bluuebunny/crossref_metadata_2025 huggingface dataset:
Change of Crystal Phases and Microstructure of Amorphous Si‐C‐N Powder by Hot Pressing
Authors: Park Jin‐Joo , Komura Osamu , Yamakawa Akira , Niihara Koichi
Published: July 2010

An amorphous Si‐C‐N powder with Y2O3 and Al2O3 powder as sintering additives was hot‐pressed at 1900°C for 120 min in a nitrogen atmosphere. Changes in the crystalline phases and microstructure of the amorphous Si‐C‐N powder during sintering were investigated by X‐ray diffractometry (XRD) and transmission electron microscopy (TEM). The defects at the fracture origins of the sintered bodies after bending tests also were investigated by scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). XRD showed that alpha‐Si3N4 was formed initially from the amorphous Si‐C‐N by 1530°C, which then transformed to ß‐Si3N4 at 1600°C. Also, a slight formation of crystalline SiC occurred during the transformation from alpha‐ to ß‐Si3N4, and it increased after the transformation was completed at 1900°C. TEM revealed that many SiC nanoparticles were incorporated into ß‐Si3N4 grains after the transformation from alpha‐ to ß‐Si3N4 at 1600°C. They were located at the triple points of the grain boundaries of ß‐Si3N4 after continued Si3N4 grain growth at 1900°C. Besides the SiC nanoparticles, large agglomerations of carbon or SiC particles of 20‐60 µm size were observed by SEM and EPMA at the fracture origins of the sintered bodies after the bending tests.
Hertzian‐Crack Suppression in Ceramics with Elastic‐Modulus‐Graded Surfaces
Authors: Jitcharoen Juthamas , Padture Nitin P. , Giannakopoulos Antonios E. , Suresh Subra
Published: July 2010

Hertzian (spherical) indentation experiments were carried out in a graded alumina‐glass composite whose Young's modulus increased with depth beneath the indented surface. An in situprocessing method involving impregnation of a dense, fine‐grained alumina by an aluminosilicate glass was employed to fabricate such a composite. With this technique, a monotonic, unidirectional variation in Young's modulus of as much as 50% was introduced over a distance of approximately 2 mm, while keeping the coefficient of thermal expansion and the Poisson ratio for the glass and the alumina nearly the same. The macroscopically graded, elastic composite so produced with nearly full density has essentially no macroscopic, long‐range residual stresses following processing. The unidirectional variation in Young's modulus under the indenter is shown to fully suppress the formation of Hertzian cone cracks. Without these elastic‐modulus gradients, cone‐crack formation was observed in bulk glass and alumina. Finite‐element analyses of spherical indentation on elastically graded substrates were also performed to develop a quantitative understanding of the experimental trends. It is reasoned that the present innovations, involving functionally graded surfaces and their in situprocessing, provide new possibilities for enhancing certain contact‐damage resistance characteristics in various ceramic materials for a broad range of engineering applications. Furthermore, this contact‐damage‐resistance phenomenon in functionally graded ceramics is elastic in nature, and is, therefore, likely to be immune to mechanical fatigue within the elastic limit.
Finite Element Simulation of Thermal Residual Stresses in Joining Ceramics with Thin Metal Interlayers
Authors: Kovalev Serguei P. , Miranzo Pilar , Osendi Maria Isabel
Published: July 2010

Finite element analysis was used to estimate thermal residual stresses developed in silicon nitride bodies bonded by metallic interlayers. Stresses were calculated for various characteristic metals, namely, Ni, Al, and Si, assuming elastic and elastic‐plastic behavior. The relative importance of the metal properties, such as thermal expansion coefficient, stiffness and ductility, has been evaluated. Two different joint geometries, butt and lap, have been used in stress calculations, and special care was taken in the mesh generation, to obtain comparable results. The yield stress of the interlayer material rather than thermal expansion mismatch is the critical factor in thermal residual tensile stress buildup inside ceramic adherents.
Contact Damage and Strength Degradation in Brittle/Quasi‐Plastic Silicon Nitride Bilayers
Authors: Lee Kee Sung , Lee Seung Kun , Lawn Brian R. , Kim Do Kyung
Published: July 2010

A study is made of the damage resistance of silicon nitride bilayers consisting of a hard overlayer (coating) on a soft underlayer (substrate). The two layers are fabricated with different starting powders, to provide distinctive elongate‐grain microstructures, and are cosintered, to provide strong interfacial bonding and thus to minimize subsequent delamination. Contact testing with spherical indenters is used to characterize the damage response. The elastic‐plastic mismatch between the layers is sufficiently high as to produce distinctive damage modes in the two layers: predominantly cone cracking in the coating, and quasi‐plasticity in the substrate. However, the mismatch is also sufficiently low as to preclude secondary transverse cracks of the kind observed in other bilayer systems to initiate immediately beneath the contact at the coating/substrate interface and propagate upward within the coating. The dominant damage mode shifts from coating fracture to substrate quasi‐plasticity with increasing contact load and decreasing coating thickness. Significantly, the presence of the soft underlayer inhibits growth of the coating cone cracks as the latter approach and intersect the interface. The underlayer also substantially diminishes strength losses from the contact‐induced damage, especially in bilayers with thinner coatings. The implication is that bilayer structures with thin, hard coatings can preserve benefits from the inherent toughness of soft substrate materials, and at the same time afford surface protection (high wear resistance) to the underlayer.
Colloidal Processing of Silicon Nitride with Poly(acrylic acid): II, Rheological Properties
Authors: Hackley Vincent A.
Published: July 2010

