Chemical vapour infiltration

As already mentioned, the first pyrolysis cycle leads to an open porosity of about 20-30 %. This high porosity limits the interlaminar shear strength (ILS). A reduction in the porosity is possible by reimpregnation with polymers and subsequent pyrolysis or CVI (Chemical Vapour Infiltration). 

There are many methods to manufacture a CMC. Only a small selection is discussed in this section. Let us first have a look at the production process of a SiC matrix reinforced with SiC fibres. First a model is made of fibres, the so-called preform, then CVI (Chemical Vapour Infiltration) is applied to produce a coating on the fibres in order to ensure a better attachment to the matrix. The next step is resin infiltration. After pyrolysis (heating to a high temperature without oxygen) a network matrix of the porous carbon arises. Silicon which has first been melted in an oven is then introduced into this network it reacts with the carbon to form the following matrix ... 

Various researchers have used different techniques for the fabrication of ceramic matrix composite (CMC) by using (a) chemical vapour deposition (CVD), (b) chemical vapour infiltration (CVI) and (c) modelling of CVI [43-54], but it is difficult to fabricate glass/glass-ceramic composite using these techniques. 

CMCs with 2-D woven fibre reinforcements have been found to possess higher resistance to thermal shock than unidirectional or cross-ply CMCs of the same constituents (Nicalon fibres and SiC matrices) and prepared by the same method (Chemical Vapour Infiltration-CVI) (Wang et al., 1997). 

There is also scope for the development of new techniques such as chemical vapour infiltration (CVI) (Caputo and Lackey, 1984 Caputo et al., 1985), normal chemical reaction bonding processes, laminar sialon composites, etc. More recently, laminated composites in non-oxide and sialons have demonstrated very promising results for strengthening (Goto and Kato, 1998) and even achieved a non-brittle failure behaviour accompanied by high damage tolerance (Yu and Krstic, 2003 Yu et al., 2005). 

Caputo, A.J. and Lackey, W.J., (1984), Fabrication of fibre-reinforced ceramic composites by chemical vapour infiltration , Ceram. Eng. Sci. Proc., 5(7-8), 654—667. 

The increasing use of light ceramic composites for high temperature and space applications has stimulated the development and optimization of the Chemical Vapour Infiltration technique. The use of conventional ceramic techniques for the fabrication of fibre-reinforced composites damages the fibres both mechanically as chemically. Also, the high process temperature causes a thermal degradation of the fibres. 

Figure 13.5 Schematic representation of chemical vapour infiltration process.

Much research has been performed on silica membranes produced by Chemical Vapour Infiltration for hydrogen separation purposes. In chapter 7, CVI experiments are described and a concise literature review is provided as well. Below some highlights will be presented briefly. 

Apart from the silica membranes prepared by dipcoating, also Chemical Vapour Infiltration (CVI)-type membranes have been prepared. Chapter 7 is dedicated to this type of membrane. 

High-performance Ceramic Matrix Composites and Chemical Vapour Infiltration... 

Chemical vapour infiltration (CVI) is an extension of CVD processes only when a CVD process occurs on an internal surface of a porous substrate (especially for the fibre preform). As compared with CVD, the CVI process for ceramics is much more effective and important because it is the optimal technique to fabricate fibre reinforced ceramics and particularly carbon fibre reinforced carbon and advanced ceramic matrix composites. Both CVI and CVD techniques share some common features in overall chemistry, however, the CVI is much more complex than the CVD process in mass transport and chemical reactions. 

Review, status, and future of the chemical vapour infiltration process for fabrication of fibre-reinforced ceramic composites, Lackey, 1989 [138]... 

Fabrication of fibre-reinforced ceramic composites by chemical vapour infiltration, Lackey and Starr, 1990 [140]... 

Lackey WJ, Starr TL (1990) Fabrication of fibre-reinforced ceramic composites by chemical vapour infiltration processing, structure and properties. In Mazdiyasni K S (ed) Fibre reinforced ceramics. Noyes, Park Ridge, NJ, pp397 150... 

Isothermal and Isobaric Chemical Vapour Infiltration Process Model... 

Forced-Flow-Chemical Vapour Infiltration Model... 

Thermal Gradient Chemical Vapour Infiltration 5.4.1 General Description... 

Some Typical Thermal Gradient/Isobaric Chemical Vapour Infiltration Techniques... 

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