Sharif Digital Repository

Plasma electrolytic oxidation (PEO) is currently recognized as an effective coating method on active metals such as magnesium. In this method, through occurrence of strong electric discharges on the surface of the anode accompanied by electrochemical and thermo-chemical reactions at plasma environment, a relatively thick ceramic coating with complex compounds grows on the metal surface which significantly improves its properties. Regarding the influence of PEO electrical parameters on the morphology and other properties of the coating, the objective of the present study is to prepare a quality ceramic coating on AZ31 magnesium alloy substrate via setting the process parameters, such as... 

Magnesium alloys are used in various industries, due to their excellent combination of low density, high strength to weight ratio and biocompatibility. However, a main drawback of Mg alloys is their poor corrosion and tribological behavior which could be improved by different surface treatments such as plasma electrolytic oxidation (PEO). Recently, PEO method as a simple and economic process is used to provide thick ceramic coating on Mg alloys. Based on some problems in zirconia coating on Mg substrates, two step PEO coating was introduced. The aim of the present study is to prepare and investigate the properties of zirconia-containing coating by two-step PEO process on the AZ31 Mg alloy... 

This thesis demonstrate a new hybrid Plasma Electrolytic Oxidation (PEO)-Hydrothermal method to produce a nano-structured TiO2 layer over a titanium substrate. Microstructural characterization was carried out by using a FE-SEM to explore nano scale structural changes due to hydrothermal treatment. More over EDS was used to analyse elements of the coating. The FE-SEM images confirmed formation of a 3D network consisting “nano flakes+nano fibers”after 6 or 12 hours and a ”sea urchin like nanostructure+nano fibers” after 24 hour. To improve the performance of nano-structured photoelectrodes, different electrolytes were studied to achieve maximum amount of anatase phase. the best results was... 

Nitinol alloy is important and increasingly used in medicine and industry due to its unique properties such as shape memory and superelasticity. Plasma Electrolytic Oxidation (PEO) is a relatively new method which in electrical discharge occurrence and formation of small plasma arcs on the anode surface and the electrochemical and thermochemical reactions in plasma environment prepare ceramic coating on the substrate. This method is taken into consideration because of its simplicity and effectiveness in the preparation of oxide ceramic coatings with porous structure on the surface of certain metals and alloys to improve their corrosion and wear properties. In this study, to improve the... 

Aluminum and its alloys have wide applications in industry and recently researches have been expanded in this area. The main reasons are unique features of aluminum corrosion resistance and high strength to weight ratio. The fundamental problem of aluminum is low wear resistance that leads to be worn in industrial applications. For more efficiency of titanium, extensive efforts have been made for solving this problem, one of the best solutions is coating. Plasma electrolyte Oxidation (PEO) is a novel method to create ceramic coatings on metals to improve wear and corrosion resistance. In this research micro and nano Si3N4 particles were added to electrolyte to create alumina-silicate... 

In recent years, magnesium and its alloys have been considered as biodegradable implants, but they corrode in the body before natural process of damaged organs recovery is completed. In this investigation PEO operation was used for corrosion control and effect of different parameter such as number of operation steps, electrolyte type, time and operation voltage on coating properties was studied. Scanning electron microscopy was used for investigating of morphology of coats and to determine chemical composition and phase of coats EDS analysis and X-ray diffraction were used. The corrosion resistance of samples were evaluated by potentiodynamic polarization and electrochemical impedance (EIS)... 

In recent years lithium-air batteries captured worldwide attention because of their high energy density. Solid state electrolytes is one of the main components of lithium-air batteries. Lithium almunium titanium phosphate(LATP) is a nasicon type ion conduction which may be of great potential as solid electrolyte. The object of this thesis was the preparation of LATP solid electrolyte which can be used in a lithium-air battery. To reach this goal LATP powder was synthesized using a solution-based method and an appropriate crystallization temperature was selected based on obtained results of X-ray diffraction analysis. In the next step solid electrolytes was prepared under different pressing... 

