US3444013A - High-velocity gun propellants containing solid nitrogen hydrides or boron compounds - Google Patents

Description

United States Patent 3,444,013 HIGH-VELOCITY GUN PROPELLANTS CONTAIN- ING SOLID NITROGEN HYDRIDES R BORON COMPOUNDS Joseph Green, Dover, and Paul F. Schaetrer, Denville, NaL, assignors to Thiokol Chemical Corporation, Trenton, N .J a corporation of Delaware No Drawing. Filed Dec. 3, 1964, Ser. No. 416,683 Int. Cl. C0611 /00 U.S. Cl. 149-22 5 Claims The present .invention relates to novel compositions adapted for use as ballistic propellants and especially advantageous for use as hypervelocity gun propellants. This invention also relates to cartridges comprising such propellants.

The term hypervelocity is used in relation to the terms low-velocity guns and high-velocity guns into which artillery has been roughly divided. Low-velocity guns are those from which projectiles are fired at not much higher than 2000 feet per second; high-velocity guns are those from which projectiles are fired at up to about 3000 feet per second. The term hypervelocity is used to refer to muzzle velocities of 3500 feet per second or higher.

. Ballistic projectiles having hypervelocity have long been considered desirable for both military and domestic uses. Discharging a projectile such as a bullet, shell, etc., from a weapon at high velocity has a number of advantages. For example, higher projectile speed can result in longer range and improved penetration of armored objects. Furthermore, improved accuracy may be obtained when using hypervelocity projectiles. This improved accuracy is due to such factors as (l) the allowance of a flatter ballistic trajectory and (2) the reduction of time between firing and target impact. This reduction in time is important, not only because the target will have less time to change position, but also because the time in which outside forces such as wind, etc., may act on the projectile is reduced.

There are a number of practical problems which hindered the wide scale use of hypervelocity weapon systems. Erosion of the gun itself is promoted by the high temperatures and pressures ordinarily required for obtaining hypervelocity projectiles with conventional gun propellants. In moderate size weapons, only a few rounds may be fired before the enlargement of the bore becomes a problem and interferes with the accurate aiming of subsequent rounds. In a 12-inch gun about a pound of material is often removed on firing a single round at a muzzle velocity of 2600 feet per second. This erosion would be several times greater were the velocity increased a 50 percent, i.e., to 3900 feet per second.

Furthermore, high temperatures required for hypervelocity projectiles energized with conventional gun propellants also contribute to the erosion problem. This is especially true when the rate of fire is high. Moreover, the high temperatures per se are undesirable. In machine guns for example, barrels often heat to 750 C. and more, swell, bend, and often blow up.

Therefore, it is readily seen that projectiles may not be fired repeatedly at hypervelocities with any degree of accuracy from gun barrels which are subjected to the aforementioned severe stresses. Projectiles are normally afforded stability in flight by a spinning motion imparted by the rifiing in the bore of the gun to the projectile by means of a rotating band on the projectile. An additional problem which is encountered when sufiicient conventional propellant is fired to provide hypervelocity to a projectile is the frequent exceeding of the strength limit of this rotating band by the high pressure and temperature "ice conditions; thus, band failure may limit the muzzle velocities attainable with conventional propellants.

All of these problems arise not from the velocity of the projectile itself, but only from the extreme conditions existing in the bore of a gun when sufiicient conventional propellant is burned to impart hypervelocity to a projectile.

It is apparent that a propellant which could be utilized to impart higher velocity projectiles with lower temperatures and pressures in the gun barrel would not only be useful in improved marksmanship but also would allow a significant decrease in gun erosion.

It is known that the maximum muzzle velocity obtainable with a given charge of propellant will be determined by the distribution of kinetic energy released by the decomposition of the propellant between the projectile and the propellant gas. That part of the kinetic energy imparted to the gas will be determined in large part by its molecular weight. Assuming the projectile mass has been reduced to the minimum mass adequate for a particular use, it is seen that the muzzle velocity obtainable is determined in large part by the molecular weight of the gas. The lighter the gas, the greater the muzzle velocity will be. The weight of the combustion products of the nitro cellulose powder, a typical conventional propellant, is about 28. In general, conventional propellants decompose to gases having molecular weights from about 25 to 28.

