bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Dopants on Nucleation and Growth of High‐Quartz Solid Solution in Lithium Aluminosilicate Glass
Authors: Tkalčce Emilija , Šenija Davor , Dondur Vesna , Petranović Nada
Published: March 2005

The kinetic parameters of nucleation and crystal growth of high‐quartz solid solution in multicomponent lithium aluminosilicate glasses doped with various transition‐metalions were studied by nonisothermal DTA. The crystallization of glasses nucleated at different temperatures was carried out, and plots of the DTA peak versus the nucleation temperatures were used to determine the maximum nucleation rate temperature. Peak temperature data of nucleated samples at varying heating rates (5–20 K/min) were used to determine the activation energy for crystallization via the JMA equation. The temperature of maximum nucleation rate depends greatly on the doped transition‐ metal ions present. The activation energy for crystallization obtained for undoped glass or glasses doped with Fe2O3 is of the same order as that already published, and the Avrami exponent is consistent with predominantly three‐dimensional crystal growth. The much higher activation energy values for glasses doped with CoO could be a consequence of two crystallization processes proceeding simultaneously.
Shape Memory‐Like Effect Phenomena in a Ce‐TZP/Al2O3 Composite
Authors: Schmid Chiari , Sbaizero Orfeo , Sergo Valter , Meriani Sergio
Published: March 2005

During an investigation of the role of alumina particles in ceria‐stabilized tetragonal zirconia polycrystals (Ce‐TZP)1 we observed that a group of samples (based on a Ce‐TZP matrix (8.5 mol% Ceria) containing 15 vol% dispersed alumina particles), exhibited an extended plastic deformation after the first elastic response. This deformation could be retained upon a prompt unloading from a fourpoint bend jig. These deformed (bent) specimens recovered their original straight shape when heated above 200°C, exhibiting features like the shape memory effect (SME). A careful examination of the samples revealed the presence of wedgelike transformation zones intruding the bulk of the specimen inwards from the tensioned side.

In an attempt to increase the degree of bending, other samples of the same composition and microstructure have been placed under a static load and maintained under that condition for ≅15 min. The penetration depth of the transformation zone reached the opposite face of the samples and the monoclinic‐phase concentration rose about 50% on both sides. Through this inwards movement, these samples, that were initially bent, showed an elongation of about 0.5% and became straightened. These samples returned to their original size after heating at ≅250°C. To get a deeper insight, samples have been examined by X‐ray diffraction (XRD), differential thermal analysis (DTA), and thermodilatometry (TD).
Influence of ZrO2 Grain Size and Content on the Transformation Response in the Al2O3─ZrO2 (12 mol% CeO2) System
Authors: Becher Paul F. , Alexander Kathleen B. , Bleier Alan , Waters Shirley B. , Warwick Wilbur H.
Published: March 2005

Based on experimental and modeling studies, the rate of increase in the martensite start temperature Ms for the tetragonal‐to‐monoclinic transformation with increase in zirconia grain size is found to rise with decrease in ZrO2 content in the zirconia‐toughened alumina ZTA system. The observed grain size dependence of Ms can be related to the thermal expansion mismatch tensile (internal) stresses which increase with decrease in zirconia content. The result is that finer zirconia grain sizes are required to retain the tetragonal phase as less zirconia is incorporated into the alumina, in agreement with the experimental observations. At the same time, both the predicted and observed applied stress required to induce the transformation are reduced with increase in the ZrO2 grain size. In addition, the transformation‐toughening contribution at temperature T increases with increase in the Ms temperature brought about by the increase in the ZrO2 grain size, when T > Ms. In alumina containing 20 vol% ZrO2 (12 mol% CeO2), a toughness of ∼10 MPa. √m can be achieved for a ZrO2 grain size of ∼2 μm (Ms∼ 225 K). However, at a grain size of ∼2 μm, the alumina–40 vol% ZrO2 (12 mol% CeO2) has a toughness of only 8.5 MPa. √m (Ms∼ 150 K) but reaches 12.3 MPa. ∼m (Ms∼ 260 K) at a grain size of ∼3 μm. These findings show that composition (and matrix properties) play critical roles in determining the ZrO2 grain size to optimize the transformation toughening in ZrO2‐toughened ceramics.
Acoustic Characterization of Silica Glasses
Authors: Jen Cheng‐Kuei , Neron Christian , Shang Alain , Abe Koich , Bonnell Lee , Kushibiki Junichi
Published: March 2005

Acoustic characterization of doped silica glasses with a GeO2, P2O5, F, TiO2, Al2O3, or B2O3dopant having different concentrations is presented. Quantitative measurements were performed with a 225‐MHz line‐focus‐beam scanning acoustic microscope. The acoustic velocity variation due to different dopant concentrations is given. It has been found that the Al2O3dopant increases, but the other dopants decrease, the acoustic velocity as compared with that of the pure fused silica. We have also found that the fractional change in acoustic velocity is greater than that in refractive index for a given dopant concentration.
Apparent Enhanced Fatigue Resistance under Cyclic Tensile Loading for a HIPed Silicon Nitride
Authors: Jenkins Michael G. , Ferber Mattison K. , Lin Chih‐Kuang J.
Published: March 2005

