Patent Publication Number: US-2016229754-A1

Title: Method of producing a ceramic article, intermediate article and composition therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application No. 61/879,784, filed Sep. 19, 2013. 
    
    
     BACKGROUND 
     Ceramic structures, such as silicon carbide-containing structures, can be produced using any of various known ceramic processing techniques. One example structure includes a matrix of silicon carbide and fibers that are dispersed in the matrix. The silicon carbide matrix can be deposited among the fibers using a polymer-infiltration-pyrolysis (“PIP”) process, for example. The PIP process typically involves infiltrating a fiber structure with a pre-ceramic polymer, and then thermally converting the pre-ceramic polymer to ceramic material. The infiltration process can be repeated to achieve a desired density in the structure. However, using this or other known ceramic processing techniques often results in deficiencies, such as incomplete densification, microcracking and residual unreacted material. These deficiencies can later debit the properties of the structure, such as long term oxidative stability and environmental durability. 
     SUMMARY 
     A method of producing a ceramic article according to an example of the present disclosure includes heating solid silicon monoxide to provide gaseous silicon monoxide and exposing a structure having a free-carbon-containing material to the gaseous silicon monoxide to convert free carbon of the free-carbon-containing material to silicon carbide. 
     A further embodiment of any of the foregoing embodiments includes providing the solid silicon monoxide as a particulate dispersed in a coating on at least a portion of the structure. 
     In a further embodiment of any of the foregoing embodiments, the coating includes a polymeric carrier phase and the particulate of the solid silicon monoxide is dispersed in the polymeric carrier phase. 
     In a further embodiment of any of the foregoing embodiments, the exposing includes heating the coated structure to convert the particulate of the solid silicon monoxide in the polymeric carrier phase to the gaseous silicon monoxide. 
     In a further embodiment of any of the foregoing embodiments, the particulate of the solid silicon monoxide is provided in an amount that is stoichiometrically equal to or greater than the amount of free carbon. 
     In a further embodiment of any of the foregoing embodiments, the polymeric carrier phase is a preceramic polymer, and further including converting the preceramic polymer phase to a ceramic material. 
     In a further embodiment of any of the foregoing embodiments, the free carbon is residual free carbon from a prior thermal process used to form the structure. 
     In a further embodiment of any of the foregoing embodiments, the free carbon is in a coating on the structure. 
     In a further embodiment of any of the foregoing embodiments, the structure is an elongated, uniform diameter fiber. 
     In a further embodiment of any of the foregoing embodiments, the structure is a porous body. 
     An intermediate article according to an example of the present disclosure includes a solid structure having free carbon and a solid, in-situ source of silicon monoxide gas. 
     In a further embodiment of any of the foregoing embodiments, the solid structure is selected from the group consisting of an elongated, uniform diameter fiber and a porous body. 
     In a further embodiment of any of the foregoing embodiments, the solid, in-situ source of silicon monoxide gas is a particulate that is dispersed in a polymeric carrier phase. 
     In a further embodiment of any of the foregoing embodiments, the polymeric carrier phase is a preceramic polymer. 
     In a further embodiment of any of the foregoing embodiments, the free carbon is in a coating of the solid structure. 
     A composition according to an example of the present disclosure includes a polymeric carrier phase and particulate of solid silicon monoxide dispersed in the polymeric carrier phase. 
     In a further embodiment of any of the foregoing embodiments, the polymeric carrier phase is a preceramic polymer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The various features and advantages of the present disclosure will become apparent to those skilled in the art from the following detailed description. The drawings that accompany the detailed description can be briefly described as follows. 
         FIG. 1  illustrates an example method of producing a ceramic article. 
         FIG. 2  illustrates an example method of producing a ceramic article from another structure. 
         FIG. 3  illustrates another example method of producing a ceramic article from another structure including a porous body. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  schematically depicts a method  20  of producing a ceramic article. As will be described, the method  20  is applicable in a variety of different circumstances to produce a ceramic article that can have enhanced densification, reduced microcracking and reduced amounts of residual unreacted material. 
     For the purpose of description, the method  20  will be described with respect to a structure  22  that has a free-carbon-containing material  24 . For example, the free-carbon-containing material  24  can be free carbon alone or free carbon that is interdispersed with another material or materials. The structure  22  can be a fiber or fiber structure, porous body or other type of structure that has free carbon. 
     The method  20  includes heating solid silicon monoxide  26  to provide gaseous silicon monoxide, represented at  28 . The structure  22 , including the free-carbon-containing material  24 , is exposed to the gaseous silicon monoxide  28 . The gaseous silicon monoxide  28  reacts with the free carbon of the free-carbon-containing material  24  to convert the free carbon to silicon carbide. The conversion of the free carbon can be used to enhance densification, reduce microcracking and/or reduce amounts of residual unreacted carbon. 
