Phosphoric acid, also known as orthophosphoric acid, is the most important oxygen acid of phosphorus with the chemical formula H3PO4. It is also the most common orthophosphoric acid. Pure form of phosphoric acid is a crystalline solid with a 42.35°C melting point. Its gravity is 1.834 at the temperature of 18°C and soluble in water and alcohol. It is a colourless, syrupy liquid form in less concentrated form. It can also combine with them to form a range of compounds that are also referred to as phosphoric acids.
Phosphoric acid is usually produced by three commercial methods, including wet process, thermal process and dry kiln process. Among these three methods, wet process is the most common route. The phosphate first reacts with the recycled phosphoric acid from the process and then mixed with sulfuric acid as a leaching agent. Then after the evaporator condensate, the gypsum separates with phosphoric acid and obtains the product acid.
Phosphoric acid is applied as a "rust converter", by direct application to rusted iron, steel tools, or surfaces. The phosphoric acid will transform reddish-brown iron(III) oxide, Fe2O3 (rust) to black ferric phosphate, FePO4. "Rust converter" is in a form of a greenish liquid, but it is more often formulated as a gel, usually called "naval jelly". Sometimes, it is sold in other names, such as "rust remover" or "rust killer". As a thick gel, it is applied to sloping, vertical, or even overhead surfaces.
It is used to produce hydrogen halide by reacting it with halide. Phosphoric acid finds important place as electrolyte in phosphoric acid fuel cells, oxy-hydrogen generators and Copper electro polishing. It is used as a wet etching agent for making impressions on surface. Most of the industries using iron and steel use phosphoric acid as a rust converter thanks to its ability to transform reddish-brown iron(III) oxide, Fe2O3(rust) to black ferric phosphate, FePO4.
Used as reaction fertilizer in the soil around a granule acidification is generated that improves the utilization of phosphorus applied and available in the rhizosphere. Due to its nitrogen content (present as ammonia), it is good for crops that require these nutrients in its initial phase.