Waste conversion into high-value ceramics: Carbothermal nitridation synthesis of titanium nitride nanoparticles using automotive shredder waste

Environmental concern about automotive shredder residue (ASR) has increased in recent years due to its harmful content of heavy metals. Although several approaches of ASR management have been suggested, these approaches remain commercially unproven. This study presents an alternative approach for ASR management where advanced materials can be generated as a by-product. In this approach, titanium nitride (TiN) has been thermally synthesized by nitriding pressed mixture of automotive shredder residue (ASR) and titanium oxide (TiO2). Interactions between TiO2 and ASR at non-isothermal conditions were primarily investigated using thermogravimetric analysis (TGA) and differential scanning calorimetry. Results indicated that TiO2 influences and catalyses degradation reactions of ASR, and the temperature, at which reduction starts, was determined around 980 °C. The interaction between TiO2 and ASR at isothermal conditions in the temperature range between 1200 and 1550 °C was also studied. The pressed mixture of both materials resulted in titanium nitride (TiN) ceramic at all given temperatures. Formation kinetics were extracted using several models for product layer diffusion-controlled solid-solid and solid-fluid reactions. The effect of reactants ratio and temperature on the degree of conversion and morphology was investigated. The effect of reactants ratio was found to have considerable effect on the morphology of the resulting material, while temperature had a lesser impact. Several unique structures of TiN (porous nanostructured, polycrystalline, micro-spherical and nano-sized structures) were obtained by simply tuning the ratio of TiO2 to ASR, and a product with appreciable TiN content of around 85% was achieved after only one hour nitridation at 1550 °C.