Hollow Glass Microspheres Research Articles

Light scattering in a three-phase photosensitive system via Monte Carlo approach.

Digital light processing (DLP)-based additive manufacturing has emerged as a powerful technique for fabricating structures from filled resin systems, in which the light scattering behavior is critical to the dimensional fidelity of the cured part. Recently created low density filled resins that incorporate hollow microspheres introduce a third optically active phase, producing yet more complex scattering and cure behaviours that existing empirical relationships cannot predict. This study simulates light scattering in these systems via Mie theory and a novel Monte Carlo model, providing insight into the relationship between filler volume fraction and cured dimensions, and proposes an inversion parameter for predicting film dimensions. Cured resin geometry dimensions such as cured depth (CD) and cured width (CW) are predicted using the developed model for 10, 30, and 50 vol% hollow glass microsphere filled resin systems. In contrast to standard two-phase models, our three-phase model predicts a positive relationship between cured depths and half-widths and the filler volume fraction, consistent with experimental data. By elucidating the intricacies of light scattering in three-phase systems, this work provides valuable insights for advancing DLP-based additive manufacturing and designing filled resin formulations to achieve the desired cured dimensions.

Lightweight shear stiffening gel with enhanced mechanical and thermal-insulating performance for advanced fire suit

A lightweight and thermal-insulating shear stiffening gel (LT-SSG) with anti-impact was developed via introducing hollow glass microspheres BR20 into shear stiffening gel (SSG). It was lightweight enough to be placed on a leaf. LT-SSG showed the ability to resist impact. Finally, a multifunctional Kevlar safeguarding suit (MKSS) with flame retardant property was fabricated. It exhibited good adiabatic effect which could isolate heat at high temperatures and prevent heat loss at low temperatures. • LT-SSG with lightweight, heat-insulation and anti-impact properties was prepared. • LT-SSG showed enhanced protective effect due to the existence of BR20 particles. • A multifunctional Kevlar safeguarding suit (MKSS) was assembled. • MKSS was capable to resist fire combustion and displayed good adiabatic effect. • MKSS effectively prevented the heat loss from humans in cold environment. Herein, a lightweight and thermal-insulating shear stiffening gel (LT-SSG) with anti-impact was prepared by introducing insulating glass microspheres BR20 into SSG. The density of LT-SSG was 48.97% lower than that of SSG. Meantime, LT-SSG showed excellent energy absorption effect. The remained impact force of LT-SSG was only 0.23 kN compared with 0.41 kN of SSG when impacted from 20 cm. Moreover, LT-SSG with good thermal insulation performance could effectively isolate surrounding temperature to 42.6 ℃ at 80 ℃ and block external cold temperature to protect the heat loss from human body. While SSG as well as the breakage of BR20 particles absorbed and dissipated much impact energy, proving its excellent protective properties. Finally, a multifunctional Kevlar safeguarding suit (MKSS) was developed. It showed the ability to resist low-speed drop hammer and high-speed ballistic impact. To this end, the reported LT-SSG showed promising application in fire suit and body armors.

Copper-coated hollow glass microspheres filled rubber composites: Lightweight, interface bonding and mechanical properties

Copper-coated hollow glass microspheres filled rubber composites: Lightweight, interface bonding and mechanical properties

Tailoring asymmetric filler arrangement by hollow glass microspheres towards polymer composites with improved through-plane thermal conductivity

Highly anisotropic thermal conductivity, i.e., a limited through-plane thermal conductivity (λ⊥), is normally observed in polymer composites with asymmetric fillers that are vulnerable to orientate along the flow field during melt-processing. We herein explored the possibility to tailor the filler arrangement and λ⊥ of polymer composites with asymmetric fillers using nonconductive hollow glass microspheres (HGμS). The results showed that λ⊥ of ultrahigh-filled polyamide 6/flake graphite (PA6/FG) composites with 70 wt% (54.7 vol%) FG increased by 27% instead of decreasing when replacing 3 wt% FG platelets with HGμS (i.e., 8.1 vol%, and 12.2 vol% HGμS with a diameter of 18 μm and 38 μm, respectively). The increase of λ⊥ from diluting FG with HGμS was attributed to the reduced structural anisotropy of the FG network, i.e., the in-plane orientation of FG platelets within the polymer matrix was inhibited. A synergistic effect on the improvement of λ⊥ was achieved by replacing FG platelets with combination of HGμS and alumina (Al2O3) microspheres. This synergy takes the effects from the “bridging” of FG platelets by Al2O3 and the inhibiting of in-plane FG orientation by HGμS.

