bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Stress and Chemical Homogeneity on Dielectric Properties of BaTi0.9Zr0.1O3
Authors: van der Gijp Sven , ten Elshof Johan E. , Steigelmann Oliver , Verweij Henk
Published: July 2010

The influence of mechanical stress and chemical homogeneity on the permittivity of BaTi0.9Zr0.1O3 ceramics prepared from mixed‐oxide and hydrothermal powders was studied. To reduce stress, liquid‐phase sintering was applied in conjunction with a low heating rate to stimulate the formation of large grains. The influence of chemical homogeneity was studied by variations in sintering temperatures and times. For both types of ceramics, the dielectric constant at the Curie temperature was influenced by both factors, but to a different extent. In the mixed oxide ceramic, chemical homogeneity played a more prominent role, while internal stress appeared to exert a larger influence in the hydrothermal ceramics. The dielectric constant at the Curie temperature could be increased by 5%–10% by an annealing treatment at 200°C, followed by slow cooling.
Effects of Residual Stress and Loading Geometry on Single‐Edge Precracked‐Beam (SEPB) Fracture‐Toughness Test Results
Authors: Grendahl Scott , Bert Raymond , Cho Kyu , Bar‐On Isa
Published: July 2010

The single‐edge precracked‐beam (SEPB) specimen test, using the “bridge indentation” method, is one of the standard test methods in the new ASTM standard for the determination of the fracture toughness of ceramics. In support of this effort, the effect of several test parameters on the fracture‐toughness (KIC) values was established. The effect of the residual stress, because of the indent and the alignment in three‐ and four‐point bending, on the KIC values was determined using aluminum nitride specimens. The results show that indent loads should be kept below 10 kgf, and the crack‐plane angle should be <5°, to prevent artificially high KIC values.
Synthesis of Nanosized Aluminum Nitride Powders by Pulsed Laser Ablation
Authors: Grigoriu Constantin , Hirai Makoto , Nishiura Koji , Jiang Weihua , Yatsui Kiyoshi
Published: July 2010

The influence of the target material, fluence, laser wavelength, and nitrogen pressure on the synthesis of AlN nanosized powders via reactive laser ablation has been investigated. Using infrared laser radiation and fluences of ≥11 J/cm2, pure AlN nanosized powders were produced at nitrogen pressures of ≥1.3 kPa via ablation of an AlN target and ≥13.3 kPa via ablation of an aluminum target. With ultraviolet laser radiation, AlN powders could be synthesized at a lower fluence (9 J/cm2 at a pressure of 8 kPa). The mean powder size was 7.5−15 nm.
Hydrothermal Preparation of Nanosized Brookite Powders
Authors: Zheng Yanqing , Shi Erwei , Cui Suxian , Li Wenjun , Hu Xingfang
Published: July 2010

Titania powders in pure brookite form were synthesized by hydrothermal treatment of titanium(IV) salt solutions. Two kinds of starting materials, titanium sulfate and titanium tetrachloride, were used in the hydrothermal reactions. The effects of preparation conditions on the polymorphous form and morphology of the titanium dioxide powders were studied. These conditions included precursor species, precursor pretreatment, pH, and reaction temperature. The conditions that lead to brookite formation versus other phases, such as anatase and rutile, are generalized. The morphologic differences of the three polymorphous powders are shown.
Solvothermal Synthesis and Characterization of Barium Titanate Powders
Authors: Chen Dairong , Jiao Xiuling
Published: July 2010

Cubic BaTiO3 powders have been synthesized from gel powders after thermal treatment in an alcohol solution and characterized using X‐ray diffractometry, transmission electron microscopy, and other techniques in detail. The borderline reaction conditions, such as the reaction temperature and time, for the synthesis of crystalline BaTiO3 powder in different solvents are established. The single‐phase BaTiO3 powder has low agglomeration and seems to have a regular morphology. The formation of BaTiO3 powders via solvothermal reaction is more difficult, in comparison to hydrothermal processing. The crystalline powders, which have a small particle size (∼20–60 nm) and narrow particle‐size distribution, can be synthesized in methanol, ethanol, or n‐propanol systems. Unlike the hydrothermal reaction, tetragonal‐phase BaTiO3 powders cannot be prepared via the solvothermal reaction, even with alkali catalysts.
Role of Length Scale on Pressure Increase and Yield of Poly(vinyl butyral)–Barium Titanate–Platinum Multilayer Ceramic Capacitors during Binder Burnout
Authors: Liau Leo C.‐K. , Peters Baron , Krueger Daniel S. , Gordon Al , Viswanath Dabir S. , Lombardo Stephen J.
Published: July 2010

The binder‐burnout kinetics of poly(vinyl) butyral from BaTiO3 multilayer ceramic capacitors with platinum metal electrodes were analyzed by combining thermogravimetric analysis with infrared spectroscopy. The rate of weight loss was accelerated when both BaTiO3 and platinum metal were present, and the presence of both metal and ceramic enhanced the production of CO2. The activation energy and pre‐exponential factor were determined by analysis of the weight‐loss data with a first‐order kinetics model. Then, the decomposition kinetics were incorporated into a coupled heat‐ and mass‐transport model to predict pressure increases as a function of the heating cycle. The heating cycles determined in this manner then were used to evaluate the yield of capacitors 1.3–3.8 cm long and 0.3–1.3 cm high. The optimum yield was realized at an aspect ratio (height:length) of 1:3.
Properties of Boron Nitride (BxNy) Films Produced by the Spin‐Coating Process of Polyborazine
Authors: Kho Joong‐Gon , Moon Kyo‐Tae , Kim Jong‐Hee , Kim Dong‐Pyo
Published: July 2010

