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Materials, Volume 12, Issue 4 (February-2 2019) – 134 articles

Cover Story (view full-size image): Aqueous suspensions of soda lime glass and coal fly ash were activated with NaOH (3M). Despite the relatively low molarity (compared to geopolymer-yielding mixtures), the suspensions underwent gelation and presented a marked pseudoplastic behaviour. A significant foaming could be achieved by air incorporation, in turn resulting from intensive mechanical stirring (with the help of a surfactant), before complete hardening. Dried foams were later transformed, by heat treatment at 700-900 °C, into porous glass-ceramics, exhibiting a remarkable crushing strength (6 MPa, with a porosity of about 70%) and a low thermal conductivity, coupled with good stabilization of pollutants from the starting waste. View this paper.
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9 pages, 16000 KiB  
Article
Effects of High-Temperature Storage on the Elasticity Modulus of an Epoxy Molding Compound
by Ruifeng Li, Daoguo Yang, Ping Zhang, Fanfan Niu, Miao Cai and Guoqi Zhang
Materials 2019, 12(4), 684; https://doi.org/10.3390/ma12040684 - 25 Feb 2019
Cited by 16 | Viewed by 6283
Abstract
Changes in the elasticity modulus of an epoxy molding compound (EMC), an electronic packaging polymer, under high-temperature air storage conditions, are discussed in this study. The elasticity modulus of EMC had two different compositions (different filling contents) under different temperatures (175, 200, and [...] Read more.
Changes in the elasticity modulus of an epoxy molding compound (EMC), an electronic packaging polymer, under high-temperature air storage conditions, are discussed in this study. The elasticity modulus of EMC had two different compositions (different filling contents) under different temperatures (175, 200, and 225 °C) and aging times (100, 500, and 1500 h), which were analyzed by using dynamic mechanic analysis technology. The results revealed that the elasticity modulus increased in the thermal aging process, with an increase in the temperature and the aging time. The increments of the glassy and rubbery states were similar. However, the growing rate was significantly different, and the growth of the rubbery state was significantly higher than that of the glassy state. The filling content influenced the degree of aging of the materials significantly. At a low filling content, long-term aging under high temperatures completely changed the material structure, and the mechanical properties of the polymer were reduced. Full article
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8 pages, 1548 KiB  
Article
Release of Cationic Drugs from Charcoal
by Chiara Di Ruocco, Maria Rosaria Acocella and Gaetano Guerra
Materials 2019, 12(4), 683; https://doi.org/10.3390/ma12040683 - 25 Feb 2019
Cited by 2 | Viewed by 3790
Abstract
The goal of this research is to improve preparation of charcoal adducts in a manner suitable for cationic drug release, possibly using an eco-friendly procedure. Charcoal, widely commercialized for human ingestion, is oxidized by hydrogen peroxide in mild conditions. Adducts of a cationic [...] Read more.
The goal of this research is to improve preparation of charcoal adducts in a manner suitable for cationic drug release, possibly using an eco-friendly procedure. Charcoal, widely commercialized for human ingestion, is oxidized by hydrogen peroxide in mild conditions. Adducts of a cationic drug (lidocaine hydrochloride, a medication used as local anesthetic) with charcoal are prepared after basification of charcoal and characterized mainly by elemental analysis, wide-angle X-ray diffraction, infrared spectroscopy and thermogravimetry. The drug in the prepared adducts is present in amount close to 30% by weight and can be readily released to both neutral and acidic aqueous solutions. Cation release, as studied by UV spectra of aqueous solutions, is faster in acidic solutions and is faster than for adducts with graphite oxide, which can be prepared only in harsh conditions. Full article
(This article belongs to the Special Issue Graphene Oxide: Synthesis, Reduction, and Frontier Applications)
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15 pages, 3344 KiB  
Article
Atomic Layer Deposited TiO2 and Al2O3 Thin Films as Coatings for Aluminum Food Packaging Application
by Vanessa Dias, Homero Maciel, Mariana Fraga, Anderson O. Lobo, Rodrigo Pessoa and Fernanda R. Marciano
Materials 2019, 12(4), 682; https://doi.org/10.3390/ma12040682 - 25 Feb 2019
Cited by 36 | Viewed by 7338
Abstract
Titanium dioxide (TiO2) and aluminum oxide (Al2O3) coatings have been investigated in a wide range of bio-applications due to their biodegradation and biocompatibility properties, that are key parameters for their use in the food packaging and biomedical [...] Read more.
Titanium dioxide (TiO2) and aluminum oxide (Al2O3) coatings have been investigated in a wide range of bio-applications due to their biodegradation and biocompatibility properties, that are key parameters for their use in the food packaging and biomedical devices fields. The present study evaluates and compares the electrochemical behavior of the non-coated, commercial resin-coated, TiO2-coated and Al2O3-coated aluminum in commercial beer electrolyte. For this, TiO2 and Al2O3 thin films were deposited on aluminum (Al) substrates using atomic layer deposition (ALD). The evaluation of the corrosion barrier layer properties was performed by linear sweep voltammetry (LSV) during 10 min and electrochemical impedance spectroscopy (EIS). In addition, profilometry, grazing incidence X-ray diffractometry (GIXRD), scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FT-IR) analyses were performed to investigate the physical and chemical properties of the pristine and / or corroded samples. TiO2 and Al2O3 films presented an amorphous structure, a morphology that follows Al substrate surface, and a thickness of around 100 nm. Analysis of LSV data showed that ALD coatings promoted a considerable increase in corrosion barrier efficiency being 86.3% for TiO2-coated Al and 80% for Al2O3-coated Al in comparison with 7.1% of commercial resin-coated Al. This is mainly due to the lower electrochemical porosity, 11.4% for TiO2-coated Al and 20.4% for Al2O3-coated Al in comparison with 96% of the resin-coated Al, i.e. an increase of up to twofold in the protection of Al when coated with TiO2 compared to Al2O3. The EIS results allow us to complement the discussions about the reduced corrosion barrier efficiency of the Al2O3 film for beer electrolyte once SEM and FT-IR analyzes did not show drastic changes in both investigated ALD films after the corrosion assays. The above results indicate that ALD TiO2 and Al2O3 films may be a viable alternative to replace the synthetic resin coatings frequently used in aluminum cans of use in the food industry. Full article
(This article belongs to the Special Issue Selected Papers from NanoBio Symposium- XVII B-MRS Meeting)
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15 pages, 5759 KiB  
Article
Numerical Study on the Potential of Cavitation Damage in a Lead–Bismuth Eutectic Spallation Target
by Tao Wan, Takashi Naoe, Hiroyuki Kogawa, Masatoshi Futakawa, Hironari Obayashi and Toshinobu Sasa
Materials 2019, 12(4), 681; https://doi.org/10.3390/ma12040681 - 25 Feb 2019
Cited by 3 | Viewed by 3322
Abstract
To perform basic Research and Development for future Accelerator-driven Systems (ADSs), Japan Proton Accelerator Research Complex (J-PARC) will construct an ADS target test facility. A Lead–Bismuth Eutectic (LBE) spallation target will be installed in the target test facility and bombarded by pulsed proton [...] Read more.
