Materials

1386 KiB

Open AccessArticle

Potential Soil Contamination in Areas Where Ferronickel Slag Is Used for Reclamation Work

by Seong Seung Kang, Kyungho Park and Daehyeon Kim

Materials 2014, 7(10), 7157-7172; https://doi.org/10.3390/ma7107157 - 23 Oct 2014

Cited by 30 | Viewed by 6028

This study aims to analyze contamination with the use of soil reclaimed with ferronickel slag (FNS). In order to investigate any contamination due to FNS disposal, soils were collected from three sites. The contamination analysis was done on these samples through a series [...] Read more.

This study aims to analyze contamination with the use of soil reclaimed with ferronickel slag (FNS). In order to investigate any contamination due to FNS disposal, soils were collected from three sites. The contamination analysis was done on these samples through a series of laboratory tests. Furthermore, laboratory tests simulating field conditions were performed in a soil chamber. In the lab test, three leaching agents, namely fresh water, acidic water and seawater, were used. The soil samples used were sand and silt with a relative density of 40% and a compaction ratio of 90%, respectively. The pH of the effluent discharged from the experimental soil chamber was also analyzed. After leaching, soil samples were subjected to analysis. The results showed that pH was higher in the silt than in the sand. The results of the laboratory tests exhibited that leaching of hazardous elements from FNS is limited, so that it can be used as a substitute for natural aggregate in the cement industry or construction applications. Full article

(This article belongs to the Special Issue Recycled Materials)

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1011 KiB

Open AccessArticle

Co-Precipitation of YAG Powders for Transparent Materials: Effect of the Synthesis Parameters on Processing and Microstructure

by Paola Palmero and Rebecca Traverso

Materials 2014, 7(10), 7145-7156; https://doi.org/10.3390/ma7107145 - 22 Oct 2014

Cited by 22 | Viewed by 7098

Abstract

The fabrication of transparent polycrystalline Y₃Al₅O₁₂ (YAG) is still a challenge, requiring the achievement of highly pure and fully dense, homogeneous materials. An important role is played by the powder characteristics: pure, fine and unagglomerated powders are essential [...] Read more.

The fabrication of transparent polycrystalline Y₃Al₅O₁₂ (YAG) is still a challenge, requiring the achievement of highly pure and fully dense, homogeneous materials. An important role is played by the powder characteristics: pure, fine and unagglomerated powders are essential for achieving full density and the required microstructural features. Keeping in mind these requirements, the aim of this work was to investigate the role of different synthesis parameters during co-precipitation, which is widely used to prepare YAG powders for transparent devices. The key role of the precipitant solution is here illustrated, by comparing the effect of aqueous ammonia (AA) versus ammonium hydrogen carbonate (AHC). This latter allowed the preparation of softly agglomerated powders, characterized by a very good sinterability. However, when AHC is used, attention should be paid to its concentration. By comparing the effect of two AHC precipitant solutions (at 0.5 M and 1.5 M, respectively), only the former one allowed the preparation of pure YAG powders, free from secondary phases. In this last condition, by using both chlorides and nitrates as YAG precursors, pressureless sintering at 1500–1600 °C/3 h gave rise to pure materials, highly dense and characterized by a fine and homogeneous microstructure. Full article

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990 KiB

Open AccessArticle

Application of Various NDT Methods for the Evaluation of Building Steel Structures for Reuse

by Masanori Fujita and Tomoya Masuda

Materials 2014, 7(10), 7130-7144; https://doi.org/10.3390/ma7107130 - 22 Oct 2014

Cited by 19 | Viewed by 10047

Abstract

The reuse system proposed by the authors is an overall business system for realizing a cyclic reuse flow through the processes of design, fabrication, construction, maintenance, demolition and storage. The reuse system is one of the methods to reduce the environmental burden in [...] Read more.

