The membrane aerated bioreactor (MABR) is a unique technological innovation where a gas permeable membrane is applied to biological processes. In an MABR, oxygen and other substrates diffuse from the opposite directions into a biofilm, and thus simultaneous chemical oxygen demand (COD) and nitrogen removal can be achieved. However, controlling biofilm thickness, stability, and attachment is challenging. The objectives of this research were to study the effect of oxygen partial pressure on process performance with respect to nitrogen removal and examine the biomass properties in MABRs at different oxygen partial pressures and COD loadings. The conditions within the bioreactors were based on a low hydrodynamic condition (average fluid velocity 22 cm/min along the membrane surface), with the intention of minimizing the impact of the hydrodynamic shear on biomass properties. Simultaneous nitrification and denitrification were achieved in the reactors, and increasing oxygen partial pressure enhanced the total nitrogen removal. The biomass at the membrane-biofilm interface was more porous at a loading of 11.3 kg COD/1000 m2/day (areal porosity about 0.9) as compared with a loading of 22.6 kg COD/1000 m2/day (areal porosity about 0.7), indicating carbon substrate was limiting near the membrane. Long-term (over 30 days) experimental results showed that at the loading of 11.3 kg COD/1000 m2/day, the oxygen partial pressures of 0.59 atm and 0.88 atm caused over 80% of the biomass to become suspended in the bulk phase while at 0.25 atm and 0.41 atm oxygen over 97% of the biomass was immobilized on the membrane. There is a critical oxygen partial pressure that can sustain the biofilm, which increases with an increasing COD loading. The nitrifying population in the reactors was examined by applying fluorescence in situ hybridization (FISH). At the loading of 22.6 kg COD/1000 m2/day, there were 12% beta-proteobacterial ammonia oxidizing bacteria (AOB) and 17%Nitrobacter in homogenized biofilm biomass at 0.59 atm oxygen while there were 7% beta-proteobacterial AOB and 4% Nitrobacter at 0.25 atm oxygen. The ratio of protein to carbohydrate in extracellular polymeric substances (EPS) of the homogenized biomass in the reactor decreased with increasing oxygen partial pressure. Surface characterization of the biomass revealed that the higher the oxygen partial pressure, the lower the biomass hydrophobicity and surface charge. The ratio of EPS protein to carbohydrate in a membrane aerated biofilm decreased when approaching the membrane-biofilm interface. The distribution of nitrifiers and dissolved oxygen profiles inside the biofilm suggested that dual substrate limitations exist, and it was concluded that the membrane aerated biofilm had an aerobic region in the inner layer and an anoxic region in the outer layer. It is proposed that the loss of EPS due to secondary substrate consumption, especially the loss of EPS proteins, at the bottom of the biofilm was responsible for biofilm detachment subjected to a critical oxygen partial pressure.

