Dense Substrates Research Articles

Novel poly(vinylidene fluoride)/thermoplastic polyester elastomer composite membrane prepared by the electrospinning of nanofibers onto a dense membrane substrate for protective textiles

ABSTRACTConventionally, electrospun thin‐film composite (TFC) membranes used in protective clothing are fabricated on the basis of an electrospinning substrate coated with a nonporous hydrophilic polymer layer. However, the incompatibility of common coating solvents with inertia substrate materials requires that the support material should be surface‐modified to promote the crosslinking of the dense and porous layers. In this study, we attempted to fabricate a novel TFC membrane for use in protective clothing by the one‐step deposition of poly(vinylidene fluoride) (PVDF) nanofibers onto a dense, hydrophilic thermoplastic polyester elastomer (TPEE) membrane substrate via electrospinning. The proposed approach has the advantage of no need for further surface modification of the substrate membrane. The optimized TFC membrane exhibited a better tensile strength than the dense substrate TPEE film. The testing results for the moisture resistance show that the new TFC membrane had a comparatively high water vapor transmission rate, notwithstanding that the value was slightly lower than that of the single‐layered TPEE film. Simultaneously, a resistance‐in‐series model based on Henis–Tripodi's model for explaining the water vapor permeation behavior of the TFC membrane was proposed. The moisture resistance values predicted by the analyzed model were in good agreement with these experimental data. This verified the validity of this in‐series moisture resistance model for the TFC membrane. The influence of the PVDF porosity on the water vapor permeation resistance throughout the TFC membrane was calculated and is discussed. More work is needed to establish the applicability of the new TFC membrane for lamination with nonwoven fabric to form the multilayered fabrics used in firefighters’ protective clothing. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42170.

Synthesis of porous LSM films on dense YSZ substrates for use in SOFC

Ceramic thin films are of great importance in the development and fabrication of devices such as SOFC. The porous microstructure of the electrodes is crucial for the overall performance of the SOFC and it is quite influenced by the fabrication process. In this sense, LSM films were obtained over 0,25 µm rough YSZ dense substrates heated at 650°C, using a salts solution and an airbrush. By XRD patterns the LSM perovskite phase was identified in both samples. The obtained films showed very high porosity with great pore size distribution. The LSM films exhibit grains with size around 60 nm in average. A more continuous film, practically without cracks, was obtained depositing 2 mL of the solution. The presence of microstructural defects in the film obtained wjth 1,5 mL of solution increased the cathode polarization compared with the one obtained with 2,0 mL of solution.

Optical properties of the glass composites with nanofilms: the relationship to the dispersed phase of sol

It has been found that the particles size, volume fraction of the film-forming sol disperse phase, the pack-density of the particles in the layer, affect the optical properties of nanodimensional films and composites consisting of a glass substrate coated with the surface film. The threshold energy density of the laser ablation destruction of the films being components of the composites also depends largely on the state of the sol dispersed phase. This value needed for the ablation under the laser radiation with nanosecond pulse duration was found to increase with the dispersed phase particles pack-density in the layer. Moreover, this value increased with the particle size and decreased as the fraction by volume of that phase and particles pack-density rose when using microsecond pulse duration. These relationships are due to low thickness and density of the nanofilm, and as a result the laser beam interacted practically with the dense glass substrate.

Microstructural characteristics and elastic modulus of porous solids

Porous La0.6Sr0.4Co0.2Fe0.8O3−δ ceramic films with different porosities were fabricated by constrained sintering on dense substrates of Gd-doped ceria at 900-1200°C. The actual digital three dimensional microstructures of the as-sintered films were reconstructed using focused ion beam/scanning electron microscope tomography and their elastic moduli were calculated using finite element modelling based on the reconstructed microstructures. The calculated moduli were found to be in good agreement with experimental results. Porosity was found to be the primary factor influencing the elastic modulus. In order to explore the influence of microstructural features other than porosity the real microstructures, and artificial microstructures based on spherical mono-size particles, were coarsened numerically at constant porosity using a cellular automaton method. The simulation results showed that in the initial stages of sintering, when interparticle necks are small, the modulus increases with the neck size. However, as the coarsening increases further, the modulus becomes insensitive to the details of the microstructure and only depends on porosity. The results also show that simulation gives inaccurate results if the ratio of characteristic length of the simulated volume to the characteristic length of the microstructure is too small (less than approximately a factor of 8).

