US3726730A - Pyrotechnic delay composition containing heavy metal soap - Google Patents

Abstract

THIS INVENTION RELATES TO A PYRROTECHNIC TIME DELAY COMPOSITION WHICH COMPRISES TUNGSTEN, POTASSIUM PERCHLORATE, BARIUM CHROMATE, DIATOMACEOUS EARTH, AND A HEAVY METAL SOAP.

Description

3,726,730 PYROTECC DELAY COMPOSITION CONTAINING HEAVY METAL SOAP James E. Rose, Bryans Road, Md., and Roswitha Zimmer- Galler, Niceville, Fla, assignors to the United States of America as represented by the Secretary at the Navy N Drawing. Filed Mar. 20, 1972, Ser. No. 236,173 Int. Cl. C061: 15/00 US. Cl. 149-40 11 Claims ABSTRACT OF THE DISCLOURE This invention relates to a pyrotechnic time delay composition which comprises tungsten, potassium perchlorate, barium chromate, diatomaceous earth, and a heavy metal soap.

BACKGROUND OF THE INVENTION Compressed columns of solid powder mixtures have long been used for initiating some desired pyrotechnic result at the end of a predetermined time-delay period. The earliest form of such pyrotechnic device consisted of a confined column of black powder which could be ignited at one end so that the flame and glow front could advance along the column to the other end at a substantially uniform and predetermined rate.

So called delay mixtures have been developed consisting of powdered manganese, silicon, boron, and zirconium nickel alloys in combination with solid oxidizers, such as barium chromate, lead chromate, and potassium perchlorate. Many of these existing type delay mixtures are subject to a number of serious limitations. Very often the range of burning time per lineal inch is restricted to a narrow range, i.e., -13 seconds. Many are subject to undesirable variations in burning rate responsive to change in pressure and temperature. Many are not ignitible in a rarified atmosphere or, at least, do not burn consistently under such conditions. In addition, very often the electricalconductivity of the mixture, both before and after the pyrotechnic reaction, is low, and this is undesirable when the delay train is to be used in multi stage rockets and similar modern applications.

In an effort to overcome these disadvantages Olander, in Letters Patent No. 3,028,229 formulated pyrotechnic time delay compositions which were easily ingitible, were consistently burning, were chemically stable, were supposedly relatively unaffected by temperature and pressure, had a broad range of burning times and were electrically conductive. Olander achieved these results by combining either chromium, molybdenum or tungsten with potassium perchlorate and a second oxidizer, such as barium chromate; with the quantity of potassium perchlorate being less than the stoichiometric equivalent of the metal powder present in the mixture.

Olander used chromium and molybdenum mixtures to produce compositions which have a burning rate between about one and about ten seconds per inch. Tungsten Was used to form compositions with a burning rate of about 40 seconds per inch. However, the tungsten containing compositions of Olander have a disadvantage in that the burning rate is atfected by a change in temperature and this is undesirable. In the past, delay times unaffected by temperature have been achieved by mechanical time fuzes. However, in such device there is a high cost in clockworks involved and, in addition, there is delay time and functioning unreliability where mechanical shock occurs, as in certain ordnance items. Pyrotechnic delays, such as those of Olander, have been used to provide delay times which are minimaly affected by temperature.

tats tet 3326,73 Patented Apr. 10, 1973 SUMMARY OF THE INVENTION It is an object of this invention to provide tungsten containing delay compositions having all of the desirable properties of previously known delay compositions while eliminating some of the inherent disadvantages thereof.

It is a further object of this invention to provide improved tungsten delay compositions by reducing or eliminating the effect of temperature change on delay burn time.

These and other objects are accomplished by incorporating a heavy metal soap into the tungsten containing compositions.

