sodium hexametaphosphate

Chemical properties

white granular solid

Chemical properties

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).

The Uses of sodium hexametaphosphate

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

The Uses of sodium hexametaphosphate

For industrial use, such as oil field, paper-making, textile, dyeing, petrochemical industry,tanning industry, metallurgical industry and building material industry, It is mainly used as a water sortening agent in solution for printing, dyeing ,and boiler; Diffusant in papermersing medium, high temperature agglomerant,detergent and soil analytical chemistry reagent,

The Uses of sodium hexametaphosphate

Sodium Hexametaphosphate is a sequestrant and moisture binder that is very soluble in water but dissolves slowly. solutions have a ph of 7.0. it permits peanuts to be salted in the shell by making it possible for the salt brine to penetrate the peanuts. in canned peas and lima beans, it functions as a tenderizer when added to the water used to soak or scald the vegetables prior to canning. it improves whipping properties in whipping proteins. it functions as a seques- trant for calcium and magnesium, having the best sequestering power of all the phosphates. it prevents gel formation in sterilized milk. it is also termed sodium metaphosphate and graham’s salt.

Preparation

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.

Agricultural Uses

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.

Industrial uses

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.

Safety Profile

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.

Properties and Applications

TEST ITEMS	SPECIFICATION
APPEARANCE	WHITE POWDER
TOTAL PHOSPHATE(P 2 O 5 )	68.0% min
INACTIVE PHOSPHATE (P 2 O 5 )	7.5% max
WATER-INSOLUBLE MATTER	0.05% max
Fe CONTENT	0.05% max
pH VALUE 1% AQUEOUS SOLUTION	5.8-7.3
As	-
Pb	-
F	-