Bulk Stability Research Articles

Bulk and Surface Stabilization Process of Metastable Li-Rich Disordered Rocksalt Oxyfluorides as Efficient Cathode Materials

Manganese based disordered rocksalt systems have attracted attention as Co-free and high capacity cathode materials for Li-ion batteries. However, for a practical application these materials are considered as metastable and exhibit too limited cyclability. In order to improve the structural stability of the disordered rocksalt Li1+xMn2/3Ti1/3O2Fx (0 ≤ x ≤ 1) system during cycling, we have introduced a mild temperature heat treatment process under reducing atmosphere, which is intended to overcome the structural anomalies formed during the mechanochemical synthesis. The heat-treated samples presented better electrochemical properties, which are ascribed to a structural defect mitigation process both at the surface and in the bulk, resulting in improved crystal structure stability. In addition, the optimized particle size and the smaller BET surface area induced by the recrystallization contributes to the observed enhanced performance. Among the studied compositions, the heat treated Li2Mn2/3Ti1/3O2F sample displayed better electrochemical performance with a discharge capacity of 165 mAh g−1 after 100 cycles at 0.1 C (∼80% of the initial capacity), when combined with further conditioning of the cells. The results point explicitly towards a guided stabilization approach, which could have a beneficial effect regarding the application of DRS oxyfluoride materials for sustainable LIBs.

Exploring the Promise of Multifunctional "Zintl-Phase-Forming" Electrolytes for Si-Based Full Cells.

Li-M-Si ternary Zintl phases have gained attention recently due to their high structural stability, which can improve the cycling stability compared to a bulk Si electrode. Adding multivalent cation salts (such as Mg2+ and Ca2+) in the electrolyte was proven to be a simple way to form Li-M-Si ternary phases in situ in Si-based Li-ion cells. To explore the promise of Zintl-phase-forming electrolytes, we systematically investigated their application in pouch cells via electrochemical and multiscale postmortem analysis. The introduction of multivalent cations, such as Mg2+, during charging can form LixMySi ternary phases. They can stabilize Si anions and reduce side reactions with electrolyte, improving the bulk stability. More importantly, Mg2+ and Ca2+ incorporate into interfacial side reactions and generate inorganic-rich solid-electrolyte interphase, thus enhancing the interfacial stability. Therefore, the full cells with Zintl-phase-forming electrolytes achieve higher capacity retentions at the C/3 rate after 100 cycles, compared to a baseline electrolyte. Additionally, strategies for mitigating the electrode-level fractures of Si were evaluated to make the best use of Zintl-phase-forming electrolytes. This work highlights the significance of synergistic impact of multifunctional additives to stabilize both bulk and interface chemistry in high-energy Si anode materials for Li-ion batteries.

Calcium hydroxide and porous silicon-impregnated silicon carbide-based composites for thermochemical energy storage

Thermal energy storage has a prospect for large-scale storage of renewable energy. Thermochemical energy storage using reversible gas–solid reactions can store thermal energy for unlimited periods with high energy density. Calcium hydroxide (Ca(OH)2), which is abundant and environmentally friendly, is one of the most promising materials for thermochemical energy storage systems. However, pure Ca(OH)2 powder has poor power density and bulk stability owing to its low thermal conductivity, volume change, and agglomeration over dehydration–rehydration cycles. Practical composites that can simultaneously overcome these problems have not been reported yet. This study combines Ca(OH)2 with ceramic foam and honeycomb structures of silicon-impregnated silicon carbide (Si–SiC) and demonstrates the improved power density and bulk stability of the resulting composites. The Si–SiC foam composite, loaded in a laboratory-scale fixed-bed reactor, exhibits a thermal discharging power density of 0.71 MW mbed−3, which is 1.6 times that of the pure Ca(OH)2 powder. In addition, the foam composite reduces the volume change by 80% and does not form centimeter-scale agglomerates even after 15 cycles, unlike the pure powder. The results suggest that embedding solid storage materials into thermally conductive open-cell foams can simultaneously enhance power density and bulk stability.

Effect of carbonated beverages on the color stability of bulk and flowable composite resin.

