Cast Double Base Research Articles

BuNENA-DNDA57 Combined Energetic Plasticizer for Modified Cast Double Base Propellants

K ziskani kvalitnich nasakovaných TPH je nutne najit vhodný kompromis mezi energii TPH (danou obsahem energetických komponent) a dalsimi vlastnosti TPH. Tato prace je zaměřena na charakterizaci TPH, v nichž je nitroglycerin nahrazen energetickými aditivy hexogenem a plastifikatory BuNENA a DNDA57. Sledovan byl pak vliv těchto aditiv na nasledujici vlastnosti: na rychlost hořeni TPH v zavislosti na okolnim tlaku (měřeno v uzavřene bombě SV-2), na termicke a stabilitni parametry (měřeno metodami DTA a DSC) a na citlivost TPH k narazu. Nejvyssi rychlost hořeni, nevyssi aktivacni energii a zaroveň nejnižsi citlivost maji směsi jen s obsahem energetických plastifikatorů.

Laser ignition of elastomer-modified cast double-base (EMCDB) propellant using a diode laser

An experimental study was conducted to investigate laser ignition using a diode laser for elastomer-modified cast double-base (EMCDB) propellant in order to develop more liable and greener laser ignitors for direct initiation of the propellant. Samples of the propellant were ignited using a 974nm near-infrared diode laser. Laser beam parameters including laser power, beam width and pulse width were investigated to determine their effects on the ignition performance in terms of delay time, rise time and burn time of the propellant which was arranged in several different configurations. The results have shown that the smaller beam widths, longer pulse widths and higher laser powers resulted in shorter ignition delay times and overall burn times, however, there came a point at which increasing the amount of laser energy transferred to the material resulted in no significant reduction in either delay time or overall burn time. The propellant tested responded well to laser ignition, a discovery which supports continued research into the development of laser-based propellant ignitors.

Radiographic Sensitivity of Flaw Detection in Solid Rocket Propellants

The sensitivity of flaw detection with x-ray radiographic methods is investigated here qualitatively in case of cast double base and cast composite propellants and for air pockets it is found to be 1.5 and 0.9 percent of the web respectively. General guidelines for the inspection of sustainer charges have also been laid down.

Studies into Laser Ignition of Unconfined Propellants

Prior to laser ignition tests, spectral absorption properties of three different solid motor propellants were analysed. The extruded double base (EDB) propellant exhibited >95 % absorption over the 250–550 nm wavelength band whereas, the cast double base (CDB) showed similar absorption over a wider band extending between 375–800 nm. The composite sample (CP) showed a uniform spectral absorption at about 90 % over 250–800 nm band. Ignition tests using an average of 500 nm output from an Ar-ion laser showed that the double base propellants undergo deflagration prior to ignition due to the presence of carbon black material. Within the laser power density range of 24–125 Wċcm−2, the threshold laser energy densities for deflagration and ignition in the double base propellant were found to␣be between 2–2.5 Jċcm−2, and 40–215 Jċcm−2, respectively. No deflagration was observed for the composite propellant, and the threshold ignition energy was found to be within the range, 11–18 Jċcm−2 for the same range of laser power densities. From the ignition map for this propellant, the threshold energy for ignition at this wavelength was found to be approximately 18 Jċcm−2 and was practically independent of laser power density. In the near infrared wavelength (780 nm) the EDB propellant was not readily ignitable due to its comparatively much higher reflectance at this wavelength. The ignition threshold values were found to be between 19–23 Jċcm−2 for a similar power density level. The results indicate that the ignitability of propellants is enhanced through the promotion of deflagration.

