Exergy analysis of ceramic composite manufacturing processes. The case of liquid silicon infiltration

A relevant barrier for the massive use of composite materials is the high energy consumption needed for their manufacturing, what affects negatively to their cost. For this reason, exergy analysis of these processes is proposed in order to quantify this consumption by using the Second Law of Thermodynamics. Since this analysis would lead to the identification of the main issues affecting this energy consumption, it can contribute to the detection and quantification of potentials of energy savings. As an example of this application, an energy and exergy study of a Liquid Silicon Infiltration process (LSI) is carried out. In the LSI process, silicon is melted and infiltrated in a ceramic porous preform (usually C or SiC) in order to obtain a final fully dense ceramic composite through a reaction bonding between the silicon and the carbon preform. These preforms are placed on a silicon powder bed, into a vacuum-reaction chamber. After that, temperature increases until the silicon melting point is exceeded and thereafter, melted silicon penetrates into the carbon porous body and reacts with it forming silicon carbide. In this study, a whole process found in the literature [1] is analyzed, knowing the volume fraction of every component along the reaction stage and the changes in the preform porosity. In order to determine the time-evolution of furnace energy consumption, a simple model of the furnace is also developed. This kind of furnace is considered as a typical lab-scale equipment to carry out a LSI process. Besides the global exergy analysis, the time-evolution of exergy balance terms are computed.