The demand for lightweight materials in the automobile and aerospace industries has led to various researches on graphite and graphite‐aluminum composites. The aim of this study was to investigate ...the effect of the addition of micron/nano TiB2 particles on the properties of graphite‐aluminum composite particularly the wear resistance. The powders were sintered at 550 °C and 50 MPa with more attention on the effect of the sintering temperature on densification, microhardness, coefficient of thermal expansion, wear and frictional force. The results show that the addition of nano TiB2 reduces the densification while improving the hardness of Gr−Al composite with the lowest value being 96.0 % of relative density and the highest microhardness of 43.58 HV 0.1. The coefficient of thermal expansion and frictional force of the composite materials increases with increasing TiB2 content and heating rate (100 °C/min–150 °C/min). TiB2 particles enhance the wear resistance of graphite‐aluminum composite. The addition of micro/nanoparticles of TiB2 to graphite‐aluminum composite increases its corrosion rate with improved passivation behavior in 3.5 wt.% NaCl solution. Nevertheless, 5 wt.% nano (100 °C/min) TiB2 additions do not affect the overall corrosion rate. This work has shown that we can take advantage of some of the properties of TiB2 to improve the performance of graphite‐aluminum composite.
Acute rheumatic fever (ARF) and rheumatic heart disease (RHD) remain major causes of heart failure, stroke and death among African women and children, despite being preventable and imminently ...treatable. From 21 to 22 February 2015, the Social Cluster of the Africa Union Commission (AUC) hosted a consultation with RHD experts convened by the Pan-African Society of Cardiology (PASCAR) in Addis Ababa, Ethiopia, to develop a 'roadmap' of key actions that need to be taken by governments to eliminate ARF and eradicate RHD in Africa. Seven priority areas for action were adopted: (1) create prospective disease registers at sentinel sites in affected countries to measure disease burden and track progress towards the reduction of mortality by 25% by the year 2025, (2) ensure an adequate supply of high-quality benzathine penicillin for the primary and secondary prevention of ARF/RHD, (3) improve access to reproductive health services for women with RHD and other non-communicable diseases (NCD), (4) decentralise technical expertise and technology for diagnosing and managing ARF and RHD (including ultrasound of the heart), (5) establish national and regional centres of excellence for essential cardiac surgery for the treatment of affected patients and training of cardiovascular practitioners of the future, (6) initiate national multi-sectoral RHD programmes within NCD control programmes of affected countries, and (7) foster international partnerships with multinational organisations for resource mobilisation, monitoring and evaluation of the programme to end RHD in Africa. This Addis Ababa communiqué has since been endorsed by African Union heads of state, and plans are underway to implement the roadmap in order to end ARF and RHD in Africa in our lifetime.
ObjectiveIsoniazid preventive therapy initiation and completion rates are suboptimal among children. Shorter tuberculosis (TB) preventive treatment (TPT) regimens have demonstrated safety and ...efficacy in children and may improve adherence but are not widely used in high TB burden countries. Understanding preferences regarding TPT regimens’ characteristics and service delivery models is key to designing services to improve TPT initiation and completion rates. We examined paediatric TPT preferences in Eswatini, a high TB burden country.DesignWe conducted a sequential mixed-methods study utilising qualitative methods to inform the design of a discrete choice experiment (DCE) among HIV-positive children, caregivers and healthcare providers (HCP). Drug regimen and service delivery characteristics included pill size and formulation, dosing frequency, medication taste, treatment duration and visit frequency, visit cost, clinic wait time, and clinic operating hours. An unlabelled, binary choice design was used; data were analysed using fixed and mixed effects logistic regression models, with stratified models for children, caregivers and HCP.SettingThe study was conducted in 20 healthcare facilities providing TB/HIV care in Manzini, Eswatini, from November 2018 to December 2019.ParticipantsNinety-one stakeholders completed in-depth interviews to inform the DCE design; 150 children 10–14 years, 150 caregivers and 150 HCP completed the DCE.ResultsDespite some heterogeneity, the results were fairly consistent among participants, with palatability of medications viewed as the most important TPT attribute; fewer and smaller pills were also preferred. Additionally, shorter waiting times and cost of visit were found to be significant drivers of choices.ConclusionPalatable medication, smaller/fewer pills, low visit costs and shorter clinic wait times are important factors when designing TPT services for children and should be considered as new paediatric TPT regimens in Eswatini are rolled out. More research is needed to determine the extent to which preferences drive TPT initiation, adherence and completion rates.
