Grain Size Dependence Research Articles

Study of thermal material properties for Ta- and Al-substituted Li7La3Zr2O12 (LLZO) solid-state electrolyte in dependency of temperature and grain size

Investigating thermal material properties such as thermal conductivity (κ), specific heat capacity (Cp) and decomposition temperature of Ta- and Al-substituted solid state electrolyte Li7La3Zr2O12 (LLZO) in dependency of temperature and grain size.

Correction: Study of thermal material properties for Ta- and Al-substituted Li7La3Zr2O12 (LLZO) solid-state electrolyte in dependency of temperature and grain size

Correction for ‘Study of thermal material properties for Ta- and Al-substituted Li7La3Zr2O12 (LLZO) solid-state electrolyte in dependency of temperature and grain size’ by Julian Neises et al., J. Mater. Chem. A, 2022, 10, 12177–12186, https://doi.org/10.1039/D2TA00323F.

MCMC inversion of the transient and steady-state creep flow law parameters of dunite under dry and wet conditions

The rheology of the upper mantle impacts a variety of geodynamic processes, including postseismic deformation following great earthquakes and post-glacial rebound. The deformation of upper mantle rocks is controlled by the rheology of olivine, the most abundant upper mantle mineral. The mechanical properties of olivine at steady state are well constrained. However, the physical mechanism underlying transient creep, an evolutionary, hardening phase converging to steady state asymptotically, is still poorly understood. Here, we constrain a constitutive framework that captures transient creep and steady state creep consistently using the mechanical data from laboratory experiments on natural dunites containing at least 94% olivine under both hydrous and anhydrous conditions. The constitutive framework represents a Burgers assembly with a thermally activated nonlinear stress-versus-strain-rate relationship for the dashpots. Work hardening is obtained by the evolution of a state variable that represents internal stress. We determine the flow law parameters for dunites using a Markov chain Monte Carlo method. We find the activation energy 430pm 20 and 250pm 10 kJ/mol for dry and wet conditions, respectively, and the stress exponent 2.0pm 0.1 for both the dry and wet cases for transient creep, consistently lower than those of steady-state creep, suggesting a separate physical mechanism. For wet dunites in the grain-boundary sliding regime, the grain-size dependence is similar for transient creep and steady-state creep. The lower activation energy of transient creep could be due to a higher jog density of the corresponding soft-slip system. More experimental data are required to estimate the activation volume and water content exponent of transient creep. The constitutive relation used and its associated flow law parameters provide useful constraints for geodynamics applications.Graphical

Dependence of Surface Profile on Diamond Impregnation Characteristics

The paper presents the results of studies of the profile of the impregnated diamond surface depending on the grain size and initial roughness of the matrix. The experiments were carried out by impregnating powders of different grit size into a matrix made of low-carbon low-alloy steel with HB180 hardness using a ball indenter. The roughness parameters were measured using a contact profilometer. The height and step parameters of roughness and the curve of the profile bearing length were evaluated. In studying the effect of grain size on the surface profile, it was found that the optimal grain size should be 0.5...0.8 of the initial surface mean spacing profile irregularities. The shape of the Abbott-Firestone curve in this case corresponds to a flat profile. Experiments carried out with varying the initial roughness of the samples confirmed the dependence of the optimum grain size on the mean spacing of the profile irregularities. The developed research procedure can be used to design technological processes of hardening parts, tools and accessories by diamond impregnation.

Modeling of Random Quasi-Phase-Matching in Birefringent Disordered Media

We provide a vectorial model to simulate second-harmonic generation (SHG) in birefringent, transparent media with an arbitrary configuration of non-linear ($\chi^{(2)}$) crystalline grains. We apply this model on disordered assemblies of LiNbO$_3$ and BaTiO$_3$ grains to identify the influence of the birefringence on the random quasi-phase-matching process. We show that in monodispersed assemblies, the birefringence relaxes the grain-size dependence of the SHG efficiency. In polydispersed assemblies with sufficiently large grains, we find that the birefringence introduces an SHG efficiency enhancement of up to 54% compared to isotropic reference crystals, which is grain size independent. This enhancement increases linearly with the grain size, if the birefringent grains can be phase matched. These two different scaling behaviours are used in Kurtz and Perry's powder-technique to identify the phase-matchability of a material. We show on the example of LiNbO$_3$ and ADP that this technique cannot be applied when the grains get smaller than the coherence length, because the SHG scaling with the grain size becomes material specific.

