Author Topic: Standards for Sulfur  (Read 2964 times)

knshugart

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Standards for Sulfur
« on: May 23, 2016, 12:49:02 pm »
At the EPMA TC, there was a discussion of good versus bad standards for Sulfur. And I forgot to write down the advice I heard, whoops!

What are your favorite standards for Sulfur? Which ones are extremely beam sensitive and should be avoided?

And while you're thinking about beam sensitive standards: are there any others for other elements that those new in the field frequently chose without thinking carefully enough? Trying to avoid these pitfalls before I jump right into them.

Thanks!

Probeman

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Re: Standards for Sulfur
« Reply #1 on: May 23, 2016, 03:27:31 pm »
At the EPMA TC, there was a discussion of good versus bad standards for Sulfur. And I forgot to write down the advice I heard, whoops!

What are your favorite standards for Sulfur? Which ones are extremely beam sensitive and should be avoided?

And while you're thinking about beam sensitive standards: are there any others for other elements that those new in the field frequently chose without thinking carefully enough? Trying to avoid these pitfalls before I jump right into them.

Thanks!

Hi Kathleen (?),
It kind of depends on whether these are sulfides or sulfates. There is a pretty significant peak shift between the two due to the chemical bond- which by the way can be used to get an idea on the chemical state of sulfur.  This sulfur peak shift measurement is often used by igneous petrologists to get oxygen fugacity information in  basaltic glasses.  Jeez, I almost sound like a geologist!   ;D

So for sulfides I would use a natural single crystal pyrite.  Analyze it for traces but it will be stoichiometric.

For sulfates synthetic BaSO4 (Barite) can be obtained and is more stable than CaSO4 (Anhydrite).

As for other difficult elements/standards, I would say that a good fluorine standard can be hard to find, but I've used a synthetic BaF2 single crystal electronic material with success.

Also the other halides and alkalis can be problematic.  See here for more discussion:

http://probesoftware.com/smf/index.php?topic=301.msg2921#msg2921
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Ben Buse

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Re: Standards for Sulfur
« Reply #2 on: May 24, 2016, 05:23:10 am »
Hi,

For sulphur in basaltic glass VG2 and VG99 are good secondary standards - one has 1000 ppm and one has 100 ppm. The one with a 1000 ppm also allows you to peak-up on the sulphur which will be closer than pyrite or basalt if you can't peak up on the actual sample.

Ben

Probeman

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Re: Standards for Sulfur
« Reply #3 on: May 24, 2016, 05:43:01 am »
Hi,

For sulphur in basaltic glass VG2 and VG99 are good secondary standards - one has 1000 ppm and one has 100 ppm. The one with a 1000 ppm also allows you to peak-up on the sulphur which will be closer than pyrite or basalt if you can't peak up on the actual sample.

Ben

Yes, VG2 makes a good secondary standard. It's actually about 1350 PPM sulfur.

What we do is peak up on both pyrite and say, anhydrite, then calculate the spectrometer position 1/3 down from pyrite towards anhydrite and that's usually very close to where you will find the sulfur peak in basaltic glasses.

Here's some references:

http://probesoftware.com/smf/index.php?topic=343.msg1803#msg1803

And interestingly, the sulfur peak position changes but not it's shape, so you can pretty much use any sulfur standard so long as you are at the peak position for your standard, and also at the peak position for your unknown as shown here:

http://probesoftware.com/smf/index.php?topic=127.msg502#msg502

« Last Edit: May 24, 2016, 05:46:23 am by Probeman »
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Probeman

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Re: Standards for Sulfur
« Reply #4 on: December 05, 2017, 02:08:08 pm »
A grad student here wants to perform some scans on different sulfur containing compounds, one of them being elemental sulfur.

A quick look at Wikipedia shows 1 Pa vapor pressure at 375 K (~100 C), that might be OK though a little high for my comfort. But its vapor pressure would be 10 Pa at 400 K, so obviously that would not be good.

But using the CalcZAF temperature rise dialog, and assuming a thermal conductivity of .2 W/(MC) for sulfur, we would see only about an 18 C increase in temperature at 15 keV and 50 nA and 1 um beam, so maybe that would be OK? Only 1.8 C with a 10 um beam.

Has anybody tried hitting elemental sulfur with the beam in an EPMA?   Does any one have data for sulfur vapor pressure at say 50 C?
john
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