Glass Microballoons Research Articles

The Influence of Gas Diffusion on the Dynamics of A Spherical Layer of Viscous Incompressible Liquid and Heat and Mass Transfer in it

The formation of spherical microballoons in the case of short-term weightlessness is investigated numerically. The algorithm of the numerical solution of the problem is described and the results of numerical studies of the formation of liquid glass microballoons, saturated with carbon dioxide, are presented. The results of calculations for the problem in the full statement (mathematical model includes the influence of inertial, thermal and diffusive factors) and simplified statement, when the process of gas diffusion is not taken into account, are compared.

Compressive Behaviour of Low Density Polymeric Syntactic Foams

The combinations of polymer resin and glass microballoon are the main materials used to produce syntactic foams. Syntactic foam is a lightweight material that has good mechanical properties and is commonly used as a component for structural materials in civil construction, aerospace and marine applications. Hence, it should have suitable mechanical properties, particularly good compression behaviour. In the present study, the results obtained from compression tests are compressive strength, elastic modulus and specific compression that decrease when increasing of glass microballoon contents (2.0 wt.%, 4.0 wt.%, 6.0 wt.%, 8.0 wt.% and 10.0 wt.%) and also neat resin. The highest strength value for compression testing is owned by 2.0 wt.% which is 88.9 MPa, while the lowest strength is 43 MPa that belongs to 10.0 wt.% of glass microballoon. This shows that the density and weight percentage of glass microballoon in these syntactic foams affect compression properties. Therefore, a further study should be conducted, which includes the effect of compressive failure mechanism.

Accelerated environmental degradation and residual flexural analysis of carbon nanofiber reinforced composites

Hollow particle filled composites known as syntactic foams presently find numerous applications in structures exposed to high moisture and high temperature environments. Carbon nanofiber (CNF) reinforcement is attractive in these composites because of the possibility of increased strength with negligible density variation. In the present study, syntactic foams containing 15–50 vol% glass microballoons (GMB) and 1–5 wt% CNF reinforcement as well as CNF/epoxy composites containing 1–5 wt% CNF were exposed to accelerated weathering by immersion in 90 °C water for two weeks and characterized for their residual flexural properties. In the worst performing composites, a maximum weight gain of 3.5% and 10% was observed for CNF/epoxy and CNF/syntactic foam composites, respectively. The syntactic foams tested were observed to generally decrease in strength after weathering with the exception of the composites containing 5 wt% CNF and 15 vol% GMB, which were observed to increase in strength by 41–51% after weathering. The composite containing 5 wt% CNF was also shown to increase in strength by 27% after weathering. Strength retention is attributed to the presence of CNF, along with competing weathering effects on composite structure and morphology.

Elastic behaviour and failure mechanism in epoxy syntactic foams: The effect of glass microballoon volume fractions

A representative elementary volume (REV) in epoxy syntactic foams was generated to incorporate randomly distributed glass microballoons that followed a log-normal size distribution. Finite element modelling of the REV foam was developed and experimentally validated to investigate the elastic behaviour and failure mechanism in the foams with different microballoon volume fractions (V). The localised stresses concentrate in various zones within the foam, and can cause the vertical splitting fracture of microballoons and the micro-crack formation in the matrix. Dependent on the microballoon volume fraction, micro-cracks can propagate to join adjacent micro-cracks and voids left by fractured microballoons, and finally develop into a macro-crack either in the preferred longitudinal (for low V) or diagonal (for high V) directions. This is consistent with the macroscopic observations of the fracture process in the foam specimens. It was also found that elastic characteristics of the foam vary with microballoon volume fractions.

Temperature of the detonation front of an emulsion explosive

This paper presents a new look at the structure of the radiance signal recorded by an optical pyrometer in measuring the brightness temperature of the detonation front of an emulsion explosive with glass microballoons as a sensitizer. The structure of the optical signal is typical of heterogeneous explosives: first a short temperature spike of up to 2500–3400 K occurs related to the formation of a layer of hot spots igniting the matrix capable of releasing energy, after which the radiance decreases to the quasi-equilibrium level corresponding to a temperature of 1880–2370 K at a detonation pressure of 0.7–11 GPa. There is satisfactory agreement between the experimental data and the results of independent calculations.

