Laminated tape propellants

Dec. 1, 1964

Filed Nov. 2, 1959

J. E. HODGSON 3,159,104

LAMINATED TAPE PROPELLANTS 2 Sheets-Sheet 1

<img file="US3159104A_D0001.tif" />

-ATTORNEYS

Dec. 1, 1964

3,159,104

J. E. HODGSON

LAMINATED TAPE PROPELLANTS

Filed Nov. 2, 1959

Sheets-Sheet 2

<img file="US3159104A_D0002.tif" />

3,159,104

Patented Dec. 1, 1964

United States Patent Office

3,159,104

LAMINATED TAPE PROPELLANTS

James E. Hodgson, Cleveland, Ohio, assignor to Solid Fuels Corporation, Cleveland, Ohio, a corporation of Ohio

Filed Nov. 2, 1959, Ser. No. 850,387

Claims. (CI. 102—98)

The present invention relates to a propellant suitable for use in rocket engines, ram-jet engines, and torpedo engines, as well as a method of making the same. This application is continuation-in-part of application No. 849,130, filed February 18, 1959.

At the present time solid propellants are generally considered to be limited in performance by the amount of high energy metals or metalloids that can be included in their compositions. Thus, the solid propellants capable of delivering the highest performance in terms of high energy release generally contains some finely divided metals such as aluminum powder, beryllium powder and the like. However, these metal particles are included as a dispersed phase in a binder along with oxidizer particles. The amount of metal particles which can be put into a solid propellant is limited since too many metal particles and subequent reduction in organic binder concentration greatly effect the physical quality of the propellant as far as structural properties, stability, handling and storage are concerned. As the metal concentration rises in the propellant, the metal particles and oxidizer particles are brought into more intimate contact and generally this contact results in even faster burning rates which can be detrimental because, although, often a high energy release is desired, the energy is preferably delivered at a nonexplosive or even a relatively slow rate. Again, as the amount of metal particles rise, the higher the combustion temperature and the higher the thermal conductivity of the propellant. The high combustion temperature, and close particles proximity, etc. is dangerous because it can lead to detonation rather than burning.

Another problem in preparing solid propellants is that very difficult to incorporate metal hydride particles therein because they are much more sensitive to oxidation and to degradation by reaction with any moisture and moisture sensitized oxidizer present than are the metal particles.

It is therefore an object of the present invention to provide an improved solid propellant in which the oxidizer and fuel particles are supplied partly or completely in the form of separate layers, the fuel layer being rich in metal particles including highly desired metal hydride particles.

It is an object of the present invention to incorporate oxidizer particles and metal particles and to a propellant by means of separate fuel layers and oxidizer layers, said layers being relatively thin and so constructed and arranged that the burning of the layers provides a very high release of energy with a fast or relatively slow burning rate as desired.

It is an object of the present invention to provide a solid propellant in which fuel particles are provided in a first layer and oxidizer particles are provided in a second layer, the layers being relatively thin and laminated together so that burning of the two layers provides a high energy release at a fast or relatively slow burning rate as desired.

It is an object of the present invention to provide a method of incorporating in a solid propellant metal hydride particles which are not easily subject to deterioration by moisture or by oxidation and in which the metal hydride particles are supplied in the form of a thin fuel layer and disposed in the propellant generally adjacent the oxidizer layers so that burning of the two layers provides a large amount of energy at a slow burning rate.

It is an object to provide a cylindrical propellant comprising a plurality of fuel layers and a plurality of oxidizer layers in which the fuel and oxidizer layers are alternatively laminated to form a structure in which the layers of fuel and oxidizer are so constructed and arranged that the layers burn with a high release of energy at the desired rate.

It is an object of the present invention to provide a propellant comprising a fuel layer and an oxidizer layer laminated so that said layers are disposed adjacent each other and at least one of said layers has a thin combustible plastic backing.

It is an object of the present invention to provide a method of forming a solid propellant by mixing a fuel material in a liquid binder, hardening said binder to suspend said fuel particles therein to thereby form a fuel layer sheet by casting, extrusion or other means, forming an oxidizer layer by mixing oxidizer particles in a liquid binder and hardening said binder to suspend oxidizer particles therein to form an oxidizer sheet by casting, extrusion or other means, and alternately laminating said fuel and oxidizer sheets with a very thin adhesive film to form a propellant or laminating the semi-polymerized sheets with or without extra adhesive.

