US3788908A

US3788908A - Tracer incendiary composition of alkylaluminum,inorganic oxidizer,and zirconium

Info

Publication number: US3788908A
Application number: US00287067A
Authority: US
Inventors: U Lehikoinen; G Franklin
Original assignee: Ethyl Corp
Current assignee: Ethyl Corp
Priority date: 1972-09-07
Filing date: 1972-09-07
Publication date: 1974-01-29
Anticipated expiration: 1991-01-29

Abstract

AN ALKYLALUMINUM-BASE MATERIAL SUITABLE FOR TRACER APPLICATIONS HAVING A LOWER ALKYLALUMINUM COMPOUND SUCH AS TRIETHYLALUMINUM OR MIXTURES THEREOF, AN INORGANIC OXIDIZER, AND OPTIONALLY A FINELY DIVIDED METAL OR METAL HYDRIDE.

Description

United States Patent 3,788,908 TRACER INCENDIARY COMPOSITION OF ALKYL- INORGANIC OXIDIZER, AND

U. Albert Lehikoinen, Detroit, Mich., and Gerald Franklin, Philadelphia, Pa., assignors to Ethyl Corporation, Richmond, Va.

No Drawing. Filed Sept. 7, 1972, Ser. No. 287,067

Int. Cl. C06]: 11/00 US. Cl. 149-42 8 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION This invention relates to materials which are suitable for use as the active ingredient in a tracer projectile. The invention relates to novel compositions which have the necessary characteristics to fulfill the special requirements of tracer materials.

Tracer ammunition (referred to hereinafter as tracers) is used to mark the flight of a bullet or projectile after firing from a weapon. Thus, the accuracy of fire directed at a target can be assessed and corrected, if necessary. However, special problems are encountered in tracers because the visible flight path or tracer signature may also serve to locate the gunners position. Thus, a short ignition delay is desirable. Other considerations of tracer materials involve afiect on ballistics of the projectile, burning time length, rate of burning, light intensity and muzzle flash. The muzzle blast or flash when firing tracers should not be brighter than ordinary and should avoid blinding the gunner temporarily, as well as marking his location. The light intensity required should be sufficient to enable the flight path of the projectile to be marked at distances of from several hundred to well over thousands of yards depending on the type of weapon being fired. The rate of burning should be fast enough to obtain good combustion but slow enough to burn throughout the flight of the projectile. Thus, the ideal agent should have a short ignition delay, a fast burning rate and considerable flaring.

Previous tracer materials have contained a metal and an oxidizer with a suitable amount of resin or polymeric binder. Several recipes for tracer formulations can be found in Military and Civilian Pyrotechnics, Ellern, Chemical Publishing Co., New York, 1968, pages 362- 365. According to Dr. Ellem, page 129, tracers are very small flares pressed into a cavity at the base of a smallarms or artillery projectile. They must be able to withstand high pressures without igniting and yet ignite very shortly after being fired from the weapon.

The object of this invention is to provide a novel tracer composition based on alkylaluminum compounds. Another object of this invention is to provide a tracer with short ignition delay, fast burning rate and considerable flaring. Another object of this invention is to provide a tracer material which is self-igniting but safe to handle and store. These and further objects will become apparent from the following description of the invention.

SUMMARY OF THE INVENTION Accordingly, the foregoing and other objects of the invention are met by providing a composition suitable for use as a tracer material, said composition comprising (a) an alkylaluminum compound having not more than about 4 carbon atoms in each alkyl radical attached to the aluminum, and

(b) an inorganic oxidizer.

Preferable alkylaluminum compounds are triethylaluminum, trimethylaluminum, and mixtures of these. The inorganic oxidizer can be any inorganic oxidizing agent compatible with the alkylaluminum; and preferably is an oxygen-containing compound of sodium or strontium. The most preferred inorganic oxidizers are sodium chlorate and strontium perchlorate, although a number of other compounds are satisfactory. In another aspect of this invention is provided a three component tracer material. Specifically, it is a composition suitable for use as a tracer material comprising (a) an alkylaluminum compound having not more than 4 carbon atoms in each alkyl group attached to the aluminum,

(b) an inorganic oxidizer, and

(c) a metal or metal hydride in finely divided form.

