Author Topic: Smithsonian Standard Sample Preparation  (Read 12508 times)

SCGene

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Re: Smithsonian Standard Sample Preparation
« Reply #15 on: May 02, 2024, 01:28:04 PM »
Just a little more clarification about how this mount was built. You purchased a 1-inch acrylic rod that you cut into disks? Then drilled holes in the disk and the holes appear to be roughly a tenth of an inch in diameter (maybe 9/100). Then fill all the holes with epoxy and grains and you polished everything at once?  This does not involve polishing each standard in a small diameter tube and then inserting the tube in the mount?  Is that correct?

Probeman

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Re: Smithsonian Standard Sample Preparation
« Reply #16 on: May 02, 2024, 02:47:29 PM »
Just a little more clarification about how this mount was built. You purchased a 1-inch acrylic rod that you cut into disks? Then drilled holes in the disk and the holes appear to be roughly a tenth of an inch in diameter (maybe 9/100). Then fill all the holes with epoxy and grains and you polished everything at once?  This does not involve polishing each standard in a small diameter tube and then inserting the tube in the mount?  Is that correct?

If you are talking about the sample/standard mounting method developed at UC Berkeley by Tim Teague:

https://probesoftware.com/smf/index.php?topic=172.0

Then yes.  Here are the main steps:
1. Obtain 1" (~25 mm) acrylic rod.

2. Slice into disks of appropriate thickness. For samples, we would slice thin say 10 mm. For standard mounts that will get re-polished for decades, say 20 mm thick.

3. Drill small holes all the way through, yes about 0.09" I think we used a 3/32" drill.  There's a trade off- small holes mean less material area, but more material to expose on re-polishing- important for standard mounts, but small holes mean more trouble getting all the bubbles out.

4. Then place the mount on some double sticky tape so the bottoms of the holes are sealed.

5. Fill the holes halfway with epoxy.  Tim Teague almost always used Petropoxy because it stays liquid until heated up, giving time to get all 35 (or whatever) holes filled with epoxy and material.

https://probesoftware.com/smf/index.php?topic=1163.msg7946#msg7946

6. Then drop your material grains into each hole one by one.  If there is an air bubble is attached to the grain, it won't sink, but if there is no air bubble attached to the grain it will sink to the bottom.  Use a thin wire to dislodge the air bubbles and you probably want to do this under a binocular scope.  A good idea to try and have enough material to get several mms of height in each hole for repeated re-polishing (for standard mounts anyway).

7. Now once all the material is added to all the holes, fill the holes with epoxy all the way to the top.  This prevents small places for polishing agent to get into.

8. Cure the epoxy on a hot plate. For Petropoxy I think it's 135F.

9. Grid the side with material until the material is exposed in all the holes. Then polish as usual.

It's tedious work, but you'll have a mount that will last decades and hold up to repeated re-grinding/polishing.  I found that one can re-polish with colloidal silica or alumina 5 to 10 times before we start getting too much relief and have to go back to fixed diamond to get everything flat again. Then final polish with colloidal silica/alumina.

The really cool thing about this method is that because (if you got all the air bubbles out), there are no holes or cracks for grinding/polishing agents to get into, this method makes cleaning the mount quick and easy by simply squirting with 100% ethanol and wiping with a (non abrasive) KimWipe.

Also you can scribe three fiducials into the mount for quick re-location in the instrument:

https://probesoftware.com/smf/index.php?topic=46.msg9615#msg9615

But all this won't help you much since the Smithsonian gives out "fly speck" amounts of material, which is why we shouldn't be using these natural heterogeneous, inclusion filled materials that available only in limited amounts as "standards" (the food was terrible and the portions so small!).

No one should be using heterogeneous natural materials that cannot be replicated. See here for my rant on this topic:

https://probesoftware.com/smf/index.php?topic=1415.0
« Last Edit: May 02, 2024, 06:11:40 PM by Probeman »
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