Hydrothermal synthesis of pure Talc, Mn and Ni-Doped Talc and their impact on stoneware tiles sintering

The present study investigates the hydrothermal synthesis of undoped talc and talc doped with Mn2+ and Ni2+ cations, to probe the effectiveness on stoneware tiles sintering. Undoped, Mn- and Ni-doped talc samples were synthesized at constant pressure (2 kbar) and reaction time (160 h), under different hydrothermal conditions (temperatures of 300 °C and 650 °C, pH values of 5 and 7). Characterization techniques including Powder X-Ray Diffraction (PXRD), Scanning and Transmission Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM/EDS, TEM/EDS), Differential Scanning Calorimetry (DSC), and micro-Raman Spectroscopy (μR) were employed to analyse the starting materials, synthesized products as well as stoneware tiles. The study revealed a direct correlation between the amount of NiO in the initial mixture and the presence of Ni-dopant in the resulting talc, yielding a full substitution of Mg2+ by Ni2+ and the consequent formation of Ni3Si4O10(OH)2. However, in the same experimental conditions, the formation of Mn3Si4O10(OH)2 is not achieved. Indeed, a saturation point for Mn2+ doping in talc has been identified, and its nature will be discussed. Furthermore, undoped-talc, Mn doped talc and Ni-talc have all been employed for the sintering of stoneware tiles. This present study demonstrates that Mn- and Ni-doped synthetic talc act as highly effective fluxing agents in stoneware tile bodies. Their addition promotes a more rapid consumption of crystalline phases, specifically albite, at lower firing temperatures compared to undoped talc. Notably, Mn2+-doping (even at low concentration of dopant) exhibits a more pronounced effect than Ni-doping. This process may offer a direct pathway to substantial energy and cost savings in industrial ceramic production.