Plasma chemical synthesis. II: Effect of wall surface on the synthesis of ammonia

The plasma synthesis of ammonia was studied at pressures of 1-5 torr and flow rates of up to 200 torr cm/sup 3/ min/sup -1/ using Pyrex and silver surfaces cooled to 77 K. The N conversion to ammonia was about 13% in experiments in which the afterglow was trapped on the Pyrex surface. By quenching the plasma rather than the afterglow, the percent N conversion could be doubled using the Pyrex surface and quadrupled using the silver surface. Increasing the hydrogen pressure and/or hydrogen discharge cleaning decreased the percent N conversion; nitrogen discharge conditioning had no significant effect. With increasing nitrogen flow rate the percent N conversion decreased linearly in the quenched plasma reaction on the silver surface, suggesting nitriding and reduction by hydrogen to form ammonia. The exponential decrease of the percent N conversion in the quenched afterglow reaction of the Pyrex surface is explained by the formation and/or dissociation of adsorbed N/sub 2/ determining the ammonia yield at 77 K.