Electron-Probe Microanalysis of Alkali Metals in Glasses

Abstract

The mechanism of alkali ion movement in glasses during electron-probe analysis must include a dependence on the temperature of the volume irradiated. Experimental results of the composition changes of binary oxide glasses of Na2O and K2O with SiO2 during electron bombardment indicate that there is a critical temperature for alkali ions in the diffusion process. Dependence of the critical temperature on composition and a comparison of these temperatures to the equilibrium temperature that can be produced from heat flow consideration indicates that for small beam diameters the actual temperature may be lower than that predicted. The rate of change of temperature may be more important to a probe operator than the equilibrium temperature.

Hydrophilic nature of silicate glass surfaces as a function of exposure condition

“…Increasing treatment time and temperature increases the effect of the plasma on the glass [28]. Plasma treatment has also been known to cause glass surface composition changes [30][31][32]. Because of the compositional change, there is an increase in the refractive index of the glass and a decrease in the surface layer thickness, which continues after treatment during air storage at room temperature [33].…”

Microanalysis of Glass Containing Alkali Ions

“…The effect was always reported as a nuisance and optimum conditions were sought under which the decay could be eliminated to enable a reliable analysis of such samples [3]. The decay was interpreted as caused by a temperature change [4] or as an effect of the electric ®eld created by the incident electron beam [1] based on the model used to explain oxygen outgassing from glass during electron bombardment [5]. However, the temperature and electric ®eld effects could not be separated in most cases and had to be taken into account together.…”

Electron Probe Microanalysis

“…The resulting electric field within the specimen may result in the redistribution of mobile ions. (27)(28)(29) It will also tend to produce a more shallow electron profile (and therefore a more shallow distribution of generated x-ray photons) in the nonconductor compared to a metallic specimen. The effect on quantitative analyses is that the absorption and fluorescence corrections tend to overcorrect.…”

“…The movement of sodium and potassium ions in glasses during electron bombardment has been observed by several investigators. (27)(28)(29) The writer has recently noted the redistribution of cadmium in complex glasses and mixed oxides, The motion of these ions may be toward or away from the bombarded volume, depending on the specimen and the experimental conditions. Organic or biological specimens tend to decompose (e.g., paper becomes charred) and elements of interest may be volatilized or redistributed, These instabilities can generally be detected by observing the emitted x-ray intensity as a function of time..…”