Showing papers in "Frontiers in Materials in 2019"
TL;DR: In this paper, the authors have reviewed the different sources of natural fibers, their properties, modification of natural fiber, the effect of treatments on natural fibers and their effective use as reinforcement for polymer composite materials.
Abstract: The increase in awareness of the damage caused by synthetic materials on the environment has led to the development of eco-friendly materials. The researchers have shown a lot of interest in developing such materials which can replace the synthetic materials. As a result, there is an increase in demand for commercial use of the natural fiber-based composites in recent years for various industrial sectors. Natural fibers are sustainable materials which are easily available in nature and have advantages like low-cost, lightweight, renewability, biodegradability and high specific properties. The sustainability of the natural fiber-based composite materials has led to upsurge its applications in various manufacturing sectors. In this paper, we have reviewed the different sources of natural fibers, their properties, modification of natural fibers, the effect of treatments on natural fibers, etc. We also summarize the major applications of natural fibers and their effective use as reinforcement for polymer composite materials.
441 citations
TL;DR: The Mo-TiO2@NC electrode as discussed by the authors showed initial discharge and charge capacities of 850.7 and 548.3 mAh g-1 at a current density of 85 mA g −1, respectively, with a remarkable discharge capacity maintained at 449.2mAh g−1 after 100 cycles.
Abstract: For improving the capability, cycling stability and rate capacity of anatase TiO2-based electrode, Mo-doped TiO2 anatase encapsulated in nitrogen-doped amorphous carbon (denoted for Mo-TiO2@NC) were synthesized through a facile hydrothermal method and followed by coating with polyaniline (PANI) and heating treatment. When tested as anode for lithium ion batteries, the Mo-TiO2@NC electrode showed initial discharge and charge capacities of 850.7 and 548.3 mAh g-1 at a current density of 85 mA g-1, respectively, with a remarkable discharge capacity maintained at 449.2 mAh g-1 after 100 cycles. Even at high current density of 850 mA g-1, a reversible capacity of 154 mAh g-1 after 200 cycles is obtained, displaying good rate capacity and long-term cycling stability. The outstanding electrochemical performance of Mo-TiO2@NC could be attributed to the synergistic effect of aliovalent ions doping and carbon coating.
245 citations
TL;DR: It is shown that experiment- and simulation-based data mining in combination with machine leaning tools provide exceptional opportunities to enable highly reliant identification of fundamental interrelations within materials for characterization and optimization in a scale-bridging manner.
Abstract: Machine learning tools represent key enablers for empowering material scientists and engineers to accelerate the development of novel materials, processes and techniques. One of the aims of using such approaches in the field of materials science is to achieve high-throughput identification and quantification of essential features along the process-structure-property-performance chain. In this contribution, machine learning and statistical learning approaches are reviewed in terms of their successful application to specific problems in the field of continuum materials mechanics. They are categorized with respect to their type of task designated to be either descriptive, predictive or prescriptive; thus to ultimately achieve identification, prediction or even optimization of essential characteristics. The respective choice of the most appropriate machine learning approach highly depends on the specific use-case, type of material, kind of data involved, spatial and temporal scales, formats, and desired knowledge gain as well as affordable computational costs. Different examples are reviewed involving case-by-case dependent application of different types of artificial neural networks and other data-driven approaches such as support vector machines, decision trees and random forests as well as Bayesian learning, and model order reduction procedures such as principal component analysis, among others. These techniques are applied to accelerate the identification of material parameters or salient features for materials characterization, to support rapid design and optimization of novel materials or manufacturing methods, to improve and correct complex measurement devices, or to better understand and predict fatigue behavior, among other examples. Besides experimentally obtained datasets, numerous studies draw required information from simulation-based data mining. Altogether, it is shown that experiment- and simulation-based data mining in combination with machine leaning tools provide exceptional opportunities to enable highly reliant identification of fundamental interrelations within materials for characterization and optimization in a scale-bridging manner. Potentials of further utilizing applied machine learning in materials science and empowering significant acceleration of knowledge output are pointed out.
222 citations
TL;DR: Urea hydrolysis is the most applied in concrete repair mechanisms and is clearly evident that microbiological and molecular components are essential to improve the process and performance of bioconcrete.
