Flames color, fuel composition

T. Fish, Green and Other Colored Flame Metal Fuel Compositions Using Parlon , PyrotechnicaVll, 1981. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

Flame color depends on fuel composition. Gas often burns blue, but heavy fuel oil burns yellow. A yellow flame is caused by thermal cracking of the fuel. There is nothing wrong with a yellow flame it is the general shape of the flame which is important. If in doubt as to the right flame shape for a particular furnace, contact the burner manufacturer for details. 

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 (see Chapter 7). 

To use potassium nitrate in colored flame mixtures, it is necessary to include magnesium as a fuel to raise the flame temperature. A source of chlorine is also needed for formation of volatile BaCl (green), or SrCl (red) emitters. The presence of chlorine in the flame also aids by hindering the formation of magnesium oxide and strontium or barium oxide, all of which will hurt the color quality. Shidlovskiy suggests a minimum of 15% chlorine donor in a color composition when magnesinm metal is nsed as a fuel [5]. 

The use of chlorate or perchlorate oxidizers (KCIO 3> KC10 , 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. Table 7.8 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 [11]. 

With good fuels (charcoal or active metals), potassium nitrate will burn well. Its use in colored flame compositions is limited, primarily due to low reaction temperatures. Magnesium may be added to these mixtures to raise the temperature (and hence the light intensity), but the color value is diminished by "black body" emission from solid MgO. 

Colored smoke mixtures also contain either sulfur or a carbohydrate as the fuel, and a volatile organic dye that sublimes from the reaction mixture to produce the colored smoke. These compositions contain a large excess of potential fuel, and their explosive properties are greatly diminished as a result. Smoke mixtures react with low flame temperatures (500°C or less)... 

---