bluuebunny/crossref_metadata_2025 huggingface dataset:
Photolithographic Patterning of Particulate Films
Authors: Garino Terry J. , Bowen H. Kent
Published: March 2005

A method has been developed to produce an arbitrary pattern with a minimum feature size of 5 μm in a thin particle film on a snbstrate. In this method, a layer of photoresist is spun onto a continuous, uniform ceramic film which is then exposed to ultraviolet light under a mask with the desired pattern. After development of the photoresist the regions of the film no longer covered with photoresist are removed by immersion in an ultrasonic bath. The vacant regions in this first layer can then be filled with a second material, and multiple layers can be built up by slight modifications to this procedure.
Effect of Heating Rate on the Microstructural Evolution During Sintering of BaTiO3 Ceramics
Authors: Yoo Young‐Sung , Kim Jeong‐Joo , Kim Doh‐Yeon
Published: March 2005

When compacts of BaTiO3 powder containing small amounts of uncombined TiO2 were sintered, marked differences in microstructural evolution were observed under varying heating rates. In fast heating, the liquid formed during heating agglomerated at the center of the specimen and resulted in an inhomogeneous microstructure. A slower heating rate resulted in a homogeneous microstructure.
Effect of Agglomerate Strength on Sintered Density for Yttria Powders Containing Agglomerates of Monosize Spheres
Authors: Ciftcioglu Mushin , Akinc Mufit , Burkhart Lawrence
Published: March 2005

The effect of agglomerate strength on sintered density, was determined for several yttria powders made by intentionally agglomerating 0.1‐μm, monodisperse yttrium hydroxycarbonate precursor spheres and calcining separate portions of the precursor at different temperatures to vary the strength of the intraagglomerate bonds. In this way, the effects of differences in particle morphology and other characteristics among the powders were minimized and the effect of agglomerate strength could be seen more clearly. The sintered density of the yttria powders decreased with increasing agglomerate strength, and even a small fraction of unbroken fragments of agglomerates in the pressed powder caused a substantial decrease in the sintered density.
Statistical Study of Thermal Fracture of Ceramic Materials in the Water Quench Test
Authors: ROGERS WAYNE P. , EMERY ASHLEY F. , BRADT RICHARD C. , KOBAYASHI ALBERT S.
Published: March 2005

The Weibull statistical theory of fracture was applied to thermal shock of ceramics in the water quench test. Transient thermal stresses and probability of failure were calculated for a cylindrical specimen cooled by convection. The convective heat transfer coefficient was calibrated using the time to failure which was measured with an acoustic emission technique. Theoretical failure probability distributions as a function of time and quench temperature compare favorably with experimental results for three high‐alumina ceramics and a glass.
Modulated Structures in SiC‐AIN Ceramics
Authors: Kuo Shih‐Yee , Virkar Anil V. , Rafaniello William
Published: March 2005

Single‐phase solid solutions of2H crystal type in the SiC‐AIN system containing 50 and 75 mol% AIN were fabricated by hot‐pressing mixtures of SiC and AIN powders. Dense samples were subjected to thermal treatments over a range of temperatures between 1600° and 1900°C for a period of time up to 320 h. Transmission electron microscopy revealed the existence of modulated structures indicative of spinodal decomposition.
Oxidation States of Chromium Dissolved in Glass Determined by X‐ray Photoelectron Spectroscopy
Authors: Brow R.K.
Published: March 2005

The oxidation states of chromium dissolved in binary sodium silicate glasses were analyzed by X‐ray photoelectron spectroscopy (XPS). The measured “equilibrium” Cr6+ fractions in glasses with varying Na2O contents are shown to be in good agreement with results obtained by other techniques reported in the literature. XPS was then used to analyze the interface of a sodium silicate glass/chromium alloy (Inconel 718) seal. It is shown that Cr2+ and Cr3+ were the major chromium species dissolved in the glass interfacial region.
Combined Homogeneous and Heterogeneous Crystal Nucleation in Glasses
Authors: WEINBERG MICHAEL C.
Published: March 2005

The temperature dependence of combined homogeneous and heterogeneous crystal nucleation is examined within the framework of the classical theory. It is demonstrated that nucleation can have a local maximum rate at one or two temperatures. The physical parameters which cause large changes in the structure of the nucleation curve are elucidated. Also, the influence of saturation effects on the structure of nucleation curves is illustrated. The utilization of these results for the interpretation of experiments and for the production of controlled crystal nucleation in glass is considered.
A Modified Barium Titanate for Capacitors
Authors: Syamaprasad U. , Galgali R. K. , Mohanty B. C.
Published: March 2005

The modified barium titanate ceramic Ba0.80Pb0.20 (Ti0.88Zr0.12) O3 doped with 0.8 mol% CaO and 1 mol%ZrO2 was prepared. Investigation of the electrical and dielectric properties shows that the material has a room‐temperature dielectric constant of 3550 with a variation of 5.7% in the temperature range 10° to 60°C, a loss factor of 0.005, a dc resistivity 1.3 × 1012Ω‐cm, and a linear variation of resistivity in the log (resistivity) vs temperature plot. This material is a good choice for the fabrication of ceramic capacitors.
Kinetics of the Growth of Spinel on Alumina Using Rutherford Backscattering Spectroscopy
Authors: Simpson Y. Kouh , Colgan E. G. , Carter C. B.
Published: March 2005

