EPMA Sample Preparation Discussion Board

[John Donovan]

This board is intended to focus attention on topic related to EPMA sample preparation, including but not limited to polished sections, polished thick mounts, drop and spin cast nano-particles and thin film samples.

Topics may include sample procurement, handling, storage, grinding, polishing, and coating.

[dawncruth]

This might be the appropriate location for this question.

I am finally going to make new standard acrylic standard blocks that will make regular re-polishing easier.

Given that the block will consist of materials that polish more/less easily do folks have a recommended polishing protocol? For example, should I load the hard materials and start polishing those and then load my softer materials?
Or should I consider standard placement in the puck?

The reason I ask is that I have a lot of Smithsonian standards I'll need to prep and we all know how tiny those are. I will also have other small, hard to obtain materials to polish as well.

[Probeman]

It is quite painful to mount small fly specks in a large mount. The curvature produced from the epoxy cure will become your bane.

Also I would avoid the Smithsonian standards unless you can get larger quantities, enough to not worry about sample prep.  Personally I hope such inhomogeneous, inclusion ridden materials (and in such miniscule amounts!) will soon become obsolete for reasons discussed here:

https://probesoftware.com/smf/index.php?topic=1415.0

The future (I believe) are high purity, stoichiometric synthetic standard materials.  We've already started with MgO, Al2O3 and MgAl2O4. Next we will be obtaining synthetic SiO2 and silicates such as Mg2SiO4. Along with synthetic Fe3O4 and YIG, etc.  *Globally* available standards!

Instead concentrate on high purity synthetic standards and calibrate your dead time constants carefully.  Making standard mounts is a lot of work, so we might as well utilize the best materials available.

[Alejandro Cortes]

Any thoughts on resin/hardener brands? The current mixture we are using results in epoxy mounts that contain sulphur which is a pain when measuring apatite.

[Probeman]

Any thoughts on resin/hardener brands? The current mixture we are using results in epoxy mounts that contain sulphur which is a pain when measuring apatite.

My favorite epoxy is "Petropoxy" which is sold here:

https://www.burnhampetrographics.com/petropoxy/ppp.php

It's stay liquid until heated so give one a long working time which is useful for complicated mounts like this:

https://probesoftware.com/smf/index.php?topic=172.msg12595#msg12595

[Anette von der Handt]

I actually had bad long-term results with Petropoxy where, after two years, the epoxy had shrunk enough to create gaps between my standard grains and the epoxy. Maybe I did something wrong when curing the Petropoxy but I am a big believer in cold-setting, slow-curing epoxies for epoxy mounts that are supposed to last a long time (like standard mounts).

We use Stuers Epofix.

[Alejandro Cortes]

Any thoughts on resin/hardener brands? The current mixture we are using results in epoxy mounts that contain sulphur which is a pain when measuring apatite.

My favorite epoxy is "Petropoxy" which is sold here:

https://www.burnhampetrographics.com/petropoxy/ppp.php

It's stay liquid until heated so give one a long working time which is useful for complicated mounts like this:

https://probesoftware.com/smf/index.php?topic=172.msg12595#msg12595

When using sticky tape or vaseline to mount grains, heating up the petropoxy will get rid of the tape and vaseline. Grains will more or start floating around. Any alternative to this problem?

[Probeman]

You might want to watch these videos of Tim Teague (master technical petrologist) discussing his methods:

https://probesoftware.com/smf/index.php?topic=1163.0

He used Petropoxy for almost everything and could obtain a mirror polish on lead metal!

With respect to your question I think he would heat the sample slightly until the Petropoxy "gelled", and then removed all the tape and only then cured it fully with more heat.

He was able to get very amazing grain mounts of anything using this method:

https://probesoftware.com/smf/index.php?topic=172.msg12595#msg12595

https://probesoftware.com/smf/index.php?topic=172.msg8991#msg8991