united states patent 3,915,379

8/6/2019 United States Patent 3,915,379

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United States Patent [19]Burkardt et al,

3,915,37911][45] Oct. 28, 1975

[54] METHOD OF CONTROLLING WEATHER[75] Inventors: Lohr A. Burkardt; William G.Finnegan; Frederick K. Odencrantz;

Pierre St.Amand; Charles D.Stanifer, all of China Lake, Calif.

[73] Assignee: The United States of America asrepresented by the Secretary of theNavy, Washington, D.C.

[22] Filed: Mar. 22, 1971[21] Appl. No.: 126,879

Related U.S. Application Data[62] Division ofSer. No. 767,068, Oct. 10, 1968, Pat. No.

3,802,971.

Brandau 239/2 RDeMent 149/81 XBurkardt et al... 149/87 XMerriweather 239/2 RFinnegan et al. 239/2 R XVetter 149/19Power 239/2 R

2,550,3242,995,5263,046,1683,127,1073,375,1483,418,1843,545,677

4/19518/19617/19623/19643/196812/196812/1970

PrimaryExaminer-Benjamin R. PadgettAssistant Examiner-E. A. MillerAttorney, Agent, or Firm-R. S. Sciascia; Roy Miller;Lloyd E. K. Pohl

ABSTRACT57]A pyrotechnic formulation for use in weather modifi-cation comprising a fuel and an oxidizer and a mixtureof a metal iodate and an alkali iodate. Upon combus-tion metal iodide and alkali iodide are generated asmixtures and complexes which show ice nuclei activityat from -50 to -200 C. depending on the molar rangeof metal iodide to alkali iodide.

[52] U.S. CI 239/2 R[51] Int. CI.2 AOIGI5/00; EOIH 13/00[58] Field of Search 239/2 R; 149/19,20,81[56] References Cited

UNITED STATES PATENTS2,527,231 10/1950 Vonnequt 239/2RX 2 Claims, 3 Drawing Figures

15.----------------.----------------r---------------~------~

wCIa /a:w 14>,U S"-CI."

:wD o.W_ ,u 13::tzw>;: : M OLE RATIOc c"- Ag i K ICI . , 3 - 1a:w 0 1 1il -~ 12 0 - 2::tzCI - 3~ I t::. - 12CI_ , A - 65

I STD

11-4 -8 -12 -16TEMPERATURE, D C


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u.s . Patent Sheet 1 of 2 3,915,379

15r---------------r---------------,---------------1I----~

Oct. 28, 1975

wc /1:1a: 14>...JC i5u..1:1en :wa..jjj...Jt..:I 13::l2w>j:: MOLE R ATIO..:Ic( Agi KI,1:1 3 - 1a: 0 1-'": 12 0 - 2::l2

- 3::>. . . . . / 6 - 12:l1:1 1 - 65..JI

STD11 -164 -8 -12

TEMPERATURE,DCFig. 1


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u .s . Patent Oct. 28, 1975 Sheet 2 of 2

Na _-- Li- ~ - - - -- _ Rb//'7 ;.,/------- A g S TA ND AR D

,,/ - : ~ - - - - - -' " "" " /-/ . '/c;,ct2t:JW....Jc. .>: : : : >2w 1012>i=c. .>wu. .u. .w

1011

. ' C s

3,915,379

TEMPERATURE, D C

10L_-- ~ -L~ _L ~ L_~o -5 -10 -15 -20 -25

F ig . 2

5%Li 103~1%LiI03________ 0.1%u 103

W....Jc . . >: : : : >2w> 1012i=c . . >wu. .u. .w

TEMPERATURE, D C

10L_------_L--------~------~---------L--------~~o -5 -10 -15 -20 -25

F ig . 3


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3,915,3791METHODOF CONTROLLINGWEATHER

GOVERNMENT INTERESTThe invention herein described may be manufac-

tured and used by or for the Government of the United 5States of America for governmental purposes withoutthe payment of any royalties thereon or therefor.

BACKGROUNDOF THE INVENTIONThis invention is a division of patent application Ser.

