Zr Metal Research Articles

Enhanced adsorption of dyes by functionalized UiO-66 nanoparticles: Adsorption properties and mechanisms

UiO-66-based metal-organic framework (MOF) materials are a class of porous crystalline materials consisting of Zr metal clusters compounded with organic ligands of terephthalic acid group. In this study, functionalized UiO-66-X (X=H, NH2, (COOH)2) nanoparticles were synthesized. The morphology of UiO-66-X nanoparticles were characterized by SEM, while the crystal structure was analyzed using XRD and TGA. Chemical composition of UiO-66-X nanoparticles were analyzed through TFIR and XPS. The adsorption capacities of UiO-66-X nanoparticles for anionic dye of Congo red (CR), and cationic dyes of methylene blue (MB) and rhodamine B (Rh B) dyes were evaluated. Furthermore, the adsorption mechanisms of UiO-66-X nanoparticles for dyes were analyzed and summarized. Results showed that the adsorption capacities of UiO-66 and UiO-66-NH2 on CR were 93.05 mg/g and 94.20 mg/g, respectively. In particular, the adsorption capacities of UiO-66-(COOH)2 on MB and Rh B were significantly increased with the adsorption capacities of 80.66 mg/g and 72.64 mg/g, respectively. Due to the strong π-π effect and hydrogen bonding interactions between UiO-66 and CR dyes. UiO-66-NH2 has stronger hydrophilicity and has electrostatic interactions, Lewis acid-base interactions and hydrogen bonds with CR. The abundant -COOH groups and higher negative Zeta potential (-23.43 mV) in UiO-66-(COOH)2 led to strong electrostatic interactions and Lewis acid-base interactions with the cationic dyes MB and Rh B. Therefore, the adsorption performance of UiO-66-(COOH)2 on cationic dyes was improved.

Microstructure and Corrosion Behavior of the Modified Layers Grown In Situ by Plasma Nitriding Technology on the Surface of Zr Metal

Preparing protecting coatings on the surface of Zr claddings has been regarded as one of the accident tolerant fuel (ATF) strategies. In this study, a series of nitride-modified layers were in situ grown by hollow cathode plasma nitriding on the surface of Zr metal. The influence of nitriding currents and time on the phases, composition, microstructure and corrosion resistance of the modified layers was investigated by X-ray diffraction (XRD), X-ray Photoemission Spectroscopy (XPS), transmission electron microscope (TEM), scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS) and potentiodynamic polarization curves. The ZrO2 layer with loose microstructure and cracks prefers to form under low nitriding current of 0.4 A, which also causes poor corrosion resistance. The high temperature caused by high nitriding currents (0.6 A and 0.8 A) promote the formation of compact nanocrystalline layers, made up of nitride and oxynitride. Below the nanocrystalline layer, it is Zr2N caused by N penetration. Besides this, a double-layer structure of the nanocrystalline layer, i.e., an equiaxed crystal zone with a grain size of ~10–50 nm on the surface and a long strip grain region beneath it was observed. The compact nitride/oxynitride layer with excellent interface bonding can improve the corrosion resistance effectively.

Understanding the Mechanism and Selectivity of 1,1-Diborylalkanes from Alkenes Catalyzed by a Zirconium Complex.

The synthesis of 1,1-diborylalkanes from readily available alkenes is an appealing method. The density functional theory (DFT) method was employed to investigate the reaction mechanism of 1,1-diborylalkanes, which was synthesized from alkenes and a borane, and the reaction was catalyzed by a zirconium complex Cp2ZrCl2. The entire reaction is divided into two cycles: dehydrogenative boration to form vinyl boronate esters (VBEs) and hydroboration of VBEs. This article focuses on the hydroboration cycle and elaborates on the role of the reducing reagents in the equilibrium of self-contradictory reactivity (dehydrogenative boration and hydroboration). The H2 and HBpin pathways were investigated as the reducing reagents in the hydroboration process. The calculated results showed that it is more advantageous to use H2 as a reducing agent (path A). Furthermore, the σ-bond metathesis is the rate-determining step (RDS) with an energetic span of 21.4 kcal/mol. This is consistent with the self-contradictory reactivity balance proposed in the experiment. The reaction modes of the hydroboration process were also discussed. These analyses revealed the origin of selectivity in this boration reaction, in which the σ-bond metathesis of HBpin needs to overcome the strong interaction between HBpin and the Zr metal. Meanwhile, the origin of the selectivity of different positions of H2 is the interaction between the σ(H1-H2) → σ*(Zr1-C1) overlap and these findings have implications for catalyst design and application.