To perform basic Research and Development for future Accelerator-driven Systems (ADSs), Japan Proton Accelerator Research Complex (J-PARC) will construct an ADS target test facility. A Lead–Bismuth Eutectic (LBE) spallation target will be installed in the target test facility and bombarded by pulsed proton beams (250 kW, 400 MeV, 25 Hz, and 0.5 ms pulse duration). To realize the LBE spallation target, cavitation damage due to pressure changes in the liquid metal should be determined, preliminarily, because such damage is considered to be very critical, from the viewpoint of target safety and lifetime. In this study, cavitation damage due to pressure waves caused by pulsed proton beam injection and turbulent liquid metal flow, were studied, numerically, from the viewpoint of single cavitation bubble dynamics. Specifically, the threshold of cavitation and effects of flow speed fluctuation on cavitation bubble dynamics, in an orifice structure, were investigated in the present work. The results showed that the LBE spallation target did not undergo cavitation damage, under normal nominal operation conditions, mainly because of the long pulse duration of the pulsed proton beam and the low liquid metal flow velocity. Nevertheless, the possibility of cavitation damage in the orifice structure, under certain extreme transient LBE flow conditions, cannot be neglected. Full article
(This article belongs to the Special Issue Damage and Mechanical Properties of Steels)
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26 pages, 12606 KiB  
Article
Unified Theory for Flexural Strengthening of Masonry with Composites
by Giancarlo Ramaglia, Francesco Fabbrocino, Gian Piero Lignola and Andrea Prota
Materials 2019, 12(4), 680; https://doi.org/10.3390/ma12040680 - 25 Feb 2019
Cited by 14 | Viewed by 3425
Abstract
Recent calamitous events have shown the fragility of the existing masonry buildings. Many of them are heritage structures, such as churches and monumental buildings. Therefore, optimized strengthening strategies are necessary. Experimental studies performed on masonry elements strengthened with composite systems have shown the [...] Read more.
Recent calamitous events have shown the fragility of the existing masonry buildings. Many of them are heritage structures, such as churches and monumental buildings. Therefore, optimized strengthening strategies are necessary. Experimental studies performed on masonry elements strengthened with composite systems have shown the performance of these materials. However, further development is necessary to optimize the intervention strategies. In fact, due to the lack of general validity models, the design is usually based on prescriptive approaches according to manufacturers’ broad instructions, often producing systems with low efficiency and overestimations of the amount of reinforcement. In this paper a generalized approach is proposed to assess the flexural behavior of masonry sections strengthened with composites. The proposed theory has allowed performance of a sensitivity analysis assessing the impact both of the mechanical parameters of masonry and of the strengthening system. In particular, the impact of several constitutive relationships of composites (linear, bilinear, or trilinear) have been evaluated in terms of ultimate behavior of the strengthened masonry. For strengthening systems more compatible with the masonry substrate, the form of the stress–strain relationship becomes a key aspect. For such cases, the modeling of the reinforcement plays a fundamental role and the form of the relationship is strongly correlated to the type of reinforcement selected, e.g., organic versus inorganic matrix. Full article
(This article belongs to the Special Issue Fiber Reinforced Polymers for Structural Strengthening)
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16 pages, 11684 KiB  
Article
Investigation on Cf/PyC Interfacial Properties of C/C Composites by the Molecular Dynamics Simulation Method
by Yuan Zhou, Tianyuan Ye, Long Ma, Zixing Lu, Zhenyu Yang and Shouwen Liu
Materials 2019, 12(4), 679; https://doi.org/10.3390/ma12040679 - 25 Feb 2019
Cited by 7 | Viewed by 3325
Abstract
In this paper, a molecular dynamics (MD) simulation model of carbon-fiber/pyrolytic-carbon (Cf/PyC) interphase in carbon/carbon (C/C) composites manufactured by the chemical vapor phase infiltration (CVI) process was established based on microscopic observation results. By using the MD simulation method, the mechanical [...] Read more.
In this paper, a molecular dynamics (MD) simulation model of carbon-fiber/pyrolytic-carbon (Cf/PyC) interphase in carbon/carbon (C/C) composites manufactured by the chemical vapor phase infiltration (CVI) process was established based on microscopic observation results. By using the MD simulation method, the mechanical properties of the Cf/PyC interphase under tangential shear and a normal tensile load were studied, respectively. Meanwhile, the deformation and failure mechanisms of the interphase were investigated with different sizes of the average length L ¯ a of fiber surface sheets. The empirical formula of the interfacial modulus and strength with the change of L ¯ a was obtained as well. The shear properties of the isotropic pyrolysis carbon (IPyC) matrix were also presented by MD simulation. Finally, the mechanical properties obtained by the MD simulation were substituted into the cohesive force model, and a fiber ejection test of the C/C composite was simulated by the finite element analysis (FEA) method. The simulation results were in good agreement with the experimental ones. The MD simulation results show that the shear performance of the Cf/PyC interphase is relatively higher when L ¯ a is small due to the effects of non-in-plane shear, the barrier between crystals, and long sheet folding. On the other hand, the size of L ¯ a has no obvious influence on the interfacial normal tensile mechanical properties. Full article
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13 pages, 3521 KiB  
Article
Dense Sm and Mn Co-Doped BaTiO3 Ceramics with High Permittivity
by Qiaoli Liu, Junwei Liu, Dayong Lu, Tingqu Li and Weitao Zheng
Materials 2019, 12(4), 678; https://doi.org/10.3390/ma12040678 - 25 Feb 2019
Cited by 29 | Viewed by 4533
Abstract
The structure, valence state, and dielectric properties of (Ba1−xSmx)(Ti0.99Mn0.01)O3 (BSTM) (x = 0.02‒0.07) ceramics prepared via a high temperature (1400 °C/12 h) solid state reaction were investigated. A homogeneous and dense microstructure [...] Read more.
