bluuebunny/crossref_metadata_2025 huggingface dataset:
Pulmonary Edema After Extensive Radiofrequency Ablation for Atrial Fibrillation
Authors: WEBER REINHOLD , MINNERS JAN , RESTLE CHRISTIAN , BUERKLE GERD , NEUMANN FRANZ‐JOSEF , KALUSCHE DIETRICH , KEYL CORNELIUS , ARENTZ THOMAS
Published: February 2008

Background: More extensive ablation strategies for the treatment of atrial fibrillation (AF) have increased success rates but are associated with new and sometimes serious complications. We describe a new complication after extensive radiofrequency (RF) ablation in the left atrium (LA) for persistent AF.

Methods and Results: Electroanatomic guided circumferential ablation around both ipsilateral pulmonary veins (PV) was performed with the endpoint of complete conduction block. When necessary, supplementary RF applications were added, including ablation of complex fractionated potentials and/or isolation of other thoracic veins and/or linear left atrial lesions. RF energy was delivered via an irrigated tip catheter with a maximum power of 30–35 W. Four out of 120 patients undergoing extensive RF ablation for persistent AF (including two patients with additional LA substrate modification) developed dyspnea, bilateral pulmonary edema, and signs of a systemic inflammatory response syndrome (SIRS) (rise in body temperature, leukocyte count, and C‐reactive protein (CRP levels) 18–48 hours after the procedure. There were no signs of PV stenosis, focal lung injury, left ventricular dysfunction, circulatory failure, or infection. All patients had complete recovery with supportive therapy within 3–4 days after the onset of symptoms.

Conclusions: Extensive LA radiofrequency ablation bears the risk of a severe pulmonary edema. Although the precise mechanism is elusive, clinical features point toward a systemic inflammatory response.
ECHO ROUNDS: Percutaneous Balloon Valvuloplasty for Pulmonic Stenosis: The Role of Multimodality Imaging
Authors: Jassal Davinder S. , Thakrar Amar , Schaffer Stephen A. , Fang Tielan , Kirkpatrick Iain , Tam James W. , Kashour Tarek
Published: February 2008

Pulmonic valvular stenosis represents the most frequent cause of right ventricular outflow obstruction. Transthoracic echocardiography is the imaging modality of choice in the diagnosis, evaluation and longitudinal follow‐up of individuals with pulmonic stenosis (PS). Although valvular PS is usually diagnosed by two‐dimensional imaging, Doppler echocardiography allows for the quantification of severity of the valvular lesion. In patients with limited acoustic windows, computed tomography and cardiac magnetic resonance imaging may provide complementary anatomical characterization of the pulmonic annulus and valve prior to percutaneous balloon valvuloplasty.
Circular Plate‐Based YBO3:Eu3+ Assemblies: Synthesis and Photoluminescence Properties
Authors: Chen Limiao , Cheng Hua , Liu Guocong , Duan Xuechen
Published: February 2008

Uniform cake‐like YBO3:Eu3+ assemblies were successfully synthesized by a poly(vinylpyrrolidone)‐assisted hydrothermal method. The products were characterized by X‐ray diffraction, scanning electron microscopy, and photoluminescence spectroscopy. The results revealed that these particles were actually composed of many circular plates, which aligned well along their longitudinal direction. A high annealing temperature (≥1100°C) led to the formation of a new phase (Y3BO6) and the disappearance of the cake‐like morphology. Photoluminescence measurements indicated that the cake‐like YBO3:Eu3+ exhibited a higher ratio (R/O value) compared with the bulk YBO3:Eu3+, and the emission intensity enhanced with increasing annealing temperature up to 1000°C and then declined with further increasing temperature due to the formation of a new phase.
Dense Alumina–Zirconia Coatings Using the Solution Precursor Plasma Spray Process
Authors: Chen Dianying , Jordan Eric H. , Gell Maurice , Ma Xinqing
Published: February 2008

For the first time, dense coatings have been made by the solution precursor plasma spray (SPPS) process. The conditions are described for the deposition of dense Al2O3–40 wt% 7YSZ (yttria‐stabilized zirconia) coatings; the coatings are characterized and their thermal stability is evaluated. X‐ray diffraction analysis shows that the as‐sprayed coating is composed of α‐Al2O3 and tetragonal ZrO2 phases with grain sizes of 72 and 56 nm, respectively. The as‐sprayed coating has a 95.6% density and consists of ultrafine splats (1–5 μm) and unmelted spherical particles (<0.5 μm). The lamellar structure, typical of conventional plasma‐sprayed coatings, is absent at the same scale in the SPPS coating. The formation of a dense Al2O3–40 wt% 7YSZ coating is favored by the lower melting point of the eutectic composition, and resultant superheating of the molten particles. Phase and microstructural thermal stabilities were investigated by heat treatment of the as‐sprayed coating at temperatures of 1000°–1500°C. No phase transformation occurs, and the grain size is still in the nanometer range after the 1500°C exposure for 2 h. The coating hardness increases from 11.8 GPa in the as‐coated condition to 15.8 GPa following 1500°C exposure due to a decrease in coating porosity.
Microstructural Phenomena Controlling Losses in NiCuZn‐Ferrites as Studied by Transmission Electron Microscopy
Authors: Sakellari Despoina , Tsakaloudi Vasiliki , Polychroniadis Efstathios K. , Zaspalis Vassilios
Published: February 2008

The magnetic losses of NiCuZn‐ferrites with the chemical formula (Ni0.37−δZn0.63Cuδ)Fe1.93O4 (0<δ<0.22) are found to exhibit a minimum as a function of the copper content. This minimum corresponds to a certain sintering temperature, which is also a function of the copper content. At sintering temperatures lower than the optimum, insufficient densification is considered to be the reason for increased losses. At sintering temperatures higher than the optimum, the increased losses are caused by the presence of copper segregation to the grain boundaries and by some identified microstructural defects such as subgrain boundaries and compositional modulations. Internal stress relaxation is believed to be the reason for those chemical and morphological imperfections. In contrast to the power losses, the magnetic permeability does not show the previous dependency and increases monotonically with increased density or grain size.
Role of Spray Drying of Nanoagglomerates in Morphology Evolution in Nanostructured APS Coatings
Authors: Viswanathan Venkatachalapathy , Rea Keith E. , Vaidya Anirudha , Seal Sudipta
Published: February 2008

