Metal-filled composites

The defects caused by the high contact resistance especially manifest themselves in the metal-filled composites where the value of the percolation threshold may reach 0.5 to 0.6 [30]. This is caused by the oxidation of the metal particles in the process of CPCM manufacture. For this reason, only noble metals Ag and Au, and, to a lesser extent, Ni are suitable for the use as fillers for highly conductive cements used in the production of radioelectronic equipment [32]. 

Experimental [23] as well as theoretical [24-26] studies of percolation phenomena have been reported. In random and macroscopically homogeneous materials it has been demonstrated [27-29] that at concentrations of metal particles below the percolation threshold (p < Pc) a short-range percolation coherence length, exists. Electrical conductivity is probable for length scales less than Thus even if the metal-filled composite exhibits no bulk electrical conductivity, conduction can occur within domains that are smaller than As the concentration of metal particles approaches oo and the composite becomes isotropically conductive. 

Static decay rates of carbon or metal-filled versus metal-painted or neat polycarbonate are shown in Table 18.6. All the filled polycarbonates performed similarly, a charge of 5 kV decayed in less than 0.06 s compared to more than 100 s for neat PC [63]. Metal-filled composites may show ohmic behavior in the interior but appear nonohmic overall due to surface depletion of the conductive species [68]. 

First, a few studies on metal-filled composite bipolar plates are briefly described. At Los Alamos National Laboratory (LANL) composite bipolar plates filled with porous graphite and stainless steel and bonded with polycarbonate (Hermann, 2005) has been developed. Kuo (2006) investigated in composite bipolar plates based on austenitic chromium-nickel-steel (SS316L) incorporated in a matrix of PA 6. Their results showed that these bipolar plates are chemically stable. Furthermore, Bin et al. (2006) reported a metal-filled bipolar plate using polyvinylidene fluorid (PVDF) as the matrix and titanium silicon carbide (TijSiCj) as the conductive filler and obtained an electrical conductivity of 29 S cm" with 80 wt% filling content. 

Developments in metal-matrix composites technology has resulted in aluminum matrix materials filled with siUcon carbide [409-21 -2] SiC, (see Carbides, silicon carbide) particles (15 to 60 vol %) that provide the possibihty of weight reduction for brakes (20). These composite materials are being tested and evaluated. 

The aerospace field is a broad one and has a complex history. A comprehensive review of structural adhesive applications on currently flying aerospace vehicles alone could fill its own book. Hence this chapter will concentrate on the aerospace commercial transport industry and its use of adhesives in structural applications, both metallic and composite. Both primary structure, that is structure which carries primary flight loads and failure of which could result in loss of vehicle, and secondary structure will be considered. Structural adhesives use and practice in the military aircraft and launch vehicle/spacecraft fields as well as non-structural adhesives used on commercial aircraft will be touched on briefly as well. 

Encapsulation of other material into carbon nanotubes would also open up a possibility for the applications to electrodevices. By applying the template method, perfect encapsulation of other material into carbon nanotubes became possible. No foreign material was observed on the outer surface of carbon nanotubes. The metal-filled uniform carbon nanotubes thus prepared can be regarded as a novel onedimensional composite, which could have a variety of potential applications (e.g novel catalyst for Pt metal-filled nanotubes, and magnetic nanodevice for Fe304-filled nanotubes). Furthermore, the template method enables selective chemical modification of the inner surface of carbon nanotubes. With this technique, carbon... 

Numerous filler characteristics influence the properties of composites [14,15]. Chemical composition and, in particular, purity of the filler both have a direct and an indirect effect on its application possibilities and performance. Traces of heavy-metal contamination decrease stability. Insufficient purity leads to discoloration, high purity CaC03 has the advantage of a white color, while the grey shade of talc filled composites excludes them from some fields of application. 

Conductive composites are obtained when powdered metal fillers or metal-plated fillers are added to resins. These composites nave been used to produce forming tools for the aircraft industry. Powdered lead-filled polyolefin composites have been used as shields for neutron and gamma radiation, and metal-filled plastics have been used to prevent interference from stray electrons (EMI). 

Armand (1994) has briefly summarised the history of polymer electrolytes. A more extensive account can be found in Gray (1991). Wakihara and Yamamoto (1998) describe the development of lithium ion batteries. Sahimi (1994) discusses applications of percolation theory. Early work on conductive composites has been covered by Norman (1970). Subsequent edited volumes by Sichel (1982) and Bhattacharya (1986) deal with carbon- and metal-filled materials respectively. Donnet et al. (1993) cover the science and technology of carbon blacks including their use in composites. GuF (1996) presents a detailed account of conductive polymer composites up to the mid-1990s. Borsenberger and Weiss (1998) discuss semiconductive polymers with non-conjugated backbones in the context of xerography. Bassler (1983) reviews transport in these materials. 

The retainer may be completely fabricated from a composite material, or may consist mainly of a composite with reinforcement by metal rings. Alternatively it may be conventionally fabricated of steel or other suitable metals, with composite components bonded, rivetted or pressed onto it, or with holes or grooves filled with the lubricant composite. 

Cermets, which are mixtures of ceramic and metal powders, heat treated and compressed. (4) Fabrics, e.g., woven combinations of wool or cotton and a synthetic fiber. (5) Filled composites in which a bonding material, i.e., linseed oil, resin, or asphalt, is loaded with a filler in the form of flakes or small particles examples are linoleum, glass flake-plastic mixtures for battery cases, and asphalt-gravel road-surfacing mixtures. 

Figure 19.17. Comparative cost of metal filled PES composites. Courtesy of Transmet Corporation, Columbus, USA.

Parts produced having a gradient in porosity could be used to fabricate composites with a gradient in composition. For graded ceramic-ceramic composites, the graded porosity in a partially sintered compact could be filled with a suitable liquid precursor to produce composites by the infiltration processing route [6, 7]. In the case of metal-ceramic composites, liquid metal infiltration of the sintered ceramic piece could be employed to introduce the metal phase [8],... 

It was mentioned above that the simulation method of Termonia [67-72] can be used to calculate the stress-strain curves of many fiber-reinforced or particulate-filled composites up to fracture, including the effects of fiber-matrix adhesion. Such systems are morphologically far more complex than adhesive joints. Many matrix-filler interfaces are dispersed throughout a composite specimen, while an adhesive joint has only the two interfaces (between each of the bottom and top metal plates and the glue layer). If one considers also the fact that there will often he a distribution of filler-matrix interface strengths in a composite, it can be seen that the failure mechanism can become quite complex. It may even involve a complex superposition of adhesive failure at some filler-matrix interfaces and cohesive failure in the bulk of the matrix. 

PDX. [LNP] Nylon 6/10 or 11, PEEK, PPS, PC, ABS, PEI, PC, OT PBT, some metal filled conductive attenuating composites effectivdy shielding electromagnetic and/or radio fiequeiK y interference used in avionics housings, business machine endosutes, and other electronic devices. 

---