ResearchPad - 117 https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Microstructure-sensitive critical plastic strain energy density criterion for fatigue life prediction across various loading regimes]]> https://www.researchpad.co/article/Nec259dea-eba2-4023-a087-8d1097f40458 In the present work, we postulate that a critical value of the stored plastic strain energy density (SPSED) is associated with fatigue failure in metals and is independent of the applied load. Unlike the classical approach of estimating the (homogenized) SPSED as the cumulative area enclosed within the macroscopic stress–strain hysteresis loops, we use crystal plasticity finite element simulations to compute the (local) SPSED at each material point within polycrystalline aggregates of a nickel-based superalloy. A Bayesian inference method is used to calibrate the critical SPSED, which is subsequently used to predict fatigue lives at nine different strain ranges, including strain ratios of 0.05 and −1, using nine statistically equivalent microstructures. For each strain range, the predicted lives from all simulated microstructures follow a lognormal distribution. Moreover, for a given strain ratio, the predicted scatter is seen to be increasing with decreasing strain amplitude; this is indicative of the scatter observed in the fatigue experiments. Finally, the lognormal mean lives at each strain range are in good agreement with the experimental evidence. Since the critical SPSED captures the experimental data with reasonable accuracy across various loading regimes, it is hypothesized to be a material property and sufficient to predict the fatigue life.

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<![CDATA[Quasi-Herglotz functions and convex optimization]]> https://www.researchpad.co/article/Nf93cfa79-431d-45b1-bce6-01ec489aef85

We introduce the set of quasi-Herglotz functions and demonstrate that it has properties useful in the modelling of non-passive systems. The linear space of quasi-Herglotz functions constitutes a natural extension of the convex cone of Herglotz functions. It consists of differences of Herglotz functions and we show that several of the important properties and modelling perspectives are inherited by the new set of quasi-Herglotz functions. In particular, this applies to their integral representations, the associated integral identities or sum rules (with adequate additional assumptions), their boundary values on the real axis and the associated approximation theory. Numerical examples are included to demonstrate the modelling of a non-passive gain medium formulated as a convex optimization problem, where the generating measure is modelled by using a finite expansion of B-splines and point masses.

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<![CDATA[Enhanced visible-light photocatalytic activity of anatase-rutile mixed-phase nano-size powder given by high-temperature heat treatment]]> https://www.researchpad.co/article/N1f8ef2f2-e69e-49ee-905c-dcf79febf823

Nano-size EVONIK AEROXIDE® P25 titanium dioxide, TiO2, powder was heat-treated at temperatures, 700–900°C, in air. An X-ray diffraction study showed that the P25 powder is composed of approximately 20 and approximately 80 mass% of rutile and anatase phases, respectively. It was also shown that the transformation from anatase to rutile induced by high-temperature heat treatment was almost completed at 750°C, whereas a small amount (less than 3 mass%) of anatase phase was still left even in the powder heat-treated at 900°C. The transformation behaviour was consistent with results obtained by Raman scattering spectroscopy. Raman experiments also indicated that high-temperature heating induced the formation of oxide ion vacancies. Powders were dispersed in methyl orange (MO) aqueous solution, and the bleach rate of MO was measured to evaluate photocatalytic activity under ultraviolet (UV)- and visible-light irradiation. After the heat treatment, the UV-light photocatalytic performance sharply deteriorated. Interestingly, visible-light photocatalytic activity was enhanced by high-temperature heating and reached the highest performance for an 800°C-heated sample, indicating that the P25 powder obtained high visible-light photocatalytic performance after heat treatment. Even after 900°C heat treatment, the photocatalytic performance was higher than that of as-received powder. Enhancement of photocatalytic activities was discussed in relation to visible light absorption and charge carrier transfer.