Nanostructured coatings undergo many processing challenges during atmospheric plasma spray if the feedstock is not well prepared. The effects of using spray drying on achieving a suitable feedstock for an even flow of nanoparticles through the gun, the selection of plasma gases for optimum heat transfer, and the velocity of the agglomerates during flight are highlighted in this communication. Analytical heat transfer calculations are used for coating property optimization. The physical characteristics of the nanoagglomerates are studied using diagnostics sensor and scanning electron microscopy. Transmission electron microscopy revealed the retention of nanostructures.
Bulk Concentration Effects on the Structure and Orientation of Adsorbed Silane on the Surface of Nanosized SiO2 Particles
Authors: Hsiang Hsing‐I. , Chen Chi‐Yu
Published: February 2008

In this study, the concentration effects of 3‐methacryloxypropyltrimethoxysilane (MEMO) on the surface coverage extent, orientation, and structures of MEMO silane grafted onto the surface of SiO2 particles are investigated using Fourier transform infrared (FTIR) and 29Si‐NMR spectroscopy. The MEMO silane concentration effects on the rheological behaviors of the SiO2 particles–1,6‐hexanedioldiacrylate (HDDA) suspensions are discussed in terms of the surface coverage extent and the MEMO silane structures grafted onto the surface of SiO2 particles. At low MEMO concentrations, many free silanol SiOH groups were observed for the MEMO grafted onto the SiO2 surface and the adsorbed MEMO molecules tended to orient parallel to the SiO2 surface due to the hydrogen bonding of the MEMO‐carbonyl and the hydroxyl group of the oxides. At high MEMO concentrations, the condensation reactions between neighboring grafted MEMO molecules result in the predominance of a T2 and T3 silicon atom structure and complete coverage of the SiO2 surface by the grafted MEMO. The enhanced steric hindrance and compatibility between the MEMO‐modified SiO2 particles and HDDA monomer, which originate from the complete coverage of the SiO2 surface by MEMO silane and a higher proportion of free carbonyl groups on the grafted MEMO, may improve the dispersibility of nanosized SiO2 in acrylate suspensions.
Nanocrystalline Scandia Powders Via Oxalate Precipitation: The Effects of Solvent and Solution pH
Authors: Xiu Zhimeng , Li Ji‐Guang , Li Xiaodong , Huo Di , Sun Xudong , Ikegami Takayasu , Ishigaki Takamasa
Published: February 2008

Nanocrystalline Sc2O3 was synthesized via precipitation with scandium nitrate as the scandium source and oxalic acid as the precipitant, with investigations into the influences of solution pH and solvent type on powder properties. Three types of scandium precursors (normal oxalate, double oxalate, and oxyhydroxide) have been obtained from aqueous media by adjusting pH of the precipitant solution with ammonia water. All the precursors, however, yield severely aggregated Sc2O3 powders of low surface areas. Replacing water with pure ethanol as the solvent was shown to be able to yield Sc2O3 nanopowders of high specific surface area (35.7 m2/g) and good dispersion. The mechanisms of solution pH and solvent type on precursor properties were also discussed.
Flexible Ceramics in the System KZr2(PO4)3–KAlSi2O6 Prepared by Mimicking the Microstructure of Itacolumite
Authors: Sato Isshu , Ichikawa Yoshitaka , Sakanoue Junji , Mizutani Mamoru , Adachi Nobuyasu , Ota Toshitaka
Published: February 2008

A ceramic composite mimicking the pervasively cracked microstructure of flexible sandstone (itacolumite) was successfully synthesized by sintering two ceramic materials with different thermal expansion coefficients. A combination of granular KZr2(PO4)3 (high thermal expansion) and powdered KAlSi2O6 (low thermal expansion) resulted in a material with a jigsaw‐like three‐dimensional cracking microstructure similar to that of itacolumite. The synthesized composite was found to exhibit ductile deformation.
Phase Evolution in Heat‐Treated Si3N4 with Additions of Yb2O3
Authors: Guo Gang Feng , Li Jianbao , Kong Xiang Yang , Lin Hong , Liang Long , He Mingsheng , Yang Liu , Wu Jiang , Cui Bai
Published: February 2008

The heat treatment of silicon nitride (Si3N4) ceramics with additions of 8, 12, and 16 wt% Yb2O3 was carried out at different temperatures and the evolution of grain boundary (GB) phase was investigated systematically by X‐ray diffraction (XRD) as well as scanning electron and transmission electron microscopic analyses. XRD results reveal that the extent and the ease of GB crystallization increase with increasing the Yb2O3 content, and that high heat‐treatment temperatures in general favor crystallization of the quaternary compounds such as the Yb4Si2O7N2 phase. These results provide an insight into the GB phase evolution in the Yb‐system Si3N4 ceramics subjected to a postsintering heat treatment.
High‐Temperature Plastic Behavior of TZP–Ni Cermets
Authors: Morales‐Rodríguez Ana , Bravo‐León Alfonso , Domínguez‐Rodríguez Arturo , Jiménez‐Melendo Manuel
Published: February 2008

