Formation of an amorphous phase and its crystallization in the immiscible Nb-Zr system by mechanical alloying

Mechanical alloying of binary Nb-Zr powder mixtures was carried out to evaluate the formation of metastable phases in this immiscible system. The milled powders were characterized for their constitution and structure by X-ray diffraction and transmission electron microscopy methods. It was shown that an amorphous phase had formed on milling the binary powder mixture for about 10 h and that it had crystallized on subsequent milling up to 50-70 h, referred to as mechanical crystallization. Thermodynamic and structural arguments have been presented to explain the formation of the amorphous phase and its subsequent crystallization

Development of Al- and Mg-based nanocomposites via solid-state synthesis

Mechanical milling (alloying) is one of the non-equilibrium techniques used to prepare alloys with exceptional properties. This technique was employed in this research to develop a new class of Al- and Mg-based nanocomposite alloys using SPEX high energy milling. These nanocomposites are characterized by the dispersion of nanocrystals in an amorphous matrix. Zirconium was added to the Al-Mg alloys for the purpose of promoting glass formability. As-milled samples were annealed at 400°C for 1 hour to investigate the thermal stability of the nanostructure. The phase evolution of the resulting alloys was studied using XRD and TEM/EDS, which showed a strong dependence of the resulting metastable phases on the starting alloys compositions.The nanocomposite structure was developed at Zr concentrations of 20 and 35 at.% regardless of the Al/Mg ratio and with some traces of oxidation. However, the amount of amorphous phase was varied in each case depending on the Al concentration into the alloy, since in low Al-containing alloys the amount of amorphous phase was less pronounced. It was found that higher Zr concentrations will lead to greater refinement of the nanostructure. These nanocomposites showed improved mechanical properties, in terms of higher hardness values, in addition to improved thermal stability. The improvement in thermal stability was attributed to the presence of Al3Zr which proved to contribute significantly to retarding grain growth via grain boundary pinning.Additionally, the employment of mechanical alloying was beneficial in producing Al3Zr in the cubic L12 ordered structure which improves the ductility of the alloy. Moreover, the homogeneity ranges of gamma-Al 12Mg17 and Al3Zr were extended significantly due to the nature of the non-equilibrium processing. In this research, the alloy with the maximum hardness was Al40Mg25Zr35, which has an average hardness value close to 780 HV and average crystallite size of about 10 nm. A common observation in the alloys that showed a higher hardness values combined with improved thermal stability, is that they contain higher Al and Zr concentrations.Le broyage mécanique est une technique hors équilibre qui permet la fabricationde nouveaux alliages avec des propriétés exceptionnelles. Lors de cette recherche, unbroyeur SPEX 8000 a été utilisé pour développer une nouvelle classe denanocomposites à base d'aluminium et de magnésium. Ces nanocomposites tirent leurspécificité de leur dispersion de nanocrystaux dans une matrice amorphe. Duzirconium a été ajouté aux alliages d'aluminium et de magnésium pour promouvoirl'amorphisation. Les échantillons de poudres broyées ont été recuits à 400°C pour 1heure pour évaluer la stabilité thermique des différentes phases. Leur évolution a étécaractérisée par diffraction par rayon-X et par MEBIEDS. TI fut démontré que lesphases métastables obtenues dépendent fortement de la composition des alliages dedépart

THE USE OF AN OPEN CYCLE ABSORPTION SYSTEM IN AUTOMOBILES AS AN ALTERNATIVE TO CFCS

Increased awareness of the impact of chlorofluorocarbons (CFCs) on the global environment has become the impetus in searching for alternative refrigerants and cooling methods for automotive air conditioning. Automotive air conditioning is one industry that heavily uses CFC compounds, and the leakage of CFCs from such air conditioners is substantial compared to that from stationary air conditioners. Therefore, the use of non-CFC air conditioners in automobiles is apparently becoming very important. The main objective of this paper is to study the feasibility and design of an air conditioning system for automobiles using the Open Cycle Absorption System, with LiBr-H2O as the working fluid. Also, some suggestions are given to minimize the power loss like making use of the exhaust gas to pre-heat the weak desiccant. Evaluating the COP, of the designed air conditioning system for buses is the main scope, and it is found that the COP of the system is increasing with the increase in regeneration temperature at fixed evaporator and absorber temperatures. The system components are plotted in a schematic and flow chart as well as psychometric chart showing the complete process of conditioning and dehumidifying air

Evaluation of single reservoir performance for flood risk reduction using a developed simulation model: case study of Makhoul reservoir

