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Materials, Volume 13, Issue 18 (September-2 2020) – 308 articles

Cover Story (view full-size image): In a water-based composite dispersant system, liquid phase exfoliation theory was used to balance the van der Waals force between the expanded graphite sheets. A water-based graphene dispersion with few layers, good dispersion stability, and economical efficiency was quickly prepared. The exfoliation and dispersion mechanisms of graphene in various dispersant systems in pure water were analyzed. View this paper
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74 pages, 7635 KiB  
Review
Porous Carbon-Based Supercapacitors Directly Derived from Metal–Organic Frameworks
by Hyun-Chul Kim and Seong Huh
Materials 2020, 13(18), 4215; https://doi.org/10.3390/ma13184215 - 22 Sep 2020
Cited by 17 | Viewed by 6049
Abstract
Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to [...] Read more.
Numerously different porous carbons have been prepared and used in a wide range of practical applications. Porous carbons are also ideal electrode materials for efficient energy storage devices due to their large surface areas, capacious pore spaces, and superior chemical stability compared to other porous materials. Not only the electrical double-layer capacitance (EDLC)-based charge storage but also the pseudocapacitance driven by various dopants in the carbon matrix plays a significant role in enhancing the electrochemical supercapacitive performance of porous carbons. Since the electrochemical capacitive activities are primarily based on EDLC and further enhanced by pseudocapacitance, high-surface carbons are desirable for these applications. The porosity of carbons plays a crucial role in enhancing the performance as well. We have recently witnessed that metal–organic frameworks (MOFs) could be very effective self-sacrificing templates, or precursors, for new high-surface carbons for supercapacitors, or ultracapacitors. Many MOFs can be self-sacrificing precursors for carbonaceous porous materials in a simple yet effective direct carbonization to produce porous carbons. The constituent metal ions can be either completely removed during the carbonization or transformed into valuable redox-active centers for additional faradaic reactions to enhance the electrochemical performance of carbon electrodes. Some heteroatoms of the bridging ligands and solvate molecules can be easily incorporated into carbon matrices to generate heteroatom-doped carbons with pseudocapacitive behavior and good surface wettability. We categorized these MOF-derived porous carbons into three main types: (i) pure and heteroatom-doped carbons, (ii) metallic nanoparticle-containing carbons, and (iii) carbon-based composites with other carbon-based materials or redox-active metal species. Based on these cases summarized in this review, new MOF-derived porous carbons with much enhanced capacitive performance and stability will be envisioned. Full article
(This article belongs to the Special Issue Metal-Organic Frameworks towards Energy Conversion and Storage)
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16 pages, 4363 KiB  
Article
Aerodynamic Performance of an Adaptive GFRP Wind Barrier Structure for Railway Bridges
by Yiqing Dai, Xuewei Dai, Yu Bai and Xuhui He
Materials 2020, 13(18), 4214; https://doi.org/10.3390/ma13184214 - 22 Sep 2020
Cited by 15 | Viewed by 2770
Abstract
Wind barrier structures on railway bridges are installed to mitigate the wind effects on travelling trains; however, they cause additional wind loads and associated aerodynamic effects on the bridge. An innovative concept was developed for a wind barrier structure in this study that [...] Read more.
Wind barrier structures on railway bridges are installed to mitigate the wind effects on travelling trains; however, they cause additional wind loads and associated aerodynamic effects on the bridge. An innovative concept was developed for a wind barrier structure in this study that used a glass–fibre–reinforced polymer (GFRP) that may deform properly when subjected to a crosswind. Such deformation then allows for wind to pass, therefore reducing the wind loads transferred to the bridge. Wind tunnel experiments were conducted on a 1/40-scale train and bridge models with the proposed GFRP barrier subjected to airflow at different speeds up to 20 m/s. The side-force and overturning-moment coefficients of both the train and the bridge were evaluated to characterise the aerodynamic effects. The results show that favourable side-force and overturning-moment coefficients of the train were provided by wind barriers taller than 10 cm. The aerodynamic coefficients of the train were not significantly affected by the airflow speeds; meanwhile, the overturning-moment coefficient of the bridge decreased with the increase in airflow speed due to smaller wind resistance of the barrier after deformation. A numerical analysis was conducted on both the reduced- and full-scale models of the train–barrier–bridge system and the results supported the findings obtained from the wind tunnel experiments. Full article
(This article belongs to the Special Issue Advances in Fiber-Reinforced Polymer Composites)
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20 pages, 5537 KiB  
Article
Simultaneous Synthesis and Nitrogen Doping of Free-Standing Graphene Applying Microwave Plasma
by D. Tsyganov, N. Bundaleska, J. Henriques, E. Felizardo, A. Dias, M. Abrashev, J. Kissovski, A. M. Botelho do Rego, A. M. Ferraria and E. Tatarova
Materials 2020, 13(18), 4213; https://doi.org/10.3390/ma13184213 - 22 Sep 2020
Cited by 17 | Viewed by 3367
Abstract
An experimental and theoretical investigation on microwave plasma-based synthesis of free-standing N-graphene, i.e., nitrogen-doped graphene, was further extended using ethanol and nitrogen gas as precursors. The in situ assembly of N-graphene is a single-step method, based on the introduction of N-containing precursor together [...] Read more.
An experimental and theoretical investigation on microwave plasma-based synthesis of free-standing N-graphene, i.e., nitrogen-doped graphene, was further extended using ethanol and nitrogen gas as precursors. The in situ assembly of N-graphene is a single-step method, based on the introduction of N-containing precursor together with carbon precursor in the reactive microwave plasma environment at atmospheric pressure conditions. A previously developed theoretical model was updated to account for the new reactor geometry and the nitrogen precursor employed. The theoretical predictions of the model are in good agreement with all experimental data and assist in deeper understanding of the complicated physical and chemical process in microwave plasma. Optical Emission Spectroscopy was used to detect the emission of plasma-generated ‘‘building units’’ and to determine the gas temperature. The outlet gas was analyzed by Fourier-Transform Infrared Spectroscopy to detect the generated gaseous by-products. The synthesized N-graphene was characterized by Scanning Electron Microscopy, Raman, and X-ray photoelectron spectroscopies. Full article
(This article belongs to the Special Issue Atmospheric Pressure Plasmas in Material Science)
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18 pages, 13256 KiB  
Article
Mechanical Properties of Corner Joints Made of Honeycomb Panels with Double Arrow-Shaped Auxetic Cores
by Adam Majewski, Tomasz Krystofiak and Jerzy Smardzewski
Materials 2020, 13(18), 4212; https://doi.org/10.3390/ma13184212 - 22 Sep 2020
Cited by 7 | Viewed by 3328
Abstract
The development of both light and strong wood-derived materials is an interesting research area, particularly in terms of usability in, e.g., furniture constructions. Honeycomb panels being current industry standard are relatively thick (32 mm and 40 mm), thus their attractiveness in designing furniture [...] Read more.
