bluuebunny/crossref_metadata_2025 huggingface dataset:
Texture Assessment of Magnetically Processed Iron Titanate
Authors: Zimmerman Michael H. , Faber K. T. , Fuller Edwin R. , Kruger Keith L. , Bowman Keith J.
Published: September 2005

Untextured and highly textured iron titanate specimens were produced by vacuum filtering iron titanate‐ethanol suspensions in the absence and presence of a strong magnetic field, respectively. Crystallographic texture was assessed by measuring X‐ray pole figures on surfaces parallel and perpendicular to the field direction for several peaks in each system. Morphological texture was assessed by measuring grain size as a function of angle to a reference direction. Results indicate that magnetic field processing imposes a strong, fiber‐type texture on the order of 30 times random, with the b‐axis parallel to the applied field. Additionally, morphological texturing is absent for the grain sizes studied in this work.
Raman Line Widths in Rare‐Earth Sesquisulfide Solid Solutions
Authors: Knight Diane S. , White William B.
Published: September 2005

High‐resolution Raman spectra were measured on two solid solution series of rare‐earth sesquisulfldes: The La2S3‐Gd2S3sequence with the orthorhombic a structure and the Dy2S3‐Er2S3 sequence with the monoclinic δ structure. Precise line widths, measured on the most intense line, showed a pronounced maximum in the middle of the solid solution series, demonstrating the relationship between Raman line width and structural disorder. The magnitude of the effect scaled with the difference in ionic radii of the cations making up the solid solution.
Subsurface Defect Detection in Ceramics Using an Optical Gated Scatter Reflectometer
Authors: Bashkansky Mark , Battle Phillip R. , Duncan Michael D. , Kahn Manfred , Reintjes J.
Published: September 2005

We demonstrate the use of optical gating techniques for determining the size and location of defects in advanced ceramic materials. The subsurface region in various silicon nitride ceramic materials is probed using an optical gated reflectometer based on a low‐coherence fiber interferometer. Experimental results indicate that the size and distribution of small subsurface defects can be determined with depth and lateral resolutions of 10 and 7 μm, respectively.
High‐Frequency Piezoceramic Equivalent Circuit
Authors: Ballato Arthur , Ballato John
Published: September 2005

Ferroelectric ceramics are strong candidates to provide thin‐film resonant microstructures for future telecommunications applications. The frequency ranges of greatest commercial interest are the VHF and UHF bands. In these bands it is especially difficult to obtain adequate and reproducible characterizations of resonance behavior. We have developed a highly accurate equivalent network for these frequencies. Descriptions in circuit terms permit representation of the ceramic properties in a form directly accessible to the designer of the equipment in which the resonator will be embedded. In this communication we introduce the new network, and give typical parameters for a practical application.
Ultrafine Spinel Powders by Flame Spray Pyrolysis of a Magnesium Aluminum Double Alkoxide
Authors: Bickmore Clint R. , Waldner Kurt F. , Treadwell David R. , Laine Richard M.
Published: September 2005

Ultrafine crystalline spinel powder has been prepared using flame spray pyrolysis of alcoholic solutions of a novel double alkoxide precursor. The particles produced are spherical, dense, single crystals with diameters of 10–100 nm and specific surface areas ranging from 40 to 60 m2/g. Powder production rates of 50–100 g/h are achieved using a bench‐top apparatus. Particle formation appears to occur by rapid oxidation of the organic ligands followed by nucleation and growth from oxide species.
Sol‐Gel Processing and Pyroelectric Properties of Highly Oriented Pb(Mg,Zn)1/3Nb2/3O3 Thin Films
Authors: Jang Hyun M. , Cho Mun K.
Published: September 2005

Thin films of Pb(Mg,Zn)1/3Nb2/3O3 (PMZN) were fabricated by spin casting the partially hydrolyzed Pb‐Mg‐Zn‐Nb‐O complex alkoxide sols on (111)Pt‐coated MgO (100) planes. A strong preferential orientation of (100) perovskite was observed in the thin film derived from the sol exhibiting pseudoplastic behavior. A small‐angle X‐ray scattering experiment in the Porod region was performed to correlate the observed preferential orientation with the network structure of precursor in the PMZN sol. It was shown that weakly branched precursor systems led to highly oriented perovskite grains after thin‐film formation. The highly (100) oriented PMZN film exhibited a larger pyroelectric coefficient (>2 μC/(cm2‐K)) and pyroelectric figure‐of‐merit (FD > 4 × 101–4 Pa−1/2) than the PMZN thin film having randomly oriented grains.
Formation of Complex Ceramic Miniaturized Structures by Pyrolysis of Poly(vinylsilazane)
Authors: Freimuth Herbert , Hessel Volker , Kölle Harald , Lacher Manfred , Ehrfeld Wolfgang , Vaahs Tilo , Brück Martin
Published: September 2005

