Sharif Digital Repository

First atomistic simulation was used to study the deformation and fracture mechanisms of Ni-Si interfaces under tensile and shear loads dependent on the crystal structure of interface zone. Modified embedded atom method (MEAM) potential was utilized for molecular dynamics (MD) modeling. The simulation includes analysis of common neighbors, coordination number, least-square atomic local strain, and radial distribution function. The profound effect of interface crystallography on the tensile and shear deformation is shown. The highest tensile strength is obtained for interfaces with high plane density due to lowest atomic disorder while under shear loading planes with low density exhibit a high... 

In this study solid lubricants MoS2 nanoparticles with average size 50 nm and hard ZrO2 nanoparticles with average size 51 nm were used in watts bath and Ni/ZrO2-MoS2 composite coatings were prepared by pulse plating technique. Effect of current density, frequency, duty cycle, surfactant type and concentration of particles in the electrolyte on the amount of particles in the coatings were investigated and optimum conditions were determined to create composite coatings. Scanning Electron Microscopy (SEM) and x-ray diffraction (XRD) analysis were performed to study the morphology, structure, chemical composition of coatings. Corrosion testing of coatings by potentiodynamic polarization in... 

WC-Co hardmetals that are produced through powder metallurgy rout are vastely used as wear resistant parts. In these materials hard particles of wolfram carbide are embodied in a cobalt binder. Because of their high hardness and adequate toughness, hardmetals have found wide range of applications in cutting tool industry. During the last decades a number of researches have been carried out to improve their mechanical and wear properties by different binders and carbide particle sizes. Because of high hardness, Tungsten carbide has a good wear resistant. It has very low thermal expansion coefficient and high wetting ability with molten metals. Unlike high hardness, it has limited toughness.... 

In this work, mechanical behavior of Ni nanowires with various dimensions under tensile loading at different temperatures and strain rates was simulated by molecular dynamics. Lennard-Jones and Sutton-Chen potential functions were utilized. The relationship between the tensile properties of Ni nanowires and temperature, strain rate, aspect ratio and crystal orientation was studied. It was shown that with increasing the aspect ratio of the nanowires the strength of the material decreases. A change in the fracture mode of the nanowire from slippage at low strain rates (<10 m/s) to amorphous deformation at high loading rates was observed. The crystal orientation was found to influence the... 

Well worn gas turbine blade made of Nickel based superalloy, IN738LC was remelted due to remove inclusion and use it in casting process of new blade after microstrucrure investigation in neutral atmosphere and vacuum. The composition of slags for removing inclusions used for this practice were 70CaF2-20CaO-10Al2O3 and 55CaO-45Al2O3. The microstructural characterization involved use both optical as well as electron microscope including application of EDS technique for denoted the type of carbides and inclusion investigation. Chemical composition was determined by despersive spectroscopy method. The changing in main elements were reported too low. Number of inclusions were decreased in the... 

In this research, for optimization of repair welding of control valve and flange that use in East Oil& Gas Company, effect of chemical composition, microstructure, hardness and stress relive on sulfide stress cracking (SSC) investigated with select of four electrodes. All welds were prepared by shielded metal arc welding (SMAW) and investigated with optical microscope, hardness test, tensile test and SSC test. The results showed that increase of nickel content in the range of 0.032–1.58 wt. % in weld metals, decrease of acicular ferrite and increase of side plate ferrite, grain boundary ferrite and M/A micro constituent in microstructure. Ni3S2 decrease SSC resistance and (FeCu).S increase... 

Adding solid lubricant particles such as PTFE, Graphite and MoS2, has major influence on electroless composite nickel coatings in order to make low friction surfaces. Among these lubricants, MoS2 has attracted great attention due to its highest stability under wearing condition. In this work Ni-P-MoS2 composite coatings using MoS2 nano-particles have been made and in the next step, we evaluated tribological properties of these coatings. For exploring these coatings different experiments were utilized, like Scanning Electron Microscope study (SEM), chemical composition analysis exploiting AAS and XRF method, and thickness measurements. Two kinds of surfactants, CTAB and PVP, have been applied... 

The current work is carried out to characterize welding of AISI 304 Austenitic Stainless Steel to Ductile Cast Iron. The welding method was SMAW and the welds were produced using a Nickel-Buttering by a pure Nickel electrode(ENi1) on Cast Iron side, then by 4 types of filler materials the joints were produced; Ni-base electrode(Ni1), E308 and E309 Austenitic stainless steel electrodes and E7018 electrode. The preheat temperature of Cast Iron has been selected to be 250○ and 500 ○C to avoid crack of weldments. The comparative evaluation was based on metallography, chemical composition, hardness and corrosion behavior on two different preheat temperatures. According to metallography, the best... 

Electrodeposition of composite coatings containing nano particles is very important because this technique is simple and economic. In this research, in order to produce a coating with high hardness and wear resistance, Ni-Co/WC nano composite was co-deposited. Watt’s based bath containing cobalt and tungsten carbide was used and parameters such as preparation of solution, concentration of ingredients and current density were controlled and adjusted. Surface morphology, microstructure and mechanical properties of coatings were studied by SEM and AFM microscopes. Mechanism of electrodeposition was investigated by cyclic voltametry, cronoamperometry and cronopotentiometry techniques and... 

The purpose of this project is to survey the created kind of inclusion in super alloyed based nickel. primarily, for this matter for the preparing of super alloyed based nickel, the vacuum induction melting furnace has been designed and built , then for surveying the kind of inclusion the effective parameters such as temperature , timing and material of crucible has been considered accordingly , the material of crucibles was considered based on mud-clay- graphitic- pure graphitic- aluminum- zirconium. From the obtained analysis samples of SEM has been distinguished which, with increasing of the temperature and the time ,the percentage of impurity will go up in super- alloyed and the... 