The reuse system proposed by the authors is an overall business system for realizing a cyclic reuse flow through the processes of design, fabrication, construction, maintenance, demolition and storage. The reuse system is one of the methods to reduce the environmental burden in the field of building steel structures. These buildings are assumed to be demolished within approximately 30 years or more for physical, architectural, economic and social reasons in Japan. In this paper, focusing on building steel structures used for plants, warehouses and offices without fire protection, the performance of steel structural members for reuse is evaluated by a non-destructive test. First, performance evaluation procedures for a non-destructive test, such as mechanical properties, chemical compositions, dimension and degradation, are shown. Tensile strengths are estimated using Vickers hardness measured by a portable ultrasonic hardness tester, and chemical compositions are measured by a portable optical emission spectrometer. The weldability of steel structural members is estimated by carbon equivalent and weld crack sensitivity composition using chemical compositions. Finally, the material grade of structural members of the building steel structure for reuse is estimated based on the proposed procedures. Full article

(This article belongs to the Special Issue Recycled Materials)

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942 KiB

Open AccessArticle

Influence of Sulfate-Reducing Bacteria on the Corrosion Residual Strength of an AZ91D Magnesium Alloy

by Xianyong Zhu, Yaohui Liu, Qiang Wang and Jiaan Liu

Materials 2014, 7(10), 7118-7129; https://doi.org/10.3390/ma7107118 - 21 Oct 2014

Cited by 15 | Viewed by 6739

Abstract

In this paper, the corrosion residual strength of the AZ91D magnesium alloy in the presence of sulfate-reducing bacteria is studied. In the experiments, the chemical composition of corrosion film was analyzed by a scanning electron microscope with energy dispersive X-ray spectroscopy. In addition, [...] Read more.

In this paper, the corrosion residual strength of the AZ91D magnesium alloy in the presence of sulfate-reducing bacteria is studied. In the experiments, the chemical composition of corrosion film was analyzed by a scanning electron microscope with energy dispersive X-ray spectroscopy. In addition, a series of instruments, such as scanning electronic microscope, pH-meter and an AG-10TA materials test machine, were applied to test and record the morphology of the corrosion product, fracture texture and mechanical properties of the AZ91D magnesium alloy. The experiments show that the sulfate-reducing bacteria (SRB) play an important role in the corrosion process of the AZ91D magnesium alloy. Pitting corrosion was enhanced by sulfate-reducing bacteria. Corrosion pits are important defects that could lead to a significant stress concentration in the tensile process. As a result, sulfate-reducing bacteria influence the corrosion residual strength of the AZ91D magnesium alloy by accelerating pitting corrosion. Full article

(This article belongs to the Special Issue Corrosion of Materials)

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1302 KiB

Open AccessArticle

Bulk TiB₂-Based Ceramic Composites with Improved Mechanical Property Using Fe–Ni–Ti–Al as a Sintering Aid

by Chao Yang, Hao Guo, Daguang Mo, Shengguan Qu, Xiaoqiang Li, Weiwen Zhang and Laichang Zhang

Materials 2014, 7(10), 7105-7117; https://doi.org/10.3390/ma7107105 - 21 Oct 2014

Cited by 16 | Viewed by 7058

Abstract

The densification behavior, microstructure and mechanical properties of bulk TiB₂-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB₂ and TiB₂–5 [...] Read more.

The densification behavior, microstructure and mechanical properties of bulk TiB₂-based ceramic composites, fabricated using the spark plasma sintering (SPS) technique with elements of (Fe–Ni–Ti–Al) sinter-aid were investigated. Comparing the change of shrinkage displacement of pure TiB₂ and TiB₂–5 wt% (Fe–Ni–Ti–Al), the addition of elements Fe–Ni–Ti–Al into TiB₂ can facilitate sintering of the TiB₂ ceramics. As the sintering temperature exceeds 1300 °C, the relative density does not significantly change. Alumina particles and austenite (Fe–Ni–Ti) metallic binder distributed homogeneously in the grain boundary of TiB₂ can inhibit the growth of the TiB₂ grains when the sintering temperature is below 1300 °C. The density and particle size of TiB₂ greatly influence the mechanical behavior of TiB₂–5 wt% (Fe–Ni–Ti–Al) composites. The specimen sintered at 1300 has the highest microhardness of 21.1 ± 0.1 GPa with an elastic modulus of 461.4 GPa. The content of secondary borides (M₂B, being M = Fe, Ni), which are more brittle than TiB₂ particles, can also influence the fracture toughness. The specimen sintered at 1500 °C has the highest fracture toughness of 6.16 ± 0.30 MPa·m^1/2 with the smallest M₂B phase. The results obtained provide insight into fabrication of ceramic composites with improved mechanical property. Full article

