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Materials, Volume 5, Issue 6 (June 2012), Pages 1005-1175

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Research

Jump to: Review, Other

Open AccessArticle Influences of Sample Preparation on Nanoindentation Behavior of a Zr-Based Bulk Metallic Glass
Materials 2012, 5(6), 1033-1039; doi:10.3390/ma5061033
Received: 6 April 2012 / Revised: 16 May 2012 / Accepted: 29 May 2012 / Published: 1 June 2012
Cited by 8 | PDF Full-text (112 KB) | HTML Full-text | XML Full-text
Abstract
Influences of two different sample preparation methods, mechanical polishing and plunge cutting, on nanoindentation behavior of a Zr-based bulk metallic glass were studied. Mechanical polishing suppresses the serrated flow but promotes the creep. In contrast, plunge cutting promotes the serrated flow but [...] Read more.
Influences of two different sample preparation methods, mechanical polishing and plunge cutting, on nanoindentation behavior of a Zr-based bulk metallic glass were studied. Mechanical polishing suppresses the serrated flow but promotes the creep. In contrast, plunge cutting promotes the serrated flow but suppresses the creep. However, hardness and elastic modulus obtained from these two methods are nearly the same. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
Open AccessArticle Atomistic Modeling of the Negative Thermal Expansion in δ- Plutonium Based on the Two-State Description
Materials 2012, 5(6), 1040-1054; doi:10.3390/ma5061040
Received: 11 April 2012 / Revised: 3 May 2012 / Accepted: 1 June 2012 / Published: 7 June 2012
Cited by 3 | PDF Full-text (534 KB) | HTML Full-text | XML Full-text
Abstract
The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an [...] Read more.
The δ phase of plutonium with the fcc structure exhibits an unusual negative thermal expansion (NTE) over its narrow temperature range of stability, 593–736 K. An accurate description of the anomalous high-temperature volume effect of plutonium goes beyond the current capability of electronic-structure calculations. We propose an atomistic scheme to model the thermodynamic properties of δ-Pu based on the two-state model of Weiss for the Invar alloys, inspired by the simple free-energy analysis previously conducted by Lawson et al. The two-state mechanism is incorporated into the atomistic description of a many-body interacting system. Two modified embedded atom method potentials are employed to represent the binding energies of two competing electronic states in δ-Pu. We demonstrate how the NTE takes place in δ-Pu by means of Monte Carlo simulations implemented with the two-state mechanism. Full article
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
Open AccessArticle Glass Fiber Reinforced Polypropylene Mechanical Properties Enhancement by Adhesion Improvement
Materials 2012, 5(6), 1084-1113; doi:10.3390/ma5061084
Received: 10 April 2012 / Accepted: 26 May 2012 / Published: 18 June 2012
Cited by 24 | PDF Full-text (6162 KB) | HTML Full-text | XML Full-text
Abstract
Glass fibers (GF) are the reinforcement agent most used in polypropylene (PP) based composites, as they have good balance between properties and costs. However, their final properties are mainly determined by the strength and stability of the polymer-fiber interphase. Fibers do not [...] Read more.
Glass fibers (GF) are the reinforcement agent most used in polypropylene (PP) based composites, as they have good balance between properties and costs. However, their final properties are mainly determined by the strength and stability of the polymer-fiber interphase. Fibers do not act as an effective reinforcing material when the adhesion is weak. Also, the adhesion between phases can be easily degraded in aggressive environmental conditions such as high temperatures and/or elevated moisture, and by the stress fields to which the material may be exposed. Many efforts have been done to improve polymer-glass fiber adhesion by compatibility enhancement. The most used techniques include modifications in glass surface, polymer matrix and/or both. However, the results obtained do not show a good costs/properties improvement relationship. The aim of this work is to perform an accurate analysis regarding methods for GF/PP adhesion improvement and to propose a new route based on PP in-situ polymerization onto fibers. This route involves the modification of fibers with an aluminum alkyl and hydroxy-α-olefin and from there to enable the growth of the PP chains using direct metallocenic copolymerization. The adhesion improvements were further proved by fragmentation test, as well as by mechanical properties measurements. The strength and toughness increases three times and the interfacial strength duplicates in PP/GF composites prepared with in-situ polymerized fibers. Full article
(This article belongs to the Special Issue Fibre-Reinforced Composites)