The development of both light and strong wood-derived materials is an interesting research area, particularly in terms of usability in, e.g., furniture constructions. Honeycomb panels being current industry standard are relatively thick (32 mm and 40 mm), thus their attractiveness in designing furniture is limited. In a few studies, it has been shown that honeycomb panels with paper cores are characterized by unsatisfactory mechanical properties, especially when the composite thickness is less than 20 mm. From the literature, it is also evident that mechanical properties might be improved by introducing auxetic features into the core structure. Even though it is a concept with great potential, there are a few studies dealing with honeycomb panels with auxetic cores made of paper. Furthermore, there is no research on the corner joints made from such material. For this reason, the aim of the study was to test the bending behavior of the corner adhesive joints made of honeycomb panels with double arrow-shaped auxetic cores. Within the research, the core cell was adopted based on literature and preliminary studies, paper auxetic cores were produced by the use of the designed and 3d printed device, and joints stiffness and strength were calculated analytically based on the experiment results. Evaluated corner joints stiffness, both in compression and tension test, is greater for samples made of panels with designed auxetic cores. Surprisingly, in the analyzed range of elasticity, it was statistically proved that the values of joint stiffness coefficient K did not vary significantly between compared joints pairs. Full article
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10 pages, 3041 KiB  
Article
Effects of Surface Roughness on the Electrochemical Properties and Galvanic Corrosion Behavior of CFRP and SPCC Alloy
by YoungHwan Kim, MyeongHan Yoo and MinSeok Moon
Materials 2020, 13(18), 4211; https://doi.org/10.3390/ma13184211 - 22 Sep 2020
Cited by 7 | Viewed by 2251
Abstract
This study investigated the potentiodynamic corrosion behavior of carbon fiber reinforced plastic (CFRP) and automotive rolled mild steel alloy (SPCC alloy) under different surface roughness conditions. Electrochemical characterization was performed using a potentiodynamic corrosion test with 5.0 wt.% NaCl aqueous solution at 25 [...] Read more.
This study investigated the potentiodynamic corrosion behavior of carbon fiber reinforced plastic (CFRP) and automotive rolled mild steel alloy (SPCC alloy) under different surface roughness conditions. Electrochemical characterization was performed using a potentiodynamic corrosion test with 5.0 wt.% NaCl aqueous solution at 25 ± 2 °C, while microstructural and compositional changes before and after corrosion were evaluated using field emission scanning electron microscopy (FE-SEM) and energy dispersive spectroscopy (EDS), respectively. The CFRP and SPCC corrosion rate increased as surface roughness increased. Generally, SPCC corroded faster than CFRP. The surface composition of CFRP was not affected by corrosion, regardless of the surface roughness conditions. Conversely, SPCC exhibited remarkable changes due to the formation of oxides, and its corrosion was more severe than that of CFRP as surface roughness increased. We used a double flat electrode cell to conduct a galvanic corrosion test in this study at 25 ± 2 °C. In this galvanic corrosion test, we studied different kinds of surface roughness for SPCC specimens under the CFRP material in its as-received condition and #200 condition. We confirmed that the results of galvanic corrosion for this study have a difference in corrosion amount and corrosion rate of SPCC specimens according to the surface roughness of CFRP. Full article
(This article belongs to the Section Corrosion)
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24 pages, 30691 KiB  
Article
Flexural and Shear Tests on Reinforced Concrete Bridge Deck Slab Segments with a Textile-Reinforced Concrete Strengthening Layer
by Viviane Adam, Jan Bielak, Christian Dommes, Norbert Will and Josef Hegger
Materials 2020, 13(18), 4210; https://doi.org/10.3390/ma13184210 - 22 Sep 2020
Cited by 18 | Viewed by 4053
Abstract
Many older bridges feature capacity deficiencies. This is mainly due to changes in code provisions which came along with stricter design rules and increasing traffic, leading to higher loads on the structure. To address capacity deficiencies of bridges, refined structural analyses with more [...] Read more.
Many older bridges feature capacity deficiencies. This is mainly due to changes in code provisions which came along with stricter design rules and increasing traffic, leading to higher loads on the structure. To address capacity deficiencies of bridges, refined structural analyses with more detailed design approaches can be applied. If bridge assessment does not provide sufficient capacity, strengthening can be a pertinent solution to extend the bridge’s service lifetime. For numerous cases, applying an extra layer of textile-reinforced concrete (TRC) can be a convenient method to achieve the required resistance. Here, carbon fibre-reinforced polymer reinforcement together with a high-performance mortar was used within the scope of developing a strengthening layer for bridge deck slabs, called SMART-DECK. Due to the high tensile strength of the carbon and its resistance to corrosion, a thin layer with high strength and low additional dead load can be realised. While the strengthening effect of TRC for slabs under flexural loading has already been investigated several times, the presented test programme also covered increase in shear capacity, which is the other crucial failure mode to be considered in design. A total of 14 large-scale tests on TRC-strengthened slab segments were tested under static and cyclic loading. The experimental study revealed high increases in capacity for both bending and shear failure. Full article
(This article belongs to the Special Issue Advanced Structural Concrete Materials in Bridges)
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18 pages, 8032 KiB  
Article
An Efficient and Adaptable Path Planning Algorithm for Automated Fiber Placement Based on Meshing and Multi Guidelines
by Hong Xiao, Wei Han, Wenbin Tang and Yugang Duan
Materials 2020, 13(18), 4209; https://doi.org/10.3390/ma13184209 - 22 Sep 2020
Cited by 7 | Viewed by 2585
Abstract
Path planning algorithms for automated fiber placement are used to determine the directions of the fiber paths and the start and end positions on the mold surfaces. The quality of the fiber paths determines largely the efficiency and quality of the automated fiber [...] Read more.
Path planning algorithms for automated fiber placement are used to determine the directions of the fiber paths and the start and end positions on the mold surfaces. The quality of the fiber paths determines largely the efficiency and quality of the automated fiber placement process. The presented work investigated an efficient path planning algorithm based on surface meshing. In addition, an update method of the datum direction vector via a guide-line update strategy was proposed to make the path planning algorithm applicable for complex surfaces. Finally, accuracy analysis was performed on the proposed algorithm and it can be adopted as the reference for the triangulation parameter selection for the path planning algorithm. Full article
(This article belongs to the Special Issue “3D” Parametric and Nonparametric Description of Surface Topography in Manufacturing Processes)
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15 pages, 5872 KiB  
Article
Applications of Micro-Indentation Technology to Estimate Fracture Toughness of Shale
by Qiang Han, Zhan Qu, Ping Wang, Gang Bi and Guanzheng Qu
Materials 2020, 13(18), 4208; https://doi.org/10.3390/ma13184208 - 22 Sep 2020
Cited by 8 | Viewed by 2368
Abstract
The fracture toughness of shale is a basic parameter that can provide effective theoretical support for wellbore stability and hydraulic fracturing of a shale reservoir. Due to the composition and microstructure, there are many problems in evaluating the mechanical properties of shale in [...] Read more.
