Materials

4901 KiB

Open AccessArticle

Study of the Corrosion Resistance of Austenitic Stainless Steels during Conversion of Waste to Biofuel

by Marina Cabrini, Sergio Lorenzi, Tommaso Pastore, Simone Pellegrini, Mauro Burattini and Roberta Miglio

Materials 2017, 10(3), 325; https://doi.org/10.3390/ma10030325 - 22 Mar 2017

Cited by 17 | Viewed by 4301

Abstract

The paper deals with the corrosion behavior of stainless steels as candidate materials for biofuel production plants by liquefaction process of the sorted organic fraction of municipal solid waste. Corrosion tests were carried out on AISI 316L and AISI 304L stainless steels at [...] Read more.

The paper deals with the corrosion behavior of stainless steels as candidate materials for biofuel production plants by liquefaction process of the sorted organic fraction of municipal solid waste. Corrosion tests were carried out on AISI 316L and AISI 304L stainless steels at 250 °C in a batch reactor during conversion of raw material to bio-oil (biofuel precursor), by exposing specimens either to water/oil phase or humid gas phase. General corrosion rate was measured by weight loss tests. The susceptibility to stress corrosion cracking was evaluated by means of U-bend specimens and slow stress rate tests at 10⁻⁶ or 10⁻⁵ s⁻¹ strain rate. After tests, scanning electron microscope analysis was carried out to detect cracks and localized attacks. The results are discussed in relation with exposure conditions. They show very low corrosion rates strictly dependent upon time and temperature. No stress corrosion cracking was observed on U-bend specimens, under constant loading. Small cracks confined in the necking cone of specimens prove that stress corrosion cracking only occurred during slow strain rate tests at stresses exceeding the yield strength. Full article

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4905 KiB

Open AccessArticle

Development of AlN and TiB₂ Composites with Nb₂O₅, Y₂O₃ and ZrO₂ as Sintering Aids

by José C. González, Miguel Á. Rodríguez, Ignacio A. Figueroa, María-Elena Villafuerte-Castrejón and Gerardo C. Díaz

Materials 2017, 10(3), 324; https://doi.org/10.3390/ma10030324 - 22 Mar 2017

Cited by 5 | Viewed by 4218

Abstract

The synthesis of AlN and TiB₂ by spark plasma sintering (SPS) and the effect of Nb₂O₅, Y₂O₃ and ZrO₂ additions on the mechanical properties and densification of the produced composites is reported and discussed. [...] Read more.

The synthesis of AlN and TiB₂ by spark plasma sintering (SPS) and the effect of Nb₂O₅, Y₂O₃ and ZrO₂ additions on the mechanical properties and densification of the produced composites is reported and discussed. After the SPS process, dense AlN and TiB₂ composites with Nb₂O₅, Y₂O₃ and ZrO₂ were successfully prepared. X-ray diffraction analysis showed that in the AlN composites, the addition of Nb₂O₅ gives rise to Nb₄N₃ during sintering. The compound Y₃Al₅O₁₂ (YAG) was observed as precipitate in the sample with Y₂O₃. X-ray diffraction analysis of the TiB₂ composites showed TiB₂ as a single phase in these materials. The maximum Vickers and toughness values were 14.19 ± 1.43 GPa and 27.52 ± 1.75 GPa for the AlN and TiB₂ composites, respectively. Full article

(This article belongs to the Section Advanced Composites)

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41645 KiB

Open AccessArticle

Integration of Electrodeposited Ni-Fe in MEMS with Low-Temperature Deposition and Etch Processes

by Giuseppe Schiavone, Jeremy Murray, Richard Perry, Andrew R. Mount, Marc P. Y. Desmulliez and Anthony J. Walton

Materials 2017, 10(3), 323; https://doi.org/10.3390/ma10030323 - 22 Mar 2017

Cited by 7 | Viewed by 6429

Abstract

This article presents a set of low-temperature deposition and etching processes for the integration of electrochemically deposited Ni-Fe alloys in complex magnetic microelectromechanical systems, as Ni-Fe is known to suffer from detrimental stress development when subjected to excessive thermal loads. A selective etch [...] Read more.

This article presents a set of low-temperature deposition and etching processes for the integration of electrochemically deposited Ni-Fe alloys in complex magnetic microelectromechanical systems, as Ni-Fe is known to suffer from detrimental stress development when subjected to excessive thermal loads. A selective etch process is reported which enables the copper seed layer used for electrodeposition to be removed while preserving the integrity of Ni-Fe. In addition, a low temperature deposition and surface micromachining process is presented in which silicon dioxide and silicon nitride are used, respectively, as sacrificial material and structural dielectric. The sacrificial layer can be patterned and removed by wet buffered oxide etch or vapour HF etching. The reported methods limit the thermal budget and minimise the stress development in Ni-Fe. This combination of techniques represents an advance towards the reliable integration of Ni-Fe components in complex surface micromachined magnetic MEMS. Full article

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

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1743 KiB

Open AccessArticle

Enhanced Unipolar Resistive Switching Characteristics of Hf_0.5Zr_0.5O₂Thin Films with High ON/OFF Ratio

by Zhipeng Wu and Jun Zhu

Materials 2017, 10(3), 322; https://doi.org/10.3390/ma10030322 - 22 Mar 2017

Cited by 10 | Viewed by 5751

Abstract

A metal–insulator–metal structure resistive switching device based on H_0.5Z_0.5O₂ (HZO) thin film deposited by pulse laser deposition (PLD) has been investigated for resistive random access memory (RRAM) applications. The devices demonstrated bistable and reproducible unipolar resistive switching (RS) [...] Read more.

A metal–insulator–metal structure resistive switching device based on H_0.5Z_0.5O₂ (HZO) thin film deposited by pulse laser deposition (PLD) has been investigated for resistive random access memory (RRAM) applications. The devices demonstrated bistable and reproducible unipolar resistive switching (RS) behaviors with an extremely high OFF/ON ratio over 5400. The retention property had no degradation at 6 × 10⁴ s. The current–voltage characteristics of the HZO samples showed a Schottky emission conduction in the high voltage region (V_reset < V < V_set), while at the low voltage region (V < V_reset), the ohmic contact and space charge limited conduction (SCLC) are suggested to be responsible for the low and high resistance states, respectively. Combined with the conductance mechanism, the RS behaviors are attributed to joule heating and redox reactions in the HZO thin film induced by the external electron injection. Full article

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25405 KiB

Open AccessArticle

3D Molding of Veneers by Mechanical and Pneumatic Methods

by Milan Gaff and Miroslav Gašparík

Materials 2017, 10(3), 321; https://doi.org/10.3390/ma10030321 - 22 Mar 2017

Cited by 1 | Viewed by 5025

Abstract

This paper deals with the influence of selected methods (mechanical and pneumatic) as well as various factors (wood species, moisture content, veneer shape, punch diameter, laminating foil thickness, holding method, plasticizing) on 3D molding of veneers. 3D molding was evaluated on the basis [...] Read more.

