The steel sample is ground by a high-speed rotating grinding wheel, ground into scrapy particles, and is projected forward in a tangential direction along the rotation of the grinding wheel. Steel particles with a certain temperature are violently oxidized by oxygen in the air, and the degree of stagnation increases sharply. A solid FeO film (2 Fe + O2-->2FeO) is formed on the surface of the steel particles. Since the steel particles contain carbon, at high temperatures, carbon is easily combined with oxygen to form carbon monoxide (FeO + C -> Fe + Co ), and iron is reduced. The reduced iron is then oxidized again by air and then restored again. Repeated repetitions of this reaction accumulate a considerable amount of CO gas inside. Initially, the solid FeO film constrains the escape of the Co gas. When the expansion force is greater than the film tension, the CO breaks through the constraint of the surface iron oxide film, causing the steel particles to pulverize and escape. The trajectory emitted by the high-temperature steel particles beside the grinding wheel is a bright line (streamline) and a bright flower (popped flower) felt by the human eye.
The color of the streamline and the burst (the shade of the color) characterizes the temperature of the pellet when it is emitted. The higher the temperature, the brighter the color of the fire bouquet (yellow white, bright white), and vice versa, the color of the fire bouquet is dark (dark red). However, the heat gain of steel particles is not only related to the formation of carbon monoxide, but also affected by many other factors. Therefore, the color of the fire bouquet is not only related to the carbon content, but also the alloying element content of steel and the oxidation performance of steel particles. It is related to factors such as the degree of oxidation.