# Manufacture an artifact with compression

Room-temperature superconductivity has finally been demonstrated, as reported by Quanta (and others), with the caveat that it requires compression of the substrate at nearly 2 Mbar. Obviously, this is an impractically high pressure, but if a different material were found that only required a much lower pressure, would it be feasible to manufacture wires under compression? If so, what is the current state of the art? I have not been able to find any examples of such a product. Most apropos to chemistry, what is a practical upper-bound on tension/compression we can expect from currently known materials?

A trivial example would be to put a spring in a box, which only requires compressing the spring and sliding it into a box. For the wire, one could perhaps imagine a strange "cylindrical press" (not sure if there is such a device) and a jacketing material with extremely high tensile strength into which the wire is thus threaded (or, more likely, the jacket is somehow rolled onto it).

A more sophisticated system would be a compressive jacket which is applied in a relaxed state, possibly at high temperature, and then cools/shrinks into a high-tension state which applies the necessary compression.

• I doubt that any sort of high pressure superconductor has any practical value. However it would of immense interest to theoreticians to help understand the nature of superconductivity.
– MaxW
Oct 14 '20 at 19:27
• @MaxW suppose that further research reduces the pressure requirements but only gets down to, say, 10 bar, or even 2 bar. Are you saying even that is infeasible? I find that hard to believe. Oct 14 '20 at 19:30
• It is not forbidden to dream. But the conductivity of practically all known substances and mixtures have already been studied so far, at ordinary pressure. It would be extremely improbable that a superconductor at room pressure and room temperature could be discovered. Why was this substance not yet studied ? The substance reported by Quanta is a mixture $\ce{CH4 + H2S}$. and this is a gas at room pressure and temperature. It becomes a superconductor under 1 Mbar. Oct 14 '20 at 19:40
• @LawnmowerMan - your Pyrex glassware in the kitchen has undergone ion exchange to form a compressive layer on the surface. This reduces crack formation and growth, toughening the Pyrex. Shot peening does similar things on metal surfaces. Oct 14 '20 at 21:27
• If it were only a few hundred or thousand bars, run the cable underwater. 10 m depth = ~1 bar. Challenger Deep ~1,000 bar. Oct 14 '20 at 23:10

Jon Custer helpfully noted (in a comment) two common production processes that result in compression of the final product. I did some research to discover the typical pressures involved.

# Tempered Glass

Glass may be tempered by cooling the outer layer quickly, while letting the inner layer cool slowly. As the inner layer cools, it shrinks; but because the surface layer is already cool, it cannot continue shrinking, so it experiences compression instead. One can think of glass tempering as producing an end result in which the core glass is literally pulling the surface inward. Very cool!

According to J.H. Nielsen, tempered glass retains compressive stress on the order of 100 MPa, if I am reading Figure 12 correctly. This is equal to 1 Kbar. That's 3 orders of magnitude short of the Mbar pressures created by the diamond anvil, not to mention the difficulties entailed by embedding wires in molten glass, and yet, this is at least a plausible way forward.

# Shot Peening

The surface of a cold metal can be further compressed simply by banging on it really hard. Most commonly this is accomplished by firing small metal shot at the surface at high velocity and volume. This induces plastic deformations which have a higher density than the underlying metal, and thus a compressive strain within the surface which helps strengthen various industrial products like springs, crankshafts, and jet engine blades.

According to this source, shot peening can induce compressive strain on the order of 800-1000 MPa, according to Figure 1. However, it should be noted that the compressive layer is only about 100 μm deep. So, this gets us up to 10 Kbar or so which is even better than glass tempering, and doesn't require high temperatures. Very interesting!