US3751311A - Gelation of hydrazine and hydrazine-type rocket fuels - Google Patents

Abstract

This patent describes novel gelled hydrazine-type fuels suitable for use in rockets, missiles and the like. The gelling agents are quaternary ammonium slats of polyacrylic acid.

Description

ilniied Siaies Pateni [1 1 Vander Wall et a1.

[ 1 Aug. 7, 11973 1 1 GELATlON 0F HYDRAZINE AND HYDRAZlNE-TYPE ROCKET FUELS [75] Inventors: Eugene M. Vander Wall, Citrus Heights; James M. Lucas, El Dorado Hills, both of Calif.

[73] Assignee: Aerojet-General Corporation, El

Monte, Calif.

[22] Filed: July 27, 1967 [21] Appl. No; 658,982

[52] US. Cl. 149/36, 49/20 3,164,505 1/1965 Hsieh et a1 149/36 3,196,059 7/1965 Godfrey 149/36 X 3,197,348 7/1965 Skolnik et al.... 149/36 X 3,232,801 2/1966 Bost et a1 149/36 X Primary ExaminerCar1 D. Quarforth Assistant Examiner-Stephen .I. Lechert, Jr. Attorney-Edward O. Ansell, D. Gordon Angus and Donald W. G rauer [57] ABSTRACT This patentdescribes novel gelled hydrazine-type fuels suitable for use in rockets, missiles and the like. The gelling agents are quaternary ammonium slats of polyacrylic acid.

7 Claims, N0 Drawings GELATION OF HYDRAZINE AND HYDRAZINE-TYPE ROCKET FUELS BACKGROUND OF THE INVENTION The field of the present invention pertains to gelled rocket fuels.

Various hydrazine-type fuels are well known for use in liquid rocket engines. However, liquid hydrazinetype materials are characterized by several problems. One of these is the tendency to slosh within fuel tanks during flight. Sloshing has been found to adversely affect the stability of the rocket. Liquid hydrazene fuels also present a safety hazard since they can easily escape through ruptured or perforated tanks or fuel lines. For these and other reasons, various gelling agents have been proposed to thicken or produce a mechanically stable gel of hydrazine. One example of such a gelling agent is polyacrylic acid which is disclosed in assignees U.S. Pat. No. 3,232,801 issued Feb. 1, 1966. This patent describes the use of polyacrylic acid as a gelling agent to produce a mechanically stable, thixotropic hydrazine-type gel. The compositions of this patent are quite satisfactory in most respects. However, certain significant improvements have now been discovered and the present patent application is directed to these improvements.

SUMMARY OF THE INVENTION Briefly, the present invention comprises a gelled, mechanically stable, thixotropic liquid fuel composition comprising a hydrazine-type fuel containing an effective gelling amount of a gelling agent which is a quaternary ammonium salt of polyacrylic acid. The invention further comprises a method of preparing novel gelled fuel compositions.

As has been indicated above, it is desirable to gel rocket fuels so that the liquid is immobilized to reduce seepage and leakage hazards, and prevent sloshing of the liquid in propellant tanks. It is also desirable to gel rocket fuels so that solid energetic particles, usually solid metals, can be permanently and uniformly suspended in the fuels to increase the fuel value. Gelation also aids in holding the propellant in its position in fuel tanks under conditions of gravity. The quaternary ammonium salts of the present invention are superior to known gelling agents in that at concentration levels of less than percent, they will gel fuels that cannot be gelled by the incorporation of ordinary polyacrylic acid. The quaternary ammonium salts of the present invention can also be used to gel several different types of hydrazine-type fuels and are not restricted in their use to the gellation of ordinary hydrazine or hydrazinecontaining mixtures.

The gels of the present invention are also less sensitive to ionic contamination than are other polymers used for gelation. The hydrazine gels of the present invention have been found to be stable over a greater temperature range than hydrazine gelled with polyacrylic acid. Further, the gelling agents of the present invention can be completely neutralized so that no acidic species are introduced into the fuels, making the fuels less reactive with acid-sensitive metals and compounds.

Accordingly, it is a principal object of the present invention to provide a mechanically stable, thixotropic gelled hydrazine-type fuel composition.

Another object of the present invention is to provide a means of gelling hydrazine-type fuel compositions having a wider applicability than has previously been available.

Still another object of the present invention is to provide a gelled hydrazine fuel composition which is stable over a greater temperature range than known gelled hydrazines.

It is still another object of the present invention to provide a gelled hydrazine-type fuel which is less sensitive to ionic contamination.

A further object of the present invention is the provision of a gelled fuel composition which is less reactive with acid-sensitive metals and other fuel additives.

