Mario Caccia

Wetting and Navier-Stokes Equation — The Manufacture of Composite Materials

It is well known that there are several processes to manufacture composite materials, a large part of which consist in the infiltration of a liquid (matrix) through a porous medium (reinforcement). To perform these processes, both thermodynamics (wet‐ ting) and kinetics (Navier-Stokes) must be considered if a good quality composite material is sought. Although wetting and the laws that govern it have been well known for over 200 years, dating back to the original works of Young and Laplace, this is not the case with the Navier-Stokes equation, which remains so far unsolved. Although the Navier-Stokes equation, which describes the motion of a fluid, has been solved for many particular cases, such as the motion of a fluid through a pipe, which has resulted in the well-known Poiseuille equation, or the motion of a fluid through a porous media, described by the Darcy’s law (empirical law obtained by Darcy), its general solution remains one of the greatest challenges of mathematicians today. Therefore, the objective of this chapter is to present the resolution of the Navier-Stokes equation with the laws of wetting for different cases of interest in the manufacture of composite materials.

Production of SiC Materials by Reactive Infiltration

The use of oak sawdust as carbon precursor for SiC manufacture via reactive infiltration was studied. The effect of oak sawdust pressing parameters, temperature and pressure, on the final SiCs properties was studied. Final products quality was evaluated through density measurement, and microstructure and pore size distribution variations were characterized with optical microscopy and mercury porosimetry. Pressed oak sawdust preforms were carbonized to obtain a carbon porous preform which was then infiltrated with melted silicon. Successful infiltration of preforms pressed at room temperatures were performed, to obtain a porous SiC. Hot pressed preforms were not satisfactory infiltrated due to a narrowing of their pores caused by SiC formations expansiveness.

Graphene Translucency and Interfacial Interactions in the Gold/Graphene/SiC System

Integration of graphene into electronic circuits through its joining with conventional metal electrodes (i.e., gold) appears to be one of the main technological challenges nowadays. To gain insight into this junction, we have studied the physicochemical interactions between SiC-supported graphene and a drop of molten gold. Using appropriate high-temperature experimental conditions, we perform wetting experiments and determine contact angles for gold drops supported on graphene epitaxially grown on 4H-SiC. The properties of the metal/graphene interface are analyzed using a wide variety of characterization techniques, along with computational simulations based on density functional theory. In contrast with the established literature, our outcomes clearly show that graphene is translucent in the gold/graphene/SiC interface, and therefore its integration into electronic circuits primarily depends on the right choice of the support to produce favorable wetting interactions with liquid gold.