Materials

6498 KiB

Open AccessArticle

Giant Strain and Induced Ferroelectricity in Amorphous BaTiO₃ Films under Poling

by Pegah Mirzadeh Vaghefi, Ali Baghizadeh, Armando A.C.S. Lourenço, Vitor S. Amaral and Andre L. Kholkin

Materials 2017, 10(9), 1107; https://doi.org/10.3390/ma10091107 - 20 Sep 2017

Cited by 3 | Viewed by 4291

Abstract

We report an effect of giant surface modification of a 5.6 nm thick BaTiO₃ film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under [...] Read more.

We report an effect of giant surface modification of a 5.6 nm thick BaTiO₃ film grown on Si (100) substrate under poling by conductive tip of a scanning probe microscope (SPM). The surface can be locally elevated by about 9 nm under −20 V applied during scanning, resulting in the maximum strain of 160%. The threshold voltage for the surface modification is about 12 V. The modified topography is stable enough with time and slowly decays after poling with the rate ~0.02 nm/min. Strong vertical piezoresponse after poling is observed, too. Combined measurements by SPM and piezoresponse force microscopy (PFM) prove that the poled material develops high ferroelectric polarization that cannot be switched back even under an oppositely oriented electric field. The topography modification is hypothesized to be due to a strong Joule heating and concomitant interface reaction between underlying Si and BaTiO₃. The top layer is supposed to become ferroelectric as a result of local crystallization of amorphous BaTiO₃. This work opens up new possibilities to form nanoscale ferroelectric structures useful for various applications. Full article

(This article belongs to the Special Issue Scanning Probe Microscopy of Ferroics)

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Graphical abstract

5779 KiB

Open AccessArticle

Microstructural Investigation of Heat-Treated Ultra-High Performance Concrete for Optimum Production

by Sung-Hoon Kang, Ji-Hyung Lee, Sung-Gul Hong and Juhyuk Moon

Materials 2017, 10(9), 1106; https://doi.org/10.3390/ma10091106 - 20 Sep 2017

Cited by 81 | Viewed by 6686

Abstract

For optimum production of ultra-high performance concrete (UHPC), the material and microstructural properties of UHPC cured under various heat treatment (HT) conditions are studied. The effects of HT temperature and duration on the hydration reaction, microstructure, and mechanical properties of UHPC are investigated. [...] Read more.

For optimum production of ultra-high performance concrete (UHPC), the material and microstructural properties of UHPC cured under various heat treatment (HT) conditions are studied. The effects of HT temperature and duration on the hydration reaction, microstructure, and mechanical properties of UHPC are investigated. Increasing HT temperature accelerates both cement hydration and pozzolanic reaction, but the latter is more significantly affected. This accelerated pozzolanic reaction in UHPC clearly enhances compressive strength. However, strength after the HT becomes stable as most of the hydration finishes during the HT period. Particularly, it was concluded that the mechanical benefit of the increased temperature and duration on the 28 day-strength is not noticeable when the HT temperature is above 60 °C (with a 48 h duration) or the HT duration is longer than 12 h (with 90 °C temperature). On the other hand, even with a minimal HT condition such as 1 day at 60 °C or 12 h at 90 °C, outstanding compressive strength of 179 MPa and flexural tensile strength of 49 MPa are achieved at 28 days. Microstructural investigation conducted herein suggests that portlandite content can be a good indicator for the mechanical performance of UHPC regardless of its HT curing conditions. These findings can contribute to reducing manufacturing energy consumption, cost, and environmental impact in the production of UHPC and be helpful for practitioners to better understand the effect of HT on UHPC and optimize its production. Full article

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59767 KiB

Open AccessArticle

Nanocrystalline Al7075 + 1 wt % Zr Alloy Prepared Using Mechanical Milling and Spark Plasma Sintering

by Orsolya Molnárová, Přemysl Málek, Jozef Veselý, Michaela Šlapáková, Peter Minárik, František Lukáč, Tomáš Chráska, Pavel Novák and Filip Průša

Materials 2017, 10(9), 1105; https://doi.org/10.3390/ma10091105 - 20 Sep 2017

Cited by 6 | Viewed by 5866

Abstract

The microstructure, phase composition, and microhardness of both gas-atomized and mechanically milled powders of the Al7075 + 1 wt % Zr alloy were investigated. The gas-atomized powder exhibited a cellular microstructure (grain size of a few µm) with layers of intermetallic phases along [...] Read more.

The microstructure, phase composition, and microhardness of both gas-atomized and mechanically milled powders of the Al7075 + 1 wt % Zr alloy were investigated. The gas-atomized powder exhibited a cellular microstructure (grain size of a few µm) with layers of intermetallic phases along the cell boundaries. Mechanical milling (400 revolutions per minute (RPM)/8 h) resulted in a grain size reduction to the nanocrystalline range (20 to 100 nm) along with the dissolution of the intermetallic phases. Milling led to an increase in the powder’s microhardness from 97 to 343 HV. Compacts prepared by spark plasma sintering (SPS) exhibited negligible porosity. The grain size of the originally gas-atomized material was retained, but the continuous layers of intermetallic phases were replaced by individual particles. Recrystallization led to a grain size increase to 365 nm in the SPS compact prepared from the originally milled powder. Small precipitates of the Al₃Zr phase were observed in the SPS compacts, and they are believed to be responsible for the retainment of the sub-microcrystalline microstructure during SPS. A more intensive precipitation in this SPS compact can be attributed to a faster diffusion due to a high density of dislocations and grain boundaries in the milled powder. Full article

(This article belongs to the Section Advanced Materials Characterization)

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4269 KiB

Open AccessFeature PaperArticle

A Method for Medical Diagnosis Based on Optical Fluence Rate Distribution at Tissue Surface

by Omnia Hamdy, Jala El-Azab, Tarek A. Al-Saeed, Mahmoud F. Hassan and Nahed H. Solouma

Materials 2017, 10(9), 1104; https://doi.org/10.3390/ma10091104 - 20 Sep 2017

Cited by 33 | Viewed by 5704

Abstract

Optical differentiation is a promising tool in biomedical diagnosis mainly because of its safety. The optical parameters’ values of biological tissues differ according to the histopathology of the tissue and hence could be used for differentiation. The optical fluence rate distribution on tissue [...] Read more.