The kinetics of the initial stage of the formation of a nickel aluminate spinel on the surface of alumina substrates has been studied. The NiO layer was formed by evaporating a thin film Ni onto the surface of single‐crystal alumina substrates and oxidizing the specimens in air at 700°C. This method gave a thin layer of NiO film that was uniform in thickness on top of the alumina substrates. The alumina surfaces studied include (0001), [1120], [1102], and [1100]. After the initial oxidation, the samples were annealed in air at 1020°C. The interaction of the thin‐film and the single‐crystal substrates was examined using Rutherford back‐scattering spectroscopy. The crystallography of the alumina substrates was found to influence greatly the kinetics of the spinel formation. For example, the rate of the spinel formation reaction is fastest for the lsqb;1102rsqb; and lsqb;1100rsqb; orientations and slowest for the (0001) orientation. The roughness of the surface of the alumina substrate has also been shown to influence directly the rate of the spinel formation. The presence of surface scratches accelerated the spinel formation.
Study of the Al‐Al2O3 Bond Interface
Authors: Otsuka Kanji , Ishida Hisashi , Tsuboi Toshihiko
Published: March 2005

The adhesion of an aluminum evaporation layer onto an alumina substrate was strong despite attack from the liquid gold‐silicon eutectic during an integrated circuit chip attachment process. Evidence of the resultant layer, which contained an oxygen concentration gradient from the interface into the Al, is presented.
Subsolidus Compatibilities in the Y2O3‐BaO‐CuO System via Diamagnetic Susceptibility
Authors: Hwu S.‐J. , Song S.N. , Ketterson J.B. , Mason T. O. , Poeppelmeier K. R.
Published: March 2005

Subsolidus compatibilities in the YO1.5‐BaO‐CuO system involving the superconducting 1:2:3 compound have been determined via optical microscopy, X‐ray diffraction, and diamagnetic susceptibility measurements. The susceptibility is particularly sensitive to the presence or absence of the superconducting phase.
Low‐Temperature Aging of t‐ZrO2 Polycrystals with 3 mol% Y2O3
Authors: LU HONG‐YANG , CHEN SAN‐YUAN
Published: March 2005

A kinetic study of the aging behavior of tetragonal zirconia polycrystals (TZPs) from 100° to 500°C suggests that there exists a cricital grain size of 0.52 μm below which the tetragonal symmetry can be retained. Property degradation of TZPs at low temperatures is connected with transformation‐induced microcracking. It is reported here that the temperature range of 100° to 400°C in which degradation occurs could be explained by an infinite incubation time for the lower limit and by the martensite starting temperature for the upper limit.
Finite‐Element Analysis of Network Dilatation in Ion‐Exchanged Glass Rods After Slicing
Authors: JAIN VIJAY , VARSHNEYA ARUN K.
Published: March 2005

Finite‐element analysis performed for the sliced glass rods exchanged by larger ions for various diffusion distances showed bulging of the cylindrical surface and concaving of the flat faces. Though these deformations result in the appearance of an apparent compression maximum at around 6 μm below the surface, they do not fully explain the presence of a compression maximum at 30‐ to 40‐μm depths observed by many workers using photoelastic techniques. Introduction of plasticity in the exchanged layers renders the computed stress profile to resemble the experimental profiles, but is followed with a decrease in the computed depth of the compression maximum. Lowering of the glass transition temperature of the exchanged layers, which results in increased stress relaxation and the superimposition of varying thermal contraction of the layers, could account for the disagreements.
Production of Controlled‐Morphology Pore Arrays: Implications and Opportunities
Authors: Rödel J. , Glaeser A. M.
Published: March 2005

A technique, combining photolithographic methods, ion beam etching, and hot‐pressing, has been developed, which permits the generation of a wide range of controlled pore structures. Pores in almost any number, and of almost any size and spacing, can be produced at grain boundaries with controlled misohentation. This new method has permitted the development of novel experiments, which are being used to study pore‐drag effects during grain growth, pore morphology evolution during crack healing, faceting behavior, interfacial energies, and Ostwald ripening of pores.
Topotaxy between BaTiO3 and Ba6Ti17O40
Authors: Kraševec Viktor , Drofenik Miha , Kolar Drogo
Published: March 2005

The orientational relationship between intergrown lamellae of tetragonal (t) BaTiO3 and monoclinic (m) Ba6Ti17O40 was found to be (111)t||(001)m, (001)t||(101)m, and [110]t||[010]m. On the basis of this relationship a model of a topotactic boundary between these two phases was constructed.
Chemical Durability of Fluoride Glasses: III, The Effect of Solution pH
Authors: SIMMONS CATHERINE J.
Published: March 2005

The aqueous corrosion behavior of glasses from two heavy‐metal fluoride families (ZrF4‐based and BaF2‐ThF4‐based) was studied as a function of controlled solution pH and of glass composition. Leach test results demonstrate a profound pH dependence of corrosion over the range pH 2 to 13. Whereas the glasses readily undergo congruent matrix dissolution in acidic media, they exhibit a marked increase in chemical durability in neutral and basic solutions, with the optimum aqueous environment occurring near pH 7. Results of this study are discussed and compared with results reported earlier for leach tests of these two compositional families in unbuffered de‐ionized water. In addition, several testing methods, both static and dynamic, are described and point to the importance of appropriate test selection in predicting the corrosion resistance of these glasses over prolonged periods.
Electrical Conductivity of Iron‐Doped NiO Single Crystal at Equilibrium and During Internal Oxidation
Authors: RICOULT DANIEL L. , SCHMALZRIED HERMANN
Published: March 2005

The dc electrical conductivity of (Ni1‐xFex)O single crystals (0.01 < x < 0.09) has been measured at controlled oxygen partial pressure, at temperatures ranging from 1170 to 1490 K. The behavior of single‐phase (Ni,Fe)O is characterized as a function of temperature, oxygen partial pressure, and iron content, and interpreted in terms of diffusive transport of the electronic charge carriers. From in situ electrical conductivity measurements performed during the internal oxidation of (Ni,Fe)O to a two‐phase mixture of “NiO”+ NiFe2O4, kinetics data for the internal oxidation are inferred.
Anisotropic Calcium Segregation to the Surface of Al2O3
Authors: BAIK SUNGGI , WHITE CALVIN L.
Published: March 2005