Thermal insulation and structural reliability of modified epoxy resin‐based ablation thermal protection coatings in aerothermal‐vibration coupling environment

AbstractNovel hybrid ablation thermal protection coatings (FHMP‐ATPCs), employing iron trioxide (Fe2O3) powder, hollow glass microspheres, and mica powder as the fillers in hydroxyl‐terminated silicone oligomer‐bridged epoxy resins (PSG) copolymer, is investigated using an aerothermal‐vibration coupling test system. The ablation behavior and structural reliability of FHMP‐ATPCs with varying coating thickness were studied. During the test, the total enthalpy of airflow and dynamic pressures are 23 MJ/kg and 300 Pa, accompanied by the random vibration with a frequency of 20–2000 Hz and a total root‐mean‐square acceleration of 14.9g. The maximum surface and back‐face temperatures of the coating with the thickness of 2 mm reached 836.2°C and 156.4°C, respectively. Results also showed that the reduction of thickness obviously suppressed the surface temperature and increase in back‐face temperature yet maintaining high structural reliability. Compared with DGEBA‐based coatings, the PSG‐based coatings showed excellent structural reliability during the test. The study provides a solution for obtaining high performance ATPCs, which are highly desired for supersonic vehicles.

Ultralow‐k hollow glass microsphere filled perfluoroalkoxy composites

AbstractPerfluoroalkoxy (PFA) composites filled with different volume fractions of hollow glass microsphere (HGM) and HGM/PFA–HGM/HBO3–HGM/PFA sandwich layered composites were prepared by simple dry mixing and hot‐pressing process. The dielectric frequency and temperature response characteristics, thermal expansion coefficient, and mechanical strength were investigated as a function of the loading fraction of HGM fillers. The obtained .6VfHGM/.4VfPFA composite demonstrates ultralow‐k (εr ∼ 1,63@1 MHz; 1.57@10 GHz) with low‐dielectric loss (∼7.2 × 10−4@1 MHz; ∼1.73 × 10−3@10 GHz), water absorption of ∼1.21%, in‐plane thermal expansion coefficient of 42 ppm/°C, and temperature coefficient of dielectric permittivity (τεr) of ∼−92 ppm/°C. The temperature stabilities of dimension and dielectric permittivity for the .6VfHGB/.4VfPFA composite could be substantially improved by forming .6VfHGM/.4VfPFA–.6VfHGM/.4VfHBO3–.6VfHGM/.4VfPFA sandwich–layered composite, which still maintained reasonable dielectric properties and mechanical rigidity with flexural strength of ∼8.1 MPa.

Effect of Hollow Glass Microspheres with Different Contents and Types on Properties of Polypropylene Composites

AbstractIn this paper, hollow glass microspheres (HGM) reinforced polypropylene (PP) composites were prepared. The effects of the type and content of HGM on the mechanical properties of the composite materials were investigated. It is found that the introduction of HGM leads to a decrease in the density of the composites, where the smallest density is 0.85 g cm−3. The tensile, bending, and impact strengths of the HGM/PP composites are slightly lower than those of pure PP resin. For a given type of HGM, as the filler content increases, the tensile properties of the HGM/PP composite decrease. A similar trend is observed in the impact strength, however, it is not observed in the bending performance. The mechanical properties of the HGM/PP composites are not only affected by the density of HGM fillers, but also by its content. The maximum bending modulus of the composites could be 24 % higher than that of the pure PP resins. In addition, the PP sample with HGM modified with γ‐aminopropyl triethoxysilane (KH550) showed promising interfacial bonding strength.

Tunable Energy Absorbing Property of Bilayer Amorphous Glass Foam via Dry Powder Printing.

