Optimisation d'interconnecteurs métalliques pour la production d'hydrogène par électrolyse de la vapeur d'eau à haute température (EVHT)

La technologie de l électrolyse de la vapeur d eau à haute température (EVHT) est unesolution alternative à la production d hydrogène. Le principe est inversé à celui d une pile àcombustible de type SOFC : on utilise la vapeur d eau et de l électricité afin de produire del hydrogène. Une difficulté technique majeure repose sur la mise au point d interconnecteursfonctionnant efficacement sur le long terme. Sur le plan électrique, l interconnecteur doitprésenter une valeur de résistance de contact aux électrodes la plus faible possible, car elleaffecte directement le rendement de conversion électrochimique (eau en hydrogène) et peutpénaliser le procédé. Il ne doit donc pas présenter une cinétique d oxydation élevée ni formerdes oxydes isolants électriquement. Sur le plan chimique, l interconnecteur doit être résistantà l oxydation sous atmosphère riche en oxygène côté anode et riche en vapeur d eau côtécathode. De plus, le problème de la volatilisation des oxydes de chrome, qui peuvent diffuseret empoisonner les électrodes, déterminant ainsi une réduction de l activité électrochimique etdes performances du stack sur des longues durées de fonctionnement, doit être réduit. Latempérature de fonctionnement comprise entre 700 et 900C permet l utilisationd interconnecteurs métalliques, qui présentent l avantage d une mise en oeuvre plus facile etd un coût plus faible par rapport aux interconnecteurs céramiques.Dans cette étude, deux matériaux ont été testés en tant qu interconnecteurs pour lessystèmes EVHT : un acier ferritique chromino-formeur K41X et un alliage Fe-Ni-Co necontenant pas de chrome. Le comportement envers la corrosion à haute température et laconductivité électrique des deux alliages ont été évalués à 800C sous un mélange 95%O2-5%H2O, pour le côté anodique, et 10%H2-90%H2O, pour le côté cathodique. Pour l alliageK41X, l effet de l état initial de la surface des échantillons sur la nature des oxydes formés àhaute température sous mélange H2-H2O a été pris en compte, à travers une comparaison desalliages bruts de laminage avec des surfaces polies miroir. L effet d une pré-oxydation decourte durée à 800C sur le comportement à haute température de l alliage K41X brut deréception sous atmosphère H2-H2O a également été évalué. Mais, le travail le plus original decette étude a consisté à effectuer des essais de marquage à l or et des marquages isotopiquessous mélange H216O-H218O, H2-D2O et D2-H2O. Ces tests ont permis d étudier lesmécanismes responsables de la croissance de la couche de corrosion de l alliage K41X brut deréception et poli miroir à 800C sous atmosphère H2-H2O et d évaluer le rôle de la vapeurd eau et de l hydrogène dans le mécanisme d oxydationThe high temperature water vapour electrolysis offers a promising method for highlyefficient hydrogen production. It works as an inverse solid oxide fuel cell, using water vapourand electricity in order to produce hydrogen. A major technical difficulty related to hightemperature water vapour electrolysis (HTVE) is the development of interconnects workingefficiently on a long period. From the electrical point of view, the interconnect must have alow contact resistance with the electrodes. Indeed, it directly affects the electrochemicalconversion efficiency (water into hydrogen) and it can penalize the process. The interconnectmust present a slow oxidation kinetics and form as less as possible electrical insulatingoxides. From the chemical point of view, the interconnect has to be resistant against oxidationin an oxygen rich atmosphere (anode side) and water vapour rich atmosphere (cathode side).Moreover, the problem of the volatility of chromium oxide species, which might migrate andpoison the electrodes, leading to a decrease in their electrochemical activity and degradationof stack performance, over long-term operation, needs to be reduced. The operatingtemperature between 700C and 900C allows the use of metallic interconnects, which havehigher electrical and thermal conductivities, easier shaping and lower cost, with respect to theceramic materials.In this study, two materials were tested as interconnects for the HTVE systems: a ferriticchromia-forming alloy, the K41X, and a Fe-Ni-Co alloy, which does not contain chromium.High temperature corrosion behaviour and electrical conductivity were tested in both anode(95%O2-5%H2O) and cathode (10%H2-90%H2O) atmospheres at 800C. Moreover, for theK41X alloy, the effect of the initial surface state of the samples on the chemical nature of theoxides formed at 800C in H2-H2O atmosphere was evaluated, by comparing as received andmirror polished surfaces. The effect of a short-term air preoxidation at 800C on the hightemperature behaviour of the K41X as received sample in H2-H2O atmosphere was tested.The most original part of this study consisted in the investigation of the oxidation mechanismsof both as received and mirror polished K41X samples at 800C in H2-H2O atmosphere bymeans of marking experiments using Au and isotopes (H216O-H218O mixture). Moreover,marking tests using H2-D2O and D2-H2O were carried out, in order to further investigate therole of hydrogen and water vapour in the oxidation mechanismDIJON-BU Doc.électronique (212319901) / SudocSudocFranceF

