Yellow Flame Compositions
Yellow flame color is achieved by atomic emission from sodium. The emission intensity at 589 nanometers increases as the reaction temperature is raised; there is no molecular emitting species here to decompose. Ionization of sodium atoms to sodium ions will occur at very high temperatures, however, so even here there is an upper limit of temperature that must be avoided for maximum color quality. The emission spectrum of a yellow flare is shown in the figure.
Emission spectrum of a yellow flare
Most sodium compounds tend to be quite hygroscopic, and therefore simple compounds such as sodium nitrate (NaNO 3 ), sodium chlorate (NaG10 3 ), and sodium perchlorate (NaC10,,) - combining the oxidizing anion with the metallic emitter - can not be used unless precautions are taken to protect against moisture before, during, and after the manufacturing process. Sodium oxalate (Na2C 204) and cryolite (Na3AlF G ) are low in hygroscopicity and they are therefore the color agents used in most commercial yellow flame mixtures. Some representative yellow compositions are given in the table.
Yellow Flame Compositions