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Author: Subject: Low T precipitation of crystalline refractory metals
Joe Skulan
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[*] posted on 16-3-2016 at 07:38
Low T precipitation of crystalline refractory metals


Refractory metals can be precipitated in pure, crystalline form at low temperatures by thermal decomposition of organometallic complexes. For example, OsO4 can be reduced by thermal decomposition of an OsO4-olefin complex to thin 500-100 Å) films of bright Os metal for mirrors, etc. Similar processes can be used for W, Re, Ir, etc.

In everything I’ve read, these processes have been used only to produce thin films of metal. Why? Is this because thin films are what people want, or because it is the only thing that can be made in this way? If the latter, what constrains the thickness of the films?

I can’t see any obvious constraint. A 1000 Å layer of Os, while thin, still is 500-1000 atoms thick, which is far too thick for the original non-Os surface to have any effect on the outer, growing surface of the crystal. From the point of view of that surface the existing crystal is infinitely thick. It seems to me that the thermal decomposition process could build a metal film of any thickness. Am I missing something?

And to forestall the obvious comment, yes, I know how dangerous OsO4 is. I am very far from actually trying this myself, and if I ever do it will all proper precautions and containment. It’s just the theory I’m curious about now.
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elementcollector1
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[*] posted on 16-3-2016 at 09:05


I think the practical constraint might be speed of deposition. How long did it take to produce a 1000-atom-thick layer of Os?



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Joe Skulan
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[*] posted on 16-3-2016 at 09:19


3-5 minutes. At that rate it would take a few weeks to get to 1mm (not unreasonable), but the time it took the film to form was not an issue in the published work. They just wanted to get a metallic film, and that is just how long it took when they dipped a glass slide in the complex and fired it under H2 or N2 at 300°. 3-5 minutes is a maximum time. Presumably it could be tweaked to make it faster.
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violet sin
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[*] posted on 16-3-2016 at 22:05


One thing I came across a while back when researching electroplating Ni w/ sulfamic acid; thickness constraints on plated layers was from crystal latis strain. It was stated thick nickel layers plated from standard baths had enough pent up force to "cup" a sheet of steel if only plated on one side. Or even forcibly crack the base metal.

Ni from the sulfamic was much more pliable/soft in nature and allowed the electroforming of complete parts, ie. Rocket thruster cones complete with all cooling/preheating plumbing internal. Big rocket, space bound main thrust stages :)

I have no documentation, it was on hathi book trust site from an old military report if I'm not mistaken I used sulfamic, amidosulfonic, amidosulfuric, aminosulfonic or sulfamidic acid + nickel as the search terms.

Working out of town again, cell phone only so it would be a BIG pain to go digging for them. A 12hr day :(
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Joe Skulan
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[*] posted on 17-3-2016 at 04:33


I wonder if electroplated crystals would be more prone to building strain than crystals formed by the thermal decomposition process. In electroplating crystals are "forced" to form by adding energy to the system, and it makes sense that some of that excess energy would be trapped in the crystal. In thermal decomposition energy is added to the system as well, but that energy goes into breaking chemical bonds and releasing Os metal. Once the metal is released, though, crystal formation is spontaneous and involves a loss of free energy. So crystals grown by thermal decomposition should be more "relaxed" than crystals grown by electroplating.

In any event, I was thinking that any thick layer of Os formed by thermal decomposition might need to be annealed.
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