Papers by Keyword: Potentiodynamic

Abstract: This study examined the corrosion inhibition characteristics of Launaea taraxacifolia on mild steel in 1M H₂SO₄ solution, considering the demand for environmentally benign and effective corrosion inhibitors in acid media. The work aimed at elucidating the adsorption behavior, inhibition mechanism, and thermodynamic properties of L. taraxacifolia. Gravimetric and potentiodynamic techniques were employed in assessing inhibitor performance for variations in inhibitor concentrations (0.3%–1.2% W/V), immersion time (10–60 minutes), and temperature (303K–323K). The results indicated that corrosion rates increased with temperature, showing that the inhibitory process is dependent on the adsorption of L. taraxacifolia onto the steel surface. Adsorption obeyed Freundlich and Temkin isotherms, and the calculated heat of adsorption was -11 kJ/mol, which indicated physical adsorption. The presence of key phytochemicals, aromatic compounds, and heteroatoms in the inhibitor played an important role in the process, making it a mixed-type inhibitor. The maximum inhibition efficiency of 97.78% was recorded at higher inhibitor concentrations and longer immersion times. The weight loss measurements were within the range of 0.001g to 0.038g across the temperatures. This study illustrates the potential of L. taraxacifolia as a green inhibitor, evidenced by its thermodynamic and kinetic properties. It concludes that L. taraxacifolia might serve as a good substitute for synthetic inhibitors, especially in those industries where environmental considerations are essential.

Abstract: It is well known that the mechanical resistance of austenitic stainless steels can be increased considerably by cold rolling process.¶ The cold rolling effect on corrosion resistance of AISI 304L stainless steel in 3% Sodium Chloride solution was investigated by potentiodynamic polarisation and by Scanning Electronic Microscopy (SEM). The pitting corrosion in this environment is related to the rate of cold deformation. The cold rolling induces important changes in the microstructure and involves phase transformation (γ→a'). The AISI 304L developes martensitic structure after 16% cold working. The potentiodynamic results show a moderate variation of the passivity zone, a remarkable decrease in the pitting potential and a free potential. The results also show an increase in the current density. However, it seems that the critical deformation rate appears to start at approximately 50% of the rolling deformation where the passivation current is minimal. After the polarisation tests, metastable pits are observed using SEM and the most probable initiation causes are discussed

Abstract: Aluminium alloys are covered spontaneously by a natural oxide layer, well adherent to the surface. For improving the material’s anticorrosion performance surface pre-treatments are needed in order to remove the superficial oxide and to prepare the alloy surface to subsequent treatments. The pre-treatment process involves several steps, including desmutting. The last requires the immersion of the part in an appropriate solution, typically composed of several chemicals, able to remove the oxide layer. In this work, the effect of the fluorides addition into a sulfuric acid-based solution, when used in a desmutting industrial process, was evaluated. Potentiodynamic curves, glow discharge optical emission spectrometry and contact angle techniques were used to characterize the surface of the aluminium alloy AA8006 after desmutting.

Abstract: Aluminium alloy 6061 T6 circular specimens were joined using TIG welding method. AlMg5 was used as filler. The corrosion behavior of welded and un-welded AA 6061 T6 was investigated using potentiodynamic and open circuit potential (OCP) measurements. Specimens were immersed in 3.5 (wt %) NaCl solution. Different zones with different corrosion properties were created as a result of the welding process. Results reveals that sever pitting corrosion has taken place on the heat affected zone (HAZ); the corrosion current of HAZ was increased. The measured potential of HAZ was more negative and largely fluctuated comparing to base metal (BM).

Abstract: The purpose of the study was the evaluation of the electrochemical corrosion resistance of extruded magnesium alloy AZ61 in solutions with concentration of 0.012 M NaCl. Resistance to electrochemical corrosion was evaluated on the ground of registered anodic polarisation curves by means of potentiodynamic method. Immersion tests were performed in NaCl solution and time periods of 1-6 days. Scanning microscopy was used to obtain images of the alloy microstructure after immersion tests. Electrochemical impedance spectroscopy was used to evaluate phenomena that take place on the surface of the tested alloy. The results of all performed tests prove explicitly deterioration of corrosion properties of magnesium alloy AZ31 with the increase of molar concentration of NaCl solution. It was found that irrespective of molar concentration of NaCl solution, pitting corrosion can be detected on the surface of the tested alloy. Test results prove that it is necessary to apply protective layers on elements made of the tested alloy.