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<![CDATA[Influence of the slight adjustment of oxides on the structural and physico-chemical properties of thin film transistor-liquid crystal display substrate glass]]> https://www.researchpad.co/article/Nee482e52-3dd6-4b95-8d37-faa83760b65d

By the slight adjustment of oxides constituting thin film transistor-liquid crystal display (TFT-LCD) substrate glass, including equal mole fraction substitution of Al2O3, GeO2, B2O3, P2O5 and ZrO2 for SiO2, as well as the substitution of CaO for SrO with the total contents unchanged, the structural and physico-chemical properties of the glass was investigated by Raman spectroscopy and other measurements. The results showed that the short-range disorder brought by the substitution of GeO2, B2O3 and P2O5 for SiO2 could weaken the stability and compactness of the glass network, and the physico-chemical properties deteriorated, while the process of glass melting would become easier accordingly. The short-range disorder by the substitution of ZrO2 for SiO2 with 1% mole fraction showed a little difference with other samples. Finally, the substitution of modified cations, such as CaO and SrO, showed a smaller variation compared with the substitution of network formers. On the condition of 1% mole fraction substitution of oxides investigated, the variation of samples showed a reasonable change and the performance was basically all satisfied for the use of TFT-LCD substrate.

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<![CDATA[Preparation and characterization of waterborne alkyd-amino baking coatings based on waste polyethylene terephthalate]]> https://www.researchpad.co/article/Nc5593182-acdc-4e08-9fb5-0eb4adba91ae

The recycling of polyethylene terephthalate (PET) is the most attractive method for PET waste management because it not only decreases the load on landfill space, but also provides opportunities for reducing the use of raw petrochemical products. Therefore, in this investigation, neopentyl glycol is used for alcoholysis of waste PET, and glycolyzed PET product was applied for preparation of the waterborne alkyd resin. Furthermore, the waterborne alkyd-amino baking coatings were prepared from the waterborne alkyd based on glycolyzed waste PET and melamine formaldehyde resin and applied on tinplate. The waterborne alkyd-amino resin films showed excellent adhesion, balanced hardness and flexibility, high gloss and outstanding chemical resistance except for alkali resistance owing to hydrolysis of ester bonds.

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<![CDATA[Liquid cell transmission electron microscopy and its applications]]> https://www.researchpad.co/article/Nf4ae0955-65b8-49c2-85ee-a2291b7bdd4f

Transmission electron microscopy (TEM) has long been an essential tool for understanding the structure of materials. Over the past couple of decades, this venerable technique has undergone a number of revolutions, such as the development of aberration correction for atomic level imaging, the realization of cryogenic TEM for imaging biological specimens, and new instrumentation permitting the observation of dynamic systems in situ. Research in the latter has rapidly accelerated in recent years, based on a silicon-chip architecture that permits a versatile array of experiments to be performed under the high vacuum of the TEM. Of particular interest is using these silicon chips to enclose fluids safely inside the TEM, allowing us to observe liquid dynamics at the nanoscale. In situ imaging of liquid phase reactions under TEM can greatly enhance our understanding of fundamental processes in fields from electrochemistry to cell biology. Here, we review how in situ TEM experiments of liquids can be performed, with a particular focus on microchip-encapsulated liquid cell TEM. We will cover the basics of the technique, and its strengths and weaknesses with respect to related in situ TEM methods for characterizing liquid systems. We will show how this technique has provided unique insights into nanomaterial synthesis and manipulation, battery science and biological cells. A discussion on the main challenges of the technique, and potential means to mitigate and overcome them, will also be presented.

