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Materials, Volume 11, Issue 8 (August 2018)

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Cover Story (view full-size image) Inspired by the problems associated with osteochondral defects, we fabricated cytocompatible, [...] Read more.
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Open AccessArticle Annealing Behaviour of Pt and PtNi Nanowires for Proton Exchange Membrane Fuel Cells
Materials 2018, 11(8), 1473; https://doi.org/10.3390/ma11081473 (registering DOI)
Received: 20 July 2018 / Revised: 11 August 2018 / Accepted: 14 August 2018 / Published: 19 August 2018
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Abstract
PtNi alloy and hybrid structures have shown impressive catalytic activities toward the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, such promise does not often translate into improved electrode performances in PEMFC devices. In this contribution, a Ni
[...] Read more.
PtNi alloy and hybrid structures have shown impressive catalytic activities toward the cathodic oxygen reduction reaction (ORR) in proton exchange membrane fuel cells (PEMFCs). However, such promise does not often translate into improved electrode performances in PEMFC devices. In this contribution, a Ni impregnation and subsequent annealing method, translatable to vertically aligned nanowire gas diffusion electrodes (GDEs), is shown in thin-film rotating disk electrode measurements (TFRDE) to enhance the ORR mass activity of Pt nanowires (NWs) supported on carbon (Pt NWs/C) by around 1.78 times. Physical characterisation results indicate that this improvement can be attributed to a combination of Ni alloying of the nanowires with retention of the morphology, while demonstrating that Ni can also help improve the thermal stability of Pt NWs. These catalysts are then tested in single PEMFCs. Lower power performances are achieved for PtNi NWs/C than Pt NWs/C. A further investigation confirms the different surface behaviour between Pt NWs and PtNi NWs when in contact with electrolyte ionomer in the electrodes in PEMFC operation. Indications are that this interaction exacerbates reactant mass transport limitations not seen with TFRDE measurements. Full article
(This article belongs to the Special Issue Metallic Nanowires and Their Applications)
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Open AccessArticle Multi Jet Fusion PA12 Manufacturing Parameters for Watertightness, Strength and Tolerances
Materials 2018, 11(8), 1472; https://doi.org/10.3390/ma11081472 (registering DOI)
Received: 16 July 2018 / Revised: 15 August 2018 / Accepted: 16 August 2018 / Published: 18 August 2018
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Abstract
The aim of this paper is to explore the watertightness behaviour for high pressure applications using Multi Jet Fusion technology and polyamide 12 as a material. We report an efficient solution for manufacturing functional prototypes and final parts for water pressure applications and
[...] Read more.
The aim of this paper is to explore the watertightness behaviour for high pressure applications using Multi Jet Fusion technology and polyamide 12 as a material. We report an efficient solution for manufacturing functional prototypes and final parts for water pressure applications and provide manufacturing rules for engineers in the pressurized product development process for up to 10 MPa of nominal pressure. The research findings show manufacturers the possibility of using additive manufacturing as an alternative to traditional manufacturing. Water leakage was studied using different printing orientations and wall thicknesses for a range of pressure values. An industrial ball valve was printed and validated with the ISO 9393 standard as also meeting tolerance requirements. This paper is a pioneering approach to the additive manufacturing of high-performance fluid handling components. This approach solves the problem of leakage caused by porosity in additive manufacturing technologies. Full article
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Open AccessArticle The Effect of Alloying Elements on the Structural Stability, Mechanical Properties, and Debye Temperature of Al3Li: A First-Principles Study
Materials 2018, 11(8), 1471; https://doi.org/10.3390/ma11081471 (registering DOI)
Received: 26 June 2018 / Revised: 11 August 2018 / Accepted: 14 August 2018 / Published: 18 August 2018
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Abstract
The structural stability, mechanical properties, and Debye temperature of alloying elements X (X = Sc, Ti, Co, Cu, Zn, Zr, Nb, and Mo) doped Al3Li were systematically investigated by first-principles methods. A negative enthalpy of formation ΔHf is predicted
[...] Read more.
The structural stability, mechanical properties, and Debye temperature of alloying elements X (X = Sc, Ti, Co, Cu, Zn, Zr, Nb, and Mo) doped Al3Li were systematically investigated by first-principles methods. A negative enthalpy of formation ΔHf is predicted for all Al3Li doped species which has consequences for its structural stability. The Sc, Ti, Zr, Nb, and Mo are preferentially occupying the Li sites in Al3Li while the Co, Cu, and Zn prefer to occupy the Al sites. The Al–Li–X systems are mechanically stable at 0 K as elastic constants Cij has satisfied the stability criteria. The values of bulk modulus B for Al–Li–X (X = Sc, Ti, Co, Cu, Zr, Nb, and Mo) alloys (excluding Al–Li–Zn) increase with the increase of doping concentration and are larger than that for pure Al3Li. The Al6LiSc has the highest shear modulus G and Young’s modulus E which indicates that it has stronger shear deformation resistance and stiffness. The predicted universal anisotropy index AU for pure and doped Al3Li is higher than 0, implying the anisotropy of Al–Li–X alloy. The Debye temperature ΘD of Al12Li3Ti is highest among the Al–Li–X system which predicts the existence of strong covalent bonds and thermal conductivity compared to that of other systems. Full article
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Open AccessArticle Characterization of a New Dry Drill-Milling Process of Carbon Fibre Reinforced Polymer Laminates
Materials 2018, 11(8), 1470; https://doi.org/10.3390/ma11081470 (registering DOI)
Received: 2 July 2018 / Revised: 7 August 2018 / Accepted: 13 August 2018 / Published: 18 August 2018
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Abstract
Carbon Fibre Reinforced Polymer (CFRP) composites are widely used in aerospace applications that require severe quality parameters. To simplify the assembly operations and reduce the associated costs, the current trend in industry is to optimize the drilling processes. However, the machining of CFRP
[...] Read more.