Improvements in the Chemical Stability of Double-Base Solid Rocket Propellants

The effect of copper, compared with lead salt-based ballistic modie ers on the reaction of the propellant stabilizers, para-nitro-N-methylaniline and 2-nitrodiphenylamine, during the aging of nitroglycerin solutions and on the reactions of these stabilizers with the individual reactive species known to be generated during double-base propellant decomposition, namely NO 2, HNO2, and HNO3, have been thoroughly investigated in an attempt to deduce some key parameters that ine uence the reactions that take place in these propellant systems during aging. It was found that copper modie ers greatly differ from lead ones in their effect on the depletion of stabilizers and in their reactivity toward the reactive species. All of the copper salts have a dramatic effect on the reactions of propellant stabilizers. They cause more rapid depletion of stabilizers when compared with that produced by lead salts, the effect of basic copper salicylate being more dramatic than that of copper oxide. The results have shown thattheorganicmoiety oftheballisticmodie erplaysanimportantroleinitsine uenceonthereactionsofstabilizers with propellant degradation species, and that the higher reactivity of copper salts compared with that of lead salts is attributable to the combined effect of both the copper ion and the salt anion. In particular, this investigation has helped contribute information on the propellant compositions that should fule ll the requirements for propellant service use. To overcome the deleterious effect of some copper modie ers on the chemical stability of double-base propellants, the stabilizer system must include resorcinol and the copper salt should be used at a low level. OPPER salts, in combination with lead salt-based ballistic modie ers, are used in nitroglycerin-(NC)-based propellants to modify the combustion characteristics of solid rocket propellants. Nearly all solid propellants based on nitrate esters contain a uniformly distributed stabilizer. The function of the stabilizer is the removal of NO 2, which is formed as a primary decomposition product during the storage of propellants, 1 and which would otherwise autocatalytically accelerate the decomposition. Stabilizer mixture systems are widely used in double-base rocket propellant formulations,wheretheyhavebeenfound 2 tobemosteffectiveinprolonging the crack-free life of the propellant grain during storage. It is generally assumed that the more reactive stabilizer reacts rapidly with the propellantdegradation productsduring theearly stagesofaging, whereas the second stabilizer reacts more slowly. Stabilizerslikeresorcinol,andthe combinationofresorcinolwith other stabilizers, are reported to be useful. 3,4 The effectiveness of resorcinolhasbeenexplained 5 asbeingaresultofactivatedaromatic ring formation, which helps in the absorption of nitrogen oxides quickly and more effectively, resulting in further control of growth of autocatalytic reactions. It was indicated 6 that the chemical stability of double-base propellants is signie cantly ine uenced by different lead-based ballistic modie ers, and that the organic moiety of the ballistic modie er is an important ine uence on the reactions of the stabilizers. In this work, systematic investigations have been carried out to obtain a deeper insight into 1 ) a comparison of the effect of lead and copper salt-based modie ers on the reaction of stabilizers commonly used in the cast double-base (CDB) rocket propellants, namely para-nitro-N-methylaniline (pNMA) and 2-nitrodiphenylamine (2NDPA),duringtheagingofNGsolutionsin acetonitrile-containing identical quantities of the ballistic modie ers that are also commonly used in the propellant matrix, and 2 )a study of the effect of copper modie ers on the reactions of the stabilizers with propellant degradation products (namelyNO2, HNO2, and HNO3). Studying the reaction of these compounds is very impor

Stabilizer Reaction is Cast Double Base Rocket Propellants. Part VIII: Characterization of propellant gassing properties during simulated aging

AbstractThe decomposition process of two cast double base (CDB) propellant compositions was measured in vacuum. The process of gas evolution during heating of propellant compositions in vacuum has been studied using Vacuum Stability Test (VST) and Gas chromatography/ Mass Spectrometry (GC‐MS) techniques. The results for the two different compositions aged at different storage temperatures for different periods of time were compared.VST has been used to quantify the amount of gases evolved during heating of propellant (aged and unaged) compositions at 100°C in vacuum, while quantitative GC‐MS has been used to identify and quantify the evolved gases when the same propellant compositions were heated at 60 °C and 70 °C at low free volume.The results have shown that the amount and type of gases evolved depend on the composition of propellant, percentage of stabilizer etc. Composition 1 evolved CO2, CO, N2, NO and N2O and produced the greater total gas volume, while Composition 2 evolved C02, CO and N2 only. In each case C02 was the predominant gas and Composition 1 produced more COz but less CO than Composition 2. It is suggested that these differences in gas evolution profiles are due to the presence of different ballistic modifiers in the two propellant compositions.Gas evolution assessment using VST technique cannot be the strict measure of double base propellants stability.