Boron‐rich boron nitride (BN) films have been prepared on Si and SiO2/Si substrates by the vacuum pyrolysis of spin‐coated polyborazine films. Physical properties of the prepared films such as film strength, thermal conductivity, and dielectrics were determined. The BN films vacuum‐pyrolyzed at 900°C showed residual N–H bonds with a 0.75 N/B ratio, interdiffusion phenomena, and preferred orientation at the interfacial zone. Hardness and the elastic modulus of the film increased to 1.6 GPa and 50 GPa by nanoindentation loading. It had a thermal conductivity of 134 W/(m·K) at 296.5 K, and a dielectric constant in the range of 5–7, with tan ∂ between 0.01 and 0.47, depending on the film thickness.
Formation of Potential Barrier Related to Grain‐Boundary Character in Semiconducting Barium Titanate
Authors: Hayashi Katsuro , Yamamoto Takahisa , Ikuhara Yuichi , Sakuma Taketo
Published: July 2010

Resistance–temperature (R–T) characteristics were measured directly at single‐grain boundaries in 0.1‐mol%‐niobium‐doped barium titanate bicrystals that had been fabricated from polycrystalline sinters, to determine a geometrical grain‐boundary character dependence of the positive temperature coefficient of resistivity (PTCR) effect. Both random boundaries and low‐Σ boundaries exhibit a similar grain‐boundary character dependence of the PTCR effect through a simple geometrical analysis, using the coincidence of reciprocal lattice points. Differences of the R–T characteristics in individual boundaries have been explained in terms of the formation of a potential barrier that is associated with the oxidation of grain boundaries during cooling, after sintering or annealing. The grain‐boundary character is likely to affect the diffusivity of O2− ions and, hence, is crucial to the formation of the potential barrier.
Complex Impedance Analysis on the Orientation Effect of Whiskers in Oriented Silicon Carbide Whisker/Silicon Nitride Composites
Authors: Wang Chang‐An , Huang Yong , Xie Zhipeng , Li Ying , Zhang Zhongtai
Published: July 2010

The effect of whisker orientation on the electrical properties of SiCw/Si3N4 composites was investigated, using the principle of complex impedance. The impedance spectra of the composites exhibited significant dependence on whisker orientation. Based on the experimental results and the microstructure of the composites, the impedance mechanisms were discussed and a corresponding equivalent‐circuit model was presented, which agreed well with the experiments.
Characterization of Electrical Properties of Li(FexAl1−x)5O8 Solid Solutions by Impedance Spectroscopy
Authors: Arakawa Shuichi , Sano Junya , Hayashi Shinsuke
Published: July 2010

To examine polaronic transport properties in Li(FexAl1−x)5O8 spinel solid solutions, a scaling analysis for their conductivity spectra and modulus spectra was performed. As in the case of ionic conductors, two significant parameters of a crossover frequency and a power‐law exponent were extracted from the conductivity spectra which displayed the universal dynamic response behavior. Both the mobility and the concentration of carriers were successfully determined from the crossover frequency. The power‐law exponent and the stretching parameter obtained from the modulus spectra varied with composition, implying that the increase in Fe concentration would enhance the Coulomb interactions between small polarons.
Behavior of Silver and Palladium Mixtures during Heating
Authors: Garino Terry , Rodriguez Mark
Published: July 2010

The behavior of mixtures of silver and palladium during heating in both air and an inert atmosphere was studied using X‐ray diffractometry (XRD), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), dilatometry, and scanning electron microscopy (SEM). In situ high‐temperature XRD studies on a commercial 20% palladium material with submicrometer‐sized particles indicated that an intermetallic phase, most likely Ag3Pd, formed in air between 300° and 400°C, the same temperature range where a 13% linear expansion was measured by dilatometry. The DSC data indicated an exothermic peak at 340°C, a temperature where the TGA results indicated that the material had picked up only 0.2% oxygen, compared with the maximum of 1.4% at 525°C. No PdO was detected by XRD at 400°C, which suggests that oxygen was being incorporated in the intermetallic. Microstructural examination using SEM indicated that larger particles, with internal pores, had formed after heating in air to 375°C. When the material was heated in argon for 1 h at 400°C, no intermetallic phase or alloy formed, and minimal expansion occurred. When mixtures of larger silver particles (5–30 μm) with palladium particles (1–3 μm) were heated in air, the maximum amount of expansion that occurred increased from 0% for pure palladium up to a maximum of 18% at 75% silver. This result supports the conclusion that expansion is a result of formation of this new phase, in the presence of oxygen, not of the oxidation of the palladium.
Electrical Characterization of Sr0.97Ti1−xFexO3−δ by Complex Impedance Spectroscopy: I, Materials with Low Iron Contents
Authors: Jurado Jose R. , Colomer Marie T. , Frade Jorge R.
Published: July 2010

Impedance spectroscopy has been used to characterize Sr0.97Ti1−xFexO3−δ materials. This technique was suitable to evaluate the grain and grain‐boundary conductivities of samples with ≤5% iron. The role of grain boundaries was changed by sintering in different conditions, and this was interpreted by accounting for microstructural differences. The corresponding relaxation times were also used to confirm the interpretation of complex impedance spectra. The values of grain‐boundary conductivity and the corresponding values of activation energy obtained by this method were relatively close to predictions obtained on assuming a p→n inversion at the grain‐boundary core, as proposed by Waser and coauthors.1–3 The temperature dependence of relaxation times confirmed this finding.
Strength Degradation of Nonrandom Porous Ceramic Structures under Uniaxial Compressive Loading
Authors: Hattiangadi Ashwin , Bandyopadhyay Amit
Published: July 2010