Study on the preparation of molecularly imprinted ZrO2-TiO2 photocatalyst and the degradation performance of hydroquinone.

In this paper, molecularly imprinted Zr-doped TiO2 photocatalysts (MIP-ZrO2-TiO2) were prepared by the molecularly imprinted sol-gel method for the photocatalytic degradation study of hydroquinone (HQ) as the target pollutant. For the effectiveness of the MIP-ZrO2-TiO2 catalyst in degrading HQ, the effects of Zr doping ratio, imprinted molecule dosage, calcination conditions, and pollutant concentration on its photocatalytic activity were investigated. XRD, TEM, XPS, and other techniques were used to evaluate the materials, and the findings revealed that MIP-ZrO2-TiO2 films with imprinted HQ were successfully produced on the ZrO2-TiO2 surface. The optimal preparation conditions were n(Ti):n(Zr) = 100:8, m(HQ) = 1.5g, 550°C for the calcination temperature, and 2h for the calcination duration. The optimum reaction conditions were 10mg/L HQ concentration, 1g/L catalyst dose, and a pH of 6.91. According to the findings of photocatalytic tests, during 30min of UV lamp (365nm) irradiation, the degradation rates of MIP-ZrO2-TiO2, ZrO2-TiO2, and TiO2 for HQ were 90.58%, 83.94%, and 58.30%, respectively. The findings revealed that the doping of Zr metal and the addition of imprinted molecules improved the photocatalytic activity of TiO2, which can be used for the efficient treatment of low concentrations of hard-to-degrade hydroquinone.

Highly selective ratiometric fluorescent sensing of fleroxacin via functionalized Zr metal–organic frameworks

The fluoroquinolone antibacterial agent fleroxacin (FLO) has been widely used for the treatment of urinary infections. Quantitatively analyzing the amount of FLO is vital for human health and the ecological system, but still proves challenging due to the complex environmental interference. In this work a ratiometric fluorescence sensor MOF-808-TPY is successfully constructed by incorporating a functional ligand, 2,2′:6′,2′'-terpyridine-4′-carboxylic acid (TPY), to the zirconium node of MOF-808 via post-synthetic modification. With the addition of fleroxacin, the prepared MOF-808-TPY sensor exhibits decreased fluorescence intensity at 370 nm, while the intrinsic fluorescence from fleroxacin at 440 nm is greatly enhanced. The yielded ratiometric response can effectively eliminate interference from environmental factors, and is able to discriminate FLO from other fluoroquinolone antibiotics efficiently, demonstrating high selectivity towards FLO analysis. A linear relationship of the fluorescence ratio F370/F440 against the concentration of FLO is observed in the range of 0 ∼ 13.50 μM with the detection of limit down to 0.01 μM. Excellent recoveries of FLO levels in real water samples for practical application are also achieved. Additionally, MOF-808-TPY could be easily integrated onto nanofibers for FLO sensing in aspect of potential sensing device. This work represents a promising strategy for constructing MOFs-based ratiometric sensors in monitoring fluorescent antibiotics.

