US3923564A - Double base propellant with thorium containing ballistic modifier - Google Patents

Abstract

The addition of thorium to a low energy double base propellant containing a small amount of a crystalline high explosive filler to produce a mesa burning rate versus pressure curve.

Description

Uite States atent 1 1 1111 3,923,564

Lantz 1 1 Dec. 2, 1975 1 DOUBLE BASE PROPELLANT WITH 3,088,858 5/1963 Camp 149/97 x THORIUM CONTAINING BALLISTIC 3,326,732 6/1967 ScurlOck et al 149/198 3,379,588 4/1968 Corsi ct a1. 1 1 149/97 X MODIFIER 3,726,729 4/1973 Pierce l49/l9.8 [75] Inventor: Robert Lantz, Chester, NJ.

OTHER PUBLICATIONS [73] Assignee: The United States of America as represented by h Secretary f the Fields et al., Lanthanide/Actinide Chemistry." page Army, Washington, C 73, American Chemical Society, (1967), Washington,

D.C. [22] Filed: Sept. 27, 1973 PP N05 398,920 7 Primary Examine1 -Benjamin R. Padgett Related Us. Application Data Assistant Examirie rE. A. Miller [63] Continuation of Ser. No 155,639, June 22, 1971, 7" Frm. Nathan Edelberg; Robert Glbson, A. Victor Erkkila abandoned.

U-S- [51] Int. Cl. C06D 5/06 The addition of thorium to a low energy double base [58] Field of Search 149/92, 97, 98, 19.8 pr p ll n n aining a small amount of a crystalline high explosive filler to produce a mesa burning rate References Cited versus pressure Curve.

UNITED STATES PATENTS 2,890,108 6/1959 Toulmin 149/87 X 4 Claims, 1 Drawing Figure U, atent Dec. 2, 1975 PRESSURE, IOO PSI INVENTOR.

ROBERT LANTZ DOUBLE BASE PROPELLANT WITH THORIUM CONTAINING BALLISTIC MODIFIER The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalty thereon.

This is a continuation of application Ser. No. 155,639, filed June 22, 1971, now abandoned.

BACKGROUND OF THE INVENTION During the last 20 years, there has been continuous activity in the development of novel ballistically modified double-base propellants. Yet, in all of these compositions, regardless of energy or ballistic activity, a lead salt and frequently an additional metallic salt have been incorporated. These propellants offer a wide variety of physical and ballistic properties. The incorporation of the metal salts in these compositions has been primarily to produce a plateau or a mesa effect. It is widely known that generally the pressure at which a propellant burns bears a direct relationship to its burning rate at a given temperature. This relationship can be expressed as: r cp" where r is the burning rate, p is the pressure and c and n are constants determined by the type of propellant used. Propellants exhibiting plateau and mesa effects deviate from the direct relationship over certain pressure ranges. If the exponent n exhibits a negative value the burning rate shows a decrease. This decrease in burning rate is called a mesa effect. If the exponent n is the burning rate remains constant and this ballistic property is called a plateau effect. If a logarithmic graph of burning rate vs pressure for a particular propellant is prepared the mesa effect shows as a segment of negative slope on the curve, the plateau effect as a segment of zero slope. Propellants exhibiting a mesa effect give an actual decreased burning rate over a particular pressure range and as a result have a built-in safety factor to insure against overpressurization of a container. The plateau effect results in a propellant with a constant thrust over the pressure range of the plateau.

Many propellant actuated devices are well known to the art and have been used to advantage in systems requiring a short-duration high force application, for example, supplying gas pressure to operate hydraulic pumps in missiles, ejecting signalling devices from aircraft, jettisoning cargo from aircraft and ramming projectiles into the breech of large guns. These devices are generally simple, light, reliable and small. There are basically two types of these devices, short duration initiators and long duration gas generators. This invention is directed to providing a propellant composition for use in a gas generator.

Desirable characteristics for a gas generating composition include: a low heat of explosion value of about 900 cal/g. or less; a low burning rate, to achieve a long burn time; a temperature dependence of low magnitude to minimize pressure change at both high and low temperatures; a very low flame temperature to minimize erosive effects on metal parts; good physical properties for ease of machining and handling; and a plateau or mesa effect to provide a built-in safety factor and relatively constant thrust.

