Core-shell Microstructure Research Articles

Electrolytic synthesis of ZrSi/ZrC nanocomposites from ZrSiO4 and carbon black powder in molten salt

Abstract ZrSi/ZrC nanocomposites have stable high-temperature properties, where conventional materials cannot meet increasingly demanding high-temperature environments. In this paper, the microstructure and electrochemical reduction mechanism of ZrSi/ZrC nanocomposites have been studied. A mixture of ZrSiO4 and carbon black powder was processed using ball grinding, sheet pressing, and sintering, and cylindrically-sintered sheet was prepared as the cathode for the electrolytic work. A high purity graphite rod was utilized as the anode.The microstructure of the electrolytic product was characterized and analyzed using X-ray diffraction, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The experimental results showed that the diameter of the as-synthesized ZrSi/ ZrC fibers typically range between 100-400 nm when produced by the electrolysis of sintered pellets in equimolar CaCl2-NaCl molten salt at 850°C with a cell voltage of 2.8 V for 20 h under an argon atmosphere. The nanofibers were formed in core-shell microstructures that overlap and grow.

Microstructure-driven self-assembly and rheological properties of multi-responsive soft microgel suspensions

HypothesesThe deformation and swelling ability of microgels is influenced by the crosslinking distribution. Varying microgels microstructure is expected to obtain suspensions with different flow behavior and thereby, different rheological properties. ExperimentsDifferent multi-responsive microgels were synthesized using two different crosslinkers and varying their amounts: N,N-methylene bis-acrylamide (MBA) and oligo(ethylene glycol) diacrylate (OEGDA). The rheological results were obtained by zero-shear viscosity and long-time creep measurements on concentrated microgel suspensions Microgel microstructure was analyzed by 1H nuclear magnetic resonance transverse relaxation measurements. FindingsAt a constant crosslinking rate, we show that the viscosity of OEGDA-crosslinked microgels diverges at a higher concentration than MBA ones, suggesting a looser shell and less restricted dangling chains at the periphery for the later. By scaling with the effective volume fraction, the viscosity curves of the different microgel suspensions reduce into a single curve and closely follow hard sphere models up to ϕeff < 0.45. The results from creep tests revealed a much higher yield stress for MBA-crosslinked microgels, strengthening the hypothesis of a looser shell for the later. Finally, transverse relaxation (T2) NMR measurements demonstrated that, although all microgels exhibit a core–shell microstructure, MBA samples present a less crosslinked shell corroborating with the rheological results.

Equilibrium Multi-precipitate Configurations

In this paper, we formulate a phase-field model for the computation of equilibrium configurations of multiple phases that arise out of a solid-state precipitate reaction, in the presence of coherency stresses. Here, we utilize the phase-field framework to minimize the sum of the elastic and the interfacial energies for a given volume of the precipitates using an extension of the volume-preserved Allen–Cahn algorithm (Garcke et al. in Math Models Methods Appl Sci 18(08):1347–1381, 2008; Bhadak et al. in Metall Mater Trans A 49A(11):5705–5726, 2018). Using this technique, we investigate the precipitate organization for three solid-state reactions. The first is the classical two-phase precipitate reaction that leads to the formation of core–shell microstructures, where we clarify the influence of elasticity on the formation of such clusters. Following this, we investigate two symmetry-breaking transitions (cubic to tetragonal) and (hexagonal to orthorhombic), that lead to the formation of multi-variant clusters where we study the organization of the precipitates as a function of the elastic properties of the precipitate and the matrix.

