NL194727C - Nitrogen-based propellant composition. - Google Patents

Description

1 194727

Nitrogen-based propellant composition

The present invention relates to a nitrocellulose-based propellant composition containing a platonizing ballistic modifier.

The preparation of nitrocellulose-containing propellants is described in Chapter 17 of the book "High Explosives and Propellants" by S. Fordham, 2nd edition, Pergamon Press 1980. The manufacture of cast double-based nitrocellulose propellants is also described in GB 827,012 and GB 1,095,471. .

In general, for a given ignition temperature, there is a relationship between the combustion rate of a propellant in a combustion chamber and the pressure to which the propellant is subjected, in a manner that can be mathematically expressed by the equation r = kp "where r is the combustion rate , p is the pressure and k and n are constituents characteristic of the propellant, so the combustion rate r increases exponentially with rising p and log r increases linearly with log p so that the graph of log r against log p is a line with a slope n. In conventional propellants without ballistic modifier, the pressure exponent n has a value of 0.5 to 0.8 and for the propulsion of rockets, the progressive increase in the combustion rate with increasing pressure poses problems in designing engines which pressures that could occur, to overcome this problem, propellant compositions have been developed based on of nitrocellulose (NC) containing ballistic modifiers, the modifier effectively changing the relationship between the combustion rate and the pressure so that the pressure exponent n is lowered over a useful range for the operating pressure. In the area where n = 0, the graph of log r against log p has a flat part which is called a "plateau" and in which the combustion is referred to as "plateau combustion". In some cases, n is reduced to a negative value over a given pressure range, in which case the combustion of the propellant is referred to as "mesa combustion". Ballistic modifiers that cause a reduction of the pressure exponent to a level characteristic of plateau burning or mesa burning are called platonizing agents. Plateau-fired propellants provide reduced variability in the operation of the engine in the plateau area and mesa combustion provides further safety against the development of high pressures in the propellant container.

Commonly used platonizing ballistic modifiers (platonizing agents) include organic salts such as lead salicylate, lead stearate or lead B resorcylate and may also include further metal salts such as copper salicylate, copper stearate or copper benzoate. The use of such ballistic modifiers is described, for example, in US 3,088,858, US 3,923,564, GB 2,121,399 and JP 55071690. A preferred modifier for relatively fast-burning propellants comprises the reaction product of lead B resorcylate and basic cupric salicylate, as described in US 3,138,499, US 3,994,757, US 3,989,776 and US 4,001,287.

GB 1,279,961 describes a solid nitrocellulose propellant containing nitroglycerol as an energetic plasticizer. By adding ferrocene to the propellant composition, it becomes possible to include more nitroglyc roll plasticizer in the composition and thus improve the low temperature properties. The propellant may contain conventional additives in a total amount of no more than 7% by weight and preferably no more than 3% by weight. As additives to be used, GB mentions 1,279,967 modifiers, including lead compounds as ballistic modifiers, stabilizers and fillers and pigments, among which zinc oxide is mentioned as an example.

GB 1,170,695 describes a loose powdered propellant charge on a nitrocellulose basis. The powder is treated with a plasticizer or coating agent to delay the ignition of the powder. In order to prevent too much delay and to obtain the required ignition sensitivity, 0.1 to 1.0% by weight of an inorganic pigment is used. The list of useful inorganic oxides mentions zinc oxide, among other things.

US 3,639,183 describes a propellant composition for a rocket engine. The composition contains propellant, energetic plasticizer, non-energetic plasticizer, stabilizer and ballistic modifier selected from dibutyl tin maleate, lead salicylate, manganese dioxide, tin (IV) oxide, zinc carbonate, monobasic copper (II) salts, monobasic lead B resorcylate, monobasic lead salicylate and mixtures thereof.