Complex ceramic miniaturized structures that have much smaller dimensions and better precision than that which has been reported previously were prepared by a combination of X‐ray synchrotron lithography, casting, and pyrolysis processes. Poly(methyl methacrylate) and poly(tetrafluorethylene) miniaturized structures were prepared with high precision via a combination of X‐ray synchrotron lithography, electroplating, and molding (the German Lithographie, Galvanoformung, and Abformung (LIGA) process). Casting of a solution of a preceramic polymer, poly(vinylsilazane), in these miniaturized structures was performed for the first time, similar to the slurry‐casting technique of macroscopic bodies. Subsequent pyrolysis led to nearly perfect, complementary bodies of the original structures because of the high smoothness of the pyrolyzed ceramics. This was demonstrated by the complex spool and meander‐like miniaturized structures with internal dimensions <2 μm and an aspect ratio as high as 5. To evaluate optimal process parameters for the preparation of these complex ceramic miniaturized structures, the pyrolysis process of poly(vinylsilazane) was investigated using Fourier transform infrared spectrometry, X‐ray diffractometry, atomic force microscopy, and scanning electron microscopy. The first step of pyrolysis involved dehydrocoupling of –CH and –NH groups and nucleophilic substitution of the Si–CxHy groups, which led to the elimination of the CxHy substituents and the formation of an amorphous silicon carbonitride (Si:C:N) at 800°C. The residual hydrogen content, which was chemically bonded as Si‐H, decreased as temperatures decreased from 800° to 1400°C. Heating to 1500°C converted the amorphous structure to a semicrystalline phase‐separated ceramic composed of α‐Si3N4 crystals embedded in a carbon‐silicon amorphous matrix. The amorphous phase could be partially etched with a KOH solution. Because of the absence of grains, the amorphous material revealed a much smoother surface than that of the crystalline material or that possible by conventional slurry processes.
Self‐Consistent Method to Calculate Fiber Interactions in a SiC/Al2O3 Ceramic Composite
Authors: Bertinetti María A. , Turner Pablo A. , Bolmaro Raú E. , Tomé Carlos N.
Published: September 2005

The sintering of Al2O3/SiC ceramic composite leads to a state of high internal stresses in the composite material at room temperature because of the difference in thermal contraction between matrix and particles. It has been shown in a previous work1 that the interaction among fibers must be accounted for in order to predict correctly the residual stresses. In the present paper we develop a numerical scheme that permits taking into account such interaction for an arbitrary distribution of fiber directions (DFD) and for completely anisotropic properties of the phases. We apply the formulation to calculate the average strain in the matrix (due to the interaction among fibers) and the effective thermal coefficients of the composite. We find that the average strain in the matrix depends strongly on the DFD and that the predictions agree with measurements done by Majumdar and Kupperman.3 We prove that the effective thermal coefficients of the composite are not sensitive to the DFD when the matrix and the fibers exhibit isotropic thermal and elastic properties. Finally, we analyze the effect of the DFD and of the fiber interaction on the internal stresses inside the SiC fibers and compare with experimental values.
Effect of Incorporation of Nitrogen on the Structure and Dielectric Properties of Modified Oxide Sol‐Precipitated Borosilicate Glasses and Glass‐Ceramics
Authors: K Jin Yong , Hsu Richard , Kumta Prashant N.
Published: September 2005

Glasses and glass‐ceramics have received considerable attention as substrate materials in electronic packaging because of their low (<5) dielectric constant at 1 MHz. It is also known that low molecular weight species lower the contribution to electronic polarization which is primarily responsible for changes in the dielectric constant at these frequencies. In this study, borosilicate gels have been synthesized using a modified oxide sol‐precipitation process utilizing oxide precursors. Nitridation of these gels has been initiated by combining air and ammonia heat treatments at different temperatures. The effects of incorporation of nitrogen on the structure of these gels have been studied using scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR). Similarly, the effects of nitrogen on the densification behavior of these gels have also been analyzed. At the same time, the dielectric constants of these glasses have been measured using impedance techniques. FTIR results indicate that the incorporation of nitrogen helps to decrease the borosiloxy (B‐O‐Si) bonds, causing a corresponding increase in B‐N and Si‐N bonds. Introduction of nitrogen into the gel network was seen to retard the densification kinetics and delay the crystallization onset for most of the nitrided glasses, while causing a gradual lowering of the dielectric constant.
Microstructure and Crystallographic Orientation of Anatase Coatings Produced from Chemically Modified Titanium Tetraisopropoxide
Authors: Kato Kazumi , Tsuge Akira , Niihara Ko‐ichi
Published: September 2005

Poly(ethylene glycol) was coordinated to a structure formed by the controlled hydrolysis and polycondensation reactions of titanium tetraisopropoxide chelated with diethanolamine. From the resulting chemically modified precursor solution, anatase coatings consisting of nanometer‐sized pores and grains with diameters of ∼30 nm and a preferred orientation along the c‐axis were prepared on quartz‐glass plates by a dip coating method. In contrast, anatase coatings consisting of submicrometersized pores and randomly orientated grains were prepared from the solution in which the poly(ethylene glycol) had been isolated.
Atmosphere Control of Interface Migration and Its Effect on Dielectric Property of CuO‐Infiltrated Strontium Titanate
Authors: Jeon Jae‐Ho , Kim Joo Seon , Kang Suk‐Joong L. , Yang Myung Seung
Published: September 2005

The control of interface migration and its effect on dielectric properties of SrTiO3 based materials have been investigated. SrTiO3 specimens with or without Nb2O5 doping were prepared, and the atmospheres of sintering and heat treatment were varied during the processing. It has been demonstrated that the change in defect structure at the interface of Nb‐doped SrTiO3 grains by atmosphere change was the cause of interface migration observed during CuO infiltration or heat treatment. The interface migration caused by sintering in a reducing atmosphere and infiltration in air could be suppressed by preoxidizing grain interfaces before the CuO infiltration in air. The suppression of migration increased the effective dielectric constant of the material.
Indentation Thermal Shock Test for Ceramics
Authors: Andersson Tomas , Rowcliffe David J.
Published: September 2005

