bluuebunny/crossref_metadata_2025 huggingface dataset:
Characterization of Interfacial Properties in Fiber‐Reinforced Cementitious Composites
Authors: Li Zongjin , Mobasher Barzin , Shah Surendra P.
Published: July 2005

For calculating interface properties from pullout tests, a simple theoretical model is proposed. The model enables calculating of the following material parameters: the parameter of shear stiffness of the fiber–matrix boundary layer, the shear bond strength, the frictional bond strength and the specific interfacial fracture energy. These parameters can be determined from the slope of the load‐slip curve, the maximum pullout load and the corresponding slip value. Slip‐controlled, multiple‐fiber pullout tests were conducted in a closed‐loop test system. The effects of embedment length of fibers on the model‐predicted material parameters were examined. The model predictions were satisfactorily compared with some previously published test data.
X‐ray Photoelectron Spectroscopy Characterization of Ion‐Beam Sputter‐Deposited Calcium Phosphate Coatings
Authors: Ong Joo L. , Harris Larry A. , Lucas Linda C. , Lacefield William R. , Rigney Douglas
Published: July 2005

X‐ray photoelectron spectroscopy (XPS) analysis of sputter‐deposited calcium phosphate coatings on titanium substrates revealed four distinct zones. The ambient‐exposed surface exhibited elevated concentrations of carbon because of atmospheric contamination. The bulk zone contained relatively constant concentrations of calcium, oxygen, phosphorus, and fluorine indicating the chemistry for calcium fluoride (CaF2) and fluorapatite (Ca5 (PO4),F) formation. The transitional zone exhibited elevated titanium and oxygen photoelectron peaks suggesting the coexistence of calcium phosphate compounds within the titanium oxide. The substrate was shown to be identical to the passivated titanium surface prior to deposition.
Crystallization of Lead Titanate Prepared by Wet Chemical Methods
Authors: Lee Moon‐Ho , Choi Byung‐Cheul
Published: July 2005

The crystallization behavior of PbTiO3 powder prepared by sol‐gel and coprecipitation techniques was investigated by DTA, XRD, and Raman spectral analyses. PbTiO3 precursor powders were derived from a mixed solution of Pb(NO3)2 and TiCl4 at 40o to 43oC and pH of 9.0 to 9.7. The dried gel and coprecipitated powders are both amorphous but have different structures. The room‐temperature Raman spectra from heat‐treated powders changed continuously from an amorphous to a crystalline state with increasing annealing temperature. By annealing coprecipitated powders, a dramatic change in the Raman spectra, caused by the structural relaxation as the annealing temperatures increased, was clearly visible, i.e., coprecipitated, gel, and crystalline structure, in turn.
Bonding of Dense Silicon Nitride with Carbon Interlayers
Authors: Krishnarao Raghavarapu Venkata , Malhar Godkhindi Mahadev
Published: July 2005

Diffusion bonding of dense Si3N4 containing 10% Ce2O3, 7% A12O3, and 2% Y2O3 was attempted through hot pressing at temperatures of 1000° to 1400°C. Physically vapor‐deposited (PVD) carbon and paraffin‐wax candle soot were tried as interlayers. The interfaces were analyzed through optical and scanning electron microscopy, and through X‐ray photoelectron spectroscopy. The bonding temperature could be reduced from 1400° (without interlayers) to 1100°C with PVD carbon or candle soot. From C Is and Si 2p spectra, the formation of SiC at the interface through the reaction of C with the silicon oxynitride layer has been identified.
The Ba(Ti,Zr)O3–(Zr,Ti)O2 Field in the Phase System BaO–TiO2–ZrO2
Authors: Hedges Michelle M. , Bannister Michael J. , Gani Mary S. J.
Published: July 2005

The two‐phase field involves a ZrO2‐TiO2 solid solution containing no more than 4 mol% TiO2, and a BaTiO3‐BaZrO3 solid solution containing a maximum of 75 mol% BaTiO3. The field narrows above 1300°C, probably because of the intrusion of a liquid‐phase field into the ternary, beginning near the BaO‐TiO2 edge.
Oxygen Fugacity Control in Nonflowing Atmospheres: II, Theoretical Model
Authors: Wirtz Gerald P. , Marques Fernando M. B.
Published: July 2005

Experimentally observed deviations from ideal isothermal behavior of solid electrolyte sensors are explained on the basis of gas‐phase diffusion in the furnace atmosphere. The presence of small amounts of CO/CO2 or other oxygenbearing gas species is essential to the theoretical explanation of these effects. Solution of the basic transport equations for limiting conditions appropriate to the control of a stagnant atmosphere by a sensor/pump combination indicates that stable fugacity fronts may exist, separating regions of relatively uniform oxygen fugacity which differ from each other by many orders of magnitude. The position of the front depends on the oxygen fugacity difference between the two regions of the furnace and can be moved through the furnace by electrochemically pumping oxygen from one end of the furnace. The relative output of two sensors separated by some finite distance in the direction in the direction of oxygen transport will depend on the position of this front, and as the front passes between the sensors a plateau in the curve of one sensor emf versus the other is predicted.
Oxidation Effects on the Mechanical Properties of a SiC‐Fiber‐Reinforced Reaction‐Bonded Si3N4 Matrix Composite
Authors: Bhatt Ramakrishna T.
Published: July 2005

