Alkali emission accompanying fracture of sodium silicate glasses

Measurements of atomic Na emission accompanying the fracture of sodium trisilicate glass and a soda lime glass in vacuum were made by quadrupole mass spectroscopy and surface ionization techniques. Peak Na° emission intensities occur some 3–6 ms after the fracture event and decay over tens of milliseconds. This behavior is attributed to the diffusion of Na⁺ ions into a layer of damaged material at the surface where the ions are subsequently neutralized and thermally emitted as Na°. Charge carriers generated during fracture and subsequently trapped at defect sites apparently play important roles in charge compensating Na⁺ diffusion and in neutralizing Na⁺. During the first 300 ms following fracture, we also observe intense, short lived (400 μs) bursts in Na° emission which may be associated with catastrophic relaxation of residual stresses. The kinetics of Na emission suggest that the relaxation of newly formed glass surfaces involves rather complex surface physical and chemical processes.