bluuebunny/crossref_metadata_2025 huggingface dataset:
Interface Reactions between Silicon Dioxide‐Lead Oxide Glass and Manganese Zinc Ferrite
Authors: Nitta Atsumi , Nakamura Hideyuki , Komatsu Takayuki , Matusita Kazumasa
Published: March 2005

The interface reations between SiO2–PbO melt and Mn‐Zn ferrite were studied using electron probe microanalysis (EPMA) and X‐ray diffraction (XRD). Intermediate layers were formed at the interface between the glass and the Mn‐Zn ferrite which were heated at 800° and 900°C, although those layers were not found in specimens heated at 1000°C. Using EPMA and XRD, the intermediate layers were found to be Pb2(Mn, Fe)2Si2O9 and Pb8(Mn, Fe)Si6O21. The mechanisms of interface reactions are discussed, related to glassforming regions. It was concluded that the interface reaactions between SiO2–PbO melt and Mn‐Zn ferrite are controlled by the dissolution of Zn ions and Mn ions from the Mn‐Zn ferrite.
Low‐Temperature Route to Lead Magnesium Niobate
Authors: Chaput Frédéric , Boilo Jean‐Pierre , Lejeune Martine , Papiernik Renée , Hubert‐Pfalzgraf Liliane G.
Published: March 2005

Lead magnesium sniobate, Pb(Mg1/3Nb2/3)O3 (PMN), was prepared by a sol‐gel technique using alkoxide precursors. The hydrolysis‐condensation mechanism leads to a translucent gel which is dried under hypercritical conditions to avoid collapse of the porous texture. After drying, the aerogel exhibits a B‐deficient pyrochlore structure which progressively inserts magnesium oxide when the temperature increases. Near 700°C, this pyrochlore phase completely transforms into the PMN‐perovskite phase. Above 1000°C, the loss of lead oxide leads to the destabilization of the PMN‐perovskite with formation of an A‐deficient pyrochlore phase.
Electrical Discharge Machining of Tungsten Carbide‐Cobalt Composites
Authors: Gadalla A. M. , Tsai W.
Published: March 2005

Increasing the current, the frequency, or the pulse duration up to certain values increased the speed of cutting and rate of removal. The amount of liquid smearing the cavities prcduced by dislodging the WC grain and microcracks increased with increasing cobalt content and/or WC grain size. Depletion of carbon and formation of W2C and WC1−x were detected on the surface. An analysis of debris showed that, in addition to melting the cobalt matrix, metallic vapors are formed and condense to hollow noncrystalline spheres which deformed and condense to hollow noncrystalline spheres which deform and crystallize if crushed.
Sintering of the Mechanochemically Activated Powders of Hexagonal Boron Nitride
Authors: Hagio Tsuyoshi , Kobayashi Kazuo , Yoshida Hisayoshi , Yasunaga Hiroaki , Nishikawa Hiroshi
Published: March 2005

Pressureless sintering of hexagonal boron nitride (BN) was performed using a powder activated by mechano‐chemical treatments. Physical properties of the sintered BN bodies depend on the type of starting powder and the conditions of the treatments. The BN body, which was obtained at 2000°C using an appropriate activated powder, was 99 wt% pure and was excellent in mechanical and physical properties, in spite of its low density (1.64 g/cm3).
Effect of Oxygen Loss on Densification When Hot Isostatic Pressing YBa2Cu3O7−δ
Authors: Niska John , Loberg Bengt , Easterling Kenneth
Published: March 2005

Hot isostatic pressing of the high‐Tc superconductor YBa2Cu3O7−δ can lead to loss of oxygen and transformation of the material from the high‐Tc orthorhombic phase to the nonsuperconducting tetragonal phase. It is shown that glass encapsulation helps retain the orthorhombic structure, whereas steel encapsulation resulted in formation of the tetragonal phase. Reasons for this phenomenon are discussed. The equilibrium oxygen gas pressure for the oxygen decomposition reaction in YBa2Cu3O7, however, prevents full densification of this material in glass when employing hot isostatic pressing conditions of 200 MPa and 845°C.
Thermodynamic Benefit of Abnormal Grain Growth in Pore Elimination During Sintering
Authors: Xue Liang A.
Published: March 2005

Free‐energy analyses performed on closed particle‐pore arrays show that the presence of an abnormal grain thermodynamically favors the shrinkage of large pores to which is is adjacent. This gives an explanation to the experimentally observed phenomenon of abnormal‐grain‐growth‐promoted densification in barium titanate.
Effect of Nonstoichiometry on Fracture Toughness and Hardness of Yttrium Oxide Ceramics
Authors: Fantozzi Gilbert , Orange Gilles , Liang Kaiming , Gautier Martine , Duraud Jean‐Paul , Maire Philippe , Le Gressus Claude , Gillet E.
Published: March 2005

This work deals with the changes in mechanical properties of yttrium oxide ceramics induced by nonstoichiometry. The maximum fracture toughness, Klc, is observed at the stoichiometric composition. For an oxygendeficient ceramic, a decrease of Klc is observed from 3.5 to 2.3 MPa.m1/2. On the other hand, the Vickers hardness seems to be less dependent on stoichiometry. These results are discussed in the frame of the evolution of the Y‐O bond with the stoichiometry. They set in particular the problem of the role of electrostatic energy stored in a brittle material containing charged defects in the energy balance controlling crack propagation.
Sintering and Crystallization of Glass at Constant Heating Rates
Authors: Panda Prakash C. , Raj Rishi
Published: March 2005

