A novel and potentially economical microwave route has been developed for the synthesis
and sintering of mullite from the naturally available minerals kaolinite and alumina. Mullite
obtained by this route could be sintered to as high as 98% of theoretical density in under 60
min. A detailed structural investigation has been carried out using XRD, IR, and MAS NMR.
It is clearly evident from the structural studies that there is a partial conversion of octahedral
Al to tetrahedral Al with time during the formation of mullite. Also, it is evident that the
exsolved SiO2 reacts with the added Al2O3 to form secondary mullite over primary mullite
which is nucleated from the decomposition of kaolinite. A detailed microstructural evolution
of this conversion has been followed. A possible microwave−material interaction has been
discussed for the rapid formation of mullite.
A novel and fast microwave route is described for the synthesis of yttrium aluminum garnet (YAG) and for its sintering to translucent bodies. Precursor was made by microwave decomposition (20 min) of aluminum tri-sec-butoxide and yttrium nitrate dissolved in ethyl acetate. The precursor, conventionally calcined at 1000 °C (1 h), was sintered in microwave using SiC as secondary heater for just 35 min. Resulting translucent YAG has a microhardness (HV) of 18.1 GPa and fracture toughness (KIC) of 4.3 MPa m1/2. A 0.86-mm-thick sintered pellet exhibits approximately 45% transmission for 520-nm radiation. The entire microwave process requires less than 3 h.
Layered bismuth titanate, Bi 4 Ti 3 O 12 (BTO) (Aurivillus phase) has been synthesized using microwave route. BTO has been prepared using conventional ceramic method also for comparison. Li + intercalation into BTO has been attempted using a soft chemistry route. Inductively coupled plasma (ICP) has been used to estimate Li + quantitatively and the lithiated sample is found to be Li 2.38 Bi 4 Ti 3 O 12 . Infrared and UV-visible spectroscopies along with ESR and 7 Li MAS NMR have been used to characterize the lithiated compound. Electrical conductivity of lithiated sample has also been examined. The pristine BTO has been sintered both using microwave and conventional heating. Sintered samples reveal very interesting morphology. The characteristic plate like growth in sintered samples appears more prominently in microwave sintering. Schematic molecular orbital (MO) diagram based band structure has been proposed which provides consistent rationalization of the observed properties.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.