Optical differentiation is a promising tool in biomedical diagnosis mainly because of its safety. The optical parameters’ values of biological tissues differ according to the histopathology of the tissue and hence could be used for differentiation. The optical fluence rate distribution on tissue boundaries depends on the optical parameters. So, providing image displays of such distributions can provide a visual means of biomedical diagnosis. In this work, an experimental setup was implemented to measure the spatially-resolved steady state diffuse reflectance and transmittance of native and coagulated chicken liver and native and boiled breast chicken skin at 635 and 808 nm wavelengths laser irradiation. With the measured values, the optical parameters of the samples were calculated in vitro using a combination of modified Kubelka-Munk model and Bouguer-Beer-Lambert law. The estimated optical parameters values were substituted in the diffusion equation to simulate the fluence rate at the tissue surface using the finite element method. Results were verified with Monte-Carlo simulation. The results obtained showed that the diffuse reflectance curves and fluence rate distribution images can provide discrimination tools between different tissue types and hence can be used for biomedical diagnosis. Full article

(This article belongs to the Special Issue Laser in Nanotechnology and Biomedical Applications)

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9217 KiB

Open AccessArticle

Superplastic Deformation Mechanisms of Superfine/Nanocrystalline Duplex PM-TiAl-Based Alloy

by Xuebo Gong, Zhenxin Duan, Wen Pei and Hua Chen

Materials 2017, 10(9), 1103; https://doi.org/10.3390/ma10091103 - 19 Sep 2017

Cited by 9 | Viewed by 4339

Abstract

In this paper, the equiaxed superfine/nanocrystalline duplex PM-TiAl-based alloy with (γ + α₂) microstructure, Ti-45Al-5Nb (at %), has been synthesized by high-energy ball milling and vacuum hot pressing sintering. Superplastic deformation behavior has been investigated at 1000 °C and 1050 °C [...] Read more.

In this paper, the equiaxed superfine/nanocrystalline duplex PM-TiAl-based alloy with (γ + α₂) microstructure, Ti-45Al-5Nb (at %), has been synthesized by high-energy ball milling and vacuum hot pressing sintering. Superplastic deformation behavior has been investigated at 1000 °C and 1050 °C with strain rates from 5 × 10⁻⁵ s⁻¹ to 1 × 10⁻³ s⁻¹. The effects of deformation on the microstructure and mechanical behaviors of high Nb containing TiAl alloy have been characterized and analyzed. The results showed that, the ultimate tensile strength of the alloy was 58.7 MPa at 1000 °C and 10.5 MPa at 1050 °C with a strain rate of 5 × 10⁻⁵ s⁻¹, while the elongation was 121% and 233%, respectively. The alloy exhibited superplastic elongation at 1000 and 1050 °C with an exponent (m) of 0.48 and 0.45. The main softening mechanism was dynamic recrystallization of γ grains; the dislocation slip and γ/γ interface twinning were responsible for superplastic deformation. The orientation relationship of γ/γ interface twinning obeyed the classical one: (001)_γ//(110)_γ. Full article

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3280 KiB

Open AccessArticle

Modification of 13X Molecular Sieve by Chitosan for Adsorptive Removal of Cadmium from Simulated Wastewater

by Yan Shi, Ken Sun, Lixin Huo, Xiuxiu Li, Xuebin Qi and Zhaohui Li

Materials 2017, 10(9), 1101; https://doi.org/10.3390/ma10091101 - 19 Sep 2017

Cited by 8 | Viewed by 4479

Abstract

Chitosan was used to modify a 13X molecular sieve to improve its cadmium removal capability. After being modified with 2% chitosan-acetate for 2 h at 30 °C, significant uptake of Cd²⁺ could be achieved. The uptake of Cd²⁺ on the modified [...] Read more.

Chitosan was used to modify a 13X molecular sieve to improve its cadmium removal capability. After being modified with 2% chitosan-acetate for 2 h at 30 °C, significant uptake of Cd²⁺ could be achieved. The uptake of Cd²⁺ on the modified 13X molecular sieve followed the Langmuir isotherms with a capacity of 1 mg/g. The kinetics of Cd²⁺ removal by modified 13X molecular sieve followed a pseudo second-order reaction, suggesting chemisorption or surface complexation. The Cd²⁺ removal with a sorbent dose of 2 g/L from an initial concentration of 100 μg/L reached more than 95% in 90 min. The equilibrium Cd²⁺ concentration was <5 μg/L, which meets the requirements of “Standards for Irrigation Water Quality” (GB5084-2005) (10 μg/L) and MCL and MCLG for groundwater and drinking water (5 μg/L) set by United States Environmental Protection Agency. Full article

(This article belongs to the Special Issue Advances in Pillared Clays and Similar Materials: Synthesis, Characterization and Applications)

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4591 KiB

Open AccessArticle

Precipitation Behavior and Quenching Sensitivity of a Spray Deposited Al-Zn-Mg-Cu-Zr Alloy

by Xiaofei Sheng, Qian Lei, Zhu Xiao and Mingpu Wang

Materials 2017, 10(9), 1100; https://doi.org/10.3390/ma10091100 - 19 Sep 2017

Cited by 12 | Viewed by 5099

Abstract

Precipitation behavior and the quenching sensitivity of a spray deposited Al-Zn-Mg-Cu-Zr alloy during isothermal heat treatment have been studied systematically. Results demonstrate that both the hardness and the ultimate tensile strength of the studied alloy decreased with the isothermal treatment time at certain [...] Read more.

Precipitation behavior and the quenching sensitivity of a spray deposited Al-Zn-Mg-Cu-Zr alloy during isothermal heat treatment have been studied systematically. Results demonstrate that both the hardness and the ultimate tensile strength of the studied alloy decreased with the isothermal treatment time at certain temperatures. More notably, the hardness decreases rapidly after the isothermal heat treatment. During isothermal heat treatment processing, precipitates readily nucleated in the medium-temperature zone (250–400 °C), while the precipitation nucleation was scarce in the low-temperature zone (<250 °C) and in the high-temperature zone (>400 °C). Precipitates with sizes of less than ten nanometers would contribute a significant increase in yield strength, while the ones with a larger size than 300 nm would contribute little strengthening effect. Quenching sensitivity is high in the medium-temperature zone (250–400 °C), and corresponding time-temperature-property (TTP) curves of the studied alloy have been established. Full article

(This article belongs to the Section Advanced Materials Characterization)

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5107 KiB

Open AccessArticle

Strengthening of Existing Bridge Structures for Shear and Bending with Carbon Textile-Reinforced Mortar

by Martin Herbrand, Viviane Adam, Martin Classen, Dominik Kueres and Josef Hegger

Materials 2017, 10(9), 1099; https://doi.org/10.3390/ma10091099 - 19 Sep 2017

Cited by 57 | Viewed by 7166

Abstract

Increasing traffic loads and changes in code provisions lead to deficits in shear and flexural capacity of many existing highway bridges. Therefore, a large number of structures are expected to require refurbishment and strengthening in the future. This projection is based on the [...] Read more.

