Faculty Publications

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Author: search.filters.author.Mahendra, K.

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    Synthesis and Optical Characterization of Amaranth Dye Doped Thiourea Barium Chloride (TBC) Single Crystals
    (Elsevier Ltd, 2018) Mahendra, K.; D'Souza, A.; Ifthekarahmed; Udayashankar, N.K.
    Thiourea barium chloride (TBC), Amaranth doped (0.05, 0.1 mM) TBC(ADTBC) crystals were synthesized at room temperature by solvent evaporation process. Structural analysis of TBC and ADTBC were studied using powder XRD, results confirmed that dye got incorporated into the host lattice. Optical analysis of the TBC and ADTBC crystals were carried using UV-Visible and photoluminescence spectrophotometer. Results showed that both pure and dye doped crystals had an absorption peak at around 264 nm. Optical bandgap of the crystal was found to be decreasing as the doping percentage of the crystal increased. Pure and doped crystals exhibit a strong emission peak in the blue region. © 2017 Elsevier Ltd.
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    Synthesis and optical characterization of Nickel doped Thiourea Barium Chloride (TBC) single crystals
    (Institute of Physics Publishing helen.craven@iop.org, 2018) Mahendra, K.; Udayashankar, N.K.
    Organometallic Thiourea barium chloride (TBC) single crystals were synthesized using solution evaporation process at room temperature. Synthesized thiourea barium chloride crystals were recrystallized and during the recrystallization process 1M%, 2M% and 5M% of nickel (Ni) was added to the solution and kept for crystallization. The variation of intensity peaks and the shift in the XRD peaks were observed due to the incorporation of nickel in the host matrix. Variations in the absorbance and transmittance spectra of the pure and Ni doped crystals further confirms the presence of nickel in TBC single crystal. The optical bandgap of the pure and nickel doped single crystals were calculated using Touc's relation. The results show that bandgap decreased with the dopant concentration in the thiourea barium chloride crystal. The optical constants such as extinction coefficient and reflectance were also studied using the absorption spectrum. The FTIR absorption also shows minute shift in the absorption peaks due to the presence of nickel in the host matrix. Photoluminescence spectra of pure and doped crystals were studied. © Published under licence by IOP Publishing Ltd.
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    Effect of waste ceramic tiles as a partial replacement of aggregates in concrete
    (Elsevier Ltd, 2019) Bommisetty, J.; Sai Keertan, T.S.; Ravitheja, A.; Mahendra, K.
    In recent constructions, the consumption of ceramic materials is increasing day by day in the form of tiles, sanitary fittings, electrical insulators etc. But a large quantity of ceramic materials changes into wastage during processing, transporting and fixing due to its brittle nature. Therefore, using these wastes in concrete production could be an effective measure in maintaining the environment and improving the properties of concrete. Hence, the crushed waste ceramic tiles were used in concrete as a replacement for natural coarse aggregates with 0%, 5%, 10%, 15% 20% and 25% of substitution. After analyzing results, the optimum value of waste ceramic tile to be used within the concrete mix with a water/cement ratio of 0.5 was determined as about 20%. The findings revealed that using waste ceramic tile lead to enhancing the properties of concrete. © 2019 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the 1st International Conference on Manufacturing, Material Science and Engineering.
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    One part alkali-activated materials for construction - A review
    (Elsevier Ltd, 2023) Mahendra, K.; Narasimhan, M.C.
    With the present-day call for sustainability in concrete constructions, alkali-activated materials (AAM) - both mortar and concrete mixes, are attracting immense interest owing to their enhanced strength and durability characteristics, and lower environmental impact. However, the utilization of the conventional two-part AAM's is generally restricted to precast sector, primarily due to the inherent difficulties associated with the transporting, storage, and handling of alkaline activator solutions which are generally aggressive in nature. This has led to the development of one-part type (or "Just add water"- type) geopolymers in which liquid activator solution is replaced with a solid or anhydrous activator. The performance of a one-part geopolymer is significantly influenced by the type of aluminosilicate precursors and solid activators used. Notably, in most of the studies, fly ash and/or GGBFS are used as the precursors, while any of anhydrous sodium silicate, sodium hydroxide, sodium carbonate, calcium hydroxide, and sodium metasilicate is used as the activator. This review article discusses the various studies that have focused on the production and placement, and the fresh, and hardened properties of one-part alkali-activated materials. Various issues associated with efforts to make such binder systems more amenable also to cast-in-situ applications are addressed. © 2023 Elsevier Ltd. All rights reserved.