This paper presents an indentation‐quench method to determine the resistance of ceramics to thermal cycling. The method defines a critical quench temperature difference, ΔTc, based on a criterion which includes a minimum amount of crack growth and a minimum fraction of growing cracks. The method is applied to three different materials, which are ranked according to the individual values of ΔTc. The variation of ΔTc with different indentation loads and indentation positions is investigated. This technique uses a small number of specimens, avoids subsequent mechanical testing, and provides information about the ΔTC of the materials. The effect of repeated cycling on crack extension is also discussed.
Vacuum Plasma Spray Deposition of Titanium Particle/Glass‐Ceramic Matrix Biocomposites
Authors: Ferraris Monica , Rabajoli Paolo , Paracchini Luigi , Brossa Francesco
Published: September 2005

The vacuum plasma spray technique (VPS) has been successfully employed to coat Ti‐6A1‐4V substrates with bioactive glasses and Ti‐particle/glass‐ceramic matrix biocomposites. The composites were prepared by sintering, under an Ar flow, green bars of bioactive glass powders and 30% volume Ti particles. The bioactive glasses have the two following compositions: SCB (48.8SiO2−48.8CaO−2.4B2O3) and TSCB (46.6SiO2−48.7CaO−2.5B2O3−2.2TiO2) (mol%). The VPS bioactive coatings were characterized by means of scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X‐ray diffraction (XRD), and mechanical tests (Vickers indentations and tensile and shear tests). Their bioactivity was tested by soaking the samples in a simulated body fluid (SBF) and by analyzing the growth of hydroxylapatite (HA) by SEM, EDS, and XRD. Leaching tests of Ca, Si, and P in SBF were made by inductively coupled plasma‐atomic emission spectroscopy (ICP‐AES, Perkin‐Elmer 5000) to study the in vitro bioactivity of the samples versus time. Each coating was found to be bioactive and well bonded to the substrate; the composites showed better mechanical properties than the pure glass matrices and the hydroxylapatite coatings deposited by the same VPS technique.
High‐Temperature Tensile Behavior of a Boron Nitride‐Coated Silicon Carbide‐Fiber Glass‐Ceramic Composite
Authors: Sun Ellen Y. , Nutt Steven R. , Brennan John J.
Published: September 2005

Tensile properties of a cross‐ply glass‐ceramic composite were investigated by conducting fracture, creep, and fatigue experiments at both room temperature and high temperatures in air. The composite consisted of a barium magnesium aluminosilicate (BMAS) glass‐ceramic matrix reinforced with SiC fibers with a SiC/BN coating. The material exhibited retention of most tensile properties up to 1200°C. Monotonic tensile fracture tests produced ultimate strengths of 230–300 MPa with failure strains of ∼1%, and no degradation in ultimate strength was observed at 1100° and 1200°C. In creep experiments at 1100°C, nominal steady‐state creep rates in the 10−9 s−1 range were established after a period of transient creep. Tensile stress rupture experiments at 1100° and 1200°C lasted longer than one year at stress levels above the corresponding proportional limit stresses for those temperatures. Tensile fatigue experiments were conducted in which the maximum applied stress was slightly greater than the proportional limit stress of the matrix, and, in these experiments, the composite survived 105 cycles without fracture at temperatures up to 1200°C. Microscopic damage mechanisms were investigated by TEM, and microstructural observations of tested samples were correlated with the mechanical response. The SiC/ BN fiber coatings effectively inhibited diffusion and reaction at the interface during high‐temperature testing. The BN layer also provided a weak interfacial bond that resulted in damage‐tolerant fracture behavior. However, oxidation of near‐surface SiC fibers occurred during prolonged exposure at high temperatures, and limited oxidation at fiber interfaces was observed when samples were dynamically loaded above the proportional limit stress, creating micro‐cracks along which oxygen could diffuse into the interior of the composite.
Grain Size Effect on Creep Deformation of Alumina‐Silicon Carbide Composites
Authors: Lin Hua‐Tay , Alexander Kathleen B. , Becher Paul F.
Published: September 2005

A study of the flexural creep response of aluminas reinforced with 10 vol% SiC whiskers was conducted at 1200° and 1300°C at stresses from 50 to 230 MPa in air to evaluate the effect of matrix grain size. The average matrix grain size was varied from 1.2 to 8.0 μm by controlling the hot‐pressing conditions. At 1200°C, the creep resistance of alumina composites increases with an increase in matrix grain size, and the creep rate (at constant applied stress) exhibits a grain size exponent of approximately 1. The stress exponent of the creep rate at 1200°C is approximately 2, consistent with a grain boundary sliding mechanism. On the other hand, the creep deformation rate of 1300°C was not sensitive to the alumina grain size. This was seen to be a result of enhanced nucleation and coalescence of creep cavities and the development of macroscopic cracks as the grain size increases. Observations also indicated that the prevalent site for nucleation and growth of creep cavities in coarsegrained materials is at two‐grain junctions (grain faces), whereas in fine‐grained materials cavities nucleate primarily at triple‐grain junctions (grain edges). Electron microscopy studies revealed that the content of any amorphous phase present at whisker‐alumina interfaces is independent of alumina grain size (and hot‐pressing conditions). In addition, the alumina grain boundaries are quite devoid of amorphous phase(s). This variation in amorphous phase content does not appear to be a factor in the present creep results.
Preparation and Properties of Borosilicate‐Coated Alumina Particles from Alkoxides
Authors: Harmer Mark A. , Bergna Horacio , Saltzberg Michael , Hu Yu H.
Published: September 2005

This paper describes the synthesis of borosilicate‐coated alumina particles. Coated particles are agglomerate‐free and contain up to 50 vol% coating. The ability to form uniform coatings is highly dependent upon both the solution chemistry and the control of the nucleation and growth of the borosilicate on the alumina. The coated particles show markedly improved densification compared to that of a mechanical mixture of borosilicate and alumina. These composite powders (borosilicate‐coated alumina particles) are moisture‐sensitive, resulting in a leached, phase‐separated, boric oxide. The particles can be stabilized by further encasing the particle with a thin layer of silica.
Evaluation of Brazed Silicon Nitride Joints: Microstructure and Mechanical Properties
Authors: Peteves Stathis D. , Nicholas Michael G.
Published: September 2005