Cyclic tensile loading tests of a commercial HIPed silicon nitride at elevated temperatures have indicated apparent “enhanced” fatigue resistance compared to static tensile loading tests under similar test conditions. At 1150°C, stress rupture results plotted as maximum stress versus time to failure did not show significant differences in failure behavior between static, dynamic, or cyclic loading conditions, with all failures originating from preexisting defects (slow crack growth failures). At 1260°C, the stress rupture results showed pronounced differences between static, dynamic, and cyclic loading conditions. Failures at low static stresses (<175 MPa) originated from environmentally assisted (oxidation) and generalized creep damage, while failures at similar times but much greater (up to 2 x) cyclic stresses originated from preexisting defects (slow crack growth failures). At 1370°C, stress rupture results did not show as pronounced differences between static, dynamic, and cyclic loading conditions, with most failures originating from environmentally assisted (oxidation) and generalized creep damage.
Electrical Conductivity of Zirconia Stabilized with Scandia and Yttria
Authors: Kaneko Hiroyuki , Jin Fuxue , Taimatsu Hitoshi , Kusakabe Hirotatsu
Published: March 2005

Electrical conductivity of zirconia stabilized with scandia and yttria (Sc2O3+Y2O3= 8 mol%) has been measured by the complex impedance method in the temperature range 573 to 1173 K. With increasing Sc2O3concentration, electrical conductivity increases at temperatures above 640 K, but it decreases below this temperature. Electrical conductivity in the electrolytes examined is a result of two processes: an activation energy of 59 to 79 kJ·mol−1predominant at high temperatures and an activation energy of 109 to 125 kJ·mol−1predominant at low temperatures.
Correlation between the Width of the Glass Transition Region and the Temperature Dependence of the Viscosity of High‐Tg Glasses
Authors: Moynihan Cornelius T.
Published: March 2005

A correlation exists between the width of the glass transition region measured using DTA or DSC during heating and the activation enthalpy ΔHη* for the shear viscosity of high‐Tginorganic glasses. This is demonstrated by the constancy of a dimensionless parameter C= (ΔHη*/R)(1/Tg – 1/Tg′), where Tg and Tg′ are temperatures marking the extrapolated onset and finish of the transition region on the DTA or DSC trace. The logarithm of the shear viscosity at Tg, log η (Tg), is also approximately constant for high‐Tg glasses. Using the universal values of C and log η (Tg), fairly reliable estimates of shear viscosities from the transition range through the working range can be made from the Tg and Tg′ values obtained using DTA or DSC.
Vibrational Spectroscopy of Aluminum Nitride
Authors: McNeil Laurie E. , Grimsditch Marcos , French Roger H.
Published: March 2005

A complete description of the first‐order Raman and Brillouin spectra of single‐crystal aluminum nitride is provided. The frequency has been measured and the symmetry identified of each of the Raman‐active zone‐center optic modes, and the five independent elastic constants have been measured. The widths of the principal Raman modes increase with increasing oxygen content up to a critical value of approximately 1 at.%, after which they are constant. This behavior supports the hypothesis of a change in the nature of the oxygen defect at that concentration.
Transmission High‐Energy Electron Energy Loss Spectrometry (EELS) Analysis of Hole Formation and Charge Transfer in p‐type Doped Cuprate Superconductors
Authors: Zhang Hong , Dravid Vinayak P.
Published: March 2005

The technique of transmission high‐energy electron energy loss spectrometry (EELS) in TEM has been applied to analyze the formation of charge carriers (holes) and charge transfer in p‐type doped cuprate superconductors. The O‐K absorption edges of these compounds exhibit a distinct pre‐edge feature which is related to the formation of holes on oxygen sites. The newly discovered Ga‐based cuprate superconductors display additional significant spectral features. O‐K absorption edge fine structure analysis reveals two types of holes in this system, one induced by hole doping alone and the other by high‐pressure oxygenation treatment. Only the second type of hole appears to be associated with the occurrence of superconductivity. The Cu L3 edge of the doped and oxygenated compounds also exhibits a pronounced shoulder on the higher‐energy side of the Cu L3 edge which represents the charge transfer between copper and oxygen. EELS absorption data are consistent with the doped charge‐transfer insulator or Mott‐Hubbard model description of the electronic states. Necessary experiments to distinguish between the above two models are also suggested.
Solid‐State Sintering of YBa2Cu3Ox in Different Oxygen Partial Pressures
Authors: Poisl W. Howard , Chaklader Asoke C. D.
Published: March 2005

The effect of oxygen partial pressure, ranging from 0.001 to 1.0 atm, and temperature, in the range of 930°–955°C, on the solid‐state sintering kinetics of the superconducting ceramic YBa2Cu3O7‐δ has been studied. Isothermal compaction rates between 930° and 955°C reached a maximum at some critical PO2 (PO2CRIT), with decreasing rates both above and below this oxygen partial pressure. This behavior was not observed for YBa2Cu3O7‐δ sintered at 960°C, when a liquid phase is present. The activation energy for sintering above PO2CRIT has been estimated to be ∼190 kJ/mol, whereas below PO2CRIT it was found to be ∼130 kJ/mol. The oxygen ion diffusion was considered to be the rate‐determining step above PO2CRIT, while it is hypothesized that lattice strain caused by the formation of oxygen ion vacancies below PO2CRIT affected the rate of sintering.
Thermochemistry of the U─O and Zr─O Systems
Authors: Wang Wei‐E , Olander Donald R.
Published: March 2005