This paper deals with the influence of selected methods (mechanical and pneumatic) as well as various factors (wood species, moisture content, veneer shape, punch diameter, laminating foil thickness, holding method, plasticizing) on 3D molding of veneers. 3D molding was evaluated on the basis of maximum deflection of birch and beech veneers. Cracks and warping edges were also evaluated in selected groups of mechanical molding. Mechanical methods tested veneers with various treatments (steaming, water and ammonia plasticizing and lamination). The pneumatic method was based on veneer shaping using air pressure. The results indicate that birch veneers are more suitable for 3D molding. The differences between the mechanical and pneumatic methods were not considerable. The most suitable method for mechanical 3D molding was the veneer lamination by polyethylene foils with thicknesses of 80 and 125 μm, inasmuch as these achieved better results than veneer plasticized by steam. The occurrence of cracks was more frequent in beech veneers, whereas, edge warping occurred at similar rates for both wood species and depends rather on holding method during 3D molding. Use of the ammonia solution is more suitable and there occurs no marked increase in moisture as happens when soaking in water. Full article

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5548 KiB

Open AccessArticle

The Effect of Thickness of Resorbable Bacterial Cellulose Membrane on Guided Bone Regeneration

by You-Jin Lee, Sung-Jun An, Eun-Bin Bae, Hui-Jeong Gwon, Jong-Seok Park, Sung In Jeong, Young-Chan Jeon, So-Hyoun Lee, Youn-Mook Lim and Jung-Bo Huh

Materials 2017, 10(3), 320; https://doi.org/10.3390/ma10030320 - 21 Mar 2017

Cited by 33 | Viewed by 5100

Abstract

This study introduces the effect of the thickness of a bacterial cellulose membrane by comparing the bone regeneration effect on rat skulls when using a collagen membrane and different thicknesses of resorbable bacterial cellulose membranes for guided bone regeneration. Barrier membranes of 0.10 [...] Read more.

This study introduces the effect of the thickness of a bacterial cellulose membrane by comparing the bone regeneration effect on rat skulls when using a collagen membrane and different thicknesses of resorbable bacterial cellulose membranes for guided bone regeneration. Barrier membranes of 0.10 mm, 0.15 mm, and 0.20 mm in thickness were made using bacterial cellulose produced as microbial fermentation metabolites. Mechanical strength was investigated, and new bone formation was evaluated through animal experimental studies. Experimental animals were sacrificed after having 2 weeks and 8 weeks of recovery, and specimens were processed for histologic and histomorphometric analyses measuring the area of bone regeneration (%) using an image analysis program. In 2 weeks, bone-like materials and fibrous connective tissues were observed in histologic analysis. In 8 weeks, all experimental groups showed the arrangement of osteoblasts surrounding the supporting body on the margin and center of the bone defect region. However, the amount of new bone formation was significantly higher (p < 0.05) in bacterial cellulose membrane with 0.10 mm in thickness compared to the other experimental groups. Within the limitations of this study, a bacterial cellulose membrane with 0.10 mm thickness induced the most effective bone regeneration. Full article

(This article belongs to the Section Biomaterials)

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1569 KiB

Open AccessCommunication

High Performance Complementary Circuits Based on p-SnO and n-IGZO Thin-Film Transistors

by Jiawei Zhang, Jia Yang, Yunpeng Li, Joshua Wilson, Xiaochen Ma, Qian Xin and Aimin Song

Materials 2017, 10(3), 319; https://doi.org/10.3390/ma10030319 - 21 Mar 2017

Cited by 41 | Viewed by 7306

Abstract

Oxide semiconductors are regarded as promising materials for large-area and/or flexible electronics. In this work, a ring oscillator based on n-type indium-gallium-zinc-oxide (IGZO) and p-type tin monoxide (SnO) is presented. The IGZO thin-film transistor (TFT) shows a linear mobility of [...] Read more.

Oxide semiconductors are regarded as promising materials for large-area and/or flexible electronics. In this work, a ring oscillator based on n-type indium-gallium-zinc-oxide (IGZO) and p-type tin monoxide (SnO) is presented. The IGZO thin-film transistor (TFT) shows a linear mobility of 11.9 cm²/(V∙s) and a threshold voltage of 12.2 V. The SnO TFT exhibits a mobility of 0.51 cm²/(V∙s) and a threshold voltage of 20.1 V which is suitable for use with IGZO TFTs to form complementary circuits. At a supply voltage of 40 V, the complementary inverter shows a full output voltage swing and a gain of 24 with both TFTs having the same channel length/channel width ratio. The three-stage ring oscillator based on IGZO and SnO is able to operate at 2.63 kHz and the peak-to-peak oscillation amplitude reaches 36.1 V at a supply voltage of 40 V. The oxide-based complementary circuits, after further optimization of the operation voltage, may have wide applications in practical large-area flexible electronics. Full article

(This article belongs to the Special Issue Oxide Semiconductor Thin-Film Transistor)

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12250 KiB

Open AccessArticle

Hot Deformation and Processing Window Optimization of a 70MnSiCrMo Carbide-Free Bainitic Steel

by Ying Han, Yu Sun, Wei Zhang and Hua Chen

Materials 2017, 10(3), 318; https://doi.org/10.3390/ma10030318 - 21 Mar 2017

Cited by 12 | Viewed by 4042

Abstract

The hot deformation behavior of a high carbon carbide-free bainitic steel was studied through isothermal compression tests that were performed on a Gleeble-1500D thermal mechanical simulator at temperatures of 1223–1423 K and strain rates of 0.01–5 s⁻¹. The flow behavior, constitutive [...] Read more.

