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Chemical vapor infiltration

The decomposition of ammonia increases above 850°C, a temperature at virhich nitridation begins to increase. As a result active hydrogen breaks the Si-0 bonds while active nitrogen reacts with unbonded silicon to form silicon nitride fibers (Equation 8b). The process does not only yield straight fibers but also well defined, coiled fibers. [Pg.22]

The formation of titanium carbide fibers by chemical vapor infiltration with titanium at 1200 C (Equation 9) can be carried out with short vapor grown carbon fibers. The flow rates of TiCU [Pg.22]


Figure 5.16. Forced-flow thermal-gradient chemical vapor infiltration. Figure 5.16. Forced-flow thermal-gradient chemical vapor infiltration.
Chemical vapor infiltration of carbon-carbon structures (reentry heat shields, rocket nozzles, and other aerospace components). [Pg.193]

Present oxidation-protection systems are based on silicon carbide (SiC), which is applied by pack cementation or by chemical-vapor infiltration (CVI) (see Ch. 4).d ] Boron, zirconium, and other... [Pg.443]

Other ceramic cutting-tool materials include alumina, Si-Al-0-N, alumina-carbide composites and, more recently, a composite of silicon nitride reinforced with silicon carbide whiskers. This last material can be produced by chemical-vapor infiltration (CVI) and has high strength and toughness as shown in Table 18.3.Cl... [Pg.457]

The reinforcing fibers are usually CVD SiC or modified aluminum oxide. A common matrix material is SiC deposited by chemical-vapor infiltration (CVI) (see Ch. 5). The CVD reaction is based on the decomposition of methyl-trichlorosilane at 1200°C. Densities approaching 90% are reported.b l Another common matrix material is Si3N4 which is deposited by isothermal CVI using the reaction of ammonia and silicon tetrachloride in hydrogen at 1100-1300°C and a total pressure of 5 torr.l" " ] The energy of fracture of such a composite is considerably higher than that of unreinforced hot-pressed silicon nitride. [Pg.481]

Pyrolytic carbon was inserted into the pores of these silica matrices by chemical vapor infiltration (CVI). The silica template was contacted with a flow of propylene Pr, (2.5 vol%) diluted in argon at 750°C during 15 hours. A quite uniform pore filling can be obtained by CVI. At the end, the carbon represents about 50 wt% of the C/Si02 material. Since the deposition... [Pg.32]

Table 1 Typical tensile properties of isothermal chemical vapor infiltration processed C/SiC... Table 1 Typical tensile properties of isothermal chemical vapor infiltration processed C/SiC...
Chemical Vapor Infiltration) [9]. As the carbon fiber itself is the main material, a low cost production process for the composite itself and for coating the composite might be advantageously investigated. [Pg.120]

The majority of work done on VGCF reinforced composites has been carbon/carbon (CC) composites [20-26], These composites were made by densifying VGCF preforms using chemical vapor infiltration techniques and/or pitch infiltration techniques. Preforms were typically prepared using furfuryl alcohol as the binder. Composites thus made have either uni-directional (ID) fiber reinforcement or two-directional, orthogonal (0/90) fiber reinforcement (2D). Composite specimens were heated at a temperature near 3000 °C before characterization. Effects of fiber volume fraction, composite density, and densification method on composite thermal conductivity were addressed. The results of these investigations are summarized below. [Pg.168]

CVI [Chemical Vapor Infiltration] A ceramic manufacturing process in which the pores of a matrix are filed by CVD. [Pg.76]

MOCVD as, 22 153-154 in silicon carbide fiber manufacture, 22 534 thermally activated, 24 744-745 Chemical vapor infiltration (CVI), 26 767 ceramics and, 5 664 Chemical warfare, 5 813-840 defense against, 5 830-837 Chemical warfare agents, detection of, 22 716-717... [Pg.171]

The molded plate with the large volume of pores was further coated by chemical vapor-infiltrated (CVI) graphitic carbon at 1,500°C with 5 kPa... [Pg.317]

