Ionization potential:
IP is the energy, expressed in electron volts, necessary to remove an electron from a gas atom, making it an ion or an electrically charged gas atom.
IP decreases as the molecular weight of gas increases.
IP is measurement of electrical conductivity of the arc shielding gas.
Eg. argon has 18 electrons while helium has 2 electrons.
as 2 electrons are near to nucleus, attractive forces are more. Thus, it will take 15.7 electron volts to remove the first electron in Argon compared to 24.5 electron volts in helium. Thus, it creates free electrons necessary to support current flow forming plasma.
as heat in the arc is roughly measured by the product of current and voltage,
– the use of helium yields a much higher available heat than does argon.
Thus, helium is reflected as ‘hotter’ gas.
ARC STARTING & ARC STABILITY are also largely dependent on the IP of shielding gas.
Gases with low IP, such as argon, give up electrons more easily, helping to initiate and maintain the arc in a stable operating mode.
Keep reading, Happy welding…
Thank you,
KP Bhatt
weldknowledge 
In last para of this blog , dose we say that argon’s molecular weight is higher compared to helium’s molecular weight hence the arc stability is more for argon than helium?
LikeLike
IP decreases as the molecular weight of the shielding gas increases.. So yes arc starting will be easier and stability will be more for argon than helium.
LikeLike