It is an object of this invention to provide propellant compositions adapted for obtaining hypervelocity projectiles. It is another object of this invention to provide dependable propellant compositions of relatively low molecular weight. It is still another object of this invention to provide gun propellants adapted for low temperature and low pressure operation. It is still a further object of this invention to provide cartridges comprising the aforementioned gun propellants. It is a still further object of the invention to provide .a propellant which contains a higher energy content per unit mass than conventional propellants.

Applicants have met these objects by providing low molecular weight propellant compositions having favorable thermodynamic characteristics and favorable chemical characteristics so as to avoid undue erosion of gun barrels. The propellant comprises boron-containing nitrogen compounds which yield BN+hydrogen gas on decomposition and nitrogen hydrides yielding N and H on dc.- composition.

The primary ingredients in applicants propellant composition are hydrogen-nitrogen-boron compounds and/or solid nitrogen hydride compounds such as hydrazine bisborane, diammonodecaborane (B N H diammonodecaborane hydrazinate (B N H and dihydrazinium perhydrodecaborane. Other propellants that c an be utilized in forming the propellant compositions include nitrogen hydrides which yield N and H gases upon combustion such as hydrazinium azide and triaminoguanidinium azide can also be used.

Minor portions of other atoms may be found in such compounds, but the quantity is too small to affect the favorable properties of the propellant.

These propellant-forming compounds are characterized by their low isochoric flame temperature, advantageously less than 2300 K. and the low molecular weight of the gases formed 'by their decomposition, preferably a mole formed for each 16 grams or less of the propellant-forming compound.

In general, these compounds may be broken down into two types, those decomposing into BN and hydrogen and those decomposing into hydrogen and nitrogen.

Of course, to be useful as propellants it is also nec essary that the compounds formed in the gun breech and barrel are not excessively corrosive and are sufficiently dense so that a sufficient quantity of propellant may be inse'rted into the gun for effective firing. The above-identified compounds meet these qualifications and are thereby uniquely advantageous for use as propellants in hypervelocity ballistic applications.

To demonstrate the improved ballistic properties of these new propellants, the following data, obtained in a test firing is presented. Propellant A is formulated of 80 parts hydrazine bisborane, 20 parts nitrocellulose and one part graphite. The pellets had a 0.25 inch diameter, a 0.063 inch diameter core therein, and a density of 0.82 gram per cc. Propellant B is a commercial single-base standard sold'under the'trade name'IMR 4227. The'difierence in propellant weight used in each test is due to the different densities of the propellants. Each setof data 'represents the average of three firings. Cartridges with propellant A were primed with magnum primer of the trade name CCI 250 obtainable from Cascade Cartridge Inc.

Thus it is seen that applicants novel propellant with only one-half the mass charge of the standard propellant causes the projectile to leave the muzzle at a speed nearly 38% faster than the speed imparted by the standard propellant. Moreover, the pressure reached in the gun on firing of the standard propellant is about 11% higher than that caused by applicants propellant. Moreover, the total amount of kinetic energy imparted to the projectile is 90% greater when 83.8 grains of applicants propellant is used than when 160 grains of the standard is utilized.

This improvement in performance has been found to be due in part to the low molecular weight of the novel propellants which contributes to their favorable low heatgenerating properties.

When applicants compounds are compared with standards such as the commercially available Hercules Bullseye propellant (a commercial double-base propellant containing 40% nitroglycerin) and the commercially available M-lO propellant (a single base propellant containing 98% of nitrocellulose), the importance of the low molecular weight decomposition products is made more evident.

T K. is the isochoric flame temperature. M is the average molecular weight of the products produced by decomposition of the propellant.

It is clear that applicants propellants provide larger quantities of gas and provide for greater impetus at far lower flame temperatures than the standard propellants.

Compositions comprising these unique and energetic gun propellants should also preferably include minor amounts of compounding additives. For example lubricants like stearic acid, metal stearates, magnesium silicate and metal carbonates aid in contributing compacting and free-flowing properties to the compositions so that they may be more easily manufactured into grains having optimum configuration. Among other additives are silica powders like that known to the art by the trade name Cab-O-Sil, complexes of silica and aluminum oxide, diatomaceous earth and other such antiblock additives known to the art.