The research in this paper entails the design of material systems with tunable energy-absorbing properties. Hollow glass microspheres of different densities are layered using dry powder printing and subsequently sintered to form a cellular structure. The tunability of the bilayer foams is investigated using various combinations of hollow microspheres with different densities and different thickness ratios of the layers. The mechanical responses to quasi-static uniaxial compression of the bilayer foams are also investigated. These bilayer samples show different mechanical responses from uniform samples with a distinctive two-step stress-strain profile that includes a first and second plateau stress. The strain where the second plateau starts can be tuned by adjusting the thickness ratio of the two layers. The resulting tunable stress-strain profile demonstrates tunable energy absorption. The tunability is found to be more significant if the density values of each layer differ largely. For comparison, bilayer samples are fabricated using epoxy at the interface instead of a sintering process and a different mechanical response is shown from a sintered sample with the different stress-strain profile. Designing the layered foams allows tuning of the stress-strain profile, enabling desired energy-absorbing properties which are critical in diverse impact conditions.

Experimental investigation of the shear bond strength between HGM cement and shallow formation in deepwater environments

Due to its low density and high strength, hollow glass micro-sphere (HGM) has become a popular additive to cement slurry in deepwater cementing. The shear bond strength (SBS) between the well cement and formation ensures the safety and integrity of oil and gas wells. We designed a simulation experiment to measure the SBS between HGM cement and shallow formations in deepwater environments. We studied the evolution of the tensile force when pulling a simulated pipe string and cement ring out of the soil layer with a constant force. The results suggest that the HGM content and size of the cement ring have no effect on the change in the tensile force over time. At the peak of the tension curve, the cement ring and soil begin to slip, causing the tensile force to decrease with time. We divided this curve into two sections, with the peak value as the dividing point. The first section is the accumulating section where the tension increases without displacement of the cement ring and the soil. The second section is the dynamic slip section. Additionally, we proposed the concepts of static SBS and dynamic shear bond coefficient. The static SBS is the strength at the pull-off position, and the dynamic shear bond coefficient is the cementation coefficient of the cement ring in the dynamic slip stage. We divided the cement ring into segments along its length, calculated the shear bond coefficient of the cement ring at different depths, and studied the variation in the dynamic shear bond coefficient with depth. The static SBS increases with decreasing HGM content and casing size, and the static SBS of the small casing is significantly greater than those of the middle casing and the large casing. The dynamic shear bond coefficient decreases after the occurrence of dynamic slip. This study provides important insights into the evolution of the cement-formation SBS, and the results can provide guidance for future cementing design.

Development of Novel Polypropylene Syntactic Foams Containing Paraffin Microcapsules for Thermal Energy Storage Applications

polypropylene (PP) syntactic foams (SFs) containing hollow glass microspheres (HGMs) possess low density and elevated mechanical properties, which can be tuned according to the specific application. A possible way to improve their multifunctionality could be the incorporation of organic Phase Change Materials (PCMs), widely used for thermal energy storage (TES) applications. In the present work, a PCM constituted by encapsulated paraffin, having a melting temperature of 57 °C, was embedded in a compatibilized polypropylene SF by melt compounding and hot pressing at different relative amounts. The rheological, morphological, thermal, and mechanical properties of the prepared materials were systematically investigated. Rheological properties in the molten state were strongly affected by the introduction of both PCMs and HGMs. As expected, the introduction of HGMs reduced both the foam density and thermal conductivity, while the enthalpy of fusion (representing the TES capability) was proportional to the PCM concentration. The mechanical properties of these foams were improved by the incorporation of HGMs, while they were reduced by addition of PCMs. Therefore, the combination of PCMs and HGMs in a PP matrix generated multifunctional materials with tunable thermo-mechanical properties, with a wide range of applications in the automotive, oil, textile, electronics, and aerospace fields.

