BITS Faculty Publications
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Item An assessment of residual stresses and micro-structure during single point incremental forming of commercially pure titanium used in biomedical applications(Elsevier, 2020) Kumar, GulshanSingle point incremental forming (SPIF) is a branch of incremental sheet forming where a very small portion of the sheet is deformed plastically at any moment. The highly localized point deformation is done by a simple hemispherical tool, whose path is numerically monitored by a Computer numerical control (CNC) machine, performs this progressive extremely localized deformation. Since no die is required during forming, highly customized and user-oriented sheet metal products can be manufactured employing the process. SPIF can be readily employed in the manufacturing of customized orthopaedic implants and braces, e.g., cranial implants, ankle implants, elbow and knee support braces. The forming of these sheets through SPIF would results in the generation of residual stresses in the sheet metal. With time and other physical factors, these residual stresses would be relieved resulting in dimensional inaccuracy. This inaccuracy is highly detrimental in the case of implants and highly undesirable for supporting braces. The objective of this work is to investigate, experimentally, the state and magnitude of residual stresses on commercially pure titanium grade 2 by SPIF for biomedical applications. The important process parameters: forming angle and incremental step depth are used for this investigation in the present study. The X-ray diffraction technique was used for the experimental measurements of the residual stresses. Microstructural behaviour of the final product at different incremental step depth and forming angles are also observed by EBSD (Electron backscattered diffraction) technique. The experimental findings showed the formation of increased tensile residual stresses with an increase in incremental step depth and steepness of forming angles.Item Novel lime-silica fume-modified limestone calcined clay cement (LC3) binder system for sustainable pavement construction(Springer, 2025-07) Lahoti, MukundLimestone calcined clay cement (LC3) has emerged as a promising sustainable alternative to ordinary Portland cement (OPC), offering comparable mechanical properties while significantly reducing carbon emissions. Conventional LC3 cement typically consists of approximately 50% ordinary Portland cement (OPC), 30% calcined clay, 15% limestone, and 5% gypsum. In this study, we refer to the binary blend of limestone and calcined clay as LC2 for convenience. This study explores two strategies to enhance LC3’s sustainability: (i) increasing the LC2-to-binder ratio and (ii) replacing OPC entirely with a calcium oxide (lime)–silica fume blend, where silica fume acts as a pozzolan to enhance hydration and strength development (all mixes contain 5% gypsum as well). A detailed investigation of 22 mix designs is conducted to evaluate compressive strength and feasibility for pavement applications, with comparison to conventional OPC-based LC3 and OPC-fly ash mortars. Microstructural analyses, including X-ray diffraction (XRD), scanning electron microscopy (SEM)-energy dispersive X-ray spectrometry (EDS), Fourier transform infrared spectroscopy (FT-IR), and thermogravimetric analysis (TGA), further corroborate the findings. Results indicate that a balanced CaO/silica fume ratio is crucial for achieving strength comparable to 70:30 OPC-based LC3; excessive CaO leads to detrimental expansion and mix instability. A maximum compressive strength of 27.6 MPa was observed for LCS-70 mixes (LCS-70-4.0), and a maximum of 29.2 MPa was observed for the LCS-50 mixes (LCS-50-1.8). Among the investigated mixes, LCS-70-1.0—where LCS refers to the LC2-CaO–silica fume system, 70 represents the LC2-to-binder ratio (70:30), and 1.0 denotes the CaO-to-silica fume ratio—emerges as the most optimal, offering a sustainable balance of strength, cost, and environmental impact. A total score of 4.46 is observed for this mix, which is higher than any other. The study concludes that lime-silica fume-modified LC3 is a viable alternative to both OPC and conventional LC3, making it suitable for low-volume pavement applications while significantly reducing embodied carbon and energy consumption.Item Glucoconjugated dinuclear copper(ii) complex: an efficient catalyst for stereoselective synthesis of trisubstituted propargylamines via solvent-free A3 coupling reaction(Wiley, 2024-08) Sah, Ajay KumarDevelopment of catalytic systems using nontoxic natural precursors is the need of the era, and along this line, we have synthesized a new D-glucose derived ligand (4,6-O-ethylidene-N-(2-hydroxy-4-(octyloxy)benzylidene)-β-D-glucopyranosylamine) and its dinuclear copper(II) complex. The molecular structure of the complex has been established by single-crystal X-ray diffraction studies and detailed