Hydrothermal Corrosion Research Articles

Hydrothermal Corrosion Behaviors of Constituent Materials of SiC/SiC Composites for LWR Applications

The corrosion behaviors of SiC/SiC composite constituent materials in pure water at operating conditions, such as 300 °C and 8.5 MPa, were studied for potential application in accident-tolerant light water reactor (LWR) fuel cladding and core structures. Five kinds of SiC fibers, four kinds of SiC matrices, and three kinds of fiber/matrix interphase materials were examined in autoclaves. The potential constituent materials for future use in SiC/SiC composites were selected by considering corrosion rates and residual strength characteristics. The mass changes and the residual strength of each specimen were measured. SEM images of the surface layers were also inspected. The SiC fibers, regardless of their purity, crystallinity or stoichiometric ratio, decreased in strength due to the hydrothermal corrosion. For its part, the hydrothermal corrosion resistance of CVD-SiC, as a SiC matrix, was found to be affected by manufacturing conditions such as raw material gas type and synthesis temperature, as well as post-machining morphology. The CVD-carbon (CVD-C), as a fiber/matrix interphase material, showed good hydrothermal corrosion resistance. In order to protect the SiC fibers and the SiC matrices from hydrothermal corrosion, it would appear to be necessary to apply a dense CVD-C coating to both every fiber and the entire surface of the SiC matrices.

A study of designer amine 4-amino-1-propyl-piperidine against the corrosion of carbon steel for application in CO2 capture

We investigated the relationship between amine structure and corrosion rates in a study of the corrosion behaviour of carbon steel in CO2-loaded 4-amino-1-propyl-piperidine (4A1PPD) solution and a series of related amines. Electrochemical measurements showed that 4A1PPD displayed the lowest corrosion rate of the amines studied, and that the corrosion rate decreased with the increase of the number of substituents on amino groups and a structural change from linear amines to cyclic amines. We also carried out a hydrothermal corrosion study using selected amines to analyse the surface morphology and composition formed on the surface of corroded carbon steel. The results suggested that the formation of a protective film was dependant on the ratio of bicarbonate/carbamate species. We confirmed that a dense FeCO3 protective film was produced on the carbon steel surface after hydrothermal corrosion treatment with CO2 rich 4A1PPD solution. Our results demonstrate that the 4A1PPD designer amine with a cyclic structure shows good corrosion properties for use in post-combustion CO2 capture and resulted in significantly reduced corrosion on carbon steel compared to the benchmark amine, monoethanolamine.

Comparison of hydrothermal corrosion behavior of SiC with Al2O3 and Al2O3 + Y2O3 sintering additives

AbstractFully dense SiC bulks with Al2O3 and Al2O3 + Y2O3 sintering additives were prepared by spark plasma sintering and the effect of sintering additives on the hydrothermal corrosion behavior of SiC bulks was investigated in the static autoclave at 400°C/10.3 MPa. The SiC specimen with Al2O3 sintering additive exhibited a higher weight loss and followed a linear law. However, the SiC specimen with Al2O3 + Y2O3 additive exhibited a lower weight loss and followed a parabolic law, indicating that the corrosion kinetic and mechanism were different for these two SiC bulks. Further examination revealed that, a deposited layer was formed on the surface of SiC specimen with Al2O3 + Y2O3 sintering additive after corrosion, which can effectively protect the SiC specimen from further corrosion, and thereby improved the corrosion resistance of the SiC specimen with Al2O3 + Y2O3 sintering additive.

The role of microstructural development in the hydrothermal corrosion of cast and HIPed Stellite 6 analogues in simulated PWR conditions

The corrosion behaviour of cast and HIPed Stellite 6 analogue materials in PWR-simulating conditions was investigated. The cast alloy exhibited localised corrosion at the boundary between the matrix and the M7C3 carbides, with this being attributed to chromium depletion in the matrix associated with the carbide growth. In contrast, the HIPed alloy exhibited no localised corrosion. The carbon content of the cast Stellite 6 analogue was right at the top end of the range indicated in the Stellite 6 specification: this results in a high fraction of carbides and a general depletion of the chromium content of the matrix.

