Synthesis of Hexacelsian Barium Aluminosilicate by a Solid‐State Process

Synthesis of hexacelsian barium aluminosilicate (BaAl 2 Si 2 O 8 or BAS) from BaCO 3 , Al 2 O 3 , and amorphous SiO 2 was examined. BaCO 3 can react with SiO 2 and Al 2 O 3 to form barium silicates (Ba 2 SiO 4 or B 2 S, BaSiO 3 or BS, and BaSi 2 O 5 or BS 2 ) and barium aluminate (BaAl 2 O 4 or BA). It is shown that there are two competitive reactions leading to the formation of hexacelsian BAS. One involves a reaction between BS 2 and Al 2 O 3 and the other involves a reaction between BA and SiO 2 . In experiments with the model BS 2 –Al 2 O 3 and BA–SiO 2 systems it is shown that the reaction between BS 2 and Al 2 O 3 is much faster than the reaction between BA and SiO 2 . However, in the BAS system, Al 2 O 3 suppresses the reactions which form BS 2 and instead reacts with B 2 S and BS to form BA. The kinetics of hexacelsian BAS formation are greatly enhanced when BS 2 is made separately and fired with Al 2 O 3 to yield BAS.