Abstract:
A yellow smoke composition useful in hand held signals, such as the U.S. Army M194 yellow smoke parachute signal; which composition contains the nontoxic, environmentally safe, quinoline solvent yellow 33 color agent and critically exhibits the requisite dense yellow smoke for the requisite 9 to 18 second burn time upon use. Further, this inventive yellow smoke composition can be used in current metal tubes and in other media, such as biodegradable cardboard tubes.

Description:
FEDERAL RESEARCH STATEMENT 
       [0001]    The inventions described herein may be manufactured, used and licensed by, or for, the U.S. Government, for U.S. Government purposes. 
     
    
     BACKGROUND OF INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to hand held signal pyrotechnic smoke compositions, and more particularly, to such an compositions that are free of the conventional, but toxic yellow smoke agents Vat Yellow 4 (dibenzochrysenedione) and benzanthrone, and still continue to provide the requisite density, burn time, and good color quality. 
         [0004]    2. Background Art 
         [0005]    Hand held signal (HHS) pyrotechnic smoke compositions are useful for multiple military purposes—including signaling troop locations or distress, during combat or training operations, or to serve as a beacon for target or landing zone marking. One such pyrotechnic smoke formulation is contained within the US Army M194 HHS—which HHS is launched via a rocket to a height of about 725 feet, at which point the signal is ignited. The M194 HHS provides a dense, highly visible yellow smoke as it falls back to earth via parachute—burning for 9 to 18 seconds (ideally about 13 to about 15 seconds), while producing the desired yellow smoke during this period, before burnout at about 500 to 600 feet. Unfortunately, the current M194 HHS yellow smoke formulation contains two toxic anthraquinone dyes, namely Vat Yellow 4 (aka (dibenzochrysenedione) and benzanthrone. Benzanthrone is a known dermal sensitizer, and is reported as causing liver and nervous system damage; plus, it is also known to be highly toxic to aquatic life. Vat Yellow 4, felt to contain small but significant amounts of dibenzochrysene (an extremely potent carcinogen) is classified as a Group 3 material by the International Agency for Research on Cancer (IARC)—because of evidence of its potential carcinogenic impact remains unsubstantiated. 
         [0006]    In the current M194 pyrotechnic formulation, the dense yellow smoke is formed by the cost effective reduction-oxidation (redox) reaction of relatively inexpensive potassium chlorate (an oxidizer), with sugar (a fuel, or reducing agent)—which generates significant heat. The heat, in turn, causes the dye molecules, i.e. the VAT Yellow 4 and benzanthrone—to enter the gas phase (via sublimation) and begin to disperse. After dispersion of the dye molecules, contact with the cool ambient air causes them to condense back to the solid phase, helped by the presence of sodium bicarbonate, which functions as an evaporative cooling agent. Lastly, the formulation contains a binder to “glue” it together, i.e. vinyl alcohol acetate resin (VAAR). 
         [0007]    As the binder in the current yellow smoke M194 formulation is available only in a solvent media—the manufacturing process requires that this solvent be driven-off prior to the consolidation of the yellow smoke formulation and its packing into a steel canister within the M194 HHS. 
         [0008]    An alternative yellow pyrotechnic smoke formulation has been developed for the simulation of the smoke signature related to ground-launched missiles—part of a Battle Effects Simulator (BES) system. These yellow smoke formulations use an alternative yellow smoke agent, quinoline yellow spirit solution, also commonly known as quinoline yellow ss or solvent yellow 33, in combination with potassium chlorate (the oxidizer), sugar (the fuel/reducing agent), magnesium carbonate (a coolant), stearic acid (a lubricant), and VAAR (a binder). However, while these alternative BES yellow smoke formulations are much safer and more environmentally friendly than the M194 yellow smoke formulations—the burn times are far outside that required for the M194 HHS application, i.e about 37.5 seconds (over twice the maximum time allowed for the M194 yellow smoke application of 9 to 18 seconds). 
         [0009]    Therefore, there is a need in the art for a replacement M194 HHS yellow smoke composition that continues to utilize the relatively inexpensive potassium chlorate and sugar redox reaction, and contains an alternative yellow smoke agent that is non-toxic and environmentally safe; which composition will burn for the requisite 9 to 18 seconds, while producing the desired dense, highly visible yellow smoke. Further, there is also a need in the art for an all solid ingredient alternative M194 HHS smoke composition that will rot require any solvent to be driven off during its manufacture—thereby simplifying and making the manufacturing process more effective, efficient, and economical. 
       SUMMARY OF INVENTION 
