3,677,840 United States P Patented July 18, 1972

iodide of the invention is obtained in a highly active form 3,677,840 ideally suited for nucleating purposes. PYROTECHNICS COMPRISING OXDE OF The metathesis reaction proceeds substantially accord FOR WEATHERMODIFICATION USE ing to the following equation: Graham C. Shaw, Garland, and Russell Reed, Jr. Brigham City, Utah, assignors to Thiokol Chemical Corporation, Bristol, Pa. No Drawing. Filed Sept. 18, 1969, Ser. No. 859,165 In accordance with the invention, the pyrotechnic com int, C. C06d 3/00 o position comprises, by weight, the cured product produced U.S. C. 149-19 5 Claims by mixing and curing together from about 0.5% to about 10 20% of of silver; from about 2% to about 45% of an alkali iodate present in about a stoichiometric amount ABSTRACT OF THE DISCLOSURE relative to the amount of oxide of silver present in the A pyrotechnic composition which upon combustion composition; from about 25% to about 75% of a solid in produces mixed silver halide nuclei for use in influencing organic oxidizer selected from the and the weather comprises a composition made by curing a mix 5 of ammonium and of Group I-A and Group II-A ture comprising , an alkali iodate, an alkali of the Periodic Table; and from about 10% to and a curable oxygenated or fluorinated or about 20% of a curable, fluid polymer for pyro ganic liquid polymer binder. The composition burns technic compositions, especially a combined-halogen-rich smoothly to provide by metathesis a mixture of silver or combined--rich polymer binder, preferably a halides as substantially the only solid or condensed phase 20 polyester-urethane terminated with amine or hydroxyl reaction products, and leaves substantially no residue. The groups. reaction products form nuclei for causing nucleation of DESCRIPTION OF THE PREFERRED water in clouds. EMBODEMENTS 25 The pyrotechnic compositions of the invention are pre pared by compounding of the ingredients according to pro BACKGROUND OF THE INVENTION cedures known in the manufacutre of pyrotechnic compo Field of the invention sitions, using equipment and safety precautions usually used and necessary in carrying out the manufacturing pro The present invention relates to a substantially residue 30 cedures involved. free pyrotechnic composition which upon combustion pro The following specific descriptions and illustrative ex vides a mixture of silver halides including, essentially, amples set forth preferred embodiments of the invention. nuclei for causing nucleation of water in In the accompanying table are listed typical ingredients, clouds, e.g. for "cloud seeding," and for thereby influenc and their amounts, which are used in preparing representa ing weather conditions. 35 tive preferred pyrotechnic compositions according to the Description of the prior art invention. Pyrotechnics useful for meterological seeding purposes TABLE are known. Such pyrotechnics are taught, for example, in Percent by weight U.S. Pats. 3,046,168; 3,140,207; 3,375,148; and 3,418,- 184. Pyrotechnic compositions described in these patents, 40 Example number------2 3 4. 5 6 Ingredients: upon combustion, produce silver iodide nuclei from silver Silver oxide------15 15.4 ------0.5 20 5 iodate. However, chemical reduction of the silver iodate in Silver peroxide------16 ------5 Ammonium perchlorat - 30 30.8 31 78.5 30 63 such compositions to silver iodide may proceed, in part, Binder------115 115.4 15 220 810 15 further to reduction of the silver iodide to metallic silver, Ammonium iodate------38.4 38 1.0 ------6 thereby diminishing the surface activity of the silver iodide 45 .------40 ------40 6 particles for cloud seeding purposes. 1 Polyester-urethane. Hydroxy-terminated polybutadiene. SUMMARY OF THE INVENTION 8 Amine-terminated polypropyleneglycol. 4 Copolymer of vinylidene flouride and perfluoropropylene dissolved The present invention provides a means for avoiding in 1,1,7-trihydroperfluoroheptyl acrylate. the above-described reduced activity of silver iodide as 50 The oxide of silver used in practicing the invention well as providing a means for producing nascent silver may be silver oxide (AgaO) or silver peroxide (AgO). iodide by an advantageous method of metathesis. Silver oxide is preferably used. The oxide of silver is used The present invention is directed to providing a pyro as a powder, preferably a powder having a particle size technic composition for weather influencing purposes in 55 of from about 10 to about 250 microns in diameter. which the silver-providing compound used to make the In addition to the benefits derived from the advan nuclei for nucleation purposes is an oxide of silver, prefer tageous use of oxide of silver because of the formation of ably, silver oxide, AgO. The oxide of silver is preferably nascent silver iodide, the use of the oxide of silver also is used in combination with an alkali iodide anion-providing economically advantageous over use of silver iodate as compound, preferably an iodate, e.g. ammonium iodate or 60 the source of the silver cation for the nucleating function potassium iodate. The iodate compound serves also as according to the