The ceramic additives used to be hard to find at least. There were 3 manufacturers, only one of which would sell their product. The other three were using it in house for R&D and probably various high end contracts. The purpose of the ceramic additives is for improving matrix properties in a fabric layup - which is essentially the same thing one wants to do with these fillets. I was looking because I was making a bladder molded composite part and I keep my eyes open for ways to make small refinements. These are a nano powder ceramic likely with a particle morphology that is not too far from spherical as flow properties needed to be maintained for their original purpose of fabric wetout.
As usual, whenever someone asks about it, I failed to find it in a moderate search. I probably have some info buried on this computer somewhere but it would take me an hour to find it. So I'll suggest others do their own search. Google does not make it as easy to find things as used to be the case. I get pages of scholarly articles nowdays.
The product one is looking for is available in pound quantities in jars and they would sell to the public. The price wasn't even all that bad. One just mixes up a batch of laminating resin and then mixes in the ceramic nanoparticles (I'd suggest having a HEPA filter near by and being careful not to get dust floating in the air). Then use like normal. The more one adds, the thicker it gets, just like most any other filler. In an ideal world one would vacuum or ultrasonic degas of course. But these internal injected fillets people are doing likely don't add all that much strength anyway, so I doubt it matters much. The little fillet naturally present from getting a good glue bond in the first place is likely fully sufficient. A bigger fillet on the inside probably adds more mass than it adds strength.
For fillers more easily obtainable, of good quality:
https://www.westsystem.com/ss/filler-selection-guide/ I'd probably use a blend of 404 and 407 as a starting point and see how it goes.
Anecdotally I can tell you that 3 micron aluminum oxide platelet crystals (closest to spherical morphology) makes an interesting structural additive. But the price would have been a bit prohibitive for a hobbyist. I played with it a bit, close to 30 years ago. I probably should have persued it. It would still flow out to form a nice white glassy fillet at fairly high concentrations, and there was no cutting or sanding it when it was done unless one was using diamond tools. It's probably cheap now if one can find it. But one would need to test, rather than trust my old info.
Gerald
