Mitigation of Single‐Point‐of‐Failure: Development of M127A1 White Star Illuminant Compositions Containing an Epoxy Binder System

A replacement for the M127A1 hand‐held signal illuminant was developed to alleviate concerns associated with single‐point‐of‐failure. In addressing single‐point‐of‐failure, Laminac 4116/Lupersol binder system were replaced with Epon 813/Versamid 140 binder system. Powdered sodium nitrate was replaced with prilled sodium nitrate in the disclosed formulations to minimize hygroscopicity concerns associated with this oxidizer. The performance of the prilled sodium nitrate‐based formulations, their burning behaviors, and the sensitivities of the best performing illuminant toward various ignition stimuli are also described in detail.     

Effect of ductility on the fatigue behavior of epoxy resins

The effect of ductility on fatigue behavior was studied using two DGEBA-based (diglycidyl ether of bisphenol A) epoxies: a ductile Epon 815/Versamid 140 and a brittle Epon 828/Epon Z. Failure modes were different although normalized stress-life relations were similar for both resins. Two competing failure mechanisms were identified: viscoelastic creep, and nucleation and coalescence into a main crack of microcracks. No signs of crazing or fibrillation were detected. The plastic elongation during fatigue was larger in Epon 815/Versamid 140. Fracture sources showed cracked material surrounded by a region of stable growth of the main crack. In the brittle Epon 828/Epon Z cracked material was scarce and the crack initiation region was clean, especially at high stress levels. Discontinuous crack growth bands and striations were seen in the stable crack growth regions. During unstable propagation the crack advanced at different levels joined by deep cleavage steps. Branching of the main crack occurred only in the brittle resin at the final stage of propagation.     

Applications of High‐Nitrogen Energetics in Pyrotechnics: Development of Perchlorate‐Free Red Star M126A1 Hand‐Held Signal Formulations with Superior Luminous Intensities and Burn Times

Perchlorate‐free hand‐held signal illuminant formulations for the M126A1 red star parachute have been developed. The formulations exhibited longer burn times and higher luminous intensities compared to the US Army in‐service M126A1 formulation. The perchlorate‐free formulations derive their enhanced performance from the inclusion of strontium bis‐(1‐methyl‐5‐nitriminotetrazolate) monohydrate, the choice of magnesium used, and replacing a polyester binder system with an epoxy binder system.     

腰果壳油改性酚醛胺环氧树脂固化剂性能研究

对比了酚醛胺NX-2003D及聚酰胺Versamid140与环氧树脂Epon828胶粘剂的力学强度,及在室温、低温、潮湿面的粘接强度。通过设计的建筑胶配方,研究了其室温及低温的粘接强度增长速度,及耐湿热老化性能。结果表明,在常温固化时,NX-2003D体系具有与Versamid140体系相近的良好力学强度及粘接性能;但在低温条件下,NX-2003D体系表现出优于聚酰胺140体系的固化性能,在0℃固化7 d及14 d后,NX-2003D体系的拉伸剪切强度分别达到5 MPa及11 MPa以上,可以满足使用要求。NX-2003D体系的耐湿热老化性能及对潮湿面的粘接强度,也明显优于聚酰胺140体系。     

Thermochemical Calculations for Potassium Ferrate(VI), K2FeO4, as a Green Oxidizer in Pyrotechnic Formulations

This paper documents the first‐time assessment of a novel oxidizer, potassium ferrate(VI), as an alternative to perchlorate and hazardous metal‐containing oxidizers in energetic formulations, using thermochemical calculations. Calculations were performed for several different types of pyrotechnic formulations using the NASA Chemical Equilibria with Applications (NASA‐CEA) program. Formulations used in devices including smokes, illuminants, signals, igniters, delays, and flashes were evaluated to determine the feasibility of using potassium ferrate(VI) as an alternative oxidizer. The calculated adiabatic flame temperatures and equilibrium combustion products for the proposed formulations were compared to those of common baseline formulations for different pyrotechnic applications to determine the likelihood of functional success of potassium ferrate(VI)‐based formulations. Based on these initial data, it is highly probable that formulations incorporating potassium ferrate(VI) will result in reactive compositions for a variety of pyrotechnic applications. This material could address environmental concerns about perchlorate and heavy metal contamination by offering an environmentally‐friendly alternative oxidizer.     