The room‐temperature mechanical properties of a SiC‐fiberreinforced reaction‐bonded silicon nitride composite were measured after 100 h treatment in nitrogen and oxygen environments to 1400°C. The composite heat‐treated in nitrogen to 1400°C showed no appreciable loss in properties. In contrast, composites heat‐treated in oxygen from 600° to 1000°C retained ∼65% and 35% of the matrix fracture and ultimate strength, respectively, of the as‐fabricated composites, and those heat‐treated from 1200° to 1400°C retained greater than 90% and 65% of the matrix fracture and ultimate strength, respectively, of the as‐fabricated composites. For all nitrogen and oxygen treatments, the composite displayed strain capability beyond the matrix fracture strength. Oxidation of the fiber surface coating, which caused degradation of bond between the fiber and matrix and reduction in fiber strength, appears to be the dominant mechanism for property degradation of the composites oxidized from 600° to 1000°C. Formation of a protective silica coating at external surfaces of the composites at and above 1200°C reduced oxidation of the fiber coating and hence degrading effects of oxidation on their properties.
Recovery of Crack‐Tip Transformation Zones in Zirconia After High‐Temperature Annealing
Authors: Shaw Michael C. , Marshall David B. , Heuer Arthur H. , Inghels Eric
Published: July 2005

Annealing at temperatures between 500° and 1000°C reverses the stress‐induced tetragonal‐to‐monoclinic phase transformation in precipitates within crack‐tip zones in MgO‐partially‐stabilized ZrO2 (Mg‐PSZ). The stability of such reverse‐transformed tetragonal precipitates during subsequent room‐temperature aging has been examined using Raman spectroscopy, surface displacement measurements, and crack‐opening measurements. Partial spontaneous retransformation of material within the original zone from tetragonal‐to‐monoclinic symmetry occurred over periods of several months.
Statistical Analysis of the Intergranular Film Thickness in Silicon Nitride Ceramics
Authors: Kleebe Hans‐Joachim , Cinibulk Michael K. , Cannon Rowland M. , Rüble Manfred
Published: July 2005

Silicon nitride materials typically reveal thin amorphous intergranular films along grain boundaries, with only the exception of special boundaries. It is known that such grainboundary films strongly affect the high‐temperature properties of the bulk material. High‐resolution electron microscopy (HREM) was used to study these amorphous films in different Si3N4 ceramics. The observed film thicknesses at grain boundaries in these materials varied between 5and 15 Å. It was shown that the grain‐boundary film thickness strongly depends on film chemistry. Careful inspections of film‐thickness measurements across grain boundaries in a given material suggest that the film widths vary on the order of 1 Å. Therefore, a quantitative evaluation should allow for the determination of the standard deviation of the film thickness. The amorphous film widths along grain boundaries in four materials were measured over the entire length (up to 1 μm) of the grain boundary between two triple points. Forty to fifty data points were evaluated for each boundary, giving a Gaussian‐like distribution of the film thickness around a median value, which corresponded well with the film width measured from single HREM micrographs. The accuracy achieved by the statistical method was better than ± 1 Å.
Alumina as a Devitrification Inhibitor during Sintering of Borosilicate Glass Powders
Authors: Jean Jau‐Ho , Gupta Tapan K.
Published: July 2005

Cristobalite is formed when borosilicate glass (Corning Code 7740) is sintered at temperatures ranging from 700o to 1000o C. The precipitation kinetics, determined by XRD analysis, exhibit a characteristic incubation period which decreases with increasing sintering temperature, from 60‐120 min at 700oC to 3‐5 min at 1000o C. Activation analysis of precipitation shows an activation energy of 75 kJ/mol, which is close to that for the diffusion of Na+ in borosilicate glass, suggesting mass‐transport controlled kinetecs. 1.,5With added alumina content greater than a critical value, however, the cristobalite formation in the borosilicate glass is completely prevented at the sintering temperatures investigated. The critical alumina content is found to decrease with decreasing alumina particle size but with increasing sintering temperature. The above result, similar to observations previously made in a binary glass mixture containing a low‐softening borosilicate glass (BSG) and a high‐softening high silica glass (HSG) 3 is attributed to a strong coupling between Al3+ from alumina and Na+ from borosilicate glass. The coupling reaction causes segregation of Na+ in boraosilicate glass to alumina, thus forming a Na+‐and Al3+‐rich reaction layer around alumina particles far too rapid for cristobalite formation.
Phase Relationships in the ZrO2‐Sc2O3 and ZrO2‐In2O3 Systems
Authors: Sheu Tzer‐Shin , Xu Jae , Tien Tseng‐Ying
Published: July 2005

Zirconia‐rich subsolidus phase relationships in the ZrO2–Sc2O3 and ZrO2–In2O3 systems were investigated. Phase inconsistencies in the ZrO2–Sc2O3 system resulted from a diffusionless cubic‐to‐tetragonal (t') phase transformation not being recognized in the past. Through three different measuring techniques, along with microstructural observations, the solubility limits of the tetragonal and cubic phases were determined.
Characterization of Pore Size Distribution by Infrared Scattering in Highly Dense ZnS
Authors: Chen William W. , Dunn Bruce
Published: July 2005

A model based upon Mie theory was developed to calculate the amount of spectral infrared scattering caused by the presence of a porous second phase. Various in‐line transmission curves were calculated and used to characterize the scattering effects of pore size and concentration. The in‐line transmission from 2.5 to 10 fjim of ZnS samples hot‐pressed at 137.8,172.3, and 206.7 MPa was measured using Fourier transform infrared spectrophotometry and compared with calculated transmission curves. Good agreement with measured results was obtained only when a size distribution effect was included. From the analysis, a bimodal distribution of pores was found to give the best agreement which duplicates the measured transmission.
“Alumina” Surface Modification of Silicon Nitride for Colloidal Processing
Authors: Luther Erik E , Lange Fred F. , Pearson Dale S.
Published: July 2005

