Nitrogen: The Universal Gas for Industry, Protection, and Precision Measurements

Introduction

Nitrogen (N₂) is a gas without which modern industry is unimaginable. It does not burn, reacts with almost nothing under normal conditions, and makes up nearly 80% of the air we breathe. It is precisely this chemical inertness, multiplied by its availability, that has made it an indispensable tool in dozens of industries: from petrochemicals and metallurgy to pharmaceuticals and analytical instrumentation.

In this article, I have compiled key information about nitrogen as an industrial gas: its physical and chemical properties, production methods, main application areas, and its special role in gas analytical measurements. I have previously written in detail about calibration and verification procedures for gas analyzers — here we will touch on this topic only to the extent necessary to understand the functions of nitrogen itself.

Physical Properties: The Foundation of Practical Application

Nitrogen is a colorless, tasteless, and odorless gas. Its N₂ molecule is extremely strong due to the triple bond between atoms (dissociation energy of 941 kJ/mol), which explains its chemical passivity.

Parameter	Value
Density (at 0 °C and 0.1 MPa)	1.25 kg/m³
Relative density (air = 1)	0.97 (slightly lighter than air)
Boiling point	–195.8 °C
Melting point	–210.0 °C
Solubility in water (at 20 °C)	1.55 mL/100 mL

Three practically important consequences follow from these figures. First, the density of nitrogen is close to that of air — it does not rush upwards like hydrogen, nor does it accumulate at floor level like propane. In the event of a leak, it distributes relatively evenly throughout the volume of a room, which simplifies ventilation design. Second, liquid nitrogen at –196 °C is a powerful and safe refrigerant (latent heat of vaporization ~199 kJ/kg), used everywhere — from cryosurgery to freezing food and cooling infrared detectors. Third, nitrogen is a good thermal insulator, which is why it is used to fill double-glazed windows.

Chemical Properties: Inertness as a Superpower

The chemical "calling card" of nitrogen is its reluctance to enter into reactions under ordinary conditions. It is precisely this quality that determines 90% of its industrial use.

At room temperature, N₂ reacts only with lithium. Nitrogen begins to interact noticeably with oxygen only at temperatures above 1200–1500 °C, forming nitrogen oxides (NOₓ) — this reaction is the main source of "thermal NOₓ" in boiler furnaces and engines.

At high temperatures and pressure in the presence of a catalyst, nitrogen reacts with hydrogen to form ammonia (NH₃) — this is the Haber process, one of the most important industrial syntheses. It can also form nitrides with certain metals, which is used for surface hardening of steel (nitriding).

For industrial safety, it is critically important that nitrogen does not support combustion. This makes it an effective means of fire suppression and the phlegmatization of combustible mixtures.

How Nitrogen Is Produced

Nitrogen is obtained from atmospheric air. The choice of method depends on the required purity and volumes.

Cryogenic rectification. The main method for large-scale production. Air is compressed, cleaned of impurities, and cooled to ultra-low temperatures. Due to the difference in boiling points (nitrogen: –196 °C, oxygen: –183 °C), the components are separated in a rectification column. This method allows obtaining nitrogen with a purity of up to 99.9999% (grade 6.0).

Membrane separation. Air is forced under pressure through polymer membranes that allow oxygen to pass through faster than nitrogen. The output is gas with a purity of up to 99.5%, suitable for fire suppression and pipeline purging, but not for analytics.

Pressure Swing Adsorption (PSA). Air is forced under pressure through carbon molecular sieves that selectively absorb oxygen. When the pressure is released, the adsorbent regenerates. Product purity is up to 99.999%. Generators based on PSA and membrane technology are increasingly being used by enterprises for autonomous nitrogen supply without purchasing cylinders.

Where Nitrogen Is Used

Nitrogen is one of the most in-demand technical gases. Let's look at the key industries.

Chemicals and Petrochemicals. The main direction is the production of ammonia for mineral fertilizers (about 80% of all ammonia produced). In the oil and gas industry, nitrogen is used to purge and pressure-test pipelines, create inert blankets in tanks with flammable liquids, and maintain reservoir pressure.

Metallurgy. Protective atmospheres for heat treatment, annealing, sintering, and welding. Nitriding — the diffusion saturation of steel surfaces to increase hardness and wear resistance.

Electronics. Ultra-high purity nitrogen creates an inert environment in the production of semiconductors and printed circuit boards, preventing the oxidation of sensitive materials.