Biosynthesis of a tri‐metallic nanoalloy for magnetic and biomedical applications

The tri‐metallic magnetic nanoalloy synthesized via the eco‐friendly procedure discussed here contains cobalt (Co), nickel (Ni), and zirconium (Zr) metals in a 3:1:1 M ratio (Co3O4.NiO.ZrO2 nanoalloy). Two different plant extracts which are rich in biologically active compounds from Spermacoce hispida and Vernonia cinereum were combined to get a multispecies nanoalloy with magnetic properties and medicinal values. The Fourier transform infrared, X‐ray diffraction, and transmission and scanning electron microscopes analyses confirmed the spherical shape of the bioinspired Co3O4.NiO.ZrO2 nanoalloy. The average size of our nanoalloy was 32 nm, but the individual nanoparticles are between 21 and 73 nm in size. A vibrating sample magnetometer study of the magnetic characteristics of the nanoalloy reveals strong saturation magnetization (12.42 emu/g), low retentivity (Mr), and low coercivity (Hc) (282.36 Oe). The higher saturation magnetization in nanoalloy is attributed to their larger particle size, a high degree of crystalline structure, and slight external spinning deformation. The low coercive field (Hc) value reveals the unique soft nature of our nanoalloy. The disc diffusion study confirms that a 6.3 μg/mL solution of the nanoalloy kills almost 96% of the harmful bacteria like Bacillus subtilis (29 mm), Bacillus cereus (26 mm), and Escherichia coli (21 mm). It shows a moderate effect of 85% killing factor against Staphylococcus albus (17 mm), Pseudomonas aeruginosa (13 mm), and Klebsiella pneumoniae (15 mm) bacteria.

Optimization of high ionic conducting Br-rich and metal (Sb and Zr) substituted Li-argyrodite and their enhanced air stability and compatibility in lithium batteries

Sulfide solid electrolyte has attracted much interest in the field of lithium solid-state batteries due to its high ionic conducting nature and good compatibility with lithium metal. However, improving the ionic conductivity, air stability, and electrochemical compatibility of sulfide solid electrolytes remains elusive. In this work, the Li-argyrodite system was optimized through halogen (Br) and metal (Sn and Zr) substitution using a high-energy ball milling process followed by heat treatment. The ionic conductivity analysis revealed that the optimized composition of Li5.3PS4.3Cl1.0Br0.7 solid electrolyte demonstrates an ionic conductivity of 16.6 mS cm−1 at 30 °C, which was ∼3 fold higher than that of Li6PS5Cl electrolyte. The metal substitution in the optimized composition slightly reduced the ionic conductivity, but increased the air stability and lithium compatibility. The optimized Sb- substituted electrolyte utilized in the Li-battery delivered a high discharge capacity of 72 mAh g−1 at 1 C rate than other electrolytes.

Catalytic upgrading of bio-oil model mixtures in the presence of microporous HZSM-5 and γ-Al2O3 based Ni, Ta and Zr catalysts

Bio-fuel production from bio-oil was investigated in the presence of microporous HZSM-5 and Al2O3 (MA) based catalysts. This study focused on the catalytic upgrading of a model bio-oil compound with ethanol for bio-fuel production. The model compound containing hydroxypropanol/furfural/formic acid: 4/6.5/5 by volume was used as a bio-oil mixture. Activity tests were performed under atmospheric pressure with a volumetric feed ratio of 30/70 bio-oil mixture/ethanol using a 0.5 g catalyst. In the reaction studies performed on the commercial microporous HZSM-5 catalyst, the optimum co-cracking temperature was determined as 400 °C. Mesoporous γ-Al2O3 support was synthesized by the evaporation-induced self-assembly (EISA) synthesis method, and Ni, Ta, and Zr metals were incorporated into the structure of the catalyst by the impregnation method to improve the surface acidity. The synthesized catalysts were characterized by X-ray diffraction (XRD), X-ray absorption near edge spectroscopy (XANES), N2 adsorption–desorption, scanning electron microscopy energy dispersive spectroscopy (SEM/EDS), X-ray fluorescence (XRF), Fourier-transformed infrared spectroscopy (FTIR), pyridine adsorbed diffuse reflectance FTIR spectroscopy (DRIFTS), and thermogravimetric/differential thermal analysis (TGA-DTA). Monometallic and pure alumina catalysts indicated an ordered mesoporous structure with surface area values 106–389 m2/g. Lewis and Brønsted acid sites associated with mild acidity were observed in the DRIFTS results of the 10 wt% Zr-containing alumina catalyst (10Zr@MA). The highest oil phase selectivity and isoparaffin selectivity in oil phase values were obtained in the presence of 10Zr@MA as 17.22% and 80.96%, respectively. 10Zr@MA catalyst showed the best catalytic activity compared to other catalysts, with 9.54% coke formation.