A multi-branch finite deformation constitutive model for a shape memory polymer based syntactic foam

A multi-branch thermoviscoelastic-themoviscoplastic finite deformation constitutive model incorporated with structural and stress relaxation is developed for a thermally activated shape memory polymer (SMP) based syntactic foam. In this paper, the total mechanical deformation of the foam is divided into the components of the SMP and the elastic glass microballoons by using the mixture rule. The nonlinear Adam-Gibbs model is used to describe the structural relaxation of the SMP as the temperature crosses the glass transition temperature (Tg). Further, a multi-branch model combined with the modified Eying model of viscous flow is used to capture the multitude of relaxation processes of the SMP. The deformation of the glass microballoons could be split into elastic and inelastic components. In addition, the phenomenological evolution rule is implemented in order to further characterize the macroscopic post-yield strain softening behaviors of the syntactic foam. A comparison between the numerical simulation and the thermomechanical experiment shows an acceptable agreement. Moreover, a parametric study is conducted to examine the predictability of the model and to provide guidance for reasonable design of the syntactic foam.

Improved Thermal Conductivity in Carbon Nanotubes-Reinforced Syntactic Foam Achieved by a New Dispersing Technique

Syntactic foams are composite materials in which the matrix phase is reinforced with hollow micro-particles. Traditionally, syntactic foams are used for many high strength applications and as insulating materials. However, for applications demanding better heat dissipation, such as thermal management of electronic packaging, conductive fillers need to be added to syntactic foam. Carbon nanotubes (CNTs), although extremely conductive, have issues of agglomeration in the matrix. In this research, CNT-reinforced syntactic foam was developed based on our approach through which CNTs were dispersed throughout the matrix by growing them on the surface of glass microballoons. The thermal conductivity of nanotube-grown syntactic foam was tested with a Flashline® thermal analyzer. For comparison purposes, plain and nanotube-mixed syntactic foams were also fabricated and tested. Nanotube-grown microballoons improved the thermal conductivity of syntactic foam by 86% and 92% (at 50°C) compared to plain and nanotube-mixed syntactic foams, respectively. The improved thermal conductivity as well as the microstructural analysis proved the effectiveness of this approach for dispersing the carbon nanotubes in syntactic foams.

The mechanical response of a syntactic polyurethane foam at low and high rates of strain

Quasi-static and dynamic experiments are conducted to characterise the mechanical response of a syntactic foam comprising hollow glass microballoons in a polyurethane matrix. Stress versus strain histories are measured in uniaxial tension and compression as well as in pure shear, at strain rates ranging from 10−4 to 103 s−1, via non-standard experimental techniques; quasi-static in-situ tests are conducted to visualise the deformation mechanisms in tension and compression. The material displays a pronounced sensitivity to the imposed strain rate and relatively high tensile and shear ductility at both low and high strain rates. A tension/compression asymmetry is displayed in quasi-static tests but is lost at high rates of strain.

A novel carbon nanofibers grown on glass microballoons immunosensor: a tool for early diagnosis of malaria.

This paper presents a novel method for direct detection of Plasmodium falciparum histidine rich protein-2 (PfHRP-2) antigen using carbon nanofiber (CNF) forests grown on glass microballoons (NMBs). Secondary antibodies specific to PfHRP-2 densely attached to the CNFs exhibit extraordinary ability for the detection of minute concentrations of Plasmodium species. A sandwich immunoassay protocol was employed, where a glass substrate was used to immobilize primary antibodies at designated capture zones. High signal amplification was obtained in both colorimetric and electrical measurements due to the CNFs through specific binding. As a result, it was possible to detect PfHRP-2 levels as low as 0.025 ng/mL concentration in phosphate buffered saline (PBS) using a visual signal within only 1 min of test duration. Lower limits of 0.01 ng/mL was obtained by measuring the electrical resistivity of the capture zone. This method is also highly selective and specific in identifying PfHRP-2 and other Plasmodium species from the same solution. In addition, the stability of the labeling mechanism eliminates the false signals generated by the use of dyes in current malaria rapid diagnostic test kits (MRDTs). Thus, the rapid, sensitive and high signal amplification capabilities of NMBs is a promising tool for early diagnosis of malaria and other infectious diseases.

