Papers by Keyword: EIS

Abstract: To determine the sealing system of arc-spraying aluminum coating for steel structures in high humidity and harsh environments, electrochemical impedance spectroscopy (EIS) was used to study the corrosion resistance and matrix protection of three arc-sprayed aluminum /organic composite coatings in 3.5% NaCl solution. The results indicated that during the 660-day soaking experiment, the coating capacitance of the epoxy-sealing paint system was consistently lower than that of the phosphating primer system and the nano-sealing primer system. The coating resistance showed a decreasing-increasing-decreasing trend but remained above the level of 105 Ω· cm², and it was higher than the other two systems. The coating reaction resistance remained above 107 Ω· cm² throughout the entire experimental period, and in the later stage of the experiment, it was 2-3 orders of magnitude higher than the other two systems. It showed that the epoxy sealer system has better shielding performance and corrosion resistance. The protective process of arc-spraying composite coating on the substrate can be divided into four stages: water penetration of organic sealing coating, contact of aluminum coating with medium, formation of shielding layer by corrosion products of aluminum coating, and penetration of corrosion products of aluminum coating to seal pores of organic sealing coating.

Abstract: Corrosion behavior of three carbon steels with increasing galvanized coating thickness of 5.6, 8.4 and 19.2 μm named as T₁, T₂ and T₃, respectively, was studied by immersion test, potentiodynamic polarization and electrochemical impedance spectroscopy in freely aerated 3.5% NaCl solution. The major phase in the corrosion product of all the samples after immersion test was found to be zincite, as determined by X-Ray Diffraction and Fourier Transform Infrared Spectroscopy techniques. The corrosion product on sample T₁was well adhered and was compact in most regions. Samples T₂ and T₃ showed porous and non-adherent growth of corrosion product. Corrosion rates were found to increase with increasing coating thickness. The impedance provided by the coating as well as the substrate was the highest for the sample with thinnest coating (T₁). The early exposure of the underlying steel in sample T₁ resulted in higher corrosion resistance, which was probably due to the combined effect of zinc corrosion products and Fe-Zn alloy layer. Higher amount of protective γ-FeOOH as well as compact corrosion product could have also improved the corrosion resistance of sample T₁. Although the average uniform corrosion resistance was higher for T₁, the localized pitting corrosion was also observed, probably due to the thin galvanized layer.

Abstract: The plasma electrolytic oxidation (PEO) process was used to form an oxide layer on an Al5754 aluminum alloy for subsequent application of organic coating. The effect of the oxidation time on the morphology and anticorrosion properties of PEO-coatings was investigated. The oxide layer possess low apparent porosity and provides high adhesion to the paint. The resulting composite coating (CC) is characterized by high barrier properties in chloride solution.

Abstract: High requirements in biomedical application are associated with biocompatibility and high corrosion resistance of metal biomaterials, which are used equally in joint and bon substitution and the healing and renewal of bone weaknesses. In this paper the surface morphology and electrochemical properties of samples manufactured by Selective Laser Melting SLM method using pure titanium Grade II powder material are explored. The tested samples were produced divided into four group, depended on the values of basic process parameters – laser power P, scanning speed SP and point distance PD. The value of energy density E delivered to the sintered material was constants and was an approximately E = 75 ± 2 J/mm³. In the paper, the pitting corrosion test by recording anodic polarization curves and electrochemical spectroscopy test were carried out. Additionally the microscopic observation and microchemical analysis by SEM/EDS analysis and material density measurements were performed too. Based on the obtained results it can be concluded that the laser power P and scanning speed SP have a significant affect on the obtained full density defect free material with high corrosion resistance.

Abstract: The binary metal oxides of ZnO and MoO₃ (ZMO) nanostructured thin films were prepared by pulsed laser deposition at different temperatures such as 298(as deposited), 623, 773 and 923K at 10Hz laser repetition rates for 30 min. The films were characterized by XRD, UV-Visible spectroscopy and IV measurements. The XRD discloses the amorphous nature of the film deposited below 773K. Few peaks which were seen in 923K sample revealed the formation of ZnMoO₄ and Zn₃Mo₂O₉ for the binary ZMO thin films. The optical energy band-gap was measured using Tauc plot and was found to be 2.4 to 2.7eV. These films were investigated by electrochemical impedance spectroscopy over a frequency range of 1Hz–1MHz, for measuring temperatures lying in 298K-473K domain. The frequency response of the imaginary impedance (Z′′) shows relaxation behavior along every measuring temperature. The binary ZMO pulsed laser deposited at high temperatures demonstrates better semiconducting behavior. The activation energy (E_a) which is minimum for high temperature PLD thin films was determined from the Arrhenius plot based on impedance.

