bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Surface Roughness on the Acid Etching of Amorphous Silica
Authors: Affatigato Mario , Osborne Danny H. , Haglund Richard F.
Published: July 2010

The effect of the root‐mean‐square (rms) roughness on the acid etching of roughened amorphous silica was studied as a function of time using atomic force microscopy and laser light scattering. The initial size and distribution of micrometer‐sized surface flaws are shown to influence the time evolution of the etching by hydrofluoric acid. The increase in the optical transparency of the samples is linked to the large increases in the correlation lengths of the sample surfaces, an effect which counteracts the accompanying rise in the rms roughness.
Growth of Nickel Oxide Single Crystals and Bicrystals via hemical Vapor Transport
Authors: Chung Yong‐Chae , Wuensch Bemhardt J.
Published: July 2010

A chemical vapor transport (CVT) method was successfully used to grow NiO single crystals and bicrystals heteroepitaxially on single‐crystal MgO substrates. The most favorable growth conditions were obtained at 1400 K using 250 torr (∼3.33 × 104 Pa) of HCl(g) as the transport agent. Average growth rates greater than 100 μm/h were easily achieved under these conditions. The CVT‐grown NiO single crystals and bicrystals usually displayed highly reflective facets along the growth direction that suggest high mechanical quality. The grain boundaries in the bicrystals were observed to be perpendicular to the (001) growth surface. The epitaxial NiO crystals were easily separated from the MgO substrate by dissolving away the latter in 85% H3PO4 at 190°C. The crystallinity and purity of the deposits were checked using these free‐standing NiO crystals. The concentration of cation impurities and the Cl content in the CVT‐grown crystals were investigated by inductively coupled plasma (ICP) mass‐spectrometric analysis and neutron activation analysis, respectively. High‐resolution transmission electron microscopy of a Σ13 (510) boundary revealed a structure at the atomic scale that provided no evidence for segregated phases.
Effect of Plasma Treatment of Polyethylene Fibers on Interface and ementitious Composite Properties
Authors: Li Victor C. , Wu Hwai‐Chung , Chan Yin‐Wen
Published: July 2010

It is well known that interfaces in composites play an important role in determining composite properties. In this paper, preliminary results of the improvement in tensile properties of a fiber‐reinforced cementitious composite due to plasma treatment of the discontinuous polyethylene fibers are reported. Specific focus is placed on the pseudo strain‐hardening composite properties induced by fiber reinforcements and associated load transfer from crackbridging fibers to matrix. Single fiber pullout tests support that the composite property improvement is indeed derived from interfacial property enhancement of the plasma treatment process.
High‐Temperature Electrical Properties in the ThO2‐Rich Region of ThO2‐RE2O3 Systems
Authors: Hufschmidt Heike , Weyl Axel , Janke Dieter
Published: July 2010

In the present study the n‐type electronic conduction in terms of the parameter pe, and the phase relations in several ThO2‐RE2O3 systems were examined. Large fluorite solid solution regions exist at elevated temperatures. It was demonstrated that RE2O3‐doped thoria compositions feature lower parameters pe, and higher chemical stability than the conventional stabilized ZrO2 electrolytes. The results are given in terms of the characteristic parameter pe, in the temperature range from 1000° to 1600°C. The experimental investigations were made using a new thermodynamic measuring system.
Ultrasonic and Dielectric Characterization of Microwave‐Sintered and Conventionally Sintered Zinc Oxide
Authors: Martin Louis Peter , Dadon David , Rosen Moshe , Gershon David , Birman Amnon , Levush Baruch , Carmer Yuval
Published: July 2010

Zinc oxide samples were prepared by microwave‐ and conventional‐sintering processes using identical time‐temperature profiles. Comparison of postsintering properties as a function of residual porosity over the range of 0%‐35% indicated no significant difference in the ultrasonic velocity‐porosity relations or the elastic moduli for the samples prepared by the two techniques. The real and imaginary parts of the permittivity of the samples processed by the two techniques were measured over a wide frequency range. In both cases, there was an increase in the measured permittivity values with decreasing porosity; however, the microwave‐sintered samples had considerably higher values. Porosity levels were evaluated using bulk density measurements and scanning electron microscopy analysis. Significantly more densification was observed at intermediate temperatures for microwave sintering than for conventional sintering.
Dynamic Consolidation of Combustion‐Synthesized Alumina‐Titanium Diboride Composite Ceramics
Authors: Kecskes Laszlo J. , Niiler Andrus , Kottke Thomas , Logan Kathryn V. , Villalobos Guillermo R.
Published: July 2010

A mixture of TiO2, B2O3, and Al powders was reacted exo‐thermically to form a low‐density Al2O3–TiB2 foamed product. After the cessation of the combustion synthesis reaction, this hot foam was densified by the pressure waves generated by the detonation of an explosive charge. The delay time between the initiation of the combustion synthesis and detonation of the explosive, the thickness of the explosive charge, and the strength of sample confinement were found to influence the effectiveness of the consolidation. Analysis of the combustion synthesis reaction temperature histories and microscopy of the reacted product sponge are used to develop additional information about this reaction/consolidation process. These results, and the microstructural properties of the combustion‐synthesized and dynamically consolidated products, are discussed.
Desintering Process in the Gas‐Pressure Sintering of Silicon Nitride
Authors: Hwang Shyh‐Lung , Becher Paul F. , Lin Hua‐Tay
Published: July 2010