Titanium Substrate Surfaces Coated with Hydroxyapatite by Magnetron Sputtering

The deposition of hydroxyapatite coatings on titanium via sputtering techniques has been quite studied on commercial dense substrates, for use as a biomaterial. In this work, porous titanium samples produced by powder metallurgy and commercially dense titanium sheet, used as control, were used as substrates. The coatings were deposited by radio frequency magnetron sputtering using a hydroxyapatite target in argon atmosphere with different deposition times. Samples characterization was performed by Optical Microscopy, Scanning Electron Microscopy/Energy Dispersive Spectroscopy and low-angle X-ray Diffraction. Hydroxyapatite coating depositions were obtained on both titanium substrates. The results indicated the potential of this methodology for titanium substrates with homogeneous hydroxyapatite coatings.

Densification of Ce0.9Gd0.1O1.95 barrier layer by in-situ solid state reaction

A novel methodology, called in-situ solid state reaction (SSR), is developed and achieved for the densification of gadolinia doped ceria (CGO) barrier layer (BL) within the solid oxide fuel cell (SOFC) technology. The method is based on the combined use of impregnation technique and a designed two-step sintering process to promote the densification of the CGO-BL on dense yttria stabilized zirconia (YSZ) electrolyte. A pre-sintering step is carried out at temperature T1 (1150–1250 °C) to obtain porous and interconnected CGO-BL on dense electrolyte substrate. Impregnation of the porous BL is then carried out with small amount of either cobalt or copper nitrate solutions as sintering aids. Final sintering of the CGO-BL at temperature T2 (1250–1275 °C, T2 > T1) is used to promote an SSR between the sintering aid and CGO-BL to obtain densification and grain growth. The approach proposed in this work was proved on both screen printed and tape cast CGO-BL, showing feasibility for the densification of generic ceramic multilayer systems undergoing different constrained sintering conditions and for a large variety of materials.

Impedance As a Diagnostic Tool to Characterize Mixed-Potential Sensor Response

Commercial tape casting and screen-printing methods have been used to fabricate a planar, self-heated, mixed-potential NOx sensor for application in vehicle on-board emission control systems. The device consists of dense La0.8Sr0.2CrO3 (LSCrO) and Pt electrodes and a porous YSZ electrolyte on one side of a dense ceramic substrate and a Pt-heater with independent leads on the backside of the substrate. While these sensors have demonstrated high sensitivity and selectivity to NOx when operated at a positive bias, optimization of the sensor device geometry remains an open question. In this work, we used circular cells of dense YSZ with LSCrO working and Pt counter electrodes in order to identify the impedance response of each individual sensor component. The impedance response measured on the cell was then used to identify the rate-limiting processes underlying the response of the planar sensor device.

The effect of a constraint on the sintering and stress development in alumina thick films

The microstructural and stress evolution of thick (25μm) alumina films on dense alumina substrates sintered at temperatures from 1300°C to 1600°C has been investigated. In this study the constraint on sintering was monitored in the absence of significant differences in thermal expansion between the film and the substrate. For comparison purposes unconstrained alumina pellets sintered at 1300°C–1600°C were also examined. Overall, the constrained alumina densified less than the free alumina, as expected, although at intermediate temperatures densification rates were comparable. Sintering in the direction perpendicular to the substrate was enhanced with respect to that parallel to the substrate as a means of stress relaxation. Using fluorescence spectroscopy the residual stresses of the films parallel to the substrates were measured; residual tensile stresses as high as 450±40MPa were exhibited by the films. The considerable stress development resulted in cracking and delamination of the film from the substrate, subsequently film constraint was reduced and densification was not impeded.