Tooth discoloration is considered as one of the most common dental problems among people, and in dentistry, the most common cases are claimed after the restoration. Therefore, in this research, we aim to evaluate the effect of carbonated beverages on the color stability of bulk and flowable composite resin. For the study, 12 composite disc samples were made using the standard dimensions of 10 mm diameter and 2 mm thick. To find the color stability, we used a VITA Easyshade spectrophotometer. We used two different composites of bulk fill and flowable composite resin; the composite brand we used was Tetric ecom plus; as an immersion medium, we used two different carbonated beverages, and the chosen beverages were Appy Fizz and 7Up. 24-h and 7-day postimmersion color stability was evaluated. In the results of postimmersion, we have found the Delta E value for 24 h immersion of flowable and bulk fill composite as 5.8115 and 7.4378, respectively; similarly, the Delta E value for 7 days immersion of flowable and bulk fill composite was 9.9559 and 10.1028, respectively. Using the independent "t"-test, we found that the significance is 0.633 and 0.328, which was statistically not significant. In the present study, when immersed in Appy Fizz juice and 7Up juice, bulk fill composite resins have shown greater discoloration when compared to flowable composite resin material. Thus, the flowable composite resin samples were more color stable.

Tantalum Oxide Coating of Ni-rich Cathode Active Material via Atomic Layer Deposition and its Influence on Gas Evolution and Electrochemical Performance in the Early and Advanced Stages of Degradation

Detrimental side-reactions of Ni-rich cathode active materials (CAMs) with the electrolyte have historically impeded the extension of the utilized voltage window to higher upper cut-off voltages. Doping and coating approaches are studied widely to further improve these materials and to reduce the intensity of bulk and surface degradation but suffer from poor control of film thickness and homogeneity, leading to partial doping of the bulk. We herein report the singular effect of a tantalum oxide (Ta2O5) thin film on Li[Ni0.8Mn0.1Co0.1]O2 (NMC811), generated by atomic layer deposition, offering the possibility of a high-level homogeneity and thickness control. After chemical analysis using X-ray photoelectron spectroscopy the composition of the deposited thin film is identified as a lithium tantalate chemistry (LiTaO3). At an early degradation stage, clear improvements directly attributed to the coating, such as suppressed exothermic side-reactions (−51%), reduced released gas amounts (−14.8%) and less charge-transfer resistance growth (2× lower) are observed. However, at an advanced degradation stage, the materials show similar cycle life, as well as similar gassing behavior and an even higher charge-transfer resistance growth as compared to the uncoated material. This study highlights the necessity of bulk stabilization and identifies the effect of surface coatings on undoped NMC811 without any doping influence.

Roles of hydrogen in structural stability and electronic property of bulk hydrogenated amorphous silicon

Hydrogenated amorphous silicon (a-Si:H) has been widely used due to its unique photoelectric properties, but the information about its structure is patchy and the factors that affect its electronic properties are also unclear. In this work, we predicted the bulk a-Si:H structures based on the particle swarm optimization (PSO) technique and explored its structural characteristics under different hydrogen content conditions, then the effect of structural characteristics such as hydrogen content, void size and hydrogen-bonding configuration on structural stability and electronic properties of these structures are revealed. The results indicate that the structures with lower hydrogen content are conductors whereas the structures with higher hydrogen content are semiconductors. The band gaps of bulk a-Si:H structures show a trend with an increase followed a decrease with the increase of hydrogen content, which can be reduced by increasing the void size or adding some Si-H2, Si-H3 or Si-H-Si bonds to structures. The transition-state structure containing Si-H-Si bonds should have better conductivity than the steady-state structures. These results provide comprehensive understanding of the structural characteristics and electronic properties of bulk a-Si:H structures, which provides a theoretical support for the application of a-Si:H in semiconductor devices or as secondarybatteryanodes and have broad implications for further investigating other physical properties of a-Si:H structures.