Abstract: In this review, microbiological and molecular concepts of Microbially induced Calcium Carbonate Precipitation (MICP) and their role in bioconcrete are discussed. MICP is a widespread biochemical process in soils, caves, freshwater, marine sediments and hypersaline habitats. MICP is an outcome of metabolic interactions between diverse microbial communities with organic and/or inorganic compounds present in environment. Some of the major metabolic processes involved in MICP at different levels are urea hydrolysis, denitrification, dissimilatory sulfate reduction and photosynthesis. Currently, MICP directed by urea hydrolysis, denitrification and dissimilatory sulfate reduction has been reported to aid in development of bioconcrete and demonstrated improvement in mechanical and structural properties of concrete. Bioconcrete is a promising sustainable technology in reducing the negative environmental impacts due to CO2 emission from construction sector and as well as in terms of economic benefits by way of promoting self-healing process of the concrete structures. Among the metabolic processes mentioned above, urea hydrolysis is the most applied in concrete repair mechanisms. MICP by urea hydrolysis is induced by a series of reactions driven by urease (Ur) and carbonic anhydrase (CA). Catalytic activity of these two enzymes depends on diverse parameters, which are currently being studied under laboratory conditions to understand the biochemical mechanisms involved and their regulation in microorganisms. It is clearly evident that microbiological and molecular components are essential to improve the process and performance of bioconcrete.
170 citations
TL;DR: In this article, the authors have attempted to highlight the advances taking place in the field of magnetic nanoparticles as theranostic agents by developing suitable procedures like precipitation, co-precipitation, thermal decomposition, hydrothermal synthesis, microemulsion synthesis and plant mediated synthesis.
Abstract: Substances at nanoscale commonly known as “nanomaterials” have always grabbed the attention of the researchers for hundreds of years Among these different types of nanomaterials, magnetic nanomaterials have been the focus of overwhelming attention during the last two decades as evidenced by an extraordinary increase in number of research papers Iron oxide magnetic nanoparticles have occupied a vital position in imaging phenomena; as drug vehicles, controlled/sustained release phenomena and hyperthermia; atherosclerosis diagnosis; prostate cancer In fact, these are wonderful “theranostic” agents with some are under clinical trials for human use In this review, we have attempted to highlight the advances taking place in the field of magnetic nanoparticles as theranostic agents Extensive progress has been made in the two most important parameters viz control over size and shape which decide the importance of iron oxide magnetic nanoparticles by developing suitable procedures like precipitation, co-precipitation, thermal decomposition, hydrothermal synthesis, microemulsion synthesis and plant mediated synthesis After suitable synthetic route, workers encounter the most daunting task linked with the materials at nanoscale ie the protection against corrosion Only properly protected iron oxide magnetic nanoparticles can be further connected to different functional systems to make building blocks for application in catalysis, biology and medicines Finally, iron oxide magnetic nanoparticles play a key role in imaging applications for diagnostic purposes, drug delivery vehicles and above all the combined effect of previous two phenomena “theranostics” With all the potential uses, toxicity of the of iron oxide magnetic nanoparticles has also been discussed In the end, attention has been drawn to address the future of research trends of iron oxide magnetic nanoparticles in theranostics
166 citations
TL;DR: In this paper, the controllable electrodeposition of CoNiCu alloy nanotubes electrodes using anodic aluminum oxide (AAO) as template was reported for non-enzymatic glucose sensing.
Abstract: Transition metal alloys are good candidate electrodes for non-enzymatic glucose sensors due to their low cost and high performance. In this work, we reported the controllable electrodeposition of CoNiCu alloy nanotubes electrodes using anodic aluminum oxide (AAO) as template. Uniform CoNiCu alloy arrays of nanotubes about 2 μm in length and 280 nm in diameter were obtained by optimizing the electrodeposition parameters. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) measurements indicated that the as-prepared alloy nanotubes arrays are composed of 64.7 wt% Co-19.4 wt% Ni-15.9 wt% Cu. Non-enzymatic glucose sensing measurements indicated that the CoNiCu nanotubes arrays possessed a low detection limit of 0.5 μM, a high sensitivity of 791 μA mM −1 cm −2 from 50 to 1,551 μM and 322 μA mM −1 cm −2 from 1,551 to 4,050 μM. Besides, they showed high reliability with the capacity of anti-jamming. Tafel plots showed that alloying brought higher exchange current density and faster reaction speed. The high performance should be due to the synergistic effect of Co, Ni, and Cu metal elements and high surface area of nanotubes arrays.
156 citations
TL;DR: In this article, a novel biodegradable material, polyvinyl alcohol (PVA)/starch (ST)/ glycerol (GL)/ halloysite nanotube (HNT) nanocomposite films were prepared by solution casting at the HNT contents of 0.25, 0.5, 1, 3 and 5 wt%.