The thermodynamic constraint relating the standard free energy of formation of an oxide (MOc) to its oxygen potentials by ΔGf0(MOc) =½ƒocΔḠ(O2) dC′ has been used to develop the full spectrum of oxygen potentials of the U─O and Zr─O systems at high temperatures. Henry's law is applied to the metal region in the U─O system. Oxygen dissolution in liquid Zr has been shown to deviate only slightly from Henry's law, despite the high solubility. Minor modifications of the previously reported oxygen pressures in the two‐phase regions of both of the U─O and Zr─O systems result from the requirement of satisfying the integral constraint. Oxygen pressures in the oxygen‐containing metal regions where no data are available have also been estimated. The ensemble of the results is displayed in the form of oxygen isobars superimposed on the phase diagrams of the U─O and Zr─O systems. The oxygen pressure‐temperature–composition relation of tetragonal (β) ZrO2±x has also been established.
Diameter Dependence of the Refractive Index of Melt‐Drawn Glass Fibers
Authors: Corpus Joey M. , Gupta Prabhat K.
Published: March 2005

The diameter dependence of the refractive index of as‐formed glass fibers is examined. It is shown that the measured results on fibers of a soda–lime–silica glass can be satisfactorily explained by combining three factors: the diameter dependence of the cooling rate, the cooling rate dependence of the fictive temperature, and the dependence of glass properties on its fictive temperature.
Positron Annihilation Studies of the Internal Surfaces of Selected Zeolites and the Effect of Hydration
Authors: Surapanani Srinivas , Mullins Michael E. , Waber James T.
Published: March 2005

Positron annihilation techniques have been applied to study the pore diameters and volumes of 11 crystalline and amorphous zeolites. The data, consisting of the number of counts per channel recorded on a multichannel analyzer, were analyzed by means of the POSITRONFIT program. The data were presented as four lifetimes, τ1 to τ4, with their associated intensities, I1 to I4. The pore volumes reported here were based on a quantum mechanical model. The derived volumes are in reasonable agreement with pore volumes obtained with X‐ray and other data. The intensity of our fourth positron lifetime correlates with Brunauer–Emmett–Teller measurements of the surface area of the powders. These results are consistent with two studies by other authors.
Active Gaseous Corrosion of Porous Silicon Carbide
Authors: Sickafoose Robert R. , Readey Dennis W.
Published: March 2005

In a reducing atmosphere, SiO2 as an impurity in SiC can react to form SiO and CO gases. Likewise, oxygen in the atmosphere can also lead to the same gaseous species. Experimental data are reported on the rate of weight loss in H2‐H2O atmospheres of porous SiC containing residual SiO2. The amount of residual SiO2 was varied by passive oxidation of the porous SiC prior to heating in the reducing atmosphere. The data are compared to a model of active corrosion to determine the mechanism of weight loss and to identify the gas species present in SiC with SiO2 as an impurity.
Excimer Laser Surface Processing of Ceramics: Process and Properties
Authors: Jervis Thomas R. , Nastasi Michael , Hubbard K. M. , Hirvonen J.‐P.
Published: March 2005

Surface modification of ceramics has proved to be of benefit in a number of applications. Excimer laser light provides a rapid and efficient means for surface alloying and modification of ceramic materials. The laser pulse can melt the surface of the ceramic as well as a deposited metal layer. This results in diffusional mixing in the liquid state, which is followed by rapid resolidification. The high temperatures involved can overcome kinetic barriers to mixing found in ion beam experiments. Tribological measurements on surface treated materials show reduced friction and increased surface toughness. Increased fracture toughness in laser surface alloyed ceramics has also been observed. Excimer laser processes therefore may enable the use of ceramic materials in applications for which they are not now suitable.
Neutron Reflectometry Characterization of Interface Width between Sol‐Gel Titanium Dioxide and Silicon Dioxide Thin Films
Authors: Keddie Joseph L. , Norton Laura J. , Kramer Edward J. , Giannelis Emmanuel P.
Published: March 2005

Neutron reflectometry (NR) was used to directly measure the interface width between a titanium dioxide and a silicon dioxide film deposited by sol‐gel processing. In a bilayer heated to 450°C, NR measurements showed that the interface width is 0.8 nm. This width is the same as the roughness of a sol‐gel silicon dioxide surface after the same heat treatment, suggesting no interdiffusion or mixing at the bilayer interface.
Error Propagation Biases in the Calculation of Indentation Fracture Toughness for Ceramics
Authors: Kelly J. Robert , Cohen Mark E. , Tesk John A.
Published: March 2005

Indentation fracture toughness models generally share the derived parameter Pc−3/2, where P is the indentation load and c the measured crack length. Biases, inherent to error propagation through this nonlinear transformation (c to c3/2), can be introduced into calculated values for KIC, depending upon the amount of averaging of crack length data performed prior to the transformation. This work utilizes Monte Carlo simulations to evaluate the bias in KIC calculated using both mean and linear regression methods. Significant positive biases were demonstrated when using mean‐based calculations where coefficients of variation (cv) in c exceeded 10%. Regression methods produced significantly less bias. With cv < 10% or when c is averaged per load, both methods produce essentially unbiased estimates for KIC.
Crystal Structure of Metastable Tetragonal Zirconia by Neutron Powder Diffraction Study
Authors: Igawa Naoki , Ishii Yoshinobu , Nagasaki Takanori , Morii Yukio , Funahashi Satora , Ohno Hideo
Published: March 2005

The crystal structure of metastable tetragonal zirconia prepared by the alkoxide method without any dopant has been examined by neutron diffraction at room temperature. The lattice parameters of this sample were a= 0.3591 ± 0.0001 nm and c= 0.5169 ± 0.0001 nm. The oxygen ions are shifted from their lattice sites in the 〈001〉 direction with a magnitude of Δ/c= 0.046 ± 0.004.
Thermal Expansion Discontinuities of Mullite
Authors: Schneider Hartmut , Rodewald Katia , Eberhard Emil
Published: March 2005