The creep behavior of tetragonal zirconia TZP–Ni cermets with metal contents below, close to, and above the percolation limit has been studied. Compressive creep tests were performed on as‐received materials and samples in which the metal phase was chemically removed (ceramic skeletons). The stress exponent and the activation energy for plastic flow are independent of the nickel content and decrease continuously on increasing the stress and/or the temperature; skeleton structures display the same trend, suggesting that creep is controlled by the zirconia matrix. The steady‐state constitutive equation for high‐purity monolithic zirconia applies to the cermets when the stress is corrected with the porosity and volume fraction of percolated nickel.
Novel Coagulation Method for Direct Coagulation Casting of Aqueous Alumina Slurries Prepared Using a Poly(Acrylate) Dispersant
Authors: Prabhakaran Kuttan , Raghunath Sooraj , Melkeri Anand , Gokhale Nitin Madusudhan , Sharma Suresh Chandra
Published: February 2008

Coagulation of concentrated aqueous alumina slurries prepared using an ammonium poly(acrylate) dispersant by MgO has been studied for direct coagulation casting (DCC). A small amount of MgO (0.2 wt% of alumina) increased the viscosity of the concentrated alumina slurry with time and finally transformed it into a stiff gel. The mechanism of coagulation is proposed such that the time‐delayed in situ generation of Mg2+ ions from the sparingly soluble MgO forms Mg–poly(acrylate) with the unadsorbed ammonium poly(acrylate) molecules in solution that shift the poly(acrylate) adsorption equilibrium toward the left by depleting the poly(acrylate) molecules adsorbed on the alumina particle surface. This leads to insufficient dispersant coverage on the particle surface and coagulation of the slurry. DCC using MgO is possible only if the slurry is prepared at a dispersant concentration higher than that required for optimum dispersion as the slurries prepared at the optimum dispersant concentration underwent premature coagulation. The gelation time could be tailored within 20 min to a few hours by maintaining the temperature in the range of 70°–30°C. The wet coagulated bodies prepared from 50 vol% alumina slurry showed a compressive strength of nearly 0.05 MPa.
Characteristics of a Nonstoichiometric Gd3+δ(Al,Ga)5−δO12:Ce Garnet Scintillator
Authors: Kanai Tsuneyuki , Satoh Makoto , Miura Ichiro
Published: February 2008

We have developed a new nonstoichiometric Gd3+δ(Al,Ga)5−δO12:Ce garnet scintillator for an X‐ray CT scanner. For commercially used scintillators, reproducible luminescence properties are of great importance. We have found that the afterglow properties of the garnet change drastically in the vicinity of the stoichiometric compositions. The most suitable properties are obtained at slightly excess (Gd,Ce) compositions from the stoichiometry. In order to investigate the afterglow properties, crystallography arrangements, phase equilibrium relationship between crystal phases, and luminescence characteristics of host material doped with different valence ions have been examined. The luminescence properties are explained by isoelectronic traps based on the difference in the electronegativity of the dopant and host ions, which would act as electron trap centers and hole trap centers within the band gap.
Highly Texturing β‐Sialon Via Strong Magnetic Field Alignment
Authors: Zhu Xinwen , Suzuki Tohru S. , Uchikoshi Tetsuo , Sakka Yoshio
Published: February 2008

This paper reports the texturing behavior of β‐sialon by strong magnetic field alignment (SMFA) during slip casting, followed by reaction pressureless sintering, using either α or β‐Si3N4, Al2O3, and AlN as the starting materials. It is found that the β‐Si3N4 crystal exhibits a substantially stronger orientation ability than the α‐Si3N4 crystal regardless of the Si3N4 raw powders in the magnetic field of 12 T. The β‐raw powder produces a highly a, b‐axis‐oriented β‐Si3N4 green body with a Lotgering orientation factor of up to 0.97. During sintering, the β‐raw powder allows the a, b‐axis‐oriented β‐sialon to retain the Lotgering orientation factor similar to and even higher than that of β‐Si3N4 in the green body. In contrast, the α‐raw powder leads to a faster transformation rate of α/β‐Si3N4 to β‐sialon but a substantially lower texture in β‐sialon. The results indicate that the use of the β‐raw powder is more efficient for producing highly textured β‐sialon via SMFA than that of the α‐raw powder as well as the prolonged sintering.
Experimental Establishment of the CaAl2O4–MgO and CaAl4O7–MgO Isoplethal Sections within the Al2O3–MgO–CaO Ternary System
Authors: Durán Teresa , Serena Sara , Pena Pilar , Caballero Ángel , De Aza Salvador , De Aza Antonio H.
Published: February 2008

The isoplethal sections CaAl2O4–MgO and CaAl4O7–MgO of the Al2O3–MgO–CaO ternary system have been experimentally established at 1 bar total pressure and air of normal humidity. The sections obtained provide new data and information that are in disagreement with thermodynamic evaluations and optimizations of the Al2O3–MgO–CaO ternary system published to date. These differences arise mainly from the inclusion, or exclusion, of the binary compound Ca12Al14O33, mayenite, as a stable phase in the reported studies of the system. The presence or absence of this compound within the system has an important impact on the solid state and melting relationships of the whole ternary system. The present study confirms the solid‐state compatibility CaAl2O4–MgO and CaAl2O4–MgO–MgAl2O4up to 1372°± 2°C, the peritectic melting point of the later mentioned subsystem.
Multiferroic BiFeO3 Thin Films Buffered by a SrRuO3 Layer
Authors: Zheng Rongyan , Gao Xingsen , Wang John , Ramakrishna Seeram
Published: February 2008

Multiferroic BiFeO3 thin films of huge polarization have been successfully realized by using SrRuO3 as a buffer layer on a Pt/TiO2/SiO2/Si substrate. They consist of a single perovskite phase and are nearly randomly orientated, where the SrRuO3 buffer layer lowers the crystallization temperature and improves the crystallinity of BiFeO3. With increasing deposition temperature during magnetron sputtering, they undergo an apparent grain growth and reduction in surface roughness. The multiferroic thin films deposited on the SrRuO3‐buffered Pt/TiO2/SiO2/Si substrate at higher temperatures show much improved polarization and reduced coercive field, together with a lowered leakage current. A huge remnant polarization (2Pr) of 150 μC/cm2 and a coercive field (2Ec) of 780 kV/cm were measured for the BiFeO3 film deposited at 650°C.
Effect of MnO on the Phase Development, Microstructures, and Dielectric Properties of 0.95Na0.5K0.5NbO3–0.05LiTaO3 Ceramics
Authors: Bomlai Pornsuda , Sinsap Penprapa , Muensit Supasarute , Milne Steven J.
Published: February 2008