Stabilizer reactions in cast double base rocket propellants. Part VII: Effect of lead‐based ballistic modifiers on the reactions of propellant stabilizers during simulated aging of cast double base solid propellants

AbstractThe effect of lead‐based ballistic modifiers on the reactions of stabilizers during accelerated aging at 80°C and 90°C of cast double base propellants has been investigated in order to obtain information on the reactions taking place in these propellant systems. It was found that the ballistic modifiers lead β‐resorcylate (LBR) and lead salicylate (LS) have a significant effect on the depletion of para‐nitro‐N‐methylaniline (pNMA) and 2‐nitrodiphenylamine (2NDPA). Model studies have shown that both LBR and LS reduce the rate of depletion of pNMA to a similar degree, but only LBR reduces the rate of depletion of 2NDPA, with LS having the opposite effect.

Stabilizer reactions in cast double base rocket propellants. Part VI: Reactions of propellant stabilizers with the known propellant decomposition products NO2, HNO2, and HNO3

AbstractThe reactions of stabilizers with the individual reactive species known to be generated during double base propellant decomposition, viz. NO2, HNO2 and HNO3, have been thoroughly investigated in an attempt to obtain information on the reactions that take place in these propellant systems. It was found that the various stabilizers differ in their behaviour towards these reactive species, and this should help to give a clearer picture of the chemistry occuring during aging of double base propellants.

Stabilizer reactions in cast double base rocket propellants. Part V: Prediction of propellant safe life

AbstractPropellant deterioration can be kinetically analysed by both Berthelot's law and Arrhenius' law. Kinetic analysis of the mixed stabilizer para‐nitro‐N‐Methylaniline(pNMA)/2‐nitrodiphenylamine (2NDPA) based propellant deterioration at different temperatures, during the time necessary for the complete consumption of the more reactive stabilizer pNMA, which can be taken as a measure of the safe life of these propellant compositions, gave results for both Berthelot's law and the Arrhenius' law which are satisfactory. However, it was found that the predicted safe life for the propellant compositions according to the Arrhenius law was much longer than that obtained from Berthelot's law. Therefore, from the safety point of view, it is preferable to use Berthelot's law analysis to assess the safe life of double base propellant compositions.

Stabilizer Reactions in Cast Double Base Rocket Propellants. Part IV: A Comparison of Some Potential Secondary Stabilizers for Use with the Primary Stabilizer 2‐Nitrodiphenylamine

AbstractReaktionen des Stabilisators in gegossenen Doublebase‐Treibladungspulvern. IV. Vergleich einiger potentieller Sekundär‐Stabilisatoren für die Anwendung mit dem Primär‐Stabilisator 2‐NitrodiphenylaminVersuche werden beschrieben in der Absicht, die Wirksamkeit des Sekundär‐Stabilisators p‐Nitro‐N‐methylanilin (pNMA) und der potentiellen Sekundär‐Stabilisatoren p‐Nitro‐N‐ethylanilin (pNEA), 4‐Nitrodiphenylamin (4NDPA) und Resorcin zu vergleichen bei der Reduzierung der Abbaugeschwindigkeit des Primär‐Stabilisators 2‐Nitrodiphenylamin (2NDPA) in nitroglycerinhaltiger Acetonitrillösung bei Alterung bei 75°C. Die HPLC‐Bestimmung der Stabilisatorkonzentrationen als Funktion der Zeit zeigt, daß 4NDPA am meisten wirksam ist und deshalb erfolgreicher eingesetzt werden könnte als Sekundär‐Stabilisator in Nitratester‐Treibstoffen als das meist verwendete p‐NMA.

