US3542610A - Composition for the pyrotechnic dissemination of screening oil smokes - Google Patents

Description

United States Patent Olfice US. Cl. 149-20 9 Claims ABSTRACT OF THE DISCLOSURE The present invention is a non-flowable combination of a heat producing means and a fog oil which when ignited produces an oil smoke screen. The heat producing means, when ignited, produces sufficient heat to vaporize the fog oil but insufiicient heat to ignite it.

BACKGROUND OF THE INVENTION The invention herein described was made in the course of or under a contract with the Department of the Air Force.

The use of smoke screens to obscure observation by others is Well known. Various compositions have been used to produce such obscuration. For example, TiCl has been disseminated to form effective smoke screens. The use of TiCl and other common screening agents has the disadvantage of forming smoke screens which are toxic and corrosive.

Oil smokes have been used to produce non-toxic, noncorrosive smoke screens. Such oil smoke screens are produced by vaporizing a fog oil and disseminating the vapor into the atmosphere around the area to be obscured. By fog oil it is meant those oils which may be vaporized without degrading and the vapor of which will form an obscuring cloud. The oil vapor condenses into fog particles capable of obscuration.

The known methods of vaporizing and disseminating fog oils require the utilization of bulky equipment such as devices having compressors, blowers, nozzles, tanks and heater. The use of such devices must be limited to accessible terrain or highly specialized equipment aboard aircraft. Pulse jet engines have also been employed to create oil smoke screens.

It is an object of the present invention to provide a composition which will produce a non-toxic, non-corrosive, highly effective smoke screen.

It is a further object to provide a composition which will produce such a smoke screen without the use of specialized equipment for dissemination.

It is an additional object to provide such a composition which may be formed into a pyrotechnic munition.

SUMMARY OF THE INVENTION The present invention is a composition for the pyrotechnic dissemination of smoke. The munition comprises an inorganic oxidizer, a fuel and a fog oil. The fuel is selected from those substances which are more readily oxidized by the oxidizer than the fog oil. The combination of fuel and oxidizer is characterized by burning at a temperature which will not cause ignition and flaming of the fog oil and yet produce sufiicient heat to vaporize the fog oil.

The composition is prepared from oxidizers, fuels and fog oils, which when combined in the proper ratios will form a non-flowable munition. The munition need not be hard, but the consistency must be such that the oxidizer, fuel and fog oil will remain in dispersion with each other.

3,542,610 Patented Nov. 24, 1970 DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred fuels for use in the present invention are compounds which are rich in sulfur, nitrogen or both. The presence of nitrogen and/or sulfur provides a fuel which will burn in combination with an inorganic oxi' dizer at a rate and temperature proper to avoid burning the fog oil and yet provide enough heat to vaporize it.

Fuels which are especially useful in the present composition are selected from the group consisting of nitramines such as 3 amino 1 nitroguanidine, ethylenedinitramine and dinitroethyleneurea; aminoguanidinium azide and nitrate salts; autocondensation products of aminoguanidinium salts; thiourea or amine-substituted derivatives thereof such as thiosemicarbazide, ethylene bis(thiosemicarbazide), thiocarbohydrazide and dithiobiurea.

Preferred inorganic oxidizers are alkali metal or ammonium nitrates, chlorates or perchlorates. Potassium chlorate is an especially preferred oxidizer.

In one embodiment of the present invention, the fueloxidizer combination is homogeneously mixed with a fog oil having a viscosity sufficient to prevent the solid particles from settling therein. The fog oil may be selected from those greases which have sufficient viscosity to maintain the oxidizer and fuel in dispersion. Greases having a viscosity of at least about 10 centipoises at 25 C. may be used in this embodiment of the invention. Those greases which maintain their viscosities at moderately elevated temperatures are preferred. Greases which have been prepared by thickening low viscosity oils by conventional means may be used in the present invention.

A fog oil of sufilciently high viscosity may be prepared by gelling a low viscosity oil with a polymer which is soluble in or swellable by the oil. Preferred polymers are those fusible, low molecular weight, heat stable thermoplastics such as polyethylene, polypropylene, polystyrene and alkyl polystyrene polymers. By heat stable, it is meant those polymers which will not flow at temperatures below about C. Thus, the smoke disseminating composition may be prepared by gelling a low viscosity fog oil to a composition of at least about 10 centipoises at 25 C. and mixing the fuel and oxidizer therewith.

