Tungsten (W) is a transition element known for its exceptional density and the highest melting point among all metals. This grayish-white metal is widely used in applications requiring high strength and resistance to extreme conditions. Its interaction with water—specifically, whether it corrodes or “gets wet” chemically—is determined by its chemical structure and the protective layer it naturally forms. This article explains tungsten’s stability when exposed to moisture and the specific, extreme conditions under which this stability breaks down.
Tungsten’s Chemical Stability at Standard Temperatures
Tungsten is characterized by its chemical inertness, meaning it is largely unreactive under normal environmental conditions. At standard room temperature, solid tungsten metal exhibits no significant reaction when immersed in liquid water or exposed to moisture in the air.
The primary reason for this resistance is the immediate formation of a thin, passive layer of tungsten oxide (\(\text{WO}_3\)) on the metal’s surface. Like aluminum, tungsten oxidizes instantly upon contact with oxygen in the air, creating a barrier that is chemically stable and non-porous. This oxide layer acts as a shield, isolating the underlying bulk tungsten metal from water molecules and preventing further chemical exchange or oxidation.
This protective mechanism explains why tungsten does not “rust” in the way iron does, which forms a flaky, non-protective layer. The tungsten oxide layer is highly adherent and insoluble, meaning water cannot penetrate it to react with the metal underneath. Consequently, tungsten maintains its structural integrity even after prolonged exposure to moisture.
Common Applications Exposed to Moisture
Tungsten’s use in items routinely exposed to water confirms its chemical stability. For instance, tungsten and its compounds are utilized in high-density weights for fishing and racing applications, where they are constantly submerged or exposed to spray. These components require no special corrosion-preventing coatings or drying processes after water contact.
Tungsten is alloyed with carbon to create tungsten carbide, an extremely hard material used to manufacture jewelry, such as wedding rings. These rings are worn daily and subjected to frequent washing without showing signs of degradation or tarnishing from moisture. Furthermore, tungsten is incorporated into specific grades of stainless steel used in offshore environments, demonstrating its contribution to corrosion resistance in chloride-rich seawater.
In specialized fields, like medicine and high-performance electronics, tungsten is used for electrodes and shielding materials. Its robust nature means that equipment containing tungsten components can be safely sterilized or operate in environments where condensation or liquid contact is possible. These applications rely on the metal’s stability to maintain performance.
Reactions Under Extreme Heat and Steam
While tungsten is inert at ambient temperatures, its stability breaks down when exposed to water vapor at extremely high temperatures. The metal reacts with steam when heated to a threshold temperature, typically starting around \(700^\circ\text{C}\) and becoming significant above \(800^\circ\text{C}\). This phenomenon is confined to industrial or scientific settings.
In this high-energy environment, the steam acts as a strong oxidizing agent, overcoming the protective passive oxide layer. The reaction produces tungsten oxide and releases hydrogen gas. This process is known as oxidative vaporization because the resulting tungsten oxide is volatile at these temperatures.
The continuous vaporization of the oxide layer exposes fresh tungsten metal to the steam, allowing the reaction to sustain itself and cause material loss. This high-temperature interaction results in the formation of white smoke, aerosolized tungsten oxide condensing as it moves away from the hot surface. This chemical behavior necessitates the use of inert gas environments for tungsten filaments in incandescent light bulbs, preventing them from reacting with oxygen at operating temperatures of over \(2,000^\circ\text{C}\).