Abstract:
A heating device is provided comprising a heating chamber for receiving and storing a substance to be heated having at least two walls, a reaction chamber affixed to a wall of the heating chamber, a solid-state modified thermite reaction composition located within the reaction chamber and an actuatable trigger mechanism affixed to the reaction chamber such that the trigger mechanism is in contact with the reaction composition. According to another aspect, a heating device is provided comprising a heating chamber defining an interior space for receiving and storing a substance to be heated, a reaction chamber, a solid-state modified thermite reaction composition disposed within the reaction chamber such that it is physically isolated from and in thermal communication with the interior space of the heating chamber and an activator mechanism affixed to either reaction chamber or heating chamber such that the activator mechanism is in communication with the reaction composition.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Continuation-In-Part of U.S. patent application Ser. No. 12/419,917, filed on Apr. 7, 2009, entitled “Solid-State Thermite Composition Based Heating Device,” and a Non-Provisional Application of U.S. Provisional Patent Application 61/224,395, filed on Jul. 9, 2009 entitled “Solid-State Thermite Composition Based Heating Device,” both upon which a claim of priority is based. 
     
    
     TECHNICAL FIELD 
       [0002]    This disclosure relates to precisely controlled solid-state thermite reaction compositions and incorporation of those compositions into an integrated heating device for various applications such as heating of prepared foods or beverages in their containers. 
       BACKGROUND 
       [0003]    Situations arise in which it would be convenient to have a distributed means of providing heat in circumstances where heating appliances are not available. For example, producers of prepared foods have indicated that there could be significant market potential for self-heating food packaging (SHFP) systems that could heat prepared foods in their containers to serving temperature, simply, safely, and efficiently. 
         [0004]    For a mass consumer SHFP product, safety is paramount and should be inherent; preferably there should be no extreme temperatures, no fire, no smoke or fumes under anticipated use and abuse conditions. Practical considerations mandate that any system be reasonably compact and lightweight with respect to the food to be heated. Thus, the system should have a good specific energy and high efficiency. The system must also be capable of extended storage without significant loss of function or accidental activation of the heater. There should be some simple means of activating the heating component of the system, after which the required heat load should be delivered efficiently within a specified time period, perhaps just a few minutes. Operation must be very reliable with low failure rates in millions of units of production. For a single use food application, material components should be food-safe, low-cost, environmentally friendly and recyclable. 
         [0005]    The only SHFP technology currently in the consumer market uses an onboard system for mixing separated compartments of quicklime and water, yielding an exothermic heat of solution. These products are bulky (literally doubling package size and weight), complex, unreliable, costly, and have achieved very low market penetration. There have also been reported instances of the heater solution leaking and coming into contact with food or consumers. 
         [0006]    An exothermic reaction in which the component reactants could be premixed yet be inert until such time as the user initiates the reaction would be beneficial in terms of providing for a simpler, more compact, and low cost package design. A solid-state reaction system could offer advantage over wet chemical systems since solid systems will be less prone to spill or leak. 
         [0007]    Thermites are a class of exothermic solid-state reactions in which a metal fuel reacts with an oxide to form the more thermodynamically stable metal oxide and the elemental form of the original oxide. Thermites are formulated as a mechanical mix of the reactant powders in the desired stoichiometric ratio. The powders may be compressed into a unitary mass. These compact reactions generate substantial heat, with system temperatures that can reach several thousand degrees, often high enough to melt one or more of the reagents involved in the reaction. However, thermite reactions typically require a very high activation energy (e.g., welding thermites [Al/FeO x ] are ignited with a burning magnesium ribbon). Thus, a thermite reagent composition can be formulated to be quite stable to prevent inadvertent initiation due to electrostatic shock or mechanical impact. This generally inert character is an advantage in storage and transportation. 
         [0008]    The most widely known thermite system is the Al/FeO x  system described in Table 1. Once initiated, this system reacts virtually instantaneously to generate molten iron and is in fact used for welding rail lines. The only other significant known applications of thermites are in pyrotechnics and military weapons technologies. “A Survey of Combustible Metals, Thermites, and Intermetallics for Pyrotechnic Applications,” S. H. Fischer, M. C. Grubelich,  Proc. Of  32 nd    AIAA/ASME/SAE/ASEE Joint Propulsion Conference  (1996) and “Thermite Reactions: their utilization in the synthesis and processing of materials,” L. L. Wang, Z. A. Munir, Y. M. Maximov,  Journal of Material Science  28(14), 3693-3708 (1993) provide useful surveys of various classes of solid-state reactions including thermites. 
         [0000]    
       
         
               
             
               
               
               
               
               
               
             
               
               
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Characteristics of FeOx/Al and SiO2/Al Thermite Reactions 
               
             
          
           
               
                   
                   
                   
                 Adiabatic 
                   
                 Gas 
               
               
                   
                   
                 Heat of 
                 Reaction 
                   
                 production 
               
               
                   
                 Density 
                 reaction 
                 Temperature 
                   
                 (moles of gas 
               
               
                 Reaction 
                 (g cm −3 ) 
                 (kJ g −1 ) 
                 (K) 
                 State of Products 
                 per 100 g) 
               
