CARBONIZATION OF MIXTURES OF COAL-TAR PITCH AND GRAPHITE FECL3 COMPOUNDS - A MOSSBAUER STUDY

Mixtures of coal tar pitch (CTP) and first-stage FeCl3-graphite interc alation compounds (GIC) have been synthesized with different GIC conce ntrations, then pyrolysed at different final temperatures and at sever al heating rates. Mossbauer spectroscopy has been used to characterize the iron states after these thermal treatments. The initial GIC is ch aracterized by a typical singlet of high-spin Fe(III) and we have stud ied the thermal stability of the GIC under nitrogen flow by X-ray meas urements: FeCl3 is progressively reduced to FeCl2 and reduction is com plete at 500 degrees C. At 750 degrees C, all iron has been removed fr om the graphene layers. After pyrolysis of the CTP and GIC mixture, di fferent phases are identified in the resulting green-coke: metallic ir on (alpha-Fe), which is present in greater quantities at high GIC conc entrations and at higher pyrolysis temperatures, ferrous chloride, iro n sulfide (FeS, troilite), nonstoichiometric Fe(1-)xS (pyrrhotite), an d a not-well-determined fourth phase that could be austenitic iron (ga mma-Fe). After steam activation of the green-coke at 750 degrees C, mo st of the iron is oxidized into magnetite as confirmed by X-ray measur ements and Mossbauer spectroscopy.