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Sunanda Mukhopadhyay

Bio: Sunanda Mukhopadhyay is an academic researcher from University of Calcutta. The author has contributed to research in topics: Graphite & Spinel. The author has an hindex of 8, co-authored 19 publications receiving 193 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, a transparent willemite, Zn 2 SiO 4 (ZS) glass-ceramic nanocomposites were prepared from melt-quench derived ZnO-Al 2 O 3 -B 2 O3 -SiO 2 (ZABS) precursor glass by an isothermal heat-treatment process.

62 citations

Journal ArticleDOI
TL;DR: In this article, a thin sol-gel film of magnesium aluminate spinel (MgAl 2 O 4 ) was applied to graphite flakes to increase their oxidation resistance and water wettability.
Abstract: Oxidation resistance and water wettability of graphite flakes have been improved by a thin sol-gel film of magnesium aluminate spinel (MgAl 2 O 4 ) over its surface. The hydrosol has been synthesized by less expensive precursors and the spinel formation has been studied by scanning electron microscopy (SEM), supplemented with energy dispersive spectral analysis. After an easy-to-use mixing procedure, drying (110°C), and subsequent calcination (550°C), coated graphites were sieved to below 75 μm. The coating over the powder contained 1.5 wt% MgAl 2 O 4 , which enormously increased the oxidation resistance (performed at 600°, 900°, and 1200°C) and water wettability, as revealed by hydrophilic functional groups from infrared spectra. Defective, intermediate spinel structure of fine, lamellar Mg-doped γ-Al 2 O 3 has been considered to be significant for this improvement. An approximate (1:2) stoichiometry of (Mg:Al) in the coating composition was confirmed by an X-ray photoelectron spectroscopy test. Castables prepared by this graphite remarkably improved their bulk density and apparent porosity compared with those prepared by the as-received graphite. Casting water was reduced along with the amount of antioxidants. This also enhanced the resistance toward the basic slag by retaining the graphite in the refractory.

39 citations

Journal ArticleDOI
TL;DR: In this article, the performance of high alumina castables containing mullite and spinel coated graphites was investigated to explore their commercial application in carbon containing refractory composites, compared in terms of thermal shock resistance, refractoriness under load, static slag resistance test, pore size distribution, and physical properties, e.g., apparent porosity and cold crushing strength.
Abstract: The performance of high alumina castables containing mullite and spinel coated graphites was investigated to explore their commercial application in carbon containing refractory composites. It was compared in terms of thermal shock resistance, refractoriness under load, static slag resistance test, pore size distribution, and physical properties, e.g., apparent porosity and cold crushing strength. The microstructures of these two castables, along with the other containing uncoated graphites, were also studied. Differential thermal analysis and X-ray diffraction patterns of heat-treated carbon-containing castable composites have also been noted. Castables containing mullite-coated graphite were found to be more resistant to repeated thermal shock cycles, whereas those containing spinel-coated graphites were more encouraging when slag resistance and overall physical properties are concerned.

22 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of three rare earth oxides, viz., La2O3, CeO2 and YbO3 on reaction sintering of magnesium aluminate spinel having molar ratio of MgO:Al 2O3 = 1:2 from its solid oxide precursors was investigated in static and dynamic heating conditions.

21 citations

Journal ArticleDOI
TL;DR: In this article, the Eu3+-doped novel precursor glass in the K2O-SiO2-SrO-Bi2O3-Ta2O5 system was prepared using the melt-quench technique.
Abstract: The Eu3+-doped novel precursor glass in the K2O-SiO2-SrO-Bi2O3-Ta2O5 system was prepared using the melt-quench technique. The transparent SrBi2Ta2O9 (SBT) glass-ceramic nanocomposites were derived from this glass using a controlled crystallization process. The formation of SBT crystal phase, size, and morphology with increase in heat-treatment time was examined using X-ray diffraction, field emission scanning electron microscopy, and fourier transform infrared transmission spectroscopy. Vicker's hardness study indicates marked improvement of hardness in the glass-ceramics compared to precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of D-5(0)-> F-7(j) (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 467 nm. These spectra reveal that the Eu3+ ions are gradually entering into the SBT nanocrystals present in the glass-ceramics. This study indicates that the incorporation of Eu3+ ions into SBT crystal lattice enhances the photoluminescence performance of the glass-ceramics by two-fold. It is believed that this work would generate significant impact in the exploration of SBT glass-ceramic nanocomposites.

16 citations


Cited by
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Journal Article
Pei Li-zhai1
TL;DR: Transparent glass-ceramic is a new kind of functional material with homogenous and dense structure composed of fine crystal particles as mentioned in this paper, and its preparation technique, species and properties were reviewed, and the development direction was discussed in the paper.
Abstract: Transparent glass-ceramic is a new kind of functional material with homogenous and dense structure composed of fine crystal particles.Its preparation technique,species and properties were reviewed,and the development direction was discussed in the paper.

93 citations

Journal ArticleDOI
TL;DR: In this paper, the crystal structure and phase analysis of the as-prepared phosphor has been carried out by X-ray Diffraction (XRD) studies and Morphology and functional groups present in the phosphor have been investigated thoroughly by using Scanning Electron Microscope (SEM) and Fourier Transform Infrared (FT-IR) spectral measurements, respectively.

76 citations

Journal ArticleDOI
TL;DR: In this paper, Dy3+ ions doped Na2O-ZnO-Al 2O3-B2O3 (BAZN) glasses with variable doping concentrations were synthesized by melt-quenching technique.

66 citations

Journal ArticleDOI
TL;DR: In this paper, the formation of willemite crystal phase, size, and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) techniques.
Abstract: The precursor glass in the ZnO–Al2O3–B2O3–SiO2 (ZABS) system doped with Eu2O3 was prepared by the melt-quench technique. The transparent willemite, Zn2SiO4 (ZS) glass–ceramic nanocomposites were derived from this precursor glass by a controlled crystallization process. The formation of willemite crystal phase, size, and morphology with increase in heat-treatment time was examined by X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM) techniques. The average calculated crystallite size obtained from XRD is found to be in the range 18–70 nm whereas the grain size observed in FESEM is 50–250 nm. The refractive index value is decreased with increase in heat-treatment time which is caused by the partial replacement of ZnO4 units of ZS nanocrystals by AlO4 units due to generation of vacancies. Fourier transform infrared (FTIR) reflection spectroscopy was used to evaluate its structural evolution. Vickers hardness study indicates marked improvement of hardness in the resultant glass-ceramics compared with its precursor glass. The photoluminescence spectra of Eu3+ ions exhibit emission transitions of 5D0→7Fj (j = 0, 1, 2, 3, and 4) and its excitation spectra show an intense absorption band at 395 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 17-fold with the process of heat treatment. This enhancement is caused by partitioning of Eu3+ ions into glassy phase instead of into the willemite crystals with progress of heat treatment. Such luminescent glass–ceramic nanocomposites are expected to find potential applications in solid-state red lasers, phosphors, and optical display systems.

65 citations

Journal ArticleDOI
TL;DR: In this paper, a transparent willemite, Zn 2 SiO 4 (ZS) glass-ceramic nanocomposites were prepared from melt-quench derived ZnO-Al 2 O 3 -B 2 O3 -SiO 2 (ZABS) precursor glass by an isothermal heat-treatment process.

62 citations