Interaction of ammonia and hydrogen with tungsten at elevated temperature studied by gas flow through a capillary

Abstract

The interaction of ammonia and hydrogen (H2 and D2) was studied by flowing pure gas or gas mixture through a hot tungsten capillary. The composition of the gas after passing the capillary was analyzed by mass spectrometry as a function of capillary temperature. Specific temperatures were identified where changes in mass spectra take place indicating thermal decomposition and isotope exchange channels. Measurements with pure ammonia and deuterium provided new data for the thermal decomposition of these molecules on hot tungsten. Ammonia gets effectively decomposed at around 900 K in the tungsten capillary, and only 7% of ammonia survives through the capillary at temperatures above 1100 K. By studying the production and desorption of HD in ammonia and deuterium mixture, the authors show that D2 molecules can get adsorbed on tungsten dissociatively only at temperatures above 1300 K in the presence of nitrogen or ammonia fragments. An adsorption barrier of 0.17 eV is determined for this case. A comparison of ...