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United States Patent (19) 3,977,990 Beckert et al. |45) Aug. 31, 1976

54 CONTROLLED GENERATION OF COOL 3,450,638 6/969 Edwards ...... 252, 188 FROM SOLID MIXTURES 3,676,07 7/1972 Speed...... 252/188 X 3,734,863 5/1973 Beckert et al...... 252/88 E75 Inventors: Werner F. Beckert, Las Vegas, 3,862,052 1 (1975 Beckert et al...... 252/88.3 Nev., William H. Barber, Brandywine, Md., Ottmar H. Dengel, Front Royal, Va.; Robert A. Primary Examiner-Benjamin R. Padgett Robb, Bryans Road, Md. Assistant Examiner-David Leland 73 Assignee: The United States of America as represented by the Secretary of the Navy, Washington, D.C. 22 Filed: Oct. 30, 1974 57 ABSTRACT 21 Appl. No.: 519,312 The hydrogen gas evolution rates and the gas tempera 52 U.S. Cl...... 252/188.3 R; 252/188; tures of certain hydrogen gas generating compositions 423/648 are modified by adding compounds such as LiAlH 51 Int. Cl.’...... C01B 1/02; COB I/O5 which thermally decompose in the reaction zone pro 58 Field of Search...... 252/88, 88.3; ducing hydrogen while lowering the reaction tempera 423/646-648 ture, and acetonates, metal , and the like which, when added in relatively small amounts accelerate the 56 References Cited hydrogen gas evolution rate. UNITED STATES PATENTS 3,405,068 10/f 968 Hiltz...... 252/88 X 19 Claims, No Drawings

3,9 / 1,99U 2 produced in less than 15 seconds, using these mixtures. CONTROLLED GENERATION OF COOL However, the recorded gas temperatures are as high as HYDROGEN FROM SOLID MIXTURES 500°C, or higher depending on the nature and amount of the material reacted and on the mode of firing. The BACKGROUND OF THE INVENTION high gas temperature prevents this hydrogen gas gener This invention relates to hydrogen gas generating ating system from being used as a direct hydrogen compositions and more specifically to compositions for source for balloon inflation, as outlined below. generating hydrogen gas at an adjustable rate and at In order to inflate a balloon with hydrogen the gas relatively low temperatures. has to be relatively cool for two reasons: Simple means for generating relatively small amounts 10 1. The dependence of the mechanical properties of of hydrogen gas are desirable for many applications. the balloon material on temperature sets an upper ten Examples are inflation of lighter-than-air devices such perature limit. as balloons and buoyant markers. Obviously, hydrogen Suitable balloon materials include natural or Syn gas thus generated is also suitable for use as a reactant thetic resins such as rubber, or polyethylene tere in chemical reactions. Parameters, which are critical 15 phthalate (trademarked Mylar) for those and other applications, include the ratios of 2. When a balloon is inflated to volume V with hot the volume of hydrogen gas generated to the weight hydrogen of temperature T (K) without over-pressu and volume of the reactants, both ratios preferably rization, and the gas, after removal of the gas source, being as high as possible. Other parameters are the subsequently cools to temperature Ti (K), a volume hydrogen gas evolution rate, the hydrogen gas tempera 20 decrease AV takes place which is, according to the ture, the expendability of the gas generating systems ideal gas law, after use, or a combination of the above. As is readily apparent, conventional methods such as using a pres surized hydrogen gas cylinder or generating hydrogen a 7- - T from the reaction of metals or metal hydrides with 25 Av-v ( #) or water do not meet the above criteria. U.S. Pat. No. 3,734,863 to Beckert et al. issued May resulting in a lift decrease of 22, 1973, which is incorporated herein by reference, describes a method for generating hydrogen gas on a AL, - -AVX22.4 27(g) small scale under conditions which satisfy most of the 30 above parameters. The method is based on the reaction of ammonium or hydrazonium salts with suitable metal The variety of applications for a composition which hydrides as expressed by the following general equa generates hydrogen gas requires both generation of tions: hydrogen at a relatively low temperature and a means 35 for either increasing or decreasing the rate of hydrogen evolution. An increasing rate of hydrogen evolution is desirable for inflation purposes and some chemical reactions. A decreasing rate of hydrogen evolution is useful for either gas laser applications, other chemicals 40 reactions, or fuel cells. A composition, which has an where X is an group such as an inorganic acid adjustable gas evolution rate is desirable because of the group like halogen (Cl, Br, F), sulfate (SO), and the simplicity of varying a standard composition compared like, n is the valency of the acid group, Y is a mono-or to the difficulty of maintaining a variety of composi divalent metal capable of forming complex hydrides tions for each individual use. such as alkali and alkaline earth metals like Li, Na, K, 45 Mg, Ba, Ca, etc., m is the valency of said metal and Z SUMMARY OF THE INVENTION is a trivalent metal capable of forming complex hy Therefore, it is an objective of this invention to pro drides such as B, Al, and the like. vide a composition and method for generating rela Some of these reactions are highly exothermic as can tively cool hydrogen gas. be seen from the data in Table I, resulting in high gas 50 Another object of this invention is to provide a rela temperatures. tively cool hydrogen gas generating composition which has a high hydrogen gas output per weight and volume TABLE I units of the compositions. CALCULATED HEATS OF REACTION A further object of this invention is to provide a - H(kcal) HImole Ha(kcal) - 55 NHF - LiBH -20.36 -51 relatively cool hydrogen gas generating composition NHF + LiAlH. -66.2 -16.6 which has a high hydrogen gas output per weight and NHCI + LiAlH4 -53.82 -135 NHCL + NaAlH. -53.5 -13.4 volume unit of the compositions and which can be NHBr -- LiAlH -50.61 -12.7 modified to adjust the hydrogen gas evolution rates NH + NaAlH -5.24 -2.8 within certain limits. NHCl2 + 2 LiAlH - 68.4 -24. 60 NHSO + 2 NaAlH. - 60.7 -23.0 It is a still further object of this invention to provide NHF.HF + 2 LiAlH. - 07. - 6.5 compositions for generating relatively cool hydrogen gas having a maintained pressurizing ability. Also, it is an object of this invention to provide com Experimentally it is found that mixtures consisting of positions for generating relatively cool hydrogen gas NHCI/NaAlH4 or NH4F/LiAlH4 in stoichiometric pro 65 suitable for use with light duty materials. portions and containing varying amounts of binder Another object of this invention is to provide compo reliably produce hydrogen gas in a short time with sitions for generating relatively cool hydrogen gas suit yields between 0.7 and 1.0 l/g; 100 l of hydrogen can be able for use as a propellant composition.

3,977,990 3 4 Yet another object of this invention is to provide a mental data. The stability of the mixtures varies ac composition for generating relatively cool hydrogen cording to composition; the initiation temperature T of gas suitable for use in a chemical reaction. No. 3 in Table III was 84.5°C, T of No. 6 was found to These and other objects are accomplished by adding be between 121 and 128.5°C. Impact, sliding friction by hydrogen gas generating compositions a compound 5 and electrostatic tests on compositions No. 3 and No. 6 or a combination of compounds such as LiAlH, LiBH, show them to be of medium sensitivity. Mgha, or AlH3, which decompose in the reaction zone As can be seen from the information outlined above, while producing hydrogen gas; and by further adding mixture No. 6 in Table III, most promising with respect small amounts of certain metals, metal oxides, organo to stability, yield, and temperature, requires approxi metallic compounds, metal chelates, or mixtures 10 mately 18 seconds for the generation of 66 l of hydro thereof which influence the evolution rate of the gener gen gas. Based on analogies, the evolution time for 120 ated hydrogen gas. l of hydrogen gas or more using this composition was projected to be 24 seconds or higher, whereas for some DESCRIPTION OF THE PREFERRED applications (e.g. in-flight inflation of lighter-than-air EMBODIMENTS 15 markers) an evolution time of less than 15 seconds is A hydrogen generating composition is cooled, by the required. TABLE III CORRELATION BETWEEN COMPOSITION AND YIELD, TEMPERATURE AND EVOLUTION TEME Amount Maximum Total Evolution Mode of Fired Gas Gas Yield Time No. Composition Binder Firing (g) Temperature /g Seconds 1 1 NHF, 1.3 LiAlH Hot Wire 21.15 475°C 23.7 12 2 2 1 NHF, 3 LiAlH Hot Wire 530 350 56.3 1.06 6 3. 