The foregoing preferred alkylaluminums and inorganic oxidizers are also applicable to this tracer composition. Moreover, the metal compound preferably employed can be either a metal, such as magnesium, aluminum or boron, or a metal hydride such as zirconium hydride or lithium aluminum hydride.

DESCRIPTION OF PREFERRED EMBODIMENTS A preferred embodiment of this invention is a composition suitable for use as the active material in a tracer projectile, said composition comprising an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical and an inorganic oxidizer. The alkylaluminum compound of these tracer compositions can be any alkylaluminum which is capable of independent ignition when exposed to the atmosphere. Generally, the lower alkyl groups attached to aluminum provide an alkylaluminum sufficiently active to self-ignite upon short exposure to the atmosphere. By the term lower alkyl is meant alkyl radicals having not more than 4 carbon atoms in each alkyl radical attached to the aluminum atom. Thus, preferred alkylaluminum compounds are those having lower alkyl groups. Typical of these are methyl, ethyl, propyl, and butyl groups. Therefore, preferred alkylaluminum compounds are trimethylaluminum, triethylaluminum, tri-n-propylaluminum, and tri-n-butylaluminum. Isomeric forms of the propyl and butyl groups are also typical such as tri-isopropylaluminum, tri-isobutylaluminum, and tri-tert-butylaluminum. Mixtures of these compounds and of the alkyl groups such as triethylaluminum/ trimethylaluminum, triethylaluminum/tri-n-propylaluminum, and the like, and diethylmethylaluminum, dimethylethylaluminum, diethylpropylaluminum, diethyl-tert-butylaluminum, methylethylpropylaluminum, and the like are typical. The hydrides are also examples of alkylaluminum compounds typical of this invention and such compounds as diethylaluminum hydride, diisobutylaluminum hydride, ethylmethylaluminum hydride, and the like can be used. The alkylaluminum halides may also be employed in this invention. Typical of these are diethyaluminum chloride, ethylaluminum dichloride, methylaluminum sesquichloride, ethylaluminum sesquichloride, and the like.

When using a mixture of alkylaluminum compounds, such as triethylaluminum and trimethylaluminum, it should be recognized that a certain amount of disproportionation of the alkyl groups may occur either during manufacture or on storage. Thus, it may be ditiicult to exactly pinpoint the composition at any particular time when using mixtures of alkylaluminum compounds. To rectify this, the final composition is always referred to by the amount and type of materials originally included.

The amount of alkylaluminum compounds used in the tracers should be sufficient to cause ignition readily and to sustain a rapid burning rate. Typically from at least about 15 percent by weight to about 60 weight percent of the total composition is the alkylaluminum compound. Of course, the best amount of alkylaluminum to use will vary depending on the other components of the tracer material and the particular alkylaluminum compound used. However, below about 15 weight percent there is not suflicient material to sustain burning for the entire flight of a projectile and to initiate combustion. On the other hand, above about 60 weight percent the tendency is to intensify the muzzle blast elfect of the weapon without sulficient ignition delay to provide for a satisfactory tracer signature. Preferably, the alkylaluminum compound is present at from about 40 weight percent to about 60 weight percent. Most preferably the alkylaluminum compound is an equimolar mixture, that is to say, a 50:50 mole percent mixture of trimethylaluminum and triethylaluminum at from about 40 to about 60 weight percent of the total composition.

The oxidizer is present because sufiicient oxygen to maintain combustion may not be present in the cavity of the projectile. Traveling at great speed, a partial vacuum is created behind the projectile as it moves through the air and not enough oxygen can get to the tracer to continue the combustion started on firing. Hence, if an oxidizer was not provided, the combustion would cease and the tracer go out prior to reaching the target.

