From the results obtained in this investigation, the following conclusions can be drawn: 1. A substance inhibits corrosion only under certain conditions, and under other conditions it may not be an inhibitor, but may be inert or an accelerator. 2. No compounds tested in concentrations of 0.01 and 0.10 percent nitrogen, were found to inhibit the corrosion of steel in 5 percent phosphoric acid at 25°C. and under the conditions of aeration and agitation used. 3. Sodium chromate is an inhibitor in concentrations of 1 percent for the corrosion of steel by a 5 percent, aerated, agitated, phosphoric acid solution at 25°C. 4. The mechanism of the corrosion of copper proposed by Whaley is not substantiated. Chelation probably is not the mechanism by which 2-nitro-l-butanol inhibits the corrosion of copper in a 5 percent phosphoric acid solution. 5. Inhibitors that are used and are efficient for one acid under certain conditions cannot always be said to work for other acids under other conditions. / M.S.

This project presents a study of iron technology in Early Medieval (fifth to eleventh centuries AD) Britain through the examination of iron found in settlement contexts. This is a period characterized by significant cultural, political and social changes. The effect of these changes on iron technology has never been investigated on a large scale. Previous studies on iron focused either on individual sites or on single artefact types, and did not provide any clear multi-region interpretive framework. A longstanding problem has been in identifying the extent of usage of a key alloy: phosphoric iron. This research project examined iron assemblages from eight settlement sites of varying size, culture, economic and social status from across Britain. From each settlement a mixed assemblage of iron artefacts was sampled, including edged tools, items of personal adornment, construction materials, and craft tools. Analysis was by traditional archaeometallurgical techniques alongside SEM-EDS elemental analysis. Alloy usage, specifically relating to phosphoric iron, was examined and the manufacturing techniques assessed. It was shown that elemental analysis is the only reliable method to determine the presence of phosphorus in iron and demonstrated that the traditional phosphoric indicators as observed during optical microscopy are insufficient. Results were subjected to a series of comparisons based on settlement size, the inferred social status, and cultural affinities. The results demonstrate the high technological level of iron artefact production across the country. All areas had access to the full range of iron alloys and employed a highly developed range of smithing techniques. Phosphoric iron was a prevalent alloy in this period. Based on these results, a model of the Early Medieval iron industry is generated, suggesting a vibrant economy in which both local and traded irons were significant.

Les minerais de phosphates, principalement exploités pour la production d'acide phosphorique et d'engrais, contiennent une quantité non-négligeable d'uranium (50 à 300 ppm) qui suscite l'intérêt de l'industrie nucléaire. Notre étude s'inscrit dans ce contexte de valorisation de l'uranium en tant que sous-produit de l'industrie des fertilisants.L'objectif de ce travail de thèse a été de mettre au point un matériau hybride, constitué d'un support inorganique sur lequel est greffée une molécule complexante, capable d'extraire sélectivement l'uranium du milieu acide phosphorique. La première étape de notre démarche a consisté à identifier un support inorganique capable de résister aux conditions particulières du milieu acide phosphorique (acidité élevée et milieu très complexant). Pour ce faire, la stabilité chimique et mécanique de différents matériaux, silice, verre et carbone mésoporeux, a été étudiée. Dans un deuxième temps, nous nous sommes intéressés à l'identification et l'optimisation de molécules complexantes spécifiques de l'uranium en milieu acide phosphorique. Ces dernières ont ensuite été greffées sur les supports les plus stables. Enfin, l'efficacité de ces systèmes hybrides a été évaluée lors de tests d'extraction, de sélectivité et de désextraction. / Phosphate rocks are industrially processed in large quantities to produce phosphoric acid and fertilisers. These rocks contain significant concentration of uranium (50 to 300 ppm) which could be interesting for nuclear industry. This work deals with the valorisation of uranium as a by-product from fertiliser industry.The aim of this study is to develop a hybrid material, constituted of an inorganic solid support grafted with an extractant (complexing molecule), which can extract selectively uranium from phosphoric acid medium. The first step of our approach was to identify an inorganic support which is stable under these particular conditions (strong acidity and complexing medium). The chemical and mechanical stability of different mesoporous materials, such as silica, glass and carbon was studied. In a second phase, we focused on the identification and the optimisation of complexing molecules, specific of uranium in phosphoric acid. These ligands were then grafted on the most stable solids. Finally, the efficiency of these hybrid systems was evaluated through different tests of extraction, selectivity and desextraction.

