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Materials, Volume 5, Issue 8 (August 2012), Pages 1336-1527

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Research

Jump to: Review

Open AccessArticle The Effect of Structural Design on Mechanical Properties and Cellular Response of Additive Manufactured Titanium Scaffolds
Materials 2012, 5(8), 1336-1347; doi:10.3390/ma5081336
Received: 7 May 2012 / Revised: 29 July 2012 / Accepted: 31 July 2012 / Published: 10 August 2012
Cited by 23 | PDF Full-text (2447 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Restoration of segmental defects in long bones remains a challenging task in orthopedic surgery. Although autologous bone is still the ‘Gold Standard’ because of its high biocompatibility, it has nevertheless been associated with several disadvantages. Consequently, artificial materials, such as calcium phosphate [...] Read more.
Restoration of segmental defects in long bones remains a challenging task in orthopedic surgery. Although autologous bone is still the ‘Gold Standard’ because of its high biocompatibility, it has nevertheless been associated with several disadvantages. Consequently, artificial materials, such as calcium phosphate and titanium, have been considered for the treatment of bone defects. In the present study, the mechanical properties of three different scaffold designs were investigated. The scaffolds were made of titanium alloy (Ti6Al4V), fabricated by means of an additive manufacturing process with defined pore geometry and porosities of approximately 70%. Two scaffolds exhibited rectangular struts, orientated in the direction of loading. The struts for the third scaffold were orientated diagonal to the load direction, and featured a circular cross-section. Material properties were calculated from stress-strain relationships under axial compression testing. In vitro cell testing was undertaken with human osteoblasts on scaffolds fabricated using the same manufacturing process. Although the scaffolds exhibited different strut geometry, the mechanical properties of ultimate compressive strength were similar (145–164 MPa) and in the range of human cortical bone. Test results for elastic modulus revealed values between 3.7 and 6.7 GPa. In vitro testing demonstrated proliferation and spreading of bone cells on the scaffold surface. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application)
Open AccessArticle Effect of AlF3 on the Density and Elastic Properties of Zinc Tellurite Glass Systems
Materials 2012, 5(8), 1361-1372; doi:10.3390/ma5081361
Received: 9 July 2012 / Revised: 20 July 2012 / Accepted: 27 July 2012 / Published: 13 August 2012
Cited by 6 | PDF Full-text (712 KB) | HTML Full-text | XML Full-text | Correction | Supplementary Files
Abstract
This paper presents the results of the physical and elastic properties of the ternary zinc oxyfluoro tellurite glass system. Systematic series of glasses (AlF3)x(ZnO)y(TeO2)z with x = 0–19, y = 0–20 and z [...] Read more.
This paper presents the results of the physical and elastic properties of the ternary zinc oxyfluoro tellurite glass system. Systematic series of glasses (AlF3)x(ZnO)y(TeO2)z with x = 0–19, y = 0–20 and z = 80, 85, 90 mol% were synthesized by the conventional rapid melt quenching technique. The composition dependence of the physical, mainly density and molar volume, and elastic properties is discussed in term of the AlF3 modifiers addition that are expected to produce quite substantial changes in their physical properties. The absence of any crystalline peaks in the X-ray diffraction (XRD) patterns of the present glass samples indicates the amorphous nature. The addition of AlF3 lowered the values of the densities in ternary oxyfluorotellurite glass systems. The longitudinal and transverse ultrasonic waves propagated in each glass sample were measured using a MBS8020 ultrasonic data acquisition system. All the velocity data were taken at 5 MHz frequency and room temperature. The longitudinal modulus (L), shear modulus (G), Young’s modulus (E), bulk modulus (K) and Poisson’s ratio () are obtained from both velocities data and their respective density. Experimental data shows the density and elastic moduli of each AlF3-ZnO-TeO2 series are found strongly depend upon the glass composition. The addition of AlF3 modifiers into the zinc tellurite causes substantial changes in their density, molar volume as well as their elastic properties. Full article
Open AccessArticle Volume Holograms in Photopolymers: Comparison between Analytical and Rigorous Theories
Materials 2012, 5(8), 1373-1388; doi:10.3390/ma5081373
Received: 4 June 2012 / Revised: 1 August 2012 / Accepted: 2 August 2012 / Published: 15 August 2012
Cited by 5 | PDF Full-text (590 KB) | HTML Full-text | XML Full-text
Abstract
There is no doubt that the concept of volume holography has led to an incredibly great amount of scientific research and technological applications. One of these applications is the use of volume holograms as optical memories, and in particular, the use of [...] Read more.