Performance optimization of core-shell HMX@(Al@GAP) aluminized explosives

The energy release of aluminized explosives was impeded by the aggregation of aluminum powders, especially for nano-aluminum powders. The core-shell HMX@(Al@GAP) explosives with 5 wt% to 15 wt% aluminum were fabricated, with systematical investigation of morphology, mechanical properties, thermal decomposition, combustion and detonation properties. Compared with the physical mixtures, the aluminized explosives with core-shell microstructure showed better creep resistance and mechanical strength. The thermal decomposition of HMX in core-shell HMX@(Al@GAP) was slightly advanced due to good dispersion of Al@GAP particles. Delayed but more vigorous and longer burning during combustion process was witnessed for the core-shell explosive. For HMX@15 wt%(Al@GAP) aluminized explosives, the detonation velocity and specific kinetic energy was 8567 m/s and 1.412 kJ/g, which was 1.3% and 5.1% higher than the corresponding physical mixtures. The reaction of the core-shell HMX@(Al@GAP) and the physical mixtures were calculated by ReacFF-/g force field, showing remarkable dependent of the average temperature on the microstructure. Present research might provide new insight for synergistically improvement of mechanical and detonation properties in aluminized explosives.

A novel self-thermoregulatory electrode material based on phosphorene-decorated phase-change microcapsules for supercapacitors

Phosphorene is a promising candidate for the pseudocapacitive electrode material, because it offers a huge number of ion-accessible sites for multiphase active materials. A high working temperature is bound to deteriorate the electrochemical behavior of supercapacitors due to exothermic redox reactions during the charge–discharge process. To address this problem in supercapacitors, a self-thermoregulatory electrode material is designed and constructed to enhance the electrical energy-storage performance of supercapacitors for use in a wider temperature range. This electrode material is fabricated by microencapsulating n-docosane phase-change material (PCM) with a SiO2 inner shell and then coating a polyaniline/phosphorene hybrid outer layer as an electrochemical active material. A well-defined core-shell microstructure and expected components of the resultant electrode material are confirmed by morphological observations and structural characterizations. In this electrode material, while the polyaniline/phosphorene hybrid layer performs charge storage/release behaviors according to the faradic mechanism, the PCM core can effectively regulate the microenvironmental temperature for the electrode system in situ through phase transitions, thus improving the rate capability and specific capacitance of the electrode system. Furthermore, the hybridization of polyaniline and phosphorene contributes to the enhancement of capacitive behavior and charge–discharge cycle stability by offering more ion-accessible site in the polyaniline active material. In view of a unique combination of phosphorene and PCM, the novel electrode material developed by this work exhibits a potential application for high-performance supercapacitors suitable for use at high working temperatures.

Layer-by-layer assembly of low-temperature in-situ polymerized pyrrole coated nanofiber membrane for high-efficiency electromagnetic interference shielding

Electromagnetic pollution often interferes with nearby electronic equipment and poses a serious threat to the health of people. There is an urgent need to develop soft and lightweight electromagnetic interference (EMI) shielding materials. In this study, a layer-by-layer self-assembly strategy was used implemented to prepare PAN@Ag@PDA@PPy (PAP@PPy) films with unique core-shell and sandwich composite microstructures for electromagnetic interference (EMI) shielding. Results showed that the conductivity of the composite films was the highest at 898.72 S/m after in situ polymerization of pyrrole at low temperatures. The mechanical properties of the conductive films also increased from the initial 16.81 MPa to 22.54 MPa. The average shielding effectiveness (SE) and SSE/t of the composite films with two layers reached as high as 23.81 dB and 6764.20 dB cm2 g−1, respectively. This performance was caused originates from by the layer structure of the PAN film and multiple internal reflections from the interconnected core-shells and sandwich microstructures in of the PAP@PPy films. Therefore, this work study gave provides a new novel strategy for fabricating conductive polymer composites (CPCs) with high-performance EMI shielding.