Sintered Si3N4 has been bonded to itself and to AISI 316 steel by the active‐metal brazing route. A commercial Ag‐35Cu‐1.6Ti filler has been used with joining taking place during a 30 min hold at 850°C under vacuum. Si3N4/ Si3N4 joints have been produced with strength distribution (average bend strength = 773.5 MPa, Weibull modulus = 11.2) similar to that of the monolithic ceramic. Direct brazing of the Si3N4 to AISI 316 steel was unsuccessful. However, reliably strong (bend strength of 250–400 MPa) ceramic/ steel joints with 20 × 20 mm2 cross sections were fabricated by using Cu, Mo, or Nb interlayers. The most potent inter‐layer used in this work was Mo, whose coefficient of thermal expansion matches best that of the ceramic.
Mechanism of Phase Formation in Pb(ZrxTi1–x)O3 Synthesized by a Partial Oxalate Method
Authors: Leite Edson R. , Cerqueira Marinalva , Perazoli Lenig A. , Nasar Ricardo S. , Longo Elson , Varela José A.
Published: September 2005

The phase formation mechanism, as well as the morpho‐tropic phase boundary, of lead zirconate titanate (PZT) processed by a partial oxalate method was investigated by simultaneous thermal analysis (TG‐DTA) and by qualitative and quantitative X‐ray diffraction (XRD). The results show that the ZrxTi1–xO2 (ZT) phase reacts with PbO forming the PZT phase without intermediate phases. XRD analysis showed the coexistence of rhombohedral and tetragonal phases for 0.47 ≤x≤ 0.55 with the phase boundary composition for x= 0.51. For low calcination temperatures, preferential formation of the PZT rhombohedral phase was observed. A model for phase formation of PZT by the partial oxalate method is proposed based on the existence of two interfaces of reaction (PbO‐PZT and PZT‐ZT) and diffusion of cations.
Structural Degradation of Tobermorite during Vibratory Milling
Authors: Sasaki Kaori , Masuda Tsuguya , Ishida Hideki , Mitsuda Takeshi
Published: September 2005

Mechanochemistry of hydrothermally prepared Al‐free and Al‐substituted 1.1 nm tobermorite was studied using 29Si NMR, XRD, and TGA‐DTA. Tobermorite has a double‐chain structure and Al/Si substitution occurs preferentially at bridging tetrahedra. By using the vibration mill, both tobermorites were observed to decompose as a function of milling time to form amorphous C‐S‐H‐like phases. The decomposition rate was higher for the Al‐substituted tobermorite. The decomposition process occurs mainly at the bridge portion of the silicate double chain. In the Al‐substituted tobermorite, the breakage seems to occur preferentially at the points where Al has replaced Si. On heating the amorphous C‐S‐H‐like phase, wollastonite is formed. However, no decrease was observed at the wollastonite formation temperature.
Fabrication of Dense, Shaped Barium Cerate by the Oxidation of Solid Metal‐Bearing Precursors
Authors: Schmutzler Hans J. , Sandhage Kenneth H. , Nava Juan C.
Published: September 2005

Some rare‐earth‐doped alkaline‐earth cerates (e.g., Nd2O3‐doped BaCeO3) are proton conductors that can act as solid state electrolytes in hydrogen or steam sensors, hydrogen pumps, steam electrolyzers, and fuel cells. In the present study, dense tapes of neodymia‐doped barium cerate were produced by the oxidation of malleable Ba‐CeH3‐Nd2O3precursor tapes. Precursor tapes were produced by cold‐rolling either blended or milled mixtures of Ba, CeH3, and Nd2O3 within a silver can. X‐ray diffraction, electron microprobe analyses, and thermogravimetric analyses were used to study the phase transformations resulting from heat treatments conducted at 300° to 900°C in pure, flowing oxygen. Barium peroxide and cerium dioxide, produced during oxidation at ≤300°C, reacted at ≤500°C to form barium cerate. The rate of formation of barium cerate depended on the degree of milling of the solid metal‐bearing precursor powder. Dense barium cerate tapes were obtained after heat treatment at 1080°C.
17O MAS NMR Investigation of the Structure of Calcium Silicate Hydrate Gel
Authors: Cong Xiandong , Kirkpatrick R. James
Published: September 2005

This paper presents the results of a systematic investigation of the structure of hydrothermally synthesized calcium silicate hydrate gel using 17O MAS NMR at 11.7 T and MAS frequencies up to 12 kHz. The results support the previously proposed defect‐tobermorite structural model for C‐S‐H. At least six O‐sites have been identified, two NBO, BO, Ca‐OH, Si‐OH, and H2O. The compositional variation of the relative intensities of the signal for different sites measured by 17O NMR is consistent with that calculated from 29Si NMR results for the same samples. The chemical shifts of the NBO and BO sites become more deshielded (more positive) with increasing C/S ratio.
Point Defects of La2CuO4‐Based Ceramics, Part I: Oxygen Interstitials
Authors: Wu Yue , Ellis Donald E. , Shen Li , Mason Thomas O.
Published: September 2005