Poly(acrylic acid) (PAA) was the focus of an investigation in the role and behavior of polyelectrolyte dispersants in aqueous‐based colloidal processing of silicon nitride. The steady‐shear flow properties of dense suspensions were examined as a function of pH, particle volume fraction, chain length, and polymer concentration. Suspensions exhibited shear‐thinning behavior, which was analyzed using the constitutive Bingham equation for plastic flow. The data showed that polyelectrolyte charge and configuration were important in the observed flow behavior. In acidic media, PAA behaved similar to a neutral polymer in a poor solvent, whereas, in alkaline media, PAA behaved similar to a rigid asymmetric particle. Although electrostatic forces dominated flow properties in alkaline media, where PAA was predominantly in the free‐polymer form, at lower pH values, PAA interactions with the particle surface resulted in a complex array of suspension effects, including polymer bridging, electrosteric stabilization, and flocculation.
Electrical Properties of Laser‐Synthesized Aluminum Oxide‐Tungsten Oxide Ceramics
Authors: Zheng Fang , Yuan Renzhang , Li Xingjiao , Li Zaiguang , Tao Xingzhi , Zheng Qiguang , Zhan Chang‐Guo
Published: July 2010

Electronic ceramics of the Al2O3‐WO3 system were synthesized by using a high‐powered CO2 laser. It was shown that these ceramics can be used as linear thermistor materials. The linear temperature range of the Al2O3‐WO3 system was ~200°C, the nonlinear deviation epsilon was <2%, the thermistor constant B was <103, and the temperature coefficient was between ‐0.2%/°C and ‐0.8%/°C. These parameters could be adjusted by changing the composition of the samples and the laser‐synthesis parameters. The present study showed that the materials should be encapsulated if they are to be used in an oxidizing atmosphere. The current‐voltage curves of the present materials were symmetrical around the coordinate origin, which also is a necessary condition for judging whether or not a thermistor is linear.
Fabrication of Fine YAG‐Particulate‐Dispersed Alumina Fiber
Authors: Towata Atsuya , Hwang Hae Jin , Yasuoka Masaki , Sando Mutsuo , Niihara Koichi
Published: July 2010

This paper involves novel fabrication processes for polycrystalline α‐Al2O3‐matrix composite fibers that contain nanosized yttrium aluminum garnet (YAG) particles. Dense α‐Al2O3/YAG nanocomposite fibers with a fine and homogeneous microstructure can be successfully fabricated via a modified sol‐gel process and α‐Al2O3 seed‐particle addition. YAG nanoparticles have been homogeneously dispersed within Al2O3‐matrix grains as well as at grain boundaries. Effects of α‐Al2O3 seed particles and YAG nanodispersions on crystallization and microstructure development of nanocomposite fibers are discussed.
Piezoelectric Properties of Pb[Zr0.45Ti0.5‐xLux(Mn1/3Sb2/3)0.05]O3 Ceramics
Authors: Yoon Seok‐Jin , Kang Hyung‐Won , Kucheiko Sergey I. , Kim Hyun‐Jai , Jung Hyung‐Jin , Lee Dong‐Kyun , Ahn Hyung‐Keun
Published: July 2010

The piezoelectric properties of Pb[Zr0.45Ti0.5‐xLux(Mn1/3‐Sb2/3)0.05]O3 ceramics, with 0 lessthan equal to x lessthan equal to 0.03, have been investigated. The partial substitution of Ti4+ with Lu3+ permitted improvement of the electromechanical coupling factor (kp), the dielectric constant (epsilonT33), and the piezoelectric constant (d33), while the dielectric loss (tan delta) increased and the mechanical quality factor (Qm) decreased with an increase of x. A pertinent piezoelectric material for actuator applications was Pb[Zr0.45Ti0.48Lu0.02(Mn1/3Sb2/3)0.05]O3, and the piezoelectric properties were kp = (58.5 ± 0.5)%, epsilonT33 = 32 ± 25, d33 = (373 ± 6) 10‐12 C/N, Qm = 714 ± 22, and tan delta = (0.98 ± 0.03)%.
Enhanced Densification of In2O3 Ceramics by Presintering with Low Pressure (5 MPa)
Authors: Son Ji‐Won , Kim Doh‐Yeon , Boch Philippe
Published: July 2010

Sintering of In2O3 has been carried out in air to full density. Because of the difference in densification between the agglomerates and the matrix, large interagglomerate pores were observed to form at the initial stage of sintering. Such pore formation could be prevented by applying a small external pressure which resulted in the beneficial rearrangement of agglomerates.
Kinetics of Oxidization Processes of Ruthenium Particles
Authors: Tanaka Masahiro , Ami Miho
Published: July 2010

The oxidation of ruthenium using rapid thermal processing (RTP) was investigated by thermogravimetric analysis. Ruthenium single‐crystal particles with 10 µm diameter were used in the present study. The result showed that the early stage of RTP was controlled primarily by the oxygen diffusion process through the RuO2reacted layer.
Optical Properties of Aluminum Oxide: Determined from Vacuum Ultraviolet and Electron Energy‐Loss Spectroscopies
Authors: French Roger H. , Müllejans Harald , Jones David J.
Published: July 2010