Thermal expansion data of mullite were collected between 25° and 800°C with high accuracy by means of an X‐ray high‐temperature Guinier powder camera, and high‐resolution single‐crystal Bond techniques. 3/2‐type mullites, synthesized from chemically coprecipitated precursors and 2/1‐type fused‐mullite single crystals, were used for the measurements. Mullite displays low and nonlinear thermal expansions along the crystallographic a, b, and c axes below about 200°C, and linear expansions between 200° and 400°C. Between about 400° and 500°C, expansion curves are discontinuous. Above 500°C, a, b, and c expansions are linear again. The temperature‐induced expansion discontinuities are relatively strong parallel to a, but are much weaker parallel to b and c. The slopes of the a and volume expansion curves are higher above the expansion discontinuity than below, while there is no significant tendency for those of b and c. Thermal expansion coefficients and discontinuity effects are reversible without any hysteresis. The increase of the a and volume expansion curves above the expansion discontinuities may be due to possible deformations, rotations, and tiltings of the [AlO6] octahedra. Another factor responsible for the higher a and volume expansion coefficients at high temperatures may be a geometrical deformation of the [Al⋆O4] tetrahedra. At present, no conclusive model exists to explain the discontinuous change of thermal expansion coefficients between 400° and 500°C.
Reaction of CaTiO3 with PbO–B2O3 and PbO–SiO2 Glasses
Authors: Yamaguchi Takashi , Ayaki Hiroko , Asai Lika
Published: March 2005

Interfacial and powder reactions between CaTiO3 and 90PbO–10B2O3 and 75PbO–25SiO2 binary glasses were studied. The reaction has been analyzed as the effect of B2O3 and SiO2 additions on the interaction between CaTiO3 and PbO, and discussed from thermodynamic and kinetic points of view. For a fixed CaTiO3/PbO ratio2 the product perovskite phase became enriched with lead as the amount of additives increased, which is more pronounced with B2O3 addition. The reaction of CaTiO3 with the lead–boron glass was controlled by a dissolution‐precipitation mechanism, and that with the lead‐silica glass by a diffusion mechanism.
Precursor Morphology Effects in Combustion‐Synthesized and Dynamically Consolidated Titanium Carbide and Titanium Boride
Authors: Kecskes Laszlo J. , Niiler Andrus , Kottke Thomas
Published: March 2005

The combustion synthesis/dynamic consolidation (CS/DC) technique was applied to titanium–carbon and titanium–boron mixtures with different initial precursor carbon and boron powder morphologies. The evolution of the CS/DC product structure was investigated by analyzing and comparing the combustion synthesis products following three fabrication process steps: reacted loose powders, reacted green compacts, and reacted green compacts which were dynamically consolidated shortly after the synthesis. In all cases, the purity of the precursor carbon and boron powders was found to affect the residual porosity of the products. However, the dependence of the resultant product grain morphology on the morphology of the precursors was not as straightforward. Correlations between the respective product structures and possible reaction mechanisms are discussed.
Microstructure of Hardened Cement Paste—A New Interpretation
Authors: Diamond Sidney , Bonen David
Published: March 2005

Morphological features of hydrated portland cement paste exhibited on carefully polished surfaces have been critically examined using backscatter mode scanning electron microscopy. A new interpretation and classification of such features is proposed. The microstructure is seen to consist of distinct grains of the order of 10 μm and larger (“phenograins”) set in a cellular groundmass of smaller particles and pores. Most of the phenograins are dense pseudomorphs of the larger cement grains, but some are large calcium hydroxide crystals, and in some cements a few may represent inert filler grains added to the cement. The phenograins that are pseudomorphs of cement particles may be solid, gapped, or hollow; and, at a given age, various stages of hydration are represented in different grains. While many pseudomorph phenograins consist of a simple core of unhydrated material surrounded by a uniform shell of hydration product, more complex and irregular structures are also found. Relationships between these features and earlier classifications of cement hydration product particles are discussed, and implications with respect to difficulties in image analysis of hardened cement paste are examined.
α‐Dicalcium Silicate Hydrate: Preparation, Decomposed Phase, and Its Hydration
Authors: Ishida Hideki , Yamazaki Satoru , Sasaki Kaori , Okada Yoshihiko , Mitsuda Takeshi
Published: March 2005

α‐C2SH can be synthesized by hydrothermal treatment of lime and silicic acid for 2 h at 200°C. When heated to 390–490°C, α‐C2SH dissociates through a two‐step process to form an intermediate phase plus some γ‐C2S. This appears to be a new dicalcium silicate different from known dicalcium silicates—α, α′L, α′H, β, and γ phase—and is stable until around 900°C. At 920–960°C, all the phases are transformed to the α′L phase. The intermediate phase has high crystallinity and is stable at room temperature. 29 Si MAS NMR measurements indicate the possibility that it contains both protonated and unprotonated monosilicate anions. The intermediate phase that has passed through the α’phase at higher temperature yields β‐C2S on cooling. The intermediate phase is highly active, and completed its hydration in 1 day (w/s= 1.0, 25°C). Among the crystalline calcium silicate hydrates with Ca/Si = 2.0, it is hillebrandite that yields β‐C2S at the lowest temperature.
Damage Development and Moduli Reductions in Nicalon—Calcium Aluminosilicate Composites under Static Fatigue and Cyclic Fatigue
Authors: Karandikar Prashant G. , Chou Tsu‐Wei
Published: March 2005