Electrolytic synthesis of ZrSi/ZrC nanocomposites from ZrSiO4 and carbon black powder in molten salt

Abstract ZrSi/ZrC nanocomposites have stable high-temperature properties, where conventional materials cannot meet increasingly demanding high-temperature environments. In this paper, the microstructure and electrochemical reduction mechanism of ZrSi/ZrC nanocomposites have been studied. A mixture of ZrSiO4 and carbon black powder was processed using ball grinding, sheet pressing, and sintering, and cylindrically-sintered sheet was prepared as the cathode for the electrolytic work. A high purity graphite rod was utilized as the anode.The microstructure of the electrolytic product was characterized and analyzed using X-ray diffraction, scanning electron microscopy equipped with energy-dispersive X-ray spectroscopy, and transmission electron microscopy. The experimental results showed that the diameter of the as-synthesized ZrSi/ ZrC fibers typically range between 100-400 nm when produced by the electrolysis of sintered pellets in equimolar CaCl2-NaCl molten salt at 850°C with a cell voltage of 2.8 V for 20 h under an argon atmosphere. The nanofibers were formed in core-shell microstructures that overlap and grow.

Microstructure and properties of aluminium-high entropy alloy composites fabricated by mechanical alloying and spark plasma sintering

High-quality aluminium-CuZrNiAlTiW high-entropy alloy (HEA) composites were fabricated by mechanical alloying and spark plasma sintering (SPS). The microstructures, mechanical properties and corrosion resistance of these composites were investigated. The as-milled HEA powders consist of a single body-centered cubic (BCC) solid solution phase. Besides the Al and BCC phases, the NiAl-rich B2 and WAl12 phases were in-situ formed in the sintered composites due to the large concentration gradient of Al between the matrix and HEA reinforcement. Compared to the SPS-ed Al bulk, the Al-HEA composites show higher microhardness and strength, caused by the dispersion strengthening of BCC phase and precipitation strengthening of B2 and WAl12 phases, as well as the serious lattice distortion. The core-shell microstructure in the composite with 10 vol.% HEA (Al10) contributes to its good compression properties with high yield strength and good plasticity. The Al20 composite exhibits a high fracture strength of 544 MPa, owing to the uniform size and distribution of BCC particles. Additionally, W and Ni could improve the stability of protective layer, and thus enhance the pitting resistance of the Al-HEA composites in seawater. The Al10 composite possesses the relatively positive corrosion potential and low corrosion rate, revealing a good general corrosion resistance.

Inhibition of exothermic runaway of batch reactors for the homogeneous esterification using nano-encapsulated phase change materials

Reaction inhibition is a promising option as an emergency measure to mitigate hazards caused by exothermic runaway reactions. The applications of phase change materials (PCMs) as inhibitors of runaway reactions have been influenced by thermal energy storage technologies. In this work, nano-PCMs powders with silica shells were fabricated using the sol–gel method at alkaline conditions. The prepared nano-PCMs had perfect core–shell microstructures and spherical morphologies, with an average encapsulated PCM particle diameter of 717.34 nm. In addition, the nano-PCMs exhibited high latent heats of fusion (129.1 J g−1), which could inhibit the uncontrolled self-heating caused by runaway reactions through conversion of the heats of reaction to the latent heats of PCMs. The homogeneous esterification of propionic anhydride with n-butanol catalyzed by sulfuric acid was chosen as target reaction with risk of exothermic runaway. Inhibition experiments was conducted in a batch reactor coupled with an in situ FTIR spectrometer. The heat transfer performance of reactant flow was studied to analyze the mechanism of thermal runaway inhibition with nano-PCMs. The results revealed that thermal runaway can be halted by applying nano-PCMs and that the reaction can proceed to completion steadily. The effect of Re on heat transfer performance was enlarged with addition of nano-PCMs. The enhancement in the heat transfer coefficient for PCM slurry was proved. Furthermore, the effectiveness of the thermal runaway inhibition can be significantly influenced by the warning temperature, stirring rate, and mass of added nano-PCMs. The applications of nano-PCMs for runaway reaction inhibition holds great potential for use in industrial processes.

