Effects of Precipitation Hardening Variables on Al–Zn–Mg-Sn Alloy as Sacrificial Anode in Seawater: Experimental and Statistical Analysis

This research investigated the effects of tin composition and heat treatment variables on the Al-Zn-Mg alloy as sacrificial anode in seawater using gravimetric technique and statistical analysis. Tin was alloyed with Al-Zn-Mg in varied proportions (0%, 0.01%, 0.05% and 0.1%) to determine the optimum anode efficiency in the marine environment. Precipitation heat treatment was performed by first subjecting the samples to solution treatment at 5380C for 2 hours and later subjected to varying hardening temperatures and times. The samples were hardened for 4, 8 and 12 hours at each of the hardening temperatures of 1300, 1600 and 1900 centigrade. The anode efficiency increases as the tin concentration increases. The experimental result of this study showed that the Al-Zn-Mg alloy with 0.1% tin gives the optimum anode efficiency. It was revealed that the Al-Zn-Mg alloy without tin composition exhibited high output current capacity when hardened at 1900C for 4 hours. Predictive model developed in this work was in consonance with experimental observation except the following; at hardening temperature of 1600C, the model recommended 12 hours as against 4 hours of laboratory experiment and at hardening temperature of 1300C it advocated 8 hours as against 12 hours

Wear and corrosion of wrought a6061 aluminium alloy in dot3 brake fluid

Abstract: The twofold impact of wear and corrosion on wrought A6061 alloy in hydraulic DOT3 brake fluid environment was studied. The wear studies were performed on the samples using a developed wear-jig. Weight loss corrosion test method was used to determine the corrosion rate of the wrought A6061 alloy samples immersed in the brake fluid for a total of 1680 hours. From the results of wear tests carried out on the A6061 alloy sample with brake oil, the highest wear value of 5.24x10-7 mg/mm2/cycle (approx.) was obtained from 6 N (approx) force after 130 minutes. The wrought A6061 alloy material demonstrated the highest corrosion rates nearly 3.0 x10-2 mg/mm2/yr within the early 168 hours of immersion in brake fluid. The result is practically lower than the corrosion rate of cast specimen in DOT3 brake oil or some other alloys immersed in other corrosive media that were previously reported in the literature. The results show that small amount of chemical corrosion is sufficient to cause and accelerate mechanical wear of the material in usage

Fabrication of forced air cool austempered ductile iron and exploring its corrosion behaviour in a simulated mine water

Abstract: The production of austempered ductile iron (ADI) with uniform microstructure and properties is constrained by the austempering process vis-à-vis the quenching medium. This is as a result of the stringent operating parameters with costly facilities. This limitation has restricted the application of ADI, despite its inherent mechanical and chemical properties. An emerging technology of overcoming this limitation is by austempering with force air cooling equipment, which is accessible, available and cost-efficient. This work characterizes the behaviour of the forced air cool ADI in simulated mine water due to the strategic importance of the mining industry in the global economy. The study establishes the influence of sample section thickness on the corrosion performance. The sample’s thickness were 5, 15, and 20 mm. Electrochemical experiments were performed on the forced air cool ADI at atmospheric pressure and room temperature with method such as open circuit potential (OCP). The post-corrosion analyses were performed using X-ray diffractometry (XRD) and field emission scanning electron microscopy (FESEM). The research highlighted that small section thickness has a more favourable performance compared with larger section. Consideration is also accorded to the capability of the ADI in the studied environment

Wear behaviour of cast aluminium silicon (Al-Si) alloy in dot 4 brake fluid

Abstract : The frictional sliding behaviour of cast Al-Si alloy was investigated with and without DOT 4 hydraulic brake fluid lubrication/environments. Cast Al-Si specimen was produced from wrought alloy and the specimen surface was metallurgically prepared. The as- cast product was characterized with aid of micro-hardness tester, the chemical composition was analysed by X-ray fluorescence (XRF), while X-ray diffraction (XRD) was used to identify phases present, microstructures and surface examinations were done on a high resolution metallurgical Optical Microscope. The properties of the polished and worn sample surfaces were examined by Scanning electron microscope (SEM) equipped with Energy dispersive X- ray (EDS) facilities. A 6mm diameter alumina ball under varying normal loads (3-10 N) was rubbed against the surface of the cast Al-Si coupon specimen. The dry and wet sliding wear behaviour was assessed based on the CoF-sliding time behaviour. From the results, the average CoF values of 0.9064 for dry and 0.2038 for wet contacts were obtained. Comparatively, 1.03E-06 and 4.21E-07 minimum wear intensities; and 467290 and 132170 wear resistances were obtained for dry and wet contacts respectively. Behaviour of cast Al-Si in DOT4 were compared with its performance in DOT3 regarding the hydraulic brake system application

Platinum degradation mechanisms in proton exchange membrane fuel cell (PEMFC) system: A review

