bluuebunny/crossref_metadata_2025 huggingface dataset:
Viscosity and Surface Tension of Oxynitride Glass Melts
Authors: Kaplan‐Diedrich Hannelore , Eckebracht Andrea , Frischat Günther H.
Published: September 2005

The viscosities and surface tensions of three MgO‐Al2O3‐Y2O3‐SiO2‐based oxynitride glass melts were measured. Glass transition temperature, Littleton temperature, and sink‐in temperature were obtained, and by using the Vogel‐Fulcher‐Tammann equation the viscosities were calculated from Tg (820° to 940°C) to 1600°C. The surface tensions were measured by the drop weight and the drop geometry methods and displayed values between about 500 and 600 N.mm−1. These values are about a factor of two higher than the surface tensions of oxide glass melts.
Mechanism of Preventing Crystallization in Low‐Firing Glass/Ceramic Composite Substrates
Authors: Park Jeong‐Hyun , Lee Sang‐Jin
Published: September 2005

The formation of a crystal phase in the glass matrix of low‐firing glass/ceramic composite substrates limits the efficiency of the ceramic substrate when it is used in circuit boards. In the present study, adding approximately 30 vol % or more of alumina to a borosilicate‐glass/ceramic composite system as a ceramic filler caused the diffusion of aluminum ions from the alumina filler into the glass matrix and prevented the formation of a cristobalite crystal phase. The diffusion distance between the aluminum ions was ∼30 μm when the system was fired at 900°C for 10 min. Raman spectroscopic analysis proved that some of the aluminum ions had diffused into the glass matrix during firing, working as a network former in the glass matrix. Raman spectra near 460 and 1100 cm−1 indicate the change of network structure in the borosilicate glass. These phenomena indicate that crystallization of the borosilicate glass was prevented in the alumina‐filled borosilicate system.
Technique for Monitoring Densification during Chemical Vapor Infiltration
Authors: Lackey W. Jack , Vaidyaraman Sundar , Freeman Garth B. , Agrawal Pradeep K.
Published: September 2005

A new technique for studying the progression of densification during the fabrication of composites by chemical vapor nfiltration is presented. The preparation of a carbon‐matrix composite was investigated by momentarily inter‐rupting, at various times, the carbon infiltration process to permit deposition of very thin layers of SiC. Microscopic examination of these layers on a polished cross section per‐mitted determination of the extent of infiltration at various locations within the preform as a function of infiltration time. The technique also distinguishes open from closed pores and provides information on the existence of temperature gradients within the preform.
Comment on “Effect of Al2O3 and Bi2O3 on the Formation Mechanism of Sn‐Doped Ba2Ti9O20”
Authors: Wang Hong‐Wen
Published: September 2005

in a recent article of the Journal, Yu et al.1 reported their experimental results on the effect of Al2O3 and Bi2O3 on the formation mechanism of Sn‐doped Ba2Ti9O20. They claimed that both Al2O3 and Bi2O3 can dramatically assist the formation of Sn‐doped Ba2Ti9O20 but are based on different mechanisms. They concluded that first, Bi2O3 melts above 830°C and accelerates the migration of the involved reactants to form Ba2Ti9O20; second, Al2O3 can reduce the height of the potential energy barrier of the formation of Ba2Ti9O20 due to the intergrowth of BaAl2Ti6O16 phase. They explained their results from a point of view that the formation of Ba2Ti9O20 is controlled by (1) the migration of reactants to the interfaces and (2) the height of the potential‐energy barrier of the reaction at the interfaces. However, based on their results, we feel their conclusions are incautious and may be misleading, as will be discussed later.
Critical Stresses for Extension of Filament‐Bridged Matrix Cracks in Ceramic‐Matrix Composites: An Assessment with a Model Composite with Tailored Interfaces
Authors: Danchaivijit Sawai , Shetty Dinesh K. , Eldridge Jeffrey
Published: September 2005

Matrix cracking was studied in a model unidirectional composite of SiC filaments in an epoxy‐bonded alumina matrix. The residual clamping stress on the filaments due to the shrinkage of the epoxy was moderated with the addition of the alumina filler, and the filament surface was coated with a releasing agent to produce unbonded frictional interfaces. Uniaxial tension specimens with controlled through‐cracks with bridging filaments were fabricated by a two‐step casting technique. Critical stresses for extension of the filament‐bridged cracks of various lengths were measured in uniaxial tension using a high‐sensitivity extensometer. The measured crack‐length dependence of the critical stress was in good agreement with the prediction of a stress‐intensity analysis that employed a new force‐displacement law for the bridging filaments. The analysis required independent experimental evaluation of the matrix fracture toughness, the interfacial sliding friction stress, and the residual tension in the matrix. The matrix‐cracking stress for the test specimens without the deliberately introduced cracks was significantly higher than the steady‐state cracking stress measured for the long, filament‐bridged cracks.
Preparation of Blue Vanadium‐Zircon Pigments by Aerosols Hydrolysis
Authors: Tartaj Pedro , Serna Carlos J. , Ocaña Manuel
Published: September 2005

A continuous procedure for the preparation of V‐ZrSiO4 powders based on the hydrolysis of liquid aerosols composed of a mixture of TEOS, zirconium propoxide, and VOCl3 is reported. These powders consist of spherical amorphous particles, having a high degree of Si‐Zr mixing and a homogeneous distribution of vanadium in the ceramic matrix. The raw composition (Zr/Si ratio and V content) was systematically varied in order to optimize the color of the final pigments. The color changes produced in the samples during heating are discussed in terms of the location of the vanadium species in the zircon matrix. In vanadium‐zircon blue pigments, evidence of the substitution of Si by V+4 in tetrahedral sites forming a solid solution with the zircon matrix is observed by infrared spectroscopy.
Voltammetric Study of Silver in a Glass Melt
Authors: Yata Kunio , Hanyu Naohiko , Yamaguchi Takashi
Published: September 2005