by Wong Ping Shing. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1995. / Includes bibliographical references (leaves 97-112). / ACKNOWLEDGMENTS --- p.i / ABSTRACT --- p.ii / ABBREVIATIONS --- p.viii / Chapter 1. --- INTRODUCTION --- p.1 / Chapter 1.1 --- General properties of zinc / Chapter 1.1.1 --- Biochemistry of zinc --- p.2 / Chapter 1.1.2 --- Distribution of zinc in body --- p.3 / Chapter 1.1.3 --- Roles of zinc in protein function --- p.4 / Chapter 1.2 --- Zinc and zinc-binding proteins in brain / Chapter 1.2.1 --- Distribution of zinc in brain --- p.7 / Chapter 1.2.2 --- Metabolism of zinc in brain --- p.9 / Chapter 1.2.3 --- Compartments of zinc in brain --- p.10 / Chapter 1.2.4 --- Zinc-binding proteins in brain --- p.12 / Chapter 1.3 --- Pathological conditions of brain in relation to zinc --- p.15 / Chapter 1.4 --- Aim of the project --- p.20 / Chapter 2. --- MATERIALS AND METHODS --- p.22 / Chapter 2.1 --- Detection of zinc-binding proteins / Chapter 2.1.1 --- Sodium-Dodecyl Sulphate Polyacrylamide Gel Electrophoresis (SDS-PAGE) --- p.22 / Chapter 2.1.2 --- Electroblotting --- p.24 / Chapter 2.1.3 --- Radioactive zinc blotting --- p.25 / Chapter 2.1.4 --- Autoradiography --- p.25 / Chapter 2.2 --- Subcellular fractionation of porcine brain --- p.26 / Chapter 2.3 --- Purification and structural characterization of a 19 kDa zinc-binding protein / Chapter 2.3.1 --- Purification of a 19 kDa protein --- p.27 / Chapter 2.3.2 --- Sequencing of N-terminal blocked 19 kDa protein --- p.30 / Chapter 2.4 --- Characterization of the binding and biological properties of the 19 kDa zinc-binding protein / Chapter 2.4.1 --- Effect of divalent metal ions on zinc binding to the 19 kDa protein --- p.33 / Chapter 2.4.2 --- Effect of pH on the dissociation of radioactive zinc from the19 kDa protein --- p.34 / Chapter 2.4.3 --- Radioactive calcium blotting --- p.34 / Chapter 2.4.4 --- Interaction of radioactive zinc and radioactive calcium binding to the 19 kDa protein --- p.35 / Chapter 2.4.5 --- Calmodulin activity assay --- p.35 / Chapter 3. --- RESULTS / Chapter 3.1 --- Specificity of radioactive zinc-blot on zinc-binding protein detection --- p.38 / Chapter 3.2 --- Zinc-binding proteins in porcine brain --- p.38 / Chapter 3.3 --- Purification and identification of a cytosolic 19 kDa zinc- binding protein in porcine brain / Chapter 3.3.1 --- Zinc-dependent hydrophobic interaction chromatography --- p.44 / Chapter 3.3.2 --- N-terminal amino acid sequencing --- p.51 / Chapter 3.3.3 --- High pH native gel electrophoresis of 19 kDa protein --- p.51 / Chapter 3.4 --- The zinc and calcium binding properties of the 19 kDa protein / Chapter 3.4.1 --- Effect of pre-exposure to divalent cations on zinc binding --- p.54 / Chapter 3.4.2 --- Competition by divalent cations for zinc binding --- p.56 / Chapter 3.4.3 --- pH dependency of zinc dissociation --- p.56 / Chapter 3.4.4 --- Effect of zinc on radioactive calcium binding --- p.61 / Chapter 3.5 --- The biological activity of the 19 kDa protein / Chapter 3.5.1 --- Effect of the 19 kDa protein on the activity of calmodulin- dependent phosphodiesterase --- p.66 / Chapter 3.5.2 --- Effect of zinc on calmodulin-dependent phosphodiesterase activity --- p.69 / Chapter 3.5.4 --- "Effect of zinc on calcium-deficient, calmodulin-dependent phosphodiesterase activity" --- p.72 / Chapter 4. --- DISCUSSION / Chapter 4.1 --- Detection and Purification of zinc-binding proteins / Chapter 4.1.1 --- Strategy for the detection of zinc-binding proteins --- p.77 / Chapter 4.1.2 --- Purification of zinc-binding protein --- p.79 / Chapter 4.2 --- Amino acid sequencing of the 19 kDa protein --- p.82 / Chapter 4.3 --- Binding properties of the 19 kDa zinc-binding protein --- p.86 / Chapter 4.4 --- Effect of zinc and 19 kDa zinc-binding protein on calmodulin dependent phosphodiesterase --- p.92 / Chapter 4.5 --- Effect of zinc on the properties of calmodulin --- p.90 / Chapter 4.6 --- Significance of the ability of zinc to affect calmodulin activity --- p.94 / Chapter 5. --- CONCLUSION --- p.95 / Chapter 6. --- REFERENCES --- p.97

