Heterogeneous Materials Research Articles

Role of Metal-Organic Framework Topology on Thermodynamics of Polyoxometalate Encapsulation.

Polyoxometalates (POMs) are discrete anionic clusters whose rich redox properties, strong Bro̷nsted acidity, and high availability of active sites make them potent catalysts for oxidation reactions. Metal-organic frameworks (MOFs) have emerged as tunable, porous platforms to immobilize POMs, thus increasing their solution stability and catalytic activity. While POM@MOF composite materials have been widely used for a variety of applications, little is known about the thermodynamics of the encapsulation process. Here, we utilize an up-and-coming technique in the field of heterogeneous materials, isothermal titration calorimetry (ITC), to obtain full thermodynamic profiles (ΔH, ΔS, ΔG, and Ka) of POM binding. Six different 8-connected hexanuclear Zr-MOFs were investigated to determine the impact of MOF topology (csq, scu, and the) on POM encapsulation thermodynamics.

Modeling and evaluation of the fracture resistance of alkali-resistant glass fibre reinforced concrete under different loading rates

Alkali-resistant glass fibre reinforced concrete (AR-GFRC) has garnered significant interest due to its economic and environmental friendliness. Given the critical importance of evaluating the crack resistance of AR-GFRC under dynamic loading conditions and the size effect inherent in determined fracture parameters using traditional methods, this study aims to propose an analytical approach based on the boundary effect model. The goal is to predict the realistic dynamic tensile strength (ft) and fracture toughness (KIC) while elucidating the rate sensitivity of fracture resistance. Three-point bending tests were conducted on AR-GFRC with three different fibre volumes to investigate dynamic fracture behaviors under varying loading rates. By introducing discrete parameter and the microstructure characteristic parameter that account for material discontinuity and heterogeneity, the realistic dynamic ft and KIC of AR-GFRC can be directly obtained as closed-form solutions upon determining the maximum fracture load from the tests. The results revealed a substantial increase in ft and KIC with an improvement in the loading rate. However, due to relatively weakened fibre activities, the enhancement of dynamic fracture resistance decreases with the increase in fibre content and loading rate.

Identification of the Spallation Properties and Ultimate Spall Strength of Heterogeneous Materials in Dynamic Processes

Identification of the Spallation Properties and Ultimate Spall Strength of Heterogeneous Materials in Dynamic Processes

Two-scale finite element simulations for UT inspection of micro-structured materials in CIVA

Ultrasonic testing (UT) of highly heterogeneous structures is an important issue for many industrial applications in civil engineering for concrete inspection as well as in nuclear and oil & gas, where it applies to cast steels and weld joints. In these materials, performance is limited by the phenomenon of multiple wave scattering at the microstructure scale. In this context, the use of effective simulation tools is particularly useful both for improving interpretation of UT and for optimizing or demonstrating the performance of inspections. However, the scales of heterogeneity to be taken into account are often smaller than fractions of a tenth of a wavelength. In 3D simulations, it is therefore difficult, if not impossible, to combine computational performances with the refinement of the modelled interactions. To meet this challenge, CEA is developing an original approach based on two applications of the finite element (FE) method implemented in CIVA. The first application uses micro-scale heterogeneous material data on small representative elemental volumes (REVs) to feed a second code dedicated to macro-scale with effective medium characteristic. This second code relies on a high-order finite element model that is very efficient at the scale of the inspected industrial component. In this communication we present the main features of these FE tools and illustrate their performances on different application cases for welded parts and concrete

Sorption behavior of low specific activity 99Mo on Ti- and Zr-xerogels as an alternative to fission-based 99Mo/99mTc generators

Abstract In order to contribute to the sufficient supply of clinical 99mTc(VII), the sorption behavior of neutron-produced 99Mo(VI) was investigated on synthetized single and binary Ti and Zr xerogels treated at different temperatures, under normal operating conditions. Materials were prepared by the sol–gel method and characterized by several techniques. Sorption batch systems were performed using 99Mo radiotracer to determine the metallic affinity as a function of pH, and a methodology was developed in order to obtain the maximum capacities by surface saturation, where the Ti-388, TiZr-388 (3:1) and Zr-388 samples showed the most noteworthy sorption behaviors (33.1 ± 0.34 mg/g at pH ∼ 6.0, 31.7 ± 0.27 mg/g at pH ∼ 6.5, and 23.5 ± 0.61 mg/g at pH ∼ 6.8, respectively). The molybdenum-99 sorption behavior was also studied by fitting to the Freundlich and Langmuir models, and all xerogels could be described as heterogeneous materials with favorable 99Mo sorption properties. Finally, preliminary studies of clinical-scale 99Mo/99mTc generators were performed, the results revealed the next maximum 99mTc elution yield order Ti-388 (89.6 %) > TiZr-388 (3:1) (86.7 %) > Zr-388 (77.7 %).