Stabilizer Reactions in Cast Double Base Rocket Propellants. Part III: Evidence for stabilizer interaction during extraction of propellant for HPLC quantitative analysis

AbstractThe use of a refined HPLC technique for analysis of the stabilizers para‐nitro‐N‐n ethylaniline (pNMA) and 2‐nitrodiphenylamine (2NDPA) and their N‐nitroso derivatives, in a mixed‐stabilizer, cast, double base rocket propellant composition subjected to accelerated aging at 70°C for 18 weeks has shown that (1) the time of hot extraction of the propellant samples for HPLC analysis significantly affects the relative quantities of the stabilizers and their corresponding N‐nitroso derivatives, and (2) pNMA is completely consumed during aging. The results presented in the first two parts of this series require some qualification on the basis of these observations, but the suggestion that the N‐nitroso derivative of pNMA participates in transnitrosation with 2NDPA remains valid, and is further substantiated by its occurrence during hot extraction of the propellant.

Assessment scheme for the chemical compatibility of materials with cast double base propellants

AbstractThe scheme for the compatibility assessment of materials with cast double base propellants as operated at Royal Ordnance Summerfield is described. Central to the scheme is the recognition that evaluation of the compatibility of materials must consider two areas of safety. These are on‐site process safety requirements, and rocket motor service life which includes safe chemicalstability and the long term functioning and reliability of a store. To rationalize testing, a system of compatibility testing to defined categories classified by the application and usage of a material is followed.

Stabilizer reactions in cast double base rocket propellants. Part II: Formation and subsequent reactions of N‐nitroso derivatives of para‐nitro‐N‐methylaniline and 2‐nitrodiphenylamine in mixed‐stabilizer propellants aged at 80°C and 90°C

AbstractThe HPLC determination of the stabilizers para‐Nitro‐N‐methylaniline (pNMA) and 2‐Nitrodiphenylamine (2NDPA) and their derivatives in two mixed‐stabilizer cast double base rocket propellants undergoing accelerated aging at 80°C and 90°C has led to the conclusion that N‐nitroso derivatives play a critical role in the stabilizer depletion processes in this type of propellant. In order to account for the principal stabilizer products in the aged propellants it is suggested that pNMA enters into an equilibrium with its N‐nitroso derivative (formed during the initial stages of aging) and that this reacts with 2NDPA in a transnitrosation reaction, to give mainly N‐nitroso‐2NDPA from which the observed C‐nitro derivatives of 2NDPA are in part generated by rearrangement and subsequent oxidation.

Stabilizer reactions in cast double base rocket propellants. Part I: HPLC Determination of Stabilizers and their derivatives in a propellant containing the stabilizer mixture para‐nitro‐N‐methylaniline and 2‐nitrodiphenylamine aged at 80°C and 90°C

AbstractReverse phase high performance liquid chromatography (HPLC) employing an acctonitrile/methanol/water (45/10/45) mobile phase has been used to separate and quantitate the stabilizaers para‐nitro‐N‐methylaniline, (pNMA) and 2‐nitrodiphenylamine, (2NDPA) and their derivatives in a mixed‐stabilizer cast double hase rocket propellant composition undergiong acceterated aging at 80°C adn 90°C. Quantitative measurements show that pNMA is converted almost cntirely into N‐nitroso‐pNMA during the carly stages of aging and that this derivative persists for the remainder of the aging period. 2NDPA, on the other hand, reacts more slowly to give both N‐nitroso and C‐nitro derivatives.

Chromatographic determination of a polyol and/or sucrose octa‐acetate in CDB casting liquid

AbstractA quantitative method for the determination of a polyol and/or sucrose octa‐acetate in cast double base (CDB) casting solvent formulations is presented. The procedure utilizing liquid chromatography is based on the separation of components by differences in molecular weight during the development of the method it became apparent that this analytical approach may be of general interest where a species to be a quantified has no other conveniently exploitable property.

Assessment of the response of rocket propellants to high-velocity projectile impact using small-scale laboratory tests

Two small-scale laboratory testing methods (Hopkinson Bar and Shotgun tests) for assessing the response of rocket propellants to high-velocity projectile impact are described. The impact ignition sensitivities of several composite propellants and cast double base (CDB) propellants have been determined. Composite propellants with different mechanical properties, oxidizer loading, and oxidizer and binder types, and CDB propellants with different nitrocellulose (NC)-to-nitroglycerine (NG) ratios have been examined. The two tests give comparable results, except for very “soft” propellants. Results from the Hopkinson Bar and Shotgun tests correlate with bullet impact field trials of end-burning rocket motors and suggest that the information obtained from these small-scale tests are relevant to propellant ignition and burning and can predict, to some extent, the response of rocket propellants to projectile impact.

