Ammonium Perchlorate (NH,,CIO,,)
The "newest" oxidizer to appear in pyrotechnics, ammonium perchlorate has found considerable use in modern solid-fuel rocket propellants and in the fireworks industry. The space shuttle alone uses approximately two million pounds of solid fuel per launch; the mixture is 70% ammonium perchlorate, 16% aluminum metal, and 14% organic polymer.
Ammonium perchlorate undergoes a complex chemical reaction on heating, with decomposition occurring over a wide range, beginning near 200°C. Decomposition occurs prior to melting, so a liquid state is not produced - the solid starting material goes directly to gaseous decomposition products. The decomposition reaction is reported by Shimizu to be
This equation corresponds to the evolution of 80 grams (2.5 moles) of oxygen gas per 2 moles (235 grams) of NH C1O,, , giving an "active oxygen" content of 34% (versus 39.2% for KC1O 3 and 46.2% for KC10,,). The decomposition reaction, above 350 1C, is reported to be considerably more complex.
Mixtures of ammonium perchlorate with fuels can produce high temperatures when ignited, and the hydrogen chloride (HCl) liberated during the reaction can aid in the production of colors. These two factors make ammonium perchlorate a good oxidizer for colored flame compositions.
Ammonium perchlorate is more hygroscopic than potassium nitrate or potassium chlorate, and some precautions should be taken to keep mixtures dry. The hygroscopicity problem can be substantial if a given composition also contains potassium nitrate, or even comes in contact with a potassium nitrate-containing mixture. Here, the reaction
can occur, especially in the presence of moisture. The exchange product, ammonium nitrate (NH,,N0 3 ) is very hygroscopic, and ignition problems may well develop. Also, ammonium perchlorate should not be used in combination with a chlorate-containing compound, due to the possible formation of unstable ammonium chlorate in the presence of moisture.
Magnesium metal should also be avoided in ammonium perchlorate compositions. Here, the reaction
can occur in the presence of moisture. Spontaneous ignition may occur if the heat buildup is substantial.
Under severe initiation conditions, ammonium perchlorate can be made to explode by itself. Mixtures of ammonium perchlorate with sulfur and antimony sulfide are reported to be considerably more shock sensitive than comparable KC1O 3 compositions. Ammonium perchlorate can be used to produce excellent colors, with little solid residue, but care must be exercised at all times with this oxidizer. The explosive properties of this material suggest that minimum amounts of bulk composition should be prepared at one time, and large quantities should not be stored at manufacturing sites.