(This article belongs to the Section Advanced Composites)

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1156 KiB

Open AccessArticle

Effect of Spark Plasma Sintering on the Structure and Properties of Ti_1−xZr_xNiSn Half-Heusler Alloys

by Ruth A. Downie, Srinivas R. Popuri, Huanpo Ning, Mike J. Reece and Jan-Willem G. Bos

Materials 2014, 7(10), 7093-7104; https://doi.org/10.3390/ma7107093 - 20 Oct 2014

Cited by 23 | Viewed by 7056

Abstract

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This [...] Read more.

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti_0.5Zr_0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m⁻¹·K⁻¹ at 350 K and 3 W·m⁻¹·K⁻¹ at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti_0.5Zr_0.5NiSn composition. Full article

(This article belongs to the Special Issue New Energy Materials)

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2647 KiB

Open AccessArticle

Property Relationship in Organosilanes and Nanotubes Filled Polypropylene Hybrid Composites

by Alejandra J. Monsiváis-Barrón, Jaime Bonilla-Rios and Antonio Sánchez-Fernández

Materials 2014, 7(10), 7073-7092; https://doi.org/10.3390/ma7107073 - 20 Oct 2014

Cited by 2 | Viewed by 6635

Abstract

Polypropylene composites with different filler contents were prepared by creating a masterbatch containing 3 wt%. filler. A variety of silanol groups were used to synthetized three compounds in different media trough a sol-gel process with acetic acid, formic acid and ammonium hydroxide as [...] Read more.

Polypropylene composites with different filler contents were prepared by creating a masterbatch containing 3 wt%. filler. A variety of silanol groups were used to synthetized three compounds in different media trough a sol-gel process with acetic acid, formic acid and ammonium hydroxide as catalysts. Besides, four different nanotubular fillers were also used to analyze their behavior and compare it with the effect caused by the silanol groups. These tubular structures comprise: unmodified halloysite, carbon nanotubes and functionalized halloysite and carbon nanotubes. Morphological characterization in SEM and STEM/TEM showed dispersion in the polypropylene matrix. According to TGA and DSC measurements thermal behavior remain similar for all the composites. Mechanical test in tension demonstrate that modulus of the composites increases for all samples with a major impact for materials containing silanol groups synthetized in formic acid. Rheological measurements show a significantly increment in viscosity for samples containing unmodified and modified carbon nanotubes. No difference was found for samples containing silanol groups and halloysite when compared to neat polypropylene. Finally, the oxygen transmission rate increased for all samples showing high barrier properties only for samples containing natural and functionalized halloysite nanotubes. Full article

(This article belongs to the Special Issue Selected Papers from the 1st International e-Conference on Materials)

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1311 KiB

Open AccessArticle

Flux-Aided Synthesis of Lu₂O₃ and Lu₂O₃:Eu—Single Crystal Structure, Morphology Control and Radioluminescence Efficiency

by Justyna Zeler, Lucjan B. Jerzykiewicz and Eugeniusz Zych

Materials 2014, 7(10), 7059-7072; https://doi.org/10.3390/ma7107059 - 20 Oct 2014

Cited by 29 | Viewed by 6419

Abstract

Li₂SO₄ or (Li₂SO₄ + SiO₂)-mixture fluxes were used to prepare a Lu₂O₃:Eu powder phosphor as well as an undoped Lu₂O₃ utilizing commercial lutetia and europia as starting reagents. [...] Read more.

Li₂SO₄ or (Li₂SO₄ + SiO₂)-mixture fluxes were used to prepare a Lu₂O₃:Eu powder phosphor as well as an undoped Lu₂O₃ utilizing commercial lutetia and europia as starting reagents. SEM images showed that the fabricated powders were non-agglomerated and the particles sizes varied from single microns to tens of micrometers depending largely on the flux composition rather than the oxide(s)-to-flux ratio. In the presence of SiO₂ in the flux, certain grains grew up to 300–400 μm. The lack of agglomeration and the large sizes of crystallites allowed making single crystal structural measurements and analysis on an undoped Lu₂O₃ obtained by means of the flux technique. The cubic structure with a = 10.393(2) Å, and Ia space group at 298 K was determined. The most efficient radioluminescence of Lu₂O₃:Eu powders reached 95%–105% of the commercial Gd₂O₂S:Eu. Full article