invention in that the unit cost of silver an additional source of oxygen for the combustion of iodide (AgI) prepared from the oxide is less than half the organic polymeric binder used in making the pyro that of Agderived from the iodate. technic composition. The amount of oxide of silver present in the composi The use of an oxide of silver as a source of the silver tion is preferably as great an amount as can be reasonably cation in silver iodide formed in the products of combus 65 completely metathesized to AgI by the tion of a pyrotechnic composition for cloud seeding pur of the composition. poses has not heretofore been known, particularly in com The iodate used in practicing the invention serves as bination with an alkali iodate which serves as the source the source of the iodide anion of the Agi. Accordingly, the of the iodide anion. Nascent silver iodide, which is formed iodate must be a compound which will decompose or in the highly oxidizing environment of the combustion, is 70 react to liberate the iodide anion at the temperatures the product of a metathesis reaction. Therefore, the silver created during combustion of the pyrotechnic composi

3,677,840 3 4. tion. Alkali iodates have been found especially suitable perchlorates of the Group II-A metals. Of the per for this purpose. The iodates of ammonium and potassium the compound is prefer are preferably used in the compositions of this invention. ably used in the pyrotechnic compositions. Examples of Other alkali iodates may also be used to obtain similar the nitrates of the Group I-A and II-A metals which are benefits and advantages. These include iodate, employed in preparing compositions of this invention are lithium iodate, iodate, and iodate. Be compounds such as sodium , , cause the amount of residue is particularly low when nitrate, , , stron ammonium iodate is used as the source of the iodide tium nitrate, etc. is also useful. Also, anion, ammonium iodate is preferably used. newer perchlorate compounds, particularly hydroxylam The amount of alkali iodate present in the composition O monium perchlorate, may be used. preferably is at least a stoichiometric amount needed to The amount of solid inorganic oxidizer present in the combine with the amount of oxide of silver present to composition preferably is at least an amount sufficient to form a silver iodide. combust completely the binder and to generate sufficient The polymer of the curable polymer binder used in the heat thereby to carry out the metathesis reaction between composition may be any fluid polymer which has a high 5 the oxide of silver and the alkali iodate. combined-oxygen or combined-halogen content and which In formulations where a metal iodate is present, e.g. further has physical properties such that it may be used barium iodate, it will be desirable in some cases to use in the arts. A wide variety of suitable, curable, finely-divided fuel metal in the formulation to aid in fluid polymers are known to the art and such polymers minimizing slag formulation, as taught, for example, in can be mixed with the other ingredients hereof to form 20 the use of iodate formulations of U.S. 3,418,184. The fuel the curable mixture. These include, for example, poly metal ingredient, then, of the composition of this inven alkylhydrocarbons, e.g., and polybutadiene, tion will be a particulate form, e.g. finer than about 100 particularly amine- or hydroxyl-terminated polymers, and mesh, of fuel metal, especially a powder of aluminum, polyfluorocarbons. Examples of highly-oxygenated bind magnesium, , , or . The pow ers, which are preferred, include polyethers and polyesters 25 ders may be used individually or admixed with each terminated in hydroxyl or isocyanate groups. Polyethers other. The fuel metal ingredient may also contain in used include polyols derived from polymerization of admixture a minor amount of a non-metallic fuel pow ethylene, propylene, and butylene oxide and tetrahydro der, including powders of , tellurium and . furan. These may also be isocyanate terminated by reac Aluminum and magnesium powders having a mesh size tion with di- or tri-functional isocyanates such as toluene 30 of less than 100 mesh U.S. Standard are preferred. diisocyanate, isophorone diisocyanate, and arylmethylene Other substances which are employed in the prepara isocyanates. Polyesters, hydroxyl-terminated, include those tion of the pyrotechnic composition of this invention in derived from esterification of high-oxygen-content acids clude minor amount of burning catalysts, well known in Such as succinic, glutaric, adipic, and citric. The diols used pyrotechnic compositions. These are composed of one include ethylene, diethylene, triethylene, propylene and 35 or a mixture of two or more metal oxide powders in butylene glycols. amounts sufficient to improve the burning rate of the Other suitable, curable, fluid polymeric binders will be composition. The amounts usually range from about 0.01 found among those described in U.S. 3,235,589, U.S. 3 to about 3 weight percent, based on the weight of the 257,801, U.S. 3,260,208, U.S. 3,158,991, and U.S. 3,068,- oxidizer employed. The particle size of the powders can 129, all incorporated herein by reference. 