Difference between revisions of "Salts of oxoacids"

Revision as of 15:04, 1 July 2021

The X-O-X bonds present in those compounds increase the space between the spacially linking X atoms. This lead to a lower density of bonds in cross sections inclusion of bigger voids thus higher porousity. Due to the porousness of these compounds it is harder to get the surfaces flat - figuratively like the surface of a pumice stone. It's impossible to get them as smooth as passivated diamond. [todo: investigate wheter superlubricating bearings can be constructed from these types of diamondoid compounds]

(wikipedia:oxoacid)

Silicates (& Quartz)

Silicates typically have pretty good mechanical properties.
Typically Mohs 5-6 sometimes up to almost ~8.

Of interest as base materials may be the pure end members of the mixing series of olivine (wikipedia) / peridot (wikipedia)
From Mg₂SiO₄ forsterite to Fe₂SiO₄ fayalite.
And especially the associated high pressure modifications.
High pressure modifications tend to have higher crystal symmetries and mechanical strength at the cots of a bit of thermal stability.

Olivin/Peridot end-members and their low pressure stable stable high pressure modifications

Low pressure magnesium endmember forsterite:

• Mg₂SiO₄ Forsterite – orthorhombic dipyramidal – Mohs 7

High pressure modifications of fortserite:

• Mg₂SiO₄ wadseylite (wikipedia) – sorosilicate – ortorhombic – dipyramidal – Mohs ?? – mid pressure crystal structure
• Mg₂SiO₄ ringwoodite (wikipedia) – nesosilicate – cubic – Mohs ?? – 3.9g/ccm – high pressure crystal structure – 3D structure (de)

Low pressure iron endmember fayalite:

• Fe₂SiO₄ Fayalite – orthorhombic dipyramidal – Mohs 6.5-7.0 – 4.39g/ccm – 3D structure (de)

High pressure modifications of fayalite:

• γ-Fe₂SiO₄ ahrensite – cubic – 4.85g/ccm – high pressure crystal structure of fayalite – 3D structure (de)

Neo-polymorphic transitions

The low pressure modifications forsterite and fayalite (and tephroite, ... see further below) are all isostructural (atoms at the same places).
This allows for neo-polymorphs spanning the natural mixing series. Just checkerpatterned as deisred.
(wiki-TODO: Magnesium and iron are pretty far apart in the periodic table – find out why they behave so similar electronically in these minerals)

Q: Is there an iron analog to wadseylite?

Ringwoodite (Mg) and ahrensite (Fe), while both cubic, have quite different structure. No neo-polymorphs here.
But Maybe unnatural iron-ringwoodite and magnesium-ahrensite can be piezosynthesized.
At least a little bit of substitution should work if electronic similarity still holds in these high pressure modifications

Silicates of further rather common elements

Calcium:

• γ-Ca₂SiO₄ Calcio-Olivine – Mohs 4.5 – orthorhombic
• β-Ca₂SiO₄ Larnite – Mohs 6 – monoclinic (?)

• Ni₂SiO₄ Liebenbergite (de) – (Mohs 6-6.5 or 4.5?) -- orthorhombic
• Mn₂SiO₄ Tephroite (maybe less interesting since Mn is more scarce) – orthorhombic dipyramidal – Mohs 6
• TiSiO₄ Titanium Silicate (no natural mineral here?) [1] (broken)

Beyond that adding one more element there are an innumerable amount of natural silicates around.

Some semi random picks of other silicates

Misc, Not exactly a salt but related ...

• PbCa₃Zn₄(SiO₄)₄ esperite [2] Mohs 5-5.5 (unabundant zinc | exceptionally hard lead mineral) Specific gravity: 4.28-4.42

Other pages listing silicates of interest

Context specific silicates are also listed on these pages:

• Ternary and higher gem-like compounds
• s-block metals – lists some alkali and earth alkali silicates (among other compounds)
• Iron – lists a few iron silicates

Phosphate minerals

(wikipedia)

Calciumphosphates (bone biominaeral):

• Especially interesting: Hydoxy- Fluor- & Clorapatite Ca₅(PO₄)₃(F,Cl,OH) - (Mohs 5 defining mineral) - a biomineral [3]

Magnesium and iron (aluminium) phosphates lazulite, scorcalite, wagnerite (naturally 75%iron 25%magnesium) (anhydrous low pressure modifications):

