Microstructure Size Research Articles

Operando Ultrasonic Characterization of Lithium Metal Batteries

Significant progress has been made in understanding and engineering rechargeable lithium metal batteries. Here, I discuss ultrasound as a technique to probe cell-level dynamics for lithium metal batteries in liquid and solid electrolytes. Multiple imaging modalities provide information on physical properties of lithium metal cells, including electrode wetting and consumption, lithium microstructural change and gas evolution. In a first case study, I discuss correlations between ultrasonic transmission signals and lithium microstructure size in liquid electrolytes, as a function of stack pressure and temperature. Anode and cathode effects can be decoupled. In a second case, acoustic amplitude is used to detect void formation in solid-state electrolytes. Third, ultrasound is used to characterize the formation process for various anode-free cells, where the improved chemical and electrochemical stability of localized ether electrolytes is correlated with decreased rates of cell swelling and minimal gas formation. Ultrasonic characterization and imaging is a portable and non-invasive means of probing commercial lithium metal cells after manufacturing, during use, or at the end-of-service.

Solid-state sensor for direct and real-time assay of p-phenylenediamine in cosmetics and herbal products

p-Phenylenediamine (p-PDA) is a common ingredient in hair dyes, cosmetics and herbal products. The current study used graphene nanoparticles and phosphotungstic acid in a quality-by-design approach to develop and optimize a carbon-paste sensor for p-PDA. Twenty-three sensors with different compositions were tested, and the results were computationally analyzed to generate prediction models. The optimized sensor consisted of graphite, graphene, o-nitrophenyloctylether, and phosphotungstic acid in a 62.83: 4.01: 27.1: 5.34 (wt %) ratio. The optimized sensor displayed a Nernstian slope of 29.1±0.22 mV decade−1, a detection limit of 1.0×10−7 mol L−1, thermal and pH stabilities and a fast equilibration time of 10 s over ten weeks. The sensor accurately measured p-PDA concentrations within a wide linear range (1.0×10−7–1.0×10−3 mol L−1) with high sensitivity and selectivity (even over its isomers o- and m-phenylenediamine). The developed electrochemical method outperformed the commonly used high performance liquid chromatography methods in simplicity, speed, cost-effectiveness, linear range width and enabled real-time detection. The sensor's microstructure, morphology, and particle size were examined using the scanning electron microscope and energy-dispersive X-ray analysis. Spiked samples (3.60×10−3–10.8 % w/w) were analyzed for p-PDA content, including tea, henna, synthetic dye, black pepper, and cosmetics. The work provides quality control laboratories with a validated, fast, and reliable tool to support data-based decisions that can have important implications for health and safety.

Microstructural size effect on the notch fatigue behavior of a Ni-based superalloy using crystal plasticity modelling approach

Fatigue performances of critical structures are strongly affected by the microstructural (e.g. grain, defect, inclusion, etc.) size effect, and it is thus important to quantify their detrimental effect. In this work, a numerical procedure is constructed to quantify the influence of microstructure on the mechanical and fatigue behaviors of Ni-based superalloy GH4169. Specifically, by combining sub-modelling approach with crystal plasticity constitutive model, a dual-scale modelling approach is developed for studying grain-level mechanical behavior of Ni-based superalloy GH4169 notched components. In addition, the dislocation-based Tanaka-Mura-Wu model is applied for fatigue crack initiation life prediction. The Paris law is then utilized for fatigue crack propagation analysis based on the simulated short crack. To study the microstructural size effect on fatigue crack initiation and propagation behaviors, sub-models containing various grain orientation, grain size, defect size/shape are built and analysed. Finally, a series of fatigue tests on notched specimens of Ni-based superalloy GH4169 were carried out for method validation. Results indicate that the established dual-scale modelling approach and fatigue life prediction framework yields good agreement with experimental results.

Alkaline Hydrolysis of Waste Acrylic Fibers Using the Micro-Water Method and Its Application in Drilling Fluid Gel Systems.

