Gillian M. Bond

Matrix molecular weight cut-off for encapsulation of carbonic anhydrase in polyelectrolyte beads.

The enzyme bovine carbonic anhydrase (BCA) has been immobilized in the chitosan-alginate system for the first time, to catalyze the conversion of CO2 to HCO3-. Chitosan-coated alginate beads are a biodegradable and environmentally benign matrix, chosen for application of the enzyme in a novel biomimetic CO2 sequestration system. The feasibility of the system and immobilization of the enzyme were demonstrated in our earlier studies [1–3]. Optimization of the matrix to improve the retention time of the enzyme in an encapsulated form is the subject of the present study. The improvement in the molecular weight cut-off of the beads was accomplished by adjusting the crosslinking conditions, coating composition, and molecular weight of the system. The quantity of enzyme released from the system was measured by a Bio-Rad protein assay. Poly-L-lysine was also used as a coating reagent for comparison purposes. The presence of a coating on the alginate beads was verified by Kjeldahl analyses. The difference in the microstructures of alginate and chitosan/alginate beads was demonstrated by SEM studies. Mineralization of the chitosan/alginate matrix in the presence of CaCO3 was also studied by FT-IR, to assess the possibility of using the beads continuously in a bioreactor.

Microstructural evolution in modified 9Cr–1Mo ferritic/martensitic steel irradiated with mixed high-energy proton and neutron spectra at low temperatures

Modified 9Cr–1Mo ferritic/martensitic steel was exposed at 32–57 °C to a mixed proton/neutron particle flux and spectrum at the Los Alamos Neutron Science Center. The microstructure of unirradiated 9Cr–1Mo consists of laths, dislocations and carbides. Examination of electron diffraction patterns obtained from extraction replicas of unirradiated 9Cr–1Mo revealed that the precipitate microstructure was primarily dominated by M23C6 carbides. The post-irradiation microstructure contained black-spot damage in addition to precipitates and dislocations. Examination of electron diffraction patterns revealed diffuse rings from M23C6 carbides, indicating amorphization and/or nanocrystallinity. Crystalline MC carbides were also found. No cavity formation was found although a significant amount of helium and hydrogen generation had been generated. TEM–EDS examination of extraction replicas for carbides from unirradiated and irradiated samples did not show any detectable changes in composition of either M23C6 or MC carbides. There was also no evident change in carbide size. Lattice images of M23C6 carbides revealed an amorphous microstructure following irradiation, but MC carbides were still crystalline.

Microstructural evolution of Alloy 718 at high helium and hydrogen generation rates during irradiation with 600–800 MeV protons

When precipitation hardened Alloy 718 is irradiated with high-energy protons (600–800 MeV) and spallation neutrons at temperatures below ∼60∘C, it quickly hardens and loses almost all uniform elongation. It later softens somewhat at higher exposures but does not regain any elongation. This behavior is explained in terms of the evolution of Frank loop formation, disordering and eventual dissolution of the γ′ and γ″ strengthening phases, and the steady accumulation of very large levels of helium and hydrogen. These gases must be dispersed on a very fine scale in the matrix since no cavities could be found.

Evolution of mechanical properties in ErT2 thin films

The mechanical properties of rare earth tritide films evolve as tritium decays into H3e, which forms bubbles that influence long-term film stability in applications such as neutron generators. Ultralow load nanoindentation, combined with finite-element modeling to separate the mechanical properties of the thin films from their substrates, has been used to follow the mechanical properties of model ErT2 films as they aged. The size of the growing H3e bubbles was followed with transmission electron microscopy, while ion beam analysis was used to monitor total T and H3e content. The observed behavior is divided into two regimes: a substantial increase in layer hardness but elasticity changed little over ∼18 months, followed by a decrease in elastic stiffness and a modest decease in hardness over the final 24 months. We show that the evolution of properties is explained by a combination of dislocation pinning by the bubbles, elastic softening as the bubbles occupy an increasing fraction of the material, and de...