Stability of Metal Hydroxide Organic Frameworks for Oxygen Evolution

The oxygen evolution reaction (OER) is central to storing electrical energy via chemical bonds in energy carriers and fuels through reactions such as electrochemical water splitting to produce hydrogen, CO2 reduction for CO and liquid hydrocarbons, and nitrogen to ammonia. While there has been considerable work towards the engineering of inexpensive yet highly active OER catalysts, current state-of-the-art materials are still at least an order of magnitude less active than oxygen evolving complexes found in biological systems that intricately combine inorganic metal-oxo clusters with organic ligands.1 As a result, metal organic frameworks (MOFs) have drawn considerable attention as hybrid organic-inorganic systems that can potentially mimic the unique structure of biological oxygen evolving complexes. Recently, metal hydroxide organic frameworks (MHOFs),2 a new class of MOFs that combine layered hydroxides with aromatic carboxylate linkers that stabilize the structure via π-π interactions, have been shown to display three times the tunability of layered hydroxides, offering extensive opportunities for further engineering of its electrochemical properties for numerous applications. However, the long-term stability of these material during OER is still unclear, which would be paramount to understand for further rational design of this class of material.In this study, we investigated Ni-based MHOFs with carboxylate linkers of varying π-π interaction strengths to understand how these differences affect the electrochemical stability of these materials during OER. We observed that the MHOFs all undergo activation during OER leading to two orders of magnitude increase in OER activity, where the MHOFs with weaker π-π interaction strengths tend to transform at a faster rate than the MHOFs with stronger π-π interaction strengths. We further characterized the MHOFs using a wide range of analytical techniques, including scanning transmission electron microscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and hard x-ray absorption spectroscopy, before and after extended OER cycling and galvanostatic tests to understand the transformed phase, which suggested that while the bulk structure largely remains unchanged, the surface undergoes significant restructuring into a Ni(OH)2-like phase during OER. Using operando UV-vis and Raman spectroscopy measurements on the MHOFs during OER to understand the factors that induce the transformation process, we found that there was a clear link between the Ni2+/3+, 4+ redox couple observed around 1.4 VRHE and a loss in the carboxylate organic linkers for the linkers with weak π-π interactions. However, for the MHOFs synthesized with linkers exhibiting strong π-π interaction strengths, there were smaller changes to the overall material during OER, suggesting that the bulk stability of these materials is largely dictated by the linker interaction strength and activation are primarily only surface transformations. These results directly demonstrate that linker selection also plays a key role in the stability MOFs under electrochemical conditions and are pertinent for rational design and understanding of the stability and activity of hybrid organic-inorganic materials as electrocatalysts.

Enhancing Thermal and High-Voltage Cycling Stability of Ni-Rich Layered Cathodes through a Ti-Doping-Induced Surface-Disordered Structure

Due to the high-energy density and potential cost advantage, Ni-rich layered oxide cathodes have attracted attention in electric vehicles. However, the inferior thermal stability and long-term cycling stability in a deeply charged state seriously restrict their large-scale applications. The oxygen topotactic lattice structure degradation caused by the irreversible anionic redox reaction has been considered one of the main reasons that cause the abovementioned electrochemical issues. Herein, we propose a modification strategy by constructing a surface-disordered structure to improve the thermal and high-voltage oxygen lattice structure stability of Ni-rich layered cathodes. Density functional theory calculations indicate that Ti4+ with a d0 electronic structure can be used as the inducer of surface-disordered structures. We directly demonstrate the successful design of a surface-disordered structure on the LiNi0.8Mn0.1Co0.1O2 model compound through neutron diffraction and scanning transmission electron microscopy measurements. The constructed surface-disordered structure can enhance the thermal and high-voltage cycling stability of LiNi0.8Mn0.1Co0.1O2. Furthermore, in situ X-ray diffraction and surface structure analyses indicate that this surface-disordered structure can improve the reversibility of bulk structure transition and stability of the formed cathode electrolyte interphase. This facile construction method of the surface-disordered structure provides a reference for industry and other layered oxide cathodes.