Theoretical and experimental studies are reported on oxygen excess defect structure of lanthanum cuprate, La2CuO4+δ. The local density functional formalism is applied to theoretical analysis. The self‐consistent discrete variational method has been used to find energy levels, densities of states, charge transfer, wavefunctions, and potentials for a fragment consisting of N (30–44) atoms embedded in the infinite crystal. Calculations have been performed on three interstitial oxygen models, with and without local relaxations. These models include sites proposed on the basis of neutron diffraction and interstitial dimers [O2]q. The dimer charge q is found to be consistent with that of normal oxygens, and not ‐1 as proposed in “superoxide” models. Electrostatic energies are used to estimate the relative stabilities of the proposed interstitial structures. The experimental Seebeck coefficient also shows that the charge of interstitial oxygen is ‐2. Effective atomic configurations for the ideal lattice are compared with those in the vicinity of the defects, and defect‐related spectro‐scopic consequences are examined.
Barium Neodymium Titanate Electroceramics: Phase Equilibria Studies of Ba6–3xNd8+2xTi18O54 Solid Solution
Authors: Cruickshank Karen M. , Jing Xiping , Wood Graeme , Lachowski Eric E. , West Anthony R.
Published: September 2005

A solid‐solution phase with the general formula Ba6‐3x Nd8+2x Ti18O54, where 0.25(5) ≤×≤ 0.75(5), has been characterized at 1250°C; this phase has been variously described as BaNd2Ti4O12 and BaNd2Ti5O14 in the literature. Variation in its stoichiometry is accommodated via the cation substitution mechanism, 3Ba2⇆2Nd3+. The location and extent of the solid solution were demonstrated by a combination of phase diagram studies and X‐ray diffraction techniques, including lattice parameter measurements and electron microscopy. A combination of techniques was employed due to the insensitivity of secondary phase detection by X‐ray diffraction in this system. Using this approach, a second possible solid‐solution mechanism, Ba2+2Nd3+⇆2Ti4+, is discounted.
Sources of Strain‐Measurement Error in Flag‐Based Extensometry
Authors: Luecke William E. , French Jonathan D.
Published: September 2005

This paper examines the sources of error in strain measurement using flag‐based extensometry that uses either scanning laser or electrooptical extensometers. These errors fall into two groups: errors in measuring the true gauge length of the specimen, which arise from the method of attachment of the flags, and errors arising from unanticipated distortions of the specimen during testing. The sources of errors of the first type include gauge‐length errors from nonparallel flags and uncertainties in the true attachment point of the flag. During the test, strain‐measurement errors of the second type can arise from horizontal translation of nonparallel flags, flag rotation that is induced by slippage, and flag motion from bending of the gauge length. Proper care can minimize the effect of these potential errors, so that flag‐based extensometry can give accurate strain measurement, if appropriate precautions are taken. Measurements on silicon nitride indicate that the strain measurements are accurate to better than 10%.
Effect of Composition on the Oxygen Tracer Diffusion in Transparent Yttrium Aluminium Garnet (YAG) Ceramics
Authors: Sakaguchi Isao , Haneda Hajime , Tanaka Junzo , Yanagitani Takakimi
Published: September 2005

The grain boundary structure and oxygen tracer diffusion in transparent yttrium aluminum garnet (YAG) ceramics varying from 2% excess of Y2O3 to 0.5% excess of Al2O3 were studied. The characterization of the specimens is as follows: (i) For the Y2O3‐excess specimen, a second phase (yttrium aluminum perovskite: YAP) containing silicon in the grain boundary was found, (ii) For the Al2O3‐excess specimen, both aluminum‐rich particles (alumina) and a silicon‐rich segregant layer were observed in the grain boundary. The volume diffusion of the oxygen tracer is little influenced by the excess composition. In contrast, the grain boundary diffusion of the oxygen tracer is suppressed in the Y2O3‐excess specimens, compared to Al2O3‐excess specimens. These differences are thought to result from the chemical reaction between the second phase and the intergranular liquid phase during the sintering.
Impedance Spectroscopy of Undoped BaTiO3Ceramics
Authors: Hirose Naohiro , West Anthony R.
Published: September 2005

The electrical properties of ceramic BaTiO3were investigated by ac impedance spectroscopy over the ranges 25°‐330°C and 0.03 Hz‐1 MHz. Results are compared with those obtained from fixed‐frequency measurements, at 1 kHz and 100 kHz. Fixed‐frequency Curie‐Weiss plots show deviations from linearity at temperatures well abovetc. The ac measurements show that grain boundary impedances influence Curie‐Weiss plots in two ways: at high temperatures, they increasingly dominate the fixed‐frequency permittivities; at lower temperatures, closer toTc, the high‐frequency permittivity contains a contribution from grain boundary effects. Methods for extraction of bulk and grain boundary capacitances from permittivity and electric modulus complex plane plots are discussed. The importance of selecting the appropriate equivalent circuit to model the impedance response is stressed. A constriction impedance model for the grain boundary in BaTiO3ceramics is proposed: the grain boundary capacitance is neither temperature‐independent, nor shows Curie‐Weiss behavior. The grain boundary is ferroelectric, similar to the grains, but its impedance is modified by either air gaps or high‐impedance electrical inhomogeneity in the region of the necks between grains; the activation energy of theconstriction grain boundaryimpedance differs from that of the bulk, suggesting differences in defect states or impurity levels.
Domain Boundary and Domain Switching in a Ceramic Rare‐Earth Orthoniobate LaNbO4
Authors: Jian Li , Wayman C. Marvin
Published: September 2005

