Corrosion and corrosion protection of support structures for offshore wind energy devices (OWEA)

The paper provides a review about the corrosion and corrosion protection of offshore wind energy devices (OWEA). Firstly, special features resulting from location and operation of OWEA are being discussed. Secondly, types of corrosion and corrosion phenomena are summarized in a systematic way. Finally, practical solutions to the corrosion protection of OWEA, including steel allowances, cathodic protection and coatings and linings, are discussed.     

Enhanced Photocurrent Production by Photosystem I Multilayer Assemblies

The long‐term success of photosynthetic organisms has resulted in their global superabundance, which is sustained by their widespread, continual mass‐production of the integral proteins that photocatalyze the chemical processes of natural photosynthesis. Here, a fast, general method to assemble multilayer films composed of one such photocatalytic protein complex, Photosystem I (PSI), onto a variety of substrates is reported. The resulting films, akin to the stacked thylakoid structures of leaves, consist of a protein matrix that is permeable to electrochemical mediators and contain a high concentration of photoelectrochemically active redox centers. These multilayer assemblies vastly outperform previously reported monolayer films of PSI in terms of photocurrent production when incorporated into an electrochemical system, and it is shown that these photocatalytic properties increase with the film thickness. These results demonstrate how the assembly of micron‐thick coatings of PSI on non‐biological substrates yields a biohybrid ensemble that manifests the photocatalytic activity of the film’s individual protein constituents, and represent significant progress toward affordable, biologically‐inspired renewable energy conversion platforms.     

Nanoindentation reveals mechanical properties within thermally sprayed hydroxyapatite coatings

Nanoindentation offers a unique capability to assess the mechanical properties of polished cross-sections of thermal spray coatings. This study set out to investigate the suitability of nanoindentation to extend the analysis of the cross-section to multiple points for a more detailed insight into variations through the thickness of the coating. Hydroxyapatite (HAp) was classified to three different particle sizes (20-40, 40-60 and 60-80 μm) and then thermally sprayed to produce a structurally homogeneous coating. Micro-Raman Spectroscopy (MRS) revealed dehydroxylation of the powder during the traverse in the thermal zone. Multiple indentations with a separation of 4 μm showed a transition within the thickness of the coating. Use of smaller particles led to higher hardness and elastic modulus compared to powder containing larger particles. The mechanical property profile provides valuable information for optimizing the processing of such coatings and feedback for the design of coating properties.     

The Electrodeposition of Chromium from Tervalent Chromium Salt Solutions. Part I. Chromium Chloride and Chromium Sulphate Baths

The “imponderables” which affect the framework within which the Plating Shop must be planned are listed. The grouping of vats, cleaners and rinses are discussed and alternative methods of hand operation of plating vats described. The importance of depth of plating vats is stressed and various methods of constructing floors, drainage and vat supports are briefly indicated. Layouts for barrel plating shops both with inclined and horizontal barrels are suggested, and the importance of correct housing for electrical and other ancillary plant is emphasised.     

Formation of dicalcium phosphate dihydrate on magnesium alloy by micro-arc oxidation coupled with hydrothermal treatment

A layer containing dicalcium phosphate dihydrate (DCPD) and β-Ca₃(PO₄)₂ was prepared on magnesium alloy by hydrothermal treatment of micro-arc oxide (MAO) layer. The biocorrosion resistance of the oxide layers before and after hydrothermal treatment was analyzed by anodic polarization and electrochemical impedance spectroscopy (EIS) in Hank’s solution. The prepared MAO layers consisted mainly of MgO and MgAl₂O₄, and Ca and P inside the oxide layers existed with amorphous phase. Hydrothermal treatments not only made the amorphous Ca and P change into DCPD and β-Ca₃(PO₄)₂ crystals, but also improved the biocorrosion resistance of magnesium alloys, especially the pitting corrosion resistance.     

