Current distribution in double-cylinder electrolyte cells: Application to the study of corrosion properties of organic coatings

The ionic conductivity of an applied organic coating has been investigated using numerical finite element modelling and a double-cylinder electrochemical cell. The experimental results show that electrochemical impedance spectroscopy is able to account for ionic conductivity property of applied organic coatings in a flexible manner.     

A method for identifying the interface shear stress of unidirectional ceramic matrix composites

A method for identifying the interface shear stress of unidirectional ceramic matrix composites (CMCs) under fatigue loading was proposed. A functional relationship between the interface shear stress and the area of the hysteresis loop, the slip strain of the hysteresis loop was established based on the shear lag model by the method of symbolic-graphic combination. A fatigue test of SiC/SiC mini-composites was performed and the hysteresis curves were obtained. Then the interface shear stress under a different number of cycles was identified by inserting the experimental data of the area and slip strain of the hysteresis curves into the functional relationship. The identification results using previously introduced methods based on the area or the secant modulus of the hysteresis loop were also examined. To verify these methods, the interface shear stress identified by the three different methods was entered into the shear lag model to simulate the hysteresis curves for the different number of cycles. A comparison between the simulated results and experimental data shows that the proposed method is more appropriate for the composites used in this paper.     

Failure analysis of thermally cycled columnar thermal barrier coatings produced by high-velocity-air fuel and axial-suspension-plasma spraying: A design perspective

Axial-suspension-plasma spraying (ASPS) is a fairly recent thermal spray technology which enables production of ceramic top coats in TBCs, incorporating simultaneously the properties of both the conventional-plasma sprayed (highly insulating porous structures) and electron-beam-physical-vapor-deposited (strain-tolerant columnar structures) top coats. TBCs are required to insulate the hot components in a gas turbine engine against high temperature and harsh operating conditions. Periodic heating and cooling of turbine engines during operation can create severe thermal cyclic fatigue conditions which can degrade the performance of these coatings eventually leading to the failure. An in-depth experimental investigation was performed to understand the failure behavior of columnar TBCs subjected to thermal cyclic fatigue (TCF) test at 1100?C. The study revealed that the TCF performance was influenced to an extent, by the top coat microstructure, but was primarily affected by the severity of thermally grown oxide (TGO) growth at the bond coat-top coat interface. Mixed failure modes comprising crack propagation through the bond coat-TGO interface, through TGO and within the top coat were identified. Based on the analysis of the experimental results and thorough discussion a novel design of microstructure for the high TCF performance columnar TBC is proposed.     

Direct esterification of a hydroxyl functional polyester resin with p-hydroxybenzoic acid: Part A: investigation of the direct esterification reaction scheme and characterisation of products

Direct esterification of a hydroxyl functional polyester resin with p-hydroxybenzoic acid (PHBA) was carried out at 200–230°C in the presence of p-toluene sulphonic acid and xylene. Acid value, molecular weight distribution, differential scanning calorimetry and both ¹H and ¹³C NMR analysis were used to monitor the reaction. The optical texture of the final products were examined using a polarising optical microscope. The products from the reaction were the polyester with approximately 1 PHBA molecule per polymer chain end and unreacted PHBA. The dominant reaction in the system appears to be transesterification, resulting in a decrease of the molecular weight during the reaction. A liquid crystalline phase was not formed as multiple grafts of PHBA were not formed.     

A new method for the preparation of ultra-sharp V-notches to measure fracture toughness in ceramics

The preparation of an ultra-sharp V-notch on structural ceramics is a prerequisite for reliable fracture toughness assessment. Femtosecond lasers are used to cut ultra-sharp V-notch on the Si₃N₄ and Al₂O₃ ceramics for fracture toughness testing by single-edge V-notched beam method. The radius of the V-notch tip is smaller than 0.5 μm. The K_Ic of Si₃N₄ and Al₂O₃ ceramics determined by this method is much close to the actual fracture toughness. This method exhibits obvious advantage in good reproducibility, high accuracy and precision for reliable fracture toughness testing of structural ceramics.     

