Sr Diffusion Research Articles

Modification of Ti3C2Tx nanostructure with KH2PO4 and chitosan for effective removal of strontium from nuclear waste.

Nanostructure titanium carbide MXene (Ti3C2Tx) was modified with KH2PO4 and chitosan to effectively remove strontium from nuclear wastewater. Nuclear waste includes radionuclides of uranium, thorium, strontium, and cesium, which are classified depending on the concentration of radionuclides. Nuclear waste with a high strontium concentration is the production waste of radiopharmaceutical production centers. Ti3C2Tx was synthesized from Ti3AlC2 using HF40% and HF in situ (MILD-Ti3C2Tx) in 24h at 313.15 and 333.15K. Morphology, structure, and functional groups were investigated using the XRD, SEM, EDS, FTIR, and BET analyses. The Sr(II)'s adsorption capacity on Ti3C2Tx-HF and Ti3C2Tx-HF in situ was obtained as 61.9 and 253.5mgg-1, respectively (temperature, 298.15K; pH, 7.00; contact time, 180min; and Sr(II) concentration, 150mgl-1). Ti3C2Tx-HF in situ showed fourfold adsorption due to more hydroxyl functional groups and larger interlayer spacing. Ti3C2Tx was modified with KH2PO4 and chitosan to investigate the mechanism of change of Sr(II)'s adsorption capacity, which increased to 370 and 284mgg-1, respectively. The structural results of modified Ti3C2Tx showed that the surface functional groups increased when modified with chitosan. In addition, modification with KH2PO4, through encapsulating large amounts of KH2PO4 between Ti3C2Tx layers, increased the possibility of Sr(II) diffusion between layers and electrochemical interactions with hydroxyl groups, and thus, increased its adsorption. Some experiments were designed to investigate the effect of parameters like initial concentration of Sr(II), contact time, temperature, and pH solution, as well as modified- and unmodified-Ti3C2Tx on adsorbent. The results revealed that the adsorption process of Sr(II) with pristine and modified-Ti3C2Tx follows pseudo-second-order kinetics and Freundlich heterogeneous isotherm model. Freundlich model isotherm indicates the presence of various functional groups on the surface and between the pristine and modified Ti3C2Tx layers. Electrostatic reactions and intra-sphere complexation were the two dominant mechanisms of the adsorption process.

An excellent bismuth-doped perovskite cathode with high activity and CO2 resistance for solid-oxide fuel cells operating below 700 °C

Lowering the operating temperatures of solid-oxide fuel cells (SOFCs) is critical, although achieving success in this endeavor has proven challenging. Herein, Bi0.15Sr0.85Co0.8Fe0.2O3−δ (BiSCF) is systematically evaluated as a carbon dioxide (CO2)-tolerant and highly active cathode for SOFCs. BiSCF, which features Bi3+ with an ionic radius similar to Ba2+, exhibits activity (e.g., 0.062 Ω cm2 at 700 °C) comparable to that of Ba0.5Sr0.5Co0.8Fe0.2O3−δ and PrBaCo2O5+δ, while demonstrating a considerable advantage over Bi-doped cathodes. Moreover, BiSCF exhibits long-term stability over a period of 500 h, and an anode-supported cell with BiSCF achieves a power density of 912 mW cm−2 at 650 °C. The CO2-poisoned BiSCF exhibits quick reversibility or slight activation after returning to normal conditions. The exceptional CO2 tolerance of BiSCF can be attributed to its reduced basicity and high electronegativity, which effectively restrict surface Sr diffusion and hinder subsequent carbonate formation. These findings highlight the substantial potential of BiSCF for SOFCs operating below 700 °C.

Plutonic Nature of a Transcrustal Magmatic System: Evidence from Ultrahigh Resolution Sr-Disequilibria in Plagioclase Microantecrysts from the Southern Taupo Volcanic Zone, New Zealand

Abstract The residence timescales of antecrystic minerals contribute a key piece of information regarding the petrologic evolution of transcrustal magmatic systems and may be inferred using a combination of observations derived from microanalytical chemistry and diffusion modelling. Here, we present state-of-the-art stacked CMOS-type active pixel sensor (SCAPS) isotopographic images of tephra-hosted plagioclase microantecrysts from Tongariro Volcanic Centre in the southern Taupo Volcanic Zone, New Zealand. These crystals exhibit high-frequency Sr and anorthite zonation at sub-micron spatial resolution. We also find that all crystals display high-frequency intracrystalline Sr chemical potential variations, indicating that they have not resided at magmatic temperature for diffusive relaxation to advance significantly. To quantify crystal residence times at the well-constrained magmatic temperatures of these tephras, we first forward-modeled intracrystalline Sr diffusion over time using numerical methods. Results were then analyzed using novel spatial Fourier-transform techniques developed to understand the systematics the diffusive decay of Sr disequilibria in the spatial frequency domain. This ultimately permitted the estimation of Sr concentration profiles at crystal formation, prior to uptake into the carrier melt at the onset of eruption. Our data imply residence times of hours to days for the studied microantecrysts. This is inconsistent with long antecryst residence times in magmatic mushes at elevated temperatures, pointing instead to a cool plutonic nature of the magmatic plumbing system beneath the southern Taupo Volcanic Zone.