A scalable synthesis route for multiscale defect engineering in the sustainable thermoelectric quaternary sulfide Cu26V2Sn6S32

In recent years, thermoelectric materials inspired from the natural mineral colusite have emerged as a new class of environmentally-friendly copper-based sulfides composed of abundant elements. Herein, high performance bulk colusite Cu26V2Sn6S32 materials were synthesized using mechanical alloying and spark plasma sintering of low-cost industrial-grade metal sulfides. This new synthesis route has led to the formation of various types of nano-to-microscale defects, from local Sn-site structural disorder to nano-inclusions and vanadium-rich core-shell microstructures. These multiscale defects have a strong impact over phonon scattering, making it possible to reach ultra-low lattice thermal conductivity. Simultaneously, the electrical transport properties are impacted through variations in charge carrier concentration and effective mass, leading to a synergistical improvement of both electrical and thermal properties. The resulting power factor, over 1 mW m−1 K−2 above 623 K with an average value of 0.86 mW m−1 K−2 over the temperature range 300 ≤ T / K ≤ 650 K, is the highest reported for a germanium-free colusite to date. Our optimization strategy based on defect engineering in bulk materials is an exciting prospect for new low-cost thermoelectric systems.

A General Synthetic Strategy to a Library of Luminescent All-Organic Core–Shell Microstructures

Achieving good control over all-organic core–shell configurations represents an enormous challenge due to the difficulties in pairing appropriate constituent materials and tuning their growth kinet...

Evolution of morphology and morphology stability in PP/PA6/EPDM-g-MA reactive ternary blends using viscoelastic measurements

The relationship between the morphology and rheological properties of PP/PA6/EPDM-g-MA ternary blends, at relatively low rubber phase contents, was studied in detail. The results showed that the size of composite droplets of core-shell microstructures decreased and increased after passing through a minimum due to competitive effects of the emulsification role of EPDM-g-MA and viscosity ratio. This trend in morphology development was well reflected in the relaxation spectrums of the blends. The morphology of discrete core-shell particles altered to the large clusters of core-shell particles at higher rubbery phase contents which led to alteration of viscoelastic behavior from liquid-like to solid-like. The morphology of high EPDM-g-MA content ternary blends was unstable particularly at higher temperatures which was evaluated using time-sweep rheological experiments and confirmed via direct SEM analysis.

Strength–Ductility Trade-Off in Dual-Phase Steel Tailored via Controlled Phase Transformation

The controlled phase transformation approach is a new generation of microstructure engineering for enhancing ductility in ultrafine-grained materials. The present study aims to extend this concept to dual-phase steel for enhanced tensile ductility at high strength. In this study, cold-rolled steel was subjected to annealing at different processing conditions to develop the core–shell microstructure constituting martensite core and ferrite as shell in the matrix. Controlled austenite decomposition was adopted in designing a core–shell-type structure. The evolved microstructure was characterized using a scanning electron microscope and electron backscatter diffraction technique. The results showed that the uniaxial tensile deformation of dual-phase structured steels had a remarkable strength–ductility trade-off. The ductility was increased anomalously at high martensite fractions. Further, the mechanism of damage activity leading to void nucleation and microcrack formation was studied in post-tensile fractured specimens to establish a correlation with tensile deformation characteristics. The possibility and outcomes of this approach are also reported here.

Gelatin-stabilized traditional emulsions: Emulsion forms, droplets, and storage stability

Fish oils are important substances in the field of food and drug delivery. Due to their unstable double bonds, fishy taste, and poor water solubility, it is pivotal to investigate novel dosage forms for fish oils, such as encapsulated droplets. In this work, we primarily prepared gelatin-stabilized fish oil-loaded traditional emulsions and investigated their emulsion forms, droplets, and storage stability under different preparation and storage conditions. Our results showed that higher gelatin solution pH, higher storage temperature in the range of 4–37 °C, and increased storage time induced the emulsion form switch from a liquid form to a redispersible gel form of the fish oil emulsion. The droplets had core-shell microstructures and a trimodal size distribution, which decreases linearly with increasing gelatin solution pH and homogenizing time, but decreases exponentially with increasing homogenizing speed. In addition, storage temperature showed a notably different effect on traditional emulsion storage. This work provides a fundamental knowledge for the formation, microstructure, and properties of gelatin-based traditional emulsions. It also provides a promising new application for fish oil-loaded emulsions in food beverages, soft candy, and other food products.

