Materials

729 KiB

Open AccessArticle

Quantitative Study of Porosity and Pore Features in Moldavites by Means of X-ray Micro-CT

by Giovanni Pratesi, Stefano Caporali, Francesca Loglio, Gabriele Giuli, Lenka Dziková and Roman Skála

Materials 2014, 7(4), 3319-3336; https://doi.org/10.3390/ma7043319 - 24 Apr 2014

Cited by 5 | Viewed by 6497

Abstract

X-ray micro-computer aided tomography (μ-CT), together with optical microscopy and imaging, have been applied to the study of six moldavite samples. These techniques enabled a complete characterization to be made of the textural features of both Muong Nong-type and common splashform moldavites. A [...] Read more.

X-ray micro-computer aided tomography (μ-CT), together with optical microscopy and imaging, have been applied to the study of six moldavite samples. These techniques enabled a complete characterization to be made of the textural features of both Muong Nong-type and common splashform moldavites. A detailed study of the size and distribution of pores or bubbles confirmed the marked variability in pore size among the samples, as well as within each sample, and indicated in the Muong Nong-type moldavites the presence of at least two deformation stages which occurred before and after pore formation. Full article

(This article belongs to the Section Porous Materials)

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376 KiB

Open AccessArticle

Distributional Fate of Elements during the Synthesis of Zeolites from South African Coal Fly Ash

by Pieter W. Du Plessis, Tunde V. Ojumu, Ojo O. Fatoba, Richard O. Akinyeye and Leslie F. Petrik

Materials 2014, 7(4), 3305-3318; https://doi.org/10.3390/ma7043305 - 23 Apr 2014

Cited by 24 | Viewed by 7888

Abstract

The synthesis of zeolites from South African coal fly ash has been deemed a viable solution to the growing economical strain caused by the disposal of ash in the country. Two synthesis routes have been studied thus far namely the 2-step method and [...] Read more.

The synthesis of zeolites from South African coal fly ash has been deemed a viable solution to the growing economical strain caused by the disposal of ash in the country. Two synthesis routes have been studied thus far namely the 2-step method and the fusion assisted process. Fly ash contains several elements originating from coal which is incorporated in the ash during combustion. It is vital to determine the final destination of these elements in order to unveil optimization opportunities for scale-up purposes. The aim of this study was to perform a material balance study on both synthesis routes to determine the distributional fate of these elements during the synthesis of zeolites. Zeolites were first synthesized by means of the two synthesis routes. The composition of all raw materials and products were determined after which an overall and elemental balance were performed. Results indicated that in the 2-step method almost all elements were concentrated in the solid zeolite product while during the fusion assisted route the elements mostly report to the solid waste. Toxic elements such as Pb, Hg, Al, As and Nb were found in both the supernatant waste and washing water resulting from each synthesis route. It has also been seen that large quantities of Si and Al are wasted in the supernatant waste. It is highly recommended that the opportunity to recycle this liquid waste be investigated for scale-up purposes. Results also indicate that efficiency whereby Si and Al are extracted from fused ash is exceptionally poor and should be optimized. Full article

(This article belongs to the Special Issue Molecular Sieving and Materials)

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742 KiB

Open AccessArticle

Limits of ZnO Electrodeposition in Mesoporous Tin Doped Indium Oxide Films in View of Application in Dye-Sensitized Solar Cells

by Christian Dunkel, Till Von Graberg, Bernd M. Smarsly, Torsten Oekermann and Michael Wark

Materials 2014, 7(4), 3291-3304; https://doi.org/10.3390/ma7043291 - 23 Apr 2014

Cited by 6 | Viewed by 7917

Abstract

Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to improve [...] Read more.

Well-ordered 3D mesoporous indium tin oxide (ITO) films obtained by a templated sol-gel route are discussed as conductive porous current collectors. This paper explores the use of such films modified by electrochemical deposition of zinc oxide (ZnO) on the pore walls to improve the electron transport in dye-sensitized solar cells (DSSCs). Mesoporous ITO film were dip-coated with pore sizes of 20–25 nm and 40–45 nm employing novel poly(isobutylene)-b-poly(ethylene oxide) block copolymers as structure-directors. After electrochemical deposition of ZnO and sensitization with the indoline dye D149 the films were tested as photoanodes in DSSCs. Short ZnO deposition times led to strong back reaction of photogenerated electrons from non-covered ITO to the electrolyte. ITO films with larger pores enabled longer ZnO deposition times before pore blocking occurred, resulting in higher efficiencies, which could be further increased by using thicker ITO films consisting of five layers, but were still lower compared to nanoporous ZnO films electrodeposited on flat ITO. The major factors that currently limit the application are the still low thickness of the mesoporous ITO films, too small pore sizes and non-ideal geometries that do not allow obtaining full coverage of the ITO surface with ZnO before pore blocking occurs. Full article

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

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Graphical abstract

1020 KiB

Open AccessReview

Donor-Acceptor Block Copolymers: Synthesis and Solar Cell Applications

by Kazuhiro Nakabayashi and Hideharu Mori

Materials 2014, 7(4), 3274-3290; https://doi.org/10.3390/ma7043274 - 22 Apr 2014

Cited by 38 | Viewed by 10689

Abstract

Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor [...] Read more.

