Dependence Of Properties Research Articles

Investigation of Metal–H2O Systems at Elevated Temperatures: Part I. Development of a Solubility Apparatus Specialized for Super-Ambient Conditions

Abstract Metals used in aqueous environments where high temperatures and pressures are present are susceptible to corrosion. This is the case for nuclear power plants, especially CANDUTM reactors, where the liquid water systems can reach over 300 °C at pressures well above 101.325 kPa (1 atm). In such situations, failure to control corrosion has economic and safety consequences. To extend corrosion modeling tools, such as Pourbaix diagrams, to harsh aqueous conditions, there is a need for experimental thermochemical data performed at elevated temperatures. This is particularly true for metal and alloy systems where such information is unavailable or unreliable. A relatively simple approach to obtaining temperature dependent thermodynamic properties is the investigation of solid–liquid phase, or solubility, equilibria. However, this requires specially designed instrumentation that can withstand harsh temperatures and extreme pH conditions, while providing accurate data. In this work, an apparatus developed for super-ambient highly acidic and alkaline solubility experiments is presented. Solubility measurements were made in the zinc oxide system, which has been extensively studied. Using these equilibrium data and comparing to the literature, allowed the instrumentation and analysis process to be validated. In situ pH measurements using a constant volume, batch reactor system are described along with a brief presentation of the ZnO dissolution equilibria results at 85 °C (358.15 K).

Study on the properties of Sm3+-Doped CaTbAl3O7 phosphors

New single phase and adjustable emission phosphors have attracted a lot of attention because of the good luminous properties. In this work, Sm3+ doped CaTbAl3O7 phosphors are prepared in air by solid-state method. The crystal structure, concentration dependent spectra, lifetimes, and luminescence properties are investigated. Because of the 4f8 → 4f75d1 and 4f → 4f transitions of Tb3+ ion, host (CaTbAl3O7) shows an excitation spectrum in the range of 220–520 nm under monitored at 544 nm and emits yellow-green light under excitation 248, 284, and 368 nm due to the 5D4 → 7FJ (J = 0, 1, 2, 3, 4, 5, and 6) transitions of Tb3+ ion. CaTbAl3O7:Sm3+ under monitored 598 nm contains the excitation spectral peaks of both CaTbAl3O7 and Sm3+ ion. With excitation at 368 nm, CaTbAl3O7:Sm3+ glows orange-red light, its PL spectrum has both host (CaTbAl3O7) and Sm3+ ion contributing, and the chromaticity coordinates are about (0.5499, 0.4351). Under excitation 402 nm, the red-orange emission of CaTbAl3O7:Sm3+ is only the contribution of Sm3+ ion and the chromaticity coordinates are about (0.5823, 0.4168). The energy transfer process from Tb3+ in host (CaTbAl3O7) to Sm3+ ions can be confirmed via the spectral properties. We explain the luminous mechanism of CaTbAl3O7:Sm3+ by the energy level diagrams of Tb3+ and Sm3+.

RAFT polymerization assisted P(NIPAm-co-AAc)-AEMR integrated PVA hydrogels: Dual responsive features, texture analysis, and cytotoxicity studies

Modified P(NIPAm-co-AAc) copolymers are prepared using Radical Addition Fragmentation Chain Transfer (RAFT) copolymerization by varying the concentration of castor oil sourced acrylated epoxy methyl ricinoleate (AEMR). Subsequently, hydrogels are prepared by integrating copolymers with polyvinyl alcohol (PVA) via freeze-thaw process. The employment of RAFT polymerization yielded copolymers with dispersity (D) value of 1.2–1.3 revealing the formation of structurally well controlled polymer chains. The lower critical solution temperature (LCST) of the copolymers (∼30–35 °C) are tuned to the range of physiological temperature (∼37 °C) in PVA hydrogel system. Temperature dependent viscoelastic properties indicated that the characteristics of copolymeric solutions and hydrogels are composition dependent while undergoing noncovalent interactions and the conformational changes and the samples showed extremely elastic behaviour beyond LCST. Swelling ratio of hydrogels are also found to be pH dependent, which displayed higher swelling ratio in alkaline and reduced swelling ratio in acidic medium. Cytotoxicity studies with L929 cells showed that the copolymers and hydrogels exhibited desirable biocompatibility, which gets improved with AEMR concentrations. Thus, these dual responsive PA-AEMR-PVA smart hydrogels can be used as a viable functional material for possible bio-medical applications.

