US3133842A - Propellant compositions containing oxyphylic and halophylic metals - Google Patents

Description

May 19, 1964 D. K. KUE HL PROPELLANT CO MPOSITIONS CONTAINING OXYPI-IYLIC AND HALOPHYLIC METALS Filed Feb. 2, 1961 0 o O o 0 0 use FIG-

N BINARY MIXTURE METAL BY WEIGHT I I0 20 PERCENT OF EACH o o 7 n 4 I I G. 2.

INVENTOR. DONALD K.

BY b Way,

KUEI-IL ATTORN EYS United States Patent ()fi 3,133,842 Patented May 19, 1964 ice 3,133,842 PROPELLANT COMPOSETIONS CONTAINENG OXYPHYLIC AND HALOPHYLIC METALS Donald K. Kuehl, Manchester, Conan, assignor to United Aircraft Corporation, East Hartford, Conn, 21 corporation of Delaware Filed Feb. 2, 1961, Ser. No. 86,613 11 Claims. (Cl. 149-19) I This invention relates to jet propulsion and more particularly to propellants having enhanced performance characteristics which are useful in connection therewith.

Although the present invention is capable of use in connection with a wide variety of transportation and military equipment, it is especially applicable in the field of aviation, to propel, for example, missiles, rockets, jet aircraft, and the like.

It is an object of the present invention to provide means for enhancing the burning rate, efficiency of combustion and specific impulse of fuels.

It is another object of the present invention to provide fuels having enhanced burning rates, efiiciency of combustion, and specific impulse.

Still another object of the present invention is to provide metal additives which may be incorporated into fuel to improve the performance characteristics thereof.

' Other objects 'of the present invention will in part be obvious and will in part appear hereinafter.

According to the present invention, it has been discovered that fuel performance characteristics are improved by the addition of a mixture of particular metals or metal alloys to propellants of the type that comprise chemically combined oxygen and halogen.

The mixtures of metals or metal alloys may be described as systems which comprise one or more oxyphylic metals, i.e., metals having an affinity for oxygen, and one or more halophylic metals, i.e., metals which have an affinity for halogen. By afiinity for halogen or oxygen is meant the preference of the metals to combine chemically with halogen or oxygen, respectively, at the temperature of combustion of the fuel. Whether the metallic additives are alloys or mixtures of halophylic metals and oxyphylic metals, the proportion .of the halophylic metal or metals to the oxyphylic metal or metals in the additives should be carefully controlled.

Assigning the halophylic and oxyphylic metals making up the additives disclosed herein their normal valences, the gram equivalent weight ratio of halophylic metal or metals to oxyphylic metal or metals in the mixtures and alloys making up the additives may vary between about 0.25 and 3.0, is usually between about 0.5, and 2.0, and is preferably between about 0.75 and 1.5 times the gram equivalent weight ratio of available halogen to available oxygen in the solid propellant. Optimum results are achieved when the gram equivalent weight ratio'of halophylic metal or metals to oxyphylic metal or metals mak- .ing up the metal additives is approximately equal to, or

varies within percent of, the gram equivalent weight ratio of available halogen to available oxygen in the propellant. j f

By available halogen and available oxygen is meant halogen and oxygen which would leave the fuel or propellant, uponcombustion, uncombined with other materials "were it not for the presence of the additives disclosed -herein.- I r e a Preferably, enough of the metallic additives disclosed ,herein should be' added to the propellants to insure that -there is adequate halophylic metal or metals present in 1 the propellant to stoichiometn'cally react with the avail- :able halogen in the propellant, and enough of the oxyphylic metal or metals present to stoichiometrically react With the available oxygen present in the propellant. Although the amounts of halophylic and oxyphylic metals present in the fuels may vary, respectively, between about 25 and 300 percent of stoichiometric requirements, the amounts are usually between about and 150 percent, and preferably between about and percent of stoichiometric requirements.

As will be clear from the following, the amounts of the additives incorporated into the fuel will generally be a function of the oxygen and halogen stoichiometry of the fuel. In general, the additive will comprise at least about 1 percent, and usually at least about 5 percent or between about 5 and 40 percent by weight of the fuel.

In calculating the requirements of the oxyphylic metal, the amount of oxygen required to combine with the carbon in the binder may be taken into consideration, and deducted from the total available oxygen, inasmuch as the oxygen combining with the carbon does not have to be taken up by the oxyphylic metal or metals. Likewise, in calculating the halophylic metal requirements, the halogen content of the binder, or other materials incorporated into the fuel, it any, may be taken into consideration and added to the total halogen. Also, when chemicals are incorporated into the fuel which have halogen already combined with a metal, e.g., K010 LiClO and so forth, the amount of halogen already combined with a metal may be deducted from the total available halogen.

