Author Topic: Explain This If You Can!  (Read 31812 times)

Probeman

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Re: Explain This If You Can!
« Reply #15 on: January 14, 2014, 03:27:09 PM »
Ok, I'll start with this recent image of mapping a glass melt inclusion in olivine about 120 um in size. Conditions were 15 keV, 30 nA and 2 sec (2000 ms) per pixel. 256 x 256 pixels.



It is quite reproducible and also seen to a much lesser degree in the other elements (e.g., K) as might be expected.

When I zoom in on the Na x-ray map I count around 10 pixels between the "high points" in the map attached in this post:

http://probesoftware.com/smf/index.php?topic=144.msg595#msg595

Since the stage scan utilized 2 seconds per pixel that mean that the "frequency" of these "high points" is around 20 seconds.

Now, here is where it gets weird: has anyone else noticed an apparent "cyclic" appearance to their TDI plots that seems to be reproducible? I couldn't find a good example so I'd appreciate someone else posting a better example, but this "cyclic" appearance looks something like this plot here with 3 sigma statistics.



Edit by John: here's a better example of the sinusoidal variation in x-ray intensities:

http://probesoftware.com/smf/index.php?topic=40.msg4006#msg4006
« Last Edit: February 03, 2016, 02:05:23 PM by John Donovan »
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John Donovan

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Re: Explain This If You Can!
« Reply #16 on: February 07, 2014, 12:45:14 PM »
Ok folks, what is this sample? (see attachment below).

A couple of hints: it is a pure element, it is in a vacuum chamber.
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Gareth D Hatton

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Re: Explain This If You Can!
« Reply #17 on: February 11, 2014, 03:05:10 AM »
I thought red mercury was a myth ;)

John Donovan

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Re: Explain This If You Can!
« Reply #18 on: February 11, 2014, 09:14:52 AM »
Ha!    :D

Nope, not mercury.  Two more hints: The actual size is roughly fist sized.  The color is from its temperature.
« Last Edit: February 11, 2014, 09:20:24 AM by John Donovan »
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Philipp Poeml

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Re: Explain This If You Can!
« Reply #19 on: February 11, 2014, 11:28:14 PM »
Let me help you with this: The isotope mass of this is 238.049553 u.


John Donovan

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Re: Explain This If You Can!
« Reply #21 on: February 12, 2014, 08:49:55 AM »
Let me help you with this: The isotope mass of this is 238.049553 u.
And getting a little bit lighter all the time...  ;D
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John Donovan

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Re: Explain This If You Can!
« Reply #22 on: February 12, 2014, 08:52:58 AM »
John J. Donovan, Pres. 
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Probeman

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Re: Explain This If You Can!
« Reply #23 on: March 05, 2014, 10:36:06 AM »
OK, here's a new one. What is this specimen?

See attached.
« Last Edit: March 05, 2014, 10:38:28 AM by Probeman »
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Probeman

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Re: Explain This If You Can!
« Reply #24 on: April 01, 2014, 03:01:00 PM »
OK, here's a new one. What is this specimen? See attached.

Well it turns out that the customer had etched the surface with nitric acid, so as is often the case, if you see something weird- it probably is!   ;)

A couple more weird ones (no acid etch this time!) are below... any guesses?



Hint: CL image...



Hint: BSE image...

These are from my old JEOL 6400 SEM taken many moons ago.
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Les Moore

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Re: Explain This If You Can!
« Reply #25 on: November 11, 2014, 02:49:47 PM »
Occums razor might suggest that a very simple reason for the Na depletion matrix - has someone put down a matrix of analyses before you mapped it?
1. Reprep and map again.
2. If it is present, is it dose dependant? Kv or current?

re the fine structure, it could be a solid state eutectoid decomposition or a spinodal decomposition.  Both are free energy minimisation reactions driven by local activity reductions. The spacing of the lamella is diffusion (in the solid state) controlled and would give some indication of the cooling rate through the reaction. 