               
                   
               
             
          
           
               
                 2Al + Fe 2 O 3 → 
                 4.175 
                 3.95 
                 3135 
                 molten Al 2 O 3  slag 
                 0.1404 
               
               
                 2Fe + Al 2 O 3   
                   
                   
                 (2862° C.) 
                 Fe (liq./gas) 
               
               
                 8Al + 3Fe 3 O 4  → 
                 4.264 
                 3.67 
                 3135 
                 Molten Al 2 O 3  slag 
                 0.0549 
               
               
                 9Fe + 4Al 2 O 3   
                   
                   
                 (2862° C.) 
                 Fe (liq./gas) 
               
               
                 4Al + 3SiO 2  → 
                 2.668 
                 2.15 
                 1889 
                 solid Al 2 O 3   
                 0 
               
               
                 3Si + 2Al 2 O 3   
                   
                   
                 (1616° C.) 
                 Si (liq.) 
               
               
                   
               
             
          
         
       
     
         [0009]    Since thermite reactions are generally vigorous with intense heat, they have not yet been successfully adapted for moderate-temperature consumer applications. Therefore, it would be highly beneficial to harness the energy release from a kinetically moderated thermite reaction thus transforming a reaction with generally pyrotechnic character to a precisely controlled power source for thermal energy and to then integrate that thermal energy into a heating device for consumer applications. 
       SUMMARY 
       [0010]    A solid-state modified thermite reaction composition is provided comprising a fuel component, a primary oxidizer, one or more initiating oxidizers and a thermal diluent. The composition can be further comprised of a fluxing agent. The composition can also further be comprised of a high energy oxidizer. 
         [0011]    According to another aspect, a heating device or package is provided comprising a heating chamber defining an interior space for receiving and storing a substance to be heated, a reaction chamber disposed adjacent to the interior space of the heating chamber, a solid-state modified thermite reaction composition disposed within the reaction chamber such that it is physically isolated from and in thermal communication with the interior space of the heating chamber; and an activator mechanism connected to either the reaction chamber or the heating chamber such that the activator mechanism is in communication with the reaction composition; wherein the reaction composition is inert until the activator mechanism is actuated. 
         [0012]    According to another aspect, a solid-state modified thermite reaction activation mechanism is provided comprising a first compound substantially in contact with a modified thermite reaction fuel, a second compound and a removable barrier located between the first and second compounds preventing any contact between the first and second compounds. When the barrier is removed, the first and second compounds contact one another and generate heat sufficient to initiate a thermite reaction using the modified thermite reaction fuel. 
         [0013]    Other aspects will be apparent to those of ordinary skill in the art upon consideration of the description, drawings and claims that follow. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    To understand the present invention, it will now be described by way of example, with reference to the accompanying drawings in which: 
           [0015]      FIG. 1  is a perspective cross-sectional view of an illustrative embodiment of a food packaging application with an integrated solid-state modified thermite heating element; 
           [0016]      FIG. 2  is a perspective cross-sectional view of the heating element depicted in  FIG. 1 ; 
           [0017]      FIG. 3  is a side cross-sectional view of another illustrative embodiment of a food packaging application with an integrated solid-state modified thermite heating element; 
           [0018]      FIG. 4  is a side cross-sectional view of an illustrative embodiment of a re-useable bowl with a port to removably insert a solid-state modified thermite heating element; 
           [0019]      FIG. 5  is a side cross-sectional view of the embodiment of  FIG. 4  with a re-useable activation mechanism removably attached; 
           [0020]      FIG. 6  is a perspective cross-sectional view of a solid-state modified thermite activation mechanism with a tear-off seal; 
           [0021]      FIG. 7  is a perspective cross-sectional view of a solid-state modified thermite activation mechanism with a foil barrier and foil piercing element; 
           [0022]      FIG. 8  is a side cross-sectional view of a solid-state modified thermite activation mechanism with a membrane coated with activation reagents on both sides; 
           [0023]      FIG. 9  is a side cross-sectional view of a solid-state modified thermite activation mechanism with a peizoelectric spark ignitor; 
           [0024]      FIG. 10  is a graphical depiction of a least squares fit of thermite reaction flame position versus time data; 
           [0025]      FIG. 11  is a graphical depiction of calorimetry data of solid-state thermite reactions. 
           [0026]      FIG. 12A  is a perspective view of an embodiment of the present invention. 
           [0027]      FIG. 12B  is a side cross-sectional view of the embodiment of  FIG. 12A . 
           [0028]      FIG. 12C  is a side cross-sectional view of the embodiment of  FIG. 12A . 