Microstructures, geochemistry, and geochronology of mica fish: Review and advances

Shear zones are one of the most conspicuous structures in orogenic and rifting settings, accommodating high strain, rock displacement and influencing magma emplacement and fluid flow. Since shear zones may be simultaneously or sequentially affected by multiple processes involving mineral reactions, variations in pressure-temperature conditions, fluid-rock interaction, and diffusion, determining the timing of such structures has been one of the major challenges for modern geochronology. Although low- (up to lower greenschist facies) and high-temperature shear zones (above amphibolite facies) are well-dated through low- and high-closure temperature minerals, medium-temperature shear zones developed within the critical temperature window of ∼450–550 °C, in which conventional chronometers such as 40Ar/39Ar and Rb–Sr applied to mica fish may or may not record the timing of deformation for multiple reasons (e.g., grain size, cooling rate, mineral composition, fluid activity, deformation, neo- and recrystallization). Here, we review the current knowledge on the evolution of mica fish and the effect of deformation on its chemical and isotopic systems. We evaluate the effect on the widely deployed in situ 40Ar/39Ar technique. Furthermore, we demonstrate the potential to assess mica fish evolution applying high-spatial resolution microstructural and chemical mapping techniques such as electron backscatter diffraction (EBSD), time-of-flight secondary ion mass spectrometry (ToF–SIMS) and in situ Rb–Sr via triple quadrupole inductively coupled plasma mass spectrometry (TQ-ICP-MS) to a case study of medium-temperature mylonites from the well-characterized Taxaquara shear zone, SE Brazil. We show that mica fish display complex microstructures with variable strain intensity, commonly with low strain inner cores and high strain edges and along kink planes. Strain shadows in mica fish are commonly characterized by low-strain fine-grained muscovite, suggesting recrystallization coeval with ductile deformation. Despite being intensely deformed, muscovite fish Rb–Sr retain the protolith age (c. 600 Ma), whereas recrystallized fine-grained muscovite yields the timing of deformation (c. 550–540 Ma). Synthetic shear bands cross-cutting coarse-grained muscovite fish induce muscovite recrystallization consistent with their distinct chemistry, with recrystallized muscovite characterized by higher Fe–Mg and lower Na suggesting fluid-assisted recrystallization under lower temperature compared to the muscovite fish host. We propose that these shear bands across mica fish play an important role by accommodating grain size reduction and subsequent deformation, leading to the formation of smaller individual mica fish. Grain size reduction, likely enhanced by dynamic precipitation (i.e., coeval crystal-plastic deformation and dissolution-precipitation creep), appears as the key recrystallization mechanism that allows low strain muscovite in strain shadows and shear bands to record the timing of deformation in medium-temperature shear zones, consistent with qualitative Sr diffusion modelling.

Reversible Solid Oxide Cells: Cycling and Long-Term Durability of Air Electrodes

Introduction Reversible solid oxide cell (r-SOC) enables both power generation and electrolysis, when the cell can be operated as a solid oxide fuel cell (SOFC) and as a solid oxide electrolysis cell (SOEC). Many studies are being conducted to improve their performance and durability (1,2).Lanthanum strontium cobalt ferrite (LSCF) is an air electrode material with a perovskite-type crystal structure which exhibits high electronic and ionic conductivity, oxygen diffusivity, and electrocatalytic activity (3). However, performance and durability of the cells with Sr-containing oxide air electrodes have to be carefully analyzed, as Sr ions tend to easily diffuse during sintering and in long-term operation, reacting with Zr ions from the solid electrolyte to form a highly resistance reaction layer such as SrZrO3 (4-6). While the performance and durability of LSCF-based air electrodes and the Sr diffusion in SOFC operation have been studied, there are still limited number of studies on the SOEC operation, and especially on the r-SOC operation. The diffusion of constituent ions such as Co and Fe may not be negligible in SOCs.Here in this study, we fabricate YSZ electrolyte-supported r-SOCs and conduct durability studies in both SOFC and SOEC modes. STEM-EDS observation of the air electrode materials is also made to investigate the durability and diffusion of various elements in the LSCF-based air electrode of r-SOCs. Experimental R-SOCs with yttria stabilized zirconia electrolytes (YSZ, 200 µm thick) were prepared. Ni-GDC co-impregnated fuel electrode was prepared, where a mixture of La0.1Sr0.9TiO3 (LST) and Gd0.1Ce0.9O2 (GDC) at a volume ratio of 50:50 was used as the porous electrode backbone, onto which Ni-containing solution of 1 µL was impregnated for Ni loading of 0.167 mg cm-2 (7). Gd0.1Ce0.9O2 (GDC) buffer layer was prepared between the electrolyte and the air electrode to prevent elemental diffusion (8). La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) was used for the air electrode. In addition, a Pt reference electrode was deposited onto the electrolyte on the fuel electrode side. The voltage measurement terminals of the electrochemical measurement setup were connected between the reference electrode and the air electrode to evaluate the air electrode potential. 50%-humidified hydrogen (100 ml min-1) was supplied to the fuel electrode, and air (150 ml min-1) was supplied to the air electrode. Negative current density means the value in the SOEC mode, while positive current density in the SOFC mode. Results and discussion As shown in Fig. 2 describing one cycle, current density was varied at 800°C for the 1000-cycle durability tests in the r-SOC operation. The range of current density was between -0.2 A cm-2 and 0.2 A cm-2. The air electrode potential at different current densities and the electrode impedance in every 100 cycles were measured. For the 1000-hour electrolysis durability test in the SOEC mode, current density of -0.2 A cm-2 was applied for 1000 hours at 800°C. The air electrode potential and the impedance in every 100 hours were measured (9). It has been found that a gradual degradation of the r-SOCs associated with an increase in air electrode potential in the SOEC mode and a decrease in the potential in the SOFC mode could be distinguished. However, such degradation tended to be stabilized with the number of cycles.STEM-EDS observations were performed to analyze the elemental distribution around the air electrode and the electrolyte in the cell. It was found that such elemental diffusion could occur during sintering and durability experiments.AcknowledgmentsA part of this study was supported by “Research and Development Program for Promoting Innovative Clean Energy Technologies Through International Collaboration” of the New Energy and Industrial Technology Development Organization (NEDO) (Project No. JPNP20005). Collaborative support by Prof. H. L. Tuller, and Prof. B. Yildiz at Massachusetts Institute of Technology (MIT) for their continuous support is gratefully acknowledged. Figure 1

