Infiltration of macroporous carbon materials with silicon oxycarbide modified by carbon nanotubes

Abstract

Two types of carbon, i.e. carbon electrode (CE) and carbon furnace lining (CFL) were modified with silicon oxycarbide (SiOC) or carbon nanotubes-containing SiOC (SiOC/fCNT) by means of polysiloxane impregnation and pyrolysis. The two carbon materials differed in pore size and in surface chemical state. The impact of these factors on the infiltration efficiency was investigated by comparing the physical, electrical and mechanical properties in samples before and after infiltration. It was shown that SiOC phase is formed in the CE macropores, leading to a reduction in the average pore size from 8.2 to 5.3 μm, and in porosity from 12.6 to 7.3%. For CFL, which contains both meso- and macropores, the observed changes in porosity are smaller. Introducing fCNT into the resin changes its surface nature from hydrophobic to hydrophilic. This modified solution better wets a CE surface containing functional groups and provides an enhanced interface contact between this carbon and SiOC. The fCNT-modified SiOC phase improves the compressive strength and modulus of both types of carbon. The electrical resistivity of CE modified with SiOC/fCNT is slightly higher, whereas for CFL it does not change. Oxidation tests in air up to 1000 °C showed a significant reduction in the mass loss of both carbon materials after their modification with pure SiOC and SiOC/fCNT. The proposed infiltration procedure can be applied to conventional carbon and graphite technology, in particular to porous carbons containing a macropore fraction.