Barium metaphosphate

Not to be confused with barium phosphate.

Barium metaphosphate is an inorganic substance with the molecular formula Ba(PO₃)₂. It is a colourless solid that is insoluble in water, though is soluble in acidic solutions through "slow dissolution".^[3] X-ray crystallography shows that this material is composed of Ba²⁺ cations attached to a polyphosphate ((PO₃⁻)_n) anion.^[4] A number of hydrated forms are known which are actually cyclic metaphosphates, Ba₂(P₄O₁₂)·3.5H₂O, Ba₃(P₃O₉)₂·6H₂O.^{[citation needed]}

Structure of a subunit of linear polyphosphate anion.

Barium metaphosphate

Names
IUPAC name barium(2+); dioxido(oxo)phosphanium
Identifiers
CAS Number	13762-83-9 N
3D model (JSmol)	Interactive image
ChemSpider	2341276
ECHA InfoCard	100.033.951
EC Number	237-362-6
PubChem CID	3084168
CompTox Dashboard (EPA)	DTXSID30872575
InChI InChI=1S/Ba.2HO3P/c;2*1-4(2)3/h;2*(H,1,2,3)/q+2;;/p-2 Key: XNJIKBGDNBEQME-UHFFFAOYSA-L
SMILES [O-][P+](=O)[O-].[O-][P+](=O)[O-].[Ba+2]
Properties
Chemical formula	Ba(PO3)2
Molar mass	295.27 g/mol
Appearance	Powder[1]
Density	3.63 g/cm3
Melting point	1,560[2] °C (2,840 °F; 1,830 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Preparation

Barium metaphosphate can be prepared by the reaction of barium carbonate with metaphosphoric acid:^{[citation needed]}

BaCO₃ + 2HPO₃ → Ba(PO₃)₂ +CO₂ +H₂O

or alternatively by the aqueous reaction of barium chloride and sodium metaphosphate:^{[citation needed]} BaCl₂(aq) + 2NaPO₃(aq) → Ba(PO₃)₂ + 2NaCl

Applications

The combination of soda and barium polyphosphate forms a low-melting glass with a high coefficient of thermal expansion. The melting point of the glass increases with barium content. This glass makes seals with low melting metals like aluminium (melting point 650 °C). Normal borosilicate glasses soften above the melting point of aluminium. This mixture is prepared by heating a mixture of diammonium phosphate, sodium carbonate, and barium carbonate.^[5]