Estimating plastic waste generation using supervised time-series learning techniques in Johannesburg, South Africa.

In recent times, many investigators have delved into plastic waste (PW) research, both locally and internationally. Many of these studies have focused on problems related to land-based and marine-based PW management with its attendant impact on public health and the ecosystem. Hitherto, there have been little or no studies on forecasting PW quantities in developing countries (DCs). The key objective of this study is to provide a forecast on PW generation in the city of Johannesburg (CoJ), South Africa over the next three decades. The data used for the forecasting were historical data obtained from Statistics South Africa (StatsSA). For effective prediction and comparison, three-time series models were employed in this study. They include exponential smoothing (ETS), Artificial Neural Network (ANN), and the Gaussian Process Regression (GPR). The exponential kernel GPR model performed best on the overall plastic prediction with a determination coefficient (R2) of 0.96, however, on individual PW estimation, ANN was better with an overall R2 of 0.93. From the result, it is predicted that between 2021 and 2050, the total PW generated in CoJ is forecasted to be around 6.7 megatonnes with an average of 0.22 megatonnes/year. In addition, the estimated plastic composition is 17,910 tonnes PS per year; 13,433 tonnes PP per year; 59,440 tonnes HDPE per year; 4478 tonnes PVC per year; 85,074 tonnes PET per year; 34,590 tonnes LDPE per year and 8955 tonnes other PWs per year.

Phase stability and microstructural properties of high entropy alloy reinforced aluminium matrix composites consolidated via spark plasma sintering.

Spark plasma sintering (SPS) technique was employed in the consolidation of Cr20Mn20Ni20Cu20Nb10Co10 high entropy alloy (HEA) reinforced aluminium matrix composites. Phase stability and prediction expressions were used in the determination of the powder combination for the HEA. The microstructural analysis showed that an interdiffusion layer was formed between the aluminium matrix and the HEA particles in the sintered composites. Further investigation of the composites by X-ray diffraction (XRD) showed that in addition to the Al matrix phase present, other new phases (BCC, FCC and other intermetallics) were formed as a result of the reaction between the Al matrix and the atoms precipitated from the added HEA during sintering. The density of the HEA-reinforced Al matrix composites decreases with an increase in the wt.% of HEA from 98.6 % for pure aluminium to 98.1 % for the reinforced alloy with 10 % HEA, while the microhardness increases with an increase in the wt.% of the HEA from 35 HV for pure aluminium to 96.0 HV for the alloy reinforced with 10 % HEA.

Nanoindentation and Structural Analysis of Sintered TiAl(100-x)-xTaN Composites at Room Temperature.

The nanohardness, elastic modulus, anti-wear, and deformability characteristics of TiAl(100-x)-xTaN composites containing 0, 2, 4, 6, 8, and 10 wt.% of TaN were investigated via nanoindentation technique in the present study. The TiAl(100-x)-xTaN composites were successfully fabricated via the spark plasma sintering technique (SPS). The microstructure and phase formation of the TiAl sample constitute a duplex structure of γ and lamellar colonies, and TiAl2, α-Ti, and TiAl phases, respectively. The addition of TaN results in a complex phase formation and pseudo duplex structure. The depth-sensing indentation evaluation of properties was carried out at an ambient temperature through a Berkovich indenter at a prescribed load of 100 mN and a holding time of 10 s. The nanoindentation result showed that the nanohardness and elastic modulus characteristics increased as the TaN addition increased but exhibited a slight drop when the reinforcement was beyond 8 wt.%. At increasing TaN addition, the yield strain (HEr), yield pressure (H3Er2), and elastic recovery index (WeWt) increased, while the plasticity index (WpWt) and the ratio of plastic and elastic work (RPE) reduced. The best mechanical properties were attained at the 8 wt.%TaN addition.

Sintering of nanocrystalline materials: Sintering parameters.