Growth of single crystals in the (Na1/2Bi1/2)TiO3\u2013(Sr1\u2013xCax)TiO3 system by solid state crystal growth

Ceramics based on (Na1/2B1/2)TiO3 are promising candidates for actuator applications because of large strains generated by an electric field-induced phase transition. For example, the (1−x)(Na1/2Bi1/2)TiO3-xSrTiO3 system exhibits a morphotropic phase boundary at x = 0.2–0.3, leading to high values of inverse piezoelectric constant d*33, which can be further improved by the use of single crystals. In our previous work, single crystals of (Na1/2B1/2)TiO3-SrTiO3 and (Na1/2B1/2)TiO3-CaTiO3 were grown by the solid state crystal growth technique. Growth in the (Na1/2B1/2)TiO3-SrTiO3 system was sluggish whereas the (Na1/2B1/2)TiO3-CaTiO3 single crystals grew well. In the present work, 0.8(Na1/2Bi1/2)TiO3-0.2(Sr1−xCax)TiO3 single crystals (with x = 0.0, 0.1, 0.2, 0.3, 0.4) were produced by the solid state crystal growth technique in an attempt to improve crystal growth rate. The dependence of mean matrix grain size, single crystal growth distance, and electrical properties on the Ca concentration was investigated in detail. These investigations indicated that at x = 0.3 the matrix grain growth was suppressed and the driving force for single crystal growth was enhanced. Replacing Sr with Ca increased the shoulder temperature Ts and temperature of maximum relative permittivity Tmax, causing a decrease in inverse piezoelectric properties and a change from normal to incipient ferroelectric behavior.

Dielectric behavior of graphite, with assimilation of the AC permittivity, DC polarization and DC electret

The dielectric behavior of polycrystalline graphite is addressed by assimilating the DC electric polarization, AC permittivity, DC electret behavior, and their grain-size dependence. The AC-permittivity-related polarization is weaker than the DC-electret-related polarization, involving fewer carriers, because the depolarization is slower than polarization. The DC-current-induced polarization is even weaker than the AC-permittivity-related polarization, involving even fewer carriers. A decrease in the grain size increases the fraction of carriers that participate in the DC-polarization/AC-permittivity/DC-electret through carrier-atom interaction at the grain boundaries, thereby increasing the permittivity and the electret's electric field. The electric field increases with increasing resistivity and increasing inter-electrode distance l. DC-polarization/DC-depolarization and electret discharge/charge are faster for a smaller grain size. Both electric field and the reciprocal of the capacitance increase linearly with l, suggesting a model of dipoles in series. The amount of charge at each end of the overall dipole is greater for a smaller grain size, while the discharge time per unit electret-participating charge is shorter. In spite of the decrease in the fraction of carriers that participate with increasing l, the electret energy density is much increased by increasing l, because it depends on the power density and discharge time, both of which increase with l.

Enhancing strength-ductility of the aluminum bronze alloy by generating high-density ultrafine annealing twins

In this work, nickel aluminum bronze (NAB) alloys with high-density nano/ultrafine annealing twins were fabricated by heavy hot rolling (HHR) and the subsequent annealing treatment at 800 °C for different times. The dependence of grain size on annealing twin density of prior α matrix phase over a range from 1.0 to 10 μm and its effect on mechanical properties were investigated. The results show the high-density annealing twins generation in α phase substantially enhances the strength-ductility combinations and work hardening of the HHRed NAB. The HHRed NAB annealing at 800 °C for 2 min, with the highest twin boundary density, exhibits and excellent comprehensive mechanical properties with a yield strength of 843.2 MPa, ultimate strength of 1148.3 MPa, and uniform elongation of 15.2%. The analysis shows that the formation of these high-density ultrafine twins is mainly attributed to the large amount of deformation energy storage, high-density defects, and ultrafine precipitates of the dispersion distribution induced by HHR. It was found that the dependence of the twin density with grain size has some deviations from the classical Pande's model in the fine-grained stage (1– 2 μm), which is closely associated with the promotion effect of the ultrafine precipitates on the annealing twins generation in the fine-grained stage.

