METHOD OF MANUFACTURING POROUS SINTERED REACTION-BONDED SILICON NITRIDE CERAMICS FROM GRANULAR Si MIXTURE POWDER AND POROUS SINTERED REACTION-BONDED SILICON NITRIDE CERAMICS MANUFACTURED THEREBY
Disclosed is a porous sintered reaction-bonded silicon nitride ceramic, which includes an array of sintered granules having fine pore channels in the sintered granules and coarse pore channels formed between the sintered granules, and in which the pore channel size is controlled so that both coarse pores and fine pores are formed together in the ceramic, thus simultaneously enhancing air permeability and capturing efficiency. A method of manufacturing the porous sintered reaction-bonded silicon nitride ceramic is also provided.
1 . A porous sintered reaction-bonded silicon nitride ceramic, comprising an array of sintered granules having fine pore channels in the sintered granules and coarse pore channels formed between the sintered granules.
2 . The porous sintered reaction-bonded silicon nitride ceramic according to claim 1 , which exhibits a bimodal pore distribution having a first peak and a second peak having a pore size larger than that of the first peak, and the first peak is based on the fine pore channels and the second peak is based on the coarse pore channels.
3 . The porous sintered reaction-bonded silicon nitride ceramic according to claim 1 , wherein the pore size of the first peak falls in a range of less than 1 μm, and the pore size of the second peak falls in a range of 1 μm or more.
4 . The porous sintered reaction-bonded silicon nitride ceramic according to claim 1 , wherein the pore size of the first peak falls in a range of less than 1 μm, and the pore size of the second peak falls in a range of 5˜20 μm.
5 . The porous sintered reaction-bonded silicon nitride ceramic according to claim 1 , wherein an average diameter of the sintered granules falls in a range of 30˜150 μm.
6 . The porous sintered reaction-bonded silicon nitride ceramic according to claim 1 , wherein a maximum frequency diameter of the sintered granules falls in a range of 50˜150 μm.
7 . A method of manufacturing a porous sintered reaction-bonded silicon nitride ceramic, comprising:
granulating a material comprising silicon and a sintering additive for preparing a sintered silicon nitride from the silicon, thus obtaining material granules;
subjecting the material granules to pressureless compacting in a mold, thus producing a material compact; and
subjecting the material compact to reaction-bonding in a nitriding gas atmosphere and post-sintering in a nitrogen atmosphere.
8 . The method according to claim 7 , wherein the sintering additive comprises yttria and alumina.
9 . The method according to claim 7 , wherein the sintering additive is used in an amount of 2˜10 wt % based on complete nitridation of the silicon.
10 . The method according to claim 7 , wherein a maximum weight frequency of the granules falls in a range of 30˜150 μm.
11 . A method of manufacturing a porous sintered reaction-bonded silicon nitride ceramic, comprising:
granulating a material comprising silicon and a sintering additive for preparing a sintered silicon nitride from the W silicon, thus obtaining material granules;
pre-sintering the material granules in an inert atmosphere, thus obtaining pre-sintered granules;
subjecting the pre-sintered granules to pressing, thus producing a material compact; and
subjecting the material compact to reaction-bonding in a nitriding gas atmosphere and post-sintering in a nitrogen atmosphere.
12 . The method according to claim 11 , wherein the sintering additive comprises at least one of alkali earth metal oxides.
13 . The method according to claim 11 , wherein the post-sintering is performed at 1700˜1900° C.
14 . The method according to claim 11 , wherein the sintering additive is used in an amount of 2˜10 wt % based on complete nitridation of the silicon.
15 . The method according to claim 11 , wherein the pressing is performed at a pressure of 1˜20 MPa.
16 . A pre-sintered granular powder for sintered reaction-bonded silicon nitride ceramics, which is a spherical porous granular powder having open pores and comprising silicon and a sintering additive for high-temperature liquid phase sintering conducted after nitridation of the silicon, the sintering additive comprising yttria, alumina and a compound thereof, the granular powder having a yield strength of 1˜20 MPa.
17 . The pre-sintered granular powder according to claim 16 , wherein the yield strength is 5 MPa or more.
18 . The pre-sintered granular powder according to claim 16 , wherein the granular powder has a flowability of 0.2˜0.5 g/sec.
19 . A compact for sintered reaction-bonded silicon nitride ceramics, which is a compact of spherical porous granules having fine pore channels and comprising silicon and a sintering additive for high-temperature liquid phase sintering conducted after nitridation of the silicon, the sintering additive comprising yttria, alumina and a compound thereof, the porous granules having a maximum weight frequency in a range of 30˜150 μm, the compact having a pore structure including fine pore channels in the porous granules and coarse pore channels between the porous granules.
20 . The compact according to claim 19 , wherein the coarse pore channels comprise coarse pores of 1 μm or more.