US2982638A - Nitrocellulose propellants containing lead salts of aliphatic acids - Google Patents

Description

, temperature.

United States Patent INITROCELLULOSE PROPELLANT S CONTAININ LEAD SALTS F ALIPHATIC ACIDS Robert: A. Cooley, East Alton, Ill., and Herman A.

Bruson, North Haven, Conn., assignors to Olin Mathieson Chemical Corporation, East Alton, 11]., a corporation of Virginia 7 No Drawing. Filed Oct. 12, 1956, Ser. No. 615,501

10 Claims. c1. 52-5 This invention relates generally to propellent powder and more particularly to an improved smokeless powder particularly well adapted for use as the propellant in rockets and other guided missiles.

Smokeless powder base propellants are utilized as the fuel in rocket motors and guided missiles. The smokeless powder base is largely nitrocellulose that has been gelatinized by means of a suitable substantially nonvolatile solvent such as a plasticizer for nitrocellulose. This plasticizer may be a nonexplosive or it may be a liquid nitric ester of a polyhydric alcohol such as, for example, nitroglycerine. Propellants having this composition have a burning rate that is influenced by the temperature at the time of ignition and by the pressure created: in the vessel or chamber in, which the propellant is burned. In other words, the pressure developed by a burning grain of propellant is proportional to the rate of burning which is influenced by the temperature of the propellant when ignition occurs, and by the pressure at which the propellant burns. Because of the influence of temperature and pressure on the burning rate of the propellant, propellants having a nitrocellulose base have not been entirely suitable, heretofore, for universal utilicontaining such a lead salt will burn at a constant rate over a range of pressure and with some variation in This effect of the lead salts is known as the mesa or plateau effect and it is possible to prepare propellent powder with custom built mesa effects. The burning rate over a given pressurerange can be reliably predicted and propellants can be designed to burn at a desired rate at a particular pressure level by utilizing one or more of the lead salts to modify the burning characteristics of the grain.

It is, therefore, an object of the invention to provide a novel smokeless powder propellant having burning characteristics that are substantially unaifected by variations in atmospheric pressure and pre-ignition temperature. A further object of the invention is to provide grains of smokeless powder base composition having burning rates substantially independent of variations in pressure and ignition temperature over the range of pressures and temperatures at which such propellants are utilized. A more specific object of the invention is to provide a propellant having novel mesa or plateau effects..-

j for nitrocellulose and particles of a lead salt of an ali-1 phatic organic acid having more than six carbon atoms tially uniformly dispersing a lead salt of an alkoxy acid,

2,982,638 Patented May 2, 1961 and adapted to be dispersed uniformly through the gel and to retard variation in burning rate with change in temperature and pressure. More specifically, it has been found that a smokeless powder base grain having improved burning characteristics is produced by substana lead salt of a keto acid, or a lead salt of a nitrogen substituted amino acid in the nitrocellulose gel that is.

shaped into the propellent grain. Lead N,N di 2 ethylhexyl B aminopropionate, lead 12 ketostearate, which may be either the normal or basic, lead 9(l0)- acetamidostearate, lead cyclohexylacetate, and lead butoxyacetate are examples of the group of aliphatic organic acids that have been found particularly advantageous for modifying the burning characteristic of the'propellent grain.

In order to determine the effect of the various ballistic modifying lead salts of the aliphatic acids on the burning of the propellent grain, a grain of the desired composition is burned under a given pressure and the burning rate is measured. The burning rate of the propellant provided by this invention will increase rapidly with increase in pressure up to a'certain pressure level and then the burning rate will remain substantially constant over a range of pressure. For example, it was found that a propellant having a nominal composition of about 57.8 percentnitrocellulose, about 24.7 percent nitroglycerine, about 9.2 percent triacetin, about 3.3 percent dioctylphthalate, about 1.7 percent 2-nitrodiphenylamine and about 3.3 percent of one of the group of lead salt ballistic modifiers indicated in the following table had a substantially constant burning rate when burned at an external pressure between about 1000 and about 2000 pounds per square inch at a temperature of about 70 F. and F. as evidenced by the following results:

Pounds per square inch.

