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Materials, Volume 12, Issue 7 (April-1 2019)

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Cover Story (view full-size image) Designers of structures with cellular materials are faced with four important questions: how does [...] Read more.
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Open AccessArticle
Effect of Aluminum Addition on the Microstructure and Properties of Non-Eutectic Sn-20Bi Solder Alloys
Materials 2019, 12(7), 1194; https://doi.org/10.3390/ma12071194
Received: 15 March 2019 / Revised: 3 April 2019 / Accepted: 7 April 2019 / Published: 11 April 2019
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Abstract
This study investigates the effect of aluminum (Al) on the microstructure, micro-hardness, and wettability of environmentally friendly Sn-20Bi-xAl (x = 0, 0.1, 0.3, 0.5 (wt.%)) solder alloys. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis, and X-ray diffraction (XRD), were used [...] Read more.
This study investigates the effect of aluminum (Al) on the microstructure, micro-hardness, and wettability of environmentally friendly Sn-20Bi-xAl (x = 0, 0.1, 0.3, 0.5 (wt.%)) solder alloys. Scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis, and X-ray diffraction (XRD), were used to identify the microstructure morphology and composition. The spreading area and contact angle of the Sn-20Bi-xAl alloys on Cu substrates were used to measure the wettability of solder alloys. The results indicate that Al increased the hardness to a maximum value of ~27.1 HV for x = 0.5. When the content of Al was more than 0.3 wt.%, the hardness change value gradually flattened. From the spreading test results, Al reduced the wettability of solder alloys. When the content of Al was 0.1 wt.%, the change was slight. When more than 0.3 wt.%, the wettability of Sn-20Bi-xAl solder alloys sharply dropped. The corrosion resistance of Sn-20Bi-0.1Al alloy was the best, and the corrosion rate was at the lowest value at 0.092 mm/a due to the dense corrosion products. Full article
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Open AccessArticle
Ordered ZnO/Ni Hollow Microsphere Arrays as Anode Materials for Lithium Ion Batteries
Materials 2019, 12(7), 1193; https://doi.org/10.3390/ma12071193
Received: 27 March 2019 / Revised: 9 April 2019 / Accepted: 10 April 2019 / Published: 11 April 2019
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Abstract
Well-designed nanostructures are very important for the electrochemical performance of lithium-ion electrode materials. In order to improve the electrochemical performance of ZnO-based anode materials, ZnO/Ni composite film, assembled by ordered hollow microsphere arrays, is designed and fabricated by means of magnetron sputtering technique [...] Read more.
Well-designed nanostructures are very important for the electrochemical performance of lithium-ion electrode materials. In order to improve the electrochemical performance of ZnO-based anode materials, ZnO/Ni composite film, assembled by ordered hollow microsphere arrays, is designed and fabricated by means of magnetron sputtering technique using a colloidal crystal template composed of a monolayer of ordered polystyrene (PS) microspheres. The ordered hollow microsphere structure as well as the constituent Ni component of the ZnO/Ni film show major advantages of homogenizing electrode reactions, enhancing electrode reaction kinetics and accommodating volume change of active materials, so they can reduce electrode polarization and stabilize electrode structure. Consequently, the resulting ordered ZnO/Ni hollow microspheres arrays deliver an initial charge capacity of 685 mAh g−1, an initial coulombic efficiency of 68%, and a capacity retention rate of 69% after 100 cycles, all of which are higher than those of the pure ZnO film. These results show progress in developing more stable ZnO-based anode materials for lithium ion batteries. Full article
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Open AccessArticle
Mechanical Behavior of Undoped n-Type GaAs under the Indentation of Berkovich and Flat-Tip Indenters
Materials 2019, 12(7), 1192; https://doi.org/10.3390/ma12071192
Received: 20 March 2019 / Revised: 5 April 2019 / Accepted: 10 April 2019 / Published: 11 April 2019
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Abstract
In this research, the mechanical behavior of undoped n-type GaAs was investigated by nanoindentation experiments using two types of indenters—Berkovich and flat-tip—with force applied up to 1000 mN. From the measured force-depth curves, an obvious pop-in phenomenon occurred at force of 150 mN [...] Read more.
In this research, the mechanical behavior of undoped n-type GaAs was investigated by nanoindentation experiments using two types of indenters—Berkovich and flat-tip—with force applied up to 1000 mN. From the measured force-depth curves, an obvious pop-in phenomenon occurred at force of 150 mN with the flat-tip indenter representing elastic–plastic transition. The Young’s modulus and hardness of GaAs were calculated to be 60–115 GPa and 6–10 GPa, respectively, under Berkovich indenter. Based on the observation of indent imprints, the fracture characteristics of GaAs were also discussed. A recovery of crack by the next indentation was observed at 1000 mN with Berkovich indenter. In the case of flat-tip indentation, however, surface material sank into a wing shape from 400 mN. In this sinking region, a density of fork-shaped sinking, slip lines, and crossed pits contributed to the slip bands, and converging crossed twinning deformations inside the GaAs material were generated. Since cracks and destructions on GaAs surface took place more easily under the flat-tip indentation than that of Berkovich, a machining tool with a sharp tip is recommended for the mechanical machining of brittle materials like GaAs. Full article
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Open AccessArticle
Basic Properties of Calcined Underground Ant Nest Materials and Its Influence on the Compressive Strength of Concrete
Materials 2019, 12(7), 1191; https://doi.org/10.3390/ma12071191
Received: 20 March 2019 / Revised: 5 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
Underground ant nests are typically made of soil and rubble mixed with dead plant bodies, ant secretions, and other organic substances. The clay content is high, and the natural clay materials show pozzolanic activity after calcination. In this study, the underground ant nest [...] Read more.
Underground ant nests are typically made of soil and rubble mixed with dead plant bodies, ant secretions, and other organic substances. The clay content is high, and the natural clay materials show pozzolanic activity after calcination. In this study, the underground ant nest materials of Iridomyrmex anceps, which is a common ant in the Shanghai area, are calcined and ground, and the material properties of calcined ant nest clay powder (CANCP) are characterized from six aspects: chemical composition, particle morphology, specific gravity, specific surface area, particle size distribution and pozzolanic activity index. The pozzolanic activity of CANCP is evaluated by the strength contribution rate of pozzolanic activity, revealing that CANCP is beneficial to the strength of the mortar system from an early age. The influence of CANCP on the compressive strength of concrete is analyzed using three aspects, namely, content, curing age and calcination temperature, and it is found that the three aspects of CANCP have a strong influence on the compressive strength of concrete. Full article
(This article belongs to the Special Issue Concrete and Construction Materials)
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Open AccessArticle
Microstructure, and Mechanical and Wear Properties of Grp/AZ91 Magnesium Matrix Composites
Materials 2019, 12(7), 1190; https://doi.org/10.3390/ma12071190
Received: 4 March 2019 / Revised: 6 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
Based on semi-solid mixing technology, two kinds of as-cast Grp (Graphite particles)/AZ91 composites with different Grp volume fractions (5 vol %, 10 vol %) were prepared; these are called 5 vol % Grp/AZ91 composites and 10 vol % Grp/AZ91 composites, respectively. In order [...] Read more.