The densification and shear behavior of glass powder compacts were determined by measuring their axial strain and radial strain during uniaxial compression. The experiments were conducted nonisothermally at constant rates of heating. The densification and the shear strain were plotted as a function of temperature. Both showed sigmoidal behavior, reaching a plateau at high temperature. The density saturated because the powder compact had sintered to completion, but the shear strain saturated because of the onset of crystallization. The technique offers a method for studying the interaction between densification and crystallization of glass powders.
High‐Temperature Oxidation of Chemically Vapor‐Deposited Silicon Carbide in Wet Oxygen at 1823 to 1923 K
Authors: Narushima Takayuki , Goto Takashi , Iguchi Yasutaka , Hirai Toshio
Published: March 2005

The oxidation of chemically vapor‐deposited SiC in wet O2 (water vapor partial pressure = 0.01 MPa, total pressure = 0.1 MPa) was examined using a thermogravimetric technique in the temperature range of 1823 to 1923 K. The oxidation kinetics follow a linear‐parabolic relationship over the entire temperature range. The activation energies of linear and parabolic rate constants were 428 and 397 kJ · mol−1, respectively. The results suggested that the rate‐controlling step is a chemical reaction at an SiC/SiO2 interface in the linear oxidation regime, and the rate‐controlling step is an oxygen diffusion process through the oxide film (cristobalite) in the parabolic oxidation regime.
Microstructure of 96% Alumina Ceramics: III, Crystallization of High‐Calcia Boundary Glasses
Authors: Powell‐Doǧan Cynthia A. , Heuer Arthur H.
Published: March 2005

The crystallization characteristics of a group of 96% Al2O3 ceramics containing a high‐CaO boundary glass were examined using a combination of electron microscopy techniques. As many as six crystalline phases formed at the boundaries during anneals between 1000° and 1350°C. Devitrification was rapid, and little glass remained following a 1‐h anneal. Despite the extensive changes in grain‐boundary microstructure, heat treatment had little effect on the room‐temperature mechanical properties of these Al2O3 materials; however, high‐CaO bodies fractured intergranularly, whereas high‐MgO bodies fractured transgranularly.
Hot Isostatic Pressing of Alumina and Examination of the Hot Isostatic Pressing Map
Authors: Uematsu Keizo , Itakura Kazuhisa , Uchida Nozomu , Saito Katsuichi , Miyamoto Akira , Miyashita Tsuneo
Published: March 2005

The hot isostatic pressing (HIP) of four alumina powders is studied in the temperature range 1100° to 1400°C, at 5‐ to 200‐MPa applied pressure, and for times ranging from 0.5 to 4 h. Density increases with increasing HIP temperature, pressure, and time; decreasing grain size results in increased density after HIP. An empirical relation is derived for grain growth during HIP, and the HIP map proposed by Helle et al. is found applicable to the present results. Densification is governed by the grain‐boundary diffusion of aluminum ions; with the transport coefficient and the grain‐growth values found in the present study, the map can be used to express experimental results to within a factor of 4 for all densification stages except near full density.
Initial Sintering of Submicrometer Titania Anatase Powder
Authors: Hébrard Jean‐Luc , Nortier Patrice , Pijolat Michèle , Soustelle Michel
Published: March 2005

Measurements of surface area reduction of TiO2 anatase powder (of initially 100 m2· g−1) were carried out for various partial pressures of water and oxygen at 823 K. The kinetic equation obtained for the experimental rates has the formulation r=k[PH2O]1/α [PO2]1/β where α and β are equal to 2 and ‐12, respectively. A mechanistic model involving six consecutive elementary steps was developed, in which hydroxyl species play a dominant role. No geometrical assumption is required. The general expression of the deduced theoretical rates has the same form as previously given. The comparison between the experimental and the predicted rates points out that the rate‐limiting step is the surface diffusion of hydroxyl species. This model can easily be used for any other compounds, for particle growth, and for porosity elimination.
Processing and Properties of Cellular Silica Synthesized by Foaming Sol‐Gels
Authors: Fujiu Takamitsu , Messing Gary L. , Huebner Wayne
Published: March 2005

A novel process for fabricating lightweight, cellular ceramics from sols is presented. The process utilizes the rapid viscosity change during gelation to stabilize the structure of a foamed silica sol. Manipulation of gel viscosity and foaming agent concentration resulted in a minimum cell size of 90 μm at 31% density and minimum density of 17% with average cell size of 400 μm. The flexural strength compared favorably with space shuttle tiles and sintered hollow glass spheres. From −50° to 150°C, the dielectric constant ranged from 1.51 to 1.55 for a 20% dense foam and was slightly dispersive, whereas the dielectric loss was comparable with fused silica.
Grain Growth in Sintered ZnO and ZnO‐Bi2O3 Ceramics
Authors: Senda Tetsuya , Bradt Richard C.
Published: March 2005

Grain growth in a high‐purity ZnO and for the same ZnO with Bi2O3 additions from 0.5 to 4 wt% was studied for sintering from 900° to 1400°C in air. The results are discussed and compared with previous studies in terms of the phenomenological kinetic grain growth expression: Gn—Gn0=K0t exp(—Q/RT). For the pure ZnO, the grain growth exponent or n value was observed to be 3 while the apparent activation energy was 224 ± 16 kJ/mol. These parameters substantiate the Gupta and Coble conclusion of a Zn2+ lattice diffusion mechanism. Additions of Bi2O3 to promote liquidphase sintering increased the ZnO grain size and the grain growth exponent to about 5, but reduced the apparent activation energy to about 150 kJ/mol, independent of Bi2O3 content. The preexponential term K0 was also independent of Bi2O3 content. It is concluded that the grain growth of ZnO in liquid‐phase‐sintered ZnO‐Bi2O3 ceramics is controlled by the phase boundary reaction of the solid ZnO grains and the Bi2O3‐rich liquid phase.
The System Bi2O3‐SiO2
Authors: Takamori Takeshi
Published: March 2005

