Composite Modified Double-base Research Articles

Applying Mechanically Activated Al/PTFE in CMDB Propellant

AbstractA novel reactive powder (aluminum/polytetrafluoroethylene, Al/PTFE 75/25 mass %) containing two kinds of PTFE (pre‐sintering PTFE and fresh PTFE, P‐PTFE and F‐PTFE) was prepared by a two‐step mechanical activation (MA) method. By introducing it into composite modified double base (CMDB) propellant, an attempt to improve the propellant performance of this mechanically activated Al/PTFE was made. Scanning electron microscopy (SEM) characterization indicated that F‐PTFE in activated powders deformed to abundant fibers under uniform shear forces. These fibers significantly enhanced propellant tensile properties and show improved safety performance. Compared to blank CMDB propellant (without PTFE), the elongation at maximum strength for propellant with activated Al/PTFE inclusions was increased to 3.7 times at −40 °C and to 3.9 times at −70 °C, the friction sensitivity and impact sensitivity were reduced by 88.9 % and 20.4 %, respectively. P‐PTFE in activated powders promoted the Al reaction activity, thereby reducing the propellant combustion agglomeration. The average diameter (D50) of coarse products for propellant with activated Al/PTFE 75/25 mass‐% was reduced by 82 % compared to that of blank CMDB propellant with spherical aluminum. This novel activated Al/PTFE shows increased propellant mechanical performance, decreased sensitivity and improved combustion efficiency of Al, which might expand the application field of CMDB propellants.

Experimental and theoretical studies on stability of new stabilizers for N-methyl-P-nitroaniline derivative in CMDB propellants

Although N-methyl-P-nitroaniline (MNA) was a quite effective stabilizer in composite modified double base (CMDB) propellants, it undergoes crystallization easily from nitroglycerin (NG) during storage. In order to improve its solubility in nitroglycerin (NG) and the stability in propellants, several new stabilizers including N-ethyl-p-nitroaniline (ENA), N-n-propyl-p-nitroaniline (n-PNA), N-i-propyl-p-nitroaniline (i-PNA), N-n-butyl-p-nitroaniline (n-BNA) and N-t-butyl-p-nitroaniline (t-BNA) were designed and synthesized to replace MNA by increasing the carbon chain length. The interaction between NG and different stabilizers was simulation by Materials Studio 5.5 and the stability and the high temperature stability performance of those new stabilizers in propellants were calculated by Gaussian 09. It was found that both the solubility of new stabilizers in NG and the stability and the high temperature stability performance of those in propellants were improved when the carbon chain length of substitution groups on nitrogen atom was increased. Thus, the n-BNA was a most potential stabilizer. Then all properties of the stabilizers were studied experimentally, which was agreement well with the theoretical analysis.

Influence of strain rate on the compressive yield stress of CMDB propellant at low, intermediate and high strain rates

The mechanical properties of composite modified double base (CMDB) propellant significantly depend on the strain rate. In particular, the yield stress increases dramatically at higher strain rates. To study this behaviour, low, intermediate and high strain rate compression testing (1.7 × 10−4 to 4 × 103 s−1) of CMDB propellant at room temperature was conducted by using a universal testing machine, a hydraulic testing machine and a split Hopkinson pressure bar (SHPB) system, respectively. The yield stress was observed to increase bilinearly with the logarithm of strain rate, with a sharp increase in slope at a strain rate of 5 × 101 s−1, which was supported by dynamic mechanical analysis (DMA) testing. The Ree-Eyring model, involving two rate-activated processes, was employed to predict the yield behaviour of CMDB propellant over a wide range of strain rates. The predictions are in excellent agreement with the experimental data.

Strain rate and temperature dependence of the compressive behavior of a composite modified double-base propellant

The quasi-static and dynamic compressive properties of a composite modified double-base (CMDB) propellant were studied over a wide range of strain rates from 10−4s−1 to 103s−1 at low temperatures of −40°C to 0°C, using a conventional universal testing machine and a split Hopkinson pressure bar apparatus. The experimental results show that the mechanical properties of the CMDB propellant, in terms of yield stress, initial compressive modulus, and ultimate strain, were greatly affected by the applied strain rate and the temperature, and the stress–strain responses exhibited an initial viscoelastic phase, followed by yielding, and then a subsequent strain hardening or softening stage, which was strongly dependent on the strain rate and temperature. It was found that the yield stress increased with both increasing strain rate and decreasing temperature. According to the experimental results, the strain rate effect, but not the temperature effect, was accentuated at higher rates. Moreover, the Eyring cooperative model was employed to predict the yielding behavior, and a master curve of reduced yield stress versus strain rate was built. The results show that the Eyring cooperative model provides reasonable prediction over a wide range of strain rates under low temperatures.

