Surface analysis of environmentally exposed painted composites manufactured from Quickstep and autoclave processes

The surface finishes of laminates produced by Quickstep&trade; and autoclave processes for use in automotive outer skin panels were compared. Automotive quality, painted carbon fibre samples, manufactured via both processes, were exposed to typical exposure environments including combinations of temperature (70, 120, 170&deg;C), UV-B, humidity (95% RH) and immersion in water.The microscopy and surface roughness results demonstrated that the surfaces produced by the Quickstep process were less susceptible to damage in the aging environments than the surfaces of the autoclaved samples. Quickstep samples displayed surface bubbling of only 5 &mu;m, compared to the autoclaved surface bubbles which reached a diameter of 30 mm before bursting, with complete delamination occurring between the paint and the composite. The surface roughness measurements revealed the autoclave samples (Ra = 0.72 &mu;m) were up to three times the roughness of the Quickstep samples (Ra = 0.23 &mu;m).<br /

Dual function of rare earth carboxylate compounds on the barrier properties and active corrosion inhibition of epoxy coatings on mild steel

In this work, two rare earth carboxylate compounds, lanthanum 4-hydroxycinnamate (La(4-OHcin)3) and yttrium 3-(4-methylbenzoyl)propanoate (Y(mbp)3), were incorporated into bisphenol-based epoxy resin to investigate their effectiveness in coating barrier properties and active corrosion inhibition. EIS results showed that the incorporation of rare earth carboxylate inhibitors significantly improved corrosion resistance compared to the inhibitor free coating, with the global impedance modulus remaining at a level higher than 1 GΩ cm2 after 219 days immersion. Following EIS experiments, cross-sectional views of the coatings exhibited a pore-plugging behavior by rare earth containing precipitates, which reinforced the coating barrier properties and delayed the electrolyte diffusion process. These effects were also reflected from the electrochemical parameters extracted from breakpoint frequency analysis and equivalent circuit modelling. Filiform corrosion experiments for artificially scratched coatings suggest that the addition of rare earth carboxylates effectively suppressed the initiation and growth of filaments as well as the development of the coating delamination front. The active corrosion inhibition is possibly related to the formation of a surface protective film consisting of bimetallic complexes and rare earth metal rich precipitates. The electrochemical measurements and surface analyses evidence the dual function of rare earth carboxylate species for enhancing coating barrier properties against electrolyte penetration and providing active corrosion inhibition for the underlying AS1020 mild steel

Leaching behavior and corrosion inhibition of a rare earth carboxylate incorporated epoxy coating system

While paint coatings act as important barriers to corrosion, defects can lead to localized, rapid metal loss. The addition of corrosion inhibitors that are capable of leaching from a coating to protect the metal surface at a defect can prevent this type of corrosion. This work investigates the release and corrosion protection capabilities of two rare earth (RE) carboxylate inhibitors from an epoxy coating as an initial step to understanding their leaching behavior and interaction with the coating system. Leaching experiments were performed via inductively coupled plasma mass spectroscopy (ICP-MS) analyses of the solutions in which free-standing coatings loaded with varying concentrations of inhibitor compounds had been immersed. Inhibitor release from the epoxy coating was observed to be dependent on initial inhibitor concentration, inhibitor chemistry, and solution pH conditions. The coating systems with greater initial inhibitor loadings showed higher leaching rates, particularly in acidic environments. Following immersion, the absence of characteristic inhibitor peaks in the FTIR spectra of the coatings also confirmed leaching had taken place. Cross-sectional views of the coatings after exposure to the pH 1 environment presented a chloride infusion zone at the coating/solution interface where the inhibitor had leached out. The RE active inhibition provided by the leached RE carboxylate inhibitors was verified by exposure of a coating defect to a chloride contaminated environment

A study of rare-earth 3-(4-methylbenzoyl)-propanoate compounds as corrosion inhibitors for AS1020 mild steel in NaCl solutions

In this work two novel rare-earth (RE) 3-(4-methylbenzoyl)-propanoate (mbp) complexes (RE(mbp)₃; RE = La, Y) have been investigated and compared with the well-researched inhibitor, lanthanum 4-hydroxycinnamate (La (4-OHcin)₃), for AS1020 mild steel in 0.01 M NaCl solutions. The electrochemical results reveal a high corrosion inhibition performance of Y(mbp)₃ which is attributed to the build-up of a protective surface film with a high level of corrosion resistance particularly after 24 h. Surface analyses indicate that the metal surface is protected during the immersion in Y(mbp)₃-inhibited solutions and the presence of Y is confirmed on the substrate surface