It can be seen from the foregoing table that the propellant provided by this invention has a more uniform burning rate than one containing a lead salt of an aromatic compound such as tetraphenyl lead over the pressure range of from about 1000 to about 2000 pounds per square inch which is the pressure range ordinaril encountered in practice. The composition of the propellent grain can vary from .about 40 percent to about 70 percent by weight nitrocellulose, from about 4 percent to about 45 percent substantially non-volatile solvent for the nitrocellulose, from about 0.5 percent to about 5 percent of the lead salt ballistic modifier, and from about 0.5 percent to about 2.5 percent of a suitable stabilizer for smokeless powder base propellants such as, for example, 2-nitrodiphenylamine, diethyldiphenylurea, methylethyldiphenylurea, diphenylamine, or the like. In shaping the grain, it has been found that from about 0.2 to about 0.5 part casting solvent per part of nitrocellulose particles should be utilized to insure that the grain upon the simultaneous dissolution of nitrocellulose and solidification of the, gel will be of substantially uniform composition throughout cellulose.

the grains length. The solvent may contain from about 60 percent to about 85 percent nitroglycerine or similar energizing modifier with the balance being one of the class of non-explosive substantially non-volatile solvents hereinbefore described. A typical solid propellent grain has the composition of about 58 percent nitrocellulose, about 25 percent nitroglycerine, about 9 per cent triacetin, about 3 percent dioctyl phthalate, about 3.5 percent lead cyclohexyloxyacetate, and about 1.5 percent Z-nitrodiphenylamine.

The propellent grain may be formed by any conventional extrusion or casting process. With large grains, however, it is preferred and, in some instances it is mandatory, that the grains be shaped by a casting process. In one type of casting process suitable for the purpose, nitrocellulose base spherical pellets such as those formed by the process disclosed by Olsen et al. in US. Patent 2,027,114 may be placed in a suitable mold and the interstices between the pellets may then be filled with a substantially non-volatile solvent for nitrocellulose.

The contents of the mold are then heated to a temperatrue at which the pellets of gelatinized nitrocellulose will dissolve in the solvent and the mass will set into a substantially homogeneous gel. The lead salt utilized to modify the burning characteristics of the propellent grain is incorporated in the gel either by incorporating it into the smokeless powder pellets as they are formed or by dispersing the lead salt in the casting solvent. Smokeless powder base pellets may also be made by the process disclosed in the Cox U.S. Patent 2,715,574 or by conventional extrusion processes or any other suitable process. It is essential in order to be able to consistently produce a propellant having a predetermined burning rate within a given pressure range that the lead salt be well dispersed in the gel that constitutes the shaped propellent grain.

A preferred casting solvent has the composition of about 72 percent by weight nitroglycerine, about 27 percent plasticizer and about 1 percent stabilizer, but the solvent may be varied in composition, and in some instances it may consist of a plasticizer for the nitro- Anv suitable substantially non-volatile solvent fornitrocellulose may be utilized as the solvent. Typical examples of such solvents are triacetin, dioctyl phthalate, dibutyl phthalate, dimethyl phthalate, dimethyl sebacate, dibutyl succinate, dibutyl adipate, ethyl diphenyl phosphate, tributyl phosphate, dimethyl phthalate, dioctyl sebacate, orthonitrobiphenyl, butyl benzyl phthalate, octyldiphenyl phosphate, triethylene glycol, di-Z-ethyl butyrate, and the like. .Best results are obtained with a solvent containing a liquid nitric ester of a polyhydric alcohol such as, for example, nitroglycerine or nitroglycol. In many compositions, the major portion of solvent for the nitrocellulose may be one of the liquid explosive nitric esters of the polyhydric alcohols which are energizing modifiers of the burning characteristics of the grain.

In order better to describe and further clarify the invention, the following is a detailed description of one embodiment of a process for making powder grains in accordance with this invention:

About 58 parts by weight nitrocellulose pellets formed by the process disclosed by Olsen et al. in U.S. Patent 2,027,114 are placed in a suitable mold. The pellets were formed by suspending nitrocellulose in water, dissolving the suspended particles in ethyl acetate, breaking up the resulting lacquer into globules and removing the solvent from the globules while they are suspended in water containing a protective colloid, such as, for example, gum arabic.

