Pressureless joining of SiC ceramics with magnesia-alumina-silica glass ceramics

Liquid phase sintered SiC ceramics were joined using magnesia-alumina-silica (MAS) glass-ceramic fillers without applied pressure. Four different filler compositions with 9.3–25.2 wt.% MgO, 20.7–33.6 wt.% Al₂O₃, and 49.2–68.1 wt.% SiO₂ were studied. The effects of filler composition and joining temperature (1450–1600°C) on the joint strength were investigated. All compositions exhibited an optimum joining temperature at which the maximum joint strength was obtained. A low joining temperature resulted in poor wetting of the SiC substrate due to the high viscosity of the filler. Whereas a high joining temperature caused dewetting and large unfilled sections in the interlayer due to the deleterious interfacial reactions. The joint strength was inversely proportional to the interlayer thickness, which was a function of filler composition and joining temperature. The SiC ceramic joined at 1525°C with MgO-25 wt.% Al₂O₃-60 wt.% SiO₂ filler exhibited a four-point bending strength of 286 ± 40 MPa.     

XAS and XPS analysis of double magnetic transition,canonical spin glass behavior and magnetoresistance in LaMn1-xCoxO3 (0.1 ≤ x ≤ 0.5) system

Polycrystalline LaMn_1-xCo_xO₃ (0.1≤ x ≤ 0.5) samples were synthesized using conventional ceramic method. Rietveld refined X-ray diffraction pattern revealed the single-phase orthorhombic crystal structure of all the samples with the space group Pbnm. Temperature-dependent magnetic measurements performed in field cooled (FC) and zero field cooled (ZFC) mode at 10² Oe exhibit the onset of double transition in x = 0.3–0.5 compositions. The ordering temperature rises with an increase in Co concentration. FC and ZFC studies show the presence of glassy state below the ordering temperature in all samples; confirmed using a. c. susceptibility measurements. The a. c. susceptibility data are analyzed using power law and the existence of canonical spin glass is revealed. Magnetic hysteresis studies demonstrate the enhanced ferromagnetism amid the presence of unsaturated magnetization with an increase in Co doping. The presence of double transition and spin glass state is attributed to the competing ferromagnetic and anti-ferromagnetic interactions between the Co and Mn ions present in the system. The system also depicts the presence of appreciable value of magnetoresistance ~42% at 8 T magnetic field in x = 0.5 sample. These properties are interpreted through valence and spin states of Mn and Co ions, being confirmed from electronic structure studies using X-ray absorption spectroscopy (XAS) at L_3,2- edges of respective ions along with O K-edge for all samples (0.1≤ x ≤ 0.5). After meticulous analysis and conjoining the results obtained from magnetization and XAS studies, it is found that cobalt is present in high spin Co²⁺ and high/low spin Co³⁺-state. Charge transfer multiplet calculation done at L_3,2 edges of Mn and Co ions confirm the presence of Mn³⁺/Mn⁴⁺ and Co²⁺/Co³⁺ states consistent with XAS results. X-ray photoelectron spectroscopy performed at Mn2p, Co2p, and O1s -edges further substantiate the reasons behind the properties exhibited by the present system.     

Green synthesis and characterisation of silver nanoparticles and their effects on antimicrobial efficacy and biochemical profiling in Citrus reticulata

