Sharif Digital Repository

Asphaltene deposition, the heaviest and most polar component of crude oil, which causes great economic damage inside the reservoir, near wells, pipelines and well equipment, is an important challenge in the production of oil reservoirs. The main purpose of this study is to prob the adsorption kinetics and the mechanism of asphaltene adsorption on the metal surface by a quartz crystal microbalance device under different conditions of temperature, flow rate and degree of asphaltene instability. In this study, indirect uv-vis spectroscopic method was used to determine the onset of asphaltene precipitation, then experiments were designed using Taguchi method. A new QCM device has been designed... 

Crude oil production could cause the thermodynamic equilibrium of the crude oil to be disturbed in the well column which results in asphaltene precipitation and deposition. The thickness of the deposited material grows over time until it completely blocks the well column.Due to the hard and insoluble nature of deposited asphaltene, the two main chemical and mechanical methods are found to be more effective. It should be noted that the actual organic sediments in the piping are not pure and consist of three components: asphaltene, resin and paraffin. Therefore, it is very important to know the composition of the deposited material before selecting the appropriate chemical solvent.The samples... 

Direct Metal Deposition is one of the methods of Additive manufacturing that has seen the most spread in recent years. In this method metal powder is directed towards the free surface of the workpiece through a nuzzle, and is simultaneously heated to become molten in a melting pool by a laser beam and begins the deposition process. One of the parts that make up a DMD system is powder feeding nuzzle. These nuzzles usually encounter a similar fundamental problem: that the effect of gravity on the stream of metal powder and the carrier fluid causes this stream to deviate from its intended position. To prevent this, nuzzles are usually designed with a fixed downward angle and the angle of the... 

In the preceding years, hydroxyapatite (HA)-based coatings and scaffolds have been known as the best biomaterials for dental and orthopedics applications. Biocompatible and bioactive hydroxyapatite-based Coatings on metallic implants is one of the best methods for reaching both suitable mechanical properties and appropriate bioactivity, leading to better osseointegration and osteoblast proliferation. The ultimate goal of this project is characterization as well as mechanical and electrochemical behavior investigation of Hydroxyapatite- Chitosan nanocomposite coating by electrophoretic deposition (EPD) method on Plasma Electrolyte Oxidation (PEO) treated titanium substrates and Magnesium (Mg)... 

Methane steam reforming (MSR) is an assuring reaction using steam to produce H2 as clean energy over a nickel-based catalyst. We synthesized monometallic NiMgAl2O4 and bimetallic NiCoMgAl2O4 catalysts in a two-step combustion method using urea, glycine, and sucrose, as fuel. BET-BJH, XRD, TGA, TPR, FESEM, and EDX-mapping characterized surface area, porosity, morphology, crystalline structure, and metal-support interaction behavior. The products exhibited well-structured, simple MgAl2O4 spinel and NiO without NiAl2O4, in both specimens. The MSR evaluation tests at 750℃ under atmospheric pressure, CH4: H2O feed ratio of 1:1.6 showed the bimetallic catalyst has the highest conversion (99.30%)... 

Perovskite solar cells with 25.5% efficiency and fast and cheap manufacturing process are among the most promising technologies in this field to replace silicon cells. Despite the challenges of stability and toxicity to these cells, their manufacturing technology has recently shifted to the development of large-scale manufacturing methods in module dimensions. In the present study, the fabrication of perovskite cells in large dimensions to achieve the perovskite module has been aimed and studied that to achieve this, the method of large-scale spraying and printing using the vacuum system was used to create cell-forming films and, consequently, to make the final cell and module. To... 

In recent years, additive manufacturing has been widely used in prototyping and production of industrial-commercial pieces. Additive manufacturing or three-dimensional (3D) printing is able to easily produce any piece for initial prototyping, no matter how complex it is. The fused deposition modeling (FDM) is a type of additive manufacturing process that produces the piece with the mechanism of feeding the PLA filament, then the molten polymer extrusion and depositing the fluid layer by layer with a high viscosity. Since the thickness of the layers is directly proportional to the diameter of the nozzle and the diameter of the used nozzles cannot be in the micron range (lower than 100... 

Zinc oxide is a wide band gap semiconductor material with wide applications as conductive oxides used in electro-optical devices. Thin films of doped zinc oxide (e.g. Al:ZnO, B:ZnO) are already used in thin-film solar cell technologies as electrodes. Chemical bath deposition (CBD) is a promising method for fabricating transparent and conductive ZnO layers at low temperatures (<100 °C) on nonconductive and temperature-sensitive substrates. Having a natural crystal habit, ZnO readily grows rod-like arrays when grown in an aqueous solution by CBD, posing challenges when attempting to deposit dense and conductive layers. The purpose of this study was to deposit dense and conductive zinc oxide... 

Efforts to identify, predict, and resolve problems linked to asphaltenes and flow assurance have resulted in the development of numerous laboratory and modelling techniques. However, there has been little research on the molecular structure of asphaltenes and how it relates to solubility, stability, aggregation, and deposition behavior. Not only was a thorough structural analysis of asphaltene extracted from three samples of light, medium, and heavy oil performed in this study, but medium oil asphaltene was also fractionated into three sub-fractions based on solubility, with minimum, medium, and maximum solubility, and each subfraction was subjected to a structural analysis. All asphaltene... 

Fabrication of porous hybrid coatings, specially in combination with carbon compounds, can improve the electrochemical behavior of the coating. In this study, graphene oxide (GO) was first synthesized by tour method. After examining different methods to create a porous coating, the electrochemical coating method for simultaneous deposition of GO and nickel on the copper substrate was selected. CTAB was used to form nanometer porosity in the coating structure. In order to investigate the effect of GO on the properties of the deposited coating, two porous coatings of nickel (Ni) and nickel reduced-graphene oxide (Ni-rGO) were investigated by different analyzes. These analyzes include FESEM... 

