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Materials, Volume 12, Issue 11 (June-1 2019)

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Cover Story (view full-size image) This study presents the synthesis and characterization of lanthanum-modified alumina supported [...] Read more.
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Open AccessArticle
In Vitro and In Vivo Evaluation of Starfish Bone-Derived β-Tricalcium Phosphate as a Bone Substitute Material
Materials 2019, 12(11), 1881; https://doi.org/10.3390/ma12111881 - 11 Jun 2019
Viewed by 527
Abstract
We evaluated starfish-derived β-tricalcium phosphate (Sf-TCP) obtained by phosphatization of starfish-bone-derived porous calcium carbonate as a potential bone substitute material. The Sf-TCP had a communicating pore structure with a pore size of approximately 10 μm. Although the porosity of Sf-TCP was similar to [...] Read more.
We evaluated starfish-derived β-tricalcium phosphate (Sf-TCP) obtained by phosphatization of starfish-bone-derived porous calcium carbonate as a potential bone substitute material. The Sf-TCP had a communicating pore structure with a pore size of approximately 10 μm. Although the porosity of Sf-TCP was similar to that of Cerasorb M (CM)—a commercially available β-TCP bone filler—the specific surface area was roughly three times larger than that of CM. Observation by scanning electron microscopy showed that pores communicated to the inside of the Sf-TCP. Cell growth tests showed that Sf-TCP improved cell proliferation compared with CM. Cells grown on Sf-TCP showed stretched filopodia and adhered; cells migrated both to the surface and into pores. In vivo, vigorous tissue invasion into pores was observed in Sf-TCP, and more fibrous tissue was observed for Sf-TCP than CM. Moreover, capillary formation into pores was observed for Sf-TCP. Thus, Sf-TCP showed excellent biocompatibility in vitro and more vigorous bone formation in vivo, indicating the possible applications of this material as a bone substitute. In addition, our findings suggested that mimicking the microstructure derived from whole organisms may facilitate the development of superior artificial bone. Full article
(This article belongs to the Special Issue Design of Materials for Bone Tissue Scaffolds)
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Open AccessArticle
α-Fe2O3 Nanoparticles/Vermiculite Clay Material: Structural, Optical and Photocatalytic Properties
Materials 2019, 12(11), 1880; https://doi.org/10.3390/ma12111880 - 11 Jun 2019
Viewed by 506
Abstract
Photocatalysis is increasingly becoming a center of interest due to its wide use in environmental remediation. Hematite (α-Fe2O3) is one promising candidate for photocatalytic applications. Clay materials as vermiculite (Ver) can be used as a carrier to accommodate and [...] Read more.
Photocatalysis is increasingly becoming a center of interest due to its wide use in environmental remediation. Hematite (α-Fe2O3) is one promising candidate for photocatalytic applications. Clay materials as vermiculite (Ver) can be used as a carrier to accommodate and stabilize photocatalysts. Two different temperatures (500 °C and 700 °C) were used for preparation of α-Fe2O3 nanoparticles/vermiculite clay materials. The experimental methods used for determination of structural, optical and photocatalytic properties were X-ray fluorescence (ED-XRF), X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive X-ray spectrometry (EDS), N2 adsorption method (BET), diffuse reflectance UV-Vis spectroscopy (DRS), photoluminescence spectroscopy (PL) and photocatalytic reduction of CO2, respectively. The data from XRD were confronted with molecular modeling of the material arrangement in the interlayer space of vermiculite structure and the possibility of anchoring the α-Fe2O3 nanoparticles to the surface and edge of vermiculite. Correlations between structural, textural, optical and electrical properties and photocatalytic activity have been studied in detail. The α-Fe2O3 and α-Fe2O3/Ver materials with higher specific surface areas, a smaller crystallite size and structural defects (oxygen vacancies) that a play crucial role in photocatalytic activity, were prepared at a lower calcination temperature of 500 °C. Full article
(This article belongs to the Special Issue Photocatalysts for Environmental Applications)
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Open AccessArticle
Preparation of Bi2O3/Al Core-Shell Energetic Composite by Two-Step Ball Milling Method and Its Application in Solid Propellant
Materials 2019, 12(11), 1879; https://doi.org/10.3390/ma12111879 - 11 Jun 2019
Viewed by 425
Abstract
In this article, Bi2O3/Al high-density energetic composites with a core-shell structure were prepared by a two-step ball milling method using a common planetary ball milling instrument, and their morphology, structure, and properties were characterized in detail. Through a reasonable [...] Read more.
In this article, Bi2O3/Al high-density energetic composites with a core-shell structure were prepared by a two-step ball milling method using a common planetary ball milling instrument, and their morphology, structure, and properties were characterized in detail. Through a reasonable ratio design and optimization of the ball milling conditions, the density of the Bi2O3/Al core-shell energetic composite is increased by about 11.3% compared to that of the physical mixed sample under the same conditions. The DSC (Differential Scanning Calorimetry) test also showed that the exothermic quantity of the thermite reaction of the energetic composite reached 2112.21 J/g, which is very close to the theoretical exothermic quantity. The effect of Bi2O3/Al core-shell energetic composite on the energy performance of insensitive HTPE propellant was further studied. The theoretical calculation results showed that replacing the partial Al with Bi2O3/Al core-shell energetic composite can make the density of propellant reach 2.056 g/cm3, and the density specific impulse reach 502.3 s·g/cm3, which is significantly higher than the density and density specific impulse of the conventional composite solid propellant. The thermal test showed that the explosive heat of the HTPE (Hydroxyl terminated polyether) propellant also increased with the increase of the content of Bi2O3/Al core-shell energetic composite. Full article
(This article belongs to the Section Energy Materials)
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Open AccessArticle
Multidimensional Phononic Bandgaps in Three-Dimensional Lattices for Additive Manufacturing
Materials 2019, 12(11), 1878; https://doi.org/10.3390/ma12111878 - 11 Jun 2019
Viewed by 647
Abstract
We report on numerical modelling of three-dimensional lattice structures designed to provide phononic bandgaps. The examined lattice structures rely on two distinct mechanisms for bandgap formation: the destructive interference of elastic waves and internal resonance. Further to the effect of lattice type on [...] Read more.