Increasing traffic loads and changes in code provisions lead to deficits in shear and flexural capacity of many existing highway bridges. Therefore, a large number of structures are expected to require refurbishment and strengthening in the future. This projection is based on the current condition of many older road bridges. Different strengthening methods for bridges exist to extend their service life, all having specific advantages and disadvantages. By applying a thin layer of carbon textile-reinforced mortar (CTRM) to bridge deck slabs and the webs of pre-stressed concrete bridges, the fatigue and ultimate strength of these members can be increased significantly. The CTRM layer is a combination of a corrosion resistant carbon fiber reinforced polymer (CFRP) fabric and an efficient mortar. In this paper, the strengthening method and the experimental results obtained at RWTH Aachen University are presented. Full article

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5933 KiB

Open AccessArticle

On the Role of Processing Parameters in Producing Recycled Aluminum AA6061 Based Metal Matrix Composite (MMC-Al_R) Prepared Using Hot Press Forging (HPF) Process

by Azlan Ahmad, Mohd Amri Lajis and Nur Kamilah Yusuf

Materials 2017, 10(9), 1098; https://doi.org/10.3390/ma10091098 - 19 Sep 2017

Cited by 23 | Viewed by 7745

Abstract

Solid-state recycling, which involves the direct recycling of scrap metal into bulk material using severe plastic deformation, has emerged as a potential alternative to the conventional remelting and recycling techniques. Hot press forging has been identified as a sustainable direct recycling technique that [...] Read more.

Solid-state recycling, which involves the direct recycling of scrap metal into bulk material using severe plastic deformation, has emerged as a potential alternative to the conventional remelting and recycling techniques. Hot press forging has been identified as a sustainable direct recycling technique that has fewer steps and maintains excellent material performance. An experimental investigation was conducted to explore the hardness and density of a recycled aluminum-based metal matrix composite by varying operating temperature and holding time. A mixture of recycled aluminum, AA6061, and aluminum oxide were simultaneously heated to 430, 480, and 530 °C and forged for 60, 90, and 120 min. We found a positive increase in microhardness and density for all composites. The hardness increased approximately 33.85%, while density improved by about 15.25% whenever the temperature or the holding time were increased. Based on qualitative analysis, the composite endures substantial plastic deformation due to the presence of hardness properties due to the aluminum oxide embedded in the aluminum matrix. These increases were significantly affected by the operating temperature; the holding time also had a subordinate role in enhancing the metal matrix composite properties. Furthermore, in an effort to curb the shortage of primary resources, this study reviewed the promising performance of secondary resources produced by using recycled aluminum and aluminum oxide as the base matrix and reinforcement constituent, respectively. This study is an outline for machining practitioners and the manufacturing industry to help increase industry sustainability with the aim of preserving the Earth for our community in the future. Full article

(This article belongs to the Special Issue Recycled Materials, Eco-design and 3D Printing)

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5107 KiB

Open AccessArticle

Towards an Ultrasonic Guided Wave Procedure for Health Monitoring of Composite Vessels: Application to Hydrogen-Powered Aircraft

by Slah Yaacoubi, Peter McKeon, Weina Ke, Nico F. Declercq and Fethi Dahmene

Materials 2017, 10(9), 1097; https://doi.org/10.3390/ma10091097 - 19 Sep 2017

Cited by 13 | Viewed by 5541

Abstract

This paper presents an overview and description of the approach to be used to investigate the behavior and the defect sensitivity of various ultrasonic guided wave (UGW) modes propagating specifically in composite cylindrical vessels in the framework of the safety of hydrogen energy [...] Read more.

This paper presents an overview and description of the approach to be used to investigate the behavior and the defect sensitivity of various ultrasonic guided wave (UGW) modes propagating specifically in composite cylindrical vessels in the framework of the safety of hydrogen energy transportation such as hydrogen-powered aircrafts. These structures which consist of thick and multi-layer composites are envisioned for housing hydrogen gas at high pressures. Due to safety concerns associated with a weakened structure, structural health monitoring techniques are needed. A procedure for optimizing damage detection in these structural types is presented. It is shown that a finite element method can help identify useful experimental parameters including frequency range, excitation type, and receiver placement. Full article

(This article belongs to the Special Issue Structural Health Monitoring for Aerospace Applications 2017)

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3090 KiB

Open AccessArticle

Can More Nanoparticles Induce Larger Viscosities of Nanoparticle-Enhanced Wormlike Micellar System (NEWMS)?

by Mingwei Zhao, Yue Zhang, Chenwei Zou, Caili Dai, Mingwei Gao, Yuyang Li, Wenjiao Lv, Jianfeng Jiang and Yining Wu

Materials 2017, 10(9), 1096; https://doi.org/10.3390/ma10091096 - 18 Sep 2017

Cited by 38 | Viewed by 5324

Abstract

There have been many reports about the thickening ability of nanoparticles on the wormlike micelles in the recent years. Through the addition of nanoparticles, the viscosity of wormlike micelles can be increased. There still exists a doubt: can viscosity be increased further by [...] Read more.

