Materials Science

Kaolin is a clay mineral that has a wide application in the industry, depending on its purity. The quality of kaolin mined around the world is depleting especially with depth and rate of mining. Consequently the usability of this mineral is threatened by the presence of some inherent impurities. Beneficiation enhances kaolin applications; hence, it becomes imperative to understudy comparative means of upgrading kaolin, for the process integration and optimization. The amenability of using magnetic separation for removing the iron oxide and titanium oxide impurities from the Egyptian Kaolin has been studied. Different variables affecting of magnetic separation process such as solid percent, magnetic field, matrix loading capacity, and retention time were studied. The results indicated that substantial decrease in iron oxide (from 1.69 % to 0.75 %) and TiO2 (from 3.1 % to 0.71 %) contents as well as improving iso-brightness (from 63.76 % to 75.21 % and whiteness (from 79.85 % to 86.72 %) of the product could be achieved.

This study presents the impact of dust on the electrical performance parameters of CIGS PV modules installed in a Sahelian environment. The study concerns two PV (photovoltaic) modules of the same technologies (CIGS), of the same power, (90W) each, of the same electrical parameters and manufactured by the same company. These modules, respectively denoted M1 (SN-CIGS90) and M2 (SN-CIGS90) were tested under the initial conditions to ensure their correct operation and to determine the initial values of the electrical parameters before exposure. After that, the modules are exposed under actual CERER operating conditions for three months, in which the module M1 undergoes weekly cleaning and M2 is exposed without cleaning for three months. The comparison of the variation rates obtained on the experimental values of the two modules shows that, like other technologies, the deposition of dust constituting the environmental constraint that most influences the electrical parameters of a CIGS module. In fact, the M2, has respective variation rates of -38,581% for the maximum power (Pmax) and -37,430% for the short-circuit current (Isc), +1.520% for the open circuit voltage and (Vco) -3.309% for the form factor (FF), unlike the M1 module, which undergoes the following variations: -7.5% for the Pmax -3.163% for the Isc, + 1.467% for the Vco and-5,861% for the FF.

This paper mainly explain the lowering of band gap energy of synthesized ZnO nanoparticles (3.263eV) than their bulk counterparts (3.37 eV), which indicate the high conductivity than the bulk ZnO powder. Zn1-xLixO, Zn1-xNaxO and Zn1-xKxO (where x= 0.005, 0.01, 0.015 and 0.02 M for all dopants) doped ZnO nanoparticles and their solution was then characterized by UV-vis spectrophotometer. All concentration of Li+ doped ZnO nanoparticles was more narrowing the band gap of the undoped ZnO nanoparticles than Na+ and K+ doped ZnO nanoparticles. Both the size and concentration of dopants were affecting the band gap energy of ZnO nanoparticles. As the concentration and ionic radii of the dopants increases the optical band gap energy was also increasing. So the highest band gap energy was obtained by 0.015 and 0.02M K+ doped ZnO nanoparticles.

In this paper, we have studied the photoluminescence spectroscopy of several HEMTs AlGaN/GaN high electron mobility transistors produced by molecular beam epitaxy growth. The heteroepitaxy of the nitrides of elements III is made on substrates of different nature: Silicon, Si [111]), Sapphire Al2O3 and Free-standing GaN. We thus observed constraints during growth, related to the disagreements of the mesh parameters. The EA activation energy of the free exciton A, measured by photoluminescence, varies linearly with the biaxial strain ?xx, obtained by X-ray diffraction. In addition we noticed that an evolution of the aluminum assay of 0.5% from one sample to another 5% reveals a shoulder that evolves respectively to a plateau, reproducible at different levels of excitation. This is how we interpret this phenomenon as a manifestation of 2D gas on the photoluminescence spectrum

The present work deals with the study of mechanical properties of epoxy filled with coconut shell powder and egg shell powder. Epoxy with coconut spell powder and egg shell powder composite was prepared with different filler concentration using hand lay-up technique. Specimens were cut according to the ASTM standards for different experiments, such as flexural test, vickers hardness test and water absorption test. It is observed that at 10 wt% of filler content, coconut shell powder gives the best results for Vickers hardness, flexural strength and flexural modulus. In water absorption test 20% C.S.P absorbs more water compared to other samples.

