Melt infiltration processing

Let us consider two hypothetical phases in our composite, A and B, without specifying their physical state. They conld be a polymer melt and a glass fiber reinforcement during melt infiltration processing, a metal powder and ceramic powder that are being snbjected to consolidation at elevated temperatnre and pressure, or two immiscible polymer melts that will be co-extruded and solidified into a two-phase, three-dimensional object. In any case, the surface that forms between the two phases is designated AB, and their individual surfaces that are exposed to their own vapor, air, or inert gas (we make no distinction here) are labeled either A or B. The following three processes are defined as these surfaces interact and form ... 

Figure 4.14 Schematic diagram of the melt infiltration process for flow past a unidirectional fiber assembly.

Ylv = 0.581 N m and rm = 667°C), the capillary pressure reaches up to 1000bar for a pore radius of 1 nm. Obviously, capillary forces of such magnitude can strongly enhance the infiltration process. Since pore filling is only promoted in the case of 0 < 90°, specific surface modification might be essential for a successful melt infiltration process. 

FIGURE 35.13 Wood converted into ceramics by a reactive melt-infiltration process. 

Chakrabarti, O., Weisensel, L., and Sieber, H. (2005) Reactive melt infiltration processing of biomorphic Si-Mo-C ceramics from wood, J. Am. Ceram. Soc. 88(7), 1792. 

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). 

Wall, N., Yang, J. M. (2012). Reactive melt infiltration processing of fiber-reinforced ceramic matrix composites. In Bansal, N. P., Boccaccini, A. R. (Eds.), Ceramics and composites processing methods (pp. 351-385). Hoboken, NJ John Wiley Sons, Inc. doi 10.1002/9781118176665.chl0. 

Reactive fibers, 9 486-489 Reactive flame retardants, 11 474-479 brominated, ll 475-477t Reactive gases, 13 456 Reactive groups, types of, 9 178 Reactive hot melt butyl sealants, 22 44 Reactive hot melt polyurethanes, 22 37-38 Reactive hot melt silicones, 22 35 Reactive ion-beam etching (RIBE), 22 184 Reactive ion etching (RIE), 20 278 22 183 of lotus effect surfaces, 22 120 Reactive lead alloys, 14 779 Reactive liquid metal infiltration process, 16 168... 

At the start of the melting process, the pressure in the channel is relatively low and the solid bed may not be fully compacted. In this case, molten resin from all films has the ability to flow into the voids between the individual pellets. This process is often referred to as melt infiltration. A photograph of a cross section of a Maddock solidification experiment at the start of the melting process is shown by Fig. 6.21. For this figure, the molten material prior to the solidification was black. Melt infiltration is shown by the black resin that has flowed from the films and in between the pellets. The flow of resin into the solid bed will likely cause the pressure in the films to decrease. 

Figure 6.21 Photograph of a cross section from a Maddock solidification experiment at the start of the melting process. The black material shows the melt films and the regions where the melt infiltrated the loosely packed solid bed...

Whiskers can be incorporated into the metallic matrix using a number of compositeprocessing techniques. Melt infiltration is a common technique used for the production of SiC whisker-aluminum matrix MMCs. In one version of the infiltration technique, the whiskers are blended with binders to form a thick slurry, which is poured into a cavity and vacuum-molded to form a pre-impregnation body, or pre-preg, of the desired shape. The cured slurry is then fired at elevated temperature to remove moisture and binders. After firing, the preform consists of a partially bonded collection of interlocked whiskers that have a very open structure that is ideal for molten metal penetration. The whisker preform is heated to promote easy metal flow, or infiltration, which is usually performed at low pressures. The infiltration process can be done in air, but is usually performed in vacuum. 

Liquid-phase infiltration of preforms has emerged as an extremely useful method for the processing of composite materials. This process involves the use of low-viscosity liquids such as sols, metal- or polymer-melts. Using this infiltration process, it is possible to design new materials with unique microstructures (e.g. graded, multiphase, microporous) and unique thermomechanical properties (graded functions, designed residual strains and thermal shock). 

A great advantage of any silica-based glass is its ease of fabrication, which allows processes such as melt infiltration and compression molding to be used. 

It depends on the nature of the active phase, whether the hydrogenated form (i.e., metal hydride) or the dehydrogenated form (i.e., metal) is more suitable for the synthesis. In the first case, it has to be considered that hydrides can decompose before or during the melting process (e.g., NaAlHJ, so it might be necessary to conduct the infiltration process under hydrogen pressure. For a successful melt infiltration, the following key requirements should be met ... 

The opals obtained by self-assembly are mechanically unstable because there is only Van der Waals force between spheres. The subsequent infiltration process could easily destroy the ordered colloid arrays. So we annealed the opals of polymer sphere to increase their stability. As a result, there would form interconnections between spheres, which come from the slight melting of the sphere surfoces. These necks can provide the opal with necessary mechanical stability. In addition, they are important for producing inverse opal structure. After infiltration, when the samples are treated with calcinations, these necks can act as channels for the transport of the products formed during calcination like CO2. 

While many refractory peridotites were likely produced by melt-rock reactions at nearly constant or increasing melt mass (Kelemen, 1990 Kelemen et al., 1990), some fertile peridotites were conversely refertUized as the result of the solidification of infiltrated melt (a process also referred to as percolative fractional crystallization by Harte et al., 1993). (Re)fertilization processes have been invoked for several types of orogenic, ophiolitic, and oceanic peridotites, such as ... 

As it provides easy access to a variety of metasomatized mantle rocks, the Lherz massif has been recently the focus of detailed geochemical studies—as well as the source of debates—concerning melt infiltration and melt-rock interaction processes in wall rocks of... 

Figure 24 Chondrite-normalized abundances of REEs in a wall-rock harzburgite from Lherz (dotted lines— whole-rock analyses), compared with numerical experiments of ID porous melt flow, after Bodinier et al. (1990). The harzburgite samples were collected at 25-65 cm from an amphibole-pyroxenite dike. In contrast with the 0-25 cm wall-rock adjacent to the dike, they are devoid of amphibole but contain minute amounts of apatite (Woodland et al., 1996). The strong REE fractionation observed in these samples is explained by chromatographic fractionation due to diffusional exchange of the elements between peridotite minerals and advective interstitial melt (Navon and Stolper, 1987 Vasseur et al, 1991). The results are shown in (a) for variable t t ratio, where t is the duration of the infiltration process and t the time it takes for the melt to percolate throughout the percolation column (Navon and Stolper, 1987). This parameter is proportional to the average melt/rock ratio in the percolation column. In (b), the results are shown for constant f/fc but variable proportion of clinopyroxene at the scale of the studied peridotite slices (<5 cm). All model parameters may be found in Bodinier et al. (1990). As discussed in the text, this model was criticized by Nielson and Wilshire (1993). An improved version taking into account the gradual solidiflcation of melt down the wall-rock thermal gradient and the isotopic variations was recently proposed by Bodinier et al. (2003).

Infiltration is accomplished by immersion, dipping, or flooding, either in vacuum, inert gas, or, preferably, in reducing atmosphere at 1150-1250 °C. Oxide layers disturb the infiltration process and must be removed prior to infiltration by reduction with hydrogen. Trace impurities can impair the wetting between tungsten and the melt (for example, silicon) but can also improve it (nickel, cobalt, iron) [6.47]. Densities of 96% up to near-... 

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