Category Archives: General

Electrochemical Deposition and Microstructure Characterization of Lead-Tin-Layers

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Fig. 3

The present study investigated the formation of a binary alloy of lead and tin. Both elements represent a thermodynamic system with strongly limited miscibility in solid state. The deposition of the layers was carried out under potentiostatic conditions at various deposition potentials from a sulfonate-based electrolyte. The layer formation was characterized by electrochemical techniques (cyclovoltammetry, chronoamperometry). The microstructure development was investigated by SEM/EDX measurements and X-ray diffraction. The layer formation is compliant with the Stranski-Krastanov growth mode. The current efficiency of the deposition was approximately 100%. According to the thermodynamic theory the layers show a dual-phase microstructure. The composition of the Pb-Sn layers was depending on the deposition potential. Supersaturated α-Pb-solid solution could not be observed. The morphology is also strongly depending on the deposition potential. The diffusion coefficient of the metal ions in the sulfonat-based electrolyte was measured by rotating disc electrode experiments. The formal diffusion coefficient in the electrolyte containing Pb2+– and Sn2+– ions is close to the diffusion coefficient of lead ions.

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A Tribological Study on the Ball-on-Disc (BOD) Method, Taking Steel and Galvanic Hard Gold as Examples

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This work was motivated by utilisation of the widespread ball-on-disc (BOD) method for potentially characterizing galvanically deposited layers, especially gold/copper/cadmium alloy layers (“hard gold”) deposited on polished 100Cr6-steel discs (Φ 18 mm) using a special module. The friction balls consisted of smooth alumina and exhibited a diameter of 6 mm. For comparison, similar experiments were made on pure steel-discs. Besides of friction diagrams, profiles were detected by means of a separated profilometer allowing the volumetric determination of the abrasion (wear). To visualize their often irregular shapes, the shape of the friction ball was placed computationally onto the grooves. Due to the semi-chaotic process, the reproducibility was only minor. Nevertheless, some fundamental tribological relations could be found. In particular, the established hypothesis of Achard and the related assumption of a material-specific, time-independent wear coefficient appeared to be inappropriate and thus untenable. Rather, observation showed that wear decreases not linearly but over-proportionally over time, particularly implicating the number of cycles (laps). Furthermore, when the rotation rate increases, a higher load is required to ensure steady abrasion. Although this method allows numerical characterizations of galvanic layers by means of specific constants such as the friction impact constant KW, revealing an obvious qualitative difference between steel and hardgold-plated steel, it is probably not optimum for such systems since it deviates too much from the real conditions of operation. However, the hereby found tribological laws could be of eminent general interest.

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  • DOI: <a href="http://dx.doi.org/10.12850/ISSN2196-0267.JEPT318">10.12850/ISSN2196-0267.JEPT318</a>

Sol-Gel Coating for Aluminum Alloy: Self-Healing Characteristics

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Water-based sol-gel coatings have been developed in the last years as cost-efficient and environmentally friendly protective layers. The stability of sol-gel films is often limited in the absence of functional compounds to generate self-healing. In this work, a water-based sol-gel coating was applied on aluminum alloy 6082. Benzotriazole and cerium nitrate were used as dopants and added to the sol after aging. The coating was injured in order to generate self-healing. The self-repairing feature of the defected specimen was evaluated by electrochemical impedance spectroscopy (EIS) in chloride solution. Healing qualification was examined by monitoring the defect size during the immersion test. The experiments show that the samples coated with an inhibitor-doped film are better protected against corrosion even after long-time immersion in chloride solution. The defect size after healing was smaller than that of the samples coated with non-doped film, which exhibited low stability in chloride solution. The defect size was several times bigger after the corrosion test. A contact stylus instrument and a scanning electron microscope (SEM) were used to characterize the defect surface profiles before and after healing.

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Anodic Film Formation in Oxalic Acid on AlMn0.5Mg0.5 Alloy

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The microstructure of oxalic-acid-anodized layers on AlMn0.5Mg0.5 alloy is compared to such layers on aluminum. Differences originate from four types of precipitates occurring in the alloy, forming inclusions in the layers, roughening surface and interface, and modifying typical pore structures of anodized aluminum oxides. A characteristic feature of this modification is the appearance of transverse channels in pore walls. Nanoscaled precipitates are suggested as their origin. Correlation to functional properties such as microhardness and electrical isolation behavior is discussed.

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Environmental Issues of Chromium(VI) Compounds

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This article focuses on ecotoxicological properties of chromium(VI) compounds, their behavior in the environment, as well as consequences for safe handling such compounds. In natural environments, chromium is usually part of complex compounds. Therefore, higher concentrations of biologically available chromium compounds are mostly due to human activity. Trivalent and hexavalent chromium remain stable in natural environments. Both oxidation states are inter-convertible via redox reactions. As studies on organisms at all levels of the food chain show, hexavalent chromium is characterized by relatively high acute and chronic aquatic toxicity. From a regulatory point of view, this implies that additional risk management measures are necessary in order to reduce the input of chromium(VI) compounds into the environment as far as possible. At the same time, the properties of the substance call for an intensive search for substitute materials and processes that guarantee the functionality needed but cause less problems for human health and the environment. Further details are available in European Risk Assessment Report 53 [1].

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