There have been many reports about the thickening ability of nanoparticles on the wormlike micelles in the recent years. Through the addition of nanoparticles, the viscosity of wormlike micelles can be increased. There still exists a doubt: can viscosity be increased further by adding more nanoparticles? To answer this issue, in this work, the effects of silica nanoparticles and temperature on the nanoparticles-enhanced wormlike micellar system (NEWMS) were studied. The typical wormlike micelles (wormlike micelles) are prepared by 50 mM cetyltrimethyl ammonium bromide (CTAB) and 60 mM sodium salicylate (NaSal). The rheological results show the increase of viscoelasticity in NEWMS by adding nanoparticles, with the increase of zero-shear viscosity and relaxation time. However, with the further increase of nanoparticles, an interesting phenomenon appears. The zero-shear viscosity and relaxation time reach the maximum and begin to decrease. The results show a slight increasing trend for the contour length of wormlike micelles by adding nanoparticles, while no obvious effect on the entanglement and mesh size. In addition, with the increase of temperature, remarkable reduction of contour length and relaxation time can be observed from the calculation. NEWMS constantly retain better viscoelasticity compared with conventional wormlike micelles without silica nanoparticles. According to the Arrhenius equation, the activation energy E_a shows the same increase trend of NEWMS. Finally, a mechanism is proposed to explain this interesting phenomenon. Full article

(This article belongs to the Section Advanced Materials Characterization)

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6127 KiB

Open AccessFeature PaperReview

Carrier Multiplication Mechanisms and Competing Processes in Colloidal Semiconductor Nanostructures

by Stephen V. Kershaw and Andrey L. Rogach

Materials 2017, 10(9), 1095; https://doi.org/10.3390/ma10091095 - 18 Sep 2017

Cited by 23 | Viewed by 7522

Abstract

Quantum confined semiconductor nanoparticles, such as colloidal quantum dots, nanorods and nanoplatelets have broad extended absorption spectra at energies above their bandgaps. This means that they can absorb light at high photon energies leading to the formation of hot excitons with finite excited [...] Read more.

Quantum confined semiconductor nanoparticles, such as colloidal quantum dots, nanorods and nanoplatelets have broad extended absorption spectra at energies above their bandgaps. This means that they can absorb light at high photon energies leading to the formation of hot excitons with finite excited state lifetimes. During their existence, the hot electron and hole that comprise the exciton may start to cool as they relax to the band edge by phonon mediated or Auger cooling processes or a combination of these. Alongside these cooling processes, there is the possibility that the hot exciton may split into two or more lower energy excitons in what is termed carrier multiplication (CM). The fission of the hot exciton to form lower energy multiexcitons is in direct competition with the cooling processes, with the timescales for multiplication and cooling often overlapping strongly in many materials. Once CM has been achieved, the next challenge is to preserve the multiexcitons long enough to make use of the bonus carriers in the face of another competing process, non-radiative Auger recombination. However, it has been found that Auger recombination and the several possible cooling processes can be manipulated and usefully suppressed or retarded by engineering the nanoparticle shape, size or composition and by the use of heterostructures, along with different choices of surface treatments. This review surveys some of the work that has led to an understanding of the rich carrier dynamics in semiconductor nanoparticles, and that has started to guide materials researchers to nanostructures that can tilt the balance in favour of efficient CM with sustained multiexciton lifetimes. Full article

(This article belongs to the Special Issue Colloidal Quantum Dots)

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1853 KiB

Open AccessArticle

Expanding the Applicability of Poly(Ionic Liquids) in Solid Phase Microextraction: Pyrrolidinium Coatings

by David J. S. Patinha, Liliana C. Tomé, Mehmet Isik, David Mecerreyes, Armando J. D. Silvestre and Isabel M. Marrucho

Materials 2017, 10(9), 1094; https://doi.org/10.3390/ma10091094 - 18 Sep 2017

Cited by 15 | Viewed by 4555

Abstract

Crosslinked pyrrolidinium-based poly(ionic liquids) (Pyrr-PILs) were synthesized through a fast, simple, and solventless photopolymerization scheme, and tested as solid phase microextraction (SPME) sorbents. A series of Pyrr-PILs bearing three different alkyl side chain lengths with two, eight, and fourteen carbons was prepared, characterized, [...] Read more.

Crosslinked pyrrolidinium-based poly(ionic liquids) (Pyrr-PILs) were synthesized through a fast, simple, and solventless photopolymerization scheme, and tested as solid phase microextraction (SPME) sorbents. A series of Pyrr-PILs bearing three different alkyl side chain lengths with two, eight, and fourteen carbons was prepared, characterized, and homogeneously coated on a steel wire by using a very simple procedure. The resulting coatings showed a high thermal stability, with decomposition temperatures above 350 °C, excellent film stability, and lifetime of over 100 injections. The performance of these PIL-based SPME fibers was evaluated using a mixture of eleven organic compounds with different molar volumes and chemical functionalities (alcohols, ketones, and monoterpenes). The Pyrr-PIL fibers were obtained as dense film coatings, with 67 μm thickness, with an overall sorption increase of 90% and 55% as compared to commercial fibers of Polyacrylate (85 μm) (PA85) and Polydimethylsiloxane (7 μm) (PDMS7) coatings, respectively. A urine sample doped with the sample mixture was used to study the matrix effect and establish relative recoveries, which ranged from 60.2% to 104.1%. Full article

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1562 KiB

Open AccessArticle

Large Electrocaloric Effect in Lead-Free (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ Ceramics Prepared via Citrate Route

by Jing Shi, Rongfeng Zhu, Xing Liu, Bijun Fang, Ningyi Yuan, Jianning Ding and Haosu Luo

Materials 2017, 10(9), 1093; https://doi.org/10.3390/ma10091093 - 18 Sep 2017

Cited by 33 | Viewed by 5377

Abstract

The 1 wt % Li-doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT-Li) ceramics prepared by the citrate method exhibit improved phase purity, densification and electrical properties, which provide prospective possibility to develop high-performance electrocaloric materials. The electrocaloric effect was [...] Read more.

The 1 wt % Li-doped (Ba_0.85Ca_0.15)(Zr_0.1Ti_0.9)O₃ (BCZT-Li) ceramics prepared by the citrate method exhibit improved phase purity, densification and electrical properties, which provide prospective possibility to develop high-performance electrocaloric materials. The electrocaloric effect was evaluated by phenomenological method, and the BCZT-Li ceramics present large electrocaloric temperature change ∆T, especially large electrocaloric responsibility ξ = ∆T_max/∆E_max, which can be comparable to the largest values reported in the lead-free piezoelectric ceramics. The excellent electrocaloric effect is considered as correlating with the coexistence of polymorphic ferroelectric phases, which are detected by the Raman spectroscopy. The large ξ value accompanied by decreased Curie temperature (around 73 °C) of the BCZT-Li ceramics prepared by the citrate method presents potential applications as the next-generation solid-state cooling devices. Full article

(This article belongs to the Section Energy Materials)

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2256 KiB

Open AccessFeature PaperArticle

N-Doped Carbon Xerogels as Pt Support for the Electro-Reduction of Oxygen

by Cinthia Alegre, David Sebastián, María E. Gálvez, Estela Baquedano, Rafael Moliner, Antonino S. Aricò, Vincenzo Baglio and María J. Lázaro

Materials 2017, 10(9), 1092; https://doi.org/10.3390/ma10091092 - 17 Sep 2017

Cited by 30 | Viewed by 5918

Abstract

Durability and limited catalytic activity are key impediments to the commercialization of polymer electrolyte fuel cells. Carbon materials employed as catalyst support can be doped with different heteroatoms, like nitrogen, to improve both catalytic activity and durability. Carbon xerogels are nanoporous carbons that [...] Read more.