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<![CDATA[Comparative study on photocatalytic activity of transition metals (Ag and Ni)-doped ZnO nanomaterials synthesized via sol–gel method]]> https://www.researchpad.co/article/N8515f4a3-7379-4f2f-96c9-816eecb7742e

Ag and Ni/ZnO photocatalyst nanostructures were successfully synthesized by a sol–gel method. In this work, the photocatalyst sample was systematically studied based on several factors affecting the performance of photocatalyst, which are size, morphology, band gap, textural properties and the number of active sites presence on the surface of the nanocatalyst. X-ray diffraction revealed that Ag/ZnO nanomaterials experienced multiple phases, meanwhile for Ni/ZnO the phase of nanomaterials were pure and single phase for stoichiometry less than 5%. Field emission scanning electron microscope (FESEM) showed almost all of the synthesized nanomaterials possessed a mixture of nanorods and spherical-like shape morphology. The Ag/ZnO showed high photocatalytic activity, producing at least 14th trials of nanocatalyst reusability on degradation of methyl orange under UV irradiation. Interestingly, this phenomenon was not observed in larger surface area of Ni/ZnO nanomaterials which supposedly favour photocatalytic activity, but instead producing poor photocatalytic performance. The main reasons were studied and exposed by temperature-programmed desorption of carbon dioxide (TPD–CO2) which showed that incorporation of Ag into ZnO lattice has enhanced the number of active sites on the surface of the nanocatalyst. Whereas incorporation of Ni in ZnO has lowered the number of active sites with respect to undoped ZnO. Active sites measurement is effective and significant, providing opportunities in developing an intensive study as an additional factor.

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<![CDATA[Moulding three-dimensional curved structures by selective heating]]> https://www.researchpad.co/article/N2da92343-9e26-4dba-8b67-a4f60d3c8a08

It is of interest to fabricate curved surfaces in three dimensions from homogeneous material in the form of flat sheets. The aim is not just to obtain a surface which has a desired intrinsic Riemannian metric, but to get the desired embedding in R3 up to translations and rotations. In this paper, we demonstrate three generic methods of moulding a flat sheet of thermo-responsive plastic by selective contraction induced by targeted heating. These methods do not involve any cutting and gluing, which is a property they share with origami. The first method is inspired by tailoring, which is the usual method for making garments out of plain pieces of cloth. Unlike usual tailoring, this method produces the desired embedding in R3. The second method just aims to bring about the desired new Riemannian metric via an appropriate pattern of local contractions, without directly controlling the embedding. The third method is based on triangulation, and seeks to induce the desired local distances. This results in getting the desired embedding in R3. The second and the third methods, and also the first method for the special case of surfaces of revolution, are algorithmic in nature. We explain these methods and show examples.

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<![CDATA[Effect of storage condition on the physico-chemical properties of corn–wheat starch/zein edible bilayer films]]> https://www.researchpad.co/article/N30cb9f16-7c82-4280-aa8f-76217ca1ac39

The functional properties of biopolymer-based film packaging materials are susceptible to external storage conditions. The effects of different storage temperature, relative humidity (RH) and duration on the apparent form, barrier properties, mechanical properties and microstructure of corn–wheat starch/zein bilayer films were studied. From 0 to 150 days, storage temperature and RH, but not storage time, affected the appearance and colour of the bilayer films. The increase in haze of the bilayer films stored at 25°C was much greater than that at low temperatures. With increased storage time, the moisture content first increased and then decreased, while the water resistance and oxygen barrier properties of the bilayer films worsened. After 150 days, the bilayer film stored at 25°C with 54% RH had better water resistance properties. The oxygen barrier properties of the bilayer film stored at 25°C with 43% RH were preferable to those of other groups because the peroxide value of vegetable oil packed in the former bilayer film was the lowest. The tensile strength of bilayer films stored at 25°C with RH of 43, 54 and 65% decreased, but was still better than those stored at low temperatures (−17°C, 4°C), which were tough due to their high elongation at break. Scanning electron microscopy results showed tight bonds between the bilayer films, and the network structure inside the films disappeared and reappeared during storage. The cross-sectional compactness changed, and there was no film separation after 150 days.

