US3234059A - Igniter composition comprising pyrotechnic dispersion in solid propellant - Google Patents

Description

United States Patent 3,234,059 IGNITER COMPOSITION COMPRISING PYRO- TECHNIC DISPERSION IN SOLID PROPELLANT Wayne A. Proell, Seymour, Ind., assignor to Standard Oil Company, Chicago, 11]., a corporation of Indiana No Drawing. Filed Nov. 18, 1963, Ser. No. 324,247 8 Claims. (Cl. 149-19) This invention relates to an igniter composition for solid propellants and more particularly to an igniter composition comprising an admixture of a pyrotechnic and a solid propellant composition.

The development of a satisfactory igniter for propellant systems has been very desirable. Igniters suitable for the ignition of rocket engines and associated devices, such as starter cartridges, have relied in many instances upon complex granular or pelleted pyrotechnic materials. In general, the eificiency of these igniters has varied considerably, with even the best requiring a large amount of igniter charge, showing low reproducibility, and generating dirt and smoke. Furthermore, these igniters require care in loading in order to obtain consistent results, are moisture sensitive due to their granular texture, show a poor temperature coefficient, and charge characteristics with age.

It has been discovered that an igniter composition made up of a compacted, dense admixture of pyrotechnic, such as gunpowder; and a solid propellant, such as an ammonium nitrate propellant, compressed into a coherent cake having the propellant as an essentially continuous phase, exhibits improved results upon ignition in respect to many of the above problems. This is surprising, as .the solid propellant is not an igniter and might be predicted to reduce the burning to such a low degree that the combination would not be an igniter.

In addition, the inventive igniter composition exhibits a highly reproducible performance of burning times in a range not generally possible with mechanical mixtures of pyrotechnics. This permits easier formulation of the igniter composition and provides greater expectancy of a predetermined performance.

The inventive igniter composition is a compacted, dense admixture comprising a dispersion of pyrotechnic in an essentially continuous phase of a solid propellant. This means that the dispersion of the pyrotechnic is essentially surrounded by the solid propellant. It is desirable that the propellant of the admixture exhibit a low porosity, usually less than about 8% and preferably less than about 4%. The admixture includes a pyrotechnic such as gunpowder, aluminum powder-alkali perchlorate, nitrocellulose grains, and boron powder-potassium nitrate, preferably gunpowder and boron powder-potassium nitrate and especially gunpowder. In many instances, the pyrotechnic is granular and porous. Its porosity may range up to about 50% but preferably is lower.

The admixture also includes a solid propellant, present as essentially a continuous phase. An especially suitable propellant is the ammonium nitrate propellant which is primarily made up of ammonium nitrate, an oxidizable organic binder material, and a combustion catalyst.

The ammonium nitrate propellant has been previously described in US. 2,999,462 and copending application S.N. 715,987 filed February 18, 1958, now Patent No. 3,148,096, which are incorporated into and made a part of this specification. In general, the ammonium nitrate propellant contains ammonium nitrate as the predominant component usually in amounts in excess of about 60 weight percent, an oxidizable organic binder, usually between about 10 and about 40 weight percent; and a catalyst, usually between about 0.5 and about 10 weight percent.

The oxidizable organic binder is utilized to permit the shaping of the ammonium nitrate composition into definite configurations and to consume the excess oxidizing power of the ammonium nitrate. A binder may be a single compound; such as rubber or asphalt, or a mixture of materials, commonly a polymeric base material (such as cellulose acetate) and a plasticizer for the base material. Both thermoplastic and thermosetting materials may be utilized as the binder. Many of the common thermoplastic materials are identified in the above cited references. Polyurethane serves to illustrate a thermosetting material which is suitable as a binder material.

In addition to the catalyst covered in the above references, suitable catalysts include alkali metal salts of nitriloacetic acid, anthranilic acid, and nitrosalicylic acid; and amine salts of nitrosalicylic acid. Commonly, the alkali metal salt is the sodium salt, and the amine salt is prepared from piperazine or guanidine.

In addition to the basic components, i.e., ammonium nitrate, binder and catalyst, the ammonium nitrate propellant may contain other commonly utilized materials such as asphalt and carbon to improve cold temperature ignition, and amines to chemically stabilize the propellant against decomposition in hot storage. These additional components are described in the above cited copending application S.N. 715,897.

It is desirable that the admixture contain about 20 to 60 weight percent of the pyrotechnic and about 40 to weight percent of the solid propellant. Especially suitable admixtures have about 30 to 50 weight percentof the pyrotechnic and about 50 to 70 weight percent of the propellant, especially when the pyrotechnic is gunpowder and the propellant is ammonium nitrate propellant. Particularly suitable combinations of gunpowder and ammonium nitrate propellant are 45% gunpowder and 55% propellant, and 40% gunpowder and 60% propellant.

The pyrotechnic and propellant are mixed together and pressed or otherwise treated until the propellant of the admixture is a compact, dense mass having a low porosity normally below about 8%. Compression molding is usually 'very suitable in most instances, although when the propellant utilizes a thermosetting such as polyure: thane, the admixture is usually cast. Usually, the pyrotechnic is in grain-form, to which the propellant is added. It is preferred that the water absorbed or adsorbed on the pyrotechnic be removed prior to the preparation of the admixture. This may be conveniently carried out by heating the combination of pyrotechnic and propellant (prior to pressing) at temperatures on the order of about C. for a short time, or by treating with a desiccant. Compression molding is then carried out, usually at about 100 C.

The following example serves to illustrate an embodiment of the invention. It is understood that this is given by way of exemplification and does not in any way serve as a limitation on the invention.