Based on semi-solid mixing technology, two kinds of as-cast Grp (Graphite particles)/AZ91 composites with different Grp volume fractions (5 vol %, 10 vol %) were prepared; these are called 5 vol % Grp/AZ91 composites and 10 vol % Grp/AZ91 composites, respectively. In order to eliminate casting defects, refine grains, and improve mechanical properties, thermal deformation analysis of these composites was conducted. The effect of the addition of Grp and thermal deformation on the microstructure, mechanical properties, and wear resistance of AZ91 composite was explored. The results showed that after 5 vol % Grp was added into the as-cast AZ91 alloy, Mg17Al12 phases were no longer precipitated reticularly along the grain boundary, and Al4C3 phases were formed inside the composite. With the increase in the volume fraction of Grp, the grains of the AZ91 composites were steadily refined. With the increase of forging pass, the grain size of 5% Grp/AZ91 composites decreased first, and then increased. Additionally, the Grp size decreased gradually. There was little change in the yield strength, and the tensile strength and elongation were improved to a certain extent. After forging and extrusion of 5% Grp/AZ91 composites once, the grain size and Grp size were further reduced, and the yield strength, tensile strength, and elongation were increased by 23%, 30%, and 65%, respectively, compared with the composite after forging. With the increase of the number of forging passes before extrusion, the grain size decreased little by little, while the Grp size remained unchanged. The average yield strength, tensile strength, and elongation of the composites after forging and extrusion six times were increased by 3%, 3%, and 23%, respectively, compared with the composite after forging and extrusion once. The wear rate and friction coefficient of the 5% Grp/AZ91 composites decreased after forging once, and the wear mechanism was mainly due to ploughing wear. By comparison, the wear rate and friction coefficient of the 5% Grp/AZ91 composites increased in the extrusion state, and the main wear mechanism was from wedge formation and micro-cutting wear. Full article
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Open AccessArticle
Aging Mechanism and Properties of SBS Modified Bitumen under Complex Environmental Conditions
Materials 2019, 12(7), 1189; https://doi.org/10.3390/ma12071189
Received: 13 March 2019 / Revised: 28 March 2019 / Accepted: 5 April 2019 / Published: 11 April 2019
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Abstract
Bitumen aging can lead to the deterioration of asphalt pavement performance, shortening the service life of road. In order to solve the problem that current studies on the ultraviolet (UV) aging of bitumen either ignore the effects of natural environmental conditions or only [...] Read more.
Bitumen aging can lead to the deterioration of asphalt pavement performance, shortening the service life of road. In order to solve the problem that current studies on the ultraviolet (UV) aging of bitumen either ignore the effects of natural environmental conditions or only consider the effects of water. In this study, different aqueous media and UV coupled simulated aging tests were carried out on virgin bitumen and styrene butadiene styrene (SBS) modified bitumen in a UV environment chamber. The combination of macroscopic performance tests and microstructure tests was used to analyze the physical, rheological, and microstructure changes of virgin bitumen and SBS modified bitumen after The film oven test (TFOT) aging and UV aging in different environments (UV, UV + Water, UV + Acid, UV + Salt). Dynamic shear rheometer (DSR) results indicated that UV aging results in the increase of rutting factor and the improvement of rutting resistance at high temperature. The Fourier transform infrared spectrum (FTIR) results illustrated that the bitumen would be oxidized and SBS would be degraded under ultraviolet radiation. The four-component analysis test results showed that light component migrated to the heavy component during the aging process. Moreover, water will aggravate the UV aging of bitumen, and the presence of acid or salt worsens ultraviolet aging. Full article
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Open AccessArticle
Effect of Al Content in the Mg-Based Alloys on the Composition and Corrosion Resistance of Composite Hydroxide Films Formed by Steam Coating
Materials 2019, 12(7), 1188; https://doi.org/10.3390/ma12071188
Received: 16 March 2019 / Revised: 4 April 2019 / Accepted: 5 April 2019 / Published: 11 April 2019
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Abstract
Mg alloys are expected to be used in fields of the transportation industry because of their lightweight property, however, they show low corrosion resistance. To improve the corrosion resistance, preparation of the protective film on Mg alloys is essential. In this study, composite [...] Read more.
Mg alloys are expected to be used in fields of the transportation industry because of their lightweight property, however, they show low corrosion resistance. To improve the corrosion resistance, preparation of the protective film on Mg alloys is essential. In this study, composite hydroxide films were prepared on three types of Mg alloys with different aluminum contents—that is, AZ31, AZ61, and AZ91D—by steam coating to investigate the relationship between the Mg-Al layered double hydroxide (LDH) content in the film and the Al content in the Mg alloys. Scanning electron microscopy (SEM) observation demonstrated that films were formed densely on all Mg alloy surfaces. X-ray diffraction (XRD) analyses revealed that all films prepared on AZ61 and AZ91D were composed of Mg(OH)2, AlOOH, and Mg-Al LDH, while the film containing Mg(OH)2 and Mg-Al LDH were formed only on AZ31. The Mg-Al LDH content in the film prepared on AZ61 was relatively higher than those prepared on AZ31 and AZ91D. The content of AlOOH in the film increased with an increase in the Al content in the Mg alloys. The film thickness changed depending on the treatment time and type of Mg alloy. Polarization curve measurements in 5 mass% NaCl solution demonstrated that the film prepared on the AZ61 showed complete passive behavior within the potential range of −1.0 to −0.64 V. In addition, immersion tests in 5 mass% NaCl aqueous solution for 480 h demonstrated that the film on the AZ61 had superior durability against 5 mass% NaCl aqueous solution. These results indicated that the film on the AZ61 had the most superior corrosion resistance among all samples. The results obtained in this study suggest that the LDH content in the film could be related to the corrosion resistance of the film. Full article
(This article belongs to the Special Issue Corrosion and Corrosion Protection for Light Metals/Alloys)
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Open AccessArticle
A Clue to the Existence of Bonding between Bone and Implant Surface: An In Vivo Study
Materials 2019, 12(7), 1187; https://doi.org/10.3390/ma12071187
Received: 1 April 2019 / Revised: 9 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
We evaluated the shear bond strength of bone–implant contact, or osseointegration, in the rabbit tibia model, and compared the strength between grades 2 and 4 of commercially pure titanium (cp-Ti). A total of 13 grades 2 and 4 cp-Ti implants were used, which [...] Read more.
