Method for making a SiC based ceramic porous body
View Patent ↗The invention relates to a process for fabrication of a porous refractory ceramic product made from SiC, by heat treatment and sintering at high temperature, starting from a fraction of fine particles of SiC and from a fraction of larger-sized particles of SiC, said process being characterized in that, in a step preliminary to the heat treatment and to the sintering at high temperature, the finest particles of SiC are agglomerated then, in a second step, the granules thus obtained are added to the SiC powder with particles of larger size. The invention also relates to a porous body made from recrystallized SiC in an essentially α form, in particular a particulate filter for automobile application, obtained by such a process.
1. The process for fabricating a sintered porous body, comprising:
a) mixing a first powder of SiC particles, whose median diameter is less than 20 μm, in a solvent and in the presence of a binder,
b) agglomerating said particles in order to form granules whose average size is in a range between 5 and 500 μm,
c) mixing the granules from b) with a second powder of SiC particles whose median diameter is greater than 5 μm and at least twice that of said first powder, in the presence of a solvent and of a binder, in proportions designed to allow shaping of the mixture,
d) shaping the mixture obtained during c) so as to obtain a hollow body,
e) eliminating the solvent and the binders from the body by thermal treatment and/or by use of microwaves, and
f) heat treating the body at a sintering temperature in a range between 1600° C. and 2400° C. in order to obtain a sintered porous body.
2. The process as claimed in claim 1 , in which the median diameter of the particles of said first SiC powder is less than 10 microns.
3. The process as claimed in claim 1 , in which the median diameter of the particles of the second SiC powder is in a range between 5 and 50 μm.
4. The process as claimed in claim 1 , in which the median diameter of the particles of the second SiC powder is at least five time greater than the median diameter of the SiC particles of said first powder.
5. The process as claimed in claim 1 , in which agglomerating is performed under conditions allowing granules whose size is in the range between 5 and 200 μm-to be obtained.
6. The process as claimed in claim 1 , in which, in the mixture of granules and particles, the fraction of granules represents between 95 and 5% by weight of the dry mixture.
7. The process as claimed in claim 1 , in which said first SiC powder is composed of several fractions which differ by the median diameter of the particles forming them, one of these fractions formed by particles whose median diameter is of the order of 1 to 20 microns and another fraction formed by particles of nanometric size.
8. The process as claimed in claim 1 , in which the binder in a) or c) is formed by a thermo-hardening resin, silicone, polyimide, polyester, a phenolic resin, PVA, optionally associated with a mineral or organo-mineral binder or an acrylic resin.
9. The process as claimed in claim 1 , in which a dispersing agent or a deflocculant is added to the binder in a) and/or c).
10. The process as claimed in claim 1 , in which agglomerating is implemented by atomization or by granulation.
11. The process as claimed in claim 1 , in which the shaping of the hollow body in d) is obtained by pressing, extrusion, vibration or by molding, or casting under pressure or otherwise, in a porous plaster or resin mold.
12. The process as claimed in claim 1 , wherein the solvent in a) is water.
13. The process as claimed in claim 1 , wherein the solvent in c) is water.
14. The process as claimed in claim 1 , wherein the median diameter of the particles of said first SiC powder is less than 5 microns.
15. The process as claimed in claim 1 , wherein the median diameter of the particles of said first SiC powder is less than 1 micron.
16. The process as claimed in claim 1 , in which the median diameter of the particles of the second SiC powder is in a range between 5 and 20 μm.
17. The process as claimed in claim 1 , in which the median diameter of the particles of the second SiC powder is at least ten times greater than the median diameter of the SiC particles of said first powder.
18. The process as claimed in claim 1 , in which agglomerating is performed under conditions allowing granules whose size is in the range between 10 and 50 μm to be obtained.
19. The process as claimed in claim 1 , in which, in the mixture of granules and particles, the fraction of granules represents between 90 and 10% by weight of the dry mixture.