D-mannitol@silica/graphene oxide nanoencapsulated phase change material with high phase change properties and thermal reliability

Sugar alcohols have considerable potential for usage in medium-temperature thermal energy storage applications; however, they suffer from poor thermal reliability and low thermal conductivity. Nanoencapsulation is an effective approach to improve the thermal energy storage performance of the phase-change materials. Until now, nanoencapsulation of sugar alcohols with a high phase-change performance has been rarely reported. The objective of this study is to develop a method for the nanoencapsulation of sugar alcohols with an enhanced phase-change performance. D-mannitol nanocapsules with a silica–graphene oxide composite shell were synthesized and investigated to demonstrate the validity of this novel method. The morphology, size distribution, and core–shell microstructure of the nanocapsules were observed using a scanning electron microscope, particle size and zeta potential analyzer, and transmission electron microscope. In addition, the phase-change performance of the nanocapsules was studied using a differential scanning calorimeter, a thermogravimetric analyzer, and weight loss and appearance investigation. The results demonstrate that the melting and solidifying latent heat of the nanocapsules are 216.7 and 174.4 kJ/kg, respectively. The energy storage efficiency of the nanocapsules was 75.8% and its 96.1% was maintained after repeated thermal cycling. Compared with pure D-mannitol, the thermal conductivity of the nanocapsules was observed to increase by up to 128.6%. The novel nanocapsules exhibited good medium-temperature thermal energy storage prospects.

Synthesis Chemistry and Properties of Ni Catalysts Fabricated on SiC@Al2O3 Core-Shell Microstructure for Methane Steam Reforming

Heat and mass transport properties of heterogeneous catalysts have significant effects on their overall performance in many industrial chemical reaction processes. In this work, a new catalyst micro-architecture consisting of a highly thermally conductive SiC core with a high-surface-area metal-oxide shell is prepared through a charge-interaction-induced heterogeneous hydrothermal construction of SiC@NiAl-LDH core-shell microstructures. Calcination and reduction of the SiC@NiAl-LDH core-shell results in the formation of Ni nanoparticles (NPs) dispersed on SiC@Al2O3, referred to as Ni/SiC@Al2O3 core-shell catalyst. The Ni/SiC@Al2O3 exhibit petal-like shell morphology consisting of a number of Al2O3 platelets with their planes oriented perpendicular to the surface, which is beneficial for improved mass transfer. For an extended period of methane-stream-reforming reaction, the Ni/SiC@Al2O3 core-shell structure remained stable without any significant degradation at the core/shell interface. However, the catalyst suffered from coking and sintering likely associated with the relatively large Ni particle sizes and the low Al2O3 content. The synthesis procedure and chemistry for construction of supported Ni catalyst on the core-shell microstructure of the highly thermal conductive SiC core, and the morphology-controlled metal-oxide shell, could provide new opportunities for various catalytic reaction processes that require high heat flux and enhanced mass transport.

Enhanced electromagnetic wave absorption of hybrid-architectures Co@ SiOxC

Rational design on the well wrapped core-shell microstructure of Co@ SiO x C composites was successfully conducted through reduction process of cobalt, efficient condensation reaction of KH-550 silane coupling agent as well as high temperature calcination. The SiO x C shell possessed 3D cross-linked network structure consisting of dielectric carbon and silicon composition for optimal electromagnetic matching. The microstructure, morphology, elements distribution, electromagnetic property and microwave absorption performance were fully characterized, respectively. This SiO x C shell effectively inhibited the agglomeration of cobalt particles, and regulated the complex electromagnetic parameters by decreasing permittivity and introducing polarization relaxation, all of which determined the efficient reflection loss with RL min value of −60.3 dB at 16.2 GHz and matching thickness of only 2.05 mm. Meanwhile, the effective absorption band is up to 7.1 GHz at 2.3 mm. By optimizing of core-shell structure and material components, the high-absorption performance was obtained through impedance matching, multi-interfacial polarizations, dipole (or defects) polarization and magnetic loss. Therefore, the Co@ SiO x C composites present a facile and promising route toward the design of large-scale-preparation and excellent microwave absorbing materials. • First use KH-550 as a preliminary coating toward core-shell absorber. • The EAB of Co@SiO x C composites is of 7.1 GHz and RL min is up to −60.3 dB at 2.05 mm. • It is convenient to synthesize.