Whether or not a metal is oxyphylic or halophylic depends on a number of considerations, including free energy and temperature. Some materials, for example, exhibit halophylic characteristics at a given temperature and oxyphylic characteristics at other temperatures. Such metals, as will be obvious, may change from oxyphylic to halophylic, and yice versa, with temperature change. Whether or not a given material is halophylic also depends to a certain extent 011 other metals in the environment in which it finds itself. Thus, in the systems of metals described herein, a certain metal may be halophylic or oxyphylic depending upon the nature of the other metal or metals in the system. The appropriately calculated free energies of the metals can be referred to, to indicate whether a particular metal will exhibit oxyphylic or halophylic characteristics in the system.

Although based on free energy considerations there are potentially a large number of metal pairs or pairs of mixture of metals which will be sufiiciently different in their afiinities for oxygen and halogens to be classified as oxyphylic-halophylic combinations, some of the metals in such potential combinations are more suitable for use in the present invention than are others. Thus, for example, some of the metals suitable for use in such combinations, although satisfying the free energy requirements to be oxyphylic or halophylic may have low heats of reaction, or low density, or other adverse properties, thereby rendering them less suitable for use than are metals which have, for example, high heats of reaction and/or high density. Although all such metal pairs or pairs of mixtures of metals will follow the principles described hereinabove, the metals in the following series, because of density, heats of reaction and other pertinent properties, are especially suitable for use, and

are preferred:

As arranged in this series, the afiinity of the metals for oxygen decreases from top to bottom, and the aifinity of the metals for halogen decreases from bottom to top.

As arranged in this series, if any pair of metals is selected, the first listed will be oxyphylic and the second listed will be halophylic for that particular pair. For example, beryllium, in combination with any other metal on the list, will be oxyphylic while the o'ther metal will be halophylic. Lithium, on the other hand, will be halophylic with any other metal on the list except sodium, for which case lithium is oxyphylic and sodium halophylic.

When pairs of mixtures of metals are employed, the metals making up the oxyphylic portion of the. additive will be higher in the series than the metals making up the halophylic portion of the additive. Thus, for example, a suitable additive may comprise beryllium and aluminum as the oxyphylic portion and calcium and lithium as the halophylic portion. Other suitable pairs of metals or pairs of mixtures of metals will readily suggest themselves from the foregoing description.

The pairs of metals or pairs of mixtures of metals forming an oxyphylic-halophylic system as described above enhance the burning time, efficiency of combustion and specific impulse, and, accordingly, the payload capacity of weight limited solid propellant rockets. Although systems of these oxyphylic and halophylic metals may enhance the described characteristics of volume limited solid propellant rockets, in general, it may be said that the improvement in these characteristics with volume limited rockets is not as great as the improvement with weight limited rockets.

For volume limited solid propellant rockets, a mixture of aluminum and beryllium has been found to considerably enhance the performance characteristics of the fuel, as will be made clear hereinoelow. In this system, aluminum acts as the halophylic metal and beryllium as the oxyphylic metal. The proportion of aluminum (halophylic metal) and beryllium (oxyphylic metal) added to the fuel is based on maximum density specific impulse, rather than on stoichiometry, however.

Although the metal additives comprising oxyphylic and halophylic metals may be added to a wide variety of fuels comprising oxygen and halogen, they are especially useful with propellants, and more particularly solid propellants, containing chemically combined oxygen and halogen as, for example, in the oxidant portion of the propellant.

As examples of oxidants having halogen chemically combined therewith may be mentioned ammonium and nitronium chlorate, bromate, iodate, fiuorate, perchlorate, perbromate, periodate, perfiuorate, and so forth. It is clear from the foregoing that the oxidants for use in this invention are halogen containing non-metallic oxidants which release, on heating, free oxygen and free halogen. Other oxidants of this type will readily suggest themselves to those skilled in the art.

In addition to the halogenated oxidizers described above, the solid propellants useful in carrying out the present invention may include a binder such as saturated or unsaturated hydrocarbons, halogenated hydrocarbons, polymeric organic compounds, and so forth. Thus, if desired, the binder for the solid fuel can be asphalt, cellulose, rubber, including natural rubber and synthetic rubbers such as butadiene-methylvinyl-pyridine copolymer or butadiene-styrene copolymer, or other suitable organic binder materials. If desired, a high energy nitropolymer, which could provide additional energy for the system, can also be used as the binder.

Depending on the nature of the binder, curing agents such as quaternizing or vulcanizing agents may be incorporated thereinto. The propellant may also include suitable burning catalysts such as rouge, ammonium dichromate, Prussian blue, Milori blue, and the like.

