The Initiation Threshold Sensitivity of HNS Explosive as a Function of its Grain Size

The initiation threshold sensitivity of HNS versus explosive grain size has been measured, using an electric gun, with two flyer thicknesses. The initiation threshold, (kinetic energy of flyer plate), versus explosive grain size shows that the threshold curve increases dramatically at grain size over 5.4 m̈m (for flyer thickness 76.2 m̈m at explosive density 1.6 g/cm³). Minimum critical energies were calculated to be 12.15 ± 0.5 J/cm² and less than 7.0 J/cm², for flyer thicknesses 76.2 m̈m and 20.0 m̈m, respectively.     

Evaluation of the Energy Fluence in the Small Scale Gap Test

The Small Scale Gap Test is a relatively simple experimental tool to obtain a measure of the shock sensitivity of explosives. An evaluation of this test is carried out with use of a computer simulation. The simulated pressures in the water gap compare to experimental data and justify the obtained energy fluence in the shock wave versus distance in the water gap. The initiating shock pulse can be represented by an equivalent planar shock with an effective diameter of only 15 mm and a pulse duration of ≈1 µs. For the type of explosives that show some non‐ideal behavior and that have a relatively large critical diameter, the initiation pressure might provide an inadequate value for the shock sensitivity. It is recommended that besides using a critical shock pressure criterion also a critical energy fluence criterion is applied to rank the shock sensitivity of explosives.     

A Miniature Device for Shock Initiation of Hexanitrostilbene by High‐Speed Flyer

A miniature device for shock initiation of the hexanitrostilbene (HNS) through micro‐charge detonation‐driven flyer was fabricated. This device consisted of the substrate, micro‐charge, flyer, and barrel. Four types of flyer (titanium of 28 μm, aluminum of 22 μm, copper of 22 μm and polyimide (PI) of 55 μm in thickness) were studied and the effect of micro‐charge thickness, diameter, and barrel length were investigated by measuring the average flyer velocities using polyvinylidene fluoride (PVDF) films. The results show that the titanium flyer is more proper for such initiation device compared to aluminum, copper, and polyimide flyer. The average velocity of the flyer increased with the thickness of micro‐charge and the increment was larger when the thickness increases from 0.3 mm to 0.4 mm than when the thickness increases from 0.4 mm to 0.6 mm. The flyer velocity significantly increased with the increase in the diameter of micro‐charge until a plateau appeared at 0.8 mm. The flyer velocity increased first and then decreased sharply with the increase in barrel length. The average velocity for a 28 μm thick titanium flyer was measured to be as high as 2468 m s⁻¹ when the thickness, micro‐charge diameter and the length of barrel were 0.6 mm, 0.8 mm and 659 μm, respectively. The HNS‐IV explosive with density 1.57 g cm⁻³ was initiated by this miniature device.     

Initiation Pressure Thresholds from Three Sources

Pressure thresholds are minimum pressures needed to start explosive initiation that ends in detonation. We obtain pressure thresholds from three sources. Run‐to‐detonation times are the poorest source but the fitting of a function gives rough results. Flyer‐induced initiation gives the best results because the initial conditions are the best known. However, very thick flyers are needed to give the lowest, asymptotic pressure thresholds used in modern models and this kind of data is rarely available. Gap test data are in much larger supply but the various test sizes and materials are confusing. We find that explosive pressures are almost the same if the distance in the gap test spacers are in units of donor explosive radius. Calculated half‐width time pulses in the spacers may be used to create a pressure‐time curve similar to that of the flyers. The very‐large Eglin gap tests give asymptotic thresholds comparable to extrapolated flyer results. The three sources are assembled into a much‐expanded set of near‐asymptotic pressure thresholds. These thresholds vary greatly with density: for TATB/LX‐17/PBX 9502, we find values of 4.9 and 8.7 GPa at 1.80 and 1.90 g/cm³, respectively.     

Evaluation of the James Initiation Criterion in the 21 mm and 50 mm PMMA Gap Test

The gap test has been used for several decades as a measure for the shock sensitivity of high explosives. Normally the axial pressure in the gap is used as the necessary initiation pressure of a high explosive for a shock to detonation transition. But it has been shown in the past that the pressure in the gap is not a suitable measure for shock sensitivity and other criteria like the James criterion in terms of critical energy fluence and critical specific kinetic energy should be used. To evaluate the James criterion in the 21 mm and 50 mm polymethylmethacrylate (PMMA) gap test numerical simulations are conducted. To validate the simulations a 21 mm water gap test is simulated and compared to experimental results, where the axial pressure calibration can be reproduced with high accuracy. With the results from the simulation of the 21 mm and 50 mm gap test it is shown that at the same maximum axial pressure the energy fluence is higher in the 50 mm gap test. This explains to some extent the higher initiation pressures observed in smaller gap tests. The James criterion is derived and it is shown that the two gap tests probe very different regions in the energy fluence vs. specific kinetic energy plane. The results can be used as a calibration for the gap tests and are intended to improve the comparability of gap test results among each other and with different initiation experiments like flyer or heavy fragment impact testing.     

