Дигидрофосфат аммония

Description

Ammonium dihydrogen phosphate (monoammonium phosphate, MAP, ADP) is a monobasic ammonium salt of orthophosphoric acid NH4H2PO4. White crystalline powder, one of the key components of ABC type fire extinguishing powders and phosphate fertilizers. The dump for this product in the source data is empty, so the description is compiled according to open chemical reference books.

Basic Attributes

• CAS No.: 7722-76-1
• Chemical formula: NH4H2PO4
• Molecular weight: 115.03

Physico-chemical characteristics

• Appearance: White crystalline powder
• Density: 1.80 g/cm3
• Melting point: 190 °C
• Solubility in water: 280 g/l at 10 °C, 360 g/l at 20 °C, 440 g/l at 30 °C, 560 g/l at 40 °C, 660 g/l at 50 °C, 810 g/l at 60 °C, 990 g/l at 70 °C, 1180 g/l at 80 °C, 1730 g/l at 100 °C
• Solubility in alcohol and acetone: insoluble
• pH: 3.8–4.4 (5% solution, 25 °C)

Substance class and mechanism of action

Acid (monobasic) ammonium salt of orthophosphoric acid - unlike dibasic diammonium hydrogen phosphate, here there is only one molecule of ammonia per molecule of phosphoric acid, so the solution of the substance is noticeably more acidic. As an active component of ABC fire extinguishing powders, when heated, the substance melts and decomposes to form a glassy film of metaphosphoric acid and polyphosphates that covers the burning surface and prevents the access of oxygen, and also releases non-flammable vapors of ammonia and water, diluting the combustion zone.

Application

• the main active component of ABC type powder fire extinguishers for extinguishing solid, liquid and gaseous flammable materials
• source of nitrogen and phosphorus in water-soluble fertilizers for drip irrigation and foliar feeding
• fire retardant - impregnation of wood and textiles to reduce flammability
• buffer component and reagent in analytical chemistry

Storage

Store in a dry, well-ventilated area, in a sealed container - the substance is hygroscopic and when moistened it cakes, losing its flowability, which is important for powder fire extinguishers. Separated from strong bases with which neutralization with generation of heat is possible.

Compatibility with other substances

Like most acid ammonium salts, ammonium dihydrogen phosphate reacts with strong bases to produce heat and is not compatible with strong oxidizing agents that accelerate the decomposition of the ammonium group. When mixing with fertilizers and agrochemicals, take into account the acidic reaction of the solution (pH 3.8–4.4), which can affect the solubility of other components of the working mixture.

Difference from diammonium hydrogen phosphate

Ammonium dihydrogen phosphate (monobasic salt, acidic solution with a pH of 3.8–4.4) and diammonium hydrogen phosphate (dibasic salt, weakly alkaline solution) are neighboring members of the same series of ammonium phosphates, differing in the number of ammonia molecules per phosphoric acid molecule. Due to its more pronounced acidity and better thermal stability of the melt, it is the monoammonium form that is preferred for fire extinguishing compositions, while the dibasic form is more often used as a pure fertilizer and feed additive.