       [0010]    In order to overcome the above stated problems of the prior art—the present inventive HHS yellow pyrotechnic smoke formulation preferably contains all solid, powder ingredients which are easily combined via a conventional dry-tumble process—the ingredients being: potassium chlorate (KClO 3 ), an oxidizing agent; sugar (sucrose), a fuel (reducing agent); solvent yellow 33 (SY33, otherwise known as quinoline yellow ss, or as D&amp;C Yellow No. 11), the yellow smoke agent; hydromagnesite (Mg5(CO3)4(OH)2.4H2O), a coolant; stearic acid, a lubricant; hydrophobic fumed silica (available from the Cabot Corporation, under the trademark Cab-O-Sil®), an anti-caking agent; and polyvinyl alcohol (PVA), a binder. These ingredients provide an inventive yellow smoke formulation wherein a redox reaction of the potassium chlorate and sugar forms potassium chloride, carbon dioxide, water vapor, and soot/carbon—which reaction is exothermic. This exothermic reaction releases sufficient heat to cause the yellow smoke agent SY33 to sublimate, disperse over a wide area, and then condense into the desired dense, highly visible yellow smoke. Further, and most importantly, the burn time is within the 9 to 18 second desired, required, smoke production time, when the inventive formulation is compressed into a smoke pellet usable in an M194 HHS. 
         [0011]    In an alternative embodiment of the present invention, a small quantity of fumed silica (also known as pyrogenic silica or Cab-O-Sil®),) can be substituted for an equal quantity of the fuel, sugar—the silica acting as an anticaking agent—to aid in the flowability of the inventive formulation during its handling, transport, and packing into the desired HHS container. 
         [0012]    If desired, the inventive formulation can contain the alternative binders polyvinyl alcohol (PVA) and/or nitrocellulose (NC). The NC alternative embodiment, wherein the nitrocellulose ingredient is contained within solvent media, will require that after the ingredients are added to the mixture, the resulting now wet mixture will have to be dried in a dryer or oven. When the preferred alternative binder polyvinyl alcohol is utilized in the inventive mixture, the resulting dry mix is useful for the subject application as is, i.e. no drying step is required. 
         [0013]    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 DRAWINGS 
         [0014]      FIG. 1  is a cross-sectional diagram of the current U.S. Army M194 HHS; regarding which HHS, the inventive yellow smoke “candle” may be substituted with that of the present invention. 
           [0015]      FIG. 2  is the structural chemical formulation of solvent yellow 33, SY33, the preferred non-toxic yellow dye material useful in the present invention. 
           [0016]      FIG. 3  is a cross-sectional view of a yellow smoke formulation test prototype using the present inventive formulation therein. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0017]    The present inventive HHS yellow pyrotechnic smoke composition is preferably a mixture of solid materials, including about 34.5 weight percent of potassium chlorate (KClO 3 ), an oxidizing agent; about 21.5 to about 22.0 weight percent of a sugar (sucrose), a fuel (reducing agent); about 36 to about 37 weight percent of solvent yellow 33 (SY33, also known as quinoline yellow ss, or as D&amp;C Yellow No. 11), the yellow smoke agent; about 5.5 weight percent hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O), a cooling agent; about 0 to about 1.0 weight percent stearic acid, a lubricant; and about 0 to about 0.5 weight percent hydrophobic fumed silica, an anti-caking agent. To this mixture of solid powdered materials, a binder or combination of binders may be added, where the most preferred binder is about 0 to about 1.0 weight percent polyvinyl alcohol (PVA), also a solid (such that the resulting mixture need only be dry-tumbled to be completed). 
         [0018]    As stated above, in an alternative embodiment of the present invention, a smal quantity, about 0.5 wt. %, of fumed silica (also known as pyrogenic silica) can be substituted for an equal quantity of the fuel, sugar—the silica acting as an anticaking agent—to aid in the flowability of the inventive formulation during its handling, transport, and packing into the desired HHS container. 
         [0019]    An alternative binder useful in the present invention includes nitrocellulose (NC)—but, this alternative binder is standardly available in a liquid form, i.e. in a solvent media—such that about 10% by weight must be added and then the solvent driven-off in an oven or dryer—whereby the final quantity of the nitrocellulose is at the desired about 0 to about 1.0 weight percent of the total inventive yellow smoke formulation. 
         [0020]    The particular yellow smoke agent useful in the present invention is, as stated above, solvent yellow 33—which material is abbreviated as SY33, and also known as quinoline yellow ss, or as D&amp;C Yellow No. 11. As shown in  FIG. 2 , the chemical structure of SY33 consists of a quinoline carbon skeleton and may be described as 2-(2-quinolyl)-1,3-indandione. This material is conventionally used as a coloring agent in topical drugs and cosmetics, in spirit lacquers, acrylic resins, polystyrene, polycarbonates, polyamides and to color hydrocarbon solvents. Most importantly, SY33 has been deerred admissible by the U.S. Army Public Health Command (PHC) in colored smoke formulations and this dye is presently used in M18 smoke grenade production. Also, inhalation studies of SY33 as a smoke dye indicates that this compound is cleared from the lungs very rapidly. 
         [0021]    The specification of the various ingredients in the above detailed inventive formulation preferably meet the criteria and specifications shown in Table 1 below. 
         [0000]    
       