Quasi-static and high strain rates compressive response of iron and Invar matrix syntactic foams

Abstract The present work is focused on developing iron and FeNi36 Invar matrix syntactic foams and studying their properties under quasi-static and high strain rate compression. The quasi-static compression is conducted at a strain rate of 10−3 s−1. High strain rate testing is performed using a split-Hopkinson pressure bar (SHPB) at strain rates up to 2500 s−1. One of the limitations of the SHPB method is that it does not provide useful results at the intermediate strain rates where the specimens do not fail completely during the test. In the present study, a recently developed repeated testing scheme is applied to obtain results at such intermediate strain rates. Syntactic foams containing 5 and 10 wt.% hollow glass microballoons (GMBs) are synthesized using the metal powder injection molding (MIM) process for this study. The results show that the yield strength decreases with increasing GMB content. The quasi-static yield strengths of 5 and 10 wt.% GMB syntactic iron foams were found to be 14% and 17% lower than that of iron. Similarly, 5 and 10 wt.% GMB syntactic Invar foams had 35% and 51% lower yield strength than Invar alloy. However, weight-related strength was found to increase with GMB content and exceed the respective data of other iron and steel foams. High strain rate testing revealed a weak trend towards yield strength increase with strain rate. However, the indication of strain rate sensitivity is not very strong due to scatter in data. Metallographic analyses conducted on failed specimens showed that the extent of matrix plastic deformation decreased with increasing strain rate. Particle crushing was observed at all strain rates.

Differences between the detonation behavior of emulsion explosives sensitized with glass or with polymeric micro-balloons

The differences between the detonation behaviour of ammonium nitrate based emulsion explosives sensitized with polymeric and those sensitized with glass micro-balloons is presented and discussed. Expancel® are hollow polymeric micro-balloons that contain a hydrocarbon gas. The mean particle size of these particles is 30 μm with a wall thickness of about 0.1 μm. The detonation velocity and the failure diameter of the emulsion explosive sensitized with different amounts of these particles have been measured in cylindrical charges by optical fibers. The detonation velocity demonstrates non-linear behaviour in relation to density and reaches the maximum value for a density lower than that of the matrix. The detonation fails when the density approaches that of the matrix. The detonation in the emulsion explosives extinguishes itself at a porosity value that seems to be independent from the nature of the sensitizing agent. For low densities, the detonation velocity is almost independent of the charge diameter, and is close to the values predicted by BKW equation of state.

Achieving Ultra-Low Detection Limit Using Nanofiber Labels for Rapid Disease Detection

Early diagnosis of diseases is critical in its effective management. Traditional disease detection methods require specialized equipment and trained personnel. With the introduction of rapid diagnostic test kits (RDTs), disease detection has become easier and faster. However, these RDTs have failed to compete with the specialized laboratory equipment due to their high detection limits and false alarm rates. This paper presents a novel method of using carbon nanofibers (CNFs) grown on glass microballoons (NMBs) to achieve ultra-low detection limits in RDTs. The NMBs have millions of nanosized CNFs grown on each microballoon, with each CNF having a strong bonding affinity for antibodies. The NMBs conjugated with secondary antibodies have therefore a significantly higher probability of capturing minute antigen concentrations in solution. Furthermore, the dark color formation at the capture zone makes visual disease detection possible. Human Immunoglobulin G (IgG) was selected as the model analyte to study the performance of NMBs using a sandwich immunoassay protocol. Ultra-low electrical detection limit of (4 pg/ml) and rapid re- sponse (~1 minute) was achieved using this method.

