OK, I took a deeper look.
It turns out that the STEEL component of J-B Weld comes apart nicely in acetone. I use those words carefully -- "comes apart" -- because most of the material doesn't actually dissolve. Instead, what I think happens is that the uncured resin component does dissolve, revealing that the bulk of the material is already solid crystals of something or other.
In any case, after three washings in acetone followed by a thorough drying, what's left over is a substantial pile of fine powder. When completely dry, the color of the pile is light gray, but when wetted, it goes very dark gray. Scattered throughout the pile of light gray powder are larger flakes of dark stuff that are just barely visible to the naked eye in diffused light but obviously sparkle in directional light.
I transferred a small pile of this stuff to a microscope slide and slid it around over a 1/4" cube rare earth magnet to see if anything moved. Nothing did, in any component of the powder.
Then I put on a drop of acetone, stirred to mix, dropped on a cover slip, and slid that around while pressing it down. I waited for the acetone to dry, and photographed through the cover slip using a 40X NA 0.65 objective with the diaphragm stopped slightly for maximum contrast. Shown here are the results.
Direct projection onto Canon T1i (APS-C), most of the whole frame, ZS PMax stacked at 1.25 microns.
Crop:
Now I understand why my first impression of the squeezed-thin resin was "like trying to look through stippled glass". I was actually trying to look through a bunch of these clear crystals suspended in resin. By the way, there's no reason to think that this sample is representative of the size distributions. Certainly there was a lot of separation by size as the stuff was settling out of suspension.
It remains an open question what this stuff is. I haven't tried dissolving the crystals in anything. In any case, my guess is that we're looking at that large percentage of the STEEL component that is not covered by the MSDS for J-B Weld.
Some suggestive guidance might be provided by the MSDS of a competing product, Loctite Weld. According to the
MSDS for that product, its ingredients are:
Code: Select all
3. COMPOSITION / INFORMATION ON INGREDIENTS
Hazardous Component(s) CAS Number Percentage*
Epoxy resin Proprietary 30 - 60
Calcium carbonate 471-34-1 10 - 30
Barium sulfate 7727-43-7 10 - 30
Triiron tetraoxide 1317-61-9 10 - 30
Epoxy resin Proprietary 1 - 5
Kaolin 1332-58-7 1 - 5
Titanium dioxide 13463-67-7 0.1 - 1
Quartz (SiO2) 14808-60-7 0.1 - 1
* Exact percentage is a trade secret.
Concentration range is provided to assist users in providing appropriate protections.
In reading the Loctite Weld MSDS, I'm struck by what a very different approach it takes from that of J-B Weld.
Here is the J-B Weld MSDS, Section 3:
Code: Select all
3. COMPOSITION/INFORMATION ON INGREDIENTS
Substance/mixture Mixture
Ingredient name % by weight CAS number
reaction product: bisphenol-A-(epichlorhydrin); epoxy resin 10 - 30 25068-38-6
crystalline silica non-respirable 0.1 - 1 14808-60-7
carbon black respirable 0.1 - 1 1333-86-4
Occupational exposure limits, if available, are listed in Section 8.
I've copied here both Section 3's in their entirety.
In my admittedly naive interpretation, I think what I'm looking at are close to opposite ends of the spectrum of completeness for writing an MSDS. This is speculation of course, but Loctite appears to have listed everything in the stuff, just on the off chance that it might be relevant, while J-B Weld lists only what they think they have to. It's an interesting distinction. (Both suppliers list U.S. addresses, by the way.)
--Rik