The structure, valence state, and dielectric properties of (Ba1−xSmx)(Ti0.99Mn0.01)O3 (BSTM) (x = 0.02‒0.07) ceramics prepared via a high temperature (1400 °C/12 h) solid state reaction were investigated. A homogeneous and dense microstructure was observed in all samples. With increasing Sm content, the crystal structure changed from tetragonal (x ≤ 0.06) to cubic (x = 0.07) and unit cell volume (V0) decreased continuously, which was mainly due to the substitution of Ba2+ ions by smaller Sm3+ ions in the perovskite lattice. Electron paramagnetic resonance investigation revealed that Mn ions were reduced from high valence to low valence under the role of Sm3+ donor, and only Mn2+ ions were observed at x = 0.07. The Curie temperature (Tc) moved to lower values, from 105.5 down to 20.4 °C, and the x = 0.07 sample satisfied Y5V specification with high permittivity (ε′RT > 13,000) and low loss (tan δ < 0.03). Full article
(This article belongs to the Section Advanced Materials Characterization)
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13 pages, 23791 KiB  
Article
Theoretical Study of As2O3 Adsorption Mechanisms on CaO surface
by Yaming Fan, Qiyu Weng, Yuqun Zhuo, Songtao Dong, Pengbo Hu and Duanle Li
Materials 2019, 12(4), 677; https://doi.org/10.3390/ma12040677 - 25 Feb 2019
Cited by 30 | Viewed by 4487
Abstract
Emission of hazardous trace elements, especially arsenic from fossil fuel combustion, have become a major concern. Under an oxidizing atmosphere, most of the arsenic converts to gaseous As2O3. CaO has been proven effective in capturing As2O3 [...] Read more.
Emission of hazardous trace elements, especially arsenic from fossil fuel combustion, have become a major concern. Under an oxidizing atmosphere, most of the arsenic converts to gaseous As2O3. CaO has been proven effective in capturing As2O3. In this study, the mechanisms of As2O3 adsorption on CaO surface under O2 atmosphere were investigated by density functional theory (DFT) calculation. Stable physisorption and chemisorption structures and related reaction paths are determined; arsenite (AsO33−) is proven to be the form of adsorption products. Under the O2 atmosphere, the adsorption product is arsenate (AsO43−), while tricalcium orthoarsenate (Ca3As2O8) and dicalcium pyroarsenate (Ca2As2O7) are formed according to different adsorption structures. Full article
(This article belongs to the Special Issue Micro/Nano Materials for Clean Energy and Environment)
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8 pages, 2403 KiB  
Article
First-Principles Investigation of the Adsorption Behaviors of CH2O on BN, AlN, GaN, InN, BP, and P Monolayers
by Chuang Feng, Hongbo Qin, Daoguo Yang and Guoqi Zhang
Materials 2019, 12(4), 676; https://doi.org/10.3390/ma12040676 - 25 Feb 2019
Cited by 30 | Viewed by 4733
Abstract
CH2O is a common toxic gas molecule that can cause asthma and dermatitis in humans. In this study the adsorption behaviors of the CH2O adsorbed on the boron nitride (BN), aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), [...] Read more.
CH2O is a common toxic gas molecule that can cause asthma and dermatitis in humans. In this study the adsorption behaviors of the CH2O adsorbed on the boron nitride (BN), aluminum nitride (AlN), gallium nitride (GaN), indium nitride (InN), boron phosphide (BP), and phosphorus (P) monolayers were investigated using the first-principles method, and potential materials that could be used for detecting CH2O were identified. The gas adsorption energies, charge transfers and electronic properties of the gas adsorption systems have been calculated to study the gas adsorption behaviors of CH2O on these single-layer materials. The electronic characteristics of these materials, except for the BP monolayer, were observed to change after CH2O adsorption. For CH2O on the BN, GaN, BP, and P surfaces, the gas adsorption behaviors were considered to follow a physical trend, whereas CH2O was chemically adsorbed on the AlN and InN monolayers. Given their large gas adsorption energies and high charge transfers, the AlN, GaN, and InN monolayers are potential materials for CH2O detection using the charge transfer mechanism. Full article
(This article belongs to the Special Issue Fabrication of 1D and 2D Nanomaterials)
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8 pages, 2167 KiB  
Article
Laser-Assisted Thermal Imprinting of Microlens Arrays—Effects of Pressing Pressure and Pattern Size
by Keisuke Nagato, Yuki Yajima and Masayuki Nakao
Materials 2019, 12(4), 675; https://doi.org/10.3390/ma12040675 - 25 Feb 2019
Cited by 13 | Viewed by 4087
Abstract
Polymer films with nano- or microstructured surfaces have been widely applied to optical devices, bioplates, and printed electronics. Laser-assisted thermal imprinting (LATI), in which a laser directly heats the surfaces of a mold and a thermoplastic polymer, is one of the high-throughput methods [...] Read more.
Polymer films with nano- or microstructured surfaces have been widely applied to optical devices, bioplates, and printed electronics. Laser-assisted thermal imprinting (LATI), in which a laser directly heats the surfaces of a mold and a thermoplastic polymer, is one of the high-throughput methods of replicating nano- or microstructures on polymer films. Only the surfaces of the mold and polymer film are heated and cooled rapidly, therefore it is possible to replicate nano- or microstructures on polymer films more rapidly than by using conventional thermal nanoimprinting. In this study, microlens arrays (MLAs) were replicated on polymethylmethacrylate (PMMA) films using LATI, and the effects of the pressing pressure (10−50 MPa) and the pattern size (33- and 5-μm pitch) of the MLA on the filling ratio were investigated by analyzing a microlens replicated using different laser-irradiation times (0.1−2 ms). The filling ratio increased with increasing pressing pressure and laser-irradiation time in the replication of MLAs with varying sizes, while the flow of the PMMA varied with the pressing pressure and laser-irradiation time. It was found that during filling, the shape of the polymer cross-sectional surface demonstrated a double and single peak in the 33- and 5-μm-pitch patterns, respectively. This was because the depth of the heated area in the 33-μm-pitch pattern was smaller than the pattern size, whereas that of the 5-μm-pitch pattern was comparable to (or larger) than the pattern size. Full article
(This article belongs to the Special Issue Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties)
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17 pages, 8489 KiB  
Article
Solid-State Limited Nucleation of NiSi/SiC Core-Shell Nanowires by Hot-Wire Chemical Vapor Deposition
by Mahdi Alizadeh, Najwa binti Hamzan, Poh Choon Ooi, Muhammad Firdaus bin Omar, Chang Fu Dee and Boon Tong Goh
Materials 2019, 12(4), 674; https://doi.org/10.3390/ma12040674 - 24 Feb 2019
Cited by 6 | Viewed by 3931
Abstract
This work demonstrated a growth of well-aligned NiSi/SiC core-shell nanowires by a one-step process of hot-wire chemical vapor deposition on Ni-coated crystal silicon substrates at different thicknesses. The NiSi nanoparticles (60 to 207 nm) acted as nano-templates to initially inducing the growth of [...] Read more.
