Combined DTA and XRD study of sintering steps towards YAl3(BO3)(4)

Sintering processes in the Y2O3-Al2O3-B2O3 system and its subsystems (Y2O3- B2O3 and Al2O3-B2O3) have been investigated by using combined DTA and XRD m easurements to get a better understanding of solid state chemical changes r esulting in the formation of yttrium aluminum borate (YAl3(BO3)(4), YAB) ph ase and to study the possible role and contribution of various simple borat es 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 980 degreesC. In the Al2O3-B2O3 sy stem a new experimental XRD profile of Al4B2O9 was observed. Formation of t hese borates seems to promote the nucleation of double borate YAB below 100 0 degreesC. Conversion of Al4B2O9 to Al18B4O33 was observed after a long te rm (10 h) sintering at 1050 degreesC. Similarly, an increased formation of YAB has been observed as a product of the sintering reaction between YBO3 a nd Al18B4O33 at 1150 degreesC. The two latter single borates are found to b e identical with the high temperature decomposition products of YAB.