The hot deformation behavior of a high carbon carbide-free bainitic steel was studied through isothermal compression tests that were performed on a Gleeble-1500D thermal mechanical simulator at temperatures of 1223–1423 K and strain rates of 0.01–5 s⁻¹. The flow behavior, constitutive equations, dynamic recrystallization (DRX) characteristics, and processing map were respectively analyzed in detail. It is found that the flow stress increases with increasing the strain rate and decreases with increasing the temperature, and the single-peak DRX can be easily observed at high temperatures and/or low strain rates. The internal relationship between the flow stress and processing parameters was built by the constitutive equations embracing a parameter of Z/A, where the activation energy for hot deformation is 351.539 kJ/mol and the stress exponent is 4.233. In addition, the DRX evolution and the critical conditions for starting DRX were discussed. Then the model of the DRX volume fraction was developed with satisfied predictability. Finally, the processing maps at different strains were constructed according to the dynamic material model. The safety domains and flow instability regions were identified. The best processing parameters of this steel are within the temperature range of 1323–1423 K and strain rate range of 0.06–1 s⁻¹. Full article

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

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6692 KiB

Open AccessArticle

Towards Highly Performing and Stable PtNi Catalysts in Polymer Electrolyte Fuel Cells for Automotive Application

by Sabrina C. Zignani, Vincenzo Baglio, David Sebastián, Ada Saccà, Irene Gatto and Antonino S. Aricò

Materials 2017, 10(3), 317; https://doi.org/10.3390/ma10030317 - 21 Mar 2017

Cited by 24 | Viewed by 5434

Abstract

In order to help the introduction on the automotive market of polymer electrolyte fuel cells (PEFCs), it is mandatory to develop highly performing and stable catalysts. The main objective of this work is to investigate PtNi/C catalysts in a PEFC under low relative [...] Read more.

In order to help the introduction on the automotive market of polymer electrolyte fuel cells (PEFCs), it is mandatory to develop highly performing and stable catalysts. The main objective of this work is to investigate PtNi/C catalysts in a PEFC under low relative humidity and pressure conditions, more representative of automotive applications. Carbon supported PtNi nanoparticles were prepared by reduction of metal precursors with formic acid and successive thermal and leaching treatments. The effect of the chemical composition, structure and surface characteristics of the synthesized samples on their electrochemical behavior was investigated. The catalyst characterized by a larger Pt content (Pt₃Ni₂/C) presented the highest catalytic activity (lower potential losses in the activation region) among the synthesized bimetallic PtNi catalysts and the commercial Pt/C, used as the reference material, after testing at high temperature (95 °C) and low humidification (50%) conditions for automotive applications, showing a cell potential (ohmic drop-free) of 0.82 V at 500 mA·cm⁻². In order to assess the electro-catalysts stability, accelerated degradation tests were carried out by cycling the cell potential between 0.6 V and 1.2 V. By comparing the electrochemical and physico-chemical parameters at the beginning of life (BoL) and end of life (EoL), it was demonstrated that the Pt₁Ni₁/C catalyst was the most stable among the catalyst series, with only a 2% loss of voltage at 200 mA·cm⁻² and 12.5% at 950 mA·cm⁻². However, further improvements are needed to produce durable catalysts. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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4587 KiB

Open AccessArticle

Negative Temperature Dependence of Recrystallized Grain Size: Formulation and Experimental Confirmation on Copper

by Mohamed Elmasry, Fan Liu, Yao Jiang, Ze Ning Mao, Ying Liu and Jing Tao Wang

Materials 2017, 10(3), 308; https://doi.org/10.3390/ma10030308 - 21 Mar 2017

Cited by 5 | Viewed by 4880

Abstract

The catalyzing effect on nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous nucleation. Analytical formulation of the effective nucleation site for recrystallization leads to a negative temperature [...] Read more.

The catalyzing effect on nucleation of recrystallization from existing grains resulting from previous lower temperature deformation is analyzed, analogous to the size effect of foreign nucleus in heterogeneous nucleation. Analytical formulation of the effective nucleation site for recrystallization leads to a negative temperature dependence of recrystallized grain size of metals. Non-isochronal annealing—where annealing time is set just enough for the completion of recrystallization at different temperatures—is conducted on pure copper after severe plastic deformation. More homogeneous and smaller grains are obtained at higher annealing temperature. The good fit between analytical and experimental results unveils the intrinsic feature of this negative temperature dependence of recrystallized grain size. Full article

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4959 KiB

Open AccessArticle

Experimental Study on the Fire Properties of Nitrocellulose with Different Structures

by Ruichao Wei, Yaping He, Jiahao Liu, Yu He, Wenzhong Mi, Richard Yuen and Jian Wang

Materials 2017, 10(3), 316; https://doi.org/10.3390/ma10030316 - 20 Mar 2017

Cited by 30 | Viewed by 5937

Abstract

In order to ensure the safety of inflammable and explosive chemical substance such as nitrocellulose (NC) mixtures in the process of handing, storage, and usage, it is necessary to obtain the fire properties of NC with different exterior structures. In present study, fire [...] Read more.

In order to ensure the safety of inflammable and explosive chemical substance such as nitrocellulose (NC) mixtures in the process of handing, storage, and usage, it is necessary to obtain the fire properties of NC with different exterior structures. In present study, fire properties of two commonly used nitrocelluloses with soft fiber structure and white chip structure were investigated by scanning electron microscope (SEM) and the ISO 5660 cone calorimeter. Experimental findings revealed that the most important fire properties such as ignition time, mass loss rate and ash content exhibited significant differences between the two structures of NC. Compared with the soft fiber NC, chip NC possesses a lower fire hazard, and its heat release rate intensity (HRRI) is mainly affected by the sample mass. In addition, oxygen consumption (OC) calorimetry method was compared with thermal chemistry (TC) method based on stoichiometry for HRRI calculation. HRRI results of NC with two structures obtained by these two methods showed a good consistency. Full article

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

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1078 KiB

Open AccessArticle

Microwave-Assisted Catalytic Synthesis of Bio-Based Copolymers from Waste Cooking Oil

by Mahrzadi Noureen Shahi, Muhammad Arshad and Aman Ullah

Materials 2017, 10(3), 315; https://doi.org/10.3390/ma10030315 - 20 Mar 2017

Cited by 2 | Viewed by 4440

Abstract

Solvent-free copolymerization of epoxides derived from fatty esters of waste cooking oil with phthalic anhydride using (salen)Cr^IIICl as catalyst and n-Bu₄NCl/DMAP (tetrabutylammonium chloride/4-(dimethylamino)pyridine) as co-catalysts was carried out for the first time under microwave irradiation, where reaction time was [...] Read more.

