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Reddy A.A.,University of Aveiro | Tulyaganov D.U.,University of Aveiro | Tulyaganov D.U.,Turin Polytechnic University in Tashkent | Goel A.,Sterlite Technologies Ltd. | And 4 more authors.
International Journal of Hydrogen Energy | Year: 2012

Diopside (CaMgSi 2O 6) based glasses compositions containing magnesium orthosilicate or barium aluminosilicates phases have been appraised for sealing applications in solid oxide fuel cells (SOFCs) and other solid-electrolyte devices. The sintering behavior and crystalline phase evolution of glass powders has been investigated under isothermal and non-isothermal conditions in the SOFC operating temperature range (800-900°C). All the glass compositions exhibited two-stage shrinkage behavior resulting in well sintered and mechanically strong glass-ceramics with Augite as the primary crystalline phase. The appropriate coefficient of thermal expansion (CTE), long term thermal stability (300 h at 900°C), high electrical resistivity, good adhesion and minimal reactivity with SOFC components makes the investigated glass-ceramics potential candidates for further experimentation as SOFC sealants. © 2012 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. Source

Kapoor S.,University of Aveiro | Goel A.,Sterlite Technologies Ltd. | Pascual M.J.,CSIC - Institute of Ceramics and Glass | Ferreira J.M.F.,University of Aveiro
Journal of Non-Crystalline Solids | Year: 2013

We report on the influence of SrO and ZnO co-doping on thermo-mechanical behaviour of alkali free bioactive glass-ceramics in system: (mol%) (36.07 - x) CaO-x SrO-(19.24 - y) MgO-y ZnO-5.61 P2O5-38.49 SiO 2-0.59 CaF2 (x = 2-10, y = 2-10). Hot-stage microscopy and differential thermal analysis revealed that densification of all the glass powders occurs before the onset of crystallization, resulting in well sintered and mechanically strong glasses/glass-ceramics after heat treating for 1 h under non-isothermal conditions at 800, 850 and 900 C. The crystalline phase assemblage in the sintered compacts included diopside (CaMgSi2O 6) and fluorapatite [Ca5(PO4)3F] with partial replacement of Ca for Sr with increasing strontium contents. The effect of heat treatment temperature on mechanical reliability was assessed by Weibull statistical analysis applied to the flexural strength data. The results obtained revealed that a better balance of properties was achieved for the samples sintered at 850 C. These results provide an insight into the choice of final material/experimental conditions for the development of three-dimensional porous scaffolds for bone tissue engineering. © 2013 Elsevier B.V. Source

Reddy A.A.,University of Aveiro | Goel A.,University of Aveiro | Goel A.,Sterlite Technologies Ltd. | Tulyaganov D.U.,University of Aveiro | And 5 more authors.
Journal of Power Sources | Year: 2013

A parent glass within the CaO-MgO-Al2O3-SiO 2 system and resulting glass-ceramics (GCs) have been appraised for solid oxide fuel cells (SOFCs) sealing applications. The sintering behavior was investigated by differential thermal analysis and hot stage microscopy. The glass composition exhibited single-stage shrinkage behavior with high sintering ability, and a suitable viscosity of 107.1 dPa s at the SOFCs operating temperature 900 °C. X-ray diffraction in conjunction with the Rietveld-RIR technique were employed to quantify the crystalline and amorphous phases in the GCs sintered at 900 °C for 1 h and 850 °C for 300 h. The coefficients of thermal expansion (CTE) measured were 9.7 × 10 -6 K-1 (200-500 °C) and ∼10.1 × 10 -6 K-1 (200-700 °C) for glass and GCs, respectively, in good agreement with those typical for SOFC components. Weibull analysis was applied on the three-point bend data of GCs in order to obtain the mechanical strength distribution, characteristic strength and Weibull modulus. Well matching CTE, flexural strength values, good sintering behavior and adhesion to the other components in air atmosphere allow proposing this glass composition as promising candidate for further experimentation as sealant for SOFCs. © 2012 Elsevier B.V. All rights reserved. Source

Bagga R.,Kanya Maha Vidyalaya | Achanta V.G.,TIFR | Goel A.,Sterlite Technologies Ltd. | Ferreira J.M.F.,University of Aveiro | And 4 more authors.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2013

The radiative emission properties of the Dy3+ ions in oxyfluoride glasses and glass ceramics have been investigated for the generation of white light. The X-ray diffraction pattern of the glass ceramics reveals the presence of NaAlSiO4 nanocrystals along with secondary phase of NaY9Si6O26 in the glass matrix after a suitable thermal treatment of the pristine glasses. Intense white light emission has been observed when the samples are excited with 350 nm light. Yellow to blue emission intensity ratios and chromaticity color coordinates have been determined from the visible luminescence spectra. All color coordinates are found to lie in the white region of the chromaticity color diagram proposing the suitability of the present studied materials for color display devices. © 2012 Elsevier B.V. Source

Goel A.,Sterlite Technologies Ltd. | Kapoor S.,University of Aveiro | Tilocca A.,University College London | Rajagopal R.R.,University of Aveiro | Ferreira J.M.F.,University of Aveiro
Journal of Materials Chemistry B | Year: 2013

We report on the effect of varying the Zn2+/Mg2+ ratio on the structure and biodegradation of glasses in an alkali-free system designed in the glass forming region of diopside (CaMgSi2O 6)-fluorapatite [Ca5(PO4)3F]-TCP (3CaO·P2O5). The zinc-containing glasses designed in the as-mentioned ternary system are potential materials for their application in bone regeneration and tissue engineering. The melt-quenched glasses with compositions (mol%), 36.07CaO - (19.24 - x) MgO - xZnO - 5.61P2O 5 - 38.49SiO2 - 0.59CaF2, where x varies between 0 and 10, have been investigated for their structure by molecular dynamics simulations as well as by nuclear magnetic resonance spectroscopy. In all the investigated glasses silicate and phosphate components are mainly present as Q2 (Si) and Q0 (orthophosphate) species, respectively. Zinc retains structural features similar to magnesium, with predominant five-fold coordination. The apatite-forming ability of glasses has been investigated by X-ray diffraction and infrared spectroscopy after immersion of glass powders in simulated body fluids for time durations varying between 1 h and 7 days, while their chemical degradation has been studied in Tris-HCl in accordance with ISO-10993-14. The increasing Zn2+/Mg2+ ratio decreases the chemical degradation of glasses as well as reducing their apatite forming ability. The results allowed us to discuss the biodegradation of alkali-free bioactive glasses on the basis of the structural role of zinc and magnesium. This journal is © The Royal Society of Chemistry 2013. Source

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