Semiconductor nanocrystals (NC's) are the materials with dimensions less than 10 nm. When the dimensions of nanocrystals are reduced the bulk bohr diameter, the photo generated electron-hole pair becomes confined and nanocrystal exhibits size dependent upon optical properties. This work is focused on the studying of CdSe semiconductor nanocrystals. These nanocrystals are considered as one of the most widely studies semiconductors because of their size -tunable optical properties from the visible spectrum. CdSe-nanocrystals are produced and obtained throughout the experimental setup initiated at Nano-NRIAG Unit (NNU), which has been constructed and assembled at NRIAG institute. This unit has a specific characterization for preparing chemical compositions, which may be used for solar cell fabrications and space science technology. The materials prepared included cadmium oxide and selinid have sizes ranging between 2.27 nm and 3.75 nm. CdSe-nanocrystals are synthesized in ''TOP/TOPO (tri-octyl phosphine/tri-octyl phosphine oxide). Diagnostic tools, include UV analysis, TEM microscope, and X-ray diffraction, which are considered for the analytical studies of the obtained materials. The results show that, in this size regime, the generated particles have unique optical properties, which is achieved from the UV analysis. Also, the TEM image analysis shows the size and shape of the produced particles. These studies are carried out to optimize the photoluminescent efficiency of these nanoparticles. Moreover, the data revealed that, the grain size of nanocrystals is dependent upon the growth time in turn, it leads to a change in the energy gap. Some applications of this class of materials are outlined. ª 2014 Production and hosting by Elsevier B.V. on behalf
Anodic oxide coatings on aluminum alloys are used for space environment applications. These provide specific thermo-optical properties to spacecraft surface. Fragments of these coatings lead to generate the contamination in satellites and affect the mission lifetime. The current work concerns studying of the anodic processes applied on aluminum and different groups of aluminum alloys as Al7075, Al2024 and Al6061. Experimental procedures are performed using sulfuric acid at different values of current density (1 -2 A/dm 2 ). The influence of the parameters of anodic film formation on the coating characteristics and layer thickness of aluminum alloys has been investigated. Reflectance and optical properties of the anodized aluminum alloy coatings are determined and found to be dependent on the alloying elements. Changes in anodic coating weight and film thickness of aluminium alloys with the process parameters as current density, temperature, time duration, acid concentration, and sealing system have been studied. Moreover, morphology and surface structure of the considered samples are carried out in attempt to understand the physical characteristics. The obtained results are compared and briefly outlined.
Because of the unique combination of light weight, high strength, and ease of fabrication, aluminum alloys have the mainstay of the aerospace industry. This report provides a brief overview of the types and series of aluminum alloys “AA” used for space industries and aerospace applications such as spacecraft surface structures and both of aircraft construction and satellite subsystems. The alloy compositions, manufacturing processes, and treatment classify the alloy properties and characteristics. According to these characteristics alloy compositions, the report outlines how to identify the suitable and optimum one to meet specific application needs and mission requirements. Also, the report clarifies how these alloys can be improved by a suitable tailoring of the composition through the addition of some of the alloying elements, which considerably are useful to refine the microstructure, thus improving the mechanical properties. Different types of aluminum alloys such as the series AA 2XXX, AA 5XXX, AA 6XXX, and AA7XXX are outlined. The discussion is performed to give view point on the alloy series with the emphasis on the improved of the alloy type AA6061, as example, with the heat treatment T6 “AA6061-T6” that is significantly more suitable alloy for spacecraft and satellite’ surface structures.
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