Lead‐free piezoelectric ceramics in the system 0.95Na0.5K0.5NbO3–0.05LiTaO3 were modified with ≤1 mol% MnO. Maximum densities occurred at a sintering temperature of 1050°C. Characteristic changes in the relative intensity of X‐ray diffraction peaks were consistent with Mn ions substituting on the perovskite lattice to produce a change from orthorhombic to a mixture of tetragonal and orthorhombic phases. Grain growth during secondary recrystallization was also affected, leading to increased grain sizes. The dielectric constant increased from ∼600 in unmodified ceramics to ∼1040 in ceramics prepared with 0.5 mol% MnO.
Synthesis and Characterization of (Zn,Cd)TiO3 by a Modified Sol–Gel Method
Authors: Zheng Mingzhen , Yu Ranbo , Chen Jun , Zhao Jie , Liu Guirong , Xing Xianran , Meng Jian
Published: February 2008

Ilmenite‐type (Zn1−xCdx)TiO3 (0≤x≤0.15 and 0.8≤x≤1.0) was synthesized by a modified sol–gel route including the Pechini process via two‐step heat treatments. The thermal stability of (Zn1−xCdx)TiO3 depended on the amount of cadmium content. The as‐synthesized (Zn1−xCdx)TiO3 (0≤x≤0.15 and 0.8≤x≤1.0) showed higher thermal stability than that of ZnTiO3. The variation of the dielectric constant of all synthesized (Zn1−xCdx)TiO3 samples for all measurement frequencies showed a similar tendency. The dielectric constant of each (Zn1−xCdx)TiO3 sample decreased first with increasing frequencies and then increased slightly when the frequency was up to 107 Hz. Moreover, the dielectric loss tangent of all synthesized (Zn1−xCdx)TiO3 samples for all measurement frequencies also changed in similar patterns. The dielectric loss tangent decreased with increasing measurement frequencies. The microwave dielectric properties of (Zn1−xCdx)TiO3 were changed with the cadmium doping content in the range of microwave frequency.
Formation of Titania Nanoarrays by Hydrothermal Reaction and Their Application in Photovoltaic Cells
Authors: Wang Wenli , Lin Hong , Li Jianbao , Wang Ning
Published: February 2008

In the present study, titania (TiO2) nanoarrays were prepared by hydrothermally oxidating a titanium substrate in aqueous alkali and then postannealed at 300°–550°C for 2 h. The nanoarrays were composed of oriented one‐dimensional nanowires or nanobelts. The growth mechanism of the nanoarrays was discussed by observing the structure under different synthesis conditions. The TiO2 nanoarray film was transferred to a transparent conductive glass substrate, used as a photoanode of a dye‐sensitized solar cell (DSC). A light‐to‐energy conversion efficiency of 6.58% for the DSC was obtained.
Crystallization and Phase Transition of Titanium Oxide Nanotube Arrays
Authors: Yang Yang , Wang Xiaohui , Li Longtu
Published: February 2008

The crystallization and phase transition of TiO2 nanotubes that are >4 μm in length were investigated. The nanotubes initially crystallized in the anatase and rutile phases at 300° and 550°C, respectively. The rutile nucleation occured initially in the nanotube–support interface. On elevating the calcination temperature above 550°C, the rutile crystallites in the nanotube–support interface merged with the nanotubes and finally formed a compact rutile layer at 800°C. During the anatase‐to‐rutile phase transition processing, a (004) preferential orientation occurred due to the regular arrangements of the nanotubes onto the titanium substrate.
Carrier Generation and Inherent Off‐Stoichiometry in Zn, Sn Codoped Indium Oxide (ZITO) Bulk and Thin‐Film Specimens
Authors: Harvey Steven P. , Mason Thomas O. , Buchholz D. Bruce , Chang Robert P. H. , Körber Christoph , Klein Andreas
Published: February 2008

Electrical studies of the Zn, Sn codoped bixbyite (In2O3) phase (ZITO), a promising alternative to indium–tin oxide (ITO) for transparent conductor applications, indicate that an inherent cation off‐stoichiometry in favor of Sn donors versus Zn acceptors dominates the defect chemistry of this important transparent conducting oxide. This was shown by bulk phase diagram and conductivity studies, thin‐film electrical/optical measurements, and photoelectron spectroscopy on both bulk and thin‐film specimens. The Sn‐excess character explains the persistent n‐type behavior of bulk ZITO, the relative redox insensitivity of codoped compositions, the existence of “special” (optimized conductivity) compositions in phase space for pulsed laser‐deposited films, and the propensity for surface chemical depletion in both bulk and thin‐film specimens.
Crystal Structure of V4AlC3: A New Layered Ternary Carbide
Authors: Hu Chunfeng , Zhang Jie , Wang Jiemin , Li Fangzhi , Wang Jingyang , Zhou Yanchun
Published: February 2008

V4AlC3, a new MAX phase, was synthesized by reactive hot pressing of a V, Al, and C powder mixture at 1700°C. Using a combination of Rietveld refinement with X‐ray diffraction data and ab initio calculations, the crystal structure was determinated. It was found that V4AlC3 has a Ti4AlN3‐type crystal structure. The lattice constants are a=0.29310 nm and c=2.27192 nm. And the atomic positions are V1 at (4f) (1/3, 2/3, 0.0544), V2 at (4e) (0, 0, 0.1548), Al at (2c) (1/3, 2/3, 1/4), C1 at (2a) (0, 0, 0), and C2 at (4f) (2/3, 1/3, 0.1080).
New Red‐ and Green‐Emitting Phosphors, AYP2O7.5:RE3+ (A=Ca and Sr; RE=Eu and Tb) under Near‐UV Irradiation
Authors: Thomas Suman Mariam , Rao P. Prabhakar , Nair K. Ravindran , Koshy Peter
Published: February 2008