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<![CDATA[Utilization of metakaolin-based geopolymer as a mud-cake solidification agent to enhance the bonding strength of oil well cement–formation interface]]> https://www.researchpad.co/article/N089adae7-2535-4254-99f4-a0753c58e3f2

This research work designed a novel mud-cake solidification method to improve the zonal isolation of oil and gas wells. The calculation methodology of mud-cake compressive strength was proposed. The optimal formula of activator and solid precursors, the proper activating time and the best activator concentration were determined by the compressive strength test. The effects of solid precursors on the properties of drilling fluid were evaluated. Test results show that the respective percentage of bentonite, metakaolin, slag and activator is 1 : 1 : 0.3 : 0.8, as well as the optimum ratio of Na2SiO3/NaOH is 40 : 1. The optimum concentration of activator is 0.21 and the activating time should be more than 10 min. The solid precursors did not show any bad influence on the rheological property of drilling fluids. Even though the compressive strength decreased when the solid precursors blended with barite, the strength values can still achieve 8 MPa. The reaction of metakaolin and activator formed cross-link structure in the mud-cake matrix, which enhanced the connection of the loose bentonite particles, lead to the significant enhancement of shear bonding strength and hydraulic bonding strength. This mud-cake solidification method provides a new approach to improve the quality of zonal isolation.

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<![CDATA[Correction to ‘Photocatalytic inactivation of Escherichia coli under UV light irradiation using large surface area anatase TiO2 quantum dots’]]> https://www.researchpad.co/article/Nefa53c87-577c-4416-a62d-684094a76b60 ]]> <![CDATA[Preparation and structure of SiOCN fibres derived from cyclic silazane/poly-acrylic acid hybrid precursor]]> https://www.researchpad.co/article/N56bbadc6-3262-4db5-aded-4276bad8010e

Ceramic matrix composite (CMC) materials have been considered a desired solution for lightweight and high-temperature applications. Simultaneously, among all different CMC reinforcements, polymer-derived ceramic (PDC) fibres have gained attention for the intrinsic thermal stability and mechanical strength with simple and cost-effective synthesis techniques. Here, carbon-rich SiOCN fibres were synthesized via hand-drawing and polymer pyrolysis of a hybrid precursor of 1,3,5,7-tetramethyl-1,3,5,7-tetravinylcyclotetrasilazane (TTCSZ) and poly-acrylic acid (PAA). The type of silazane reported in this work is considered as a major precursor for SiCN; however, it is unspinnable, due to its unfavourable physical properties (low viscosity) and chemical structure (cyclic rather than linear structure). The introduction of PAA to TTCSZ to create a hybrid precursor remarkably improved the spinnability of the silazane and should be widely applicable to other unspinnable PDC pre-ceramic polymers. Investigations on the structural and compositional development of the fibres were mainly conducted via Raman spectroscopy, Fourier-transform infrared spectroscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, nuclear magnetic resonance and thermo-gravimetric analysis to determine spinnability, free carbon content, cross-linking and pyrolysis behaviour of the fibres, respectively.

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<![CDATA[Enhancement of thermoelectric properties of La-doped SrTiO3 bulk by introducing nanoscale porosity]]> https://www.researchpad.co/article/N4a33b185-bc40-4dcf-9f26-8ca4ab92d764

Electron-doped SrTiO3 is a well-known n-type thermoelectric material, although the figure of merit of SrTiO3 is still inferior compared with p-type metal oxide-based thermoelectric materials due to its high lattice thermal conductivity. In this study, we have used a different amount of the non-ionic surfactant F127 during sample preparation to introduce nanoscale porosities into bulk samples of La-doped SrTiO3. It has been observed that the porosities introduced into the bulk sample significantly improve the Seebeck coefficient and reduce the thermal conductivity by the charge carrier and phonon scattering respectively. Therefore, there is an overall enhancement in the power factor (PF) followed by a dimensionless figure of merit (zT) over a wide scale of temperature. The sample 20 at% La-doped SrTiO3 with 600 mg of F127 surfactant (SLTO 600F127) shows the maximum PF of 1.14 mW m−1 K−2 at 647 K which is 35% higher than the sample without porosity (SLTO 0F127), and the same sample (SLTO 600F127) shows the maximum value of zT is 0.32 at 968 K with an average enhancement of 62% in zT in comparison with the sample without porosity (SLTO 0F127).

