Argon 4.6, 4.8 and 5.0 — Shielding Gas Purity Compared
Purity grades, air separation and the question of which grade really pays off
AI generated What 4.6, 4.8 and 5.0 mean, why 100% does not exist, and which purity really pays off for steel, aluminum, titanium and spectrometry.
What 4.6, 4.8 and 5.0 actually mean
Argon is sold as in purity grades. The number counts the nines after the decimal point: 4.6 = 99.996%, 4.8 = 99.998% and 5.0 = 99.999% purity. The rest is foreign matter – mainly , and moisture.
How argon is produced – and why 100% does not exist
Argon comes from fractional cryogenic air separation, the Linde process: air is liquefied and split into its components in a distillation column. The problem: the boiling point of argon (−185.8 °C) sits extremely close to the oxygen boiling point (−182.96 °C). The two gases can only be separated with great effort – so traces of the other always remain. Thermodynamically, 100% purity does not exist.
What residual oxygen does
When stainless steel and , even a tiny amount of residual oxygen reacts with the hot pool. The result: – the colored edges next to the weld everyone knows. On titanium that is already enough to make the part brittle and unusable.
Which purity is really worth it?
• Structural steel, unalloyed steel and ordinary repair welds → 4.6 is the economical standard and fully sufficient for most TIG/MIG jobs.
• TIG welding of → 4.8 gives measurably cleaner, bright seams with fewer oxide inclusions ("pepper").
• , , and spectrometry → 5.0 is mandatory so that ppm-level oxygen and nitrogen traces cannot cause embrittlement.
The practical tip
Do not blindly buy the most expensive gas. Check what your material needs: standard → 4.6, aluminum TIG → 4.8, reactive metals and analytics → 5.0.