           [0029]      FIG. 12D  is a perspective cross-sectional view of the embodiment of  FIG. 12A . 
           [0030]      FIG. 12E  is a top view of an embodiment of the present invention. 
           [0031]      FIG. 12F  is a side view of the embodiment of  FIG. 12E . 
           [0032]      FIG. 12G  is a perspective view of the embodiment of  FIG. 12E . 
           [0033]      FIG. 12H  is a perspective view of an embodiment of the present invention. 
           [0034]      FIG. 12I  is a top cross-sectional view of the embodiment of  FIG. 12H . 
           [0035]      FIG. 12J  is a side cross-sectional view of the embodiment of  FIG. 12H . 
           [0036]      FIG. 12K  is a perspective view of an embodiment of the present invention. 
           [0037]      FIG. 12L  is a side cross-sectional view of the embodiment of  FIG. 12K . 
           [0038]      FIG. 12M  is a top cross-sectional view of the embodiment of  FIG. 12K . 
           [0039]      FIG. 13A  is a perspective view of an embodiment of the present invention. 
           [0040]      FIG. 13B  is a side cross-sectional view of the embodiment of  FIG. 13A . 
           [0041]      FIG. 13C  is a side cross-sectional view of the embodiment of  FIG. 13A . 
           [0042]      FIG. 13D  is a perspective view of the embodiment of  FIG. 13A . 
           [0043]      FIG. 13E  is a perspective view of the embodiment of  FIG. 13A . 
           [0044]      FIG. 13F  is a perspective view of the embodiment of  FIG. 13A . 
           [0045]      FIG. 13G  is a perspective view of the embodiment of  FIG. 13A . 
           [0046]      FIG. 13H  is a perspective view of the embodiment of  FIG. 13A . 
           [0047]      FIG. 13I  is a perspective view of an embodiment of the present invention. 
           [0048]      FIG. 13J  is a top cross-sectional view of the embodiment of  FIG. 13I . 
           [0049]      FIG. 13K  is a perspective cross-sectional view of the embodiment of  FIG. 13I . 
           [0050]      FIG. 13L  is a perspective view of an embodiment of the present invention. 
           [0051]      FIG. 13M  is a side cross-sectional view of the embodiment of  FIG. 13L . 
           [0052]      FIG. 13N  is a perspective view of an embodiment of the present invention. 
           [0053]      FIG. 13O  is a side cross-sectional view of the embodiment of  FIG. 13N . 
           [0054]      FIG. 14A  is a top view of an embodiment of the present invention. 
           [0055]      FIG. 14B  is a perspective view of the embodiment of  FIG. 14A . 
           [0056]      FIG. 14C  is a side view of the embodiment of  FIG. 14A . 
           [0057]      FIG. 14D  is a side cross-sectional view of the embodiment of  FIG. 14A . 
           [0058]      FIG. 14E  is a bottom view of the embodiment of  FIG. 14A . 
           [0059]      FIG. 14F  is a perspective cross-sectional view of the embodiment of  FIG. 14A . 
           [0060]      FIG. 14G  is a perspective cross-sectional view of the embodiment of  FIG. 14A . 
           [0061]      FIG. 14H  is a perspective cross-sectional view of the embodiment of  FIG. 14A . 
           [0062]      FIG. 15A  is a top view of an embodiment of the present invention. 
           [0063]      FIG. 15B  is a perspective view of the embodiment of  FIG. 15A . 
           [0064]      FIG. 15C  is a side view of the embodiment of  FIG. 15A . 
           [0065]      FIG. 15D  is a bottom view of the embodiment of  FIG. 15A . 
           [0066]      FIG. 15E  is a side cross-sectional view of the embodiment of  FIG. 15A . 
           [0067]      FIG. 15F  is a perspective cross-sectional view of the embodiment of  FIG. 15A . 
           [0068]      FIG. 15G  is a perspective cross-sectional view of the embodiment of  FIG. 15A . 
           [0069]      FIG. 15H  is a side cross-sectional view of a stack of the embodiments of  FIG. 15A . 
           [0070]      FIG. 16  is a perspective exploded view of an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0071]    The description that follows describes, illustrates and exemplifies one or more particular embodiments of the present invention in accordance with its principles. This description is not provided to limit the invention to the embodiments described herein, but rather to explain and teach the principles of the invention in such a way to enable one of ordinary skill in the art to understand these principles and, with that understanding, be able to apply them to practice not only the embodiments described herein, but also other embodiments that may come to mind in accordance with these principles. The scope of the present invention is intended to cover all such embodiments that may fall within the scope of the appended claims, either literally or under the doctrine of equivalents. 
         [0072]    It should be noted that in the description and drawings, like or substantially similar elements may be labeled with the same reference numerals. However, sometimes these elements may be labeled with differing numbers, such as, for example, in cases where such labeling facilitates a more clear description. Additionally, the drawings set forth herein are not necessarily drawn to scale, and in some instances proportions may have been exaggerated to more clearly depict certain features. Such labeling and drawing practices do not necessarily implicate an underlying substantive purpose. The present specification is intended to be taken as a whole and interpreted in accordance with the principles of the present invention as taught herein and understood to one of ordinary skill in the art. 
         [0073]    Food-safety and cost are two primary considerations in the selection of potential materials for use in the illustrative embodiments described herein. The Al/FeO x  and Al/SiO 2  thermites described in Table 1 involve only abundant, low-cost, food-safe materials and are therefore in this regard good candidates for SHFP. However, those of ordinary skill in the art will understand that many different materials could be selected without departing from the novel scope of the present invention. 
