conditions induce new cracks and/or cause propagation of the existing cracks. In this study, a TP316L stainless steel pipe subjected to four-point bend testing was examined to predict the propagation of fatigue cracks in a part-through cracked pipe using the CASCA and FRANC2D programs. Two different methods based on “rigidity” and “stress intensity factor” have been proposed for converting a three-dimensional pipe into a two-dimensional beam for modeling.

Materiali in tehnologije

In this paper, friction-stir spot welding (FSSW) is performed on 3 mm thick AA1060 and C11000 usi... more In this paper, friction-stir spot welding (FSSW) is performed on 3 mm thick AA1060 and C11000 using different process parameters and tool geometries. The microstructure-and the microhardness-profile analyses were conducted and the probability distribution function (PDF) of the obtained microhardness values was determined. Optical images showed a good material mixing in most of the spot welds produced, whereas the energy-dispersive-spectroscopy (EDS) analysis showed the presence of intermetallic compounds. Microhardness results revealed that process parameters and tool geometries have significant effects on the distribution of microhardness values in different locations of the produced spot welds. Furthermore, goodness-of-fit values showed that most of the R 2 values ranged between 0.8842 and 0.9999, which indicated how well the model fits with the experimental data. On the other hand, the residuals comprised positive and negative runs which also indicated the existence of a certain correlation with the experimentation.

Trace Elements in the Environment - New Approaches and Recent Advances [Working Title]

In the Blesbokspruit area of Ekuhurleni, South Africa, previous gold mining activities resulted i... more In the Blesbokspruit area of Ekuhurleni, South Africa, previous gold mining activities resulted in many tailings dump sites. 20 representative soil samples were used in describing the distribution of metals. The soils were very strongly acidic ranging from 3.86 to 4.34 with a low cation exchange capacity (CEC). Based on X-ray fluorescence (XRF) analysis, elemental composition of the soils revealed average values of major elements such as Na2O (0.18%), MgO (0.63%), Al2O3 (6.51%), SiO2 (81.83%), P2O5 (0.04%), SO3 (3.40%), K2O (1.98%), CaO (0.45%), TiO2 (0.51%), Cr2O3 (0.17%), MnO (0.04%), Fe2O3 (3.59%), NiO (0.04%), As2O3 (0.02%), with Rb2O and SrO falling below 0.01%. Trace metals (TM) contamination levels in the soils were evaluated using various pollution indices which revealed that over 60% of the soils were between the high degree and the ultra-high degree of contamination classes. The concentration of various trace metals varies from 860.3-862.6 mg/kg for Cr; 324.9-328.4 mg/kg for Al; 200.9-203.4 mg/kg for As; 130.1-136.2 mg/kg for Fe; 121.9-125.8 mg/kg for Pb; 27.3-30.2 mg/kg for Co; 23.8-26.8 mg/kg for Ni; 7.2-9.2 mg/kg for Ti; 7.1-9.2 mg/kg for Cd; 4.0-5.6 mg/kg for Zn and 0.1-0.6 mg/kg for Cu.

Materials Today: Proceedings

Abstract Jarosite wastes are produced daily from the refineries and contain toxic elements. In th... more Abstract Jarosite wastes are produced daily from the refineries and contain toxic elements. In this study, the characterization of jarosite/clay/fly ash admixture is carried out to explore the possibility of using the produced bricks in the construction industry. The XRD results showed that the major phases in jarosite are Coesite and Mackinawite while Kaolinite and Mullite were found in clay and fly ash respectively.The major chemical elements in jarosite are Fe (41.46%), S (7.29%) and Si (5.61%) whereas Si (24.4%), Al (20.01%) and Fe (2.26%) were found in clay. On the hand, the major elements in fly ash are Si (22.44%), Al (18.42) and Ca (3.47).The microstructure of jaroriste and clay showed non-uniform particles in structure and irregular in shape while fly ash particles were uniform in structure and spherical/cenospherical in shape. The compressive strength results of the produced bricks revealed that all the 1:1 and 2:1 ratios with 15% and 20% met the minimum required compressive strengthof common building bricks. The chemical analysis of the leachates heated samples at 900˚C showed that toxic elements such as Pb, Fe and Ni were detoxified except for the Arsenic

