Carbon-Bonded Alumina Refractories with Reduced Carbon Content due to the Addition of Semi-Conductive Silicon and/or Nanoparticles

This study investigated the combined effect of nanoscaled additives (carbon nanotubes and nanoscaled alumina) and semi-conductive silicon on carbon-bonded alumina with a reduced primary carbon content of 20 wt%. It focused on the initial cold modulus of rupture and its evolution on exposure to thermal shock. The use of the single additive groups or their combination yielded an increased initial strength compared to the reference without additives. It was shown that the combination of the additives resulted in a material that exhibited no statistically significant decrease of the cold modulus of rupture in up to five thermal shock cycles. To understand these effects, physical properties (total porosity, open porosity, true density) were observed. The data showed that the microstructural reactions were complex. The combination of all additives caused a decrease in the open porosity. The available data of the true density analysis matched partly with the possible reactions. Especially the formation of SiC whiskers was considered to be important during the coking process and the thermal shocks. Furthermore, it was proposed that a deposition of carbon because of oxidation processes followed by reactions with the additives, especially the semi-conductive silicon, occurred, which might have a self-healing effect on the refractory matrix.