Materials

15 pages, 2080 KiB

Open AccessArticle

Improvement of Surface Roughness and Hydrophobicity in PETG Parts Manufactured via Fused Deposition Modeling (FDM): An Application in 3D Printed Self–Cleaning Parts

by Juan M. Barrios and Pablo E. Romero

Materials 2019, 12(15), 2499; https://doi.org/10.3390/ma12152499 - 6 Aug 2019

Cited by 55 | Viewed by 7677

Abstract

The fused deposition modeling (FDM) technique is used today by companies engaged in the fabrication of traffic signs for the manufacture of light-emitting diode LED spotlights. In this sector, the surface properties of the elements used (surface finish, hydrophobic features) are decisive because [...] Read more.

The fused deposition modeling (FDM) technique is used today by companies engaged in the fabrication of traffic signs for the manufacture of light-emitting diode LED spotlights. In this sector, the surface properties of the elements used (surface finish, hydrophobic features) are decisive because surfaces that retain little dirt and favor self–cleaning behavior are needed. A design of experiments (L27) with five factors and three levels has been carried out. The factors studied were: Layer height (LH), print temperature (T), print speed (PS), print acceleration (PA), and flow rate (F). Polyethylene terephthalate glycol (PETG) specimens of 25.0 × 25.0 × 2.4 mm have been printed and, in each of them, the surface roughness (R_a,0, R_a,90), sliding angle (SA₀, SA₉₀), and contact angle (CA₀, CA₉₀) in both perpendicular directions have been measured. Taguchi and ANOVA analysis shows that the most influential variables in this case are printing acceleration for R_{a, 0} (p–value = 0.052) and for SA₀ (p–value = 0.051) and flow rate for R_{a, 90} (p–value = 0.001) and for SA₉₀ (p–value = 0.012). Although the ANOVA results for the contact angle are not significant, specimen 8 (PA = 1500 mm/s² and flow rate F = 110%) and specimen 10 (PA =1500 mm/s² and F = 100%) have reached contact angle values above or near the limit value for hydrophobia, respectively. Full article

(This article belongs to the Special Issue Industrial Additive Manufacturing Process Planning: Process Evaluation, Metrology, and Post-Processing Techniques)

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17 pages, 9280 KiB

Open AccessFeature PaperArticle

Leaf Age-Dependent Effects of Foliar-Sprayed CuZn Nanoparticles on Photosynthetic Efficiency and ROS Generation in Arabidopsis thaliana

by Ilektra Sperdouli, Julietta Moustaka, Orestis Antonoglou, Ioannis-Dimosthenis S. Adamakis, Catherine Dendrinou-Samara and Michael Moustakas

Materials 2019, 12(15), 2498; https://doi.org/10.3390/ma12152498 - 6 Aug 2019

Cited by 33 | Viewed by 4047

Abstract

Young and mature leaves of Arabidopsis thaliana were exposed by foliar spray to 30 mg L⁻¹ of CuZn nanoparticles (NPs). The NPs were synthesized by a microwave-assisted polyol process and characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and transmission electron [...] Read more.

Young and mature leaves of Arabidopsis thaliana were exposed by foliar spray to 30 mg L⁻¹ of CuZn nanoparticles (NPs). The NPs were synthesized by a microwave-assisted polyol process and characterized by dynamic light scattering (DLS), X-ray diffraction (XRD), and transmission electron microscopy (TEM). CuZn NPs effects in Arabidopsis leaves were evaluated by chlorophyll fluorescence imaging analysis that revealed spatiotemporal heterogeneity of the quantum efficiency of PSII photochemistry (Φ_PSΙΙ) and the redox state of the plastoquinone (PQ) pool (q_p), measured 30 min, 90 min, 180 min, and 240 min after spraying. Photosystem II (PSII) function in young leaves was observed to be negatively influenced, especially 30 min after spraying, at which point increased H₂O₂ generation was correlated to the lower oxidized state of the PQ pool. Recovery of young leaves photosynthetic efficiency appeared only after 240 min of NPs spray when also the level of ROS accumulation was similar to control leaves. On the contrary, a beneficial effect on PSII function in mature leaves after 30 min of the CuZn NPs spray was observed, with increased Φ_PSΙΙ, an increased electron transport rate (ETR), decreased singlet oxygen (¹O₂) formation, and H₂O₂ production at the same level of control leaves.An explanation for this differential response is suggested. Full article

(This article belongs to the Special Issue The Role of Metal Ions in Biology, Biochemistry and Medicine)

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13 pages, 20881 KiB

Open AccessArticle

Fluorescent PCDTBT Nanoparticles with Tunable Size for Versatile Bioimaging

by Srujan Cheruku, Lien D’Olieslaeger, Nick Smisdom, Joeri Smits, Dirk Vanderzande, Wouter Maes, Marcel Ameloot and Anitha Ethirajan

Materials 2019, 12(15), 2497; https://doi.org/10.3390/ma12152497 - 6 Aug 2019

Cited by 8 | Viewed by 5039

Abstract

Conjugated polymer nanoparticles exhibit very interesting properties for use as bio-imaging agents. In this paper, we report the synthesis of PCDTBT (poly([9-(1’-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophene-diyl)) nanoparticles of varying sizes using the mini-emulsion and emulsion/solvent evaporation approach. The effect of the size of the particles on the [...] Read more.

Conjugated polymer nanoparticles exhibit very interesting properties for use as bio-imaging agents. In this paper, we report the synthesis of PCDTBT (poly([9-(1’-octylnonyl)-9H-carbazole-2,7-diyl]-2,5-thiophenediyl-2,1,3-benzothiadiazole-4,7-diyl-2,5-thiophene-diyl)) nanoparticles of varying sizes using the mini-emulsion and emulsion/solvent evaporation approach. The effect of the size of the particles on the optical properties is investigated using UV-Vis absorption and fluorescence emission spectroscopy. It is shown that PCDTBT nanoparticles have a fluorescence emission maximum around 710 nm, within the biological near-infrared “optical window”. The photoluminescence quantum yield shows a characteristic trend as a function of size. The particles are not cytotoxic and are taken up successfully by human lung cancer carcinoma A549 cells. Irrespective of the size, all particles show excellent fluorescent brightness for bioimaging. The fidelity of the particles as fluorescent probes to study particle dynamics in situ is shown as a proof of concept by performing raster image correlation spectroscopy. Combined, these results show that PCDTBT is an excellent candidate to serve as a fluorescent probe for near-infrared bio-imaging. Full article

(This article belongs to the Special Issue Functional Conjugated Polymers for Bioimaging and Biosensing)

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(top) Schematic illustration of the PCDTBT NP synthesis. (bottom) Chemical structure of PCDTBT. Full article ">Figure 2
TEM micrographs of the different sized nanoparticles: (A) NP1, (B) NP2, (C) NP3, (D) NP4, and (E) NP5. The inset shows the morphology of a single particle in an enlarged view. Full article ">Figure 3
UV-Vis absorption (solid lines) and fluorescence (dashed lines) spectra of (A) PCDTBT in NP (NP1) and MD form, and (B) the differently sized PCDTBT NPs (NP1, NP2, NP3, NP4, NP5). The UV-Vis absorption spectrum of the NPs is hypsochromically shifted and fluorescence spectrum bathochromically shifted, compared to its MD form. Full article ">Figure 4
Dose-dependent cytotoxicity of the different PCDTBT NPs after 24 h of exposure, as determined by the Alamar blue assay on A549 cells, showing no significant cytotoxicity. Error bars show the standard deviations of the measurements (n = 3). Full article ">Figure 5
Two-photon microscopic images of A549 cells incubated for 18 h with 50 µg/mL of (A–E) NP1–NP5 respectively. The NPs are seen in green; they are superimposed on transmission images of the cells. All the NPs are internalized by the A549 cells. Scale bar: 25 µm. Full article ">Figure 6
Diffusion coefficients of the different PCDTBT NP samples as measured by RICS. The diffusion coefficients increase as the hydrodynamic size (as measured by DLS) of the particles decreases. Full article ">

15 pages, 5370 KiB

Open AccessArticle

Microstructural Evolution and Refinement Mechanism of a Beta–Gamma TiAl-Based Alloy during Multidirectional Isothermal Forging

by Kai Zhu, Shoujiang Qu, Aihan Feng, Jingli Sun and Jun Shen

Materials 2019, 12(15), 2496; https://doi.org/10.3390/ma12152496 - 6 Aug 2019

Cited by 10 | Viewed by 3540

Abstract

Multidirectional isothermal forging (MDIF) was used on a Ti-44Al-4Nb-1.5Cr-0.5Mo-0.2B (at. %) alloy to obtain a crack-free pancake. The microstructural evolution, such as dynamic recovery and recrystallization behavior, were investigated using electron backscattered diffraction and transmission electron microscopy methods. The MDIF broke down the [...] Read more.

