Gemstone-like compound

Diamondoid materials encompass all materials that:

• do not diffuse at room temperature
• are stiff enough to keep their shape under thermal movement
• have dense three dimensional networks of covalent bonds - (short bond loops => no polymeres)
• (not necessarily but desirable) do not react or dissolve in water

The main reason why diamondoid materials are the material of choice for diamondoid molecular elements DMEs (the constituents of artificial advanced AP systems) is that they do not jitter and wobble or even diffuse away while they are built robotically (a blind process) and that products out of those systems can be made so that they only have one to a few tightly controlled degrees of freedome. This way one can test one action at a time which enables engineering with fast progress. A systems design that poses the necessity for scientific entangling of convoluted relationships is usually considered bad. Natural nanosystems are like this because of random incremental evolution in small steps without lookahead. In this regard one obviously shouldn't copy from nature.

Wikipedia has its own page about diamondoid materials. See here: [1]

Carbons versatility

By now (2014) carbon is the only building material for which extensive studies about tooltip chemistry have been undertaken.
Note that just by structuring carbon (and adding a bit hydrogen as passivation agent) many material properties will be archivable. This is because diamondoid materials go far beyond the known allotropes and thermodynamically stable phases. They extend into the set of low level and high level metamaterials.

Low level metamarterials include very stable patterns that are highly ordered. Those patterns may include vacancies and may have periods of repitition of arbitrary length. Their structural alterations are small enough to influence properties that originate at such low size levels e.g. chemical electrical magnetical and other properties (especially relevant for the non mechanical technology path). A simple example of a low level metamaterial is when donation atoms are embedded in a checkerboard or other exactly periodic pattern. The set of sufficiently metastable low level metamaterials is significantly bigger than the set of designed materials that can today (2014) be cooked together by macroscopic means. This set of designed materials favours random mixing because they require very restrictive good thermodynamic accessibility.

The distinction between low level metamaterials and high level metamaterials may be difficult in some cases. Conventially doped semiconductors for example are not called metamaterials.

Beyond carbon from acetylene and methane many further studies are needed most importantly:

• machanosynthetic splitting of water for scavenging usable oxygen
• direct splitting of oxygen
• splitting of nitrogen - artificial and different to current natural or industrial methods of nitrogen fixation.
• splitting of carbon dioxide
• fluorine and the nonmetal elements of the third period

Carbon nanotubes can replace the scarce element copper for electrical cables.

Diamondoid compounds

list of potential structural compounds

Compounds that are synthesizable under solution are of interest for technology level II to bridge the gap between technology level I and III.

binary compounds that do not react or dissolve in water

• carbon sp3 network allotropes: diamond, lonsdaleite; sp2 allotropes: fullerenes, graphitic networks
• silicon carbide (also cubic or hexagonal)
• silicon (also cubic or hexagonal)
• B₄C boron carbide
• SiB₄; SiB₆ ?
• four allotropes of elementar boron
• AlB₁₂
• β-C₃N₄ beta carbon nitride [2] (possibly a health hazard if cyanide release can occur - to investigate)
• Si₃N₄ silicon nitride
• cubic BN cubic boron nitride
• BP boron phosphide
• SiO₂ quartz (it's actually slightly water soluble) & allotropes like dense and hard stishovite
• Tectosilicates: [3] [4]
• Al₂O₃ aluminum oxide - aka sapphire
• Fe₃C iron carbide aka cementite
• iron silicides & iron borides ? - unknown properties
• FeS₂ FeS iron sulfides - pyrite marcasite ...
• Fe₂O₃ Fe₃O₄ hämatite magnetite
• Cu₃P CuS (copper is not too abundant)
• B₆O boron suboxide (hardest known oxide)

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.

• TiC titanium carbide
• TiSi₂ titanium disilicide (unknown mechanical properties ?)
• TiB₂ titanium diboride
• TiN titanium nitride
• TiP titanium(III) phoshide (metallic conductivity)
• titanium sulphides TiS (goldbrown), TiS₂ (bronze/golden yellow), Ti₂S₃ (black,graphitic), TiS₃, Ti₃S₄, Ti₄S₅, Ti₄S₈, Ti₈S₉
• TiO₂ Ti₂O₃ titanium oxide polymorphs: rutile anatase brookite

drawn from the atmosphere

Oxygen and nitrogen rich compounds like SiO₂ and Si₃N₄ are interesting because more than half of this material can be drawn directly from the atmosphere. When atmospheric carbon dioxide is used carbon allotropes and β-C₃N₄ can be drawn 100% from the air.

back to the atmosphere

When burning diamondoid materials (hopefully in a smart way - thus only in traces - see recycling) it strongly depends on the type of chosen material whether they convert to gasses or just reform to a glassy slag. In the latter case it will be more difficult to recover the elements in pure form. The rough rule is: When heated under oxygen mainly carbon based materials burn up almost completely while silicon or metal oxide based materials just melt to a slag. Everything in between could be possible. Certain combinations of elements can become dangerous when burned together as we know from the PVC dioxine problem.