We report on numerical modelling of three-dimensional lattice structures designed to provide phononic bandgaps. The examined lattice structures rely on two distinct mechanisms for bandgap formation: the destructive interference of elastic waves and internal resonance. Further to the effect of lattice type on the development of phononic bandgaps, we also present the effect of volume fraction, which enables the designer to control the frequency range over which the bandgaps exist. The bandgaps were identified from dispersion curves obtained using a finite element wave propagation modelling technique that provides high computational efficiency and high wave modelling accuracy. We show that lattice structures employing internal resonance can provide transmissibility reduction of longitudinal waves of up to −103 dB. Paired with the manufacturing freedom and material choice of additive manufacturing, the examined lattice structures can be tailored for use in wide-ranging applications including machine design, isolation and support platforms, metrology frames, aerospace and automobile applications, and biomedical devices. Full article
(This article belongs to the Special Issue Damping Materials)
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Open AccessArticle
The Influence of Surface Wettability and Topography on the Bioactivity of TiO2/Epoxy Coatings on AISI 316L Stainless Steel
Materials 2019, 12(11), 1877; https://doi.org/10.3390/ma12111877 - 11 Jun 2019
Viewed by 408
Abstract
Epoxy/TiO2/epoxy and epoxy/FAS-TiO2/epoxy coatings were applied to the surface of AISI 316L stainless steel with the aim to improve the biocompatibility and antibacterial properties. Contact-angle measurements were used to evaluate the wetting properties of the epoxy, epoxy/TiO2/epoxy [...] Read more.
Epoxy/TiO2/epoxy and epoxy/FAS-TiO2/epoxy coatings were applied to the surface of AISI 316L stainless steel with the aim to improve the biocompatibility and antibacterial properties. Contact-angle measurements were used to evaluate the wetting properties of the epoxy, epoxy/TiO2/epoxy and epoxy/FAS-TiO2/epoxy coatings. The epoxy and epoxy/TiO2/epoxy coatings were hydrophilic compared with the strongly hydrophobic epoxy/FAS-TiO2/epoxy coating. The average surface roughness (Sa) of the epoxy/FAS-TiO2/epoxy coating was higher than that of the epoxy/TiO2/epoxy coating due to the formation of agglomerates. The biocompatibility evaluation revealed that the cell attachment was significantly higher on the epoxy/FAS-TiO2/epoxy and epoxy/TiO2/epoxy coatings compared with the pure epoxy coating. We also observed improved antibacterial properties for the epoxy coatings with the addition of both TiO2 and FAS-TiO2 nanoparticles. Full article
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Open AccessArticle
Investigation of the Quench Sensitivity of an AlSi10Mg Alloy in Permanent Mold and High-Pressure Vacuum Die Castings
Materials 2019, 12(11), 1876; https://doi.org/10.3390/ma12111876 - 11 Jun 2019
Viewed by 428
Abstract
The quench sensitivities of an AlSi10Mg alloy in permanent mold (PM) and high-pressure vacuum die (HPVD) castings were investigated with time–temperature–transformation and time–temperature–property diagrams using an interrupted quench technique. The quench-sensitive temperature range of the HPVD casting sample is 275–450 °C, and its [...] Read more.
The quench sensitivities of an AlSi10Mg alloy in permanent mold (PM) and high-pressure vacuum die (HPVD) castings were investigated with time–temperature–transformation and time–temperature–property diagrams using an interrupted quench technique. The quench-sensitive temperature range of the HPVD casting sample is 275–450 °C, and its nose temperature is 375 °C. The quench-sensitive range of the PM casting sample is 255–430 °C, and the nose temperature is 350 °C. The mechanical strength versus the cooling rate in both casting samples were predicted via a quench factor analysis and verified experimentally. The critical cooling rate of the HPVD casting sample is 20 °C/s whereas it is 17 °C/s for the PM casting sample. With a shorter critical time, higher nose temperature, and higher critical cooling rate, the HPVD casting sample exhibits a higher quench sensitivity than the PM casting sample. The differences in the quench sensitivities of the AlSi10Mg alloy due to the different casting processes is explained via the different precipitation behavior. At the nose temperature, coarse β-Mg2Si precipitates mainly precipitate along the grain boundaries in the HPVD casting sample, whereas rod-like β-Mg2Si precipitates distribute in the aluminum matrix in the PM casting. Full article
(This article belongs to the Special Issue Alloys Casting: Materials, Technologies, and Applications)
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Study on the Viscoelasticity Measurement of Materials Based on Surface Reflected Waves
Materials 2019, 12(11), 1875; https://doi.org/10.3390/ma12111875 - 10 Jun 2019
Viewed by 434
Abstract
The reflected waves received from ultrasonic waves propagating in materials contain information that constitutes the physical properties, material composition, defects, and degradation states. When measuring the dynamic viscoelasticity, the traditional bottom reflection method (BRM) cannot be used to measure the bottom irregular samples. [...] Read more.
The reflected waves received from ultrasonic waves propagating in materials contain information that constitutes the physical properties, material composition, defects, and degradation states. When measuring the dynamic viscoelasticity, the traditional bottom reflection method (BRM) cannot be used to measure the bottom irregular samples. In this paper, the storage modulus, loss modulus, and loss tangent are extracted by the surface reflection method (SRM) to evaluate the elastomer sample viscoelasticity. A theoretical study on the phase change caused by multiple reflections in the case of non-thin layer coupling is conducted. Based on this research, the experimental system is built. The results show that considering the thickness of the coupling layer can optimize the determination of viscoelasticity and reduce the error of the viscoelastic evaluation results of an elastomer with the traditional BRM. Finally, based on the principle of the SRM, the density of the elastomers is measured, and the feasibility and overall efficiency of this method are verified by experiments. Full article
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Open AccessArticle
Effect of Chitin Nanofibrils on Biocompatibility and Bioactivity of the Chitosan-Based Composite Film Matrix Intended for Tissue Engineering
Materials 2019, 12(11), 1874; https://doi.org/10.3390/ma12111874 - 10 Jun 2019
Viewed by 417
Abstract
This paper discusses the mechanical and physicochemical properties of film matrices based on chitosan, as well as the possibility of optimizing these properties by adding chitin nanofibrils. It is shown that with the introduction of chitin nanofibrils as a filler, the mechanical stability [...] Read more.
