Crystallization of a niobium phosphate glass
| Autor: | L. Ghussn, J. R. Martinelli, Miguel Oscar Prado, D. O. Russo |
|---|---|
| Rok vydání: | 2006 |
| Předmět: |
Arrhenius equation
Chemistry Nucleation Analytical chemistry Crystal growth Atmospheric temperature range Condensed Matter Physics Electronic Optical and Magnetic Materials Phosphate glass law.invention Crystal symbols.namesake Crystallography law Phase (matter) Materials Chemistry Ceramics and Composites symbols Crystallization |
| Zdroj: | Journal of Non-Crystalline Solids. 352:3391-3397 |
| ISSN: | 0022-3093 |
| Popis: | Niobium phosphate glasses with composition 37P 2 O 5 · 23K 2 O · 40Nb 2 O 5 are stable in relation to crystallization during the heating process, exhibit a low critical cooling rate, and are potentially good for nuclear wasteforms. The crystallization of these glasses was evaluated by optical microscopy after proper heat treatments, showing that surface crystallization is the main process occurring during the heat treatment. Two main crystalline phases were observed. These crystalline phases were KNb 3 O 8 and K 3 NbP 2 O 9 . Surface crystal growth rates were measured in the temperature range of 806-972 °C (T g = 683 °C) for both crystalline phases. Apparent crystallization enthalpies were determined through the Arrhenius plots of lnU vs. 1/T. The enthalpies are 496 kJ/mol and 513 kJ/mol for each crystalline phase, respectively. The surface density of nucleation sites (N s ) on 3 μm diamond paste polished surfaces is (2.4 ± 0.7) x 10 8 nuclei/ m 2 for one crystalline phase and (9.8 ± 0.8) × 10 9 nuclei/m 2 for the other crystalline phase, when revealed at 838 °C/17.5 h, and these values show a slight variation depending on the time and the temperature. At the tested temperatures, only one crystal phase appeared inside the volume, and a volume density of nucleation sites N v = 5 × 10 6 nuclei/m 3 was measured. |
| Databáze: | OpenAIRE |
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