bluuebunny/crossref_metadata_2025 huggingface dataset:
Ultrasonic Imaging of Porosity Variations Produced During Sinteriing
Authors: Generazio Edward R. , Roth Don J. , Stang David B.
Published: October 2005

A silicon carbide disk was sintered from 2090° to 2190°C in 25°C steps. After each sintering step, the disk was examined using a precision acoustic scanning system to determine acoustic attenuation and velocity. The bulk density was found to vary non‐monotonically with sintering temperature. The density varied as much as 10% from its value at 2090°C during the sintering process. Local density fluctuations occurred in an organized and history‐dependent way. These local density fluctuations varied up to ±7% of the bulk density and were made visible by acoustic attenuation and velocity mapping.
Hot‐Gas‐Jet Method and Apparatus for Thermal‐Shock Testing
Authors: Wei George C. , Walsh John
Published: October 2005

In the hot‐gas‐jet thermal‐shock‐testing method, a stream of high‐temperature air is impinged on the center of a ceramic disk. This test is suitable for determining the relative resistance of ceramics to thermal shock that involves fast heating from ambient, with convection as the principal heat‐transfer mode. The feasibility of this testing method was established using transparent polycrystalline La2O3‐doped Y2O3. Thermal‐shock fracture initiates from the cold face of the disk. A smaller grain size in transparent Y2O3 results in a higher probability of survival for a given critical temperature difference in the test. Toughened Y2O3 shows more resistance to thermal‐shock fracture than the standard material.
Anisotropic Electrical Conductivity in Quartz During γIrradiation
Authors: Miyazaki Tetsuo , Kato Noriyuki , Fueki Kenji , Ohshima Nobumitsu
Published: October 2005

Electrical conductivity of quartz during y‐irradiation has been studied at 295 K. A significant electric current was observed in z‐cut quartz, but it could not be measured at all in x‐cut quartz, y‐cut quartz, and amorphous silica. The mobile ionic species produced during y‐irradiation migrate eflciently along the c axis of a quartz crystal. The G value (i.e., the number of product molecules (or ions) formed on irradiations per 100 eV of energy absorbed) of the mobile free ions was determined to be 0.018 from the field dependence of current at low dose rates.
Microstructure Development in Mullite‐Cordierite Ceramics
Authors: Hodge James D.
Published: October 2005

The evolution of the microstructure in mullite‐cordierite bodies containing 36 wt% cordierite has been studied in samples fired at 1490°C for varying times. This material reaches its final density very quickly once the cordierite becomes molten. However, densification, which is not accompanied by any significant coarsening of the mullite phase, appears almost entirely to result from particle–particle rearrangement. Consequently, the ultimate density of these materials appears to be limited by the inability of molten cordierite to penetrate all mullite‐mullite grain boundaries.
Oxidation of Ba2YCu3Ox at High Po2
Authors: O'Bryan Henry M. , Gallagher Patrick K. , Laudis Robert A. , Caporaso Anthony J. , Sherwood Richard C.
Published: October 2005

Dense large‐grain ceramic samples of Ba2YCu2Ox have been oxidized at 400° to 500°C in 10 to 30 MPa of oxygen for 1 to 10 d. The high‐pressure treatment has increased the equilibrium content x slightly above 7 but there is no concomitant increase in Tc. At x = 7.03 the superconducting transition, measured by ac susceptibility, has an onset temperature of ∼91 K and ΔT∼4 K and no change in lattice parameter is observed. High oxygen pressure increases the rate of oxidation.
Laser‐Chemical Vapor Precipitation of Submierometer Silicon and Silicon Nitride Powders from Chlorinated Silanes
Authors: Bauer Robert A. , Smulders Robert , Becht Johanna G. M. , van der Put Paul J. , Schoonman Joop
Published: October 2005

The laser‐chemical vapor precipitation (L‐CVP) of Si3N4 powders from miktures of SiH2Cl2 and NH3 or SiC1,4 and NH3, was studied. The reactant gases were mixed in the laser beam, thus preventing low‐temperature reactions. In a high‐temperature electrostatic precipitator (ESP), Si3N, was collected and separated from the waste product NH4Cl. In the ESP, Si was collected at a lower temperature. A major problem in utilizing chlorinated silanes was their poor absorption of the 10.6‐μm radiation. SF6 was explored for use as an inert sensitizer. Si was prepared from SiH2Cl2. Particle diameters were typically 20 to 40 nm for Si3N4 and 50 nm for Si.
Tensile Strength of Yttria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Noguchi Kenichi , Fujita Michihiko , Masaki Takaki , Mizushina Masahiro
Published: October 2005

Tensile strengths of 2.0 to 5.0 mol% Y2O3‐stabilized ZrO2 polycrystals were described using the newly developed tensile testing method. The tensile test was conducted by attaching three strain gauges on both sides of a rectangular bar that was 10 mm by 1 mm by 200 mm. The tensile strength of tetragonal ZrO2 polycrystals (TZP) containing 2.0 mol% Y2O3 showed 745 MPa, whereas the bend strength of this material was 1630 MPa. Inelastic behavior of the stress‐strain curve was observed at critical stresses and strains of 500 to 700 MPa and 0.25% to 0.35%, respectively. Although deviation from proportionality was observed to be small, it increased with the increase of temperature from −100° to 200°C.
Experimental Whisker Growth and Thermodynamic Study of the Hafnium‐Carbon System for Chemical Vapor Deposition Applications
Authors: Lackey W. J. , Hanigofsky John A. , Freeman Garth B.
Published: October 2005