The optical properties of alpha‐Al2O3 have been determined by two independent methods, vacuum ultraviolet (VUV) spectroscopy and electron energy‐loss spectroscopy (EELS) over the energy range from 6 to 142 eV. For each experimental method two sets of high‐quality data have been measured and analyzed from alpha‐Al2O3. The evolution of the differences between the data for each experimental method and its associated analytical method indicate the reliability of the results, and the comparison between the methods emphasizes the relative advantages of each. VUV spectroscopy offers a higher energy resolution, resolving sharper features in the spectra, whereas EELS significantly extends the energy range, which has been exploited here to 140 eV but can be extended even further. Good overall consistency is found, but there are pronounced differences in the valence region from 10 to 30 eV, where strong absorptions are present, increasing the relative variability of the analysis. This demonstrates that accuracy estimates of the optical properties are meaningful only when supplied as a function of energy, because both strong intrinsic absorptions and weak experimental signals make accurate determinations difficult. Moreover, variations in the optical properties are observed most easily in the interband transition strength, Jcv, and are less evident when the optical properties are represented as the complex index of refraction. Because the optical properties can change with specimen origin and preparation and because of the details of data acquisition and numerical analysis procedures, assessing the contributions of each of these methods to our accurate knowledge of the optical constants is essential.
A New Mechanism of Nonstoichiometric 1:1 Short‐Range Ordering in NiO‐Doped Pb(Mg1/3Nb2/3)O3 Relaxor Ferroelectrics
Authors: Lee Kyu‐Mann , Jang Hyun M.
Published: July 2010

The oxidation of ruthenium using rapid thermal processing (RTP) was investigated by thermogravimetric analysis. Ruthenium single‐crystal particles with 10 µm diameter were used in the present study. The result showed that the early stage of RTP was controlled primarily by the oxygen diffusion process through the RuO2 reacted layer.
Lead Zirconate Titanate Prepared from Different Zirconium and Titanium Precursors by Sol‐Gel
Authors: Wu Aiying , Salvado Isabel M. Miranda , Vilarinho Paula M. , Baptista João L.
Published: July 2010

Modified sol‐gel processes have been developed for the preparation of lead zirconate titanate (PZT) (52/48) powders. These processes use different starting sources to introduce the titanium and zirconium components, namely tetraethyl orthotitanate, titanium isopropoxide, or titanium diisopropoxide bis(2,4‐pentanedionate) for titanium and zirconium propoxide or zirconium acetylacetonate for zirconium. To achieve stable and homogeneous precursor systems, several solvents (acetic acid, 1,2‐propanediol, propanol, and distilled water) and chemical modifying additives, such as acetylacetone and nitric acid, were also introduced for the preparation processes. The influence of the different precursors on the crystallization behavior of the sol‐gel‐derived powders was studied. Well‐crystallized single‐phase PZT powders were obtained after heat treatment at 600°C for 1 h. The powders obtained sintered well at 1000°C/2 h and a homogeneous microstructure with small grain sizes was obtained.
Preparation of Macroporous Titania Films by a Sol‐Gel Dip‐Coating Method from the System Containing Poly(ethylene glycol)
Authors: Kajihara Koichi , Nakanishi Kazuki , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2010

Macroporous titania (TiO2) films have been prepared via a sol‐gel dip‐coating method from a titanium tetraisopropoxide solution that contains poly(ethylene glycol) (PEG). The macroporous morphology‐i.e., the size, distribution, and shape of the macropores‐is controlled by varying the content and molecular weight of PEG, the withdrawal speed, and the temperature of the dipping solution. The morphology of the TiO2 film is determined by competitive contributions of the following factors: (i) decrease in fluidity, because of the evaporation of solvent; (ii) network formation by polycondensation reactions; and (iii) domain formation during phase separation into gel phases and solvent phases.
Low‐Pressure Flame Deposition of Nanostructured Oxide Films
Authors: Skandan Ganesh , Glumac Nick , Chen Yi‐Jia , Cosandey Fredric , Heims Eric , Kear Bernard H.
Published: July 2010

The influence of electroless nickel plating on lead‐based relaxor ferroelectric multilayer ceramic capacitors (MLCs) was studied by a comparison experiment. It was found that the influence is related to reactions in the electroless plating. It is proposed that adsorbed hydrogen atoms generated in electroless plating can diffuse into the ceramic bodies of MLCs and undergo some reduction reaction with them, resulting in the failure of electroless nickel plating. The implications for the negative influence of electroplating on MLCs and for the degradation in MLCs are also included, in which much attention is paid to the reduction reaction of hydrogen atoms generated by electrolysis of water.
Superplastic Flow of Fine‐Grained Yttria‐Stabilized Zirconia Polycrystals: Constitutive Equation and Deformation Mechanisms
Authors: Jiménez‐Melendo Manuel , Domínguez‐Rodríguez Arturo , Bravo‐León Alfonso
Published: July 2010

Available deformation data for superplastic yttria‐stabilized zirconia polycrystals with grain size <1 µm have been analyzed at temperatures between 1250° and 1450°C as a function of stress, grain size, and impurity content. The apparent stress exponentnfor the higher‐purity materials (residual impurity content <0.10 wt%) varies from 2 (region II) to greaterthan equal to3 (region I), and then toward 1 when the stress is decreased. The stress for transition between region II and region I decreases when the temperature and/or grain size is increased. The activation energyQfor flow in region II is 460 kJ/mol, which is approximately that for cation lattice diffusion. The grain‐size exponentpdecreases continuously andQincreases continuously with decreasing stress in region I. The constitutive equation for superplastic flow in region II is identical to that for metallic systems when lattice diffusion is the rate‐controlling mechanism. The experimental results have been correlated with a single deformation process that incorporates a threshold stress, below which grain‐boundary sliding does not contribute to strain. The threshold stress may result from yttrium segregation at grain boundaries and its interaction with grain‐boundary dislocations. A single deformation regime withn= 2 exists for low‐purity materials (impurity content >0.10 wt%) over the entire stress range. The strain‐rate enhancement with respect to high‐purity materials is related to the grain‐boundary amorphous phase present in such materials.
Reactions between Hot‐Pressed Calcium Hexaluminate and Silicon Carbide in the Presence of Oxygen
Authors: Cinibulk Michael K.
Published: July 2010