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1094 KiB

Open AccessArticle

Effect of Isomorphous Substitution on the Thermal Decomposition Mechanism of Hydrotalcites

by Sergio Crosby, Doanh Tran, David Cocke, El-Shazly M. Duraia and Gary W. Beall

Materials 2014, 7(10), 7048-7058; https://doi.org/10.3390/ma7107048 - 17 Oct 2014

Cited by 7 | Viewed by 6530

Abstract

Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere [...] Read more.

Hydrotalcites have many important applications in catalysis, wastewater treatment, gene delivery and polymer stabilization, all depending on preparation history and treatment scenarios. In catalysis and polymer stabilization, thermal decomposition is of great importance. Hydrotalcites form easily with atmospheric carbon dioxide and often interfere with the study of other anion containing systems, particularly if formed at room temperature. The dehydroxylation and decomposition of carbonate occurs simultaneously, making it difficult to distinguish the dehydroxylation mechanisms directly. To date, the majority of work on understanding the decomposition mechanism has utilized hydrotalcite precipitated at room temperature. In this study, evolved gas analysis combined with thermal analysis has been used to show that CO₂ contamination is problematic in materials being formed at RT that are poorly crystalline. This has led to some dispute as to the nature of the dehydroxylation mechanism. In this paper, data for the thermal decomposition of the chloride form of hydrotalcite are reported. In addition, carbonate-free hydrotalcites have been synthesized with different charge densities and at different growth temperatures. This combination of parameters has allowed a better understanding of the mechanism of dehydroxylation and the role that isomorphous substitution plays in these mechanisms to be delineated. In addition, the effect of anion type on thermal stability is also reported. A stepwise dehydroxylation model is proposed that is mediated by the level of aluminum substitution. Full article

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1216 KiB

Open AccessArticle

Decomposition of Cyclohexane on Ni₃Al Thin Foil Intermetallic Catalyst

by Paweł Jóźwik, Marco Salerno, Wojciech J. Stępniowski, Zbigniew Bojar and Krzysztof Krawczyk

Materials 2014, 7(10), 7039-7047; https://doi.org/10.3390/ma7107039 - 17 Oct 2014

Cited by 7 | Viewed by 6477

Abstract

Micro-grained thin foils made of Ni₃Al intermetallic alloy were fabricated, according to a previously described procedure, and tested as catalyst for decomposition of cyclohexane. The conversion efficiency of the catalyst was evaluated in a synthetic air atmosphere, and found to be [...] Read more.

Micro-grained thin foils made of Ni₃Al intermetallic alloy were fabricated, according to a previously described procedure, and tested as catalyst for decomposition of cyclohexane. The conversion efficiency of the catalyst was evaluated in a synthetic air atmosphere, and found to be as high as 98.7% ± 1.0% at 600 °C and 86.7% ± 3.6% at 500 °C. During the reaction, the growth of carbon nanofibers on the catalysts surface was observed. The chemical and phase composition of the nanofibers was investigated with scanning electron microscopy (SEM), energy dispersive spectrometry (EDS) and X-ray diffraction (XRD), finding them to be made of graphitic carbon. Additionally, nanoparticles of nickel appear to be incorporated in the fibers. The obtained material is promising for large scale fabrication in industrial applications because of its high efficiency in the hydrocarbon decomposition, the simple fabrication procedure, and the form of self-supporting foils with the presence of additional carbon nanofibers that increase its efficiency. Full article

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968 KiB

Open AccessArticle

Photocatalytic H₂ Production Using Pt-TiO₂ in the Presence of Oxalic Acid: Influence of the Noble Metal Size and the Carrier Gas Flow Rate

by Ákos Kmetykó, Károly Mogyorósi, Viktória Gerse, Zoltán Kónya, Péter Pusztai, András Dombi and Klára Hernádi

Materials 2014, 7(10), 7022-7038; https://doi.org/10.3390/ma7107022 - 17 Oct 2014

Cited by 18 | Viewed by 7683

Abstract

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO₂ photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO [...] Read more.