Carbon Fibre Reinforced Polymer (CFRP) composites are widely used in aerospace applications that require severe quality parameters. To simplify the assembly operations and reduce the associated costs, the current trend in industry is to optimize the drilling processes. However, the machining of CFRP composites is very challenging compared with metals, and several defect types can be generated by drilling. The emerging process of orbital drilling can greatly reduce the defects associated with the traditional drilling of CFRP, but it is a more complex process requiring careful process parameters selection and it does not allow for the complete elimination of the thrust force responsible for delamination damage. As an alternative to traditional and orbital drilling, this work presents a new hole making process, where the hole is realized by a combination of drilling and peripheral milling performed using the same cutting tool following a novel tool path strategy. An original tool design principle is proposed to realize a new drill-milling tool, made of a first drilling and a subsequent milling portion. Two different tool configurations are experimentally tested to evaluate the performance of the newly-conceived combined drill-milling process. This process is quick and easy, and the experimental results show an improvement in the drilled hole quality. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessArticle Product Lifecycle Management as Data Repository for Manufacturing Problem Solving
Materials 2018, 11(8), 1469; https://doi.org/10.3390/ma11081469 (registering DOI)
Received: 2 July 2018 / Revised: 9 August 2018 / Accepted: 14 August 2018 / Published: 18 August 2018
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Abstract
Fault diagnosis presents a considerable difficulty to human operators in supervisory control of manufacturing systems. Implementing Internet of Things (IoT) technologies in existing manufacturing facilities implies an investment, since it requires upgrading them with sensors, connectivity capabilities, and IoT software platforms. Aligned with
[...] Read more.
Fault diagnosis presents a considerable difficulty to human operators in supervisory control of manufacturing systems. Implementing Internet of Things (IoT) technologies in existing manufacturing facilities implies an investment, since it requires upgrading them with sensors, connectivity capabilities, and IoT software platforms. Aligned with the technological vision of Industry 4.0 and based on currently existing information databases in the industry, this work proposes a lower-investment alternative solution for fault diagnosis and problem solving. This paper presents the details of the information and communication models of an application prototype oriented to production. It aims at assisting shop-floor actors during a Manufacturing Problem Solving (MPS) process. It captures and shares knowledge, taking existing Process Failure Mode and Effect Analysis (PFMEA) documents as an initial source of information related to potential manufacturing problems. It uses a Product Lifecycle Management (PLM) system as source of manufacturing context information related to the problems under investigation and integrates Case-Based Reasoning (CBR) technology to provide information about similar manufacturing problems. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessArticle Hydrothermal Synthesis of Co-Doped NiSe2 Nanowire for High-Performance Asymmetric Supercapacitors
Materials 2018, 11(8), 1468; https://doi.org/10.3390/ma11081468 (registering DOI)
Received: 20 June 2018 / Revised: 11 July 2018 / Accepted: 15 August 2018 / Published: 18 August 2018
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Abstract
Co@NiSe2 electrode materials were synthesized via a simple hydrothermal method by using nickel foam in situ as the backbone and subsequently characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and a specific surface area analyzer. Results show that the
[...] Read more.
Co@NiSe2 electrode materials were synthesized via a simple hydrothermal method by using nickel foam in situ as the backbone and subsequently characterized by scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, and a specific surface area analyzer. Results show that the Co@NiSe2 electrode exhibits a nanowire structure and grows uniformly on the nickel foam base. These features make the electrode show a relatively high specific surface area and electrical conductivity, and thus exhibit excellent electrochemical performance. The obtained electrode has a high specific capacitance of 3167.6 F·g−1 at a current density of 1 A·g−1. To enlarge the potential window and increase the energy density, an asymmetric supercapacitor was assembled by using a Co@NiSe2 electrode and activated carbon acting as positive and negative electrodes, respectively. The prepared asymmetrical supercapacitor functions stably under the potential window of 0–1.6 V. The asymmetric supercapacitor can deliver a high energy density of 50.0 Wh·kg−1 at a power density of 779.0 W·kg−1. Moreover, the prepared asymmetric supercapacitor exhibits a good rate performance and cycle stability. Full article
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Open AccessArticle Microstructures, Mechanical and Corrosion Properties of the Extruded AZ31-xCaO Alloys
Materials 2018, 11(8), 1467; https://doi.org/10.3390/ma11081467 (registering DOI)
Received: 18 July 2018 / Revised: 9 August 2018 / Accepted: 12 August 2018 / Published: 18 August 2018
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Abstract
The effects of the extrusion process and CaO addition amount on microstructure, mechanical, and corrosion properties of AZ31 alloys were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), standard tensile testing, and so on. The grain
[...] Read more.
The effects of the extrusion process and CaO addition amount on microstructure, mechanical, and corrosion properties of AZ31 alloys were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), standard tensile testing, and so on. The grain size of AZ31 or AZ31-1%CaO alloy becomes larger with increasing extrusion temperature. The grain size of AZ31-1%CaO alloy is much smaller than that of AZ31 alloy at the same extrusion temperature. In addition, the formation of the Al2Ca phase caused by CaO addition refines the grain size, and the recrystallization of AZ31-1%CaO alloy is improved significantly. The recrystallization grains distribute more uniformly as the increase of extrusion ratio, and the completely recrystallized grains distribute uniformly in the form of equiaxed crystals with an extrusion ratio of 9. Tensile testing results show that extruded AZ31-1%CaO alloy at the extrusion temperature of 300 °C and an extrusion ratio of 9 exhibits the best mechanical properties. While corrosion properties of AZ31 alloys decreases due to the addition of CaO. Full article
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Open AccessArticle Experimental Study of Macro and Microgeometric Defects in Drilled Carbon Fiber Reinforced Plastics by Laser Beam Machining
Materials 2018, 11(8), 1466; https://doi.org/10.3390/ma11081466 (registering DOI)
Received: 1 July 2018 / Revised: 13 August 2018 / Accepted: 13 August 2018 / Published: 18 August 2018
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Abstract
Plastic matrix composite materials are an excellent choice for structural applications where high strength-weight and stiffness-weight ratios are required. These materials are being increasingly used in diverse industrial sectors, particularly in aerospace. Due to the strict tolerances required, they are usually machined with
[...] Read more.
