Hollow Microspheres Research Articles

Lightweight, hydrostatic pressure‐resistance, thermal insulating epoxy syntactic foam with a multiscale ternary structure for marine engineering application

AbstractThe study of lightweight epoxy syntactic foams is of great significance for the exploitation of marine resources. In this work, glass fibers reinforced epoxy hollow spheres (GFs‐EHS) were first prepared using a template method, and a lightweight three‐phase epoxy syntactic foam (LWTP‐ESF) with a multiscale ternary structure was prepared using a molding pressing method with epoxy resin as matrix, hollow glass microspheres (HGMs), and GF‐EHS as the lightweight fillers. The effect of HGMs content on the density, uniaxial compression properties, water absorption, and thermal conductivity of obtained LWTP‐ESF was evaluated. The results indicated that the density, uniaxial compression strength, and thermal conductivity of LWTP‐ESF were consistently decreased, while the water absorption was increased with the increase in HGMs content. The highest specific compression strength and lowest thermal conductivity of LWTP‐ESF could reach 52.77 ± 0.82 MPa·cm3/g and 0.113 ± 0.005 W/(m·K), respectively. Moreover, the effect of hydrostatic pressure on the water absorption and thermal conductivity of LWTP‐ESF were also systematically analyzed. This study provides a novel system and method to prepare lightweight epoxy syntactic foams, and the prepared composites have potential applications in the field of lightweight thermal insulation materials for marine.Highlights The composites with a multiscale ternary structure were designed. The composites possessed significantly lower density and thermal conductivity. The water absorption of composites under hydrostatic pressure was evaluated. The thermal conductivity of composites under hydrostatic pressure was evaluated. The water absorption mechanism and thermal insulation mechanism were proposed.

Unraveling the synergistic role of oxygen vacancy and Co dual-site pairs in MOFs-derived defect-engineered Co3O4 catalysts with a hollow architecture for photothermal OVOCs degradation: Formation of reactive oxygen species

Herein, we developed a solvent regulation strategy with dual organic ligands to synthesize a series of Co-MOF-74 isomer derivatives as model materials that were investigated the formation of reactive oxygen species (ROS) and photothermal OVOCs (methanol, acetone and ethyl acetate) degradation. As a result, the defect-engineered Co3O4-DIW-100 with hollow microsphere synthesized under an equivalent volume ratio of N, N-dimethylformamide (DMF), isopropanol and H2O, can efficiently improve the photothermal catalytic conversions for methanol (97 %), acetone (96 %) and ethyl acetate (93 %) oxidation under Xenon lamp irradiation, compared with unremarkable Co3O4-M catalyst. Thanks to its hollow architecture, the optimal Co3O4-DIW-100 possessed the enhanced low-temperature redox capability and more exposed Co3+ and VO sites. Furthermore, DFT and EPR results revealed that the VO and Co dual-site pairs at surrounding structural defects synergistically participated in the generation of abundant ROS (O2−) through a specific O2 activation configuration (Co2+=O–O–Co3+). Meanwhile, light irradiation could induce the separation and transfer of charge carriers to accelerate the formation of O2−. The superior absorption of visible light derived from the narrow Eg value on Co3O4-DIW-100 can boost a higher light-driven temperature to perform the photothermal OVOCs oxidation. The formation and transformation of sectional key reaction intermediates, such as CH3COOH, CH3OH and HCOOH, were accurately identified and investigated by in-situ DRIFTS results on the methanol, acetone and ethyl acetate oxidation.

Composite ZnFe2O4/SrWO4 hollow microspheres as catalyst for high-performance photo-Fenton degradation

Low degradation rate for a long degradation time and poor cycle stability caused by rapid recombination of generated electron-hole pairs are tough challenges for photo-Fenton degradation The unique microstructure catalyst can provide enough catalytic surface to prevent the recombination of electron-hole pairs and facilitate the barrier-free transport of active species. In addition, the special hollow microsphere structure can effectively accelerate the Rhodamine B (RhB) penetration and the photo-Fenton process. Introducing SrWO4 can increase oxygen vacancies and optimize the electronic structure of ZnFe2O4, thus enhancing electron transport and RhB degradation in the photo-Fenton process. This kind of catalytic material ZnFe2O4/SrWO4 (ZFO/SW) in the photo-Fenton process can effectively degrade the 99.18 % RhB dye only within 20 min with remarkable cycling stability. This work demonstrates the high efficiency of ZFO/SW as a photocatalyst and confirms the contribution of the current design concept to the development of photo-Fenton degradation materials.

