Materials

254 KiB

Open AccessReview

Delocalization of Electrons in Strong Insulators at High Dynamic Pressures

by William J. Nellis

Materials 2011, 4(6), 1168-1181; https://doi.org/10.3390/ma4061168 - 21 Jun 2011

Cited by 3 | Viewed by 6900

Systematics of material responses to shock flows at high dynamic pressures are discussed. Dissipation in shock flows drives structural and electronic transitions or crossovers, such as used to synthesize metallic liquid hydrogen and most probably Al₂O₃ metallic glass. The term [...] Read more.

Systematics of material responses to shock flows at high dynamic pressures are discussed. Dissipation in shock flows drives structural and electronic transitions or crossovers, such as used to synthesize metallic liquid hydrogen and most probably Al₂O₃ metallic glass. The term “metal” here means electrical conduction in a degenerate system, which occurs by band overlap in degenerate condensed matter, rather than by thermal ionization in a non-degenerate plasma. Since H₂ and probably disordered Al₂O₃ become poor metals with minimum metallic conductivity (MMC) virtually all insulators with intermediate strengths do so as well under dynamic compression. That is, the magnitude of strength determines the split between thermal energy and disorder, which determines material response. These crossovers occur via a transition from insulators with electrons localized in chemical bonds to poor metals with electron energy bands. For example, radial extents of outermost electrons of Al and O atoms are 7 a₀ and 4 a₀, respectively, much greater than 1.7 a₀ needed for onset of hybridization at 300 GPa. All such insulators are Mott insulators, provided the term “correlated electrons” includes chemical bonds. Full article

(This article belongs to the Special Issue Hard Materials: Advances in Synthesis and Understanding)

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687 KiB

Open AccessArticle

In Vivo Corrosion of Two Novel Magnesium Alloys ZEK100 and AX30 and Their Mechanical Suitability as Biodegradable Implants

by Tim Andreas Huehnerschulte, Nina Angrisani, Dina Rittershaus, Dirk Bormann, Henning Windhagen and Andrea Meyer-Lindenberg

Materials 2011, 4(6), 1144-1167; https://doi.org/10.3390/ma4061144 - 21 Jun 2011

Cited by 57 | Viewed by 9539

Abstract

In magnesium alloys, the components used modify the alloy properties. For magnesium implants in contact with bone, rare earths alloys are commonly examined. These were shown to have a higher corrosion resistance than other alloys and a high mechanical strength, but their exact [...] Read more.

In magnesium alloys, the components used modify the alloy properties. For magnesium implants in contact with bone, rare earths alloys are commonly examined. These were shown to have a higher corrosion resistance than other alloys and a high mechanical strength, but their exact composition is hard to predict. Therefore a reduction of their content could be favorable. The alloys ZEK100 and AX30 have a reduced content or contain no rare earths at all. The aim of the study was to investigate their in vivo degradation and to assess the suitability of the in vivo µCT for the examination of their corrosion. Implants were inserted in rabbit tibiae. Clinical examinations, X-rays and in vivo µCT scans were done regularly. Afterwards implants were analyzed with REM, electron dispersive X-ray (EDX), weighing and mechanical testing. The in vivo µCT is of great advantage, because it allows a quantification of the corrosion rate and qualitative 3D assessment of the corrosion morphology. The location of the implant has a remarkable effect on the corrosion rate. Due to its mechanical characteristics and its corrosion behavior, ZEK100 was judged to be suitable, while AX30, which displays favorable degradation behavior, has too little mechanical strength for applications in weight bearing bones. Full article

(This article belongs to the Special Issue Orthopaedic Biomaterials)

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471 KiB

Open AccessArticle

Optical Properties of ZnO Nanoparticles Capped with Polymers

by Shingo Tachikawa, Atsushi Noguchi, Takeharu Tsuge, Masahiko Hara, Osamu Odawara and Hiroyuki Wada

Materials 2011, 4(6), 1132-1143; https://doi.org/10.3390/ma4061132 - 17 Jun 2011

Cited by 119 | Viewed by 13876

Abstract

Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the [...] Read more.

