bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Processing Parameters on Alumina Coatings Deposited on Nickel Substrates by Reacting Aluminum Chloride and Hydrogen/Carbon Dioxide Gas Mixtures
Authors: Bae Yong W. , Lee Woo Y. , Besmann Theodore M. , Cavin O. Burl , Watkins Thomas R.
Published: July 2010

Pure nickel coupons were used as substrates in the deposition of alumina (Al2O3) from the reaction of aluminum chloride (AlCl3) with hydrogen/carbon dioxide gas mixtures in the temperature range of 954°–1100°C and system pressures of 2.7–13.3 kPa. The apparent activation energy estimated from the coating growth rate averaged 320 kJ/mol at 13.3 kPa. At temperatures <1000°C, transition theta, kappa, and delta modifications were codeposited with alpha‐Al2O3, whereas single‐phase alpha‐Al2O3 was deposited at higher temperatures. At high AlCl3 partial pressures, nickel aluminide phases were sometimes codeposited with Al2O3, which was attributed to the reaction of AlCl3 with the nickel substrate in the presence of hydrogen gas.
Oxidation of Chemically‐Vapor‐Deposited Silicon Carbide in Carbon Dioxide
Authors: Opila Elizabeth J. , Nguyen QuynhGiao N.
Published: July 2010

Chemically‐vapor‐deposited silicon carbide (CVD SiC) was oxidized in carbon dioxide (CO2) at temperatures of 1200–1400°C for times between 96 and 500 h at several gas flow rates. Oxidation weight gains were monitored by thermogravimetric analysis (TGA) and were found to be very small and independent of temperature. Possible rate‐limiting kinetic mechanisms are discussed. Passive oxidation of SiC by CO2 is negligible compared to the rates measured for other oxidants that are also found in combustion environments, oxygen and water vapor.
Novel Doping Mechanism for Very‐High‐Permittivity Barium Titanate Ceramics
Authors: Morrison Finlay D. , Sinclair Derek C. , Skakle Janet M. S. , West Anthony R.
Published: July 2010

Barium titanate (BaTiO3) can be doped with La3+ ions via partial substitution for Ba2+ ions; charge balance is maintained by the creation of Ti4+ vacancies. Samples processed in an atmosphere of 1 bar O2 and a temperature of 1350°C are insulating and free from electronic defects associated with either O2 loss or reduction of Ti4+ to Ti3+. The Curie temperature (Tc) decreases approximately linearly as the lanthanum content increases and, at the same time, an increase in the permittivity (ɛ′) maximum at Tc occurs. For the composition Ba1‐xLaxTi1‐x/4O3, where x= 0.05, ɛ′ has a maximum value of 19000 at 18°C, compared with a typical value of 10000 at 130°C in undoped BaTiO3 ceramics. This value is the highest value reported for A‐site‐doped BaTiO3 and is linked to the mechanism of combined A‐site doping and Ti‐vacancy creation.
Chemical Shifts of Silicon X‐ray Photoelectron Spectra by Polymerization Structures of Silicates
Authors: Okada Kiyoshi , Kameshima Yoshikazu , Yasumori Atsuo
Published: July 2010

The binding energy of Si 2p electrons and the kinetic energy of the Si(KLL) X‐ray‐excited state were measured by using X‐ray photoelectron spectroscopy (XPS) and X‐ray Auger electron spectroscopy (XAES), respectively, for silicates with SiO4 tetrahedra of various polymerization types. The resulting Si 2p XPS binding energies varied from 101.3 eV in merwinite (monomeric structure) to 103.4 eV in quartz and cristobalite (three‐dimensional framework structure). A clear chemical‐shift relation was observed, relating the polymerization structures of SiO4 tetrahedra to the plots of their Si 2p XPS binding energy versus the kinetic energy of their Si(KLL) XAES spectra. Thus, the structural state of the surface silicates in various substances can be deduced from this chemical‐shift relationship.
Nonuniform Heating in Zinc Oxide Varistors Studied by Infrared Imaging and Computer Simulation
Authors: Wang Hsin , Bartkowiak Miroslaw , Modine Frank A. , Dinwiddie Ralph B. , Boatner Lynn A. , Mahan Gerald D.
Published: July 2010