Development of tunable porous alumina monolith using hollow microspheres via extrusion-based 3D printing

Hierarchical cellular ceramics have attracted considerable interest due to their versatility and unique physico-mechanical effectiveness for advanced applications. Tailorable alumina foams with low shrinkage were fabricated through an innovative combination of 3D printing and sacrificial templating with low environmental footprint. The viscoelastic pastes were formulated using the aqueous-based solution of binder, dispersant, and plasticizer with different volumes of α-alumina and lightweight hollow microspheres (HMs) as a template. The solid-to-liquid ratio increased 53–80 vol% with the inclusion of HMs for printable rheology. Cellular architectures of alumina were structured through a material extrusion-based technique and then thermally treated at 1200 °C. Finally, the alumina monoliths achieved a ∼55–93 % porosity with three different types of adjustable pores, produced by combining 3D printing, burning of templates, and inter-particle voids. The HMs generated spherical pores (7–47 µm) in the printing struts with reduced CO2 emissions compared to conventional sacrificial porogens during the burnout process.

Transition Metal‐Cross‐Linked‐Starch Aerogel‐Derived Porous Carbon‐Based Monolithic Chainmail Electrodes for High‐Current‐Density and Durable Alkaline Water Splitting

AbstractA porous carbon‐based monolithic chainmail electrode, namely Co2P@CSA, is fabricated via direct carbonization of Co2+‐cross‐linked‐starch aerogel (Co2+‐SA) followed by low‐temperature vapor phosphorization. During successive carbonization‐phosphorization, the SA framework is formulated into 3D hierarchically porous carbon membrane matrix comprising hollow open carbon microspheres while the cross‐linked Co species are converted into uniformly distributed carbon‐encapsulated Co2P nanoparticles on carbon microspheres. Thanks to the high porosity, excellent electrolyte wettability, unique chainmail structure, and good mechanical strength, the monolithic Co2P@CSA can be directly used as a binder‐free bifunctional electrocatalyst for alkaline water splitting, and it can afford a high current density of 100 mA cm−2 for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at low overpotentials of 140.0 and 305.5 mV, respectively, with outstanding stability at 50 mA cm−2 for >30 h. More significantly, an alkaline electrolyzer assembled using Co2P@CSA achieves a current density of 100 mA cm−2 for overall water splitting (OWS) at a cell voltage of 1.94 V with unit Faradaic efficiency and provides a high solar‐to‐hydrogen (STH) conversion efficiency of 13.4 % when driven by a commercial silicon solar cell. This work offers an effective strategy towards cost‐effective fabrication of high‐performance carbon‐based monolithic chainmail electrocatalysts for energy conversion reactions.

Construction of thermally resistant and flame-retardant multifunctional polyester composite fabrics

The development of thermally resistant textiles with fire safety using thermo-expandable hollow microsphere (TEHM) has garnered significant interest. In this study, TEHM and ammonium polyphosphate (APP) were bonded to polyester fabric surface by using polyurethane coating. The surface morphology, thermally resistant, flame-retardant performance and mechanism of the developed PET@TEHM/APP composite fabric were investigated. The PET@TEHM/APP composite fabric exhibited the reduced thermal conductivity of 0.07458 W/m·K from 0.13120 W/m·K of pristine PET fabric. The thermal conduction and radiation performance of the PET@TEHM/APP composite fabric decreased owing to the low thermal conductivity of the expanded TEHM. The PET@TEHM/APP composite fabric presented a damaged length of 13.5 cm without melt dripping, achieving the B1 classification. The peak heat release of the PET@TEHM/APP composite fabric decreased by 58.3 % versus pristine PET fabric according to cone calorimetry test. PET@TEHM/APP composite fabric also had an FRI of 1.001, showing ‘Good’ flame retardancy performance. TG-IR and char residue analyses suggested that the flame retardancy of PET@TEHM/APP composite fabric improved by the synergic flame-retardant action in both gas and condensed phases.