Aging of ADN Rocket Propellant Formulations with Desmophen®‐Based Elastomer Binder

Desmophen® binder‐based rocket propellant formulations containing ammonium dinitramide (ADN) and different fuel filler types (Al, HMX) were manufactured and investigated. Desmophen® D2220 is a polyesterpolyol. Polyesters are seen as a binder possibility, because of the relatively low temperature of the glass transition region compared to polyether‐based prepolymers such as GAP. The analogous formulations with AP instead of ADN were also included for comparison. The aging was followed by SEM, DSC, and DMA measurements. The accelerated aging program was developed on the principle of thermal equivalent load and the generalized van’t Hoff rule with a scaling factor equal to F=2.9. The aging was performed in air (RH<10 %) at temperature values between 65 and 85 °C and aging times adjusted to a thermal equivalent load of 15 years at 25 °C. DMA measurements of the aged ADN/Desmophen®‐based propellants identified changes in the loss factor curve. In contrast to HTPB‐Al‐AP rocket propellant formulations, the loss factor curve of the ADN formulations with Desmophen®‐based elastomer binder shows only one main apparent peak. The loss factor curves were modeled with exponentially modified Gaussian functions, which have revealed the presence of a second hidden peak. It was found that the aging could be characterized by the time‐temperature dependence of the areas of the hidden peak. The area increased with aging, which is explained by scissioning of the polymer in the shell around the ADN particles. By this process the strength is reduced, which was recognized by the decrease in storage shear modulus.     

Preliminary Characterization of Propellants Based on p(GA/BAMO) and pAMMO Binders

In previous papers, the synthesis and characterization of OH‐terminated glycidyl azide‐r‐(3,3‐bis(azidomethyl)oxetane) copolymers (GA/BAMO) and poly‐3‐azidomethyl‐3‐methyl oxetane (pAMMO) by azidation of their respective polymeric substrates were described. The main objective was the preparation of amorphous azido‐polymers, as substitutes of hydroxy‐terminated polybutadiene (HTPB) in new formulations of energetic propellants. Here, the subsequent characterization of both the binders is presented. First of all, several isocyanates were checked in order to optimize the curing reaction, and then two small‐scale formulations of a propellant, based on aluminium and ammonium perchlorate, were prepared and characterized. Finally, the mechanical properties and burning rate were compared to those of a similar propellant based on HTPB as binder.     

Laser Ignition of Pyrotechnics – Effects of Wavelength,Composition and Confinement

Ignition tests were carried out using three different laser systems and three different pyrotechnic compositions. Pyrotechnic materials investigated are: sulfur/charcoal/potassium nitrate based composition (gunpowder, GP), Shellac binder‐based boron/potassium nitrate composition (SR 44) and acaroid resin binder based magnesium/potassium nitrate composition (SR 371C). The laser sources were the multimode output from an Ar‐ion laser (λ=500 nm average), a high‐power commercial diode laser (λ=784 nm) and a small laser diode operating at around the same wavelength but controlled by a customized electronic circuitry. Lasers operating in the visible wavelength range provided more reproducible and quicker ignition than the infrared output from the diode lasers. It was found that unconfined gunpowder exhibits more reproducible ignition for both the visible and the infrared wavelengths compared to the other two compositions. The composition based on magnesium, SR 371C appeared to be very sensitive to laser intensity variations and gave erratic and therefore, irreproducible ignition delay times. The threshold laser energies to initiate reproducible ignition for the different wavelengths were measured and ignition maps were constructed. From these maps, the required laser power density for any value of the ignition delay time, i.e. laser energy density was determined. Tests were also conducted on gunpowder samples, partially confined in a modified pyrogen igniter capsule and a small laser diode. The diode was operated in single pulse mode using a current surge, which was much higher than the recommended value for CW operation. This provided ~1 W pulses at the end of a 1 mm diameter fiber optic cable and caused reproducible ignition in the semi‐confined pyrotechnic bed within the capsule. The threshold ignition energy under semi‐confined conditions was found to be substantially less than that required in the unconfined environment under similar experimental conditions.     