By using TEM and X‐ray diffraction, the domain structure in ceramic LaNbO4 has been studied. It has been found that the domains have two different orientations, separated by a boundary with_irrational Miller indexes between (20)I/ (402)II and (20)I/(602)II lattice planes, which is in good agreement with the boundary indexes calculated from elasticity theory and spontaneous strain tensor. The orientation relationship between the domains has been determined as a rotation of 95.6° about the [010] axis. A model for domain boundary configuration, a diffuse boundary with a transition zone, has been proposed according to TEM diffraction patterns and HRTEM images. Based on this domain boundary model, a domain switching mechanism is suggested, and the corresponding driving force for domain switching is considered.
Development of Drying Schedules for One‐Side‐Heating Drying of Refractory Concrete Slabs Based on a Finite Element Model
Authors: Gong Zhen‐Xiang , Mujumdar Arun S.
Published: September 2005

A finite element model is presented for drying of refractory concrete pieces cast into various shapes. Simulations are carried out for one‐side‐heating drying of refractory concrete slabs. The effects of permeability, heating rate, and slab thickness on pore pressure and moisture removal rate are investigated. Different drying schedules are modeled and analyzed. New schedules are proposed to provide guidelines for on‐site drying operations.
Grain Orientation Dependence of the PTCR Effect in Niobium‐Doped Barium Titanate
Authors: Hayashi Katsuro , Yamamoto Takahisa , Sakuma Taketo
Published: September 2005

The positive temperature coefficient of resistivity (PTCR) effect is directly measured in single grain boundaries in 0.1‐mol%‐Nb‐doped BaTiO3 with 1 mm coarse grains. The PTCR effect largely depends on grain boundary structure. Random grain boundaries exhibit the PTCR effect as in polycrystalline samples, but the PTCR effect does not appear in highly coherent boundaries such as small‐angle boundaries, twin boundaries, and coincidence site lattice (CSL) boundaries with low Σ values. For Σ= 3 boundaries, the resistance increase above the Curie temperature is a function of deviation angle. A small PTCR effect is observed in Σ= 3 boundaries with a deviation angle of about 9° in contrast with ideal Σ= 3 boundaries and boundaries with a deviation of about 4°.
Polymerized Complex Route to Synthesis of Pure Y2Ti2O7 at 750°C Using Yttrium‐Titanium Mixed‐Metal Citric Acid Complex
Authors: Kakihana Masato , Milanova Maria M. , Arima Momoko , Okubo Toru , Yashima Masatomo , Yoshimura Masahiro
Published: September 2005

A polymerized complex technique was used to prepare high‐purity pyrochlore Y2Ti2O7 powders at 750°C. Heating of a mixed solution of citric acid (CA), ethylene glycol (EG), and yttrium and titanium ions, with a molar ratio of CA:EG:Y:Ti = 5:20:1:1, at 130°C produced a yellowish transparent polymeric gel without any precipitation; this material was used subsequently as a precursor for Y2Ti2O7. Based on the results of 13C‐NMR spectroscopy, it was suggested that a mixed‐metal (Y,Ti)‐CA3 chelate complex formed in a starting CA/EG solution. The formation of pure pyrochlore Y2Ti2O7 occurred when the precursor was heat‐treated in a furnace set at 750°C in static air for 4 h.
A New “Incipient‐Wetness” Method for the Synthesis of Chemically Stabilized β‐Cristobalite
Authors: Alcalá Mariá D. , Real Concha , Criado José M.
Published: September 2005

A new “incipient‐wetness” method is proposed for the synthesis of chemically stabilized β‐cristobalite (CSC) that avoids the need to handle liquid phases as required by the sol‐gel routes proposed in the literature. Stoichiometric compounds with the composition Si1–xAl*xCa1/2O2 have been investigated. ×= 0.07 represents the optimal composition for obtaining an extremely well‐crystallized material consisting of a single β‐cristobalite phase. XRD, FTIR, DSC, and differential dilatometry have been used for the physicochemical characterization of the samples.
Role of Niobium in Magnesium Titanate Microwave Dielectric Ceramics
Authors: Ferreira Victor M. , Baptista João L.
Published: September 2005

The effect of niobium doping on MgTiO3 ceramics was evaluated in terms of microstructure and microwave dielectric properties. Pure and doped MgTiO3 dense ceramics were produced. Doping levels of niobium were 0.5,1, and 2 at.% of Nb5+. Phase assemblages were examined by XRD and checked by EDS during microstructural observations by SEM. Microwave dielectric properties were measured at 8 GHz. Dielectric permittivity was not much affected by doping. Q decreased for the sample with the higher Nb content because of the presence of a second phase. For low Nb contents, a solid solution was formed and Q even increased. An explanation is presented based on the elimination of lattice defects.
Growth of Boric Acid Crystallites on the Surface of Boron‐Doped Silicon Carbide Samples
Authors: Vassen Robert , Stöver Detlev
Published: September 2005

White crystallites were visually observed on fractured or polished surfaces of SiC samples (grain sizes below ∼500 nm) during exposure to air at room temperature for several days. Characterization of the crystallites by scanning electron microscopy, secondary ion mass spectroscopy, and X‐ray diffraction identified B(OH)3 crystals with a strong (002) texture. The rate of boric acid formation was determined by a gravimetric experiment. The rate of weight gain increased significantly after an incubation period of 1 week. Nucleation is initially the rate‐limiting process. Subsequently small B(OH)3 crystals form on the surface, whose growth rate is determined by grain boundary diffusion of boron to the SiC surface. An estimated grain boundary diffusion coefficient of boron in SiC was many orders of magnitude higher than extrapolated literature values.
Sequestration of Cesium and Strontium by Tobermorite Synthesized from Fly Ashes
Authors: Ma Weiping , Brown Paul W. , Komarneni Sridhar
Published: September 2005

