Preparation of porous pyrophoric iron using sol-gel methods

Abstract

New sol-gel methods can be employed to generate high surface area porous iron (III) oxide-based solids. Chemical reduction of such porous solids at low temperatures allows the preparation of high surface area porous iron with little sintering, with the only byproduct being water. The material is readily pyrophoric and has utility in new decoy flares. The material, prepared by this synthetic route, eliminates the use of hot caustic leaching solutions. It does not require the incorporation of any hazardous materials or processes that are not already used in current production methods.

1 . A method for producing porous nanostructured pyrophoric metal, comprising: 
 forming a solution containing at least one hydrated-metal ion inorganic salt and at least one solvent;    adjusting the pH of said solution with a proton scavenger to induce gel formation of said solution to form a nanostructured metal-oxide-based gel;    drying said nanostructured metal-oxide-based gel to form a nanostructured metal-oxide-based porous material;    thermally treating said nanostructured metal-oxide-based porous material to produce a thermally treated nanostructured metal-oxide-based porous material; and    heating said thermally treated nanostructured metal-oxide-based porous material in the presence of a chemical reductant diluted with an inert carrier gas to produce a porous nanostructured pyrophoric metal.    
   
   
       2 . The method of  claim 1 , wherein said nanostructured metal-oxide-based porous material is selected from the group consisting of a xerogel and an aerogel.  
   
   
       3 . The method of  claim 1 , wherein the step of drying comprises drying said nanostructured metal-oxide-based gel by atmospheric evaporation, wherein said nanostructured metal-oxide-based porous material comprises nanostructured metal-oxide-based xerogel.  
   
   
       4 . The method of  claim 1 , wherein the step of drying comprises drying said nanostructured metal-oxide-based gel by super critical solvent extraction, wherein said nanostructured metal-oxide-based porous material comprises nanostructured metal-oxide-based aerogel.  
   
   
       5 . The method of  claim 1 , wherein the step of thermally treating said nanostructured metal-oxide-based porous material includes removing at least one impurity from said nanostructured metal-oxide-based porous material  
   
   
       6 . The method of  claim 1 , wherein the step of thermally treating said nanostructured metal-oxide-based porous material includes removing at least one surface bound chemical species from said nanostructured metal-oxide-based porous material.  
   
   
       7 . The method of  claim 1 , wherein the step of thermally treating said nanostructured metal-oxide-based porous material is carried out while said nanostructured metal-oxide-based porous material is under a dynamic vacuum.  
   
   
       8 . The method of  claim 1 , wherein said chemical reductant is selected from a group consisting of hydrogen gas (H 2 ) and carbon monoxide (CO).  
   
   
       9 . The method of  claim 1 , wherein said porous nanostructured pyrophoric metal comprises porous nanostructured pyrophoric iron.  
   
   
       10 . The method of  claim 9 , wherein said at least one hydrated-metal ion inorganic salt comprises Fe (III) salt.  
   
   
       11 . The method of  claim 10 , wherein said Fe (III) salt is selected from the group consisting of Ferric nitrate nonahydrate, Fe(NO 3 ) 3 .9H 2 O, ferric chloride hexahydrate, FeCl 3 .6H 2 O, and FeCl 3    
   
   
       12 . The method of  claim 9 , wherein said at least one solvent is selected from the group consisting of ethanol (200 proof), 1-propanol, t-butanol, acetonitrile, water (distilled), ethyl acetate, 2-ethoxy ethanol, N,N-dimethylformamide, methanol, tetrahydrofuran (THF), acetone, ethylene glycol, propylene glycol, formamide, 1,4-dioxane, benzyl alcohol, nitrobenzene, hexanes, and dimethyl sulfoxide (DMSO).  
   
   
       13 . The method of  claim 9 , wherein said at least one solvent is selected from the group consisting of ethanol and water.  
   
   
       14 . The method of  claim 13 , wherein said of ethanol is about 200 proof and said water is distilled.  
   
   
       15 . The method of  claim 9 , wherein said nanostructured metal-oxide-based gel comprises Fe 2 O 3  gel.  
   
   
       16 . The method of  claim 9 , wherein the step of forming a solution is carried out under ambient conditions.  
   
   
       17 . The method of  claim 10 , wherein said solution comprises about 0.65 g of Fe(NO 3 ) 3 .9H 2 O (1.6 mmol) dissolved in 3.25 mL of 200 proof ethanol.  
   
   
       18 . The method of  claim 17 , wherein the step of adjusting the pH comprises providing an epoxide/Fe ratio of about 11.  
   
   
       19 . Porous nanostructured pyrophoric metal produced by a method comprising: 
 forming a solution containing at least one hydrated-metal ion inorganic salt and at least one solvent;    adjusting the pH of said solution with a proton scavenger to induce gel formation of said solution to form a nanostructured metal-oxide-based gel;    drying said nanostructured metal-oxide-based gel to form a nanostructured metal-oxide-based porous material;    thermally treating said nanostructured metal-oxide-based porous material to produce a thermally treated nanostructured metal-oxide-based porous material; and    heating said thermally treated nanostructured metal-oxide-based porous material in the presence of a chemical reductant diluted with an inert carrier gas to produce a porous nanostructured pyrophoric metal.    
   
   
       20 . The porous nanostructured pyrophoric metal of  claim 19 , wherein said nanostructured metal-oxide-based porous material is selected from the group consisting of a xerogel and an aerogel.  
   
   
       21 . The porous nanostructured pyrophoric metal of  claim 19 , wherein said porous nanostructured pyrophoric metal comprises porous nanostructured pyrophoric iron.  
   
   
       22 . The porous nanostructured pyrophoric metal of  claim 21 , wherein said at least one hydrated-metal ion inorganic salt comprises Fe (III) salt.  
   
   
       23 . The porous nanostructured pyrophoric metal of  claim 22 , wherein said Fe (III) salt is selected from the group consisting of Ferric nitrate nonahydrate, Fe(NO 3 ) 3 .9H 2 O, ferric chloride hexahydrate, FeCl 3 .6H 2 O, and FeCl 3    
   
   
       24 . The porous nanostructured pyrophoric metal of  claim 21 , wherein said at least one solvent is selected from the group consisting of ethanol (200 proof), 1-propanol, t-butanol, acetonitrile, water (distilled), ethyl acetate, 2-ethoxy ethanol, N,N-dimethylformamide, methanol, tetrahydrofuran (THF), acetone, ethylene glycol, propylene glycol, formamide, 1,4-dioxane, benzyl alcohol, nitrobenzene, hexanes, and dimethyl sulfoxide (DMSO).  
   
   
       25 . The porous nanostructured pyrophoric metal of  claim 21 , wherein said at least one solvent is selected from the group consisting of ethanol and water.  
   
   
       26 . The porous nanostructured pyrophoric metal of  claim 21 , wherein said nanostructured metal-oxide-based gel comprises Fe 2 O 3  gel.  
   
   
       27 . The porous nanostructured pyrophoric metal of  claim 22 , wherein said solution comprises about 0.65 g of Fe(NO 3 ) 3 .9H 2 O (1.6 mmol) dissolved in 3.25 mL of 200 proof ethanol.