US3767489A - Nitrasol propellant - Google Patents

Abstract

1. A propellant composition consisting essentially of from about 25 to 100 percent binder and up to 75 percent solid loading, said binder comprising from about 10 to 50 percent of plastisol nitrocellulose and from about 15 to 85 percent plasticizer material of the formula (O2 NOCH2)3 C-R wherein R is a member of the class consisting of hydrogen, NO2, lower alkyl and a lower alkyl carbinol radical, said solid loading consisting of up to 60 percent of a metal and from about 20 to 100 percent of a material from the class consisting of perchlorate oxidizing agents, cyclotetramethylene tetranitramine, trinitroethylorthocarbonate and mixtures thereof; said plastisol nitrocellulose being made by placing 90 grams of nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite and 1.4 liters of nitromethane in a flask and stirring vigorously until dissolution occurs, stirring slowly for an additional 10 minutes to insure homogeniety, adding to the resulting lacquer 19.2 grams of a petroleum sulfonate emulsifying agent for nitrocellulose in about 900 ml of water and circulating through a colloid mill for about 10 minutes, draining the resulting emulsion from the mill into about 30 liters of water and stirring about 15 minutes until a nitrocellulose percipitate is formed which is filtered from the liquid, washed in hexane, dried for about 16 hours and sifted through a 200 mesh screen.

Description

United States Patent [1 1 Reinhart et al.

[ Oct. 23, 1973 Julian S. Davidson, all of China Lake, Calif.

[73] Assignee: The United States of America as represented by the Secretary of the Navy, Washington, DC.

[22] Filed: Sept. 16, 1958 [2l] Appl. No.: 761,448

521 U.S. c1 149/18, 149/19, 149/20, 149/76, 149/89, 149/92, 149/96 511 Int. Cl C06d /06 [58] Field of Search ..s2/50,13,13.1, 52/5.1; 149/18, 19, 20, 76, 89, 92, 96

[56] References Cited UNITED STATES PATENTS 2,417,090 3/1947 Silk et al 264/3 FOREIGN PATENTS OR APPLICATIONS 485,662 8/l952 Canada 485,661 8/l952 Canada OTHER PUBLICATIONS Military Explosives, Dept. of the Army Technical Manual, TM-9-l9l0 Dept. of the Air Force Tech. Order to llA-l-34 Apr. 14, 1955, p. 247. Warren, Rocket Propellants, Remhold Publ. Corp., NY. 1958, p. 37.

Primary Examiner-Benjamin R. Padgett AttorneyW. O. Quesenberry and P. H. Firsht EXEMPLARY CLAIM l. A propellant composition consisting essentially of from about 25 to I00 percent binder and up to 75 percent solid loading, said binder comprising from about 10 to 50 percent of plastisol nitrocellulose and from about to 85 percent plasticizer material of the formula (O NOCI-l CR wherein R is a member of the class consisting of hydrogen, N0 lower alkyl and a lower alkyl carbinol radical, said solid loading consisting of up to 60 percent of a metal and from about to 100 percent of a material from the class consisting of perchlorate oxidizing agents, cyclotetramethylene tetranitramine, trinitroethylorthocarbonate and mixtures thereof; said plastisol nitrocellulose being made by placing 90 grams of nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite and 1.4 liters of nitromethane in a flask and stirring vigorously until dissolution occurs, stirring slowly for an additional l0 minutes to insure homogeniety, adding to the resulting lacquer 19.2 grams of a petroleum sulfonate emulsifying agent for nitrocellulose in about 900 ml of water and circulating through a colloid mill for about l0 minutes, draining the resulting emulsion from the mill into about liters of water and stirring about 15 minutes until a nitrocellulose percipitate is formed which is filtered from the liquid, washed in hexane, dried for about 16 hours and sifted through a 200 mesh screen.

5 Claims, N0 Drawings NITRASOL PROPELLANT The invention herein described may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to rocket propellants; more specifically it relates to improved propellent binders.

1n the past, many propellants have been developed, but the best of these has a specific impulse of only about 240 lb-sec/lb. A rocket propelled with such a propellant of course has performance limitations due to the energy limitations of the propellant.

Propellent grains often cannot stand the stresses of great temperature changes, or ignition without cracking. As is well known, a cracked grain when fired usually results in a ruptured motor tube.

Propellants utilizing a resinous binder usually have a pot life of only a few hours; once the components are mixed, rapid casting is necessary so that the propellant will not cure before it is shaped.

