E342 Antioxidant

Agriculture

The largest use of E342 by weight is in agriculture, as an ingredient of fertilizers. It supplies the soil with the elements nitrogen and phosphorus in a form usable by plants. Its NPK label is 12-61-0 (12-27-0), meaning that it contains 12% by weight of elemental nitrogen and (nominally) 61% of phosphorus pentoxide P
2O
5, or 27% of elemental phosphorus.

Fire extinguishers

The compound is also a component of the ABC powder in some dry chemical fire extinguishers.

Optics

E342 is a widely used crystal in the field of optics due to its birefringence properties. As a result of its tetragonal crystal structure, this material has negative uniaxial optical symmetry with typical refractive indices no = 1.522 and ne = 1.478 at optical wavelengths.

Electronics

E342 are piezoelectric, a property required in some active sonar transducers (the alternative being transducers that use magnetostriction). In the 1950s ADP crystals largely replaced the quartz and Rochelle salt crystals in transducers because they are easier to work than quartz and, unlike Rochelle salt, are not deliquescent.