Abstract:
An improved armor piercing and pyrotechnic projectile for use in .50″ military caliber rounds. Such projectiles contain a core, jacket, a base and a hollow nose housing pyrotechnic mixtures composed of sodium periodate and magnalium. The improved projectiles exhibit increased luminosity, and are non-toxic, safer, and environmentally benign compared to current state-of-the-art projectiles.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation-in-part application that claims the benefit of pending non-provisional patent application entitled “Armor Piercing Projectile Incendiary Composition” filed Jan. 29, 2013, as Ser. No. 13/752,444. 
    
    
     FEDERAL RESEARCH STATEMENT 
     The inventions described herein may be manufactured, used and licensed by, or for, the U.S. Government, for U.S. Government purposes. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to armor piercing projectiles containing improved incendiary compositions having mixtures of sodium periodate and magnalium. Such projectiles have improved performance over state of the art compositions with the added benefit of being non-toxic and environmentally safe. 
     BACKGROUND OF THE INVENTION 
     The U.S. military utilizes M2 and M85 machine guns, firing fifty caliber (hereinafter ‘.50″ caliber’) projectiles, to penetrate and destroy hard targets at long ranges, up to and about 800 meters. The .50″ caliber projectiles including M2 armor piercing rounds are designed to penetrate light-armored vehicles or breach hard unarmored targets such as concrete walls or shelters. 
     Other .50″ caliber projectiles, such as the M1 or M23 incendiary rounds contain an incendiary composition, such that upon impact the composition bursts into flame, to ignite any flammable material in proximity thereof. These incendiary rounds may be used against aircraft. 
     Certain .50″ machine gun projectiles of particular interest include the M8 armor piercing incendiary (API) round and the MK257 armor piercing incendiary dim tracer (API-DT) round, which rounds combines the functionality of the M2 armor piercing round and the M1/M23 incendiary rounds; so as to be useful against hard targets containing a flammable component, such as lightly armored targets containing volatile fuels, e.g. aviation fuel, gas, diesel fuel, etc. Upon impact with such a hard target, the M8/MK257 round will penetrate the target, the kinetic energy of the impact is converted by friction to heat which causes an incendiary material within the projectile to ignite, such as U.S. incendiary composition IM-11 (50% barium nitrate and 50% powdered aluminum/magnesium alloy) or IM-28. Importantly, in addition to providing a means for igniting flammable materials, including fuel vapors, in or about the target; the ignition of the incendiary provides an incandescent flash, which is very useful for marking the impact point—as a pyrotechnic signal to other military units. 
     The M8 API, MK257 (API-DT) and other similar in-service U.S. military incendiary projectiles, such as the 20 mm PGU-28/B semi armor piercing high explosive incendiary (SAPHEI) and the 20 mm M940 multi-purpose tracer with self destruct (MPT-SD) round, contain potassium perchlorate (KClO 4 ) and/or barium nitrate, as an oxidizer, within their oxidizer/fuel incendiary composition. These compounds however, have been associated with toxic effects in humans. For instance, potassium perchlorate has been associated with increasing thyroid dysfunction and teratogenicity while barium nitrate has been reported as being cardiotoxic. Further, while recent work has shown that sodium nitrate (NaNO 3 ) can be a substitute for such environmentally toxic oxidizers, the hygroscopic nature of NaNO 3  promotes agglomeration upon exposure to water vapor in the air which poses risks during manufacturing and affects performance of the pyrotechnic projectiles. 
     Therefore, a need exists in the art for a less toxic alternative oxidizer to potassium perchlorate and barium nitrate in armor piercing incendiary projectile compositions—an alternative that does not suffer from being hygroscopic. In addition, the alternative oxidizer must provide equally reliable ignition, burn time and pyrotechnic visual intensity to the current incendiaries based on barium nitrate and potassium perchlorate oxidizers. 
     SUMMARY OF INVENTION 
     The present invention provides an economical, non-hygroscopic, non-toxic and environmentally safe oxidizer/fuel incendiary composition useful in incendiary .50″ caliber rounds—such as the M8 API, MK257 API-DT. The oxidizer, sodium periodate (NaIO 4 , which is also known as sodium (meta) periodate), is blended with a fuel system consisting of magnalium. Surprisingly, the luminous efficiency, i.e. the integrated luminous intensity per unit mass in (cds-grn) −1 , of the flash provided by the preferred sodium periodate was almost 20% greater than the current IM-28 incendiary—with substantively corresponding burn times. Such significantly improved luminous efficiency indicates that the inventive formulation will not only provide enhanced incendiary effects; but, clearly will also provide significantly more pyrotechnic flash for a given quantity thereof, providing a significantly more observable marking of the impact point. And, finally, and also surprisingly, the impact sensitivity of the inventive incendiary formulations is significantly less than the current IM-28 incendiary—indicating that the new inventive formulation is much safer for transport and handling. 