Example ammonium nitrate, 62.30%; cellulose acetate, 10.40%;'

acetyl triethyl citrate, 11.85%; dinitrophenoxyethanol, 10.45%; sodium barbiturate, 1.00%; carbon, 3.00%; and 2,4-toluenediamine, 1.00%.

The pressed cake igniter was then subjected to burning tests to determine its percent temperature coeflicient. This .3 coefficient is calculated by determining the pressure generated by the igniter at temperatures of 160 F., and 65 F The difierence between the pressures at 160 F. and 65 F. is then divided by the pressure at 65 F. The result is a measure of the uniformity of performance with temperature.

Seven tests were carried out on the pressed igniter and a percent temperature coefiicient for each was calculated.

The average of the seven was 118%.

For comparison purposes, gunpowder and ammonium nitrate propellant were mixed together to form a mechanical mixture which was burned to determine its performance. The relative proportions of each component were present in amounts to give approximately the same igniter pressure versus time characteristics as for the pressed igniter. Seven individual tests were carried out on the mixture. The percent temperature coefficient for each test was calculated and their average was determined to be 152%.

The above results demonstrate the superior performance of the pressed cake igniter over an igniter which has not been compacted. The average percent temperature coefficient of the pressed cake igniter was 118% as contrasted to the average of 152% for the mixture of gunpowder and propellant which have not been consolidated into a pressed cake.

Very similar results are also obtainable from the above composition when the proportions of the components are within the following ranges: ammonium nitrate, 6080%; cellulose acetate, 23-12%; acetyl triethyl citrate, 1014%; dinitrophenoxyethanol, 23-12%; sodium barbiturate, 0.5-5%; carbon, 0.5-5%; and 2,4-toluenediamine,

Thus having described the invention, what is claimed is:

1. As an improved igniter composition, a compacted, dense admixture comprising a dispersion of pyrotechnic selected from the class consisting of gunpowder, aluminum powder-alkali perchlorate, and boron powder-potassium nitrate, in an essentially continuous phase of a solid propellant comprising ammonium nitrate as the predominant component, between about 0.5' to about weight percent of a combustion catalyst, and about 10 to about 40 weight percent of an oxidizable organic binder material, said admixture containing about 20 to 60 weight percent of said pyrotechnic and about 40 to 80 percent of said solid propellant.

2. The admixture of claim 1 wherein said pyrotechnic is gunpowder. 7

3. As an improved igniter composition, a compacted, dense admixture comprising about 30 to weight percent of a dispersion of gunpowder in about 50 to weight percent of an essentially continuous phase of solid ammonium nitrate propellant.

4. The admixture of claim 3 wherein the propellant of said admixture has a porosity less than about 8%.

5. The admixture of claim 3 wherein said ammonium nitrate propellant comprises ammonium nitrate as the predominant component, between about 0.5 to about 10 weight percent of a combustion catalyst, and about 10'to about 40 weight percent of an oxidizable organic binder material.

6. The admixture of claim 5 wherein the propellant phase of said admixture has a porosity less than about 8%.

7. As an improved igniter composition, a compacted, dense admixture comprising about 30 to 50 weight percent of a dispersion of gunpowder in about 50 to 70 weight percent of an essentially continuous phase of a solid propellant consisting essentially by weight of about 60 to percent of ammonium nitrate, 8 to 12 percent of cellulose acetate, 10 to 14 percent of acetyl triethyl citrate, 8 to 12 percent of dinitrophenoxyethanol, 0.5 to 5 percent of sodium barbiturate, 0.5 to 5 percent of carbon, and 0.5 to 3 percent of 2,4-toluenediamine, the propellant of said admixture having a porosity less than about 4%.

8. Theadmixture of claim 7 wherein said gunpowder, propellant, ammonium nitrate, cellulose acetate, acetyl triethyl citrate, dinitrophenoxyethanol, sodium barbiturate, carbon and toluenediamine are present in the respective weight percentages of about 45, 55, 62.3, 10.4, 11.9, 10.4, 1.0, 3.0, and 1.0.

References Cited by the Examiner UNITED STATES PATENTS 2,988,876 6/1961 \Valden 149--41 3,000,311- 9/1961 Stanley 149--60 X 3,017,300 1/19 62 Herring 14941 3,031,347 4/1962 Philipson 149-19 X CARL D. QUARFORTH, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,234,059 February 8, 1966 Wayne A. Proell It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 1, line 24, for "charge" read change, column 2, lines 14 and 15, for "nitrosalicylic", each occurrence, read nitrosalicyclic same column 2, line 41, before "such" insert binder Signed and sealed this 3rd day of January 1967.

ERNEST W. SWIDER EDWARD J. BRENNER Anesting Offioer Commissioner of Patents

Claims (1)

1. AS AN IMPROVED IGNITER COMPOSITION, A COPACTED, DENSE ADMIXTURE COMPRISING A DISPERSION OF PYROTECHNIC SELECTED FROM THE CLASS CONSISTING OF GUNPOWDER, ALUMINUM POWDER-ALKALI PERCHLORATE, AND BORON POWDER-POTASSIUM NITRATE, IN AN ESSENTIALLY CONTINUOUS PHASE OF A SOLID PROPELLANT COMPRISING AMMONIUM NITRATE AS THE PREDOMINANT COMPONENT, BETWEEN ABOUT 0.5 TO ABOUT 10 WEIGHT PERCENT OF A COMBUSTION CATALYST, AND ABOUT 10 TO ABOUT 40 WEIGHT PERCENT OF AN OXIDIZABLE ORGANIC BINDER MATERIAL, SAID ADMIXTURE CONTAINING ABOUT 20 TO 60 WEIGHT PERCENT OF SAID PYROTECHNIC AND ABOUT 40 TO 80 PERCENT OF SAID SOLID PROPELLANT.