Review

Jump to: Research, Other

Open AccessReview Extrinsic and Intrinsic Frequency Dispersion of High-k Materials in Capacitance-Voltage Measurements
Materials 2012, 5(6), 1005-1032; doi:10.3390/ma5061005
Received: 28 December 2011 / Revised: 24 April 2012 / Accepted: 11 May 2012 / Published: 1 June 2012
Cited by 16 | PDF Full-text (717 KB) | HTML Full-text | XML Full-text
Abstract
In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such [...] Read more.
In capacitance-voltage (C-V) measurements, frequency dispersion in high-k dielectrics is often observed. The frequency dependence of the dielectric constant (k-value), that is the intrinsic frequency dispersion, could not be assessed before suppressing the effects of extrinsic frequency dispersion, such as the effects of the lossy interfacial layer (between the high-k thin film and silicon substrate) and the parasitic effects. The effect of the lossy interfacial layer on frequency dispersion was investigated and modeled based on a dual frequency technique. The significance of parasitic effects (including series resistance and the back metal contact of the metal-oxide-semiconductor (MOS) capacitor) on frequency dispersion was also studied. The effect of surface roughness on frequency dispersion is also discussed. After taking extrinsic frequency dispersion into account, the relaxation behavior can be modeled using the Curie-von Schweidler (CS) law, the Kohlrausch-Williams-Watts (KWW) relationship and the Havriliak-Negami (HN) relationship. Dielectric relaxation mechanisms are also discussed. Full article
(This article belongs to the Special Issue High-k Materials and Devices)
Open AccessReview Formation of Degenerate Band Gaps in Layered Systems
Materials 2012, 5(6), 1055-1083; doi:10.3390/ma5061055
Received: 3 April 2012 / Revised: 30 May 2012 / Accepted: 31 May 2012 / Published: 7 June 2012
Cited by 3 | PDF Full-text (948 KB) | HTML Full-text | XML Full-text
Abstract
In the review, peculiarities of spectra of one-dimensional photonic crystals made of anisotropic and/or magnetooptic materials are considered. The attention is focused on band gaps of a special type—the so called degenerate band gaps which are degenerate with respect to polarization. Mechanisms [...] Read more.
In the review, peculiarities of spectra of one-dimensional photonic crystals made of anisotropic and/or magnetooptic materials are considered. The attention is focused on band gaps of a special type—the so called degenerate band gaps which are degenerate with respect to polarization. Mechanisms of formation and properties of these band gaps are analyzed. Peculiarities of spectra of photonic crystals that arise due to the linkage between band gaps are discussed. Particularly, it is shown that formation of a frozen mode is caused by linkage between Brillouin and degenerate band gaps. Also, existence of the optical Borrmann effect at the boundaries of degenerate band gaps and optical Tamm states at the frequencies of degenerate band gaps are analyzed. Full article
(This article belongs to the Special Issue Photonic Materials and Applications)
Figures

Open AccessReview Strain Measurements within Fiber Boards. Part I: Inhomogeneous Strain Distribution within Medium Density Fiberboards (MDF) Loaded Perpendicularly to the Plane of the Board
Materials 2012, 5(6), 1115-1124; doi:10.3390/ma5061115
Received: 16 May 2012 / Revised: 14 June 2012 / Accepted: 15 June 2012 / Published: 19 June 2012
Cited by 3 | PDF Full-text (381 KB) | HTML Full-text | XML Full-text
Abstract
Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with [...] Read more.
Internal bond strength testing is a widely used approach for testing quality traits of wood based panels. Generally, failure of internal bond specimens is due to adhesion and/or wood failure in the specimen. It has been reported that a composite product with a large variation in the vertical density profile fails in the center part of the board which is either the middle of the core layer or the transition zone between core layer and face layer. The density in the failure zone is typically 50% lower than the maximum density in the face layers. The aim of this study was to analyze the strain distribution in a specimen under tension perpendicular to the panel plane. The results showed that a high variety of strain magnitude occurred in the specimen. The strain is either aligned with the tension direction or a tension zone is built in one of the edge zones leading to failure. Vector graphics of the specimen show the problematic test setup of internal bond strength measurement. Strain spots in the edges lead to the assumption of an uneven stress distribution due to the momentum which results from non-perfect alignment or irregularities in the test setup. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
Open AccessReview Two Decades of Negative Thermal Expansion Research: Where Do We Stand?
Materials 2012, 5(6), 1125-1154; doi:10.3390/ma5061125
Received: 16 April 2012 / Revised: 1 June 2012 / Accepted: 15 June 2012 / Published: 20 June 2012
Cited by 85 | PDF Full-text (807 KB) | HTML Full-text | XML Full-text
Abstract
Negative thermal expansion (NTE) materials have become a rapidly growing area of research over the past two decades. The initial discovery of materials displaying NTE over a large temperature range, combined with elucidation of the mechanism behind this unusual property, was followed [...] Read more.
Negative thermal expansion (NTE) materials have become a rapidly growing area of research over the past two decades. The initial discovery of materials displaying NTE over a large temperature range, combined with elucidation of the mechanism behind this unusual property, was followed by predictions that these materials will find use in various applications through controlled thermal expansion composites. While some patents have been filed and devices built, a number of obstacles have prevented the widespread implementation of NTE materials to date. This paper reviews NTE materials that contract due to transverse atomic vibrations, their potential for use in controlled thermal expansion composites, and known problems that could interfere with such applications. Full article
(This article belongs to the Special Issue Negative Thermal Expansion Materials)
Figures

Open AccessReview Transition Metal Compounds Towards Holography
Materials 2012, 5(6), 1155-1175; doi:10.3390/ma5061155
Received: 26 March 2012 / Revised: 14 June 2012 / Accepted: 14 June 2012 / Published: 20 June 2012
Cited by 10 | PDF Full-text (5265 KB) | HTML Full-text | XML Full-text
Abstract
We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from microseconds up to hours at room [...] Read more.
We have successfully proposed the application of transition metal compounds in holographic recording media. Such compounds feature an ultra-fast light-induced linkage isomerization of the transition-metal–ligand bond with switching times in the sub-picosecond regime and lifetimes from microseconds up to hours at room temperature. This article highlights the photofunctionality of two of the most promising transition metal compounds and the photophysical mechanisms that are underlying the hologram recording. We present the latest progress with respect to the key measures of holographic media assembled from transition metal compounds, the molecular embedding in a dielectric matrix and their impressive potential for modern holographic applications. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
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Other

Jump to: Research, Review

Open AccessCorrection Correction: Dense CO2 as a Solute, Co-solute or Co-solvent in Particle Formation Processes: A Review. Materials 2011, 4, 2017-2041.
Materials 2012, 5(6), 1114; doi:10.3390/ma5061114
Received: 29 May 2012 / Accepted: 18 June 2012 / Published: 18 June 2012
PDF Full-text (31 KB) | HTML Full-text | XML Full-text
Abstract Due to a lapse the Acknowledgements section was missed from the original article version. [...] Full article

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