Filtrate reducer is a drilling fluid additive that can effectively control the filtration loss of drilling fluid to ensure the safe and efficient exploitation of oilfields. It is the most widely used treatment agent in oilfields. Due to its moderate conditions and controllable procedure, alkaline hydrolysis of high-purity waste polyacrylonitrile has been utilized for decades to produce filtrate reducer on a large scale in oilfields. However, the issues of long hydrolysis time, high viscosity of semi-finished products, high drying cost, and tail gas pollution have constrained the development of the industry. In this study, low-purity waste acrylic fiber was first separated and purified using high-temperature hydroplastization, and the hydrolyzed product was obtained using alkaline hydrolysis with the micro-water method, which was called MW-HPAN. The hydrolysis reaction was characterized using X-ray diffraction, scanning electron microscopy, infrared spectroscopy, and thermogravimetric analysis, and the elemental analysis showed a hydrolysis degree of 73.21%. The experimental results showed that after aging at 180 °C for 16 h, the filtration volume of the freshwater base slurry with 0.30% dosage and 4% brine base slurry with 1.20% dosage was 12.7 mL and 18.5 mL, respectively. The microstructure and particle size analysis of the drilling fluid gel system showed that MW-HPAN could prevent the agglomeration of clay and maintain a reasonable particle size distribution even under the combined deteriorating effect of high temperature and inorganic cations, thus forming a dense filter cake and achieving a low filtrate volume of the drilling fluid gel system. Compared with similar commercially available products, MW-HPAN has better resistance to temperature and salt in drilling fluid gel systems, and the novel preparation method is promising to be extended to practical production.

Formation of nano-wire and ring-like microstructures in LC media via self-assembly of NiO quantum dots and investigation of their optoelectronic properties

Nickel oxide nano-dot wire and ring like structures were synthesized via self-assembly of nickel-oxide quantum dots in the presence of liquid crystal media. The sizes of the ring-like microstructures extend up-to a few tens of microns. After doping NiO QDs in 4-(trans-4-n-hexylcyclohexyl) isothiocyanatobenzoate (6CHBT), we characterize the LC and quantum dot hybrid system using optical microscopy, fluorescence, UV–vis-nir, FTIR, FESEM-EDX and Raman spectroscopy methods. The sizes of the synthesized NiO QDs are observed in the range of 5.38 nm–10.17 nm. Our FTIR data confirms for the purity as well as the nonbonding interactions of NiO NPs and LC molecules with each other. We have used theoretical models based on nanoscale principles to further validate our experimental findings. The predictive theoretical model match with the experimentally obtained particle size data and the corresponding band gap values for the case of spherical NiO nanoparticles very well. The band gap value of the hybrid system corresponds to spherical nanoparticle clusters of sizes 25 nm. This allows us to estimate the effective size of the nanoclusters of NiO QDs in the hybrid system. We have correlated the findings of fluorescence, Raman and optical microscopy to verify the formation of nanodot wires and nanodot-ring like microstructures in LC media. FESEM images further confirm for the formation of NiO nanodot-wire-like structures and presence of LC molecules anchoring over nano-dot hierarchical structures. Elemental analysis done using EDX, confirm for the presence of LC molecules and NiO.

Spontaneous nucleation of vortex–antivortex pairs in confined magnetic microstructures

Vortex–antivortex pairs have shown great potential in spintronics, where they can be used for information storage and logical devices. However, the physical mechanism for the nucleation of vortex–antivortex pairs is still unclear due to its metastability. We report on spontaneous nucleation of vortex–antivortex pairs in patterned Fe20Ni80 films (circular, square, hexagonal islands). By using a complex approach involving micromagnetic simulations, more in-depth understanding of vortex pair nucleation was achieved. A large amount of vortex–antivortex pairs appear in the as-grown magnetic film, which is the unstable high-energy state. Then, vortex and antivortex moves towards each other and annihilate, transforming magnetic structures and lowering the total energy of the system. With the decrease of sizes of microstructures, isolated vortex becomes stabilized due to confinement effect. These results provide a physical view for the nucleation of vortex–antivortex pairs and may be useful for design and optimization of magnetic microstructures for future spintronic applications.