         
               
             
               
               
             
           
               
                 TABLE 1 
               
             
             
               
                   
               
               
                 Preferred chemical specifications for the 
               
               
                 ingredients useful in the present invention. 
               
             
          
           
               
                 Ingredient 
                 Specification (US Military Specifications) 
               
               
                   
               
               
                 Potassium chlorate (KClO 3 ) 
                 MIL-P-150D, Grade B, Class 7 
               
               
                 Sugar (sucrose) 
                 MIL-AA-20135D, Type 1, Style C 
               
               
                 Solvent yellow 33 
                 MIL-DTL-51485B(EA), Type II, 
               
               
                   
                 from Nation Ford Chemical 
               
               
                 Sodium bicarbonate 
                 Technical grade, from Hummel Croton 
               
               
                 (NaHCO 3 ) 
               
               
                 Hydromagnesite 
                 Technical grade, from Pine Bluff Arsenal 
               
               
                 (Mg 5 (CO 3 ) 4 (OH) 2 •4H 2 O) 
               
               
                 Stearic acid 
                 MIL-S-271B 
               
               
                 Hydrophobic fumed silica 
                 From Cabot 
               
               
                 (Cabosil) 
               
               
                 VAAR 
                 MIL-V-50433 
               
               
                 Polyvinyl alcohol 
                 Molecular weight range: 
               
               
                   
                 77,000-79,000 g/mol 
               
               
                 Nitrocellulose 
                 Technical grade, from Alliant Techsystems 
               
               
                   
               
             
          
         
       
     
         [0022]    In preparing the inventive yellow smoke formulation, the potassium chlorate was initially oven dried overnight at 140 degrees F.—to ensure its dryness. Then, in the case of the inventive formulation embodiments containing only solid ingredients, the potassium chlorate and other ingredients were tumbled end-over-end in conductive plastic containers for 60 min; while, those containing wet NC were blended in a Hobart mixer for 30 min. Dry-tumbled formulations were taken directly to loading operations without further processing, while NC-based formulations were oven-cured overnight at 140° F. prior to loading. Following blending, the dry mixture was hydraulically pressed into kraft cardboard tubes—which is a distinct advantage over formulations of the prior art. Specifically, the current inventive yellow smoke formulation can be consolidated and delivered in the prior art steel canister, or in other canister materials, such as an aluminum, or even cardboard canisters—and still give the requisite smoke density, color, and duration of burn. And, after consolidation and coating with first-fire composition, the pressed pellets are ready for evaluation/testing. 
         [0023]    The inventive formulations were tested and proved to meet the requisite smoke density, color, and burn time in biodegradable cardboard tubes (as shown in  FIG. 3 )—using static ignition tests. Referring to  FIG. 3 , a 70-gram, cylindrical smoke pellet was pressed in 2-3 increments (at about 4,000 to about 12,000 pound dead load, for about 4 seconds dwell time) inside of a Kraft paper tube—to form a smoke candle. A thin coat of igniter slurry (first-fire composition) was applied to the top surface (shallow recess on the left side of the pressed smoke composition) and tapered inner bore of the pellet. After oven-curing at 140° F. for 16 hours, the pellet (smoke candle) was ready to be ignition-tested and its resulting smoke density, color, and burn time evaluated. 
         [0024]    The inventive formulations were tested against the current BES yellow smoke formulation, which was considered a baseline, as it is similar in many respects; but, as stated, has a burn time that is totally unacceptable (twice the maximum allowed rate of 18 seconds). The results of the tests are shown in Table 2, and the summarized below:
       (1) replacement of the binder present in BES—samples designated 12 and 14, or eliminating the binder altogether, designated 13—resulted in burn times on the outer cusp of the requirement ˜18 s in each case—and were judged not acceptable;   (2) increasing oxidizer content in 5 wt. % increments, designated 15 and 16, yielded burn times more-or-less equivalent to that of the BES control—i.e. not acceptable;   (3) increasing dye content in 5 wt. % increments, designated 17 and 18 yielded burn times that were both longer than the BES control—i.e. not acceptable;   (4) substituting the coolant NaHCO 3  for hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O) the in the BES control, was met with a significant improvement in burn time, demonstrated by burning of the formulation designated 19—however, not to the extent as to be acceptable. This coolant effect was also explored in the alternative formulations, designated 22, 24, and 25, which were identical to formulations designated 12, 13, and 14, again only using NaHCO 3  instead of (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O) as a coolant. These too, unfortunately, burned outside the acceptable/target time range;   (5) a mix identical to 12 only with 2 wt. % NC, designated 23, gave a burn time that was still too long; despite efforts to reduce burn time and the improvements exhibited by 12, 13, and 14, more formulation development was necessary to fit more comfortably within the target time range (ideally 13-15 seconds);   (6) tests at 10.5 wt. % coolant weight percentage for all four binder systems (NC, PVA, binder-free, and VAAR) designated 89 through 117, and 118 through 121 proved unacceptably long, with the (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O)-based formulations generally burning faster than the NaHCO 3 -based formulations;   (7) however, surprisingly, three formulations in the grouping designated 27, 28, and 29, at 5.5 wt. % (Mg 5 (CO 3 ) 4 (OH) 2 .4H 2 O) met the target burn time range, each at about 15 seconds; but   (8) the alternative NaHCO 3 -based formulations, designated 26 through 64 at this 5.5 wt. % coolant level—still burned outside the target range;   (9) further, and also surprisingly, as the coolant level was progressively lowered, while we expected to see even shorter burn times by cutting the coolant level to 2.5 wt. % in the grouping designated 77 through 80, and 81 through 84—these formulations, however, generally gave smoke plumes of drastically reduced color quality. Apparently, the coolant level in this last grouping was not sufficiently high to moderate the reaction temperature and to suppress flaming.       
 
