Low-Temperature Densification Sintering and Properties of Monoclinic-SrAl sub(2)Si sub(2)O sub(8) Ceramics

The dense monoclinic-SrAl sub(2)Si sub(2)O sub(8) ceramics have been prepared by a two-step sintering process at a sintering temperature of 1173 K (900 degree C). Firstly, the pre-sintered monoclinic-SrAl sub(2)Si sub(2)O sub(8) powders containing small SiO sub(2).Al sub(2)O sub(3) crystal phases were obtained by continuously sintering a powder mixture of SrCO sub(3) and kaolin at 1223 K (950 degree C) for 6 hours and 1673 K (1400 degree C) for 4 hours, respectively. Subsequently, by the combination of the pre-sintered ceramic powders with the composite flux agents, which are composed of a SrO.3B sub(2)O sub(3) flux agent and alpha -Al sub(2)O sub(3), the low-temperature densification sintering of the monoclinic-SrAl sub(2)Si sub(2)O sub(8) ceramics was accomplished at 1173 K (900 degree C). The low-temperature sintering behavior and microstructure evolvement of the monoclinic-SrAl sub(2)Si sub(2)O sub(8) ceramics have been investigated in terms of Al sub(2)O sub(3) in addition to the composite flux agents. It shows that due to the low-meting characteristics, the SrO.3B sub(2)O sub(3) flux agent can urge the dense microstructure formation of the monoclinic-SrAl sub(2)Si sub(2)O sub(8) ceramics and the re-crystallization of the grains via a liquid-phase sintering. The introduction of alpha -Al sub(2)O sub(3) to the SrO.3B sub(2)O sub(3) flux agent can apparently lead to more dense microstructures for the monoclinic-SrAl sub(2)Si sub(2)O sub(8) ceramics but also cause the re-precipitation of SiO sub(2).Al sub(2)O sub(3) compounds because of an excessive Al sub(2)O sub(3) content in the SrO.3B sub(2)O sub(3) flux agent.