Two different methods are used to coat silicon nitride particles with an alumina precursor to make Si3N4 behave like Al2O3 in aqueous slurries. The first method involves the precipitation of an aluminum hydroxycarbonate from dissolved Al(NO3)3 during the decomposition of urea. In the second method, dry silicon nitride powder is reacted with aluminum tri‐sec‐butoxide in hexane at room temperature. Both methods produce a coated powder in which the electrophoretic and rheological properties of aqueous slurries mimic those of alumina. When salt is added to slurries consisting of coated Si3N4 powder, all rheological evidence suggests the presence of a short‐range repulsive potential that produces a weakly attractive particle network similar to that previously reported for Al2O3 powder. Although electrophoretic and rheological data showed that the coated powder behaved like Al2O3, consolidation data indicated that slurries of coated powder with added salt did not pack to high density. In addition, these bodies were not plastic as found for bodies consolidated from dispersed and salt‐added Al2O3 slurries.
Incommensurately Modulated Polar Structures in Antiferroelectric Sn‐Modified Lead Zirconate Titanate: The Modulated Structure and Its Influences on Electrically Induced Polarizations and Strains
Authors: Viehland Dwight , Forst Donald , Xu Z. , Li Jie‐Fang
Published: July 2005

Tin‐modified lead zirconate titanate ceramics, Pb(0.99)Nb0.02‐[(Zr0.55Sn0.45)0.98Tiy]O3 (PZST 45/y/2), have been studied by hot‐stage transmission electron microscopy (TEM), dielectric spectroscopy, Sawyer‐Tower polarization (P—E) measurements, and electrically induced strain (ε‐E) techniques. The compositional range chosen for investigation was 0 < y < 0.09. Electron diffraction confirmed the existence of 1/x〈110〉 superlattice reflections in the previously designated antiferroelectric tetragonal state. For PZST 45/0/2, the room‐temperature modulated structure was found to be commensurate with the lattice and isomorphous with the antiferroelectric orthorhombic phase of PbZrO3. With increasing Ti content, the modulation wavelength (λ) increased and became incommensurate. At high temperatures, λ was found to be incommensurate for all compositions. A model is discussed which suggests that the origin of incommensuration is due to a competition between anti‐ferroelectric and ferroelectric tendencies. P—E studies revealed antiferroelectric‐ferroelectric (AFE—FE) polarization curves which possessed no hysteresis in the incommensurate region, indicating a thermally reversible AFE—FE transformation. On cooling, strong hysteresis developed as the incommensurate structure became metastably locked. Investigations then revealed that the electrically induced strain associated with the AFE—FE transformation was not realized until field strengths were attained significantly above that required for polarization saturation. It is believed that the electrically induced strain is decoupled from the polarization due to AFE—FE switching by the field modulation of the incommensurately modulated polar structure.
Effect of Temperature on the Slurry Characteristics and Green Bodies of Alumina
Authors: Tomita Yosinori , Guo Lu‐Cun , Zhang Yao , Uchida Nozomu , Uematsu Keizo
Published: July 2005

The importance of temperature in colloidal processing was examined by investigating its effect on the characteristics of a ceramic slurry and on the subsequent processing before firing. An aqueous alumina slurry was used as a model system in the present study. The viscosity of the slurry was found to vary significantly with temperature, and the structure of the resultant green bodies made by centrifugation varied correspondingly. The importance of temperature in the production of ceramics is discussed in light of these results.
Effect of Particle Size on Colloidal Zirconia Rheology at the Isoelectric Point
Authors: Leong Yee‐Kwong , Scales Peter J. , Healy Thomas W , Boger David V
Published: July 2005

This paper examines the effects of particle concentration and size on the yield stress of ZrO2 suspensions at a well‐defined surface chemistry condition of the isoelectric point (IEP). At the IEP, the relationship between yield stress τYmax and particulate volume fraction φs and mean particle size d was evaluated to be τYmax =Kφs4.0/d2.0. The difference in size distribution of the various ZrO2 suspensions examined causes some degree of scatter in the data used to establish the τYmax, φs, and d relation. The use of particle concentration nt based on the fine size fraction instead of volume fraction φs provided a better correlation, because the fine particles govern the properties of the flocculated network structure.
Tetragonal—Monoclinic Phase Transition Enthalpy and Temperature of ZrO2‐CeO2 Solid Solutions
Authors: Yashima Masatomo , Mitsuhashi Takefumi , Takashina Hiroyuki , Kakihana Masato , Ikegami Takayasu , Yoshimura Masahiro
Published: July 2005

DSC (differential scanning calorimeter) measurements were performed to investigate the tetragonal‐monoclinic (t‐m) transition enthalpy of the compositionally homogeneous ZrO2‐X mol% CeO2 solid solution of X= 0, 4, 8, and 12. The transition enthalpy decreases linearly with an increase of CeO2 content. The m → t transition enthalpy on heating agreed well with the inverse t → m one obtained during cooling. With increasing X, the DSC peak broadens and the transition temperature distribution of each sample increases, while the thermal hysteresis is almost independent of X.
Dynamic Characteristics of Rainbow Ceramics
Authors: Elissalde Catherine , Cross Leslie Eric
Published: July 2005

The piezoelectric resonance behavior of end‐clamped bimorph structures made from the rainbow monolithic ceramic have been evaluated. Thickness, width, width flexure, and length bending modes have been identified and measured. Using a very crude model in which the cermet component of the rainbow is assumed to have the same density × elasticity product as the bulk, surprisingly good agreement is obtained between observed and calculated frequency behavior. By appropriate processing it is possible to delaminate the bimorph, and work is now in progress to measure the properties of the two separate phases so that a proper composite resonator model may be developed.
Effect of High‐Voltage Screening on Strength Distribution for Titanium Dioxide Ceramics
Authors: Kishimoto Akira , Endo Koretomo , Nakamura Yoshinobu , Motohira Naobumi , Yanagida Hiroaki , Sugai Kazuhito
Published: July 2005

