Uses of Argon Gas

The short answer

Argon is used mainly as a shielding gas in welding — the standard for TIG and a major component of MIG mixtures — along with root purging of stainless pipework, controlled-atmosphere heat treatment, degassing and blanketing molten metal, plasma cutting, carrier and plasma gas for analytical instruments, and as the fill gas in double glazing and specialist lighting.

Unlike nitrogen, which is merely unreactive at ordinary temperatures, argon is a noble gas and will not react even with molten titanium. That is what justifies its higher cost where nitrogen would be cheaper.

Welding: why argon and not nitrogen

A weld pool at 1,500 °C or more will pull nitrogen and oxygen out of the surrounding air and take them into the metal, causing porosity, embrittlement and loss of corrosion resistance. The shielding gas exists to keep air away from the pool until it solidifies.

Nitrogen cannot do this job in most alloys, because at arc temperatures nitrogen is no longer inert — it dissolves into the weld metal and forms nitrides. Argon is inert at any temperature the arc produces. It is also 38% denser than air, so it blankets the pool and stays there rather than drifting off.

Root purging: the application people skip

When stainless steel pipe is welded, the inside of the joint is exposed to air while the outside is shielded. Without an internal argon purge the root of the weld oxidises into a rough grey scale known as sugaring, which destroys corrosion resistance exactly where the pipe carries product.

In food, pharmaceutical and chemical pipework this is not cosmetic — a sugared root is a rejected weld. Purge dams and inflatable purge systems exist solely to make this affordable on large-diameter pipe by limiting the volume that must be filled.

Metals and heat treatment

• ✓Degassing molten aluminium — argon bubbled through the melt strips dissolved hydrogen that would otherwise cause porosity in the casting
• ✓Blanketing molten metal to prevent oxidation losses
• ✓Argon-oxygen decarburisation (AOD) in stainless steelmaking
• ✓Bright annealing, sintering and controlled-atmosphere furnaces where even nitrogen would react
• ✓Plasma cutting and plasma welding as the plasma gas
• ✓Growing silicon and specialty crystals under an inert atmosphere

Analysis, lighting and glazing

Argon is the plasma and carrier gas for ICP-OES and ICP-MS instruments, and a carrier gas in gas chromatography. Analytical work needs ultra-high purity — 99.9995% and above — because the instrument measures at the concentration the impurities occupy.

In double glazing, argon fills the cavity between panes: it conducts heat about a third less readily than air, measurably improving the insulation value of the unit. Incandescent and specialist lamps are argon-filled to stop the filament oxidising.

The safety point worth repeating

Argon is non-toxic and non-flammable, and it is 38% denser than air. It sinks and pools in pits, trenches, tank bottoms and any low-lying enclosed space, silently displacing the oxygen there.

Welders are the group most exposed, because good shielding means a continuous argon flow into whatever space they are working in. Welding inside a tank, vessel or trench with argon shielding is a confined-space operation and must be treated as one — ventilated, monitored and attended.