Fullerene derivatives have been widely used for conventional acceptor materials in organic photovoltaics (OPVs) because of their high electron mobility. However, there are also considerable drawbacks for use in OPVs, such as negligible light absorption in the visible-near-IR regions, less compatibility with donor polymeric materials and high cost for synthesis and purification. Therefore, the investigation of non-fullerene acceptor materials that can potentially replace fullerene derivatives in OPVs is increasingly necessary, which gives rise to the possibility of fabricating all-polymer (polymer/polymer) solar cells that can deliver higher performance and that are potentially cheaper than fullerene-based OPVs. Recently, considerable attention has been paid to donor-acceptor (D-A) block copolymers, because of their promising applications as fullerene alternative materials in all-polymer solar cells. However, the synthesis of D-A block copolymers is still a challenge, and therefore, the establishment of an efficient synthetic method is now essential. This review highlights the recent advances in D-A block copolymers synthesis and their applications in all-polymer solar cells. Full article

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

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2137 KiB

Open AccessArticle

Anodic Fabrication of Ti-Ni-O Nanotube Arrays on Shape Memory Alloy

by Qiang Liu, Dongyan Ding and Congqin Ning

Materials 2014, 7(4), 3262-3273; https://doi.org/10.3390/ma7043262 - 22 Apr 2014

Cited by 20 | Viewed by 7146

Abstract

Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. The [...] Read more.

Surface modification with oxide nanostructures is one of the efficient ways to improve physical or biomedical properties of shape memory alloys. This work reports a fabrication of highly ordered Ti-Ni-O nanotube arrays on Ti-Ni alloy substrates through pulse anodization in glycerol-based electrolytes. The effects of anodization parameters and the annealing process on the microstructures and surface morphology of Ti-Ni-O were studied using scanning electron microscope and Raman spectroscopy. The electrolyte type greatly affected the formation of nanotube arrays. A formation of anatase phase was found with the Ti-Ni-O nanotube arrays annealed at 450 °C. The oxide nanotubes could be crystallized to rutile phase after annealing treatment at 650 °C. The Ti-Ni-O nanotube arrays demonstrated an excellent thermal stability by keeping their nanotubular structures up to 650 °C. Full article

(This article belongs to the Special Issue Shape Memory Materials)

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1308 KiB

Open AccessArticle

Aggregates of Chemically Functionalized Multiwalled Carbon Nanotubes as Viscosity Reducers

by Angelo Petriccione, Mauro Zarrelli, Vincenza Antonucci and Michele Giordano

Materials 2014, 7(4), 3251-3261; https://doi.org/10.3390/ma7043251 - 22 Apr 2014

Cited by 11 | Viewed by 5157

Abstract

Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed to [...] Read more.

Confinement and surface effects provided by nanoparticles have been shown to produce changes in polymer molecules affecting their macroscopic viscosity. Nanoparticles may induce rearrangements in polymer conformation with an increase in free volume significantly lowering the viscosity. This phenomenon is generally attributed to the selective adsorption of the polymer high molar mass fraction onto nanoparticles surface when the polymer radius of gyration is comparable to the nanoparticles characteristic dimensions. Carbon nanotubes seem to be the ideal candidate to induce viscosity reduction of polymer due to both their high surface-to-volume ratio and their nanometric sizes, comparable to the gyration radius of polymer chains. However, the amount of nanotube in a polymer system is limited by the percolation threshold as, above this limit, the formation of a nanotubes network hinders the viscosity reduction effect. Based on these findings, we have used multiwalled carbon nanotubes MWCNT “aggregates” as viscosity reducers. Our results reveal both that the use of nanotube clusters reduce significantly the viscosity of the final system and strongly increase the nanotube limiting concentration for viscosity hindering. By using hydroxyl and carboxyl functionalized nanotubes, this effect has been rather maximized likely due to the hydrogen bridged stabilization of nanotube aggregates. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Graphical abstract

3237 KiB

Open AccessReview

A Review on Breathing Behaviors of Metal-Organic-Frameworks (MOFs) for Gas Adsorption

by Mays Alhamami, Huu Doan and Chil-Hung Cheng

Materials 2014, 7(4), 3198-3250; https://doi.org/10.3390/ma7043198 - 21 Apr 2014

Cited by 278 | Viewed by 24913

Abstract

Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, “tailor-made” framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In [...] Read more.

Metal-organic frameworks (MOFs) are a new class of microporous materials that possess framework flexibility, large surface areas, “tailor-made” framework functionalities, and tunable pore sizes. These features empower MOFs superior performances and broader application spectra than those of zeolites and phosphine-based molecular sieves. In parallel with designing new structures and new chemistry of MOFs, the observation of unique breathing behaviors upon adsorption of gases or solvents stimulates their potential applications as host materials in gas storage for renewable energy. This has attracted intense research energy to understand the causes at the atomic level, using in situ X-ray diffraction, calorimetry, Fourier transform infrared spectroscopy, and molecular dynamics simulations. This article is developed in the following order: first to introduce the definition of MOFs and the observation of their framework flexibility. Second, synthesis routes of MOFs are summarized with the emphasis on the hydrothermal synthesis, owing to the environmental-benign and economically availability of water. Third, MOFs exhibiting breathing behaviors are summarized, followed by rationales from thermodynamic viewpoint. Subsequently, effects of various functionalities on breathing behaviors are appraised, including using post-synthetic modification routes. Finally, possible framework spatial requirements of MOFs for yielding breathing behaviors are highlighted as the design strategies for new syntheses. Full article

(This article belongs to the Section Porous Materials)

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588 KiB

Open AccessArticle

Corrosion Behavior of Steel Reinforcement in Concrete with Recycled Aggregates, Fly Ash and Spent Cracking Catalyst

by Hebé Gurdián, Eva García-Alcocel, Francisco Baeza-Brotons, Pedro Garcés and Emilio Zornoza

Materials 2014, 7(4), 3176-3197; https://doi.org/10.3390/ma7043176 - 21 Apr 2014

Cited by 48 | Viewed by 7894

Abstract

The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to evaluate [...] Read more.