Microstructural origins of radiation-induced changes in mechanical properties of 316 L and 304 L austenitic stainless steels irradiated with mixed spectra of high-energy protons and spallation neutrons

Abstract A number of candidate alloys were exposed to a particle flux and spectrum at Los Alamos Neutron Science Center (LANSCE) that closely match the mixed high-energy proton/neutron spectra expected in accelerator production of tritium (APT) window and blanket applications. Austenitic stainless steels 316 L and 304 L are two of these candidate alloys possessing attractive strength and corrosion resistance for APT applications. This paper describes the dose dependence of the irradiation-induced microstructural evolution of SS 316 L and 304 L in the temperature range 30–60°C and consequent changes in mechanical properties. It was observed that the microstructural evolution during irradiation was essentially identical in the two alloys, a behavior mirrored in their changes in mechanical properties. With one expection, it was possible to correlate all changes in mechanical properties with visible microstructural features. A late-term second abrupt decrease in uniform elongation was not associated with visible microstructure, but is postulated to be a consequence of large levels of retained hydrogen measured in the specimens. In spite of large amounts of both helium and hydrogen retained, approaching 1 at.% at the highest exposures, no visible cavities were formed, indicating that the gas atoms were either in solution or in subresolvable clusters.

Development of bubble microstructure in ErT2 films during aging

Helium bubbles form in metal tritide films as tritium decays into H3e, influencing mechanical properties and long-term film stability. The bubble nucleation and growth mechanisms comprise an active research area, but there has been only one previous systematic experimental study of helium bubble growth in metal tritides, on zirconium tritides. There have been no such studies on tritides such as ErT2 that form platelike bubbles and lack a secondary bubble population on a network of line dislocations, and yet such a study is needed to inform the modeling of helium bubble microstructure development in a broader range of metal tritides. Transmission electron microscopy has been used to study the growth and evolution of helium bubbles in ErT2 films over a four-year period. The results have been used to test the present models of helium bubble nucleation and growth in metal tritides, particularly those forming platelike bubbles. The results support the models of Trinkaus and Cowgill. The observations of nonunif...

Polyelectrolyte Cages For A Novel Biomimetic CO2 Sequestration System

Development of a novel biomimetic approach to safe, long-term CO2 sequestration is the overall goal of our research program. The objective is to develop a system resembling a CO2 scrubber that can be used to reduce CO2 emissions from, for example, fossil-fuel-burning power plants. It is becoming increasingly clear that some form or forms of carbon sequestration will have to be among the range of carbon management strategies to be implemented if meaningful reductions in CO2 emissions are to be achieved in response to concerns about global climate change. This is particularly true if reductions are to be effected in the short to medium term. Our main focus is on electric power generation, which represents a relatively small number of very large stationary sources. For example, a “typical” plant (based on a hypothetical new 300 MW(e) plant in a Kenosha, Wisconsin, location, burning an Appalachian coal) produces 2.32 tonnes of CO2 per tonne of coal, or 290 tonnes of CO2 per hour. Such large sources are likely to be among those to be addressed first in the event that limits are placed on CO2 emissions.

Early results from a laboratory-scale pilot-plant demonstration of enzyme-catalyzed CO2 sequestration with produced waters as cation source

Publisher Summary This chapter develops a system resembling a CO2 scrubber that can provide a route to safe, long-term sequestration of CO2 from, for example, fossil-fuel-burning power plants. It has been estimated that an amount of carbon equivalent to 150,000 × 1012 tonnes of CO2 is naturally sequestered in the form of carbonate minerals, such as calcite, aragonite, dolomite, and dolomitic limestone, which thus constitute the earths largest CO2 reservoir. Mineralization is attractive as a possible route to carbon sequestration because it offers the potential for safe storage of very large quantities of CO2 over very long time periods, as demonstrated by the geological record. This would, of course, minimize risks and monitoring requirements, and facilitate licensing. Produced waters offer a particularly attractive because of the potential to improve cost effectiveness for sequestration while also benefiting the oil and gas industry. In active production areas such as the Permian Basin, substantial amounts of brine are already being produced, transported, and re-injected. Some of these produced waters are used in water flooding for secondary production, but most constitute a waste product requiring disposal.