Structural Integrity

Aluminium and copper are widely used in engineering structures, due to their unique performances,... more Aluminium and copper are widely used in engineering structures, due to their unique performances, such as higher electrical conductivity, heat conductivity, corrosion resistance and mechanical properties even though they have considerable differences in their melting points. In this study, the microstructure of the friction stir spot welds of aluminium and copper produced at various parameter combinations were analyzed by using a scanning electron microscope; while the residual stresses were studied by using the X-ray diffraction technique. Furthermore, the electrical resistivities of the joints was also measured. The evolving microstructure shows a good mixing in the produced spot welds with Cu particles present in the aluminium matrix. The formation of a copper ring/hook was evident in all the spot welds; and the length thereof increased with the shoulder plunge depth variation; while the spot welds produced at 1200 rpm for the two tool geometries exhibited a decrease and a slight increment in the length of the copper ring using a flat pin/flat shoulder and conical pin/concave shoulder, respectively. The obtained residual stresses results were compressive. The maximum residual stress of −116.8 MPa was measured on the copper ring of the welds produced at 800 rpm and 0.5 mm shoulder plunge depth, when using a flat pin and a flat shoulder tool. This was due to the generation of stress, when the copper was extruded into the aluminium sheets. Furthermore, the intensity of all the peaks using different process parameters decreased in comparison to the peaks generated by the parent materials and the effect of shoulder plunge depth on the full width at half the maximum (FWHM) was observed. The values of the measured electrical resistivities of the joints were higher than those of the parent materials.

Fullerenes, Nanotubes and Carbon Nanostructures

Abstract Conductive polymer nanocomposites are receiving lots of research attention in the field ... more Abstract Conductive polymer nanocomposites are receiving lots of research attention in the field of material science due to their fascinating properties and potentials in many areas of applications. In this work, reduced graphene oxide (RGO); a highly conducting nanofiller was synthesized and incorporated into the matrix of insulating expanded polystyrene (EPS); a recycled polymer, by solution mixing, then electrospun under the effect of optimized processing parameters. A filler loading of between 0.01 and 3 wt% was used at 15% (w/v) concentration of EPS in mixed solvent of DMF and THF to obtain composite nanofibers in submicron range. Analytical tools such as SEM, XRD, FTIR, and RAMAN were used for the investigation of the morphology of the synthesized RGO and electrospun composite nanofibers. Electrical, thermal, and mechanical properties of EPS/RGO composite nanofibers were investigated and compared with that of EPS/Carbon Black composite nanofibers. Keithely 2000 multimeter with four-point probes was used for electrical characterization. A significant drop in resistivity at a very low filler loading of RGO with percolation threshold of 0.7 wt% was recorded for EPS/RGO at conductivity value of 0.132 × 10−4S/m as compared to percolation threshold of 3.0 wt% obtained from EPS/Carbon Black composite nanofibers. A drastic improvement in thermal stability, Young Modulus, and tensile strength were also observed in all the nanocomposites compared with pure electrospun EPS. A sustainable reuse pathway for post-consumer plastic is also hereby presented.

Materials Today: Proceedings

Abstract Mesoporous titania was prepared using a sol-gel method with a synthetic (Pluronic P123) ... more Abstract Mesoporous titania was prepared using a sol-gel method with a synthetic (Pluronic P123) and a natural (Gum Arabic) templating agent. The precursor used was titanium methoxide, and the aims of this study were to compare the effects of a synthetic and natural template on the physical-chemical properties of the titania product, elucidate the effect of the surfactants on the pore size, specific surface area and overall structure of the mesoporous material. The synthesized titania materials were characterized by X-ray diffraction (XRD), nitrogen sorption at 77 K, Diffuse Reflectance Spectroscopy (DRS) and Fourier Transform Infrared (FTIR) techniques. From the XRD analysis, all the samples showed phases of anatase and rutile, while the DRS measurements revealed a decrease in band gap for samples prepared with P123, and samples prepared with Gum Arabic also showed a decrease in the band gap, when compared to bulk titania. Moreover, the BET surface area of the P123 samples was 65.34 m2/g and that with Gum Arabic was 41.75 m2/g.

Materials Today: Proceedings

Abstract Various evolving applications in power generation and the chemical, petrochemical, nucle... more Abstract Various evolving applications in power generation and the chemical, petrochemical, nuclear, aerospace, industries and manufacturing led to the development of techniques such as friction stir welding (FSW) and friction stir spot welding (FSSW) for similar and dissimilar materials. Many challenges include different melting temperatures arise during the joining of aluminium and copper. Therefore, obtaining sound aluminium to copper joints is a challenging task for researchers. Friction stir spot welding is a variant of the friction stir welding which is found to be an efficient and environmental friendly process. This paper present the current state on the joining of aluminium to copper using friction stir spot welding (FSSW) technique. A brief summary in terms of materials, microstructure evolution and chemical analysis are presented. Furthermore, mechanical and electrical properties aresummarized. Sound spot welds were successfully obtained by many researchers and the technique is gaining ground and could be used as an alternative to resistance spot welding and riveting. This technique could successfully be used in various industries include, automobile, ship building and aerospace.