The main strategy to reduce the environmental impact of the concrete industry is to reuse the waste materials. This research has considered the combination of cement replacement by industrial by-products, and natural coarse aggregate substitution by recycled aggregate. The aim is to evaluate the behavior of concretes with a reduced impact on the environment by replacing a 50% of cement by industrial by-products (15% of spent fluid catalytic cracking catalyst and 35% of fly ash) and a 100% of natural coarse aggregate by recycled aggregate. The concretes prepared according to these considerations have been tested in terms of mechanical strengths and the protection offered against steel reinforcement corrosion under carbonation attack and chloride-contaminated environments. The proposed concrete combinations reduced the mechanical performance of concretes in terms of elastic modulus, compressive strength, and flexural strength. In addition, an increase in open porosity due to the presence of recycled aggregate was observed, which is coherent with the changes observed in mechanical tests. Regarding corrosion tests, no significant differences were observed in the case of the resistance of these types of concretes under a natural chloride attack. In the case of carbonation attack, although all concretes did not stand the highly aggressive conditions, those concretes with cement replacement behaved worse than Portland cement concretes. Full article

(This article belongs to the Section Advanced Composites)

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1415 KiB

Open AccessArticle

Quantitative X-ray Elemental Imaging in Plant Materials at the Subcellular Level with a Transmission Electron Microscope: Applications and Limitations

by Shaoliang Chen, Heike Diekmann, Dennis Janz and Andrea Polle

Materials 2014, 7(4), 3160-3175; https://doi.org/10.3390/ma7043160 - 21 Apr 2014

Cited by 12 | Viewed by 6733

Abstract

Energy-dispersive X-ray microanalysis (EDX) is a technique for determining the distribution of elements in various materials. Here, we report a protocol for high-spatial-resolution X-ray elemental imaging and quantification in plant tissues at subcellular levels with a scanning transmission electron microscope (STEM). Calibration standards [...] Read more.

Energy-dispersive X-ray microanalysis (EDX) is a technique for determining the distribution of elements in various materials. Here, we report a protocol for high-spatial-resolution X-ray elemental imaging and quantification in plant tissues at subcellular levels with a scanning transmission electron microscope (STEM). Calibration standards were established by producing agar blocks loaded with increasing KCl or NaCl concentrations. TEM-EDX images showed that the salts were evenly distributed in the agar matrix, but tended to aggregate at high concentrations. The mean intensities of K⁺, Cl⁻, and Na⁺ derived from elemental images were linearly correlated to the concentrations of these elements in the agar, over the entire concentration range tested (R > 0.916). We applied this method to plant root tissues. X-ray images were acquired at an actual resolution of 50 nm ´ 50 nm to 100 nm ´ 100 nm. We found that cell walls exhibited higher elemental concentrations than vacuoles. Plants exposed to salt stress showed dramatic accumulation of Na⁺ and Cl⁻ in the transport tissues, and reached levels similar to those applied in the external solution (300 mM). The advantage of TEM-EDX mapping was the high-spatial-resolution achieved for imaging elemental distributions in a particular area with simultaneous quantitative analyses of multiple target elements. Full article

(This article belongs to the Section Biomaterials)

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697 KiB

Open AccessArticle

Characterization of High-k Nanolayers by Grazing Incidence X-ray Spectrometry

by Matthias Müller, Philipp Hönicke, Blanka Detlefs and Claudia Fleischmann

Materials 2014, 7(4), 3147-3159; https://doi.org/10.3390/ma7043147 - 17 Apr 2014

Cited by 39 | Viewed by 8785

Abstract

The accurate characterization of nanolayered systems is an essential topic for today’s developments in many fields of material research. Thin high-k layers and gate stacks are technologically required for the design of current and future electronic devices and can be deposited, e.g., by [...] Read more.

The accurate characterization of nanolayered systems is an essential topic for today’s developments in many fields of material research. Thin high-k layers and gate stacks are technologically required for the design of current and future electronic devices and can be deposited, e.g., by Atomic Layer Deposition (ALD). However, the metrological challenges to characterize such systems demand further development of analytical techniques. Reference-free Grazing Incidence X-ray Fluorescence (GIXRF) based on synchrotron radiation can significantly contribute to the characterization of such nanolayered systems. GIXRF takes advantage of the incident angle dependence of XRF, in particular below the substrate’s critical angle where changes in the X-ray Standing Wave field (XSW) intensity influence the angular intensity profile. The reliable modeling of the XSW in conjunction with the radiometrically calibrated instrumentation at the PTB allows for reference-free, fundamental parameter-based quantitative analysis. This approach is very well suited for the characterization of nanoscaled materials, especially when no reference samples with sufficient quality are available. The capabilities of this method are demonstrated by means of two systems for transistor gate stacks, i.e., Al₂O₃ high-k layers grown on Si or Si/SiO₂ and Sc₂O₃ layers on InGaAs/InP substrates. Full article

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

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Graphical abstract

1068 KiB

Open AccessArticle

Evaluation and Observation of Autogenous Healing Ability of Bond Cracks along Rebar

by Choonghyun Kang and Minoru Kunieda

Materials 2014, 7(4), 3136-3146; https://doi.org/10.3390/ma7043136 - 17 Apr 2014

Cited by 13 | Viewed by 6409

Abstract

Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing the [...] Read more.