The fracture toughness of shale is a basic parameter that can provide effective theoretical support for wellbore stability and hydraulic fracturing of a shale reservoir. Due to the composition and microstructure, there are many problems in evaluating the mechanical properties of shale in a macroscopic test. In this paper, the composition and pore distribution of shale were studied by X-ray diffraction and nuclear magnetic resonance. Scanning electron microscopy was used to characterize the pore structure. The setting of experimental parameters and the selection of the indenter were discussed. Micro-indentation technique was proposed and applied to fracture toughness analysis of shale. The results show that Berkovich indenter is more suitable for shale indentation test than Vickers indenter. Fracture toughness of shale indentation is obviously affected by surface roughness and indentation position. Fracture toughness of shale decreases slightly with the increase of the indentation load. The energy analysis result presents that the effect of cracking on the ratio of total/unloading work is minimal when there is no significant stripping on the shale surface. Compared with the experimental method, energy methods can obtain all the analysis parameters from a single indentation test. The results of comparative analysis with macroscopic experiments display that micro-indentation test can effectively predict the macroscopic fracture toughness of shale. Full article
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21 pages, 6749 KiB  
Article
Effect of Alumina Nano-Particles on Physical and Mechanical Properties of Medium Density Fiberboard
by Hisham Alabduljabbar, Rayed Alyousef, Waheed Gul, Syed Riaz Akbar Shah, Afzal Khan, Razaullah Khan and Abdulaziz Alaskar
Materials 2020, 13(18), 4207; https://doi.org/10.3390/ma13184207 - 22 Sep 2020
Cited by 14 | Viewed by 3483
Abstract
This research aims to explore the effects of nanoparticles such as alumina (Al2O3) on the physical and mechanical properties of medium density fiberboards (MDF). The nanoparticles are added in urea-formaldehyde (UF) resin with different concentration levels e.g., 1.5%, 3%, [...] Read more.
This research aims to explore the effects of nanoparticles such as alumina (Al2O3) on the physical and mechanical properties of medium density fiberboards (MDF). The nanoparticles are added in urea-formaldehyde (UF) resin with different concentration levels e.g., 1.5%, 3%, and 4.5% by weight. A combination of forest fibers such as Populus Deltuidess (Poplar) and Euamericana (Ghaz) are used as a composite reinforcement due to their exceptional abrasion confrontation as well as their affordability and economic value with Al2O3-UF as a matrix or nanofillers for making the desired nanocomposite specimens. Thermo-gravimetric analysis (TGA) and thermal analytical analysis (TAA) in the form of differential scanning calorimetry (DSC) are carried out and it has been found that increasing the percentage of alumina nanoparticles leads to an increase in the total heat content. The mechanical properties such as internal bonding (IB), modulus of elasticity (MOE) and modulus of rupture (MOR), and physical properties such as density, water absorption (WA), and thickness swelling (TS) of the specimens have been investigated. The experimental results showed that properties of the new Nano-MDF are higher when compared to the normal samples. The results also showed that increasing the concentration of alumina nanoparticles in the urea-formaldehyde resin effects the mechanical properties of panels considerably. Full article
(This article belongs to the Collection Manufacturing Engineering and Mechanical Properties of Composite Materials)
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15 pages, 2607 KiB  
Article
Portland Cements with High Content of Calcined Clay: Mechanical Strength Behaviour and Sulfate Durability
by Carlos H. Aramburo, César Pedrajas and Rafael Talero
Materials 2020, 13(18), 4206; https://doi.org/10.3390/ma13184206 - 22 Sep 2020
Cited by 14 | Viewed by 3342
Abstract
Calcined clay has become the supplementary cementitious materials with the greatest potential to reduce the clinker/cement. In this research, the mechanical strengths and sulphate resistance of blended cements with a high content of calcined clay as a pozzolanic addition were evaluated to demonstrate [...] Read more.
Calcined clay has become the supplementary cementitious materials with the greatest potential to reduce the clinker/cement. In this research, the mechanical strengths and sulphate resistance of blended cements with a high content of calcined clay as a pozzolanic addition were evaluated to demonstrate that these cements could be designed as CEM (cement) type IV/A-SR and IV/B-SR cements by the current European standard UNE-EN 197-1: 2011. The blended cements were prepared by two Portland cements (P1 and PY6) with different mineralogical compositions and a calcined clay. The level of replacement was greater than 40% by weight. The results obtained confirm the decrease in the mechanical strengths and the increase in the sulfate resistance of the two Portland cements when they are replaced by calcined clay at a level of replacement greater than 40%. These results are a consequence of the chemical effect from the pozzolanic activity of the calcined clay. Therefore, there is an important decrease in portlandite levels of paste liquid phase that causes the increase in sulfate resistance and the decrease of the mechanical strengths. Full article
(This article belongs to the Special Issue Low Carbon Cements)
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11 pages, 4898 KiB  
Article
Effect of Annealing on the Microstructure and SERS Performance of Mo-48.2% Ag Films
by Haoliang Sun, Xinxin Lian, Yuanjiang Lv, Yuanhao Liu, Chao Xu, Jiwei Dai, Yilin Wu and Guangxin Wang
Materials 2020, 13(18), 4205; https://doi.org/10.3390/ma13184205 - 22 Sep 2020
Cited by 13 | Viewed by 2455
Abstract
Mo-48.2% Ag films were fabricated by direct current (DC) magnetron sputtering and annealed in an argon atmosphere. The effects of annealing on the surface morphology, resistivity and surface-enhanced Raman scattering (SERS) performance of Mo-48.2% Ag films were investigated. Results show a mass of [...] Read more.
Mo-48.2% Ag films were fabricated by direct current (DC) magnetron sputtering and annealed in an argon atmosphere. The effects of annealing on the surface morphology, resistivity and surface-enhanced Raman scattering (SERS) performance of Mo-48.2% Ag films were investigated. Results show a mass of polyhedral Ag particles grown on the annealed Mo-48.2% Ag films’ surface, which are different from that of as-deposited Mo-Ag film. Moreover, the thickness and the resistivity of Mo-48.2% Ag films gradually decrease as the annealing temperature increases. Furthermore, finite-difference time-domain (FDTD) simulations proved that the re-deposition Ag layer increases the “hot spots” between adjacent Ag nanoparticles, thereby greatly enhancing the local electromagnetic (EM) field. The Ag layer/annealed Mo-48.2% Ag films can identify crystal violet (CV) with concentration lower than 5 × 10−10 M (1 mol/L = 1 M), which indicated that this novel type of particles/films can be applied as ultrasensitive SERS substrates. Full article
(This article belongs to the Section Thin Films and Interfaces)
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17 pages, 14880 KiB  
Article
Characteristics of CO2 and Energy-Saving Concrete with Porous Feldspar
by Jung-Geun Han, Jin-Woo Cho, Sung-Wook Kim, Yun-Suk Park and Jong-Young Lee
Materials 2020, 13(18), 4204; https://doi.org/10.3390/ma13184204 - 21 Sep 2020
Cited by 5 | Viewed by 3262
Abstract
In this study, to reduce the use of cement and sand, porous feldspar with excellent economic efficiency was used as a substitute in the heat storage concrete layer. When porous feldspar and four other silicate minerals were used as substitute materials for sand [...] Read more.
