Contribution to the understanding of cathodic carbon swelling under pressure

Many laboratory experiments on carbon swelling under pressure with a Rapoport and Samoilenko type apparatus were performed using different carbon samples and experimental conditions. The Young’s modulus, characterizing the mechanical properties of carbon, was measured at different temperatures, mainly at 970 °C under electrolysis conditions. Cathodic carbon swelling was interpreted in terms of partial molar volumes, and the observed results were rationalized by the compressibility of the sodium in solution in the carbon lattice. Its compressibility coefficient was found to be 1.43 · 10−7 MPa−1. The relationship between the apparent Young’s modulus of impregnated carbon and the sodium content was derived. The consequence of this peculiar behavior on the mechanical properties of carbon blocks was discussed.