This paper discusses the mechanical and physicochemical properties of film matrices based on chitosan, as well as the possibility of optimizing these properties by adding chitin nanofibrils. It is shown that with the introduction of chitin nanofibrils as a filler, the mechanical stability of the composite materials increases. By varying the concentration of chitin nanofibrils, it is possible to obtain a spectrum of samples with different bioactive properties for the growth of human dermal fibroblasts. Film matrices based on the nanocomposite of chitosan and 5 wt % chitin nanofibrils have an optimal balance of mechanical and physicochemical properties and bioactivity in relation to the culture of human dermal fibroblasts. Full article
(This article belongs to the Special Issue Chitosan-based Materials)
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Open AccessArticle
Synthesis, Characterization, and Crystal Structures of Imides Condensed with p-Phenylamino(Phenyl) Amine and Fluorescence Property
Materials 2019, 12(11), 1873; https://doi.org/10.3390/ma12111873 - 10 Jun 2019
Viewed by 449
Abstract
A series of aromatic diimide and monoimide compounds condensed with p-phenylamino(phenyl)amine were synthesized and confirmed by Proton Nuclear Magnetic Resonance (1H NMR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Elemental Analysis (EA), and High [...] Read more.
A series of aromatic diimide and monoimide compounds condensed with p-phenylamino(phenyl)amine were synthesized and confirmed by Proton Nuclear Magnetic Resonance (1H NMR), Carbon-13 Nuclear Magnetic Resonance (13C NMR), Fourier Transform Infrared Spectroscopy (FT-IR), Elemental Analysis (EA), and High Resolution Mass Spectroscopy (HRMS). Meanwhile, single crystal X-ray diffraction showed the existence of intermolecular N···O hydrogen bonds, which affected the thermal stabilities of corresponding compounds by the support of Thermalgravimetric Analysis (TGA) curves. The steady-state UV-vis absorption peaks of synthetic compounds 16 appeared in the range of 220–380 nm. Fluorescence emission spectra showed peaks in the range of 290–420 nm. Meanwhile, deep-blue or violet-blue emissions for 2, 4, and 5 in THF under excitations of 254 nm and 365 nm, respectively, were observed at room temperature in air. Furthermore, Differential pulse voltammetry (DPV) and cyclic voltammogram CV were conducted within −1.5–+1.5 V to show quasi-reversible behavior for conjugated compounds and irreversible behavior for less conjugated ones. Full article
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Open AccessArticle
Structural Evolution in Isothermal Crystallization Process of Poly(L-lactic acid) Enhanced by Silk Fibroin Nano-Disc
Materials 2019, 12(11), 1872; https://doi.org/10.3390/ma12111872 - 10 Jun 2019
Cited by 1 | Viewed by 541
Abstract
The nucleating effect of silk fibroin nano-disc (SFN) on the crystallization behavior of poly(L-lactic acid) (PLLA) was investigated by simultaneous synchrotron small- and wide-angle X-ray scattering measurements. For the isothermal crystallization at 110 °C from the melt, the induction period of the PLLA [...] Read more.
The nucleating effect of silk fibroin nano-disc (SFN) on the crystallization behavior of poly(L-lactic acid) (PLLA) was investigated by simultaneous synchrotron small- and wide-angle X-ray scattering measurements. For the isothermal crystallization at 110 °C from the melt, the induction period of the PLLA specimens containing 1% SFN was reduced compared to that of the neat specimens, indicating the acceleration of the nucleation of PLLA. The final degree of crystallinity was also increased, and the crystallization half-time was decreased, which indicates that the overall crystallization process was accelerated. Furthermore, the final value of the crystallite size (the lateral size of the crystalline lamella) was slightly lower for the specimens containing 1% SFN than that for the PLLA neat specimen, although the crystallites started growing much earlier. However, it was found that there was no effect of SFN on the growth rate of the crystallite size. The lamellar thickening process was also accelerated with a clear overshooting phenomenon with the inclusion of 1% SFN. As for the polymorphism, the α’ phase is dominant with about 96%, but a small amount of the α phase (4%) is found to exist. It was found that the SFN can also accelerate the formation of the minor α phase as well as the major α’ phase. Full article
(This article belongs to the Special Issue Biobased Polymers)
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Open AccessArticle
Molybdenum Dopped Copper Ferrites as Active Catalysts for Alcohols Oxidative Coupling
Materials 2019, 12(11), 1871; https://doi.org/10.3390/ma12111871 - 10 Jun 2019
Viewed by 417
Abstract
Copper ferrites dopped with molybdenum were studied in an oxidative coupling reaction between methanol and ethanol in the gas phase. The catalysts have been characterized by X-ray diffraction, where the presence of ferrite, magnetite, and tenorite phases was observed; scanning electron microscopy; UV-Vis [...] Read more.