State‐of‐the‐art infrared (IR) thermal imaging was used to monitor the heating of ZnO varistors by electrical transients. On a macroscopic scale (e.g., 10 mm), heating in large varistor blocks (i.e., diameter of 42 mm) was found to be the greatest near the block edges and to be approximately radially symmetric in blocks fabricated at a low aspect ratio. In blocks fabricated at a higher aspect ratio, the heating was less symmetric, presumably because uniform properties are more difficult to achieve. Nonuniform heating in large blocks can be attributed to processing‐induced variations in the electrical properties of the blocks. On an intermediate size scale (e.g., 1 mm), the heating in small varistor disks (e.g., diameter of 10 mm) was observed to be most intense along localized electrical paths. The high electrical conductivity of these paths originates from the statistical fluctuations in properties that inevitably occur in polycrystalline materials. On a microscopic scale (e.g., 10 μm), the heating in thin varistor slices (e.g., thickness of 100 μm) was observed to be localized in strings of tiny hot spots. The hot spots occur at the grain boundaries in a conducting path, where the potential is decreased across Schottky‐type barriers and the heat is generated. The experimentally observed heating is interpreted by applying transport theory and using computer simulations. It is shown that, on the scale of the grain size, the heat transfer is too fast to permit temperature differences that could cause a varistor failure. Current localization and nonuniform heating on an intermediate size scale can have a microstructural origin (e.g., statistical fluctuations of grain sizes and grain‐boundary properties). However, these are shown to be significant only in small varistors, whereas destructive failures (puncture and cracking) of large varistor blocks can be caused only by nonuniform heating on a macroscopic scale.
Optical Properties of Rare‐Earth Ions in Lead Germanate Glasses
Authors: Wachtler Mario , Speghini Adolfo , Gatterer Karl , Fritzer Harald P. , Ajò David , Bettinelli Marco
Published: July 2010

Glasses of composition (x ‐ 1)PbO(100 ‐ x)GeO21Ln2O3, with x= 30 mol% (Ln = Nd, Eu, Er), 40 mol% (Ln = Pr, Nd, Sm, Eu, Dy, Ho, Er, Tm), and 50 mol% (Ln = Eu, Er), have been prepared by quenching the oxidic melts. From the optical absorption and emission spectra in the ultraviolet‐visible‐near‐infrared (UV‐VIS‐NIR) region, the intensity parameters, spontaneous emission probabilities, branching ratios, radiative lifetimes, and, for selected NIR transitions, peak stimulated emission cross sections have been obtained. The trends observed in the intensity parameters have been discussed, as a function of the number of f electrons as well as a function of the lead content. As the amount of lead increases, the covalency of the Ln‐O bond increases, the symmetry of the rare‐earth site increases, and the dopant site distribution narrows. The peak stimulated emission cross sections rank among the highest found for oxide glasses.
Effects of Milling Liquid on the Reaction‐Bonded Aluminum Oxide Process
Authors: Watson Matthew J. , Chan Helen M. , Harmer Martin P. , Caram Hugo S.
Published: July 2010

The reaction‐bonded aluminum oxide process begins with aluminum, Al2O3, and usually ZrO2 powders that have been attrition‐milled in an organic liquid. The attrition‐milled powder is then compacted and heat‐treated in air to produce polycrystalline, Al2O3‐based ceramics. Safety considerations have made it desirable for the milling liquid to be changed from acetone to a less‐flammable solvent. In this paper, mineral spirits, ethanol, and mineral spirits that contains 2 wt% stearic acid are presented as viable alternatives to acetone. The effects of changing the milling liquid on the reaction process and the properties of the final fired ceramic are investigated.
General Observations of Constant Flow Rate Filter Pressing
Authors: Lin Ching‐Yao , Kellett Bruce J.
Published: July 2010