         [0074]    Table 1 compares various characteristics of Al/FeO x  and Al/SiO 2  thermite systems. In both cases aluminum is the fuel, with either FeO x  or SiO 2  as oxidizer. However the reaction character of the two systems are distinctly different. The high heat of reaction (3.8 kJ g −1 ) of the Al/FeO x  thermite leads to an adiabatic reaction temperature of over 3000 K (well above the melting point of both metals: T M, Fe =1809 K, T M, Al =933 K), with excess heat generating gases that can spew molten reaction product. The heat of reaction for Al/SiO 2  thermite is somewhat lower (2.15 kJ g −1 ) leading to an adiabatic reaction temperature of only 1889 K. This temperature is insufficient to melt the alumina slag formed during reaction. This slag acts as a thickening barrier to mass transfer in this type of system, and thus, thermal losses at the reaction front can quench the Al/SiO 2  thermite reaction. 
         [0075]    The rate-limiting step in thermite reactions is typically diffusion of material to the reaction zone. Accordingly, heat transfer and mass transfer are closely coupled in determining reaction rate. Thermite kinetics are typically modeled as a combustion system in which a solid flame front moves through preheat, reaction and quench zones. For reaction self-propagation to occur, the heat generated in the reaction zone must trigger reaction ahead of the wave front. The parameter used to quantify reaction rate of thermites is combustion wave speed. These can range anywhere from approximately 1 m s −1  for conventional thermites to greater than 1000 m s −1  for superthermites based on nanoscale powdered reactants. 
         [0076]    While reasonably exothermic, the Al/SiO 2  system is inherently both non-detonative and self-extinguishing. Based on this more controlled reaction character, this system comprises the foundation of the moderated thermite composition of the embodiments of the present invention described herein. In one embodiment the foundational solid-state chemistry is modulated via a combination of physical and chemical reaction modifiers to prepare Al/SiO 2  thermite fuel formulations that are inherently self-regulating at an optimal bounded temperature and give high utilization of the chemical energy content of the reaction materials at the requisite rate of heating. 
         [0077]    Another aspect of these embodiments is maximization of energy content in the solid thermite composition. “Mixed” thermites can be prepared, for example using a combination of oxidizers, and, as shown in Table 1, substituting any portion of the SiO 2  oxidizer with FeO x  to create a ternary system, which can beneficially increase the specific energy content of the system from approximately 2 to 4 kJ g −1  depending on FeO x  content. Aluminum, SiO 2 , and iron oxides are readily available in various commercial powder grades with food grade purity. 
         [0078]    Factors that can be altered to adjust the reaction rate and combustion temperature of thermite systems include: particle size of reactants, composition, diluent (inert) additives, pre-combustion density, ambient pressure and temperature, and physical and chemical stability of reactants. 
         [0079]    Because mass diffusion is the rate controlling step for thermites and diffusion-controlled reactions are inherently slower than temperature dependent chemical kinetics, increasing the diffusion coefficient or reducing the diffusion length between fuel and oxidizer species within an energetic composite can be used to accelerate the reaction rate. Particle shape can be highly influential. For efficient thermite fuel utilization, the solid-state reaction must be self-sustaining throughout its volume and there should not be extensive un-reacted regions. Those of ordinary skill in the art will understand that the degree and intimacy of mixing between the silica, aluminum, and additive constituents can be altered to satisfy a myriad of desired outcome parameters without departing from the novel scope of the present invention. 
         [0080]    In a preferred embodiment of an Al/SiO 2  thermite fuel formulation as shown in Table 2 below, the thermite fuel is an aluminum flake. In order to achieve an appropriate balance of reactive surface area and relatively low thermal conductivity to reduce combustion rate, a portion of the silica used is fumed silica, which is in fact an agglomerated nanoparticulate that is easily dispersed into mixtures. Certain materials can act as a “coolant” to lower the burning temperature of the mixture and/or slow down the reaction rate. Other additives can act as binders or stabilizers to regulate mass and heat transfer. Accordingly, in a particular embodiment, a nanoscale clay material is used as a thermal buffer to moderate temperature. Other materials may be used as well. 
         [0081]    In order to render self-sustaining character to the Al/SiO 2  system while operating at lower temperatures, an accelerant is incorporated to reduce the activation energy for the reaction or enable a lower energy reaction path. For example, as shown in Table 2, potassium chlorate, a strong oxidizer is used as an accelerant. Those of ordinary skill in the art will understand that there are many other possible chemical accelerants that could be incorporated without departing from the novel scope of the present invention. Further, the high boiling point, inert salt calcium fluoride is provided as a fluxing agent to increase the fluidity of the reacting system and thereby facilitate mass transport. 
         [0000]    
       