Abstract: As a novel biodegradable material, poly (vinyl) alcohol (PVA)/starch (ST)/ glycerol (GL)/ halloysite nanotube (HNT) nanocomposite films were prepared by solution casting at the HNT contents of 0.25, 0.5, 1, 3 and 5 wt%. Water absorption capacity and water solubility of nanocomposite films were decreased remarkably by 44.24 and 48.05%, respectively, with increasing the HNT content from 0 to 5 wt% when compared with those of biopolymer matrices. Moreover, the water contact angle of nanocomposite films increased by 21.36o with the incorporation of HNTs. The presence of HNTs appeared to reduce the overall migration rates for PVA/ST/GL/HNT nanocomposite films when interacting with either hydrophilic or lipophilic food simulants. However, the migration rates of HNTs alone were enhanced with increasing the HNT contents in hydrophilic, lipophilic and acidic food simulants. On the other hand, the biodegradation rate and light transmittance of nanocomposite films were reduced linearly by 18.56 and 26.90% with increasing the HNT content from 0 to 5 wt%. Overall, novel PVA/ST/GL/HNT nanocomposite films in this study offer highly competitive material with excellent water resistance, good biodegradability and acceptable transparency to be potentially used for sustainable food packaging particularly targeting lipophilic and acidic foodstuffs.
133 citations
TL;DR: In this paper, a state-of-the-art review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical and durability performance, environmental impacts, and their potentials in applications is presented.
Abstract: Chemically activated materials (often termed as geopolymer) have received attracting attentions in civil, material and environmental research fields as a toolkit alternative to traditional Portland cement in specific applications. This paper presents a state-of-the-art review on silico-aluminophosphate (SAP) geopolymers in terms of definition, chemistries involved during geopolymerization, mechanical and durability performance, environmental impacts, and their potentials in applications as compared to conventional alkali-aluminosilicate (AAS) geopolymers. Recommendations for future applications are also highlighted. It is found that S-A-P gels with six-coordinated aluminum environment dominate in SAP geopolymers, while the aluminum in N-A-S-H gels formed in the AAS geopolymers is characterized by four-coordinated features. Besides, the slow performance development of SAP geopolymer matrix under ambient temperature curing can be compensated through incorporating additional countermeasures (e.g., metal sources) which allow the tailored design of such geopolymers for certain in-situ applications, i.e., calcium-bearing C-(A)-S-H gels co-existed with N-A-S-H gels are dominant in AAS geopolymers, while S-A-P gels enhanced by phosphate-containing crystalline/amorphous phases are the main products in SAP geopolymers. Another advantage of SAP geopolymers is their environmental friendliness relative to the AAS geopolymers due to the utilization of phosphate activators that require lower production energy relative to silicate-containing activators. However, the higher cost of phosphate activators may confine the applications of SAP geopolymers in some exquisite or special fields.
121 citations
TL;DR: In this article, a review of the current progress in pseudocapacitive electrode materials, fabrication techniques and new materials for electric double layer capacitor, and different flexible substrates are highlighted.
Abstract: Flexible supercapacitors are highly attractive for the large number of emerging portable lightweight consumer devices. The novelty of a flexible supercapacitor is the incorporation of flexible electrode or substrate material to combine structural flexibility with the inherently high power density of supercapacitors. Flexible supercapacitors can use non-Faradaic energy storage process as seen in the electric double layer capacitor type or a Faradaic mechanism as seen in the pseudocapacitors. In this review, we account the current progress in pseudocapacitive electrode materials, fabrication techniques and new materials for electric double layer capacitor, and different flexible substrates. Future directions in developing new materials towards improved energy density and cost-effectiveness of the flexible supercapacitors and their usage in combination with lithium-ion batteries are highlighted.
113 citations
TL;DR: In this article, the synthesis, properties, and applications of tungsten-oxide-based nanomaterials as a new type of photothermal material are reviewed, and promising insights into this rapidly growing field that may inspire additional research leading to practical applications.
Abstract: Among several active photothermal nanomaterials, tungsten-oxide-based materials have received considerable attention recently because of their ability to absorb near-infrared (NIR) light and their efficient light-to-heat conversion properties. In addition, tungsten-oxide-based materials have an unusual oxygen defect structure and strong local surface plasma resonance (LSPR), which offers strong photoabsorption in a broad wavelength range of the NIR region. In the past, several light-absorbing nanomaterials such as noble metals, polymeric materials, and other inorganic nanomaterials were of interest for their use in photothermal therapy for cancer treatment. In this study, we review the synthesis, properties, and applications of tungsten-oxide-based nanomaterials as a new type of photothermal material. The basic ideas behind photothermal nanomaterial development as well as the factors that influence their structural designs are also discussed in this study. In addition, recent progress in various fields such as NIR light-shielding, pyroelectric, water evaporation, photocatalysis, gas sensors, and energy-related applications for WO3-x- and MxWO3-based nanomaterials (including their hybrids) are highlighted. Finally, this review presents promising insights into this rapidly growing field that may inspire additional research leading to practical applications.
109 citations
TL;DR: The main applications of 3D-printed HAp scaffolds in bone tissue engineering are presented and discussed and the most recent achievements towards the development and testing of multifunctional HAp-based systems combining multiple properties for advanced therapy are emphasized.