Characterization of Aging Behavior of Butacene® Based Composite Propellants by Loss Factor Curves

Butacene® is a polymeric binder with ferrocenyl groups chemically bonded to HTPB backbone. Through incorporation in the AP−Al composite propellant formulation, it leads to high burning rates (BR) >20 mm/s at 7 MPa, and low pressure exponents n<0.5, allowing more flexibility to the rocket design, keeping the characteristics (process, mechanical properties, pot‐life) of HTPB binder formulations together with a lower vulnerability (IM) contribution by Butacene®. The key molecular level characteristic of such HTPB based elastomeric binder systems of solid composite rocket propellants (SCRP) is the glass‐rubber transition region, which is mainly defined by the molecular mobility of the components in the polymeric network during the transition from energy to entropy elasticity with respect to temperature. The molecular rearrangement regions or binder mobility fractions related to the glass‐rubber transition of such composite propellants during storage are important in terms of in‐service time estimations. They are detectable by dynamic mechanical analysis (DMA). Formulations with and without Butacene® were prepared and analyzed using the loss factor curves obtained by torsion DMA. A special modelling with so named Exponentially Modified Gaussian (EMG) distribution was used to define and quantify sub‐transition regions in the loss factor curve. SEM images revealed the network formation connected with AP bonding, which correlate to the tensile results. DMA loss factors revealed a strong oxidation with Butacene® containing formulations during aging. Burning rates of the formulations show slight increases with aging.     

Issues Related with Pot Life Extension for Hydroxyl‐Terminated Polybutadiene‐Based Solid Propellant Binder System

Extension of the pot life for hydroxyl‐terminated polybutadiene (HTPB) based propellant binder systems was attempted through employing a bicurative system comprising of toluene‐di‐isocyanate (TDI) and isophorone‐di‐isocyanate (IPDI). Pot life characteristics were studied through evaluating curing kinetics for the HTPB‐bicurative binder formulations. Curing kinetics were studied through viscosity buildup during the cure reaction and estimation of the rate constants for viscosity build‐up. Introduction of IPDI slowed down the curing process, but at the same time, has not adversely affected the mechanical characteristics. One of the discouraging factors in adopting IPDI as curative is the poor interface characteristics between liner and insulator of the solid propellant grains, and it has been proposed that the root cause for the same is the permeation of IPDI through the insulator. Quantification of such permeation was attempted from the numerical values for cross‐link density evaluated for various binder compositions. Remedy for poor interface characteristics is suggested in this study.     

Burn‐through resistance of fibre/felt materials for aircraft fuselage insulation blankets

Light‐weight fire barrier materials for aircraft thermal/acoustical insulation blankets were investigated. The burn‐through test on blankets inserted with these fire‐blocking materials was performed using a small‐scale kerosene burner apparatus. The burner system generated a turbulent flame at 1000°–1100°C and a front heat‐flux at 160–180 kW/m². The rear or back‐side heat flux of blankets and their corresponding burn‐through time were monitored by a computerized data acquisition system. The blankets with ceramic or polymeric fire barrier materials provided a significantly additional burn‐through time compared with the regular blankets. Blanket samples inserted with an alumino‐silicate‐based ceramic layer were not burned‐through after 6 min. For fire resistant polymeric‐based materials, the burn‐through time varied from 2 to 6 min. The burn‐through resistance was correlated with the stable structure of SiO₂ at high temperature for the ceramic sheets and with the formation of a char layer for polymeric layers.Copyright © 2002 John Wiley & Sons, Ltd.     