Fine-Tuning of Air Electrode Microstructure and Its Composition as a Way to Enhance the Performance and Durability of Solid Oxide Electrolyzer - preliminary results

Among actions undertaken to reach a net-zero economy by 2050, implementation of the hydrogen technologies into various sectors e.g. energy and transport seems to be crucial. The significant increase of the installed capacity of electrolyzer in the last few years has been observed, which will accelerate in next decades to meet declared by many countries goals of their national hydrogen strategies. Nowadays, a dominant role on the electrolyze markets possess low temperature solution, namely, alkaline and PEM electrolyzes. However, due to higher efficiency – lower energy demand for hydrogen production, it is forecast that solid oxide electrolyzers (SOE) will take part of the market. The development of SOE, which are on the final R&D phase, is mainly focused on the extension of their lifespan and minimizing their manufacturing costs.The La1-xSrxCoO3-δ (LSC) and La1-xSrxCoyFe1-yO3-δ (LSCF) oxides due to their good catalytic activity and high mixed ionic-electronic conductivity are recognized as state-of-the-art air electrodes for SOC. However, Co-based perovskites are characterized by high thermal and chemical expansion, which might cause a mechanical mismatch with electrolyte, resulting in intensified SOC degradation. To mitigate mentioned issues different strategies have been proposed in the literature. Through the combined approach focused on modification of the bulk properties, simultaneously tailoring the microstructure of the electrodes and electrode/solid electrolyte interface, it is possible to overcome the kinetic limitations of operation at decreased temperatures.To maximize cell performance, and prevent the potential electrode degradation (i.e. its delamination) composite GDC-LSC/LSFC electrodes with gradual changes of the composition from electrolyte-electrode interphase to the electrode surface, were proposed. Furthermore, the impact of modification of electrode microstructure by an increase of its porosity and infiltration of the electrode surface with catalytically active oxides (e.g. PrxOy) was investigated. Fine-tuning of electrode porosity was achieved by the addition of the pore-forming agent, and the selection of its type (graphite or PMMA), amount, and size of its grains. Moreover, the work presents an approach to optimize the buffer layer, inter alia by its densifying, to mitigate Sr diffusion to the electrolyte and prevent air electrode delamination.The developed composite air electrodes were screen-printed (with an active area of 16 cm2) on the fuel electrode-supported cell and evaluated in the SOE mode at the 650-750 °C temperature range. Tests included measurements of j-V dependences and EIS spectra (at different temperatures, current densities, and for different gas flow delivered at the air side of the cell). In order to assess the impact of the added amount and type of pore-forming agent on the microstructure of the electrode layer, as well as to investigate possible microstructural changes of the cell after testing SEM, SEM-EDS, and FIB-SEM analysis were performed. The proposed modification of the composition and microstructure resulted in higher current densities and reduced cell polarization compared to standard cells with LSC and LSCF as the air electrode.AcknowledgmentsThe presented research was financially supported by: the National Centre for Research and Development, Poland, within project no. LIDER/1/0003/L-12/20/NCBR/2021 (research related to composite GDC-LSC/LSFC electrodes), and Ministry of Science and Higher Education through the statutory grant, within grant no. CPE.4000.001.2023 (research related to the improvement of the buffer layer-electrode interphase).

