Hollow Spheres Research Articles

Rheology of Suspensions Thickened by Cellulose Nanocrystals.

The steady rheological behavior of suspensions of solid particles thickened by cellulose nanocrystals is investigated. Two different types and sizes of particles are used in the preparation of suspensions, namely, TG hollow spheres of 69 µm in Sauter mean diameter and solospheres S-32 of 14 µm in Sauter mean diameter. The nanocrystal concentration varies from 0 to 3.5 wt% and the particle concentration varies from 0 to 57.2 vol%. The influence of salt (NaCl) concentration and pH on the rheology of suspensions is also investigated. The suspensions generally exhibit shear-thinning behavior. The degree of shear-thinning is stronger in suspensions of smaller size particles. The experimental viscosity data are adequately described by a power-law model. The variations in power-law parameters (consistency index and flow behavior index) under different conditions are determined and discussed in detail.

A study on syntactic aluminum foams manufactured infiltrating sintered preforms of iron hollow spheres

This work analyzes the microstructure, porosity, and mechanical properties of syntactic foams obtained infiltrating 3 mm in diameter Fe hollow spheres with an Al–12Si eutectic alloy. The hollow spheres were first sintered at 800, 900, and 1000 °C for 1h to obtain composite porous preforms, focusing on the effect of this sintering on the manufactured syntactic foams. Results showed that the increase in the sintering temperature led to an increase in the porosity from 51 to 56 %, also increasing the percentage of Fe in the solid part of the foams and decreasing the pore cell thickness. This led to significantly higher strength and a brittle behavior for the foams obtained using spheres sintered at 1000 °C, while the foams manufactured using lower temperatures presented a ductile behavior and lower mechanical properties. α (Al8Fe2Si) and β (Al5FeSi) were obtained during infiltration, decreasing the wall thickness of the Fe spheres.

Lightweight porous mullite-silica ceramics with multistage pore structure, low thermal conductivity and improved strength

Thermal protection was always a prominent issue in the aerospace industry. For vehicle safety, reliability and payload requirements, thermal protection materials were usually expected to possess low density, superior mechanical and thermal insulation properties. Here, lightweight and high-strength porous mullite-silica ceramics were manufactured using particle-stabilized foaming technique. The strength and thermal insulation properties of porous ceramics modified with hollow silica spheres were significantly enhanced. A 10 wt% hollow spheres addition achieved a 28.9 % increase in strength and a 33.4 % decrease in thermal conductivity with almost constant porosity (from 86.39 % to 87.04 %). Considering the characteristics of light weight, high compression strength and superior thermal insulation performance, porous ceramics could be applied as thermal protection materials in the aerospace sector.

Radial channel boosting stress release in hollow carbon spheres for high-rate sodium ions storage

Carbon spheres are appealing anode materials for advanced sodium ions batteries. However, several major hurdles to address are the stress-accumulation associated with the drastic volume change, the sluggish sodium ions diffusion kinetics, and poor electrochemically active sites inside. Herein, the von Mises stress distribution uncovers the critical role of the radial channel on the strain relaxation behavior based on the finite element method. Based on the finite element simulation, the radial porous hollow carbon spheres are proposed and synthesized by a universal strategy with a hard-template approach and dynamic graphitization. RPHCSs dominate opened micro-mesoporous features through the shell. With fast sodium ion diffusivity kinetics and much more accessible electrochemical active sites in shell, RPHCSs electrodes deliver a high specific capacity of 103.0 mAh g−1 even at 4000 mA g−1 with a high capacity contribution ratio > 0.1 V (81.1 %), suggesting its great superiority in the application of high-rate sodium ions storage. Such architecture provides a promising structural platform for the fabrication of high-performance carbon spheres material for other electrochemical energy storage systems.

