1,415 research outputs found
The influence of a Zr-based conversion treatment on interfacial bonding strength and stability of epoxy coated carbon steel
No full textThe effect of a zirconium (Zr)-based pretreatment on interfacial bonding properties of a fusion bonded epoxy (FBE) coating on carbon steel is investigated. The initiation and kinetics of delamination of epoxy coatings applied on differently pretreated carbon steel surfaces is studied with scanning Kelvin probe (SKP). In-situ attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) is applied to study interfacial coating-oxide chemistry changes upon electrolyte diffusion towards the buried interface. Corresponding coating degradation is analyzed with the use of electrochemical impedance spectroscopy (EIS). pull off experiments showed a clear beneficial effect of the Zr-based pretreatment improving the dry and wet adhesion properties of the fusion bonded epoxy coating to the carbon steel surface particularly upon exposure to wet and corrosive conditions. This increase in interfacial bonding stability is confirmed by the ATR-FTIR and EIS experiments and delayed and slower delamination was observed in the SKP measurements.Accepted Author Manuscript(OLD) MSE-6(OLD) MSE-
On the importance of irreversibility of corrosion inhibitors for active coating protection of AA2024-T3
No full textInhibitor leaching, fast, effective and irreversible passivation are essential for active protective coatings to protect aluminium alloys. This study presents the comparison of the active protective properties of lithium carbonate and two organic corrosion inhibitors, benzotriazole and 2-mercaptobenzothiazole, on aluminium alloy 2024-T3 with a special focus on the irreversibility of the inhibition. A combined approach of electrochemical measurements, optical observations, surface roughness and weight-loss measurements revealed the reversible inhibition behaviour of benzotriazole and 2-mercaptobenzothiazole on AA2024-T3. On the contrary, lithium carbonate demonstrated fast, effective and irreversible corrosion inhibition, providing the essential characteristics needed for effective active corrosion protection from coatings.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.(OLD) MSE-6(OLD) MSE-
In-situ interfacial approaches on chemisorption and stability of buried metal oxide-polymer interfaces
No full textUntil today, interfacial bond formation and degradation between polymer coatings and metal substrates is still far from fully understood, whilst it is a limiting factor for the durability of metal-polymer hybrid systems. To improve the corrosion resistance and adhesion properties of metal substrates, a chemical surface treatment is applied prior to painting. However, due to ecological and health related issues, traditional well established surface treatments containing hexavalent chromate or high phosphate loads are being replaced by a new generation of ecologically-justified surface treatments. This comes with the need of gaining fundamental insights on the impact of substrate and pretreatment variations on the (chemical) adhesion of polymers to guarantee the lifetime of newly developed metal-polymer hybrid systems. A challenge in this regard is the hardly accessible buried interface, which until today requires the use of model systems when using non-destructive surface sensitive techniques. Yet, industrial metal-polymer hybrid systems are typically highly heterogeneous, creating a distinct gap between model and industrial systems. This dissertation aims to close this gap starting from simplified model systems to which complexity is gradually added. This has been done using the thin organic film approach on one hand, and the thin (thermally vaporized) metal substrate approach on the other hand, allowing non-destructive access of the metal-polymer interface from the polymer side and metal side, respectively. Complementary use of both approaches allows systematically comparison of model systems to industrially relevant paint and metal substrates.(OLD) MSE-
Corrosion and Corrosion Inhibition Studies of Aerospace Aluminium Alloys at the Nanoscale using TEM Approaches
No full textFor many decades, corrosion and corrosion inhibition of high-strength aluminium alloys have been studied indirectly and through traditional and separately performed electrochemical, spectroscopic and microscopic techniques. These approaches employed to date commonly lack sufficient lateral and time resolution to unravel early-stage events which is controlled at the nanoscopic levels at which microstructural heterogeneities actually steer local and dynamic electrochemical activities. Besides, techniques with appropriate resolution like transmission electron microscopy (TEM) have been applied to the field, but carried out ex-situ, normally providing no detailed on-site time-resolved information to investigate distinctive-but-consecutive stages of corrosion and corrosion inhibition phenomena. That is why theories of relevance are established through bridging and linking separately-obtained information and therefore are described in rather stochastic than deterministic terms. This is particularly the case for the legacy alloy AA2024-T3 which is prone to complicated forms of local corrosion resulting from extremely complex and heterogeneous local microstructures.Local corrosion in AA2024-T3 is site-specific where complicated local degradation events predominantly take place at surface intermetallic particles (IMPs) dispersed in the alloy matrix and eventually lead to pitting and intergranular forms of corrosion. Thus, the detailed understanding of space- and time-resolved local corrosion mechanisms of engineered microstructures is of pivotal importance to developing reliable and active protection strategies. However, despite the high demand for time- and space-resolved mechanistic information of local corrosion, it has not yet been possible to unambiguously define the morphological and micro-electrochemical characteristics during local corrosion and corrosion inhibition owing to extremely demanding experimental challenges. Nevertheless, this thesis put efforts into carrying out dedicated TEM experimental approaches including in-situ liquid-phase, quasi in-situ and ex-situ TEM to provide time-resolved and direct nanoscopic evidence of local corrosion and corrosion inhibition processes from early surface initiation to an advanced stage of propagation. Team Yaiza Gonzalez Garci