         [0000]    
       
         
               
             
               
               
               
               
               
               
               
               
               
             
               
               
               
               
               
               
               
               
               
             
           
               
                 TABLE 2 
               
             
             
               
                   
               
               
                 Chemical composition and performance of invented yellow smoke 
               
               
                 formulations a , 27, 28, 29, and similar compositions which 
               
               
                 failed to meet the burn time standard 
               
             
          
           
               
                   
                   
                   
                   
                   
                   
                   
                 Wt. % 
                 Burn 
               
               
                 Ref. 
                 Wt. % 
                 Wt. % 
                 Wt. % 
                 Wt. % 
                 Wt % 
                   
                 fumed 
                 Time 
               
               
                 No. 
                 KClO 3   
                 Sugar 
                 Coolant c   
                 NaHCO 3   
                 SY 33 
                 Binder 
                 silica 
                 (sec) 
               
               
                   
               
             
          
           
               
                 BES 
                 29.5 
                 22 
                 15.5 
                   
                 31 
                 VAAR 
                   
                 38 
               
               
                 12 
                 29.5 
                 22 
                 15.5 
                   
                 31 
                 NC 
                   
                 19 
               
               
                 13 
                 29.5 
                 22 
                 15.5 
                   
                 32 
                 None 
                   
                 17 
               
               
                 14 
                 29.5 
                 22 
                 15.5 
                   
                 31 
                 PVA 
                   
                 18 
               
               
                 15 
                 29.5 
                 27 
                 10.5 
                   
                 31 
                 VAAR 
                   
                 42 
               
               
                 16 
                 29.5 
                 32 
                 5.5 
                   
                 31 
                 VAAR 
                   
                 34 
               
               
                 17 
                 29.5 
                 22 
                 10.5 
                   
                 36 
                 VAAR 
                   
                 43 
               
               
                 18 
                 29.5 
                 22 
                 5.5 
                   
                 41 
                 VAAR 
                   
                 45 
               
               
                 19 
                 29.5 
                 22 
                   
                 15.5 
                 31 
                 VAAR 
                   
                 22 
               
               
                 22 
                 29.5 
                 22 
                   
                 15.5 
                 31 
                 NC 
                   
                 30 
               
               
                 24 
                 29.5 
                 21.5 
                   
                 15.5 
                 31 
                 PVA 
                 0.5 
                 42 
               
               
                 25 
                 29.5 
                 21.5 
                   
                 15.5 
                 32 
                 None 
                 0.5 
                 36 
               
