Sunanda Mukhopadhyay

Bio: Sunanda Mukhopadhyay is an academic researcher from University of Calcutta. The author has contributed to research in topic(s): Graphite & Spinel. The author has an hindex of 8, co-authored 19 publication(s) receiving 193 citation(s).

Fabrication and enhanced photoluminescence properties of Sm3+-doped ZnO–Al2O3–B2O3–SiO2 glass derived willemite glass–ceramic nanocomposites

Abstract: The transparent willemite, Zn 2 SiO 4 (ZS) glass–ceramic nanocomposites were prepared from melt-quench derived ZnO–Al 2 O 3 –B 2 O 3 –SiO 2 (ZABS) precursor glass by an isothermal heat-treatment process. The generation 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 80–120 nm. The decreased refractive index with increase in heat-treatment time attributed to partial replacement of ZnO 4 units of willemite nanocrystals by AlO4 units and simultaneous generation of vacancies in the Zn-site. Fourier transform infrared (FTIR) reflection spectroscopy exhibits the structural evolution of willemite glass–ceramics. The photoluminescence spectra of Sm 3+ ions exhibit emission transitions of 4 G 5/2 → 6 H J ( J = 5/2, 7/2, 9/2, 11/2) and its excitation spectra shows an intense absorption band at 402 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 14-fold with crystallization into willemite.

Spinel-Coated Graphite for Carbon Containing Refractory Castables

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.

Characteristics of Refractory Castables Containing Mullite and Spinel Coated Graphites

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.

Nanoscale calcium aluminate coated graphite for improved performance of alumina based monolithic refractory composite

Abstract: The synthesis and properties of high alumina castable containing nanostructured calcium aluminate coated graphite were studied in terms of slag resistance and overall physical characteristics. Raman spectroscopy, BET surface area and field emission scanning electron microscopy (FESEM) were performed to exclusively understand the coating characteristics and its compatibility in refractory composite. The coating not only secured graphite in castable for prolonged period but also noticeably improved matrix to aggregate contact. The microstructural aspects of castables were investigated, with special emphasis on a representative matrix prepared and infiltrated with slag at elevated temperature. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) of fired composite containing surface-treated graphite was quite prospective. It circumvented the problems of incorporating as-received graphite in castables and should be in the attention of refractory researchers and producers.

Synthesis and Properties of SrBi2Ta2O9‐Based Glass‐Ceramics Modified with Eu3+

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.

Transparent Glass-ceramics

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.

Easy-to-use mullite and spinel sols as bonding agents in a high-alumina based ultra low cement castable

Abstract: This paper deals with the preparation of colloidal suspensions of mullite and magnesium-aluminate spinel via a cheaper precursor of alumina sol. Viscosity, pH, solid content, DTA, TGA and XRD studies at different temperatures were performed to characterize those two sols. These mullite and spinel sols were used separately as bonding agents in a high-alumina based ultra low cement castable composition prepared by simple tapping technique and their performances have been compared in terms of bulk density, apparent porosity, cold crushing strength, flexural strength, slag corrosion, thermal shock, XRD and SEM reports. The results confirm that the mullite sol excels while the spinel sol degrades the refractory castable quality.

Spectroscopic and photoluminescence characteristics of Sm3+ doped calcium aluminozincate phosphor for applications in w-LED

Abstract: Monophase Calcium Aluminozincate (Ca 3 Al 4 ZnO 10 ) phosphor doped with Sm 3+ ions by varying concentrations have been prepared at 1300 °C using conventional solid state reaction technique. The crystal structure and phase analysis of the as-prepared phosphor has been carried out by X-ray Diffraction (XRD) studies. 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. Under 401 nm excitation, the as-prepared phosphor exhibit intense visible orange emission at 601 nm. It has been observed that 1.0 mol% of Sm 3+ ions concentration is optimum to give intense visible orange emission. The PL analysis reveals that the dipole-dipole interaction is primarily responsible for the concentration quenching observed beyond 1.0 mol% of Sm 3+ ions. The TR-PL study reveals a bi-exponential behavior of decay curves with an average lifetime of the order of microseconds. The CIE coordinates ( x =0.574 and y =0.424) measured for the optimized phosphor are very close to the intense orange emission coordinates specified by Nichia Corporation developed Amber LED NSPAR 70BS (0.570, 0.420). The spectroscopic, PL and TR-PL studies suggest the potential use of Sm 3+ doped calcium aluminozincate phosphors for display and white light emitting devices.

Thermal, Structural, and Enhanced Photoluminescence Properties of Eu3+-doped Transparent Willemite Glass–Ceramic Nanocomposites

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.

Fabrication and enhanced photoluminescence properties of Sm3+-doped ZnO–Al2O3–B2O3–SiO2 glass derived willemite glass–ceramic nanocomposites

Abstract: The transparent willemite, Zn 2 SiO 4 (ZS) glass–ceramic nanocomposites were prepared from melt-quench derived ZnO–Al 2 O 3 –B 2 O 3 –SiO 2 (ZABS) precursor glass by an isothermal heat-treatment process. The generation 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 80–120 nm. The decreased refractive index with increase in heat-treatment time attributed to partial replacement of ZnO 4 units of willemite nanocrystals by AlO4 units and simultaneous generation of vacancies in the Zn-site. Fourier transform infrared (FTIR) reflection spectroscopy exhibits the structural evolution of willemite glass–ceramics. The photoluminescence spectra of Sm 3+ ions exhibit emission transitions of 4 G 5/2 → 6 H J ( J = 5/2, 7/2, 9/2, 11/2) and its excitation spectra shows an intense absorption band at 402 nm. These spectra reveal that the luminescence performance of the glass–ceramic nanocomposites is enhanced up to 14-fold with crystallization into willemite.