Nanostructured materials (NsM) are typical materials with structural length scales of one, two, or three dimensions in the range of 1-100 nm. In the development of NsM, the microstructure of a material, which is an integral factor in determining the intrinsic performance of a material, is susceptible to changes that may hinder the desired nano-state properties under different processing routes and associated varying processing parameters. NsM exhibits distinct superior properties when compared to conventional coarse-structured materials. They exhibit distinct and rapid development during production due to their unique surface area, which requires concise control measures over coarse materials. These promising excellent properties of nanocrystalline materials have caught the attention of material scientists and engineers towards their developments. In order to exploit the abundance of excellent properties of NsM, investigations on the processing-structure-property correlations have been employed in recent years to understand their complications and subsequent development of novel materials. This review aims to understand the sintering of nanomaterials, with a clear focus on the spark plasma sintering technique and its associated sintering parameters, bordering on intricate issues on densification, coarsening of particles, and grain growth.

Evaluation of the Wear and Mechanical Properties of Titanium Diboride-Reinforced Titanium Matrix Composites Prepared by Spark Plasma Sintering.

The synthesis of x-wt.% (where x = 2.5, 5, 7.5, and 10) TiB2-reinforced titanium matrix was accomplished through the spark plasma sintering technique (SPS). The sintered bulk samples were characterized, and their mechanical properties were evaluated. Near full density was attained, with the sintered sample having the least relative density of 97.5%. This indicates that the SPS process aids good sinterability. The Vickers hardness of the consolidated samples improved from 188.1 HV1 to 304.8 HV1, attributed to the high hardness of the TiB2. The tensile strength and elongation of the sintered samples decreased with increasing TiB2 content. The nano hardness and reduced elastic modulus of the consolidated samples were upgraded due to the addition of TiB2, with the Ti-7.5 wt.% TiB2 sample showing the maximum values of 9841 MPa and 188 GPa, respectively. The microstructures display the dispersion of whiskers and in-situ particles, and the X-ray diffraction analysis (XRD) showed new phases. Furthermore, the presence of TiB2 particles in the composites enhanced better wear resistance than the unreinforced Ti sample. Due to dimples and large cracks, ductile and brittle fracture behavior was noticed in the sintered composites.

A Review on Heat Treatment of Cast Iron: Phase Evolution and Mechanical Characterization.

The isothermal heat treatment process has been identified as a unique process of fabricating exceptional graphite cast iron due to its remarkable mechanical properties, such as excellent machinability, toughness, and high level of ultimate tensile strength. Austempered ductile iron (ADI), ductile iron (DI), and gray cast iron (GCI), known as spheroidal cast irons, are viable alternative materials compared to traditional steel casting, as well as aluminum casting. The graphite nodules from the microstructures of DI, ADI, and GCI are consistently encompassed by acicular ferrite and carbon-saturated austenite in the matrix, forming a distinctive ausferritic structure. All these materials are extensively used in the fabrication of engine sleeves, engine blocks, valves, gears, and camshafts in the automobile sector. With relative motion and outward loads, these components are regularly exposed to surface contact. In this project, it was observed that austempering temperature and a shorter holding period could also be used to manufacture needle-like ferrite platelets for austempered ductile iron (ADI) and other graphite cast irons. To overcome the brittleness challenges and catastrophic failures encountered by applied loads in present-day applications, it is essential to comprehend the isothermal treatments, morphological behaviors, phase analyses, processing techniques, and mechanical properties needed to properly incorporate these materials into future designs. This review article provides detailed information on the characterization and relevant potential mechanisms of ADI, DI, and GCI.

Additive manufacturing of titanium-based alloys- A review of methods, properties, challenges, and prospects.