No. 767,068, filed Oct. 10, 1968 now U.S. Pat. No.3,802,971.Weather modification has been applied in different

parts of the world and several methods and means havebeen used to modifythe physical and dynamical condi-tions of the atmosphere. Particles exist in the atmo-sphere which have the ability to form ice crystals in su-percooled clouds. These are called natural or atmo-spheric ice nuclei and are responsible primarily formost of the natural ice formation in the cloud and their 20absence is strongly related to the supercooling of thecloud.When a supercooled cloud isseeded with ice nu-clei, ice crystals are formed which start growing by ab-stracting water vapor from the surrounding atmosphere 25or by freezing the cloud droplets by accretion. Thereare two widely used artificial ice nuclei: dry ice (solidcarbon dioxide) used successfully for cloud modifica-tion bySchaefer in 1946, and silver iodidewhose excel-lent activity was discovered by Vonnegut in 1947. Re- 30search has been conducted on the generation of solidparticulate matter by pyrotechnic and rocket propul-sion techniques and studies made of the nucleatingproperties of these materials asfunctions of their chem-ical and physical properties. The generation of pure sil- 35ver iodide has been studied in the past to characterizethe generation process and to establish ice nuclei char-acteristics as a function of silver iodate concentrationin the pyrotechnic. The present invention provides anumber of new pyrotechnic compositions which upon 40combustion showice nuclei activityat from -5 to -20C. and provide more effective cloud seeding.

2SUMMARY OF THE INVENTION

This invention is for improved pyrotechnic composi-tions. The compositions comprise a fuel and oxidizermixture to which a mixture consistingof a metal iodateand an alkali iodate is added. The products of decom-position are the metal iodide-alkali iodide in varyingmolar ratios, complexes and other mixtures which in-duce the freezing of supercooled water droplets in cold

10 clouds and fogs in an effective manner.The general object of this invention is to provide acomposition which upon combustion yields freezingnuclei having greatly increased activity, especially atthe higher temperatures approaching 0C. Another ob-

15 ject is to provide pyrotechnic compositions which areinexpensive to formulate and are simple to use in dis-pelling fog, suppressing hail formation and increasingrainfall.

BRIEF DESCRIPTION OF THE DRAWINGFIG. 1shows nuclei activity of the potassium iodide-silver iodide complex wherein the mole ratio of AgI-KI

ranges froni 3:I to 1:65;FIG. 2 shows the ice nuclei activity for the initial se-ries of formulations (Examples 4, 5, 7, 8, and 9)

wherein silver iodide is shown as the working standard;andFIG. 3 shows the nuclei activityof the lithium iodide-silver iodide complex.

DESCRIPTIONOF THE INVENTIONIn accordance with the present invention formula-

tions comprising a fuel, an oxidizer, a metal iodate se-lected from the group consisting of silver, lead, copper,and bismuth iodates and an alkali iodate selected fromthe group consisting of lithium, sodium, potassium, ru-bidium, cesium and ammonium iodates were blended.The formulations were then pressed, cast, or extrudedinto the desired shape and cured.The followingexamplesset forth inTable Iwillbetterillustrate the invention but should not be considered aslimiting thereof.

TABLE IPyrotechnic Compositions(Ingredients % by Weight)