40 range from about 10 to about 250 microns in diameter. The amount of binder present in the composition should Non-limiting examples of metals that serve as burning be at least sufficient to form a castable, fluid mass with the catalysts are , vanadium, chromium, silver, molyb Solid ingredients and to bind the ingredients into a tough, denum, Zirconium, , , iron, cobalt, Solid mass when the binder is cured. An additional amount and . Examples of metal oxide burning catalysts of the polymeric binder may be used, as is known in the 45 are ferric oxide, aluminum oxide, copper oxide, chromic pyrotechnic art, to serve as the fuel component to burn oxide, as well as the of the other metals mentioned with the oxidizer components of the composition. Both the above. Other burning rate catalysts which may be used alkali iodate and the solid inorganic oxidizer used in the will be found among those described in U.S. 2,969,638, composition serve as oxidizers. The stoichiometric balance incorporated herein by reference. needed among these components will be readily determin 50 Curing catalysts are often added in minor amounts to able by one skilled in the art of formulating pyrotechnic cure the polymer in the curable composition of this inven compositions, tion. Non-limiting examples of catalysts used for this pur Solid inorganic oxidizers employed in the pyrotechnic pose are aluminum , tristrimethylsilyl borate, compositions of this invention can be compounds such benzoyl peroxide, and other catalysts well known in the as ammonium and metal perchlorates and ammonium and 55 curing of plastics, , polymers, and rubbers. Exam metal nitrates. The perchlorates employed as oxidizing ples of various catalysts may be found in text books such agents or oxygen carriers in the compositions are anhy as “Synthetic Rubber,” by G. S. Whitley, pp. 892-933, drous and have the general formula M(CIO), wherein 1954 ed., published by John Wiley and Sons, Inc., New M is NH4 or a metal, and x is the valence of M, and ordi York. The curing catalysts are added in amounts of from narily has a value of 1 or 2. Since the pyrotechnic com 60 0.1 to about 10 weight percent based on the weight of the position is required to withstand high temperature storage, polymer. The particular catalyst and amount employed it is preferable that the and the decomposi depend on the state of cure desired, the nature of the polymeric material employed in the composition, and the tion temperatures of the oxidizer be as high as possible. heating and storage compatibility of the catalyst with the The perchlorates of ammonium and of the Group I-A and 65 high explosive, fuel metal and oxidizer ingredients, as Group II-A metals are found to have the required high well as with the binder. temperature stability and are employed in the preparation The blending of the ingredients in preparing the pyro of pyrotechnic composition for use in practice of this technic composition is carried out at a temperature suf invention. The metal perchlorates used in the preparation ficiently high to maintain fluidity of the polymer binder of the compositions include lithium perchlorate, sodium 70 ingredient but sufficiently low enough to minimize curing perchlorate, potassium perchlorate, rubidium perchlorate, of the polymer binder in the blender. A temperature in and cesium perchlorate, which are the perchlorates of the the range of about 120 to 135 F. will usually be found metals of Group I-A of the Periodic Table of Elements; suitable. The blending is carried out in accordance with and magnesium perchlorate, calcium perchlorate, stron known procedures for a period of time sufficient to homo tiun perchlorate, and barium perchlorate, which are the geneously mix all the ingredients to form a putty-like mass w 3,677,840 5 6 which can be flowed upon application of moderate pres nuclei in the products of combustion dur See O. Wac ing burning, thus further ensuring a minimum of slag The curable pyrotechnic composition which results formation, from the blending operation is deaerated and then is ex Following the procedures described above, one skilled truded or otherwise drawn or forced into a rocket, shell 5 in the art will be able to prepare many suitable combina or cannister. Where the composition cures on stand tions of the disclosed ingredients to obtain the cured ing for a period of several hours to several days at a tem silver oxide-containing pyrotechnic composition essential perature of about 135 to 150 F. depending on the type for the practice of the invention. Thus, one may readily and amount of fluid polymer binder and curing agent Substitute silver peroxide for silver oxide, or other binders, therefor which is used. A suitable procedure for filling O e.g. epoxy curable hydroxy-terminated polybutadiene the tubes by means of vacuum is described in U.S. 3,341 or amine-terminated polypropylene glycol for the binders 636, incorporated herein by reference. in the above examples to obtain the advantages and bene The following examples further illustrate the invention. fits thereof. Also, one may readily