A screening field at or below which 30% of TiO2 ceramic samples break electrically was applied to the samples. After high‐voltage screening, the surviving samples were subjected to mechanical strength measurement and the resulting strength distribution was compared to the original distribution. The effect of high‐voltage screening and the correlation between mechanical and dielectric strength are discussed. There is a correlation between mechanical and dielectric strengths with a correlation coefficient of 0.77, which indicates the validity of high‐voltage screening.
A Simultaneous Loading System to Evaluate the Structural Reliability of Brittle Materials
Authors: Kishimoto Akira , Sugai Kazuhito , Nakamura Yoshinobu , Motohira Naobumi , Yanagida Hiroaki
Published: July 2005

An alternative method to obtain a strength distribution of many test pieces simultaneously has been proposed. In this method, the bending stress of all subjected samples is simultaneously increased by utilizing their elastic modulus constancy, and the fractured sample number is monitored by the change in electric conductance.
Growth of Monoclinic ZrO2 Thin, Flaky Crystals by Hydrothermal Decomposition of Zirconium Oxide Sulfate Crystals
Authors: Kato Eturo , Hirano Masanori , Nagai Akihiro
Published: July 2005

Thin platelike hexagonal crystals of zirconium oxide sulfate (ZOS) with a chemical composition of Zr3O5SO4.nH2O were previously synthesized by the hydrolysis of an aqueous solution of 2 mol/L ZrOSO4 at 240°C. The ZOS particles obtained were hydrothermally treated again in dilute sulfuric acid solution (<0.15 mol/L) at 240°C. The decomposition of ZOS and the nucleation and growth morphology of the monoclinic ZrO2 crystals were automatically controlled with increasing sulfuric acid released by the decomposition of ZOS, and were influenced by the morphology of ZOS as precursors. Anisotropic monoclinic ZrO2 single crystals, elongated thin and flaky particles (length: >2 (Am; width: about 0.1 μm; thickness:«0.01 μm), could be obtained under some conditions without the coexistence of another type of anisotropic ZrO2 fibrous twin crystal.
Characteristics of Lead Magnesium Niobate Thin Film Prepared by Sol‐Gel Processing Using a Complexing Agent
Authors: Yoon Ki Hyun , Park Jeong Hwan , Kang Dong Heon
Published: July 2005

The effects of a complexing agent on the synthesis of a Pb(Mg1/3Nb2/3)O3(PMN) solution and the dielectric properties of a PMN thin film were investigated. When triethanolamine (TEA) was used as a complexing agent, a homogeneous and stable precursor solution was synthesized in air and a crack‐free thin film with the nearly pure perov‐skite phase and an average grain size of 0.2–0.4 μm was prepared by heating at 800°C for 5 min. The PMN thin film showed a relative permittivity of 1800 and tan δ of 0.01 at room temperature. The voltage dependence of polarization for the thin film was also presented.
Compositional Modifications of 10%‐Pb‐Doped Bi0.5Na0.5Tio3 for High‐Temperature Dielectrics
Authors: Kuharuangrong Sutin , Schulze Walter
Published: July 2005

Modifications of 10%‐Pb‐doped Bi0.5Na0.5TiO3 were studied for consideration as possible high‐temperature dielectrics. Composition with potassium gave a broader dielectric response and a lower temperature of the ferroelectric‐antiferroelectric transition. With La doping, a low‐temperature‐stable dielectric constant was obtained. Barium modifications increased the dielectric constant and also lowered the first transition temperature. However, doped with 10% Ba, the composition ordered and the first transition ceased to exist.
Synthesis of Silicon Carbide from Rice Husk in a Packed Bed Arc Reactor
Authors: Mishra Pratima Kumari , Nayak Bijan Bihari , Mohanty Bishnucharanarabinda
Published: July 2005

Silicon carbide in the form of powder was prepared from boiler burnt rice husk in a new type of packed bed arc reactor where the raw materials were processed in briquette form. X‐ray diffraction analysis identified the presence of both β and α SiC. Microstructural characterization revealed the presence of triangular, truncated triangular, and hexagonal crystallites, along with platelets.
Effect of Chloride on the Structure of Fluoroaluminate Glasses Studied by XPS
Authors: Zhang Lipeng , Wang Paul W.
Published: July 2005

The effect of chlorine on the structure of AlF3/YF3‐based fluoride glasses was studied by XPS. The changes in the bonding state of cations with increase of chlorine content were all investigated by measuring the composition‐depend‐ dent changes in the relative concentration and binding energy of related cations. It was proposed that the chlorine replaces the bridging fluorine by which the [AlFn] and [YFm] polyhedra are connected and result in the formation of [AlFn‐uClu] and [YFm‐vClv] polyhedra. In the low BaCl2 content region (<6 mol%), as many chlorine as possible attack [A1FJ and [YFm] polyhedra, and with the increase of chlorine content, they replace more fluorines in [YFm] polyhedra, while the number of chlorines in [AIFn‐uClu] polyhedra remains a low constant value. In the high BaCl2 content region (>6 mol %), the chlorines replace more fluorines in the already formed [AlFn‐uClu] polyhedra and do not attack other [AlF] polyhedra, while the composition of [YFm‐vClv] polyhedra does not change.
Bioactivity of Na2O‐CaO‐SiO2 Glasses
Authors: Kim Hyun‐Min , Miyaji Fumiaki , Kokubo Tadashi , Ohtsuki Chikara , Nakamura Takashi
Published: July 2005

