High Temperature Aqueous Environments Research Articles

High Temperature Self-Regenerative Granular Hydrogels for Fracture Treatments During Subsurface Energy Recovery.

The uses of granular hydrogels to assemble macroscopic bulk hydrogels display numerous distinct advantages. However, prior assembly of bulk hydrogels is accomplished by interparticle linking strategy, which compromised mechanical property and thermal stability under hostile conditions. To expand their applications as engineering soft materials, self-regenerative granular hydrogels via a seamless integrating approach to regenerate bulk hydrogels is highly desirable. Herein, covalent regenerative granular hydrogels (CRHs) are prepared at low-temperature synthetic conditions and re-construct bulk seamless hydrogels at high-temperature aqueous environments. The re-formed bulk hydrogels display rubber-like viscoelastic behaviors over a wide range of temperatures from 90 to 150°C, where the covalent re-crosslinking reactions homogeneously occurr along the periphery and in the matrix of granular hydrogels, accounting for the increased structural integrity at high temperatures. The bulk hydrogel shows increased elasticity and long-term thermal integrity at 150°C for more than six months in the confined fractures. Moreover, regenerative granular CRH-based bulk hydrogels significantly improve mechanical robustness under destructive pressure. Thus, high temperature water induced regenerative granular hydrogels present the paradigm to treat engineering scenarios such as large fractures for hydraulic fracturing, drilling operation, and disproportionate permeability reduction under extremely hostile conditions during subsurface energy recovery.

Novel design constructed In2S3@SnO2 hollow heterojunctions by insufficiently etched MOFs as framework for photoelectrochemical bioanalysis

Compared to sufficiently etched MOFs materials, insufficiently etched MOFs materials tend to display unsatisfactory performance due to their immature structure and have been eliminated from scientific research. Herein, this work reported a novel In2S3@SnO2 heterojunction (In2S3@SnO2-HSHT) materials, which were stably synthesized in high temperature aqueous environment and equipped extraordinary photoelectrochemical (PEC) properties, fabricated by a succinct hydrothermal synthesis method using insufficiently etched MIL-68 as a self-sacrificing template. Compared with the control groups and In2S3@SnO2 heterojunctions with collapse morphology synthesized by sufficiently etched MIL-68 in high temperature aqueous environment, In2S3@SnO2-HSHT synthesized from insufficiently etched MIL-68 as a template had a massively enhanced light-harvesting capability and generated more photoinduced charge carriers due to its well-preserved hollow structure. Therefore, based on outstanding PEC performance of In2S3@SnO2-HSHT, the established PEC label-free signal-off immunosensor to detect CYFRA 21-1, revealing vivid selectivity, stability, and reproducibility. This novel strategy adopted the insufficient chemical etching method neglected by the mainstream chemical etching approaches, which solved the challenge that the stability of the sufficient etched MOFs with hollow structure cannot be maintained under the subsequent high temperature aqueous reaction conditions, and was further applied to the design of hollow heterojunction materials for photoelectrochemical fields.

The Role of Determinism in the Prediction of Corrosion Damage

This paper explores the roles of empiricism and determinism in science and concludes that the intellectual exercise that we call “science” is best described as the transition from empiricism (i.e., observation) to determinism, which is the philosophy that the future can be predicted from the past based on the natural laws that are condensations of all previous scientific knowledge. This transition (i.e., “science”) is accomplished by formulating theories to explain the observations and models that are based on those theories to predict new phenomena. Thus, models are the computational arms of theories, and all models must possess a theoretical basis, but not all theories need to predict. The structure of a deterministic model is reviewed, and it is emphasized that all models must contain an input, a model engine, and an output, together with a feedback loop that permits the continual updating of the model parameters and a means of assessing predictions against new observations. This latter feature facilitates the application of the “scientific method” of cyclical prediction/assessment that continues until the model can no longer account for new observations. At that point, the model (and possibly the theory, too) has been “falsified” and must be discarded and a new theory/model constructed. In this regard, it is important to stress that no amount of successful prediction can prove a theory/model to be “correct”, because theories and models are merely the figments of our imagination as developed through imperfect senses and imperfect intellect and, hence, are invariably wrong at some level of detail. Contrariwise, a single failure of a model to predict an observation invalidates (“falsifies”) the theory/model. The impediment to model building is complexity and its impact on model building is discussed. Thus, we employ instruments such as microscopes and telescopes to extend our senses to examining smaller and larger objects, respectively, just as we now employ computers to extend our intellects as reflected in our computational prowess. The process of model building is illustrated with reference to the deterministic Coupled Environment Fracture Model (CEFM) that has proven to be highly successful in predicting crack growth rate in metals and alloys in contact with high-temperature aqueous environments of the type that exist in water-cooled nuclear power reactor primary coolant circuits.