Proton Exchange Membrane Fuel Cells (PEMFCs) have the perspective to intensely decrease global emission through environmentally-friendly potential. This review paper summarizes the degradation of platinum catalyst layer that has become a significant issue in the improvement of PEMFCs. The review intends to categorise and provide a clear understanding between disintegration and agglomerate that occurs during platinum degradation. In each process, different degradation mechanisms and their migration processes are presented. The improvement in platinum degradation as a function of increasing the performance of PEMFC is established. Prospects for addressing platinum degradation through the exploration of further experimental and numerical research are recommended. Lastly, this paper through recommendation attempts to prevent platinum degradation and reduces high costs associated with the replacement of catalysts in the PEMFCs

A review of bipolar plates materials and graphene coating degradation mechanism in proton exchange membrane fuel cell

Proton exchange membrane fuel cells (PEMFCs) have the perception to strongly reduce global emissions through an environmentally friendly perspective. Graphene has drawn global attention and has positioned itself as a potential material for bipolar plates application. This study reviews the application of graphene and summarizes the degradation of graphene coating that has become a significant issue in the improvement of PEMFC's performance. In the analysis, the degradation and its dissolution processes are presented. The need to improve the material selection focused mitigation on fabrication defects that act as initiation sites for graphene coating degradation is recommended. Finally, this review through recommendation endeavors to prevent graphene coating degradation and reduces high costs associated with the replacement of bipolar plates in the PEMFCs

Microstructural characterization and corrosion behaviour of heat treated standard stainless steels in tar sand

This paper aims to investigate the corrosion behaviour of heat-treated standard duplex stainless steel (UNS S32205) in the recovery of bitumen from Nigerian-rich tar sand, using sodium hydroxide (NaOH) as the process solution. Appropriate material family needs to be identified for the exploitation of tar sand resources to ensure sustainable extraction of bitumen. UNS S32205 offers exceptional mechanical properties and excellent corrosion resistance which makes it a great material choice for demanding applications, including offshore platforms and construction projects. Samples of UNS 32205 were heat-treated and immersed in the digested tar sand, maintaining a process temperature of 90°C. The microstructure of the corrosion coupons was studied using SEM/EDS (Scanning Electron Microscope/Energy Dispersive Spectroscope), and the corrosion rate of the samples was derived using gravimetric technique following ASTM G31 standard. The SEM micrographs indicated varying degrees of pits associated with the passivity of UNS 32205 and an imbalance between its ferrite and austenite phases due to the presence of secondary precipitates formed during heat treatment.The normalized sample, having a corrosion rate of 0.053 mm/year, exhibited the best corrosion resistance, followed by oil quenching (0.054 mm/year), then annealing (0.076 mm/year), and water quenching (0.077 mm/year), where they all showed improved corrosion resistance over the as-received sample having a corrosion rate of 0.078 mm/year

Productivity and Unemployment in Nigeria

Productivity and employment are issues that are central to the social and economic life of every country. The extant literature refers to productivity and unemployment as constituting a vicious circle that explains the endemic nature of poverty in developing countries. And it has been argued that continuous improvement in productivity is the surest way to breaking this vicious circle. Growth in productivity provides a significant basis for adequate supply of goods and services thereby improving the welfare of the people and enhancing social progress. As pointed out by Dernburg (1985:63), "Without it there would be no growth in per capita income, and inflation control would be all the more difficult". In fact, the observation has been made that continuous enhancement of productivity has been very central to the brilliant performance of the Asian Tigers and Japan in recent years (Simbeye, 1992; World Bank 1993). Recent developments in the world economy have also shown that countries with high productivity are not only central to the determination of global balance of powers (e.g Japan and Germany), but also serve as centres of stimulus, where world resources (including labour) are redirected to, as opposed to countries with low or declining productivity. Recent studies, for example, Rensburg and Nande (1999) and Roberts and Tybout (1997) have also shown that high productivity increases competitiveness in terms of penetrating the world market. Thus, a country with high productivity is often characterized by a very high capacity utilization (optimal use of resources), high standard of living, low rate of unemployment and social progress. Unemployment, on the other hand, has been categorized as one of the serious impediments to social progress. Apart from representing a colossal waste of a country's manpower resources, it generates welfare loss in terms of lower output thereby leading to lower income and well-being (Akinboyo, 1987; and Raheem, 1993). Unemployment is a very serious issue in Africa (Vandemoortele, 1991 and Rama, 1998) and particularly in Nigeria (Oladeji, 1994 and Umo, 1996). The need to avert the negative effects of unemployment has made the tackling of unemployment problems to feature very prominently in the development objectives of many developing countries. Incidentally, most of these countries' economies are also characterized by low productivity. Thus, it seems obvious to many policy makers that there must be a straight forward connection between productivity and employment/unemployment. However, the theoretical linkage between productivity and unemployment is yet to be settled in the literature. While some researchers posit that higher productivity may increase unemployment (e.g. Diachavbre, 1991; Krugman, 1994), some others argue that it could increase employment (e.g Yesufu, 1984; Akerele, 1994; CEC, 1993). In view of the unfolding reality coupled with the protracted debates this paper attempts to examine the linkage between productivity and unemployment. Specifically, it examines the dimensions of productivity and unemployment in Nigeria as well as the direction of causality between them. To this end, the rest of the paper is organized thus. Following this introduction is part II, which examines the conceptual and theoretical is sues. Part III discusses the profile of productivity and unemployment in Nigeria while the empirical link between them is examined in part IV. The final part contains the policy implications and conclusions