               
                 23 
                 29.5 
                 22 
                 14.5 
                   
                 31 
                 NC (2%) 
                   
                 25 
               
               
                 89 
                 29.5 
                 22 
                 10.5 
                   
                 36 
                 NC 
                   
                 23 
               
               
                 90 
                 29.5 
                 21.5 
                 10.5 
                   
                 37 
                 None 
                 0.5 
                 34 
               
               
                 116 
                 29.5 
                 21.5 
                 10.5 
                   
                 36 
                 PVA 
                 0.5 
                 33 
               
               
                 117 
                 29.5 
                 22 
                 10.5 
                   
                 36 
                 VAAR 
                   
                 86 
               
               
                 118 
                 29.5 
                 22 
                   
                 10.5 
                 36 
                 NC 
                   
                 49 
               
               
                 119 
                 29.5 
                 21.5 
                   
                 10.5 
                 37 
                 None 
                 0.5 
                 42 
               
               
                 120 
                 29.5 
                 21.5 
                   
                 10.5 
                 36 
                 PVA 
                 0.5 
                 33 
               
               
                 121 
                 29.5 
                 22 
                   
                 10.5 
                 36 
                 VAAR 
                   
                 65 
               
               
                 27 
                 34.5 
                 22 
                 5.5 
                   
                 36 
                 NC 
                   
                 16 
               
               
                 28 
                 34.5 
                 21.5 
                 5.5 
                   
                 37 
                 None 
                 0.5 b   
                 15 
               
               
                 29 
                 34.5 
                 21.5 
                 5.5 
                   
                 36 
                 PVA 
                 0.5 b   
                 15 
               
               
                 63 
                 34.5 
                 22 
                 5.5 
                   
                 36 
                 VAAR 
                   
                 49 
               
               
                 26 
                 34.5 
                 22 
                   
                 5.5 
                 36 
                 NC 
                   
                 24 
               
               
                 33 
                 34.5 
                 21.5 
                   
                 5.5 
                 37 
                 None 
                 0.5 
                 21 
               
               
                 34 
                 34.5 
                 21.5 
                   
                 5.5 
                 36 
                 PVA 
                 0.5 
                 20 
               
               
                 64 
                 34.5 
                 22 
                   
                 5.5 
                 36 
                 VAAR 
                   
                 88 
               
               
                 77 
                 34.5 
                 22 
                 2.5 
                   
                 39 
                 NC 
                   
                 21 
               
               
                 78 
                 34.5 
                 21.5 
                 2.5 
                   
                 40 
                 None 
                 0.5 
                 24 
               
               
                 79 
                 34.5 
                 21.5 
                 2.5 
                   
                 39 
                 PVA 
                 0.5 
                 17 
               
               
                 80 
                 34.5 
                 22 
                 2.5 
                   
                 39 
                 VAAR 
                   
                 55 
               
               
                 81 
                 34.5 
                 22 
                   
                 2.5 
                 39 
                 NC 
                   
                 28 
               
               
                 82 
                 34.5 
                 21.5 
                   
                 2.5 
                 40 
                 None 
                 0.5 
                 26 
               
               
                 83 
                 34.5 
                 21.5 
                   
                 2.5 
                 39 
                 PVA 
                 0.5 
                 26 
               
               
                 84 
                 34.5 
                 22 
                   
                 2.5 
                 39 
                 VAAR 
                   
                 54 
               
               
                   
               
               
                   a All formulations contain 1 wt. % stearic acid as a lubricant and, except those noted otherwise or those binder-free, 1 wt. % binder (NC or PVA or VAAR - as stated). 
               
               
                   b The fumed silica, e.g. Cab-O-Sil ® available from the Cabot Corporation, can be omitted entirely and the sugar content increased correspondingly to 22 wt. % with no difference in performance. 
               
               
                   c The coolant being: hydromagnesite (Mg 5 (CO 3 ) 4 (OH) 2 •4H 2 O). 
               
             
          
         
       
     
         [0034]    The procedure used in the static ignition tests, whose results are detailed above, involved using the cylindrical smoke pellets, or smoke candles, (produced as detailed above), wherein the pellet were clamped vertically with the top slurry-coated end facing up. The head of an electric match was placed on the top slurried end. After passing an energy of 2 volts through the electric match, the resulting spit of the electric match lights the igniter slurry. The heat from this ignition event then initiates a reduction-oxidation reaction between the fuel (sugar) and the oxidizer (potassium chlorate) in the tested pressed smoke compositions. The burning of the pressed pellet propagated in a core-burning fashion, from top-down and from inside-out (but surprisingly, not bottom-up). The burn times, linear burning rates, and mass consumption rates were measured for all smoke candles tested—and the results presented above. 
         [0035]    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.