It is possible to use carbon dioxide (CO2) in place of nitrogen atmosphere. Before making the substitution several issues should be considered. Nitrogen is considered an inert atmosphere. It does not react with any other gases present. It displaces them. Nitrogen is a good choice as long as the purge is sufficient to completely remove all other gas products. Carbon dioxide (CO2) is a good more reactive, protective gas. It displaces other gases but can also react with any remaining undesired products. The negative is that CO2 could react during the welding process. The CO2 in the presence of the weld energy might break down. Oxygen would be generated and that could lead to oxidation/discoloration of the TO-39 package.
A trial with carbon dioxide (CO2)or other protective gas may be worthwhile but the following must be considered:
1. Is the current Nitrogen purge sufficient (flow/time)?
2. Will the change to a more reactive gas cause a reaction with the part and alter oxidation, corrosion or microstructure?
3. Will the process have to be recertified?