The oxidizer of this invention must be compatible with the alkylaluminum, that is, it must be capable of being mixed with the alkylaluminum without reacting until the proper time. Nevertheless, it must, on ignition of the alkylaluminum, decompose easily and rapidly to provide sufficient oxidizing agent to continue combustion. Organic oxidizers and some inorganic oxidizers react with alkylaluminum compounds. It is easy to test for this interaction by simply mixing small quantities of the oxidizer and alkylaluminum together in an inert atmosphere. Any evidence of reaction, such as increase in temperature, sparks, smoking or ignition eliminates the particular oxidizers. Therefore, the oxidizer of this invention is preferably an inorganic oxidizer which is compatible with alkylaluminum compounds, that is, one which is substantially inert when mixed with alkylaluminum compounds under anhydrous conditions in an inert atmosphere. Without limiting the invention, it has been found that such inorganic oxidizers are substantially insoluble in alkylaluminum compounds. In other words, they tend to form physical mixtures when blended with alkylaluminum compounds. Typical of compatible oxidizers are certain oxygen-containing inorganic oxidizers called per compounds. For example, peroxides, perchlorates, perchromates, permanganates, periodates, and the like are typical. Also, some inorganic nitrates and oxides are compatible inorganic oxidizers. More preferred inorganic oxidizers which are compatible with alkylaluminum compounds are selected from alkali metal and alkaline earth metal compounds. Either alkali metal or alkaline earth metal compounds alone can be suitable inorganic oxidizers by themselves or as mixtures. Typical are sodium nitrate, sodium chlorate, sodium iodate, sodium chromate, sodium peroxide, potassium nitrate, potassium chromate, potassium dichromate, potassium permanganate, strontium peroxide, strontium nitrate, strontium perchlorate, barium peroxide, barium nitrate, and the like. Most preferable inorganic oxidizers compatible in the tracer material are sodium chlorate and strontium perchlorate. Without limiting the invention to the alkali metal and alkaline earth metal compounds, it should be recognized that other inorganic oxidizers are compatible with the alkylaluminum-based tracer materials of this invention; such as, copper oxide, manganese oxide, boron oxide, for example.

The inorganic oxidizer should be present in an amount sufficient to provide oxygen or other oxidizing agent to sustain combustion of the tracer material. Of course, this will vary because of the flight characteristics of the projectile, since some projectiles tumble end over end in flight and present only small oxygen dilficiences, and the amount and type of alkylaluminum and other components in the tracer material. Generally speaking, the Weight of inorganic oxidizer should be from at least about 40 weight percent to about 85 weight percent of the total tracer material weight. Preferably, the inorganic oxidizer should be present in an amount of from about 40 to about 60 weight percent of the tracer material.

Therefore, a preferred embodiment of this invention is a composition suitable for use as the active material in a tracer projectile, said composition comprising an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical and an inorganic oxidizer. A more preferred embodiment is the above composition wherein the alkylaluminum compound is present at from at least about to about 60 percent by weight and said inorganic oxidizer is present at from at least about to about 85 percent by weight; all percentages based on the total Weight of the active material.

In some instances it is preferred to add, as a third component, a metal or metal compound or mixtures thereof to the tracer formulations of this invention. While massive metals themselves would not, except in very special cases, lend themselves to use in tracer materials, it is known that finely divided metals ignite and burn intensely. This property makes a number of metals extremely advantageous to use in finely divided form as a component of tracer materials. Preferably, a metal or a metal hydride is suitable in the tracers of this invention, and more preferred are a metal or a metal hydride when used in finely divided form. The metal need not be so fine as to cause dusting, sticking, or other handling problems; but the particle size should be sufficiently small to oxidize easily, rapidly, and with intense light being given off. Of course, the metal is not critical so long as it meets the requirements set forth above. Finely divided iron, copper, steel, magnesium, aluminum, boron, silicon, selenium, tellurium, titanium, zirconium, lead, manganese, tungsten, zinc, and the like are illustrative examples of suitable metals. More preferred for inclusion in tracer materials are metals selected from magnesium, aluminum, and zirconium Most preferred is finely divided or powdered magnesium.

Not only are the metals themselves suitable, but in addition metal compounds such as the hydrides and complex metal hydrides are suitable for the tracer materials of this invention. For example, titanium hydride, zireonium hydride, lithium aluminum hydride, boron hydride, sodium borohydride, sodium hydride, sodium aluminum hydride, calcium hydride, and the like are illustrative of typical metal hydrides and complex metal hydrides. Zirconium hydride is a preferred metal hydride. Without limiting the invention to the foregoing metal compounds, it should be clear that any metal compound which is readily decomposable or which provides a highly active form of the metal for oxidation or which is normally susceptible of the drastic oxidation in combustion and not merely oxidative degradation over a prolonged period would be suitable as a component of the tracer material of this invention.

