Materials

1301 KiB

Open AccessArticle

Influence of Material Microstructures in Micromilling of Ti6Al4V Alloy

by Aldo Attanasio, Marcello Gelfi, Annalisa Pola, Elisabetta Ceretti and Claudio Giardini

Materials 2013, 6(9), 4268-4283; https://doi.org/10.3390/ma6094268 - 24 Sep 2013

Cited by 71 | Viewed by 8150

In the most recent decades the introduction of unconventional machining processes allowed the development of micromachining techniques. In this work, the influence of material microstructures on the micromilling process was investigated. Ti6Al4V alloy was selected as workpiece material since it is a very [...] Read more.

In the most recent decades the introduction of unconventional machining processes allowed the development of micromachining techniques. In this work, the influence of material microstructures on the micromilling process was investigated. Ti6Al4V alloy was selected as workpiece material since it is a very common material for micro applications and because its duplex microstructure can be easily changed by proper thermal treatments. Four different microstructures (namely bimodal, fully equiaxed, fully lamellar and mill annealed) were obtained through recrystallization annealing treatments carried out at different times and temperatures. The mechanical properties of the samples were assessed by microhardness measurements. Nano-indentations were also performed on single grains to understand how the different hardness of phases and structures present in the Ti6Al4V alloy can affect the micromilling process. Microchannels using two flute flat end mills with a diameter equal to 200 µm were realized on the treated samples. Two different feed-per-tooth values were used during the tests. Cutting force, channel shape and burr dimension were investigated. Morphological and energy dispersive spectroscopy (EDS) analyses were performed on tools by means of a scanning electron microscope (SEM): in this way the phenomena mainly influencing the tool status were also identified. Lower cutting forces and reduced tool wear were observed when working fully lamellar microstructures compared to the other ones. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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496 KiB

Open AccessArticle

Dislocation Energetics and Pop-Ins in AlN Thin Films by Berkovich Nanoindentation

by Sheng-Rui Jian, Yu-Chin Tseng, I-Ju Teng and Jenh-Yih Juang

Materials 2013, 6(9), 4259-4267; https://doi.org/10.3390/ma6094259 - 23 Sep 2013

Cited by 27 | Viewed by 6027

Abstract

Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected [...] Read more.

Nanoindentation-induced multiple pop-ins were observed in the load-displacement curves when the mechanical responses of AlN films grown on c-plane sapphire substrates were investigated by using Berkovich indenters. No evidence of phase transformation is revealed by cross-sectional transmission electron microscopy (XTEM) and selected area diffraction (SAD) analyses. Instead XTEM observations suggest that these “instabilities” resulted from the sudden nucleation of dislocations propagating along the slip systems lying on the {0001} basal planes and the pyramidal planes commonly observed in hexagonal compound semiconductors. Based on this scenario, an energetic estimation of dislocation nucleation is made. Full article

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957 KiB

Open AccessCommunication

Co-Dispersion Behavior of ZrB₂–SiC–B₄C–C Powders with Polyethyleneimine

by Jie Yin, Jian Chen, Xuejian Liu, Hui Zhang, Yongjie Yan, Zhengren Huang and Dongliang Jiang

Materials 2013, 6(9), 4249-4258; https://doi.org/10.3390/ma6094249 - 23 Sep 2013

Cited by 9 | Viewed by 6364

Abstract

The aqueous dispersion behavior of ZrB₂, SiC powders with B₄C and C as sintering aids was investigated. Well co-dispersed suspension can be obtained in acidic solutions in presence of polyethyleneimine (PEI). The adsorption of PEI on the powder surface [...] Read more.

The aqueous dispersion behavior of ZrB₂, SiC powders with B₄C and C as sintering aids was investigated. Well co-dispersed suspension can be obtained in acidic solutions in presence of polyethyleneimine (PEI). The adsorption of PEI on the powder surface was measured by thermal gravimetric (TG) analysis. Rheological measurements displayed the effect of dispersant on the flow behavior of as-prepared slurries. An optimum condition was obtained with 1 wt % PEI. The viscosity of 40 vol % ZrB₂–SiC–B₄C–C (ZSBC) suspension at 100 s⁻¹ was as low as 0.74 Pa·s, which was suitable for aqueous processing. Full article

(This article belongs to the Special Issue Ultra-high Temperature Ceramics)

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1869 KiB

Open AccessArticle

Unified Formulation for a Triaxial Elastoplastic Constitutive Law for Concrete

by Rabah Hammoud, Rachid Boukhili and Ammar Yahia

Materials 2013, 6(9), 4226-4248; https://doi.org/10.3390/ma6094226 - 23 Sep 2013

Cited by 5 | Viewed by 6329

Abstract

A constitutive model to describe the triaxial load-response spectrum of plain concrete in both tension and shear was developed. The inelastic phenomena are described using the plastic flow with direction determined by the gradient of the plastic potential. A new plastic potential is [...] Read more.

A constitutive model to describe the triaxial load-response spectrum of plain concrete in both tension and shear was developed. The inelastic phenomena are described using the plastic flow with direction determined by the gradient of the plastic potential. A new plastic potential is introduced and experimentally fitted to ensure better estimate of the load direction. This approach allows to control the inelastic dilatancy in terms of the inelastic deformation of the material. By overlaying the plastic potential on modified Etse and Willam’s yield surface (both defined on the Haigh–Westergaard coordinates), the results showed that the two curves do not undergo similar stress states for a given strength level. It is, therefore, necessary that each surface goes through the current stress state to ensure adequate evaluation of normal vectors. A closed-form solution to accurately predict the triaxial stress state in concrete has been proposed. The predictive capabilities of the proposed model are evaluated by comparing predicted and measured stresses. The proposed model is shown to be accurate in predicting stress state of concrete. Full article

(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)

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858 KiB

Open AccessArticle

Healing of Fatigue Crack by High-Density Electropulsing in Austenitic Stainless Steel Treated with the Surface-Activated Pre-Coating

by Atsushi Hosoi, Tomoya Kishi and Yang Ju

Materials 2013, 6(9), 4213-4225; https://doi.org/10.3390/ma6094213 - 23 Sep 2013

Cited by 43 | Viewed by 9083

Abstract

A technique to heal a fatigue crack in austenitic stainless steel SUS316 by applying a controlled, high-density pulsed current was developed. A surface-activated pre-coating (SAPC), which eliminates the oxide layer and coats a Ni film on the crack surface, was used to improve [...] Read more.