In order to produce compositions which will yield a high level of obscuring power per pound of composition, the ratio of oxidizer to fuel to fog oil should be such that the composition consists of 10 to 50 weight percent oxidizer, 5 to 35 weight percent fuel and 35 to '75 weight percent fog oil.

An especially effective composition is made up of 6.6% to 10.5% thiourea as fuel, 33.4% to 34.5% KClO as oxidized and 55% to 60% of fog oil having at least the minimum viscosity herein set forth.

In another embodiment of the invention, the munition is brought to a viscosity sufiicient to maintain the fuel, oxidizer and fog oil in dispersion by using a binder fuel which is a polymeric compound which when combined with the fog oil and oxidizer will maintain the composition in a stable configuration and combine with the oxidizer upon ignition to produce sufiicient heat to disseminate the fog oil, but insufficient heat to ignite it. The binder fuel must be more readily oxidized than the fog oil. Fog oils of low viscosity do not work well with a binder fuel due to phase separation. By using a thickened fog oil in combination with the binder fuel, this problem may be eliminated. The fog oil should have a viscosity sufficient to prevent phase separation with the binder fuel, i.e. remain dispersed therein. This viscosity will vary depending on the fog oil and binder fuel selected. The minimum viscosity of the fog oil necessary to prevent phase separation may readily be determined for a given composition.

Preferred binder fuels are epoxy resins which contain sulfide or ether groupings or are copolymerized with polysulfide resins. Amines are normally used as curing agents. An especially effective binder fuel is prepared by copolymerizing a polyfunctional glycidyl ether of glycerine with a mercapto terminated resin containing about 40% sulfur. Benzyl dimethyl amine is normally used as curing agent to enhance the copolymerization reaction. Binder fuels containing 25% to 100% of the glycidyl ether of glycerine, to 75% 0f the mercapto terminated resin are normally used. Usually to 25 parts of benzyl dimethyl amine per 100 parts of the glycidyl ether is used as curing agent. The binder fuel, oxidizer fog oil ratio should be about to 40 weight percent binder fuel, 10 to 50 weight percent oxidizer and 35 to 75 weight percent fog oil. The binder fuel is normally set by heat curing at temperatures of between 40 and 80 C. for from 1 to about hours.

Preferred fog oils are low molecular weight lubricating and processing oils. Parafiinic processing oils having a viscosity of about 10 centipoises are especially preferred. The fog oils must be thickened to the minimum viscosity set out herein in order to be used in the present invention. Low viscosity naphthenic oils which have been thickened to a sufficient viscosity have also been found to produce good oil smoke screens.

In order to aid dissemination, a gas generating agent may be added to the composition. Gas disseminating agents suitable for use with the present invention are those materials which upon heating liberate carbon dioxide, nitrogen or mixtures thereof, including for example, alkali metal acid carbonates, ammonium acid carbonates, guanidine carbonate, oxamide, oxalic dihydrazine and urea oxalate.

The composition may be ignited by using any of those ignition systems and igniters normally used to initiate thermal disseminating munitions.

The following examples will serve to further illustrate the invention.

Example I A fog oil of suflicient viscosity was prepared by gelling 41.5% of a paraflinic processing oil having a viscosity of about 10 centipoises with 6.3% of a polyethylene having a melt index of 28. The mixture was heated to a temperature of approximately 200 C. with vigorous stirring until a homogeneous mixture was obtained. It was then cooled with vigorous stirring. To the gelled fog oil was added 9.8% thiourea as fuel, 31.4% KClO as oxidizer and 9.8% NaHCO as gas generating agent. All percentages represent weight percent of the completed composition. The fuel oxidizer and gas generating agent were thoroughly mixed with the gelled fog oil. The resulting composition was a self-supporting petrolatumlike gel with a flow point of about 90 C.

A 30 gm. portion of the composition was ignited. No flaming occurred upon ignition. The ignition produced a smoke cloud with a Total Obscuring Power (TOP) in square feet per pound of composition of 3,900.

After storage for 48 hours at 72 C., the composition remained self-supporting.

Example II Several compositions were made incorporating a high temperature grease as the fog oil. The grease selected was a lubricating oil which had been thickened by the addition of inorganic thickeners. The grease was determined to have a viscosity of between 9.37 10 and 1.0 X 10 centipoise at C. by use of a Brookfield RVF viscometer having a spindle designation of TE. The viscometer was run at a speed of 4 revolutions per minute.