Single metal-doped silicon (Si59X; X = Nb, Mo, Y, Zr) nanostructured as nanosensors for N-Nitrosodimethylamine (NDMA) pollutant: Intuition from computational study

The present work examines the efficacy of metal-doped silicon (Si59X; X = Nb, Mo, Y, Zr) nanocages as an efficient nanosensors for N-Nitrosodimethylamine (NDMA). A suitable computational approach employing the exchange-correlation functional (PBE) along the Lanl2DZ basis set was utilized to this end to investigate the potential of silicon nanostructure, doped transition metal as a detector for NDMA. To comprehend the nature of the interaction between the nanostructure and adsorbate (NDMA), diverse computational descriptors including the adsorption energy of interaction, electronic attributes of the surfaces, sensing mechanism and recovery time of the modelled nanostructures were examined. The results show that doping all Si60 fullerene nanostructure with transition metals (Nb, Mo, Y, and Zr) enhanced the sensing attributes of the nanostructure towards NDMA. The average adsorption energy was calculated to be − 169.43 kcal/mol. The doped metals were also observed to influence the surface conductivity and binding affinity; the obtained adsorption energy was found to decrease with the doping of Zr metal whereas an increase was observed in the case of Nb doping. Other molecular descriptors also pointed out favourable results and affirmed the suitability of the surfaces to detect NDMA. Moreover, the recovery of NDMA from the surfaces was calculated to be in the milliseconds’ range and therefore suggests the recyclability of the surfaces. Finally, classical MD simulations affirmed the stabilities of the surfaces and disclosed that adsorption the adsorbate does not result in considerable deformation of the modelled surfaces. It is, therefore, concluded that the modelled surfaces could be further explored as potential candidates for the construction of amperometric nano-sensors.

Effect of Transition Metals Addition on the Nickel Oxide Catalyst toward Reduction Behaviour in Carbon Monoxide Atmosphere

The chemical reduction progression behaviour of transition metals (Mo, Zr, W, Ce, and Co) doped on NiO was studied using temperature programmed reduction (TPR) analysis. A wet impregnation method was applied to synthesise the doped NiO series catalysts. The reduction progress of the catalysts was attained by using a reductant gas at the concentration of 40% v/v CO/N2. X-ray diffraction (XRD) was employed to determine the composition of the reduced phases. Undoped NiO was reduced at 384℃ to obtain a cubic phase of NiO. It was observed that Ce/NiO exhibited the lowest reduction temperature of 370℃ among all catalysts. This phenomenon might be due to a higher surface area of Ce/NiO compared to undoped NiO, which facilitated a faster reduction reaction. The rest of the doped NiO series catalysts (Co/NiO, Mo/NiO, W/NiO and Zr/NiO) demonstrated a higher reduction temperature compared to undoped NiO. New peaks in the XRD pattern were observed only for the reduced catalysts of Mo/NiO and W/NiO, which were associated with monoclinic MoO2 and WO2.72 phases, respectively. The formation of new compounds or more stable nickel alloys led to a slower reduction reaction than undoped NiO. Therefore, Ce/NiO was the most efficient catalyst in promoting the formation of Ni under the CO atmosphere.