Plastic matrix composite materials are an excellent choice for structural applications where high strength-weight and stiffness-weight ratios are required. These materials are being increasingly used in diverse industrial sectors, particularly in aerospace. Due to the strict tolerances required, they are usually machined with drilling cycles due to the type of mounting through rivets. In this sense, laser beam drilling is presented as an alternative to conventional drilling due to the absence of tool wear, cutting forces, or vibrations during the cutting process. However, the process carries with it other problems that compromise the integrity of the material. One of these is caused by the high temperatures generated during the interaction between the laser and the material. In this work, variance analysis is used to study the influence of scanning speed and frequency on macro geometric parameters, surface quality, and defects (taper and heat affected zone). Also, in order to identify problems in the wall of the drill, stereoscopic optical microscopy (SOM) and scanning electron microscopy (SEM) techniques are used. This experimental procedure reveals the conditions that minimize deviations, defects, and damage in machining holes. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessArticle Biological Compatibility of a Polylactic Acid Composite Reinforced with Natural Chitosan Obtained from Shrimp Waste
Materials 2018, 11(8), 1465; https://doi.org/10.3390/ma11081465 (registering DOI)
Received: 14 May 2018 / Revised: 1 June 2018 / Accepted: 1 June 2018 / Published: 18 August 2018
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Abstract
The aim of this work is to evaluate the effect of chitosan content (1, 3 and 5 wt %) dispersed in polylactic acid (PLA) on the structure and properties of composites. Also, the hydrolytic degradation, and the cell viability and adhesion of human
[...] Read more.
The aim of this work is to evaluate the effect of chitosan content (1, 3 and 5 wt %) dispersed in polylactic acid (PLA) on the structure and properties of composites. Also, the hydrolytic degradation, and the cell viability and adhesion of human MG-63 osteoblasts are analyzed to determine the composites’ suitability for use in tissue engineering. For the manufacture of the materials, natural chitosan was extracted chemically from shrimp exoskeleton. The composites were fabricated by extrusion, because it is a low-cost process, it is reproducible, and it does not compromise the biocompatibility of the materials. FT-IR and XRD show that the chitosan does not change the polymer structure, and interactions between the composite components are discarded. In vitro degradation tests show that the composites do not induce significant pH changes in phosphate buffer solution due to their low susceptibility to hydrolytic degradation. The adhesion and morphological characteristics of the osteoblasts are evaluated using confocal microscopy and scanning electron microscopy. The cell viability is determined by the MTT assay. Osteoblasts adhesion is observed on the surface of PLA and composites. A higher amount of chitosan, higher number of cells with osteoblastic morphology, and mineralized nodules are observed on the composite surface. The highest metabolic activity is evidenced at 21 days. The results suggest that the Polylactic acid/chitosan composites are potentially suitable for use as a biomaterial. Full article
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Open AccessArticle Effects of Cr and Zr Addition on Microstructures, Compressive Properties, and Abrasive Wear Behaviors of In Situ TiB2/Cu Cermets
Materials 2018, 11(8), 1464; https://doi.org/10.3390/ma11081464 (registering DOI)
Received: 13 July 2018 / Revised: 12 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
In situ micro-TiB2/Cu cermets with a different TiB2 content (40, 50, and 60 vol %) were successfully fabricated by combustion synthesis (CS) and hot press consolidation in Cu-Ti-B systems. In addition, different contents of Cr and Zr were added to
[...] Read more.
In situ micro-TiB2/Cu cermets with a different TiB2 content (40, 50, and 60 vol %) were successfully fabricated by combustion synthesis (CS) and hot press consolidation in Cu-Ti-B systems. In addition, different contents of Cr and Zr were added to the Cu-Ti-B systems. The microstructure, mechanical properties, and abrasive wear properties of the TiB2/Cu cermets were investigated. As the ceramic content increased, the yield strength and compressive strength of the cermets were found to increase, while the strain decreased. An increase in load and abrasive particle size caused the wear volume loss of the TiB2/Cu cermets to increase. When the ceramic content was 60 vol %, the wear resistance of the TiB2/Cu cermets was 3.3 times higher than that of pure copper. The addition of the alloying elements Zr and Cr had a significant effect on the mechanical properties of the cermets. When the Cr content was 5 wt %, the yield strength, ultimate compressive strength, and microhardness of the cermets reached a maximum of 997 MPa, 1183 MPa, and 491 Hv, respectively. Correspondingly, when the Zr content was 5 wt %, those three values reached 1764 MPa, 1967 MPa, and 655 Hv, respectively, which are 871 MPa, 919 MPa, and 223 Hv higher than those of the unalloyed cermets. The wear mechanism of the in-situ TiB2/Cu cermets, and the mechanisms by which the strength and wear resistance were enhanced by the addition of Zr, were preliminarily revealed. Full article
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Open AccessArticle Fused Filament Fabrication of Small Ceramic Components
Materials 2018, 11(8), 1463; https://doi.org/10.3390/ma11081463 (registering DOI)
Received: 16 July 2018 / Revised: 8 August 2018 / Accepted: 15 August 2018 / Published: 17 August 2018
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Abstract
With respect to rapid prototyping of ceramic components, there are known only a few processes (stereo lithography, binder jetting). In this work, a new process chain is described in detail, showing that ceramics can be printed in a very cost-efficient way. We developed
[...] Read more.
With respect to rapid prototyping of ceramic components, there are known only a few processes (stereo lithography, binder jetting). In this work, a new process chain is described in detail, showing that ceramics can be printed in a very cost-efficient way. We developed a ceramic–polymer composite as filament material that can be printed on a low-cost fused filament fabrication (FFF) desktop printer, even with very small nozzle sizes enabling very small geometric feature sizes. The thermal post-processing, with debinding and sintering, is very close to the ceramic injection molding (CIM) process chain. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Corrosion Behaviors of Q345R Steel at the Initial Stage in an Oxygen-Containing Aqueous Environment: Experiment and Modeling
Materials 2018, 11(8), 1462; https://doi.org/10.3390/ma11081462 (registering DOI)
Received: 31 May 2018 / Revised: 3 August 2018 / Accepted: 10 August 2018 / Published: 17 August 2018
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Abstract
The ingress of oxygen into pressure vessels used in oil & gas production and transportation could easily result in serious corrosion. In this work, the corrosion behaviors of Q345R steel at the initial stage in 1 wt.% NaCl solution were investigated using electrochemical
[...] Read more.