These and other objects and advantages of the present invention will become apparent from a more detailed description which follows.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The gelling agents of the present invention are normally employed in effective gelling amounts up to about 10 percent by weight of the total fuel composition. However, it should be understood that even greater amounts of the gelling agent may be employed, although this is normally to be avoided since the gelling agents are completely effective at low concentration and the use of more gelling agent is of no further benefit.

There may be included in the gelled hydrazine-type fuels of the present invention, as an optional ingredient, powdered metals such as aluminum or beryllium. These metals serve to increase the specific impulse of the fuel. The amount of powdered metal employed is not critical. Normally, if the powdered metal is added, it should be used in amounts up to about percent by weight of the total weight of the gelled fuel compositions. When these metals are incorporated in the gelled hydrazine compositions, it has been found that the resulting fuel is mechanically stable and there is no tendency for the powdered metal to settle out of the gel.

The quaternary ammonium polyacrylate salts used as the gelling agents of the present invention are prepared by neutralizing a suitable polyacrylic acid with a quaternary ammonium hydroxide in a solvent. The solvent is removed after neutralization and the salt is dried in vacuum at room temperature.

The amount of quaternary ammonium hydroxide used may be enough to neutralize all of the free carboxyl groups in the polyacrylic acid. However, in many cases, less than a stoichiometric amount of quaternary ammonium hydroxide is used. The use of partially neutralized polyacrylic acid has been found to reduce the quantity of a gelling agent which is required for gellation compared to that required when the completely neutralized salt is used. In other cases where acid sensitive metals or other additives are to be employed, it has been found that it is preferred to employ a completely neutralized gelling agent which introduced no acidic species into the fuels. Thus, based upon the foregoing criteria, those skilled in the art will be able, within the scope of the present invention and in accordance with the teachings of this patent, to select a gelling agent to provide optimum gelation in each specific fuel composition while minimizing the amount of gelling agent required.

The following examples are presented solely to illustrate the invention and should not be regarded as limiting in any way. In the examples, the parts and percentages are by weight unless otherwise indicated.

EXAMPLE 1 The following example illustrates the preparation of the gelling agent of the present invention. 5.42 grams (0.72 equivalents) of suitable polyacrylic acid, Cartetrapropyl ammonium hydroxide in the above example, tetramethyl ammonium polyacrylate and tetraethyl ammonium polyacrylate were obtained.

TABLE I Components of gels Physical properties High shear Gallant viscosity Gel is cone. (01).) (17,300 stable lolyacrylate gelling agent (percent) Fuel sec. to-( F.)

Tr-tramr-thyl-ammoniurn 1.37 Hydrazine 37 165 Tetraethyl-ammonium 1. 83 .d 165 Tetrapropyl-ammoniu 1.40 26 165 Tetraethyl-ammonium. 8. 1 3-1 'Ietrapropyl-ammonium. 4.1 24 165 Tetrapropyl-ammonium 34 neutr 2.0 ..do 23 133 Tetrapropyl-ammonium 3.7 33 212 D0 6 {50% unsymmetrical (limethyl hydrazine. "II;

bopol-940, a polyacrylic acid manufactured by B. F. The hydrazine gels prepared with quaternary ammo- Goodrich Company, are dispersed in 550 ml of methanium salts do not break down upon prolonged exposure nol. As this solution is stirred, 142 grams of a 10 perto the atmosphere, while hydrazine gels prepared with 35 cent aqueous solution of tetrapropyl ammonium hydroxide (0.072 equivalents) available from Eastman Chemical Products Company are gradually added. The entire addition requires five minutes. A gel forms, and stirring is continued for two hours to assure complete mixing. Methanol and water are removed by evaporation under vacuum. The product is vacuum-dried at a pressure of 5 mm Hg for four days at room temperature. The product is a glass-like material which requires grinding to facilitate dispersal in liquids. The yield is 19 grams of tetrapropyl ammonium polyacrylate which corresponds to 97 percent of the theoretical yield. Losses are primarily incurred in handling. The pH of an 0.01 N solution of tetrapropyl ammonium polyacrylate in water is 8.8. The equivalent weight of this salt is 260.

By substituting tetramethyl ammonium hydroxide and tetraethyl ammonium hydroxide, respectively, for

the polyacrylic acid itself break down upon brief exposure.

The following tables illustrate the properties various gels within the scope of this invention.

High Yield Gel Gelling shear stress, breakdown agent, vlseosdynes/ tempera- Gelling agent percent ity, cp. cm! ture, F.

Tetramethyl ammonium polyacry ate 0. 94 25 600 165 D0 1. 47 64 2, 800 165 Tetrapropyl ammonium polyacrylate 1. 40 26 165 Do 1. 88 46 600 165 Tetrabutyl ammomum aerylate 2. 92 14 300 Property not determined.

TABLE 1II.-PROPERTIES OF METALIZED HYDRAZINE GELS Yield High Gel-liquid Composition stress, shear transition dynes/ viscostempera- Gelling agent- Pereent Metal em. ity, cp. ture. F.

