Part III. On Backgrounds of Color Flame Spectra

ABSTRACT: Blank runs were made with nominal colorproducing compositions to investigate the lines, bands or continuous spectra that appear as background and interfere with the desired spectra of red, yellow, green, etc. These sample compositions consisted of solid materials such as oxidizers (ammonium perchlorate, potassium chlorate, potassium perchlorate, potassium nitrate, etc.), low temperature fuels (shellac, rosin, pine root pitch, etc.), and magnesium powder for the high temperature fuel.

For low flame temperatures sodium D (Na-D) lines (5890 and 5896 Å, caused by impurities contained mainly in the oxidizers), continuous spectra (caused by carbon particles and potassium atoms) and potassium (K) lines (5802, 5783, 5832, 5813; 5340, 5324, 5360, 5343; 5090, 5084, 5113, 5080; 4044, 4048 Å) are observed. For high flame temperatures Na-D lines are also observed, and in addition to the above, MgO bands and continuous spectra (the latter are caused by solid metal oxide particles and K atoms) are found.

The main interfering spectra are the Na-D lines and continuous spectra. Purification of ingredients is very important to remove Na-D lines and to obtain fine colored flames. For high flame temperatures, the addition of chlorine- containing compounds such as polyvinyl chloride, ammonium chloride, etc. to a composition is effective in decreasing the intensity of the continuous spectra, and it is assumed that the metal oxide of the solid phase is converted into the metal chloride of the vapor phase in the presence of chlorine or hydrogen chloride in the flame, but this should be ascertained by further experiments of higher accuracy. The addition of shellac is also effective in weakening the intensity of the continuous spectra and decreasing the black body temperature of the flame.

The permeability coefficients and black body temperature of flames of basic compositions are measured for reference .

Ref: Selected Pyrotechnic Publication of Dr. Takeo Shimizu, Part 3,  pp 39-56

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