An effort was made toward modifying the Si3N4-SiC phase ratio in bulk nanocomposites obtained from polymer precursors. While pyrolyzing the polymer, flowing ammonia was introduced, to facilitate a chemical exchange, resulting in a different C/N ratio in the ceramic pyrolysis product. A pre-pyrolysis/binding/pyrolysis approach was used for sample consolidation. Comparison was made between the crystallization behavior of the pyrolysis-derived ceramic powders and consolidated bulk samples. A profound enhancement in crystallization tendency was observed in the consolidated samples whose nitrogen content was increased by ammonia treatment. A mechanism based on the particle/binder interface energy was proposed to account for this observation.