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<![CDATA[Irradiation-catalysed degradation of methyl orange using BaF 2 –TiO 2 nanocomposite catalysts prepared by a sol–gel method]]> https://www.researchpad.co/article/N12ab3ad5-6cdf-4ed3-bc28-843d877051cd

BaF2–TiO2 nanocomposite material (hereinafter called the composite) was prepared by a sol–gel method. The composite surface area, morphology and structure were characterized by Brunauer–Emmett–Teller method, X-ray diffraction analysis and a scanning electron microscopy. The results showed that BaF2 and TiO2 form a PN-like structure on the surface of the composite. Composites were used to catalyse the degradation of methyl orange by irradiation with ultraviolet light, γ-rays and an electron beam (EB). It was demonstrated that the composite is found to be more efficient than the prepared TiO2 and commercial P25 in the degradation of methyl orange under γ-irradiation. Increasing the composite catalyst concentration within a certain range can effectively improve the decolorization rate of the methyl orange solution. However, when the composite material is used to catalyse the degradation of organic matter in the presence of ultraviolet light or 10 MeV EB irradiation, the catalytic effect is poor or substantially ineffective. In addition, a hybrid mechanism is proposed; BaF2 absorbs γ-rays to generate radioluminescence and further excites TiO2 to generate photo-charges. Due to the heterojunction effect, the resulting photo-charge will produce more active particles. This seems to be a possible mechanism to explain γ-irradiation's catalytic behaviour.

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<![CDATA[Modelling the coefficient of thermal expansion in graphite crystals: implications of lattice strain due to irradiation and pressure]]> https://www.researchpad.co/article/5c2bbc71d5eed0c484741d80

Theoretical models for the coefficient of thermal expansion (CTE) first proposed in the 1970s are expanded upon, allowing them, for the first time, to be implemented over a wide temperature range. The models are of interest because they predict the effects of the changes in the crystal lattice spacing and crystallite modulus on the CTE. Hence, they can in turn be used to investigate the influence of pressure and irradiation on the CTE. To date, typographical and mathematical errors and incomplete or conflicting assumptions between the various papers had made the complex mathematical formulations difficult, if not impossible, to follow and apply. This paper has two main aims: firstly to revisit and review the CTE models, correcting the errors and compiling and updating various input data, secondly to use the revised models to investigate the effect of loading and irradiation on the CTE. In particular, the models have been applied to data for natural and highly orientated pyrolytic graphite and compared with experimental data, giving an insight into the influence of temperature, loading and irradiation on both single crystal and polycrystalline graphite. The findings lend credence to postulated microstructural mechanisms attributed to the in-reactor behaviour of nuclear graphite, which finds a wide use in predictive multiscale modelling.

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<![CDATA[Electrochemical performance of ZnO-coated Li4Ti5O12 composite electrodes for lithium-ion batteries with the voltage ranging from 3 to 0.01 V]]> https://www.researchpad.co/article/5c1522cad5eed0c4840bd63a

Oxide is widely used in modifying cathode and anode materials for lithium-ion batteries. In this work, a facile method of radio magnetron sputtering is introduced to deposit a thin film on Li4Ti5O12 composite electrodes. The pristine and modified Li4Ti5O12 electrodes are characterized at an extended voltage range of 3–0.01 V. The reversible capacity reaches a high level of 286 mAh g−1, which is a little less than its theoretical capacity (293 mAh g−1). Electrodes modified by ZnO thin films with various thickness show elevated rate capability and improved cycle performance.