BTATz–HNIW–CMDB propellants

The high nitrogen compound 3,6-bis(1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine and the high energy density material hexanitrohexaazaisowurtzitane (HNIW), were used as substitute of hexogen (RDX) in the composite modified double base (CMDB) propellant formulations, the propellant samples were prepared, the thermal behaviors, nonisothermal reaction kinetics, and thermal safety were carried out, and the eight important parameters were calculated and obtained as the self-accelerating decomposition temperature (T SADT), thermal ignition temperature (T TIT), critical temperatures of thermal explosion (T b), critical temperature of hot-spot initiation (T cr,hot-spot), characteristic drop height of impact sensitivity (H 50), critical thermal explosion ambient temperature (T acr), safety degree (S d), and thermal explosion probability (P TE). It shows that the content of HNIW has a large effect on the decomposition reaction mechanism of the CMDB propellant, when the content of HNIW is 10 %, the decomposition reaction are controlled by the random nucleation and subsequent growth (n = l), and the reaction mechanism obeys Mampel law; but when the content of HNIW is 20 %, the decomposition reaction are controlled by the chemical reaction (n = 1/4). The mechanism can not be changed by the catalysts, and they just make the apparent activation energy change slightly. For the sample, from BC01 to BC04, the values of T SADT and T TIT making an upward tendency, show the resistivity to heat: BC04 > BC03 > BC02 > BC01; the values of T acr and S d, BC01 are the maximum and BC02 are the minimum, show the heat sensitivity: BC01 > BC03 > BC04 > BC02. For the same radius, the thermal safety of the sphere sample is greater than that of the infinite cylinder one.

Study on the Notch Strength and Notch Sensitivity of Composite Modified Double-Base Propellants

To obtain the notch strength of the composite modified double base (CMDB) propellant, three-point bending tests on the single-edge U-notched thin plate specimens and uniaxial tensile tests on standard tensile specimens were carried out at 20°C. Experimental data include three parts in different range of the stress concentration factor Kt of specimens. The stress concentration factor Kt of the specimens have a distinct effect on the notch strength in a specific range. When Kt is less than the notch sensitivity factor KbN which is approximately equal to 1.35, the notch strength of CMDB propellant is approximately equal to its fracture strength and independent of the stress concentration factor of test specimens. When Kt is upper than 2.41, the notch strength change to be steady to a proper value which associate with the fracture toughness of the propellant . This shows that the CMDB propellant is insensitive to notch. The tensile test data is used to predict the value of the notch strength and notch sensitivity factor,and the prediction fit well with the test results of the notched specimens in a specific range.

Surface Coating of Nitroamine Explosives and Its Effects on the Performance of Composite Modified Double-Base Propellants

T HE traditional high-energy nitroamine explosives, cyclotrimethylene trinitramine (RDX) and cyclotetramethylene tetranitramine (HMX), have been widely used in many plasticbonded explosives, propellants, and powders due to their high energy performance, smokeless combustion products, and low price [1–4]. The content of nitroamine explosives exceeds 80% in some composite modified double-base (CMDB) and nitrate ester plasticized polyether propellants, respectively [5]. Nitroamine explosives can greatly enhance the specific impulse of propellants. It can, however, degrade the safety, mechanical properties, and processing properties of the propellants, which restricts the application of these highenergy propellants. More recently, much interest has been generated on how to improve the propellant’s overall properties. The main approaches include the following: 1) using advanced binders or plasticizers, such as glycidyl azide polymer [6,7] or 3,3diazidomethyloxetane [8,9]; 2) improving the particle properties of the solid fillers by reducing the particle size [10–13] or changing the particle morphology [14–16]; and 3) optimizing the propellant’s formulation and charge structure [17,18]. An acutely popularmethod to improve the propellant properties is to coat its sensitive fillers. Manning and Thelma [19] used graphite to surface-coat RDX fillers by solvent-evaporation and investigated the application in propellants. Their experimental results showed that, by such surface coating, the drop heightH50 of RDX andRDX-containing propellant increased by 40%and115%, respectively. In addition, some previous researchers have also indicated that the mechanical properties of propellants were improved via coating of the nitroamine fillers with polymer or bonding agent [20–23]. The properties of the coated particles depend on the kind of coating materials. For the nitroamine explosive used in some propellants, the best coating materials should be selected from the propellant ingredients [5]. Nitrocellulose (NC) is necessary for the energy and mechanical properties of double-based propellants. In our previous work, RDX particles coated with NC were prepared by solvent evaporation. These coated samples exhibited par dispersion [24]. Another coating technology, slurry solution distillation (SSD), has also been used to prepare themolding powders [25,26].However, there are two limitation to this method: 1) the energy of the explosive is greatly decreased because the addition of coating materials is higher than 5%; and 2) agglomerates composed of multiple particles can be formed easily, which leads to a change in particle size distribution. Herein, a new method, slurry emulsion distillation (SED), was exploited to coat NC and centralite-1 (C-1) onto the nitroamine particles by introducing a high-shear force in the SSDmethod. Also, the effects of such surface coating on properties of nitroamine explosives and CMDB propellants were investigated.