The surface enrichment of Ca on various crystalloraphic planes of CaO‐doped sapphire has been measured as a function of annealing temperature using Auger electron spectroscopy (AES). Strong Ca enrichment was found on the (1010) prism plane at ≥1300°C, whereas no evidence or Ca segregation could be observed on the (0001) basal plane up to 1500°C. The surface enrichment factor estimated at 1300°C was at least 3 × 103 for the prism plane, while that for the basal plane was below 50, which corresponds to the detectability limit of AES. The Ca segregation to the prism plane was uniform and limited to the surface monolayer; an apparent heat of segregation determined in the range of 1300° to 1500°C was–169 kJ/mol. Low‐energy electron diffraction studies of annealed surfaces revealed that Ca segregation was concurrent with a two‐dimensional surface phase transition. The anisotropic segregation behavior of Ca may explain why CaO is not an effective additive for alumina sintering.
Phase Compatibilities in the System Y2O3‐BaO‐CuO at 950°C
Authors: Frase Katharine‐G. , Liniger E. G. , Clarke David R.
Published: March 2005

We report the compatibility relationships between compounds, including the newly discovered superconducting Y1Ba2Cu3Ox phase, in the Y2O3‐BaO‐CuO system at 950°C. In addition to the previously reported ternary compounds, there is a new compound with a composition YlBa3Cu2Ox. The new compound is a perovskite 'space group P4mm) with lattice parameters a =4.078 Å (0.4078 nm) and c =4.01 Å (0.401 nm). There are also at least two structurally distinguishable binary phases between barium oxide and the known BaCuO2, but they appear to be hygroscopic and are beyond our current capabilities of analysis.
Dielectric Loss to Detect Liquid Phase in Ceramics at High Temperatures
Authors: Ho William W. , Morgan Peter E. D.
Published: March 2005

Rapidly increasing dielectric loss values, coinci nt with the formation, with increasing temperature, of small amounts of liquid phase, have been seen in an alumina doped with titania and soda (Al2O3‐l molc TiO2‐0.5 mol% NaO12). The method appears to have the sensitivity to detect liquids in ceramics down to 0.1% in favorable cases.
Structural Transformation in Cubic Zirconia
Authors: Usha Devi Subba Rao , Ming Li Chung , Manghnani Murli H.
Published: March 2005

The structure of CaO‐stabilized cubic zirconia has been investigated by X‐ray diffraction at high temperatures and pressures up to 1000°C and ∼35 GPa, using a diamond‐anvil cell interfaced with aYAG laser heating system. At ∼1000°C and 15 GPa, the cubic phase transforms directly into an orthorhombic phase with the PbCl2 structure. This high‐pressure phase is quenchable. The zero‐pressure lattice parameters are a=0.3327±0.0004 nm, b=0.5566±0.0003 nm, and c =0.6487±0.0005 nm, the volume change being 10.5%.
Microstructure and Growth Model for Rice‐Hull‐Derived SiC Whiskers
Authors: NUTT STEVEN R.
Published: March 2005

The microstructure of silicon carbide whiskers grown from rice hulls has been studied using methods of high‐resolution analytical electron microscopy. Small, partially crystalline inclusions (∼10 nm) containing calcium, manganese, and oxygen are concentrated in whisker core regions, while peripheral regions are generally inclusion free. The distinct microphase distribution is evidence of a two‐stage growth process in which the core region grows first, followed by normal growth toward whisker sides. Partial dislocations extend radially from the core region to the surface and tend to be paired in V‐shaped configurations. Whisker surfaces exhibit microroughness due to a tendency to develop small facets on close‐packed planes. The microstructural data obtained from TEM observations are used as a basis for discussion of the mechanisms involved in whisker growth, and a model of the growth process is proposed. The model includes a two‐dimensional growth mechanism involving vapor, liquid, and solid phases, although it is significantly different from the classical vapor‐liquid‐solid (VLS) process of whisker growth.
Anisotropy in an Oriented Ba2YCu3O7 Superconductor
Authors: Lynds L. , Galasso Francis , Otter F. , Weinberger B.R. , Budnick J.I. , Yang D.P. , Filipkowski M.
Published: March 2005

A highly oriented Ba2YCu3O7 ceramic disk was prepared with the c axis perpendicular to the flat faces. The use of high pressures during cold‐pressing tends to enhance the orientation of the fired sample. A nitric acid procedure for forming the material produces a powder which orients most readily. Magnetic measurements show that the critical current is larger in the layers perpendicular to the pressing direction.
Measurement of Crack Tip Displacement Fields in Mixed Mode I–Mode III Fracture
Authors: Tossel David A. , Ashbee Kenneth H. G.
Published: March 2005

A new method has been devised to propagate stable subcritical mixed mode I–mode III cracks in soda–lime–silicate and borosilicate glasses. The mode I content was measured using an original optical tunneling technique and mode III content via multiple‐beam interferometry. Measurement of the mode III displacement field allows values of mode III fracture toughness, KIII, to be derived. KIII vs crack velocity (v) diagrams have been constructed for both glasses, and, in the case of the soda–lime–silicate glass, v vs KIII relationships have been determined for a variety of humidities. Comparison has been made with published KI vs v data for this glass.
Noble Metals as a Source of Continuous Scattering in Fluoride Glasses
Authors: Lu Grant , Aggarwal Ishwar , Bradley John P.
Published: March 2005

Submicrometer scattering centers in fluorozirconate glasses were analyzed in an analytical electron microscope. Spherical platinum particles were found most frequently; other morphologies and noble metals such as gold, rhodium, and iridium were also observed.
Characteristics of ZrO2‐Dispersed Si3N4 without Additives Fabricated by Hot Isostatic Pressing
Authors: Terao Koichi , Miyamoto Yoshinari , Koizumi Mitsue
Published: March 2005