The Measurement of Internal Stress in Electrodeposits

The fundamental principles and underlying methods of measuring internal stress in electrodeposits are reviewed and special attention is given to the bent strip methods. The advantages of the Hoar-Arrowsmith continuous measuring null instrument (Trans Inst Metal Finishing, 1957, 34, 354) are emphasized and a refined theoretical treatment is presented. A comparison is made between the formulae derived by various authors, and approximations involved are examined. Percentage errors, which are frequently quite large, are presented for many of the cases.     

In situ infrared reflection spectroscopy studies of the initial atmospheric corrosion of Zn–Al–Mg coated steel

NaCl induced atmospheric corrosion of ZnAl2Mg2 coated, electrogalvanised (EG) and hot dipped galvanised (HDG) steel was studied using in situ infrared reflection absorption spectroscopy, XRD and SEM. Initial corrosion leads to the formation of Mg/Al and Zn/Al layered double hydroxides (LDHs) on ZnAl2Mg2, due to the anodic dissolution of Zn–MgZn2 phases and cathodic oxygen reduction on Zn–Al–MgZn2, Al-phases and on zinc dendrites. In contrast to EG and HDG, were no ZnO and Zn₅(OH)₈Cl₂⋅H₂O detected. This is explained by the buffering effect of Mg and Al which inhibit the ZnO formation, reduce the cathodic reaction and corrosion rate on ZnAl2Mg2.     

Novel approach to correlate degree of surface deterioration to coating impedance for laboratory test panels coated with two types of primers

Abstract

Relationships between deteriorated coating surface conditions of laboratory test panels determined by image processing software and coating impedance data collected with electrochemical impedance spectroscopy (EIS) were investigated. A unique relationship was found between the log?|Z|_0·1 values of experimental EIS data and the corresponding deteriorated area ratios determined by the image processing method. A well defined one to one relationship was also found between log?|Z|_0·1 values and log?(R_po) values extracted through EIS data fitting analysis. This study demonstrates that estimation of log?(R_po) at a certain deterioration stage is feasible via field image processing alone without running in situ EIS measurements and going through time consuming EIS fitting analysis. A field coating maintenance program established by this methodology can be an effective tool for bridge maintenance engineers who need to make timely decisions on coating repair/rehabilitation work based on the quantitative ‘visual’ image scan results and ‘invisible’ coating pore resistance.     

Characterisation of amorphous phosphate coatings onto carbon steel surfaces

Abstract

This study continues the authors’ investigation of the newly developed product KAF-09OF and concerns the preparation and characterisation of amorphous phosphate coatings on carbon steels. KAF-09OF is a liquid concentrate of ammonium and alkaline phosphates, stabilising additives – buffers, softeners, activators (both inorganic and organic), as well as surfactants – a non-ionic and an anionic detergents. Gravimetric and polarisation methods, X-ray fluorescence analysis, transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy have been used to determine the effect of pH (2–6), temperature conditions (20–80°C) and agitation rate (0–2000 rev min^?1) on the process of phosphating using this developed product. Coating thicknesses, compositions, structures and passivation characteristics in the phosphating baths with different concentrations of KAF-09OF have been analysed.     

The influence of experimental conditions on the morphology and phase composition of Nb-doped ZrO2 films prepared by spark anodization

This paper reports the morphological and microstructural characterization of Nb-doped ZrO₂ films obtained by anodic doping in conditions of spark electrolytic breakdown. The oxide films were prepared by galvanostatic anodization of metallic Zr in oxalic acid solution containing ammonium oxaloniobate, NH₄H₂[NbO(C₂O₄)₃]⋅3H₂O using Nb(V) ions as the precursor dopant. The characterization was performed by SEM and XRD. A factorial design was used to optimize the experiments and study the influence of experimental variables on morphology and phase composition. The results demonstrated that the dopant concentration is the most important factor that affected the analyzed responses. A significant influence of this variable was observed on the pore average diameter and on the percentage of the stabilized tetragonal phase. The temperature also affected the phase composition, however no effect was observed on the morphological response.