We evaluated the shear bond strength of bone–implant contact, or osseointegration, in the rabbit tibia model, and compared the strength between grades 2 and 4 of commercially pure titanium (cp-Ti). A total of 13 grades 2 and 4 cp-Ti implants were used, which had an identical cylinder shape and surface topography. Field emission scanning electron microscopy, X-ray photoelectron spectroscopy, and confocal laser microscopy were used for surface analysis. Four grades 2 and 4 cp-Ti implants were inserted into the rabbit tibiae with complete randomization. After six weeks of healing, the experimental animals were sacrificed and the implants were removed en bloc with the surrounding bone. The bone–implant interfaces were three-dimensionally imaged with micro-computed tomography. Using these images, the bone–implant contact area was measured. Counterclockwise rotation force was applied to the implants for the measurement of removal torque values. Shear bond strength was calculated from the measured bone–implant contact and removal torque data. The t-tests were used to compare the outcome measures between the groups, and statistical significance was evaluated at the 0.05 level. Surface analysis showed that grades 2 and 4 cp-Ti implants have similar topographic features. We found no significant difference in the three-dimensional bone–implant contact area between these two implants. However, grade 2 cp-Ti implants had a higher shear bond strength than grade 4 cp-Ti implants (p = 0.032). The surfaces of the grade 2 cp-Ti implants were similar to those of the grade 4 implants in terms of physical characteristics and the quantitative amount of attachment to the bone, whereas the grade 2 surfaces were stronger than the grade 4 surfaces in the bone–surface interaction, indicating osseointegration quality. Full article
(This article belongs to the Special Issue Dental Implant Materials 2019)
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Open AccessArticle
In Vitro Physico-Chemical Characterization and Standardized In Vivo Evaluation of Biocompatibility of a New Synthetic Membrane for Guided Bone Regeneration
Materials 2019, 12(7), 1186; https://doi.org/10.3390/ma12071186
Received: 25 January 2019 / Revised: 8 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
This study’s aim was to evaluate the biocompatibility and bioabsorption of a new membrane for guided bone regeneration (polylactic-co-glycolic acid associated with hydroxyapatite and β-tricalcium phosphate) with three thicknesses (200, 500, and 700 µm) implanted in mice subcutaneously. Scanning electron [...] Read more.
This study’s aim was to evaluate the biocompatibility and bioabsorption of a new membrane for guided bone regeneration (polylactic-co-glycolic acid associated with hydroxyapatite and β-tricalcium phosphate) with three thicknesses (200, 500, and 700 µm) implanted in mice subcutaneously. Scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, and the quantification of carbon, hydrogen and nitrogen were used to characterize the physico-chemical properties. One hundred Balb-C mice were divided into 5 experimental groups: Group 1—Sham (without implantation); Group 2—200 μm; Group 3—500 μm; Group 4—700 μm; and Group 5—Pratix®. Each group was subdivided into four experimental periods (7, 30, 60 and 90 days). Samples were collected and processed for histological and histomorphometrical evaluation. The membranes showed no moderate or severe tissue reactions during the experimental periods studied. The 500-μm membrane showed no tissue reaction during any experimental period. The 200-μm membrane began to exhibit fragmentation after 30 days, while the 500-μm and 700-µm membranes began fragmentation at 90 days. All membranes studied were biocompatible and the 500 µm membrane showed the best results for absorption and tissue reaction, indicating its potential for clinical guided bone regeneration. Full article
(This article belongs to the Special Issue Current and Future Trends in Dental Materials)
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Open AccessArticle
On the Thickness Quantification of Composite Materials by Using Lock-In Thermography
Materials 2019, 12(7), 1185; https://doi.org/10.3390/ma12071185
Received: 4 March 2019 / Revised: 3 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
Many structural components made of composite materials need an accurate thickness control during fabrication and/or maintenance. In this regard, various non-destructive techniques can be used for the online measuring of thickness of large components such as wings and fuselage in the aerospace industry. [...] Read more.
Many structural components made of composite materials need an accurate thickness control during fabrication and/or maintenance. In this regard, various non-destructive techniques can be used for the online measuring of thickness of large components such as wings and fuselage in the aerospace industry. In this work, the capabilities of lock-in thermography technique in thickness measurement of glass fiber reinforced plastic material were investigated and a correct procedure has been proposed to ensure the best measurement accuracy. An analytical approach and several tests were carried out on a sample specimen with the aim to study the main test parameters. Finally, the limits of technique have been discussed. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Biodentine Boosts, WhiteProRoot®MTA Increases and Life® Suppresses Odontoblast Activity
Materials 2019, 12(7), 1184; https://doi.org/10.3390/ma12071184
Received: 5 March 2019 / Revised: 6 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
(1) Background: When pulp exposure occurs, reparative dentinogenesis can be induced by direct pulp capping to maintain the vitality and function of the tissue. The aim of this work was to assess the cytotoxicity and bioactivity of three different direct pulp capping materials, [...] Read more.
(1) Background: When pulp exposure occurs, reparative dentinogenesis can be induced by direct pulp capping to maintain the vitality and function of the tissue. The aim of this work was to assess the cytotoxicity and bioactivity of three different direct pulp capping materials, calcium hydroxide (Life®), mineral trioxide aggregate (WhiteProRoot®MTA) and calcium silicate (Biodentine), in an odontoblast-like mouse cell line (MDPC-23). (2) Methods: Metabolic activity was assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide test (MTT)assay, viability by the sulforhodamine B (SRB) assay, and the type of death and cell cycle analysis by flow cytometry. Alkaline phosphatase was evaluated by polymerase chain reaction (PCR), and dentin sialoprotein expression was assessed by immunocytochemistry. Mineralization was determined by the Alizarin Red S colorimetric assay and quantified by spectrophotometry. (3) Results: Life® induced a decrease in metabolic activity and viability, which is associated with an increase cell death. WhiteProRoot®MTA and Biodentine™ induced similar effects in cytotoxicity assays, with an increase in the expression of dentin sialoprotein (DSP) and formation of mineralized deposits, especially with Biodentine™. (4) Conclusions: The results of WhiteProRoot®MTA confirm its indication for these therapies, justifying its recognition as the “gold standard”. Biodentine™ may be an alternative, since they promote the same cellular response that mineral trioxide aggregate (MTA) does. Full article
(This article belongs to the Special Issue Biomaterials for Dental Healing)
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Open AccessArticle
Reduction Temperature-Dependent Nanoscale Morphological Transformation and Electrical Conductivity of Silicate Glass Microchannel Plate
Materials 2019, 12(7), 1183; https://doi.org/10.3390/ma12071183
Received: 4 March 2019 / Revised: 21 March 2019 / Accepted: 8 April 2019 / Published: 11 April 2019
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Abstract
Lead silicate glasses are fundamental materials to a microchannel plate (MCP), which is a two dimensional array of a microscopic channel charge particle multiplier. Hydrogen reduction is the core stage to determine the electrical conductivity of lead silicate glass MCP multipliers. The nanoscale [...] Read more.