Consolidating powder compacts to a uniform and high particle packing density is a central aspect of ceramic processing. Experiments on the formation of powder compacts from slurries of differing properties and filter pressed under different conditions are presented. The influence of (1) piston velocity, (2) the solid content of the slurry, and (3) slurry viscosity are discussed. A simplified theory of nonuniform cake growth is developed. This theory is based on the assumption that the cake profile is time independent in a reference plane moving with the cake/slurry interface. Classical theory assumes uniform cake density, while more difficult finite element methods are required for calculating nonuniform cake growth conditions. This theory simplifies nonuniform cake consolidation mechanics and allows simple spread‐sheet‐type calculations on cake uniformity. Cake uniformity is an important goal in processing. Piston stress‐displacement behavior can be reasonably simulated from the fundamental cake properties (permeability and yield curve). The inverse, estimating the fundamental cake properties from piston stress‐displacement behavior, appears to provide only rough estimates of these characteristic parameters. The Kozeny‐Carman equation appears to reasonably fit the permeability behavior of these filter cakes.
Stress Rupture of an Enhanced Nicalon/Silicon Carbide Composite at Intermediate Temperatures
Authors: Steyer Todd E. , Zok Frank W. , Walls David P.
Published: July 2010

The stress rupture characteristics of an enhanced Nicalon/SiC composite at 900°C have been examined. This temperature has been identified as being in the regime wherein oxidation embrittlement is operative. The enhancement of the composite involves the use of a coating around the fiber tows, comprising a C‐rich matrix and B‐containing particulates. The efficacy of this oxidation protection scheme has been evaluated by comparing the stress rupture characteristics with those of both Nicalon/SiC composites without the enhancement and the fibers alone. Such comparisons indicate that a substantial portion of the strength loss is attributable to a degradation of the fibers, and that the performance of the enhanced material is marginally better than that of the reference (nonenhanced) composite. Moreover, at stress levels greater than the matrix cracking limit, oxidation embrittlement occurs rapidly and the rupture times (several hours) are short in relation to the targeted service lives of most ceramic composite components. The mechanisms associated with the embrittlement have been identified using scanning electron microscopy and Auger spectroscopy.
Numerical Simulation of Viscous Sintering by a Periodic Lattice of a Representative Unit Cell
Authors: Van de Vorst Alfred
Published: July 2010

In this paper numerical simulations of the viscous sintering phenomenon are presented, i.e., of the process that occurs (for example) during the densification of a porous glass heated to such a high temperature that it becomes a viscous fluid. The numerical approach consists of simulating the shrinkage of a two‐dimensional unit cell which is in some sense representative for the porous glass. Hence it is assumed that the microstructure of the glass can be described by a periodic continuation in two directions of this unit cell. In this way it is possible to obtain insights into the viscous sintering process with respect to both pore size and pore distribution of the material. In particular this model is able to examine the consequences of microstructures on the evolution of the pore size distribution. The major finding is that the pores vanish in order of size one after another‐the smallest pores first, followed by the larger ones. Moreover, it is shown that pores with concave boundary parts may initially grow before they start shrinking at a later stage.
Experimental Phase Diagram in the Ag‐Cu2O‐CuO System
Authors: Nishiura Hiroshi , Suzuki Ryosuke O. , Ono Katsutoshi , Gauckler Ludwig J.
Published: July 2010

Phase equilibria in the Ag‐CuO‐Cu2O system were experimentally determined using thermal analysis, and structural and compositional studies. Three reactions were observed in air: (1) L1= CuO + Ag, (2) L2= CuO + L1, and (3) Cu2O = CuO + L2. The evolution and absorption of oxygen accompanied these reactions. At oxygen partial pressures below 0.02 bar, the reactions L1= Cu2O + Ag and L2= Cu2O + L1 were found. Based on isobaric projections in the Ag‐CuO‐Cu2O system, two invariant reactions, L1= CuO + Cu2O + Ag and L2= CuO + Cu2O + L1, were deduced.
Incommensurately Modulated Polar Structures in Antiferroelectric Tin‐Modified Lead Zirconate Titanate: II, Dependence of Structure‐Property Relations on Tin Content
Authors: Forst Donald , Li Jie‐Fang , Xu Zhengkui , Viehland Dwight
Published: July 2010

