Department of Metallurgical and Materials Engineering

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Coating thin liquid films with complex rheological behaviour on permeable substrates is often an important requirement in several applications such as contact lenses, textiles, and paper-based electronics. Here, we extend the classical Landau-Levich problem of dip coating of Newtonian liquids on rigid substrates to liquids of power-law rheology on permeable substrates. Our results suggest distinct deviation from the classical Landau-Levich relation through exhibition of different regimes of varying dependence of coating film thickness on withdrawal speed. A process map is presented depicting these coating thickness regimes for a wide range of operating parameters such as the substrate permeability factor, power-law exponent of the liquid, and a rescaled capillary number. © 2021 Elsevier Ltd

World University root node

International Communications in Heat and Mass Transfer

Thickness regimes of power law liquids dip coated onto permeable substrates

Ceria, its Eu-based (Ce0.9Eu0.1O2), and Cr-based (Ce0.9Cr0.1O2) derivatives are investigated as supercapacitor-electrode material. In this work, doping standalone is used to enhance specific capacitance by 218% over pristine ceria. The Mott-Littleton method is used to predict the appropriate trivalent dopant (Cr in this case). The experimental study is found to be consistent with the prediction. Specifically, the XPS analysis indicates a higher vacancy concentration in the case of Ce0.9Cr0.1O2 vis-à-vis Ce0.9Eu0.1O2. The former material exhibits a maximum specific capacitance of 328 F g−1, which is 3 times that of undoped-ceria; the rate capability is reasonable even at 10 A g−1. A Swagelok cell consisting of Ce0.9Cr0.1O2@Ni-foam shows 100% capacitance retention even after 10,000 cycles. The cell exhibits a low steady-state leakage current of 17 μA with an overall leakage charge of 49.72 μAh. This study indicates that the Mott-Littleton approach can be used to guide superior dopant selection for supercapacitor application. © 2020

Department Of Chemistry

Applied Materials Today

Ceria for supercapacitors: Dopant prediction, and validation in a device

Present work studies 126 quaternary and 126 quinary equiatomic refractory high entropy alloys (RHEAs), made from Group IV (Ti, Zr, Hf), Group V (V, Nb, Ta) and Group VI (Cr, Mo, W) elements. Rule-of-mixtures (ROM) technique is used to calculate liquidus temperature, density (ρ), Young's modulus (E), % atomic size difference (δ), valence electron concentration (VEC) and specific heat at constant pressure and at 1273 K (Cp). CALPHAD technique is used to predict the number of phases formed at 298 K, ρ and liquidus temperature. ROM calculated densities are matching perfectly with CALPHAD values. Densities and E are directly proportional to the VEC and liquidus temperature of the alloys. Ti, Zr, Hf are ductilizing the alloys and making them light; whereas Cr, Mo and W, are reducing the alloys' ductility and making them heavy. For quinary RHEAs, Cp shows six distinct groups with δ, but a similar trend is not observed in quaternary RHEAs. A methodology is developed to screen a large number of alloys based on various properties. Correlations between those properties are also studied. © 2020

Department Of Civil Engineering

Intermetallics

CALPHAD and rule-of-mixtures: A comparative study for refractory high entropy alloys

The study focuses on the design of an energy harvesting nonlinear dynamic vibration absorber (DVA) for possible vibration attenuation and energy generation. As an application vibration mitigation of a base-excited single degree of freedom (SDOF) system is considered. Conventional DVAs are widely used as vibration control devices that undergo large displacements in order to dissipate the energy from the primary structure. For an energy harvester higher the vibration higher is the energy generated. Therefore, if an energy harvester is attached to the DVA, the primary structure DVA interaction can be used for dual purposes. In this study, a duffing-type nonlinear DVA system with a piezo patch is proposed as energy harvesting nonlinear DVA to mitigate the vibration and to obtain electricity. The modeling of the total system is carried out considering the electromechanical interactions between the harvester-DVA and structural system. The formulation is done in time domain and a simulation study is carried out for harmonic base excitation to understand the effect of nonlinearity in voltage generation. A frequency sweep study is carried out to locate the frequency band in which the system responses are consistently higher. Further, the important design parameters are identified. A parametric study to obtain optimal design parameters is also reported. The advantages of nonlinear energy harvesting DVA over the linear ones are many. A nonlinear harvester provides power over a broad range of frequencies and, therefore would be able to dissipate energy from the primary structure over wideband excitations. Finally, the performance of the designed nonlinear DVA system with harvester is examined for vibration mitigation of SDOF primary system. © 2021, The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd.

