Modification from rod-shaped β-LiAlO2 crystals to γ-LiAlO2 crystals without morphology change and stability of γ-LiAlO2 crystals in alkali carbonates

The phase transformation of rod-shaped β-LiAlO2 crystals synthesized in the LiOH-Al2O3-NaOH system with a molar ratio of 43.0:10.8:46.2 to γ-LiAlO2 crystals was examined. It was revealed that rod-shaped β-LiAlO2 crystals (1.5μm in diameter and 13 to 14μm in length) modified to γ-LiAlO2 crystals without morphology change by heating to 700°, 750°, 800°, 900° and 1000°C for 10 to 30h. The surface areas of resulting rod-shaped γ-LiAlO2 crystals were larger than 10m2/g. The stability of rod-shaped β-LiAlO2 and γ-LiAlO2 crystals in alkali carbonates, an electrolyte of molten carbonate fuel cells, was examined. The original rod-shaped β-LiAlO2 crystals mixed with alkali carbonates deformed by the heat treatment at 650°C for 500h, whereas rod-shaped γ-LiAlO2 crystals derived from β-LiAlO2 at 900°C for 10h underwent no deformation by the heat treatment at 650°C for 1000h.