Ternary explosive compositions
The present invention is concerned with ternary explosive compositions having very good shattering properties. 
     Explosive compositions based on trinitrotoluene (or TNT) and on hexogen (or RDX), which appeared in the period between the two wars, are now well known. They are called hexolites or cyclotols and are characterised by their good shattering properties and their ease of processing, especially by casting. 
     We have previously made significant improvements in hexolites which increased the detonation rate and the degradation resistance, for example by replacing the finest fraction of the hexogen in a conventional hexolite by octogen or hexo-octo having a fine particle size, as described in French Pat. No. 2,182,599. 
     However, hexogen and octogen are relatively expensive explosives and it would be desirable to be able to replace them in hexolites, at least in part, by crystalline explosives which have a high detonation rate and are less expensive. In this respect, pentrite is not suitable because it imparts to compositions in which it is present substantially poorer shattering properties and much greater sensitivity to impact than in the case of hexogen compositions containing the same proportion of crystalline explosives. 
     We have now found that mixtures comprising trinitrotoluene, hexogen and dinitroglycoluril have shattering properties which are as good as, or even better than, those of hexolites having the same proportion of trinitroltoluene, and such dinitroglycoluril-containing compositions are less expensive than such hexolites. 
     According to the present invention, therefore, there is provided an explosive composition which comprises trinitrotoluene, hexogen and dinitroglycoluril. 
     Preferred compositions according to the invention contain, by weight, from 10 60% of trinitrotoluene, from 10 to 85% of hexogen, and from 5 to 50% of dinitroglycoluril. 
     Dinitroglycoluril or DINGU is a compound of the formula: ##STR1## 
     The explosive properties of DINGU are described in French Pat. No. 2,238,703. Its detonation rate of 7,580 m/second, determined on a fuse having a silver sheath of 4 mm external diameter and for a charge density of 1.76, means that this explosive has shattering properties which are inferior to those of pentrite. 
     For this reason, it is entirely surprising that the incorporation of DINGU into a hexolite substantially enhances its shattering properties, as shown in Table I (of the compositions given in this Table, only those of Examples 6 and 7 are in accordance with the invention): 
     
                       TABLE I                                                     
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                            Deto-                                         
                            nation        Shatter                         
                            rate          ing Pro-                        
Ex.  TNT    Hexogen  DINGU  (km/          perties                         
No.  (%)    (%)      (%)    second)                                       
                                   Density                                
                                          (1)                             
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1    60     40       --     7.520  1.69    95.6                           
2    60     --       40     7.330  1.73    93.0                           
3    36.9   63.1     --     7.840  1.73   106.3                           
4    30     --       70     7.500  1.81   101.8                           
5    26.4   73.6     --     8.098  1.74   114.1                           
6    26.7   56.9     16.4   8.072   1.769 115.3                           
7    37.6   32.2     30.2   7.744   1.770 106.1                           
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 .sup.(1) equal to the product:density × (detonation rate).sup.2    
 
    
     The invention is applicable to both cast and compressed charges. For the latter, a relatively small proportion of trinitrotoluene, preferably about 10%, is advantageously used. 
     The invention is also applicable to the ternary compositions described in French Pat. No. 2,182,599. In these compositions, part of the hexogen having a particle size of less than 300 μm can be replaced by fine DINGU. The compositions obtained possess all the advantages described in said French Pat. No. 2,182,599 and those mentioned in this specification. The compositions containing octogen and/or hexo-octo (that is to say crystals of hexogen and octogen which are crystallised together and obtained during the manufacture of octogen, by the French process having a particle size of less than 300 μm, therefore form part of the present invention. 
     Compositions according to the invention may also comprise modifying agents which are known in the field of the hexolites, for example waxes, agents for ensuring uniform crystallisation, such as hexanitrostilbene (HNS), or plasticisers, such as mononitrotoluene. However, the use of HNS is not essential in view of the excellent appearance of the compositions according to the invention. 
     Apart from their detonating qualities, which compare very favourably with the corresponding hexolites, the compositions according to the invention possess other very appreciable advantages for the user: 
     Exudation. As shown in Examples 15 to 37 below, the trinitrotoluene exudes much less in compositions containing DINGU than in compositions containing only hexogen. The use of DINGU enables an anti-exuding agent, such as polyvinyl nitrate, to be dispensed with. 
     Sedimentation. The compositions according to the invention produce an exceptionally small amount of sediment during charging by casting. The homogeneity of the charges is substantially improved and the density gradient is substantially eliminated. A considerable reduction in the size of the top layer results. 
     Degradation on successive melting operations. The compositions according to the invention retain a substantially constant low viscosity when they are subjected to melting cycles which reproduce the conventional charging conditions for hexolites. It is known that a disadvantage of conventional hexolites is the increase in their viscosity after a small number of melting operations. 
     Sensitivity to the impact of bullets. It is lower than that of hexolites. It is not possible to obtain positive results (i.e. detonation) with conventional tests for this property; this also applies to more rigorous tests (i.e. with very high speed firings). 
     Crushing strength. This is greater for compositions according to the invention than for the corresponding hexolites (by about 25%). 
     Evenness of texture and cracking. After melting, the compositions according to the invention have an attractive appearance and a fine and even texture. They exhibit practically no cracking. 
     By virtue of their performance, the compositions according to the invention can be used in all the applications known for hexolites and, because DINGU is less expensive than hexogen, they provide new prospects for this type of explosive. Furthermore, the use of DINGU having a fine particle size (of less than 10 μm) is particularly advantageous, the conventionally synthesised crude DINGU being in this form. 
     In order that the invention may be more fully understood, the following examples (some of which are not in accordance with the invention are are given for the purpose of comparison) are given by way of illustration. 
     EXAMPLES 8 to 14 
     Several compositions according to the invention were prepared by casting, the DINGU being introduced into the molten TNT at the same time as the hexogen. 
     For each of the compositions prepared, the density and the detonation rate were measured and the shattering properties were calculated. The results are given in Table II. 
     
