Porous ceramic materials for investment casting

Abstract

Methods and compositions for forming porous ceramic articles are provided. The method is forming a composition including liquid siloxanes, ceramic particles, a catalyst, and a pore-former; shaping the composition; curing the composition to form a green body; volatilizing the pore-former before or after curing the composition; and firing the green body. The pore-former is a silicon-bearing agent with an average molecular weight under 1300 grams per mole, or a molecule with a molecular weight under 1,000 grams per mole and a freezing point between −40° C. and 25° C. that is soluble in the liquid. The composition comprises liquid siloxanes, ceramic particles, a catalyst, and a pore-former, which is an agent with an average molecular weight under 1300 grams per mole or a molecule with a molecular mass under 1,000 grams per mole and a freezing point between −40° C. and 25° C. that is soluble in the liquid.

1 . A method for creating a porous ceramic structure comprising:
 creating a composition, wherein the composition comprises a liquid, a plurality of particles disposed within the liquid, a catalyst material disposed within the liquid, and a pore-forming agent disposed within the liquid;   wherein the liquid comprises one or more siloxane species;   the plurality of particles comprises a ceramic material;   the pore-forming agent comprises an agent that is substantially inert with respect to the liquid, further comprising (a) a silicon-bearing agent that has a number average molecular weight less than about 1,300 grams per mole, or (b) a molecule having a molecular mass less than approximately 1,000 grams per mole and a freezing point between −40° C. and 25° C. that is soluble in the liquid, or any combination of the two;   disposing the composition in any desired shape;   volatilizing at least a portion of the pore-forming agent;   curing the composition to form a green body; and   firing the green body.   
     
     
         2 . The method of  claim 1 , wherein the one or more siloxane species of the liquid comprise an alkenyl functional group, a hydride functional group, or any combination of the two. 
     
     
         3 . The method of  claim 1 , wherein the pore-forming agent comprises cyclohexane, benzene, p-xylene, o-xylene, cyclooctane, cyclononane, bicyclohexyl, tridecane, dodecane, 3,4-dichlorotoluene, cycloundecane, cycloheptane, 2,2,3,3-tetramethylpentane, and 2,2,5,5-tetramethylhexane, or combinations including one or more of these. 
     
     
         4 . The method of  claim 3 , wherein volatilizing at least a portion of the pore-forming agent occurs before curing the composition to form said green body and comprises lowering a temperature of the composition to below the freezing point of the pore-forming agent, freezing at least a portion of the pore-forming agent to phase-separate said portion of the pore-forming agent from another component of the composition, and reducing atmospheric pressure to below a vapor pressure of the pore-forming agent but above a vapor pressure of another component of the composition at said temperature for a period of time sufficient to volatilize at least some of said portion of the pore-forming agent. 
     
     
         5 . The method of  claim 4  wherein a pore-forming agent is cyclohexane. 
     
     
         6 . The method of  claim 1 , wherein the pore-forming agent is a silicone-bearing agent comprising: decamethylcyclopentasiloxane; tetramethyltetraphenyltrisiloxane; phenyltrimethylsilane; tetra-n-butylsilane; p-tolyltrimethylsilane; methyltri-n-trioctylsilane; dimethyldiphenylsilane; methyltri-n-hexylsilane, hexamethyl disiloxane; octamethyl trisiloxane; decamethyl tetrasiloxane; dodecamethyl pentasiloxane; phenyl-tris(trimethylsiloxy)silane; methyl-tris(trimethylsiloxy)silane;
 3,3,3-trifluoropropyl-tris(trimethylsiloxy)silane; tetrakis(trimethylsiloxy)silane; or a compound of the formula (R 3 SiO) 3 SiR or (R 3 SiO) 4 Si wherein R is a monovalent hydrocarbon, a halocarbon, or a halogenated hydrocarbon, and with which the siloxane species of the liquid is not reactive; or a combination including one or more of these.   
     
     
         7 . The method of  claim 6 , wherein volatilizing at least a portion of the pore-forming agent comprises raising the temperature of said green body to above the cure temperature and up to the boiling point for said silicon-bearing agent for a period of time sufficient to volatilize said portion of the pore-forming agent before firing. 
     
     
         8 . The method of  claim 6  wherein curing the composition to form a green body comprises phase-separating at least a portion of the pore-forming agent from another component of the composition. 
     
     
         9 . The method of  claim 7 , wherein the silicon-bearing agent comprises 1,3,5-tris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane. 
     
     
         10 . The method of  claim 3 , wherein the pore-forming agent is present at a concentration of at least about 5 percent by volume of the entire composition. 
     