         
               
             
               
               
               
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Compositions in Weight Percent for Examples 
               
             
          
           
               
                   
                   
                 Example I 
                 Example II 
               
               
                 Component 
                 Function 
                 (BC03A04) 
                 (BC12A02) 
               
               
                   
               
             
          
           
               
                 Flaked Aluminum 
                 Fuel component 
                 17.9% 
                 17.3% 
               
               
                 powder (Toyal America 
               
               
                 5621) 
               
               
                 KClO 3   
                 Initiating oxidizer 
                 14.3% 
                 13.8% 
               
               
                 (Sigma-Aldrich 31247) 
               
               
                 SiO 2 −325 mesh 
                 Oxidizer, dense 
                 17.9% 
                 13.0% 
               
               
                 (Sigma-Aldrich 342890) 
                 form 
               
               
                 Fumed silica 
                 Oxidizer, high 
                  3.5% 
                 3.5% 
               
               
                 (Sigma-S5130) 
                 surface area form 
               
               
                 CaF 2   
                 Fluxing agent 
                 10.7% 
                 10.4% 
               
               
                 (Sigma-Aldrich 31247) 
               
               
                 Bentonite nanoclay 
                 Thermal Diluent 
                 35.7% 
                 34.3% 
               
               
                 (Aldrich 682659) 
               
               
                 Fe 2 O 3  &lt; 5 micron 
                 High energy 
                   0% 
                 7.7% 
               
               
                 (Sigma-Aldrich 31247) 
                 oxidizer 
               
               
                   
               
             
          
         
       
     
