Infrared signature powder and methods of controlling the temperature, duration, and intensity of infrared signature radiation

Abstract

In accordance with aspects of the invention, an infrared signature powder (“IR powder”) suitable for marking targets and other objects is provided. The IR powder primarily includes porous, pyrophoric iron and moderators. The duration, temperature, and intensity of the emitted infrared radiation can be tailored during the powder's production process by adjusting the proportion or properties of the moderators in the IR powder. Additionally, a method of producing the IR powder is provided. The method can include the following general steps: heat a blend of aluminum and iron powders to cause an inter-metallic reaction; leach the aluminum from the iron; and mix a selected moderator and a binder with the iron in selected proportions to create the IR powder. Many of these steps are performed in an oxygen-free environment to prevent the iron from prematurely oxidizing. Similarly, the IR powder is encapsulated in an oxygen-free frangible ampoule or other container.

1 . A method of manufacturing infrared signature powder, the method comprising:
 mixing granular first and second metals;   heating the mixture of the metals to form an intermetallic compound;   leaching the second metal from the intermetallic compound to provide a porous pyrophoric metal;   processing the porous pyrophoric metal to provide a pyrophoric metal powder;   coating the pyrophoric metal powder with a moderator, wherein the ratio of moderator to pyrophoric metal powder is selected to control oxidation properties of the coated pyrophoric metal powder; and   encapsulating the coated pyrophoric metal powder.   
     
     
         2 . The method of  claim 1  wherein mixing granular first and second metals comprises mixing iron and aluminum. 
     
     
         3 . The method of  claim 1  wherein mixing granular first and second metals comprises mixing at least one of nickel, cobalt, titanium, manganese, iron, tin, or zirconium with aluminum. 
     
     
         4 . The method of  claim 1  wherein processing the porous pyrophoric metal comprises grinding the porous pyrophoric metal to 200 mesh particle size. 
     
     
         5 . The method of  claim 1  wherein leaching the second metal from the intermetallic compound comprises leaching the second metal with a sodium hydroxide leaching solution. 
     
     
         6 . The method of  claim 1  wherein coating the pyrophoric metal powder with a moderator comprises mixing the pyrophoric metal powder, the moderator, and a binder solution comprising a resin dissolved in solvent, and wherein the solvent is at least one of toluene, hexane, cyclohexane, or acetone. 
     
     
         7 . The method of  claim 1  wherein the moderator includes a binder comprising of at least one of polyvinyl alcohol, pine resin, or Kraton. 
     
     
         8 . The method of  claim 1  wherein coating the pyrophoric metal powder with a moderator comprises coating the pyrophoric metal powder with a moderator at a ratio of from about 1:9 to about 9:1 by mass. 
     
     
         9 . The method of  claim 1  wherein the moderator comprises a mixture of boron nitride and activated carbon, mixed at a ratio of from about 1:3 to about 3:1 by mass. 
     
     
         10 . The method of  claim 1  wherein the first metal comprises iron, the second metal comprises aluminum, and the moderator comprises an approximately 50/50 mixture of boron nitride and activated carbon. 
     
     
         11 . The method of  claim 1  wherein encapsulating the coated pyrophoric metal powder comprises encapsulating the coated pyrophoric metal powder in a frangible, airtight container. 
     
     
         12 . A method of controlling the duration and temperature of infrared signature radiation, the method comprising:
 forming an intermetallic compound of a first metal and aluminum;   leaching the aluminum from the intermetallic compound to provide a porous pyrophoric metal;   grinding the porous pyrophoric metal into a pyrophoric metal powder;   selecting an amount of a moderator in proportion to an amount of the pyrophoric metal powder, wherein the proportion is controlled to achieve a pre-selected temperature and duration of emitted radiation;   coating the pyrophoric metal powder with the moderator; and   encapsulating the coated pyrophoric metal powder.   
     
     
         13 . The method of  claim 12  wherein forming an intermetallic compound of a first metal and aluminum comprises forming an intermetallic compound of iron and aluminum. 
     
     
         14 . The method of  claim 12  wherein selecting the amount of a moderator in proportion to the amount of the pyrophoric metal powder comprises selecting a proportion of moderator to pyrophoric metal powder from about 48%/52% to about 52%/48% to achieve low-intensity infrared radiation emission for at least 3 minutes at about 200 degrees Celsius or hotter. 
     
     
         15 . The method of  claim 12  wherein selecting the amount of a moderator in proportion to the amount of the pyrophoric metal powder comprises selecting no moderator to achieve high-intensity infrared radiation emission for approximately 2-5 seconds at about 800 degrees Celsius or hotter. 
     
     
         16 . The method of  claim 12  wherein selecting the amount of a moderator in proportion to the amount of the pyrophoric metal powder comprises selecting a proportion of moderator to pyrophoric metal powder from about 60%/40% to about 55%145% to achieve low-intensity infrared radiation emission for at least 3 minutes at about 60 degrees Celsius to about 80 degrees Celsius. 
     
     
         17 . A munitions round, comprising:
 a projectile having an internal portion and an external portion;   a frangible ampoule positioned in the internal portion; and   an infrared signature powder sealed within the ampoule, the infrared signature powder comprising pyrophoric porous metal powder coated with a moderator, wherein the proportion of the moderator to the porous metal powder in the infrared signature powder is controlled to emit radiation at a pre-selected temperature and intensity for a pre-selected duration upon exposure to ambient air.   
     
     
         18 . The munitions round of  claim 17  wherein the projectile comprises a tracer, and wherein the frangible ampoule is configured to break upon launch of the tracer to expose the infrared signature powder to ambient air. 
     
     
         19 . The munitions round of  claim 17  wherein the frangible ampoule is configured to break upon impact with a target, thereby exposing the infrared signature powder to the ambient air. 
     
     
         20 . The munitions round of  claim 17  wherein the infrared signature powder comprises a powder that is about 200 mesh particle size or smaller.