A new design and synthesis approach of supported metal catalysts via interfacial hydrothermal-oxidation/reductive- exolution chemistry of Al metal substrate

Supported metal catalysts of high intrinsic catalytic activities with significant mass and heat-transport properties are constructed via in situ synthesis based on the interfacial hydrothermal-oxidation/reductive-exolution (HO/RE) chemistry of Al metal substrates. The hydrothermal reaction of Al metal particles in an aqueous solution of Ni salt gives rise to the formation of NiAl-LDH@Al core-shell microstructure consisting of an Al core and a NiAl layered double hydroxide (LDH) shell with petal-like surface morphology. A reduction of the NiAl-LDH@Al leads to exolution of Ni atoms from the NiAl-LDH shell, developing fine Ni metal nanoparticles (NPs) with high surface dispersion and size uniformity. The mechanism of heterogeneous formation of MeAl-LDH (Me = hetero-metals) structures from Al metal substrate is suggested in detail. For CO2 methanation, the Ni/Al2O3@Al exhibits a three-fold greater turnover frequency (TOF) than the Ni/Al2O3 catalyst prepared by the conventional impregnation method, indicating the marked intrinsic catalytic properties of the Ni/Al2O3@Al catalyst.

Electrospun Core–Shell Fibrous 2D Scaffold with Biocompatible Poly(Glycerol Sebacate) and Poly-l-Lactic Acid for Wound Healing

Biomimetic scaffolds made by synthetic materials are usually used to replace the natural tissues aimed at speeding up the skin regeneration. In this study, a flexible and cytocompatible poly(glycerol sebacate)@poly-l-lactic acid (PGS@PLLA) fibrous scaffold with a core–shell structure was fabricated by coaxial electrospinning, where the shell PLLA was used to be a skeleton with pores on the fibrous surface. The fibrous morphology with pores on the surface of the prepared fibers was observed by SEM. The core–shell microstructure of PGS@PLLA fibers was confirmed by TEM and Laser Scanning Confocal Microscopy (LSCM). In addition, the prepared fibers exhibited a strong ability to repair tissues of the skin wound, where the stability of cell security and proliferation, and the lower inflammatory response were all superior to those of pure PLLA scaffold. It’s worth noting that the percentage of skin tissue was regenerated by 95% within 14 days, which suggests the potential application for electrospun-based synthetic fibrous scaffolds on wound healing.

Study on the flame retardancy of high impact polystyrene composites filled with organic-modified carbon nanotubes

ABSTRACTCarbon nanotubes (CNTs) were organic modified by the synthesized flame retardant (FR) named as spirocyclic pentaerythritol bisphosphorate disphosphoryl chloride/10-(2,5-dihydroxyphenyl)-9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (SPDH). CNTs-g-SPDH with a core-shell microstructure was successfully obtained, and its grafting efficiency was calculated to be about 65%. Effects of pristine CNTs and modified CNTs on flame retardation, structure and mechanical properties of high impact polystyrene (HIPS) were investigated. Cone calorimeter results showed that the heat release rate (HRR) and smoke production rate (SPR) of HIPS nanocomposites filled with CNTs or CNTs-g-SPDH were reduced. Moreover, addition of CNTs-g-SPDH resulted in better charring performance than that of pristine CNTs. Modification of CNTs improved compatibility and dispersion in the polymer matrix. Mechanical measurements showed that the Young’s modulus increased, while the tensile strength and elongation at break decreased. The negative effect of CNTs-g-SPDH on tensile strength of HIPS resin was obviously minimized by organic modification of CNTs.