The reactions between hot‐pressed calcium hexaluminate (CaAl12O19, hibonite) and silicon carbide (SiC) at 1100°‐1400°C in air and nominal argon atmospheres were investigated. In inert atmospheres, there was no evidence of reaction at temperatures up to at least 1400°C. In air, the oxidation of SiC produced a layer of silica or a multicomponent amorphous silicate (depending on impurities) that reacted with CaAl12O19. At temperatures below 1300°C, the reaction resulted in the stratification of two distinct interfacial layers: a partially devitrified CaO‐Al2O3‐SiO2 glass adjacent to SiC and a CaAl2Si2O8 (anorthite) layer adjacent to hibonite. At 1400°C, a large amount of liquid was formed, the majority of which was squeezed out from between the reaction couple. No distinct layer of anorthite was present; instead, the anorthite was replaced by a layer of alumina between the glass‐rich layer and hibonite. An activation energy of 290 kJ/mol was determined for the reaction, which is consistant with oxygen diffusion through a calcium aluminosilicate glass. The reaction between rare‐earth hexaluminates and SiO2 was predicted to produce a more‐viscous glass than CaAl12O19 and SiO2 and, therefore, have slower reaction kinetics, because of lower mass transport in the glass.
Chemical Preparation of the Binary Compounds in the Calcia‐Alumina System by Self‐Propagating Combustion Synthesis
Authors: Tas A. Cüneyt
Published: July 2010

The binary compounds Ca3Al2O6 (C3A), Ca12Al14O33 (C12A7), CaAl2O4 (CA), CaAl4O7 (CA2), and CaAl12O19 (CA6) in the CaO‐Al2O3 system have been synthesized as high‐compound‐purity ceramic powders by using the self‐propagating combustion synthesis (SPCS) method. Materials characterization of the above‐mentioned phases was performed via powder X‐ray diffractometry (XRD), Fourier transform infrared spectroscopy, scanning electron microscopy, and energy‐dispersive X‐ray spectroscopy. The structural characterization of the C12A7 phase has been performed via Rietveld analysis on the powdered XRD samples. It has hereby been shown that, by using this synthesis procedure, it should be possible to manufacture high‐purity ceramic powders of CA, CA2, and C12A7 at 850°C, C3A at 1050°C, and CA6 at 1200°C in a dry‐air atmosphere.
Kinetics of Thin‐Film Reactions of Nickel Oxide with Alumina: I, (0001) and {1120} Reaction Couples
Authors: Kotula Paul G. , Carter C. Barry
Published: July 2010

Solid‐state reactions between thin films of nickel oxide (NiO) that had been grown on four different orientations of alpha‐alumina (alpha‐Al2O3), each with an intermediate layer of spinel, have been studied by using electron microscopy. The starting reaction geometry consists of a nickel aluminate (NiAl2O4) buffer layer 20 nm thick and a NiO overlayer 400 nm thick, both of which were grown via pulsed‐laser deposition and epitactically aligned to the alpha‐Al2O3. In the first of a series of three papers, the reaction on (0001)‐ and {[1120}‐oriented monocrystals of alpha‐Al2O3 is discussed. When heat treatment is applied, the reaction layers thicken linearly as the time increases, which is indicative of kinetic control via an interfacial reaction. The activation energy for reaction on the (0001) face is 697 kJ/mol, whereas that for reaction on the {1120} reflection is 536 kJ/mol. Because the spinel and NiO have the same orientations (i.e., (111), parallel to the substrate surface plane) for both of these orientations, the NiO/spinel interfaces are the same. Thus, the difference in the kinetics is associated with the differences that occur at the spinel/alumina interface; hence, the kinetics of the interfacial reaction are dependent upon the interfacial structure. Observations of the location of the initial interfaces, relative to their final locations, lead to the conclusion that these reactions do not only occur via a counterdiffusion of cations, but rather must also involve the diffusion of oxygen.
Kinetic Analyses of Solid‐State Reactions with a Particle‐Size Distribution
Authors: Koga Nobuyoshi , Criado Jose M.
Published: July 2010

Kinetic analyses for the solid‐state reactions of reactant particles in an assemblage with a particle‐size distribution (PSD) have been reexamined for the reactions that proceed by the advance of the reaction interfaces inward toward the center of the individual reactant particles. The experimental kinetic curves for a particle assemblage are influenced by the existing PSD. It has been demonstrated that, even if PSD exists, a reliable activation energy E can be obtained from such overall kinetic curves by the empirical isothermal analysis without accounting for the PSD. The isoconversion methods, which enable us to determine the E value from the data points at a given fractional reaction of a series of experimental kinetic curves, are methodologically independent of the PSD. It is neccessary to incorporate the PSD into the kinetic equation to select an appropriate kinetic model and to evaluate the preexponential factor A. The method of kinetic calculation accounting for the PSD can be generalized, for the kinetic data under any thermal profiles, by extrapolating all the analytical conditions to infinite temperature. For the reaction characterized by the well‐defined PSD and kinetic model function, the meaningful A value is obtained by the kinetic analysis at infinite temperature. Although the ability to discriminate the contracting geometry of the reaction interface in a single particle from the overall kinetic curve decreases with increasing PSD, the rate‐controlling steps for the advance of the reaction interface, i.e., chemical reaction controlled or diffusion controlled, can be distinguised from each other even for the reactions with a fairly large PSD.
Direct Measurement and Interpretation of Electrostatic Potentials at 24° [001] Tilt Boundaries in Undoped and Niobium‐Doped Strontium Titanate Bicrystals
Authors: Mao Zhigang , Dunin‐Borkowski Rafal E. , Boothroyd Christopher B. , Knowles Kevin M.
Published: July 2010

