Electro-chemo-mechanical effects of lithium incorporation in zirconium oxide

Understanding the response of functional oxides to extrinsic ion insertion is important for technological applications including electrochemical energy storage and conversion, corrosion, and electronic materials in neuromorphic computing devices. Decoupling the complicated chemical and mechanical effects of ion insertion is difficult experimentally. In this work, we assessed the effect of lithium incorporation in zirconium oxide as a model system, by performing first-principles based calculations. The chemical effect of lithium is to change the equilibria of charged defects. Lithium exists in ZrO_{2} as a positively charged interstitial defect, and raises the concentration of free electrons, negatively charged oxygen interstitials, and zirconium vacancies. As a result, oxygen diffusion becomes faster by five orders of magnitude, and the total electronic conduction increases by up to five orders of magnitude in the low oxygen partial pressure regime. In the context of Zr metal oxidation, this effect accelerates oxide growth kinetics. In the context of electronic materials, it has implications for resistance modulations via ion incorporation. The mechanical effect of lithium is in changing the volume and equilibrium phase of the oxide. Lithium interstitials together with zirconium vacancies shrink the volume of the oxide matrix, release the compressive stress that is needed for stabilizing the tetragonal phase ZrO_{2} at low temperature, and promote tetragonal-to-monoclinic phase transformation. By identifying these factors, we are able to mechanistically interpret experimental results in the literature for zirconium alloy corrosion in different alkali-metal hydroxide solutions. These results provide a mechanistic and quantitative understanding of lithium-accelerated corrosion of zirconium alloy, as well as, and more broadly, show the importance of considering coupled electro-chemo-mechanical effects of cation insertion in functional oxides

Predicting point defect equilibria across oxide hetero-interfaces: model system of ZrO2/Cr2O3

We present a multi-scale approach to predict equilibrium defect concentrations across oxide/oxide hetero-interfaces. There are three factors that need to be taken into account simultaneously for computing defect redistribution around the hetero-interfaces: the variation of local bonding environment at the interface as epitomized in defect segregation energies, the band offset at the interface, and the equilibration of the chemical potentials of species and electrons via ionic and electronic drift-diffusion fluxes. By including these three factors from the level of first principles calculation, we build a continuum model for defect redistribution by concurrent solution of Poisson's equation for the electrostatic potential and the steady-state equilibrium drift-diffusion equation for each defect. This model solves for and preserves the continuity of the electric displacement field throughout the interfacial core zone and the extended space charge zones. We implement this computational framework to a model hetero-interface between the monoclinic zirconium oxide, m-ZrO[subscript 2], and the chromium oxide Cr[subscript 2]O[subscript 3]. This interface forms upon the oxidation of zirconium alloys containing chromium secondary phase particles. The model explains the beneficial effect of the oxidized Cr particles on the corrosion and hydrogen resistance of Zr alloys. Under oxygen rich conditions, the ZrO[subscript 2]/Cr[subscript 2]O[subscript 3] heterojunction depletes the oxygen vacancies and the sum of electrons and holes in the extended space charge zone in ZrO[subscript 2]. This reduces the transport of oxygen and electrons thorough ZrO[subscript 2] and slows down the metal oxidation rate. The enrichment of free electrons in the space charge zone is expected to decrease the hydrogen uptake through ZrO[subscript 2]. Moreover, our analysis provides a clear anatomy of the components of interfacial electric properties; a zero-Kelvin defect-free contribution and a finite temperature defect contribution. The thorough analytical and numerical treatment presented here quantifies the rich coupling between defect chemistry, thermodynamics and electrostatics which can be used to design and control oxide hetero-interfaces

Doping in the Valley of Hydrogen Solubility: A Route to Designing Hydrogen-Resistant Zirconium Alloys