Bulk and interface-strengthened Li7P2.9Sb0.1S10.65O0.15I0.2 electrolyte via dual-source doping for all-solid-state lithium-sulfur batteries

Sulfide solid electrolyte is a promising candidate for the development of high-energy lithium-sulfur (Li-S) batteries. However, the concurrent improvement of ionic conductivity, bulk air stability, and compatibility of the electrolyte/electrode interface of sulfide solid electrolyte remains a huge challenge. Herein, we propose a dual-source doping (Sb2O3 and LiI) strategy to prepare a multifunctional sulfide solid electrolyte. Sb2O3 can broaden the transmission path of lithium ions and improve the bulk stability, and LiI can inhibit the generation of lithium dendrites and reduce the electrolyte/electrode resistance. Therefore, the sulfide solid electrolyte can be strengthened in terms of its bulk and interface, thus exhibiting a high ionic conductivity of 1.69 × 10−3 S cm−1 at 30°C, high air stability, and high electrochemical stability with lithium metal. On this basis, the as-prepared all-solid-state Li-S batteries (ASSLSBs) can exhibit a high specific discharge capacity after being cycled at 0.05 C for 100 cycles at room temperature (833 mA h g−1) or 60°C (949 mA h g−1). This work provides a rational scheme for the preparation of practical sulfide solid electrolytes and high-performance ASSLSBs.

Modeling the Shallow Cumulus-Topped Boundary Layer at Gray Zone Resolutions

Abstract This study investigates simulated fair-weather shallow cumulus-topped boundary layer (SCTBL) on kilometer- and subkilometer-scale horizontal resolutions, also known as the numerical gray zone of boundary layer turbulence. Based on a priori analysis of a simulated classic SCTBL with large-eddy simulation, its gray zone scale is determined. The dominant length scale of the cloud layer (CL) is found to be the effective cloud diameter, while that of the underlying mixed layer (ML) is the size of organized convection. The two scales are linked by a simple geometric argument based on vertically coherent updrafts, and are quantified through spectral analysis. Comparison to a simulated dry convective boundary layer (CBL) further reveals that the ML gray zone scale does not differentiate between clear and cloudy conditions with the same bulk stability. A posteriori simulations are then performed over a range of resolutions to evaluate the performance of a recently developed scale-adaptive planetary boundary layer (PBL) scheme. Simulation results suggest indifferences to the scale-adaptive capability. Detailed analyses of flux partition reveal that, in the absence of a shallow cumulus scheme, overly energetic resolved fluxes develop in the CL at gray zone and coarse resolutions, and are responsible for overpredicted resolved convection in the ML. These results suggest that modifications are needed for scale-adaptive PBL schemes under shallow cumulus-topped conditions. Significance Statement Shallow cumulus (ShCu) clouds play an important role in the dynamical and radiative processes of the atmospheric boundary layer. As the grid resolution of modern numerical weather prediction models approach kilometer and subkilometer scales, also known as the gray zone, accurate modeling of ShCu clouds becomes challenging due to difficulties in their parameterization. This study identifies the spatial scale that sets the gray zone of ShCu clouds, providing the key to building better parameterizations. Performance of existing parameterizations developed for clear-sky conditions is evaluated for cloudy conditions, exposing deficiencies and motivating further development.

Revealing the electronic, optical, phonon and thermoelectrical characteristics of bulk and monolayered RbLiS and RbLiSe compounds by DFT

Materials displaying anomalous quantum confinement effects (aqce) comprise the significant materials for recent optoelectronics, two-dimensional (2D) heterojunctions and band-gap engineering. Although available literature involves numerous works for regular 2D materials, there is still a lack of the key physical properties of aqce materials. So, in this work, density functional theory (DFT) calculations have been performed for the electronic, optical, phonon and thermoelectric properties of bulk and monolayered counterparts of recently introduced RbLiS and RbLiSe (aqce) compounds. The bulk RbLiS demonstrated a bandgap of 2.53 eV, whereas its monolayer has a lower bandgap of 1.20 eV. In addition, the bulk bandgap of RbLiSe was determined to be 2.10 eV being higher than the 1.26 eV of its monolayered counterpart. The optical properties of the addressed compounds are reported to be complex in nature, where bulk RbLiS and monolayers of RbLiS and RbLiSe can be intended as low-dielectric materials. Also, both bulk and monolayered RbLiS and RbLiSe compounds may be used as demanded photoconductors for possible UV purposes. In addition, both bulk RbLiS and RbLiSe exhibit high-refractive indices and are determined to be feasible for practical IR goals in contrast to their monolayer counterparts. Also, both bulk and monolayered RbLiS and RbLiSe compounds can be used as effective optical absorbers in ultraviolet (UV) applications. Phonon dispersions indicated dynamical stability of both bulk and monolayered structures of RbLiS and RbLiSe, which means the possibility of their experimental synthesis. Bulk and monolayered structures of RbLiS and RbLiSe compounds with high Seebeck coefficients suggest the possibility of new thermoelectric materials from bulk (3000 μV/K) and monolayered (2200 μV/K) RbLiS and RbLiSe compounds.