The membrane aerated bioreactor (MABR) is a unique technological innovation where a gas permeable membrane is applied to biological processes. In an MABR, oxygen and other substrates diffuse from the opposite directions into a biofilm, and thus simultaneous chemical oxygen demand (COD) and nitrogen removal can be achieved. However, controlling biofilm thickness, stability, and attachment is challenging. The objectives of this research were to study the effect of oxygen partial pressure on process performance with respect to nitrogen removal and examine the biomass properties in MABRs at different oxygen partial pressures and COD loadings. The conditions within the bioreactors were based on a low hydrodynamic condition (average fluid velocity 22 cm/min along the membrane surface), with the intention of minimizing the impact of the hydrodynamic shear on biomass properties. Simultaneous nitrification and denitrification were achieved in the reactors, and increasing oxygen partial pressure enhanced the total nitrogen removal. The biomass at the membrane-biofilm interface was more porous at a loading of 11.3 kg COD/1000 m2/day (areal porosity about 0.9) as compared with a loading of 22.6 kg COD/1000 m2/day (areal porosity about 0.7), indicating carbon substrate was limiting near the membrane. Long-term (over 30 days) experimental results showed that at the loading of 11.3 kg COD/1000 m2/day, the oxygen partial pressures of 0.59 atm and 0.88 atm caused over 80% of the biomass to become suspended in the bulk phase while at 0.25 atm and 0.41 atm oxygen over 97% of the biomass was immobilized on the membrane. There is a critical oxygen partial pressure that can sustain the biofilm, which increases with an increasing COD loading. The nitrifying population in the reactors was examined by applying fluorescence in situ hybridization (FISH). At the loading of 22.6 kg COD/1000 m2/day, there were 12% beta-proteobacterial ammonia oxidizing bacteria (AOB) and 17%Nitrobacter in homogenized biofilm biomass at 0.59 atm oxygen while there were 7% beta-proteobacterial AOB and 4% Nitrobacter at 0.25 atm oxygen. The ratio of protein to carbohydrate in extracellular polymeric substances (EPS) of the homogenized biomass in the reactor decreased with increasing oxygen partial pressure. Surface characterization of the biomass revealed that the higher the oxygen partial pressure, the lower the biomass hydrophobicity and surface charge. The ratio of EPS protein to carbohydrate in a membrane aerated biofilm decreased when approaching the membrane-biofilm interface. The distribution of nitrifiers and dissolved oxygen profiles inside the biofilm suggested that dual substrate limitations exist, and it was concluded that the membrane aerated biofilm had an aerobic region in the inner layer and an anoxic region in the outer layer. It is proposed that the loss of EPS due to secondary substrate consumption, especially the loss of EPS proteins, at the bottom of the biofilm was responsible for biofilm detachment subjected to a critical oxygen partial pressure.

The erosion or dissolution of stainless steel grade 304 as base metal by molten brazing fillermetal was investigated using one nickel and two iron based filler metals. The difference betweentwo iron filler metal is 5 % Manganese content in one of the filler metal. The Wettability of fillermetal is effected by oxidation of base or filler metal for which high vacuum or non reacting gasis used as a furnace atmosphere to reduce the partial pressure of oxygen. The furnace parameterseffecting erosion of base metal was observed e.g. peak temperature and brazing time. The effectof filler mass was also observed. The erosion depth was measured by light optical microscope.All the three filler metal shows different erosion behavior in nitrogen atmosphere compare tohigh vacuum. In high vacuum some of the elements evaporates at brazing temperature whichchanges the properties of filler metal. This change of composition in filler metal was observed byEDX analysis. SEM analysis was used to identify different element rich phases.

La température et la pression partielle d’oxygène (PO2) constituent les paramètres majeurs contrôlantles évolutions thermochimiques en réacteur des combustibles nucléaires de type oxyde, et notammentla spéciation des produits de fission potentiellement corrosifs (Cs, I, Te). Pour limiter les risques derupture de la gaine en Zr par corrosion, une solution innovante consiste à imposer au combustible defonctionner dans un domaine de PO2 où les espèces chimiques des gaz de fission sont inoffensives, pardopage in-situ avec un tampon oxydo-réducteur solide. Le niobium, avec ses couples redoxNbO2/NbO et Nb2O5/NbO2, a été identifié comme le candidat le plus prometteur. Un procédé defabrication d’un combustible dopé niobium répondant à cet objectif et conforme aux spécificationsd’usage (densité, microstructure) a été optimisé. L’étude expérimentale du système UO2-NbOx a révélél’existence à 810°C d’une phase liquide entre UO2 et NbO2, non identifiée à ce jour. La caractérisationdes phases solides et en solution du niobium nous a conduit à proposer un modèle thermodynamiquede solubilité du dopant dans UO2 à 1700°C. Une étude approfondie de la spéciation du niobiumprécipité a permis d’identifier la présence simultanée dans le matériau des phases majeures NbO2 etNbO, ainsi que Nb en moindre teneur. La coexistence du niobium sous deux degrés d’oxydationdifférents constitue un élément-clé de démonstration d’un possible effet tampon in-situ, dont l’impactest observé sur certaines propriétés du combustible dépendantes de la PO2, la densification notamment.Les résultats confirment le potentiel prometteur des combustibles tamponnés en PO2 au regard de sesperformances en réacteur. / Temperature and oxygen partial pressure (PO2) of nuclear oxide fuels are the main parametersgoverning both their thermochemical evolution in reactor and the speciation of volatile fissionproducts such as Cs, I or Te. An innovative way to limit the risk of cladding rupture by corrosionunder irradiation consists in buffering the oxygen partial pressure of the fuel under operation in a PO2domain where the fission gas are harmless towards Zr clad, by using solid redox buffers as additives.Niobium, with its NbO2/NbO and Nb2O5/NbO2 redox couples has been found to be a promisingcandidate to this end. A manufacturing process of a buffered UO2 fuel, doped with niobium has beenoptimized, in order to fulfill usual specifications (density, microstructure). The experimental study ofthe UO2-NbOx system has shown the existence of a liquid phase between UO2 and NbOx at 810°C,which was not reported in the literature. The characterization of Nb containing phases present in UO2both in solid solution and as precipitates has lead us to propose a solubility thermodynamic model ofniobium in UO2 at 1700°C. An extensive study of the niobium precipitates shows the co-existence inthe fuel of NbO2 and NbO as major phases, together with small amounts of metallic Nb. The coexistenceof niobium under two oxidation states inside the fuel is a key element of demonstration of apossible in-situ buffering effect, which is likely to impact some properties of the material that aredependent upon PO2, such as densification. These results confirm the promising potential of oxygenbuffered fuels as regard to their performance in reactor.

