Reaction Behavior of High-purity Mullite Container with Melted Solar Salts

High-purity and good sinterable mullite powder (3Al2O3･2SiO2) was synthesized by a sol-gel process to prepare a high-purity mullite crucible.The densified mullite crucible was fabricated by slip casting with the powder followed by sintering at 1600 ℃.Solar salt was put into the mullite crucible and then fired at the temperature of 1000 ℃ and 1250 ℃ with 4~24 h holding time.The inside surface of the crucible which was in contacted with the melted salt was analyzed using XRD, SEM and EDS.Corrosion of the crucible by the melted solar salt was insignificant.The reacted surface area displayed mullite, spinel and forsterite crystal phases, with a very thin reactant layer of 10~20 m.The EDAX result of the very thin surface layer showed a relatively higher Na and Mg contents in the sample heat-treated at 1250 ℃ for 4 h compared to the sample heat-treated at 1000 ℃ for 24 h.EDS mapping showed that the reactant layer are mainly consisted of MgO, SiO2 and Al2O3.From these results, it can be speculated that mullite is attacked by the Mg component in the solar salt, rather than Na and S. Finally, the very thin reactant layer of the mullite surface at high temperature means that a pure mullite crucible can be used as a commercial ceramic container for the firing of solar salt.