Chapter 38. Pseudo-Binary Eutectic Between Y4Al2O9 and y203
- John B. Wachtman Jr.
Published Online: 26 MAR 2008
Copyright © 1992 The American Ceramics Society
Proceedings of the 16th Annual Conference on Composites and Advanced Ceramic Materials, Part 2 of 2: Ceramic Engineering and Science Proceedings, Volume 13, Issue 9/10
How to Cite
Mah, T. and Petry, D. (2008) Pseudo-Binary Eutectic Between Y4Al2O9 and y203, in Proceedings of the 16th Annual Conference on Composites and Advanced Ceramic Materials, Part 2 of 2: Ceramic Engineering and Science Proceedings, Volume 13, Issue 9/10 (ed J. B. Wachtman), John Wiley & Sons, Inc., Hoboken, NJ, USA. doi: 10.1002/9780470313978.ch38
- Published Online: 26 MAR 2008
- Published Print: 1 JAN 1994
Print ISBN: 9780470375198
Online ISBN: 9780470313978
- thermal expansion;
- crystal structure;
The pseudo-binary eutectic composition between Y4Al2O9 and Y2O3 was determined using an electron microprobe on specimens with hypo-and hyper- eutectic compositions. Directional solidification using the modified-Bridgeman technique was used to produce these specimens and others of differing compositions. For each composition a mixture of commercially available or alkoxy-derived alumina and yttria powders with a total weight of about 50g was used. For each composition a molybdenum crucible containing sintered pellets was lowered at a velocity of 6 cm/hr out of a graphite susceptor heated inductively to and held at a temperature of 2050°C. A portion of the resulting directionally solidified melt was powdered for characterization with x-ray diffraction and showed the presence of only Y4Al2O9 and Y2O3 in all experiments. Each crucible was sectioned and the transverse sections were polished for examination with a SEM. Four distinctively different microstructures were observed depending upon the composition; two phases with no eutectic, eutectic with yttria cuboids, eutectic, and eutectic with alumina cuboids. The polished transverse sections of the alumina-rich specimen (hypo-eutectic composition) and the yttria-rich specimen (hyper-eutectic composition) were subjected to electron microprobe analysis. The EPMA was carried out using an accelerating voltage of 15kV and a beam current of 30nA. Thirty analyses were made on each specimen on areas that exhibited a fine eutectic microstructure. By averaging the 60 analyses, 30 from each specimen, the mean, taken as the eutectic composition, was 29.5 mol% Al2O3 and 70.5 mol% Y2O3. Based on these results and other published phase diagrams, the revised pseudobinary system between Al2O3 and Y2O3 was proposed.