Material Grain Research Articles

Research of influence of adhesive additives on physical and chemical properties of road bitumens

To increase the adhesion strength (wetting ability) of bitumen, and, consequently, reduce the likelihood of premature occurrence of defects formed on asphalt concrete coatings, it is necessary to use various kinds of surfactants that increase the adhesion ability of bitumen. Adhesive additives to road bitumens increase the mobility of the organic binder, help reduce the number of uncoated grains of mineral material, which facilitates the compaction of asphalt concrete mix. One of the problems of durability of asphalt concrete pavements is the lack of strong adhesion of the bitumen film to the surface of the mineral material. To increase this strength, various adhesive additives are used, which affect not only the adhesive properties of bitumen, but also its physical and chemical properties. The main task of the work is aimed at solving the issues of the influence of adhesive additives on the physicochemical properties of organic binders used in road construction. The quality assessment of the modified bitumen was carried out according to GOST 22245-90, which, at present, is guided by the selection of the composition of the asphalt concrete mixture. As a result of the study, effective adhesive additives were identified that contribute to the minimal change in the physicochemical properties of viscous road bitumen and possess thermal stability under prolonged exposure to elevated temperatures. Studies have shown that almost all adhesive additives not only improve the adhesive properties of organic binders to mineral materials, but also can alter and even worsen the physicochemical properties of the original organic binder, which can adversely affect the properties of asphalt concrete. The study used the original bitumen from only one manufacturer and the negative effect of adhesive additives may be due to the incompatible chemical composition of the adhesive additive with the group composition of bitumen and the mineralogical composition of the mineral material.

The Al<sub>2</sub>O<sub>3</sub>-3D-ceramics' structure changing when sintering

It was proposed to regard the ceramic products with periodic topology as the systems having the multilevel organized structures. The development of the structure was studied at different scales levels after the sintering at 1700 °С for the corundum ceramics prepared by 3D-printing. The peculiarities of the geometry change were shown for the 3d-printed layered structure, for the material's grain structure and for the crystal lattice parameters of the α-Al2O3grains.Ill. 5. Ref.8.

Modeling polycrystalline materials with elongated grains

SummaryA novel algorithm to reproduce the arrangement of grains in polycrystalline materials was recently published by the authors. In this original approach, a dense package of circles (or spheres) with the same distribution as the grains is generated to produce a set of Voronoi cells that are later modified to Laguerre cells representing the original structure. This algorithm was successfully applied to materials with somewhat equidimensional grains; however, it fails for long‐shaped grains. In this paper, modifications are provided in order to overcome these drawbacks. This is accomplished by moving each vertex of the Voronoi cells in such a way that the vertex should be equidistant from the particles with respect to the Euclidean distance. The algorithm is applied to packages of ellipses and spherocylinders in 2D. An example for a package of spheres is also provided to illustrate the application for a simple 3D case. The adherence between the generated packages and the corresponding tessellations is verified by means of the Jaccard coefficient (J). Several packages are generated randomly and the distribution of J coefficients is investigated. The obtained values satisfy the theoretical restraints and the quality of the proposed algorithm is statistically validated.

Invited Article: Scalable high-sensitivity optomechanical magnetometers on a chip

The dual-resonant enhancement of mechanical and optical response in cavity optomechanical magnetometers enables precision sensing of magnetic fields. In previous working prototypes of such magnetometers, a cavity optomechanical system is functionalized by manually epoxy-bonding a grain of magnetostrictive material. While this approach allows proof-of-principle demonstrations, practical applications require more scalable and reproducible fabrication pathways. In this work, we developed a multiple-step method to scalably fabricate optomechanical magnetometers on a silicon chip, with reproducible performance across different devices. The key step is to develop a process to sputter coat a magnetostrictive film onto high quality toroidal microresonators, without degradation of the optical quality factor. A peak sensitivity of 585 pT/Hz is achieved, which is comparable with previously reported results using epoxy-bonding. Furthermore, we demonstrate that thermally annealing the sputtered film can improve the magnetometer sensitivity by a factor of 6.3.

