Metallographic Preparation Procedures - Glass

Alumino-silicate Glass Ceramic

Glass ceramics have been crystallized to have a very fine crstalline structure. The primary advantage of glass ceramics is that tehy have very interesting thermomechanical properties because they are impervious to thermal shock.

This Alumino-Silicate glass has been crystallized to form a glass ceramic. Proper microstructural preparation of these materials requires proper cutting or sectioning of this material. Therefore, the most important step in the preparation of glass ceramics is in sectioning. If the glass ceramic is chipped or excessively cracked during sectioning it may be impossible to remove the damage. Wafer sectioning with a fine grit diamond blade is essential. Figure 1 shows a properly cut specimen with a fine grit blade, where the fibers edges are intact. In comparison, Figure 2 shows the severe damage that occurs even with a medium grit blade.

Planar grinding is accomplished with diamond on a metal mesh cloth to minimize cracking and subsurface damage. For rough polishing, the use of a low napped pads such as TEXPAN and DACRON with polycrystalline diamond and colloidal silica eliminates most of the surface and subsurface damage. Final polishing is accomplished easily with a resilient polishing pad such as BLACK CHEM using SIAMAT colloidal silica (Figure 3).

SECTIONING
Diamond Wafering blade - fine grit / low concentration

MOUNTING
Castable Mounting with Epoxy or Acrylic resins

POLISHING

Figure 1. Fine grit diamond cut of glass		Figure 2. Medium grit diamond cut of glass

Alumino-silicate glass ceramic, 400X (Polarized light) as polished