New red‐ and green‐emitting phosphors, AY1−xP2O7.5:xRE3+ (A=Ca and Sr; x=0.01, 0.03, 0.05, 0.10; RE=Eu and Tb) were synthesized by the conventional ceramic route and their photoluminescence properties under near‐ultraviolet (UV) irradiation were investigated. It was found that CaYP2O7.5: Eu3+ phosphor emits strong red light when excited by a radiation of 394‐nm wavelength and SrYP2O7.5:Eu3+ gives intense orange light when excited by a radiation of 396‐nm wavelength. Strong green emission for AY1−xP2O7.5:Tb3+ is also observed under near‐UV irradiation (378 nm). When compared with emission intensity from a standard YPO4:0.05Tb3+, the emission from SrYP2O7.5:0.05Tb3+ showed greater intensity values under the same excitation wavelength (378 nm). X‐ray powder diffraction analysis showed that AYP2O7.5 has xenotime‐type structure.
Effect of Milling Time on the Rheology of Highly Loaded Aqueous‐Fused Silica Slurry
Authors: Mohanta Kalyani , Bhargava Parag
Published: February 2008

The effects of milling time on the rheological behavior of 70‐vol% loaded fused silica slurries were studied. A transition from shear thickening to shear thinning behavior was observed with milling time. Slurry viscosity and thixotropy attained a minimum after 18 h of milling and remained almost unchanged with additional milling. Infrared spectroscopy and particle surface charge measurements confirmed the development of increasing amount of surface hydroxide and surface charge respectively with progress in milling time, leading to shear thinning behavior. An initial static aging treatment of 24 h aided the development of silanol groups, indicating that the milling time can be reduced to save energy and time.
Self‐Constrained Sintering of a Multilayer Low‐Temperature‐Cofired Glass–Ceramics/Alumina Laminate
Authors: Liao Chien‐Hong , Jean Jau‐Ho , Hung Yao‐Yi
Published: February 2008

A self‐constrained low‐temperature‐cofired ceramic system with a multilayer structure of a low‐temperature cofirable CaO–B2O3–SiO2 glass (CBSG) tape and a pure alumina tape has been developed. Because the densification temperature range required for the CBSG layer is much lower than that needed for pure alumina, its lateral shrinkage is inhibited by the presence of a nondensified alumina layer during cofiring. Porosity in the alumina layer is later filled by the capillary infiltration of free glass in the densified CBSG. This leads the linear shrinkage of the multilayer CBSG/alumina laminate to take place only in the Z direction with little shrinkage in the X–Y directions, which exhibits unique characteristics of self‐constrained densification.
Influence of Microstructure on the Wear Behavior of SiC‐Reinforced Titanium‐Matrix Composites Lubricated by Water and by Ethanol
Authors: Hibi Yuko , Murakami Takashi , Miyake Koji , Sasaki Shinya
Published: February 2008

Two kinds of SiC‐reinforced titanium‐matrix composites were slid against themselves in water and in ethanol to evaluate the influence of their microstructure on the wear behavior. The composites had a structure in which the SiC particles were coated with interfacial layers that consisted of Ti5Si3Cx and TiC, and the TiC particles were dispersed in a titanium matrix. The wear resistance of the composites was much better than that of titanium metal. The wear of the composites prepared from starting materials with a high SiC content was lower than that with a low SiC content.
Fabrication and Characterization of Colossal Electroresistance Chip Devices Composed of Polycrystalline Lanthanum‐Doped Strontium Titanate and Palladium Electrodes
Authors: Hirose Sakyo , Nakayama Akinori , Niimi Hideaki
Published: February 2008

A colossal electroresistance (CER) multilayered chip device composed of polycrystalline 0.8‐at% La‐doped SrTiO3 and Pd electrodes has been successfully fabricated. Polycrystalline SrTiO3 devices exhibit large hysteresis in their current–voltage (I–V) characteristics after the forming process. Further, their resistance states can be switched by applying voltage pulses above ±50 V, and the resistance changes by approximately two orders of magnitude (from ∼600 Ω to ∼80 kΩ). These resistance‐switching behaviors demonstrate that even ceramics can exhibit resistance changes as large as thin‐film devices and provide the possibility of new switching devices with the memory effect composed of ceramics.
Synthesis and Characterization of Crystallizable Anorthite‐Based Glass for a Low‐Temperature Cofired Ceramic Application
Authors: Dileep Kumar C. J. , Sunny E. K. , Raghu N. , Venkataramani N. , Kulkarni Ajit R.
Published: February 2008

We report successful identification and preparation of a glass composition in the CaO–Al2O3–SiO2 phase diagram with a judicious choice of fluxes that met all dielectric, electrical, and thermal property requirements for low‐temperature cofired ceramic (LTCC) applications. The glass composition sintered at 900°C attains good density (2.45 g/cc) and does not precipitate any crystalline phase. However, when this glass powder is sintered at the same temperature in the presence of 30 vol% cordierite, crystallization of the anorthite phase is observed, which improves the properties of the composite for LTCC application.
Neutron Diffraction of Zirconia‐Dispersed Alumina with Increasing Stress and Temperature
Authors: Carter Geoffrey A. , Van Riessen Arie
Published: February 2008

Neutron and X‐ray diffraction were used to investigate changes in the phase composition and lattice parameters with temperature and pressure of a 20‐wt% zirconia‐dispersed alumina composite. Neutron diffraction was used to determine the variation of tetragonal/monoclinic zirconia phase abundance for the bulk with stress. The bulk tetragonal/monoclinic ratio decreased by 40% for a stress of 550 MPa. A difference in the tetragonal/monoclinic ratio between the near‐surface and the bulk of the processed samples is believed to contribute to observed variations in nonuniform strain in the matrix, which has the effect of prestressing the sample. Placing a stress on the sample initially releases this prestressing.
Optimized Nanosecond Pulsed Laser Micromachining of Y‐TZP Ceramics
Authors: Wang Xin , Shephard Jonathan D. , Dear Fraser C. , Hand Duncan P.
Published: February 2008