Investigation on the feasibility of the interaction between NiO and Mo oxide for self-healing intelligence on the nuclear fuel cladding

ABSTRACT The feasibility of NiO-MoO3 reaction as a complement for the self-healing reaction proposed in our previous study is assessed in high-temperature aqueous environment. NiMoO4·nH2O and crystal α-NiMoO4 are produced in an aqueous environment by Ni(OH)2-MoO3 and NiO-MoO3 reactions, of which the starting temperature is about 100°C. NiMoO4·nH2O is completely dehydrated into β-NiMoO4 when annealed at about 600°C in air. Therefore, NiO-MoO3 reaction is expected to self-heal the cracks as a supplement of Fe2O3-MoO3 reaction in the high-temperature aqueous environment.

Structure of the Oxide Films Formed on Hydrogen-Charged and Uncharged 316L Stainless Steels in Oxygenated High Temperature Water

Austenitic stainless steels (SSs) are commonly used in pressurized water reactors (PWRs) nuclear power systems as key structural materials. The corrosion resistance are closely related to the passive film formed on the surfaces of austenitic alloys in high-temperature aqueous environments. It has been reported that hydrogen can affect corrosion, localized corrosion as well as stress corrosion cracking of materials in aqueous solutions. It is necessary to investigate the influence of hydrogen on the corrosion behavior of stainless steels material in high temperature water environments. In the present study, the oxide films formed on 316L SS with uncharged (316L) and hydrogen-charged (316L-H) in oxygenated simulated PWR primary water at 300℃were investigated. Oxygen was added in high temperature water to simulated occlude region condition or faulted water chemistry. The aim of this work is to clarify the effect of hydrogen in stainless steel on the corrosion behavior. The surface morphologies of the oxide films formed on 316L (uncharged) and 316L-H (charged) specimens after exposure to oxygenated PWR primary water at 300 oC for168 h were observed. The regular and irregular oxides particles homogeneous distributed on the outer surface of 316L specimen, and compact filamentary oxides in the sub-surface. On 316L-H specimen, large oxides dispersed and inhomogeneous distributed on the outer surface, and compact minor polyhedral oxide particles packed on the sub-surface. The number of the large oxides on the outermost surface of 316L specimen was more than that on the 316L-H sample. The cross-section of the oxide films formed on 316L specimens after exposed to oxygenated PWR primary water was analyzed by FIB-TEM. The interface front between the inner oxide layer and the base metal was wavy-shaped. There were compact Cr-rich oxides in the inner layer, and filamentary (Fe, Ni)-rich oxides in the outer layer. There was slightly Ni-enrichment near the inner oxides/matrix interface and Fe-enrichment beneath the inner oxides/matrix interface from EDS line scan profile. Some discontinuous cellular oxides distributed on the inner oxides/matrix interface on 316L-H after the exposure test, which was Fe-rich oxides identified by EDS maps and line scan. Similar to the 316L specimen, the inner layer oxide was compact and Cr-edriched, showing a slightly Fe-enriched beneath the inner oxides/matrix interface, but no Ni-enrichment close to the interface of inner oxides/matrix was observed. Figure 1

Effect of oxide film on ECT detectability of surface IGSCC in laboratory-degraded alloy 600 steam generator tubing

Abstract Stress corrosion cracking (SCC) widely found in both primary and secondary sides of steam generator (SG) tubing in pressurized water reactors (PWR) has become an important safety issue. Using eddy-current tests (ECTs), non-destructive evaluations are performed for the integrity management of SG tubes against intergranular SCC. To enhance the reliability of ECT, this study investigates the effects of oxide films on ECT’s detection capabilities for SCC in laboratory-degraded SG tubing in high temperature and high pressure aqueous environment.

