Mullite Ceramic from Diphasic Precursor Powder

Abstract

The use of mullite as a ceramic material proliferate from the field of conventional ceramic to the most advanced structural and functional area of ceramic due to its many advantageous properties. The properties of a sintered mullite ceramic are very much dependent on the type of processing route by which powder precursor was prepared.
In the present work, the stoichiometric diphasic mullite precursor powder was prepared by reverse addition technique using fume silica and aluminium nitrate nonahydrate as raw material. The effects of solution pH on the properties of the prepared powder have been investigated. The precursor powder made at ph-6, pH-8 and pH-10 were studied by TG-DSC analysis to know about the thermal decomposition behavior. Phase analysis of the precursor powder and calcined powder at different temperatures was done by XRD study. The presence of the different functional group in the precursor powder and calcined powder is confirmed by the FTIR study. The particle morphology, tendency of agglomeration and surface area, was investigated by microstructure analysis, particle size distribution and surface area analysis respectively. It was found that though the desired mullite phase formation is not very much affected by the variation of solution pH but the other properties are pH dependent.
The precursor powder formed at pH-8 exhibited better properties compared to the other batches. Therefore, the sintering study of the precursor powder in the presence of the different quantity of TiO2 additive is continued with that powder only. Samples made from different batches were sintered at three different temperatures i.e. 1450 ˚C, 1550 ˚C and 1650 ˚C under ambient atmosphere. The sintered pellets were characterized with respect to shrinkage, percent apparent porosity and bulk density. The phases formed in the sintered pellets were analyzed by X-Ray diffraction study. Morphology and microstructure were evaluated by FESEM.