The validity of SIMS observations of alkali metal segregation into intergranular regions of ceramics

Abstract

Secondary ion mass spectroscopy has been used in the static mode to study fracture faces of ceramic materials and glasses. The static SIMS conditions minimize interlayer mixing, and equivalent etch rates down to 0.001 nm min^-1 can be used with reasonable sensitivity, e.g. count rates > 50 s^-1. A comparison between a caesium aluminosilicate ceramic (pollucite, CsAlSi₂O₆), a titania-based multiphase ceramic (Synroc C) and a borosilicate glass will be described. The multiphase ceramic Synoc C gives evidence that alkali metal cations are enhanced by factors greater than three on fracture face surfaces compared with bulk levels or polished faces. The fracture mechanism appears to be predominantly intergranular. Under the same conditions enhancement is not observed on fracture faces of the single-phase ceramic pollucite or on the borosilicate glass. The evidence suggests that selective sputtering, ion beam-induced diffusion, changes in secondary ion/neutral ratios and interlayer mixing are not responsible for the enhancement but that intergranular regions retain higher levels of Cs, Na and K. Interlayer mixing effects can be observed on the pollucite and glass samples at higher beam currents and voltages. The paper discusses the validity of SIMS results by comparison with scanning Auger and XPS evidence from similar surfaces.