The metal or metal compound can be normally present in amounts sufficient to add a bright, intensive flaring to the tracer combustion. Without limiting the invention, when the metal or metal compound is present in an amount of at least about 30 to about 75 weight percent of the total tracer material, a suitable tracer material is produced. Preferably, the metal is present at from about to about weight percent of the tracer material.

Therefore, another preferred embodiment of this invention is a composition suitable for use as the active material in a tracer projectile, said composition comprising an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical, an inorganic oxidizer, and a metal or metal hydride or mixtures thereof in finely divided form. The alkylaluminum compound can be any alkylaluminum compound hereinabove described. However, the amounts required are not as great as in the two component system. Preferably from about 5 to about 60 weight percent of the total weight of the active material can be alkylaluminum; more preferably from at least about to about 30 weight percent should be used. Similarly, the inorganic oxidizer is also as hereinabove described. Again, the amounts required are not so great and preferably from at least about 10 to about 40 percent by weight and more preferably from about to about percent by weight based on the total weight of material may be used. Thus, in a more preferred embodiment of this invention the active material for a tracer projectile comprises from at least about 5 to about 60 percent by weight of an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical, from at least about 10 to about percent by weight of an inorganic oxidizer, and from at least about 30 to about 75 percent by weight of a metal, metal hydride, or mixture thereof in finely divided form.

In addition to the foregoing, various other components may be added to the tracer material of this invention. For example, binders, coloring agents, ignition-delay enhancers, destruct devices, light intensifiers, and the like may be used to produce a better tracer material or improve its properties. Without limiting the invention, typical binders are those which when added to the tracer material cause stiffening of the material and increase its cohesion, while at the same time altering the burning characteristics little, if any. Typically, the binder may be a natural or synthetic polymer or gelling agent; for example, polyolefins, such as polyethylene, polypropylene, and polyisobutylene, paraffin wax, high molecular weight polyethers, and the like.

Various coloring agents can also be used in the tracer materials of this invention without departing from the scope thereof. Basically, the colors red and green are produced by the elements strontium and barium, respectively, usually as their relatively volatile chlorides. They are usually present either as the perchlorates or their less hazardous nitrate forms are used in conjunction with a halogen donor such as inorganic metal salts, such as sodium, barium, strontium, and calcium chlorides and the like. Copper powders may be added to formulas producing green light as an intensifier. Yellow may be produced by the strong tintorial power of sodium, for example, as with a sodium salt. Blue may be produced by including copper in the presence of chlorine (in its absence green is produced).

The use of additional pyrotechnic or explosive devices in tracer materials is convenient because the tracer usually burns in cigarette fashion" and thus serves as a delay for the later ignition of the explosive. Operating in this manner the tracer may destroy the projectile after a definite interval.

The tracer materials of this invention can conveniently be prepared by simply mixing the dry ingredients together and then adding the liquid components thereto forming a pasty mass which can be shaped as desired. The entire operation of mixing should be carried out under anhydrous conditions in an inert atmosphere, such as for example, under a nitrogen blanket.

The method or order of mixing the materials is not considered critical. Thus, the inorganic oxidizer may be added to the alkylaluminum, but for convenience it appears easier to blend the liquid alkylaluminum compound into the oxidizer. When a metal or metal hydride is used,

it is preferred to blend the oxidizer and metal or metal hydride and then add the alkylaluminum. The resultant tracer material may range from a pasty mass to particles of a solid depending on the type and amount of the various materials used.

The materials may be admixed at any convenient temperature although extreme temperatures should generally be avoided. The tracer material can be formulated conveniently at room temperature or at any temperature below which the inorganic oxidizer is substantially insoluble in the alkylaluminum.

In practice the tracer material can be premixed and packed into the projectile cavity or the cavity can be partially filled with the proper amount of premixed dry ingredients and the desired amount of alkylaluminum added to the cavity. Also, the entire premixed tracer material can be extruded into the cavity. When filling the cavity precautions should continually be observed to avoid air and water, until the cavity is appropriately sealed.

