DETAILED DESCRIPTION The use of flexible pre-sintered electrolyte or other structural layers for the fabrication of fuel cell structures in accordance with the invention offers a number of processing and performance advantages over co-sintering approaches to fuel cell fabrication.
Particularly important is the ability to prefabricate and select sintered electrolyte sheet at thicknesses easily adjustable within a range from less than 4 micrometers to 45 micrometers or more, and in compositions which can be optimized for each particular cell design.
As noted in U.
S.
Pat.
No.
5,089,455, expressly incorporated herein by reference, zirconia and a wide variety of related stabilized zirconia compositions, as well as many other oxide and non-oxide ceramic compositions, can be successfully sintered to thin flexible sheet or tape in accordance with the methods therein described.
Particular examples of ceramics which can be so processed include, in addition to zirconia and stabilized or partially stabilized zirconia, various oxides selected from the group consisting of hafnia, alumina, .
beta.
-alumina, .
beta.
"-alumina, silica, titania, mullite, spinel, chromium oxide, zircon, sialon, and nasicon, as well as non-oxides including silicon or titanium carbides and/or nitrides, zirconium carbide, and titanium diboride.
Particularly preferred for fuel cell electrolytes are zirconia and the stabilized zirconias, most particularly stabilized zirconias containing at least one stabilizer selected from the group consisting of yttria (Y.
sub.
2 O.
sub.
3) and calcia (CaO).
However, a variety of other stabilizers, including any of the well-known alkaline earth oxide and rare earth oxide stabilizers, may additionally or alternatively be present.
The fabrication of flat thin sheets of ceramic is best achieved in accordance with the preferred method of the aforementioned patent, i.
e.
, by drawing continuous lengths of green sheet through a sintering furnace.
Conventional sheet sintering methods, involving the firing of discrete green sheets disposed on setter plates or setter sand, can produce sheet defects such as sheet curling or sheet texturing, due to non-uniform static or dynamic frictional forces arising between the sheet and the support during sintering
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