All
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2
decomposition problems, but mixtures of aluminum and non-hygro-Cu +2 + Mg _
+ Mg+
Cu
scopic barium nitrate can be stored with a minimum of precautions, This process becomes much more probable if a composition is mois-as long as the composition does not actually get wet. Mixtures of magnesium metal with nitrate salts do not have this alkaline-cata-tened, again pointing out the variety of problems that can be created if water is added to a magnesium-containing mixture. The lyzed decomposition problem.
A magnesium hydroxide (Mg(OH) 2 ]
coating on the metal surface apparently protects it from further standard potential for the Cu +2 /Mg system is +2.72 volts, indicating a very spontaneous process. Therefore, Cu +2 , Pb +2 , and reaction.
This protection is not provided to aluminum metal by
-
other readily-reducible metal ions must not be used in magnesium-the alkaline soluble aluminum hydroxide, Al(OH) 3 .
containing compositions.
Magnesium (Mg)
"Magnalium" (Magnesium-Aluminum Alloy) Magnesium is a very reactive metal and makes an excellent fuel A material finding increasing popularity in pyrotechnics is the under the proper conditions. It is oxidized by moist air to form 50/50 alloy of magnesium and aluminum, termed "magnalium."
magnesium hydroxide, Mg(OH) 2 , and it readily reacts with all Shimizu reports that this material is a solid solution of Al acids, including weak species such as vinegar (5% acetic acid) 3 Mg 2 in
and boric acid. The reactions of magnesium with water and an Al 2 Mg 3 , with a melting point of 460°C [2]. The alloy is considerably more stable than aluminum metal when combined with ni-acid (HX) are shown below:
trate salts, and reacts much more slowly than magnesium metal Water:
Mg + 2 H
+ H
2 O } Mg(OH) 2
2
with weak acids. It therefore offers stability advantages over Acids (HX): Mg + 2 HX ; MgX
both of its component materials.
2 + H 2 (X = Cl, NO 3 , etc.)
The Chinese make wide use of magnalium in fireworks items Even the ammonium ion, NH 4+, is acidic enough to react with to produce attractive white sparks and "crackling" effects.
magnesium metal.
Therefore, ammonium perchlorate and other
Shimizu also reports that a branching spark effect can be pro-ammonium salts should not be used with magnesium unless the duced using magnalium with a black powder-type composition metal surface is coated with linseed oil, paraffin, or a similar
[2] .
material.
Chlorate and perchlorate salts, in the presence of moisture, I ron
will oxidize magnesium metal, destroying any pyrotechnic effect during storage.
Nitrate salts appear to be considerably more Iron, in the form of fine filings, will burn and can be used to stable with magnesium [2].
Again, coating the metal with an
produce attractive gold sparks, such as in the traditional wire organic material - such as paraffin - will increase the storage sparkler.
The small percentage (less than 1%) of carbon in steel lifetime of the composition.
A coating of potassium dichromate
can cause an attractive branching of the sparks due to carbon on the surface of the magnesium has also been recommended to dioxide gas formation as the metal particles burn in air.
aid in stability [21, but the toxicity of this material makes it of Iron filings are quite unstable on storage, however. They questionable value for industrial applications.
readily convert to iron oxide (rust - Fe 2 0 3 ) in moist air, and Magnesium has a heat of combustion of 5. 9 kcal /gram, a melt-filings are usually coated with a paraffin-type material prior to ing point of 649°C, and a low boiling point of 1107°C. This low use in a pyrotechnic mixture.
boiling point allows excess magnesium in a mixture to vaporize and burn with oxygen in the air, providing additional heat (and Other Metals
light) in flare compositions.
No heat absorption is required to
decompose an oxidizer when this excess magnesium reacts with Titanium metal (Ti) offers some attractive properties to the high-
-
atmospheric oxygen; hence, the extra heat gained by incorpor energy chemist. It is quite stable in the presence of moisture ating the excess magnesium into the mixture is substantial.
and most chemicals, and produces brilliant silver-white spark Magnesium metal is also capable of reacting with other metal and light effects with oxidizers. Lancaster feels that it is a ions in an electron-transfer reaction, such as safer material to use than either magnesium or aluminum, and
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recommends that it be used in place of iron filings in fireworks
"fountain" items, due to its greater stability [11] . Cost and lack of publicity seem to be the major factors keeping titanium from being a much more widely used fuel.
Zirconium (Zr) is another reactive metal, but its considerable expense is a major problem restricting its wider use in high-energy compositions. It is easily ignited - and therefore quite hazardous - as a fine powder, and must be used with great care.
Non-Metallic Elements
Several readily-oxidized nonmetallic elements have found widespread use in the field of pyrotechnics. The requirements again are stability to air and moisture, good heat-per-gram output, and reasonable cost. Materials in common use include sulfur, boron, silicon, and phosphorus. Their properties are summarized in Table 3.5.
Sulfur
The use of sulfur as a fuel in pyrotechnic compositions dates back over one thousand years, and the material remains a widely-used component in black powder, colored smoke mixtures, and fireworks compositions. For pyrotechnic purposes, the material termed "flour of sulfur" that has been crystallized from molten sulfur is preferred. Sulfur purified by sublimation - termed
"flowers of sulfur" - often contains significant amounts of oxidized, acidic impurities and can be quite hazardous in high-energy mixtures, especially those containing a chlorate oxidizer
[11].
Sulfur has a particularly low (119°C) melting point. It is a rather poor fuel in terms of heat output, but it frequently plays another very important role in pyrotechnic compositions. It can function as a "tinder," or fire starter. Sulfur undergoes exothermic reactions at low temperature with a variety of oxidizers, and this heat output can be used to trigger other, higher-energy reactions with better fuels. Sulfur's low melting point provides a liquid phase, at low temperature, to assist the ignition process. The presence of sulfur, even in small percentage, can dramatically affect the ignitibility and ignition temperature of high-energy mixtures. Sulfur, upon combustion, is converted to sulfur dioxide gas and to sulfate salts (such as potassium sulfate - K 2SOy). Sulfur is also found to act as an oxidizer in some