Topology characteristics of three-dimensional grains in polycrystalline materials

The quantitative microstructural analysis in recrystallized pure iron is carried out by serial sectioning experiment coupled with three-dimensional (3-D) grain reconstruction technique. The full 3-D morphology of 16254 pure iron grains, which is the largest experimental 3-D grain dataset to date, is obtained. It is shown that the peak and the mean of the grain face number distribution were 10 and 13.5, respectively. For individual grains, the average trends that the highest and lowest face classes exhibited the highest affinity for mutual contact but the lowest affinity for contact with themselves are experimentally confirmed by 3-D pure iron grains. The pure iron grains are observed to have much more three-edged faces than Monte Carlo grains, resulting in relatively higher average dispersions of the grain edge distribution.

Interpretation of the Phase Functions Measured by the OSIRIS Instrument for Comet 67P/Churyumov–Gerasimenko

Abstract We show that the scattering phase functions of the coma and the nucleus of the comet 67P/Churyumov–Gerasimenko measured by the Rosetta/Optical, Spectroscopic, and Infrared Remote Imaging System (OSIRIS) instrument can be reproduced by a particle model involving clustered, densely packed submicrometer-sized grains composed of organic material and larger micrometer-sized silicate grains. The simulated and measured coma phase functions suggest that near the nucleus scattering is dominated by large particles, and the size distribution of dust particles varies with time and/or local coma environment. Further, we show that the measured nucleus phase function is consistent with the coma phase function by modeling a nucleus-sized object consisting of the same particles that explain the coma phase functions.

Enhancing the electrochemical performance of LiNi0.8Co0.15Al0.05O2 by a facile doping method: Spray-drying doping with liquid polyacrylonitrile

In this paper, a simple one-step doping spray method using liquid polyacrylonitrile (LPAN) is reported, for the preparation of LiNi0.8Co0.15Al0.05O2 (NCA) precursor, after calcination, to obtain a loose and porous sphere-shaped NCA (LPAN@NCA). The initial discharge specific capacity was found to be 227.9 mA h g−1 at 0.1C, which is 26.6% higher than that of the pristine sample. Its capacity retention rate was found to be 93.59% after 200 cycles, and the surface morphology of the material grains after the cycles remains intact. X-ray diffraction (XRD) analysis reveals that doping with LPAN can effectively decrease the amount of disorder of Ni2+ in Li + position that gets reduced by 2.72%. The X-ray photoelectron spectroscopy (XPS) analysis shows that after the carbonization of LPAN, the C atoms replace part of O atoms, effectively forming a new compound. The decrease in the impedance of the battery materials before and after the cycle and the increase of lithium ion mobility also confirms the effectiveness of LPAN doping. The LPAN@NCA prepared by in-situ doping of LPAN by spraying method is simple and effective, which exhibits high specific capacities, superior rate performance and excellent recycling stability, that has a good commercial application prospect.

Numerical mode matching for sound propagation in silencers with granular material

This work presents an efficient numerical approach based on the combination of the mode matching technique and the finite element method (FEM) to model the sound propagation in silencers containing granular material and to evaluate their acoustic performance through the computation of transmission loss ( TL ). The methodology takes into account the presence of three-dimensional (3D) waves and the corresponding higher order modes, while reducing the computational expenditure of a full 3D FEM calculation. First, the wavenumbers and transversal pressure modes associated with the silencer cross section are obtained by means of a two-dimensional FEM eigenvalue problem, which allows the consideration of arbitrary transversal geometries and material heterogeneities. The numerical approach considers the possibility of using different filling levels of granular material, giving rise to cross sections with abrupt changes of properties located not only in the usual central perforated passage, but also in the transition between air and material, that involves a significant change in porosity. After solving the eigenvalue problem, the acoustic fields (acoustic pressure and axial velocity) are coupled at geometric discontinuities between ducts through the compatibility conditions to obtain the complete solution of the wave equation and the acoustic performance ( TL ). The granular material is analysed as a potential alternative to the traditional dissipative silencers incorporating fibrous absorbent materials. Sound propagation in granular materials can be modelled through acoustic equivalent properties, such as complex and frequency dependent density and speed of sound. TL results computed by means of the numerical approach proposed here show good agreement with full 3D FEM calculations and experimental measurements. As expected, the numerical mode matching outperforms the computational expenditure of the full 3D FEM approach. Different configurations have been studied to determine the influence on the TL of several parameters such as the size of the material grains, the filling level of the chamber, the granular material porosity and the geometry of the silencer cross section. • Numerical mode matching is applied to sound waves in silencers with granular medium. • It allows efficient computation of geometries with arbitrary cross section. • TL curves show good agreement with full 3D FEM results and experimental measurements. • The acoustic influence of granular size and silencer cross section is analysed.

