Barium metaphosphate

Barium metaphosphate

Names
IUPAC name barium(2+); dioxido(oxo)phosphanium
Identifiers
CAS Number	13762-83-9
PubChem	3084168
Properties
Chemical formula	Ba(PO3)2
Molar mass	295.27 g/mol
Appearance	Powder
Density	3.63 g/cm3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Infobox references

Barium metaphosphate is an inorganic substance with the molecular formula Ba(PO₃)₂. It is a colourless solid that is insoluble in water. X-ray crystallography shows that this material is composed of Ba²⁺ cations attached to a polyphosphate ((PO₃⁻)_n) anion. A number of hydrated forms are known which are actually cyclic metaphosphates, Ba₂(P₄O₁₂)·3.5H₂O, Ba₃(P₃O₉)₂·6H₂O.

File:PolyphosphateChainP4.png

Structure of a subunit of linear polyphosphate anion.

Preparation

Barium metaphosphate can be prepared by the reaction of barium carbonate with metaphosphoric acid:-

BaCO₃ + 2HPO₃ → Ba(PO₃)₂ +CO₂ +H₂O

or alternatively by the aqueous reaction of barium chloride and sodium metaphosphate:- BaCl₂(aq) + 2NaPO₃(aq) → Ba(PO₃)₂ + 2NaCl

Applications

The combination of sodium 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.