Researches on Thermal Decomposition Kinetics of Composite Modified Double‐base Propellants

AbstractThe thermal decomposition kinetics of composite modified double‐base (CMDB) propellants with a series of contents of hexogeon (RDX) was investigated by using parameters of Teo, Ti, Tp, Tf, Tb, Ta, E, lg A and ΔH, which were obtained from using a CDR‐4P differential scanning calorimeter (DSC) and Perkin‐Elmer Pyris 1 thermogravimetric analyzer (TG) analyses with heating rates of 5, 10, 15 and 20 K/min. Reliable activation energy was calculated using Flynn‐Wall‐Ozawa method before analyzing the thermal decomposition mechanism. TG‐DTG curves were treated with Malek method in order to obtain the reaction mechanisms. The obtained results show that the thermal decomposition mechanisms with the conversion from 0.2 to 0.4 was f(α)1/2α, and with the conversion from 0.5 to 0.7 was f(α)(1/4)(1−α)[−ln(1−α)]−3.

BTATz-CMDB propellants

Abstract The high-pressure thermal properties and their correlation with burning rates of the composite modified double base (CMDB) propellants containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz), a substitute of hexogen (RDX), were investigated using the high-pressure differential scanning calorimetry (PDSC). The results show that there is a main exothermal decomposition process with the heating of each propellant. High pressure can restrain the volatilization of NG, accelerate the main decomposition reaction, and make the reaction occur easily. High pressure can change the main decomposition reaction mechanism function and kinetics, and the control process obeys the rule of Avrami–Erofeev equation at high pressure and chemical reaction at normal pressure. However, the mechanism function can not be changed by the ballistic modifier. The correlation between PDSC characteristic values and burning rates was carried out and found that u and keep a good linear relation, ku keeps a si...

Thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates of BTATz-CMDB propellant

The composite modified double base (CMDB) propellants (nos. RB0601 and RB0602) containing 3,6-bis (1H-1,2,3,4-tetrazol-5-yl-amino)-1,2,4,5-tetrazine (BTATz) without and with the ballistic modifier were prepared and their thermal behaviors, nonisothermal decomposition reaction kinetics, thermal safety and burning rates were investigated. The results show that there are three mass-loss stages in TG curve and two exothermic peaks in DSC curve for the BTATz-CMDB propellant. The first two mass-loss stages occur in succession and the temperature ranges are near apart, and the decomposition peaks of the two stages overlap each other, inducing only one visible exothermic peak appear in DSC curve during 350–550 K. The reaction mechanisms of the main exothermal decomposition processes of RB0601 and RB0602 are all classified as chemical reaction, the mechanism functions are f( α) = (1 − α) 2, and the kinetic equations are d α / d t = 10 19.24 ( 1 − α ) 2 e − 2.32 × 10 4 / T and d α / d t = 10 20.32 ( 1 − α ) 2 e − 2.43 × 10 4 / T . The thermal safety evaluation on the BTATz-CMDB propellants was obtained. With the substitution of 26% RDX by BTATz and with the help of the ballistic modifier in the CMDB propellant formulation, the burning rate can be improved by 89.0% at 8 MPa and 47.1% at 22 MPa, the pressure exponent can be reduced to 0.353 at 14–20 MPa.

