US2974026A - Solid composite, smokeless, slow burning, low flame propellant - Google Patents

Description

' turbines and the like.

SOLID COMPOSITE, SMOKELESS, SLOW BURN- ING, LOW FLAME PROPELLANT No Drawing. Filed Mar. 14, 1952, Ser. No. 276,703

5 Claims. (Cl. 52-5 This invention relates to propellants or self-combustible compositions adapted for the generation of large volumes mes 5 m of gas useful in the performance of'work, such as jet 1.;

propulsion, driving turbines, press'urizing liquids, operat- .ing mechanical pistons, and the like.

. The principal object of the invention is to provide a substantially smokeless, slow burning, low flame temperature propellant that is .easy to manufacture and can be produced at a relatively low cost. A further object of the invention is to provide a propellant that can be .safely, manufactured -'and does'not subject .the' user to :undue hazards.-

A propellant composition of the solid type ordinarily 1 comprises a fuel ingredient having an oxidizer intimately mixed in it so that it contains the oxygen for its" own combustion. The fuel may be a combustible substance such as a resin which acts as a binder for the oxidizer which is ordinarily present in a finelydivided state.

Heretofore propellant formulations have been proposed for the generation of large volumes of gas to operate However, ,in most of the proposed propellants an objection has been that the temice . 2 satisfactory operation of the mechanism in which the gases are employed. g f By my present invention I have succeeded in producing a propellant that is capable of generating," large volumes of substantially solid-free gases at a low flame temperature which are smokeless and slow burning, making it particularly desirable for application to equipmerit such as gas turbines and the like. I have further dis;- covered that such a propellant may be compounded .by using ammonium nitrate as the oxidizer, preferably inan unstabilized form, by using as a binder for the oxidizer, a particular fuel composition which providesahighdegree of toughness and flexibility, thereby enabling the binder to adjust itself to the expansion or contraction of the ammonium nitrate oxidizer when this substance under"- goes changes at the various transition points. I n A feature of this invention resides in the fact that the fuel contains sufiicient oxygen in the molecule toinsure against the formation of carbon in the form of smoke in the exhaust gas. The particular fuel composition which I have discovered to have this desirable property inconjunction with ammonium nitrate is the resinous condensation product of adipic acid, maleic anhydride and diethylene glycol to which is added methyl. acrylate and styrene. .Ordinary resins containing ammonium nitrate will not avoid cracking when the temperatures vary wideily; but the foregoing polyester resin when provided with the styrene and methylacrylate additive and in thejfollowing indicated proportions, is an exception which an result in a substantially non-cracking propellant/ 'I'h'e proportions *ofthe components should be held substanperature at which the gases are generated is .usually too However, up to the present time this ex- -fuel some undesirable cracking of the propellant has .occurred when the propellant is subjected to wide tem :peratures variation. The formation of cracks in the propellant material is undesirable as it has the effect of :increasing the burning area and rate beyond what is intended; and such increased burning rate maybe dangerous as it maycause an explosion.

; ,I have discovered that this; cracking of thepropellant containing ammonium nitrate as an oxidizer is generally .due. to the fact that the fuel or hinder portion of the propellantsis; incapable-of adjusting itself to expansion :or contraction to which the ammonium nitrate oxidizer is subjected when the substance is cooled or heatedto cause it to undergo its transition change in physical state.

3 -;One expedient; that has, been propo'sedto minimize the a, ;-transition change of ammonium nitrate; has been to sta- Qbiliz'g: the ammonium nitrate before introducing it'in'to she-prope l nts. and this-has been .donezby adding modifyg in red e ts to-theammeniemnitrateyflHo e'ver, such cle 'thefigasesliferrn; and" havez..the- ;undesirable feature-that they lower {the .speicifiefimpul'se ;of. itheprom lantha g The; exis ence of .solid particles 'ini'itlre gass ge a d. y; theLpropellant cannot: be.- ,tolerated ito anygreat. extent 138. .it would; soon; interfere with the fyins-ingl edientshaye thefefifect; ofucreating solid 1 tially withinthe tfairly narrow limits whichihave been I'determined,.as indicated below. The adipic acid should be presentin an amount of at least 4 moles adipic acid to one mole of maleic anhydride. The amount of the glycol to the combined acids (adipic'acid plus maleic anhydride). should range from about 0.5 to 2 moles 1th -1 mole of the glycol, the preferred ratio: being about '1 mole of the glycol toone mole of the combined acids. The ratio of adipic acid to maleic anhydride may vary from about 4 to 9' moles of adipic acid to 1" mole of maleic anhydride.

Suitable polyesters are those restricted to the following ingredients and range of proportions:

Moles Diethylene glycol l0l1 Adipic acid Y 8 9 Maleic anhydridel- '2 An example of a particularly suitable polyester resin within the foregoing range is one having the following proportions:

10.5 moles diethylene glycol 9.0 moles adipic acid 1.0 moles maleic anhydride This resin is hereinafter referred to 'as Resin A; a 1' Another somewhat similar resin found very satisfactory .for use in formulating the propellant one having the following proportions:

10.5 moles diethylene glycol 8.0 molesadipic acid v 24) molesmalei'c anhydride This resin will hereinafter be referred to as Re'sinB. r ."KT'hecondensation process by. which the polyester is termed. is briefly as follows:;-... 2-; a r M Z The-ingredients' comprising the'adip'ic acid/M81916 nzhydride; 'andQ diethylene glycol are mixed together"ahd heatedito .a temperature .of approximately C.

away. This is carried out in an atmosphere of inert gas such as hydrogen, nitrogen,.- carbon dioxide, helium, etc. When the water hasbeen substantially removed thet-reaction product may then be subjected to alligher temperaturenot to exceed about 250 (Land preferably between 200 C. and, 230" C. The condensationis, con- Itinued until the polyester has reached a desired degree 0tv polymerization which may be determined either by ascertaining, the acidnumber inthe mixture -or by measure ing the viscosity of the resin. The preferred degree of polymerization. lies between 5. and 100 and. will usually take around 70 hours of condensation. product is generally a viscous liquid which can be cooled and stored, making it available for further polymerization with the additives.