Functionally Graded Material (FGM)is attaining more and more interests recently due to its outstanding feature of possessing benefits of physical and mechanical properties of two materials in one part. One of the common processes to fabricate FGM is laser directed energy deposition of pre-mixed powder of two materials. The powder stream and laser attenuation in LDED of FGM is studied in this dissertation by the aid of numerical simulation and experimental investigations. Due to numerical simulation results, which is done in FLUENT software, powder particle size and axial shielding gas flow rate has significant effect on composition of powder mixture falling into the molten pool. Considering... 

The multilayer coating (Zn-Ni)1/(Zn-Ni)2 is deposited from a single bath with a zincate-sulfate compound and by changing the current density. The effect of current density and the number of layers on the chemical composition, surface morphology, roughness, phase structure, and corrosion resistance of multilayer coatings respectively using atomic absorption spectroscopy, FE-SEM microscope, roughness tests, X-ray analysis, and electrochemical techniques such as Tafel polarization and impedance was investigated and compared with single-layer coatings. Because the amount of nickel in the composition of the coatings is less than 27%, in all the studied currents, the deposition is anomalous. The... 

Additive manufacturing can be considered as a revolution in the manufacturing industry. The unique capabilities of this technology have led to the removal of many obstacles to the construction of complex and special parts. In this study, with the aim of further understanding how the gradient region is formed, the possibility of detecting the microstructure and finally the properties of the gradient piece made, a solidification process has been simulated in direct metal deposition. The results of this study include calculating the heat distribution during the process and obtaining a thermal history of the fabricated part, calculating the dimensions of the molten pool and the heat affected... 

With advancement of science of aircraft design and limitations of traditional manufacturing methods, using new ones in order to improve efficiency is needed. Among those methods to improve structure efficiency are weight reduction or increase in strength. Increasing strength-to-weight ratio and reduction of weight could be achieved by using composite materials and topology optimization respectively. Manufacturing such parts with efficient design using traditional methods is hard or impossible. Additive manufacturing as a new technology which is being developed every day, can be a big help to aerospace industry. Considering the importance of strength-to-weight ratio in aerospace industry and... 

Direct metal deposition (DMD) process is an additive manufacturing technology that is rapidly gaining laser importance due to its various capabilities in applications such as coating, repairing high-value damaged parts, rapid prototyping and even production in small quantities. Among the equipment needed for this process, nozzle is perhaps the most important component because its performance affect the efficiency of powders trapped in the molten pool, and is crucial to the quality of the deposited layer. The existing nozzle designs can be categorized in two groups; lateral and coaxial nozzles; and the coaxial ones are divided into continuous and discontinuous types. Coaxial nozzles have... 

Decomposition of seawater with the help of sunlight is one of the most promising ways to produce hydrogen as a clean and acceptable fuel in the future. Tungsten photoelectrode is a suitable option for seawater decomposition due to its medium bandwidth, excellent load transfer properties, good chemical stability in acidic and neutral environments, abundance and cost-effectiveness. On the other hand, intermediate metal catalysts (Fe, Ni, Co) are very important due to their abundance in the earth's crust and their stability in alkaline and neutral environments instead of oxides of precious metals (RuO2, IrO2). In this study, tungsten plate (WO3) nanostructures were grown on the surface of a... 

A novel optoelectronic property of two-dimensional (2D) materials suggests they can be used for high-performance photodetector design. There has been a lot of attention paid to MoS2 and Despite its higher optical absorbance, MoSe2 has received little attention. A chemical vapor deposition system was used to prepare atomically thin MoSe2 films. Our research developed a method of preparing hexagon-shaped MoSe2 photodetector on Si/SiO2 substrates in atmospheric pressure with sawtooth edges, leading to large-scale MoSe2 layers with the size of ∼ 70µm . The Raman characterization of the grown flakes indicated that they possessed high quality few layers of MoSe2 and the distance between the two... 

Memristor is a modern circuit element that demonstrates resistance memory function and can have important applications in emerging memories and artificial synapses. Binary oxides and perovskite oxides are two major classes of materials that are promising for memory resistances. Among the binary oxides, TiO2, and among the perovskite oxides, SrTiO3 (STO), are particularly promising in research on electrical resistance switching. In this thesis, by using two deposition techniques of sputtering and pulsed laser deposition (PLD), we have constructed single-layer and multi-layer memristor devices based on these two materials. Two general mechanisms control the behavior of memristors: bulk-control... 

Polylactic acid (PLA) is considered as a great option to be employed as 3D porous scaffold in tissue engineering applications owing to its excellent biocompatibility and processability. However, relatively weak mechanical properties, low degradation rate and inappropriate biodegradability limit its extensive usage. In order to overcome the mentioned challenges, micrometric magnesium (Mg) particles were incorporated into the PLA matrix by the fused deposition modeling (FDM) technique. The effects of various Mg contents (i.e., 2, 4, 6, 8 and 10 wt%) on the mechanical, thermal, structural, wettability, rheological, biodegradability characteristics and cellular behavior of the 3D porous PLA-Mg... 

This thesis aim to the study of the effect of bank’s branching decisions on deposit market. Using panel data banks from Iran, we study effect of branching on market share and market size. In theoretical part, we assume that banks maximize discounted flow of the profits. We also assume that the banks take into account the reaction from rival banks in setting number of branches. Banks are assumed to expect the rival banks react by a lag of one period. In empirical part, in order to distinguish between aggregate market size effect and market share effect, we rewrite quantity of deposit in banks as the product of aggregate deposit and market share. We specify deposit market share function with...