In the past, solid, gas generator propellants have been used in a variety of devices, however it was difficult to produce a low energy propellant composition which exhibited plateau or mesa ballistic effects, with the result that high energy propellants were the only ones available even though they were not suited for special applications required by designers. A solid propellant used to generate gas must be chosen primarily according to ballistic properties which are appropriate for operating pressure, environmental storage and actual use conditions. Consideration must also be given to the criteria of reliability of ignition, smoothness of burning and wide temperature range stability. Thus it is seen that the production of a new low energy propellant composition provides a much broader choice for the design of propellant actuated devices. In addition a low flame temperature minimizes the erosion of metal parts that come in contact with the exhaust gases of the propellant. A low flame temperature will allow design tolerances, for these metal parts, which would be inapplicable with a higher flame temperature.

It is therefore an object of this invention to provide a new ballistic modifier which produces mesa and plateau effects when incorporated into a double base propellant.

A further object is to provide a new low energy composition which exhibits mesa and plateau ballistic characteristics and which has a low burning rate.

A still further object is to provide a low energy propellant composition, exhibiting mesa and plateau ballistic characteristicsand having an extremely low flame temperature to minimize corrosion of metal parts in contact with the propellant.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same become better understood by reference to the following detailed description.

These objects are attained and the prior art deficiencies are overcome by the use of thorium as a ballistic modifier with conventional double base propellants. This novel ballistic modifier produces a smooth low burning rate and allows the use of low energy propellants for applications which require mesa or plateau ballistic characteristics. In addition the flame temperature is very low and thus minimizes the corrosive and erosive effect of the exit exhaust gases. This minimization of deleterious effects introduces greater flexibility into the field of propellant actuated device design.

This discovery, herein described, is quite unexpected and forms, in effect, the basis for an advance in the art. The production of mesa and plateau ballistic characteristics by the use of thorium salts is a major technological advance in the field of propellant ballistics. Additionally, the use of this novel ballistic modifier allows the production of a low energy, low flame temperature propellant having ballistic modification.

The effects of this invention are numerous. Initially it provides a new ballistic modifier which will provide new parameters for further research into the basic nature of ballistic modification. It also provides a composition which exhibits mesa ballistics at pressures between 2000 and 3000 psi. It provides a composition which has a very low flame temperature so that its exhaust gas reaction products are much less corrosive and erosive towards exposed metal parts. Further, this composition with its low flame temperature permits a flexibility in the design of propellant actuated devices previously unattainable. In addition this composition allows the incorporation of crystalline fillers into a double base composition with retention of mesa ballistics.

The following range of compositions can be used to prepare the propellants of our invention:

N. by weight Nitrocellulose 12.2 to 14.6 40 60 Nitroglycerin 10 30 Plasticizers l 30 Thorium Ballistic Modifier l Carbon Black 0.02 0.10 Heterocyclic nitramine Crystalline explosive filler 0 10 Stabilizer 1 5 In general, the procedure used for preparing our novel propellants is conventional and includes:

1. Mixing the ingredients with the required amount and type of solvent to achieve proper colloidization;

2. Preparing the colloided propellant for extrusion;

3. Extruding the prepared propellant; and

4. Curing the extruded propellant to a maximum v01- atile content of about 0.4% weight.

More specifically, the propellant composition of our invention can be formulated in the following manner:

Dehydrated nitrocellulose, stabilizer, plasticizer and carbon black are blended together for about 30 minutes in a sigma blade mixer. The ballistic modifier is added and blended for about minutes. If desired the crystalline explosive filler, wet with alcohol, is then added and blended for 15 minutes. Nitroglycerin, any remaining plasticizer and the balance of any solvents necessary to effectuate homogeneous mixing are then added and mixed in for about 60 minutes or until properly colloided. The mixer temperature is maintained at 40 i 5F. throughout the mixing cycle. The colloided propellant is then screened, dried, extruded and cured in the conventional manner, then finally extruded and machined to the final design dimensions desired. Sample grains obtained in the above process are then tested.

The stabilizers which can be utilized to advantage with this invention are any compounds or mixture of compounds which prevent the decomposition of nitrocellulose while not interfering with the ballistic or structural properties of the final propellant, for example; diphenylamine, 2-nitrodiphenylamine, ethyl centralite and N-methyl p-nitroaniline. These stabilizers may be present in an amount of from about 1.0% to 5% by weight. If less than 1.0% is added the low pressure mesa is adversely affected, if more than 5% is added again the mesa is adversely affected. Preferably in our invention about 2 to 4% by weight is added to insure proper placement of the mesa effect on the pressure vs burning rate curve.

