Sharif Digital Repository

The effect of the bath chemistry and operating conditions on the chemical composition, microstructure and properties of NiWmdashB alloys deposited from tartrate baths on working electrode was studied for the first time by the pulsed current method. The investigations included the measurement of the current efficiencies and determination of the tungsten content in the electrodeposits. UV spectrometry was used for characterisation of complex formation. The grain size of deposits was determined by XRD. Also, the morphology of the deposits was studied by SEM. Amorphous NimdashWB alloys were successfully obtained by electrodeposition from the tartrate bath. The corrosion behaviour of NiWmdashB... 

Electrochemical deposition of aluminum and lead from basic molten AlCl3-NaCl-KCl mixture on an aluminum electrode at 180 °C was studied by the methods of voltammetry, potential and current transient and constant current deposition. The deposition of aluminum was found to proceed via a nucleation/growth mechanism, while the deposition of lead was found to be diffusion controlled. The diffusion coefficient calculated for Pb2+ ions in basic melt by voltammetry was in agreement with the deductions of transient method. The analysis of the chronoamperograms indicates that the deposition process of lead on Al substrates was controlled by 3D diffusion control, nucleation and growth. The processes... 

A simple process for the chemical vapor deposition of ultra SD single-wall carbon nanotubes has been developed. In this process, an iron nitrate nonahydrate solution in isopropyl alcohol with a concentration of (400 μgr/milt) was used to catalyst nanoparticle formation on an oxidized silicon wafer. The oxide on the substrate was made of a thick layer of wet oxide sandwiched between two thin layers of dry oxide. The process results in semiconducting Single-Walled carbon Nano Tubes (SWNTs) with diameters of less than 0.7 nm and more than a 1 ev band gap energy, which are amongst the smallest diameters of SWNTs ever reported. © Sharif University of Technology, June 2009  

During recent years, many investigations have been carried out to determine how to select different materials for the making of Micro Electro Mechanical Systems (MEMS) and bio-MEMS. The NiTi shape memory alloy thin film has been much regarded as a promising candidate for MEMS due. to its unique shape memory effect and high energy output. In this research, NiTi thin film was fabricated using a sputtering technique from separate elemental Ni and Ti targets. The characterizations of the deposited films were, investigated using different analysis techniques, such as Field Emission SEM, DSC, XR.D, electrical resistivity measurement and nanoindentation. © Sharif University of Technology, June 2009... 

Modeling fate of nitrogen in unsaturated and saturated zone is a complex process, which requires detailed geochemical data. Complexities of the process as well as data insufficiencies are two major issues, which make quantitative assessment of the problem more complicated. In this work, a lumped-parameter model (LPM) is proposed that has been evaluated for a data-limited case to study temporal and steady-state behavior of Nitrate and Ammonium in unsaturated zone. The concentration of components in the model are assumed as the depth-averaged concentrations, and dispersive fluxes have been neglected. The case study area is Tehran City aquifer, which is highly contaminated by domestic... 

Laser cutting characteristics including power level and cutting gas pressure are investigated in order to obtain an optimum kerf width. The kerf width is investigated for a laser power range of 50-170 W and a gas pressure of 1-6 bar for steel and mild steel materials. Variation of sample thickness, material type, gas pressure and laser power on the average cut width and slot quality are investigated. Optimum conditions for the steel and mild steel materials with a thickness range of 1-2 mm are obtained. The optimum condition for the steel cutting results in a minimum average kerf width of 0.2 mm at a laser power of 67 W, cutting rate of 7.1 mm/s and an oxygen pressure of 4 bar. A similar... 

The effect of titanium addition on the SAW weld metal microstructure of API 5L-X70 pipeline steel was investigated. The relationship between microstructure and toughness of the weld deposit was studied by means of full metallographic, longitudinal tensile, Charpy-V notch and HIC tests on the specimens cut transversely to the weld beads. The best combination of microstructure and impact properties was obtained in the range of 0.02-0.05% titanium. By further increasing of titanium content, the microstructure was changed from a mixture of acicular ferrite, grain-boundary ferrite and Widmanstätten ferrite to a mixture of acicular ferrite, grain-boundary ferrite, bainite and ferrite with M/A... 