Chemical vapor deposition of nonstoichiometric hafnium carbide is studied by computer minimization of the Gibbs free energy of the system. Isostoichiometric curves in the HfC1‐x region of the deposition diagram are calculated as a function of HfCI4, CH4, and H2 concentration and reaction temperature. Possible experimental reactions are investigated using thermodynamic efficiency and partial pressure diagrams. A comparison between the calculated solid‐phase regions and the HfC phase diagram is given, and experimental results for HfC whiskers are also compared with the calculations.
Effect of a liquid Phase on Superplasticity of 2‐moI%‐Y203‐StabiIlzed Tetragonal Zirconla Polycrystals
Authors: Hwang Chin‐Mau James , Chen Lwei
Published: October 2005

A small addition of CuO to 2‐mol%‐Y2O3‐stabilized tetragonal zirconia polycrystals significantly enhances superplasticity by forming an amorhous grain‐boundary phase containing primarily Cu+, Y3+, Zr4+, and O2−. This phase apparently melts at around 1130°C, but it already provides a fast diffusion path even below the melting temperature. There are abrupt changes in stress exponent, activation energy, and grain size exponent across the melting temperature. Superplasticity is diffusion‐controlled below the melting temperature and is interfaced‐controlled above that.
dc Electrical Degradation of Perovskite‐Type Titanates: III, A Model of the Mechanism
Authors: Baiatu Tudor , Waser Rainer , Härdtl Karl‐Heinz
Published: October 2005

A quantitative model for the dc voltage‐induced resistance degradation is based on the defect structural material constants and a numerical solution of the general transport problem for the mixed‐conducting perovskite‐type titanates. During degradation, a demixing of the initially homogeneous oxygen vacancy concentration in nominally undoped and acceptor‐doped systems occurs since the ionic transfer is (at least partially) blocked at the electrodes. Because of the specific defect structure, the concentration polarization of the oxygen vacancies leads to a pronounced increase of the p‐conductivity in the anodic region and formation of an n‐conducting cathodic region. The results of our phenomenological degradation studies concerning the influence of external parameters and material parameters as well as the time evolution of the field distribution and the electro‐coloration are described by our simulation model with reasonable precision. The thermodynamic and kinetic aspects of the demixing process are discussed and compared to related phenomena.
Investigation of Lithium Diffusion in Octalithium Plumbate by Conductivity and NMR Measurements
Authors: Konishi Satoshi , Ohno Hideo , Hayashi Takumi , Okuno Kenji , Matsuo Toru
Published: October 2005

Diffusion of lithium ion and tritium in octalithium plumbate (LisPbO6) was studied. The electrical conductivity of the polycrystalline pellets measured by the two‐terminal ac method in the temperature range of 300 to 973 K was one of the highest among oxide lithium ceramics. The temperature dependence of the conductivity is consistent with the nuclear magnetic resonance of lithium‐7 powder samples, suggesting that the temperature dependence of the diffusion of lithium consists of three regions in this temperature range. Preliminary measurements of the diffusion coefficient of tritium in neutron‐irradiated LisPbO6 powder were also carried out. The results were compared with the diffusion of lithium ion, and the relationship between diffusion of lithium ion and tritium is discussed.
Epitaxial Growth of Nickel(II) Hydroxide on layer Silicate and Derived Nickel‐(Layer Silicate) Nanocomposite
Authors: Ohtsuka Kunio , Koga Johji , Tsunoda Masakiyo , Suda Mitsuru , Ono Mikiya
Published: October 2005

Nickel(II) hydroxide crystals were deposited on a substrate of layer silicates from the liquid phase by decomposing nickel(II) ammine complex solutions dispersed with expandable layer silicates; the (001) planes of the nickel(II) hydroxide aligned parallel to the basal (001) plane of the layer silicates. From these layer silicate complexes with nickel(II) hydroxide, nickel‐coated layer silicate composite particulates were derived. Moreover, metal–ceramics alloys, composed of nickel containing uniformly dispersed layer silicates several tens of angstroms in thickness, were produced by sintering the metal‐coated ceramic powders.
Silica to Silicon: Key Carbothermic Reactions and Kinetics
Authors: Filsinger Daniel H. , Bourrie Daniel B.
Published: October 2005

The primary carbothermic reactions for the reduction of silica to produce silicon were defined and the reaction kinetics were determined. Most possible reactions between silicon oxide and carbon or carbon compounds were studied by a series of thermogravimetric analyses at temperatures up to 2000°C. Four key sequential reactions occur with SiC and SiO as intermediate reactants; two reactions involve SiO2 and two involve SiO. Reaction rate versus temperature, activation energy, and preexponential factors were determined for each of six reactions involving SiO2 or SiO. These kinetic studies show that SiO, when combined with either carbon or Sic, reacts in the gaseous state, and the sublimation of SiO is not the rate‐limiting reaction for forming silicon.
Strength of Slip‐Cast, Sintered Silicon Nltrlde
Authors: Govila Ratan K.
Published: October 2005

The flexural strength of slip‐cast, sintered silicon nitride was evaluated as a function of temperature (20° to 1300°C in air), applied stress, and time. The flexural strength was independent of temperatures from 20° to 800°C, and the mode of crack propagation was primarily transgranular. Above 800°C, the flexural strength decreased because of viscous flow of the glassy phase present in the material resulting in subcritical crack growth (SCG). The mode of crack propagation during SCG was essentially intergranular. Flexural stress‐rupture evaluation in the temperature range 800° to 1000°C was used to identify the stress levels for time‐dependent and time‐independent failures.
Processing of Amorphous Calcium Aluminate Powders at < 900°C
Authors: Uberoi Mohit , Risbud Subhash H.
Published: October 2005