Durability and limited catalytic activity are key impediments to the commercialization of polymer electrolyte fuel cells. Carbon materials employed as catalyst support can be doped with different heteroatoms, like nitrogen, to improve both catalytic activity and durability. Carbon xerogels are nanoporous carbons that can be easily synthesized in order to obtain N-doped materials. In the present work, we introduced melamine as a carbon xerogel precursor together with resorcinol for an effective in-situ N doping (3–4 wt % N). Pt nanoparticles were supported on nitrogen-doped carbon xerogels and their activity for the oxygen reduction reaction (ORR) was evaluated in acid media along with their stability. Results provide new evidences of the type of N groups aiding the activity of Pt for the ORR and of a remarkable stability for N-doped carbon-supported Pt catalysts, providing appropriate physico-chemical features. Full article

(This article belongs to the Special Issue Advanced Materials in Polymer Electrolyte Fuel Cells)

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32700 KiB

Open AccessArticle

Effects of Pulse Parameters on Weld Microstructure and Mechanical Properties of Extra Pulse Current Aided Laser Welded 2219 Aluminum Alloy Joints

by Xinge Zhang, Liqun Li, Yanbin Chen, Zhaojun Yang, Yanli Chen and Xinjian Guo

Materials 2017, 10(9), 1091; https://doi.org/10.3390/ma10091091 - 15 Sep 2017

Cited by 16 | Viewed by 5791

Abstract

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The [...] Read more.

In order to expand the application range of laser welding and improve weld quality, an extra pulse current was used to aid laser-welded 2219 aluminum alloy, and the effects of pulse current parameters on the weld microstructure and mechanical properties were investigated. The effect mechanisms of the pulse current interactions with the weld pool were evaluated. The results indicated that the coarse dendritic structure in the weld zone changed to a fine equiaxed structure using an extra pulse current, and the pulse parameters, including medium peak current, relatively high pulse frequency, and low pulse duty ratio benefited to improving the weld structure. The effect mechanisms of the pulse current were mainly ascribed to the magnetic pinch effect, thermal effect, and electromigration effect caused by the pulse current. The effect of the pulse parameters on the mechanical properties of welded joints were consistent with that of the weld microstructure. The tensile strength and elongation of the optimal pulse current-aided laser-welded joint increased by 16.4% and 105%, respectively, compared with autogenous laser welding. Full article

(This article belongs to the Special Issue Laser Materials Processing)

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4174 KiB

Open AccessCommunication

Enhanced Interface Structure and Properties of Titanium Carbonitride-Based Cermets with the Extra Solid Phase Reaction

by Nan Lin, Yuehui He and Xiyue Kang

Materials 2017, 10(9), 1090; https://doi.org/10.3390/ma10091090 - 15 Sep 2017

Cited by 14 | Viewed by 5806

Abstract

In this paper, the influence of the extra solid phase reaction on the interface structure and mechanical properties of titanium carbonitride-based cermets were investigated. The extra solid phase reaction in the preparation process of cermets could induce the formation of a core/rim/binder interface [...] Read more.

In this paper, the influence of the extra solid phase reaction on the interface structure and mechanical properties of titanium carbonitride-based cermets were investigated. The extra solid phase reaction in the preparation process of cermets could induce the formation of a core/rim/binder interface with the coherent structure and reinforce the interface bonding strength in cermets. The existence of a coherent structure interface can inhibit crack spread and improve the toughness and abrasion resistance of titanium carbonitride-based cermets significantly. Cermets can exhibit the high hardness Rockwell Hardness A (HRA) 92.3, fracture toughness of 11.6 MPa·m^1/2, and transverse rupture strength of 2810 MPa. Full article

(This article belongs to the Section Advanced Materials Characterization)

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15465 KiB

Open AccessArticle

Dynamic Recrystallization of the Constituent γ Phase and Mechanical Properties of Ti-43Al-9V-0.2Y Alloy Sheet

by Yu Zhang, Xiaopeng Wang, Fantao Kong and Yuyong Chen

Materials 2017, 10(9), 1089; https://doi.org/10.3390/ma10091089 - 15 Sep 2017

Cited by 11 | Viewed by 4562

Abstract

A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The [...] Read more.

A crack-free Ti-43Al-9V-0.2Y alloy sheet was successfully fabricated via hot-pack rolling at 1200 °C. After hot-rolling, the β/γ lamellar microstructure of the as-forged TiAl alloy was completely converted into a homogeneous duplex microstructure with an average γ grain size of 10.5 μm. The dynamic recrystallization (DRX) of the γ phase was systematically investigated. A recrystallization fraction of 62.5% was obtained for the γ phase in the TiAl alloy sheet, when a threshold value of 0.8° was applied to the distribution of grain orientation spread (GOS) values. The high strain rate and high stress associated with hot-rolling are conducive for discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX), respectively. A certain high-angle boundary (HAGB: θ = 89° ± 3°<100>), which is associated with DDRX, occurs in both the recrystallized and deformed γ grains. The twin boundaries play an important role in the DDRX of the γ phase. Additionally, the sub-structures and sub-boundaries originating from low-angle boundaries in the deformed grains also indicate that CDRX occurs. The mechanical properties of the alloy sheet were determined at both room and elevated temperatures. At 750 °C, the alloy sheet exhibited excellent elongation (53%), corresponding to a failure strength of 467 MPa. Full article

(This article belongs to the Section Advanced Materials Characterization)

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3548 KiB

Open AccessArticle

Multi-Aperture Shower Design for the Improvement of the Transverse Uniformity of MOCVD-Derived GdYBCO Films

by Ruipeng Zhao, Qing Liu, Yudong Xia, Fei Zhang, Yuming Lu, Chuanbing Cai, Bowan Tao and Yanrong Li

Materials 2017, 10(9), 1088; https://doi.org/10.3390/ma10091088 - 15 Sep 2017

Cited by 7 | Viewed by 4094

Abstract

A multi-aperture shower design is reported to improve the transverse uniformity of GdYBCO superconducting films on the template of sputtered-LaMnO₃/epitaxial-MgO/IBAD-MgO/solution deposition planarization (SDP)-Y₂O₃-buffered Hastelloy tapes. The GdYBCO films were prepared by the metal organic chemical vapor deposition [...] Read more.