Allosteric probe-triggered isothermal amplification to activate CRISPR/Cas12a for sensitive electrochemiluminescence detection of Salmonella

We report an electrochemiluminescence (ECL) sensor for Salmonella detection based on allosteric probe as a bio-recognition element and CRISPR/Cas12a as a signal amplification strategy. In the presence of Salmonella, the structure switching occurs on allosteric probes, resulting in their hybridization with primers to trigger isothermal amplification. Salmonella is then released to initiate the next reaction cycle accompanying by generating a large amount of dsDNA, which are subsequently recognized by CRISPR-gRNA for activating the trans-cleavage activity of Cas12a. Furthermore, the activated Cas12a can indiscriminately cut the ssDNA which is bound to the electrode, enabling the release of the ECL emitter porphyrinic Zr metal − organic framework (MOF, PCN-224) and exhibiting a decreased ECL signal accordingly. The linear range is 50 CFU·mL−1–5 × 106 CFU·mL−1 and the detection limit is calculated to be 37 CFU·mL−1. This method sensitively detects Salmonella in different types of real samples, indicating it is a promising strategy for Salmonella detection

Electrochemical CO2 reduction over surface-modified Cd-based electrodes and reaction paths for long-chain hydrocarbons

Using an electrocatalyst to convert CO2 into useful chemicals is a promising strategy for sustainable energy and environmental solutions. In this study, cadmium (Cd) was modified with different transition metals (Ti, Zr, Au, Cu, and Pt) and used as an electrode for electrochemical CO2 reduction. The resulting chemicals produced, such as CO, H2, and formate, were dependent on various factors, including the applied potential, electrolyte concentration, and overlayer metal. By increasing the NaHCO3 concentration, the production of CO and formate decreased, but long-chain hydrocarbons (CnH2n and CnH2n+2, n = 2–6) were produced. These hydrocarbons were further increased by sputter deposition of Zr and Ti on the Cd electrode, which followed a Fischer-Tropsch synthesis mechanism. Despite the low production efficiency, the results obtained provide significant insights into the mechanisms underlying C–C coupling and the electrochemical generation of long-chain hydrocarbons. By modifying the Cd surface with other metals (Au, Cu, and Pt), the resulting chemicals were compared, and Cd was found to recrystallize to CdCO3 cuboid/cube morphology after electrochemistry. These results provide valuable insights for the development of surface-modified Cd-based electrocatalysts and long-chain hydrocarbon productions for energy and the environment.

Predicting properties of high entropy carbides from their respective binaries

Using Density Functional Theory calculations, this paper addresses two questions: (1) to what degree can the properties of high entropy carbides created by equi-molar combinations of five of the set of eight refractory metals Hf, Nb, Mo, Ta, Ti, V, W, and Zr be predicted from their respective binary compounds, and (2) can empirical relationships from properties of the binary compounds be used to predict phase stability for these materials. For the former question, it is found that lattice constant, binding energy and bulk modulus are well approximated by binary carbide averages, but carbon vacancy formation energies are less predictable. To address the second question, correlations are explored between binary properties and the entropy forming ability (EFA) of all 56 possible five-element combinations of the eight refractory elements. Significant correlations are not found between cohesive energies or lattice constants of the binary constituents of each composition and that composition’s EFA, but there is a correlation between EFA and the standard deviation of the distribution of bulk moduli of the constituent binaries.

Removal Effectiveness for Washing Ce(IV), U(VI), and Zr(IV) Ions from Contaminated Purex Solvent by Hydrazine Carbonate