The redox reaction and the oxidation state of silver in a glass melt were studied by cyclic voltammetry and chronopotentiometry between 800° and 1200°C. Silver ions in glass were reduced at a less noble potential than the rest potential of a platinum electrode. A reversible redox reaction of silver in glass was indicated from the analysis of the cyclic voltammogram. An analysis based on the electron transference number revealed that the solubility of reduced silver increased with increasing temperature. Ag+/Ag0 equilibrium in glass was suggested because the rest potential of the platinum electrode in glass was a mixed potential. No relation was observed between the redox behavior of silver in glass and optical basicity. O‐type redox behavior of silver in glass was shown.
Microwave Characteristics of BaO‐TiO2 Ceramics Prepared via a Citrate Route
Authors: Choy Jin‐Ho , Han Yang‐Su , Sohn Jeong‐Ho , Itoh Mitsuru
Published: September 2005

Microwave dielectrics of the TiO2‐rich BaO‐TiO2 system (BaTi4O9 and Ba2Ti9O20) were prepared by the citrate route. Pure and well‐crystallized BaTi4O9 and Ba2Ti9O20 particles of nanometer size (30–50 nm) could be obtained by thermal decomposition of citrate gel precursors. After sintering at 1200°–1350°C (for 2–10 h), dense compounds with >90% of theoretical density could be obtained. Dielectric properties of disk‐shaped sintered specimens, in the microwave frequency region, were measured in the TE01δ mode. They were found to have excellent microwave characteristics: for BaTi4O9, εr= 36, Q= 4900 at 10.3 GHz, and τf= 16 ppm/°C; and for Ba2Ti9O20, εr= 37, Q= 5300 at 10.7 GHz, and τf=−6.0 ppm/°C.
Effects of Silver Doping on the Reliability of (Pb0.875 Ba0.125)[(Mg1/3 Nb2/3) 0. 5(Zn1/3 Nb2/3)0.3 Ti0.2] O3 Relaxor Dielectric Ceramics
Authors: Kanai Hideyuki , Furukawa Osamu , Nakamura Shin‐ichi , Hayashi Masaru , Yoshiki Masahiko , Yatnashita Yohachi
Published: September 2005

The reliability of the silver‐doped dielectric ceramic (Pb0.875Ba0.25)0.995[(Mg1/3Nb2/3)0.5(Zn1/3Nb2/3)0.3Ti0.2]O3 was investigated to speculate on the effects of silver diffusion from internal electrodes into dielectric layers on the reliability of multilayer ceramic capacitors (MLCs). The addition of silver into the dielectric ceramic degraded the insulation resistance under humid loading conditions. Scanning transmission electron microscopy (STEM) revealed that a Pb‐rich grain boundary phase exists at triple points of Ag‐doped specimens. The Pb‐rich phase appeared to be PbO by X‐ray photoelectron spectroscopy (XPS). Degradation of insulation resistance was interpreted as a result of silver migration from the anode to the cathode through a grain boundary phase dissolved in water. Although silver diffusion from internal electrode layers in MLCs into dielectric layers was confirmed by STEM, a secondary phase was not observed. Intensive study is needed to clarify the effect of silver diffusion on degradation of insulation resistance of MLCs under humid loading conditions.
Formation of Calcium Lanthanum Sulfide by Carbonate Coprecipitation and CS2 Sulfurization
Authors: Tsai Ming‐Shyong , Wang Li‐Hsing , Hon Min‐Hsiung
Published: September 2005

Pure calcium lanthanum sulfide (CLS) powders with various La/Ca ratios were prepared by a carbonate coprecipitation method and CS2 sulfurization. Four coprecipitation processes were investigated by conventional titration, and a suitable means for coprecipitating CLS was found. By that process, a cation solution containing La3+ and Ca2+ ions was added to the precipitation medium (an anion solution of ammonium carbonate) with stirring. Precursors with various La/Ca ratios were synthesized and then sulfurized for 3 h using CS2 as a sulfurizing agent. In the range of La/Ca ratios from 2 to 5, the intermediate phase of sulfide powder was LaS2, and the CLS formation temperature could be increased by increasing the La/Ca ratio. For powder with high La/Ca ratios (La/Ca = 10, 15), and LaS2intermediate phase formed at low temperature (700°C), a (β‐La2S3 minor phase at 800°C, and a pure CLS phase after 950°C treatment. The resulting pure CLS powder was spherical, with slight necking in the submicrometer range.
Processing and Properties of Alumina‐Graphite Platelet Composites
Authors: Kellett Bruce J. , Wilkinson David S.
Published: September 2005

Fine‐grain Al2O3‐graphite platelet composites have been fabricated by both filter pressing and tape casting with up to 50 vol% of fine or coarse graphite flakes. Filter pressing behavior remains unchanged with coarse graphite flake additions. Strength of hot‐pressed specimens decreases from about 350 to about 50 MPa with 50 vol% graphite. Preliminary experiments indicate that platelet orientation has a significant effect on strength: Platelets oriented perpendicular to the fracture plane and face‐on to the crack front are about 20% weaker than composites with platelets oriented both perpendicular to the fracture plane and edge‐on to the crack front. This suggests that the flakes behave as oriented voids in the microstructure.
Determination of Fracture Toughness in 2‐D Woven SiC Matrix Composites Made by Chemical Vapor Infiltration
Authors: Droillard Christine , Voisard Patrick , Heibst Cyril , Lamon Jacques
Published: September 2005

An approach to the R‐curve behavior of 2‐D woven ceramic matrix composites is proposed. This approach takes into account the presence of a process zone at the crack tip. The strain energy release rate is determined using an equivalent system of two specimens free of process zones. The process zone size is determined independently by assimilating a notch tip region to a beam of bimaterial. Compact tension specimens having different dimensions and single‐edge notched beam specimens were used for the analysis. Important trends in toughening of ceramic matrix composites were anticipated.
Mechanical Properties of Mica Glass‐Ceramics
Authors: Baik Dong Soo , No Kwang Soo , Chun John Soung‐Soon , Yoon Yong Joon
Published: September 2005

