Sintering of Mixed-Conducting Composites for Hydrogen Membranes from Nanoscale Co-Synthesized Powders
The potential for highly selective, nongalvanic permeation of hydrogen through dense mixed conducting composites at elevated temperatures makes them attractive as hydrogen separation membranes. The glycine-nitrate combustion synthesis technique has been used to co-synthesize a cation-doped barium cerate protonic conducting phase together with a metallic nickel electronic conducting phase (15-35 vol% Ni). Co-synthesis of these phases results in an intimately mixed powder with particle sizes on the order of 10 nm. DTA/TGA of all as-synthesized compositions determined that a calcination temperature of 1000°C was required for full reaction of the cerate components. DTA/TGA and sintering shrinkage dilatometry were performed on calcined powders to determine that a sintering temperature of 1250°C would be adequate for achieving >90% relative density in all compositions. Bars of the material containing 25 vol% Ni were reduced at three different points in the heat treatment process (e.g., before, during, or after sintering). It was determined that there was less porosity in the sample reduced during sintering than any other. It was also seen on SEM that the primary grain size, regardless of when reduction occurred compared to sintering of the material, is less than 5 8m.
T. Chandra, K. Tsuzaki, M. Militzer , C. Ravindran
N. L. Canfield et al., "Sintering of Mixed-Conducting Composites for Hydrogen Membranes from Nanoscale Co-Synthesized Powders", Materials Science Forum, Vols. 539-543, pp. 1415-1420, 2007