Combined Effects of Boron Carbide, Silicon, and MWCNT s in Alumina‐Carbon Refractories on Their Microstructural Evolution

The phase and microstructure evolutions of multiwalled carbon nanotubes ( MWCNT s) in B 4 C‐ and Si‐containing Al 2 O 3 –C specimens under elevated temperatures were investigated by means of X‐ray diffraction, scanning electron microscopy, and transmission electron microscopy. The results show that the incorporation of B 4 C decreases the partial pressure of SiO(g) in Al 2 O 3 –C specimens due to the oxidation of B 4 C prior to Si at lower temperature, which prevents the transformation of MWCNT s at 1000°C and suspends the transformation under higher temperature. B 2 O 3 vapor resulting from oxidation of B 4 C powder reacts with C sources to generate nanoscaled B 4 C droplets, which facilitate the catalytic formation of new MWCNT s and nano onion‐like carbon. In addition, B‐doped MWCNT s and BN tubes with the coexistence of B 2 O 3 , MWCNT s, and N 2 are obtained under evaluated temperatures.