Peridynamic simulation of micro-internal damage and macro-mechanical properties of cement paste under freeze-thaw cycles

Concrete is a multi-phase, multi-component, heterogeneous composite material and a typical porous medium with a complex microstructure. Under freeze-thaw cycles (FTCs), pressures from the freezing and migration of water within the pores of the concrete cause freeze-thaw damage, which is influenced by its microstructure. To effectively simulate and understand the freeze-thaw damage mechanism, it is crucial to use a geometric structure that reflects the actual pore distribution. This study employs the μic model to create a geometric structure of hardened cement paste, capturing the spatial distribution of pores. The study utilizes the peridynamics (PD) method based on ice formation and crystallization thermodynamics to investigate the freeze-thaw damage evolution and the deterioration of mechanical properties in cement paste under FTCs. The simulations revealed the entire freeze-thaw damage process of cement paste, including internal crack initiation and propagation, as well as surface freeze-thaw spalling. The freeze-thaw damage of cement paste intensifies with increasing FTCs, and the extension of cracks diminishes the interconnection among the skeletons constituting the cement paste microstructure, leading to decreased tensile strength and elastic modulus. Additionally, the stress-strain evolution behavior of freeze-thaw cement paste under uniaxial tensile loads was obtained. The tensile strength and elastic modulus of cement paste decrease with increasing FTCs, and the higher the water-cement (w/c) ratio, the greater the reduction in strength and modulus.

The property and mechanism of peroxymonosulfate activation boosted carbon cage encapsulated Mo2C/Bi2O2CO3 Z-scheme heterojunction for enhanced catalytic degradation and antibacterial activity

The regulation of heterogeneous material properties for the synergistic degradation of pollutants remains a challenge. Herein, cobalt-nitrogen co-doped carbon cage (NCC) encapsulated Mo2C nanoparticles boosting Bi2O2CO3 photocatalyst (Mo2C@NCC/BOC) we designed to achieve photoexcitation synergistic PMS activation. The degradation results revealed Mo2C@NCC/BOC could achieved 96.4 % tetracycline (TC) removal after only 5 min. The degradation rate was 3.1 times and 5.9 times higher than those of pure Bi2O2CO3 and pure Mo2C@NCC, respectively. The improved TC degradation performance could be attributed to the Z-scheme heterostructure, resulting in a higher conversion rate of photo-generated electrons into radicals. In addition, Co2+/Co3+ and Mo5+/Mo6+ dual ions redox cycle system effectively triggers the activation of HSO5− under visible light. The TC degradation pathways and intermediate toxicity, including the photocatalyticmechanism were evaluated in detail. This study provides novel perspectives on the rational design of atom co-sharing heterojunction photocatalysts in activating PMS for water remediation.

PINN enhanced extended multiscale finite element method for fast mechanical analysis of heterogeneous materials

PINN enhanced extended multiscale finite element method for fast mechanical analysis of heterogeneous materials

Mechanics of gradient nanostructured metals

The emergence of heterogeneous nanostructured materials (HNMs) offers exciting opportunities to achieve outstanding mechanical properties. Among these materials, gradient nanotwinned (GNT) Cu is a prominent class of HNMs, demonstrating superior strengths by gaining extra strengths compared to non-gradient counterparts. Its layered gradient structure provides a simplified quasi-one-dimensional model system for understanding the extra strengthening effects of structural gradients and resulting plastic strain gradients. This paper presents a comprehensive report for recent experimental and modeling studies on the mechanics of GNT Cu, covering advances in controlled material processing, back stress measurement, deformation field characterization, dislocation microstructure analysis, and strain gradient plasticity modeling. These studies unveil the spatiotemporal evolution of both plastic strain gradients and extra back stresses originating from structural gradients. Direct connections are established between the sample-level extra strength of GNT Cu and the synergistic strengthening effects induced by local nanotwin structures and their gradients. We emphasize the critical role of the size of the representative volume element in assessing the effects of plastic strain gradient and extra back stress. Moreover, lower-order strain gradient plasticity models are validated through experimental characterizations of GNT Cu, paving the way for future investigation into the mechanics of gradient nanostructured metals. Finally, we provide an outlook on research needs for understanding the mechanics of gradient nanostructured metals and, more broadly, HNMs, towards achieving exceptional mechanical properties.