Thesis (M.S.); Submitted to the University of California, Berkeley, 210 Hearst Mining Memorial Bldg., Berkeley, CA 94720 (US); 15 Dec 2003. / Published through the Information Bridge: DOE Scientific and Technical Information. "LBNL--54116" Li, Sonny X. USDOE Director. Office of Science. Basic Energy Sciences (US) 12/15/2003. Report is also available in paper and microfiche from NTIS.

An induction setup for levitation studies of molten metals was built. The setup was used to levitate and heat stainless steel samples of 2.00 g to 1600 °C and subject them to different atmospheres. Changes in shape and temperature were recorded by video and infrared thermocouple. Oxide films forming on the droplets during levitation were observed. It was possible to notice an immediate surface reaction when the reaction gas was introduced. This reaction is concluded to influence the surface and bulk composition, and therefore have an effect on the shape evolution of the droplet. A more oxidizing atmosphere resulted in a more conical droplet shape; this is thought to be an effect of lowered surface tension and the conically shaped volumetric force caused by the magnetic field. Changes in temperature after the sample is molten are thought to be an effect of changes in emissivity, caused by surface oxidization. Post mortem analysis show a difference in surface morphology for samples subjected to different gases, as well as a difference in amount of oxidization.

Chromium is an important alloying element in stainless steel but also environmentally harmful element. A number of mineralogical phases present in the slag matrix can contain chromium and lead to chromium leaching. Chromium in slag if not stabilized, could oxidize to the cancerogenic hexavalent state, and leach out if exposed to acidic and oxygen rich environment. Other environmental concerns are slag dusting and chromium escape to the atmosphere. Despite the fact that there is a certain risk of Cr-emission from slags at operating conditions, still very little is known regarding the emission of the oxides of chromium during the slag tapping. Spinel phase is known to be important for controlling the leaching properties of chromium from the slag. The objective of the present study was to get an understanding of the phase relationships and chromium partition in the chromium-containing industrial slags and synthetic slags with a view to control the chromium stabilization in spinel phase. The impact of slag basicity, heat treatment, oxygen partial pressure and Al2O3 addition, on the phase relationships and chromium partition has been determined. The experimental results were compared with the phase equilibrium calculations. It was found that the oxygen partial pressure in the gas phase had a strong impact on chromium partition. The experimental results show that the impact of the slag basicity on chromium partition at lower oxygen partial pressures was negligible in contrast to that in air. The amount of spinel phase was found to increase with increased Al2O3 content. Slow cooling of slag and soaking at low oxygen partial pressure would improve the spinel phase precipitation. This treatment will also lead to less Cr dissolved in the unstable matrix phases. Chromium oxide was found to be emitted when chromium containing slags were exposed to oxidizing atmosphere. The results indicate that chromium oxide evaporation increases with increase in temperature and oxygen partial pressure, but decreases with slag basicity and sample thickness. / <p>QC 20131114</p> / Steel Eco-Cycle