There is no doubt that the concept of volume holography has led to an incredibly great amount of scientific research and technological applications. One of these applications is the use of volume holograms as optical memories, and in particular, the use of a photosensitive medium like a photopolymeric material to record information in all its volume. In this work we analyze the applicability of Kogelnik’s Coupled Wave theory to the study of volume holograms recorded in photopolymers. Some of the theoretical models in the literature describing the mechanism of hologram formation in photopolymer materials use Kogelnik’s theory to analyze the gratings recorded in photopolymeric materials. If Kogelnik’s theory cannot be applied is necessary to use a more general Coupled Wave theory (CW) or the Rigorous Coupled Wave theory (RCW). The RCW does not incorporate any approximation and thus, since it is rigorous, permits judging the accurateness of the approximations included in Kogelnik’s and CW theories. In this article, a comparison between the predictions of the three theories for phase transmission diffraction gratings is carried out. We have demonstrated the agreement in the prediction of CW and RCW and the validity of Kogelnik’s theory only for gratings with spatial frequencies higher than 500 lines/mm for the usual values of the refractive index modulations obtained in photopolymers. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
Open AccessArticle Time-Dependent Damage Investigation of Rock Mass in an In Situ Experimental Tunnel
Materials 2012, 5(8), 1389-1403; doi:10.3390/ma5081389
Received: 28 March 2012 / Revised: 7 August 2012 / Accepted: 8 August 2012 / Published: 16 August 2012
Cited by 4 | PDF Full-text (1171 KB) | HTML Full-text | XML Full-text
Abstract
In underground tunnels or caverns, time-dependent deformation or failure of rock mass, such as extending cracks, gradual rock falls, etc., are a costly irritant and a major safety concern if the time-dependent damage of surrounding rock is serious. To understand [...] Read more.
In underground tunnels or caverns, time-dependent deformation or failure of rock mass, such as extending cracks, gradual rock falls, etc., are a costly irritant and a major safety concern if the time-dependent damage of surrounding rock is serious. To understand the damage evolution of rock mass in underground engineering, an in situ experimental testing was carried out in a large belowground tunnel with a scale of 28.5 m in width, 21 m in height and 352 m in length. The time-dependent damage of rock mass was detected in succession by an ultrasonic wave test after excavation. The testing results showed that the time-dependent damage of rock mass could last a long time, i.e., nearly 30 days. Regression analysis of damage factors defined by wave velocity, resulted in the time-dependent evolutional damage equation of rock mass, which corresponded with logarithmic format. A damage viscoelastic-plastic model was developed to describe the exposed time-dependent deterioration of rock mass by field test, such as convergence of time-dependent damage, deterioration of elastic modules and logarithmic format of damage factor. Furthermore, the remedial measures for damaged surrounding rock were discussed based on the measured results and the conception of damage compensation, which provides new clues for underground engineering design. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
Open AccessArticle Effect of the Milling Time of the Precursors on the Physical Properties of Sprayed Aluminum-Doped Zinc Oxide (ZnO:Al) Thin Films
Materials 2012, 5(8), 1404-1412; doi:10.3390/ma5081404
Received: 21 March 2012 / Revised: 29 June 2012 / Accepted: 24 July 2012 / Published: 16 August 2012
Cited by 2 | PDF Full-text (483 KB) | HTML Full-text | XML Full-text
Abstract
Aluminum doped zinc oxide (ZnO:Al) thin films were deposited on soda-lime glass substrates by the chemical spray technique. The atomization of the solution was carried out by ultrasonic excitation. Six different starting solutions from both unmilled and milled Zn and Al precursors, [...] Read more.