Solvent-free copolymerization of epoxides derived from fatty esters of waste cooking oil with phthalic anhydride using (salen)Cr^IIICl as catalyst and n-Bu₄NCl/DMAP (tetrabutylammonium chloride/4-(dimethylamino)pyridine) as co-catalysts was carried out for the first time under microwave irradiation, where reaction time was reduced from a number of hours to minutes. The polyesters were obtained with molecular weight (Mw = 3100–6750 g/mol) and dispersity values (D = 1.18–1.92) when (salen)Cr^IIICl/n-Bu₄NCl was used as catalysts. Moreover, in the case of DMAP as a co-catalyst, polyesters with improved molecular weight (Mw = 5500–6950 g/mol) and narrow dispersity values (D = 1.07–1.28) were obtained even at reduced concentrations of (salen)Cr^IIICl and DMAP. The obtained products were characterized and evaluated by attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR), proton nuclear magnetic resonance (¹H-NMR) spectroscopy, gel permeation chromatography (GPC), thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) Techniques. Full article

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3165 KiB

Open AccessArticle

VO₂ Thermochromic Films on Quartz Glass Substrate Grown by RF-Plasma-Assisted Oxide Molecular Beam Epitaxy

by Dong Zhang, Hong-Jun Sun, Min-Huan Wang, Li-Hua Miao, Hong-Zhu Liu, Yu-Zhi Zhang and Ji-Ming Bian

Materials 2017, 10(3), 314; https://doi.org/10.3390/ma10030314 - 19 Mar 2017

Cited by 27 | Viewed by 6743

Abstract

Vanadium dioxide (VO₂) thermochromic thin films with various thicknesses were grown on quartz glass substrates by radio frequency (RF)-plasma assisted oxide molecular beam epitaxy (O-MBE). The crystal structure, morphology and chemical stoichiometry were investigated systemically by X-ray diffraction (XRD), atomic force [...] Read more.

Vanadium dioxide (VO₂) thermochromic thin films with various thicknesses were grown on quartz glass substrates by radio frequency (RF)-plasma assisted oxide molecular beam epitaxy (O-MBE). The crystal structure, morphology and chemical stoichiometry were investigated systemically by X-ray diffraction (XRD), atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) analyses. An excellent reversible metal-to-insulator transition (MIT) characteristics accompanied by an abrupt change in both electrical resistivity and optical infrared (IR) transmittance was observed from the optimized sample. Remarkably, the transition temperature (T_MIT) deduced from the resistivity-temperature curve was reasonably consistent with that obtained from the temperature-dependent IR transmittance. Based on Raman measurement and XPS analyses, the observations were interpreted in terms of residual stresses and chemical stoichiometry. This achievement will be of great benefit for practical application of VO₂-based smart windows. Full article

(This article belongs to the Special Issue Metal-Insulator Transition)

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5142 KiB

Open AccessArticle

Two 8-Hydroxyquinolinate Based Supramolecular Coordination Compounds: Synthesis, Structures and Spectral Properties

by Chengfeng Zhu, Yunfei Wang, Qingqing Mao, Fang Li, Yougui Li and Changle Chen

Materials 2017, 10(3), 313; https://doi.org/10.3390/ma10030313 - 18 Mar 2017

Cited by 13 | Viewed by 5322

Abstract

Two new Cr(III) complexes based on 2-substituted 8-hydroxyquinoline ligands, namely [Cr(L₁)₃] (1), (HL₁=(E)-2-[2-(4-nitro-phenyl)-vinyl]-8-hydroxy-quinoline) and [Cr(L₂)₃] (2), (HL₂=(E)-2-[2-(4-chloro-phenyl)vinyl]-8-hydroxy-quinoline), were prepared by a facile hydrothermal method and characterized thoroughly [...] Read more.

Two new Cr(III) complexes based on 2-substituted 8-hydroxyquinoline ligands, namely [Cr(L₁)₃] (1), (HL₁=(E)-2-[2-(4-nitro-phenyl)-vinyl]-8-hydroxy-quinoline) and [Cr(L₂)₃] (2), (HL₂=(E)-2-[2-(4-chloro-phenyl)vinyl]-8-hydroxy-quinoline), were prepared by a facile hydrothermal method and characterized thoroughly by single crystal X-ray diffraction, powder X-ray diffraction, FTIR, TGA, ESI-MS, UV-Visible absorption spectra and fluorescence emission spectra. Single crystal X-ray diffraction analyses showed that the two compounds featured 3D supramolecular architectures constructed from noncovalent interactions, such as π···π stacking, C-H···π, C-H···O, C-Cl···π, C-H···Cl interactions. The thermogravimetric analysis and ESI-MS study of compounds 1 and 2 suggested that the Cr(III) complexes possessed good stability both in solid and solution. In addition, the ultraviolet and fluorescence response of the HL₁ and HL₂shown marked changes upon their complexation with Cr(III) ion, which indicated that the two 8-hydroxyquinolinate based ligand are promising heavy metal chelating agent for Cr³⁺. Full article

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4578 KiB

Open AccessArticle

New Developments in Cathodoluminescence Spectroscopy for the Study of Luminescent Materials

by Daniel den Engelsen, George R. Fern, Paul G. Harris, Terry G. Ireland and Jack Silver

Materials 2017, 10(3), 312; https://doi.org/10.3390/ma10030312 - 17 Mar 2017

Cited by 5 | Viewed by 6225

Abstract

Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band [...] Read more.

Herein, we describe three advanced techniques for cathodoluminescence (CL) spectroscopy that have recently been developed in our laboratories. The first is a new method to accurately determine the CL-efficiency of thin layers of phosphor powders. When a wide band phosphor with a band gap (E_g > 5 eV) is bombarded with electrons, charging of the phosphor particles will occur, which eventually leads to erroneous results in the determination of the luminous efficacy. To overcome this problem of charging, a comparison method has been developed, which enables accurate measurement of the current density of the electron beam. The study of CL from phosphor specimens in a scanning electron microscope (SEM) is the second subject to be treated. A detailed description of a measuring method to determine the overall decay time of single phosphor crystals in a SEM without beam blanking is presented. The third technique is based on the unique combination of microscopy and spectrometry in the transmission electron microscope (TEM) of Brunel University London (UK). This combination enables the recording of CL-spectra of nanometre-sized specimens and determining spatial variations in CL emission across individual particles by superimposing the scanning TEM and CL-images. Full article

(This article belongs to the Special Issue Techniques and Methods for Advanced Characterization of Luminescent Materials)

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4574 KiB

Open AccessArticle

Fabrication of Cellulose Nanofiber/AlOOH Aerogel for Flame Retardant and Thermal Insulation

by Bitao Fan, Shujun Chen, Qiufang Yao, Qingfeng Sun and Chunde Jin

Materials 2017, 10(3), 311; https://doi.org/10.3390/ma10030311 - 17 Mar 2017

Cited by 58 | Viewed by 8610

Abstract

Cellulose nanofiber/AlOOH aerogel for flame retardant and thermal insulation was successfully prepared through a hydrothermal method. Their flame retardant and thermal insulation properties were investigated. The morphology image of the cellulose nanofiber/AlOOH exhibited spherical AlOOH with an average diameter of 0.5 μm that [...] Read more.