Copper ferrites dopped with molybdenum were studied in an oxidative coupling reaction between methanol and ethanol in the gas phase. The catalysts have been characterized by X-ray diffraction, where the presence of ferrite, magnetite, and tenorite phases was observed; scanning electron microscopy; UV-Vis spectroscopy; and Fourier-transform infrared spectroscopy, which highlighted the presence of octahedral coordination of isolated molybdena species. The catalyst with the highest activity in this reaction and with the highest selectivity to hydroxyacetone is the one that presents Lewis sites with weak acidity. The methyl and ethyl acetate selectivities are directly proportional to the Cu/Fe ratio. It has been observed that the presence of reduced copper sites is responsible for the selectivity in esters, while the presence of reduced iron and molybdenum sites is responsible for the acetol production. Full article
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Open AccessArticle
Mechanical and Surface-Chemical Properties of Polymer Derived Ceramic Replica Foams
Materials 2019, 12(11), 1870; https://doi.org/10.3390/ma12111870 - 10 Jun 2019
Viewed by 451
Abstract
Polymer derived ceramic foams were prepared with the replica method using filler free and filler loaded polysiloxane containing slurries for the impregnation of open celled polyurethane foams. A significant change in mechanical strength, porosity and surface energy, i.e., wettability after thermal treatment between [...] Read more.
Polymer derived ceramic foams were prepared with the replica method using filler free and filler loaded polysiloxane containing slurries for the impregnation of open celled polyurethane foams. A significant change in mechanical strength, porosity and surface energy, i.e., wettability after thermal treatment between 130 °C (crosslinking) and 1000 °C (pyrolysis) in argon atmosphere was observed. While low-temperature pyrolyzed foams are elastic and hydrophobic, foams pyrolyzed at high temperatures are brittle and hydrophilic, and they possess higher compression strength. Changes of these properties were correlated with the polymer-to-ceramic transformation. Full article
(This article belongs to the Special Issue Advances in Functional Cellular Structures and Composites)
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Open AccessArticle
Surface Characterization and Corrosion Behavior of 90/10 Copper-Nickel Alloy in Marine Environment
Materials 2019, 12(11), 1869; https://doi.org/10.3390/ma12111869 - 10 Jun 2019
Cited by 1 | Viewed by 446
Abstract
Surface characterization and corrosion behavior of 90/10 copper-nickel alloy in seawater from Xiamen bay at 30 °C for 56 days were investigated in this study. The results indicated that the corrosion product layer was mainly a mixture of CuO, Cu2O, and [...] Read more.
Surface characterization and corrosion behavior of 90/10 copper-nickel alloy in seawater from Xiamen bay at 30 °C for 56 days were investigated in this study. The results indicated that the corrosion product layer was mainly a mixture of CuO, Cu2O, and Cu(OH)2, with a transition to CuCl, CuCl2, and Cu2(OH)3Cl during the corrosion process. However, as corrosion proceeds, the resistance of the product film was reduced due to its heterogeneous and fairly porous structures, which led to local corrosion of the alloy. The corrosion potentials (Ecorr) increase while corrosion current densities (Icorr) decrease with time because of the formation of protective oxide film. Full article
(This article belongs to the Section Structure Analysis and Characterization)
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Open AccessArticle
Microstructure and Mechanical Properties of Spark Plasma Sintered Si3N4/WC Ceramic Tools
Materials 2019, 12(11), 1868; https://doi.org/10.3390/ma12111868 - 10 Jun 2019
Cited by 1 | Viewed by 514
Abstract
Silicon nitride (Si3N4) based ceramic tools exhibit good machinability in cutting materials such as gray cast iron, ductile iron, malleable cast iron, and superalloys due to excellent high-temperature mechanical properties. In this paper, high-performance Si3N4-based [...] Read more.
Silicon nitride (Si3N4) based ceramic tools exhibit good machinability in cutting materials such as gray cast iron, ductile iron, malleable cast iron, and superalloys due to excellent high-temperature mechanical properties. In this paper, high-performance Si3N4-based ceramic tools containing tungsten carbide (WC) and cobalt (Co) were studied. Effects of the WC content and Co content on mechanical properties and a microstructure of Si3N4-based ceramic materials were analyzed. Results showed that Si3N4-based ceramic material containing 10 wt % WC and 1 wt % Co had the best comprehensive mechanical properties at a sintering temperature of 1650 °C and holding time of 6 min, achieving Vickers hardness, fracture toughness, and room temperature bending strength of 16.96 GPa, 7.26 MPa·m1/2, and 1132 MPa, respectively. The microstructure of Si3N4-based ceramic tool material is uniform without obvious abnormal growth. The Si3N4-based ceramic tool was mainly composed of α-Si3N4, β-Si3N4, and WC phases. Full article
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Open AccessArticle
Fabrication and Application of Carboxymethyl Cellulose-Carbon Nanotube Aerogels
Materials 2019, 12(11), 1867; https://doi.org/10.3390/ma12111867 - 09 Jun 2019
Viewed by 583
Abstract
In this study, composite aerogels with excellent mechanical properties were prepared by using carboxymethyl cellulose (CMC) as raw materials, with carboxylic carbon nanotubes (CNTs) as reinforcement. By controlling the mass fraction of CNTs, composite aerogels with different CNTs were prepared, and the surface [...] Read more.
In this study, composite aerogels with excellent mechanical properties were prepared by using carboxymethyl cellulose (CMC) as raw materials, with carboxylic carbon nanotubes (CNTs) as reinforcement. By controlling the mass fraction of CNTs, composite aerogels with different CNTs were prepared, and the surface morphology, specific surface area, compressive modulus, density and adsorption capacities towards different oils were studied. Compared to the pure CMC aerogel, the specific surface areas of CMC/CNTs were decreased because of the agglomeration of CNTs. However, the densities of composite aerogels were lower than pure CMC aerogel. This is because the CNTs were first dispersed in water and then added to CMC solution. The results indicated that it was easy for the low CMC initial concentration to be converted to low density aerogel. The compressive modulus was increased from 0.3 MPa of pure CMC aerogel to 0.5 MPa of 5 wt % CMC/CNTs aerogel. Meanwhile, the prepared aerogels showed promising properties as the adsorption materials. Because of the high viscosity, liquid possesses strong adhesion to the pore wall, the adsorption capacity of the CMC aerogel to the liquid increases as the viscosity of the liquid increases. Full article
(This article belongs to the Section Porous Materials)
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Open AccessArticle
Comparative Analysis of the Chemical Composition and Microstructure Conformation Between Different Dental Implant Bone Drills
Materials 2019, 12(11), 1866; https://doi.org/10.3390/ma12111866 - 09 Jun 2019
Viewed by 545
Abstract
Background: Hardness is considered an important parameter for evaluating the clinical performance of dental implant bone drills. It is connected to the chemical composition, microstructure conformation and manufacture of the surgical drills. Methods: Microstructure of five dental implant drills using scanning electronic microscopy [...] Read more.