The synthesis of nanoparticles by utilising plant extract has revolutionised the field of nanotechnology. In the present study, AgNPs were synthesised by utilising the leaves of Moringa oleifera as reducing and stabilising agent. UV‐visible spectroscopy showed characteristic surface plasmon band in the range of 413–420 nm. Scanning electron microscopy (SEM) elucidated rectangular segments fused together. X‐ray diffraction (XRD) analysis confirmed the crystalline nature of AgNPs and presence of metallic silver ions was confirmed by energy dispersive X‐ray (EDX). The different concentrations (10, 20, 30 and 40 ppm) of AgNPs were exogenously applied on Citrus reticulata to record the disease incidence at different day intervals. The disease intensity was progressively increased in all the applied treatments with the passage of time. The 30 ppm concentration of AgNPs was found to be most suitable concentration for creating the resistance against brown spot disease. Moreover, the effects of AgNPs were also assessed for biochemical profiling in C. reticulata. The enhanced production of endogenous enzymes and non‐enzymatic components was observed in response to 30 ppm concentration of AgNPs. The present work highlighted that green synthesised AgNPs can be as used as biological control of citrus diseases and the enhanced production of secondary metabolites antioxidants.Inspec keywords: nanoparticles, silver, nanofabrication, nanomedicine, biomedical materials, biochemistry, enzymes, molecular biophysics, plant diseases, ultraviolet spectra, visible spectra, scanning electron microscopy, surface plasmon resonance, X‐ray diffraction, X‐ray chemical analysisOther keywords: green synthesis, silver nanoparticles, antimicrobial efficacy, biochemical profiling, Citrus reticulata, plant extract, nanotechnology, medical sciences, environment friendly AgNPs, biomedical fields, leaves, Moringa oleifera, reducing agent, stabilising agent, ultraviolet‐visible spectroscopy, characteristic surface plasmon band, scanning electron microscopy, rectangular shape, X‐ray diffraction analysis, crystalline nature, energy dispersive X‐ray spectroscopy, disease incidence, disease intensity, applied treatments, Alternaria brown spot disease, total phenolic content, dry weight, total flavonoid content, T4 treatment, superoxide dismutase activity, fresh weight, maximum peroxidase production, DPPH radical scavenging assay, biological control, citrus disease, secondary metabolites antioxidants     

Hierarchically structured, hyaluronic acid-based hydrogel matrices via the covalent integration of microgels into macroscopic networks

We aimed to develop biomimetic hydrogel matrices that not only exhibit structural hierarchy and mechanical integrity, but also present biological cues in a controlled fashion. To this end, photocrosslinkable, hyaluronic acid (HA)-based hydrogel particles (HGPs) were synthesized via an inverse emulsion crosslinking process followed by chemical modification with glycidyl methacrylate (GMA). HA modified with GMA (HA-GMA) was employed as the soluble macromer. Macroscopic hydrogels containing covalently integrated hydrogel particles (HA-c-HGP) were prepared by radical polymerization of HA-GMA in the presence of crosslinkable HGPs. The covalent linkages between the hydrogel particles and the secondary HA matrix resulted in the formation of a diffuse, fibrilar interface around the particles. Compared to the traditional bulk gels synthesized by photocrosslinking of HA-GMA, these hydrogels exhibited a reduced sol fraction and a lower equilibrium swelling ratio. When tested under uniaxial compression, the HA-c-HGP gels were more pliable than the HA-p-HGP gels and fractured at higher strain than the HA-GMA gels. Primary bovine chondrocytes were photoencapsulated in the HA matrices with minimal cell damage. The 3D microenvironment created by HA-GMA and HA HGPs not only maintained the chondrocyte phenotype but also fostered the production of cartilage specific extracellular matrix. To further improve the biological activities of the HA-c-HGP gels, bone morphogenetic protein 2 (BMP-2) was loaded into the immobilized HGPs. BMP-2 was released from the HA-c-HGP gels in a controlled manner with reduced initial burst over prolonged periods of time. The HA-c-HGP gels are promising candidates for use as bioactive matrices for cartilage tissue engineering.     

Neural network approach for estimating the residual tensile strength after drilling in uni-directional glass fiber reinforced plastic laminates

The drilling of fiber reinforced plastics (FRP) often results in damage around the drilled hole. The drilling induced damage often serves to impair the long-term performance of the composite products with drilled holes. The present research investigation focuses on developing a predictive model for the residual tensile strength of uni-directional glass fiber reinforced plastic (UD-GFRP) laminates with drilled hole which has not been developed worldwide till now. Artificial neural network (ANN) predictive approach has been used. The drill point geometry, the feed rate and the spindle speed have been used as the input variables and the residual tensile strength as the output. The results of the predictive model are in close agreement with the training and the testing data.     