A unique desintering phenomenon has been observed in gas‐pressure sintering of silicon nitrides with additives of yttria and alumina. The desintering phenomenon occurred, simultaneous with weight increase, only when a boron nitride crucible was used in combination with the application of high nitrogen pressure (5 MPa). When the nitrogen pressure was low (0.5 MPa), or when the boron nitride crucible was replaced by a graphite crucible, this desintering phenomenon was not observed. These results could be rationalized by the chemical dissolution of nitrogen into the oxynitride melts and the resultant evolution of carbon monoxide. This indicates that the high nitrogen overpressure employed in gas‐pressure sintering of silicon nitride ceramics is not always beneficial.
Preparation and Analysis of a Silicon Carbide Composite Membrane
Authors: Lin Ping‐Kun , Tsai Dah‐Shyang
Published: July 2010

Silicon carbide (SiC) porous substrates, containing alumina (Al2O3) dopant levels of 3, 5, and 8 wt%, are prepared by slip casting and sintering in the temperature range of 1450°–1800°C. The linear shrinkage, bulk density, and pore size of the sintered substrate increase as the sintering temperature and the amount of dopant increase. A large amount of β‐phase SiC is transformed to α‐phase SiC if the dopant concentration is 5 or 8 wt%. The flexural strength of the substrate doped with 8 wt% Al2O3 is higher than that of the substrate doped with 3 wt% Al2O3; however, the Weibull modulus of the former is lower. SiC composite membranes of improved selectivity and strength are fabricated by coating the porous substrate with layers of lower Al2O3 contents at lower sintering temperatures.
Effects of Shape and Size of Inclusions on the Sintering of ZnO—ZrO2 Composites
Authors: Nakada Yohsuke , Kimura Toshio
Published: July 2010

The densification behavior and microstructure development of ZnO matrices containing rigid Zro2 inclusions were studied, with special emphasis on the effect of inclusion shape and size. The inclusions retarded the densification of the matrix, regardless of the inclusion shape and size. For large inclusions with diameters of 10 μm, dense regions developed between inclusion particles. The inclusion particles and dense regions formed a continuous network, which constrained the densification of the composites. The inclusion shape had a small effect on the development of dense regions. Severe retardation in densification was observed for compacts containing inclusions with diameters of 10 μm. In these cases, dense regions between inclusion particles did not develop. The formation of the continuous network cannot be applicable to small inclusions as an origin of retardation of densification.
Corrosion of MgO—MgAl2O4 Spinel Refractory Bricks by Calcium Aluminosilicate Slag
Authors: Goto Kiyoshi , Argent Bernard B. , Lee William E.
Published: July 2010

Microstructural analysis of MgO—MgAl2O4 refractory bricks corroded at 1400–1450°C by calcium aluminosilicate slag reveals secondary spinel, monticellite, merwinite, and MgO as microscopic corrosion products, generally forming in this sequence as the brick is penetrated. The secondary spinel forms an incomplete layer close to (but not at) the MgO grain. Thermodynamic calculations are used to support a detailed model of the corrosion mechanism.
Silicon Carbide Powder Synthesis from Silicon Monoxide and Methane
Authors: Setiowati Utami , Kimura Shoichi
Published: July 2010

SiC was synthesized via the gas‐phase reaction between SiO and CH4 at 1500° and 1560°C in a tubular flow reactor. SiO vapor was generated from equimolar powder mixtures of Si and SiO2 in the reactor while CH4 was externally supplied. Products of different morphologies were collected at different longitudinal locations: whiskers, crystal aggregates, scale, and powder. The total yield of SiC, based on the amount of SiO generated, reached as high as 99%, of which 25–46% by mass was fine powder with sizes ranging from 60 to 300 nm.
Monoclinic‐to‐Tetragonal Phase Transformation in a Ceramic Rare‐Earth Orthoniobate, LaNbO4
Authors: Jian Li , Wayman C. M.
Published: July 2010

The monoclinic‐to‐tetragonal phase transformation in LaNbO4 has been investigated by X‐ray diffraction and dilatometry. Based on the experimental results and theoretical concerns (Landau theory and thermodynamics), it is suggested that this transformation is second order in nature.
High‐Temperature Ionic Conduction in Multicomponent Solid Oxide Solutions Based on Zirconia
Authors: Weyl Axel , Janke Dieter
Published: July 2010

High‐temperature ionic conductivity of zirconia–calcia (ZrO2–CaO), zirconia–yttria (ZrO2Y2O3), and zirconia–rareearth‐oxide (ZrO2RE2O3) solid solutions was measured at temperatures of 1000°–1600°C. The emf polarization method and a thermodynamic emf method using a new reference system (aluminum melt coexisting with solid alumina) were applied to obtain the parameterspe'characterizing ionic conductivity. In the present study, the parameterpe'has been investigated as a function of temperature, of dopant radius, of dopant concentration, and of conditions of preparation. In the range of the investigated dopant concentrations, parameterpe'was shown to decrease as the dopant radius decreased. For the system ZrO2Y2O3, a minimum of the parameter pe was observed at 25 mol% Y2O3. In addition to this, it is important to take into account the sintering parameters, the purity, and the grain size of the used samples to compare the results with previous data. A comparison of the parameter pe of CaO‐ and Y2O3‐doped ZrO2and of RE2O3‐doped ZrO2indicates that the relevant values of ZrO2RE2O3solid solutions are one to two orders lower. Additional studies on new multicomponent solid solutions based on ZrO2also revealed promising high‐oxygen‐ion‐conductive solid electrolyte materials in view of low values of parameter pe. Wide ranges of cubic solid solutions were identified by X‐ray diffractometry. It was demonstrated that the two experimental techniques can successfully be used to determine mixed ionic and electronic conduction in commonly used solid oxide electrolyte materials, e.g., for practical oxygen sensors in metal melts.
Fabrication and Sintering of Fine Yttria‐Doped Ceria Powder
Authors: Van Herle Jan , Horita Teruhisa , Kawada Tatsuya , Sakai Natsuko , Yokokawa Harumi , Dokiya Masayuki
Published: July 2010