Owing to the inherent difficulty of mechanically machining hard, ytrria‐stabilized tetragonal zirconia polycrstal (Y‐TZP) ceramics, laser processing has recently been investigated as an alternative. However, owing to the vast range of variables such as wavelength, focus position, pulse width, power, and repetition rate, finding the optimum processing conditions can be difficult. In this report, we examine the parameters for a nanosecond pulsed (60 ns) Nd:YAG laser. It was found that at room temperature, the absorption of Y‐TZP at 1064 and 532 nm is very low; however, it becomes highly absorbing above a “machining threshold” with a penetration depth of 1.6 μm above the threshold. In this condition, we have found the combination of processing variables that provides the optimum material removal rate (up to ∼2 mm3/min). Additionally, it was found that the pulse overlap has a significant influence on the efficiency of the processing and therefore the combination of scan speed and repetition rate must be carefully considered.
Preparation of High Solids Content Nanozirconia Suspensions
Authors: Santacruz Isabel , Anapoorani Ketharam , Binner Jon
Published: February 2008

A new colloidal route leading to the production of ∼99% dense 3‐mol% yttria‐stabilized zirconia nanostructured ceramics, while retaining a final average grain size of ∼75 nm, has been developed. The process was based on the production of stable, homogeneous nanosuspensions with solids contents of up to 28 vol% (70 wt%), but viscosities <0.05 Pa·s at any shear rate in the range of study were obtained. The suspensions were formed by the concentration and optimization of precursor, dilute (5.0 vol%) commercial nanosuspensions, the approach requiring a change of pH, from the 2.4 of the as‐received suspension to 11.5, and the use of an appropriate anionic dispersant. Exposure of the nanosuspensions to ultrasound also helped to reduce the viscosity further, although it only worked when the dispersant was optimized. The nanosuspension was slip cast to form homogenous green bodies with densities of ∼55% of the theoretical without agglomeration in the nanostructure; these were subsequently densified using a two‐step sintering technique.
Oxidation Kinetics and Stress Effects for the Oxidation of Continuous Carbon Fibers within a Microcracked C/SiC Ceramic Matrix Composite
Authors: Halbig Michael C. , McGuffin‐Cawley James D. , Eckel Andrew J. , Brewer David N.
Published: February 2008

Carbon fiber‐reinforced silicon carbide (C/SiC) composites have the potential to be utilized in many high‐temperature structural applications, particularly in aerospace. However, the susceptibility of the carbon fibers to oxidation has hindered the composite's use in long‐term reusable applications. In order to identify the composites limitations, fundamental oxidation studies were conducted to determine the effects of such variables as temperature, environment, and stress. The systematic studies first looked at the oxidation of the plain, uncoated carbon fiber, then when fiber was utilized within a C/SiC composite, and finally when a stress was applied to the C/SiC composite (stressed oxidation). The first study, oxidation of just the carbon fibers, showed that the fiber oxidation kinetics occurs in two primary regimes: chemical reaction control and diffusion control. The second study, oxidation of the C/SiC composite, showed the self‐protecting effects from the SiC matrix at elevated temperatures when the composite was not stressed. The final study, stressed oxidation of the C/SiC composite, more closely simulated application conditions in which the material is expected to encounter thermal and mechanical stresses. The applied load and temperature will affect the openings of the as‐fabricated cracks, which are an unavoidable characteristic of C/SiC composites. The main objective of the paper was to determine the oxidation kinetic regimes for the oxidation of carbon fibers in a cracked silicon carbide matrix under stressed and unstressed conditions. The studies help to provide insights in to the protective approaches, that could be used to prevent oxidation of the fibers within the composite.
Infiltration‐Inhibiting Reaction of Gadolinium Zirconate Thermal Barrier Coatings with CMAS Melts
Authors: Krämer Stephan , Yang James , Levi Carlos G.
Published: February 2008

The thermochemical interaction between a Gd2Zr2O7 thermal barrier coating synthesized by electron‐beam physical vapor deposition and a model 33CaO–9MgO–13AlO3/2–45SiO2 (CMAS) melt with a melting point of ∼1240°C was investigated. A dense, fine‐grained, ∼6‐μm thick reaction layer formed after 4 h of isothermal exposure to 1300°C. It consisted primarily of an apatite phase based on Gd8Ca2(SiO4)6O2 and fluorite ZrO2 with Gd and Ca in a solid solution. Remarkably, melt infiltration into the intercolumnar gaps was largely suppressed, with penetration rarely exceeding ∼30 μm below the original surface. The microstructural evidence suggests a mechanism in which CMAS infiltration is arrested by rapid filling of the gaps with crystalline reaction products, followed by slow attack of the column tips.
Sintering Arches for Cosintering Camber‐Free SOFC Multilayers
Authors: Lee Sang‐Ho , Messing Gary L. , Awano Masanobu
Published: February 2008

We describe a series of experiments to learn how to produce flat LaSrMnO3/YSZ/NiO‐YSZ multilayer packages typically used for solid oxide fuel cells, in a single cosintering cycle, by applying a load during cosintering using sintering arches. We demonstrate that the key step is to apply the load gradually after the multilayer components are stronger and at their minimum viscosity of ∼6 GPa·s during sintering. Alumina sintering arches, which support an alumina loading plate above the multilayer laminate, were designed to yield slowly at the intermediate stage of cosintering and thus apply the loading plate to the multilayer package. The primary design features of sintering arches are the arch material viscosity behavior, and the arch width, thickness, and curvature.
Growth of Tabular α‐Al2O3 Grains on Porous Alumina Substrate
Authors: Yu Bang‐Ying , Wei Wen‐Cheng J.
Published: February 2008