The following table represents the formulations and efiiciency of smoke producing compositions employing the grease as fog oil.

Various compositions were prepared which incorporated either the gelled low viscosity parafiinic oil of Example I or the high temperature grease of Example II. The following table indicates the formulations and efficiency of various compositions.

Formulation a b c d e Ingredients [Weight percent of composition] Thiourea 10. 5 10. 5 8. 6 8. 6 6. 6 K0103- 34. 5 34. 5 33. 4 33. 4 33. 4 Grease 55. 0 0 60 Polyethylene 7. 1 Parafinic o 47. 9 Flaming None None None None None Cloud: TOP (ftJ/lb.) 8, 410 3, 950 3, 360 3, 775 3, 690

Example IV A composition having a rubbery texture was prepared by combining a fog oil with a binder fuel and oxidizer. The low viscosity paraffinic oil was employed as the fog oil after having been gelled with polyethylene to give it sufficient viscosity to be compatible with the binder fuel. 39.2% oil was gelled with 5.8% polyethylene as in Example I. With constant stirring, the gelled oil was combined with 6.0% of a polyfunctional glycidyl ether of glycerine and 18% of a mercapto terminated resin containing about 40% sulfur. Benzyl dimethyl amine was employed as a curing agent in the amount of 1%. All percentages represent weight percent of the completed composition. The composition was then cast and cured at 70 C. for 4 hours.

A 20 gm. sample was ignited and a good cloud formation resulted.

TOP values which are given in the preceding examples were obtained by the visual target and light transmission methods which are well known to those skilled in the art of obscuration.

Attempts were made to produce smoke disseminating compositions by mixing low viscosity fog oils with solid oxidizers and fuels. The result was a mixture which provided improper combustion and obscuration due to separation of the fuel and oxidizer from the fog oil.

We claim:

1. A munition for the pyrotechnic dissemination of smoke which comprises an inorganic salt as an oxidizer, a fuel and a fog oil, the oxidizer fuel combination being selected so that it will burn at a temperature sufficient to vaporize the fog oil but insufficient to ignite the fog oil and the fuel being more readily oxidized than the fog oil, wherein the fog oil is gelled to a viscosity sufficient to prevent solid particles from settling out and the oxidizer, fuel and fog oil combination has a viscosity sufiicient to maintain the fuel, oxidizer and fog oil in dispersion with each other.

2. A munition for the pyrotechnic dissemination of smoke which comprises:

(a) 35 to 75 weight percent of a low viscosity oil which has been gelled to a viscosity of at least about 10 centipoises as fog oil;

(b) 10 to 50 weight percent of an inorganic salt as oxidizer; and

(c) 5 to 35 weight percent of a fuel, the oxidizer fuel combination being selected so that it will burn at a temperature sufficient to vaporize the fog oil but insufficient to ignite the fog oil and the fuel being more readily oxidized than the fog oil.

3. The munition of claim 2 in which the fuel is a nitramine, aminoguanidinium azide or nitrate, a condensation product of an aminoguanidinium salt, thiourea or an amine substituted derivative of thiourea.

4. The munition of claim 2 in which the oxidizer is an alkali metal or ammonium nitrate, chlorate or perchlorate.

5. The munition of claim 2 which consists essentially of 6.6 to 10.5 weight percent thiourea, 33.4 to 34.5 weight percent KC1O and to weight percent fog oil.

6. A munition for the pyrotechnic dissemination of smoke which comprises an inorganic salt as oxidizer, a fog oil and a binder fuel, the binder fuel being a polymeric compound which will maintain the munition in a stable configuration and combine with the oxidizer upon ignition to produce sufiicient heat to disseminate the fog oil but insuflicient heat to ignite it and is more readily oxidized than the fog oil and the fog oil being gelled to a suflicient viscosity to remain dispersed in the binder fuel.

7. The munition of claim 6 in which the binder fuel References Cited UNITED STATES PATENTS 2,707,695 5/1955 Courtier 149--46 X 2,791,178 5/1957 Thompson 10290 X 2,955,526 8/1961 De Ment. 3,323,958 6/1967 Penn et al 149-83 X 3,335,040 8/1967 Niles 149-83 X CARL D. QUARFORTH, Primary Examiner S. J. LECHERT, JR., Assistant Examiner US. Cl. X.R.