Lithographically Patterned Thin Activated Carbon Films as a New Technology Platform for On-Chip Devices

Continuous, smooth, visibly defect-free, lithographically patterned activated carbon films (ACFs) are prepared on the surface of silicon wafers. Depending on the synthesis conditions, porous ACFs can either remain attached to the initial substrate or be separated and transferred to another dense or porous substrate of interest. Tuning the activation conditions allows one to change the surface area and porosity of the produced carbon films. Here we utilize the developed thin ACF technology to produce prototypes of functional electrical double-layer capacitor devices. The synthesized thin carbon film electrodes demonstrated very high capacitance in excess of 510 F g(-1) (>390 F cm(-3)) at a slow cyclic voltammetry scan rate of 1 mV s(-1) and in excess of 325 F g(-1) (>250 F cm(-3)) in charge-discharge tests at an ultrahigh current density of 45,000 mA g(-1). Good stability was demonstrated after 10,000 galvanostatic charge-discharge cycles. The high values of the specific and volumetric capacitances of the selected ACF electrodes as well as the capacity retention at high current densities demonstrated great potential of the proposed technology for the fabrication of various on-chip devices, such as micro-electrochemical capacitors.

Application of Commercial Manufacturing Methods to Mixed-Potential NOx Sensors

Commercial manufacturing methods have been used to fabricate a planar, self-heated, tape-cast, mixed-potential NOx sensor for application in vehicle on-board emission control systems. The device consists of dense La0.8Sr0.2CrO3 (LSCrO) and Pt electrodes and a porous YSZ electrolyte on one side of a dense ceramic substrate and a Pt-heater with independent leads on the backside of the substrate. These planar mixed-potential sensors are capable of selectively detecting ppm levels of NOx when operated at a positive bias. Additionally, the device has yielded stable performance under months of testing as a result of the stable morphology of the electrode/electrolyte/gas phase interface.

The effect of vermiculite on the degradation and spallation of plasma sprayed thermal barrier coatings

A study has been made of the effect of vermiculite (VM) on the sintering-induced spallation of plasma sprayed zirconia thermal barrier coatings (TBCs). The glass transition (~1040°C) and melting (~1360°C) temperatures of VM are representative of a broad class of so-called CMAS (calcia–magnesia–alumina–silica) particulates likely to be ingested into gas turbines. Selected loadings of VM powder were introduced onto the surface of free-standing coatings, followed by heating (1500°C) for periods of up to 80h. The presence of VM induces various microstructural changes in the coatings and also accelerates the rise in their (in-plane) Young's modulus. Finally, results are presented concerning the effect of VM on spallation resistance, using coatings sprayed onto dense alumina substrates. Spallation lifetimes can be substantially reduced by VM, even at relatively low levels (~1wt.%). This is related to acceleration of the sintering-induced increases in coating stiffness.

Influence of the process parameters on the spray pyrolysis technique, on the synthesis of gadolinium doped-ceria thin film

This work presents the results of a process of optimization applied to gadolinia-doped ceria (Ce0.8Gd0.2O1.9−x, or CGO) thin films, deposited by spray pyrolysis (SP). Spray pyrolysis is a high thermal deposition method that combines material deposition and heat treatment. This combination is advantageous since the post-deposition heat treatment step is not necessary. However, stresses are solidified in the coating during the deposition, which may lead to the initiation of a crack in the coating. The aim of this work was to achieve thin, dense, and continuous CGO coatings, which may be used as gas separation membranes and as a solid state electrochemical interfaces. Dense, flat, low-defect substrates such as silica slides, silicon mono crystal wafers, and porous substrates were used as substrates in this work. Cerium ammonium nitrate and gadolinium acetylacetonate were dissolved in ethanol and butyl carbitol to form a precursor solution that was sprayed on the heated substrates. Process parameters such as solvent composition, deposition rate and different heating regimes were analyzed. The microstructure was analyzed by secondary electron microscopy (SEM) and was found that thin, dense, and defect-free films could be produced on dense and porous substrates. The results obtained show that it is possible to obtain a CGO dense film deposited by spray pyrolysis. X-ray diffraction (XRD) analysis showed that the films were crystalline after the deposition without requiring post-deposition heat treatment. The crystallite size does not vary significantly as a function of the annealing temperature.