Gradient, porous alumina ceramics were prepared with the characteristics of microsized tabular α‐Al2O3 grains grown on a surface with a fine interlocking feature. The samples were formed by spin‐coating diphasic aluminosilicate sol on porous alumina substrates. The sol consisted of nano‐sized pseudo‐boehmite (AlOOH) and hydrolyzed tetraethyl orthosilicate [Si(OC2H5)4]. After drying and sintering at 1150°–1450°C, the crystallographic and chemical properties of the porous structures were investigated by analytical electron microscopy. The results show that the formation of tabular α‐Al2O3 grains is controlled by the dissolution of fine Al2O3 in the diphasic material at the interface. The nucleation and growth of tabular α‐Al2O3 grains proceeds heterogeneously at the Al2O3/glass interface by ripening nano‐sized Al2O3 particles.
A Soft Chemistry Route for the Synthesis of Nanostructured Pb2Ru2O6.5 with a Controlled Stoichiometry
Authors: Esposito Vincenzo , Marani Debora , Wachsman Eric D. , Traversa Enrico
Published: February 2008

A new chemical route to synthesize nanostructured lead ruthenium pyrochlore (Pb2Ru2O6.5) powders was developed. The synthesis was performed starting from a metal nitrate aqueous solution and N, N, N′, N′ tetramethylethylendiamine (TMEDA). The amine, which is a mild basic chelating agent, was able to control the simultaneous precipitation of lead and ruthenium oxo/hydroxides. For the sake of comparison, Pb2Ru2O6.5 powders were prepared using the more conventional polymeric precursor method. The new method was effective for the synthesis of nanostructured Pb2Ru2O6.5 powders already stable at 400°C and up to 1000°C.
Low‐Temperature Preparation of Titanium Carbide Coatings on Graphite Flakes from Molten Salts
Authors: Liu X. , Zhang S.
Published: February 2008

Titanium carbide (TiC)‐coated graphite for refractory castable applications was prepared via reacting titanium metal powder (∼45 μm) and natural graphite flakes (100–300 μm) for 5 h at 950°C in a KCl‐based salt in Ar atmosphere. TiC coatings formed on graphite flakes were uniform, crack‐free, and composed of nanosized particles (20–40 nm). The “template‐growth” mechanism played a dominant role in the coating formation process.
Sintering Kinetics of a MgAl2O4Spinel Doped with LiF
Authors: Rozenburg Keith , Reimanis Ivar E. , Kleebe Hans‐Joachim , Cook Ron L.
Published: February 2008

The sintering kinetics of a pure magnesium aluminate spinel, MgAl2O4, and that doped with LiF were determined through the use of the master sintering curve technique developed by Su and Johnson.20Powders with 0%, 0.5%, and 1.0% by mass LiF were densified in a vacuum hot press under a range of unaxial pressures. After the sintering mechanisms in each temperature and pressure regime were determined, an optimized vacuum hot‐pressing schedule was formulated for spinel powders doped with 1.0% by mass of LiF. In addition to forming a transient liquid phase, the presence of LiF leads to the formation of oxygen vacancies that promote late‐stage sintering in MgAl2O4.
Characterization of Bulk Structure in Zinc Orthotitanate: A Density Functional Theory and EXAFS Investigation
Authors: Rankin Rees B. , Campos Andrew , Tian Hanjing , Siriwardane Ranjani , Roy Amitava , Spivey James J. , Sholl David S. , Johnson J. Karl
Published: February 2008

Development of high‐efficiency multicontaminant sorbents is critical for commercialization of power plants utilizing integrated gasification combined cycle technologies. A known prototypical sorbent for this application is the compound zinc orthotitanate, Zn2TiO4 (ZTO). Previous work has not completely resolved the atomic‐level structure of ZTO. Results from both experimental X‐ray absorption fine structure measurements and density functional theory (DFT) calculations are presented and are in quantitative agreement. The DFT calculations identify the octahedral site occupation of Zn and Ti atoms that give the lowest energy ground state structure. We have supplemented our DFT calculations with a cluster expansion model used to parameterize Monte Carlo (MC) simulations. The results of the MC simulations reveal the temperature dependence of the equilibrium octahedral site occupation in Zn2TiO4.
Hydrothermal Treatment of Si3N4 for the Improvement of Oxidation Resistance at 1400°C
Authors: Lee Sea‐Hoon , Kaiser Gerhard , Rixecker Georg , Aldinger Fritz , Park Jae‐Young , Auh Keun‐Ho , Choi Sung‐Churl
Published: February 2008

The surface of Si3N4 ceramics was hydrothermally treated with HCl or H2SO4 using an autoclave. The thickness of the oxide layers formed on the Si3N4 samples decreased to one‐fourth after oxidation at 1400°C by the treatment. The oxide layer of the treated samples was dense, and flaw formation in and beneath the layer did not occur at 1400°C. The avoidance of low melting Y‐silicates by leaching Y2O3 is the reason for the improved oxidation resistance of the hydrothermally treated Si3N4, despite an increase in surface porosity through a 70 μm layer.
Elastic, Piezoelectric, and Dielectric Properties of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 Crystals Obtained by Solid‐State Crystal Growth
Authors: Zhang Shujun , Lee Sung‐Min , Kim Dong‐Ho , Lee Ho‐Yong , Shrout Thomas R.
Published: February 2008

