Zinc (Zn), atomic number 30, is a metal that exists as a solid under standard room temperature conditions. Although it has a relatively low melting point of 419.53°C, it maintains a stable, crystalline structure at ambient temperatures. Zinc is the 24th most abundant element in the Earth’s crust, found naturally in various minerals, most commonly sphalerite. Its physical and chemical characteristics at ambient temperatures explain why it is a widely used industrial material.
Defining the Physical State and Appearance
In its pure form, zinc exhibits a bright, lustrous, bluish-white or silvery-gray appearance. Exposure to the atmosphere, however, quickly leads to a duller, more matte finish due to a thin layer of surface oxidation. The density of zinc at 20°C is 7.14 grams per cubic centimeter, which is denser than aluminum but lighter than iron or copper.
The internal atomic arrangement of zinc is characterized by a hexagonal close-packed (HCP) crystal structure. This specific structure, where layers of atoms are stacked in an ABAB pattern, influences many of the metal’s mechanical properties. The relatively high density for a non-ferrous metal means it provides substantial mass for applications like ballast or die-casting.
Mechanical Properties and Workability
At room temperature, pure zinc is considered a brittle material. Applying stress or attempting to bend or roll the metal often results in cracking or fracturing rather than smooth deformation. This brittleness is a consequence of its hexagonal crystal structure, which restricts the number of planes along which the atoms can easily slide past one another. The limited capacity for slip makes the metal resistant to substantial plastic deformation when cold.
This mechanical behavior changes when the metal is warmed slightly above ambient temperature. Zinc becomes more malleable and ductile when heated into the range of 100°C to 150°C. Within this temperature window, the metal can be readily rolled into sheets, drawn into wire, or otherwise shaped without breaking. Above 210°C, the metal becomes brittle again, a characteristic that limits certain high-temperature forming processes. This temperature sensitivity influences how zinc is processed for applications like galvanized steel or zinc-based alloys.
Room Temperature Chemical Interaction
The most significant chemical characteristic of zinc at room temperature is its slow, self-limiting reaction with the surrounding air and moisture. When exposed to the atmosphere, zinc actively oxidizes to form a thin, adherent layer of zinc oxide (ZnO). This layer then further reacts with carbon dioxide and water vapor to create a denser layer of basic zinc carbonate.
This resulting film, often called a patina, is dull gray and serves an important protective function. The dense, insoluble nature of the zinc carbonate layer prevents oxygen and water from reaching the underlying metal. This process effectively halts further corrosion, making zinc a durable material despite its relatively high chemical reactivity. This slow, ambient passivation reaction is the foundation for its widespread use in galvanizing, where a zinc coating protects steel from rust.