The most commonly used gas for industrial inerting purposes is molecular nitrogen (\(\text{N}_2\)). This gas is utilized across countless applications to prevent unwanted chemical reactions, particularly those involving oxygen or moisture. While nitrogen serves as the bulk, cost-effective agent, the most common noble gas used for inerting is argon (\(\text{Ar}\)). This distinction is important because the absolute chemical stability of noble gases like argon is sometimes required for specialized, high-performance environments where nitrogen is unsuitable.
Defining Inert Gases and Inerting
An inert gas is chemically non-reactive under typical conditions, meaning it does not readily combine with other substances to form new chemical compounds. This stability stems from the gas’s electron configuration, which makes it unwilling to gain, lose, or share electrons with other atoms.
The practical application of using these non-reactive gases is known as inerting, which involves replacing a reactive atmosphere, primarily air, with the inert gas. The purpose of inerting is to create an oxygen-free or moisture-free environment to prevent undesirable events like combustion, material degradation, or contamination. This process is frequently referred to as “blanketing” or “purging,” where the inert gas displaces the reactive air within a container or over a surface.
Nitrogen: The Most Common Industrial Inerting Agent
Nitrogen’s dominance as the primary industrial inerting agent is a direct result of its overwhelming abundance and low cost. It comprises approximately 78% of the Earth’s atmosphere, making it easily and cheaply obtainable through large-scale cryogenic distillation of air.
Although not a noble gas, molecular nitrogen achieves a high degree of inertness due to the exceptionally strong triple covalent bond between its two nitrogen atoms (\(\text{N} \equiv \text{N}\)). Breaking this triple bond requires significant energy input, meaning nitrogen remains highly non-reactive at standard temperatures and pressures. This characteristic makes it the workhorse for bulk applications like tank blanketing, where it forms a protective layer over liquids to prevent contact with atmospheric oxygen.
Nitrogen’s cost-effectiveness and general stability make it the optimal choice for processes requiring large volumes of inert gas, such as purging pipelines or suppressing fire hazards in storage vessels. Its non-reactive nature at ambient conditions effectively prevents oxidation, corrosion, and the formation of explosive mixtures. The ability to generate nitrogen on-site from ambient air further reduces logistical costs, cementing its role as the most widely used inerting agent globally.
Specialized Uses of Noble Gases
While nitrogen is the most common inert gas overall, argon is the most frequently used noble gas in industrial inerting applications. Argon is less abundant than nitrogen, making up about 0.93% of the atmosphere, which contributes to its higher production cost. Despite this, its superior chemical inertness is necessary for specific high-performance environments where nitrogen is inadequate.
The key difference lies in thermal stability; at extremely high temperatures, such as those found in arc welding, the strong triple bond in the nitrogen molecule can break apart. This dissociation allows the individual nitrogen atoms to react with surrounding materials, potentially forming undesired compounds like metal nitrides that compromise integrity. As a noble gas, argon has a complete, stable electron shell and cannot break down or react even under these intense thermal conditions.
This absolute chemical stability makes argon the standard shielding gas for high-temperature metal fabrication processes, including Gas Tungsten Arc Welding (GTAW) and Gas Metal Arc Welding (GMAW). Argon is also employed in specialized lighting, such as incandescent bulbs, where it prevents the hot metal filament from evaporating or reacting with residual gases.
Large-Scale Commercial Applications of Inerting
In the food and beverage industry, nitrogen is extensively used in Modified Atmosphere Packaging (MAP) to extend the shelf life of perishable goods. By injecting nitrogen into packaging, oxygen is displaced, which prevents the oxidative degradation that causes rancidity and spoilage.
Chemical and petrochemical industries rely on inerting for safety and process control, frequently utilizing nitrogen to purge vessels and pipelines. This displacement of oxygen prevents the formation of explosive vapor-air mixtures before maintenance or during the transfer of flammable liquids. This safety protocol ensures that the oxygen concentration remains below the Limiting Oxygen Concentration (LOC) required for combustion.
In the production of semiconductors and electronics, both nitrogen and argon are essential for maintaining ultra-clean manufacturing environments. These processes require atmospheres free of oxygen, moisture, and other contaminants that could interfere with the delicate fabrication of microchips. Inerting protects sensitive components and high-purity materials, ensuring the required level of quality and performance in advanced electronic devices.