Aluminum doped zinc oxide (ZnO:Al) thin films were deposited on soda-lime glass substrates by the chemical spray technique. The atomization of the solution was carried out by ultrasonic excitation. Six different starting solutions from both unmilled and milled Zn and Al precursors, dissolved in a mix of methanol and acetic acid, were prepared. The milling process was carried out using a planetary ball mill at a speed of 300 rpm, and different milling times, namely, 15, 25, 35, 45, and 60 min. Molar concentration, [Al]/[Zn] atomic ratio, deposition temperature and time, were kept at constant values; 0.2 M, 3 at.%, 475 °C, and 10 min, respectively. Results show that, under the same deposition conditions, electrical resistivities of ZnO:Al thin films deposited from milled precursors are lower than those obtained for films deposited from unmilled precursors. X-ray diffraction analysis revealed that all films display a polycrystalline structure, fitting well with the hexagonal wurtzite structure. Changes in surface morphology were observed by scanning electron microscopy (SEM) as well, since films deposited from unmilled precursors show triangular shaped grains, in contrast to films deposited from 15 and 35 min milled precursors that display thin slices with hexagonal shapes. The use of milled precursors to prepare starting solutions for depositing ZnO:Al thin films by ultrasonic pyrolysis influences their physical properties. Full article
(This article belongs to the Special Issue Advances in Transparent Conducting Oxides)
Open AccessArticle On the Effects of Hot Forging and Hot Rolling on the Microstructural Development and Mechanical Response of a Biocompatible Ti Alloy
Materials 2012, 5(8), 1439-1461; doi:10.3390/ma5081439
Received: 15 May 2012 / Revised: 23 July 2012 / Accepted: 26 July 2012 / Published: 20 August 2012
Cited by 5 | PDF Full-text (3507 KB) | HTML Full-text | XML Full-text
Abstract
Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To [...] Read more.
Zr, Nb, and Ta as alloying elements for Ti alloys are important for attaining superior corrosion resistance and biocompatibility in the long term. However, note that the addition of excess Nb and Ta to Ti alloys leads to higher manufacturing cost. To develop low-cost manufacturing processes, the effects of hot-forging and continuous-hot-rolling conditions on the microstructure, mechanical properties, hot forgeability, and fatigue strength of Ti-15Zr-4Nb-4Ta alloy were investigated. The temperature dependences with a temperature difference (ΔT) from β-transus temperature (Tβ) for the volume fraction of the α- and β-phases were almost the same for both Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys. In the α-β-forged Ti-15Zr-4Nb-4Ta alloy, a fine granular α-phase structure containing a fine granular β-phase at grain boundaries of an equiaxed α-phase was observed. The Ti-15Zr-4Nb-4Ta alloy billet forged at Tβ-(30 to 50) °C exhibited high strength and excellent ductility. The effects of forging ratio on mechanical strength and ductility were small at a forging ratio of more than 3. The maximum strength (σmax) markedly increased with decreasing testing temperature below Tβ. The reduction in area (R.A.) value slowly decreased with decreasing testing temperature below Tβ. The temperature dependences of σmax for the Ti-15Zr-4Nb-4Ta and Ti-6Al-4V alloys show the same tendency and might be caused by the temperature difference (ΔT) from Tβ. It was clarified that Ti-15Zr-4Nb-4Ta alloy could be manufactured using the same manufacturing process as for previously approved Ti-6Al-4V alloy, taking into account the difference (ΔT) between Tβ and heat treatment temperature. Also, the manufacturing equivalency of Ti-15Zr-4Nb-4Ta alloy to obtain marketing approval of implants was established. Thus, it was concluded that continuous hot rolling is useful for manufacturing α-β-type Ti alloy. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application)
Open AccessArticle Replication of Holograms with Corn Syrup by Rubbing
Materials 2012, 5(8), 1462-1476; doi:10.3390/ma5081462
Received: 3 April 2012 / Revised: 19 July 2012 / Accepted: 30 July 2012 / Published: 21 August 2012
PDF Full-text (271 KB) | HTML Full-text | XML Full-text
Abstract
Corn syrup films are used to replicate holograms in order to fabricate micro-structural patterns without the toxins commonly found in photosensitive salts and dyes. We use amplitude and relief masks with lithographic techniques and rubbing techniques in order to transfer holographic information [...] Read more.