A multi-aperture shower design is reported to improve the transverse uniformity of GdYBCO superconducting films on the template of sputtered-LaMnO₃/epitaxial-MgO/IBAD-MgO/solution deposition planarization (SDP)-Y₂O₃-buffered Hastelloy tapes. The GdYBCO films were prepared by the metal organic chemical vapor deposition (MOCVD) process. The transverse uniformities of structure, morphology, thickness, and performance were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), step profiler, and the standard four-probe method using the criteria of 1 μV/cm, respectively. Through adopting the multi-aperture shower instead of the slit shower, measurement by step profiler revealed that the thickness difference between the middle and the edges based on the slit shower design was well eliminated. Characterization by SEM showed that a GdYBCO film with a smooth surface was successfully prepared. Moreover, the transport critical current density (J_c) of its middle and edge positions at 77 K and self-field were found to be over 5 MA/cm² through adopting the micro-bridge four-probe method. Full article

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Open AccessFeature PaperReview

Hole-Transporting Materials for Printable Perovskite Solar Cells

by Paola Vivo, Jagadish K. Salunke and Arri Priimagi

Materials 2017, 10(9), 1087; https://doi.org/10.3390/ma10091087 - 15 Sep 2017

Cited by 101 | Viewed by 16056

Abstract

Perovskite solar cells (PSCs) represent undoubtedly the most significant breakthrough in photovoltaic technology since the 1970s, with an increase in their power conversion efficiency from less than 5% to over 22% in just a few years. Hole-transporting materials (HTMs) are an essential building [...] Read more.

Perovskite solar cells (PSCs) represent undoubtedly the most significant breakthrough in photovoltaic technology since the 1970s, with an increase in their power conversion efficiency from less than 5% to over 22% in just a few years. Hole-transporting materials (HTMs) are an essential building block of PSC architectures. Currently, 2,2’,7,7’-tetrakis-(N,N’-di-p-methoxyphenylamine)-9,9’-spirobifluorene), better known as spiro-OMeTAD, is the most widely-used HTM to obtain high-efficiency devices. However, it is a tremendously expensive material with mediocre hole carrier mobility. To ensure wide-scale application of PSC-based technologies, alternative HTMs are being proposed. Solution-processable HTMs are crucial to develop inexpensive, high-throughput and printable large-area PSCs. In this review, we present the most recent advances in the design and development of different types of HTMs, with a particular focus on mesoscopic PSCs. Finally, we outline possible future research directions for further optimization of the HTMs to achieve low-cost, stable and large-area PSCs. Full article

(This article belongs to the Special Issue Highly Ordered Organic Thin Films)

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2420 KiB

Open AccessArticle

Impact of Source and Manufacturing of Collagen Matrices on Fibroblast Cell Growth and Platelet Aggregation

by Stefanie Böhm, Christine Strauß, Stefan Stoiber, Cornelia Kasper and Verena Charwat

Materials 2017, 10(9), 1086; https://doi.org/10.3390/ma10091086 - 15 Sep 2017

Cited by 31 | Viewed by 6828

Abstract

Collagen is a main component of the extracellular matrix. It is often used in medical applications to support tissue regeneration, hemostasis, or wound healing. Due to different sources of collagen, the properties and performance of available products can vary significantly. In this in [...] Read more.

Collagen is a main component of the extracellular matrix. It is often used in medical applications to support tissue regeneration, hemostasis, or wound healing. Due to different sources of collagen, the properties and performance of available products can vary significantly. In this in vitro study, a comparison of seven different collagen matrices derived from bovine, equine, and porcine sources was performed. As performance indicators, the scaffold function for fibroblasts and platelet aggregation were used. We found strong variation in platelet aggregation and fibroblast growth on the different collagen materials. The observed variations could not be attributed to species differences alone, but were highly dependent on differences in the manufacturing process. Full article

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Open AccessFeature PaperArticle

Enhanced Plasmonic Wavelength Selective Infrared Emission Combined with Microheater

by Hiroki Ishihara, Katsuya Masuno, Makoto Ishii, Shinya Kumagai and Minoru Sasaki

Materials 2017, 10(9), 1085; https://doi.org/10.3390/ma10091085 - 14 Sep 2017

Cited by 2 | Viewed by 4825

Abstract

The indirect wavelength selective thermal emitter that we have proposed is constructed using a new microheater, demonstrating the enhancement of the emission peak generated by the surface plasmon polariton. The thermal isolation is improved using a 2 μm-thick Si membrane having 3.6 and [...] Read more.

The indirect wavelength selective thermal emitter that we have proposed is constructed using a new microheater, demonstrating the enhancement of the emission peak generated by the surface plasmon polariton. The thermal isolation is improved using a 2 μm-thick Si membrane having 3.6 and 5.4 mm outer diameter. The emission at around the wavelength of the absorption band of CO₂ gas is enhanced. The absorption signal increases, confirming the suitability for gas sensing. Against input power, the intensity at the peak wavelength shows a steeper increasing ratio than the background intensity. The microheater with higher thermal isolation gives larger peak intensity and its increasing ratio against the input power. Full article

(This article belongs to the Special Issue Advance in Plasmonics and Metamaterials)

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Open AccessArticle

Multiple Fatigue Failure Behaviors and Long-Life Prediction Approach of Carburized Cr-Ni Steel with Variable Stress Ratio

by Hailong Deng, Wei Li, Hongqiao Zhao and Tatsuo Sakai

Materials 2017, 10(9), 1084; https://doi.org/10.3390/ma10091084 - 14 Sep 2017

Cited by 16 | Viewed by 5505

Abstract

Axial loading tests with stress ratios R of −1, 0 and 0.3 were performed to examine the fatigue failure behavior of a carburized Cr-Ni steel in the long-life regime from 10⁴ to 10⁸ cycles. Results show that this steel represents continuously [...] Read more.