The mechanical properties of fluorophlogopite mica‐based glass‐ceramics, such as fracture toughness, flexural strength, and machinability, were investigated. It has been shown that toughening increments in the glass‐ceramics occurred by crack deflection and branching by crystals with a high aspect ratio. All the glass‐ceramics heat treated at 1000°–1150°C exhibited a higher fracture toughness of 1.2–2.2 MPa‐m1/2 as compared to 0.8 MPa‐m1/2 for the parent glass, and showed average flexural strengths of 140–160 MPa. It has been suggested that (H/KIc)2 of the mica glass‐ceramic be used to estimate the machinability, because it decreases linearly with machinability.
Polytypes, Grain Growth, and Fracture Toughness of Metal Boride Particulate SiC Composites
Authors: Tanaka Hidehiko , Iyi Nobuo
Published: September 2005

In order to understand the relation between microstructure and toughening behavior in SiC materials, NbB2, TaB2, TiB2, and ZrB2 particulate SiC composites were fabricated with pressureless sintering. In the composites, 3(cubic)‐SiC powder was used as starting material for the matrix. The p‐SiC powder transformed to a(noncubic) phase during sintering. The transformation, the behavior of which was influenced by the existence of metal boride particles, was accompanied by normal or exaggerated grain growth. The metal boride particles suppressed large‐scale exaggerated grain growth of SiC, and it had a tendency to simulate grain growth with a high aspect ratio of the SiC grains. Increase in the fracture toughness of the composites was observed when the grain size and the aspect ratio of the SiC grains increased together. The toughening behavior is discussed based on a grain bridging mechanism.
Flexural Creep of Coated SiC‐Fiber‐Reinforced Glass‐Ceramic Composites
Authors: Sun Ellen Y. , Nutt Steven R. , Brennan John J.
Published: September 2005

This study reports the flexural creep behavior of a fiber‐reinforced glass‐ceramic and associated changes in micro‐structure. SiC fibers were coated with a dual layer of SiC/BN to provide a weak interface that was stable at high temperatures. Flexural creep, creep‐rupture, and creep‐strain recovery experiments were conducted on composite material and barium‐magnesium aluminosilicate matrix from 1000° to 1200°C. Below 1130°C, creep rates were extremely low (∼10−9 S−1), preventing accurate measurement of the stress dependence. Above 1130°C, creep rates were in the 10−8 s−1 range. The creep‐rupture strength of the composite at 1100°C was about 75–80% of the fast fracture strength. Creep‐strain recovery experiments showed recovery of up to 90% under prolonged unloading. Experimental creep results from the composite and the matrix were compared, and microstructural observations by TEM were employed to assess the effectiveness of the fiber coatings and to determine the mechanism(s) of creep deformation and damage.
Indentation Crack‐Shape Evolution during Subcritical Crack Growth
Authors: Dwivedi Priya , Green David J.
Published: September 2005

Indentation crack‐shape evolution during subcritical crack growth was examined in soda‐lime glass. Crack‐arrest markings were generated on the fracture surfaces by temporary unloading during subcritical crack growth. Crack shapes were determined from these crack‐arrest markings by optical microscopy. The shapes were found to be semielliptical, but the ellipticity changed significantly with crack extension under an applied bending stress. Crack‐shape evolution was predicted by using the stress intensity factor equation for a semielliptical crack for the applied stress distribution and the subcritical crack growth parameters for the material/environment system. Experimental results were found to be in excellent agreement with the predictions. The influence of the initial crack size and shape, the loading configuration, and the subcritical crack growth exponent n on crack‐shape evolution was also investigated in the simulations. It was found that, for the particular loading configuration and material, there is an equilibrium shape associated with the subcritically growing crack. The variation in crack shape with its extension during subcritical crack growth was found to be an important factor in lifetime prediction.
Preparation of Silicon Nitride‐Titanium Nitride and Titanium‐Titanium Nitride Composites from (CH3)3SiNHTiCl3‐Coated Si3N4 and Ti Particles
Authors: Narula Chaitanya K. , Demczyk Brian G. , Czubarow Paul , Seyferth Dietmar
Published: September 2005

[(Trimethylsilyl)amino]titanium trichloride, (CH3)3‐SiNHTiClj, was isolated as a red‐orange crystalline solid in 58% yield from the reaction of TiCl4 with [(CH3)3Si]2NH in 1:1 molar ratio in dichloromethane at —78°C. Pyrolysis of (CH3)3SiNHTiCl3 at 600°C furnished titanium nitride. This precursor is suitable for the preparation of composites and was employed to prepare Si3N4‐TiN and Ti‐TiN powders by adding Si3N4 particles or titanium powders to a solution of (CH3), SiNHTiCl3 in dichloromethane, drying and pyrolyzing the resulting solid. This precursor also has been used as a binder to prepare Si3N4‐TiN and Ti‐TiN bodies. High‐resolution transmission electron microscopic studies of the Si3N4‐TiN composite showed that titanium nitride is concentrated on the surface of the Si3N4 particles.
Boehmite Coating as a Consolidation and Forming Aid in Aqueous Silicon Nitride Processing
Authors: Shih Wei‐Heng , Pwu Leh‐Lii , Tseng Ampere A.
Published: September 2005