Hydrophobic-treated yolk-shell SnS2@CSs Z-scheme confinement reactor for solar-electro-driven hydrogen peroxide production in neutral media

The diffusion and adsorption properties of the O2/H2O corpuscles at active sites play a crucial role in the fast photo-electrocatalytic reaction of hydrogen peroxide (H2O2) production. Herein, SnS2 nanosheets with abundant interfacial boundaries and large specific areas are encapsulated into hollow mesoporous carbon spheres (CSs) with flexibility, producing a yolk-shell SnS2@CSs Z-scheme photocatalyst. The nanoconfined microenvironment of SnS2@CSs could enrich O2/H2O in catalyst cavities, which allows sufficient internal O2 transfer, improving the surface chemistry of catalytic O2 to O2− conversion and increasing reaction kinetics. By shaping the mixture of SnS2@CSs and polytetrafluoroethylene (PTFE) on carbon felt (CF) using the vacuum filtration method, the natural air-breathing gas diffusion photoelectrode (AGPE) was prepared, and it can achieve an accumulated concentration of H2O2 about 12 mM after a 10 h stability test from pure water at natural pH without using electrolyte and sacrificial agents. The H2O2 product is upgraded through one downstream route of conversion of H2O2 to sodium perborate. The improved H2O2 production performance could be ascribed to the combination of the confinement effect of SnS2@CSs and the rich triple phase interfaces with the continuous hydrophobic layer and hydrophilic layer to synergistically modulate the photoelectron catalytic microenvironment, which enhanced the transfer of O2 mass and offered a stronger affinity to oxygen bubbles. The strategy of combining the confined material with the air-breathing gas diffusion electrode equips a wide practical range of applications for the synthesis of high-yield hydrogen peroxide.

Characterization of resistance welded hybrid sandwich sheets with additively manufactured core structure

Abstract Production of additively manufactured sandwich sheets is limited to small sizes. In the new introduced process route, additively manufactured core structures are joined with rolled face sheets by resistance welding, and the formability of the hybrid sandwich sheets is investigated. The necessity of developing the humps to improve the quality of resistance welding is initially investigated. Two different core structures, namely honeycomb and hollow sphere, are selected, and electrical-thermal coupled simulations with the ABAQUS software are performed to study the temperature distribution during resistance welding without and with hump. The strength of the joints for the fabricated sandwich sheets is verified by a quasi-static shear test. It is experimentally proven that the sandwich sheets without a hump in the core structure are not fully joined, and desired temperature localization is possible only by applying the hump. This is because the hump reduces the contact area, which leads to an increase in current density at the point where the resistance ratios are changed. This leads to higher temperatures in the intended joining zone. Different hump geometries for the core structure are designed, fabricated, and joined to the face sheets under different process parameters. The spot contact yields up to 50% higher shear strength than the linear or area contact. The free air bending results show that the double weld is essential for successful subsequent bending. It is also concluded that increasing the resistance welding time by more than 120 ms does not affect the joining strength of hybrid sheets.

Simulation study of compressive mechanical properties of spheroidal cytosolic lattice structures

Ultra-lightweight metallic lattice structures are lightweight functional materials, and the design of their cell elements is a focus of research. Based on the idea of hollow sphere and lattice structure, this paper designs a kind of spherical cytosolic lattice structure, investigates its mechanical properties when compressed by numerical simulation, analyzes its deformation law, derives the nominal stress-strain curve, and investigates the effects of the rod diameter and the cytosolic sphere center distance on the structure’s properties of the effective modulus of elasticity, yield limit, plateau stress, energy absorption and specific energy absorption. The results of the study show that the compressive deformation of the structure exhibits three types depending on the spherical center distance. The mechanical properties of the structure, such as effective modulus of elasticity, yield limit, and plateau stress, show a pattern of decreasing and then increasing with the increase of the spherical center distance, and the minimum value is reached when the spherical center distance is 9.0, but the specific energy absorption of the structure shows a pattern of increasing and then decreasing, and it reaches the maximum value when the spherical center distance is 9.6 mm. The validity of the numerical analog simulation analysis was experimentally verified by 3D printing specimens.