Active corrosion protection of aerospace aluminium alloys by lithium-leaching coatings
No full textFor decades, scientists and engineers are searching for a safe and environmentally friendly alternative for the toxic chromate corrosion inhibitors in active protective coatings for the protection of aerospace aluminium alloys. In this search many different compounds have been investigated as leachable corrosion inhibitor, but no alternative with equal or better performance compared to chromates has been found yet. In 2010 it was discovered that organic coatings loaded with lithium-salts (Li) as leachable corrosion inhibitor provided very effective and promising corrosion inhibition on aluminium alloys when exposed to industrial accelerated corrosion tests. Initial investigations showed the formation of a corrosion protective layer on the aluminium alloy in a defect area, which appears to be a key feature of these Li-leaching coatings.(OLD) MSE-
Cr(VI)-free pre-treatments for adhesive bonding of aerospace aluminium alloys
No full textFor more than six decades, chromic acid anodizing (CAA) has been the central process in the surface pre-treatment of aluminium for adhesively bonded aircraft structures in Europe. Unfortunately, this electrolyte contains hexavalent chromium (Cr(VI)), a compound known for its toxicity and carcinogenic properties. The approaching ban on the use of hexavalent chromium (Cr(VI)) makes its elimination a high-priority R&D topic within the aerospace industry and the Cr(VI)-era will soon have to come to an end. Anodizing aluminium in acid electrolytes produces a self-ordered porous oxide layer with a thin barrier layer underneath. This special type of oxide readily adheres to the organic resin and provides protection against corrosion. Although Cr(VI)-free candidates such as sulphuric acid- (SAA), phosphoric acid- (PAA) and mixtures of phosphoric-sulphuric acid anodizing (PSA) can be used to create this type of structure, the excellent adhesion and corrosion resistance that is currently achieved by the Cr(VI)-based process is not easily matched. To gain a better understanding of the underlying physical and chemical mechanisms that contribute to the adhesion and durability in these structures, this study investigates the correlation between the oxide’s chemical and morphological characteristics, as influenced by the anodizing electrolyte, and bond performance. The major challenge in the mechanistic understanding of the adhesion in bonded components is to differentiate between the different forces acting at the oxide/resin interface. In the first part of this PhD thesis, studies focus on the role of surface chemistry. To exclude the contribution of mechanical interlocking between the oxide and the resin, featureless oxides were prepared by stopping the anodizing during the formation of the barrier layer. Surface characterization of the different anodic oxides by means of Fourier transform infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) revealed no significant net change in the acid-base properties of the different anodic oxides. It was found that local chemical changes were introduced due to the incorporation of electrolyte-driven anions. Therefore, a model was developed to quantify the relative amounts of O2-, OH−, PO4 3−, and SO4 2−, showing significant changes in the type and amount of surface species. Consequently, measurements showed that the pretreatments and the molecule type affected oxide/molecule interfacial interactions. To evaluate the contribution of adsorptive interaction in practice, peel tests were performed on featureless oxides bonded with commercial aerospace adhesives. Results showed that significant initial dry adhesion is achieved with FM 73 epoxy without mechanical interlocking, and independent of the type of pretreatment. However, the formed bonding was not water resistant, with the amount of applied stress needed for peeling linearly increasing with the amount of surface hydroxyls. Moreover, the application of a thin γ-APS silane layer before bonding with epoxy has confirmed that the stability of the interface is also determined by the nature of the bond, showing much more stable interfaces in the presence of covalent interactions. When peel tests were performed with a phenolic-based adhesive (Redux 775), no correlation to the surface chemistry was found. Nevertheless, the bonded joints on the basis of the weakly acidic character of the phenolic adhesive showed better resistance to corrosion in salt spray tests, compared to those on the basis of the epoxy adhesive. Therefore, we conclude that both oxide surface- and adhesive chemistries play a role in the formation and long-term stability of the oxide/resin interface. In the second part of this thesis industrial porous oxides were applied. Fundamental investigations show that changing the voltage during anodizing can produce morphological variations across the oxide thickness. The effect of the initial voltage sweeps, however, was limited by the oxide dissolution action of phosphoric acid in PSA, since prolonged anodizing in this electrolyte not only leads to an increase of the pore diameter, but also completely dissolves the upper most part of the oxide. Morphological changes were distinguished between geometrical