Silicon nitride powders were coated by boehmite via a solgel process to improve the consolidation and forming of aqueous silicon nitride suspensions. The coated silicon nitride suspensions had a significantly higher solids loading than the pure silicon nitride in water. Viscosity measurements and centrifugation showed that the coating changed the long‐range interaction between the silicon nitride particles, whereas the pressure filtration study indicated that the oxide coating modified the short‐range interaction at particle contacts. Preliminary rheological studies indicated that at pH 3, the boehmite‐coated silicon nitride suspensions can gel, as indicated by a wide linear viscoelastic region in dynamic rheological tests. The gelation of coated silicon nitride at pH 3 offers the potential for net‐shape forming. Our study establishes a water‐based green body consolidation and forming technique of silicon nitride without polymeric additives or organic solvents.
Solid Solutions within Selected SrO‐LnO1.5‐TiO2 Systems
Authors: Shoup Shara S. , Haverlock Tamara J. , Bamberger Carlos E.
Published: September 2005

A region of selected SrO‐LnO1.5‐TiO2 (Ln = La, Ce, Pr, or Nd) systems was studied experimentally using X‐ray diffractometry (XRD). A series of solid solutions with composition Sr4xLn2x/ 3Ti4O12 having tetragonally distorted per‐ovskite structures was found to exist along the tie line connecting SrTiO3 and Ln2Ti3O9. Reactions of SrLn2Ti4O12, representative compounds of the series, with SrO were also studied. Additionally, the solubility of TiO2 in Ln2O3‐(3TiO2‐m (Ln = La, Pr, or Nd) at 1300°C was investigated using XRD.
Cristobalite Phase Formation in Glass/Ceramic Composites
Authors: Imanaka Yoshihiko , Aoki Shigenori , Kamehara Nobuo , Niwa Koichi
Published: September 2005

The effect of several different aluminum‐containing ceramic additions to borosilicate glass on suppressing cris‐tobalite precipitation has been examined. The results showed that mullite or aluminum nitride suppresses cristo‐balite formation more effectively than alumina or spinel. Although both follow a simple rule of mixtures, glass/mullite composites can be fabricated with lower dielectric constants than glass/alumina composites, while maintaining a thermal expansion coefficient close to Si. Electron micro‐analysis using X‐ray energy dispersive spectroscope showed that the measured interdiffusion coefficient between alumina and glass is in good agreement with the data which have already been published.
The SiO2‐Si3N4 Interface, Part I: Nature of the Interphase
Authors: Ogbuji Linus U. J. T. , Bryan Scott R.
Published: September 2005

Recent reports in the literature have suggested that Si2N2O forms in the oxidation of Si3N4 as a buffer suboxide below the silica crust, and that equilibrium between SiO2 and Si3N4 requires the presence of this buffer. Here we report the examination of SiO2/Si3N4 boundaries of different genesis, by a variety of techniques, all of which failed to detect Si2N2O. What was found in each case is a graded suboxide whose composition merges seamlessly with the higher oxide above and the Si3N4 below. Part I presents the results of compositional depth profiling across the suboxide. In Part II a model is proposed to explain how O2 diffusion in the graded suboxide limits Si3N4 oxidation kinetics.
The SiO2‐SI3N4 Interface, Part II: O2 Permeation and Oxidation Reaction
Authors: Ogbuji Linus U. J. T.
Published: September 2005

Previous analyses of Si3N4 oxidation on the basis of diffusion control by a suboxide layer yielded impossibly high N2 pressures. Those models assumed interfacial reactions as the oxidation mechanism. However, it is now thought that the oxidation process is in situ substitution of O for N in silicon oxynitride of graded composition rather than interfacial reaction. In this paper, diffusional and thermodynamic analyses appropriate to this mode of oxidation are developed for both the permeation and reaction aspects of oxidation; O2 diffusivities are calculated from permeation energies; gas pressures in the oxide are derived from solution thermodynamics and found to be moderate.
Characterization and X‐ray Photoelectron Spectroscopy Investigation of PbO‐Bi2O3‐Ga2O3 Glasses
Authors: Heo Jong , Kim Choon Gon , Kim You Song
Published: September 2005

XPS Ols spectra were recorded for glasses in the binary PbO‐Ga2O3 and ternary PbO‐Bi2O3‐Ga2O3 systems. Large shoulders with chemical shifts of 1.4 to 1.9 eV were observed in the Ols spectra recorded from PbO‐Ga2O3 glasses. These shoulders were attributed to the presence of nonbridging oxygens in the structure. The shoulders indicated that, contrary to previous results, PbO was a network modifier as well as a charge compensator and network former. The addition of Bi2O3 reduced the number of nonbridging oxygens and, therefore, it was classified as an intermediate. Ga2O3 seemed to form GaO4− tetrahedra, constituting the backbone of the network structure. Glasses in the PbOBi2O3‐Ga2O3 system had their IR cutoff edges located at 7 μm with glass transition temperatures in the range of 320° to 400°C.
Effects of Organotitanate Additions on the Dispersion of Aluminum Nitride in Nonpolar Solvents
Authors: Liao Hongmei , Coyle Thomas W.
Published: September 2005

Organotitanate additives are known to reduce the viscosity of many filled polymer systems, including formulations of interest for ceramic powder injection molding. Mineral oil was used as a model solvent for these systems to examine the effects of Organotitanate additions on the stability and rheology of A1N dispersions. Addition of the titanate coupling agents neoalkoxy tri(neodecanoyl) titanate and neoalkoxy tri(dioctylphosphato) titanate resulted in better dispersion as measured by sedimentation tests and rheological characterizations. Excellent correlation of the sediment heights and measured viscosities with adsorption isotherms for the organotitanates was shown, with both lower sediment height and lower viscosity obtained when a monolayer of the titanate molecules was present on the powder surface. Comparison of the behavior of the mineral oil based systems with the viscosity of corresponding polypropylene based binder systems indicates that the titanate additions are effective in reducing particle‐particle interaction effects in both systems.
Computer‐Aided, Single‐Specimen Controlled Bending Test for Fracture‐Kinetics Measurement in Ceramics
Authors: Borovik Valeri G. , Chushko Victor M. , Kovalev Sergei P.
Published: September 2005

