Sharif Digital Repository

To improve the biocompatibility and corrosion resistance of 316L SS (Stainless Steel) metal implants, HAp(hydroxyapatite)/TiO2/Al2O3 nanocomposite coating was created using dip sol-gel method sintered at 550 °C. The weight percentage of TiO2+ Al2O3 in these coatings was 20, 30, and 40% wt. In this study, characterization was performed using FTIR (Fourier-Transform Infrared Spectroscopy), XRD, FE-SEM (Field Emission Scanning Electron Microscope), EDS (Energy Dispersive Spectroscopy), DLS (Dynamic Light Scattering), Pull-off, and AFM (Atomic Force Microscopy) analysis. The potentiodynamic polarization and EIS (Electrochemical Impedance Spectroscopy) were performed in the simulated body fluid... 

In this project, the protective effect of Biebersteinia multifida root extract (BMRE) against corrosion of 1018 low carbon steel (1018LCS) in HCl solutions was appraised by assessing weight loss, electrochemical impedance spectroscopy (EIS), and polarization at 25 °C. The maximum inhibitory efficacy for the concentration of 1 g/l of the BMRE was 92.8% at 25 °C after 2 h and increased to 95.3% after 24 h of immersion. Polarization experiments have shown that the extract in acidic solutions can act as a mixed corrosion inhibitor. The corrosion inhibitory efficacy of BMRE decreased with increasing temperature, and at all temperature settings studied, the adsorption of BMRE molecules on 1018 LCS... 

One effective method for preventing corrosion of steel reinforcement and improving the mechanical properties of concrete is changing the physical nature of concrete by adding different materials. In this study, we have used polypropylene fibers as an additional material. We have compared the corrosion rate of rebar using different volume ratios and sizes of polypropylene fibers. Reinforcement potential increased as the amount of fibers increased from 0 to 2 kg m -3. The polypropylene fibers delay the initial corrosion process by preventing cracking, thereby decreasing permeability of the concrete. In addition, the corrosion rate of concrete samples made with Kish Island coral aggregate was... 

Carbon nanocapsules doped separately with epoxy and polyamine were used to fabricate an epoxy nanocomposite coating. Carbon nanospheres with dual-encapsulated epoxy/polyamine were dispersed uniformly in the epoxy resin at concentrations of 2, 5, and 10 wt %. The mechanical properties of the nanocomposites were studied by tensile testing and scratch hardness measurements. Furthermore, nanocomposites were applied on mild steel substrates, and their corrosion protection and barrier performance were evaluated using electrochemical impedance spectroscopy (EIS). Adhesion loss measurements of coatings after 240 h exposure to 3.5 wt % NaCl solution were performed by pull-off adhesion testing. Also,... 

The high aspect ratio and unique thermal and electrical characteristics of carbon nanofiber (CNF) made it an ideal physical barrier against the penetration of corrosive ions. However, the poor compatibility of the CNF with the polymer matrix and the lack of active corrosion inhibitors are the key limitations of this nanomaterial, resulting in short-term anti-corrosion resistance. An intelligent self-healing epoxy (EP) coating, including CNF modified with a polydopamine (PDA)-La3+ complex, was successfully fabricated to overcome these issues. Electrochemical impedance spectroscopy (EIS) evaluation implied that mild steel (MS) submerged in a 3.5 wt % NaCl solution containing the CNF-PDA-La... 

Anatase nanostructured coating has been prepared on 316 L stainless steel by sol-gel dip coating. The topography of the coatings surface has been analyzed using atomic force microscopy. The anticorrosion performance of the coatings has been evaluated using polarization curves. Effects of calcination temperature, withdrawal speed and times of coating on corrosion protection have been studied. The results showed calcination temperature of 400°C and withdrawal speed of 10 cm/min are desirable conditions to achieve high corrosion protection of 316 L stainless steel in chloride containing environments. Coatings with 3 times exhibit better resistance against corrosion in 0.5 molar NaCl solutions.... 

In this research, microstructure and corrosion properties of plasma nitriding and post-oxidation treated AISI 316 austenitic stainless steel have been studied. The plasma nitriding treatment was carried out at 450 C for 5 h in a D.C. plasma setup with a gas mixture of 25% N2-75% H2 followed by post-oxidation in gas mixtures of O2/H2: 1/3, 1/5, 1/9 and 1/12 for 30 min. The treated samples were characterized by SEM, XRD and roughness testing. Potentiodynamic and cyclic polarization tests were also employed to evaluate the corrosion resistance of the samples. The results showed that plasma nitriding treatment decreases corrosion resistance of the steel substrate. However, post-oxidizing... 