Multidirectional isothermal forging (MDIF) was used on a Ti-44Al-4Nb-1.5Cr-0.5Mo-0.2B (at. %) alloy to obtain a crack-free pancake. The microstructural evolution, such as dynamic recovery and recrystallization behavior, were investigated using electron backscattered diffraction and transmission electron microscopy methods. The MDIF broke down the initial near-lamellar microstructure and produced a refined and homogeneous duplex microstructure. γ grains were effectively refined from 3.6 μm to 1.6 μm after the second step of isothermal forging. The ultimate tensile strength at ambient temperature and the elongation at 800 °C increased significantly after isothermal forging. β/B2→α₂ transition occurred during intermediate annealing, and α₂ + γ→β/B2 transition occurred during the second step of isothermal forging. The refinement mechanism of the first-step isothermal forging process involved the conversion of the lamellar structure and discontinuous dynamic recrystallization (DDRX) of γ grains in the original mixture-phase region. The lamellar conversion included continuous dynamic recrystallization and DDRX of the γ laths and bugling of the γ phase. DDRX behavior of γ grains dominated the refinement mechanism of the second step of isothermal forging. Full article

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13 pages, 3179 KiB

Open AccessArticle

Cold Isostatic Pressing to Improve the Mechanical Performance of Additively Manufactured Metallic Components

by Isidoro Iván Cuesta, Emilio Martínez-Pañeda, Andrés Díaz and Jesús Manuel Alegre

Materials 2019, 12(15), 2495; https://doi.org/10.3390/ma12152495 - 6 Aug 2019

Cited by 13 | Viewed by 5063

Abstract

Additive manufacturing is becoming a technique with great prospects for the production of components with new designs or shapes that are difficult to obtain by conventional manufacturing methods. One of the most promising techniques for printing metallic components is binder jetting, due to [...] Read more.

Additive manufacturing is becoming a technique with great prospects for the production of components with new designs or shapes that are difficult to obtain by conventional manufacturing methods. One of the most promising techniques for printing metallic components is binder jetting, due to its time efficiency and its ability to generate complex parts. In this process, a liquid binding agent is selectively deposited to adhere the powder particles of the printing material. Once the metallic piece is generated, it undergoes a subsequent process of curing and sintering to increase its density (hot isostatic pressing). In this work, we propose subjecting the manufactured component to an additional post-processing treatment involving the application of a high hydrostatic pressure (5000 bar) at room temperature. This post-processing technique, so-called cold isostatic pressing (CIP), is shown to increase the yield load and the maximum carrying capacity of an additively manufactured AISI 316L stainless steel. The mechanical properties, with and without CIP processing, are estimated by means of the small punch test, a suitable experimental technique to assess the mechanical response of small samples. In addition, we investigate the porosity and microstructure of the material according to the orientations of layer deposition during the manufacturing process. Our observations reveal a homogeneous distribution independent of these orientations, evidencing thus an isotropic behaviour of the material. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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11 pages, 1196 KiB

Open AccessArticle

Influence of Solution Deposition Process on Modulating Majority Charge Carrier Type and Quality of Perovskite Thin Films for Solar Cells

by Chuangchuang Chang, Xiaoping Zou, Jin Cheng, Tao Ling, Yujun Yao and Dan Chen

Materials 2019, 12(15), 2494; https://doi.org/10.3390/ma12152494 - 6 Aug 2019

Cited by 11 | Viewed by 4411

Abstract

In the past ten years, extensive research has witnessed the rapid development of perovskite solar cells (PSCs) and diversified preparation processing craft. At present, the most widely used methods of preparing perovskite solar cells are the one-step method and the two-step method. The [...] Read more.

In the past ten years, extensive research has witnessed the rapid development of perovskite solar cells (PSCs) and diversified preparation processing craft. At present, the most widely used methods of preparing perovskite solar cells are the one-step method and the two-step method. The main work of this paper is to study the effect of the solution deposition process on the quality of perovskite thin films, as well as modulating majority charge carrier types. Perovskite film was prepared in air by designing different processes, which were then adequately analyzed with corresponding methods. It was demonstrated that the preparation process plays a crucial role in modulating the type of majority carrier and in achieving high-quality perovskite thin film. The one-step prepared perovskite layer is enriched in MA⁺, leading to a P type majority carrier type thin film. The two-step prepared perovskite layer is enriched in Pb²⁺, leading to a N type majority carrier type thin film. In addition, we found that the one-step method caused PbI₂ residue due to component segregation, which seriously affects the interface and film quality of the perovskite layer. This work aims to modulate the majority carrier type of perovskite film through different preparation processes, which can lay the foundation for the study of homojunction perovskite solar cells to improve the device performance of PSCs. Full article

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32 pages, 4954 KiB

Open AccessReview

Nanotechnology in Transportation Vehicles: An Overview of Its Applications, Environmental, Health and Safety Concerns

by Muhammad Shafique and Xiaowei Luo

Materials 2019, 12(15), 2493; https://doi.org/10.3390/ma12152493 - 6 Aug 2019

Cited by 74 | Viewed by 12005

Abstract

Nanotechnology has received increasing attention and is being applied in the transportation vehicle field. With their unique physical and chemical characteristics, nanomaterials can significantly enhance the safety and durability of transportation vehicles. This paper reviews the state-of-the-art of nanotechnology and how this technology [...] Read more.

Nanotechnology has received increasing attention and is being applied in the transportation vehicle field. With their unique physical and chemical characteristics, nanomaterials can significantly enhance the safety and durability of transportation vehicles. This paper reviews the state-of-the-art of nanotechnology and how this technology can be applied in improving the comfort, safety, and speed of transportation vehicles. Moreover, this paper systematically examines the recent developments and applications of nanotechnology in the transportation vehicle industry, including nano-coatings, nano filters, carbon black for tires, nanoparticles for engine performance enchantment and fuel consumption reduction. Also, it introduces the main challenges for broader applications, such as environmental, health and safety concerns. Since several nanomaterials have shown tremendous performance and have been theoretically researched, they can be potential candidates for applications in future environmental friendly transportation vehicles. This paper will contribute to further sustainable research and greater potential applications of environmentally friendly nanomaterials in healthier transportation vehicles to improve the transportation industry around the globe. Full article

(This article belongs to the Special Issue Advanced Materials for Transport Applications 2020)

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12 pages, 4642 KiB

Open AccessArticle

The Interface and Mechanical Properties of a CVD Single Crystal Diamond Produced by Multilayered Nitrogen Doping Epitaxial Growth

by Yun Zhao, Chengming Li, Jinlong Liu, Kang An, Xiongbo Yan, Lifu Hei, Liangxian Chen, Junjun Wei and Fanxiu Lu

Materials 2019, 12(15), 2492; https://doi.org/10.3390/ma12152492 - 6 Aug 2019

Cited by 11 | Viewed by 4400

Abstract

In the present investigation, a nitrogen-doped multilayer homoepitaxial single crystal diamond is synthesized on a high-pressure high temperature (HPHT) Ib-type diamond substrate using the microwave plasma chemical vapor deposition (MPCVD) method. When 0.15 sccm of nitrogen was added in the gas phase, the [...] Read more.

In the present investigation, a nitrogen-doped multilayer homoepitaxial single crystal diamond is synthesized on a high-pressure high temperature (HPHT) Ib-type diamond substrate using the microwave plasma chemical vapor deposition (MPCVD) method. When 0.15 sccm of nitrogen was added in the gas phase, the growth rate of the doped layer was about 1.7 times that of the buffer layer, and large conical and pyramidal features are formed on the surface of the sample. Raman mapping and photoluminescence imaging of the polished cross sectional slice shows a broadband emission, with a characteristic zero phonon line (ZPL) at 575 nm in the doped layers, and large compressive stress was formed in the nitrogen-doped layers. X-ray topography shows that the defects at the interface can induce dislocation. The pyramid feature is formed at the defect, and more nitrogen-related defects are formed in the pyramid region. Thin nitrogen-doped multilayers were successfully prepared, and the thickness of the nitrogen-doped and buffer layers was about 650 nm each. The indentation measurements reveal that the thin nitrogen-doped multilayers are ultra-tough (at least ~22 MPa m^1/2), compared to the Ib-type HPHT seed substrate (~8 MPa m^1/2) and the unintentionally doped chemical vapor deposition (CVD) single crystal diamond (~14 MPa m^1/2). Full article

(This article belongs to the Special Issue Functional Surface Structures and Thin Solid Films)

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16 pages, 16419 KiB

Open AccessArticle

3D Printing of Conductive Tissue Engineering Scaffolds Containing Polypyrrole Nanoparticles with Different Morphologies and Concentrations

by Chunyang Ma, Le Jiang, Yingjin Wang, Fangli Gang, Nan Xu, Ting Li, Zhongqun Liu, Yongjie Chi, Xiumei Wang, Lingyun Zhao, Qingling Feng and Xiaodan Sun

Materials 2019, 12(15), 2491; https://doi.org/10.3390/ma12152491 - 6 Aug 2019

Cited by 38 | Viewed by 6281

Abstract

Inspired by electrically active tissues, conductive materials have been extensively developed for electrically active tissue engineering scaffolds. In addition to excellent conductivity, nanocomposite conductive materials can also provide nanoscale structure similar to the natural extracellular microenvironment. Recently, the combination of three-dimensional (3D) printing [...] Read more.