     
         11 . The method of  claim 3 , wherein the pore-forming agent is present in the composition at a concentration in a range from about 7 volume percent to about 35 volume percent of the entire composition. 
     
     
         12 . The method of  claim 6 , wherein the pore-forming agent is present at a concentration of at least about 5 percent by volume of the entire composition. 
     
     
         13 . The method of  claim 6  wherein the pore-forming agent is present in the composition at a concentration in a range from about 7 volume percent to about 35 volume percent of the entire composition. 
     
     
         14 . The method of  claim 1 , wherein the pore-forming agent comprises a mixture of components, wherein the components of the mixture have freezing points, boiling points, or vapor pressures at a given temperature that differ from each other. 
     
     
         15 . The method of  claim 14 , wherein at least one component of said mixture is said (a) silicon-bearing agent that has a number average molecular weight less than about 1,300 grams per mole and at least one component of said mixture is said (b) molecule having a molecular mass less than approximately 1,000 grams per mole and a freezing point between −40° C. and 25° C. that is soluble in the liquid. 
     
     
         16 . The method of  claim 1 , further comprising disposing the ceramic body within an investment casting mold, and solidifying molten metal within the investment casting mold. 
     
     
         17 . The method of  claim 1 , wherein disposing comprises injecting the material via a printer nozzle. 
     
     
         18 . The method of  claim 1 , wherein disposing comprises disposing a plurality of layers of the material in successive deposition actions. 
     
     
         19 . A composition comprising:
 a liquid that comprises one or more siloxane species;   a plurality of particles, comprising a ceramic material, disposed within the liquid;   a catalyst material disposed within the liquid; and   a pore-forming agent comprising an agent that is substantially inert with respect to the liquid, further comprising (a) a silicon-bearing agent that has a number average molecular weight less than about 1,300 grams per mole, or (b) a molecule having a molecular mass less than approximately 1,000 grams per mole and a freezing point between −40° C. and 25° C. that is soluble in the liquid, or any combination of the two.   
     
     
         20 . The composition of  claim 19 , wherein the pore-forming agent comprises cyclohexane, benzene, p-xylene, o-xylene, cyclooctane, cyclononane, bicyclohexyl, tridecane, dodecane, 3,4-dichlorotoluene, cycloundecane, cycloheptane, 2,2,3,3-tetramethylpentane, and 2,2,5,5-tetramethylhexane, or combinations including one or more of these. 
     
     
         21 . The composition of  claim 20 , wherein the pore-forming agent comprises cyclohexane. 
     
     
         22 . The method of  claim 19 , wherein the pore-forming agent is a silicone-bearing agent comprising decamethylcyclopentasiloxane; tetramethyltetraphenyltrisiloxane;
 phenyltrimethylsilane; tetra-n-butylsilane; p-tolyltrimethylsilane; methyltri-n-trioctylsilane; dimethyldiphenylsilane; methyltri-n-hexylsilane, hexamethyl disiloxane; octamethyl trisiloxane; decamethyl tetrasiloxane; dodecamethyl pentasiloxane; phenyl-tris(trimethylsiloxy)silane; methyl-tris(trimethylsiloxy)silane; 3,3,3-trifluoropropyl-tris(trimethylsiloxy)silane; tetrakis(trimethylsiloxy)silane; and a compound of the formula (R 3 SiO) 3 SiR or (R 3 SiO) 4 Si wherein R is a monovalent hydrocarbon, a halocarbon, or a halogenated hydrocarbon, and with which the siloxane species of the liquid is not reactive; or a combination including one or more of these.   
     
     
         23 . The method of  claim 22 , wherein the silicon-bearing agent comprises 1,3,5-tris(3,3,3-trifluoropropyl)trimethylcyclotrisiloxane. 
     
     
         24 . The composition of  claim 19 , wherein the pore-forming agent comprises a mixture of said molecules, wherein the freezing point, boiling point, or vapor pressure at a given temperature of one molecule of said mixture differs from that of another molecule of said mixture. 
     
     
         25 . The composition of  claim 19 , wherein the pore-forming agent is present at a concentration of at least about 5 percent by volume of the entire composition. 
     
     
         26 . The composition of  claim 19 , wherein the pore-forming agent is present in the composition at a concentration in a range from about 7 volume percent to about 35 volume percent of the entire composition. 
     
     
         27 . The composition of  claim 19 , wherein the one or more siloxane species of the liquid comprises an alkenyl functional group, a hydride functional group, or any combination of the two.