Aluminum chelate and calcium nitrate precursors were used to synthesize amorphous calcium aluminate powders by solgel processing at < 900°C. The method of preparation and results of characterization of the gels by thermogravimetric analysis, X‐ray diffraction, scanning Auger microscopy, and single‐point BET analysis are presented. An optimum heat‐treatment schedule consisting of heating the gel to 900°C at 5°C/min and holding for 16 h was developed to produce highly reactive, X‐ray amorphous calcium aluminate powders.
Effects of Sm2O3 and Gd2O3+ Nd2O3 on Electromechanical Properties of PbTiO3 Ceramics
Authors: Xue W. R. , Schulze Walter A. , Newnham Robert E.
Published: October 2005

The electromechanical properties of PbTiO3 ceramics, modified by substitution of Sm or Gd + Nd (same average atomic radius as Sm) for Pb, were studied in the range of 6% to 14% substitution. The modified PbTiO3 ceramics were stable, and the Curie temperature decreased linearly over this composition range. The 10% Sm composition had a large anisotropy in the coupling factor ratio, kt/kp, and a similar, but weaker, effect developed for 12% (1/2 Gd + 1/2 Nd). This indicates that other than average ion size may influence the electromechanical coupling factor ratio.
Joining of Carbon‐Carbon Composites by Graphite Formation
Authors: Dadras Parviz , Mehrotra Gopal M.
Published: October 2005

Joining of carbon‐carbon (C‐C) composites by graphite formation, using manganese, magnesium, and aluminum interlayers, has been investigated. The process involved the formation of a metal carbide by chemical reaction between the metal interlayer and the composite, followed by the decomposition of the carbide and evaporation of the metal at elevated temperatures. The maximum bonding temperature in these experiments was 2200°C. Bonding of composite specimens occurred when manganese or a powder mixture of aluminum and graphite was used as interlayers. Attempts to join C‐C pieces using a magnesium interlayer were unsuccessful. The double notch shear strengths of the joints produced using Mn interlayers were very low and ranged from 0.15 to 1.61 MPa at test temperatures of 1200° and 1400°C. The interlayer, after completion of the joining operation, consisted, in most cases, only of graphite. The joints produced with aluminum plus graphite interlayers were even weaker, with strength values of 0.11 MPa or less. The presence of aluminum could be detected in some of these joints, suggesting incomplete dissociation of Al4C3 at the maximum bonding temperature of 2150°C.
Methodology for Relating the Tensile Constitutive Behavior of Ceramic‐Matrix Composites to Constituent Properties
Authors: Evans Anthony G. , Domergue J.‐M. , Vagaggini E.
Published: October 2005

A methodology for the straightforward and consistent evaluation of the constituent properties of ceramic‐matrix composites (CMCs) is summarized, based on analyses from the literature. The results provide a constitutive law capable of simulating the stresshain behavior of these materials. The approach is illustrated using data for two CMCs: SiC/CAS and SiC/SiC. The constituent properties are also used as input to mechanics procedures that characterize stress redistribution and predict the effect of strain concentrations on macroscopic performance.
YBCO Oxalate Coprecipitation in Alcoholic Solutions
Authors: Shter Gennady E. , Grader Gideon S.
Published: October 2005

A process for synthesis of ultrafine YBa2Cu3O7–x powder by oxalate coprecipitation from nearly saturated solutions of the metal acetates and a 2‐propanol solution of oxalic acid was developed. The coprecipitation was complete within 5 min in an ice bath at 0–2°C. The final stoichiometry was Y:Ba:Cu = 1:1.994:2.991, while the particle size and surface area in the homogeneous coprecipitated powder were 0.1–0.2 pm and 24.9 m2.g−1, respectively. Because of the uniformity and particle size of the coprecipitated material, reactive YBCO powder with a surface area of 1.7 m2.g−1 can be obtained at 780°C in about 12 h.
Temperature‐Stable lead‐Relaxor‐Based Ceramic Dielectrics with Chemical lnhomogeneity
Authors: Tsuzuku Koichiro , Fujimoto Masayuki
Published: October 2005

Matrix grains of Pb‐relaxor ceramics with chemical inhomogeneity, showing the so‐called core‐shell structure already reported for BaTiO3‐based X7R ceramics, were obtained by a controlled sintering process in a MgO‐excess and PbO‐excess PMN‐PMW‐PT system. Multilayer ceramic capacitors exhibiting the X7T specifications were then fabricated from the 8 mol% MgO excess and 4 mol% PbO excess powder. Their chemical inhomogeneity was stable, showing a decrease of capacitance of only 2.9% after an 800‐h aging test.
Dislocation Activity, Stable Crack Motion, and the Warm‐Prestressing Effect in Magnesium Oxide
Authors: Booth Andrew S. , Roberts Steven G.
Published: October 2005

Four‐point bend tests were performed on precracked single‐crystal MgO specimens at different temperatures and strain rates. A large amount of stable crack growth before fracture occurred; etching revealed dislocations in the crack advance region. We believe that dislocation sources near the crack tip emit loops, producing shielding and antishielding dislocations; the latter promote crack advance by a repeated microcleavage mechanism. “Warm‐prestressing” experiments, which improve the room‐temperature fracture toughness by dislocation shielding, were performed. There was a prestress below which no “warmprestressing effect” (WPSE) was exhibited and the magnitude of the WPSE increased with increasing prestressing temperature.
Structure Development Study of Pb (Zr, Ti)O3 Thin Films by an Optical Method
Authors: Peng Chien H. , Desu Seshu B.
Published: October 2005