The behavior of biomolecules in mixtures is affected by the presence of electrolytes. For instance, in the presence of an electrolyte, solubility of most biomolecules like proteins,peptids and amino acids can be increased or decreased. As a biomolecule, urea is a protein denaturant and influences protein folding and protein-DNA binding. The presence of ions can affect the interactions between urea and water In this thesis, experimental data of density and electrical conductance of aqueous solutions of urea-NaCl were obtained at different physical conditions. Density measurement experiments were carried out at different temperatures from 20-40 oC. Apparent and infinite dilution molar volumes... 

Saturation molality for a number of single and mixed aqueous electrolyte solutions containing NaCl, Na2CO3, and K2SO4, was measured at atmospheric pressure over a wide range of temperature. In order to check the repeatability of the experimental data, the experiments were replicated three times and average of the results was considered as final saturation molality. Experimental data of saturation molality for single electrolyte solutions were correlated using the modified UNIFAC–Dortmund model to account for the shortrange interaction. Binary interaction parameters, between water molecules and ionic species were also reported. For the long-range interactions between the ionic species in... 

In this study, the aging of the LiFePO4/graphite cell was investigated in two different types of 18650 Li-ion batteries during cycling at various C-rates (0.5, 1, 2, 3, 4C) and high temperature under long-term cycling. An amount of 20% Capacity loss was considered as the end of the cycling. Batteries with a capacity of 1500 mAh after this capacity drop, experience 60, 120, 1502, and 2155 cycles, at the rates of 4, 3, 2, and 1C , and batteries with capacity of 1400 mAh was also 60, 360, 1100, 1000, and 805 cycles at a rate of 0.5C. Capacity decrease of the cell is in linear relationship with cycle number and the slope of the capacity-fading line increases with elevating current rate. Aging... 

Plasma electrolytic oxidation (PEO) was implemented to produce a ceramic coating on AZ31 magnesium alloy, using an alternate power source (AC), in a silicate based electrolyte containing zirconia nanoparticles in different concentrations. Prior to adding nanoparticles to electrolyte, working parameters such as current density, frequency and coating duration were examined and studied concerning the equipment and coating conditions. And after reaching the optimized condition, ZrO2 nanoparticles were added to the electrolyte to create composite coatings. To examine the properties of the coatings before and after the creation of composite PEO coatings, scanning electron microscopy (SEM) was used... 

This thesis deals with a theoretical and experimental investigation of different approaches for reduction of electronic recombination in the semiconductor/Dye interface of dye sensitized solar cells (DSSC) including dye coverage, core-shell structures and energy level distributions. Interface of ZnO/TiO2 in the core-shell structure have been studied by density functional theory and the energy level distribution of surface atoms, recombination and Fermi level changes, open circuit voltage and surface dipole distributions have been discussed.
The presence of TiO2 shell increases the ZnO surface dipole moment, and shifts the ZnO conduction and valence bands to higher energies. Also, it... 

In this study a systematic effort was made to investigate the poisoning effect of sulfur-containing materials on the electro- oxidation of methanol and ethanol on Ni and Cu electrodes in alkaline solutions by the methods of cyclic voltammetry, chronoamperometry and electrochemical impedance spectroscopy. Activation energy of methanol electro-oxidation in the absence of Na2S was obtained 30.7 kJ/mol by cyclic voltammetric at different temperatures, and its values increased by increase in Na2S concentrations to 97kJ/mol. Na2S adsorption isotherms corresponded with Langmuire isotherm, equilibrium constants of adsorption – desorption and adsorption enthalpy (ΔHads= -62kJ/mol) were calculated for... 

