Transparent Nano‐Composites Ceramics by Annealing of Amorphous Phase in the HfO₂‐Al₂O₃‐GdAlO₃ System

Abstract

We have succeeded in fabricating transparent nano‐structured ceramics by annealing of the amorphous phase obtained by the solidification of the eutectic melt in the ternary system HfO2− Al2O3− GdAlO3. The ceramics annealed at 1273 K for 6 hr contained 5‐10‐nm cubic hafnia grains, and those annealed at 1273 K for 72 hr contained both cubic hafnia and gadolinium aluminum garnet grains 5‐10 nm in size. They showed high transparency. Annealing at 1473 K, however, resulted in grain growths that brought about non‐transparency.

Crystallization behavior of the eutectic glass in the C12A7–CaYAlO4 system

“…Detailed procedures for the arc-image furnace (UF-10001, Ushio Inc., Tokyo, Japan) are mentioned in our previous papers. 4,5,11,16 The sample after the solidification had globule shape due to the surface tension of the melt and vitrified caused by rapid cooling rate about 200-500 • C/s. The sample globules were annealed at several temperatures and several time periods, i.e.…”

Fabrication of Crack‐Free C12A7 Nano‐Ceramics Composite from Eutectic Glass in the C12A7–CaYAlO4 System

“…Yoshimura et al 14,15 . recently pointed out that those reasons are rather superficial but the real reason for the sintering processes is mainly to avoid the excess grain growth to prevent the stress accumulation which often exceeds the critical fracture stress due to grain growth of the crystallized phase(s) during melt solidification.…”

“…The motives for preferring the powder processes are generally believed that sintering at a lower temperature is easier and/or more economical than melting at high temperature. 12,13 Yoshimura et al 14,15 recently pointed out that those reasons are rather superficial but the real reason for the sintering processes is mainly to avoid the excess grain growth to prevent the stress accumulation which often exceeds the critical fracture stress due to grain growth of the crystallized phase(s) during melt solidification. According to this concept, we have proposed the meltsolidification processes for eutectic melts in binary and ternary systems where grain growths can be avoided during eutectic solidification.…”

“…Moreover, the amorphous phase (supercooled liquid) can be produced in the eutectic systems more easily than from the melt of a single phase and/or a stoichiometric compound. [15][16][17] Based on new findings on the eutectic solidification in the ternary Al 2 O 3 -Y 2 O 3 -ZrO 2 system 18-20 and amorphous formation in the Al 2 O 3 -Gd 2 O 3 -HfO 2 system, 15,21 we have studied the melt-solidification and amorphous phase formation in the system Al 2 O 3 -CaO-Y 2 O 3 . 22 In the present study, we demonstrate the fabrication of the C12A7 bulk materials with an arbitrary shape and size from the eutectic melts in the pseudobinary C12A7-CaYAlO 4 system, which should have more advantages to fabricate the C12A7 bulk materials than the composition of the stoichiometric C12A7.…”

“…The experimental procedures of the fabrication process by the arc imaging furnace is described in previous reports. 15,[18][19][20][21][22] After heating the sample at 8301C for 15 min in order to remove the residual stress, two parallel flat planes were prepared by mirror polishing on the sample globules in order to measure the precise linear expansion. The linear expansion behavior with crystallization of the glass samples were measured by loading 0.5 g weight, vertical to the mirror planes and at a heating rate of 101C/min from room temperature to 12001C using thermodilatometry (TD) (TD5000SA, Bruker AXS K.K., Tsukuba, Japan).…”