                       TABLE II                                                    
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                                 Detonation                               
Ex.  TNT    RDX     DTNGU  Den-  rate (km/                                
                                         Shattering                       
No.  (%)    (%)     (%)    sity  second  properties                       
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 8   25.3   63.9    10.8    1.7615                                        
                                 8.092   115.3                            
 9   25.4   69.4    11.2    1.7615                                        
                                 8.118   116.1                            
10   28.6   54.5    16.9   1.767 8.030   113.9                            
11   28.7   54.7    16.6   1.767 7.975   112.4                            
12   31.4   54.7    13.9   1.761 7.910   110.2                            
13   38.1   31.5    30.4   1.766 7.710   105.0                            
14   38.3   30.8    30.9   1.768 7.726   105.5                            
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     EXAMPLES 15 to 37 
     (In this series of examples, Examples 16, 18, 20, 27-30, 32, 33, 35 and 36 show the use of compositions according to the invention and the remaining examples are given for the purpose of comparison). 
     Exudation tests were carried out as follows. The composition to be tested was melted at 85° C. and poured into a steel mould which had been pre-heated to about 50° C. up to the brim. The upper part of this cylindrical mould (bore 21 mm, height 40 mm) had the shape of a funnel. 
     When it had completely cooled, the composition was withdrawn from the mould and the upper part, in the shape of a funnel, was cut off so as to leave only the cylinder having a height of 40 mm. The roughnesses on the lower part of this cylinder were removed by rubbing this part for a short time on a surface of (laminated) wood. 
     Squares of constant weight and having sides of 90 mm were cut out of dry filter paper, and the sample was placed in the centre of a first quarter of the square of filter paper, which was supported, with the smooth side facing upwards, on a glass plate with a flat surface. 3 or 4 successive 16 hour cycles at 70° C. were carried out, measuring the diameter of the spot and the increase in the weight of the paper after each cycle. The results obtained are summarised in Table III. 
     
                                           TABLE III                               
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                                           Total                          
RDX                                        loss in                        
                                               Summed                     
315-      RDX  DINGU                                                      
                    1st cycle                                             
                          2nd cycle                                       
                                3rd cycle                                 
                                      4th cycle                           
                                           weight                         
                                               diameters                  
No.                                                                       
   TNT                                                                    
      800 μm                                                           
          2- 10 μm                                                     
               1- 20 μm                                                
                    mm mg mm mg mm mg mm   (mg)                           
                                               (mm)                       
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15 40 48  12   --   32 126                                                
                          30 51 23 44 22   221 107                        
16 40 48  --   12   24 32 22 6  21 12 21    50  88                        
17 40 42  18   --   34 102                                                
                          33 52 25 28 23   182 115                        
18 40 42  --   18   21 20 21 2  21  4 21   206  84                        
19 40 30  30   --   28 79 26 2  23 16 24    97 101                        
20 40 30  --   30   21 18 21 1  21  2 21   201  84                        
21 40 60  --   --   33 166                                                
                          31 20 23 46 23   232 110                        
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     A further series of experiments was carried out at 70° C. (Table IV), the duration of the cycle being 20 hours. The loss in weight of the sample was measured. Hexogen was used in some of the compositions, which had a very fine particle size, of about 3 microns, equal to the modal value of the particle size of the DINGU used. Hexolite additives, hexanitrostilbene (HNS) and polyvinyl nitrate (PVN), were also included in some of the compositions. 
     
