Transport of Electrolyte in Organic Coatings on Metal

Organic coatings form an effective barrier between metals and their environment, providing them protection against corrosion. Corrosion on coated metals depends mainly on the diffusion of water through the coating, the loss of adhesion at the interface between the coating and the metal (delamination), the rate of the chemical and electrochemical reactions under the coating and the treatment of the metal surface before the coating application. Many aggressive ions are transported toward and inside the coating through water. In organic coatings, typically, the water absorbed by the coating affects the polymer matrix structure, and it causes swelling and stresses, which may result in cracks. Swelling and cracks enhance the transport of water into the solid polymer, and concurrently the diffusion of ions. Over time also, the chemical structure of the polymer may change, adversely affecting its barrier properties and overall performance. In this chapter, we focus on methods to quantify the transport of electrolyte in organic coatings. We mark out the main characteristics, advantages and limitations of each one of them

Patterning of graphene on silicon-on-insulator waveguides through laser ablation and plasma etching

We present the use of femtosecond laser ablation for the removal of monolayer graphene from silicon-on-insulator (SOI) waveguides, and the use of oxygen plasma etching through a metal mask to peel off graphene from the grating couplers attached to the waveguides. Through Raman spectroscopy and atomic force microscopy, we show that the removal of graphene is successful with minimal damage to the underlying SOI waveguides. Finally, we employ both removal techniques to measure the contribution of graphene to the loss of grating-coupled graphene-covered SOI waveguides using the cut-back method. This loss contribution is measured to be 0.132 dB/μm

An In-Situ EC-STM Study and DFT Modeling of the Adsorption of Glycerol on Cu(111) in NaOH Solution

International audienceOrganic coatings are often required for the protection of metals against environmental degradation. Despite their extensive use, only limited information is available on the initial stages of adsorption and formation of protective films, especially at the molecular and atomic level. As a model system for coating formation, this study investigates the adsorption of glycerol molecules on the single-crystalline Cu(111) surface. A combined electrochemical and scanning tunneling microscopy (EC-STM) study in NaOH aqueous solution enabled following the adsorption process in detail, providing molecular information on the glycerol film structure. A potential-driven adsorption of glycerol was observed, suppressing the adsorption of hydroxyl molecules and copper oxidation. The adsorbed species assembled in a nearest neighbor arrangement fitting a (√3 × √3) R30° hexagonal structure with respect to the Cu(111) lattice. This experimentally observed configuration was confirmed by density functional theory (DFT) calculations. DFT modeling indicates that a mixed adsorption mode involving the two primary alcohol groups adsorbed at different z-positions relative to the surface is the most favorable. This mixed configuration enabled the formation of an extended network of hydrogen bonds that aids to stabilize the glycerol film. This implies that interactions between glycerol molecules play a non-negligible effect in the growth process of such an organic film, allowing the formation of organic layers in the absence of strong interfacial interactions

Development of an electrochemical procedure for monitoring hydrogen sorption/desorption in steel

Hydrogen embrittlement leads to mechanical degradation of metals. Hence, hydrogen sorption/desorption properties of metals need to be characterized. An electrochemical procedure based on cyclic voltammetry (CV) and potentiostatic polarization is elaborated on plain-carbon steel. The procedure consists of first two consecutive CV cycles (pretreatment and reference CV), followed by cathodic H-charging, and subsequent CV scans to study and quantify the H-sorption/desorption. Best practice in this procedure is to perform all steps consecutively without interruption or sample manipulations between steps to avoid spontaneous H-loss. The H-related interaction with the steel is clearly identified in the CV and can be differentiated from the electrolyte contribution coming from thiourea. The study confirms the role of thiourea as H-recombination poison in alkaline solution, and also demonstrates that it contributes to the CV response. Additionally, various charging times are investigated to study the time to H-saturation, and also the scan rate during the CV procedure is varied to study time-related phenomena. Dedicated discharging experiments were included in the study to complement the CV data, giving additional insights in the H-steel interaction. Moreover, hydrogen related findings are successfully verified by using a complimentary method, i.e. hot extraction. The better understanding of the peaks in the CV and the continuous procedure result in a reliable methodology to characterize the H-sorption/desorption in steel

Effect of hydrogen peroxide on bovine serum albumin adsorption on Ti6Al4V alloy: A scanning Kelvin probe force microscopy study

Abstract Protein adsorption on the surface of implant materials greatly affects the performance of the implants, such as their stability as well as the release of metal ions from and the adhesion of cells to their surface. In addition, the production of extracellular H2O2 from the activation of inflammatory cells could interfere with protein–metal interactions and/or modify the conformation of adsorbed proteins. In this study, we utilised scanning Kelvin probe force microscopy (SKPFM) to visualise the impact of H2O2 on bovine serum albumin (BSA) adsorption on the positively polarised Ti6Al4V alloy in a phosphate-buffered saline (PBS) solution. We show that the negatively charged BSA adsorbs onto the surface of polished and anodically polarised Ti6Al4V in a dense layer with a continuous network-like morphology or cluster shape and reduces the variation in the total surface potential compared to that of blank Ti6Al4V. However, addition of H2O2 to the PBS solution interferes with the formation of the dense protein network, and only a thin and discontinuous protein layer adsorbs onto the surface of the Ti6Al4V alloy, lowering the total surface potential difference. The information presented in this work provides new insights into the adsorption distribution of proteins on metallic substrates in biomaterials field

The Role of Cu-Based Intermetallic on the Direct Growth of a ZnAl LDH Film on AA2024

The direct ZnAl layered double hydroxide growth on AA2024 is a fast-occurring reaction, yet is characterized by an inhomogeneous film thickness. It has been shown that at the periphery of Cu-rich intermetallic, the flakes tend to be larger and denser. A combination of in situ and ex situ measurements were used to monitor the changes in the layered double hydroxide film grown on the regions of intermetallics. Immediately after immersion, an activation of the intermetallic phases is observed due to the dealloying process with an almost immediate film growth. Dealloying is followed by trenching of the adjacent Al matrix leading to an excessive production of large and dense layered double hydroxide flakes at the periphery of the intermetallic. However, the scanning electron microscopy cross-section images revealed that the trenching process leads to defects in the area surrounding the intermetallic. This could weaken the corrosion resistance performance of the layered double hydroxide conversion coating and lead to adhesion failure of consecutive polymer coatings. Nevertheless, this work highlights a few advantages and drawbacks of the layered double hydroxide conversion coatings and pathways to its potential optimization and improvement

Corrosion protection of Cu by atomic layer deposition

Atomic layer deposition (ALD) is a vapor phase technique that is able to deposit uniform, conformal thin films with an excellent thickness control at the atomic scale. 18 nm thick Al2O3 and TiO2 coatings were deposited conformaly and pinhole-free onto micrometer-sized Cu powder, using trimethylaluminum and tetrakis(dimethylamido)titanium(IV), respectively, as a precursor and de-ionized water as a reactant. The capability of the ALD coating to protect the Cu powder against corrosion was investigated. Therefore, the stability of the coatings was studied in solutions with different pH in the range of 0-14, and in situ raman spectroscopy was used to detect the emergence of corrosion products of Cu as an indication that the protective coating starts to fail. Both ALD coatings provide good protection at standard pH values in the range of 5-7. In general, the TiO2 coating shows a better barrier protection against corrosion than the Al2O3 coating. However, for the most extreme pH conditions, pH 0 and pH 14, the TiO2 coating starts also to degrade. Published by the AVS