The Bi2O3‐rich side of the system Bi2O3‐SiO2 was studied with powder X‐ray diffraction and differential thermal analysis. In the composition 6Bi2O3. xSiO2, the metastable γ phase (bcc) was observed to exist over the range of 0 < x≤ 1. In most of the compositions studied, metastable phases of water‐quenched melts transformed into another metastable phase before reaching stable phases. A modification of the phase diagram is proposed.
Simulation of the Viscous Sintering of Two Particles
Authors: Jagota Anand , Dawson Paul R.
Published: March 2005

The viscous sintering of two initially spherical particles is modeled as creeping flow in response to surface tension. The governing equations are solved using the finite‐element method. The condensed results of this simulation, the center‐to‐center approach velocity, and the rate of change of contact area were presented earlier. Some details of the flow field during sintering and the evolution of the neck geometry in the early stages of sintering are presented here. Important numerical issues are detailed.
Infrared Spectroscopy of Lead and Alkaline‐Earth Aluminosilicate Glasses
Authors: Roy Bimalendu N.
Published: March 2005

Infrared spectroscopic studies of lead and alkaline‐earth aluminosilicate glasses in the series xMO‐xAl2O3 (1 ‐ 2x)SiO2 M = Mg, Ca, Sr, Ba, and Pb; 0.05 x 0.275] were carried out in the range 2000 to 200 cm−1. Three major absorption bands were observed in the 1100‐, 800‐, and 500‐cm−1 regions. The frequency and the intensity of the 1100‐cm−1 band varied linearly with composition. For a specific value of x, the changes in the frequency, intensity, and bandwidth of this band decreased in the order Mg > Ca > Sr > Pb > Ba and the apparent disorder in the glass structure, effected by the substitution of aluminum, increased in the direction Mg < Ca < Sr < Ba, with Pb in between Mg and Ca. The force constants and the bond orders of the Si‐O and Al‐O stretching vibrations in each of the glasses increased monotonically as Al/(Al + Si) decreased.
Ductile‐Regime Machining of Germanium and Silicon
Authors: Blake Peter N. , Scattergood Ronald O.
Published: March 2005

Precision machining of germanium and silicon was studied using single‐point diamond turning. Special attention was directed to the so‐called ductile regime wherein optical quality surface finishes can be machined directly on brittle materials. A novel interrupted‐cutting test and a new model of the machining process were used to measure a critical‐depth parameter experimentally. This parameter governs the transition from plastic flow to fracture along the tool nose. The critical‐depth parameter can be used to provide physical insight into the effect of various machining parameters such as tool rake angle or tool clearnace angle. Because of a complex interplay between tool geometry, machining parameters, and material response, a large fraction of material removal occurs by fracture even when ductile‐regime conditions are achieved.
Synthesis and Characterization of Silicon Oxycarbide Glasses
Authors: Zhang Hanxi , Pantano Carlo G.
Published: March 2005

It has been found that X‐ray amorphous silica glasses containing up to 18% carbon can be synthesized using a sol/gel process. In this study, the sols were prepared using four different organometallic precursors—methyl‐, ethyl‐, propyl‐, and phenyltrimethoxysilanes. 1H NMR,13C NMR, and TGA revealed that the methoxy groups are hydrolyzed in the solutions and, therefore, are absent in the gels. But the alkyl groups are retained in the dry gels. The 29Si NMR data verified that the Si—C bonds associated with these alkyl groups are intact in the dry gels. Most importantly, however, Si—C bonds are found in the glasses obtained after heat‐treating the gels at high temperature in an inert atmosphere; i.e., the synthesis does, in fact, create an oxycarbide network structure. TGA showed that the dense oxycarbide glasses are stable to 1000°C in argon and in air.
Hot Corrosion of Silica
Authors: Lawson Mark G. , Kim Hei R. , Pettit Fred S. , Blachere Jean R.
Published: March 2005

The high‐temperature corrosion of bulk silica glass was studied in pure oxygen and in SO3‐containing oxygen atmospheres in the presence of liquid sulfate deposits at temperatures of 700° and 1000°C. No reaction and devitrification were observed without Na2SO4 on the surface. The wetting of the silica by the sulfate, the tendency toward basic fluxing, and the crystallization of the silica incrased with the activity of Na2O. The most extensive degradation of vitreous silica occurred by crystallization, and the resulting spalling under basic conditions and thermal cycling at basic conditions were parabolic. This behavior is explained by a model in which the crystallization is controlled by sodium at the glass‐crystal interface and its diffusion into the glass. This sodium diffuses into the glass before crystallization and is swept ahead of the crystallization front.
Solid‐State Epitaxial Effects in Structurally Diphasic Xerogel of Pb(Mg1/3Nb2/3)O3
Authors: Ravindranathan P. , Komarneni Sridhar , Roy Rustum
Published: March 2005

Lead magnesium niobate (PMN), Pb(Mg1/3Nb2/3)O3, with perovskite structure has been prepared using structurally diphasic PMN gels. The diphasic gels were made using various concentrations of perovskite PMN seeds. The unseeded gel calcined at 775°C for 2 h gave ∼98% of perovskite PMN phase. The use of 1% PMN perovskite seed not only led to a pure perovskite phase but also lowered the crystallization temperature of these gels by about 75°C. These results show that isostructural seeding helps to lower the crystallization temperature of perovskite PMN phase.
Stress‐Biased Anisotropic Microcracking in Zirconia Polycrystals
Authors: Reyes‐Morel Patricio E. , Chen I‐Wei
Published: March 2005

