Similar Composite Systems Research Articles

Sorption Properties of ZrO2-Analcime Composites in Relation to Cs(I) and Sr(II)

Composite zeolite sorbents based on analcime with inclusions of hydrated zirconium dioxide (ZrO2-analcime) have been obtained by hydrothermal treatment of coal fly ash cenospheres with a high glass phase content in the presence of a zirconium compound and an alkaline activating agent at 150 °C and different stirring modes of the reaction mixture. The synthesis products were characterized by XRD, SEM-EDS, STA and low-temperature nitrogen adsorption; their sorption properties with respect to Cs+ and Sr2+ were studied in the pH range of 2–10. It was found that the ZrO2-analcime compositions surpass unmodified analcime by 2–5 times in terms of sorption of Cs+ and Sr2+ and by two orders of magnitude in terms of the distribution coefficient value (KD ~106 ml/g). The process of high-temperature solid-phase transformation of Cs+/Sr2+-exchanged forms of the compositions was studied, which simulates the process of conversion of water-soluble forms of Cs‑137 and Sr‑90 radionuclides into a mineral-like form. It was shown that at 1000 °C the ZrO2-analcime compositions with sorbed Cs+ and Sr2+ undergo the phase transformation resulting in polyphase systems of similar composition based on nepheline, tetragonal ZrO2, and glass phase

Thermal and electrical properties enhancement of a nanocomposite of industrial silicone rubber filled with reduced graphene oxide

In this work, a nanocomposite was developed by in-situ polymerization using industrial-grade diatom-containing silicone rubber (SR) as the matrix and reduced graphene oxide (RGO) as filler. The Concentration of RGO, was very low, varying from 0 to 1 wt%. In these nanocomposites, diatoms as well as RGO flakes of sizes smaller than 20 µm were dispersed homogeneously within the SR. According to thermogravimetric analysis (TGA), the thermal stability of the composite is improved by increasing the decomposition temperature of SR from 497 °C to 546 °C at 0.8 wt% of RGO. A TGA signal between 620 °C and 670 °C is identified as due to C-C bonds thermal breaking, whose integrated intensity increases in proportion to the concentration of RGO and can be used to determine the concentration of RGO in similar composite systems. When 1.0 wt% of RGO is added thermal conductivity increases by 47.5% and the electrical resistivity decreases four orders of magnitude, respect to SR values. The SR/RGO nanocomposite is flexible and represents a good candidate for applications in the development of sensors and biomedical applications. The use of industrial-grade SR reduces production costs of composites in comparison to those prepared with more expensive analytical grade rubbers.

Homogenization method for microscopic characterization of the composite magnetoelectric multiferroics

Tuning of magnetization or electrical polarization using external fields other than their corresponding conjugate fields (i.e., magnetic field for the former or electric field for the latter response) attracts renewed interest due to its potential for applications. The magnetoelectric effect in multiferroic 1–3 composite composed of alternating magnetic and ferroelectric layers operating in linear regime consequent to external biasing fields is simulated and analysed theoretically. Two-scale homogenization procedure to arrive at the equilibrium overall physical properties of magnetoelectric multiferroic composite is formulated using variational analysis. This procedure is extended to quantify the underlying local (microscopic) electric, magnetic and elastic fields and thereby compute local distribution of stresses and strains, electrical and magnetic potentials, the electric and magnetic fields as well as the equivalent von Mises stresses. The computational model is implemented by modifying the software POSTMAT (material postprocessing). Computed local stress/strain profiles and the von Mises stresses consequent to biasing electrical and magnetic fields provide insightful information related to the magnetostriction and the ensuing electrical and magnetic polarization. Average polarization and magnetization against magnetic and electric fields respectively are computed and found to be in reasonable limits of the experimental results on similar composite systems. The homogenization model covers multiferroics and its composites regardless of crystallographic symmetry (with the caveat of assuming an ideal and semi-coherent interface connecting the constituent phases) and offer computational efficiency besides unveiling the nature of the underlying microscopic field characteristics.