Application of chemical interaction between (Fe, Cr) oxides and Mo oxide at high temperature for self-healing intelligence on nuclear fuel cladding in LWRs

ABSTRACT A novel scheme for a bilayer coating with self-healing ability is proposed in this study. The candidate materials for the coatings and the potential self-healing reaction are assessed in high-temperature aqueous environments and high-temperature air. The pure Cr2O3 layer and the composite of Cr2O3 and MoO3 are the candidate materials for the outer layer and inner layer, respectively, due to their compatibility under normal condition and fabricability. Fe2O3–MoO3 reactions exhibit a potential ability to heal the cracks because of a high reaction rate under normal condition. The self-healing process proceeds via the following mechanism under normal condition: Fe2O3 (a corrosion product in the coolant) diffuses into the cracks on the coating and reacts with MoO3 (inner layer) to produce the insoluble Fe2(MoO4)3, which deposits and repairs the cracks. In the loss-of-coolant accident (LOCA) situation, Cr2O3–MoO3 reaction is expected to strengthen the adhesion of the coating.

Structural evolution of oxidized surface of zirconium-silicide under ion irradiationm

Irradiation-induced structural evolution and compositional alterations on nanometer length scales of ZrO2-SiO2 nanocomposite and crystalline ZrSiO4, produced by oxidation of ZrSi2 at 1000 °C and 1400 °C, respectively, have been investigated. Irradiations were performed with 3.9 MeV Si2+ at 305 °C up to damage levels of 60 displacements per atom (dpa), and post-irradiation characterization was conducted by cross-sectional scanning- and transmission electron microscopy (STEM and TEM) in conjunction with energy dispersive spectroscopy (EDS), as well as glancing-angle X-ray diffraction (XRD). The multilayered nanocomposite oxide showed extensive phase mixing so that the originally distinct interfaces between ZrO2 and SiO2 phases were obliterated resulting in the formation of a single amorphous Zr-Si-O phase. Crystalline ZrSiO4 grains were completely amorphized at damage levels of 5–15 dpa, as evidenced by disappearance of grain boundaries and as confirmed by electron diffraction. The irradiation-induced phase transformation for both types of oxide structures has the potential to dramatically enhance corrosion resistance in high temperature aqueous and steam environments.

Effects of lead on oxidation behavior of Alloy 690TT within a high temperature aqueous environment

The chemical compositions, phases and structures of two oxide films on Alloy 690TT following exposure for 4400h in pure water with and without lead at 320°C were studied by surface analysis techniques. The analysis of a lead-doped oxide film prepared by a focused ion beam (FIB) demonstrated that both Cr-rich and Ni-rich oxides were alternatively distributed within the outer layer, whereas the inner layer was porous and poorly protected, causing severe corrosion of the alloy and a thicker film was formed. A duplex film model was proposed for the effects discussion of lead on the oxidation mechanism.

Effects of hydrogen on corrosion of pure Ni in high temperature water

A specially designed cyclic hydrogenated and oxygenated water chemistry in a high temperature aqueous environment was used, and the consequential corrosion behavior of pure Ni was investigated by in situ electric/electrochemical measurements and ex situ surface oxides analyses. The penetrated hydrogen in Ni from the hydrogenated water can enhance oxidation taking place in the subsequent oxygenated water. Ni oxide formed in oxygenated water can be reduced in the following hydrogenated water with a much slower reduction rate than that in gaseous environments. Practical implications of the phenomena in structural materials in nuclear power plants were also discussed.

Copper-Copper Sulfate Reference Electrode for Operating in High Temperature and High Pressure Aqueous Environments

A copper-copper sulfate electrode (CSE) was constructed and tested at elevated temperatures. Experimental cell potentials versus a silver-silver chloride electrode were compared against results from Gibbs energy minimization (GEM) calculations. After accounting for irreversible thermodynamic processes, experimental and calculated CSE potentials, were generally within 3% of the observed potential from 25 to 150°C at 3MPa. The CSE potentials changed by less than 20mV with increasing temperature, compared to 120mV for the silver-silver chloride electrode. With its repeatability and small temperature dependence, the CSE electrode appears to be a viable reference electrode for measuring in-situ real time cell potentials in aqueous phase-containing media at elevated temperature and pressure.