Lead zirconate titanates (Pb (ZrxTi1–x)O3 or PZT) are well‐known materials with useful ferroelectric properties for nonvolatile memory applications. The device applications usually require processes which form the ferroelectric perovskite phase at low temperatures. Understanding the various aspects of structure development of PZT films is the key to develop low‐temperature processes. An effective, versatile, and nondestructive optical method was developed for the study of the structure development in PZT films. Also, models for the structure development were proposed and were verified by this optical method. Using this method, the characteristic temperatures at which both pyrochlore phase and perovskite phase are initiated and completed were identified. The pyrochloreperovskite transformation was initiated at lower temperature and completed faster for the films on the titanium‐rich side than those on the zirconium‐rich side. In addition, the volume fractions of the perovskite phase were obtained as a function of annealing temperature by this optical method.
Degradation of Stressed Optical Fibers in Water: New Worst‐case Lifetime Estimation Model
Authors: Hasløv Peter , Jensen Knud Bundgaard , Skovgaard Niels H.
Published: October 2005

Simultaneously determined results from zero‐stress aging and static fatigue measurements in water at 65°, 80°, and 95°C have been combined into a worst‐case fiber lifetime model which shows good agreement between predicted and observed failure times. The model shows that the lifetime in a wet environment of the largest crack at normal service strain (0.1%) is nearly identical to the lifetime of the pristine fiber and that the initial strength and the stress corrosion exponent are of minor importance for the lifetime. In a separate experiment, it is shown that degradation in a water‐saturated, jelly‐filled cable is significantly slower than when fibers are directly immersed in water. For a fast‐degrading fiber, evidence of a strength‐increasing mechanism is presented.
Time‐Temperature‐Transformation Curves for Kaolinite‐α‐Alumina
Authors: Liu Kuo‐Chung , Thomas Gareth , Caballero Angel , Moya Jose S. , de Aza Salvador
Published: October 2005

The C‐shaped time‐temperature‐transformation curves (T‐T‐T curves) of cristobalite formation and the L‐shaped T‐T‐T curves of α‐alumina reaction were established for a high‐purity kaolinite‐α‐alumina mixture during heating. The results revealed that cristobalite formation in kaolinite was retarded by the presence of α‐alumina between 1250° and 1350°C and was totally prohibited above 1380°C due to the reaction of kaolinite with α‐alumina to form secondary mullite. The reaction of α‐alumina with kaolinite was initiated at about 1250°C. It became quite extensive above 1380°C and was extremely fast at 1600°C and above, indicating the strong effect of the eutectic liquid formation at ∼1587°C in silica‐alumina. The effectiveness of the established T‐T‐T curves was demonstrated and discussed.
New Development of the J‐Based Fracture Testing Technique for Ceramic‐Matrix Composites
Authors: Hashida Toshiyuki , Li Victor C. , Takahashi Hideaki
Published: October 2005

The J‐based fracture testing technique is newly extended to experimentally determine the tension‐softening (σ–δ) relations in ceramic‐matrix composites. The J‐based technique originally proposed for concrete has been well established for quasi‐brittle materials where the fracture process is primarily dominated by the formation of a fracture process zone and the contribution of the crack tip toughness is negligibly small. In this study, the J‐based technique is further developed to cover a more general case, i.e., a material in which the crack tip stress singularity coexists with the fracture process zone. This is the case, in particular, for modern fiber‐reinforced ceramic composites and coarse‐grained ceramics. The newly derived testing technique has been applied to foam glass composites reinforced with SIC and stainless steel short fibers. The validity of the deduced tension‐softening relations has been examined by microscopy observations and by comparing with other conventional testing methods: the fracture energy method and the R‐ curve approach. It is suggested that the J‐based fracture testing technique can provide reasonable tension‐softening relationships and fracture parameters in modern ceramics and ceramic‐matrix composites.
Residual Stresses in Polycrystalline Diamond Compacts
Authors: Lin Tze‐Pin , Hood Michael , Cooper George A. , Smith Redd H.
Published: October 2005

The effects of residual stress on the integrity of polycrystalline diamond compact (PDC) cutters was investigated. When the compact cooled from the sintering temperature to room temperature, very high radial compressive stresses were induced in the diamond table, and (generally) much lower radial tensile stresses were induced in the cemented tungsten carbide backing. The magnitudes of these residual stresses were not affected very much by the diameter of the compact. However, the residual stresses were affected significantly by the thickness ratio of the carbide layer to the diamond layer. The higher this ratio the greater was the radial compressive stress in the diamond and the lower was the radial tensile stress in the carbide. This same effect was obtained by sintering a relatively thin layer of tungsten carbide on top of the diamond table.
Neutron Diffraction Measurements of the Residual Stresses in Al2O3‐ZrO2 (CeO2) Ceramic Composites
Authors: Wang Xun‐Li , Hubbard Camden R. , Alexander Kathleen B. , Becher Paul F. , Fernandez‐Baca Jaime A. , Spooner Steve
Published: October 2005

