Instructables

How to mount, polish, and etch a sample for optical microscopy.

In order to view a metal specimen under an optical microscope, the sample must be prepared using several steps. It must be mounted onto bakelite puck, polished using finer and finer grits as well as polishing slurry, and finally it needs to be etched. These instruction are intended for the Leco mounting press and Leco polishing stations. Figure 1 above shows an example of what a sample should look like after it has been mounted.

Useful Terms:
Grit - The measure of the fineness of an material to grind or polish a surface.
Slurry
- A diamond paste used to polish metal.
Mounting - The process of compressing and heating bakelite powder around a piece of metal in order to form a solid disk or puck that can be used to handle the sample easier.
Etching - The process of using nital to reveal the grain structure in a sample for viewing under an optical microscope.
Ram - The upper and lower rods of the mounting press that are used to compress the sample. The upper one is attached by turning the levers on it and screwing it into place. The lower one is raised and lowered using a dial/knob on the machine.
Microstructure - The microscopic structure of a material.

Required Materials:
Gloves, Apron, and Safety Glasses
Sink with running water
Fume Hood
Blow Hose Gun
Bakelite (polyoxybenzylmethylenglycolanhydride)
Leco Mounting Press
Polishing Machines with 500, 400, 300, 200 and 100 grit
Diamond Slurry of 5, 1, and 0.5 micrometers
Nital Solution
A Metal Specimen (usually a steel or an alloy of steel)
Beaker
Tongs

 
Remove these adsRemove these ads by Signing Up

Step 1: Preparing the Mounting Press

Turn the handles on the upper ram until it is fully loose. Raise the lower ram in the mounting press using the knob until the upper ram sticks out. Remove the upper ram. Clean the surface of the lower ram as shown in figure 2 and remove any leftover Bakelite.