A technique to heal a fatigue crack in austenitic stainless steel SUS316 by applying a controlled, high-density pulsed current was developed. A surface-activated pre-coating (SAPC), which eliminates the oxide layer and coats a Ni film on the crack surface, was used to improve the adhesion between crack surfaces. Cracks were observed by scanning electron microscopy before and after the application of high-density electropulsing. To evaluate the healing effect of the SAPC during crack propagation, fatigue tests were conducted under a constant stress intensity factor. The fatigue crack treated with the SAPC was found to be effectively healed as a result of electropulsing, and also showed a slower rate of crack propagation. Full article

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733 KiB

Open AccessArticle

Preparation and Morphology Studies of Nano Zinc Oxide Obtained Using Native and Modified Chitosans

by Munusamy Thirumavalavan, Kai-Lin Huang and Jiunn-Fwu Lee

Materials 2013, 6(9), 4198-4212; https://doi.org/10.3390/ma6094198 - 18 Sep 2013

Cited by 89 | Viewed by 7391

Abstract

Nano zinc oxide (ZnO) with moderate surface area and high pore volume were prepared using a facile preparation method. Chitosan was utilized as both chelating and structure directing agent. The application of chitosans in this study suggested that even biowastes can be served [...] Read more.

Nano zinc oxide (ZnO) with moderate surface area and high pore volume were prepared using a facile preparation method. Chitosan was utilized as both chelating and structure directing agent. The application of chitosans in this study suggested that even biowastes can be served in a productive manner economically. The surface modification of chitosan was carried out in order to increase the interaction between chitosan and zinc ions. The effect of sodium chloroacetate and isopropyl alcohol on the surface modification process was also explored. FT-IR (Fourier transform-infrared spectrometer) and TGA (Thermogravimetric analyses) analyses revealed that modified chitosans are more stable than those of unmodified chitosan. Among surface modified chitosans, CMC1 (1.5 M sodium chloroacetate and 75% isopropyl alcohol) showed enhanced surface properties. Freundlich adsorption isotherms as preliminary studies confirmed that modified chitosan showed enhanced interaction with zinc ions. The interaction of zinc salt with chitosans produced a zinc-chitosan polymer. This finally cleaved upon calcination to produce nano ZnO. The effects of different calcination temperatures indicated that 450 °C is the optimum calcination temperature to produce the nano ZnO with favored surface area (15.45 m²/g) and pore size (221.40 nm). SEM (Scanning electron microscope) and TEM (Transmission electron microscope) of ZnO indicated that uniform particle and shape distributions were obtained at low calcination temperature (450 °C). Full article

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906 KiB

Open AccessArticle

Effect of Thermal Treatment on Fracture Properties and Adsorption Properties of Spruce Wood

by Koji Murata, Yasuhiro Watanabe and Takato Nakano

Materials 2013, 6(9), 4186-4197; https://doi.org/10.3390/ma6094186 - 18 Sep 2013

Cited by 38 | Viewed by 5679

Abstract

The effect of thermal treatment on spruce is examined by analyzing the fracture and hygroscopic properties. Specimens were heated at temperatures within the range 120–200 °C for 1 h. Fracture energy was measured using a single-edge notched bending test and the strain-softening index [...] Read more.

The effect of thermal treatment on spruce is examined by analyzing the fracture and hygroscopic properties. Specimens were heated at temperatures within the range 120–200 °C for 1 h. Fracture energy was measured using a single-edge notched bending test and the strain-softening index was estimated by dividing the fracture energy by the maximum load. Adsorption properties were estimated using adsorption isotherms. Fiber saturation points (FSPs) were estimated by extrapolating the moisture adsorption isotherm curve. Langmuir’s adsorption coefficient and number of adsorption sites were obtained using Langmuir’s theory and the Hailwood-Horrobin theory, respectively. The fracture energy, FSPs, and specimen weights decreased at temperatures higher than 150 °C, but the critical point for the strain-softening index and the number of adsorption sites was shown to be 180 °C. We hypothesize that the fracture energy and FSP depend on the chemical structure of the cell wall, whereas the strain-softening behavior may be influenced by the number of adsorption sites, and in turn the number of hydrogen bonds in hemicellulose. Full article

(This article belongs to the Section Biomaterials)

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808 KiB

Open AccessArticle

Th(IV) Adsorption onto Oxidized Multi-Walled Carbon Nanotubes in the Presence of Hydroxylated Fullerene and Carboxylated Fullerene

by Jing Wang, Peng Liu, Zhan Li, Wei Qi, Yan Lu and Wangsuo Wu

Materials 2013, 6(9), 4168-4185; https://doi.org/10.3390/ma6094168 - 17 Sep 2013

Cited by 13 | Viewed by 6704

Abstract

The adsorption of Th(IV) onto the surface of oxidized multi-walled carbon nanotubes (oMWCNTs) in the absence and presence of hydroxylated fullerene (C₆₀(OH)_n) and carboxylated fullerene (C₆₀(C(COOH)₂)_n) has been investigated. C₆₀(OH)_n [...] Read more.