                                           TABLE IV                                
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                         Losses in weight                                 
      RDX RDX               after 1st                                     
                                 after 2nd                                
                                      after 3rd                           
                                           after 4th                      
      315-                                                                
          1.5-                                                            
              DINGU      total                                            
                            cycle                                         
                                 cycle                                    
                                      cycle                               
                                           cycle                          
No.                                                                       
   TNT                                                                    
      800 μm                                                           
          6 μm                                                         
              1-20 μm                                                  
                   PVN                                                    
                      HNS                                                 
                         mg mg   mg   mg   mg                             
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22 40 54  6   --   -- -- 57 19   10   12   16                             
23 40 48  12  --   -- -- 59 21   15   12   11                             
24 40 60  --  --   -- -- 54 21   11   11   11                             
25 40 42  18  --   -- -- 52 17   13   12   10                             
26 40 30  30  --   -- -- 43 15   10   10   8                              
27 40 54  --  6    -- -- 33 11   8    8    6                              
28 40 8   --  12   -- -- 34 12   8    8    6                              
29 40 42  --  18   -- -- 28 9    5    8    6                              
30 40 30  --  30   -- -- 27 8    6    7    6                              
31 39.8                                                                   
      53.7                                                                
          6   --   -- 0.5                                                 
                         58 18   16   13   11                             
32 39.8                                                                   
      53.7                                                                
          --  6    -- 0.5                                                 
                         25 9    5    6    5                              
33 39.7                                                                   
      53.6                                                                
          --  6    -- 0.7                                                 
                         33 13   8    4    8                              
34 39.7                                                                   
      53.7                                                                
          6   --   0.6                                                    
                      -- 27 9    7    7    4                              
35 39.7                                                                   
      53.7                                                                
          --  6    0.6                                                    
                      -- 22 6    7    6    3                              
36 39.6                                                                   
      53.4                                                                
          --  6    1.0                                                    
                      -- 25 9    6    6    4                              
37 39.7                                                                   
      59.7                                                                
          --  --   0.6                                                    
                      -- 29 10   7    7    5                              
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     The foregoing tests with compositions, some of which comprised a fine hexogen fraction, show that these compositions were subject to significant exudation. 
     On the other hand, when DINGU was used, the exudation was reduced by 40 to 90%. The visual comparison of the filter papers from each test was spectacular: the exudation was practically zero when at least 15% by weight of DINGU was used. 
     It is known that the incorporation of a small amount of PVN has the effect of reducing the exudation of hexolites. This is confirmed by Example 34. Nevertheless, it can be seen, for example from Examples 29, 30 and 32, that the use of DINGU enables PVN to be dispensed with in order to reduce exudation. 
     Examples 35 and 36 show that the effects of DINGU and PVN are slightly additive from the point of view of exudation. 
     Example 31 shows that HNS has no influence on the exudation of hexolites. The incorporation of HNS into compositions according to the invention does not detract from the improvement in exudation provided by DINGU. 
     EXAMPLES 38 to 40 
     (In this series of examples, only Example 40 is in accordance with the invention, the other two examples being given for the purpose of comparison.) 
     Sedimentation tests were carried out so as to judge the behaviour of the explosive according to the invention during the charging of ammunition. 
     The test consisted of melting the mixture in a stirred vat at 90° C. and removing it from the vat. The molten mixture was then cast into steel tubes, having a length of 200 mm and an internal diameter of 50 mm, which were slightly conical and were pre-heated to 90° C. Sedimentation was allowed to proceed for 3 hours, after which cooling to 50° C. was carried out in 25 mm stages, every 30 minutes. After 3 hours, the moulded article was withdrawn, the top layer of TNT was removed and the remaining piece was cut into three equal parts, the density of which was measured. 
     The results are summarised in Table V which follows: 
     
