Beryllium

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Unusability despite benefits

Due to their extreme hardness beryllium compounds would be an excellent building material for products of advanced atomically precise gem-gum technology. Beryllium oxide BeO also known as the gemstone Brommelite e.g. has a Mohs hardness of 9. The problem though is that:

  • A) Compounds of beryllium are highly toxic and often slightly water soluble. A bad combination.
  • B) The element beryllium is rather rare.

Gemstones

In hard and water insoluble gemstones beryllium can be contained pretty safely. Simple berylliumoxide (Brommelite) - a due to it's high hardness (Mohs 9) mechanically interesting compound - is slightly water soluble though and thus toxic.

The presence of beryllium in the crystal structure usually can in cases improve the hardness of a compound.

With aluminium Al (and magnesium Mg)

With silicon Si

With silicon and aluminium

  • Beryl Be3Al2(SiO3)6 (aka Emerald, Aquamarine, ...) (Mohs 7.5-8)
  • Euclase BeAlSiO4(OH) (Mohs 7.5) - there are forms that do not cleave easily

With other elements

  • Hambergite Be2BO3OH (Mohs 7.5) - with not so common boron
  • Pezzottaite Cs(Be2Li)Al2Si6O18 (Mohs 8) - with not so common cesium and lithium; hard but complex unit cell

The following compounds are below Mohs 7 and may release critical amounts of Beryllium into the environment via abrasion.

  • Danalite Fe4Be3(SiO4)3S (Mohs 5.5-6) - silicate; contains iron and sulfur
  • Nabesite Na2BeSi4O10·4(H2O) (Mohs 5-6) - silicate; rich in crystal water
  • Herderite CaBe(PO4)(F,OH) (Mohs 5-5.5) - phosphate => maybe slightly water soluble => probably more toxic
  • Beryllonite NaBePO4 (Mohs 5.5-6) - phosphate => maybe slightly water soluble => probably more toxic

Atypical covalent salts (may be incorrect - there is a note of E. Drexlers on a wikipedia talk page on that!)

Compounds of beryllium behave quite unusual. (They could be counted to the oddball compounds.)
Its location in the earth alkali group would suggest that it forms purely ionic bonds. But instead even in compounds where one would expect to find highly ionic salt bonds like BeF2 abd BeCl2 the bonds have strong covalent character. Such covalent (directed) character of bonds is very desirable in diamondoid systems. It makes it possible to passivate surfaces and have sliding interfaces. So the material is usable for more than just structural elements.

The "brother compound" of BeO is Magnesium oxide MgO. It is also known as the gemstone Periclase and has strong ionic character bonds and forms a rock salt crystal structure. Wile excellently friendly to the biological environment it does not feature the benefit of covalent bond character.

Another less directly related compound is Al2O3 Leukosapphire. It has similar hardness and aluminium has low toxicity and high abundance. Those two things that beryllium lacks.

Beryllium often can be better bound (that is safer contained) in garnet like compounds. But then the material strength benefit got lost.
(TODO: investigate this in more detail)

Nuclear

As a side-note: Molten beryllium fluoride along with a greater mass of lithium fluoride is considered for usage in nuclear molten salt fission reactors of non atomically precise technology. The disadvantage of salts tending to form no covalent character bonds turns in an advantage in high radiation environments where the recombining ionic bonds in a structurless soup of molten salt prevent material destruction by radiolysis and metamictisation. Looked at this reversely radiation is the natural enemy of atomically precise technology since the in APM desired directed covalent bonds are susceptible to irreversible breakage and due to the densely packed functionality there's lots of structure that needs to be preserved.

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