Process for the infiltration of porous carbon composites
A process form producing ceramic composites comprising metal carbides, which comprises the steps production of a porous carbon-containing intermediate body, infiltration of the intermediate body with the melt of a carbon-forming metal, reaction of at least part of the carbon of the intermediate body with the carbide-forming metal to form a metal carbide, with at least part of the carbide-formed metal being supplied via at least one wick made of porous carbon material having pore channels and the wick being produced by carbonization of wood materials or of essentially unidirectionally reinforced CFRP, such wicks and their use in the abovementioned process.
1. A process for producing ceramic composites comprising metal carbides, which comprises the following steps:
drying wood at a temperature of from 40° C. to 95° C.,
carbonizing the dried wood at a temperature of from 700° C. to 1500° C., to obtain a body having a density of from 0.1 g/cm 3 to 0.9 g/cm 3
forming a wick from the carbonized wood having a total porosity of from 40% to 90%, and an open porosity of from 15% to 60%, with mesopores in the carbonized wood running parallel to a longitudinal direction of the wick,
producing a porous carbon-containing green body by placing the green body on the wick so that pore channels in the wick impinge on the surface of the green body at an angle of from 0° to not more than 45° to the normal of the surface,
infiltrating the green body with the melt of a carbide-forming metal via the wick,
reacting at least part of the carbon of the green body with the carbide-forming metal to form a metal carbide,
wherein at least part of the carbide-forming metal is supplied via the wick.
2. The process as claimed in claim 1 , wherein the green body is placed directly on the wicks whose lower ends dip into a metal melt.
3. The process as claimed in claim 1 , wherein the porous carbon-containing green body used is a C/C composite.
4. The process as claimed in claim 1 , wherein the carbide-forming metal used is selected from the group consisting of silicon, iron, nickel, titanium, zirconium, vanadium, chromium, molybdenum, tungsten, boron and alloys of at least two of these elements.
5. The process as claimed in claim 3 , wherein at least one of the compounds selected from the group consisting of SiC, ZrC, TiC, TiSi x and MoSi x is formed in by the infiltration and reaction steps.
6. The process as claimed in claim 1 , wherein the wick is produced by the carbonisation from a wood material selected from the group consisting of natural wood, pressed wood, wood molding compositions and synthetic wood.
7. The process as claimed in claim 6 , wherein the natural wood is selected from the group consisting of balsa, pine, oak, maple, beech, ebony and bamboo.
8. A process for producing ceramic composites comprising metal carbides, which comprises the following steps
providing a CFRP body reinforced with unidirectionally aligned carbon fibers, with a proportion of fibers running transverse thereto to stabilize the material perpendicular to the unidirectional fibers,
carbonizing the CFRP body at a temperature in excess of 650° C. to form a wick consisting of a carbonized CFRP body reinforced with unidirectional carbon fibers having an open porosity of from 15% to 60%, and having pores forming continuous parallel channels with pore diameters of from 50 pm to 600 pm,
producing a porous carbon-containing green body by placing the green body on the wicks so that the pore channels in the wick impinge on the surface of the green body at an angle of from 0° to not more than 45° to the normal of the surface,
infiltrating the green body with the melt of a carbide-forming metal via the wick,
reacting at least part of the carbon of the green body with the carbide-forming metal to form a metal carbide, wherein at least part of the carbide-forming metal is supplied via the wick.
9. The process as claimed in claim 1 , wherein the wick material has an open porosity in the range from 21% to 44%.
10. The process as claimed in claim 8 , wherein the predominant proportion of the pore channels of the wick impinge on the green body at an angle in the range from 45° to 0° to the normal of the surface of the green body.