Phase contrast techniques in the transmission electron microscope are used to measure electrostatic potentials at 24° [001] tilt boundaries in nominally undoped and Nb‐doped SrTiO3 bicrystals. All of the boundaries are found to have lower scattering potentials than the surrounding bulk crystal. Origins for the measured changes in potential are investigated through the application of high‐resolution transmission electron microscopy, diffuse dark‐field imaging, energy dispersive X‐ray spectroscopy, and parallel electron energy loss spectroscopy. Significantly, we show that space charge is not the dominant contribution to the potential because the magnitudes of the potentials seen cannot be explained on the basis of ionic space charge theory alone.
Microstructure and Nonlinear Properties of Microwave‐Sintered ZnO‐V2O5 Varistors: I, Effect of V2O5 Doping
Authors: Kuo Cheng‐Tzu , Chen Chang‐Shun , Lin I‐Nan
Published: July 2010

The modification of the densification behavior and the grain‐growth characteristics of the microwave‐sintered ZnO materials, caused by the incorporation of V2O5 additives, have been systematically studied. Generally, the addition of V2O5 markedly enhances the densification rate, such that a density as high as 97.9% of the theoretical density and a grain size as large as 10 µm can be attained for a sintering temperature as low as 800°C and a soaking time as short as 10 min. Increasing the sintering temperature or soaking time does not significantly change the sintered density of the ZnO‐V2O5 materials but it does monotonously increase their grain size. Varying the proportion of V2O5 in the range of 0.2‐1.0 mol% does not pronouncedly modify such behavior. The leakage current density (JL) of these high‐density and uniform‐granular‐structure samples is still large, which is amended by the incorporation of 0.3 mol% of Mn3O4 in the ZnO materials, in addition to 0.5 mol% of the V2O5 additives. Samples that are obtained using such a method possess good nonohmic characteristics (α= 23.5) and a low leakage current density (JL= 2.4 10‐6 A/cm2).
Crystallization of Pseudo‐orthorhombic Anorthite on Basal Sapphire
Authors: Mallamaci Michael P. , Carter C. Barry
Published: July 2010

Anorthite‐glass films were grown on basal Al2O3 substrates using pulsed‐laser deposition. The substrates were cleaned and annealed in air at 1400°C to produce crystallographically flat (0001) terraces. The films were deposited in an oxidizing environment. X‐ray microanalysis confirmed the composition of the glass films to be close to that of anorthite (CaO·Al2O3·2SiO2). Although anorthite usually has triclinic symmetry, subsequent crystallization of these films in air at 1200°C resulted in the formation of pseudo‐orthorhombic CaAl2Si2O8 (o‐anorthite), a known metastable form of the mineral. Microstructural characterization was performed using visible‐light microscopy, scanning electron microscopy, and transmission electron microscopy. The films dewetted the substrate either before or after crystallization to form o‐anorthite islands which had strong orientation relationships to the Al2O3 substrate. The epitaxy of the o‐anorthite islands was accompanied by a small lattice mismatch parallel to the substrate plane. The formation of three orientational variants is consistent with the symmetry of the basal Al2O3 surface. The dislocation network observed at the o‐anorthite/Al2O3 interface indicates that nucleation and growth of the anorthite occurs directly on the substrate surface without an intervening interfacial amorphous layer. The study of anorthite‐glass films is important because they are present in liquid‐phase‐sintered Al2O3, and may be devitrified by postsintering heat treatments.
Development of Zirconium/Magnesium Phosphate Composites for Immobilization of Fission Products
Authors: Singh Dileep , Tlustochowicz Marcin , Wagh Arun S.
Published: July 2010

Novel chemically bonded phosphate ceramics have been investigated for the capture and stabilization of volatile fission‐product radionuclides. We have used low‐temperature processing to fabricate zirconium phosphate and zirconium/magnesium phosphate composites. A zirconium/magnesium phosphate composite has been developed and shown to stabilize ash waste that has been contaminated with a radioactive surrogate of the 137Cs and 90Sr species. Excellent retention of cesium in the phosphate matrix system was observed in both short‐ and long‐term leaching tests. The retention factor determined by the USEPA Toxicity Characteristic Leaching Procedure was one order of magnitude better for cesium than for strontium. The effective diffusivity, at room temperature, for cesium and strontium in the waste forms was estimated to be as low as 2.4 × 10−13 and 1.2 ×10−11 cm2/s, respectively. This behavior was attributed to the capture of cesium in the layered zirconium phosphate structure via an intercalation ion‐exchange reaction, followed by microencapsulation. However, strontium is believed to be precipitated out in its phosphate form and subsequently microencapsulated in the phosphate ceramic. The performance of these final waste forms, as indicated by the compression strength and the durability in aqueous environments, satisfies the regulatory criteria.
Development of Short‐Range Repulsive Potentials by Short‐Chain Surfactants in Aqueous Slurries
Authors: Luther Erik P. , Lange Fred F. , Pearson Dale S. , Colic Miroslav
Published: July 2010