     Preferred embodiments of the present inventive incendiary compositions include from about 30 to 50 weight percent of the sodium periodate oxidizer, and about 70 to about 50 weight percent of magnalium, a chemical alloy of aluminum and magnesium said magnalium comprising 10:90 to a 20:80 ratio and more preferably 50:50 ratio of aluminum to magnesium. A small quantity of a flow agent such as fumed silica (aka Cab-o-sil®) or calcium stearate at about 0.01 to about 0.05 percent of the total weight of the composition may be added prior to mixing with about 70 to about 50 weight percent magnalium. The flow agent was found to aid in the mixing of the oxidizer and fuel and creating a more uniform incendiary product and to avoid any potential undesired agglomeration. 
     Additional features and advantages of the present invention will be set forth in, or are apparent from, the detailed description of preferred embodiments thereof which follows. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood, and further objects, features, and advantages thereof will become more apparent from the following description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
       The FIGURE is a cross-section of the armor piercing incendiary projectile of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Disclosed herein are armor piercing incendiary projectiles containing an incendiary composition that is an improvement over current projectiles as being less toxic and environmentally safe while having enhanced incendiary effects and pyrotechnic flash. 
     Generally armor piercing incendiary projectiles such as those for M8 API, MK257 APT-DT .50″ caliber rounds will disperse incendiary material upon impact to disclose the location of the target as well as causing collateral damage by igniting flammable material. 
     The FIGURE is an illustration of an exemplary armor piercing incendiary projectile. The projectile contains a core  1 , which is typically comprised of a metal such as steel or lead fitted inside a metal jacket  2 . The front of the core is shorter than the jacket leaving a space at the tip of the jacket (i.e. hollow nose) when the core is seated inside the jacket. The hollow space  3  at the nose of the jacket houses the incendiary composition  4 . At the rear of the jacket and core is the base  5 , which may be sealed off to prevent exposure of the powder flame from the cartridge propellant to the incendiary composition. Optionally, a tracer composition may be placed on the rear of projectiles, i.e. on or near the base, to indicate the projectile&#39;s path during flight. 
     The incendiary composition provided herein comprises an oxidizer such as sodium periodate. The composition further comprises magnalium a binary fuel system comprising a chemical alloy of aluminum and magnesium. The incendiary composition may further comprise a flow agent such as fumed silica or calcium stearate. 
     The current, prior art IM-28 U.S. military incendiary composition formulation is shown in Table 1, below, wherein the Ba(NO 3 ) 2  and the KCIO 4  serve as oxidizers and the 50:50 magnesium-aluminum alloy (magnalium) serves as the fuel. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Composition of current in-service 
               
               
                 US military IM-28 incendiary 
               
             
          
           
               
                   
                   
                 Weight 
               
               
                   
                 Component 
                 Percentage (%) 
               
               
                   
                   
               
               
                   
                 Ba(NO 3 ) 2   
                 40% 
               
               
                   
                 KClO 4   
                 10% 
               
               
                   
                 magnalium 
                 50% 
               
               
                   
                   
               
             
          
         
       
     
     The preferred incendiary embodiment of the present invention is shown in Table 2. As shown in the table below, the preferred weight percentage range for the oxidizer is 30-50 wt. %, 50-70% for the fuel, along with an additional 0.01 to 0.05 percent of a flow agent per the total weight of the composition. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Alternative preferred embodiment of the 
               
               
                 present inventive incendiary composition. 
               