Cellulose nanofiber/AlOOH aerogel for flame retardant and thermal insulation was successfully prepared through a hydrothermal method. Their flame retardant and thermal insulation properties were investigated. The morphology image of the cellulose nanofiber/AlOOH exhibited spherical AlOOH with an average diameter of 0.5 μm that was wrapped by cellulose nanofiber or adhered to them. Cellulose nanofiber/AlOOH composite aerogels exhibited excellent flame retardant and thermal insulation properties through the flammability test, which indicated that the as-prepared composite aerogels would have a promising future in the application of some important areas such as protection of lightweight construction materials. Full article

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2107 KiB

Open AccessArticle

In-Situ Studies of Structure Transformation and Al Coordination of KAl(MoO₄)₂ during Heating by High Temperature Raman and ²⁷Al NMR Spectroscopies

by Min Wang, Jinglin You, Alexander Sobol, Liming Lu, Jian Wang and Yingfang Xie

Materials 2017, 10(3), 310; https://doi.org/10.3390/ma10030310 - 17 Mar 2017

Cited by 7 | Viewed by 5881

Abstract

Recent interest in optimizing composition and synthesis conditions of functional crystals, and the further exploration of new possible candidates for tunable solid-state lasers, has led to significant research on compounds in this family M^IM^III(M^VIO₄)₂ [...] Read more.

Recent interest in optimizing composition and synthesis conditions of functional crystals, and the further exploration of new possible candidates for tunable solid-state lasers, has led to significant research on compounds in this family M^IM^III(M^VIO₄)₂ (M^I = alkali metal, M^III = Al, In, Sc, Fe, Bi, lanthanide; M^VI = Mo, W). The vibrational modes, structure transformation, and Al coordination of crystalline, glassy, and molten states of KAl(MoO₄)₂ have been investigated by in-situ high temperature Raman scattering and ²⁷Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy, together with first principles density functional simulation of room temperature Raman spectrum. The results showed that, under the present fast quenching conditions, Al is present predominantly in [AlO₆] octahedra in both KAl(MoO₄)₂ glass and melt, with the tetrahedrally coordinated Al being minor at approximately 2.7%. The effect of K⁺, from ordered arrangement in the crystal to random distribution in the melt, on the local chemical environment of Al, was also revealed. The distribution and quantitative analysis of different Al coordination subspecies are final discussed and found to be dependent on the thermal history of the glass samples. Full article

(This article belongs to the Section Advanced Materials Characterization)

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849 KiB

Open AccessArticle

ZT Optimization: An Application Focus

by Richard Tuley and Kevin Simpson

Materials 2017, 10(3), 309; https://doi.org/10.3390/ma10030309 - 17 Mar 2017

Cited by 9 | Viewed by 4543

Abstract

Significant research has been performed on the challenge of improving thermoelectric materials, with maximum peak figure of merit, ZT, the most common target. We use an approximate thermoelectric material model, matched to real materials, to demonstrate that when an application is known, average [...] Read more.

Significant research has been performed on the challenge of improving thermoelectric materials, with maximum peak figure of merit, ZT, the most common target. We use an approximate thermoelectric material model, matched to real materials, to demonstrate that when an application is known, average ZT is a significantly better optimization target. We quantify this difference with some examples, with one scenario showing that changing the doping to increase peak ZT by 19% can lead to a performance drop of 16%. The importance of average ZT means that the temperature at which the ZT peak occurs should be given similar weight to the value of the peak. An ideal material for an application operates across the maximum peak ZT, otherwise maximum performance occurs when the peak value is reduced in order to improve the peak position. Full article

(This article belongs to the Special Issue Advances in Thermoelectric Materials)

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11415 KiB

Open AccessArticle

Biodegradation Resistance and Bioactivity of Hydroxyapatite Enhanced Mg-Zn Composites via Selective Laser Melting

by Cijun Shuai, Yuanzhuo Zhou, Youwen Yang, Pei Feng, Long Liu, Chongxian He, Mingchun Zhao, Sheng Yang, Chengde Gao and Ping Wu

Materials 2017, 10(3), 307; https://doi.org/10.3390/ma10030307 - 17 Mar 2017

Cited by 45 | Viewed by 5779

Abstract

Mg-Zn alloys have attracted great attention as implant biomaterials due to their biodegradability and biomechanical compatibility. However, their clinical application was limited due to the too rapid degradation. In the study, hydroxyapatite (HA) was incorporated into Mg-Zn alloy via selective laser melting. Results [...] Read more.

Mg-Zn alloys have attracted great attention as implant biomaterials due to their biodegradability and biomechanical compatibility. However, their clinical application was limited due to the too rapid degradation. In the study, hydroxyapatite (HA) was incorporated into Mg-Zn alloy via selective laser melting. Results showed that the degradation rate slowed down due to the decrease of grain size and the formation of protective layer of bone-like apatite. Moreover, the grain size continually decreased with increasing HA content, which was attributed to the heterogeneous nucleation and increased number of nucleation particles in the process of solidification. At the same time, the amount of bone-like apatite increased because HA could provide favorable areas for apatite nucleation. Besides, HA also enhanced the hardness due to the fine grain strengthening and second phase strengthening. However, some pores occurred owing to the agglomerate of HA when its content was excessive, which decreased the biodegradation resistance. These results demonstrated that the Mg-Zn/HA composites were potential implant biomaterials. Full article

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Open AccessArticle

Hybrid Coatings Enriched with Tetraethoxysilane for Corrosion Mitigation of Hot-Dip Galvanized Steel in Chloride Contaminated Simulated Concrete Pore Solutions

by Rita B. Figueira, Emanuela Callone, Carlos J. R. Silva, Elsa V. Pereira and Sandra Dirè

Materials 2017, 10(3), 306; https://doi.org/10.3390/ma10030306 - 17 Mar 2017

Cited by 20 | Viewed by 4957

Abstract

Hybrid sol-gel coatings, named U(X):TEOS, based on ureasilicate matrices (U(X)) enriched with tetraethoxysilane (TEOS), were synthesized. The influence of TEOS addition was studied on both the structure of the hybrid sol-gel films as well as on the electrochemical properties. The effect of TEOS [...] Read more.