The effect of both cationic (n‐trimethylammonium bromide, CnTAB) and zwitterionic (phosphocholine, CnCnPC) surfactants on the properties of aqueous slurries of Si3N4 was studied. These surfactants were expected to adsorb to the surface of Si3N4 particles to produce short‐range repulsive interparticle potentials that might be useful for the colloidal processing of advanced ceramic powders. Electrophoretic, adsorption, and viscosity measurements showed that longer‐chain‐length surfactants (CnTAB, n≥ 12, and CnCnPC, n≥ 9) strongly adsorb. Surfactants with shorter chain lengths were highly soluble and did not adsorb. Although the CnTAB, n≥ 12, surfactants produced very weak particle networks with a low viscosity, the packing density during consolidation was very low, and the bodies were brittle (cracked before plastic deformation). The less‐soluble, longer‐chained CnCnPC, n≥ 9, surfactants did produce high particle‐packing densities but also produced brittle bodies. In all cases, it appeared that the surfactants could be pushed away from the surface during particle packing.
Structural and Dielectric Properties of PLZT Ceramics Modified with Lanthanide Ions
Authors: Park Hyu‐Bum , Park Chan Young , Hong Young‐Sik , Kim Keon , Kim Si‐Joong
Published: July 2010

Lanthanide‐modified lead lanthanum zirconate titanate (PLZT) ceramics were prepared through a hydroxide co‐precipitation method, and the effects of the lanthanide ions on the structural and dielectric properties of the PLZT ceramics were investigated. The substitution site of the lanthanide ions was found to change from the A site to the B site with decreased lanthanide ionic radius by comparing theoretically calculated and experimentally measured unit‐cell volumes and densities. The variation of structural and dielectric properties in the lanthanide‐modified PLZT series was highly correlated to the change of substitution site, leading to the compositional change of the unit cell. Raman spectra showed that the B‐site local structures were affected by the substitution type.
Tip Deflection and Blocking Force of Soft PZT‐Based Cantilever RAINBOW Actuators
Authors: Wang Qing‐Ming , Cross L. Eric
Published: July 2010

A piezoelectric/electrostrictive RAINBOW actuator is a monolithic bending device consisting of an electromechanically active layer and a reduced passive layer formed in a high‐temperature reduction treatment. When the piezoelectric or electrostrictive layer is driven under an electric field or when the environmental temperature changes, bending deflection is produced because of the constraint of the reduced inactive layer or because of the thermal expansion coefficient difference of the two layers. In this study, general analytical expressions relating tip deflection, blocking force, and equivalent moment with an applied electric field and temperature change are derived for a cantilevered RAINBOW actuator. It is shown that optimal actuator performance can be achieved in the RAINBOW actuator by choosing a suitable thickness ratio of the reduced layer to the PZT layer. A series of RAINBOW cantilever actuators have been experimentally prepared from high‐density, soft, lead zirconate titanate (PZT) ceramics. Different reduction layer thickness is obtained by adjusting the processing parameters, such as reduction temperature and time. The measured results on tip deflection and blocking force agree well with theoretical prediction under a weak electric field. However, when a high driving electric field is used, deviation is observed, which can be attributed to a nonlinear piezoelectric response and a nonlinear elastic behavior associated with soft PZT materials under high driving electric fields.
Radial Variations in Modulus and Hardness in SCS‐6 Silicon Carbide Fibers
Authors: Mann Adrian B. , Balooch Mehdi , Kinney John H. , Weihs Timothy P.
Published: July 2010

The mechanical properties of SCS‐6 SiC fibers were measured as a function of fiber radius using nanoindentation techniques. Hardness and Young's modulus were characterized for the material in all of the major regions of these fibers: the carbon core, the graphitic core coating, the inner SiC sheath, and the outer SiC sheath. The carbon core of the fibers was determined to be uniform in properties but extremely compliant. Young's modulus of 28 GPa and a hardness of 4.2 GPa were measured. The graphitic core coating was found to exhibit considerable anelasticity and to have both a low modulus (21 GPa) and a low hardness (1.7 GPa). The inner sheath of the fiber, which contained a varying chemistry, showed a sharp increase in stiffness and hardness from the inner core. Modulus and hardness increased by an order of magnitude over just 1 or 2 μm when transversing radially away from the core into the SiC. This change in properties was pronounced and clearly defined. The outer sheath, which contained a uniform chemistry and microstructure, was consistently stiff and hard when transversing radially. The average modulus and hardness for the full fiber was 333 GPa. The values reported for Young's modulus and hardness clearly showed that the mechanical properties of SCS SiC fibers exhibit dramatic changes across their diameters.
Novel Processing for Mesoporous Silica Films with One‐Dimensional Through Channels Normal to the Substrate Surface
Authors: Kondoh Shinji , Iwamoto Yuji , Kikuta Koichi , Hirano Shin‐ichi
Published: July 2010

Mesoporous silica films with one‐dimensional through channels perpendicular to the substrate surface have been fabricated successfully by a novel process, which was a combination of eutectic decomposition of amorphous films and subsequent chemical etching. In the case of the Fe–Si–O system, amorphous precursor films annealed under oxidizing conditions were decomposed to a regular array of needlelike hematite (Fe2O3) crystals with a diameter of ∼4 nm surrounded by an amorphous silica matrix. Then, hematite crystals were preferentially removed by chemical etching. The pore surface areas of the remaining mesoporous SiO2 films were found to be more than 1000 m2/g by an isothermal N2 gas adsorption and desorption measurement.
Fabrication of Lead Zirconate Titanate Microrods for 1–3 Piezocomposites Using Hot Isostatic Pressing with Silicon Molds
Authors: Wang Shinan , Li Jing‐Feng , Watanabe Ryuzo , Esashi Masayoshi
Published: July 2010

