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From: Richard Smith <null@void.com>
Newsgroups: rec.crafts.metalworking
Subject: Re: A small welding job
Date: Mon, 23 Jan 2023 08:08:37 +0000
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"Jim Wilkins" <muratlanne@gmail.com> writes:

> "Richard Smith"  wrote in message news:lycz763kcp.fsf@void.com...
>
>> ...

> ...

> -------------------
> Raman lidar.
> -------------------

> ...
>
> https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5090567/
> "Only at higher temperatures are the values from different works
> [diffusion rate measurements] close to each other; at room temperature
> differences in the order of three magnitudes are observed. This is a
> direct result of the interaction of hydrogen dissolved interstitially
> in the crystal lattice and lattice defects in the iron, such as
> vacancies, foreign atoms, dislocations, grain boundaries, voids and
> other defects. Most of these defect sites tend to react exothermally
> with interstitial hydrogen, as opposed to the endothermic dissolution
> of hydrogen in the lattice, and constitute traps for hydrogen uptake,
> respectively sources for hydrogen release. The effective diffusion
> coefficient of hydrogen in the presence of defect sites is always
> smaller than that of ideally dissolved hydrogen in the defect-free
> perfect crystalline lattice."
>
> Is the rate of diffusion through a thin sheet relatable to the rate of
> diffusion the same distance into a solid?
>
> For real-time measurement:
> https://unisense.com/products/h2-microsensor/
>
> For integrated measurement, hydrogen can reduce silver and copper
> compounds to the metal, and increase the sensitivity of photo film.

Correct.  Exactly so.  "Trapping".  By 300degC and upwards all steels
are showing the same diffusivity to hydrogen accordign to all
experimental data - they all interlock to say that.

Thanks
"Raman Lidar"