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<![CDATA[Facile synthesis of hierarchical CNF/SnO2/Ni nanostructures via self-assembly process as anode materials for lithium ion batteries]]> https://www.researchpad.co/article/5c06e1ecd5eed0c484c4f0ab

Hierarchical carbon nanofibre (CNF)/SnO2/Ni nanostructures of graphitized carbon nanofibres and SnO2 nanocrystallines and Ni nanocrystallines have been prepared via divalent tin–alginate assembly on polyacrylonitrile (PAN) fibres, controlled pyrolysis and ball milling. Fabrication is implemented in three steps: (1) formation of a tin–alginate layer on PAN fibres by coating sodium alginate on PAN in a water medium followed by polycondensation in SnCl2 solution; (2) heat treatment at 450°C in a nitrogen atmosphere; (3) ball milling the mixture of CNF/SnO2 fibres and Ni powder. The CNF/SnO2/Ni nanocomposite exhibits good lithium ion storage capacity and cyclability, providing a facile and low-cost approach for the large-scale preparation of anode materials for lithium ion batteries.

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<![CDATA[Synthesis and photocatalytic activity of mesoporous g-C3N4/MoS2 hybrid catalysts]]> https://www.researchpad.co/article/5c02bbdfd5eed0c484454e53

The key to solving environmental and energy issues through photocatalytic technology requires highly efficient, stable and eco-friendly photocatalysts. Graphitic carbon nitride (g-C3N4) is one of the most promising candidates except for its limited photoactivity. In this work, a facile and scalable one-step method is developed to fabricate an efficient heterostructural g-C3N4 photocatalyst in situ coupled with MoS2. The strong coupling effect between the MoS2 nanosheets and g-C3N4 scaffold, numerous mesopores and enlarged specific surface area helped form an effective heterojunction. As such, the photocatalytic activity of the g-C3N4/MoS2 is more than three times higher than that of the pure g-C3N4 in the degradation of RhB under visible light irradiation. Improvement of g-C3N4/MoS2 photocatalytic performance is mainly ascribed to the effective suppression of the recombination of charge carriers.

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<![CDATA[Chromium deposition and poisoning of La2NiO4 cathode of solid oxide fuel cell]]> https://www.researchpad.co/article/5c1522c1d5eed0c4840bd5fc

Chromium deposition and poisoning of La2NiO4 cathode of solid oxide fuel cell were studied. La2NiO4 cathode showed stable performance in the presence of metallic interconnects. Comparing with the polarization resistance (Rp) of La2NiO4 cathode in the absence of metallic interconnects, Rp did not change in the presence of metallic interconnect. After electrical conductivity relaxation method, La2NiO4 with high surface oxygen diffusion coefficients working under Cr atmosphere improved the oxygen reduction kinetics and increased cathode O2 reduction reaction rates. No chromium deposition was observed on the La2NiO4 cathode surface after polarization for 20 h at 800°C. The chemical compatibility of La2NiO4/Cr2O3 and La2NiO4/Gd0.1Ce0.9O1.95 (GDC) study indicates that La2NiO4 did not react with Cr2O3 and GDC under the operating temperature. The results indicate that La2NiO4 cathode is a potential chromium-tolerant material of solid oxide fuel cell.

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<![CDATA[Study of complex impedance spectroscopic properties of La0.7−xDyxSr0.3MnO3 perovskite oxides]]> https://www.researchpad.co/article/5c22c6bfd5eed0c484aa19f8

The dysprosium perovskite La0.7−xDyxSr0.3MnO3 (x = 0.00 [LSMO] and 0.03 [LDSMO]) compounds were prepared by the sol–gel reaction and characterized by the X-ray diffraction technique. The electrical conductivity and modulus characteristics of the system have been investigated in the temperature and the frequency range 311–356 K and 209–5 × 107 Hz, respectively, by means of impedance spectroscopy. The ac and dc conductivities were studied to explore the mechanisms of conduction of LSMO and LDSMO. The insertion of a small amount of Dy3+ in the La-site of LSMO perovskite oxide increases the value of the activation energy from 0.2106 to 0.5357 eV and enhances electrical resistivity values for almost two orders of magnitude.

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