Lead silicate glasses are fundamental materials to a microchannel plate (MCP), which is a two dimensional array of a microscopic channel charge particle multiplier. Hydrogen reduction is the core stage to determine the electrical conductivity of lead silicate glass MCP multipliers. The nanoscale morphologies and microscopic potential distributions of silicate glass at different reduction temperatures were investigated via atomic force microscope (AFM) and Kelvin force microscopy (KFM). We found that the bulk resistance of MCPs ballooned exponentially with the spacing of conducting islands. Moreover, bulk resistance and the spacing of conducting islands both have the BiDoseResp trend dependence on the hydrogen reduction temperature. Elements composition and valence states of lead silicate glass were characterized by X-ray photoelectron spectroscopy (XPS). The results indicated that the conducting island was an assemblage of the Pb atom originated from the reduction of Pb2+ and Pb4+. Thus, this showed the important influence of the hydrogen temperature and nanoscale morphological transformation on modulating the physical effects of MCPs, and opened up new possibilities to characterize the nanoscale electronic performance of multiphase silicate glass. Full article
(This article belongs to the Special Issue In Situ TEM and AFM for Investigation of Materials)
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Open AccessArticle
One-Step Synthesis of Environmentally Friendly Superhydrophilic and Superhydrophobic Sponges for Oil/Water Separation
Materials 2019, 12(7), 1182; https://doi.org/10.3390/ma12071182
Received: 15 March 2019 / Revised: 28 March 2019 / Accepted: 5 April 2019 / Published: 11 April 2019
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Abstract
Environmentally friendly superhydrophilic and superhydrophobic sponges were synthesized using a one-step approach for oil/water separation. A superhydrophilic or superhydrophobic sponge (MFS/CC-DKGM or MFS/CC-PDMS) was synthesized by one-step coating of melamine formaldehyde sponge (MFS) with a mixture of calcium carbonate (CC) rods and deacetylized [...] Read more.
Environmentally friendly superhydrophilic and superhydrophobic sponges were synthesized using a one-step approach for oil/water separation. A superhydrophilic or superhydrophobic sponge (MFS/CC-DKGM or MFS/CC-PDMS) was synthesized by one-step coating of melamine formaldehyde sponge (MFS) with a mixture of calcium carbonate (CC) rods and deacetylized Konjac glucomannan (DKGM) [or polydimethylsiloxane (PDMS)]. The MFS/CC-PDMS showed excellent absorption capacity, which reached 52–76 g/g following immersion into various types of oil/water mixtures. Furthermore, the MFS/CC-DKGM and MFS/CC-PDMS exhibited excellent water- and oil-flux performances, which reached 4,702 L/m2 h and 19,591 L/m2 h, respectively, when they were used as filters. The MFS/CC-DKGM and MFS/CC-PDMS maintained their wettability characteristics relatively well after the chemical, thermal, and mechanical stability tests. Full article
(This article belongs to the Special Issue Smart Nanomaterials for Environmental Remediation)
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Open AccessArticle
Effect of Urchin-Like Mullite Whiskers on the High-Temperature Performance of Porous SiO2-Based Ceramic Molds
Materials 2019, 12(7), 1181; https://doi.org/10.3390/ma12071181
Received: 12 March 2019 / Revised: 5 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
Urchin-like mullite whiskers synthesized by the vapor–liquid–solid growth method were used to improve the high-temperature performance of porous gelcast SiO2-based ceramic molds. Aluminum was used to facilitate the synthesis of polycrystal urchin-like mullite whiskers which acted as bridges between particles. Scanning [...] Read more.
Urchin-like mullite whiskers synthesized by the vapor–liquid–solid growth method were used to improve the high-temperature performance of porous gelcast SiO2-based ceramic molds. Aluminum was used to facilitate the synthesis of polycrystal urchin-like mullite whiskers which acted as bridges between particles. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were used to investigate the microstructures and phase compositions of the sintered ceramic samples, respectively. Urchin-like mullite whiskers with diameters of 0.2~1.0 µm and lengths of 1.0~8.0 µm were successfully synthesized in SiO2-based ceramic. When 15 vol% Al was added, the high-temperature strength at 1200 °C was improved from 8.5 to 27.5 MPa, and the creep deformation was decreased to 0.56 mm. Meanwhile, a sintering shrinkage below 0.3% was obtained, and the de-coring rate was accelerated by 67% compared to that of the pure SiO2-based ceramic. This method showed excellent high-temperature strength and high precision, having remarkable potential in the fabrication of hollow turbine blades. Full article
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Open AccessArticle
A Nanocomposite Based on Reduced Graphene and Gold Nanoparticles for Highly Sensitive Electrochemical Detection of Pseudomonas aeruginosa through Its Virulence Factors
Materials 2019, 12(7), 1180; https://doi.org/10.3390/ma12071180
Received: 24 March 2019 / Revised: 8 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
Pyoverdine is a fluorescent siderophore produced by Pseudomonas aeruginosa that can be considered as a detectable marker in nosocomial infections. The presence of pyoverdine in water can be directly linked to the presence of the P. aeruginosa, thus being a nontoxic and [...] Read more.
