Thermal Expansion of Nb₂O₅

Abstract

The high-temperature thermal expansion of monoclinic Nb,O, was studied with X-ray and dilatometric techniques. The X-ray axial thermal expansion was anisotropic; the mean coefficients in the a, b, and c directions, respectively, were 5.3, 0, and 5.9X10-" "C-' from room temperature to 1000°C. It is proposed that this anisotropy causes microcrack formation in sintered polycrystalline samples. The bulk linear thermal expansion of both sintered and hot-pressed samples was determined with a dilatometer from room temperature to 1200OC. A hysteresis effect between heating and cooling data observed for sintered samples was attributed to the occurrence and recombination of internal microcracks.

Thermal expansion of specimens of niobium and tantalum pentoxides obtained by melting in an optical furnace

“…This allows the authors to infer that a network of microcracks responsible for the negative values of CLTE can form in the volume of an ingot [6]. This is confirmed by the positive values of temperature changes in the volume of an elementary cell of the main (monoclinic) phase of niobium pentoxide obtained in [7].…”

“…The behavior of the temperature dependence of the lattice parameters of monoclinic Nb 2 O 5 differs somewhat from the data of [7]. The differences can be explained by the use of purer initial materials for the study.…”

“…The data on the temperature-induced variation of the volume of an elementary cell of the monoclinic Nb 2 O 5 phase ( Table 1 and curve 4 of the present work and curve 2 plotted from the data of [7]) presented in Fig. 2 show that an elementary cell of monoclinic Nb 2 O 5 phase changes with growth in the temperature.…”

“…The differences can be explained by the use of purer initial materials for the study. Figure 2 presents the curves of relative variation (the range of 20 -800°C) of the volume of Nb 2 O 5 specimens obtained by the method of melting in optical furnace [3] and by sintering by the traditional ceramic process [7].…”

Síntese De Pós Nanometricos Do Al2mo3o12 Para Otimização De Seu Coeficiente De Expansão Térmica Na Forma Maciça

“…O gráfico 12 ilustra uma correlação entre a densidade (% da teórica) e o tamanho de cristal, que apresenta uma relação semelhante a uma das razões possíveis listadas por Manning et al [27] …”