Inspired by electrically active tissues, conductive materials have been extensively developed for electrically active tissue engineering scaffolds. In addition to excellent conductivity, nanocomposite conductive materials can also provide nanoscale structure similar to the natural extracellular microenvironment. Recently, the combination of three-dimensional (3D) printing and nanotechnology has opened up a new era of conductive tissue engineering scaffolds exhibiting optimized properties and multifunctionality. Furthermore, in the case of two-dimensional (2D) conductive film scaffolds such as periosteum, nerve membrane, skin repair, etc., the traditional preparation process, such as solvent casting, produces 2D films with defects of unequal bubbles and thickness frequently. In this study, poly-l-lactide (PLLA) conductive scaffolds incorporated with polypyrrole (PPy) nanoparticles, which have multiscale structure similar to natural tissue, were prepared by combining extrusion-based low-temperature deposition 3D printing with freeze-drying. Furthermore, we creatively integrated the advantages of 3D printing and solvent casting and successfully developed a 2D conductive film scaffold with no bubbles, uniform thickness, and good structural stability. Subsequently, the effects of concentration and morphology of PPy nanoparticles on electrical properties and mechanical properties of 3D conductive scaffolds and 2D conductive films scaffolds have been studied, which provided a new idea for the design of both 2D and 3D electroactive tissue engineering scaffolds. Full article

(This article belongs to the Special Issue Electro-Active Scaffolds for Tissue Engineering)

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9 pages, 3427 KiB

Open AccessArticle

Bending Strain and Bending Fatigue Lifetime of Flexible Metal Electrodes on Polymer Substrates

by Tae-Wook Kim, Jong-Sung Lee, Young-Cheon Kim, Young-Chang Joo and Byoung-Joon Kim

Materials 2019, 12(15), 2490; https://doi.org/10.3390/ma12152490 - 6 Aug 2019

Cited by 59 | Viewed by 10765

Abstract

As the technology of flexible electronics has remarkably advanced, the long-term reliability of flexible devices has attracted much attention, as it is an important factor for such devices in reaching real commercial viability. To guarantee the bending fatigue lifetime, the exact evaluation of [...] Read more.

As the technology of flexible electronics has remarkably advanced, the long-term reliability of flexible devices has attracted much attention, as it is an important factor for such devices in reaching real commercial viability. To guarantee the bending fatigue lifetime, the exact evaluation of bending strain and the change in electrical resistance is required. In this study, we investigated the bending strains of Cu thin films on flexible polyimide substrates with different thicknesses using monolayer and bilayer bending models and monitored the electrical resistance of the metal electrode during a bending fatigue test. For a thin metal electrode, the bending strain and fatigue lifetime were similar regardless of substrate thickness, but for a thick metal film, the fatigue lifetime was changed by different bending strains in the metal electrode according to substrate thickness. To obtain the exact bending strain distribution, we conducted a finite-element simulation and compared the bending strains of thin and thick metal structures. For thick metal electrodes, the real bending strain obtained from a bilayer model or simulation showed values much different from those from a simple monolayer model. This study can provide useful guidelines for developing highly reliable flexible electronics. Full article

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(a) Schematic illustrations and equations for calculating bending strain using monolayer and bilayer models. (b) Schematic and image of a bending fatigue test and an electrical resistance monitoring system. Full article ">Figure 2
(a) Normalized electrical resistance changes of 100 nm thick Cu film on 50, 75, and 125 µm thick polyimide (PI) as a function of the number of bending cycles under bending strain amplitudes of 0.7%, 1%, and 1.5%. (b) SEM images of 100 nm thick Cu film after the bending fatigue test. Full article ">Figure 3
(a) Normalized electrical resistance changes of 1 μm thick Cu film on 50, 75, and 125 μm thick PI as a function of the number of bending cycles under bending strain amplitudes of 0.7%, 1%, and 1.5%. (b) SEM images of 1 μm thick Cu film after the bending fatigue test. Full article ">Figure 4
Calculated bending strains of (a) 100 nm thick Cu film and (b) 1 μm thick Cu film using monolayer and bilayer models. Full article ">Figure 5
Finite-element method (FEM) modeling and strain distributions: (a) 100 nm thick Cu on 50 μm thick PI, (b) 100 nm thick Cu on 125 μm, (c) 1 μm thick Cu on 50 μm thick PI, and (d) 1 μm thick Cu on 125 μm thick PI. Full article ">

21 pages, 12152 KiB

Open AccessArticle

Efficacy of Bacterial Cellulose as a Carrier of BMP-2 for Bone Regeneration in a Rabbit Frontal Sinus Model

by Takashi Koike, Jingjing Sha, Yunpeng Bai, Yuhei Matsuda, Katsumi Hideshima, Takaya Yamada and Takahiro Kanno

Materials 2019, 12(15), 2489; https://doi.org/10.3390/ma12152489 - 6 Aug 2019

Cited by 21 | Viewed by 4172

Abstract

If the alveolar bone height of patients requiring dental implants in the maxillary molar region is inadequate, it is difficult to achieve satisfactory outcomes using existing bone graft materials. We previously reported the possible utility of bacterial cellulose (BC) as a new dental [...] Read more.

If the alveolar bone height of patients requiring dental implants in the maxillary molar region is inadequate, it is difficult to achieve satisfactory outcomes using existing bone graft materials. We previously reported the possible utility of bacterial cellulose (BC) as a new dental treatment material. BC has a high absorptive capacity, good mechanical strength, and good volume retention. BC loaded with bone morphogenetic protein-2 (BMP-2) might allow effective alveolar bone augmentation. We created critical frontal bone defect models in 12 male Japanese white rabbits and divided them into four groups: sham; BC (BC grafting only); BMP-2 (treated with BMP-2 solution only); and BC+BMP-2 (grafted with BC loaded with BMP-2). Newly formed bone volume was calculated via hematoxylin-eosin staining evaluation. The proliferating cell nuclear antigen and osteocalcin levels were determined by the immunohistochemical staining analysis. All measured indices of the BC+BMP-2 group were significantly superior to those of the other groups (all p < 0.05). BC maintained the graft space and released BMP-2 in a sustained manner, promoting optimal bone formation. The BC+BMP-2 combination enhanced bone regeneration and shows promise as a useful means of clinical pre-dental implant bone augmentation in the maxillary sinus. Full article

(This article belongs to the Special Issue Micro and Nanotechnologies in Biomedicines)

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20 pages, 8095 KiB

Open AccessArticle

Isothermal Crystallization Kinetics of Poly(4-hydroxybutyrate) Biopolymer

by Ina Keridou, Luis J. del Valle, Lutz Funk, Pau Turon, Ibraheem Yousef, Lourdes Franco and Jordi Puiggalí

Materials 2019, 12(15), 2488; https://doi.org/10.3390/ma12152488 - 6 Aug 2019

Cited by 13 | Viewed by 4168

Abstract

Thermal properties and crystallization kinetics of poly(4-hydroxybutyrate) (P4HB) have been studied. The polymer shows the typical complex melting behavior associated to different lamellar populations. Annealing processes had great repercussions on properties and the morphology of constitutive lamellae as verified by X-ray scattering data. [...] Read more.

Thermal properties and crystallization kinetics of poly(4-hydroxybutyrate) (P4HB) have been studied. The polymer shows the typical complex melting behavior associated to different lamellar populations. Annealing processes had great repercussions on properties and the morphology of constitutive lamellae as verified by X-ray scattering data. Kinetics of isothermal crystallization was evaluated by both polarizing optical microscopy (POM) and calorimetric (DSC) measurements, which indicated a single crystallization regime. P4HB rendered banded spherulites with a negative birefringence when crystallized from the melt. Infrared microspectroscopy was applied to determine differences on the molecular orientation inside a specific ring according to the spherulite sectorization or between different rings along a determined spherulitic radius. Primary nucleation was increased during crystallization and when temperature decreased. Similar crystallization parameters were deduced from DSC and POM analyses (e.g., secondary nucleation parameters of 1.69 × 10⁵ K² and 1.58 × 10⁵ K², respectively). The effect of a sporadic nucleation was therefore minimized in the experimental crystallization temperature range and a good proportionality between overall crystallization rate (k) and crystal growth rate (G) was inferred. Similar bell-shaped curves were postulated to express the temperature dependence of both k and G rates, corresponding to the maximum of these curves close to a crystallization temperature of 14–15 °C. Full article

(This article belongs to the Special Issue Biomedical Applications of Polyesters and Related Polymers)

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10 pages, 2343 KiB

Open AccessArticle

Annealing-Induced Changes in the Nature of Point Defects in Sublimation-Grown Cubic Silicon Carbide

by Michael Schöler, Clemens Brecht and Peter J. Wellmann

Materials 2019, 12(15), 2487; https://doi.org/10.3390/ma12152487 - 6 Aug 2019

Cited by 3 | Viewed by 3867

Abstract

In recent years, cubic silicon carbide (3C-SiC) has gained increasing interest as semiconductor material for energy saving and optoelectronic applications, such as intermediate-band solar cells, photoelectrochemical water splitting, and quantum key distribution, just to name a few. All these applications critically depend on [...] Read more.