Dense, ZrO2‐dispersed Si3N4 composites without additives were fabricated at 180 MPa and ∼1850° to 1900°C for l h by hot isostatic pressing using a glass‐encapsulation method; the densities reached >96% of theoretical. The dispersion of 20 wt% of 2.5YZrO2 (2.5 mol% Y2O3) in Si3N4 was advantageous to increase the room‐temperature fracture toughness (∼7.5 MPa˙m1/2) without degradation of hardness (∼15 GPa) because of the high retention of tetragonal ZrO2. The dependence of fracture toughness of Si3N4–2.5YZrO2 on ZrO2 content can be related to the formation of zirconium oxynitride because of the reaction between ZrO2 and Si3N4 matrix in hot isostatic pressing.
Modification of the Hydrofluoric Acid Leaching Technique: I, Corundum–Mullite–Glassy Phase Materials
Authors: WANCHENG ZHOU , LITONG ZHANG , HENGZHI FU
Published: March 2005

A method to modify the HF leaching technique is proposed. By the use of this method, the error caused by the dissolution of mullite can be measured and removed from the analysis results, and satisfying accuracy of the results can be reached. Experimental comparison shows that the accuracy of the modified HF leaching technique is much higher than that of the unmodified HF leaching technique and the X‐ray diffraction technique when these techniques are used to determine the amount of glassy phase in Al2O3–SiO2 ceramics. An example is given to show how to use the modified HF leaching technique.
Identification of t' Phase in ZrO2‐7.5 wt% Y2O3 Thermal‐Barrier Coatings
Authors: Muraleedharan Kuttanellur , Subrahmanyam Jandhyala , Bhaduri Sarit B.
Published: March 2005

The presence of nontransformable tetragonal (t') phase in plasma‐sprayed ZrO2‐Y2O3 coatings enhances the stability of the coating during high‐temperature exposure. In this paper, we describe the importance and procedure for correctly identifying t’phase in X‐ray diffraction patterns of the as‐sprayed and heat‐treated coatings. The results agree with the phase diagram. We also point out that in the heat‐treated materials, the durability should be specified in terms of t'‐ZrO2.
Change in the Fracture Mode of PLZT Ceramics by Chemically Induced Grain‐Boundary Migration
Authors: Kim Jeong‐Joo , Kim Doh‐Yeon
Published: March 2005

The undulating grain‐boundary structure formed by chemically induced grain‐boundary migration in lanthanum‐modified‐lead‐zirconium‐titanium ceramics causes a change in the fracture mode and an increase in room‐temperature fracture toughness. Specimens with normal and undulating grain‐boundary structure exhibit intergranular and transgranular fracture, respectively. The grain‐boundary undulation is suggested to be effective for improving high‐temperature creep resistance.
Mass Transport and Chemical Demixing of Y‐Ba‐Cu‐O Compounds During Sintering in Temperature Gradients
Authors: Rahaman Mohamed N. , De Jonghe Lutgard C. , Chu May‐Ying
Published: March 2005

A thin cylindrical powder compact (3‐mm diameter by 20‐mm) with a nominal composition of YBa2Cu3Ox was sintered in a static temperature gradient of 25°C/mm in air for 12 h. The temperature at the hot end of the sample was maintained at 940°±5°C. Considerable mass transport and chemical demixing occurred along the length of the sample. The results are consistent with the formation of a liquid phase at the hot end of the sample, transport of the liquid down the temperature gradient, and the formation of different eutectic compositions along the length of the sample. The implications for processing high‐Tc superconductors in the system Y‐Ba‐Cu‐O are discussed.
Polymorphic Mixes of Zirconia from a Borate Glass Melt
Authors: De Villiers Dan R. , Kingon Angus I. , Res Miloslav A.
Published: March 2005

Yttria‐stabilized zirconia crystals were produced by devitrification within a sodium borate glass containing zirconia and yttria. Yttria (3, 6, or 10 mol%) in zirconia was added as part of the starting material of the glass batch. Phase separation and crystallization occurred during the cooling and subsequent heat treatment of the glasses. The zirconia powders obtained after leaching away the sodium borate had surface areas between 16 and 48 m2/g. X‐ray diffraction traces revealed a mixture of monoclinic, tetragonal, and cubic phases, the phase ratios of which depended on the composition of the glass.
Formation and Transformation of Solid Solutions in the System Nb2O5–Ta2O5
Authors: Yamaguchi Osamu , Tomihisa Daijo , Shirai Masakazu , Shimizu Kiyoshi
Published: March 2005

In the system Nb2O5–Ta2O5, a continuous series of δ‐Nb2O5 (δ‐Ta2O5) solid solutions with a hexagonal cell is formed while heating amorphous materials prepared by the simultaneous hydrolysis of niobium and tantalum alkoxides. The lattice parameters a and c change linearly with increasing Ta2O5 content; the former value increases from 0.3604 to 0.3620 nm, and the latter value decreases from 0.3923 to 0.3883 nm. They transform to γ‐Nb2O5 (β‐Ta2O5) solid solutions with an orthorhombic cell at higher temperatures. The changes in lattice parameters a and c as functions of composition are the same as those of hexagonal solid solutions, whereas parameter b is relatively constant.
Solid Phase Relations at 950°C in La‐Ba‐Cu‐O
Authors: Klibancw D. , Sujata K. , Mason T. O.
Published: March 2005