Grain-size dependence of magnetic microstructure and high-frequency susceptibility of nanocrystalline thin films: A micromagnetic simulation study

The size of crystallites is one of the most important factors that determine the key characteristics of nanocrystalline thin magnetic films that make them very promising media for various applications. In this paper, using micromagnetic simulation, we study in detail the influence of the grain size on the magnetic microstructure of the films and its relation with high-frequency dynamics of magnetization. When the grain size exceeds some critical value Dcr, a sharp broadening and shift of the ferromagnetic resonance line are observed at certain frequencies of the alternating magnetic field. Using a two-magnon scattering model, it is shown that these effects are caused by the scattering of spin waves on the inhomogeneous stochastic magnetic structure—magnetization ripple. An expression for the determination of the critical size Dcr is obtained. The micromagnetic simulation results agree with the main conclusions of the static and dynamic theories of magnetization ripple and also confirmed by experimental data reported by other authors.

Non-polar a-plane oriented ZnO:Al thin films for optoelectronic applications

This paper reports the details of fabrication of aluminum-doped zinc oxide (AZO) thin films on Corning glass substrates by pulsed laser deposition technique at different laser ablation fluences: 8.75, 17.5 and 35 J/cm2. The influence of laser fluence on the structural, optical and electrical properties of the prepared thin films is analyzed and discussed. X-ray diffraction pattern of AZO thin film confirmed a non-polar a-plane oriented crystal growth in the AZO film prepared at higher fluences. Field emission scanning electron microscopic images indicate the dependence of grain size of AZO on the laser fluence. The highest transmittance (>86%) and the lowest resistivity is attained in thin film prepared at 35 J/cm2 fluence. A remarkable switching behavior from p-type to n-type semiconductivity is observed. The achieved optoelectronic properties of non-polar a–plane oriented AZO thin film, suggests the prepared thin film is a promising material in the fabrication of LED device.

Characteristics of thermal- and strain-induced ε-martensite in Fe50Mn30Co10Cr10 multi-component alloy: Effect of grain size

Electron backscatter diffraction technique is used to systematically investigate the characteristics of thermal- and strain-induced ε-martensite in Fe50Mn30Co10Cr10 multi-component alloy, focusing on the grain size effect. Results show that a clear morphological distinction between thermal- and strain-induced ε-martensite cannot be made, both exhibiting laminate- and blocky-shaped features. The amount of thermal-induced ε-martensite dependence of initial γ-austenite grain sizes is evidenced, revealing the formation of multiple initial ε variants in coarse γ-austenite grains, rather than in fine γ-austenite grains. The external strain effect is advantageous of the formation of secondary ε variants and εtwins, but not the thermal effect. Decreasing γ-austenite grain size hinders the activation of secondary ε variants and εtwin, confirming secondary ε variants and εtwin can be produced in coarse γ-austenite grains under the small strain, rather than in fine γ-austenite grains. Furthermore, under the heavy strain, the saturated ε-martensite is almost dominated by one persisting ε variant in coarse and fine γ-austenite grains.

Dynamic recrystallization of friction welded AISI 316 stainless steel joints

Abstract The microstructural characteristics of friction welded AISI 316 stainless steel samples in a welding zone and a heat affected zone were investigated. Inhomogeneous plastic deformation occurred due to friction welding. Individual grains in the final microstructure underwent various evolution mechanisms. These were caused by the growth of the initially recrystallized grains or as a result of the dynamic recrystallization of the sub-grains formed. The grains within the welding zone and the heat affected zone exhibited different densities of dislocations and experienced various degrees of recovery. Using reasonable estimates of the strain, strain rate and temperature of the friction welding, the dependence of the dynamic recrystallization grain size was found to have the same dependence on the Zener-Hollomon parameter as material deformed via a conventional hot working process.

Dynamic recrystallization of friction welded AISI 316 stainless steel joints

Abstract The microstructural characteristics of friction welded AISI 316 stainless steel samples in a welding zone and a heat affected zone were investigated. Inhomogeneous plastic deformation occurred due to friction welding. Individual grains in the final microstructure underwent various evolution mechanisms. These were caused by the growth of the initially recrystallized grains or as a result of the dynamic recrystallization of the sub-grains formed. The grains within the welding zone and the heat affected zone exhibited different densities of dislocations and experienced various degrees of recovery. Using reasonable estimates of the strain, strain rate and temperature of the friction welding, the dependence of the dynamic recrystallization grain size was found to have the same dependence on the Zener-Hollomon parameter as material deformed via a conventional hot working process.