Thickness dependent structural and electrical properties of pulsed laser deposited Y0.95Ca0.05MnO3 thin films and the effect of high energy oxygen ion irradiation

Thickness dependent structural and electrical properties of pulsed laser deposited Y0.95Ca0.05MnO3 thin films and the effect of high energy oxygen ion irradiation

Insights into the dynamics of supported Au nanoparticles in the wet environments from first-principles and ReaxFF MD simulations

The interactions between metal and oxide supports have been widely studied, where the size effect of metal nanoparticles (NPs) and the gas environment play critical roles in catalytic performance. We employed density functional theory and ReaxFF reactive force field to investigate the size dependent properties of gold NPs supported on cerium dioxide, such as structural dynamics, adsorption, and electronic properties under wet environments. Distinct dynamic behaviors were observed in wet environments compared to vacuum conditions. In the wet environments, the hydroxide (OH) species preferentially adsorbs on the low coordination sites, such as edge sites, of NPs. This selective absorption induces a reconstruction effect on small NPs. Moderate-sized NPs exhibit significant surface reconstruction due to abundant OH adsorption at interface sites. However, this effect is negligible in larger NPs. A high interfacial population of OH significantly contributes the high catalytic performance of moderate-sized NPs. Moreover, OH adsorption modulates the charge distribution within the NPs, leading to their stabilization through OH-induced charge transfer. These findings provide insights into understanding and optimizing reactions in wet environments, offering a foundation for the development of more effective catalyst.

Model based study of temperature dependent thermodynamic and surface properties of Al-Ti-Ni-Cr system in liquid state

Thermodynamic and surface properties of Al-Ti-Ni liquid alloy with adding Cr, Al-Ti-Ni-Cr, were studied at 2000 K, 2100 K, 2200 K, 2300 K, and 2400 K using different theoretical models. The self-consistent energy interaction parameters of constituent binary subsystems were taken from the literature for the purpose. The thermodynamic properties like excess Gibbs free energy of mixing and the activities of the components in the alloy were investigated using the General Solution Model (GSM). Surface tension of the liquid alloy and surface concentrations of components in it were calculated using Butler's model with the aid of determined thermodynamic functions. The mixing tendency of the Al-Ti-Ni-Cr liquid alloy was found to decrease with the addition of Cr atoms for all compositions at its melting temperature, 2000 K. The activity of Cr decreased while those of the remaining components increased with the temperature rise. The surface tension of both Al-Ti-Ni and Al-Ti-Ni-Cr liquid alloys decreased linearly at elevated temperatures.

Disentangling different interfacial effects of reduced thin layer magnetizations

Abstract Thin buried magnetic layers ranging from thicknesses of a few atomic monolayers to several nanometers are omnipresent in the fields of magnetism and spintronics. For the functionality and fine tuning of devices build with such layers, exact knowledge of the depth dependent magnetic properties is essential. Especially the interfacial magnetic properties are important. Hence, understanding how magnetism is affected by structural variations, such as thickness or interface roughness, is mandatory. In this study, we use x-ray resonant magnetic reflectometry and magnetometry to study the high-resolution depth dependent magnetization profiles of thin magnetic transition metal layers sandwiched between an oxide and chromium layer. Compared to bulk materials, the room temperature saturation magnetization of these layers is reduced by up to 67%. These reductions are extremely sensitive to small structural variations. From the magnetic depth profiles, we disentangle different effects contributing to the magnetization reduction and the exact magnetic properties of the interface.

Size dependent dielectric properties in BaTiO3 nanopowders for application of MLCC

With the development of technology, electronic devices are constantly improving in performance, leading to an increase in the number of components. Consequently, there is a need to downsize passive components such as multi-layer ceramic capacitors (MLCCs). As a result, the size of the dielectric material used in MLCCs, namely BaTiO3, must also be reduced. However, previous studies have primarily investigated the dielectric properties of BaTiO3 nanopowders using the slurry method, of which approach has limitations as it combines the dielectric properties of both nanopowders and solvent. In this study, we employed scanning dielectric microscopy (SDM) to individually measure the dielectric constants of single BaTiO3 nanopowders. We demonstrate dielectric constant dependent on the size of nanopowder. Furthermore, the variation in dielectric constant can be attributed to the surface cubic layer of BaTiO3 nanopowders. Our findings revealed a peak dielectric constant of 60 occurring at an approximate nanopowder size of 55 nm, a phenomenon explicable through a three-phase structural model. This exploration into the nanoscale characteristics of BaTiO3 holds promise for advancing the development of next-generation MLCCs.

