Dual composites consisting of an oxide conducting ceramic and molten salts have been given attention in recent years as electrolytes in intermediate temperature fuel cells and as highly selective membranes for CO₂ separation operating at high temperatures. Their performance, preparation procedures and operating mechanisms have been addressed. [1] Our contribution to the subject has been directed to providing micron sized porosity stabilized zirconia ceramics, with size homogeneity and low tortuosity in the porosity as well as in the ceramic, and using these ceramics to investigate CO₂ membrane performance with the aim to investigate the operating mechanisms. [2] These porous ceramics result from the acid etching of MgO out of directionally solidified eutectic MgO- Mg stabilized Zirconia composites, and show high CO₂ permeability.

The procedures to fabricate the solidified composite with the desired microstructure have to allow coupled solidification of a eutectic melting at 2100 °C with relatively large solidification gradients. Laser melting is one such procedure which allows both. Usually, only small volumes of material can be molten at a time, resulting in solidified pieces with at least one dimension in the mm range, which result in thin rods, solidified coatings or layer-by-layer manufactured composites. [3].

We report here on the porous MgO stabilized Zirconia plates prepared by laser melting of a preheated ceramic, their structure, microstructure and ion transport characterization. Plates with microstructural size between 0.4 and 4 microns were obtained. The zirconia phase is mainly cubic, with less than around 10 % volume of tetragonal phase and traces of monoclinic phase, consequence of some solid state segregation of phases at the processing temperatures. It shows an ionic conductivity up to one order of magnitude larger than the one of the material solidified by the laser floating zone (LFZ) method, which should be beneficial for the performance of the CO₂ separation membrane.

MgO etching in these composites is as effective as in the LFZ produced material, with 23 % weight loss and around 30 % volume porosity. More important, even if the macroscopic alignment of the microstructure is not perfect, corresponding to a position-dependent solidification direction, the ionic conductivity of the molten-carbonate infiltrated plates is similar to that of the molten carbonates above the melting point.