Micro cracks occurring in concrete around tensile rebar is well known latent damage phenomenon. These micro cracks develop, and can be detected after reaching the surface of the concrete. Detection of these cracks before they are fully formed is preferable, but observing the whole crack structure is difficult. Another problem is repairing micro cracks under the concrete surface. The autogenous ability of bond cracks along rebar was evaluated using the air permeability test. Air permeability coefficients were measured before and after tensile loading, and experimental air permeability coefficients became larger near cracks along rebar as a result of tensile loading. Recuring for 28 days after tensile loading made the air permeability coefficients smaller, but this restriction only occurred during water recuring. Observation of crack patterns helped the understanding of change in the air permeability coefficients. Several small cracks along rebar were observed after tensile loading, and most cracks along rebar were not found after water recuring. On the other hand, the crack pattern did not change after air recuring. These results indicate that bond cracks along rebar can be closed by autogenous healing, and cause the air permeability coefficients. Full article

(This article belongs to the Special Issue Self-healing Concrete)

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1157 KiB

Open AccessReview

Gelatin-Based Materials in Ocular Tissue Engineering

by James B. Rose, Settimio Pacelli, Alicia J. El Haj, Harminder S. Dua, Andrew Hopkinson, Lisa J. White and Felicity R. A. J. Rose

Materials 2014, 7(4), 3106-3135; https://doi.org/10.3390/ma7043106 - 17 Apr 2014

Cited by 263 | Viewed by 23351

Abstract

Gelatin has been used for many years in pharmaceutical formulation, cell culture and tissue engineering on account of its excellent biocompatibility, ease of processing and availability at low cost. Over the last decade gelatin has been extensively evaluated for numerous ocular applications serving [...] Read more.

Gelatin has been used for many years in pharmaceutical formulation, cell culture and tissue engineering on account of its excellent biocompatibility, ease of processing and availability at low cost. Over the last decade gelatin has been extensively evaluated for numerous ocular applications serving as cell-sheet carriers, bio-adhesives and bio-artificial grafts. These different applications naturally have diverse physical, chemical and biological requirements and this has prompted research into the modification of gelatin and its derivatives. The crosslinking of gelatin alone or in combination with natural or synthetic biopolymers has produced a variety of scaffolds that could be suitable for ocular applications. This review focuses on methods to crosslink gelatin-based materials and how the resulting materials have been applied in ocular tissue engineering. Critical discussion of recent innovations in tissue engineering and regenerative medicine will highlight future opportunities for gelatin-based materials in ophthalmology. Full article

(This article belongs to the Special Issue Biocompatibility of Materials 2013)

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1891 KiB

Open AccessArticle

R-HPDC Process with Forced Convection Mixing Device for Automotive Part of A380 Aluminum Alloy

by Bing Zhou, Yonglin Kang, Mingfan Qi, Huanhuan Zhang and Guoming Zhu

Materials 2014, 7(4), 3084-3105; https://doi.org/10.3390/ma7043084 - 15 Apr 2014

Cited by 21 | Viewed by 14468

Abstract

The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical stirring [...] Read more.

The continuing quest for cost-effective and complex shaped aluminum castings with fewer defects for applications in the automotive industries has aroused the interest in rheological high pressure die casting (R-HPDC). A new machine, forced convection mixing (FCM) device, based on the mechanical stirring and convection mixing theory for the preparation of semisolid slurry in convenience and functionality was proposed to produce the automotive shock absorber part by R-HPDC process. The effect of barrel temperature and rotational speed of the device on the grain size and morphology of semi-solid slurry were extensively studied. In addition, flow behavior and temperature field of the melt in the FCM process was investigated combining computational fluid dynamics simulation. The results indicate that the microstructure and pore defects at different locations of R-HPDC casting have been greatly improved. The vigorous fluid convection in FCM process has changed the temperature field and composition distribution of conventional solidification. Appropriately increasing the rotational speed can lead to a uniform temperature filed sooner. The lower barrel temperature leads to a larger uniform degree of supercooling of the melt that benefits the promotion of nucleation rate. Both of them contribute to the decrease of the grain size and the roundness of grain morphology. Full article

(This article belongs to the Special Issue Light Alloys and Their Applications)

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Graphical abstract

2366 KiB

Open AccessArticle

Numerical Study of Variation of Mechanical Properties of a Binary Aluminum Alloy with Respect to Its Grain Shapes

by Hamid Sharifi and Daniel Larouche

Materials 2014, 7(4), 3065-3083; https://doi.org/10.3390/ma7043065 - 15 Apr 2014

Cited by 3 | Viewed by 6813

Abstract

To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes into [...] Read more.

To study the variation of the mechanical behavior of binary aluminum copper alloys with respect to their microstructure, a numerical simulation of their granular structure was carried out. The microstructures are created by a repeated inclusion of some predefined basic grain shapes into a representative volume element until reaching a given volume percentage of the α-phase. Depending on the grain orientations, the coalescence of the grains can be performed. Different granular microstructures are created by using different basic grain shapes. Selecting a suitable set of basic grain shapes, the modeled microstructure exhibits a realistic aluminum alloy microstructure which can be adapted to a particular cooling condition. Our granular models are automatically converted to a finite element model. The effect of grain shapes and sizes on the variation of elastic modulus and plasticity of such a heterogeneous domain was investigated. Our results show that for a given α-phase fraction having different grain shapes and sizes, the elastic moduli and yield stresses are almost the same but the ultimate stress and elongation are more affected. Besides, we realized that the distribution of the θ phases inside the α phases is more important than the grain shape itself. Full article

(This article belongs to the Special Issue Selected Papers from the International Aluminium Conference (INALCO) 2013)

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Graphical abstract

1000 KiB

Open AccessArticle

Physical Characterization of Cementitious Materials on Casting and Placing Process

by Hong Jae Yim and Jae Hong Kim

Materials 2014, 7(4), 3049-3064; https://doi.org/10.3390/ma7043049 - 15 Apr 2014

Cited by 13 | Viewed by 6237

Abstract

Coagulation of cement particles is an inevitable phenomenon of fresh cement-based materials undergoing solidification. Coagulation can be classified into two types, reversible flocculation and irreversible coagulation, wherein microstructural change affects the rheological properties, including shear thinning and thixotropy, and the hydration process. This [...] Read more.