Pyoverdine is a fluorescent siderophore produced by Pseudomonas aeruginosa that can be considered as a detectable marker in nosocomial infections. The presence of pyoverdine in water can be directly linked to the presence of the P. aeruginosa, thus being a nontoxic and low-cost marker for the detection of biological contamination. A novel platform was developed and applied for the electrochemical selective and sensitive detection of pyoverdine, based on a graphene/graphite-modified screen-printed electrode (SPE) that was electrochemically reduced and decorated with gold nanoparticles (NPs). The optimized sensor presenting higher sensitivity towards pyoverdine was successfully applied for its detection in real samples (serum, saliva, and tap water), in the presence of various interfering species. The excellent analytical performances underline the premises for an early diagnosis kit of bacterial infections based on electrochemical sensors. Full article
(This article belongs to the Special Issue Graphene Oxide: Synthesis, Reduction, and Frontier Applications)
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Open AccessArticle
Analysis of Surface Geometry Changes after Hybrid Milling and Burnishing by Ceramic Ball
Materials 2019, 12(7), 1179; https://doi.org/10.3390/ma12071179
Received: 20 March 2019 / Revised: 3 April 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
The production of modern machines requires parts with much greater geometric accuracy and surface geometry (SG) precision than several years ago. These requirements are met by so-called hybrid technologies that must simultaneously be inexpensive to implement. The integration of treatment procedures (usually in [...] Read more.
The production of modern machines requires parts with much greater geometric accuracy and surface geometry (SG) precision than several years ago. These requirements are met by so-called hybrid technologies that must simultaneously be inexpensive to implement. The integration of treatment procedures (usually in one operation) is geared towards achieving a synergistic effect. Combining different treatments from various technologies produces synergy, i.e., benefits greater than the optimization of each individual process done separately. This paper presents experimental results and numerical experiment data on surface plastic deformation. The hybrid technology used in the study was a combination of milling and finishing with plastic burnishing using a ceramic ball. These processes were integrated on a multi-axis CNC machining center. The plastic deformations of real surfaces were determined in simulations. The paper also discusses the structure of the model and how to use it to conduct a finite element method (FEM) computer simulation. The aim of the study was to determine how to use the potential developed model of hybrid treatment to predict the surface performance expressed by the amplitude, volume, and functional parameters of the surface geometry, with the EN-ISO 25178-2 profile. Full article
(This article belongs to the Special Issue Microstructure and Mechanical Properties of Steels)
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Open AccessArticle
DNA Adsorption Studies of Poly(4,4′-Cychlohexylidene Bisphenol Oxalate)/Silica Nanocomposites
Materials 2019, 12(7), 1178; https://doi.org/10.3390/ma12071178
Received: 27 January 2019 / Revised: 5 March 2019 / Accepted: 6 March 2019 / Published: 11 April 2019
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Abstract
The present study deals with the synthesis, characterization, and DNA extraction of poly(4,4′-cyclohexylidene bisphenol oxalate)/silica (Si) nanocomposites (NCs). The effects of varying the monomer/Si (3.7%, 7%, and 13%) ratio towards the size and morphology of the resulting NC and its DNA extraction capabilities [...] Read more.
The present study deals with the synthesis, characterization, and DNA extraction of poly(4,4′-cyclohexylidene bisphenol oxalate)/silica (Si) nanocomposites (NCs). The effects of varying the monomer/Si (3.7%, 7%, and 13%) ratio towards the size and morphology of the resulting NC and its DNA extraction capabilities have also been studied. For the NC synthesis, two different methods were followed, including the direct mixing of poly(4,4′-cyclohexylidene bisphenol oxalate) with fumed Si, and in situ polymerization of the 4,4′-cyclohexylidene bisphenol monomer in the presence of fumed silica (11 nm). The formed NCs were thoroughly investigated by using different techniques such as scanning electron microscopy (SEM), fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), powdered X-ray diffraction (XRD), and Brunauer–Emmett–Teller (BET) analysis where the results supported that there was the successful formation of poly(4,4′-cyclohexylidene bisphenol oxalate)/Si NC. Within the three different NC samples, the one with 13% Si was found to maintain a very high surface area of 12.237 m2/g, as compared to the other two samples consisting of 7% Si (3.362 m2/g) and 3.7% Si (1.788 m2/g). Further, the solid phase DNA extraction studies indicated that the efficiency is strongly influenced by the amount of polymer (0.2 g > 0.1 g > 0.02 g) and the type of binding buffer. Among the three binding buffers tested, the guanidine hydrochloride/EtOH buffer produced the most satisfactory results in terms of yield (1,348,000 ng) and extraction efficiency (3370 ng/mL) as compared to the other two buffers of NaCl (2 M) and phosphate buffered silane. Based on our results, it can be indicated that the developed poly(4,4′-cyclohexylidene bisphenol oxalate)/Si NC can serve as one of the suitable candidates for the extraction of DNA in high amounts as compared to other traditional solid phase approaches. Full article
(This article belongs to the Special Issue Organic and Carbon Gels: Properties and Application)
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Open AccessReview
Conventional and Microwave Hydrothermal Synthesis and Application of Functional Materials: A Review
Materials 2019, 12(7), 1177; https://doi.org/10.3390/ma12071177
Received: 5 March 2019 / Revised: 29 March 2019 / Accepted: 9 April 2019 / Published: 11 April 2019
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Abstract
With the continuous development and progress of materials science, increasingly more attention has been paid to the new technology of powder synthesis and material preparation. The hydrothermal method is a promising liquid phase preparation technology that has developed rapidly during recent years. It [...] Read more.
With the continuous development and progress of materials science, increasingly more attention has been paid to the new technology of powder synthesis and material preparation. The hydrothermal method is a promising liquid phase preparation technology that has developed rapidly during recent years. It is widely used in many fields, such as the piezoelectric, ferroelectric, ceramic powder, and oxide film fields. The hydrothermal method has resulted in many new methods during the long-term research process, such as adding other force fields to the hydrothermal condition reaction system. These force fields mainly include direct current, electric, magnetic (autoclaves composed of non-ferroelectric materials), and microwave fields. Among them, the microwave hydrothermal method, as an extension of the hydrothermal reaction, cleverly uses the microwave temperature to compensate for the lack of temperature in the hydrothermal method, allowing better practical application. This paper reviews the development of the hydrothermal and microwave hydrothermal methods, introduces their reaction mechanisms, and focuses on the practical application of the two methods. Full article
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Open AccessFeature PaperArticle
Chitosan Nanoparticles Rescue Rotenone-Mediated Cell Death
Materials 2019, 12(7), 1176; https://doi.org/10.3390/ma12071176
Received: 13 March 2019 / Revised: 1 April 2019 / Accepted: 4 April 2019 / Published: 11 April 2019
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Abstract
The aim of the present investigation was to study the anti-oxidant effect of chitosan nanoparticles on a human SH-SY5Y neuroblastoma cell line using a rotenone model to generate reactive oxygen species. Chitosan nanoparticles were synthesized using an ionotropic gelation method. The obtained nanoparticles [...] Read more.