The primary objective of the experiments was to investigate the differences in the photocatalytic performance when commercially available Aeroxide P25 TiO₂ photocatalyst was deposited with differently sized Pt nanoparticles with identical platinum content (1 wt%). The noble metal deposition onto the TiO₂ surface was achieved by in situ chemical reduction (CRIS) or by mixing chemically reduced Pt nanoparticle containing sols to the aqueous suspensions of the photocatalysts (sol-impregnated samples, CRSIM). Fine and low-scale control of the size of resulting Pt nanoparticles was obtained through variation of the trisodium citrate concentration during the syntheses. The reducing reagent was NaBH₄. Photocatalytic activity of the samples and the reaction mechanism were examined during UV irradiation (λ_max = 365 nm) in the presence of oxalic acid (50 mM) as a sacrificial hole scavenger component. The H₂ evolution rates proved to be strongly dependent on the Pt particle size, as well as the irradiation time. A significant change of H₂ formation rate during the oxalic acid transformation was observed which is unusual. It is probably regulated both by the decomposition rate of accumulated oxalic acid and the H⁺/H₂ redox potential on the surface of the catalyst. The later potential is influenced by the concentration of the dissolved H₂ gas in the reaction mixture. Full article

(This article belongs to the Special Issue Photocatalytic Materials)

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1060 KiB

Open AccessArticle

Suppression of 3C-Inclusion Formation during Growth of 4H-SiC Si-Face Homoepitaxial Layers with a 1° Off-Angle

by Keiko Masumoto, Hirokuni Asamizu, Kentaro Tamura, Chiaki Kudou, Johji Nishio, Kazutoshi Kojima, Toshiyuki Ohno and Hajime Okumura

Materials 2014, 7(10), 7010-7021; https://doi.org/10.3390/ma7107010 - 17 Oct 2014

Cited by 7 | Viewed by 6768

Abstract

We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed [...] Read more.

We grew epitaxial layers on 4H-silicon carbide (SiC) Si-face substrates with a 1° off-angle. The suppression of 3C-inclusion formation during growth at a high C/Si ratio was investigated, because a growth technique with a high C/Si ratio is needed to decrease residual nitrogen incorporation. 3C inclusions were generated both at the interface between the substrate and epitaxial layer, and during epitaxial growth. 3C-SiC nucleation is proposed to trigger the formation of 3C inclusions. We suppressed 3C-inclusion formation by performing deep in situ etching and using a high C/Si ratio, which removed substrate surface damage and improved the 4H-SiC stability, respectively. The as-grown epitaxial layers had rough surfaces because of step bunching due to the deep in situ etching, but the rough surface became smooth after chemical mechanical polishing treatment. These techniques allow the growth of epitaxial layers with 1° off-angles for a wide range of doping concentrations. Full article

(This article belongs to the Special Issue Compound Semiconductor Materials 2014)

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1014 KiB

Open AccessArticle

Fabrication of Cellulose ZnO Hybrid Nanocomposite and Its Strain Sensing Behavior

by Hyun-U Ko, Seongcheol Mun, Seung-Ki Min, Gi-Woo Kim and Jaehwan Kim

Materials 2014, 7(10), 7000-7009; https://doi.org/10.3390/ma7107000 - 16 Oct 2014

Cited by 40 | Viewed by 6200

Abstract

This paper reports a hybrid nanocomposite of well-aligned zinc oxide (ZnO) nanorods on cellulose and its strain sensing behavior. ZnO nanorods are chemically grown on a cellulose film by using a hydrothermal process, termed as cellulose ZnO hybrid nanocomposite (CEZOHN). CEZOHN is made [...] Read more.