Anisotropic elastic response of microcracked bodies has been studied using transformation‐toughened Mg‐PSZ and Ce‐TZP as model materials. These zirconias have been previously deformed in triaxial compression to effect various extents of phase transformation. Microcracks were found to align with the compression axis and their normalized density increases linearly with the extent of transformation plasticity. The measured elastic constants are anisotropic and well described by an elasticity theory. An additional anomalous elastic anisotropy was also found in Ce‐TZP due to a transformation texture of both the remaining tetragonal phase and the newly formed monoclinic phase. The terminal crack density ω=Na3, where N is the number of cracks per unit volume and a is the crack radius, reaches 0.05 in Mg‐PSZ and 0.1 in Ce‐TZP at the completion of transformation plasticity.
Crystallization of MgO‐CaO‐SiO2‐P2O5 Glass
Authors: Shyu Jiin‐Jyh , Wu Jenn‐Ming
Published: March 2005

The crystallization behavior of a glass with a composition of 40 wt% 3CaO · P2O5−60 wt% CaO · MgO · 2SiO2 was investigated. The primary crystalline phase was apatite with a dendritic form and ellipsoidal shape. β‐(3CaO · P2O5) and CaO · MgO · 2SiO2 were crystallized as samples heated to 990°C, and a three‐layer structure was obtained. The development and morphology of this construction were explained by both the surface crystallization of the apatite and CaO · MgO · 2SiO2 and the bulk crystallization of apatite and the CaO · MgO · 2SiO2‐β‐(3CaO · P2O5) composite.
On the Thermoelastic Martensitic Transformation in Tetragonal Zirconia
Authors: Heuer Arthur H. , Ruhle Manfred , Marshall David B.
Published: March 2005

Recent evidence is summarized showing that the tetragonal (t) → monoclinic (m) martensitic transformation in ZrO2 can occur thermoelastically in certain ZrO2‐containing ceramics, and that microcracking accompanying the transformation is more common than had previously been recognized. The implications of these new data for the conditions under which the stress‐induced transformation is irreversible, and for the particle size dependence of the transformation start (Ms), temperature, are discussed.
Estimate of the Activation Energies for Boundary Diffusion from Rate‐Controlled Sintering of Pure Alumina, and Alumina Doped with Zirconia or Titania
Authors: Wang Jenqdaw , Raj Rishi
Published: March 2005

Sintering experiments at constant heating rates were employed to estimate the activation energy for sintering in alumina and in alumina containing 5 vol% zirconia or 5 vol% titania. Grain growth, which can complicate the analysis of sintering kinetics data, was suppressed by using uniformly and densely packed grain compacts prepared by colloidal processing. Grain‐boundary diffusion is believed to have been the dominant sintering mechanism. The activation energies were 440 ± 40 kJ/mol for pure alumina, 585 ± 40 kJ/mol for alumina (titania), and 730 ± 60 kJ/mol for alumina (zirconia). The alumina and alumina (titania) results are in agreement with the values reported in the literature. The possibility that the higher activation energies for doped alumina reflect a stronger bonding at alumina interfaces in the presence of zirconium and titanium is discussed.
In Situ Tensile Measurements of Single Fibers by Scanning Electron Microscopy
Authors: Krönert Wolfgang , Raith Angelika
Published: March 2005

A newly developed tensile module allows tensile experiments of single fibers to be carried out under visual observation in the scanning electron microscope. This allows correlation of measured data with observed changes in the microstructure, such as surface irregularities and crack formation. With point heating, the thermal behavior of the fibers may be studied up to 2500°C. The results are presented with tensile elongation recordings and micrograph sequences of the structural changes. Carbon fibers with and without an aluminum coating were selected as testing specimens.
Elevated‐Temperature R‐Curve Behavior of a Polycrystalline Alumina
Authors: Grimes Robert E. , Kelkar Girish P. , Guazzone Laurent , White Kenneth W.
Published: March 2005

The fracture behavior of a polycrystalline alumina was examined at temperatures ranging from ambient through 1400°C, using three‐point bend bar test specimens. R‐curves were determined at all temperatures studied, and when accompanied by renotching procedures, a wake removal technique, conclusive evidence was provided to support the existence of a following wake region in this monolithic ceramic material. The crack closure stresses identified in this region are responsible for all toughening with crack extension observed in this study. Room‐temperature “KIC” fracture toughness values of 4.5 MPa · m1/2 for the chevron‐notch specimen and 3.9 MPa · m1/2 for the straight‐notch configuration were obtained. The critical stress intensity factor of the renotched chevron‐notch specimen compared very closely with that of the straight‐notch specimen. These findings further confirm the toughening role of the microstructural features found in the following wake region. This paper considers, in detail, these observations in terms of the microstructure and its role in the toughening mechanism.
Electrical Properties of TiO2‐K2Ti6O13 Porous Ceramic Humidity Sensor
Authors: Yeh Yuan‐Chang , Tseng Tseung‐Yuen , Chang De‐An
Published: March 2005

Porous ceramic humidity sensors using pure TiO2 doped with a few molar percent K2CO3 were studied. The conductance versus relative humidity (rh) sensitivity of the sensor sintered at 1200°C was as high as 4 orders of magnitude in the range of 15% to 95% rh at 200 Hz and 25°C. The sensors were reversible without repeated high‐temperature thermal desorption processes. The electrical properties of the sensors under different rh were determined by both direct current (dc) and alternating current (ac) analysis techniques. The sensors could be polarized similar to electrolytes in a charging process as a result of the electrode and water molecular polarization effects, and the effects were enhanced with increasing rh. The conduction carriers of the sensors in a moist atmosphere were ions and electrons, and the dominant conduction carrier was ions. By complex impedance plots with a “non‐Debye” capacitor concept, an equivalent circuit model was established which can simulate well all the electrical properties of the sensors in the range of 65% to 95% rh for all measured frequencies (5 Hz to 13 MHz). The relative dielectric dispersion k’(ω) increased with increasing rh and was almost proportional to ω−1.85 at low frequencies. The relative dielectric absorption k″(ω) increased with increasing rh and was almost proportional to ω−1 at low and median frequencies.
R‐Curve Behavior of Long Cracks in Alumina
Authors: Steinbrech R.W. , Reichl A. , Schaarwächter W.
Published: March 2005