DJ. Hewkin et al. In Combustion Science and Technology 2 (1971) pages 307-327 describe the use of lead compounds as ballistic modifiers that have a plateau or mesa burning effect. Tests with the use of different metal oxides in an amount of 0.1 gram metal / kg composition are also described. It is stated that zinc oxide in an amount of 8 g / kg does not cause a plateau or mesa burning effect.

194727 2

The known ballistic modifiers are inadequate in some respects. For example, platinumised propellant compositions often have poor reproducibility of plateau characteristic from batch to batch, are chemically unstable on long-term storage and exhibit combustion instability on burning and ballistic drift on storage. There is therefore a need for improved ballistic-modified propellant compositions, and in particular for well-platelized, high-burning, high-burning compositions which, if necessary, contain aluminum or high levels of energetic fillers such as a nitramine, e.g., RDX (cyclo-1,3,5). trimethylene-2,4,6-trinitramine).

It has now been found that nitrocellulose-based propellants with improved plateau or mesa combustion characteristics can be obtained by using zinc oxide as a ballistic modifier optionally in admixture with one or more lead or copper compounds known as ballistic modifiers in a certain amount.

Therefore, the invention provides a nitrocellulose-based propellant composition containing a platonizing ballistic modifier, characterized in that the platonizing ballistic modifier comprises a total of 2.0 to 8.0% by weight of the propellant composition that comprises zinc oxide or a mixture with one or more lead or copper compounds known as ballistic modifier, and the amount of zinc oxide makes up from 0.15% by weight to no more than 5.0% by weight of the propellant composition.

The propellant compositions of the invention have reproducible combustion characteristics from batch to batch and do not undergo ballistic drift on storage.

Zinc oxide is an effective ballistic modifier for nitrocellulose-based propellants, including cast and extruded propellants. If zinc oxide is used in combination with one or more lead or copper compounds that are known as ballistic modifiers, the platatonized burning rate can be further increased.

With such mixed ballistic modifiers, the platinumized combustion rate of a propellant can be "adjusted" to the requirements of a particular rocket engine and the combustion rate can be increased even for very fast-burning propellants, in some cases by 19%. The modified propellants have improved chemical stability as reflected in improved results in bursting tests. This is due to a reaction between the zinc oxide and protic acid impurities which are present in the propellant composition and which cause the decomposition of nitric acid esters in the absence of zinc oxide. We have also found that the incorporation of zinc oxide as a modifier in nitrocellulose propellants improves or eliminates combustion instability, which is caused by acoustic resonance waves that develop in a rocket engine cavity during combustion of the propellant and cause strong fluctuations in pressure All-time combustion characteristics. It is believed that the improvement is due to the zinc oxide due to its high melting point, thereby acting as a resonance suppressing agent.

Preferably, the propellant composition of the invention contains lead stearate, lead phthalate, lead acetophthalate, lead salicylate, lead B resorcylate, basic copper salicylate, copper B resorcate or copper oxide.

In addition to the nitrocellulose and the ballistic modifier, the propellant compositions of the invention may (also) contain conventional propellant components including NG (double-based propellants); stabilizers, for example paranitro-N-methylaniline, 2-nitrodiphenylamine or resorcinol; plasticizers, for example sucrose octoacetate, triacetin or dibutyl phthalate; energetic components, for example a nitramine such as RDX or metal powder such as aluminum; means for moderating the burning rate, for example soot; lubricants, for example candelilla wax; polymeric binders, for example polycaprolactone cross-linked with isocyanate; "flash" suppressants, for example, 45 potassium nitrate, and resonance suppressors, e.g., silicon carbide.

Platonized propellant compositions according to the invention can vary over widened ranges for the energy and combustion rates. For example, suitable compositions can be formulated that cover the energy range from about 800 calories / g to 1200 calories / g and burn rates from about 4 mm / s to about 45 mm / s. The composition can be prepared using the conventional methods of making propellants suitable for the respective types of nitrocellulose propellants.

The invention is further illustrated by the following examples in which all percentages are weight percentages.