The objectives of this study were firstly, to develop a simulation model (SM) for a single reservoir to identify the standard operating policy (SOP) of a reservoir based on a monthly operating period, and secondly, to evaluate the performance of the proposed Makhoul reservoir using a Developed Simulation Model (DSM) in reducing flood risk. This reservoir is located on the River Tigris, approximately 180 km upstream of Baghdad, Iraq. The performance of the reservoir in reducing flood risk was evaluated using two designs and records of flood waves gathered over two years. The first design was the present one, while the second was developed by increasing the operational storage to its maximum, based on the digital maps of the region. The flows downstream of the reservoir were compared, with and without the reservoir in the two years in question. Four parameters resulting from the two designs were compared: storage, surface area, elevation and power. The results suggested that the reservoir would be ineffective in reducing flood risk, but it would have the ability to provide hydroelectric power using the two designs, with the new one showing better ability at doing this. The reservoir can also serve purposes such as irrigation, fish wealth development and recreation. This DSM proved its effectiveness in evaluating the performance of the single storage system used for reservoirs

Characterization of Environmental Dust in the Dammam Area and Mud After-Effects on Bisphenol-A Polycarbonate Sheets

Owing to recent climate changes, dust storms are increasingly common, particularly in the Middle East region. Dust accumulation and subsequent mud formation on solid surfaces in humid environments typically have adverse effects on surface properties such as optical transmittance, surface texture, and microhardness. This is usually because the mud, which contains alkaline and ionic species, adheres strongly to the surface, often through chemical bonds, and is therefore difficult to remove. In this study, environmental dust and the after-effects of mud formed on a polycarbonate sheet, which is commonly used as a protective glass in photovoltaic cells. Ionic compounds (OH−) are shown to significantly affect the optical, mechanical, and textural characteristics of the polycarbonate surface, and to increase the adhesion work required to remove the dry mud from the polycarbonate surface upon drying. Such ability to modify characteristics of the polycarbonate surface could address the dust/mud-related limitations of superhydrophobic surfaces

Spark Plasma Sintering of Metals and Metal Matrix Nanocomposites: A Review

Metal matrix nanocomposites (MMNCs) are those metal matrix composites where the reinforcement is of nanometer dimensions, typically less than 100 nm in size. Also, it is possible to have both the matrix and reinforcement phases of nanometer dimensions. The improvement in mechanical properties of MMNCs is attributed to the size and strength of the reinforcement as well as to the fine grain size of the matrix. Spark plasma sintering has been used extensively over the past years to consolidate wide range of materials including nanocomposites and was shown to be effective noneconventional sintering method for obtaining fully dense materials with preserved nanostructure features. The objective of this work is to briefly present the spark plasma sintering process and review published work on spark-plasma-sintered metals and metal matrix nanocomposites

Fabrication and Assessment of Crumb-Rubber-Modified Coatings with Anticorrosive Properties

Scrap tires continue to be a major source of waste due to the lack of valuable and effective disposal routes. A viable solution to this problem is to recycle crumb rubber (CR)—a granulated material derived from scrap tires—and use it to develop other valuable products. Herein we report the fabrication and characterization of CR-modified coatings with anticorrosive properties on metal substrates. By varying the particle size and concentration of CR, we have determined the coating composition that offers the highest level of erosion protection. Images from a scanning electron microscope (SEM) reveal that CR is homogenously dispersed in the coating, especially when fine particles are used. As the concentration of CR increases, the hardness of the coating decreases as a result of the elastic properties of CR. More importantly, the erosion rate of the coating decreases due to increased ductility. Following Potentiodynamic tests, the utilization of these coatings proved to be beneficial as they showed good protection against aqueous corrosion when tested in 0.5 M NaCl solution. Our newly developed coatings offer an incentive to recycling CR and open up a safe and sustainable route to the disposal of scrap tires

Processing of CNTs Reinforced Al-Based Nanocomposites Using Different Consolidation Techniques

In this work, the development of two types of Al-based alloys with different concentrations of Si reinforced with MWCNT’s at 0.5–2.0 wt% is presented. Sonication of the CNT’s in ethyl alcohol was carried out for dispersion, and the mixtures were ball milled for 1, 3, and 5 hrs. SEM/EDS were used to study the morphology and the effects of changing milling parameters in addition to changes caused due to increasing concentration of the CNT’s. Furthermore, three sintering techniques, namely, Spark Plasma Sintering (SPS), Microwave Sintering (μWS), and Hot Isostatic Press Sintering (HIP) were employed to consolidate the ball milled powders at varying temperatures of 400, 450, and 500°C. It was found that SPS consolidated samples showed the most promising results amongst the three with the highest hardness values; around 100% densification, as well as the finest microstructure. On the other hand, microwave sintered samples showed the least appealing results, this could be attributed to the poor temperature distribution and the pressureless nature of the technique. A sintering temperature of 500°C was found to be the most suitable for these types of alloys