US3753811A - Igniter composition - Google Patents

Abstract

1. A composition consisting essentially of about 30 to about 85 weight percent of a material selected from the class consisting of polytetrafluoroethylene and polytrifluorochloroethylene; about 15 to about 70 weight percent of a material selected from the class consisting of magnesium, aluminum, boron, titanium, ziroconium, thorium, mixtures thereof and lithium nitride; about 1 to about 10 weight percent of a material selected from the class consisting of potassium dichromate, manganese dioxide, ammonium nitrate and ammonium perchlorate; and from about 1 to about 10 weight percent of a material selected from the class consisting of lead fluoride and sodium fluoride.

Description

United States Patent [191 Julian et al.

[ Aug. 21, 1973 IGNITER COMPOSITION [22] Filed: June 13, 1957 [21] Appl. No.: 665,613

FOREIGN PATENTS OR APPLICATIONS 628,247 8/ 1949 Great Britain Primary Examiner-Carl D. Quarforth Assistant ExaminerE. A. Miller Attorneyl(. F. Ross and Q. B. Warner EXEMPLARY CLAIM 1. A composition consisting essentially of about 30 to about 85 weight percent of a material selected from the class consisting of polytetrafluoroethylene and polytrifluorochloroethylene; about 15 to about 70 weight percent of a material selected from the class consisting of magnesium, aluminum, boron, titanium, ziroconium, thorium, mixtures thereof and lithium nitride; about 1 to about 10 weight percent of a material selected from the class consisting of potassium dichromate, manganese dioxide, ammonium nitrate and ammonium perchlorate; and from about 1 to about 10 weight percent of a material selected from the class consisting of lead fluoride and sodium fluoride.

2 Claims, 3 Drawing Figures PATENTEDAUGZI ma 3.75331 1 SHEET 1 0F 3 INVENTORS ELMO C. JULIAN FRANK G. CRESCENZO ROBERT C. MEYERS, DECEASED, av BETTE C. MEYERS,exEcuTR|x,

R Y" m/- ATTORNEYS IGNITER COMPOSITION The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates to a new igniter, more particularly, it relates to an igniter mixture for gas producing charges such as propellants, fuels and explosives.

The ideal igniter should produce short ignition delays with reproducible output characteristics independent of environmental temperature and pressure conditions without causing damage to any component parts. In addition, igniter materials should be sufficiently inert to avoid hazard when handling. They should have good surveillance characteristics. The principal igniter materials used in the past have consisted of black powder used alone, or a mixture of 80 percent black powder and 20 percent magnesium. The above materials are subject to the disadvantages that they are highly sensitive to static electricity and friction, thus making their handling extremely dangerous. Also, they absorb moisture from humid air, this factor adversely affecting their ignition characteristics in that it leads to delayed ignition and complete ignition failures. Additionally, the above materials are highly sensitive in their operation to changes in temperature and pressure. Further, mixtures of black powder and magnesium have a tendency to segregate, thus vitiating the advantages of the combination.

It is therefore an object of this invention to provide an igniter which has an acceptable range of ignition time delay.

It is another object of this invention to provide igniter mixtures which are inert to static electricity, impact and friction. It is another object of this invention to provide an igniter mixture which is inert to temperatures below 400C.

It is another object of this invention to provide an igniter mixture which has good surveillance characteristics and which is unaffected in its operation by moisture in the atmosphere.

It is a further object of this invention to provide an igniter which gives reproducible output characteristics which are independent of environmental temperature and pressure conditions.

It has been found that the above objectives are accomplished by an igniter incorporating a composition comprising a mixture of a material from the class consisting of magnesium, aluminum, thorium, zirconium, titanium, molybdenum, boron and lithium nitride, with a fluorinated alkene. To this composition may be added oxidizing agents such as lithium perchlorate, potassium dichromate, manganese dioxide and ammonium nitrate. Catalytic agents, such as, inorganic fluorides may also be added. Examples of these inorganic fluorides are fluorides of the alkali metals and lead.

The invention is best understood by reference to the following description taken in connection with theaccompanying drawings hereby made a part of this specification and in which:

FIG. 1 is a cut-away showing of an ignition testing semi-vented bomb, used to test the compositions of the invention;

FIG. 2 is a horizontal cross-section of a two inch steel static firing motor for testing the ignition of end burning propellent charges; and

FIG. 3 is a typical pressure-time graph showing the igniter performance characteristics of interest obtained from test firing the two inch semi-vented bomb of FIG. 1.