Department of Applied Mechanics

Lecture Notes in Mechanical Engineering

Design of a Nonlinear Energy Harvesting Dynamic Vibration Absorber

A suspended layer made up of ferromagnetically ordered spins could be created between two- monolayer or multilayer graphene through intercalation. Stability and electronic structure studies show that, when fluorine molecules are intercalated between two mono/multilayer graphene, their bonds get stretched enough (∼1.9-2.0Å) to weaken their molecular singlet eigenstate. Geometrically, these stretched molecules form a pseudoatomized fluorine layer by maintaining a van der Waals separation of ∼2.6Å from the adjacent carbon layers. As there is a significant charge transfer from the adjacent carbon layers to the fluorine layers, a mixture of triplet and doublet states stabilizes to induce local spin moments at each fluorine site and in turn form a suspended two-dimensional spin lattice. The spins of this lattice align ferromagnetically with nearest-neighbor coupling strength as large as ∼100meV. Our finite-temperature ab initio molecular dynamics study reveals that the intercalated system can be stabilized up to a temperature of 100 K with an average magnetic moment of ∼0.6μB/F. However, if the graphene layers can be held fixed, the room-temperature stability of such a system is feasible. © 2020 American Physical Society.

Department Of Physics

Fulltext

Physical Review Materials

Fluorine intercalated graphene: Formation of a two-dimensional spin lattice through pseudoatomization

Hot workability characteristics of a recently developed rare-earth-free creep-resistant magnesium alloy Mg-3Ca-2Sn-1Al (XTA321) is evaluated using the processing map approach. The processing map is established using the flow stress data from constant strain rate compression tests conducted in the temperature and strain rate range of 300°C-500°C and 10−3-10 s−1, respectively. The processing map exhibits a hot workability domain between 475°C to 500°C and in the strain rate range of 10−2 to 10−1 s−1. Correlation of post-deformation microscopy with kinetic analysis is carried out to identify the possible softening mechanism in the hot working domain. The significant portion of the processing map falls in the instability regime, having shear band formation as the prime microstructural feature. The poor workability of the XTA321 vis-a-vis most of the magnesium alloys can be attributed to the presence of a high volume fraction of the strong second phase in the microstructure. Copyright © 2020 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959

Materials Performance and Characterization

Exploring the safe hot working regime of creep-resistant Mg-3Ca-2Sn-1Al alloy

A series of (D-π)2-An-A based organic dyes containing a boron dipyrromethene (BODIPY) moiety as an ancillary acceptor (An) derivative were chosen, and the effect of donor moieties (diarylamine, carbazole, azepine, and dibenzazepine) was investigated to understand their photophysical and photoelectrochemical properties by employing density functional theory (DFT) and time-dependent DFT. It is experimentally proved that BODIPY enhances light-harvesting in the red and near IR regions of visible light. Electron density distribution analysis was performed for all the dyes to confirm the intramolecular charge transfer, envisioned from the simulated absorption spectra of the dyes. Carbazole donor-based dyes exhibited the lowest reorganization energy. A dye attached to the TiO2(1 0 1) surface was modeled to estimate the adsorption energy of the dyes. The density of states analysis revealed that the absence of defect states in the bandgap of TiO2 facilitates smooth electron transfer from the excited state of the dye to the conduction band of TiO2. Considering the lowest unoccupied molecular orbital (LUMO) energy level of the dyes and the conduction band energy level of TiO2, it is understood that all the dyes studied in this report are capable of electron injection upon photoexcitation. Considering the driving force for dye regeneration and the magnitude of reorganization energy, a carbazole donor-based dye (D2) would be the best performing dye in DSSCs. Previously, the power conversion efficiencies of the dyes have been reported, and the carbazole donor-based dye (D2) exhibited the highest efficiency among all the dyes. Our computational investigations are in good agreement with the experimental results. © 2020 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.

