Abstract:
A ramjet solid fuel composed of Hydroxyl terminated polybutadiene aluminum,agnesium, and boron carbide is described. The high volumetric heating value fuel of the present invention significantly increases the distance range of missiles.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to ramjet fuels and more particularly to those solid ramjet fuels which are composed of hydroxyl terminated polybutadiene (HTPB). 
     Though the performance of presently available standard solid fuel for ramjets containing HTPB is considered adequate, it is highly desirable to have ramjet solid fuel compositions of increased performance, as the range of missiles would be significantly increased and they could be deployed for tactical air launched missiles. 
     OBJECTS OF THE INVENTION 
     It is, therefore, an object of this invention to provide a novel ramjet solid fuel composition. 
     A further object of this invention is to increase the distance range of weapons using solid ramjet fuels. 
     It is still another object of this invention to provide additives which would increase the volumetric heating value of HTPB. 
     BRIEF SUMMARY OF THE INVENTION 
     These and still further objects of the present invention are achieved, in accordance therewith, by providing a ramjet solid fuel composition which contains hydroxyl terminated polybutadiene and a combination of additives, aluminum, magnesium and boron carbide. 
     These and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed disclosure. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The invention will be illustrated by, but is not intended to be limited to, the following description and examples. 
     EXAMPLE I 
     78% by weight hydroxyl terminated polybutadiene (HTPB) and 22% by weight dimeryl diisocyanate (DDI) are thoroughly mixed and then degassed. The composite is then cured at 50° C. for 24 hours. This fuel composition is used as standard against which the other compositions containing additives of the present invention are compared with. Other fuel compositions were prepared under similar conditions and in similar fashion. HTPB and DDI are mixed in the ratio of 78-22 by weight percent to form a composite and various additives singly or a mixture thereof are then added to the composite in a weight percent ratio corresponding to the weight of HTPB. The amount of curative is not taken in account. The composition containing HTPB, DDI and the additive is then degassed and cured at 50° C. for 24 hours. 
     The examples 2 to 22 are prepared containing HTPB with various proportions of additives as shown in Table I. 
     
                       TABLE I______________________________________Example______________________________________ 1               100% HTPB 2      5% AP    95% HTPB 3      10% AP   90% HTPB 4      15% AP   85% HTPB 5      5% Al    95% HTPB 6      13% Al   87% HTPB 7      23% Al   77% HTPB 8      31% Al   69% HTPB 9      40% Al   60% HTPB10      45% Al   55% HTPB11      50% Al   50% HTPB12      55% Al   45% HTPB13      5% Mg    95% HTPB14      10% Mg   15% Al     25% B.sub.4 C                               50% HTPB15      5% Mg    5% AP      30% B.sub.4 C                               60% HTPB16      5% Mg    30% B.sub.4 C                       65% HTPB17      10% Mg   30% B.sub.4 C                       60% HTPB18      15% Mg   30% B.sub.4 C                       55% HTPB19      20% Mg   30% B.sub.4 C                       50% HTPB20      35% Mg   35% B.sub.4 C                       30% HTPB21      15% B.sub.4 C            85% HTPB22      30% B.sub.4 C            70% HTPB______________________________________ 
    
     The physical properties of these additives used are as follows: 
     
         ______________________________________Ammonium Perchlorate (AP)Average particle size  50 micronsDensity                1.53 g/cm.sup.3Properties of Aluminum Powder (Valley Metallurgical Co. H-5)Test required          Test values obtainedMaterial volatile at 105° C.                  0.006%Oil and grease         0.002%Iron (as Fe)           0.13%Free metallic aluminum 99.0%Average particle size (Fisher subsieve sizer)                  5.4 μmTap density            1.53 g/mlParticle shape         sphericalProperties of B.sub.4 C (Carborundum 800F).Particle size          20 μm and finerParticle shape         AngularPercent boron, wt. %   &gt;76Particle size median    4 micronsMax 1%                 20 microns______________________________________ 
    
     Mg Powder 
     Magnesium powder used is known as Granulation No. 16 (nominal mesh size 200-325 and has 65-70 micron diameter. It meets the specification of MIL-M-382-C(A.R.) Aug. 10, 1978). 
     
         ______________________________________Fuel Ingredients         Density Heat of CombustionIngredient     Formula   g/cm.sup.3                         kcal/g kcal/cm.sup.3______________________________________HTPB/DDI  C.sub.4 H.sub.6 O.sub.0.15               0.92      10.16   9.34AP        NH.sub.4 Cl0.sub.4               1.95      0.32    0.62Mg        Mg        1.74      6.01   10.46Al        Al        2.70      7.41   20.0B.sub.4 C B.sub.4 C 2.50      12.235 30.58______________________________________ 
    
     Tests were conducted on the cured compositions of these examples and tabulated as shown in Table II. 
     The comparison shows that aluminum, magnesium, and boron carbide, alone or in combination with each other when added to HTPB binder and DDI curative systems improve the performance of ramjet solid fuel. More particularly the combination of Mg and B 4  C when added to HTPB and cured improves the performance of the fuel significantly. 
     