modifications that affect the pore size and changes in the surface roughness that was caused by extended chemical dissolution at higher anodizing temperatures and/or phosphoric acid concentration. Measured carbon concentration profiles within the pores using high-resolution transmission electron microscopy (TEM) coupled with energy-dispersive X-ray spectroscopy (EDS) indicated that resin penetration is affected by both aspects. Moreover, mechanical performance in peel tests indicates that these parameters, rather than the oxide layer thickness are critical for moisture-resistant adhesion. Both adhesion mechanisms: adsorption and mechanical interlocking seem to contribute to the adhesion in these structural bonds. A higher degree of dissolution during anodizing is beneficial for the adhesion, facilitating a composite-like interphase. Too much dissolution, however, reduces the resistance to bondline corrosion. Overall, the presented results illustrate the need to consider both chemical and morphological changes in the selection of Cr(VI)-free alternatives for structural adhesive bonding
The Journey That Saved Curious George: The True Wartime Escape of Margret and H.A. Rey
No full textMany years ago, two Jewish artists from Germany met in Brazil, started a business, fell in love, and got married. The Brazilians could not pronounce their German names, so the couple shortened them to H.A. and Margret Rey. While honeymooning in Europe, the Reys decided to stay in Paris so H.A. could pursue a career as a children\u27s book author and illustrator. During this time, H.A. started developing stories about a curious little monkey, influenced by the many monkeys he saw in Brazil. But Hitler\u27s forces delayed H.A.\u27s plans for the little monkey until he and Margret could safely escape Europe
The importance of the time-effect in electrochemical studies of corrosion inhibitors
No full textThe corrosion protection of metallic substrates with corrosion inhibitors, either in solution or dispersed in a coating formulation, has been the focus of many research topics for many decades and has intensified in recent years even more with industry moving away from hexavalent chromium (Cr(VI))- based corrosion inhibitors. While mainly concentrating on the electrochemical behaviour and the underlying corrosion protective mechanism, the study of the time-effect, i.e. the study of how the electrochemical system behaves and the stabilization of the electrochemical system is altered over time, is often not taken into account when studying corrosion inhibitor-containing electrochemical systems. To gain a better understanding of the kinetic aspect of corrosion inhibitors changing the overall electrochemistry, this study focusses on the quantification of the time-effect of corrosion inhibitors’ electrochemical behaviour. Therefore odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected, a multisine alternative to the classical electrochemical impedance spectroscopy (EIS) technique, capable to measure and quantify the stability of electrochemical systems over time. Two different electrochemical systems are considered: lithium-based corrosion inhibitor technology on aluminium alloy AA2024-T3 and silica- and phosphate-based corrosion inhibitors for hot-dip galvanized steel. The former, already well-understood system, served as the proof of concept to design a well-defined methodology to study corrosion inhibitor-containing electrochemical systems, and gain deeper knowledge of the latter system.(OLD) MSE-
Out and All About: Fables for Old and Young
No full textThe title-page is missing in this book, and the only reference on the web is to a reprint of a book before 1923. At least this reference gives us an author. “Routledge” appears on the spine. I read only the first fable, “The Spider and the Ants,” which lasted some 20 pages and seemed to me to lose some of its focus along the way. The book is generously illustrated with partial-page black-and-white illustrations of various sizes along the way. As the beginning T of C shows, there are here some 31 fables on 256 pages before 18 pages of advertisements. Pretty cover and spine, including gold and black on red cloth.H.A. Pag
A Complementary Electrochemical Approach for Time-Resolved Evaluation of Corrosion Inhibitor Performance
No full textIn this paper, different macroscopic electrochemical techniques are applied to study the corrosion inhibitor efficiency, protection mechanism and stability of a calcium aluminum polyphosphate silicate hydrate inhibitor on hot-dip galvanized steel in the time-domain. Potentiodynamic polarization (PP) measurements are applied to study the anodic and cathodic mechanistic behavior as well as inhibitor efficiencies at discrete and single times of exposure. Open circuit potential (OCP) with superimposed linear polarization resistance (LPR) measurements are applied as a faster, non-invasive alternative to PP, characterizing the overall performance of the system in terms of the polarization resistance. Electrochemical impedance spectroscopy (EIS) measurements are applied to detail both the overall performance of the system as well as the corrosion inhibition mechanism related to the electrochemical system’s physicochemical representation over time. Electrochemical noise (EN) measurement are used to evaluate the inhibition efficiency as a function of exposure time, represented by the electrochemical noise resistance. Odd random phase electrochemical impedance spectroscopy (ORP-EIS) is selected as the electrochemical tool to study the system’s instability, by evaluation of the non-linearities and non-stationarities over time. The non-stationarities present in the inhibitor-containing electrochemical system are shown to cause the overall instability of the system and should be taken into account when interpreting results from the different techniques over time
- …
