Steam Oxidation Research Articles

Effect of aging and α’ segregation on oxidation and electrochemical behavior of FeCrAl alloys

FeCrAl alloys are promising candidates for next generation nuclear fuel cladding applications due to their high resistance to hydrothermal corrosion, high temperature steam oxidation, fretting, and creep properties. However, a potential area of concern for FeCrAl alloys is the precipitation of Cr-enriched α’ phase which could have an implication on the mechanical, oxidative degradation as well as electrochemical behavior. Studies in this area are limited since most of the past applications of FeCrAl alloys have been in high temperatures above the miscibility gap. In this work, we investigate the high temperature oxidation and electrochemical behavior of a modified APMT (Fe21Cr5Al3Mo) alloy in unaged condition in comparison with a thermally aged condition having α’ phase segregation. The α’ is shown to have no major role in steam oxidation resistance of FeCrAl alloys. The electrochemical behavior in chloride environments shows that the presence of α’ slightly reduces the pitting potential but shows an overall increase in polarization resistance indicating that α’ may enhance corrosion resistance in chloride environments by increasing passivation.

Oxidation performance and limitations of additively manufactured SiC/Si─O─C composites at elevated temperatures

AbstractSiC preforms were infiltrated with polycarbosiloxane preceramic polymer to create low‐cost SiC—SixOyCz matrix composites for possible high temperature application. The effect of specimen annealing conditions on the steam and air oxidation resistance was analyzed. Air exposures from 900–1500°C showed stability of the SixOyCz matrix phase with moderate oxidation resistance. After 900°C exposures, oxidation of the composite is primarily limited to the matrix phase, and only at 1200 and 1500°C was SiC consumption visualized. Steam cycle exposures at 1200°C resulted in rapid linear oxidation of the composites with induced specimen swelling from volume expansion associated with internal oxidation. Specimens annealed in argon were found to be the most oxidation resistant due to increased matrix crystallinity and carbon retention. The results of this work were used to develop clear strategies for improving the high‐temperature properties of SiC—SixOyCz composites.

Oxidation behaviour of Ni-base superalloy 617 in simulated Advanced Ultra Supercritical (AUSC) steam

Alloy 617 was exposed in a simulated Advanced Ultra Supercritical (AUSC) steam oxidation test loop at 650–710 ℃, 31 MPa for 600 h. Detailed characterization of the oxide scales was carried out using Transmission Electron Microscopy coupled with Precession Electron Diffraction. The alloy 617 showed insignificant weight gains with super-parabolic kinetics. The oxide scale formed on the alloy consisted of a thin inner Cr2O3 layer and outer islands of (Mn,Ni,Fe)Cr2O4 spinel with negligible internal oxidation zone comprising Al2O3. The mechanistic aspect of AUSC steam oxidation is discussed.

Microstructure dependent burst behavior of oxide dispersion–strengthened FeCrAl cladding

Oxide dispersion–strengthened (ODS) FeCrAl alloys are an advanced cladding material that combines the high-temperature steam oxidation resistance of conventional wrought FeCrAl with the irradiation resistance and high-temperature strength of nanostructured ferritic alloys. In the present study, the effect of microstructure on the performance of the ODS FeCrAl alloy system in light-water reactor–accident scenarios is evaluated using a combination of experimentation and modeling. ODS FeCrAl alloy with nominal composition Fe-12Cr-6Al-0.3Zr-0.3Y2O3 was produced into a thin-walled tube via high-precision tube rolling. A portion of the as-received (AR) tube was subjected to a full recrystallization heat treatment. Both variants were subjected to burst testing at Oak Ridge National Laboratory’s Severe Accident Test Station. The recrystallized tube exhibited burst temperature margins 200 °C higher than that of C26M, whereas the AR tube only achieved burst properties comparable to the wrought FeCrAl alloy. The burst experiments were simulated in the BISON finite element code through the development of new viscoplastic material databases for each heat treatment condition, informed by high temperature tensile tests of tube specimens and existing literature data on creep mechanisms. Finally, an ODS FeCrAl burst criterion was obtained using simulated burst experiments across the entire range of test conditions.