Studies of the structure‐property relations in Pb0.98Nb0.02‐ [(Zr1‐xSnx)0.97Ti3]1‐zO3 (PZST x/3/2) were performed for 0 < x < 0.50 by transmission electron microscopy, dielectric spectroscopy, and electrically induced polarization and strain methods. As the tin content increased, a general sequence of changes in phase stability was observed, including (i) a ferroelectric rhombohedral (FEr) phase (x < 0.15), (ii) a coexistence of FEr and antiferroelectric incommensurate (AFEin) states (x = 0.15), and (iii) an AFEin state (x > 0.15). Evidence will be presented that incommensurately modulated structures become pinned into long‐lived metastable states by quenched tin impurities, rather than evolving toward a commensurate phase. Maximum electrically induced strains (epsilon) and polarizations (P) were found in the compositional range of x similar/congruent 0.15, where FEr and AFEin regions coexisted. Values of epsilon as large as 0.5% were found at field strengths of <80 kV/cm. In addition, these studies demonstrated evidence for two electrically induced phase transitions (x = 0.15): (i) an antiferroelectric‐ferroelectric (AFE‐FE) transition near 40 kV/cm, and (ii) a secondary ferroelectric‐ferroelectric (FE‐FE) transition near 60‐80 kV/cm. The dominate contribution to epsilon was associated with the secondary transition, whereas the dominate contribution to P was associated with the first. For x < 0.15, evidence of an induced FE‐FE transition was found. For x > 0.15, an induced AFE‐FE transition was evident. However, no indications of a secondary FE‐FE transition were observed. Large epsilon values were not induced until field levels significantly greater than that required to induced polarization saturation were obtained, which indicates a decoupling of epsilon and P.
Effect of Precrack “Halos” on Fracture Toughness Determined by the Surface Crack in Flexure Method
Authors: Swab Jeffrey J. , Quinn George D.
Published: July 2010

The surface crack in flexure method, which is used to determine the fracture toughness of dense ceramics, necessitates the measurement of precrack sizes by fractographic examination. Stable crack extension may occur from flaws under ambient, room‐temperature conditions, even in the relatively short time under load during fast fracture strength or fracture toughness testing. In this article, fractographic techniques are used to characterize evidence of stable crack extension, a “halo,” around Knoop indentation surface cracks. Optical examination of the fracture surfaces of a high‐purity Al2O3, an AlN, a glass‐ceramic, and a MgF2 reveal the presence of a halo around the periphery of each precrack. The halo in the AlN is merely an optical effect due to crack reorientation, whereas the halo in the MgF2 is due to indentation‐induced residual stresses initiating crack growth. However, for the Al2O3 and the glass‐ceramic, environmentally assisted slow crack growth is the cause of the halo. In the latter two materials, this stable crack extension must be included as part of the critical crack size to determine the appropriate fracture toughness.
Creep and Fatigue Behavior in an Enhanced SiC/SiC Composite at High Temperature
Authors: Zhu Shijie , Mizuno Mineo , Nagano Yasuo , Cao Jianwu , Kagawa Yutaka , Kaya Hiroshi
Published: July 2010

The monotonic tension, creep, and fatigue behavior of an enhanced SiC/SiC composite was investigated at a temperature of 1300°C in air and argon. The improved creep and fatigue resistances were determined and compared to those of the standard SiC/SiC composite. The effects of additives (glass‐forming, boron‐based particulates) in the matrix on the creep and environmental resistance of the enhanced SiC/SiC composite were discussed. Crack propagation in the matrix of the enhanced SiC/SiC composite was different from that in the standard SiC/SiC composite. The filling of the glassy phases in the cracks prohibited the diffusion of oxygen from the environment. As a result, creep and fatigue properties in the enhanced SiC/SiC composite in air at high temperatures was improved.
Low‐Temperature Transient Glass‐Phase Processing of Monoclinic SrAl2Si2O8
Authors: Chinn Richard E. , Haun Michael J. , Kim Chan Young , Price David B.
Published: July 2010