Effect of Habit Modifiers on Morphology and Properties of Nano‐HNS Explosive in Prefilming Twin‐Fluid Nozzle‐Assisted Precipitation

This article was published in Early View with DOI 10.1002/prep.200800071 – what is wrong. It has appeared with the correct DOI 10.1002/prep.200900071 – in Propellants, Explosives, Pyrotechnics 2009 (34) issue 1/2009 on pp 72‐77.     

The Initiation Threshold Sensitivity of LX-15 Explosive as a function of its grain size

The effect of the explosive binder 5 w/o-Kel-F-800 on the initiation threshold sensitivity of LX-15 had been measured. The initiation threshold (kinetic energy of flyer plate) versus explosive grain size shows constant difference of 5.5 ± 0.5 J/cm² between threshold curves of HNS and LX-15 explosives (HNS plus 5 w/o-Kel-F-800). This result can be explained by hot spots model.     

HMX as an Impurity in RDX Particles: Effect on the Shock Sensitivity of Formulations Based on RDX

Two main kinds of heterogeneities are pointed out in RDX particles in using optical microscopy with matching refractive index and scanning electron microscopy. These are HMX impurities and solvent inclusions.     

The Poly‐Rho Test as a Screening Tool for Explosive Performance

A screening test was developed at Los Alamos National Laboratory [1] that can be used to decide if a newly synthesized/formulated explosive might warrant further development. The test consists of firing a rate‐stick composed of 12.7 mm diameter by 12.7 mm high pellets of different densities ordered from lowest to highest, initiated by a detonator at the low‐density end of the stick. This poly‐rho test yields detonation velocities over a range of densities using only the small amount of the explosive typically generated by the synthetic organic chemist at an early stage of the scale‐up process. The amount of material required is far less than that required for the typical rate‐stick series. This paper presents results on poly‐rho tests that were conducted on three explosives commonly used at Los Alamos National Laboratory, namely PBX 9501, PBX 9502 and PETN. The results are compared with empirical detonation‐theory predictions and existing explosive experimental data, with good agreement in all cases.     

Design and Analysis of a Shock Generator

The purpose of this study is to design a high‐shock acceleration apparatus that can be used in a laboratory, alleviating the need for expensive and complex experiments. The key components of this device include a detonator, dynamite, a shock transmission bar, the housing for the test object, and an accelerometer. The device uses the detonation of the dynamite to generate instantaneous accelerations of up to 10⁵ m s⁻², which last for hundreds of microseconds. The acceleration forces over the most significant frequency range of the system were analyzed using the shock response spectrum (SRS) method. The device output provides a test sample of 1 kg with the high‐acceleration shock condition required by the Mil‐Std‐810F shock test specification.     

Mathematical Modeling of Monovalent Permselectivity of a Bilayer Ion-Exchange Membrane as a Function of Current Density

Modification of an ion-exchange membrane with a thin layer, the charge of which is opposite to the charge of the substrate membrane, has proven to be an effective approach to obtaining a composite membrane with permselectivity towards monovalent ions. However, the mechanism of permselectivity is not clear enough. We report a 1D model based on the Nernst–Planck–Poisson equation system. Unlike other similar models, we introduce activity coefficients, which change when passing from one layer of the membrane to another. This makes it possible to accurately take into account the fact that the substrate membranes usually selectively sorb multiply charged counterions. We show that the main cause for the change in the permselectivity coefficient, P_1/2, with increasing current density, j, is the change in the membrane/solution layer, which controls the fluxes of the competing mono- and divalent ions. At low current densities, counterion fluxes are controlled by transfer through the substrate membrane, which causes selective divalent ion transfer. When the current increases, the kinetic control goes first to the modification layer (which leads to the predominant transfer of monovalent ions) and then, at currents close to the limiting current, to the depleted diffusion layer (which results in a complete loss of the permselectivity). Thus, the dependence P_1/2 − j passes through a maximum. An analytical solution is obtained for approximate assessment of the maximum value of P_1/2 and the corresponding fluxes of the competing ions. The maximum P_1/2 values, plotted as a function of the Na⁺ ion current density at which this maximum is reached, gives the theoretical trade-off curve between the membrane permselectivity and permeability of the bilayer monovalent selective ion-exchange membrane under consideration.     

