Time of hot-spot formation in shock compression of microballoons in a condensed medium

The optical thermal radiation arising from the shock collapse of glass or polymer microballoons in a transparent condensed medium (water or polymerized epoxy resin) was detected. The temporal characteristics of the detected radiation in the pressure range 0.5–29 GPa at different viscosities of the material surrounding the pore were determined. The brightness temperature of hot spots was estimated to be 1600–3200 K at a pressure of 2–29 GPa. The length of the leading edge of the radiation pulse corresponding to the time of hot-spot formation increases from 2 · 10^?8 to 30 · 10^?8 s, depending on the shock-wave intensity and the viscosity of the material surrounding the pore. Analysis of the data shows that in the pressure range 5–29 GPa, hot-spot formation is dominated by the hydrodynamic mechanism of collapse and in the range 0.5–5 GPa, by the viscoplastic mechanism.     

Phase transformations in shock-compressed ytterbium

In order to study the phase transformations of ytterbium under shock compression, the electrical resistance of ytterbium at the initial temperatures of 77 and 290 K and a shock pressure of p ? 20 GPa is measured. The dependence of ytterbium resistance on pressure is nonmonotonic and indicates three successive phase transitions. At p ≈ 2 GPa, ytterbium enters a state with a high electrical resistance of the semiconductor type. The ytterbium bandgap at p ≈ 1.8 GPa is estimated as ≈0.02 eV. At p ≈ 3 GPa, the electrical resistance of ytterbium decreases due to a polymorphic phase transition The electrical resistance grows with further increase in pressure, and at p > 11 GPa, it does not change. The nature of the third transition is determined by calculating the temperature of the sample under shock compression. Analysis of the dependence of sample temperature on shock pressure, together with the phase diagram of ytterbium, suggests that the third transition is caused by ytterbium melting.     

Possible Negative Value of the Grüneisen Coefficient of Hydrogen in the Area of Pressures from 40 to 75 GPa and Temperatures from 3500 to 7500 K

Experimental data on single and double shock compression of initially liquid and gaseous (compressed by initial pressure) hydrogen isotopes (protium and deuterium) at pressures of ≈10–180 GPa and temperatures of ≈3000–20 000 K are considered. The mean values of the measured variables (pressure, density, internal energy, and temperature) show that hydrogen at a pressure of ≈41 GPa in the temperature interval of ≈3500–5700 K and at a pressure of ≈74 GPa in the temperature interval of ≈5000–7500 K is characterized by a negative value of the Grüneisen coefficient. Such an anomaly may play a key role in some processes, including those proceeding in the Jupiter gas envelope, which mainly consists of protium (≈90%) and helium (≈10%). In the range of pressures (depths) of its manifestation, convection in the protium envelope is forbidden with an increase in temperature in the envelope with increasing pressure. Possibly, a comparatively low fraction of helium does not suppress the anomaly, and it serves as a barrier for large-scale convection in the Jupiter envelope. Additional refining experiments are required to confirm this anomaly.     

轻质环氧复合材料的制备与性能研究

制备了一种以空心玻璃微珠为填充材料的轻质环氧复合材料,确定了材料的固化工艺,并对不同型号的空心玻璃微珠进行了筛选.研究了玻璃微珠填充量对材料密度及力学性能的影响.研究发现,复合材料的密度随空心玻璃微珠填充量的加大呈现先降低后略有升高的趋势;拉伸强度和压缩强度均随填充量的增加而减小;拉伸弹性模量和压缩弹性模量随着填充量提...     

Shock Wave Properties of Inert and Chemically Active Porous Media

Shock wave properties of porous specimens made on the basis of matrices composed of inert and chemically active media (silicon rubber and emulsion, which is an aqueous solution of ammonium nitrate with mineral oil and emulsifier) are studied. The porosity of the specimens is generated by using a filler composed of glass microspheres. The wave velocity profiles are measured by a VISAR laser Doppler interferometer. It is shown that the shock compressibility of porous silicon rubber at pressures below 0.1 GPa displays an anomalous behavior, resulting in smearing of the compression pulse front propagating over the specimen. In the emulsion matrices without microspheres, there are no noticeable chemical transformations up to the pressure of 15 GPa. Addition of microspheres drastically decreases the threshold of chemical reaction initiation and leads to the formation of a steady detonation wave.     

