Solid-State Reaction Mechanism and Deliquescence Phenomenon of K0.5Na0.5Nb0.7Al0.3O3 Ceramic

Abstract

Development of (K,Na)NbO3-based ceramics has attracted much attention in recent decades. In this work, K0.5Na0.5Nb0.7Al0.3O3 ceramic was prepared using conventional solid-state processing. A deliquescence phenomenon was observed when the specimen was exposed to moist atmosphere. The reaction mechanism and cause of deliquescence were investigated using x-ray diffraction analysis, scanning electron microscopy, energy-dispersive spectrometry, electron microprobe analysis, inductively coupled plasma mass spectrometry, and thermogravimetric/differential scanning calorimetric analysis. The results revealed interactions mainly amongst the raw materials K2CO3, Na2CO3, and Nb2O5 as well as K2CO3, Na2CO3, and Al2O3, which can influence the sintering behavior of the mixture. (K,Na)NbO3 and (K,Na)AlO2 were present in the sintered K0.5Na0.5Nb0.7Al0.3O3 ceramic, with the latter leading to deliquescence. During the sintering process, Al2O3 reacts with alkali oxides (Na2O and K2O), which are the decomposition products of carbonates, to form (K,Na)AlO2. In addition, Al2O3 is more likely to react with K2O compared with Na2O.