Other objects will be apparent from the description that follows, the appended claims, and the drawings, in which:

FIG. 1 is a perspective view of a laminated propellant made according to the present invention showing an alternate arrangement of fuel layer and oxidizer layers;

FIG. 2 is another embodiment of the present invention showing a laminated propellant having a generally rectangular cross section;

FIG. 3 shows a cross sectional view of a propellant having a laminated structure and in the form of another embodiment, the view being taken along the lines indicated at 3—3 in FIG. 1;

FIG. 4 shows a cross sectional view of a laminated propellant made according to the present invention and carried in a combustion chamber of a rocket engine;

FIG. 5 is a cross sectional view of a laminated propellant utilized in a combustion chamber of a torpedo engine;

FIG. 6 is a sectional view taken along the lines indicated at 6—6 in FIG. 5; and

FIG. 7 is a sectional view of another embodiment of a laminated propellant on an enlarged scale.

The present invention provides an improved solid propellant in which the metal particles are incorporated therein by means of a separate relatively thin fuel layer and the oxidizer particles are incorporated therein also by means of a thin separate layer. The layers are laminated to be positioned approximately adjacent each other in the propellant and the oxidizer and fuel layers are so constructed and arranged that the burning thereof produces a very high release of energy but at a fast or relatively slow burning rate as desired. The propellant of the present invention and the method of making the same can be used even to incorporate metal hydride particles therein with little danger of deterioration in handling and storage due to oxidization or moisture attack, or degradation during manufacture.

FIG. 1 shows a preferred form of a laminated solid propellant according to the present invention. As seen therein, an improved propellant 5 is made by laminating a relatively thin fuel layer sheet 6 and a relatively thin oxidizer sheet 7 together by preferably winding them around each other to build up a generally circular cross sectional area. When the laminated propellant of FIG. 1

3,159,104 is burned, the alternate arrangement and positioning of the oxidizer particles with respect to the metal particles by virtue of their respective oxidizer and fuel layers provide a high release of energy and yet the laminated structure slows such high release of energy down to a controllable desirable burning rate which is especially desirable in large diameter rockets so that not all the energy is released too rapidly and detonation results. The laminated structure of FIG. 1 also tends to reduce the combustion flame propagation rate and, thus, the tendency of the propellant to detonate. It is understood that the sheets may be wound together in spiral fashion to produce an excellent propellant material.

FIG. 2 shows a laminated and burning propellant 9 in which the cross sectional area is generally rectangular. The propellant 9 is made of relatively thin fuel layer 10, a relatively thin oxidizer layer 11. The thin fuel layer 10 has a very thin backing layer 13 of a combustible plastic material such as poly tetrafluoroethylene or polyethylene. The oxidizer layer 11 also has a thin combustible backing layer 14 of poly tetrafluoroethylene or polyethylene, or cellulose nitrate.

Still another form of a laminated structure is shown in FIG. 3 in which a propellant 16 is depicted comprising relatively thin fuel layers 17 disposed radially between disposed oxidizer layers 18 which are generally thicker than the fuel layers. The cross section of propellant 16 is generally circular and the layers 17 and 18 run longitudinally the length thereof so that the layers in the cross sectional view are radially disposed about the 30 central longitudinal axis of the propellant, the general appearance being similar to an orange sliced in half and having frusto conical shaped sections about the center.

FIG. 4 shows another improved solid propellant 19 in the form of laminated fuel and oxidizer sheets having 35 alternate fuel layers 20 and oxidizer layers 21. As shown in FIG. 4, the right side of the figure is a generally forward portion of the propulsion device. The engine shown may be utilized in a fully controllable rocket since additional oxidizing material is supplied in the form of a 40 tank of hydrogen peroxide or perchloryl fluoride 31 in the left side of the figure. The oxidizer tank is auto pressurized by heat taken as demanded by a pressure sensitive valve 36 from the oxidizer nozzle coolant 38 return line, which may be diverted through the oxidizer 45 pressurizing coil 37 before injection at 34 for reaction with the laminated propellant and aiding and controlling combustion thereof.