Facile synthesis of Ag Bi25GaO39Bi2WO6 heterostructure with enhanced photocatalytic performance based on interface structure design

Abstract Composite photocatalytic system based on interface structure design is deemed to be a feasible method to improve the photocatalytic efficiency of sillenite-type photocatalytic material. Therefore, we reported the successful construction of novel tetrahedron-like Ag Bi25GaO39 Bi2WO6 heterostructure through a partial chemical conversion strategy coupling with the photo-reduction method. Experiment indicated that the as-prepared Ag Bi25GaO39 Bi2WO6 heterogeneous structure possessed excellent photo-degradation activity for the decomposition of Rhodamine B (RhB) and 95% of RhB molecules could be decomposed after 20 min of UV–vis light irradiation by comparison of single Bi25GaO39 and Bi2WO6, as well as the Bi25GaO39 Bi2WO6 heterostructure. Moreover, the resulted Ag Bi25GaO39 Bi2WO6 product also exhibited outstanding photocatalytic activity for the decomposition of other pollutant such as phenol and toxic Cr(VI) solutions. Due to the resulted advantages derived from the rational design of interface structure (matching band structure, intimate interfacial contacts, “face-to-face” contact mode of hetero-interface and the famous “schottky barriers), the photo-generated charges generated in the composite photocatalytic system could be separated quickly, thus exhibiting excellent photocatalytic ability. This design concept can provide new ideas for the construction of other similar composite photocatalytic systems.

Fiber orientation measurement from mesoscale CT scans of prepreg platelet molded composites

X-ray computed tomography (CT) analysis is used to measure the heterogeneous fiber orientation fields in a 20 cm3 composite bracket made from prepreg platelet-based molding compound (PPMC). The as-molded mesostructure of the complete geometry is captured using material density gradients in 50 µm resolution CT scans without the need to resolve individual fibers. Fiber collimation and physical density gradients within intact platelets of this material system facilitates nondestructive assessment of average local fiber orientation at the component scale. Microscopy-based validation of the local orientation measurements indicate the accuracy that can be attained utilizing the density-based structure tensor CT analysis method. Local orientation field measurements for the complete geometry can be mapped into a “digital twin” model, for purposes such as experimental performance simulation and validation of molding process orientation state predictions. Composite designers, analysts, and material suppliers can employ this methodology to more confidently utilize PPMCs and morphologically similar composite material systems.

Structural properties of melt versus sol-gel derived yttrium aluminosilicate systems

The present study reports results regarding the structure of yttrium aluminosilicate systems of similar composition obtained by melting and sol-gel methods. The samples were investigated both in non-crystalline state and partially crystallised by 1200 °C heat treatment. The differences already noticed in the local order of non-crystalline samples prepared by the two methods appear much more pronounced after partial crystallization as evidenced by X-ray diffraction and infrared spectroscopy analysis. The infrared absorption bands recorded in the low wavenumber range after heat treatment denote the yttrium involvement in crystalline phases. According to X-ray diffraction results, the embedding of yttrium in Y2Si2O7 crystalline phase is undeniably evidenced after 1200 °C treatment of melt derived sample while in the corresponding sol-gel derived sample yttrium embedding is presumed by partial replacement of aluminium atoms in Al6Si2O13 mullite phase.

Study on magnetocapacitance effect of magnetic particle polymer matrix composite system by finite element method

In this paper, the magnetocapacitance effect of magnetic particles Fe3O4 embedded in polymer insulating matrix polydimethylsiloxane is investigated using finite element method by commercial software Comsol Multiphysics. With this method, the process of the capacitance variation under different magnetic field is simulated, and the factors influencing magnetocapacitance effect are studied. In particular, we apply the micro-macro coupling method for simulation analysis due to a large amount of calculation in the actual model. First, a three-dimensional microscopic model is calculated to obtain the effect of the magnetic field on the equivalent permittivity of the composite. The relationship is then substituted into the material property of the macroscopic model to simulate the magnetocapacitance effect. The results show that the composite exhibits magnetocapacitance characteristics that are related to the magnetic field intensity, particle size, and particle concentration. The capacitance value increases with the magnetic field at certain particle size and particle volume fraction. Meanwhile, the capacitance value at the same magnetic field increases with the particle size and particle volume fraction. The numerical results are consistent with the experimental results. The simulation model can provide a reference for research on the magnetocapacitance effect involving similar composite systems composed of magnetic particles and polymer matrix.