Bioactivities of Na2O‐CaO‐SiO2 glasses were evaluated by examining the formation of bonelike apatite, which is responsible for their bonding to living bone, on their surfaces in a simulated body fluid, using thin‐film X‐ray diffraction and Fourier‐transform infrared reflection spectroscopy. It was found that glasses in a wide compositional region in the P2O5‐free Na2O‐CaO‐SiO2 system can show bioactivity, as those in the P2O5‐containing system. The rate of apatite formation on the surfaces of glasses varied largely with the composition of the glasses. Under a constant SiO2 content of 50 mol%, a glass containing equimole of Na2O and CaO showed the highest rate of the apatite formation. Variation in the rate of apatite formation with the glass composition corresponded well with the rate of increase in the degree of the supersaturation of the simulated body fluid with respect to the apatite due to dissolution of sodium and calcium ions from the glasses. Little difference was observed in the rates of ion dissolution and of apatite formation between P2O5‐containing Bioglass 45S5‐type and a corresponding P2O5‐free Na2O‐CaO‐SiO2 glass. It is believed that P2Os‐free Na2O‐CaO‐SiO2 glasses also show bioactivity as high as that of Bioglass.
Fracture Strength and Dynamic Elastic Modulus of Ce‐ and Er‐TZP at Low Temperature
Authors: Zhang Zhong , Jin Duo , Li Laifeng , Tu Zhihua , Zhao Lizhong , Zhang Peiqiang , Zhao Jianhua
Published: July 2005

Fracture strength of TZP containing 14.5, 15.5, and 16.5 mol % CeO2 is studied using static three‐point bending at low temperature. There is 22 %–46 % increase from 300 to 77 K and 47 %–92 % increase from 300 to 4.2 K in fracture strength of Ce‐TZP. The temperature dependencies of dynamic elastic modulus and damping capacity of CeO2/Er2O3‐alloyed tetragonal zirconia ceramics (Ce‐/Er‐TZP) between 300 and 77 K are characterized using flexural vibration. System identification techniques in time domain are used to identify dynamic parameters from strain vibration signals of the ceramic samples. The results indicate that there is 15 %–22 % increase of Ce‐TZP and 9%–22% increase of Er‐TZP in dynamic elastic modulus from 300 to 77 K. The microhardness of Ce‐/Er‐TZP was measured at room temperature.
Internal Stresses and the Martensite Start Temperature in Alumina‐Zirconia Composites: Effects of Composition and Microstructure
Authors: Alexander Kathleen B. , Becher Paul F. , Wang Xun‐Li , Hsueh Chun‐Hway
Published: July 2005

n alumina‐based composites containing ceria‐stabilized tetragonal zirconia, the martensite start temperature (Ms) of the tetragonal‐to‐monoclinic zirconia phase transformation exhibits a grain size dependence that becomes increasingly pronounced as the zirconia content decreases. Neutron diffraction experiments confirm earlier dilatometry measurements of Ms in composites containing ≥20 vol% ZrO2 and were instrumental in obtaining Ms values in lower zirconia content (i.e., 10 vol%) composites. The dependence of Ms on zirconia content is related to the internal stresses that arise from differences in thermal expansion coefficients between the two phases. Neutron diffraction measurements show that the internal tensile stresses in the zirconia grains increase with decreasing zirconia content. The measured internal stresses are in quantitative agreement with predictions based on models assuming isolated ZrO2 particles at low zirconia contents and a continuous ZrO2“matrix” phase at higher zirconia contents. This assumption is consistent with the observed microstructural development in which the low zirconia contents result in isolated zirconia grains, whereas higher zirconia contents result in more interconnected zirconia grains.
Microstructure and Oxidation‐Resistant Property of Sol‐Gel‐Derived ZrO2‐Y2O3 Films Prepared on Austenitic Stainless Steel Substrates
Authors: Miyazawa Kun'ichi , Suzuki Kunio , Wey Myeong Yong
Published: July 2005

The effect of Y2O3 addition to the oxidation resistance of sol‐gel‐derived zirconia films coated on austenitic stainless steel substrates was examined. The oxidation weight gain measurement and XRD analyses of oxides showed that addition of Y2O3 reduces oxide formation. TEM observations revealed that the films are joined to the substrates via an amorphous layer with concentrated Si, and the layer grew thicker by adding Y2O3 or elevating the firing temperature. Lattice constants of the films were shown to be more expanded than the zirconia powders prepared from the coating liquids.
Microstructure and Physicochemical Studies of Pure and Zinc‐Substituted Lithium Ferrites Sintered above 1000°C
Authors: Bermejo Edelio , le Mercier Thierry , Quarton Michel
Published: July 2005

The effects of sintering temperature above 1000°C and of cooling rate on the microstructual development of pure and Zn‐substituted spinel lithium ferrites are discussed. The strong dependence of microstructural features on cooling rate can be explained on the basis of the precipitation of α‐Fe2O3 or the formation of a solid solution of ferrite phase with Fe3O4 occurring during sintering above 1000°C. These two phenomena are studied by detailed characterization analyses: SEM, XRD, magnetization, and ac electrical resistivity measurements.
Processing of Silicon Carbide‐Mullite‐Alumina Nanocomposites
Authors: Sakka Yoshio , Bidinger Donald D. , Aksay Ilhan A.
Published: July 2005

Nanocomposite materials in the form of nanometer‐sized second‐phase particles dispersed in a ceramic matrix have been shown to display enhanced mechanical properties. In spite of this potential, processing methodologies to produce these nanocomposites are not well established. In this paper, we describe a new method for processing SiC‐mullite‐Al2O3 nanocomposites by the reaction sintering of green compacts prepared by colloidal consolidation of a mixture of SiC and Al2O3 powders. In this method, the surface of the SiC particles was first oxidized to produce silicon oxide and to reduce the core of the SiC particles to nanometer size. Next, the surface silicon oxide was reacted with alumina to produce mullite. This process results in particles with two kinds of morphologies: nanometer‐sized SiC particles that are distributed in the mullite phase and mullite whiskers in the SiC phase. Both particle types are immersed in an Al2O3 matrix.
Electromechanical Properties of Some Pb(Mg1/3Nb2/3)O3‐PbTiO3‐(Ba,Sr)TiO3 Ceramics: Part Two
Authors: Pilgrim Steven M. , Massuda Mona , Prodey Jackie D.
Published: July 2005