Coagulation of cement particles is an inevitable phenomenon of fresh cement-based materials undergoing solidification. Coagulation can be classified into two types, reversible flocculation and irreversible coagulation, wherein microstructural change affects the rheological properties, including shear thinning and thixotropy, and the hydration process. This paper attempts to measure the mechanical property and the coagulation of cement particles according to the mix proportions of cement paste. Experimental setups were proposed for two different types of coagulations using a laser backscattering instrument. Volume fraction and size distribution of coagulated particles were obtained, and their variations were discussed. From the obtained results the microstructural buildup of freshly mixed cement pastes can be divided into three categories: permanent coagulation and strong and weak flocculation. Full article

(This article belongs to the Special Issue Construction Materials)

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1683 KiB

Open AccessArticle

Physical Characterization of Natural Straw Fibers as Aggregates for Construction Materials Applications

by Marwen Bouasker, Naima Belayachi, Dashnor Hoxha and Muzahim Al-Mukhtar

Materials 2014, 7(4), 3034-3048; https://doi.org/10.3390/ma7043034 - 11 Apr 2014

Cited by 126 | Viewed by 10344

Abstract

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat [...] Read more.

The aim of this paper is to find out new alternative materials that respond to sustainable development criteria. For this purpose, an original utilization of straw for the design of lightweight aggregate concretes is proposed. Four types of straw were used: three wheat straws and a barley straw. In the present study, the morphology and the porosity of the different straw aggregates was studied by SEM in order to understand their effects on the capillary structure and the hygroscopic behavior. The physical properties such as sorption-desorption isotherms, water absorption coefficient, pH, electrical conductivity and thermo-gravimetric analysis were also studied. As a result, it has been found that this new vegetable material has a very low bulk density, a high water absorption capacity and an excellent hydric regulator. The introduction of the straw in the water tends to make the environment more basic; this observation can slow carbonation of the binder matrix in the presence of the straw. Full article

(This article belongs to the Section Advanced Materials Characterization)

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791 KiB

Open AccessArticle

Preparation of Nanocomposite Plasmonic Films Made from Cellulose Nanocrystals or Mesoporous Silica Decorated with Unidirectionally Aligned Gold Nanorods

by Michael G. Campbell, Qingkun Liu, Aric Sanders, Julian S. Evans and Ivan I. Smalyukh

Materials 2014, 7(4), 3021-3033; https://doi.org/10.3390/ma7043021 - 11 Apr 2014

Cited by 38 | Viewed by 8474

Abstract

Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of [...] Read more.

Using liquid crystalline self-assembly of cellulose nanocrystals, we achieve long-range alignment of anisotropic metal nanoparticles in colloidal nanocrystal dispersions that are then used to deposit thin structured films with ordering features highly dependent on the deposition method. These hybrid films are comprised of gold nanorods unidirectionally aligned in a matrix that can be made of ordered cellulose nanocrystals or silica nanostructures obtained by using cellulose-based nanostructures as a replica. The ensuing long-range alignment of gold nanorods in both cellulose-based and nanoporous silica films results in a polarization-sensitive surface plasmon resonance. The demonstrated device-scale bulk nanoparticle alignment may enable engineering of new material properties arising from combining the orientational ordering of host nanostructures and properties of the anisotropic plasmonic metal nanoparticles. Our approach may also allow for scalable fabrication of plasmonic polarizers and nanoporous silica structures with orientationally ordered anisotropic plasmonic nanoinclusions. Full article

(This article belongs to the Special Issue Liquid Crystals)

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1677 KiB

Open AccessArticle

A Procedure to Measure the in-Situ Hygrothermal Behavior of Earth Walls

by Pierre-Antoine Chabriac, Antonin Fabbri, Jean-Claude Morel, Jean-Paul Laurent and Joachim Blanc-Gonnet

Materials 2014, 7(4), 3002-3020; https://doi.org/10.3390/ma7043002 - 11 Apr 2014

Cited by 29 | Viewed by 6574

Abstract

Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount of [...] Read more.

Rammed earth is a sustainable material with low embodied energy. However, its development as a building material requires a better evaluation of its moisture-thermal buffering abilities and its mechanical behavior. Both of these properties are known to strongly depend on the amount of water contained in wall pores and its evolution. Thus the aim of this paper is to present a procedure to measure this key parameter in rammed earth or cob walls by using two types of probes operating on the Time Domain Reflectometry (TDR) principle. A calibration procedure for the probes requiring solely four parameters is described. This calibration procedure is then used to monitor the hygrothermal behavior of a rammed earth wall (1.5 m × 1 m × 0.5 m), instrumented by six probes during its manufacture, and submitted to insulated, natural convection and forced convection conditions. These measurements underline the robustness of the calibration procedure over a large range of water content, even if the wall is submitted to quite important temperature variations. They also emphasize the importance of gravity on water content heterogeneity when the saturation is high, as well as the role of liquid-to-vapor phase change on the thermal behavior. Full article

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1162 KiB

Open AccessReview

Precursor Mediated Synthesis of Nanostructured Silicas: From Precursor-Surfactant Ion Pairs to Structured Materials

by Peter Hesemann, Thy Phung Nguyen and Samir El Hankari

Materials 2014, 7(4), 2978-3001; https://doi.org/10.3390/ma7042978 - 11 Apr 2014

Cited by 25 | Viewed by 8730

Abstract

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. [...] Read more.