Curvature radius measurement by optical profiler and determination of the residual stress in thin films

The Stoney formula, based on the measurement of the substrate curvature, is often used for the determination of the thin films' residual stress. In this study, titanium nitride coatings were deposited by DC reactive magnetron sputtering on silicon substrates. An optical profiler was used to determine the curvature of the surface before and after coating. Two radii were then obtained, along the principal perpendicular directions of the surface curvature. A simple and efficient method to determine the experimental error on the stress calculation was developed taking into account the film thickness dispersion and the radii dispersion. Using constant deposition parameters, some samples' characteristics were tested: film and substrate thickness, size, shape and crystallographic orientations of the substrates. With the help of the developed error method, we analyzed what can be conclude about the influence of these characteristics on the calculated stress values, obtained from the experimental measurements

Development of Ti PVD Films to Limit the Carburization of Metal Powders during SPS Process

Spark plasma sintering technique is used for the fabrication of dense materials with a fine-grained microstructure. In this process, a powder is placed into a graphite mold and a uniaxial pressure is applied by two graphite punches. A graphite foil is inserted between the punches and the powder and between the mold and the powder to ensure good electrical, physical and thermal contact. One of the major drawbacks during sintering of metal powders is the carburization of the powder in contact with the graphite foils. In this study, a PVD coating of titanium was applied on the graphite foils in contact with the metal powder (pure iron). The results are promising, as the investigations show that the application of a Ti PVD film of 1.5 and 1.1 µm thickness is effective to completely avoid the carburization of iron powder. Carbon diffuses inside the PVD film during sintering. In parallel, iron diffusion was revealed inside the Ti coating of 1.5 µm thickness. On the other hand, a Ti PVD film of 0.5 µm thickness provides a protection against carbon diffusion just on the sides in contact with the mold, proving that the coating thickness represents an important parameter to consider

Effect of Pre-Oxidation on a Ti PVD Coated Ferritic Steel Substrate during High-Temperature Aging

A PVD coating is often applied on the surface of metallic alloys to improve their high-temperature resistance. In the present work, a thin titanium layer (1.2 µm) was deposited by PVD on the surface of a stainless steel substrate before high-temperature exposure (800 °C in ambient air). The underlying idea is that metallic Ti converts into Ti oxide (TiO2) during high-temperature aging at 800 °C, thereby slowing down the substrate oxidation. The stability of the coating with and without substrate pre-oxidation was investigated. Morphological, structural, and chemical characterizations were performed and completed by simulation of the film growth and measurement of the mechanical state of the film and the substrate. In the case of the sample that was not pre-oxidized, the oxidation of the steel was slowed down by the TiO2 scale but spallation was observed. On the other hand, when the steel was pre-oxidized, TiO2 provided more significant protection against high-temperature oxidation, and spalling or cracking did not occur. A combination of different kinds of stress could explain the two different behaviors, namely, the mechanical state of the film and the substrate before oxidation, the growing stress, and the thermal stress occurring during cooling down

Optimisation of metallic interconnects for hydrogen production by high temperature water vapour electrolysis (HTVE)