The ingress of oxygen into pressure vessels used in oil & gas production and transportation could easily result in serious corrosion. In this work, the corrosion behaviors of Q345R steel at the initial stage in 1 wt.% NaCl solution were investigated using electrochemical techniques. The effects of oxygen concentration, temperature and pH on corrosion behaviors were discussed. Simultaneously, a numerical model based on the mixed potential theory was proposed. The results show that the proposed model accords well with the experimental data in the pH range from 9.0 to 5.0. In this pH range, the oxygen reduction reaction, H+ reduction, water reduction, and iron oxidation can be quantitatively analyzed using this model. However, this model shows a disagreement with the experimental data at lower pH. This can be attributed to the fact that actual area of reaction on the electrode is much smaller than the preset area due to the block effect resulted from hydrogen bubbles adsorbed on the electrode surface. Full article
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Open AccessArticle Analysis of Surface Extraction Methods Based on Gradient Operators for Computed Tomography in Metrology Applications
Materials 2018, 11(8), 1461; https://doi.org/10.3390/ma11081461 (registering DOI)
Received: 6 July 2018 / Revised: 13 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
Among the multiple factors influencing the accuracy of Computed Tomography measurements, the surface extraction process is a significant contributor. The location of the surface for metrological applications is generally based on the definition of a gray value as a characteristic of similarity to
[...] Read more.
Among the multiple factors influencing the accuracy of Computed Tomography measurements, the surface extraction process is a significant contributor. The location of the surface for metrological applications is generally based on the definition of a gray value as a characteristic of similarity to define the regions of interest. A different approach is to perform the detection or location of the surface based on the discontinuity or gradient. In this paper, an adapted 3D Deriche algorithm based on gradient information is presented and compared with a previously developed adapted Canny algorithm for different surface types. Both algorithms have been applied to nine calibrated workpieces with different geometries and materials. Both the systematic error and measurement uncertainty have been determined. The results show a significant reduction of the deviations obtained with the Deriche-based algorithm in the dimensions defined by flat surfaces. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessArticle Fabrication of Polymer Microstructures of Various Angles via Synchrotron X-Ray Lithography Using Simple Dimensional Transformation
Materials 2018, 11(8), 1460; https://doi.org/10.3390/ma11081460 (registering DOI)
Received: 7 July 2018 / Revised: 6 August 2018 / Accepted: 15 August 2018 / Published: 17 August 2018
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Abstract
In this paper, we developed a method of fabricating polymer microstructures at various angles on a single substrate via synchrotron X-ray lithography coupled with simple dimensional transformations. Earlier efforts to create various three-dimensional (3D) features on flat substrates focused on the exposure technology,
[...] Read more.
In this paper, we developed a method of fabricating polymer microstructures at various angles on a single substrate via synchrotron X-ray lithography coupled with simple dimensional transformations. Earlier efforts to create various three-dimensional (3D) features on flat substrates focused on the exposure technology, material properties, and light sources. A few research groups have sought to create microstructures on curved substrates. We created tilted microstructures of various angles by simply deforming the substrate from 3D to two-dimensional (2D). The microstructural inclination angles changed depending on the angles of the support at particular positions. We used convex, concave, and S-shaped supports to fabricate microstructures with high aspect ratios (1:11) and high inclination angles (to 79°). The method is simple and can be extended to various 3D microstructural applications; for example, the fabrication of microarrays for optical components, and tilted micro/nanochannels for biological applications. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessCommunication CVD Synthesis of Monodisperse Graphene/Cu Microparticles with High Corrosion Resistance in Cu Etchant
Materials 2018, 11(8), 1459; https://doi.org/10.3390/ma11081459 (registering DOI)
Received: 27 June 2018 / Revised: 27 July 2018 / Accepted: 2 August 2018 / Published: 17 August 2018
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Abstract
Copper powder has broad applications in the powder metallurgy, heat exchanger, and electronic industries due to its intrinsically high electrical and thermal conductivities. However, the ease of formation of surface oxide or patina layer raises difficulty of storage and handling of copper powder,
[...] Read more.
Copper powder has broad applications in the powder metallurgy, heat exchanger, and electronic industries due to its intrinsically high electrical and thermal conductivities. However, the ease of formation of surface oxide or patina layer raises difficulty of storage and handling of copper powder, particularly in the case of Cu microparticles. Here, we developed a thermal chemical vapor deposition chemical vapor deposition (CVD) process for large-scale synthesis of graphene coatings on Cu microparticles, which importantly can remain monodisperse without aggregation after graphene growth at high temperature by using removal spacers. Compared to other protective coating methods, the intrinsic electrical and thermal properties of Cu powder would not be degraded by uniform growth of low defect few-layer graphene on each particle surface. As a result, when the anticorrosion performance test was carried out by immersing the samples in Cu etchant, the corrosion rate of graphene/Cu microparticles was significantly improved (ca three times slower) compared to that of pristine Cu powder, also showing a comparable anticorrosion ability to commercial CuZn30 alloy. Full article
(This article belongs to the Special Issue Recent Advances in 2D Nanomaterials)
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Open AccessArticle Virtual Extensometer Analysis of Martensite Band Nucleation, Growth, and Strain Softening in Pseudoelastic NiTi Subjected to Different Load Cases
Materials 2018, 11(8), 1458; https://doi.org/10.3390/ma11081458 (registering DOI)
Received: 27 June 2018 / Revised: 6 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
Pseudoelastic NiTi shape memory alloys exhibit different stress–strain curves and modes of deformation in tension vs. compression. We have recently shown that under a combination of compression and shear, heterogeneous deformation can occur. In the present study, we use digital image correlation to
[...] Read more.