Plasticizers that may be used to advantage include both explosive types such as nitroglycerin, diethylene glycol dinitrate, triethylene glycol dinitrate, 1,2,4- butanetriol trinitrate, trimethylolethane trinitrate and other common polyhydroxylic compounds that form nitrate esters and fuel types such as glycerol triacetate, esters such as dimethyl phthalate, diethyl phthalate, din-butyl phthalate, di-octyl phthalate and analogous adipate and sebacate compounds and nitro compounds such as dinitrotoluene.

Additives may be used in small quantities to produce desired effects, for example, a small amount of carbon black can be used beneficially as an opacifying agent and as a burning rate control agent. Any common extrusion lubricant such as candelilla wax can be used if necessary.

The thorium containing ballistic modifiers suitable for use with our invention are finely divided metallic thorium, as well as inorganic thorium compounds such as thorium oxide and thorium carbonate and organic thorium compounds including organo-metallic thorium compounds. Preferably, organic and organo-metallic thorium compounds are used, such as thorium malonate, thorium malate, thorium tartrate, thorium cyclopentane carboxylate, thorium stearate, thorium salicylate, thorium resorcylate, thorium succinate, thorium pimelate, thorium adipate and the like and mixtures thereof. The amount of modifier that can be used is from about 0.1 to about 10% by weight based on the thorium content depending on the modification desired; at less than 0.1% there is negligible modification and above 10% the mesa or plateau becomes very small. Preferably from about 2 to about 5% and particularly from about 2.5 to about 3.5% by weight is used to achieve proper modification. The ballistic modifier will, of course, be chosen to produce the desired mesa or plateau effect and this choice will depend on the nature and amount of the constituents used in the propellant. I

Crystalline explosive fillers that may be used to advantage can be any heterocyclic nitramine such as HMX (cyclotetramethylene tetranitramine), RDX (cyclotrimethylenetrinitramine), 1,3 dinitroimidoledone 2, and 1,3,5-trinitro-l ,3,5-triazacycloheptane. These fillers. can be used alone or in admixture with each other in any proportion.

The amount of cyclic nitramine that may be used with our invention is from 0 to about 10% by weight; preferably from about 4 to about 8% by weight and especially about 5% by weight is used to achieve an optimum balance of physical handling characteristics, eg machinability, dimensional stability. If no crystalline filler is used physical properties suffer although ballistic modification is still effective. If more than 10% is used then the ballistic modification becomes disadvantageous.

The composition of this invention, which may be used to produce a propellant having the properties desired, is set forth in the following examples. It is, of course, understood that these examples are meant to be illustrative and not restrictive of our invention.

EXAMPLE I 143 Pounds of nitrocellulose (12.6%N) were treated with ethyl alcohol to remove any water and screened through a U.S.S. 8 sieve, where necessary the other materials to be used were also prepared by screening through a U.S.S. 20 sieve. The dehydrated nitrocellulose was added to a sigma blade mixer. Mixing was begun and 3 pounds of ethyl centralite, 3 pounds of N- methyl p-nitroaniline and 0.09 pounds of carbon black were then added to the nitrocellulose and blended in for about 30 minutes. 9 pounds of thorium stearate ballistic modifier was introduced into the batch and mixing was continued for about 15 minutes. 15 pounds of l-IMX (cyclotetramethylene tetranitramine) wet with ethyl alcohol was added and mixed in for about 15 minutes. A mixture of 61.2 pounds of nitroglycerin and 65.8 pounds of triacetin was slurried with enough of a mixture of ethyl alcohol and ethyl ether to insure safe handling and proper mixing. This nitroglycerin mixture was then added to the batch. The whole mass was mixed thoroughly for about 60 minutes with enough solvent addition to guarantee uniform dispersal and proper gelatinization of the propellant components. The total amount of solvent used was about 40% by weight of the propellant. The solvent composition was about 35% by weight of ethyl ether to about 65% by weight of ethyl alcohol, and amounted to about 40% by weight of the total propellant weight. Any other solvent exist within which the composition can be varied. Selection of the proper components is largely empirical and depends on desirable design conditions within the limits prescribed. The thorium compounds will achieve or solvent mixture which will insure homogeneity and 5 ballistic modification with many double base propelproper colloidization of the propellant can also be used lants within these prescribed limits. to advantage. The temperature of the mixer was main- I wish it to be understood that I do not desire to be tained at 40F 1 5. The properly colloided propellant limited to the exact details shown and described, for was then blocked, screened through a U.S.S. l2 and 24 obvious modification will occur to a person skilled in mesh screen series, reblocked and extruded. The exthe art. truded strands were cut and dried to achieve a maxi- I claim: mum volatile content of 0.4% by weight. The dried l. A propellant composition consisting essentially of: grains were then used to form burning rate strands for testing of propellant characteristics. Testing was accomplished by standard methods. The following Table by weight illustrates additional compositions of our invention. Nitrocellulose 12.2% to 14.6% N -60 Table I Additional Examples (Composition is expressed in by weight Example No. 2 3 4 5 6 7 8 Nitrocellulose 40.0 44.5 53.2 58.0 50.8 59.6 50.0 (12.6% N.) Nitro- 20.6 14.7 26.9 27.0 19.2 10.7 22.6 glycerine Crystalline I-IMX RDX l-IMX HMX HMX RDX Filler 9.4 7.1 4.3 5.2 5.0 5.2 Plasticizers diethylenetrimethyloldiethylenetriacetin glycol ethane triacetin triacetil-l glycol triacetin dinitrate trinitrate dinitrate 15.0 13.6 4.1 9.8 9.8 10.7 l8.0

