SYNTHESIS OF NIOBIUM CARBIDE FROM NIOBIUM OXIDE AEROGELS

Niobium carbide (NbC) synthesis was studied by the temperature-program med reaction (TPR) between niobium oxide precursors of different textu ral properties and a 20% (v/v) CH4-H-2 mixture. Surface areas ranging between 13 and 74 m(2)/g were obtained depending on the temperature an d on the nature of the precursor (Nb2O5 or an aerogel precursor). The high synthesis temperatures (1173-1373 K) caused surface contamination by carbon from methane decomposition and led to low CO uptakes (15-28 mu mol/g). Environmental scanning electron microscopy (ESEM) analysis showed that the transformation oxide carbide is a pseudomorphous proc ess. The results suggest that the reaction occurs in two steps: reduct ion by H-2 leading to NbO2 formation and carburization/reduction of th e NbO2 to NbC.