Distinguishing Bulk-Diffusion from Surface-Desorption Limited Gas Release Processes

TL;DR

This paper presents a method to distinguish between surface desorption and bulk diffusion limited gas release processes by analyzing temperature ramp experiments and their effects on release curves.

Contribution

A novel approach is proposed to identify whether gas release is limited by surface desorption or bulk diffusion using temperature ramp comparisons.

Findings

The peak position remains unchanged in first-order desorption.

The peak shifts to higher temperature in other cases.

The method differentiates kinetics types based on Arrhenius analysis.

Abstract

The release of a gas limited by surface desorption, or by diffusion from the bulk of spherical pebbles is revisited. A method is proposed to identify the release limiting process, by comparing a partial temperature ramp, up to slightly beyond the release peak, followed by a rapid temperature drop, to a second, full release ramp. Comparing the release curve from the second ramp to that of the first one: i) the peak is unmoved in first order desorption kinetics, and moves to higher temperature in the other cases, ii) as compared to the Arrhenius analysis of the first curve, that of the second is, again, identical in first order kinetics, in second order desorption it maintains the slope but lowers the intercept at the reciprocal temperature origin, and it is inapplicable in bulk diffusion kinetics.