Procedia Materials Science最新文献

The purpose of this paper is to use software package ATK-SE package, in combination with virtual Nano-Lab (VNL), can be used to investigate a Nano-scale transistor. For the transistor structure we will use a graphene junction device, where ATK is used to investigate the properties of a similar system. The effect of various parameters on the structure of graphene Nano-ribbon checked. It consists of 3 regions and forms a metal-semiconductor-metal junction. By applying a gate potential to the central region, the system can function as a field effect transistor, which is able to calculate properties, Transmission spectrum, Temperature dependent conductance, Conductance and Current as function of gate potential and temperature. So in this paper, the device design and simulation parameters are associated with improved performance.

The aim of this development is to optimize a bone substitute (BS) for use in tissue engineering. This is achieved through the combination of three phases in a biocomposite (BCO), in which each is reabsorbed in the site of implantation and replaced by autologous bone (patient's own). The inorganic phases are composed of irregular particles (150-300 microns) obtained by milling and sieving of a biphasic bioceramic (BC) of hydroxyapatite (HA of bovine origin) with 40% (wt.) β-tricalcium phosphate (β- TCP, obtained by chemical synthesis) and Bioglass type 45S5 (45SiO₂ -24,5CaO - 24,5Na2O - 6P2O5, in % wt.). Instead, the organic phase consists of collagen extracted from Wharton's jelly (part of the human embryonic tissue) from physical and chemical self-developed process. The BC is produced by mixture of HA and β-TCP (< 45 μm) and molding by gelcasting with albumin in aqueous solutions, drying and sintering at 1200 °C for 2 hours. The BG is obtained from the mixture of the oxides, melting at 1350 °C and cast onto metal. Each phase and BCO is subjected to studies by electron microscopy (SEM and EDS), X-ray diffraction (DRX) and infrared spectrometry (FT-IR). The biocompatibility is evaluated by in vivo studies using the laminar implant model in Wistar rats (n=40). Histological samples show high biocompatibility and ability to integrate with the bone tissue. 30 days after implantation, the material is completely reabsorbed and the bone regeneration process starts, the primary objective. The process developed allows the synthesis of a new BS with excellent biological properties for clinical use.

In this study, titanium scaffolds with porosity of 60 volume percent were produced by Ti powder and urea space holder, using powder metallurgy technique. Dip-coating sol-gel process was used to coat titanium scaffolds with fluorohydroxyapatite (FHA) ceramics in order to improve their osteointegration for medical implant purposes. Scanning electron microscopy (SEM) with energy dispersive spectrometers (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES) and X-ray diffraction (XRD) were employed to ensure removal of urea particles, non-oxidized samples caused by sintering process as well as evaluation of nanocrystalline fluorohydroxyapatite coating structure. Results implied that ultrasonic irradiation could promote transferring of coating slurry into the pores and using a low temperature process improve crystallization and decreases the crystallite size of fluorohydroxyapatite to about 50 nm. Moreover, ICP-OES analysis indicated that Ca:P molar ratio was 1.69, which was quite close to the molar ratios of the natural bone calcium and phosphor elements.

In this paper the fault diagnosis of multiple faults in linear circuits is studied for distortion analysis for 2nd and 3rd harmonic components by considering a state variable filter circuit. To study the testability of the circuit the distortion analysis is plotted for various fault conditions. The sensitivity of the output signal with respect to the faults along with pole-zero analysis is obtained. The transfer function of the state variable filter considered for the analysis is given by:

One-dimensional Zinc oxide is among the most promising nanostructures due to their exceptional properties in wide range of applications such as electronic, optoelectronic, electrochemical, and electromechanical devices. The ZnO nanorods are synthesized by the means of chemical bath deposition. Among all of the parameters affecting chemical bath deposition method, the seed layer properties are vitally important to control the structural, morphological, and optical features of the ZnO nanorods. In this study the effect of seed layer sol concentration is investigated. Zinc acetate dihydrate (ZAD) as precursor, triethylamine as an additive, and 1-propanol as an alcoholic solvent are used to provide the sol to synthesize the seed layers. X-ray diffraction patterns show that all the ZnO seed layers and nanorods have hexagonal wurtzite structure. The preferred orientation along (002) polar surface is enhanced by increasing the ZAD concentration. Field emission scanning electron microscope images show that the morphological properties of ZnO nanorods are strongly depended on the seed layer sol concentration. As the ZAD concentration increases, the alignment of ZnO nanorods is enhanced. Furthermore, the diffuse reflectance spectroscopy analysis shows that the transmittance of nanorods is decreased by increasing the density of the ZnO nanorods.