Pseudoelastic NiTi shape memory alloys exhibit different stress–strain curves and modes of deformation in tension vs. compression. We have recently shown that under a combination of compression and shear, heterogeneous deformation can occur. In the present study, we use digital image correlation to systematically analyze how characteristic features of the nominally uniaxial engineering stress–strain curves (particularly the martensite nucleation peak and the plateau length) are affected by extensometer parameters in tension, compression, and the novel load case of shear-compression. By post-experimental analysis of full surface strain field data, the effect of the placement of various virtual extensometers at different locations (with respect to the nucleation site of martensite bands or inhomogeneously deforming regions) and with different gauge lengths is documented. By positioning an extensometer directly on the region corresponding to the nucleating martensite band, we, for the first time, directly record the strain-softening nature of the material—a specific softening behavior that is, for instance, important for the modeling community. Our results show that the stress–strain curves, which are often used as a basis for constitutive modeling, are affected considerably by the choice of extensometer, particularly under tensile loading, that leads to a distinct mode of localized deformation/transformation. Under compression-shear loading, inhomogeneous deformation (without lateral growth of martensite bands) is observed. The effects of extensometer gauge length are thus less pronounced than in tension, yet systematic—they are rationalized by considering the relative impact of differently deforming regions. Full article
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Open AccessFeature PaperArticle Sinus Membrane Elevation with Heterologous Cortical Lamina: A Randomized Study of a New Surgical Technique for Maxillary Sinus Floor Augmentation without Bone Graft
Materials 2018, 11(8), 1457; https://doi.org/10.3390/ma11081457 (registering DOI)
Received: 19 July 2018 / Revised: 8 August 2018 / Accepted: 14 August 2018 / Published: 17 August 2018
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Abstract
Background: The aim of this randomized controlled clinical trial was to compare the efficacy of two different techniques for maxillary sinus augmentation using a lateral window approach: Heterologous cortical lamina without any grafting material versus 100% collagenated granular collagen porcine bone. Methods: Twenty-three
[...] Read more.
Background: The aim of this randomized controlled clinical trial was to compare the efficacy of two different techniques for maxillary sinus augmentation using a lateral window approach: Heterologous cortical lamina without any grafting material versus 100% collagenated granular collagen porcine bone. Methods: Twenty-three healthy patients with not relevant past medical history (14 women and 9 men, non-smokers, mean age 52 years, range 48–65 years) were included. In Group I, the sinus was filled with collagen porcine bone (Geno-os, OsteoBiol, Turin, Italy) and a collagen membrane (Evolution, OsteoBiol, Turin, Italy) was used to close the lateral window of the sinus. In Group II, the sinus was treated with heterologous cortical lamina only (Lamina, OsteoBiol, Turin, Italy). Results: There was a statistically significant difference in the surgical time required to complete the augmentation procedures: 18.3 ± 2.1 min for lamina treated sites versus 12.5 ± 3.1 min for porcine bone treated sites. In Group I, the mean volume of the graft was 3101 ± 321 mm3 in the immediate postoperative examination (5–7 days), while after a six-month healing period it was 2716.7 ± 432 mm3. Conclusion: This study demonstrates that the use of heterologous cortical lamina is a valid technique for the mechanical support of sinus membranes resulting in only bone tissue formation and not mixed with the graft. The graft material was biocompatible and not completely resorbed after six months, although the remains were integrated into the bone. Full article
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Open AccessArticle Effects of Loading Frequency and Loading Type on High-Cycle and Very-High-Cycle Fatigue of a High-Strength Steel
Materials 2018, 11(8), 1456; https://doi.org/10.3390/ma11081456
Received: 24 July 2018 / Revised: 14 August 2018 / Accepted: 14 August 2018 / Published: 16 August 2018
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Abstract
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on
[...] Read more.
High-cycle and very-high-cycle fatigue tests via rotary bending (52.5 Hz), electromagnetic resonance (120 Hz) axial cycling, and ultrasonic (20 kHz) axial cycling were performed for a high-strength steel with three heat treatment conditions, and the effects of loading frequency and loading type on fatigue strength and fatigue life were investigated. The results revealed that the loading frequency effect is caused by the combined response of strain rate increase and induced temperature rise. A parameter η was proposed to judge the occurrence of loading frequency effect, and the calculated results were in agreement with the experimental data. In addition, a statistical method based on the control volume was used to reconcile the effect of loading type, and the predicted data were consistent with the experimental results. Full article
(This article belongs to the Special Issue Deformation, Fatigue and Fracture of Materials)
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Open AccessArticle Mechanical Properties Study of Fe-Mn-Si Shape Memory Alloys Welding Seam Formed by Laser Welding with Filler Powder
Materials 2018, 11(8), 1454; https://doi.org/10.3390/ma11081454
Received: 11 July 2018 / Revised: 1 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
To reduce the residual stress and improve the fatigue property of the laser weldment by using the stress self-accommodation characteristic of Fe-Mn-Si shape memory alloys (SMAs), a Fe15Mn5Si12Cr6Ni memory alloy welding seam was formed inside 304 stainless steel by laser welding with filler
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To reduce the residual stress and improve the fatigue property of the laser weldment by using the stress self-accommodation characteristic of Fe-Mn-Si shape memory alloys (SMAs), a Fe15Mn5Si12Cr6Ni memory alloy welding seam was formed inside 304 stainless steel by laser welding with filler powder. The combination of the hole-drilling method and the ANSYS software was used to research the distribution law of residual stress inside the laser welding specimen. The fatigue strength of the laser welded specimens with the Fe-Mn-Si SMAs welding seam (experimental materials) and 304 stainless steel welding seam (comparative materials) was measured by cycle bending fatigue test. The microhardness of the welding specimens was measured by the microhardness tester. The thermodynamic model of the laser welding process and the phase transition crystallography of Fe-Mn-Si SMAs were evaluated to analyze the strengthening mechanism of the mechanical properties in the experimental materials. The results show that the distribution law for residual stress in the experiment and simulation are consistent. The experimental materials possess low residual stress, high fatigue strength and high microhardness. The strengthening mechanism for mechanical properties is the welding residual stress-induced γ→ε martensitic transformation inside the experimental materials, which causes the tensile plastic strain of the welding seam to resist residual compression strain, and the residual stress, as the transition driving force, is released in shear processing. Full article
