THERMAL-DECOMPOSITION OF NF3 BY TI, SI, AND SN POWDERS

The thermal decomposition of NF3 by Ti, Si, and Sn powders was investigated using gas chromatography, X-ray photoelectron spectroscopy, BET surface areas, and X-ray powder diffraction. The decomposition of NF3 using Ti powder starts at 160 degrees C, with >99.8% conversion occurring at 325 degrees C. Using Si powder, NF3 starts to decompose at 250 degrees C, with >99.8% conversion at 500 degrees C. Sn powder starts to decompose NF3 at 160 degrees C; however, complete conversion could not be obtained due to the low melting point of tin. In all cases, nitrogen and the corresponding metal fluorides were the only major products from the reaction. XPS revealed no nitrogen on the metal surface of the reacted powders, but metal fluoride species were observed. The XRD pattern for the reacted Ti showed crystalline TiF3 as well as Ti metal. The reacted Si and Sn patterns showed no new peaks. BET measurements revealed increases in surface area after reaction of Si and Ti with NF3. From these studies, it has been concluded that of the three powders, Ti powder is the best getter for NF3.