The allotropic behavior of titanium is affected by many factors such as processing temperature and alloying elements. Using processing method with parameters that enhaces properties of the resulting ...alloy is imperative. In this study, CP-Ti, binary systems Ti-1Nb, Ti-1Zr and ternary Ti-1Nb-1Zr, were produced using spark plasma sintering method at 1200˚C at the heating rate of 100˚C/min, a 10 min holding time and pressure of 50 MPa. The microstructures were analyzed by an optical microscope and scanning electron microscope and the XRD was used to examine phases formed. Furthermore, the microhardness and the compressive behavior of the materials were analyzed for mechanical properties. The microstructures obtained were of α phase for the CP Ti and Ti-1Nb binary alloy, and it was found to be α׳ for Ti-1Zr and Ti-1Nb-1Zr. The α׳ alloys had relatively the highest hardness at about 218HV and 225 HV for Ti-1Zr and Ti-1Nb-1Zr respectively. The developed alloys had densities above 99%. The results also showed that even at low additions, Zr and Nb improved the properties of CP-Ti, making them good contenders for biomedical implant applications.
Graphite–copper (Gr–Cu) and graphite–aluminum (Gr–Al) composites are potential candidates for enhanced thermal management for different engineering applications. However, their applications are ...limited by inadequate thermal conductivity, high coefficient of thermal expansion (CTE) and low microhardness. In this study, SiC and ZrB
2
were incorporated into Gr–Cu and Gr–Al powders, and then sintered in a spark plasma sintering (SPS) system to produce Gr–Cu + 8wt%SiC, Gr–Cu + 4wt%SiC + 4wt%ZrB
2
, Gr–Al + 8wt%SiC and Gr–Al + 4wt%SiC + 4wt%ZrB
2
composites. After sintering, the physical, morphological, thermal, electrical and mechanical properties of the composites were evaluated. Results indicated 8.5% increase in relative density for reinforced Gr–Cu composites over the unreinforced Gr–Cu. The porosity of the reinforced Gr–Cu composites is 40.5% lower than that of the unreinforced and ~ 8% for reinforced Gr–Al. For all the sintered samples, Gr–Cu + 4wt%SiC + 4wt%ZrB
2
sample has the highest hardness value of 44.5 HV
0.1
, highest peak intensity ratio of 80.19% and minimum CTE of 2.02 × 10
–5
/K. The huge increase in the microhardness and peak intensity ratio of Gr–Cu + 4wt%SiC + 4wt%ZrB
2
is partially attributed to the formation of hard ZrC phase and three-bond system in ZrB
2
. This composite is recommended for thermal management of heat sinks and heat spreaders in electronics and pistons in automobiles.
Friction stir processing (FSP) is a solid-state processing technique that has proven to be an efficient surface modification process for producing aluminium matrix composites (AMCs). However, ...practical challenges still occur during the processing of AMCs even though extensive progress has been made in recent years. In the present study, the influence of FSP process parameters on the tensile property of Al-Ni-Fe composite has been investigated. The process parameters studied were rotational speed and advancing speed. The rotational speed varied between 600 and 1000 rpm while the advancing speed varied between 70 and 210 mm/min. The rotational speed was kept constant at each setting and the advancing speed varied. Other processing parameters were kept constant throughout the experiments. The results were compared with those of the base metal (Al). The results showed that the tensile strength decreased as the advancing speed increased. The highest tensile strength was obtained at a rotational speed of 1000 rpm and an advancing speed of 70 mm/min.