Corn syrup films are used to replicate holograms in order to fabricate micro-structural patterns without the toxins commonly found in photosensitive salts and dyes. We use amplitude and relief masks with lithographic techniques and rubbing techniques in order to transfer holographic information to corn syrup material. Holographic diffraction patterns from holographic gratings and computer Fourier holograms fabricated with corn syrup are shown. We measured the diffraction efficiency parameter in order to characterize the film. The versatility of this material for storage information is promising. Holographic gratings achieved a diffraction efficiency of around 8.4% with an amplitude mask and 36% for a relief mask technique. Preliminary results using corn syrup as an emulsion for replicating holograms are also shown in this work. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
Open AccessArticle Quickly Updatable Hologram Images Using Poly(N-vinyl Carbazole) (PVCz) Photorefractive Polymer Composite
Materials 2012, 5(8), 1477-1486; doi:10.3390/ma5081477
Received: 27 June 2012 / Revised: 1 August 2012 / Accepted: 20 August 2012 / Published: 22 August 2012
Cited by 10 | PDF Full-text (583 KB) | HTML Full-text | XML Full-text
Abstract
Quickly updatable hologram images using photorefractive (PR) polymer composite based on poly(N-vinyl carbazole) (PVCz) is presented. PVCz is one of the pioneer materials of photoconductive polymers. PR polymer composite consists of 44 wt % of PVCz, 35 wt % of [...] Read more.
Quickly updatable hologram images using photorefractive (PR) polymer composite based on poly(N-vinyl carbazole) (PVCz) is presented. PVCz is one of the pioneer materials of photoconductive polymers. PR polymer composite consists of 44 wt % of PVCz, 35 wt % of 4-azacycloheptylbenzylidene-malonitrile (7-DCST) as a nonlinear optical dye, 20 wt % of carbazolylethylpropionate (CzEPA) as a photoconductive plasticizer and 1 wt % of 2,4,7-trinitro-9-fluorenone (TNF) as a sensitizer. PR composite gives high diffraction efficiency of 68% at E = 45 V μm−1. Response speed of optical diffraction is the key parameter for real-time 3D holographic display. The key parameter for obtaining quickly updatable holographic images is to control the glass transition temperature lower enough to enhance chromophore orientation. Object image of the reflected coin surface recorded with reference beam at 532 nm (green beam) in the PR polymer composite is simultaneously reconstructed using a red probe beam at 642 nm. Instead of using a coin object, an object image produced by a computer was displayed on a spatial light modulator (SLM) and used for the hologram. The reflected object beam from an SLM was interfered with a reference beam on PR polymer composite to record a hologram and simultaneously reconstructed by a red probe beam. Full article
(This article belongs to the Special Issue Advanced Materials for Modern Holographic Applications)
Open AccessArticle Synthesis of Uniform Polyaniline Nanofibers through Interfacial Polymerization
Materials 2012, 5(8), 1487-1494; doi:10.3390/ma5081487
Received: 4 July 2012 / Revised: 31 July 2012 / Accepted: 13 August 2012 / Published: 22 August 2012
Cited by 26 | PDF Full-text (329 KB) | HTML Full-text | XML Full-text
Abstract
The present paper aims to study the preparation of polyaniline nanofibers through simple interfacial polymerization. Ammonium persulfate, hydrochloric acid and chloroform were used as oxidant, dopant and organic solvent respectively. Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction and Fourier Transform Infrared [...] Read more.