Superlong cycle-life sodium-ion batteries supported by electrode/active material interaction and heteroatom doping: Mechanism and application

To achieve both the capacity and stability of metal sulfides simultaneously remains a significant challenge. In this study, we have synthesized the manganese-doped copper sulfide three-dimensional (3D) hollow flower-like sphere (M/CuS-NSC), encapsulated in a nitrogen and sulfur co-doped carbon. The hollow lamellae structure allows the rational self-aggregation process of numerous active surface area enlarged nanosheets, thereby enhancing electrochemical activity. The subsurface framework characterized by CSC bonds enhances the pseudo-capacitive properties. Furthermore, the transformation of sulfur and the isomerization of carbon contribute to the enhancement of sodium ion storage. The incorporation of Mn into CuS lattice increases the interplanar distance, providing additional space for the accommodation of sodium ions. Mn doping facilitates the localization of electrons near the Fermi level, thereby improving conductivity. Additionally, Cu foils coated with M/CuS-NSC-2 engage with the electrolyte and sulfur, initiating the reaction sequence through the formation of Cu9S8. Consequently, M/CuS-NSC-2 exhibits highly reversible capacities of 676.24 mAh g−1 after 100 cycles at 0.1 A g−1 and 511.52 mAh g−1 after 10000 cycles at 10 A g−1, with an average attenuation ratio of only 0.009 %. In this study, we propose an effective strategy that combines structural design with heteroatom doping, providing a novel approach to enhance the electrochemical performance of monometallic sulfide.

Design strategy of TiO2/AgInSe/CdS/CdSe/ZnS photoanode and optimization of CdSe nanoparticles layer for increasing the efficiency of quantum dot-sensitized solar cells

In this study, ternary AgInSe (AISe) quantum dots compound were synthesized using a novel chemical precipitation method followed by a controlled hydrothermal treatment. The as-prepared particles were deposited onto a mesoporous TiO2 substrate to be applied as the photoelectrode of quantum dot sensitized solar cells (QDSSCs). Two configurations of multilayer photoanodes i.e. the TiO2 NCs/AgInSe/CdS/ZnS and TiO2 NCs/AgInSe/CdS/CdSe/ZnS were fabricated and employed for higher photovoltaic performance. The co-sensitizing CdS and CdSe nanocrystals layers were synthesized and deposited through successive ionic layer adsorption and reaction (SILAR) and chemical bath deposition (CBD) techniques, respectively. The results revealed that the QDSSCs with TiO2 NCs/AgInSe/ZnS photoanode initially showed an efficiency of 0.45 %. Incorporating CdS NCs as a quasi-shell film increased the efficiency to 3.9 % in the optimized TiO2/AgInSe/CdS(3 cycle)/ZnS configuration. Adding CdSe nanocrystals over-layer did not improve the efficiency of corresponding cells due to the increased thickness and resistance. Instead, the TiO2/AgInSe/CdS(2 cycle)/CdSe(12 min)/ZnS photoanode resulted in the efficiency of 4.10 % with 34 % improvement. Using the sub-micron size TiO2 hollow spheres (HSs) as the light scattering layer created further light absorption and enhanced performance. It was shown that the photovoltaic parameters were increased to short circuit current density (Jsc) of 23.25 mA/cm2, open-circuit voltage (Voc) of 512 mV and overall efficiency equal to 4.55 %

NiCo2S4 nanotubes in situ anchored double-layered hollow carbon nanospheres towards enhanced overall water splitting

An efficient approach is developed to fabricate hybrid nanomaterials by anchoring in situ NiCo2S4 components on hollow double-layered carbon nanospheres (DCs). NiCo(CO3)(OH)2 is deposited on DCs and then reacted with S ions to create NiCo2S4 phase. Because of the homogeneous distribution of nanoparticles and well-developed interface, samples reveal excellent electrochemical activity. The compositions of NiCo2S4/hollow DCs (denoted as DCs-x-y, x and y are the molar ratios of Ni and Co in precursors) are adjusted to test the growth kinetics and morphology evolution. Under optimized conditions, the capabilities of composite sample DCs-0.20–0.30 outperform DCs and NiCo2S4 alone, which is ascribed to the high specific surface area and the existence of monodispersed hollow carbon spheres improving the distribution of NiCo2S4 and the overall conductivity to increase active sites. Especially, the optimized sample DCs-0.20–0.30 exhibits high performances and stability for enhanced hydrogen evolution reaction (HER) in both acidic and alkaline conditions and oxidation evolution reaction (OER) in alkaline electrolyte. Furthermore, using DCs-0.20–0.30 sample as both the cathode and anode in the alkaline electrolyzer, the current density of 10 and 100 mA cm−2 at 1.736 and 2.171 V are obtained. The sample also displays excellent durability for 20 h at 10 mA cm−2.