Abstract: Hydroxyapatite (HAp) has been considered for decades an ideal biomaterial for bone repair due to its compositional and crystallographic similarity to bio-apatites in hard tissues. However, fabrication of porous HAp acting as a template (scaffold) for supporting bone regeneration and growth has been a challenge to biomaterials scientists. The introduction of additive manufacturing technologies, which provide the advantages of a relatively fast, precise, controllable and potentially scalable fabrication process, has opened new horizons in the field of bioceramic scaffolds. This review focuses on 3D-printed HAp scaffolds and related composite systems, where the calcium phosphate phase is combined with other ceramics or polymers improving the mechanical properties and/or imparting special extra-functionalities. The main applications of 3D-printed HAp scaffolds in bone tissue engineering are presented and discussed; furthermore, this review also emphasizes the most recent achievements towards the development and testing of multifunctional HAp-based systems combining multiple properties for advanced therapy (e.g. bone regeneration, antibacterial effect, angiogenesis and cancer treatment).
TL;DR: In this article, a review summarizes some of the recent approaches considered in our research group for the preparation of efficient catalysts for the production of hydrogen via dehydrogenation of formic acid by using Pd-based heterogeneous catalysts supported on carbon or carbon-containing materials.
Abstract: The urgency of finding clean energy sources is nowadays latent and the role of hydrogen in the future energy scenario is well-recognized. However, there are still various barriers that limit the widespread utilization of hydrogen, which are mainly related to its storage and transportation. Chemical hydrogen storage stands out as a suitable alternative to those traditional physical storage methods and formic acid holds tremendous promise within the molecules studied so far. This review summarizes some of the recent approaches considered in our research group for the preparation of efficient catalysts for the production of hydrogen via dehydrogenation of formic acid by using Pd-based heterogeneous catalysts supported on carbon or carbon-containing materials. Several routes were considered to attain efficient catalysts, covering from the optimization of the size and composition of the nanoparticles to the modulation of important features of the support, such as the porous texture and nitrogen doping level.
TL;DR: In this article, the attenuation performance of metaconcrete specimens characterized by a lattice-like pattern of bi-material resonant inclusions was verified through nondestructive transmission tests spanning the sonic range of frequencies.
Abstract: The attenuation performance of metaconcrete specimens characterized by a lattice-like pattern of bi-material resonant inclusions was verified through nondestructive transmission tests spanning the sonic range of frequencies. Seven cubic specimens of metaconcrete with regularly disposed resonant inclusions have been cast from a standard concrete matrix. Inclusions were regularly spaced and symmetrically disposed in a three-dimensional setting. Specimens differ in terms of inclusion spacing, controlled by varying the number of inclusions (0, 8, 27, and 64) and the cement cover. Three-month cured specimens have been tested along the three symmetry axes, under a sinusoidal excitation with four linearly variable frequency sweeping ranges centered at the eigenfrequencies of the inclusions, to assess the relevance of inclusion packing and arrangement on the dynamic behavior of metaconcrete. With respect to the plain concrete specimen, all engineered specimens showed a marked attenuation of the transmitted signal at a frequency close or very close to the theoretical eigenfrequency of the resonant inclusion. The attenuation was weakly dependent on the density of the inclusions and apparently not affected by interspacing, cement cover, and direction of the excitation along the axes of the specimen. Experimental results confirmed the behavior of metaconcrete as predicted by theoretical investigations, and further proved that the attenuation properties of metaconcrete are due to the resonant behavior of the inclusions.
TL;DR: In this paper, the authors analyzed the toughness of polylactic acid/polycaprolactone (PLA/PCL) blends with respect to the PCL particle size, PLA matrix crystallinity, and presence of a compatibilizer.
Abstract: Results of the studies dealing with the toughness of polylactic acid/polycaprolactone (PLA/PCL) blends are analyzed with respect to the PCL particle size, PLA matrix crystallinity, and presence of a compatibilizer. It is shown that a high toughness or even »super-toughness« of PLA/PCL blends without a compatibilizer can be achieved for blends with the proper size of PCL particles. Nevertheless, the window for obtaining the super-tough PLA/PCL blends is quite narrow, as the final impact strength is very sensitive to multiple parameters: namely the blend composition, PLA matrix crystallinity, and PCL particle size. Available literature data suggest that the optimal composition for PLA/PCL blends is around 80/20 (w/w). The PLA/PCL(80/20) blends keep high stiffness of PLA matrix and the concentration of PCL particles is sufficient to achieve high toughness. The PLA/PCL(80/20) blends with low-crystallinity PLA matrix (below ca 10 %) exhibit the highest toughness for bigger PCL particles (weight average diameter above 1 μm), while the blends with high-crystallinity PLA matrix (above ca 30 %) exhibit the highest toughness for smaller PCL particles (weight average diameter below 0.5 μm). The addition of a compatibilizer may improve the toughness only on condition that it helps to achieve a suitable particle size. The toughness of both non-compatibilized and compatibilized PLA/PCL blends with optimized morphology can be more than 15 times higher in comparison with neat PLA.
