Reaction speed
Thermite welding of railways rails

The speed of reaction is difficult for the operator to assess, as the retraction of the flame, the sign of the end of the reaction, is not easy to appreciate.

On the other hand, the start of casting at the bottom of the crucible is perfectly visible, and the ignition-casting time is clearly defined and measured.

The experiment involved equipping a crucible with an accelerometer and recording its movements due to the internal agitation of the oxide-aluminium reaction (figure 4 , solid line curve). The graph recorded on the computer shows a hump bristling with oscillations, and the end of the reaction is well defined.