Oxidation of a chromia-forming nickel base alloy at high temperature in mixed diluted CO/H2O atmospheres

International audienceCorrosion of a chromia-forming nickel base alloy, Haynes 230_, has been investigated under impure helium containing a few Pa of CO and H2O at 900 °C. It has been found that this alloy reacts simultaneously with CO and H2O. Oxidation by CO has been revealed to occur mainly in the first hours. CO diffuses through the scale via short-circuit pathways and oxidizes Al, Cr and Si at the oxide/metal interface. Kinetics of CO oxidation has been investigated and several rate limiting steps are proposed. In the long term, H2O is the major oxidant of chromia-forming nickel base alloys in impure helium

Etude des premiers instants d'oxydation d'un acier ferrito-martensitique FE-12CR dans le CO2

Dans le cadre du développement des réacteurs nucléaires de 4ème génération et plus particulièrement du réacteur à neutrons rapides refroidi au sodium (SFR), le CO2 supercritique, dans un cycle de Brayton, a été identifié comme fluide potentiel en remplacement de la vapeur d'eau dans le cycle de conversion de l'énergie. Les aciers ferrito-martensitiques contenant 9 à 12 % en poids de Cr sont de bons candidats pour la réalisation d'échangeurs thermiques car ils présentent de bonnes propriétés mécaniques jusqu'à une température de 600C, une forte conductivité thermique, un faible coefficient d'expansion thermique ainsi qu'un coût plus faible que celui des aciers austénitiques. Cependant, il a été montré que ces aciers forment une couche d oxyde à croissance rapide et carburent fortement dans les conditions du circuit de conversion d'énergie (550C, 250 bar).Cette étude a pour objectif d étudier l influence de différents paramètres (les impuretés présentes dans le CO2, les vitesses de rampe thermique ainsi que l état de surface) sur le mécanisme d oxydation d un acier Fe-12Cr dans le CO2 à 550C. Il est montré qu en fonction de la valeur de ces paramètres, il est possible de former une couche d oxyde fine protectrice en surface sans carburation. Un modèle permettant de rendre compte de l ensemble des résultats expérimentaux est proposé.In the framework of the development of Sodium Fast Reactors in France, supercritical carbon dioxide integrated in the Brayton cycle is proposed as new cycle energy conversion system to replace current steam generators. Ferritic-Martensitic steels with 9-12 wt% Cr are good candidates for heat exchanger application because they have good mechanical properties up to a temperature of 600C, a high thermal conductivity, a low coefficient of thermal expansion and a lower cost than that of austenitic steels. However, it has been found that these steels present a high parabolic oxide growth rate and a strong carburization in the temperature and pressure conditions of the SC-CO2 cycle (550C, 250 bar).This study aims to investigate the influence of different parameters (impurities present in CO2, thermal ramp rate and surface state) on the oxidation mechanism of a Fe-12 Cr steel in CO2 at 550C. It has been shown that depending on these parameters, a thin protective oxide scale without any strong carburization can be obtained. A model is proposed to explain the experimental results.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

Etude de l'Evolution Physico-Chimique du Substrat lors de l'Oxydation à Haute Température des Alliages Modèle Ni-Cr à Faible Teneur en Chrome et de l'Alliage Modèle Ni-16Cr-9Fe