The propellants of today which are capable of specific impulses of 240 lb-sec/lb are of the composite type which contain an oxidizer and light metal incorporated in a polymeric binder. After prolonged storage, the oxidizer tends to migrate away from the surface of the grain, making the grain difficult to ignite.

It is therefore an object of this invention to provide rocket propellants which have higher specific impulses than previous propellants.

Another object is to provide propellants which will not crack under the stresses of ignition or stresses caused by expansion and contraction due to extreme changes in temperature.

Still another object is to provide propellants having a relatively long pot life, being measured in weeks instead of hours.

A final object is to provide a grain which will ignite reliably even after long periods of storage.

The above objects are accomplished by an elastomeric high energy binder which incorporates a solid oxidizer with or without a light metal fuel and which may be cast into a motor tube and cured in situ. The binder alone or in combination with an oxidizer is a fairly good propellant but when loaded with the oxidizer and metals aforementioned, gives especially high energy formulations. The solids loading runs as high as 75 percent by weight.

The binder consists of a mixture of from about to 85 percent high energy plasticizer, zero to percent inert plasticizer, and about 10 to 50 percent plastisol nitrocellulose. The high energy plasticizer is one selected from the group consisting of primary and secondary nitrate esters, both liquid and solid. Preferred nitrate esters are pentaerythritol trinitrate and trimethylolethane trinitrate.

The inert plasticizer is conventional and may or may not be added to modify ballistic and physical properties. Dibutyl phthlate is commonly employed as such a plasticizer.

Plastisol nitrocellulose is made in batches by placing 90 gms of dry nitrocellulose (12.6 percent N), 1.2 grns ethyl centralite, and 1.4 liters of nitromethane in a flask and stirring vigorously until apparent dissolution occurs, then stirring slowly for 10 minutes more to insure homogeneity in the resulting lacquer. About 19.2 gms ofa suitable petroleum sulfonate emulsifying agent, for example Petromix No. 9, in about 900 ml of water is added to the lacquer and the mixture circulated and recirculated through a colloid mill wherein the liquid has to pass between a stator and a rotor which have only a small clearance while the rotor rotates at about 10,000

rpm.

After 10 minutes, the emulsion is drained from the colloid mill into about 30 liters of stirred water and stirred for about 15 minutes whereupon a precipitate of nitrocellulose forms. Then the precipitate is filtered out of the liquid, washed in hexane and dried for about 16 hours. Then the nitrocellulose is sifted through a 200 mesh screen.

The above procedure yields dense, spherical nitrocellulose particles of l 30p, median diameter. This form of nitrocellulose is not substantially attacked by the plasticizers until cure at elevated temperature is initiated.

Small amounts of conventional stabilizers are added in accordance with good practice. Ethyl centralite and N-methyl-p-nitroaniline are widely used to stabilize nitrocellulose.

The solids which are incorporated in the binder to make the improved propellant are normally ammonium perchlorate and a metal such as aluminum, magnesium, boron, zirconium and titanium. Other perchlorate and nitrate oxidizers could be used. Particle size is not critical from the standpoint of operability but does affect the burning rate. The smaller the particle size, the more rapid the burning rate, generally.

The proportion of aluminum or other light metal may run as high as 60 percent of the weight of the propellant.

The propellant is made by placing the powdered plastisol nitrocellulose in a sigma blade mixer and pouring in about 45 percent of the liquid plasticizer (s). The mixture is agitated for about 15 minutes. Then the remainder of the plasticizer (s) is added and the mixture agitated for about 30 minutes under vacuum to remove entrapped air.

The powdered metal is added, if metal is to be used, and stirred into the mixture until it is thoroughly wetted; the solid oxidizer is added and the mixture agitated again for about 30 minutes under vacuum. During the last 15 minutes, warm water at F. is run through the jacket surrounding the mixer in order to bring the temperature of the mixture up to 110 F. Then the mixing is discontinued and the mixture-simply poured into a rocket motor tube, in the absence of pressure or vacuum, and the tube placed in an oven and maintained at F. for 1 to 2 hours. At the end of the period, the propellant is cured and ready for firing. A pentaerythritol trinitrate containing binder can be stored for several days at room temperature and a trimethylolethane trinitrate containing binder even longer without curing.

In Table l which follows there is given a comparison of two different high energy binders.

Elongation",

77F. 107 128 F. 80 62 Closed-bomb specific impulse, sec. 222 216 Taliani, mm Hg/minute 0.72 0.44

obtained from duplicate specimens cut from propellant sheets 1/4 inch thick.

Of particular interest is the low viscosity of binder 1 in the uncured state which affords higher solids loading and greater flexibility in propellant formulation because of a wider range of possible compositions with good castability.