Hollow ultra-microporous carbon spheres as high-rate anode nanomaterials for sodium-ion batteries

Hollow porous carbon spheres are considered as promising anode nanomaterials for sodium-ion batteries (SIBs), but suffer from the problems of poor rate and cycling performances. Typical improvement strategies by creating micropores or mesopores are used to boost cycling and rata performances. Herein, hollow porous carbon spheres (HPCS) with ultra-micropores are prepared as anode nanomaterials for SIBs. The optimized HPCS-2 delivers a decent capacity of 272.3 mAh g−1 at 0.1 A g−1, a capacity retention rate of 96.62% over 500 cycles at 2 A g–1, and, in particular, a remarkable rate performance of 233.64 mAh g–1 at 10 A g–1. The great enhancement is elucidated predominantly by the abundant ultra-micropores that provide rapid ion-transport pathways and accelerated sodium-ion diffusion coefficient. The results promise rational design and preparation of high-rate carbon anode nanomaterials for sodium storage.

Sea Urchin-Like NiCo-LDH Hollow Spheres Anchored on 3D Graphene Aerogel for High-Performance Supercapacitors.

To enhance the inherent poor conductivity and low cycling stability of dimetallic layered double hydroxides (LDHs) materials, designing a synergistic effect between EDLC capacitors and pseudocapacitors is an efficient strategy. In this paper, we utilized a solvothermal technique employing Co-glycerate as a precursor to prepare sea urchin-like NiCo-LDH hollow spheres anchored on a 3D graphene aerogel. The unique morphology of these hollow microspheres significantly expand the specific surface area and exposes more active sites, while reducing the volume changes of materials during long-term charging and discharging processes. The 3D graphene aerogel serves as a conductive skeleton, improving the material's electrical conductivity and buffering high current. The sea urchin-like NiCo-LDH hollow spheres anchored on 3D graphene aerogel (H-NiCo-LDH@GA) has a specific surface area of 51 m2 g-1 and the ID/IG value is 1.02. The H-NiCo-LDH@GA demonstrate a significant specific capacitance of 236.8 mAh g-1 at 1 A g-1, with a remarkable capacity retention rate of 63.1 % even at 20 A g-1. Even after 8000 cycles at 10 A g-1, the capacity retention still remains at 96.3 %, presenting excellent cycling stability.

Mesoporous carbon hollow spheres with controllable pore structure for efficient lithium and aluminum ion storage

Mesoporous carbon hollow nanospheres (MCHS), synthesized via a block copolymer-mediated supramolecular self-assembly process, serve as both anode materials for lithium-ion batteries (LIBs) and cathode materials for aluminum-ion batteries (AIBs). By adjusting the carbonization temperature and the dosage of the pore extender, 1,3,5-trimethylbenzene (TMB), insights into the relationships among pore structure, crystal structure, and electrochemical properties of MCHS in Li/Al-ion batteries are gained. Their exceptional properties, including hierarchically porous structure, large surface area, tailored inner voids, mesoporous shells, and high electronic conductivity, contribute to high specific capacity, improved rate performances, and remarkable electrochemical stability. Crystallographic insights reveal that highly porous MCHS facilitate the intercalation of ionic lithium and aluminum species into the carbon crystal lattices while maintaining structural integrity. The appropriate mesopore size significantly impacts the storage of lithium or aluminum ions, with relatively larger mesopore sizes being more beneficial for aluminum ion storage compared to lithium ions. The optimal MCHS exhibit a stable discharge specific capacity of 330.8 mAh·g−1 after 800 cycles at a current density of 372 mA·g−1 (1C) in LIBs and 41.6 mAh·g−1 after 500 cycles at 74.4 mA·g−1 in AIBs.