Optimization of ultrasonic levitation bearing load characteristics based on rotor surface microstructure

Ultrasonic levitation bearings have lower load capacity and stiffness than other non-contact bearings, which restricts their practical use. This study proposes a method to improve the load characteristics of the bearings by adding microstructure on the rotor surface. The effects of different microstructure shapes, sizes, and quantities on the bearing load capacity and stiffness were investigated, and the mechanism of how the microstructures and their parameters affect the bearing static performance was revealed by analyzing the air film pressure field analysis of the bearing. Using the groove microstructure as an example, an optimization design was carried out to maximize the load capacity and stiffness of the ultrasonic levitation bearing, and the validity of this optimization was verified by the experiment.

Numerical simulation and experimental study of micro-structured surface of sapphire ground by structured grinding wheel

The efficiency and form accuracy of micro-structured surface preparation can be greatly improved by using structured wheels to grind micro-structured surfaces. In this study, the structural design of the grinding wheel surface was first carried out. Then, the geometric analysis of the designed structured 3D model of the grinding wheel is carried out to establish a numerical model for grinding micro-structured surfaces with structured grinding wheels and to investigate the effects of different velocity ratio, grinding depth and dressing angle on the size and distribution of surface microstructures. Finally, the surface of the grinding wheel is structured using wire electrical discharge machining (WEDM) technology, and the microgroove grinding experiment on the sapphire surface is carried out. The research results show that the established numerical simulation can accurately describe the formation mechanism of micro-structured surfaces ground by structured grinding wheels. At the same time, it is found that the shape of micro-grooves on the sapphire surface ground by the structured grinding wheel is basically complete. This further shows that the technology developed in this research can produce the micro-structured surfaces with good quality.

Effect of recrystallization annealing on microstructure and properties of cold-deformed CoCrCu1.2FeNi high entropy alloy

In this paper, CoCrCu1.2FeNi high entropy alloy (HEA) was prepared by vacuum suspension melting. After 50 % cold-deformation, recrystallization annealing experiments involving the annealing temperatures of 650–950 ℃ and the annealing times of 30–120 min were carried out on the cold-deformed HEA. The microstructure and properties of the alloy were compared before and after annealing. The results showed that with the extension of annealing time and temperature, the microstructure of the alloy was gradually uniform and coarsening occurred after spheroidization. In addition, fusion and engulfment occurred in the microstructure and the microstructure size decreased first and then increased. Both the fracture strength and fracture strain of the alloy increased first and then decreased. The alloy had the best compression performance at 850 ℃/60 min. Compared with the alloy after cold-deformation, the fracture strength was increased by 79.3 %, the fracture strain was increased by more than 1 time, and the comprehensive mechanical properties were the best at 750–850 ℃. The average hardness decreased with the increase of temperature and annealing time, and the initial recrystallization temperature of the alloy was determined to be about 650 ℃. The formation of annealing twins refined the microstructure and improved the properties of the alloy.

Hardening Behavior and Model of a 316L Sheet Considering Macro and Micro Size Effects

316L stainless steel is often used as the metal bipolar plate, which is a key component of fuel cells. For the thinner metal bipolar plates, the mechanical properties may be different for different specimen sizes. In this paper, the mechanical properties, metallographic structure, and hardening behavior of 316L stainless steel sheets with different grain sizes and specimen thickness were studied. Several mathematical models were selected to describe the hardening behavior of 316L stainless steel sheet. A correlated hardening model of 316L stainless steel was established, considering the specimen and grain size effect. The results show that the specimen thickness has no effect on the microstructure and grain size, but the austenite grain size increases gradually with an increase in holding time. With a decrease in plate thickness and an increase in grain size, the strength decreases. Compared to the 0.1 mm sheet, the yield strength and tensile strength for the 0.9 mm sheet are increased by 48% and 24%, respectively. The yield strength and tensile strength are decreased by nearly half after 20 min heat treatment due to the grain size growth. The thicker the sample and higher the grain size is, the higher the hardening rate is. The predicted stress–strain by established correlated hardening model has a good agreement with the experiment curves.