Electrochemical characterization of nano zinc ferrite coating on carbon steel by pulsed laser deposition

The structural materials in water-cooled nuclear power reactors are mainly iron and nickel based alloys. Continuous operation of these nuclear reactors at high temperature and high pressure aqueous environment leads to the formation of various oxides due to corrosion of the structural materials. Since the corrosion process is mainly interfacial and electrochemical in nature, the interfaces formed between the alloys/oxide and oxide/solution plays a crucial role in deciding the overall corrosion resistance of the structural materials. In this context, efforts are being made to modify the size of the oxide particles (surface morphology) to nano size and/or change the composition of the oxides by the addition of an external metal ion (Metal Ion Passivation) both of which are likely to improve the adherence and protectiveness of the interfacial film. In this paper, attempts were made to form an additional nano zinc ferrite (ZnFe2O4) coating by pulsed laser deposition technique on the magnetite (Fe3O4) layer formed on carbon steel for improving the corrosion resistance of the base metal. The ZnFe2O4 was synthesized by co-precipitation method and its phase purity was confirmed by Raman Spectroscopy and X-Ray Diffraction studies. 10mm diameter ferrite targets were prepared and a thin film of ZnFe2O4 was deposited on the Fe3O4 coated carbon steel specimens using pulsed laser deposition technique. Characterization of this deposited ferrite film was carried out by Raman spectroscopy, X-Ray Diffraction, X-ray Photoelectron Spectroscopy and Secondary Electron Microscopy. The semiconductor properties of these oxides were investigated by Mott-Schottky plots. The mechanism of corrosion resistance/improvement in the deposited layer was studied by electrochemical techniques and the results are presented in detail in this paper.

Acoustic emission behavior of 316LN stainless steel during oxide film formation in high temperature aqueous environment

Acoustic emission (AE) technique was used to study the oxide film formation of 316LN stainless steel (SS) in high temperature aqueous environment. The morphology and chemical compositions of oxide films of 316LN SS base metal and weld were also investigated by using scanning electron microscopy (SEM), energy dispersive X‐ray spectroscopy (EDX), and X‐ray photoelectron spectroscopy (XPS). The results indicated that 316LN SS weld had a higher oxidation resistance than that of base metal due to higher amount of chromium and nickel in the weld material. AE activity and intensity were high during the oxide film formation and decreased gradually with increasing immersion time. The evolution of AE hits was consistent with the oxidation kinetics of 316LN SS base metal and weld. The formation of Cr‐enrichment layer and Ni(OH)2 contributed to the enhancement of oxidation resistance, leading to a continuous decrease of AE activity and intensity. Two types of AE waveforms were detected and the frequency spectra of both types mainly ranged from 0.3 to 0.6 MHz. According to the analyses of AE based b‐values and parameters, it could be deduced that AE sources during oxide film formation were the plastic deformation of base metal/weld and oxide film.

The Effect of Hydrogen on the Corrosion and Anodic Behavior of 13Cr Stainless Steel in Chloride Solution

