Thermocapillary effects in two-phase medium and applications to metal-silicate separation

The separation of a liquid phase from a solid but deformable matrix made of mineral grains is controlled at small scale by surface tension. The role of interfacial surface tension is twofold as it explains how a small volume of liquid phase can infiltrate the grain boundaries, be distributed and absorbed in the matrix, but after complete wetting of the grains, surface tension favors the self-separation of the liquid and solid phases. Another consequence of surface tension is the existence of Marangoni forces, which are related to the gradients of surface tension that are are usually due to temperature variations. In this paper, using a continuous multi-phase formalism we clarify the role of these different effects and quantify their importances at the scale of laboratory experiments and in planets. We show that Marangoni forces can control the liquid metal-solid silicate phase separation in laboratory experiments. The Marangoni force might help to maintain the presence of metal at the surface of asteroids and planetesimals that have undergone significant melting.