The synthesis of nanostructured anionic-surfactant-templated mesoporous silica (AMS) recently appeared as a new strategy for the formation of nanostructured silica based materials. This method is based on the use of anionic surfactants together with a co-structure-directing agent (CSDA), mostly a silylated ammonium precursor. The presence of this CSDA is necessary in order to create ionic interactions between template and silica forming phases and to ensure sufficient affinity between the two phases. This synthetic strategy was for the first time applied in view of the synthesis of surface functionalized silica bearing ammonium groups and was then extended on the formation of materials functionalized with anionic carboxylate and bifunctional amine-carboxylate groups. In the field of silica hybrid materials, the “anionic templating” strategy has recently been applied for the synthesis of silica hybrid materials from cationic precursors. Starting from di- or oligosilylated imidazolium and ammonium precursors, only template directed hydrolysis-polycondensation reactions involving complementary anionic surfactants allowed accessing structured ionosilica hybrid materials. The mechanistic particularity of this approach resides in the formation of precursor-surfactant ion pairs in the hydrolysis-polycondensation mixture. This review gives a systematic overview over the various types of materials accessed from this cooperative ionic templating approach and highlights the high potential of this original strategy for the formation of nanostructured silica based materials which appears as a complementary strategy to conventional soft templating approaches. Full article

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

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2127 KiB

Open AccessArticle

Influence of Layer-by-Layer Polyelectrolyte Deposition and EDC/NHS Activated Heparin Immobilization onto Silk Fibroin Fabric

by M. Fazley Elahi, Guoping Guan, Lu Wang and Martin W. King

Materials 2014, 7(4), 2956-2977; https://doi.org/10.3390/ma7042956 - 11 Apr 2014

Cited by 45 | Viewed by 13307

Abstract

To enhance the hemocompatibility of silk fibroin fabric as biomedical material, polyelectrolytes architectures have been assembled through the layer-by-layer (LbL) technique on silk fibroin fabric (SFF). In particular, 1.5 and 2.5 bilayer of oppositely charged polyelectrolytes were assembled onto SFF using poly(allylamine hydrochloride) [...] Read more.

To enhance the hemocompatibility of silk fibroin fabric as biomedical material, polyelectrolytes architectures have been assembled through the layer-by-layer (LbL) technique on silk fibroin fabric (SFF). In particular, 1.5 and 2.5 bilayer of oppositely charged polyelectrolytes were assembled onto SFF using poly(allylamine hydrochloride) (PAH) as polycationic polymer and poly(acrylic acid) (PAA) as polyanionic polymer with PAH topmost. Low molecular weight heparin (LMWH) activated with 1-ethyl-3-(dimethylaminopropyl) carbodiimide hydrochloride (EDC) and N-hydroxysuccinimide (NHS) was then immobilized on its surface. Alcian Blue staining, toluidine blue assay and X-ray photoelectron spectroscopy (XPS) confirmed the presence of heparin on modified SFF surfaces. The surface morphology of the modified silk fibroin fabric surfaces was characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM), and obtained increased roughness. Negligible hemolytic effect and a higher concentration of free hemoglobin by a kinetic clotting time test ensured the improved biological performance of the modified fibroin fabric. Overall, the deposition of 2.5 bilayer was found effective in terms of biological and surface properties of the modified fibroin fabric compared to 1.5 bilayer self-assembly technique. Therefore, this novel approach to surface modification may demonstrate long term patency in future in vivo animal trials of small diameter silk fibroin vascular grafts. Full article

(This article belongs to the Section Biomaterials)

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521 KiB

Open AccessCommunication

Non-enzymatic Hydrogen Peroxide Sensors Based on Multi-wall Carbon Nanotube/Pt Nanoparticle Nanohybrids

by Zhiying Miao, Di Zhang and Qiang Chen

Materials 2014, 7(4), 2945-2955; https://doi.org/10.3390/ma7042945 - 10 Apr 2014

Cited by 59 | Viewed by 7698

Abstract

A novel strategy to fabricate a hydrogen peroxide (H₂O₂) sensor was developed by using platinum (Pt) electrodes modified with multi-wall carbon nanotube-platinum nanoparticle nanohybrids (MWCNTs/Pt nanohybrids). The process to synthesize MWCNTs/Pt nanohybrids was simple and effective. Pt nanoparticles (Pt [...] Read more.

A novel strategy to fabricate a hydrogen peroxide (H₂O₂) sensor was developed by using platinum (Pt) electrodes modified with multi-wall carbon nanotube-platinum nanoparticle nanohybrids (MWCNTs/Pt nanohybrids). The process to synthesize MWCNTs/Pt nanohybrids was simple and effective. Pt nanoparticles (Pt NPs) were generated in situ in a potassium chloroplatinate aqueous solution in the presence of multi-wall carbon nanotubes (MWCNTs), and readily attached to the MWCNTs convex surfaces without any additional reducing reagents or irradiation treatment. The MWCNT/Pt nanohybrids were characterized by transmission electron microscope (TEM), and the redox properties of MWCNTs/Pt nanohybrids-modified Pt electrode were studied by electrochemical measurements. The MWCNTs/Pt-modified electrodes exhibited a favorable catalytic ability in the reduction of H₂O₂. The modified electrodes can be used to detect H₂O₂ in the range of 0.01–2 mM with a lower detection limit of 0.3 μM at a signal-to-noise ratio of 3. The sensitivity of the electrode to H₂O₂ was calculated to be 205.80 μA mM⁻¹ cm⁻² at working potential of 0 mV. In addition, the electrodes exhibited an excellent reusability and long-term stability as well as negligible interference from ascorbic acid, uric acid, and acetaminophen. Full article

(This article belongs to the Section Advanced Composites)

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1040 KiB

Open AccessReview

Emerging Applications for High K Materials in VLSI Technology

by Robert D. Clark

Materials 2014, 7(4), 2913-2944; https://doi.org/10.3390/ma7042913 - 10 Apr 2014

Cited by 143 | Viewed by 26556

Abstract

The current status of High K dielectrics in Very Large Scale Integrated circuit (VLSI) manufacturing for leading edge Dynamic Random Access Memory (DRAM) and Complementary Metal Oxide Semiconductor (CMOS) applications is summarized along with the deposition methods and general equipment types employed. Emerging [...] Read more.

