Defects In Matrix Research Articles

Simulating changes of packing structures, locally loading states and mechanical behaviors for Si lattices with double vacancies at elevated temperatures

The vacancy defects in silicon matrix have important influences on processing or manufacturing novel microelectronic devices as well as their performances related to structures and mechanical properties. Molecular dynamics simulations were performed for the evolution of the atomic packing structures and locally loading states as well as tensile tests for silicon matrixes having three types of double vacancies at atomic scale. Through analysis from Young's modulus, Poisson's ratios, Lode-Nadai parameters and atomic strain energy density as well as visually packing images, the simulation results show that there exists just one type of adjacent vacancies at room temperature, and the external energy provided from high temperature results in vacancy's migration. On heating, the matrixes having vacancies present apparent different stages from elasticity to plasticity, and their temperature regimes are identified. Under applying uniaxial tension at room temperature, the strain energy density of the matrix near the vacancies is significantly higher than those in the other regions in the elasticity stage. There are differences of the elongation and tensile strength of the matrixes having different types of vacancies.

Influence of multi-walled carbon nanotubes in polytetrafluoroethylene on the parameters of electronic structure and absorption of ultra-high-frequency radiation

Using the methods of angular correlation of annihilation radiation (ACAR), attenuation of electromagnetic radiation in 1.5–2.2 GHz frequency range, and optical ellipsometry, it was shown that in composites of polytetrafluoroethylene (PTFE) + multi-walled carbon nanotubes (MWCNTs), a 2% decrease in the probability of annihilation of positrons in free volumes in PTFE leads to changes in other parameters of electronic structure of composites by 8–29%. Polytetrafluoroethylene is transparent to electromagnetic radiation, but after the addition of 10 wt.% or more of MWCNTs, the composites demonstrate 200–410-fold decrease in the electromagnetic radiation intensity when the radiation passes through a specimen with a thickness of ≈2 mm. It was found that the average radius of the free volumes and the probability of annihilation of positrons are determined by the defect and electronic structures of the polymer matrix only. The Fermi angle and the probability of positrons annihilation with free electrons are determined by the analogous structures of MWCNTs only. Since the electronic characteristics of the atoms and defects in the polymer matrix (at least outside the interphase) do not change, the changes in the other ACAR parameters are mainly due to changes in the imperfect MWCNTs’ atomic and electronic structures. The average radius of free volumes reaches its maximum value in the composite with 10 wt.% MWCNTs. It was found that in a specimen with 10 wt.% MWCNTs, the highest density of free electrons is observed due to charge transfer from free volumes to MWCNTs, and the highest electron density is observed on defects. A disorder of MWCNTs and their branched conductive network can form the ‘tails’ of electronic density of states in a band gap. Thus, composite with 10 wt.% MWCNTs has the highest absorption coefficient for electromagnetic radiation.

Dopant–free edge–rich mesoporous carbon: Understanding the role of intrinsic carbon defects towards oxygen reduction reaction

• E–MC–1000 can be fabricated by a facile template–induced pyrolytic strategy. • E–MC–1000 possesses abundant intrinsic carbon defects. • Increasing pyrolytic temperature leads to decreased intrinsic carbon defects. • E–MC–1000 exhibits much better ORR performance than the counterparts. Except heteroatoms doping, intrinsic defects in carbon matrix exert a profound influence on the performance of carbon–based electrocatalysts, but the relevant understanding is limited. Herein, a template–induced pyrolytic strategy is proposed to prepare dopant–free edge–rich mesoporous carbon (E–MC–1000, 1000 represents pyrolytic temperature). The obtained E–MC–1000 with short–range ordered bent graphene–like nanosheets possesses abundant intrinsic carbon defects (including edge defects and sp 3 –type carbon), thus displaying favorable oxygen reduction reaction (ORR) performance. Obviously, our finding is valuable to understanding the role of intrinsic carbon defects towards ORR.