             
          
           
               
                   
                   
                 Subject Invention 1 
               
               
                   
                 Component 
                 Weight Percentage (%) 
               
               
                   
                   
               
               
                   
                 NaIO 4   
                   30-50 
               
               
                   
                 magnalium 
                   70-50 
               
               
                   
                 Flow agent 
                 +0.01-0.05 
               
               
                   
                   
               
             
          
         
       
     
     The performance of the alternative preferred embodiments of the present incendiary composition shown in Table 2 is compared to the current state-of-the-art IM-28 incendiary composition in Table 3, below. 
     
       
         
               
             
               
               
               
               
               
             
           
               
                 TABLE 3 
               
             
             
               
                   
               
               
                 Laboratory performance of the present invention vs. the  
               
               
                 current in-service IM-28 incendiary composition 
               
             
          
           
               
                   
                   
                 Burn 
                 Luminous 
                 Impact 
               
               
                   
                   
                 Time 
                 Efficiency 
                 Sensitivity 
               
               
                   
                 Formulation 
                 (seconds) 
                 (cd·s-gm −1 ) 
                 (Joules) 
               
               
                   
                   
               
               
                   
                 Current IM-28 
                 0.109 
                 11,294 
                 2.94 
               
               
                   
                 Subject composition 
                 0.185 
                 13,504 
                 9.80 
               
               
                   
                   
               
             
          
         
       
     
     Table 3 illustrates that the subject composition containing NaIO 4  in the formulation exhibits up to about 20% more luminous efficiency vs. the current IM28 formulation. Furthermore, that exhibited brightness will appear to be enhanced because of the spectral emission corresponding to gaseous atomic sodium which gives off a more discernible yellow light than the blueish white light from the current IM-28. 
     As stated above, an important attribute of the present invention, containing NaIO 4  as the oxidizing agent, is the fact that it is non-hygroscopic. The non-hygroscopic nature of this preferred embodiment is demonstrated in Table 4, below, in relation to other common pyrotechnic oxidizers, such as Sr(NO 3 ) 2  and NaNO 3 , known as alternatives to Ba(NO 3 ) 2  and KCIO 4  in the present IM-28 composition. 
     
       
         
               
             
               
               
               
             
           
               
                 TABLE 4 
               
             
             
               
                   
               
               
                 Water solubility data for current inventive preferred  
               
               
                 oxidizer vs. known nitrate oxidizer alternatives. 
               
             
          
           
               
                   
                   
                 Water Solubility 
               
               
                   
                 Ingredient 
                 [g per 100 g H 2 O] 
               
               
                   
                   
               
               
                   
                 NaNO 3   
                 91.2 
               
               
                   
                 Sr(NO 3 ) 2   
                 80.2 
               
               
                   
                 NaIO 4   
                 14.4 
               
               
                   
                   
               
             
          
         
       
     
     The ballistic performance of the inventive composition exceeds that of the currently specified IM-28 incendiary filler for M8 .50″ caliber APIs. Table 5 below compares the performance of the subject composition and IM-28 when each is charged into actual bullets and gun-fired during the “Incendiary Flash” and “Penetration” qualification tests. These tests are part of the typical lot acceptance testing and both must be passed with the minimum scores in the “Success Criteria” column. From Table 5, it is clear that the subject composition, while being free of environmentally objectionable materials, also offers superior performance to the currently specified art. 
     