Subsolidus phase relations in the La2O3–BaO–CuO system were studied at 950°C. Three previously reported binary compounds exist (La2CuO4, BaLa2O4, and BaCuO2) and five previously reported ternary phases occur (La2‐xBaxCuO4‐(x/2)+δ, La4‐2xBa2+2xCu2‐xO10‐2x, La2‐xBa1+xCu2O6‐(x‐2), La3‐xBa3+xCu6O14±δ, and La4BaCu5O13+δ). Of the seven phases in the diagram, all but BaLa2O4, BaCuO2, and La4BaCu5O13+δ were shown to exhibit significant ranges of solubility. The diagram is important in that both >30 K (La2‐xBaxCuO4‐(x/2)+δ) and >90 K (La3‐xBa3+xCu6O14+δ, x=1) superconductors occur.
Indentation Creep in Single‐Crystal Cubic Zirconia at Room Temperature
Authors: Carter Graham M. , Henshall John L. , Hooper Robert M.
Published: March 2005

Indentation creep of yttria‐ and calcia‐fully‐stabilized single‐crystal zirconia has been observed at room temperature. The Knoop hardnesses decreased by 15% and 12% of their conventional short‐time values, respectively, for indentation times of 100000 s.
Sol–Gel Processing of Lead Titanate in 2‐Methoxyethanol: Investigations into the Nature of the Prehydrolyzed Solutions
Authors: Dekleva Thomas W. , Hayes James M. , Cross Leslie E. , Geoffroy Gregory L.
Published: March 2005

A previously developed system for the sol–gel processing of lead titanate powders and films has been analyzed by a variety of spectroscopic, chromatographic, and wet‐chemical means. The results indicate that refluxing Pb(OAc)2˙3H2O in 2‐methoxyethanol is accompanied by the volatilization of 0.5 equiv of organic acetate and results in solutions containing what is believed to be anhydrous basic lead acetate, 3Pb(OAc)2˙PbO. This has been isolated as its monohydrate, which has been fully characterized by elemental (C, H, Pb), infrared, 1H NMR, and XRD analyses. The anhydrous salt generated in situ reacts further with Ti(OR)4 under reflux conditions to liberate more organic acetates. The final stoichiometries (one volatilized acetate per lead) tend to preclude the possibility that significant amounts of polymeric intermediates are generated. Analyses of the organic volatiles also indicate that, at least under our conditions, significant trans‐alcoholysis of the precursor Ti(OR)4 (R=Et, i‐Pr, n‐Pr) occurs (80% to 90% replacement). The conclusions and consequences of these and related observations are presented.
Aluminum Titanate Formation by Solid‐State Reaction of Coarse Al2O3 and TiO2 Powders
Authors: FREUDENBERG B. , MOCELLIN A.
Published: March 2005

Reaction kinetics in a coarse equimolar powder mixture were slow enough to allow for the different stages to be identified, notably in the lower and higher temperature ranges, respectively. In the former (T≤ 1600 K), Al2TiO5 nucleation was hindered by the strain energy contribution to the overall driving force. The setting up of metastable layer sequences Al2TiO5/TiO2/Al2O3 was found to occur generally during subsequent growth. The high Al mobility in the TiO2 provided a rapid aluminum transport from the metastable Al2O3/TiO2 interface to the TiO2/Al2TiO5 front. At temperatures above ∼1700 K the Al2O3/TiO2 interface was very rapidly sealed off by Al2TiO5 formation. Reactant transport across the Al2TiO5 was slow because of the low mobilities in the product phase. Therefore, much lower product growth velocities were observed at higher temperatures than at lower temperatures.
Hydrolysis in the Aluminum sec‐Butoxide—Water—Isopropyl Alcohol System: I, Rheology and Gel Structures
Authors: CHANE‐CHING J‐Y. , KLEIN LISA C.
Published: March 2005

Solutions representing a wide range of compositions in the aluminum sec‐butoxide‐water‐isopropyl alcohol system were prepared. Viscosity measurements were made on solutions hydrolyzed at 20°C, Large differences were observed between low‐water solutions and high‐water solutions, both in the time evolution of the viscosity and in the effect of isopropyl alcohol content on the viscosity. Higher values of viscosity were attributed to polycondensation of partially hydrolyzed species, while lower values of viscosity were attributed to hydrolyzed clusters. The reduced viscosity was independent of oxide content for low‐water solutions, but decreased with increasing oxide content for high‐water solutions.
Hydrolysis in the Aluminum sec‐Butoxide—Water—Isopropyl Alcohol System: II, Aging and Microstructure
Authors: CHANE‐CHING J‐Y. , KLEIN LISA C.
Published: March 2005

Solutions representing a wide range of compositions in the aluminum sec‐butoxide‐water‐isopropyl alcohol system were prepared. Solutions were mixed at room temperature, then gelled and evaporated at 80°C. Regions within this system were distinguished where translucent gels formed instead of precipitates or powders. Translucent gels formed in compositions with high water content and high isopropyl alcohol content. The stages of sol‐gel process were investigated by Fourier transform infrared spectroscopy in the early stages and in gels before and after solvent evaporation. The microstructure was characterized by nitrogen sorption analysis.
Annealing of Test Specimens of High‐Toughness Magnesia‐Partially‐Stabilized Zirconia
Authors: Readey Michael J. , Heuer Arthur H. , Steinbrech Rolf W.
Published: March 2005

The peak toughness of a commercial magnesia‐partially‐stabilized zirconia was strongly dependent on a postprocessing, postspecimen preparation, and modest annealing (1000°C for 20 min), increasing it from ∼9 to almost ∼18 MP a·m1/2. Further study of this surprising phenomenon revealed that increases in toughness occurred for annealing temperatures as low as 275°C. The low toughness of the as‐received materials is due to a post‐manufacture room‐temperature aging.
Hot Isostatic Pressing of Si3N4 Powder Compacts and Reaction‐Bonded Si3N4
Authors: Heinrich Juergen , Backer Eberhard , Böhmer Manfred
Published: March 2005