The development of materials for biomedical, aerospace, and automobile industries has been a significant area of research in recent years. Various metallic materials, including steels, cast iron, nickel-based alloys, and other metals with exceptional mechanical properties, have been reportedly utilized for fabrication in these industries. However, titanium and its alloys have proven to be outstanding due to their enhanced properties. The ß-titanium alloys with reduced modulus compared with the human bone have found more usage in the biomedical industry. In contrast, the α and α+ß titanium alloys are more utilized to fabricate parts in the automobile and aerospace industries due to their relatively lightweight. Amongst the numerous additive manufacturing (AM) techniques, selective laser and electron beam melting techniques are frequently used for the fabrication of metallic components due to the full densification and high dimensional accuracy they offer. This paper reviews and discusses the different types of AM techniques, attention is also drawn to the properties and challenges associated with additively manufactured titanium -based alloys. The outcome from this study shows that 3D printed titanium and titanium-alloys exhibit huge prospects for various applications in the medical and aerospace industries. Also, laser-assisted 3D technologies were found to be the most effective AM method for achieving enhanced or near-full densification.

Prediction of electronic properties of novel ZnS-ZnO-recycled expanded polystyrene nanocomposites by DFT.

DFT calculations using Material Studio (2019) were used to ascertain the changes in electronic properties of recycled expanded polystyrene (rEPS) after modification with nanoparticles of ZnS and ZnO. The nanocomposites were obtained using rEPS and suitable metal salt precursors via a solvothermal method. The XRD analysis was conducted to obtain the crystallography data of the new rEPS-based nanocomposites. Using Material Studio simulation software, the potential photocatalytic properties of the new prepared material was predicted and information on the electronic band structure was extracted. The calculated band gap values for rEPS and ZnS-ZnO-rEPS nanocomposite were 4.217 eV and 2.698 eV, respectively. Furthermore, our results showed that the nanocomposite is a p-type semiconductor. From the electronic structure and the band gap narrowing, these nanocomposites obtained from a waste material may have some potential in photocatalytic applications.

Nondestructive measurement of the mechanical properties of graphene nanoplatelets reinforced nickel aluminium bronze composites.

Nanoindentation is a viable method to assess the mechanical properties of developed alloys and composites at the nanometer scale without hampering the microstructure and integrity of materials. In this study, nondestructive measurement was conducted on spark plasma sintered nickel aluminium bronze (NAB), and graphene nanoplatelets (1, 2, 3 wt.%) reinforced NAB composites using the nanoindentation technique. The nondestructive measurements were conducted under loads of 50 mN and 100 mN to assess the nanohardness and reduced elastic modulus of the fabricated NAB alloy and composites. Further investigations were carried to evaluate the elastic recovery index, plasticity index, the nanohardness and reduced modulus ratio, and the yield pressure to reveal the nanomechanical responses of the fabricated materials. Scanning electron microscopy was used to analyze and reveal the dispersibility of the graphene nanoplatelets (GNP) in the NAB matrix. The nondestructive measurements showed that the nanohardness, reduced elastic modulus, yield pressure, resistance to elastic strain to failure and the elastic recovery index improved with the presence and increase in the concentration of GNP in the NAB matrix. The reduced elastic modulus and nanohardness values range from 34.2 - 43.0 GPa and 4407.2-6598.8 MPa respectively, which declined with nanoindentation loads. The fabricated NAB alloy experienced the maximum plastic deformation and least resistance to impact loading.

Challenges of plastic waste generation and management in sub-Saharan Africa: A review.

Recently, the issues of land-based plastics and their associated challenges in the marine world have been widely publicised in the media and scientific literature. Thus far, despite these communications, there have been few reports that have focused on the issues that acute plastic waste generation and its poor management pose to human health and the global environment. Also, articles on ways to mitigate these issues particularly in sub-Saharan Africa have not been documented. Indeed, there is significant scope for improvements in plastic waste management in developing countries, which offer a wide range of economic and environmental benefits. Plastic waste generation in sub-Saharan Africa is dependent on many factors like urbanization, etc. Currently, the population of sub-Saharan Africa is around 1 billion as of the year 2019, the amount of generated waste is 180 million tonnes at the rate of 0.5% per capita per day, the amount that is openly dumped is 70% and the plastic waste generated annually is 17 million tonnes. Therefore, this study aims to provide an overview of the plastic lifecycle and problems associated with plastic waste management in sub-Saharan Africa, including current practices, public participation and opinion, and government regulations. In addition, this highlight aims to outline the impact of plastic waste proliferation on man and the environment; and the economic and environmental benefits of proper plastic waste management. Critical discussion of current processes and the suitability of potential solutions provide the basis for proposition on mitigation measures to avert the negative impact of plastic waste.