Conductometric ozone sensor based on mesoporous ultrafine Co3O4 nanobricks

Monitoring the ozone concentration is widely needed in manufacturing. In this work, mesoporous Co3O4 nanobricks were prepared by a facile hydrothermal corrosion method followed by thermal decomposition from CoSn(OH)6 precursor. The morphologies, phase, surface composition, nanostructures and exposed crystal facet of the Co3O4 were investigated by using XRD, SEM, TEM, XPS and Raman method. The Co3O4 nanobricks are composed of ultrafine tricobalt tetroxide spinel nanocrystal with size about 10 nm, and the dominant exposed facet is {110}. It is found that those Co3O4 nanobricks show good response to n-butanol and xylene gases, especially to ozone, which reaches the highest response of 130 to 100 ppm ozone at 85°C. In the end, the formation and gas-sensing mechanism of the mesoporous Co3O4 nanobricks were discussed. The good gas sensing properties of the Co3O4 nanobricks can be ascribed to the ultrafine crystallite and mesoporous structure. The high ozone sensitivity can be explained by the {110} exposed facet with Co2+ active sites. Based on the investigate, the Co3O4 nanobricks is proved to be a promising material for ozone sensing.

U3Si2-SiC fuel performance analysis in BISON during normal operation

U3Si2-SiC is an accident-tolerant fuel concept currently under development by Westinghouse that has potential to improve economic performance and safety of light water reactors. Since U3Si2 fuel suffers from poorer hydrothermal corrosion performance relative to UO2, it is paramount in an U3Si2-SiC fuel rod to lower the stress in the cladding to prevent any inward leakage of coolant. This motivates a detailed fuel-clad analysis of U3Si2-SiC during normal operation. The SiC cladding is modeled with a layer of SiCf/SiC composite followed by a layer of monolithic SiC. The dependence of thermomechanical properties for each SiC layer on temperature and neutron fluence is considered in the BISON fuel performance code. Particularly, pseudo-ductile deformation and anisotropic swelling models of SiCf/SiC composite are updated. While SiC thermal conductivity is commonly known to decrease as a consequence of irradiation damage, its additional degradation by mechanical damage is also modeled. Owing to limited availability of U3Si2 irradiation behavior models and experimental data under power reactor conditions, several assumptions are made to perform the initial detailed assessment of the fuel system. The results show that the fuel rod designs with larger pellet radius, thinner SiC cladding and larger initial gap width (thus larger cladding inner radius) can be beneficial to lower cladding stress during power operation and reactor shutdown.

The preparation and ozone-sensing performance of Co3O4 nanobricks

Co3O4 nanobricks were prepared using the method of the hydrothermal corrosion, in which CoSn(OH)6 was the precursor, and it was corroded by NaOH and transformed into Co3O4. The phase composition and morphology of the CoSn(OH)6 and the Co3O4 nanobricks prepared were examined by using XRD, SEM, and TEM. The Co3O4 nanobricks have a face-centered cubic structure with the average nanocrystals size of 10.2 nm. The sensor made by the Co3O4 nanobricks showed an ultra-sensitivity to ozone at low operating temperatures. It exhibited a fast rate of response and recovery, as well as a high stability and repeatability. The Co3O4 nanobricks can be a promising material for sensing ozone.

Factors affecting the hydrothermal corrosion behavior of chemically vapor deposited silicon carbides

The hydrothermal corrosion behavior of chemical-vapor-deposited SiC was investigated for application as nuclear fuel cladding in a pressurized water reactor (PWR). This paper presented the effect of grain size, stacking fault, electrical conductivity, and electrochemical properties on the hydrothermal corrosion behavior of the CVD SiC in a simulated PWR water loop at 360 °C and 18.5 MPa. The hydrothermal corrosion of SiC was strongly influenced by electrical conductivity. It was revealed that high electrical conductivity leads to high exchange current density, which allows SiO2/Si(OH)4 to form easily on the SiC surface, allowing it to dissolve rapidly in the hydrothermal environment.

Effect of hydrothermal corrosion on the fracture strength of SiC layer in tristructural‐isotropic fuel particles

AbstractThe hydrothermal corrosion behavior of SiC layer in tristructural‐isotropic (TRISO) fuel particles and its effect on the fracture strength were investigated. The corrosion test was performed using the static autoclave at 400°C/10.3 MPa. The SiC layer exhibited a thickness loss and the corrosion rate followed a linear law. During corrosion, carbon was formed on the SiC surface due to the loss of Si. The corrosion was found preferentially occurred at the grain boundary of SiC, leading to the grain detachment and pit formation. The rate determining step of the corrosion was SiO2 formation rather than SiO2 dissolution in the hydrothermal environment. The fracture strength of SiC shell after corrosion was evaluated using the crush test. It showed a slight decrease with an increase in corrosion time, due to the thickness reduction in SiC layer. The results of this study demonstrated that the SiC in TRISO particles has good corrosion resistance in the hydrothermal environment.