The use of transient glass‐phase processing to lower the glass‐melting temperature and subsequent heat‐treatment temperature of stoichiometric SrAl2Si2O8 to produce the stable monoclinic form has been described. Two nonstoichiometric, low‐melting, alumina‐deficient, strontium aluminosilicate compositions were melted, quenched, and milled into glass powders. B2O3 was dissolved into one of the glass compositions to control the crystallization behavior. The glass powders were then wet‐mixed with enough alpha‐Al2O3 powder so that the overall composition was that of stoichiometric SrAl2Si2O8 (B2O3 neglected). The four compositions were dry‐pressed into pellets and sintered in three processes. Glass‐alumina pellets with dissolved B2O3 were densified via viscous‐phase sintering at 1100°C, followed by complete dissolution of the alumina and crystallization to ~100% monoclinic SrAl2Si2O8. Pellets without dissolved B2O3 required considerably higher temperatures to form ~100% monoclinic SrAl2Si2O8 in a modified process.
Stress Relaxation, Creep Recovery, and Newtonian Viscous Flow in Silicon Nitride
Authors: Woodford David A.
Published: July 2010

A new approach to tensile creep testing and analysis based on stress relaxation is described for sintered silicon nitride. Creep rate data covering up to 5 orders of magnitude are generated in tests lasting less than 1 day. Tests from various initial stresses at temperatures up to 1300°C are analyzed and compared with creep rates measured during conventional constant load testing. It is shown that at least 40% of the creep strain accumulated under all test conditions is recoverable, and that the deformation may properly be described as viscoelastic. A regime which approximated as Newtonian viscous behavior (creep rate directly proportional to stress) was observed during decreasing stress at temperatures between 1200° and 1300°C. This resulted in anomalous behavior at low strains in pseudo stress‐strain curves generated from the stress relaxation data. However, the otherwise systematic rate dependence provides a possible basis for design in terms of a secant modulus analysis. The anelastic, recoverable component of creep may lead to complex deformation history‐dependent phenomena.
Chemistry of the Aqueous Phase of Ordinary Portland Cement Pastes at Early Reaction Times
Authors: Kelzenberg Anthony L. , Tracy Sharon L. , Christiansen Bruce J. , Thomas Jeffrey J. , Clarage Matthew E. , Hodson Simon , Jennings Hamlin M.
Published: July 2010

The chemistry of the aqueous phase of ordinary portland cement paste at early ages (<2 h) has been analyzed in terms of the concentrations of the elemental components in the pore fluid. The concentrations of calcium, sulfur, aluminum, and silicon are rationalized by plotting the data on “phase diagrams.” To simplify the analysis, the portland cement system is described using two subsystems: (i) CaO‐Al2O3‐CaSO4‐H2O, modified by the presence of sodium and potassium, and (ii) CaO‐SiO2‐H2O. During the first 10 min of hydration, the calcium, sulfur, and aluminum concentrations all decrease, roughly in proportion, which suggests a precipitation process, a conversion of calcium sulfate hemihydrate to gypsum, and the initial formation of ettringite. The CaO‐Al2O3‐CaSO4‐H2O subsystem seems to move from a phase assemblage of gypsum, Al2O3·3H2O, and ettringite to an assemblage of gypsum, calcium hydroxide, and ettringite during the first 15‐30 min after the water and the cement are mixed. The silicate equilibrium is approached more slowly. The intensity of mixing has relatively little effect on the concentrations beyond the first few minutes.
Kinetics of Metal‐Ceramic Composite Formation by Reactive Penetration of Silicates with Molten Aluminum
Authors: Saiz Eduardo , Tomsia Antoni P.
Published: July 2010

Wetting and reactions between molten Al and silicate substrates (particularly mullite) are studied to determine both how substrate tensity and p(O2) influence wetting behavior, reaction rates, composition, and reaction product microstructure and what key steps control penetration kinetics. Guidelines are provided for using reactive penetration or infiltration when fabricating metal/ceramic composites. For dense substrates, a reactive penetration process occurs. For a certain range, the chemical reaction between Al and the ceramic is a limiting kinetic step resulting in fast reaction rates. Maximum dense mullite substrate reaction rates are between 1000° and 1200°C independent of p(O2), unlike fused silica, which has faster penetration rates at higher temperatures. For mullite, reaction layer microstructure evolution halts reaction at higher temperatures. For porous substrates, reactive infiltration alone occurs. Either a critical temperature or p(O2) must be reached before infiltration starts.
Effect of Zirconia Content on the Oxidation Behavior of Silicon Carbide/Zirconia/Mullite Composites
Authors: Tsai Cheng‐Yuan , Lin Chien‐Cheng , Zangvil Avigdor , Li Ai‐Kang
Published: July 2010

