NF3 Compatibility Testing
WHA was the coordinator of an industry sponsored program that funded the development of test systems to determine the compatibility of materials in nitrogen trifluoride (NF3). The NF3 test systems include:
- Autogenous Ignition Temperature (AIT)
- The minimum temperature at which non-metallic materials ignite in pressurized NF3. The method is consistent with ASTM G72 for oxygen.
- NF3 Index
- The minimum concentration of NF3 mixed with nitrogen that supports self-sustained burning of non-metals. The method is consistent with Oxygen Index Testing except it is performed in a combustion chamber at pressures from atmospheric to 1500 psig.
- Promoted Combustion
- The threshold pressure of metals in NF3 is determined in a promoted combustion chamber by determining the maximum no-burn pressure and minimum burn pressure. The test method is consistent with ASTM G124 for oxygen.
Although initially designed on equivalent oxygen tests, these tests systems were modified to tolerate the powerful oxidizing capabilities of NF3. WHA's paper, Material Compatibility with Nitrogen Trifluoride, summarizes the results of the testing on various nonmetals and metals. WHA has recently developed a new AIT test system with Fourier Transform Infrared (FTIR) technology. The AIT chamber is capable of receiving an external beam FTIR to characterize the species produced as NF3 is heated and non-metallic materials ignite and react.
WHA can also provide custom NF3 testing which would involve long duration exposure of materials to NF3 under specific conditions and promoted ignition testing of NF3 valves and other components. The promoted ignition testing applies a unique ignition source within the valve to promote the seat or other nonmetals and evaluate whether the reaction extinguishes after the nonmetal is consumed or continues to the surrounding materials.