Browsing by Author "Tsanev A."

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    Characterization of anodized Al 1050 with electrochemically deposited Cu, Ni and Cu/Ni and their behavior in a model corrosive medium
    (2021-01-01) Girginov C.; Kozhukharov S.; Tsanev A.; Dishliev A.
    The specific benefits of the modified films formed on preliminary anodized aluminum, including the versatility of their potential applications impose the need for evaluation of the exploitation reliability of these films. In this aspect, the dura-bility of Cu and Ni modified anodized aluminum oxide (AAO) films on the low-doped AA1050 alloy was assessed through extended exposure to a 3.5% NaCl model corrosive medium. The electrochemical measurements by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) after 24 and 720 hours of exposure have revealed that the obtained films do not change their obvious barrier properties. In addition, supplemental analyses of the coatings were performed, in order to elucidate the impact of the AC-deposition of Cu and Ni inside the pores. The scanning electron microscopy (SEM) images have shown that the surface topology is not affected and resembles the typical surface of an etched metal. The subsequent energy dispersive X-ray spectroscopy (EDX) tests have revealed a predominance of Cu in the combined AAO-Cu/Ni layers, whereas additional X-ray photoelectron (XPS) analyses showed that both metals form oxides with different oxidation states due to alterations in the deposition conditions, promoted by the application of AC-polarization of the samples.
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    Characterization of anodized Al 1050 with electrochemically deposited Cu, Ni and Cu/Ni and their behavior in a model corrosive medium
    (2021-01-01) Girginov C.; Kozhukharov S.; Tsanev A.; Dishliev A.
    The specific benefits of the modified films formed on preliminary anodized aluminum, including the versatility of their potential applications impose the need for evaluation of the exploitation reliability of these films. In this aspect, the dura-bility of Cu and Ni modified anodized aluminum oxide (AAO) films on the low-doped AA1050 alloy was assessed through extended exposure to a 3.5% NaCl model corrosive medium. The electrochemical measurements by means of electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) after 24 and 720 hours of exposure have revealed that the obtained films do not change their obvious barrier properties. In addition, supplemental analyses of the coatings were performed, in order to elucidate the impact of the AC-deposition of Cu and Ni inside the pores. The scanning electron microscopy (SEM) images have shown that the surface topology is not affected and resembles the typical surface of an etched metal. The subsequent energy dispersive X-ray spectroscopy (EDX) tests have revealed a predominance of Cu in the combined AAO-Cu/Ni layers, whereas additional X-ray photoelectron (XPS) analyses showed that both metals form oxides with different oxidation states due to alterations in the deposition conditions, promoted by the application of AC-polarization of the samples.
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    Evaluation of the electrochemical performance of Ag containing aao layers after extended exposure to a model corrosive medium
    (2020-01-01) Kozhukharov S.; Girginov C.; Kiradzhiyska D.; Tsanev A.; Avdeev G.
    The coating procedure appears to be an indispensable finishing stage in the production of Al based industrial products, engineering facilities and equipment. For this reason, there is an ever-increasing interest towards the elaboration of reliable corrosion protective layers with apparent coverage, adhesion, and barrier properties. In this sense, both the formation of anodized aluminum oxide (AAO) layer and its further modification with silver enable the elaboration of advanced (Al-O-Ag) films with extended beneficial characteristics. The present research activities are aimed at the determination of the corrosion protective properties of electrochemically synthesized Al-O-Ag layers on the technically pure AA1050 alloy. The structures and compositions of the obtained Al-O-Ag layers were characterized by X-ray diffractometry (XRD) and X-ray photoelectron spectroscopy (XPS). The research activities were accomplished by means of two independent electrochemical characterization methods: electrochemical impedance spectroscopy (EIS) and potentiodynamic scan-ning (PDS). The electrochemical measurements were performed after 24, 168 and 672 hours of exposure to 3.5 % NaCl solution used as a model corrosive medium (MCM), in order to determine the barrier properties and durability of the elaborated Al-O-Ag layers. The analysis of the obtained results has undoubtedly shown that the proposed electrochemical Al-O-Ag layer formation can successfully be used for the creation of self-standing layers with apparent corrosion protective properties. Besides, Al-O-Ag system can be used as a basis for development of efficient protective layers suitable for application in biologically contami-nated media.
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    INFLUENCE OF THE FINAL THERMAL SEALING ON THE PROPERTIES OF COMBINED ANODIC ALUMINA/CERIUM CONVERSION COATINGS ON AA2024-T3 AIRCRAFT ALLOY
    (2023-01-01) Girginov C.; Kozhukharov S.; Tsanev A.; Georgieva M.; Petrova M.; Lilov E.; Petkov P.
    The current research presents results following corrosion tests, performed on combined anodic alumina/cerium conversion coatings (Al2O3/CeCC), thermally sealed for 15 min at 100°C either in boiling water or in hot-air medium. The coatings were formed on AA2024-T3 aircraft alloy substrates, at the optimum conditions of anodization and cerium conversion coating deposition, described in previous works. Prior to the corrosion tests, both the color characteristics and wetting ability of the combined films were evaluated. The corrosion protective properties of the sealed films were assessed by means of Electrochemical Impedance Spectroscopy (EIS) and Potentiodynamic Polarization (PDP). The measurements were performed after 672 hours of exposure to a 5 % NaCl model corrosive medium (MCM). Additional long term (up to 1344 hours of exposure) durability tests were then performed under the same conditions for the samples and superior performance was established. The electrochemical measurements were conducted regularly, once a week. Low and high-resolution Scanning Electron Microscopy (SEM) studies were performed on selected samples. The experimental results have shown that the sealing procedure in an aqueous environment enhances the corrosion protective ability and durability of the coating, probably due to formation of a hydrate layers, that suppresses the access of corrosive species to the surface of the substrate. This inference was additionally confirmed by the subsequent chemical analysis by means of X-Ray Photoelectron Spectroscopy (XPS). The results acquired have also shown that the incorporated Ce is predominantly in the form of Ce(IV)-oxides/hydroxides and after the thermal treatment almost entirely consists of cerium.