Difference between revisions of "Calcium"

Revision as of 14:15, 18 December 2016

Calcium as pure metal is unsuitable as building material for advanced atomically precise manufacturing since:

• as metal it has meatllic interelemental bonds that is the bonds have have low directionality
• it has weak interelemental bonds
• => diffusion jumps at low twmperatures are likely
• it is also highly electropositive and reacts strongly with oxygen and even water (this actually is less of a problem since parts can perfectly be sealed)

Just oxidizing calcium may solve the problem of weak undirected metallic bonds but the formed compound is still highly reactive. Calcium oxide CaO is commonly known as burnt lime. It strongly reacts with water to calcium hydroxide. The resulting compound calcium hydroxide is slightly water soluble (it is what makes water hard / slightly basic) and very soft. Hardly usable as building material.

• Portlandite Ca(OH)₂ (Mohs 2 soft| Trigonal)

Calcium oxide does also react with carbon dioxide to calcium carbonates which (albeit still pretty soft) are a better candidate for building materials. Only silicates and phosphates of calcium though form decently hard and more water resistant compounds.

Calcium silicates (hard)

• Wollastonite (Mohs 4.5-5 | Triclinic)
• ...

Calcium phosphates (hard)

• Hydroxylapatite Ca₅(PO₄)₃(OH) (Mohs 5 | Hexagonal)
• Fluorapatite Ca₅(PO₄)₃F (Mohs 5 | Hexagonal)
• Chloroappatite Ca₅(PO₄)₃Cl (Mohs 5 | Hexagonal)

Polymorphs of calcium carbonate CaCO₃ (soft)

• Aragonite (Mohs 3.5-4 | Orthorhombic)
• Calcite (Mohs 3 by definition | Trigonal)
• Vaterite μ-CaCO₃ (Mohs 3 | Hexagonal)

• Monohydrocalcite CaCO₃·H₂O
• Ikaite CaCO₃·6H₂O (Mohs 3 | Monoclinic)

Calcium sulfates (very soft)

• Anhydrite γ-CaSO₄ (Mohs 3 | Orthorhombic)

• Gypsum CaSO₄·2H₂O (Mohs 2 by definition | Monoclinic)
• alpha & beta hemihydrate (CaSO₄)₂·H₂O

Calcium nitrates (very soft and highly water soluble)

• Nitrocalcit Ca(NO₃)₂•4(H₂O) (Mohs 1-2)

Halogenides

• Fluorite CaF₂ (Mohs 4 by definition | Cubic) All other calcium halogenides are water soluble salts.
• Antarcticite CaCl₂·6H₂O (Mohs 2-3 | Trigonal)
• Calcium hydride CaH₂ is reactive similar to calcium oxide.

Misc

• Calcium hexaboride CaB₆ is a good ceramic
• calcium silicide CaSi₂ is pretty stable
• Calcium carbide CaC₂ strongly reacts with water (it's commonly known as carbide)

Calcium carbide may be of interest since on contact with water it releases ethyne which is due to its low hydrogen content a good resource for mechanosynthesis of diamond.
Mechanosynthetic means though will allow indepencence of crude chemical means of storage like in calcium carbide.

• Calcium titanate: Perovskite CaTiO₃ (Mohs 5-5.5 | Orthorhombic)

External Links

• Wikipedia: Calcium compounds
• Wikipedia: Calcium aluminates