Nonrandom porous mullite ceramics with controlled pore geometry have been fabricated using a lost mold process, where the molds were fabricated using the fused deposition process from CAD data. The pore geometry of molds was varied to achieve different pore sizes and shapes. These porous ceramic structures were then tested under uniaxial compression to evaluate their strength degradation for different pore volumes created by varying pore sizes and shapes. The finite element method (FEM) has been used to understand the effect of these porosity parameters based on stress concentrations along pore boundaries. Strength degradation of porous ceramics was found to be related to the increase in stress concentration along the pore boundaries in three‐dimensional nonrandom porous ceramics.
Crack Healing Behavior of Silicon Carbide Ceramics
Authors: Korouš Jan , Chu Min Cheol , Nakatani Masahiko , Ando Kotoji
Published: July 2010

This study focuses on the crack healing behavior of three kinds of commercial SiC ceramics. Specimens with and without cracks were subjected to thermal treatment at different temperatures, and their strengths were measured by a three‐point bending test in accordance with JIS standards. The tests were performed in air at both room temperature and elevated temperatures between 600° and 1500°C. The healed specimens showed a complete recovery of strength at room temperature for the investigated crack sizes of 2c≅ 100 μm and 2c≅ 200 μm, and their strength increased in accordance with the healing temperature. The behavior of the healed specimens at elevated temperatures was influenced by the material used and the test temperature. Generally, the strength decreased at a high temperature, but the degree of strength reduction was determined by the kind of ceramic. The most important difference between the healed and smooth specimens was exhibited in material A. It was observed that at 1400°C, the bending strength of the healed specimens made from this ceramic was about 37% of the value for specimens in an as‐received state. Static fatigue tests were also performed for ceramic B at 900° and 1000°C. The experiment demonstrated that the static fatigue limit of a healed specimen is about 75% of the monotonic bending strength at the same temperature.
Ion‐Exchange Loading of Yttrium Acetate as a Sintering Aid on Aluminum Nitride Powder via Aqueous Processing
Authors: Shimizu Yasuhiro , Hatano Jun , Hyodo Takeo , Egashira Makoto
Published: July 2010

A novel fabrication process of AlN ceramics via aqueous colloidal processing and pressureless sintering has been presented. The chemical stability of AlN powder in water was improved by the surface chemical modification with sebacic acid, while maintaining a hydrophilic surface. The treatment of the sebacic acid‐modified powder with yttrium acetate tetrahydrate resulted in strong immobilization of Y3+ ions, as a sintering aid, at a highly dispersive level on the AlN powder surface through ion exchange with the free carboxyl groups of the sebacic acid molecules attached to the AlN surface. By selecting slip compositions for a well‐deflocculated condition and firing conditions to burn out organic components in the slip cast compacts, a thermal conductivity of about 250 W/(m·K) could be attained by the pressureless sintering at 1900°C for 5 h.
Anisotropic Abnormal Grain Growth in TiO2/SiO2‐Doped Alumina
Authors: Kim Young‐Min , Hong Seong‐Hyeon , Kim Doh‐Yeon
Published: July 2010

The effect of TiO2/SiO2 addition on the grain growth of alumina was reinvestigated. TiO2 promoted the grain growth, but there was no abnormal grain growth. However, codoping of TiO2 and SiO2 resulted in a duplex microstructure consisting of large platelike grains, ∼800 μm long and ∼100 μm thick, and fine matrix grains. The observed anisotropic abnormal grain growth was explained in terms of liquid formation during heat treatment.
Influence of Fluorine Content in Apatite–Mullite Glass‐Ceramics
Authors: Rafferty Aran , Clifford Anton , Hill Robert , Wood David , Samuneva Bisserka , Dimitrova‐Lukacs Margarita
Published: July 2010

The nucleation and crystallization of a series of glasses based on 4.5SiO2·3Al2O3·1.5P2O5·(5 −z)CaO ·zCaF2 with a Ca:P ratio corresponding to apatite were studied. In these glasses, the objective was to investigate the influence of fluorine content and z was varied from 3 to 0. All the glasses studied crystallized to fluorapatite (FAP) and mullite with the exception of the glass containing no fluorine, which crystallized to β‐tricalcium phosphate (Ca3(PO4)2) and anorthite (CaAl2Si2O8). Glasses that contained sufficient fluorine to form FAP bulk nucleated to give FAP without a nucleation hold. Thermal gravimetric analysis demonstrated a significant weight loss corresponding to the crystallization of mullite, which increased with the fluorine content of the glass and also with decreased particle size. The loss was attributed to volatile SiF4. The glass transition temperature decreased with increased fluorine content of the glass.
Anisotropic Grain Growth in α‐Al2O3 with SiO2 and TiO2 Additions
Authors: Kebbede Anteneh , Parai John , Carim Altaf H.
Published: July 2010

Microstructural changes caused by doping α‐Al2O3 with small amounts of SiO2 and TiO2 added singly or together were investigated. When they were sintered at 1450°C for 120 min, singly doped samples developed equiaxed microstructures, but codoped material developed an anisotropic microstructure that contained platelike grains with an average aspect ratio of 3.4. The development of anisotropy thus resulted from a cooperative effect of silicon and titanium. Amorphous material was present at most grain boundaries in the silicon‐doped sample. In the codoped sample, only boundaries that exhibited a basal facet were penetrated by amorphous material. Energy dispersive X‐ray spectroscopy analysis showed strong titanium enrichment at the edges of platelets. Additional experiments demonstrated that the volume fraction of highly anisotropic platelike grains interspersed with equiaxed grains could be adjusted by using varying amounts of titanium with a constant amount of silicon content. The fracture toughnesses of such materials increased as the structure became more anisotropic.
Preparing Low‐Loss Low‐Temperature Cofired Ceramic Material without Glass Addition
Authors: Jantunen Heli , Rautioaho Risto , Uusimäki Antti , Leppävuori Seppo
Published: July 2010