Relevance of diffuse-layer, Stern-layer and interlayers for diffusion in clays: A new model and its application to Na, Sr, and Cs data in bentonite

The diffusive flux of cations is enhanced and that of anions is decreased compared to that of water tracers in bentonite or other clays, as a result of electrostatic interactions between ions and the charged clay surfaces. Clays are often used or foreseen as barriers in waste disposal in order to protect the environment from hazardous materials. A consistent description of diffusion of various ions and uncharged species is important in this context, especially if long-term interactions between clays and other materials shall be predicted by reactive transport simulations. Here, diffusion of a suite of tracers (HTO, Cl, Na, Sr and Cs) in bentonite was investigated. Experimental through-diffusion data at different bentonite dry densities were described with models of increasing complexity. First, ‘standard’ empirical single ion transport models (uncoupled, simple Fickian diffusion) were applied for each density. These models served as reference cases for comparisons. For sorbing tracers (Na, Sr, Cs), surface diffusion models were used in a next step, where average surface mobilities for the cations were determined based on comparisons with transport parameters from HTO diffusion. Finally, a more complex model was developed in order to describe anion and cation diffusion in a coupled way. This model accounts for locally parallel diffusion in different environments, namely in ‘free’ water unaffected by surface charges, in diffuse (Donnan) layer water, within the Stern layer, and within interlayer water (D-S-I model). This coupled model requires additional parameters related to the bentonite microstructure as well as to cation mobilities in the Stern layer and in the interlayer. The latter were taken from literature. Microstructural parameters were constrained in a manner that overall anion exclusion matches anion accessible porosities found by the simple Fickian diffusion model. This was possible with a reasonable choice of microstructure parameters that are consistent with literature values. A good agreement between the experimental data and the simulated cation diffusion coefficients of the D-S-I model was found, using constraints by the HTO and Cl diffusion data. The interlayer pathway was found to be most important for diffusion of Na, Sr and Cs through bentonite. Stern layer diffusion was significant and more important than diffusion through the diffuse layer for Cs and Sr, while for Na the two pathways were of equal importance.

The effect of Fe2O3 sintering aid on Gd0.1Ce0.9O1.95 diffusion barrier layer and solid oxide fuel cell performance

Solid oxide fuel cells (SOFCs) with the Gd0.1Ce0.9O1.95 (GDC) diffusion barrier layer require the densification of GDC to improve the performance of the cells. In this work, the addition of 0.5 mol% Fe2O3 in GDC diffusion barrier layer as sintering aid is studied. The symmetrical cell and the fuel cell are fabricated by hot-pressing, co-sintering and screen-printing technologies. It is found that the addition of Fe2O3 can make GDC barrier layer denser at a reduced sintering temperature of 1250 °C and prevent diffusion of Sr to form ionic insulating interface between YSZ (Y2O3 stabilized ZrO2) and La0.6Sr0.4Co0.8Fe0.2O3-δ (LSCF). The fuel cell based on the GDC-Fe2O3 barrier layer achieves better maximum power density of 0.89 W cm−2 at 800 °C than that of 0.68 W cm−2 without Fe2O3 addition. No obvious degradation was observed on fuel cell based on the GDC-Fe2O3 diffusion barrier layer after a stability test at 750 °C for 100 h under 0.75 V and the thermal cycling between 750 and 400 °C. The results indicate that the addition of Fe2O3 sintering aid in GDC diffusion barrier layer can promote the densification of GDC and exhibit good long-term stability and thermal cycle stability.

Synthesis and Structure of an Ion‐Exchanged SrTiO3 Photocatalyst with Improved Reactivity for Hydrogen Evolution

AbstractBaTiO3 heated in an excess of SrCl2 at 1150 °C converts to SrTiO3 through an ion exchange reaction. The SrTiO3 synthesized by ion exchange produces hydrogen from pH 7 water at a rate more than twice that of conventional SrTiO3 treated identically. The apparent quantum yield for hydrogen production in pure water of the ion exchanged SrTiO3 is 11.4% under 380 nm illumination. The catalyst resulting from ion‐exchange differs from conventional SrTiO3 by having ≈2% residual Ba, inhomogeneous Cl‐doping at a concentration less than 1%, Kirkendall voids in the centers of particles that result from the unequal rates of Sr and Ba diffusion together with the transport of Ti and O, and nanoscale regions near the surface that have lattice spacings consistent with the Sr‐excess phase Sr2TiO4. The increased photochemical efficiency of this nonequilibrium structure is most likely related to the Sr‐excess, which is known to compensate donor defects that can act as charge traps and recombination centers.

Hydrogeochemical processes of critical zone developed in Tégulines Clay, Paris Basin: Hydrogeochemical and multi-isotopic approach (δ13C, δD, δ18O, 87Sr/86Sr and 14C)