Gas hydrates are ice-like clathrate compounds. Methane, carbon dioxie and natural gas compounds can form gas hydrate and plug pipelines, in order to preventing of gas hydrate formation, inhibitors like electrolytes are added to the natural gas pipelines. In this work a model proposed to predict the hydrate formation conditions in presence of some inhibitors such as NaCl, KCl, NaBr, KBr, [BMIM][BF4] and [BMIM][Br]. So a new equation of state that can be applied to both electrolyte and associating solutions called GV-SAFT-MSA is developed. Two dialkylimidazolium ionic liquids [BMIM][BF4] and [BMIM][MS] have been investigated for their potential application as novel gas hydrate inhibitors. The... 

Surfactants are widely used in enhancing oil recovery. But application of worm-like micelles which seem to be a perfect candidate for enhancing heavy oil recovery have been less studied despite their significant ability in reducing interfacial tension and their high viscosity. This research consists of three parts. In the first part, the kinetic and equilibrium adsorption of surfactant on reservoir rock is experimentally investigated, and its appropriate kinetic and equilibrium adsorption model is specified. According to the adsorption models, the pseudo second order kintic coefficient of adsorption is proved to have a linear relationship with concentration, so its value at different... 

Plasma Electrolytic oxidation has recently been known as a new technology in surface engineering. It is one of the low-cost techniques used for improving corrosion and wear resistance in Al-Mg alloys. The purpose of this study first is to attach aluminum and magnesium alloys safely and without any defects, and then finding the optimum coating condition in connection line to achieve most possible corrosion resistance. For this purpose, first of all optimization of Al-Mg alloys friction stir welding (FSW) condition is required. After required investigations, it was shown that the weld created between Aluminum and Magnesium sheets by the cylindrical pin moving in a rotational speed of 550... 

Recent developments in improving lighting efficiency and cost reduction of LED’s have caused them to be a suitable alternative for the current lighting systems. In this thesis a novel off-line structure is proposed to drive LED’s. The proposed circuit has a high power factor and high efficiency and a long lifetime. To increase the life time of the converter, the proposed circuit doesn’t use any electrolytic capacitors in the power stage. The proposed circuit consists of a transition mode (TM) flyback converter in order to have power factor correction (PFC), a buck converter is added to the third winding of the flyback transformer in order to create two paths for the electrical power. DC... 

In this work, butyl methylimidazolium tetrafluoroborate and butyl methylimidazolium hexafluorophosphate are used as ionic liquid and lithium perchlorate and lithium hexafluorophosphate as lithium salt. Dimethyl carbonate and propylene carbonate are used as solvent to prepare diffrent kinds of organic - ionic liquids solvent for lithium ion batterries. In preliminary expriment it was distinguished that in the mixture of organic solvent lithium hexaflourophosphat has more conductivity in comparison with lithium perchlorate. There for,in this work, all organic-ionic liquid solvent electrolytes are considered based on lithium hexaflourophosphat salt. Different compositions of organic-ionic... 

LED Drivers with near 1 power factor, Because of using electrolytic capacitors (to become flicker-free) have lifetime drawbacks. This research will focus on solutions to use magnetic energy storage instead of electrolytic capacitors (used for energy storage) to solve lifetime drawbacks and decrease output light flicker. Calculations show that magnetic energy density using iron powder cores are lower than electrolytic capacitors, also a little lower than ceramic capacitors, but obviously higher than film capacitors. After calculations, conventional isolated and non-isolated LED drivers will be reviewed and new non-isolated off-line 230v with 10w output power LED driver with magnetic energy... 

Li7La3Zr2O12 (LLZO) solid-state electrolyte is a very promising electrolyte for a variety of ion lithium solid-state batteries, due to high conductivity of Li ions at room temperature as well as its chemical stability with Li metal anode. LLZO phase has two tetragonal and cubic symmetries. The conductivity of the cubic phase is two times higher than that for the tetragonal phase. To stabilize the cubic phase at room temperature, 0.2, 0.25, and 0.3 mol% Aluminum was doped to LLZO solid-state electrolyte. This powder was synthesized by sol-gel combustion method at 1000˚C. The cubic phase and lack of impurity of the samples doped with 0.25 and 0.3% Aluminum were determined by X-ray Diffraction...