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Systematic study on the effect of Ag doping in shaping the magnetic properties of sol-gel derived TiO2 nanoparticles.
No full textEffect of Silver (Ag) doping in shaping magnetic properties of sol-gel derived TiO2 nanoparticles (NPs) is studied using different characterisation techniques. An interconnection between the results of characterizations and the magnetic behavior of the Ag doped samples has been established. XRD patterns show an anatase to rutile phase transition in NPs at 14 at. % Ag doping. XRD peaks related to metallic Ag are found in the TiO2 NPs containing 10 and 14 at. % Ag whereas secondary phase of Ag2O is noticed in all the samples. FESEM images exhibit the presence of segregated silver clusters attached to the TiO2 nanostructures for 10 and 14 at. % Ag doping. XPS detects the presence of several cationic states in doped TiO2 NPs. UV–Vis measurements reveal that the quantum size effect enhances the band gap at initial level of doping and afterwards it continiously decreases due to sp-d exchange interactions. M − H study shows the emergence of soft ferromagnetism (FM) in the sample doped with a critical Ag+ ion concentration of 5 at. % due to d-orbital mediated spin information transfer between two hole trapped Ag+ ion and a Ti3+ defect leading to the formation of BMP. Temperature dependent FC and ZFC magnetization measurements indicate coexistence of ferromagnetic and antiferromagnetic domains. The investigations culminate in identification of not only the optimum processing conditions for enhanced FM properties along with good physical characteristics but also the probable cause behind the origin of FM in Ag doped TiO2 NPs. Such Ag doped TiO2 NPs can be useful for development of futuristic spintronic and magneto-optical devices
Consistent derivation of non-constant material function for one-dimensional shape memory alloy phenomenological model.
No full textConstitutive modelling of shape memory alloys with new material functions is presented within the frame work of thermodynamic consistency. A one- dimensional constitutive model based on the previous work of constant and non-constant material functions is redefined from first principles. In the first step Clausius-Duhem inequality condition for stress is rewritten and an alternate form of differential equation is proposed. The initial and final condition of evolution are applied to obtain a new form of non-constant transformation tensor, which is independent of residual strain the SMA material. As a result in the present work the residual strain is purely defined as a function of transformation stress and not as a function of transformation modulus. The proposed form of new transformation tensor is compared with previously proposed material function and validation results for the consistency are presented. It is observed that newly derived non-constant material function is compatible in both differential and integrated form of the one-dimensional shape memory alloy constitutive relation and satisfies the evolution conditions of phase transformations
Investigating the wetting phenomena and fabrication of sticky, para-hydrophobic cerium oxide coating
No full textWe report fabrication of a novel sticky parahydrophobic cerium oxide (CeO2) coating using a facile and industrially viable plasma spray technique, which has prospective applications in microfluidic chips, no loss microdroplet transportation and chemical microreactors. Our coating displays significantly high water contact angle (∼159.02˚) along with high contact angle hysteresis (CAH≥90˚), very much similar to a ‘Rose petal’. This is further strengthened by the fact that the coating displayed remarkable adhesion even with large inverted water droplets of 70 μL, which is significantly higher than the reported values of 18 μL for polymer and 20 μL for drop casted CeO2 nanotubes. We also present systematic characterization results to clarify the ongoing confusion regarding the hydrophobicity of CeO2 coatings often reported in literature. Meanwhile, our parahydrophobic coating also showed remarkable thermal and mechanical stability even at a significantly high temperature of 200 °C for 14 h and with 50 g abrasive paper
Effect of the addition of diurethane dimethacrylate on the chemical and mechanical properties of tBA-PEGDMA acrylate based shape memory polymer network
No full textThere is a great demand for the synthesis of acrylate based thermoset shape memory polymer (SMP) associated with one monomer and one crosslinker such as tert-butyl acrylate (t-BA) with poly (ethylene glycol) dimethacrylate (PEGDMA). The present work describes the synthesis of a new thermoset SMP wherein a second monomer such as diurethane dimethacrylate (DUDMA) has been added to the existing tBA + PEGDMA SMP matrix. The synthesized thermoset shape memory polymer exhibited a glass transition temperature (Tg) of 55 °C, higher Young's Modulus of 3.23 GPa, transmittance of 95% and 100% shape recovery. The SMP exhibited response to both thermal and chemical stimuli. The shape recovery rate of the SMP network is 20 s compared to 24 s observed for SMP based on tBA + PEGDMA. The obtained SMP is very transparent and possesses higher stiffness (8 MPa) and hence may be suitable for biomedical shape memory lens and orthopedic application
Flow visualization and supersonic combustion studies of an acoustically open strut cavity