The adsorption of Th(IV) onto the surface of oxidized multi-walled carbon nanotubes (oMWCNTs) in the absence and presence of hydroxylated fullerene (C₆₀(OH)_n) and carboxylated fullerene (C₆₀(C(COOH)₂)_n) has been investigated. C₆₀(OH)_n, C₆₀(C(COOH)₂)_n and oMWCNTs have been chosen as model phases because of their representative in carbon nano-materials family. Adsorption experiments were performed by batch procedure as a function of contact time, pH, ionic strength, and temperature. The results demonstrated that the adsorption of Th(IV) was rapidly reached equilibrium and the kinetic process could be described by a pseudo-second-order rate model very well. Th(IV) adsorption on oMWCNTs was dependent on pH but independent on ionic strength. Adsorption isotherms were correlated better with the Langmuir model than with the Freundlich model. The thermodynamic parameters calculated from temperature-dependent adsorption isotherms suggested that Th(IV) adsorption on oMWCNTs was spontaneous and endothermic. Compared with the adsorption of Th(IV) on the same oMWCNTs free of C₆₀(OH)_n or C₆₀(C(COOH)₂)_n, the study of a ternary system showed the inhibition effect of C₆₀(OH)_n at high concentration on the adsorption of Th(IV) in a pH range from neutral to slightly alkaline; whereas the promotion effect of C₆₀(C(COOH)₂)_n, even at its low concentration, on Th(IV) adsorption was observed in acid medium. Full article

(This article belongs to the Special Issue Carbon Nanotubes)

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697 KiB

Open AccessReview

SBA-15 Mesoporous Silica as Catalytic Support for Hydrodesulfurization Catalysts—Review

by Rafael Huirache-Acuña, Rufino Nava, Carmen L. Peza-Ledesma, Javier Lara-Romero, Gabriel Alonso-Núez, Barbara Pawelec and Eric M. Rivera-Muñoz

Materials 2013, 6(9), 4139-4167; https://doi.org/10.3390/ma6094139 - 17 Sep 2013

Cited by 175 | Viewed by 18566

Abstract

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated [...] Read more.

SBA-15 is an interesting mesoporous silica material having highly ordered nanopores and a large surface area, which is widely employed as catalyst supports, absorbents, drug delivery materials, etc. Since it has a lack of functionality, heteroatoms and organic functional groups have been incorporated by direct or post-synthesis methods in order to modify their functionality. The aim of this article is to review the state-of-the-art related to the use of SBA-15-based mesoporous systems as supports for hydrodesulfurization (HDS) catalysts. Full article

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

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1069 KiB

Open AccessArticle

High Density Polyethylene Composites Reinforced with Hybrid Inorganic Fillers: Morphology, Mechanical and Thermal Expansion Performance

by Runzhou Huang, Xinwu Xu, Sunyoung Lee, Yang Zhang, Birm-June Kim and Qinglin Wu

Materials 2013, 6(9), 4122-4138; https://doi.org/10.3390/ma6094122 - 17 Sep 2013

Cited by 88 | Viewed by 12474

Abstract

The effect of individual and combined talc and glass fibers (GFs) on mechanical and thermal expansion performance of the filled high density polyethylene (HDPE) composites was studied. Several published models were adapted to fit the measured tensile modulus and strength of various composite [...] Read more.

The effect of individual and combined talc and glass fibers (GFs) on mechanical and thermal expansion performance of the filled high density polyethylene (HDPE) composites was studied. Several published models were adapted to fit the measured tensile modulus and strength of various composite systems. It was shown that the use of silane-modified GFs had a much larger effect in improving mechanical properties and in reducing linear coefficient of thermal expansion (LCTE) values of filled composites, compared with the use of un-modified talc particles due to enhanced bonding to the matrix, larger aspect ratio, and fiber alignment for GFs. Mechanical properties and LCTE values of composites with combined talc and GF fillers varied with talc and GF ratio at a given total filler loading level. The use of a larger portion of GFs in the mix can lead to better composite performance, while the use of talc can help lower the composite costs and increase its recyclability. The use of 30 wt % combined filler seems necessary to control LCTE values of filled HDPE in the data value range generally reported for commercial wood plastic composites. Tensile modulus for talc-filled composite can be predicted with rule of mixture, while a PPA-based model can be used to predict the modulus and strength of GF-filled composites. Full article

(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)

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2214 KiB

Open AccessArticle

The Tension and Puncture Properties of HDPE Geomembrane under the Corrosion of Leachate

by Qiang Xue, Qian Zhang, Zhen-Ze Li and Kai Xiao

Materials 2013, 6(9), 4109-4121; https://doi.org/10.3390/ma6094109 - 17 Sep 2013

Cited by 11 | Viewed by 7393

Abstract

To investigate the gradual failure of high-density polyethylene (HDPE) geomembrane as a result of long-term corrosion, four dynamic corrosion tests were conducted at different temperatures and durations. By combining tension and puncture tests, we systematically studied the variation law of tension and puncture [...] Read more.

To investigate the gradual failure of high-density polyethylene (HDPE) geomembrane as a result of long-term corrosion, four dynamic corrosion tests were conducted at different temperatures and durations. By combining tension and puncture tests, we systematically studied the variation law of tension and puncture properties of the HDPE geomembrane under different corrosion conditions. Results showed that tension and puncture failure of the HDPE geomembrane was progressive, and tensile strength in the longitudinal grain direction was evidently better than that in the transverse direction. Punctures appeared shortly after puncture force reached the puncture strength. The tensile strength of geomembrane was in inversely proportional to the corrosion time, and the impact of corrosion was more obvious in the longitudinal direction than transverse direction. As corrosion time increased, puncture strength decreased and corresponding deformation increased. As with corrosion time, the increase of corrosion temperature induced the decrease of geomembrane tensile strength. Tensile and puncture strength were extremely sensitive to temperature. Overall, residual strength had a negative correlation with corrosion time or temperature. Elongation variation increased initially and then decreased with the increase in temperature. However, it did not show significant law with corrosion time. The reduction in puncture strength and the increase in puncture deformation had positive correlations with corrosion time or temperature. The geomembrane softened under corrosion condition. The conclusion may be applicable to the proper designing of the HDPE geomembrane in landfill barrier system. Full article

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415 KiB

Open AccessArticle

Complete Permittivity Tensor in Sputtered CuFe₂O₄ Thin Films at Photon Energies between 2 and 5 eV

by Martin Veis, Roman Antos, Stefan Visnovsky, Prasanna D. Kulkarni, Narayanan Venkataramani, Shiva Prasad, Jan Mistrik and Ramanathan Krishnan

Materials 2013, 6(9), 4096-4108; https://doi.org/10.3390/ma6094096 - 16 Sep 2013

Cited by 10 | Viewed by 5336

Abstract

This work is devoted to the systematic study of the optical and magneto-optical properties of sputter deposited CuFe₂O₄ thin films in the photon energy region between 2 and 5 eV using spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The spectral dependence [...] Read more.