Fracture testing of ceramics by using controlled crack growth is proposed to allow study of crack‐kinetics behavior under a given loading history. A computer‐aided, real‐time data acquisition system improves the quality of crack‐growth parameters obtained in a simple, single‐specimen bend test. Several ceramic materials were tested in the present study: aluminum nitride as a linear‐elastic material; and alumina and yttria‐stabilized zirconia, both representative of ceramics with microstructure‐dependent nonlinear fracture properties. Ambiguities in the crack‐growth diagrams are discussed to show the importance of accounting for crack‐growth history in correctly describing nonequilibrium fracture behavior.
Perturbed‐Angular‐Correlation Study of Zirconias Produced by the Sol‐Gel Method
Authors: Rivas Patricia C. , Martinez J. A. , Caracoche M. C. , Lopez Garcia Alberto R. , Klein Lisa C. , Pavlik Robert S.
Published: September 2005

Zirconia powders, prepared by a sol‐gel method using zirconium n‐propoxide (ZNP) and different H2O/ZNP and alcohol/ZNP ratios, were investigated by the perturbed‐angular‐correlation method, along with X‐ray diffraction (XRD), Raman spectroscopy, differential thermal analysis (DTA), and thermogravimetric analysis (TGA) techniques. The hyperfine interaction was measured after annealing the samples at increasing temperatures up to 1080°C. Two disordered structures, giving tetragonal patterns in XRD and Raman analysis, were identified in as‐produced powders, which consisted of chains of fully hydrolyzed species and chains containing residual organic groups. As the annealing temperature was increased, crystallization occurred, producing the tetragonal and monoclinic phases of zirconia. All powders were essentially monoclinic at the highest temperatures. Those representing low H2O/ZNP ratios retained a large amount of tetragonal phase over a wide temperature range and transformed to monoclinic with a higher activation energy.
Reaction Condition for the Synthesis of Ultrafine Particles of the High‐Vacancy‐Content Zn(II)‐ Bearing Ferrites from Iron(III) Tartrate Solution
Authors: Kodama Tatsuya , Tamaura Yutaka
Published: September 2005

Reaction conditions for the synthesis of ultraflne particles of ferrite solid Solutions between ZnFe2O4 and γ‐Fe2O3 rep‐resented by x(ZnFe2O4)‐ y(Fe3O4)‐ z(γ‐Fe2O3), where x + y + z = 1 (0.09 x 0.73, y 0.08,0.22 z 0.88) (high‐vacancy‐content Zn(II)‐ bearing ferrites), were studied using the strongly alkaline Solutions of Fe(III) tartrate con‐taining Zn(II) ions at 100°C. The crystal growth of the ferrite particles was enhanced with the Zn(II) ions in the reaction solution. The number of nuclei of the ferrite was dependent on the Fe(III) or the tartrate concentration, which influenced the ultraflne particle size of the ferrite. The average particle size of the high‐vacancy‐content Zn(II)‐ bearing ferrites ranged from 7 to 38 nm. The room‐temperature Mössbauer effect of the high‐vacancy‐content Zn(II)‐ bearing ferrite (x = 0.34–0.37, y 0.02, z = 0.62–0.65) revealed the superparamagnetic nature for ultrafine particle sizes less than 20 nm. The ferrite was transferred from superparamagnetic to ferrimagnetic with an increase in the particle size (>20 nm) at room temperature.
Grain‐Size Effects on Diffuse Phase Transitions of Sol‐Gel Prepared Barium Titanate Ceramics
Authors: Lobo R. P. S. M. , Mohallem Nelcy D. S. , Moreira Roberto L.
Published: September 2005

Barium titanate ceramic samples, obtained by sol‐gel methods, having different grain sizes have been analyzed by diffuse phase transition techniques. We performed a study of the influence of each method on the phase transition interval and on the Landau parameters of the ferroelectric phase transition of these materials. The results show the existence of a relationship between the diffuse character of the transition and the grain size of the sample. The method of fitting dielectric data presented here allows us to compare ceramics with single crystals and then analyze the sol‐gel process used to obtain them.
Determination of the Piezospectroscopic Coefficients for Chromium‐Doped Sapphire
Authors: He Jun , Clarke David R.
Published: September 2005

The coefficients of the piezospectroscopic tensor for a 0.05 wt% ruby are evaluated by direct measurement of the frequency shift for uniaxial compression along the three principal crystallographic directions and for loading in the three principal shear directions. Although the numerical value of the trace of the tensor is the same äs previously reported, the piezospectroscopic coefficients along the c and m directions are slightly different. Contrary to expectation from the rotational symmetry of sapphire about the c axis, the coefflcient along the a direction was found to be different from that along the m direction. It also varies nonlinearly with strain in the a direction. The difference is attributed to the applied stress breaking the rotational symmetry about the c axis and is interpreted in terms of the relative motion of the Cr3+ ion with respect to the nearest‐neighbor oxygen ions. An additional finding is that there is a signiflcant difference in the piezospectroscopic tensor for the Rl and R2 lines. This will facilitate a more complete determination of the stress tensor from fluorescence measurements than has hitherto been possible.
Grain Growth of ZnO in ZnO‐Bi2O3 Ceramics with TiO2 Additions
Authors: Suzuki Hironori , Bradt Richard C.
Published: September 2005