Yttria–doped ceria powder was prepared from oxalate precursors. The oxalate coprecipitation bath parameters were closely monitored and found to influence the sintering behavior of the subsequently obtained oxide powders strongly. The use of concentrated (Ce,Y) metal nitrate solutions and dilute neutralized oxalic acid for coprecipitation were identified as the most–important parameters. Following calcination at 700°C, compacts of such powders were sintered to high density (98%) at 1400°C (4 h). Ball milling of the powder further reduced the sintering temperature. Dry milling, for tape–casting applications of the powder in particular, was more effective than wet milling. Tape–cast membranes were fired at 1400°C (2 h), with resulting densities of 98%.
Effect of Additives on the Electromechanical Properties of Pb(Zr,Ti)O3–Pb(Y2/3W1/3)O3 Ceramics
Authors: Yoon Seok‐Jin , Joshi Amod , Uchino Kenji
Published: July 2010

Dielectric and piezoelectric properties of 0.02Pb(Y2/3W1/3)O3 0.98Pb(Zr0.52Ti0.48)O3 ceramics doped with additives (Nb2O5, La2O3, MnO2, and Fe2O3) were investigated. The grain sizes of these ceramics decreased with increasing amounts of additives. For additions of MnO2 and Fe2O3, dielectric losses decreased, while for Nb2O5 and La2O3, these values increased. The maximum values of the mechanical quality factor Qm were found to be 956 and 975 for additions of 0.9 wt% Fe2O3 and 0.7 wt% MnO2, respectively, but donor dopants (Nb2O5 and La2O3) did not change the values of Qm. On the other hand, the piezoelectric constant d33 and the electromechanical coupling factor kp decreased with additions of MnO2 and Fe2O3, but improved with additions of Nb2O5 and La2O3.
Space‐Charge Distribution across Internal Interfaces in Electroceramics Using Electron Holography: II, Doped Grain Boundaries
Authors: Ravikumar Venkataraman , Rodrigues Richard P. , Dravid Vinayak P.
Published: July 2010

Transmission high‐energy electron holography has been utilized to quantitatively determine the magnitude, sign, and spatial extent of the electrical potential, electric field, as well as the charge and stress field distributions across electrically active grain boundaries (GBs) in polycrystalline SrTiO3. The polycrystalline compacts utilized were bulk‐doped with Fe and GB‐doped with Mn, which is diffused into them under a nonequilibrium situation. The holography results reveal negatively charged GBs with associated positive space‐charge, indicating that Mn resides as an acceptor dopant on the Ti site, creating a negative bound charge at the GBs. A large heterogeneity in the electrical activity is observed among various GBs; while some GBs show high Schottky barriers, others have very small barriers. The distribution of the bound charge and the compensating free charge, which together contribute to the formation of GB charge and space‐charge, has been estimated. The bound charge experiences an outward stress field due to the force of the electric field on either side of the GB. The height of the double Schottky barrier, the Debye length, as well as the spatial extent of the bound charge and space‐charge at the GB are derived from these holography results. The results also provide a quantitative measure of the defect densities as well as of the contribution of the electrostatic stress field to the lattice relaxation at the GBs and yield a point defect model for the GB.
Texture Development by Templated Grain Growth in Liquid‐Phase‐Sintered α‐Alumina
Authors: Seabaugh Matthew M. , Kerscht Ingrid H. , Messing Gary L.
Published: July 2010

The distribution and orientation of platelet‐shaped particles of α‐alumina in a fine‐grained alumina matrix is shown to template texture development via anisotropic grain growth. The textured microstructure ranges from 4 wt% oriented platelet particles in calcined samples to nearly 100% oriented α‐Al2O3 grains after sintering at 1400°C. A CaO + SiO2 liquid phase creates favorable thermodynamic and kinetic conditions for anisotropic grain growth and grain reorientation during sintering. Important criteria for templated grain growth include (1) anisotropic crystal structure and growth, (2) high thermodynamic driving force for template grain growth, and (3) modification of diffusion in the system to continuously provide material to the anisotropically growing template grains.
Composite Laminates in Plane Stress: Constitutive Modeling and Stress Redistribution due to Matrix Cracking
Authors: Genin Guy M. , Hutchinson John W.
Published: July 2010

Plane‐stress constitutive relations for laminate composites undergoing matrix cracking are developed that can be fit to data from uniaxial tests. The constitutive equations are specialized to brittle‐matrix composites in the form of crossplies and quasi‐isotropic laminates. The effect of nonlinear stress–strain behavior on stress redistribution around holes and notches in laminate plates is illustrated.
Effect of Crystallinity on Strength and Fracture Toughness of Li2O‐Al2O3‐CaO‐SiO2 Glass‐Ceramics
Authors: Anusavice Kenneth J. , Zhang Nai‐zheng
Published: July 2010

The influence of crystal volume fraction on fracture toughness (KIC) and indentation strength was analyzed for Li2O‐Al2O3‐CaO‐SiO2 (LACS) and LACS glass‐ceramics containing 0.58 mmol% AgNO3 (LACS‐0.58Ag) or 0.78 mmol% AgNO3 (LACS‐0.78Ag). The mean flexure strength, indentation strength, and KIC values of the LACS‐0.78Ag groups increased with volume fraction of crystallinity. To achieve the greatest strength and KIC in LACS‐Ag specimens, a high volume fraction of crystallinity (95%) had to be produced. However, the relationship between volume fraction of crystal phase and translucency had to be analyzed to determine the influence of crystallization on the potential esthetic results that are essential for dental applications. Addition of AgNO3 to LACS glass produced a change from surface crystallization to bulk crystallization.
Combined Mode I–Mode II Fracture of 12‐mol%‐Ceria‐Doped Tetragonal Zirconia Polycrystalline Ceramic
Authors: Tikare Veena , Choi Sung R.
Published: July 2010