Food Industry. Nitrogen is a safe food additive (E941). It is used to displace oxygen from packaging (meat, coffee, snacks), extending shelf life. Liquid nitrogen is used for quick freezing, while gaseous nitrogen protects wines and oils from contact with air.

Medicine. Liquid nitrogen is a tool of cryosurgery. In pharmaceuticals, gaseous nitrogen creates a sterile, oxygen-free environment for drug synthesis.

Energy and Construction. Purging turbines, inert environment in transformers, metal cutting and welding, filling double-glazed windows to improve thermal insulation.

Nitrogen in Climatic and Environmental Testing

Liquid and gaseous nitrogen are widely used in testing technology.

Cold resistance testing of materials. Many polymers and composites become brittle at low temperatures. Liquid nitrogen allows for rapidly cooling a sample and checking its behavior under conditions simulating the Far North or high altitudes.

Thermal cycling. Repeated alternation of heating and cooling using liquid nitrogen reveals hidden defects associated with the difference in the coefficients of thermal expansion of materials.

Electronics testing. Testing thermal imagers, semiconductor matrices, and infrared detectors often requires temperatures of 70–80 K, which liquid nitrogen provides.

Environmental chambers. Dry nitrogen allows testing at relative humidity close to zero, which is important for assessing the corrosion resistance of materials and coatings.

The Role of Nitrogen in Gas Analysis

Nitrogen occupies a special place in the field of environmental monitoring and gas analytical measurements. I have previously written in detail about procedures for calibration, verification, and validation of gas analyzers, as well as the proper selection of calibration gas mixtures. Here, I will focus on the properties of nitrogen itself that make it indispensable in this area.

Ultra-high purity nitrogen (grade 5.0 and above) serves as a zero gas — the standard against which the "zero" of an instrument is set. Purity requirements in Russian practice are regulated by GOST 9293-74 (ISO 2435-73) . For metrological purposes, gaseous nitrogen of special purity, first grade (at least 99.999% N₂, oxygen — no more than 0.0005% vol.), is required, which corresponds to the international Nitrogen 5.0 grade. For the most demanding applications (accredited laboratories, FID detectors), grade 6.0 (99.9999%) is recommended.

Why nitrogen?

• It contains no measurable impurities (CO, CO₂, NOₓ, SO₂, hydrocarbons) and is an ideal "blank page" for zero calibration.

• N₂ is a homonuclear molecule that does not absorb infrared radiation. It does not create cross-sensitivity with any component measured by NDIR and FTIR analyzers.

• The vast majority of calibration gas mixtures are prepared using nitrogen as the balance gas, making it doubly indispensable: for both zero setting and span calibration.

It is fundamentally important to distinguish between zero nitrogen (ultra-high purity N₂ without measurable impurities or oxygen) and zero air (purified atmospheric air with ~21% O₂). The choice between them depends on the type of analyzer. For most optical instruments (NDIR, UV, FTIR, TDLAS), nitrogen is the preferred zero gas. For paramagnetic and zirconia oxygen analyzers, air is used.

Storage and Transportation

The method of storing nitrogen depends on consumption volumes and required purity.

Cylinder nitrogen. Steel cylinders at a pressure of 150–200 bar (6.2–10 m³ of gas). The primary supply method for laboratories and small production facilities. According to Russian standards, cylinders are painted black with a brown stripe and the yellow inscription "АЗОТ" (NITROGEN).

Liquid nitrogen. Stored in Dewar vessels with vacuum insulation. 1 liter of liquid yields about 700 liters of gas upon evaporation. Convenient for consumers who need large volumes without high purity requirements.

Nitrogen generators (PSA, membrane). Economically viable for large consumers with a constant demand for gas. They eliminate logistics and cylinder rental costs but require initial capital investment and regular service.

Conclusion

Nitrogen is a rare example of a substance whose natural properties have perfectly matched the demands of numerous industries. Its inertness makes it an indispensable shielding gas in metallurgy and electronics. Its low boiling point opens up the possibilities of cryogenic technology and medicine. Its environmental neutrality allows unrestricted use in the food industry. And its high purity and absence of interfering impurities make it the benchmark zero gas in analytical instrumentation.

Understanding these properties, knowing the purity requirements, and following the rules for the safe handling of nitrogen is a mandatory minimum for any specialist dealing with industrial equipment or gas analytical instruments. Without a high-quality zero gas, all subsequent measurements lose their meaning, and it is nitrogen that serves as the foundation upon which metrological accuracy is built.