Hybrid sol-gel coatings, named U(X):TEOS, based on ureasilicate matrices (U(X)) enriched with tetraethoxysilane (TEOS), were synthesized. The influence of TEOS addition was studied on both the structure of the hybrid sol-gel films as well as on the electrochemical properties. The effect of TEOS on the structure of the hybrid sol-gel films was investigated by solid state Nuclear Magnetic Resonance. The dielectric properties of the different materials were investigated by electrochemical impedance spectroscopy. The corrosion behavior of the hybrid coatings on HDGS was studied in chloride-contaminated simulated concrete pore solutions (SCPS) by polarization resistance measurements. The roughness of the HDGS coated with hybrids was also characterized by atomic force microscopy. The structural characterization of the hybrid materials proved the effective reaction between Jeffamine^® and 3-isocyanate propyltriethoxysilane (ICPTES) and indicated that the addition of TEOS does not seem to affect the organic structure or to increase the degree of condensation of the hybrid materials. Despite the apparent lack of influence on the hybrids architecture, the polarization resistance measurements confirmed that TEOS addition improves the corrosion resistance of the hybrid coatings (U(X):TEOS) in chloride-contaminated SCPS when compared to samples prepared without any TEOS (U(X)). This behavior could be related to the decrease in roughness of the hybrid coatings (due TEOS addition) and to the different metal coating interaction resulting from the increase of the inorganic component in the hybrid matrix. Full article

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11940 KiB

Open AccessArticle

Process Parameter Optimization of Extrusion-Based 3D Metal Printing Utilizing PW–LDPE–SA Binder System

by Luquan Ren, Xueli Zhou, Zhengyi Song, Che Zhao, Qingping Liu, Jingze Xue and Xiujuan Li

Materials 2017, 10(3), 305; https://doi.org/10.3390/ma10030305 - 16 Mar 2017

Cited by 102 | Viewed by 10773

Abstract

Recently, with a broadening range of available materials and alteration of feeding processes, several extrusion-based 3D printing processes for metal materials have been developed. An emerging process is applicable for the fabrication of metal parts into electronics and composites. In this paper, some [...] Read more.

Recently, with a broadening range of available materials and alteration of feeding processes, several extrusion-based 3D printing processes for metal materials have been developed. An emerging process is applicable for the fabrication of metal parts into electronics and composites. In this paper, some critical parameters of extrusion-based 3D printing processes were optimized by a series of experiments with a melting extrusion printer. The raw materials were copper powder and a thermoplastic organic binder system and the system included paraffin wax, low density polyethylene, and stearic acid (PW–LDPE–SA). The homogeneity and rheological behaviour of the raw materials, the strength of the green samples, and the hardness of the sintered samples were investigated. Moreover, the printing and sintering parameters were optimized with an orthogonal design method. The influence factors in regard to the ultimate tensile strength of the green samples can be described as follows: infill degree > raster angle > layer thickness. As for the sintering process, the major factor on hardness is sintering temperature, followed by holding time and heating rate. The highest hardness of the sintered samples was very close to the average hardness of commercially pure copper material. Generally, the extrusion-based printing process for producing metal materials is a promising strategy because it has some advantages over traditional approaches for cost, efficiency, and simplicity. Full article

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2715 KiB

Open AccessArticle

Xylan-Modified-Based Hydrogels with Temperature/pH Dual Sensitivity and Controllable Drug Delivery Behavior

by Wei-Qing Kong, Cun-Dian Gao, Shu-Feng Hu, Jun-Li Ren, Li-Hong Zhao and Run-Cang Sun

Materials 2017, 10(3), 304; https://doi.org/10.3390/ma10030304 - 16 Mar 2017

Cited by 27 | Viewed by 5746

Abstract

Among the natural macromolecules potentially used as the scaffold material in hydrogels, xylan has aroused great interest in many fields because of its biocompatibility, low toxicity, and biodegradability. In this work, new pH and thermoresponsive hydrogels were prepared by the cross-linking polymerization of [...] Read more.

Among the natural macromolecules potentially used as the scaffold material in hydrogels, xylan has aroused great interest in many fields because of its biocompatibility, low toxicity, and biodegradability. In this work, new pH and thermoresponsive hydrogels were prepared by the cross-linking polymerization of maleic anhydride-modified xylan (MAHX) with N-isopropylacrylamide (NIPAm) and acrylic acid (AA) under UV irradiation to form MAHX-g-P(NIPAm-co-AA) hydrogels. The pore volume, the mechanical properties, and the release rate for drugs of hydrogels could be controlled by the degree of substitution of MAHX. These hydrogels were characterized by swelling ability, lower critical solution temperature (LCST), Fourier-transform infrared (FTIR), and SEM. Furthermore, the cumulative release rate was investigated for acetylsalicylic acid and theophylline, as well as the cytocompatibility MAHX-based hydrogels. Results showed that MAHX-based hydrogels exhibited excellent swelling–deswelling properties, uniform porous structure, and the temperature/pH dual sensitivity. In vitro, the cumulative release rate of acetylsalicylic acid for MAHX-based hydrogels was higher than that for theophylline, and in the gastrointestinal sustained drug release study, the acetylsalicylic acid release rate was extremely slow during the initial 3 h in the gastric fluid (24.26%), and then the cumulative release rate reached to 90.5% after sustained release for 5 h in simulated intestinal fluid. The cytotoxicity experiment demonstrated that MAHX-based hydrogels could promote cell proliferation and had satisfactory biocompatibility with NIH3T3 cells. These results indicated that MAHX-based hydrogels, as new drug carriers, had favorable behavior for intestinal-targeted drug delivery. Full article

(This article belongs to the Section Porous Materials)

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1706 KiB

Open AccessArticle

Novel PEFC Application for Deuterium Isotope Separation

by Hisayoshi Matsushima, Ryota Ogawa, Shota Shibuya and Mikito Ueda

Materials 2017, 10(3), 303; https://doi.org/10.3390/ma10030303 - 16 Mar 2017

Cited by 9 | Viewed by 5089

Abstract

The use of a polymer electrolyte fuel cell (PEFC) with a Nafion membrane for isotopic separation of deuterium (D) was investigated. Mass analysis at the cathode side indicated that D diffused through the membrane and participated in an isotope exchange reaction. The exchange [...] Read more.

The use of a polymer electrolyte fuel cell (PEFC) with a Nafion membrane for isotopic separation of deuterium (D) was investigated. Mass analysis at the cathode side indicated that D diffused through the membrane and participated in an isotope exchange reaction. The exchange of D with protium (H) in H₂O was facilitated by a Pt catalyst. The anodic data showed that the separation efficiency was dependent on the D concentration in the source gas, whereby the water produced during the operation of the PEFC was more enriched in D as the D concentration of the source gas was increased. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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4475 KiB

Open AccessArticle

The Synthesis of a Core-Shell Photocatalyst Material YF₃:Ho³⁺@TiO₂ and Investigation of Its Photocatalytic Properties

by Xuan Xu, Shiyu Zhou, Jun Long, Tianhu Wu and Zihong Fan

Materials 2017, 10(3), 302; https://doi.org/10.3390/ma10030302 - 16 Mar 2017

Cited by 14 | Viewed by 6360

Abstract

In this paper, YF₃:Ho³⁺@TiO₂ core-shell nanomaterials were prepared by hydrolysis of tetra-n-butyl titanate (TBOT) using polyvinylpyrrolidone K-30 (PVP) as the coupling agent. Characterization methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) [...] Read more.