Hot isostatically pressed silicon nitride was produced by densifying Si3N4 powder compacts and reaction‐bonded Si3N4 (RBSN) parts with yttria as a sintering additive. The microstructure was analyzed using scanning electron microscopy, X‐ray diffraction, and density measurements. The influence of the microstructure on fracture strength, creep, and oxidation behavior was investigated. It is assumed that the higher amount of oxygen in the Si3N4 starting powder compared with the RBSN starting material leads to an increased amount of liquid phase during densification. This results in grain growth and in a larger amount of grain boundary phase in the hot isostatically pressed material. Compared with the hot isostatically pressed RBSN samples therefore, strength decreases whereas the creep rate and the weight gain during oxidation increase.
Thermodynamic Stability of K+‐β‐Alumina
Authors: Itoh Mitsuru , Kozuka Zensaku
Published: March 2005

K2O activity in K+‐(α+β)‐alumina was determined from emf data of the galvanic cell Pt,O2,(α+β)‐alumina/K+‐β‐alumina/K2SO4,SO2+SO3+O2,Pt. K2O activity in the K+‐(α+β)‐alumina was expressed by the equation log ak2o (±0.038)=(−18295±120)(K/T)+(0.998±0.110), where 961 K<T<1274 K. Using the activity data, the following thermodynamic properties of K+‐β‐alumina are discussed: the standard Gibbs energy of formation of K2O·11Al2O3 from K2O and α‐Al2O3 and from K, O, and Al; the thermodynamic stabilities of K+‐β‐alumina in the atmospheres of SOx (x=2, 3) and CO2; the equilibrium vapor pressure of potassium over K+‐β‐alumina under a constant O2 pressure; and the stability of K+‐β‐alumina in the molten Na‐K alloy.
High‐Temperature/Field Alternating‐Current Behavior of ZnO‐Based Varistors
Authors: Alim Mohammad A. , Seitz Martin A. , Hirthe Richard W.
Published: March 2005

The ac electrical response of the grain boundary in the ZnO–Bi2O3‐based varistor system (in the frequency range 10−2≤f≤107 Hz) has been analyzed using complex plane analysis techniques as a function of temperature (90°≤T≤150°C) and electric field (E60%lmA/cm2≤E≤ElmA/cm2). The high‐temperature/field data were best represented in the impedance plane. The lumped parameter equivalent circuit representation, containing a voltage variable resistive element associated with the grain boundary, was in agreement with a model previously reported in the literature. The resulting equivalent circuit representation of the grain‐boundary response consisting of a resistance and a capacitance are interpreted in terms of various phenomena occurring at the electrical thickness of the grain boundary.
Sinter‐Forging Characteristics of fine‐Grained Zirconia
Authors: Panda Prakash C. , Wang Jenqdaw , Raj Rishi
Published: March 2005

Powder preforms of zirconia, containing 2.85 mol% yttria, were sinter‐forged in simple uniaxial compression at 1400°C by applying constant displacement rates to the specimens. Shear and densification strains and the uniaxial stress were measured as a function of time. In contrast with alumina and silicon nitride, zirconia appears to densify by a dislocation mechanism. As a consequence, the densification rate is linked to the applied strain rather than to the applied hydrostatic pressure; the powder compact requires a critical amount of compressive strain to consolidate to full density, irrespective of the strain rate or the stress at which that strain is applied.
Interfacial Layers in Brittle Cracks
Authors: ROACH DAVID H. , LATHABAI SRINIVASARAO , LAWN BRIAN R.
Published: March 2005

A study has been made of interfacial layers that form within cracks in mica and silicate glass. The layers are the result of interactions with environmental species behind the crack tip. Deposition processes are associated with precipitation from aqueous solutions and corrosion of the crack walls. The level of precipitation depends on such factors as “impurity” content, temperature, etc. It is demonstrated that the layers can bridge the interface and thereby significantly increase the apparent toughness and the strength. These retardation effects are modeled as an “internal”(negative) contribution to the net stress intensity factor on the crack from closure tractions over a near‐tip area of the interface. The results highlight the potential importance of surface chemistry as a determinant of both equilibrium and kinetic fracture properties.
Statistical Approaches to Failure for Ceramic Reliability Assessment
Authors: LAMON JACQUES
Published: March 2005

The paper examines the respective merits of the main statistical approaches to brittle failure. These approaches based upon the weakest‐link concept are the Weibull approach, Batdorf's approach, and a multiaxial elemental strength model. The purpose of this paper is to determine whether these theories are capable of meeting the requirements of ceramic reliability prediction and component design. Also discussed is the legitimacy of these weakest‐link theories for treating delayed fracture. Alternative solutions are outlined.
Determination of Diffusion Coefficients of Dopants in Wet Gels During Leaching
Authors: Shingyouchi Kazuo , Makishima Akio , Konishi Shirou
Published: March 2005

Diffusion of germanium and titanium ions during the leaching of GeO2‐SiO2 wet gel in water and TiO2‐SiO2 wet gel in HCl was studied. The gels were densified by heating, and the composition profiles of the densified glasses were observed with a transmission interference microscope. In order to calculate the apparent diffusion coefficients, the observed results were fitted to a solution of the diffusion equation. The diffusion coefficients for germanium and titanium ions in the gels are about 3.0×10−6 and 1.1×10−6 cm2/s, respectively.
Early Stages of Alumina Sol‐Gel Formation in Acidic Media: An 27Al Nuclear Magnetic Resonance Spectroscopy Investigation
Authors: Nazar Linda F. , Klein Lisa C.
Published: March 2005

The effects of processing conditions on the formation of alumina sols from the hydrolysis of alkoxide precursors have been investigated using 27Al nuclear magnetic resonance (NMR) spectroscopy. In the range of acid ratios between ∼0.3 to 1.0 mol of HNO3 per mole of alumina sec‐butoxide, the NMR data show that sols processed at 20°C, low temperature (LT), differ greatly from those processsed at 90° to 95°C, high temperature (HT). In the LT sols, the aluminum is predominantly in the form of the polyoxycation species, Al13O4(OH)24(H2O)xn+ (where n is probably 7), rather than a folded defect boehmite structure as suggested by Pierre and Uhlmann. Furthermore, heating the LT sols at 90°C does not transform them to the HT form directly, but rather results in the growth of new tetrahedral and octahedral alumina species.
Preparation of Manganese Zinc Ferrite Powders by Alcoholic Dehydration of Citrate/Formate Solution
Authors: Sainamthip Prinya , Amarakoon Vasantha R.W.
Published: March 2005