The mode I, mode II, and combined mode Imode II fracture behavior of ceria‐doped tetragonal zirconia polycrystalline (Ce‐TZP) ceramic was studied. The single‐edge‐precracked‐beam (SEPB) samples were fractured using the asymmetric four‐point‐bend geometry. The ratio of mode I to mode II loading was varied by varying the degree of asymmetry in the four‐point‐bend geometry. The minimum strain energy density theory best described the mixed‐mode fracture behavior of Ce‐TZP with the mode I fracture toughness, KIC= 8.2 ± 0.6 MPa·m1/2, and the mode II fracture toughness, KIIC= 8.6± 1.3 MPa·m1/2.
Computer Simulations of Diffraction Effects due to Stacking Faults in β‐SiC: I, Simulation Results
Authors: Pujar Vijay V. , Cawley James D.
Published: July 2010

X‐ray diffraction (XRD) patterns from nominally β‐SiC specimens often differ from those expected for the cubic crystal structure. These differences include the presence of additional peaks, enhanced background intensities, peak broadening, changes in relative peak heights, and shifts in peak positions. It has long been recognized that they are due to the presence of stacking faults, and models relating the experimental observations to stacking fault population have continued to evolve. The presence and relative magnitude of these features vary among different β‐SiC specimens. In this work, computer simulations were used to show that the variations are closely related to differences in the type and spatial distribution of stacking faults in each specimen. In these simulations, stacking sequences were generated using a selectively activated 1‐D Ising model with a Boltzmann‐type probability function for specifying errors, which allows a wide variety of fault configurations to be generated. Direct correlations between different features in the XRD data to the underlying fault population are demonstrated, which are discussed in this paper. It is also shown that this computer model is general, in the sense that many of the models presented in prior work can be interpreted as limiting cases of it.
Microstructure Evolution of ZrO2‐(Fe2O3, Al2O3) Materials Synthesized with Solution Precursors
Authors: Narwankar Pravin K. , Lange Fred F. , Levi Carlos G.
Published: July 2010

Aqueous Zr‐nitrate solutions containing appropriate amounts of Fe(NO3)3·6H2O and Al(NO3)3·6H2O were used to synthesize ZrO2‐Fe2O3 compositions (up to 40 mol% Fe2O3) and one ZrO2‐Al2O3‐Fe2O3 composition. An amorphous phase was produced after pyrolysis, which subsequently crystallized to a single‐phase Zr(Fe)O2 solid solution (or Zr(Fe,Al)O2 ss) that appeared cubic by X‐ray diffraction, but tetragonal (c/a→ 1) by electron diffraction. The crystallization temperature increased with Fe2O3 content. At higher temperatures, the single phase partitioned to two phases, tetragonal‐ZrO2+γ‐Fe2O3. The γ‐ to α‐Fe2O3 transformation occurred at still higher temperatures to produce a two‐phase microstructure composed of two interpenetrating phases (ZrO2+α‐Fe2O3), each with equiaxed grains. This microstructure was relatively stable to grain coarsening, even to temperatures just below the apparent eutectic temperature. With the exception of the lower transition temperatures and the equiaxed grains observed for both phases, these observations are similar to that previously reported for the ZrO2‐Al2O3 system. The microstructure development reported here is another example for the synthesis via solution processing that involves diffusion‐limited crystallization. Namely, a two‐phase material can be produced where the grain size of each can be very small, and can be prevented from growing rapidly at high temperatures due to the constraint of each phase on one another.
Feasibility of Using Cordierite Glass‐Ceramics as Tile Glazes
Authors: Ferrari Anna Maria , Barbieri Luisa , Leonelli Cristina , Manfredini Tiziano , Siligardi Cristina , Corradi Anna Bonamartini
Published: July 2010

Basic principles of fabricating tile glazes based on cordieritic glass‐ceramics are explained. Glass compositions from the MgO‐Al2O3‐SiO2 three‐component phase diagram have been melted with and without the nucleating agent TiO2. Additionally, a sodium borosilicate glass that is commonly used in the tile glaze industry has been wet milled, together with the previous compositions, to produce a coating slip. Studies are focused on the role of the nucleating agent and glassy formulation in the crystallization of the glass‐ceramic system using differential thermal analysis, X‐ray diffractometry, and scanning electron microscopy. When added to a borosilicate glass, only one composition is capable of crystallizing cordierite under a fast‐firing cycle used for “monoporosa” production. The porosity of the glaze layer is sufficiently low and the crystal size is small to ensure good mechanical and chemical properties. The presence of cordierite crystals in the glaze should enhance abrasion and acid resistance, in comparison to a traditional matte glaze that contains mostly enstatite or diopside crystals.
Spherical Indentation and Fracture of Glass Plates
Authors: Lardner Thomas J. , Ritter John E. , Zhu Gao‐Qiu
Published: July 2010

Spherical indentation of thick and thin glass plates was investigated numerically and experimentally. The energy release rate at the tip of a cone crack was calculated by using finite element techniques and used to investigate the applicability in thick plates of Roesler's law relating the cone crack radius to the indentation load. Indentations of thin glass specimens resting on different substrates were also studied numerically and experimentally. The stresses in the thin specimens were calculated and correlated with the observed failures. On the basis of these results, a crack initiation mechanism map was developed for glass specimens on different substrates.
Three‐Dimensional Carbon/Silicon Carbide Composites Prepared by Chemical Vapor Infiltration
Authors: Xu Yongdong , Zhang Litong
Published: July 2010