Unidirectional and cross‐ply Nicalon fiber‐reinforced calcium aluminosilicate (CAS) glass‐ceramic composite specimens were subjected to tension–tension cyclic fatigue and static fatigue loadings. Microcrack densities, longitudinal Young's modulus, and major Poisson's ratio were measured at regular intervals of load cycles and load time. The matrix crack (0° plies) density and transverse crack (90° plies) density increased gradually with fatigue cycles and load time. The crack growth is environmentally driven and depends on the maximum load and time. Young's modulus and Poisson's ratio decreased gradually with fatigue cycles and load time. The saturation crack densities under fatigue loadings were found to be comparable to those under monotonic loading. A matrix crack growth limit strain exists, below which matrix cracks do not grow significantly under fatigue loading. This limit coincides with the matrix crack initiation strain. Linear correlations between crack density and moduli reductions obtained from quasi‐static data can predict the moduli reductions under cyclic loading, using experimentally measured crack densities. A logarithmic correlation can predict the Young's modulus reduction in a limited stress range. A fatigue crack growth model is proposed to explain the presence of two distinct regimes of crack growth and Young's modulus reduction.
Mullite with Lattice Constants a > b
Authors: Schneider Hartmut , Fischer Reinhard X. , Voll Dietmar
Published: March 2005

The mullite phase was synthesized in a sol–gel process using aluminum sec‐butylate and silicon chloride in proportions corresponding to an Al/Si ratio of 4:1. Heat treatment at 1000°C yielded a mullite‐type phase, γ‐alumina, and amorphous fractions. Conventional indexing based on the orthorhombic (Pbam) mullite unit cell with b > a showed that X‐ray diffraction peaks with high k and l but low h indices are strongly shifted toward higher d‐spacings as compared with a “normal” mullite. Furthermore, the relative positions of reflection pairs hkl and khl are interchanged. The Rietveld analysis yielded the following constants: a= 7.760(2) Å, b= 7.595(2) Å, c= 2.9192(4) Å confirming a > b.
Optical Study of Domains in Ba(Ti,Sn)O3 Ceramics
Authors: Oh KCi‐Young , Uchino Kenji , Cross L. Eric
Published: March 2005

Domain structures of Ba(Ti1−xSnx)O3 (x = 0, 0.05, 0.1, 0.13) ceramics were observed dynamically under an electric field at various temperatures using a high‐resolution charge‐coupled‐device (CCD) microscope system. The Ba(Ti1−xSnx)O3 ceramics showed a significant difference in domain structure and motion with changing composition: the domain structure became tiny and complex with increasing x, and the domain reorientation was easily induced with increasing and decreasing electric field. The results of the domain observations coincided well with electrical measurement data.
Notch Effects in Carbon Matrix Composites
Authors: Heredia Fernando E. , Spearing S. Mark , Mackin Thomas J. , He Ming Y. , Evans Anthony G. , Mosher Paul , Brøndsted Povl
Published: March 2005

The tensile properties of various carbon matrix composites, reinforced with C and SiC fibers, have been evaluated. The objective is to assess mechanics procedures for characterizing the influence of holes and notches. Interpretation has been attempted using large‐scale bridging mechanics, with linear elastic fracture mechanics as one limit and notch insensitivity as the other. Important differences between the materials, associated primarily with the fiber/matrix interfaces and the in‐plane shear strength, have been identified and attempts made to rationalize these differences.
Growth of Strontium Titanate Thin Films of Controlled Thickness by the Hydrothermal–Electrochemical Method
Authors: Kajiyoshi Koji , Tomono Kunisaburo , Hamaji Yukio , Kasanami Torn , Yoshimura Masahiro
Published: March 2005

Strontium titanate thin films were grown on titanium electrodes up to ca. 2 μm in thickness by a hydrothermal–electrochemical method using electrolysis performed potentiostatically by the three‐electrode cell technique. The film thickness increased monotonically with an increase in the quantity of electricity passed through the Ti electrode, and could be controlled accurately by this factor. Grown films were composed of a surface layer having an invariant thickness of ca. 0.2 μm and an inner layer grown by electrolysis. The lattice parameter of the cubic SrTiO3 film was analyzed to be 3.919 A.
Silver‐Palladium Thick‐Film Conductors
Authors: Wang Sea Fue , Dougherty Joseph P. , Huebner Wayne , Pepin John G.
Published: March 2005

The trends in integrated circuit packaging technology are toward high speed, high density, reliability, and low cost. These demand the improvement of material formulations and processing technology. Among the thick‐film materials systems, conductor materials generally represent an important and the most expensive element. Therefore, attention has been centered on the performance of the fired metal film and its cost. Silver and palladium (Ag/Pd) conductors are important components of thick‐film paste technology. Thick‐film Ag/Pd conductors find applications in many aspects of electronics and electronic packaging, such as hybrid microcircuits, multichip modules, packaging for integrated microcircuits, and in passive electronic components such as multilayer capacitors, varistors, and inductors. In this paper, the performance and properties of fired Ag/Pd films are discussed through their physical and chemical aspects. The final film properties are correlated to a number of factors, including thermodynamics and kinetics of Pd oxidation during burnout and firing; chemical and physical reaction of the Ag/Pd with the ceramic substrate, organic vehicle, and solder; Ag diffusion and migration; inorganic and organic additives; powders characteristics; and paste properties.
Synthesis and Dielectric Properties of Subsituted Lanthanum Aluminate
Authors: Vanderah Terrell A. , Lowe‐Ma Charlotte K. , Gagnon David R.
Published: March 2005

