Study on the pyrolysis of ammonium thiocyanate and its product formation characteristics in H2

Abstract

The thermal decomposition and products generation characteristics of ammonium thiocyanate (NH4SCN) have been studied in Ar and H2 by thermogravimetry - differential scanning calorimetry, thermogravimetry-Fourier transform infrared spectroscopy, Fourier transform infrared spectroscopy and X-ray diffraction. The results show that NH4SCN undergoes four endothermic processes between 40–850 °C in Ar and H2. The first two processes are dominated by the crystal transformation of NH4SCN, melting, and sublimation, and the isomerization of NH4SCN occurred in the third stage due to the pyrolysis process. H2 can inhibit the isomerization slightly and obviously promote the pyrolysis of NH4SCN. The pyrolysis end temperature in H2 was reduced to 603.80 °C, which is 120.55 °C lower than that using an Ar atmosphere. This difference is due to the higher thermal conductivity of H2 than Ar and the participation of H2 in the generation of HNCS and NH3. The main gaseous products are HNCS, NH3, CS2, and H2S. They were found to peak at 240.61 °C, which is 24.62 °C lower than in Ar. Thiourea, guanidine thiocyanate, cyanamide, dicyandiamide and melamine are main intermediates, while graphitic carbon nitride (g-C3N4) was formed at the end of pyrolysis.