This paper reports a hybrid nanocomposite of well-aligned zinc oxide (ZnO) nanorods on cellulose and its strain sensing behavior. ZnO nanorods are chemically grown on a cellulose film by using a hydrothermal process, termed as cellulose ZnO hybrid nanocomposite (CEZOHN). CEZOHN is made by seeding and growing of ZnO on the cellulose and its structural properties are investigated. The well-aligned ZnO nanorods in conjunction with the cellulose film shows enhancement of its electromechanical property. Strain sensing behaviors of the nanocomposite are tested in bending and longitudinal stretching modes and the CEZOHN strain sensors exhibit linear responses. Full article

(This article belongs to the Section Advanced Composites)

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1019 KiB

Open AccessArticle

Statistical Optimization for Acid Hydrolysis of Microcrystalline Cellulose and Its Physiochemical Characterization by Using Metal Ion Catalyst

by Md. Ziaul Karim, Zaira Zaman Chowdhury, Sharifah Bee Abd Hamid and Md. Eaqub Ali

Materials 2014, 7(10), 6982-6999; https://doi.org/10.3390/ma7106982 - 13 Oct 2014

Cited by 79 | Viewed by 8816

Abstract

Hydrolyzing the amorphous region while keeping the crystalline region unaltered is the key technology for producing nanocellulose. This study investigated if the dissolution properties of the amorphous region of microcrystalline cellulose can be enhanced in the presence of Fe³⁺ salt in acidic [...] Read more.

Hydrolyzing the amorphous region while keeping the crystalline region unaltered is the key technology for producing nanocellulose. This study investigated if the dissolution properties of the amorphous region of microcrystalline cellulose can be enhanced in the presence of Fe³⁺ salt in acidic medium. The process parameters, including temperature, time and the concentration of metal chloride catalyst (FeCl₃), were optimized by using the response surface methodology (RSM). The experimental observation demonstrated that temperature and time play vital roles in hydrolyzing the amorphous sections of cellulose. This would yield hydrocellulose with higher crystallinity. The factors that were varied for the production of hydrocellulose were the temperature (x₁), time (x₂) and FeCl₃ catalyst concentration (x₃). Responses were measured in terms of percentage of crystallinity (y₁) and the yield (y₂) of the prepared hydrocellulose. Relevant mathematical models were developed. Analysis of variance (ANOVA) was carried out to obtain the most significant factors influencing the responses of the percentage of crystallinity and yield. Under optimum conditions, the percentage of crystallinity and yield were 83.46% and 86.98% respectively, at 90.95 °C, 6 h, with a catalyst concentration of 1 M. The physiochemical characteristics of the prepared hydrocellulose were determined in terms of XRD, SEM, TGA and FTIR analyses. The addition of FeCl₃ salt in acid hydrolyzing medium is a novel technique for substantially increasing crystallinity with a significant morphological change. Full article

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808 KiB

Open AccessArticle

Hysteresis in Lanthanide Aluminum Oxides Observed by Fast Pulse CV Measurement

by Chun Zhao, Ce Zhou Zhao, Qifeng Lu, Xiaoyi Yan, Stephen Taylor and Paul R. Chalker

Materials 2014, 7(10), 6965-6981; https://doi.org/10.3390/ma7106965 - 13 Oct 2014

Cited by 10 | Viewed by 7703

Abstract

Oxide materials with large dielectric constants (so-called high-k dielectrics) have attracted much attention due to their potential use as gate dielectrics in Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). A novel characterization (pulse capacitance-voltage) method was proposed in detail. The pulse capacitance-voltage [...] Read more.

Oxide materials with large dielectric constants (so-called high-k dielectrics) have attracted much attention due to their potential use as gate dielectrics in Metal Oxide Semiconductor Field Effect Transistors (MOSFETs). A novel characterization (pulse capacitance-voltage) method was proposed in detail. The pulse capacitance-voltage technique was employed to characterize oxide traps of high-k dielectrics based on the Metal Oxide Semiconductor (MOS) capacitor structure. The variation of flat-band voltages of the MOS structure was observed and discussed accordingly. Some interesting trapping/detrapping results related to the lanthanide aluminum oxide traps were identified for possible application in Flash memory technology. After understanding the trapping/detrapping mechanism of the high-k oxides, a solid foundation was prepared for further exploration into charge-trapping non-volatile memory in the future. Full article

(This article belongs to the Special Issue High-k Materials and Devices 2014)

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737 KiB

Open AccessArticle

New Methods of Enhancing the Thermal Durability of Silica Optical Fibers

by Karol Wysokiński, Tomasz Stańczyk, Katarzyna Gibała, Tadeusz Tenderenda, Anna Ziołowicz, Mateusz Słowikowski, Małgorzata Broczkowska and Tomasz Nasiłowski

Materials 2014, 7(10), 6947-6964; https://doi.org/10.3390/ma7106947 - 13 Oct 2014

Cited by 32 | Viewed by 6481

Abstract

Microstructured optical fibers can be precisely tailored for many different applications, out of which sensing has been found to be particularly interesting. However, placing silica optical fiber sensors in harsh environments results in their quick destruction as a result of the hydrolysis process. [...] Read more.

