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 that 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:[2]

(NH4)2HPO4(s) ⇌ NH3(g) + NH4H2PO4(s)

log PmmHg = −3063 / T + 175 log T + 3.3


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

At 100 °C, the dissociation pressure of diammonium phosphate is approximately 5 mmHg.[3] Accordingly, to MSDS of DiammoniumPhosphate from CF Industries inc. decomposition starts as low as 70*C "Hazardous Decomposition Products: Gradually loses ammonia when exposed to air at room temperature. Decomposes to ammonia and monoammonium phosphate at around 70°C (158°F). At 155°C (311°F), DAP emits phosphorus oxides, nitrogen oxides and ammonia." Uses[edit] DAP is used as a fertilizer.[4] When applied as plant food, it temporarily increases the soil pH, but over a long term the treated ground becomes more acidic than before upon nitrification of the ammonium. It is incompatible with alkaline chemicals because its ammonium ion is more likely to convert to ammonia in a high-pH environment. The average pH in solution is 7.5–8.[5] The typical formulation is 18-46-0 (18% N, 46% P2O5, 0% K2O).[5] DAP can be used as a fire retardant. It lowers the combustion temperature of the material, decreases maximum weight loss rates, and causes an increase in the production of residue or char.[6] These are important effects in fighting wildfires as lowering the pyrolysis temperature and increasing the amount of char formed reduces that amount of available fuel and can lead to the formation of a firebreak. It is the largest component of some popular commercial firefighting products.[7] DAP is also used as a yeast nutrient in winemaking and mead brewing; as an additive in some brands of cigarettes purportedly as a nicotine enhancer; to prevent afterglow in matches, in purifying sugar; as a flux for soldering tin, copper, zinc and brass; and to control precipitation of alkali-soluble and acid-insoluble colloidal dyes on wool.[1] External links[edit]

International Chemical Safety Card 0217 Diammonium phosphate
Diammonium phosphate
fertilizer manufacturing process flowsheet


^ a b Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8 ^ John R Van Wazer (1958). Phosphorus And Its Compounds - Volume I: Chemistry. New York: Interscience Publishers, Inc. p. 503.  ^ McKetta Jr, John J., ed. (1990). Encyclopedia of Chemical Processing and Design (Chemical Processing and Design Encyclopedia). New York: Marcel Dekker, Inc. p. 478. ISBN 0-8247-2485-2.  ^ IPNI. "Diammonium Phosphate" (PDF). International Plant Nutrition Institute. Retrieved 21 July 2014.  ^ a b International Plant Nutrition Institute. "Nutrient Source Specifics: Diammonium Phosphate" (PDF). Retrieved 2012-12-10.  ^ George, C.W.; Susott, R.A. (April 1971). "Effects of Ammonium Phosphate and Sulfate on the Pyrolysis
and Combustion of Cellulose". Research Paper INT-90. Intermountain Forest and Range Experiment Station: USDA Forest Service.  ^ Phos-Chek MSDS[permanent dead link], Phos-