Niobium carbide synthesis from niobium oxide: Study of the synthesis conditions, kinetics, and solid-state transformation mechanism

Journal Article · Mon Apr 01 04:00:00 EST 1996 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1006/jssc.1996.0165· OSTI ID:274263

Teixeira da Silva, V L.S.; Schmal, M ^[1]; Oyama, S T ^[2]

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1. Universidade Federal do Rio de Janeiro (Brazil)
2. Virginia Polytechnic Inst. and State Univ., Blacksburg, VA (United States)

The carburization of B-niobium oxide (B-Nb{sub 2}O{sub 5}) to niobium carbide (NbC) in 20% (v/v)CH{sub 4}/H{sub 2} was studied at temperature-programmed conditions, the reaction required high temperatures, greater than 1370K, and variations of heating rate (0.04-0.17 K s{sup {minus}1}) and molar space velocity (400-1600 h{sup {minus}1}) had only a minor effect on the product specific surface are (S{sub g}). In the course of the transformation S{sub g} increased from 1 m{sup 2}g{sup {minus}1} to about 20 m{sup 2}g{sup {minus}1}, and scanning electron microscopy showed the development of macropores of about 100 nm. The progress of the reaction was followed by mass spectroscopic analysis of the gaseous products, which identified two distinct stages. X-ray diffraction analysis of reaction intermediates showed that in the first stage B-Nb{sub 2}O{sub 5} was reduced to NbO{sub 2}, and in the second stage NbO{sub 2} was simultaneously reduced and carburized to NbC. The first reduction occurred by a nucleation mechanism with an activation energy of 100 kJ mol{sup {minus}1}. Independent experiments with NbO indicated that it was not involved in the reaction pathway. However, X-ray photoelectron spectroscopy revealed the presence of an oxycarbide phase which was probably the intermediate in the final transformation. The oxycarbide phase transformed rapidly to the product NbC and was not observable as a bulk phase by XRD.

• OSTI ID: 274263
• Journal Information: Journal of Solid State Chemistry, Journal Name: Journal of Solid State Chemistry Journal Issue: 1 Vol. 123; ISSN 0022-4596; ISSN JSSCBI
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ACTIVATION ENERGY
CHEMICAL PREPARATION
CHEMICAL REACTION KINETICS
MASS SPECTROSCOPY
NIOBIUM CARBIDES
REACTION INTERMEDIATES
REDUCTION
SCANNING ELECTRON MICROSCOPY
X-RAY DIFFRACTION
X-RAY SPECTROSCOPY