Monodispersed hollow ceramic microspheres fabricated based on preceramic polymers and pulse‐controlled coaxial injection

AbstractHollow ceramic microspheres (HCMs) have widespread applications in aerospace and electronic areas owing to their multiple merits such as low density, low thermal conductivity, oxidation, and high‐temperature resistance. In this work, monodispersed HCMs were fabricated based on preceramic polymers and the pulse‐controlled coaxial injection approach. The size and shell morphology of hollow ceramic spheres can be flexibly tailored by adjusting the diameters of coaxial needles, and the composition and flow rates of inner and outer liquids. As‐obtained HCMs were comprised of ultrafine nanocrystals of ZrO2, SiO2, ZrC, and SiC, which can enhance the interfacial polarization effect. Through optimization of microstructure and composition, the electromagnetic shielding performance of HCMs reached up to 45 dB in the frequency range of 12–18 GHz. This work demonstrates a facile and general method for the fabrication of monodispersed HCMs.

Effect of hollow glass microspheres surface modification on the compressive strength of syntactic foams

Polymer matrix syntactic foams made of hollow glass microspheres (HGMs) and epoxy resin are widely used in underwater vehicles providing buoyancy due to their advantages of low density and high mechanical strength. When HGMs is strong enough, surface modification of HGMs is an effective method to improve the compressive strength of syntactic foams. However, the effects of different surface modifiers on the physical properties of HGMs and the compressive strength of syntactic foams have rarely been systematically studied. It is of great significance to enhance the interfacial strength of syntactic foams. Herein, the T40 HGMs was treated by different modifiers (HCl, NaOH, Li2SiO3, Me3SiONa, KH550, KH560, KH570, and Volan), physical properties of modified HGMs were studied, including true density, angle of repose, isostatic compressive strength, specific surface area, and contact angle. Furthermore, the effects of modified HGMs on the compressive strength of syntactic foams were also studied. The results showed that the compressive strength depend largely on the interface bonding between HGMs and resin matrix. This work can provide some references for mechanical property reinforcement of syntactic foams with high filling ratio and plenty of interface zones.

Preparation of RDX/F2311/Fe2O3/Al Composite Hollow Microspheres by Electrospray and Synergistic Energy Release during Combustion between Components.

Nanothermites and high-energy explosives have significantly improved the performance of high-energy composites and have broad application prospects. Therefore, in this study, RDX/F2311/Fe2O3/Al composite hollow microspheres were successfully prepared utilizing the electrospray method using F2311 as a binder between components. The results show that the combustion time of the composite hollow microspheres is shortened from 2400 ms to 950 ms, the combustion process is more stable, and the energy release is more concentrated. The H50 of the composite hollow microspheres increased from 14.49 cm to 24.57 cm, the explosion percentage decreased from 84% to 72%, and the sensitivity of the composite samples decreased significantly. This is mainly the result of the combination of homogeneous composition and synergistic reactions. The combustion results show that F2311 as a binder affects the tightness of the contact between the components. By adjusting its content, the combustion time and the intensity of the combustion of the composite microspheres can be adjusted, which provides a feasible direction for its practical application.

Template Synthesis of SnO2 Hollow Microspheres and Enhanced Photocatalytic Activity

Template Synthesis of SnO₂ Hollow Microspheres and Enhanced Photocatalytic Activity

Processing, Microstructure, and Performance of Robocast Clay-Based Ceramics Incorporating Hollow Alumina Microspheres.