The current status of High K dielectrics in Very Large Scale Integrated circuit (VLSI) manufacturing for leading edge Dynamic Random Access Memory (DRAM) and Complementary Metal Oxide Semiconductor (CMOS) applications is summarized along with the deposition methods and general equipment types employed. Emerging applications for High K dielectrics in future CMOS are described as well for implementations in 10 nm and beyond nodes. Additional emerging applications for High K dielectrics include Resistive RAM memories, Metal-Insulator-Metal (MIM) diodes, Ferroelectric logic and memory devices, and as mask layers for patterning. Atomic Layer Deposition (ALD) is a common and proven deposition method for all of the applications discussed for use in future VLSI manufacturing. Full article

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

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681 KiB

Open AccessArticle

Interaction and UV-Stability of Various Organic Capping Agents on the Surface of Anatase Nanoparticles

by Mohsin Raza, Angelika Bachinger, Nina Zahn and Guido Kickelbick

Materials 2014, 7(4), 2890-2912; https://doi.org/10.3390/ma7042890 - 10 Apr 2014

Cited by 35 | Viewed by 8767

Abstract

Anatase nanoparticles synthesized by the sol-gel method were surface-functionalized with long alkyl chain coupling agents as compatibilizers for a nonpolar environment, containing different anchor groups for surface interaction namely phosphonate (dodecyl phosphonate), carboxylate (dodecanoic acid), sulfate (sodium dodecyl sulphate), and amine (dodecyl amine). [...] Read more.

Anatase nanoparticles synthesized by the sol-gel method were surface-functionalized with long alkyl chain coupling agents as compatibilizers for a nonpolar environment, containing different anchor groups for surface interaction namely phosphonate (dodecyl phosphonate), carboxylate (dodecanoic acid), sulfate (sodium dodecyl sulphate), and amine (dodecyl amine). It was shown that the surface of the nanoparticles can be functionalized with the various surface groups applying similar reaction conditions. The kind of surface interaction was analyzed applying FTIR spectroscopy. The phosphonate and the carboxylate groups interact with the surface via quite strong covalent or coordinative interactions, respectively. The sulfate and amine based coupling agents on the other hand exhibit electrostatic interactions. UV stability studies of the surface bound groups revealed different degradation mechanisms for the various functionalities and moreover showed that phosphonates are the most stable among the investigated surface capping groups. Full article

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

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755 KiB

Open AccessArticle

Hot Corrosion Behavior of Sputtered Nanocrystalline Coating with Yttrium Addition at 900 °C

by Wei Jiang, Ping Yu, Wen Wang, Shenglong Zhu and Fuhui Wang

Materials 2014, 7(4), 2882-2889; https://doi.org/10.3390/ma7042882 - 9 Apr 2014

Cited by 3 | Viewed by 6143

Abstract

The high temperature corrosion behavior of sputtered nanocrystalline K38 coating with and without yttrium addition under mixed molten salt film in air was investigated. Accelerated corrosion occurred on the coating without yttrium (Y) addition locally after 60 h exposure at 900 °C, which [...] Read more.

The high temperature corrosion behavior of sputtered nanocrystalline K38 coating with and without yttrium addition under mixed molten salt film in air was investigated. Accelerated corrosion occurred on the coating without yttrium (Y) addition locally after 60 h exposure at 900 °C, which resulted in negative weight gain in kinetics. A uniform and protective alumina scale formed on surface of the coating containing yttrium in comparison. Y enriched particle as corrosion product was observed on the top of alumina scale. The results indicated the beneficial influence of Y on the chemical stability of the protective scale in the presence of chloride. The mechanism was discussed. Full article

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

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1548 KiB

Open AccessReview

Zinc Oxide—From Synthesis to Application: A Review

by Agnieszka Kołodziejczak-Radzimska and Teofil Jesionowski

Materials 2014, 7(4), 2833-2881; https://doi.org/10.3390/ma7042833 - 9 Apr 2014

Cited by 2002 | Viewed by 123276

Abstract

Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel [...] Read more.

Zinc oxide can be called a multifunctional material thanks to its unique physical and chemical properties. The first part of this paper presents the most important methods of preparation of ZnO divided into metallurgical and chemical methods. The mechanochemical process, controlled precipitation, sol-gel method, solvothermal and hydrothermal method, method using emulsion and microemulsion enviroment and other methods of obtaining zinc oxide were classified as chemical methods. In the next part of this review, the modification methods of ZnO were characterized. The modification with organic (carboxylic acid, silanes) and inroganic (metal oxides) compounds, and polymer matrices were mainly described. Finally, we present possible applications in various branches of industry: rubber, pharmaceutical, cosmetics, textile, electronic and electrotechnology, photocatalysis were introduced. This review provides useful information for specialist dealings with zinc oxide. Full article

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748 KiB

Open AccessArticle

Base Catalytic Approach: A Promising Technique for the Activation of Biochar for Equilibrium Sorption Studies of Copper, Cu(II) Ions in Single Solute System

by Sharifah Bee Abdul Hamid, Zaira Zaman Chowdhury and Sharifuddin Mohammad Zain

Materials 2014, 7(4), 2815-2832; https://doi.org/10.3390/ma7042815 - 9 Apr 2014

Cited by 62 | Viewed by 8152

Abstract

This study examines the feasibility of catalytically pretreated biochar derived from the dried exocarp or fruit peel of mangostene with Group I alkali metal hydroxide (KOH). The pretreated char was activated in the presence of carbon dioxide gas flow at high temperature to [...] Read more.