Giant spin seebeck effect with highly polarized spin current generation and piezoelectricity in flexible V2SeTeO altermagnet at room temperature

Studies on altermagnetic materials are attracting extensive research efforts owing to their directional dependent spin split band structure. However, it is rare to find reports on the possibility of multifunctionality in altermagnetic systems. Here, we explore the spin dependent transport properties and piezoelectricity of two-dimensional V2SeTeO altermagnet. The V2SeTeO system has a direct band gap of 0.32 eV with a Neel temperature of 510 K. We find a giant effective Seebeck coefficient of 0.64 mV/K at 300 K. This is several times larger than that found in bulk and other two-dimensional materials. Moreover, the effective Seebeck effect is entirely determined by either only spin-up or spin-down component. This feature implies that we can generate highly spin polarized current by temperature gradient at room temperature. We attribute this pure spin current generation to the directional dependent spin split band structure. Along with the spin dependent transport properties, we also find that the Janus V2SeTeO altermagnet shows outstanding flexibility and piezoelectric response with out-of-plane piezoelectric coefficient of d31=0.245pm/V. Overall, we propose that the V2SeTeO altermagnet system exhibits multifunctional physical properties at room temperature, and this can be utilized for potential spintronics and flexible piezoelectric applications simultaneously.

Generative diffusion models for synthetic trajectories of heavy and light particles in turbulence

Heavy and light particles are commonly found in many natural phenomena and industrial processes, such as suspensions of bubbles, dust, and droplets in incompressible turbulent flows. Based on a recent machine learning approach using a diffusion model that successfully generated single tracer trajectories in three-dimensional turbulence and passed most statistical benchmarks across time scales, we extend this model to include heavy and light particles. Given the particle type – tracer, light, or heavy – the model can generate synthetic, realistic trajectories with correct fat-tail distributions for acceleration, anomalous power laws, and scale dependent local slope properties. This work paves the way for future exploration of the use of diffusion models to produce high-quality synthetic datasets for different flow configurations, potentially allowing interpolation between different setups and adaptation to new conditions.

Simulating the near-field dynamic plume behavior of disposed fine sediments

Projections of the effects of fine sediment disposals, relevant for managed estuaries and tidally influenced coastal areas, are typically based on numerical far-field models. For an accurate consideration of the disposal itself, near-field models are often needed. The open source near-field model, PROVER-M, simulates the relevant processes of the physics based, dynamic behavior of disposed fine sediments in coastal waters and is applied in this study. First, new small scale laboratory experiments of instantaneous disposals are presented, documenting the dynamic behavior of fine material disposed in shallow waters. Second, results of the PROVER-M model are shown for disposals in three different settings: (1) a field-scaled study complementary to the laboratory set-up, (2) a parametric study of sequentially varied model input and (3) a far-field model coupling for estimation of the PROVER-M impact. By comparing results of the laboratory experiments to the PROVER-M model, the physical behavior of PROVER-M is successfully validated. The impact of the ambient setting and dredged material parameters is evaluated by the PROVER-M simulations, where the results show non-linear, complex interdependencies of the input parameters on disposal properties in dependence of ambient site conditions and material composition. In this context, limits of the model application are assessed and critically discussed. Finally, an exemplary coupling to a far-field model based on a real set of disposals in the tidally influenced Weser estuary (Germany) illustrates the potential impact of PROVER-M for assessing far-field suspended sediment concentration (SSC), with increased maximum SSC values of up to 10%.

Temperature and Tension Speed-Dependent Interface Properties Between Polymers and Ceramics or Metals

Interfaces between polymers and ceramics or metals have wide applications in mechanical, electronic and chemical engineering. Loading speed and temperature have certain influence on interface properties, which affect their application in the service environment. In this paper, the interface intrinsic strength of polypropylene (PP)/silicon oxide (SiO[Formula: see text] and polyethylene (PE)/aluminum are studied based on molecular dynamic (MD) tensile method at low temperature and loading speed first. Then changes of interface properties are studied by increasing loading speed and temperature, respectively. The results indicate that interface strength increases or decreases with increasing loading speed or temperature. The interface damage mechanism related to the evolution of free volume is revealed.

Existence of weak solutions to a Cahn–Hilliard–Biot system

We prove existence of weak solutions to a diffuse interface model describing the flow of a fluid through a deformable porous medium consisting of two phases. The system non-linearly couples Biot’s equations for poroelasticity, including phase-field dependent material properties, with the Cahn–Hilliard equation to model the evolution of the solid, and is further augmented by a visco-elastic regularization of Kelvin–Voigt type. To obtain this result, we approximate the problem in two steps, where first a semi-Galerkin ansatz is employed to show existence of weak solutions to regularized systems, for which later on compactness arguments allow limit passage. Notably, we also establish a maximal regularity theory for linear visco-elastic problems.