         [0082]    The exemplary thermite fuel compositions described above were tested to determine their specific energy and reaction rate as follows: 
       Example I 
     Specific Energy and Reaction Rate Determination on a Moderated Al/SiO2 Thermite—Initiated By Hot Wire 
       [0083]    An approximately 30 g batch of the formulation in column 3 of Table 2 is prepared using the following steps. The powdered components are all first sieved through a 60-mesh screen and weighed in correct proportions into a mill jar. They are mixed in the jar by tumbling on a roll mill for 30 minutes. 
         [0084]    As discussed previously, the rate of reaction and hence heat generation or power is a key metric for an energetic material in consumer heating applications. Kinetic measurements were made on the Example I material by flame tube experiments in which the energetic material is placed in a Pyrex tube and initiated with a hot wire. A video of the reaction is made and then the position data of the reaction front versus time are least square analyzed to extract reaction propagation velocity.  FIG. 10  shows the reaction propagation velocity for the Example I material to be 0.691 mm s −1 . This low combustion rate is significantly below that previously reported for conventional thermite reactions and allows efficient calorimetric heat transfer to take place. 
         [0085]    Calorimetric data was measured on a sample prepared by packing approximately 7 g of the powder mix into an open top cylindrical steel can (14 mm diameter×50.5 mm high). The filled can is held immersed in a stirred beaker containing approximately 120 g of water. A small nichrome wire heating element connected to a current source is placed in contact with the upper surface of the packed powder. Current is passed momentarily to initiate the mix and then switched off. The temperature of the water vs. time is recorded, and the maximum temperature increase is used to calculate the thermal energy transferred to the water. The curve labeled Example I on  FIG. 11  shows calorimetric time vs. temperature data on the Example I formulation. With the Example I formulation, it takes less than 2 minutes for the water to reach its peak temperature and deliver an energy content of 1.61 kJ g −1 . 
       Example II 
     Specific Energy Determination on a Moderated Al/SiO 2  Thermite Containing Fe 2 O 3 —Initiated By Hot Wire 
       [0086]    Example II is prepared in a similar manner and tested as Example I except that some stoichiometric fraction of the SiO 2  in the formulation is replaced by Fe 2 O 3  to yield the formulation given in Column 4 of Table 2. The curve labeled Example II on  FIG. 11  shows calorimetric time vs. temperature data on the Example II formulation. The greater specific oxidizing power of the Fe 2 O 3  substituent is evidenced by a higher peak temperature of the water. This corresponds to a transferred energy content of 1.76 kJ g −1 . 
         [0087]    Another embodiment of the present invention is the inclusion of a means for activating a solid-fuel modified thermite composition. The solid fuel should not be prone to inadvertent activation, yet a simple means of activating the reactive material in the heater at the desired time of use is beneficial. 
         [0088]    In some embodiments, a more complex and costly activation device that is re-useable would couple to disposable heater elements for activation. For example, as shown in  FIGS. 4 and 5 , a re-useable container is provided with a re-useable activating device such as a battery powered hot wire or a piezoelectric spark ignitor, as shown in  FIG. 9 . Referring to  FIG. 4 , a heating bowl  410  is provided with a port  420  to receive heating elements  430  containing a solid-state modified thermite fuel composition. The heating element  430  is held in place by holding tabs or standoffs  440 . An activation device port  450  is provided on the bottom of the bowl to receive and temporarily attach a modified thermite activation device. The activation device could be a simple battery and wire device  510  as shown in  FIG. 5 . The battery  520  is connected to a wire  530  that can be extended through the activation device port  450  into the modified thermite fuel composition within the heating element  430 . The battery can be used to send enough current down the wire to initiate a thermite reaction using the modified thermite fuel composition. In addition, the activation device could be a piezoelectric spark ignitor as shown in  FIG. 9 . Those of ordinary skill in the art will understand that many types of activation devices can be employed without departing from the novel scope of the present invention. 
         [0089]    In a particular embodiment that enables the greatest ease of use, a simple, low-cost, small (or even miniature) activation device as a built-in component of the heating device is provided. This embodiment is particularly useful in the disposable food packaging context. For example, as shown in  FIGS. 6 ,  7  and  8 , the activation device could be comprised of minute quantities of an exothermic A/B chemical couple separated by a partition. When the partition is breached mechanically by a simple action of the user, the reactive A/B components mix into contact with each other as well as with the bulk solid modified thermite fuel composition. Reaction of the A/B components generates a highly localized hot spot in contact with the fuel composition, thereby initiating its controlled combustion. 
         [0090]    While those of ordinary skill in the art will understand that there are many exothermic couples that can be used,  FIGS. 6 ,  7  and  8  show three designs that incorporate reagents which produce sufficient heat to activate thermite reactions.  FIG. 6  shows a pyrophoric iron/air couple where the removal of an internal seal  610  exposes a small mass of pyrophoric iron  620 , which is in contact with a solid modified thermite fuel composition  630 , to the surrounding atmosphere. The pyrophoric iron reacts with the air to generate the requisite heat to initiate the thermite reaction. 
         [0091]    A potassium permanganate/glycerin couple, as shown in  FIG. 7 , is easily prepared, low-cost and food-safe while reliably generating very high temperatures with minute quantities of reagents.  FIG. 7  shows an amount of potassium permanganate  710  placed directly onto the modified thermite fuel composition  720 . An aluminum foil barrier  730  is placed over the potassium permanganate  710  and glycerin  740  is placed onto the foil. A cover  760  made of a malleable material with an integrated piercing member  750  is placed over the entire system. A user can then activate the mechanism by pressing down on the cover  760  thus pushing the piercing member  750  through the foil barrier  730 , allowing the potassium permanganate  710  and glycerin  740  to mix and generate enough heat to initiate the thermite reaction. 
         [0092]    This embodiment is capable of being produced in high volume based on a multi-laminate paper making process in which a thin septum layer is interposed between sheets coated with each reactant as shown in  FIG. 8 . As shown in  FIG. 8 , the potassium permanganate  810  and glycerin  840  are disposed on either side of a thin membrane  830 . A user can rupture the membrane  830  by applying pressure thus allowing the potassium permanganate  810  and glycerin  840  to mix and contact the modified thermite fuel composition  820 , thus initiating the desired thermite reaction. 
