[Phalcone42]

Hi all,

Time to bridge the gap between Mat Sci and Inorganic Chem. I was wondering if it were possible for a small molecule that would normally form a complex with a metal in aqueous or organic solutions to also form in an alloy as a solute in the solid solution. I'm looking at this in the context of using asymmetric solutes to create asymmetric lattice distortions.

Example: Au can complex with SCN- . If I were to add solid AuSCN to a melt of Au, would the SCN act as a solute in a similar way as Sn being a solute in a Cu rich bronze? (idk the thermal decomposition data of AuSCN, but lets say I picked a system where T_{decomp,complex} < T_{m, Alloy})

[AWK]

I only heard about ammonium, hydrazinium and tetramethylammonium amalgams.

[Phalcone42]

I had not thought of amalgams, I'll have to see if they strengthen by forming a solid solution, or if the salts they make with the metals form precipitates.

I still wonder if the general question I posed holds for all complexes (with a decomposition temp lower than that of the melt of course)

[Enthalpy]

For most metals including gold, it looks badly difficult to find organic complexes that withstand the melting temperature (hence T decomposition > T melting). Amalgams and low-melting alloys look more promising indeed.

If gold is the target (and I would enjoy harder gold), maybe a ceramic like MgO or denser BaO would stay bound within molten gold, but I don't see how to introduce atom pairs of MgO. Dissolve Mg in Au if feasible, introduce O₂ somehow, quench Au before MgO coalesces and buoys to the surface?

[Phalcone42]

@Enthalpy: My intuition is that most ceramics that I would add to the solution would phase separate before entering solution (see FeC₃ in steel, nitrides in Ti alloys, silver chloride impurities in gold). And that would lead to precipitate strengthening rather than solute strengthening.

I'll look into this more though; see if I can find any papers about Mg/Au alloys.
Edit:  I've been thinking about this from a purely theoretical perspective. For what application do you want stronger gold?

@AWK: On ammonium amalgams I found this (Translated from german; taken from doi:10.1002/zaac.200600163):
"Our X-ray experiments, in agreement with earlier studies, show a strong structural similarity of tetramethylammonium amalgam and α-Hg. The packing of Hg atoms in the Amalgam is slightly contracted at the ab plane and strongly disordered towards the c axis. In this direction, the platelets expand as they decompose. It is suggested that tetramethylammonium molecules are intercalated between layers or layer packets of α-Hg. The content of tetramethylammonium in the phase is evidently constant, as the reproducible values ​​for different prepared samples show."

The intercalated ammonium molecules sound to me like a phase separation effect, rather than a solute effect. I may be wrong about that though.

[AWK]

See Hume-Rothery rules for solid solutions.

[Phalcone42]

I'm familiar with those rules. IIRC, they are empirically determined guidelines for metal solubility, but not physical laws. I'm specifically looking for an exception to them.

[Enthalpy]

I too believe ceramics will precipitate from liquid metals rather than dissolve. That's why I put "I don't see how to introduce atom pairs of MgO" and suggested to dissolve the ceramic-forming metal, then introduce oxygen, and quench before the ceramic coalesces.

Maybe a melt is the wrong direction. Accumulative roll bonding might disperse a complex in a metal at a reasonable temperature. It wouldn't be bonding here, but the same process.

Or you might insert the precursors to the solute in different sheets of the base alloy, then bond the sheets finely by accumulative roll, and once the precursors are very close to an other, heat moderately to let them diffuse and react with an other.

If the base metal is very unreactive, as gold is, maybe CO would dissolve. At least, it won't precipitate. Advantage of all gases.

[Phalcone42]

Thanks for the feedback. I will look into accumulative roll bonding.
The diffusive idea is also interesting.