Le travail réalisé au cours de cette thèse concerne l analyse des conséquences de l oxydation à 950C des alliages base Ni sur la composition de l alliage à proximité de l interface alliage/oxyde. Deux catégories d alliages ont été analysées : alliages à faible teneur en chrome conduisant à l oxydation interne et l alliage chromino-formeur Ni-16Cr-9Fe.Une description complète des mécanismes de l oxydation interne du chrome est obtenue à partir du développement du modèle analytique de Wagner d oxydation interne et du développement du modèle numérique de Feulvarch. Ces modèles décrivent l évolution de l oxydation interne jusqu à la transition oxydation interne / oxydation externe à 11 %poids de chrome environ.L analyse par la spectroscopie d électrons Auger de l alliage modèle Ni-16Cr-9Fe à 950C oxydé pendant 10 heures a permis d explorer la zone à proximité immédiate de l interface alliage/oxyde et de déterminer la concentration en chrome à l interface à 0,5%poids (i.e. dans 20 premiers nanomètres), ce qui est en accord avec le modèle analytique de Wagner d oxydation en couche compacte. La description des profils de déchromisation et des profils de cavités pour plusieurs temps d exposition allant de 100h à 5000h a permis de mettre en évidence une corrélation forte entre ces deux phénomènes (même constante parabolique). Pour ces durées d oxydation les profils de déchromisation présentent un point d inflexion ce qui se traduit par l augmentation de la teneur en chrome à l interface. Les résultats sont interprétés dans le cadre d un nouveau modèle analytique avec l hypothèse d injection des lacunes produites par l effet Kirkendall au point d inflexion.The present work is focused on the consequences of oxidation at 950C on the nature of a chromium-depleted area in Ni-based alloys. Two classes of alloys were analysed : low chromium Ni-Cr alloys and a typical chromia-former Ni-16Cr-9Fe.A complete description of the mechanisms of nodular oxidation is obtained from the development of both the Wagner s analytical model of internal oxidation and the Feulvarch s numerical model. These models describe the evolution of nodular oxidation up to the transition between internal to external oxidation which happens at around 11 wt%Cr.Auger Electron Spectroscopy (AES) measurements on a model Ni-16Cr-9Fe alloy oxidised at 950C during 10 hours has allowed a detailed analysis in the immediate vicinity of the oxide/alloy interface and resulted in a very low Cr content in first 20 nm of the subsurface layer. This result is in agreement with Wagner s theory of external oxidation of binary alloys. Higher oxidation times, from 100h to 5000h, have resulted in extensive cavitation and chromium depletion, both quantified respectively by image analysis and EDX. These profiles appear to be strongly correlated (same parabolic constant). Higher oxidation times result in an inflection point on chromium depletion profile and higher Cr interface content, which are due to the increased chromium diffusivity. The overall results are interpreted in the frame of a new analytical model based on the assumption of Kirkendall vacancy injection at the inflection point.ST ETIENNE-ENS des Mines (422182304) / SudocSudocFranceF

Perceptual model for adaptive local shading and refresh rate

When the rendering budget is limited by power or time, it is necessary to find the combination of rendering parameters, such as resolution and refresh rate, that could deliver the best quality. Variable-rate shading (VRS), introduced in the last generations of GPUs, enables fine control of the rendering quality, in which each 16×16 image tile can be rendered with a different ratio of shader executions. We take advantage of this capability and propose a new method for adaptive control of local shading and refresh rate. The method analyzes texture content, on-screen velocities, luminance, and effective resolution and suggests the refresh rate and a VRS state map that maximizes the quality of animated content under a limited budget. The method is based on the new content-adaptive metric of judder, aliasing, and blur, which is derived from the psychophysical models of contrast sensitivity. To calibrate and validate the metric, we gather data from literature and also collect new measurements of motion quality under variable shading rates, different velocities of motion, texture content, and display capabilities, such as refresh rate, persistence, and angular resolution. The proposed metric and adaptive shading method is implemented as a game engine plugin. Our experimental validation shows a substantial increase in preference of our method over rendering with a fixed resolution and refresh rate, and an existing motion-adaptive techniqu

Mechanism of destruction of the protective oxide layer on Alloy 230 in the impure helium atmosphere of Very High Temperature Reactors.

International audienceAlloy 230 which contains 22wt.% chromium could be a promising candidate material for structures and heat exchangers (maximum operating temperature: 850°-950°C) in Very High Temperature Reactors (VHTR). The feasibility demonstration involves to valid its corrosion resistance in the reactor specific environment namely impure helium. The alloys surface reactivity was investigated at temperatures between 850 and 1000°C. Two main behaviours have been revealed: the formation of a protective Cr/Mn rich oxide layer at 900°C and its following destruction at higher temperatures. Actually, above a critical temperature called TA, oxide is reduced at the oxide/metal interface by carbon in solution in the alloy. To ascribe the scale destruction, a model is proposed based on thermodynamic interfacial data for the alloy (chromium and carbon activity), oxide layer morphology and carbon monoxide partial pressure in helium. The proposed mechanism is then validated regarding experimental results and observations on alloy 230 and model alloys

Hydrogen induced cracking of ultra high strength 350 grade maraging steel

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The role of 401A>G polymorphism of methylenetetrahydrofolate dehydrogenase gene (MTHFD1) in fetal hypotrophy

Introduction: Important role is attributed to genetic polymorphisms influencing enzymatic activity in folate metabolism. These inherited genetic variants may influence fetal growth and fetal hypotrophy development. The aim of the study was to investigate the connection of 401A>G polymorphism of methyleneterahydrofolate dehydrogenasegene (MTHFD1) with increased risk of fetal hypotrophy. Material and methods: To the study group 120 women who delivered children with fetal hypotrophy and to the control group 120 healthy women were enrolled. Study group was divided into subgroups according to gestational age at delivery (52 patient

A model of internal crack extension due to a continuous build-up of hydrogen pressure: Application to a pressure vessel component

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Palliative chemotherapy with kapecytabine and gemcytabine in patients with advenced gallbladder cancer

