Supercritical CO2 is heavy like a liquid, with weird and useful properties

https://www.brianneltner.com/thin-films

The key is conformal films and aspect ratio. If you're familiar with CVD, you might have encountered "duning" where film growth can produce unstable interfaces or find that a trench will get filled in at the top and leave a void underneath.

One common option is using ALD which uses alternating precursors so you can fully coat every surface of an arbitrarily high surface area material with a monolayer of your precursor, and then a second step converts that precursor to metal so you get atomically thick layers.

The downside of ALD is that it's quite slow in terms of growth rate because you can only grow one atom thick layer at a time. Additionally, the precursor has to have a vapor pressure high enough that the often solid precursors can actually be flowed through a reactor under vacuum. But it can get super thin films that can be conformal and which have incredible aspect ratios.

What I did was use sCO2 to dissolve chemicals like those ALD or CVD precursors in an "organic solvent" (sCO2 itself) to deliver it at super high concentrations to the reactor (at like 5000PSI) instead of at super low concentrations under vacuum. It stays supercritical through the full fluidized bed. But the reactor itself is hot so the precursors spontaneously decompose and do so preferentially on surfaces. But! The key difference is that because of the high precursor concentration, instead of the film growth rate being dictated by how fast precursor can get to the particle surface (diffusion limited) it's limited by how fast the precursor reacts on the surface (kinetically limited). The prior is notorious for unstable interfaces, the latter is much better because it's just growing at max speed at all locations simultaneously.

So the real difference is that it let me deposit thin films from a high concentration precursor stream.

My actual application was trying to coat copper flake with chromium metal to increase the oxidation temperature for use as a replacement to silver conductive pastes used in solar panel manufacturing. Silver was (might still be) like 10% of the total cost of making one, so this was of keen interest and would be pretty awesome. Ultimately, I was able to make it so that copper showed no oxidation at 300C over a minute while uncoated copper did show a lot of oxidation.

However, the amount of coating I needed to keep the oxygen away from the copper was too thick (or at least I couldn't make it thinner with that tech) and the chromium was expensive enough that it'd have ended up more expensive than just using silver.

So I moved on =) A project worth doing for sure, everyone I talked to about it simply could not guess if it would work. Sadly it worked but wasn't commercially interesting in the end.

Here's the phase diagram:

https://en.wikipedia.org/wiki/File:Carbon_dioxide_pressure-t...

I'm no engineer, but I like to work with engineers that are good at not just established "engines" but imaginary ones too.

I always thought any engineer should be able to understand this well-established graph just by looking at it, regardless of whether they had any ChE background.

Engineers already exposed to material phase behavior sometimes still take a little while, but there's not much there, it's a pretty straightforward graph.

Studying it alone should bring understanding, not of the full implications of the dynamic physico-chemical properties of course, just the states of matter that exist under the conditions indicated by the data.

Some engineers can never get this, I don't get that.

While I would prefer an engineer with an appreciation for what it takes to turn the imagination of some PhDs into apparatus capable of creating drawings like this, using commercially available components when possible, based primarily on drawings like this.

I'm no capitalist without other people's money (I personally owned two of the automated positive-displacement high-pressure [syringe] pumps), but a good capitalist to work with would have enough imagination for an intuitive understanding of the leverage used to assemble advanced equipment into money-making machines, when the majority of operators must accept the high-dollar components as unrecoverable costs.

https://greenfield.com/wp-content/uploads/2018/11/Spec-Sheet...

This fungible specification has no specific limit for Diacetone Alcohol content, a common impurity and one which increases during storage.

Diacetone Alcohol is an industrial solvent with properties of its own, not nearly as low-boiling as Acetone. Clean Diacetone Alcohol will also show negligible Residue After Evaporation and Non-Volatile Residue under conditions of the tests, which report mostly solids content along with many higher-boiling liquid impurities but not components as moderately volatile as Diacetone Alcohol itself.

However Diacetone Alcohol can still be a significant component of the extract once the bulk Acetone has fully evaporated, depending on the conditions of the processing. Rotovap would help a lot and more than 135F would reduce residual solvent better from a viscous matrix.

The USP Purity minimum of 99.5 basically means that the water content plus any other chemical impurities such as Iso-Propyl Alcohol & Methanol (specified) and implying things like Diacetone Alcohol or Benzene, etc (but unspecified) must not add up to more than 0.5 percent.

You might even prefer to explicitly specify a maximum limit For some other target toxins, less than some low detectable amount if you were picky.

Some legitimate laboratories may not be able to detect the difference between Acetone which contains unlisted impurities and that where it is negligible.

Take a look at the associated weaselwords from legal:

https://greenfield.com/wp-content/uploads/2018/11/OVI-Residu...

Which references this as the closest applicable guideline, even though it was intended to apply to the residual solvent content of pharmaceutical products not solvents themselves:

https://www.uspnf.com/sites/default/files/usp_pdf/EN/USPNF/g...

Better than nothing but not as cautious as it could be. You may want fewer impurities than marginal drug companies anyway, you're allowed to do that. This particular supplier does look nicely better than marginal, which is good, with typicals looking well better than the limit.

Regardless with two lots of USP Acetone having apparently identically suitable certificates, one may result in its Diacetone Alcohol or other not-so-volatile components comprising a significant portion of the extract, while the other lot would not, under the same solvent-removal conditions which are excellent for the latter batch of Acetone having only the lighter impurities such as IPA & Methanol.

I would still want to test it myself first.

Source: pioneered laboratory techniques which some other testers and chemical plants eventually adopted years later, still state-of-the-art today, including this particular material. Certified billions of dollars worth of commodities like this, single-handedly more than some single petro-chemical companies can manufacture. Less than a year ago deployed a further advanced system with two backups for 100 percent uptime in a 24hr staffed operation, for when a big oil/chemical client has their ships come in, and it was Acetone. There is still no adequate publication within ASTM, been at it since dirt was rocks, and Acetone has been around even longer. Documentation not found elsewhere.