bluuebunny/crossref_metadata_2025 huggingface dataset:
The Maize Transcription Factor KNOTTED1 Directly Regulates the Gibberellin Catabolism Genega2ox1
Authors: Bolduc Nathalie , Hake Sarah
Published: July 2009

KNOTTED1 (KN1)-like homeobox (KNOX) transcription factors are involved in the establishment and maintenance of plant meristems; however, few direct targets of KNOX proteins have been recognized. Using a combination of double mutant analysis and biochemistry, we found that in maize (Zea mays), KN1 negatively modulates the accumulation of gibberellin (GA) through the control of ga2ox1, which codes for an enzyme that inactivates GA. The ga2ox1 mRNA level is elevated in immature leaves of dominant KNOX mutants and downregulated in reproductive meristems of the null allele kn1-e1. KN1 binds in vivo to an intron of ga2ox1 through a cis-regulatory element containing two TGAC motifs. VP16-KN1 activates transcription in planta from a chimeric promoter containing this binding site. The domains of expression of kn1 and ga2ox1 mRNAs overlap at the base of the shoot apical meristem and the base of newly initiated leaves, suggesting that KN1-mediated activation of ga2ox1 maintains a boundary between meristem cell identity and rapidly elongating cells of the shoot. The KN1 binding site is conserved in ga2ox1 genes of different grasses, suggesting that the local regulation of bioactive GA levels through KNOX proteins is a common theme in grasses.
Synthesis of Hexacelsian Barium Aluminosilicate by a Solid‐State Process
Authors: Lee Kuo‐Tong , Aswath Pranesh B.
Published: July 2009

Synthesis of hexacelsian barium aluminosilicate (BaAl2Si2O8 or BAS) from BaCO3, Al2O3, and amorphous SiO2 was examined. BaCO3 can react with SiO2 and Al2O3 to form barium silicates (Ba2SiO4 or B2S, BaSiO3 or BS, and BaSi2O5 or BS2) and barium aluminate (BaAl2O4 or BA). It is shown that there are two competitive reactions leading to the formation of hexacelsian BAS. One involves a reaction between BS2 and Al2O3 and the other involves a reaction between BA and SiO2. In experiments with the model BS2–Al2O3 and BA–SiO2 systems it is shown that the reaction between BS2 and Al2O3 is much faster than the reaction between BA and SiO2. However, in the BAS system, Al2O3 suppresses the reactions which form BS2 and instead reacts with B2S and BS to form BA. The kinetics of hexacelsian BAS formation are greatly enhanced when BS2 is made separately and fired with Al2O3 to yield BAS.
Spontaneous Infiltration of Iron Silicides into Silicon Carbide Powder Preforms
Authors: Pan Yi , Baptista João L.
Published: July 2009

The infiltration of liquid Fe3Si (mp of ∼1300°C), Fe5Si3 (mp of ∼1210°C), and FeSi (mp of ∼1410°C) into SiC powder preforms was performed at various infiltration temperatures for 60 min under either argon flow or dynamic vacuum. The amount of infiltration under various infiltration conditions was studied as a function of infiltration temperature. For the preforms as‐pressed from raw SiC powder, the amount of infiltration of the three silicides under argon flow was independent of their melting points, but suddenly increased within a common temperature range from 1450° to 1550°C. Thermodynamic analyses indicated that the common temperature range corresponded to the temperature at which the SiO2 on the surface of the SiC particles was decreased under argon flow. Infrared spectroscopy showed SiO2 on the surfaces of as‐received SiC powder particles, but not on the surfaces of the SiC powder particles fired under argon at 1600°C. The amount of infiltration of the as‐pressed SiC under vacuum and of fired SiC under argon and vacuum exhibited an obvious dependence on the silicide melting points. This was attributed to the SiO2 reduction taking place at temperatures lower than the melting points of the silicides. The amount of infiltration was then controlled by the melt viscosity.
Sol–Gel‐Prepared Pure and Lithium‐Doped Hexacelsian Polymorphs: An Infrared, Raman, and Thermal Expansion Study of the β‐Phase Stabilization by Frozen Short‐Range Disorder
Authors: Colomban Philippe , Courret Hellène , Romain François , Gouadec Gwenaël , Michel Daniel
Published: July 2009

Monoclinic and hexagonal forms of celsians (BaAl2Si2O8) were synthesized by hydrolysis–polycondensation of Si/Al alkoxide mixtures. Dilatometry, Raman scattering, IR absorption, and X‐ray diffraction techniques were used to identify various hexacelsian phases and their conversion into the monoclinic phase as a function of thermal treatments and doping. Emphasis is given to the relationship between the shrinkage behavior and the static and dynamic short‐range disorders in the XO4 tetrahedra (X = Si/Al) arrangement. The α hexagonal phase exhibits a well‐defined α–βHT transition at about 300°C but a “statically disordered”βSD form, which does not vary very much with temperature and is very similar to the βHT form obtained below 300°C for some materials. This statically disordered phase is preferentially observed for fast‐sintered lithium‐free compositions and transforms gradually in the ordered form by annealing above 1100°C. Such stabilization of the high‐temperature phase by the static disorder arising from the peculiar synthesis through alkoxide hydrolysis and the gel route, which freeze the dynamic disorder of gel‐forming entities in a static disorder at the gelation step, is discussed in the light of previously observed cases. The thermal expansion behavior is very sensitive to the synthesis conditions, doping, and thermal treatments. The ordered α phase is more easily achieved with lithium‐doped compositions, but lithium addition shifts the hexagonal‐to‐monoclinic phase transformation onset toward lower temperatures and promotes complete transformation with thermal annealing.
Mullite Suspensions for Reticulate Ceramic Preparation
Authors: Roncari Edoardo , Galassi Carmen , Bassarello Carla
Published: July 2009