Surface science insight note: Imaging X‐ray photoelectron spectroscopy

Quantification of X‐ray photoelectron spectroscopy (XPS) data is often limited by the heterogeneous nature of the material surface. However, it is often the case that heterogeneous material contains areas within the analyzed area that are effectively homogeneous. In this Insight note, concepts, and methods used to analyze both XPS data are presented to extract both spatial and spectral information from heterogeneous surfaces. These concepts and methods are applied to a specific material surface that contains three chemical compounds separated spatially. The analysis entails converting XPS image data to spectral data and is designed to highlight the potential of XPS imaging in revealing compositional information correlation with spatial information. Properties of algorithms used to evaluate XPS images and spectra are described to outline their application to image data. A case study of an imaging XPS data set is presented that demonstrates how poor signal‐to‐noise images, where the signal is recorded for 4 s per image, are still open to analysis yielding useful information. Ultimately, the methods presented here will aid in interpreting complex XPS data obtained from spatially complex materials often obtained during extensive cycling, such as conventional or electrocatalysts.

Structural concrete measurements: New distributed approach for standard specimens

Concrete structures are widely used in construction because of their many advantages, including high corrosion resistance, durability, low operating costs, and the ability to design any geometry. However, they also have some disadvantages, such as their high dead weight and susceptibility to cracking. Although this material is widely used globally, new types of concrete, such as high-strength or lightweight aggregate-based, are still being developed. This requires constant control and testing in both laboratory and field conditions. Concrete is a heterogeneous material due to the influence of aggregate grains and local discontinuities, voids or pores. Given these characteristics, it is clear that most conventional diagnostic solutions, such as spot foil strain gauges or extensometers, are unable to accurately analyse these localised effects as they average local strains over the measurement base. In contrast, distributed fibre optic sensing (DFOS) enables strain readings to be taken with millimetre geometric resolution, significantly extending the structural assessment capability. The article describes research on standard concrete cylinders equipped with surface-mounted optical fibres for simultaneous measurements of distributed strains in both the longitudinal direction (compression zone) and circumference direction (tension zone). The novelty of the proposed approach, apart from the way of arranging the sensing fibres on the specimens, lies mainly in the new diagnostic approach that allow (1) the evaluation of the homogeneity of the concrete using statistical parameters, (2) the identification of microcracking and (3) the identification of near-to-failure state based on Poisson’s ratio analysis. Twenty cylindrical specimens were laboratory tested using reference techniques to validate the performance of the DFOS-based system and to provide data for statistical evaluation. The results indicate the possibility of detecting the approaching damage even without knowledge of the material properties of the specimen or the initial stress level at the moment of starting the measurements. The discussion also covered future research directions and potential improvements.

Research on Macroscopic Mechanical Behavior of Recycled Aggregate Concrete Based on Mesoscale.

Recycled concrete is a heterogeneous composite material, and the composition and volume fraction of each phase affect its macroscopic properties. In this paper, ANSYS APDL was used to construct a two-dimensional numerical model of recycled aggregate concrete with different replacement rates of recycled aggregate (0%, 25%, 50%, 75% and 100%), and a uniaxial compression test was carried out to explore the relationship between recycled aggregate content and its macroscopic mechanical behavior. On this basis, the numerical simulation of different strain rates (0.1 s-1, 0.05 s-1, 0.01 s-1, 0.005 s-1 and 0.001 s-1) was carried out. It was found that with the increase in the recycled aggregate replacement rate, the peak stress decreases first and then increases, and the peak strain increases continuously. When the replacement rate of recycled aggregate exceeds 50%, the overall damage area of the material increases rapidly. The strain rate will change the path of the micro-crack initiation and expansion of recycled concrete, as well as the process of damage accumulation and evolution. As a result, the unit area and shape of recycled concrete are different at different strain rates, and the damage degree of each phase material is also different.

