Electron microscopy and EDX-microanalysis of photochromic silver halide glasses of the composition systems Al2O3-B2O3-SiO2 and Na2O-CaO-SiO2

The microstructure and microanalysis study of two glasses containing AgCl precipitated particles have been carried out by transmission electron microscopy (TEM, replica method), scanning electron microscopy (SEM) and SEM/EDX (energy dispersive X-ray spectrometry). The composition of these glasses doped with silver halide and CuO was formulated from the Al₂O₃-B₂O₃-SiO₂ and Na₂O-CaO-SiO₂ systems respectively. In both glasses the seeds, nuclei, crystals and matrix were analysed, and the mean size and number of crystals were evaluated from the TEM and SEM observations. The microstructure in both glasses is different because of the different shape of the silver halide particles; the particles of the Al₂O₃-B₂O₃-SiO₂ glass are rounded while Na₂O-CaO-SiO₂ shows square precipitated particles. Likewise, the darkening behaviour is basically different; the Al₂O₃-B₂O₃-SiO₂ glass shows a higher darkening velocity than the Na₂O-CaO-SiO₂ glass, showing for this glass a very small slope value.