Tetramethyl ammonium polyacrylate 0.58 43% A1 1,800 50 D0 0.48 43% Al 30 160 Tetramethyl ammonium polyacrylate 50% neutralized 0. 48 43% -18 160 'Ietrapropyl ammonium polyacrylate 1. 2T 43% Al 1, 200 52 160 Do 0.58 43% Al 28 160 Do 0.91 LM-Q 1,000 39 160 Property not determined.

lNG AGENTS Gelling agent High Yield G el conccnshear stress, stability tratiou, viscosdynes/ temperature (iclling agent Fuel percent ity, op. cm.'- limits, F.

Totravthyl ammonium polyacrylate Monomethyl hydrazine 8. 1 34 t) (l 'letrapropyl ammonium polyacrylatm 4. O 20 100 65, 16a Do 8.6 67 2,200 65, 165 'lotrabutyl ammonium polyaciylatc "do 12.9 16 t) 65, 165

Property not determined.

in general, it can be seen from the foregoing examples that the stable hydrazine gels of this invention are produced by mixing a gelling agent with hydrazine. it is to be understood that powdered metals such as powdered aluminum, can be blended either before, after, or along with the gelling agent. The ingredients are normally blended by shaking or by mechanical agitation to uniformly distribute the gelling agent and to deagglomerate the powdered metal.

The significant improvement in the gel stability in the presence of ions is shown by the comparative data on the following table.

TRA'IION ON THE HIGH SHEAR VISCOSITY OF HYDRA- ZINE GELLED WITH SALTS OF POLYACRYLIC ACIDS Monomethylhydrazonium salt of TF/I RAP ROI YLAMMONIUM SAL'I OF POLYAC RYLIC ACID Gallant Sodium concentration nitrate Viscosity /O) (m -l (an) 1. 40 0 26.011. 2 1.33 51 23. 110. 8 1. 33 98 19. :121. 2 1. 33 337 16. Git). 2

Nora-All viscosity measurements are reported at a shear rate of 17,300 secf While the present invention has been specifically illustrated with hydrazine monomethyl hydrazine and unsymmetrical dimethyl hydrazine, it is to be understood that it is applicable to all types of hydrazine-type fuels, including mixtures of various hydrazine-type fuels.

The gelled fuels of the present invention are highly energetic and are directly useful as fuels in liquid rocket motors.

As can be seen from the foregoing discussion, the gelled fuels of the present invention can be made quite insensitive to acidic reacting liquid propellant additives. The gels of this invention are also stable over a wide range of temperatures. In addition, the gelling agents employed in the present invention can be varied in accordance with the particular fuel to be gelled. Thus, if the fuel is to contain an acid-reacting ingredient, the gelling agent can be completely neutralized. On the other hand, if no acid-reacting additive is to be employed, then, the gelling agent. need only be partly neutralized, and in this case the amount of gelling agent required can be reduced. it is therefore apparent that the present invention will find wide application in the space and defense missile efforts.

Having fully described the invention, it is intended that it be limited only by the lawful scope of the appended claims.

We claim:

1. A gelled mechanically stable thixotropic highenergy fuel composition comprising a hydrazine-type fuel selected from the group consisting of hydrazine and alkyl substituted hydrazines containing therein an effective gelling amount of a gelling agent comprising a quaternary ammonium salt of polyacrylic acid.

2. The composition of claim 1 wherein the gelling agent is tetramethyl ammonium polyacrylate.

3. The composition of claim 11 wherein the gelling agent is tetraethyl ammonium polyacrylate.

4. The composition of claim 11 wherein the gelling agent is tetrapropyl ammonium polyacrylate.

5. The composition of claim 11 wherein the gelling agent is tetrabutyl ammonium pol yacrylate.

6. The composition of claim 1 wherein the gelling agent comprises a partially neutralized quaternary ammonium salt of polyacrylic acid.

7. The composition of claim 1 wherein there is additionally present finely divided metal fuel in an amount up to about 60 percent by weight of. the composition.

, a a t a a

Claims (6)

1. 2. The composition of claim 1 wherein the gelling agent is tetramethyl ammonium Polyacrylate.
2. 3. The composition of claim 1 wherein the gelling agent is tetraethyl ammonium polyacrylate.
3. 4. The composition of claim 1 wherein the gelling agent is tetrapropyl ammonium polyacrylate.
4. 5. The composition of claim 1 wherein the gelling agent is tetrabutyl ammonium polyacrylate.
5. 6. The composition of claim 1 wherein the gelling agent comprises a partially neutralized quaternary ammonium salt of polyacrylic acid.
6. 7. The composition of claim 1 wherein there is additionally present finely divided metal fuel in an amount up to about 60 percent by weight of the composition.