The dispersing behavior of MgO‐doped mullite suspension suitable for the production of reticulate ceramics by sponge impregnation was studied. Three deflocculants were tested and the optimum dispersing conditions for the mullite suspension were found. Electrokinetic studies of magnesia in water evidence that it undergoes pronounced solubilization that strongly affects the performance of the mullite suspension when added at the 1 wt% concentration, in terms of solid loading and aging effects. The optimum composition of the slurry was found, reticulate mullite samples were produced, and the green and sintered bodies were characterized.
Properties of Highly Porous Hydroxyapatite Obtained by the Gelcasting of Foams
Authors: Sepulveda Pilar , Ortega F. S. , Innocentini Murilo D. M. , Pandolfelli Victor C.
Published: July 2009

Open‐cell hydroxyapatite (HA) foams, produced through the novel technique of gelcasting foams with relative porosities ranging from 0.72 to 0.90, were characterized for pore‐size distribution, surface area, permeability, compressive strength, elastic modulus, and microstructural features. The porous structure, which is composed of an array of spherical cells interconnected through windows, had a mode pore diameter in the range 17–122 μm, as demonstrated by mercury porosimetry. The BET specific surface area increased from 1.5 to 3.8 m2/g as the sample porosity increased. The compressive strength and elastic modulus were in the range 1.6–5.8 MPa and 3.6–21.0 GPa, respectively. The permeability constants, k1 (Darcian) and k2 (non‐Darcian), were strongly dependent on porosity fraction and varied widely, from 1.22 × 10−11 to 4.31 × 10−10 m2 and from 1.75 × 10−6 to 8.06 × 10−5 m, respectively. This combination of properties make the HA foams suitable for a variety of potential applications in the biomedical field, preferentially nonloading, including materials for bone repair, carriers for controlled drug‐delivery systems, and matrixes for tissue engineering.
Elastic Properties of Model Porous Ceramics
Authors: Roberts Anthony P. , Garboczi Edward J.
Published: July 2009

The finite‐element method (FEM) is used to study the influence of porosity and pore shape on the elastic properties of model porous ceramics. Young's modulus of each model is practically independent of the solid Poisson's ratio. At a sufficiently high porosity, Poisson's ratio of the porous models converges to a fixed value independent of the solid Poisson's ratio. Young's modulus of the models is in good agreement with experimental data. We provide simple formulas that can be used to predict the elastic properties of ceramics and allow the accurate interpretation of empirical property–porosity relations in terms of pore shape and structure.
Deformation Mechanisms in Compression‐Loaded, Stand‐Alone Plasma‐Sprayed Alumina Coatings
Authors: Trice Rodney W. , Prine David W. , Faber K. T.
Published: July 2009

Cylindrical, stand‐alone tubes of plasma‐sprayed alumina were tested in compression in the axial direction at room temperature, using strain gauges to monitor axial and circumferential strains. The primary compression‐loading profile used was cyclic loading, with monotonically increased peak stresses. Hysteresis was observed in the stress–strain response on unloading, beginning at a peak stress of 50 MPa. The modulus decreased as the maximum applied stress increased. The stress–strain response was only linear at low stresses; the degree of nonlinearity at high stresses scaled with the stress applied. One‐hour dwells at constant stress at room temperature revealed a time‐dependent strain response. Using transmission electron microscopy and acoustic emission to investigate deformation mechanisms, the stress–strain response was correlated with crack pop‐in, growth, and arrest. It is proposed that the numerous defects in plasma‐sprayed coatings, including porosity and microcracks, serve as sites for crack nucleation and/or propagation. As these small, nucleated cracks extend under the applied stress, they propagate nearly parallel to the loading direction along interlamellae boundaries. With increasing stress, these cracks ultimately link, resulting in catastrophic failure.
Effect of Moisture on the High‐Temperature Stability of Unidirectionally Solidified Al2O3/YAG Eutectic Composites
Authors: Bahlawane Naoufal , Watanabe Tadahiko , Waku Yoshiharu , Mitani Atsuyuki , Nakagawa Narihito
Published: July 2009

The corrosion resistance of a unidirectionally solidified alumina/yttrium aluminum garnet (Al2O3/YAG) eutectic mixture was investigated at high temperature. Samples were exposed to high temperature (1200°–1800°C) in different atmospheres, which included argon, argon/water vapor, air, and air/water vapor. The most important microstructural changes occurred at the interface between the YAG and the Al2O3. Those changes consisted of localized thermal grooving, especially when the corrosive atmosphere contained water vapor. The samples exhibited significant weight loss at high temperature (1800°C) after 20 h of exposure. The calculated volume gain that was induced by the increased surface relief was low and limited, except when the corrosive atmosphere contained air, which indicated that the presence of air (particularly oxygen) induced a more‐active corrosion process. On the other hand, no change in the flexural strength was observed, even after 100 h at 1800°C in a humid atmosphere, because of the cross‐linked structure of the composite, which limited propagation of the groove.
Phase Equilibrium in the Fluorapatite–Anorthite–Diopside System
Authors: Tulyaganov Dilshat Ubaydullayevich
Published: July 2009

The binary systems Ca5[PO4]3F–CaAl2Si2O8 and Ca5[PO4]3F–CaMgSi2O6 have been investigated, via annealing and quenching in the experimental method, direct observation of the melting behavior of the samples, X‐ray diffraction analysis, petrography, and transmission electron microscopy. Phase equilibrium in the ternary system Ca5[PO4]3F–CaAl2Si2O8–CaMgSi2O6 was determined by combining information from the structure of the binary boundary systems and additional experimental data that were obtained from ternary compositions. The glass‐formation region of the fluorapatite–anorthite–diopside system was studied, and the glass compositions for the development of glass‐ceramics for technical and medical applications were identified.
Ruddlesden–Popper Planar Faults and Nanotwins in Heteroepitaxial Nonstoichiometric Barium Titanate Thin Films
Authors: Suzuki Toshimasa , Nishi Yuji , Fujimoto Masayuki
Published: July 2009