TL;DR: The nonvolatility, structure-tunability and high CO2 uptake capacity render ionic liquids (ILs) the most exciting materials for the carbon dioxide (CO2) capture and fixation to value-added chemical compounds.
Abstract: The nonvolatility, structure-tunability and high CO2 uptake capacity render ionic liquids (ILs) the most exciting materials for the carbon dioxide (CO2) capture and fixation to value-added chemical ...
TL;DR: In this article, a comprehensive review of the effect of nanostructured energy materials on the electrochemical properties of carbon nanotube-based fibers is presented, which covers the various compositions, spinning and fabrication conditions on the performance of wearable energy storage.
Abstract: Energy storage is a key requirement for the emerging wearable technologies. Recent progress in this direction includes the development of fiber based batteries and capacitors and even some examples of such fibers incorporated into prototype textiles. Herein we discuss the advantages of using the wet-spinning process to create nanostructured carbon based materials as wearable energy storage. The ability to control the physical, mechanical, electrical and electrochemical properties of carbon nanotube based fibers holds great promise to develop smart polymeric structure as an energy storing materials including fibers and textiles. This is the first comprehensive review to discuss effect of nanostructured energy materials on the electrochemical properties of carbon nanotube based fibers which covers the various compositions, spinning and fabrication conditions on the performance of wearable energy storage.
TL;DR: In this article, a review of the literature related to efflorescence in geopolymers is presented, where the authors highlight that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control efforescence rate and changes in mechanical behavior.
Abstract: Even with the rapid development of the alkali-activated cement (AAC) technology in the past few years, some phenomena still needs to be better understood, that may alter the durability of the material. In many industrial uses and laboratory researches the formation of the salts on the surface alkali-activated type cements was observed, which was identified as efflorescence. This occurs due to the presence of an alkali transported in contact with the humidity and CO2 environment. It may present externally from the formation of salts on the surface and internally with the carbonation of the alkalis in capillary pores. The effects of efflorescence on the material in use, as well as all factors that can influence its formation are not yet fully understood or reported. The search for papers was conducted using the search words efflorescence and geopolymer/alkali-activated, combined in the electronic data base. Due to the limited quantity of papers published related to efflorescence in geopolymers, the review was complemented using papers that discuss this behavior in Portland cement (PC) and based on the main properties that can influence the formation of efflorescence. In this paper, to understand the nature of efflorescence, upon which proper methods of minimizing of this issue can be based, the following aspects are discussed and re-examined: (1) the development of efflorescence's in PC concrete, (2) the role of alkalis in AACs, (3) efflorescence in AACs, and (4) effect from a physical and microstructural point of view of efflorescence's on the ACCs. This paper highlights that the nature of the pore structure and the design parameters (such as alkali concentration, presence of soluble silicates, and water content in the activator) are the two most important factors that control efflorescence rate and changes in mechanical behavior. However, the stability of the alkalis and their relationship with the formed gel, which are determining factors in the formation of efflorescence, remain not completely understood. In the same way, the effect of efflorescence in tensile strength and shrinkage needs to be evaluated.
TL;DR: Coupled cluster theory as discussed by the authors provides a compelling framework of approximate infinite-order perturbation theory in the form of an exponential of cluster operators describing the true quantum many-body effects of the electronic wave function at a computational cost that scales polynomially with system size.
Abstract: The workhorse method of computational materials science is undeniably density functional theory in the Kohn-Sham framework of approximate exchange and correlation energy functionals. However, the need for highly accurate predictions of ground and excited state properties in materials science motivates the further development and exploration of alternative as well as complementary techniques. Among these alternative approaches, quantum chemical wavefunction based theories and in particular coupled cluster theory hold the promise to fill a gap in the toolbox of computational materials scientists. Coupled cluster (CC) theory provides a compelling framework of approximate infinite-order perturbation theory in the form of an exponential of cluster operators describing the true quantum many-body effects of the electronic wave function at a computational cost that, despite being significantly more expensive than DFT, scales polynomially with system size. The hierarchy of size-extensive approximate methods established in the framework of CC theory achieves systematic improvability for many materials properties. This is in contrast to currently available density functionals that often suffer from uncontrolled approximations that limit the accuracy in the prediction of materials properties. In this tutorial-style review we will introduce basic concepts of coupled cluster theory and recent developments that increase its computational efficiency for calculations of molecules, solids and materials in general. We will touch upon the connection between coupled cluster theory and the random-phase approximation to bridge the gap between traditional quantum chemistry and many-body Green’s function theories that are widely-used in the field of solid state physics. We will discuss various approaches to improve the computational performance without compromising accuracy. These approaches include large-scale parallel design as well as techniques that reduce the prefactor of the computational complexity. A central part of this article discusses the convergence of calculated properties to the thermodynamic limit which is of significant importance for reliable predictions of materials properties and constitutes an additional challenge compared to calculations of large molecules. Furthermore we mention technical aspects of computer code implementations of periodic coupled cluster theories in different numerical frameworks of the one-electron orbital basis; the projector-augmented-wave formalism using a plane wave basis set and the numeric atom-centered-orbital with resolution-of-identity.