Background: Hardness is considered an important parameter for evaluating the clinical performance of dental implant bone drills. It is connected to the chemical composition, microstructure conformation and manufacture of the surgical drills. Methods: Microstructure of five dental implant drills using scanning electronic microscopy (SEM) integrated with energy dispersive X-ray spectrometry. Vickers microhardness was measured using a CV 2000 microhardness tester with an indentation force of 500 g. Results: Composition of the implant drills was typical of martensitic stainless steel (MSS). The drills contained 13%–17% of Cr; Mo, Si and Mn were present as minor ligands. The examined bone drills showed different external surface conformation and hardness in relation to the different industrial production processes. A rougher external surface and a higher hardness value are characteristics of the surgical bone drills produced by hot forming; the implant drills produced by machining showed mailing lines on their external surface and a lower hardness. Conclusions: Different compositions and treatments were used by the manufacturers to improve the hardness of the external layer of the dental implant drills making them prone to a diverse heat generation during the implant site preparation. Full article
(This article belongs to the Special Issue Advanced Materials for Oral and Dentofacial Surgery)
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Open AccessArticle
Using the Steady-State Chloride Migration Test to Evaluate the Self-Healing Capacity of Cracked Mortars Containing Crystalline, Expansive, and Swelling Admixtures
Materials 2019, 12(11), 1865; https://doi.org/10.3390/ma12111865 - 09 Jun 2019
Cited by 2 | Viewed by 594
Abstract
Interest in self-healing-crack technologies for cement-based materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. Therefore, this study proposes a test method to evaluate [...] Read more.
Interest in self-healing-crack technologies for cement-based materials has been growing, but research into such materials remains in the early stage of development and standardized methods for evaluating healing capacity have not yet been established. Therefore, this study proposes a test method to evaluate the self-healing capacity of cement-based materials in terms of their resistance to chloride penetration. For this purpose, the steady-state chloride migration test has been used to measure the diffusion coefficients of cracked mortar specimens containing crystalline, expansive, and swelling admixtures. The results of the present study show that the time to reach a quasi-steady-state decreased and the diffusion coefficients increased as the potential increased because of the potential drop inside the migration cell and self-healing that occurred during the test. Therefore, use of a high potential is recommended to minimize the test duration, as long as the temperature does not rise too much during the test. Using this test method, the self-healing capacity of the new self-healing technologies can be evaluated, and an index of self-healing capacity is proposed based on the rate of charged chloride ions passing through a crack. Full article
(This article belongs to the Special Issue Self-Healing and Smart Cementitious Construction Materials)
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Open AccessArticle
Preparation of Carbon Aerogel Electrode for Electrosorption of Copper Ions in Aqueous Solution
Materials 2019, 12(11), 1864; https://doi.org/10.3390/ma12111864 - 09 Jun 2019
Viewed by 559
Abstract
Carbon aerogel (CA) has a rich porous structure, in which micropores and mesopores provide a huge specific surface area to form electric double layers. This property can be applied to the application of capacitive deionization (CDI). The adsorption effect of CA electrode on [...] Read more.
Carbon aerogel (CA) has a rich porous structure, in which micropores and mesopores provide a huge specific surface area to form electric double layers. This property can be applied to the application of capacitive deionization (CDI). The adsorption effect of CA electrode on Cu2+ in an aqueous solution was explored for solving heavy metal water pollution. The CAs were synthesized by a sol-gel process using an atmospheric drying method. The structure of CAs was characterized by scanning in an electron microscope (SEM) and nitrogen adsorption/desorption techniques. The adsorption system was built using Cu2+ solution as the simulation of heavy metal pollution solution. The control variate method was used to investigate the effect of the anion species in copper solution, the molar ratio of resorcinol to catalyst (R/C) of CA, and the applied voltage and concentration of copper ion on the adsorption results. Full article
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Open AccessArticle
Mechanical Properties of Natural Rubber Filled with Foundry Waste Derived Fillers
Materials 2019, 12(11), 1863; https://doi.org/10.3390/ma12111863 - 09 Jun 2019
Viewed by 516
Abstract
The main aim of this study is to evaluate the possibility of applying foundry dust (FD) derived filler for the preparation of natural rubber (NR) based composites by characterizing the mechanical properties. The as-received FD was processed via a simple and low-cost procedure, [...] Read more.
The main aim of this study is to evaluate the possibility of applying foundry dust (FD) derived filler for the preparation of natural rubber (NR) based composites by characterizing the mechanical properties. The as-received FD was processed via a simple and low-cost procedure, including sieving, deironing and milling using a variety of industrial equipment. FD powders before and after silane coupling agent (Si 69) modification were used as fillers for NR. NR composites inserted with different content of modified and unmodified FD up to 50 phr were prepared via dry-mixing method. Then, comprehensive mechanical performances were performed on the corresponding vulcanizates. It was demonstrated that NR composite filled with 50 phr of modified FD exhibited optimized comprehensive mechanical performance. Tear strength and hardness is increased by 21.3% and 12.8% than pure NR, respectively. Tensile strength is reduced by 21% and elongation at break remained nearly unchanged. Additionally, the composite showed a large increment of 50.9% for its wet grip property, while exhibited an increment of only 11.9% for its rolling resistance in comparison with the composite containing 10 phr of FD. The findings of this study may provide a new application area for the large amounts of utilization of foundry waste with a high level of value being added. Full article
(This article belongs to the Section Advanced Composites)
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Open AccessArticle
Surface Characterization and Tribological Performance of Anodizing Micro-Textured Aluminum-Silicon Alloys
Materials 2019, 12(11), 1862; https://doi.org/10.3390/ma12111862 - 09 Jun 2019
Viewed by 501
Abstract
Eutectic aluminum-silicon alloys present high frictional coefficient and a high wear rate due to the low hardness under sliding friction conditions. In this paper, the eutectic aluminum-silicon alloy was textured firstly by micro-milling operations. Then, the micro-textured specimen was subjected to anodizing to [...] Read more.