Journal of Bio- and Tribo-Corrosion

Corrosion inhibitor has been successfully used for the protection of 3CR12 stainless steel surfac... more Corrosion inhibitor has been successfully used for the protection of 3CR12 stainless steel surface against corrosion in 1–2.5 M HCl. The performance of this inhibitor was correlated to the chemical composition and microscopic structures in accordance with the adsorption on the metal surface. Deoxyribonucleic acid (DNA) was extracted from the thymus gland of a calf, a component of the immune system of mammals. The study investigated the use of DNA extracted from calf thymus gland as a protective coat for 3CR12 stainless steel in the presence of a hydrochloric (HCl) medium. The mechanism of the potential inhibitor was understudied at different conditions of temperature and concentration in order to be able to explain the influence of the inhibitor on the metal. The highest CTGDNA inhibition efficiency was attained at 10 °C and at 20 mg/L. The micrographs revealed by scanning electron microscopy show that bio-macromolecules of CTGDNA were adsorbed on stainless steel surfaces. Nonetheless, the best micrograph result was achieved at 10 °C. The study of the Tafel polarization demonstrated that CTGDNA inhibitors at different concentration represented some mixed-type inhibitors. An inhibition mechanism was proposed which was confirmed by X-ray powder diffraction analysis. The results indicated that the corrosion inhibition efficiency increased with increase in HCl concentration.

SN Applied Sciences

This study explored the synthesis of activated carbon from olive seeds by chemical and thermal ac... more This study explored the synthesis of activated carbon from olive seeds by chemical and thermal activation, and evaluated the energy efficiency of the process. The oilseed samples were carbonized at varying temperature (600-840 °C). The produced activated carbons were used for dye removal, studying the effect of temperature. The materials were analyzed using X-ray diffraction and scanning electron microscopy (SEM). The pores and interpore spacing porous of the activated carbons were identified from the SEM images using ImageJ software. The results show that the yield of activated carbon and energy efficiency significantly decreased with increasing carbonization temperature. This reveals that a higher yield of activated carbon and higher energy efficiency was attained at lower carbonization temperature, meaning that producing activated carbon from olive seed is cost effective. Moreover, the activated carbon obtained at 600 °C exhibits the optimum removal efficiency for methylene blue, however, the increase in the removal efficiency upon increasing the temperature from 600 to 720 °C is insignificant (about 1%).

The International Journal of Advanced Manufacturing Technology

Corrosion and wear phenomenon has been responsible for the gradual deterioration of components in... more Corrosion and wear phenomenon has been responsible for the gradual deterioration of components in industrial plants. This deterioration of components results in loss of plant efficiency, total shutdown and aggressive damage in a number of industries. Hence, surface modification and coating technique with enhanced surface properties is desirable. The study was designed to investigate the enhancement in the corrosion, hardness and wear properties of Al-Sn binary coatings on AISI 1015 steel by laser alloying technique using ytterbium laser system (YLS). A laser power of 1000 W, scanning speeds of 0.6 and 0.8 m/min, and alloy compositions of Al-75Sn, Al-50Sn and Al-25Sn were used in this study. Decrease in Sn content from 75 to 25% at different laser processing conditions resulted in improved properties. The enhanced properties were obtained at 75Al-25Sn alloy at laser power of 1000 W and speeds of 0.6 and 0.8 m/min. At optimum composition and speed of 0.8 m/min, there was enhancement of 53.63% in microhardness. At scanning speed of 0.6 m/min, 75Al-25Sn alloy exhibited the highest polarization resistance, Rp, (1.06 × 108 Ω cm2); lowest corrosion current density, Icorr, (3.12 × 10−7 A/cm2); and lowest corrosion rate, Cr, (0.00363 mm/year) in 3.65 wt% NaCl solution. In addendum, significant reduction in wear volume loss of 75Al-25Sn alloy at 0.8 m/min was attributed to excellent wear resistance performance due to metastable intermetallic phases. This research has established the enhanced surface properties of laser alloyed Al-Sn binary coatings on AISI steel for engineering applications.

Arsenic - Analytical and Toxicological Studies, 2018

The work represents the bio-adsorption of arsenic(III) from standard solutions and real water sam... more The work represents the bio-adsorption of arsenic(III) from standard solutions and real water samples using a powdered avocado seed as a bio-adsorbent. The adsorbent was synthesized, demineralized, and characterized by X-ray diffraction (XRD), scanning electron microscope coupled with energy dispersive spectroscopy (SEM-EDS), Fourier transformation infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) theory. Batch adsorption studies were carried out by using avocado seed, and As III was analyzed by using inductively coupled plasma optical emission spectroscopy (ICPOES) after optimizing the following parameters: pH 6, analyte concentration 2 mg L À1 , bio-adsorbent dosage 0.8 g, contact time 120 min between analyte and adsorbent, and temperature from 22 to 40 C. The adsorption capacity of 93.75 mg/g was obtained, and the Langmuir isotherm was adopted by the adsorbent due to the chemisorption that occurs on the surface between the functional groups of the bio-adsorbent and As III .

