Self-powdering phenomenon of ^|^beta;^|^prime;-RE2(MoO4)3 formed in crystallization of glasses and its mechanism (RE: Gd, Sm, Dy)
Journal of the Ceramic Society of Japan
Some glasses in the RE 2 O 3 MoO 3 B 2 O 3 system (RE: Gd, Sm, Dy) were prepared by using a conventional melt quenching method, and the self-powdering phenomenon of ¢¤-Gd 2 (MoO 4 ) 3 crystals, i.e., the breaking into small pieces during the crystal growth, was examined using polarized optical microscope observations in a heating stage. In Gd 2 O 3 MoO 3 B 2 O 3 glasses with Gd 2 O 3 / MoO 3 = 1/3 and with different B 2 O 3 contents (1530 mol %) such as 20Gd 2 O 3 60MoO 3 20B 2 O 3 , ¢¤-Gd 2
... 2 O 3 , ¢¤-Gd 2 (MoO 4 ) 3 crystals were formed and the self-powdering phenomenon was observed irrespective of B 2 O 3 content. The crack formation radiating out from the center part was clearly observed in the inside of crystals (diameter >40¯m) formed at 570°C in the glasses with Gd 2 O 3 or Dy 2 O 3 . But, any clear crack formation was not observed in the glass with Sm 2 O 3 . It was found that the base glasses have larger densities at room temperature compared with ¢¤-RE 2 (MoO 4 ) 3 crystals formed, which is a unique feature in the RE 2 O 3 MoO 3 B 2 O 3 system compared with the crystallization of other glass systems. Such differences in the density might induce the accumulation of extremely large stresses in the inside of crystals, eventually causing the breaking of crystals.