The aim of the present investigation was to study the anti-oxidant effect of chitosan nanoparticles on a human SH-SY5Y neuroblastoma cell line using a rotenone model to generate reactive oxygen species. Chitosan nanoparticles were synthesized using an ionotropic gelation method. The obtained nanoparticles were characterized using various analytical techniques such as Dynamic Light Scattering, Scanning Electron Microscopy, Transmission Electron Microscopy, Fourier Transmission Infrared spectroscopy and Atomic Force Microscopy. Incubation of SH-SY5Y cells with 50 µM rotenone resulted in 35–50% cell death within 24 h of incubation time. Annexin V/Propidium iodide dual staining verified that the majority of neuronal cell death occurred via the apoptotic pathway. The incubation of cells with chitosan nanoparticles reduced rotenone-initiated cytotoxicity and apoptotic cell death. Given that rotenone insult to cells causes oxidative stress, our results suggest that Chitosan nanoparticles have antioxidant and anti-apoptotic properties. Chitosan can not only serve as a novel therapeutic drug in the near future but also as a carrier for combo-therapy. Full article
(This article belongs to the Special Issue Environmentally Friendly Polymers and Polymer Composites)
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Open AccessArticle
Hot-Deformation Behavior of High-Nitrogen Austenitic Stainless Steel under Continuous Cooling: Physical Simulation of Surface Microstructure Evolution of Superheavy Forgings during Hot Forging
Materials 2019, 12(7), 1175; https://doi.org/10.3390/ma12071175
Received: 26 March 2019 / Revised: 6 April 2019 / Accepted: 9 April 2019 / Published: 10 April 2019
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Abstract
Superheavy forgings are increasingly used in the nuclear industry. The strain rate is extremely low during hot forging due to the huge size of the superheavy forging; in fact, the surface temperature of the forging decreases obviously during each deformation step. Hot-deformation behavior [...] Read more.
Superheavy forgings are increasingly used in the nuclear industry. The strain rate is extremely low during hot forging due to the huge size of the superheavy forging; in fact, the surface temperature of the forging decreases obviously during each deformation step. Hot-deformation behavior differs from that of isothermal deformation. In this study, 18Mn18Cr0.6N steel was selected as a model material. Hot-compression tests were conducted using a Gleeble 3800 simulator at a strain rate of 10−4 s−1 and continuous cooling rates of 0.0125 Ks−1 and 0.025 Ks−1. The microstructure was observed using electron backscatter diffraction analysis and transmission electron microscopy. The flow stress increased with increasing strain: the higher the cooling rate, the higher was the hardening rate. Continuous cooling inhibited dynamic recrystallization by delaying its nucleation. The subgrain/cell size increased linearly with increasing final temperature of deformation in the temperature range 1273 to 1448 K. An intense <001> texture formed in 0.8-strained specimens and the matrix exhibited a low Taylor factor orientation. Most dislocations were separately distributed in subgrains and did not entangle with each other or with the subgrain boundary. Dislocation arrays transferred easily through boundaries and dislocation accumulation at boundaries was weak. This study contributes to understanding the hot-forging process of superheavy forgings. Full article
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Open AccessArticle
Biomechanical Behaviour and Biocompatibility of Ureidopyrimidinone-Polycarbonate Electrospun and Polypropylene Meshes in a Hernia Repair in Rabbits
Materials 2019, 12(7), 1174; https://doi.org/10.3390/ma12071174
Received: 5 March 2019 / Revised: 4 April 2019 / Accepted: 9 April 2019 / Published: 10 April 2019
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Abstract
Although mesh use has significantly improved the outcomes of hernia and pelvic organ prolapse repair, long-term recurrence rates remain unacceptably high. We aim to determine the in vivo degradation and functional outcome of reconstructed abdominal wall defects, using slowly degradable electrospun ureidopyrimidinone moieties [...] Read more.
Although mesh use has significantly improved the outcomes of hernia and pelvic organ prolapse repair, long-term recurrence rates remain unacceptably high. We aim to determine the in vivo degradation and functional outcome of reconstructed abdominal wall defects, using slowly degradable electrospun ureidopyrimidinone moieties incorporated into a polycarbonate backbone (UPy-PC) implant compared to an ultra-lightweight polypropylene (PP) textile mesh with high pore stability. Twenty four New-Zealand rabbits were implanted with UPy-PC or PP to either reinforce a primary fascial defect repair or to cover (referred to as gap bridging) a full-thickness abdominal wall defect. Explants were harvested at 30, 90 and 180 days. The primary outcome measure was uniaxial tensiometry. Secondary outcomes were the recurrence of herniation, morphometry for musculofascial tissue characteristics, inflammatory response and neovascularization. PP explants compromised physiological abdominal wall compliance from 90 days onwards and UPy-PC from 180 days. UPy-PC meshes induced a more vigorous inflammatory response than PP at all time points. We observed progressively more signs of muscle atrophy and intramuscular fatty infiltration in the entire explant area for both mesh types. UPy-PC implants are replaced by a connective tissue stiff enough to prevent abdominal wall herniation in two-thirds of the gap-bridged full-thickness abdominal wall defects. However, in one-third there was sub-clinical herniation. The novel electrospun material did slightly better than the textile PP yet outcomes were still suboptimal. Further research should investigate what drives muscular atrophy, and whether novel polymers would eventually generate a physiological neotissue and can prevent failure and/or avoid collateral damage. Full article
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Open AccessArticle
The Potential of Ladle Slag and Electric Arc Furnace Slag use in Synthesizing Alkali Activated Materials; the Influence of Curing on Mechanical Properties
Materials 2019, 12(7), 1173; https://doi.org/10.3390/ma12071173
Received: 5 March 2019 / Revised: 1 April 2019 / Accepted: 9 April 2019 / Published: 10 April 2019
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Abstract
Alkali activation is studied as a potential technology to produce a group of high performance building materials from industrial residues such as metallurgical slag. Namely, slags containing aluminate and silicate form a useful solid material when activated by an alkaline solution. The alkali-activated [...] Read more.
