Porous silicon carbide
A porous refractory product includes a matrix of sintered silicon carbide having a porosity of about 45% to about 65%. The matrix is formed by heating in a noble gas atmosphere a cast preform including a mixture of alpha-silicon carbide and boron carbide each having a particle size of less than about 1 micron. The heating causes the formation of gaseous SiO within the silicon carbide matrix, which, in turn, forms pores having an average size of less than about 1 micron. The porous refractory products herein are suitable for use in a variety of applications including for use in high temperature particulate filtering applications.
1. A method of making a permeable refractory product having a porosity of about 45% to about 65%, comprising forming by spray drying and heating in a noble gas atmosphere a mixture comprising alpha-silicon carbide and boron carbide each having a particle size of less than about 1 micron, the silicon carbide particles forming gaseous SiO within the silicon carbide matrix to form pores having an average size of less than about 1 micron.
2. The method of claim 1 , wherein the heating is carried out at a temperature of about 2000 to about 2200° C. for such a time as required to achieve an average porosity of about 45% to about 65% by volume.
3. The method of claim 1 , wherein the heating is carried out at about 2100 to about 2200° C.
4. The method of claim 1 wherein the sintering is carried out at about 2125 to about 2175° C.
5. A method of making a porous silicon carbide article comprising:
a. combining to form a mixture
i. 100 parts by weight of α-silicon carbide having a particle size of 0.5 microns to 10 microns;
ii. 0.2-1 parts by weight of boron carbide; and
iii. 1-10 parts by weight of an organic vehicle;
b. milling the mixture for homogeneity and particle size reduction such that the carbide particle sizes (D 50 ) are less than about 1 micron;
c. forming the mixture into a desired shape and
d. sintering the formed mixture in a noble gas atmosphere at a temperature of about 2000 to about 2200° C. for such a time as required to achieve an average porosity of about 45% to about 65% by volume.
6. The method of claim 5 , wherein the sintering is carried out at about 2100 to about 2200° C.
7. The method of claim 6 , wherein the sintering is carried out at about 2125 to about 2175° C.
8. The method of claim 6 , wherein forming the mixture into a desired shape comprises:
a. combining the silicon carbide and boron carbide with an organic vehicle to form a green body, wherein the binder comprises a dispersant and a solvent, and
b. forming a slurry having a viscosity of about 200 to about 700 cps, and a solids loading of about 45 to about 70 wt %.
9. A method of making a porous silicon carbide article comprising:
a. combining to form a mixture that is devoid of free carbon and free silicon
i. 100 parts by weight of α-silicon carbide having a particle size of 0.5 microns to 10 microns;
ii. 0.2-1 parts by weight of boron carbide; and
iii. 1-10 parts by weight of an organic vehicle;
b. milling the mixture for homogeneity and particle size reduction such that the carbide particle sizes (D 50 ) are less than about 1 micron;
c. forming the mixture into a desired shape and
d. sintering the formed mixture in a noble gas atmosphere at a temperature of about 2000 to about 2200° C. for such a time as required to achieve an average porosity of about 30% to about 70%.
10. The method of claim 9 , wherein the sintering is carried out at about 2100to about 2200° C.
11. The method of claim 9 , wherein the sintering is carried out at about 2125 to about 2175° C.
12. The method of claim 9 , wherein forming the mixture into a desired shape comprises
a. combining the silicon carbide and boron carbide with an organic vehicle to form a green body, wherein the binder comprises a dispersant and a solvent selected from the group consisting of PVA, PEG, and combinations thereof,
b. forming a slip from the green body, the slip having a viscosity of about 200 to about 700 cps, and a solids loading of about 45 to about 75 wt %.