In this study, to reduce the use of cement and sand, porous feldspar with excellent economic efficiency was used as a substitute in the heat storage concrete layer. When porous feldspar and four other silicate minerals were used as substitute materials for sand in cement mortar, the specimen with the porous feldspar exhibited approximately 16–63% higher compressive strength, thereby exhibiting a higher reactivity with cement compared to the other minerals. To compensate for the reduction in strength owing to the decreased cement content, mechanical and chemical activation methods were employed. When the specific surface area of porous feldspar was increased, the unit weight was reduced by approximately 30% and the compressive strength was increased by up to 90%. In addition, the results of the thermal diffusion test confirmed that thermal diffusion increased owing to a reduction in the unit weight; the heat storage characteristics improved owing to the better porosity of feldspar. When chemical activation was performed after reducing the cement content by 5% and replacing the sand with porous feldspar, the compressive strength was found to be approximately twice that of an ordinary cement mortar. In a large-scale model experiment, the heat storage layer containing the porous feldspar exhibited better heat conduction and heat storage characteristics than the heat storage layer composed of ordinary cement mortar. Additionally, energy savings of 57% were observed. Full article
(This article belongs to the Special Issue Supplementary Cementitious Materials in Concrete)
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21 pages, 5979 KiB  
Article
Thermochemical Route for Extraction and Recycling of Critical, Strategic and High-Value Elements from By-Products and End-of-Life Materials, Part II: Processing in Presence of Halogenated Atmosphere
by Ndue Kanari, Eric Allain, Seit Shallari, Frédéric Diot, Sébastien Diliberto, Fabrice Patisson and Jacques Yvon
Materials 2020, 13(18), 4203; https://doi.org/10.3390/ma13184203 - 21 Sep 2020
Cited by 7 | Viewed by 2636
Abstract
During the treatment of copper anode slime (CAS) under an air atmosphere, several aspects of the interactions of its main components (CuAgSe, Cu2−xSeyS1−y, Ag3AuSe2) with oxygen were described in Part I. As a [...] Read more.
During the treatment of copper anode slime (CAS) under an air atmosphere, several aspects of the interactions of its main components (CuAgSe, Cu2−xSeyS1−y, Ag3AuSe2) with oxygen were described in Part I. As a comparative and complementary study, this work deals with the thermal behavior of CAS under air in the presence of polyvinyl chloride (PVC) between 195 and 770 °C. The preliminary thermal treatment of an e-waste sample containing brominated substances was also performed. The reaction products were systematically analyzed by scanning electron microscopy through energy-dispersive spectroscopy (SEM-EDS) and X-ray diffraction (XRD) to investigate the thermal behaviors of the studied samples in a halogenated medium. At low temperatures, the copper, silver and selenium compounds of the CAS reacted with the HCl, issued from PVC degradation, leading to the formation of their respective chlorides. Bromides of valuable metals (Cu, Pb, Sn…) were synthesized during the e-waste treatment at 500 °C and they were distributed between the solid residue and gaseous phase. The data obtained give an insight into the reactivity of several metals towards halogenated substances, which may be valuable information for conducting the extraction and recycling of targeted elements from industrial by-products and end-of-life materials by a thermochemical route. Full article
(This article belongs to the Special Issue Characterization and Processing of Complex Materials)
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16 pages, 26850 KiB  
Article
Formation of Geopolymers Using Sodium Silicate Solution and Aluminum Orthophosphate
by Stephan Partschefeld, Torben Wiegand, Frank Bellmann and Andrea Osburg
Materials 2020, 13(18), 4202; https://doi.org/10.3390/ma13184202 - 21 Sep 2020
Cited by 7 | Viewed by 4394
Abstract
This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, [...] Read more.
This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, 3 and 2). Reaction kinetics of binders were determined by isothermal calorimetric measurements at 20 °C. X-ray diffraction analysis as well as nuclear magnetic resonance (NMR) measurements were performed on binders to determine differences in structure by varying the alkalinity of the sodium silicate solutions and the Si/Al-ratio. The calorimetric results indicated that the higher the alkalinity of the sodium silicate solution, the higher the solubility and degree of conversion of the aluminum orthophosphate. The results of X-ray diffraction and Rietveldt analysis, as well as the NMR measurements, confirmed the assumption of the calorimetric experiments that first the aluminum orthophosphate was dissolved and then a polycondensation to an amorphous aluminosilicate network occurred. The different amounts of amorphous phases formed as a function of the alkalinity of the sodium silicate solution, indicate that tetrahydroxoaluminate species were formed during the dissolution of the aluminum orthophosphate, which reduce the pH value. This led to no further dissolution of the aluminum orthophosphate, which remained unreacted. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
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8 pages, 2423 KiB  
Article
Improved Intrinsic Nonlinear Characteristics of Ta2O5/Al2O3-Based Resistive Random-Access Memory for High-Density Memory Applications
by Ji-Ho Ryu and Sungjun Kim
Materials 2020, 13(18), 4201; https://doi.org/10.3390/ma13184201 - 21 Sep 2020
Cited by 13 | Viewed by 3560
Abstract
The major hindrance for high-density application of two-terminal resistive random-access memory (RRAM) array design is unintentional sneak path leakage through adjacent cells. Herein, we propose a bilayer structure of Ta2O5/Al2O3-based bipolar type RRAM by evaluating [...] Read more.
The major hindrance for high-density application of two-terminal resistive random-access memory (RRAM) array design is unintentional sneak path leakage through adjacent cells. Herein, we propose a bilayer structure of Ta2O5/Al2O3-based bipolar type RRAM by evaluating the intrinsic nonlinear characteristics without integration with an additional transistor and selector device. We conducted X-ray photoelectron spectroscopy (XPS) analysis with different etching times to verify Ta2O5/Al2O3 layers deposited on the TiN bottom electrode. The optimized nonlinear properties with current suppression are obtained by varying Al2O3 thickness. The maximum nonlinearity (~71) is achieved in a Ta2O5/Al2O3 (3 nm) sample. Furthermore, we estimated the comparative read margin based on the I-V characteristics with different thicknesses of Al2O3 film for the crossbar array applications. We expect that this study about the effect of the Al2O3 tunnel barrier thickness on Ta2O5-based memristors could provide a guideline for developing a selector-less RRAM application. Full article
(This article belongs to the Special Issue Physics, Electrical and Structural Properties of Dielectric Layers)
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24 pages, 6525 KiB  
Article
Ultimate Bearing Capacity Analysis of CFRP-Strengthened Shield Segments Using Bonding Slip Behavior Experiments
by Hong-bin Nie and Shuan-cheng Gu
Materials 2020, 13(18), 4200; https://doi.org/10.3390/ma13184200 - 21 Sep 2020
Cited by 4 | Viewed by 2649
Abstract
Shield segments of subway tunnels are often exposed to the combined actions of several hygrothermal factors that could lead to accidents such as water seepage and tunnel collapse. Further, they often break and deform owing to formation pressure. In addition, uncertainties related to [...] Read more.