1 NHF, 4 LiAlH. SCID-k 61.7 245 52.0 0.84 7 4 1 NHF, 5 LiAlH Hot Wire 59.3 175 47.3 0.8O 27 5 1 NHCl, NaAlH, 1 LiAlH SCID 20.0 290 6.0 0.80 , 10.5 6 1 NHCt, NaAlH, 2 LiAlH 4 SCID 81 235 65.9 0.81 18 7 l NHCl, i NaAlH, 3 LiAlH SCID 61.6 150 44.0 0.71 60 8 NHC, 1 NaAlH4 LiAlH 1 SCID 65.9 125 326 0.49) 45 'Reaction apparently incomplctic "Ignitcr in tube addition of compounds which thermally decompose in the reaction zone to produce hydrogen, and has the In order to adjust the hydrogen generation rate, small rate of evolution adjusted by addition of metals, metal amounts of certain chemical compounds, or mixtures oxides, or organometallic compounds. 35 thereof, which can significantly influence the hydrogen The composition results in the temperature of the evolution rate of the above mixtures are added thereto. hydrogen gas being lowered, without significantly low These compounds comprise a wide variety of chemical ering the hydrogen gas yield per gram of the hydrogen compositions. gas generating composition, by adding compounds In general, all compounds tested consisting of a metal such as LiAlH4, LiBH, MgH2, or AlHa which thermally 40 or metal radical combined with organic ligands decompose in the reaction zone and ultimately produce such as the acetylacetonates, influence generation rates hydrogen. The resulting lower gas temperature is when about 5% are added to the basic mixtures. Most caused by two factors: of these compounds produce a rate increase. Only a. the decomposition reactions of the added com acetylacetonate, and to a lesser degree titanyl pounds are more or less endothermic thus using up 45 acetylacetonate, acetylacetonate, and ferro part of the heat generated by the basic reaction; cene show a distinct rate decrease. b. the added compounds and their decomposition While most oxides tested show no or little activity, products act as a heat sink. (III) oxide, oxide, and silicium dioxide (as The thermally decomposable compounds are added Cab-o-sil) proved to be very active. Platinum dioxide, to hydrogen gas generating compositions such as those 50 which is known to be easily reduced to finely divided of U.S. Pat. No. 3,734,863 above referenced. platinum, a hydrogenation catalyst, caused a spontane Table. II presents calculated heats of reaction for ous decomposition of the mixtures during preparation some systems where an excess of LiAlH is used to at ambient temperature in the dry box atmosphere. lower the gas temperature. Finely divided metal causes a similar decom 55 position, whereas metal on charcoal and palla TABLE II dium chloride have little effect. The following com NFLUENCE OF EXCESS HYDRDES ON HEATS OF pounds produce a significant hydrogen gas evolution REACTION CALCULATED VALUES). A/nole rate increase when 5% by weight are incorporated into No. CoMPOST on AH (kcal) H(kcal) a mixture of NHCl -- NaAlH -- LiAlH. (molar ratios 1. NHF -- 3 LiAlH. -56-5 -8.1 1:1:2): acetylacetonate, (II) acetylac 2. NHF -- 4 LiAlH -52.O. -6. etonate, (II) acetylacetonate, iron(II) acetylac 3. NHC -- NaAH -- LiAlH -49.O. -8.9 etonate, iron(III) acetylacetonate, manganic acetylac 4. NHC -- NaAH -- 2 LiAlH -44.5 -64 etonate, molybdenyl (VI) acetylacetonate, ace 5. NHC -- Naal -- 3 Lial H -39.9 -47 tylacetonate, uranyl acetylacetonate, acetyl 65 acetonate, vanady acetylacetonate, acetylaceton Yield, temperature, and rate of gas evolution of these ate, iron(III) oxide, platinum dioxide, silicium dioxide systems depend on nature, ratio and total amount of (Cab-O-Sil) silver oxide, palladium metal powder, sil the components, as illustrated in Table III by experi wer carbonate.

