Tin

Tins identity crisis

Tin is quite far on the right in the periodic table sharing its group with the non metal carbon and the semi metals silicon and geranium.

Nonetheless tin in the form commonly encountered is metallic (it's tetragonal β-Tin). But it has a second (usually unwanted) crystal form (face centered cubic α-tin - the diamond lattice). In fact this second crystal structure is more characteristic for its group.

Under low temperature conditions (below 11°C) and especially under the presence of a bit of catalyzing α-tin β-tin can start to convert to α-tin destroying the materials structural integrity due to a large change in unit cell geometry.

Since α-tin has strong covalent character it is a good target for direct mechanosynthesis. Mechanosynthesized α-tin would not be a fine powder but likely a stronger material akin to germanium. The production path through mechanosynthesis would probably not change much on its low thermal stability though. Note that long before the material melts unwanted diffusion may kick in that destroys carefully arranged atomically precise structures. (Side-note: mechanosynthesized chunks lacking vacations and featuring perfeclty flat surfaces may be pretty resillient to diffusion)

Stabilizing the more diamondoid and exotic α-Tin

To increase thermal stability some of the tin atoms in the lattice could be replaced by elements that are located above tin in the periodic table in a systematic checkerboard pattern.

Germanium is to rare for large scale construction materials. (SnGe) Carbon is not abundant but highly accessible but it might have a little low atomic radius. (SnC) Silicon is abundant and has a bigger radius and is thus likely a good candidate (SnSi).

Thermodynamically produced alloys of tin and silicon (melting and mixing) do not form an intermetallic highly ordered stochiometric phase and have thus likely very different (inferior) properties than mechanosynthesized checkerboard SnSi.

Mechanosynthesis may even allow to coax the element below tin which is lead into a diamond lattice with covalent character by combining it with carbon. This compound (PbC) is to current knowledge (2017) not thermodynamically accessible but when mechanosynthesized it may be stable enough to not blow up in your face on the slightest disturbance.

Misc

• Cassierite SnO₂ (Mohs 6-7; ~7.1g/ccm; tetragonal; rutile structure)
• Plattnerite PbO₂ (Mohs 5.5; ~9.63g/ccm; tetragonal; rutile structure)

Cassierite has a quite high density.
It's not quite as high as plattnerite but when the tin slowly leaches out into the biosphere its a non issue unlike with the lead.

Of course going for solid non oxidized metals gives far higher densities.
Mechanosynthesis just need to take into account then, that some geometries (e.g. single metal atoms on flat metal surfaces) show extreme diffusion rates and speeds at room temperature or even lower. Thus these geometries need to be either avoided or mechanosynthesized at very low temperatures and then permanently sealed by a covalent sell that does FAPP not diffusion at room temperature.

Related

• Silicon
• Germanium
• Lead

External Links

• Thermodynamic phase diagram of Sn & Si: [1]
• Wikipedia: Tin pest
• Wikipedia: Hypothetical compound lead carbide