Carbothermal-sulfurization of TiO2 into Ti2SC MAX phase in TiO2/C/FeS2 ternary system.

The conventional method for synthesizing Ti 2 SC depends on the reaction between TiS and TiC, which requires the utilization of costly Ti, TiC, or TiS 2 powders. Utilizing TiO 2 as the raw material for the synthesis of Ti 2 SC enables the cost-effective preparation of this compound. However, the optimization of the TiO 2 /C/X n S m (sulfides) system is of utmost importance when aiming to synthesize Ti 2 SC through carbothermal-sulfurization of TiO 2 , as the formation temperature of TiS and TiC greatly depends on the X n S m. In this study, the identification of the thermodynamically dominant region for the formation of TiS and TiC in the TiO 2 /C/X n S m systems was conducted by utilizing various sulfides (63 types). Considering factors such as the challenges associated with removing by-products, accessibility, and toxicity, FeS 2 was ultimately chosen as a highly promising candidate. Thanks to the low melting point of FeS 2 , Ti 3 O 5 , the preliminary carbothermal reduction product of TiO 2 , has achieved rapid-deep deoxidation and phase reconstruction processes in the molten phase. Meanwhile, unlike the conventional solid-solid sintering reaction, which often results in residual reactants that are challenging to eliminate. This novel one-step phase transformation process that occurs in the molten phase exhibits minimal impurity phases, apart from the by-product Fe. Ti 2 SC with a purity greater than 99 wt% was obtained when the TiO 2 /C/FeS 2 was pickled to remove Fe after sintering at 1600 °C for 5 min. This work will provide the theoretical basis and a new path for the low-cost preparation of sulfur-containing MAX phases. [ABSTRACT FROM AUTHOR]