This work is devoted to the systematic study of the optical and magneto-optical properties of sputter deposited CuFe₂O₄ thin films in the photon energy region between 2 and 5 eV using spectroscopic ellipsometry and magneto-optical Kerr spectroscopy. The spectral dependence of both the diagonal and off-diagonal elements of the permittivity tensor is determined. A complete picture about the electron transitions in CuFe₂O₄ is suggested in the frame of intervalence charge transfer and intersublattice charge transfer transitions. The effect of deposition conditions and post-deposition treatment in CuFe₂O₄ films upon the optical and magneto-optical properties is discussed. Full article

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697 KiB

Open AccessArticle

Aqueous ZrO₂ and YSZ Colloidal Systems through Microwave Assisted Hydrothermal Synthesis

by Kenny Vernieuwe, Petra Lommens, José C. Martins, Freya Van Den Broeck, Isabel Van Driessche and Klaartje De Buysser

Materials 2013, 6(9), 4082-4095; https://doi.org/10.3390/ma6094082 - 16 Sep 2013

Cited by 10 | Viewed by 6319

Abstract

In this paper, the formation of ZrO₂ and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 [...] Read more.

In this paper, the formation of ZrO₂ and yttria-stabilised-zirconia (YSZ) aqueous colloidal systems via microwave assisted hydrothermal synthesis is studied. Microwave synthesis allows a fast screening of the influence of different parameters such as time and temperature. The temperature varied from 140 °C up to 180 °C and the used reaction time varied from 5 min up to 1 h. The synthesised zirconia nanoparticles have a particle size of 50 nm confirmed by TEM. A ¹H NMR (nuclear magnetic resonance) study helped to understand the stabilization mechanism of the synthesised particles. By the addition of ytrrium ions into the zirconia colloidal solution, YSZ could be formed via an additional thermal treatment. Hereby, the samples are heated up to 400 °C for 1 h. YSZ colloidal solutions are synthesised by making use of complexing agents such as nitrilotriacetic acid, ethylenediaminetetraacetic acid and citric acid to control the hydrolysis and condensation of both ions to avoid non-stoichiometric phases. The ratio of Zr/Y in the particles is quantified by XRF. The amorphous structure of those particles necessitates an additional thermal treatment up to 600 °C during 1 h in order to obtain crystalline YSZ. Full article

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971 KiB

Open AccessArticle

Experimental Study on Cementitious Composites Embedded with Organic Microcapsules

by Xianfeng Wang, Feng Xing, Ming Zhang, Ningxu Han and Zhiwei Qian

Materials 2013, 6(9), 4064-4081; https://doi.org/10.3390/ma6094064 - 16 Sep 2013

Cited by 125 | Viewed by 7697

Abstract

The recovery behavior for strength and impermeability of cementitious composites embedded with organic microcapsules was investigated in this study. Mortar specimens were formed by mixing the organic microcapsules and a catalyst with cement and sand. The mechanical behaviors of flexural and compression strength [...] Read more.

The recovery behavior for strength and impermeability of cementitious composites embedded with organic microcapsules was investigated in this study. Mortar specimens were formed by mixing the organic microcapsules and a catalyst with cement and sand. The mechanical behaviors of flexural and compression strength were tested. The results showed that strength could increase by up to nine percent with the addition of a small amount of microcapsules and then decrease with an increasing amount of microcapsules. An orthogonal test for investigating the strength recovery rate was designed and implemented for bending and compression using the factors of water/cement ratio, amount of microcapsules, and preloading rate. It is shown that the amount of microcapsules plays a key role in the strength recovery rate. Chloride ion permeability tests were also carried out to investigate the recovery rate and healing effect. The initial damage was obtained by subjecting the specimens to compression. Both the recovery rate and the healing effect were nearly proportional to the amount of microcapsules. The obtained cementitious composites can be seen as self-healing owing to their recovery behavior for both strength and permeability. Full article

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

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1719 KiB

Open AccessReview

Consolidation of Hierarchy-Structured Nanopowder Agglomerates and Its Application to Net-Shaping Nanopowder Materials

by Jai-Sung Lee, Joon-Phil Choi and Geon-Yong Lee

Materials 2013, 6(9), 4046-4063; https://doi.org/10.3390/ma6094046 - 16 Sep 2013

Cited by 28 | Viewed by 8168

Abstract

This paper provides an overview on our recent investigations on the consolidation of hierarchy-structured nanopowder agglomerates and related applications to net-shaping nanopowder materials. Understanding the nanopowder agglomerate sintering (NAS) process is essential to processing of net-shaped nanopowder materials and components with small and [...] Read more.

This paper provides an overview on our recent investigations on the consolidation of hierarchy-structured nanopowder agglomerates and related applications to net-shaping nanopowder materials. Understanding the nanopowder agglomerate sintering (NAS) process is essential to processing of net-shaped nanopowder materials and components with small and complex shape. The key concept of the NAS process is to enhance material transport through controlling the powder interface volume of nanopowder agglomerates. Based upon this concept, we have suggested a new idea of full density processing for fabricating micro-powder injection molded part using metal nanopowder agglomerates produced by hydrogen reduction of metal oxide powders. Studies on the full density sintering of die compacted- and powder injection molded iron base nano-agglomerate powders are introduced and discussed in terms of densification process and microstructure. Full article

(This article belongs to the Special Issue Progress in Net-shaped PM (Powder Metallurgical) Parts)

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755 KiB

Open AccessArticle

Thermally Activated Composite with Two-Way and Multi-Shape Memory Effects

by Abdul Basit, Gildas L'Hostis, Marie José Pac and Bernard Durand

Materials 2013, 6(9), 4031-4045; https://doi.org/10.3390/ma6094031 - 12 Sep 2013

Cited by 18 | Viewed by 6707

Abstract

The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the [...] Read more.