Initiators usefully incorporated into these compositions include nitrocellulose-based blank-fire powder, polyethylene hydrazine nitrate, and ethylenedi(aminoguanidinium)- azide/ formaldehyde copolymer. Initiators are usually necessary for the hydrazine-bisborane based propellants and should be incorporated in levels of up to 10 to 30% or more based on the total Weight of initiator and hydrazinebisborane. Nitrocellulose is a particularly useful material.

When it is desirable to lower the burning rate of the propellant, small quantities of burning rate modifiers known to the art may be incorporated. For example, graphite is often conveniently used in such formulations.

A number of processing problems must be overcome in order to produce propellants containing reactive boroncontaining compounds such as hydrazine bisborane or reactive compound like hydrazinium azide.

Nitrocellulose, when used in the compositions, must be incorporated into the process in a nonaqueous medium because both hydrazinium azide and hydrazine bisborane Will bedegraded by water. A hydrocarbon such as hexane V An ester such as propyl acetate and/ or ethyl acetate, preferably diluted by a hydrocarbon, is used as a solvent medium for mixing about a 10% lacquer of nitrocellulose *with reactive boron-containing compounds. Conventional ether/ alcohol mixtures are not acceptable because of their reactivity.

The mixing operation is carried out in a mixer of the type known to the art, for example a Baker-Perkins planetary vertical mixer. It is necessary, of course, to provide an explosion barrier between the mixture and any attendant personnel. The mixer is fitted with vacuum fittings and excess ester solvent and hydrocarbon are evaporated under vacuum before the mixture is extruded into propellant grains.

Additives such as graphite and burning rate modifiers are conveniently added to the mix after up to three hours of processing, i.e., just prior to extrusion.

Extrusion of the propellant grains can be carried out by a Loomis extrusion press of a 7-ton capacity in a manner known to the art. Another method of fabricating grains is to press pellets of the required size with or without perforations using a pellet press such as a Stokes pellet press.

We claim:

1. A gun propellant comprising granules of a mixture of a gas-forming constituent consisting of at least one member selected from the group consisting of hydrogennitrogen-boron compounds and normally solid nitrogen hydrides and a minor amount of a molding lubricant.

2. A gun propellant comprising as its essential gasforming compounds a major portion of hydrazine bisborane and a minor portion of nitrocellulose.

3. The process of forming gun propellants having hydrogen-nitrogen-boron compounds and nitrocellulose as their essential gas-forming constituents comprising wetting nitrocellulose in a nonpolar solvent With said solvent, mixing said nitrocellulose into an ester-based lacquer, admixing said lacquer with said boron-containing compound to form a mixture in which the solids comprise a major proportion of the boron-containing compounds and a minor proportion of nitrocellulose, and drying excess solent from the mixture.

4. A gun propellant comprising granules of a mixture of a gas-forming constituent consisting of at least one member selected from the group consisting of hydrazine bisborane, hydrazinium azide, diammonodecaborane, diammonodecaborane hydrazinate, dihydrazinium perhydrodecaborane, and triaminoguanidinium azide, and a minor amount of a molding lubricant.

5. A gun propellant comprising as its essential gasforrning compounds a major proportion of hydrazinium azide and a minor proportion of nitrocellulose.

References Cited UNITED STATES PATENTS 3,148,938 9/1964 Knoth 149-22X 3,153,567 10/1964 Fetter.

6 3,170,283 2/1965 Sayles 149-36 X 3,250,651 5/1966 Bell et a1 149-22 X 3,268,376 8/1966 Haldeman et al 149-22 X 5 BENJAMIN R. PADGE'IT, Primary Examiner.

US. Cl. X.R. 149-18, 36, 94

Claims (1)

1. A GUN PROPELLANT COMPRISING GRANULESS OF A MIXTURE OF A GAS-FORMING CONSTITUENT CONSISTING OF HYDROGENNITROGEN-BORON COMPOUNDS AND NORMALLY SOLID NITROGEN HYDRIDES AND A MINOR AMOUNT OF A MOLDING LUUBRICANT.