Abstract: To improve the corrosion resistance on Q235 low carbon steel, in this paper, tetraethyl orthosilicate (TEOS), N-dodecyl trimethoxysilane and γ-(2,3-epoxypropoxy) propytrimethoxysilane (KH560) were used to make organic-inorganic hybrid sol-gel film. Cross cut test adhesion method, neutral salt spray test, electrochemical test and film protective efficiency were taken to value the corrosion resistance property. The corrosion topography was studied by optical microscope. In addition, potentiodynamic polarization, electrochemical impedance spectroscopy (EIS) curves and equivalent electric circuit fitting were used to analyze the corrosion mechanism. The cross cut adhesion of sol-gel film can reach 1 class and the protection class can attain 5 class after 72 hours neutral salt spray test. According to the potentiodynamic polarization curve analysis, the corrosion potential of sol-gel film coating sample after 0.5 hours immersion was -0.46 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.74×10^-7 A·cm^-2. The corrosion potential of bare Q235 low carbon steel plate after 0.5 hours immersion was -0.78 V (vs. SCE) on the 0.1 Hz, and its corrosion current density was 4.75×10^-6 A·cm^-2. The impedance value on 0.1 Hz (|Z|_0.1Hz) (1.27×10⁶ Ω·cm²) of sol-gel film coating sample was more than three orders of magnitude higher than the value of the low carbon steel plate. Even dipping in 3.5 wt. % NaCl for 72 hours, the |Z|_0.1Hz value of sol-gel coating sample was still one order of magnitude higher than the low carbon steel plate with 0.5 hours immersion. Sol-gel film with excellent adhesion can significantly improve the corrosion resistance of low carbon steel plate. Sol-gel film can increase the protection efficiency of low carbon steel plate by 90%.

Abstract: Corrosion performance of graphene oxide (GO) coatings from different sheets sizes in 3.5 wt% NaCl solution was investigated. The GO dispersion was subjected to 5 and 10 hours of ultrasonication before electrophoretically deposited (EPD) onto the copper substrate. It was found that the EPD-GO coating from smaller sheets (10h ultrasonication) possess hydrophobic, thinner film and smooth surfaces. It is suggested that the corrosion performance of the coating from smaller GO sheets is improved due to the surface texture and compactness of the coating as compared to the larger GO sheets.

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: Solid electrolytes such as lithium lanthanum zirconate have shown a lot of promise in an all-solid-state Lithium-based battery since the discovery of its highly conductive cubic garnet structure. In this study, different concentrations of Al-doped Lithium Lanthanum Zirconate (Al-doped LLZ) having the formula of Li_7-.3xAl_xLa₃Zr₂O₁₂ with x = 0.1,0 .2, 0.3, were synthesized via modified Pechini method and the effect of sintering temperatures, 1150 and 1200 °C, on the resulting properties were investigated. X-ray diffraction results have shown that cubic Al-doped LLZ can be obtained at a lower temperature using Pechini method. Significant effect to the conductivity on the different sintering temperatures was observed for the 0.1 Al-doped LLZ. With the different studied compositions synthesized via modified Pechini method, it was revealed that the 0.2 Al doped LLZ sintered either at 1150 or 1200 °C showed the highest conductivity of about 1.4x10^-4 S/cm.

Abstract: The present study investigates the effect of lanthanide chlorides conversion coatings on the corrosion response of the 2009 Al alloy and SiC_p reinforced 2009 Al MMCs. Electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization studies showed that the localized corrosion resistance increased after treatments with solutions having various combinations of CeCl₃.7H₂O and LaCl₃.7H₂O, with maximum increase noticed for 5000ppm CeCl₃.7H₂O. It was found that the protection degree effect obtained under similar coating conditions for 25 vol.% SiC_p/2009 Al was relatively higher than 15vol.% SiC_p/ 2009 Al MMC, but both of them were less than that of the unreinforced alloy. Scanning electron microscopy (SEM) accompanied with energy dispersive spectroscopy (EDS) analysis revealed the deposition of Ce and/ or La oxides/ hydroxides on cathodic intermetallics/ SiC_p and the existence of crevices at the SiC_p/ matrix interfaces. X-ray photoelectron spectroscopy (XPS) results indicated that Ce was incorporated as Ce³⁺ and Ce⁴⁺ species in the coatings.