As shown in FIG. 4, the rocket engine consists of a casing 30 with a forward oxidizer cell 31α, a nozzle 32 and a central portion 33. The oxidizer cell 31 houses control valve 36 and 39, the auto pressurizing coil 37 and the injector 34. The central chamber 33 contains a propellant made up of the alternate fuel layers 20 and oxidizer layers 21. In the embodiment shown in FIG. 4 55 the propellant has its outer surface adapted to conform with the inner surface of the casing 30 and may be treated with combustion inhibiter in the usual way. Passing through the charge 19 is a longitudinal passage 35. -.-- - —----- vaauy uepusiung

Tbis passageway may be cylindrical but also may be star- 60 oxidizer particles and a liquid binder therefor shaped, or, instead of one central longitudinal passageway, -there may be a plurality of relatively smaller passageways or any other well known burning surface design to provide suitable mass flow according to the requirements of the rocket.

fh FIG. 5, a laminated tape propellant 40 is shown in a torpedo engine 41. As therein illustrated, the propellant 40 comprises a plurality of fuel layers 45 alternately sandwiched between a plurality of oxidizer layers ΎΙαλ ΙολλΙ-, ______11. , · J shape and generally circular in cross section'and'has a central cavity longitudinally extending the length thereof which is filled with a fuel composition 48 comprising and^C°K^i^^{S p}“^ticl®^{s such as llth}ium uj. uuu jiiopeiiani layers with thin fuel and lithium hydride which may be bound with a low 75 thin oxidizer layers. In the embodiment shown, the melting waxy material or other suitable binder. A chamber 50 is provided to house the propellant and disposed between the laminated layers of fuel and oxidizer, layers 45 and 46 respectively, is a relatively thin outer jacket layer 49 comprising a low melting, semi-solid easily fusible material such as petroleum jelly. The semi-solid layer 49 provides lubrication between the chamber and the main propellant charge when it is extruded or moved towards the rear of the engine.

A combustion chamber 52 is provided for burning the propellant. The propellant is pushed into the combustion chamber 52 where it is burned with a liquid oxidizer 55 which is hydrogen peroxide. The hydrogen peroxide is carried in an annular chamber 56 which is jacketed around the propellant housing chamber 50.

In accordance with the present invention, a piston 58 pushes the laminated propellant through a ring 59 which has a central opening 60 which is smaller in cross sectional area than the chamber 50. The piston 58 is forced against the fuel slug by a propellant charge 62 which can be cordite, a smokeless powder which is a mixture of nitrocellulose and nitroglycerin. The burning of the propellant 62 causes pressure to be exerted against the piston 58 as well as pistons 63 and 64 which, in turn, pressurize the hydrogen peroxide.

The hydrogen peroxide, thus, is forced into the combustion chamber 52 through conduits 67 and injected therein by injector means comprising a series of slits 69 which are disposed around the inner periphery of the combustion chamber near the point at which the propellant slug enters said chamber.

In any of the above described engines, sometimes it is advantageous to place a conventional propellant layer (containing both fuel and oxidizer particles) between the fuel layers and the oxidizer layers. It has been found also that when the oxidizer layer contains some aluminum particles or other metal in finely divided form which may or may not be coated with a protective film of polymerized resin, good results are obtained aparently, the aluminum particles present in 2 to 25% by weight are needed to vaporize the fuel layer and thus promotes combustion since the burning generally starts at the interface of the oxidizer and fuel layers.

As seen in FIG. 6, the hydrogen peroxide 55 is injected into the combustion chamber to combine chemically with the portion of the propellant that has been pushed therein to provide an end burning surface for the release of energy for propulsion. In addition to the energy obtained from the laminated propellant portion, the ^core’.which preferably has a high concentration of lithium, lithium hydride particles or can be even an exotic metal or metalloid powder solidly or even loosely packed therein, also provides a large amount of energy for propulsion when burned with the hydrogen peroxide. In FIG. 7, a. cross sectional view of a laminated propellant 70 comprising a plurality of oxidizer layers 72 containing an oxidizer material 73 which is embedded in and around the wires of an aluminum wire screen 75. The layer 72 can be made easily by depositing a mixture of the surface tension, etc. of the liquid holding the mixture on the wire until it is hardened. The propellant also contains a plurality of fuel layers 77 which contain metal particles such as lithium particles and a suitable binder gg therefor.