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Open AccessArticle Fabrication of Cu Based Metallic Binder for Diamond Tools by Microwave Pressureless Sintering
Materials 2018, 11(8), 1453; https://doi.org/10.3390/ma11081453
Received: 30 May 2018 / Revised: 10 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
Microwave pressureless sintering (MPS) method is successfully applied in the fabrication of Cu based metallic matrix for diamond tools. The main purpose of this work is to obtain better mechanical properties when the metal binder of the diamond tools was prepared by the
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Microwave pressureless sintering (MPS) method is successfully applied in the fabrication of Cu based metallic matrix for diamond tools. The main purpose of this work is to obtain better mechanical properties when the metal binder of the diamond tools was prepared by the MPS method. The orthogonal experimental method is adopted to design the sintering process parameters. The optimized experimental conditions are suggested as 880 °C of sintering temperature, 375 MPa of cold pressure, and 35 min of withholding time. The contrastive investigation of the MPS and conventional pressureless sintering (CPS) are performed under optimized conditions. The microstructures information are obtained by scanning electron microscopy (SEM), X-ray diffraction (XRD), electron probe microanalysis (EPMA), and the necessary mechanical properties, such as relative density, hardness, and flexural strength are tested. Experimental results show that the MPS method, compared with CPS, can significantly improve the mechanical properties of the metallic matrix. The factors of relative density, hardness, and flexural strength increase 1.25%, 3.86%, and 6.28%, respectively. The possible sintering mechanism of the MPS method is also discussed. This work may provide a reference for the fabrication of metal-based diamond tools by microwave heating method. Full article
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Open AccessArticle Graphene Quantum Dots Decorated Al-Doped ZnS for Improved Photoelectric Performance
Materials 2018, 11(8), 1452; https://doi.org/10.3390/ma11081452
Received: 9 July 2018 / Revised: 12 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
Graphene quantum dots (GQDs) decorated Al-doped ZnS composites were prepared using the solvothermal process, and the hydrothermal method was used to prepare GQDs. Various spectroscopic techniques were used to characterize the products, and the results show that Al-ZnS attached GQD composites present lattice
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Graphene quantum dots (GQDs) decorated Al-doped ZnS composites were prepared using the solvothermal process, and the hydrothermal method was used to prepare GQDs. Various spectroscopic techniques were used to characterize the products, and the results show that Al-ZnS attached GQD composites present lattice fringes that can be assigned to ZnS and GQDs, respectively. The absorption peaks of Al-ZnS/GQDs are red-shifted because of the doping of aluminum and the incorporation of GQDs. The luminescence intensity of Al-ZnS/GQDs shows a downward trend with the addition of GQDs. As the GQD content changes from 0.6 wt % to 1.8 wt %, the photocurrent density achieves a maximum at the addition of 1.2 wt %. The photocurrent of Al-ZnS/GQDs composites are about 700% and 200% of pure ZnS and Al-ZnS, respectively. The results indicate that Al doping can reduce the energy bandgap of ZnS and produce more photogenerated electrons. The photogenerated electrons from Al-ZnS can be extracted and transferred to GQDs, which act as conducting materials to decrease the recombination rate and improve the photogenerated electron-transfer. Full article
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Open AccessArticle The Effect of Plasma Pretreatment and Cross-Linking Degree on the Physical and Antimicrobial Properties of Nisin-Coated PVA Films
Materials 2018, 11(8), 1451; https://doi.org/10.3390/ma11081451
Received: 13 July 2018 / Revised: 12 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
Stable antimicrobial nisin layers were prepared on the carrying medium-polyvinyl alcohol (PVA) films, crosslinked by glutaric acid. Surface plasma dielectric coplanar surface barrier discharge (DCSBD) modification of polyvinyl alcohol was used to improve the hydrophilic properties and to provide better adhesion of biologically
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Stable antimicrobial nisin layers were prepared on the carrying medium-polyvinyl alcohol (PVA) films, crosslinked by glutaric acid. Surface plasma dielectric coplanar surface barrier discharge (DCSBD) modification of polyvinyl alcohol was used to improve the hydrophilic properties and to provide better adhesion of biologically active peptide-nisin to the polymer. The surface modification of films was studied in correlation to their cross-linking degree. Nisin was attached directly from the salt solution of the commercial product. In order to achieve a stable layer, the initial nisin concentration and the following release were investigated using chromatographic methods. The uniformity and stability of the layers was evaluated by means of zeta potential measurements, and for the surface changes of hydrophilic character, the water contact angle measurements were provided. The nisin long-term stability on the PVA films was confirmed by tricine polyacrylamide gel electrophoresis (SDS-PAGE) and by antimicrobial assay. It was found that PVA can serve as a suitable carrying medium for nisin with tunable properties by plasma treatment and crosslinking degree. Full article
(This article belongs to the Special Issue Surface Modification to Improve Properties of Materials)
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Open AccessArticle Comparative Research on the Rebound Effect in Direct Electromagnetic Forming and Indirect Electromagnetic Forming with an Elastic Medium
Materials 2018, 11(8), 1450; https://doi.org/10.3390/ma11081450
Received: 24 July 2018 / Revised: 12 August 2018 / Accepted: 14 August 2018 / Published: 16 August 2018
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Abstract
In the process of electromagnetic forming (EMF), the rebound effect caused by high speed collision between sheet and die will affect the fittability, which results in a bad forming quality of workpiece. In this paper, finite element models of direct EMF and indirect