Eutectic aluminum-silicon alloys present high frictional coefficient and a high wear rate due to the low hardness under sliding friction conditions. In this paper, the eutectic aluminum-silicon alloy was textured firstly by micro-milling operations. Then, the micro-textured specimen was subjected to anodizing to fabricate alumina films. The surface topography, surface roughness, and bearing area ratio of micro-textured and anodizing micro-textured specimens were measured and characterized. For the anodizing micro-textured specimens, the surface roughness and superficial hardness increase compared with those for micro-textured ones. Tribological tests indicate that anodizing micro-textured samples present lower friction coefficient of 0.37 than that of flat samples of 0.43 under dry sliding conditions. However, they exhibit higher friction coefficient at 0.16 than that of flat samples of 0.13 under oil-lubricated conditions. The difference between the friction coefficient of anodizing micro-textured and flat samples under dry and oil-lubricated conditions is ascribed to the influence mechanism of surface roughness, bearing area ratio curves, and its relative parameters on the tribological performance of testing samples. The dry sliding friction coefficient has a positive correlation with bearing area ratio curves, while they present negative correlation with bearing area ratio curves under oil-lubricated conditions. The synergy method treated with micro-milling and anodizing provides an effective approach to enhance the dry sliding friction property of eutectic aluminum-silicon alloys. Full article
(This article belongs to the collection Textures and Anisotropy in Advanced Materials)
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Open AccessArticle
Effect of the Content of Micro-Active Copper Tailing on the Strength and Pore Structure of Cementitious Materials
Materials 2019, 12(11), 1861; https://doi.org/10.3390/ma12111861 - 09 Jun 2019
Viewed by 552
Abstract
This study investigates the effect of micr-oaggregate filling with copper tailing on the pore structure of cement paste containing copper tailing (CPCT). The particle size of the CPCT and the pore structure of CPCT were analyzed by laser particle size analysis and mercury [...] Read more.
This study investigates the effect of micr-oaggregate filling with copper tailing on the pore structure of cement paste containing copper tailing (CPCT). The particle size of the CPCT and the pore structure of CPCT were analyzed by laser particle size analysis and mercury instruction porosimetry (MIP). Results showed that at the early stage of curing time, with increasing copper tailing content, the compressive strength of cement mortar with copper tailing (CMCT) was lower, and the porosity and pore diameter of CPCT were higher and greater; with the extension of curing age, when the content of copper tailing was less than 30%, the compressive strength of CMCT and the porosity of CPCT changed slightly with the increase of the content of copper tailing. However, the maximum hole diameter of CPCT decreased gradually (a curing age between 7 d and 365 d under standard conditions). Scanning electron microscopy analysis showed that at the early stage of cement hydration in the CPCT, the copper tailing did not fill the pores in CPCT well, while in the later stage of cement hydration, the microaggregates of copper tailing filled the pores well and closely combined with the surrounding hydration products. In the later stage of cement hydration, the microaggregate filling of copper tailing was primarily responsible for the strength increase of the CMCT. Full article
(This article belongs to the Special Issue Sustainability in Construction and Building Materials)
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Open AccessArticle
Probing Slip Differential Heat of Magnetorheological Fluids Subjected to Shear Mode Operation and Its Effect on the Structure
Materials 2019, 12(11), 1860; https://doi.org/10.3390/ma12111860 - 08 Jun 2019
Viewed by 507
Abstract
The paper probes slip differential heat of magnetorheological fluids (MRFs) subjected to shear mode operation and its effect on the structure. To begin, we present a novel model for measurement of slip differential heat to describe temperature rise of MRFs mainly caused by [...] Read more.
The paper probes slip differential heat of magnetorheological fluids (MRFs) subjected to shear mode operation and its effect on the structure. To begin, we present a novel model for measurement of slip differential heat to describe temperature rise of MRFs mainly caused by friction between magnetorheological particles. It includes two stages: (1) The micro-macro analysis of slip differential heat of MRFs including force, movement and heat between neighboring particles based on magnetic dipole and Hertzian contact theories, and (2) the further application to two basic disc-type and cylinder-type magnetorheological clutches combined with finite element simulations involving electromagnetic field and thermal analysis. The model takes into account the effect of each of the main influencing factors, such as the input current of excitation coil, the rotational speed difference of the clutches, the size and volume fraction of particles, the saturation magnetization of particles, and the structural size of the clutches, etc., on the slip differential heat of MRFs. Then the thermal structure analysis of MRFs comprising thermal deformation and equivalent thermal stress is carried out. Moreover, the effect of typical governing parameters on the slip power of MRFs and the influence of slip differential heat on the structure of MRFs are investigated individually. We show that such a model is effective in reflecting the temperature-slip time relation of MRFs. It is shown that the input current and the rotational speed difference have great effect on the slip power, and the slip differential heat has a certain influence on the micro-structure of MRFs. Full article
(This article belongs to the Special Issue Electrorheological and Magnetorheological Materials)
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Open AccessFeature PaperArticle
Antimicrobial Wound Dressings as Potential Materials for Skin Tissue Regeneration
Materials 2019, 12(11), 1859; https://doi.org/10.3390/ma12111859 - 08 Jun 2019
Viewed by 667
Abstract
The most important properties of performant wound dressings are biocompatibility, the ability to retain large amount of exudate and to avoid complications related with persistent infection which could lead to delayed wound healing. This research aimed to obtain and characterize a new type [...] Read more.