The bomb of FIG. 1 comprises generally an internal pressure chamber in which the propellent grain is ignited by means of a conventional squib and the igniter composition of this invention. The pressure chamber is provided with means for measuring internal pressures at various times and intervals of space along the bomb. Referring to FIG. 1, the outer case of the bomb is represented by numeral 10 and the internal pressure chamber by the numeral 11. The case 10 is provided with threaded end plugs 12 and 13 for engagement with the ends of case 10. The end plug 12 contains the igniter assembly and the end plug 13 contains the pressure relief assembly. A three inch section of an internal burning, externally inhibited, star perforated propellent grain is shown at 14. The grain has an outside diameter of 1.9 inches. The igniter material is shown at 15. For igniting the igniter material 15 a conventional squib is provided at 16 which in turn is provided with a pressure seal electrical lead 17. For measuring pressure in the chamber at various intervals of time and space, pressure taps 18, 19, 20, 21, and 22 are provided. These taps are connected by hydraulic lines to Wiancko conventional type pressure gages. A cap 23 is provided for pressure tap 18 to prevent pressure leak when the device is inoperative. Rupture discs 26 and 27 designed to rupture at predetermined pressures are provided as shown. For adjusting the distance between propellent grain and igniter, removable collars 28 are provided in the pressure chamber. A thermocouple assembly 29 is supported by end plug 13.

In operation of the test bomb, a propellent charge 14 is placed in the inner cavity 11 of the bomb as shown, and the igniter composition 15 of the invention is inserted in the case 4 inches from the propellant l4 and adjacent the squib 16. After the pressure gages have been connected to suitable recorders, the igniter is ignited by introduction of current to the squib 16 through electrical lead 17. During the process of ignition of the squib, igniter and propellant, pressure-time measurements are recorded.

Referring to FIG. 2, there is shown a static testing rocket motor having an outer casing 30 and provided with head end closure 31. Head end closure 31 is sealed to the rocket body by means of threaded ring 32 at tached to the case 31 by fillet 33, and internally threaded cap 34 as shown. 0 ring 35 is provided to furnish a gas tight seal. The rocket nozzle is shown at 36 having an exhaust port 37. The nozzle 36 is attached to the rocket body by means of threaded ring 38 secured to the outer casing or rocket tube 30 by means of fillet 39, and internally threaded cap 40. Nozzle shear ring 41 is provided as shown. The end assembly is made gas tight by means of O ring 44. Pressure plugs 46 are provided for measuring pressure in the cavity aft of the rocket grain. A series of these plugs located circumferentially in the outer casing may be used. Spacing ring 47 is provided for holding the grain secure. For testing the igniter, a double base end burning propellent grain 48 having an outer inhibiting coating 49 is located in the rocket motor chamber as shown. The grain is provided with a conical shaped burning surface 50. The igniter material of the invention in a plastic bag 52 with a conventional squib 53 in proximity thereto is positioned as shown. Electrical leads 54 are provided as shown for conducting current from a source not shown to squib 53. In operation of the motor, current is introduced to ignite the squib, igniter material and propellant in turn. Internal pressure is measured by means of the pressure plugs 46 which are hydraulically connected to pressure gages.

Referring to FIG. 3, there is shown a typical pressuretime graph used to present important igniter test data obtained by testing compositions of the invention in the test device of FIG. 1. The compositions are operative as igniter materials under actual operating conditions. ln the graph, pressure is plotted on the ordinate against time delay in milliseconds on the abscissa. The legend for the numerals is shown on the drawing. Squib time is the interval of time between the application of current to fusion of the bridge wire in the squib. lgniter time is the time elapsing from fusion of the bridge wire to ignition of the igniter or until the first indication of initial pressure, this later indicating the ignition of the igniter. The ignition duration is the time between ignition of the igniter and ignition of the propellant and is indicated on the graph by the inflection of the pressure time curve as indicated by the numeral 3. The propellant ignition delay is the sum of the igniter time and the ignition duration as represented by the numerals 2 and 3 on the graph. This is the most significant factor in the evaluation of igniter mixtures. Numerals 5, 6, 7 and 8 represent supplementary pressure information shown on the graph.

