Epoxy Vacuum Impregnation

[Probeman]

I was informed recently that we had a vacuum issue in the Sx100, that seems to have been caused by an improperly cured epoxy mount that had been "vacuum impregnated". That is the specimen had been pumped in a bell jar under liquid epoxy in a small plastic beaker to remove air bubbles and to "push" the epoxy into the sample pores when the bell jar is finally vented...

There is nothing wrong with using vacuum impregnation to remove air bubbles and impregnate a specimen with epoxy, but one has to learn to distinguish air bubbles coming from within the specimen, from bubbles of volatile reagents in the uncured epoxy.

If the epoxy looks like it's "boiling", you might be losing important reagents that are necessary for a proper cure.

I always give every finished sample a quick "smell test" before I place it in the instrument airlock. If I can smell epoxy, then the sample is not going in one of my electron beam instruments!

[Ben Buse]

On the Edinburgh Ion Probe website, they suggest that epoxy boiling is due to using too high a vacuum, and suggest using a vacuum of 20inHg - 250 Torr

https://www.ed.ac.uk/geosciences/facilities/ionprobe/technical/prep

[Gseward]

My home brew efforts (the remit: cheap,effective, idiot-proof):

See attached

The advantage of the syringe is that I don't need to pump on the epoxy - typically I pump, dump in the epoxy and vent. Ideally I would also add a leak valve, although this would be costly.
I typically centrifuge the syringe full of epoxy first, to minimise bubbles of air, and then purge the air and a little epoxy through the unused 3-way valve port
For our typical samples, the vacuum is used to prevent air bubbles getting trapped between the edges of tiny grains and the substrate when the epoxy is introduced, but would also be fine for 'impregnation' samples.
I also have a larger home brew chamber with a multiple liquid feed-through approach using tubes rather than a syringe.

Gareth