Abstract: Electrochemical behaviour of cast Al-Zn alloys in natural chloride solution were investigated by potentiodynamic measurements and electrochemical impedance spectroscopy (EIS). Results from open circuit potential (OCP) measurement against immersion time showed a stable free corrosion process was achieved after 15 kiloseconds and alloys with more Sn contents had shifted OCP value towards more negative direction. Potentiodynamic polarisation curves showed that the corrosion potential (Ecorr) of aluminium alloys with Sn addition were much active compared to alloy without Sn. The anodic curves were characterized by no sign of passive current due active dissolution on the surface of the Al-Zn-Sn alloy. SEM images show that the presence of Sn in Al-Zn alloys produces better and uniform dissolution morphology. EIS results confirm that the presence of Sn is beneficial in improving anodic dissolution of Al-Zn alloys by reducing resistance to polarization (Rp). The presence of 0.1%wt. Sn in Al-Zn alloy has been found to be useful in activating electrochemical reaction at alloy-solution interface based on inductive loop in EIS diagram.

Abstract: High strength aluminium alloys are widely used in the civil and military aerospace industry due to their low weight and high mechanical properties, achieved by selected alloying elements and heat treatments. The resulting multiphase alloy system, a solid solution of alloying elements in the aluminium matrix and a variety of second phase material, requires specific anticorrosion measures in order to prevent localized corrosion, which is promoted by microgalvanic coupling between the different metallographic phases. Traditionally, the anticorrosion performances are achieved by chromic acid anodizing (CAA), followed by painting. However, environmental issues and associated costs for the disposal of chromate wastes, require the development of new approaches for anodizing of aluminium alloys. In this work, the potential for tailoring the porous anodic film morphology through the film thickness by controlled variations of the anodizing potential is inspected. The procedure developed is, in principle, applicable to any aluminium alloy in any anodizing electrolyte and results in the generation of innovative graded porous anodic film morphologies which promise improvement of anticorrosion properties and replacement of CAA .

Abstract: In order to investigate the intergranular and pitting corrosion behavior of Fe-25Al-6Cr intermetallic compounds containing Mo, Nb and B, 11 kinds of Fe-25Al were prepared by arc melting in Ar gas, using high purity aluminum and iron. The fabricated materials were heat treated for homogenious structure and stabilization of the iron aluminides. The electrochemical methods were used for interganular and pitting corrosion. Effects of Mo, Cr, Nb and B on the repassivation current density(Ir) and the active current density(Ia) of Fe-25Al-6Cr were recorded in the following order: MoCr>Nb>B, from the highest to the lowest respectively.

Abstract: In this study, in order to fabricate dental and medical bone plates, the effects of hydroxyapatite(HA) coating made of tooth ash and TiN coating prepared by electron-beam physical vapor deposition(EB-PVD) method on corrosion resistance and surface phenomena of Ti alloyed bone plates were investigated using various test methods. The coatings were deposited on the Ti-6Al-4V alloy fabricated by using a vacuum induction furnace. The corrosion behaviors of the samples were examined through potentiodynamic method in 0.9% NaCl solutions at 36.5±1°C and corrosion surface was observed using SEM and XPS. The surface roughness of TiN coated bone plates was lower than that of HA coated plates. The structure of TiN and HA coated layers showed the columnar structure. The corrosion potential was observed to be higher on the TiN and HA coated specimens than that of the non-coated alloy. The active current density was drastically lowered by both of TiN and HA coatings. The pit number and pit size of TiN and HA coated alloy were smaller in comparison with those of non-coated alloy. From the experimental results, it is suggested that TiN coated Ti alloy sample with rough surface has good protective propertiy against corrosion as well as HA coated bone plate alloy.