A low‐temperature cofired ceramic (LTCC) composition for radio‐frequency purposes was accomplished without prior glass preparation. In this process, the formulation was made by mixing the glass‐forming oxides (ZnO, SiO2, and B2O3) with the commercial microwave ceramic MgTiO3–CaTiO3. The sintering, microstructure, and microwave properties were compared to a formulation with exactly the same composition, but a conventional production route, including glass preparation. The novel preparation route resulted in improved firing properties of the mixture. Also, the densities, porosities, and phases of the samples were almost the same as those of the conventional samples, but the phase fractions were different. Finally, this preparation route produced better dielectric values.
Fabrication of Translucent Magnesium Aluminum Spinel Ceramics
Authors: Li Ji‐Guang , Ikegami Takayasu , Lee Jong‐Heun , Mori Toshiyuki
Published: July 2010

A precursor for magnesium aluminum spinel powder, composed of crystalline ammonium dawsonite hydrate (NH4Al(OH)2CO3·H2O) and hydrotalcite (Mg6Al2(CO3)(OH)16·4H2O) phases, was synthesized via precipitation, using ammonium bicarbonate as the precipitant. The precursor was characterized by differential thermal analysis/thermogravimetry, X‐ray diffractometry, and scanning electron microscopy. Reactive spinel powder, which could be densified to translucency under vacuum at 1750°C in 2 h without additives, was obtained by calcining the precursor at 1100°C for 2 h.
Two Types of Domain Boundaries in Lanthanum Magnesium Niobate
Authors: Lee Hwack Joo , Park Hyun Min , Cho Yang Koo , Song Yong Won , Paik Jong Hoo , Nahm Sahn , Byun Jae‐Dong
Published: July 2010

Microstructural studies of the domain boundaries in the complex perovskite compound lanthanum magnesium niobate (La[Mg2/3Nb1/3]O3, LMN) were conducted using transmission electron microscopy. Both the 1:1 chemical ordering of B‐site cations and the tilting of oxygen octahedra affected the domain boundaries. Two types of domain boundaries were observed. In addition to the presence of antiphase boundaries, which were insensitive to the crystallographic planes, ferroelastic domain boundaries that were caused by the phase transition due to the tilting of oxygen octahedra also were present. In some grains, only one type of oxygen tilting was present, which resulted in a single domain in one grain. Two or three domains were observed in a grain where the walls were parallel to the {110} plane. Many domains also were observed in a grain that had boundaries whose linear characteristics were gradually reduced.
Roles of Poly(propylene glycol) during Solvent‐Based Lamination of Ceramic Green Tapes
Authors: Suppakarn Nitinat , Ishida Hatsuo , Cawley James D.
Published: July 2010

Solvent lamination of alumina green tapes is readily accomplished using a mixture of ethanol, toluene, and poly(propylene glycol), or PPG. After lamination, the PPG is clearly present as a discrete film at the interface between the laminated tapes, and direct particle–particle contact does not, in general, exist across the joined surfaces. This condition, however, does not generate delamination during firing. Instead, stacks of green tapes laminated using this mixture routinely sinter to full density and no evidence of original joint persists through the firing process. This paper presents the results of experiments undertaken to determine the role of PPG in the lamination process and, specifically, the mechanism by which it is redistributed during subsequent processing. PPG slowly diffuses through the organic binder film at room temperature. The PPG diffusion rapidly increases as the temperature is increased to 80°C. The key to the efficiency of adhesives during green‐tape lamination is mutual solubility of the nonvolatile component of the glue and the base polymeric binder.
Monolayer Packing of Submicrometer Ceramic Spheres by Employing a Langmuir–Blodgett Film of Dicarboxylic Acid
Authors: Shimizu Yasuhiro , Kawanabe Kazuyuki , Takao Yuji , Egashira Makoto
Published: July 2010

A closely packed monolayer of spherical SiO2 or SiO2–TiO2 particles of submicrometer size has been fabricated on a silicon or glass substrate by employing a Langmuir–Blodgett (LB) film of 1,12‐dodecanedicarboxylic acid, followed by dehydration–condensation reaction between carboxyl groups of the dicarboxylic acid and surface hydroxyl groups of both the substrate and the ceramic spheres. Deposition of the LB film on the substrate was essential for immobilization of ceramic spheres. The flexibility of an alkyl chain in the dicarboxylic acid may have resulted in better capturing of ceramic spheres compared with surface hydroxyl groups on the substrate. Two‐dimensional packing of the ceramic spheres immobilized became dense with decreasing molecular area of the dicarboxylic acid in the LB film and the temperature of the LB medium (water), although partial three‐dimensional attachment of ceramic spheres was observed, especially when an LB film of quite small molecular area was used. In addition, the amount of surface hydroxyl groups on the substrate was found to significantly affect the microstructure of the two‐dimensionally packed ceramic spheres. The closest two‐dimensional packing was observed on a glass substrate by employing an LB film with a molecular area of 0.03 nm2·molecule−1 at 20°C.
Design of Ceramic Materials for Chemical Sensors: Effect of SmFeO3 Processing on Surface and Electrical Properties
Authors: Aono Hiromichi , Sato Masaki , Traversa Enrico , Sakamoto Masatomi , Sadaoka Yoshihiko
Published: July 2010

