Dynamic wetting of porous Ni substrate under MCFC conditions

Abstract

The dynamic contact angle of molten carbonate in first contact with porous Ni was measured as a function of porosity and thickness of the substrate, and of the amount of carbonate as a fraction of the empty pore volume available (“degree-of-filling”). The spreading of molten carbonate on the outer surface, and its penetration inside the porous Ni substrate were observed separately, and the time to complete absorption of a known mass of melt was measured under different conditions of substrate porosity, thickness and degree-of-filling. The average absorption rate and the average linear velocity over the initial void cross-section were determined and correlated with substrate characteristics. A straightforward quasi-linear correlation with control variables was found. However, although initial filling is capillary-force controlled, later stages of absorption appear slowed down significantly by viscous and inertial effects. This helps to understand why capillary equilibrium models do not accurately predict electrolyte redistribution in long-term performance. Moreover, post-test analysis indicates that on first contact of porous Ni substrates with molten carbonate, sintering of Ni particles occurs even at the relatively low temperature of 580 °C. Models for initial filling need to account for this initial accelerated sintering. The result of this work may be used to optimize the infiltration process of electrolyte into the porous MCFC electrodes.