Modeling of surface evolution in plasma etching for SiC microgroove fabrication

Monocrystalline silicon carbide (SiC) has attracted attention for applications in devices operating in harsh environments due to its excellent physicochemical properties. However, it is difficult to obtain extremely small-feature sizes with undamaged surfaces due to its extremely high hardness. Herein, a novel method to fabricate SiC microgrooves is proposed that combines molding with inductively coupled plasma (ICP) etching process. First, a Ni–P microgroove master mold was fabricated by ultraprecision cutting and replicated on a polydimethylsiloxane (PDMS) surface, which was then used as the microgroove mold for hot embossing. Then, the patterned mask fabricated by hot embossing was transferred to the SiC substrate by ICP etching. To obtain customized microgrooves, an interface-evolution model based on angular dependence theory was established. A numerical method based on a string algorithm approach is developed for interface-evolution simulations. During ICP etching, the characteristic size d of homogeneous materials and the sidewall angle in heterogeneous materials varied with the sidewall angle of the SU-8 mask due to the angular dependence of etch rate. Finally, seven sets of microgrooves were machined on SU-8 to study the interface-evolution process. Variations in the characteristic size Δd and sidewall angle θ for each unit in homogeneous material, as well as the variations in sidewall angle before and after etching in heterogeneous materials are described. The high accuracy of the proposed interface-evolution model was experimentally validated.

Investigations of the specific heat capacity of selected heterogeneous materials

Investigations of the specific heat capacity of selected heterogeneous materials

Structure heterogeneity in polycrystalline and single-crystal high-nickel cathode materials by synchrotron radiation XAS

Structure heterogeneity in polycrystalline and single-crystal high-nickel cathode materials by synchrotron radiation XAS

ON THE QUESTION OF THE COEXISTENCE OF NICKEL AND COBALT SPINEL

For the development of composite materials based on alumina and high-alumina cements using resource-saving technology when replacing the original raw materials with substandard raw materials and chemical wastes, there is a need for a physical and chemical substantiation of the coexistence of newly formed phases in the composition of the binder, which necessitated the study of the subsolidus structure of the system. The paper presents the results of calculations characterising the elements of the subsolidus structure of the CoO - NiO - Al2O3 system. The results of the study revealed the predominance of solid-phase exchange reactions and determined the structure of the CoO - NiO - Al2O3 system in the subsolidus region. It was found that the sub-solidus structure of the system is simple and consists of three elementary triangles. The analysis of the area of the elementary triangles and the low degree of asymmetry indicate that there are no significant risks of deviation from the specified phase composition of the synthesised materials due to the preparatory technological stages, and no special measures are required during the synthesis of materials to ensure the accuracy of the dosage of the starting ingredients. Based on the results of the calculations, the most thermodynamically stable compound in the studied system (aluminocobalt spinel) was identified, and the maximum probability of its existence was determined. Aluminium-nickel spinel has a lower probability of existence because it does not coexist with CoO and is not represented in the elementary triangle with the maximum area. Aluminium-nickel spinel has a lower probability of existence, and the least likely is the identification of Al2O3 in the composition of heterophase combinations. Based on the results of the study, the geometric-topological and statistical characteristics of the subsolidus structure of the system were analysed, which are important for the accuracy of predicting phase combinations in the synthesis of new heterogeneous composite materials.

3D imaging of magnetic domains in Nd2Fe14B using scanning hard X-ray nanotomography.

Nanoscale structural and electronic heterogeneities are prevalent in condensed matter physics. Investigating these heterogeneities in 3D has become an important task for understanding material properties. To provide a tool to unravel the connection between nanoscale heterogeneity and macroscopic emergent properties in magnetic materials, scanning transmission X-ray microscopy (STXM) is combined with X-ray magnetic circular dichroism. A vector tomography algorithm has been developed to reconstruct the full 3D magnetic vector field without any prior noise assumptions or knowledge about the sample. Two tomographic scans around the vertical axis are acquired on single-crystalline Nd2Fe14B pillars tilted at two different angles, with 2D STXM projections recorded using a focused 120 nm X-ray beam with left and right circular polarization. Image alignment and iterative registration have been implemented based on the 2D STXM projections for the two tilts. Dichroic projections obtained from difference images are used for the tomographic reconstruction to obtain the 3D magnetization distribution at the nanoscale.