In this study WO x films were deposited by laser ablation of ultra-pure (5N) tungsten trioxide targets onto SiO2 or silicon substrates at 250°C temperature, 100 mTorr oxygen partial pressure and 1×10-5 Torr vacuum. Surface chemical states and compositions of the deposits were determined by X-ray photoelectron spectroscopy. The results showed that deposits in oxygen partial pressure contain W6+ with x ∼ 3.1, while vacuum-deposited films have different W states with various percentage distributions as W4+>W5+>W 6+>W0, and x ∼ 1. We used fast electrical resistance measurement as a probe to study the deposition process. Film resistance as a function of deposition time in vacuum revealed some... 

Modified tungsten oxide films by vanadium oxide provide neutrally coloring electrochromic electrodes for smart windows technology. In this study W-V-O mixed oxide films were fabricated by Nd:YAG pulsed laser deposition (PLD), λ=1064 nm, from mixed pressed powders of (WO3)1-x(V2O5)x, x=0, 0.09, 0.17, 0.23, 0.29 and 0.33, at 13.3 Pa oxygen partial pressure and 200 °C temperature on glass substrates. X-ray photoelectron spectroscopy (XPS) revealed V5+, V4+, W6+ and W5+ surface oxide states, where the ratio of W5+/W6+ enhances by the amount of vanadium in the films. Surface morphology was studied by scanning electron microscope (SEM) and optical properties by transmission-reflection spectra.... 

Nickel and nickel-copper alloy modified glassy carbon electrodes (GC/Ni and GC/NiCu) prepared by galvanostatic deposition were examined for their redox process and electrocatalytic activities towards the oxidation of methanol in alkaline solutions. The methods of cyclic voltammetery (CV) and chronoamperometry (CA) were employed. The cyclic voltammogram of NiCu alloy demonstrates the formation of β/β crystallographic forms of the nickel oxyhydroxide under prolonged repetitive potential cycling in alkaline solution. In CV studies, in the presence of methanol NiCu alloy modified electrode shows a significantly higher response for methanol oxidation. The peak current of the oxidation of nickel... 

A numerical model for the deposition of silicon nitride using silane and ammonia mixture in a radio frequency plasma reactor has been developed. Plasma enhanced chemical vapor deposition process is simulated by combined analysis for the glow discharge, fluid flow and chemical reactions. The main goal is to investigate the effect of variations of the process parameters on the deposition rate, and uniformity of the resulting layer. The approach used is based on the theoretical partial differential equation models, without any empirical approximation of the critical data being used. Owing to the fact that the relevant equations are highly nonlinear, the discretization method is of great... 

The majority of the city of Tehran, Iran has been developed on cemented coarse-grained alluvium. In order to understand the mechanical behavior of this soil, a series of triaxial compression tests (CD, CU) were performed on uncemented and artificially cemented samples. Hydrated lime was used as the cementation agent for sample preparation to model the Tehran cemented deposit. The tests were performed on artificially cemented samples after an appropriate curing time. The effect of confining pressure, cement content and fine content is investigated in this research. The tests results show that peak shear strength is followed by strain softening for all cemented samples. Shear strength... 

A comparison of various hydrogen production processes indicates that the thermal decomposition of methane (TDM) provides an attractive option from both economical and technical points of view. The main problem for this process is the deposition of the nano-carbon particles on the reactor wall (or catalyst surface). This research concentrates on the numerical simulation of the TDM process without use of a catalyst to find a technique that decreases the carbon accumulation in a tubular reactor. In this model, the produced carbon particles are tracked with the Lagrangian method under thermophoretic, Brownian, van der Waals, Basset, drag, lift, gravity, pressure and virtual mass forces. In... 

