Sample prep for water-soluble materials

[alerner]

Hello,

(First post to the forum, very exciting)

I am hoping people can share their experiences for best sample polishing practices for materials that are water soluble. Basically, what are the best lubricants and cleaning agents that won't dissolve H2O-soluble salts and sulfates, and also will not negatively affect epoxy mounts.

I had been using isopropyl alcohol during polishing, but just learned of the "moating" effect in epoxy around grain edges.

Thanks!
Allan

[Probeman]

I had been using isopropyl alcohol during polishing, but just learned of the "moating" effect in epoxy around grain edges.

Hi Alan,
I learned from Tim Teague at UC Berkeley many years ago that the sharp edge of epoxy around the edges of a polished grain can be eaten away (at microscopic levels) by isopropyl alcohol (and even worse is acetone), but that pure (*undenatured*) 190 proof ethanol works excellently and does not damage epoxy.  The concern being that the conductive coating might not "bridge" the "moat" you describe above.

I also remember him telling me " always rub the excess ethanol off with a KimWipe (lint free and non scratching) until the surface is dry".  The idea being, I think, that if one allows the ethanol to dry by evaporation, the dissolved residues will be left deposited on the surface.

But it further occurs to me that Tim Teague's slow RPM oil based polishing methods would be better for prepping such water soluble materials as you mentioned above, but that's about all I know on that subject.  Could one use hexane as a polishing lubricant for water sensitive materials I wonder?
john

[Anette von der Handt]

Hi,
We have people dealing with water-soluble samples (carbonates and carbonatites) and they simply polish their samples dry with diamond powder on a soft polishing cloth.

I also know that people have good results by polishing with petroleum ether as the lubricant.

[neko]

I checked with our thin section lab operator and they use a 50/50 mix of ethylene glycol and pure ethanol, a formulation based on... some ancient thing they read. Seems to work, but we work more with hygroscopic than water-soluble materials. They said they weren't sure whether or not changing the ratio would have any effect on anything, as they understand it the ethylene glycol is there to help slow down the evaporation of the ethanol.

Back in school we used kerosene with grit in Vibromet polishers on metal samples, but I think kerosene has fallen out of favor as a polishing solvent.

edit: I know the user titles on the forum are just automatically generated based on post count, but we should all just take a nerd moment to appreciate that this thread was started by "A lerner, Student"

[Probeman]

edit: I know the user titles on the forum are just automatically generated based on post count, but we should all just take a nerd moment to appreciate that this thread was started by "A lerner, Student"

Ha!  Nice catch. 

Well I just hope we're all "a lerner", when it comes to EPMA, regardless of our user titles!   

[jeffchen]

I had been using isopropyl alcohol during polishing, but just learned of the "moating" effect in epoxy around grain edges.

Hi Alan,
I learned from Tim Teague at UC Berkeley many years ago that the sharp edge of epoxy around the edges of a polished grain can be eaten away (at microscopic levels) by isopropyl alcohol (and even worse is acetone), but that pure (*undenatured*) 190 proof ethanol works excellently and does not damage epoxy.  The concern being that the conductive coating might not "bridge" the "moat" you describe above.

I also remember him telling me " always rub the excess ethanol off with a KimWipe (lint free and non scratching) until the surface is dry".  The idea being, I think, that if one allows the ethanol to dry by evaporation, the dissolved residues will be left deposited on the surface.

But it further occurs to me that Tim Teague's slow RPM oil based polishing methods would be better for prepping such water soluble materials as you mentioned above, but that's about all I know on that subject.  Could one use hexane as a polishing lubricant for water sensitive materials I wonder?
john

I used oil-based diamond paste with kerosene as lubricant for polishing water sensitive material, the results were generally satisfactory. One thing I wasn't totally sure about was that the resin block would have kerosene smell even I put it in vacuum oven at 60oC for over 48hours...I guess some kerosene got absorbed by the resin but unsure about how much it would be still in there... yeah, so I got same question as John...can we use hexane as lubricant? hexane has much higher vapour pressure compared to kero so I reckon it would go away quicker? Thanks!

[crystalgrower]

Polish with oil.  Degrease with dried hexane.  Keep the total work time to a minimum to control the exposure to humidity.