Dense and porous titanium substrates with a biomimetic calcium phosphate coating

The present work studied a biomimetic method using a simplified solution (SS) with calcium and phosphorus ions for coating titanium substrates, in order to improve their bioactivity. Commercially pure titanium dense sheet, microporous and macroporous titanium samples, both produced by powder metallurgy, were treated in NaOH solution followed by heat-treating and immersed in SS for 7, 14 or 21 days. The samples characterization was performed by quantitative metallographic analysis, confocal scanning optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and low angle X-ray diffraction. The results showed coatings with calcium phosphate precipitation in all samples, with globular or plate-like morphology, typical of hydroxyapatite and octacalcium phosphate, respectively, indicating that the solution (SS) has potential for coating titanium substrates. In addition, the different surfaces of substrates had an effect on the formed calcium phosphate phase and thickness of coatings, depending on the substrate type and imersion time in the simplified solution.

A methodology, based on sintering-induced stiffening, for prediction of the spallation lifetime of plasma-sprayed coatings

This study concerns the effect of sintering-induced stiffening in promoting spallation of plasma-sprayed yttria-stabilized zirconia thermal barrier coatings. Coatings with thickness in the range 350–800μm were sprayed onto dense alumina substrates. In order to ensure a tough interface, the surface of the alumina substrates were first roughened by laser treatment. Specimens were heat treated at 1500°C and periodically quenched to ∼100°C, using nitrogen jets. During cooling, specimens were monitored for spallation via a webcam. Spallation lifetimes were observed to be shorter for thicker coatings. Using a simple fracture mechanics approach, with the strain energy release rate obtained using measured coating stiffness values, the behaviour was found to be consistent with an approximately constant interfacial fracture energy value of the order of 300Jm−2. If this interfacial toughness had been known beforehand, then the rationale presented here could have been used for prediction of coating lifetime. While the experiments are based on use of a ceramic substrate, the approach could be applied to conventional metallic substrate systems.

Properties of Titanium Foams for Biomedical Applications

AbstractTitanium foams are presently used in various load bearing orthopedic applications. Such foams are characterized by an open network of porosity with high surface area. This paper presents the structure, microstructure, and properties of titanium foams produced with a powder metallurgy process. Fully porous CpTi and Ti6Al4V cylinders and CpTi foam coating on CpTi and Ti6Al4V substrates were produced and characterized. The microstructure of the foam cell walls is representative of annealed CpTi and Ti6Al4V. Alloying elements and oxygen in solution increase the mechanical strength of the foams but lower their ductility. Ductility affects the fatigue life of the material. When CpTi foam is bonded to Ti6Al4V substrates, migration of alloying elements in the foam cell walls is observed. Good metallurgical bonding is created between the coatings and the dense substrate and shear strength above the requirements of the FDA guidelines are obtained.

The co-operative, transformative organization of human action and knowledge

Focusing on a range of features that are central to the constitution of action, this article is an empirically based theoretical contribution to the field of research attempting to understand how human sociality is established and sustained. Human action is intensely, perhaps uniquely, co-operative. Individual actions are constructed by assembling diverse materials, including language structure, prosody, and visible embodied displays. Semiotically charged objects, such as maps, when included within local action, incorporate ways of knowing and acting upon the world that have been inherited from predecessors. New action is built by performing systematic, selective operations on these public configurations of resources. The way in which a single action encompasses different kinds of resources makes possible 1) distinctive forms of co-operative social organization as alternatively positioned actors contribute different kinds of structure to a single shared action (e.g., the talk of a speaker and the silent visible displays of hearer work together to construct a turn-at-talk and the utterance emerging within it); and 2) the accumulation and differentiation through time within local co-operative transformation zones of dense substrates that create a multiplicity of settings for action. Each setting for action must be inhabited by competent members who have mastered the culturally specific practices required to perform the activities that animate the lifeworld of a particular community. Through the progressive development of, and apprenticeship within, diverse epistemic ecologies, communities invest their members with the resources required to understand each other in just the ways that make possible the accomplishment of ongoing, situated action. Human beings inhabit each other's actions.