The seal is important because its function is to prevent premature exposure of the tracer material to the atmosphere and, thus, prevent undesirable ignition. In another sense, however, the seal is not critical to this invention in that any nonpermeable membrane which is inert t0 the tracer material, provides suitable storage life, ruptures easily, or is ejected on firing the projectile and does not intefere with the pyrotechnical aspects of the tracer may be conveniently employed. For example, sealing membranes such as aluminum foil, viton, and Teflon are typical, but non-limiting illustrations.

The following examples serve to illustrate the tracer compositions of this invention.

EXAMPLE 1 TABLE L-COMPATIBILITY OF OXIDIZING AGENTS WITH TRIETHYLALUMIN UM Not compatible K104, FeCh, KClOa,

Compatible NaNO NaClOs, NaIOs, NmCrOt, Nazor, NaF, KNO; moto K2Cr2O1, KMnOt, BT02, sioroiii. Sr(ClOla, B802, Ba(N0a)2, CuO, MnOz, B20:

Similar results are obtained when the alkylaluminum used for compatibility testing is trimethylaluminum, an equimolar mixture of triethylaluminum and trimethylaluminum, tripropylaluminum, tri-n-butylaluminum, and the like.

The burning characteristics of compatible systems were qualitatively tested for ignition delay, burning rate, and flaring by exposing the compatible compositions of Table l to the atmosphere. Comparative observations of ignition delay were rated as long, average, or short. These terms are used to mean a delay of about 3 to 10 seconds, about 1 to 3 seconds, and less than 1 second, respectively. The burning rate was compared and the results re ported as slow, average, and fast. As used in this application, these terms mean a rate of about 5 to 15 seconds, about 2 to 5 seconds, and less than 1 to 2 seconds respectively. The flaring characteristics of the compositions were rated visually as none, fair, bright, or very bright. The burning characteristics of compatible compositions are given in Table 2 as follows:

TABLE 2.BURNING CHARACTERISTICS OF SYSTEMS CONTAINING TRIETHYLALUMINUM AND AN OXIDI- ZING AGENT Ignition delay Burning rate Flaring None.

Bright.

N one.

Bright.

None.

Fair.

Agent NaNGs Average Average NaClOa Short Fast Similar burning characteristics are observed when the alkylaluminum compound used is trimethylaluminum, mixtures of trimethyland triethyialuminum, tripropylaluminum, tri-n-butylaluminum, and the like.

From the results shown in Tables 1 and 2, it can be seen that a wide variety of oxidizing compounds may be used in the tracer materials of this invention. Preferred tracer compositions are prepared from sodium peroxide and sodium chlorate with triethylaluminum. Most preferred is the system comprising triethylaluminum and sodium chlorate.

Tracer formulations containing an equimolar mixture of triethylaluminum and trimethyialuminum are especial ly preferred. While other mixtures can also be used, a tracer having shorter ignition delay than either individual component alone is conveniently prepared from 50 mole percent of triethyialuminum and 50 mole percent of trimethylaluminum. Typical formulations having such an equimolar mixture are given below:

A trademark of Badische Anilinand Soda-Fabrik, for B. commercially available form of polyisobutylene.

In another formulation, a metal or metal hydride was added to a tracer formulation comprising triethylalumi num and either NaClO or Na The procedure for this is shown in the following illustrative example.

8 EXAMPLE 2 In a nitrogen box was cautiously blended 3 grams of NaClO and 2 grams of powdered magnesium. To this mixture were added 2 ml. of triethylaluminum; the pasty mass was sealed in a glass vial and then exposed to the atmosphere by breaking the vial in a suitable test location. The burning characteristics, according to the ratings for Table 2, were observed and recorded. The results of exposing the formulation prepared in Example 2 and of several other formulations prepared in the same manner are given in Table 3.

TABLE 3.BURNING CHARACTERISTICS OF SYSTEMS CONTAINING TRIETHYLALUMINUM, AN OXIDIZING AGENT, AND METAL OR METAL HYDRIDE Agents Ignition delay Burning rate Flaring NaCl0;tZrHz Long Fast. Bright. NaCl0sAl o.-. d Do. NaClOz-Mg Short... Very bright. NaC10; Bright. NaClO;LiAlHi Averag do Do.