Synergistically Promoting Coking Resistance of a La0.4Sr0.4Ti0.85Ni0.15O3-δ Anode by Ru-Doping-Induced Active Twin Defects and Highly Dispersed Ni Nanoparticles.

The development of anodes with highly efficient electrochemical catalysis and good durability is crucial for solid oxide fuel cells (SOFCs). This paper reports a superior Ru-doped La0.4Sr0.4Ti0.85Ni0.15O3-δ (L0.4STN) anode material with excellent catalytic activity and good stability. The doping of Ru can inhibit the agglomeration of in situ-exsolved Ni nanoparticles on the surface and induce the formation of abundant multiple-twinned defects in the perovskite matrix, which significantly increase the concentration of oxygen vacancies. The reduced L0.4STRN (R-L0.4STRN) anode shows an area-specific resistance (ASR) of 0.067 Ω cm2 at 800 °C, which is only about one-third of that of stochiometric R-L0.6STN (0.212 Ω cm2). A single cell with the R-L0.4STRN anode shows excellent stability (∼50 h at 650 °C) in both H2 and CH4. Furthermore, R-L0.4STRN exhibits outstanding resistance to carbon deposition, which can be attributed to the synergistic effect of highly dispersed Ni nanoparticles and active twinned defects induced by Ru doping.

Local stress within a granular molecular solvent matrix, a mechanism for individual ion hydration

• Individual ion hydration values are estimated from a matrix of full hydration values for complete salts. • Ionic volume relative to the volume of water shown to dictate hydration requirements. • Solutes may conceptually behave as substitutional defects in a water matrix, inducing tensile or compressive stresses. • This model may advance the understanding of solute activity, ion diffusion, solution viscosity, and the Hofmeister series. The activity of water is important in many natural systems and directed processes. To better understand water activity, the hydration of individual ions is approximated for a recently developed speciation-based solution model. A matrix of values for hydration of complete salts (anion and cation) was used as source data to calculate individual ion hydration values. Some electrolytes were excluded from calculations of individual ion hydration due to the prevalence of ion pairing and resulting liberation of water upon ion pairing. Evaluation of the periodic trends emerging from individual ion hydration values suggests that ionic volume, relative to the volume of molecular water, dictates both modeled hydration requirements (related to vapor–liquid-equilibrium-derived activity) as well as properties historically described by hydrodynamic radius (ion diffusion and solution viscosity). When water is conceptualized as a granular three-dimensional matrix, solutes may function as substitutional defects (dilation or constriction) inducing local compressive or tensile stress. These results have implications on the mechanism of the Hofmeister series and series reversals.

Ultrafast regulation of nano-scale matrix defects using electrical property discrepancies to delay material embrittlement

Nano-scale phases can enhance or reduce the mechanical properties of materials, so it is very important to control the size of the phases. Copper-rich nanoclusters as matrix defects will significantly reduce the performance of materials for key nuclear power components, while traditional heat treatment method has a technical bottleneck for the dissolution of nanoclusters. A new method of using the inherent electrical property discrepancies between the matrix material and the nanoclusters to effectively dissolve the nanoclusters through pulsed electric current to realize the recovery of material aging degradation performance is proposed. The performance evolution of simulated steel in the aging-external field repair cycle was studied, and it was found the dislocations as the preferred nucleation sites of nanoclusters were regulated in virtue of the non-thermal effect of current, resulting in a decrease in dislocation density and entanglement release. In the subsequent thermal aging process, the embrittlement rate of the aged and tempered material trained by the electric pulse was slower than that of the untreated sample. When moving dislocations are pinned by nanoclusters under high stress, nano-scale dislocations can be induced into the clusters. The dislocations near the nanoclusters and the newly formed nano-scale dislocations in the nanoclusters act as fast diffusion channels, which can further accelerate the dissolution of the nanoclusters.

Emerging roles of oxidative stress in the pathogenesis of pseudoexfoliation syndrome (Review).