Study of Ceramic Hollow Buoyant Balls Prepared Based on Slip Mold Casting and Brazing Process

In the domain of deep-sea buoyancy material applications, hollow ceramic spheres, known for their high strength and low mass-to-drainage ratio, contribute to increased buoyancy and payload capacity enhancement for deep submersibles, constituting buoyancy materials of exceptional overall performance. This study entails the brazing of two ceramic hemispherical shells, obtained through slurry molding, to form a ceramic float. This process, which integrates slurry molding and ceramic brazing, facilitates buoyancy provision. Further refinement involves welding a ceramic connector onto the ceramic shell, incorporating a top opening to create a ceramic float equipped with an observation window seat. The ceramic float maintains uniform wall thickness, while the observation window facilitates external environmental observation in deep-sea research. Two pressure-resistant spherical shells, produced using this process, underwent testing, revealing the wall thickness of the prepared alumina ceramic hollow spheres to be 1.00 mm, with a mass-to-drainage ratio of 0.47 g/cm3 and a buoyancy coefficient of 53%. The resultant ceramic hollow floating ball can withstand hydrostatic pressure of 120 MPa, while the pressure-resistant ball shell with an observation window seat can endure hydrostatic pressure of 100 MPa, ensuring safe operation at depths of 5000–6000 m. This process provides a production method for subsequent large-scale ceramic float manufacturing for the transportation of objects or personnel.

Construction of hollow sphere MnOX with abundant oxygen vacancy for accelerating VOCs degradation: Investigation through operando spectroscopycombined with on-line mass spectrometry

To clarify the key role of oxygen vacancy defects on enhancing the oxidative activity of the catalysts, metal–organic frameworks (MOFs) derived MnOX catalysts with different morphologies and oxygen vacancy defects were successfully prepared using a facile in-situ self-assembly strategy with different alkali moderators. The obtained morphologies included three-dimensional (3D) triangular cone stacked MnOX hollow sphere (MnOX-H) and 3D nanoparticle stacked MnOX nanosphere (MnOX-N). Compared to MnOX-N, MnOX-H exhibited higher activity for the oxidation of toluene (T90 = 226 °C). This was mainly due to the large number of oxygen vacancy defects and Mn4+ species in the MnOX-H catalyst. In addition, the hollow structure of MnOX-H not only facilitated toluene adsorption and activation of toluene and also provided more active sites for toluene oxidation. Reaction mechanism studies showed that the conversion of toluene to benzoate could be realized over MnOX-H catalyst during toluene adsorption at room temperature. In addition, abundant oxygen vacancy defects can accelerate the activated oxidation of toluene and the formation of oxidation products during toluene oxidation.

Enhanced visible-light photocatalytic activity of N-doped C/Na2Ti6O13/TiO2 hollow spheres for efficient dye degradation

Doping and hybridization with other semiconductors are highly effective ways to address the limitations, including their weak response to visible light and significant recombination of photogenerated carriers. In addition, the assisted carbon on the catalyst surface and the structural design have the advantage of being catalytically active. Herein, visible-light-active N-doped C/Na2Ti6O13/TiO2 hollow spheres (denoted as N–C/NTO/TiO2 HS) were successfully prepared using a facile two-step method and evaluated for methylene blue (MB) aqueous solution degradation under visible-light irradiation.The as-obtained N–C/NTO/TiO2 HS demonstrated improved photocatalytic efficiency (94 %) and pseudo-first-order kinetic degradation rate (0.023 min−1). Moreover, after three cycles of testing, N–C/NTO/TiO2 HS showed a 91 % degradation rate in its photostability. The enhanced photocatalytic performance was attributed to the combined effects of N-doping, carbon species on the surface, and the coupling of TiO2 and Na2Ti6O13 using morphology engineering. Finally, based on the experimental results, a possible photocatalytic mechanism was proposed. This study provides a rational approach toward the development of high-performance titanate-based photocatalysts for solar energy-assisted wastewater treatment.

Repairable body-centered cubic Fe0 anchoring on porous hollow nitrogen-doped carbon spheres with adjusting electron distribution for efficient electrocatalytic ammonia synthesis

Electrocatalytic nitrogen reduction reaction (ENRR) is a promising and efficient method for ammonia production. However, ENRR is restricted by the adsorption and activation of N2. Herein, an efficient nitrogen reduction reaction (NRR) electrocatalyst loaded with zero valent iron (ZVI) particles onto porous nitrogen-doped carbon (NC) hollow spheres is reported. The optimal Fe@10N3C-950 exhibits excellent performance with high ammonia (NH3) yield (152.28 µg h−1 mgcat−1) and Faradaic efficiency (FE, 54.55 %) at − 0.3 V (versus reversible hydrogen electrode, vs. RHE). Bader charge shows that the adsorbed N2 acquires more electrons from Fe sites with body-centered cubic (BCC) structure to better activate N2. Moreover, i-t experiments are performed before electrocatalytic NH3 production to effectively eliminate the effect of oxidation on ZVI and thus, maintain high ENRR activity for Fe@10N3C-950. Theoretical calculations indicate that nitrogen doping not only reduces the Gibbs free energy of rate determining step (RDS), but the BCC-structured Fe can also decrease the energy barriers of N2 activation and RDS.