In recent years, cubic silicon carbide (3C-SiC) has gained increasing interest as semiconductor material for energy saving and optoelectronic applications, such as intermediate-band solar cells, photoelectrochemical water splitting, and quantum key distribution, just to name a few. All these applications critically depend on further understanding of defect behavior at the atomic level and the possibility to actively control distinct defects. In this work, dopants as well as intrinsic defects were introduced into the 3C-SiC material in situ during sublimation growth. A series of isochronal temperature treatments were performed in order to investigate the temperature-dependent annealing behavior of point defects. The material was analyzed by temperature-dependent photoluminescence (PL) measurements. In our study, we found a variation in the overall PL intensity which can be considered as an indication of annealing-induced changes in structure, composition or concentration of point defects. Moreover, a number of dopant-related as well as intrinsic defects were identified. Among these defects, there were strong indications for the presence of the negatively charged nitrogen vacancy complex (N_C–V_Si)⁻, which is considered a promising candidate for spin qubits. Full article

(This article belongs to the Special Issue Silicon Carbide and Related Materials for Energy Saving Applications—Select Papers from E-MRS 2019—Symposium “Silicon Carbide and Related Materials for Energy Saving Applications")

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As-grown bulk cubic silicon carbide (3C-SiC) sample and typical temperature dependent photoluminescence (PL) spectra of the sample: (a) backlight image of the as-grown bulk 3C-SiC sample prepared by epitaxial sublimation growth. The inhomogeneities of the coloring originate from carbon inclusions, protrusions, and, primarily, residuals from the seed mounting on the back side of the layer; (b) typical temperature-dependent PL-spectra of the as-grown 3C-SiC. The spectra were acquired with a 405 nm laser. Three sections were classified and labeled as second-order-diffraction (SOD), near-infrared (NIR), and visible (VIS) luminescence. Full article ">Figure 2
Identification of peak positions in the second-order-diffraction (SOD) and visible (VIS) regimes: (a) Within the SOD regime, four distinct peaks can be identified. Two of them were assigned to SOD of VIS and two originated from point defects. The spectra were acquired with the 405 nm laser and the InGaAs detector. (b) Within the VIS regime, four distinct peaks can be identified. Two of them were assigned to donor–acceptor pairs (DAP) and two of them were assigned to defect centers originating from point defects. The spectra were acquired with the 405 nm laser and the charge-coupled device (CCD) detector after the annealing step at 100 °C. Full article ">Figure 3
Behavior of (a) SOD and (b) VIS during temperature treatments. For improved clarity, only distinct temperatures of “as-grown” (without T-treatment), 700 °C, 850 °C, and 1300 °C are shown. The arrows indicate the shift of PL spectra after annealing. All spectra in both diagrams were acquired at a PL temperature of 50 K after temperature treatment. For excitation, the 405 nm laser was used in combination with the InGaAs detector. The shaded areas describe the variance of the reproducible reaching of the measuring position. Full article ">Figure 4
Integrated intensities of the VIS regime (1.5–2.15 eV) and SOD regime (0.73–1.08 eV) as a function of annealing temperature. Mechanisms explaining the curve characteristics are indicated in the diagram. The spectra were acquired with the 405 nm laser and the InGaAs detector at a measuring temperature of 50 K. Full article ">

16 pages, 4027 KiB

Open AccessArticle

Biosorption of Methylene Blue Dye Using Natural Biosorbents Made from Weeds

by Francisco Silva, Lorena Nascimento, Matheus Brito, Kleber da Silva, Waldomiro Paschoal and Roberto Fujiyama

Materials 2019, 12(15), 2486; https://doi.org/10.3390/ma12152486 - 5 Aug 2019

Cited by 74 | Viewed by 4980

Abstract

The purpose of this work is to make use of vegetables that, although widely found in nature, there are few applications. The weeds used here, Cyanthilium cinereum (L.) H. Rob (CCLHR) and Paspalum maritimum (PMT) found in the Amazon region of Belém state [...] Read more.

The purpose of this work is to make use of vegetables that, although widely found in nature, there are few applications. The weeds used here, Cyanthilium cinereum (L.) H. Rob (CCLHR) and Paspalum maritimum (PMT) found in the Amazon region of Belém state of Pará-Brazil, contribute to the problem of water contamination by the removal of the methylene blue dye through the biosorption process, taking advantage of other materials for economic viability and processing. The influences of parameters such as, biosorbent dose, contact time, and initial concentration of dye were examined. The characterizations were realized using SEM to verify the morphology of the material and spectroscopy in the FTIR region. As for the adsorption mechanism, the physical adsorption mechanism prevailed. The time required for the system to reach equilibrium for both biosorbents was from 50 min, following a kinetics described by the pseudo-second order model. The adsorption isotherm data for PMT were better adjusted to the Langmuir model and the biosorption capacity (

q_{m a x}

) value was (56.1798 mg/g). CCLHR was better adjusted to the Freundlich model and its maximum biosorption capacity was 76.3359 mg/g. Thus, these weed species are promising for the biosorption of methylene blue dye in effluents. Full article

(This article belongs to the Special Issue Porous Materials for Environmental Applications)

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24 pages, 19652 KiB

Open AccessArticle

GFRP Bars Anchorage Resistance in a GFRP-Reinforced Concrete Bridge Barrier

by Michael Rostami, Khaled Sennah and Saman Hedjazi

Materials 2019, 12(15), 2485; https://doi.org/10.3390/ma12152485 - 5 Aug 2019

Cited by 4 | Viewed by 5502

Abstract

In the present paper, experimental and numerical investigations were conducted on concrete bridge barriers utilizing glass fiber reinforced polymer (GFRP) bars with a hook at their ends. Implementation of these hooked bars instead of the bent bars or headed-end bars in the bridge [...] Read more.

In the present paper, experimental and numerical investigations were conducted on concrete bridge barriers utilizing glass fiber reinforced polymer (GFRP) bars with a hook at their ends. Implementation of these hooked bars instead of the bent bars or headed-end bars in the bridge barriers presented in the Canadian Highway Bridge Design Code (CHBDC) was investigated on American Association for State Highway and Transportation Officials (AASHTO) test level 5 (TL-5) concrete bridge barriers. This research aimed to reach a cost effective and safe anchorage method for GFRP bars at the barrier–deck junction, compared to the conventional bend bars or headed-end bars. Therefore, an experimental program was developed and performed to qualify the use of the recently-developed, small radius hooked bars at the barrier–deck junction. The experimental findings were compared with the design factored applied transverse load specified in CHBDC for the design of the barrier–deck junction as well as factored applied bending moment obtained at the barrier–deck junction using a recently-conducted finite-element modeling. Satisfactory behavior for the developed hooked GFRP bars as well as their anchorage resistance was established and a reasonable factor of safety in design of barrier–deck joint was achieved. Full article

(This article belongs to the Special Issue Polymer in/on Concrete)

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10 pages, 3737 KiB

Open AccessArticle

A New Reversible Phase Transformation of Intermetallic Ti₃Sn

by Minshu Du, Lishan Cui and Feng Liu

Materials 2019, 12(15), 2484; https://doi.org/10.3390/ma12152484 - 5 Aug 2019

Cited by 10 | Viewed by 3893

Abstract

Ti₃Sn has received increasing attention as a high damping metallic material and as an anode material for rechargeable lithium-ion batteries. However, a heated dispute concerning the existence of solid state phase transformation of stoichiometric Ti₃Sn impedes its development. Here, [...] Read more.