Hydrothermal Corrosion of SiC and FeCrAl for Accident Tolerant Fuel Cladding

Since the Fukushima incident in 2011, the nuclear industry has sought to replace Zircaloy fuel cladding with a material which will better withstand a beyond-design-basis incident. A suitable material must possess superior oxidation resistance in high temperature steam (1200-1700°) to withstand a loss of coolant accident, while maintaining good hydrothermal corrosion properties for environmental compatibility during normal operating conditions (288-320°C water). In addition to corrosion issues, a suitable material must also demonstrate sufficient mechanical strength, creep resistance, radiation tolerance, and favorable neutronics. Researchers at Oak Ridge National Laboratory are engaged in testing of two leading candidates for accident tolerant fuel cladding: iron-chomium-aluminum (FeCrAl) alloys, and silicon carbide ceramic matrix composites (SiC/SiC). FeCrAl alloys have shown excellent oxidation resistance due to the formation of a passive alumina film in high temperature steam, and a protective Fe-Cr spinel layer in water. SiC/SiC has shown excellent corrosive properties in high temperature steam, but a tendency to dissolve in LWR water. To improve performance of SiC normal operating conditions, several candidate coatings are being considered, including Cr, CrN, and TiN. This work presents results of hydrothermal corrosion experiments on FeCrAl alloys and coated SiC in boiling water reactor hydrogen water chemistry (BWR-HWC) and normal water chemistry (BWR-NWC) (288°C with 150 ppb H2 or 2 ppm O2 respectively). FeCrAl samples generally exhibited low corrosion rates. Hydrothermal corrosion properties of current FeCrAl alloys are compared to older generations. CVD-SiC and SiC/SiC exhibited significant mass loss during exposure. SiC samples coated with Cr and CrN adhered well to their substrates, and effectively mitigated dissolution, with acceptable corrosion rates. This work was funded by the DOE Office of Nuclear Energy Advanced Fuels Campaign

Atomic-Level Simulation Study of n-Hexane Pyrolysis on Silicon Carbide Surfaces.

Ethylene production plays a key role in the petrochemical industry. The severe operation conditions of ethylene thermal cracking, such as high-temperature and coke-formation, pose challenges for the development of new corrosion-resistant and coking-resistant materials for ethylene reactor radiant coils tubes (RCTs). We investigated the performance of ceramic materials such as silicon carbide (SiC) in severe pyrolysis conditions by using reactive force field molecular dynamics (ReaxFF MD) simulation method. Our results indicate that β-SiC surface remains fully stable at 1500 K, whereas increased temperature results in melted interface. At 2500 K, fully grown cross-linked-graphene-like polycyclic aromatic hydrocarbon coking structure on SiC surfaces was observed. Such coking was particularly severe in the carbon-side of the surface slab. The coking structures were mainly derived from surface atoms at the initial 3.0 ns, as a result of the loss of interfacial hydroxyl layer and further hydrothermal corrosion. The SiC substrate surface enhances the ethylene cracking rate and also leads to different intermediate-state compounds. Our fundamental research will have significant and broad impact on both petrochemical industry and academic research in materials science, petrochemistry, and combustion chemistry.

Protective coatings on zirconium-based alloys as accident-tolerant fuel (ATF) claddings

AbstractSurface-modified zirconium (Zr)-based alloys, mainly by fabricating protective coatings, are being developed and evaluated as accident-tolerant fuel (ATF) claddings, aiming to improve fuel reliability and safety during normal operations, anticipated operational occurrences, and accident scenarios in water-cooled reactors. In this overview, the performance of Zr alloy claddings under normal and accident conditions is first briefly summarized. In evaluating previous studies, various coating concepts are highlighted based on coating materials, focusing on their performance in autoclave hydrothermal corrosion tests and high-temperature steam oxidation tests. The challenges for the utilization of coatings, including materials selection, deposition technology, and stability under various situations, are discussed to provide some valuable guidance to future research activities.