Hydrogen pickup and embrittlement pose a challenging safety limit for structural alloys used in a wide range of infrastructure applications, including zirconium alloys in nuclear reactors. Previous experimental observations guide the empirical design of hydrogen-resistant zirconium alloys, but the underlying mechanisms remain undecipherable. Here, we assess two critical prongs of hydrogen pickup through the ZrO[subscript 2] passive film that serves as a surface barrier of zirconium alloys; the solubility of hydrogen in it—a detrimental process—and the ease of H[subscript 2] gas evolution from its surface—a desirable process. By combining statistical thermodynamics and density-functional-theory calculations, we show that hydrogen solubility in ZrO[subscript 2] exhibits a valley shape as a function of the chemical potential of electrons, μ[subscript e]. Here, μ[subscript e], which is tunable by doping, serves as a physical descriptor of hydrogen resistance based on the electronic structure of ZrO[subscript 2]. For designing zirconium alloys resistant against hydrogen pickup, we target either a dopant that thermodynamically minimizes the solubility of hydrogen in ZrO[subscript 2] at the bottom of this valley (such as Cr) or a dopant that maximizes μ[subscript e] and kinetically accelerates proton reduction and H[subscript 2] evolution at the surface of ZrO[subscript 2] (such as Nb, Ta, Mo, W, or P). Maximizing μ[subscript e] also promotes the predomination of a less-mobile form of hydrogen defect, which can reduce the flux of hydrogen uptake. The analysis presented here for the case of ZrO[subscript 2] passive film on Zr alloys serves as a broadly applicable and physically informed framework to uncover doping strategies to mitigate hydrogen embrittlement also in other alloys, such as austenitic steels or nickel alloys, which absorb hydrogen through their surface oxide films.United States. Dept. of Energy. Energy Innovation Hub for Modeling and Simulation of Nuclear Reactors. Consortium for Advanced Simulation of Light Water Reactors (Contract DE-AC05-00OR22725)MIT-China Scholarship Council (Fellowship

Performance of Isolated Footing with Several Corrosion Levels under Axial Loading

This research aims to illustrate the corrosion process and its effect on the deterioration of reinforced concrete (RC) isolated footings using a small-scale model (1/8) and present the results of a prototype-scale study using a numerical model with different concrete depths and corrosion levels under axial load. The experimental program consisted of testing five small-scale (1/8) model RC isolated footings under axial loading after subjecting them to accelerated corrosion tests with a constant current. The main variable in the small-scale sample test was the corrosion level. This study presents an experimental approach, using the constant current method and the finite element method (FEM) with the ABAQUS package, to examine its effect on the axial load behavior under different corrosion ratios, which were 0%, 4.21%, 9.11%, 24.56%, and 30.67%. On the prototype scale, the variables were the corrosion level and the RC depths of 300 mm, 400 mm, and 500 mm. The results indicated that the average deviation in ultimate load between the experimental and FEM outcomes for the small-scale was below 5.6%, while the average deflection deviation was 6.8%. Also, the study found that an increase in the depth of the RC footing and corrosion ratio led to a more pronounced impact of the cracking pattern in the concrete and corroded bars, as well as a greater difference in the failure load. The experimental results suggest that the proposed numerical model is accurate and effective. These findings have important implications for the evaluation of isolated footings affected by corrosion damage using FEM, and can help inform decisions related to their design and maintenance. The failure loads of non-corroded footings with different depths were compared with the ECP-203 provisions of the 2018 Egyptian Code, and how corrosion ratios can be simulated by numerical models. The percentage variation between the design loads by code and the numerical loads by ABAQUS for controlled footings with thicknesses of 300, 400, and 500 mm was found to be 73%, 80%, and 78%, respectively. Using the derived relationship, the equivalent corrosion ratio percentages were 23.8%, 20.2%, and 32%, respectively. Doi: 10.28991/CEJ-2023-09-06-011 Full Text: PD

Thermomechanical Stabilization of Electron Small Polarons in SrTiO₃ Assessed by the Quasiharmonic Approximation

We predict a predominance diagram for electron defects in the temperature-hydrostatic stress space for SrTiO₃ by combining density functional theory and the quasiharmonic approximation. We discovered two regimes where small polarons dominate: under tensile stress at lower temperature due to a larger relaxation volume of the defect Ω, and under compressive stress at higher temperature due to a smaller Ω and larger formation entropy. This provides a means to modulate the electronic conductivity via controlling the underlying charge carrier. Furthermore, the results challenge the common association between larger Ω and charge localization by demonstrating that at high temperature the free electron can induce larger Ω compared to the small polaron. This finding is attributed to the ability of the free electron to generate greater vibrational entropy upon finite isothermal expansion.National Science Foundation (U.S.). Materials Research Science and Engineering Centers (Program) (DMR-1419807)National Science Foundation (U.S.) (TG-DMR 140065

Accessible Switching of Electronic Defect Type in SrTiO₃ via Biaxial Strain

Elastic strain is used widely to alter the mobility of free electronic carriers in semiconductors, but a predictive relationship between elastic lattice strain and the extent of charge localization of electronic defects is still underdeveloped. Here we considered SrTiO₃, a prototypical perovskite as a model functional oxide for thin film electronic devices and nonvolatile memories. We assessed the effects of biaxial strain on the stability of electronic defects at finite temperature by combining density functional theory (DFT) and quasiharmonic approximation (QHA) calculations. We constructed a predominance diagram for free electrons and small electron polarons in this material, as a function of biaxial strain and temperature. We found that biaxial tensile strain in SrTiO₃ can stabilize the small polaron, leading to a thermally activated and slower electronic transport, consistent with prior experimental observations on SrTiO₃ and distinct from our prior theoretical assessment of the response of SrTiO₃ to hydrostatic stress. These findings also resolved apparent conflicts between prior atomistic simulations and conductivity experiments for biaxially strained SrTiO₃ thin films. Our computational approach can be extended to other functional oxides, and for the case of SrTiO₃ our findings provide concrete guidance for conditions under which strain engineering can shift the electronic defect type and concentration to modulate electronic transport in thin films