The contaminated solvent from the Purex process is washed with alkaline detergents such as sodium carbonate, which generates a large amount of secondary wastes. Therefore, hydrazine carbonate as a salt-free reagent deserves to be studied in depth. In this study, the Ce(IV), U(VI), and Zr(IV) metal ions in organic phases containing dibutyl phosphate (HDBP) of 30% tributyl phosphate (TBP)–dodecane were washed with hydrazine carbonate. The effects of the oscillation time (1 to 15 min); temperature (25°C to 85°C); cumulative number of washes (one to four times); mass fraction of hydrazine carbonate (0.1% to 20%); volume ratio of the aqueous phase to the organic phase (0.2 to 5); HDBP concentration (0 to 0.4 M); HNO3 concentration (0.05 to 8 M); and concentration of Ce(IV), U(VI), and Zr(IV) metal ions on the removal percentages of Ce(IV), U(VI), and Zr(IV) metal ions in polluted solvents were studied. The results showed that when the organic phase containing 0.02 M HDBP was washed three times with 5% hydrazine carbonate at 25°C, the removal percentages of the Ce(IV), U(VI), and Zr(IV) ions were 96%, 98%, and 94%, respectively. Meanwhile, the retention concentrations of the three in the organic phase were 35, 28, and 78 mg/L, respectively. The increase of the mass fraction of hydrazine carbonate enhances the removal of the metal ions from the organic phase into the aqueous phase. High acid is not conducive to alkaline washing of metal ions. The increase of HDBP concentration not only promotes extraction but also increases the retention capacity of the organic phase and has the most significant effect on Zr(IV). U(VI) promotes the preferential washing of Zr(IV) while Ce(IV) increases the metal retention concentration of Zr(IV) in the organic phase.

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A new study of double beta decay processes in natural Zr isotopes using Zr metal samples and an ultra-low-background high-purity germanium detectors was performed at Laboratori Nazionali del Gran Sasso of INFN (Italy). Two data sets were collected with a 736.35 g and a 129.94 g Zr metal over 59.7 days and 37.3 days, respectively, and were used for a detailed analysis. A new limit on the double beta decay of 94\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{94}$$\\end{document}Zr to the 1st excited level of 94\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{94}$$\\end{document}Mo was set as T1/2ββ>2.1×1020year\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$T_{1/2}^{\\beta \\beta } > 2.1\ imes 10^{20}~\ ext {year}$$\\end{document}, which is a factor of three better than the previous result. It is shown that the current radiopurity of Zr metal (tens of Bq/kg), produced via two methods, do not comply with the radiopurity requirements for low-background experiments. Hence, we propose to use a purified ZrCl4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$_{4}$$\\end{document} powder in an optimized geometry as a new approach for future experiments with extended sensitivity focused on studies of rare nuclear processes in Zr isotopes.

Effect of different valence metals doping on methane activation over La2O3(001) surface

La2O3 as a catalyst is used for oxidative coupling of methane (OCM) reactions due to its excellent stability and high C2 selectivity, but poor activity on methane dissociation limits its wide application. Different valence metals are doped on the La2O3(001) surface to improve the methane conversion activity, and the activation of methane on metal-doped La2O3(001) surfaces has been investigated via the density functional theory (DFT) calculations. The relationship between the valence states of doped metals and the methane conversion activities shows that doping low valence metals (Li, Na, K, Mg, Ca, Sr and Ba) and equivalent metals (Al, Ga, In) can significantly improve the conversion activity of methane. Among them, the activation energy of methane on the Li-La2O3(001) surface is the lowest, which is only 13.0 kJ/mol. However, doping of high valence metals (Zr, Nb, Re and W) cannot improve the CH4 dissociation activity. Furthermore, the relationships between surface oxygen vacancy formation energies, acid-base properties and the activation energies of CH4 have also been investigated. The results show that with the increase of metal valence state, the oxygen vacancy formation energy increases, while the dissociation activity of CH4 decreases. The introduction of alkali and alkaline earth metals increases the alkalinity of La2O3(001) surface, and the alkalinity of La2O3(001) doped with the alkali metal is stronger than that with the alkaline earth metal, exhibiting higher dissociation activity of CH4. Our research may provide a guide for improving methane conversion activity on La2O3 catalysts.

