Hydrophobic Coatings for Corrosion Control of Aluminum Heat Exchangers

The production of thin films (nanocoatings) is a technological field with many applications to elaborate materials with new properties to be used as corrosion protection of traditional metals. Hydrophobicity is an example of such properties. In this chapter, an example of two hydrophobic corrosion coatings for possible use over aluminum heat exchanger geothermal power plants is discussed. Material substrate preparation, synthesis of hydrophobic sol‐gel nanocoating, characterization, and electrochemical evaluation as a function of time of immersion, which are compared to another commercial fluorinated compound, are presented. Good corrosion protection was found for both hydrophobic coatings for possible application in geothermal heat exchangers

Electrochemical behaviour of Iron in chlorinated alkaline media: the effect of slurries from granite processing

Porriño is a well known zone of quarry and stone working of the SW of Galicia, Spain. In granite's working processes 3 <FONT FACE=Symbol>&times;</FONT> 10(5) ton year-1 of granite powder are generated in this area, causing an important environmental problem. This dust has proved to be an efficient addition to high-strength concrete to improve mechanical properties. Nevertheless, no works have been published concerning the effect of this admixture in the passivation of steel reinforcements. The objective of the present work is to analyze the electrochemical behaviour of iron and carbon steel electrodes in alkaline solutions resulting from these slurries. The growth and evolution of the passive layers formed on the tested electrodes are studied by Cyclic Voltammetry and Electrochemical Impedance Spectroscopy. Scanning Electron Microscopy and X-ray powder Diffraction have been used for the morphological and chemical characterisation of the generated passive films. The effect of the presence of Cl- ions is also considered

Repetitive corrugation and straightening effect on the microstructure, crystallographic texture and electrochemical behavior for the Al-7075 alloy

Anti-corrosion susceptibility is one of the top criteria for selecting metallic materials for several industrial applications. This work studies the corrosion performance on an Al-7075 alloy obtained by Repetitive Corrugation and Straightening (RCS). This processing method generated a microstructure formed by randomly distributed micro-, submicro-, and nano- metric grain sizes. The samples exhibited a drop in corrosion resistance for a longer duration in the electrolyte and higher deformation. However, the samples processed by RCS showed better electrochemical stability in comparison with the non-deformed condition. The improvement of electrochemical stability could be associated with the particular microstructure generated during the RCS process.Postprint (published version

Caracterización electroquímica de recubrimientos Zn-Al sobre fundición nodular grado 2, obtenidos por proyección térmica por flama con alambre

Thermal spray is a technology that involves heating a material in the form of powder or wire, which is brought to a molten or semi-molten state, then propelled by a stream of gas or compressed air and deposited on a metallic, ceramic or polymeric substrate, with appropriate roughness conditions. The main objective of this research is to perform electrochemical characterization employing electrochemical impedance spectroscopy and electrochemical noise techniques of a Zn-15Al alloy deposited on a ductile iron grade 65-45-12 (2) through flame thermal spray technique with wire to the Zn-Al coating shows good homogeneity, good adhesion and a substantial improvement in corrosion resistance. &nbsp;La proyección térmica o rociado térmico es una tecnología que implica calentar un material que está en forma de polvo o alambre y llevarlo a un estado fundido o semifundido, para luego propulsarlo mediante una corriente de gas o aire comprimido y depositarlo sobre un sustrato metálico, cerámico o polimérico, que tenga condiciones de rugosidad adecuadas. La investigación realizó la caracterización electroquímica mediante las técnicas de espectroscopia de impedancia electroquímica y ruido electroquímico de una aleación Zn-15Al depositada sobre una fundición nodular grado 65-45-12 (2), por medio de la técnica de proyección térmica por llama con alambre, donde el recubrimiento de Zn-Al presenta buena homogeneidad, buena adherencia y una mejora sustancial en la resistencia a la corrosión

Electrochemical Polarization as a Sustainable Method for the Formation of Bronze Patina Layers on a Quaternary Copper Alloy: Insight into Patina Morphology and Corrosion Behaviour

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO3 were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected

Electrochemical Polarization as a Sustainable Method for the Formation of Bronze Patina Layers on a Quaternary Copper Alloy: Insight into Patina Morphology and Corrosion Behaviour

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO3 were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected

Caracterización electroquímica de recubrimientos Zn-Al sobre fundición nodular grado 2, obtenidos por proyección térmica por flama con alambre

Thermal spray is a technology that involves heating a material in the form of powder or wire, which is brought to a molten or semi-molten state, then propelled by a stream of gas or compressed air and deposited on a metallic, ceramic or polymeric substrate, with appropriate roughness conditions. The main objective of this research is to perform electrochemical characterization employing electrochemical impedance spectroscopy and electrochemical noise techniques of a Zn-15Al alloy deposited on a ductile iron grade 65-45-12 (2) through flame thermal spray technique with wire to the Zn-Al coating shows good homogeneity, good adhesion and a substantial improvement in corrosion resistance.  La proyección térmica o rociado térmico es una tecnología que implica calentar un material que está en forma de polvo o alambre y llevarlo a un estado fundido o semifundido, para luego propulsarlo mediante una corriente de gas o aire comprimido y depositarlo sobre un sustrato metálico, cerámico o polimérico, que tenga condiciones de rugosidad adecuadas. La investigación realizó la caracterización electroquímica mediante las técnicas de espectroscopia de impedancia electroquímica y ruido electroquímico de una aleación Zn-15Al depositada sobre una fundición nodular grado 65-45-12 (2), por medio de la técnica de proyección térmica por llama con alambre, donde el recubrimiento de Zn-Al presenta buena homogeneidad, buena adherencia y una mejora sustancial en la resistencia a la corrosión