Date of Award

Spring 1983

Degree Type

Thesis - Restricted

Degree Name

Master of Science (MS)



First Advisor

Blumenthal, Robert N.

Second Advisor

Fournelle, Raymond A.

Third Advisor

Hirthe, W. M.


Despite many published listings of thermodynamic data for the equilibrium conditions of carburizing atmospheres, the question of whether equilibration of the carburizing atmosphere components actually occurs has not been fully examined. Some investigators have recently claimed that the partial pressure of H20 is not in equilibrium with carbon concentration in austenite according to H2 + CO = C + H20. This non-equilibrium condition, if valid, would require re-evaluation of the traditional carbon potential control via controlling water-vapor concentration (dew point) of the furnace atmosphere. This study evaluates the validity of the equilibrium assumption, clarifies the conditions under which it may be obtained, and treats some of the experimental subleties required for obtaining and evaluating samples of carburizing atmosphere. Equilibration of an endothermic carburizing atmosphere was accomplished with the aid of catalysts at several selected carburizing ternperatures. As predicted by the equilibrium condition, carbon activities obtained independently from the partial pressures of H20, C02, CH4 and 02 corresponded well with each other. The carbon activity was found to be approximately constant at all temperatures of interest. Fast quenching of the sampled furnace gas was determined to be essential for preventing soot formation which upsets the partial pressure of C02, and H20 leads to erroneously low carbon activities. Finally, some preferred free energy equations for the carburizing gas reactions are recommended.