Process for preparing ceramic materials with reduced carbon levels

A process for preparing ceramic materials with reduced carbon levels is described. The process involves treating a silicon-containing preceramic polymer with ammonia at a temperature of 550 DEG -800 DEG C. for a time sufficient to reduce the carbon content prior to pyrolysis at 900 DEG -1500 DEG C. Another process also involves the pyrolysis of a silicon-containing preceramic polymer in an ammonia atmosphere. The carbon level of ceramic materials produced by this invention can be controlled to a given, desired level by varying the process conditions. Suitable silicon-containing preceramic polymers include polycarbosilanes, polysilazanes, polysilanes, organosilsesquioxane-containing sol-gels, and organopolysiloxanes which are capable of being converted to ceramic materials when fired to elevated temperatures. Ceramic fibers can be prepared by the processes disclosed which contain less than 0.25 weight percent carbon.