Гексаметафосфат натрия

Химические свойства

The sodium polyphosphates class consists of several amorphous, water soluble polyphosphates composed of linear chains of metaphosphate units, (NaPO3)x where x ≥ 2, terminated by Na2PO4- groups. They are usually identified by their Na2O/ P2O5 ratio or their P2O5 content. The Na2O/P2O5 ratios vary from about 1.3 for sodium tetrapolyphosphate, where x = approximately 4; through about 1.1 for Graham’s salt, commonly called sodium hexametaphosphate, where x = 13 to 18; to about 1.0 for the higher molecular weight sodium polyphosphates, where x = 20 to 100 or more. The pH of their solution varies from about 3 to 9. For additional details of description, refer to Burdock (1997).

Использование

sodium hexametaphosphate is a chelating agent and a corrosion inhibitor. This is an inorganic salt.

Подготовка

Sodium hexametaphosphate is prepared by heating monosodium phosphate (NaH2PO4) rapidly to a clear melt, which occurs slightly above 625°C. Rapid chilling of this melt produces a very soluble glass, which is then crushed or milled.

Сельскохозяйственное использование

Sodium metaphosphate is the salt of metaphosphoric acid having a molecular formula (NaPO₃)_n, where n ranges from 3 to 10 (for cyclic molecules) or may be much larger (for polymers).
Cyclic molecules have alternate phosphorus and oxygen atoms in the rings and start with trimetaphosphate (NaPO₃)₃ to at least decametaphosphate.
Sodium hexametaphosphate may be a polymer where n is between 10 and 20.
Vitreous sodium phosphates have a Na₂O:P₂O₅ ratio near unity and are called Graham's salts. The average number of phosphorus atoms in these vitreous glasses ranges from 25 to infinity.

Промышленное использование

Sodium hexametaphosphate (SHMP) or water glass Na₆P₆O₁₈ is basically the salt of metaphosphoric acid. SHMP is difficult to dissolve. By mixing SHMP for 1-3 h, a solution of 8-10% can be obtained. The pH of this solution is about 5. Because of a weak acid reaction, the SHMP reacts with cations of bivalent metals forming Na₂MeP₆O₁₈ or Na₄MeP₆O₁₈. In the presence of oxygen, SHMP slowly decomposes into pyrophosphate and orthophosphate.

Профиль безопасности

Poison by intravenous route. Moderately toxic by intraperitoneal and subcutaneous routes. Wdly toxic by ingestion. When heated to decomposition it emits toxic fumes of PO, and Na2O. See also PHOSPHATES.