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.

• Al₄C₃
• AlN (oxidizes on air)
• the three natural allotropes of elementar phosphorus
• S₂N₂ S₄N₄ (SN)_X - diamondoid?
• allotropes of elementar sulfur

simplest most water stable compounds of abundant alkaline eart metals

• MgB₂ magnesium diboride (high temperature superconductor)
• MgO magnesium oxide aka magnesia
• CaB₂ calcium diboride
• CaS calcium sulfite

most water stable solid fluorides

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

ternary and higher compounds

Look out for rock forming minarals here.
Alkali and earth alkali compounds tend to be rather soluble in binary compounds.

• Ca(OH)₂ calcium hydroxide aka slaked lime (rather water soluble) [5]
• CaCO₃ calcium carbonate (very slightly soluble) [6]
• MgCO₃ magnesium carbonate aka magnesite (slightly soluble) [7]
• ... many more

In the earths mantle and crust silicon and oxygen are the most abundant elements. On the borther to earths outer core this changes to iron and nickle. Down there the most abundant minearls are made from mixture of those elements: olivine/peridot Of interest as diamondoid materials may be the pure end members of the mixing series:

• Fayalite Fe₂SiO₄
• Forsterite Mg₂SiO₄
• Tephroite Mn₂SiO₄ (less interesting since Mn is more scarce)
• TiSiO₄
• Titanite or Sphene CaTiSiO₅

In nature when metal is available in stochiometric excess heterogenous pallasite is formed. This rock looks really beautiful and can be found in some meteroids.

compounds which contain relatively scarce elements

Those may be useful in the lower technology levels or special tooltip chemistry where only very small amounts are needed (e.g. germaium containing tips).

• molybdenium oxide structures
• germanium compounds
• ... many more

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.

Sources for elements

Carbon is planned to be drawn from [ethyne] more commonly known as the welding gas acetylene. It has the advantage of a triple bond that when partly split up provides four unpassivated bonds and it's carrying around a minimal amount of hydrogen. Since DMEs are compact and crystal like they have a lot less surface than the source molecules and thus require a lot less hydrogen passivation. Ethyne cant be delivered in highly compressed gasseous form since it explosively decomposes. It is hardly soluble in water but well soluble in acetone ethanol or dimethylformamide. Ethyne can be manufactured by the partial combustion of methane and thus potentially be gained from renewable resources.

If one looks at the most common or most easily accessible elements and their simplest compounds one finds a list of potential structural building materials:
Link to a graphic of the most common elements in the earths crust from Wikimedia Commons.

Most easily accessible are nitrogen oxygen and argon since they can direcly be drawn from the atmosphere.
To investigate:

• Means for filtering/capturing N₂ and O₂ each selectively from the atmosphere.
• Mechanosynthetic tooltips and manipulations to gain reactive moieties out captured N₂ and O₂.

Chlorine could be drawn from common salt leaving behind sodium. To get this residual into a nonreactive environmentally acceptable form that could be used as structural material rather than just constituting waste one could chose from sodium minerals. To prefer are compounds with no crystal water and simple formulas with only elements of high importance for APM (that is which we are likely to gain control of soon after reaching technology level III) like e.g. jadeite and further ones to find.

The 13th group

Elements of the 13th group (the boron group) are special in that they can form electron deficiency bonds.

If elements of this group come into play (are used in DMEs) the view of atoms as construction blocks with a fixed number of connection points breaks down. E.g. when boron comes in contact with nitrogen the lone pair of nitrogen plucks into the electron deficient hull of boron making the two atoms more behave like two four valenced carbon atoms (with a little polar/ionic character). Prime example: ammonia borane. This is not yet handeled correctly by the software Nanoengineer-1 so it is advised to refrain from using 13th group elements for DME design for now.

In high quanities both solvated aluminum and boron compounds are alien to human and natural biology. Intake can lead to bad or unknown effects. Thus one might refrain from using strongly water soluble compounds of 13th group elements. Some information can be found here: boron and water (de); aluminum and water (de)

In tooltip chemistry boron and aluminum may be useful as tool-tips for the handling of atoms with almost full electron shells like oxygen fluorine sulfur and chlorine effectively increasing their normally low bond number. (To verify!)