Nonstoichiometric 10‐mol%‐excess‐BaO–BaTiO3 (Ba1.1TiO3.1) thin film grown on a (100) SrTiO3 substrate consisted of heteroepitaxial c‐axis‐oriented BaTiO3 perovskite crystals including Ruddlesden–Popper planar faults and nanometer‐scale multiple (111) twin lamellae. High‐resolution electron microscopy and electron energy‐loss spectroscopy revealed that nanotwins with coherent (111) Σ3 coincident site lattice boundaries were terminated in the BaTiO3 matrix to form incoherent (211) Σ3 boundaries accommodating excess barium ions. Both Ruddlesden–Popper planar fault and incoherent (211) boundary formation were proposed as possible accommodation mechanisms of excess barium ions in the perovskite film.
Phase Diagram of the System KF–AlF3
Authors: Chen Rong , Wu Genhua , Zhang Qiyun
Published: July 2009

The system KF–AlF3 was reinvestigated precisely by differential thermal analysis, X‐ray diffractometry, and visual observation. All of the samples for the present investigation were prepared by solution synthesis. The results verified the existence of 2KF·AlF3 (K2AlF5) and KF·4AlF3 in the phase diagram; both compounds were orthorhombic. The cell parameters of the compounds were, respectively, a= 10.87 ± 0.03 Å, b= 10.36 ± 0.01 Å, c= 7.83 ± 0.03 Å, and a= 7.89 ± 0.01 Å, b= 7.57 ± 0.01 Å, c= 6.94 ± 0.01 Å. KAlF4 was confirmed to melt congruently at 575°± 2°C by careful examination.
Oxygen Position, Octahedral Distortion, and Bond‐Valence Parameter from Bond Lengths in Ti1−xSnxO2 (0 ≤x≤ 1)
Authors: Hirata Toshiya
Published: July 2009

Based on the virtual crystal approximation (or Vegard's law), the bond lengths of Ti1−xSnxO2 were deduced from those of TiO2 and SnO2, to allow the oxygen position and octahedral distortion to be determined as a function of x. The oxygen positional parameter (u) increased linearly when the Sn4+ cation (which has a larger ionic radius) was substituted for the Ti4+ cation, whereas the octahedral distortion exhibited a nonlinear decay with increasing x in Ti1−xSnxO2. At the same time, the bond‐valence parameter, which relates bond valence to bond length, so that the central atom in the octahedron can retain a constant valence of +4.0, exhibited a correlation with u for Ti1−xSnxO2. The present results indicate that the different phonon/physical properties of TiO2 and SnO2 and/or their dependence on x in Ti1−xSnxO2 can be associated with different octahedral distortions.
Self‐Catalyzed Synthesis of Organo‐Silica Nanoparticles
Authors: Ottenbrite Raphael M. , Wall Jason S. , Siddiqui Junaid A.
Published: July 2009

A procedure has been developed which utilizes aminopropyltriethoxysilane (APS) as the catalyst and a comonomer in the production of hybrid organo‐silica nanoparticles. Particles ranging from ca. 100 to 500 nm can be prepared using organo‐silanes of the type R′Si(OR)3, where R′= Me, vinyl, allyl, or other hydrophobic groups and R = Me or Et, in a water/surfactant solution. Based on elemental analysis, up to 10 mol% of APS was incorporated into the siloxane particle network. It is thought that the amino groups are located mainly on the surface due to their hydrophilicity and APS′ relatively slow rate of hydrolysis and condensation.
Crack Deflection in Composites with Very Thin Interlayers
Authors: Winn E. Jenny , Chen I‐Wei
Published: July 2009

Composites with very thin second‐phase interlayers were made by painting zirconia tapes with a slurry that contained alumina and a fugitive polymer. Warm uniaxial pressing was used to produce microstructures that contained either straight or wavy interlayers. Through the use of the fugitive polymer and a carefully selected sintering temperature, porosity was introduced into the second phase. Samples that were tested in bending displayed high strengths (540–580 MPa), whereas examination of polished and fractured test bars revealed crack deflection at weak interlayers.
Laser Ablation Synthesis and Optical Characterization of Silicon Carbide Nanowires
Authors: Shi Wensheng , Zheng Yufeng , Peng Hongying , Wang Ning , Lee Chun Sing , Lee Shuit‐Tong
Published: July 2009

Silicon carbide (SiC) nanowires were synthesized at 900°C by the laser ablation technique. The growth morphology, microstructure, and defects in SiC nanowires were characterized by scanning electron microscopy (SEM) and high‐resolution transmission electron microscopy (HRTEM). The Raman scattering study indicated that the Raman peaks corresponding to the TO and LO phonon modes of the SiC nanowires had larger red shifts compared to those of bulk SiC material. The red shift, broadening peak, and the asymmetry of the Raman peak could be explained by the size confinement effect in the radial and growth directions. The growth mechanism of SiC nano‐wires was discussed based on the vapor–liquid–solid reaction.
Effect of Bridged Boron Nitride Coatings on the Flexure Behavior of a Unidirectional Ceramic‐Fiber Ceramic‐Matrix Composite
Authors: Jessen Todd L. , Bender Barry A. , Greenhut Victor A.
Published: July 2009

A series of 50 vol/% unidirectional Nicalon™ fiber/zirconium titanate matrix composites were fabricated by alkoxide infiltration of the fiber tows. The fibers had a thin, amorphous boron nitride coating that was either heavily or lightly bridged. The bridged coatings were a result of localized excess boron nitride deposits and had the effect of binding adjacent fibers at boron nitride nodules during the immersion process. The resultant composites contained matrix‐rich ribbons, which exhibited laminate‐like mechanical behavior reported previously. Highest strength was obtained when the composites were loaded parallel to the ribbon orientation, and highest toughness (WOF) was obtained when the composites were loaded perpendicular to the ribbons. The ribbon orientation had a more pronounced effect on composite behavior than the presence or lack of bridging boron nitride nodules. However, the bridging nodules altered the relative orientation of the matrix‐rich ribbons during fabrication and, thus, the direction of optimal strength or toughness.
Fabrication of Ceramic–Polymer Photonic Crystals by Stereolithography and Their Microwave Properties
Authors: Kirihara Soshu , Miyamoto Yoshinari , Kajiyama Kenji
Published: July 2009

