Binary gem-like compound

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binary compounds that do not react or dissolve in water

Theres is a big stable group of B-C-N compounds, a few aluminum (Al2O3,AlB) and few silicon (SiC,SiO2,N4Si3) compounds.

There seem to be no binary iron minerals that have hardness above mohs 6.5

Titanium forms chemically and mechanically rather stable compounds with many nonmetals.

binary compounds which very slowly dissolve in water and are thought to be rather nontoxic

Solubility is good for an envirounmental viewpoint (decay time of abandoned scrap material) but bad for engineering materials. Especially in nanosystems the slightes bit of dissolvation completely destroys the outermost layer of nanomachinery. This makes sealing of products and high system reduncancy even more necessary than it is when more stable materials are used.

simplest most water stable compounds of abundant alkaline eart metals

most water stable solid fluorides from abundant metals

  • TiF3 titanium fluoride
  • MgF2 magnesium fluoride aka sellaide
  • CaF2 calcium fluoride aka fluorite

dangerous compounds to stay away from

  • solid nitrogen (except you want to make highly potent explosives)
  • AlP extremely toxic
  • Al2S3 toxic - H2S generation
  • sulphur phosphorus compounds - highly toxic
  • Fe3P highly toxic
  • BF3 BCl3 PCl3 all highly toxic (but gasseous anyway)

reactive but useful compounds

Many other highly reactive compounds may be useful when encapsulated and serving a non structural like electronic or other function.

Passivation layer minerals of today's industrial metals

We do have daily skin contact with these minerals without even realizing it.
Often these minerals are naturally present as ores from which the metals are extracted.

wikipedia: passivation in general

Passivation of passivation layer minerals

Here an interesting problem occurs. To prevent two atomically precisely flat blocks from fusing seamlessly together on contact their surfaces must look differently than their insides. Specifically it is often a good idea to cover the whole surface with lone pairs of electrons. But further oxidation of an already oxidized material will probably not work or be rather unstable [to investigate]. What should be doable almost always is hydrogen passivation. (Such passivation may cause higher friction due to high lateral spacing between the small hydrogen atoms sitting atop larger atoms and the low lateral stiffness of the single bonded hydrogen atoms) It may be necessary to find a special solution for each indivitual material - nitrogen phosphorus and sulfur may often be useful for plugging surfaces closed.

Pseudo phase diagrams

For orientation what kind of low level metamaterials can be built with binary compounds one can create something like "pseudo phase diagrams". "pseudo" since the structure of the material at a specific point in the diagram is not defined by the thermodynamic history of the material but by the way it was mechanosynthesized. There are lots of special positions in the diagram that arise due to the specific choosen crystal structure and checkerbord pattern.

An example of such an pseudo phase diagram would be a square with CO2 (upper left) SiO2 (upper right) beta-C3N4 (lower left) Si3N4 (lower right) as their "end members". (solid CO2 is likely to be explosive but with a sufficient number of C atoms substituted with Si atoms it will be stable - it may be possible to draft a frobidden zone around the solid CO2 corner). In this specific diargam from top to bottom from oxides to nitrides the crystal structure must change significantly (due to the changing valence number) making a less continuous transition.

[todo: add existing images of such diagrams]

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