The examples were propellant batches with the compositions listed in Tables 1 and 55 prepared using standard propellant manufacturing methods as described in Chapter 17 of the book "High Explosives and Propellants" by S. Fordham, 2® edition, Pergamon Press 1980. Apart from the zinc oxide, the ingredients used were components commonly used in propellants.

Examples 3-6 were molded double-base propellants made according to a standard method in which a double-base propellant powder containing the majority of the ingredients was prepared by a method using a recording solvent and (this powder was then mixed with a pouring liquid containing about half the nitroglycerin, all the triacetin and a portion of the stabilizer. For testing the combustion rates, plates and final combustion charges were cut from the cast propellant and burned in an engine at an initial temperature of 21 ° C (unless otherwise specified).

Examples 1 and 2 were made by the solvent process. The propellant according to these examples was extruded into wires with a diameter of 2 mm and a length of 18 cm the surface of which was inhibited by treatment with a vinyl lacquer to obtain a constantly burning end surface. The burning rates of the wires were measured over a range of pressures where the wires were burned from the untreated end surface in a "Crawford Bombe" as a device for burning a wire, under a nitrogen atmosphere at an initial temperature of 21 ° C (unless stated otherwise).

Example 1

This example relates to a platatonized, solvent-extruded double-base propellant composition containing 4.00% zinc oxide as the only ballistic modifier. The ballistic properties (burning speed against pressure) are graphically represented in Figure 1 as a graph of the log burning speed against log pressure. The graph shows that the zinc oxide gave a plateau combustion rate of 18 mm / s in a pressure range of 175-225 bar.

Example 2 This example relates to a platatonized, solvent-extruded double-base propellants of the same composition as Example 1, except that the ballistic modifier consisted of 2.0% zinc oxide and 2.0% lead B resorcylate. The ballistic test results of this composition, which are graphically shown in Figure 2, show that this composition gave a plateau combustion at a higher combustion rate of approximately 27 mm / s over a pressure range of approximately 85-200 bar.

30

Examples 3 (a) and 3 (b)

These examples concern platinumized cast double base propellants with substantially the same composition, except that (the agent of) Example 3 (b) contained 0.34% zinc oxide in addition to 1.99% lead B resorcylate and 1.99% lead salicylate as ballistic modifier. The ballistic test results of these compositions are shown graphically in Figure 3. These results show that the zinc oxide had a higher combustion rate plateau over a larger pressure range of about 80-175 bar.

Plates of the compositions were stored at 60 ° C for 12 weeks after which the burning rates were again determined. Example 3 (a) exhibited a ballistic drift to a lower value of 7% over this storage period while Example 3 (b) showed practically unchanged ballistic properties, indicating that the zinc oxide has the effect of reducing the ballistic drift to lower values usually attributed to reaction between the lead B resorcylate and lead salicylate in the composition.

Example 4 45 This example relates to a platatonized, elastomer-modified cast double base propellant composition containing 0.66% zinc oxide, 1.98% lead resorcylate, 1.98% lead salicylate and 3.53% of a polymer binder consisting of polycaprolactone cross-linked with isocyanate. The combustion rate tested at initial temperatures of -40, 21 and 60 ° C was 25-26 m / s in all cases over a platatonized combustion range of 100-175 bar, as shown in Figure 4.

50 In the plateau incineration area, the combustion rate did not vary much with the initial temperature (i.e., the temperature coefficient was low) over the range of -40 to 60 ° C.