Computer Simulation of an Electrode of Lithium-Ion Battery: Estimation of Ohmic Losses for Active-Material Grains Covered by a Conducting Film

The use of active materials with high resistivity in lithium-ion batteries necessitates covering the surface of active particles with electron-conducting films. If this measure is insufficient, then carbon black is added to the electrode active layer. The ohmic losses are assessed by computer simulation of electrode’s active layers with active grains covered by a carbon film. Electrode’s active layer is modeled as a set of equal-sized cubic grains of the active material (covered with a conducting film) and the electrolyte; the grains are randomly distributed throughout the active layer. It is shown how the effective conductivity of the active layer decreases in this case. Furthermore, account is taken of the fact that carbon films represent a set of islets, which results in an additional decrease in the effective conductivity of the active layer. By computer simulations in combination with the percolation theory, it is found how the addition of carbon black can increase the conductivity of electrode’s active layer.

Evaluación de la erosión de riberas de ríos en regiones semiáridas mediante datos de teledetección y SIG: caso del río Rdat (Marrakech, Marruecos)

La erosión de riberas es el proceso de desprendimiento de los granos materiales que constituyen las orillas de los ríos bajo el efecto del agua. En regiones semiáridas, las inundaciones se caracterizan por su irregularidad. Este fenómeno tiene varios impactos ambientales en el ecosistema fluvial, por lo que es esencial realizar estudios al respecto. En este contexto, el propósito de este trabajo es proporcionar un enfoque sencillo que permita estimar las alturas de los bancos con el fin de evaluar la tasa de contribución de la erosión de riberas a la carga sedimentaria de los ríos durante los últimos 32 años y sus consecuencias en el sistema fluvial. La base de datos considerada son las imágenes Landsat de 1984 a 2016 y los datos de elevación ALOS PALSAR de la cuenca del Rdat, que se encuentra en el sureste de Marrakech en Marruecos, así como pruebas de campo. Estos datos se procesaron utilizando herramientas de teledetección y SIG y luego se combinaron para mejorar los resultados. Los resultados obtenidos muestran que la ribera de la cuenca del Rdat es, de forma significativa, inestable y contribuye al suministro de sedimentos al río, con una tasa de retroceso en la ribera de 5 m/yr y una tasa de erosión volumétrica anual de 286,82 m3/yr en promedio. Los sedimentos liberados en el río, cuando se erosionan desde las orillas, pueden ser el origen de sedimentos contaminados (fósforo, mercurio...), así como la causa principal del relleno del cauce del río.

Higher Temperatures Yield Smaller Grains in a Thermally Stable Phase-Transforming Nanocrystalline Alloy.

Grains in crystalline materials usually grow with increased thermal exposure. Classical phenomena such as recrystallization may lead to a purely temporary decrease in the grain size, while recent advances in alloy design can yield thermally stable nanocrystalline materials in which grain growth stagnates. But grains never shrink, since there is a lack of interface-generating mechanisms at high temperatures, which are required to decrease the grain size if such was the system's thermodynamic tendency. Here we sidestep this paradigm by designing a nanocrystalline alloy having an allotropic phase transformation-an interface-generating mechanism-such that only the high-temperature phase is stabilized against grain growth. We demonstrate that for an Fe-Au alloy cycled through the α↔γ transformation, the high-temperature phase (γ-Fe) has a stable fine grain size, smaller than its low-temperature counterpart (α-Fe). The result is an unusual material in which an increase in temperature leads to finer grains that are stable in size.

Three-dimensional X-ray diffraction imaging of dislocations in polycrystalline metals under tensile loading

The nucleation and propagation of dislocations is an ubiquitous process that accompanies the plastic deformation of materials. Consequently, following the first visualization of dislocations over 50 years ago with the advent of the first transmission electron microscopes, significant effort has been invested in tailoring material response through defect engineering and control. To accomplish this more effectively, the ability to identify and characterize defect structure and strain following external stimulus is vital. Here, using X-ray Bragg coherent diffraction imaging, we describe the first direct 3D X-ray imaging of the strain field surrounding a line defect within a grain of free-standing nanocrystalline material following tensile loading. By integrating the observed 3D structure into an atomistic model, we show that the measured strain field corresponds to a screw dislocation.