Axial loading tests with stress ratios R of −1, 0 and 0.3 were performed to examine the fatigue failure behavior of a carburized Cr-Ni steel in the long-life regime from 10⁴ to 10⁸ cycles. Results show that this steel represents continuously descending S-N characteristics with interior inclusion-induced failure under R = −1, whereas it shows duplex S-N characteristics with surface defect-induced failure and interior inclusion-induced failure under R = 0 and 0.3. The increasing tension eliminates the effect of compressive residual stress and promotes crack initiation from the surface or interior defects in the carburized layer. The FGA (fine granular area) formation greatly depends on the number of loading cycles, but can be inhibited by decreasing the compressive stress. Based on the evaluation of the stress intensity factor at the crack tip, the surface and interior failures in the short life regime can be characterized by the crack growth process, while the interior failure with the FGA in the long life regime can be characterized by the crack initiation process. In view of the good agreement between predicted and experimental results, the proposed approach can be well utilized to predict fatigue lives associated with interior inclusion-FGA-fisheye induced failure, interior inclusion-fisheye induced failure, and surface defect induced failure. Full article

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Open AccessArticle

Shape Memory Polyurethane Materials Containing Ferromagnetic Iron Oxide and Graphene Nanoplatelets

by Magdalena Urban and Michał Strankowski

Materials 2017, 10(9), 1083; https://doi.org/10.3390/ma10091083 - 14 Sep 2017

Cited by 31 | Viewed by 6747

Abstract

Intelligent materials, such as memory shape polymers, have attracted considerable attention due to wide range of possible applications. Currently, intensive research is underway, in matters of obtaining memory shape materials that can be actuated via inductive methods, for example with help of magnetic [...] Read more.

Intelligent materials, such as memory shape polymers, have attracted considerable attention due to wide range of possible applications. Currently, intensive research is underway, in matters of obtaining memory shape materials that can be actuated via inductive methods, for example with help of magnetic field. In this work, an attempt was made to develop a new polymer composite—polyurethane modified with graphene nanoplates and ferromagnetic iron oxides—with improved mechanical properties and introduced magnetic and memory shape properties. Based on the conducted literature review, gathered data were compared to the results of similar materials. Obtained materials were tested for their thermal, rheological, mechanical and shape memory properties. Structure of both fillers and composites were also analyzed using various spectroscopic methods. The addition of fillers to the polyurethane matrix improved the mechanical and shape memory properties, without having a noticeable impact on thermal properties. As it was expected, the high content of fillers caused a significant change in viscosity of filled prepolymers (during the synthesis stage). Each of the studied composites showed better mechanical properties than the unmodified polyurethanes. The addition of magnetic particles introduced additional properties to the composite, which could significantly expand the functionality of the materials developed in this work. Full article

(This article belongs to the Special Issue Improving Performance of Nanocomposite Materials)

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Open AccessArticle

Bonding Behavior of Deformed Steel Rebars in Sustainable Concrete Containing both Fine and Coarse Recycled Aggregates

by Sun-Woo Kim, Wan-Shin Park, Young-Il Jang, Seok-Joon Jang and Hyun-Do Yun

Materials 2017, 10(9), 1082; https://doi.org/10.3390/ma10091082 - 14 Sep 2017

Cited by 19 | Viewed by 6345

Abstract

In order to assess the bond behavior of deformed steel rebars in recycled-aggregate concrete (RAC) incorporating both fine and coarse recycled aggregate, pull-out tests were carried out in this study on 16-mm diameter deformed steel rebars embedded concentrically in RAC. The concrete was [...] Read more.

In order to assess the bond behavior of deformed steel rebars in recycled-aggregate concrete (RAC) incorporating both fine and coarse recycled aggregate, pull-out tests were carried out in this study on 16-mm diameter deformed steel rebars embedded concentrically in RAC. The concrete was designed using equivalently mixed proportions of both recycled coarse aggregate and recycled fine aggregate. The tests employed five types of recycled aggregate replacement combinations and three types of rebar placement orientation (i.e., vertical bars and two-tiered and three-tiered horizontal bars). Based on the pull-out test results, the maximum bond strength tended to decrease and the slip at the maximum bond strength increased as the average water absorption of the aggregate increased, irrespective of the rebar orientation or placement location within the concrete member. The pull-out test results for the horizontal steel rebars embedded in RAC indicate that the casting position effect could be determined from the mid-depth of the concrete member, irrespective of the member’s height. The normalized bond versus slip relationship between the deformed rebar and the RAC could be predicted using an empirical model based on regression analysis of the experimental data. Full article

(This article belongs to the Special Issue Recycled Materials, Eco-design and 3D Printing)

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4990 KiB

Open AccessFeature PaperArticle

The Role of Controlled Surface Topography and Chemistry on Mouse Embryonic Stem Cell Attachment, Growth and Self-Renewal

by Melanie Macgregor, Rachel Williams, Joni Downes, Akash Bachhuka and Krasimir Vasilev

Materials 2017, 10(9), 1081; https://doi.org/10.3390/ma10091081 - 14 Sep 2017

Cited by 25 | Viewed by 5183

Abstract

The success of stem cell therapies relies heavily on our ability to control their fate in vitro during expansion to ensure an appropriate supply. The biophysical properties of the cell culture environment have been recognised as a potent stimuli influencing cellular behaviour. In [...] Read more.

The success of stem cell therapies relies heavily on our ability to control their fate in vitro during expansion to ensure an appropriate supply. The biophysical properties of the cell culture environment have been recognised as a potent stimuli influencing cellular behaviour. In this work we used advanced plasma-based techniques to generate model culture substrates with controlled nanotopographical features of 16 nm, 38 nm and 68 nm in magnitude, and three differently tailored surface chemical functionalities. The effect of these two surface properties on the adhesion, spreading, and self-renewal of mouse embryonic stem cells (mESCs) were assessed. The results demonstrated that physical and chemical cues influenced the behaviour of these stem cells in in vitro culture in different ways. The size of the nanotopographical features impacted on the cell adhesion, spreading and proliferation, while the chemistry influenced the cell self-renewal and differentiation. Full article

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

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4906 KiB

Open AccessArticle

Facile Preparation of a Robust and Durable Superhydrophobic Coating Using Biodegradable Lignin-Coated Cellulose Nanocrystal Particles

by Jingda Huang, Siqun Wang and Shaoyi Lyu

Materials 2017, 10(9), 1080; https://doi.org/10.3390/ma10091080 - 14 Sep 2017

Cited by 30 | Viewed by 7530

Abstract

It is a challenge for a superhydrophobic coating to overcome the poor robustness and the rough surface structure that is usually built using inorganic particles that are difficult to degrade. In this study, a robust superhydrophobic coating is facilely prepared by using commercial [...] Read more.