The oxidation of hot‐pressed SiC‐particle (SiCp)/zirconia (ZrO2)/mullite composites with various ZrO2 contents, exposed in air isothermally at 1000° and 1200°C for up to 500 h, was investigated; an emphasis was placed on the effects of the ZrO2 content on the oxidation behavior. A clear critical volume fraction of ZrO2 existed for exposures at either 1000° or 1200°C: the oxidation rate increased dramatically at ZrO2 contents of >20 vol%. The sharp transition in the oxidation rate due to the variation of ZrO2 content could be explained by the percolation theory, when applied to the oxygen diffusivity in a randomly distributed two‐phase medium. Morphologically, the composites with ZrO2 contents greater than the critical value showed a large oxidation zone, whereas the composites with ZrO2 contents less than the critical value revealed a much‐thinner oxidation zone. The results also indicated that the formation of zircon (ZrSiO4) at 1200°C, through the reaction between ZrO2 and the oxide product, could reduce the oxidation rate of the composite.
Fracture of Alumina with Controlled Pores
Authors: Zimmermann André , Hoffman Mark , Flinn Brian D. , Bordia Rajendra K. , Chuang Tze‐Jer , Fuller Edwin R. , Rödel Jürgen
Published: July 2010

Fracture from artificial spherical pores, as well as natural defects, in alumina in a grain‐size range of 0.8‐9.2 µm has been studied experimentally and compared with a fracture‐mechanics model. Results from fracture‐strength measurements have been combined with detailed fractographic analysis to elucidate the ensuing crack instability. Two existing models of possible crack configurations have been extended and contrasted. The semicircular crack as well as the circumferential crack both are described as flaws in the stress‐concentrating field of a spherical pore. Surface correction terms afforded by the presence of the pore have been incorporated. A comparative computation shows that fracture occurs more likely from the semicircular crack configuration than the circumferential crack configuration.
Sintering and Phase Evolution of Electroless‐Nickel‐Coated Alumina Powder
Authors: Lin Yung‐Jen , Jiang Bor‐Feng
Published: July 2010

Alumina‐nickel powders have been prepared via electroless‐nickel (EN) coating of submicrometer‐sized alumina powder. The EN layers contain 5.1 ± 0.4 wt% phosphorus and are very unevenly distributed on the surfaces of the alumina particles. These layers consist of amorphous and microcrystalline phases. At temperatures greaterthan equal to1300°C, the EN layers de‐wet from the alumina surfaces to become discrete, round particles in the alumina matrix. The alumina‐EN pellets can be sintered to reach ~95% of the theoretical density at 1500°C for 4 h in graphite crucibles. The phases of the sintered samples consist of alumina, nickel, and nickel phosphides. However, in the exterior region of the sample sintered at 1500°C for 4 h, Ni3Al will also form.
A New Low‐Brittleness Glass in the Soda‐Lime‐Silica Glass Family
Authors: Sehgal Jeetendra , Ito Setsuro
Published: July 2010

In the soda‐lime‐silica glass family, the effect of each constituent of the composition on the brittleness was first investigated. Vickers indentation was employed to estimate the brittleness (ratio of harness (H) to fracture toughness (Kc)) by measuring the C/a ratios (where C and a are the characteristic crack and indentation diagonal lengths, respectively). It was observed that a higher silica content and a lower lime content helped to lower the brittleness. Substitution of potash and magnesia for soda and calcia, respectively, was effective in lowering the brittleness. From these results, a higher molar volume was found to be a key factor for reducing the brittleness. A new low‐brittleness glass was then developed with a brittleness as low as 5.1 µm‐1/2 as compared with the brittleness of 7.1 µm‐1/2 for commercial soda‐lime‐silica glass. The crack initiation load (P*), measured by the Vickers indentation method, for this new low‐brittleness glass was almost 10 times as high as P* of commercial soda‐lime‐silica glass. The new glass shows lower hardness and higher fracture toughness than the commercial soda‐lime‐silica glass.
Experimental Phase Equilibria in the PbOx‐CaO System
Authors: Suzuki Ryosuke O. , Nagata Jun‐ichi , Risold Daniel
Published: July 2010