The mold is closed and about 42 parts by weight casting solvent made up of about 25 parts nitroglycerine, about 9 parts triacetin, about 3 parts dioctyl phthalate, about 3.5 parts lead cyclohexyloxyacetate, and about 1.5 parts Z-nitrodiphenylamine are introduced into the mold under pressure and into the interstices between 4 the nitrocellulose pellets. then heated to about 60 C. and held at this temperature for about 48 hours or until the casting solvent has dis-- solved the nitrocellulose particles and the mass has solidified without any solvent removal into a homogeneous gel resulting suspension is poured into a mold having the desired configuration. elevated temperature until the particles have dissolved The mold is then stored .at an and a gel has been formed. The lead salt may be incorporated in the gel formed by this process or in any of the other processes by dispersing it in the nitrocellulose particles as they are formed or by dissolving it in the casting solvent.

The relatively constant burning rate, or plateau as it 'is commonly referred to in the art, will occur at different pressure levels as was indicated in the foregoing table, depending upon which of the lead salts is utilized. Moreover, the extent of the pressure range at which the burning rate will remain substantially constant will vary depending upon the particular lead salt in the gel.

Although the invention has been described in considerable detail in the foregoing, it is to be understood that many variations may be made by those skilled in the art without departing from the spirit and scope of the invention except as it is limited by the appended claims.

We claim:

1. A smokeless powder grain consisting essentially of gelatinized nitrocellulose and between about 0.5 percent and about 5 percent of a lead salt of an aliphatic acid selected from the group consisting of keto aliphatic acids, alkoxy aliphatic acids, acylamino aliphatic acids, and dialkylamino aliphatic acids. said lead salt having more than 6 carbon atoms and being substantially uniformly dispersed throughout the grain.

2. A smokeless powder grain consisting essentially of a propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of a lead salt of an alkoxy aliphatic acid having more than 6 carbon atoms, said salt being substantially uniformly dispersed throughout the grain.

3. A smokeless powder grain consisting essentially of a propellant powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of a keto aliphatic acid lead salt having more than 6 carbon atoms, said salt being substantially uniformly dispersed throughout the grain.

4. A smokeless powder grain consisting essentially of a propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of a lead salt of a nitrogen substituted amino aliphatic acid having more than 6 carbon atoms, said salt being substantially uniformly dispersed throughout the grain.

5. A smokeless powder grain consisting essentially of a propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of a ballistic modifier selected from the group of lead salts of aliphatic acids having more than 6 carbon atoms consisting of lead N,N-di-2-ethylhexyl 3 aminopropionate, lead 12 ketostearate, lead 9(10)-acetamidostearate, lead cyclohexyloxyacetate, and lead butoxyacetate, said modifiers being substantially uniformly dispersed throughout the grain.

6. A smokeless powder grain consisting essentially of The contents of the mold area propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of lead N,N di 2 ethylhexyl- B aminopropionate dispersed substantially u n i f o r m l y throughout the grain.

7. A smokeless powder grain consisting essentially of a propellent powder base selected from thegroup consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between about 0.5 percent and about 5 percent of lead l2-ketostearate dispersed substantially uniformly throughout the grain.

8. A smokeless powder grain consisting essentially of a propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and nitrocellulose-nitroglycol, and between'about 0.5 percent and about 5 percent of lead 9(10)-acetamidostearate dispersed substantially uniformly throughout the grain.

9. A smokeless powder grain consisting essentially of a propellent powder base selected from the group consisting of nitrocellulose, nitrocellulose-nitroglycerin, and

and about 5 percent of lead butoxyacetate dispersed substantially uniformly throughout the grain.

References Cited in the file of this patent UNITED STATES PATENTS 2,498,388 Ball Feb. 21, 1950 FOREIGN PATENTS Canada Aug. 12, 1952 OTHER REFERENCES Colver: High Explosives, Crosby Lockwood and Son, London (1918), pp. 135, 169, 253 and 342. Copy in Scientific Lib.

Claims (1)

1. A SMOKELESS POWDER GRAIN CONSISTING ESSENTIALLY OF GELATINIZED NITROCELLULOSE AND BETWEEN ABOUT 0.5 PERCENT AND ABOUT 5 PERCENT OF A LEAD SALT OF AN ALIPHATIC ACID SELECTED FROM THE GROUP CONSISTING OF KETO ALIPHATIC ACIDS, ALKOXY ALIPHATIC ACIDS, ACYLAMINO ALIPHATIC ACIDS, AND DIALKYLAMINO ALIPHATIC ACIDS, SAID LEAD SALT HAVING MORE THAN 6 CARBON ATOMS AND BEING SUBSTANTIALLY UNIFORMLY DISPERSED THROUGHOUT THE GRAIN.