This work demonstrated a growth of well-aligned NiSi/SiC core-shell nanowires by a one-step process of hot-wire chemical vapor deposition on Ni-coated crystal silicon substrates at different thicknesses. The NiSi nanoparticles (60 to 207 nm) acted as nano-templates to initially inducing the growth of these core-shell nanowires. These core-shell nanowires were structured by single crystalline NiSi and amorphous SiC as the cores and shells of the nanowires, respectively. It is proposed that the precipitation of the NiSi/SiC are followed according to the nucleation limited silicide reaction and the surface-migration respectively for these core-shell nanowires. The electrical performance of the grown NiSi/SiC core-shell nanowires was characterized by the conducting AFM and it is found that the measured conductivities of the nanowires were higher than the reported works that might be enhanced by SiC shell layer on NiSi nanowires. The high conductivity of NiSi/SiC core-shell nanowires could potentially improve the electrical performance of the nanowires-based devices for harsh environment applications such as field effect transistors, field emitters, space sensors, and electrochemical devices. Full article
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13 pages, 2955 KiB  
Article
Low-Frequency Noise Investigation of 1.09 μm GaAsBi Laser Diodes
by Justinas Glemža, Vilius Palenskis, Andrejus Geižutis, Bronislovas Čechavičius, Renata Butkutė, Sandra Pralgauskaitė and Jonas Matukas
Materials 2019, 12(4), 673; https://doi.org/10.3390/ma12040673 - 24 Feb 2019
Cited by 7 | Viewed by 3531
Abstract
GaAsBi is a suitable and very attractive material system to be used as an active layer in laser diodes (LDs). To understand the performance and the reliability of such devices and also for further laser diode improvements, the origin of noise sources should [...] Read more.
GaAsBi is a suitable and very attractive material system to be used as an active layer in laser diodes (LDs). To understand the performance and the reliability of such devices and also for further laser diode improvements, the origin of noise sources should be clarified. A detailed study of near-infrared 1.09 μm wavelength GaAsBi type-I laser diodes using the low-frequency noise spectroscopy in a temperature range of (180–300) K is presented. Different types of voltage fluctuation spectral density dependencies on the forward current far below the lasing threshold have been observed. According to this, investigated samples have been classified into two groups and two equivalent noise circuits with the corresponding voltage noise sources are presented. Calculations on the voltage spectral density of the electrical noise and current-voltage characteristic approximations have been performed and the results are consistent with the experimental data. The analysis showed that one group of LDs is characterized by 1/fα-type electrical fluctuations with one steep electrical bump in the electrical noise dependence on forward current, and the origin of these fluctuations is the surface leakage channel. The LDs of the other group have two bumps in the electrical noise dependence on current where the first bump is determined by overall LD defectiveness and the second bump by Bi-related defects in the active area of LD with characteristic Lorentzian-type fluctuations having the activation energy of (0.16–0.18) eV. Full article
(This article belongs to the Special Issue Materials for Sources and Detectors in the GIGA-TERA-MIR Range)
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24 pages, 8222 KiB  
Article
Investigation of the Corrosion Behavior of Atomic Layer Deposited Al2O3/TiO2 Nanolaminate Thin Films on Copper in 0.1 M NaCl
by Michael A. Fusco, Christopher J. Oldham and Gregory N. Parsons
Materials 2019, 12(4), 672; https://doi.org/10.3390/ma12040672 - 24 Feb 2019
Cited by 27 | Viewed by 5290
Abstract
Fifty nanometers of Al2O3 and TiO2 nanolaminate thin films deposited by atomic layer deposition (ALD) were investigated for protection of copper in 0.1 M NaCl using electrochemical techniques. Coated samples showed increases in polarization resistance over uncoated copper, up [...] Read more.
Fifty nanometers of Al2O3 and TiO2 nanolaminate thin films deposited by atomic layer deposition (ALD) were investigated for protection of copper in 0.1 M NaCl using electrochemical techniques. Coated samples showed increases in polarization resistance over uncoated copper, up to 12 MΩ-cm2, as measured by impedance spectroscopy. Over a 72-h immersion period, impedance of the titania-heavy films was found to be the most stable, as the alumina films experienced degradation after less than 24 h, regardless of the presence of dissolved oxygen. A film comprised of alternating Al2O3 and TiO2 layers of 5 nm each (referenced as ATx5), was determined to be the best corrosion barrier of the films tested based on impedance spectroscopy measurements over 72 h and equivalent circuit modeling. Dissolved oxygen had a minimal effect on ALD film stability, and increasing the deposition temperature from 150 °C to 250 °C, although useful for increasing film quality, was found to be counterproductive for long-term corrosion protection. Implications of ALD film aging and copper-based surface film formation during immersion and testing are also discussed briefly. The results presented here demonstrate the potential for ultra-thin corrosion barrier coatings, especially for high aspect ratios and component interiors, for which ALD is uniquely suited. Full article
(This article belongs to the Special Issue Corrosion and Protection of Materials)
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16 pages, 8541 KiB  
Article
3D Numerical Simulation of Reactive Extrusion Processes for Preparing PP/TiO2 Nanocomposites in a Corotating Twin Screw Extruder
by Dapeng Sun, Xiangzhe Zhu and Mingguang Gao
Materials 2019, 12(4), 671; https://doi.org/10.3390/ma12040671 - 23 Feb 2019
Cited by 19 | Viewed by 6215
Abstract
To better understand the relationship between flow, mixing and reactions in the process of preparing PP/TiO2, a 3D numerical simulation in a co-rotating twin screw extruder (TSE) was firstly employed using commercial CFD code, ANSYS Polyflow. The effects of rotating speed [...] Read more.
To better understand the relationship between flow, mixing and reactions in the process of preparing PP/TiO2, a 3D numerical simulation in a co-rotating twin screw extruder (TSE) was firstly employed using commercial CFD code, ANSYS Polyflow. The effects of rotating speed of screws, stagger angle of knead blocks, inlet flow rate and initial temperature of barrel on the mixing and reaction process in the TSE were investigated. The results reveal that the studied operational and geometric parameters, which determine mixing efficiency, residence time distribution, and temperature of the flows in the TSE, affect the local species concentration, reaction time and reaction rate, and hence have great influences on the conversion rate. The results show that increasing the rotating speed and inlet flow rate can decrease the time for sufficient mixing, which is not conducive to intensive reaction, and increasing the stagger angle has the opposite effect. Moreover, the conversion rate greatly affected by the initial temperature of barrel. Full article
(This article belongs to the Special Issue Polymer Processing: Modeling and Correlations Finalized to Tailoring the Plastic Part Morphology and Properties)
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15 pages, 6110 KiB  
Article
Enhancing Interfacial Bonding and Tensile Strength in CNT-Cu Composites by a Synergetic Method of Spraying Pyrolysis and Flake Powder Metallurgy
by Xiangyang Chen, Rui Bao, Jianhong Yi, Dong Fang, Jingmei Tao and Yichun Liu
Materials 2019, 12(4), 670; https://doi.org/10.3390/ma12040670 - 23 Feb 2019
Cited by 18 | Viewed by 3781
Abstract
Carbon nanotube (CNT)-reinforced metal matrix composites (MMCs) face the problems of dispersion and interfacial wetting with regard to the matrix. A synergetic method of spray pyrolysis (SP) and flake powder metallurgy (FPM) is used in this paper to improve the dispersibility and interfacial [...] Read more.