         [0093]    A still further aspect of the present invention is integration of a heating element comprised of a modified thermite fuel composition and an activation mechanism into the packaging of a food product to be heated by a consumer. An appropriate design of package can be used in conjunction with the moderated composite fuel formulation to provide for ease of use and additional consumer safety. The solid-state fuel can be integrated into a package in a way that provides for efficient transfer of the heat generated to the material to be heated. To illustrate this aspect of the invention, several illustrative embodiments describing designs for incorporating solid fuel compositions into self-heating food packaging follow. 
         [0094]      FIGS. 1 and 3  show heater device, apparatus, or package designs that are suited to heating foods with a high fluid content, such as canned soups or beverages. In  FIG. 1 , the fuel composite  110  is packed into a metal tube  120  that is formed into the shape of a complete or partial annular ring to provide a heating surface near the bottom of the container  100  while at least one end of the tube is located near the top of the container to allow access for user activation of the device. In the alternative design of  FIG. 3  the fuel composite  310  is packed into a cylindrical metal can  320  which is then affixed to the bottom of the container  300 . However, those of ordinary skill in the art will understand that a myriad of heater component shapes can be used without departing from the novel scope of the present invention. 
         [0095]    In both designs, the thin metal wall enclosing the fuel provides excellent heat transfer to the surrounding fluid and the simple constructions are amenable to low cost methods of manufacture. As shown in  FIG. 2 , the tube  120  or cylinder  320  can be lined with a ceramic layer  210  to provide more efficient heat transfer through the metal wall. Various means can be provided for closing the open ends of the packed cylinders so that the fuel materials will not come into direct contact with the food. The packed tubing may be held in place by stand-off mechanical contacts  130 , such as for example welded tabs to the interior of the container, so that heat transfers efficiently to the surrounding fluid and heat losses to the exterior food container wall are minimized. The heater elements can be offset from the center in order to facilitate filling, stirring, and spooning material from the container. Those of ordinary skill in the art will understand that numerous methods for attaching or integrating the heating component into the packaging structure are available without departing from the novel scope of the present invention. 
         [0096]    Further embodiments of this aspect can include the bowl configurations shown in  FIGS. 12A-12M . As shown in  FIGS. 12A-12D , a bowl  1210  that can be filled with the liquid or food to be heated  1220  has an amount of solid-state modified thermite fuel  1230  located in the bottom of the bowl  1210 . However, as shown in  FIGS. 12E-12G , the modified thermite fuel  1230  can be configured as a flat ring located in the interior of bowl  1210 . The modified thermite fuel can be encapsulated to prevent contact with the liquid or food to be heated  1220 . Alternatively, a liner  1290  may be placed into the interior of the bowl  1210  to prevent the modified thermite fuel  1230  from contacting the liquid or food to be heated  1220  as shown in  FIGS. 12C and 12D . An activation device  1240  is disposed in contact with the modified thermite fuel  1230  such that a thermite reaction is triggered upon user actuation of the activation device  1240 . The activation device  1240  is accessible by a user from the outside of the bowl  1210  and is covered by a safety seal  1250  which prevents inadvertent actuation of the activation device  1240  but can be removed by a user. Those of ordinary skill in the are will understand that safety seal  1250  can be comprised of various materials and be configured into a variety of shapes to correspond to a specific bowl geometry without departing from the novel scope of the present invention. 
         [0097]    The outer wall of bowl  1210  can have a corrugated configuration  1260  to prevent heat transfer through certain sections of the bowl thereby controlling the heating profile of the liquid or food to be heated  1220  or preventing the user from being burned when touching the bowl  1210 . The bowl  1210  is sealed at the top by a food seal  1270  that prevents the liquid or food to be heated  1220  from escaping or spoiling during storage or transport. Those of ordinary skill in the art will understand that the food seal  1270  may be comprised of a variety of materials and configurations without departing from the novel scope of the present invention. The bowl  1210  may also have a lid  1280 . The lid  1280  may have ventilation holes to aid in the heating process and may also be configured with various shaped grooves or other shapes to allow multiple bowls  1210  to be stacked easily and efficiently for transportation or storage. Finally, those of ordinary skill in the art will understand that the bowl  1210  can be a variety of shapes and configurations to accommodate various types of liquids and foods including but not limited to the oblong configuration shown in  FIGS. 12H-12J  and the square configuration shown in  FIGS. 12K-12M  without departing from the novel scope of the present invention. 
         [0098]    In another embodiment, shown in  FIGS. 13A-130 , an amount of solid-state modified thermite fuel  1330  is integrated into a beverage can  1310 . As shown in  FIG. 13A , the can  1310  may have corrugated sections  1360  to prevent the user from being burned and a temperature indicator  1380  to let the user know the temperature of the liquid  1320  inside the can  1310 . The temperature indicator  1380  may be a sticker or decal that changes color at different temperatures. The can  1310  may also have a safety seal  1350  to prevent inadvertent activation of modified thermite fuel  1330 . Those of ordinary skill in the art will understand that the can  1310  may be a variety of shapes, sizes and configurations including but not limited to the square configuration shown in  FIGS. 13I-13K , the handled-mug configuration shown in  FIGS. 13L and 13M  and the bottle configuration shown in  FIGS. 13N and 13O  without departing from the novel scope of the present invention. 
         [0099]    As shown in  FIGS. 13B-13H , the can  1310  contains an encapsulated amount of modified thermite fuel  1330  in contact with an activation device  1340  that is integrated into the top of the can  1310 . The activation device  1340  may function in a variety of ways to trigger a thermite reaction. As shown in  FIG. 13B , the activation device  1340  is a push-button initially covered by opener tab  1370 . A user can open the can  1310  with opener tab  1370  and then actuate activation device  1340  to heat the beverage  1320 . As shown in  FIG. 13C , the activation device is integrated into opener tab  1370  such that a user can simultaneously open the can  1310  and actuate the activation device  1340 . As shown in  FIGS. 13D-13H , the can  1310  may include a separate activation tab  1390  connected to the activation device  1340 . A user can pull the activation tab  1390  first, allow the beverage  1320  to reach a desired temperature and then open the can with opener tab  1370 . Those of ordinary skill in the art will understand that the activation device may be located at various places around the can  1310  including but not limited to the side of the can  1310  as shown in  FIGS. 13I and 13J  without departing from the novel scope of the present invention. 
