Liquid silicon infiltration

Gern, F.H. and Kochendoerfer, R., Liquid silicon infiltration description of infiltration dynamics and silicon carbide formation. Composites, 28A, 355-364, 1997. 

Silicon carbide (SiC) matrix composites have been fabricated by chemical vapor infiltration (CVl), polymer impregnation and pyrolysis (PIP), and reaction sintering (RS). The RS process can be recognized as an attractive technique, because it offers a high density and good thermal conductivity, compared to those of CVl and PIP process. In general, the fabrication of fiber reinforced SiC matrix composites by reaction sintering involves melt infiltration (Ml) or liquid silicon infiltration (LSI). However, the fabrication of continuous fiber reinforced SiC matrix composites by RS focused in melt infiltration (Ml) such as liquid silicon infiltration (LSl) Vapor silicon infiltration was rarely used for SiC matrix composites. 

For liquid silicon infiltration, Capillary force is the driving force. It can be stated... 

When liquid silicon infiltration are conducted at 1427°C (1700K),... 

From the above calculation, it is found that there is much less heat delivery per unit time during vapor silicon infiltration than liquid silicon infiltration. It is also noted that the driving force of molten silicon is greatly affected by the pore size (diameter), which might result in problem (clogging, etc.). However, gaseous silicon, acting like ideal gas, can enter into any open pore. 

Fabrication by Liquid Silicon Infiltration (reaction bonding) (LSI) A leading candidate for use in industrial gas turbine engine is a SiC matrix composite named toughened Silcomp [175]. It is produced by melt infiltration of molten silicon into a porous preform containing carbon as well as BN-coated SiC fibers (e.g. Textron SCS - 6). The composites thus produced consist of a fully dense matrix of SiC + Si, reinforced with continuous SiC fibers. Moreover, the melt infiltration process is net shape and fast. Ultimate strength and strain at ultimate strength are 220 MPa and 0.8 /o, respectively at room temperature (LSI-SiC/SiC Si). 

Historically, the processing routes moved from the isothermal CVI process to more cost-effective techniques such as gradient-CVI and liquid polymer or liquid silicon infiltration. These routes are faster and lead to shorter manufacture cycles than isothermal CVI and, especially the two liquid phase processes LPI and LSI, use technologies already developed for polymer matrix composites (PMC). 

R. Kochendbrfer and N. Liitzenburger, Applications of CMCs made via the Liquid Silicon Infiltration (LSI) Technique, High Temperature Ceramic Matrix Composites (Eds. W. Krenkel, R. Naslain, H. Schneider), WILEY-VCH, Weinheim, Germany (2001), p. 277-287. 

SiC- Sic and SiC-C (Continuous Fiber-Reinforced SiC Matrix Composites) Three different processes are commonly used to manufacture carbon fiber-reinforced SiC materials (i) chemical vapor infiltration (CVI) [340] (ii) liquid polymer infiltration (LPI also termed polymer infiltration and pyrolysis, PIP) [341]) and (iii) melt infiltration or liquid silicon infiltration (MI/LSI) [342]. 

Patel, M., Saurabh, K., Prasad, V. V. B., Subrahmanyam, J. (2012). High temperature C/C-SiC composite by liquid silicon infiltration A literature review. Bulletin of Materials Science, 35(1), 67-77. doi 10.1007/sl2034-011-0247-5. 

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