3,977,990 S 6 The following compounds produce a moderate hy rials which preferably have high heats of fusion and drogen gas evolution rate increase when 5% by weight heat capacities (Wood's metal, Rose's metal, or chemi were incorporated into a mixture of NHCl -- NaAlH.-- cal compounds such as Na2HPO. 12H2O) or low-boil LiAlH4 (molar ratios 1:1:2): acetylacetonate, ing liquids. acetylacetonate, chloranilate, nickel benzoylacetonate, palladium chloride, copper(I) The following examples are intended to illustrate the oxide. invention without unduly limiting the invention. The following compounds produce no detectable hydrogen gas evolution rate change when 5% by weight EXAMPLE I are incorporated into a mixture of NHCl -- NaAlH -- O A mixture of ammonium chloride, aluminum LiAlH4 (molar ratios l: 1:2): Aluminum oxide, , and aluminum hydride with isobutyl oxide, , copper-chromium oxide, magne styrene copolymer as binder and CONCO oil as plasti sium oxide, vanadium pentoxide, amorphous cizer, and 5% by weight of iron (III) oxide as additive, powder, 5% rhodium on charcoal, silver powder, tung pressed into the desired shape and fired in a suitable sten powder, chromium trichloride, copper(I) bro 5 aluminum gas generator produces gas in excess of 120 mide, ammonium vanadate, nickel chromate. at a temperature below 250°C in 10-15 seconds at a The following compounds produce a moderate hy yield of approximately 0.8 l/g. Thus; this material is drogen gas evolution rate decrease when 5% by weight especially suitable for in-flight inflations of lighter are incorporated into a mixture of NHCl -- NaAlH4 -- than-air markers and similar purposes where fast hy LiAlH4 (molar ratio 1:1:2): Ferrocene, (titanyl acetyl 20 drogen generation is required. acetonate, zirconium acetylacetonate, thorium oxide, The material is prepared in a drybox as a slurry of the dioxide, iron powder (reduced), tet components with the binder and the plasticizer dis rachloride. solved in toluene as solvent; after evaporation of the The following compound produces a significant hy solvent, the material is ground in a blender before drogen gas evolution rate decrease when 5% by weight 25 pressing. The reaction is started as outlined in U.S. Pat. is incorporated into a mixture of NHCl -- NaAlH4 -- No. 3,734,863, incorporated herein by reference. LiAlHa (molar ratio 1:1:2): Thorium acetylacetonate. Use of an optional binder greatly improves the me EXAMPLE II chanical properties of the material; up to 10% of butyl The procedure of Example I is repeated substituting styrene or isobutylstyrene copolymer only slightly in 30 other additives for the iron (III) oxide. The results are fluences yield, rate and temperature. Addition of up to summarized in Table IV. 30% of the binder level of CONCO oil, a plasticizer, TABLE IV further improves the mechanical properties of the grain, again without drastically influencing yield, rate, INFLUENCE OF ADDITIVES ON GAS EVOLUTION RATE and temperature. Small particle sizes (< 100pu) of the 35 COMPOUND EFFECT2) ingredients are desirable especially for the components Barium acetylacetonate of the basic reaction. Larger particle sizes generally Calcium acetylacetonate Chromium acetylacetonate decrease rate and yield significantly. Applications of Cobalt(II) acetylacetonate pressure to obtain various shapes of the material in Copper(II) acetylacetonate 40 Iron(II) acetylacetonate crease up to 97% of the theoretical value. Rate Iron(III) acetylacetonate and yield generally decrease with increasing density. Ferrocene Thus, by varying the amount of the endothermically Lanthanum chloranilate Manganic acetylacetonate decomposing component and the kind and amount of Molybdenyl(VI) acetylacetonate the secondary additive, as well a by varying the particle Nickel acetylacetonate sizes of the ingredients and the density of the final 45 Nickel benzoylacetonate Thorium acetylacetonate