Pseudoexfoliation syndrome (PEXS) is a systemic disease caused by defects in the extracellular matrix (ECM) remodelling process leading to the chronic deposition of extracellular, fibrillary, white flaky pseudoexfoliation material (PEXM) throughout the body. Specifically, PEXM deposits on the lens capsule cause open-angle glaucoma, cataracts and blindness in patients with PEXS. Several gene single nucleotide polymorphisms are linked to the development of PEXS in humans, including lysyl oxidase-like 1 gene, clusterin and fibulin-5. The exact reason for the PEXM generation and its resulting pathogenesis is not well understood. However, defective ECM remodelling and oxidative stress (OS) have been hypothesized as significant events leading to the PEXM. Specifically, the link between OS and PEXS has been well studied, although the investigation is still ongoing. The present review explored recent advances in various aspects of PEXS and the involvement of OS in the eye for PEXS development.

Toughen and strengthen alginate fiber by incorporation of polyethylene glycol grafted cellulose nanocrystals

Excellent strength regenerated alginate composite fibers mixed with Poly (ethylene glycol) grafted cellulose nanocrystals (CNC-g-PEG) were prepared through a simple and scalable blending strategy. Firstly, high modulus cellulose nanocrystals (CNCs) were fabricated based on waste cotton fabrics by the chemical treatment. Poly (ethylene glycol) (PEG) with different molecular weight was grafted onto the CNC surface. The composite fibers were prepared from CNC-g-PEG/sodium alginate spinning dope by wet spinning. The CNC-g-PEG/Alginate fibers were characterized using FTIR, XRD, scanning electron microscopy, and mechanical testing. The morphology of the SEM image showed that CNC-g-PEG partially eliminated the defects of the alginate matrix and increased the roughness of the fracture cross-section, constructing material with a denser microstructure. Under the same load, the addition of CNC-g-PEG has better effects on the mechanical properties of alginate fibers than CNCs. The maximum strength and elongation at the break for alginate composite fibers were increased by 56.3% and 81.6% as a result of the CNC-g-PEG reinforcement, respectively. Besides, the salt tolerance and antibacterial activity of the CNC-g-PEG/Alginate composite fibers were improved as the molecular weight of PEG increased. This study provides the possibility for the development of high-performance, green alginate fibers.Graphical abstract

Direct Observation of Cu Clusters and Dislocation Loops by Cs-Corrected STEM in Fe-0.6wt%Cu Alloy Irradiated in BR2

The neutron irradiation of Fe-based fusion and fission reactor materials leads to an increase in ductile-to-brittle transition temperature with a decrease in upper shelf energy. It is well known that Cu content has a strong influence on the embrittlement phenomenon, as Cu-rich clusters (CRPs) are thought to be directly responsible for embrittlement. In contrast, mechanical property studies for steels with different Cu levels exhibit dominant matrix defects in the embrittlement of both low-Cu steels and high-Cu steels at high fluences. To determine the effects of dislocation loops and CRPs on radiation hardening in those steels, neutron irradiation was conducted on Fe-0.6wt%Cu alloy. The neutron irradiation was performed in BR2 at 290 °C up to a dose of 4.1 × 1024 n/m2. After irradiation, the microstructure was observed and analyzed by spherical aberration-corrected transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) combined with X-ray energy-dispersive spectroscopy, using a JEOL ARM200FC. This technique enabled simultaneous observation of ~10 nm CRPs and dislocation loops. Additional high-voltage electron irradiation was performed at room temperature, and the dislocation loops were identified as interstitial-type dislocation loops. Radiation-induced hardening due to neutron irradiation was estimated by measuring the size and density of the dislocation loops and the CRPs. These results suggest that simultaneous observation of dislocation loops and CRPs using the Cs-corrected STEM with EDS analysis is essential for the study of radiation-induced hardening in Fe-based alloys.

