Pyrotechnics hygroscopicity

Cost is always a factor in selecting a component for a pyrotechnic composition, as is the water-attracting abiHty of a substance (hygroscopicity). In general, substances that attract water from the atmosphere are avoided in pyrotechnic formulations for a variety of reasons, thereby supporting the centuries-old adage, "Keep your powder dry."... 

Another matter of concern in pyrotechnic formulations is the possibiHty of exchange reactions occurring between components. Addition of ammonium salts to compositions containing nitrate oxidizers can produce ammonium nitrate, a very hygroscopic material. The composition then becomes quite prone to pick up water and its performance deteriorates. The addition of an ammonium salt to a chlorate-based formulation can lead to the... 

Lithium chlorate [13453-71 -9] LiClO, has rhombic needles mp 124—129°C decomposes on heating to 270°C. It is one of the most soluble salts known and it is very hygroscopic. LiClO is prepared by adding lithium chloride [7447-41-8] to sodium chlorate solution. Sodium chloride precipitates, the hquor is concentrated, and the lithium chlorate is filtered and dried. It has limited use in pyrotechnics. 

As mentioned earlier, chlorates are also a major ingredient in various pyrotechnic formulations. Typically potassium chlorate is utilized in this capacity due to the more hygroscopic nature of the sodium analog. Mixed with powdered aluminum and/or sulfur, potassium chlorate produces a mixture commonly referred... 

The best flame emission in the red region of the visible spectrum is produced by molecular strontium monochloride, SrCl. This species - unstable at room temperature - is generated in the pyrotechnic flame by a reaction between strontium and chlorine atoms. Strontium dichloride, SrCl 2, would appear to be a logical precursor to SrCl, and it is readily available commercially, but it is much too hygroscopic to use in pyrotechnic mixtures. 

Ellern, Pyrotechnics(1968) Particle Size Determination of Pyrotechnic Compositions (pp 259-61) Heats of Combustion of Elements and Compounds Used in Pyrotechnics (pp 276-80) Measurement of Stability and Reactivity of Pyrotechnic Compositions (pp 291-94) Ignition, Initiation and Decomposition of Pyrotechnic Compositions (pp 294-300) Hygroscopicity and Self-Destructive Interaction (pp 300-304) Survival and Surveillance of Finished Pyrotechnic Items (pp 304-307)... 

Some of the important properties which are considered when choosing the ingredients for pyrotechnic formulations are density, hygroscopicity, melting and boiling points and decomposition temperatures, oxygen content of oxidizers, thermal conductivity of fuels and containers, nature of combustion products and toxicity etc. 

Refs l)Colver(l918),639 2)C.E.Munroe, ChemMetEngrg 26, 541(1922) 3)J-L-Sherick, ArOrdn 24, 329 395(1924) 4)G.W.Jones, ArOrdn 5, 599(1924) 5)D-B.Gawchrop, ArOrdn 6, 47(1925) 6)Cook(l958),29-31 Absorption of Moisture by Explosives, Propellants and Pyrotechnic Compositions. See Hygroscopicity Action of Light on Explosives, etc. See Light, Action on Explosives, etc Aptitude a I inflammation, Es ai. Same as Capability to Inflame Test... 

Some bitumens have been used in coml expls and pyrotechnic compos as a coating for those ingredients which are either too hygroscopic or too sensitive to impact or friction to be used uncoated. Izzo(Ref 5) lists the following Ital pyro compns a)Bitumen 10, hexachloroethane 50 Zn powd 30 KNOs 10% b)Bitumen 10, hexachloroethane 45, Zn powd 25, KN03 15 ZnO 5%... 

Lithium nitrate is soluble in water and is highly hygroscopic. Its only use is as a flame-coloring oxidizer in pyrotechnical formulations. 

Tessier introduced the use of cryolite (AlNaaF ) for the yellow coloring of stars, lances, and Bengal lights. In his second edition he includes a chapter on the small pyrotechnic pieces which are knonm as Japanese fireworks, giving formulas for them, and another on the picrates, which he studied extensively. The picrates of sodium, potassium, and ammonium crystallize in the anhydrous condition. Those of barium, strontium, calcium, magnesium, zinc, iron, and copper are hygroscopic and contain considerable water of crystallization which makes them unfit for use in pyrotechnic compositions. Lead picrate, with 1 H3O, detonates... 

The presence of sodium compounds in certain flame pyrotechnics is to be avoided on account of the masking influence of the sodium flame and also on account of the hygroscopic nature of sodium nitrate which might interfere with the proper functioning of the p>rotechnic. The sodium nitrate can be estimated by the method of Ball. Wher a mixture of potassium nitrate, bismuth nitrate and caesium nitrate in nitric acid is added to a dilute solution of sodium nitrate, even in presence of large an>ount3 of potassium salts, the sodium is precipitated... 

Clive Jennings-White "Hygroscopicity and Double Decomposition of Pyrotechnic Oxidizers", PyrotechnicaXVI, page 11 (1995). 

C. Jennings-White, Hygroscopicity and Double Decomposition of Pyrotechnic Oxidizers , Pyrotechnica XVI, 1995. 

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