The most important properties of performant wound dressings are biocompatibility, the ability to retain large amount of exudate and to avoid complications related with persistent infection which could lead to delayed wound healing. This research aimed to obtain and characterize a new type of antimicrobial dressings, based on zinc oxide/sodium alginate/polyvinyl alcohol (PVA). Zinc oxide nanostructures, obtained with different morphology and grain size by hydrothermal and polyol methods, are used as antimicrobial agents along with sodium alginate, which is used to improve the biocompatibility of the dressing. The nanofiber dressing was obtained through the electrospinning method. Characterization techniques such as X-ray diffraction (XRD) and scanning electron microscopy (SEM) were performed to determine the structural and morphological properties of the obtained powders and composite fibers. Their antimicrobial activity was tested against Gram negative Escherichia coli (E. coli), Gram positive Staphylococcus aureus (S. aureus) bacteria and Candida albicans (C. albicans) yeast strains. The in vitro biocompatibility of the obtained composites was tested on human diploid cells. The obtained results suggest that the composite fibers based on zinc oxide and alginate are suitable for antimicrobial protection, are not toxic and may be useful for skin tissue regeneration if applied as a dressing. Full article
(This article belongs to the Special Issue Novel Materials for Antimicrobial Application)
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Open AccessArticle
Mesh-Based and Meshfree Reduced Order Phase-Field Models for Brittle Fracture: One Dimensional Problems
Materials 2019, 12(11), 1858; https://doi.org/10.3390/ma12111858 - 08 Jun 2019
Cited by 1 | Viewed by 614
Abstract
Modelling brittle fracture by a phase-field fracture formulation has now been widely accepted. However, the full-order phase-field fracture model implemented using finite elements results in a nonlinear coupled system for which simulations are very computationally demanding, particularly for parametrized problems when the randomness [...] Read more.
Modelling brittle fracture by a phase-field fracture formulation has now been widely accepted. However, the full-order phase-field fracture model implemented using finite elements results in a nonlinear coupled system for which simulations are very computationally demanding, particularly for parametrized problems when the randomness and uncertainty of material properties are considered. To tackle this issue, we present two reduced-order phase-field models for parametrized brittle fracture problems in this work. The first one is a mesh-based Proper Orthogonal Decomposition (POD) method. Both the Discrete Empirical Interpolation Method (DEIM) and the Matrix Discrete Empirical Interpolation Method ((M)DEIM) are adopted to approximate the nonlinear vectors and matrices. The second one is a meshfree Krigingmodel. For one-dimensional problems, served as proof-of-concept demonstrations, in which Young’s modulus and the fracture energy vary, the POD-based model can speed up the online computations eight-times, and for the Kriging model, the speed-up factor is 1100, albeit with a slightly lower accuracy. Another merit of the Kriging’s model is its non-intrusive nature, as one does not need to modify the full-order model code. Full article
(This article belongs to the Special Issue Randomness and Uncertainty)
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Open AccessFeature PaperArticle
Insight on the Interplay between Synthesis Conditions and Thermoelectric Properties of α-MgAgSb
Materials 2019, 12(11), 1857; https://doi.org/10.3390/ma12111857 - 07 Jun 2019
Viewed by 581
Abstract
α-MgAgSb is a very promising thermoelectric material with excellent thermoelectric properties between room temperature and 300 °C, a range where few other thermoelectric materials show good performance. Previous reports rely on a two-step ball-milling process and/or time-consuming annealing. Aiming for a faster and [...] Read more.
α-MgAgSb is a very promising thermoelectric material with excellent thermoelectric properties between room temperature and 300 °C, a range where few other thermoelectric materials show good performance. Previous reports rely on a two-step ball-milling process and/or time-consuming annealing. Aiming for a faster and scalable fabrication route, herein, we investigated other potential synthesis routes and their impact on the thermoelectric properties of α-MgAgSb. We started from a gas-atomized MgAg precursor and employed ball-milling only in the final mixing step. Direct comparison of high energy ball-milling and planetary ball-milling revealed that high energy ball milling already induced formation of MgAgSb, while planetary ball milling did not. This had a strong impact on the microstructure and secondary phase fraction, resulting in superior performance of the high energy ball milling route with an attractive average thermoelectric figure of merit of z T avg = 0.9. We also show that the formation of undesired secondary phases cannot be avoided by a modification of the sintering temperature after planetary ball milling, and discuss the influence of commonly observed secondary phases on the carrier mobility and on the thermoelectric properties of α-MgAgSb. Full article
(This article belongs to the Special Issue Novel Thermoelectric Materials and Their Applications)
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Open AccessArticle
Cross-Influence between Intra-Laminar Damages and Fibre Bridging at the Skin–Stringer Interface in Stiffened Composite Panels under Compression
Materials 2019, 12(11), 1856; https://doi.org/10.3390/ma12111856 - 07 Jun 2019
Viewed by 473
Abstract
In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this [...] Read more.
In this paper, the skin–stringer separation phenomenon that occurs in stiffened composite panels under compression is numerically studied. Since the mode I fracture toughness and, consequently, the skin–stringer separation can be influenced by the fibre bridging phenomenon at the skin–stringer interface, in this study, comparisons among three different material systems with different fibre bridging sensitivities have been carried out. Indeed, a reference material system has been compared, in terms of toughness performance, against two materials with different degrees of sensitivity to fibre bridging. A robust numerical procedure for the delamination assessment has been used to mimic the skin–stringer separation. When analysing the global compressive behaviour of the stiffened panel, intra-laminar damages have been considered in conjunction with skin–stringer debonding to evaluate the effect of the fibre and matrix breakage on the separation between the skin and the stringer for the three analysed material systems. The latter are characterised by different toughness characteristics and fibre bridging sensitivities, resulting in a different material toughness. Full article
(This article belongs to the Special Issue Carbon Fibre Reinforced Plastics)
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Open AccessArticle
Experimental Study on the Vegetation Growing Recycled Concrete and Synergistic Effect with Plant Roots
Materials 2019, 12(11), 1855; https://doi.org/10.3390/ma12111855 - 07 Jun 2019
Viewed by 533
Abstract
Vegetation growing recycled concrete (VGRC) is a relatively new building material that has both biocompatibility and engineering function. The basic performance of VGRC was investigated by experimental analysis, and the hydration products and pore structure of different VGRC mix proportions were studied by [...] Read more.