Phase equilibria in the PbOx‐CaO system at oxygen partial pressures of 1.01 105 and 1.01 103 Pa were experimentally investigated. The temperatures of the eutectic reaction between PbO and PbCa2O4 and of the peritectic melting of PbCa2O4 were measured via differential thermal analysis at five oxygen partial pressures. The phase transition in air between PbO and Pb3O4 was not affected by the coexistence of PbCa2O4.
Fabrication, Microstructure, and Mechanical Properties of Cr2O3/ZrO2(2.5Y) Composite Ceramics in the Cr2O3‐Rich Region
Authors: Takano Yoshihiko , Komeda Tetsuya , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Intimate mixtures of Cr2O3/ZrO2(2.5Y) in the Cr2O3‐rich region are produced at low temperatures from amorphous materials prepared by the hydrazine method. Spark plasma sintering (SPS) has been performed for 10 min at 1300°C and 30 MPa. Composite ceramics with homogeneously dispersed fine ZrO2 (0.2 µm) give 99.8% of theoretical densities. Their mechanical properties are examined in connection with increased ZrO2 content. A high fracture toughness of 9.3 MPam1/2 and an excellent bending strength of 1290 MPa are achieved in the composite ceramics containing 50 mol% ZrO2.
Preparation of Transparent Thick Films by Electrophoretic Sol‐Gel Deposition Using Phenyltriethoxysilane‐Derived Particles
Authors: Katagiri Kiyofumi , Hasegawa Koichi , Matsuda Atsunori , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2010

Thick films were prepared on glass substrates coated with indium tin oxide (ITO) via electrophoretic deposition using sols that contained phenylsilsesquioxane (PhSiO3/2) particles derived from phenyltriethoxysilane. The transparency of the thick PhSiO3/2 films was significantly improved via heat treatment at temperatures >200°C. Scanning electron microscopy observation showed that the thick films changed in morphology, from aggregates of particles with several open spaces among the particles to a monolith with no open spaces after the heat treatment. Transparent films ~3 µm thick were obtained when the films were heat‐treated at a temperature of 400°C for 2 h.
Generalized Orowan‐Petch Plot for Brittle Fracture
Authors: Zimmermann André , Rödel Jürgen
Published: July 2010

The fracture of brittle solids is considered to be based on a defect configuration consisting of a stress concentrator, in our case a hemispherical pore, and a starter crack, in our case either a semicircular crack, a circular crack, or a circumferential crack. Computation of the stress field, application of the relevant weight functions, and an averaging scheme based on the assumption of a virtual crack increment provides stress intensity factors for all defect configurations considered. A normalization scheme yields a generalized version of the Orowan‐Petch plot in the form of a normalized strength to normalized defect size relationship.
Crystallization and Densification of Nano‐Size Amorphous Cordierite Powder Prepared by a PVA Solution‐Polymerization Route
Authors: Lee Sang‐Jin , Kriven Waltraud M.
Published: July 2010

A homogeneous and stable amorphous‐type cordierite (2MgO2Al2O35SiO2) powder was prepared by a solution‐polymerization route employing a Pechini resin or a poly(vinyl alcohol) (PVA) solution as the polymeric carrier. After calcination at 800°C for 1 h under atmospheric conditions, the bulky precursor changed into a very soft and porous powder. A 30 nm size, amorphous‐type cordierite powder was prepared by attrition milling the calcined powder, which was made using a PVA precursor solution. The nano‐size powder, which had a high specific surface area of 181 m2/g, was obtained after milling for <1 h. The sintered cordierite grains did not show the presence of any amorphous SiO2 phase and had a dense microstructure with a relative density of 99% and a thermal expansion coefficient of 2.1 10‐6/°C.
Effects of Chemical Species on the Crystallization Behavior of a Sol‐Derived Zirconia Precursor
Authors: Ong Chiau Ling , Wang John , Ng Ser Choon , Gan Leong Ming
Published: July 2010