Grain growth of ZnO in liquid‐phase‐sintered ZnO‐Bi2O3ceramics containing systematic additions of TiO2 to the 0.55 wt% level has been studied for flring in air from 900° to 1400°C. The Bi2O3 melts during flring, and then the TiO2dissolves into the Bi2O3‐rich liquid. The TiO2 initially reacts with the Bi2O3 to form the compound Bi4Ti3Oi2. Above ∼1050°C, the Bi4Ti3O12 reacts with ZnO to form the Zn2TiO4 spinel phase. This results in two distinct regions of ZnO grain growth in this System; one below 1050°C, where the Bi4Ti3O12 affects the process, and the other above 1050°C, where the Zn2TiO4 spinel dominates. The exponent for ZnO grain growth decreases from 5 for TiO2‐free ZnO‐Bi2O3 to 3 for ZnO‐Bi2O3‐TiO2 at temperatures below 1050°C, but increases to 6 at temperatures above 1050°C. The exponents are related to the presence of Bi4Ti3O12 in the Bi2O3‐rich liquid phase below 1050°C and the Zn2TiO4particles that are present above 1050°C. The activation energy for grain growth of the ZnO is ∼300 kJ/mol below 1050°C, but 360 kj/mol above 1050°C. It is suggested that diffusion of ZnO through the Bi2O3‐rich liquid phase is the rate‐controlling mechanisrn for ZnO grain growth below 1050°C and that grain‐boundary drag by the pores and Zn2TiO4 spinel particles is the rate‐controlling mechanism above 1050°C.
Phase and Microstructure Evolution in Alkoxide‐Derived Mullite/MgO‐Partially‐Stabilized Zirconia
Authors: Lin Chien‐Cheng , Zangvil Avigdor , Ruh Robert
Published: September 2005

The microstructure and phase evolution of a mullite/MgO‐partially‐stabilized‐zirconia alkoxide‐derived composite was studied by XRD and TEM/EDS in samples hot pressed at 850° to 1400°C for various periods of time. Upon hot press‐ing, Al‐Si spinel, with a composition close to that of (2;1) mullite, crystallized at a temperature as low as 850°C. It converted to (3;2) mullite at temperatures above 1200°C. Eine spherical metastable cubic‐ZrO2 particles, uniformly distributed in the amorphous matrix, precipitated at T ∼ 850°C. They coarsened at higher temperatures and trans‐formed to tetragonal or monoclinic ZrO2, depending upon the grain size. These primary precipitates grew to become intergranular zirconia in the final structure. The solid solu‐tion of zirconia in mullite decreased with increasing temperature, so that secondary zirconia particles precipitated at higher temperatures and remained as inclusions inside mullite grains. Irregularly shaped elongated zircon was found at T ∼ 1200°C. It decomposed at higher temperatures to form zirconia particles, which existed at the grain bound‐aries of the final mullite. Other phases found in hot‐pressed samples included MgAl2O4 spinel and sapphirine (2MgO‐2Al2O3‐SiO2). For powders heat treated in air, γ‐Al2O3(instead of Al‐Si spinel) was formed at temperatures above 900°C. The γ→α‐Al2O3 phase transformation occurred at T 1300°C, followed by a rapid grain growth. In contrast with the hot‐pressed samples, mullite in heat‐treated powders crystallized only at temperatures above 1400°C. Previous studies on phase evolution during pressureless heat treatment of powders were generally unindicative of phase and microstructural evolution upon hot pressing.
Sol‐Gel Processing and Conduction Mechanism of RuO2‐Glass Thick‐Film Resistors
Authors: Yamaguchi Takashi , Nakamura Yuko
Published: September 2005

Sol‐gel processing was used to study the conduction mechanism in RuO2‐glass thick‐film resistors (TFRs). The relation between resistance and conductive particle concentration was studied on TFRs with uniformly dispersed RuO2 particles in lead silicate glass. The resistance‐concentration relation was best expressed by the percolation theory, whereas conventional TFRs showed a marked deviation. Conductivity measurements and Auger spectroscopy of glass films heated in contact with RuO2 films revealed appreciable dissolution of RuO2 in glass. Summarizing the experimental results, a percolation theory has been proposed as a possible conduction mechanism.
Defect Formation during Plastic Deformation of Y2O3‐Partially‐Stabilized ZrO2 Single Crystals
Authors: Baither Dietmar , Baufeld Bernd , Messerschmidt Ulrich
Published: September 2005

Y2O3‐partially‐stabilized ZrO2 single crystals have been deformed at 1400°C and subsequently investigated in the high‐voltage electron microscope. At an yttria concentration of 6.8 mol%, elongated planar defects with APB‐like contrast arose on four (101) planes. This unusual [101](101) glide system was activated due to a more favorable atomic arrangement of the planar defects on (101) planes instead of (010) ones.
Electrical Resistivity of Titanium Diboride and Zirconium Diboride
Authors: Rahman Matiur , Wang Ching C. , Chen Weihua , Akbar Sheikh A. , Mroz Cathleen
Published: September 2005

The electrical resistivities of hot‐pressed samples of Ti1‐xZrxB2 (x= 0.0, 0.3, 0.5, 0.7, 1.0) were measured by a four‐point ac technique over the range 298 to 1573 K in an argon atmosphere. The hot‐pressed samples for the intermediate compositions were found to be mixtures of two solid‐solution phases. The resistivities for all compositions were found to increase linearly with temperature and can be described by ρ(T) =ρ298+φ(T ‐ 298). The room‐temperature resistivity ρ298 (μΩ cm) and the temperature coefficient of resistivity φ (nΩ·cm/K) for ZrB2 were determined to be 7.8 and 10, both of which increase with the content of TiB2. These values for TiB2 were determined to be 20.4 and 36, respectively.
Investigation of Low‐Temperature‐Fired Strontium Titanate Multilayer Grain‐Boundary Layer Capacitors
Authors: Zhang Shuren , Zhong Chaowei , Qin Xiaoliang , Ye Yaohong
Published: September 2005

Newly developed low‐temperature‐flred semiconducting SrTiO3 ceramics were used to prepare multilayer grain‐boundary layer capacitors (MBLCs) based on the conventional manufacturing process for multilayer capacitors (MLCs). The compatibilities of ceramic materials with organic binder and inner electrodes and the effects of preparation methods were investigated. The experiment results showed that the method proposed by this study is a practicable technique for preparation of MBLCs.
Effect of Fictive Temperature on Dynamic Fatigue Behavior of Silica and Soda‐Lime Glasses
Authors: Li Hong , Agarwal Anand , Tomozawa Minoru
Published: September 2005