Stabilizing photo-induced vacancy defects in MOF matrix for high-performance SERS detection

Stabilizing photo-induced vacancy defects in MOF matrix for high-performance SERS detection

Carbon driven oxygen retention in uranium oxycarbide (UCO) fluorite phase

The behavior of oxygen in uranium oxycarbide (UCO) has been investigated using density functional theory. To assess the role of carbon on the stability of oxygen point defects, we first determined the formation energies of oxygen vacancy and interstitial for different carbon configurations. Subsequently, we evaluated the barriers for migration of various oxygen defects in the UCO matrix. Our results show that carbon atoms create strong attraction centers for oxygen atoms, as a consequence the spontaneous formation of oxygen Frenkel pairs in the fluorite structure is promoted. Moreover, the strong affinity of oxygen atoms for sites in the first coordination shell of a carbon center leads to the formation of CO, and thus reducing the mobility of oxygen atoms in the UCO fuel. Upon formation, the CO remains fixed at the carbon site due to significant hybridization with uranium atoms, therefore behaving as trap sites for oxygen atoms. Our findings indicate that the formation of CO molecules increases the retention of oxygen atoms inside the UCO matrix. Consequently, carbon atoms in the UCO matrix contribute to mitigating the deleterious effects that oxygen release from the fuel kernel has on the structural integrity of the silicon carbide layer in tristructural isotropic (TRISO) particles.

Vapor/gas separation through carbon molecular sieve membranes: Experimental and theoretical investigation

The separation of H2O vapor from (hydrogen-rich) gaseous streams is a topic of increasing interest in the context of CO2 valorisation, where the in situ water removal increases product yield and catalyst stability. In this work, composite alumina carbon molecular sieve membranes (Al-CMSM) were prepared from phenolic resin solutions loaded with hydrophilic boehmite (γ-AlO(OH)) nanosheets (0.4–1.4 wt. % in solution) which partially transform to γ-Al2O3 nanosheets upon thermal decomposition of the resin, improving the hydrophilicity and thus the adsorption-diffusion contribution of the H2O permeation. The γ-Al2O3 nanosheets showed no influence on the pore size distribution of the membranes in the range of micropores, but they increased the membrane hydrophilicity. In addition, the use of boehmite in the resin solution causes an increase in the viscosity and thus an increase in the carbon layers thickness deposited on the porous α-Al2O3 support (from 1 to 3.3 μm). Furthermore, the alumina sheets introduce defects in the carbon matrix, increasing the tortuosity of the active layer, as concluded via phenomenological modelling and parametric fitting of the experimental results. As a consequence, the water permeability exhibits a maximum (1.3ꞏ10−6 molꞏs−1 Pa−1 m−1 at 150 °C) with boehmite/alumina content of ca. 0.8 wt. %, as the combined effects of increasing hydrophilicity (which favour H2O permeability) and increasing thickness and tortuosity (which hamper permeability) upon increasing boehmite loading. Similarly, the H2O/gas perm-selectivity is optimum at 1.2 wt. % boehmite loading. We further investigated the H2O permeation mechanism by modelling the mono- and multi-layer adsorption and capillary condensation of water in microporous media, which result as the main transport mechanisms in the explored conditions.

A DMA-Based Approach to Quality Evaluation of Digitally Manufactured Continuous Fiber-Reinforced Composites from Thermoplastic Commingled Tow

Direct digital manufacturing of continuous fiber-reinforced thermoplastics exhibits the potential to relieve many of the constraints placed on the current design and manufacture of composite structures. At present, the additive manufacturing of continuous fiber-reinforced thermoplastics is demonstrated to varying extents; however, a comprehensive investigation of manufacturing defects and the quality of additively manufactured high fiber volume fraction continuous fiber-reinforced thermoplastic composites is limited. Considering the preliminary nature of the additive manufacturing of continuous fiber-reinforced thermoplastics, composites processed in this manner are typically subject to various manufacturing defects, including excessive void content in the thermoplastic matrix. Generally, quality evaluation of processed composites in the literature is limited to test methods that are largely influenced by the properties of the continuous fiber reinforcement, and as such, defects in the thermoplastic matrix are usually less impactful on the results and are often overlooked. Hardware to facilitate the direct digital manufacturing of continuous fiber-reinforced thermoplastic matrix composites was developed, and specimens were successfully processed with intentionally varied void content. The quality of the additively manufactured specimens was then evaluated in terms of the measured maximum storage modulus, maximum loss modulus, damping factor and the glass transition temperature by means of dynamic mechanical analysis (DMA). DMA allows for thermomechanical (i.e., highly matrix sensitive) evaluation of the composite specimens, specifically in terms of the measured elastic storage modulus, viscous loss modulus, damping factor and the glass transition temperature. Within the tested range of void contents from roughly 4–10%, evaluation by DMA resulted in a distinct reduction in the maximum measured storage modulus, maximum loss modulus and glass transition temperature with increasing void content, while the damping factor increased. Thus, the results of this work, which focused on the effect of void content on DMA measured properties, have demonstrated that DMA exhibits multi-faceted sensitivity to the presence of voids in the additively manufactured continuous fiber-reinforced thermoplastic specimens.

