Diffusion of Neon Isotopes in Fused Quartz

Abstract

The diffusion of Ne²⁰ and Ne²² through the walls of high‐purity fused quartz hollow cylinders was studied using a mass spectrometer as a detecting device. The diffusion process was found to be relatively simple and fairly well described by Fick's laws. Diffusion coefficients and permeabilities were measured for both isotopes in the temperature range of 440° to 985°C. The D₀'s for Ne²⁰ and Ne²² were (2.21±0.12) × 10^—4 cm²/sec and (2.08±0.17) × 10^—4 cm²/sec respectively. The activation energy for diffusion for Ne²⁰ was 11 370±80 cal/g atom and the value for Ne²² was found to be statistically equivalent to this. The best estimate of the ratio of the D₀'s was 1.05±0.01. Solubilities were calculated by dividing the permeabilities by the diffusion coefficients. The heats of solution for the two isotopes were the same and equal to — 1950±150 cal/g atom. The significance of the isotope effect in diffusion is discussed.