• FeAl2(PO₄)₂ iron-lazulite (wikipedia) – monoclinic – Mohs 6
• MgAl2(PO₄)₂ magnesium-lazulite
• FeAl2(PO₄)₂ iron-scorzalite (wikipedia) – monoclinic (does not look so) – (Mohs 5.5-6.0)
• MgAl2(PO₄)₂ magnesium-scorcalite
• Fe2PO4F iron-wagnerite [4] – monoclinic – Mohs 5.0-5.5
• Mg2PO4F magnesium wagnerite

• Al₂(PO₄)(OH)₃ augelite [5] – monoclinic – Mohs 4-4.5
• FePO₄ heterosite Wikipedia:Heterosit(de) – orthorhombic dipyramidal – Mohs 4-4.5

• MnPO₄ purpurite [6] – ortorhombic dipyramidal – Mohs 4-5 (manganese is not too abundant) – (is that impressive color material inherent rather due to impurities?)
• Zn₂Fe(PO₄)₂•4H₂O Phosphophyllite (wikipedia) – monoclinic – zinc iron phosphate - rather soft (Mohs 3.5) – rather soft
• Pb₅(PO₄)₃Cl pyromorphite (wikipedia) – hexahonal dipyramidal – Mohs 3.5 – (relatively hard for a lead mineral)
• Y(PO₄) Xenotime (wikipedia) – tetragonal dipyramidal – Mohs 4.5 – (yttrium is not too abundant)

Carbonate minerals

(wikipedia - minerals) (wikipedia - artificial)

Many may be isostructural and amenable to making neo-polymorphs (to check).
The relatively low symmetry crystal structure may be a bit annoying.
Degradability solubility properties when exposed to the weather as spill may be decent.
(Only relevant if that is the design goal).

Calcium:

• CaCO₃ Calcite Mohs 3 (defining mineral)
• CaCO₃ Aragonite Mohs 3.5-4

Magnesium:

• MgCO₃ Magnesite [7] – trigonal – Mohs 3.5-4.5

Both:

• CaMg(CO₃)₂ Dolomite [8] – trigonal rhombohedral – Mohs 3.5-4
• Mg₃Ca(CO₃)₄ Huntite [9] – trigonal – Mohs 1-2 (way too soft!)

Copper:

• Cu2CO3(OH)2 malachite [10] – Monoclinic – Mohs 3.5-4.0
• Cu3(CO3)2(OH)2 azurite – Monoclinic – Mohs 3.5-4.0 – (complex structure)

Iron, zinc, manganese, lead:

• FeCO₃ Siderite [11] – Trigonal – Mohs MgCO₃
• ZnCO₃ Smithsonite (mindat) – trigonal – Mohs 4.0-4.5 – 4.44g/ccm
• MnCO₃ Rhodochrosite – trional – Mohs 3.5-4.0 – manganese is not too abundant
• PbCO₃ Cerussite [12] – orthorhombic dipyramidal – Mohs 3.0-3.5 (soft) – 6.57g/ccm

Sulfate minerals

(wikipedia)

Sulfate minerals are generally rather soft with few exceptions.
One of the harder ones is brochantite (wikipedia) - (Mohs 3.5-4)

• CaSO₄ anhydrite [13] (decomposes slowly to hydroxyde gypsum)

Very common chemical. Not at all useful as structural material though:

• Copper(II) sulfate – copper sulfate pentahydrate Chalcanthite – Mohs 2.5 – very soft

Borate minerals

(wikipedia)

• Mg₃B₇O₁₃Cl Boracite (wikipedia) - (Mohs 7-7.5)
• Mn₃B₇O₁₃Cl Chambersite (wikipedia) - (Mohs 7)

• Al₆B₅O₁₅(F,OH)₃ Jeremejevite (wikipedia) - (Mohs 6.5-7.5)
• Mg₇(BO₃)₃(OH)₄Cl Karlite (wikipedia) - (Mohs 5½)
• Ca₂B₅SiO₉(OH)₅ Howlite (wikipedia) - soft (Mohs 3.5)
• MnSn(BO₃)₂ Tusionite (wikipedia) - (Mohs 5-6) - tin
• CaZrAl₉O₁₅(BO₃) Painite (wikipedia) - rare zirconium (Mohs 8)
• ...

Nitrate and Aluminates

Nitrates are typically rather water soluble.
While that migh be desired for intentional degradability of inner normally sealed structures
nitrates are also typically extremely soft, strongly limiting their applicability for mechanical purposes.
See: (wikipedia - natural nitrate minerals) and (wikipedia - artificial nitrates)

Aluminates:
(wikipedia)

Salts of metal oxoacids

TODO ...

Related

• Oxygen

External links

Wikipedia:

• Solubility chart: https://en.wikipedia.org/wiki/Solubility_chart
• Oxoacid
• Category:Oxoacids