Analytical Methods in Diffusion Studies

Abstract

In this chapter, we provide an overview of analytical methods used in diffusion studies. These methods fall into two broad categories-direct profiling and bulk release/exchange. Direct profiling methods, where the concentration of diffusant vs. depth is determined, can employ a variety of techniques, and can access diffusivities ranging from ~10 −9 to 10 −24 m 2 /s. Among these methods are the "classical" techniques of serial sectioning and autoradiography, which, despite a long history of application in diffusion studies, are now rarely used, having been superseded by other analytical methods with better depth resolution and greater flexibility. Direct profiling can also be subdivided into methods involving step-scanning, with measurements made by stepping across a sample cut normal to the diffusion interface, and depth profiling, where analyses are performed parallel to the diffusion direction. Step-scanning may be used in cases where diffusion profiles are at least many tens of micrometers long, as it is limited by the beam spot size (typically ≥ 2 mm; although transmission electron microscopes have much better spatial resolution, they are not used extensively in diffusion studies dues to the difficulties in sample preparation) of the analytical tool used and the minimum number of points necessary to define the diffusion profile. The electron microprobe is used for diffusion measurements by step-scanning, as is the ion microprobe (Secondary Ion Mass Spectrometry, SIMS), and IR spectroscopy. SIMS instruments can also be used in depth profiling mode when smaller diffusion distances are measured. The accelerator-based ion beam techniques Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection (ERD) are also applied in measuring short diffusion distances. This group of techniques is capable of high depth resolution (~10 to a several tens of nm) and thus can be used

Oxygen and Hydrogen Diffusion in Minerals

“…A detailed outline and discussion of the analytical methods employed in diffusion studies is presented by Cherniak et al (2010) and only a brief overview of analytical methods commonly employed for oxygen and hydrogen diffusion studies is presented below.…”

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“…The total amount of dissolved water is denoted as H 2 O t and herein sometimes referred to as water. Both H 2 O m and OH can be quantified using infrared and Raman spectroscopy (e.g., Stolper, 1982b;Ihinger et al, 1994;Cherniak et al, 2010;Ni et al, 2013). H 2 O m and OH can interconvert through the reaction (e.g., Stolper, 1982a,b) …”

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“…Information about analytical techniques to measure diffusion profiles can be found in Cherniak et al (2010). In most of the sulfur diffusion studies, chemical diffusion coefficients were measured, meaning that a gradient in sulfur concentration was present in the experimental diffusion samples.…”