Shield segments of subway tunnels are often exposed to the combined actions of several hygrothermal factors that could lead to accidents such as water seepage and tunnel collapse. Further, they often break and deform owing to formation pressure. In addition, uncertainties related to the stress relaxation characteristics and bonding performance of carbon-fiber-reinforced plastics (CFRPs) under a hygrothermal environment make their application in subway systems difficult. This study analyzes the effects of the slip-on-bending strength of CFRP-strengthened shield segments in a hygrothermal environment. In the study, the shield segments are damaged at ambient pressure under a combination of humidity (0%, 5%, and 10%) and temperature (20 °C, 25 °C, 30 °C, and 40 °C). An experimental procedure is designed to evaluate a CFRP-reinforced concrete arch. The method predicts the load–slip relationship and maximum shearing stress and strain. Moreover, confined compression tests are conducted on a tunnel segment lining strengthened with CFRP to evaluate the bearing capacity of the CFRP-strengthened shield segments. An equation for the latter’s ultimate bearing capacity is developed based on the elastic layer system theory, stress boundary condition, and bending stress characteristics of axisymmetric elements. It was found that the results from the developed model are compared with the experimental values of CFRP-strengthened shield segments under different humidity values (0%, 5%, and 10%) and a constant temperature. The ultimate strength—the debonding deflection of the CFRP-strengthened shield segment—can be predicted using the proposed ultimate bearing capacity equation with sufficient accuracy. Full article
(This article belongs to the Special Issue Advanced and Emerging Materials-2022)
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14 pages, 4747 KiB  
Article
Investigation on the Curvature Correction Factor of Extension Spring
by P. S. Tan, Ali Akhavan Farid, Atefeh Karimzadeh, Seyed Saeid Rahimian Koloor and Michal Petrů
Materials 2020, 13(18), 4199; https://doi.org/10.3390/ma13184199 - 21 Sep 2020
Cited by 8 | Viewed by 3466
Abstract
The curvature correction factor is an important parameter in the stress calculation formulation of a helical extension spring, which describes the effect of spring wire curvature on the stress increase towards its inner radius. In this study, the parameters affecting the curvature correction [...] Read more.
The curvature correction factor is an important parameter in the stress calculation formulation of a helical extension spring, which describes the effect of spring wire curvature on the stress increase towards its inner radius. In this study, the parameters affecting the curvature correction factor were investigated through theoretical and numerical methods. Several finite element (FE) models of an extension spring were generated to obtain the distribution of the tensile stress in the spring. In this investigation, the hook orientation and the number of coils of the extension spring showed significant effects on the curvature correction factor. These parameters were not considered in the theoretical model for the calculation of the curvature correction factor, causing a deviation between the results of the FE model and the theoretical approach. A set of equations is proposed for the curvature correction factor, which relates both the spring index and the number of coils. These equations can be applied directly to the design of extension springs with a higher safety factor. Full article
(This article belongs to the Special Issue Machine Design: Numerical Simulation and Experimental Tests of Engineering Materials and Devices)
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20 pages, 9598 KiB  
Article
The Influence of the Addition of Plant-Based Natural Fibers (Jute) on Biocemented Sand Using MICP Method
by Md Al Imran, Sivakumar Gowthaman, Kazunori Nakashima and Satoru Kawasaki
Materials 2020, 13(18), 4198; https://doi.org/10.3390/ma13184198 - 21 Sep 2020
Cited by 47 | Viewed by 4803
Abstract
The microbial-induced carbonate precipitation (MICP) method has gained intense attention in recent years as a safe and sustainable alternative for soil improvement and for use in construction materials. In this study, the effects of the addition of plant-based natural jute fibers to MICP-treated [...] Read more.
The microbial-induced carbonate precipitation (MICP) method has gained intense attention in recent years as a safe and sustainable alternative for soil improvement and for use in construction materials. In this study, the effects of the addition of plant-based natural jute fibers to MICP-treated sand and the corresponding microstructures were measured to investigate their subsequent impacts on the MICP-treated biocemented sand. The fibers used were at 0%, 0.5%, 1.5%, 3%, 5%, 10%, and 20% by weight of the sand, while the fiber lengths were 5, 15, and 25 mm. The microbial interactions with the fibers, the CaCO3 precipitation trend, and the biocemented specimen (microstructure) were also evaluated based on the unconfined compressive strength (UCS) values, scanning electron microscopy (SEM), and fluorescence microscopy. The results of this study showed that the added jute fibers improved the engineering properties (ductility, toughness, and brittleness behavior) of the biocemented sand using MICP method. Furthermore, the fiber content more significantly affected the engineering properties of the MICP-treated sand than the fiber length. In this study, the optimal fiber content was 3%, whereas the optimal fiber length was s 15 mm. The SEM results indicated that the fiber facilitated the MICP process by bridging the pores in the calcareous sand, reduced the brittleness of the treated samples, and increased the mechanical properties of the biocemented sand. The results of this study could significantly contribute to further improvement of fiber-reinforced biocemented sand in geotechnical engineering field applications. Full article
(This article belongs to the Special Issue Innovative Materials for Construction)
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17 pages, 6730 KiB  
Article
Estimating the Impact of Nanophases on the Production of Green Cement with High Performance Properties
by Inas A. Ahmed and Najlaa S. Al-Radadi
Materials 2020, 13(18), 4197; https://doi.org/10.3390/ma13184197 - 21 Sep 2020
Cited by 2 | Viewed by 2600
Abstract
Ordinary Portland cement (OPC) production is energy-intensive and significantly contributes to greenhouse gas emissions. One method to reduce the environmental impact of concrete production is the use of an alternative binder, calcium sulfoaluminate cement, which offers lower CO2 emissions and reduces energy [...] Read more.