High‐resolution neutron powder diffraction was used to study the residual stresses in Al2O3‐ZrO2 (12 mol% CeO2) ceramic composites containing 10, 20, and 40 vol% ZrO2 (CeO2). The diffraction data were analyzed using the Rietveld structure refinement technique. The analysis shows that for all samples, the CeO2‐stabilized tetragonal ZrO2 particles are in tension and the Al2O3 matrix is in compression. For both the ZrO2 particles and the Al2O3 matrix, the average lattice strains are anisotropic and increase approximately linearly with a decrease in the corresponding phase content. It is shown that these features can be qualitatively understood by taking into consideration the thermal expansion mismatch between the ZrO2 and Al2O3 grains. Also, for all composite samples, the diffraction peaks are broader than the instrumental resolution, indicating that the strains in these samples are inhomogeneous. From an analysis of the refined peak shape parameters, the average root‐meansquare strain, which describes the distribution of the inhomogeneous strain field, was determined. Finally, the average residual stresses were evaluated from the experimentally determined average lattice strains and compared with recent results of X‐ray measurements on similar composites.
Thermodynamic Equilibria in Two‐Phase, Elastically Stressed Ionic Crystals
Authors: Johnson William C.
Published: October 2005

The conditions for thermodynamic equilibrium in two‐phase, multicomponent, elastically stressed ionic crystals are derived within the realm of phenomenological thermodynamics using a Gibbsian variational approach. Equilibria between a stressed ionic crystal and a fluid and between two elastically stressed crystals possessing a coherent interface are examined, and an expression for the dependence of the electrochemical potential on stress is derived. The equilibrium conditions are used to calculate composition changes in a ternary (Mg, Ni)O film and the corresponding change in the thermodynamic stability of the film owing to substrate‐induced stress. In this example, a substrateinduced strain of 1% yields an absolute shift in composition of 1.1 at.% at 1000 K. Significantly smaller or larger shifts are possible depending upon material parameters.
Interrelationship between Densification, Crystallization, and Chemical Evolution in Sol‐Gel Titania Thin Films
Authors: Keddie Joseph L. , Braun Paul V. , Giannelis Emmanuel P.
Published: October 2005

The mechanisms contributing to densification during non‐isothermal heat treatments in sol‐gel titania films have been studied. At low temperatures, shrinkage is attributed to condensation reactions between hydroxyls located primarily within the oxide skeleton. At higher temperatures, densification is due to both continued condensation between surface hydroxyls and structural relaxation. Shrinkage stops when films attain a level of crystallinity corresponding to the percolation threshold. At conventional rates, densification is delayed by faster heating; however, at very fast heating rates provided by rapid thermal annealing (8000°C/min), condensation is highly arrested and densification is faster. Similarly, the onset of crystallization increases with conventional heating rates, but crosses over to a lower temperature with rapid thermal annealing.
Characteristics of Alumina Powders Prepared by Spray‐Drying of Boehmite Sol
Authors: Varma Hari Krishna , Mani Themanam Veetil , Damodaran Alathoor D. , Warrier Krishna Gopakumar , Balachandran Uthamalingam
Published: October 2005

Boehmite sol prepared from aluminum nitrate has been spray‐dried to obtain micrometer‐size spherical particles consisting of submicrometer crystallites. The spray‐dried powder was further washed with solvents of varying polarities such as acetone, 2‐propano1, and 2‐methyl‐2‐propanol. Particle‐size distribution, morphology, density, compaction, and sintering characteristics of powders washed with different solvents are reported. The effect of posttreatments on the boehmite‐sol‐derived powders toward reducing agglomeration and obtaining high‐density bodies is discussed.
Hydrothermal Strontium Titanate Films on Titanium: An XPS and AES Depth‐Profiling Study
Authors: Pilleux Mauricio E. , Grahmann Carlos R. , Fuenzalida Víctor M.
Published: October 2005

SrTiO3 films in the 100‐nm thickness range were grown on Ti foils by a 2–4 h hydrothermal treatment at 225°C in an aqueous solution of Sr(OH)2. X‐ray diffraction showed the principal reflections of cubic SrTiO3. Photoelectron analysis revealed the presence of carbon contamination and suggested the presence of hydroxyl groups on the surface, which disappeared in the film bulk. The Auger depth profiles showed three distinct zones. The outermost layer, besides the common carbon contamination, had a large number of OH groups. The second zone was a clean, almost carbon‐free SrTiO3 film. The third zone was a diffuse interface region where the Sr and O concentrations slowly decreased toward the substrate.
Dynamic Compaction of Al2O3‐ZrO2 Compositions
Authors: Tunaboylu Bahadir , McKittrick Joanna , Nellis W. J. , Nutt Steven R.
Published: October 2005

Shock compaction of Al2O3‐ZrO3 binary and ternary powder compositions resulted in dense, one‐piece samples without visible cracks for pressures ≤12.6 GPa. Dynamic pressures were achieved by using a 6.5‐m‐long two‐stage gas gun. It is believed that plastic deformation by dislocation slip of α‐Al2O3 partially accommodates the tensile stresses created during the release of shock pressures. A fine and narrow particle size distribution is necessary to achieve high bulk densities, but the bulk structural integrity was not strongly related to the distribution. A high‐pressure phase of ZrO2, which was formed from the monoclinic polymorph, was found at and above shock pressure of 6.3 GPa. No evidence of the orthorhombic cotunnite structure was observed. Compaction of glassy and submicrocrystalline rapidly solidified starting materials showed good structural integrity, although the bulk density was relatively low. It is not clear what the densificationhonding mechanism is in these materials, although it appears not to be plastic deformation. Microstructural analysis showed that fine and uniform microstructures are retained after compaction at appropriate dynamic pressures for all compositions, with some interparticle cohesion present.
Interaction of Yttria with Uranium Fluoride Gases (UFn, n= 4, 6) at High Temperatures
Authors: Erkmen Z. Engin , Anghaie Samim
Published: October 2005