Aqueous Molecular Sieving and Strong Gas Adsorption in Highly Porous MOFs with a Facile Synthesis

Aqueous molecular sieving is demonstrated in a new series of isostructural metal organic frameworks based on the perylene tetracarboxylate (PTC) ligand. The frameworks can be formed in water at room temperature with Mg, Ni, and other first row transition metal ions and adopt a highly porous topology that results in predicted surface areas of over 2000 m² g^–1 and periodic channels of around 6 Å in diameter. Unusually, the M-PTC MOFs are highly resistant to moisture and can be readily synthesized on multigram scales. The frameworks have been shown to exhibit molecular sieving in the absorption from mixtures of organic molecules at low aqueous concentrations, with an application demonstrated on a dangerous water-borne herbicide, Paraquat. Ni-PTC also exhibits a structural flexibility that leads to strong and selective gas adsorption characteristics, with an IAST selectivity of 300 for carbon dioxide being adsorbed over nitrogen. Binding enthalpies for hydrogen and carbon dioxide are also very strong in comparison to other MOFs, at 10.75 and 52.50 kJ/mol respectively

Aqueous Molecular Sieving and Strong Gas Adsorption in Highly Porous MOFs with a Facile Synthesis

Aqueous molecular sieving is demonstrated in a new series of isostructural metal organic frameworks based on the perylene tetracarboxylate (PTC) ligand. The frameworks can be formed in water at room temperature with Mg, Ni, and other first row transition metal ions and adopt a highly porous topology that results in predicted surface areas of over 2000 m² g^–1 and periodic channels of around 6 Å in diameter. Unusually, the M-PTC MOFs are highly resistant to moisture and can be readily synthesized on multigram scales. The frameworks have been shown to exhibit molecular sieving in the absorption from mixtures of organic molecules at low aqueous concentrations, with an application demonstrated on a dangerous water-borne herbicide, Paraquat. Ni-PTC also exhibits a structural flexibility that leads to strong and selective gas adsorption characteristics, with an IAST selectivity of 300 for carbon dioxide being adsorbed over nitrogen. Binding enthalpies for hydrogen and carbon dioxide are also very strong in comparison to other MOFs, at 10.75 and 52.50 kJ/mol respectively

Tailoring the Chain Packing in Ultrathin Polyelectrolyte Films Formed by Sequential Adsorption: Nanoscale Probing by Positron Annihilation Spectroscopy

Depth profiling experiments by positron annihilation spectroscopy have been used to investigate the free volume element size and concentration in films assembled using the layer-by-layer (LbL) adsorption method. Films prepared from strong polyelectrolytes, weak polyelectrolytes, hydrogen-bonding polymers, and blended polyelectrolyte multilayers have different chain packing that is reflected in the free volume characteristics. The influence of various parameters on free volume, such as number of bilayers, salt concentration, solution pH, and molecular weight, has been systematically studied. The free volume cavity diameters vary from 4 to 6 Å, and the free volume concentrations vary from (1.1–4.3) × 10²⁰ cm^–3, depending on the choice of assembly polymers and conditions. Films assembled from strong polyelectrolytes have fewer free volume cavities with a larger average size than films prepared from weak polyelectrolytes. Blending the weak polyanion poly­(acrylic acid), PAA, with the strong polyanion poly­(styrene sulfonate), PSS, to layer alternately with the polycation poly­(allyamine hydrochloride), PAH, is shown to be a viable method to achieve intermediate free volume characteristics in these LbL films. An increase in salt concentration of the adsorption solutions for films prepared from strong polyelectrolytes makes these films tend toward weaker polyelectrolyte free volume characteristics. Hydrogen-bonded layered films show larger free volume element size and concentration than do their electrostatically bonded counterparts, while reducing the molecular weight of these hydrogen-bonded polymers results in slightly reduced free volume size and concentration. A study of the effect of solution pH on films prepared from weak polyelectrolytes shows that when both polyelectrolytes are substantially charged in solution (assembly pH = 7.5), the chains pack similarly to strong polyelectrolytes (i.e., lower free volume concentration), but with smaller average cavity sizes. These results give, for the first time, a clear indication of how the free volume profile develops in LbL thin films, offering numerous methods to tailor the Ångström-scale free volume properties by judicious selection of the assembly polymers and conditions. These findings can be potentially exploited to tailor the properties of thin polymer films for applications spanning membranes, sensing, and drug delivery