Stable Sodium-Based Batteries with Advanced Electrolytes and Layered-Oxide Cathodes.

Sodium-ion batteries offer a promising alternative to the more expensive, resource-limited lithium-ion batteries, in particular to accommodate the growing demand for large-scale energy storage. One of the main challenges for sodium-ion batteries, however, is the poor electrolyte stability, which leads to rapid capacity fade during cycling. Recent advances in the lithium-ion-battery field have expanded our understanding of electrolyte compositions and stability, paving the way for better sodium-ion-battery electrolytes. Two of the most promising new classes of electrolytes are evaluated herein with a sodium layered-oxide cathode, for the first time: a localized high-concentration electrolyte (LHCE) composed of sodium bis(fluorosulfonyl)imide, dimethyl ether, and tetrafluoropropyl ether and a "highly fluorinated" electrolyte (HFE) composed of 20% fluoroethylene carbonate with a lithium difluorophosphate additive. With a combination of electrochemical and post-mortem characterization techniques, the stability of each electrolyte is assessed with the O3-type Na(Ni0.3Fe0.4Mn0.3)O2 cathode and sodium metal anode. Both electrolytes significantly improve the surface and bulk stability of the cathode, but only the LHCE has a meaningful improvement on sodium metal stability. For the purpose of developing a long-lasting, sodium-ion full cell, both classes of electrolyte show great promise.

Bilateral political relations, space spillovers and the import expansion of China’s bulk commodity

The stability of bulk commodities imports is crucial to the development and stability of the country’s economy. Because its political attribute is more significant than other commodities, the trade of bulk commodities is more easily affected by bilateral political relations. However, there are only few studies examine the impact of political relations between countries and their spatial spillovers on bulk commodities’ imports. Based on “United Nations (UN) Voting General Assembly Voting Data” and “China Import and Export Statistics Data” from 1996 to 2014, this paper empirically examines the influence of the spatial spillover of China’s political relations with countries other than potential importing countries on the import expansion of China’s bulk commodity from the potential importing country. The results show that the improvement of bilateral political relations between China and other countries has a negative spatial spillover effect on the import of bulk commodities. However, this negative effect will be changed as China starts to establish a sound bilateral political relation with the potential importing country. Meanwhile, the more significant the political attributes of commodities, the greater the negative effect of spatial spillover. The import expansion of commodities with significant political attributes requires an improvement in direct bilateral relations.

Hotmelt tissue adhesive with supramolecularly-controlled sol-gel transition for preventing postoperative abdominal adhesion

Postoperative adhesion is a serious and frequent complication, but there is currently no reliable anti-adhesive barrier available due to low tissue adhesiveness, undesirable chemical reactions, and poor operability. To overcome these problems, we report a single-syringe hotmelt tissue adhesive that dissolves upon warming over 40 °C and coheres at 37 °C as a postoperative barrier. Tendon-derived gelatin was conjugated with the ureidopyrimidinone unit to supramolecularly control the sol-gel transition behavior. This functionalization improved bulk mechanical strength, tissue-adhesive properties, and stability under physiological conditions through the augmentation of intermolecular hydrogen bonding by ureidopyrimidinone unit. This biocompatible adhesive prevented postoperative adhesion between cecum and abdominal wall in adhesion models of rats. This hotmelt tissue adhesive has enormous potential to prevent postoperative complications and may contribute to minimally invasive surgery. Statement of significanceThere is a strong need to develop medical tissue adhesives with high biocompatibility, tissue adhesiveness, and operatability to prevent postoperative complications. In this report, single syringe, hotmelt-type tissue adhesive was developed by controlling sol-gel transition behavior of gelatin through supramolecular approach. The functionalization of gelatin with quadruple hydrogen bonding improved key features necessary for anti-adhesive barrier including bulk mechanical strength, tissue adhesive property, stability under physiological conditions, and anti-adhesive property. The hotmelt tissue adhesive can be used for a sealant, hemostatic reagent, and wound dressing to prevent postoperative complications including delayed bleeding, perforation, and inflammation and contribute to minimally invasive surgery.