The corrosion mechanism and microstructural characteristics of yttria (Y2O3) exposed to uranium hexafluoride (UF4) and uranium tetrafluoride gases at temperatures above 900°C were investigated. Processed yttria samples were exposed for times ranging from 5 to 40 min. A weight increase was observed after each test exposure. An outer corrosion scale composed of UO2 and YF3, and an inner corrosion layer of YF3, were observed following the UF6 reaction at nearly 1200 K. During the UF4 exposure, an outer layer containing a liquid mixture of fluoride, oxygen, yttrium, uranium compounds, a secondary reaction layer of UO2 followed by an inner layer composed of a solution of Y2O3 and YF3, possibly in the form of YOF inner layer, were observed. It was found that the corrosion process is controlled by the diffusion which is evidenced by the parabolic growth rate of the secondary layer. After completion of the solidification process, the formation of a eutectic region and dendrites were observed throughout the outer scale. In general, at temperatures above 1173 K, high corrosion rates were observed, and yttria did not appear to be a viable containment material for UF4 and UF6.
Effect of Polynuclear Complex Content on the Synthesis of Aluminum Nitride from Aluminum Polynuclear Complex
Authors: Hashirnoto Noboru , Deki Shigehito , Yato Hisanari , Kanaji Yukio
Published: October 2005

Aluminum nitride powders were synthesized from an aluminum polynuclear complex and glucose. Basic aluminum chloride (BAC) was used as the aluminum polynuclear complex. The effect of the polynuclear complex content on the nitridation reaction and particle size of the AIN powder synthesized was investigated. BAC solutions with various polynuclear complex contents were synthesized using an aqueous solution prepared from AlCl3and Al metal with various compositions. In this system, AlN was synthesized through γ‐Al2O3as an intermediate regardless of the polynuclear complex content. Polynuclear complex content affects the reactivity of nitridation and the particle size of the synthesized AIN powder. The reactivity of nitridation and specific surface area of the products increased with the polynuclear complex content. When the precursor with a polynuclear complex content of 94% was calcined at 1400°C, the AlN content reached 95%. Crystallite size by X‐ray diffraction measurement and particle size calculated from the specific surface area for the products were in good agreement, indicating that AlN particles formed in the synthesis process are in the form of single crystals. AlN powder synthesized from the precursor with a polynuclear complex content above 80% had a fine particle size and narrow size distribution.
Phase Characterization of Precipitated Zirconia
Authors: Gutzov Stoyan , Ponahlo Johann , Lengauer Christian L. , Beran Anton
Published: October 2005

The phase compositions of undoped and europium‐doped zirconia samples, obtained by precipitation and thermal treatment from 350° to 1000°C, have been investigated by powder X‐ray diffractometry, infrared spectroscopy, and cathodoluminescence spectroscopy. The low‐temperature stabilization of tetragonal zirconia is mainly controlled by the presence of anion additives, such as ammonium chloride. The influence of the crystallite size is less important. Cathodoluminescence spectra show a structural similarity between tetragonal and amorphous zirconia.
Grinding Forces and Elastic Recovery in Ceramic Materials
Authors: Kondo Yoshihito , Tsukuda Akira , Takada Atsushi , Okada Shojiro
Published: October 2005

Understanding grinding technology using a diamond grinding wheel is very important to achieve the dimensional accuracy of the final product in structural application of ceramics. Because Si3N4 is very difficult to grind, its grindability, which is estimated from the grinding force, is examined with regard to some of its physical properties. The difficult‐to‐grind nature of Si3N4 depends on its high elastic recovery energy.
Synthesis and Characterization of Sr2Ce2Ti5O16 in the System SrO‐CeO2‐TiO2
Authors: Bamberger Carlos E. , Havedock Tamara J. , Kopp Otto C.
Published: October 2005

The ternary system SrO‐CeO2‐TiO2 was investigated using X‐ray diffractometry. The formation of a new compound, Sr2Ce2Ti5O16, was established, and its compatibilities with SrO, SrCeO3, and SrTiO3 were studied. The results revealed the existence of a series of compounds Sr6–12xCe6xTi5O16 and solid solutions Sr2+nCe2Ti5+nO16+3n (n≤ 6).
Carbon Dioxide laser Synthesis of Ultrafine Silicon Carbide Powders from Diethoxydimethylsilane
Authors: Li Ya‐li , Liang Yong , Zheng Fen , Hu Zhuang‐qi
Published: October 2005

Ultrafine SiC powders have been synthesized from diethoxydimethylsilane by laser‐induced vapor‐phase reactions. The powders produced under different flow rates of the reactant vapor have been characterized by chemical analysis, transmission electron microscopy, infrared spectros‐copy, and X‐ray diffractometry. The results show that the powders are less than 30 nm in average particle diameter, uniformly distributed, spherical in shape, and amorphous. The oxygen and free carbon of the powders vary with the vapor flow rate of the reactant. Annealing of the powders at 1873 K in nitrogen for 1 h results in a complete transformation from amorphous SiC to β‐SiC and a small amount of α‐SiC.
Thickness of Cubic Surface Phase on Barium Titanate Single‐Crystalline Grains
Authors: Takeuchi Tomonari , Ado Kazuaki , Asai Takashi , Kageyama Hiroyuki , Saito Yuria , Masquelier Christian , Nakamura Osamu
Published: October 2005