Diffusion of Active Ingredients in Textiles

Most practical textile models are based on a two scale approach: a one-dimensional fiber model and a fabric model, see Fan et al. (Commun Comput Phys 4(4):929–948, 2008). No meso-level is used in between, i.e. the yarn scale is neglected in this setup. For dense textile substrates this seems appropriate as the yarns connect everywhere, but for loose fabrics or scrims this approach cannot be kept. Specifically when one is interested in tracking an active component released by the fibers, the yarn level plays an important role. This is because the saturation vapor pressure will influence the release rate from the fibers, and its value will vary over the yarn cross-section. Therefore, in this work we present a three step multiscale model: the active component is tracked in the fiber, the yarn, and finally at the fabric level. At the fiber level a one-dimensional reduction to a non-linear diffusion equation is performed, and solved on an as needed basis. At the yarn level both a two-dimensional or a one-dimensional model can be applied, and finally the yarn result is upscaled to the fabric level.

Stress Assisted Grain Growth and Dielectric Properties of BaLa4Ti4O15 Thick Films

Thick films of BaLa4Ti4O15 (BLT) are potential candidates for applications in telecommunications devices, operating at microwave frequencies, in which miniaturization is required. The production of thick films usually involves the powder deposition on top of a dense substrate, followed by the constrained sintering of the powder layer. Constrained sintering of functional complex oxides as BLT has not been addressed. In this work we demonstrated that in opposition to isotropic constrained sintering model predictions, BLT films with density equivalent to freely sintered bulk samples were obtained after 180 min at 1500 ºC. Another unexpected observation is that films showed a larger grain size than the bulk sample sintered under the same conditions. A high degree of anisotropy was detected in grain's shape, with high aspect ratio, and in film's orientation, with grains oriented parallel to the substrate. In comparison, in freely sintered bulk sample, lower aspect ratio and lower grain orientation are observed. Stress assisted grain growth is shown to be responsible for the increased grain growth and high texturization observed in the films. Dielectric characterization was also performed in films and bulk and the electrical response correlated with the microstructural features. Both showed near-zero temperature coefficients of permittivity, revealing a dielectric response with great temperature stability, interesting for microelectronic applications.

Relevance of Hydrophobic and Oleophobic Properties of Antigraffiti Systems on Their Cleaning Efficiency on Concrete and Stone Surfaces

The problem of graffiti is not entirely restricted to urban areas, but also appears frequently in rural communities and along traffic infrastructure. Besides its aesthetic and societal effects, graffiti cause considerable removal costs and subsequent costs for repairing damages caused by improper graffiti removal. Over the last two decades, strategies have been developed to combat graffiti in the built environment, including the development of protective measures in the form of antigraffiti systems (AGSs). Antigraffiti systems promise to be affordable and easily applicable for a wide range of substrates, and many products have already been on the market for many years. In practice, however, successful application of AGS and removal of graffiti depend on many factors in which the type of coating and condition of the substrate play critical roles. The optimal environmental goal is to use AGS without any cleaning chemicals except for pure water. Available studies on the behavior of the same AGS on various substrates can show completely different results concerning the cleaning efficacy and the durability of the AGS under different climatic conditions. The question of which properties of an AGS are most essential for its efficiency has still not been fully investigated. The goal of this study was to investigate cleaning efficacy in conjunction with hydrophobic and oleophobic properties of the AGS on different substrates. The results showed that hydrophobicity and oleophobicity are important for dense substrates but have a low influence on porous substrates. In this case, cleaning efficiency is majorly determined by the physical properties of the substrates.

Influence of Substrate Temperature in the Morphology and Microstructure of YSZ Films Obtained on LSM Porous Substrate via Spray Pyrolysis

Many studies have been reported in the literature related to YSZ films deposited on dense substrate or applied directly on the SOFC anode. However, there are not a lot of studies about the YSZ deposition on the cathode. The present work aims to obtain yttria-stabilized zirconia (YSZ), using the spray pyrolysis technique, for their application as electrolyte in solid oxide fuel cells (SOFC). The films were obtained from a precursor solution containing zirconium and yttrium salts, dissolved in ethanol and propylene glycol (1:1), this solution was sprayed onto a heated LSM porous substrate. The substrate temperature was varied in order to obtain dense and homogeneous films. After deposition, the films were heat treated, aiming to crystallize and stabilize the zirconia cubic phase. The films were characterized by Scanning Electron Microscopy (SEM), thermal analysis, X-ray diffraction and Fourier transform Infrared Spectroscopy (FT-IR).