Tobermorites were synthesized from oxides and from fly ashes under mild hydrothermal conditions. The bulk compositions of the ash‐based formulations were adjusted to give the same [Ca]/[Si + Al] ratio as for the oxides. Selective Cs and Sr exchange with these tobermorites was measured. Compared to those prepared from the oxides and from class C fly ash, the tobermorites obtained from class F fly ash exhibited superior Cs and Sr selective properties. This is apparently a result of more extensive Al incorporation with class F fly ash. For example, tobermorite synthesized from class F fly ash exhibited a cesium Kd (mL/g) of 3826 while those prepared from oxides and from class C fly ash showed Kd values of 1112 and 796, respectively, under the same conditions. These results suggest that fly ash waste materials can be converted into tobermorite, which can serve as a resource in the separation, immobilization, and disposal of radioactive species such as Cs and Sr.
In S/Yu‐Toughened Silicon Carbide‐Titanium Carbide Composites
Authors: Cho Kyeong‐Sik , Kim Young‐Wook , Choi Heon‐Jin , Lee June‐Gunn
Published: September 2005

A process based on liquid‐phase sintering and subsequent annealing for grain growth is presented to obtain in situ‐toughened SiC‐30 wt% TiC composites. Its microstructures consist of uniformly distributed elongated α‐SiC grains, matrixlike TiC grains, and yttrium aluminum garnet (YAG) as a grain boundary phase. The composites were fabricated from β‐SiC and TiC powders with the liquid forming additives of A12O3 and Y2O3 by hot pressing. During the subsequent heat treatment, the β→α phase transformation of SiC led to the in situ growth of elongated α‐SiC grains. The fracture toughness of the SiC‐30 wt% TiC composites after 6‐h annealing was 6.9 MPa‐m1/2, approximately 60% higher than that of as‐hot‐pressed composites (4.4 MPa‐m1/2). Bridging and crack deflection by the elongated α‐SiC grains appear to account for the increased toughness of this new class of composites.
Links between Electrical and Optical Fatigue in Pb (Zr,Ti)O3 Thin Films
Authors: Warren William L. , Dimos Duane , Al‐Shareef Husam N. , Raymond Mark V. , Turtle Bruce A. , Pike Gordon E.
Published: September 2005

Switchable polarization can be significantly suppressed in ferroelectric (FE) materials by electrical or optical processes. Electrical suppression can occur by subjecting the FE to repeated polarization reversals; optical suppression can occur while biasing the FE near the switching threshold and illuminating with bandgap light. A link between the two processes in Pb(Zr,Ti)O3 (PZT) thin film capacitors is demonstrated by showing a relationship between the amount of the suppressed polarization induced by the two methods. This observation suggests that the optical method may be a useful, simple, and time‐saving probe of a material's susceptibility to fatigue. These results further support the view that polarization suppression in PZT thin films induced by electrical fatigue largely involves electronic charge trapping.
Solid‐Liquid Reaction in the Si3N4‐AlN‐Y2O3 System under 1 MPa of Nitrogen
Authors: Huang Zhen‐Kun , Tien Tseng‐Ying
Published: September 2005

The melting behaviors of selected compositions in the Si3N4‐AlN‐Y2O3 system were determined under 1 MPa of nitrogen. The phase diagrams of the ternary and their binary systems are presented. The lowest melting composition of the ternary system contains 15 mol % Si3N4, 25 mol % AIN, and 60 mol % Y2O3 and has a melting temperature of 1650°C. The binary eutectic compositions and temperatures are 15 mol % Si3N4 and 85 mol % Y2O3 at 1720°C, and 20 mol % AIN and 80 mol% Y2O3 at 1730°C.
Generation of Cracklike Voids during Sintering of Al2O3‐10ZrO2 Ceramics and Their Prevention by Presintering with Low Pressure (2 MPa)
Authors: Oh Kyung‐Sik , Kim Doh‐Yeon , Cho Seong‐Jai
Published: September 2005

During sintering of Al2O3‐10ZrO2 ceramics, cracklike voids were formed due to the differential in densification between agglomerates and the matrix. The small external pressure (2 MPa) applied during presintering at 1200°C prevented the formation of these cracklike voids. The results are explained in relation to the microstructural development during the initial stage of sintering.
Dislocation‐Related Plasticity of Ceria‐Stabilized Zirconia Polycrystals
Authors: Zhe Xiaoli , Wang Chongmin , Hendry Alan
Published: September 2005

Much higher plastic strain of 4% in Ce‐TZP ceramics was produced by a novel thermal‐mechanical process below 450°C. Observation by TEM showed that there were abundant dislocation pile‐ups associated with a few martensitic laths in the deformed samples. The density of dislocations increased with thermal‐mechanical cycles. These suggested that dislocation multiplication was caused by the high local stress concentration in front of a martensitic lath during the thermal‐mechanical deformation. The generation and movement of dislocations introduced extra plasticity beside the transformation plasticity caused by martensite. Meanwhile, movement of dislocations relaxes the interface stress at martensitic laths to prevent reverse martensitic transformation and early cracking of the specimens. The results are discussed in terms of thermal‐mechanical action and dislocation multiplication.
Structural–Property Relations in a Reduced and Internally Biased Oxide Wafer (RAINBOW) Actuator Material
Authors: Elissalde Catherine , Cross L. Eric , Randall Clive A.
Published: September 2005

Reduced and internally biased oxide wafer (RAINBOW) actuators are fabricated by a controlled reduction of Pb(Zr, Ti)O3‐based piezoelectric material. The reduction process results in a conductive layer composed of an interconnected metallic lead phase and refractory oxides (ZrTiO4, ZrO2, La2O3, etc.). The nature of the reduction is discovered to be the result of a complex volume change leading to a nanoscale interconnected metallic structure. The distribution of phases within the cermet vary within the thickness of the wafer. Within the piezoelectric ceramic phase, the reduction process modifies the grain‐boundary structure to give two distinct types of fracture: transgranular and intergranular. The complexed microstructures of the RAINBOW actuator materials are discussed in relation to their dielectric and piezoelectric properties.
Relationship between Field Direction and Wave Propagation in Activated Combustion Synthesis
Authors: Feng Aiguo , Munir Zuhair A.
Published: September 2005

