Zinc (Zn) is a silvery-white metal used extensively in everything from batteries and sunscreens to preventing rust on steel. It is the fourth most common metal in industrial production, valued for its ability to resist corrosion and form useful alloys like brass. Understanding how zinc behaves under heat is fundamental to its applications and safe handling. The boiling point is the specific temperature at which zinc changes from a liquid into a gas, making it a metric for metallurgists and engineers.
The Specific Temperature of Vaporization
The boiling point of a metal is the temperature at which its liquid form transitions entirely into a gaseous vapor at standard atmospheric pressure. For pure zinc, this temperature is precisely 907 degrees Celsius (907 °C). This is equivalent to 1,665 degrees Fahrenheit (1,665 °F). This temperature is significantly higher than the melting point of the metal, which occurs at 420 °C. The difference between the melting point and the boiling point represents the temperature range where zinc exists as a liquid metal.
Context: Why Zinc Boils So Easily
Compared to many other structural metals, zinc’s boiling point of 907 °C is relatively low. This characteristic relates directly to the structure of the zinc atom and the nature of its metallic bonds. Zinc’s atomic structure, with a full d-shell, results in weaker metallic bonding compared to the strong bonds found in typical transition metals. This weaker attraction requires less energy to break the bonds and allow the atoms to escape as a vapor.
For perspective, aluminum boils at approximately 2,470 °C, copper at about 2,562 °C, and iron requires temperatures of around 2,870 °C to vaporize. Zinc’s significantly lower boiling point made it historically challenging to smelt, as the metal would vaporize and be lost in the flue gas of early furnaces. This property makes zinc one of the most volatile of the commercially produced metals, a trait that must be carefully managed in high-temperature applications.
Industrial Uses Requiring High Heat
The relatively low boiling point of zinc is leveraged in several key industrial processes. One application is the purification of zinc metal through distillation. By heating impure zinc past its boiling point, the zinc turns into a vapor, leaving behind impurities like iron and lead, which have much higher boiling points. The zinc vapor is then collected and condensed back into a highly pure liquid metal.
This volatility is also central to creating zinc oxide, a compound used in sunscreens, paints, and rubber manufacturing. In the indirect (French) process for making zinc oxide, pure zinc metal is heated to temperatures exceeding its boiling point, often between 1,000 °C and 1,100 °C. This intense heat generates a stream of zinc vapor, which is immediately reacted with oxygen in the air. The rapid oxidation of the vapor produces extremely fine particles of white zinc oxide powder.
The temperature is also an important factor in the widely used process of galvanizing, where steel is coated with molten zinc to prevent rust. Although the hot-dip galvanizing bath is maintained well below the boiling point, the metal still produces zinc fumes, or zinc oxide smoke, at high rates. This fume generation must be managed for environmental and safety reasons, as it is a direct consequence of the metal’s tendency to vaporize and react with oxygen at elevated temperatures.