In the last decade, a great deal of attention has been paid to the study of synthesis of Nanoparticles, because of the widespread use of this material in applications involving Fuel cells and magnetic devices. In this thesis, we report some interesting features in the electrodeposition of metallic nanoparticles. The electrochemical phase formation of rhenium and nickel on the surface of P-Si (100) substrate plus morphological, topographical and fractal aspects of the accumulated surface were investigated in this research by means of chronoamperometry method and by utilization of AFM and SEM. The nucleation and growth mechanisms on silicon electrode are characterized using cyclic voltammetry... 

Today, due to the decreasing of fossil fuel reserves and the need to use clean fuels, hydrogen is a suitable alternative, and hydrogen production has received considerable attention. One of the best methods of hydrogen production is water splitting. Overall water splitting can be divided into two half reactions including the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which selecting the appropriate electrocatalyst for these half reactions plays an important role. The four-electron transfer process in OER leads to slow kinetics of the reaction and a large overpotential. The noble metal-based oxides, including IrO2 and RuO2, are known as outstanding OER... 

Carbon dioxide photocatalytic reduction is one of the promising methods used to produce a wide range of renewable hydrocarbon fuels using sunlight in the presence of photocatalysts. In this study, a series of Nickel and Bismuth doped titanium dioxide samples were synthesized by Sol-gel method. After performing photocatalytic carbon dioxide recovery experiments and finding the optimum percentage of Nickel and Bismuth doped titanium dioxide,Ni and Bi co-doped TiO2 sample showed the highest photocatalytic activity. Amount of methane production was 21.13 μmol/gcat in the presence of co-doped sample that was about 6.5 times higher than the amount of methane produced in the presence of pure TiO2... 

In this study, the effect of nano-structure mesoporous supports on the performance of the nickel catalysts in the combined reforming process was investigated. In the first part, magnesium aluminate spinel was prepared using a sol-gel method and employed as a catalyst support for the preparation of nickel catalysts with various nickel contents. The samples were characterized using BET, XRD, TPR, TPO, CO chemisorption and SEM techniques. The results showed that increasing the nickel content up to 7.5 wt.% improved the catalytic activity, but further increase in nickel content decreased the activity due to the decrease in the nickel dispersion. The catalysts except of the sample with 2.5 wt.%... 

Polycrystalline materials are solids that are composed of many crystallites of varying size and orientation called “Grain”. As the grain size reduces to the values below 100nm, the overall material properties are remarkably changed, and thus the resulting nanocrystalline materials have provided much better engineering properties at the same chemical composition compared to the microcrystalline. The main objective of the present study is to synthesize a nanocrystalline (22nm-25nm) coating based on Nickel over the yellow-brass plates. To do this, an electroplating technique in a modified Watts bath is employed in which the current density and stirring speed varied between 3 to 9.5 Ampere per... 

Silicon carbide due to its noticeable mechanical and thermal properties, uses in various industries either main substrate or reinforcement. SiC has low specific surface area according to its resistivity against sintering. Recently, a lot of scientists have been worked on SiC in order to fabricating small ones ; subsequently, better sintering will be achieved. Chemical vapor deposition method (CVD) is a method to produce fine SiC with deposition of products by reacting of initial materials from gas environment. In this study normal CVD as proper method and hydrogen, silicon tetrachloride and activated carbon as initial materials are chosen. Using of iron and nickel catalysts in temperature... 

In this project, nonocrystalline nickel coatings with grain sizes within the range of 9-27 nanometers were produced on yellow-brass plates by electroplating in a modified Watts bath applying current densities from 2 to 6 A/dm2 and bath stirring speeds from 0 to 400 rpm. To determine crystallite size, X-ray diffraction technique (XRD) was utilized; it was observed that grain size declined continuously with increase in current density and then in bath stirring speed. The experimental results coming from XRD tests were compared with a theoretical model in order to verify their reliability; the obtained curve indicated a good correspondence between the experimental data and the theoretical... 

Synthesis gas is a gaseous mixture which mainly consists of carbon monoxide and hydrogen. Different methods are used to produce synthesis gas but the most important method is auto thermal reforming. This method is based upon catalytic reactions. Steam, oxygen and natural gas are the influents to the reactor and synthesis gas will be the effluent. Ni catalysts on alpha-alumina as the support media are usually used in this process. These catalysts are highly heat resistant and insure great qualifications for reactions. This thesis tries to find best solutions of synthesis gas production suitable for feeding to a methanol production unit. There are four main reactions. Three of which are highly... 

Ammonia (NH3) is the second most synthesized chemical in the world which is used about 80% for the production of chemical fertilizers. Industrial production of ammonia commonly relies on Haber-Bosch method that is produced from gaseous N2 and H2, at very high pressure (200-400 atm) and high temperature (400-600oC) on the surface of an iron-based catalyst. But due to required high pressure and temperature researchers are looking for alternative methods that are environmentally friendly. In this research, we applied electrochemical nitrogen reduction reaction (NRR) used nickel oxide (NiO) deposited on nickel foam substrate by hydrothermal method. The prepared samples were treated by nitrogen... 

Hydrogen is emerging as a clean and ideal fuel. However, its dependency on freshwater resources will be a threat to a sustainable environment. Considering the abundance of seawater and the scarcity of freshwater resources, direct electrolysis of seawater to produce hydrogen fuel can be a promising and potential alternative to pure water electrolysis technologies. Seawater contains electrochemically active ions with the nature of competition with the oxidation reaction of water, thus affecting the catalytic activity and, subsequently, the selectivity. From the thermodynamic and kinetic aspect in the electrolysis of seawater, the unfavorable reaction related to the formation of chlorine...