Continuous‐carbon‐fiber‐reinforced silicon carbide composites (C/SiC) were prepared by chemical vapor infiltration in which the preforms were fabricated with the three‐dimensional braid method. The mechanical properties and microstructures were investigated. For the composites with no interfacial layer, flexural strength and fracture toughness increased with density of the composites, and the maximum values were 520 MPa and 16.5 MPa·m1/2, respectively. The fracture behavior was dependent on the interfacial bonding between fiber/matrix and fiber bundle/bundle which was determined by the density of the composites. Heat treatment had a significant influence on the mechanical properties and fracture behavior. The composites with pyrolysis interfacial layers exhibited characteristic fracture and relatively low strength (300 MPa).
Mechanical Properties of Dry‐Pressed Ceramic Green Products: The Effect of the Binder
Authors: Baklouti Samir , Chartier Thierry , Baumard Jean François
Published: July 2010

The strength of alumina green samples prepared by uniaxial pressing of powders spray‐dried with two binders such as poly(ethylene glycol) or poly(vinyl alcohol) is discussed in terms of (i) the adhesive properties of the polymer‐rich external layer of spray‐dried granules and (ii) the mechanical properties of this layer. A transition from intra‐ to intergranular fracture is observed when the glass transition temperature of the binder increases. The influence of the binder on the defect size distribution in the green products is investigated using the classical Weibull statistics.
Microstructure and High‐Temperature Mechanical Behavior of Alumina/Alumina–Yttria‐Stabilized Tetragonal Zirconia Multilayer Composites
Authors: Jiménez‐Melendo Manuel , Clauss Carolina , Doḿnguez‐Rodŕguez Arturo , Sánchez‐Herencia Antonio J. , Moya José S.
Published: July 2010

Layered composites of alternate layers of pure Al2O3(thickness of 125 μ m) and 85 vol% Al2O3‐15 vol% ZrO2 that was stabilized with 3 mol% Y2O3(thickness of 400 μ m) were obtained by sequential slip casting and then fired at either 1550° or 1700°C. Constant‐strain‐rate tests were conducted on these materials in air at 1400°C at an initial strain rate of 2 × 10‐5 s‐1. The load axis was applied both parallel and perpendicular to the layer interfaces. Catastrophic failure occurred for the composite that was fired at 1700°C, because of the coalescence of cavities that had developed in grain boundaries of the Al2O3 layers. In comparison, the composite that was fired at 1550°C demonstrated the ductility of the Al2O3+YTZP layer, but at a flow stress level that was determined by the Al2O3 layer.
Colloidal Processing of Silicon Nitride with Poly(acrylic acid): I, Adsorption and Electrostatic Interactions
Authors: Hackley Vincent A.
Published: July 2010

The role of poly(acrylic acid) (PAA) in the dispersion of silicon nitride suspensions was investigated experimentally. The effects of concentration, relative molecular mass, and suspension pH were evaluated. The ionization of PAA was characterized by potentiometric titration and indicated a pH‐dependent conformational transition. The isoelectric point for silicon nitride decreased from pH 6.3 to pH 3 as the PAA concentration increased, roughly independent of relative molecular mass. A broadening of the stability region for silicon nitride was attributed to this effect. Redispersion in alkaline media, subsequent to destabilization by surface‐charge neutralization, improved following preadsorption of PAA in acidic media. This effect was attributed to formation of a protective polymer adlayer on the surface, which prevented primary minimum aggregation; an electrosteric contribution also may be present. The influence of free polymer on the suspension properties also is discussed.
A Strong and Damage‐Tolerant Oxide Laminate
Authors: Kuo Dong‐Hau , Kriven Waltraud M.
Published: July 2010

A novel laminar oxide composite was developed. This oxide laminate, which was fabricated by hot pressing, consisted of three types of layers, which were stacked in a repeating sequence of YPO4, yttria‐stabilized ZrO2, 30 vol% yttria‐stabilized ZrO2‐70 vol% Al2O3, and yttria‐stabilized ZrO2. The behavior of the oxide laminate was evaluated by four‐point flexural testing and the indentation technique. The flexural strength from one test was 358 MPa, and the load‐displacement curve of this test displayed a graceful failure. Pronounced interfacial delamination contributed to a high work of fracture and damage tolerance. These properties have rarely been observed in oxide composites and are comparable to those of non‐oxide composites, such as SiC/graphite, SiC/BN, and Si3N4/BN laminates.
Defect Chemistry of Donor‐Doped and Undoped Strontium Titanate Ceramics between 1000° and 1400°C
Authors: Moos Ralf , Hardtl Karl Heinz
Published: July 2010

The electrical conductivity, sigma, of donor‐doped and undoped strontium titanate (SrTiO3) ceramics and, in some cases, single crystals, Sr1‐xLaxTiO3 (0 ≤ to x ≤ 0.1), was investigated in the temperature range of 1000°‐1400°C under oxygen partial pressures, PO2, of 10‐20‐1 bar. In conjunction with Hall data and thermopower data from related papers, a set of constants for a defect‐chemical model was determined, precisely describing point‐defect concentrations and transport properties of these materials. In contrast to former works, temperature‐dependent transport parameters and their non‐negligible influence on the determination of the constants was considered, as well as the equilibrium restoration phenomena of the cation sublattice, which can be studied only at such high temperatures. It was shown that defects in the cation sublattice completely govern the electrical behavior of donor‐doped and undoped SrTiO3. In the latter case, frozen‐in strontium vacancies act as intrinsic acceptors, determining the sigma(PO2) curves at lower temperatures. This intrinsic acceptor concentration also can be calculated with this model. The very good agreement between calculation and measurement is shown in many examples.
A Processable Mullite Precursor Prepared by Reacting Silica and Aluminum Hydroxide with Triethanolamine in Ethylene Glycol: Structural Evolution on Pyrolysis
Authors: Kansal Pallavi , Laine Richard M. , Babonneau Florence
Published: July 2010