The crystallographic structure of BaTiO3 particles prepared by conventional solid‐state reaction has been investigated by X‐ray diffractometry and dielectric measurements. The systematic analysis of the diffraction pattern has clearly shown the coexistence of tetragonal and cubic phases at room temperature. The relative amount of cubic phase increases and the dielectric constant decreases with decreasing particle size. These experimental results are consistent with the model that the cubic phase is located at the surface of BaTiO3 grains. The thickness of the surface layer is estimated to be approximately 5 nm, irrespective of the grain size.
Lead Zirconate Titanate Hollow‐Sphere Transducers
Authors: Meyer Richard , Weitzing Holger , Xu Qichang , Zhang Qiming , Newnham Robert E. , Cochran Joe K.
Published: October 2005

Millimeter‐sized, hollow spheres of lead zirconate titanate were fabricated by blowing gas through a fine‐grained slurry of PZT‐5. After they were sintered, the spheres were poled in two ways: radially between inside and outside electrodes, and tangentially between two outside electrodes. The capacitance and vibration modes were modeled and measured for these two poling configurations. The two principal modes of vibration were a breathing mode near 700 kHz and a wall thickness mode near 10 MHz. These spheres have potential uses in medical ultrasound, nondestructive testing, and low‐density transducer arrays.
Strength and Toughness of Slip‐Cast Fused‐Silica Composites
Authors: Lyons Jed S. , Starr Thomas L.
Published: October 2005

The effects of fiber composition, size, and surface treatment on the mechanical behavior of slip‐cast fused‐silica composites were investigated. The ambient and 1000°C stiffness and strength, fracture toughness, GR ‐curve behavior, and fiber‐matrix interface bond strength were determined. Quantitative fractography and scanning electron microscopy were used to ascertain the mechanisms of toughening and strengthening. Composites with weak interface bonding exhibited good strength retention and rising GR ‐curve behavior. The fracture resistance was improved primarily through crack deflection.
Erosion of Glass as Modeled by indentation Theory
Authors: Buijs* Maarten
Published: October 2005

The relation between the mechanical properties of brittle surfaces and an expression for removal rate obtained from the modeling of solid‐particle erosion has been investigated with the aid of indentation‐fracture theory. Different types of glass have been used in this investigation to avoid the complications that microstructure introduces to the description of the mechanical properties of ceramics in general. It appears that the dependence of the removal rate on the material parameters of elasticity, hardness, and fracture toughness can be well described by indentation‐fracture theory. Although different types of glass allow a much more accurate validation of theory than other ceramics, they still do not discriminate between the various expressions for crack length and cracking depth that coexist in indentation‐fracture theory.
Presintering Heat Treatment, Densification, and Mechanical Properties of Silicon Carbide
Authors: Ohji Tatsuki , De Jonghe Lutgard C.
Published: October 2005

Silicon carbides were subjected to extended heat treatments at 1400° or 1600°C prior to a 1‐h isochronal sintering at 2000°C in argon, and the resulting microstructures, final densities, and room‐temperature four‐point bend strengths were compared to those of samples prepared without the pretreatments. The samples heat‐treated at 1600°C exhibited higher relative densities and flexure strengths. Microstructural observation revealed that the heat treatment at 1600°C modified the initial powder compact microstructure, decreasing the development of large, dense domains in the early and intermediate sintering stages. This evolution was considered to promote a more uniform subsequent densification. The final size and distribution of the grains as well as of the pores were found to be affected favorably by the pretreatment.
Effect of Sintering Atmosphere on Interface Migration of Niobium‐Doped Strontium Titanate during Infiltration of Oxide Melts
Authors: Jeon Jae‐Ho , Kang Suk‐Joong L.
Published: October 2005

The solid/liquid interface migration in Nb‐doped SrTiO3 has been investigated. The specimen sintered in air shows no migration during oxide infiltration in air, whereas the specimen sintered in 5H2.95N2 shows appreciable migration during similar infiltration. In the migrated layers of the specimen sintered in the reducing atmosphere and infiltrated in the oxidizing atmosphere, no cations of the infiltrants are detected by wavelength dispersive spectroscopy. These results show that the change in defect concentration due to the atmosphere change can induce the interface migration as in the case of frequently observed migrations due to solute concentration change. The driving force for the migration is discussed in terms of the coherency strain energy in a thin diffusional oxidized layer of the receding grain.
Preparation of Silicon Carbide Fiber from Activated Carbon Fiber and Gaseous Silicon Monoxide
Authors: Okada Kaoru , Kato Hitoshi , Nakajima Keihachiro
Published: October 2005

Crystalline silicon carbide (SiC) fiber was produced by a new, simple procedure. Activated carbon fiber (ACF) was reacted with gaseous silicon monoxide and was converted to SiC fiber at elevated temperature and reduced pressure. The reaction was completed at temperatures as low as 1473 K. The reacted fiber consisted of submicrometer particles which were not observed in the original ACF. The SiC crystal size in the reacted fiber was approximately 30 nm. The microstructure of the fiber became dense after it was heat‐treated in air at 1573 K or in nitrogen gas at 1873 K.
Concept of Functionally Graded Materials for Advanced Thermal Barrier Coating Applications
Authors: Lee Woo Y. , Stinton David P. , Berndt Christopher C. , Erdogan Fazil , Lee Yi‐Der , Mutasim Zaher
Published: October 2005