Disposed between some of the fuel and oxidizer layers are propellant layers 80 which comprise metal containing particles 81 such as lithium hydride in a suitable binder therefor along with oxidizer particles comprising an oxwhich is jacketed with a tough thin piasticffim 85 of a material such as an epoxy resin.

The laminated propellant in FIG. 7, thus, provides a combination of thin propellant layers with thin fuel and , . _: pro50 'Tt.^ 1 _· A J n . ^J xajcia — c*xv»x±_e wilai MA1U1Z.C1 DcU LiUlcS ΟΟΠ1ΡΓ18ΙΠ£ &amp;Π OX.^d⁷⁰ 1°?J³ °* ^a “^{aterial Such as} lithium perchlorate

3,159,104 pellant layer advantageously and unexpectedly provides active oxidizer particles with usually reactive lithium hydride particles without the danger of premature reaction, the thin tough plastic film prevents any reaction of the oxidizer particles until it is melted or burned away.

The aluminum wire screening material may be any screen of a fine mesh size such as 200 to 325 mesh screens or finer. The screening may also be made of fine guage magnesium or lithium wire, or of their alloys with or without aluminum.

A quilted metal foil preferably of aluminum may also be used in place of the fine aluminum screening. In that case, the oxidizer material is deposited mainly in the valleys between the peaks in the foil.

The thin plastic film 85 may be any tough combustible film such as one of polyethylene, polyurethane, etc. or any of those plastic materials described as useful as backing layers for the laminated tapes.

As previously indicated it is important in the present invention that at least some of the metal particles, and preferably a majority of the metal or metalloid particles are incorporated in the propellant charge by means of thin fuel layers in which the fuel particles, preferably metal and metalloid (metal hydrides borides and carbides) particles, are dispersed uniformly in a suitable binder therefor. The metal particles which are bound up in the fuel layers may comprise high energy, high heat releasing, exotic metal and metalloid particles such as metals including magnesium, lithium, aluminum, boron, beryllium or even titanium and their borides carbides and hydrides such as decaborane aluminum hydride, lithium hydride, beryllium hydride, lithium boro hydride, lithium aluminum hydride, beryllium carbide, lithium carbide, aluminum carbide, beryllium carbide, boron carbide, silicon carbide, carbon, silicon, etc.

Suitable binders may be any plastic or rubbery binder such as organic polyurethanes polysulphide rubber, natural rubber, butadiene styrene copolymers, polyethylene, polytetrafluoroethylene, and all binders well known in the propellant art, including double base nitro and nitrated compositions such as cordite, or metal binders such as lithium alloys of lithium with magnesium and aluminum and alloys of aluminum with lithium and magnesium or waxy binders such as petroleum jelly, paraffin wax, naphthalene and triphenyl methane.

Of the above binders, a higher energy release is provided by the metal binders, of which lithium, magnesium, and alloys of magnesium and aluminum and alloys of lithium with magnesium and aluminum are highly preferred. With these metal binders, heavy metals such as copper may be added in small amounts, say up to 2%, to improve physical properties. On the other hand, if there are any applications in which a laminated propellant can be extruded into a burning chamber and combined therewith with oxygen and/or fluorine, a low melting waxy binder such as petroleum jelly is preferred for easy handling and its excellent extrudability characteristics at normal room temperature, say 20 to 30° C.

In some applications, for increased combustion rate the fuel or oxidizer binder may comprise a homogenous mixture of nitro-cellulose and nitro-glycerine such as cordite. While the above double-base type of explosive material is preferred, triple-base binders can also be used in which a third explosive base such as dinitro-toluene, mono-nitro phenol and dinitro phenol as used in place of part of the nitro-glycerine.

