[1] The Ostwald process is a mainstay of the modern chemical industry, and it provides the main raw material for the most common type of fertilizer production.
Ammonia burns in oxygen at temperature about 900 °C (1,650 °F) and pressure up to 8 standard atmospheres (810 kPa)[4] in the presence of a catalyst such as platinum gauze, alloyed with 10% rhodium to increase its strength and nitric oxide yield, platinum metal on fused silica wool, copper or nickel to form nitric oxide (nitrogen(II) oxide) and water (as steam).
[6] Another side reaction produces nitrous oxide: The platinum and rhodium catalyst is frequently replaced due to decomposition as a result of the extreme conditions which it operates under, leading to a form of degradation called cauliflowering.
[7] The exact mechanism of this process is unknown, the main theories being physical degradation by hydrogen atoms penetrating the platinum-rhodium lattice, or by metal atom transport from the centre of the metal to the surface.
[citation needed] This gas is then readily absorbed by the water, yielding the desired product (nitric acid in a dilute form), while reducing a portion of it back to nitric oxide:[5] The NO is recycled, and the acid is concentrated to the required strength by distillation.