A simple, processable precursor to mullite can be synthesized in quantities of 100 g in a few hours by direct reaction of silica, aluminum hydroxide, and triethanolamine in ethylene glycol. To delineate a processing window whereby precursor shapes can be transformed into mullite, the chemical and phase microstructural evolution of this precursor on pyrolysis to selected temperatures in air is followed by thermal gravimetric analysis, differential thermal analysis, diffuse reflectance infrared Fourier transform spectroscopy, solid‐state 27Al and 29Si nuclear magnetic resonance, X‐ray diffractometry, and Brunauer‐Emmett‐Teller analytical methods. The precursor behaves as a single‐phase, atomically mixed material that initially transforms to a porous, amorphous aluminosilicate when heated to temperatures as high as 950°C. Above 950°C, the precursor first transforms to tetragonal mullite, based on comparison with the literature, and, on continued heating above 1200°C, to orthorhombic mullite with coincident loss of porosity.
Nucleation and Crystallization of a Lithium Aluminosilicate Glass
Authors: Barbieri Luisa , Leonelli Cristina , Manfredini Tiziano , Siligardi Cristina , Corradi Anna Bonamartini , Mustarelli Piercarlo , Tomasi Corrado
Published: July 2010

An aluminosilicate glass of composition 61SiO26Al2O310MgO6ZnO·12Li2O·5TiO2 (mol%) has been prepared by a melting process and investigated as far as crystallization is concerned. Glass‐ceramic is easily obtained because glass shows a high tendency to crystallize starting from 700°C. The crystalline phases evolve with temperature, showing the aluminosilicates to be the main phase up to 1050°C, followed by metasilicates and silicates, some of which have lower melting points. The titanates of Mg and Zn develop from the phase‐separated glass, soon after Tg, and grow to form nucleation centers for the other crystalline phases. The evolution from phase‐separated glass to glass‐ceramic has been followed by many thermal, diffractometric, spectroscopic, and microscopic techniques.
Leakage and Reliability Characteristics of Lead Zirconate Titanate Thin‐Film Capacitors
Authors: Al‐Shareef Husam N. , Dimos Duane
Published: July 2010

Resistance degradation in lead zirconate titanate (Pb(Zr,Ti)O3, PZT) thin‐film capacitors has been studied as a function of applied voltage, temperature, and film composition. The mean time‐to‐failure (lifetime, or tf) of the capacitors shows a power‐law dependence on voltage of the form tf∝V−n (n similar/congruent 4‐5). The capacitor lifetime also exhibits a temperature dependence of the form tf∝ exp[Ea/(kT)], with an activation energy of 0.6‐1.0 eV. The steady‐state leakage current in these samples seems to be bulk controlled. The voltage V, temperature T, and polarity dependence of the leakage current collectively suggest a leakage‐current mechanism that is most similar to a Frenkel‐Poole process. The tf value and the leakage current of niobium‐doped PZT films are superior to those of undoped PZT films. This result can be explained on the basis of the point‐defect chemistry of the PZT system. Finally, the results indicate that the niobium‐doped PZT films meet essential tf requirements for decoupling‐capacitor applications.
Low‐Temperature Electrochemical Synthesis of ZrO2 Films on Zirconium Substrates: Deposition of Thick Amorphous Films and in situ Crystallization on Zirconium Anode
Authors: Tsukada Takayuki , Venigalla Sridhar , Adair James H.
Published: July 2010

The feasibility of synthesizing crystalline ZrO2 films at low temperatures was evaluated using an electrochemical method. Anodization of zirconium‐metal substrates in tetraethyl ammonium hydroxide (TEAOH) solutions under constant applied voltage conditions at ∼25° and ∼100°C was investigated. The chemistry and microstructure of the anodic oxide films deposited on the zirconium‐metal substrates under the above conditions were characterized using X‐ray diffractometry and scanning electron microscopy. The results indicated that, with sufficiently high applied voltages (in the range of 300 V) at pH ∼9.5, the initial dissolution of the zirconium anode resulted in the local saturation of the electrolyte solution with Zr4+, forming Zr(OH)−5, which deposited electrophoretically on the anode as a thick, gelatinous film at 25°C. Similar treatments at 100°C resulted in an in situ crystallization of Zr(OH)4 gel to monoclinic ZrO2.
Oxidation‐Resistant Fiber Coatings for Non‐oxide Ceramic Composites
Authors: Luthra Krishan L.
Published: July 2010

Oxidation of fiber/matrix interfaces can degrade the strength and toughness of ceramic composites containing non‐oxide constituents. Oxidation can occur when the fiber ends are exposed or in the presence of cracks. Theoretical considerations indicate that, contrary to popular belief, oxide fiber coatings should be worse than non‐oxide fiber coatings for protection against oxidation. Furthermore, oxidation of fiber/matrix interfaces is a composite system problem rather than that of the fiber coating.
Defect Chemistry of (La,Sr)MnO3
Authors: Nowotny Janusz , Rekas Mieczyslaw
Published: July 2010