One-pot synthesis of amphiphilic nanogels from vinylated SPIONs/HEMA/PEG via a combination of click chemistry and surfactant-free emulsion photopolymerization: Unveiling of the protein-nanoparticle interactions

In this study, freshly prepared Fe₃O₄ nanoparticles (MNP1) were coated with 3-aminopropyltriethoxysilane (APTES) to produce core–shell Fe₃O₄@SiO₂ nanoparticles (MNP2), amine terminated nanoparticles was converted into the triazide in the presence of as-prepared triflic azide (MNP3). Propargyl acrylate (PgA) was synthesized from propargyl alcohol and acryloyl chloride and their structures were characterized by FT-IR and ¹H NMR spectroscopy. MNP3 were modified by PgA via click reaction to produce fully decorated triazole product (MNP4). Photopolymerization of MNP4 in the presence of hydroxyethyl methacrylate (HEMA) and acrylated methyl ether poly (ethylene glycol) (ACMPEG) were carried out by emulsion method without any surfactant (MNP5). The in-vitro release behavior of quercetin from MNP5s was investigated at two pHs (7.4 and 5.8). The effect of fetal bovine serum (FBS) on MNPs and its ability to cover magnetite nanoparticles was investigated.     

Preparation of TiO2/carbon nanotubes photocatalysts: The influence of the method of oxidation of the carbon nanotubes on the photocatalytic activity of the nanocomposites

A method for the preparation of efficient TiO₂/multi-wall carbon nanotubes nanocomposite photocatalysts by precipitation of anatase TiO₂ nanoparticles onto differently oxidized carbon nanotubes is presented. The precursor compound titanium(IV) bromide was hydrolyzed producing pure anatase phase TiO₂ nanoparticles decorated on the surface of the oxidized carbon nanotubes. The oxidative treatment of the carbon nanotubes influenced the type, quantity and distribution of oxygen-containing functional groups, which had a significant influence on the electron transfer properties, i.e., the photocatalytic activity of the synthesized nanocomposites. The results of C.I. Reactive Orange 16 photodegradation in the presence of all the synthesized nanocomposites showed their better photocatalytic activity in comparison to the commercial photocatalyst Degussa P-25.     

SEraMic: A semi-automatic method for the segmentation of grain boundaries

The SEraMic method, implemented in the SEraMic plugin for Fiji or ImageJ software, was developed to calculate a segmented image of a ceramic cross section that shows the grain boundaries. This method was used to accurately and automatically determine grain boundary positions and further assess the grain size distribution of monophasic ceramics, metals, and alloys. The only required sample preparation is polishing the cross section to a mirror-like finish. The SEraMic method is based on at least six backscattered electron scanning electron microscopy images of a unique region of interest with various tilt angles ranging from -5° to +5°, which emphasises the orientation contrasts of the grains. Because the orientation contrast varies with the incident beam angle on the sample, the set of images contains information related to all the grain boundaries. The SEraMic plugin automatically calculates and builds a segmented image of the grain boundaries from the set of tilted images. The SEraMic method was compared with classical thermal etching methods, and it was applied to determine the grain boundaries in various types of materials (oxides, phosphates, carbides, and alloys). The method remains easy to use and accurate when the average grain diameter is greater than or equal to 0.25 μm.     

A novel method to prepare self‐lubricity of Si3N4/Ag composite: Microstructure,mechanical and tribological properties

Si₃N₄/Ag composites were firstly prepared through SPS technology, using Si₃N₄ and AgNO₃ as raw materials. Utilizing the coordination bonding of Ag⁺ ions with nitrogen atoms of Si₃N₄, in situ generated Ag particles about 1 μm were tightly anchored on Si₃N₄ surface, thereby preventing the outflow of silver during sintering process. Meanwhile, smaller silver particles about 20 nm were located at the grain boundaries of Si₃N₄, which effectively improved the mechanical and tribological properties of Si₃N₄‐based composites. Finally, the Si₃N₄/Ag composites reinforced by Ag particles showed a friction coefficient of 0.48 ± 0.01, wear rate of 1.79 × 10^?6 mm³ N^?1 m^?1 and fracture toughness of 7.05 ± 0.2 MPa m^1/2, respectively.     

