What happens when : manganese dioxide is heated with aluminium powder ? 

When manganese dioxide $(Mn{O}_2)$ is heated with aluminium powder , displacement reaction takes place , and manganese is obtained as the product along with aluminium oxide. It is an exothermic reaction and hence Mn is obtained in molten form. 

$3Mn{O}_2(s)+4Al(s)\to 3Mn(l)+2A{l}_2{O}_3(s)+$ heat