     In further examples, the method  20  can be employed using either of two techniques. The first technique is an ex-situ technique and the second technique is an in-situ technique. In the ex-situ technique, the solid silicon monoxide  26  is provided separate from, i.e., outside or exterior of, the structure  22 . The in-situ technique involves providing the solid silicon monoxide  26  as an integral constituent in, or of, the structure  22  rather than as a separate or separated material. For example, each technique can be conducted in a heating chamber under vacuum and/or inert gas environment (e.g., argon gas). Upon heating to a target temperature range, the solid silicon monoxide  26  vaporizes to the gaseous silicon monoxide  28  that contacts and infiltrates the structure  22 . For example, the target temperature can be 1250° C.-1900° C., or more preferably 1280° C.-1540° C. For the ex-situ technique, the gaseous silicon monoxide  28  can infiltrate through pores into the structure  22  to contact and react with the free carbon, although the degree of infiltration may be limited if porosity is low and/or if pore size is small or the porosity is substantially closed rather than interconnected. For the in-situ technique, the gaseous silicon monoxide  28  can infiltrate through pores of the structure  22  to contact and react with the free carbon. Further, since the solid silicon monoxide  26  is an integral constituent in, or of, the structure  22 , the transport distance for the gaseous silicon monoxide  28  to the free carbon is reduced compared to the ex-situ technique. Thus, the in-situ technique can in some instances be more effective. 
     The ex-situ technique can be used separately from or in combination with the in-situ technique. The in-situ technique involves providing the solid silicon monoxide  26  in the structure  22 . In this regard, as will be described in further detail below, the solid silicon monoxide  26  can be incorporated into the structure  22  as a filler material, as a coating, or combinations thereof. 
     As can be appreciated, the free-carbon-containing material  24  can be present in the structure  22  from any of a variety of different circumstances. In one example, the free-carbon-containing material  24  is residual carbon from a prior thermal process used to form the structure  22 . For instance, the free carbon can be residual carbon from a prior thermal process used to convert a pre-ceramic polymer into a ceramic material that forms the structure  22 . In this regard, the free carbon can be present in residual amounts of 5 to 30 atomic %, depending upon the efficiency of the conversion and composition of the pre-ceramic polymer. In another example, the free carbon is residual carbon in or on the surfaces of silicon carbide fibers. The free carbon on the fiber surfaces can be converted to a silicon carbide surface layer that can enhance the surface roughness of the fiber and/or serve as a relatively weak interface with a ceramic matrix, such as a silicon carbide matrix. In another example, the free carbon is from the pyrolyzation of an organic fiber and/or fiber sizing to free carbon. Additionally or alternatively, the free carbon can be intentionally incorporated into the structure  22 , with the intent of later converting it to silicon carbide using the method  20 . 
       FIG. 2  illustrates another exemplary application of the method  20  to a structure  122  according to the in-situ technique. In this example, the solid silicon monoxide  26  is provided in a composition  130  that is coated onto a surface  132  of the structure  122 . As can be appreciated, the surface  132  can be an internal surface, such as a pore surface, or an external surface, such as a fiber surface. The composition  130 , in addition to the solid silicon monoxide  26 , can include a polymeric carrier phase  134  throughout which the solid silicon monoxide  26  is dispersed. That is, the solid silicon monoxide  26  is a filler within the matrix provided by the polymeric carrier phase  134 . For example, the polymeric carrier phase  134  is an organic polymer or silicon-containing polymer. 
     Portion  136  of the structure  122  serves as a substrate for the coating of the composition  130 . For example, the substrate  136  can be an elongated, uniform diameter fiber, in which case the surface  132  is an exterior surface of the fiber, or a porous body, such as a fiber structure onto which the coating of the composition  130  is deposited. As previously described, upon the application of heat in the prescribed temperature range, the solid silicon monoxide  26  vaporizes to gaseous silicon monoxide  28  that reacts with the free-carbon-containing material  24  to form silicon carbide in the structure  122 . 
       FIG. 3  illustrates another example application of the method  20  to a structure  222 . In this example, the structure  222  includes a porous body  236 , only a portion of which is shown in the illustration. The porous body  236  includes pores  238  (one shown) in which the composition  130  is infiltrated into. For example, the composition  130  is infiltrated into the pores  238  using a polymer impregnation technique, which can be conducted under vacuum. The porous body  236  includes the free-carbon-containing material  24 , which as described above can be residual free carbon that is unintentionally/undesirably present or intentionally added free carbon. Prior to the application of heat, the structure  222  is an intermediate article that includes a solid structure, here the porous body  236 , having the free carbon of the free-carbon-containing material  24 , along with a solid, in-situ source of silicon monoxide gas, which is the solid silicon monoxide  26  of the composition  130 . Upon the application of heat to the prescribed temperature, the solid silicon monoxide  26  vaporizes into the gaseous silicon monoxide  28 , which reacts with the free carbon to form silicon carbide. Subsequently, one or more additional infiltration cycles can be conducted to infiltrate additional amounts of the composition  130  into the pores  238 , followed by one or more additional cycles of heat to react the gaseous silicon monoxide  28  with free carbon in the porous body  236 . 
     Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments. 
     The preceding description is exemplary rather than limiting in nature. Variations and modifications to the disclosed examples may become apparent to those skilled in the art that do not necessarily depart from the essence of this disclosure. The scope of legal protection given to this disclosure can only be determined by studying the following claims.