LaAlO3 was chemically modified in order to ascertain the effects of substitution of larger cations on the compound's slight rhombohedral distortion from cubic symmetry—a property that often degrades the performance of LaAlO3 substrates for epitaxial high‐temperature superconducting films. La1–xSrxAl1–xTixO3 (x = 0–05, 0.10, 0.15, 0.25),La1–xSrxAl1–xZrxO3, La1–xSrxAl1–xMgxO3–2xF2x and La1–x,SrxAl1–xScxO3–x (x = 0.05, 0.10, 0.15) were prepared in polycrystalline form and 1–2 mm single crystals of the Sr,Ti‐ and Sr,Zr‐substituted systems were grown using a PbO–PbF2–B2O3–PbO2 flux. Shifts in the peak positions of the X‐ray powder diffraction patterns confirmed subsitution of the larger cations. The diffraction patterns were also typified by the line‐broadening and the decrease in the rhombohedral splitting at all doping levels. The dielectric constant of LaAlO3 was unchanged for all of the fluoride‐containing systems and for the 5% Sr, Ti‐ and Sr,Zr‐systems.
Microstructure and Mechanical Properties of the in situβ‐Si3N4/α′‐SiAlON Composite
Authors: Sheu Tzer‐Shin
Published: March 2005

The in situβ‐Si3N4/α′‐SiAlON composite was studied along the Si3N4–Y2O3: 9 AlN composition line. This two phase composite was fully densified at 1780°C by hot pressing Densification curves and phase developments of the β‐Si3N4/α′‐SiAlON composite were found to vary with composition. Because of the cooperative formation of α′‐Si AlON and β‐Si3N4 during its phase development, this composite had equiaxed α′‐SiAlON (∼0.2 μm) and elongated β‐Si3N4 fine grains. The optimum mechanical properties of this two‐phase composite were in the sample with 30–40%α′, which had a flexural strength of 1100 MPa at 25°C 800 MPa at 1400°C in air, and a fracture toughness 6 Mpa·m1/2. α′‐SiAlON grains were equiaxed under a sintering condition at 1780°C or lower temperatures. Morphologies of the α°‐SiAlON grains were affected by the sintering conditions.
Refractive‐Index Dispersion of Tellurite Glasses in the Region from 0.40 to 1.71 μm
Authors: Takebe Hiromichi , Pujino Shigeru , Morinaga Kenji
Published: March 2005

The refractive index of binary tellurite glasses with various modifiers was measured down to the fifth decimal place in the wavelength range of 0.40–1.71 μm using the minimumedeviation method. An empirical equation based on the single‐oscillator Drude–Voigt dispersion equation. nd2=A·Nfλ02+B, is obtained, where nd is the refractive index at 0.5876 μm, N is the number of molecules in a unit volume, f is the average oscillator strength, λ0 is the average resonance wavelength, and A and B are constants. The refractive index nd of tellurite glasses is substantially determined by the resonance wavelength at the ultraviolet region, which is affected by the main constituent, TeO2.
Crack‐Shape–Wake‐Area Effects on Ceramic Fracture Toughness and Strength
Authors: Rice Roy W.
Published: March 2005

It is argued that, where crack wake‐area effects are a significant factor in the toughness of ceramics, the rate of change of wake area with crack growth normalized by the instantaneous wake area should be a factor in their mechanical behavior. Simple geometrical considerations show that differences in such wake area changes can vary by a factor of two or more for different test/crack geometries. This raises key questions regarding the (1) applicability of certain toughness tests for predicting strengths, (2) possible favoring of certain initial crack shapes or shape changes during failure, and (3) interaction with fracture mechanics, e.g., how stress intensity and such geometrical wake effects balance to control crack shape and failure.
Superplastic Forming of SiAlON Ceramics
Authors: Hwang Shyh‐Lung , Chen I‐Wei
Published: March 2005

Superplastic SiAlON's of the nominal composition Ym/3‐Si12‐(m+n)ALm+nOnN16–n are reported in this study using a transient‐phase‐forming approach. They encompass the fields of single‐phase α′‐SiAlON, single‐phase β′‐SiAlON, and their two‐phase mixtures. Excellent formability is obtained at 1550°C for the β’and α’+β’materials, and at 1600°C for the α’material. Typically in the nonequilibrium state before deformation, these fine‐grained materials undergo dramatic phase and microstructure evolutions during superplastic forming. In particular, the stress‐biased α‐Si3N4→β′‐SiAlON reaction is found to result in elongated and aligned grains with fiber‐strengthening effect and excellent formability.
Solid–Liquid Reaction in the System Si3N4–Y3Al5O12–Y2Si2O7 under 1 MPa of Nitrogen
Authors: Huang Zhen‐Kun , Tien Tseng‐Ying
Published: March 2005

The melting behaviors of selected compositions in the system–Si3N4‐Y3Al5O12–Y2Si2O7 were determined under 1 MPa of nitrogen. The behavior phase diagrams of the ternary and their binary systems are presented. The ternary eutectic composition contains 10 wt% Si3N4, 27 wt% Y3Al5O12, and 63 wt% Y2Si2O7 with a eutectic temperature of 1430°C. The binary eutectic compositions and temperatures are 25 wt% Si3N4 and 75 wt% Y3Al5O12 at 1650°C, 10 wt% Si3N4 and 90 wt% Y2Si2O7 at 1570°C, and 35 wt% Y3Al5O12 and 65 wt% Y2Si2O7 at l520°C.
Improvement of Tensile Creep Displacement Measurements
Authors: Lin Hua‐Tay , Becher Paul F. , Ferber Mattison K.
Published: March 2005