TL;DR: In this article, an approach preventing contact to ambient air during transfer from liquid environment for electrochemical treatment to UHV environment for surface analysis by X-Ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry was applied to study the mechanisms of Cr and Mo enrichments in the passive oxide film formed on 316L austenitic stainless steel.
Abstract: An approach preventing contact to ambient air during transfer from liquid environment for electrochemical treatment to UHV environment for surface analysis by X-Ray Photoelectron Spectroscopy and Time-of-Flight Secondary Ion Mass Spectrometry was applied to study the mechanisms of Cr and Mo enrichments in the passive oxide film formed on 316L austenitic stainless steel. Starting from the air-formed native oxide-covered surface, exposures were conducted in aqueous sulfuric acid solution first at open circuit potential and then under anodic polarization in the passive range. At open circuit potential the thickness of the bi-layered oxide film was observed to decrease and the enrichments of both Cr(III) and Mo, mostly Mo(VI), to markedly increase as well as the film hydroxylation. This is due to preferential dissolution of the Fe(III) oxide/hydroxide, not compensated by oxide growth in the absence of an electric field established by anodic polarization. Anodic polarization in the passive domain causes the bi-layered structure of the oxide film to re-grow by oxidation of iron, chromium and molybdenum, without impacting the Cr enrichment and only slightly mitigating the Mo enrichment. De-hydroxylation of the inner layer is also promoted upon anodic polarization. These results show that the treatment of the surface oxide film in acid solution at open circuit potential enhances Cr and Mo enrichments and promotes hydroxylation. Passivation by anodic polarization allows dehydroxylation, yielding more Cr oxide, without markedly affecting the Mo enrichment, also beneficial for the corrosion resistance.
TL;DR: In this article, the authors classified the mainstream technologies into two categories: top-down and bottom-up, and discussed the challenges for both types of technologies, including costs, synthesis and choice of ink for printing technologies, the limited choice of metal for bottom-down technologies, and the mass production of these methods.
Abstract: Printed electronic technologies draw tremendous attention worldwide due to their ability to surpass the limitations of traditional high-cost electronics based on rigid silicon and manufacture various devices on flexible substrates. As a critical component of flexible electronics, electrodes fabricated on soft, bendable and stretchable substrates are of great importance. Based on the fabrication process, this paper classifies the mainstream technologies into two categories: top-down and bottom-up. To be specific, the top-down technology includes physical evaporation methods, printing technologies and soft lithography and the bottom-up technology involves polymer-assisted-metal-deposition methods and ion-exchange methods, respectively. In contrast to the top-down technology that transfers the functional ink onto the substrate directly, the bottom-up methods achieve great improvement in the adhesion between the substrates and the metal electrodes. In the end of the paper, the challenges for top-down technologies, including costs, synthesis and choice of ink for printing technologies, the limited choice of metal for bottom-up technologies and the mass production of these methods are also discussed.
TL;DR: A quantitative comparison between segmentation results indicates that the 3D U-Net performs best among the considered U-nets, where the latter was trained at a lower resolution due to memory limitations.
Abstract: In this paper, various kinds of applications are presented, in which tomographic image data depicting microstructures of materials are semantically segmented by combining machine learning methods and conventional image processing steps. The main focus of this paper is the grain-wise segmentation of time-resolved CT data of an AlCu specimen which was obtained in between several Ostwald ripening steps. The poorly visible grain boundaries in 3D CT data were enhanced using convolutional neural networks (CNNs). The CNN architectures considered in this paper are a 2D U-Net, a multichannel 2D U-Net and a 3D U-Net where the latter was trained at a lower resolution due to memory limitations. For training the CNNs, ground truth information was derived from 3D X-ray diffraction (3DXRD) measurements. The grain boundary images enhanced by the CNNs were then segmented using a marker-based watershed algorithm with an additional postprocessing step for reducing oversegmentation. The segmentation results obtained by this procedure were quantitatively compared to ground truth information derived by the 3DXRD measurements. A quantitative comparison between segmentation results indicates that the 3D U-Net performs best among the considered U-Net architectures. Additionally, a scenario, in which "ground truth" data is only available in one time step, is considered. Therefore, a CNN was trained only with CT and 3DXRD data from the last measured time step. The trained network and the image processing steps were then applied to the entire series of CT scans. The resulting segmentations exhibited a similar quality compared to those obtained by the network which was trained with the entire series of CT scans.