Preparation and characterization of electrospun poly(2,5-dicyclohexylphenylene-1,4-ethynylene) (C<Subscript>24</Subscript>H<Subscript>30</Subscript>)<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>/poly(ethylene oxide) (PEO) hybrid nanofibers

We report the preparation of poly(2,5-dicyclohexylphenylene-1,4-ethynylene) (PDE)/poly(ethylene oxide) (PEO) hybrid nanofibers by electrospinning technique. The hybrid nanofibers were characterized by a host of characterization techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, atomic force microscopy, optical and scanning electron microscopy. The results showed a successful preparation of PDE/PEO composite nanofibers. The diameter of the hybrid nanofibers ranges between 500 and 1000 nm. The results showed that this kind of hybrid nanofibers could be a possible candidate in color display devices.     

Modular fixture planning for minimum three-dimensional tolerances using a neutral part data exchange format

Machining accuracy and tolerances achieved using modular fixtures are inferior to those achieved using dedicated fixtures. This is mainly because they are built by assembling individual components, which results in positional and dimensional inaccuracies due to their manufacturing tolerances being added up. It is therefore important to plan the fixture configuration such that the effect of fixture elements tolerances is least at the critical machining regions. In this work, an attempt is made to minimize the deviation at the machining zone due to the variation in size and thereby selecting the position of locating and supporting elements. The definition of a solid is considered in the most accurate form by taking NURBS-based IGES/STEP part model as input. All feasible (unique and accessible) triplets of locating positions at different locating heights are determined. It is demonstrated that the modular fixture plans can be significantly improved by changing the locating plane height. The fixturing plans are graded using three-dimensional tolerance analysis for a given machining set-up with respect to the deviation at the critical machining features. The most appropriate locating scheme for which the tolerance errors at selected machining zones is minimum is chosen.     

Amorphous carbon films in direct current magnetron sputtering from regenerative sooting discharge

We present results of carbon coatings on metal substrates in cylindrical hollow cathode (CHC) direct current magnetron sputtering. This is a new technique for making amorphous carbon films by CHC magnetron sputtering from a regenerative sooting discharge. The carbon films are deposited on Cu and Al substrates in a Ne atmosphere and compared with the films of carbon soot on the same materials produced from a conventional 80A arc discharge between graphite electrodes in a He background gas. Raman spectroscopy reveals the existence of graphite and diamond-like structures from the arc discharge while in CHC magnetron sputtering, graphite-like structures are dominant. X-ray diffraction data of samples from the arc discharge show nano-size precipitates of Al₄C₃ of rhombohedral and hexagonal form for the aluminium sample and probable formation of diamond and hexagonal carbon in copper whilst in magnetron sputtering we obtain amorphous carbon films. Scanning electron microscope images of the surface show a collection of loose agglomerates of carbon particles in the arc discharge whereas, for magnetron sputtering, structures are regular with smooth edges and fine grains.     

Single step synthesis of Ce doped CaAl2O4 and CaAl4O7 systems

Both CaAl₂O₄ (CA2) and CaAl₄O₇ (CA4) oxide-systems possess monoclinic crystal structure. Herein, we have prepared CA2 and CA4 systems via single step combustion route. A good correlation is observed between calculated and the standard lattice parameters. Ce³⁺ ions were deliberately doped as extrinsic impurities in order to understand the crystal symmetry effects on the emission characteristics in the as-prepared matrices. Large red-shift was observed in CA4-emission spectrum despite of their same crystal structures. Possible reasons are discussed.     

Behaviour of RC beams strengthened by partial jacketing under cyclic loading

This work presents a study on the behaviour under cyclic loading of reinforced concrete beams strengthened in bending by the addition of concrete and steel on their tension side using expansion bolts as shear connectors, denominated here as partial jacketing. The experimental program included tests on six full scale reinforced concrete beams, simply supported, with rectangular cross section 150 mm wide and 400 mm high, span of 4,000 mm and total length of 4,500 mm. All the beams, after receiving two cycles of static loading in order to create a pre-cracking condition, were strengthened in bending by partial jacketing and then subjected to cyclic loading until the completion of 2 × 10⁶ cycles or the occurrence of fatigue failure. Following the cyclic loading, the beams that did not fail by fatigue were subjected to a static load up to failure. The main variables were the flexural reinforcement ratio in the beam and in the jacket, the beam–jacket interface condition (smooth or rough) and cyclic load amplitude. On the basis of the obtained test results and the results of previous study of similar beams tested only under static loading, the behaviour of the strengthened beams is discussed and a proposal for their design is given.