Compositional change within the Pb(Mg1/3Nb2/3)O3‐PbTiO3‐(Ba,Sr)TiO3 ternary, hereafter known as PMN‐PT‐BT,ST, results in major variations in properties. When coupled with the temperature and processing dependence of the relaxor materials near their diffuse phase transition, the compositional dependence significantly complicates the selection of an optimum composition for transducer use. Noncompositional variations in dielectric and electromechanical properties with temperature and processing are easily noted among the many publications on the PMN family of relaxors. In this work, we concentrate on the effects of composition on the electromechanical properties over the 0°–40°C range. The specific compositions include a total of 17 compositions within the PMN‐PT‐BT,ST family (6.4%≤ PT%≤ 14.1%, 1.25%≤ BT,ST%≤ 2.5%). By careful processing of matched pairs of BT‐ and ST‐containing compositions, we demonstrate compositional effects on the properties without an associated processing effect. In this work, we present weak‐field (relative permittivity and dielectric loss) and high‐field (induced strain, polarization, and hysteresis) data for a total of 17 compositions synthesized by a modified columbite precursor route. As previously reported on a more limited compositional suite, the shift in weak‐field Tmax with the logarithm of frequency is nearly linear. There is a minor departure from linearity at low frequencies. Strontium additions are shown to be more effective at reducing Tmax than the equivalent barium addition. All compositions showed dielectric aging which was easily reset by short exposure to elevated temperature. A method for selecting a composition for a specific temperature regime based on the concept of a lower and upper use temperature is presented. This works well for low levels of PT, but decoupling between Tmax and the lower use temperature invalidates the method for PT > 12 mol%.
Tensile Behavior of Microcracking SiC‐TiB2 Composites
Authors: Gu W‐H. , Faber K. T.
Published: July 2005

The stress–strain behavior of microcracking SiC‐TiB2 composites was studied using uniaxial tensile tests. The nonlinear stress–strain behavior provided the critical stresses for microcracking (defined as the proportional limit) and the magnitude of residual strain release as a consequence of stress‐induced microcracking. The release of residual strain was confirmed using the loading–unloading process. Both the critical stress for the nonlinear stress–strain curve and the release of residual strain were used to establish the maximum principal stress as the stress criterion for microcracking.
Ceramic Composites of Monazite and Alumina
Authors: Morgan Peter E. D. , Marshall David B.
Published: July 2005

A new family of high‐temperature, oxidation‐resistant, ceramic composites, with (La)‐monazite (LaPO4) serving as a weakly bonded interphase, is proposed. Monazite is stable and phase‐compatible with alumina at temperatures at least as high as 1750°C in air. Especially important for use in high‐toughness composites, the monazite‐alumina interface is shown to be sufficiently weak that interfacial debonding prevents cracks from growing from monazite into alumina. Observations of fracture responses of fibrous and laminar reinforcements are presented.
Role of PbO and Ag on Insulation Resistance Degradation in Relaxor‐Based MLCs
Authors: Kanai Hideyuki , Furukawa Osamu , Nakamura Shin‐ichi , Yamashita Yohachi
Published: July 2005

The relationship between the grain boundary phase and insulation resistance of dielectric layers in multilayer ceramic capacitors (MLCs) was clarified, leading to a proposal for the mechanism of insulation resistance degradation. A Pb‐rich secondary phase was present at grain boundaries, and a small amount of Ag was detected from the secondary phase, while no secondary phase existed in dielectric layers with normal insulation resistance. These results suggest that diffusion from an internal electrode into the secondary phase in dielectric layers is responsible for the extremely low insulation resistance: oxygen vacancies, formed as a result of substitution of Ag for Pb, may play a role in lowering insulation resistance.
Bimodal Sintering of Al2O3/Al2O3 Platelet Ceramic Composites
Authors: Belmonte Manuel , Moya Jose S. , Miranzo Pilar
Published: July 2005

The sintering behavior of an Al2O3 compact containing uniformly dispersed Al2O3 platelets has been investigated. The results reveal a significant decrease in the sintering rate as well as the formation of voids and cracklike defects in the presence of nonsinterable platelets. The addition of a small amount (2 vol%) of tetragonal‐ZrO2 particles enhances the sintering rate, increases end‐point density (∼99.5% of theoretical density) and prevents formation of sintering defects.
Processing Strategy for Producing Highly Anisotropic Silicon Nitride
Authors: Hirao Kiyoshi , Ohashi Masayoshi , Brito Manuel E. , Kanzaki Shuzo
Published: July 2005

Silicon nitride with a preferred orientation of large elongated grains was obtained by tape casting of raw powder slurry seeded with rodlike β‐Si3N4 particles, followed by a gas pressure sintering under 1 MPa nitrogen pressure. The large elongated grains developed from seeds lay in planes parallel to the casting direction in a two‐dimensional distribution. Increased fracture toughness (11.1 MPa·m1/2) and bending strength (1100 MPa) were achieved in the direction perpendicular to the grains alignment compared to specimens with a random distribution of elongated grains. Morover, the specimens exhibited a high Weibull modulus of 46 due to the uniform distribution of large grains.
Reaction between Calcium‐Doped Lanthanum Chromite and Silica
Authors: Horita Teruhisa , Choi Jin‐Sam , Lee You‐Kee , Sakai Natsuko , Kawada Tatsuya , Yokokawa Harumi , Dokiya Masayuki
Published: July 2005