U 4 chorych na zaawansowanego raka pęcherzyka żółciowego (III lub IV stopień klinicznego zaawansowania) podjęto próbę paliatywnej chemioterapii. U wszystkich chorych wykluczono możliwość leczenia chirurgicznego. Schemat chemioterapii GX obejmował podawanie kapecytabiny (doustnie w dawce 2500 mg/m2 codziennie przez 14 dni) i gemcytabiny (dożylnie w dawce 1000 mg/m2 w dniach pierwszym i ósmym; cykle powtarzane w odstępie 21 dni). U wszystkich chorych uzyskano normalizację lub znaczne obniżenie wartości wyjściowo nieprawidłowych parametrów czynności wątroby (transaminazy i bilirubiny) oraz markerów surowiczych (CEA i CA 19.9), a także stwierdzono złagodzenie lub ustąpienie dolegliwości. Powyższe obserwacje uzasadniają podjęcie prospektywnej oceny wartości chemioterapii z zastosowaniem kapecytabiny i gemcytabiny pod względem wpływu na wskaźniki przeżycia chorych z rozpoznaniem zaawansowanego raka pęcherzyka żółciowego.Palliative chemotherapy was attempted in 4 patients with advanced gallbladder carcinoma (stage III or IV).The possibility of surgical treatment was excluded at all patients. Chemotherapy regimen GX included capecitabine (orally in the daily dose of 2500 mg/m2 day 1 to 14) and gemcitabine (intravenously in the dose 1000 mg/m2 day 1 and 8; repeated every 21 days). Normalization or significant reduction of initially elevated liver function tests (transaminases and bilirubin) and serum markers (CEA and CA 19.9) as well as symptom improvement or disapearance were found in all patients. These findings justify prospective study evaluating capecitabine- and gemcitabine-containing chemotherapy with regard of its impact on survival rates in patients with advanced gallbladder carcinoma

Udział polimorfizmu Hind III C>G genu PAI-1 w etiologii poronień nawracających

Objectives: The goal of the study was to assess the relationship of HindIII C>G PAI-1 gene polymorphism with increased risk of recurrent miscarriages. Material and methods: A whole of 152 women with a history of at least two miscarriages were classified into analysis. The study group was divided twice (114 subjects with 2 miscarriages and 38 subjects with >3 miscarriages, 123 subjects with miscarriages at 3 miscarriages (50.0% vs. 42.2% in controls, OR=1.37, p=0.13). A tendency of higher frequency of HindIII GG genotype and HindIII G allele was also noted in the subgroup of patients with miscarriages in the first and second trimester (HindIII GG: 31.0% vs. 20.0% in controls, OR=1.80, p=0.14, HindIII G: 51.7% vs. 42.2% in controls, OR=1.47, p=0.11). Conclusions: Mutated HindIII G allele and HindIII GG genotype of HindIII C>G polymorphism probably augment the risk of recurrent miscarriages.Cel pracy: Ocena związku polimorfizmu HindIII C>G genu PAI-1 z występowaniem poronień nawracających. Metody: W badaniu uwzględniono dwie grupy kobiet: 152 pacjentki z obciążonym wywiadem w kierunku występowania poronień (dwóch lub więcej) oraz 180 pacjentek, u których potwierdzono w wywiadzie co najmniej jedną ciążę o niepowikłanym przebiegu, zakończoną urodzeniem zdrowego, donoszonego noworodka oraz wykluczono wystąpienie poronień. W grupie kobiet z poronieniami nawracającymi dokonano podziału na podgrupy (114 kobiet z dwoma poronieniami w wywiadzie oraz 38 kobiet z >3 poronieniami w wywiadzie, 123 pacjentki, u których poronienia występowały poniżej 13 tc. oraz 29 kobiet, u których poronienia miały miejsce poniżej 21 tc.). Analizę genetyczną przeprowadzono przy zastosowaniu metody PCR/RFLP. Wyniki: Zmutowany genotyp HindIII GG w grupie badanej występował z częstością 25,7%, natomiast wśród kobiet z grupy kontrolnej z częstością 20,0% (OR=1,38, p=0,14). Podobna obserwacja dotyczyła częstości występowania zmutowanego allela HindIII G (45,7% vs. 42,2% w grupie kontrolnej, OR=1,15, p=0,20). W podgrupie pacjentek z >3 poronieniami frekwencja genotypu HindIII GG była wyraźnie wyższa niż w grupie kontrolnej (31,6% vs. 20,0% w grupie kontrolnej, OR=1,85, p=0,09). Również frekwencja allela HindIII G była wyższa w tej podgrupie (50,0% vs. 42,2% w grupie kontrolnej, OR=1,37, p=0,13). Tendencja do częstszego występowania genotypu HindIII GG i allela HindIII G była także obserwowana u pacjentek z poronieniami G genu PAI-1 prawdopodobnie zwiększają ryzyko występowania poronień nawracających