International Journal of Corrosion and Scale Inhibition, Mar 26, 2021

One of the ways to protect aluminum metal from corrosion in polymer electrolyte membrane (PEM) hy... more One of the ways to protect aluminum metal from corrosion in polymer electrolyte membrane (PEM) hydrogen fuel cells is through the use of the chemical inhibition method. In this work, we present unsubstituted (NiPc) and tetrasubstituted nickel phthalocyanines (TNNiPc) as corrosion inhibitors for aluminum (Al) metal in 1 mol•L-1 hydrochloric acid (HCl) solution. The synthesized inhibitors were characterized using several techniques. The XRD patterns demonstrated that NiPc was more crystalline than TNNiPc (a nitro group at a peripheral position). The FTIR spectra for all the inhibitors showed a similar vibration band at around 730 cm-1 , which was due to C-H deformations. The TNNiPc inhibitor showed additional asymmetric and symmetric NO2 vibrations around 1336 and 1525 cm-1 , respectively. The UVvis spectrum of NiPc showed an intense Q-band at around 774 nm in 1 mol•L-1 H2SO4, whereas TNNiPc resulted in a blue shift of the Q-band due to the electron-withdrawing properties of the NO2 group. The TGA supported the presence of NO2 by the degradation step as indicative of decomposition of NO2 group in the TNNiPc inhibitor. Electrochemical studies showed that the inhibitors prevent Al metal sheet corrosion by adsorbing on Al surface to form a pseudocapacitive interface. The inhibitive effect of NiPc and TNNiPc inhibitors increased with increasing concentration. Furthermore, potentiodynamic polarization measurements revealed that the dyes are mixed-type corrosion inhibitors.

The International Journal of Advanced Manufacturing Technology

β-type titanium alloys are acquiring research interest in orthopaedic applications because of the... more β-type titanium alloys are acquiring research interest in orthopaedic applications because of their exceptional properties such as moderate strength, good biocompatibility and corrosion resistance, high ductility and low elastic modulus. The study aims at designing a series of binary Ti-Mo alloys (Ti-8.71 Mo, Ti-10.02 Mo, Ti-11.78 Mo and Ti-15.05 Mo (wt%)) using the cluster plus glue atom model to design the compositions. The prediction methods such as the molybdenum equivalence, the average electron ratio and the d-electron methods were used to predict the stability of the β phase. Microstructural evolution and phases of the designed alloys were characterized using the optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffractometry (EBSD) and X-ray diffractometry (XRD), while the microhardness and tensile properties were measured using the Vickers hardness tester and tensile testing machine. The microstructure of the cast Ti-Mo alloys comprised primarily the β phase and secondary orthorhombic martensitic α″ and athermal omega (ω) phases. Their elastic moduli (96.8–70.5 GPa) decreased with the amount of Ti in the glue side and were found to be lower than the commercially available 316 L stainless steel, Co-Cr and Ti6Al4V alloys. The microhardness values of the as-cast Ti-Mo alloys decreased as the amount of Ti in the glue side decreased in the cluster formula. The tensile strength of the as-cast alloys ranges from 796.76 to 593.48 MPa with Ti-8.71 wt% Mo alloy showing the highest tensile strength owing to the amount of Ti in the glue side. The yield strength of all the designed alloys decreased as the amount of Ti atoms placed in the glue side decreased. The elongation at fracture ranged between 0.28 and 0.71%, indicating that all the designed alloys fractured in a brittle manner. The elastic admissible strain of the designed alloys (Ti-15.05 wt% Mo) was significantly higher than the conventional orthopaedic implant materials (CP-Ti, Ti6Al4V) indicating that this study is promising for the development of excellent biomedical materials.

Minerals

Mining of minerals such as gold, copper, and platinum has been one of several activities sustaini... more Mining of minerals such as gold, copper, and platinum has been one of several activities sustaining the economy of South Africa. However, the mining sector has contributed significantly to environmental contamination through the improper disposal of mine tailings which covers vast areas of land. Therefore, this study utilised a vitrification process to manufacture glass from gold mine tailings. X-ray fluorescence was used to determine the chemical composition of the tailings while X-ray diffraction was adopted for the mineralogy. The tailings were of granitic composition enriched in potentially toxic elements such as copper, cadmium, zinc, lead, arsenic, and chromium. A representative sample of gold mine wastes of sandy grain size was used in making the glass. Based on composition, the glass was formulated by adding an average 10.0 mass% of CaCO3 and 5.0 mass% of Na2CO3 to 35.0 mass% of SiO2, which resulted in the production of a green-coloured glass.