Three‐dimensional photonic crystals with periodic variations in the dielectric constant were fabricated using a stereolithographic rapid prototyping method. The structures were composed of millimeter‐scale ordered epoxy lattices in which ceramic particles with high dielectric constants (such as silica and titania) were dispersed. These crystals were designed to reflect microwaves via the formation of photonic band gaps in a gigahertz range. The attenuation of transmission amplitude through the photonic crystals, which was measured as a function of frequency using a network analyzer, clearly showed the formation of band gaps in the microwave range.
New Materials and Processes for Integrated Optics
Authors: Wilkinson James S.
Published: July 2009

Materials and processes for integrated optics are faced with increasing demands from telecommunications and instrumentation applications. Progress in three aspects of novel materials and processes are described: titanium‐diffused sapphire waveguides and lasers, interferometric excimer laser ablation of waveguide gratings, and surface studies by waveguide surface plasmon resonance.
Tellurite Glasses for Broadband Amplifiers and Integrated Optics
Authors: Shen Shaoxiong , Jha Animesh , Liu Xiaobo , Naftaly Mira , Bindra Kushvinder , Bookey Henry J. , Kar Ajoy K.
Published: July 2009

The present investigation discusses the advantage of using RE‐ion‐doped (Nd3+, Tm3+, and Er3+) TeO2glasses for developing fiber and planar broadband amplifiers and lasers. The spectroscopy of RE‐ion‐doped fibers and glasses is discussed along with the thermal properties of glass hosts. The results of emission from the3H4level in single‐mode Tm3+‐doped tellurite fiber show that the emission band overlaps with Er3+emission from the4I13/2level and Nd3+emission from the4F3/2level in silicate and tellurite glasses, thereby enabling the development of amplifiers and lasers between 1350 and 1650 nm. Recent results using Z‐scan measurements of nonlinear refractive index and absorption demonstrate that the third‐order nonlinearity in undoped TeO2glasses is of the order of 2 × 10−15to 3 × 10−15cm2·W−1between 1300 and 1550 nm. These results are briefly discussed in view of an amplifier operation combined with ultrafast all‐optical switching.
Fabrication of Highly Porous Yttria‐Stabilized Zirconia by Acid Leaching Nickel from a Nickel‐Yttria‐Stabilized Zirconia Cermet
Authors: Kim Hyuk , da Rosa Calvin , Boaro Marta , Vohs John M. , Gorte Raymond J.
Published: July 2009

Porous Y2O3‐stabilized ZrO2 (YSZ) samples were synthesized by preparing NiO/YSZ composites by tape casting and calcining at 1800 K, reducing the NiO to nickel in H2 at 973 K, and finally leaching the nickel out of the structure with 2.2M HNO3 at 353 K. Porous YSZ was prepared from NiO/YSZ composites containing 0, 20, 40, and 50 wt% NiO. Complete removal of the nickel was demonstrated by XRD, weight changes, and porosity increases. Porosities >75% could be achieved without structural collapse of the YSZ phase. Finally, the method was applied to the fabrication of a solid oxide fuel cell with a copper‐based anode operating on H2 and n‐butane.
Chemical Vapor Infiltration Rates of ZrO2 into MoSi2 Porous Bodies and Comparison with Model Calculation
Authors: Yoshikawa Noboru , Evans James W.
Published: July 2009

Zirconia (ZrO2) was chemical vapor infiltrated (CVI) into a partially sintered MoSi2 body (preform) by using zirconium n‐propoxide (Zr(OC3H7)4) as a gas precursor. Infiltration distances at different conditions were compared with the calculated results. Chemical vapor deposition (CVD) film growth rates of ZrO2 were measured, and the data were incorporated into the model calculations. Two models were used to analyze the observed infiltration distances. Initially a conventional model assuming a pore with constant radius (SP model) was used. With this model, it was possible to predict the approximate infiltration distance. However, the model cannot predict pore closure and the infiltration distances for a variety of CVI conditions. Secondly, a newly proposed model (PC model) from a previous paper was applied to calculate the infiltration distance. Using this model, it was possible to predict the occurrence of pore closure or the formation of the deposition layer on the preform surface.
Modeling of Chemical Vapor Infiltration Rate Considering a Pore Size Distribution
Authors: Yoshikawa Noboru , Evans James W.
Published: July 2009

To analyze chemical vapor infiltration (CVI) rates, a simulation model (PC model) was proposed, which is capable of considering difficulties of densification in the internal regions of porous bodies and the pore closure phenomena. In the model, a fictitious tapered pore is constructed based on the pore size distribution of the preform body, and variation of the pore shape during the process is calculated. For simulation study, fictitious tapered pores were constructed using different pore size distribution functions of Gaussian, δ‐function, and flat distribution, and their shapes and characteristics were compared. In the case of the Gaussian flat distribution (large dispersion), the fraction of fine pores was large and these pores became closed near their mouths. Reconversion of temporal fictitious pore shape into the pore distribution function was attempted and the PC model was successfully applied to monitor variations in the pore size distributions during the CVI process.
Defect and Mixed Conductivity in Nanocrystalline Doped Cerium Oxide
Authors: Suzuki Toshio , Kosacki Igor , Anderson Harlan U.
Published: July 2009

