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To assist in the failure analysis of a rocket thruster, the ignition temperature in oxygen-enriched atmospheres of titanium and titanium alloys was investigated. The open literature indicated melting temperatures in the range of 1,660°C (3,020°F) and ignition temperatures ranging from 250 to 1,627°C (482 to 2,961°F) for titanium powder and solid titanium, respectively. Vertically mounted test samples of varying diameters were ignited by induction heating in 66 % oxygen (O2)/balance nitrogen (N2) and in 99.5 + % O2 at 1,000 psia. Ignition was measured by either a platinum/platinum-rhodium (Type S) thermocouple comprised of 0.05-mm (0.002 in.) and 0.076-mm (0.003 in.) diameter wires welded to the samples or by a two-color pyrometer. The ignition temperatures in 66 % O2 and 99.5 + % O2, with various surface treatments and configurations, ranged from 1,623 to 1,659°C (2,953 to 3,018°F). The lack of an effect on ignition temperature as a function of oxygen concentration suggests that the ignition process is controlled by subsurface rather than surface-related processes. One unexpected result was that although sample nitriding did not change the autogenous ignition temperature (AIT), it did change the rate of combustion after ignition.
titanium autogenous ignition temperature, induction heating, pyrometer, oxygen concentration effects
Material and Components Laboratories Office, NASA Johnson Space Center White Sands Test Facility, Las Cruces, NM
Gallus, Timothy D.
NASA Johnson Space Center White Sands Test Facility, Las Cruces, NM