A micromechanical model for quasi-brittle compressive failure of glass-microballoons/thermoset-matrix syntactic foams

We propose a micromechanical model for the quasi-brittle failure of syntactic foams subject to uniaxial compression. We focus on a failure characterised by shear bands inclined of about 45° with respect to the loading axis, often observed in thermoset polymers filled with glass microballoons. Our objective is to develop a three-dimensional Finite Element (FE) model for the effective compressive strength. Towards this aim, we extend our previous FE models, which include fifty randomly placed balloons and were developed to assess the accuracy of linear elastic homogenisation procedures for syntactic foams. Here, we account for the filler polydispersion and introduce a novel structural failure criterion for the glass microballoons. The proposed models are shown to be macroscopically isotropic with respect to the effective strength. We find good agreement with experimental results from the literature on syntactic foams with filler volume fraction of 60%, for which we assume the matrix to be linear elastic.

Flexural properties of epoxy syntactic foams reinforced by fiberglass mesh and/or short glass fiber

Epoxy syntactic foams containing 15wt.% hollow glass microballoon were reinforced by fiberglass mesh and/or short glass fiber, and the flexural behavior of these foams were investigated. Flexural tests results showed that the presence of glass fiber or fiberglass mesh led to increased values of strength and modulus in syntactic foams compared with unreinforced syntactic foams. And fiberglass mesh was found to be much more efficient. By adding two-layer fiberglass mesh to the glass fiber reinforced syntactic foams, the flexural strength and modulus further increased almost 2.5 and 2times, respectively, while the density of the reinforced foam only increased by 9.3%. In addition, it was found that the position and layers of fiberglass mesh had significant influence of the flexural properties. The failure modes and mechanisms of different reinforced syntactic foams are examined and the underlying differences are discussed.

Dependence of Critical Diameter of Emulsion Explosive on Density in Steel Confinement

Emulsion explosives (EMX) based on fine emulsion matrix are characterized by high detonation ability. Critical diameter (as minimum diameter when detonation occurs) and reaction zone length are known in the case of thin confinement with low acoustic impedance. The dependence of critical diameter of EMX in steel confinement with high acoustic impedance was examined in the range of initial density 0,75–1,37 g/cm3 . Density was varied by the concentration of glass microballoons, which were used as the sensitizer. It was shown experimentally, that characteristic value is /2 1 cr R d a  in the case of strong confinement. This can be due to the decrease of detonation front curvature. Comparison was made between the values of critical diameter in weak and strong confinement. The main distinction is that such dependence in strong confinement is lower and almost monotonic. This can indicate the influence of some processes besides lateral rarefaction wave. Period of reaction is closely connected with critical diameter and reaction zone length. Model based on heterogeneous kinetic of heating of emulsion surrounding single microballoon was proposed to describe the experimental dependence of the reaction zone time of EMX on concentration of microballons

The strain sensing property of carbon nanofiber/glass microballoon epoxy nanocomposite

This work reports the strain sensing property of a nanocomposite made from a free standing multi-scale structure that consisted of glass microballoons and carbon nanofibers. An epoxy system was infiltrated into the structure in order to fabricate a nanocomposite sensor. The electrical resistance of the sensor when subjected to a tensile strain was investigated. The change in electrical resistance of the sensor versus the applied strain was found to have linear and non-linear regions. In the linear region, the sensor exhibited a similar sensitivity to conventional resistance-type strain gages. A single equation that relates the change in electrical resistance to the applied strain for the linear and non-linear regions was developed.