The present paper aims to study the preparation of polyaniline nanofibers through simple interfacial polymerization. Ammonium persulfate, hydrochloric acid and chloroform were used as oxidant, dopant and organic solvent respectively. Field Emission Scanning Electron Microscopy (FESEM), X-ray diffraction and Fourier Transform Infrared Spectroscopy (FTIR) techniques were used to analyze the product. FESEM results show that polyaniline has nano-fiber morphology. XRD results show the crystalline properties of polyaniline nanofiber, and FTIR results confirmed the formation of polyaniline in different monomer/oxidant molar ratios. This study provides a better understanding on the synthesis of uniform polyaniline nanofibers through interfacial polymerization. Full article
Open AccessArticle Strain Measurements within Fibre Boards. Part II: Strain Concentrations at the Crack Tip of MDF Specimens Tested by the Wedge Splitting Method
Materials 2012, 5(8), 1495-1507; doi:10.3390/ma5081495
Received: 27 June 2012 / Revised: 17 August 2012 / Accepted: 21 August 2012 / Published: 23 August 2012
Cited by 1 | PDF Full-text (1131 KB) | HTML Full-text | XML Full-text
Abstract
This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the [...] Read more.
This is the second part of an article series where the mechanical and fracture mechanical properties of medium density fiberboard (MDF) were studied. While the first part of the series focused on internal bond strength and density profiles, this article discusses the fracture mechanical properties of the core layer. Fracture properties were studied with a wedge splitting setup. The critical stress intensity factors as well as the specific fracture energies were determined. Critical stress intensity factors were calculated from maximum splitting force and two-dimensional isotropic finite elements simulations of the specimen geometry. Size and shape of micro crack zone were measured with electronic laser speckle interferometry. The process zone length was approx. 5 mm. The specific fracture energy was determined to be 45.2 ± 14.4 J/m2 and the critical stress intensity factor was 0.11 ± 0.02 MPa. Full article
(This article belongs to the Special Issue Creep and Fracture of Engineering Materials and Structures)
Open AccessArticle Heterogeneous Coordination Environments in Lithium-Neutralized Ionomers Identified Using 1H and 7Li MAS NMR
Materials 2012, 5(8), 1508-1527; doi:10.3390/ma5081508
Received: 29 June 2012 / Revised: 14 August 2012 / Accepted: 17 August 2012 / Published: 23 August 2012
Cited by 7 | PDF Full-text (868 KB) | HTML Full-text | XML Full-text
Abstract
The carboxylic acid proton and the lithium coordination environments for precise and random Li-neutralized polyethylene acrylic acid P(E-AA) ionomers were explored using high speed solid-state 1H and 7Li MAS NMR. While the 7Li NMR revealed only a single Li [...] Read more.
