Duritanium (or duratanium) was a type of alloy used in construction.
In late 2151, Tucker noted to D'Marr that Enterprise was in need of such supplies as raw duratanium and dilithium ore. Although D'Marr did not carry such supplies, he did direct them to a small system, located about two days from their present location that might have what they were looking for. (ENT: "Oasis")
In 2152, Captain Archer ordered Tucker to bring him two hatches from the shuttlepods as they were reinforced with duratanium alloy. He used them as shields against a quarter of a kiloton thermokinetic explosion from a Romulan mine. (ENT: "Minefield")
An alien probe destroyed by a Cardassian ATR-4107, dubbed "Dreadnought", was composed primarily of duritanium polyalloy. When the debris was later discovered by the USS Voyager, it was noted that very few weapon types were capable of damaging a spacecraft with a duritanium hull to that extent. (VOY: "Dreadnought")
The primary test chamber, designed by Allos' species to construct the Omega molecule, was protected by a door constructed of solid duritanium that was thirteen centimeters thick. The door became melted into the door frame following the loss of containment in the test chamber, requiring phasers to cut through the metal. (VOY: "The Omega Directive")