High-performance thin-layer chromatographic analysis of the organic components of composite modified double-base propellants

Qualitative and quantitative analysis of the organic components of composite modified double-base (CMDB) propellants have been performed by HPTLC. The method enabled analysis of a five-component mixture in less than 10 min. The relative distribution of the components of the mixture was determined by means of a UV absorbance detector capable of monitoring at several different wavelengths and of providing UV spectra which could be used to assess peak purity. Detection limits were at nanogram levels.

Studies on azotetrazolate based high nitrogen content high energy material spotential additives for rocket propellants

This paper reports the synthesis, characterisation and thermolysis studies of a series of azotetrazolate salts, viz., ammonium/guanidinium/triaminoguanidinium [azotetrazolate]. TG-DTA and DSC results of these compounds exhibited their thermal stability up to 180°C. DSC indicated the highest heat release (2804 J g−1) for guanidinium azotetrazolate salt during exothermic decomposition. FTIR of the decomposition products of azotetrazolate salts showed bands at 3264 and 2358 cm−1 which may be attributed to gaseous species such as NH3 and HCN or NH2CN. The sensitivity data suggests low vulnerability of ammonium and guanidinium salts. In cyclic voltammetric studies all the salts showed similar response in reduction reactions. Triamino guanidinium azotetrazolate (TAGAZ) was incorporated into solid propellant formulations in order to establish the compatibility of this class of compounds. DSC results revealed that it does not have adverse effect on thermal stability of double base matrix. The burning rate data obtained indicated that TAGAZ acts as an efficient energetic additive in composite modified double base (CMDB) propellant formulations in high-pressure region.

Combustion and Thermal Studies on Al/Ti/Ni/Zr Composite Modified Double-Base Systems

Slurry-cast metallized ammonium perchlorate (AP)-composite modified double-base (CMDB) propellants incorporating Ni, Ti, and Zr were studied. Aluminized formulations were investigated as reference. Selected ballistic modifiers, namely, copper chromite (Cu-chromite)/ferric oxide (Fe 2 O 3 )/ferric acetyl acetonate (FeAA)/basic lead salicylate (BLS)+Cu 2 O+carbon black (C-black) combinations were also evaluated for their effectiveness. An acoustic emission technique was applied to determine the burning rates in the pressure range of 1-10.8 MPa, and thermal data were generated by applying differential thermal analysis, thermogravimetry, and differential scanning calorimetry techniques. The control formulation based on 30% AP dispersed in a 70% double base matrix, gave stable combustion in the entire pressure range studied. Inclusion of metals (2.5-17.5% at the expense of AP) resulted in a decrease in the burning rates with the increase in metal content. Ni-based formulations exhibited burning rates superior to aluminized formulations particularly with high metal content. The overall best burning-rate results were obtained with Zr, followed by Ti. Among ballistic modifiers, Cu-chromite was found to be the most effective, followed by the BLS + Cu 2 O + C-black combination. An interesting composition with super-burning-rate characteristics (10-60 mm/s in the 1-10.8 MPa pressure range) emerged during the research. Thermal studies show the heat sink effect of metals. However, Ni, Ti, and Zr appear to produce compensating heat feedback to a greater extent than Al. Cu-chromite appears to be highly effective in facilitating both condensed- and gas-phase combustion reactions.

Tailoring of unsaturated polyesters for inhibition of double-base and composite modified double-base rocket propellants†

Unsaturated polyesters have proved their potential for inhibition of double-base (DB) and composite modified double-base (CMDB) rocket propellants but usually suffer from slightly higher nitroglycerine (NG) absorption andlower flame retardant characteristics. This requires tailoring of their properties through different techniques. This review summarizes different techniques for this purpose and presents the data generated. The present status of these tailored/modified systems is also discussed in detail followed by future scope of research in this field.

Studies on effect of incorporation of BDNPF/A on burning rates of RDX/AP/AI filled CMDB propellants

This paper reports the effect of replacement of non -energetic plasticizer diethyl phthalate (DEP) by nitroplasticizer [1:1 mixture of bis (2,2 dinitro propyl) formal (BDNPF) and bis (2,2 dinitro propyl) acetal (BDNPA)] on burning rates and Isp of nitramine (RDX) / ammonium perchlorate (AP) based composite modified double base (CMDB) propellants. Addition of BDNPF/A led to overall 9–46% increase in burning rates, as well as gain in Isp to the order of 5–10 s in both the systems. Inclusion of copper chromite (C.C.) led to further improvement in burning rates. A typical aluminized (17.5%)- ecofriendly RDX (12.5%)-CMDB formulation gave burning rates of the order of 8–22 mm/s in the pressure range of 2.9–10.8 MPa with Isp (theoretical) of 264 s. Aluminized AP-CMDB propellant with low pressure combustion limit of 1.9 MPa and burning rates of 15–31 mm/s was also realized during this work. Superior oxygen balance and heat of formation of BDNPF/A compared to DEP appear to play contributory role in this regard. Heat feed back from intensified combustion near the deflagrating propellant surface may be facilitating the decomposition of condensed phase. This is clearly brought out from estimated activation energy values for BDNPF/A plasticized RDX propellants.

