Thermotransport of carbon in two-phase V-C and Nb-C alloys

Thermotransport experiments were performed on two-phase V-C and Nb-C alloys for various times, temperature ranges, and compositions. A one-phase region develops in the hotter portion of the sample accompanied by an increase in carbide concentration in the colder region. A mathematical equation in which the direction of transport is described by the sum of the heat of solution,A―H, and the heat of transport,Q*, was fitted to the experimental data for all of the alloys studied. No evidence was found to support the physical motion of the carbide particles predicted by some models. On the assumption that local equilibrium exists between the particles and the matrix, points on the V-C solvus were determined from the temperature corresponding to the one-phase/two-phase interface in the different experiments. The solid solubility for carbon in vanadium was determined to be log C (at. pct C) = 2.918 - 4536/T with a heat of solution of 86.8 ± 2.9 kJ/mol. Formerly a Graduate Research Assistant, Ames Laboratory, Iowa State University