Alkali activation is studied as a potential technology to produce a group of high performance building materials from industrial residues such as metallurgical slag. Namely, slags containing aluminate and silicate form a useful solid material when activated by an alkaline solution. The alkali-activated (AA) slag-based materials are promising alternative products for civil engineering sector and industrial purposes. In the present study the locally available electric arc furnace steel slag (Slag A) and the ladle furnace basic slag (Slag R) from different metallurgical industries in Slovenia were selected for alkali activation because of promising amorphous Al/Si rich content. Different mixtures of selected precursors were prepared in the Slag A/Slag R ratios 1/0, 3/1, 1/1, 1/3 and 0/1 and further activated with potassium silicate using an activator to slag ratio of 1:2 in order to select the optimal composition with respect to their mechanical properties. Bending strength of investigated samples ranged between 4 and 18 MPa, whereas compressive strength varied between 30 and 60 MPa. The optimal mixture (Slag A/Slag R = 1/1) was further used to study strength development under the influence of different curing temperatures at room temperature (R.T.), and in a heat-chamber at 50, 70 and 90 °C, and the effects of curing time for 1, 3, 7 and 28 days was furthermore studied. The influence of curing time at room temperature on the mechanical strength at an early age was found to be nearly linear. Further, it was shown that specimens cured at 70 °C for 3 days attained almost identical (bending/compressive) strength to those cured at room temperature for 28 days. Additionally, microstructure evaluation of input materials and samples cured under different conditions was performed by means of XRD, FTIR, SEM and mercury intrusion porosimetry (MIP). Full article
(This article belongs to the Section Construction and Building Materials)
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Open AccessLetter
Contrastive Studies between Laser Repairing and Plasma Arc Repairing on Single-Crystal Ni-Based Superalloy
Materials 2019, 12(7), 1172; https://doi.org/10.3390/ma12071172
Received: 12 March 2019 / Revised: 29 March 2019 / Accepted: 3 April 2019 / Published: 10 April 2019
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Abstract
Laser repairing and plasma arc repairing experiments on the single-crystal Ni-based superalloy DD407(Ni-7.82Cr-5.34Co-2.25Mo-4.88W-6.02Al-1.94Ti-3.49Ta in wt.%) were carried out in this paper, and the differences in microstructures and mechanical properties varying with depth between the two repairing methods were studied. Comparing the two repairing [...] Read more.
Laser repairing and plasma arc repairing experiments on the single-crystal Ni-based superalloy DD407(Ni-7.82Cr-5.34Co-2.25Mo-4.88W-6.02Al-1.94Ti-3.49Ta in wt.%) were carried out in this paper, and the differences in microstructures and mechanical properties varying with depth between the two repairing methods were studied. Comparing the two repairing processes, both the fusion zone can maintain single-crystal epitaxial growth with no significant cracks and have similar fine γ′ precipitates. Nevertheless, the columnar-to-equiaxed transition phenomenon occurred on the top of the fusion zone during the laser re-melting process but was not very obvious on the top surface of the fusion zone during the plasma arc re-melting process. In addition, both the DD407 superalloy conducted with the two repairing processes had a large microhardness and a great Young’s modulus in the fusion zone. Full article
(This article belongs to the Special Issue Advanced Technology for Materials Synthesis and Processing)
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Open AccessArticle
Combined Strengthening Techniques to Improve the Out-of-Plane Performance of Masonry Walls
Materials 2019, 12(7), 1171; https://doi.org/10.3390/ma12071171
Received: 18 February 2019 / Revised: 8 March 2019 / Accepted: 8 March 2019 / Published: 10 April 2019
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Abstract
The purpose of this study is to improve the performance of walls under out-of-plane loads especially when subjected to the hammering action of the floors. The idea behind the paper is to provide the masonry walls with a device that behaves like a [...] Read more.
The purpose of this study is to improve the performance of walls under out-of-plane loads especially when subjected to the hammering action of the floors. The idea behind the paper is to provide the masonry walls with a device that behaves like a buttress, without having to build a traditional buttress. The solution presented in this paper consists of a mechanical coupling between the three-dimensional net of steel ribbons of the CAM (Active Confinement of Masonry) system and the CFRP (Carbon Fiber Reinforced Polymer) strips. Since the steel ribbons of the CAM system have a pre-tension, the mechanical coupling allows the steel ribbons to establish a semi-rigid transverse link between the CFRP strips bonded on the two opposite sides of a wall. Therefore, two vertical CFRP strips tied by the steel ribbons behave like the flanges of an I-beam and the flexural strength of the ideal I-beam counteracts the out-of-plane displacements of the wall. The experimental results showed that the combined technique inherits the strong points of both constituent techniques. In fact, the delamination load is comparable to that of the specimens reinforced with the CFRP strips and the overall behavior is as ductile as for the specimens reinforced with the CAM system. They also inspired a more performing combined technique. Full article
(This article belongs to the Special Issue Reinforcement and Repair Materials for Masonry Structures)
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Open AccessArticle
A Multiscale Model of Oxidation Kinetics for Cu-Based Oxygen Carrier in Chemical Looping with Oxygen Uncoupling
Materials 2019, 12(7), 1170; https://doi.org/10.3390/ma12071170
Received: 23 January 2019 / Revised: 28 March 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
Copper oxide is one of the promising oxygen carrier materials in chemical looping with oxygen uncoupling (CLOU) technology, cycling between Cu2O and CuO. In this study, a multiscale model was developed to describe the oxidation kinetics of the Cu-based oxygen carrier [...] Read more.
Copper oxide is one of the promising oxygen carrier materials in chemical looping with oxygen uncoupling (CLOU) technology, cycling between Cu2O and CuO. In this study, a multiscale model was developed to describe the oxidation kinetics of the Cu-based oxygen carrier particle with oxygen, including surface, grain, and particle scale. It was considered that the solid product grows with the morphology of disperse islands on the grain surface, and O2 contacts with two different kinds of grain surfaces in the grain scale model, that is, Cu2O surface (solid reactant surface) and CuO surface (solid product surface). The two-stage behavior of the oxidation reaction of the Cu-based oxygen carrier was predicted successfully using the developed model, and the model results showed good agreement with experimental data in the literature. The effects of oxygen partial pressure, temperature, and particle structure on the oxidation performance were analyzed. The modeling results indicated that the transition of the conversion curve occurs when product islands cover most part of the grain surface. The oxygen partial pressure and particle structure have an obvious influence on the duration time of the fast reaction stage. Furthermore, the influence of the external mass transfer and the change of effectiveness factor during the oxidation reaction process were discussed to investigate the controlling step of the reaction. It was concluded that the external mass transfer step hardly affects the reaction performance under the particle sizes normally used in CLOU. The value of the effectiveness factor increases as the reaction goes by, which means the chemical reaction resistance at grain scale increases resulting from the growing number of product islands on the grain surface. Full article
(This article belongs to the Special Issue Micro/Nano Materials for Clean Energy and Environment)
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Open AccessFeature PaperArticle
Toward a Fully Analytical Contact Resistance Expression in Organic Transistors
Materials 2019, 12(7), 1169; https://doi.org/10.3390/ma12071169
Received: 7 March 2019 / Revised: 8 April 2019 / Accepted: 9 April 2019 / Published: 10 April 2019
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Abstract
Contact resistance is a major characteristic of organic transistors, and its importance has received renewed attention due to the recent revelation of mobility overestimation. In this article, we propose a method to describe the contact resistance as a closed-form compact equation of the [...] Read more.