Nitrogen-doped hollow carbon sphere composite Mn3O4 as an advanced host for lithium-sulfur battery

As the most promising advanced energy storage system, lithium-sulfur batteries (LSBs) are highly favored by the researchers because of their advantages of high energy density (2500 W h kg−1), low cost and non-pollution. However, the low conductivity, volume expansion of sulfur, and shuttle effect are still the great hindrance to the practical application of LSBs. Herein, the above problems can be addressed through the following strategies: (1) Hollow carbon microspheres with high specific surface area were constructed as sulfur hosts to increase sulfur loading while also being able to enhance the physical adsorption of polysulfides; (2) the loading of Mn3O4 particles on the basis of hollow carbon microspheres facilitates the capture and adsorption of polysulfides; (3) the hollow carbon sphere structure as a conductive network can provide more pathways for rapid electrical/ionic transport and also accelerate electrolyte wetting. Moreover, the thinner shell of hollow carbon microsphere is conducive to ion diffusion and speed up the reaction rate. Thus, the NHCS/Mn3O4/S composites exhibit a high discharge specific capacity of 1010.3 mAh g−1 at first and still maintained a reversible capacity of 269.2 mAh g−1 after 500 cycles. This work presents a facile sustainable and efficient synergistic strategy for the development of advanced LSBs.

Generalized magneto-thermoelasticity problem in an orthotropic hollow sphere under thermal shock

This article addresses the magneto-thermoelasticity problem within an orthotropic hollow sphere. The governing equations are formulated based on the Lord-Shulman coupled theory of thermoelasticity. Time-dependent thermal and mechanical boundary conditions are imposed on the inner and outer surfaces of the hollow sphere. The analytical solution is obtained using the finite Hankel transform. A thermal shock in the form of heat flux is prescribed on the sphere’s inner surface, and subsequently, the transient thermal response of the sphere, along with radial displacement and radial, tangential, and circumferential stresses, are derived. The influence of different magnetic field values, orthotropic material properties, and relaxation time is investigated and presented graphically. The obtained results exhibit excellent agreement with existing literature, validating the robustness of the proposed model. The findings not only contribute to the fundamental understanding of magneto-thermoelasticity but also offer practical insights for engineering applications involving orthotropic materials in complex thermal and magnetic environments. The availability of an exact solution facilitates the validation of numerical models, ensuring their accuracy and reliability in capturing the intricate behavior of orthotropic materials under coupled fields.

Optimizing large porous mannitol-leucine microparticles via spray drying technique

The development of large porous microparticles (LPPs) has gained attention for dry powder in-halation (DPI) formulations due to their potential to enhance the efficiency of drug delivery into the lungs. In this work, large porous mannitol-leucine microparticles (MALs) were developed using a spray drying technique. Mannitol was co-spray dried with ammonium bicarbonate (0–50 % w/w) and leucine (1–20 % w/w). The morphology of MAL particles was spherical hollow with corrugated surface. The MAL with 10 % leucine (MAL-10) showed the lowest bulk density (0.08 g/cm3) with the highest surface area (7.85 m2/g), while the aerodynamic diameter (Daer) was within 1–5 μm, indicating the suitability to penetrate the lung. The DSC and XRD results indicated that the MALs exhibited a mixture of β- and α-polymorphs, while the FT-IR spectra con-firmed that no chemical interaction during co-processing. The leucine co-processing significantly improved powder flowability of the MAL-10 (28.33° for angle of repose). In addition, the co-processing with high leucine concentration (10–20 %) significantly reduced moisture sorption, while the polymorph of MALs did not change after 30 days of hygroscopicity study that indicated good stability. According to all results, the MALs could potentially be applied as drug carriers for DPI formulations.