In this study, the self-diffusion coefficients of carbon monoxide in the Cu-BTC nanoporous have been studied by molecular dynamics simulation. Metal-organic framework (MOF) materials pose an interesting substitute to more traditional nanoporous materials for a variety of separation processes. Separation processes including nanoporous materials can be controlled by two factors: diffusive transport rates and adsorption equilibrium. Adsorption equilibrium has been studied for some of gases in MOFs, but almost nothing is about molecular diffusion rates in MOFs. One of the known MOF is Cu-BTC that is formed of copper as metal center and benzene-1, 3, 5–tricarboxylate as linker molecule. The MD simulations have been carried out in the NVT and NVE ensemble. For simulation equilibration of the system at the desired temperature, an NVT simulation is used and for computing the self-diffusion coefficient, the ensemble is switched to NVE. The simulations have been performed at 100, 150, 200, 250, 298, 350, 400, 450 and 500 K with loading of 40 guest molecules per unit cell. The Mean square displacement, self-diffusion coefficient and activation energy have been calculated in total and in the X, Y and Z direction. The calculated MSD for the center of mass of the carbon monoxide molecules in the X, Y and Z-directions shows that the motion of carbon monoxide is homogeneous in the Cu-BTC and there is isotropic translational diffusion for carbon monoxide in the Cu-BTC. The calculated self-diffusion coefficients increase as temperature is increased. We use the Arrhenius equation to calculate the activation energy. The calculated activation energy is 4.43 kJ.mole^-1.

Laser shock peening (LSP) is one of the modern surface treatment methods in which surface of the work-piece is peened using short and intense laser pulses. In this process, favorable compressive residual stresses are induced on and near the surface of the material. This process is usually used to improve fatigue life of the component and has been applied in different industries such as aerospace, automotive, nuclear, medical, etc. Many researchers have used the finite element method (FEM) to simulate the LSP. In the majority of the conducted researches, results are in good agreement with the experimental data which shows FEM is capable of accurately simulating the LSP process. Simulations reduce the costs related to experimental measurement. Moreover with simulations, it is easier to understand, and is possible to analyze and optimize the process. To conduct a parametric study, it is first necessary to be able to simulate a single shot. After verification of the results, it is necessary to investigate the effect of multiple close impacts on the final results. Therefore, three dimensional analysis should be used. Since deformation is caused by the generated shockwave, there is a high strain rate (in the order of 10⁶ s^-1) in this process which necessitates the use of a very fine mesh. This in conjunction with a 3D simulation significantly increases the computational cost. This analysis is crucial for the design and optimization process of laser shock peening for a specific application. The present article, investigates the effect of overlapping laser pulses. Residual stress distribution on a range of overlap ratios (0 to 80% overlap) with square laser spot shape has been presented. With a laser intensity of 8GW/cm², and a desirable compressive stress of 300 MPa, it was found that the optimum choice of overlap is between 0 to 20 percent.

In this work, the fine grains of Phosphate rocks forming minerals (francolite-Ca₅(PO₄,CO₃)₃F,OH) which belong to the geological formation of phosphate rocks of Zagros mountains in IRAN were detected, analyzed and interpreted by SEM-EDX in nano-scale. Moreover, the results are compared with the results of XRD analysis and straight observations of samples through the polarized microscope. Finding the composition of elements in minerals is the best path finder and also is very important in many geological investigations. The fine grain Phosphate minerals perform as traps which attract some kinds of elements. But sometimes these minerals are very fine and it is too difficult to determine and separate them for further studies. For instance, interpretation and investigation of the composition of fine minerals in Nano-scale by using single crystal X-ray Diffraction (Single-crystal XRD) analysis is impossible. Due to variety of minerals phases in a rock sample, the interpretations of the results of total elemental analysis, for example XRF, ICP, are not so real. Therefore, the best method for determination of elements in fine grain rock forming minerals is the study of minerals by the Scanning Electron Microscopy (SEM), with Energy Dispersive X-Ray Analysis (EDX).

Silicene has been recently synthesized in the form of nanoribbons on the anisotropic Ag (110) surface. The effects of disorder on silicene nanoribbons are expected to exhibit remarkable properties in the form of nanostructures. It has been found that the electronic structures of the doped zigzag silicene nanoribbons (ZSiNRs) are different from those of pristine ZSiNRs. In this paper, we study the spin dependent electron conductance of ZSiNRs substitutionally doped with Boron/Nitrogen (B/N) atoms by using Green's Function method based on Tight Binding approximation and Landauer-Buttiker formalism. B/N atoms place on different sites of ZSiNRs from edge to center. The B/N atoms have influence on spin dependent transport. Also, conductance varies with the position of B/N atoms. Our findings are comparable with recent DFT calculations. These doping effects can be used to design novel spintronic devices.

Cordierite based materials are widely used in high temperature applications due to their good thermo-mechanical properties and thermal shock resistance. They are generally employed in the kiln furniture (shelves, brackets, bearing plates) for firing ceramic pieces. Because of its low expansion coefficient and dielectric properties, cordierite is also used in advanced ceramics, catalyst supports automotive, industrial waste gas purification and parts subjected to sudden temperature changes. The low intrinsic strength of the cordierite may be compensated by the presence of mullite, forming a composite material of cordierite-mullite, extending its use to somewhat higher temperatures, at the expense of a slight increase in the thermal expansion coefficient. In this work a cordierite-mullite precursor was prepared from a mixture of magnesium oxide, calcined alumina, silica fume and monoaluminum phosphate solution that produces fast setting at room temperature (∼20 minutes) and then, by calcination, cordierite-mullite is generated. The evolution of the mineralogical phases was studied from room temperature to 1350 °C by X-ray diffraction, differential thermal analysis and thermogravimetry. A possible sequence of chemicals reactions throughout the heat treatment is also proposed. Adding refractory aggregates to this precursor leads to obtaining a fast-setting concrete, suitable for the formation of individual pieces or repair service at moderately high temperatures. A summary of its main properties is also included.