Water transfers and processes governing the chemistry of groundwaters and clay pore waters were investigated in the critical zone developed in Tégulines Clay in the area of Brienne-Le-chateau, at east of the Aube alluvium plain (France). A pit-digging campaign along two-stepped west-facing hillslopes along the Brevonne valley and the Aube/Brevonne paleo-valley gives evidence of a thin Quaternary clay silty and carbonate-free loams overlying Tégulines Clay, mobile regolith along the slopes and the presence of a carbonate alluvium layer in pits of the Brevonne valley. Groundwaters at the first ridgetop attest of a temporary perched water table, while groundwaters at top of Tégulines Clay along the first west-facing steep slope toward the Brevonne River provide evidence of lateral groundwater transfers and runoff of waters toward the valley which is a discharge zone belonging to the present-day Aube alluvium plain. Groundwaters have low concentrations of Total Dissolved Solids (TDS < 600 mg/L) and are calcic-carbonate waters. Their δ18O and δD of groundwaters are consistent with local meteoric values. An 18O and D enrichment in groundwaters at the bottom of the second hillslope and in waters from reservoirs indicates evaporation processes. The δ13CCO2 of dissolved inorganic carbone in groundwaters is essentially due to degradation of organic matter. The composition of the pore waters from Tégulines Clay in boreholes are chemically heterogeneous and different from groundwaters. They are Ca-Mg-SO4-rich and show a large range of TDS concentrations (592–6457 mg/L). The highest values are measured in the most intensely weathered clay developed in the first 10–15 m under the first ridge top and the low east-facing slope of the Aube/Brevonne paleo-valley. This latter seems to represent a large intermediate discharge zone between the coarse ridgetops (recharge zones) and the current Aube alluvium plain. The δ18O and δD of pore waters are alined along the local meteoric water line, indicating that meteoric waters have diffused through the clay formation during post-depositional history and replaced original connate seawater. On contrary the 87Sr/86Sr ratios of pore waters remain almost similar to that of Lower Cretaceous seawater, suggesting a limited diffusion of Sr since the formation deposition. Toward the top of the formation in the Aube/Brevonne paleovalley, major cation and anion concentrations, 18O and D enrichment and a slight increase of the 87Sr/86Sr ratios suggest the diffusion of evaporated waters. The δ13C, δ18O,87Sr/86Sr ratios and 14C activity of concretions at top of Tégulines Clay show that they precipitated from evaporated old groundwaters, the oldest one at ∼ 34 ky in the TPH2-1 pit at the ridgetop of the second hillslope and a younger age of ∼ 8 ky in the TV4-1 pit.

Three-dimension titanium phosphate aerogel for selective removal of radioactive strontium(II) from contaminated waters

The effective removal of radioactive strontium (especially 90Sr) from nuclear wastewater is crucial to environmental safety. Nevertheless, materials with excellent selectivity in Sr removal remain a challenge since the similarity with alkaline earth metal ions in the liquid phase. In this work, a novel titanium phosphate (TiP) aerogel was investigated for Sr(II) removal from the radioactive wastewater based on the sol-gel method and supercritical drying technique. The TiP aerogel has amorphous, three-dimensional and mesoporous structures with abundant phosphate groups, which was confirmed by X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), atomic force microscope (AFM) and Fourier transform infrared spectroscopy (FT-IR). The adsorbent exhibited high efficiency and selectivity for the removal of Sr(II) with an extensive distribution coefficient up to 4740.03 mL/g. The adsorption equilibrium reached within 10 min and the maximum adsorption capacity was 373.6 mg/g at pH 5. And the kinetics and thermodynamics data fitted well with the pseudo-second-order model and Langmuir model respectively. It can be attributed to the rapid trapping and slow intraparticle diffusion of Sr(II) inside the mesoporous channels of the TiP aerogel. Furthermore, TiP aerogel exhibited over 80% removal for 50 mg/L Sr2+ in real water systems (seawater, lake water and tap water). X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that strong ionic bonding formed during Sr(II) adsorption with the phosphate group on TiP aerogel. These results indicated that TiP aerogel is a promising high-capacity adsorbent for the effective and selective capture of Sr(II) from radioactive wastewater.

Performance and Durability of Solid Oxide Electrolysis Cell Air Electrodes Prepared By Various Conditions

