Best method to verify NI/CR plating composition? 2

[rollingcloud]

Out of ICP, OES, SEM, EDS, and XRF, I guess XRF would be the cheapest method. However, since XRF penetrates thin layers and we have a portable XRF gun, would it just include elements from both the plating and the underlying base metal given that nickel/Cr plating is often very thin (e.g. 0.0005'')?

 

[EdStainless]

Penetration will depend on the voltage of the tube.
For handheld devices it likely won't be very deep, unless you are talking about real XRF.
Do you care about light elements? Such as B, P, S, C and so on.
If so, then XRF is not the choice.
OES is the fastest and easiest.

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[mrfailure]

With field XRF (aka PMI) you would need toc clean the surface thoroughly of oxides and contaminants that would throw the results off, and also make sure the beam does not penetrate to the substrate, which may also may throw off results. I question whether OES is really viable as well for such a thin coating. I approach this issue instead by making a transverse mount, polishing it, and then use EDS in an SEM. Also give you the added benefit (if you need it) of confirming the substrate. Note with EDS and XRF that you can confirm material, but you can't use tese techniques for determining compositional conformance as they are not considered fully quantitative.

 

[EdStainless]

With OES you can choose how deep to penetrate the surface.
XRF uses reference standards and calibration curves to give accurate quantitative results.
This is the same as with OES.
ICP on the other hand is an absolute method.
But it requires sample preparation into a liquid form.

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[mrfailure]

Ed, is 0.0005" a feasible distance for an accurate OES quantification?

The advantage of using EDS in cross-section is penetration depth becomes irrelevant so you can select the energy you need to identify plating.

 

[rollingcloud]

Thanks Ed and mrfailure.
Yes, we are only required to verify the Ni & Cr, not light elements. Often, we're also required to verify the coating thickness, which the XRF gun can't measure. So, I guess it depends on the handheld XRF device? If it's not penetrating the coating layer, then for cases where we need to verify the base metal elements, we would have to remove the coating?

 

[mrfailure]

This is another advantage to using EDS from a mounted cross-section. You can measure coating thickness in the SEM at the same time you are collecting your EDS data.

 

[EdStainless]

A handheld device will only give you good enough information to say if it matches a known alloy.
This is not an analysis.
Real XRF machines will generate >10e8 counts of the major elements, not just tens of thousands.
This how you get statistically significant accuracy.

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