Microstructured optical fibers can be precisely tailored for many different applications, out of which sensing has been found to be particularly interesting. However, placing silica optical fiber sensors in harsh environments results in their quick destruction as a result of the hydrolysis process. In this paper, the degradation mechanism of bare and metal-coated optical fibers at high temperatures under longitudinal strain has been determined by detailed analysis of the thermal behavior of silica and metals, like copper and nickel. We furthermore propose a novel method of enhancing the lifetime of optical fibers by the deposition of electroless nickel-phosphorous alloy in a low-temperature chemical process. The best results were obtained for a coating comprising an inner layer of copper and outer layer of low phosphorous nickel. Lifetime values obtained during the annealing experiments were extrapolated to other temperatures by a dedicated model elaborated by the authors. The estimated copper-coated optical fiber lifetime under cycled longitudinal strain reached 31 h at 450 °C. Full article

(This article belongs to the Special Issue New Materials and Processing Methods for Microstructured Optical Fibres)

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1004 KiB

Open AccessArticle

Pull-Out Strength and Bond Behavior of Prestressing Strands in Prestressed Self-Consolidating Concrete

by Wu-Jian Long, Kamal Henri Khayat, Guillaume Lemieux, Soo-Duck Hwang and Feng Xing

Materials 2014, 7(10), 6930-6946; https://doi.org/10.3390/ma7106930 - 10 Oct 2014

Cited by 10 | Viewed by 6902

Abstract

With the extensive use of self-consolidating concrete (SCC) worldwide, it is important to ensure that such concrete can secure uniform in-situ mechanical properties that are similar to those obtained with properly consolidated concrete of conventional fluidity. Ensuring proper stability of SCC is essential [...] Read more.

With the extensive use of self-consolidating concrete (SCC) worldwide, it is important to ensure that such concrete can secure uniform in-situ mechanical properties that are similar to those obtained with properly consolidated concrete of conventional fluidity. Ensuring proper stability of SCC is essential to enhance the uniformity of in-situ mechanical properties, including bond to embedded reinforcement, which is critical for structural engineers considering the specification of SCC for prestressed applications. In this investigation, Six wall elements measuring 1540 mm × 2150 mm × 200 mm were cast using five SCC mixtures and one reference high-performance concrete (HPC) of normal consistency to evaluate the uniformity of bond strength between prestressing strands and concrete as well as the distribution of compressive strength obtained from cores along wall elements. The evaluated SCC mixtures used for casting wall elements were proportioned to achieve a slump flow consistency of 680 ± 15 mm and minimum caisson filling capacity of 80%, and visual stability index of 0.5 to 1. Given the spreads in viscosity and static stability of the SCC mixtures, the five wall elements exhibited different levels of homogeneity in in-situ compressive strength and pull-out bond strength. Test results also indicate that despite the high fluidity of SCC, stable concrete can lead to more homogenous in-situ properties than HPC of normal consistency subjected to mechanical vibration. Full article

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953 KiB

Open AccessArticle

Mechanical and Thermal Properties of Polypropylene Composites Reinforced with Lignocellulose Nanofibers Dried in Melted Ethylene-Butene Copolymer

by Shinichiro Iwamoto, Shigehiro Yamamoto, Seung-Hwan Lee, Hirokazu Ito and Takashi Endo

Materials 2014, 7(10), 6919-6929; https://doi.org/10.3390/ma7106919 - 9 Oct 2014

Cited by 32 | Viewed by 7644

Abstract

Lignocellulose nanofibers were prepared by the wet disk milling of wood flour. First, an ethylene-butene copolymer was pre-compounded with wood flour or lignocellulose nanofibers to prepare master batches. This process involved evaporating the water of the lignocellulose nanofiber suspension during compounding with ethylene-butene [...] Read more.