Ti₃Sn has received increasing attention as a high damping metallic material and as an anode material for rechargeable lithium-ion batteries. However, a heated dispute concerning the existence of solid state phase transformation of stoichiometric Ti₃Sn impedes its development. Here, thermal-induced reversible phase transformation of Ti₃Sn is demonstrated to happen at around 300 K by the means of in-situ variable-temperature X-ray diffraction (XRD) of Ti₃Sn powder, which is also visible for bulk Ti₃Sn on the thermal expansion curve by a turning at 330 K. The new phase’s crystal structure of Ti₃Sn is determined to be orthorhombic with a space group of Cmcm and the lattice parameters of a = 5.87 Å, b = 10.37 Å, c = 4.76 Å respectively, according to selected area electron diffraction patterns in transmission electron microscope (TEM) and XRD profiles. The hexagonal → orthorhombic phase transformation is calculated to be reasonable and consistent with thermodynamics theory. This work contributes to a growing knowledge of intermetallic Ti₃Sn, which may provide fundamental insights into its damping mechanism. Full article

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Phase transformation characterization of intermetallic Ti3Sn. (a) DSC result. (b) Thermal expansion test result. Full article ">Figure 2
Comparison of conventional X-ray diffraction (XRD) patterns between (a) bulk Ti3Sn sample and (b) Ti3Sn powder during the cooling process. (a) XRD peaks of bulk Ti3Sn near hexagonal D019 phase (002), (201) and (203) crystal faces. (b) XRD peaks of Ti3Sn powder near hexagonal D019 phase (002), (201) and (203) crystal faces, respectively. Full article ">Figure 3
Overlapping twins in bulk Ti3Sn sample. (a) Extensively distributed twins; (b) lamellar nano-twins; (c) multiple twins distributed with 120° crossover; (d) stepped twins and inner lamellar twins. Full article ">Figure 4
Lattice d-spacing variations of Ti3Sn powder during in-situ cooling and heating process. (a) D-spacing change of D019-(110) plane; (b) d-spacing change of D019-(200) plane; (c) d-spacing change of D019-(201) plane in a temperature range of 93–320 K, respectively. The D019 (201) peak still existed after phase transformation to the lowest temperature of 93 K. Full article ">Figure 5
A set of selected area electron diffraction (SAED) patterns of Ti3Sn at the room temperature. The crystal zone axis and experimental tilting angle between the neighboring SAED patterns are indicated in the figure. Full article ">Figure 6
Rietveld refinement result of XRD profile of Ti3Sn powder at 93 K, in which the hexagonal phase and the orthorhombic phase positions were indicated by green bars and red bars, respectively. The phase contents were also shown by the pie sub-figure as inserted. Full article ">Figure 7
Temperature dependence of lattice parameters a, b and c of orthorhombic Ti3Sn during cooling and heating processes, in which the schematic unit cell is also showed. Full article ">Figure 8
Comparison of the projection drawings of the hexagonal structure (drawn in black) and the orthorhombic structure (drawn in pink) of Ti3Sn from c axis, in which a, b axes of the hexagonal structure and a’, b’ axes of the orthorhombic structure were also indicated. Full article ">

12 pages, 4402 KiB

Open AccessArticle

Effect of Eggshell Powder on the Hydration of Cement Paste

by Natnael Shiferaw, Lulit Habte, Thriveni Thenepalli and Ji Whan Ahn

Materials 2019, 12(15), 2483; https://doi.org/10.3390/ma12152483 - 5 Aug 2019

Cited by 60 | Viewed by 9679

Abstract

Eggshells are one of the solid wastes in the world and are considered hazardous according to European Commission regulations. The utilization of solid wastes, like eggshells, will help create a sustainable environment by minimizing the solid wastes that are disposed into the environment. [...] Read more.

Eggshells are one of the solid wastes in the world and are considered hazardous according to European Commission regulations. The utilization of solid wastes, like eggshells, will help create a sustainable environment by minimizing the solid wastes that are disposed into the environment. The utilization of eggshell powder in cement also helps to reduce the carbon dioxide emissions from cement factories by reducing clinker production. In this study, the effect of eggshell powder on the hydration of cement products was investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM). Pastes were made with 10% and 20% eggshell powder and examined for 1, 14, and 28 days of hydration. The addition of eggshell powder transformed ettringite to monosulfoaluminate and to monocarboaluminate. In 20% eggshell powder, the formation of monocarboaluminate was detected in the early stages and accelerated the hydration reaction. The CaCO₃ from the eggshells reacted with the C₃A and changed the hydration products of the pastes. The addition of eggshell powder provided nucleation sites in the hydration products and accelerated cement hydration. Full article

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12 pages, 4397 KiB

Open AccessFeature PaperArticle

Biocompatibility and Mineralization Activity of Three Calcium Silicate-Based Root Canal Sealers Compared to Conventional Resin-Based Sealer in Human Dental Pulp Stem Cells

by Deog-Gyu Seo, Donghee Lee, Yong-Min Kim, Dani Song and Sin-Young Kim

Materials 2019, 12(15), 2482; https://doi.org/10.3390/ma12152482 - 5 Aug 2019

Cited by 54 | Viewed by 5916

Abstract

The purpose of this study was to compare the cytotoxic effects and mineralization activity of three calcium silicate-based root canal sealers to those of a conventional resin-based sealer. Experiments were performed using human dental pulp stem cells grown in a monolayer culture. The [...] Read more.

The purpose of this study was to compare the cytotoxic effects and mineralization activity of three calcium silicate-based root canal sealers to those of a conventional resin-based sealer. Experiments were performed using human dental pulp stem cells grown in a monolayer culture. The root canal sealers tested in this study were EndoSequence BC Sealer (Brasseler), BioRoot RCS (Septodont), Endoseal MTA (Maruchi), and AH Plus (Dentsply DeTrey). Experimental disks 6 mm in diameter and 3 mm in height were made and stored in a 100% humidity chamber at 37 °C for 72 h to achieve setting. The cytotoxicity of various root canal sealers was evaluated using a methyl-thiazoldiphenyl-tetrazolium (MTT) assay. To evaluate cell migration ability, a scratch wound healing method was used, and images of the scratch area were taken using a phase-contrast microscope. Cell morphology was evaluated by a scanning electron microscope after direct exposure for 72 h to each sealer disk. In the cell viability assay, there were no significant differences between the EndoSequence BC, BioRoot RCS, Endoseal MTA, and control groups in any experimental period (p > 0.05). In the cell migration assay, there were no significant differences between the EndoSequence BC, Endoseal MTA, and control groups in any experimental period (p > 0.05). BioRoot RCS exhibited slower cell migration relative to EndoSequence BC and Endoseal MTA for up to 72 h (p < 0.05). Conversely, it showed a similar wound healing percentage at 96 h (p > 0.05). In an evaluation of cell morphology, cells in direct contact with EndoSequence BC, BioRoot RCS, and Endoseal MTA disks showed superior spreading compared to those in contact with the AH Plus disk. In an Alizarin red staining assay, EndoSequence BC, BioRoot RCS, and Endoseal MTA showed a significant increase in mineralized nodule formation compared to the AH Plus group (p < 0.05). In conclusion, all calcium silicate-based root canal sealers tested in this study showed good biological properties and mineralization activity compared to conventional resin-based sealer. Full article

(This article belongs to the Special Issue Contemporary Endodontic Materials)

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Experimental procedure of biocompatibility tests of each experimental sealer disk. Full article ">Figure 2
Relative cell viability rate based on a methyl-thiazoldiphenyl-tetrazolium (MTT) assay. Asterisks indicate statistically significant differences between the control group and experimental groups. Full article ">Figure 3
Relative wound healing rate based on the cell migration assay. Asterisks indicate statistically significant differences between the control group and experimental groups. Full article ">Figure 4
Representative image of wound healing percentage based on the cell migration assay. (a) Control group, (b) AH Plus group, (c) EndoSequence BC Sealer group, (d) BioRoot RCS group, (e) Endoseal MTA group. Full article ">Figure 5
Scanning electron microscope (SEM) results of direct contact of human dental pulp stem cells (hDPSCs) with each experimental sealer. (a) Control group, (b,c) cells with control disk, (d) AH Plus disk, (e,f) cells with AH Plus disk, (g) EndoSequence BC Sealer disk, (h,i) cells with EndoSequence BC Sealer disk, (j) BioRoot RCS disk, (k,l) cells with BioRoot RCS disk, (m) Endoseal MTA disk, (n,o) cells with Endoseal MTA disk. Full article ">Figure 6
Relative mineralized nodule formation rate based on Alizarin red staining assay. Asterisk indicates a statistically significant difference between the control group and experimental groups. Different superscript letters indicate statistically significant differences. Full article ">

20 pages, 6141 KiB

Open AccessArticle

Effects of Transverse Crack on Chloride Ions Diffusion and Steel Bars Corrosion Behavior in Concrete under Electric Acceleration

by Fengyin Du, Zuquan Jin, Chuansheng Xiong, Yong Yu and Junfeng Fan

Materials 2019, 12(15), 2481; https://doi.org/10.3390/ma12152481 - 5 Aug 2019

Cited by 13 | Viewed by 4071

Abstract

Cracks greatly impact the durability of concrete structures due to their influence on the migration of chloride ions and the corrosion process of steel bars. This study investigates the effects of transverse cracks on chloride diffusion and the corrosion behavior of two types [...] Read more.

