fire
CuCl. Flame emission from this molecular species yields a series Polyvinyl chloride
22
of bands in the region from 428-452 nanometers, with additional Magnesium
19
peaks between 476-488 nanometers [1, 11].
In an oxygen-rich flame, and at temperatures above 12000C, CuCl is unstable and will react to form CuO and CuOH. CuOH
emits in the 525-555 nanometer region (green!) and substantial emission may overpower any blue effect that is also present. Copper oxide, CuO, emits a series of bands in the red region, and among the materials used in blue flame mixtures. Potassium per-this reddish emission is often seen at the top of blue flames, where chlorate and ammonium perchlorate are the oxidizers found in most sufficient oxygen from the atmosphere is present to convert CuCI blue compositions. Potassium chlorate would be an ideal choice to Cu0 [111.
because of its ability to sustain reaction at low temperatures (reParis green - copper acetoarsenite, (CuO) 3 As2 O3 Cu(C2H302) -
member, CuCl is unstable above 1200°C), but copper chlorate is was widely used in blue flame mixtures until a few years ago. It an extremely reactive material. The chance of it forming should produces a good blue flame, but it has all but vanished from com-a blue mixture get wet precludes the commercial use of KC1O
mercial formulas because of the health hazards associated with its 3 .
Several formulas for blue flame compositions are given in Table use. (It contains arsenic! )
7.11. An extensive review of blue and purple flames, concentra-Copper oxide (CuO), basic copper carbonate - CuCO 3 • C u(OH) 2 , ting on potassium perchlorate mixtures, has been published by and copper sulfate - available commercially as CuS0,, • 5H
Shimizu [131.
20 - are
162
Chemistry o f Pyrotechnics
'
Color and Light Production
163
TABLE 7.12 Purple Flame Compositions
Composition
% by weight
Commenta
I. Potassium perchlorate, KC10,, 70
"Excellent"
Polyvinyl chloride
10
Red gum
5
Copper oxide, CuO
6
Strontium carbonate, SrCO 3
9
Rice starch
5 (additional %)
II. Potassium perchlorate, KC10,,
70
"Excellent"
Polyvinyl chloride
10
Red gum
5
Copper powder, Cu
6
Strontium carbonate, SrCO 3
9
Rice starch
5 (additional %)
a Reference 13.
Purple Flame Compositions
A purple flame, a relative newcomer to pyrotechnics, can be achieved by the correct balance of red and blue emitters. The additive blending of these two colors produces a perception of purple by an observer. Several comprehensive review articles on purple flames have recently been published [131.
The compositions given in Table 7.12 received an "excellent"
rating in the review article written by Shimizu [131.
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 Figure 7.2.
164
Chemistry of Pyrotechnics
Color and Light Production
165
TABLE 7.13 Yellow Flame Compositions
% by
Refer-
Composition
weight
Use
ence
I.
Potassium perchlorate, KC104
70
Yellow fire-
6
Sodium oxalate, Na 2C 204
14
works star
Red gum
6
Shellac
6
Dextrine
4
II.
Potassium perchlorate, KC10 4
75
Yellow fire
6
Cryolite, Na 3A1F6
10
Red gum
15
III. Sodium nitrate, NaN03
56
Yellow fire
5
Magnesium
17
(Russian)
Polyvinyl chloride
27
IV. Potassium nitrate, KNO 3
37
Yellow fire
5
Sodium oxalate, Na 2C 20y
30
(Russian)
Magnesium
30
Resin
3
FIG. 7.2 Emission spectrum of a yellow flare. The primary emit-V.
Barium nitrate, Ba(N0 3) 2
17
Yellow flare
8
ting species is atomic sodium, with intensity centered near 589 nm.
Strontium nitrate, Sr(N0 3) 2
16
A background continuum of "blackbody" emission and bands from Potassium perchlorate, KC104
17
vaporized BaO, BaOH, and BaCl are also observed. The compo-Sodium oxalate, Na 2C 20,,
17
sition of the flare was potassium perchlorate (21.0%), barium ni-Hexachlorobenzene, C 6 C16
12
trate (20.0%), magnesium (30.3%), sodium oxalate (19.8%), as-Magnesium
18
phaltum (3.9%), and binder (5.0%). This is apparently a former Linseed oil
3
green flare formula to which sodium oxalate was added to obtain a yellow flame. The intense atomic sodium emission at 589 nm overwhelms the green bands from barium-containing species!
Source: H. A. Webster III, "Visible Spectra of Standard Navy Colored Flares," Proceedings, Explosives and Pyrotechnics Appli-before, during, and after the manufacturing process. Sodium cations Section, American Defense Preparedness Association, Fort oxalate (Na