substitute other metal oxidizers and metal fuels, as described above. EXAMPLE I The means for deploying the cloud seeding munition to A curable, flowable pyrotechnic composition is pre its target will be obvious to those skilled in the munitions pared by blending together in a propellant mixer at 135 arts, whether as a rocket propelled projectile, a drop flare, 145 F. the following ingredients until a homogeneous or a mortar shell, or other device and therefore are not flowable mixture is obtained: further described herein. Ingredient: Percent by weight 20 Although specific embodiments have been shown and Liquid hydroxy - terminated polybutadiene described, it is to be understood that they are illustrative polymer ------10.65 and are not to be construed as limiting on the scope and Polyisocyanate such as isophorone diisocya spirit of the invention. nate ------2.35 We claim: Silver oxide powder ------10.00 25 1. A pyrotechnic composition for producing silver Ammonium perchlorate powder ------60.00 iodide by metathesis for use in influencing weather, said Ammonium iodate powder ------17.00 composition comprising, by weight, from about 0.5% to about 20% of an oxide of silver; EXAMPLE I from about 2% to about 45% of a heat decomposable The pyrotechnic composition made according to the 30 alkali iodate present in about a stoichiometric amount method described in Example I is loaded into a dispersing relative to the amount of oxide of silver present in means cannister similar to that of an aircraft parachute the composition; type drop flare and cured therein. The cannister is assem from about 25% to about 75% of a solid inorganic bled into the parachute-type drop unit. To achieve the oxidizer selected from the perchlorates and the ni objective of the invention, the unit is dropped into a 35 trates of Group I-A and Group II-A metals of the cloud bank from an aircraft and is ignited in the usual Periodic Table; and Way. As the pyrotechnic composition burns, silver halides from about 10% to about 20% of a polymer binder in the form of submicron sized silver iodide and silver for pyrotechnic compositions present in at least a chloride particles form and serve as nuclei for nucleating Stoichiometric amount relative to amounts of the the Water vapors in the cloud bank, causing rainfall. 40 alkali iodate and solid inorganic oxidizer present in the composition. EXAMPLE III 2. The composition of claim 1 wherein the oxide of 13.2 percent by weight of Morester 905 binder, a hy silver is silver oxide. droxy terminated polyester, are mixed with 1.8 parts of 3. The composition of claim wherein the iodate is PAPI (polymethylene polyphenylisocyanate). To this 45 Selected from an iodate of ammonium, potassium, sodium, mixture are added 15 percent of silver oxide powder, 30 lithium, calcium and barium. percent KClO4 and 40 percent of KIO. This formulation 4. The composition of claim 1 wherein the iodate is is then thoroughly mixed at 135-145 F. until a flowable ammonium iodate. mixture is obtained. The mixture is then deaerated and 5. The composition of claim 1 wherein the binder is cast into the dispersing cannister for use in a delivery mu 50 Selected from a fluid, curable , hydroxy-ter inition according to the invention. The mixture is then minated polybutadiene, amine-terminated polypropylene. cured to a solid, tough mass by heating to 135 F. for 24 glycol, and copolymer of vinylidene fluoride, perfluoro hours. The mass has a specific gravity of 1.50 or greater. propylene dissolved in 1,1,7-trihydroperfluorohepty The pyrotechnic composition so made is then used to seed acrylate, hydroxy-containing polyethers, isocyanate-con a cloud bank with silver halide nuclei to cause rainfall. 55 taining polyethers, hydroxy-containing polyesters, and EXAMPLE IV isocyanate-containing polyesters. 16 percent by weight of a liquid fluorocarbon binder References Cited (Viton A, 8-10%, a copolymer of vinylidene fluoride and perfluoropropylene dissolved in 1,1,7-trihy 60 UNITED STATES PATENTS droperfluoroheptyl acrylate to which a catalytic amount, 2,995,526 8/1961 De Ment 149-81 X about 0.2%, of benzoyl peroxide has been added as a 3,000,174 9/1961 Vose ------149-87 X curing catalyst), 20 percent of silver oxide powder of 3,046,168 7/1962 Burkardt et al. 149-42 about 100 mesh size, 30 percent of NHClO4, and 34 3,140,207 7/1964 Williams et al. 149-19 percent of NHIO are mixed together at 125 F. for 20 65 3,375,148 3/1968 Finnegan et al. 149-18 to 30 minutes. The mixture is deaerated and flowed under 3,418,184 / 1968 Vetter ------149-19 pressure into dispersing cannisters. The formulation is 3,467,558 9/1969 Wernette et al. 149-19 cured at 135 F. for 24 hours. A tough, solid elastomeric mass is formed, having a specific gravity of 1.80 to 1.85. CARL. D. QUARFORTH, Primary Examiner The pyrotechnic composition so made is ready for use in 70 E. A. MILLER, Assistant Examiner preparing a cloud seeding munition Substantially as de scribed above. The high combined-fluorine content of the U.S. C. X.R. fluorocarbon binder in this composition results in the formation of silver fluoride as well as silver iodide and 149-61, 81, 83, 85