Question

The ignition mixture in “alumina thermite” process consists of a mixture of:
(A) Magnesium powder and $Ba{O_2}$ or $KCl{O_3}$
(B) Magnesium powder, aluminium and $Ba{O_2}/KCl{O_3}$
(C) Magnesium and aluminium powder
(D) Magnesium and aluminium oxides

Answer 1

Hint: The alumina thermite process uses a metal powder and a metal oxide, heating them to ignition where they undergo a highly exothermic, oxidation-reduction reaction.

Complete answer:
-Aluminothermic reactions are exothermic reactions which use aluminium as their reducing agent at high temperatures. These reactions are used industrially for production of alloys of iron.
-The thermite reaction was first discovered by Hans Goldschmidt in 1893.
-Any pyrotechnic composition of a metal powder and metal oxide is known as thermite. If this thermite mixture is heated to ignition it undergoes an exothermic, oxidation-reduction reaction. Thermites have diverse compositions of fuels and oxidizers.
Fuels can be magnesium, aluminium, titanium, zinc, boron or silicon. But mostly aluminium is used due to its high boiling point and low price cost. Oxidisers can be boron (lll) oxide, silicon (lV) oxide, iron (lll, ll) oxide, copper (ll) oxide, bismuth (lll) oxide, etc.
-The alumina thermite process will usually contain oxides of chromium and manganese which have a high melting point and so cannot be reduced by carbon. But aluminium can reduce them. The ignition mixture will contain magnesium powder along with $Ba{O_2}$ or $KCl{O_3}$. The involved reactions can be written as:
                                 $C{r_2}{O_3} + 2Al \to A{l_2}{O_3} + 2Cr + heat(q)$
                              $3M{n_3}{O_4} + 8Al \to 4A{l_2}{O_3} + 9Mn + heat(q)$
-We know that thermite is basically a correct mixture of metallic fuels which when combined, can be easily ignited. Since metals burn without releasing cooling gases, they have the potential to burn at extremely high temperatures. Magnesium being reactive can very easily reach temperatures high enough to undergo thermite ignition. Magnesium is also easily available.

So, the correct option is: (A) Magnesium powder and $Ba{O_2}$ or $KCl{O_3}$.

Note: The extreme high temperatures produced and the difficulty in smothering the reaction once ignited makes thermite use highly hazardous. If thermite is mixed with water or water is poured into it. Steam explosions (hot fragments sprayed in all directions) can occur. In some cases it can also explode violently.