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RISS 인기검색어
- 검색키워드
- 저자 : Ramaraghavulu Rajavaram (검색결과 2 건)
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Rajavaram, Ramaraghavulu,Park, Junwoo,Lee, Joonho Elsevier 2017 JOURNAL OF ALLOYS AND COMPOUNDS Vol.712 No.-
<P><B>Abstract</B></P> <P>Structure modification of tetragonal BaTiO<SUB>3</SUB> (t-BaTiO<SUB>3</SUB>) and corresponding phase transition by microwave heating were investigated. The sample compound was heated by 1.8 kW power and 2.45 GHz frequency microwave irradiation under N<SUB>2</SUB> atmosphere in a short experimental duration of 14 min. The maximum temperature of the surface of the sample was 1115 °C. The structure of the microwave irradiated BaTiO<SUB>3</SUB> was then analyzed by employing X-ray diffraction (XRD), Rietveld refinement analysis, Raman spectroscopy, and field emission scanning electron microscopy techniques. From XRD and Rietveld refinement analysis, the microwave irradiated BaTiO<SUB>3</SUB> sample was composed of hexagonal 89%, cubic 5% and tetragonal 6%. Due to the direct internal heating mechanism of microwaves, the core temperature of the sample might be higher than the phase transition temperature. The magnetic behavior of the sample was investigated using a vibrating sample magnetometer. The results indicated that the microwave irradiated BaTiO<SUB>3</SUB> exhibited mixed magnetism: ferromagnetic nature at low applied magnetic fields and diamagnetic nature at high applied magnetic fields.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Synthesis of hexagonal BaTiO<SUB>3</SUB> by microwave irradiation at low temperatures. </LI> <LI> Heating of BaTiO<SUB>3</SUB> by microwave irradiation was significant above ∼830 °C. </LI> <LI> Structure of the prepared samples were investigated by XRD, rietveld refinement and Raman spectra analysis. </LI> <LI> VSM analysis has revealed a mixed magnetic behaviours of ferromagnetism and diamagnetism at low and high magnetic fields. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
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Microwave Heating Characteristics of Magnetite Ore
Ramaraghavulu Rajavaram,Jaehong Lee,Joon Seok Oh,Han Gyeol Kim,Joonho Lee 대한금속·재료학회 2016 METALS AND MATERIALS International Vol.22 No.6
The heating characteristics of magnetite ore under microwave irradiation were investigated as a function ofincident microwave power, particle size, and magnetite ore mass. The results showed that the heating rate ofmagnetite ore is highly dependent on microwave power and magnetite ore mass. The maximum heating ratewas obtained at a microwave irradiation power of 1.70 kW with a mass of 25 g and particle size between53-75 μm. The volumetric heating rate of magnetite ore was investigated by measuring the temperature at differentdepths during microwave irradiation. Microwave irradiation resulted in modification of the microstructure of themagnetite ore, but new phases such as FeO or Fe2O3 were not formed. In addition, the crystal size decreasedfrom 115 nm to 63 nm after microwave irradiation up to 1573 K.
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