Carbon nanotube (CNT)-reinforced metal matrix composites (MMCs) face the problems of dispersion and interfacial wetting with regard to the matrix. A synergetic method of spray pyrolysis (SP) and flake powder metallurgy (FPM) is used in this paper to improve the dispersibility and interfacial bonding of CNTs in a Cu matrix. The results of the interface characterization show interface oxygen atoms (in the form of Cu2O) and a high density of dislocation areas, which is beneficial for interfacial bonding. The tensile results show that the tensile strength of the SP-CNT-Cu composites is much higher than that of the CNT-Cu composites when the mass fraction of the CNTs does not reach the critical value. This can be explained by the nanoparticles which are found on the surface of the CNTs during the SP process. These nanoparticles not only increase the tensile strength of the SP-CNT-Cu composites but also improve the dispersion of the CNTs in the Cu matrix. Thereby, uniform dispersion of CNTs, interfacial bonding between CNTs and the Cu matrix, and the enhancement of tensile strength are achieved simultaneously by the synergetic method. Full article
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9 pages, 2356 KiB  
Article
Anisotropic Properties of Polylactic acid–carbon Fiber Composites Prepared by Droplet spray Additive Manufacturing
by Yongfeng Li, Qingjun Ding, Hongyuan Zhao, Tingting Wu, Mingming Zhang and Yaqi Zhang
Materials 2019, 12(4), 669; https://doi.org/10.3390/ma12040669 - 23 Feb 2019
Cited by 5 | Viewed by 4232
Abstract
Anisotropic materials are important functional materials in many fields. The use of these materials is currently being expanded through the rapid development of additive manufacturing. However, there is still no universal method for fabricating two-dimensional anisotropic polymer composites. Here, polylactic acid–carbon fiber composites [...] Read more.
Anisotropic materials are important functional materials in many fields. The use of these materials is currently being expanded through the rapid development of additive manufacturing. However, there is still no universal method for fabricating two-dimensional anisotropic polymer composites. Here, polylactic acid–carbon fiber composites were prepared using the droplet spray method, and their mechanical and friction properties were studied. The tensile strength in the X–Y plane perpendicular to the direction of the droplet spray was significantly higher than that in the direction of droplet ejection. Similar trends were observed for the elongation at breaking and the impact strength. The friction coefficient was smallest in the X–Y plane. Scanning electron microscopy showed that carbon fibers were oriented in the X–Y plane, which enhanced the mechanical and friction properties in this plane. Full article
(This article belongs to the Section Advanced Composites)
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25 pages, 11010 KiB  
Review
“Traditional” Sol-Gel Chemistry as a Powerful Tool for the Preparation of Supported Metal and Metal Oxide Catalysts
by Serena Esposito
Materials 2019, 12(4), 668; https://doi.org/10.3390/ma12040668 - 23 Feb 2019
Cited by 231 | Viewed by 19885
Abstract
The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, [...] Read more.
The sol-gel method is an attractive synthetic approach in the design of advanced catalytic formulations that are based on metal and metal oxide with high degree of structural and compositional homogeneity. Nowadays, though it originated with the hydrolysis and condensation of metal alkoxides, sol-gel chemistry gathers plenty of fascinating strategies to prepare materials from solution state precursors. Low temperature chemistry, reproducibility, and high surface to volume ratios of obtained products are features that add merit to this technology. The development of different and fascinating procedure was fostered by the availability of new molecular precursors, chelating agents and templates, with the great advantage of tailoring the physico-chemical properties of the materials through the manipulation of the synthesis conditions. The aim of this review is to present an overview of the “traditional” sol-gel synthesis of tailored and multifunctional inorganic materials and their application in the main domain of heterogeneous catalysis. One of the main achievements is to stress the versatility of sol-gel preparation by highlighting its advantage over other preparation methods through some specific examples of the synthesis of catalysts. Full article
(This article belongs to the Special Issue Supported Metal and Metal Oxide Catalysts by Sol-Gel Chemistry: Synthesis and Applications)
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20 pages, 6878 KiB  
Article
Residual Lattice Strain and Phase Distribution in Ti-6Al-4V Produced by Electron Beam Melting
by Tuerdi Maimaitiyili, Robin Woracek, Magnus Neikter, Mirko Boin, Robert C. Wimpory, Robert Pederson, Markus Strobl, Michael Drakopoulos, Norbert Schäfer and Christina Bjerkén
Materials 2019, 12(4), 667; https://doi.org/10.3390/ma12040667 - 23 Feb 2019
Cited by 22 | Viewed by 5518
Abstract
Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental [...] Read more.
Residual stress/strain and microstructure used in additively manufactured material are strongly dependent on process parameter combination. With the aim to better understand and correlate process parameters used in electron beam melting (EBM) of Ti-6Al-4V with resulting phase distributions and residual stress/strains, extensive experimental work has been performed. A large number of polycrystalline Ti-6Al-4V specimens were produced with different optimized EBM process parameter combinations. These specimens were post-sequentially studied by using high-energy X-ray and neutron diffraction. In addition, visible light microscopy, scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD) studies were performed and linked to the other findings. Results show that the influence of scan speed and offset focus on resulting residual strain in a fully dense sample was not significant. In contrast to some previous literature, a uniform α- and β-Ti phase distribution was found in all investigated specimens. Furthermore, no strong strain variations along the build direction with respect to the deposition were found. The magnitude of strain in α and β phase show some variations both in the build plane and along the build direction, which seemed to correlate with the size of the primary β grains. However, no relation was found between measured residual strains in α and β phase. Large primary β grains and texture appear to have a strong effect on X-ray based stress results with relatively small beam size, therefore it is suggested to use a large beam for representative bulk measurements and also to consider the prior β grain size in experimental planning, as well as for mathematical modelling. Full article
(This article belongs to the Special Issue Progress in Metal Additive Manufacturing and Metallurgy)
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14 pages, 3320 KiB  
Article
Electroanalytical Performance of Nitrogen-Doped Graphene Films Processed in One Step by Pulsed Laser Deposition Directly Coupled with Thermal Annealing
by Florent Bourquard, Yannick Bleu, Anne-Sophie Loir, Borja Caja-Munoz, José Avila, Maria-Carmen Asensio, Gaëtan Raimondi, Maryam Shokouhi, Ilhem Rassas, Carole Farre, Carole Chaix, Vincent Barnier, Nicole Jaffrezic-Renault, Florence Garrelie and Christophe Donnet
Materials 2019, 12(4), 666; https://doi.org/10.3390/ma12040666 - 23 Feb 2019
Cited by 14 | Viewed by 5362
Abstract
Graphene-based materials are widely studied to enable significant improvements in electroanalytical devices requiring new generations of robust, sensitive and low-cost electrodes. In this paper, we present a direct one-step route to synthetize a functional nitrogen-doped graphene film onto a Ni-covered silicon electrode substrate [...] Read more.