Hierarchically Porous Iron Alloys with High Sintering Resistance During Cyclic Steam Oxidation and Hydrogen Reduction

AbstractHydrogen release/storage materials for iron/air batteries are fabricated as Fe‐16Mo and Fe‐24Ni (at.%) lattices via 3D‐extrusion printing of foamed inks containing oxide microparticles, followed by H2 reduction and sintering. A hierarchical open porosity is designed: (i) channels between walls created during printing, (ii) mesopores within walls, created during ink foaming, and (iii) micropores within ligaments between mesopores, created from partial sintering metal particles and gas escape during cycling. When subjected to H2/H2O redox cycling at 800 °C, the lattices of both compositions gradually undergo sintering. The Fe‐16Mo lattice remains fully redox‐active after 50 cycles unlike the Fe‐24Ni lattice, which loses 90% of its redox capacity after 30 cycles. The increased lifetime of the Fe‐16Mo lattice is attributed to the sintering inhibition of Mo, the formation of a mixture of oxide phases in the oxidized state, and the cyclic formation of submicron Fe2Mo by reduction of MoO2 and Fe2Mo3O8. The microstructure of the foamed walls is examined throughout cycling to track changes in morphology and composition. These are correlated to volume and porosity changes in the lattice. A comparison is made to previously‐studied Fe‐Mo and Fe‐Ni freeze‐cast lamellar foams, and variations in performance are discussed in the context of the different architectures.

Improved oxidation resistance of Cr/FeCrAl coating on Zr alloy in high-temperature steam environment

A new bi-layer Cr/FeCrAl coating was successfully fabricated on the Zr-4 plates through multi-arc ion plating in order to take advantage of the two materials of FeCrAl and Cr. The high-temperature steam oxidation behavior of the Cr/FeCrAl-coated Zr-4 at 1000–1200 °C was investigated and compared with that of bare and single-layer FeCrAl-coated Zr-4. Various analytical techniques including scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS), X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used for the microstructural and compositional analysis of the as-deposited and oxidized samples. Results indicated that the FeCrAl-coated Zr-4 could only withstand up to 1000 °C because of the severe FeZr interdiffusion. Whereas the introduction of the Cr interlayer effectively prevented fast FeZr interdiffusion and consequently improves the overall oxidation resistance of the Zr substrate below 1200 °C steam environment. After 1100 °C steam oxidation, the weight gain of the Cr/FeCrAl-coated Zr-4 was about 8 times and 2 times lower than that of the uncoated and FeCrAl-coated Zr-4 alloys, respectively. These facts make possible the use of FeCrAl coating on Zr cladding which has excellent high-temperature mechanical properties and oxidation resistance.

Effect of Bias Voltage on the Microstructure, Mechanical Properties, and High-Temperature Steam Oxidation Behavior of Cr Coatings Prepared by Magnetron Sputtering on Zircaloy-4 Alloy

Effect of Bias Voltage on the Microstructure, Mechanical Properties, and High-Temperature Steam Oxidation Behavior of Cr Coatings Prepared by Magnetron Sputtering on Zircaloy-4 Alloy

Investigation of Surface Oxide Layer Structure to Improve Durability of Stainless Steels Under Humidified Hydrogen

We study degradation mechanism of stainless steels under SOFC operating conditions to improve durability of SOFC stack. To reduce material cost, a low-cost stainless steel is preferred because metal interconnect occupies considerable amount in the stack. From commercially available stainless steels, four types of alloy composition were chosen as model materials, which are widely used in the other applications. The alloy test pieces were exposed to hydrogen with 10%-50% H2O at 600oC-700oC, and mass gain after the test was measured. The mass gain increased with time, indicating that steam oxidation proceeded. The oxidation rate was smaller for JIS SUS430J1L than the other three types of the alloy for all the test conditions. The proficient durability came mainly from the thin Cr-rich oxide layer covering the alloy uniformly with little defect or segregation. The additives in the alloy such as Nb also may have an effect on suppressing elemental diffusion through the oxide layer. Because morphology of the surface oxide layer initially formed on the surface should affect the process of steam oxidation during SOFC operation, we investigated influence of pre-heat treatment condition (700oC-900oC) of the alloy. The surface oxide layer formed by the pre-heat treatment at 900oC in air for 2 h had an effect of reducing steam oxidation rate. Microstructure of the surface oxide layer before and after the durability test was analyzed by STEM. From the difference in the microstructure of the surface oxide layer, predominant factor to improve durability will be discussed. This paper is based on results obtained from a project, (JPNP20003), commissioned by the New Energy and Industrial Technology Development Organization (NEDO). Figure 1