         [0100]    In another embodiment, shown in  FIGS. 14A-14H , an amount of solid-state modified thermite fuel  1430  is integrated into a storage can  1410  for a food or liquid  1420 . As shown in  FIGS. 14A-14C , the storage can  1410  is sealed at the top by a removable lid  1470 . An opener tab  1480  is integrated onto the removable lid  1470  to aid a user in opening the can  1410 . As shown in FIGS.  14 D and  14 F- 14 G, the bottom of the storage can  1410  is formed with an indented groove or pocket  1490  that allows an amount of modified thermite fuel  1430  to be encapsulated inside the bottom of the storage can  1410 . As best shown in  FIGS. 14F and 14G , the modified thermite fuel is encapsulated within a fuel housing  1434  disposed within the pocket  1490 , wherein the activation device  1440  is in communication with the modified thermite fuel  1430  via an aperture  1436  within the housing  1434 . A cover  1438  retains the fuel housing  1434  and the activation device  1440  in place and provides a cover portion  1439  over the activation device  1440 . The cover portion  1439  is configured to deflect and allow activation of the activation device  1440 . An annular shroud  1460  is disposed adjacent to the cover  1438  and has an aperture  1442  therein to allow access to the cover portion  1439 . A safety seal  1450  is disposed over the aperture  1442  to prevent access to the cover portion  1439  and accidental activation of the activation device  1440 . As shown in  FIG. 14G , those of ordinary skill in the art will understand that safety seal  1450  can be comprised of various materials and be configured into a variety of shapes without departing from the novel scope of the present invention. The annular shroud  1460  is preferably rigid in structure so that it cannot deflect inwardly toward the activation device  1440  and allow activation without removing the safety seal  1450 . In an alternate embodiment, the annular shroud  1460  and cover  1438  are integrated into a single structure. The pocket  1490  can be trapezoidal to allow a disc-shaped modified thermite fuel  1430  to be situated therein. Those of ordinary skill in the art will also understand that the pocket  1490  can be a variety of shapes, sizes and configurations including but not limited to the cylindrical configuration shown in  FIG. 14H  without departing from the novel scope of the present invention. 
         [0101]    Among others, an advantage of the embodiment depicted in  FIG. 14D , wherein the fuel or fuel device is fully integrated or “built into” the packaging, is that there are fewer parts and material requirements for assembly. On the other hand, among others, an advantage of the embodiment depicted in  FIG. 14G  is that the fuel or fuel device is a discrete component, which may be encapsulated or have its own device structure and be utilized in a modular arrangement. One of ordinary skill in the art will recognize that each of the embodiments depicted and described herein may have unique characteristics or configurations that may translate into one or more advantages over other depicted and described embodiments depending on a particular application. 
         [0102]    In another embodiment, shown in  FIGS. 15A-15H , an amount of solid-state modified thermite fuel  1530  is integrated into a food container  1510  particularly suitable for a liquid food, such as soup  1520 . As shown in  FIGS. 15A-15C , the container  1510  is sealed at the top by a removable lid  1570 . A opener tab  1580  is integrated onto the removable lid  1570  to aid a user in opening the container  1510 . As shown in  FIGS. 15E-15G , the bottom of the container  1510  is formed with an indented groove or pocket  1590  that allows an amount of modified thermite fuel  1530  to be encapsulated inside the bottom of the container  1510 . The modified thermite fuel  1530  can be applied pre- or post-retort processing. The pocket  1590  can be trapezoidal to allow a disc-shaped modified thermite fuel  1530  to be situated therein without protruding outside the container  1510 . This integration of the modified thermite fuel  1530  allows for multiple containers to be efficiently stacked during storage or transport as shown in  FIG. 15H . 
         [0103]    An activation device  1540  is located in contact with the modified thermite fuel  1530  such that a thermite reaction is triggered upon user actuation of the activation device  1540 . As shown in  FIG. 15G , the construction is similar to that shown in the embodiment of  FIG. 14G . As shown in  FIGS. 15D-15G , the activation device  1540  is accessible through an aperture in an annular shroud  1560  that is covered by a safety seal  1550  which prevents inadvertent actuation of the activation device  1540  but can be removed by a user. Those of ordinary skill in the art will understand that safety seal  1550  can be comprised of various materials and be configured into a variety of shapes without departing from the novel scope of the present invention. 
         [0104]    Increased weight and volume of packaging relative to the net food content translates to higher shipping costs and shelf space requirements. Therefore, in order to keep packaging overhead low, a compact SHFP heater device is preferred. However, a compact geometry means less surface area is available for heat transfer, which can be an important consideration in cases where the food to be heated is not readily stirred to provide convective heat transfer. Conductive heat transfer from a small heater to a larger mass of solid or non-stirrable food material will provide inefficient and uneven heating. 
         [0105]    In order to overcome these limitations, the heater element of this invention may be implemented so that the heat it generates raises steam that distributes throughout the package interior and transfers sensible and latent heat (via condensation) to the food. An exemplary embodiment of this aspect of the present invention is shown in  FIG. 16 . A modified thermite fuel  1630  is layered in the bottom of a steamer pan  1610 . An activation device  1640  is located in contact with the modified thermite fuel  1630  at one corner of the pan  1610 . A liner  1690  is located on the interior of the pan  1610  to prevent the modified thermite fuel  1630  from contacting the food to be heated  1620 . The food to be heated  1620  is placed on a steaming rack  1650  inside the pan  1610  and then covered with lid  1680 . A user can then use the activation device  1640  to trigger the modified thermite fuel and steam the food  1620 . 
         [0106]    The principle of using a chemical reaction to raise steam for heat transfer is efficiently used in the “flameless ration heaters” (FRH) used by the US Army to heat the “meal ready to eat” (MRE) field ration. However, the FRH is a wet system based on mixing magnesium metal powder with water and is not well suited to widespread consumer use, whereas in the present invention, the water to be vaporized is not a component of the dry reaction mixture. Rather a small quantity of water is maintained in contact with the outer surface of the heater. For example, the cylindrical heater design of  FIG. 3  could be wrapped in a dampened wicking material or located in a small condensate sump in the base of the package. The combustion characteristics of the heater are designed so that in operation, the exterior surface of the heater maintains a temperature sufficient to vaporize water to steam. 
         [0107]    Applications of the present invention are not limited to the SHFP applications described above. A heating component in accordance with the present invention could be incorporated into a wide array of applications where heating would be desirable such as camping equipment as noted above or gloves for skiiers or mountain climbers. 
         [0108]    While one or more specific embodiments have been illustrated and described in connection with the present invention, it is understood that the present invention should not be limited to any single embodiment, but rather construed in breadth and scope in accordance with recitation of the appended claims.