Graphene-based materials are widely studied to enable significant improvements in electroanalytical devices requiring new generations of robust, sensitive and low-cost electrodes. In this paper, we present a direct one-step route to synthetize a functional nitrogen-doped graphene film onto a Ni-covered silicon electrode substrate heated at high temperature, by pulsed laser deposition of carbon in the presence of a surrounding nitrogen atmosphere, with no post-deposition transfer of the film. With the ferrocene methanol system, the functionalized electrode exhibits excellent reversibility, close to the theoretical value of 59 mV, and very high sensitivity to hydrogen peroxide oxidation. Our electroanalytical results were correlated with the composition and nanoarchitecture of the N-doped graphene film containing 1.75 at % of nitrogen and identified as a few-layer defected and textured graphene film containing a balanced mixture of graphitic-N and pyrrolic-N chemical functions. The absence of nitrogen dopant in the graphene film considerably degraded some electroanalytical performances. Heat treatment extended beyond the high temperature graphene synthesis did not significantly improve any of the performances. This work contributes to a better understanding of the electrochemical mechanisms of doped graphene-based electrodes obtained by a direct and controlled synthesis process. Full article
(This article belongs to the Special Issue Element-Doped Functional Carbon-based Materials)
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11 pages, 2150 KiB  
Article
An On-Line System for High Temperature Dielectric Property Measurement of Microwave-Assisted Sintering Materials
by Li Wu, Yi Zhang, Fengxia Wang, Weiquan Ma, Tian Xie and Kama Huang
Materials 2019, 12(4), 665; https://doi.org/10.3390/ma12040665 - 22 Feb 2019
Cited by 13 | Viewed by 3981
Abstract
Microwave-assisted sintering materials have been proven to deliver improvements in the mechanical and physicochemical properties of the materials, compared with conventional sintering methods. Accurate values of dielectric properties of materials under high temperatures are essential for microwave-assisted sintering. In view of this, this [...] Read more.
Microwave-assisted sintering materials have been proven to deliver improvements in the mechanical and physicochemical properties of the materials, compared with conventional sintering methods. Accurate values of dielectric properties of materials under high temperatures are essential for microwave-assisted sintering. In view of this, this paper, proposes an on-line system to measure the high temperature dielectric properties of materials under microwave processing at a frequency of 2450 MHz. A custom-designed ridge waveguide is utilized, where samples are heated and measured simultaneously. An artificial neural network (ANN) trained with the corresponding simulation data is integrated into this system to reverse the permittivity of the measured materials. This whole system is tested at room temperature with different materials. Accuracies of measuring dielectric property with an error lower than 9% with respect to theoretical data have been achieved even for high loss media. The functionality of the dielectric measurement system has also been demonstrated by heating and measuring Macor and Duran ceramic glass samples up to 800 °C. All the preliminary experiments prove the feasibility of this system. It provides another method for dielectric property measurement and improves the understanding of the mechanism between microwave and media under high temperatures, which is helpful for optimizing the microwave-assisted sintering of materials. Full article
(This article belongs to the Special Issue Conventional and Microwave Sintering Techniques in Materials)
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20 pages, 4722 KiB  
Article
The Preparation and Characterization of Polyacrylonitrile-Polyaniline (PAN/PANI) Fibers
by Iwona Karbownik, Olga Rac-Rumijowska, Marta Fiedot-Toboła, Tomasz Rybicki and Helena Teterycz
Materials 2019, 12(4), 664; https://doi.org/10.3390/ma12040664 - 22 Feb 2019
Cited by 114 | Viewed by 7981
Abstract
The paper presents a method of modifying polyacrylonitrile (PAN) fibers using polyaniline (PANI). The PAN fibers were doped with polyaniline that was obtained in two different ways. The first consisted of doping a spinning solution with polyaniline that was synthesized in an aqueous [...] Read more.
The paper presents a method of modifying polyacrylonitrile (PAN) fibers using polyaniline (PANI). The PAN fibers were doped with polyaniline that was obtained in two different ways. The first consisted of doping a spinning solution with polyaniline that was synthesized in an aqueous solution (PAN/PANI blended), and the second involved the synthesis of polyaniline directly in the spinning solution (PAN/PANI in situ). The obtained fibers were characterized by the methods: X-ray powder diffraction (XRD), scanning electron microscope (SEM), fourier-transform infrared spectroscopy (FTIR), thermogravimetry (TG) and differential scanning calorimetry (DSC). Analysis of the results showed strong interactions between the nitrile groups of polyacrylonitrile and polyaniline in the PAN/PANI in situ fibers. The results of mechanical strength tests indicated that the performance of the PAN/PANI mixture significantly improved the mechanical parameters of polyaniline, although these fibers had a weaker strength than the unmodified PAN fibers. The fibers obtained as a result of the addition of PANI to PAN were dielectric, whereas the PANI-synthesized in situ were characterized by a mass-specific resistance of 5.47 kΩg/cm2. Full article
(This article belongs to the Special Issue Textile-Based Advanced Materials: Construction, Properties and Applications)
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18 pages, 11366 KiB  
Article
Alternative Process Routes to Manufacture Porous Ceramics—Opportunities and Challenges
by Uwe Scheithauer, Florian Kerber, Alexander Füssel, Stefan Holtzhausen, Wieland Beckert, Eric Schwarzer, Steven Weingarten and Alexander Michaelis
Materials 2019, 12(4), 663; https://doi.org/10.3390/ma12040663 - 22 Feb 2019
Cited by 25 | Viewed by 5565
Abstract
Porous ceramics can be realized by different methods and are used for various applications such as cross-flow membranes or wall-flow filters, porous burners, solar receivers, structural design elements, or catalytic supports. Within this paper, three different alternative process routes are presented, which can [...] Read more.