Ordinary Portland cement (OPC) production is energy-intensive and significantly contributes to greenhouse gas emissions. One method to reduce the environmental impact of concrete production is the use of an alternative binder, calcium sulfoaluminate cement, which offers lower CO2 emissions and reduces energy consumption for cement production. This article describes the effect of adding nanophases, namely belite, calcium sulfoaluminate, calcium aluminum monosulfate (β-C2S, C4A3S, and C4AS, respectively) on OPC’s properties. These phases are made from nanosubstances such as nano-SiO2, calcium nitrate (Ca(NO3)2), and nano-aluminum hydroxide Al(OH)3 with gypsum (CaSO4·2H2O). The impact of β-C2S, C4A3S, and C4AS nanophases on the capabilities of cements was assessed by batch experimentations and IR, XRD, and DSC techniques. The results showed that the substituting of OPC by nano phases (either 10% C4A3S or 10% C4A3S and 10% β-C2S) reduced setting times, reduced the water/cement ratio and the free-lime contents, and increased the combined water contents as well as compressive strength of the cement pastes. The blends had high early and late compressive strength. The IR, XRD, and DSC analyses of the blends of 10% C4A3S or 10% C4A3S and 10% β-C2S cement displayed an increase in the hydrate products and the presence of monosulfate hydrate. The addition of 10% C4AS or 10% C4AS and 10% β-C2S to OPC reduced the setting times, decreased the W/C ratio, free lime, the bulk density, and increased the chemically-combined water and compressive strength. Overall, the results confirmed that the inclusion of the nanophases greatly enhanced the mechanical and durability properties of the OPCs. Full article
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14 pages, 29473 KiB  
Article
Corrosion Fatigue Fracture Characteristics of FSW 7075 Aluminum Alloy Joints
by Qingna Ma, Fei Shao, Linyue Bai, Qian Xu, Xingkun Xie and Mei Shen
Materials 2020, 13(18), 4196; https://doi.org/10.3390/ma13184196 - 21 Sep 2020
Cited by 9 | Viewed by 3144
Abstract
The corrosion fatigue properties and fracture characteristics of friction stir welding joints of 7075 aluminum alloys were studied via corrosion fatigue tests, electrochemical measurements, and corrosion fatigue morphology and microstructure observations. The results show that the corrosion fatigue crack of the friction stir [...] Read more.
The corrosion fatigue properties and fracture characteristics of friction stir welding joints of 7075 aluminum alloys were studied via corrosion fatigue tests, electrochemical measurements, and corrosion fatigue morphology and microstructure observations. The results show that the corrosion fatigue crack of the friction stir welding (FSW) joint of 7075 aluminum alloys originated in the junction zone between the thermomechanically affected zone and the weld nugget zone. The corrosion fatigue life of the joint decreased with increasing stress amplitude, with an S–N curve equation of lgN = 5.845 − 0.014S. Multiple crack sources were observed in the corrosion fatigue fracture. The main crack source originated from the corrosion pits at the interface between the thermomechanically affected zone and the weld nugget zone due to the influence of the coarse microstructure and the large potential difference between both zones. Corrosion morphologies of a rock candy block and an ant nest appeared in the crack propagation zone and the grain boundary of the weld nugget zone. In addition, fatigue speckles and intergranular fractures were observed, as well as brittle fracture characterized by cleavage steps and secondary cracks in the final fracture zone. Full article
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13 pages, 2765 KiB  
Article
Pullout Behavior of Recycled Waste Fishing Net Fibers Embedded in Cement Mortar
by Jun Kil Park, Min Ook Kim and Dong Joo Kim
Materials 2020, 13(18), 4195; https://doi.org/10.3390/ma13184195 - 21 Sep 2020
Cited by 15 | Viewed by 2798
Abstract
In this study, recycled waste fishing net (WFN) short fibers were proposed to be used as short fiber reinforcements. The pullout resistance of WFN short fibers embedded in cement mortar was investigated by conducting fiber pullout tests. Three types of WFN short fibers [...] Read more.
In this study, recycled waste fishing net (WFN) short fibers were proposed to be used as short fiber reinforcements. The pullout resistance of WFN short fibers embedded in cement mortar was investigated by conducting fiber pullout tests. Three types of WFN short fibers and two types of commercial polypropylene (CP) fibers were investigated. To quantitatively compare the pullout resistance of WFN short fibers and CP fibers, pullout parameters, including peak pullout load (peak bond strength), peak fiber stress, slip at peak load, and pullout energy (equivalent bond strength) of the pullout specimens, were analyzed. In addition, the analysis of fiber images, captured by using a stereoscopic digital microscope, before and after pullout tests, elucidated the different mechanisms of fiber pullout corresponding to the type of fibers. The bundled structures of the WFN fibers generated mechanical interaction between fiber and matrix during fiber pullout; consequently, they produced higher bond resistance and more damage on the surface of fibers after the pullout. Therefore, the bundled WFN fibers showed comparable pullout resistance with CP fibers. Full article
(This article belongs to the Special Issue Advanced Fiber-Reinforced Concrete Composites)
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12 pages, 2381 KiB  
Article
THz Fingerprints of Cement-Based Materials
by Jorge S. Dolado, Guido Goracci, Eduardo Duque, Pavel Martauz, Yibing Zuo and Guang Ye
Materials 2020, 13(18), 4194; https://doi.org/10.3390/ma13184194 - 21 Sep 2020
Cited by 11 | Viewed by 2815
Abstract
To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of [...] Read more.
To find materials with an appropriate response to THz radiation is key for the incoming THz technology revolution. Unfortunately, this region of the electromagnetic spectra remains largely unexplored in most materials. The present work aims at unveiling the most significant THz fingerprints of cement-based materials. To this end transmission experiments have been carried out over Ordinary Portland Cement (OPC) and geopolymer (GEO) binder cement pastes in combination with atomistic simulations. These simulations have calculated for the first time, the dielectric response of C-S-H and N-A-S-H gels, the most important hydration products of OPC and GEO cement pastes respectively. Interestingly both the experiments and simulations reveal that both varieties of cement pastes exhibit three main characteristic peaks at frequencies around ~0.6 THz, ~1.05 THz and ~1.35 THz, whose origin is governed by the complex dynamic of their water content, and two extra signals at ~1.95 THz and ~2.75 THz which are likely related to modes involving floppy parts of the dried skeleton. Full article
(This article belongs to the Special Issue Modeling of Cementitious Materials and Structures)
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15 pages, 89900 KiB  
Article
The Collapse of Titanium C-Column due to Thermal Compression
by Leszek Czechowski, Adrian Gliszczyński and Nina Wiącek
Materials 2020, 13(18), 4193; https://doi.org/10.3390/ma13184193 - 21 Sep 2020
Cited by 3 | Viewed by 1930
Abstract
The analysis of structures under higher temperature is important for predicting the ultimate strength of a structure. Therefore, many experimental tests on samples should be undertaken to observe their behaviour and to determine ultimate load. The present work includes the study on a [...] Read more.