Using experimental and modeling studies, the effect of field direction on the field‐activated combustion synthesis of SiC was investigated. Field application imposed in a direction perpendicular to wave propagation resulted in enhancement: the wave velocity increased linearly with an increase in field strength. For field application parallel to wave propagation, two cases were considered: confined and nonconfined areas of impacted energy from an ignition source. In the confined case both experimental (using laser ignition) and simulation studies were made. Both showed the establishment of a two‐front combustion with waves moving to opposite sides in a direction perpendicular to the field. In the nonconfined case, initial waves propagated in a direction parallel to the field but were independent of field strength. The results are interpreted in terms of a model in which the current is confined to the combustion zone, adding another source of heat to the combustion process, at a rate of σE2 (J·cm‐3·s‐1).
Low‐Temperature Synthesis of Ba(Mg1/3Ta2/3)O3 Ceramics from Ba‐Mg‐Ta Alkoxide Precursor
Authors: Katayama Shingo , Yoshinaga Ikuko , Yamada Noriko , Nagai Toru
Published: September 2005

BMT perovskite ceramics were synthesized at low temperature (∼100°C) by chemical processing comprised of the hydrolysis of Ba‐Mg‐Ta alkoxide precursor. FT‐IR and Raman spectroscopic studies of the Ba‐Mg‐Ta ethoxide precursor reveal that barium, magnesium, and tantalum ethoxides are bonded with each other via alkoxy bridging to form a trimetallic alkoxide. The hydrolysis of the Ba‐Mg‐Ta ethoxide with a large amount of water under refluxing results in the direct formation of a crystalline BMT phase with the pseudocubic perovskite structure at a low temperature of ∼100°C. The alkoxide‐derived BMT powder has high sinterability to provide a high‐density sintered body with a density of 94.0–98.0% at a low firing temperature of 1400°C.
Mechanical Properties of Single‐Crystal α‐Si3N4
Authors: Reimanis Ivar E. , Suematsu Hisayuki , Petrovic John J. , Mitchell T. E.
Published: September 2005

Single crystals of α‐Si3N4 several millimeters in diameter and several millimeters long have been grown by chemical vapor deposition. Some of the microstructural and mechanical properties have been evaluated using X‐ray diffracometry, optical and transmission electron microscopy, and high‐temperature microhardness testing. The crystallographic growth direction determines the quality of the crystals, including the density of internal microcracks and the nature and quantity of special boundaries. The measurement of crack lengths associated with microindentations has shown that cleavage in α‐Si3N4 is relatively isotropic. Finally, indentation fracture toughness values agree well with theoretical predictions based on recent bond‐energy calculations.
SiAlON Composites Containing Rare‐Earth Melilite and Neighboring Phases
Authors: Huang Zhen‐Kun , Liu Shih‐Yu , Rosenflanz Anatoly , Chen I‐Wei
Published: September 2005

Sintering aids with a formulation of rare‐earth (R) melilite solid solution M'(R) have been introduced to several SiAlON composites to obtain high‐density bodies by pressureless and gas‐pressure sintering. These compositions include ones along the Si3N4–R2O3:9AlN line, which contain no Al2O3 and are known to have excellent strength but very poor sinterability. Phase analysis and property (hardness, toughness, strength, and oxidation resistance) measurements reveal a complex set of structure–property–processing relationships that are composition‐dependent. Of the most importance is the Al—O content in various phases, which is dictated by the starting composition as well as Al—O solubility in M'(R). This influences the sinterability, strength, and phase assemblage through the compositions of the intermediate liquid and the final β'‐SiAlON. La2O3 is further established as an effective sintering aid that does not affect the equilibrium phase assemblage. Overall, M'(R) and La2O3 show promise as SiAlON sintering aids that allow high density to be achieved without compromising intrinsic mechanical and thermal properties.
Effect of Mn on Aging of (Pb0.63Ba0.37)(Zr0.7Ti0.3)O3 Dielectric Ceramics
Authors: Harada Kouichi , Kanai Hideyuki , Yamashita Yohachi
Published: September 2005

An aging model for relaxors is suggested on the basis of the transformation of a supercooled cubic lattice into a tetragonal lattice. Manganese ions distort the crystal lattice, and the distortion affects the phase transformation rate. As a result, the aging rate may be expected to change. The lattice constant of (Pb0.63Ba0.37)(Zr0.7Ti0.3)O3+χ MnO mol% dielectric ceramics was used as a measure of the degree of the distortion. As the lattice constant decreased up to 0.5 MnO mol%, the aging rate increased, justifying the proposed model.
Phase Transformations and Melting Effects During the Sintering of Bismuth‐Doped Zinc Oxide Powders
Authors: Peigney Alain , Rousset Abel
Published: September 2005

ZnO ceramics used as varistors are prepared with bismuth oxide as an essential additive. Some of its effects during the first step of liquid‐phase sintering remain unexplained. Therefore, in this work, we characterize the Bi distribution and identify the Bi‐rich phases in spherical Bi‐chemically‐doped ZnO powders. By a suitable method of differential thermal analysis conducted during sintering, we detect thermal phenomena. Characterization of ceramics quenched during sintering allows us to describe them and to analyze their influence on sintering. We also study the parameters which determine the occurrence of these events during sintering.