Introduction Fuel electrode materials are important for achieving higher performance and durability of Solid Oxide Fuel Cell (SOFC), Solid Oxide Electrolysis Cell (SOEC), and Reversible Solid Oxide Cells (r-SOCs). On the other hand, the air electrode also faces performance and durability issues. For example, the diffusion of Sr ions from the air electrode materials has been reported.1, 2 In SOECs, if electrolysis can be performed at a thermoneutral potential balancing heat absorption by electrolysis and heat generation by the internal resistance of the electrolysis cell, hydrogen can be generated theoretically without heat supply. The purpose of this study is to evaluate the electrochemical performance and durability of the SOECs by conducting electrolysis performance tests of LSCF-based air electrodes with different preparation conditions, and electrolysis durability tests at the thermoneutral potential. Experimental Each test was conducted using a cell with a scandia-stabilized zirconia electrolyte (ScSZ, 200 µm thick) as a substrate. For the fuel electrode, Ni-GDC co-impregnated fuel electrode was used3. A mixture of Ni(NO3)2･6H2O, Gd(NO3)3･6H2O, and Ce(NO3)3･6H2O was impregnated into the porous LST-GDC framework, a mixture of LST powder (La0.1Sr0.9TiO3) and GDC powder (Gd0.9Ce0.1O₃). LSCF, (La0.6Sr0.4)(Co0.2Fe0.8)O3, was used for the air electrodes. GDC was inserted between the LSCF layer and the electrolyte plate as a buffer layer. In fabricating air electrodes, four types of air electrodes were applied, at shown in Table 1. For the electrochemical measurements of the air electrodes, Pt reference electrode was attached to the electrolyte on the fuel electrode side, and the voltage terminals of the electrochemical measurement system were connected between the reference electrode and the air electrode to measure air electrode voltage.In the performance tests, the voltage (potential) and impedance of the air electrode were measured at operating temperatures of 800°C, 750°C, and 700°C. In the durability tests, the air electrode was maintained at thermoneutral potentials at 800°C and 700°C (1.286 V and 1.283 V, respectively), and the voltage and impedance of the air electrodes were measured before and after the durability tests to evaluate the degradation of the air electrodes. Results and discussion Figure 1 shows the air electrode voltage obtained from the performance tests at each operating temperature for the four types of air electrodes shown in Table 1. First, regarding the dependence of the electrolysis performance on operating temperature, an increase in air electrode voltage (degradation of the air electrode) was found at 800°C.The increase in air electrode voltage with current density was almost linear, but at lower operating temperatures, the increase in air electrode voltage at lower current densities becomes larger. In other words, the I-V curve was rather ohmic at 800°C, but non-ohmic at 700°C.Figure 2 shows the results of an 80-hour durability test at different temperatures. The current density of the cell corresponding to the thermoneutral potential was -0.298 Acm-2 when operated at 800°C and -0.018 Acm-2 when operated at 700°C.The degradation rate was calculated from the difference in air electrode voltage before and after the performance and durability test at these current densities: 0.172% at 800°C and 0.792% at 700℃. The degradation rate increased as the operating temperature decreased in the SOEC mode, despite the low current density. Microstructural observation of the air electrode after the durability test showed that Sr diffused to the LSCF/GDC interface similar to SOFCs mode4, and that the diffusion of Sr was accelerated at 700°C. In addition, Co diffusion was also observed. Such diffusion may occur during LSCF firing process and/or during SOEC operation. More detailed investigation is in progress. Acknowledgements This research was supported in part by NEDO (New Energy and Industrial Technology Development Organization). We thank all parties involved. References (1) V. Subotić, S. Futamura, G. F. Harrington, J. Matsuda, K. Natsukoshi, and K. Sasaki, J. Power Sources, 492, 229600 (2021).(2) S. P. Simner, M. D. Anderson, M. H. Engelhard, and J. W. Stevenson, Electrochem. Solid-State Lett., 9 A478 (2006).(3) K. Natsukoshi, K. Miyara, Y. Tachikawa, J. Matsuda, S. Taniguchi, G. F. Harrington, and K. Sasaki, ECS Trans., 03, 203 (2021).(4) S. Kanae, Y. Toyofuku, T. Kawabata, Y. Inoue, T. Daio, J. Matsuda, J,-T. Chou, Y. Shiratori, S. Taniguchi, and K. Sasaki, ECS Trans., 68, 2463 (2015). Figure 1

A new design of metal supported micro-tubular solid oxide fuel cell with sandwich structure

Micro-tubular solid oxide fuel cell (MT-SOFC) is considered as a promising choice for portable applications. In this work, we developed a novel metal supported MT-SOFC with porous 430 stainless steel support| 430 stainless steel-SSZ| SSZ| porous SSZ sandwich structure by dip coating and one-step co-sintering technology. The metal supported MT-SOFC showed good connection between each function layer and exhibited a significant maximum power density of 271 mW cm−2 at 800 °C. Although the power density showed about 19.6% off after 14 thermal cycles between 600 °C and 800 °C, and about 5% per 100 h degradation rate during the 200 h long-term stability test at 700 °C and 0.7 V, the structure of the single cell could be maintained well and no crack and Sr diffusion was observed. As the result, the ohmic resistance of the cell kept unchanged during the thermal cycling and long-term test. The relatively fast degradation was attributed to the Ni and LSM particles coarsening and agglomeration, which will be improved in the further work. This work presented a low-cost and simple way to fabricate the metal supported MT-SOFCs with good electrochemical performance.

Investigating the thermal stability of nanocrystalline aluminum-lithium alloy by combining different mechanisms: Reinforcing with graphene and alloying with Sr

