It seems like the typical laboratory methods for determining the carbon content of steel are to cuppellate it in a stream of oxygen and then measure the volume of the evolved $\ce{CO}$ and $\ce{CO2}$, which involves many high-temperature complexities.

Why can't the carbon content of steel be measured by dissolving it in acid and reacting out the carbon at low temperature?

  • $\begingroup$ I am interested to know what happens the the carbon when steel when it is reacted with acid. Would the reaction be different in nitric acid vs hydrochloric? $\endgroup$ – Brinn Belyea Jun 22 '15 at 2:54
  • $\begingroup$ I don't know much about metallurgy. I think reaction of steel with acid leads to corrosion. So does corrosion play any role here? $\endgroup$ – Freddy Jun 22 '15 at 6:49

I think cuppellate is a foreign word meaning "burn" essentially.

The basic technique would be to have the iron sample in a small ceramic boat which is put into a hot stream of $\ce{O2}$ so the iron and carbon both oxidize. The iron oxide stays in the boat, and the $\ce{CO2}$ is sweep away and trapped/reacted somehow. We talking small samples 10 grams perhaps.

If you try to dissolve the steel in an acid solution then the $\ce{CO2}$ gas is formed in solution. It is really hard to get a small amount of $\ce{CO2}$ out of solution given that you are starting with a small amount to begin with. Also if you try to scale up such a reaction it gets to be a problem. A $2~\mathrm{cm^3}$ block of iron takes a long time to dissolve in acid.

So choosing the analytical method depends on a lot of factors. Time per sample, sensitivity, and overall cost being the main ones.

  • $\begingroup$ May I introduce you to the \ce{...} notation? Use that in MathJax to get upright chemical expressions. E.g. $\ce{C + O2 -> CO2}$ gives $\ce{C + O2 -> CO2}$. Learn more on meta $\endgroup$ – Jan Oct 31 '15 at 0:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.