Coarse‐grained alumina is among those monolithic ceramics which can exhibit an increase in crack resistance with crack extension. This R‐curve behavior is most pronounced for intergranular fracture and does not depend exclusively on material properties. Crack and specimen geometries also influence the shape of the R‐curves. The magnitude of the effect increases with increasing crack surface roughness, which is microstructure‐dependent, and with crack‐opening displacement, which is geometry‐dependent. Based on experimental observations, a “dynamic”R‐curve model is presented which relates the increasing resistance to an increasing crack tip shielding caused by crack surface bridging. Applying a J‐integral approach, R‐curves are calculated for two specimen geometries (short double cantilever beam and single‐edged notched beam) and different grain sizes. The good agreement between calculation and experiment indicates that the R‐curve behavior of long cracks in alumina can be predicted by a simple wake model.
Energetics of the Charge‐Coupled Substitution Si4+→ Na++ T3+ in the‐Glasses NaTO2–SiO2 (T = Al, Fe, Ga, B)
Authors: De Yoreo James J. , Navrotsky Alexandra , Dingwell Don B.
Published: March 2005

Heats of solution in molten 2PbO·B2O3 at 973 K are reported for glasses xNaT3+O2–(1 –x)SiO2 for T = Fe, Ga. These measurements, combined with previous data for T = Al, B, give a relative measure of the enthalpy of the charge‐coupled substitution Si4+→ Na++ T3+. The heats of solution become more endothermic with increasing x for x→ 0.5 and exhibit a maximum near x= 0.5. This indicates an exothermic enthalpy for the substitution and an overall stabilization of the glasses. The degree to which the glasses are stabilized decreases in the order Al > Ga > Fe > B. On the basis of molecular orbital calculations, X‐ray scattering, and Raman spectroscopy, it is argued that this trend is primarily due to a decrease in the range of energetically favorable T–O–T bond angles as Al, Ga, Fe, and B are substituted for Si.
Preparation of Small‐Particle‐Size, Semiconductor CdS‐Doped Silica Glasses by the Sol–Gel Process
Authors: Nogami Masayuki , Nagaska Katsumi , Kato Etsuro
Published: March 2005

The sol–gel process has been applied successfully to the preparation of small‐particle‐size CdS‐doped silica glasses with a significant quantum size effect. Gels prepared through the hydrolysis of a complex solution of Si(OC2H5)4 and Cd(CH3COO)2·2H2O were heated at 500°C, then reacted with H2S gas to form fine, hexagonal, CdS‐microcrystal‐doped glasses. The optical absorption edge is blue shifted by ∼0.4 eV compared with the bulk absorption value of CdS crystal. This result is interpreted in terms of a quantum‐confinement effect of small crystal size.
Impurity Distribution in Polycrystalline Aluminum Nitride Ceramics
Authors: Callahan Daniel L. , Thomas Gareth
Published: March 2005

Convergent‐beam electron diffraction and diffuse darkfield imaging of transmission electron microscopy were used to obtain qualitative information regarding the distribution of impurities in polycrystalline AIN. Impurities are distributed homogeneously within the grains of a given ceramic, but an amorphous grain‐boundary phase on the order of 1 to 2 nm in thickness is observed between the AIN matrix grains.
Local Density Approximation Total Energy Calculations for Silica and Titania Structure and Defects
Authors: Allan Douglas C. , Teter Michael P.
Published: March 2005

Theoretical structural predictions are presented for three polymorphs of silica (α‐quartz, α‐cristobalite, and stishovite) and the rutile structure of titania. Several defects within the silica system (the oxygen vacancy, a puckering distortion in quartz with no oxygen vacancy, and titanium in silica) are also studied. These ab initio studies are conducted using the local density approximation for electronic structure and total energies and are implemented using some very recent advances in improved pseudopotentials and energy minimization algorithms. Results include two metastable conformations of the oxygen vacancy in silica, similar Si—O and Ti—O bond energies, and equilibrium structures of several defects.
Kinetics of Tricalcium Silicate Hydration in Diluted Suspensions by Microcalorimetric Measurements
Authors: Damidot Denis , Nonat André , Barret Pierre
Published: March 2005

Investigations of tricalcium silicate (C3S) suspensions using different techniques have shown the initial hydration kinetics of C3S are strongly dependent on the water/C3S ratio. In order to provide new experimental data on the hydration, we have adapted a Tian‐Calvet heat flow isothermal microcalorimeter to study thermal flow variation released by C3S stirred suspensions in water and saturated lime water. We observed three exothemic peaks and one endothermic peak. Their relative magnitude and duration depend on the W/C ration and the lime solution concentration. The protective layer theory appears to be consistent with our results for high W/C ratio. Moreover, portlandite precipitation seems to be a consequence and not the cause of the acceleratory period.
Instability of Thallium‐Containing Superconductor Phases in Isothermal Equilibrium with Thallium Oxide
Authors: Aselage Terry L. , Voigt Jim A. , Keefer Keith D.
Published: March 2005

Knowledge of the equilibrium conditions under which the superconducting phases in the Tl‐Ca‐Ba‐Cu‐O system are stable would enable the controlled preparation of these materials. Isothermal equilibrium between samples in this quaternary system and Tl2O vapor from a condensed thallium oxide source has been studied. None of the superconductor phases coexisted in equilibrium with thallium oxide under the conditions employed. Instead, two previously unknown ternary thallium‐calcium‐barium oxides and one previously unknown thallium‐calcium oxide were observed. The equilibrium phase assemblage at temperatures between 825° and 925°C consisted of the most thallium‐rich ternary oxide plus CuO, although small amounts of the other thallium‐rich phases may be required to balance stoichiometry. The vapor pressure of Tl2O established by pure, condensed thallium oxide clearly exceeds the stability limit for the superconductor phases. If the thallium‐containing superconductors are stable phases at high temperature, they will exist over some range of lower Tl2O partial pressure.
Elastic Properties of Porous Silica Derived from Colloidal Gels
Authors: Ashkin Daniel , Haber Richard A. , Wachtman John B.
Published: March 2005

