[pcm81]

I have been lately experimenting with some hot caustic bluing solutions. There seem to be many recipes on the internet for the bath composition. The problem I am having is that most of these baths function with an excess of one chemical or another, hence it it difficult to figure out the balanced reactions that govern the process, which in turn is needed for me better understand the contribution of each of the chemicals involved to overall process.

The bath usually consists of H2O + NaOH + NaNO3 and in some cases additions of Sodium Nitride and / or sodium dichromate.
I see recipes that range from 5 to 8 pounds of NaOH per gallon of water with NaNO3 ranging from couple ounces to couple pounds per gallon.

The output of the chain reaction is Fe3O4 plus other stuff.

the reaction temperature is usually between 290 and 310 degrees F.

I am GUESSING that sodium nitrate combines with metallic iron and then iron nitrate is reduced to magnetite by sodium hydroxide?

Can someone please help me understand the balanced reactions for this process or point out what I may have missed? Why would some recipes also have sodium nitride and sodium dichromate in them as well?

Thanks ahead

[pcm81]

I have been lately experimenting with some hot caustic bluing solutions. There seem to be many recipes on the internet for the bath composition. The problem I am having is that most of these baths function with an excess of one chemical or another, hence it it difficult to figure out the balanced reactions that govern the process, which in turn is needed for me better understand the contribution of each of the chemicals involved to overall process.

The bath usually consists of H2O + NaOH + NaNO3 and in some cases additions of Sodium Nitride and / or sodium dichromate.
I see recipes that range from 5 to 8 pounds of NaOH per gallon of water with NaNO3 ranging from couple ounces to couple pounds per gallon.

The output of the chain reaction is Fe3O4 plus other stuff.

the reaction temperature is usually between 290 and 310 degrees F.

I am GUESSING that sodium nitrate combines with metallic iron and then iron nitrate is reduced to magnetite by sodium hydroxide?

Can someone please help me understand the balanced reactions for this process or point out what I may have missed? Why would some recipes also have sodium nitride and sodium dichromate in them as well?

Thanks ahead

I am guessing this is what actually happens:
Fe + NaNO3 --> Na + FeNO3
FeNO3 + NaOH --> FeOH + NaNO3
FeOH + H+ --> Fe3O4 +H2O

So, it would seem that Sodium hydroxide is consumed, but Sodium Nitrate is retained?

Ultimately the goal is to know what to add to the bath to adjust the boiling point. It seens to raise BP i'd need to add NaOH sine that is actually consumed in he reaction?

Wht would Sodium nitride and dichromate contribute to this reaction?

EDIT:
Actually looks like NaOH is not consumed, since Na from step 1 reacts woth H2O producing NaOH and the leftover proton is consumed in step 3.