Thermal Expansion of NbC, HfC, and TaC at High Temperatures

Abstract

The thermal expansion of niobium monocarbide, hafnium monocarbide, and tantalum monocarbide was determined from room temperature to 2700°C by dilatometric measurements. The apparatus and experimental procedure were described earlier by Miccioli and Shaffer.1 All carbides used in the present investigation were prepared at The Carborundum Company by hot pressing at 3150°C and 3000 psi. The bulk thermal expansion results of these three monocarbides are compared with other published dilatometric data1–3 and also with x-ray lattice expansion data.4–6 The high-temperature divergence between the bulk thermal expansion data and the lattice expansion data is due to the effect of nonstoichiometry, caused by noncongruent vaporization7–9 at high temperature in these cubic monocarbides. The previously reported inversion phenomena were observed in the vicinity of 2000°C on several refractory monocarbides which were prepared by hot pressing at about 2000°C. This inversion was not detected in the present investigation. The inversion is due to the densification at the temperature apparently at which the specimens were fabricated.