Propellants double-base

W. G. Clark, Evaluation of 1,2,4-Butanetriol Trinitrate as the EiquidExplosive Plasticiserfor Cast Double Base Propellant Report 4, PTA, Dover, N.J., 1960. 

The Beckstead-Derr-Price model (Fig. 1) considers both the gas-phase and condensed-phase reactions. It assumes heat release from the condensed phase, an oxidizer flame, a primary diffusion flame between the fuel and oxidizer decomposition products, and a final diffusion flame between the fuel decomposition products and the products of the oxidizer flame. Examination of the physical phenomena reveals an irregular surface on top of the unheated bulk of the propellant that consists of the binder undergoing pyrolysis, decomposing oxidizer particles, and an agglomeration of metallic particles. The oxidizer and fuel decomposition products mix and react exothermically in the three-dimensional zone above the surface for a distance that depends on the propellant composition, its microstmcture, and the ambient pressure and gas velocity. If aluminum is present, additional heat is subsequently produced at a comparatively large distance from the surface. Only small aluminum particles ignite and bum close enough to the surface to influence the propellant bum rate. The temperature of the surface is ca 500 to 1000°C compared to ca 300°C for double-base propellants. 

Solventless Extrusion Process. The solvendess process for making double-base propellants has been used ia the United States primarily for the manufacture of rocket propellant grains having web thickness from ca 1.35 to 15 cm and for thin-sheet mortar (M8) propellant. The process offers such advantages as minimal dimensional changes after extmsion, the elimination of the drying process, and better long-term baUistic uniformity because there is no loss of volatile solvent. The composition and properties of typical double-base solvent extmded rocket and mortar propellant are Hsted ia Table... 

R. C. Strittmater, E. M. Wineholt, and M. E. Holmes, The Sensitivity of Double Base Propellant Burning Rate to Initial Temperature, MR-2593, BRL, Aberdeen, Md., 1976. 

Development of an Indicator Test Paper for Detecting Stability of Double-Base Propellants , PATR 1782 (1950)... 

Kaufman et al, Nitriles as Plasticizers for Double Base Propellants , NDTS 1299 (NAVORD 4973) (1956) 8) D.N. Lapedes, Ed, Ency-... 

M.C, Philpot, Gas Chromatographic Determination of Plasticizers and Stabilizers in Composite Modified Double-Base Propellants , AnalChem 41 (1), 166-8 (1969) CA 70, 49143 (1969) 49) J. Trauchant, Chromato-... 

Burning Rates of Double-base Propellants (IPCA Modifier)... 

A Comparison of Crosslinkable Double-Base Propellants With and Without Burning Rate Catalyst... 

A third type of propellant, the composite modified-double-base propellant, represents a combination of the other two types. These propellants are made from mixtures of nitroglycerine and nitrocellulose or similar materials, but with crystalline oxidizers such as ammonium perchlorate also included in the matrix. 

Altman and Nichols (A4) were the first to test the constant ignition-temperature approach experimentally. These investigators ignited samples of double-base propellants with electrically heated wires located on the propellant surface. The ignition delay was measured from the time of application... 

Price (P9) has also investigated the ignition characteristics of JPN, a double-base propellant, in an arc-imaging furnace. Price s data show agreement with the predictions of Eq. (8b) for heat fluxes below 1.5 cal/cm2-sec. Above this flux level, the data deviated from the theoretical predictions. 

Although the thermal-ignition theory was developed for double-base propellants, several investigators have attempted to correlate the ignition characteristics of composite propellants using this approach. Baer and Ryan (Bl) have correlated ignition data for a polysulfide-ammonium perchlorate... 

With these goals in mind, several investigators have undertaken to set down quantitative expressions which will predict propellant burning rates in terms of the chemical and physical properties of the individual propellant constituents and the characteristics of the ingredient interactions. As in the case of ignition, the basic approach taken in these studies must consider the different types of propellants currently in use and must make allowances for their differences. In the initial combustion studies, the effort was primarily concerned with the development of combustion models for double-base propellants. With the advent of the heterogeneous composite propellants, these studies were redirected to the consideration of the additional mixing effects. 