Prediction of the Behavior of a Liquid‐Fluidized Bed of Inert Particles Used for Separation by Density

A liquid‐fluidized bed of inert particles was used to separate a pure object from a mixture. One (binary solid‐liquid‐fluidized bed) or two (tertiary solid‐liquid‐fluidized bed) types of objects with relatively large‐sized particles were immersed in an inert‐particle bed, and the bed behavior was observed for different liquid velocities. The void fraction and apparent density of the inert‐particle suspension were predicted by considering the effect of the change in object position for different liquid velocities. The prediction method, which considers the change in the minimum fluidization velocity, accurately expressed the changes in the void fraction and the apparent density of the bed with the position of the objects in the bed. Using this method, the liquid velocity required to separate a certain kind of object from a mixture can be predicted.     

The Decomposition of some RDX and HMX Based Materials in the One Dimensional Time to Explosion Apparatus. Part 2. Estimating the Violence of the Cook‐Off Event

Various methods of assessment have been applied to the One Dimensional Time to Explosion (ODTX) apparatus and experiments with the aim of allowing an estimate of the comparative violence of the explosion event to be made. Non‐mechanical methods used were a simple visual inspection, measuring the increase in the void volume of the anvils following an explosion and measuring the velocity of the sound produced by the explosion over 1 metre. Mechanical methods used included monitoring piezo‐electric devices inserted in the frame of the machine and measuring the rotational velocity of a rotating bar placed on the top of the anvils after it had been displaced by the shock wave. This last method, which resembles original Hopkinson Bar experiments, seemed the easiest to apply and analyse, giving relative rankings of violence and the possibility of the calculation of a “detonation” pressure.     

Effect of Volume Fraction of Material on Separation by Density Difference in a Liquid‐Fluidized Bed of Inert Particles

A liquid‐fluidized bed was used to separate a pure material from a mixture. A quantity of relatively large sized material was immersed in an inert‐particle fluidized bed and the behavior of materials was examined for different liquid velocities. In particular, the volume fraction of the material was varied and its effect on the separation characteristics was examined. The material floats on the inert‐particle fluidized bed when the density of the material is lower than the apparent density of the bed, regardless of the volume fraction of the material. The apparent density of the bed can be adjusted by changing the liquid velocity. The materials in the upper portion of the bed affect the properties of the bed below them, i.e., the void fraction decreases and the apparent density increases in the inert‐particle suspension when materials are present in the upper portion of the bed. Therefore, the materials float on the bed although the apparent density of the inert‐particle suspension obtained from the case without material is less than the density of the material at a relatively high volume fraction of material. This phenomenon occurs more easily for lighter and smaller materials. This means that small inert particles and low liquid velocities are the optimum operating conditions for the separation.     

The Decomposition of some RDX and HMX Based Materials in the One‐Dimensional Time to Explosion Apparatus. Part 1. Time to Explosion and Apparent Activation Energy

A One‐Dimensional Time to Explosion (ODTX) apparatus has been used to study the times to explosion of a number of compositions based on RDX and HMX over a range of contact temperatures. The times to explosion at any given temperature tend to increase from RDX to HMX and with the proportion of HMX in the composition. Thermal ignition theory has been applied to time to explosion data to calculate kinetic parameters. The apparent activation energy for all of the compositions lay between 127 kJ mol⁻¹ and 146 kJ mol⁻¹. There were big differences in the pre‐exponential factor and this controlled the time to explosion rather than the activation energy for the process.     

Small‐Angle Neutron Scattering and Contrast Variation Measurement of the Interfacial Surface Area in PBX 9501 as a Function of Pressing Intensity

Small‐angle neutron scattering with contrast variation was used to measure the interfacial surface area in a composite high explosive formulated with a deuterated binder. Continuing our work on the effect of varying the pressing intensity on void and binder size distribution, the effect of pressing intensity on the three interfaces (HMX‐binder, HMX‐voids and binder‐voids) of the PBX 9501 microstructure was studied. Formulation of PBX 9501 with a deuterated binder allowed the neutron scattering length density contrast to be varied and thus allowed differentiation of the three interfaces. Porod analysis was used to measure the surface area. The surface area at the interfaces of HMX and binder was found to increase with increasing pressing intensity, while the surface area between HMX and voids may have decreased slightly. No evidence was found for voids within the binder at any pressing intensity.     