Relationship between impact ignition sensitivity and kinetics of the thermal decomposition of solid propellants

The impact ignition sensitivities of a series of composite propellants and a cast double base (nitrocellulosenitroglycerine) propellant were measured and related to the fracture behavior and thermal properties (decomposition kinetics, thermal stability, and burning rate) of the propellants. The kinetics of the thermal degradation of the propellants were studied over a temperature range of 30–450°C at various heating rates. The composite propellants showed a two-step decomposition mechanism, the initial decomposition being due mainly to reactions involving the oxidizer. The major decomposition, which takes place at higher temperatures, was due to several simultaneous reactions involving the oxidizer, the binder, and their decomposition products. At heating rates of 5–15°C min −1, the second-step decomposition followed 0.5–1-order kinetics, but at heating rates above 20°C min −1, the reaction became zero order (attributed to autocatalysis). The critical impact velocity showed a very strong dependence on the fracture toughness of the propellant, whereas the slope of the plot of ignition probability versus impact velocity showed good correlation with the decomposition kinetics and thermal stability and, to some extent, with the burning rate of the propellant. Our results suggest that two distinct mechanisms are involved in impact ignition: (1) an initiation step where fracture, viscoelastic plastic deformation and cracking occur, and are means by which not spots are formed (mechanical properties of the propellant predominate in this initiation step); and (2) a flame propagation step, which involves burning and is governed by several interrelated factors, such as the decomposition kinetics, thermal stability, and burning rate of the propellant.

Temperature dependence of high strain-rate impact fracture behaviour in highly filled polymeric composite and plasticized thermoplastic propellants

The effect of temperature and strain-rate on the fracture behaviour during high strain-rate (∼ 103 sec−1) impact of two highly filled polymeric composite propellants (containing segmented polyurethanes based on hydroxy-term inated polybutadiene (HTPB) or glycidyl azide polymer (GAP) filled with ammonium perchlorate (AP) particles) and a plasticized thermoplastic (cast double base (CDB) nitrocellulose-nitroglycerine) propellant have been examined over a wide temperature range encompassing the ⋊ittle-ductile” transition. In the “elastic” region of the loaddisplacement curve, the yield stress and fracture toughness is highest for GAP/AP and lowest for HTPB/AP. In the “elastic” and post-yield “ductile” regions CDB is more fracture-resistant than GAP/AP and HTPB/AP over the temperature range −20 to 50° C, but below −40° C, where both CDB and GAP/AP are brittle, GAP/AP is more fracture-resistant than CDB (as observed in the “elastic” region). Although all the propellants are known to develop small cracks in the “elastic” and post-yield “ductile” regions of the load-displacement curve, the overall fracture behaviour is largely governed by viscoelastic properties (because the cracks close up in compression). The good mechanical properties of CDB, above the “brittle-ductile” transition temperature, can be attributed to the presence of a largeβ-transition loss peak. In the composites, the fracture behaviour is also influenced to a lesser extent by the degree of filler-binder interactions. Dynamic mechanical analysis indicates that GAP/AP has a slightly higher degree of filler-binder interactions than HTPB/AP. A temperature-strain rate reduction has been obtained for the yield stress and the composite curve can be expressed by the equation σy =K1 +K2 log (ĠeaT) whereK1 andK2 are constants andaT is a shift factor.K2 is a material constant which reflects the temperature and strain-rate sensitivity.

Influence of Phenolic Compounds in the Combustion of Cast Double Base Propellants Containing Lead Stearate

Abstract The effect of different cresols (o, m, p), resorcinol and pyrogallol in the presence and absence of lead stearate on the burning rates of cast double base propellants has been studied in the 35−140 kg/cm2 pressure range. While their effect is not significant without lead stearate, these phenolic compounds increased burning rates in the presence of lead stearate. Their mode of action is explained on the basis of differential thermal analysis data.