Materials Today: Proceedings

Abstract Shea nut shell (SNS) is an agrowaste obtained from Vitellaria paradoxa tree and discarde... more Abstract Shea nut shell (SNS) is an agrowaste obtained from Vitellaria paradoxa tree and discarded by burning. The extraction of nanocellulose from this agrowaste is expected to be a value addition to Shea farming and processing. However, the isolation of quality nanocellulose begins with optimal pretreatment of the agrowaste material. In this work, the mercerization of SNS collected from local processing centers was carried out by varying the treatment conditions such as temperature, time, liquor ratio (LR) and concentration of the alkali solution. The resulting samples were characterized using FTIR, TGA and DTGA. From the results obtained, the minimum treatment conditions required to isolate cellulose from SNS was obtained as 100 °C for treatment temperature, 2 h for treatment time, 1:20 for LR and 20% for alkali solution concentration. The isolated cellulose was also found to be of good thermal properties when compared to cellulose from other agrowaste. However, these conditions can be varied to give desired properties for specific application.

Transactions of the Indian Institute of Metals

The environmental consciousness and consumer pressure have forced manufacturing industries to use... more The environmental consciousness and consumer pressure have forced manufacturing industries to use natural fibres as a substitute for conventional non-renewable reinforcing materials. In the present investigation, the effect of rate of loading on jute fibre-reinforced polymer composite was studied. The mechanical properties (in three-point bend test) like interlaminar shear strength, yield strength and energy at break were examined as a function of strain rate. It was observed that the untreated fibre-reinforced composites were not very sensitive to the rate of loading; however, loading rate sensitivity was observed in alkali-treated fibre-reinforced composites. It has been proposed that fibre pull-out dominates over mechanism of composite failure in alkali-treated condition, and the interlaminar shear strength/yield strength was increased due to the increase in stiffness of the composite with rate of loading (in initial stage); however, at higher strain rate, matrix became susceptible to brittleness as there was lesser time available for crack-blunting to take place. All the microstructures were generated using a scanning electron microscope, and mechanical testing was done using tensile testing machine Instron 1195.

International Journal of Environmental Research and Public Health

The problem of environmental pollution is a global concern as it affects the entire ecosystem. Th... more The problem of environmental pollution is a global concern as it affects the entire ecosystem. There is a cyclic revolution of pollutants from industrial waste or anthropogenic sources into the environment, farmlands, plants, livestock and subsequently humans through the food chain. Most of the toxic metal cases in Africa and other developing nations are a result of industrialization coupled with poor effluent disposal and management. Due to widespread mining activities in South Africa, pollution is a common site with devastating consequences on the health of animals and humans likewise. In recent years, talks on toxic metal pollution had taken center stage in most scientific symposiums as a serious health concern. Very high levels of toxic metals have been reported in most parts of South African soils, plants, animals and water bodies due to pollution. Toxic metals such as Zinc (Zn), Lead (Pb), Aluminium (Al), Cadmium (Cd), Nickel (Ni), Iron (Fe), Manganese (Mn) and Arsenic (As) ar...

Transactions of the Indian Institute of Metals

In the present study, microstructural analysis of post-deformation annealed sample has been carri... more In the present study, microstructural analysis of post-deformation annealed sample has been carried out for 23Cr–6Ni–3Mo duplex stainless steel. It was observed that the restoration mechanism and substructural characteristics were different for austenite and ferrite during post-deformation annealing. In the initial stage of post-deformation annealing, the restoration mechanism of austenite envisaged meta-dynamic recrystallization (MDRX), while the dominating mechanism of softer ferrite showed static recovery (SRV) with a minimal of static recrystallization (SRX). In the intermediate stage, the austenite showed SRX followed by coarsening of meta-dynamically recrystallized grains, and ferrite revealed mostly SRV. The last stage of post-deformation annealing showed the disintegration of substructures in both austenite and ferrite. The microstructure after 20 min of post-deformation annealing displayed coarse subgrains. Finer austenite subgrains were observed as compared to ferrite subgrains after the post-deformation annealing of 20 min. High-resolution EBSD was used to study substructural characteristics of microstructure, and post-processing of microstructural results was made by HKL Channel 5 software. Misorientation angle distribution, subgrain size as well as restoration mechanism corresponding to both austenite and ferrite were determined over intensive sample area.

