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... 

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... 

Alloy coating of nickel - molybdenum with 20-25 wt% Mo, exhibits excellent protective properties against corrosion in different corrosive environments, therefore it has received much attention. In comparison with Ni coatings, Ni-Mo coatings reduce hydrogen evolution reaction overpotential(HER) significantly, therefore it has suitable catalytic properties for HER.
A few researches on pulse reverse palting of Ni-Mo coatings have been published. in this work, we have evaluated effects of PRC on some properties of Ni-Mo coating such as chemical composition, morphology, catalytic properties for HER, crystaline structure and hardness property. The results of atomic absorption spectroscopy(AAS)... 

Chromium oxide coatings (Cr2O3) have been widely used due to their remarkable properties in corrosion, wear, optical and mechanical applications. So far, several methods have been used to prepare Cr2O3 thin films. In this study, the chromium oxide was produced by the sol-gel method and dip coated on the low carbon steel and glass substrates. In this context, we encountered with the problem of incoherency of the Cr2O3 ceramic coating to the steel substrates. It is highly likely that this problem be due to causes such as: a) thermal stresses due to the difference between the thermal expansion coefficients of the substrate and the coating, b) incoherent substrate/coating interface due to their... 

Silver is a resistant metal against the oxidation under normal atmospheric conditions, but it reacts readily with sulfur bearing species in the environment and corrodes. Alloying silver with more noble elements, such as Palladium, is a promising approach for increasing corrosion resistance against the sulfur pollutants. The purpose of this research is to develop a plating bath for deposition of Silver-Palladium alloy with acceptable appearance and higher corrosion resistance than pure silver. For this purpose, a bath based on thiosulfate complexing agent was investigated. In this solution, with a bath containing 10 mM of each cation, deposits with palladium content of 6, 11 and 14 % were... 

In this project, graphene oxide was produced by chemical method (modified hummers method) because of simplicity and reproductiblity in the manufacuring process. Zinc nanoparticles were produced from pure zinc anode in the graphene oxide solution (anodic dissolution). Nanocomposite coating of reduced graphene oxide – zinc was created by electrochemical reduction with voltage pulse. Optimization of corrosion current density of the coating was done by design of experiments software (central composite design). To achieve this goal, several parameters such as cycles of zinc dissolution, frequency, duty cycle, total time of coating and applied voltage were examined. Using analysis of variance... 

316L stainless steel is used in implants under load in orthopedics and dentistry due to its high strength and corrosion resistance. Therefore, to improve their biocompatibility properties, bioceramic coatings with more suitable biocompatibility properties are used. Therefore, in the present study, to improve the biocompatibility and corrosion properties on 316 L metal implants, HAp / TiO2 / Al2O3 nanocomposite coating was created using the cost-effective sol-gel method. Titanium + alumina by weight percentage in these coatings were 20, 30, and 40% by weight. In this study, FTIR, XRD, DSC / TG, FE-SEM EDS, DLS tests were performed to investigate the chemical bases in nanocomposites,... 

Today, in our beloved country of Iran and other parts of the world, reinforced concrete structures are used in large industrial projects, in some cases we see their very early failure even before the time of operation. This issue in the southern coasts of the country due to special weather conditions (humidity and high temperature) and the existence of the offensive ions such as chlorine and sulfate in seawater are more important and we always face with severe corrosion of reinforcement and reduced service life of concrete structures in these areas. Despite this, little research has been done on the reliability of concrete facilities in the vicinity of the Caspian Sea in the north of the... 

Plasma Electrolytic Oxidation (PEO) method was used for the preparation of ceramic coatings on Aluminum 5052 substrate in a silicate-based electrolyte containing different concentrations of ZrO2 nanoparticles. Before the addition of nanoparticles into the electrolyte, determining process parameters including current density, coating time, and frequency were examined carefully. After studying corrosion behavior, thickness, and coating morphology in different circumstances, the frequency of 50Hz, the current density of 150mA/cm2, and the coating time of 20 minutes were chosen as the optimum parameters. After that and with the usage of those parameters, ZrO2 nanoparticles were added to the... 

The aim of this project is to investigate the effect of adding nano-silica on reinforcement corrosion in concrete caused by chloride. Because concrete is a porous composite, which is exposed to a corrosive environment such as the sea, it needs more protection to control the corrosion of steel reinforcement. This has led to the necessity of using nanoparticles in concrete mortar. This research was done by evaluating the effect of adding nanosilica gel as a partial replacement of type 2 Portland cement and hydrophobic nanosilica, respectively, to mortar and concrete surface on the corrosion resistance of reinforcement. In the project, three models of concrete samples with a cement grade of 550... 

Corrosion is an electrochemical process that results in the degradation of metallic materials in a corrosive environment. Localized corrosion is a destructive form of corrosion that can lead to catastrophic failure of structures. In developed countries, corrosion costs more than 3% of gross national product every year, much more than the costs arisen from all-natural disasters combined. It is very important to understand this process to prevent sudden accidents and also develop high strength corrosion resistant metallic materials. This study presents the formulation and implementation of a phase field model for simulating the activation- and diffusion-controlled pitting corrosion phenomena...