La technologie de l’électrolyse de la vapeur d’eau à haute température (EVHT) est unesolution alternative à la production d’hydrogène. Le principe est inversé à celui d’une pile àcombustible de type SOFC : on utilise la vapeur d’eau et de l’électricité afin de produire del’hydrogène. Une difficulté technique majeure repose sur la mise au point d’interconnecteursfonctionnant efficacement sur le long terme. Sur le plan électrique, l’interconnecteur doitprésenter une valeur de résistance de contact aux électrodes la plus faible possible, car elleaffecte directement le rendement de conversion électrochimique (eau en hydrogène) et peutpénaliser le procédé. Il ne doit donc pas présenter une cinétique d’oxydation élevée ni formerdes oxydes isolants électriquement. Sur le plan chimique, l’interconnecteur doit être résistantà l’oxydation sous atmosphère riche en oxygène côté anode et riche en vapeur d’eau côtécathode. De plus, le problème de la volatilisation des oxydes de chrome, qui peuvent diffuseret empoisonner les électrodes, déterminant ainsi une réduction de l’activité électrochimique etdes performances du « stack » sur des longues durées de fonctionnement, doit être réduit. Latempérature de fonctionnement comprise entre 700 et 900°C permet l’utilisationd’interconnecteurs métalliques, qui présentent l’avantage d’une mise en oeuvre plus facile etd’un coût plus faible par rapport aux interconnecteurs céramiques.Dans cette étude, deux matériaux ont été testés en tant qu’interconnecteurs pour lessystèmes EVHT : un acier ferritique chromino-formeur K41X et un alliage Fe-Ni-Co necontenant pas de chrome. Le comportement envers la corrosion à haute température et laconductivité électrique des deux alliages ont été évalués à 800°C sous un mélange 95%O2-5%H2O, pour le côté anodique, et 10%H2-90%H2O, pour le côté cathodique. Pour l’alliageK41X, l’effet de l’état initial de la surface des échantillons sur la nature des oxydes formés àhaute température sous mélange H2-H2O a été pris en compte, à travers une comparaison desalliages bruts de laminage avec des surfaces polies miroir. L’effet d’une pré-oxydation decourte durée à 800°C sur le comportement à haute température de l’alliage K41X brut deréception sous atmosphère H2-H2O a également été évalué. Mais, le travail le plus original decette étude a consisté à effectuer des essais de marquage à l’or et des marquages isotopiquessous mélange H216O-H218O, H2-D2O et D2-H2O. Ces tests ont permis d’étudier lesmécanismes responsables de la croissance de la couche de corrosion de l’alliage K41X brut deréception et poli miroir à 800°C sous atmosphère H2-H2O et d’évaluer le rôle de la vapeurd’eau et de l’hydrogène dans le mécanisme d’oxydationThe high temperature water vapour electrolysis offers a promising method for highlyefficient hydrogen production. It works as an inverse solid oxide fuel cell, using water vapourand electricity in order to produce hydrogen. A major technical difficulty related to hightemperature water vapour electrolysis (HTVE) is the development of interconnects workingefficiently on a long period. From the electrical point of view, the interconnect must have alow contact resistance with the electrodes. Indeed, it directly affects the electrochemicalconversion efficiency (water into hydrogen) and it can penalize the process. The interconnectmust present a slow oxidation kinetics and form as less as possible electrical insulatingoxides. From the chemical point of view, the interconnect has to be resistant against oxidationin an oxygen rich atmosphere (anode side) and water vapour rich atmosphere (cathode side).Moreover, the problem of the volatility of chromium oxide species, which might migrate andpoison the electrodes, leading to a decrease in their electrochemical activity and degradationof stack performance, over long-term operation, needs to be reduced. The operatingtemperature between 700°C and 900°C allows the use of metallic interconnects, which havehigher electrical and thermal conductivities, easier shaping and lower cost, with respect to theceramic materials.In this study, two materials were tested as interconnects for the HTVE systems: a ferriticchromia-forming alloy, the K41X, and a Fe-Ni-Co alloy, which does not contain chromium.High temperature corrosion behaviour and electrical conductivity were tested in both anode(95%O2-5%H2O) and cathode (10%H2-90%H2O) atmospheres at 800°C. Moreover, for theK41X alloy, the effect of the initial surface state of the samples on the chemical nature of theoxides formed at 800°C in H2-H2O atmosphere was evaluated, by comparing as received andmirror polished surfaces. The effect of a short-term air preoxidation at 800°C on the hightemperature behaviour of the K41X as received sample in H2-H2O atmosphere was tested.The most original part of this study consisted in the investigation of the oxidation mechanismsof both as received and mirror polished K41X samples at 800°C in H2-H2O atmosphere bymeans of marking experiments using Au and isotopes (H216O-H218O mixture). Moreover,marking tests using H2-D2O and D2-H2O were carried out, in order to further investigate therole of hydrogen and water vapour in the oxidation mechanis

Optimisation d'interconnecteurs métalliques pour la production d'hydrogène par électrolyse de la vapeur d'eau à haute température (EVHT)