Hydrogen evolution is one of the common cathodic reactions involved in corrosion of metals and alloys in aqueous solutions. The reduction of hydrogen ions is a source of atomic hydrogen on the surfaces of metals. Corrosion reactions, the application of cathodic protection and electroplating, etc., can introduce hydrogen into metals via diffusion. The presence of hydrogen in metals can have a significant influence on the mechanical properties and electrochemical behavior of metals depending on the environments. Stainless steels generally corrode at very low rates in high temperature aqueous environments because of their tendency to form a protective oxide film. Hydrogen is incorporated into the structural alloys during production, fabrication, processing, from in service conditions, and from the electrochemical reaction during corrosion. The transport of hydrogen through passive films is involved in many corrosion processes such as pitting, stress corrosion cracking and corrosion fatigue. The nature of passive films on metals and alloys is a decisive factor that controls their corrosion behavior. Mmuch work has been devoted to the study of the electronic properties and chemical composites of passive films on metals and alloys. Based on the fact that the potential-dependent transpassive dissolution varies with the electronic properties of the passive film, Sato proposed a breakdown mechanism of the passive film on metals, the electrochemical stability of a passive film strongly depends on the electron energy band structure in the film. Bianchiet al. concluded that the high susceptibility of stainless steel to pitting nucleation was connected to n-type conductivity of the oxide film. Cr-bearing stainless steels have been widely used in power generation systems and other industrial systems. The effects of hydrogen on the surface film and electrochemical behavior of 13Cr stainless steel in a chloride solution were investigated in the present work. Hydrogen was introduced into the samples by cathodic charging under galvanostatic condition at 25 oC in sulfuric acid solution with thiourea. The specimens were charged at a current density 2 mA/cm2 for 2 h. Electrochemical measurements were carried out on both uncharged and hydrogen charged specimens for evaluating their corrosion resistance. Potentiodynamic anodic polarization curves were carried out in 200 ppm wt.% NaCl solution at 25 oC, as shown in Figure. 1. Pre-charged hydrogen specimen showed a significantly lower open-circuit potential of about -0.67 V(SCE), and the non-charged specimen showed OCP of about -0.11V (SCE). Anodic current density in the anodic polarization curves of the hydrogen-charged specimen was significantly higher than that of the non-charged specimen. These results indicate that the corrosion resistance of 13Cr steel was significantly reduced by charged-hydrogen. Figure 2 show the electrochemical impedance spectra (EIS) for hydrogen-charged and non-charged specimens after different immersion periods in 200ppm wt.% NaCl solution at 25 oC. EIS diagrams of hydrogen-charged and non-charged specimens exhibited two parts: a capacitive loop in the high-frequency region and a capacitive loop in the low-frequency region. The second capacitive arc radius for the hydrogen-charged specimen was significantly less than that of the non-charged specimen. The scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) was used for the element and surface morphology analysis of the specimens after immersion tests in 200ppm wt.% NaCl solution at 25 oC for 68 h. Little corrosion product could be found on the non-charged specimen surface while more corrosion product appeared on the hydrogen-charged specimen surface, as shown in Fig. 3. Cr content in the film formed on hydrogen-charged specimen was lower than that on non-charged specimen, indicating the effect of hydrogen on the chemical composition of surface film. Figure 1

The corrosion behavior of Alloy 182 in a cyclic hydrogenated and oxygenated water chemistry in high temperature aqueous environment

The corrosion behavior of Alloy 182 in a cyclic hydrogenated and oxygenated water chemistry in high temperature water is studied using various in situ and ex situ oxide characterization methods. The electrochemical potential and film resistance show a large change when the environment is changed from hydrogenated water to oxygenated water and are changeable with changing environment. The morphology and composition of the oxide film also exhibit a cyclic change accompanying with the cyclic changed environment. The phenomenon of hydrogen enhanced oxidation behavior is observed when the environment is changed from hydrogenated water to oxygenated water.

Influence of Conductivity on Corrosion Behavior of 304 Stainless Steel in High Temperature Aqueous Environment

The influence of conductivity on corrosion behavior of 304 stainless steel (SS) in high temperature water was investigated by using in-situ potentiodynamic polarization curves, electrochemical impedance spectra (EIS) at 300 °C, and ex-situ scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The structures of oxide films formed on 304 SS change with different conductivities at 300 °C. With the increase in conductivity, the passive current density increases while the resistances of oxide films decrease. But the resistances do not decrease lineally with the increase in conductivity. A modified double-layer model for oxide structure was proposed to explain the influence mechanism of conductivity on the oxide films on 304 SS in high temperature water. Improving the 10B enrichment level can reduce the conductivity of primary water and increase the corrosion resistance of 304 SS.

The corrosion behavior of Alloy 52 weld metal in cyclic hydrogenated and oxygenated water chemistry in high temperature aqueous environment

The corrosion behavior of Alloy 52 weld metal in cyclic hydrogenated and oxygenated water chemistry in high temperature water is studied by in situ monitoring corrosion potential (Ecorr), contact electric resistance (CER) and electrochemical impedance measurements (EIS), and ex situ scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) analysis. The Ecorr and film resistance show large change when the environment is changed from hydrogenated water to oxygenated water and changeable with changing environment while the morphology and composition only show obvious distinction in the first cycle. The main factor controlling the electric/electrochemical properties of the oxide film is Ecorr.

