Abstract:
The invention relates to a heat-generating mixture, to a method and a device for generating heat, especially for heating food such as water, coffee, etc.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a heat-generating mixture and to a method and a device for heat generation, especially for heating foodstuffs such as water, coffee, instant meals, etc. 
     Heat generation by the thermite process is known per se in traditional welding technology. However, thermite cannot be used in heat generation for foodstuffs because it forms a molten ball that can lead to mechanical instability to the point of melting through the casing of the device for heat generation. 
     U.S. Pat. No. 6,267,110 B1 discloses a disposable heating unit for a food container. As the heat-generating mixture, the device disclosed in this document also contains components that react together spontaneously at room temperature when they are brought into contact with one another, at least one of these components being in liquid form. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The object of the present invention was therefore to provide heat-generating mixtures that overcome the disadvantages of the state of the art. 
     The solution according to the invention provides a heat-generating mixture containing one or more of the constituents metal silicide, iron oxide and silicon, optionally together with additives and processing aids such as silicon dioxide or water glass. The heat-generating mixture according to the invention is accommodated in a device which contains, in and/or on a casing, inter alia in addition to the substance to be heated, a booster charge and an igniter capable of being actuated mechanically or electrically, preferably piezoelectrically. The casing can be made of metal and/or plastic. If necessary, in the heat generation according to the invention, the booster charge is ignited by the igniter and in turn reliably and uniformly ignites the heat-generating mixture according to the invention. In a suitable mechanical casing, the slow and smoke-free combustion of the heat-generating mixture heats e.g. water, The thermomechanical stresses on the casing are markedly reduced because, on burning, a desirable non-melting, porous slag is formed in which the beads of iron cannot combine to form a molten ball. The temperature and the time taken to reach the maximum temperature can be controlled by way of the formulation, the amount of mixture used, the amount of water and/or the type of mechanical casing. Thus, for example, 25 g of the mixture according to the invention heat 125 ml of water from 20° C. to 98° C. within 60 seconds in a suitable apparatus. 
     Only solids that do not react with one another at room temperature are used in the heat-generating mixture according to the invention, in the associated booster charge and in the igniting mixture. The heat-generating mixture used according to the invention is e.g. a mixture containing 40 to 55 wt. % of metal silicide, preferably calcium silicide and/or iron silicide, 40 to 60 wt. % of iron(III) oxide, 0 to 10 wt. % of silicon, and additives and processing aids such as silicon dioxide or water glass. The booster charge for the heat-generating mixture can consist e.g. of mixtures containing light metals such as titanium, magnesium and/or aluminium, and metal silicides such as calcium silicide and/or iron silicide, iron oxide, silicon and additives, or other mixtures known from the state of the art. The igniters used for the booster charge are preferably anvil-shaped igniter caps that are capable of being actuated mechanically and are based on igniting mixtures free of lead and heavy metals. These are known from the state of the art and contain e.g. potassium dinitrobenzo-furoxanate or diazodinitrophenol, tetrazene, zinc peroxide, nitrocellulose, and additives such as powdered glass and titanium. The heat-generating mixtures according to the invention are prepared by methods known per se: the components are mixed in the indicated amounts and optionally compressed. The same applies to the igniting mixture and the booster charge. 
     The batch formulations are illustrated by the Examples below without thereby limiting the invention: 
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Heat-generating mixture 
               
             
          
           
               
                   
                 Example 1.1 
                 Example 1.2 
                 Content [wt. %] 
               
               
                   
               
               
                   
                 Calcium silicide 
                 Iron silicide 
                 40-55 
               
               
                   
                 Iron(III) oxide 
                 Iron(III) oxide 
                 40-60 
               
               
                   
                 Silicon 
                 Silicon 
                  0-10 
               
               
                   
                 Silicon dioxide 
                 Silicon dioxide 
                 0-5 
               
               
                   
                 Water glass 
                 Water glass 
                  0-20 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Booster charge 
               
             
          
           
               
                   
                 Example 2.1 
                 Example 2.2 
                 Content [wt. %] 
               
               
                   
               
               
                   
                 Magnesium 
                 Titanium 
                 10-30  
               
               
                   
                 Calcium silicide 
                 Calcium silicide 
                 25-35  
               
               
                   
                 Silicon 
                 Silicon 
                 0-10 
               
               
                   
                 Iron(III) oxide 
                 Iron(III) oxide 
                 40-55  
               
               
                   
                 Additives: 
                 Additives: 
                   
               
               
                   
                 Binder 
                 Binder 
                 0-10 
               
               
                   
                 Silicon dioxide 
                 Silicon dioxide 
                 0-10 
               
               
                   
                 Graphite 
                 Graphite 
                 0-10 
               
               
                   
                 Boron nitride 
                 Boron nitride 
                 0-10 
               
               
                   
               
             
          
         
       
     
     
       
         
               
             
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Igniting mixture 
               
             
          
           
               
                   
                 Example 3.1 
                 Example 3.2 
                 Content [wt. %] 
               
               
                   
               
               
                   
                 Potassium dinitro- 
                 Diazodinitrophenol 
                 20-40  
               
               
                   
                 benzofuroxanate 
                   
                   
               
               
                   
                 Zinc peroxide 
                 Zinc peroxide 
                 20-40  
               
               
                   
                 Tetrazene 
                 Tetrazene 
                 0-10 
               
               
                   
                 Titanium 
                 Titanium 
                 0-20 
               
               
                   
                 Nitrocellulose 
                 Nitrocellulose 
                 0-40 
               
               
                   
                 Powdered glass 
                 Powdered glass 
                 0-20 
               
               
                   
               
             
          
         
       
     
     The following compositions may be mentioned as preferred embodiments without thereby excluding other possible formulations: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
             
             
               
                   
                 Heat-generating mixture: 
                 iron silicide: 
                 48 
                 wt. % 
               
               
                   
                   
                 iron(III) oxide: 
                 50 
                 wt. % 
               
               
                   
                   
                 silicon: 
                 2 
                 wt. % 
               
               
                   
                 Booster charge: 
                 magnesium: 
                 20 
                 wt. % 
               
               
                   
                   
                 calcium silicide: 
                 30 
                 wt. % 
               
               
                   
                   
                 silicon: 
                 3 
                 wt. % 
               
               
                   
                   
                 iron(III) oxide: 
                 47 
                 wt. % 
               
               
                   
                 Igniting mixture: 
                 potassium dinitro- 
                 30 
                 wt. % 
               
               
                   
                   
                 benzofuroxanate: 
                   
                   
               
               
                   
                   
                 zinc peroxide: 
                 25 
                 wt. % 
               
               
                   
                   
                 tetrazene: 
                 5 
                 wt. % 
               
               
                   
                   
                 titanium: 
                 5 
                 wt. % 
               
               
                   
                   
                 nitrocellulose: 
                 35 
                 wt. % 
               
               
                   
               
             
          
         
       
     
     The heat-generating mixture according to the invention can be used e.g. to prepare for consumption foodstuffs such as water, coffee, instant meals, etc., in a suitable device.