Compositions of polycrystalline Mg-Zn mixed ferrites with the general formula Mg(1-x)Zn(x)Fe(2)O(4) (0 (less-than or equal to) x (less-than or equal to) 1) were prepared by the standard double ...sintering ceramic method. The structural properties of these ferrites have been investigated using X-ray diffraction and infrared absorption spectroscopy. The lattice parameter, particle size, bonds length, force constants, density, porosity, shrinkage and cation distribution of these samples have been estimated and compared with those predicted theoretically. Most of these values were found to increase with increasing Zn content. The energy dispersive (EDS) analysis confirmed the proposed sample composition. The scanning electron microscope (SEM) and transmission electron microscope (TEM) micrographs showed aggregates of stacked crystallites of about 200-800 nm in diameter. Far infrared absorption spectra showed two significant absorption bands. The wave number of the first band, v(1), decreases with increasing Zn content, while the band, v(2) shifts linearly towards higher wave numbers with Zn contents, over the whole composition range. The room temperature electrical resistivity was found to decrease as Zn-content increases. Values of the vacancy model parameters showed that the packing factors P(a) and P(b) decrease, the fulfillment coefficient, a, remains almost constant and the vacancy parameter, beta, strongly increases with increasing Zn content in the sample. The small values of P(a), P(b), alpha and the strong increase of the vacancy parameter, beta, indicate the presence of cation or anion vacancies and the partial participation of the Zn(2+) vacancies in the improvement of the electrical conductivity in the Mg-Zn ferrites.
This work studied the correlation between Vickers and nano-hardness of SAF 2205 reinforced with TiN nanoparticles for the convenience of assessing its mechanical properties. Spark plasma sintering ...was used to fabricate the composites. Micro and nanoindentations were performed to determine micro and nanohardness values of the fabricated composite. Optical microscope was used to assess the microstructure. The microstructure revealed that the TiN dominated the ferrite/ferrite, ferrite/austenite and austenite/austenite grain boundaries. The micro and nanohardness at the TiN dominated grain boundaries were higher compared to the grain hardness. Hardness also increased considerably as the TiN nanoparticles increases. This is also owed to the strengthening effect played by TiN at the grain boundaries by disrupting dislocation motion in the composite. The determined Vickers hardness was plotted as a function of the corresponding nanohardness, a good linear relation was found between Vickers hardness and nanohardness. A linear relationship (HV = 215.15 + 15.03Hnano) was established which indicates that there is no difference in behavior for the Vickers hardness and nanohardness.
Abstract
The demand for lightweight materials in the automobile and aerospace industries has led to various researches on graphite and graphite‐aluminum composites. The aim of this study was to ...investigate the effect of the addition of micron/nano TiB
2
particles on the properties of graphite‐aluminum composite particularly the wear resistance. The powders were sintered at 550 °C and 50 MPa with more attention on the effect of the sintering temperature on densification, microhardness, coefficient of thermal expansion, wear and frictional force. The results show that the addition of nano TiB
2
reduces the densification while improving the hardness of Gr−Al composite with the lowest value being 96.0 % of relative density and the highest microhardness of 43.58 HV 0.1. The coefficient of thermal expansion and frictional force of the composite materials increases with increasing TiB
2
content and heating rate (100 °C/min–150 °C/min). TiB
2
particles enhance the wear resistance of graphite‐aluminum composite. The addition of micro/nanoparticles of TiB
2
to graphite‐aluminum composite increases its corrosion rate with improved passivation behavior in 3.5 wt.% NaCl solution. Nevertheless, 5 wt.% nano (100 °C/min) TiB
2
additions do not affect the overall corrosion rate. This work has shown that we can take advantage of some of the properties of TiB
2
to improve the performance of graphite‐aluminum composite.
The use of nickel-based superalloys has extended to different fields such as turbines, rocket motors, chemical equipment, space vehicles and power plants due to their excellent mechanical properties. ...This study investigates the effect of heat treatment on the microstructure and microhardness of spark plasma sintered Ni-Fe-Co ternary alloy. 50wt.% Ni and varying percentages of Fe and Co powders were milled and fabricated by Spark Plasma Sintering (SPS) technique at a temperature of 900 °C, pressure and holding time were kept at 50 MPa and 10 min respectively. The sintered compacts were heat-treated at 1000 °C, soaked for 1 hr and quenched in distilled water for 5 min. Subsequently, the sintered and heat-treated samples were characterized by scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (EDS) and X-ray Diffraction (XRD) to determine the microstructural evolution and phase transformation accompanying the process. XRD results revealed the evolution of strengthening phases in the heat treated of the samples. The as-sintered and heat-treated compacts Vickers hardness was also investigated before and after the heat treatment. The results show a general improvement in the microstructure after the heat treatment which translated to the observed increase in the hardness of the heat-treated samples.
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