The use of shape memory polymer composites is growing rapidly in smart structure applications. In this work, an active asymmetric composite called “controlled behavior composite material (CBCM)” is used as shape memory polymer composite. The programming and the corresponding initial fixity of the composite structure is obtained during a bending test, by heating CBCM above thermal glass transition temperature of the used Epoxy polymer. The shape memory properties of these composites are investigated by a bending test. Three types of recoveries are conducted, two classical recovery tests: unconstrained recovery and constrained recovery, and a new test of partial recovery under load. During recovery, high recovery displacement and force are produced that enables the composite to perform strong two-way actuations along with multi-shape memory effect. The recovery force confirms full recovery with two-way actuation even under a high load. This unique property of CBCM is characterized by the recovered mechanical work. Full article

(This article belongs to the Special Issue Smart Polymers and Polymeric Structures)

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3442 KiB

Open AccessArticle

Observations of Ball-Lightning-Like Plasmoids Ejected from Silicon by Localized Microwaves

by Yehuda Meir, Eli Jerby, Zahava Barkay, Dana Ashkenazi, James Brian Mitchell, Theyencheri Narayanan, Noam Eliaz, Jean-Luc LeGarrec, Michael Sztucki and Oleg Meshcheryakov

Materials 2013, 6(9), 4011-4030; https://doi.org/10.3390/ma6094011 - 11 Sep 2013

Cited by 20 | Viewed by 9945

Abstract

This paper presents experimental characterization of plasmoids (fireballs) obtained by directing localized microwave power (<1 kW at 2.45 GHz) onto a silicon-based substrate in a microwave cavity. The plasmoid emerges up from the hotspot created in the solid substrate into the air within [...] Read more.

This paper presents experimental characterization of plasmoids (fireballs) obtained by directing localized microwave power (<1 kW at 2.45 GHz) onto a silicon-based substrate in a microwave cavity. The plasmoid emerges up from the hotspot created in the solid substrate into the air within the microwave cavity. The experimental diagnostics employed for the fireball characterization in this study include measurements of microwave scattering, optical spectroscopy, small-angle X-ray scattering (SAXS), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Various characteristics of these plasmoids as dusty plasma are drawn by a theoretical analysis of the experimental observations. Aggregations of dust particles within the plasmoid are detected at nanometer and micrometer scales by both in-situ SAXS and ex-situ SEM measurements. The resemblance of these plasmoids to the natural ball-lightning (BL) phenomenon is discussed with regard to silicon nano-particle clustering and formation of slowly-oxidized silicon micro-spheres within the BL. Potential applications and practical derivatives of this study (e.g., direct conversion of solids to powders, material identification by breakdown spectroscopy (MIBS), thermite ignition, and combustion) are discussed. Full article

(This article belongs to the Special Issue Microwave Processing of Materials)

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297 KiB

Open AccessArticle

New Coating Technique of Ceramic Implants with Different Glass Solder Matrices for Improved Osseointegration-Mechanical Investigations

by Enrico Mick, Jana Markhoff, Aurica Mitrovic, Anika Jonitz and Rainer Bader

Materials 2013, 6(9), 4001-4010; https://doi.org/10.3390/ma6094001 - 11 Sep 2013

Cited by 8 | Viewed by 6492

Abstract

Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the [...] Read more.

Ceramics are a very popular material in dental implant technology due to their tribological properties, their biocompatibility and their esthetic appearance. However, their natural surface structure lacks the ability of proper osseointegration, which constitutes a crucial process for the stability and, thus, the functionality of a bone implant. We investigated the application of a glass solder matrix in three configurations—consisting mainly of SiO₂, Al₂O₃, K₂O and Na₂O to TZP-A ceramic specimens. The corresponding adhesive strength and surface roughness of the coatings on ceramic specimens have been analyzed. Thereby, high adhesive strength (70.3 ± 7.9 MPa) was found for the three different coatings. The obtained roughness (R_z) amounted to 18.24 ± 2.48 µm in average, with significant differences between the glass solder configurations. Furthermore, one configuration was also tested after additional etching which did not lead to significant increase of surface roughness (19.37 ± 1.04 µm) or adhesive strength (57.2 ± 5.8 MPa). In conclusion, coating with glass solder matrix seems to be a promising surface modification technique that may enable direct insertion of ceramic implants in dental and orthopaedic surgery. Full article

(This article belongs to the Section Manufacturing Processes and Systems)

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572 KiB

Open AccessArticle

Effect of Nanopore Length on the Translocation Process of a Biopolymer: Numerical Study

by Suresh Alapati, Woo Seong Che and Yong Kweon Suh

Materials 2013, 6(9), 3989-4000; https://doi.org/10.3390/ma6093989 - 11 Sep 2013

Cited by 4 | Viewed by 5237

Abstract

In this study, we simulate the electrophoretic motion of a bio-polymer through a synthetic nanopore in the presence of an external bias voltage by considering the hydrodynamic interactions between the polymer and the fluid explicitly. The motion of the polymer is simulated by [...] Read more.