The restoration of ancient ceramics has attracted widespread attention as it can reveal the overall appearance of ancient ceramics as well as the original information and artistic charm of cultural relics. However, traditional manual restoration is constrained due to its time-consuming nature and susceptibility to damaging ancient ceramics. Herein, a three-dimensional (3D) printing technique was employed to accurately restore Chinese Yuan Dynasty Longquan celadon using hollow Al2O3 microsphere-modified 3D printing paste. The results show that the hollow Al2O3 microsphere content plays a vital role in the printability, physical properties, and firing performance of the modified 3D printing paste. The printed green bodies show no noticeable spacing or voids under moderate rheological conditions. The as-prepared ceramic body modified with 6 wt.% hollow Al2O3 microspheres and fired at 1280 °C exhibits optimal bending strength of 56.66 MPa and a relatively low density of 2.16 g∙cm-3, as well as a relatively uniform longitudinal elastic modulus and hardness along the interlayer. This 3D printing technique based on hollow Al2O3 microsphere-modified paste presents a promising pathway for achieving non-contact and damage-free restoration of cultural relics.

Effects of the ZrO2 Crystalline Phase and Morphology on the Thermocatalytic Decomposition of Dimethyl Methylphosphonate.

Thermocatalytic decomposition is an efficient purification technology that is potentially applicable to degrading chemical warfare agents and industrial toxic gases. In particular, ZrO2 has attracted attention as a catalyst for the thermocatalytic decomposition of dimethyl methylphosphonate (DMMP), which is a simulant of the nerve gas sarin. However, the influence of the crystal phase and morphology on the catalytic performance of ZrO2 requires further exploration. In this study, monoclinic- and tetragonal-phase ZrO2 (m- and t-ZrO2, respectively) with nanoparticle, flower-like shape and hollow microsphere morphologies were prepared via hydrothermal and solvothermal methods, and their thermocatalytic decomposition of DMMP was systematically investigated. For a given morphology, m-ZrO2 performed better than t-ZrO2. For a given crystalline phase, the morphology of hollow microspheres resulted in the longest protection time. The exhaust gases generated by the thermocatalytic decomposition of DMMP mainly comprised H2, CO2, H2O and CH3OH, and the by-products were phosphorus oxide species. Thus, the deactivation of ZrO2 was attributed to the deposition of these phosphorous oxide species on the catalyst surface. These results are expected to help guide the development of catalysts for the safe disposal of chemical warfare agents.

MICROBALLOONS: A PROMISING APPROACH FOR GASTRORETENTIVE DRUG DELIVERY SYSTEM AND THEIR ADVANTAGES, LIMITATIONS, RECENT ADVANCEMENT IN DRUG DELIVERY SYSTEM, PATENTS AND FUTURE ASPECTS

The key objective of the present review was to collect the latest literature on technological advancements towards microballoons as novelistic buoyant drug delivery systems. Microballoons are hollow microspheres with a potential approach for gastric retention, offering controlled release of the drugs. It offers prominent targeting of drugs in the stomach. More significantly, it is an anticipated drug delivery system in the gastrointestinal tract’s upper section. At a high pH environment, this drug delivery system improves the solubility of less soluble drugs. It is an innovative and authenticated drug delivery system, specifically for those drugs which are unable to tolerate the acidic pH. The microballoons are developed by several techniques like Solvent Evaporation, Solvent Diffusion-Evaporation, Solvent Diffusion and Spray Drying techniques, to develop the space of empty inner core. Moreover, this manuscript covers significance, limitations, applications, list of polymers used, characterization, formulation design and evaluation parameters of microballoons.

Crystallographic types depended energy storage mechanism for zinc storage

As a new type cathode material for aqueous zinc-ion batteries (ZIBs), manganese-based sulfides have gradually received researchers’ concern in recent years due to their lower electronegativity, higher electronic conductivity and better electrochemical activity compared with the corresponding manganese-based oxides. However, the revelation of energy storage mechanism for manganese-based sulfides is full of great challenges, which largely restricts their application. Herein, inspired by density functional theory calculations, we design and synthesize the γ-MnS and α-MnS hollow microspheres with different crystallographic types for the first time, delivering significantly different energy storage mechanisms of the two MnS electrodes. Impressively, the γ-MnS electrode can stably exist and store energy during the whole charging/discharging processes, while the α-MnS electrode first undergoes irreversible in situ oxidation to generate ZnMnO3/MnOx during the initial charging process, and then the reversible H+/Zn2+ co-insertion/extraction energy storage behavior occurs during the subsequent discharging/charging processes. This unique phase transition mechanism caused by in situ electrochemical oxidation enables the α-MnS electrode to achieve enhanced ion diffusion kinetics, thereby improving the rate capability and cyclic stability. This work not only enriches the energy storage mechanism of manganese-based sulfide cathodes, but also offers research ideas for the design and development of advanced manganese-based cathodes.