The elastic properties were determined for gel‐derived vitreous silica sintered from a relative density of 0.15 to full density. The gels were made from colloidal silica, potassium soluble silicate, and formamide. The soluble silicate was found to reinforce the gel network during gelation and its concentration relative to the colloidal silica affected Young's modulus for samples of relative density, 0.15 to 0.6 Young's modulus varied from 300 to 700 MPa at a relative density of 0.15 as a function of the soluble silicate concentration. Young's modulus at full density was measured to be 72.6 GPa. Poisson's ratio was found to be a function of relative density.
High‐Temperature Defect Structure of Lanthanum Cuprate
Authors: Su M.‐Y. , Cooper E. A. , Elsbernd C. E. , Mason T. O.
Published: March 2005

High‐temperature (650° to 8507deg;C) electrical conductivity and Seebeck coefficient measurements as functions of oxygen partial pressure and temperature in polycrystalline lanthanum cuprate support a defect model consisting of oxygen interstitials charge compensated by electron holes. The La:Cu ratio was therefore estimated to be 2.000 ± 0.001. By comparison with existing oxygen nonstoichiometry data, the high‐temperature electron hole mobility and density‐of‐states were estimated.
Reaction‐Controlled Binder Burnout of Ceramic Multilayer Capacitors
Authors: Verweij H. , Bruggink W. H. M.
Published: March 2005

Reaction‐controlled binder burnout of ceramic multilayer capacitors (CMCs) is conducted in a series of small‐scale experiments. the burnout process is followed by monitoring the weight of the CMCs. The observed maximum weight loss rate, obtained with a conventional linear heating process, is used to design a weight‐time program for a reaction‐controlled process. In this process the actual CMC weight is controlled to closely follow the weight program by means of continuous control with the batch temperature. The advantages of this procedure are discussed. The results of the present study, although being restricted to oxidative burnout of a special product, are thought to be of some use for other ceramic burnout situations. The relevant parts of controller design are discussed together with some comments on scale‐up.
Morphology of Zinc Sulfide Particles Produced from Various Zinc Salts by Homogeneous Precipitation
Authors: Celikkaya Ahmet , Akinc Mufit
Published: March 2005

Colloidal sols of ZnS were prepared by thermal decomposition of thioacetamide in acidic zinc solutions. Precipitation was carried out in the presence of nitrate, acetate, chloride, and sulfate ions. Particle morphology was influenced by the chemical nature of the anions present in the solution as well as the rate of sulfide ion generation. Spherical, monodisperse particles having a specific type of particle size distribution, i.e., monosized, bimodal, or continuous distribution, with mean sizes in the range of 0.15 to 3 μm, were formed depending on the anion type and sulfide ion generation rate. Individual particles always consisted of clusters of sphalerite crystallites except when sulfide ions were generated at low rates and sulfate ions were present. In such cases a mixture of α‐ and β‐ZnS was formed.
Properties and Structure of Lead Halosilicate Glasses
Authors: Coon Jeffrey , Shelby James E.
Published: March 2005

The glass transformation temperature, thermal expansion coefficient, dc electrical conductivity, and IR transmission have been measured for four series of lead halosilicate glasses of the general composition (65–x)PbO·xPbX2·35 SiO2 (X=F, Cl, Br, I). Although results of these and other measurements suggest that the halide ions play similar structural roles in the glass, there appear to be significant differences in physical property behavior between glasses containing F− anions and those containing the other three halide anions. These results are explained by a proposed model incorporating both bridging and nonbridging halide species.
Preparation and Photoproperties of a Transparent Alumina Film Doped with Energy‐Transfer‐Type Laser Dye Pair
Authors: Sasaki Hideaki , Kobayashi Yoshio , Muto Shinichi , Kurokawa Youichi
Published: March 2005

Doping of an energy‐transfer‐type laser dye pair into an alumina film was tried in order to increase the efficiency of its photoproperties. A transparent alumina film was prepared from an aqeous sol solution by the sol—gel process. Changes in the fluorescence of the pyranine were monitored during the process from aqueous sol solution to the dried gel. The undesirable dye aggregation usually observed in aqueous solution was largely reduced in the film. The laser emission of rhodamine B by N2 laser pumping can be increased by the addition of rhodamine 6G, which enhances pumping efficiency. It indicates that this doped film operates as a compact dye laser film.
Reduction in Aluminum Alloy Attack on Aluminosilicate Refractories by Addition of Rare‐Earth Oxides
Authors: O'Brien Michael H. , Akinc Mufit
Published: March 2005

Several aluminosilicate compositions were tested for molten 7075 aluminum alloy attack with and without the addition of 10% Na2CO3. The extent of corrosion was proportional to the silica content of the refractory and especially of the matrix phase. The addition of rare earths up to 15% by weight to the aluminosilicates virtually eiiminated corrosion. Bastnasite, a rare‐earth concentrate, was found to be a more effective additive at low concentrations than either CeO2 or La2O3 alone in rendering the aluminosilicates corrosion resistant.
Bonding Mechanisms in Silicon Nitride Brazing
Authors: Loehman Ronald E. , Tomsia Antoni P. , Pask Joseph A. , Johnson Sylvia M.
Published: March 2005

