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".

X-ray crystallography X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...

shows that this material is composed of Ba²⁺ cations attached to a

polyphosphate A polyphosphate is a Salt (chemistry), salt or ester of polymeric oxyanions formed from tetrahedral PO4 (phosphate) structural units linked together by sharing oxygen atoms. Polyphosphates can adopt linear or a cyclic (also called, ring) structure ...

((PO₃⁻)_n) anion. A number of hydrated forms are known which are actually cyclic metaphosphates, Ba₂(P₄O₁₂)·3.5H₂O, Ba₃(P₃O₉)₂·6H₂O. PolyphosphateChainP4

Preparation

Barium metaphosphate can be prepared by the reaction of

barium carbonate Barium carbonate is the inorganic compound with the formula BaCO3. Like most alkaline earth metal carbonates, it is a white salt that is poorly soluble in water. It occurs as the mineral known as witherite. In a commercial sense, it is one of ...

with metaphosphoric acid: :BaCO₃ + 2HPO₃ → Ba(PO₃)₂ +CO₂ +H₂O or alternatively by the aqueous reaction of

barium chloride Barium chloride is an inorganic compound with the formula . It is one of the most common water-soluble salts of barium. Like most other water-soluble barium salts, it is a white powder, highly toxic, and imparts a yellow-green coloration to a flam ...

and sodium metaphosphate: BaCl₂(aq) + 2NaPO₃(aq) → Ba(PO₃)₂ + 2NaCl

Applications

The combination of soda and barium polyphosphate forms a low-melting

glass Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...

with a high

coefficient of thermal expansion Thermal expansion is the tendency of matter to increase in length, area, or volume, changing its size and density, in response to an increase in temperature (usually excluding phase transitions). Substances usually contract with decreasing temp ...

. 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 Borosilicate glass is a type of glass with silicon dioxide, silica and boron trioxide as the main glass-forming constituents. Borosilicate glasses are known for having very low coefficient of thermal expansion, coefficients of thermal expansion ( ...

glasses soften above the melting point of aluminium. This mixture is prepared by heating a mixture of

diammonium phosphate Diammonium phosphate (DAP; IUPAC name diammonium hydrogen phosphate; chemical formula (NH4)2(HPO4)) is one of a series of water- soluble ammonium phosphate salts that can be produced when ammonia reacts with phosphoric acid. Solid diammonium ph ...

sodium carbonate Sodium carbonate (also known as washing soda, soda ash, sal soda, and soda crystals) is the inorganic compound with the formula and its various hydrates. All forms are white, odourless, water-soluble salts that yield alkaline solutions in water ...

, and

.Wilder Jr., J.A. "Glasses and glass ceramics for sealing to aluminum alloys" Journal of Non-Crystalline Solids Volume 38-39, Issue PART 2, May 1980, Pages 879-884. Hart, Patricia E.; Mesko, Melissa G.; Shelby, James E. "Crystallization and phase equilibrium in the sodium barium metaphosphate system" Journal of Non-Crystalline Solids (2000), 263&264, 305-311.

References

{{Barium compounds Barium compounds Metaphosphates