DESCRIPTION OF THE PREFERRED EMBODIMENTS We have found that by incorporating from about 0.5 percent to about 1.5 percent, by weight, of a heavy metal soap such as zinc or barium stearate into the tungsten compositions of Olander, the problem of burning rate dependent upon temperature can be virtually eliminated. Normally there is a direct relationship between reaction rate and temperature, in which an increase in temperature brings about a corresponding increase in the rate of a chemical reaction. Thus, the rate at 71 F. should normally be greater than the rate at 65 F. However, it has been found that at room temperatures, such as 71 F the reaction rate can be slowed by the incorporation of a heavy metal soap. On the other hand, at low temperatures, such as 65 F., the reaction rate is quickened by the addition of the additive. This effect, i.e. speeding up at lower temperatures and slowing down at higher temperatures, compensates for the normal direct dependency of reaction rate upon temperature. Thus, it is possible to obtain a composition which will burn more quickly at 65 -F. than at room temperature. Furthermore, by adjusting the present level of the heavy metal soap additive in the formulation, it has been found that a zero temperature coefficient can be approached. As the level of additive is reduced, a point will be reached below which the compositions temperature coefiicient is normal, i.e., decreasing burning rate (seconds/inch) with increasing temperature.

The amount of heavy metal soap present in the composition should be from about 0.5 percent by weight to about 1.5 percent by weight of the composition. The proportion of soap to the rest of the mixture will control the effect of temperature. This proportion will depend on the nature of the other ingredients and must be determined empirically but should be within the limits specified. There will be one point within the range of 0.5 to 1.5 at which the temperature coeflicient will be reduced to a minimum.

The other ingredients in the instant invention are potassium perchlorate as a primary oxidizer, tungsten, diatomaceous earth and barium chromate as a secondary oxidizer. The ingredients are either in powdered or finely divided form. Generally, any of the tungsten containing compositions of US. Pat. No. 3,028,229 can be utilized. Thus, the instant invention contemplates the use of any of the substitutes for barium chromate taught by Olander such as strontium chromate, calcium chromate, silver oxide, barium peroxide, manganese dioxide, cupric oxide and lead dioxide. The amount of tungsten can vary from about 10-90 percent by weight of the composition and the amount of tungsten present will determine the time of burning. The amount of perchlorate varies from about 4.5l5 percent, with the proviso that the quantity of potassium perchlorate is less than the stoichiometric equivalent of tungsten powder present in the mixture. The amount of barium chromate, which acts as a reaction modifier to slow the burning rate, will vary from about 1060 percent. The amount of diatomaceous earth will vary from about 3-12 percent by weight of the compositron.

As the heavy metal soap we mean the salts of a metal with an atomic number of 25 or above with a higher fatty acid, such as lauric, oleic, palmitic, stearic, etc. It is generally preferred to use either barium stearate or zinc stearate.

The soap additive is added to the rest of the composition by means of a wet mix method wherein the whole composition, including the soap, is first dry blended and then a solvent such as toluene is utilized to disperse the soap throughout the composition. For example, warm toluene at 60 C. can be added to the dry ingredients and the resultant dough agitated until a damp earth consistency is achieved. The damp mixture is then forced through a 16 mesh USS sieve and dried at least 48 hours at 140 F. The optimal temperature of the solvent will be affected by the nature or" the heavy metal soap. For zinc stearate, this is around 100 C.

The following compositions are exemplary of the many combinations which may be made without departing from the principle of the invention.

EXAMPLE I Tungsten, percent by weight 35 Barium chromate, percent by Weight 48.5 Potassium perchlorate, percent by weight 10 Diatomaceous earth, percent by weight 5 Zinc stearate, percent by weight 1.5 Burning time (sec/inch) at +71 F. 12.9790 65 F. 11.8768 T [Temperature coetf. (see/inch/degree] +.008164 Percent T gf Xl 062 EXAMPLE II Tungsten, percent 35 Barium chromate, percent 49 Potassium perchlorate, percent 10 Diatomaceous earth, percent Zinc stearate, percent 1 Buring time, sec./in. at-