       
         
               
               
               
               
               
             
           
               
                   
               
               
                 Qualification 
                   
                 Success 
                   
                 Subject 
               
               
                 Test 
                 Reference 
                 Criteria 
                 IM-28 
                 Composition 
               
               
                   
               
             
             
               
                 Incendiary  
                 TECP 700-700, 
                   &gt;70% 
                   93% 
                  96% 
               
               
                 Flash 
                 Vol. III 
                   
                   
                   
               
               
                 Penetration 
                 TECP 700-700, 
                 &gt;87.5% 
                 97.5% 
                 100% 
               
               
                   
                 Vol. III 
               
               
                   
               
             
          
         
       
     
     The subject preferred inventive incendiary composition was prepared by first oven drying the oxidizer(s), screening the oxidizer(s) through a 60-mesh sieve. The dried and screened oxidizer(s) was then combined with the fuel in a conductive container, and the binary mixture was dry-tumbled therein for a period of up to about 30 minutes to ensure thorough mixing/blending. The thoroughly blended composition therefrom was manually pressed into pellets for static ignition testing—to establish the reported burn times and luminous efficiencies—or subjected to a variety of physical stimuli as small, loose powder samples (ca. 20 mg)—to determine sensitivity data—or alternatively, charged as a loose powder into bullet hardware for ballistic tests. Further, as noted above, a small quantity of hydrophobic fumed silica or calcium stearate (about 0.01 to about 0.05 wt. % per total weight of composition) can be added to the oxidizer after it is screened; but, before it is blended with a metal fuel, to enhance uniformity of the resulting inventive incendiary composition—i.e. the oxidizers ability to be thoroughly mixed with the metal fuel, esp. 50/50 magnalium fuel, is enhanced. And, where the 50/50 magnalium (having a preferred mean particle diameter of about 18.4 μm) is available from Magnesium Elektron Powder Products N.A. (Reade Manufacturing Company), Manchester, N.J. 08759. 
     NaIO 4  oxidizing agent is available from William Blythe, Ltd, Lancashire, England BB5 4PD, or Alfa Aesar, a Johnson Matthey Company, located in Ward Hill, Mass. 01835—having a preferred mean particle diameter of about 61.8 μm. 
     The luminous efficiency, the integrated luminous intensity per unit mass, as reported above was established using a single-element photopic light detector. The light detector was manufactured by International Light and is composed of a SED 033 silicon detector (33 mm 2  area silicon detector with quartz window) coupled to a photopic filter (Y-filter) and a field of view limited hood (H-hood). The current output of the detector was converted to a voltage using a DL Instruments 1211 transimpedance amplifier. Voltage output was collected and analyzed form the amplifier using a NI-6115 National Instruments data card and in-house developed Labview based data acquisition and analysis software. 
     Ballistic test data for the subject composition were obtained by standard methods described in TECP 700-700, Volume III. For incendiary flash, 20 rounds derived from the subject composition were fabricated and gun-fired in a test tunnel. The flash resulting from each shot was recorded by high speed camera and compared to the flash silhouettes on a standard drawing. Scores ranged from 0 (no flash, “dud”) to 5 (robust, bright flash) and an overall percentage was obtained by simply adding up all 20 individual scores. For .50″ caliber rounds, a minimum flash score of 70% is required for lot acceptance. For the penetration tests, 20 more rounds were fabricated and gun-fired at a 1.00″ thick steel plate. The terminal effect at the target plate was noted for each shot and only those shots resulting in complete perforation of the plate were credited; other outcomes such as “bulge rear no cracks,” spall, or partial penetration were not credited. A final penetration score was obtained by adding the number of credited shots and multiplying by five. For .50″ caliber rounds, a minimum penetration score of 87.5% is required for lot acceptance. 
     Although the invention has been described above in relation to preferred embodiments thereof, it will be understood by those skilled in the art that variations and modifications can be effected in these preferred embodiments without departing from the scope and spirit of the invention. Further, while specific weights or ratios may have been used by way of example/specific embodiments, it is also understood by those skilled in the art that quantities of the materials between and about the ratios are equally functional.