On the grain size dependence of shock responses in nanocrystalline sic ceramics at high strain rates

Shock induced plasticity, structural phase transitions, as well as dynamic failure in nanocrystalline SiC ceramics, with grain sizes varying from ~2 to ~32 nm, are investigated systematically using large scale molecular dynamics simulations. Shock particle velocities are varied from 1 to 5 km/s in order to study elastic and plastic behavior. Multiple non-monotonic grain-size dependent mechanical properties of nanocrystalline SiC are elucidated. Deformation twinning identified at Up = 2 km/s is reduced with decreasing grain size with a breakdown between dG = 6 to 10 nm. Statistics from grain size effects on the phase transformation from Zinc-Blend to Rock-Salt structure at different particle velocities are obtained. The characteristics of failure shift from classical spall to micro-spall as Up is increased from 1 to 5 km/s. Spall strengths are evaluated by an indirect free-surface method, akin to experimental measurements, and a direct method evaluating the atomic stress tensor at the point of spallation. Differences between the two methods at high strain rates are discussed in detail. The direct method provides a measure of ultimate spall strength, while the indirect method shows pronounced agreement with the nucleation stress. An unexpected grain size dependence of the tensile strengths is also identified, which is similar to a theoretically predicted trend in nanoscale systems. Our results provide new support to the grain size dependence of mechanical properties of nanocrystalline system at high strain rates, which could benefit the design of nanocrystalline ceramics.

Tensile strength of glacial ice deduced from observations of the 2015 eastern Skaftá cauldron collapse, Vatnajökull ice cap, Iceland

AbstractThe representation of iceberg calving in numerical models is a key source of uncertainty in century-scale sea-level rise projections. Parameters central to model representations of calving, including the tensile strength of glacier ice, remain poorly constrained. Grain-size and sample-size dependence make it difficult to reconcile laboratory and in situ estimates of ice tensile strength. Further, assumptions of various numerical models obscure comparison of the ‘strength’ parameter with a physically observable value. Here, we address the problem of fracture during calving using an analogous natural laboratory: a viscoelastic analysis of observed surface deformation and associated stresses in the 2015 collapse of eastern Skaftá cauldron, Vatnajökull ice cap, Iceland. We find that the ice within the cauldron could have experienced instantaneous elastic stress on the order of several MPa. We observe surface crevasses at the cauldron edges and center, but find that large areas of ice remain intact despite high stress. Our findings suggest a tensile strength of glacier ice on the order of 1 MPa, consistent with laboratory estimates but exceeding previous glacier-specific estimates.

Microstructure, dielectric and microwave features of [Ni0.4Cu0.2Zn0.4](Fe2−xTbx)O4 (x ≤ 0.1) nanospinel ferrites

Tb-substituted Ni0.4Cu0.2Zn0.4TbxFe2−xO4 (0.0≤x≤0.10) nanospinel ferrites were formed by sonochemical technique. It was first time established correlation between chemical composition of the nanosized NiCuZn spinels and their structural, electrical and microwave properties. The structure of nanospinel ferrites (NSFs) was proved through XRD. Microstructural were analyzed from SEM. It was observed a non-linear dependence of the average grain size with Tb concentration. The conduction mechanism and dielectric function has been extensively studied as functions of frequency, temperature, and Tb ions substitution ratio using complex impedance spectroscopy. It is obvious to see that the substitutions ratio showed a substantial influence on dielectric features, while Tb ion substitution has little but notable effect on AC/DC conductivity change. From the Arrhenius plots, the activation energies for all substitution ratios were calculated. The reflection losses as a function frequency dependences of the were calculated from S-parameters data within 1–4.5GHz. The occurrences of the electromagnetic absorption in the frequency interval of 1.85–3.79GHz were observed. Non-linear behaviour of the amplitude–frequency features were verified as a function of the level of chemical substitution (x) with Tb ions concentration. It was found microstructural parameters correlates well with the main absorption characteristics. It was discussed the nature of the electromagnetic absorption for partially substituted nanospinels. The decline of the reflected electromagnetic radiations was explicated along with domain-boundary resonance, which well correlates with the microstructure data. The low dimensional magnetic oxides having the domain-boundary resonance have a role in nature of absorption.