It is a challenge for a superhydrophobic coating to overcome the poor robustness and the rough surface structure that is usually built using inorganic particles that are difficult to degrade. In this study, a robust superhydrophobic coating is facilely prepared by using commercial biodegradable lignin-coated cellulose nanocrystal (L-CNC) particles after hydrophobic modification to build rough surface structures, and by choosing two different adhesives (double-sided tape and quick-setting epoxy) to support adhesion between the L-CNC particles and the substrates. In addition to excellent self-cleaning and water repellence properties, the resulting coatings show outstanding mechanical strength and durability against sandpaper abrasion, finger-wipe, knife-scratch, water jet, UV radiation, high temperature, and acidic and alkali solutions, possessing a wide application prospect. Full article

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3193 KiB

Open AccessArticle

Low-Temperature Self-Healing of a Microcapsule-Type Protective Coating

by Dong-Min Kim, Yu-Jin Cho, Ju-Young Choi, Beom-Jun Kim, Seung-Won Jin and Chan-Moon Chung

Materials 2017, 10(9), 1079; https://doi.org/10.3390/ma10091079 - 14 Sep 2017

Cited by 30 | Viewed by 5811

Abstract

Low-temperature self-healing capabilities are essential for self-healing materials exposed to cold environments. Although low-temperature self-healing concepts have been proposed, there has been no report of a microcapsule-type low-temperature self-healing system wherein the healing ability was demonstrated at low temperature. In this work, low-temperature [...] Read more.

Low-temperature self-healing capabilities are essential for self-healing materials exposed to cold environments. Although low-temperature self-healing concepts have been proposed, there has been no report of a microcapsule-type low-temperature self-healing system wherein the healing ability was demonstrated at low temperature. In this work, low-temperature self-healing of a microcapsule-type protective coating was demonstrated. This system employed silanol-terminated polydimethylsiloxane (STP) as a healing agent and dibutyltin dilaurate (DD) as a catalyst. STP underwent a condensation reaction at −20 °C in the presence of DD to give a viscoelastic product. The reaction behavior of STP and the viscoelasticity of the reaction product were investigated. STP and DD were separately microencapsulated by in situ polymerization and interfacial polymerization methods, respectively. The STP- and DD-loaded microcapsules were mixed into a commercial enamel paint, and the resulting formulation was applied to glass slides, steel panels, and mortars to prepare self-healing coatings. When the self-healing coatings were damaged at a low temperature (−20 °C), STP and DD were released from broken microcapsules and filled the damaged area. This process was effectively visualized using a fluorescent dye. The self-healing coatings were scratched and subjected to corrosion tests, electrochemical tests, and saline solution permeability tests. The temperature of the self-healing coatings was maintained at −20 °C before and after scratching and during the tests. We successfully demonstrated that the STP/DD-based coating system has good low-temperature self-healing capability. Full article

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11004 KiB

Open AccessArticle

Largest Magnetic Moments in the Half-Heusler Alloys XCrZ (X = Li, K, Rb, Cs; Z = S, Se, Te): A First-Principles Study

by Xiaotian Wang, Zhenxiang Cheng and Guodong Liu

Materials 2017, 10(9), 1078; https://doi.org/10.3390/ma10091078 - 14 Sep 2017

Cited by 47 | Viewed by 8405

Abstract

A recent theoretical work indicates that intermetallic materials LiMnZ (Z = N, P) with a half-Heusler structure exhibit half-metallic (HM) behaviors at their strained lattice constants, and the magnetic moments of these alloys are expected to reach as high as 5 μ_B [...] Read more.

A recent theoretical work indicates that intermetallic materials LiMnZ (Z = N, P) with a half-Heusler structure exhibit half-metallic (HM) behaviors at their strained lattice constants, and the magnetic moments of these alloys are expected to reach as high as 5 μ_B per formula unit. (Damewood et al. Phys. Rev. B 2015, 91, 064409). This work inspired us to find new Heusler-based half-metals with the largest magnetic moment. With the help of the first-principles calculation, we reveal that XCrZ (X = K, Rb, Cs; Z = S, Se, Te) alloys show a robust, half-metallic nature with a large magnetic moment of 5 μ_B at their equilibrium and strained lattice constants in their most stable phases, while the excellent HM nature of LiCrZ (Z = S, Se, Te) alloys can be observed in one of their metastable phases. Moreover, the effects of uniform strain in LiCrZ (Z = S, Se, Te) alloys in type II arrangement have also been discussed. Full article

(This article belongs to the Special Issue Intermetallic Alloys: Fabrication, Properties and Applications 2017)

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2671 KiB

Open AccessArticle

Material Viscoelasticity-Induced Drift of Micro-Accelerometers

by Wu Zhou, Peng Peng, Huijun Yu, Bei Peng and Xiaoping He

Materials 2017, 10(9), 1077; https://doi.org/10.3390/ma10091077 - 14 Sep 2017

Cited by 12 | Viewed by 5152

Abstract

Polymer-based materials are commonly used as an adhesion layer for bonding die chip and substrate in micro-system packaging. Their properties exhibit significant impact on the stability and reliability of micro-devices. The viscoelasticity, one of most important attributes of adhesive materials, is investigated for [...] Read more.

Polymer-based materials are commonly used as an adhesion layer for bonding die chip and substrate in micro-system packaging. Their properties exhibit significant impact on the stability and reliability of micro-devices. The viscoelasticity, one of most important attributes of adhesive materials, is investigated for the first time in this paper to evaluate the long-term drift of micro-accelerometers. The accelerometer was modeled by a finite element (FE) method to emulate the structure deformation and stress development induced by change of adhesive property. Furthermore, the viscoelastic property of the adhesive was obtained by a series of stress–relaxation experiments using dynamic mechanical analysis (DMA). The DMA curve was imported into the FE model to predict the drift of micro-accelerometers over time and temperature. The prediction results verified by experiments showed that the accelerometer experienced output drift due to the development of packaging stress induced by both the thermal mismatch and viscoelastic behaviors of the adhesive. The accelerometers stored at room temperature displayed a continuous drift of zero offset and sensitivity because of the material viscoelasticity. Moreover, the drift level of accelerometers experiencing high temperature load was relatively higher than those of lower temperature in the same period. Full article

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