Defect‐disorder models are derived for undoped and strontium‐doped LaMnO3. A random‐defect model and a cluster‐defect model are both considered within the regimes that correspond to oxygen deficit and oxygen excess. The models are constructed based on the experimental nonstoichiometry data that was reported by previous researchers. According to both models, the addition of strontium leads to an increase of the concentration of electron holes and oxygen nonstoichiometry. The defect clusters that are predicted by the cluster model have a marked concentration only at very low oxygen partial pressures. Both models are verified against the electrical‐conductivity data. A good agreement between the random‐defect model and the experimental data is shown.
Possible Role of the Oxygen Potential Gradient in Enhancing Diffusion of Foreign Ions on α‐Al2O3 Grain Boundaries
Authors: Pint Bruce A. , Garratt‐Reed Anthony J. , Hobbs Linn W.
Published: July 2010

Thermally grown, alpha‐Al2O3 external scales formed on alloys after oxidation in pure oxygen at temperatures between 1000° and 1500°C were analyzed using FEG‐STEM/XEDS. Alloy dopants such as Y, Zr, La, Hf, and Ti were found to segregate to the alpha‐Al2O3 grain boundaries and to the alloy‐scale interface. With increasing oxidation time and temperature, the amount of segregant on the oxide grain boundaries near the gas interface increases until a critical level is reached and precipitates begin to nucleate and grow. These observations are a result of the outward transport of dopants from the alloy, through the external alumina scale, to the gas interface. The apparent driving force for the dopant diffusion is the oxygen potential gradient in the growing oxide scale.
Influence of Thermal and Electrical Histories on Domain Structure and Polarization Switching in Potassium‐Modified Lead Zirconate Titanate Ceramics
Authors: Tan Qi , Viehland Dwight
Published: July 2010

The dependence of domain evolution and polarization switching on thermal and electrical histories has been investigated for K1+‐ion‐modified lead zirconate titanate (PZT) ceramics by using hot‐stage transmission electron microscopy and Sawyer—Tower polarization methods. In each case, the domains were very narrow, on the order of several hundred angstroms. In the aged condition, the domain structure was dominated by a “wavy” morphology. In the as‐quenched condition, fine and straight 180° domains were found that extended across entire grains. In the field‐cooled condition, fine and straight 70° and 110° domains were found. Corresponding polarization studies revealed double‐loop characteristics in the as‐quenched and aged conditions. In both these cases, the switchable polarization was much less than that of the base PZT composition. In the field‐cooled condition, a single polarization loop was observed. However, the polarization—electric field (P—E) curve was skewed from the origin, and the polarization was not completely switchable on field reversal. These changes in domain stability and P—E properties have then been explained in terms of the dependence of a spatial distribution of polarizable defect complexes on thermal and electrical histories.
In Situ Processing and Properties of SiC/MoSi2 Nanocomposites
Authors: Lee Jong Ik , Hecht Norman L. , Mah Tai‐Il , Mah Tai‐Il
Published: July 2010

A novel concept for in situ processing of SiC/MoSi2 nanocomposites has been developed that combines the pyrolysis of MoSi2 particles coated with polycarbosilane and subsequent densification by hot pressing. After densification, a uniform dispersion of SiC particles is obtained in the MoSi2 matrix. The strength at both room and elevated temperature is dramatically improved by the processing protocol employed. The average room‐temperature flexural strength measured for the SiC/MoSi2 nanocomposite was 760 versus 150 MPa for unreinforced MoSi2. The average 1250°C flexural strength measured for the SiC/MoSi2 nanocomposite was 606 versus 77 MPa for unreinforced MoSi2.
Dynamics of Consolidation and Crack Growth in Nanocluster‐Assembled Amorphous Silicon Nitride
Authors: Tsuruta Kenji , Nakano Aiichiro , Kalia Rajiv K. , Vashishta Priya
Published: July 2010

Consolidation and fracture dynamics in nanophase amorphous Si3N4 are investigated using 106‐atom molecular‐dynamics simulations. At a pressure of 15 GPa and 2000 K, the nanophase system is almost fully consolidated within a fraction of a nanosecond. The consolidation process is well‐described by the classical theory of sintering. Under an applied strain the consolidated system develops several cracks which propagate parallel to each other, causing failure at multiple sites. The critical strain at which the nanophase system fractures is much larger than that for crystalline Si3N4.
Contact‐Induced Transverse Fractures in Brittle Layers on Soft Substrates: A Study on Silicon Nitride Bilayers
Authors: Lee Kee Sung , Wuttiphan Sataporn , Hu Xiao‐Zhi , Lee Seung Kun , Lawn Brian R.
Published: July 2010

An analysis of transverse cracks induced in brittle coatings on soft substrates by spherical indenters is developed. The transverse cracks are essentially axisymmetric and geometrically conelike, with variant forms dependent on the location of initiation: outer cracks that initiate at the top surface outside the contact and propagate downward; inner cracks that initiate at the coating/substrate interface beneath the contact and propagate upward; intermediate cracks that initiate within the coating and propagate in both directions. Bilayers consisting of hard silicon nitride (coating) on a composite underlayer of silicon nitride with boron nitride platelets (substrate), with strong interfacial bonding to minimize delamination, are used as a model test system for Hertzian testing. Test variables investigated are contact load, coating/substrate elastic‐plastic mismatch (controlled by substrate boron nitride content), and coating thickness. Initiation of the transverse coating cracks occurs at lower critical loads, and shifts from the surface to the interface, with increasing elastic‐plastic mismatch and decreasing coating thickness. This shift is accompanied by increasing quasi‐plasticity in the substrate. Once initiated, the cracks pop in and arrest within the coating, becoming highly stabilized and insensitive to further increases in contact load, or even to coating toughness. A finite element analysis of the stress fields in the loaded layer systems enables a direct correlation between the damage patterns and the stress distributions: between the transverse cracks and the tensile (and compressive) stresses; and between the subsurface yield zones and the shear stresses. Implications of these conclusions concerning the design of coating systems for damage tolerance are discussed.
Growth of TiO2 Single Crystals and Bicrystals by the Laser‐Heated Floating‐Zone Method
Authors: Kotani Toshihiro , Tuller Harry L.
Published: July 2010

