Advanced Multifunctional Corrosion Protective Coating Systems for Light-Weight Aircraft Alloys—Actual Trends and Challenges

The present chapter is devoted to the recent trends in the field of the advanced corrosion protective layers elaboration. The chapter begins with brief classification of the standard aluminum alloys, remarking their importance for the transport sector, as well as the basic corrosion forms, typical for these alloys. It continues with the basic requirements regarding the elaboration of durable and reliable coating systems and the factors of detrimental effect during the service life time. The concept for passive and active corrosion protection capabilities is remarked as well. After description of the need for multilayered coating systems elaboration, the function of each layer is described beginning from (i) UV light–absorbing exterior layers, (ii) self-repairing reinforced intermediate barrier layers, and (iii) cerium oxide primer layers (CeOPL). The importance and the basic approaches for metallic alloy preliminary treatment are remarked, as well. Finally, the basic concepts and the function of each layer in advanced multilayered coating system are summarized in a special section. The chapter finishes with brief conceptual description of two advanced versatile technological synthesis methods, which enable elaboration of organic/inorganic hybrid polymers and reinforcing nanoparticles

Enhancement of the cerium oxide primer layers deposited on AA2024-T3 aircraft alloy by preliminary anodization

The possibility for combination between anodized aluminum oxide (AAO) and cerium oxide primer layer (CeOPL) for elaboration of efficient protective coatings for AA2024-T3 aircraft alloy is proposed in the present research. The combined AAO/CeOPL coating characterizations include electrochemical impedance spectroscopy (EIS) combined with linear voltammetry (LVA), for extended times (until 2520 hours) to a model corrosive medium (3.5 % NaCl). Topographical and cross-sectional (SEM and EDX) observations were performed in order to determine the AAO/CeOPL film thickness and composition. The AAO/CeOPL layer durability tests were confirmed by standard neutral salt spray (NSS). The data analysis from all the used measurement methods has undoubtedly shown that the presence of AAO film significantly improves the cerium oxide primer layer (CeOPL) protective properties and performance

Alternative technological approach for synthesis of ceramic pigments by waste materials recycling

AbstractAlternative technological approach is proposed enabling utilization of raw materials from an oil refinery, such as waste guard layers from reactors. Reagent grade and purified MgO, Cr2O3, Fe2O3, and nitric acid (HNO3), were used as additional precursors. The homogeneous mixtures obtained were formed into pellets and sintered at different temperatures. The main phase was proved by X-ray phase analysis (XRD) and compared to ICPDS database. The main phase in the ceramics synthesized was solid solution of spinel MgAl2O4 and magnesiochromite. These minerals are classified as chromspinelide MgCr1.2Al0.4Fe0.4O4 and alumochromite MgCr1.6Al0.4O4. Additional SEM observations, combined with EDX analysis were performed, evincing agglomeration at lower temperatures, followed by agglomerate crumbling, at elevated calcination temperature.The complete transformation of initial precursors into the final ceramic compounds was found to occur at 800°C – 1h. The ceramic samples synthesized had high density of 1.72–1.93g/cm3 and large absorption area – 32.93% which is probably due to the high porosity of the sample

Impact of the final thermal sealing of combined zinc/cerium oxide protective coating primers formed on low carbon steel

The final sealing possesses a proven beneficial effect on the protective properties of anodic oxide films on aluminum. In this sense, the present research is devoted to the evaluation of the impact of this procedure on the barrier ability of combined Zn/Ce oxide layers deposited on low carbon steel samples. For this purpose, four samples were submitted to galvanic zinc deposition, followed by spontaneous formation of cerium oxide primer layer (CeOPL). Afterwards, two of the samples underwent thermal sealing in boiling water in order to enhance their barrier ability. Its evaluation was performed by two electrochemical methods: electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) after 24 hours of exposure to a diluted model corrosive medium (MCM). Other instrumental methods were used in order to describe the effect of this final procedure on the color characteristics and hydrophobicity of the films. The results were collected from multiple tests, followed by statistical data treatment. In addition, the surfaces of the obtained films were submitted to direct observation by scanning electron microscopy (SEM), coupled with energy dispersion X-ray (EDX). Their composition was determined by means of X-ray Photoelectron Spectroscopy (XPS). The acquired data have revealed a detrimental effect of the final sealing in boiling water. It was expressed by the loss of the barrier properties of the Zn/CeOPL films, combined with additional decolorization and hydrophilization. Finally, the mechanism of this detrimental effect was determined by further SEM, EDX and XPS analyses