Thermal insulating and mechanical properties of high entropy pyrochlore oxide ceramic with hierarchical porous structures

High entropy pyrochlore oxide ceramics with hierarchical porous structures were prepared by coprecipitation, freeze-casting, and press-less sintering methods. In the fabrication process, a Ca2+-crosslinked alginate network was utilized to control the growth of ice crystals, resulting in uniformly dispersed micro-scale circular pores. The submicron pores were formed in the high entropy oxide ceramic during the press-less sintering method. The XRD was employed to explore the phase of the high entropy pyrochlore oxide ceramic. The porous structures of high-entropy ceramic were analyzed through the discussion of microstructure and pore size distribution. The tests show that the prepared series of ceramics with high porosity have optional compressive strength and thermal insulation properties. The high entropy oxide ceramic (La0.2Y0.2Gd0.2Sm0.2Nd0.2)2Zr2O7 with hierarchical porous structures possess moderate density (0.4 g/cm3) and low thermal conductivity (0.04 W m−1 K−1). The excellent comprehensive performance makes the porous high entropy oxide ceramic could be applied as a thermal insulating material.

Effect of N Content on the Microstructure and Impact Properties of Normalized Vanadium Micro-Alloyed P460NL1 Steel

In this work, the effect of nitrogen doping on vanadium micro-alloyed P460NL1 steel is studied in terms of microstructures and impact toughness. As the nitrogen content increased from 0.0036% to 0.0165%, the number of V (C,N) particles increased. The fine precipitates of V (C,N) effectively pin the prior austenite grain boundary, resulting in the refinement of the austenite grain. The intragranular and intergranular V-containing coarse particles enhanced the nucleation of intragranular ferrite and the grain boundaries of polygonal ferrite during air cooling. Accordingly, the proportion of heterogeneously nucleated ferrite increased, and the grain size of ferrite decreased. Notably, the size of the pearlite microstructure decreased, and the bainite microstructure appeared with a high doping of N. With the increase in N content, the impact toughness of vanadium micro-alloyed P460NL1 steel was enhanced. This can be attributed to the refinement of ferrite and the reduction in pearlite, which, in turn, was ascribed to the increase in nitrogen.

Processing of Carbon Nanoparticle-Enriched AISI H11 Tool Steel Powder Mixtures in DED-LB/M for the AM of Forging Tools with Tailored Properties (Part II): Influence of Nanoscale Carbon Additives on Microstructure and Mechanical Properties

A promising approach for producing parts with outstanding properties in directed energy deposition (DED-LB/M) provides the application of tailored powder mixtures processed by applying in situ alloying strategies. In this work, DED-LB/M was used to manufacture multilayer specimens from AISI H11 steel powders enriched with carbon nanoparticles (C-np) in concentrations of 0.1 wt.-% and 0.2 wt.-%. The scientific aim was to investigate the impact of C-np on the microstructural (particularly retained austenite content (RA-c) and grain size) and mechanical properties (specifically hardness and compression yield strength) of the manufactured specimens. It was shown that the addition of C-np to the H11 powder leads to a stronger distortion of martensite as well as significantly enhancing the RA-c. Furthermore, the C-np seem to favor the formation of finer martensite, as can be verified with XRD and EBSD. Under as-built conditions, the mean hardness increases from 653 ± 10 HV1 for the H11 sample to 770 ± 14 HV1 for the sample reinforced with 0.2 wt.-% C-np. At the same time, Y0.2% rises up from 1839 ± 61 MPa to 2134 ± 68 MPa. The hardness- and strength-increasing effect of the added C-np is retained even after heat treatment, similarly to the industrial standard.

Surface nano-crystallisation and mechanical properties of Ti[sbnd]Ta composite materials after surface mechanical grinding treatment

Surface mechanical milling generates gradient nano-structure surfacial layers that enhance the mechanical properties of titanium (Ti)–tantalum(Ta) composites for medical implants. Herein, the effect of surface mechanical grinding treatment (SMGT) on the surface nano-crystallisation of TiTa laminated composites was investigated in terms of micro-structure and Coherent Scattering Regions (CSRs) size using X-ray diffraction, scanning electron microscopy and transmission electron microscopy. A strengthening effect was verified using a micro-hardness tester and tensile testing machine, and the fracture mechanism was analysed through fracture observation. The experimental results showed that gradient nano-structures were formed on the surface of the TiTa laminated composites after SMGT, with the smallest CSRs size of the outer surface layer of approximately 13.3 ± 0.4 nm. The plastic deformation mechanism of the TiTa laminated composites during SMGT was a dislocation cutting mechanism. The micro-hardness and tensile strength of the TiTa laminated composites increased after SMGT up to 440 HV and 1097.528 MPa, respectively. The fracture mechanism of the TiTa laminated composites after SMGT was a combination of ductile fracture and quasi-cleavage fracture mechanisms. After SMGT, the TiTa laminated composite performed well and exhibited excellent potential for use in biomaterials.

