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P2O5 (Phosphorus Pentoxide)
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 is not in any way a substitute for silica and does not enter the silica chain, but remains as a separate colloidal presence in the silicate matrix. -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 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. Mechanisms
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