The invention is illustrated by the examples included in Tables 1-4, inclusive, which are illustrative only of the invention but not limiting thereof. Tables 1 and 2 present comparative results of ignition tests performed on black powder, black powder-magnesium mixture, and a polytetrafluoroethylene-magnesium mixture of the invention. Tables 3 and 4 present examples of ignition mixtures of the invention and test data therefor. The data for the examples was obtained with the ignition testing, semi-vented bomb of FIG. 1.

The compounding of the igniter mixtures is illustrated by the following: Metal powder 100 mesh or finer was added to powdered Teflon polymer of 50 mesh or finer in ratios of 50 to 800 percent of the stoichiometric quantities. These materials were then thoroughly mixed. They may be blended, rolled or treated in a signal blade mixer. Alternate methods of making the mixtures is as follows: Teflon is reduced to less than 5 micron particle size by techniques well known in the art and introduced to a Waring blendor. An inert solvent such as acetone or a hydrocarbon is added and the mixture blended for seconds in the blendor. This material is transferred to a suitable vessel where the metal is added and the mixture is stirred for 5 minutes. The material is then filtered to remove the bulk of the solvent and transferred to a mixer where the remainder of the components are added. Complete grinding followed by further mixing completes the compounding.

The fluorocarbon compound is a polymeric halogenated alkene, preferably, polytetrafluoroethylene or polytrifluorochloroethylene or mixtures thereof. Other fluorinated alkenes may be used, such as, the fluorinated higher alkenes. By the term fluorinated as used in this specification and claims is meant either totally or partially fluorinated. The polytetrafluoroethylene may have a molecular weight range from 100,000 to 9,000,000. This compound is known commercially as Teflon and its chemical composition is published in the literature. The polychlorotrifluoroethylene may have a molecular weight range from 303 to 10,000. This compound is known commercially as Kel-F. It may be used in the composition in liquid, solid or waxy form depending upon the amount of plasticization which is to be effected by its use in non-solid fonn. Plasticization to a degree, may be effected through the use of liquid polymers such as KEL -F polymer oil of various molecular weights. A portion of the solid polymer may thus be replaced by a chemically equivalent weight of the liquid polymer. When used in solid form the fluorocarbon compound is a powder of less than 20 mesh particle size.

The following is an example of compounding the composition when plasticization is required. The metal powder, mesh or finer, is added to somewhat less than the intended quantities of the powdered solid polymer, 50 mesh or finer. Enough liquid polymer to realize the intended ratio of total polymer to powdered metal, 50 200 percent of the stoichiometric quantities, is added. The liquid polymer may be added in the form ofa solution in a solvent such as benzene or methylene chloride. In this case the solvent must be removed by evaporation. The material may be mixed in a sigma blade mixer.

As respects the metals used, the heat of formation of the metal-fluorine bond must exceed 67 kilocalories per gram molecule of the condensed halide. As the examples show, the nitrides of these metals may be used. The carbides and hydrides, having similar chemical properties and similar heats of formation as the nitrides may be used also. The metals and their compounds may be in divided form of less than twenty mesh, or part of the finely divided metal may be replaced by wire of 0.0020 inches in diameter or granules of 20 25 mesh particle size.

Oxidation of one of the reaction products, carbon, may be effected by the addition of an oxidant, such as, ammonium nitrate, or lithium perchlorate in amounts of not more than 10 percent by weight. A small increase in gas production is thus effected. The oxidant may be added to the mixture without affecting the polymer-metal ratio. The oxidant may be in powdered or pellet form.