N azOr-ZTH: do -do Do. NazO2Al. Do. NaaO:Mg. Do. NEL202B-. D0. NflzOr-LLUHA do Slow Fair.

1 Very fast-taster than one second by an order of magnitude.

Similar results can be obtained when the alkylaluminum compound used is trimethylaluminum, an equimolar mixture of triethylaluminum and trimethylaluminum, tripropylaluminum, tri-n-butylaluminum, and the like. Further, similar results can be obtained when the inorganic oxidizer is potassium diohromate, potassium permanganate, strontium peroxide, barium peroxide, and the like.

The formulations of Table 3 all produce a yellow light when burned. A suitable tracer formulation producing red light can be prepared by using a strontium compound as the inorganic oxidizing agent, for example,

43 weight percent ISrO 29 weight percent powdered Mg;

and 28 weight percent triethylaluminum 43 percent Sr(NO 29 weight percent powdered Mg;

and 28 weight percent triethylaluminum 43 weight percent Sr(ClO 29 weight percent powdered Mg; and 28 weight percent triethylaluminum.

A bright-red, flare-like fire resulted from combustion of the above formulations. Similar formulations may be obtained when the triet hylaluminum is replaced with trimethylaluminum, mixtures of triethylaluminum and trimethylaluminum, tripropylaluminum, tri n butylaluminum, diethylaluminum hydride, diisobutylaluminum hydride, and the like.

Using the Procedure of Example 2, various formulations were prepared and tested. These illustrative examples are found in Table 4.

TAB LE 4.-COMPOSITION AND COMBUSTION CHARACTERISTICS OF ALUMINUM ALKYL-BASED TRACER FORMULATIONS Weight percent Total Example wt., mg. Physical appearance Combustion characteristics B00 Liquid mostly absorbed by solids. 800 Pastas; liquid just absorbed 3(0)?) Pastazliquid completely absorbed Bright yellow sustained flare.

Dglayed ignition. Bright yellow sporadic are.

-- No spontaneous ignition.

Sporadic, spread-out yellow ilare.

Sporadic yellow flare.

Sustained yellow flare.

Sustained light-yellow iiare.

Do. Fast, light-yellow flash. Bright, yellow sustained flare. Delayed ignition. Slightly sporadic bright,

yellow flare. No spontaneous ignition. Spontaneous ignition. Red flare. Sporlgdie, very bright, red flare.

No spontaneous ignition. Sporadic red flare.

Do. Sustained red flare. Two discrete sustained red flares. Sustained flare, red at first turning to white.

l TEA/TMA is a :50 mole percent mixture of triethylaluminum and trimethylaluminum.

EXAMPLES 25-32 According to the procedure set forth in Example 2, suitable tracer formulations are prepared having the following compositions:

Weight percent of component Example TEA number Mg Zr NaClOs Sr(ClO4)a TEA TMA TMA 1 TEA/'IMA is a 50:50 mole percent mixture of triethylaluminum and ri methylaluminum.

EXAMPLE 33 In a nitrogen box under anhydrous conditions, a blend of 250 mg. of powdered magnesium and 150 mg. of sodium chlorate was made in a 10 x 75 mm. test tube. A 5.56 mm. tracer projectile was placed nose down in a holder and 100 mg. of the blend was added to the tracer cavity. This blend filled the projectile to about ,4,; of an inch below the top of the cavity opening. Then 25 mg. of an equimolar mixture of triethylaluminum and trimethylaluminum was added dropwise from a calibrated dropping pipette. The final mixture was 50 weight percent magnesium, 30 weight percent sodium chlorate, and 20 weight percent TEA/TMA. A square of aluminum foil tape containing an acrylic adhesive was cut to fit, placed over the cavity, and the corners pressed down along the sides to seal the tracer material into the cavity. The projectile was removed from the holder, inverted in the nitrogen box, and left standing for 24 hours. After this time there appeared to be no leakage of the tracer material from the cavity.

