  The synthesis of Si3N4 nanowires from the reaction of silicon nanoparticles
with N2 in the 1200-1440 C temperature range is reported. The nitridation
conditions are such that the reaction with nitrogen is favoured by the presence
of silicon oxide in the particles and by the active oxidation of silicon
without a catalyst. It is shown that the Si to Si3N4 conversion rate depends on
the amount of silicon particles used in the experiments and that, in general,
the reaction slows down for greater amounts. This trend is explained by
particle stacking, which restricts the exchange of gases between the furnace
atmosphere and the atmosphere around the inner particles. In a first stage,
local oxygen partial pressure increases around the inner particles and inhibits
nitridation locally. If the amount of reactant Si nanoparticles is small
enough, this extrinsic effect is avoided and the intrinsic nitridation kinetics
can be measured. Experiments show that intrinsic kinetics does not depend on
temperature.