The oxidizer particles may include percentages of well known explosive material such as RDX (trinitrotrimethylenetriamine) or penta erythritol tetranitrate or any solid nitro compounds i.e. gelignite, trinitro toluene, picric acid, nitro starches, nitro cellulose, nitro guanidine, or usually any conventional solid nitrate, chlorate, perchlorate (both organic and inorganic), such as ammonium nitrate, ammonium perchlorate, hydroxylamine nitrate, hydrazine nitrate, hydrazine dinitrate, hydrazine perchlorate, lithium nitrate, lithium chlorate, lithium perchlorate, urea nitrate, quarternary amine perchlorate, guanidine perchlorate, etc.

In accordance with the present invention, the metal and/or metalloid particles incorporated in a pure fuel layer preferably comprise about 35 to 95 percent by weight of the fuel layer and the balance is then preferably about 5 to 65 percent by weight of binder, whether this be organic or metallic since the fuel can be pure metal such as commercial aluminum foil or its lithium or lithium-aluminummagnesium alloy.

The oxidizer particles incorporated within the thin oxidizer layers preferably comprise about 35 to 95 percent by weight of the oxidizer layer and the balance preferably being a suitable binder therefore, suitable binders being generally the same organic binders described as suitable for suspending the metal fuel particles.

With respect to the binders used for both the metal containing fuel particles and the oxidizer particles, some binders with built-in oxygen and fluorine provide advantage in many applications. These binders are fluorinated polyurethanes, fluorinated polyethylenes or nitro substituted polyurethanes and nitro substituted polyethylenes or polyurethanes or polyethylenes having perchloro substitutents on their main chains, or other hydrocarbon polymers having hydrogen, carbon, with or without oxygen atoms, and in which some of the hydrogen atoms are replaced by nitro or fluorine groups or even perchloro groups.

In one aspect of the present invention, polyurethanes, whether they are fluoro substituted or nitro substituted or nonsubstituted, which are made with excess isocyanate so that they have some isocyanate end groups are particularly advantageous in binding reactive metal and metal hydride particles and the like since the NCO groups are highly reactive towards water and react with any moisture present before admixing the hydride during manufacture and absorbed during storage etc. which might otherwise deteriorate the propellant charges.

Thus, in accordance with the present invention, polyurethanes are suitable as highly adhesive binders or as combustible backing material upon which a fuel and/or oxidizer layer can be deposited or otherwise formed. Polyurethanes, as is well known in the art, are made by reacting polyhydric materials such as polyethers, polyesters or polyamines containing reactive hydrogen atoms with polyisocyanates (which are preferably diisocyanates although some triisocyanates may be used).

Generally, the linear rubbery polyurethanes are formed on the molar ratio of polyether or polyester to polyisocyanate of about 1 to 1. However, as previously discussed, when the diisocyanate or triisocyanate, or mixture of the two are used in amounts in excess over a 1 to 1 ratio of mole equivalent weights, the excess isocyanate groups are present in the polymer which tend to scavange any moisture present during storage, etc. to prevent reaction of moisture with exotic metal or metalloid particles such as lithium, lithium hydride particles etc. to deteriorate the charge prematurely. Suitable polyethers are polyethylene glycol, polypropylene glycol, polytetramethylene ether glycol and fluorinated and nitro substituted derivatives of the same. Suitable polyesters are polyethylene adipate, polypropylene adipate and poly (ethylene-propylene) adipates or succinates, or polyesters such as above with —NO₂ groups and fluorine atoms as substituents on their polymer chains.

Suitable polyisocyanates are ρ,ρ'-diisocyanato diphenylmethane, 2,4-toluene diisocyanate, mixtures of 2,4- and 2,6-tolylene diisocyanates, naphthalene 1,5-diisocyanate, hexamethylene diisocyanate, and ρ,ρ',ρ''-triisocyanato triphenyl methane. As previously indicated, nitro-substituted and fluoro substituted polyurethanes are particularly advantageous because they have built-in oxygen and fluorine for combination with the metal fuel particles. Examples of said fluoro- and nitro-substituted polyisocyanates are 3,5-fluoro, 2,4-toluene diisocyanate, 3,5-ni3,159,104 tro, 2,4-tohiene diisocyanate, 3,3'-difluoro-4,4'-biphenylene diisocyanate, 3,3'-dinitro-4,4'-phenylene diisocyanate, 3,3'-difluoro-4,4'-diisocyanato diphenylmethane, 2,3,5,6tetrafluoro para phenylene diisocyanate.