Developing a Combustion Model of a Solid Propellant Containing Capsules of Liquid Oxidizer

A combustion model of a solid propellant containing liquid oxidizer capsules was developed. The model is based on the combustion cycle of a unit cell, an oxidizer droplet surrounded by the adjusting amount of binder. Three combustion stages are considered: (1) binder decomposition parallel to oxidizer heating up to boiling temperature, (2) simultaneous binder and oxidizer gasification, and (3) gasification of the remaining condensed phase species. Simple global kinetics are assumed for the gas phase reactions and binder decomposition abiding Arrhenius law, and boiling process for the oxidizer abiding Clausius‐Clapeyron curves. The obtained results show similar trends as do other relevant models and experimental results, especially for the effect of droplet size and propellant composition on the burn rate. The predicted effect of initial temperature on the burn rate is less significant than for common solid propellants. The results indicate that for small droplets the oxidizer will heat up to boiling temperature even before it is revealed on the burning surface, due to heat conduction through the surrounding binder.     

Application of the BAMO‐AMMO Alternative Block Energetic Thermoplastic Elastomer in Composite Propellant

A BAMO‐AMMO alternative block (BAAB)‐based thermoplastic composite propellant with 80 % solid content was prepared using BAAB energetic thermoplastic elastomer (ETPE) as the binder, and the formulation was optimized through energy calculation. The densities, heats of explosion, glass‐transition temperatures, and mechanical properties of the samples were determined by surface tension measurements, oxygen bomb calorimetry, differential scanning calorimetry and static tensile tests, respectively. The results showed that this composite propellant can reach a standard theoretical specific impulse of 275.45 s (10 MPa), a density of 1.8102 g cm⁻³, a heat of explosion of 6256 kJ kg⁻¹, a T_g of −50.46 °C, a tensile strength of 1.56 MPa and an elongation at break of 20 %, thus presenting a superior comprehensive property to BAMO‐AMMO random block (BARB)‐based thermoplastic composite propellant.     

Studies of IR‐Screening Smoke Clouds

This paper contains some results of research on the IR‐screening capability of smoke clouds generated during the combustion process of varied pyrotechnic formulations. The smoke compositions were made from some oxygen or oxygen‐free mixtures containing metal and chloroorganic compounds or mixtures based on red phosphorus. The camouflage effectiveness of clouds generated by these formulations was investigated under laboratory conditions with an infrared camera. The technique employed enables determination of radiant temperature distributions in a smoke cloud treated as an energy equivalent of a grey body emission. The results of the analysis of thermographs from the camera were the basis on which the mixtures producing screens of the highest countermeasure for thermal imaging systems have been chosen.     

Spectroscopic Investigations of High‐Nitrogen Compounds for Near‐Infrared Illuminants

Alkaline metal salts are widely used in pyrotechnic formulations. For NIR pyrotechnics, potassium, and cesium nitrate are mainly used as oxidizers and infrared emitters. Herein, new NIR illuminant formulations were tested using several potassium and cesium salts of high‐nitrogen compounds such as tetrazole and triazole derivatives. The research of new formulations comprises the evaluation of sensitivity data and radiometric measurements of new formulations. It was further investigated whether the IR emission can be improved using different nitrogen releasing agents like aminotetrazole or diethylene triamine trinitrate (DETT) as hexamethylenetetramine replacements.     

The effect of ultraviolet‐curable water‐borne polyurethane acrylate binder concentration on the printing performance of synthetic leather

In this paper, synthetic leather samples were screen printed with pigmented pastes including two types of photoinitiators and three different concentrations of ultraviolet (UV)‐curable water‐borne polyurethane acrylate binder. The curing process was conducted under different combinations of lamps (gallium, mercury, gallium/mercury and gallium/gallium/mercury) at three power levels. Abrasion resistance, crock fastness, hardness and colour strength were investigated. Chemical changes in the clear and pigmented film structures because of UV curing were analysed by Fourier Transform‐infrared spectroscopy measurements. In hardness measurements, the highest hardness values were obtained with clear and pigmented formulations which have the highest solid content (57%). In colour measurements, higher K/S values were obtained in samples printed with the formulation having a binder concentration of 46%. Wet crock fastness values improved as the energy level increased during curing, and the highest values were obtained with a formulation which had a binder concentration of 57%. Greater amounts of binder in the formulations and increased amounts of energy applied to the surface during curing increased the hardness value of the prints, thus better abrasion resistance was obtained. Overall results suggested that the highest hardness, crock fastness and abrasion resistance values were obtained with the formulation with a binder concentration of 57%. However, for ease of application, printing efficiency and colour strength, the formulation with a binder concentration of 46% is recommended for printing, and curing under consecutive passes with gallium and mercury lamps at 120 W/cm is proposed in terms of energy efficiency and printing performance.     

