chemical analysis of unknown alloy

[durable_oreo]

I recently was reading about traditional inorganic analysis of an unknown alloy. From an idiot's POV, it's a series of precipitations, interleaved with centrifugation or filtration, followed by another precipitation, etc. Some color changes and lots of fussy details, like how to dry a particular precipitate without overheating. Order is important and there are flow charts to keep it all straight.

As far as I know, these traditional tests are qualitative. How is a quantitative analysis done? Perhaps you have an unknown copper alloy and you need to know what percentage is aluminum. How would you do that?

Is this ever done outside of college lab work?

What other methods of analysis are available? What is used in industry? Atomic absorption spectroscopy and XRF come to mind.

 

[mrfailure]

When I don't know what I have, I start with energy dispersive spectroscopy (EDS) in a scanning electron microscope. It tells what elements are present in identifiable quantities and will give a rough idea of the quantities, especially if you look at a polished surface in a mount. Once you have these, you than can send the sample for quantitative analysis (for example, by OES - optical emission spectroscopy - or other means) to get an exact composition. You will need to quantify all elements even if you are only trying to get one like Al.

 

[weldstan]

Wet chemical analysis is still done but I don't know how often. When I worked in LA many years ago, a wet chemist at a small met lab there was the final arbiter of unknown analysis in many law suits, including 2 cases where my company was involved. When I worked on the Space Shuttle, we tested five different OES labs in the area for the chemistry of one specific alloy that was used therein and compared them to that produced by that wet chemist. We chose the lab that was closest to the analysis of the wet chemist to perform all the future work for us. Note all five labs produced different analyses for the same specimen.

 

[mfgenggear]

Spectro analysis

 

[mrfailure]

There are caveats in the analysis approach I mentioned that I left out to streamline the general approach. Beside OES, ICP (Inductively Coupled Plasma) is often used for quantifying some or all of the elements. Carbon/Sulfur analysis (commercially called Leco analysis) may also be needed in addition to the other proceesses.

 

[mfgenggear]

I personally have run it but I would forward the specimen to a met lab. They would run the test.
Seemed to give pretty good results.

 

[EdStainless]

I worked with a we chem lab back in the early 80's.
Each of those filtrates is a known compound.
By drying and weighing them you can get the exact composition.
and there is no interference between elements.
But it would take a skilled chemist two or three days to run a set of 10 samples.
Which was actually only 5 alloys because everything was run in duplicate.
We had them testing samples for us that we then used as XRF calibration standards.
It was an alloy class for which no standards were available.

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P.E. Metallurgy, consulting work welcomed