Processing and performance evaluation of hollow microspheres filled epoxy composites

Microspheres filled epoxy composites are fabricated, using two types of hollow glass microspheres, namely, Fillite‐500 and K‐15. Fillite‐500 microspheres are relatively stronger and denser (avg. crushed strength ∼17 MPa and density ∼0.45 kg/m³) than K‐15 microspheres (avg. crushed strength ∼2 MPa and density ∼0.15 kg/m³). Each type of microspheres in the range of 10–70 vol% are added into a low viscosity two‐part epoxy resin (SC‐15) system in several steps and are mixed together meticulously to avoid breakage of the microspheres during mixing. The epoxy/microspheres mixture is then cured at room temperature (about 70°F) inside an oven for 24 h followed by post curing at 200°F for 4 h. One of the objectives of this research is to determine the maximum amount of microspheres that can be mixed uniformly without aid of diluents. Microstructural examinations reveal that the microspheres are fairly distributed uniformly through out the epoxy matrix up to 70 vol% for Fillite‐500 and 60 vol% for K‐15. It is found that addition of microspheres results in the reduction of density of the neat epoxy up to 28% with Fillite‐500 and up to 54% with K‐15. Thermo mechanical analysis results show that the coefficient of thermal expansion of epoxy matrix is reduced up to 66% with Fillite‐500 and up to 51% with K‐15.Compressive behavior for the epoxy/Fillite‐500 system is found to be different than the epoxy/K‐15 system. Failure analysis results indicate that the failure processes are also different for both the systems. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

Shock compression of an emulsion matrix at pressures up to 37 GPa

This paper presents an experimental study of the shock compression of an emulsion matrix based on an aqueous solution of ammonium and sodium nitrates at pressures up to 37 GPa, which is significantly higher than the calculated detonation pressure. The data obtained were used to determine the parameters of the Hayes equation of state and calculate the shock heating temperature of the matrix. At a pressure of more than 17 GPa, the input pressure profiles shows a rise associated with the chemical transformation of the emulsion.     

空心玻璃微球高压贮氢技术

利用炉内成球技术制备的亚毫米量级空心玻璃微球进行实验,系统研究了玻璃微球高压贮氢技术.玻璃微球直径150～250 μm,壁厚0.9～4.0 μm.采用气体渗透法充氢,在高温时,气体扩散进入微球内,温度降低后气体不容易扩散出来,即可实现贮氢.通过控制外界温度和气氛可实现氢气的贮存和释放.对于直径200 μm,壁厚1 μm的空心玻璃微球,在350℃充气的平衡时间约6～10 h,充气平衡后,微球内外压基本相等.在室温条件下,微球的保气半寿命约40～50 d.对于直径200 μm,壁厚2 μm的空心玻璃微球,球内氢气最高压力可达20～25 MPa,单位质量贮氢效率为13%～16％.     

Stepwise shock compression of C70 fullerene

Shock-induced phase transitions of C₇₀ fullerene are experimentally studied up to a pressure of 36 GPa and a temperature of 1200 K. Pressure–temperature histories of C₇₀ specimens are estimated and overlaid on the tentative phase diagram of C₇₀. The crystalline phase of fullerene C₇₀ with a hexagonal close-packed structure remained practically unchanged under stepwise shock compression up to а pressure of 8 GPa. Contrariwise the crystalline phase of fullerene C₇₀ with a rhombohedral structure fully converted to the phase with a cubic structure under similar conditions. Shock-induced transformation of the hexagonal phase into the face-centered cubic phase was observed at pressures in the range of 9–19 GPa. The amount of transformed material increases with the shock intensity. Upon further increase in the shock pressure, the destruction of C₇₀ molecules begins. In the sample recovered from 26 GPa, we observed the traces of C₇₀ with a face centered cubic structure only. The destruction of C₇₀ is accompanied by formation of graphitic carbon.     

Improved epoxy-amine matrices for composites

The physical and mechanical properties of epoxy-amine matrices can be improved by the use of additives known as epoxy fortifiers. The tensile strength of a typical aminecured epoxy increased from 82 MPa to 123 MPa, the tensile modulus form 2.5 GPa to 4.1 GPa, and the tensile test specimens also failed in a ductile fashion. The improvements in matrix properties translated into improved performance for filament-wound and cloth-reinforced composites. For example, the transverse moduli and compression strengths of carbon fiber/epoxy filament-wound tubes and plates increased at least 20 percent with the addition of fortifiers, while the compression strength of glass cloth/epoxy laminates increased by up to 41 percent.     

Measurement of the brightness temperature of shock-compressed epoxy resin

The brightness temperature of shock-compressed EC141 NF epoxy resin was measured by a pyrometric method in the pressure range of 19–42 GPa. The experimental points are in good agreement within the error with the calculation performed in the work. From the results of experiments, it follows that the presumed phase-transition region is not apparent in the pressure—temperature plane. Particle velocity records at the epoxy-water interface suggest the absence of a chemical reaction in EC141 NF epoxy compound at a pressure of 22.5 GPa during the observation time.     

