The multifarious aspects of the thermal conversion of Ba-exchanged zeolite A to monoclinic celsian

The thermal transformation of Ba-exchanged zeolite A into the monoclinic polymorph of Ba feldspar celsian (BaAl2Si2O8, a ceramic material of great technological interest) was found to be affected by a number of different parameter, such as the temperature and duration time of the thermal treatment, the forming pressure, the presence of the mineralizing cation Na+ and Li+, and Sr2+ doping. These facts were investigated in a long term study which is critically reviewed in this work, thus supplying the reader with an overall vision of this complex matter. Moreover, it is evidenced that the thermal transformation of Ba-exchanged zeolite A appears the most profitable and simple way to obtain the synthesis of the monoclinic polymorph of Ba feldspar celsian, which can be attained in few hours thermal treatments at 1000–1100 °C. The mechanisms on which these transformations are based and the sintering of monoclinic celsian powders obtained from Ba-exchanged zeolite A are discussed.