Crystallization behavior of calcium–magnesium–alumina–silicate coupled with NaCl/Na2SO4

Abstract

Promoting molten calcium–magnesium–alumina–silicate (CMAS) crystallization can highly reduce the melt penetration into thermal barrier coatings (TBCs), which alleviates its corrosion to TBCs. In marine environments, many salts are coupled with CMAS. In this study, we investigated the crystallization behavior of CMAS + NaCl/NaSO₄, and pointed out its influence on the corrosion behavior of TBCs. At 1200 ℃, CMAS + NaCl was crystalized into CaMgSi₂O₆, CaSiO₃ and CaAl₂Si₂O₈, while the crystallization products of CMAS + NaSO₄ depended on NaSO₄ content, i.e., 4 wt.% and 10 wt.% NaSO₄ addition leading to CaAl₂Si₂O₈ and Ca₂Al(AlSiO₇) phases, respectively, in addition to CaMgSi₂O₆ and CaSiO₃. At 1100 ℃, CMAS + NaSO₄ crystalized, while CMAS + NaCl had no crystallization. At lower temperatures, both NaCl and NaSO₄ additions could suppress CMAS crystallization. It reveals that CMAS coupled with molten salt is hard to crystallize, which is detrimental to corrosion protection.