Volume relaxation in a borosilicate glass hot compressed by three different methods

The temperature dependence of glass relaxation has been intensively studied; however, the effect of an imposed pressure history on relaxation behavior is poorly understood. In this study, we subjected SCHOTT N-BK7^® borosilicate glasses to isostatic compression in a Paterson press (PP) and a gas pressure chamber (GPC). The pressure ranged from 0.1 GPa to 2 GPa for various dwell temperatures and times near the glass transition region. Comparison with our recent results on the same glass using the piston-cylinder apparatus (PC, 0.5-1.5 GPa) reveals that the density of a glass, which has been quenched from the equilibrium state under high pressure at 2 K/min (pressure quench), increases approximately linearly with increasing pressure up to 2 GPa. Considering the volume recovery results at ambient pressure, we assert that the preceding high-pressure treatment in PC (uniaxial loading) generates a similar isostatic pressure effect on N-BK7 glass as those of PP and GPC treatments. Finally, we verify the previously proposed two-internal-parameter relaxation model on the volume recovery data using the three different compression methods. With a new set of parameters in the model, we can account for the pressure and temperature dependence of volume relaxation even for the samples quenched from nonequilibrium states at high pressure.     

Preparation and characterization of three phase epoxy syntactic foam filled with carbon fiber reinforced hollow epoxy macrospheres and hollow glass microspheres

The present study focuses on the preparation and characterization of three phase epoxy syntactic foam (ESF) filled with carbon fiber reinforced hollow epoxy macrospheres (CFR‐HEMS) and hollow glass microspheres (HGMS). The ESF was produced by embedding CFR‐HEMS into a mixture of epoxy‐hardener and 30 wt% HGMS. An innovative approach and simple procedure was implemented in the preparation of CFR‐HEMS where expanded polystyrene (EPS) beads were used as initiation template. The EPS beads were coated with epoxy resin and carbon fiber using “rolling ball method,” and these coated EPS beads were later cured and post‐cured at high temperature which will shrink the EPS beads thus producing a hollow macrosphere structure. The compressive property of ESF was characterized and the mechanical model was issued. The ESF (450 kg/m³, 30.74 MPa) can withstand 2049 m water pressure and provide 550 kg/m³ buoyancy, the higher strength are due to the fiber spherical x–y network throughout the macrosphere epoxy matrix, which can give some support to the preparation of buoyancy material used in deepwater oil exploration. POLYM. COMPOS., 37:497–502, 2016. © 2014 Society of Plastics Engineers     

Equation of state of polytetrafluoroethylene for calculating shock compression parameters at megabar pressures

Semi-empirical equations of state (thermal and caloric) are obtained to calculate not only the kinematic parameters (shock wave velocity, particle velocity, and reverberation of waves) but also the thermodynamic parameters (temperature, pressure, and compression) of monolithic and porous polytetrafluoroethylene at high shock pressures. The equations of state are used to model wave interaction in shock-wave experiments using the developed hydrocode. The equations are verified by comparison simulation results with published results of experiments and the data of our shock compression tests of solid and porous samples of PTFE in the range of 10–170 GPa.     

Reaction Behavior of Polytetrafluoroethylene/Al Granular Composites Subjected to Planar Shock Wave

The shock‐compression responses of PTFE (polytetrafluoroethylene)/Al granular composites subjected to planar shock waves of various pressures are investigated. A 57‐mm diameter single‐stage gas‐gun and 50‐mm diameter plane‐wave lenses are employed to perform planar shock wave experiments. High frequency manganin piezoresistance stress gauges are used to monitor the stress (regarded as pressure in consideration of the high pressure state) at four Lagrangian positions of the PTFE/Al granular composites specimens. Planar shock wave experiments show characteristics of densification at measured input pressure of 0.5 GPa to 1.27 GPa using single‐stage gas‐gun and shock‐induced reaction (SIR) indicated by growth of shock pressure and specific volume expansion at measured input pressure of 7.29 GPa to 12.25 GPa using plane‐wave lenses. The pressure and relative volume states behind the shock wave front are calculated from the experimental recorded pressure profiles using Lagrangian analysis method, which are used to determine the reaction ratios under different shock pressures by comparing with partial reacted Hugoniot calculations. It was shown that the reaction ratios obtained in this research have good agreement with the thermochemical modeling calculations. The corresponding results indicate that the shock‐induced reactions of PTFE/Al granular composites occur in the shock wave rising period and the reaction ratios are intimately related to the shock wave pressure.     