Vegetation growing recycled concrete (VGRC) is a relatively new building material that has both biocompatibility and engineering function. The basic performance of VGRC was investigated by experimental analysis, and the hydration products and pore structure of different VGRC mix proportions were studied by X-ray diffraction (XRD), scanning electron microscope (SEM), and industrial computed tomography (CT). The results show that ultrafine slag can reduce Ca(OH)2 content in cementing material and has a filling effect on micropores. VGRC has the best performance; the internal pore distribution is uniform when porosity is 20–25%, and the ultrafine slag content is 40%. The compressive strength of VGRC is greatly damaged by the quick-freezing method, while the degree of damage from natural freeze–thaw cycles is relatively small. Soaking in acid solution can effectively reduce the internal pore alkalinity of VGRC. Most plants can grow normally in vegetation concrete, and plant roots can penetrate 6-cm thick concrete blocks after being planted for 60 days. The compressive strength of VGRC decreased after turf planting of 30 days and then increased slowly. The permeability coefficient of VGRC increases with the increase in porosity and aggregate size and decreases after planting and covering. The frost resistance of VGRC is enhanced, and the influence of aggregate size and porosity is small after turf planting. Full article
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Open AccessArticle
Fabrication and Tribological Properties of Copper Matrix Solid Self-Lubricant Composites Reinforced with Ni/NbSe2 Composites
Materials 2019, 12(11), 1854; https://doi.org/10.3390/ma12111854 - 07 Jun 2019
Viewed by 518
Abstract
This paper presents a facile and effective method for preparing Ni/NbSe2 composites in order to improve the wettability of NbSe2 and copper matrix, which is helpful in enhancing the friction-reducing and anti-wear properties of copper-based composites. The powder metallurgy (P/M) technique [...] Read more.
This paper presents a facile and effective method for preparing Ni/NbSe2 composites in order to improve the wettability of NbSe2 and copper matrix, which is helpful in enhancing the friction-reducing and anti-wear properties of copper-based composites. The powder metallurgy (P/M) technique was used to fabricate copper-based composites with different weight fractions of Ni/NbSe2, and tribological properties of composites were evaluated by using a ball-on-disk friction-and-wear tester. Results indicated that tribological properties of copper-based composites were improved by the addition of Ni/NbSe2. In particular, copper-based composites containing 15 wt.% Ni/NbSe2 showed the lowest friction coefficient (0.16) and wear rate (4.1 × 10−5 mm3·N−1·m−1) among all composites. Full article
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Open AccessReview
Scalable Synthesis of Mesoporous TiO2 for Environmental Photocatalytic Applications
Materials 2019, 12(11), 1853; https://doi.org/10.3390/ma12111853 - 07 Jun 2019
Cited by 2 | Viewed by 933
Abstract
Increasing environmental concern, related to pollution and clean energy demand, have urged the development of new smart solutions profiting from nanotechnology, including the renowned nanomaterial-assisted photocatalytic degradation of pollutants. In this framework, increasing efforts are devoted to the development of TiO2-based [...] Read more.
Increasing environmental concern, related to pollution and clean energy demand, have urged the development of new smart solutions profiting from nanotechnology, including the renowned nanomaterial-assisted photocatalytic degradation of pollutants. In this framework, increasing efforts are devoted to the development of TiO2-based nanomaterials with improved photocatalytic activity. A plethora of synthesis routes to obtain high quality TiO2-based nanomaterials is currently available. Nonetheless, large-scale production and the application of nanosized TiO2 is still hampered by technological issues and the high cost related to the capability to obtain TiO2 nanoparticles with high reaction yield and adequate morphological and structural control. The present review aims at providing a selection of synthetic approaches suitable for large-scale production of mesoporous TiO2-based photocatalysts due to its unique features including high specific surface area, improved ultraviolet (UV) radiation absorption, high density of surface hydroxyl groups, and significant ability for further surface functionalization The overviewed synthetic strategies have been selected and classified according to the following criteria (i) high reaction yield, (ii) reliable synthesis scale-up and (iii) adequate control over morphological, structural and textural features. Potential environmental applications of such nanostructures including water remediation and air purification are also discussed. Full article
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Open AccessArticle
Effect of Turning Amount on Metallurgical Qualities and Mechanical Properties of GH4169 Superalloy
Materials 2019, 12(11), 1852; https://doi.org/10.3390/ma12111852 - 07 Jun 2019
Viewed by 443
Abstract
The determination of an appropriate amount of turning for superalloy ingot surfaces, in a scientific and reasonable manner, is vital to the improvement of the metallurgical quality and comprehensive performance of superalloy ingots. In the present study, scanning electron microscopy with energy-dispersive spectroscopy, [...] Read more.
The determination of an appropriate amount of turning for superalloy ingot surfaces, in a scientific and reasonable manner, is vital to the improvement of the metallurgical quality and comprehensive performance of superalloy ingots. In the present study, scanning electron microscopy with energy-dispersive spectroscopy, a high-temperature testing machine, a Brinell hardness tester and the Image-Pro Plus software were used to analyze and compare the types and amounts of inclusions, the average area of the (Al,Mg)O inclusions, and the mechanical properties of points at different distances from the edge of the GH4169 superalloy vacuum arc remelting (VAR) ingot edge. The effects of the amount of turning to which the superalloy is subjected, the metallurgical qualities, and the mechanical properties were systematically studied. The results showed that the five inclusion types did not change as the sampling locations moved away from the ingot edge, but the amount of inclusions and the average area of the (Al,Mg)O inclusions first decreased and then stabilized. Similarly, the tensile strength, elongation, section shrinkage, hardness, and fatigue life first increased and then stabilized. Finally, this experiment tentatively determined that an appropriate amount of turning for a GH4169 superalloy ingot is 36–48 mm. Full article
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