Endowing versatility and superamphiphobicity to composite coating via a bioinspired strategy

The strong adhesion by crude oil and the deposition of wax in petrochemical pipeline systems are notorious problems, which seriously threaten the safety and economic production of the petroleum industry. Superamphiphobic coatings that repel water/oil offer exciting opportunities to solve these problems, but there are formidable challenges in developing elaborate structures facilely. Herein, a springtail-inspired and multifunctional superamphiphobic coating (OCA = 152.1 ± 0.4°, OSA = 8.2 ± 0.8°) was prepared by a straightforward spraying technique. To emulate the cuticular characteristics of the springtail, the micro-/nano-hierarchical fillers prepared by loading silica nanoparticles on the surface of hollow glass microspheres and then chemical modification (F-HGM@SiO2) and the fluorinated nano-silica (F-SiO2) were simultaneously introduced into polyvinylidene fluoride (PVDF) to construct a micro-/nano-/nano-hierarchical structure on the PVDF/F-HGM@SiO2/F-SiO2 surface. Hence, a durable air layer was formed due to the suitable rough structure in conjunction with low-surface-energy groups, which endows the coating with outstanding crude-oil-repellency. Moreover, based on the self-designed test device, the coating showed an excellent anti-waxing deposition ratio (R = 82.76 %). Significantly, on the basis of the morphologies, wettability, and anti-waxing performance of the coatings, the main liquid-wettability, and anti-waxing mechanisms were illustrated, which revealed the inseparable relationship between them. The durability of the coating was investigated through mechanical/chemical damage tests (the OCA and OSA were kept above 140° and below 30°, respectively). Therefore, this bioinspired superamphiphobic coating is expected to open up new avenues for the design and fabrication of anti-waxing coating, which present enormous application value in oily/corrosive environments.

A Controlled Experiment of Surface Albedo Modification to Reduce Ice Melt

AbstractLoss of reflectivity in the Arctic and the wider cryosphere is known to increase global temperature rise through an ice‐albedo feedback loop, which has the potential to lead to loss of summertime ice cover in the Arctic Ocean, and to accelerate global warming. Despite the urgency of this situation, there are few options being developed to preserve and restore ice reflectivity. Localized surface albedo modification using reflective materials offers a potential pathway to restore Arctic ice. We conducted a controlled experiment to determine effects of surface albedo modification on ice melt and thermodynamic processes of a pond. We applied a coating of hollow glass microspheres (HGMs) to a test section, while leaving a control section unmodified. Laboratory measurements show that the loading of HGM materials used corresponds to a reflectivity of 30%. We measured ice and snow thickness, albedo, incoming and outgoing shortwave and longwave radiation, and ice, water, and ambient temperatures. A 1‐D thermodynamic model was developed to quantify the effect of albedo modification on the processes of heat transfer, energy absorption and ice melt. The albedo increased from 0.17 on a control section to 0.36 on a test section. During the 2‐week melt period, there was a 29% reduction in net radiative energy into the test section and a 33% reduction of ice melting rate measured by volume. This experiment using quantitative methods elucidates the mechanisms of ice preservation through surface albedo modification and demonstrates its effectiveness.

Cu-Co Hybrid Crystals Assembled on Hollow Microsphere: Temperature-Dependent Top-Down Synthesis and Aggregation-Induced Conversion from Microwave Shielding to Absorption.

The construction of hollow metallic microspheres with rationally designed building blocks of the metal shell is a promising way to achieve low density and functionality control, but the microengineering of the metallic structures on a micrometer spherical surface is a great challenge. In the present work, a novel and simple calcination-induced aggregation strategy is developed to realize the distribution status and microstructure control of Co-Cu bimetal building blocks assembled on a hollow glass microsphere support, and thus a series of low-density (0.58gcm-3 ) dual shell composite hollow microspheres are constructed with gradient in electromagnetic property depending on the calcination temperature (CT). The optimized microwave shielding performance can be achieved at a CT of 500°C, while further increasing CT to 700°C leads to an interesting conversion from microwave shielding to absorption with an optimized effective absorption bandwidth of 4.64GHz at a low matching thickness of 1.33mm. The mechanism underlying the CT-dependent metallic shell structure variation and further the decisive effect of the shell structure on the microwave response behavior are proposed based on a series of contrast experiments.