Fabrication of Plasmonic Microcubes by Laser Ablation of Au‐Nanoparticles‐Loaded Acrylate

The fabrication of plasmonic 3D microstructures is still a challenge. In this study, the fabrication of gold‐nanoparticle (Au‐NP)‐filled acrylate‐based micron‐scale cuboids forming plasmonic 3D particles is investigated. UV curable acrylate is mixed with HAuCl4 and spin‐coated onto a fused silica wafer. UV light and heat treatment of the layer result in polymerization of the acrylate and formation of Au‐NPs with a plasmonic resonance ranging from 535 to 550 nm. The plasmonic resonance wavelength decreases slightly with increasing UV dose. The resonance wavelength can be shifted by a subsequent annealing process. The decreasing resonance wavelength with increasing annealing temperature is discussed as a result of the increasing Au‐NPs. The size and the distribution of the resulting gold particles in the acrylate matrix is investigated by transmission electron microscopy. The Au‐NPs‐filled acrylate layer is laser structured using a UV‐femtosecond laser, which allows the fabrication of adjustable micro‐cuboids with edge lengths down to 15 μm. The laser‐cut micro‐cuboids are transferred into isopropanol and the plasmonic properties of the structures in the liquid are successfully demonstrated. The presented concept allows easy and large‐scale fabrication of plasmonic microstructures with independently adjustable plasmonic properties and microstructural size and shape.

Strain rate effects on intact deep-sea sediments under different confining pressures and overconsolidation ratios

Underwater construction has gone to greater depths below the sea level for the extraction of resources such as oil and minerals. During different construction stages of deep-sea structures, different loading rates may be applied to deep-sea sediments. Generally, the strength of soil usually increases with the loading rate, and the sensitivity to strain rate effects may be more pronounced in deep-sea sediments. Previously, the strain rate effects were mainly studied on shallow marine deposits, but rarely on deep-sea sediments due to the difficulty of sampling. In this study, the strain rate effects on intact deep-sea sediments were investigated by a series of undrained triaxial tests with different strain rates of 0.5%/h, 2.6%/h and 13.2%/h under normally and over-consolidated conditions. In addition, scanning electron microscopy (SEM), nitrogen adsorption (NA) and mercury intrusion porosimetry (MIP) tests were conducted to illustrate the unique microstructure and pore size distributions of the deep-sea sediments, which showed a flocculent structure with abundant mesopores and macropores. It is found that higher strain rate leads to higher undrained shear strength due to the delay of increase of excess pore pressure as a result of low permeability. Strain rate effects are more obvious with the increase of confining pressure and then become less significant when the confining pressure is increased further. This change of trend is attributed to the increase of particle contact and more particle rearrangements when the confining pressure is first increased, but the particle rearrangement is suppressed under higher confining pressure. The sensitivity to strain rate effects increases with the overconsolidation ratio as more particle rearrangement is enabled under less confinement.

Multifield asymptotic homogenization for periodic materials in non-standard thermoelasticity