The results obtained from a study on the microstructure and the electrical properties of Gd‐doped CeO2 thin films were reported. Dense, nanocrystalline films on sapphire substrates are prepared using a polymeric precursor spin coating technique. The electrical conductivity was studied as a function of temperature and oxygen activity and correlated with the grain size. For nanocrystalline Gd‐doped CeO2 thin films, the ionic conductivity increased with decreasing activation energy as the grain size decreased. A conductivity model was developed to analyze PO2 behavior of the electrical conductivity. Using the conductivity model, the hopping energy of electron conduction and the enthalpy of oxygen vacancy formation were determined for different microstructures.
Weight Function Analysis on the R‐Curve Behavior of Multilayered Alumina–Zirconia Composites
Authors: Moon Robert J. , Hoffman Mark , Hilden Jon , Bowman Keith , Trumble Kevin , Rödel Jürgen
Published: July 2009

The single‐edge V‐notched‐beam (SEVNB) testing geometry was used to measure the crack growth resistance (R‐curve) behavior of multilayered alumina–zirconia composites. Fracture mechanics weight function analysis was applied to predict the R‐curve behavior of multilayered composites having a stepwise change in composition. These results were then used to differentiate the influence of residual stresses from crack‐bridging stresses on the measured R‐curve behavior.
Microstructure and Mechanical Properties of Silicon Nitride Ceramics with Controlled Porosity
Authors: Yang Jian‐Feng , Ohji Tatsuki , Kanzaki Shuzo , Díaz Aranzazu , Hampshire Stuart
Published: July 2009

Porous silicon nitride ceramic with a porosity from 0–0.3 was fabricated by partial hot‐pressing of a powder mixture of α‐Si3N4 and 5 wt% Yb2O3 as sintering additive. Irrespective of the porosity, the samples exhibited almost the same microstructural features including grain size, grain aspect ratio, and pore size. Porosity dependences of Young's modulus, flexural strength, and fracture toughness (KIC) were investigated. All these properties decreased with increasing porosity. However, because of the fibrous microstructure, the decreases of flexural strength and fracture toughness were moderate compared with the much greater decrease of Young's modulus. Thus, the strain tolerance (fracture strength/Young's modulus) increased with increasing porosity. The critical energy release rate also increased slightly with an increasing volume fraction of porosity to 0.166 and remained at the same level with that of the dense sample when the porosity was 0.233. They decreased as porosity increased further.
Elastoplastic Indentation on Heat‐Treated Carbons
Authors: Sakai Mototsugu , Nakano Y. , Shimizu S.
Published: July 2009

A Vickers indenter, as an efficient mechanical microprobe, was applied to carbon materials heat‐treated at temperatures in the range 880°–2600°C. The plasticity of the carbon materials, which was enhanced by increasing the heat‐treatment temperature (HTT), was assessed from the relation between the indentation load, P, and the penetration depth, h. Using the concept of the true hardness, H, as a measure of plasticity and the experimental estimate of the H‐value, the plasticity of the carbon materials was examined as a function of their crystallographic parameters. The residual impression of the carbons at HTT > 1800°C was hardly visible on the indented surface after unloading, because of the nearly complete elastic recovery of the indented surface, yielding a very unique indentation P–h hysteresis in the loading/unloading cycle. The microscopic processes associated with this unique elastic recovery during unloading are discussed here in relation to the reversible slip of the dislocation‐network structures on the graphitic basal planes.
Chemical Durability of Silicon Oxycarbide Glasses
Authors: Sorarù Gian Domenico , Modena Stefano , Guadagnino Emanuel , Colombo Paolo , Egan James , Pantano Carlo
Published: July 2009

Silicon oxycarbide (SiOC) glasses with controlled amounts of Si—C bonds and free carbon have been produced via the pyrolysis of suitable preceramic networks. Their chemical durability in alkaline and hydrofluoric solutions has been studied and related to the network structure and microstructure of the glasses. SiOC glasses, because of the character of the Si—C bonds, exhibit greater chemical durability in both environments, compared with silica glass. Microphase separation into silicon carbide (SiC), silica (SiO2), and carbon, which usually occurs in this system at pyrolysis temperatures of >1000°–1200°C, exerts great influence on the durability of these glasses. The chemical durability decreases as the amount of phase separation increases, because the silica/silicate species (without any carbon substituents) are interconnected and can be easily leached out, in comparison with the SiOC phase, which is resistant to attack by OH− or F− ions.
Structural Analysis of a New Layered Compound: La0.05Sr0.95MnO3
Authors: Nakano Hiromi , Mori Takanori , Horikubi Takayoshi , Kamegashira Naoki
Published: July 2009

We have found a new phase of La0.05Sr0.95MnO3 with a 30‐layer rhombohedral structure by using electron microscopy. The lattice constants were hexagonal axes of a= 0.5444 nm and c= 6.7582 nm. Both weak and strong intensities appeared in selected area diffraction (SAD) patterns. The strong intensities were caused by the periodicity of 15 (Sr,La)O3 layers that had a new stacking sequence of (cchch)3. However, the weak intensities indicated that the 15‐layer structure has modulation along the c‐direction that is twice as long as that of the structure indicated by the strong intensities. We concluded that the modulation of the 30‐layer structure was produced by the introduction of two kinds of oxygen octahedra, Mn3+O6 and Mn4+O6.
Abnormal Grain Growth in Alumina with Anorthite Liquid and the Effect of MgO Addition
Authors: Park Chan Woo , Yoon Duk Yong
Published: July 2009

