Liquid infiltration technique

It is also interesting to note that electroless plating of silver on carbon fiber surface improves the wettability between molten aluminum and PAN based carbon fibers using the liquid infiltration technique in vacuum (Warrier et al., 1993). This is attributed to the formation of an eutectic phase between silver and aluminum, and the silver coating of the fibers during processing. 

Dacres CM, Reamer SM, Sutula RA, Larrick BF, Proc Electrochem Soc, 83(1), 76-95, 1983. Wang C, Ying M, Yue D, In Matthews FL, Buskell NCR, Hodgkinson JM, Morton J, Proc 6th Int Conf Compos Mater 2nd Eur Conf Compos Mater, Vol 2, Elsevier, London, 2.183-2.188, 1987. Cheng HM, Lin ZH, Zhou BL, Zhen ZG, Kobayashi K, Uchiyama Y, Preparation of carbon-fiber-reinforced aluminum via ultrasonic liquid infiltration technique. Mater Sci Technol, 9(7), 609-619, 1993. 

Less-conventional processing techniques are also used to make ceramic matrix composites. Siliconized silicon carbide, for example, is made by liquid infiltration.16,17 A compact of SiC particles is formed and then presintered, or reaction bonded. Liquid silicon is then infiltrated into the structure. Many different microstructures of siliconized silicon carbide can be made in this manner. The volume fraction of SiC particles can be as high as 90vol.%. Bimodal structures have also been made by this technique. These materials are used for radiant heaters and heat exchangers.17,19... 

The main drawback of the CVI techniques is the long processing time of infiltration, normally in the range of a hundred hours. This is coupled with a very slow rate of deposition associated with a relatively low conversion efficiency of the precursor. To address this deficiency new manufacturing approaches have been explored to develop rapid infiltration techniques and so far most of these attempts remain as research work being investigated in laboratories. Another potential problem is that CVI composites exhibit some residual open porosity. This would be a drawback for applications where gas or liquid tightness is strictly required. 

The range of processing techniques that can be employed to produce FGMs is also broad [1]. Vapor-phase methods e.g., CVD, CVI, and PVD methods), liquid-phase methods e.g., electrodeposition, sol-gel, plasma spraying and molten metal infiltration methods), and a variety of solid-phase methods based on powder metallurgy are available. The solid-state methods include powder stacking techniques, powder infiltration techniques, slurry techniques e.g., sedimentation... 

Despite their heterogeneous microstructure and their complex processing, hybrid processes show a promising route to combine the high material purity and process controllability of the chemical vapour infiltration technique with the less time consuming and in most cases cheaper liquid phase infiltration techniques of LSI and LPI, However, additional research and development have to be done in order to take benefit of the whole potential of combined processes. 

Method //was designed for a bonded microreactor. After the channel was sealed with a Pyrex top plate using the anodic bonding technique, the liquid precursor was infiltrated into the microreactor through the outlet of the reactor under slight pressure and withdrawn. A thin film of solution remained on the walls of the microchannel. 

In this technique cyclohexane (C6H12) is selected as a liquid precursor because of its suitable boiling point, low toxicity and low cost. In addition, some other hydrocarbons also exhibit infiltration properties similar to those of cyclohexane,... 

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. 

The infiltration of carbonaceous structures by liquid silicon or silicon vapor is also an interesting technique to produce SiC components. Especially the Si-inhltration of C-structures coining from natural materials like wood offers the possibility for low cost fabrication of SiC, and has already been described in Sect. 4. Infiltration of polymer-matrix derived carbon fiber reinforced carbon is schematically drawn in Fig. 14 [255, 256]. The production of complex SiC-composite parts and components as well as big parts is possible by this route. 

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). 

FIGURE 11. The technique for making C/SiC components by liquid polymer infiltration (LPI)... 

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. 

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