Prediction of crack growth rate in Type 304 stainless steel using artificial neural networks and the coupled environment fracture model

A crack growth rate (CGR) database has been developed to train an artificial neural network (ANN). The trained ANN and the extended coupled environment fracture model (CEFM) were used to predict the CGR in Type 304SS as a function of each of the principal variables of the system. The ANN revealed the underlying relationships that map the dependencies of the CGR on the various input independent variables. A sensitivity analysis revealed that IGSCC in sensitized Type 304SS in high temperature aqueous environments is primarily electrochemical in character. Comparison between the ANN-predicted CGR and CEFM-predicted CGR reveal good agreement.

In situ monitoring of the adsorption of Co2+ on the surface of Fe3O4 nanoparticles in high-temperature aqueous fluids

Developing an understanding of the reaction processes occurring at the surface⿿fluid interface at the atomic level of nanostructured materials in high-temperature aqueous environments is necessary for establishing general principles of behavior of nanomaterials operating in such extremes. In situ Co K-edge X-ray absorption spectroscopy (XAS) measurements were made on Fe3O4 nanoparticles in the presence of Co2+ ions in aqueous fluids to 500°C and approximately 220MPa. The results from analysis of the in situ EXAFS data, along with SEM-EDX spectra measured from reacted nanoparticles, indicate that adsorption of Co2+ ions on the surface of Fe3O4 nanoparticles is negligible at temperatures below 200°C but becomes significant in the 250⿿500°C temperature range. The low reaction temperature threshold of the Co2+ aqua ion with Fe3O4 nanoparticles is consistent with a relatively low value of the crystal field stabilization energy (CFSE) of Co2+ in octahedral site symmetry in spinels. Modeling of the pre-edge feature of the XANES and analysis of the extended X-ray absorption fine structure (EXAFS) shows that Co2+ adsorbs predominantly on octahedral sites of the surface of nanoparticles in aqueous fluids. Structural analyses using EXAFS and high resolution TEM show that the inverse spinel structure is preserved in the Co-incorporated surface atomic layers of the Fe3O4 nanoparticles. Our results suggest that the dissolved radioactive isotope 60Co in the primary cooling loop of supercritical water-cooled nuclear reactors have a high likelihood of precipitating on the surfaces of spalled ferrite nanomaterial.

The effect of Sn on autoclave corrosion performance and corrosion mechanisms in Zr–Sn–Nb alloys

The desire to improve the corrosion resistance of Zr cladding material for high burn-up has resulted in a general trend among fuel manufacturers to develop alloys with reduced levels of Sn. While commonly accepted, the reason for the improved corrosion performance observed for low-tin zirconium alloys in high-temperature aqueous environments remains unclear. High-energy synchrotron X-ray diffraction was used to characterize the oxides formed by autoclave exposure on Zr–Sn–Nb alloys with tin concentration ranging from 0.01 to 0.92wt.%. The alloys studied included the commercial alloy ZIRLO® (ZIRLO® is a registered trademark of Westinghouse Electric Company LLC in the USA and may be registered in other countries throughout the world. All rights reserved. Unauthorized use is strictly prohibited.) and two variants of ZIRLO with significantly lower tin levels, referred to here as A-0.6Sn and A-0.0Sn. The nature of the oxide grown on tube samples from each alloy was investigated via cross-sectional scanning electron microscopy. Atom probe analysis of ZIRLO demonstrated that the tin present in the alloy passes into the oxide as it forms, with no significant difference in the Sn/Zr ratio between the two. Synchrotron X-ray diffraction measurements on the oxides formed on each alloy revealed that the monoclinic and tetragonal oxide phases display highly compressive in-plane residual stresses with the magnitudes dependent on the phase and alloy. The amount of tetragonal phase present and, more importantly, the level of tetragonal-to-monoclinic phase transformation both decrease with decreasing tin levels, suggesting that tin is a tetragonal oxide phase stabilizing element. It is proposed that in Zr–Nb–Sn alloys with low Sn, the tetragonal phase is mainly stabilized by very small grain size and therefore remains stable throughout the corrosion process. In contrast, alloys with higher tin levels can in addition grow larger, stress stabilized, tetragonal grains that become unstable as the corrosion front continues to grow further inwards and stresses in the existing oxide relax.