Transactions of the Indian Institute of Metals

In the present investigation, the effect of substructures on hardness and conductivity during par... more In the present investigation, the effect of substructures on hardness and conductivity during partial annealing of cold-rolled copper was studied. Substructures were observed after annealing at lower temperature; however, the annealed sample (at higher temperature) was mostly free from substructures. Therefore, it is proposed that the restoration mechanism at lower temperature envisages recovery in copper; however, it is partial recrystallization at higher temperature. There was an increase in hardness observed at lower temperature due to higher fraction of substructures, while an increase in conductivity was observed at higher temperature due to partial recrystallization. It was confirmed that the twin boundaries produced during cold rolling provided dislocations pinning, leading to greater tensile strength.

Transactions of the Indian Institute of Metals

The pipes are subjected to different load conditions such as internal stress, compression, tensio... more The pipes are subjected to different load conditions such as internal stress, compression, tension, bending and/or any combination thereof. These various types of load conditions induce new cracks and/or cause propagation of the existing cracks. In this study, a TP316L stainless steel pipe subjected to four-point bend testing was examined to predict the propagation of fatigue cracks in a part-through cracked pipe using the CASCA and FRANC2D programs. Two different methods based on “rigidity” and “stress intensity factor” have been proposed for converting a three-dimensional pipe into a two-dimensional beam for modeling.

Materiali in tehnologije

In this paper, friction-stir spot welding (FSSW) is performed on 3 mm thick AA1060 and C11000 usi... more In this paper, friction-stir spot welding (FSSW) is performed on 3 mm thick AA1060 and C11000 using different process parameters and tool geometries. The microstructure-and the microhardness-profile analyses were conducted and the probability distribution function (PDF) of the obtained microhardness values was determined. Optical images showed a good material mixing in most of the spot welds produced, whereas the energy-dispersive-spectroscopy (EDS) analysis showed the presence of intermetallic compounds. Microhardness results revealed that process parameters and tool geometries have significant effects on the distribution of microhardness values in different locations of the produced spot welds. Furthermore, goodness-of-fit values showed that most of the R 2 values ranged between 0.8842 and 0.9999, which indicated how well the model fits with the experimental data. On the other hand, the residuals comprised positive and negative runs which also indicated the existence of a certain correlation with the experimentation.

Trace Elements in the Environment - New Approaches and Recent Advances [Working Title]

In the Blesbokspruit area of Ekuhurleni, South Africa, previous gold mining activities resulted i... more In the Blesbokspruit area of Ekuhurleni, South Africa, previous gold mining activities resulted in many tailings dump sites. 20 representative soil samples were used in describing the distribution of metals. The soils were very strongly acidic ranging from 3.86 to 4.34 with a low cation exchange capacity (CEC). Based on X-ray fluorescence (XRF) analysis, elemental composition of the soils revealed average values of major elements such as Na2O (0.18%), MgO (0.63%), Al2O3 (6.51%), SiO2 (81.83%), P2O5 (0.04%), SO3 (3.40%), K2O (1.98%), CaO (0.45%), TiO2 (0.51%), Cr2O3 (0.17%), MnO (0.04%), Fe2O3 (3.59%), NiO (0.04%), As2O3 (0.02%), with Rb2O and SrO falling below 0.01%. Trace metals (TM) contamination levels in the soils were evaluated using various pollution indices which revealed that over 60% of the soils were between the high degree and the ultra-high degree of contamination classes. The concentration of various trace metals varies from 860.3-862.6 mg/kg for Cr; 324.9-328.4 mg/kg for Al; 200.9-203.4 mg/kg for As; 130.1-136.2 mg/kg for Fe; 121.9-125.8 mg/kg for Pb; 27.3-30.2 mg/kg for Co; 23.8-26.8 mg/kg for Ni; 7.2-9.2 mg/kg for Ti; 7.1-9.2 mg/kg for Cd; 4.0-5.6 mg/kg for Zn and 0.1-0.6 mg/kg for Cu.

Materials Today: Proceedings

Abstract Jarosite wastes are produced daily from the refineries and contain toxic elements. In th... more Abstract Jarosite wastes are produced daily from the refineries and contain toxic elements. In this study, the characterization of jarosite/clay/fly ash admixture is carried out to explore the possibility of using the produced bricks in the construction industry. The XRD results showed that the major phases in jarosite are Coesite and Mackinawite while Kaolinite and Mullite were found in clay and fly ash respectively.The major chemical elements in jarosite are Fe (41.46%), S (7.29%) and Si (5.61%) whereas Si (24.4%), Al (20.01%) and Fe (2.26%) were found in clay. On the hand, the major elements in fly ash are Si (22.44%), Al (18.42) and Ca (3.47).The microstructure of jaroriste and clay showed non-uniform particles in structure and irregular in shape while fly ash particles were uniform in structure and spherical/cenospherical in shape. The compressive strength results of the produced bricks revealed that all the 1:1 and 2:1 ratios with 15% and 20% met the minimum required compressive strengthof common building bricks. The chemical analysis of the leachates heated samples at 900˚C showed that toxic elements such as Pb, Fe and Ni were detoxified except for the Arsenic