In accordance with the present invention, the thick- 5 ness of the oxidizer and fuel layers is of importance. Generally, the thickness of each of the above layers may be from about 1 thousandth or thinner to about 250 or even up to 300 thousandths of an inch to provide benefits of the present invention. However, for best results 10 in burning to obtain a high release of energy and at the same time have a relatively controllable burning rate, the thinner the layers the better. Thus, generally a range from about 1 or 2 up to 20 thousandths of an inch in thickness is preferred for most applications. While the 15 thickness may, in some cases, go down below 3 thousandths of an inch down to one-half, one or two thousandths of an inch; such layers are difficult to form and difficult to handle in attempting to form the laminate.

The layers of the present invention as previously in- 20 dicated may be formed on a backing layer which may be very thin, say, from %o,ooo of an inch to about 3 thousandths of an inch of a combustible plastic material such as polyethylene, polytetrafluoroethylene, and polyurethanes or even a thin aluminum, magnesium or lithium 25 foil or a thin metal alloy foil. In this respect, an oxidizer layer or a fuel layer can be adhered to a metal foil or plastic backing layer by a suitable adhesive (polyurethane or epoxide) or merely deposited upon a thin metal or plastic layer mixed but in liquid form and 30 hardened thereon such as one made of aluminum or to secure the same to the backing to provide some benefits of the present invention. However, propellants made with metal foils usually have lower burning rates and only do not have as wide a range of application as do 35 the propellants in which the fuel particles are provided dispersed in a layer rather than in a densified compact foil. Metal foils provide a very rigid and strong propellant when made in the roll form and can be used as an outer case for end or axial burning powder and poly- 40 mer bases.

While the above described metal foils can be used advantageously as backing layers, they may also be used to wrap the whole laminated propellant to add a surprisingly large amount of strentgh to the propellant structure. If the metal foil is devoid of oxidizer and 45 has no thin oxidizer layer adhered thereto, the outer foil also inhibits combustion on the outer surfaces of the propellant structure which is helpful in end-burning propellant applications.

In one aspect of the present invention, the fuel layers 50 and oxidizer layers may be formed advantageously by dispersing metal particles or oxidizer particles in a liquid binder and then hardening the binder suspend the particles homogenously therein. In such a case the liquid binder might be a polyurethane, a polysulphide rub- 55 ber, a polytetrafluoroethylene or the like. The resultant dispersal of particles within the liquid binder can be cast upon a surface such as a thin layer of a polyfluoroethylene backing material. The cast material is then hardened by cooling the material, by driving off any 60 solvent therein or by cross linking or vulcanizing the polymer to obtain a stable homogenous dispersion of the metal particles and metalloid particles or oxidizer particles. The fuel or oxidizer layers also may be produced by extrusion means in which the material is extruded in 65 a thin sheet and rolled down to the required thickness which is generally 3 to 250 thousandths of an inch. The layers may also be produced by casting a liquid binder containing metal particles or oxidizer particles on a surface and hardening the binder to suspend the fuel or 70 oxidizer particles in the sheet, the liquid binder being spread thinly on a sheet. Upon hardening, the layer can be stripped therefrom or can be left then as in the case of a polyfluoroethylene, polyurethane, or metal foil backing sheet. 75

The following examples illustrate the formation of laminated propellants according to the present invention:

Example I

A tape containing fuel particles was made by mixing finely divided decaborane Bi₀H₁₄ particles in an organic binder which was an epoxide based elastomer. The mixture used was 20 parts by weight epoxide and 80 parts by weight of decaborane powder.

The epoxide used was a low molecular weight epoxy resin, EPON 828, which is one of the epoxy resins having molecular weights of 350 to 4000 sold by the Shell Chemical Corporation. EPON 828 is believed to be a liquid condensation product of epichlorhydrin and bisphenol A having an average molecular weight of about 384 and an epoxy equivalent of from about 105 to 200. Three parts by weight of diethylene triamine were also used per 20 parts of the epoxy resin as a curing agent therefor.