Abnormal grain growth (AGG) in alumina with anorthite liquid has been observed with varying anorthite and MgO contents, at 1620°C. When only anorthite is added to form a liquid matrix, the grain–liquid interfaces have either flat or hill‐and‐valley shapes indicating atomically flat (singular) structures. The large grains grow at accelerated rates to produce AGG structures with large grains elongated along their basal planes. This is consistent with the slow growth at low driving forces and accelerated growth above a critical driving force predicted by the two‐dimensional nucleation theory of surface steps. With increasing temperature, the AGG rate increases. The number density of the abnormally large grains increases with increasing anorthite content. The addition of MgO causes some grain–liquid interfaces to become curved and hence atomically rough. The grains also become nearly equiaxed. With increasing MgO content the number density of the abnormally large grains increases until the grain growth resembles normal growth. This result is qualitatively consistent with the decreasing surface step free energy associated with partial interface roughening transition.
High‐Temperature Hydroxylation of Mullite
Authors: Rüscher Claus H. , Shimada Shiro , Schneider Hartmut
Published: July 2009

A plane‐parallel, polished, 0.9 mm thick, single‐crystal (001) plate of 2:1 mullite was treated for 6 h at 1600°C in an Ar/H2O (90/10) gas mixture at 100 kPa. Optical microscopy studies and infrared (IR) reflection spectroscopy studies of the lattice vibrations yielded no evidence for change with respect to the untreated reference crystal. However, IR absorption spectroscopy showed that structurally bound OH groups were formed by the heat treatment in the Ar/H2O gas mixture. IR absorption depth profile analysis showed a rather homogeneous OH distribution through the crystal. Five different hydroxyl groups were separated according to dipole orientations and peak positions: E‖a, ωa1= 3447 cm−1, ωa2= 3579 cm−1; E‖b, ωb1= 3456 cm−1, ωb2= 3544 cm−1; and E‖c, ωc1= 3498 cm−1. All IR peaks were strongly broadened (between 90 and 150 cm−1) because of a distribution in O‐H binding distances caused by the real structure of mullite.
Effects of B2O3 on the Phase Stability of Ba2Ti9O20 Microwave Ceramic
Authors: Wang Sea‐Fue , Chung Chiang‐Chuang , Wang Chai‐Hui , Chu Jinn P.
Published: July 2009

Preparation of dense and phase‐pure Ba2Ti9O20 is generally difficult using solid‐state reaction, since there are several thermodynamically stable compounds in the vicinity of the desired composition and a curvature of Ba2Ti9O20 equilibrium phase boundary in the BaO–TiO2 system at high temperatures. In this study, the effects of B2O3 on the densification, microstructural evolution, and phase stability of Ba2Ti9O20 were investigated. It was found that the densification of Ba2Ti9O20 sintered with B2O3 was promoted by the transient liquid phase formed at 840°C. At sintering temperatures higher than 1100°C, the solid‐state sintering became dominant because of the evaporation of B2O3. With the addition of 5 wt% B2O3, the ceramic yielded a pure Ba2Ti9O20 phase at sintering temperatures as low as 900°C, without any solid solution additive such as SnO2 or ZrO2. The facilities of B2O3 addition to the stability of Ba2Ti9O20 are apparently due to the eutectic liquid phase which accelerates the migration of reactant species.
Inhomogeneity of Grain‐Boundary Resistivity in Calcia‐Stabilized Zirconia
Authors: Lee Jong‐Heun , Lee Je Hun , Kim Doh‐Yeon
Published: July 2009

Impedance spectroscopy with millimeter‐scale electrodes was used to determine the local grain‐boundary resistivity (ρgb) of a 1‐mol%‐Al2O3‐doped CaO‐stabilized ZrO2 (CSZ) specimen. A much higher ρgb at the specimen surface was observed compared with that of the specimen interior. The result was mainly due to the difference in the dihedral angle of the intergranular phase, which was ∼20° at the surface and ∼100° at the interior.
Evolution of the Grain Size Distribution during the Sintering of Alumina at 1350°C
Authors: Nettleship Ian , McAfee Richard J. , Slaughter William S.
Published: July 2009

The objectives of this study are to provide some rare unfolded grain size distribution data for the sintering of alumina and to test for time invariance of the normalized grain size distribution as required by normal grain growth. The results show that ln ς doubled during the sintering times studied. The changes in the grain size distribution may be due to an increase in the number of relatively large grains combined with a reduction in the number of grain annihilation events compared with that required for time invariance of the normalized grain size distribution.
Sintering and Characterization of Nanophase Zinc Oxide
Authors: Hynes Anne P. , Doremus Robert H. , Siegel Richard W.
Published: July 2009

Nanocrystalline, single‐phase undoped ZnO was sintered to 95%–98% of theoretical density at 650°–700°C, using pressureless isothermal sintering. The density increased very rapidly at 500°–600°C, remained constant with sintering temperature until ∼900°C, and then decreased slightly. The estimated activation energy for densification at 600°–700°C (275 kJ/mol) was comparable to grain‐growth activation energies previously reported for microcrystalline ZnO but much greater than the grain‐growth activation energy measured in the present work. A bimodal microstructure, consisting of nanocrystalline grains within larger ensembles (“supergrains”), was observed, and both modes grew as the sintering temperature increased. The grain‐growth activation energy for the nanocrystalline grains was extremely low, ∼20 kJ/mol. The activation energy for the growth of the supergrains depended strongly on temperature but was ∼54 kJ/mol at >500°C. The important mechanisms probably are rearrangement of the nanoparticle grains, with simultaneous surface and boundary diffusion, and vapor transport above 900°C.
Complete Elastic Tensor for Mullite (∼2.5Al2O3·SiO2) to High Temperatures Measured from Textured Fibers
Authors: Palko James W. , Sayir Ali , Sinogeikin Stanislav V. , Kriven Waltraud M. , Bass Jay D.
Published: July 2009

