Combined DTA and XRD Study of Sintering Steps Towards YAl3(BO3)4

Sintering processes in the Y2O3–Al2O3–B2 O3 system and its subsystems (Y2O3–B2O3 and Al2 O3–B2O3) have been investigated by using combined DTA and XRD measurements to get a better understanding of solid state chemical changes resulting in the formation of yttrium aluminum borate (YAl3(BO3)4, YAB) phase and to study the possible role and contribution of various simple borates formed also in the former processes. Two new exothermic heat effects of YBO3 formation have been detected by DTA in the Y2O3–B2O3 system between 720 and 980C. In the Al2O3–B2O3 system a new experimental XRD profile of Al4B2O9 was observed. Formation of these borates seems to promote the nucleation of double borate YAB below 1000C. Conversion of Al4B2O9 to Al18B4 O33 was observed after a long term (10 h) sintering at 1050C. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO3 and Al18B4O33 at 1150C. The two latter single borates are found to be identical with the high temperature decomposition products of YAB.