L10 ordered phase formation at solid state reactions in Cu/Au and Fe/Pd thin films

To understand the mechanism of mass transfer during solid state reactions and order-disorder transitions the formation processes of CuAuI and L10-FePd ordered structures at solid state reactions in Cu/Au и Fe/Pd bilayer thin films have been carried out using the method of in situ electron diffraction (ED). The value of the long-range order (LRO) parameter has been estimated for the L10 type ordered structures being formed; the order-disorder transition temperatures have been determined. The formation mechanism of the L10 type ordered structures formed at the initial stages of the solid state reaction in the Cu/Au and Fe/Pd thin films has been suggested. In the case of Cu/Au it has been shown that the interdiffusion of copper and gold at the initial stage of the solid state reaction results in the reduced size of the grains of the initial materials, as a result, nanocrystalites of the Cu-Au solid solution are formed, and further, grains of the CuAuI ordered solid solution appear and their growth begins.

Experimental investigation of the equilibrium scour depth below submerged pipes both in live-bed and clear-water regimes under the wave effect

Pipelines are the key structures to carry fluids such as oil, petroleum, gas and water; any inadequate design induces bottom stability problems causing unintended consequences. In the present study, the equilibrium scour depth below submerged pipes due to regular waves was investigated experimentally. During the experiments various pipe diameters, bed material grain sizes and wave characteristics were used. The novelty of the study is that the experiments were performed both in live-bed and clear-water regime conditions. The analysis of the experimental data showed that the equilibrium scour was correlated with Shields parameter as well as Keulegan-Carpenter number, especially for live-bed scour condition. However, in the case of clear-water scour, the Keulegan-Carpenter number was found as a unique non-dimensional parameter that dominates the scour phenomenon. New empirical relations were also proposed for clear-water and live-bed scour separately.

Microstructure Evolution and Properties of Friction Stir Welding Joint for 6082-T6 Aluminum Alloy

To investigate the evolution of grain morphologies, grain boundary features, and dislocation structure in upper part of nugget zone during friction stir welding of 6082-T6 aluminum alloys, electron backscattered diffraction and transmission electron microscope techniques were employed. The results showed that the metal on retreating side of the weld zone produced thermoplastic deformation during the welding process. The substructure of the lamellar dislocation wall formed at retreating side. Motivated by the welding thermal cycle, geometric dynamic recrystallization occurred in the substructure of the lamellar grains, leading to the lamellar array of grains. Discontinuous dynamic recrystallization occurred in the lamellar grain, leading the grain to be arranged in a necklace form. Simultaneously, the coarse grain of base material was refined. Due to the inhomogenous distribution of stress during the welding process, the alternating presence of large grain and small grain regions on advancing side took place. During the process of welding joint tensile, the fracture results from dislocation piling-up at the Mg2Si interface in large grains with a (111)[110] orientation. Thus, the advancing side becomes the weakest part of the mechanical properties in the welding joint,the tensile strength of the joint was 275MPa with a break elongation of 6%.

On the grain size proportionality constants calculated in M.I. Mendelson's “Average Grain Size in Polycrystalline Ceramics”

AbstractIn 1969, M.I. Mendelson published a paper in the Journal of the American Ceramic Society that introduced a proportionality constant of 1.558 for estimating the average 3D grain size from the mean 2D lineal intercept under the assumption of lognormally distributed grains. Recent simulations by the authors revealed that the lognormal parameterization in the original work actually calculates the median grain size instead of the mean. The relationship between the mean caliper diameter and mean lineal intercept was found to be 1.60 when using common parameterizations. In addition, it is demonstrated through simulations that the correct proportionality constant can range from 1.776 to below unity depending on a material's grain size dispersion, such that 1.60 should only be used as a crude approximation.

Mechanism of the Electromigration in Ag-Pd Alloy Bonding Wires

The failure mechanism of the electromigration in Ag-Pd bonding wires was investigated through stressing with a current density of 1.23 × 105 A/cm2 at temperatures of 150 °C to 300 °C. It was found that the grains of the wire materials grew rapidly during current stressing for 100 minutes at various temperatures. In contrast, the grain structure remained almost unchanged after storage at these temperatures for 100 minutes without current stressing. The mean-time-to-failure (MTF) for various current-stressed Ag-Pd alloy wires decreased with increases in Pd content. The activation energy for the electromigration of these wire materials was measured, and the results indicated that the main driving force was surface diffusion of Ag.