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    Performance of Alternate Superplasticizers on Performance of Self-compacting Geopolymer Mortars—An Experimental Study
    (Springer Science and Business Media Deutschland GmbH, 2024) Prakash, G.B.; Mahendra, K.; Tanush, L.; Narasimhan, M.C.
    Geopolymer binders are the best alternatives to Ordinary Portland cement in the view of carbon impact on the environment. The effect of addition of different types of superplasticizers (SPs) on the flow and compressive strengths of a class of self-compacting geopolymeric mortar (SCGM) mixes is investigated in the present study. Three different kinds of SPs, namely modified Polycarboxylate Ether (MPCE), Polycarboxylate Ether (PCE), and Sulfonated Naphthalene Formaldehyde (SNF), were used in the production of SCGM with varying proportions at 1, 1.5, and 2% by weight of the binder. Results revealed that modified PCE-based SP showed better results in flow and compressive strength (CS) in comparison to PCE and SNF-based SPs. However, an increase in the dosage of SP had less/adverse effect on the flow properties. A maximum slump flow of 270 mm was observed for a modified PCE-based SP at 1.5% dosage, while the highest CS of 34 MPa was observed at 1.5% dosage of the same SP. Scanning electron microscope (SEM) analyses were carried out on a few selected SCGM mixes. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
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    Shear Strength Characteristics of One-Part Alkali Activated Concrete Mixes—A DOE Approach
    (Springer Science and Business Media Deutschland GmbH, 2024) Mahendra, K.; Prakash, G.B.; Shetty, S.; Narasimhan, M.C.
    Utilization of one-part alkali-activated concrete (OPAAC) mixes is an advantageous option for large-scale construction applications. In the present investigation, the main objective was to investigate the shear strength characteristics of OPAAC mixes that were made using GGBFS and fly ash as precursors and sodium meta-silicate as solid activator. Taguchi’s DOE approach has been used to reduce the experimental effort and to find the optimum parameters. An initial set of nine OPAAC mixes was identified based on an L-9 array, with three representative levels considered for each of three principal mix parameters and experiments were conducted to test their compressive and shear strengths. The test results revealed that the OPAAC mixes exhibited 28-day compressive strength values ranging from 55 to 70 MPa, with shear strengths varying in the range of 8.5–12.67 MPa. Multi-linear regression equations were then developed to predict the 28-day compressive and shear strengths using MINITAB 21 statistical software. The predictions of these were verified by conducting actual strength experiments on a new set of three verification mixes. Further, additionally, a generalized correlation was developed to predict the 28-day shear strength of OPAAC mixes based on the known 28-day compressive strength. Again, an examination of microstructures was carried out through the utilization of FESEM analysis, to get a general appreciation of the microstructure (morphology) and elemental composition using EDX analysis of these mixes. The outcomes of this study are anticipated to promote the extensive adoption of environmentally friendly and sustainable materials within the construction industry. The findings of this study are anticipated to promote the extensive adoption of environmentally friendly and sustainable materials in the construction industry. © The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2024.