Perovskite‐type SmFeO3 powders were prepared by the thermal decomposition of a heteronuclear complex, Sm(Fe(CN)6)·4H2O and by solid‐state reaction between the corresponding single oxides, Sm2O3 and Fe2O3. The thermal decomposition behavior of the complex was studied by thermogravimetric analysis. X‐ray diffractometry was used to investigate the structure of the products from the complex thermal decomposition and the formation of SmFeO3 from the oxide mixture. Powders prepared by both methods were used to deposit thick films onto alumina substrates with comb‐type gold electrodes. The microstructure and chemical homogeneity of the film surfaces were investigated by scanning electron microscopy and Auger electron spectroscopy. Thick SmFeO3 single‐phase films having a homogeneous elemental distribution on the surface were obtained when powder prepared by thermal decomposition of the complex was used for deposition, even when the powder was fired at low temperature (800°C). Surface chemical analysis was performed by X‐ray photoelectron spectroscopy (XPS). The O 1s XPS line was deconvoluted into two peaks, attributed to adsorbed oxygen (Oad) and oxygen in the lattice (Olattice). Quantitative analysis showed that the surface coverage of iron, expressed as Fe/(Fe + Sm), was larger for the films prepared using the solid‐state reacted powder. Although the Olattice/(Fe + Sm) atomic ratio was not influenced by the processing procedures (and, thus, by iron surface coverage), the amount of Oad decreased with increasing iron surface coverage. A model of the SmFeO3 surface was used to determine that the outermost layer of the perovskite‐type SmFeO3 prepared from the complex consisted mainly of samarium ions that could each bond four adsorbed oxygen ions. A single oxygen ion could adsorb onto an iron ion, and therefore, the content of adsorbed oxygen was lower for the film prepared from the solid‐state reacted powders, which showed larger iron surface coverage. Electrical conductance measurements, performed with increasing temperature in different gaseous environments, confirmed these findings. Higher conductances and lower activation energies were observed for the films with larger samarium surface coverage.
In‐Plane Fracture Resistance of a Crossply Fibrous Monolith
Authors: McNulty John C. , Begley Matthew R. , Zok Frank W.
Published: July 2010

The in‐plane fracture resistance of a crossply Si3N4/BN fibrous monolith in the 0°/90° and ±45° orientations is examined through tests on notched flexure specimens. The measurements and observations demonstrate the importance of fiber pullout following fiber fracture. The mechanical response is modeled using a crack‐bridging approach. Two complementary approaches to evaluating the bridging law are developed: one based on a micromechanical model of fiber pullout and the other based on the load versus crack mouth opening displacement response of the flexure specimens following fracture of all fibers. Both approaches indicate that the bridging law follows an exponential form, characterized by a bridging strength and an effective pullout length. An assessment of the bridging model is made through comparisons of simulations of the load–displacement response with those measured experimentally.
Luster Pottery from the Thirteenth Century to the Sixteenth Century: A Nanostructured Thin Metallic Film
Authors: Pérez‐Arantegui Josefina , Molera Judit , Larrea Angel , Pradell Trinitat , Vendrell‐Saz Marius , Borgia Ilaria , Brunetti Brunetto G. , Cariati Franco , Fermo Paola , Mellini Marcello , Sgamellotti Antonio , Viti Cecilia
Published: July 2010

Luster is a decorative metallic film that was applied on the surface of medieval glazed pottery. It can be obtained via the low‐temperature (∼650°C), controlled reduction of copper and silver compounds. In this paper, we show that luster is a thin layered film (200–500 nm thick) that contains metallic spherical nanocrystals dispersed in a silicon‐rich matrix and has a metal‐free outermost glassy layer that is 10–20 nm thick. Silver nanocrystals seem to be separated from those of copper, forming aggregates 5–100 μm in diameter. This composite structure exhibits optical properties that are dependent on both the particle size and the matrix. Luster is indeed the first reproducible nanostructured thin metallic film that was made by humans.
Synthesis of a Hydroxyapatite/Collagen/Chondroitin Sulfate Nanocomposite by a Novel Precipitation Method
Authors: Rhee Sang‐Hoon , Tanaka Junzo
Published: July 2010

A hydroxyapatite/collagen/chondroitin sulfate nanocomposite that partly mimicked the composition of cartilage was synthesized through a novel precipitation method, using a calcium hydroxide suspension and phosphoric acid solutions that contained several mixing ratios of type II collagen (Col) and chondroitin sulfate (ChS). The precipitates were shaped and consolidated via filter pressing and subsequent cold isostatic pressing, respectively. A preferential alignment of the crystallographic c‐axis of the hydroxyapatite nanocrystals along the longitudinal direction of the Col and ChS mixture was observed. The fracture strength and Vickers hardness of the nanocomposites were in the ranges of 35–50 and 119–219 MPa, respectively. This nanocomposite may be applicable for use as a bone substitute, because of its potential capability of bone remodeling through endochondral ossification.
Influence of Aluminum–Oxygen–Yttrium Solid Solution on the Aqueous Tribological Behavior of Silicon Nitride
Authors: Satoh Takeshi , Sakaguchi Shuji , Hirao Kiyoshi , Toriyama Motohiro , Kanzaki Shuzo
Published: July 2010

To investigate the influence of crystal structure and solid solutions of certain elements in Si3N4 on aqueous tribological properties, seven specimens were fabricated. Solid solutions of aluminum and oxygen made the friction coefficient and wear increase in both α‐type and β‐type crystal structures. In particular, α‐SiAlON, in which yttrium is also incorporated into the α‐Si3N4 lattice, showed a higher friction coefficient and wear than other specimens containing the same concentration of Al or O.
Dynamic Rheology of Agar Gel Based Aqueous Binders
Authors: Labropoulos Kyriakos C. , Rangarajan Sriram , Niesz Dale E. , Danforth Stephen C.
Published: July 2010