Cracks greatly impact the durability of concrete structures due to their influence on the migration of chloride ions and the corrosion process of steel bars. This study investigates the effects of transverse cracks on chloride diffusion and the corrosion behavior of two types of steel bars (low carbon steel and corrosion resistant steel) in fly ash concrete with 1 kg/m³ solution-polymerized super absorbent polymer. Electrochemical impedance spectroscopy was used to monitor the chloride-induced corrosion behavior of steel bars in concrete. The chloride profile around cracks was tested via chemical titration. The corrosion products diffusion area was photographed and measured to evaluate the influences of cracks on the corrosion degree of steel bars. Transverse cracks greatly influence the chloride ion transport. When their width is less than 0.15 mm, cracks exert little influence on both chloride diffusion and steel corrosion. When the crack width exceeds 0.15 mm, the chloride ion transmission coefficient is significantly improved and steel corrosion is accelerated. However, when the crack width exceeds 0.20 mm, this effect is gradually weakened. Based on the experimental data, a quantitative relationship between the crack width and the chloride ion transmission coefficient in electric acceleration was established. Full article

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10 pages, 3979 KiB

Open AccessArticle

Damping Enhancement Using Axially Functionally Graded Porous Structure Based on Acoustic Black Hole Effect

by Weiguang Zheng, Shiming He, Rongjiang Tang and Shuilong He

Materials 2019, 12(15), 2480; https://doi.org/10.3390/ma12152480 - 4 Aug 2019

Cited by 13 | Viewed by 3641

Abstract

The acoustic black hole (ABH) effect for damping flexural waves using axially functionally graded porous (FGP) structure is investigated. With proposed power-law porosity of FGP structure, ABH can be achieved and damping effect is enhanced. The physics are explained from divergent conditions of [...] Read more.

The acoustic black hole (ABH) effect for damping flexural waves using axially functionally graded porous (FGP) structure is investigated. With proposed power-law porosity of FGP structure, ABH can be achieved and damping effect is enhanced. The physics are explained from divergent conditions of the integrated wave phase at composite ends. Numerical results show the damping effect is increased with power law index. The phenomenon is expounded by the characteristics of reflection coefficient and impedance. It indicates that increasing power law index leads to smaller wavelength along to the end, then the wave needs more oscillation cycles to travel, which leads to more energy absorption. Transient analysis for 2D FGP structure also shows the focalization and ABH effect of the flexural waves. Full article

(This article belongs to the Collection Damping Materials)

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9 pages, 3741 KiB

Open AccessFeature PaperArticle

In Situ Macroscopic Tensile Testing in SEM and Electron Channeling Contrast Imaging: Pencil Glide Evidenced in a Bulk β-Ti21S Polycrystal

by Meriem Ben Haj Slama, Nabila Maloufi, Julien Guyon, Slim Bahi, Laurent Weiss and Antoine Guitton

Materials 2019, 12(15), 2479; https://doi.org/10.3390/ma12152479 - 4 Aug 2019

Cited by 12 | Viewed by 4478

Abstract

In this paper, we report the successful combination of macroscopic uniaxial tensile testing of bulk specimen combined with In situ dislocation-scale observations of the evolution of deformation microstructures during loading at several stress states. The dislocation-scale observations were performed by Accurate Electron Channeling [...] Read more.

In this paper, we report the successful combination of macroscopic uniaxial tensile testing of bulk specimen combined with In situ dislocation-scale observations of the evolution of deformation microstructures during loading at several stress states. The dislocation-scale observations were performed by Accurate Electron Channeling Contrast Imaging in order to follow the defects evolution and their interactions with grain boundaries for several regions of interest during macroscopic loading. With this novel in situ procedure, the slip systems governing the deformation in polycrystalline bulk β-Ti21S are tracked during the macroscopic uniaxial tensile test. For instance, curved slip lines that are associated with “pencil glide” phenomenon and tangled dislocation networks are evidenced. Full article

(This article belongs to the Special Issue New Progress on Electron Microscopies for Characterizing Microstructures)

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(a) Tensile sample geometry and sizes (mm); (b) Elastic deformation simulation on COMSOL. Full article ">Figure 2
Assembly of the tensile machine/sample inside the Scanning Electron Microscope (SEM); when SEM chamber is opened (left image) and inside the closed SEM chamber with the BackScattered Electrons (BSE) detector inserted (right images). Full article ">Figure 3
In situ obtained stress-strain curve of the β-Ti21S showing the positions where observations/Accurate Electron Channeling Contrast Imaging (A-ECCI) were made: before loading (1), during elastic deformation (2: no defect formation was observed), at the beginning of the plastic domain (3), and for six intermediate states of the second tensile cycle before unloading (four to 10). The dashed vertical lines correspond to the relaxation after plastic deformation. Full article ">Figure 4
Observed area of 600 × 450 µm2 with the seven zones of interest in white dashed frames. Full article ">Figure 5
(a) BSE micrographs in channeling condition (with g = (1–10) in the grain of interest) presenting the evolution of the defect structure corresponding to each deformation step of the tensile curve. The letter refers to the zone (E) and the number refers to the load state from the curve. Black arrows indicate slip lines, orange arrows indicate dislocations and yellow crosses indicate an increase in dislocation length; (b) Example of SE vs BSE images from zone (E8). Full article ">Figure 6
(a) Local section reduction to create high-strained zones (b) BSE micrographs in channeling condition post mortem test showing dislocation networks and slip lines forming and evolving during plastic deformation. Full article ">Figure 7
(a) Secondary Electron (SE) micrographs showing curved slip lines resulting from pencil glide phenomenon and (b) a corresponding schematic representation. Full article ">

18 pages, 9531 KiB

Open AccessArticle

Revealing the Nuclei Formation in Carbon-Inoculated Mg-3%Al Alloys Containing Trace Fe

by Chengbo Li, Shuqing Yang, Gan Luo, Hengbin Liao and Jun Du

Materials 2019, 12(15), 2478; https://doi.org/10.3390/ma12152478 - 4 Aug 2019

Cited by 5 | Viewed by 2888

Abstract

In this study, Fe-bearing Mg-3%Al alloys were inoculated by combining carbon with or without Ca. Both processes can significantly refine the grain size of Mg-3%Al alloys. The highest refining efficiency can be obtained by carbon combined with Ca. The synergistic grain refining efficiency [...] Read more.

In this study, Fe-bearing Mg-3%Al alloys were inoculated by combining carbon with or without Ca. Both processes can significantly refine the grain size of Mg-3%Al alloys. The highest refining efficiency can be obtained by carbon combined with Ca. The synergistic grain refining efficiency can be attributed to the constitutional undercooling produced by the addition of Ca. Two kinds of carbon-containing nuclei with duplex-phase particles and cluster particles were observed in the carbon-inoculated alloys. A thermodynamic model was established to disclose the formation mechanisms of the duplex-phase particles and Al₄C₃ cluster particles. This thermodynamic model is based on the change of Gibbs free energy for the formation of these two kinds of particles. The calculated results show that these two particles can form spontaneously, since the change of Gibbs free energy is negative. However, the Gibbs free change of the duplex-phase particle is more negative than the Al₄C₃ cluster particle. This indicates that the adsorption process is more spontaneous than the cluster process, and tiny Al₄C₃ particles are preferred to form duplex-phase particle, rather than gathering to form an Al₄C₃ cluster particle. In addition, the addition of Ca can reduce the interfacial energy between the Al₄C₃ phase and the Al–Fe phase and promote the formation of duplex-phase particles. Full article

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20 pages, 8180 KiB

Open AccessArticle

Influence of Pore Networking and Electric Current Density on the Crack Pattern in Reinforced Concrete Test Due to Pressure Rust Layer at Early Ages of an Accelerated Corrosion Test

by Ángela M. Bazán, Encarnación Reyes and Jaime C. Gálvez

Materials 2019, 12(15), 2477; https://doi.org/10.3390/ma12152477 - 4 Aug 2019

Cited by 4 | Viewed by 4384

Abstract

Research on early stages of corrosion of steel bars caused by chloride penetration is relevant in improving the durability of reinforced concrete structures. Similarly, the formation and development of cracks induced in the surrounding concrete is also of great importance. This paper uses [...] Read more.