Microstructures evolution and localized properties variation of a thick friction stir welded CuCrZr alloy plate

The welding processing between large-dimension components is a big challenge for manufacturing in modern industry. In this work, a friction stir welding technology was employed to weld 30 mm thick CuCrZr alloy plates together with high strength and conductivity. The thermal histories and temperature distributions in the welded plate produced by friction stir welding (FSW) were simulated. The microstructural evolution and variation of properties in different regions around the weld line were investigated systematically. The results revealed that the large grains in the base material (BM) were transformed into a microstructure where the grains were completely equiaxed in the weld nugget zone (WNZ) induced by continuous dynamic recrystallization (CDRX), which can be attributed to the combination of severe deformation and high welding temperature. The significant changes to the heat gradient resulted in variations of prominent microstructures and properties in the structure from the top to the bottom layers in the WNZ. In the thickness direction, the exquiaxed grain size in the WNZ were decreased gradually while the hardness and strength were increased slightly. The large strength of the BM is due to the precipitation strengthening from the Cr precipitates even though the grain size is larger than that in the WNZ, while the large strength of the bottom layer is dominant because of the grain boundary strengthening.

Revealing the sequence of switching mechanisms in polycrystalline ferroelectric/ferroelastic materials

Ferroelectric materials find application in numerous electronic devices and are continuously enabling the development of new technologies. Their versatility is intimately related to the unique property to switch the polarization with electric fields. However, the switching mechanisms in polycrystalline ferroelectric materials remain insufficiently understood. Here we reveal that switching in ferroelectric/ferroelastic materials consists of a sequence of individual events, separated into three regimes: rapid movement of non-180° domain walls, main switching phase with 180° and non-180° switching events, and creep-like non-180° domain wall movement. The determination of the mechanisms was enabled by a novel measurement approach, simultaneously tracking the time dynamics of switched polarization, macroscopic strain, and structural changes. Time-resolved in situ synchrotron diffraction allowed direct insight into the non-180° domain wall dynamics and lattice strains and gave evidence for strong time correlation of non-180° switching events in different grains of the polycrystalline material. The obtained results open new opportunities for targeted manipulation of individual switching events and tuning of material's functional properties.

Pampaloite, AuSbTe, a new mineral from Pampalo gold mine, Finland

AbstractPampaloite, AuSbTe, is a new mineral discovered in the Pampalo gold mine, 65 km east of Joensuu, Finland. It forms anhedral grains (up to ~20 μm) intergrown with gold, frohbergite and altaite. Pampaloite is brittle and has a metallic lustre. Values of VHN25lie between 245 and 295 kg/mm2, with a mean value of 276 kg/mm2, corresponding to a Mohs hardness of ~4–5 (measured on synthetic material). In plane-polarised light, pampaloite is white with medium to strong bireflectance, weak reflectance pleochroism from slightly pinkish brown to slightly bluish white (only visible in grains of synthetic material containing multiple orientations), and strong anisotropy, with blue to light brown rotation tints; it exhibits no internal reflections. Reflectance values of pampaloite in air (R1,R2in %) are: 60.0, 62.5 at 470 nm, 62.5, 64.8 at 546 nm, 63.2, 65.6 at 589 nm and 63.7, 66.0 at 650 nm. Ten electron-microprobe analyses of natural pampaloite give an average composition: Au 44.13, Sb 27.44 and Te 28.74, total 100.31 wt.%, corresponding to the empirical formula Au1.00Sb1.00Te1.00based on 3 atoms; the average of eleven analyses on synthetic pampaloite is: Au 44.03, Sb 27.26, and Te 29.08, total 100.38 wt.%, corresponding to Au0.99Sb1.00Te1.01. The density, calculated on the basis of the empirical formula, is 9.33 g/cm3.The mineral is monoclinic, space groupC2/c, witha= 11.947(3),b= 4.481(1) Å,c= 12.335(3) Å, β = 105.83(2)°,V= 635.3(3) Å3andZ= 8. The crystal structure was solved and refined from the single-crystal X-ray-diffraction data of synthetic AuSbTe. The pampaloite crystal structure can be considered as a monoclinic derivative of the CdI2structure composed of [AuTe3Sb3] octahedra. The strongest lines in the powder X-ray diffraction pattern of synthetic pampaloite [din Å (I) (hkl)] are: 4.846(24)($\bar{2}$02), 3.825(18)(111), 2.978(100)($\bar{3}$11), 2.968(50)(004), 2.242(25)(020), 2.144(55)(313), 2.063(33)($\bar{3}$15) and 1.789(18)(024).