Interest in nanocrystalline (nc) aluminum-lithium (Al-Li) alloys is motivated by the demand for lightweight and high-performance materials for light-weighting applications and superior fuel consumption. Nonetheless, nc metals, including Al are thermally unstable, which hinders their technological applications. In this study, we explore the effect of combining dilute amounts of strontium (1.0 at% Sr) and graphene nanoplatelets (1.0 wt% GNPs) to investigate the thermal stability of a nc Al-Li alloy. Ball milling was used to prepare four samples: Al-Li, Al-Li-Sr, Al-Li-GNPs, and Al-Li-Sr-GNPs, to systematically investigate the role of each added element. Isothermal annealing was conducted at different temperatures to investigate the thermal stability. Despite maintaining a nanometric grain size and high hardness of 70 nm and 1.1 GPa, respectively, after annealing at 773 K for 1 h, the Al-Li-Sr-GNPs sample suffered the most significant grain growth and the highest drop in hardness when compared to the Al-Li-Sr and Al-Li-GNPs samples. Microstructural investigations suggested that competing effects resulting from the spontaneous reaction of both Sr and GNPs with Al at higher temperatures resulted in a declining thermal stability efficiency. The formation and distribution of the rod-like Al 4 C 3 phase at the grain boundaries stood in the way of proper Sr diffusion after annealing and caused the agglomeration of the Al 4 Sr phase. • The thermal stability of nc Al-Li alloy was studied through Sr and GNPs additions. • The Al 4 Sr and Al 4 C 3 formed at the GBs contributed to the improved thermal stability. • Rod-like Al 4 C 3 formed at the grain boundaries prevented the proper Sr segregation. • Agglomeration of the Al 4 Sr resulted in a declined thermal stability efficiency.

Thermal storage conditions and origin of compositional diversity of plagioclase crystals in magmas from the 1980 and 2004-2005 eruptions of Mount Saint Helens

Abstract The thermal histories of upper crustal magma reservoirs place important constraints on the formation, evolution, and remobilization of crustal magmas, yet quantifying thermal histories remains challenging. We report new in-situ plagioclase trace-element data, Sr in plagioclase diffusion timescales, and plagioclase 238U-230Th-226Ra disequilibria data from Mount Saint Helens (MSH) 1980 cryptodome and 2004-2005 dacite domes to evaluate the thermal storage conditions and compositional diversity of recent MSH magmas. This approach allows us to more directly link the thermal (and therefore physical) conditions within the MSH magma reservoir to timescales of storage, thereby constraining the fraction of time 1980-2005 MSH magmas have spent in a mobile state. Plagioclase trace-element data and U-series characteristics reveal a compositionally heterogenous magmatic system beneath MSH and also require multi-stage plagioclase growth histories. The data also show that 2004-05 dacites contain a different plagioclase population relative to the 1980 cryptodome dacite, comprised of either a compositionally (and possibly temporally) distinct plagioclase component or composed of the same plagioclase components but in significantly different proportions. Discordant plagioclase 238U-230Th and 230Th-226Ra apparent ages require a mixture of young (likely eruption related) and old (&amp;gt;20-40 ka) plagioclase crystals in both 1980 and 2004-05 dacites. The low (230Th)/(232Th) in all measured 1980 and 2004-05 plagioclase requires a significant fraction (&amp;gt;10-30%) of the plagioclase to be old (&amp;gt;10s kyr). Maximum modeled Sr diffusion timescales at 750oC range from decades to centuries for both eruptions, with a maximum of ~600 years found in 1980 cryptodome plagioclase. However, partially equilibrated Sr in the innermost exposed parts of some crystals found in both 1980 and 2004-05 plagioclase indicate that a fraction (&amp;gt;20%) of plagioclase may have experienced a total of &amp;gt;10 kyrs at temperatures ≥750oC. Coupling Sr diffusion timescales with U-series measurements indicates that significant fraction (at least ~40%) of modeled MSH plagioclase spent &amp;lt;5% of their storage time at temperatures ≥750oC and thus in an easily mobilized rheological state. In contrast, the fraction of partially equilibrated plagioclase possibly spent &amp;gt;25-50% of their storage time at hotter conditions. Our data combined with data from other arc magmatic systems (e.g., Mt. Hood) imply that the process of remobilizing magma in arc systems towards successive eruptions requires thermally rejuvenating largely crystalline material, as opposed to sequential tapping of a persistent liquid-dominated magma body, even if successive eruptions are spaced closely in time (decades). In addition, rejuvenation events responsible for successive eruptions may sample spatially localized, but potentially overlapping, portions of the broader magma reservoir.

Thermal Budgets of Magma Storage Constrained by Diffusion Chronometry: the Cerro Galán Ignimbrite

Abstract The long-term thermochemical conditions at which large bodies of silicic magma are stored in the crust is integral to our understanding of the timing, frequency, and intensity of volcanic eruptions and provides important context for interpreting volcano monitoring data. Despite this, however, individual magmatic systems may exhibit a range of time–temperature paths, or thermal histories, that are the result of many complex and, in some cases, competing processes. This complexity contributes to an incomplete understanding of the long-term thermal evolution of magma stored within the Earth’s crust. Of recent interest to the volcanology community is the length of time large volumes of rheologically eruptible and geophysically detectable magma exist within the crust prior to their eruption. Here we use a combination of diffusion chronometry, trace element, and thermodynamic modeling to quantify the long-term thermal evolution of the 2.08 Ma, 630 km3 Cerro Galán Ignimbrite (CGI) in NW Argentina; one of the largest explosive volcanic eruptions in the recent geologic record. We find that diffusion of both Mg and Sr in plagioclase indicate that erupted magmatic material only spent decades to centuries at or above temperatures (~750°C) required to maintain significant volumes of stored eruptible magma. Calculated plagioclase equilibrium compositions reveal an array of liquids that is controlled overall by fractionation of plagioclase + biotite + sanidine, although high-resolution trace element transects record a diversity of fractionation pathways. Overall, we suggest that there is compelling evidence that the magma erupted from the CGI magmatic system spent most of its upper crustal residence in a largely uneruptible state and was rapidly remobilized shortly before eruption.