Research on early stages of corrosion of steel bars caused by chloride penetration is relevant in improving the durability of reinforced concrete structures. Similarly, the formation and development of cracks induced in the surrounding concrete is also of great importance. This paper uses integration of the analytical models examined in the published literature, combined with experimental research in corrosion induced at the concrete/steel interface, in estimating the time-to-crack initiation of reinforced concrete subjected to corrosion. This work studies the influence of the porous network and electric current density on the cracking process at early ages. The experimental program was performed by using an accelerated corrosion test. Two types of concrete were performed: A conventional concrete (CC) and a concrete with silica fume (SFC). A current density of 50 μA/cm² and 100 μA/cm² was applied to specimens of both concretes. Examination performed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) provided both qualitative and quantitative information on the penetration of the rust layer in the surrounding concrete porous network. Strain gauges were used to measure corrosion-induced deformations between steel and concrete matrices, as well as the formation of corrosion-induced cracks. A good correlation between the rate of penetration of the rust products in the surrounding pores and the delay of the cracking pressure in concrete was observed from the experimental results. This phenomenon is incorporated into the analytical model by using a reduction factor, which mainly depends on the pore size of the concrete. The crack width obtained exhibited a significant dependency on electric current density at the beginning of the test, depending mainly on the pore size of the concrete later. Full article

(This article belongs to the Special Issue Corrosion of Reinforcing Steel in Reinforced Concrete)

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23 pages, 3438 KiB

Open AccessReview

Cross-Linking Strategies for Electrospun Gelatin Scaffolds

by Chiara Emma Campiglio, Nicola Contessi Negrini, Silvia Farè and Lorenza Draghi

Materials 2019, 12(15), 2476; https://doi.org/10.3390/ma12152476 - 4 Aug 2019

Cited by 196 | Viewed by 14919

Abstract

Electrospinning is an exceptional technology to fabricate sub-micrometric fiber scaffolds for regenerative medicine applications and to mimic the morphology and the chemistry of the natural extracellular matrix (ECM). Although most synthetic and natural polymers can be electrospun, gelatin frequently represents a material of [...] Read more.

Electrospinning is an exceptional technology to fabricate sub-micrometric fiber scaffolds for regenerative medicine applications and to mimic the morphology and the chemistry of the natural extracellular matrix (ECM). Although most synthetic and natural polymers can be electrospun, gelatin frequently represents a material of choice due to the presence of cell-interactive motifs, its wide availability, low cost, easy processability, and biodegradability. However, cross-linking is required to stabilize the structure of the electrospun matrices and avoid gelatin dissolution at body temperature. Different physical and chemical cross-linking protocols have been described to improve electrospun gelatin stability and to preserve the morphological fibrous arrangement of the electrospun gelatin scaffolds. Here, we review the main current strategies. For each method, the cross-linking mechanism and its efficiency, the influence of electrospinning parameters, and the resulting fiber morphology are considered. The main drawbacks as well as the open challenges are also discussed. Full article

(This article belongs to the Special Issue Polymer-based Instructive Scaffolds for Regenerative Medicine)

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9 pages, 5168 KiB

Open AccessArticle

Electrochemistry and Rapid Electrochromism Control of MoO₃/V₂O₅ Hybrid Nanobilayers

by Chung-Chieh Chang, Po-Wei Chi, Prem Chandan and Chung-Kwei Lin

Materials 2019, 12(15), 2475; https://doi.org/10.3390/ma12152475 - 3 Aug 2019

Cited by 27 | Viewed by 4171

Abstract

MoO₃/V₂O₅ hybrid nanobilayers are successfully prepared by the sol–gel method with a spin- coating technique followed by heat -treatment at 350 °C in order to achieve a good crystallinity. The composition, morphology, and microstructure of the nanobilayers are [...] Read more.

MoO₃/V₂O₅ hybrid nanobilayers are successfully prepared by the sol–gel method with a spin- coating technique followed by heat -treatment at 350 °C in order to achieve a good crystallinity. The composition, morphology, and microstructure of the nanobilayers are characterized by a scanning electron microscope (SEM) and X-ray diffractometer (XRD) that revealed the a grain size of around 20–30 nm, and belonging to the monoclinic phase. The samples show good reversibility in the cyclic voltammetry studies and exhibit an excellent response to the visible transmittance. The electrochromic (EC) window displayed an optical transmittance changes (ΔT) of 22.65% and 31.4% at 550 and 700 nm, respectively, with the rapid response time of about 8.2 s for coloration and 6.3 s for bleaching. The advantages, such as large optical transmittance changes, rapid electrochromism control speed, and excellent cycle durability, demonstrated in the electrochromic cell proves the potential application of MoO₃/V₂O₅ hybrid nanobilayers in electrochromic devices. Full article

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22 pages, 4970 KiB

Open AccessArticle

Internal Cracks and Non-Metallic Inclusions as Root Causes of Casting Failure in Sugar Mill Roller Shafts

by Muhammad Jamil, Aqib Mashood Khan, Hussien Hegab, Shoaib Sarfraz, Neeraj Sharma, Mozammel Mia, Munish Kumar Gupta, GuLong Zhao, H. Moustabchir and Catalin I. Pruncu

Materials 2019, 12(15), 2474; https://doi.org/10.3390/ma12152474 - 3 Aug 2019

Cited by 18 | Viewed by 7545

Abstract

The sugar mill roller shaft is one of the critical parts of the sugar industry. It requires careful manufacturing and testing in order to meet the stringent specification when it is used for applications under continuous fatigue and wear environments. For heavy industry, [...] Read more.

The sugar mill roller shaft is one of the critical parts of the sugar industry. It requires careful manufacturing and testing in order to meet the stringent specification when it is used for applications under continuous fatigue and wear environments. For heavy industry, the manufacturing of such heavy parts (>600 mm diameter) is a challenge, owing to ease of occurrence of surface/subsurface cracks and inclusions that lead to the rejection of the final product. Therefore, the identification and continuous reduction of defects are inevitable tasks. If the defect activity is controlled, this offers the possibility to extend the component (sugar mill roller) life cycle and resistance to failure. The current study aims to explore the benefits of using ultrasonic testing (UT) to avoid the rejection of the shaft in heavy industry. This study performed a rigorous evaluation of defects through destructive and nondestructive quality checks in order to detect the causes and effects of rejection. The results gathered in this study depict macro-surface cracks and sub-surface microcracks. The results also found alumina and oxide type non-metallic inclusions, which led to surface/subsurface cracks and ultimately the rejection of the mill roller shaft. A root cause analysis (RCA) approach highlighted the refractory lining, the hot-top of the furnace and the ladle as significant causes of inclusions. The low-quality flux and refractory lining material of the furnace and the hot-top, which were possible causes of rejection, were replaced by standard materials with better quality, applied by their standardized procedure, to prevent this problem in future production. The feedback statistics, evaluated over more than one year, indicated that the rejection rate was reduced for defective production by up to 7.6%. Full article

(This article belongs to the Special Issue Advances in Multi-scale Mechanical Characterization of Materials with Optical Methods)

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13 pages, 2148 KiB

Open AccessArticle

Adhesive Cements That Bond Soft Tissue Ex Vivo

by Xiuwen Li, Michael Pujari-Palmer, David Wenner, Philip Procter, Gerard Insley and Håkan Engqvist

Materials 2019, 12(15), 2473; https://doi.org/10.3390/ma12152473 - 3 Aug 2019

Cited by 17 | Viewed by 7007

Abstract

The aim of the present study was to evaluate the soft tissue bond strength of a newly developed, monomeric, biomimetic, tissue adhesive called phosphoserine modified cement (PMC). Two types of PMCs were evaluated using lap shear strength (LSS) testing, on porcine skin: a [...] Read more.

The aim of the present study was to evaluate the soft tissue bond strength of a newly developed, monomeric, biomimetic, tissue adhesive called phosphoserine modified cement (PMC). Two types of PMCs were evaluated using lap shear strength (LSS) testing, on porcine skin: a calcium metasilicate (CS1), and alpha tricalcium phosphate (αTCP) PMC. CS1 PCM bonded strongly to skin, reaching a peak LSS of 84, 132, and 154 KPa after curing for 0.5, 1.5, and 4 h, respectively. Cyanoacrylate and fibrin glues reached an LSS of 207 kPa and 33 kPa, respectively. αTCP PMCs reached a final LSS of ≈110 kPa. In soft tissues, stronger bond strengths were obtained with αTCP PMCs containing large amounts of amino acid (70–90 mol%), in contrast to prior studies in calcified tissues (30–50 mol%). When αTCP particle size was reduced by wet milling, and for CS1 PMCs, the strongest bonding was obtained with mole ratios of 30–50% phosphoserine. While PM-CPCs behave like stiff ceramics after setting, they bond to soft tissues, and warrant further investigation as tissue adhesives, particularly at the interface between hard and soft tissues. Full article

(This article belongs to the Special Issue Mineral Bone Cements: Current Status and Future Prospects)

