Interaction of Low‐Expansion NZP Ceramics with Na2SO4 at 1000°C

The interaction between several low‐expansion NZP materials and Na 2 SO 4 at 1000°C in pure O 2 was studied. Ba 1.25 Zr 4 P 5.5 Si 0.5 O 24 experienced extensive cracking and delamination upon reaction with Na 2 SO 4 . On the other hand, Ca 0.5 Sr 0.5 Zr 4 P 6 O 24 remained intact in terms of visual appearance and had no significant weight loss or gain. However, the ion exchange between Na + ions and Ca +2 ions was observed to be sufficiently rapid to allow the penetration of the Na + ions into the test specimens in 100 h. The segregation of Ca to the specimen surface was observed due to the ion exchange. Ca 0.6 Mg 0.4 Zr 4 P 6 O 24 was also tested, but its stability could not be properly assessed because the as‐received specimens contained a significant amount of MgZr 4 P 6 O 24 as an impurity phase.