Simulation of interfacial debonding in hollow particle reinforced composites with VCFEM

The addition of hollow glass microsphere into composites is a method to improve mechanical properties. However, the interfacial debonding of hollow microsphere inevitably causes a decrease in the mechanical properties of the material, which ultimately leads to the failure of the composites. In the numerical simulation of such hollow particle-reinforced composites, the ordinary displacement finite element requires a large number of meshes, which undoubtedly greatly increases the computational cost. In this paper, a new VCFEM is proposed to solve this problem by establishing a two-dimensional Voronoi cell finite element model, deriving the residual energy generalized function of hollow particle-reinforced composites, and calculating the interface debonding. The simulation results are compared with the commercial software MARC, ABAQUS to verify the effectiveness of this VCFEM. The results show that this VCFEM greatly improves the computational efficiency while ensuring the accuracy. Based on this model, this paper also investigates the effect of the generation of interfacial debonding on the overall structure and the effect of different wall thickness of hollow particles on the damage of element debonding.

Tomographic analysis of segregation behavior of hollow glass microspheres in lightweight cementitious composites

Lightweight concrete must contain lightweight aggregates that are more susceptible to segregation than traditional concrete. Concrete has increasingly used lightweight fillers but research on segregation analysis is relatively scarce. To systematically investigate the segregation of hollow glass microspheres (HGMs), lightweight cementitious composites (LWCC) with a water-to-cement (w/c) ratio of 0.25–0.5 were investigated. The 3D structure of HGMs in the LWCC was observed with micro-computed tomography (μ-CT), and a rapid CT projection analysis was proposed to evaluate the segregation. The results showed that a slight segregation tendency of HGMs was observed from 0.45, while severe floating segregation occurred at 0.5 of w/c. The flowability of the LWCC increased with the increase of the w/c ratio, but it could not anticipate the segregation behavior. Meanwhile, 2D CT projection image could quickly evaluate the segregation phenomenon so it was proposed that it can be utilized for evaluating potential segregation of cement-based materials.

CdS/CdSe/PbS quantum dots sensitized TiO2 eggshell hollow microspheres photoanode to boost photocurrent and power conversion efficiency of QDSSC

Light harvesting plays crucial role for high photovoltaic performance of quantum dots sensitized solar cell (QDSSC). However, there are still issues need to be tackled, such as enlarging light response range and enhancing light scattering capability. In this work, TiO2 eggshell hollow microspheres (EHMS) were synthesized by carbonaceous microspheres (CMS) template method and co-sensitized by CdS/CdSe/PbS quantum dots (QDs) for application in QDSSC. Compared with QDSSC based on TiO2 nanoparticles (NP) and TiO2 hollow microspheres (HMS), the TiO2 EHMS based QDSSC showed a remarkable increase of short-circuit current density (Jsc) to 24.81 mA cm−2 with a power conversion efficiency (PCE) of 4.07 %. Photoelectrochemical analysis of QDSSC indicate that CdS/CdSe/PbS QDs can enlarge the light response range, and the TiO2 EHMS improve the light scattering, leading to the improvement of light harvesting efficiency. Charges dynamics tests results proved that a larger charges recombination resistance at photoanode/electrolyte interface and longer electron lifetime can be achieved with TiO2 EHMS, contributing to the boost of Jsc. The presented study introduces a simple strategy for researchers interested in designing photoanode for various photoelectrochemical applications.

Micromechanical Dilution of PLA/PETG-Glass/Iron Nanocomposites: A More Efficient Molecular Dynamics Approach.