The synthesis of enantiomerically pure compounds is of vital importance. Most biologically active natural products are chiral and require asymmetric synthesis, chiral resolution, or the use of naturally chiral starting materials for their preparation. Organocatalytic enantioselective reaction methodology is a continuously growing area in organic chemistry. The use of organocatalysts as a potentially environmentally friendly alternative to metal catalysts is appealing to the pharmaceutical industry. In this dissertation an enantioselective Mannich reaction using an organocatalyst was investigated. The reaction was between a ß-keto ester and an imine electrophile catalyzed by vaulted biphenanthrol (VAPOL) phosphoric acid. The reaction resulted in products with high yields, but low to moderate enantioselectivity and diastereoselectivity. The development of the first Brønsted acid-catalyzed desymmetrization of meso-aziridines was also investigated. This is one of the first instances where a phosphoric acid has been used to catalyze a reaction that did not involve an imine. It was shown that the chiral VAPOL phosphoric acid was an excellent catalyst for the reaction resulting in high yields and enantioselectivities for the chiral ring opened products. It was also shown, for the first time, that a vaulted binaphthol (VANOL) phosphoric acid can also catalyze the ring-opening of meso-aziridines with comparable results to the VAPOL phosphoric acid in some cases. Mechanistic NMR studies were used to probe the reaction, and it is believed that evidence leads one to conclude that a unique mechanism for phosphoric acid-catalysis is followed. The products that can be obtained from this reaction, 1,2-diamines, are of high value for synthetic chemists. They have been used as chiral auxiliaries, ligands, and precursors to natural products.

Succinic acid is a compound used for manufacturing lacquers, resins, and other coating chemicals. It is also used in the food and beverage industry as a flavor additive. It is predominantly manufactured from petrochemicals, but it can also be produced more sustainably by fermentation of sugars from renewable feedstocks (biomass). Bio-based succinic acid has excellent potential for becoming a platform chemical (building block) for commodity and high-value chemicals. In this study, we focused on the production of bio-based succinic acid from the fiber of sweet sorghum (SS), which has a high fermentable sugar content and can be cultivated in a variety of climates and locations around the world. To avoid competition with food feedstocks, we targeted the non-edible ‘bagasse’, which is the fiber part after extracting the juice. Initially, we studied various conditions of pretreating SS bagasse to remove most of the non-fermentable portions and expose the cellulose fibers containing the fermentable sugars (glucose). Concentrated (83%) phosphoric acid was utilized at mild temperatures of 50-80 °C for 30-60 minutes at various bagasse loadings (10-15%) using a partial factorial experimental design. After pretreatment, the biomass was subjected to enzymatic hydrolysis with commercial cellulase enzyme (Cellic® Ctec2) to identify the pretreatment conditions that lead to the highest glucose yield that is critical for the production of succinic acid via fermentation with the bacterium Actinobacillus succinogenes. As the pretreatment temperature and duration increased, the bagasse color changed from light brown to dark brown-black, indicating decomposition, which ranged from 15% to 72%. The pretreatment results were fitted with an empirical model that identified 50 °C for 43 min at 13% solids loading as optimal pretreatment conditions that lead to the highest glucose release from sweet sorghum bagasse. Biomass pretreated at those conditions and subjected to separate enzymatic hydrolysis and fermentation with A. succinogenes yielded almost 18 g/L succinic acid, which represented 90% of the theoretical yield, a very promising performance that warranties further investigation of bio-based succinic acid production from sweet sorghum bagasse, as a more sustainable alternative to succinic acid produced from fossil sources, such as oil.