TL;DR: In this paper, the effects of partial fly ash substitution in a series of alkali-activated concrete based on a high-MgO blast furnace slag BFS were investigated.
Abstract: The aim of this study was to determine the effects of partial fly ash substitution in to a series of alkali-activated concrete based on a high-MgO blast furnace slag BFS. Mixes were activated with ...
TL;DR: In this paper, the effect of GTA crosslinking and gelatin content on the biological response of SF/gelatin scaffolds was evaluated using 3T3 mouse fibroblast.
Abstract: Bombyx mori silk fibroin (SF) /gelatin nanofibre mats with different blend ratios of 100/0, 90/10 and 70/30 were prepared by electrospinning and crosslinked with glutaraldehyde (GTA) vapour at room temperature. GTA was shown to induce the conformational transition of SFs from random coils to β-sheets along with increasing nanofibre diameters with the addition of gelatin into SFs. It was found that by increasing the gelatin content, crosslinking degree was enhanced from 34% for pure SF nanofibre mats to 43% for SF/gelatin counterparts at the blend ratio of 70/30, which directly affected mechanical properties, porosity, and water uptake capacity (WUC) of prepared nanofibre mats. The addition of 10 and 30 wt% gelatin into SFs improved tensile strengths of SF/gelatin nanofibre mats by 10 and 27% along with significant increases in Young’s modulus by 1.1 and 1.3 times, respectively, as opposed to plain SF counterparts. However, both porosity and WUC were found to decrease from 62 and 405% for pristine SF nanofibre mats to 47% and 232% for SF/gelatin counterparts at the blend ratio of 70/30 accordingly. To further evaluate the combined effect of GTA crosslinking and gelatin content on biological response of SF/gelatin scaffolds, the proliferation assay using 3T3 mouse fibroblast was conducted. In comparison with pure SFs, cell proliferation rate was lower for SF/gelatin constructs, which declined when the gelatin content increased. These results indicated that the adverse effect of GTA crosslinking on cell response may be ascribed to imposed changes in morphology and physiochemical properties of SF/gelatin nanofibre mats. Although crosslinking could be used to improve mechanical properties of nanofibre mats, it reduced their capacity to support the cell activity. GTA optimisation is required to further modulate the physico-chemical properties of SF/gelatin nanofibre mats in order to obtain stable materials with favourable bioactive properties and promote cellular responses for tissue engineering applications.
TL;DR: In this paper, the authors acknowledge the financial support by the Ministry of Economy and Competitiveness of Spain (MINECO) and FEDER (CTQ2015-66080-R MINECO/FEDER and MAT2016-76595-R).
Abstract: We want to acknowledge the financial support by the Ministry of Economy and Competitiveness of Spain (MINECO) and FEDER (CTQ2015-66080-R MINECO/FEDER and MAT2016-76595-R).
TL;DR: A review of the phylogeny of MXenes materials in recent years, mainly focusing on the synthesis process and environmental stability, is presented in this article, where the synthesis methods and processing environment of the MXenes, which are closely strictly to the microstructure, surface chemistry, and electronic properties, have attracted great attention.
Abstract: In the past decade, MXenes family have undergone considerable development and have been widely investigated in various research fields, relying on their excellent physicochemical properties. Benefiting from the increasingly versatile preparation methods and the continued discovery of new members, their large-scale application has already been underway, with energy storage fields including supercapacitors and batteries leading. The synthesis methods and processing environment of MXenes, which are closely strictly to the microstructure, surface chemistry, and electronic properties, have attracted great attention. In this review, we review the phylogeny of MXenes materials in recent years, mainly focusing on the synthesis process and environmental stability.
TL;DR: This work presents here a method to construct, based on data, automatic corrections to existing models, particularly large strain (visco-)hyperelasticity, and focuses on solid mechanics.
Abstract: Unveiling physical laws from data is seen as the ultimate sign of human intelligence. While there is a growing interest in this sense around the machine learning community, some recent works have attempted to simply substitute physical laws by data. We believe that getting rid of centuries of scientific knowledge is simply nonsense. There are models whose validity and usefulness is out of any doubt, so try to substitute them by data seems to be a waste of knowledge. While it is true that fitting well-known physical laws to experimental data is sometimes a painful process, a good theory continues to be practical and provide useful insights to interpret the phenomena taking place. That is why we present here a method to construct, based on data, automatic corrections to existing models. Emphasis is put in the correct thermodynamic character of these corrections, so as to avoid violations of first principles such as the laws of thermodynamics. These corrections are sought under the umbrella of the GENERIC framework (Grmela and Oettinger, 1997), a generalization of Hamiltonian mechanics to non-equilibrium thermodynamics. This framework ensures the satisfaction of the first and second laws of thermodynamics, while providing a very appealing context for the proposed automated correction of existing laws. In this work we focus on solid mechanics, particularly large strain (visco-)hyperelasticity.
