Diammonium Phosphate

Diammonium phosphate (DAP) (chemical formula (NH4)2HPO4, IUPAC name diammonium hydrogen phosphate) is one of a series of water-soluble ammonium phosphate salts which can be produced when ammonia reacts with phosphoric acid. Solid diammonium phosphate shows a dissociation pressure of ammonia as given by the following expression and equation:

(NH4)2HPO4(s) NH3(g) + NH4H2PO4(s)
log PmmHg = -3063 / T + 175 log T + 3.3

where:

P = the resultant dissociation pressure of ammonia
T = absolute temperature (K)

At 100ºC, the dissociation pressure of diammonium phosphate is approximately 5 mmHg.

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