No full textIn this study, the supersonic flow over strut cavities was experimentally studied to understand flow features. Instantaneous schlieren imaging in non-reacting flow experiments exhibited the seven types of waves associated with cavity pressure oscillations and the formation of unstable shear layers on both sides. The shear layers moved in and out in synchronous and asynchronous modes at the trailing edge of the strut cavities. The symmetrical wave structure appeared on both sides in the synchronous mode, whereas the shear layers appeared in different stages of the cavity pressure oscillation cycle in the asynchronous mode, resulting in an asymmetrical wave structure. The pressure waves generated at the trailing edge of the strut cavities perturbed the shear layers during their movement toward the leading edge, creating a wavy shear layer with alternate troughs and crests. The pressure oscillations of the strut cavities had high-amplitude cavity modes with broadband noises, and their amplitude decreased from the trailing edge to the leading edge. The estimated recovery factor using the time lag between the signals of the leading and trailing edges showed that the flow inside the strut cavities was low subsonic. The measured dominant pressure oscillation modes had a closer match with the Rossiter modes. The pressure coefficient demonstrated that fluid accumulation inside the cavity increased with an increase in the aspect ratio. Furthermore, a higher fluid mass accumulated at the trailing edge than at the leading edge, and the difference in fluid accumulation increased with an increase in the aspect ratio. Supersonic combustion experiments with strut cavities showed that the strut cavity stabilized the flame. Moreover, the addition of an acoustically open strut cavity ahead of the flame-stabilizing cavity advanced the heat release location upstream
Stochastic Modeling and Reliability Analysis of Wing Flutter
No full textIn this work, a physics-based first-order reliability method (FORM) algorithm is proposed for the flutter reliability analysis of an aircraft wing in the frequency domain. The limit state function, which is an implicit function of random variables, is defined in terms of the damping ratio of the aeroelastic system in a conditional sense on flow velocity. Two aeroelastic cases, namely, an airfoil section model and a cantilever wing model, are considered for carrying out the studies. These aeroelastic models have well separated mean bending and mean torsional modal frequencies. The geometric, structural, and aerodynamic parameters of airfoil and wing systems are modeled as independent Gaussian random variables. The effects of these on the statistics of frequency and damping ratio, and the cumulative distribution functions (CDFs) of flutter velocity are studied. In the case of the wing, the effects of modeling stiffness parameters as Gaussian random fields on the CDFs of flutter velocity are also studied. Here, spectral stochastic finite element method (SFEM) based on Karhunen–Loeve (K–L) expansion is used to discretize the random fields into random variables. From the study of an airfoil system, it is observed that parameters like torsional stiffness, elastic axis location, free stream density, and mass moment of inertia are more sensitive as compared with other parameters. However, in the case of the wing parameters such as torsional stiffness, free stream density, mass moment of inertia, and mass are observed to be more sensitive. The CDFs of flutter velocity obtained using the proposed algorithm are compared with Monte Carlo simulations (MCS) and found to be accurate. A comparative study of aeroelastic reliability for the wing is also carried out by treating stiffness parameters as random variables and random fields. It is observed that the CDFs of flutter velocity in the tail region are conservative when stiffness parameters are treated as random variables
Engineering the Microstructure of Silicon Nanowires by Controlling the Shape of the Metal Catalyst and Composition of the Etchant in a Two-Step MACE Process: An In-Depth Analysis of the Growth Mechanism
No full textIn this work, slanted, kinked, and straight silicon nanowires (SiNWs) are fabricated on Si(111) and (100) substrates using a facile two-step metal-assisted chemical etching nanofabrication technique. We systematically investigated the effect of crystallography, morphology of Ag catalyst, and composition of etchant on the etch profile of Ag catalyst on Si(111) and (100) substrates. We found that the movement of AgNPs inside the Si is determined by physiochemical events such as Ag/Ag interaction, Ag/Si contact, and diffusion kinetics. Further, from detailed TEM and micro-Raman spectroscopy analyses, we demonstrate that the metal catalyst moves in the crystallographically preferred etching direction (viz., ) only when the interface effect is not predominant. Further, the metal-assisted chemical etching (MACE) system is highly stable at low-concentration plating and etching solutions, but at high concentrations, the system loses its stability and becomes highly random, leading to the movement of Ag catalyst in directions other than ⟨100⟩. In addition, our studies reveal that Ag nanostructures growth on Si(111) and (100) substrates through galvanic displacement is controlled by substrate symmetry and surface bond density. Finally, we demonstrate that by using an optimized balance between the Ag morphology and concentration of the etchant, the angle in slanted SiNWs, kink position in kinked SiNWs, and aspect ratio of straight SiNWs can be controlled judiciously, leading to enhanced optical absorption in the broadband solar spectrum
Processing of Cf/SiC composites by hot pressing using polymer binders followed by polymer impregnation and pyrolysis.