The development of novel asymmetric reaction methodologies has been invaluable in both the academic and industrial world. In just 15 years, organocatalysis has provided a new means of developing asymmetric reaction methodologies using catalysts that are environmentally benign, relatively inexpensive, bench stable, and non-toxic. One development in organocatalysis that is important to our group in particular is chiral phosphoric acid-catalysis. BINOL-derived and VAPOL-derived phosphoric acids have proven to be excellent catalysts for a number of reactions. The two projects I will discuss my efforts on are acetalization and iso-Pictet-Spengler reactions. These were projects that I performed during my first two years as a graduate student. The acetalization was particularly fascinating as only one literature report existed for the catalytic asymmetric variant of a reaction that makes such important compounds--O,O-acetals. The acetalization reaction proved to be a formidable opponent, and to this date no research report has been published documenting the intra-, or intermolecular catalytic asymmetric acetalization of vinyl ethers or the intermolecular catalytic asymmetric transacetalization. The iso-Pictet-Spengler reaction is one that is interesting because exhaustive research has been conducted into the development of catalytic asymmetric Pictet-Spengler reactions, but at the time of my research, not a single catalytic asymmetric method existed to synthesize tetrahydro-γ-carbolines, the product of the iso-Pictet-Spengler reaction. Structurally, the tetrahydro-γ-carboline is isomeric to the tetrahydro-β-carboline, the product of the Pictet-Spengler reaction. They differ only in the position of nitrogen in the annulated product. This reaction seemed attractive to investigate, since independent elegant reports by Professors Benjamin List, Henk Hiemstra, and Darren Dixon documented the excellent control over enantioselectivity that chiral phosphoric acid have in the Pictet-Spengler reaction. Concurrent with the beginning stages of this project, Professor Eric Jacobsen reported the enantioselective thiourea-catalyzed iso-Pictet-Spengler reaction. The results were very good but not as great as the Pictet-Spengler work he pioneered. Around the time this report came out I commenced my reaction studies, and this thesis is the sum of just two projects I worked on. There were many more including halolactonization, VAPOL synthesis, chiral phosphoric acid synthesis, catalytic asymmetric hydroamination, and others.