Mechanical response of additively manufactured foam: A machine learning approach

This paper uses ensemble and automated machine learning algorithms to predict the mechanical properties (tensile and flexural strength) of a three-dimensionally printed (3DP) foamed structure. The closed cell foams were made from the most commonly used thermoplastic, High-Density Polyethylene (HDPE). The hollow glass microspheres are infused in HDPE at varying volume %. The available data on these foams' mechanical properties are used by the chosen machine learning (ML) algorithms to propose the best suited algorithm for such a three-phased microstructure as these closed cell foams exhibit. Finally, the strength predictions from the models were validated using experimental data. The models were trained with nozzle temperature, bed temperature, and force values as input parameters. The output parameters predicted were the tensile and flexural strength. LightGBM outperforms all other models in terms of performance among ensemble-based models, while H2OAutoML outperforms all other models. All the ML algorithms produced models with greater than 95% accuracy. Finally, memory and time consumption for each model are presented.

Near Infrared Reflection and Hydrophobic Properties of Composite Coatings Prepared from Hollow Glass Microspheres Coated with Needle-Shaped Rutile Shell

Infrared thermal reflective coating is an effective material to reduce building energy consumption and carbon emission. In this work, needle-shaped-rutile-shell-coated hollow glass microbeads (HGM) were prepared by surface modification of HGM and thermohydrolysis of TiCl4, and the possible shell formation mechanism was also proposed. The near infrared (NIR) reflectance of the coated HGM reached 93.3%, which could be further increased to 97.3% after the rutile shell crystallinity was improved by heat treatment. Furthermore, HGM/styrene-acrylic composite reflective coating was prepared on the surface of gypsum board by facile blending and coating methods, and the thermal insulation performance was measured by an indigenously designed experimental heat set-up. The results show that the composite coating prepared by HGM coated with rutile shell shows better NIR reflectance and thermal insulation performance than that prepared by pure organic coating and uncoated HGM. Meanwhile, it also shows better surface hydrophobicity, which is conducive to long-term and stable infrared reflection performance.

Dynamic Response of Components Containing Polymer Composites in the Resonance Region for Vibration Amplitudes up to 5g.

This paper focuses on high-speed-operation textile machines with the aim of increasing the rotational speed by operating within the resonance region to vibration amplitudes up to 5g. The native design does not allow keeping the vibration amplitude under 5g, which is a safe operation mode, for revolutions more than 120,000 min-1. The innovative modification of the design was made by the incorporation of polymer composite materials with carbon dust, glass hollow microspheres, and silica sand fillers to the rotor-bearing casing; moreover, through the incorporation of a multilayered foam composite structure and particle damper to the pressure plate of the mechanical machine system. By using the approach of supplementing with high-damping composites, the existing native design can be used, thus avoiding the costly production of new components and subassemblies with modified shapes and dimensions. Twelve possible combinations of mentioned modifications were tested, evaluated and compared with the native design made of steel, as standard structure material in mechanical engineering. The average vibration amplitudes were evaluated in the region before the resonance peak and in the range of the resonance peak, i.e., 120,000-135,000 min-1. Significant vibration amplitude reductions in the range from 30 to 70% of the average vibration amplitude were obtained. The vibration amplitude reduction results were evaluated considering the mass through the amplitude reduction efficiency coefficient.

Enhanced energy absorption and microstructural studies on hollow glass microsphere filled closed cell aluminum matrix syntactic foam

The research on lightweight materials for advanced engineering applications attracted the development of metal matrix syntactic foams. The automobile sector has started using Al-based alloys in structural components such as crash-box, underride-guard, fenders, dampers, A, B, and C Pillars. The present study explores the energy absorption behavior; microstructural characterization such as SEM, EDS, and XRD analysis of hollow glass microsphere (HGM) filled aluminum matrix syntactic foam. A380 aluminum alloy reinforced with different volume fractions 10%, 20%, 30%, and 35% of hollow glass microspheres were used in the fabrication of syntactic foam using the stir casting technique. The quasi-static compression test conducted, evaluated the plateau strength, which improved from 284.14 to 341.69 MPa, and energy absorption capacity was observed in the range 139.25–187.92 MJ/m3. The plateau strength and energy absorption capacity were improved by 16.82% and 25.89% for the 35 vol.% HGM sample as compared with 10 vol.% HGM filled aluminum matrix syntactic foam. The addition of a calcium thickening agent in the casting process improved the bonding between aluminum and HGM particle and also the homogeneous distribution of HGM. The XRD analysis revealed the chemical reaction that occurred between aluminum and SiO2 that produced the AlSiO2 and Al2SiO5 interfacial compounds. This reaction tends to collapse the HGM cell wall and fills it with matrix material.