TL;DR: In this paper, the fabrication of mixed structure of ZnO nanorod on SnO2 thin film via spray pyrolysis followed by thermal annealing and their gas sensing properties is reported.
Abstract: This work reports the fabrication of mixed structure of ZnO nanorod on SnO2 thin film via spray pyrolysis followed by thermal annealing and their gas sensing properties. ZnO/SnO2 nanostructures are successfully prepared on a gold interdigitated alumina substrate by spraying varying mixed precursor concentrations of zinc acetate and tin (IV) chloride pentahydrate solutions in ethanol and thermal annealing. The morphology of the nanostructures is controlled by tailoring the Zn:Sn ratio in the precursor solution mixture. Unique ZnO crystals and ZnO nanorods are observed under a field emission scanning electron microscopy (FESEM) when the Zn/Sn ratio in the precursor solution is in between 13:7 to 17:3 after thermal annealing. The fabricated nanostructures are tested for ethanol, methane and hydrogen in air ambient for various gas concentrations ranging from 25 ppm to 400 ppm and the effect of fabrication conditions on the sensitivity and selectivity are studied. Among the nanostructure sensors studied, the film fabricated with molar ratio of Zn/Sn =3:1 shows better sensitivity and selectivity to ethanol due to high sensing surface area of nanorod. The response to 25 ppm ethanol is found to be as high as 50 at an operating temperature of 400oC.
TL;DR: The authors provides a comprehensive perspective on the oxygen defects and surface chemistry of reducible oxides based on two-dimensional materials and discusses some of the main challenges and opportunities in this important field of research.
Abstract: The magic reducible oxides properties likely are mainly due to the presence of oxygen defects and their rich surface chemistry, which provide a rational pathway to the emergent of entirely new properties. Although significant progress has performed in the last years, nevertheless, it can be stated that they are not fully understood at the nanoscale level so far. This review provides a comprehensive perspective on the oxygen defects and surface chemistry of reducible oxides based on two-dimensional materials. Thus, in this perspective, we intend to discuss some of the main challenges and opportunities in this important field of research in materials chemistry and engineering. From a practical standpoint, chemical insights from defect-engineering may provide vital clues for improving synthetic methods and understanding fundamental nanoscale properties, driving innovation in the field of crystalline materials.
TL;DR: In this paper, a transparent cellulose nanowhisker (CNW)/ graphene nanoplatelet (GN) composite films were produced via sonication mixing and solution casting methods.
Abstract: Transparent cellulose nanowhisker (CNW)/ graphene nanoplatelet (GN) composite films were produced via sonication mixing and solution casting methods. Such composite films exhibited improved thermal, electrical and mechanical properties. The material morphologies and microstructures were examined using scanning electronic microscopy (SEM), X-ray diffraction (XRD) analysis and Raman spectroscopy. Strong interaction was detected when CNWs were randomly attached onto graphene sheets, as evidenced by SEM images obtained in this study. In particular, the addition of GNs into CNWs had significant effect on the thermal behavior of composite films. The melting temperature (Tm) and initial thermal decomposition temperature (Tid) of CNW films were both increased by 23.2, 29.3, 26.3oC, and 70.2, 88.4, 87.8oC with the inclusions of 0.1, 0.25 and 0.5 wt% GNs, respectively. The electrical conductivity of composite films was enhanced in a monotonically increasing manner with the maximum level of 4.0×10-5 S/m detected at the GN content of 0.5 wt%. Their tensile strength was also improved by maximum 33.7% when increasing the GN content up to 0.25 wt% as opposed to that of CNW films. Such CNW/GN composite films can be potentially used in green anti-static and electronic packaging applications.
TL;DR: In this paper, a review article surveys the latest progress in engineered metal oxide nanostructure arrays, i.e., nanoarrays, for advanced chemical sensors' design and application.
Abstract: In recent years, engineered nanostructure assemblies such as nanowire arrays have attracted much research attention due to their unique chemical and functional characteristics collectively. The engineered nano-assemblies usually carry the characteristics distinct from bulk as a result of a size effect in their comprised elemental building blocks. The nanoscale size induced high surface-to-volume ratio is a fundamental attribute responsible for various chemical and physical properties required in various technologically important applications such as catalysts and sensors. This review article surveys the latest progress in engineered metal oxide nanostructure arrays, i.e., nanoarrays, for advanced chemical sensors’ design and application. It starts with an overview of gaseous chemical sensors followed by surveys of various fabrication methods and routes for metal oxide nanoarrays. Different sensing modes and corresponding applications have been highlighted in the mixed gaseous chemical sensing, which provides new approaches and perspectives to meet the challenges of selective gas sensing, such as the cross-sensitivity and inter-correlation of multiple sensing signals.