P₂O₅ (Phosphorus Pentoxide)

Data

Frit Softening Point	Sublimates at 300C (From The Oxide Handbook)

Notes

-Phosphorus along with calcium is an essential element in plant and animal growth, thus its principal source is organic ash (i.e. calcined cattle bones).

-Phosphoric oxide is normally present in only trace amounts in ceramic materials.

-It can act as a melter in middle to high fire, but its power-per-unit-added drops drastically beyond 5% additions.

-Small amounts can produce colloidal opacity as in Chinese chun glazes. The depth of Sung glazes is attributed to phosphorus.

-P₂O₅ is a glass network former like boric oxide and silicon dioxide. Phosphoric glass tends to show as a bluish flush in glazes. It does not enter the silica chain in the matrix. However, P₂O₅ by itself (with no SiO₂ present in the matrix) is a glass former and the base of an entire class of glasses that can be doped with rare earths and metals for produce special purposes ranging from soluble medical implants to insoluble acid-resistance and even radiation resistance.

-Phosphorus can vitrify porcelains without softening and is the key to translucency in bone china.

-Phosphate ions are added to glaze frits as a color control agent during the melting of titania opacified frits.

- P₂O₅ itself can crystallize in multiple forms. It is known to influence the rate of nucleation and/or crystallization in Li₂O and MgO low expansion glaze systems.

-P₂O₅ combines with certain oxides of iron forms colorless compounds. This suggests that P₂O₅ could be used to allow the use of less pure materials in glazes and glass.

-Phosphorite mineral Ca3(PO₄)2 and Apatite 3Ca3(PO₄)2 Ca(Cl,F)2 are the parent rocks of phosphate fertilizers. The latter can thus be used to introduce phosphorus into glazes and frits.

Links

Materials	Bone Ash
Materials	Tricalcium Phosphate
Materials	Sodium Tripolyphosphate
Materials	Trisodium Phosphate
Materials	Tetrasodium Pyrophosphate Hydrated
Materials	Borax Decahydrate
Materials	Apatite
Materials	Hommel Frit 435
Materials	Phosphorus pentoxide
URLs	http://en.wikipedia.org/wiki/Phosphate_glass Phosphate glasses at Wikipedia

Mechanisms

Glaze Variegation	Phosphorus can produce variegated and mottling effects in glazes (especially low fire) when used in small amounts (e.g. up to 2%). Bone ash is a source.

By Tony Hansen
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