composition, hydrogen gas evolution rate and tempera Titanyl acetylacetonate tures are tailored for specific purposes. Other suitable Uranyl acetylacetonate Vanadium acetylacetonate binders are useful, such as those listed in the above Zinc acetylacetonate cited patent. Plasticizers and solvents are variable also, Vanadyl acetylacetonate based on the suitability for the process. Although in 50 Zirconium acetylacetonate Aluminum oxide general a small particle size of up to 100 microns is desirable to obtain a fast and nearly complete reaction, Calcium oxide large particle sizes might be useful for special purposes, Copper-Chromium oxide Copper(I) oxide e.g., to slow down the reaction, or to obtain a specific Iron(II) oxide grain structure. 55 oxide The additives or mixtures of additives can be added Platinum oxide Silicium dioxide(Cab-O-Sil) during the mixing process, or they can be added during Silver oxide the blending step, after evaporation of the solvent. Thorium oxide A number of mixing and shaping techniques can be Vanadium pentoxide used, depending on the nature of the material, such as 60 Boron, amorphous inert diluent or pneumatic mixing, casting or extrusion, Iron powder, reduced etc. Palladiurn 5% Rhodium on charcoal After generation, the hydrogen is optionally cooled Silver further by heat exchangers and/or heat sink arrange Chronium trichloride ments containing materials with a high specific heat 65 Copper(I) bromide such as copper, nickel, or cobalt, or materials which Palladium chloride Uranium tetrachloride exhibit an endothermic phase change between ambient Ammonium vanadate and the desired temperature, such as low-melting mate Nickel chromate 3,977,990 8 7 the acetylacetonates of barium and calcium; lanthanum TABLE IV-continued chloranilate; nickel benzoylacetonate; cuprous oxide; INFLUENCE OF ADDITIVES ON GAS EVOLUTION RATE and palladium chloride. 7. In a hydrogen gas generating composition compris COMPOUND EFFECT(2) ing (1) a hydride having the formula Y(ZH4), wherein Silver carbonate ---- Y is a mono- or divalent metal capable of forming '5% of the additive incorporated into a NHC/NaAH/iaih mixture complex hydrides and is selected from the group con '----- significant rate increase - modcrate rate increase sisting of alkali metals and alkaline earth metals, m is 0 - no detectable Tatc change the valency of said mono- or divalent metal and Z is a -- moderate rate decrease O trivalent metal capable of forming complex hydrides -- significant rate decrease and is selected from the group consisting of boron and aluminum, or mixtures of said hydrides; and (2) a hy Obviously numerous modifications and variations of drogen producing reactant having the formula the present invention are possible in light of the above (NH),X wherein X is an inorganic acid group and n is teachings. It is therefore to be understood that, within 15 the valency of said inorganic acid group, and mixtures the scope of the appended claims, the invention may be of said compounds, wherein components (1) and (2) practiced otherwise than as specifically described. are present in stoichiometric amounts in the hydrogen What is claimed as new and desired to be secured b gas generating composition, the improvement compris Letters Patent of the United States is: ing the incorporation in said composition of at least one 1. In a hydrogen gas generating composition compris 20 metal hydride coolant which decomposes endothermi ing ( ) a hydride having the formula Y(ZH), wherein cally to produce hydrogen gas; and a reaction rate Y is a mono- or divalent metal capable of forming modifier selected from the group consisting of the ace complex hydrides and is selected from the group con tylacetonates of thorium and zirconium; titanyl acetyl sisting of alkali metals and alkaline earth metals, m is acetonate; ferrocene; thorium oxide; titanium dioxide the valency of said mono- or divalent metal and