Theoretically, what is the smallest stable metallic lattice that can exist independently? In other words, the smallest possible grain size of a metal powder. This must be somewhere between a few atoms and a few microns. If the grain size was only a few atoms, then the substance would be essentially the same as a liquid, which would appear impossible, given that it would be existing at a temperature above the below the melting point of said metal. At sizes of many microns, particles of metal will not spontaneously bond to become one lattice, so at what point between these two extremes is the smallest possible independent lattice? And why, after that point, will two lattices of an equal size not bond together? I realise this has no practical relevance, as it would be impossible to create such a fine grained metallic powder, but I thought it an interesting question nonetheless. I wonder, does a mathematical relationship exist between the TSA of each grain and the rate of combustion/reaction?
-Oli
This subject has been extensively studied but is a fairly narrow specialization and is of interest the fields of electo-plating, electron beam lithography and (IIRC) hard drive platter engineering.
5-10 nanometers seens to be around the lower size limit for a crystalline metal “grain” as part of a metal surface. I would imagine that this would also define the lower limit that a metal could be “powered” and still maintain some degree of separation, unless other factors like incipient oxidation or magnetic polarity issues some into play, but this is just a WAG.
Your need to refine the question. Using sputtering you can easily deposit a thickness of a few atoms. This layer is not a liquid. It is also different from a non-crystalline metallic glass.
Are you asking about powder metallurgy? Here you can make very fine powders, but they can only exist in a vacuum since they oxidize rapidly. The powder itself is stable.
I guess what I’m asking is down to what point would such a powder be stable. Below what point would grains begin to clump together to form a larger lattice.
-Oli
In reply to astro:
So where does Liquidmetal fit in?
In case you haven’t heard of it, Liquidmetal is an amourphous solid that does not have a grain size - it is structured like a liquid.
-Oli
Liquidmetal is an alloy of quite a number of different metals; I suspect that this is why it does not form grains.
Perhaps partly, but I was under the impression that the main reason Liquidmetal does not formk grains was due to the cooling process involved.
-Oli
Don’t metals exhibit “vacuum welding?” Unless layers of oxide or contamination intrude, metal powders SHOULD spontaneously fuse together. Maybe the question is: how small can we make particles of a particular metal without the particles turning totally to oxide within a short time.
I remember an article within the last few years where some reseacher was suprised to find that 8-atom clusters of some ??? metal did exhibit electron band structure. Supposely the theory of the time predicted that far more atoms should be required before metal clusters start acting “metal-y.”