A study on nanofiber‐reinforced thermoplastic composites (II): Investigation of the mixing rheology and conduction properties

This article is portion of a comprehensive study on the development of nanofiber‐reinforced polymer composites for electrostatic discharge materials and structural composites. Vapor‐grown carbon fibers with an average diameter of 100 nm were used as a precursor and model fiber system for carbon nanotubes. These nanofibers were purified and functionalized to provide for an open network of high‐purity nanofibers. Banbury‐type mixing was used to disperse the nanofibers in the polymer matrix. Rheological and microscopic analysis showed that the high shear processing of the polymer/nanofiber mixture led to a homogeneous dispersion of nanofibers with no agglomerates present and no shortening of the nanofibers. The shear thinning behavior of polymeric materials helps in the mixing of the nanofibers to form the composites. A percolation threshold for electrical conduction of 9–18 wt % was observed for the highly dispersed nanofiber networks. The electrical behavior of these materials was not affected by changes in humidity. Microscopic analysis showed highly dispersed nanofibers with no indications of porosity. These conducting polymers are well suited for electrostatic discharge applications, and might well become multifunctional materials for strength/electrical applications. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 1162–1172, 2001     

Thiourea assisted one-pot easy synthesis of CdS/rGO composite by the wet chemical method: Structural,optical, and photocatalytic properties

We report on the synthesis of CdS/reduced graphene oxide (rGO) composite by a wet chemical method. Thiourea was used both as a sulfur source and as a reducing agent to convert graphene oxide to rGO. The structural and morphological confirmation for the reduction of graphene oxide and the formation of the CdS/rGO composite was demonstrated by X-ray diffractometry, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy analyses. Photoluminescence spectra of the composite exhibited a more efficient luminescence quenching in comparison with pure CdS nanoparticles. The composite demonstrated 99% photodegradation of methyl orange under UV irradiation, which is much superior than the photodegradation of methyl orange under similar conditions exhibited by CdS nanoparticles (72%).     

A method for structural characterization of the range of cylindrical nanocarbons: Nanotubes to nanofibers

Given the wealth of carbon multi-walled carbon nanotubes (MWNTs) and nanofiber synthesis strategies and resulting forms, there is an increasing need to better classify these materials in terms of their nanostructure. Apart from distinguishing the different nanoforms, such classification may be particularly useful for relating MWNT or nanofiber performance within various applications to their nanostructure. Demonstrated here is the use of image analysis algorithms applied to high resolution transmission electron microscopy (HRTEM) images of MWNTs and nanofibers. The analysis of the HRTEM images allowed for four separate measurements to quantify the graphitic content of the nanotube and nanofiber samples. Each measurement was based upon the features of individual carbon layer plane segments, which appear as fringes in HRTEM images. These measures included fringe length, separation, tortuosity and orientation. Distributions in the form of histograms serve to quantify data contained in the HRTEM images as represented by these parameters. Such information can serve as a measure of the physical characteristics and resulting chemical and mechanical properties of the nanotubes, nanofibers and their utility in applications.     

Synthetic methods in phase equilibria: A new apparatus and error analysis of the method

A new apparatus for the study of high-pressure phase equilibria using a synthetic method is described. The apparatus was especially developed for the study of solubilities of gases in condensed phases, at temperatures ranging from 243 K to 353 K and pressures up to 20 MPa. The quality of the equipment was confirmed through several tests, including measurements along the three phase co-existence line for the system ethane + methanol, the study of the solubility of methane in water, and of carbon dioxide in water.An analysis regarding the application of the synthetic isothermal method in the study of gas solubilities was performed, in order to evaluate the influence of common assumptions and of various experimental aspects on the final solubility results. The analysis revealed that the largest influence on the precision of the solubility results is related to the ratio between the volumes of the two phases in equilibrium. Experiments with small volume of the vapour phase are less susceptible to the influence of other sources of errors, resulting in a higher precision of the final results.     

