Exploring the sintering and densification behaviour of multiwalled carbon nanotube reinforced TiO₂–MnO₂ composites developed by spark plasma sintering

The quest to synthesis advanced ceramic materials with enhanced density and mechanical properties have prompted the addition of multiwall carbon nanotubes (MWCNTs) and manganese oxide to titania (TiO₂) matrix. In this research, TiO₂ based composites comprising of 0.5, 1.0 and 1.5 wt. % MWCNTs and 5 wt. % manganese oxide (MnO₂) was synthesized via spark plasma sintering (SPS) technique. Prior to the consolidation of the ceramic composites, the starting powders were milled using ball milling technique, and the dispersibility and structural evolution of the MWCNTs were investigated. The milled powders were consolidated at 1200 °C under a compressive pressure of 25 MPa using a holding time and heating rate of 5 min and 50 °C/min respectively. Furthermore, the influence of different fraction of MWCNTs and MnO₂ in the milled powders and sintered composites were evaluated using transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffraction (XRD) technique and Raman spectroscopy. The roles of MWCNTs and the presence of MnO₂ on the sintering, densification and microhardness of the sintered composites were also explored. The morphology, XRD patterns and Raman spectra of the milled powders indicated that the presence of MnO₂ influenced the dispersibility and structural integrity of the nanotubes in the composites. In addition, the presence of MnO₂ improved the densification and microhardness of the composites. The microhardness values were in the range of 11.5–13.7 GPa, which improved with the addition of MWCNTs. Whereas, higher concentrations of MWCNTs result in decrease in the densification of the ceramic composites with relative density ranging from 98 to 99%.