Entwicklung von Submikron - Pulver-Suspensionen zur Herstellung ...

Abstract
Fuel cells for the direct conversion of chemical into electrical energy are under development
worldwide . Solid oxide fuel cells (SOFCs) promise to provide the highest efficiencies . They
are being developed for stationary and mobile applications . For the planar cell concept of
Research Centre Jülich the oxygen-ion-conducting electrolyte of yttrium-stabilized Zr0 2
(8YSZ) is deposited onto the supporting anode substrate by vacuum slip casting (VSC) .
The required gas tightness of the 5 to 10 bum thick electrolyte film is obtained by sintering .
For the present work, suspensions are developed from submicron powders and investigated
for wet powder spraying (WPS) as a low-cost alternative to the VSC process .
For this purpose, fine 8YSZ powders were produced by a precipitation process, characterized
and tested for their applicability . Spray suspensions are developed from commercially
available powders by dispersann in ethanol and water with additives . The amounts of additives
are optimized by viscosity and zeta-potential measurements and by determining the particle
size characterized by the dso value . In addition, a finely dispersed commercial suspension was
used . Layer preparation an SOFC anode substrates was achieved by two different spaying
systems, a spray head and an airbrush gun . The sintered specimens were examined by optical
and scanning electron microscopy and subjected to a helium leakage test to determine their
gas tightness .
It was found that dense electrolyte films of 5 bum thickness an anode substrates can be
achieved by the airbrush technique with ethanol suspensions, to which 1 .5 % dispersant and
0 .5 % binder are added, involving short spray times and significantly shortened sintering
times compared to the VSC process . Calcining of the starting powders as performed for the
VSC process is no longer required . Helium leakage rates of the order of VSC specimens can
already be achieved after one-hour sintering for a two-layer system of commercial suspension
and optimally adjusted ethanol suspension .
Thin electrolyte films can be produced by wet powder spraying, processing selectively
adjusted suspensions . Optimized processing (e .g . short sintering times) reduces costs and
shortens production times .