New Journal of Chemistry

A computational study on boron dipyromethene ancillary acceptor-based dyes for dye-sensitized solar cells

Heterostructure interfaces play a major role in defining the performance of thin-film devices. High-k dielectric oxide-semiconductor heterostructures are being extensively investigated as promising candidates for future integrated circuits, thus it becomes important to precisely probe the interfaces at the atomic scale for technological advancements. In this work, a high-k dielectric oxide (Gd2O3)-semiconductor (Ge) interface was characterized at the atomic scale using complex-valued exit wave reconstructed from a set of focal series high-resolution transmission electron microscopy (HRTEM) images acquired without objective lens spherical aberration correction. The complexity of this characterization lies in removing image artefacts produced by amorphous layer deposited on the imaged region during ion milling which was successfully solved using an algorithm to remove amorphous background developed recently. The final result reveals that the interface of the present study is atomically sharp and flat. The thickness of the imaged region along viewing direction was estimated from channelling map. Comparing reconstructed amplitude of experimental data with that of simulated one generated using Density Functional Theory (DFT) optimized interface structure, it was found that the Gd2O3 layers were terminated at the Gd atoms in the interface. © 2019 Elsevier B.V.

GENERAL

Journal of Alloys and Compounds

Unravelling atomically resolved structure of a high-k dielectric oxide-semiconductor interface: Exit wave reconstruction and ab-initio calculation insights

Introduction: The aim of this study was to evaluate the effect of functionalized nanoparticle photodynamic therapy on Nano hardness of root dentin Methodology: Fifty single rooted lower premolars were decoronated and sectioned into two halves. Then the samples were embedded horizontally in to the acrylic resin to expose the dentin surface. Baseline nanohardness was done at midroot level using a Nanohardness tester. Exposed dentin surfaces were immersed in the following irrigating solutions • Group 1: 1 ml of Chitosan conjugated Rose Bengal (CSRB-np) activated with 540 nm for 10 min • Group 2: 1 ml of Methylene blue loaded poly lactic acid (PLGA-MB np) activated with 660 nm for 10 min • Group 3: 5 ml of 5.25 % sodium hypochlorite for 1 min + 1 ml of 17 % EDTA for 1 min • Group 4: 1 ml of 2.5 % sodium hypochlorite for 10 min + 1 ml of 17 % EDTA for 1 min + 1 ml of 2% chlorhexidine for 1 min. • Group 5: 1 ml of 0.9 % Saline for 10 min. Post treatment nanohardness testing was done and results were analyzed statistically Results: In general, all the samples in their respective groups had significant change in nanohardness following immersion in irrigant solutions except in NaOCl + EDTA and saline group. CSRB-np and PLGA-MBnp showed increased nanohardness (P = 0.005 and P = 0.007 respectively). Whereas NaOCl + EDTA + CHX showed decrease in nanohardness (P = 0.04). With regards to Modulus of elasticity (MOE), CSRB-np showed significant difference (P = 0.002) compared to the other groups. MOE increased in CSRB-np and PLGA-MBnp while it decreased in all the other groups. Conclusion: In this study, the improvement of nanohardness and modulus of elasticity following the immersion of root dentin in CSRB-np solution was demonstrated © 2020 Elsevier B.V.

Department of Mathematics

Department of Aerospace Engineering

Photodiagnosis and Photodynamic Therapy

Evaluation of effect of two different functionalized nanoparticle photodynamic therapy on nanohardness of root dentin–An in vitro study

Solid oxide fuel cell (SOFC) is a green energy technology that directly coverts chemical energy into electricity. Scandia stabilized zirconia (SSZ) shows the highest conductivity among zirconia based electrolytes for SOFCs. However, the stability of the cubic phase, which is the desirable phase for high conductivity, can be an issue in SSZ electrolytes due to its transformation to other low-conducting phases at higher temperatures. In the present investigation, SSZ electrolyte was co-doped with ytterbia, gadolinia and ceria with an objective of improving the high-temperature phase stability. Both the doped and co-doped compositions exhibited a single cubic phase in the as-processed condition. The phase stability at high temperature was studied by aging the sintered pellets at 900&nbsp;°C for 500&nbsp;h in air. X-ray diffraction and transmission electron microscopy analysis revealed formation of small amount of the low-conducting tetragonal phase in 1&nbsp;mol % ytterbia and gadolinia co-doped compositions on ageing which resulted in conductivity degradation. Increasing the doping level to 2&nbsp;mol% prevented the formation of the tetragonal phase. The ceria co-doped composition (1&nbsp;mol%), on the other hand, was clean without any sign of the secondary phases even after high-temperature ageing. The rhombohedral ‘β’ phase formed in the binary composition (SSZ) after sintering but was absent in all the co-doped compositions. The conductivity of the co-doped samples was higher than the binary SSZ. Thus, it can be said that rare earth co-doping is an effective way of improving the phase stability and conductivity of SSZ electrolytes.