+7l F. 13.142 --65 F. 12.326 T sec./in. degree +0060 Percent T 0.046 EXAMPLE III Tungsten, percent 35 Barium chromate, percent 491-(5) Potassium perchlorate, percent Diatomaceous earth, percent 5 Zinc stearate, percent 0.5 Burning time, sec./ in. at

--65 F. 12.7583 T sec./in./degree -.00488 Percent '1 0.040 Percent T ZT X 100 .062

EXAMPLE IV Tungsten, percent 39 Barium chromate, percent 45 Potassium perchlorate, percent 10 Diatomaceous earth, percent 5 Barium stearate, percent 1 Burning time, sec/in. at-

-65 F. 12.8962 T sec./in./degree .00268 Percent T 0.02

If the composition of Example 1V is varied to contain 0.5% barium stearate, it will contain 45.5% barium chromate. As can be seen by the above data, delay times are little affected by temperature over the temperature range 65 F. to +70 F. As a matter of fact, as can be seen by Examples I-III, in which the temperature coefficient varies from a positive to a negative value determined by percentage additive, there will be some proportion of additive, i.e., zinc stearate, at which the temperature coefficient will be about Zero. Thus, somewhere between 0.5 percent and 1.0 percent zinc stearate in the compositions of Examples IIII which contain 35% tungsten, 5 diatomaceous earth, 10% potassium perchlorate, from 48.549.5% barium chromate and from 0.5 to 1.5% stearate, a zero temperature coefiicient can be reached. However, it is not essential to reach this zero value, since beneficial results achieved by the temperature coefficients produced by compositions containing between 0.5 and 1.5 percent soap additive will be small enough to be of beneficial practical use. The temperature coefiicients produced by these compositions are much smaller than the temperature coefiicients of the corresponding unmodified compositions which do not contain the soap additives, i.e., the compositions of Olander.

The pyrotechnic time delay compositions of the instant invention can be used whereever time delay compositions have heretofore been used, such as in cartridges, fuzes, ordnance devices requiring time delay, etc.

Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described herein.

What is claimed as new and desired to be secured by Letters Patent of the United States is:

1. A pyrotechnic time delay composition comprising tungsten, potassium perchlorate, barium chromate and a heavy metal soap, wherein the amount of potassium perchlorate is less than the stoichiometric equivalent of the tungsten present in said composition and said heavy metal soap is present in the amount of from about 0.5 to 1.5 percent by weight of the composition.

2. A composition according to claim 1 wherein the heavy metal soap is a fatty acid salt of a metal whose atomic number is 25 or above.

3. A composition according to claim 2, wherein said heavy metal soap is selected from the group consisting of barium and Zinc stearates, palmitates, oleates, and laurates.

4. A composition according to claim 3 wherein said heavy metal soap is selected from the group consisting of Zinc stearate and barium stearate.

5. A composition according to claim 45 wherein the heavy metal soap is zinc stearate.

6. A composition according to claim 4 wherein the heavy metal soap is barium stearate.

7. A composition according to claim 11 wherein the ingredients are present in the following percentages, by weight, of the total composition:

Percent Tungsten 10-90 Barium chromate 10-60 Potassium perchlorate 4.5-15 Diatomaceous earth 3-12 Heavy metal soap 0.5-1.5

8. A composition according to claim 7 wherein the heavy metal soap is zinc stearate.

9. A composition according to claim 7 wherein the heavy metal soap is barium stearate.

10. A composition according to claim 8 which comprises:

Percent Tungsten 35 Barium chromate 48.549.5 Potassium perchlorate 10 Diatomaceous earth 5 Zinc stearate .51.5

11. A composition according to claim 9 which comprises:

6 3,028,229 4/1962 Olander 14944 2,696,429 12/1954 Hart 14940 X 2,830,885 4/1958 Kerr et a1 149---40 X 2,990,264 6/1961 CQInyn 14940 X 3,173,367 3/1965 Shinpangh 149-40 X 3,701,697 10/1972 Galler et al. 1494O STEPHEN J. LECHERT, JR.,Primary Examiner US. Cl. X.R.