                                           TABLE II__________________________________________________________________________PERFORMANCE OF EXPERIMENTAL SOLID RAMJET FUELS                   Combustion               PerformanceFUEL COMPOSITION   Efficiency                            Density                                 ΔHc.sup.b                                      ΔHc                                            Relative toExample(wt %)             (η)                         Φ.sup.a                            (gm/cc)                                 k cal/gm                                      K cal/cm.sup.3                                            HTPB.sup.c__________________________________________________________________________ 1   HTPB               .76   .85                            0.92 10.16                                      9.347 1.00 2   5% AP 95% HTPB     .81   .85                            0.94 9.668                                      9.088 1.00 3   10% AP 90% HTPB    .786  1.17                            0.971                                 9.176                                      8.910 0.98 4   15% AP 85% HTPB    .794  1.27                            0.999                                 8.684                                      8.675 0.97 5   5% Al 95% HTPB     .74   .85                            0.95 10.02                                      9.519 0.99 6   13% Al 87% HTPB    .76   .85                            1.01 9.80 9.898 1.06 7   23% Al 77% HTPB    .71   .85                            1.08 9.53 10.292                                            0.95 8   31% Al 69% HTPB    .71   .85                            1.16 9.31 10.800                                            1.08 9   40% Al 60% HTPB    .75   .85                            1.25 9.06 11.325                                            1.1910   45% Al 55% HTPB    .636  .88                            1.308                                 8.927                                      11.677                                            1.0411   50% Al 50% HTPB    .674  1.03                            1.42 8.790                                      12.482                                            1.1812   55% Al 45% HTPB    .564  .97                            1.443                                 8.653                                      12.486                                            0.9913   5% Mg 95% HTPB     .73   .85                            0.94 9.947                                      9.350 0.9614   10% Mg 15% Al 25% B.sub.4 C 50% HTPB                   .779  1.19                            1.322                                 9.842                                      13.011                                            1.4215   5% Mg 5 AP 30% B.sub.4 C 60% HTPB                   .656  1.19                            1.210                                 10.077                                      12.193                                            1.1216   5% Mg 30% B.sub.4 C 65% HTPB                   .69   .85                            1.17 10.570                                      12.367                                            1.2017   10% Mg 30% B.sub.4 C 60% HTPB                   .727  .906                            1.205                                 10.356                                      12.479                                            1.2818   15% Mg 30% B.sub.4 C 55% HTPB                   .689  .98                            1.244                                 10.144                                      12.619                                            1.2219   20% Mg 30% B.sub.4 C 50% HTPB                   .740  1.06                            1.285                                 9.931                                      12.761                                            1.3320   35% Mg 35% B.sub.4 C 30% HTPB                   .794  .80                            1.499                                 9.397                                      14.086                                            1.5721   15% B.sub.4 C 85% HTPB                   .64   .85                            1.02 10.470                                      10.679                                            0.9622   30% B.sub.4 C 70% HTPB                   .61   .85                            1.13 10.781                                      12.183                                            1.04__________________________________________________________________________ .sup.a Equivalence ratio (Stoichiometric airto-fuel ratio ÷ Actual airto-fuel ratio). .sup.b Net heat of combustion ##STR1## 
    
     Examples 16 to 20 indicate that the performance of HTPB fuel is substantially increased when it is loaded with up to 116 parts by weight of Mg and up to 116 parts by weight of B 4  C relative to 100 parts by weight of HTPB. Examples 14 and 15 indicate that improved results are obtained when Al is also added with weight HTPB-Mg-B 4  C mixture. Thus HTPB fuel could be loaded with weight percentages of Al, Mg, and B 4  C corresponding to the weight of HTPB, in quantities of up to 30 percent Al, up to 20 percent Mg and up to 50 percent B 4  C in relation to HTPB. 
     Thus the invention demonstrates that the volumetric heating values of HTPB can be increased significantly by the addition of certain metals and compounds. The high volumetric heating value fuels of the present invention have the potential not only for increasing missile range but also for reducing missile length or diameter for a given range when used in place of lower heating value fuels. 
     Though DDI has been used as curative for HTPB in the above examples, any other suitable curative will produce substantially the same results. 
     It should therefore be appreciated that the present invention as described achieves its intended purpose by providing superior ramjet fuel compositions which exhibit: 
     (1) suitable physical properties over a wide temperature range, (2) long-term storage stability, (3) low toxicity, (4) a very low degree of manufacturing and handling hazard, (5) high volumetric heats of combustion, (6) ease of ignition, and (7) high combustion efficiencies. 
     Obviously many modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.