TiO2 bicrystals with controlled misorientation have been grown by a laser‐heated floating‐zone method using a [001] oriented bicrystal seed designed for producing a (210)[001] tilt boundary. The grain boundary and crystal morphology are sensitive to the growth atmosphere, as confirmed by optical and transmission electron microscopies and by the Laue X‐ray back‐reflection method. These observations are discussed with respect to the nonstoichiometry of TiO2.
Residual Stress Fields at the Surface of Sharp Pyramid Indentations
Authors: Zeng Kaiyang , Giannakopoulos Antonios E. , Rowcliffe David , Meier Patrick
Published: July 2010

This paper describes an experimental measurement of the residual stress field around Berkovich and Knoop indentations on the surface of soda‐lime glass. The isostress contours of both the residual tensile and compressive stress are presented. The results are compared with similar measurements around Vickers indentations on the same glass. The residual stress field around all three different shapes of indentations is clearly nonequal biaxial, with characteristic differences in the form of the stress contours that relate to each specific shape. The results for Berkovich indentation are compared with finite element (FEM) numerical calculations. Some general conclusions related to the sharp indentations are deduced from this study.
Kinetics of Solid‐State Reaction of BaO2 and α‐Fe2O3
Authors: Watanabe Koichi
Published: July 2010

The reaction kinetics of an equimolar mixture of BaO2 and alpha‐Fe2O3 were investigated in an ambient atmosphere under isothermal conditions. The volume fraction of products was determined using the integrated X‐ray diffraction intensities of the most prominent peaks, and the rate constants of the reaction were calculated with the Jander equation. The apparent activation energy for the formation of BaFeO3‐x (x= 0.02‐0.08) was 82 ± 6 kJmol−1, and that for the formation of BaFe2O4 was 82 ± 7 kJmol−1.
Processing of Concentrated Aqueous Silicon Nitride Slips by Slip Casting
Authors: Albano María P. , Garrido Liliana B.
Published: July 2010

The optimization of concentrated Si3N4 powder aqueous slurry properties to achieve high packing density slipcast compacts and subsequent high sintered densities was investigated. The influence of pH, sintering aid powder (6% Y2O3, 4% Al2O3), NH4PA dispersant, and Si3N4 oxidative thermal treatment was determined for 32 vol% Si3N4 slurries. The results were then utilized to optimize the dispersion properties of 43 vol% solids Si3N4‐sintering aid slurries. Calcination of the Si3N4 powder was observed to result in significantly greater adsorption of NH4PA dispersant and effectively reduced the viscosity of the 32 vol% slurries. Lower viscosities of the optimized dispersion 43 vol% Si3N4‐sintering aid slurries resulted in higher slipcast packing density compacts with smaller pore sizes and pore volumes, and corresponding higher sintered densities.
Crystallite Size and Microstrain of Thermally Aged Low‐Ceria‐ and Low‐Yttria‐Doped Zirconia
Authors: Lin Jyung‐Dong , Duh Jenq‐Gong
Published: July 2010

The final phases of zirconia powders depend on the synthesis method employed, and the amounts of stabilizer present. In this study, ceria‐ and yttria‐doped zirconia powders were prepared by urea hydrolysis and subsequent hydrothermal treatment. The amount of tetragonal (t) vs monoclinic (m) phase in the powders increased with increasing stabilizer content, while the tetragonal phase size decreased and the microstrain of t crystals remained unchanged. The thermal degradation behavior of the metastable t phase in zirconia containing a low CeO2 or YO1.5 doping level was explored during aging treatment by means of X‐ray line profile broadening analysis. Both ultrafine yttria‐ and ceria‐doped zirconia powder pellets exhibit isothermal t→m transformation after aging at 900°C for various times. It is argued that a crystallite size effect, rather than the dopant valence, dictates the occurrence of the t→m transformation in ultrafine zirconia powders. The change in crystallite sizes of both t and m phases during aging depends significantly on the amount of stabilizer, aging time, and mechanism of t→m phase transformation. However, the change of microstrain in both t and m phases is related to the amount of stabilizers present and the matrix constraints.
Role of Microstructure in Hertzian Contact Damage in Silicon Nitride: II, Strength Degradation
Authors: Lee Seung Kun , Lawn Brian R.
Published: July 2010

In this Part II of a two‐part study of the role of microstructure on Hertzian contact damage in silicon nitride we determine strength degradation properties. As previously, three microstructures are investigated: fine (F), medium (M) and coarse (C), representing a progressive transition from brittle to quasi‐plastic damage. In both the F and M materials, failures originate from cone cracks (although limited quasi‐plasticity is evident in the latter material). These two materials show abrupt losses in strength at the critical contact loads for cone crack initiation, and steady falloff thereafter at higher contact loads. In the C material, failures occur from critical shear faults within the damage “yield” zones. The strengths in this material fall off much more gradually, without abrupt drop, above about twice the critical load for the onset of yield. Fracture mechanics models for each type of failure mode provide explicit relations for the degraded strength as a function of contact load. These models account for all the essential features in the observed strength degradation data. Particular attention is given to indenter size effects in the strength responses. Sphere radius has a profound influence on the critical loads for the onset of degradation, but relatively little influence on the degraded strengths at higher loads. Implications of the results concerning contact fatigue and wear are briefly considered.