Color Intensifiers
Chlorine is the key to the production of good red, green, and blue flames, and its presence is required in a pyrotechnic mixture to achieve a good output of these colors. Chlorine serves two important functions in a pyrotechnic flame. It forms volatile chlorine - containing molecular species with the color-forming metals, ensuring a sufficient concentration of emitters in the vapor phase. Also, these chlorine-containing species are good emitters of narrow bands of visible light, producing the observed flame color. Without both of these properties - volatility and light emission - good colors would be difficult to achieve.
The use of chlorate or perchlorate oxidizers (KC1O 3 , KC1O,,, etc.) is one way to introduce chlorine atoms into the pyrotechnic flame. Another method is to incorporate a chlorine-rich organic compound into the mixture. The table lists some of the chlorine donors commonly used in pyrotechnic mixtures. A dramatic increase in color quality can be achieved by the addition of a small percentage of one of these materials into a mixture. Shimizu recommends the addition of 2-3% organic chlorine donor into compositions that don't contain a metallic fuel, and the addition of 10 - 15% chlorine donor into the high temperature mixtures containing metallic fuels.
Chlorine Donors for Pyrotechnic Mixtures
Shimizu attributes much of the value of these chlorine donors in magnesium-containing compositions to the production in the flame of hydrogen chloride, which reacts with magnesium oxide to form volatile MgCl molecules. The incandescent emission from MgO particles is thereby reduced, and color quality improves significantly.