The analysis of structures under higher temperature is important for predicting the ultimate strength of a structure. Therefore, many experimental tests on samples should be undertaken to observe their behaviour and to determine ultimate load. The present work includes the study on a thin-walled C-column made of titanium compressed in an elevated temperature. The phenomenon of buckling and the post-buckling state of columns were investigated during heating or compressing in higher temperature. The tests of compression were conducted for several temperature increments by assuming the same preload to determine the load-carrying capacity. The deformations of columns until total damage were measured by using the non-contact Digital Image Correlation Aramis® System (DICAS). The numerical calculations based on the finite element method (FEM) were performed to validate the empirical results. The full characteristics of one-directional tension tests were taken into account in order for them to be constant or dependent on the temperature change. Numerical computations were conducted by employing Green–Lagrange equations for large deflections and strains. Based on our own experiment, the thermal property of titanium as a linear expansion coefficient was stable up to 300 °C in contrast to its mechanical properties. The paper shows the influence of varying material properties as a function of temperature on the behaviour and load-carrying capacity of columns. These aspects cause thin-walled columns made of titanium to endure, in elevated temperatures, significantly smaller maximum loads. Moreover, the critical buckling loads for several types of stiff supports were compared to the maximum loads of columns. The results obtained indicate that the temperature rise in columns by 175 K with regard to ambient temperature brings about the decrease of the maximum load by a half. Full article
(This article belongs to the Special Issue Impact Damage and Mechanical Analysis of Thin-Walled Composites)
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10 pages, 1733 KiB  
Article
A Novel Green Extraction Technique for Extracting Flavonoids from Folium nelumbinis by Changing Osmosis Pressure
by Hai-Yan Fang, Ying-Qin Wei, Meng-Li Zhang and Wei Liu
Materials 2020, 13(18), 4192; https://doi.org/10.3390/ma13184192 - 21 Sep 2020
Cited by 3 | Viewed by 2219
Abstract
A new green and sustainable extraction technique, namely osmosis extraction (OE), was developed for efficient extracting flavonoids from Folium nelumbinis by changing the osmotic pressure. The antioxidant activities of the extracted flavonoids were also evaluated. Ethanol and ammonium sulfate were selected for the [...] Read more.
A new green and sustainable extraction technique, namely osmosis extraction (OE), was developed for efficient extracting flavonoids from Folium nelumbinis by changing the osmotic pressure. The antioxidant activities of the extracted flavonoids were also evaluated. Ethanol and ammonium sulfate were selected for the OE system because they are environmentally friendly. The maximum flavonoids concentration in the top phase was obtained with an ethanol volume fraction of 42.0% and the salt mass of 1.9 g. The kinetic behavior of the extraction process showed that OE had higher efficiencies especially coupled with ultrasonication due to the accompanying and serious morphological changes of Folium nelumbinis cells observed by digital microscope and nano-computed tomography (nano-CT). Results of morphological and anatomical features showed that the higher intracellular chemical potential made the cell expand and even led to bursting. The results also showed that the extraction efficiency of flavonoids with high antioxidant activities was higher than that of the traditional method. The interface effect enhanced the extraction during the salting-out extraction and osmosis was the main factor that improved the extraction efficiency. Full article
(This article belongs to the Special Issue Fundamentals and Applications of Bionano Sensor Techniques)
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12 pages, 6737 KiB  
Article
Strengths, Microstructure and Nanomechanical Properties of Concrete Containing High Volume of Zeolite Powder
by Zhouping Yu, Weijun Yang, Peimin Zhan, Xian Liu and Deng Chen
Materials 2020, 13(18), 4191; https://doi.org/10.3390/ma13184191 - 21 Sep 2020
Cited by 12 | Viewed by 2514
Abstract
In order to save resources and reduce the carbon footprint of concrete, the addition of high volumes of supplementary cementitious materials (SCMs) to replace cement is one of the most effective and promising methods. Zeolite powder (ZP), with a high specific surface area, [...] Read more.
In order to save resources and reduce the carbon footprint of concrete, the addition of high volumes of supplementary cementitious materials (SCMs) to replace cement is one of the most effective and promising methods. Zeolite powder (ZP), with a high specific surface area, exhibits high pozzolanic reactivity in cement-based materials. This paper investigates the effects of ZP addition used to replace cement at the levels of 20%, 40% and 60% on the strength development and microstructure evolution of concrete, and the nanomechanical properties are analyzed using nanoindentation technique. The results show that the replacement of ZP for cement generally has a dilution effect on the concrete, leading to a detrimental effect on the strength development. However, the 20% ZP replacement for cement slightly enhances the 90-day compressive strength. The pore structure analysis shows that the sample with 20% ZP content has a lower total porosity than the control sample. The hydration of ZP goes against the dilution effect and reduces the total porosity of concrete to compact the microstructure. Nanoindentation investigation of the matrix shows that 20% ZP decreases the content of portlandite but increases the content of high density calcium silicate hydrate (C-S-H). This is beneficial for improving the nanomechanical properties of interface transition zone. However, further increases in the content of ZP (40% and 60%) decrease the total volume of C-S-H and increase the porosity to degrade the microstructure. Full article
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16 pages, 1122 KiB  
Article
Synthesis, Selected Transformations, and Biological Activity of Alkoxy Analogues of Lepidilines A and C
by Grzegorz Mlostoń, Małgorzata Celeda, Wiktor Poper, Mateusz Kowalczyk, Katarzyna Gach-Janczak, Anna Janecka and Marcin Jasiński
Materials 2020, 13(18), 4190; https://doi.org/10.3390/ma13184190 - 21 Sep 2020
Cited by 7 | Viewed by 2939
Abstract
Condensation of diacetyl monooxime with formaldimines derived from alkoxyamines in glacial acetic acid at room temperature leads to corresponding 2-unsubstituted imidazole N-oxides bearing an alkoxy substituent at the N(1) atom of the imidazole ring. Subsequent O-benzylation afforded, depending on the type [...] Read more.
Condensation of diacetyl monooxime with formaldimines derived from alkoxyamines in glacial acetic acid at room temperature leads to corresponding 2-unsubstituted imidazole N-oxides bearing an alkoxy substituent at the N(1) atom of the imidazole ring. Subsequent O-benzylation afforded, depending on the type of alkylating agent, either symmetric or nonsymmetric alkoxyimidazolium salts considered as structural analogues of naturally occurring imidazole alkaloids, lepidilines A and C. Some of the obtained salts were tested as precursors of nucleophilic heterocyclic carbenes (NHCs), which in situ reacted with elemental sulfur to give the corresponding N-alkoxyimidazole-2-thiones. The cytotoxic activity of selected 4,5-dimethylimidazolium salts bearing either two benzyloxy or benzyloxy and 1-adamantyloxy groups at N(1) and N(3) atoms was evaluated against HL-60 and MCF-7 cell lines using the MTT (3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide) assay. Notably, in two cases of alkoxyimidazolium salts, no effect of the counterion exchange (Br− → PF6−) on the biological activity was observed. Full article
(This article belongs to the Special Issue Research of Organic Molecules and Materials for Biological Application)
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18 pages, 3930 KiB  
Article
Influence of Crack Width in Alternating Tension–Compression Regimes on Crack-Bridging Behaviour and Degradation of PVA Microfibres Embedded in Cement-Based Matrix
by Majid Ranjbarian, Xiaomeng Ma and Viktor Mechtcherine
Materials 2020, 13(18), 4189; https://doi.org/10.3390/ma13184189 - 21 Sep 2020
Cited by 6 | Viewed by 2483
Abstract
The use of high-performance polymeric microfibres in enhancing the ductility of cementitious composites is widespread. A vivid example is the application of strain-hardening cement-based composites (SHCCs) in the construction industry. However, there are a few challenges which need to be addressed with respect [...] Read more.