A 3D coupled numerical simulation of energised fracturing with CO2: Impact of CO2 phase on fracturing process

Engineered fractures play a critical role in enhancing energy extraction efficiency. In this study, energised fracturing with CO2, as an alternative approach to conventional water-based hydraulic fracturing, is investigated via numerical simulations. We validated the CO2 finite element-based fracturing model against analytical as well as CO2-fracturing laboratory experiments, then utilised the model to investigate the effects of pressure-temperature dependent properties of CO2 on energised fracturing process. To account for the temperatures expected in a real field, four cases with injection temperatures of CO2 varying between 250 K and 350K, under both isothermal and adiabatic conditions have been considered. In the adiabatic conditions, the temperature variation during compression of CO2 is captured using the Joule-Thompson coefficient, assuming no thermal exchange between the CO2 and the surrounding medium. The results highlight the significant influence of CO2 phase on the fracturing process, during the pressurisation stage, as well as post-breakdown, the speed of fracture growth after the breakdown and subsequent depressurisation and associated cooling of CO2. In the designed cases, the phase-change from gas to liquid or supercritical occurs during the pressurisation and prior to breakdown, while the phase remains unchanged post breakdown and during fracture propagation. Liquid CO2 presents a fast-pressurising process while gaseous CO2 undergoes a lengthy compression stage. Supercritical CO2 is the best performing as the pressurisation is not too lengthy, while the instantaneous post breakdown fracturing is significant. Results show that higher temperature of supercritical CO2 is causing larger instantaneous fracture propagation as it has lower viscosity for the given in situ stresses (>10 MPa).

Bilayer period and ratio dependent structure and mechanical properties of TiN/MoN superlattices

Transition metal nitrides are widely used in the hard materials and protective coatings industry, but are limited by their low fracture toughness. Encouraged by previous studies on remarkable simultaneous improvements in strength and ductility through superlattice (SL) architectures, various TiN/MoN SL thin films were developed on MgO (100) substrates. By varying their bilayer periods (Λ) between 2 and 23 nm with bilayer ratios (Γ = ℓMoN:ℓTiN) of 0.5, 1, 2, and 2.7, their individual effects on structure and mechanical properties can be revealed. All SLs—independent of Λ, Γ, and nitrogen-to-metal (N/Me) ratio (within the analysed variations)—exhibit a rocksalt structure with high-order satellite peaks in X-ray diffraction. While the SLs with Γ = 2 have the lowest hardness (H)—presumably due to their overall lowest N/Me ratio—the SLs with Γ = 2.7 are the hardest with a neat superlattice effect. The SLs with Γ = 1 and 2.7 have a comparable superlattice effect on fracture toughness (KIC), peaking at Λ = 9.9 and 9.3 nm, respectively. Of all the SLs investigated, those with Γ = 1 provide the best blend of mechanical properties and dry sliding coefficient of friction (µ), such as H = 34.8±1.6 GPa, KIC = 4.1±0.2 MPa√m, and µ = 0.27 when Λ = 9.9 nm. Deepening current understanding of superlattice effects in general—particularly the influence of bilayer periods and ratios—in relation to the nitrogen supply and heterogeneous microstructures, our study accelerates the design of nanolayered coatings with desired structure-property combinations.

Sintering temperature dependent characterization of Ni nano ferrite with the optimization of frequency dependent properties

Ni ferrite is becoming a prominent candidate for high frequency applications. To find the best performance of Ni ferrite for high frequency devices, NiFe2O4 ferrites are synthesized by co-precipitation method at five distinct sintering temperatures (TS = 500 °C, 700 °C, 850 °C, 1000 °C, and 1200 °C). The structural properties of the synthesized samples are characterized by x-ray diffraction (XRD) with Rietveld refinement analysis. The grain formation of the ferrites is observed by field emission scanning electron microscopy (FESEM) and the gradual increase in grain size is noticed with the increment of sintering temperature. The frequency dependent properties are studied by an impedance analyzer. The real permeability values of the samples are stable in a wide frequency range (100 Hz to 100 MHz) and the imaginary permeability values are decreased at lower frequency region. It can be seen that the real part of magnetic permeability increases significantly with sintering temperature. The real and imaginary dielectric properties are reduced at the initial applied field and become constant at higher frequencies. The magnetic quality factor and dielectric quality factor are enhanced with the increase of sintering temperature. Frequency dependent properties confirm that these ferrites are strong candidates for potential high frequency applications. Finally, it is found that, comparatively a higher sintering temperature is better for permeability properties, and a lower sintering temperature is better for dielectric properties.

