Search results for " oxidation"

Effect of pH and nitrite concentration on nitrite oxidation rate

2011

The effect of pH and nitrite concentration on the activity of the nitrite oxidizing bacteria (NOB) in an activated sludge reactor has been determined by means of laboratory batch experiments based on respirometric techniques. The bacterial activity was measured at different pH and at different total nitrite concentrations (TNO 2). The experimental results showed that the nitrite oxidation rate (NOR) depends on the TNO 2 concentration independently of the free nitrous acid (FNA) concentration, so FNA cannot be considered as the real substrate for NOB. NOB were strongly affected by low pH values (no activity was detected at pH 6.5) but no inhibition was observed at high pH values (activity wa…

Resonant wavelength control of a 1.3 µm microcavity by intracavity steam oxidation

2003

Wine-making with protection of must against oxidation in a warm, semi-arid terroir

2016

In order to defend varietal aromas from oxidation before alcoholic fermentation, two musts were prepared from white grapes pre-cooled and added with ascorbic acid and solid CO2 (trial ACO2) or SO2 (trial BSO2). Experiments were performed with grapes of a white grape variety indigenous to western Sicily, the wines from which, obtained by vinification of musts protected from oxidation and poor in copper, as previously proven, have aroma descriptors ascribed to passion fruit and grapefruit skin. The smaller content in flavanols in the ACO2 trial, demonstrated that the use of solid CO2, instead of SO2, reduced the extraction of such polyphenols from grape solids. The higher content in hydroxyci…

Xanthine oxidase catalyzes the oxidation of retinol.

2007

In mammals, xanthine oxidase (E.C. 1.17.3.2) catalyzes the hydroxylation of a wide variety of heterocyclic substrates such as purines, pyrimidines, and pterins, in addition to aldehydes [1] as all-trans-retinaldehyde [2-5]. Here, we show that buttermilk xanthine oxidase was capable to oxidizing all-trans-retinol (t-ROL) to all-trans-retinaldehyde (t-RAL) that was successively oxidized to all-trans-retinoic acid (t-RA). A rise in the enzyme activity, when t-ROL-CRBP complex was assayed, with respect to the free t-ROL, was observed. Furthermore, treatment of the enzyme with Na2S and glutathione resulted in a significant increment in catalytic activity toward t-ROL and t-RAL, due to the recons…

Study of the fuel/clad bonding of pressurized water reactors fuel rods

2017

Durability and integrity of materials used in nuclear power plants is a continuous concern of the nuclear power plant owners and developers. During the fuel irradiation in pressurised water reactors (PWR), the whole fuel-clad assembly is subjected to several irradiation-induced modifications. In particular, the fuel element expansion concomitant to the cladding creeping, leads to the contacting of both materials, allowing the oxidation of the inner side of the clad, locally at first, then tending to affect the overall cladding inner surface. At high burnup, a bonding of the fuel periphery with the metallic cladding can be observed, forming the fuel-clad bonding phenomenon, which conditions …

Influence of the preparation method on the activity of ceria zirconia mixed oxides for naphthalene total oxidation

2013

Cerium/zirconium mixed oxides, with different Ce/Zr ratios, have been synthesised by a co-precipitation method using two different precipitating agents (sodium carbonate and urea) and tested for the total oxidation of naphthalene. Catalysts were characterized by N2 adsorption, XRD, Raman, TPR, XPS and DRIFTS. Ceria prepared by carbonate precipitation had low activity and this is likely to be related to the high concentration of residual surface carbonate that covers catalytic sites and inhibits reaction. For carbonate precipitation, increasing the Zr content to 1% resulted in a significant increase of activity, which is related to the decrease of surface carbonate. Increasing the Zr content…

ZrO2 based materials: preparation, characterization and photocatalytic activity for 2-propanol oxidation and CO2 reduction

2017

ZrO2 based materials: preparation, characterization and photocatalytic activity for 2-propanol oxidation and CO2 reduction

Microstructure impact on high temperature corrosion behavior of AISI 316L stainless steel additively manufactured by Selective Laser Melting (AM-SLM)

2019

International audience; Additive Manufacturing by Selective Laser Melting (AM-SLM) is a near-net shape method producing dense and geometrically complex materials from micrometric powders. This process involves complete melting and very high cooling rates who induce a refinement of microstructure, improving the mechanical properties of the material [1,2]. However, the impact of these new microstructures on real functioning properties, like for instance the high temperature durability, needs to be studied. In this purpose, AISI 316L is considered in this work. Samples elaborated by AM-SLM and by conventional metallurgy were oxidized under laboratory air at 900°C for periods up to 3000h. The r…

Coupled Modelling of ZrO 2 /α-Zr(O) Layers Growth under Thermal and Mechanical Gradients

2019

The oxidation process of a nuclear reactor fuel rod clad made of zirconium is simulated. It is assumed that the oxygen is transported by anionic diffusion in the zirconia layer (ZrO2). Part of this oxygen reacts at the interface between the zirconia layer and the metal, while the rest diffuses in the oxygen-enriched metal volume (α-Zr(O)) to the core of the metal by an interstitial mechanism. The model is based on the thermodynamics of irreversible processes and takes into account the influence of driving forces on the oxygen migration in the metal such as the oxygen concentration gradient, the temperature gradient [1] and the mechanical stress gradient [2]. The growth of both ZrO2 and α-Zr…

Interconnecteurs métalliques de piles à combustible de type SOFC - Résistance à la corrosion et conductivité électrique à haute température

2009

The need of interconnect to connect individual cells into electrical series in a SOFC stack appears as one of the most important point in fuel cell technology. The main important criteria requires for interconnect is an excellent oxidation resistance in air and in H2/H2O. The goal of this study is to determine the influence on corrosion behaviour of a reactive element oxide coating (La2O3, Y2O3) realized by MOCVD on different metallic alloys like Crofer22APU, Haynes230 and Fe30Cr. The realisation of long ageing (7 700 and 15 400 hours) proved to be insightful. The corrosion kinetic experiments, the oxide scale characterisation and ASR measurements established that the presence of perovskite…