Calcium‐doped lanthanum chromite reacted with silica to form silicates and chromium oxide at 1473‐1773 K. A reaction mechanism was proposed at each temperature. At 1473 K, a reaction zone was observed in two areas: one was the bulk reaction area where silicates and chromium oxide were formed near the reaction interface; the other was the grain boundary reaction area where chromium oxide and calcium silicate spots were formed far from the reaction interface. Above 1673 K, silicates in the La2O‐CaO‐SiO, system and chromium oxide were formed simultaneously in the reaction zone with no grain boundary reaction. No layered reaction products were observed in the reaction zone of the lanthanum chromite side. Formation of melt silicates above 1723 K at the reaction interface resulted in strong bonding between calcium‐doped lanthanum chromite and silica.
The “Direct Bond” in Magnesia Chromite and Magnesia Spinel Refractories
Authors: Gotod Kiyoshi , Lee William E.
Published: July 2005

The microstructures of several commercial refractory bricks have been characterized using scanning and transmission electron microscopy. The “direct bond” is shown to be direct at the level of resolution attainable (∼0.3 nm), and a significant number of such direct contacts occur between non‐silicate phases in the microstructures of magnesia‐chromite bricks. However, attempts to examine the direct bond in magnesia‐spinel bricks were unsuccessful due to nonuniform ion thinning of TEM specimens.
Thermal Expansion of YBa2Cu3O7_xas Determined by High‐Temperature X‐ray Diffraction under Controlled Oxygen Partial Pressures
Authors: Mizusaki Junichiro , Tagawa Hiroaki , Hayakawa Kei , Hirano Katsuhiko
Published: July 2005

The high‐temperature phase relationship and thermal expansion coefficient of YBa2Cu3O7‐x under constant oxygen nonstoichiometry, x,were determined by high‐temperature powder X‐ray diffraction analysis under controlled oxygen partial pressure at temperatures up to 800deg;C. The results are discussed based on reported nonstoichiometry data. The present study showed an orthorhombic‐to‐tetragonal transition near the composition x =0.5. The lattice parameter c,perpendicular to the Cu‐O plane, showed a maximum at around x =0.7 to 0.8. In the ortho‐rhombic phase, the lattice parameters aand balong the Cu‐O plane were essentially constant for x <0.2. For 0.2 < x < ∼0.5, aincreased and bdecreased with x.In the tetragonal phase, with x < ∼0.5, the lattice parameter adecreased with x.The thermal expansion coefficient, α, along the c‐axis ranged from 19 × 10‐6 to 25 × 10‐6‐K‐1, whereas a along the a‐and b‐axes ranged from 12 × 10‐6 to 22 × 10‐6‐K‐1 at 400° to 800deg;C, and these values were very small below 400deg;C. It was found that a, b,and α along the a‐and b‐axes are smaller when the oxygen content along the respective axes is less, while the area of the abplane and its thermal expansion coefficient are larger when the deviation of the oxygen content from the stoichiometric compositions of YBa2Cu3O7 or YBa2Cu3O6 is larger. Changes of xand temperature affected cmore strongly than aand b.
VAMAS Round Robin on Fracture Toughness of Silicon Nitride
Authors: Mizuno Mineo , Okuda Hiroshi
Published: July 2005

Eight laboratories in Germany, Japan, U.K., and U.S. participated in the VAMAS round robin. The fracture toughness of silicon nitride at room temperature and at 1200deg;C was measured by three methods: the single‐edge V‐notched beam (SEVNB), single‐edge precracked beam (SEPB), and chevron notched beam (CNB). The obtained values show hardly any crosshead speed dependence, irrespective of test temperature and atmosphere. Results may have been influenced by a small amount of slow crack growth, but distinct R‐curve behavior could not be detected within the scope of the tests. The values at 1200deg;C in N2 can be measured by the SEVNB and SEPB methods with small scatters. The oxidation of silicon nitride, caused by heating in air, increases the SEVNB and SEPB values. The CNB values are free from the effects of test temperature and atmosphere, but they show a large scatter between laboratories. However, the chevron V‐notched beam (CVNB) method, which is an improved CNB method, shows values with a small scatter, irrespective of the measurement conditions. The SEVNB and SEPB measurements in N2 and the CVNB measurement under any conditions are recommended for the measurement of high‐temperature fracture toughness.
Investigations of a Diol‐based Sol‐Gel Process for the Preparation of Lead Titanate Materials
Authors: Calzada M. Lourdes , Sirera Rafael , Carmona Francisco , Jiménez Basilio
Published: July 2005

Lead titanate sols were prepared by a sol‐gel method from lead acetate trihydrate, Pb(OOCCH3)23H2O, and titanium di‐isopropoxide bis‐acetylacetonate, Ti (OC3H7)2‐ (CH3COCHCOCH3)2, in 1,3‐propanediol, HO(CH2)3OH, as solvent. IR analysis and NMR spectroscopic techniques were used to study the reaction mechanisms and to identify possible polymer structures developed during synthesis of the solutions.
Mechanisms of Deformation and Failure in Carbon‐Matrix Composites Subject to Tensile and Shear Loading
Authors: Turner Kristofer R. , Speck James S. , Evans Anthony G.
Published: July 2005

The operative damage mechanisms in a series of C‐matrix composites loaded in tension and shear have been investigated. The composites contained either C fibers or Nicalon fibers, both with and without a carbon coating. The matrix consisted primarily of ex‐phenolic carbon with a final carbon layer introduced by chemical vapor infiltration. Some composites have a high fiber/matrix sliding stress. In these composites, failure is characterized by localized fiber pullout. Other composites have a low. Failure of these materials is characterized by stochastic fiber failure with a diffuse fracture surface. The operative damage mechanisms have been identified and used in conjunction with available models to rationalize composite performance in terms of constituent properties (fiber, matrix, interface). The properties emphasized include the inelastic strain, as well as the ultimate tensile and shear strengths.
Reaction Mechanisms of Silicon Carbide Fiber Synthesis by Heat Treatment of Polycarbosilane Fibers Cured by Radiation: II, Free Radical Reaction
Authors: Sugimoto Masaki , Shimoo Toshio , Okamura Kiyohito , Seguchi Tadao
Published: July 2005