The energies of the two binders do not vary much but, the TMETN containing binder seems to be more elastomeric at temperatures in the neighborhood of 0 F., and both are more elastomeric than double-base propellants at any temperature; TMETN has the additional advantage over PETRIN that it allows the nitrocellulose to be cross-linked with a diisocyanate to produce a stronger grain.

Table 11 which follows shows the effect of loading a particular binder with varying amounts of oxidizer.

I cal/g TABLEIII Composition and Example Properties Burning rate.

F. 1000 psi, inlsec Pressure exponent Heat of Explosion,

Taliani, mm Hg/min impact sensitivity, 50%

point, cm l5 14 7 Table [V which follows gives more specific examples, with the aluminum content reduced to 15 percent. The

TABLE 11 heats of explosion range from about 1,000 to 1,700 Example cal/g, the burning rates vary from 0.3 to 0.4 inches per composition and properties 3 I second, and the Taliani test for stability ranges from 0. mm min. Ammonium perchlorate, 2001;, about 0 4 to 6 Hg/ percent 20 3O 40 50 60 Il 3Iinderf, perlcentuulnh 80 7g 60 50 340 eato exp osion, 0 .lg 89 1,012 1 160 1, 27 Burning rate (1,000 p.s.i. and 80 30 TABLE IV F.),in./sec 0.29 0. 27 0.34 0.33 0. 41 Pressure exponent 0.52 0.43 0.48 0.47 0. 53 Formulations wt. Composition Taliani, mm. Hg/minute 1.0 0.9 0.7 0. 6 0.6 Ingredients A B C D E B Binder pomposition, weight percent; Nitrocellulose (12.6% N) 38, Manual Petnn 39, dibutyl phthalate 20, adipomtrile l, ethyl centralite 2. memo 2 28.5 '9 0 Us 7 I I V V V V PETRIN 70.0 19.5 (J Z71) As is readily apparent, the heat of explosion, burning 35 TMETN e rate and Taliani stability increase with increased oxi- 31m dizer loading, while the pressure exponent of burning pmh w v 2 mo it) varies moderately.

ccntraliu: s l 5 to 0.75 0'; Table 111 below shows the effect of including alumi- A monium num along with an oxidizer in a particular binder to 40 Aluminum 7 I 150 15.0

form the propellant.

The inclusion of aluminum has increased the heat of explosion considerably over those formulations not containing it, as is to be expected, while other proper- Table V which follows contains data relating to the physical properties of the formulations listed in Table ties do not vary greatly. 45 1V.

7 TABLE v Strength, p.s.i. at Elongation, percent at- Modulus of Temp. elasticity, Compositlon of Maximum Rupture Maximum Rupture p.s.i. X10

l --30 l, 600 1, 600 3.9 3. 9 94. 6 0 789 728 7. 6 l4. 9 25. 4 20 e +10 435 11. 6 51. 4 8.8 -10 223 373 15.7 91. 2 2. 4 77 B 72 164 B 17. 8 0.78 64 62 130 132 O. 36

Values determined at first maximum in curve.

Taliani stability, the pressure exponent of burning and the impact sensitivity are satisfactory.

The formulations C, D and E listed in Table V contain the same amount of ammonium perchlorate and aluminum, but the binder composition varies Tram? case. All the formulations are sufficiently elastomeric to be case bonded to motor tubes. HMX (cyclo-' tetramethylene tetranitramine) and TNEOC (trinitroethyl-orthocarbonate), are high energy additives which may be used, sometimes completely replacing the ammonium perchlorate oxidizer.

Table VI which follows shows the effects of these ad-' ditives.

TABLE VI Example Composition and properties 1 2 3 4 5 Binder type G G G H H HMX, 100 avg. percent... 37 22 20 30 'INEOC, percent 32 Ammonium perchlorate,

percent 12 Aluminum, atomized, percent 18 13 16 20 20 Burning rate, 70 F. and 1,000

p.s.i., iu./sec 0. 35 0. 15 0. 22 0. 34 0. 3 Pressure exponent. 0.9 0.6 0. 7 0. 8 Heat of explosion, cal./ 908 1,079 1, 433 1, 490 Taliani, mm. Hglmiragten t 0.3 0.5 0.3 0.3 Im act sensitivit 5 oin ciii .fuuif 33 25 e See the following table:

Binder formulations, weight percent:

Nitrocellulose (12.6% N) pibuti i'iiiiiiiiaiIIT II 20 Adipouitrile 1 Ethyl centralite 2 1. 5

b Uneured.