Optical properties of ZnO nanoparticles capped with polymers were investigated. Polyethylene glycol (PEG) and polyvinyl pyrrolidone (PVP) were used as capping reagents. ZnO nanoparticles were synthesized by the sol-gel method. Fluorescence and absorption spectra were measured. When we varied the timing of the addition of the polymer to the ZnO nanoparticle solution, the optical properties were drastically changed. When PEG was added to the solution before the synthesis of ZnO nanoparticles, the fluorescence intensity increased. At the same time, the total particle size increased, which indicated that PEG molecules had capped the ZnO nanoparticles. The capping led to surface passivation, which increased fluorescence intensity. However, when PEG was added to the solution after the synthesis of ZnO nanoparticles, the fluorescence and particle size did not change. When PVP was added to the solution before the synthesis of ZnO nanoparticles, aggregation of nanoparticles occurred. When PVP was added to the solution after the synthesis of ZnO nanoparticles, fluorescence and particle size increased. This improvement of optical properties is advantageous to the practical usage of ZnO nanoparticles, such as bioimaging Full article

(This article belongs to the Special Issue Luminescent Materials 2011)

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280 KiB

Open AccessArticle

Teriparatide Therapy as an Adjuvant for Tissue Engineering and Integration of Biomaterials

by Robinder S. Dhillon and Edward M. Schwarz

Materials 2011, 4(6), 1117-1131; https://doi.org/10.3390/ma4061117 - 15 Jun 2011

Cited by 17 | Viewed by 6705

Abstract

Critically sized large bone defects commonly result from trauma, radical tumor resections or infections. Currently, massive allografting remain as the clinical standard to treat these critical defects. Unfortunately, allograft healing is limited by the lack of osteogenesis and bio-integration of the graft to [...] Read more.

Critically sized large bone defects commonly result from trauma, radical tumor resections or infections. Currently, massive allografting remain as the clinical standard to treat these critical defects. Unfortunately, allograft healing is limited by the lack of osteogenesis and bio-integration of the graft to the host bone. Based on its widely studied anabolic effects on the bone, we have proposed that teriparatide [recombinant parathyroid hormone (PTH_1–34)] could be an effective adjuvant for massive allograft healing. In support of this theory, here we review studies that have demonstrated that intermittent PTH_1–34 treatment enhances and accelerates the skeletal repair process via a number of mechanisms including: effects on mesenchymal stem cells (MSC), angiogenesis, chondrogenesis, bone formation and remodeling. We also review the current literature on the effects of PTH_1–34 therapy on bone healing, and discuss this drug’s long term potential as an adjuvant for endogenous tissue engineering. Full article

(This article belongs to the Special Issue Advances in Biomaterials 2011)

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517 KiB

Open AccessReview

The Role Played by Computation in Understanding Hard Materials

by John Edward Lowther

Materials 2011, 4(6), 1104-1116; https://doi.org/10.3390/ma4061104 - 14 Jun 2011

Cited by 10 | Viewed by 6578

Abstract

In the last decade, computation has played a valuable role in the understanding of materials. Hard materials, in particular, are only part of the application. Although materials involving B, C, N or O remain the most valued atomic component of hard materials, with [...] Read more.

In the last decade, computation has played a valuable role in the understanding of materials. Hard materials, in particular, are only part of the application. Although materials involving B, C, N or O remain the most valued atomic component of hard materials, with diamond retaining its distinct superiority as the hardest, other materials involving a wide variety of metals are proving important. In the present work the importance of both ab-initio approaches and molecular dynamics aspects will be discussed with application to quite different systems. On one hand, ab-initio methods are applied to lightweight systems and advanced nitrides. Following, the use of molecular dynamics will be considered with application to strong metals that are used for high temperature applications. Full article

(This article belongs to the Special Issue Hard Materials: Advances in Synthesis and Understanding)

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305 KiB

Open AccessArticle

Correlation of Nitrogen Sorption and Confocal Laser Scanning Microscopy for the Analysis of Amino Group Distributions on Mesoporous Silica

by Nando Gartmann and Dominik Brühwiler

Materials 2011, 4(6), 1096-1103; https://doi.org/10.3390/ma4061096 - 9 Jun 2011

Cited by 7 | Viewed by 6135

Abstract

Aminopropylalkoxysilanes are frequently used for the functionalization of mesoporous silica. The analysis of amino group distributions on arrays of silica nanochannels by a combination of nitrogen sorption and confocal laser scanning microscopy provides valuable insight into the mechanisms underlying the interaction of these [...] Read more.