In this study, we simulate the electrophoretic motion of a bio-polymer through a synthetic nanopore in the presence of an external bias voltage by considering the hydrodynamic interactions between the polymer and the fluid explicitly. The motion of the polymer is simulated by 3D Langevin dynamics technique by modeling the polymer as a worm-like-chain, while the hydrodynamic interactions are incorporated by the lattice Boltzmann equation. We report the simulation results for three different lengths of the nanopore. The translocation time increases with the pore length even though the electrophoretic force on the polymer is the same irrespective of the pore length. This is attributed to the fact that the translocation velocity of each bead inside the nanopore decreases with the pore length due to the increased fluid resistance force caused by the increase in the straightened portion of the polymer. We confirmed this using a theoretical formula. Full article

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542 KiB

Open AccessArticle

Constitutive Behavior and Finite Element Analysis of FRP Composite and Concrete Members

by Ki Yong Ann and Chang-Geun Cho

Materials 2013, 6(9), 3978-3988; https://doi.org/10.3390/ma6093978 - 10 Sep 2013

Cited by 7 | Viewed by 5802

Abstract

The present study concerns compressive and flexural constitutive models incorporated into an isoparametric beam finite element scheme for fiber reinforced polymer (FRP) and concrete composites, using their multi-axial constitutive behavior. The constitutive behavior of concrete was treated in triaxial stress states as an [...] Read more.

The present study concerns compressive and flexural constitutive models incorporated into an isoparametric beam finite element scheme for fiber reinforced polymer (FRP) and concrete composites, using their multi-axial constitutive behavior. The constitutive behavior of concrete was treated in triaxial stress states as an orthotropic hypoelasticity-based formulation to determine the confinement effect of concrete from a three-dimensional failure surface in triaxial stress states. The constitutive behavior of the FRP composite was formulated from the two-dimensional classical lamination theory. To predict the flexural behavior of circular cross-section with FRP sheet and concrete composite, a layered discretization of cross-sections was incorporated into nonlinear isoparametric beam finite elements. The predicted constitutive behavior was validated by a comparison to available experimental results in the compressive and flexural beam loading test. Full article

(This article belongs to the Special Issue Constitutive Behavior of Composite Materials)

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683 KiB

Open AccessArticle

Microstructural and Wear Behavior Characterization of Porous Layers Produced by Pulsed Laser Irradiation in Glass-Ceramics Substrates

by Daniel Sola, Ana Conde, Iñaki García, Elena Gracia-Escosa, Juan J. De Damborenea and Jose I. Peña

Materials 2013, 6(9), 3963-3977; https://doi.org/10.3390/ma6093963 - 9 Sep 2013

Cited by 12 | Viewed by 6906

Abstract

In this work, wear behavior and microstructural characterization of porous layers produced in glass-ceramic substrates by pulsed laser irradiation in the nanosecond range are studied under unidirectional sliding conditions against AISI316 and corundum counterbodies. Depending on the optical configuration of the laser beam [...] Read more.

In this work, wear behavior and microstructural characterization of porous layers produced in glass-ceramic substrates by pulsed laser irradiation in the nanosecond range are studied under unidirectional sliding conditions against AISI316 and corundum counterbodies. Depending on the optical configuration of the laser beam and on the working parameters, the local temperature and pressure applied over the interaction zone can generate a porous glass-ceramic layer. Material transference from the ball to the porous glass-ceramic layer was observed in the wear tests carried out against the AISI316 ball counterface whereas, in the case of the corundum ball, the wear volume loss was concentrated in the porous layer. Wear rate and friction coefficient presented higher values than expected for dense glass-ceramics. Full article

(This article belongs to the Special Issue Advances in Surface Coatings 2013)

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989 KiB

Open AccessArticle

Synthesis and Characterization of Novel Epoxy Geopolymer Hybrid Composites

by Giuseppina Roviello, Laura Ricciotti, Claudio Ferone, Francesco Colangelo, Raffaele Cioffi and Oreste Tarallo

Materials 2013, 6(9), 3943-3962; https://doi.org/10.3390/ma6093943 - 9 Sep 2013

Cited by 58 | Viewed by 7772

Abstract

The preparation and the characterization of novel geopolymer-based hybrid composites are reported. These materials have been prepared through an innovative synthetic approach, based on a co-reticulation in mild conditions of commercial epoxy based organic resins and a metakaolin-based geopolymer inorganic matrix. This synthetic [...] Read more.

The preparation and the characterization of novel geopolymer-based hybrid composites are reported. These materials have been prepared through an innovative synthetic approach, based on a co-reticulation in mild conditions of commercial epoxy based organic resins and a metakaolin-based geopolymer inorganic matrix. This synthetic strategy allows the obtainment of a homogeneous dispersion of the organic particles in the inorganic matrix, up to 25% in weight of the resin. The materials obtained present significantly enhanced compressive strengths and toughness with respect to the neat geopolymer, suggesting their wide utilization for structural applications. A preliminary characterization of the porous materials obtained by removing the organic phase from the hybrid composites by means of heat treatments is also reported. Possible applications of these materials in the field of water purification, filtration, or as lightweight insulating materials are envisaged. Full article

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Open AccessReview

Calcium Orthophosphate-Based Bioceramics

by Sergey V. Dorozhkin

Materials 2013, 6(9), 3840-3942; https://doi.org/10.3390/ma6093840 - 6 Sep 2013

Cited by 222 | Viewed by 18056

Abstract

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In [...] Read more.

Various types of grafts have been traditionally used to restore damaged bones. In the late 1960s, a strong interest was raised in studying ceramics as potential bone grafts due to their biomechanical properties. A bit later, such synthetic biomaterials were called bioceramics. In principle, bioceramics can be prepared from diverse materials but this review is limited to calcium orthophosphate-based formulations only, which possess the specific advantages due to the chemical similarity to mammalian bones and teeth. During the past 40 years, there have been a number of important achievements in this field. Namely, after the initial development of bioceramics that was just tolerated in the physiological environment, an emphasis was shifted towards the formulations able to form direct chemical bonds with the adjacent bones. Afterwards, by the structural and compositional controls, it became possible to choose whether the calcium orthophosphate-based implants remain biologically stable once incorporated into the skeletal structure or whether they were resorbed over time. At the turn of the millennium, a new concept of regenerative bioceramics was developed and such formulations became an integrated part of the tissue engineering approach. Now calcium orthophosphate scaffolds are designed to induce bone formation and vascularization. These scaffolds are often porous and harbor different biomolecules and/or cells. Therefore, current biomedical applications of calcium orthophosphate bioceramics include bone augmentations, artificial bone grafts, maxillofacial reconstruction, spinal fusion, periodontal disease repairs and bone fillers after tumor surgery. Perspective future applications comprise drug delivery and tissue engineering purposes because calcium orthophosphates appear to be promising carriers of growth factors, bioactive peptides and various types of cells. Full article