The propellant is compounded by mixing thev poly.- ester resin, the styreneand the methyl acrylatetogether with sufli'cient quantities of ammonium nitrate in finely divided form to provide enough oxygen for the complete combustion of the fuel elements. To the ammonium nitrate there is preferably added a small percentage of ammonium dichromate to improve the burning qualities of the propellant mixture. The substances are mixed together homogeneously and to the mixture there is preferably added the usual polymerization catalysts and acceleratorssuch as methyl ethyl ketone peroxide and cobalt octoate. It is also desirable toadd a small amount of lecithin to the mixture to insure a morecastable homogeneous mixture.

"The'proportion. in which the components may be admixedwith, each other to form satisfactory propellants are astolloiwsiz Percent by: weight Resin A or Resin B 4-14 Styrene 1-6 fMethylacrylate 4-116 Ammonium nitrate 65-80 Ammonium dichromate l-S Methyl ethyl ketone peroxide 0.1-1.0 Gobalt octoate 0;01-0.10 Lecithin v 0.0l-0.5

A specific formulation which has been found panticularly satisfactory for this purpose is as follows:

Percent by weight The advantage of the above propellant formulations is that it is possible to make propellants capable of generating large volumes of substantially solid-free gases at relatively low temperatures and at the same time employ the inexpensive oxidizing-component, ammonium nitrate,

without the danger of having the propellant-massbecomecracked if subjected to a change in temperature which would normally cause the ammoniumnitrate to pass through one of its many transition points-and expand or The resulting 4 contract in an amount sufiicient to develop a separation within the propellant charges.

We .claim:

1. A substantially smokeless, slow. burning, low-flame temperature propellant comprising:rrom-4:.t 14%-by weightv based'on'the weight of the .totallpropell'ant Of a .polyester'resin obtained by condensing-1010' 11 moles of diethylene glycol with from 8 to 9 molesof adipic acid and 1 to 2 moles of maleic anhydride; from 1 to 6% by weight styrene based on the weight of the total propellant; from 4 to 16% by weight methyl acrylate based on the weight of the total propellant; from 65 to by weight ammonium nitrate based on the weight of the total propellant; from 1 to 5% by weight ammonium dichromatebased on. the weight, of. the total propellant; from 01% to 1 .0% by weight. methyl ethyl 'ketone peroxide based on the weight of the total propellant; from-.0101 to .10% by weight cobalt octoate based on the weight of the total propellant"; and from .01 to 0.5% by weight lecithin based onthe weight of the total propellant.

2. A substantially smokeless, slow burning, low flame temperature propellant comprising from 4 to 14% by -weight based on the weight of the total propellant of a total propellant; from 0.01; to- 10% by weight cobalt octoate based on the weight of -the total propellant; and from .01 to 0.5 by weight lecithin based on the weight of the: total? propellant.

3. A: substantially smokeless slow burning, low flame temperature propellant comprising. from 4 to 14% by weight; based on the weight; of the total propellant: of a polyester resintobtaine'd by'condensing 10 /2 moles of diethylene glycol with 1 mole maleic anhydride and 9 moles adipic-acid; from I to 6% by weight styrene based on the weight of the total propellantyfrom 4 to 16% by weight methyl acrylatebased on the weight ofthe total propellant; from 65 to 80% by weight ammonium nitrate based on the weight of the total propellant; from 1 to 5% by weight ammonium dichromate based on the weight of the total propellant; from 0.1 to 1.0% by weight methylethyl ketone peroxide based on the weight -0f'-the total propellant; from 0.01 to .10% by weight cobalt octoatebased. on the weight of the total pmon the-weight-of the total propellant; 72;80% byweight ammonium nitrate-based on-the'weight of the total propellant; 2% by weight ammonium dichromate based on the weightofthe total propellant; 0.30% by weight methyl ethyl ketone peroxide based on the weight of the total propellant; 0.25 %v by weight cobalt octoate (1% cobalt solution) basedontheweight of the total pro- 'pellant; and 0.05% by weight lecithin based on the weight of the total propellant.

5. A substantiallysmolceless, slow burning; low flame temperature propellant. comprising 10% by weight based onthe weight of the total propellant of a polyester resin obtained by condensing 10 /2 moles of diethylene glycol -with-1 mole'malei'c anhydrideand 9 moles: adi'pie acid;

2 .30% by weightstyrene-based on the weight ofthe total propellant; 12.40% by weight methyl acrylate based ontheweight of the total propellant; 72.80%" by-weight ammonium nitrate-based on the weight of the total propell ant; 2% by weight ammonium dichromate'based'v on the weight of the total propellant; 0.30% by. weight methyl ethyl "lcetone peroxide basedon the weight of the total propellant; 0.25% by weight cobalt octoate (1% cobalt solution) based on the weight of the total propellant; and 0.05% by weight lecithin based on the weight UNITED STATES PATENTS Gordon et a1. Ian. 12, 1937 6 Lawson Apr. 25, 1939 Holm Apr. 2, 1940 Patterson Dec. 15, 1942 DAlelio May 25, 1943 Fuller Nov. 6, 1945 King Aug. 20, 1946 Taylor et :al. Jan. 20, 1948 Geckler Aug. 23, 1949