Abstract:
A pyrotechnic mixture for producing a smoke screen includes a reduction agent comprising a light metal, at least one oxidation agent comprising potassium nitrate, combustion moderators including at least one carbonate and a nitrogen producing compound and at least one sublimable or evaporatable, smoke generating, nontoxic additive.

Description:
BACKGROUND OF THE INVENTION 
     The invention relates to a pyrotechnic mixture for producing a smoke screen. 
     Such mixtures are known per se. Hygroscopic compounds, such as metal chlorides (ZnCl 2 , FeCl 3 , AlCl 3 , TiCl 4 , SiCl 4 ) or phosphorus oxides (P 2  O 3 , P 2  O 5 ) are produced, evaporated and then hydrolyze with air to form smoke clouds suitable for camouflage. Regarding the mechanism of this method of smoke generation see H. Ellern, Military and Civilian Pyrotechnics, Chem. Publ. Comp., Inc., N.Y., 1968, pages 147-151; John A. Conkling, Chemistry of Pyrotechnics, Marcel Dekker Inc., N.Y., 1985, pages 174, 175. 
     Due to hydrolysis with humid air, the resulting smoke, particularly a smoke composed of hexachloroethane containing, so-called HC smoke, compositions, but also phosphorus smoke compositions, is highly acidic since it is primarily hydrochloric acid (HC smoke) or phosphorus acids (phosphorus smoke) that are formed. The smoke is therefore toxic and incompatible with plant life. 
     Moreover, in the smoke mixture most frequently employed which is based on hexachlorethane (HC) and zinc or zinc oxide, the heavy metal zinc is discharged into the environment. 
     There has been no lack of attempts to overcome these drawbacks. For example, the pyrotechnic smoke compositions disclosed in German Patents Nos. DE-PS 2,743,363 and DE-AS No. 2,819,850 are constructed in such a manner that the acid effect of the resulting smoke is partially or completely cancelled out by corresponding chemical complex formation or neutralization of the resulting ZnCl 2  or of the phosphorus acids. However, toxic substances that are not compatible with the environment are still generated. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to provide a smoke screen which is particularly suitable for training purposes and which is composed of a nontoxic aerosol which therefore is unable to produce a toxic effect on humans and animals and, is compatible with the environment. When NaCl is not employed as an additive, the smoke is primarily composed of macronutrients suitable for plants. 
     A pyrotechnic mixture for producing a smoke screen, the mixture comprising: 
     a reduction agent comprising magnesium powder, 
     at least one oxidation agent comprising potassium nitrate, 
     combustion moderators including at least one carbonate and a nitrogen producing compound and 
     at least one sublimable or evaporatable, smoke generating, nontoxic additive. 
     The invention as described above generates a non-toxic smoke of sufficient optical density for military training purposes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING 
     The drawing FIGURE shows the mixture of the invention as used in a smoke generating device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Smoke generation occurs in the following way: the components magnesium powder, potassium nitrate and potassium perchlorate, when converted in a range of 2500° C. will already produce smoke-like clouds. The density of the smoke is improved particularly by adding potassium chloride and/or sodium chloride whose sublimation boiling points are 1500° C. and 1450° C., respectively, far below the reaction temperature for the conversion of magnesium and potassium nitrate. The reaction products of the chemical reaction of magnesium with potassium nitrate, potassium perchlorate, calcium carbonate, etc. thus form with the sublimating potassium chloride or the evaporating sodium chloride a useful training smoke without toxic or environmentally damaging components. 
     The chemical reactions in the smoke composition can be represented in a simplified manner in the three equations below: 
     
         1. 2 KNO.sub.3 +5 Mg→5 MgO+K.sub.2 O+N.sub.2 +E 
    
     
         2. KClO.sub.4 +4 Mg→4 MgO+KCl+E 
    
     
         3. CaCO.sub.3 +2 Mg→CaO+2 MgO+C+E 
    
     The energy (E) released in the three listed basic reactions serves to sublimate/evaporate the potassium chloride and sodium chloride. 
     To improve combustion control, substances such as azodicarbonamide, oxamide or dicyandiamide which produce nitrogen are preferably added to the mixture. This produces a continuous gas stream for better transport of the aerosol particles and an increased aerosol yield since the permanently formed gases prevent the slag from flowing together and enhance sublimation and evaporation by an enlarged surface area. 
     When the mixture burns, a pure, white aerosol results which is composed primarily of the components potassium chloride, magnesium oxide, calcium hydroxide, calcium carbonate, sodium chloride and potassium carbonate. These components are compatible with the environment and nontoxic and, except for NaCl, are macronutrients for plants. 
     The pH of the resulting smoke is highest at the point where it is generated where is has 9 pH of 9. Chemical reactions of the oxides K 2  O and CaO, which are the primary oxides produced, (Equations 1, 3) with components of the air, primarily H 2  O and CO 2 , form KHCO 3 , K 2  CO 3 , Ca(OH) 2  and CaCO 3  and by dilution, cause the pH to decrease rapidly. For example, at a distance of 5 to 10 m from the source of the smoke, the pH of the ambient air reaches about 6 (≈6). 
     A pyrotechnic composition including the same components as the mixture for producing the smoke screen can be employed as an ignition mixture, with, however, the content of magnesium and oxidation agents being increased so as to raise ignition sensitivity and the reliability of ignition transfer. The ignition composition may be composed, for example, of the following percentages of the components: 25% Mg, 35% KNO 3 , 10% KClO 4 , 20% CaCO 3 , 10% KCl. 
     The smoke composition and ignition composition are pressed into casings in a known manner and are caused to react by means of conventional ignition means. 
     The drawing figure shows one embodiment of a smoke generating body including the novel mixture. In a casing 1 having a bottom 3 there is disposed the compacted mixture 4 which is capped by a pressed-on ignition mixture 5. The embodiment of the drawing includes a recess 6 for the insertion of a known initiation means. 
     Preferred embodiments of the mixture are listed in the table below: 
     
         ______________________________________(a)         Mg           15%       KNO.sub.3    30%       KClO.sub.4   0%       CaCO.sub.3   15%       KHCO.sub.3   0%       KCl          32%       NaCl         0%       azodicarbonamide                    8%(b)         Mg           12%       KNO.sub.3    25%       KClO.sub.4   5%       CaCO.sub.3   18%       KHCO.sub.3   2%       KCl          30%       NaCl         0%       oxamide      8%(c)         Mg           20%       KNO.sub.3    20%       KClO.sub.4   8%       CaCO.sub.3   0%       KHCO.sub.3   12%       KCl          15%       NaCl         15%       dicyandiamide                    10%______________________________________