The dynamic fatigue characteristics of silica glasses with fictive temperatures of 1000°, 1100°, and 1300°C and soda‐lime glasses with fictive temperatures of 470° and 530°C were measured in air. For both glasses, samples with higher fictive temperatures had a greater fatigue resistance. Inert strength of silica glasses with flctive temperatures of 1000° and 1300°C was also measured at liquid nitrogen temperature. Glass with higher flctive temperature had a greater inert strength.
Simulation of Hardness Testing on Plasma‐Sprayed Coatings
Authors: Lin Chung‐Kwei , Lin Chung‐Chieh , Berndt Christopher C.
Published: September 2005

A plasma‐sprayed thermal barrier coating consisting of a NiCoCrAlY bond coat and Ce‐stabilized zirconia ceramic coating was heat‐treated at 400°C for 1000 h. Microhardness measurements were used to evaluate microstructural variations throughout the coating. One hundred and twenty measurements were performed at both the bond coat and ceramic coating positions within the thermal barrier coating system. Both data sets were analyzed to assess whether they could be described as Gaussian (i. e., “normal”) or Weibull distributions. The influence of the sample size, i. e., the number of microhardness tests for a group, on the mean hardness value was also evaluated by a Monte Carlo simulation procedure. The mean value, the standard deviation, the coefficient of variation, and the Weibull modulus for the subsets of data were calculated to assess these effects. The confidence for the mean value was also considered. The results indicated that the reliability of the microhardness test improved as the sample size increased. At least 20 measurements were needed to distinguish differences in micro‐hardness between the bond coat and the ceramic coating at a 95% confidence level.
Direct Observation of Channel Structures in Zeolite Y and A with a Slow‐Scan, Charge‐Coupled‐Device Camera
Authors: Sasaki Yukichi , Suzuki Toshiyuki , Ikuhara Yuichi , Saji Akira
Published: September 2005

Zeolite materials are very sensitive to electron beam irradiation. Therefore, there have been only limited attempts to characterize their structures using high‐resolution electron microscopy (HREM). The sensitivity to the electron beam depends strongly on the Si/Al ratio in zeolites. A slow‐scan, charge‐coupled‐device (CCD) camera provides the possibility to observe materials using HREM with very low beam doses. In this study, this method was applied to observe sensitive materials such as zeolite type A and type Y, and HREM images were recorded without any damage caused by electron irradiation under a dose density less than 0. 2 A /cm2. It was found that fine channel structures, cleavage planes, and the electron irradiation process in the zeolites could be characterized using HREM with the slow‐scan CCD camera.
Formation and Characterization of Ce3ZrO8 Prepared by the Hydrazine Method
Authors: Hirano Shingo , Kawabata Akio , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: September 2005

A compound denoted as (Ce0.75Zr0.25)O2 (Ce, ZrO8) is formed near room temperature from cerium and zirconium nitrates using hydrazine monohydrate. It has a cubic unit cell with a= 0.5342 nm. Characterization of powders heated to various temperatures at 10°C/min demonstrates that the specific surface area does not decrease below 20 mVg until >1000°C.
Formation of Silicon Nitride Film by Plasma Decomposition of Methylsilazane
Authors: Moriwaki Takayuki , Matsumoto Osamu
Published: September 2005

Si3N4 thin films were deposited on silicon wafer or α‐Al2O3wafer substrates from methylsilazane in a microwave nitrogen‐hydrogen‐mixture plasma at substrate temperatures of 590 to 1000 K. The deposits were identified by IR spectroscopy and XPS as approximately stoichiometric Si3N4, and they contained small amounts of impurities. Decomposition of the methylsilazane in the plasma may be one of the reasons for the lower deposition temperature of the Si3N4.
Fabrication of Glass Matrix Composites by Tape Casting
Authors: Gustafson Cathleen M. , Button Rollie E. , Kerans Ronald J.
Published: September 2005

A method has been developed to fabricate borosilicate glass matrix composites reinforced with monofilament SiC fibers by tape casting. Green matrix tapes are laminated with fiber mats of a uniform fiber spacing. The resulting laminate is sintered at 710°C to >98% relative density and HIP‐consolidated to full density. The final specimens contain a high volume fraction of fibers (>35 vol%) in a uniform array. A variation of this technique can be used to mount “microcomposites” (i.e., coated fibers) in a glass matrix to facilitate fabrication of push‐out test specimens.
Synthesis and Friction Behavior of Chemically Vapor Deposited Composite Coatings Containing Discrete TiN and MoS2 Phases
Authors: Bae Yong W. , Lee Woo Y. , Yust Charles S. , Blau Peter J. , Besmann Theodore M.
Published: September 2005

Composite coatings containing discrete crystalline phases of TiN and MoS2 were deposited on Si, graphite, and Ti‐6A‐14V alloy substrates by simultaneous chemical vapor deposition. MoF6 and H2S were utilized as the precursors for MoS2 formation, while Ti((CH3)2N)4 and NH3 were used for TiN deposition. The composition and microstructure of the coatings were investigated by X‐ray diffraction, Auger electron spectroscopy, and transmission electron microscopy. The molar ratios of TiN and MoS2 in the composite microstructure could be controlled by adjusting the MoF6concentration in the reagent mixture. Encouraging friction and wear characteristics against silicon nitride were obtained for a composite coating which was rich in MoS2 at the coating surface, with TiN as the major phase near the substrate interface. Friction coefficients at room temperature in air were typically in the range of 0.07 to 0.3. The friction coefficients remained comparable at 573 K, but increased to 0.7 to 1.0 at 673 K. A friction coefficient value of −0.3 was, however, obtained from a composite coating tested at 973 K.
Microstructure of TiO2 and ZnO Films Fabricated by the Sol‐Gel Method
Authors: Ohya Yutaka , Saiki Hisao , Tanaka Toshimasa , Takahashi Yasutaka
Published: September 2005