Aminopropylalkoxysilanes are frequently used for the functionalization of mesoporous silica. The analysis of amino group distributions on arrays of silica nanochannels by a combination of nitrogen sorption and confocal laser scanning microscopy provides valuable insight into the mechanisms underlying the interaction of these silanes with mesoporous silica surfaces. Tendencies towards external surface functionalization, non-uniform distribution in the pores, and hydrolysis of the silica framework are shown to depend to a large extent on the mobility of the aminopropylalkoxysilane molecules, which can be adjusted by the number and type of alkoxy groups. Full article

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1011 KiB

Open AccessArticle

Fabrication of Multiferroic Co-Substituted BiFeO₃ Epitaxial Films on SrTiO₃ (100) Substrates by Radio Frequency Magnetron Sputtering

by Husne Ara Begum, Hiroshi Naganuma, Mikihiko Oogane and Yasuo Ando

Materials 2011, 4(6), 1087-1095; https://doi.org/10.3390/ma4061087 - 9 Jun 2011

Cited by 11 | Viewed by 7514

Abstract

The 10 at.% Co-substituted BiFeO₃ films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO₃ (100) substrates with epitaxial relationships of [001](001)Co-BiFeO₃//[001](001)SrTiO₃. In this study, a single phase Co-substituted BiFeO₃ [...] Read more.

The 10 at.% Co-substituted BiFeO₃ films (of thickness 50 nm) were successfully prepared by radio frequency (r.f.) magnetron sputtering on SrTiO₃ (100) substrates with epitaxial relationships of [001](001)Co-BiFeO₃//[001](001)SrTiO₃. In this study, a single phase Co-substituted BiFeO₃ epitaxial film was fabricated by r.f. magnetron sputtering. Sputtering conditions such as Ar, O₂ gas pressure, annealing temperature, annealing atmosphere, and sputtering power were systematically changed. It was observed that a low Ar gas pressure and low sputtering power is necessary to suppress the formation of the secondary phases of BiO_x. The Co-substituted BiFeO₃ films were crystalized with post-annealing at 600 °C in air. The process window for single phase films is narrower than that for pure BiFeO₃ epitaxial films. By substituting Fe with Co in BiFeO₃, the magnetization at room temperature increased to 20 emu/cm³. This result suggests that Co-substituted BiFeO₃ films can be used in spin-filter devices. Full article

(This article belongs to the Special Issue Multiferroics)

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1541 KiB

Open AccessReview

Storage Phosphors for Medical Imaging

by Paul Leblans, Dirk Vandenbroucke and Peter Willems

Materials 2011, 4(6), 1034-1086; https://doi.org/10.3390/ma4061034 - 9 Jun 2011

Cited by 172 | Viewed by 28731

Abstract

Computed radiography (CR) uses storage phosphor imaging plates for digital imaging. Absorbed X-ray energy is stored in crystal defects. In read-out the energy is set free as blue photons upon optical stimulation. In the 35 years of CR history, several storage phosphor families [...] Read more.

Computed radiography (CR) uses storage phosphor imaging plates for digital imaging. Absorbed X-ray energy is stored in crystal defects. In read-out the energy is set free as blue photons upon optical stimulation. In the 35 years of CR history, several storage phosphor families were investigated and developed. An explanation is given as to why some materials made it to the commercial stage, while others did not. The photo stimulated luminescence mechanism of the current commercial storage phosphors, BaFBr:Eu²⁺ and CsBr:Eu²⁺ is discussed. The relation between storage phosphor plate physical characteristics and image quality is explained. It is demonstrated that the morphology of the phosphor crystals in the CR imaging plate has a very significant impact on its performance. Full article

(This article belongs to the Special Issue Luminescent Materials 2011)

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487 KiB

Open AccessArticle

A Mechanochemical Approach to Porous Silicon Nanoparticles Fabrication

by Luigi Russo, Francesco Colangelo, Raffaele Cioffi, Ilaria Rea and Luca De Stefano

Materials 2011, 4(6), 1023-1033; https://doi.org/10.3390/ma4061023 - 7 Jun 2011

Cited by 74 | Viewed by 9875

Abstract

Porous silicon samples have been reduced in nanometric particles by a well known industrial mechanical process, the ball grinding in a planetary mill; the process has been extended to crystalline silicon for comparison purposes. The silicon nanoparticles have been studied by X-ray diffraction, [...] Read more.