sucrose diethyldioctylsucrose sucrose triacetin octaacetate phthalate phthalate octaacetate octaacetate l 2.0

10.0 l4.8 6.7 10.2 10.2 Stabilizer ethyl ethyl ethyl ethyl ethyl 2 nitro diphenycentralite centralite centralite centralite centralite diphenylamine lamine 1.0 1.0 1.0 1.0 1.0 2.0 1.0 N methyl N-methyl N-methyl N-methyl N-methyl p-nitroaniline pnitroaniline p-nitroaniline p-nitroaniline p'nitroarliline .0 .0 1.0 1.0 1.0 Thorium malonate malate tartrate salicylate succinate adipate cyclopentane containing carboxylate Ballistic 3.0 3.3 2.8 3.0 3.0 3.0 3.2 Modifier Carbon Black 0.02 0.03 0.03 0.04 0.03 0.03 0.03 (added) Referring now to the drawing, the curves shown are g ggggggf' 1&38 representative of experiments performed on the com- Thorium ballistic difi position of Example 1. The pronounced mesa is apparent in the low temperature isotherm, the 70 isotherm has a slight mesa over the same range, the higher isotherm does not exhibit a mesa but does show a marked change from the normal logarithmic increase which would be present if the propellant were not modified ballistically. The small deviation in burning rate with change in temperatures is also apparent from the drawmg.

The heat of explosion of examples 1 through 8 is uniformly under 900 cal/ g. The flame temperature is much less than in other double base propellants because of the low heat of explosion and is therefore much less corrosive and erosive than the other propellants.

The composition to be used with our invention is composed basically of high energy and low energy ingredients, usually it is necessary to proportion these ingredients according to their energy content to achieve a particular energy level. For example, if the amount of one of the high energy ingredients such as nitroglycerin or one of the explosive plasticizers such as diethylene glycoldinitrate is increased then the amount of the crystalline filler would have to be decreased. Certain limits small amount wherein said thorium ballistic modifier is an organic thorium compound of the group consisting of thorium malonate, thorium malate, thorium tartrate, thorium cyclopentane carboxylate, thorium stearate, thorium salicylate, thorium resorcylate, thorium succinate, thorium pimelate, thorium adipate and mixtures thereof, said propellant composition having a heat of explosion less than 900 calories per gram and exhibiting mesa or plateau ballistic properties.

2. The propellant composition of claim 1, wherein the amount of carbon black is 0.02-O. 10%.

3. The propellant composition of claim 1, wherein the amount of thorium ballistic modifier based on thorium content is between about 2 and about 5%.

4. The propellant composition of claim 1, wherein the amount of said nitramine is between about 4 and about 8%.

Claims (4)

1. . A PROPELLANT COMPOSITION CONSISTING ESSENTIALLY OF:

2. The propellant composition of claim 1, wherein the amount of carbon black is 0.02-0.10%.

3. The propellant composition of claim 1, wherein the amount of thorium ballistic modifier based on thorium content is between about 2 and about 5%.

4. The propellant composition of claim 1, wherein the amount of said nitramine is between about 4 and about 8%.

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