New Insight on improving foam stability and foam flooding using fly-ash in the presence of crude oil

One of the most important methods for increasing the oil recovery of petroleum reservoirs is gas injection. However, it will not result in good oil recovery in many cases due to a low volumetric sweep efficiency. Foam flooding emerged as a promising solution for improving gas flooding. Still, there are significant concerns regarding the use of foam due to its un-stability in reservoir conditions and the vicinity of crude oil.For a foam flooding process to be successful, high-performance foaming agents must be selected to produce stable foam. One of these agents could be the use of nanoparticles. In this paper, we have attempted to create foam by making a low-cost nanoparticle, which can be obtained from an industrial waste called fly ash and addressing its impact on the crucial parameters of the foam EOR process. In the current study, fly ash nanoparticles were first obtained using a specific ball milling method and then used with a surfactant solution to form foam. Foam performance at bulk volume was evaluated, and results indicated that a small amount of fly ash nanoparticles could significantly increase the foam stability in the presence of a cationic surfactant. Foam agents also changed the surface wettability from completely oil-wet to water-wet. Furthermore, it has been observed that fly ash nanoparticles can reduce the IFT between the oil and water phase. In addition to bulk stability tests, flooding tests suggested that the nano-stabilized foam could increase the ultimate oil recovery in quasi-two-dimensional (2D) porous media tests.

Theoretical investigations on the defect structures and g factors for V4+ in 30PbO-5Bi2 O3 -(65-x)SiO2 glasses at different concentrations.

For 3d1 (V4+ ) impurity in 30PbO-5Bi2 O3 -(65-x)SiO2 glass systems with different concentrations x of V2O5, the defect structures and gyromagnetic factors are theoretically investigated by using the perturbation formulas of g factors for a tetragonally compressed octahedral 3d1 group. The concentration dependences of d-d transition band and g factors are suitably explained from the Fourier type concentration functions of the cubic crystal field parameter Dq, covalency factor N and relative tetragonal compression ratio ρ. The above concentration dependences of these quantities are suitably illustrated by the modifications of the local crystal field strength and electron cloud distribution with increasing x. The concentration variations of the electrical conductivity and dielectric relaxation are further analyzed from the stability of the systems in view of two competitive factors (increasing network polymerization and bulk stability at low concentrations and decreasing former SiO2 and stability at high concentrations).

Mechanical stability, electronic, and optical properties of bulk and (001)-surfaces of Sr2RuO4-xFx quaternary alloy.

The DFT- based calculations are used to investigate the mechanical, electronic, and optical characteristics of Sr2RuO4-xFx (x = 0, 2) to elucidate the applications in renewable energy devices. The Voigt–Reuss–Hill approximation method is applied to analyze the elastic constants, Poisson ratio, bulk, shear, and Young modulus. The results demonstrate that the Sr2RuO4 and Sr2RuO2F2 tetragonal phases are mechanically stable because the elastic constants satisfy Born's mechanical stability condition. Then, Sr2RuO2F2 thin films are simulated in the (0 0 1) direction with a broad vacuum of 2.5 nm across the z-plane to eliminate the interlayer interactions. The relative stability and the feasibility of the synthesis of the different numbers of layers are proved by the positive values obtained for the surface energies. The thin films exhibited narrower band gaps compared with their bulk counterparts; gaps increased with increasing thickness of the thin films and the absorption ability is improved in the visible light (380∼790 nm). The findings suggest that all the studies’ structures with various thicknesses are significantly absorbent and productive with an optical absorption that exceeds 104 cm−1 in the visible range (λ ∼ 550 nm). Hence, the Sr2RuO2F2 films may be promising candidates in advanced optoelectronic and solar cell applications.

Fourier Transform Infrared Spectroscopic, Spectrofluorimetric Assays of Canagliflozin, and Stability-Indicating UV-Spectrophotometric Method for the Simultaneous Determination of Canagliflozin and Metformin.