Redox Tolerant Solid Oxide Electrolysis Cathode for CO2 and Steam

The production of oxygen for life support and ascent vehicle propellant oxidant is essential for human expeditions to Mars. OxEon team led the development of solid oxide electrolysis cell (SOEC) stacks for the Mars 2020 mission in collaboration with the Jet Propulsion Laboratory (JPL) and Massachusetts Institute of Technology (MIT). A stack that was installed in the Perseverance Rover has been operated twelve times so far to demonstrate the production of high purity oxygen by electrolyzing Mars atmosphere CO2.Traditionally, SOEC stacks use nickel–zirconia or nickel–ceria composite cathode to reduce the oxidized species. Nickel based electrodes are susceptible to oxidation by the feed gas (CO2 or steam) at the inlet conditions and are often irreversibly damaged during operation and start-up unless reduced species (carbon monoxide or hydrogen) are also present. Oxidation of Ni to NiO causes ~24% volume expansion, and a redox cycle with associated expansion and contraction can result in significant changes to the microstructure and loss of connectivity in the cathode and current collection layers. This challenge was encountered during early stack and testing development for the Mars mission where even short-term exposure to oxidizing dry CO2 feed caused massive performance degradation (12% of initial performance after 15 operational cycles). This necessitated a recycle loop for the stack on the Perseverance Rover that introduces a fraction of the CO-containing tail gas to the inlet to protect the cathode layers from oxidation.A simpler solution than a system recycle loop was desired for future applications. Under a NASA SBIR program OxEon investigated a combination of materials and engineering solutions to improve redox tolerance of the nickel-based cathode so that 100% dry CO2 could be fed directly into a stack without harming the electrode. A modified nickel-based cathode composition with a unique backbone and infiltrated cathode structure was developed and tested in both button cell and stack configurations. The new cathode has been shown to completely tolerate partial and full (i.e., complete oxidation of Ni to NiO before re-reduction) redox cycling, with complete performance recovery occurring in a matter of minutes even after total oxidation. It was also demonstrated that feeding a reducing gas after complete oxidation is not required since the CO generated by the applied voltage during initial CO2 electrolysis reaction is sufficient for self-reduction recovery. This self-recovery feature is particularly attractive for applications where an oxidizing gas feed cannot be easily substituted with a reducing gas feed, such as with Mars O2 generation.In-situ resource utilization (ISRU) of lunar ice and potential Martian ice for O2 and H2 generation is also of significant interest for future space missions. The redox tolerant cathode has been shown to completely tolerate steam oxidation as well, with self-generated H2 resulting in rapid reduction and recovery. Steam redox tolerance was demonstrated in both button cells and stacks and was independently verified by testing at PNNL. The redox tolerant cathode is also capable of rapid thermal cycling with ramp rates as high as 15 °C/min tested with no performance degradation. Improved coking tolerance over the traditional cathode material is an additional robustness feature that allows for higher conversion of CO2, enabling increased O2 production.This work was done under a NASA Small Business Innovation Research Contract No. 80NSSC19C0114. Validation testing at PNNL was performed under a DOE Award No. DE-FE0032105.

Steam oxidation of Cr-coated zirconium alloy claddings at 1200 °C: Kinetics transition and failure mechanism of Cr coatings

The microscopic layered structural evolution, the diffusion behavior of O, Cr and Zr elements and oxidation kinetics of the Cr-coated zirconium alloy claddings during steam oxidation at 1200 °C were systematically studied. At the initial oxidation stage (within 1 h oxidation), the protective Cr2O3 layer formed on the Cr coating, and the interdiffusion between Cr and Zr resulted in a four-layers structure from outer to inner, Cr2O3, Cr, Cr-Zr diffusion layer and Zr substrate. At this stage, the oxidation kinetics followed parabolic law. With increasing oxidation time to 1.8 h, ZrO2 networks formed in the Cr coating due to the occurrence of the redox reaction between Zr and Cr2O3, which provided a pathway for the diffusion of oxygen toward substrate. The layered structure on the Cr coating side transformed from a four-layers to a five-layers structure with the formation of a ZrO2 layer in the substrate. Meanwhile, the oxidation kinetics became linear growth. The failure of Cr coatings resulting in the oxidation of Zr substrate accounts for the parabolic-to-linear kinetics transition.

