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.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Ser. No. 60 / 583,155, filed Jun. 24, 2004, titled: “Preparation of Porous Pyrophoric Iron Using Sol-Gel Methods,” incorporated herein by reference. [0002] The United States Government has rights in this invention pursuant to Contract No. W-7405-ENG48 between the United States Department of Energy and the University of California for the operation of Lawrence Livermore National Laboratory.BACKGROUND OF THE INVENTION [0003] 1. Field of the Invention [0004] The present invention relates to sol-gel chemistry, and more specifically, it relates to sol-gel methods for producing porous pyrophoric iron. [0005] 2. Description of Related Art [0006] Pyrotechnics can be grouped into six families; decoy flares, illuminating flares, colored flares, smokes, igniters / starters and miscellaneous pyrotechnic items. Decoy flares include infrared (IR) and solid pyrophoric flares. Aircraft pyrophoric decoy flares are solid pyrot...

AI Technical Summary

Benefits of technology

[0014] It is an object of the present invention to provide “sol-gel” chemical techniques that can be used in environmentally acceptable solvents to prepare high surface area porous iron (III) oxides.

[0015] It is another object of the invention to provide a “sol-gel” methodology for producing nanostructured energetic materials while minimizing or eliminating the health and environmental hazards associated with their current fabrication.

[0018] Highly porous sol-gel derived iron (III) oxide materials can be reduced to sub-micron-sized metallic iron by heating the materials to intermediate temperatures in a hydrogen atmosphere. Through a large number of experiments, complete reduction of the sol-gel based materials was realized with a variety of hydrogen-based atmospheres (25-100% H2 in Ar, N2, CO2, or CO) at intermediate temperatures (350° C. to 700° C. Sol-gel-derived metallic iron powders that were produced were ignitable by thermal methods. The present invention teaches techniques for producing sol-gel-derived metallic iron powders that are pyrophoric. For comparison several types of commercial micron sized iron oxides (Fe2O3, and NANOCAT™) were also reduced under identical conditions. All resulting materials were characterized by thermal gravimetric analysis (TGA), differential thermal analysis (DTA), powder X-ray diffraction (PXRD), as well as scanning and transmission electron microscopies (SEM and TEM). In addition, the reduction of the iron oxide materials was monitored by TGA. In general the sol-gel materials were more rapidly reduced to metallic iron and the resulting iron powders had smaller particle sizes and were more easily oxidized than the metallic powders derived from the micron sized materials. Impurities in the smaller fine metallic powders can prevent pyrophoricity if a passivation layer is on the iron.

Problems solved by technology

These solutions are corrosive and represent both a safety and environmental hazard.

However, the iron precursor used in the MOCVD process, iron pentacarbonyl, is highly pyrophoric and toxic.

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