Thin Sections

Procedure

These procedures are for those who already have flat specimens prepared. They are a modified version of the procedures stated in "Petrographic Methods of Examining Hardened Concrete: A Petrographic Manual," US Department of Transportation, Federal Highway Administration, Publication No. FHWA-HRT-04-150, July 1006. See Chapter 5.3 THIN SECTIONS for much background information and procedural details.

Procedure by Karl Peterson.

First, you want to stabilize the surface of the specimen:

1. Set flat face down in tray of Logitech IU30 vacuum impregnation chamber
2. Pump down to a vacuum atmosphere
3. Introduce fluorescent resin
4. Release vacuum

Before the resin is set:

1. Remove from tray
2. Press impregnated surface directly onto a transparency film to remove the excess resin, let cure on film

When the resin is cured:

1. Peel off the sample from the transparency
2. Grind off the excess cured resin around the edges
3. Grind off veneer on the surface of the specimen, so that you reach the specimen’s actual face, where the pores are filled in by the resin.
4. Glue the freshly ground face to a clear glass slide using clear epoxy resin

Cut off the bulk of the specimen with diamond saw, leaving only a ~mm thick layer bonded to the glass. This can be accomplished with:

• Ingram Laboratories Model 103 thin section cut-off saw
• Logitech CS 10 thin section cut-off saw
• Buehler Isomet 1000 precision saw
• By hand with the use of glass plates and loose SiC grit,¹ with a birefringence color chart to determine thickness²

¹Reference book: Petrography of Igneous and Metamorphic Rocks, Anthony R. Philpotts, University of Connecticut, Prentice Hall, Englewood Cliffs, New Jersey, 1989.

²Birefringence chart example courtesy of Mineralogy Database.

You may choose to polish your sample, depending on your needs. This can be done by:

• Buehler Vibromet 1 vibratory polisher
• Buehler Ecomet 4 variable speed grinder/polisher with Automet 2 power head
• LECO AP-50 Automatic Polishing Machine
• LECO AP-300 Automatic Polishing Machine
• By hand

Now you have a flat, polished sample that can be mounted to a stub with carbon tape and coated to use in the electron microscope.