Friday, January 7, 2022

Chemistry compounds responsible for firework color

Fireworks are a class of low explosive pyrotechnic devices used for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks, a display of the effects produced by firework devices.

Fireworks take many forms to produce the four primary effects: noise, light, smoke, as well as floating materials.

Colors in fireworks are usually generated by pyrotechnic stars, which produce intense light when ignited. Stars contain five basic types of ingredients.
  • A fuel
  • An oxidizer—a compound that combines with the fuel to produce intense heat
  • Color-producing salts (when the fuel itself is not the colorant)
  • A binder which holds the pellet together.

The color of a compound in a firework will be the same as its color in a flame test. Not all compounds that produce a colored flame are appropriate for coloring fireworks, however. Ideal colorants will produce a pure, intense color when present in moderate concentration.
©BBC

The color of sparks is limited to red/orange, yellow/gold and white/silver. This is explained by light emission from an incandescent solid particle in contrast to the element-specific emission from the vapor phase of a flame.

Light emitted from a solid particle is defined by black-body radiation.

Low boiling metals can form sparks with an intensively colored glowing shell surrounding the basic particle. This is caused by vapor phase combustion of the metal.

Different compounds are associated with different colors:

Red- Strontium or Lithium. mostly in form of SrCO3 (strontium carbonate), Li2CO3 (lithium carbonate) LiCl (lithium chloride)

Orange- Calcium in form of CaCl2 (calcium chloride).

Yellow- Sodium in form of NaNO3 (sodium nitrate).

Green- Barium in form of BaCl2 (barium chloride).

Blue- Copper halides, for example CuCl2 (copper chloride), at low temperature.

Indigo- Caesium in form of CsNO3 (caesium nitrate).

Violet- Pottasium in form of KNO3 (potassium nitrate).

Violet-red- Rubidium in form of RbNO3 (rubidium nitrate).

Gold- Charcoal, iron or lampback

White- Titanium, aluminium, beryllium, or magnesium powders.

The brightest stars, often called Mag Stars, are fueled by aluminium. Magnesium is rarely used in the fireworks industry due to its lack of ability to form a protective oxide layer. Often an alloy of both metals called magnalium is used.

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