The pulverizer in the flour mill needs to process wheat into very fine flour, and the pulverizer needs to consume electric energy and crush the processed materials. Among them, part of the work completed by the pulverizer is converted into energy, which is stored on the surface of material particles after being pulverized. This part of energy is called surface energy in physical chemistry. In addition, for some substances, the greater the degree of crushing, that is, the smaller the particles, the greater the surface area and the greater the surface energy.
For example, the surface of 1 kg of silica can be 0.2 Joule, which is very small. It is only equivalent to the work done by lifting an object with a height of 1 kg feet by 0.02 m feet. However, if it is pressed into tiny dust like flour, its surface energy can reach 2.7? 10 6 Joule, which is equivalent to the work done by lifting an object with the same weight of 2,700 meters feet. The surface energy is increased by10 million times. Because dust has such a high surface energy, it is easy to undergo physical or chemical changes to release its energy compared with bulk materials.
This principle is like that because water at a high place has extra potential energy than water at a low place, it flows to a low place. Therefore, these tiny dust, which seem insignificant at ordinary times, will be fully mixed with the air when encountering suitable conditions. In case of fire, it will have a fierce combustion reaction soon, and in an instant, huge energy will be released, so that a terrible thing, namely flour explosion, also occurred. The earliest recorded dust explosion accident occurred in a flour mill workshop in Italy in 1785. Due to scientific and technological reasons at that time, people did not realize that dust would explode.