Fused powder of yttria-stabilised zirconia
The present invention relates to a powder of molten grains of yttria-stabilized zirconia, said grains having the following chemical analysis, in weight percent on the basis of the oxides: ZrO 2 +HfO 2 : remainder up to 100%; 11.8%≦Y 2 O 3 ≦18.6%; 0.07%≦Al 2 O 3 ≦1.8%; TiO 2 ≦0.6%, provided that 0.5<Al 2 O 3 0.3%≦TiO 2 if 0.6%<Al 2 O 3 ; and other oxides: ≦2.0%.
1. A powder formed of fused grains of yttria-stabilized zirconia, said grains exhibiting the following chemical analysis, as percentage by weight on the basis of the oxides:
ZrO 2 +HfO 2 : remainder to 100%;
11.8%≦Y 2 O 3 ≦18.6%;
0.07%≦Al 2 O 3 ≦1.8%;
TiO 2 ≦0.6%, provided that 0.5×Al 2 O 3 −0.3%≦TiO 2 if 0.6%<Al 2 O 3 ;
other oxides:
and said grains having a minimum size D 10 of greater than 3 μm.
2. The powder formed of fused grains as claimed in claim 1 , in which:
the Y 2 O 3 content is greater than 12.7%, and less than 17.8%; and/or
the Al 2 O 3 content is less than 1.5%; and/or
the TiO 2 content is less than 0.4% and greater than 0.01%; and/or
the content of “other oxides” is less than 1%.
3. The powder formed of fused grains as claimed in claim 1 , in which:
the Y 2 O 3 content is greater than 13.5% and less than 16.9%; and/or
the Al 2 O 3 content is less than 0.9%; and/or
the TiO 2 content is less than 0.3% and greater than 0.1%;
the content of “other oxides” is less than 0.5%.
4. The powder formed of fused grains as claimed in claim 1 , in which:
the Al 2 O 3 content is less than 0.5% and greater than 0.1%; and/or
the TiO 2 content is less than 0.2% and greater than 0.1%; and/or
the content of “other oxides” is less than 0.2%.
5. The powder formed of fused grains as claimed in claim 1 , in which the 90 percentile, D90, of the grains of the powder is less than 200 μm.
6. The powder formed of fused grains as claimed in claim 1 , in which more than 40% of the grains of the powder, as percentage by number, exhibit an aspect ratio R of greater than 1.5, the aspect ratio of the grain being the ratio L/W between the length L and the width W of said grain.
7. The powder formed of fused grains as claimed in claim 6 , in which more than 70% of the grains of the powder, as percentage by number, exhibit an aspect ratio R of greater than 1.5.
8. The powder formed of fused grains as claimed in claim 1 , wherein a grain exhibiting an aspect ratio R, the aspect ratio of the grain being the ratio L/W between the length L and the width W of said grain, the aspect ratios of the grains of the powder being distributed in a distribution, the distribution of the aspect ratio R being such that:
less than 90% of the grains of the powder exhibit an aspect ratio R of greater than 1.5, and/or
more than 10% and less than 60% of the grains of the powder exhibit an aspect ratio R of greater than 2, and/or
more than 5% and less than 40% of the grains of the powder exhibit an aspect ratio R of greater than 2.5, and/or
more than 2% and less than 20% of the grains of the powder exhibit an aspect ratio R of greater than 3, the percentages being percentages by number.
9. The powder formed of fused grains as claimed in claim 1 , wherein a grain exhibiting an aspect ratio R, the aspect ratio of the grain being the ratio L/W between the length L and the width W of said grain, the aspect ratios of the grains of the powder being distributed in a distribution, the distribution of the aspect ratio R being such that:
less than 80% of the grains of the powder exhibit an aspect ratio R of greater than 1.5, and/or
more than 20% and less than 40% of the grains of the powder exhibit an aspect ratio R of greater than 2, and/or
more than 10% and less than 20% of the grains of the powder exhibit an aspect ratio R of greater than 2.5, and/or
more than 5% and less than 10% of the grains of the powder exhibit an aspect ratio R of greater than 3, the percentages being percentages by number.
10. A sintered cermet obtained by sintering a feedstock comprising the powder as claimed in claim 1 .
11. An electrode comprising the sintered cermet as claimed in claim 10 .
12. A process for the manufacture of the powder as claimed in claim 1 , comprising the following successive stages:
a) mixing particulate starting materials contributing ZrO 2 , Y 2 O 3 , Al 2 O 3 , and optionally TiO 2 , and/or one or more precursors of these oxides, in order to form an appropriate feedstock so that, on conclusion of stage c), the product exhibits a composition in accordance with that of the grains of the powder as claimed in claim 1 ,
b) melting the feedstock until a molten material is obtained,
c) cooling until said molten material has completely solidified, so as to obtain a fused product,
d) optionally, grinding said fused product.
13. A process for the manufacture of a cermet, comprising the following successive stages:
A) preparing a particulate feedstock comprising (i) a powder according to claim 1 and (ii) particles of nickel oxide or of cobalt oxide and/or one or more precursors of these oxides;
B) shaping the particulate feedstock prepared in stage a), so as to form a preform;
C) sintering said preform; and
D) reducing the nickel oxide to give nickel or the cobalt oxide to give cobalt,
wherein, in stage a), the feedstock comprises between 30% and 70% of nickel oxide NiO or cobalt oxide CoO particles, as percentage by weight of the feedstock, and/or an equivalent amount of one or more precursors of these oxides.
14. A powder formed of fused grains of yttria-stabilized zirconia, said grains exhibiting the following chemical analysis, as percentage by weight on the basis of the oxides:
ZrO 2 +HfO 2 : remainder to 100%;
11.8%≦Y 2 O 3 ≦18.6%;
0.07%≦Al 2 O 3 ≦1.8%;
0.01%<TiO 2 ≦0.6%, provided that 0.5×Al 2 O 3 −0.3%≦TiO 2 if 0.6%<Al 2 O 3 ;
other oxides: ≦2.0%.