Dynamic rheology was used to study the gelation behavior of agar gel based aqueous binders (1–3 wt%) for powder injection molding. Typical gelation temperatures, Tgel, and liquefaction temperatures, Tliq, were 36° and 78°C, respectively. The thermal history of the gels was found to influence Tgel and the asymptotic storage modulus, G′. A higher degree of undercooling (ΔT=Tgel−Thold) enhanced the driving force for gelation. G′ master curves were created and revealed a relatively weak frequency dependence. G′ increased significantly with agar content. The shape of the gel's relaxation spectrum was found to be independent of agar content, indicating that the nature of the relaxation processes does not change significantly.
Conversion of Oak to Cellular Silicon Carbide Ceramic by Gas‐Phase Reaction with Silicon Monoxide
Authors: Vogli Evelina , Mukerji Joydeb , Hoffman Christiane , Kladny Ralf , Sieber Heino , Greil Peter
Published: July 2010

Oak has been converted to a porous biocarbon template by annealing in an inert atmosphere above 800°C. Subsequent infiltration with gaseous SiO at 1550–1600°C under flowing argon of atmospheric pressure finally resulted in the formation of a porous, cellular β‐SiC ceramic. The conversion retains the biomorphic cellular morphology of oak tissue. While pores in the cell walls with a diameter less than ∼1 μm vanished, two distinct pore channel maxima representing tracheidal cells and large vessels remained in the SiC ceramic. Depending on the cellular morphology of different kinds of wood, e.g., strut thickness and pore size distribution, gas‐phase conversion to single‐phase β‐SiC can be used to manufacture cellular ceramics with a wide range of pore channel diameters.
Adsorption of Hydroxypropyl Methyl Cellulose in an Aqueous System Containing Multicomponent Oxide Particles
Authors: Sawyer Constance B. , Reed James S.
Published: July 2010

The adsorption behavior of a hydroxypropyl methyl cellulose (HPMC) polymer in aqueous suspensions of alumina, silica, kaolin, and talc powders, two‐component combinations, and one three‐component combination was determined. Powders were well characterized by chemical analysis, XRD, DRIFT, SEM, particle size, surface area, and density analyses. The zeta‐potential of each powder in aqueous suspension was determined over a range of pH to determine particle charging and the isoelectric point for each material. Alumina and silica powders having heavily hydroxylated surfaces were observed not to adsorb the HPMC polymer over a range of pH. The layer‐type minerals talc, which was noticeably hydrophobic, and kaolin, which had differently hydrated basal planes, adsorbed the HPMC polymer but in different amounts per unit of surface area. In the two‐component systems, HPMC polymer adsorption for systems of dispersed particles of like electrical charge (kaolin + silica, talc + silica or alumina, and kaolin + talc) was proportionate to the sum of the fraction x specific surface area x adsorption capacity for each particle type. In systems where particles had an opposite electrical charge (kaolin + alumina, kaolin + talc + alumina), the HPMC polymer adsorption was significantly lower than that calculated for a dispersed system. SEM analysis showed very fine, nonadsorbing alumina particles predominantly on the faces of the adsorbing kaolin particles that apparently masked polymer adsorption. Results suggested a hydrophobic mechanism for the HPMC polymer adsorption and adsorption on only one face of the kaolin particles.
Dielectric Properties of the Perovskite System Pb(Mg1/3Nb2/3)O3‐PbTiO3Modified by Pb(Mg1/3Ta2/3)O3and Pb(Zn1/3Nb2/3)O3
Authors: Suh Dong‐Hwan , Lee Dong‐Ha , Kim Nam‐Kyoung
Published: July 2010

Effects of Pb(Mg1/3Ta2/3)O3and Pb(Zn1/3Nb2/3)O3substitution in the Pb(Mg1/3Nb2/3)O3‐PbTiO3ceramic system on structure formation, crystallographic aspects, and dielectric properties are discussed. Developed phases in the B‐site precursor and perovskite systems were studied by X‐ray diffraction. Crystal symmetries and dimensions of the perovskite unit cell of the two systems are compared. Changing rates of the lattice parameter with substituent PbTiO3concentration in the two modified systems are virtually identical to that of the unmodified Pb(Mg1/3Nb2/3)O3‐PbTiO3system. Weak‐field low‐frequency dielectric responses of the ceramics were investigated. The dielectric maximum temperatures of the two perovskite systems shifted almost linearly with compositional change. Dielectric constant spectra at low concentrations of PbTiO3exhibited typical diffuse phase transition behavior, whereas those at high PbTiO3concentrations were rather sharp. The phase transition modes reflected on the dielectric spectra were quantitatively analyzed in terms of diffuseness parameters.
Influence of Copper(II) Oxide Additions to Zinc Niobate Microwave Ceramics on Sintering Temperature and Dielectric Properties
Authors: Kim Dong‐Wan , Ko Kyung Hyun , Hong Kug Sun
Published: July 2010

The effect of CuO additions on the firing temperature of ZnNb2O6 ceramics was investigated using dilatometry, transmission electron microscopy, and X‐ray diffractometry. A 5 wt% CuO addition to ZnNb2O6 ceramics significantly lowered the firing temperature from 1150° to ∼900°C. The presence of a CuO‐rich intergranular phase in the specimen was observed and was evidence of the formation of a liquid phase during sintering. The composition of the liquid phase was (ZnCu2)Nb2O8. In particular, the low‐fired ZnNb2O6 ceramics had good microwave dielectric characteristics—Q×f= 59 500, ɛr= 22.1, τf=–66 ppm/oC. These properties were correlated with the formation of a second phase, (ZnCu2)Nb2O8.
Effects of Calcium Substitution on the Structural and Microwave Dielectric Characteristics of [(Pb1−xCax)1/2La1/2](Mg1/2Nb1/2)O3 Ceramics
Authors: Liu Chin‐Lin , Wu Tai‐Bor
Published: July 2010

