What Is Ammonium Phosphate?
Ammonium phosphate is an inorganic compound resulting from the acid-base reaction between phosphoric acid and ammonia.
It exists in three forms: monoammonium phosphate (NH4H2PO4), diammonium phosphate (NH4)2HPO4, and triammonium phosphate (NH4)3PO4.
Uses of Ammonium Phosphate
Monoammonium and diammonium phosphate are the two types commonly used in the industry, sharing many applications despite their differing compositions.
1. Monoammonium Phosphate
It is utilized as an extinguishing agent in ABC fire extinguishers, which are versatile in putting out various types of fires.
2. Diammonium Phosphate
Often referred to as ammonium phosphate, it is extensively employed as a chemical fertilizer. Its industrial applications include uses as a metal surface treatment agent, organic synthesis catalyst, wastewater treatment agent, dyeing aid, and enamel glaze.
In pharmaceutical and food industries, it serves as a reagent, bio-agent, brewing additive, expansion agent, emulsifier, culture medium, pH adjuster in cosmetics, buffering agent, and oral care product.
Properties of Ammonium Phosphate
1. Monoammonium Phosphate (NH4H2PO4)
A colorless or white crystalline powder, it has a molecular weight of 115.03, a specific gravity of 1.803, and melts at 190°C. It is air-stable, highly soluble in water with a slightly acidic solution pH of 4.0 to 5.0, and exhibits buffering capabilities. It forms insoluble salts with soluble alkaline earth metals and is virtually insoluble in ethanol. Decomposition occurs above 216°C, releasing ammonia.
2. Diammonium Phosphate (NH4)2HPO4
This colorless or white crystalline powder, with a molecular weight of 132.06 and specific gravity of 1.619, melts at 190°C and is relatively stable in air. It dissolves well in water, producing a slightly alkaline solution with a pH of 7.6 to 8.4 and acts as a buffer. Like the monoammonium form, it reacts with soluble alkaline earth metals to form insoluble salts and is nearly insoluble in ethanol. It decomposes above 155°C to produce ammonia.
3. Triammonium Phosphate (NH4)3PO4・3H2O
Available as a hydrate, this white crystalline powder has a molecular weight of 203.13. It is air-unstable, readily producing ammonia and converting to diammonium phosphate, hence possessing a strong ammonium phosphate odor. It dissolves well in water, resulting in an alkaline solution with a pH of about 10, and is almost insoluble in ethanol.
Other Information on Ammonium Phosphate
How Ammonium Phosphate Is Produced
Ammonium phosphate is synthesized by reacting phosphoric acid with ammonia in aqueous solution. Adjusting the ratio of phosphoric acid to ammonia allows for the production of its three forms:
- H3PO4 + NH3 → NH4H2PO4
- H3PO4 + 2NH3 → (NH4)2HPO4
- H3PO4 + 3NH3 → (NH4)3PO4
Phosphoric acid can be produced by either the wet or dry process. The wet process involves decomposing phosphate rock with sulfuric acid, while the dry process involves thermal decomposition in an electric furnace. While the dry process yields higher purity phosphoric acid and is more energy-intensive and costly, the wet process is typically used for fertilizer production where high purity is not essential. However, advancements in refining technology for the wet process have improved the quality of phosphoric acid for industrial and food applications.