Bubble Counter Sample Preparation
At a minimum, slabs should be prepared per section 8 of ASTM C457. The polishing procedure used in the NCVP lab depends upon the size of the slabs being analyzed.
Slabs that will fit in the Lapmaster (4" X 3") are prepared as follows:
- Grind the surface to be analyzed on the #60 magnetic-backed diamond wheel being sure to apply pressure evenly across the entire surface. The operating procedure for the Diamond Pacific Lapping Wheel may be found here.
- Review the Lapmaster 12 operation procedure here.
- Turn on the agitator on the Lapmaster slurry tank.
- Add about 1l water to the tank.
- Add about 1 tablespoon of #600 silicon carbide grit to the tank.
- Place the sample, side to analyze down, in a conditioning ring on the lap plate in one of the roller bearing yokes, put a sponge on the sample and place the pressure plate on top of the sponge.
- Set the timer on the Lapmaster to 15 minutes.
- Check periodically to see that the conditioning ring(s) are rotating and that slurry is being applied onto the plate. Take appropriate action as necessary.
Slabs that do not fit in the Lapmaster are prepared as follows:
- Grind the sample on the magnetic-backed diamond media progressing through the following grits: #60, #100, #200, #325 and #500. Find the operating procedure for the Diamond Pacific lapping wheel here.
The remaining steps are the same regardless of the size of the sample.
- In the wash basin located in the sample prep lab, wash the polished surface thoroughly and carefully by running compressed air through a stream of water over the face of the sample.
- Dry the slab at 50C.
- Apply a thin, even coat of 1:5 nail hardener:acetone to the polished surface and allow to dry for several minutes.
- Do a final wet polish with #600 SiC sticky-back media on the Diamond Pacific lapping wheel. Be careful as considerable force will be required to keep from having the slab pulled out of your hands.
- Dry the polished slab at 50C.
- Blacken the entire polished surface with a black marker. Any black marker will do, but opaque pigment markers are recommended (ex: SAKURA ColorProducts Corporation, Japan) . Apply marker in even, parallel strokes in one direction, turn the sample 90 degrees and repeat the application.
- Press in your white powder of choice (we like wollastonite powder). Pour sufficient powder on the blackened surface, spread and press the powder into the voids using a stiff, straight implement (a petrographic glass slide works well). Take care not to drag the powder over the surface as it will abrade away the black treatment.
- With a sharp single-sided razor, scrape off the excess powder.
- With a VERY lightly oiled finger or thumb, remove the last bit of powder, leaving a relatively shiny black surface where no voids are present and bright white, powder filled voids.
- Apply small stickers (we use the refracting squares cut from stickers) to each corner (and roughly equidistant along the longitudinal edges of long/large samples) to keep from having the hard surface of the sample come into contact with the scanner glass and potentially scratching it.