The objective of this study is to shed more light on the electrochemical interface of HTPEM fuel cell. More specifically, to understand and improve the electrochemical interface of both the anodic and cathodic electrode in HTPEM fuel cells, as well as optimize the catalyst layer structure for operation under various challenging conditions. For that reason the effect of the PA amount in the catalyst layer and the effect of the catalyst’s substrate on the fuel cell’s performance were investigated. Initially the poisoning effect of PA on the anodic electrode was investigated. The PA amount was altered in the anodic catalyst layer and its effect on the ECSA and the anode’s performance were evaluated. It was observed that the reversible performance loss of the anodic electrode was a function of the PA amount in the catalyst layer. More specifically, under low PA loading (<3 gPA/gPt) on the anodic electrode, < 10% of the Pt active surface is electrochemically active under fuel cell operating conditions. This was attributed to the blockage of the Pt surface by pyrophosphoric acid or poly-phosphates, H2 reduced polyphosphoric acid species and the shrinkage of the interface due to the displacement of the H3PO4 by the adsorbed H2 species. High PA loadings reduced the poisoning effect of these reduced PA species ( >3 gPA/gPt). It was found that the controlled and increased PA content within the catalytic layer can result even up to the tenfold decrease in the Pt loading when the anode operates under H2 rich conditions. In order to increase the fuel cell performance and increase the three phase boundary, a newly synthesized electrocatalyst was evaluated, and compared to the commercial 30wt%Pt/C. The new catalyst is based on pyridine functionalized carbon nanotubes ,30wt%Pt/oxMWCNT-Py. Pyridine groups are known to interact with PA and thus it is expected to increase the TPB and lower the Pt loading. CL employing the new catalyst were formulated and tested at the anodes. It was found that the presence of pyridine groups homogeneously distributed PA in the catalyst layer, resulting in high ECSA values, 40m2/gPt. As a result the MEA employing 30wt% Pt oxMWCNT-Py showed the same performance as the 30%Pt/C (having 1.3mgPt/cm2), for Pt loading loadings as low as 0.2mgPt/cm2. The performance of the anodic electrode was also found to be largely depended on the PA amount imbedded in the CL, when low Pt loading were used. The latter was an effect of the shrinkage of the ECSA as a result of the formation of PA poisoning species, as also mentioned in the previous paragraph. Since 30wt% Pt/oxMWCNT-Py exhibited very promising results and high ECSA values, its performance under harsh synthetic reformate gas was also evaluated. The synthetic reformate gas that was used comprised of 50.7kPa of H2, 2 kPa of CO and 33.5kPa of H2O balanced with Ar. It was found that the 30wt%Pt/oxMWCNT-Py electrocatalyst are ideal candidates for operation under those harsh reformates conditions, as they exhibited smaller voltage losses and higher stability under these conditions. The interaction of pyridine groups with phosphoric acid not only promotes its uniform distribution on the CL but also stabilizes the EI under high partial pressure of water. Additionally, the use of pyridine functionalized MWCNT based electrocatalyst gives the opportunity of lowering the Pt loading in the electrodes without sacrificing the overall cell’s performance under reformate conditions. The observed voltage loss under synthetic reformate gas rich in CO and steam was found to be a multi-step process and a function of the hydrophobicity of catalyst substrate, the PA loading in the CL as well as the water and CO molar fraction in the reformate gas. In order to optimize the cathodic catalyst layer, CL were formulated using the newly synthesized electrocatalyst (30wt%Pt/oxMWCNT-Py) and compared to the commercial 30wt%Pt/C. A full parametric analysis with respect to catalyst type, PA loading and Pt loading was conducted. It was found that the presence of pyridine groups homogeneously distributes PA