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Full article ">Figure 1
(A) Overview of the testing procedure and obtained data. Skin was removed from an entire ear, as a single piece, and subsequently sectioned into smaller strips 1 cm × 2 cm. (B) To ensure reproducible and comparable conditions each sample was held together during the curing stage using universal grips. (C) The lap shear testing setup. (D) Representative force/displacement curves for calcium metasilicate PMC (CS1), and the peak force per area was calculated for each sample. (E) Adhesive PMCs were applied to the skin surface as a viscous, tacky paste, with the failure surface. Full article ">Figure 2
Particle size distribution of PMC precursors. The particle size limit of each PMC precursor (calcium salt) below which, based upon number, surface, and volume average calculations, (A) 50% (D0.5) or (B) 90% (D0.9) of all measured particles fall. (C) A distribution plot of all PMCs using surface average calculations. The surface area of each PMC precursor (D), determined by BET (white bars) or laser diffraction (black bars). Each αTCP (i.e., αTCP2.1) refers to the average particle size (D0.5, surface, in micrometers) of the calcium salt portion of PMC. Full article ">Figure 3
Secondary electron SEM images of precursor calcium salts: (A) αTCP2.1, (B) αTCP1.9, (C) αTCP1.5, and (D) CS1 particles are shown at 1000× magnification. Inset images in the upper right corner reveal the surface topography and fine structure of respective particles at approximately 25,000× magnification. Each number following the precursor name (i.e., αTCP2.1) refers to the average particle size (D0.5, surface, in micrometers) of the calcium salt portion of PMC. Scale bars represent a 10 µm distance, while inset scale bars represent a 1 µm distance. Full article ">Figure 4
X-ray diffraction of calcium salt precursors used to make PMCs. Full article ">Figure 5
Lap shear strength of PMCs under varied testing conditions. (A) The bond strength of αTCP2.1 PMCs applied to porcine skin obtained from either the rostral (front) or caudal (back) portion of the ear. (B) Bond strength of αTCP2.1 PMCs tested at a crosshead speed of 1, 10, or 30 mm per minute. (C) Bond strength of αTCP2.1 PMCs applied to porcine skin of different sizes (overlap area). (D) The effect of using universal grips (black bars), compared to samples that were appositioned without grips (white bars) on the observed bond strength for each material. All samples contained 60 mol% of phosphoserine, unless otherwise indicated, and were cured for 90 min. Each αTCP, i.e., αTCP2.1, refers to the average particle size (D0.5, surface, in micrometers) of the calcium salt portion of PMC. * and ** indicate p < 0.05, and p < 0.01, respectively, in comparison to samples with a 1 cm2 contact area (C), or between grip and no grip samples (D). Each data point and group represents a sample size of three (n = 3), except in <a href="#materials-12-02473-f005" class="html-fig">Figure 5</a>A, which contained six samples per group (n = 6). Full article ">Figure 6
Lap shear strength of PMCs. (A) The optimal bond strength of PMCs, with varied ratio of calcium salt to phosphoserine, after curing for 90 min. (B) The optimal bond strength of αTCP PMCs of differing particle size, with varied ratios of calcium salt to phosphoserine after curing for 90 min. To ensure that the comparisons in (A) and (B) represented the true final cure strength, the cure kinetics of each PMC was compared at the optimal mole ratio for (C) CS1 PMC (53%) and (D) αTCP PMC (87%) after curing for 30, 90, or 240 min. αTCP1.5, αTCP1.9, and αTCP 2.1 refer to the average particle sizes (D0.5, surface, in micrometers) of the calcium salt portion of PMC. * and ** indicate p < 0.05 and p < 0.01, respectively, with all comparisons made against αTCP 2.1 PMC with respect to each time point or mole ratio. Each data point and group represents a sample size of six (n = 6) in <a href="#materials-12-02473-f006" class="html-fig">Figure 6</a>A–D. Full article ">

7 pages, 1921 KiB

Open AccessArticle

Effect of the Iron Reduction Index on the Mechanical and Chemical Properties of Continuous Basalt Fiber

by Lida Luo, Qichang Zhang, Qingwei Wang, Jiwen Xiao, Jin Liu, Linfeng Ding and Weizhong Jiang

Materials 2019, 12(15), 2472; https://doi.org/10.3390/ma12152472 - 3 Aug 2019

Cited by 8 | Viewed by 2923

Abstract

Basalt glass belongs to the iron-rich aluminosilicate glass system; thus, the iron content and the iron redox index (IRI=Fe²⁺/Fe_total) influence the viscosity, density, mechanical and chemical properties of basalt fiber (BF). In this work, continuous BFs with IRIs ranging [...] Read more.

Basalt glass belongs to the iron-rich aluminosilicate glass system; thus, the iron content and the iron redox index (IRI=Fe²⁺/Fe_total) influence the viscosity, density, mechanical and chemical properties of basalt fiber (BF). In this work, continuous BFs with IRIs ranging from 0.21–0.87 were prepared by adding a different amount of redox agents. An economical and easily accessible testing method—the spectral photometric method with 1,10-phenanthroline—is applied to measure the IRI with convinced accuracy, which has been approved by Mössbauer spectra and X-ray fluorescence analysis. The tensile strength of the BF samples increases approximately linearly with increasing IRI as a function of

σ = 227.9 IRI + 780.0

. The FT-IR results indicate that, with increasing IRI, the ferric ions are replaced by the much stronger network formers (Al³⁺ and Si⁴⁺), hence the increased the tensile strength. The X-ray diffraction results show an amorphous nature of BF samples. Moreover, the tensile strength is significantly decreased after the alkali corrosion, which is partly attributed to the severe surface damaging according to the SEM results. This work proved the feasibility of mechanical property improvement in BF production by controlling the iron redox index. Full article

(This article belongs to the Section Materials Chemistry)

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13 pages, 3870 KiB

Open AccessArticle

Impact of Electrocautery on Fatigue Life of Spinal Fusion Constructs—An In Vitro Biomechanical Study

by Haidara Almansour, Robert Sonntag, Wojciech Pepke, Thomas Bruckner, Jan Philippe Kretzer and Michael Akbar

Materials 2019, 12(15), 2471; https://doi.org/10.3390/ma12152471 - 3 Aug 2019

Cited by 7 | Viewed by 4104

Abstract

Instrumentation failure in the context of spine surgery is attributed to cyclic loading leading to formation of fatigue cracks, which later propagate and result in rod fracture. A biomechanical analysis of the potential impact of electrocautery on the fatigue life of spinal implants [...] Read more.

Instrumentation failure in the context of spine surgery is attributed to cyclic loading leading to formation of fatigue cracks, which later propagate and result in rod fracture. A biomechanical analysis of the potential impact of electrocautery on the fatigue life of spinal implants has not been previously performed. The aim of this study was to assess the fatigue life of titanium (Ti) and cobalt-chrome (CoCr) rod-screw constructs after being treated with electrocautery. Twelve spinal constructs with CoCr and Ti rods were examined. Specimens were divided into four groups by rod material (Ti and CoCr) and application of monopolar electrocautery on the rods’ surface (control-group and electrocautery-group). Electrocautery was applied on each rod at three locations, then constructs were cyclically tested. Outcome measures were load-to-failure, total number of cycles-to-failure, and location of rod failure. Ti-rods treated with electrocautery demonstrated a significantly decreased fatigue life compared to non-treated Ti-rods. Intergroup comparison of cycles-to-failure revealed a significant mean decrease of almost 9 × 10⁵ cycles (p = 0.03). No CoCr-rods failed in this experiment. Electrocautery application on the surface of Ti-rods significantly reduces their fatigue life. Surgeons should exercise caution when using electrocautery in the vicinity of Ti-rods to mitigate the risk of rod failure. Full article

(This article belongs to the Special Issue Novel Research about Biomechanics and Biomaterials Used in Hip, Knee and Related Joints)

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17 pages, 5797 KiB

Open AccessArticle

Mechanical Properties of High-Performance Steel-Fibre-Reinforced Concrete and Its Application in Underground Mine Engineering

by Xiang Li, Weipei Xue, Cao Fu, Zhishu Yao and Xiaohu Liu

Materials 2019, 12(15), 2470; https://doi.org/10.3390/ma12152470 - 3 Aug 2019

Cited by 18 | Viewed by 3651

Abstract

In order to economically and reasonably solve the problem of mineshaft support in complex geological conditions, the mechanical properties of high-performance steel-fiber-reinforced concrete (HPSFRC) and its application in mineshaft lining structures were investigated in this study. Firstly, the mix proportion of HPSFRC for [...] Read more.

In order to economically and reasonably solve the problem of mineshaft support in complex geological conditions, the mechanical properties of high-performance steel-fiber-reinforced concrete (HPSFRC) and its application in mineshaft lining structures were investigated in this study. Firstly, the mix proportion of HPSFRC for the mineshaft lining structure was obtained through raw material selection and preparation testing. Then, a series of mechanical property tests were conducted. The test results showed that the compressive, flexural, and tensile strengths of HPSFRC were 9%, 71%, and 53% higher than that of ordinary concrete, respectively. The fracture toughness of HPSFRC was 75% higher than that of the ordinary concrete and the fracture energy of HPSFRC was 16 times that of the ordinary concrete. Finally, the model test results of the HPSFRC shaft lining structure showed that the crack resistance, toughness, and bearing capacity of the shaft lining structure had been significantly improved under a non-uniform confining load because of the replacement of ordinary concrete with HPSFRC. HPSFRC was proved to be an ideal material for mineshaft support structures under complex geological conditions. Full article

(This article belongs to the Special Issue New and Emerging Construction Materials)

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