Rational Design of Fluorinated Phthalonitrile/Hollow Glass Microsphere Composite with Low Dielectric Constant and Excellent Heat Resistance for Microelectronic Packaging.

High-performance composites with a resin matrix are urgently required for electronic packaging due to their low dielectric constant, outstanding high temperature resistance, excellent corrosion resistance, light weight and easy molding. In this work, hollow-glass-microsphere (HGM)-filled fluorinated-phthalonitrile (PBDP) composites, with filler contents ranging from 0 to 35.0 vol.%, were prepared in order to modify the dielectric properties of the phthalonitrile. Scanning electron microscopy (SEM) observations indicate that the modified HGM particles were uniformly dispersed in the matrix. The PBDP/27.5HGM-NH2 composite demonstrates a low dielectric constant of 1.85 at 12 GHz. The 5% thermogravimetric temperature (T5) of composites with silanized HGM filler (481-486 °C) is higher than the minimum packaging-material requirements (450 °C). In addition, the heat-resistance index (THRI) of PBDP/HGM-NH2 composites reached as high as 268 °C. the storage modulus of PBDP/HGM-NH2 composites were significantly increased to 1283 MPa at 400 °C, an increase by 50%, in comparison to that of PBDP phthalonitrile resin (857 MPa). The excellent dielectric and thermal properties of the present composites may pave a way for comprehensive applications in electronic packaging and thermal management for energy systems.

Analysis of Particle Variation Effect on Flexural Properties of Hollow Glass Microsphere Filled Epoxy Matrix Syntactic Foam Composites.

Syntactic foam made from hollow glass microspheres (HGM) in an epoxy matrix has proven to be a good material with a strong structural strength. Understanding filler particle size variation is important in composite material formation, especially in syntactic foam, because of its numerous applications such as aerospace, marine, and structural purposes. In this present work, the effects of particle variation in different sizes (20-24 µm, 25-44 µm, 45-49 µm, and 50-60 µm) on the mechanical properties of the syntactic foam composites with a focus on flexural strength, modulus, and fracture surfaces are investigated. The particle sizes are varied into five volume fractions (5, 10, 15, 20, and 25 vol%). The results show that the highest flexural strength is 89 MPa at a 5 vol% fraction of 50-60 µm particle size variation with a 69% increase over the neat epoxy. This implies that the incorporation of HGM filler volume fraction and size variation has a strong effect on the flexural strength and bending modulus of syntactic foam. The highest particle size distribution is 31.02 at 25-44 µm. The storage modulus E' increased at 30 °C, 50 °C, and 60 °C by 3.2%, 47%, and 96%, respectively. The effects of wall thickness and aspect ratio on the size of the microstructure, the fracture surfaces, and the viscoelastic properties are determined and reported accordingly.

Crystallization Behavior of Poly(ε-Caprolactone)-Hollow Glass Microspheres Composites for Rotational Molding Technology

Composites suitable for rotational molding technology based on poly(ε-caprolactone) (PCL) and filled with hollow glass microspheres (HGM) or functionalized hollow glass microspheres (HGMf) were prepared via melt-compounding. The functionalization of glass microspheres was carried out by a silanization treatment in order to improve the compatibility between the inorganic particles and the polymer matrix and achieve a good dispersion of glass microspheres in the matrix and an enhanced filler–polymer adhesion. The crystallization behavior of materials was studied by DSC under isothermal and non-isothermal conditions and the nucleating effect of the glass microspheres was proven. In particular, the presence of silanized glass microspheres promoted faster crystallization rates and higher nucleation activity, which are enhanced by 75% and 50%, respectively, comparing neat PCL and the composite filled with 20 wt% HGMf. The crystalline and supermolecular structure of PCL and composites crystallized from the melt was evaluated by WAXD and SAXS, highlighting differences in terms of crystallinity index and structural parameters as a function of the adopted crystallization conditions.