Metal-matrix composites chemical vapor deposition

Molybdenum hexafluoride is used in the manufacture of thin films (qv) for large-scale integrated circuits (qv) commonly known as LSIC systems (3,4), in the manufacture of metallised ceramics (see MetaL-MATRIX COMPOSITES) (5), and chemical vapor deposition of molybdenum and molybdenum—tungsten alloys (see Molybdenumand molybdenum alloys) (6,7). The latter process involves the reduction of gaseous metal fluorides by hydrogen at elevated temperatures to produce metals or their alloys such as molybdenum—tungsten, molybdenum—tungsten—rhenium, or molybdenum—rhenium alloys. 

Small diameter ceramic fibers are needed for use in ceramic and metal matrix composites in defense and industrial applications. SiC is a useful candidate material because of its low density, high temperature strength, and resistance to oxidation and creep. By depositing a 5 pm layer of SiC onto a 5 pm diameter carbon fiber by chemical vapor... 

For this testing, the composite system interrogated was a Melt Infiltrated In-Situ BN SiC/SiC composite (Ml SiC/SiC). The interface coating for this material is form a two step process it is initially heat treated to create a fine layer in in-situ BN and then it is followed with CVI deposited Si-doped BN. The MI SiC/SiC system has a stochiometric SiC (Sylramic ) fiber in a multiphase matrix of SiC deposited by chemical vapor deposition followed by slurry casting of SiC particulates with a final melt infiltration of Si metal. The specific MI SiC/SiC tested for this effort had 36% volume fraction fibers using a 5 HS weave at 20 EPI. The fibers are 10 pm diameter and there are 800 fibers per tow. This material system was developed by NASA-GRC and is sometimes referred to as the 01/01 material [11]. A cross section of this material is shown in Figure 1. 

Ceramic fibers. The other fibers shown in Table 4.6 have varying uses, and several are still in development. Silicon carbide continuous fiber is produced in a chemical vapor deposition (CVD) process similar to that for boron, and it has many mechanical properties identical to those of boron. The other fibers show promise in metal matrix composites, as high-temperature polymeric ablative reinforcements, in ceramic-ceramic composites, and in microwave transparent structures (radomes or microwave printed wiring boards). 

Chapter 10 deals with composite films synthesized by the physical vapor deposition method. These films consist of dielectric matrix containing metal or semiconductor (M/SC) nanoparticles. The film structure is considered and discussed in relation to the mechanism of their formation. Some models of nucleation and growth of M/SC nanoparticles in dielectric matrix are presented. The properties of films including dark and photo-induced conductivity, conductometric sensor properties, dielectric characteristics, and catalytic activity as well as their dependence on film structure are discussed. There is special focus on the physical and chemical effects caused by the interaction of M/SC nanoparticles with the environment and charge transfer between nanoparticles in the matrix. 

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