sodium orthophosphate

Sodium hexametaphosphate

Sodium hexametaphosphate (SHMP) is a hexamer of composition (NaPO3)6. Sodium hexametaphosphate of commerce is typically a mixture of polymeric metaphosphates, of which the hexamer is one, and is usually the compound referred to by this name. It is more correctly termed sodium polymetaphosphate. It is prepared by melting monosodium orthophosphate, followed by rapid cooling. SHMP hydrolyzes in aqueous solution, particularly under acidic conditions, to sodium trimetaphosphate and sodium orthophosphate. SHMP is used as a sequestrant and has applications in a wide variety of industries, including as a food additive in which it is used under the E number E452i. Sodium carbonate is sometimes added to SHMP to raise the pH to 8.0-8.6, which produces a number of SHMP products used for water softening and detergents. Also used as a dispersing agent to break down clay and other soil types.

Ceramic process

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. The sodium hexametaphosphate causes the heavy particles in the slip to drop to the bottom allowing the fine particles to be siphoned off and applied to a green ware ceramic surface.

Other Uses

Sodium hexametaphosphate is also a whitening ingredient included in Crest Pro-Health, Vivid White and Vivid White Night.

It is also used as an additive in Rubicon Mango drinks, Diet Lipton teas and Life Brand naturally flavored bottled water.

Health concern

Some individuals may experience an allergic reaction to the ingestion of sodium hexametaphosphate that may produce mild chest pain. One case of this allergic reaction was reported to have been due to trace amounts of sodium hexametaphosphate found in bottled water.

Other names

  • Calgon S
  • Glassy sodium
  • Graham's Salt
  • Hexasodium metaphosphate
  • Hexasodium salt
  • Metaphosphoric acid


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