Structural Integrity

Aluminium and copper are widely used in engineering structures, due to their unique performances,... more Aluminium and copper are widely used in engineering structures, due to their unique performances, such as higher electrical conductivity, heat conductivity, corrosion resistance and mechanical properties even though they have considerable differences in their melting points. In this study, the microstructure of the friction stir spot welds of aluminium and copper produced at various parameter combinations were analyzed by using a scanning electron microscope; while the residual stresses were studied by using the X-ray diffraction technique. Furthermore, the electrical resistivities of the joints was also measured. The evolving microstructure shows a good mixing in the produced spot welds with Cu particles present in the aluminium matrix. The formation of a copper ring/hook was evident in all the spot welds; and the length thereof increased with the shoulder plunge depth variation; while the spot welds produced at 1200 rpm for the two tool geometries exhibited a decrease and a slight increment in the length of the copper ring using a flat pin/flat shoulder and conical pin/concave shoulder, respectively. The obtained residual stresses results were compressive. The maximum residual stress of −116.8 MPa was measured on the copper ring of the welds produced at 800 rpm and 0.5 mm shoulder plunge depth, when using a flat pin and a flat shoulder tool. This was due to the generation of stress, when the copper was extruded into the aluminium sheets. Furthermore, the intensity of all the peaks using different process parameters decreased in comparison to the peaks generated by the parent materials and the effect of shoulder plunge depth on the full width at half the maximum (FWHM) was observed. The values of the measured electrical resistivities of the joints were higher than those of the parent materials.

Fullerenes, Nanotubes and Carbon Nanostructures

Abstract Conductive polymer nanocomposites are receiving lots of research attention in the field ... more Abstract Conductive polymer nanocomposites are receiving lots of research attention in the field of material science due to their fascinating properties and potentials in many areas of applications. In this work, reduced graphene oxide (RGO); a highly conducting nanofiller was synthesized and incorporated into the matrix of insulating expanded polystyrene (EPS); a recycled polymer, by solution mixing, then electrospun under the effect of optimized processing parameters. A filler loading of between 0.01 and 3 wt% was used at 15% (w/v) concentration of EPS in mixed solvent of DMF and THF to obtain composite nanofibers in submicron range. Analytical tools such as SEM, XRD, FTIR, and RAMAN were used for the investigation of the morphology of the synthesized RGO and electrospun composite nanofibers. Electrical, thermal, and mechanical properties of EPS/RGO composite nanofibers were investigated and compared with that of EPS/Carbon Black composite nanofibers. Keithely 2000 multimeter with four-point probes was used for electrical characterization. A significant drop in resistivity at a very low filler loading of RGO with percolation threshold of 0.7 wt% was recorded for EPS/RGO at conductivity value of 0.132 × 10−4S/m as compared to percolation threshold of 3.0 wt% obtained from EPS/Carbon Black composite nanofibers. A drastic improvement in thermal stability, Young Modulus, and tensile strength were also observed in all the nanocomposites compared with pure electrospun EPS. A sustainable reuse pathway for post-consumer plastic is also hereby presented.

Materials Today: Proceedings

Abstract Mesoporous titania was prepared using a sol-gel method with a synthetic (Pluronic P123) ... more Abstract Mesoporous titania was prepared using a sol-gel method with a synthetic (Pluronic P123) and a natural (Gum Arabic) templating agent. The precursor used was titanium methoxide, and the aims of this study were to compare the effects of a synthetic and natural template on the physical-chemical properties of the titania product, elucidate the effect of the surfactants on the pore size, specific surface area and overall structure of the mesoporous material. The synthesized titania materials were characterized by X-ray diffraction (XRD), nitrogen sorption at 77 K, Diffuse Reflectance Spectroscopy (DRS) and Fourier Transform Infrared (FTIR) techniques. From the XRD analysis, all the samples showed phases of anatase and rutile, while the DRS measurements revealed a decrease in band gap for samples prepared with P123, and samples prepared with Gum Arabic also showed a decrease in the band gap, when compared to bulk titania. Moreover, the BET surface area of the P123 samples was 65.34 m2/g and that with Gum Arabic was 41.75 m2/g.