in the catalyst layer minimizing the blockage of the pores of the catalyst layer and increase the three phase boundary. As a result the MEA employing 30wt% Pt oxMWCNT-Py showed the same performance as the 30%Pt/C for half the Pt loading. Despite the hard operating conditions the Pt particles attached to the ox.MWCNT-Py substrate exhibit the same stability as the commercial catalyst and the pyridine groups were found to be stable, at least for short term operation at the cathodic and anodic electrode. Also optimization of the ECSA evaluation procedure at the cathodic electrode, using CO as a probe molecule, without damaging the Pt distribution was found. It is clear that the use of this newly synthesized electrocatalyts 30wt%Pt/oxMWCNT-Py , at both electrodes, has major advantages as it increase the catalyst utilization and there is no need to use a polymer-binder inside the catalytic layer. Thus avoiding problems of inhomogeneous binder distribution and/or electronic insulation of catalyst nanoparticles. Using 30wt%Pt/oxMWCNT-Py electrocatalyst opens the possibility of significant reduction of the amount of Pt on both electrodes, under various operation conditions, without sacrificing the performance and stability of the fuel cell. / Στο πλαίσιο της παρούσας διδακτορικής διατριβής έγινε σύνθεση ενός νέου βελτιωμένου ηλεκτροκαταλύτη Pt για χρήση σε κελιά καυσίμου πολυμερικής μεμβράνης υψηλών θερμοκρασιών (HTPEM), με σκοπό την αύξηση της ηλεκτροχημικά ενεργού επιφάνειας τόσο του ανοδικού όσο του καθοδικού ηλεκτροδίου. Ο καταλύτης αυτός αποτελείται από 30 % κ.β. Pt σε φορέα τροποποιημένους πολυ-φλοιϊκούς νανοσωλήνες άνθρακα (MWCNT). Οι νανοσωλήνες άνθρακα τροποποιήθηκαν σταδιακά, σε ένα πρώτο βήμα με ομάδες οξυγόνου (ox.MWCNT) και στη συνέχεια με ομάδες πυριδίνης (ox.MWCNT-Py) που προσαρτήθηκαν μέσω ομοιοπολικών δεσμών στο εξωτερικό τοίχωμά τους, ώστε να επιτευχθεί ομοιόμορφη κατανομή τους στο καταλυτικό στρώμα. Επειδή οι ομάδες πυριδίνης (Py) δεσμεύουν το φωσφορικό οξύ, το οποίο χρησιμοποιείται ως ιοντικός αγωγός, δημιουργείται ένας ιοντικά αγώγιμος δρόμος κατά μήκος του καταλυτικού στρώματος, με συνακόλουθη αύξηση της ηλεκτροχημικά ενεργού επιφάνειας, η οποία επέτρεψε τη σημαντική μείωση της ποσότητας Pt στα ηλεκτρόδια, χωρίς μείωση της απόδοσης και σταθερότητας του κελιού καυσίμου. Πλεονέκτημα αυτής της προσέγγισης για αύξηση της απόδοσης του ηλεκτροκαταλύτη Pt είναι το ότι αποφεύγεται η χρήση ενός ιονομερούς στο εσωτερικό του καταλυτικού στρώματος και τα προβλήματα που σχετίζονται με την ανομοιογενή κατανομή του. Εξετάστηκαν επίσης η επίδραση στην απόδοση του ανοδικού ηλεκτροδίου της παρουσίας CO και υψηλής μερικής πίεσης υδρατμού στην τροφοδοσία της ανόδου, στη περίπτωση χρήσης αερίου αναμόρφωσης ως καυσίμου. Για διερεύνηση του μηχανισμού ανάπτυξης υπέρτασης (ενεργειακής απώλειας σε όρους δυναμικού) στη περίπτωση αυτή και βελτιστοποίηση της λειτουργίας του κελιού καυσίμου, παρασκευάστηκαν ηλεκτρόδια με χρήση τριών διαφορετικών καταλυτών Pt, συγκεκριμένα των καταλυτών 30% κ.β. Pt/C, 30% κ.β. /oxMWCNT και 30wt%Pt/oxMWCNT-Py. Τα ηλεκτρόδια αυτά διέφεραν επίσης όσον αφορά στη ποσότητα καταλύτη ανά μονάδα επιφάνειας ηλεκτροδίου και στη ποσότητα φωσφορικού οξέος (PA) στο καταλυτικό στρώμα ανά μονάδα μάζας Pt (0.5 gPA/gPt και 2 gPA/gPt). Η ανάπτυξη υπέρτασης στις αναφερθείσες συνθήκες λειτουργίας αποδόθηκε σε ένα μηχανισμό πολλών σταδίων, ο οποίος βασίζεται στη μείωση της ηλεκτροχημικά ενεργού επιφάνειας λόγω της εκτόπισης του φωσφορικού οξέος από την ηλεκτροχημική διεπιφάνεια. Παρότι το φωσφορικό οξύ αποτελεί ιδανικό αγωγό ιόντων για τα κελιά καυσίμου υψηλών θερμοκρασιών τύπου PEM, παρουσιάζει διάφορους περιορισμούς, όπως το φαινόμενο δηλητηρίασης του ανοδικού ηλεκτροδίου εξαιτίας του, το οποίο επίσης μελετήθηκε στη διατριβή αυτή. Διαπιστώθηκε ότι η αναστρέψιμη απώλεια της απόδοσης του ανοδικού ηλεκτροδίου ήταν συνάρτηση της ποσότητας του H3PO4 στο καταλυτικό στρώμα.

No description available.

Thesis (Ph. D.)--University of Virginia, 2007. / Includes bibliographical references. Also available online through Digital Dissertations.