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2011-Sustainable Industrial Processing Summit
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| Editors: | Florian K |
| Publisher: | Flogen Star OUTREACH |
| Publication Year: | 2012 |
| Pages: | 646 pages |
| ISBN: | 978-0-9879917-6-8 |
| ISSN: | 2291-1227 (Metals and Materials Processing in a Clean Environment Series) |
Synthesis Of Superfine Nd2Hf2O7 And Study Of Its Vaporization
Vladimir Sevastyanov1; Valentina Stolyarova2; Sergey Lopatin2;1N.S. KURNAKOV INSTITUTE OF GENERAL AND INORGANIC C, Moscow, Russia; 2SAINT PETERSBURG STATE UNIVERSITY, Saint Petersburg, Russia;
Type of Paper: Regular
Id Paper: 130
Topic: 9
Abstract:
Niodimium hafnate Nd2Hf2O7 with the pyrochlore structure is the promising component of high temperature ceramics that may be used for the modern thermobarier coatings owing to the high melting temperature and the phase stability in the wide temperature range. In the present study the superfine Nd2Hf2O7 with the pyrochlore structure was prepared by the self-propagating high temperature synthesis. The composition and purity of the sample obtained was confirmed by laser mass spectrometric method with the identification of the phase composition. Microstructure of the superfine Nd2Hf2O7 was studied by scanning and transmission microscopy. The specific surface values of the sample were found using the BET method. The thermal stability of material was studied by TGA/DSC/DTA methods up to the temperature 1473 K. The kinetics of the sintering process of the Nd2Hf2O7 sample prepared was investigated at the various temperatures. The Knudsen effusion mass spectrometric method was used to study of the vaporization processes and thermodynamic properties of Nd2Hf2O7 in the temperature range 2400-2600 K. Vaporization of Nd2Hf2O7 was done from the tungsten effusion cells using mass-spectrometer MS 1301 developed for the high temperature thermodynamic studies of the low volatile inorganic substances. The NdO, Nd and oxygen vapour species were identified over sample studied in the temperature range indicated. The partial pressures of these vapour species were obtained using the ion current comparison method. The vaporization dynamics of the NdO, Nd and oxygen vapour species over Nd2Hf2O7 as the functions of time and temperature was illustrated. The Nd2O3 activities in the Nd2Hf2O7 compound were found by the comparison method using vaporization from the double effusion cell: one cell was for the investigation of the compound under consideration and second was for the corresponding individual oxide. The enthalpies of sublimation of the main vapour species over Nd2Hf2O7 were obtained as well as the equations of the temperatures dependencies of the partial pressures of these species were presented. The question on the deviations from the ideality of Nd2O in the Nd2Hf2O7 compound at high temperatures was discussed.