The carboxylic acid proton and the lithium coordination environments for precise and random Li-neutralized polyethylene acrylic acid P(E-AA) ionomers were explored using high speed solid-state 1H and 7Li MAS NMR. While the 7Li NMR revealed only a single Li coordination environment, the chemical shift temperature variation was dependent on the precise or random nature of the P(E-AA) ionomer. The 1H MAS NMR revealed two different carboxylic acid proton environments in these materials. By utilizing 1H-7Li rotational echo double resonance (REDOR) MAS NMR experiments, it was demonstrated that the proton environments correspond to different average 1H-7Li distances, with the majority of the protonated carboxylic acids having a close through space contact with the Li. Molecular dynamics simulations suggest that the shortest 1H-7Li distance corresponds to un-neutralized carboxylic acids directly involved in the coordination environment of Li clusters. These solid-state NMR results show that heterogeneous structural motifs need to be included when developing descriptions of these ionomer materials. Full article
(This article belongs to the Special Issue NMR in Materials Science)
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Review

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Open AccessReview A Review of Titanium Zirconium (TiZr) Alloys for Use in Endosseous Dental Implants
Materials 2012, 5(8), 1348-1360; doi:10.3390/ma5081348
Received: 14 June 2012 / Revised: 22 July 2012 / Accepted: 25 July 2012 / Published: 13 August 2012
Cited by 38 | PDF Full-text (129 KB) | HTML Full-text | XML Full-text
Abstract
Dental implants made from binary titanium-zirconium (TiZr) alloys have shown promise as a high strength, yet biocompatible alternative to pure titanium, particularly for applications requiring small diameter implants. The aim of this review is to summarize existing literature reporting on the use [...] Read more.
Dental implants made from binary titanium-zirconium (TiZr) alloys have shown promise as a high strength, yet biocompatible alternative to pure titanium, particularly for applications requiring small diameter implants. The aim of this review is to summarize existing literature reporting on the use of binary TiZr alloys for endosseous dental implant applications as tested in vitro, in animals and clinically. And furthermore to show that TiZr is “at least as good as” pure titanium in terms of biocompatibility and osseointergration. From the twelve papers that met the inclusion criteria, the current literature confirms that TiZr alloys produce small diameter implants with a strength up to 40% higher than conventional, cold-worked, grade IV titanium implants, and with a corrosion resistance and biocompatibility that is at least as good as pure titanium. The surface structure of TiZr is compatible with established surface treatments proven to aid in the osseointegration of titanium implants. Furthermore, binary TiZr alloys have been shown to achieve good osseointegration and high success rates both in animal and in clinical studies. Full article
(This article belongs to the Special Issue Titanium Materials for Biomedical Application)
Open AccessReview Design of Higher-k and More Stable Rare Earth Oxides as Gate Dielectrics for Advanced CMOS Devices
Materials 2012, 5(8), 1413-1438; doi:10.3390/ma5081413
Received: 2 June 2012 / Revised: 24 July 2012 / Accepted: 26 July 2012 / Published: 17 August 2012
Cited by 30 | PDF Full-text (2103 KB) | HTML Full-text | XML Full-text
Abstract
High permittivity (k) gate dielectric films are widely studied to substitute SiO2 as gate oxides to suppress the unacceptable gate leakage current when the traditional SiO2 gate oxide becomes ultrathin. For high-k gate oxides, several material properties [...] Read more.
High permittivity (k) gate dielectric films are widely studied to substitute SiO2 as gate oxides to suppress the unacceptable gate leakage current when the traditional SiO2 gate oxide becomes ultrathin. For high-k gate oxides, several material properties are dominantly important. The first one, undoubtedly, is permittivity. It has been well studied by many groups in terms of how to obtain a higher permittivity for popular high-k oxides, like HfO2 and La2O3. The second one is crystallization behavior. Although it’s still under the debate whether an amorphous film is definitely better than ploy-crystallized oxide film as a gate oxide upon considering the crystal boundaries induced leakage current, the crystallization behavior should be well understood for a high-k gate oxide because it could also, to some degree, determine the permittivity of the high-k oxide. Finally, some high-k gate oxides, especially rare earth oxides (like La2O3), are not stable in air and very hygroscopic, forming hydroxide. This topic has been well investigated in over the years and significant progresses have been achieved. In this paper, I will intensively review the most recent progresses of the experimental and theoretical studies for preparing higher-k and more stable, in terms of hygroscopic tolerance and crystallization behavior, Hf- and La-based ternary high-k gate oxides. Full article
(This article belongs to the Special Issue High-k Materials and Devices)

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