Influence of microstructure on hydrothermal corrosion of chemically vapor processed SiC composite tubes

Multi-layered SiC composites consisting of monolithic SiC and a SiCf/SiC composite are one of the accident tolerant fuel cladding concepts in pressurized light water reactors. To evaluate the integrity of the SiC fuel cladding under normal operating conditions of a pressurized light water reactor, the hydrothermal corrosion behavior of multi-layered SiC composite tubes was investigated in the simulated primary water environment of a pressurized water reactor without neutron fluence. The results showed that SiC phases with good crystallinity such as Tyranno SA3 SiC fiber and monolithic SiC deposited at 1200 °C had good corrosion resistance. However, the SiC phase deposited at 1000 °C had less crystallinity and severely dissolved in water, particularly the amorphous SiC phase formed along grain boundaries. Dissolved hydrogen did not play a significant role in improving the hydrothermal corrosion resistance of the CVI-processed SiC phases containing amorphous SiC, resulting in a significant weight loss and reduction of hoop strength of the multi-layered SiC composite tubes after corrosion.

Microstructure and hydrothermal corrosion behavior of NITE-SiC with various sintering additives in LWR coolant environments

Nano-infiltration and transient eutectic phase (NITE) sintering was developed for fabrication of nuclear grade SiC composites. We produced monolithic SiC ceramics using NITE sintering, as candidates for accident-tolerant fuels in light-water reactors (LWRs). In this work, we exposed three different NITE chemistries (yttria-alumina [YA], ceria-zirconia-alumina [CZA], and yttria-zirconia-alumina [YZA]) to autoclave conditions simulating LWR coolant loops. The YZA was most corrosion resistant, followed by CZA, with YA being worst. High-resolution elemental analysis using scanning transmission electron microscopy (STEM) X-ray mapping combined with multivariate statistical analysis (MVSA) datamining helped explain the differences in corrosion. YA-NITE lost all Al from the corroded region and the ytttria reformed into blocky precipitates. The CZA material lost all Al from the corroded area, and the YZA − which suffered the least corrosion −retained some Al in the corroded region. The results indicate that the YZA-NITE SiC is most resistant to hydrothermal corrosion in the LWR environment.

Relationships among volcanic and hydrothermal activity and faults from the Shunnan 3-D well zone in the Tadong Area (Tarim Basin, China)

Tarim Basin distributed widely two stages of Permian volcanic rocks. However, the location and timing of these rocks pinching out and the relationship between Ordovician carbonate hydrothermal reservoirs and fault activity remain unclear. The Shunnan (Shunnan here in after referred to as SN) 1 3-D well zone in the eastern Tarim Basin contains volcanic rocks, and the Ordovician layer contains a hydrothermal reservoir. This paper describes the lithology, stage, volcanic rock distribution, crater position and deposition pinch-out line of volcanic rocks based on drilling and 3-D seismic data. The Permian strata in the well zone contain only one stage of Kupkuciman Formation basalt and tuff, the Kaipeleicike Formation contains terrigenous clastic rock and the adjacent volcanic rocks of wells SN2 and GL (Gulong here in after referred to as GL) 2 exhibit an absence of deposition. Although the craters are distributed on both sides of the NNW faults that cross well SN4, their positions are also controlled by the intersection of earlier NEE and NW faults and later NNE faults. Furthermore, the Ordovician strata in the SN1 well zone developed abundant tubular high-amplitude anomalies and tabular high-amplitude anomalies via hydrothermal corrosion, and the anomaly distributions are similar to the positions of the craters, which are controlled by the intersection of multi-group faults and the density of the faults.

Hydrothermal corrosion of silicon carbide joints without radiation

Hydrothermal corrosion of four types of the silicon carbide (SiC) to SiC plate joints were investigated under pressurized water reactor and boiling water reactor relevant chemical conditions without irradiation. The joints were formed by metal diffusion bonding using molybdenum or titanium interlayer, reaction sintering using Ti–Si–C system, and SiC nanopowder sintering. Most of the joints withstood the corrosion tests for five weeks. The recession of the SiC substrates was limited. Based on the recession of the bonding layers, it was concluded that all the joints except for the molybdenum diffusion bond are promising under the reducing environments without radiation. The SiC nanopowder sintered joint was the most corrosion tolerant under the oxidizing environment among the four joints.

