Heat of Transfer for Carbon in Iron-Carbon System

The implications of the phenomenological diffusion equation for solute atoms under a temperature gradient are examined. It is pointed out that the quantity which can be derived from the steady state distribution of the solute atoms under a temperature gradient is, in principle, not the heat of transfer for the solute atoms but the partial molar enthalpy of the solute atoms less the heat of transfer for the solute atoms in the system. And it is shown that the reported value of the heat of transfer for carbon in α-iron agrees well with the value of the partial molar enthalpy for carbon in α-iron calculated using the thermodynamic database SGTE with THERMO-CALC. Correspondingly, it is concluded that the carbon distribution observed experimentally is not the result of the thermal diffusion of carbon but the distribution of carbon in equilibrium under a temperature gradient. The calculated value of the partial molar enthalpy of carbon in γ-iron, however, does not meet with the experimental value of the reduced heat of transfer for carbon in γ-iron. It is pointed out that the reported value of the reduced heat of transfer for carbon in γ-iron may have large experimental errors.