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

Abstract

Crack formation in the C12A7 nano‐composite during crystallization was successfully avoided by using the eutectic glass in the C12A7–CaYAlO4 system. The crystal phases from the eutectic glass were identified to be C12A7 (major phase) and CaYAlO4 (minor phase) by X‐ray diffraction and high‐resolution transmission electron microscope. It was indicated that origin of cracks upon crystallization of C12A7 glass was the volume expansion caused by crystallization of C12A7 in the glass and the cracking could be avoided by the volume shrinkage by crystallization of CaYAlO4. By using a conventional molding technique, we have also succeeded to fabricate a bulk C12A7 composite with arbitrary shapes.

Fabrication of Nanocomposite Ceramics by Crystallization of Rapidly Solidified Eutectic Melts

“…We also investigated crystallization behavior from the glass phase of the C12A7–CaYAlO 4 eutectic 15,16 . C12A7 is one of a hot topic in the oxide materials because it exhibits many outstanding properties, e.g., oxygen radical (O − ) emission, 17 UV light‐induced conversion from an insulator to a conductor, 18 and electride structure where the electrons act separately as anions, 19 without the need for expensive and precious elements.…”

Solution derived 12CaO·7Al2O3 thin films on MgO(100) substrate

“…C12A7:e − exhibits low work function and high electronic conductivity, it is expected to application of transparent electrode which may replace the ITO electrode due to a great deal of Ca, Al, and O resources on the earth [6]. There have been reported for fabricating C12A7 bulk material via melt processing in order to prepare C12A7 via simple method [7][8][9]. For the C12A7 film, however, most of the C12A7 thin film fabrication processes reported have been based on PLD method, which require high vacuum level and high energy consumption.…”

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

“…As reported in our previous paper, 11 glass of C12A7 stoichiometry composition cracks during annealing due to crystallization of C12A7, whereas the eutectic glass of C12A7-CaYAlO 4 system does not. We suggest the cracking mechanism by volume expansion of C12A7 during annealing 19 and surface crystallization nature of the stoichiometric glass.…”

“…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.…”

“…10 We have reported a fabrication route for the C12A7-based bulk composites using the ternary eutectic Y 2 O 3 -CaO-Al 2 O 3 system, where the C12A7 bulk composite can be easily obtained by merely annealing the molded glass. 11 The shape and size of the composite can be controlled by the glass because it does not cause any cracking during annealing, although the C12A7 stoichiometry glass cracks during annealing. In that report, we suggested a mechanism of cracking and of avoiding cracking.…”