The effect of aluminide coating on the steam oxidation behavior of SS321 steel at 700 °C

Steam oxidation is considered the main attack form involved in the destruction of superheater tubes in the superheater of water-tube boiler. In this work, the effect of an aluminide coating on the way steam reacts with SS321 steel in a superheater was studied. Aluminide coating was done by powder cementation at 800 °C for 7 h and then heat treatment at 900 °C for 1 h. The coating was made with an Al-rich Fe2Al5 phase, with an inner (diffusion) layer of 5 μm and an outer layer of 25 μm. The grains were all the same size, and there were few holes. The samples were subjected to a constant stream of supersaturated water vapor at a temperature of 700 °C. The weight gain of uncoated and coated samples was measured as 1 mg cm−2 and 0.5 mg cm−2 after 20 h, and 2.5 mg cm−2 and 0.7 mg cm−2 after 350 h, respectively. The remarkable weight loss of the coated samples after 20 h and up to 350 h was attributed to the formation of stable Al2O3 oxides. This was although in the uncoated samples, the outer and inner layers of the coating were composed of Fe-rich oxides (magnetite) and Cr-rich oxides (Cr-Fe spinel oxides), respectively. Microstructural studies showed that with the increase in oxidation time, the inner layer (diffusion) increases from 5 μm to 25 μm, which is attributed to the diffusion of substrate particles towards the coating during oxidation.

Modelling and optimization of sorption-enhanced biomass chemical looping gasification coupling with hydrogen generation system based on neural network and genetic algorithm

Chemical looping gasification of biomass (BCLG) can realize the production of pure syngas without an extra purification process. By coupling steam oxidation of oxygen carrier in BCLG, pure hydrogen can be generated meanwhile, which is a promising clean energy. An enhanced BCLG process coupling with hydrogen generation is constructed in this work, aiming to realize effective co-production of syngas and hydrogen. The coupled effects of temperature and material flows of gasifier on the gas yield, lower heating value (LHV) of syngas and gasification efficiency are numerically investigated. The effects of temperature and steam flowrate in oxidizer are changed to investigate their effects on hydrogen production. Based on the simulation results, an accurate back-propagation neural network (BPNN) is trained and tested for the performance prediction of this syngas and hydrogen co-production system. The prediction accuracy of this BPNN model is quite high with a correlation coefficient of 0.99967. Finally, the optimization of this system is conducted based on the BPNN model and genetic algorithm (GA) to make the H2/CO ratio close to 2 and maximize hydrogen production simultaneously.

Self-toughening mechanism of the ZrO2 scale and the precipitation of Sn during the steam oxidation of ZIRLO™ at 1200 °C

The steam oxidation behavior of ZIRLO™ at 1200 °C was investigated using a thermogravimetric analyzer. The microstructure of the oxide was analyzed using SEM, EBSD, and FIB+TEM in depth. Very long “spaghetti-like” columnar oxide grains were formed owing to the intracrystalline diffusion of O2− and the high oxidation temperature. These grains extended from the oxide/matrix interface to a thin outer equiaxed grain layer. The special growth mechanism of the columnar grains determines the unique properties of the oxide scale, such that their structural integrity cannot be destroyed. Therefore, the oxidation kinetics followed a parabolic law throughout the oxidation process without breakaway behavior. Observations revealed the presence of twins, slip bands, and subgrains within the ZrO2 grains, which were identified as the primary manners of oxide deformation under stress. The residual stress and phase distribution along the thickness of the oxide were investigated using synchrotron radiation X-ray diffraction. The oxide was almost completely transformed into a m phase after oxidation. The compressive stress inside the oxide was relatively low, indicating that the stress was relaxed. Transformation toughening, plastic deformation, densely arranged columnar grains, and the absence of grain boundaries parallel to the direction of compressive stress constitute the self-toughening mechanism of the ZrO2 scale. Zr5Sn3, ZrSn2, and β-Nb second phase particles were observed at the ZrO2 grain boundaries and inside the ZrO2 grains. The outward diffusion of Sn in the liquid state and the peritectic reaction can result in the formation of voids at the edges of the second phase particles.