Z is a 25 reduced iron powder; uranium tetrachloride; and mix trivalent metal capable of forming complex hydrides tures thereof. and is selected from the group consisting of boron and 8. The composition of claim 7 wherein said coolant is aluminum, or mixtures of said hydrides; and (2) a hy selected from the group consisting of LiAlH4, LiBH, drogen producing reactant having the formula MgH2 and AlH3. (NH),X wherein X is an inorganic acid group and n is 30 the valency of said inorganic acid group, and mixtures 9. The composition of claim 7 wherein the reaction of said compounds, wherein components (l) and (2) rate modifier comprises up to about 10% by weight of are present in stoichiometric amounts in the hydrogen said composition. gas generating composition, the improvement compris 10. The composition of claim 8 wherein said hydride ing the incorporation in said composition of at least one is NaAlH, said hydrogen producing reactant is NHCl, metal hydride coolant which decomposes endothermi said coolant is LiAlH4 and said rate modifier is thorium cally to produce hydrogen gas; and a reaction rate acetylacetonate. modifier selected from the group consisting of the ace 11. The composition of claim 9 wherein said modifier tylacetonates of barium, calcium, chromium, cobalt comprises about 5% by weight of said composition. (II), copper (II), iron (II), iron (III), (III), 40 12. The composition of claim 7 wherein the reaction nickel, vanadium, and zinc, molybdenyl (VI) acetylac rate modifier is selected from the group consisting of etonate; uranyl acetylacetonate; vanadyl acetylaceton zirconium acetylacetonate, titanyl acetylacetonate, ate; ferric oxide; platinum dioxide; dioxide; ferrocene, thorium oxide, titanium dioxide, reduced silver oxide; palladium metal powder; silver carbonate; iron powder and uranium tetrachloride. lanthanum chloranilate; nickel benzoylacetonate; cu 45 13. The composition of claim 1 wherein said coolant prous oxide; palladium chloride; and mixtures thereof. is selected from the group consisting of LiAlH, LiBH, 2. The composition of claim 1 wherein the reaction MgH2 and AlH. rate modifier is selected from the group consisting of 14. The composition of claim 1 further comprising a the acetylacetonates of chromium, cobalt(II), copper binder up to about 15% by weight of said composition (II), iron (II), iron (III), manganese (III), nickel, vana 50 thereby forming a solid gas generating composition. dium and zinc, molybdenyl (VI) acetylacetonate, ura 15. The composition of claim 14 additionally com nyl acetylacetonate; vanadyl acetylacetonate; ferric prising a suitable plasticizer up to about 30% by weight oxide; platinum dioxide; ; silver oxide; of said binder thereby improving the mechanical prop palladium metal powder; and silver carbonate. erties of said solid gas generating composition. 3. The composition of claim 1 wherein the reaction 55 16. The composition of claim 14 wherein said binder rate modifier comprises up to about 10% by weight of comprises an isobutyl/styrene copolymer. said composition. 17. The composition of claim 7 further comprising a 4. The composition of claim 3 wherein said hydride is binder up to about 15% by weight of said composition NaAlH, said hydrogen producing reactant is NHCl, thereby forming a solid gas generating composition. said coolant is LiAlH4 and said rate modifier is ferric 60 18. The composition of claim 17 additionally com oxide. prising a suitable plasticizer up to about 30% by weight 5. The composition of claim 4 wherein said rate mod of said binder thereby improving the mechanical prop ifier comprises about 5% by weight of said composi erties of said solid gas generating composition. tion. 19. The composition of claim 17 wherein said binder 6. The composition of claim 1 wherein the reaction 65 comprises an isobutyl/styrene copolymer. rate modifier is selected from the group consisting of sk xk k is sk