Chemically homogeneous manganese zinc ferrite powders of submicrometer size and desired stoichiometry were achieved using alcoholic dehydration and subsequent calcination of citrate/formate solution. The successful powder preparation was dependent on the water content in the starting solution, the pH of the solution, the amount of alcohol used, and the washing and drying step. Calcination temperature was also critical since the evaporation of ZnO took place above 1000°C. A two‐step calcination process was utilized to develop submicrometer ferrite powders without any Zn loss.
Melt Infiltration Approach to Ceramic Matrix Composites
Authors: Hillig William B.
Published: March 2005

Melt infiltration offers an alternative route to the synthesis of fully dense ceramic matrix composites. Necessary conditions with respect to chemical reactivity, melt viscosity, and wetting must be satisfied. Other properties of the reinforcement and matrix constituents must also be considered. With these restrictions this generic approach is applicable to a wide range of composite systems. Preliminary structure and property results are presented for the representative systems based on particulate and whisker SiC reinforcement in combination with CaSiO3, SrSiO3, and strontium feldspar matrices.
Instability of the Characteristics of the Positive Temperature Coefficient of Resistivity in High‐Curie‐Point Barium‐Lead Titanate Ceramics and Their Grain Structures
Authors: Kuwabara M. , Nakao K. , Okazaki K.
Published: March 2005

A significant isothermal increase in resistivity with time has been observed in high‐Curie‐point barium‐lead titanate ceramics in the temperature region of the Curie points, giving rise to an instability of the characteristics of the positive temperature coefficient of resistivity (PTCR). The isothermal increase in resistivity (ρ) with time (t) observed at various temperatures can be expressed by the equation log ρ=A+B√t, where A and B are both temperature‐dependent constants. The temperature dependence of A gave the usual PTCR characteristics because A is log ρ at t=0, while the temperature dependence of B was found to show a characteristic curve with a peak around the Curie point. Observation by SEM revealed a considerable difference between the grain structure of a sample showing a significant resistivity change and that of a sample showing little resistivity change.
Sequential Precipitation of MgAl2O4 on Mg1‐x CaxAl2O4 in Hot‐Pressed MgO Single Crystals
Authors: FUJIMOTO MASAYUKI , CHIANG YET‐MING , KINGERY W. DAVID
Published: March 2005

In a hot‐pressed and deformed MgO single crystal, precipitates of Mg1‐xCaxAl2O4 spinel upon which MgAl2O4 spinel subsequently precipitated were observed and analyzed using transmission electron microscopy and scanning electron microscopy. This behavior is related to the respective solubility limits of CaO and Al2O3 in MgO at the hot‐pressing temperature and may be aided by impurity segregation to the dislocations. The spinel selectively precipitated at the nodes of a dislocation network which was formed during [001] hot‐pressing deformation, as a result of the reaction b3= b1+ b2= (1/2) [011] + (1/2) = [001]. The dislocation is sessile, and the precipitates have a <100>matrix? <100>spinel coherent relationship.
Phase Equilibria and Structural Species in MgF2‐MgO, MgF2‐CaO, and MgF2‐Al2O3 Systems
Authors: SHARMA RAM A.
Published: March 2005

Partial equilibrium phase diagrams for the systems MgF2‐MgO, MgF2‐CaO, and MgF2‐Al2O3 were determined by differential thermal analysis. Simple eutectics were observed at 8.5 mol% MgO and 1228°± 3°C in the MgF2‐MgO system, at 7.5 mol% CaO and 1208°± 3°C in the MgF2‐CaO system, and at 2.5 mol% Al2O3 and 1250°± 3°C in the MgF2‐Al2O3 system. On the basis of agreements between the activities calculated by the Clausius‐Clapeyron equation and Temkin's model using the present data, the eutectic melt consists of Mg2+, F‐, and O2‐ ions in the MgF2‐MgO system; Mg2+, Ca2+, F‐, and O2‐ ions in the MgF2‐CaO system; and Mg2+, Al3+, F‐, and AlO2¯ ions in the MgF2‐Al2O3 system. Well‐defined long needles of MgO in the MgF2‐MgO system, less defined needles of CaO in the MgF2‐CaO system, and Al2O3 grains in the MgF2‐Al2O3 system were observed by optical microscopy.
Quantitative Analysis of Coexisting Byproducts in Orthorhombic YBa2Cu3Ox by X‐ray Diffraction
Authors: Itoh Takao , Uzawa Masami , Uchikawa Hiroshi
Published: March 2005

BaCuO2, Y2Cu2O5, and Y2BaCuO5 as well as YBa2Cu3Ox were synthesized and nonlinear calibration curves for mole fraction versus integrated intensity ratio of X‐ray diffraction peaks were obtained for BaCuO2‐, Y2Cu2O5‐, and Y2BaCuO5‐YBa2Cu3Ox systems. It is shown that the amount of BaCuO2 contained in orthorhombic YBa2Cu3Ox is not negligible, even if the relative intensity of the strongest diffraction peak of BaCuO2 is negligibly weak.
Factors Affecting the Porosity and Bending Strength of Ti(CN)‐TiB2 Materials
Authors: Watanabe Tadahiko , Yamamoto Hideki , Shobu Kazuhisa , Sakamoto Tadashi
Published: March 2005