Lignocellulose nanofibers were prepared by the wet disk milling of wood flour. First, an ethylene-butene copolymer was pre-compounded with wood flour or lignocellulose nanofibers to prepare master batches. This process involved evaporating the water of the lignocellulose nanofiber suspension during compounding with ethylene-butene copolymer by heating at 105 °C. These master batches were compounded again with polypropylene to obtain the final composites. Since ethylene-butene copolymer is an elastomer, its addition increased the impact strength of polypropylene but decreased the stiffness. In contrast, the wood flour- and lignocellulose nanofiber-reinforced composites showed significantly higher flexural moduli and slightly higher flexural yield stresses than did the ethylene-butene/polypropylene blends. Further, the wood flour composites exhibited brittle fractures during tensile tests and had lower impact strengths than those of the ethylene-butene/polypropylene blends. On the other hand, the addition of the lignocellulose nanofibers did not decrease the impact strength of the ethylene-butene/polypropylene blends. Finally, the addition of wood flour and the lignocellulose nanofibers increased the crystallization temperature and crystallization rate of polypropylene. The increases were more remarkable in the case of the lignocellulose nanofibers than for wood flour. Full article

(This article belongs to the Special Issue Advances in Cellulosic Materials 2014)

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Open AccessArticle

Acoustic Emission Behavior of Early Age Concrete Monitored by Embedded Sensors

by Lei Qin, Hong-Wei Ren, Bi-Qin Dong and Feng Xing

Materials 2014, 7(10), 6908-6918; https://doi.org/10.3390/ma7106908 - 2 Oct 2014

Cited by 26 | Viewed by 7396

Abstract

Acoustic emission (AE) is capable of monitoring the cracking activities inside materials. In this study, embedded sensors were employed to monitor the AE behavior of early age concrete. Type 1–3 cement-based piezoelectric composites, which had lower mechanical quality factor and acoustic impedance, were [...] Read more.

Acoustic emission (AE) is capable of monitoring the cracking activities inside materials. In this study, embedded sensors were employed to monitor the AE behavior of early age concrete. Type 1–3 cement-based piezoelectric composites, which had lower mechanical quality factor and acoustic impedance, were fabricated and used to make sensors. Sensors made of the composites illustrated broadband frequency response. In a laboratory, the cracking of early age concrete was monitored to recognize different hydration stages. The sensors were also embedded in a mass concrete foundation to localize the temperature gradient cracks. Full article

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Drying of Pigment-Cellulose Nanofibril Substrates

by Oleg Timofeev, Katariina Torvinen, Jenni Sievänen, Timo Kaljunen, Jarmo Kouko and Jukka A. Ketoja

Materials 2014, 7(10), 6893-6907; https://doi.org/10.3390/ma7106893 - 1 Oct 2014

Cited by 9 | Viewed by 8843

Abstract

A new substrate containing cellulose nanofibrils and inorganic pigment particles has been developed for printed electronics applications. The studied composite structure contains 80% fillers and is mechanically stable and flexible. Before drying, the solids content can be as low as 20% due to [...] Read more.

A new substrate containing cellulose nanofibrils and inorganic pigment particles has been developed for printed electronics applications. The studied composite structure contains 80% fillers and is mechanically stable and flexible. Before drying, the solids content can be as low as 20% due to the high water binding capacity of the cellulose nanofibrils. We have studied several drying methods and their effects on the substrate properties. The aim is to achieve a tight, smooth surface keeping the drying efficiency simultaneously at a high level. The methods studied include: (1) drying on a hot metal surface; (2) air impingement drying; and (3) hot pressing. Somewhat surprisingly, drying rates measured for the pigment-cellulose nanofibril substrates were quite similar to those for the reference board sheets. Very high dewatering rates were observed for the hot pressing at high moisture contents. The drying method had significant effects on the final substrate properties, especially on short-range surface smoothness. The best smoothness was obtained with a combination of impingement and contact drying. The mechanical properties of the sheets were also affected by the drying method and associated temperature. Full article

(This article belongs to the Special Issue Advances in Cellulosic Materials 2014)

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Materials, Volume 7, Issue 10 (October 2014) – 20 articles , Pages 6893-7172

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