NucleationSample Metal Iodate Alkali Iodate Oxidizer Fuel Temp. 0C.I AglOa 5% NH.IOa 5% NH,NOa 40% Nitrosol 50%2 Pb[Oa 5% NH,lOa 5% NH,NOa 40% Nit rosol 50%3 Ag[Oa 15% Na[Oa 28.73% Nl:I,NOa 6.27% PNC 50%4 Ag[Oa [5% Na[Oa 15% NH,NOa 20% PNC 50%5 Ag[Oa 5% uro, 5% NH,NOa 40% PNC 50%6 Ag[Oa 5% NalOa 5.44% NH,NOa 39.56% PNC 50%7 AglOa 5% KIOa 5.88% NH,NOa 39.12% PNC 50%8 AglOa 5% cao, 8.46% NH,NOa 36.54% PNC 50%9 AglOa 5% asro, 7.16% NH,NOa 37.84% PNC 50%10 AgiO a 5% cao, 1% NH,NOa 44% PNC 50%11 AglOa 5% RblOa 1% NH,NOa 44% PNC 50%12 Pb(lOa). 5% uro, 5% NH,NOa 40% PNC 50%13 AglOa 5% NalOa 1% NH,NOa 44% PNC 50%14 AglOa 5% KIOa 1% NH,NOa 44% PNC 50%15 AglOa 5% LiIOa 1% NH,NOa 44% PNC 50%16 AglOa 5% uro, 1% NH,NOa 44.9% PNC 50%17 AglOa 5% KIOa 0.1% NH,NOa 44.9% PNC . 50%18 AglOa 5% cuo, 0.1% NH,NOa 44.9% PNC 50%19 AglOa 5% KIOa 45% PNC 50%20 AglOa 5% KIOa (,26% NH,NOa 43.74% 5 0 O / CPNC21 AglOa 5% KIOa 1.89% NH,NOa 43.11% PNC 50%22 AglOa 5% KIO, 3.79% NH,NOa 41.21% PNC soc23 AgiO, 5% KIOa 7 . 5 8 o / c NH,NOa 37.42% PNC 50%24 AglOa 5% KIOa 11.35% NH,NOa 33.65'if PNC 50%25 AgiO, 1% KIOa 49% PNC 50%


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3,915,3793 4TABLE I-ContinuedPyrotechnic Compositions(Ingredients 0/,-by Weight)

NucleationSample Metal Iodate Alkali Iodate Oxidizer Fuel Temp. 0 C.26 AgiO. 5% KIO. 5.88% NH.NO. 34.12% PNC 50%

AI 50/,-27 AgiO. 1% LiIO. 10% PNC 500/,-KIO. 39%28 AgiO. 5% KIO. 5.88% NH.NO. 34.12% AI 50/0PETRIN 15%PNC 35%29 AgiO. 1% NaIO. 49% PNC 500/,-30 AgiO. 5% NaIO. 1.17% NH.NO. 43.88% PNC 500/,-31 AgiO. 5% NaIO. 3.5% NH.NO. 41.5% PNC 50'1>32 AgiO. 5% NaIO. 10.5% NH.NO. 34.5% PNC 50%33 AgiO. 12.04% uro, 1.360/,- NH,NO. 36.6% Nitrosol 500/,-34 Pb(lO.J. 10% KIO. 11.75% NH.NO. 28.25% PNC 50


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5minutes to insure homogeniety, adding to the resultinglacquer 19.2 grams of a petroleum sulfonate emulsify-ing agent for nitrocellulose in about 900 ml of waterand circulating through a collard mill for about 10min-utes, draining the resulting emulsion from the mill into 5about 30 liters of water and stirring about 15 minutesuntil a nitrocellulose precipitate is formed which is fil-tered from the liquid, washed in hexane, dried forabout 16 hours and sifted through a 200 mesh screen.The formulations shown in Table I above may be 10

modified as necessary to generate the desired complexnuclei. In place of the plastisol nitrocellulose doublebase formulations were used. They comprise about51%byweight nitrocellulose, 43% byweight nitroglyc- 15 ---- - -- - - -- - -- - -- - -- -erin, and the remainder diethylphthalate, a plasticizer,and ethyl centralite, a stabilizer. Cast double base com-prising nitrocellulose and nitroglycerin in majoramount petrin and metriol trinitrate in minor amountalso provided a good fuel for the metal iodate-alkali io- 20date mixture.The products of combustion of these examples usingnitrosol binder were collected, characterized by wetchemical and X-ray diffration analysis and the resultscompared with data on known complexes. Ice nuclei 25activity spectra were measured in a Naval WeaponsCenter cloud chamber burning small pyrotechnic sam-ples directly in supercooled fog of 1glm3liquid watercontent. These fogs evaporate in 3-8 minutes, depen- 30dent on operating conditions if not nucleated. Each ex-periment utilized 100 mg of pyrotechnic containing10%of the heavy metal derivative burned at one pointin the chamber. Nucleation temperatures were taken asthose where complete icing of the chamber occurred, 35 _but do not necessarily represent the true droplet equi-librium threshold values.The activity spectra for the initial series of formula-