Suppressing Hydrogen Evolution by Aqueous Silicon Powder Dispersions by Controlled Silicon Surface Oxidation

Aqueous silicon dispersions are used to produce pyrotechnic time delay compositions. The propensity of silicon to react with water and to produce hazardous hydrogen gas must be suppressed. To this end, the effect of air heat treatment temperature on the rate of corrosion of silicon was investigated. It was found that four hour heat treatments at temperatures below 350 °C provided significant passivation. This is attributed to the removal of the hydroxyl groups present on the SiO₂ surface scale layer. It was found that thickening the silica layer, by heat treatment at higher temperatures, causes a further reduction in the amount of hydrogen released. However, differential thermal analysis (DTA) studies showed that excessive silicon surface oxidation increased the ignition temperature and reduced the heat release of a near‐stoichiometric silicon‐lead chromate pyrotechnic composition.     

Cone calorimeter analysis of UL‐94 V‐rated plastics

Cone calorimeter analysis was conducted on 18 thermoplastics with different UL‐94 vertical burn test (V) ratings. Ratings varied from V‐0 to no rating (NR), and the types of thermoplastics included were polycarbonate (PC), acrylonitrile–butadiene–styrene (ABS), PC/ABS blends, high‐impact polystyrene (HIPS), polypropylene (PP), and poly(vinyl chloride) (PVC). Our analysis of the cone calorimeter data found that there were correlations between UL‐94 V rating and some cone calorimeter measurements (peak heat release rate (HRR) average and HRR at 60 s) and no relationship for other measurements (time to ignition and total heat release). However, no precise correlation was found due to significant differences in flame retardant mechanism and polymer fuel energy values. In this paper, we seek to explain further why a broad quantitative relationship between UL‐94 V and cone calorimeter remains elusive, and also to show how the cone calorimeter can be used to understand why a material passes or fails a particular UL‐94 V rating. Copyright © 2006 John Wiley & Sons, Ltd.     

Synthesis of GAP-PB-GAP Triblock Copolymer and Application as Modifier in AP/HTPB Composite Propellant

A new triblock copolymer polyglycidylazide-block-polybutadiene-block-polyglycidylazide (GAP-PB-GAP) has been synthesized. The synthesis was done by cationic ring opening polymerization of epichlorohydrin (ECH) with HTPB as the alcohol and boron trifluoride etherate as the catalyst followed by the conversion of the -CH₂Cl group into -CH₂N₃ group. The presence of the azido groups in the GAP polymer chain makes it more energetic and the triblock copolymer can be used as an energetic binder/additive for propellant energy modification. Since the triblock copolymer has polybutadiene (PB) as the central block, which is from HTPB itself, it can be used as an additive in HTPB based polymeric formulations to improve their properties. In the present work, a part of HTPB, the propellant binder in ammonium perchlorate (AP)/HTPB propellant was removed and replaced with the GAP-PB-GAP copolymer. Burn rate, mechanical properties, and heat of combustion properties of these propellants were measured and compared with the unmodified HTPB/AP propellant. The results show that the burn rate of the HTPB/AP solid propellant could be enhanced by the addition of the triblock copolymer.     

Mixed Explosives and Determination of Their Detonation Parameters

A model of the effective characteristics of heterogeneous systems is given. The model is based on the methods of field theory of many bodies. The suitability of the given approach for a quantitative assessment of the characteristics of explosives and detonation is shown. In particular, two‐component mixtures of TNT/RDX and three‐component mixtures of aluminum with energetic materials are considered. The values of a few parameters (density, impact sensitivity, heat of explosion, detonation velocity) calculated by means of the proposed model agree satisfactorily with known experimental data.