Examples 5 (a) and 5 (b)

These examples concern platinumized, aluminum-containing cast, double-base propellants with 55 substantially the same composition, except that Example 5 (b) contained 0.34% zinc oxide. 5.1 cm cubes (ribs) of both compositions were stored at 80 ° C and examined (by X-rays) for signs of cracking or internal cracks. Example 5 (a) showed cracks after eight

Claims (9)

194727 4 days while Example 5 (b) shows no sign of cracking hole for 21 days. Example 6 Propellant composition according to claim 1, characterized in that the lead or copper compound comprises lead stearate, lead citrate, lead phthalate, lead acetophthalate, lead salicylate, lead B resorcylate, basic copper salicylate, copper B resorcylate or copper oxide Propellant composition according to one of the preceding claims, characterized in that it further comprises a stabilizer, plasticizer, modifier for the burning rate, lubricant, "flash" suppressant and / or polymer binder. 4. Propellant composition according to claim 3, characterized in that it contains para-nitro-N-methylaniline, 2-nitrodiphenylamine, resorcinol, sucrose octoacetate, triacetin, dibutyl phthalate, carbon black, candelilla wax, polycaprolactone crosslinked with potassium nitrate and / or silicon nitrate. Propellant composition according to one of the preceding claims, characterized in that it contains at least one energetic component, such as a metal powder or a nitramine, for example cyclo-1,3,5-trimethylene-2,4,6-trinitramine. This example relates to a platinumized, elastomer-modified cast high-base double propellant containing 0.21% zinc oxide, 3.21% polymer binder (same as used in Example 4), 19.6% RDX (cyclonite) and 1 4 contains silicon carbide. The ballistic test results shown in Figure 5 show that plateau combustion occurs at approximately 20 mm / s with an acceptable (low) temperature coefficient over the pressure range of 80-150 bar. TABLE A Example 1 2 3 (a) 3 (b) 4 5 (a) 5 (b) G composition% 15 - nitrocellulose 40.50 40.50 40.09 39.89 26.47 35.57 35.40 21.15 (12.6% N) nitroglycerin 46.86 46.86 47.12 47.01 56.50 43.75 43.64 44.74 p-nitro-N- 0.7 0.7 0.67 0.66 0.66 0.60 0.60 0.69 20 methylaniline 2-nitrodiphenylamine 0.3 0.3 0.33 0.33 0.33 0.33 0.33 0.30 triacetin 7.44 7.44 7.59 7.59 7.69 7.44 7.44 6.09 zinc oxide 4.00 2.0 - 0.34 0.66 - 0.34 0.21 roet 0.2 0.2 0.2 0.2 0.2 1.14 1.13 0.11 25 lead-B resorcylate - 2.0 2.0 1-99 1.98 4.02 4.0 1.25 lead salicylate - - 2.0 1.99 1.98 - - 1.25 • polymer - - - - 3.53 - - 3.21 binder Aluminum _____ 4.56 4.54 - 30 basic cuprisali- - - - - - 1.94 1.93 - cylate resorcinol - - - - - 0.65 0.65 - RDX _______ 19.6 silicon carbide - - - - - - - - 1.4 35 - preparation method from cast cast cast cast cast cast solution · solvent medium extruded · Extruded deplatized 18 27 24 29 26 - - 20 burning speed ( mm / s) pressure range (bar) 175-225 85-200 80-130 80-175 100-175 - - 80-150 * 5 service life until ----- 8 21 - cracks occur (days at 80 ° C) 50 polycaprolactone cross-linked with isocyanate. 55 1. Nitrocellulose-based propellant composition containing a platonizing ballistic modifier, characterized in that the platonizing ballistic modifier comprises a total of 2.0 to 8.0% by weight of the propellant composition, said agent comprising zinc oxide or a mixture of zinc oxide with one or more than 194727 lead or copper compounds known as ballistic modifier, and the amount of zinc oxide makes up from 0.15% by weight to no more than 5.0% by weight of the propellant composition Propellant composition according to one of the preceding claims, characterized in that it has an energy in the range of 800 to 1,200 calories / g. Propellant composition according to one of the preceding claims, characterized in that it has a combustion rate of 4 to 45 mm / s. 8. Propellant composition according to any of the preceding claims, characterized in that the propellant is a double base propellant containing nitrocellulose and nitroglycerol Use of zinc oxide in a nitrocellulose-based propellant composition as a ballistic modifier to provide the propellant composition with improved plateau or mesa combustion properties over a printing range. Hereby 5 sheets of drawing