The reaction mechanism most likely is an indirect one. Initially some K2Cr2O7 may be formed plus tiny amounts of N2 and NO. K2Cr2O7, however, is less
stable than K2CrO4 at high temperature and loses oxygen. The resulting material then is oxidized again by the KNO3. So, after a small initial
formation of NO, further reaction products are N2, O2 (and possibly N2O). These gases do not react with each other at 300 C or so, that would require
MUCH higher temperatures and this also explains why you did not notice any brown fumes and did not smell any NO2. |