Seismic analysis of gravity dam-foundation systems using stochastic spectral finite element method

Seismic analysis of dam-foundation systems is inherently complex due to uncertainties in material properties. This study investigates the effects of material randomness and heterogeneity on the seismic response of gravity dam-foundation systems using the stochastic spectral finite element method (SSFEM) based on the Karhunen Loève expansion and the polynomial chaos expansion. The Pine Plane dam is taken as an analysis example. First, the appropriate Karhunen Loève expansion modes and polynomial chaos order are determined for SSFEM by comparing them with the Monte-Carlo simulations. Subsequently, the seismic response of the dam is analyzed in the stochastic and deterministic models, respectively. Results indicate that material randomness and heterogeneity may reduce the seismic response of gravity dams, and the deterministic model may overestimate dynamic responses. Subsequently, the parametric analysis of the correlation length, which measures the spatial correlation between variables in different positions and indicates the size of heterogeneity material patches, is conducted. It is demonstrated that the correlation length would not significantly affect the mean responses, but a larger correlation length leads to greater dispersions in responses. Finally, the effects of randomness in the foundation are investigated. The heterogeneities in the foundation affect the response of the dam in the high-frequency range. Therefore, the uncertainty in material properties should be fully considered in a structural assessment and risk analysis.

Experimental and mesoscopic simulation study of size effect on splitting tensile performance of spontaneous combustion coal gangue concrete

The spontaneous-combustion coal gangue concrete (SCGAC) demonstrates different mechanical behavior compared to ordinary concrete owing to its distinct porous structure and the presence of fibrous materials in its coarse aggregates. Presently, research on the macroscopic mechanical properties of SCGAC is reasonably comprehensive; however, it falls short of fully understanding its size effect. This study examines the splitting tensile strength of cubic SCGAC specimens with three strength grades, i.e., C30, C35, and C40, and three sizes, i.e., 100 mm, 150 mm, and 200 mm; proposes a mesoscopic modeling approach based on the computer vision; analyzes the intrinsic mechanisms of splitting failure and the size effect of different strength grades on the SCGAC by utilizing mesoscopic simulation methods. Subsequently, an analysis of the size effect on the splitting tensile strength of SCGAC is conducted based on classical size effect laws. The results reveal the following: The method proposed in this study for mesoscopic modeling is recognized for its low cost, high efficiency, and accurate simulations, fulfilling the required standards for mesoscopic mechanical analysis. SCGAC, as a heterogeneous material, demonstrates significant size effect phenomena that become more pronounced with enhancements in strength grades. The Carpinter fractal size effect law is ideally suited to characterize the size effect patterns in SCGAC. This paper enhances the comprehension of the size effect of SCGAC through a combination of macroscopic experiments and mesoscopic simulations, thereby facilitating its engineering applications.

Enhanced Fenton performance of wet-mechanochemically synthesized FeS2/Biochar: The multiple synergistic effect derived from mutual element doping

FeS2-biochar composites have been considered as promising heterogeneous Fenton materials for pollutants removal. However, the chemical synthesis of element-doped FeS2-biochar composite with superior performance and the comprehensive investigation for its underlying multiple synergistic mechanism remain a difficult endeavor. Herein, a novel FeS2/Biochar nanocomposite with mutual element doping was firstly synthesized by facile wet-mechanochemical method using iron, sulfur and bamboo-biochar for efficient organic pollutant (sulfamonomethoxine, SMM) removal. Experiment and DFT calculation results revealed that multiple synergistic effect between FeS2 and biochar derived from newly formed Fe-C and C-S-C bonds induced the abundant reactive oxygen species (ROS) and excellent electron transfer capacity. Fe-C sites facilitated the H2O2 adsorption and populated O-O bond in H2O2 for its barrierless dissociation into •OH via forming bridging C-Fe-O-O-Fe bond. Oxygen vacancy, C-S-C and Fe-C bonds, persistent free radicals (PFRs) accelerated the generation and transformation of ROS, which resulted in dominating free radical (•OH, •O2–, •SO4-) and auxiliary non-radical (1O2) pathway. Meanwhile, Fe3+/Fe2+ redox-cycle was expedited by electron donor/shuttle (S22-, BC, •O2–, C-S-C and Fe-C bonds). All these specialties contributed to the superior performance of FeS2/Biochar Fenton system for SMM removal at wide pH range (3–11) with negligible Fe release. Completely SMM (50 mg/L) removal was achieved within 20 min for 8 successive reuses. This work emphasized the concept of building mutual element doping on molecular level in enhancing FeS2-Biochar synergy towards efficient environmental remediation.