A water‐cooled copper shield is shown to minimize local temperature variations (hence, regulate the refractive index of the air) in the optical path traversed by a laser beam used to measure creep displacements in a tensile specimen. Both the scatter and the reliability of the elevated‐temperature tensile creep displacement measurements have been significantly improved from ±5 to ±0.5 μm, which is comparable to that obtained at room temperature. Results achieved with this modification were demonstrated with a hot isostatically pressed (HIPed) silicon nitride ceramic containing 4 wt% Y2O3 as a sintering additive tested at 1370°C in air. Results also indicate that the creep rates can be independent of the specimen geometry (and size) and the gripping system.
Stability Diagram for the System Yba2Cu3O7–x
Authors: Kim Jung‐Sik , Gaskell David R.
Published: March 2005

The dependence of the degree of nonstoichiometry of YBa2Cu307–x (123) on temperature and oxygen pressure has been determined by thermogravimetric analysis (TGA) in the temperature range 400° to 950°C and the oxygen pressure range 10–6 to 1 atm (1 atm = 105 Pa). The nature of the decomposition of 123 in the temperature range 750° to 950°C and the oxygen pressure range 10–6 to 10–2 atm has been determined by TGA and X‐ray diffractometry (XRD). As the oxygen pressure decreases, the decomposition of 123 follows the sequence 123→ Y2BaCuo5 (211) + BaCuO2° Cu2O→ 211 ° BaCuO2° BaCu2O2→ 211 ° YBa3Cu2Ox (132) ° BaCu2O2→ 211 ° BaCu2O2°BaO. The incongruent melting temperatures have been determined in the oxygen pressure range 10–6 to 1 atm by differential thermal analysis, and the phases formed on solidification have been identified by XRD. The stability diagram for the composition 123 has been constructed.
Low‐Temperature Fabrication of Anorthite Ceramics
Authors: Kobayashi Yuichi , Kato Etsuro
Published: March 2005

Fabrication of anorthite ceramics suitable for low temperature, sinterable, multilayered substrates is described. Anorthite ceramics were synthesized from relatively pure kaolin and calcites of varying particle sizes. Mixed powders were uniaxially pressed and fired between 900° and 1200°C. Firing at 1000°C yielded a dense anorthite ceramic when the finest calcite powder was used. The relative density and water absorption of the anorthite ceramic were 94% and almost zero, respectively. Mixtures containing coarser calcite had lower densities and higher water absorption.
Simple Technique for Observing Subsurface Damage in Machining of Ceramics
Authors: Xu Hockin H. K. , Jahanmir Said
Published: March 2005

A simple technique is proposed for directly observing subsurface damage in the machining of ceramics. The technique requires two polished specimens and an optical microscope with Nomarski illumination for examination. The subsurface damage created by the grinding of an alumina ceramic is investigated using this technique. The mode of damage is identified as intragrain twinning/slip, and intergranular and transgranular cracking. Chipping along the twinned planes and along the transgranular crack planes, and dislodgement of the intergranularly debonded grains are suggested to be the mechanisms of material removal in the machining of this alumina ceramic.
Further Investigation of the Stabilization of β‐Cristobalite
Authors: Thomas Elizabeth S. , Thompson John G. , Withers Ray L. , Sterns Meta , Xiao Yuehui , Kirkpatrick R. James
Published: March 2005

Chemical stabilization of β‐cristobalite has been achieved using two methods: (1) incorporating “stuffing” cations Na, Ca, Cu, and Sr into the cavities in the tectosilicate framework, as previously reported, and (2) without “stuffing” cations, by substituting AlPO4 into the framework. XRD, TEM, FTIR, DSC, and solid‐state variable‐temperature 29Si NMR confirm that stabilization occurs by both methods. Dynamic disorder, characteristic of the β‐cristobalite structure above the α↔β phase transition, was observed via TEM in the NaAlO2‐, CaAl2O4‐, and CuAl2O4‐stabilized cristobalites at room temperature. For AlPO4‐stabilized material intergrowths of AlPO4 regions with a tridymite‐type structure suppress the β‐ ↔α‐cristobalite phase transition.
Effect of Dopants on Zirconia Stabilization—An X‐ray Absorption Study: I, Trivalent Dopants
Authors: Li Ping , Chen I‐Wei , Penner‐Hahn James E.
Published: March 2005

Local atomic structures of Zr and dopant cations in zirconia solid solutions with Fe2O3, Ga2O3, Y2O3, and Gd2O3 have been determined. The Zr ions in both partially stabilized tetragonal and fully stabilized cubic zirconia have their own characteristic structures which are dopant‐independent. The dopant cations substitute for Zr ions despite severe local distortions necessitated by the large difference in dopant–O distance ana Zr─O distance. Dopant ionic size determines the preferred locations of oxygen vacancies. Vacancies introduced by oversized dopants (Y and Gd) are located as nearest neighbors to Zr atoms, leaving 8‐fold oxygen coordination to dopant cations. Undersized dopants (Fe and Ga) compete with Zr ions for the oxygen vacancies in zirconia, resulting in 6‐fold oxygen coordination and a large disturbance to the surrounding next nearest neighbors. Since oxygen vacancies associated with Zr can provide stability for tetragonal and cubic zirconia, these results suggest an explanation for the observation that oversized trivalent dopants are more effective than undersized trivalent dopants in stabilizing cubic and tetragonal phases.
Far‐Infrared Reflection Spectra of Dielectric Ceramics for Microwave Applications
Authors: Fukuda Koichi , Kitoh Ryozo , Awai Ikuo
Published: March 2005