A single thin layer in tape form was produced by extruding the above mixture through a die onto a conveyor and to form a flat sheet. The flat continuous sheet then was rolled to a thickness of 3 thousandths of an inch. The rolled layer was interlayered with a polyethylene tape and wound in tension on a mandrel for subsequent processing with an oxidizer layer.

An oxidizer layer was formed by mixing 85 parts by weight of finely divided anhydrous ammonium perchlorate in 15 parts by weight of an epoxide based elastomer under low pressure. The epoxide used was the same one described as suitable for the fuel layer and, again, 3 parts by weight of diethylene triamine was used. The oxidizer sheet was formed by depositing the ammonium perchlorate mixture on the fuel tape of 3 thousandths of an inch thickness, spreading the liquid oxidizer mixture with a doctor knife to obtain a thin even layer, and thereafter polymerizing the binder to form an oxidizer layer of 12 thousandths of an inch thickness bonded over said fuel tape.

The laminated propellant tapes then were simultaneously treated with a micro thick film of liquid epoxide and wound together tightly to form a cylindrical propellant having a circular cross section similar to the propellant described in FIG. 1. The resultant propellant gave a high release of energy at a suitable burning rate.

In the above example, the oxidizer tape may be prepared first and the fuel layer deposited on it.

Example II

An oxidizer mixture was made by dissolving 85 parts by weight of finely divided anhydrous lithium perchlorate particles in 15 parts by weight of a binder which was a mixture of 100 parts by weight of a polypropylene adipate having a molecular weight of about 2000, an OH number of 60, an acid number of 1 and a viscosity at 73° C. of 1000 cps. and 8 parts by weight of an 80/20 mixture of 2,4' and 2,6-tolylene diisocyanates.

Good results also are obtained by using 100 parts by weight of Multrathane R-26, a polyester sold by the Mobay Chemical Company and 8 parts by weight of Mondur T-80, an 80/20 by weight mixture of 2,4- and 2,6-tolylene diisocyanates also sold by the Mobay Chemical Company. The above polyurethane starting ingredients are well known raw materials for potting applications. The polyurethane-bound particles of oxidizer were cast upon a thin cellulose nitrate foil 0.5 thousandth of an inch thick and solidified there by heating to 120° F. for 8 hours to form a thin layer of 8 thousandths of an inch thickness on the thin cellulose nitrate foil. This laminate was then used as an oxidizer layer.

A fuel layer was made by warm (260° F.) rolling in a hydrogen atmosphere, a mixture of 20 parts lithium hydride bound by 80 parts lithium to a thickness of 4 thousandths of an inch.

The resultant separate sheets of fuel particles and oxi3,159,104 dizer particles were then cut into a circular form with a die with a central star-shaped opening cut in each of the circular disks. The separate disks, were laminated together with a micro layer of polyurethane elastomer so that the fuel sheets and oxidizer sheets were in alternate arrangement in a rocket engine such as the one shown in FIG. 4. The resultant propellant provided a good energy release at a suitable rate.

It is thus seen that improved solid propellants can be made according to the present invention in great safety because the high energy metals and metalloid fuel particles are not contacted by oxidizer particles during manufacture. This manner of preparing propellants also results in greater chemical stability in storage and in freedom from slow oxidation of the normally highly sensitive fuel material. Furthermore, another important advantage of the present invention is that the laminated propellants of the present invention can bind together sufficient metal and metalloid fuel particles with just the required amount of oxidizer particles for stoichiometric or nonstoichiometric combustion therewith without the risk of detonating the propellant during its formation or combustion.

It should be understood that other binders, other metal or metalloid fuel particles, and other oxidizer particles as previously discussed can be substituted for the finely divided metal fuel particles, the binders, and the oxidizers used in the above examples.

For example, an excellent thin oxidizer layer for use with the thin lithium hydride fuel layer of Example II, with or without some of the oxidizer layers of the same example, may be made by depositing a liquid mixture of 75 parts by weight of 200 mesh potassium perchlorate particles 2 parts by weight of ZnO₂, and 25 parts by weight of liquid polysulfide rubber on a 325 mesh screen (U.S. Sieve Standard Screen Series) made of 0.0014 inch diameter aluminum wires.