In this paper, the structure of a wall jet deflected by a baffle along with the trajectory of particles has been studied. This baffle is used to produce a stable deflected surface jet, thereby deflecting the high-velocity supercritical stream away from the bed to the surface. An elliptic relaxation turbulence model (v2̄ - f model) has been used to simulate this submerged flow. During the last few years, the v2̄ - f turbulence model has become increasingly popular due to its ability to account for near-wall damping without use of damping functions. In addition, it has been proven that the v2̄ - f model is superior to other RANS methods in many fluid flows where complex flow features are... 

NiTiHf thin films with varying hafnium contents up to 28.7at% were fabricated using simultaneous sputter deposition from separate Ni, Ti, and Hf targets onto unheated substrates. The required film composition was achieved by adjusting the power ratio to the targets. The as-deposited films were amorphous; and post deposition annealing was performed at 550°C, slightly above their crystallization temperatures. The crystallization temperature of the films varied as a function of Hf concentration, and was as high as 520°C at a Hf content of 28.7at%. 2μm thick crystallized films with I0at% or greater Hf were martensitic at room temperature. DSC analysis demonstrated that above 10at%Hf additions... 

Nowadays "as everywhere in the world", so much attention is drawn to performing safety and HSE management rules in Iran. Considering the long life of oil and it's relevant industries in Iran (since 1908, first oil well in Middle East, Masjid Soleyman), many units with more than 50 years old are still in operation. This situation posed special problems in performing safety and HSE regulations that some of them are communal among these units. This paper reveals the result of industrial projects, collecting numerous technical checklists in such units and author's experiences in recent years in Iran, which is aimed to announce some of these major problems and also present solutions for them.... 

We study the effect of quantum motion in a Mach-Zehnder interferometer where ultracold, two-level atoms cross a π2-π-π2 configuration of separated, laser illuminated regions. Explicit and exact expressions are obtained for transmission amplitudes of monochromatic, incident atomic waves using recurrence relations which take into account all possible paths: the direct ones usually considered in the simple semiclassical treatment, but including quantum motion corrections, and the paths in which the atoms are repeatedly reflected at the fields. © 2008 The American Physical Society  

In this paper the gain dynamics of an erbium-doped fiber laser (EDFL) with an inhomogeneous active medium in the presence of ion pairs is modeled. A two-level model for single ions and a three-level model for ion pairs are employed to write the propagation and rate equations of inhomogeneous laser medium. The governing equations are an uncountable system of partial differential equations (PDEs). By employing the moment method, the system of PDEs is converted to a finite system of ordinary differential equations (ODEs). The Solution of the system of ODEs is used to analyze the output power of a high concentration EDFL. As it expected, theoretical results show that the threshold pumping power... 

We prepared copper-carbon nanocomposite films by co-deposition of RF-Sputtering and RF-PECVD methods at room temperature. These films contain different copper concentration and different size of copper nanoparticles. The copper content of these films was obtained from Rutherford Back Scattering (RBS) analyze. We studied electrical resistivity of samples versus copper content. A metal-nonmetal transition was observed by decreasing of copper content in these films. The electrical conductivity of dielectric and metallic samples was explained by tunneling and percolation models respectively. In the percolation threshold conduction results from two mechanisms: percolation and tunneling. In the... 

In this work we present an ellipsoid cavity regime for the production of a bunch of quasi-monoenergetic electrons. The electron output beam is more effective than the periodic plasma wave method or the plasma-channel-guided method. A hyperbola, parabola or ellipsoid path is described for the electron trajectory motion in this model. A dense bunch of relativistic electrons with a quasi-monoenergetic spectrum is self-generated here. The obtained results show a smaller width for the electron energy spectrum in comparison with the previous results. We found that there are optimum conditions to form the ellipsoid cavity. Laser beam properties (such as the spot size, power and pulse duration) and...