The effects of calcium substitution on the structural and microwave dielectric characteristics of [(Pb1−xCax)1/2La1/2](Mg1/2Nb1/2)O3 ceramics (with x= 0.01–0.5) were investigated. All the materials were observed to have an ordered A(B1/2′B1/2″)O3‐type perovskite structure; however, the space group of the structure changed from Fm3m to Pa3 as the calcium content increased to x= 0.1, and then from Pa3 to R3¯ at the x= 0.5 composition. During the structural evolution, the lattice parameter of the perovskite cell decreased linearly, and the dielectric constant (k) also decreased, from k= 80 to k= 38. However, the product of the quality factor and the resonant frequency (Q×f) increased from 50 000 GHz to 90 000 GHz as the calcium content increased. Also, the temperature coefficient of resonant frequency (τƒ) gradually changed from 120 ppm/°C to −40 ppm/°C as the calcium content increased. At the x= 0.3 composition, a combination of properties—k∼ 50, Q×f∼ 86 000 GHz, and τƒ∼ 0 ppm/°C—can be obtained.
Long‐Term Behavior and Application Limits of Plasma‐Sprayed Zirconia Thermal Barrier Coatings
Authors: Langjahr Petra A. , Oberacker Rainer , Hoffmann Michael J.
Published: July 2010

Investigations of changes in phase composition, mechanical properties, and microstructure of ZrO2‐based plasma‐sprayed thermal barrier coatings (TBCs) with 8 mol% CeO2, 19.5 mol% CeO2/1.5 mol% Y2O3, 35 mol% CeO2, and 4.5 mol% Y2O3 after long‐term heat treatments at typical operation temperatures (1000°–1400°C) are presented. Experimental studies include X‐ray diffractometry, mechanical testing, and scanning electron microscopy. Thermal cycling experiments also have been performed. TBCs with 8 mol% CeO2 contain mainly the tetragonal equilibrium phase and, therefore, show rapid failure because of the high amount of tetragonal → monoclinic phase transformation, even after relatively short heat treatments (1250°C/1 h). In the case of the other systems that consist mainly of the tetragonal or cubic nonequilibrium phases, TBCs with 19.5 mol% CeO2/1.5 mol% Y2O3 or 35 mol% CeO2 reveal a smaller amount of monoclinic phase after long‐term heat treatments (1250°C/1000 h) compared with TBCs containing 4.5 mol% Y2O3. TBCs containing 35 mol% CeO2 show a higher degree of sintering than the TBCs with 19.5 mol% CeO2/1.5 mol% Y2O3 and, therefore, a greater increase of the elastic modulus. Among the systems investigated, TBCs containing 4.5 mol% Y2O3 exhibit the highest resistance to failure in thermal‐cycling experiments.
Effect of Shear Damage on the Fracture Behavior of Carbon–Carbon Composites
Authors: Goto Ken , Hatta Hiroshi , Takahashi Hirotsugu , Kawada Hiroyuki
Published: July 2010

The notch insensitivity of carbon–carbon composites (C/Cs) has been believed to result primarily from shear damage near sources of stress concentration. To evaluate this hypothesis, notch sensitivity has been examined for C/Cs with crossply laminates (CP‐C/Cs) and quasi‐isotropic (QI‐C/Cs) laminates. The main difference in both laminates involves their shear behavior: the QI‐C/Cs have an almost‐linear stress–strain curve and high strength, whereas the CP‐C/Cs exhibit strong nonlinearity and low strength. Thus, the effect of shear damage can be extracted by comparison of both materials. Experimental results from the present study have shown that the fracture behaviors of both C/Cs are quite similar. Finite‐element analyses also have revealed that the stress redistribution caused by shear nonlinear deformation is too small to explain its toughening behavior, even in the CP‐C/C. From these results, it is concluded that the notch‐insensitive behavior of the C/Cs cannot be explained by the already‐proposed shear‐damage mechanism. To this end, a discussion has been conducted on a new possible toughening mechanism that is capable of generating the R‐curve and notch insensitivity.
Relationship between Microstructure and Fracture Toughness of Toughened Silicon Carbide Ceramics
Authors: Lee Sung‐Gu , Kim Young‐Wook , Mitomo Mamoru
Published: July 2010

Different microstructures in SiC ceramics containing Al2O3, Y2O3, and CaO as sintering additives were prepared by hot‐pressing and subsequent annealing. The microstructures obtained were analyzed by image analysis. Crack deflection was frequently observed as the toughening mechanism in samples having elongated α‐SiC grains with aspect ratio >4, length >2 μm, and grain thickness (t) <3 μm (defined as key grains 1). Crack bridging was the dominant toughening mechanism observed in samples having grains with thickness of 1 μm < t < 3 μm and length >2 μm (key grains 2). The values of fracture toughness varied from 5.4 to 8.7 MPa·m1/2 with respect to microstructural characteristics, characterized by mean grain thickness, mean aspect ratio, and total volume fraction of key grains. The difference in fracture toughness was mainly attributed to the amount of key grains participating in the toughening processes.
Microstructure of a Complex Oxide, Er2Mn2/3Mo4/3O7, with a Pyrochlore‐Related Structure
Authors: Nakano Hiromi , Kamegashira Naoki
Published: July 2010

The ternary compound Er2Mn2/3Mo4/3O7, with a pyrochlore‐related structure, was synthesized in a vacuum‐sealed quartz tube at 1373 K. The compound was characterized by X‐ray diffractometry, electron probe microanalysis, and transmission electron microscopy. The compound possessed a monoclinic structure, with lattice parameters of a= 1.2781(2) nm, b= 0.7378(5) nm, c= 1.1643(6) nm, and β= 100.53(1)°. The compound had a large number of lamellar domains, which were composed of a microtwinned structure on the twin axis 〈1¯1¯0〉.
Effect of Surface Impurities on the Microstructure Development during Sintering of Alumina
Authors: Sone Tae‐Wook , Han Joo‐Hwan , Hong Seong‐Hyeon , Kim Doh‐Yeon
Published: July 2010

