Synthesis and growth of anorthite crystal during in situ preparation of porous anorthite ceramics by foam-gelcasting

Pure anorthite porous ceramics have been fabricated using γ-Al 2 O 3 , CaCO 3 , and SiO 2 as raw materials through foam-gelcasting method. XRD, thermal analysis, SEM, and TEM were used to study the synthesis and grain growth of anorthite during the in situ process. The results indicated that the initiator (ammonium presulfate) took part in the chemical reaction to form CaSO 4 , which played an effective role during synthesis of anorthite. Besides, CaO and CaSiO 2 were the other intermediate phase during synthesis. Anorthite first occurred at 1050°C, and it was the only phase after it sintered over 1260°C. With sintering temperature increasing from 1300°C to 1450°C, the large sphere pore wall got denser and the anorthite grains obviously showed platelike. It was deduced that the preferential growth of anorthite crystals was parallel to the (004) plane.