From the data in Table 4 it should be recognized that this invention also provides an improved tracer formulation which is useful in the same manner as the formulations given above. Thus another aspect of this invention lies in a composition suitable for use as the active material in a tracer projectile including an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical, an inorganic oxidizer, and a metal, the improvement comprising said metal being zirconium. A preferred improved tracer formulation has the following composition of from at least about 5 to about 60 percent by weight of an alkylaluminum compound having not 10 more than 4 carbon atoms in each alkyl radical, from at least about 10 to about 40 percent by weight of an inorganic oxidizer, and from at least about 30 to about 75 percent by weight of zirconium in finely divided form. In all cases the alkylaluminum and inorganic oxidizer are similar to those described hereinabove.

The tracer formulations are useful in small arms, artillery, anti-aircraft and similar weapons. With very little modification the formulations may also be useful in devices for military and civilan signalling applications, such as, flares, distress signals, and the like. Other applications will be readily apparent to skilled practitioners of military and civilian pyrotechnics.

The above description is illustrative and the invention should be limited only by the lawful scope of the following claims.

What is claimed is:

1. In a composition suitable for use as the active material in a tracer projectile, said composition including an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical, an inorganic oxidizer, compatible with alkylaluminum and a metal, the improvement comprising said metal being zirconium.

2. A composition of claim 1 wherein said alkylaluminum compound is trialkylaluminum compound.

3. A composition of claim 2 wherein said trialkylaluminum is trimethylaluminum.

4. A composition of claim 2 wherein said trialkylaluminum is triethylaluminum.

5. A composition of claim 2 wherein said trialkylaluminum compound is a mixture of triethylaluminum and trimethylaluminum.

6. A composition of claim 5 wherein said inorganic oxidizer is sodium chlorate.

7. A composition of claim 5 wherein said inorganic oxidizer is strontium perchlorate.

8. A composition of claim 1 wherein said composition comprises:

(a) from at least about 5 to about percent by weight of an alkylaluminum compound having not more than 4 carbon atoms in each alkyl radical,

(b) from at least about 10 to about 40 percent by weight of an inorganic oxidizer, and

(c) from at least about 30 to about percent by weight of zirconium in finely divided form.

References Cited UNITED STATES PATENTS 1,708,186 4/1929 Meek 149-44 X 3,005,693 10/ 1961 Thomas et al 149-87 X 3,247,261 4/1966 DAlelio 149-87 X 3,634,049 1/1972 Burns 149-87 X 3,634,156 1/1972 Batson 149-87 STEPHEN I LECHERT, 111., Primary Examiner US. Cl. X.R.

H050 UNKTED STATES PATENT QFFICE eE-rmmrt er QREC'HN Patent No. 5,788, 908 Dated January 29, 1974 i e Inventor(s) U. vAlbert Lehikoinen and Gerald Franklin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shewn below:

Col. 1, line 5,- assignors should be the said. Lehikoinen a? assignor Col. 1, line 6, after Va, add. and the said Franklin assignor to the United States of America as represented by the Secretary of the Army Signed 'and sealed this 18th day of February 1975.

(SEAL) Attest:

a 8 c. MARSHALL DANN RUTH C MASON Commissioner of Patents Attesting Officer and Trademarks 801. 1, line 5,- f'assignors" 53 3 UNITED STATES PATENT OFFICE CE'RTIFECATE 0F CORRECTION Patent No. 5,788,908 Dated January 29, 197

Inventofls) U. .Albert Lehikoinen and Gerald. Franklin It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shewn below:

should be the said Lehikoinen 1 assignor Col. 1, line 6, after Va. add. and the said Franklin assignor to the United States of America as represented. by the Secretary of the Army Signed and sealed this 18th day of February 1975.

(SEAL) Attest: v a

v c. MARSHALL DANN RUTH c. MASON Attesting Officer Commissioner of Patents and Trademarks UNITED STATES PATENT OFFICE 9 (56) CERTIFICATE OF CORRECTION Patent No. 5,788,908 Dated January 29, 197M U. Albert Lehikoinen and Gerald Franklin Inventofls) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

601. 1, line 5, "assignors" should be the said Lehikoinen .1

assignor Col. 1, line 6, after Va. add and the said Franklin assignor to the United States of America as represented by the Secretary of the Army Signed and sealed this 18th day of February 1975.

(SEAL) Attest:

C. MARSHALL DANN RUTH C MASON Commissioner of Patents Attesting Officer and Trademarks