Why is aluminum powder used to reduce chromium oxide to chromium metal?

Aluminum powder is used in the aluminothermic process to reduce chromium oxide (${\text{Cr}}_2{\text{O}}_3$) to chromium metal because the reaction is highly exothermic and efficient for industrial production. When the mixture of chromium oxide and finely divided aluminum powder is ignited, the combustion generates temperatures exceeding 2,000 °C (3,600 °F). This intense heat allows for a clean separation of the resulting chromium metal from the slag, yielding a product with a purity typically ranging from 97 to 99 percent.1

This method is preferred over carbon reduction for producing pure chromium because carbon reduction often results in the formation of chromium carbides and leaves residual carbon impurities that are difficult to eliminate in commercial practice due to the presence of other minerals in the ore.2