I would doubt it is a eutectic as the structure is so fine and would suggest a very high cooling rate as diffusion in liquids is so fast.
 

John Donovan

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Re: Explain This If You Can!
« Reply #26 on: November 12, 2014, 09:15:29 AM »
Occums razor might suggest that a very simple reason for the Na depletion matrix - has someone put down a matrix of analyses before you mapped it?
1. Reprep and map again.

Hi Les,
I assume you are talking about the Na map of the melt inclusion at the top of the topic? If so, please use the "quote" button for clarity next time...    :P

Your speculation is not unreasonable (that it was previously mapped), but no, it is a virgin material and the artifact is due to some sort of sub surface charging dynamics during the stage scan acquisition. It is also present (though less apparent), in the K image (and Si and Al). The material is essentially homogeneous. See Julie Chouinard's poster from this summer (attached below).

2. If it is present, is it dose dependent? Kv or current?

We have not tried various conditions. If it is an ion migration artifact, and I'm pretty sure it is as these glasses show extreme time dependent intensity (TDI) effects, then beam current, size and even keV should affect the artifact "wavelength".

I have an idea for a TDI map acquisition, but so little time...
« Last Edit: November 12, 2014, 02:54:15 PM by John Donovan »
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Gseward

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Re: Explain This If You Can!
« Reply #27 on: March 05, 2015, 12:52:39 AM »
Whilst browsing the 'Standards' topic I noticed a mention of the Sulphide standards produced by Gerald Czamanske. This reminded me of some images I took a while back, and the story that went with them: I rescued two 1"dia. standard mounts from an old desiccator minutes before they were thrown in a dumpster. After doing some investigation, they turned out to be a set of the Czamanske sulphides. I put them in the SEM to check out what I had. After a quick glance at low mag I was cursing myself for not doing a better job of 'dusting-off' the surface (there appeared to be a large clump of fluff on the surface of one of the standards). I zoomed-in to find a spot to take a quick EDS measurement and this is what I found:



This is an image of the surface of the pure Ag standard. As far as I can tell, the crystals growing on the surface are all the same phase: Ag2S.
I remember being told in a geochemistry class that this is why there is always a bone spoon in a silver cutlery set!
« Last Edit: March 05, 2015, 03:21:50 PM by Gseward »

Les Moore

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Re: Explain This If You Can!
« Reply #28 on: May 27, 2015, 04:27:51 PM »
Trivia on the silver sulphide:

This effect causes major problems on silver connectors in industrial (SO2 rich environments).
I have also heard that the telephone exchange at Rotaurua in NZ has a double air environment.   
It is also of great use in sepia toning of B&W prints.
The latter is employed to see the S distribution in steel.... an unexposed (or developed for that matter) piece of acid soaked photographic paper is placed on a ground/polished steel sample.  Any S rich inclusions or regions create H2S and these react with the Ag in the paper to leave brown spots.  It's called a sulphur print.

Probeman

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Re: Explain This If You Can!
« Reply #29 on: November 04, 2015, 03:27:54 PM »
This is a beam damage issue related I think to the beam damage issues in SiO2 as described here:

http://probesoftware.com/smf/index.php?topic=418.msg2269#msg2269

But this is zircon, a much more robust material I think everyone will agree. And the data was acquired at 100nA but with a 5 um defocussed beam. To me it looks like a 5 um carbon ring, with a smaller central area that appears more damaged. So what I'm wondering is whether the damage pattern seen here:



represents an uneven distribution of electrons in the defocussed beam or if the central area that appears damaged is simply an effect of the heat being concentrated in the center, since the outer regions are also being heated by the defocussed beam so the center area should get the hottest...

I guess my question is: has anyone attempted to profile the electron distribution in a defocussed beam spot?  In other words, is the electron density distribution profile across the defocussed beam like A or B:



I assume we all hope it is like A, but I suspect it is a lot more like B...
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