3.14. Optical Microscopy

The specimens were tested from the perspective of the degree of even dispersion of the filler component in the polished cross-sections (pastes) and unpolished cross-sections (composites). Polishing of composite samples was not possible due to damaging of the surface by the releasing sand particles. A digital optical microscope with a 2500× lens was used for the determination of the microstructure, as it is capable of achieving a magnification equivalent to approximately 800× of an optical microscope. The device uses an optical system and a digital camera with a high resolution, equipped with an optical cable for an immediate transfer of the captured image to a computer. Due to the different depths of focus of the individual scanned layers, the technology of a composite image was used to achieve maximum possible sharpness. A polarizing aperture was used for the differentiation of the carbon particles. This uses the fact that light is in its essence an electromagnetic wave that oscillates on all levels that are perpendicular to the direction of the ray. The insertion of the polarizing screen into the path of the light refracted from the surface of the sample creates a polarized ray. Upon interference, the recombined ray has different properties depending on the optical properties of the double-refraction object and the slight turning of the analyzer. The record of the recombined ray with an appropriately turned analyzer enables the clear distinction of spatially oriented particles of carbon in the specimen, as they have a different refraction index from the matrix.