Direct cold sintering of translucent gamma-Al2O3 ceramics

Gamma-Al2O3 ceramics can hardly be densified by conventional sintering methods because of the low surface energy of gamma-Al2O3 powder and phase transformation at elevated temperature. Here, we report the preparation of translucent gamma-Al2O3 ceramics by cold sintering process at merely 350 degrees C via using the gammaAl2O3 as starting powder. Due to the enhanced solubility and reaction of gamma-Al2O3 in alkaline solution, the nanocrystalline particles can be densified to -92% of full density via adding 10 M NaOH solution as the transient liquid. It is proved that the high concentration of alkaline solution can greatly accelerate the dissolutionprecipitation process, leading to the activation energy as low as 16.9 kJ/mol. Consequently, a translucent ceramic with in -line transmittance reaching 16% around 800 nm can be obtained, despite the residual porosity. Considering the stable hardness and translucency after water leaching or heating to 1000 degrees C, the cold sintered gamma-Al2O3 ceramic may have the potential application as optical windows under extreme environments.