Post-irradiation annealing of high flux irradiated and surveillance material reactor pressure vessel weld metal

In this study, high flux irradiated and surveillance high Ni and Mn and low Cu welds identical to those of the belt-line region of Ringhals R4 were subjected to annealing at temperatures between 390 and 455 °C for 24–30 h, in order to study the dissolution of irradiation induced clusters and possible matrix defects using hardness testing and atom probe tomography. It was found that the cluster characteristics did not change during annealing at 390 °C, meaning that the size, number density and composition of the clusters, which mainly consist of Ni and Mn, did not change. Thus, the observed decrease in hardness during annealing of the high flux irradiated material is believed to be due to dissolution of matrix defects that were stable at the operating temperature. Cluster dissolution was observed after annealing at 410 °C in the high flux irradiated material, leaving around 10% of the original clusters. These clusters contained more Cu and less Ni and Mn than before annealing. The cluster dissolution at temperatures above 400 °C correlated with the decrease in hardness. The larger clusters of the surveillance material required a higher temperature or longer time to be dissolved compared to the clusters of the high flux material.

Characterization of Eu doped ZnO micropods prepared by chemical bath deposition on p-Si substrate

The chemical bath deposition method was used to synthesize Eu-doped ZnO on p-type (100) silicon. The SEM image shows the formation of micropod-like ZnO. EDX and XPS measurements showed an increase in the Eu concentration up to 2.54% and the simultaneous presence of Eu3+ and Eu2+. XRD analysis confirmed that the interstitial Eu3+ ions distorted the four tetrahedral bonds, and the substitution of Eu2+ ions increased the c lattice parameter. Only Eu3+5D0→7F2 transition-related emission was observed, so a weak transfer energy from the ZnO matrix to the Eu ion occurred. However, the competition between the emission of deep-level defects in the host matrix and that of Eu3+ ions deforms the visible emission towards the red color. The I–V measurements of the Eu-ZnO/p-Si heterojunctions showed diode-like behavior with a low rectification ratio and a barrier height around 0.84 eV not affected by the Eu concentration.

Casticin Alleviates the Proliferation and Extracellular Matrix Deposition in Glomerular Mesangial Cells Induced by High Levels of Glucose

Diabetic nephropathy is a common complication of diabetes associated with defects in the extracellular matrix. However, its precise mechanism remains to be explored. Casticin (3′, 5-dihydroxy-3, 4′, 6, 7-tetramethoxyl flavone) is a bioactive component of Fructus vitexis known to exhibit many biological and pharmacological effects. Herein, we have explored the role and mechanism of casticin-mediated amelioration of diabetic nephropathy. Using a high glucose induced glomerular mesangial cell model, we report casticin inhibition of high glucose induced excessive glomerular mesangial cell proliferation, inflammation, and extracellular matrix deposition. Casticin suppressed TGF-β1/Smad pathway, and therefore alleviated the proliferation and extracellular matrix deposition of glomerular mesangial cells. These data suggest that casticin could serve as a promising drug for the management of diabetic nephropathy.