Shock Compression and Initiation of LX-10

LX-10 is a high energy density solid explosive consisting of 94.5% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 5.5% Viton A Binder pressed to 1.865 g/cm³ (98.4% of theoretical maximum density). In this paper the shock compression and initiation of chemical reaction in LX-10 by sustained shock pressures of 0.4 to 3 GPa are studied experimentally using embedded pressure and particle velocity gauges. The resulting pressure and particle velocity histories are evaluated theoretically using the ignition and growth reactive flow computer model of shock initiation and detonation. Manganin resistance and polyvinylidene fluoride (PVF₂) ferroelectric pressure gauges are both employed in the low pressure (0.4 – 0.7 GPa) shock compression experiments. Multiple manganin pressure and multiple electromagnetic foil particle velocity gauges measure the growth of reaction at various positions in LX-10 shocked to 1 – 3 GPa. The reactive flow modeling results imply that less than one percent of the LX-10 shocked to 0.4 – 0.7 GPa reacts in fifteen microseconds. For the higher pressure experiments, the ignition and growth model accurately calculates the pressure and/or particle velocity buildup in LX-10 as the reaction grows toward detonation. The LX-10 calculations are compared to those for the well-calibrated explosive PBX-9404, which contains 94% HMX and a reactive binder. Since it has the inert binder Viton A and better mechanical properties than PBX-9404, LX-10 is demonstrated to be significantly less reactive than PBX-9404 at these shock pressures. Therefore LX-10 is safer than PBX-9404 in many hazard and vulnerability scenarios to which solid explosives may be subjected.     

Manufacturing and impact behavior of syntactic foam

Syntactic foam made of glass hollow microspheres and epoxy vinyl ester resin is manufactured by using a new manufacturing method and its impact behavior is studied in terms of protection parameters. Experimental results for impact force and stress as functions of specimen diameter were found to be in reasonable agreement with predictions based on a model. Also, some compression properties of the foam were investigated. It was found that there is similarity in compressive failure mode between pseudostatic and impact loadings. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 1324–1328, 2000     

Melting-Temperature Measurements on alpha-Silicon Nitride to a Pressure of 37 GPa

The melting temperature of alpha-silicon nitride, up to a pressure of 37 GPa, was determined by using the diamond-anvil cell technique, together with laser heating and spectroradiometry. The melting temperature varied from 2200 ± 75 K at 3.5 GPa to 3600 ± 200 K at 37 GPa; the extrapolated temperature at 1 atm was estimated to be 2100 ± 75 K.     

Tensile creep behavior of unidirectional glass‐fiber polymer composites

The tensile creep behavior of unidirectional glass‐fiber polymer composites was studied at three different temperatures, namely 298, 333, and 353 K. Testing was performed on the pure epoxy matrix, the 0° specimens as well as off‐axis at 15, 30, and 60 degrees in respect to the axis of tension. The creep strain rate was negligible at room temperature, while it was considerable at the higher temperatures examined. The materials exhibit nonlinear viscoelastic behavior, and the creep response of the composites was treated as a thermally activated rate process. The creep strain was considered to include an elastic, a viscoelastic and a viscoplastic part. The viscoplastic part was calculated through a functional form, developed in a previous work, assuming that viscoplastic response of polymer composites arises mainly from the matrix viscoplasticity. The model predictions in terms of creep compliances were found to be satisfactory, compared with the experimental results. POLYM. COMPOS. 26:287–292, 2005. © 2005 Society of Plastics Engineers.     

Preparation of phenolic hollow microspheres via in situ polymerization

BACKGROUND: Phenolic hollow microspheres with a closed structure have a set of outstanding thermal characteristics. In the work reported here, a facile method is introduced to fabricate phenolic closed hollow microspheres by in situ polymerization in oil‐in‐water emulsion. Although in situ polymerization has been widely used to prepare hollow microspheres, it has not been utilized for the preparation of phenolic hollow microspheres. RESULTS: The average particle size of the produced microspheres was about 500 µm. Fourier transform infrared spectroscopy indicated that the phenolic microspheres were partially cured during preparation and a significant number of hydroxymethyl groups remained in the microspheres. Thermogravimetric analysis showed that the thermal decomposition temperature of the phenolic hollow microspheres was 420 °C, and residual weight at 800 °C was 62%. Differential thermal analysis showed that the glass transition temperature of the phenolic hollow microspheres was 200 °C. CONCLUSION: Using in situ polymerization, high thermal performance phenolic hollow microspheres are produced. The resultant product possesses a satisfactory closed hollow structure with controlled morphology. Copyright © 2009 Society of Chemical Industry