One extremely important point to realize is that different propellant types may have different rate-controlling processes. For example, the true double-base propellants are mixed on a molecular scale, since both fuel and oxidizing species occur on the same molecule. The mixing of ingredients and their decomposition products has already occurred and can therefore be neglected in any analysis. On the other hand, composite and composite modified-double-base propellants are not mixed to this degree, and hence mixing processes may be important in the analysis of their combustion behavior. 

The approach taken in the development of an analytical model for the combustion of double-base propellants has been based on the decomposition behavior of the two principal propellant ingredients, nitrocellulose and nitroglycerin. The results of several studies reviewed by Huggett (HI2) and Adams (Al) show that nitrocellulose undergoes exothermic decomposition between 90° and 175°C. In this temperature range, the rate of decomposition follows the simple first-order expression... 

Fig. 14. Schematic model of combustion zone of double-base propellants (HI2).

The basic approach taken in the analytical studies of composite-propellant combustion represents a modification of the studies of double-base propellants. For composite propellants, it has been assumed that the solid fuel and solid oxidizer decompose at the solid surface to yield gaseous fuel and oxidizing species. These gaseous species then intermix and react in the gas phase to yield the final products of combustion and to establish the flame temperature. Part of the gas-phase heat release is then transferred back to the solid phase to sustain the decomposition processes. The temperature profile is assumed to be similar to the situation associated with double-base combustion, and, in this sense, combustion is identical in the two different types of propellants. 

Green (G3) has proposed an alternate approach based on the concept of a critical mass-velocity required to produce a Mach number of 1 in a constant-area channel. Green showed this approach was able to correlate the erosive-burning data he obtained for both a double-base propellant and a composite propellant. 

A comparison of Horton s data for composite propellants with the theoretical results of Hart and Friedly is difficult. The theoretical studies are based on premixed flames, which are more appropriate for double-base propellants. The applicability of premixed flames to composite propellants is open to question, as indicated in Section II. Brown et al. (B13) have indicated that the data are consistent with the expected contributions of surface reactions in the transient combustion process. These comparisons are preliminary, however, and more research is required to study these observations in detail. 

Current propellent explosives may be divided into three classes single base, double base and composite however double base propellants which contain picrite are often considered a separate class and called triple base. 

The actual process of burning of single and double base propellants has been studied in some detail and shown to consist of a number of stages, as shown in Fig. 18.2. The succession of stages is as follows. 

Many methods have been proposed and are used to study the thermal stability of propellants and to ensure the absence of possible autocatalysed decompositions during storage. None are sufficiently reliable to merit individual description. In practice, stabilisers are added, the usual being diphenylamine for nitrocellulose powders and symmetrical diethyl diphenyl urea (carbamate or centralite) for double base propellants. Provided a reasonable proportion of stabiliser remains, the propellant can be assumed to be free from the possibility of autocatalytic decomposition. The best test of stability is therefore a chemical determination of the stabiliser present. 

For civilian aircraft the facility for rapid starting is not important and cartridge operation is not often employed, particularly because it involves storing and handling explosives, even though the hazards of these explosives are those of fire and not of detonation. For military purposes, however, particularly for fighter aircraft which are best scattered on an airfield, a rapid start is of considerable importance. Therefore cartridge operated starters are much used for these aeroplanes. In Britain, development has been essentially with propellants based on ballistite, namely double base propellants of the solventless type, whereas in the United States composite propellants based on ammonium nitrate have proved more popular. 

Double base propellant. A propellant based on nitrocellulose and nitroglycerine. 

Paste. In double base propellant manufacture, the initial mixture of guncotton and nitroglycerine. 

Solvent type propellant. A double base propellant in which solvent is used to assist the gelatinisation of the nitrocellulose. 

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