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Abstract

The structural, electronic and optical properties of (AlSb)m/(GaSb)n (m-n: 1-1, 2-2, 1-3 and 3-1) superlattices are investigated within the density functional theory (DFT) by using the last version of the first principles full potential linear muffin tin orbital method (FP-LMTO) as implemented in LmtART 7.0 code. The exchange and correlation potential is treated by the local density approximation (LDA) for the total energy calculations. Our calculations of the band structure show that the superlattices (n ≠ 1) have a direct band gap Γ-Γ. The optical constants, including the dielectric function ∈ (w), the refractive index n(w) and the reflectivity R(w) are calculated and discussed.

Abstract

A series of borate glasses with the composition x(SrO) · (50 – x)V2O5 ·0.5(B2O3) where x = 0, 0.1, 0.2, 0.3 and 0.4 were prepared by melt-quenching technique. The non-crystalline nature of the glasses has been established by XRD studies. Room temperature density and DC electrical conductivity of the samples were investigated in the temperature range of 300 K to 443 K. The molar volume and oxygen packing density (OPD) were estimated. The results show that the density, molar volume and OPD decrease with the increasing of SrO mole fraction. The DC electrical conductivity data has been analyzed in the light of Mott’s small polaron hopping (SPH) model and the activation energies were estimated. The conductivity was observed to rapidly fall and activation energy was found to increase when SrO was incorporated into the glass network. This may indicate that Sr+ ions have not contributed to the total conductivity and the observed conductivity may be of polaronic type only, which is due to the hopping of electrons between multivalent states of vanadium. Various small polaron hopping parameters such as small polaron radius, rp, effective dielectric constant, ∈p, polaron band width, J, optical phonon frequency, νo, small polaron coupling constant, γp, density of states at Fermi level, N(EF) were estimated and discussed.

Abstract

Copper (Cu) and nickel (Ni) nanoparticles have been grown simultaneously on glass and silicon substrates by RF sputtering method to form three Cu/Ni nanocomposites at different deposition times. The existence of Cu and Ni peaks in the X-ray diffraction (XRD) profiles confirms the crystalline structure of samples with Cu and Ni atomic content which have also been characterized by Rutherford backscattering (RBS) method. Moreover, the structural and morphological properties of the prepared nanocomposites have been compared with respect to their morphologies by means of atomic force microscopy (AFM) analysis. In order to compare the surface roughness over different spatial frequency ranges and evaluate surface quality, power spectral density (PSD) of each sample has been extracted from AFM data and also, the experimental and theoretical results have been compared. The fractal nature of these nanocomposites has been finally discussed.

Abstract

The investigation into wear resistance is an up-to-date problem from the point of view of both scientific and engineering practice. In this study, HVOF coatings such as MCrAlY (CoNiCrAlY and NiCoCrAlY) and NiCrMo were deposited on AISI 310 (X15CrNi25-20) stainless steel substrates. The microstructural properties and surface morphology of the as-sprayed coatings were examined. Cavitation erosion tests were conducted using the vibratory method in accordance with the ASTM G32 standard. Sliding wear was examined with the use of a ball-on-disc tribometer, and friction coefficients were measured. The sliding and cavitation wear mechanisms were identified with the SEM-EDS method. In comparison to the NiCrMo coating, the MCrAlY coatings have lower wear resistance. The cavitation erosion resistance of the as-sprayed M(Co,Ni)CrAlY coatings is almost two times lower than that of the as-sprayed NiCrMoFeCo deposit. Moreover, the sliding wear resistance increases with increasing the nickel content as follows: CoNiCrAlY < NiCoCrAlY < NiCrMoFeCo. The mean friction coefficient of CoNiCrAlY coating equals of 0.873, which almost 50% exceed those reported for coating NiCrMoFeCo of 0.573. The as-sprayed NiCrMoFeCo coating presents superior sliding wear and cavitation erosion resistance to the as-sprayed MCrAlY (CoNiCrAlY and NiCoCrAlY) coatings.

