Relationship between the growth of carbon nanofilaments and metal dusting corrosion

Raman scattering, X-ray diffraction, scanning electron microscopy, and transmission electron microscopy were used to study the mechanism of the catalytic crystallization of carbon and metal dusting corrosion. A mechanism is proposed for both metal dusting and the growth of carbon fibers. Carbon cannot crystallize well by deposition from carburizing gases at low temperature without catalytic activation because of its strong C-C bonds and high melting temperature. To form good crystalline carbon, the carbon atoms must dissolve, diffuse through metal particles, and crystallize on an appropriate facet that can act as a template to help the epitaxial growth of carbon crystals. In this process, metal particles are liberated from the pure metal and alloys. This liberation leads to the metal dusting phenomenon. The catalytic growth of carbon filaments is due to the transportation of carbon from one facet of a metal or carbide particle that favors carbon deposition to another facet that favors carbon precipitation. The free energy of poor crystalline carbon is higher than that of good crystalline carbon. The decrease in free energy from highly disordered carbon to well-ordered carbon is the driving force for metal dusting and for growth of carbon filaments through metal particles.