noncovalent intermolecular interactions present in it have been explored by Hirshfeld surface analysis. Further, the complex has been used as a catalyst in the enantioselective (87–99 % ee) synthesis of propargylamines in good to excellent yield (82–95 %) via aldehyde-amines-alkynes (A3) coupling reaction under solvent-free condition. The formation of aminal intermediate during the reaction has been confirmed by 1H-NMR and single-crystal X-ray diffraction studies. The catalytic system is reusable without any appreciable loss in the enantioselectivity or product yield.Item Formation of all tin oxide p–n junctions (SNO–SNO2) during thermal oxidation of thin sn films(Wiley, 2024-12) Hazra, Arnab; Gangopadhyay, SubhashisMetastable stannous oxide (SnO) phase of p-type semiconductor and all tin oxides p–n junctions of SnO–SnO2 nanostructures are formed by controlled thermal oxidation of thin tin films. High purity Sn is deposited on quartz substrates using a vacuum-assisted thermal evaporation technique. Afterwards, controlled thermal oxidation at different temperatures is performed in air ambient condition (150–800 °C). Various surface characterization techniques have been employed to analyze the structure, morphology, chemistry, optical, and electronic properties of these SnOx films. P-type SnO phase is found to be thermodynamically stable at lower oxidation temperatures (250–400 °C), while n-type SnO2 phase starts to appear above 500 °C. Highly uniform and dense SnO nanospheres along with few 1D nanorods are observed after oxidation at 400 °C. Mixed oxide phases of p–n junctions with a sudden decrease in electrical conductivity is observed for 500 °C film. Significantly lower surface conductivity of mixed oxide phase indicates the formation of depletion layers between p-type SnO and n-type SnO2 nanograins. A transition from SnO layer to SnO2 layer is also observed above 600 °C. Overall, SnOx-based nanostructures would be a potential candidate for solar cells, p-channel thin film transistors, p–n junction diodes and gas sensors.Item Novel mixed matrix membranes with indium-based 2D and 3D MOFs as fillers and polysulfone for CO2/CH4 mixed gas separation(RSC, 2025-01) Kuncharam, Bhanu Vardhan ReddyTo address the limitations of polymeric membranes, mixed matrix membranes for CO2 separation from biogas mixtures (CO2 and CH4) have been investigated utilizing various fillers. In this study, we investigated novel MMMs using 3D and 2D indium-based MOFs, MIL-68(In)–NH2 and In(aip)2, in a polysulfone polymer matrix. To confirm synthesis, both fillers were subjected to XRD and FTIR analysis, as well as FESEM characterization to assess their 2D and 3D structures. BET analysis revealed the pore size of MOFs. MMMs were characterized using XRD, FTIR, FESEM, and DSC to determine various membrane characteristics. MMMs were tested with CO2 : CH4 of 60 : 40 vol% to mimic the biogas mixture, and the CO2 permeability of 144 Barrer and 79.2 Barrer was obtained for 20 wt% In(aip)2/PSF membrane and 15 wt% MIL-68(In)–NH2/PSF membrane. The highest CO2/CH4 selectivities of 19.8 and 24.4 were obtained for 15 wt% MIL-68(In)–NH2/PSF MMM and 10 wt% In(aip)2/PSF MMM, respectively. The gas permeation findings of this study were compared with existing literature and long-term stability analysis was done to assess the performance of membranes for commercial standards.Item Electron beam deposited thin titanium films and its thermal oxidation to form rutile TiO2 thin films(AIP, 2024) Gangopadhyay, SubhashisSmooth and homogeneous titanium (Ti) thin films are formed on quartz substrate using a vacuum assisted electron beam evaporation technique. Afterwards, controlled thermal oxidation of these Ti films are performed to grow a uniform titanium dioxide (TiO2) layer. Structural, morphological, chemical and optical properties of these metal and oxide layers have been investigated using various surface characterization techniques such as x-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy and UV-Vis spectroscopy. Formation of rutile TiO2 phase is confirmed from the XRD and Raman spectroscopy, after thermal oxidation above 400°C. SEM imaging suggests the formation of a smooth and homogeneous Ti as well as TiO2 layers which appear with a nanometer scale granular surface morphology. All findings are explained in terms of surface thermodynamics and chemical reactivity.Item Growth and Characterization of ZnO Nanostructures: Materials for CO and Ethanol Sensing(Springer, 2021) Hazra, Arnab; Choudhary, Sumita; Gangopadhyay, SubhashisControlled growth of ZnO-based nanostructures, starting from a vertical nanowall surface morphology to laterally grown highly anisotropic nanorods/wires formation has successfully been achieved by controlled thermal oxidation of thin Zn films for a temperature range of 100–700 °C. The as-grown ZnO nanorods were further used for carbon monoxide gas sensing at low temperatures (down to 150 °C) as well as ethanol vapour sensing at