The structure of a fire dust particle

When we collect fire dust on the surface of water in a vessel, it is suddenly cooled and we can find the construction of a particle as shown in Fig.48. 

A single particle consists of an active and an inactive substance. 

The active substance is oxidized by the oxygen in the air to keep the particle at a high temperature. When all the active substance in a particle is oxidized, the particle is cooled and no visible light is emitted. The inactive substance adjusts the exposure of the active substance to the air and controls it to avoid a violent reaction. If there is no inactive 

Aluminium fire dust consists of melted aluminium as the active substance and melted AI2O3 as the inactive substance in a particle in the fire dust of black powder(a composition of potassium nitrate, sulphur and charcoal) charcoal is the active material along with the burning product K2SX - K2SO4, K2CO3 etc. is the inactive part. 

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