Facile corrosion synthesis and sintering of disperse pure tetragonal zirconia nanoparticles

Disperse pure tetragonal zirconia (t-ZrO2) nanoparticles smaller than 10nm are essential for preparation of structural and functional zirconia materials, but syntheses of t-ZrO2 nanoparticles using inorganic zirconium salts usually result in severe agglomeration. In this paper, we report a hydrothermal corrosion approach for improving the dispersity of t-ZrO2 nanoparticles synthesized by precipitation using zirconium oxychloride without any surfactants. Disperse pure t-ZrO2 nanoparticles with average sizes of 4.5 and 6nm and size distributions of 2–11 and 3–12nm were obtained by calcining precipitates at 400°C for 2h and 500°C for 0.5h followed by HCl corrosion at 120°C for 75h, respectively. Disperse t-ZrO2 nanoparticles with an average size of 6nm and a size distribution of 3–12nm were pressed into green compacts at 500MPa and sintered by two-step sintering (heating to 1150°C without hold and decreasing to 1000°C with a 10h hold). The sintered bodies are dense pure monoclinic ZrO2 nanocrystalline ceramic with a relative density of 99.9% and an average grain size of 110nm.

Ag@Au core-shell dendrites: a stable, reusable and sensitive surface enhanced Raman scattering substrate.

Surface enhanced Raman scattering (SERS) substrate based on fabricated Ag@Au core-shell dendrite was achieved. Ag dendrites were grown on Si wafer by the hydrothermal corrosion method and Au nanofilm on the surface of Ag dendritic nanostructure was then fabricated by chemical reduction. With the help of sodium borohydride in water, Au surface absorbates such as thiophene, adenine, rhodamine, small anions (Br– and I–), and a polymer (PVP, poly(N-vinylpyrrolidone)) can be completely and rapidly removed. After four repeatable experiments, the substrate SERS function did not decrease at all, indicating that the Ag@Au dendrite should be of great significance to SERS application because it can save much resource. Six-month-duration stability tests showed that the Ag@Au core-shell dendrite substrate is much more stable than the Ag dendrite substrates. We have also experimented on fast detection of Cd2+ at 10−8 M concentration by decorating single-stranded DNA containing adenine and guanine bases on the surface of this Ag@Au dendrite. Finite-difference time-domain simulations were carried out to investigate the influence of Au nanolayer on Ag dendrites, which showed that the local electric fields and enhancement factor are hardly affected when a 4 nm Au nanolayer is coated on Ag dendrite surface.

Hydrothermal corrosion of SiC in LWR coolant environments in the absence of irradiation

Assessment of the thermodynamics of SiC corrosion under light water reactor coolant environments suggests that silica formation is always expected in the range of applicable pH and potential. Autoclave testing of SiC-based materials in the absence of ionizing radiation was performed. The kinetics data from these tests, when compared with kinetics of silica dissolution in water and post-exposure characterization of SiC samples, suggest that oxidation of SiC to form silica is the rate-limiting step for recession of SiC in high temperature water. Oxygen activity in water was determined to play an important role in SiC recession kinetics. A simplified model of a power loop shows the effect of silica dissolution from the hot region (resembling fuel) and deposition in the cold regions.

Effect of irradiation damage on hydrothermal corrosion of SiC

The hydrothermal corrosion behavior (320°C, 20MPa, 168h) of high-purity chemical-vapor-deposited (CVD) SiC pre-irradiated with 5.1-MeV Si ions at 400 and 800°C and 0.1–2.6dpa was studied in order to clarify the effects of irradiation damage on SiC corrosion. Regardless of the pre-irradiation conditions, selective corrosion was observed at the grain boundaries and stacking faults even at the unirradiated regions. In contrast to the complete loss of the irradiated regions observed in the specimens irradiated at 400°C during the autoclave test, a number of large grains survived in the case of the specimens irradiated at 800°C. The corrosion rates at the irradiated regions increased with increasing irradiation fluence, with a significant dependence in the lower dpa regime similar to that observed in the point-defect swelling. SiO2 formation was not detected in any case. Cross-sectional scanning transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS) analyses of the surfaces of the surviving grains revealed oxygen diffusion to a depth of 3.0nm from the surface. A significant reduction of the oxygen diffusion barrier at the surface was implicated as one of the key mechanisms of the acceleration of the ion-irradiated SiC corrosion rates.