Kinetic behavior in criticality accident of two fuel solution tanks

This work aimed at criticality safety in fuel-fabrication or reprocessing facilities. To estimate the expected released energy in criticality accidents of several fuel-solution tanks based on the energy released in a single-fuel-solution-tank accident, the total energy released in a two-tank system was evaluated with different compositions of fuel solutions. The code used for the analysis took into account the neutronic coupling between the tanks. The results made clear that as the fuel enrichment increases, neutronic coupling becomes stronger. The calculated increase of the total energy released in a criticality accident of a system with two fuel-solution tanks compared to that of a system with just one was roughly the same regardless of different feedback model used for the analysis. The results show that the difference in energy release between multiple-tank and single-tank systems of similar composition may be evaluated using the developed transient analysis code.

Magnetodielectric effect in Ni0∙5Zn0∙5Fe2O4–BaTiO3 nanocomposites

Composites comprising of nanoparticles of Ni0∙5Zn0∙5Fe2O4 (NZF) and BaTiO3 (BT), respectively were synthesized by a chemical method. The particles had diameters in the range of 15–31 nm. NZF was prepared by a coprecipitation technique. This was soaked in a sol containing BT. Compositions synthesized were xNZF-(1 – x) BT, where x = 0∙7, 0∙5 and 0∙3, respectively. The composites showed ferromagnetic hysteresis loops due to NZF phase. The analysis of coercivity variation as a function of temperature gave blocking temperatures in the range of 306–384 K depending on the diameter of the ferrite nanoparticles. This implied that superparamagnetic interactions are above these temperatures. The nanocomposites also exhibited ferroelectric behaviour arising due to the presence of BT. The remanent polarization of the samples was small. This was adduced to the nanosize of BT. The specimens showed magneto-dielectric (MD) effect in the magnetic field range 0–0∙7 Tesla. The MD parameter measured at the maximum magnetic field was around 2%. This was one order of magnitude higher than that reported so far in similar composite systems. This was explained on the basis of a two-phase inhomogeneous medium model with an interface between them, the phases possessing drastically different electrical conductivities.

Determination of interfacial mechanical properties of ceramic composites by the compression of micro-pillar test specimens

A novel method to determine the fiber-matrix interfacial properties of ceramic matrix composites is proposed and evaluated; where micro-pillar samples containing inclined fiber/matrix interfaces were prepared from a SiC fiber-reinforced SiC matrix composites and then compression-tested using the nano-indentation technique. This new test method employs a simple geometry and mitigates the uncertainties associated with complex stress state in the conventional single-filament push-out method or tensile unloading–reloading hysteresis loop analysis method for the determination of interfacial properties. Based on the test results using samples with different interface orientations, the interfacial debond shear strength and the internal friction coefficient are explicitly determined and compared with values obtained by other test methods. SEM observation showed that micro compression caused an adhesive type of debonding between the fiber and the pyrolytic carbon interface. The results suggest that the debonding/failure behavior of the micro-pillars followed the Coulomb fracture criterion. The determined interfacial debond shear strength is ~100 MPa, which appears to be smaller than that determined from fiber push-out test for similar composite systems. The difference can be explained by the effect of normal stress (clamping stress) on the apparent interfacial debond shear strength.

Patterns and Drivers of Tree Mortality in Iberian Forests: Climatic Effects Are Modified by Competition

Tree mortality is a key process underlying forest dynamics and community assembly. Understanding how tree mortality is driven by simultaneous drivers is needed to evaluate potential effects of climate change on forest composition. Using repeat-measure information from c. 400,000 trees from the Spanish Forest Inventory, we quantified the relative importance of tree size, competition, climate and edaphic conditions on tree mortality of 11 species, and explored the combined effect of climate and competition. Tree mortality was affected by all of these multiple drivers, especially tree size and asymmetric competition, and strong interactions between climate and competition were found. All species showed L-shaped mortality patterns (i.e. showed decreasing mortality with tree size), but pines were more sensitive to asymmetric competition than broadleaved species. Among climatic variables, the negative effect of temperature on tree mortality was much larger than the effect of precipitation. Moreover, the effect of climate (mean annual temperature and annual precipitation) on tree mortality was aggravated at high competition levels for all species, but especially for broadleaved species. The significant interaction between climate and competition on tree mortality indicated that global change in Mediterranean regions, causing hotter and drier conditions and denser stands, could lead to profound effects on forest structure and composition. Therefore, to evaluate the potential effects of climatic change on tree mortality, forest structure must be considered, since two systems of similar composition but different structure could radically differ in their response to climatic conditions.

