Alumina-filled epoxy composites materials

Fracto-emission (FE) is the emission of particles (electrons, positive ions, and neutral species) and photons, when a material is stressed to failure. In this paper, we examine various FE signals accompanying the deformation and fracture of fiber-reinforced and alumina-filled epoxy, and relate them to the locus and mode of fracture. The intensities are orders of magnitude greater than those observed from the fracture of neat fibers and resins. This difference is attributed to the intense charge separation that accompanies the separation of dissimilar materials (interfacial failure) when a composite fractures. 

Another composite structure we have investigated recently is a particulate-filled epoxy. The epoxy is EPON 828 (Z-hardener) filled with irregularly shaped alumina particles with an average diameter of approximately 10/xm. This material is quite strong and brittle so we fractured most of the samples in a three-point flexure mode. The cross section of the sample was 2 mm x 6 mm. A typical EE curve plotted on a log scale is shown in Fig. 9, where t = 0 corresponds to the instant of failure. The material for this emission curve is filled at an Al203/epoxy ratio a of... 

Organic-ceramic composites may use an epoxy as the matrix and glass or ceramic powder as the filler. A common example is the fiberglass-reinforced epoxy used as a printed circuit laminate. An epoxy substrate filled with alumina and carbon black has also been developed. By weight, the composition is 10.8 percent epoxy resin, 89 percent alumina, and 0.2 percent carbon black. This material has a thermal conductivity of 3.0 to 4.0 W/(m K), compared to both glass-epoxy printed circuit material [0.2 W/(m K)] and glass-alumina low temperature cofired substrates [2.5 W/(m K)]. The TCE (17 ppm/°C) is substantially below that... 

K would cause a AT of almost 100 °C. For at least two decades, alumina and crystaUine silica have been used to boost the thermal conductivity of epoxy resins. When highly conductive fillers such as boron nitride, aluminum niliide, and diamond powders become commercially available, these materials have been incorporated in adhesive compositions. The expected target was the attainment of kg values of at least 10 W m K if not better. Such high values have been claimed for diamond-filled adhesives but they remain currently questionable with regard to the experimental results. summarized in the graph of Fig. 12.18. 

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