Why is helium so commonly used in welding and for growing high-purity silicon crystals?

Helium is commonly used in welding and for growing high-purity silicon crystals because of the inert gaseous properties it possess.

Explanation:

Helium is an inert gas in the periodic table with atomic number 2, possessing 2 free electrons that can involve in reaction. Being an inert gas it shows negligible reactivity towards materials.

It is used in welding mainly because of its ability to transfer high heat and also this gas acts as a perfect shield preventing oxygen and water to weld, thereby helping in the welding of alloys.

Silicon being the 2nd most abundant element and a potential semi conductor, its important to manufacture silicon crystals almost for everything. in silicon era,  ultra high purity helium in lab grade is used in semiconductor processing mainly because of its high thermal conductivity and higher ionization potential since helium absorbs high amount of energy before itself becoming ionised.