THERMAL-EXPANSION AND ATHERMAL PHASE-TRANSITION OF Y4AL2O9 CERAMICS

Thermal expansion of Y4Al2O9 ceramics prepared at 1600 degrees and 180 0 degrees C was measured from room temperature to 1500 degrees C in ai r, Volume changes at the phase transition of Y4Al2O9, along with therm al hysteresis, were observed around 1400 degrees C, The volume of the high-temperature phase was about 0.5% lower than that of the low-tempe rature phase, The hysteresis width for the sample prepared at 1600 deg rees C was 56 degrees C, wider than that (14 degrees C) for the sample prepared at 1800 degrees C, The averages of phase transition start te mperatures on heating and on cooling for these samples mere, however, almost the same at 1377 degrees C, The phase transitions did not occur at fixed temperatures, and the proportions of the high-temperature ph ase and the low-temperature phase did not change with time as long as the temperature remained constant (athermal character), The sample pre pared at 1800 degrees C also showed another thermal hysteresis behavio r from room temperature to about 1000 degrees C.