CAFFEINEAS A PROMISING ANTIFBROTIC AGENT AGAINST CCL4-INDUCED LIVER FIBROSIS

Objective: Hepatic fibrosis is a wound-healing process in the liver with chronic injury and is characterized by an excess production and deposition of extracellular matrix (ECM) components. Our aim is to investigate the hepatoprotective effects of caffeine against CCL4-induced liver fibrosis in rats and to be compared with the reference standard N-acetylcysteine (NAC).Methods: Rats were divided into 5 groups (n=8), the 1st group served as normal control, the 2nd group received corn oil, the 3rd group is a fibrosis control and the remaining two groups received in addition to CCL4, NAC (150 mg/kg/day) as a reference treatment and caffeine (15 mg/kg/day). At the end of experimental period the following parameters were measured, specific fibrosis biomarkers [hepatic transforming growth factor β1(TGF-β1) and hepatic hydroxyproline (HYP)], liver function biomarkers [serum alanine transaminase (ALT), aspartate transaminase (AST), total bilirubin and albumin], lipid profile [serum triglycerides, total cholesterol, low density lipoprotein cholesterol (LDL-Ch) and high density lipoprotein cholesterol (HDL-Ch)], inflammatory biomarkers [serum tumor necrosis factor alpha (TNF-α), hepatic myeloperoxidase (MPO)], oxidative stress biomarkers [hepatic malondialdehyde (MDA), glutathione (GSH) and catalase (CAT)], relative liver body weight and liver histopathological study.Results: Caffeine significantly improved all the aforementioned biochemical parameters and liver sections obtained from this group showed prominent histopathological improvement.Conclusion: Caffeine hepatoprotective effects may be due to modulation of the fibrous scar formation, Improvement of liver function, Anti-inflammatory and antioxidant potentials

Oral Focal Mucinosis: A case report

Oral focal mucinosis is a rare lesion with less than 60 cases reported in English literature so far, to the best of our knowledge. It is considered to be the oral counterpart of cutaneous focal mucinosis and/or cutaneous myxoid cyst. Histopathologically, Oral focal mucinosis is demonsterates a well-circumscribed area of myxomatous connective tissue containing mucinous material, surrounded by denser collagenous connective tissue. We present a case of Oral focal mucinosis occurring on the buccal gingiva of the lower jaw

Portal Venous Pressure as a Predictor of Mortality in Child’s A Cirrhotic Patients Undergoing Elective Surgery: A Prospective Study

BACKGROUND: Recently, portal venous pressure (PVP) exhibited high sensitivity and specificity in anticipating death in cirrhotic cases submitted to emergency operations. AIM: The current prospective work aimed to evaluate the utility of PVP in predicting 1st month post-operative death in Child’s A cirrhotic cases who underwent elective operations. METHODS: One-hundred and twenty cirrhotic cases that were planned to undergo elective surgery were enrolled in the current prospective work. The intraoperative (I.O) PVP and central venous pressure (CVP) were measured. The statistical analysis was performed using the SPSS version 22.0. The receiver operative curve was plotted to measure the predictive value of PVP. Multivariate analysis was done using logistic regression method for the significant variables impacting mortality on univariate analysis. RESULTS: Twenty-nine patients died in the current work. Patients who survived had statistically considerably lower PVP than patients who died (8.2 ± 1.5 vs. 12.5 ± 1.6 mmHg, respectively, p < 0.001). Similarly, patients who died had significantly higher I.O CVP (p < 0.001), body mass index (p < 0.001), and were more likely to have model for end-stage liver disease score between 9 and 16 (p = 0.003). At a cutoff value ≥10.5 mmHg, the PVP had a sensitivity of 82.8% and specificity of 93.4% for the prediction of mortality. The logistic regression analysis showed that only PVP (odds ratio [OR] =3.1, 95% confidence interval [CI] 1.25–7.5) and CVP (OR = 2.8, 95% CI 1.2–6.5) were the only independent predictors of mortality. CONCLUSION: PVP is a significant predictor of death in Child’s A cirrhotic cases submitted to elective operations

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London