Silicon carbide (SiC) fibers were synthesized by the pyrolysis of radiation‐cured polycarbosilane (PCS) fibers. The pyrolytic reaction was analyzed through free radicals by electron spin resonance (ESR). Free radicals on Si and C atoms were produced in the pyrolysis, and their yield as a function of reaction temperature depended on the oxygen content in the cured PCS fibers. There were two temperature ranges for the reactions related to Si and C atoms in PCS fibers. The radical concentration reflects the rate differences between the radical formation by the cleavage of Si‐H and C‐H bonds and the decay by recombination of radicals. The reaction of Si‐H was strongly influenced by the oxygen content in the cured PCS fibers, and the decay rate of radicals decreased with an increase of the oxygen content in PCS fibers introduced in the curing process.
High‐Temperature Mechanical Behavior of Stoichiometric Magnesium Spinel
Authors: Baudín Carmen , Martínez Rafael , Pena Pilar
Published: July 2005

The elastic and mechanical behavior, from room temperature up to 1300deg;C, of Stoichiometric polycrystalline magnesium aluminum spinel is studied. Elastic modulus, fracture toughness, and modulus of rupture measurements and observations of polished and fracture surfaces have been performed. Two well‐differentiated regions of fracture behavior as a function of temperature have been found. In the low‐temperature region, this material behaves elastically, whereas in the high‐temperature (>800deg;C) region, plastic phenomena take place.
Na2SO4‐lnduced Corrosion of Si3N4 Coated with Chemically Vapor Deposited Ta2O5
Authors: Lee Woo Y , Bae Yong W. , Stinton David E
Published: July 2005

Hot isostatically pressed Si3N4 was coated with chemically vapor‐deposited Ta2O5, and subjected to oxidative and corrosive environments to determine the feasibility of using a Ta2O5 coating for protecting Si3N4 from hot corrosion. The coated structure was relatively stable at 1000deg;C in pure O2. However, the Ta2O5‐Si3N4 system became unstable in an environment containing Na2SO4 and O2 at 1000deg;C because (1) Ta2O5 and Na2SO4 reacted rapidly to form NaTaO3 and (2) subsequently NaTaO3 interacted destructively with the underlying Si3N4 substrate to form a molten phase.
Epitaxial Aluminum‐Doped Zinc Oxide Thin Films on Sapphire: I, Effect of Substrate Orientation
Authors: Srikant V , Sergo Valter , Clarke David R.
Published: July 2005

Epitaxial thin films of Al‐doped zinc oxide have been grown on sapphire substrates by pulsed laser ablation. The effect of substrate temperature, background pressure of oxygen, and substrate orientation (A, M, R, C) on the orientation relationships between ZnO and sapphire have been evaluated using on‐ and off‐axis X‐ray diffractometry. Under all growth conditions zinc oxide, on A‐ and C‐plane sapphire, grew with the c‐axis perpendicular to the substrate. In contrast, on M and R orientations of sapphire, ZnO grew with its c‐axis parallel or perpendicular to the substrate depending on the substrate temperature and background pressure employed during growth. In all cases only one unique in‐plane relationship between the sapphire substrate and the zinc oxide film was found with the exception of the M‐plane at high substrate temperatures.
Growth of CeO2 Films on Sapphire and MgO by rf Magnetron Sputtering
Authors: Tsaih Wen‐Chou , Huang Chin‐Kuan , Tseng Tseung‐Yuen
Published: July 2005

pitaxial CeO2 films on (1102) sapphire and (100) MgO were grown by rf magnetron sputtering. Substrate temperature, total pressure, and oxygen‐to‐argon mole ratio were varied to explore the optimal deposition condition. The X‐ray diffraction spectra indicate that the degree of crystallinity of the deposited CeO2 films depends on the oxygen‐ to‐argon mole ratio and the substrate temperature. Atomic force microscopy images of the films on sapphire and MgO showed that substrate temperature and total pressure affect surface roughness. The best film surface is smooth with a 0.89 nm root‐mean‐square roughness. The quality of the films on MgO showed a strong dependence on substrate pretreatments. Epitaxial CeO2 films could be grown on pre‐ annealed or pre‐etched MgO if substrate temperatures reached higher than 790deg;C. Additionally, the effect of ion bombardment at low total pressures on the crystallinity of the films was examined by growing the films outside the plasma region. Experimental results indicate that the ion bombardment does not prevent the films from preferred orientation.
Preparation of Aragonite Whiskers
Authors: Ota Yoshio , Inui Saburo , Iwashita Tetsushi , Kasuga Toshihiro , Abe Yoshihiro
Published: July 2005

A simple synthetic method for preparing aragonite whiskers has been developed. A suspension of CaCl2‐MgCl2‐Mg(OH)2 with pH ∼9 has been prepared by adding Ca(OH)2 to MgCl2 aqueous solution. CaCO3 whiskers (aragonite phase) have been prepared easily by blowing CO2‐containing gas into the suspension. The whiskers have high aspect ratios ranging from 20 to 80 with diameters of 0.5–1 μm.
Phase Stability of Fine‐Grained (Mg,Y)‐PSZ
Authors: Meschke Frank , Claussen Nils , Portu Goffredo De , Rödel Jürgen
Published: July 2005

A fine‐grained zirconia, which has been costabilized with yttria and magnesia, has been prepared. Its stability during subeutectoid annealing at 1100deg;C, and its hydrothermal stability during hydrothermal treatment at 180deg;C, have been determined and they are compared to those of Y‐TZP and Mg‐PSZ materials.