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    Synthesis, structural, optical and electrical (DC) properties of a semiorganic Thiourea Barium Chloride (TBC) single crystal
    (Elsevier GmbH journals@elsevier.com, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present study, TBC single crystals were synthesized using solution evaporation method. The structural analysis of TBC crystal was studied using Powder X-ray diffraction. Optical properties of TBC crystals were carried out using UV–vis, FTIR, Raman and photoluminescence (PL) spectra. The crystal shows absorbance maxima at 209 nm and transparent in the visible region 300–900 nm. The various optical constants such as refractive index, reflectance, speed of light, extinction coefficient, electrical susceptibility, dielectric constant, optical and electrical conductivity were evaluated. Thus results revealed that all these optical constants shows a strong dependence on optical absorption coefficient. Using single oscillator model (Wemple ?Didomenico), lattice dielectric constant and the ratio of free charge carrier to their effective mass were evaluated. The PL study of TBC crystals shows two emission peaks (419 nm ?S, 441 nm- Ba) in blue region. The DC resistivity and conductivity of the crystal was investigated in the temperature range 26 °C–115 °C. © 2017 Elsevier GmbH
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    Effect of Zn doping on the structural, optical, photoluminescence and mechanical properties of thiourea barium chloride (TBC) crystal
    (Elsevier Ltd, 2017) Mahendra, K.; D'Souza, A.; Udayashankar, N.K.
    In the present work, a synthesis and comparative study on the effect of Zinc (Zn) on thiourea barium chloride (TBC) single crystals has been reported. Crystals of thiourea barium chloride and Zn-doped thiourea barium chloride crystals are prepared using slow evaporation from the saturated solution. The samples were subjected to single crystal and powder X-ray diffraction to study the unitcell parameters and structural variations. The functional groups present in the crystals are derived using FTIR and Raman analysis. The enhancement of transmittance with the addition of Zn and the variations in the parameters such as bandgap, extinction coefficient, reflectance, refractive index, optical and electrical conductivity, real and imaginary part of dielectric constant are studied from UV–vis spectrum analysis. Vickers hardness measurements are conducted for pure and Zinc-doped TBC single crystals. The emission spectrum of pure and Zn doped single crystals are studied using photoluminescence analysis. © 2017 Elsevier Ltd
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    Gamma irradiation effect on structural, optical and electrical properties of organometallic potassium hydrogen oxalate oxalic acid dihydrate single crystal
    (Springer New York LLC barbara.b.bertram@gsk.com, 2018) Mahendra, K.; Nayak, K.K.; Fernandes, B.J.; Udayashankar, N.K.
    Potassium oxalate oxalic acid dihydrate (KHO) single crystals were grown from solvent evaporation technique at room temperature. Crystals were optically characterized using UV–Vis and photoluminescence analysis. The gamma irradiation effects on KHO crystals were also studied optically and the results were analyzed to compare the effect of irradiation on the crystal lattice for different dosage. Structural variations were studied using powder XRD, FTIR and the results were examined to study the defect states created inside the lattice due to irradiation and the effect on the functional vibrations of the host crystal. Surface morphology of the crystal was studied using scanning electron microscope (SEM). Photo conductivity of the synthesized crystals were studied and analyzed to compare the photo response as well as the conductivity of the materials when subjected to irradiation. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.
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    Enhanced structural, optical, thermal, mechanical and electrical properties by a noval approach (nanoparticle doping) on ferroelectric triglycine sulphate single crystal
    (Springer Verlag service@springer.de, 2019) Mahendra, K.; Kumar, H.K.T.; Udayashankar, N.K.
    The pristine and AgNP-doped TGS crystals are studied using powder X-ray diffraction, density measurements, solubility studies, UV–Vis analysis, photoluminescence spectroscopic analysis, thermal gravimetric analysis, differential thermal analysis, differential scanning calorimetry, Vicker’s hardness measurements, I–V and impedance measurements. From the XRD studies, TGS crystal formation is confirmed and by further analyzing X-ray diffraction data it is noticed that the incorporation of nanoparticles induce stress in the lattice of TGS crystal, which, in turn, lead to shift in peak positions. Crystal solubility and density values are increased after doping process. From the emission spectrum it is evident that emission intensity increases as the doping concentration increased. The melting point and mechanical hardness of the crystals also showed improvement after AgNP doping. Band gap calculated by Tauc’s relation is found to decrease with increase in doping concentration. Further, electrical studies demonstrated that crystal conductivity is improved as the doping concentration increases. © 2019, Springer-Verlag GmbH Germany, part of Springer Nature.