No full textContinuous carbon fiber (Cf) reinforced silicon carbide (SiC) matrix composite (Cf/SiC) was processed through hot pressing (HP) using polycarbosilane (PCS) in matrix and polysilazane in interphase regions as polymer binders. HP experiments were conducted at 4 MPa, 1200 °C and 1 h; followed by PCS polymer impregnation and pyrolysis (PIP) at 1200 °C under vacuum. The BN/SiC-Si3N4 interphase formed on the Cf cloth during BN dispersed polysilazane polymer coating and pyrolysis. The influence of PCS quantity during HP experiments on Cf/SiC composites was studied. Results suggest that sintering of SiC matrix in Cf/SiC composite improves by increasing PCS content during HP; however, high PCS content increases the liquidity of SiC-PCS mixture to flow out of the composite structure. The Cf/SiC composites with relative density ranging from 79 to 83% and flexural strength from 67 to 138 MPa was achieved
Low-Temperature Propylene Epoxidation Activity of CuO-CeO2Catalyst with CO + O2: Role of MetalSupport Interaction on the Reducibility and Catalytic Property of CuOxSpecies
No full textEpoxidation of propylene into propylene oxide (PO) in the gas phase is a highly challenging reaction. Cu-based catalysts have been active for this reaction, but the state of Cu as an active species is still debatable. In this paper, we report the propylene epoxidation activity of solution combustion synthesized Cu/CeO2 catalysts with the CO + O2 mixture at low temperatures (50–100 °C) peaking at ∼80 °C. The highest PO yield was obtained with 20–25% Cu loading in CeO2. In contrast, the reaction over the catalyst containing nonreducible support such as Cu/SiO2 occurred above 170 °C. Detailed structural characterization indicated two types of Cu species such as Cu2+ partly (∼3%) dissolved in CeO2 forming a CuxCe1–xO2−δ phase and the remaining amount formed highly dispersed CuO as a separate phase. Thus, the highest activity relates to the optimum presence of CuO along with Ce1–xCuxO2−δ. The reducibility of the Cu species in two phases was significantly shifted toward lower temperatures, indicating strong electronic interaction between the two phases. The substituted Cu2+ was reduced first, and then, the bulk CuO reduction was initiated. In situ spectroscopic studies showed Cu+ formation from Cu2+ over Cu/CeO2 catalysts even at room temperature unlike in CeO2 or CuO + CeO2 physical mixtures, indicating strong electronic interaction between Ce1–xCuxO2−δ and CuO phases on CO adsorption in the Cu/CeO2 catalyst. It is proposed that substituted Cu2+ along with Ce4+ is reduced easily, and then, Ce3+ promotes the reduction of the interfacial CuO phase that might donate active oxygen species for epoxidation reaction
Derivation of compatibility conditions and nonconstant material function for one-dimensional constitutive relations of shape memory alloys
No full textThe present work investigates the thermodynamic inconsistencies in the definition of the compatibility conditions on stress for constant and nonconstant material functions in one-dimensional modeling of shape memory alloys based on the first principles. In this work, simplifications are provided validating inconsistencies in the earlier proposed non-constant material functions used to satisfy compatibility conditions. It is presented that the inconsistencies originate due to an incorrect definition of the compatibility conditions on stress. In the first step, it is shown that, due to inconsistent definitions of the compatibility conditions, the material functions cannot be derived from the first principles. Consequently, it is presented that the material functions result in an incorrect form of the differential constitutive equation. Furthermore, it is also analyzed that these incorrect definitions on the compatibility conditions result in an inconsistent form of nonconstant material functions as well as the differential equation, which are proposed in earlier models. As a result, in the present work the consistent definition of the compatibility conditions for one-dimensional shape memory alloy models is derived. Next, the new and correct definition for the compatibility conditions is proposed, which is used to derive a new and consistent form of nonconstant material function. Finally, a consistent form of non-constant material function and differential equation are derived from first principles, which satisfy the new definition of compatibility conditions on stress