Metallographic Cleaning Information
Introduction
Cleaning and drying is perhaps the most underrated processing step in specimen preparation. Yet improper cleaning can lead to misleading results. Cleaning is required to remove polishing residue as well as particulates on the surface. Cleaning can be classified into two categories:
- Intermediate cleaning
- Final cleaning and drying
Intermediate Cleaning
Intermediate cleaning is important in order to minimize cross contaminaton of abrasives and swarf material. Intermediate cleaning is best accomplished with rinsing and ultrasonics. For the best results the specimen and holder should be cleaned with water and a cotton swab to remove excess abrasive and swarf. A secondary cleaning with an ultrasonic cleaner and an appropriate surfactant (cleaning solution) is recommended for removing inaccessible abrasive and swarf which can be located in specimen cracks or pores, cavities in the mount, and in the specimen holder crevices. A tap water rinse is recommended in order to remove the surfactant. Air drying is recommended but not always required for this step.
Final Cleaning
Final cleaning is the most important cleaning step for removing residue prior to specimen examination. This cleaning step can be more difficult because of the tendency of the final polishing abrasives to crystallize or agglomerate on the specimen surface. Final cleaning should be performed immediately after or at the end of the final polishing step. For very fine abrasives such as SIAMAT colloidal silica and Nanometer alumina, rinsing the polishing pad with distilled or deionized water for the last 10-15 seconds of the polishing stage helps to mechanically scrub the specimen surface as well as clean the polishing pad.
For difficult to clean specimens, a cotton swab dipped in alcohol can be useful for scrubbing the specimen.
A similar procedure is also recommended following etching.
Drying
Following the pad/specimen cleaning it is recommended that the specimens be cleaned in an ultrasonic cleaner and then dipped or sprayed with an alcohol solution. The alcohol replaces the water and allows for more efficient drying. Air drying with compressed air or in a heated oven produces dried specimen surfaces.
Corrosion Inhibitors
Corrosion or staining can occur if water remains on the surface or in any pores or gaps in the mounting resin. This corrosion can lead to water stains on the metal surface. The use of an organic corrosion inhibitor dip can eliminate this problem as well as protect sensitive surfaces from air oxidation over time.
Application Guidelines (Cleaning and Drying)
- Apply distilled or filtered deionized water to the polishing pad for the last 10-15 seconds of the polishing sequence
- Remove excess abrasive and swarf from specimen holder using a cotton swab and ultrasonic cleaning solution, followed by a water rinse
- Ultrasonically clean with appropriate cleaning surfactant, followed by a water rinse
- Dip or spray specimens with an alcohol solution, and dry with compressed air
Trouble Shooting Guidelines for Cleaning and Drying
| Symptom | Cause | Action |
|---|---|---|
| Specimen surface has a thin "matte like" film | Thin coating of NANOMETER alumina particles | Lightly remove particles with a cotton swab and alcohol |
| Specimen surface has a crystallized residue on the surface | Most likely crystallized colloidal silica | Repolish and rinse polishing pad and specimen with water for last 10-15 seconds of polishing step |
| Water spots on specimen | Hard water rinsing | Lightly repolish and rinse with D.I. water followed by an alcohol rinse. Dry with compressed air |
| Pits in specimen after water rinsing | Water soluble phases corroding | Clean with organic solvents such as alcohol |
| Inability to completely dry specimen | Water seeping out of cracks or pores in the specimen or mount | Dip in an alcohol corrosion inhibitor. The corosion inhibitor provides a protective organic coating on the surface and the alcohol allows the liquid to evaporate faster from the surface of the sample |
Cleaning/ Drying Product Descriptions
Cleaning
| Description | Quantity | Catalog Number | Product Image |
|---|---|---|---|
| Ultrasonic Cleaning solution | 32 oz (0.97 l) 128 oz (3.8 l) |
UC-1000-32 UC-1000-128 |
 |
| Ultrasonic Degreasing/ Cleaning solution | 32 oz (0.97 l) 1/2 gallon (1.9l) 128 oz (3.8 l) |
UC2-1000-32 UC2-1000-64 UC2-1000-128 |
|
| Compressed Non-flammable gas | each | AIR-1000 |
Preserving Specimens for Storage
| Description | Quantity | Catalog Number |
|---|---|---|
| Organic Corrosion Inhibitor (100X concentrate in IPA) | 32 oz (0.97 l) | PCC-7500-32 |
| Urethane Spray Coating | each | URE-1000 |
| 1.25-inch plastic Storage container | 25/pkg | STORE-0125 |
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