Diammonium phosphate ( DAP , IUPAC name diammonium hydrogen phosphate , chemical formula (NH 4 ) 2 (HPO 4 ) is one of a series of water – soluble ammonium phosphate salts that can be produced when ammonia reacts with phosphoric acid solids . Diammonium phosphate shows a. The dissociation pressure of ammonia as given by the following expression and equation:
(NH4)2HPO4(s) ⇌ NH3(g) + (NH4)H2PO4(s)
- chemical formula (NH 4 ) 2 hpo 4
- molar mass 132.06 g/mol
- appearance white powder
- density 1.619 g/ cm3
- Melting point 155 °C (311 °F; 428) decomposes
- Solubility in water 57.5 g/100 mL (10 °C)
- 106.7 g/100 mL (100 °C)
- solubility Insoluble in alcohol , acetone and liquid ammonia
- refractive index ( nd ) 1.52
At 100 °C, the dissociation pressure of diammonium phosphate is about 5 mmHg.
CF Industries, Inc. According to the MSDS of diammonium phosphate, decomposition begins as low as 70 °C: “Dangerous decomposition product: slowly loses ammonia when exposed to air at room temperature. At about 70 °C into ammonia and monoammonium phosphate.” Decomposes (158 °F. At 155 °C (311 °F), DAP emits phosphorus oxides, nitrogen oxides, and ammonia.”
DAP is used as a fertilizer.  When applied as a plant food, it temporarily raises the pH of the soil, but on prolonged nitrification of ammonium the treated soil becomes more acidic than before. It is incompatible with alkaline chemicals because its ammonium ion is more likely to convert to ammonia in high-pH environments. The average pH of the solution is 7.5–8.  The typical formulation is 18-46-0 (18% N, 46% P 2 O 5 , 0% K 2 O). 
DAP can be used as a fire retardant. This lowers the combustion temperature of the material, lowers the maximum weight loss rate, and causes an increase in the production of residue or char.  These have important implications in fighting wildfires because lowering the pyrolysis temperature and increasing the amount of char formed reduces the amount of fuel available and can cause fires. It is the largest component of some popular commercial fire extinguishing products. 
DAP is also used as a yeast nutrient in winemaking and mead-making; Reportedly as a nicotine enhancer, as an additive in some brands of cigarettes; To prevent matchsticks, in purifying sugar; As a flux for soldering tin, copper, zinc and brass; and to control the precipitation of alkali-soluble and acid-insoluble colloidal dyes on wool.
The compound is found in nature as the extremely rare mineral phosphamite.   The related dihydrogen compound occurs in the form of the mineral biphosphamite. Both are related to guano deposits.