We investigated the wetting behavior and reactions of different metals on Si3N4 using sessile drop measurements, analysis of reaction layers, and measurements of strengths of joined bars. Active metals, such as Al and Ti, and alloys that contain them react with Si3N4 and cause wetting and spreading at the interface. Al‐Si3N4 reaction at 900°C produced a thin layer of Al2O3 at the interface. Reaction between Si3N4 and Ag‐Cu‐To braze alloys at 900°C resulted in a complex microstructure in the reaction zone that contained TiN and titanium silicides. Breaking strengths of Si3N4 bars joined with the Ag‐Cu‐Ti braze alloys were higher than those for Si3N4 joined with Al, primarily because of the better wetting by the Ag‐Cu‐Ti alloys. Nonreactive metals and alloys such as Sn, In, Ag‐Cu, and Ag‐Cu‐Sn neither wet, spread, nor adhere to Si3N4 substrates.
Raman Spectra of Molybednum Phosphate Glasses and Some Crystalline Analogues
Authors: Morgan Steven H. , Magruder Robert H.
Published: March 2005

The Raman spectra of a series of glasses in the system MoO3‐P2O5 and the polyerystalline compounds molybdenum metaphosphate (MoO2(P03)2) and molybdenum pyrophosphate ((MoO2)2P2O2) are reported. The spectra indicate that traces of P=O and phosphate chains are present only in glasses having less than 50 mol% MoO3. Comparison of the glass spectra with spectra of crystalline molybdenum phosphates indicates the presence of metaphosphate and orthophosphate structural groups of MoO3 concentrations of about 50 mol% or less. As the MoO3 concentration is increased, the bands characteristic of pyrophosphate groups appear in the spectra and become the dominant feature at 76 mol% MoO3 concentration. Metaphosphate groups are present in the glass even at the highest MoO3 concentrations measured.
Electrical Properties of Chemically Bonded Ceramic Insulators
Authors: Young J. Francis , Dimitry Said
Published: March 2005

The electrical properties of commercially produced, chemically bonded ceramic insulators are compared with conventional porcelain and phenolic resin insulators. The influences of relative humidity and temperature are presented and correlated with adsorption of water in a connected pore system.
Advanced Structural Ceramics: A Round Robin
Authors: Quinn George
Published: March 2005

The strength of 1500 sintered alumina and reaction‐bonded silicon nitride flexure specimens was measured by seven laboratories in four countries. Consistent results were obtained only with a well‐defined standard test method. Older procedures were less consistent or gave erroneous results. A simple statistical procedure allowed a quick estimate of consistency, and outlier samples could be appraised for the likelihood of their occurrence.
Nonstoichiometry in Pure and Zr‐Doped Yttria Ceramics: An EXAFS and XPS Study
Authors: Duraud Jean‐Paul , Jollet Francois , Thromat Nathalie , Gautier Martine , Maire Philippe , Le Gressus Claude , Dartyge Elisabeth
Published: March 2005

Nonstoichiometry is exhibited by many ceramics at very high temperatures. The high‐temperature treatment of yttria, in particular, can induce a large concentration of point defects that changes the electrical and mechanical behavior of the solid. In the present study, the electronic and geometric structures of nonstoichiometric pure and Zr‐doped yttria are examined by X‐ray photoelectron spectroscopy and X‐ray absorption. The results show that the doping atom influences the level of stoichiometry, as well as the induced disorder and the change in the partial ionic character of the Y‐O bond.
Creep Deformation and the Grain‐Boundary Resistivity of Tetragonal Zirconia Polycrystalline Materials
Authors: Badwal Sukhvinder P. S. , Ciacchi Fabio T. , Swain Michael V. , Zelizko Viktor
Published: March 2005

The grain‐boundary resistivity of tetragonal zirconia polycrystals, which had undergone creep with different applied compressive loads and at different temperatures, has been measured with impedance spectroscopy. A stress exponent of unity was determined from strain rate versus stress data. The grain‐boundary resistivity decreased significantly with increasing stress at a constant creep temperature indicating squeezing out of the glassy phase from interfaces between grains. This, however, had no effect on the activation energy for the grain‐boundary resistivity.
Foaming in Glass Melts Produced by Sodium Sulfate Decomposition under Isothermal Conditions
Authors: Kim Dong‐Sang , Hrma Pavel
Published: March 2005

The factors controlling the behavior of foam produced in molten glass by sulfate decomposition are sulfate oversaturation (determined by the initial sulfate concentration, fraction of sulfate dissolved, and melting temperature), bubble nucleation (occurring predominantly on the residual silica grains), and film stability. The connection between the foam generation and variation in melting temperature and silica grain size has been experimentally investigated by observing the melting process in a transparent silica crucible. A generation/release model for the time variation of gas‐phase volume retained in molten glass has been developed. The analysis of experimental data using this approach suggests that two forms of sulfate produce foam during melting: (1) sulfate dissolved in melt and (2) sulfate from sulfate‐rich melt surrounding sand grains.
X‐ray Diffraction Study of the Structure of Silicon Nitride Fiber Made from Perhydropolysilazane
Authors: Yokoyama Yasuharu , Nanba Tokuro , Yasui Itaru , Kaya Hiroshi , Maeshima Tsugio , Isoda Takeshi
Published: March 2005

Continuous stoichiometric silicon nitride fiber was produced by the pyrolysis of perhydropolysilazane. This high‐purity silicon nitride fiber is colorless and has high strength, modulus of elasticity, and thermal stability which are properties suitable for reinforcing plastics, metals, glasses, and even ceramics. The structures of three kinds of amorphous silicon nitride fibers (with stoichiometric, Si‐excess and O‐excess composition) were investigated by X‐ray diffraction followed by calculating the radial distribution functions. Radial distribution functions were calculated from several possible crystal structures and compared with observed radial distribution functions.
Subeutectoid Degradation of Yttria‐Stabilized Tetragonal Zirconia Polycrystal and Ceria‐Doped Yttria‐Stabilized Tetragonal Zirconia Polycrystal Ceramics
Authors: Hernandez María T. , Jurado José R. , Duran Pedro , Fierro José L. G.
Published: March 2005