The processing techniques used for CMCs can be quite exotic (and expensive), such as chemical vapor infiltration (CVI), or through pyrolysis of polymeric precursors. Their maximum use temperatures are theoretically much higher than most MMCs or PMCs, exceeding 1800°C, although the practical use temperature is often much lower... [Pg.104]

Due to the fact that industrial composites are made up of combinations of metals, polymers, and ceramics, the kinetic processes involved in the formation, transformation, and degradation of composites are often the same as those of the individual components. Most of the processes we have described to this point have involved condensed phases—liquids or solids—but there are two gas-phase processes, widely utilized for composite formation, that require some individualized attention. Chemical vapor deposition (CVD) and chemical vapor infiltration (CVI) involve the reaction of gas phase species with a solid substrate to form a heterogeneous, solid-phase composite. Because this discussion must necessarily involve some of the concepts of transport phenomena, namely diffusion, you may wish to refresh your memory from your transport course, or refer to the specific topics in Chapter 4 as they come up in the course of this description. [Pg.269]

Chemical vapor infiltration (CVl) is similar to CVD in that gaseous reactants are used to form solid products on a substrate, but it is more specialized in that the substrate is generally porous, instead of a more uniform, nominally flat surface, as in CVD. The porous substrate introduces an additional complexity with regard to transport of the reactants to the surface, which can play an important role in the reaction as illustrated earlier with CVD reactions. The reactants can be introduced into the porous substrate by either a diffusive or convective process prior to the deposition step. As infiltration proceeds, the deposit (matrix) becomes thicker, eventually (in the ideal situation) filling the pores and producing a dense composite. [Pg.272]

Figure 3.35 Classification of chemical vapor infiltration processes. From Carbide, Nitride, and Boride Materials Synthesis and Processing, A. W. Weimer, ed. p. 563. Copyright 1997 by Chapman Hall, London, UK, with kind permission of Kluwer Academic Publishers. Figure 3.35 Classification of chemical vapor infiltration processes. From Carbide, Nitride, and Boride Materials Synthesis and Processing, A. W. Weimer, ed. p. 563. Copyright 1997 by Chapman Hall, London, UK, with kind permission of Kluwer Academic Publishers.
In Section 3.4.2, we introdnced the concept of chemical vapor infiltration, CVI, in which a chemical vapor deposition process is carried out in a porous preform to create a reinforced matrix material. In that section we also described the relative competition between the kinetic and transport processes in this processing technique. In this section we elaborate npon some of the common materials used in CVI processing, and we briefly describe two related processing techniques sol infiltration and polymer infiltration. [Pg.802]

Chemical Vapor Infiltration (CVI). Recall from Section 3.4.2 that CVI is primarily nsed to create ceramic matrix composites, CMCs. Fabrication of CMCs by CVI involves a sequence of steps, the first of which is to prepare a preform of the desired shape and fiber architecture. This is commonly accomplished by layup onto a shaped form of layers from multifilament fibers using some of the techniques previously described, such as filament winding. [Pg.802]

Chung, G. Y. and Benjamin, J.M., Modeling of chemical vapor infiltration for ceramic composites reinforced with layered, woven fabrics , J. Am. Ceram. Soc., 74, 746 (1991). [Pg.97]

T.M. Besmann, Processing Science for Chemical Vapor Infiltration, Laboratory Industry I Government Briefing, Oak Ridge National Laboratory, Oak Ridge, TN, 1990. [Pg.135]

In addition to the Pd-based membranes, microporous silica membranes for hydrogen permeation [8] can be produced by a special type of chemical vapor deposition [140] named chemical vapor infiltration (CVI) [141], A large amount of studies have been carried out on silica membranes made by CVI for hydrogen separation purposes [8,121], CVI [141] is another form of chemical vapor deposition (CVD) [140] (see Section 3.7.3). CVD involves deposition onto a surface, while CVI implies deposition within a porous material [141], Both methods use almost similar equipment [140] and precursors (see Figure 3.19) however, each one functions using different operation parameters, that is, flow rates, pressures, furnace temperatures, and other parameters. [Pg.485]


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See also in sourсe #XX -- [ Pg.443 ]

See also in sourсe #XX -- [ Pg.316 ]




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