Titanium dioxide and zinc oxide films were fabricated by spin‐on and dip‐coating methods. Both types of films exhibited columnar grains when the single coating was thin, ∼10 nm. The columnar TiO2 films were dense, as confirmed by their density values calculated from the refractive index and TEM results. The addition of Al cations into the ZnO suppressed grain growth, because Zn had a lower diffusivity in the doped films. The doped ZnO films had nearly the same electrical resistivity as that of the undoped films.
Influence of Granule Character and Compaction on the Mechanical Properties of Sintered Silicon Nitride
Authors: Takahashi Hideo , Shinohara Nobuhiro , Uematsu Keizo , JunIchiro Tsubaki
Published: September 2005

The influence of granule character and compaction on the mechanical properties of sintered silicon nitride was studied as a function of the pH of the spray‐dry slurry. The character and the compaction behavior of the spray‐dried silicon nitride granules considerably affect the mechanical properties of the sintered body. Dense and hard granules resulting from a well‐dispersed slurry retained their shape in green compacts and caused numerous pore defects in sintered body. Decreasing the slurry pH to a certain value (e.g., 7.9) caused slurry flocculation and reduced the granule density as well as the diametral compression strength of the granules. Sintered bodies fabricated with these weak granules contained fewer defects and showed remarkable strength increase.
Fracture Toughness of 2‐D Woven SiC/SiC CVI‐Composites with Multilayered Interphases
Authors: Droillard Christine , Lamon Jacques
Published: September 2005

Relations between fracture toughness and fiber/matrix interphases were examined on various SiC/SiC composites made by chemical vapor infiltration (CVI) and reinforced with woven fiber bundles. Strong and weak fiber/matrix bondings were obtained using multilayered interphases consisting of various combinations of carbon and SiC layers of different thickness and using fibers which had been previously treated. Fracture toughness was estimated using the J‐ integral and using strain energy release rate computed with a model taking into account the presence of a process zone of matrix microcracks. Both approaches evidenced similar trends. It appeared that higher toughness was obtained with those composites possessing strong interphases and subject to dense matrix microcracking.
Crack Initiation in Borosilicate Glass‐SiC Fiber Composites
Authors: Dutton Rollie E. , Pagano Nicholas J. , Kim Ran Y.
Published: September 2005

The initiation of matrix microcracking was investigated in unidirectional glass matrix composites having controlled fiber spacing. Observations were taken from composites consisting of regular arrays of TiB2‐coated SIGMA 1240 and carbon‐coated SCS‐6 monofilament SiC fibers in a series of borosilicate glasses. The thermal expansion mismatch between the fibers and glass matrix was varied such that the resulting radial stresses after processing ranged from tensile to compressive. The glass strongly bonds to the TiB2‐coated SIGMA 1240 fiber but weakly bonds to the carbon coating of the SCS‐6 fiber, allowing the investigation of the effects of bonding at the fiber/matrix interface. The observed crack initiation stresses of the various composites are compared to predictions based on a previously developed semiempirical model and used to study the influence of the volume fraction of fibers, residual stress state and interface strength.
Reactive Wetting in the Liquid‐Silicon/Solid‐Carbon System
Authors: Li Jian‐Guo , Hausner Hans
Published: September 2005

The wettability of glassy carbon by liquid silicon has been investigated at 1430°C in argon by using techniques of both in situ formation and capillary formation of sessile drops. Analyses of the results showed that there are three distinct contributions of reaction to wetting: (a) dissolution of solid substrate carbon in liquid silicon; (b) formation of a continuous SiC layer at the solid side of the interface, and (c) a contribution of the free energy released by the reaction localized at the interface between liquid silicon and solid carbon.
Synthesis of Lead Barium Niobate Powders and Thin Films by the Sol‐Gel Method
Authors: Sakamoto Wataru , Yogo Toshinobu , Kikuta Ko‐ichi , Arimoto Tadashi , Hirano Shin‐ichi
Published: September 2005

Crack‐free, dense, and transparent Pb0.6Ba0.4Nb2O6 (PBN60) thin films have been prepared by a sol‐gel method with metal alkoxides and metal acetate. A homogeneous and stable precursor solution was obtained from Ba metal, Pb(CH3COO)2, and Nb(OEt)5 in 2‐methoxyethanol. PBN60 powder crystallized to the hexagonal phase at 600°C and then completely transformed to the orthorhombic phase of the tungsten bronze structure at 1250°C. The hexagonal phase was formed on SiO2 glass, MgO(lOO), and sapphire(R) substrate at 600°C, while the orthorhombic phase was only on a sapphire(C) substrate. Orthorhombic PBN60 films with c‐axis preferred orientation were successfully synthesized on sapphire(C) substrates at 600°C.
Thermally Activated Martensitic Transformations in Mg‐PSZ
Authors: Behrens Gesa , Heuer Arthur H.
Published: September 2005

The thermally activated, stress‐assisted martensitic tetragonal → monoclinic (t→m) and tetragonal → orthorhombic (t→o) transformations in a high‐toughness Mg‐PSZ were investigated by monitoring the phase assemblage with Raman spectroscopy after a variety of heat treatments and loading conditions. After a short anneal at 1000°C, which transforms m‐ and o‐ZrO2 to the t polymorph, isothermal t→m and t→o transformations occur at room temperature during the months following the anneal. The transformation rates in the annealed samples are greatly enhanced under external stress. Alternatively, samples containing regions of significant residual stress, introduced by indentation for example, and then annealed at relatively low temperatures, underwent additional thermally activated transformation in the stressed regions. The thermodynamics and kinetics of this complex transformation “plasticity,” and its effect on mechanical properties, are discussed.