HMX causes a marked decrease in burning r ate 5'63 produces a higher pressure exponent than that obtained with ammonium perchlorate. TNEOC exhibits fair heat stability and is less sensitive to impact than ammonium perchlorate.

Table Vll below presents specific impulses calculated from static firing data. Theoretical calculations for the specific impulses of these propellants range from 240 265 lb-sec/lb. The propellant contains 50 percent solids loaded into the binder E of Table IV except in examples 9 and where binder D is used, and the specific impulse is measured as a function of the aluminum content.

TABLE VII The ballistic and physical properties presented in the foregoing tables were measured by standard techniques well known in the art.

The propellants are acceptable for military purposes as relates to surveillance, electrostatic sensitivity and friction sensitivity.

From the foregoing it is evident that propellants with excellent physical properties have been produced which are sufficiently elastomeric to be case bonded to motor tubes. Excellent ballistic properties are also displayed by the formulations. The binder can be mixed and stored for as long as two weeks at room temperature without curing.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may b;

practiced otherwise than as specifically described.

What is claimed is:

l. A propellant composition consisting essentially of 5 from about to 100 percent binder and up to 75 percent solid loading, said binder comprising from about 10 to 50 percent of plastisol nitrocellulose and from about 15 to 85 percent plasticizer material of the formula (O NOCH CR wherein R is a member of the class consisting of hydrogen, N0 lower alkyl and a lower alkyl carbinol radical, said solid loading consisting of up to 60 percent of a metal and from about 20 to 100 percent of a material from the class consisting of perchlorate oxidizing agents, cyclotetramethylene tetranitramine, trinitroethylorthocarbonate and mix- 15 tures thereof; said plastisol nitrocellulose being made by placing 90 grams of nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite and 1.4 liters of nitromethane in a flask and stirring vigorously until dissolution occurs, stirring slowly for an additional 10 minutes to insure homogeniety, adding to the resulting lacquer 19.2 grams of a petroleum sulfonate emulsifying agent for nitrocellulose in about 900 ml of water and circulating through a colloid mill for about 10 minutes, draining the resulting emulsion from the mill into about liters of water and stirring about 15 minutes until a ni- 25 trocellulose percipitate is formed which is filtered from the liquid, washed in hexane, dried for about 16 hours and sifted through a 200 mesh screen.

2. A propellant composition consisting essentially of about 10 to 50 percent plastisol nitrocellulose and from 0 about 15 to 85 percent of a plasticizer material of the formula (0 NOCH CR wherein R is a member of the class consisting of hydrogen, N0 lower alkyl and a lower alkyl carbinaol radical, said plastisol nitrocellulose being made by vigorously stirring until dissolution 90 grams of dry nitrocellulose (12.6 percent N), 1.2

grams of ethyl centralite, and 1.4 liters of nitromethane in a flask, and slowly stirring for about 10 additional minutes to insure homogeneity, adding to the resulting lacquer about 19.2 grams of a petroleum sulfonate emulsifying agent for the mitrocellulose, 900 ml of water and circulating the mixture thereof through a colloid mill for about 10 minutes after which the emul sion therefrom is drained from the mill into about 30 liters of water and stirred for about 15 minutes whereupon the nitrocellulose containing percipitate forms which is filtered, washed in hexane, dried for about 16 hours and sifted through a 200 mesh screen.

3. A propellant composition consisting essentially of from about 35 to percent of a binder which comprises from about 10 to 50 percent plastisol nitrocellulose, about 15 to percent of a plasticizer selected 50 from the group consisting of pentaerithyrtol trinitrate.

and trimethylolethane trinitrate, about 15 to 20 percent aluminum and from about 30 to 35 percent ammonium perchlorate, said plastisol nitrocellulose being made by placing grams of nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite and 1.4 liters of nitromethane in a flask and stirring vigorously until dissolution occurs, stirring slowly for an additional 10 minutes to insure homogeneity, adding to the resulting lacquer 19.2 grams of a petroleum sulfonate emulsifying agent for nitrocellulose in about 900 ml of water 60 and circulating through a colloid mill for about 10 minutes, draining the resulting emulsion from the mill into about 30 liters of water and stirring about 15 minutes until a nitrocellulose percipitate is formed which is filtered from the liquid, washed in hexane, dried for about 16 hours, and sifted through a 200 mesh screen.

4. The propellant composition of claim 3 in which cyclotetramethylene tetranitramine is substituted for ammonium perchlorate.