English

The study aimed to assess concentrations of heavy metals in soil samples on both sides along the three Niles (Blue, White, and Nile Rivers) and Almogran area (Tuti Island) in Khartoum city (the capital of Sudan country) after the overflow season. Concentrations of heavy metals Br, Cu, Ni, Pb, Co, Rb, Cr, Zn, Zr, Sr, Mn, Ti, K, Ca, and Fe were determined using Xray fluorescence (XRF) techniques compatible with direct analysis of soils. The results showed that the element's concentration along the Blue Nile is higher than White Nile, Nile river, and Almogran area. In addition, Enrichment Factor (EF) and Geoaccumulation index (GI) factor was calculated, and both are in recommended ranges except EF for Ni high at Blue Nile 2.58, which is more than recommended value (2).

Atomic structure evolution and linear regression fitting models for pre-breakdown electric field strength of FCC, BCC and HCP metal nano-emitters under high electric field from PIC-ED–MD simulations

Multi-scale and multi-physics simulations are carried out for nano-emitters consisting of FCC (Al, Cu and Au), BCC (V, Mo and W) and HCP (Ti, Zn and Zr) metals, using hybrid electrodynamics coupled with molecular dynamics-particle in cell simulations (PIC-ED–MD). We show that the tilting of the nano-emitter at low temperature and small electric field (E-field) is mainly caused either by the movement of partial dislocations at the apex of the nanotip or by the elastic local distortions of atomic registries away from their ideal lattice sites (FCC/BCC/HCP). At high E-field, the intense resistive heating due to the strong electron emission leads to the direct melting of the apex of nano-emitters. For nano-emitters consisting of low melting point metals such as Al, Zn and Au, the thermal runaway is driven by the elongation, thinning and necking of the molten region. Meanwhile, the elongation, thinning and sharpening produce the nano-protrusion at the apex of metal nano-emitters, and the detachment of atoms or atomic clusters from the nano-protrusion mainly contributes to the thermal runaway event for refractor metals such as Ti, Zr, Mo and W. The critical E-field strength of metal nano-emitters is found to be strongly correlated with structural parameters (atomic coordination number of liquid and equilibrium lattice constant), thermodynamic quantities (cohesive energy and enthalpy of evaporation) and phase transition temperatures (melting point and boiling point). These correlations enable us to establish either single-variable linear fitting models or multi-variable linear regression models to predict the critical E-field value for metal nano-emitters with good credibility.

Nitriding model for zirconium based fuel cladding in severe accident codes

A model has been developed to describe the nitriding of partially oxidized zirconium based cladding during an air ingress sequence when the reaction has become starved of oxidant (oxygen and/or steam), and the subsequent re-oxidation of nitride following of restoration of coolant. Key aspects of the model are the estimation of oxygen-stabilised alpha zirconium, α-Zr(O), formed during pre-oxidation and its reaction with the nitrogen. Nitriding of metallic Zr is much slower than α-Zr(O), and plays a comparatively minor role. The model is based on data from separate-effects tests comprised pre-oxidation, nitriding in the absence of oxidant, and re-oxidation in the absence of nitrogen, which were used to derive the kinetic parameters for the main reaction processes. Developmental assessment was performed using the test results, demonstrating favourable agreement for the main reaction signatures. Independent assessment against Integral Test data is underway.

Investigation of Solid–Solid Transition in Ti and Zr at High Pressure by Electrical Resistivity

The group IV metals Ti and Zr are isoelectronic and crystallize in a hexagonal closed packed structure at ambient conditions. Herein, the electrical resistivity of Ti and Zr at room temperature with increasing pressure up to 20 GPa is reported using a 4‐wire resistivity method. The slope of their resistivity against pressure changes value at various pressures. At 10 GPa, resistivity of Ti increases with pressure whereas Zr resistivity decreases with pressure. The opposite behavior is interpreted to be due to incoherent scattering in Ti versus coherent scattering in Zr, as both undergo solid α → ω transition. By comparing the Zr result with a previous study that combined in situ X‐ray synchrotron with compressional and shear wave velocity measurement, the boundaries of the region of α → ω phase coexistence are constrained in Zr to be 4–8 GPa. The Ti result will be valuable for constraining its boundary when such in situ velocity measurement becomes available for Ti as well.