Localized corrosion in selective laser melted SS316L in CO2 and H2S brines at elevated temperatures.

In this work, the passivation and localized corrosion of selective laser melted (SLM) stainless steel 316 L when exposed to high pressures of CO2 with the presence of H2S and Cl- at 25 °C and 125 °C were studied. Depletion of Cr/Mo was observed at the cell interiors and melt-pool boundaries (MPBs) compared to the cell boundaries. Volta potential differences obtained from scanning Kelvin probe force microscopy (SKPFM) showed that the MPBs were 8-20 mV lower than the matrix, while the cell interiors were 20-50 mV lower than the cell boundaries. Electrochemical impedance spectroscopy (EIS) and Mott-Schottky tests indicated a more defective passive film at 125 °C, and X-ray photoelectron spectroscopy (XPS) confirmed the formation of a less protective film with an increased S/O ratio at 125 °C than 25 °C. Initiation of localized corrosion was observed at the MPBs and pits formed after a week of immersion were wider by an order of magnitude at 125 °C than 25 °C, with evidence of cell-interior dissolution. While passivity was observed even at elevated temperatures, local chemical heterogeneities compromised the stability of the film and contributed to localized corrosion in SLM SS316L.

ZrO2/ZnO/TiO2 Nanocomposite Coatings on Stainless Steel for Improved Corrosion Resistance, Biocompatibility, and Antimicrobial Activity.

The ultrathin nanocomposite coatings made of zirconium oxide (ZrO2), zinc oxide (ZnO), and titanium oxide (TiO2) on stainless steel (SS) were prepared by the radio frequency sputtering method, and the effects of the nanocomposite coating on corrosion protection and antibacterial activities of nanocomposite coated SS were investigated. Scanning electron microscopy was conducted to observe surface morphology of nanocomposite coatings with distinct distribution of grains with the formation on SS substrate. From the electrochemical impedance spectroscopy results, ZrO2/ZnO/TiO2 nanocomposite coating showed excellent corrosion protection performance at 37 °C during immersion in simulated body fluid and saliva solution for 12 and 4 weeks, respectively. The impedance of ZrO2/ZnO/TiO2 (40/10/50) nanocomposite coated SS exhibited values about 5 orders of magnitude higher than that of uncoated SS with polarization at the low-frequency region. Cell viability of ZrO2/ZnO/TiO2 nanocomposite coated SS was examined under mouse fibroblasts culture (L929), and it was observed that the nanocomposite coating improves proliferation through effective cellular attachment compared to uncoated SS. From the antimicrobial activity results, ZrO2/ZnO/TiO2 nanocomposite-coated SS showed killing efficiency of 81.2% and 72.4% against Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus, respectively.

Smart Coating Embedded with pH-Responsive Nanocapsules Containing a Corrosion Inhibiting Agent.

Triethanolamine (TEA), an amine-based corrosion inhibitor, was encapsulated and then embedded into an epoxy coating to provide long-term corrosion protection of aluminum alloy 3003. TEA was encapsulated by means of free-radical polymerization, yielding an average particle size of 450 nm. An applied epoxy coating containing 10 wt % of the nanocapsules successfully protected an artificially defective area for a long period due to TEA adsorption, which resulted in the formation of an inhibiting layer. Electrochemical impedance spectroscopy showed an inhibition efficiency surpassing 85% when the metal experienced mild corrosion in its early stages, and the inhibiting layer started to form by local pH level change, which triggered the release of TEA. On the basis of the results of a scanning vibrating electrode technique, the current density of the metal surface in the presence of an encapsulated TEA coating was significantly lower than that of the control coating with no nanocapsules. Optical microscope and scanning electron microscope images revealed that the sample surface that had encapsulated TEA nearby was considerably less stained after 60 days of testing compared with that of the control sample, which indicated that the metal substrate was protected by an inhibiting layer. Elemental analysis performed by energy-dispersive X-ray spectroscopy further confirmed that the metal surface was well preserved, and a remarkably low oxygen content indicated suppressed metal oxidation. The nuclear magnetic resonance spectra also evidenced a successful release of TEA throughout the experimental period. These findings reflected a spontaneous surface repassivation with the help of encapsulated TEA coating.

Antimicrobial Activities of Thermoplastic Polyurethane/Clay Nanocomposites against Pathogenic Bacteria.

As a thermoplastic polymer with an impressive combination of mechanical properties and biological compatibility, thermoplastic polyurethane (TPU) is one of the important polymers used in various applications such as biomaterials, conducting materials, and tissue engineering. Nanocomposites made of TPUs with nanoclays were prepared by melt-compounding, and the effects of clay on antibacterial activities and physical properties of nanocomposites were investigated. X-ray powder diffraction, water contact angle, and TEM results were analyzed to investigate the effects of dispersion and modification of clays in TPU/clay nanocomposites. Using the pour plating method, scanning electron microscopy technique, and disk diffusion test, TPU/clay nanocomposites were observed to show contact killing activity against bacteria. The antibacterial activities of TPU/clay nanocomposites were found to be affected by the dispersion state and amount of organic modifier of clays. TPU nanocomposites containing 5 wt % organically modified clay showed 98.5% killing efficiency against Gram-negative Escherichia coli and 99.9% against Gram-positive Staphylococcus aureus, while neat TPU showed almost none. The positively charged quaternary ammonium salt groups of clay in TPU/clay nanocomposites interacted with the negatively charged cytoplasmic membrane of bacteria, and the dead bacteria were eliminated by weakened adhesion on hydrophobic backbone surfaces.

Integrated zwitterionic conjugated poly(carboxybetaine thiophene) as a new biomaterial platform.

An integrated zwitterionic conjugated polymer-based biomaterial platform was designed and studied to address some of the key challenges of conjugated polymers in biomedical applications. This biomaterial platform consists of conjugated polymer backbones and multifunctional zwitterionic side chains. Zwitterionic materials gain electrical conductivity and interesting optical properties through conjugated polymer backbones, and non-biocompatible conjugated polymers obtain excellent antifouling properties, enhanced electrical conductivity, functional groups of bioconjugation and response to environmental stimuli via multifunctional zwitterionic side chains. This platform can potentially be adapted to a wide range of applications (e.g. bioelectronics, tissue engineering and biofuel cell), which require high performance conducting materials with excellent antifouling/biocompatibility at biointerfaces.

Electrochemical impedance study of GaAs surface charge modulation through the deprotonation of carboxylic acid monolayers.

Modifications to the space charge region of p+ and p-GaAs due to surface charge modulation by the pH-induced deprotonation of bound carboxylic acid terminal monolayers were studied by electrochemical impedance spectroscopy and correlated to flat-band potential measurements from Mott-Schottky plots. We infer that the negative surface dipole formed on GaAs due to monolayer deprotonation causes an enhancement of the downward interfacial band bending. The space charge layer modifications were correlated to intermolecular electrostatic interactions and semiconductor depletion characteristics.