Why Optical Emission Spectrometry Requires Argon Gas?
Optical Emission Spectrometry (Spark OES), an important instrument for analyzing the composition of metal and alloy. Spark OES detected the percentage of elements in the ferrous and non-ferrous alloy, includes it's major metal matrix and other elements. The energy of spark burns the a thin surface of the metal sample, and generate the plasma. The excited atoms and ions in the plasma is detected by a spectrometer in the Spark OES instrument.
Since each elements has it's characteristic peaks in certain wavelength(s) in the spectrum, one can analyze the composition of elements in the alloy, as well as their percentage. By the percentage of elements been detected, the grade of alloy is defined. Some Spark OES even designed PMT illuminate source for specific and increase its accuracy of specific elements.
The Reasons of Using Argon Gas
Below are the reasons of using high purity argon as the shielding :
Argon is an inert gas and won’t react with the elements in the alloy during the sparking period.
Isolate the atmosphere by flushing the surface so that the spectrometer won’t detect the elements in the atmosphere.
Spectrometer can detect the element, which has its characteristic peak below the wavelength 200nm correctly.
In the composition of alloy, the element Argon is not ignored.
Price of Argon is relatively inexpensive, typically, the price of inter gases from cheapest one to most expensive one:
Argon <Helium < Neon < Krypton or Xenon
Common Usage of Three Inert Gases
Helium: ultra-low temperature cooling, vapor deposition, balloons of diving suits filling.
Neon: neon light or mercury lamp filling, plasma research, laser beam (He-Ne)
Argon: metal welding, OES spectrometer.
Why Not Using Inexpensive Nitrogen?
Some alloy are composed of nitrogen and it is needed to be analyzed. And nitrogen can react with metals in under high temperature, and result residues. (e.g. Magnesium Nitride.)
Is It The Same Principle of TIG Welding?
It is different. TIG welding uses argon as a shielding gas to oxidation on the welding point. Spark OES uses argon gas to isolate the elements in the atmosphere, which are also the composition of the alloy.
If the purity of argon does not meet the requirements during use, an argon gas purifier must be added.