• PARAG BHARGAVA

Articles written in Bulletin of Materials Science

• Stereological characterization of crack path transitions in ceramic matrix composites

All ceramic composites involve a mismatch in physical properties the extent of which differs from one composite to another. Mismatch in thermal expansion (𝛥 𝛼) and elastic modulus (𝛥E) is known to produce stresses that influence the path of a propagating crack. Thus, the relative effect of thermal and elastic mismatch on the crack path is expected to change with change in stress intensity. We propose that the crack path in ceramic composites should undergo a transition with the crack being strongly influenced by the thermal mismatch stresses at low stress intensity and elastic mismatch stresses at high stress intensities. Thus, a material in use under different applications each with its own loading conditions is expected to exhibit different crack propagation tendencies which may be reflected in the 𝑣–𝐾 characteristics of the composite material. In the present work several model composites with different combinations of thermal and elastic mismatch have been considered. Cracks propagating at different sub-critical stress intensities (velocities) were generated by a novel indentation technique. Each indentation was performed at a constant displacement rate and a peak load. A range of displacement rates were used to produce cracks propagating at different velocities. The indentations were made using a Vickers indentor fitted in a universal mechanical testing machine. The crack paths in composites were quantified by stereological technique and the proposed theory was verified.

• Fabrication of low specific resistance ceramic carbon composites by colloidal processing using glucose as soluble carbon source

Ceramic carbon composites were fabricated by colloidal processing using glucose as soluble carbon source.Glucose is converted into conducting carbon at high temperature treatment. Ceramic carbon composites were sintered inflowing argon at 1400◦C showing resistor behaviour even at low carbon content (1 wt%). In this work, ceramic carboncomposites were fabricated using alumina–clay slurries with addition of glucose as a soluble carbon source. Morphology ofthe sintered samples was characterized by field emission gun (FEG) electron microscopy. Phase analysis was done by X-raydiffraction (XRD). Electrical properties of ceramic carbon composites were measured by broad band dielectric spectrometer.Carbon produced from glucose at high temperature was characterized independently by BET surface area, dynamic lightscattering, field emission gun scanning electron microscopy, field emission gun transmission electron microscopy, XRD andRaman spectroscopy.

• Characteristics of ionic adsorption on silica nanoparticles and its impact on the long term stability of dye-sensitized solar cells

Quasi-solid electrolytes based on silica nanopowder are well known in literature and these electrolytes are able to match in performance with that of liquid electrolytes. However, contrasting results are observed in literatureregarding stability of dye-sensitized solar cells (DSSCs) with most of the reported articles projecting silica-loaded quasisolid electrolyte-based cells as a stable alternative to liquid electrolyte-based cells, while a few others contradicting thesame. The present study demonstrates the effect of ageing under heat (60$^{\circ}$C) and illumination on the performance of liquid electrolyte and silica-loaded electrolyte-based DSSCs. It has been observed that DSSC based on silica-loaded electrolyte are less stable than DSSC based on liquid electrolyte even though independent study on both electrolytes by thermal analysis shows silica-loaded electrolyte to be more stable than liquid electrolyte. Segregation of silica in electrolyte has been confirmed through cryo-field emission gun-scanning electron microscopy. Zeta potential measurements show that ions are desorbed from the surface of silica on ageing under heat and illumination.

• Bulletin of Materials Science

Volume 43, 2020
All articles
Continuous Article Publishing mode

• Dr Shanti Swarup Bhatnagar for Science and Technology

Posted on October 12, 2020

Prof. Subi Jacob George — Jawaharlal Nehru Centre for Advanced Scientific Research, Jakkur, Bengaluru
Chemical Sciences 2020

Prof. Surajit Dhara — School of Physics, University of Hyderabad, Hyderabad
Physical Sciences 2020

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Posted on July 25, 2019

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