Directionally solidified mullite fibers have been grown by the laser‐heated, float‐zone method from starting materials with a nominal composition of 3Al2O3·2SiO2. The fibers used in this study have large single‐crystal regions with composition 2.5Al2O3·SiO2 and (001) fiber axis orientation. The complete elastic tensor of these samples has been determined by Brillouin spectroscopy at room temperature and elevated temperatures up to 1200°C. Isotropic moduli (bulk, shear, and Young's) have been calculated using the Voigt–Reuss–Hill averaging scheme. The room‐temperature values obtained are KVRH= 173.5 ± 6.9 GPa, GVRH= 88.0 ± 3.5 GPa, EVRH= 225.9 ± 9.0 GPa. All moduli show gradual, linear decreases with temperature. The temperature derivatives obtained for the equivalent, isotropic moduli are dKVRH/dT=−17.5 ± 2.5 MPa/°C, dGVRH/dT=−8.8 ± 1.4 MPa/°C, dEVRH/dT=−22.6 ± 2.8 MPa/°C. Substantial differences between bulk properties calculated from the single–crystal measurements in this study and the properties reported in the literature for polycrystalline sintered mullite are identified, indicating the importance of factors such as microstructure, intergranular phases, and composition to the elasticity of mullite ceramics.
Kinetic Model for α–Tricalcium Phosphate Hydrolysis
Authors: Durucan Caner , Brown Paul W.
Published: July 2009

A mechanistic model for the kinetics of hydrolysis of α‐tricalcium phosphate (α–Ca3(PO4)2 or α‐TCP) to hydroxyapatite (Ca10−x(HPO4)x(PO4)6−x(OH)2−x or HAp) has been developed. The model is based on experimental hydrolysis rate data obtained using isothermal calorimetry. Analysis of the kinetic data according to the general kinetics models in terms of the fractional degree of reaction and time suggests the hydrolysis to be controlled by different rate‐limiting mechanisms as reaction proceeds. Initially, the hydrolysis kinetics depend on the surface area of the anhydrous α‐TCP. Subsequently, they change to a dependence on the rate of HAp product formation controlled by a nucleation and growth mechanism. The model predicts that HAp nuclei form at essentially one time and growth occurs in two dimensions, leading to a platelike morphology. The change in the reaction mechanism occurs at a fractional degree of hydrolysis, which does not change significantly with temperature in the range of 37°–56°C.
Rate Effects in Critical Loads for Radial Cracking in Ceramic Coatings
Authors: Lee Chul‐Seung , Kim Do Kyung , Sánchez Jose , Miranda Pedro , Pajares Antonia , Lawn Brian R.
Published: July 2009

Rate effects in the Hertzian contact loading of model glass/polycarbonate and silicon/polycarbonate bilayers bonded by epoxy adhesive are examined. Glass is used because of its high susceptibility to slow crack growth, making this conventional contribution to the rate dependencies easy to distinguish. Silicon is used as a control material with effectively no slow crack growth. Abrasion damage is introduced into the undersurfaces of the brittle coating layers to provide controlled flaws for the initiation of radial cracks from flexural stresses introduced by the contact loading. Critical loads are measured as a function of loading rate. Comparative flexural strength tests on free‐standing abraded specimens show a pronounced rate dependence in the glass but none in the silicon, entirely consistent with slow crack growth effects. The glass/polycarbonate bilayer critical load data show a similar trend, but with stronger loading‐rate dependence, suggesting an extraneous contribution to the kinetics from the adhesive/substrate. The silicon/polycarbonate bilayer data also show a loading‐rate dependence, albeit much smaller, confirming this last conclusion. Data from cyclic contact tests on the glass/polycarbonate bilayers coincide with the loading‐rate data on lifetime plots, eliminating the likelihood of a mechanical component in the fatigue response. It is concluded that the adhesive/substrate contribution is viscoelastic in nature, from energy‐dissipating (but noncumulative) anelastic deformation during the cyclic loading. Critical load tests on bilayers with different exposures to external water show no influence of external environment, suggesting that internal moisture is responsible for the slow crack growth in the glass‐coating bilayers.
Phase Distribution and Residual Stresses in Melt‐Grown Al2O3‐ZrO2(Y2O3) Eutectics
Authors: Harlan Nicole R. , Merino Rosa I. , Peña José I. , Larrea Angel , Orera Victor M. , González Carlos , Poza Pedro , LLorca Javier
Published: July 2009

Al2O3‐ZrO2 eutectics containing 0 to 12.2 mol% Y2O3 (with respect to zirconia) were produced by directional solidification using the laser floating zone (LFZ) method. Processing variables were chosen to obtain homogeneous, colony‐free, interpenetrating microstructure for all of the compositional range, optimum from the viewpoint of mechanical properties. The amount of cubic, tetragonal, or monoclinic zirconia phases was determined using a combination of Raman and X‐ray diffraction techniques. Monoclinic zirconia was present up to concentrations of 3 mol% Y2O3, while the amount of tetragonal zirconia gradually increased with yttria content up to 3 mol%. Cubic zirconia was the only phase detected when the yttria content reached 12 mol%. The residual stresses in alumina were measured using the shift of the ruby R lines. Compressive stresses were isotropic when measured in the samples containing tetragonal and cubic zirconia, while higher tensile, anisotropic stresses were found when monoclinic zirconia was present. They were partially relieved in the eutectic sample without yttria. These results were compared with a thermoelastic analysis based on the self‐consistent model.
Phase Transformations of Plasma‐Sprayed Zirconia–Ceria Thermal Barrier Coatings
Authors: Lee Eui Yeol , Sohn Yong‐ho , Jha Santosh K. , Holmes John W. , Sisson Richard D.
Published: July 2009