Microstructural evolution during sintering of alumina powder compacts prepared by cold isostatic pressing (CIP) was monitored. For CIP, rubber molds lubricated with silicone oil were used so that a very small amount of impurity was introduced to the surface of the powder compacts. During sintering at 1600°C, grain growth in the surface region was inhibited up to sintering for 1 h, but subsequently abnormal grain growth occurred. In the inner region, however, the grains grew uniformly without abnormal grain growth. Impurities that initially drag the boundary migration but form liquid at the end are suggested to cause abnormal grain growth.
Pore–Boundary Separation Behavior during Sintering of Pure and Bi2O3‐Doped ZnO Ceramics
Authors: Choi Jung‐Hae , Hwang Nong‐Moon , Kim Doh‐Yeon
Published: July 2010

Pore–boundary separation in ZnO and 99.95ZnO·0.05Bi2O3 (in mol%) specimens during sintering at 1200°C was investigated. In pure ZnO specimens, pores were attached to the grain boundaries and disappeared during the final stage of sintering. In the Bi2O3‐doped specimens, on the other hand, many pores were separated from the boundaries and trapped inside the grains. Observation using transmission electron microscopy showed that a thin layer of Bi2O3‐rich phase existed at the boundaries in the Bi2O3‐doped specimens. The pore separation in 99.95ZnO·0.05Bi2O3 specimens was explained in terms of the dihedral angle change and the high mobility of a liquid film boundary.
Mechanical Properties of Dry‐Pressed Alumina Green Bodies
Authors: Carneim Tamara J. , Green David J.
Published: July 2010

The elastic modulus and the tensile strength of uniaxially pressed alumina‐kaolin green bodies were measured using noncontact ultrasound and diametral compression, respectively. These properties showed a strong dependence on the green density and, therefore, the compaction stress. The dependence on density was compared with theoretical models and these did not accurately describe the observed behavior. Possible causes of the discrepancies with the theoretical derivations are discussed. The choice of binder was shown to play a critical role in determining the elastic modulus, strength, strength variability, and fracture morphology.
Preparation of Nickel Powders by Spray Pyrolysis of Nickel Formate
Authors: Xia Bin , Lenggoro I. Wuled , Okuyama Kikuo
Published: July 2010

The preparation of nickel powders by the ultrasonic spray pyrolysis of Ni(HCOO)2 was studied. Phase‐pure nickel powder was obtained at as low as 350°C. HCOOH was a reducing source for nickel formation. Moreover, metallic nickel was obtained at a residence time as short as 0.1 s at 600°C. A broad range of particle morphologies, which included agglomerated nanoparticles, nonagglomerated submicrometer particles, hollow particles, and spherical dense particles, were obtained from Ni(HCOO)2 pyrolysis and were shown to depend on the precursor solution and the operating condition.
Synthesis of Ultrafine Ceria Powders by Mechanochemical Processing
Authors: Tsuzuki Takuya , McCormick Paul G.
Published: July 2010

The synthesis of ultrafine cerium dioxide (CeO2) powders via mechanochemical reaction and subsequent calcination was studied. Anhydrous CeCl3 and NaOH powders, along with NaCl diluent, were mechanically milled. A solid‐state displacement reaction—CeCl3+ 3NaOH → Ce(OH)3+ 3NaCl—was induced during milling in a steady‐state manner. Calcination of the as‐milled powder in air at 500°C resulted in the formation of CeO2 nanoparticles in the NaCl matrix. A simple washing process to remove the NaCl yielded CeO2 particles ∼10 nm in size. The particle size was controlled in the range of ∼10–500 nm by changing the calcination temperature.
Formation of Barrier Ribs for Plasma Display Panel via Roll Forming of Green Tapes
Authors: Kim Yong‐Seog , Lee Seog‐Young , Hong Soon‐Kug , Jeon Hyung‐Jo
Published: July 2010

In an attempt to explore the possibility of forming barrier ribs for a plasma display panel by plastically deforming a green tape with a grooved roll, the effects of green tape composition and rolling parameters on the height of the barrier ribs formed were studied. For the analysis of the results, viscosity of the green tape was evaluated using a modified slit rheometer. The results indicated that the effects of organic constituents in the green tape and processing parameters on the dimension of the barrier ribs formed are closely related with the pseudoplastic characteristics of the green tape.
Microstructural Evolution in Liquid‐Phase‐Sintered SiC: Part I, Effect of Starting Powder
Authors: Xu Huiwen , Bhatia Tania , Deshpande Swarnima A. , Padture Nitin P. , Ortiz Angel L. , Cumbrera Francisco L.
Published: July 2010

The effect of starting SiC powder (β‐SiC or α‐SiC), with simultaneous additions of Al2O3 and Y2O3, on the microstructural evolution of liquid‐phase‐sintered (LPS) SiC has been studied. When using α‐SiC starting powder, the resulting microstructures contain hexagonal platelike α‐SiC grains with an average aspect ratio of 1.4. This anisotropic coarsening is consistent with interface energy anisotropy in α‐SiC. When using β‐SiC starting powder, the β→α phase transformation induces additional anisotropy in the coarsening of platelike SiC grains. A strong correlation between the extent of β→α phase transformation, as determined using quantitative XRD analysis, and the average grain aspect ratio is observed, with the maximum average aspect ratio reaching 3.8. Based on these observations and additional SEM and TEM characterizations of the microstructures, a model for the growth of these high‐aspect‐ratio SiC grains is proposed.