Yttria‐doped tetragonal zirconia containing 2 and 3 mol% Y2O3 (Y‐TZP), and CeO2‐doped Y‐TZP containing 0 to 12 mol% CeO2 were sintered at 1350°C in a tetragonal single‐phase field for 2 h in air, and the degradation behavior at low temperature in air and in hot water was observed. X‐ray photoelectron spectroscopy studies on the surface of hydrothermally treated samples show evidence for the formation of a YO(OH) species, along with the simultaneous formation of purely tetragonal zirconia nuclei that retain their coherence in the Y‐TZP matrix. Above a critical size, the tetragonal nuclei spontaneously transform to a monoclinic structure, giving rise to macro‐ and microcracking. The strong tetragonal grains degrade to produce a spalling phenomenon that facilitates further degradation. Y‐TZP ceramics alloyed with adequate amounts of CeO2 show no tetragonal‐to‐monoclinic transformation after hydrothermal treatment.
Cyclic Fatigue Life and Crack‐Growth Behavior of Microstructurally Small Cracks in Magnesia‐Partially‐Stabilized Zirconia Ceramics
Authors: Steffen Angela A. , Dauskardt Reinhold H. , Ritchie Robert O.
Published: March 2005

Cyclic fatigue stress/life (S/N) and crack‐growth properties are investigated in magnesia‐partially‐stabilized zirconia (Mg‐PSZ), with particular reference to the role of crack size. The material studied is subeutectoid aged to vary the steady‐state fracture toughness, Kc, from ∼3 to 16 MPa · m1/2·S/N data from unnotched specimens show markedly lower lives under tension—compression compared with tension—tension loading; “fatigue limits”(at 108 cycles) for the former case approach 50% of the tensile strength. Under tension—tension loading, cyclic crack‐growth rates of “long”(> 3 mm) cracks are found to be power‐law dependent on the stress‐intensity range, ΔK, with a fatigue threshold, ΔKTH, of order 50% of Kc. Conversely, naturally occurring “small”(1 to 100 μm) surface cracks are observed to grow at ΔK levels 2 to 3 times smaller than ΔKTH, similar to behavior widely reported for metallic materials. The observed small‐crack behavior is rationalized in terms of the restricted role of crack‐tip shielding (in PSZ from transformation toughening) with cracks of limited wake, analogous to the reduced role of crack closure with small fatigue cracks in metals. The implications of such data for structural design with ceramics are briefly discussed.
Cation Effects on 31P MAS NMR Chemical Shifts of Metaphosphate Glasses
Authors: Brow Richard K. , Phifer Carol C. , Turner Gary L. , Kirkpatrick R. James
Published: March 2005

We have examined a series of metaphosphate glasses with 31P magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy. Increasing the ionic potential (Z/a) of the modifying cation from sodium to magnesium causes a systematic change to more shielded isotropic chemical shifts with a concomitant increase in the peak FWHM. These spectral trends are consistent with counterion‐induced modifications to the ionic character of the P–O bond. Such modifications do not produce significant changes in either the chemical shift anisotropy or the asymmetry parameter.
Effect of Firing Atmosphere on Sintered and Mechanical Properties of Vanadium‐Doped Alumina
Authors: Wakamatsu Mitsuru , Ishida Shingo , Takeuchi Nobuyuki , Hattori Tetsuyuki
Published: March 2005

Vanadium‐doped alumina was sintered at 1650°C in both an oxidizing (O) and a reducing (R) atmosphere and the sintered bodies examined. In the O‐sintered body, vanadium was present preferentially between the alumina grains, forming a phase (AlVO4). In the R‐sintered body, on the other hand, most of the vanadium was dissolved in alumina as V3+, and a small proportion of the vanadium was present as V4+ in the grain‐boundary region. During O sintering, V2O5 doping depressed both densification and grain growth, whereas R sintering had no effect on densification but did depress grain growth. The O‐sintered, V‐doped body exhibited low flexural strength and hardness, whereas the R‐sintered body showed comparatively high hardness.
Modified Sol‐Gel Process for the Production of Lead Titanate Films
Authors: Milne Steven J. , Pyke Stephen H.
Published: March 2005

A modified sol‐gel process has been developed for the production of thin films of PbTiO3. The new route uses the mixed ligand complex titanium diisopropoxide bis(acetylacetonate), Ti(OC3H7)2(CH3COCHCOCH3)2, in place of titanium tetraisopropoxide, Ti(OC3H7)4. For base‐catalyzed conditions, the maximum thickness of crack‐free PbTiO3 films after one high‐temperature firing cycle is 1 μm. This value represents a twofold increase in thickness over that obtained using existing sol‐gel routes based on Ti(OC3H7)4.
Preparation of Magnesium Aluminate Spinel Containing Controlled Amounts of 17O Isotope
Authors: Kim Hyoun‐Ee , Zinkle Steven J. , Allen William R.
Published: March 2005

Magnesium aluminate spinel (MgAl2O4) with an 17O enrichment (17O/OTot) of about 23 at.% was prepared by reacting fine mixtures of aluminum hydroxide (enriched with 17O) and magnesium oxide of normal isotopic content. The material was prepared for experiments in which the radiation damage produced in a fusion reactor is simulated by fission reactor exposures. The powder mixtures were obtained by hydrolyzing, with water containing the 17O iostope, a mixture of aluminum isopropoxide and magnesium oxide powder. The mixture was converted into pure spinel by a series of heat treatments and grindings. Essentially fully dense bodies, which contained about 45% of the 17O isotope initially present in the water, were successfully fabricated provided that all thermal treatments were conducted in argon or vacuum atmospheres.