A novel process for the synthesis of cordierite (Mg2Al4Si5O18) powders from rice husk ash and other sources of silica and their comparative study

Cordierite (Mg2Al4Si5O18) powders were synthesised by utilising agro-based ‘waste’ material-rice husk ash and two other sources of silica, i.e. tetraethylorthosilicate (TEOS) and fumed silica, for a comparative study following sol–gel technique. The gel and calcined powders obtained from different silica sources were characterised by thermogravimetry analysis (TGA), differential thermal analysis (DTA), X-ray diffraction (XRD) study, Fourier transformed infrared (FTIR) spectroscopy, 27Al and 29Si solid state MAS NMR spectroscopy, scanning electron microscopy (SEM) and particle size analysis. For rice husk ash as the source material, DTA and XRD results confirmed that α-cordierite was formed at 1365 °C through the intermediate phases of cristobalite and MgAl2O4 spinel while in case of TEOS and fumed silica sources, α-cordierite formed at 1320 and 1360 °C respectively through the intermediate phases of μ-cordierite and magnesium aluminate (MgAl2O4) spinel for the former and via the MgAl2O4 spinel for the latter. FTIR studies showed the vibration bands of SiO4 tetrahedra, AlO6 octahedra and AlO4 tetrahedra for different sources of silica calcined at different temperatures. The 27Al solid state NMR confirmed the highly abundance of AlO6 octahedra while 29Si solid state NMR revealed the Q4 state for SiO4 tetrahedra for the sample obtained from rice husk ash after calcination at 800 °C. The SEM showed the irregular morphology of the calcined powders (1400 °C) for all the samples and comparatively wide size distribution of the particles was found for the sample obtained from rice husk ash.