This paper describes the effects that the particle size of Ti(CN) and TiB2 powder, oxygen content of the TiB2 powder, and Co impurity content in the starting raw materials have on the porosity and bending strength ofTi(CN)‐30% TiB2 materials obtained by ordinary sintering.
Purity of Aluminum Hydroxide Derived from Triethylaluminum
Authors: Tebbe Fred N. , Morris Patricia A. , French Roger H. , Chowdhry Uma , Coble Robert L.
Published: March 2005

Aluminum hydroxide obtained by hydrolysis of triethylaluminum is free of uranium and thorium at detection limits of 1 to 9 parts per billion (ppb). Other impurities commonly associated with aluminum oxides are present at low levels (Fe, ∼ 1 ppm; Si, 3 to 6 ppm). When the organoaluminum is intentionally contaminated with an iron salt, purity is restored by a simple distillation.
Surface‐Energy Determinations of Tin Oxide‐Coated Soda–Lime–Silica Glass
Authors: Smay Gary L.
Published: March 2005

The dispersive and polar surface‐energy components, as well as the total surface energy, of tin oxide coatings on soda–lime–silica glass were determined by the Owens–Wendt method. The total surface energy of tin oxide is greater than soda–lime–silica glass and, more importantly, exhibits significantly more‐dispersive and less‐polar character. These results indicate that tin oxide is significantly more covalent than soda–lime–silica glass. It is postulated that the more‐covalent tin oxide coatings increase the bond strength of organic coatings to soda–lime–silica glass. These effects improve the friction‐damage resistance of glass surfaces coated with metal oxides and organics, compared with glass surfaces coated with organics only.
A Method for Preparation of Unsupported Sol–Gel Thin Films
Authors: Huling Jeffrey C. , Messing Gary L.
Published: March 2005

Unsupported gel films 1 to 3 μm thick may be prepared from colloidal sol–gel systems by spin‐coating onto a camphor substrate. Sublimation of the camphor surface allows the film to separate and be freely sintered, giving a rapid indication of sintering behavior and microstructural development.
Crack Resistance Curves in Magnesia‐Partially‐Stabilized Zirconia
Authors: MARSHALL DAVID B. , SWAIN MICHAEL V.
Published: March 2005

Crack growth resistance curves (R curves) for the growth of surface cracks have been measured in a series of magnesia‐partially‐stabilized zirconia ceramics with varying degrees of transformation toughening. The shapes of the R curves are correlated with strength‐toughness relations and the predictions of fracture mechanics analysis of transformation toughening. Results support a previous hypothesis that the peak in the strength‐toughness relation is associated with a decreasing slope of the R curve with increasing steady‐state toughness. The role of microstructural influences due to localized regions of transformation on crack growth is assessed, and the relation between reversible and irreversible transformation and toughness is examined.
Near‐Tip Mechanics of Stress‐Induced Microcracking in Brittle Materials
Authors: CHARALAMBIDES PANAYIOTIS G. , McMEEKING ROBERT M.
Published: March 2005

A continuum‐mechanics description of stress‐induced microcracking was developed. Modulus‐reduction effects due to microcracking are taken into account through the model of Budiansky and O'Connell. This is used in conjunction with a modified microcracking criterion that stems from the work of Evans and Fu. The resulting constitutive law for a microcracking material was used in finite‐element calculations to study the near‐tip stress and strain fields and the size and shape of a small‐scale damaged zone for a stationary mode I crack in an elastic body. The finite‐element results for the stationary crack are used to predict asymptotic toughening values which correspond to a fully developed wake of microcracked material for a propagating crack. Substantial toughening can result. In contrast, the microcracking zone for a stationary crack is thought to make little or no contribution to material toughening. The theoretical results are discussed in the context of experimental observations for zirconiatoughened alumina.
Model for Ion‐Exchanged Waveguides in Glass
Authors: ABOU‐EL‐LEIL MAHMOUD , LEONBERGER FRED
Published: March 2005

An analytical model describing refractive index profiles in ion‐exchanged glass waveguides is presented. Polarizability, volume, and stress‐state changes are accounted for. Index distribution is given in terms of known or measurable physical parameters. Model predictions compare favorably with experimental results of field‐assisted ion‐exchanged waveguides fabricated in 7740 borosilicate glass. Experimental characterization of the index changes includes prism coupling, microprobe, and photoelastic measurements.
Critical Current Densities in Thin Ceramic Tapes of Superconducting Ba2YCu3O7
Authors: Johnson David W. , Grader Gideon S.
Published: March 2005

Tape‐cast slurries of Ba2YCu3O7 powders offer a convenient means of preparing sintered ceramic samples for critical current density (Jc) measurements where the transport cross section is small and the current electrode areas are large. Samples were sintered from 900° to 1000°C and characterized for bulk density, grain size, phase composition, Tc, and Jc. Bulk density and grain size both increase with sintering temperature while all samples were single‐phase perovskite except for those sintered at 900°C. The onset temperature for superconductivity is constant at about 93 K while the transition sharpens to R=0 at about 92 K for the densest samples. Jc rises with sintering temperature to a maximum of ∼103 A/cm2. A linear relationship between Jc and bulk density is predicted from microstructural considerations.
Determination of Crack‐Bridging Forces in Alumina
Authors: Reichl Andreas , Steinbrech Rolf W.
Published: March 2005

In alumina, R‐curve behavior is frequently attributed to “wake” effects which partially shield the crack tip from the applied stress. A novel method is introduced to prove the existence of crack‐bridging wake effects and to examine their influence on toughness. Short double‐cantilever‐beam (DCB) specimens were modified to contain a machined notch at the back face of the specimen. As the growing crack enters this rear notch, the load‐bearing capacity of the specimen, and thus the effectiveness of the wake to withstand fracture, is determined. This paper describes the use of such a specimen to evaluate the magnitude of the bridging stresses developed and the contribution of the wake to toughness in polycrystalline alumina.