Datasets on the measurement of mechanical properties of ferrite and austenite constitutive phases using nanoindentation and micro hardness techniques.

The major objective of this work is to study the hardness data at the domain of ferrite and Austenite phases. Nanoindentation and microhardness study has been conducted on austenite and ferrite present in the microstructure of hot rolled and heat treated duplex stainless steel (2205 DSS). Furthermore, Optical microscopy and field emission scanning electron microscope (FE-SEM) were used to identify the microstructural distribution and phases present. Austenite reveals higher nanohardness data value than ferrite, as oppose to ferrite average elastic modulus which is higher than that of austenite. Also, higher value of microhardness data was observed for austenite in comparison with the ferrite at different load application.

Fretting corrosion behaviour of Ti-6Al-4V reinforced with zirconia in foetal bovine serum.

Fretting corrosion is a critical challenge in the design of hip prosthesis used in total hip arthroplasty (THA) surgeries. Currently, the design of hip implants includes a tapered junction which introduces additional interfaces that connect different parts of the hip implant such as the femoral neck and head or stem and neck interface. Micro motions that occur under the influence of load, together with chemical changes in the host environment, make these interfaces susceptible to tribocorrosion processes, particularly fretting corrosion. Commonly used metallic biomaterials are based on stainless steels, cobalt chrome-based alloys as well as titanium and titanium alloys. Each of these materials possess some degree of limitations, particularly where tribocorrosion events are concerned. Titanium alloy Ti-6Al-4V is widely used in biomedical applications for non-bearing components of total joint arthroplasty (TJA) surgeries. Its poor wear resistance continues to remain a challenge in load-bearing joints where parts articulate against one another as in the case of modular junctions. Some of the attempts made to improve the wear properties of Ti-6Al-4V is through the incorporation of second phase particles like ceramics in its matrix to produce metal matrix composites of Ti-6Al-4V. The aim of this work is to investigate the effect of zirconia reinforcement on spark plasma sintered Ti-6Al-4V composites (zirconium oxide particles incorporated into Ti-6Al-4V matrix) on the fretting corrosion properties of Ti-6Al-4V. Fretting corrosion tests were carried out on as-sintered Ti-6Al-4V and Ti-6Al-4V with 5 and 10 wt.% ZrO2. The tests were carried out in foetal bovine serum under applied normal loads of 85 and 115 N using the cylinder-on-flat contact configuration. The evolution of OCP, dissipated energy and friction coefficient were recorded throughout the test. Microstructural analysis of the samples before fretting corrosion tests showed the presence of globular agglomerates throughout the Ti-6Al-4V matrix due to zirconia additions; the volume of the agglomerates was higher in the composites having 10 wt.% ZrO2. Ti-6Al-4V composites having zirconia additions produced a nobler OCP during fretting in foetal bovine serum, compared to pure Ti-6Al-4V. Furthermore, the fretting corrosion results showed a significant improvement in the tribocorrosion resistance of Ti-6Al-4V with 10 wt.% ZrO2 at all loads. This composition also produced the least amount of degradation. and metal ion release. Mechanical data showed that increasing the applied normal load promoted a transition from gross slip to partial slip conditions for all compositions. Partial slip was found to be prevalent at a higher normal load (drastic decrease of the dissipated energy and consequently the friction coefficient). This mechanical condition prevents a large amount of degradation.