This article presents a multifield asymptotic homogenization scheme for the analysis of Bloch wave propagation in non-standard thermoelastic periodic materials, leveraging on the Green-Lindsay theory that accounts for two relaxation times. The procedure involves several steps. Firstly, an asymptotic expansion of the micro-fields is performed, considering the characteristic size of the microstructure. By utilizing the derived microscale field equations and asymptotic expansions, a series of recursive differential problems are solved within the repetitive unit cell Q. These problems are then expressed in terms of perturbation functions, which incorporate the material’s geometric, physical, and mechanical properties, as well as the microstructural heterogeneities. The down-scaling relation, which connects the microscopic and macroscopic fields along with their gradients through the perturbation functions, is then established in a consistent manner. Subsequently, the average field equations of infinite order are obtained by substituting the down-scaling relation into the microscale field equations. To solve these average field equations, an asymptotic expansion of the macroscopic fields is performed based on the microstructural size, resulting in a sequence of macroscopic recursive problems. To illustrate the methodology, a bi-phase layered material is introduced as an example. The dispersion curves obtained from the non-local homogenization scheme are compared with those generated from the Floquet-Bloch theory. This analysis helps validate the effectiveness and accuracy of the proposed approach in predicting the wave propagation behavior in the considered non-standard thermoelastic periodic materials.

Design strategy for high-entropy alloys with enhanced microstructural stability and mechanical properties for high-temperature applications

The use of AlCoCrFeNi high-entropy alloy as high-temperature structural materials is limited because of their phase instability. To address this, we designed Co-free Al–Cr–Fe–Ni alloys with spinodal structures composed of disordered body-centered cubic (BCC) (A2) and ordered BCC (B2) phases. The effect of Al and Ni content on the phase fractions and that of the Cr content on the microstructure and B2 precipitate size were evaluated. The composition of the alloy was optimized to enhance its microstructural stability and room-temperature machinability. Finally, Al13.6Cr(x)Fe(75.2-x)Ni11.2 alloys were designed and investigated for their phase stability and mechanical properties at both ambient and elevated temperatures. The fabricated Al13.6Cr(x)Fe(75.2-x)Ni11.2 alloys exhibited adequate phase stability at high temperatures. Particularly, as the Al13.6Cr13.3Fe61.9Ni11.2 (13Cr) alloy exhibited ductility of 1.3 % at 298 K, it can be a potential candidate as a high-temperature structural material. These findings suggest a promising design strategy for high-entropy alloys.

Study on the anticorrosion and antifouling performance of magnetically responsive self-healing polyurethane coatings

The dispersivity of self-healing microcapsules plays a critical role in the self-repairing properties of coatings. However, resolving the aggregation phenomenon of self-healing microcapsules has been challenging due to their high surface energy. In this paper, we successfully developed magnetically responsive self-healing microcapsule (MS-TO@CA) and polyurethane (PU) coatings with biomimetic interface wet-adhesion patterned microstructures and realized the adsorption, automatic capture and dispersion of MS-TO@CA based on different patterned microstructure sizes, microparticle sizes and contents. COMSOL software was used to simulate the magnetic field design and distribution, and the magnetization phenomenon of the microstructure was analyzed. The optimal process for the preparation of a new type of magnetically responsive self-healing PU coating was proposed. Compared with the control group, the corrosion time of the metal under the action of the coating was delayed by 816 h, and the antifouling performance was improved by approximately 30 times. This work has guiding significance for prolonging the service life of metals and improving metal anticorrosion and antifouling.

Lower-temperature sintered high energy density fine-grained sodium bismuth titanate - strontium bismuth titanate ceramics multilayer capacitors

The breakdown field strongly determines the energy density of energy-storage ceramic capacitors. In this work, a compound sintering aid of CuO and SiO2 was preferably selected to explore the effect on sintering behavior and energy storage of sodium bismuth titanate - strontium bismuth titanate (NBT-SBT) relaxor ferroelectrics. The optimum sintering temperature promotes a dense microstructure and fined-grain size in NBT-SBT, which contributes to an increase in breakdown strength. Meanwhile, the appropriate CuO/SiO2 ratio retains the advantages of the high polarization value of NBT-SBT. Specifically, when sintered at 1040 °C with 0.2 wt% SiO2 and 0.8 wt% CuO composite sintering aids, the NBT-SBT bulk ceramics achieved an energy storage density of 4.09 J/cm3 under a high electric field of 270 kV/cm. Owing to the lower sintering temperature, the NBT-SBT achieved co-firing with 30/70 Ag/Pd electrodes. Finally, multilayer ceramic capacitors with a recoverable energy density of 8.43 J/cm3 have been successfully fabricated.