Incorporation of Flaxseed Flour as a Dietary Source for ALA Increases Bone Density and Strength in Post-Partum Female Rats

In women, bone mass undergoes changes during pregnancy and the postpartum period, which has a risk for subsequent development of osteoporosis. Thus, the present study aims to evaluate the effects of flaxseed flour in femur quality during post‐weaning of dam rats. After weaning, the rats were divided into control (C, n = 7) and experimental (F, n = 7) groups treated with a diet containing 25 g of flaxseed flour in the lactating period and 15 g in the maintenance period. After 51 days post‐partum, serum hormone, fatty acids composition, bone compartments, computed tomography, and biomechanical analyses were determined. Food intake, length, body mass, hormone analysis, and total bone compartments showed similar results. For biomechanical and computed tomography analysis and fatty acids composition, the F group showed higher maximum force (+12%, p < 0.05), breaking strength (+25%, p < 0.05), rigidity (+17%, p < 0.0001), and femoral head radiodensity (+15%, p < 0.05) and presented lower total polyunsaturated fatty acids (?17%, p < 0.0001) and arachidonic acid (?44%, p < 0.0001) and higher ALA (+695%, p < 0.0001) and EPA (+160%, p < 0.05). Fatty acids composition of flaxseed flour, as well as its protein profile and calcium content, were able to improve the bone quality, which may be associated with lower serum levels of arachidonic acid and higher EPA, showing an anti‐inflammatory profile and increased deposition of organic matrix during the post‐weaning period, and may result in prevention of future osteoporosis.     

Electrochemical Performance of a Ni and YSZ Composite Synthesised by Ultrasonic Spray Pyrolysis as an Anode for SOFCs

The electrochemical performance of an anode material for a solid oxide fuel cell (SOFC) depends highly on microstructure in addition to composition. In this study, a NiO–yttria‐stabilised zirconia (NiO–YSZ) composite with a highly dispersed microstructure and large pore volume/surface area has been synthesised by ultrasonic spray pyrolysis (USP) and its electrochemical characteristics has been investigated. For comparison, the electrochemical performance of a conventional NiO–YSZ is also evaluated. The power density of the zirconia electrolyte‐supported SOFC with the synthesised anode is ∼392 mW cm^–2 at 900 °C and that of the SOFC with the conventional NiO–YSZ anode is ∼315 mW cm^–2. The improvement is ∼24%. This result demonstrates that the synthesised NiO–YSZ is a potential alternative anode material for SOFCs fabricated with a zirconia solid electrolyte.     

The use of pure methanol as fuel at high compression ratio in a single cylinder gasoline engine

The methanol has greater resistance to knock and it emits lower emissions than neat gasoline. As single cylinder small engines have low compression ratio (CR), and they run with slightly rich mixture, their power are low and emission values are high. The performance can be increased at high CR if these engines are run with fuels which have high octane number. In this study, methanol was used at high CR to increase performance and decrease emissions of a single-cylinder engine. Initially, the engine whose CR was 6/1 was tested with gasoline and methanol at full load and various speeds. Then, the CR was raised from 6/1 to 8/1and 10/1, gradually. The knock was not observed at the CRs of 8/1 and 10/1 when using methanol while the knock was observed at the CR of 8/1 when using gasoline. The knock was determined from the cylinder pressure-time curves. The results showed that some decreases were obtained in CO, CO₂ and NO_x emissions without any noticeable power loss when using methanol at the CR of 6/1. By increasing the CR from 6/1 to 10/1 with methanol, the engine power and brake thermal efficiency increased by up to 14% and 36%, respectively. Moreover, CO, CO₂ and NO_x emissions were reduced by about 37%, 30% and 22%, respectively.     

The Use of Gaseous Ozone as a Cleaning Agent on Stainless Steel Surfaces Fouled with Bovine Protein

Facilitation of cleaning of stainless steel particles fouled with heat-treated bovine serum albumin (BSA) was studied using gaseous ozone generated from a pure oxygen-fed ozonizer at concentrations of 0.1 to 0.5% (v/v). Ozone pretreatment markedly accelerated the rate of BSA desorption during subsequent caustic alkali cleaning. The effect of ozone pretreatment depended on the concentration of ozone and it was attributed to partial decomposition of BSA molecules into some fragments. It was also found that the surface charge property of stainless steel particles was modified by ozone oxidation, resulting in the improvement of the cleanability of stainless steel surfaces.