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In the process of electromagnetic forming (EMF), the rebound effect caused by high speed collision between sheet and die will affect the fittability, which results in a bad forming quality of workpiece. In this paper, finite element models of direct EMF and indirect EMF with an elastic medium are established, the influence factors of fittability in indirect EMF are studied, the two forming processes are compared, and the mechanisms of reduced rebound effect in indirect EMF are revealed. The results show that: in indirect EMF, with the increase of the discharging voltage or thickness of rubber, the fittability increases and then decreases; when the thickness of driver plate is equal to the skin depth of the driver plate, the fittability is the best. The optimal process parameters of indirect EMF are as follows: the discharging voltage is 10 kV, the thickness of the rubber is 20 mm and the thickness of driver plate is 2 mm. The rebound effect in indirect EMF is reduced compared with direct EMF for the following reasons: the impact force caused by the collision between the sheet and die is balanced by the pressure provided by the rubber; the sheet is always under tensile stress state due to the friction force provided by rubber; the remaining kinetic energy of sheet after collision with the die is absorbed by rubber. Therefore, the rebound effect in indirect EMF is suppressed compared with direct EMF. So, the fittability of the workpiece is improved, which results in a better forming quality. Full article
(This article belongs to the Section Manufacturing Processes and Systems)
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Open AccessArticle Analysis of Favorable Process Conditions for the Manufacturing of Thin-Wall Pieces of Mild Steel Obtained by Wire and Arc Additive Manufacturing (WAAM)
Materials 2018, 11(8), 1449; https://doi.org/10.3390/ma11081449
Received: 7 July 2018 / Revised: 3 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant
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One of the challenges in additive manufacturing (AM) of metallic materials is to obtain workpieces free of defects with excellent physical, mechanical, and metallurgical properties. In wire and arc additive manufacturing (WAAM) the influences of process conditions on thermal history, microstructure and resultant mechanical and surface properties of parts must be analyzed. In this work, 3D metallic parts of mild steel wire (American Welding Society-AWS ER70S-6) are built with a WAAM process by depositing layers of material on a substrate of a S235 JR steel sheet of 3 mm thickness under different process conditions, using as welding process the gas metal arc welding (GMAW) with cold metal transfer (CMT) technology, combined with a positioning system such as a computer numerical controlled (CNC) milling machine. Considering the hardness profiles, the estimated ultimate tensile strengths (UTS) derived from the hardness measurements and the microstructure findings, it can be concluded that the most favorable process conditions are the ones provided by CMT, with homogeneous hardness profiles, good mechanical strengths in accordance to conditions defined by standard, and without formation of a decohesionated external layer; CMT Continuous is the optimal option as the mechanical properties are better than single CMT. Full article
(This article belongs to the Special Issue Special Issue of the Manufacturing Engineering Society (MES))
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Open AccessArticle Mechanical Properties of Hybrid Ultra-High Performance Engineered Cementitous Composites Incorporating Steel and Polyethylene Fibers
Materials 2018, 11(8), 1448; https://doi.org/10.3390/ma11081448
Received: 31 July 2018 / Revised: 12 August 2018 / Accepted: 13 August 2018 / Published: 16 August 2018
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Abstract
This paper presents the authors’ newly developed hybrid ultra-high performance (HUHP) engineered cementitious composite (ECC) with steel (ST) and polyethylene (PE) fibers. From this point on it will be referred to as HUHP-ECC. The volumes of steel and PE fibers were adjusted to
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This paper presents the authors’ newly developed hybrid ultra-high performance (HUHP) engineered cementitious composite (ECC) with steel (ST) and polyethylene (PE) fibers. From this point on it will be referred to as HUHP-ECC. The volumes of steel and PE fibers were adjusted to obtain different mechanical properties, including compressive strength, tensile, and flexural properties. We found that tensile and flexural properties, including bending strength and ductility indexes, increased with higher PE fiber amounts but reduced with the increased ST fiber volume. Notably, the compressive strength had the opposite tendency and decreased with increases in the PE volume. The ST fiber had a significantly positive effect on the compressive strength. The fluidity of HUHP-ECC improved with the increasing amount of ST fiber. The pseudo strain-hardening (PSH) values for all the HUHP-ECC mixtures were used to create an index indicating the ability of strain capacity; thus, the PSH values were calculated to explain the ductility of HUHP-ECC with different fiber volumes. Finally, the morphology of PE and ST fibers at the fracture surface was observed by an environmental scanning electron microscope (ESEM). Full article
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Open AccessArticle Numerical Analysis and 1D/2D Sensitivity Study for Monolithic and Laminated Structural Glass Elements under Thermal Exposure
Materials 2018, 11(8), 1447; https://doi.org/10.3390/ma11081447
Received: 3 July 2018 / Revised: 8 August 2018 / Accepted: 12 August 2018 / Published: 16 August 2018
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Abstract
Glass is largely used in architectural and engineering applications (i.e., buildings and vehicles) as a structural material, especially in the form of laminated glass (LG) sections. To achieve adequate and controlled safety levels in these applications, the well-known temperature-dependent behavior of viscoelastic interlayers
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Glass is largely used in architectural and engineering applications (i.e., buildings and vehicles) as a structural material, especially in the form of laminated glass (LG) sections. To achieve adequate and controlled safety levels in these applications, the well-known temperature-dependent behavior of viscoelastic interlayers for LG sections should be properly accounted for during the design process. Furthermore, the materials’ thermomechanical degradation with increases of temperature could severely affect the load-bearing performance of glass assemblies. In this context, uncoupled thermomechanical finite element (FE) numerical models could represent a robust tool and support for design engineers. Key input parameters and possible limits of the FE method, however, should be properly calibrated and assessed, so as to enable reliable estimations for the real behavior of glazing systems. In this paper, FE simulations are proposed for monolithic (MG) and LG specimens under radiant heating, based on one-dimensional (1D) and two-dimensional (2D) models. A special attention is focused on thermal effects, being representative of the first step for conventional uncoupled, thermomechanical analyses. Based on experimental results available in the literature, FE parametric studies are discussed, giving evidence of limits and issues due to several modeling assumptions. In particular, careful consideration is paid for various thermal material properties (conductivity, specific heat) and thermal boundaries (conductivity, emissivity), but also for other influencing parameters like the geometrical features of samples (thickness tolerances, cross-sectional properties, etc.), the composition of LG sections (interlayer type, thickness), the loading pattern (heat transfer distribution) and the presence of additional mechanical restraints (i.e., supports of different materials). Comparative FE results are hence critically discussed, highlighting the major effects of such influencing parameters. Full article