This feature article explores the concept of creating functionally graded metal‐ceramic composite microstructures for thermal barrier coatings used in gas‐turbine applications. From a thermomechanical perspective, this concept offers the possibility of significantly improving the life and reliability of thermal barrier coatings. However, prior research reveals that progress has been somewhat limited because of the oxidative instability exhibited by some metal‐ceramic composite microstructures. The present study addresses some of the materials criteria and research issues associated with preparing chemically stable, yet mechanically durable, graded metal‐ceramic microstructures for realistic application environments.
Particle‐Inhibited Grain Growth in AI2O3‐SiC: I, Experimental Results
Authors: Stearns Laura C. , Harmer Martin P.
Published: October 2005

An extensive experimental study has been conducted to examine the influence of ultraflne SiC particles on grain growth in A12O3. Grain growth has been studied as a function of annealing time, particle volume fraction, and annealing temperature. The SiC particles reduce the grain‐growth rate of A12O3 by >3 orders of magnitude, resulting in final grain sizes that decrease with increasing particle volume fraction. The fraction of SiC particles on grain boundaries, φ, has been measured as a function of annealing time, particle volume fraction, and annealing temperature. φ decreases during grain‐growth anneals, implying that grain boundaries are able to break free from particles and this is true to a greater extent for smaller volume fractions of particles. Further, it has been discovered that φ and average grain size, G, are strongly correlated, such that any increase in G results in a predictable decrease in pH. This new finding has revealed a path for microstructure development in this system that proves to be critical in the equilibrium and kinetic analyses described in a companion paper.
Direction of Liquid Film Migration Induced by Chromic Oxide in Alumina‐Anorthite
Authors: Paek Yeong‐Kyeun , Lee Ho‐Yong , Kang Suk‐Joong L.
Published: October 2005

Three kinds of single‐crystalline alumina plates with the crystallographic planes of C, m, and R were diffusion‐bonded with liquid‐phase sintered (98)alumina‐(2)anorthite (in wt%) plates (P) and then heat‐treated at 1600°C under a Cr203‐containing atmosphere. During the heat treatment, for all of the specimens studied, the anorthite liquid films between alumina plates migrated to grains with surface orientation corresponding to higher coherency strain energy. This result is in better agreement with a prediction based on the coherency strain theory than the previous one obtained for grain‐boundary migration. The discrepancy between the predicted and previously observed migration directions of some grain boundaries in alumina may therefore be attributed to an effect of grain‐boundary structure and stress transmission across the boundary.
Rheological Properties of Concentrated, Nonaqueous Silicon Nitride Suspensions
Authors: Bergström Lennart
Published: October 2005

The rheological properties of nonaqueous silicon nitride powder suspensions have been investigated using steady shear and viscoelastic measurements. The polymeric dispersant, Hypermer KD‐3, adsorbed strongly on the powder surfaces, and colloidally stable, fluid suspensions up to a volume fraction of φ= 0.50 could be prepared. The concentrated suspensions all displayed a shear thinning behavior which could be modeled using the high shear form of the Cross equation. The viscoelastic response at high concentrations was dominated by particle interactions, probably due to interpenetration of the adsorbed polymer layers, and a thickness of the adsorbed Hypermer KD‐3 layer, Δ∼10 nm, was estimated. The volume fraction dependences of the high shear viscosity of three different silicon nitride powders were compared and the differences, analyzed by using a modified Krieger‐Dougherty model, were related to effective volume effects and the physical characteristics of the powders. The significantly lower maximum volume fraction, φm= 0.47, of the SN E‐10 powder was referred to the narrow particle size distribution and the possibility of an unfavorable particle morphology.
A Theoretical Model for Compaction of Granular Materials
Authors: Kenkre V. M. , Endicott M. R. , Glass S. Jill , Hurd Alan J.
Published: October 2005

A theoretical model is developed for the description of the compaction of granular materials exemplified by granulated ceramic powders. Its predictions compare satisfactorily to results of uniaxial compaction tests of ceramic granules of lead magnesium niobate‐lead titanate (PMN‐PT), rutile, and spray‐dried alumina. The theory uses volume‐based statistical mechanics and an activation analogy to treat, in parallel, the rearrangement of granules and their deformation. Variation of the model incorporates a distribution of barriers to deformation, which can be considered to include the effects of statistical pressure distributions within the compact. Other curve‐fitting schemes available in the literature are shown to correspond to particular cases of the theory, and a justification of the equations used in those schemes is provided on physical grounds.
Cyclic‐Fatigue Behavior of SiC/SiC Composites at Room and High Temperatures
Authors: Mizuno Mineo , Zhu Shijie , Nagano Yasuo , Sakaida Yoshihisa , Kagawa Yutaka , Watanabe Makoto
Published: October 2005

Tension‐tension cyclic‐fatigue tests of a two‐dimensional‐woven‐SiC‐fiber‐SiC‐matrix composite (SiC/SiC) prepared by chemical vapor infiltration (CVI) were conducted in air at room temperature and in argon at 1000°C. The cyclic‐fatigue limit (107 cycles) at room temperature was ∼160 MPa, which was ∼80% of the monotonic tensile strength of the composite. However, the fatigue limit at 1000°C was only 75 MPa, which was 30% of the tensile strength of the composite. No difference was observed in cyclic‐fatigue life at room temperature and at 1000°C at stresses >180 MPa; however, cyclic‐fatigue life decreased at 1000°C at stresses < 180 MPa. The fracture mode changed from fracture in 0° and 90° bundles at high stresses to fracture mainly in 0° bundles at low stresses. Fiber‐pullout length at 1000°C was longer than that at room temperature, and, in cyclic fatigue, it was longer than that in monotonic tension. The decrease in the fatigue limit at 1000°C was concluded to be possibly attributed to creep of fibers and the reduction of the sliding resistance of the interface between the matrix and the fibers.