C. Garcia-Rosales (Sp), I. López Galilea, N. Ordás, University of Navarra, San Sebastian (Spain)
Carbon fiber reinforced carbon (CFC) is envisaged for the strike point areas of the ITER divertor due to its excellent thermo-mechanical properties, resulting in a greater resilience to excessive heat loads during ELMs and plasma disruptions than other candidate materials such as tungsten. Besides the high cost and manufacturing difficulties of the CFCs developed for ITER, a main drawback of carbon-based materials is their chemical erosion under hydrogen bombardment from the plasma. Doping of carbon with small amounts of certain elements is known to reduce chemical erosion. On the other hand, some dopants show a catalytic effect on the graphitization, leading to a significant increase of the graphitization degree and allowing the development of doped isotropic graphite with high thermal conductivity and high thermal shock resistance. Furthermore, very fine and homogeneous dopants dispersion is required for an effective improvement of all properties, since both the thermo-mechanical properties and the chemical erosion seems to be particularly sensitive to changes in particle size. The aim of this work is to demonstrate at laboratory scale the optimization possibilities of doped isotropic fine-grained graphites with reduced chemical erosion, high thermal conductivity, high thermal shock resistance and low costs, to make them competitive with present CFC candidate materials for ITER. As starting materials, a mixture of mesophase carbon powder and different carbide forming dopants (Ti, V, Zr, W) has been used. Previously, the particle size of some of the dopants has been reduced below 100 nm by high energy ball milling. It has been confirmed that a reduction in the dopants particle size leads to a significant improvement of thermal conductivity and mechanical strength, as well as to a strong decrease in chemical erosion, depending on the manufacturing parameters. A model based on a dissolution-precipitation mechanism in a liquid metal phase is proposed to explain the catalytic graphitization.