[en] The aim of the present work is to determine the kinetics of reaction between TiSi₂ powder and gaseous nitrogen. Isothermal nitridation of TiSi₂ powders with fine (1.4 µm) and medium (4.5 µm) particle size has been studied in pure nitrogen atmosphere from 1000 to 1200 °C for duration up to 50 h. The isothermal nitridation kinetics of TiSi₂ powders were investigated by thermogravimetry. The nitridation rate strongly depends on the particle size and temperature. Smaller size particle exhibits higher nitridation rate due to its larger surface area. The conversion process is complex with nucleation and growth of TiN at the surface of the grain and Si₃N₄ inside the grain promoted by the Kirkendall effect with an influence of the volume increase. - Graphical abstract: Backscattered electrons image of a transverse TiSi₂ grain nitrurated at 1100 °C for 50 h. - Highlights: • Influence of grain size on TiSi₂ powder nitridation. • Influence of temperature on TiSi₂ powder nitridation. • Experimental measurements of the nitridation kinetics. • An explanation of the nitridation mechanism

[en] Ceramic matrix composites have been manufactured at temperatures below 1100 C by a multistep process which consists in (i) a polymer impregnation of Si-C-O fibre preform and pyrolysis (PIP) in order to consolidate the preform; (ii) an impregnation with a slurry of submicron TiSi_2 powder, (iii) a heat treatment under nitrogen (N_2) in order to reduce the porosity thanks to the volume expansion associated with the nitridation of the active filler; and (iv) a final densification by PIP. Various liquid polymeric precursors were investigated to perform this final densification. The morphology, the chemical composition and the mechanical properties of the composites were characterized. Based on these characterizations, a pre-ceramic polymer precursor was chosen in order to produce a ceramic matrix composite. (authors)

[en] Highlights: ► Nitridation of TiSi₂ creates TiN, Si and Si₃N₃ phases. ► A study of size (micronic and sub micronic) particles is presented. ► Si₃N₄ is created at 1100 °C with the nitridation of sub micronic particles. - Abstract: This paper reports on the nitriding process of TiSi₂ micro/submicrometer-sized powders. TiSi₂ powders were treated under nitrogen flow, at 1100 °C, during various durations. The composition and morphology of the nitride powders are characterized by X-ray diffraction and observed on cross-section, prepared using ion polishing system by scanning electron microscopy whereas the chemical composition is analyzed by energy dispersive X-ray spectroscopy. All these analyses revealed that under nitrogen flow, TiSi₂ grains are first transformed into a core-shell structure composed of TiN, surrounded by Si. Long nitriding treatments result in the complete transformation of Si₃N₄. These results are discussed in terms of various diffusion limitation phenomena.