The propellants used to test the igniter composition are the double base propellants, N-S and X-l l. A representative N-S composition is as follows:

Component Wt. Percent Nitrocellulose 12.6%N) 50.00 Nitroglycerin 34.9 Diethyl Phthalate 10.50

Z-Nitrodiphenylamine 2.00 Lead 2-Ethyl Hexoate L20 Lead Salicylate 1.20 Candelilla Wax 0.20

A representative X-ll composition is the following:

Component Wt. Percent Nitrocellulose (12.6%N) 50.00 Nitroglycerin 33 .l Diethyl Phthalate 12.4 Z-Nitrodiphenylamine 2.0 Lead Salicylate 1.2 Lead B-resorcylate l.2 Candellia Wax 01 Carbon Black +0.05

As stated previously, the percentage of metal to fluorocarbon which may be used is preferably from about 6 to about 800 percent of the stoichiometric. The presame composition and ignition delay values obtained ferret] percentage range is from about l5 to about show a definite relationship between the composition percent by weight of metal and about 30 to about of the mixture and its heat of explosion. Variation in percent by weight of fluorocarbon. ignition time delay results from the extreme conditions TABLE I Summary of Performance Characteristics of Igniter Materials Test Fired at 65 F. in 2.0-Inch Diameter Experimental Test Vehicles with N -5 Propeliant Propellant Initial Initial Propellant Propeliant Igmter Squib Ignrter Ignition ignition peak rate of presignition rate of pres- Average charge time, time, duration, delay, pressure, sure rise, pressure. suro rise, heat of Igniter material wt. msec. msec. msec. msec. p.s.i. p.s.i./msec. p.s.i. p.s.i./msec. explosion Black powder 3. 0 14. 0 2. 0 12 14 326 137 510 50. 6 700 Black powder, 80%Mg, 20%... 3. 0 9.0 20. 0 3 23 460 213 505 43. 7 850 Polytetratluoroethylene, 67%- TABLE II Test Made at 65 F. in 2.0 Diameter Inch Experimental Test Vehicle with X-ll Propcliant Propellant Initial Initial Propcliant Propeilant Igniter Squib Igniter Ignition ignition peak rate of presignition rate of pres- Average charge time, time, duration, delay, pressure, sure rise, pressure, sure rise, heat of Ignitar material wt. msec. msec. msec. msec. p.s.i. p.s.i./msec. p.s.i. p.s.i./msec. explosion Black powder 3. 0 18. 6 8. 7 13. 4 22. 1 368 643 87 700 Black powder, 80%Mg, 20%." 3. 0 18. 7 8. 2 10. 2 18. 4 325 94 581 111 850 Poiytetraiiuoroeth yiene, 67%

TABLE III Three gram charge weights were used. Tests were run at 06 F. The propellent charge was spaced 4" from the ignitcr. The. examples are glvon in percentage composition by weight Component (wt. percent) Example No. Magnesium Boron PTFE PCTFE NaF KzCraOr 11.15. P.I.D

10. 0 7. 5 7. 5 1, 281 32. 0 10.0 7. 5 7. 5 1, 597 17. 5 10.0 7. 5 7. 5 1, 8-16 14. 5 l0. 0 7. 5 7. 5 l 378 4. 5 10. 0 7. 5 7. 5 1, 059 59.1 10. 0 7. 5 7. 5 1, 347 "6 I 2. 5 2. 5 l, 964 14 5 LEDoENn.-P'IFE=Polytetrafluorocthylene; PCTFE=Polychlorotritluoroethylene; H. E.=Heat of explosion in calories per gram; P. I. D.=Propeiiant ignition delay in milliseconds.

TABLE IV A three gram charge weight was used. Mixtures were tested at 65 F. with tho propellant being spaced 4 from the igniter. The examples are given in percentage compositions by weight Component (wt. percent) Example No. Th Zr Ti Mo Al LiaN PIFE KaCrzQr NBF PbFz LlClOi H.E. P.I.D.