The high temperature water vapour electrolysis offers a promising method for highlyefficient hydrogen production. It works as an inverse solid oxide fuel cell, using water vapourand electricity in order to produce hydrogen. A major technical difficulty related to hightemperature water vapour electrolysis (HTVE) is the development of interconnects workingefficiently on a long period. From the electrical point of view, the interconnect must have alow contact resistance with the electrodes. Indeed, it directly affects the electrochemicalconversion efficiency (water into hydrogen) and it can penalize the process. The interconnectmust present a slow oxidation kinetics and form as less as possible electrical insulatingoxides. From the chemical point of view, the interconnect has to be resistant against oxidationin an oxygen rich atmosphere (anode side) and water vapour rich atmosphere (cathode side).Moreover, the problem of the volatility of chromium oxide species, which might migrate andpoison the electrodes, leading to a decrease in their electrochemical activity and degradationof stack performance, over long-term operation, needs to be reduced. The operatingtemperature between 700°C and 900°C allows the use of metallic interconnects, which havehigher electrical and thermal conductivities, easier shaping and lower cost, with respect to theceramic materials.In this study, two materials were tested as interconnects for the HTVE systems: a ferriticchromia-forming alloy, the K41X, and a Fe-Ni-Co alloy, which does not contain chromium.High temperature corrosion behaviour and electrical conductivity were tested in both anode(95%O2-5%H2O) and cathode (10%H2-90%H2O) atmospheres at 800°C. Moreover, for theK41X alloy, the effect of the initial surface state of the samples on the chemical nature of theoxides formed at 800°C in H2-H2O atmosphere was evaluated, by comparing as received andmirror polished surfaces. The effect of a short-term air preoxidation at 800°C on the hightemperature behaviour of the K41X as received sample in H2-H2O atmosphere was tested.The most original part of this study consisted in the investigation of the oxidation mechanismsof both as received and mirror polished K41X samples at 800°C in H2-H2O atmosphere bymeans of marking experiments using Au and isotopes (H216O-H218O mixture). Moreover,marking tests using H2-D2O and D2-H2O were carried out, in order to further investigate therole of hydrogen and water vapour in the oxidation mechanismLa technologie de l’électrolyse de la vapeur d’eau à haute température (EVHT) est unesolution alternative à la production d’hydrogène. Le principe est inversé à celui d’une pile àcombustible de type SOFC : on utilise la vapeur d’eau et de l’électricité afin de produire del’hydrogène. Une difficulté technique majeure repose sur la mise au point d’interconnecteursfonctionnant efficacement sur le long terme. Sur le plan électrique, l’interconnecteur doitprésenter une valeur de résistance de contact aux électrodes la plus faible possible, car elleaffecte directement le rendement de conversion électrochimique (eau en hydrogène) et peutpénaliser le procédé. Il ne doit donc pas présenter une cinétique d’oxydation élevée ni formerdes oxydes isolants électriquement. Sur le plan chimique, l’interconnecteur doit être résistantà l’oxydation sous atmosphère riche en oxygène côté anode et riche en vapeur d’eau côtécathode. De plus, le problème de la volatilisation des oxydes de chrome, qui peuvent diffuseret empoisonner les électrodes, déterminant ainsi une réduction de l’activité électrochimique etdes performances du « stack » sur des longues durées de fonctionnement, doit être réduit. Latempérature de fonctionnement comprise entre 700 et 900°C permet l’utilisationd’interconnecteurs métalliques, qui présentent l’avantage d’une mise en oeuvre plus facile etd’un coût plus faible par rapport aux interconnecteurs céramiques.Dans cette étude, deux matériaux ont été testés en tant qu’interconnecteurs pour lessystèmes EVHT : un acier ferritique chromino-formeur K41X et un alliage Fe-Ni-Co necontenant pas de chrome. Le comportement envers la corrosion à haute température et laconductivité électrique des deux alliages ont été évalués à 800°C sous un mélange 95%O2-5%H2O, pour le côté anodique, et 10%H2-90%H2O, pour le côté cathodique. Pour l’alliageK41X, l’effet de l’état initial de la surface des échantillons sur la nature des oxydes formés àhaute température sous mélange H2-H2O a été pris en compte, à travers une comparaison desalliages bruts de laminage avec des surfaces polies miroir. L’effet d’une pré-oxydation decourte durée à 800°C sur le comportement à haute température de l’alliage K41X brut deréception sous atmosphère H2-H2O a également été évalué. Mais, le travail le plus original decette étude a consisté à effectuer des essais de marquage à l’or et des marquages isotopiquessous mélange H216O-H218O, H2-D2O et D2-H2O. Ces tests ont permis d’étudier lesmécanismes responsables de la croissance de la couche de corrosion de l’alliage K41X brut deréception et poli miroir à 800°C sous atmosphère H2-H2O et d’évaluer le rôle de la vapeurd’eau et de l’hydrogène dans le mécanisme d’oxydatio

316L Stainless-Steel Carburizing Close to Eutectic Transformation Using the Spark Plasma Sintering Process

