High temperature insulation utilizing zirconia-hafnia
View Patent ↗A ceramic insulating composition including monoclinic zirconia-hafnia. The zirconia-hafnia may be used as a filler powder ( 14 ) in a ceramic composition ( 10 ), or it may be used as a protective overlayer ( 50 ). The zirconia-hafnia ( 24 ) may be combined with alumina ( 22 ) to achieve a desired elastic modulus. The portion of hafnia contained in the zirconia-hafnia is selected to provide a predetermined phase transition temperature to minimize undesired phase changes during high temperature use of the material.
1. A ceramic composition comprising:
a plurality of oxide shapes;
a filler powder comprising particles of zirconia-hafnia; and
a binder material partially filling gaps between the oxide shapes and the filler powder;
wherein the filler powder particles comprise an average size of at least 30 microns and exhibit micro-cracks contained within the particles and not propagated into the binder material.
2. The composition of claim 1 , wherein the portion of hafnia in the zirconia-hafnia is in the range of 50–95 mol %.
3. The composition of claim 1 , wherein the portion of hafnia in the zirconia-hafnia is in the range of 60–75 mol %.
4. The composition of claim 1 , wherein the portion of hafnia in the zirconia-hafnia is at least 20 mol % and less than 100 mol %.
5. The composition of claim 1 , wherein the filler powder comprises composite particles each comprising zirconia-hafnia and alumina.
6. The composition of claim 5 , wherein the portion of alumina in the composite particles is in the range of 20–50 mol %.
7. The composition of claim 1 , wherein the filler powder comprises particles having an average size range of 30–50 microns.
8. The composition of claim 1 , further comprising:
the oxide shapes comprising hollow mullite spheres;
the filler powder comprising composite particles comprising zirconia-hafnia and alumina; and
the binder material comprising alumina.
9. The composition of claim 1 disposed on an oxide-oxide ceramic matrix composite substrate material.
10. The composition of claim 9 , wherein the portion of hafnia in the zirconia-hafnia is selected to limit a phase transformation of the zirconia-hafnia from a monoclinic phase to a tetragonal phase to occur throughout no more than 20% of a thickness of the material remote from the substrate material at a predetermined use temperature.