Flexoelectric Enhancement of Strain Gradient Elasticity Across a Ferroelectric-to-Paraelectric Phase Transition.

We study the temperature dependent elastic properties of Ba0.8Sr0.2TiO3 freestanding membranes across the ferroelectric-to-paraelectric phase transition using an atomic force microscope. The bending rigidity of thin membranes can be stiffer compared to stretching due to strain gradient elasticity (SGE). We measure the Young's modulus of freestanding Ba0.8Sr0.2TiO3 drumheads in bending and stretching dominated deformation regimes on a variable temperature platform, finding a peak in the difference between the two Young's moduli obtained at the phase transition. This demonstrates a dependence of SGE on the dielectric properties of a material and alludes to a flexoelectric origin of an effective SGE.

The role of interfacial Dzyaloshinskii–Moriya interaction in different heavy metal-based perpendicular magnetic systems and its application in spintronic devices

The interfacial Dzyaloshinskii–Moriya interaction (DMI) acting as an essential source to stabilize spin textures in ferromagnetic ultrathin films has revealed its significant role in spin–orbit torque (SOT)-driven magnetic switching. Based on a convincing homochiral Néel domain wall model, the in-plane (IP) magnetic field associated with the DMI effect has been confirmed as an essential prerequisite for deterministic SOT-driven switching. Although the presence of the IP field is required, the impact of IP field magnitude combined with the DMI effect on SOT-driven switching in different heavy metals (HMs) has never been considered together. In this research, SOT-induced switching under various IP fields in Pt, W, or Ta/CoFeB/MgO systems has been studied. The results show that the critical threshold current IC is almost independent of the IP field in the Pt-based structure; however, it significantly decreases with an increase in the IP field in the W- and Ta-based systems. Combining the derived DMI field and the magnetic domain nucleation, it is concluded that the significant difference in DMI fields and the domains' nucleating positions are the main reasons for the above phenomenon. Exploiting the distinct dependent properties of IC on the IP field, a six resistance state multilevel storage and five programmable spin logic gates are proposed and realized. This study provides insight into the special ability of the SOT effect modulated by the DMI, and also expands an effective way to construct spin-based devices based on this unique spintronic effect.

Bioinspired microstructure design simultaneously enhances strain-rate stiffening and toughening of composites

Keratinous biological materials, such as baleen, pangolin scales, and human hair, have similar constituent materials. However, their strain-rate dependent mechanical properties vary due to differences in their microstructures. Inspired by the microstructures observed in baleen, here we present novel microstructural designs of three types of lamellar-tubular fibers, namely the lamellar-tubular fiber (LTF), mineralized lamellar-tubular fiber (MLTF) and hollow mineralized-lamellar-tubular fiber (HMLTF). We systematically investigated their strain-rate dependent mechanical behaviors with comparison to the conventional cylinder-fiber (CF) reinforced composites. Through the finite element analysis (FEA), we found that the baleen-inspired composites have superior strain-rate stiffening and toughening effects than the conventional fiber reinforced composite. Rate-dependent constitutive models decoupling elastic and inelastic regimes were constructed for these bioinspired composites. Based on the FEA results, three constitutive parameters were obtained to quantitatively characterize the rate-dependent mechanical behaviors of these composites, especially the microstructure-induced difference. Furthermore, our study found that the baleen-inspired tubular microstructure improves stiffness and strain-rate stiffening through raising the stress levels of all phases and improves toughness and strain-rate toughening through enlarging the deformation in the inelastic region. This novel bioinspired design is hopeful to pave ways for the development of advanced composites with simultaneously enhanced strain-rate stiffening and toughening.

(Invited) Semiconductor Nanostructures for Light Energy Conversion

This talk will review some of the key developments of semiconductor quantum dots based light energy conversion. Semiconductor nanostructures are finding new ways to design light energy conversion devices (e.g., thin film solar cells and light emitting devices). The decreased consumption of energy during the manufacture and the lessened use of semiconductor materials lowers the overall carbon footprint with energy payback time less than a year for such devices. The early studies which focused on the synthesis of various semiconductor nanostructures and exploration of their size dependent optical and electronic properties have led to their their integration in high efficiency thin film solar cells.. Unlike solar cell devices, photocatalytic processes are yet to deliver conversion efficiencies and stability that can make them compatible for practical applications. Understanding the limitations imposed by interfacial charge transfer processes remains a key to further advance photocatalytic systems for chemical energy storage. Recent developments in utilizing semiconductor nanostructures for light energy conversion and storage will be discussed.