The use of high-performance polymeric microfibres in enhancing the ductility of cementitious composites is widespread. A vivid example is the application of strain-hardening cement-based composites (SHCCs) in the construction industry. However, there are a few challenges which need to be addressed with respect to material design. For instance, the ductility of SHCC diminishes under alternating tension–compression loading, where the fibres lose their crack-bridging capacity due to specific damage mechanisms. The damage development and its influence on crack-bridging capacity have been studied in previous works by the authors. The paper at hand focuses on the influence of crack width on the crack-bridging capacity of polymeric microfibres in conjunction with the number of cycles in an alternating tension–compression regime with different cyclic compressive force levels. It shows that bridging capacity can be markedly influenced by crack width: an increase in crack width leads to more severe damage to the fibres and thus to lower crack-bridging capacity. Then, after analysing the specimens by means of electron microscopy, a hypothesis is presented to address the effect of crack width on damage development. Finally, a simple approach is proposed for estimating the influence of different parameters on fibre degradation. Full article
(This article belongs to the Special Issue Mineral-Bonded Composites for Enhanced Structural Impact Safety)
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17 pages, 55800 KiB  
Article
Effects of Alloying Elements (C, Mo) on Hydrogen Assisted Cracking Behaviors of A516-65 Steels in Sour Environments
by Jin Sung Park, Jin Woo Lee, Joong Ki Hwang and Sung Jin Kim
Materials 2020, 13(18), 4188; https://doi.org/10.3390/ma13184188 - 21 Sep 2020
Cited by 13 | Viewed by 2950
Abstract
This study examined the effects of alloying elements (C, Mo) on hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) behaviors of A516-65 grade pressure vessel steel in sour environments. A range of experimental and analytical methods of HIC, SSC, electrochemical permeation, and immersion [...] Read more.
This study examined the effects of alloying elements (C, Mo) on hydrogen-induced cracking (HIC) and sulfide stress cracking (SSC) behaviors of A516-65 grade pressure vessel steel in sour environments. A range of experimental and analytical methods of HIC, SSC, electrochemical permeation, and immersion experiments were used. The steel with a higher C content had a larger fraction of banded pearlite, which acted as a reversible trap for hydrogen, and slower diffusion kinetics of hydrogen was obtained. In addition, a higher hardness in the mid-thickness regions of the steel, due to center segregation, resulted in easier HIC propagation. On the other hand, the steel with a higher Mo content showed more dispersed banded pearlite and a larger amount of irreversibly trapped hydrogen. Nevertheless, the addition of Mo to the steel can deteriorate the surface properties through localized pitting and the local detachment of corrosion products with uneven interfaces, increasing the vulnerability to SSC. The mechanistic reasons for the results are discussed, and a desirable alloy design for ensuring an enhanced resistance to hydrogen assisted cracking (HAC) is proposed. Full article
(This article belongs to the Special Issue Corrosion and Protection of Materials)
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24 pages, 8625 KiB  
Article
Corrosion Susceptibility and Allergy Potential of Austenitic Stainless Steels
by Lucien Reclaru and Lavinia Cosmina Ardelean
Materials 2020, 13(18), 4187; https://doi.org/10.3390/ma13184187 - 21 Sep 2020
Cited by 9 | Viewed by 4046
Abstract
Although called stainless steels, austenitic steels are sensitive to localized corrosion, namely pitting, crevice, and intergranular form. Seventeen grades of steel were tested for localized corrosion. Steels were also tested in general corrosion and in galvanic couplings (steels–precious alloys) used in watchmaking applications. [...] Read more.
Although called stainless steels, austenitic steels are sensitive to localized corrosion, namely pitting, crevice, and intergranular form. Seventeen grades of steel were tested for localized corrosion. Steels were also tested in general corrosion and in galvanic couplings (steels–precious alloys) used in watchmaking applications. The evaluations have been carried out in accordance with the ASTM standards which specifically concern the forms of corrosion namely, general (B117-97, salt fog test), pitting (G48-11, FeCl3), crevice (F746-87) and intergranular (A262-15, Strauss chemical test and G108-94, Electrochemical potentiodynamic reactivation test). All tests revealed sensitivity to corrosion. We have noticed that the transverse face is clearly more sensitive than the longitudinal face, in the direction of rolling process. The same conclusion has been drawn from the tests of nickel release. It should be pointed out that, despite the fact that the grade of steel is in conformity with the classification standards, the behavior is very different from one manufacturer to another, due to parameters dependent on the production process, such as casting volume, alloying additions, and deoxidizing agents. The quantities of nickel released are related to the operations involved in the manufacturing process. Heat treatments reduce the quantities of nickel released. The surface state has little influence on the release. The hardening procedures increase the quantities of nickel released. The quantities of released nickel are influenced by the inclusionary state and the existence of the secondary phases in the steel structure. Another aspect is related to the strong dispersion of results concerning nickel release and corrosion behavior of raw materials. Full article
(This article belongs to the Collection Microstructure and Corrosion Behavior of Advanced Alloys)
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16 pages, 7463 KiB  
Article
Effects of Cooling Rate during Quenching and Tempering Conditions on Microstructures and Mechanical Properties of Carbon Steel Flange
by Haeju Jo, Moonseok Kang, Geon-Woo Park, Byung-Jun Kim, Chang Yong Choi, Hee Sang Park, Sunmi Shin, Wookjin Lee, Yong-Sik Ahn and Jong Bae Jeon
Materials 2020, 13(18), 4186; https://doi.org/10.3390/ma13184186 - 21 Sep 2020
Cited by 13 | Viewed by 8326
Abstract
This study investigated the mechanical properties of steel in flanges, with the goal of obtaining high strength and high toughness. Quenching was applied alone or in combination with tempering at one of nine combinations of three temperatures TTEM and durations tTEM [...] Read more.
This study investigated the mechanical properties of steel in flanges, with the goal of obtaining high strength and high toughness. Quenching was applied alone or in combination with tempering at one of nine combinations of three temperatures TTEM and durations tTEM. Cooling rates at various flange locations during quenching were first estimated using finite element method simulation, and the three locations were selected for mechanical testing in terms of cooling rate. Microstructures of specimens were observed at each condition. Tensile test and hardness test were performed at room temperature, and a Charpy impact test was performed at −46 °C. All specimens had a multiphase microstructure composed of matrix and secondary phases, which decomposed under the various tempering conditions. Decrease in cooling rate (CR) during quenching caused reduction in hardness and strength but did not affect low-temperature toughness significantly. After tempering, hardness and strength were reduced and low-temperature toughness was increased. Microstructures and mechanical properties under the various tempering conditions and CRs during quenching were discussed. This work was based on the properties directly obtained from flanges under industrial processes and is thus expected to be useful for practical applications. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Metals and Alloys)
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