In this paper, YF₃:Ho³⁺@TiO₂ core-shell nanomaterials were prepared by hydrolysis of tetra-n-butyl titanate (TBOT) using polyvinylpyrrolidone K-30 (PVP) as the coupling agent. Characterization methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive X-ray spectroscopy (EDS) under TEM, X-ray photoelectron spectroscopy (XPS), fluorescence spectrometry, ultraviolet-visible diffuse reflectance spectroscopy, and electron spin resonance (ESR) were used to characterize the properties and working mechanism of the prepared photocatalyst material. They indicated that the core phase YF₃ nanoparticles were successfully coated with a TiO₂ shell and the length of the composite was roughly 100 nm. The Ho³⁺ single-doped YF₃:Ho³⁺@TiO₂ displayed strong visible absorption peaks with wavelengths of 450, 537, and 644 nm, respectively. By selecting these three peaks as excitation wavelengths, we could observe 288 nm (⁵D₄→⁵I₈) ultraviolet emission, which confirmed that there was indeed an energy transfer from YF₃:Ho³⁺ to anatase TiO₂. In addition, this paper investigated the influences of different TBOT dosages on photocatalysis performance of the as-prepared photocatalyst material. Results showed that the YF₃:Ho³⁺@TiO₂ core-shell nanomaterial was an advanced visible-light-driven catalyst, which decomposed approximately 67% of rhodamine b (RhB) and 34.6% of phenol after 10 h of photocatalysis reaction. Compared with the blank experiment, the photocatalysis efficiency was significantly improved. Finally, the visible-light-responsive photocatalytic mechanism of YF₃:Ho³⁺@TiO₂ core-shell materials and the influencing factors of photocatalytic degradation were investigated to study the apparent kinetics, which provides a theoretical basis for improving the structural design and functions of this new type of catalytic material. Full article

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6244 KiB

Open AccessFeature PaperArticle

Improvement of Fracture Toughness in Epoxy Nanocomposites through Chemical Hybridization of Carbon Nanotubes and Alumina

by Muhammad Razlan Zakaria, Muhammad Helmi Abdul Kudus, Hazizan Md. Akil and Mohd Hafiz Zamri

Materials 2017, 10(3), 301; https://doi.org/10.3390/ma10030301 - 16 Mar 2017

Cited by 18 | Viewed by 5159

Abstract

The current study investigated the effect of adding a carbon nanotube–alumina (CNT–Al₂O₃) hybrid on the fracture toughness of epoxy nanocomposites. The CNT–Al₂O₃ hybrid was synthesised by growing CNTs on Al₂O₃ particles via the [...] Read more.

The current study investigated the effect of adding a carbon nanotube–alumina (CNT–Al₂O₃) hybrid on the fracture toughness of epoxy nanocomposites. The CNT–Al₂O₃ hybrid was synthesised by growing CNTs on Al₂O₃ particles via the chemical vapour deposition method. The CNTs were strongly attached onto the Al₂O₃ particles, which served to transport and disperse the CNTs homogenously, and to prevent agglomeration in the CNTs. The experimental results demonstrated that the CNT–Al₂O₃ hybrid-filled epoxy nanocomposites showed improvement in terms of the fracture toughness, as indicated by an increase of up to 26% in the critical stress intensity factor, K_1C, compared to neat epoxy. Full article

(This article belongs to the Special Issue The Failure Micromechanics and Toughening Mechanisms of Materials)

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707 KiB

Open AccessArticle

The Effect of Different Storage Media on Color Stability of Self-Adhesive Composite Resin Cements for up to One Year

by Anja Liebermann, Malgorzata Roos and Bogna Stawarczyk

Materials 2017, 10(3), 300; https://doi.org/10.3390/ma10030300 - 16 Mar 2017

Cited by 12 | Viewed by 4172

Abstract

The aim of this study was to analyze the long-term color stability of eight self-adhesive composite resin cements (SACRCs) after storage in diverse media for up to one year. 480 discs (diameter: 12 mm/thickness: 1.0 ± 0.05 mm) were fabricated (n = 60/SACRC): [...] Read more.

The aim of this study was to analyze the long-term color stability of eight self-adhesive composite resin cements (SACRCs) after storage in diverse media for up to one year. 480 discs (diameter: 12 mm/thickness: 1.0 ± 0.05 mm) were fabricated (n = 60/SACRC): (1) BeautyCem (BEA); (2) Bifix SE (BIF); (3) Clearfil SA Cement Automix (CLE); (4) RelyX Unicem 2 Automix (RXU); (5) SeT (SET); (6) SmartCem 2 (SMC); (7) SoloCem (SOC); and (8) SpeedCEM (SPC). After polishing, specimens were immersed in (a) red wine (RW); (b) curry-solution (CU); (c) cress-solution (CR); and (d) distilled water (DW) at 37 °C and measured after 7, 28, 90, 180, and 365 days for color differences (ΔE) and water absorption (WA). Non-aged specimens were used as baselines. After 365 days, all of the discs were polished and their ΔE was measured. Data were analyzed using Kolmogorov-Smirnov, partial-eta-squared/η_P², 3-/1-way ANOVA with Tukey-HSD post-hoc test (α = 0.05). Significant differences occurred between all SACRCs for WA (p ≤ 0.003), except in RXU and in SET and in ΔE (p ≤ 0.002), except in SET and SPC. The significantly highest WA presented in SOC; the lowest showed in BEA. Significant ΔE differences and a decrease after polishing between all storage media were found (p < 0.001) with highest values for RW, followed by CU, CR, and DW. The lowest ΔE was measured for CLE, followed by SOC, BIF, RXU, BEA, SPC, SET, and SMC (p < 0.001) and increased significantly during aging. The highest ΔE decrease presented in BEA. SACRCs showed an increase in WA/ΔE within total aging time. Discoloration could not be removed completely by polishing. SACRCs need to be carefully selected for restorations in the esthetical zone with visible restoration margins. Polishing can significantly reduce the marginal discoloration. Full article

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9602 KiB

Open AccessArticle

Surface Roughening Behavior of 6063 Aluminum Alloy during Bulging by Spun Tubes

by Yang Cai, Xiaosong Wang and Shijian Yuan

Materials 2017, 10(3), 299; https://doi.org/10.3390/ma10030299 - 16 Mar 2017

Cited by 8 | Viewed by 4803

Abstract

Severe surface roughening during the hydroforming of aluminum alloy parts can produce surface defects that severely restrict their application in the automobile and aerospace industry. To understand the relation between strain, grain size and surface roughness under biaxial stress conditions, hydro-bulging tests of [...] Read more.

