US 3898112 A
A solid gas generating propellant based upon 5-aminotetrazole nitrate as the oxidant component and utilizing a binder matrix of a block copolymer selected from the group consisting of styrene-butadiene-styrene and styrene-isoprene-styrene.
Description (OCR text may contain errors)
United States Patent [191 Strecker et a1.
[ 51 Aug. 5, 1975 SOLID S-AMINOTETRAZOLE NITRATE GAS GENERATING PROPELLANT WITH BLOCK COPOLYMER BINDER  Inventors: Ruediger A. H. Strecker, Oxon Hill;
Hermann S. Haiss, Indian Head, both of Md.
 Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.
22 Filed: Sept. 23, 1970 211 App1.No.:74,894
 US. Cl. l49/l9.9; 149/19.91; 149/92  Int. Cl. .1 C06D 5/06  Field of Search 149/19, 19.9, 19.91, 92
Primary Examiner-Benjamin R. Padgett Assistant ExaminerE. A. Miller Attorney, Agent, or Firm-R. S. Sciascia; .1. A. Cooke  ABSTRACT A solid gas generating propellant based upon 5- aminotetrazole nitrate as the oxidant component and utilizing a binder matrix of a block eopolymer selected from the group consisting of styrene-butadiene-styrene and styrene-isoprene-styrene.
5 Claims, N0 Drawings SOLID S-AMINOTETRAZOLE NITRATE GAS GENERATING PROPELLANT WITH BLOCK COPOLYMER BINDER BACKGROUND OF THE INVENTION This invention relates generally to composite propellants and more particularly to a composite propellant especially useful as a gas generator.
In the past, the mainstay of gas generating composite propellants has been based on ammonium nitrate as the oxidizing component. Although generally acceptable the ammonium nitrate based gas generators burn very slowly; i.e., about 0.10 inches/sec., even with the addition of burning rate modifiers.
Consequently, large volumes of gas are not produced quickly by these systems and thus they are not effective for purposes where total pressure is required immediately, for example, where the guidance of a missile is dependent upon instantaneous total pressurization.
Efforts have been made to improve the burning rates of ammonium nitrate gas generators, but have not been completely successful, since the addition of burning rate modifiers, while increasing the burning rate, cause additional problems, such as the erosion of hardware due to the formation of metal oxides not otherwise present in the system. However, a desirable characteristic of the ammonium nitrate compositions, also desirable for all gas generators, is its low flame temperature.
Another gas generating propellant composition which has been employed in the past is based upon ammonium perchlorate as the oxidant. Although these have higher burning rate characteristics than the ammonium nitrate based compositions, the ammonium perchlorate generators generate deleterious corrosive gases and therefore also have limited applicability.
ln US. application Ser. No. 883,327 by Moy et al. filed Nov. 28, 1969, a gas generating propellant composition based upon S-aminotetrazole nitrate as the oxidant was disclosed. This gas generator was found to be faster burning than the ammonium nitrate type and have a comparable low flame temperature.
Other characteristics, such as a low burning rate slope and a rr value of between 0.2 and 0.3, increased temperature stability, and good aging of the propellant composition, are also highly desirable properties for a solid propellant. Furthermore, the complete absence of inorganic additives, even small amounts that are often required as curing catalysts for the binder material or ballistic modifiers, is preferred to avoid any formation ofinorganic solids upon combustion, which are intolerable in some applications.
SUMMARY OF THE INVENTION Accordingly, it is one object of the present invention to provide an improved fast burning, gas generating solid propellant composition based upon 5- aminotetrazole nitrate.
Another object of the present invention is to provide a gas generating solid propellant composition based upon S-aminotetrazole nitrate which yields only noncorrosive gases upon combustion.
Still another object of this invention is to provide a gas generating solid propellant composition based upon S-aminotetrazole nitrate which possesses improved mechanical, physical and chemical characteristics.
A still further object of the instant invention is to provide a gas generating solid propellant composition DESCRIPTION OF THE PREFERRED EMBODIMENTS The gas generating propellant compositions of this invention are based upon S-aminotetrazole nitrate, depicted by the structural formula below, as the oxidizing material ll II N c NH HNO3 The oxidizing compound of the formula is easily and conventionally prepared by the addition of nitric acid to S-aminotetrazole.
For the purposes of this invention, the 5- aminotetrazole nitrate is incorporated in a binder matrix which is a block copolymer of styrene and butadiene or styrene and isoprene. Generally, the propellant composition of this invention is comprised of from about to about 87 percent by weight of the compound of formula l and from about 13 to about 25 percent by weight of the styrene-butadiene-styrene or styrene-isoprene-styrene binder. Preferably, the present propellant compositions are comprised of from about 84 to about 87 percent by weight of oxidant.
