Wettability of molten Na2CO3–K2CO3 on coal fly ash ceramic substrates with expanded graphite

Abstract

The wettability of materials influences highly the stability of form-stable phase change materials (FSPCMs). In this study, the wetting behavior of Na2CO3–K2CO3 on the coal fly ash (CFA) ceramic substrates with different expanded graphite (EG) contents was studied through contact angle measurements at 707 °C. The influences of surface microstructure of substrates, adhesion of molten salt to the substrates, and salt infiltration during the contact angle measurements were taken into consideration. The results found that the eutectic carbonate salt on the CFA ceramic substrates generally showed a good wettability, which can be influenced by the surface microstructure of the CFA ceramic substrates and the adhesion of molten salt to the substrates. Due to the presence of salt infiltration phenomenon during the experiments, the measured contact angle should be modified to eliminate the infiltration effect. Increasing the EG content in the substrates caused a decrease of surface roughness of substrate and salt infiltration, resulting in the evident increase of modified contact angle. Besides, using high forming pressure of the prepared substrate also decreased the surface cracks and surface roughness, and increased the modified contact angle.