thermodynamic process

n the casting of metals the top of the mould can be constructed of substance which evolve heat when they come into contact with a source of heat such as molten metal this evalution of heat by the exothermic materials as they are often called keeps the metal att he top of the casting molten allowing it to feed into the casting and fill the contraction cavity which forms when the metal solidifies one of the reaction tacking place in the exthermic material is the combustion of aluminum powder,the heat change accompanying this reaction is large and negative so that alarge quantity of heat is evolved and the reaction is known as an exothermic reaction hence the name of the materials used in the top of the mould to produce heat.carbon is used to reduce zinc oxide in the commerical extraction of zinc and the reaction can be reperseented, because this reaction absorbs alarge quantity of heat energy the energy is supplied by external heating of the retorts in which the reaction is carrird out with