Contact resistance is a major characteristic of organic transistors, and its importance has received renewed attention due to the recent revelation of mobility overestimation. In this article, we propose a method to describe the contact resistance as a closed-form compact equation of the materials, interfaces, and geometrical parameters. The proposed model allows us to quantitatively understand the correlation between charge-injection and transport properties, while providing a tool for performance prediction and optimization. This theory is applied to a set of experimentally fabricated devices to exemplify how to utilize the model in practice. Full article
(This article belongs to the Section Optics and Photonics)
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Open AccessArticle
Accuracy of Eddy-Current and Radar Methods Used in Reinforcement Detection
Materials 2019, 12(7), 1168; https://doi.org/10.3390/ma12071168
Received: 4 March 2019 / Revised: 3 April 2019 / Accepted: 5 April 2019 / Published: 10 April 2019
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Abstract
This article presents results from non-destructive testing (NDT) that referred to the location and diameter or rebars in beam and slab members. The aim of paper was to demonstrate that the accuracy and deviations of the NDT methods could be higher than the [...] Read more.
This article presents results from non-destructive testing (NDT) that referred to the location and diameter or rebars in beam and slab members. The aim of paper was to demonstrate that the accuracy and deviations of the NDT methods could be higher than the allowable execution or standard deviations. Tests were conducted on autoclaved aerated concrete beam and nine specimens that were specially prepared from lightweight concrete. The most advanced instruments that were available on the market were used to perform tests. They included two electromagnetic scanners and one ground penetrating radar (GPR). The testing equipment was used to analyse how the rebar (cover) location affected the detection of their diameters and how their mutual spacing influenced the detected quantity of rebars. The considerations included the impact of rebar depth on cover measurements and the spread of obtained results. Tests indicated that the measurement error was clearly greater when the rebars were located at very low or high depths. It could lead to the improper interpretation of test results, and consequently to the incorrect estimation of the structure safety based on the design resistance analysis. Electromagnetic and radar devices were unreliable while detecting the reinforcement of small (8 and 10 mm) diameters at close spacing (up to 20 mm) and of large (20 mm) diameters at a close spacing and greater depths. Recommendations for practical applications were developed to facilitate the evaluation of a structure. Full article
(This article belongs to the Special Issue Non-destructive Testing of Materials in Civil Engineering)
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Open AccessArticle
Research on Internal Force Detection Method of Steel Bar in Elastic and Yielding Stage Based on Metal Magnetic Memory
Materials 2019, 12(7), 1167; https://doi.org/10.3390/ma12071167
Received: 8 March 2019 / Revised: 6 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
Based on the metal magnetic memory effect, this paper proposed a new non-destructive testing method for the internal tensile force detection of steel bars by analyzing the self-magnetic flux leakage (SMFL) signals. The variation of the SMFL signal of the steel bar with [...] Read more.
Based on the metal magnetic memory effect, this paper proposed a new non-destructive testing method for the internal tensile force detection of steel bars by analyzing the self-magnetic flux leakage (SMFL) signals. The variation of the SMFL signal of the steel bar with the tensile force indicates that the curve of the SMFL signal has a significant extreme point when the tensile force reaches about 65% of the yield tension, of which the first derivative curve has extreme points in the elastic and yielding stages, respectively. To study the variation of SMFL signal with the axial position of the steel bar under different tensile forces, a parameter reflecting the fluctuation of the SMFL signal along the steel bar is proposed. The linear relationship between this parameter and the tensile force can be used to quantitatively calculate the tensile force of steel bar. The method in this paper provides significant application prospects for the internal force detection of steel bar in the actual engineering. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
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Open AccessArticle
Study of the Suitability of Different Types of Slag and Its Influence on the Quality of Green Grouts Obtained by Partial Replacement of Cement
Materials 2019, 12(7), 1166; https://doi.org/10.3390/ma12071166
Received: 18 March 2019 / Revised: 4 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
This paper is part of a research line focused on the reduction of the use of cement in the industry. In this work, the study of work methodologies for the manufacture of green cementitious grout mixtures is studied. Grout is widely used in [...] Read more.
This paper is part of a research line focused on the reduction of the use of cement in the industry. In this work, the study of work methodologies for the manufacture of green cementitious grout mixtures is studied. Grout is widely used in construction and it requires an important use of raw materials. On the other hand, the steel industry faces the problem of the growing generation of slag wastes due to the increase in steel manufacturing. The green grout aims to achieve the dual objective of reducing the demand for cement and improve the slag waste valorization. Slag is not introduced as an aggregate but through the direct replacement of cement and no additives. The research seeks a product where we can use steel slag intensively, guaranteeing minimum resistance and workability. Results with substitutions between a 25% to 50% and water/cement ratio of 1 are presented. In particular, the suitability of different slags (two Ladle Furnace Slag (LFS) and one Blast Furnace Slag (GGBS)) in the quality of the final product are analyzed. The feasibility of replacing cement with slag and the importance of the origin and pretreatment are highlighted. Full article
(This article belongs to the Special Issue Novel Bioderived Composites from Wastes)
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Open AccessArticle
Forms of Damage of Bricks Subjected to Cyclic Freezing and Thawing in Actual Conditions
Materials 2019, 12(7), 1165; https://doi.org/10.3390/ma12071165
Received: 25 March 2019 / Revised: 5 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
The paper presents the characteristics of damage of bricks in masonry structures of significant historical value as a result of cyclic freezing and thawing. Based on extensive investigation, which included macroscopic description, determination of compressive strength and tensile strength, determination of the mineral [...] Read more.
The paper presents the characteristics of damage of bricks in masonry structures of significant historical value as a result of cyclic freezing and thawing. Based on extensive investigation, which included macroscopic description, determination of compressive strength and tensile strength, determination of the mineral composition, scanning microscopy observation and determination of the porosity structure of bricks, three forms of frost damage were distinguished, termed as powdering, flaking and cracking. Bricks were collected from existing historical buildings 70 years after their construction. It was observed that the particular form of frost damage of bricks is highly correlated with the structure of porosity. Additional factors affecting the form of frost destruction are the strength of the material, its mineral composition and the spatial arrangement of the texture elements. Taking the above into account, it is possible to evaluate frost resistance of bricks and specify the form of damage. Predicting frost resistance and forms of damage based on low-destructive methods using small samples is the expected solution in the case of heritage facilities. Full article
(This article belongs to the Section Construction and Building Materials)
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