This study examines the feasibility of catalytically pretreated biochar derived from the dried exocarp or fruit peel of mangostene with Group I alkali metal hydroxide (KOH). The pretreated char was activated in the presence of carbon dioxide gas flow at high temperature to upgrade its physiochemical properties for the removal of copper, Cu(II) cations in single solute system. The effect of three independent variables, including temperature, agitation time and concentration, on sorption performance were carried out. Reaction kinetics parameters were determined by using linear regression analysis of the pseudo first, pseudo second, Elovich and intra-particle diffusion models. The regression co-efficient, R² values were best for the pseudo second order kinetic model for all the concentration ranges under investigation. This implied that Cu(II) cations were adsorbed mainly by chemical interactions with the surface active sites of the activated biochar. Langmuir, Freundlich and Temkin isotherm models were used to interpret the equilibrium data at different temperature. Thermodynamic studies revealed that the sorption process was spontaneous and endothermic. The surface area of the activated sample was 367.10 m²/g, whereas before base activation, it was only 1.22 m²/g. The results elucidated that the base pretreatment was efficient enough to yield porous carbon with an enlarged surface area, which can successfully eliminate Cu(II) cations from waste water. Full article

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738 KiB

Open AccessArticle

Spin Relaxation in GaAs: Importance of Electron-Electron Interactions

by Gionni Marchetti, Matthew Hodgson, James McHugh, Roy Chantrell and Irene D'Amico

Materials 2014, 7(4), 2795-2814; https://doi.org/10.3390/ma7042795 - 9 Apr 2014

Cited by 11 | Viewed by 8042

Abstract

We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that [...] Read more.

We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into account electron-electron interactions within the simulations, results for the spin relaxation time—with respect to both electron density and temperature—will reach good quantitative agreement with corresponding experimental data. Our calculations contain no fitting parameters. Full article

(This article belongs to the Special Issue Spintronics)

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510 KiB

Open AccessArticle

Directional Scattering of Semiconductor Nanoparticles Embedded in a Liquid Crystal

by Braulio García-Cámara, José Francisco Algorri, Virginia Urruchi and José Manuel Sánchez-Pena

Materials 2014, 7(4), 2784-2794; https://doi.org/10.3390/ma7042784 - 3 Apr 2014

Cited by 7 | Viewed by 6213

Abstract

Light scattering by semiconductor nanoparticles has been shown to be more complex than was believed until now. Both electric and magnetic responses emerge in the visible range. In addition, directional effects on light scattering of these nanoparticles were recently obtained. In particular, zero [...] Read more.

Light scattering by semiconductor nanoparticles has been shown to be more complex than was believed until now. Both electric and magnetic responses emerge in the visible range. In addition, directional effects on light scattering of these nanoparticles were recently obtained. In particular, zero backward and minimum-forward scattering are observed. These phenomena are very interesting for several applications such as, for instance, optical switches or modulators. The strong dependence of these phenomena on the properties of both the particle and the surrounding medium can be used to tune them. The electrical control on the optical properties of liquid crystals could be used to control the directional effects of embedded semiconductor nanoparticles. In this work, we theoretically analyze the effects on the directional distribution of light scattering by these particles when the refractive index of a surrounded liquid crystal changes from the ordinary to the extraordinary configuration. Several semiconductor materials and liquid crystals are studied in order to optimize the contrast between the two states. Full article

(This article belongs to the Special Issue Liquid Crystals)

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1028 KiB

Open AccessArticle

Investigation on the Enhanced Oxidation of Ferritic/Martensitic Steel P92 in Pure Steam

by Juntao Yuan, Ximao Wu, Wen Wang, Shenglong Zhu and Fuhui Wang

Materials 2014, 7(4), 2772-2783; https://doi.org/10.3390/ma7042772 - 3 Apr 2014

Cited by 21 | Viewed by 7726

Abstract

Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600–800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly enhanced [...] Read more.

Oxidation of ferritic/martensitic steel P92 was investigated in pure oxygen and in pure steam at 600–800 °C by thermogravimetric analysis (TGA), optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The results showed that the oxidation of P92 was significantly enhanced and multilayer scale with an outer iron oxides layer formed in pure steam. At 700 °C, the gas switch markedly influenced the scaling kinetics and scale microstructure. It was supposed that the higher affinity of iron to steam would be attributed to the enhanced oxidation of P92 in pure steam, and the much easier transport of hydroxyl would account for the significant difference induced by gas switch. Full article

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

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856 KiB

Open AccessReview

Hybrid Organic/Inorganic Nanocomposites for Photovoltaic Cells

by Ruchuan Liu

Materials 2014, 7(4), 2747-2771; https://doi.org/10.3390/ma7042747 - 2 Apr 2014

Cited by 132 | Viewed by 14280

Abstract

Inorganic/organic hybrid solar cells have attracted a lot of interest due to their potential in combining the advantages of both components. To understand the key issues in association with photoinduced charge separation/transportation processes and to improve overall power conversion efficiency, various combinations with [...] Read more.

Inorganic/organic hybrid solar cells have attracted a lot of interest due to their potential in combining the advantages of both components. To understand the key issues in association with photoinduced charge separation/transportation processes and to improve overall power conversion efficiency, various combinations with nanostructures of hybrid systems have been investigated. Here, we briefly review the structures of hybrid nanocomposites studied so far, and attempt to associate the power conversion efficiency with these nanostructures. Subsequently, we are then able to summarize the factors for optimizing the performance of inorganic/organic hybrid solar cells. Full article

(This article belongs to the Special Issue Nanocomposites of Polymers and Inorganic Particles 2013)

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Materials, Volume 7, Issue 4 (April 2014) – 47 articles , Pages 2395-3336

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