Magnesium (Mg)
Magnesium is a very reactive metal and makes an excellent fuel under the proper conditions. It is oxidized by moist air to form magnesium hydroxide, Mg(OH) 2 , and it readily reacts with all acids, including weak species such as vinegar (5% acetic acid) and boric acid. The reactions of magnesium with water and an acid (HX) are shown below:
Even the ammonium ion, NH 4+, is acidic enough to react with magnesium metal. Therefore, ammonium perchlorate and other ammonium salts should not be used with magnesium unless the metal surface is coated with linseed oil, paraffin, or a similar material.
Chlorate and perchlorate salts, in the presence of moisture, will oxidize magnesium metal, destroying any pyrotechnic effect during storage. Nitrate salts appear to be considerably more stable with magnesium [2]. Again, coating the metal with an organic material - such as paraffin - will increase the storage lifetime of the composition. A coating of potassium dichromate on the surface of the magnesium has also been recommended to aid in stability, but the toxicity of this material makes it of questionable value for industrial applications.
Magnesium has a heat of combustion of 5. 9 kcal /gram, a melting point of 649°C, and a low boiling point of 1107°C. This low boiling point allows excess magnesium in a mixture to vaporize and burn with oxygen in the air, providing additional heat (and light) in flare compositions. No heat absorption is required to decompose an oxidizer when this excess magnesium reacts with atmospheric oxygen; hence, the extra heat gained by incorporating the excess magnesium into the mixture is substantial.
Magnesium metal is also capable of reacting with other metal ions in an electron-transfer reaction, such as
This process becomes much more probable if a composition is moistened, again pointing out the variety of problems that can be created if water is added to a magnesium-containing mixture. The standard potential for the Cu +2 /Mg system is +2.72 volts, indicating a very spontaneous process. Therefore, Cu +2 , Pb +2 , and other readily-reducible metal ions must not be used in magnesiumcontaining compositions.