                                           TABLE V                                 
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      RDX         Technical                                               
      315-                                                                
          RDX RDX grade Thickness                                         
                               Mean                                       
                                   Density                                
                                        Density                           
                                             Density                      
No.                                                                       
   TNT                                                                    
      800 μ                                                            
          2-10 μ                                                       
              1.5-6 μ                                                  
                  DINGU of TNT (mm)                                       
                               density                                    
                                   at top                                 
                                        in middle                         
                                             at bottom                    
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38 40 30  30  --  --    5      1.705                                      
                                   1.696                                  
                                        1.702                             
                                             1.715                        
39 40 30  --  30  --    8      1.727                                      
                                   1.720                                  
                                        1.726                             
                                             1.735                        
40 40 30  --  --  30    1      1.758                                      
                                   1.755                                  
                                        1.758                             
                                             1.761                        
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     The DINGU used came from a batch manufactured on an industrial scale by the process of French Pat. No. 2,238,703. 
     The results given for Examples 38 and 39 are based on measurements carried out on two tubes; Example 40 refers to the mean of 4 tubes. 
     It is seen that the production of a sediment of TNT is reduced by about 80% and that the difference betweem the extreme densities of the charge, which is of the order of 1% in the case of the hexolites, is three times smaller in the case of the composition according to the invention if the top layer of TNT is removed, and four times smaller if the latter is not removed. It follows from these results that the top layer can be substantially reduced by means of the invention (the top layer is the upper, less rich part of the charge which the charger must remove and recycle). 
     EXAMPLES 41 to 47 
     A composition according to the invention, consisting, by weight, of 40% of TNT, 54% of hexogen and 6% of fine DINGU (particle size 1-10 microns), was prepared. Several successive re-melting operations were carried out at 85° C. on this composition and its viscosity was measured on an EFFLUX viscometer (diameter of the flow orifice: 0.5 inch, that is to say about 1.2 cm). The following results, expressed in flow times (in seconds), were obtained. 
     
         __________________________________________________________________________
No. of flow test                                                          
        1  2  3  4  5  6  7  8  9  10 11 12                               
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Viscosity                                                                 
        5.0                                                               
           5.1                                                            
              4.9                                                         
                 4.8                                                      
                    4.6                                                   
                       4.7                                                
                          4.6                                             
                             4.5                                          
                                4.5                                       
                                   4.4                                    
                                      4.6                                 
                                         4.7                              
(seconds)                                                                 
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     By way of comparison, a hexolite of the same composition, but in which the DINGU fraction was replaced by a hexogen of the same particle size, had a viscosity of 27 seconds after the second melting operation, all conditions being otherwise the same. 
     Compositions according to the invention having an increasing proportion of DINGU and a constant proportion of TNT, that is 40% by weight, were prepared, and their viscosity was measured at 85° C. The results are summarised below. 
     
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                              EFFLUX viscosity                            
No.    RDX %      DINGU %     (seconds)                                   
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42     60         --          9                                           
43     54          6          3.6                                         
44     48         12          3.2                                         
45     45         15          3.2                                         
46     36         24          3.8                                         
47     30         30          5.3                                         
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     It is found that compositions according to the invention degrade to an extremely small extent during successive re-melting operations, which is an appreciable advantage for chargers. 
     As regards compositions containing a high proportion of crystalline explosive, it was found that a composition containing only 25% by weight of TNT, 55% by weight of hexogen (375-800 microns), and 20% by weight of fine DINGU was castable (viscosity: 20 seconds at 85° C.), dense (d=1.77) and very homogeneous. 
     EXAMPLES 48 to 51 
     The compositions according to the invention have an excellent insensitivity to the impact of bullets; they did not give any positive result in conventional tests. The following compositions Nos. 48 to 50 were cast into a container having dimensions 60×50×40 mm, made of 0.5 mm thick sheet metal and provided with a 10 mm thick anvil. A 7.62 mm calibre bullet was fired into the sample at speeds of 890 to 910 m/second. No positive result was found for any batch of five blocks. 
     No. 48: 40% TNT, 30% RDX, 30% DINGU, 
     No. 49: 40% TNT, 45% RDX, 15% DINGU, 
     No. 50: 30% TNT, 53% RDX, 17% DINGU, all proportions by weight. 
     For conventional 70/30 or 60/40 hexolites, positive results have already been recorded for these bullet speeds. 
     The test has been made more rigorous for the compositions according to the invention. A steel tube was used which had a length of 70 mm and diameters of 41/49 mm and which was sealed at one end by a 5 mm welded steel plate and at the other end by a cast iron cap. Firings were carried out with a 7.62 mm bullet, radially and at very high speed (1,260 m/second). 
     No positive result was obtained with composition No. 48 over ten firings, and no positive result was obtained over 5 firings with composition No. 51 comprising 15% of TNT, 40% of RDX and 45% of DINGU, all by weight. 
     EXAMPLE 52 
     The crushing strength of 10×10×10 mm cubes of 60/40 hexolite (comprising 30% of hexogen, 2-10 microns) and of a 30/30/40 composition according to the invention, that is containing 30% by weight of RDX, 30% by weight of DINGU and 40% by weight of TNT, were compared under the same conditions. 
     A mean crushing strength of 192 bars (maximum: 220 bars) was obtained for six samples of the hexolite (which had a mean density of 1.727). 
     A mean strength of 253 bars (maximum: 300 bars) was obtained for six samples of the corresponding composition according to the invention (which had a mean density of 1,760). 
     In this test, compression was carried out between two parallel faces, the crushing rate being 1 mm/minute.