Microwave Assisted Combustion (MAC) Synthesis of Mixed Oxide Electro-Ceramic Nanopowders

Microwave assisted combustion [MAC] synthesis is a rapid technique being exploited for obtaining fine-scale structural, electronic and bio ceramic powders. The main advantage of microwave energy is its accelerated molecular level reversible heating from core to surface by dielectric polarization that offers size and shape control over the end products. MAC synthesis has been well reported for many ceramic oxides such as Al2O3, ZrO2, mullite, MgAl2O4 and ceramic pigments. We have been using this technique for synthesizing single-phase and sinter-active nanocrystalline yttria (Y2O3), gadolinium doped ceria (Gd-CeO2) and zinc oxide (ZnO) with and without dopants for the potential applications as transparent ceramics, luminous pipes for high-intensity discharge lamps, laser host material, solid oxide fuel cell [SOFC] electrolytes, gas sensors, transparent electronic devices, surge-protection electric power devices (varistors), high frequency electronic and telecommunication devices and ferrite cores. The technique involves combustion of the respective oxidic precursor mixtures under microwave energy [2.45 GHz, 900 W] using organic fuels such as urea, citric acid and glycine. In this book chapter we are presenting an overview of our research on MAC synthesis to synthesize fine-scale electro-ceramic powders in the past few years. The various results such as phase purity by powder X-ray, structural evolution by Fourier transform infra red spectroscopy [FTIR], thermal decomposition by Differential thermal analysis [DTA], thermogravimetry analysis [TGA], differential scanning calorimetry analysis [DSC], and particle size, dilatometry, and morphology by scanning electron microscope [SEM], transmission electron microscope [TEM] are highlighted in addition to the sintering properties. The mechanical properties of sintered ceramics processed through MAC technique are also discussed. Interestingly we observed the mechanical fracture toughness and hardness variations depending upon the fuel systems. The phase analysis supports that the as derived ceramic powders are fully crystalline nano-scale oxides that have high specific surface area. It is also observed that fuel like glycine shows strong influence on the size and shape of the particles. In this type of fuel spherical morphology is usually obtained. The MAC synthesis shows great advantages in chemical homogeneity, high sinterability, fine-sintered grain size, and enhanced mechanical and electrical properties. In this chapter we reviewed our attempts made on MAC synthesis for obtaining electro-ceramic powders for the benefit of the academic researchers and industrial R'.

Keywords: Synthesis, Microwave assisted combustion, Electro-ceramics, Nanocrystalline powders, Organic fuels