Genesis of Nanogalvanic Corrosion Revealed in Pearlitic Steel.

Nanoscale, localized corrosion underpins billions of dollars in damage and material costs each year; however, the processes responsible have remained elusive due to the complexity of studying degradative material behavior at nanoscale liquid-solid interfaces. Recent improvements to liquid cell scanning/transmission electron microscopy and associated techniques enable this first look at the nanogalvanic corrosion processes underlying this widespread damage. Nanogalvanic corrosion is observed to initiate at the near-surface ferrite/cementite phase interfaces that typify carbon steel. In minutes, the corrosion front delves deeper into the material, claiming a thin layer of ferrite around all exposed phase boundaries before progressing laterally, converting the ferrite to corrosion product normal to each buried cementite grain. Over the following few minutes, the corrosion product that lines each cementite grain undergoes a volumetric expansion, creating a lateral wedging force that mechanically ejects the cementite grains from their grooves and leaves behind percolation channels into the steel substructure.

Tuning the Potential Energy Landscape to Suppress Ostwald Ripening in Surface-Supported Catalyst Systems.

Rational control of nanoparticle (NP) size distribution during operation is crucial to improve catalytic performance and noble metal sustainability. Herein, we explore the Ostwald ripening (OR) of metal atoms on zeolite surfaces by a coupled theoretical-experimental approach. Zeolites with the same structure (ZSM-5) but different concentrations of aluminum doped into the matrix were observed to yield systematic differences in supported nanoparticle size distributions. Our first-principles simulations suggest that NP stability at high temperature is governed by both geometric constraints and the roughness of the energetic landscape. Calculated adatom migration paths across the zeolite surface and desorption paths from the supported NPs lend insight into the modified OR sintering processes with the emergence of different binding configurations as the aluminum concentration increases from pristine to heavily doped ZSM-5. These findings reveal the potential for the rational design of support structures to suppress OR sintering.

Exo-selective, Reductive Heck Derived Polynorbornenes with Enhanced Molecular Weights, Yields, and Hydrocarbon Gas Transport Properties.

Next-generation membranes use highly engineered polymeric structures with enhanced chain rigidity, yet difficulties in polymerization often limit molecular weights required for film formation. Addition-type polynorbornenes are promising materials for industrial gas separations, but suffer from these limitations owing to endo-exo monomeric mixtures that restrict polymerization sites. In this work, a synthetic approach employing the reductive Mizoroki-Heck reaction resulted in exo-selective products that polymerized up to >99% yields for ROMP and addition-type polymers, achieving molecular weights an order of magnitude higher than addition-type polymers from endo-exo mixtures and impressive side group stereoregularity. Due to this increased macromolecular control, these polynorbornenes demonstrate unique solubility-selective permeation with mixed gas selectivities that exceed commercially used PDMS. In addition to thermal and structural characterization, XRD and computational studies confirmed the results of pure and mixed-gas transport testing, which show highly rigid membranes with favorably disrupted chain packing.