Porous silicon samples have been reduced in nanometric particles by a well known industrial mechanical process, the ball grinding in a planetary mill; the process has been extended to crystalline silicon for comparison purposes. The silicon nanoparticles have been studied by X-ray diffraction, infrared spectroscopy, gas porosimetry and transmission electron microscopy. We have estimated crystallites size from about 50 nm for silicon to 12 nm for porous silicon. The specific surface area of the powders analyzed ranges between 100 m²/g to 29 m²/g depending on the milling time, ranging from 1 to 20 h. Electron microscopy confirms the nanometric size of the particles and reveals a porous structure in the powders obtained by porous silicon samples which has been preserved by the fabrication conditions. Chemical functionalization during the milling process by a siloxane compound has also been demonstrated. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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421 KiB

Open AccessArticle

Synthesis and Properties of a Chiroptically Active Oligomer from 3,4-Ethylenedioxythiophene and (–)-Myrtenal

by Hirotsugu Kawashima and Hiromasa Goto

Materials 2011, 4(6), 1013-1022; https://doi.org/10.3390/ma4061013 - 30 May 2011

Cited by 2 | Viewed by 6456

Abstract

Oxidative polycondensation of 3,4-ethylenedioxythiophene and (–)-myrtenal was carried out with POCl₃. A p-conjugated system thus constructed consists of aromatic and quinoidal alternating structure linked via methine groups. We examined iodine doping effect for the resultant material with electron spin resonance spectroscopy. [...] Read more.

Oxidative polycondensation of 3,4-ethylenedioxythiophene and (–)-myrtenal was carried out with POCl₃. A p-conjugated system thus constructed consists of aromatic and quinoidal alternating structure linked via methine groups. We examined iodine doping effect for the resultant material with electron spin resonance spectroscopy. Circular dichroism spectra in chloroform solution showed blue-shift with increase of iodine concentration. This result indicates that the doping process can tune chiroptical activity of the chiral π-conjugated system. Full article

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252 KiB

Open AccessReview

Antiviral Activity of Metal-Containing Polymers—Organotin and Cisplatin-Like Polymers

by Michael R. Roner, Charles E. Carraher Jr., Kimberly Shahi and Girish Barot

Materials 2011, 4(6), 991-1012; https://doi.org/10.3390/ma4060991 - 27 May 2011

Cited by 42 | Viewed by 9000

Abstract

Polymers containing platinum and to a lesser extent tin, have repeatedly demonstrated antitumor activity in vitro and in vivo against a variety of cell and tumor types. The mechanisms responsible for the antitumor activity include inducing a delay in cell proliferation and sister [...] Read more.

Polymers containing platinum and to a lesser extent tin, have repeatedly demonstrated antitumor activity in vitro and in vivo against a variety of cell and tumor types. The mechanisms responsible for the antitumor activity include inducing a delay in cell proliferation and sister chromatid exchanges blocking tumor growth. As most DNA and some RNA viruses require, and even induce, infected cells to initiate DNA replication and subsequent cell division, compounds with antitumor activity will very likely also possess antiviral activity. This article examines the use of metal-containing polymers as a novel class of antivirals. Full article

(This article belongs to the Special Issue Metal-Containing Polymers)

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406 KiB

Open AccessArticle

Luminescent Afterglow Behavior in the M₂Si₅N₈: Eu Family (M = Ca, Sr, Ba)

by Koen Van den Eeckhout, Philippe F. Smet and Dirk Poelman

Materials 2011, 4(6), 980-990; https://doi.org/10.3390/ma4060980 - 27 May 2011

Cited by 85 | Viewed by 9544

Abstract

Persistent luminescent materials are able to emit light for hours after being excited. The majority of persistent phosphors emit in the blue or green region of the visible spectrum. Orange- or red-emitting phosphors, strongly desired for emergency signage and medical imaging, are scarce. [...] Read more.

