Which fumed silica are you using?

[jorj]

I've now got a half dozen types of fumed silica in my house, and another half dozen or so on the way. So far it seems like folks either get something purely labeled as "fumed silica", or they're using Aerosil 200. There are dozens of other types; I wonder what all of the unlabeled or repacked versions really are.

I have one, for example, labeled "Aerosil - cabosil". Two different brand names. I seriously doubt it's a mix of both; but even if it is, it doesn't say which Aerosil or CAB-O-SIL product. And I have another which was sold as "Aerosil 200" but is hydrophobic - which means it's *not* Aerosil 200.

So, if you're using fumed silica, I'd be interested to hear: which type? What's it labeled, and where did you get it?

(My goal here is to catalog the different properties of a dozen-ish fumed silica variants to give us some sort of baseline for comparison; if I see that folks are using something common that I don't have, I'll go pick some up to include it.)

-- Jorj

 

[Loris Medici]

Jorj, there's a hydrophobic variant of Aerosil 200 too; I think it's labeled Aerosil 200 *R* or something... In any case, you definitely need something hydrophilic!

 

[Barry S]

For small quantities--there are a lot of resellers out there, (mis)packaging various products with incorrect or poor labeling. I wish I could tell you what I'm using other than it came from Amazon, and is hydrophilic. My first package came from eBay and was incorrectly labeled as a hydrophilic type of Cabosil--it was clearly hydrophobic and made for a laughable coating session.

 

[Robert Hall]

Just order from Bostick and Sullivan and get the right stuff right off the bat. Sounds like you spent money over and over again and now don't know what you have.

I got mine off Amazon here, but again, I would just order from B&S

 

[jorj]

Thanks for the feedback, folks.

Loris, you're close - all of the Aerosil variants that are hydrophobic contain an "R". There's no Aerosil R 200, but there is an R 202. And Barry's experience is similar to my own.

Robert, I have one bag of I-don't-know-what (hydrophobic, supposedly "Aerosil 200" which can't be true); one bottle of hydrophilic FS labeled "Aerosil-Cabosil" (which is unlikely)... and 12 large bottles of specifically labeled and verified product that I sourced directly from manufacturers.

B&S is, in this case, tangled in the same problem. I've sent them mail asking *which* fumed silica they're selling, and haven't yet gotten a reply. I wonder if that's because they don't know for certain. It definitely seems to be endemic in the FS reseller trade. I've also recommended that folks buy directly from them; at least buying from them nets you a hydrophilic version.

But as far as I can tell, nobody yet knows what the "right stuff" is. As long as it's hydrophilic it seems to convey some benefit, and that's as far as the scientific analysis has gone; beyond that, each person's research is only valid to their setup, as they have a different FS than everyone else (and may not even know which FS they've got).

I could guess that Aerosil 380 is more likely to increase dmax, and Aerosil 90 more likely to streak. But those are based on other uses of those products, and not based on any evidence.

What I want to do is actually catalog how some/several/all of the variants perform, so that real qualitative comparisons can be made. And if there is indeed some particular "right stuff" that performs better, people will know to look for it. Perhaps B&S would wind up stocking that variant.

So far it sounds like this would be beneficial to those experimenting with FS, and nobody actually knows what they've got, so I might as well continue down the road I'm on...

-- Jorj

 

[Robert Hall]

If you are not getting a response from B&S, call Dana. He can help you out.