Porous ceramics can be realized by different methods and are used for various applications such as cross-flow membranes or wall-flow filters, porous burners, solar receivers, structural design elements, or catalytic supports. Within this paper, three different alternative process routes are presented, which can be used to manufacture porous ceramic components with different properties or even graded porosity. The first process route is based on additive manufacturing (AM) of macro porous ceramic components. The second route is based on AM of a polymeric template, which is used to realize porous ceramic components via replica technique. The third process route is based on an AM technology, which allows the manufacturing of multimaterial or multiproperty ceramic components, like components with dense and porous volumes in one complex-shaped component. Full article
(This article belongs to the Special Issue Advanced Porous Ceramics and Its Applications)
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37 pages, 18396 KiB  
Review
Recent Advances of Hierarchical and Sequential Growth of Macromolecular Organic Structures on Surface
by Corentin Pigot and Frédéric Dumur
Materials 2019, 12(4), 662; https://doi.org/10.3390/ma12040662 - 22 Feb 2019
Cited by 17 | Viewed by 5977
Abstract
The fabrication of macromolecular organic structures on surfaces is one major concern in materials science. Nanoribbons, linear polymers, and porous nanostructures have gained a lot of interest due to their possible applications ranging from nanotemplates, catalysis, optoelectronics, sensors, or data storage. During decades, [...] Read more.
The fabrication of macromolecular organic structures on surfaces is one major concern in materials science. Nanoribbons, linear polymers, and porous nanostructures have gained a lot of interest due to their possible applications ranging from nanotemplates, catalysis, optoelectronics, sensors, or data storage. During decades, supramolecular chemistry has constituted an unavoidable approach for the design of well-organized structures on surfaces displaying a long-range order. Following these initial works, an important milestone has been established with the formation of covalent bonds between molecules. Resulting from this unprecedented approach, various nanostructures of improved thermal and chemical stability compared to those obtained by supramolecular chemistry and displaying unique and unprecedented properties have been developed. However, a major challenge exists: the growth control is very delicate and a thorough understanding of the complex mechanisms governing the on-surface chemistry is still needed. Recently, a new approach consisting in elaborating macromolecular structures by combining consecutive steps has been identified as a promising strategy to elaborate organic structures on surface. By designing precursors with a preprogrammed sequence of reactivity, a hierarchical or a sequential growth of 1D and 2D structures can be realized. In this review, the different reaction combinations used for the design of 1D and 2D structures are reported. To date, eight different sequences of reactions have been examined since 2008, evidencing the intense research activity existing in this field. Full article
(This article belongs to the Special Issue Advances and Challenges in Organic Electronics)
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12 pages, 4310 KiB  
Article
Development of a Zeolite A/LDH Composite for Simultaneous Cation and Anion Removal
by Breno Gustavo Porfírio Bezerra, Lindiane Bieseki, Djalma Ribeiro da Silva and Sibele Berenice Castellã Pergher
Materials 2019, 12(4), 661; https://doi.org/10.3390/ma12040661 - 22 Feb 2019
Cited by 10 | Viewed by 4875
Abstract
Wastewater from the oil industry is a major problem for aqueous environments due to its complexity and estimated volume of approximately 250 million barrels per day. The combination of these petroleum pollutants creates risks to human health, and their removal from the environment [...] Read more.
Wastewater from the oil industry is a major problem for aqueous environments due to its complexity and estimated volume of approximately 250 million barrels per day. The combination of these petroleum pollutants creates risks to human health, and their removal from the environment is considered a major problem in the world today. Thus, this work has the objective of studying the treatment of this type of effluent through the adsorption method using the following exchange materials: cationic, anionic, their combination by a sequential method, and a composite material. Zeolite A, a layered double hydroxide (LDH), and the new composite material formed by zeolite A and LDH structures were synthesized for this study. All were used for the simultaneous treatment of cations and anions in a complex sample such as water produced from petroleum production. The composite demonstrated an excellent ability to simultaneously remove cations and anions. The results obtained after the different treatment modes of the effluent using different materials varied from 85% to 100% for the removal of cations and from 56% to 99.7% for the removal of anions. Full article
(This article belongs to the Special Issue Porous Materials for Environmental Applications)
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17 pages, 10174 KiB  
Article
Barkhausen Noise Emission in Hard-Milled Surfaces
by Miroslav Neslušan, Anna Mičietová, Branislav Hadzima, Branislav Mičieta, Pavel Kejzlar, Jiří Čapek, Juraj Uríček and Filip Pastorek
Materials 2019, 12(4), 660; https://doi.org/10.3390/ma12040660 - 22 Feb 2019
Cited by 19 | Viewed by 3778
Abstract
This paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled [...] Read more.
This paper reports on an investigation treating a hard-milled surface as a surface undergoing severe plastic deformation at elevated temperatures. This surface exhibits remarkable magnetic anisotropy (expressed in term of Barkhausen noise). This paper also shows that Barkhausen noise emission in a hard-milled surface is a function of tool wear and the corresponding microstructure transformations initiated in the tool/machined surface interface. The paper discusses the specific character of Barkhausen noise bursts and the unusually high magnitude of Barkhausen noise pulses, especially at a low degree of tool wear. The main causes can be seen in specific structures and the corresponding domain configurations formed during rapid cooling following surface heating. Domains are not randomly but preferentially oriented in the direction of the cutting speed. Barkhausen noise signals (measured in two perpendicular directions such as cutting speed and feed direction) indicate that the mechanism of Bloch wall motion during cyclic magnetization in hard-milled surfaces differs from surfaces produced by grinding cycles or the raw surface after heat treatment. Full article
(This article belongs to the Collection Magnetoelastic Materials)
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11 pages, 3296 KiB  
Article
Strain-Rate-Dependent Tensile Response of Ti–5Al–2.5Sn Alloy
by Bin Zhang, Jin Wang, Yang Wang, Yu Wang and Ziran Li
Materials 2019, 12(4), 659; https://doi.org/10.3390/ma12040659 - 22 Feb 2019
Cited by 15 | Viewed by 3975
Abstract
This study is an experimental investigation on the tensile responses of Ti–5Al–2.5Sn alloy over a wide range of strain rates. Uniaxial tension tests within the rate range of 10−3–101 s−1 are performed using a hydraulic driven MTS810 machine and [...] Read more.