Self-stabilized hybrid cathode for solid oxide fuel cell: A-site deficient perovskite coating as solid solution for strontium diffusion

Challenged by the surface strontium (Sr) enrichment, long-term stability of the La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode remains to be the most intractable problem hindering its further development and application in solid oxide fuel cells (SOFCs). To enhance the durability and performance of LSCF-based electrodes, we propose a novel approach by introducing a highly active A-site deficient La0.95CoO3-δ (LC95) thin film onto the surface of the porous LSCF scaffold, simultaneously working as the accepter for Sr diffusion and conformal collector for electrons conduction. Besides the inhibiting effect from the dense coating, the A-site deficiencies reserved in coating lattice enable promising stabilization for Sr diffusion and segregation. At 700 °C, the La0.6Sr0.4Co0.2Fe0.8O3-δ@La0.95CoO3-δ (LSCF@LC95) hybrid cathode shows a polarization resistance of 0.28 Ωcm2, much lower than that for pristine LSCF cathode (0.36 Ωcm2). In addition to the higher electrochemical activity, single cell with LSCF@LC95 cathode exhibits remarkable long-term stability without detectable degradation over 120 h.

Diffusion and segregation of Sr in glassy carbon: Model and analysis

Some diffusing systems segregation towards the surface also occurs. Such a system can be described by adding a force-induced velocity term to the Fick diffusion equation. The profile of an implanted material is usually Gaussian or at least very near a Gaussian function. In this paper this Fick partial differential equation in a force field was solved for an initially Gaussian profile. The simulated profiles exhibit the expected behavior. 200 keV implanted strontium into glassy carbon and isochronically annealed in vacuum from 300 °C to 900 °C for 1 h. The Sr profiles were determined by RBS (Rutherford backscattering spectrometry). They showed both diffusion and segregation between 400 °C to 900 °C. These profiles were fitted to the abovementioned solution to extract the diffusion coefficient and segregation drift velocity at each annealing temperature. In the temperature range 400 °C to 800 °C the diffusion coefficient had an activation energy for diffusion of 0.20 eV and 1.2 nm2/s for the pre-exponential factor D0. The segregation velocity, which is directly proportional to the segregating force, increased with increasing temperature. At annealing temperature of 400 °C the average drift velocity towards the surface was 39 pm/s and at 900 °C it was an order of maginitude higher at 0.34 nm/s.

Measurement of effective Sr diffusion coefficients in IG-110 graphite

Radionuclide transport and release from operating HTGR cores during normal and off-normal operations carries the possibility of increased exposure risk to reactor personnel as well as radionuclide release to the surrounding environment in the event of a depressurization accident. Diffusion is one of the primary processes by which this radionuclide transport takes place. 90Sr is one of several fission products which is commonly investigated within the context of high-temperature gas-cooled reactors due to its low volatility and ability to migrate through intact TRISO fuel particles. Effective diffusion coefficients for strontium in unirradiated IG-110 graphite have been experimentally determined over the temperature range 1773 K – 1973 K using a time-release method coupled to an inductively-coupled plasma mass spectrometer. The results of this work are: DSr,IG−110=(1.7×10−1m2/s)exp(−3.46×105J/molRT)

Sectoral and growth rate control on elemental uptake by individual calcite crystals

Heterogeneous distribution of trace elements (impurities) within individual calcite crystals is a phenomenon commonly observed in natural and laboratory systems. Changes in thermodynamic intensive parameters (mostly chemical potential and temperature) cannot always explain the inhomogeneous impurity patterns in calcite crystals and it has been suggested that growth rate and crystallographic orientation may exert strong effects on elemental incorporation into calcite. In addition, there are a number of experimental studies on micro-scale element (E) distribution between non-equivalent pairs of calcite vicinal faces (known as sectoral zoning); however, the variability of partition coefficients (e.g., KE = (E/Ca)calcite/(E/Ca)fluid) within individual crystals remains undetermined.In this study, we have extended the work on elemental distribution between crystal sectors to evaluation of partition coefficients of trace and minor elements (Li, B, Mg, and Sr) in calcite crystal faces (10–14) and (01−12), whose growth rates were assessed. Growth entrapment model (GEM) and lattice strain theory were applied to explain KE heterogeneity by varying near-surface diffusivity of Mg and Sr and by varying surface enrichment factor for Li, B, Mg, and Sr. Decoupling of sectoral and growth rate effects reveals that sectoral zoning plays a key role in elemental distribution. More specifically, KLi and KB vary by more than one order of magnitude and KMg varies by a factor of two within individual crystal faces. Strontium sectoral distribution is different from those of Li, B, and Mg and KSr varies by up to a factor of two. These behaviors likely reflect different mechanisms of incorporation of Li, B, Mg, and Sr into calcite.