Substrate protection with corrosion scales : can we depend on iron carbonate?

Controlling corrosion with naturally occurring corrosion scales is potentially a more environmentally sustainable alternative to current approaches, including dosing of organic corrosion inhibitors. We report operando grazing incidence X-ray diffractograms correlated with electrochemical measurements to elucidate the growth and corrosion protection properties of a corrosion scale composed of FeCO3 crystallites, which is encountered in various key energy industry applications. Data, acquired as a function of time from high-purity iron immersed in CO2-saturated deionized H2O at pH 6.8 and T = 80 °C, show that the FeCO3 scale not only prevents corrosion of the covered substrate but also acts as a significant interfacial diffusion barrier for corrosion reagents and/or products once sufficient coverage is achieved. Most notably, from a corrosion engineering perspective, however, it is determined that corrosion occurring in gaps between scale crystallites remains appreciable; this important insight is gained through the analysis of electrochemical impedance spectra to estimate the variation in electrochemically active surface area as scale coverage increases. These results indicate that naturally occurring FeCO3 scales are not a tenable solution for corrosion protection, as even in their intact state they are highly likely to be, at best, semiprotective

Risk of failing both methotrexate and mycophenolate mofetil from the First-line Antimetabolites as Steroid-sparing Treatment (FAST) uveitis trial.

BackgroundThe antimetabolites methotrexate (MTX) and mycophenolate mofetil (MMF) are commonly used as initial corticosteroid-sparing treatment for uveitis. There is little data examining risk factors for failing both MTX and MMF. The objective of this study is to determine risk factors for failing both MTX and MMF in patients with non-infectious uveitis.Main bodyThis is a sub-analysis of the First-line Antimetabolites as Steroid-sparing Treatment (FAST) uveitis trial, which was an international, multicenter, block-randomized, observer-masked, comparative effectiveness trial comparing MTX and MMF as initial treatments for non-infectious uveitis. This study was undertaken at multiple referral centers in India, the United States, Australia, Saudi Arabia and Mexico between 2013 and 2017. A total of 137 patients who completed all 12 months of follow-up from the FAST trial, were included in this study. The primary outcome was failing both antimetabolites over the 12 months of the trial. Potential predictors included: age, sex, bilateral involvement, anatomic location of the uveitis, presence of cystoid macular edema (CME) and retinal vasculitis at baseline visit, uveitis duration, and country/study sites as risk factors for failing both MTX and MMF. The presence of retinal vasculitis posterior to the equator on fluorescein angiogram was associated with failing both MTX and MMF.ConclusionRetinal vasculitis may be a risk factor for failing multiple antimetabolites. Clinicians could consider more quickly advancing these patients to other medication classes, such as biologics