Severe surface roughening during the hydroforming of aluminum alloy parts can produce surface defects that severely restrict their application in the automobile and aerospace industry. To understand the relation between strain, grain size and surface roughness under biaxial stress conditions, hydro-bulging tests of aluminum alloy tubes were carried out, and the tubes with different grain sizes were prepared by a spinning and annealing process. The surface roughness was measured by a laser scanning confocal microscope to evaluate the surface roughening macroscopical behavior, and the corresponding microstructures were observed using electron back-scattered diffraction (EBSD) to reveal the roughening microscopic behavior. The results obtained show that the surface roughness increased with both strain and grain size under biaxial stress. No surface defects were observed on the surface when the grain size was less than 105 μm if the strain was less than 18%, or when the grain size was between 130 and 175 μm if the strain was less than 15.88% and 7.15%, respectively. The surface roughening microscopic behavior was identified as an inhomogeneous grain size distribution, which became more pronounced with increasing grain size and resulted in greater local deformation. Concentrated grain orientation also results in severe inhomogeneous deformation during plastics deformation, and serious surface roughening. Full article

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4810 KiB

Open AccessFeature PaperArticle

Analysis of Historic Copper Patinas. Influence of Inclusions on Patina Uniformity

by Tingru Chang, Inger Odnevall Wallinder, Daniel De la Fuente, Belen Chico, Manuel Morcillo, Jean-Marie Welter and Christofer Leygraf

Materials 2017, 10(3), 298; https://doi.org/10.3390/ma10030298 - 16 Mar 2017

Cited by 17 | Viewed by 5449

Abstract

The morphology and elemental composition of cross sections of eight historic copper materials have been explored. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. All copper substrates contain inclusions [...] Read more.

The morphology and elemental composition of cross sections of eight historic copper materials have been explored. The materials were taken from copper roofs installed in different middle and northern European environments from the 16th to the 19th century. All copper substrates contain inclusions of varying size, number and composition, reflecting different copper ores and production methods. The largest inclusions have a size of up to 40 μm, with most inclusions in the size ranging between 2 and 10 μm. The most common element in the inclusions is O, followed by Pb, Sb and As. Minor elements include Ni, Sn and Fe. All historic patinas exhibit quite fragmentized bilayer structures, with a thin inner layer of cuprite (Cu₂O) and a thicker outer one consisting mainly of brochantite (Cu₄SO₄(OH)₆). The extent of patina fragmentation seems to depend on the size of the inclusions, rather than on their number and elemental composition. The larger inclusions are electrochemically nobler than the surrounding copper matrix. This creates micro-galvanic effects resulting both in a profound influence on the homogeneity and morphology of historic copper patinas and in a significantly increased ratio of the thicknesses of the brochantite and cuprite layers. The results suggest that copper patinas formed during different centuries exhibit variations in uniformity and corrosion protection ability. Full article

(This article belongs to the Special Issue Fundamental and Research Frontier of Atmospheric Corrosion)

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6410 KiB

Open AccessArticle

The Role of Geometrically Necessary Dislocations in Cantilever Beam Bending Experiments of Single Crystals

by Edgar Husser and Swantje Bargmann

Materials 2017, 10(3), 289; https://doi.org/10.3390/ma10030289 - 16 Mar 2017

Cited by 19 | Viewed by 8045

Abstract

The mechanical behavior of single crystalline, micro-sized copper is investigated in the context of cantilever beam bending experiments. Particular focus is on the role of geometrically necessary dislocations (GNDs) during bending-dominated load conditions and their impact on the characteristic bending size effect. Three [...] Read more.

The mechanical behavior of single crystalline, micro-sized copper is investigated in the context of cantilever beam bending experiments. Particular focus is on the role of geometrically necessary dislocations (GNDs) during bending-dominated load conditions and their impact on the characteristic bending size effect. Three different sample sizes are considered in this work with main variation in thickness. A gradient extended crystal plasticity model is presented and applied in a three-dimensional finite-element (FE) framework considering slip system-based edge and screw components of the dislocation density vector. The underlying mathematical model contains non-standard evolution equations for GNDs, crystal-specific interaction relations, and higher-order boundary conditions. Moreover, two element formulations are examined and compared with respect to size-independent as well as size-dependent bending behavior. The first formulation is based on a linear interpolation of the displacement and the GND density field together with a full integration scheme whereas the second is based on a mixed interpolation scheme. While the GND density fields are treated equivalently, the displacement field is interpolated quadratically in combination with a reduced integration scheme. Computational results indicate that GND storage in small cantilever beams strongly influences the evolution of statistically stored dislocations (SSDs) and, hence, the distribution of the total dislocation density. As a particular example, the mechanical bending behavior in the case of a physically motivated limitation of GND storage is studied. The resulting impact on the mechanical bending response as well as on the predicted size effect is analyzed. Obtained results are discussed and related to experimental findings from the literature. Full article

(This article belongs to the Special Issue Computational Multiscale Modeling and Simulation in Materials Science)

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3794 KiB

Open AccessArticle

Vibration Damping Analysis of Lightweight Structures in Machine Tools

by Francesco Aggogeri, Alberto Borboni, Angelo Merlo, Nicola Pellegrini and Raffaele Ricatto

Materials 2017, 10(3), 297; https://doi.org/10.3390/ma10030297 - 15 Mar 2017

Cited by 59 | Viewed by 6864

Abstract

The dynamic behaviour of a machine tool (MT) directly influences the machining performance. The adoption of lightweight structures may reduce the effects of undesired vibrations and increase the workpiece quality. This paper aims to present and compare a set of hybrid materials that [...] Read more.

The dynamic behaviour of a machine tool (MT) directly influences the machining performance. The adoption of lightweight structures may reduce the effects of undesired vibrations and increase the workpiece quality. This paper aims to present and compare a set of hybrid materials that may be excellent candidates to fabricate the MT moving parts. The selected materials have high dynamic characteristics and capacity to dampen mechanical vibrations. In this way, starting from the kinematic model of a milling machine, this study evaluates a number of prototypes made of Al foam sandwiches (AFS), Al corrugated sandwiches (ACS) and composite materials reinforced by carbon fibres (CFRP). These prototypes represented the Z-axis ram of a commercial milling machine. The static and dynamical properties have been analysed by using both finite element (FE) simulations and experimental tests. The obtained results show that the proposed structures may be a valid alternative to the conventional materials of MT moving parts, increasing machining performance. In particular, the AFS prototype highlighted a damping ratio that is 20 times greater than a conventional ram (e.g., steel). Its application is particularly suitable to minimize unwanted oscillations during high-speed finishing operations. The results also show that the CFRP structure guarantees high stiffness with a weight reduced by 48.5%, suggesting effective applications in roughing operations, saving MT energy consumption. The ACS structure has a good trade-off between stiffness and damping and may represent a further alternative, if correctly evaluated. Full article

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

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