Papers by NIBEDITA SASMAL
Foamed glass-ceramics without using foaming agent have been synthesized in a novel glass system o... more Foamed glass-ceramics without using foaming agent have been synthesized in a novel glass system of SrO-CaO-Al 2 O 3 -TiO 2 -B 2 O 3 -SiO 2 -P 2 O 5 -M x O y (where M = Ba, Mg, La, Ce and Ni) by a simple process of powder sintering. The glass and glass-ceramics are characterized by dilatometry, differential scanning calorimetry (DSC), heating stage microscopy (HSM), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), optical microscopy and Fourier transformed infrared spectroscopy (FTIR). All the glasses formed are amorphous and the glass transition temperature and dilatometric softening temperature of these glasses are found to be in the range 673-678°C and 706-728°C respectively. The glasses are highly stable as indicated by the DSC evaluated glass stability parameters of the range 195-240°C. Quantitative sintering study of glass powder compacts revealed swelling in the samples with NiO and CeO 2 corresponding to a geometry change of 75 and 108% around 900°C respectively. With reference to this finding the glass powder compacts are heated to 900°C and the foamed glass-ceramics are obtained. Characteristic crystalline silicate phases have been identified in the XRD studies and their microstructures are recorded by FESEM. Optical microscope study of the foamed samples revealed formation of bigger foamed cavity with residual pores in samples with NiO and CeO 2 in comparison to samples with BaO, MgO and La 2 O 3 . The mean pore diameters of the samples with NiO and CeO 2 are determined to be 43 and 32 μm, and their respective porosities are 2.34 and 1.82 cm 3 /g respectively. Thus NiO and CeO 2 are found to be very effective to obtain foamed glass-ceramics without using foaming agent by the viscous flow sintering of fine glass powder compacts along with the reduction of the respective polyvalent ions.
We have explored the effects of lanthanum oxide (La 2 O 3 ) on the properties of barium-free SrO-... more We have explored the effects of lanthanum oxide (La 2 O 3 ) on the properties of barium-free SrO-CaO-ZnO-B 2 O 3 -SiO 2 glass system varying its content from 0 to 6 mol%. The coefficient of thermal expansion and glass transition temperature of the glasses are found to be in the ranges 10.6-10.8 × 10 −6 /K (50-600°C) and 650-690°C respectively. Differential scanning calorimetric studies revealed an increase in crystallization peak temperature and thermal stability of the glasses up to 4 mol% and then decrease on further addition. A monotonic increase in characteristic shrinkage temperature of glass powder compact is observed on addition of La 2 O 3 as revealed in the heating stage microscopic study. X-ray diffraction studies revealed reduced crystallization peak intensity in La 2 O 3 added glasses. Fourier transformed infrared spectra disclosed that the addition of La 2 O 3 stabilized the glass structure by reducing the number of non-bridging oxygens. Vickers micro hardness of the glasses varied in the range 2.6-5.6 GPa. Scanning electron microscopy revealed the formation of particulate nature of microstructures in parent glass which is not observed in the La 2 O 3 added glasses. Activation energy of crystallization has increased from 331 to 361 kJ/mol determined by Kissinger and Augis-Bennett models. Above properties of these glasses clearly advocate their applicability as solid oxide fuel cell sealants.
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Papers by NIBEDITA SASMAL