In this thesis, the focus is on studying BaZrO3-BaCeO3 based proton conductors due to that they represent very promising proton conductors to be used for Intermediate Temperature Solid Oxide Fuel Cells (ITSOFCs). Here, dense BaZr0.5Ce0.3Y0.2O3-δ (BZCY532) ceramics were selected as the major studied materials. These ceramics were prepared by different sintering methods and doping strategies. Based on achieved results, the thesis work can simply be divided into the following parts: 1) An improved synthesis method, which included a water-based milling procedure followed by a freeze-drying post-processing, was presented. A lowered calcination and sintering temperature for a Hf0.7Y0.3O2-δ (YSH) compound was achieved. The value of the relative density in this work was higher than previously reported data. It is also concluded that this improved method can be used for mass-production of ceramics. 2) As the solid-state reactive sintering (SSRS) represent a cost-effective sintering method, the sintering behaviors of proton conductors BaZrxCe0.8-xLn0.2O3-δ (x = 0.8, 0.5, 0.1; Ln = Y, Sm, Gd, Dy) during the SSRS process were investigated. According to the obtained results, it was found that the sintering temperature will decrease, when the Ce content increases from 0 (BZCLn802) to 0.3 (BZCLn532) and 0.7 (BZCLn172). Moreover, the radii of the dopant ions similar to the radii of Zr4+ or Ce4+ ions show a better sinterability. This means that it is possible to obtain dense ceramics at a lower temperature. Moreover, the conductivities of dense BZCLn532 ceramics were determined. The conductivity data indicate that dense BZCY532 ceramics are good candidates as either oxygen ion conductors or proton conductors used for ITSOFCs. 3) The effect of NiO on the sintering behaviors, morphologies and conductivities of BZCY532 based electrolytes were systematically investigated. According to the achieved results, it can be concluded that the dense BZCY532B ceramics (NiO was added during ball-milling before a powder mixture calcination) show an enhanced oxygen and proton conductivity. Also, that BZCY532A (NiO was added after a powder mixture calcination) and BZCY532N (No NiO was added in the whole preparation procedures) showed lower values. In addition, dense BZCY532B and BZCY532N ceramics showed only small electronic conductivities, when the testing temperature was lower than 800 ℃. However, the BZCY532A ceramics revealed an obvious electronic conduction, when they were tested in the range of 600 ℃ to 800 ℃. Therefore, it is preferable to add the NiO powder during the BZCY532 powder preparation, which can lower the sintering temperature and also increase the conductivity. 4) Dense BZCY532 ceramics were successfully prepared by using the Spark Plasma Sintering (SPS) method at a temperature of 1350 ℃ with a holding time of 5 min. It was found that a lower sintering temperature (&lt; 1400 ℃) and a very fast cooling rate (&gt; 200 ℃/min) are two key parameters to prepare dense BZCY532 ceramics. These results confirm that the SPS technique represents a feasible and cost-effective sintering method to prepare dense Ce-containing BaZrO3-BaCeO3 based proton conductors. 5) Finally, a preliminary study for preparation of Ce0.8Sm0.2O2-δ (SDC) and BZCY532 basedcomposite electrolytes was carried out. The novel SDC-BZCY532 based composite electrolytes were prepared by using the powder mixing and co-sintering method. The sintering behaviors, morphologies and ionic conductivities of the composite electrolytes were investigated. The obtained results show that the composite electrolyte with a composition of 60SDC-40BZCY532 has the highest conductivity. In contrast, the composite electrolyte with a composition of 40SDC-60BZCY532 shows the lowest conductivity. In summary, the results show that BaZrO3-BaCeO3 based proton-conducting ceramic materials represent very promising materials for future ITSOFCs electrolyte applications. / <p>QC 20150423</p>