The styrene-butadiene-styrene and the styreneisoprene-styrene block copolymer binders of the pres ent invention have a molecular weight within the range of from about 60,000 to about 100,000 with a first block styrene molecular weight of from about 9,600 to about 13,600, a center block molecular weight (butadiene or isoprene) of from about 47,500 to about 69,800 and a second block styrene molecular weight of from about 9,400 to about 14,500. The styrene content is preferably maintained within the range of from about 28 to about 29 percent by weight and more specifically about 28.6 percent by weight. Higher styrene contents tend to make the material too hard for propellant composition use.
The styrene-butadiene-styrene and styrene-isoprenestyrene block copolymers are rubbery materials and are commercially available as KRATON 1 102 and KRATON l 107 respectfully, manufactured by the Shell Chemical Company, Emeryville, California.
The gas generating solid propellant compositions of this invention are readily made by conventional mixing procedures. For example, the solid styrene-butadienestyrene or styrene-isoprene-styrene copolymer is dissolved in a suitable solvent such as cyclohexane, in a ratio of, for example, 1 part to 5 parts respectfully.
Upon the substantial solution of the copolymer, the 5- aminotetrazole nitrate and other additives such as for example anti-oxidants are added with mixing and under vacuum to the copolymer solution. When all the solvent has been evaporated off, the dry mix is removed from the mixer and compression or extruded molded. The composition does not require any curing and retains its elastic properties for an extended period of time.
As a result of the low unsaturation (unsaturation is easily accessible to air oxidation), which is characteristic of the copolymer binders of the present invention, and the absence of any inorganic additives for curing purposes or ballistic modifying purposes, the gas generating propellant compositions possess excellent aging characteristics and thus have long shelf-lives. Furthermore, the excellent m, values of less than 0.3, also characteristic of the present propellant compositions, are also attributed to the copolymer binder materials employed herein.
Organic anti-oxidants and plasticizing agents also may be added in minor amounts (about 3 to percent by weight) to the propellant compositions of this invention for additional improved aging and mechanical properties. Specifically, some anti-oxidants which are applicable herein include 2.2-methylenebis(4-methyl- 6-tertiarybutylphenol) and phenyl B-naphthylamine and the like, while applicable plasticizing agents include dioctyladipate, Conco oil (an aromatic hydrocarbon made by the Continental Oil Company, New York, New York,) Circolight oil (another aromatic hydrocarbon made by the Sun Oil Company of Phil., Pa.) and the like. As herein before set forth the addition of inorganic materials, for example for curing purposes or ballistic modifying purposes, is not desirable. Their pres ence, however, is not beyond the scope of this invention.
Having generally described the invention the following example is given for purposes of illustration. It will be understood that the invention is not limited to this example, but is susceptible to different modifications that will be recognized by one of ordinary skill in the art.
butylphenol) The composition of Example 1 exhibited a burning rate of 0.420 in./sec at 1000 psi and 77F. The popular ammonium nitrate based gas generators generally burn only at about 0.10 inches/sec even with the addition of burning rate modifiers which add corrosive materials to the end combustion products. Furthermore, the composition of Example 1 is further characterized by a burning rate exponent of 0.51 and a 11 valve of 0.296. This constant 'rr represents the burning rate dependency of a propellant upon changes in temperature and pressure. Thus, a low Tl' value is generally desired since the burning rate of an ideal propellant composition would be completely independent of variations in temperature and pressure. A 11 value of between 0.2 and 0.3 is therefore noteworthy.
Furthermore, the composition of example 1 ignites at 168C and after constant heating at 120C it does not ignite or show any exotherm over a period of 24 hours, which clearly demonstrates the improved stability of the instant composition.
The gas generating compositions of this invention are especially useful, for instance, for actuating gas pres sure operated mechanical devices; e.g., for driving engines, electric generator motors, and turbines or for operating pneumatic tools, and for the propulsion and guidance of rockets or other gas escape reaction propelled devices.
Having thus described the invention, what is claimed and desired to be secured by Letters Patent of the United States is:
1. A gas generating solid propellant composition comprising 5-aminotetrazole nitrate as the oxidant and a binder matrix selected from the group consisting of a styrene-butadiene-styrene block copolymer and a styrene-isoprene-styrene block copolymer.
2. The gas generating solid propellant composition of claim 1 wherein said styrene-butadiene-styrene and said styrene-isoprene-styrene block copolymers have a molecular weight within the range of from about 60,000 to about 100,000 and a styrene content of from about 28 to 29 percent by weight.
3. The gas generating solid propellant composition of claim 2 wherein said S-aminotetrazole nitrate is present in an amount within the range of from about to 87 percent by weight and said block copolymer is present in an amount within the range of from about 13 to about 25 percent.
4. The gas generating solid propellant composition of claim 3 wherein said block copolymer is styrenebutadiene-styrene.
5. The gas generating solid propellant composition of claim 3 which further includes a minor amount of a material selected from the group consisting of an organic anti-oxidant, an organic plasticizing agent and mixtures