Sodium hexametaphosphate (SHMP), is basically a hexamer of the chemical formula (NaPO3)6. It is also called Graham’s salt or hexasodium metaphosphate. It is white and granular in appearance and hydrolyses in aqueous solution, during acidic conditions. It is soluble in water, while insoluble in organic solvents. It is a sequestrant that binds with calcium ions.
Sodium dihydrogen phosphate: The soda solution was first subject to neutralization reaction with phosphate acid at 80~100 ℃ for 2h; the resulting sodium dihydrogen phosphate solution was concentrated by evaporation, cooled and crystallized to obtain sodium dihydrogen phosphate dihydrate and heated to 110~230 ℃ to remove two crystal water; further be subject to heating to remove the structural water; further being heated to 620 ℃ for dehydration to result in the molten sodium metaphosphate and further polymerized into sodium hexametaphosphate, and discharged; apply chilling shock for 650 ℃ to 60~80 ℃ for flaking, and crush to obtain the hexametaphosphate products. Its reaction formula is as below:
Na2CO3 + 2H3PO4 + H2O → 2NaH2O4•2H2O + CO2 ↑
NaH2PO4•2H2O [△] → Na2H2PO4 + 2H2O
2NaH2PO4 [△] → Na2H2P2O7 + H2O
Na2H2P2O7 → 2NaPO3 + H2O
6NaPO3 [△] → (NaPO3)6
Phosphorus pentoxide method: put the yellow phosphorus into a steam of dry air for combustion and oxidation, the cooling obtained phosphorus pentoxide is mixed together with soda in certain ratio (Na2O: P2O5 = 1~1.1). Put the mixed powder in a graphite crucible and heated indirectly to have it dehydrated and agglomerated, the resulting sodium hexametaphosphate is subject to flaking upon chilling shock and pulverized to obtain industrial hexametaphosphate products. The reaction formula is as below:
P4 + 5O2 → 2P2O5
P2O5 + Na2CO3 → 2NaPO3 + CO2 ↑
6NaPO3 [△] → (NaPO3)6
Sodium hexametaphosphate is used as a sequestrant which improves the quality and stability of the food products. It is used under E number E425i. Artificial maple syrup, canned milk, cheese powders and dips, imitation cheese, whipped topping, packaged egg whites, roast beef, fish fillets, fruit jelly, frozen desserts, salad dressing, herring, breakfast cereal, ice cream, beer, and bottled beverages, among other foods, can contain sodium hexametaphosphate.
Sodium hexametaphosphate is used for water softening and detergents. Also used as a dispersing agent to break down clay and other soil types. One of the lesser-known uses for sodium hexametaphosphate is as a deflocculant in the making of terra sigillata, a ceramic technique using a fine particled slip.