Vacuum Impregnation

Vacuum Impregnation is a method used to infiltrate porous samples with an epoxy type resin that allows for grinding/polishing of samples with minimal damage to the samples. This was intended to help the MMC-SD group view crushed pores and potential areas of closed porosity in the carbonized wood samples.

Loss Prevention

• The vacuum impregnation machine pulls a vacuum on the samples. Safety glasses should be worn as vacuum chambers have a inherent risk to them.
• While working with the resin, nitrile gloves should be worn to avoid contact with the skin.

Procedure

Sample Prep

• Samples must be made to fit in the sample cups commonly used for metallography. It Is preferable to not have any part of the samples above the height of the cup as well.
• To reduce the amount of leaked epoxy aluminum foil can be used at be put in between both part of the sample cup, this will also aid in removal of the cap.

Vacuum Impregnation

1. The resin used is a 2 part epoxy, for our resin, a weight ratio of 20:5 was used for resin:hardener. The total weight of epoxy depends on the number of samples, for ours 100 total grams was more than enough for 4 cups.
2. The vacuum impregnator has two chambers, the left is for the resin, the right for the samples. two vaccuum fittings connected by a hose for the epoxy to flow connects the two.
3. The resin side uses a black vacuum fitting, the right uses a larger, silver one. When putting the fittings on the hose, make sure two o-rings are used between the fitting and its bolt As shown in the image.
4. Place the resin in left chamber and samples in the right, adjust the hose so that the tube reaches the bottom of the resin beaker, and the sample side fitting can be turned to point at each sample cup. Make sure the black fitting has the set screw closing off the tube before turning on the vacuum chamber.
5. The top valve is the vacuum valve and the bottom valve is the purge. Begin with vacuum open for resin, closed for samples, and purge closed for both resin and samples. The O-rings that each chamber has on the plexiglass face may need to be maneuvered to help pull the vacuum.
6. If too much bubbling occurs in the resin slowly open the purge to relieve pressure.
7. Once a vacuum is pulled close the vacuum valve and open it for sample chamber.
8. After a vacuum is pulled align the hose over a sample cup and slowly release set screw and begin filling cups.

• Adjust the set screw to adjust the flow
• Adjust the purge valve to control bubbling

Clean Up

1. Once bubbling has finished the chambers can be purged and samples removed.
2. clean the inside of the chambers with ethanol
3. Throw away hose
4. It may be necessary to weight down samples if the resin is more dense than the sample, take samples out of chamber and cover, and allow at least 24 hours to cure.