A new lost‐mold process to fabricate piezoceramic microrods for 1–3 piezocomposites has been developed. A Si wafer was machined as a mold with a regular array of columnar cavities having a negative structure of piezoceramic microrods, by deep reactive ion etching (RIE). A lead zirconate titanate (PZT) slurry was cast into the Si mold and calcinated to burn out the binder, and fully condensed in the cavities by the glass‐encapsulated hot isostatic pressing technique. Finally, the Si mold was selectively removed by XeF2etching. PZT microrods with high aspect ratios (diameter <12 μm, aspect ratio >14), which can be used to construct high‐resolution micro‐ultrasonic transducers for medical imaging, were fabricated successfully by the present process.
Effect of Gallia Addition on the Sintering Behavior of Samaria‐Doped Ceria
Authors: Yoshida Hiroyuki , Miura Kazuhiro , Fujita Jun‐ichi , Inagaki Toru
Published: July 2010

Samaria‐doped ceria (SDC) was prepared by using the solid‐state reaction method. Sintering of SDC was significantly promoted by adding a small amount of gallium. SDC that had 1% of gallium added, sintered at 1450°C, showed almost the same properties as SDC sintered at 1600°C. Measurements showed that the addition of gallia could reduce the sintering temperature by 150°C without deteriorating the properties of SDC as an electrolyte for solid oxide fuel cells.
Low‐Temperature Synthesis of BaAl2O4/Aluminum‐Bearing Composites by the Oxidation of Solid Metal‐Bearing Precursors
Authors: Citak Ramazan , Rogers Kirk A. , Sandhage Ken H.
Published: July 2010

BaAl2O4/aluminum‐bearing composites have been synthesized via the low‐temperature oxidation of Ba‐Al precursors. Ba‐Al powder mixtures that were prepared via high‐energy vibratory milling were uniaxially pressed into bar‐shaped specimens that were then exposed to a series of heat treatments in pure, flowing oxygen at temperatures up to 640°C. Oxidation at a temperature of 300°C resulted in the formation of barium peroxide (BaO2). Additional heat treatment at a temperature of 550°C resulted in the consumption of BaO2 and some aluminum to yield BaAl2O4 and Al4Ba. The oxidation of Al4Ba at a temperature of 640°C yielded additional BaAl2O4. Microstructural analyses revealed that a well‐dispersed, co‐continuous mixture of Al2O3‐excess BaAl2O4 and 99.5% pure aluminum was produced.
Varistor Ceramics
Authors: Clarke David R.
Published: July 2010

The development of varistor ceramics is reviewed with an emphasis on ZnO‐based varistors formed by liquid‐phase sintering. Particular attention is given to the effects of microstructural disorder on the properties of varistors and to the different modes of failure that can occur.
Process‐Structure‐Reflectance Correlations for TiB2 Films Prepared by Chemical Vapor Deposition
Authors: Beckloff Bruce N. , Lackey W. Jack
Published: July 2010

The process‐structure‐reflectance interrelationships for TiB2 films prepared by CVD were determined using statistically designed experiments. A hot wall CVD reactor employing graphite substrates and the TiCl4+ BCl3+ H2 reagent system were used at pressures of 2.7 and 6.7 kPa. Single‐phase polycrystalline TiB2 films were obtained. An increasing percentage of the grains were oriented with their (001) planes parallel to the substrate as the deposition temperature was increased and as the BCl3:TiCl4 ratio decreased. Grain size increased from ∼0.5 to 3 µm as the deposition temperature was increased from 900° to 1100°C and as the coating rate was decreased from 0.6 to 0.1 µm/min. Fine‐grained, smooth, highly reflective films were obtained at low deposition temperatures and high BCl3:TiCl4 ratios.
Short‐Duration Rapid‐Thermal‐Annealing Processing of Tantalum Oxide Thin Films
Authors: Ezhilvalavan Santhiagu , Tseng Tseung‐Yuen
Published: July 2010

The effect of the rapid thermal annealing (RTA) processing time on the electrical properties of reactively sputtered tantalum oxide (Ta2O5) films that was deposited onto Pt/SiO2/n‐Si substrates, which resulted in the formation of a metal‐insulator‐metal (MIM) planar capacitor structure, was studied. The Ta2O5MIM capacitors were subjected to different RTA processing times (30 s to 30 min) at temperatures in the range of 600°‐800°C in an ambient oxygen‐gas atmosphere. A very‐short‐duration RTA process at a temperature of 800°C in oxygen gas for 30 s crystallized the films, decreased the leakage current density (to 10‐10A/cm2at a stress field of 100 kV/cm), increased the dielectric constant (to 52), and resulted in the most‐reliable time‐dependent dielectric‐breakdown characteristics. The decrease in leakage current density was attributed to the reduction of oxygen vacancies and the suppression of silicon diffusion from the SiO2/n‐Si substrate into the Ta2O5grain and the grain boundary, because of the shorter‐duration annealing. Increasing the annealing time to >30 s increased the leakage current density. The annealing duration of the RTA process was more crucial in regard to obtaining optimum dielectric properties and low leakage current densities. Time‐dependent dielectric‐breakdown characteristics indicated that Ta2O5MIM film capacitors that were subjected to an RTA process at a temperature of 800°C for 30 s in oxygen gas can survive a stress field of 1.5 MV/cm for 10 years. The electrical and dielectric measurements in the MIM configuration showed that Ta2O5is a good dielectric material and is suitable for use in future dynamic random‐access memories.
Creep Behavior of Si3N4‐Whisker‐Reinforced Si3N4‐Matrix Composites Using anIn SituDynamic Beam Profiling Method
Authors: Costa Célio A. , Todd Judith A.
Published: July 2010

A four‐point flexure test, capable of simultaneously measuring load‐point and beam‐center displacements and permittingin situprofiling of the beam throughout the test, has been developed. Compressive and tensile strains in the outer fibers, together with the neutral axis displacement, were determined in real time for Si3N4‐whisker‐reinforced Si3N4‐ceramic‐matrix composites. Combining these data with the closed form solution of Chen and Chuang gave excellent correspondence between the creep exponents determined from flexure tests with those determined independently from tensile and compressive creep tests.
Highly Reactive Remelted Belite
Authors: Fukuda Koichiro , Ito Suketoshi
Published: July 2010