it will be noted that all data, with the exception of the under which the tests were made. it will lac-noted from heat of explosion tests, was taken at temperatures of 60 the results oiTables l and ii that the propellant ignition 65 F for three gram charge weights. The igniter was delay obtained with magnesium-Teflon mixtures is as spaced a distance of four inches from the propellent good as that obtained with the ignition compositions of charge. Test firings were conducted at low temperathe prior art, that is, black powder used alone and black tures with small igniter charge weights, as these condipowder-magnesium mixture. For propellant ignition in tion's indicate successful functioning at extreme condi- 65 general, it is to be noted that differences in propellant tions' as well as extend the difference in the ignition ignition delay when the total time is less than 35 millitime delays of similar compositions. Examples 1 seconds are insignificant as any ignition delay under 35 through 5 in Table iii show varying proportions of the milliseconds is highly acceptable. The advantages of the ignition mixtures of the present invention over prior art ignition mixtures stem from other properties. It will be noted from all the examples that the heat of explosion of the igniter compositions of this invention can be adjusted to fit the circumstances by choice of the metal used. in example 8 of Table IV, a composition is shown in which the heat of explosion is only 647 calories per gram. This composition could be used in applications wherein heat damage to surrounding metal parts is to be avoided. It is to be noted that in all examples, with the possible exception of examples and 8 of Tables Ill and IV, respectively, an acceptable ignition time delay is obtained. The examples show that the igniter mixtures of the invention produce extremely high energy output, and have reproducible output characteristics under severe conditions. The mixtures were tested and found to be inert to shock, friction, or static electricity, and insensitive to temperatures of 400C or less. The mixtures are simple to manufacture from readily obtainable materials; they are not subject to segregation, they are non-toxic and their operation is not affected by moisture and high humidity. The mixtures are compatible with propellent and explosive compositions in general, and can be assembled in contact with the propellant. This is in contrast to black powder which is in compatible with double base propellants, for example, and must be assembled in a cannister to avoid contact with the propellant, as well as to prevent absorbtion of moisture from the atmosphere by the black powder. To test the inertness of the mixtures to static electricity a spark from a spark coil was discharged through the ignition mixtures placed in the spark gap without ignition of the powder. Representative samples of the ignition mixtures were subjected to temperatures at 400C for four hours in a muffle furnace with no signs of ignition. Drop tests performed on representative mixtures indicate that they are highly insensitive to shock. For example, only 50 percent ignition was obtained in drops of 85 centimeters with a two kilogram weight. As will be noted from the compositions of the examples, oxidizing agents such as potassium dichromate may be added. Catalytic agents, such as, fluorides of the alkali metals and lead fluoride may also be incorporated in the mixtures. It was noticed that a slight improvement was obtained by the combinations of oxidizing agent and catalytic agent. The effect of the catalytic agent is believed to be due to probable activation of the surface of the metal, thus enhancing its reaction with the fluorinated compound.

While the effectiveness of the ignition compositions of the invention have been illustrated by the ignition of double base propellants having a nitroglycerinnitrocellulose base, they are by no means limited to this application as they are equally applicable to the ignition of other propellants and explosives in general.

Obviously, many modifications and variations of the present invention are possible in the 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.

What is claimed is:

l. A composition consisting essentially of about 30 to about 85 weight percent of a material selected from the class consisting of polytetrafluoroethylene and polytrifluorochloroethylene; about 15 to about weight percent of a material selected from the class consisting of magnesium, aluminum, boron, titanium, zirconium, thorium, mixtures thereof and lithium nitride; about t to about 10 weight percent of a material selected from the class consisting of potassium dichromate, manganese dioxide, ammonium nitrate and ammonium perchlorate; and from about 1 to about 10 weight percent of a material selected from the class consisting of lead fluoride and sodium fluoride.

2. The composition according to claim 1 wherein the material selected from the class consisting of magnesium, aluminum, boron, titanium, zirconium, thorium, mixtures thereof and lithium nitride has a particle size which does not exceed 20 mesh.

Claims (2)

1. A COMPOSITION CONSISTING ESSENTIALLY OF ABOUT 30 TO ABOUT 85 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF POLYTETRAFLUROETHYLENE AND POLYTRIFLUOROCHLORETHYLENE, ABOUT 15 TO ABOUT 70 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF MAGNESOIUM, ALUMINUM, BORON, TITANIUM ZIROCONIUM, THORIUM, MIXTURES THEREOF AND LITHIUM NITRIDE, ABOUT 1 TO ABOUT 10 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF POTASSIUM DICHROMATE, MAGANESE DIOXIDE, AMMONIUM NITRATE AND AMMONIUM PERCHLORAGE, AND FROM ABOUT 1 TO ABOUT 10 WEIGHT PERCENT OF A MATERIAL SELECTED FROM THE CLASS CONSISTING OF THE LEAD FLUORIDE AND SODIUM FLUORIDE.

2. The composition according to claim 1 wherein the material selected from the class consisting of magnesium, aluminum, boron, titanium, zirconium, thorium, mixtures thereof and lithium nitride has a particle size which does not exceed 20 mesh.

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