5. The propellant composition of claim 3 in which trinitroethylorthocarbonate is substituted for ammonium perchlorate.

Claims (5)

1. A PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF FROM ABOUT 25 TO 100 PERCENT BINDER AND UP TO 7K PERCENT SOLID LOADING, SAID BINDER COMPRISING FROM ABOUT 10 TO 50 PERCENT OF PLASTISOL NITROCELLULOSE AND FROM ABOUT 15 TO 85 PERCENT PLASTICIZER MATERIAL OF THE FORMULA (O2 NOCH2)3 C-R WHEREIN R IS A MEMBER OF THE CLASS CONSISTING OF HYDROGEN, NO2, LOWER ALKYL AND A LOWER ALKYL CARBINOL RADICAL, SAID SOLID LOADING CONSISTING OF UP TO 60 PERCENT OF A METAL AND FROM ABOUT 20 TO 100 PERCENT OF A MATERIAL FROM THE CLASS CONSISTING OF PERCHLORATE OXIDIZING AGENTS, CYCLOTETRAMETHYLENE TETRANITRAMINE, TRINITROETHYLORTHOCARBONATE AND MIXTURES THEREOF; SAID PLASTISOL NITROCELLULOSE BEING MADE BY PLACING 90 GRAMS OF NITROCELLULOSE (12.6 PERCENT N), 1.2 GRAMS OF ETHYL CENTRALITE AND 1.4 LITERS OF NITROMETHANE IN A FLASK AND STIRRING VIRGOROUSLY UNTIL DISSOLUTION OCCURS, STIRRING SLOWLY FOR AN ADDITIONAL 10 MINUTES TO INSURE HOMOGENIETY, ADDING TO THE RESULTING LACQUER 192 GRAMS OF A PETROLEUM SULFONATE EMULSIFYING AGENT FOR NITROCELLULOSE IN ABOUT 900 ML OF WATR AND CIRCULATING THORUGH A COLLOID MILL FOR ABOUT 10 MINUTES, DRAINING THE RESULTING EMULSION FROM THE MILL INTO ABOUT 30 LITERS OF WATER AND STIRRING ABOUT 15 MINUTES UNTIL A NITROCELLULOSE PERCIPITATE IS FORMED WHICH IS FILTERED FROM THE LIQUID, WASHED IN HEXANE, DRIED FOR ABOUT 16 HOURS AND SIFTED THROUGH A 200 MESH SCREEN.

2. A propellant composition consisting essentially of about 10 to 50 percent plastisol nitrocellulose and from about 15 to 85 percent of a plasticizer material of the formula (O2 NOCH2)3 C-R wherein R is a member of the class consisting of hydrogen, NO2, lower alkyl and a lower alkyl carbinaol radical, said plastisol nitrocellulose being made by vigorously stirring until dissolution 90 grams of dry nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite, and 1.4 liters of nitromethane in a flask, and slowly stirring for about 10 additional minutes to insure homogeneity, adding to the resulting lacquer about 19.2 grams of a petroleum sulfonate emulsifying agent for the mitrocellulose, 900 ml of water and circulating the mixture thereof through a colloid mill for about 10 minutes after which the emulsion therefrom is drained from the mill into about 30 liters of water and stirred for about 15 minutes whereupon the nitrocellulose containing percipitate forms which is filtered, washed in hexane, dried for about 16 hours and sifted through a 200 mesh screen.

3. A propellant composition consisting essentially of from about 35 to 55 percent of a binder which comprises from about 10 to 50 percent plastisol nitrocellulose, about 15 to 85 percent of a plasticizer selected from the group consisting of pentaerithyrtol trinitrate and trimethylolethane trinitrate, about 15 to 20 percent aluminum and from about 30 to 35 percent ammonium perchlorate, said plastisol nitrocellulose being made by placing 90 grams of nitrocellulose (12.6 percent N), 1.2 grams of ethyl centralite and 1.4 liters of nitromethane in a flask and stirring vigorously until dissolution occurs, stirring slowly for an additional 10 minutes to insure homogeneity, adding to the resulting lacquer 19.2 grams of a petroleum sulfonate emulsifying agent for nitrocellulose in about 900 ml of water and circulating through a colloid mill for about 10 minutes, draining the resulting emulsion from the mill into about 30 liters of water and stirring about 15 minutes until a nitrocellulose percipitate is formed which is filtered from the liquid, washed in hexane, dried for about 16 hours, and sifted through a 200 mesh screen.

4. The propellant composition of claim 3 in which cyclotetramethylene tetranitramine is substituted for ammonium perchlorate.

5. The propellant composition of claim 3 in which trinitroethylorthocarbonate is substituted for ammonium perchlorate.