Silicon infiltration

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

The reflection spectra of grooved silicon and grooved silicon infiltrated with nematic liquid crystal (LC) have been calculated. The grooved silicon structures with different lattice constants (A=16,1 2, 8 and 4 pm) have been designed and fabricated. The analysis of the polarised infrared spectra of Si structures infiltrated with LC allows one to determine the refractive index (Nlc) and the orientation of the liquid crystal. 

VAPOR SILICON INFILTRATION FOR FIBER REINFORCED SILICON CARBIDE MATRIX COMPOSITES... 

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. 

Vapor Silicon Infiltration for Fiber Reinforced Silicon Carbide Matrix Composites... 

At high temperature, gaseous silicon can be considered to be an ideal gas due to its vapor pressure of 100Pa. The amount of gaseous silicon can be derived with vapor silicon infiltration conducted in a sealed crucible with a diameter of 180mm and a height of 150mm. 

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. 

The microstructure of an SiC-filter made from silicon infiltrated polymer foam is shown in Fig. 19. Cell size, cell geometry, and cell anisotropy is controllable during processing [283]. The structural variability of this material reaches from tube-like anisotropic to isotropic pore nets with several pore and bridge averages. This porous SiC material cannot only be applied to filters and membrane supports it can also be used as catalyst support or heat exchanger [284]. 

Figure 12. Microstructure of various SiC ceramics (a) KSiC, nitride bonded SiC (AnnaSicon 25) (b) RSiC, recrystallized SiC (AnnaNox CK) (c) SiSiC silicon infiltrated SiC (AnnaNox CD), (d) SSiC, B/C doped (Ekasic F), (e) LPSSiC, equiaxed SiC grains (Ekasic T), (f) LPSSiC, platelet SiC grains (ESK), (g) HPSiC,Al-doped (ESK), (h) HIPSiC, undoped (ESK).

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. 

Figure 1.18 Silicon infiltration combustion nitriding completeness degree ( f) on dilution...

Wood-based composites with a phenohc resin matrix have been transformed into silicon-infiltrated silicon carbide ceramics by carbonization at about 1 650°C [46]. The bending strength and the elastic modulus of these original ceramics were better than those of conventionally manufactured counterparts, whereas the fracture toughness was lower. 

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]. 

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