This study is an experimental investigation on the tensile responses of Ti–5Al–2.5Sn alloy over a wide range of strain rates. Uniaxial tension tests within the rate range of 10−3–101 s−1 are performed using a hydraulic driven MTS810 machine and a moderate strain-rate testing system. The high-rate uniaxial tension and tension recovery tests are conducted using a split-Hopkinson tension bar to obtain the adiabatic and isothermal stress–strain responses of the alloy under dynamic loading conditions. The experimental results show that the value of the initial yield stress increases with the increasing strain rate, while the strain rate sensitivity is greater at high strain rates. The isothermal strain-hardening behavior changes little with the strain rate, and the adiabatic temperature rise is the main reason for the reduction of the strain-hardening rate during high strain-rate tension. The electron backscatter diffraction (EBSD) analysis of the post-deformed samples indicates that there are deformation twins under quasi-static and high-rate tensile loadings. Scanning electron microscope (SEM) micrographs of the fracture surfaces of the post-deformed samples show dimple-like features. The Zerilli–Armstrong model is modified to incorporate the thermal-softening effect of the adiabatic temperature rise at high strain rates and describe the tension responses of Ti–5Al–2.5Sn alloy over strain rates from quasi-static to 1050 s−1. Full article
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14 pages, 2797 KiB  
Article
Effect of Atmospheric Cold Plasma Treatment on the Adhesion and Tribological Properties of Polyamide 66 and Poly(Tetrafluoroethylene)
by Zoltán Károly, Gábor Kalácska, Jacob Sukumaran, Dieter Fauconnier, Ádám Kalácska, Miklós Mohai and Szilvia Klébert
Materials 2019, 12(4), 658; https://doi.org/10.3390/ma12040658 - 22 Feb 2019
Cited by 29 | Viewed by 3871
Abstract
The surfaces of two engineering polymers including polyamide 66 (PA66) and polytetrafluoroethylene (PTFE) were treated by diffuse coplanar surface barrier discharges in atmospheric air. We found that plasma treatment improved the adhesion of PA66 for either polymer/polymer or polymer/steel joints, however, it was [...] Read more.
The surfaces of two engineering polymers including polyamide 66 (PA66) and polytetrafluoroethylene (PTFE) were treated by diffuse coplanar surface barrier discharges in atmospheric air. We found that plasma treatment improved the adhesion of PA66 for either polymer/polymer or polymer/steel joints, however, it was selective for the investigated adhesive agents. For PTFE the adhesion was unaltered for plasma treatment regardless the type of used adhesive. Tribological properties were slightly improved for PA66, too. Both the friction coefficient and wear decreased. Significant changes, again, could not be detected for PTFE. The occurred variation in the adhesion and tribology was discussed on the basis of the occurred changes in surface chemistry, wettability and topography of the polymer surface. Full article
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21 pages, 10344 KiB  
Article
Rheological Property Criteria for Buildable 3D Printing Concrete
by Hoseong Jeong, Sun-Jin Han, Seung-Ho Choi, Yoon Jung Lee, Seong Tae Yi and Kang Su Kim
Materials 2019, 12(4), 657; https://doi.org/10.3390/ma12040657 - 21 Feb 2019
Cited by 78 | Viewed by 7880
Abstract
Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress [...] Read more.
Fresh concrete used in 3D printing should ensure adequate yield stress, otherwise the printed concrete layer may suffer intolerable deformation or collapse during the printing process. In response to this issue, an analytical study was carried out to derive the initial yield stress and hardening coefficient of fresh concrete suitable for 3D printing. The maximum shear stress distribution of fresh concrete was calculated using a stress transformation equation derived from the equilibrium condition of forces. In addition, the elapsed time experienced by fresh concrete during the printing processes was estimated and was then substituted into the elapsed time-yield stress function to calculate the yield stress distribution. Based on these results, an algorithm capable of deriving both the initial yield stress and the hardening coefficient required for printing fresh concrete up to the target height was proposed and computational fluid dynamics (CFD) analyses were performed to verify the accuracy of the proposed model. Full article
(This article belongs to the Special Issue Concrete 3D Printing and Digitally-Aided Fabrication)
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17 pages, 4871 KiB  
Article
Identification of the Degree of Degradation of Fibre-Cement Boards Exposed to Fire by Means of the Acoustic Emission Method and Artificial Neural Networks
by Krzysztof Schabowicz, Tomasz Gorzelańczyk and Mateusz Szymków
Materials 2019, 12(4), 656; https://doi.org/10.3390/ma12040656 - 21 Feb 2019
Cited by 24 | Viewed by 3988
Abstract
This paper presents the results of research aimed at identifying the degree of degradation of fibre-cement boards exposed to fire. The fibre-cement board samples were initially exposed to fire at various durations in the range of 1–15 min. The samples were then subjected [...] Read more.
This paper presents the results of research aimed at identifying the degree of degradation of fibre-cement boards exposed to fire. The fibre-cement board samples were initially exposed to fire at various durations in the range of 1–15 min. The samples were then subjected to three-point bending and were investigated using the acoustic emission method. Artificial neural networks (ANNs) were employed to analyse the results yielded by the acoustic emission method. Fire was found to have a degrading effect on the fibres contained in the boards. As the length of exposure to fire increased, the fibres underwent gradual degradation, which was reflected in a decrease in the number of acoustic emission (AE) events recognised by the artificial neural networks as accompanying the breaking of the fibres during the three-point bending of the sample. It was shown that it is not sufficient to determine the degree of degradation of fibre-cement boards solely on the basis of bending strength (MOR). Full article
(This article belongs to the Special Issue Non-destructive Testing of Materials in Civil Engineering)
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36 pages, 5117 KiB  
Review
Plastics—Villain or Hero? Polymers and Recycled Polymers in Mineral and Metallurgical Processing—A Review
by Sheila Devasahayam, R. K. Singh Raman, K. Chennakesavulu and Sankar Bhattacharya
Materials 2019, 12(4), 655; https://doi.org/10.3390/ma12040655 - 21 Feb 2019
Cited by 34 | Viewed by 11752
Abstract
This review focusses on the use of recycled and virgin polymers in mineral and metallurgical processing, both high and ambient temperature processes, including novel applications. End of life applications of polymers as well as the utilisation of polymers during its life time in [...] Read more.
This review focusses on the use of recycled and virgin polymers in mineral and metallurgical processing, both high and ambient temperature processes, including novel applications. End of life applications of polymers as well as the utilisation of polymers during its life time in various applications are explored. The discussion includes applications in cleaner coal production, iron and steel production, iron ore palletisation, iron alloy manufacturing, manganese processing, E-wastes processing and carbon sequestration. The underlying principles of these applications are also explained. Advantages and disadvantages of using these polymers in terms of energy and emission reductions, reduction in non-renewables and dematerialisation are discussed. Influence of the polymers on controlling the evolution of micro and nanostructures in alloys and advanced materials is also considered. Full article
(This article belongs to the Section Carbon Materials)
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