The liquid polysulphide rubber, a reaction product of ethylene dichloride and sodium tetrasulfide composed of —C₂H₄S₄— units, is cured by the zinc oxide at relatively low temperatures to bind the perchlorate particles in a uniform arrangement within the layer.

Another example of a material which can be used as a binder of backing tape with “built-in” fluorine is polyvinyl fluoride having a molecular weight of preferably about 100,000 to 200,000, a melting point of about 185 to 195° F. and being soluble in dimethyl formamide, butyl lactone and cyclohexanone. Copolymers of vinyl fluoride with vinylidene fluoride and hexafluoropropylene are also suitable.

Other fuels, oxidizers and binders may be used in the above examples.

For instance, excellent results are obtained when Adiprene L, a liquid linear isocyanate terminated polyurethane containing approximately 4 to 4.3% reactive polyisocyanate sold by Du Pont, is substituted in whole or part for the polyurethane binder used in Example II. Generally about 100 parts of the above polymer, which has an average molecular weight of about 2000, a viscosity of about 16,000 to 19,000 cps. at 73° C. and is prepared from about 1.2 to 1.8 moles or more of toluene diisocyanate per mole of polytetramethylene ether glycol, are used along with about 2 to 18 parts by weight of a curing agent which is preferably MOCA, a curing agent sold by Du Pont which is 4,4'-methylene bis (2-chloroaniline). Other curing agents such as glycols, including 1,4-butanediol, and polyols including trimethylol propane and glycerol may also be used and the curing may be accomplished at temperatures as high as 212° F. for 3 to 4 hours but is preferably accomplished at low temperatures, if necessary such as 8 to 10 hours.

It is also understood that combustion agents such as steam, liquid oxygen, liquid fluorine and air may be used to burn the laminated propellants in place of all or part of the oxidizers including hydrogen peroxide illustrated in the examples and in the drawings. For instance, in FIG. 4, steam alone can be used to bum the fuel once the metal particles have started to burn. Also in FIG. 4, a ram-jet diffuser can be used to replace the peroxide decomposer 34 at the forward end 31 of the engine. In this case, ram air advantageously can be used to bum with the fuel-rich propellants of the present invention, the propellant 19 being burned “in situ” in engine 30 of FIG. 4 as compared to being extraded into a combustion chamber and burned.

In all propellant forms made from individual disks or sheets, generally it is highly important that the layers be securely bonded together except in instances where it is desired to have internal burning at very high combustion rates. Generally, the cemented laminated layers of the present invention prevent interlayer burning at a high rate which might lead to detonation or otherwise would be undesirable. As previously described herein and particularly as described for binder materials, adhesive layers of polyurethanes, polyisocyanates alone, and epoxy resins, which may or may not contain oxidizer particles subject to burning requirements, are outstanding cementing materials. Generally these adhesive layers are as thin as can be made and still provide a uniform coating or unbroken film to secure the layers together. Thus, the adhesive films or layers are generally much thinner than the backing layers, except when adhesive layers are the oxidizing materials or fuel materials themselves.

The above cementing materials can be used to coat a fuel or oxidizer tape which has been sprayed with a liquid adhesive and fine particles of fuel or oxidizer coated thereon by sprinkling at a uniform rate. In this case, the salted layer can be spray coated with a liquid such as a polyisocyanate to fill in the voids between particles as well as anchor the salted layer to another layer.

It is understood that disks or sheets of solid oxidizer material such as lithium perchlorate can be adhesively laminated with elastomeric fuel layers to provide an excellent propellant, although the structure is too fragile for some applications. These disks, which are generally from about 1 to 300 thousandths of an inch thick, can be made by casting a liquid melted oxidizer or saturated alcoholic solution such as LiClO₄ in methyl alcohol, and solidifying the same. Again these disks of solid oxidizers should be adhered to the fuel rich layers with suitable cementing materials as previously described.

It is to be understood and further modification of the method, apparatus and composition of the present invention may be made without departing in spirit and scope from the present invention.