Question

Aluminium is used in thermite welding.
a.What is thermite?
b.What is the ignition mixture?
c.Write the reaction for the process?

Answer 1

The thermite reaction is also popularly known as the Goldschmidt reaction. This highly exothermic reaction involving oxides of iron creates suitable conditions of temperature that can be utilized for the purpose of welding and disabling artillery by the blocking or damaging of barrels.

Complete answer:
a.The word ‘thermite’ is derived from a generic term that is used to define the reactions that occur between metallic oxides and reducing agents. The metallic oxides that are selected to be included in thermite mixture are the ones with low enthalpy of formations. The metallic reducing agents (that themselves undergo oxidation) must have high enthalpies of formation upon getting oxidized in the thermite reaction. The high enthalpy of reaction that is released in the process is used for carrying out welding of metal surfaces.
Thus, a thermite mixture in thermite welding mainly consists of aluminium that acts as a reducing agent and iron oxide.
b.The ignition mixture that is used in the thermite reaction or the welding process is to provide the initial source of energy for the reaction to start. In order to prepare the ignition mixture a small amount of magnesium powder is mixed with barium peroxide.
c.The chemical reaction that takes place during the thermite process can be written as follows:
$F{e_2}{O_3}(s) + 2Al(s) \to A{l_2}{O_3}(s) + 2Fe(s)$

Note:
The thermite reaction is highly exothermic in nature but requires heat as part of the initiation process. Though magnesium ribbon and barium oxides are used but a better substitute is a reaction between potassium permanganate and glycerin which produces enough heat for the initiation of thermite reaction