tions were compared with silver iodide as a workingstandard (see AG. 2). The spectrum for complex ce- 40siumiodide-silver iodide nuclei did not show enhancedactivity over that for silver iodide alone. Nevertheless,sufficient cesium iodide was present in the nuclei tocomplex the silver iodide completely. The rubidium io- 45dide-silver iodide systemshowsslightlyenhanced activ-ity over that of standard silver iodide. The sodium io-dide-silver iodide, potassium iodide-silver iodide, andlithium iodide-silver iodide nuclei all show greatly en-

Pyrotechnic Nucleationhanced activity. 50 Composition Ternp., -c .The potassium iodide-silver iodide series showed the -----------------------highest activity at warmer temperatures. Formulations ~~g:.KIOa _~:~calculated to yield complex nuclei with potassium io- MoOa.2 KIOa -10.0dide-silver iodide ratios of 1:3, 2:1, 3:1, 12:1, and 65:1 ~~g::~: : 3 a = g : gare shown in FIG. 1.The 3KI - AgI complex shows the 55 Bi20a.2 KIO.highest activity. Although less effective at warmer tern- Bi203.4 KIOaBi.Oa.6 KI03peratures, the 65KI - AgI nuclei show excellent activi- Bi(IOah3 uio,. I t Bi(lOah3 KIOa'ties at ower tempera ures.Nuclei having a molar ratio of 65KI to one AgI

(97.87 wt. %KI,213 st. % Agl) are completely soluble 60when sufficient water is acquired to yield a compositionof 39 wt. %water and 61 wt. %of the nuclei material.The LiI-2AgI complex follows the behavior of the KI-Agi complex shown in FIG. 3. 65Table II gives the nucleation temperature values ob-

tained for silver iodide and several complexes of silveriodide and potassium iodide.

3,915,379 6TABLE II

PyrotechnicComposition

NucleationTemp.,oc.AgI03AgIOa.2 KIO.AgIO,.3 KIO,AgIOa.4 KIOa

o-1.0-1.0-0.8

Table III shows the temperature of nucleation of thedecomposition product of lead iodate and those if itscomplexes with several alkali iodides.

TABLE IIIIce Nucleation Temperatures

3 Pb(IOah.KI032 Pb(lO,h.KIOaPb(lOah.KIOaPb(lO,l a-2 KIOaPb(lOah.3 KIO,Pb(lOah.4 KIO,Pb(lO,l a-5 KIOaPb(103l a-7 KIOaPb(lOah8 KIOaPb(I03),9 KIOaPb(103l a-2 uio,Pb(lO,l a-3 UIO,Pb(lOal .4 LiIO.

2 Pb(103h.Na10aPb(I03h.NaIOaPb(IOal2.2 NalOa

-1.2-1.0-1.0-1.5-1.8-1.2-1.5-1.0-1.0-0.5-1.0-1.5-1.0-0.8-1.0-1.0

Table IV shows the values obtained for nuclei gener-ated by combustion or pyrotechnics containing cupriciodate alone and with added alkali iodates.

TABLE IVIce Nucleation Temperatures

PyrotechnicComposition

NucleationTemp. , C.Cu(lOahCu(103h.2 KIOaCu(lOal e-3 KI03Cu(IO,h.4 KIO.Cu(lOah.2 Lil03Cu(lOah.3 Lil03

-7.0-6.0-6.5a-2.0-1.2b

UNo nucleation occurred at -1.00 C."No nucleation 'occurred at -5.5 c.