This work focuses on the 316L austenitic stainless-steel case-hardening microstructure, after the SPS process near the solid/liquid state transition temperature. This process, faster than conventional carburizing techniques, is equivalent to weld cladding, allowing the achievement of high surface carbon contents with large-size carbide grains in the case of partial melting. Three distinct zones were formed: internal carburizing, carburizing with melting, and carburizing with melting and chromium depletion; all three composed of mixed carbides (Cr0.4Fe0.6)7C3 distributed in an austenitic matrix. The internal carburizing layer growths following a parabolic kinetic law with kp 1027 cm2/s, while the advancement of the melting front is very fast and follows a linear law with kl = 1.0 3 1024 cm2/s at 1100 °C. The Cr-depleted fusion zone microstructure is similar to a composite material with a metallic matrix, which includes graphite particles, Mo-rich intermetallic phases, and core-shell eutectic carbides. The partial melting zone without Cr depletion shows the formation of a dense carbide layer with diameters exceeding 10 µm, constituting 60% of the volume, and achieving a hardness of 850 HV5. Its wear rate is about 100 times lower than the 316L steel, indicating a significant improvement in the alloy's wear behavior

Effect of the microstructure on the tribological properties of HIPed and PTA-welded Fe-based hardfacing alloy

his work focuses on the comparison of the tribological properties of Norem02, a Fe-based hardfacing elaborated by hot isostatic pressing (HIP), a pressure-assisted sintering technique and by plasma transferred arc welding (PTAW), a more conventional coating process. The influence of the microstructural modifications induced by the elaboration process is investigated. The aim of the present study is to assess the possibility of considering HIP as an effective alternative to more conventional hardfacing techniques. Wear tests were carried out using a pin-on-disk tribometer with ball-on-plate configuration under loads of 2, 5 and 10 N against a WC-Co ball counterpart. The worn tracks present typical marks of abrasive wear followed by oxidative but also adhesive ones. HIPed sample presents a dominance of oxidative and adhesive wear, while for sample elaborated by PTAW the dominant mechanism is abrasive wear. The results indicate that in the case of the HIPed alloy the wear resistance is generally increased and under a load of 10 N the wear rate of the HIPed Norem02 is reduced of about 5.5 times. The fine microstructure obtained by HIP, containing small globular carbides well dispersed in the matrix allows the alloy to better withstand the mechanical stresses occurring during the wear tests, reducing the surface damages.Chaire Framatome. Région Bourgogne-Franche-Comt

Effect of Water Vapor on the Oxidation Mechanisms of a Commercial Stainless Steel for Interconnect Application in High Temperature Water Vapor Electrolysis.

International audienceHigh temperature water vapor electrolysis is one of the most promising methods for hydrogen production. The interconnect is a key component in the electrolyse technology. In a previous paper, the high temperature corrosion resistance and the electrical conductivity of a commercial ferritic stainless steel, K41X (AISI 441), were assessed in both anode (95 %O2–5 %H2O) and cathode atmospheres (10 %H2–90 %H2O). In cathode atmosphere, ageing tests performed up to 1,000 h revealed the formation of a duplex oxide scale: an inner layer consisting of protective chromia and an outer layer comprised of a magnetite-type iron oxide. In this study, we further investigated the oxidation mechanisms of K41X alloy in cathode atmosphere by means of marker experiments using an inert marker (Au) and isotopes. SEM-EDX and SIMS characterizations were combined in order to determine the oxide scale growth processes. The roles played by hydrogen and water vapor are discussed and a diffusion mechanism is postulated

Comparison of thermal diffusion and interfacial reactions for bulk and sputtered titanium on 316L stainless steel

International audienceAs a first step to devise a hybrid process for the production of TiC wear coatings on 316L, consisting of magnetron sputtering followed by titanium carburization, interfacial reactivity between stainless steel and titanium has to be finely understood. Systematic comparisons were carried out on diffusion couples of increasing chemical and geometrical complexity (Fe/Ti, 316L/Ti, and 316L/sputtered Ti), highlighting the formation mechanisms of interfacial structures. Transmission and scanning electron microscopy composition profiles revealed that long-range microstructures in titanium are the result of iron diffusion and oxygen impurities interactions. FeTi and Fe2Ti intermetallics formation is first kinetically driven, then favors thermodynamic stability, leading to compositional changes during thermal cycles. Their growth is shown to be non-diffusion controlled. These compounds act as diffusion barriers for chromium, and traps for carbon, indirectly generating a complex layered structure at the interface. Differences between bulk and sputtered titanium are exclusively linked to the latter smaller scale, including destabilized diffusion fronts, and superficial TiO formation by oxygen rejection after iron diffusion