Electrochemical impedance spectroscopy investigations of epoxy zinc rich coatings: Role of Zn content on corrosion protection mechanism

Effect of zinc content in the epoxy zinc rich coating on the mechanism of corrosion protection was investigated using electrochemical impedance spectroscopy (EIS). The zinc content in the coating (on dry film) was varied from 40% to 90% in steps of 10%. Open circuit potential (OCP) measurements and salt spray tests were also carried out to generate supporting evidences and to deepen the understanding in the area of zinc rich coatings. The healing or bridging ability of these coatings was studied by making a scribe on the coating and monitoring the evolution of OCP. EIS was also utilized to screen the amount of zinc particles required to provide efficient galvanic protection and to study the effect of purity of Zn on corrosion protection performance. Both EIS and OCP measurements indicate that coatings containing 40% Zn (on dry film) provides very good barrier protection coming mainly from polymer whereas the one containing >80% Zn provides excellent galvanic protection to the steel substrate. When the zinc loading is between 60% and 70%, coatings neither show barrier protection nor galvanic protection.     

High barrier sustainable co-polymerized coatings

The goal of this project was to determine the most promising co-polymerized (COP) coating for paperboard for protection against gas and water vapor transmission. The driving force for this was to create a coating that will significantly slow the permeation of water and water vapor through the paperboard, while retaining its mechanical properties. This was accomplished by creating high barrier co-polymerized coatings. This study focuses on the use of modified high shape factor engineered (HSFE) clays. In this study, acrylic co-monomers have been polymerized in the presence of three different, finely dispersed HSFE clays, to prepare the co-polymerized coatings. The wet coating structure was studied using Brookfield and Hercules Hi-Shear viscometers, water retention, and dispersion stability. The dry coating structure was studied using WYKO White Light Interferometry and burn out tests. The cylindrical laboratory coater (CLC)-coated samples were then tested for gas and water vapor permeability. Additionally, the optical and surface properties were determined. The CLC-coated board samples showed almost zero gas permeability and a significant reduction in water vapor transmission rate (water vapor permeability). The water vapor permeability was reduced up to 90% reflecting a one order of magnitude decrease in comparison to a commercially coated sample. The co-polymerized coating with high shape factor and thinner platelet clay displayed the lowest water vapor permeability and the best optical and surface properties, thereby making it the most promising barrier coating for solid bleached sulfate paperboard.     

Long time stress relaxation of amorphous networks under uniaxial tension: The Dynamic Constrained Junction Model

The constrained junction model that represents the stress-strain relations of amorphous networks in equilibrium is modified to analyze stress relaxation. Deviation of stress from equilibrium when a network is stretched suddenly is represented by a time dependent constraint contribution that is of the same form as that of the equilibrium theory. The time dependent motions of the junctions are assumed to obey the Langevin equation. The only new term in the model is a time dependent κ parameter that vanishes at long times. Results of the model are compared with uniaxial stress relaxation experiments on polyisoprene networks with different degrees of cross-linking. Experiments show that the time dependent κ parameter obeys a stretched exponential form, with β = 0.4 and τ = 40 s, both of which are the same for all extensions and cross-link densities studied. The front factor κ₀ depends on cross-link density in the same way as in the equilibrium case. Comparison with stress relaxation experiments shows satisfactory agreement at a wide range of extensions and for different degrees of cross-linking. The relatively low value of the stretched exponent parameter, β = 0.4, is interpreted in terms of a molecular picture where entanglements contribute to relaxation at a wide spectrum of time scales.     

Structural study of electrochemically synthesized TiO2 nanotubes via cross-sectional and high-resolution TEM

The as-grown structure of electrochemically synthesized titania nanotubes is investigated by a combination of cross-sectional and high-resolution transmission electron microscopy (TEM). The analysis reveals a preferred growth direction of the nanotubes relative to the substrate surface and the presence of a thin barrier oxide layer that exists between the metal substrate and the nanotubes. High-resolution TEM images also provide information about the morphology of the metal/oxide and oxide/nanotube interfaces, and the crystallinity of the different layers. In addition, compositional analysis performed via energy dispersive X-ray spectroscopy (EDS) indicates that there are differences in oxygen and titanium concentrations between nanotubes and barrier oxide. The experimental observations obtained from these analysis techniques provide additional insights about the tube formation process.     

纳米材料TiO2在汽车面漆中的应用研究探讨

分析了纳米材料对汽车面漆涂料性能的影响机理,提出了利用纳米材料TiO2提高汽车面漆涂料耐老化性能的设想.对于金红石型纳米TiO2,屏蔽紫外线的最佳粒径为65～130nm.制订了纳米涂料的研制方案,关键是解决纳米材料在涂料中的分散和稳定问题.     

Study of the correlation between corrosion resistance and semi‐conducting properties of the passive film of AISI 316L stainless steel in physiological solution

In this work the corrosion resistance of AISI 316L biomedical stainless steel was assessed through electrochemical impedance spectroscopy (EIS) measurements in Hanks' solution at 37 °C. Specimens were immersed in the electrolyte during 21 days. Semi‐conducting properties of the passive film naturally formed on the surface of the metallic material during the test were evaluated through the Mott–Schottky approach. The aim was to investigate the correlation between corrosion resistance and semi‐conducting properties in the physiological solution. The corrosion resistance was found to decrease with the immersion time. The density of defects in the passive film increased accordingly as indicated by the Mott–Schottky plots. The passive film presented a semi‐conducting behavior with a duplex character. Above the flat band potential the behavior was typical of an n‐type semiconductor whilst below such value it was typical of a p‐type semiconductor. The results from EIS measurements and Mott–Schottky were in good agreement, suggesting that the corrosion resistance of biomedical stainless steels may be associated with the semi‐conducting properties of the passive films formed during immersion in physiological medium.     

Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective

Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100?C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed.     

Fast anodization fabrication of AAO and barrier perforation process on ITO glass

Thin films of porous anodic aluminum oxide (AAO) on tin-doped indium oxide (ITO) substrates were fabricated through evaporation of a 1,000- to 2,000-nm-thick Al, followed by anodization with different durations, electrolytes, and pore widening. A faster method to obtain AAO on ITO substrates has been developed, which with 2.5 vol.% phosphoric acid at a voltage of 195 V at 269 K. It was found that the height of AAO films increased initially and then decreased with the increase of the anodizing time. Especially, the barrier layers can be removed by extending the anodizing duration, which is very useful for obtaining perforation AAO and will broaden the application of AAO on ITO substrates.