Steam oxidation behavior of T92 steel tube for high temperature reheater after long-term service in ultra-supercritical boilers

The steamside oxidation behavior of T92 steel tube for high temperature reheater after long-term service in ultra-supercritical boilers was investigated. The structure evolution process, phase composition and element distribution of the oxide film were studied. The oxide film consisted of outermost layer with hematite, subouter layer with magnetite and inner layer with Fe-Cr spinel. The structure of the transition zone of the oxide film and related oxidation mechanism was discussed in detail. A steam oxidation kinetic model of the T92 reheater based on the evolution of the inner layer thickness of the oxide film was established.

Hydrothermal corrosion of Cr[sbnd]C and Ti-Al-C carbide ceramic coatings on Zircaloy: Corrosion behavior, mechanism and influence of water exposure on pressurized steam oxidation resistance

The corrosion behavior of CrC and Ti-Al-C coatings in lithiated/borated water was studied, and the influence of hydrothermal corrosion on coating chemical stability in pressurized steam was investigated. In lithiated/borated water, CrC coating formed a protective Cr2O3 layer, and the NiAl intermediate layer remained unoxidized. The diffusion degree of O2− differed in the depth direction of the Ti-Al-C coating. O2− penetrated into the NiAl intermediate layer, facilitating oxidation and cracking. CrC coating was found to be more resistant to steam oxidation than Ti-Al-C coating. Oxidation stress led to partial delamination of the oxide scale on CrC coating, while Ti-Al-C coating suffered intergranular oxidation and exhibited microscale facets under the selective attack of steam.

Construction of Cr coatings with different columnar structure on Zircaloy-4 alloys to optimize the high-temperature steam oxidation behavior for accident tolerant fuel claddings

To optimize the oxidation behavior of chromium-coated Zircaloy-4 alloys under 1200 °C high-temperature steam for accident tolerant fuel (ATF) claddings, Cr coatings with different columnar structure are constructed by changing bias voltage using high power impulse magnetron sputtering and corresponding microstructure, mechanical and high-temperature steam oxidation properties are studied systematically. With the bias voltage increase from 0 V to − 150 V, the microstructure of Cr coatings changes from porous columnar structure to compact columnar structure. Especial for bias voltage is − 90 V, the tiny compact grains uniform distribute on the surface micrographs and optimal compact columnar structure are observed on the cross-section micrographs. The hardness and elastic modulus of as-prepared Cr coatings increase firstly and then decrease, the hardness of Cr coatings with optimal compact columnar structure is 8.65 GPa, which is elevated ∼2.28 times than Cr coatings with porous columnar structure. 1200 °C high-temperature steam oxidation test results show an interesting phenomenon that the thickness of Cr layer reduces initial and then increase with the exposure time prolong from 1 h to 4 h. The main steam oxidation mechanism, in the early oxidation stage, is formation the compact Cr2O3 oxide layer. Then, with the exposure time extend, the reduction reaction plays the significant part for steam oxidation mechanism, which is consumption of outmost Cr2O3 oxide layer and formation of subsurface Cr layer. The construction of Cr coatings with compact columnar structure and relevant oxidation mechanism are expected to offer a new idea for improving 1200 °C steam oxidation resistance of chromium-coated Zircaloy-4 alloys.

