Analysis of the crystal phases of Na+-beta-aluminas synthesized by infiltration of alkali molten salts

Na+-beta-aluminas in ternary Na2O–Al2O3–Li2O systems were synthesized by infiltration of alkali molten salts into porous α-Al2O3 pre-form. The effects of calcination temperature, infiltration time, and starting materials on phase formation were investigated. Pre-forms were fabricated by pressureless powder packing (PLPP), slip casting, and cold isostatic pressing (CIP) with fused and calcined α-Al2O3 powder. They were heated and infiltrated by alkali molten salts at [Na2O]:[Al2O3] = 1:5 (Li2O = 0.4 w/o). Each infiltrated specimen was calcined at 1100–1300 °C to form Na+-beta-aluminas, whose crystalline formations, phase fractions, and alkali ion contents were analyzed. The pre-form prepared by PLPP with 1 μm-calcined α-Al2O3 powder showed the highest Na-β″-Al2O3 phase fraction (59.5%), without residual α-Al2O3 phase.