Persistent luminescent materials are able to emit light for hours after being excited. The majority of persistent phosphors emit in the blue or green region of the visible spectrum. Orange- or red-emitting phosphors, strongly desired for emergency signage and medical imaging, are scarce. We prepared the nitrido-silicates Ca₂Si₅N₈:Eu (orange), Sr₂Si₅N₈:Eu (reddish), Ba₂Si₅N₈:Eu (yellowish orange), and their rare-earth codoped variants (R = Nd, Dy, Sm, Tm) through a solid state reaction, and investigated their luminescence and afterglow properties. In this paper, we describe how the persistent luminescence is affected by the type of codopant and the choice and ratio of the starting products. All the materials exhibit some form of persistent luminescence, but for Sr₂Si₅N₈:Eu,R this is very weak. In Ba₂Si₅N₈:Eu the afterglow remains visible for about 400 s, and Ca₂Si₅N₈:Eu,Tm shows the brightest and longest afterglow, lasting about 2,500 s. For optimal persistent luminescence, the dopant and codopant should be added in their fluoride form, in concentrations below 1 mol%. A Ca₃N₂ deficiency of about 5% triples the afterglow intensity. Our results show that Ba₂Si₅N₈:Eu(,R) and Ca₂Si₅N₈:Eu(,R) are promising persistent phosphors for applications requiring orange or red light. Full article

(This article belongs to the Special Issue Luminescent Materials 2011)

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1188 KiB

Open AccessArticle

Microstructural and Process Characterization of Conductive Traces Printed from Ag Particulate Inks

by David A. Roberson, Ryan B. Wicker, Lawrence E. Murr, Ken Church and Eric MacDonald

Materials 2011, 4(6), 963-979; https://doi.org/10.3390/ma4060963 - 26 May 2011

Cited by 56 | Viewed by 8478

Abstract

Conductive inks are key enablers for the use of printing techniques in the fabrication of electronic systems. Focus on the understanding of aspects controlling the electrical performance of conductive ink is paramount. A comparison was made between microparticle Ag inks and an Ag [...] Read more.

Conductive inks are key enablers for the use of printing techniques in the fabrication of electronic systems. Focus on the understanding of aspects controlling the electrical performance of conductive ink is paramount. A comparison was made between microparticle Ag inks and an Ag nanoparticle ink. The microstructures resulting from thermal cure processes were characterized morphologically and also in terms of their effect on the resistivity of printed traces. For microparticle inks, the variability of resistivity measurements between samples as defined by coefficient of variation (CV) was greater than 0.1 when the resistivity was 10 to 50 times that of bulk Ag. When the resistivity was lower (~1.4 times that of bulk Ag) the CV of sample sets was less than 0.1. In the case of the nanoparticle ink, resistivity was found to decrease by a factor ranging from 1.2 to 1.5 after doubling the amount of layers printed prior to curing though it was expected to remain the same. Increasing the amount of layers printed also enhanced the sintering process. Full article

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703 KiB

Open AccessArticle

Study of Ni Metallization in Macroporous Si Using Wet Chemistry for Radio Frequency Cross-Talk Isolation in Mixed Signal Integrated Circuits

by Xi Zhang, Chengkun Xu, Kyuchul Chong, King-Ning Tu and Ya-Hong Xie

Materials 2011, 4(6), 952-962; https://doi.org/10.3390/ma4060952 - 25 May 2011

Cited by 1 | Viewed by 6877

Abstract

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of [...] Read more.

A highly conductive moat or Faraday cage of through-the-wafer thickness in Si substrate was proposed to be effective in shielding electromagnetic interference thereby reducing radio frequency (RF) cross-talk in high performance mixed signal integrated circuits. Such a structure was realized by metallization of selected ultra-high-aspect-ratio macroporous regions that were electrochemically etched in p⁻ Si substrates. The metallization process was conducted by means of wet chemistry in an alkaline aqueous solution containing Ni²⁺ without reducing agent. It is found that at elevated temperature during immersion, Ni²⁺ was rapidly reduced and deposited into macroporous Si and a conformal metallization of the macropore sidewalls was obtained in a way that the entire porous Si framework was converted to Ni. A conductive moat was as a result incorporated into p⁻ Si substrate. The experimentally measured reduction of crosstalk in this structure is 5~18 dB at frequencies up to 35 GHz. Full article

(This article belongs to the Special Issue Porous Materials 2011)

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Materials, Volume 4, Issue 6 (June 2011) – 14 articles , Pages 952-1181

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