as we know there are several types of inert gases in nature. however argon helium and nitrogen (not classified as inert gas) have been chosen for this purpose.
what is so special about these gases to be used in such operation?
It is not clear to me what do you mean by "shielding gases", but...
1) Nitrogen (N2) is usually inert in many cases, and it is cheaper than argon and helium.
2) Argon is cheaper than helium.
Hence, nitrogen is the gas of choice for many purposes when an inert atmosphere is needed.
These are employed for the reactions or under various other conditions in order to produce an Oxygen free atmosphere & as these gases are completely inert to most of such reactions / Conditions. Off course , as Carlos said, the nitrogen gas is the most economical for such purposes. The generators of all these gases are available commercially.
Shielding gas also plays an important role in determining weld penetration profiles, helping maintain arc stability and achieving the desired mechanical properties in the finished weld. Shielding gas can also affect the transfer of the filler metal from the arc to the weld joint, which in turns contributes to the efficiency of the welding process and the quality of the weld. Other important factors that shielding gas help determine include the weld bead appearance, and weld toughness and strength.
These inert gases are used in gas tungsten arc welding, and also in gas metal arc welding for the welding of non-ferrous metals. Pure argon and helium are used only for some nonferrous metals. Semi-inert shielding gases, or active shield gases, include carbon dioxide, oxygen, nitrogen, and hydrogen.
Helium: Helium is generally used when welding non-ferrous metals. It is also used in a tri-mix formula of argon and CO2 for welding stainless steels.
Argon: When welding aluminum, magnesium or titanium, it is common to use 100 percent argon as a shielding gas due to its stable arc features.
The primary gases used for GTAW are argon, helium, hydrogen, and sometimes nitrogen. The composition and purity of the gas or gas mixture should be tailored to meet your process, material, and application requirements. Shielding gases are used in either pure form or in blends of varying components. Therefore, selecting a gas or gas mixture can become quite complex because of the many combinations available
One property common to all , is their inertness , that make them fit ....
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