In preparing the propellants disclosed herein, the metal additives, whether a physical admixture or an alloy of the oxyphylic and halophylic metals, are preferably employed in a finely divided state of subdivision. The average particle size of the metal additive should be small enough to insure good dispersion of the additive through out the fuel composition. In general, the average particle size of the metal additive will be less than 200 microns, and usually less than 147 microns. Particularly good results are achieved when the average particle size is between about 10 and 147 microns. The finely divided metal additive, binder, and halogenated oxidant, and other suitable ingredients, as indicated hereinabove, are then mixed together to provide a homogeneous mixture with the additive evenly dispersed throughout.

The amount of binder incorporated with the powdered metal additive and the oxidant will ordinarily be the optimum amount required to maintain the powdered metal additive, the oxidant and other materials which may be present, in a coherent mass having the required structural strength to withstand storage and handling. The utilization of ordinary techniques for the incorporation of fairly viscous polymeric compounds containing as little as 5 weight percent of binder, will produce a satisfactory solid product. A special technique will produce solid grains of powdered fuel containing as little as one Weight percent of binder. This special technique comprises intimately admixing the powderedmetal additive and oxidant, as well as the other ingredients with an excess of a fluid binder material such as lacquer or shellac and centrifuging the mixture to remove excess fluid. Although there is really no upper limit to the amount of binder employed, when the binder is carbonaceous in nature, the amount of binder employed should be low enough to insure the availability of oxygen in excess of that required to stoichiometrically react with the carbon of the binder. Otherwise, there would be no available oxygen to combine with the halophylic metal. With this thought in mind, good results have been achieved with as high as 50% or more of binder, based on the weight of the fuel or propellant. After molding, or extruding, and curing, a dense charge of high structural strength is obtained.

Typical examples of the solid rocket propellants produced in accordance with the present invention are indicated in the following table.

T able I Formula 1, Formula 2, Percent Percent By Wt. By Wt.

Ammonium perchlorate 70 70 Hydrocarbon binder (0.111%) 10 15 Burning metal alloy 20 15 Typical examples of the burning metal alloy which may be used with the fuel compositions identified as l and 2 in Table I are indicated in Table II.

The above examples of solid rocket formulations and metal alloys, it should be noted, are merely illustrative of operative embodiments of the present invention, and are not intended to limit the invention, except as such limitations may appear in the claims. The oxidizer and binder in Formulae 1 and 2, for example, may be any of those described hereinabove, and metal additives other than those described in Table 11, may be used, as will be clear from the foregoing.

In the case of volume limited solid propellant rocket fuels having the general composition identified as l and 2 in Table I, an alloy or mixture of aluminum and beryllium comprising between about 15 and 40 percent by weight beryllium is highly effective in enhancing the performance characteristics of the fuel. In general, the amount of said mixture or alloy added to the volume limited solid propellant rocket fuel may vary between about 4 and 40 percent by weight of the fuel, and is preferably between about 15 and 25 percent by weight of the fuel.

The improvement in performance characteristics of fuels by carrying out the teachings of the present invention will be clear from the accompanying drawings.

FIGURE 1 is a plot of payload capabilities for a propellant comprising, by weight, 70 percent ammonium perchlorate, percent of solid saturated hydrocarbon binder having the theoretical formula C H and 20 percent of a binary alloy of lithium and beryllium. FIGURE 1 shows the effect of varying the proportions of lithium and beryllium on the payload capacity. The calculations for determining the payload capacity shown in FIGURE 1 are made on an IBM 704 calculating machine programmed on the basis of isobaric, isenthalpic combustion and isentropic, adiabatic, reversible expansion through the nozzle from 1000 to 14.7 p.s.i.g. The payload capacities indicated in FIGURE 1 are for a weight limited rocket of 18,000 pounds gross weight and 2100 mile range. As is apparent from FIGURE 1, maximum payload capacity occurs when the binary metal additive comprises between about 18 and 40 percent by weight of lithium, and between about 82 and 60 percent by weight of beryllium.

Although FIGURE 1 is a plot of theoretical values, it is representative of the comparative improvement in performance for the fuel systems indicated hereinabove.

FIGURE 2 is a plot of relative payload capabilities in terms of density specific impulse for a propellant comprising 70 percent by weight ammonium perchlorate, 10 percent by weight of solid saturated hydrocarbon binder having the formula C H and 20 percent by weight of a binary alloy of aluminum and beryllium. As may be seen from FIGURE 2, the maximum payload capacity of the fuel is optimum when the composition of the binary alloy is between about and 40 percent by weight of beryllium and 85 and 60 percent by weight of aluminum.

Although mixtures or alloys of the metals described herein may be employed, it should be understood that alloys are preferred for the reason that they may provide greater density of the metal components than does a mixture of metals, and will have superior combustion characteristics, as will be understood by those skilled in the art.