HUMIDITY SENSING ELEMENTS BASED ON SILICA-GRAPHENE SURFACE LAYERS

The paper presents humidity sensing elements based on silica-graphene surface layers, prepared via a sol-gel method. The samples were sintered at temperatures of 400 °C, 600 °C and 800 °C. Tetraethoxysilane was used as a precursor of SiO2 and as a dopant - graphene aggregates of nanoplatelets. A description of the sample preparation procedure is provided. Using a precise impedance analyzer and a calibrator for humidity and temperature, the changes in their resistance R were investigated with variations in relative humidity in the range of 30% to 90% at a temperature of 25 °C and at a frequency of 20 Hz. Morphological observations and map data analyses were carried out by Scanning Electron Microscopy (SEM) and Energy Dispersion Spectroscopy (EDX). The developed sensor elements have a good sensitivity to the humidity, and the resistance change reaches two orders of magnitude. Additions of graphene improve the sensitivity of the elements. The characteristics of the sensing elements at different sintering temperatures and different amounts of graphene dopant were modeled using an artificial neural network.

Evaluation of the electrochemical performance of Ag containing AAO layers after extended exposure to a model corrosive medium

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 scan­ning (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 contami­nated media.</p

Elaboration of advanced glass-ceramic glaze for anti-slip porcelain stoneware

The present communication describes the synthesis of anti-slip enamel exhibiting glass-ceramic nature using new matte frits and raw materials. The glass-ceramic glazes obtained are characterized by various instrumental techniques (X-ray fluorescence (XRF), scanning electron microscopy (SEM), X-ray diffraction (XRD), mechanical profilometry and microhardness measurements) to elucidate the nature of the crystallized phases, their morphology, surface roughness and the finished tile microhardness. The quality of the glazed piece is evaluated by the regulations of chemical resistance, stain-resistance and slipperiness. The enamel obtained devitrifies in crystals of calcium and barium silicoaluminates. It complies with anti-slip and stain-resistance standards, because its surface roughness is similar to that of non-slip enamel

Sealing of cerium oxide coating primers on anodized AA2024-T3 alloy by boiling in Lourier buffers

Although their exceptional re-passivation ability, Al-alloys are susceptible to corrosion due to the amphoteric nature of the alumina passivation films. This issue is exacerbated by the disruption of these films by intermetallics on the surfaces of highly doped ones, like AA2024-T3 aircraft alloy. The combination of anodized aluminium oxide (AAO) and cerium conversion coatings (CeCC) shows promise as a coating primer. However, the defective structures of CeO2 and Al2O3 require additional sealing. This research proposes sealing the CeCC/AAO layer by boiling it for 10 minutes in two relatively neutral Lourier buffers, adjusted to pH 7.75, and in a mixture of them. The samples underwent a series of analyses to compare the impact of the sealing procedure on surface topology, properties (e.g., colour and wettability on two samples from each set), and corrosion protective ability. It was assessed after 24 hours of exposure to 3.5 % NaCl model corrosive medium on six samples from each set. The assessments included electrochemical impedance spectroscopy (EIS) and potentiodynamic scanning (PDS) techniques. The results indicate that the borate buffer improves the corrosion protection of the coating primers more effectively than the phosphate and mixed ones

Surface of Alumina Films after Prolonged Breakdowns in Galvanostatic Anodization

Breakdown phenomena are investigated at continuous isothermal (20∘C) and galvanostatic (0.2–5 mA cm−2) anodizing of aluminum in ammonium salicylate in dimethylformamide (1 M AS/DMF) electrolyte. From the kinetic ()-curves, the breakdown voltage () values are estimated, as well as the frequency and amplitude of oscillations of formation voltage () at different current densities. The surface of the aluminum specimens was studied using atomic force microscopy (AFM). Data on topography and surface roughness parameters of the electrode after electric breakdowns are obtained as a function of anodization time. The electrode surface of anodic films, formed with different current densities until the same charge density has passed (2.5 C cm−2), was assessed. Results are discussed on the basis of perceptions of avalanche mechanism of the breakdown phenomena, due to the injection of electrons and their multiplication in the volume of the film

Synthesis of pigments of Fe2O3·SiO2 system, with Ca, Mg, or Co oxide additions

AbstractThe present research work is based on the comparative evaluation of the Ca, Mg, and Co dopant impact on the properties of new ceramic pigments from the system Fe2O3·SiO2 obtained via classical ceramic technology. This approach enabled determination of the optimal temperature for the synthesis and the most appropriate mineralizer. The obtained specimens were submitted to systematical analysis, including X-ray Diffraction (XRD) spectroscopy, Electron Paramagnetic Resonance (EPR) analysis and Mössbauer spectroscopy for crystalline phase determination. The color characteristics are quantified by spectrophotometric measurements. The pigments particle size has been determined by Scanning Electron Microscopy (SEM), combined by Energy Dispersion X-ray spectroscopy (EDX). The obtained results enabled to determine the correlation between the calcination temperature and the phase compositions of the obtained pigments. In addition, some interesting magnetic properties were detected for the Co-doped composition