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A solution of bromate barium, prepared in the previous experience, cool to room temperature; the precipitate should fall out of white crystals of salt. When they had enough, RUB them with a glass rod. Maybe not the first time (requires skill), but when crushed displayed flashes of light.

Why - because the chemical processes don't go, and crystallization ended too?

Indeed, the reason here is different - friction. And this phenomenon is triboluminescence (in Greek TRIBOS - friction). There are substances, which are very sensitive to friction and begin to glow in the dark not only when grinding, but even when shaken. However, these substances are not the most common, but maybe they are in school chemistry or in chemical circle. Here are two of them: the zinc sulfide ZnS with the addition of 0.02% manganese sulfide MnS; cadmium sulfide CdS. However, among the substances that emit light by friction, there is surprisingly common. For example, sucrose.

In a large porcelain mortar and sprinkle on the bottom slightly refined (i.e., cleared) sugar. Log in to the dark room and probuditi in it for a few minutes. When your eyes adjust to the darkness, slowly at first, then gradually speeding up the tempo, RUB in circular motions sugar porcelain pestle. Soon will appear bluish sparks, which will merge into a glowing ring. If you do not speed up the rate of grinding, sparks will flare up under the pestle here and there.

Simplified experience: strong hold in my hand a piece of lump sugar and Cerknica them a few times on rough surfaces - porcelain, ceramic. Do this, as before, in the dark. If the eye is accustomed to it, you will see glowing stripes that fade, barely flushed.

The radiation at triboluminescence due to electrical discharges occurring in the destruction of the crystals. That's why it stops when the sugar crystals in a mortar already frayed. Sugar powder by friction is not lit.

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986


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