Abstract

Surface modification is one of the most intensively studied issue of technology, which is related to the almost all branches of industry. Since more than 100 years the huge number of methods has been developed and are still in growth. On this field the plasma transferred arc (PTA) hardfacing and surfacing is one of the most frequently used group of the method. The development of this method is going in three ways: (i) modification of the classic technique and the equipment, (ii) development in new materials, especially with the nanometric size and (iii) replacement dangerous materials (e.g. high cobalt alloys). In the current article the state of the art as well as the development directions of the plasma hardfacing issues are described.

Abstract

The paper discusses the problem of possibility of the detecting surface defects in carbon fibre reinforced plastics (CFRP) materials on the basis of the milling time series. First, the special defects in the hole-shaped with various depth were made. Next, the cutting forces are measured during the milling machining. Finally, the recurrence plot and quantification analysis was applied. The obtained results show that the depth defect influences the selected recurrence quantifications, which can be used as the simple defect indicators. The conducted research allow to determine the percentage share of the detectable defects. The novelty of the work and an unresolved problem is the selection of recurrence quantifications with the simultaneous use of them to detect the size of defects in carbon fibre reinforced plastics.

Abstract

Perovskite is able to sequester simultaneously, in its structure, both actinides and alkaline-earth elements. This study is an attempt to synthesize a complex perovskite Ca0.91-xCe0.09Rb0.04Csx[(Zr0.50Ti0.45)Al0.05]O3 (0.2≤x≤0.4), doped in the same time, with Ce, Cs and Rb. The synthesis is conducted by sintering at 1150°C during 16h. XRX analysis confirms the perovskite formation. SEM observations show a less porous microstructure. FTIR analysis reveals TiO6, Ti-O-Ti, Ti-O and Zr-O vibrations. Raman spectroscopy indicates many orthorhombic perovskite active modes, as: Ti-O6 and Ti-O3 torsions, ZrO7, CaO8 vibrations, the totally symmetric oxygen, and the O-octahedron cage rotation.

Abstract

The aim of this study is to increase the energy efficiency of the solar panel, to make the waste heat generated under the panel efficient and to store the electrical energy produced from solar panels in the form of hydrogen in boron nitride and boron carbide. Characterization of boron nitride and boron carbide was carried out with Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), differential thermal and thermogravimetric analysis (DTA/TG), Brunauer–Emmett–Teller (BET) and scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM/EDX). The specific surface areas and pore sizes of the boron nitride and boron carbide were determined as 78 and 20 m2/g; and 3.8 and 11.1 nm, respectively. DTA/TG thermograms showed that boron nitride degraded in one step in the temperature range of 30-550°C and boron carbide degraded in two steps. From experimental studies, approximately 8.7% energy efficiency was achieved and hydrogen energy was costless produced from a renewable energy source excluding system costs. Moreover, it was found that 276% and 208% more hydrogen could be stored in the boron compounds, the boron nitride had more hydrogen storage capacity, and the electrical efficiency of the panel was increased.

Abstract

In this paper, we use a phenomenological model based on the Jiles-Atherton-Sablik model of stress affecting the magnetic hysteresis of magnetic materials as modified when stress goes past the yield stress We use this to show that (1) the model produces sharp shearing of hysteresis curves, as seen experimentally and that (2) it also produces a step in the hysteresis loss at small residual plastic strain. We also find that the step in the hysteresis loss can be fitted to a power law, and find that the power law can be fitted by the power m=0.270, different from the mechanical Ludwik Law exponent, and reasonably close to the experimental 0.333 and 0.202. We will also suggest a method of measuring how plastically deformed the material is by suggesting how the dislocation density can be measured.

Abstract

This paper presents an investigation of impact strength of sponge gourd, coir, and jute fibers reinforced epoxy resin-based composites. Impact strength of specimens, made of composites with various proportions of wt% ratio of resin and hardener, wt% of resin and hardener, wt% ratio of sponge gourd and jute, wt% ratio of sponge gourd and coir, was measured. Design of experiment was done by Taguchi method using four control factors with three levels. Effect of the above control factors on impact strength was examined and the best combinations of control factors are advised. Confirmation test was performed by using this combination and the percentage of contribution of the above factors on impact strength was investigated by Analysis of Variance (ANOVA). Contour and interaction plots provide helpfully examines to explore the combined influences of different control factors on output characteristics. The regression equation represents a mathematical model that relates control factors with impact strength.