Polylactic acid (PLA) and poly(ethylene terephthalate glycol) (PETG) are popular thermoplastics used in additive manufacturing applications. The mechanical properties of PLA and PETG can be significantly improved by introducing fillers, such as glass and iron nanoparticles (NPs), into the polymer matrix. Molecular dynamics (MD) simulations with the reactive INTERFACE force field were used to predict the mechanical responses of neat PLA/PETG and PLA-glass/iron and PETG-glass/iron nanocomposites with relatively high loadings of glass/iron NPs. We found that the iron and glass NPs significantly increased the elastic moduli of the PLA matrix, while the PETG matrix exhibited modest increases in elastic moduli. This difference in reinforcement ability may be due to the slightly greater attraction between the glass/iron NP and PLA matrix. The NASA Multiscale Analysis Tool was used to predict the mechanical response across a range of volume percent glass/iron filler by using only the neat and highly loaded MD predictions as input. This provides a faster and more efficient approach than creating multiple MD models per volume percent per polymer/filler combination. To validate the micromechanics predictions, experimental samples incorporating hollow glass microspheres (MS) and carbonyl iron particles (CIP) into PLA/PETG were developed and tested for elastic modulus. The CIP produced a larger reinforcement in elastic modulus than the MS, with similar increases in elastic modulus between PLA/CIP and PETG/CIP at 7.77 vol % CIP. The micromechanics-based mechanical predictions compare excellently with the experimental values, validating the integrated micromechanical/MD simulation-based approach.

Impact of thermal conductivity of aerogel-enhanced insulation materials on building energy efficiency in environments with different temperatures and humidity levels

New building thermal insulation materials, such as aerogel-enhanced insulation materials, are constantly emerging. To study how cement-based aerogel-enhanced thermal insulation materials perform under temperature and humidity changes, various aerogel-enhanced hollow glass microsphere insulation boards (HGBs) have been developed as building thermal insulation materials. The thermal conductivity of aerogel-enhanced HGBs, expanded polystyrene (EPS), and foamed cement (FC) was measured at various relative humidity levels and temperatures, and the summer cooling load of buildings with aerogel-enhanced HGBs, EPS, or FC as the insulation layer was simulated for different building heights and thermal zones. The results show that (1) the new aerogel-enhanced HGB materials are more suitable for building insulation in humid and hot areas than FC; (2) the cooling load of small buildings with fewer floors is more sensitive to the variation in the thermal conductivity with temperature and humidity; (3) for buildings in areas with hot summers and warm winters, the impact of the outdoor relative humidity should be fully considered when calculating summer cooling loads.

Constructing ‘bayberry shape’ structure on HGMs surface using CNTs to enhance the mechanical properties of HGMs/epoxy composites

The lightweight composites, composed of epoxy resin (EP) and hollow glass microspheres (HGMs), have been widely applied in marine buoyancy materials, insulation for marine pipelines, and aerospace. However, achieving lower density often requires a significant addition of HGMs, leading to a compromise in mechanical properties. To address this problem, this paper proposes a method to enhance the mechanical properties of HGMs/EP composites without altering the HGMs content. Here, the ‘bayberry shape’ structure of HGMs was achieved by chemically grafting carbon nanotubes (CNTs) onto their surface through an esterification reaction. Subsequently, a lightweight CNTs-HGMs/EP composite with improved strength was fabricated using these ‘bayberry’ HGMs as fillers and EP as the matrix. The effect of different grafted-CNTs content on HGMs' surface on the mechanical properties of CNTs-HGMs/EP composites, along with the enhancement mechanism, were systematically analyzed. The tensile strength, flexural strength and compressive strength of CNTs-HGMs/EP composites demonstrated remarkable increases of 39.14%, 21.78% and 17.87%, respectively, compared to pure HGMs/EP composites. Our results demonstrate that surface modification of HGMs could significantly improved the mechanical properties of HGMs/EP composites without affecting their density. Moreover, this method was characterized by its simplicity in operation and batch preparation, which holds great significance for the efficient production of lightweight composites.