Porous graphite fabricated by liquid metal dealloying of silicon carbide

Abstract

Porous graphite was prepared by dealloying SiC in molten germanium, and then excavating the Ge phase. Dealloying is a technique whereby nanoporous materials are produced via the selective dissolution of one or more components from a homogeneous alloy. Here, the liquid metal dealloying (LMD) process was extended to non-metal precursors, demonstrating that carbide-derived carbons (CDCs) can be fabricated by this process. The dealloying depth, concentration profile and length scale of the dealloyed microstructure were examined as they varied with immersion times and temperatures. The dealloying depth h varied with time as h ∼ t1/2 and we also observed a build-up of Si concentration in the germanium near the dealloying interface. These observations are consistent with kinetics that are rate-limiting in the liquid germanium side of the moving interface. However, the measured activation barrier of 2.4–2.8 eV was too high to be consistent with diffusion in the liquid phase, so instead we propose a mechanism in which Si diffusion is impeded by unsaturated carbon bonds near the dealloying interface. The porous graphite exhibited three-dimensional connectivity and a high degree of crystallinity, with an I(D)/I(G) ratio of 0.3 for samples dealloyed at the highest temperatures.