HTPB‐based polyurethanes for inhibition of composite‐modified double‐base (CMDB) propellants

Polyurethanes were synthesized by the reaction of hydroxy-terminated poly-butadiene (HTPB) and diisocyanates such as toluene diisocyanate (TDI), diphenyl-methane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), and isophorone diisocyanate (IPDI). Carbon black and antimonytrioxide (Sb2O3) were incorporated into these formulations as fillers. Dioctyladipate (DOA) and trimethyllolpropane (TMP) were also added as a plasticizer and crosslinker, respectively. These polyurethanes were investigated as inhibitors for composite-modified double-base (CMDB) propellants. Due to superior mechanical properties, thermal properties, and low nitroglycerine absorption, HTPB–MDI–TMP-derived filled polyurethane was selected and evaluated as an inhibitor for a CMDB propellant. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:355–363, 1997

HTPB-based polyurethanes for inhibition of composite-modified double-base (CMDB) propellants

Polyurethanes were synthesized by the reaction of hydroxy-terminated poly-butadiene (HTPB) and diisocyanates such as toluene diisocyanate (TDI), diphenyl-methane diisocyanate (MDI), hexamethylene diisocyanate (HMDI), and isophorone diisocyanate (IPDI). Carbon black and antimonytrioxide (Sb2O3) were incorporated into these formulations as fillers. Dioctyladipate (DOA) and trimethyllolpropane (TMP) were also added as a plasticizer and crosslinker, respectively. These polyurethanes were investigated as inhibitors for composite-modified double-base (CMDB) propellants. Due to superior mechanical properties, thermal properties, and low nitroglycerine absorption, HTPB–MDI–TMP-derived filled polyurethane was selected and evaluated as an inhibitor for a CMDB propellant. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65:355–363, 1997

The energy and pressure exponent of composite modified double‐base propellant

AbstractThe paper describes an analysis on the energy and pressure exponents of composite modified double‐base (CMDB) propellants. The evaluation of the energy was conducted by means of a thermodynami‐ cal program. Propellant burning rates were determined by the strand burner method. In the AP‐based composition, the energy is enhanced and the pressure exponent reduced with increasing AP content. When AP is partially or entirely replaced by the nitramines HMX or RDX, Isp is improved, and the pressure exponent is inevitably increased. A mixture of lead salicylate or lead o‐amino benzoate and copper 2,4‐ or 3,5‐dihydroxy benzoate produces a remarkable effect on the burning nature of the CMDB propellant. It was noted that the pressure exponent decreases from 0.66 to 0.48 with lead and copper salts added at 3.0% in AP‐Al, 0.82 to 0.60 at 2.0% in RDX‐Al and 0.72 to 0.54 at 2.5% in RDX‐AP‐Al compositions, respectively.

Thermal Behaviour of AP Based CMDB Propellants with Stabilizers

Stability test results and DTA studies indicate the superiority of molecular sieve (MS) over zirconium silicate (ZrSiO/sub 4/) as the stabilizer for a composite modified double base (CMDB) system. Shelf life as computed from autoignition test results was 30 years for MS-based composition which is almost double the life of ZrSiO/sub 4/, but approximately half the life of resorcinol-based composition which was used as a reference. Higher stabilizing effect of MS as compared to ZrSiO/sub 4/ has been explained on the basis of the presence of channels and cavities in its structure, which makes it an effective adsorbent for decomposition catalysing species. Poor stabilization capability of m-dinitrobenzene as compared to resorcinol suggests the catalytic involvement of acidic decomposition products of nitrate esters in autodecomposition process of CMDB propellants.

Evaluation of various dihydric and trihydric phenols as stabilizers for composite modified double base (CMDB) propellants

This paper reports thermal analysis results of the various di- and trihydric phenols containing composite modified double base (CMDB) propellants. Ther