Phase constituents and transformations of plasma‐sprayed thermal barrier coatings (TBCs) with CeO2‐stabilized ZrO2 (CSZ; 16–26 wt% CeO2) have been investigated using X‐ray diffractometry (XRD), scanning electron microscopy (SEM), and energy‐dispersive spectroscopy (EDS). The as‐coated CSZ coatings with 16 and 18 wt% CeO2 consisted only of the nonequilibrium tetragonal (t′) phase. A mixture of the t′ and the nonequilibrium cubic (c′) phases was observed for the as‐coated CSZ coatings containing 20–26 wt% CeO2. During 65 min cyclic oxidation at 1135°C (45 min hold time) in air, the t′ or the mixture of the t′ and the c′ phases decomposed to the equilibrium tetragonal (t) and the equilibrium cubic (c) phases. Some of the t phase transformed to the monoclinic (m) phase on cooling. More m phase was observed to develop in the CSZ coating containing 16 wt% CeO2 than in the other coatings. More m phase was observed on the top surface than on the bottom surface of the CSZ coating. Spalling of the plasma‐sprayed CSZ coating during thermal cycling occurred after 230 cycles for the CSZ coating containing 16 wt% CeO2, whereas the lifetime of the CSZ coatings with 18–26 wt% CeO2 ranged between 320 and 340 cycles.
Quantitative Analysis of Microstructural Homogeneity and Capacitance Correlations in Palladium/Yttria‐Stabilized Zirconia Composites
Authors: Hendriks Mark G. H. M. , Heijman Marjan J. G. W. , van Zyl Werner E. , ten Elshof Johan E. , Verweij Henk
Published: July 2009

Voronoi tessellation was applied to quantify the microstructural homogeneity of palladium particles in random Pd/cubic yttria‐stabilized zirconia (YSZ) composites with the Pd concentration ranging from 0 to 30 vol%. Room‐temperature impedance measurements were used to determine the capacitance of the composites. A fourfold enhancement in capacity near the percolation threshold of Pd was obtained. The percolation threshold was estimated at ∼30 vol% Pd using the normalized percolation theory (NPT). Data obtained from Voronoi diagrams resulted in a quantitative measure for the homogeneity of the dual‐phase composite. The homogeneity was found to decrease with increasing Pd concentration in the composites. Near the theoretical value of the percolation threshold, the Pd phase appeared to be distributed too inhomogeneously for preparing insulating composites. No large increase in capacity as predicted by NPT could therefore be experimentally verified.
Assessment of Mass Loss and Permeability Changes during the Dewatering Process of Refractory Castables Containing Polypropylene Fibers
Authors: Innocentini Murilo D. M. , Ribeiro Caue , Salomão Rafael , Pandolfelli Victor C. , Bittencourt Luis R. M.
Published: July 2009

This work describes the use of a new permeametry technique to evaluate microstructural changes that take place in castables with high alumina‐fiber content during the dewatering process. It is shown that the mass loss due to cement dehydration and the permeability increase caused by fiber burnout can be independently assessed, based on the fluid dynamic conditions established for the experiment. Control of the pressure drop through the sample was the key procedure used to analyze the phenomenon of interest.
Fatigue‐Free Lead Zirconate Titanate (Pb(Zr,Ti)O3)‐Based Capacitors Co‐modified by Lanthanum and Lithium for Nonvolatile Memories
Authors: Shannigrahi Santiranjan R. , Lee Sun‐Hwa , Jang Hyun M.
Published: July 2009

Pb0.98(La1−xLix)0.02(Zr0.55Ti0.45)O3(PLLZT with 0.1 ≤x≤ 0.7) thin films were sol‐gel‐grown on Pt(111)/Ti/SiO2/Si substrates, employing a thin lead zirconate titanate (PZT) template layer. Films annealed at >550°C showed a highly (111)‐oriented preferential growth. Typical values of the switchable remanent polarization (2Pr) and the coercive field (Ec) of the PLLZT/PZT/Pt film capacitor for x= 0.3 were 50 μC/cm2 and 39 kV/cm, respectively, at 5 V. All the PLLZT/PZT/Pt capacitors (for 0.1 ≤x≤ 0.7) exhibited fatigue‐free behavior up to 6.5 × 1010 switching cycles, a quite stable charge retention profile with time, and high 2Prvalues, all which assure their suitability for nonvolatile ferroelectric memories.
Sintering of Boron Carbide Heat‐Treated with Hydrogen
Authors: Lee Hyukjae , Speyer Robert F. , Hackenberger Wesley S.
Published: July 2009

Hydrogen gas (H2) was used to extract B2O3 coatings from boron carbide (B4C) particles, permitting a lower temperature onset of sintering and restricting coarsening via solution and precipitation of B4C in B2O3 liquid. Remnant H2 had to be removed from the furnace before specimens were heated through temperature ranges in which evaporation‐condensation coarsening competed with sintering (2010°–2140°C), because the presence of H2 increased the B4C vapor pressure. Heat treatment of B4C compacts in a 50:50 H2‐He mixture at 1350°C, followed by a purge of the H2 gas and then rapid heating to 2230°C, resulted in a percentage of theoretical density of 94.7%. This is higher than the value of 92.8%, which was the highest achieved without the use of H2.
Compositional Dependence of Microwave Dielectric Properties in (1 −x)(Na1/2Nd1/2)TiO3−xNd(Mg1/2Ti1/2)O3 Ceramics
Authors: Kim Jae Beom , Yoon Ki Hyun , Cho Yong S.
Published: July 2009

The compositional dependence of microwave dielectric properties has been investigated in the (1 −x)(Na1/2Nd1/2)TiO3−xNd(Mg1/2Ti1/2)O3 (NNT‐NMT) system. The addition of NMT results in significant improvement in the quality factor and the temperature coefficient of frequency, but gradually decreases the dielectric constant from ∼100 for pure NNT to ∼25 for pure NMT. The single perovskite phase is observed with various {hkl} superlattice reflections over the entire compositional range. The increasing tendency of peak splitting with increasing x at some perovskite reflections strongly suggests that the crystal structure of the system changes to lower symmetry structures. This is confirmed using infrared reflectivity spectra. The superlattice reflections related to structural deviation become more predominant as the composition reaches pure NMT. Particularly, {111} superlattice reflections are believed to be associated with the 1:1 cation ordering and responsible for the observed abrupt increase in quality factor at x > 0.7.