Single crystals with the composition of 0.71Pb(Mg1/3Nb2/3)O3–0.29PbTiO3 (PMNT29) were grown using the solid‐state crystal growth (SSCG) method. Compared with the conventional Bridgman grown crystals, the SSCG PMNT29 crystals were found to possess comparable piezoelectric, dielectric, and electromechanical properties (d33∼1500 pC/N, ɛT33/ɛ0∼5400 and k33∼90%), with the same Curie temperature (TC) and ferroelectric phase transformation temperature (TR–T). The full set of elastic, piezoelectric, and dielectric material constants were determined by the resonance method for the SSCG grown PMNT29 crystals according to IEEE standards and compared with Bridgman grown crystals. The dielectric temperature behavior and the strain field characteristics were investigated, demonstrating excellent performance over the temperature range from room temperature to 95°C. Strain behavior at high electric fields was found to be different from Bridgman growth crystals and believed to be attributed to different domain structures.
Fabrication of Nanocomposite Powders of Carbon Nanotubes and Montmorillonite
Authors: Feng Jingdong , Wang Qingwei
Published: February 2008

Nanocomposite powders of carbon nanotubes (CNTs) and montmorillonite (MMT) were successfully synthesized by heating the mixed composites of polypropylene, nickel (Ni) catalyst, and organic‐modified montmorillonite in large quantities after the Ni catalysts were removed. Transmission electron microscopy, X‐ray diffraction, thermogravimetric analysis, Raman spectroscopy, and scanning electron microscopy show the co‐presence of CNTs and MMT. The interlayer distance of MMT was enlarged because of the CNTs, which result in MMT being partly exfoliated and buried in the CNTs. These current nanocomposite powders of CNTs and MMT with superstructure are therefore expected to be ideal fillers for high‐performance polymer nanocomposites.
Transmission Electron Microscopy Observations on the Interfacial Structures of the Pt/SrBi2Ta2O9/Pt Thin‐Film Capacitors Prepared by Metallo‐Organic Decomposition
Authors: Zhu Xinhua , Wu Di , Li Aidong , Liu Zhiguo , Ming Naiben
Published: February 2008

Interfacial structures of the Pt/SBT/Pt capacitors prepared by metallo‐organic decomposition were examined by transmission electron microscopy (TEM) and high‐resolution TEM (HRTEM) as a function of the postannealed time at 750°C to investigate the interfacial evolution developed in the Pt/SBT/Pt capacitors. The results show that after postannealing at 750°C for a short time (e.g., 300 s), a thin amorphous layer was observed at the interfaces of the SBT/Pt‐bottom and the SBT/Pt‐top electrodes in the Pt/SBT/Pt capacitors, whereas after postannealing for a moderate time (e.g., 20 min), the interfaces of the SBT/Pt‐bottom and the SBT/Pt‐top electrodes became quite smooth and uniform, and almost free of the interfacial phase. However, after postannealing for a longer time (e.g., 60 min), an interfacial phase consisting of oval‐shaped nanocrystallites was developed at both the SBT/Pt‐bottom and the SBT/Pt‐top electrode interfaces, which resulted in weakly bonded interfaces between the SBT films and Pt electrodes. This is the reason why a Pt electrode peeling phenomenon (similar to that reported in the Pt/SBT/Pt/capacitors annealed in the forming gas atmosphere) is frequently observed in the Pt/SBT/Pt capacitors postannealed for 60 min during the fabrication of cross‐sectional TEM samples. Based on two‐dimensional lattice fringes of the HRTEM images from the small nanocrystallites and the corresponding fast Fourier transform patterns, the oval‐shaped nanocrystallites precipitated at both the SBT/Pt‐bottom and the SBT/Pt‐top electrode interfaces were determined to be a PtBi2 phase with a cubic structure. The formation of the Pt–Bi‐based interfaces in the Pt/SBT/Pt capacitors is due to the reaction of bismuth (out‐diffused from the SBT films) with Pt electrodes during the postannealing process. The elliptical morphology of the interfacial PtBi2 phase can be ascribed to its different growth rates in the parallel and vertical directions of the interface, and also the limited space for grain growth perpendicular to the interface.
Synthesis and Electrical Properties of Stabilized Manganese Dioxide (α‐MnO2) Thin‐Film Electrodes
Authors: Kwon Do‐Kyun , Akiyoshi Teppei , Lee Hyeongjae , Lanagan Michael T.
Published: February 2008

Manganese dioxide (α‐MnO2) thin films have been explored as a cathode material for reliable glass capacitors. Conducting α‐MnO2 thin films were deposited on a borosilicate glass substrate by a chemical solution deposition technique. High carbon activities originated from manganese acetate precursor, (Mn(C2H3O2)2·4H2O) and acetic acid solvent (C2H4O2), which substantially reduced MnO2 phase stability, and resulted in Mn2O3 formation at pyrolysis temperature in air. The α‐MnO2 structure was stabilized by Ba2+ insertion into a (2 × 2) oxygen tunnel frame to form a hollandite structure. With 15–20 mol% Ba addition, a conducting α‐MnO2 thin film was obtained after annealing at 600–650°C, exhibiting low electrical resistivity (∼1 Ω·cm), which enables application as a cathode material for capacitors. The hollandite α‐MnO2 phase was stable at 850°C, and thermally reduced to the insulating bixbyte (Mn2O3) phase after annealing at 900°C. The phase transition temperature of Ba containing α‐MnO2 was substantially higher than the reported transition temperature for pure MnO2 (∼500°C).
A Novel Hybrid Method of Sol–Gel and Ultrasonic Atomization Synthesis and Piezoelectric Properties of SrBi4Ti4O15 Ceramics
Authors: Xu Zhijun , Chu Ruiqing , Hao Jigong , Li Guorong , Yin Qingrui
Published: February 2008

SrBi4Ti4O15(SBTi) powders were synthesized by a novel hybrid method of sol–gel and ultrasonic atomization. TiO2 particle was used as a starting material to replace other expensive soluble titanium salts. X‐ray diffraction results showed that the pure‐phase SBTi powders were obtained at 700°C for 2 h, which is much lower than the calcination temperature (800°–850°C) required in solid‐state reactions. The ceramics sintered at 1100°C for 1 h exhibited 94.5% of relative density and a piezoelectric coefficient of 21 pC/N. The results showed that this hybrid method could lead to an attractive method for the industrial fabrication of SBTi materials.