On the Cycle Stability and Macroscopic Structure of Iron Oxide Pellets for Thermochemical Hydrogen Storage: Influence of Water Content during the Pelletizing Process

Hydrogen storage based on the repeated reduction and oxidation (redox) reactions of iron oxide/iron composites represents a promising technology. This work is dedicated to studying the influence of the amount of water added during the pelletizing process on the cycle stability and structure of iron oxide pellets. The storage composites were prepared from iron oxide (Fe2O3) and 10 wt.-% support material (cement) with different amounts of water (18 and 33 wt.-%) in a laboratory-scale pelletizing disk. To evaluate the cycle stability of the composites, the kinetics of the redox reactions were experimentally measured at 800 °C in an atmosphere of 50% N2 and 50% H2 (reduction) or 50% steam (oxidation), respectively. Moreover, the structure of the pellets was analyzed by micro-computed tomography scans. It turned out that pellets with higher water contents attained faster kinetics and a higher cycle stability. The sample with the least water content (18 wt.-%) needed about 26 min and 19 min to reach a conversion rate of 80% during the reduction and oxidation reactions of the sixth redox cycle, respectively. In contrast, the sample with the highest water content (33 wt.-%) could achieve the same conversion rate after 18 min (reduction) and 13 min (oxidation) during the ninth redox cycle.

OECD/NEA R&D priorities for loss-of-cooling and loss-of-coolant accidents in Spent-Fuel-Pools

Motivated by the 2011 accident at the Fukushima Daiichi Nuclear Power Station, the Nuclear Energy Agency (NEA) Committee on the Safety of Nuclear Installations (CSNI) of the Organisation for Economic Cooperation and Development (OECD) launched several activities with the aim to support the post-Fukushima accident decision making process. One of these activities, discussed in the present paper, consisted in the production of a Phenomena Identification and Ranking Table (PIRT) in order to systematically highlight Spent-Fuel-Pool (SFP) accident-related phenomena that are of both high importance and high uncertainty, and thus of primary interest for further experimental or modeling activities. For that purpose, an international panel of experts identified and ranked more than a hundred physical phenomena with regard to their safety importance and current level of knowledge. Altogether eighteen unique phenomena were identified as having priority research needs. About half of these phenomena are related to thermal-hydraulics and heat transfer in the SFP, and they are judged to be important to the coolability of the spent fuel in loss-of-cooling and/or loss-of-coolant accidents. The other half comprises fuel-related phenomena such as fuel volatilization, cladding oxidation in mixed steam–air environment and nitrogen-assisted oxide breakaway at moderate temperature, judged as important and poorly modeled in the scope of SFP accidents. The final part of the paper discusses the research programmes performed on Spent Fuel Pool loss-of-cooling and loss-of-coolant accidents since the publication of the PIRT report in 2018 and the remaining R&D needs.

Isothermal Experiments on Steam Oxidation of Zr-Sn-Nb Alloy at 1050 °C: Kinetics and Process.

The isothermal steam oxidation behavior of the Zr-Sn-Nb alloy at 1050 °C was studied. In this study, the oxidation weight gain of Zr-Sn-Nb samples with oxidation durations ranging from 100 s to 5000 s was calculated. The oxidation kinetic properties of the Zr-Sn-Nb alloy were obtained. The macroscopic morphology of the alloy was directly observed and compared. The microscopic surface morphology, cross-section morphology, and element content of the Zr-Sn-Nb alloy were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy disperse spectroscopy (EDS). According to the results, the cross-sectional structure of the Zr-Sn-Nb alloy consisted of ZrO2, α-Zr(O), and prior-β. During the oxidation process, its weight gain versus oxidation time curve followed a parabolic law. The thickness of the oxide layer increases. Micropores and cracks gradually appear on the oxide film. Similarly, the thicknesses of ZrO2 and α-Zr versus oxidation time were in accordance with the parabolic law.

Improvement of the high-temperature steam oxidation resistance of Zirlo tubes by multilayer Cr/CrAlSiN coatings

Chromium (Cr) has been recognized as a promising candidate material for ATF coatings. Herein, multilayer Cr/CrAlSiN coatings were prepared by magnetron sputtering to improve the high-temperature steam oxidation resistance of Zirlo tubes. The key performances of specimens in terms of high-temperature steam oxidation were investigated by using X-ray diffractometer (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compared with Cr coatings, the oxidation resistance time of the Cr/CrAlSiN coatings increased from 1 h to 4 h in 1100 °C steam. A “thin Cr2O3 scale + thick Cr-rich layer” structural arrangement formed during the oxidation of the Cr/CrAlSiN coatings. The thin Cr2O3 scale means less growth stress produced in the oxidation process, and the thick residual Cr-rich layer can play a leading role in relieving the great stress and bearing the plastic deformation from the Cr2O3 layer.