Characterization of rubber-brass bonding layers by analytical electron microscopy (AEM)

The mechanical properties of rubber- brass bonding systems depend on the morphology, chemistry, and crystallography of the phases in the sulfide layers which are formed during cure. These layers contain the crystalline high-digenite and chalcocite copper sulfides. Most of the bonding layers are relatively thin and consist of several phases which can be visualized by electron microscopy (EM). Their characterization requires structural and elemental analyses with high spatial resolution. Analytical electron microscopy (AEM) fulfils these requirements. For a successful application of AEM, suitable specimen preparation is a major prerequisite. Two preparation techniques are discussed: the extraction of the bonding layers parallel to the substrate and the preparation by cryo-ultramicrotomy of cross-sections perpendicular to the brass surface. The bonding layers are characterized by means of transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM), electron diffraction, energy-dispersive X-ray spectrometry (EDXS), electron energy-loss spectrometry (EELS), and electron spectroscopic imaging (ESI). The application of these techniques to bonding layers is demonstrated with typical examples and is discussed critically.