Minerals and Metals in Ancient India v1.c26.s6.t2.4

v1.c26.s6.t2.4

Zinc melts at 432°C and under one atmospheric pressure boils at 913°C, which is below the temperature required to reduce the oxide to metal in the presence of carbon. Though the initiation of reduction of zinc oxide to zinc by carbon begins at 950°C, the minimum temperature necessary for successful extraction of the metal in a retort is of the order of 1150-1200°C. The reaction ZnO + C → Zn + CO Δ H = - 57 kcal. is highly endothermic. Therefore, before the advent of modern high-pressure reduction technology or electrolytic extraction processes, zinc had to be produced inevitably as vapour around 1200°C and then condensed as liquid much below 913°C.