Magnetization enhancement and cation valences in nonstoichiometric (Mn,Fe)3-δO4 nanoparticles

We present a study of the structural and magnetic properties of (Mn,Fe)3-δO4 nanoparticles synthesized by soft mechanochemistry using Mn(OH)2 × 2 H2O and Fe(OH)3 powders as starting compounds. The resulting nanoparticles with a composition of the (Mn,Fe)3-δO4 type are found to have a core/shell structure with different Mn/Fe ratios in the core and at the surface. XPS analysis points to valences of +2, +3, and +4 for Mn and +3 for Fe at the particle surface. Combined results of XRPD, Mössbauer spectroscopy, and EDX analysis suggest that there is a deviation from stoichiometry in the nanoparticle core compared to the shell, accompanied by creation of cation polyvalence and vacancies. The value of saturation magnetization, MS, of 73.5 emu/g at room temperature, is among the highest reported so far among nanocrystalline ferrite systems of similar composition.

Laser-induced ultrafast demagnetization in the presence of a nanoscale magnetic domain network

Femtosecond magnetization phenomena have been challenging our understanding for over a decade. Most experiments have relied on infrared femtosecond lasers, limiting the spatial resolution to a few micrometres. With the advent of femtosecond X-ray sources, nanometric resolution can now be reached, which matches key length scales in femtomagnetism such as the travelling length of excited 'hot' electrons on a femtosecond timescale. Here we study laser-induced ultrafast demagnetization in [Co/Pd](30) multilayer films, which, for the first time, achieves a spatial resolution better than 100 nm by using femtosecond soft X-ray pulses. This allows us to follow the femtosecond demagnetization process in a magnetic system consisting of alternating nanometric domains of opposite magnetization. No modification of the magnetic structure is observed, but, in comparison with uniformly magnetized systems of similar composition, we find a significantly faster demagnetization time. We argue that this may be caused by direct transfer of spin angular momentum between neighbouring domains.

Magnetic coupling mechanisms in particle/thin film composite systems.

Magnetic γ-Fe2O3 nanoparticles with a mean diameter of 20 nm and size distribution of 7% were chemically synthesized and spin-coated on top of a Si-substrate. As a result, the particles self-assembled into a monolayer with hexagonal close-packed order. Subsequently, the nanoparticle array was coated with a Co layer of 20 nm thickness. The magnetic properties of this composite nanoparticle/thin film system were investigated by magnetometry and related to high-resolution transmission electron microscopy studies. Herein three systems were compared: i.e. a reference sample with only the particle monolayer, a composite system where the particle array was ion-milled prior to the deposition of a thin Co film on top, and a similar composite system but without ion-milling. The nanoparticle array showed a collective super-spin behavior due to dipolar interparticle coupling. In the composite system, we observed a decoupling into two nanoparticle subsystems. In the ion-milled system, the nanoparticle layer served as a magnetic flux guide as observed by magnetic force microscopy. Moreover, an exchange bias effect was found, which is likely to be due to oxygen exchange between the iron oxide and the Co layer, and thus forming of an antiferromagnetic CoO layer at the γ-Fe2O3/Co interface.

Successive approximation procedure of optimal tracking control for nonlinear similar composite systems

The optimal tracking control (OTC) problem for a class of affine nonlinear composite systems with similar structure is considered. By using a modeling technique, the nonlinear similar composite system is first transformed into some quasi-decoupled subsystems. Then the high-order, strongly coupled, nonlinear two-point boundary value (TPBV) problem is transformed into a sequence of linear decoupled TPBV problems through a successive approximation procedure. The obtained OTC law consists of an accurate linear term and a nonlinear compensation term which is the limit of the adjoint vector sequence. A suboptimal tracking control law is obtained by truncating a finite iterative result of the adjoint vector sequence as its nonlinear compensation term.