Green Fourier transform infrared (FTIR) spectroscopy, using potassium bromide (KBr) disc technique, eliminates the consumption of hazardous chemicals. Spectrofluorimetry for drugs that have native fluorescence. Mean centering of ratio spectra (MCRS) analysing overlapped spectra without preliminary separation. Three simple, accurate, and sensitive methods have been developed and validated for the determination of canagliflozin (CANA); one is a stability-indicating method for CANA and metformin (MET) determination. Method A is FTIR using a KBr disc for CANA determination measuring alkyl halide C-F peak area centered on 1230/cm. Method B is spectrofluorimetry using Δ λ = 50 nm synchronous mode at a peak maximum of 291.8 nm for CANA determination using methanol as solvent. Method C is a stability-indicating MCRS method measuring the peak amplitude of CANA and MET at 306.2 and 246.6 nm, respectively, in their mixture with complete CANA oxidation degradation. The linear ranges were: FTIR spectroscopy, 1.50-24.70 μg/mg CANA; spectrofluorimetry, 100.00-600.00 ng/mL CANA; and MCRS, 1.00-25.00 μg/mL CANA and 1-30 μg/mL MET. All results were statistically compared with a reported method: no significant difference was observed. The proposed methods can be used efficiently for routine analysis in QC laboratories. A green FTIR method utilizes only one reagent, KBr. Spectrofluorimetry using a constant wavelength synchronous scan of CANA native fluorescence in nanogram concentrations overcomes conventional excitation/emission spectra drawbacks and proves that the solvent effect in the fluorescence intensity differs according to concentration used. Stability-indicating MCRS determines the studied drugs in bulk, pharmaceutical formulations, accelerated and long-term stability study samples.

Excellent thermal stability and mechanical properties of bulk nanostructured FeCoNiCu high entropy alloy

In this work, we report bulk nanostructured equiatomic FeCoNiCu high-entropy alloy (HEA) with superior thermal stability and decent mechanical properties. High pressure torsion (HPT) was employed to refine the grains in the HEA into nanoscale (80 nm), and then Cu-rich particles were in-situ introduced at grain boundaries by subsequent annealing (≥700 °C), forming a multi-phase nanostructure. The Cu-rich particles are highly stable at high temperatures and impose a pinning effect on the grain boundaries, which significantly restricts grain growth (grain size <500 nm up to 900 °C), thus leading to outstanding thermal stability. On the other hand, the nanostructures also possess high yield strengths of 643∼1165 MPa, mainly attributing to grain boundary hardening. Meanwhile, the in-situ formed Cu-rich particles can concurrently deform with the matrix during straining, resulting in large total elongation (15∼20%). This work provides a novel strategy for designing bulk nanostructured HEA with good thermal stability and mechanical properties.

Computational investigation of van der Waals corrections in the adsorption properties of molecules on the Cu(111) surface.

Here, we report a computational investigation on the role of the most common van der Waals (vdW) corrections (D2, D3, D3(BJ), TS, TS+SCS, TS+HI, and dDsC) employed in density functional theory (DFT) calculations within local and semilocal exchange-correlation functionals to improve the description of the interaction between molecular species and solid surfaces. For this, we selected several molecular model systems, namely, the adsorption of small molecules (CH3, CH4, CO, CO2, H2O, and OH) on the close-packed Cu(111) surface, which bind via chemisorption or physisorption mechanisms. As expected, we found that the addition of the vdW corrections enhances the energetic stability of the Cu bulk in the face-centered cubic structure, which contributes to increasing the magnitude of the mechanical properties (elastic constants, bulk, Young, and shear modulus). Except for the TS+SCS correction, all vdW corrections substantially increase the surface energy, while the work function changes by about 0.05 eV (largest change). However, we found substantial differences among the vdW corrections when comparing its effects on interlayer spacing relaxations. Based on bulk and surface results, we selected only the D3 and dDsC vdW corrections for the study of the adsorption properties of the selected molecules on the Cu(111) surface. Overall, the addition of these vdW corrections has a greater effect on weakly interacting systems (CH4, CO2, H2O), while the chemisorption systems (CH3, CO, OH) are less affected.