OKMC simulation of matrix defect evolution of Fe-C Alloy under irradiation

The effects of carbon traps in Fe-C alloys on matrix defects and the evolutions of matrix defects in Fe-C alloys under irradiation are investigated in this paper. The object kinetic Monte Carlo (OKMC) modeling is used to establish a bridge between the micro-computational simulation data and the macro-experimental data. The simulation results verify the evolution of the carbon (C)-vacancy (Vac) complex under ideal conditions, and at relatively low temperatures, the complex is mainly C-Vac<sub>2</sub>. Under the assumption of complex traps, the evolution of matrix defects in Fe-C systems under irradiation is simulated in this work. It is verified that the carbon vacancy complex has an obvious trapping effect on matrix defects, and the simulation results of evolution simulation of matrix defects in the Fe-C system under irradiation are consistent with the experimental results. Furthermore, the effective approximate parameters used in the simulation are compared and discussed. The present research can provide a basic support for the research on the evolution of iron-based alloy irradiation defects.

Temperature-dependent mechanical properties of Al/Cu nanocomposites under tensile loading via molecular dynamics method

Abstract Al-Cu Nanocomposites (NCs) are widely used in industrial applications for their high ductility, light weight, excellent thermal conductivity, and low-cost production. The mechanical properties and deformation mechanisms of Metal Matrix NCs (MMNCs) strongly depend on the matrix microstructure and the interface between the matrix and the second phase. The present study relies on Molecular Dynamics (MD) to investigate the effects of temperature on the mechanical properties and elastic and plastic behavior of the Al-Cu NC with single-crystal and polycrystalline matrices. The effects of heating on microstructural defects in the aluminum matrix and the Al/Cu interface were also addressed in the following. It was found that the density of defects such as dislocations and stacking fault areas are much higher in samples with polycrystalline matrices than those with single-crystal ones. Further, by triggering thermally activated mechanisms, increasing the temperature reduces the density of crystal defects. Heating also facilitates atomic migration and compromises the yield strength and the elastic modulus as a result of the increased energy of atoms in the grain boundaries and in the Al-Cu interface. The results showed that the flow stress decreased in all samples by increasing the temperature, making them less resistant to the plastic deformation.

Effects of parameters on titanium nitride formation at atomic level

The effects of parameters on nanoscale titanium nitride during the formation process in ferrite were studied via the molecular dynamics (MD) simulation. The formation of titanium nitride was executed by employing a dislocation-motivated formation model in which the atomic diffusion has a significant contribution. The roles of N/Ti atom ratio, temperature and matrix defect were identified and the according nitride formation property was analyzed.

Strength and Microstructure Characteristics of Blended Fly Ash and Ground Granulated Blast Furnace Slag Geopolymer Mortars with Na and K Silicate Solution.

Mineral geopolymer binders can be an attractive and more sustainable alternative to traditional Portland cement materials for special applications. In geopolymer technology the precursor is a source of silicon and aluminium oxides, the second component is an alkaline solution. In the synthesis of geopolymer binders the most commonly used alkaline solution is a mixture of sodium or potassium water glass with sodium or potassium hydroxide or silicate solution with a low molar ratio, which is more convenient and much safer in use. In this paper, we present the influence of sodium or potassium silicate solution on the physical and mechanical properties of fly ash and ground granulated blast furnace slag-based geopolymer mortars. Mercury intrusion porosimetry and microstructural observation allowed for comparing the structure of materials with a different type of alkaline solution. The evolution of compressive and flexural tensile strength with time determined for composites using 10%, 30% and 50% slag contents (referring to fly ash mass) was analysed. The tests were performed after 3, 7, 14 and 28 days. It was observed that, as the amount of slag used increases in the precursor, the strength of the material grows. Mortars with the sodium alkaline solution were characterised by a higher strength at a young age. However, the values of strength 28 days were higher for geopolymers with potassium alkaline solution reaching 75 MPa in compression. Geopolymer mortar microstructure observation indicates a high matrix heterogeneity with numerous microcracks. Matrix defects may be caused by the rapid kinetics of the material binding reaction or shrinkage associated with the drying of the material.