Effect of grain size distribution and size-dependent grain heating on molecular abundances in starless and pre-stellar cores

We present a new gas-grain chemical model to constrain the effect of grain size distribution on molecular abundances in physical conditions corresponding to starless and pre-stellar cores. We simultaneously introduce grain-size dependence for desorption efficiency induced by cosmic rays (CRs) and for grain equilibrium temperatures. The latter were calculated with a radiative transfer code via custom dust models built for the present work. We explicitly tracked of ice abundances on a set of grain populations. We find that the size-dependent CR desorption efficiency affects ice abundances in a highly nontrivial way that depends on the molecule. Species that originate in the gas phase, such as CO, follow a simple pattern in which the ice abundance is highest on the smallest grains and these are the most abundant in the distribution. Some molecules, such as HCN, are instead concentrated on large grains throughout the time evolution; others, such as N2, are initially concentrated on large grains, but at late times on small grains because of grain-size-dependent competition between desorption and hydrogenation. Most of the water ice is on small grains at high medium density (n(H2) ≳ 106 cm−3), where the water ice fraction, with respect to the total water ice reservoir, can be as low as ~10−3 on large (>0.1 μm) grains. Allowing the grain equilibrium temperature to vary with grain size induces strong variations in relative ice abundances in low-density conditions in which the interstellar radiation field and in particular its ultraviolet component are not attenuated. Our study implies consequences not only for the initial formation of ices preceding the starless core stage, but also for the relative ice abundances on the grain populations going into the protostellar stage. In particular, if the smallest grains can lose their mantles owing to grain-grain collisions as the core is collapsing, the ice composition in the beginning of the protostellar stage could be very different than in the pre-collapse phase because the ice composition depends strongly on the grain size.

Dependence of grain size and aspect ratio on grain boundary additives in hot-deformed Nd-Fe-B magnets

Commercial Nd13.6Fe73.6Ga0.6Co6.6B5.6 (at.%) powders were mixed with 0–10 wt% Nd80Cu15Al5 alloy powders to prepare hot-deformed Nd-Fe-B magnets. As the increasing Nd80Cu15Al5 content from 0 to 10 wt%, the grain sizes along the c-plane (Dǁ) decreased by more than 35% from 312 to 198 nm while the grain sizes along the ab-plane (D⊥) decreased by less than 7% from 58 to 54 nm, resulting in a decrease of more than 30% in the grain aspect ratio (Dǁ/D⊥) from 5.4 to 3.7. Moreover, the temperature coefficient of coercivity increased significantly from −0.469 to −0.419%/°C by 8 wt% Nd80Cu15Al5 addition. Based on microstructure observations, the improved thermal stability of the magnets without using heavy rare-earth elements is due to combined effect of the exchange decoupling between grains by the nonferromagnetic grain boundary phases, the refinement of grains and the decreased grain aspect ratio.

Залежність крупності зерна пивоварного ячменю ярого від впливу мінерального живлення

Залежність крупності зерна пивоварного ячменю ярого від впливу мінерального живлення

Sintering of Metakaolin-based Na-Pollucite ceramics and their immobilization of Cs

Metakaolin-based Na-Pollucite ceramics (high-temperature sintered Na-pollucite ceramics: HTNP), with a target composition close to Pollucite (CsAlSi2O6), were fabricated at sintering temperatures above 1000 °C to immobilize Cs as waste form material. The sintering behaviors of Metakaolin-based Na-Pollucite ceramics were investigated, in particular with respect to sintering temperature, grain size, and microstructure. The results indicate that major phases of the pollucite ceramics consist of pollucite phase and a small fraction of other mineral phases like Albite, SiO2, and Al2O3, and the microstructures greatly depends on the molar Cs/Na ratio. Furthermore, with increasing Cs content in the pollucite ceramics, the sintering temperature increases gradually, and the pollucite grain size decreases accordingly. On the other hand, to avoid the high-temperature volatilization of Cs-ions during sintering, low-temperature sintered Na-pollucite (LTNP) ceramics were prepared below 950 °C by introducing H3BO3 into the metakaolin-based Na-Pollucite ceramics. After the LTNP ceramics were sintered using a low-temperature liquid-phase process, even when the sintering temperature was decreased to 650 °C, they remained structurally as pollucite phase. In addition, the sintering-temperature and grain-size dependency on the molar Cs/Na ratio in LTNP ceramics is consistent with that in HTNP ceramics. Leaching in the PCT (Product Consistency Test) indicates that the leaching concentrations of HTNP ceramics are, in total, lower than in LTNP ceramics. However, the LTNP and HTNP ceramics samples, with the molar Cs/Na ratios 1:1.5, 1:0.67, and 1:0.25 show better immobilization abilities for the Cs ion. This indicates that, besides the pollucite phase formation, the immobilization of the Cs ion correlates also with dense microstructures, grain size, and good crystallization. More importantly, low sintering temperatures and the fabrication of Cs crystalline ceramics are the important factors to improve the Cs ion immobilization.