The invention in its broader aspects is not limited to the specific details shown and described but departures may be made therefrom within the scope of the accompanying claims without departing from the principles of the invention and without sacrificing its chief advantages.

What is claimed:

1. A volume limited solid propellant rocket fuel consisting essentially of a halogen containing non-metallic oxidant, a binder, and a mixture of metals comprising aluminum and beryllium, the amount of beryllium in said mixture being between about 15 and 40 percent by weight of said mixture and the amount of aluminum in said mixture being between about 85 and 60 percent by weight of said mixture, both the oxygen and the halogen of the non-metallic oxidant being available for chemical combination with the mixture of metals.

2. The volume limited solid propellant rocket fuel of claim 1 wherein said mixture is an alloy.

3. The fuel of claim 1 wherein said mixture comprises between about 4 and 40 percent by weight of the fuel.

4. A fuel composition comprising an intimate mixture Beryllium Boron Aluminum Titanium Zirconium Calcium Magnesium Lithium Silicon Sodium the indicated arrangement of members in said group being such that the affinity for oxygen decreases from top to bottom and the afiinity for halogen decreases from bottom to top, the gram equivalent weight ratio of the oxyphylic member to said halophylic member being approximately equal to the gram equivalent weight ratio of available oxygen to available halogen in the fuel composition, and the quantity of said metal additive being between about 1 and 40%, based upon the weight of the fuel composition.

5. The fuel composition of claim 4, wherein the gram equivalent weight ratio of the oxyphylic member to the halophylic member is within about 10 percent of the gram equivalent weight ratio of available oxygen to available halogen in said composition.

6. A fuel composition comprising an intimate mixture of a halogen containing, non-metallic oxidant, a finely divided metal, and a binder, the oxygen and halogen of the non-metallic oxidant being available for chemical combinations with the metal additive upon ignition, and the finely divided metal comprising lithium and a member selected from the group consisting of beryllium, alumi num, zirconium, magnesium, silicon, boron, titanium, calcium, and mixtures of the foregoing, the gram equivalent weight ratio of said member to lithium being between about 0.25 and 3.0 times the gram equivalent weight ratio of available oxygen to available halogen in the fuel composition, the total amount of metal being between about 1 and 40%, based on the weight of the fuel.

7. The fuel composition of claim 6 wherein said member is beryllium.

8. The fuel composition of claim 4 wherein the amount of said oxyphylic member is between about and of that stoichiometrically required to combine with the available oxygen, and the amount of the halophylic member is between about 95 and 105% of that stoichiometrically required to react with the available halogen.

9. The fuel composition of claim 4 wherein the binder contains halogen which is also available for combination with the halophylic rnetal upon ignition.

10. A solid propellant rocket fuel composition comprising, based on the weight of the composition, from about 1 to 40% of a mixture of lithium and at least one member selected from the group consisting of beryllium, aluminum, zirconium, magnesium, silicon, boron, titaniurn, calcium, and mixtures of the foregoing; a hydrocarbon binder, from about 1 to 50%; and an oxidant selected from the group consisting of ammonium and nitronium chlorates, bromates, fluorates, perchlorates, perborates, periodates, perfluorates, and mixtures of the foregoing; the quantity of lithium being between about 95 and 105% of that stoichiometrically required to react with the halogen in the oxidant, and the quantity of said member being between about 95 and 105% of that stoichiometrically required to react with the oxygen of the oxidant.

11. A solid propellant rocket fuel composition comprising up to about 70 percent by weight of a member selected from the group consisting of ammonium and nitronium chlorates, iodates, bromates, fluorates, perchlorates, perborates, periodates and perfluorates, and mixtures of the foregoing; between about 10 and 15 percent by weight of a hydrocarbon binder; and between about beryllium; and aluminum, 8 to 50 weight percent, remainder beryllium.

References Cited in the file of this patent UNITED STATES PATENTS Fox Mar. 1, 1960 Perry et al Mar. 22, 1960. Walden June 20, 1961 Bice Aug. 8, 1961 Pierce et a1. Nov. 28, 1961

Claims (1)

1. A VOLUME LIMITED SOLID PROPELLANT ROCKET FUEL CONSISTING ESSENTIALLY OF A HALOGEN CONTAINING NON-METALLIC OXIDANT, A BINDER, AND A MIXTURE OF METALS COMPRISING ALUMINUM AND BERYLLIUM, THE AMOUNT OF BERRYLLIUM IN SAID MIXTURE BEING BETWEEN ABOUT 15 AND 40 PERCENT BY WEIGHT OF SAID MIXTURE AND THE AMOUNT OF ALUMINUM IN SAID MIXTURE BEING BETWEEN ABOUT 85 AND 60 PERCENT BY WEIGHT OF SAID MIXTURE, BOTH THE OXYGEN AND THE HALOGEN OF THE

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