room temperatures. Thin films of Zn were deposited on glass and silicon substrate at room temperature, using a vacuum-assisted thermal evaporation technique. Structure, morphology and chemical property of ZnO layers were investigated using various surface characterization techniques such as X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS) and Raman spectroscopy. The XRD and SEM results are in very good correlation and showed vertical growth morphology of ZnO nanowall/sheet structures at a relatively lower oxidation temperature up to 400 °C. However, at higher oxidation temperature, lateral growths started to dominate over the vertical growth. Oxidation at 700 °C appeared with laterally grown one-dimensional (1D) ZnO nanowires/rods of high density. Raman spectroscopy and XPS results suggested that the vertical growth is mainly initiated by the metallic Zn film morphology, whereas the lateral growth is strongly dominated by the oxide (ZnO) formation. Finally, laterally grown ZnO nanorods could successfully sense CO gas and ethanol vapour. A drastic enhancement in CO gas sensitivity for a concentration of 230 ppm was clearly observed in dynamic gas flow mode even for a wide range of operating temperature.Item Highly selective formaldehyde sensing using ZnO nano-rods(AIP, 2023-03) Choudhary, Sumita; Hazra, Arnab; Gangopadhyay, SubhashisEarly detection of formaldehyde emission from any household materials is technologically very demanding as it can be a serious human health hazard. Even indirect inhaling of formaldehyde may cause significant harm to our eyes, skin, mouth or any other organs. Hence, fabrication of a simple and sensitive formaldehyde sensor would be of high practical importance. Within this work, formation of ZnO nano-rods by controlled thermal oxidation of vacuum deposited thin Zn films in air ambient, followed by fabrication of formaldehyde sensor operating at relatively lower operating temperature are reported. The crystal structure, surface morphology and optical properties of the as grown ZnO nano-rods have been investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and Raman spectroscopy, respectively. The XRD patterns of ZnO suggested the formation of highly crystalline oxide films whereas FESEM images have revealed its nano-rods surface morphology with significantly high (length to diameter) aspect ratio. Raman spectroscopy confirms the thermal oxidation of the Zn thin films. As-grown ZnO nano-rods were then subsequently used to fabricate the chemi-resistive formaldehyde sensors. These sensors showed an extremely high formaldehyde sensing performance at a relatively lower operating temperature of 200°C. In a static measurement mode, the sensor exhibited a gas response of about 53% toward 100 ppm of formaldehyde, with a reasonable fast response and recovery time. Moreover, these ZnO nano-rod based sensors have also been tested with similar type of VOCs such as benzene, xylene, alcohols and acetone and appeared with an excellent selectivity towards formaldehyde over the other VOCs.Item Development of Ni–Sn/Al2O3 Nano Catalysts for H2 Production from Biomass by Aqueous Phase Reforming(Igenta, 2014-07) Roy, BanasriPreparation and characterization of nano Ni–Sn/Al2O3 catalysts prepared by Co-precipitation technique has been reported in this paper. Two set of samples have been designed; in first one the metal/support catalyst is directly precipitated from solution mixture of precursors as one pot synthesis, while for the second one, Al2O3 support is prepared by precipitation method and then metal is loaded by standard wet impregnation. Aluminum nitrate, nickel nitrate, tin chloride, and ammonia solution are used as the starting materials. Investigations regarding the structure - property relations are being carried out through TGA, FTIR, and XRD which will be discussed in detail.Item Synthesis of Mixed-Phase TiO2 Powders in Salt Matrix and Their Photocatalytic Activity(Taylor & Francis, 2016-05) Roy, BanasriThree mixed-phase TiO2 powders, containing ∼80 volume % anatase and ∼20 volume % rutile, were prepared from amorphous titanium hydroxide and three different salt matrices—pure sodium chloride, pure Na2CO3, and pure disodium hydrogen phosphate (DSP). Amorphous titanium hydroxide and salt mixtures were heat treated at 875°C in a rapid thermal annealing system for different times, according to the time–temperature phase transformation graphs. Time-dependent UV degradation of aqueous solutions of methylene blue dye (15 ppm) in the presence of mixed-phase powders was used to monitor the activity of the catalysts. Microstructural study of the powders by scanning electron microscope and transmission electron microscope combined with phase analysis by XRD and optical absorbance by UV-absorption spectroscopy indicated that the higher photocatalytic activity of the powder obtained from pure DSP salt could be explained by its smaller rutile particle size and anatase–rutile interparticle bonding.