(This article belongs to the Special Issue Ceramics for Healthcare 2013)

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Open AccessArticle

Dopamine-Mediated Sclerotization of Regenerated Chitin in Ionic Liquid

by Dongyeop X. Oh, Sara Shin, Chanoong Lim and Dong Soo Hwang

Materials 2013, 6(9), 3826-3839; https://doi.org/10.3390/ma6093826 - 6 Sep 2013

Cited by 47 | Viewed by 8104

Abstract

Chitin is a promising structural material for biomedical applications, due to its many advantageous properties and abundance in nature. However, its usage and development in the biomedical field have been stagnant, because of chitin’s poor mechanical properties in wet conditions and the difficulties [...] Read more.

Chitin is a promising structural material for biomedical applications, due to its many advantageous properties and abundance in nature. However, its usage and development in the biomedical field have been stagnant, because of chitin’s poor mechanical properties in wet conditions and the difficulties in transforming it into an applicable form. To overcome these challenges, we created a novel biomimetic chitin composite. This regenerated chitin, prepared with ionic liquid, showed improved mechanical properties in wet conditions by mimicking insect cuticle and squid beak sclerotization, i.e., catechol-meditated cross-linking. By ionic liquid-based heat treatment, dopamine oxidation produced melanin-like compounds and dopamine-meditated cross-links without any solvent evaporation and oxidant utilization. The dopamine-meditated sclerotization increased the ultimate tensile strength (UTS) of the regenerated chitin by 2.52-fold, measured after six weeks of phosphate-buffered saline (PBS) submersion. In addition, the linear swelling ratio (LSR) of the chitin film was reduced by about 22%. This strategy raises a possibility of using regenerated chitin as an artificial hard tissue in wet conditions. Full article

(This article belongs to the Section Biomaterials)

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Open AccessArticle

Microgel Modified UV-Cured Methacrylic-Silica Hybrid: Synthesis and Characterization

by Carola Esposito Corcione, Raffaella Striani and Mariaenrica Frigione

Materials 2013, 6(9), 3805-3825; https://doi.org/10.3390/ma6093805 - 6 Sep 2013

Cited by 18 | Viewed by 7029

Abstract

An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was [...] Read more.

An innovative photopolymerizable microgel modified UV-cured acrylic-silica hybrid formulation was developed and characterized for possible use as protective coating for different substrates. A deep investigation, aiming at providing a strong scientific basis for the production of organic-inorganic (O-I) hybrids exhibiting phase co-continuity, was firstly carried out. The O-I hybrid first proposed in this study was obtained from organic precursors with a high siloxane content, which are mixed with tetraethoxysilane (TEOS) in such a way to produce co-continuous silica nanodomains dispersed within the crosslinked organic phase, as a result of the sol-gel process. The first part of the research deals with the selection and optimization of suitable systems through appropriate chemical modifications, in order to ensure that curing reactions can be carried out at room temperature and in the presence of UV radiation. Firstly, the silica domains are formed, followed by crosslinking reactions of the acrylic groups in the oligomer via a free radical polymerization. The crosslinking reaction was controlled with the use of a suitable photoinitiator. Most of the experimental work was devoted to understanding the morphology of the hybrid system, both in uncured and cured states, and to assess its final thermal and optical properties, using different experiential techniques. Full article

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

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Open AccessReview

Monitoring the Cure State of Thermosetting Resins by Ultrasound

by Francesca Lionetto and Alfonso Maffezzoli

Materials 2013, 6(9), 3783-3804; https://doi.org/10.3390/ma6093783 - 5 Sep 2013

Cited by 119 | Viewed by 8717

Abstract

The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to [...] Read more.

The propagation of low intensity ultrasound in a curing resin, acting as a high frequency oscillatory excitation, has been recently proposed as an ultrasonic dynamic mechanical analysis (UDMA) for cure monitoring. The technique measures sound velocity and attenuation, which are very sensitive to changes in the viscoelastic characteristics of the curing resin, since the velocity is related to the resin storage modulus and density, while the attenuation is related to the energy dissipation and scattering in the curing resin. The paper reviews the results obtained by the authors’ research group in the last decade by means of in-house made ultrasonic set-ups for both contact and air-coupled ultrasonic experiments. The basics of the ultrasonic wave propagation in polymers and examples of measurements of the time-evolution of ultrasonic longitudinal modulus and chemical conversion of different thermosetting resins are presented. The effect of temperature on the cure kinetics, the comparison with rheological, low frequency dynamic mechanical and calorimetric results, and the correlation between ultrasonic modulus and crosslinking density will be also discussed. The paper highlights the reliability of ultrasonic wave propagation for monitoring the physical changes taking place during curing and the potential for online monitoring during polymer and polymer matrix composite processing. Full article

(This article belongs to the Section Advanced Materials Characterization)

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Homogenized Elastic Properties of Graphene for Small Deformations

by Eduard Marenić, Adnan Ibrahimbegovic, Jurica Sorić and Pierre-Alain Guidault

Materials 2013, 6(9), 3764-3782; https://doi.org/10.3390/ma6093764 - 3 Sep 2013

Cited by 18 | Viewed by 6154

Abstract

In this paper, we provide the quantification of the linear and non-linear elastic mechanical properties of graphene based upon the judicious combination of molecular mechanics simulation results and homogenization methods. We clarify the influence on computed results by the main model features, such [...] Read more.