Far‐infrared reflection spectra of dielectric ceramics, BaSm2Ti5O14, BaTi4O9, and some pcrovskites such as Ba(Zn1/3Nb2/3)O3, have been measured at room temperature using a Fourier transform infrared spectrometer in order to investigate the effect of the crystal structure on the dielectric properties. As for perovskites, Sr(Zn1/3Nb2/3)O3 and Sr(Mg1/3Nb2/3)O3, in which B site ions are ordered, were also measured. Reflectance data were analyzed by means of a factorized form of dielectric functions instead of the classical dispersion theory, and all of the spectra were well fitted. The values of dielectric constants and tan δ calculated from the reflectance data were in good agreement with resonant cavity measurements at 5 GHz. Furthermore, results of this study have shown that the main contribution to the microwave dielectric properties is caused by low‐frequency optically active modes located at 50 to about 300 cm−1, and for perovskite structures it is suggested that the ordering of B site ions is significant in obtaining low dielectric losses.
Electric Fatigue in Lead Zirconate Titanate Ceramics
Authors: Jiang Qiyue , Cao Wenwu , Cross L. Eric
Published: March 2005

Electric fatigue is a major obstacle for some potential applications of ferroelectric materials based on reversals of spontaneous polarization, such as memory devices and high strain actuators. Our studies of finegrained hotpressed lead zirconate titanate with lanthanum dopant (PLZT 7/68/32) show that fast fatigue is actually caused by contaminated surfaces instead of intrinsic structure deterioration or the change of domain states. All of the specimens with conventionally cleaned surfaces showed significant fatigue after 105 switching cycles, but specimens cleaned with a new cleaning procedure did not fatigue even after more than 108 switching cycles. This type of fatigue is found to be due to generated microcracking at the ceramic–electrode interface.
Calculated Structures and Energies of Grain Boundaries in α‐Al2O3
Authors: Kenway Philip R.
Published: March 2005

Static‐lattice calculations of the energies and structures of {101n} (n = 0, 1, and 4) and {0001} grain boundaries in α‐AI2O3 using three different potentials are reported. It was found that the energies of boundaries perpendicular to the (0001) direction vary between 0.3 and 0.9 J·m−2. These compare favorably to experimental values, and the results are not sensitive to the choice of potential. The energies of the other boundaries do depend on the potential, but their relaxed structures do not. Using the most reliable potential, the energies of boundaries which have been studied by high‐resolution electron microscopy range from 1.0 to 1.7 J.m−2. Simulated images of the calculated structures compare favorably with high‐resolution electron microscope micrographs of these boundaries.
Oxidation Mechanisms and Kinetics of 1D‐SiC/C/SiC Composite Materials: II, Modeling
Authors: Filipuzzi Ludovic , Naslain Roger
Published: March 2005

A model, based on a simple axisymmettical fiber/interphase/ matrix assembly, is derived to depict the oxidation behavior of ID‐SiC/C/SiC composites within the temperature range 900–1300°C and for 10 < PO2 < 100 kPa. It takes into account (i) the changes versus time of the geometry of the annular pore resulting from the consumption by oxidation of the carbon interphase, (ii) the may transfers by diffusion along the pore of the reactant and products, and (iii) the chemical reactions with oxygen of both the pore walls (yielding silica) and the pore bottom (consisting of carbon). The model gives the gaseous species concentration and silica thickness profiles along the pore, the length of carbon consumed by oxidation, and the relative weight change. The model depicts in a satisfactory manner the features of the TGA curves recorded on actual composites and it is in excellent agreement with the measurements of the carbon interphase lengths consumed by oxidation. It shows that the oxidation resistance of ID‐SiC/C/SiC composites is better at high temperatures (T 1100°C) and for thin carbon interphases (e 0.1 μm). Under such conditions, the materials exhibit a self‐healing behavior.
Experimental Measurement of Residual Stress Field around Sharp Indentation in Glass
Authors: Zeng Kaiyang , Rowcliffe David
Published: March 2005

A new technique is developed to measure the residual stress field around Vickers indentations in glass and ceramics. This technique uses a small indentation as a microprobe to measure the residual stress at a specific position near a large indentation. The approach is based on the observation that the crack lengths of the small indentation are changed under the influence of the residual stress field created by the large indentation. A simple fracture mechanics model is derived to calculate the residual stress from the measurement of the changes of the crack lengths of the small indentation. The results show that the residual stress around Vickers indentations is a nonequal biaxial field; both tensile and compressive stresses exist around a sharp indentation and decrease as the distance from the center of indentation increases. This technique can be easily extended to many other cases of residual stress in ceramics and composites.
Chemical Synthesis and Characterization of Calcium Aluminate Powders
Authors: Gülgün Mehmet A. , Popoola Oludele O. , Kriven Waltraud M.
Published: March 2005

The Pechini process was used to produce high‐purity, monocalcium aluminate (CaAl2O4) powders at temperatures as low as 900°C. Absorption spectrometry and BET measurements revealed particles with sizes ranging from submicrometer to 100 μm, with specific surface areas as high as 10 m2/g. Auger electron spectrometry (AES) was used to study the progressive elimination of surface carbon from the organic burnout as a function of temperature. The growth kinetics of calcium aluminate crystallites from a polymeric precursor were studied during calcination as a function of temperature, using transmission electron microscopy (TEM). At the early stages of crystallization, the activation energy for crystallite growth was found to be 118 kJ/mol. This is substantially less than the 356 kJ/mol previously reported. A growth kinetic exponent of n = 1.68 was determined for the amorphous‐to‐crystalline transformation in the temperature range 700° to 850°C. These values were consistent with growth by short‐range diffusion.