Composite material, heat-absorbing component, and method for producing the composite material

Abstract

In a known composite material with a fused silica matrix there are regions of silicon-containing phase embedded. In order to provide a composite material which is suitable for producing components for use in high-temperature processes for heat treatment even when exacting requirements are imposed on impermeability to gas and on purity, it is proposed in accordance with the invention that the composite material be impervious to gas, have a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm 3 , and at a temperature of 1000° C. have a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 μm.

1 . A composite material comprising:
 a matrix of fused silica in which regions of a phase containing silicon in elemental form have been embedded,   wherein the composite material is impervious to gas, has a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm 3 , and, at a temperature of 1000° C., has a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 μm.   
     
     
         2 . The composite material according to  claim 1 , wherein the matrix has pores therein with a maximum pore dimension of less than 10 μm. 
     
     
         3 . The composite material according to  claim 1 , wherein the phase containing silicon in elemental form is present in a weight fraction that is not more than 5%. 
     
     
         4 . The composite material according to  claim 1 , wherein the matrix consists essentially of fused silica having a hydroxyl group content of not more than 30 ppm by weight. 
     
     
         5 . The composite material according to  claim 1 ,
 wherein the phase containing silicon in elemental form consists essentially of silicon having a metallic purity of at least 99.99% and wherein the matrix possesses a chemical purity of at least 99.99% SiO 2  and a cristobalite content of not more than 1%.   
     
     
         6 . The composite material according to  claim 1 ,
 wherein the phase containing silicon in elemental form exhibits non-spherical morphology with maximum dimensions of on average less than 20 μm.   
     
     
         7 . A heat-absorbing component, comprising:
 at least one surface formed from a composite material comprising a matrix of fused silica in which regions of a phase containing silicon in elemental form have been embedded,   said matrix being impervious to gas, having a closed porosity of less than 0.5% and a specific density of at least 2.19 g/cm 3 , and, at a temperature of 1000° C., having a spectral emissivity of at least 0.7 for wavelengths between 2 and 8 μm.   
     
     
         8 . The component according to  claim 7 , wherein the component is a reactor, fitting, or component configured to be used in an oxidizing or heat-treating operation, in epitaxy, or in chemical vapour deposition. 
     
     
         9 . The component according to  claim 7 , wherein the component is a plate, ring, flange, dome, crucible, or solid or hollow cylinder. 
     
     
         10 . A method for producing a composite material, said method comprising:
 forming a porous shaped body from a powder mixture comprising amorphous fused silica powder and a powder containing silicon in elemental form and/or from a mixed powder comprising amorphous fused silica, interspersed with a phase containing silicon in elemental form and,   compacting the shaped body so as to produce the composite material,   wherein the forming of the shaped body comprises a slipcasting process comprising producing a suspension that comprises the powder mixture and/or the mixed powder in a liquid, consolidating the suspension by removal of liquid so as to form a green body, and forming the shaped body from the green body by drying.   
     
     
         11 . The method according to  claim 10 ,
 wherein the suspension comprises a powder mixture of fused silica powder and powder containing silicon in elemental form, and   wherein the powder containing silicon in elemental form consists essentially of silicon having a metallic purity of at least 99.99%, and has a particle size distribution with a D 97  of between 1 to 20 μm and a D 10  of 2 μm, and the powder containing silicon in elemental form constituting a volume fraction in the powder mixture of not more than 5%.   
     
     
         12 . The method according to  claim 11 , wherein the powder containing silicon in elemental form is mixed into the liquid comprising the fused silica powder. 
     
     
         13 . The method according to  claim 10 ,
 wherein the fused silica powder comprises amorphous particles having particle sizes not more than 200 μm, and   wherein SiO 2  particles having particle sizes between 1 μm and 60 μm make up a largest volume fraction of the fused silica powder.   
     
     
         14 . The method according to  claim 13 , wherein the fused silica powder particles have a particle size distribution with a D 50  of less than 50 μm, and have an SiO 2  content of at least 99.99% by weight. 
     
     
         15 . The method according to  claim 10 , wherein the fused silica powder particles are produced by wet grinding of initial granular SiO 2 . 
     
     
         16 . The method according to  claim 10 , wherein the shaped body is heated to a sintering temperature below the melting temperature of silicon. 
     
     
         17 . The composite material according to  claim 1 ,
 wherein the phase containing silicon in elemental form exhibits non-spherical morphology with maximum dimensions of on average between 3 and 20 μm.   
     
     
         18 . The method according to  claim 13 ,
 wherein the amorphous particles have particle sizes not more than 100 μm.   
     
     
         19 . The method according to  claim 13 , wherein the fused silica powder particles have a particle size distribution which is characterized by a D 50  of less than 40 μm, and have an SiO 2  content of at least 99.99% by weight. 
     
     
         20 . The method according to  claim 11 ,
 wherein the D 97  of the particle size distribution is greater than 3 μm.