Materials Today: Proceedings

Abstract Various evolving applications in power generation and the chemical, petrochemical, nucle... more Abstract Various evolving applications in power generation and the chemical, petrochemical, nuclear, aerospace, industries and manufacturing led to the development of techniques such as friction stir welding (FSW) and friction stir spot welding (FSSW) for similar and dissimilar materials. Many challenges include different melting temperatures arise during the joining of aluminium and copper. Therefore, obtaining sound aluminium to copper joints is a challenging task for researchers. Friction stir spot welding is a variant of the friction stir welding which is found to be an efficient and environmental friendly process. This paper present the current state on the joining of aluminium to copper using friction stir spot welding (FSSW) technique. A brief summary in terms of materials, microstructure evolution and chemical analysis are presented. Furthermore, mechanical and electrical properties aresummarized. Sound spot welds were successfully obtained by many researchers and the technique is gaining ground and could be used as an alternative to resistance spot welding and riveting. This technique could successfully be used in various industries include, automobile, ship building and aerospace.

Journal of Bio- and Tribo-Corrosion

Corrosion inhibitor has been successfully used for the protection of 3CR12 stainless steel surfac... more Corrosion inhibitor has been successfully used for the protection of 3CR12 stainless steel surface against corrosion in 1–2.5 M HCl. The performance of this inhibitor was correlated to the chemical composition and microscopic structures in accordance with the adsorption on the metal surface. Deoxyribonucleic acid (DNA) was extracted from the thymus gland of a calf, a component of the immune system of mammals. The study investigated the use of DNA extracted from calf thymus gland as a protective coat for 3CR12 stainless steel in the presence of a hydrochloric (HCl) medium. The mechanism of the potential inhibitor was understudied at different conditions of temperature and concentration in order to be able to explain the influence of the inhibitor on the metal. The highest CTGDNA inhibition efficiency was attained at 10 °C and at 20 mg/L. The micrographs revealed by scanning electron microscopy show that bio-macromolecules of CTGDNA were adsorbed on stainless steel surfaces. Nonetheless, the best micrograph result was achieved at 10 °C. The study of the Tafel polarization demonstrated that CTGDNA inhibitors at different concentration represented some mixed-type inhibitors. An inhibition mechanism was proposed which was confirmed by X-ray powder diffraction analysis. The results indicated that the corrosion inhibition efficiency increased with increase in HCl concentration.

SN Applied Sciences

This study explored the synthesis of activated carbon from olive seeds by chemical and thermal ac... more This study explored the synthesis of activated carbon from olive seeds by chemical and thermal activation, and evaluated the energy efficiency of the process. The oilseed samples were carbonized at varying temperature (600-840 °C). The produced activated carbons were used for dye removal, studying the effect of temperature. The materials were analyzed using X-ray diffraction and scanning electron microscopy (SEM). The pores and interpore spacing porous of the activated carbons were identified from the SEM images using ImageJ software. The results show that the yield of activated carbon and energy efficiency significantly decreased with increasing carbonization temperature. This reveals that a higher yield of activated carbon and higher energy efficiency was attained at lower carbonization temperature, meaning that producing activated carbon from olive seed is cost effective. Moreover, the activated carbon obtained at 600 °C exhibits the optimum removal efficiency for methylene blue, however, the increase in the removal efficiency upon increasing the temperature from 600 to 720 °C is insignificant (about 1%).

The International Journal of Advanced Manufacturing Technology

Corrosion and wear phenomenon has been responsible for the gradual deterioration of components in... more Corrosion and wear phenomenon has been responsible for the gradual deterioration of components in industrial plants. This deterioration of components results in loss of plant efficiency, total shutdown and aggressive damage in a number of industries. Hence, surface modification and coating technique with enhanced surface properties is desirable. The study was designed to investigate the enhancement in the corrosion, hardness and wear properties of Al-Sn binary coatings on AISI 1015 steel by laser alloying technique using ytterbium laser system (YLS). A laser power of 1000 W, scanning speeds of 0.6 and 0.8 m/min, and alloy compositions of Al-75Sn, Al-50Sn and Al-25Sn were used in this study. Decrease in Sn content from 75 to 25% at different laser processing conditions resulted in improved properties. The enhanced properties were obtained at 75Al-25Sn alloy at laser power of 1000 W and speeds of 0.6 and 0.8 m/min. At optimum composition and speed of 0.8 m/min, there was enhancement of 53.63% in microhardness. At scanning speed of 0.6 m/min, 75Al-25Sn alloy exhibited the highest polarization resistance, Rp, (1.06 × 108 Ω cm2); lowest corrosion current density, Icorr, (3.12 × 10−7 A/cm2); and lowest corrosion rate, Cr, (0.00363 mm/year) in 3.65 wt% NaCl solution. In addendum, significant reduction in wear volume loss of 75Al-25Sn alloy at 0.8 m/min was attributed to excellent wear resistance performance due to metastable intermetallic phases. This research has established the enhanced surface properties of laser alloyed Al-Sn binary coatings on AISI steel for engineering applications.