(This article belongs to the Special Issue Selected Papers from the 3rd International E-Conference on Materials)
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Open AccessArticle Sol-Gel Synthesis of Silicon-Doped Lithium Manganese Oxide with Enhanced Reversible Capacity and Cycling Stability
Materials 2018, 11(8), 1455; https://doi.org/10.3390/ma11081455
Received: 12 July 2018 / Revised: 2 August 2018 / Accepted: 14 August 2018 / Published: 15 August 2018
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Abstract
A series of silicon-doped lithium manganese oxides were obtained via a sol-gel process. XRD characterization results indicate that the silicon-doped samples retain the spinel structure of LiMn2O4. Electrochemical tests show that introducing silicon ions into the spinel structure can
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A series of silicon-doped lithium manganese oxides were obtained via a sol-gel process. XRD characterization results indicate that the silicon-doped samples retain the spinel structure of LiMn2O4. Electrochemical tests show that introducing silicon ions into the spinel structure can have a great effect on reversible capacity and cycling stability. When cycled at 0.5 C, the optimal Si-doped LiMn2O4 can exhibit a pretty high initial capacity of 140.8 mAh g−1 with excellent retention of 91.1% after 100 cycles, which is higher than that of the LiMn2O4, LiMn1.975Si0.025O4, and LiMn1.925Si0.075O4 samples. Moreover, the optimal Si-doped LiMn2O4 can exhibit 88.3 mAh g−1 with satisfactory cycling performance at 10 C. These satisfactory results are mainly contributed by the more regular and increased MnO6 octahedra and even size distribution in the silicon-doped samples obtained by sol-gel technology. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle Effect of Alloying Elements Gradient on Solid-State Diffusion Bonding between Aerospace Aluminum Alloys
Materials 2018, 11(8), 1446; https://doi.org/10.3390/ma11081446
Received: 2 June 2018 / Revised: 31 July 2018 / Accepted: 7 August 2018 / Published: 15 August 2018
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Abstract
Three different bonding couples assembled by two commonly used aerospace aluminum alloys were bonded within the temperature range of 460–520 °C under 6 MPa for 60 min in vacuum atmosphere. The interface microstructure and alloying elements distribution of the bonded joints were determined
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Three different bonding couples assembled by two commonly used aerospace aluminum alloys were bonded within the temperature range of 460–520 °C under 6 MPa for 60 min in vacuum atmosphere. The interface microstructure and alloying elements distribution of the bonded joints were determined by scanning electron microscope (SEM) and Energy Dispersive Spectroscope (EDS); the bond strength was evaluated by tensile-shear strength test. The results show the bond quality improved effectively as the bonding temperature increased. Compared with the 1420-1420 and 7B04-7B04 bonding couples, the 1420-7B04 couples obtained better interface integrity and higher bond strength, the highest shear strength for 1420-7B04 couple can be as high as 188 MPa when bonded at 520 °C. Special attention was focused on the 1420-7B04 couple, the diffusion coefficient of Mg at the original interface under different temperatures were investigated, the results show the diffusion coefficient increased obviously as the bonding temperature increased. A diffusion affected zone (DAZ) without continuous intermetallic phases formed due to the diffusion of alloying elements across the bonding interface. The combined action of temperature and alloying elements gradient resulted in the increase of alloying elements diffusion fluxes, which in turn promote the bonding quality through the accelerated shrinkage of interfacial voids. Full article
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Open AccessArticle Fracture Properties and Softening Curves of Steel Fiber-Reinforced Slag-Based Geopolymer Mortar and Concrete
Materials 2018, 11(8), 1445; https://doi.org/10.3390/ma11081445
Received: 14 July 2018 / Revised: 1 August 2018 / Accepted: 2 August 2018 / Published: 15 August 2018
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Abstract
Adding short steel fibers into slag-based geopolymer mortar and concrete is an effective method to enhance their mechanical properties. The fracture properties of steel fiber-reinforced slag-based geopolymer concrete/mortar (SGC/SGM) and unreinforced control samples were compared through three-point bending (TPB) tests. The influences of
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Adding short steel fibers into slag-based geopolymer mortar and concrete is an effective method to enhance their mechanical properties. The fracture properties of steel fiber-reinforced slag-based geopolymer concrete/mortar (SGC/SGM) and unreinforced control samples were compared through three-point bending (TPB) tests. The influences of steel fiber volume contents (1.0%, 1.5% and 2.0%) on the fracture properties of SGC and SGM were studied. Load-midspan deflection (P-δ) curves and load-crack mouth opening displacement (P-CMOD) curves of the tested beams were recorded. The compressive and splitting tensile strengths were also tested. The fracture energy, flexural strength parameters, and fracture toughness of steel fiber-reinforced SGC and SGM were calculated and analyzed. The softening curves of steel fiber-reinforced SGC and SGM were determined using inverse analysis. The experimental results show that the splitting tensile strength, fracture energy, and fracture toughness are significantly enhanced with fiber incorporation. A strong correlation between the equivalent and residual flexural strengths is also observed. In addition, the trilinear strain-softening curves obtained by inverse analysis predict well of the load-displacement curves recorded from TPB tests. Full article
(This article belongs to the Special Issue New and Emerging Construction Materials)
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Open AccessEditorial Environmental Impacts of Engineered Nanomaterials—Imbalances in the Safety Assessment of Selected Nanomaterials
Materials 2018, 11(8), 1444; https://doi.org/10.3390/ma11081444
Received: 3 August 2018 / Accepted: 13 August 2018 / Published: 15 August 2018
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(This article belongs to the Special Issue Environmental Impact of Nanomaterials)
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