Remelted belite showed higher hydration activity and better grindability than the quenched material. Both properties were closely related to the belite microtextures induced by the remelting reaction; after the reaction, the belite showed disintegration of the intracrystalline lamella structure, inclusion of the liquid exsolved on the former lamella boundaries, and crystallization of the liquid during further cooling. The fractures easily penetrated the remelted crystal grains upon grinding, probably along the disintegrated lamella boundaries and/or along the inclusions. The resulting fragments were irregular in shape with high specific surface area, leading to the high hydration activity of the remelted belite.
Reactions between Strontium‐Substituted Lanthanum Manganite and Yttria‐Stabilized Zirconia: I, Powder Samples
Authors: Wiik Kjell , Schmidt Christian R. , Faaland Sonia , Shamsili Senem , Einarsrud Mari‐Ann , Grande Tor
Published: July 2010

Sintered submicrometer powder mixtures of strontium‐substituted lanthanum manganite and yttria‐stabilized zirconia have been studied in order to investigate the chemical stability of these materials as respectively electrode and electrolyte in solid oxide fuel cells. Formation of secondary phases was observed after 1 h heat treatment at 1350°C and more than 13 h at 1200°C. La2Zr2O7was formed in mixtures with LaMnO3at 1350°C, while SrZrO3was formed in mixtures containing La0.6Sr0.4MnO3or La0.4Sr0.6MnO3. Only minor amounts of secondary phases were observed in mixtures with La0.7Sr0.3MnO3. Chemical analysis revealed considerable interdiffusion between the primary phases as well as A‐site deficiency of LaMnO3and La0.7Sr0.3MnO3when exposed to cubic zirconia. The oxidative/reductive nature of the chemical reaction between strontium‐substituted lanthanum manganite and yttria‐stabilized zirconia is discussed in relation to the Sr content in LSM. The lattice parameter of cubic zirconia was observed to be quite sensitive to the interdiffusion and is an excellent tool for investigating reactions on heterophase interfaces involving stabilized zirconia.
Reactions between Strontium‐Substituted Lanthanum Manganite and Yttria‐Stabilized Zirconia: II, Diffusion Couples
Authors: Kleveland Kjersti , Einarsrud Mari‐Ann , Schmidt Christian R. , Shamsili Senem , Faaland Sonia , Wiik Kjell , Grande Tor
Published: July 2010

Formation of secondary phases and diffusion of cations in diffusion couples of yttria‐stabilized zirconia and lanthanum manganite substituted with 0 to 60 mol% strontium have been studied by scanning electron microscopy and energy dispersive X‐ray spectroscopy. Only the primary phases were observed after 120 h at 1200°C, while formation of secondary phases was identified already after 1 h heat treatment at 1350°C. The phase composition of the reaction layer altered from La2Zr2O7 to SrZrO3 at increasing Sr content in LaxSr1‐xMnO3. The thickness of the reaction layer was increasing with heat treatment time. In diffusion couples of La0.4Sr0.6MnO3 formation of manganese oxide was observed in the perovskite layer after 1 h heat treatment at 1350°C, while isolated grains of SrZrO3 relatively deep inside the zirconia were observed after longer heat treatment time. Diffusion of Mn into zirconia was observed preferenced along grain boundaries in the early stage of the interface reaction.
Phase Diagram, Short‐Range Structure, and Amorphous Phases in the ZrO2‐GeO2(‐H2O) System
Authors: Karlin Sacha , Colomban Philippe
Published: July 2010

Gels of the ZrO2‐GeO2(‐H2O) system have been prepared via the hydrolysis‐polycondensation of zirconium and germanium isopropoxides. Phase relationships have been deduced from differential thermal analysis, thermogravimetric analysis, and shrinkage analysis and are discussed on the basis of X‐ray diffractometry and Raman scattering studies. Emphasis has been given to understanding the short‐range structure. A small glass‐forming domain is observed in the temperature range of 600°−700°C for compositions of 30–40 mol% GeO2.
Synergistic Effects of Porosity and Glass on Quasi‐Ductility under Hertzian Contact in Liquid‐Phase‐Sintered Alumina
Authors: DiGiovanni Anthony A. , Chan Helen M. , Harmer Martin P. , Nied Herman F.
Published: July 2010

Direct observation of damage mechanisms in a porous liquid‐phase‐sintered alumina under Hertzian contact has been made possible through a modification of the bonded interface technique. Using high‐resolution scanning electron microscopy, subsurface regions have been examined in a pre‐indentation and post‐indentation condition at loads just beyond the yield stress. Intergranular cracking, often through large glassy regions, is observed in the vicinity of pores, whereas dense regions of the microstructure remain undamaged. Distributed subsurface microfracture is attributed to porosity that acts as a stress concentrator and the glassy phase, which provides a weak path for short‐crack propagation.
Effect of α‐Si3N4Particle Size on the Microstructural Evolution of Si3N4Ceramics
Authors: Lee C. J. , Kim Deug J. , Kang E. S.
Published: July 2010

The effects of initial particle size on the microstructure of silicon nitride ceramics produced by pressureless sintering have been investigated. The microstructures of the silicon nitride ceramics varied considerably with the size of the initial powder. With decreasing powder size, abnormal grain growth was enhanced, which resulted in significant bimodal distribution of grain size. The observed results are discussed in relation to the two‐dimensional nucleation and growth theory for faceted crystals.