This paper focuses on anti-reflective coatings on monocrystalline silicon solar cells and the impact of thickness and refractive index on reflectivity. The reference wavelength of silicon is 700nm, with its optimum refractive index (n = 3.7838) and a surface reflectivity of 33%. The calculations were based on values of layer thickness and refractive indices that meet the chosen phase and amplitude conditions, namely (HfO2), (MgF2); (SiOxNy), (SiOx), (Si3N4) and (SiNx:H). Numerical simulations have shown that low reflectivities at the surface of the single-layer coated planar cell can be obtained (3% with Si3N4) and (2% with HfO2). Multilayers such as MgF2/SiNx:H/Si, give a very low reflectivity of around 1%.

We discuss the band gap tunability of ZnO by mixing ZnO with CdO. Nanoparticles of ZnO/CdO and ZnO are prepared by decomposition of their respective metal acetates, ammonium carbonate and ethylene diamene tetra accetic acid, by chemical co precipitation method. The heat treatment of the precursor powders at their decomposition temperature and beyond, results in the evolution of heat from the combustion of carbonaceous material. This facilitates the reaction among the constituent metal ions and the desired oxide phase is formed at low temperature. The particle size is determined by X-ray diffraction and the diffractogram is compared with JCPDS data to identify the crystallographic phase. The shift in the‘d’ value and elastic micro strain was calculated .The FTIR studies are used to confirm the formation of metal oxide. The characteristic stretching and bending frequencies of the samples were also analysed. The absorption spectra and luminescence spectra are recorded. To study the effect of calcination on crystal lattice, phase, band gap and luminescence the prepared samplewas heated at 9000C. A colour change from saffron to dark brown is observed without any phase change. We also studied the dependence of excitation wavelength on the fluorescent emission of this Nano composite.

Mn-doped and Undoped Ruthenium Oxide composite nanostructures in thin film form were prepared on stainless steel substrates by sol-gel spin coating method. The at % of Mn was increased as 0.1, 0.2, 0.5, 1 and 2 %. The XRD pattern of undoped and Mn-doped Ruthenium oxide films showed crystalline nature with porous morphology. EDAX confirms the successful doping of Mn in RuO2. The infrared spectrum illustrates stretching mode of Ru= O and O-Ru-O and absorption peaks attributed to the –OH bending vibrations along with Mn atoms was also seen. Electrochemical behaviour of the deposited films was attempted in 0.1 M KOH aqueous electrolyte using cyclic voltammetry, chronopotentiometry and electrochemical impedance spectroscopy (EIS) tests. For 1 At % Mn:RuO2 thin films electrode showed maximum specific capacitance of 328 F/g. Chronopotentiometry study showed that for 1 at % Mn doping the specific energy and specific power are increased than undoped Ruthenium oxide and decrease in the charge transfer resistance .

The present paper reviews the comparative effect of different transition metal complexes derived from hexaminecobalt(III) chloride metal complex on the thermal properties of polyaniline nanocomposites. These metal complexes are obtained through photo-substitution route in which some of the amine ligands of the hexaminecobalt(III) chloride metal complex are photochemically substituted by different organic ligands like 1,10 phenenthroline, pyrazine and imidazole. It is observed that the metal complexes thus synthesised containing both organic and inorganic moieties enhance the thermal stability of polyaniline to a great extent as compared to simple hexamine metal complex filled nanocomposite. However, as far as the role of different incorporating organic ligands of metal complexes on the thermal properties of polyaniline nanocomposites are concerned, there seems to be little or no effect.

Polycrystalline bulk samples of La_0.5Ca_0.5MnO₃ were synthesized by solid state reaction method to explore their structural, electrical and magnetic properties. The Rietveld treatment of the X-Ray diffraction (XRD) profiles clearly indicated that the XRD patterns are well fitted with Orthorhombic structure. Raman peaks revealed their finger print positions and irreducible representations at the Brillouin zone center as presented by the group theory. Resistivity ‘?’ measurements revealed that  ? first increases as temperature ‘T’ decreases, exhibits a peak at T = Tp (Tp is the temperature corresponding to the resistivity peak), which is around 150 K in the present compound and then decreases as T is further reduced below Tc (Tc is the ferromagnetic curie temperature). For T > Tc, the resistivity shows activated transport as in an insulator. Magnetization study revealed that both a paramagnetic to ferromagnetic transition and an antiferromagnetic transition are involved. Possible mechanism contributing to these processes such as activated transport and Zener double exchange has been discussed.