One of the main concerns in cladding Inconel 625 superalloy on desired substrates is deterioration of corrosion resistance due to cladding process. The present study aims to compare the effect of fusion cladding and explosive cladding procedures on corrosion behavior of Inconel 625 cladding on plain carbon steel as substrate. Also, an attempt has been made to investigate the role of load ratio and numbers of fusion layers in corrosion behavior of explosive and fusion cladding Inconel 625 respectively. In all cases, the cyclic polarization as an electrochemical method has been applied to assess the corrosion behavior. According to the obtained results, both cladding methods aggravate the... 

The effect of some inhibitors consisting of sodium nitrite (NaNO 2), sodium nitrate (NaNO 3), sodium molybdate (Na 2MoO 4), and sodium silicate (Na 2SiO 3) on the corrosion behavior of aluminum alloy 3303 (UNS A93303) in a water and ethylene glycol (C 2H 6O 2) mixture was investigated. In the first part, the tests were established without any galvanic coupling. In the second part, the tests were established with galvanic connections between the aluminum alloy and mild steel, stainless steel, copper, brass, and solder. Results show that the best corrosion inhibitor in both situations is sodium nitrate, according to its abilities to reduce corrosion rate, passivate the aluminum surface, and... 

Electrophoretic technique was used to deposit micro- and nano-sized aluminum nitride coatings on stainless steel surfaces by using a well-dispersed stable suspension produced by addition of AlN powder plus a small amount of iodine to ethanol. Parabolic regime governed the deposition. Electrophoretic deposition for 240 s at 100 V resulted in formation of a uniformly dense film on the top, but a porous inhomogeneous layer at the bottom. This was attributed to fast deposition of coarse particles and/or agglomerates at large electric fields. After drying, micro-sized particles led to a uniform crack-free interface while nano-particles resulted in fragmented non-cohesive layers. Weight loss... 

The inhibitory action of N,N′-1,3-propylen-bis(3- methoxysalicylidenimine) {PMSI} on mild steel corrosion in sulfuric acid medium was investigated through electrochemical methods and evaluations based on infrared spectroscopy and scanning electron micrographs. The studies revealed that the molecule is a good mixed-type inhibitor (mostly anodic), acts as a multi-dentate ligand and repels the corrosive agents by hydrophobic forces. Its adsorption on metal surface has a physicochemical nature and obeys the Langmuir isotherm. At a critical (optimum) concentration, an anomalous inhibitory behavior was observed and interpreted at microscopic level by means of desorption/adsorption process and... 

A new Zinc phosphating bath, which produces coatings at relatively lower temperatures within a reasonable time by using of chemical accelerators has been devised. Improvement of the bath performance by the addition of divalent cations like calcium, nickel has been studied. Bath formulation and operating conditions have been optimized by coating weight determinations. Stable samples of phosphating formulations with and without calcium and nickel salts were prepared and the structure and morphology of the phosphate coatings were determined by using X-ray diffraction (XRD) techniques, scanning electron microscopy. ASTMB117 salt spray test and electrochemical impedance spectroscopy (EIS) were... 

Corrosion of mild steel in aqueous solutions containing hydrogen sulphide was modelled under the condition that an iron sulphide film was formed on the steel surface. In the present model, the iron sulphide forms on the steel surface as a result of a solid state reaction between iron and hydrogen sulphide which has several steps. First a very thin film of iron sulphide nucleates on the steel surface. Then, due to further growth of the initial thin layer, a more porous layer of iron sulphide forms on the initial film. In the present model, it is assumed that mass transfer through the thin iron sulphide layer (i.e. adjacent to the steel substrate) controls the corrosion rate of steel in H 2S... 

Resistance spot welding was used to join austenitic stainless steel sheets. Mechanical properties of the spot welds were evaluated using tensile shear test. Mechanical behaviour was described by peak load, failure energy and failure mode. The relationship between weld fusion zone attributes and failure behaviour was studied. Generally, it was observed that increasing fusion zone size is accompanied by an increase in load carrying capacity and energy absorption capability. However, when expulsion occurs, despite almost constant weld fusion zone size, energy absorption capability reduces significantly due to increase in electrode indentation depth. Considering the failure location and failure... 

A gas turbine which output 18MW power exploded after 3h of ordinary operation and after 4,785 starts. The turbine's rotor had undergone repair after 77,000 operating hours. A piece was cut from the failed marriage bolt and tested using atomic absorption spectrometry in order to know the grade of the alloy. It was found that the marriage bolt is made from ASTM A193 B16 steel which is suitable. Hardness and microhardness measurement was also determined and showed that it was within the range of the specified hardness for ASTM A193 B16 steel. The marriage bolt's mechanical properties also meet technical specifications and showed that it contained anti-corrosion properties. Visual examination...