Degradation of phenols using boron-doped diamond electrodes: A method for quantifying the extent of combustion

Boron-doped diamond (BDD) is a very promising material to be used in electrochemical processes of wastewater treatment, since it enables the efficient degradation of many persistent/recalcitrant organic pollutants, with the possibility of achieving their complete mineralization (i.e., combustion to CO₂). It was investigated in this work the electrochemical degradation of a set of phenols frequently found in industrial wastewaters, specifically, phenol, m-cresol, catechol and guaiacol, using a BDD anode. It was the aim of this study to present a method for quantifying the extent of combustion in this type of process, by introducing the concept of “combustion efficiency”, η_C, which is derived from well established theory. Experimental values of combustion efficiencies, in tests performed at different current densities were obtained for each product. The results show that the highest values of η_C are found for catechol, and that η_C increases with increasing current densities. The effect of the solute concentration on η_C was also investigated; the results show that under conditions of diffusive control η_C is independent of the concentration, pointing out that combustion and current efficiencies are independent quantities.     

An energy-efficient method for mitigating membrane fouling: A novel embodiment of the inverse fluidized bed

A novel inverse fluidized bed (IFB) was developed to improve membrane fouling mitigation vis-à-vis the conventional aeration method. The fluidized media, whose density was less than water and oleophilic, were more effective than bubbles for both feeds containing oil and particulates due to their greater inertia. The key highlights are (i) for all the conditions investigated, IFB consistently gave a lower trans-membrane pressure (TMP) than aeration at the same energy requirement; (ii) IFB performed better even when the energy input was reduced by 87.5%; (iii) IFB provided an impressive enhancement of up to 54 times that of dead-end filtration.     

Fatty acid vinyl esters as acylating agents: A new method for the enzymatic synthesis of monoacylglycerols

Lipase-catalyzed synthesis of monoacylglycerols (MAG) was performed by transesterification reactions between fatty acid vinyl esters and either glycerol (1) or 1,2-O-isopropylidene-rac-glycerol (2), without solvents or in the presence ofn-pentane. Vinyl decanoate, vinyl laurate, vinyl stearate and vinyl palmitate have been converted to the corresponding monoacylglycerols. As expected for the reaction with1, a mixture of mono-, di- and triacylglycerols was synthesized. The highest concentrations of MAG were achieved with vinyl stearate (30% 2-MAG and 15% 1-MAG). The reactions of fatty acid vinyl esters with the protected glycerol (2) led to the corresponding protected 3-monoacylglycerols with 100% conversion after short reaction times. The subsequent cleavage of these acetonides was performed by four different methods. The fastest cleavage was found with trifluoroacetic acid as catalyst, whereas the highest concentration of MAG (100%) was obtained for the boric acid-catalyzed hydrolysis of the acetonides.     

Improving the design of depth filters: A model‐based method using optimal control theory

Because there is no general design method for depth filters, especially for layered configurations, this methodological gap is addressed here. Using optimal control theory, paths of the filter coefficient, a measure for local filtration performance, are determined along the filter depth. An analytical optimal control solution is derived and used to validate the numerical algorithm. Two optimal control scenarios are solved numerically: In the first scenario, the goal of constant deposition along the filter depth is addressed. The second scenario aims at maximizing the time until some maximal pressure drop is reached. Furthermore, a computational strategy is presented to derive discrete layers suitable for practical design from the continuous optimal control solutions. All optimized scenarios are compared to one‐layered filter designs and significant improvements are found. As this work is based on strongly validated and widely used filtration models, the presented methods are expected to have broad applicability. © 2017 American Institute of Chemical Engineers AIChE J, 63: 68–76, 2018