Instructions for polishing grain mounts
- Round slides or leucite/epoxy sample mounts
- leucite slide holder (optional)
- 100 (163 microns, red), 220 (68 microns, green), and 600 (60um, yellow) diamond grit mesh laps (top drawer in probe prep lab)
- Timer (in overhead cabinet in prep lab)
- 15, 6, and <2 µm diamond powder (in probe prep lab)
- distilled water, cloth laps and glass mounting plate
It is difficult to write a generalized polishing procedure, because the length of time needed for each step is variable from sample to sample. However, here are some general guidelines.
- Take the sample, diamond grit laps, timer, and leucite sample holder to the MSEC polishing room (3rd floor).
- Find the magnetic wheel (generally in the dish drainer) and place the wheel on the polishing mount. Center the 163 µm diamond grinding lap (colored side down) on the wheel. Place the splash guard over the wheel.
- Turn on the water to a thin stream. Turn on the power to the wheel and adjust the speed (about midway through the green on the dial. Grind the sample until most of the grains are exposed, but don’t grind down too far. DO NOT press down hard on the lap, but hold the sample down with about the weight of your hand. For grain mounts, less than half of the average grains should be ground away otherwise they could be ground to nothing on the next grinding step. Take care at this step to keep the sample flat. Look at the sample occasionally, and if it has become wedged or domed, attempt to correct the problem. Once the sample is done, turn off the wheel and detach the 163 µm diamond mesh lap. Rinse the lap and place it in the drain rack to dry.
- Mount the 68 µm diamond mesh lap (green) onto the wheel,turn on water, and grind for 3 min. Apply very light pressure (basically just let the sample ride on the surface). Again, try to keep the sample flat. Rinse the lap when done and place it in the dish drainer to dry.
- Mount the 68 µm diamond mesh lap, turn on the water and repeat procedure, grinding the sample for 3 minutes on this wheel. When finished turn the wheel speed all the way to the left and shut off the power to the wheel. Turn off the water and rotate the faucet into the center sink. Remove and rinse the mesh lap and the magnetic wheel and place them in the dish drainer.
- Clean up the work area, mopping up any excess water. Finish drying the diamond laps, wrap them in paper towel and place them back in their plastic bags. Make sure the lights are off and the door is locked. Proceed to the probe prep lab.
- If using a sample holder remove the sample and place in a small beaker of water, and ultrasonify for about 20 seconds. Rinse the sample holder in tap water.
- Find the 15 micron polishing cloth. This should be stuck to a glass backing plate and stored in a ziplock bag. Remount the sample in the sample holder (if applicable). Wet the polishing cloth and sample surface with distilled water. Apply a pinch of 15 micron diamond powder to the sample and polish for 4 minutes, applying moderate pressure and changing the sample orientation occasionally.
- Remove the sample from the holder and ultrasonify in a beaker for about 40 seconds. Rinse a couple more times with DI water.
- Place the 15 micron polishing cloth on top of the water chiller, and cover with a piece of Kimwipe. Wipe the work surface with a wet cloth before proceeding to the next grit and dispose of any used kimwipes.
- Find the 6 micron polishing cloth. This should be adhered to a glass backing plate and stored in a ziplock bag. Wet with distilled water and pply a pinch of 6 micron diamond powder to the sample. Polish the sample for 6 minutes, applying moderate pressure and changing the sample orientation occasionally. You want to achieve a sample surface with few pits, and an even network of small scratches. Occasionally, you may have to polish an additional 3-6 minutes to achieve a good polish, depending on the type of sample .
- When done, ultrasonify the sample in a small beaker for about 40 seconds.
- Place the 6 micron polishing cloth on top of the water chiller, and cover with a Kimwipe. Wipe the work surface with a wet cloth before proceeding to the next grit and dispose of any used kimwipes.
- Find the <2 micron polishing cloth. Prepare in the same way as the 6 micron cloth, using the 1 micron diamond powder. Polish the sample for 1 minute on this wheel. Ultrasonify and rinse the sample. Clean the sample with petroleum ether and place in the box labeled “ready for C coat”.
- Place the <2 micron polishing cloth on the counter near the oven (away from the coarser grit polishing cloths) and cover with a Kimwipe.
- The polishing cloths need to be put back in their ziplock bags when dry, this will take around 1 hour. Come back to the lab in about an hour to put them away.
The 6 and 1 micron polishing cloths are easily contaminated, and once contaminated will not give a good polish. Always ultrasonify the sample and rinse the sample holder before using these cloths, be careful not to spill anything on them, and cover or bag them when not in use. Only have one polishing plate on the counter at a time to avoid cross-contamination.