TABLE V

The unexpectedly high threshold temperature valuesobtained suggest strongly that contact freezing of drop-lets is the major mechanism of ice crystal formation.Under the test conditions of an evaporating fog, sil-ver i~dide can function as an ice nuclei at measured air

temperatures of +0.50 C.Tentative interpretation of the data in Tables II-Vsuggests the following:


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3,915,3797Heavy metal iodides are more effective nuclei than

the corresponding oxides. Molybdenum and bismuthiodides are thermodynamically unstable and are notformed during combustion processes. Complexes of theoxides with alkali iodides are also not active at high 5temperatures. Lead and copper iodates decompose togive oxyiodides of intermediate activity. Complexingwith alkali iodides may enhance activity. Silver iodideshows the highest temperature threshold and is a stableproduct of combustion of silver iodate. Complexes of 10silver iodide and alkali iodides are equally effective asice nuclei.The new compositions disclosed herein are pyrotech-

nics which are generally low explosives that have butlittle explosive value because of their low rates of com- 15bustion and the liberation of relatively little gas per unitweight of composition. The combustion by products ofthe present compositions include the silver iodide-alkali iodide complex, lead iodate and those of its com-plexes with several alkali iodides, cupric iodate alone 20and with alkali iodates, complexes of bismuth and mo-lybdenum oxides and alkali iodides. All of the samplesare well within the safety requirements of a military py-rotechnic.Metal such as aluminum is added to raise the flame 25

temperature and additional oxidizer (in addition to theiodates) is added to ensure proper combustion.Many cloud seeding techniques have been used to in-

troduce the metal iodide-alkali iodide complexesformed upon combustion of these new pyrotechnics 30into undercooled clouds whereby rainfall was attainedand hail suppression was achieved. In several experi-ments the composition was ignited on a mountain topand the complexes entrained into the range of cloudsto be seeded by updraft. The material was also ferried 35directly into the clouds to be seeded by aircraft pro-vided with special devices for expelling the pyrotech-nics which produced the atomized seeding material.Rockets and artillery missiles have also been loadedwith the composition and fired into the appropriate 40cloud.These new pyrotechnic compositions either seed the

cloud and produce rainfall or snow if they reach thecold part of the cloud or they dissolve out. Most of thecomplexes formed upon combustion of the composi- 45tion, e.g., AgI-KI, break down with water and silver orlead iodide, as the case may be, is precipitated out. Allof the compositions in the dry state nucleate ice butthey must be dispersed into the cloud at the right tem-peratures (-20 to OC.). Most of them are quite effec- 50tive if the complex is dropped into the clouds and over-seeding the tops of connective clouds has stoppedclouds from raining.

8The herein described compositions must be brought

into a state of fine dispersion for the seeding of theclouds to successfully suppress hail, increase rainfall ordisperse fog. The present invention provides substanceswhich show better capability of forming freezing nucleias silver iodide alone, and are simple and inexpensiveto prepare.What is claimed is:1. A method for artificially influencing the weatherwhich comprisesoversee ding the tops of convective clouds with a sil-ver iodide-potassium iodide complex whereby rain-fall is suppressed.

2. A method for influencing the weather comprisingthe steps of:a. providing a pyrotechnic formulation containingthe following:

Ingredients Percent by weightFuel BinderOxidizer AdditionMetal IodateAlkali Iodate

50--555-451-10

0.1-30

said fuel binder being selected from the group con-sisting of: plastisol nitrocellulose, nitrosol, doublebase propellant binder consisting essentially of ni-trocellulose and nitroglycerine, cast double baseconsisting essentially of nitrocellulose, petrin, met-riol trinitrate, and the binder system consisting es-sentially of a carboxylated linear polybutadienehaving a carboxy end group present on both endsof the polymer chain and tris - [1-( 2 methyl) aziri-dinyl] phosphine oxide and trimethylol ethane tri-nitrate;

said oxidizer being selected from the group consistingof ammonium iodate, ammonium nitrate, and am-monium perchlorate;

said metal iodate being selected from the group con-sisting of the iodates of copper, silver, lead, bis-muth and molybdenum; and

said alkali iodate being selected from the group con-sisting of the iodates of lithium, sodium, potassium,rubidium, cesium and ammonium;b. forming the pyrotechnic formulation into a de-sired shape and curing it; and

c. burning the shaped and cured pyrotechnic for-mulation above a cloud having an air tempera-ture in the range of from -20 to OC to formcomplex metal iodide-alkali iodide ice formingnuclei. * * * * *

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united states patent 3,915,379

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