OBSERVER-BASED STABILIZATION OF DISCRETE-TIME UNCERTAIN SWITCHING SIMILAR COMPOSITE SYSTEMS

Reduced-order design of decentralized observer-based output switching controllers is presented for uncertain discrete-time switching similar composite systems with arbitrary switching rule. First, a reduced-order control design model is constructed with the dimension equal to a subsystem's dimension of the original system. Then, asymptotically stabilizing switching controller is designed. It is proved that when this controller is implemented into each subsystem of the original system then such decentralized controller asymptotically stabilizes the overall closed-loop system under arbitrary switching.

Creep and Stress–Strain Behavior after Creep for SiC Fiber Reinforced, Melt‐Infiltrated SiC Matrix Composites

Silicon carbide fiber (Hi‐Nicalon Type S, Nippon Carbon) reinforced silicon carbide matrix composites containing melt‐infiltrated silicon were subjected to creep at 1315°C at three different stress conditions. For the specimens that did not rupture after 100 h of tensile creep, fast‐fracture experiments were performed immediately following the creep test at the creep temperature (1315°C) or after cooling to room temperature. All specimens demonstrated excellent creep resistance and compared well to the creep behavior published in the literature on similar composite systems. Tensile results on the after‐creep specimens showed that the matrix cracking stress actually increased, which is attributed to stress redistribution between composite constituents during tensile creep.

Nonlinear viscoelastic micromechanical analysis of fibre-reinforced polymer laminates with damage evolution

A micromechanical model of unidirectional fibre-reinforced polymer laminates under off-axis loading is analyzed using finite element method. A three-dimensional periodic unit cell is established with the matrix described by a nonlinear viscoelastic model and the fibre by an elastic one. Matrix cracking is modeled by smeared crack method which permits a crack description in terms of stress–strain relations and stiffness reduction in particular orientations. The micromechanical analysis features material nonlinearity, damage initiation and growth, and multiaxial loading. Numerical results reveal the local and global response of the laminate including the damage mechanism. The predictions are in good agreement with the test results performed on a similar composite system.

The effect of S on the partitioning of Ni between olivine and silicate melt in MORB

The partitioning behavior of Ni between olivine and silicate melt in S-bearing systems has been investigated using mid-ocean ridge basalts (MORBs). The Nernst Ni partition coefficient between olivine and silicate melt ( D Ni) derived from the MORB samples varies between 4 and 9, values that are up to 50% lower than those derived from S-free experimental systems of similar composition. The MORB samples yield lower D Ni values because Ni 2+ and S 2− interact to form a Ni–S complex in the silicate melt. Since the Ni present as NiS contributes to the melt concentration but is not available for sequestration by olivine, the overall effect is a reduction in the D Ni value calculated from the total concentration of Ni in the silicate melt. This hypothesis is supported by the negative correlation between the ln K D Ni–Mg ( K D Ni–Mg=[MgO melt/MgO Ol]/[NiO melt/NiO Ol]) values and the contents of S in the silicate melts of the MORB samples.

Conductivity as a predictor of a total cations and salinity in Ethiopian lakes and rivers: revisiting earlier models

We used regression analyses of water samples from 18 lakes, nine rivers, and one spring in Ethiopia to (a) test the hypothesis that water bodies of relatively higher salinity ( K 25>1000 μS cm −1) have a different conductivity to salinity relationship than waters of lower salinity ( K 25 < 1000 μS cm −1), and (b) develop models to predict total cations and salinity from conductivity that can be used for Ethiopian waters and other African aquatic systems of similar chemical composition. We found no statistical difference in the bilogarithmic relationships (total cations vs. conductivity; salinity vs. conductivity) for waters of higher salinity ( K 25 > 1000 μS cm −1) and waters of lower salinity ( K 25 < 1000 μS cm −1). However, comparison among our models and models from the literature suggests that developing separate equations for low and high salinity water bodies has some merit. We believe that the equations developed in this study can be used for Ethiopian waters and other African waters within the range of conductivity in this study.