Effect of explosive characteristics on the explosive welding of stainless steel to carbon steel in cylindrical configuration

The aim of this research is to study the influence of explosive characteristics on the weld interfaces of stainless steel AISI 304L to low alloy steel 51CrV4 in a cylindrical configuration. The effect of ammonium nitrate-based emulsion, sensitized with different quantities and types of sensitizing agents (hollow glass microballoons or expanded polystyrene spheres) and Ammonium Nitrate Fuel Oil (ANFO) explosives on the interface characteristics is analyzed. Research showed that the type of explosive and the type and proportion of explosive sensitizers affect the main welding parameters, particularly collision point velocity. The morphology of the wavy weld interfaces, chiefly the amplitude and length of the waves, is affected both by the impact velocity and the type and particle size of the explosive sensitizers, and increases with particle size. All the weld interfaces, except welds done with ANFO, displayed localized melted and solidified regions, whose chemical composition resulted from the contribution of both flyer and base metal.

Comparing neutron and X-ray images from NIF implosions

Directly laser driven and X-radiation driven DT filled capsules differ in the relationship between neutron and X-ray images. Shot N110217, a directly driven DT-filled glass micro-balloon provided the first neutron images at the National Ignition Facility. As seen in implosions on the Omega laser, the neutron image can be enclosed inside time integrated X-ray images. HYDRA simulations show the X-ray image is dominated by emission from the hot glass shell while the neutron image arises from the DT fuel it encloses. In the absence of mix or jetting, X-ray images of a cryogenically layered THD fuel capsule should be dominated by emission from the hydrogen rather than the cooler plastic shell that is separated from the hot core by cold DT fuel. This cool, dense DT, invisible in X-ray emission, shows itself by scattering hot core neutrons. Germanium X-ray emission spectra and Ross pair filtered X-ray energy resolved images suggest that germanium doped plastic emits in the torus shaped hot spot, probably reducing the neutron yield.

Predicting the Effect of Underfill Filler Volume Fraction on Solder Fatigue Life and Residual Stress for Surface Mount Components Using Nonlinear Viscoelastic Analyses

Glassy thermoset polymer underfills are commonly used for reliability enhancement in modern electronics. By adding filler to the polymer, underfill mechanical properties, such as bulk and shear moduli and coefficient of thermal expansion, can be altered. Addition of underfills can affect the solder reliability and component failure during dynamic environments. By modifying the nonlinear viscoelastic simplified potential energy clock model, a generic computational tool was created for analyzing filled polymers. Together with a unified creep plasticity model for solder and the Coffin-Manson fatigue criterion, solder fatigue life for underfilled surface mount components was investigated for various underfill filler materials and filler volume fractions (FVFs) using finite element analyses. By creating models of representative components with very different geometries, the effect of adding an underfill and increasing the FVF of hard and glass micro-balloons (GMB) fillers was analyzed. For a large stiff component, the addition of an unfilled underfill reduced the localized tensile stress in the component. Underfill filler volume fractions greater than 10% for hard filler and 15% for GMB filler resulted in a positive effect on the fatigue life. The results were different for a small flexible component. The addition of an unfilled underfill slightly increased the localized tensile stress in the component, but a positive effect on the fatigue life was still demonstrated if the underfill FVFs were greater than 15% for hard filler and 30% for GMB filler.

Temperature and strain rate dependence of syntactic foam under tensile and shear loads

The behaviour of syntactic foam is strongly dependent on temperature and strain rate. This research focuses on the behaviour of syntactic foam made of epoxy and glass microballoons in the glassy, transition and rubbery regions. Both epoxy and epoxy foam are investigated separately under tension and shear loadings in order to study the strain rate and temperature effects. The results indicate that the strength and strain to failure data can be collapsed onto master curves depending on temperature reduced strain rate. The highest strain to failure occurs in the transition zone. The presence of glass microballoons reduces the strain to failure over the entire range considered, an effect that is particularly significant under tensile loading. However, as the microballoons increase the elastic modulus significantly in the rubbery zone but reduce it somewhat in the glassy zone, the effect on the strength is more complicated. Different failure mechanisms are identified over the temperature-frequency range considered. As the temperature reduced strain rate is decreased, the failure mechanism changes from microballoon fracture to matrix fracture and debonding between the matrix and microballoons.