In this paper, we provide the quantification of the linear and non-linear elastic mechanical properties of graphene based upon the judicious combination of molecular mechanics simulation results and homogenization methods. We clarify the influence on computed results by the main model features, such as specimen size, chirality of microstructure, the effect of chosen boundary conditions (imposed displacement versus force) and the corresponding plane stress transformation. The proposed approach is capable of explaining the scatter of the results for computed stresses, energy and stiffness and provides the bounds on graphene elastic properties, which are quite important in modeling and simulation of the virtual experiments on graphene-based devices. Full article

(This article belongs to the Special Issue Computational Modeling and Simulation in Materials Study)

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Construction of a Novel Magnetic Targeting Anti-Tumor Drug Delivery System: Cytosine Arabinoside-Loaded Bacterial Magnetosome

by Qiongjia Deng, Yuangang Liu, Shibin Wang, Maobin Xie, Shenjian Wu, Aizheng Chen and Wenguo Wu

Materials 2013, 6(9), 3755-3763; https://doi.org/10.3390/ma6093755 - 3 Sep 2013

Cited by 24 | Viewed by 6239

Abstract

To ease the side effects triggered by cytosine arabinoside (Ara-C) for acute leukemia treatment, a novel magnetic targeting anti-tumor drug delivery system was constructed through bacterial magnetosomes (BMs) from Magnetospirillum magneticum AMB-1 combined with Ara-C by crosslinking of genipin (GP). The results showed [...] Read more.

To ease the side effects triggered by cytosine arabinoside (Ara-C) for acute leukemia treatment, a novel magnetic targeting anti-tumor drug delivery system was constructed through bacterial magnetosomes (BMs) from Magnetospirillum magneticum AMB-1 combined with Ara-C by crosslinking of genipin (GP). The results showed that Ara-C could be bonded onto the membrane surface of BMs effectively through chemical crosslinking induced by dual hand reagents GP. The average diameters of BMs and Ara-C-coupled BMs (ABMs) were 42.0 ± 8.6 and 72.7 ± 6.0 nm respectively, and the zeta potentials (−38.1 ± 9.1) revealed that these systems were stable, confirming the stability of the system. The optimal encapsulation efficiency and drug loading were 89.05% ± 2.33% and 47.05% ± 0.64% respectively when crosslinking reaction lasted for 72 h. The system also presented long-term stability and release behaviors without initial burst release (Ara-C could be released 80% within three months). Our results indicate that BMs have great potential in biomedical and clinical fields as a novel anti-tumor drug carrier. Full article

(This article belongs to the Section Biomaterials)

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701 KiB

Open AccessReview

Nanoscale Design of Nano-Sized Particles in Shape-Memory Polymer Nanocomposites Driven by Electricity

by Haibao Lu, Wei Min Huang, Fei Liang and Kai Yu

Materials 2013, 6(9), 3742-3754; https://doi.org/10.3390/ma6093742 - 2 Sep 2013

Cited by 15 | Viewed by 6323

Abstract

In the last few years, we have witnessed significant progress in developing high performance shape memory polymer (SMP) nanocomposites, in particular, for shape recovery activated by indirect heating in the presence of electricity, magnetism, light, radio frequency, microwave and radiation, etc. In this [...] Read more.

In the last few years, we have witnessed significant progress in developing high performance shape memory polymer (SMP) nanocomposites, in particular, for shape recovery activated by indirect heating in the presence of electricity, magnetism, light, radio frequency, microwave and radiation, etc. In this paper, we critically review recent findings in Joule heating of SMP nanocomposites incorporated with nanosized conductive electromagnetic particles by means of nanoscale control via applying an electro- and/or magnetic field. A few different nanoscale design principles to form one-/two-/three- dimensional conductive networks are discussed. Full article

(This article belongs to the Section Advanced Composites)

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637 KiB

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Synthesis and Characterization of Encapsulated Nanosilica Particles with an Acrylic Copolymer by in Situ Emulsion Polymerization Using Thermoresponsive Nonionic Surfactant

by Mostafa Yazdimamaghani, Tannaz Pourvala, Elaheh Motamedi, Babak Fathi, Daryoosh Vashaee and Lobat Tayebi

Materials 2013, 6(9), 3727-3741; https://doi.org/10.3390/ma6093727 - 28 Aug 2013

Cited by 81 | Viewed by 13614

Abstract

Nanocomposites of encapsulated silica nanoparticles were prepared by in situ emulsion polymerization of acrylate monomers. The synthesized material showed good uniformity and dispersion of the inorganic components in the base polymer, which enhances the properties of the nanocomposite material. A nonionic surfactant with [...] Read more.

Nanocomposites of encapsulated silica nanoparticles were prepared by in situ emulsion polymerization of acrylate monomers. The synthesized material showed good uniformity and dispersion of the inorganic components in the base polymer, which enhances the properties of the nanocomposite material. A nonionic surfactant with lower critical solution temperature (LCST) was used to encapsulate the silica nanoparticles in the acrylic copolymer matrix. This in situ method combined the surface modification and the encapsulation in a single pot, which greatly simplified the process compared with other conventional methods requiring separate processing steps. The morphology of the encapsulated nanosilica particles was investigated by dynamic light scattering (DLS) and transmission electron microscopy (TEM), which confirmed the uniform distribution of the nanoparticles without any agglomerations. A neat copolymer was also prepared as a control sample. Both the neat copolymer and the prepared nanocomposite were characterized by Fourier transform infrared spectroscopy (FTIR), thermal gravimetric analyses (TGA), dynamic mechanical thermal analysis (DMTA) and the flame resistance test. Due to the uniform dispersion of the non-agglomerated nanoparticles in the matrix of the polymer, TGA and flame resistance test results showed remarkably improved thermal stability. Furthermore, DMTA results demonstrated an enhanced storage modulus of the nanocomposite samples compared with that of the neat copolymer, indicating its superior mechanical properties. Full article

(This article belongs to the Section Advanced Composites)

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Materials, Volume 6, Issue 9 (September 2013) – 33 articles , Pages 3676-4283

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