The thermal and crystallization behaviors of a sol‐derived zirconia precursor are affected by the chemical species (such as chloride, acetate, and hydroxyl; i.e., Cl‐, CH3COO‐, and OH‐) present in the solution in which they are aged. The crystallization temperature of zirconia precipitate increases steadily with decreasing pH when hydrochloric acid is added to the aging mother liquor. A more dramatic increase in crystallization temperature is observed when acetic acid is used to reduce the pH of the aging solution. The precursors aged in the solutions of intermediate pH range demonstrate a typical two‐step crystallization behavior, due to the transition from a OH‐‐dominated surface structure to a CH3COO‐‐dominated one. These results show that a higher crystallization temperature results when the OH‐ groups attached to the surface of precursor particles are replaced by the CH3COO‐ groups. Only a slight decrease in the crystallization temperature of aged precipitates occurs when free species, such as CH3COO‐ and OH‐, are being removed from the aging solution.
Ultrasonic and Mechanical Behavior of Green and Partially Sintered Alumina: Effects of Slurry Consolidation Chemistry
Authors: Schilling Christopher H. , García Victor J. , Smith Rachelle M. , Roberts R. A.
Published: July 2010

Green and partially sintered compacts of alpha‐Al2O3 powder were made by filtration of aqueous suspensions under three conditions: (i) electrostatic stabilization without any organic additive, (ii) strong flocculation near the isoelectric point without any organic additive, and (iii) weak flocculation by the use of maltodextrin or oxalic acid additives. We evaluated relationships between the macroscopic and interparticle mechanical behavior of these compacts using model correlations with measurements of diametral compression, ultrasonic velocity, and ultrasonic attenuation. Although type iii green specimens were less dense than type i, type iii exhibited significant increases in velocity, macroscopic Young's modulus, interparticle‐contact stiffness, and diametral compressive strength, suggesting that the mechanism of stiffening/strengthening entailed interparticle bridging of maltodextrin or oxalic acid. These properties were significantly reduced upon heating type iii specimens to 500°C, suggesting that pyrolysis of surface‐adsorbed maltodextrin and oxalic acid may have reduced the interparticle stiffness and strength. In contrast, negligible changes in these properties occurred upon heating type i specimens to the same temperature. Despite small increases in packing density, significant decreases in attenuation and significant increases in velocity, interparticle‐contact stiffness, and Young's modulus occurred upon heating all specimens to greaterthan equal to700°C, suggesting the formation of interparticle necks by solid‐state sintering.
Phase Transformation in Y2O3‐Partially‐Stabilized ZrO2 Polycrystals of Various Grain Sizes during Low‐Temperature Aging in Water
Authors: Li Jing‐Feng , Watanabe Ryuzo
Published: July 2010

ZrO2‐2 mol% Y2O3 crystals with average grain sizes from 0.51 to 0.96 µm were prepared by sintering in air at 1400°C for 2 to 100 h. The tetragonal‐to‐monoclinic phase transformation associated with the low‐temperature degradation was investigated to clarify how the presence of water directly affects the influence of grain size on transformation. The specimens were exposed to water at 80–120°C, a temperature range in which transformation by thermal activation is difficult in the absence of water. Contrary to expectations, this type of low‐temperature transformation did not accelerate monotonously with increasing grain size. Instead, the amount of phase transformation first decreased, reaching a constant value, and then increased with increasing grain size. Such interesting results can be explained satisfactorily by the combined influences of grain size on the nucleation process, because of preferential dissolution of yttrium at the grain boundaries, and the intrinsic transformability of Y2O3‐doped tetragonal ZrO2 grains.
Chemical Processing of Potassium‐Substituted Strontium Barium Niobate Thin Films through Metallo‐organics
Authors: Sakamoto Wataru , Yogo Toshinobu , Kawase Akihiro , Hirano Shin‐ichi
Published: July 2010

Transparent and highly oriented Kx(Sr0.5Ba0.5)1−x/2Nb2O6 (x= 0.2, 0.4) (KSBN) thin films have been synthesized by a chemical solution deposition method. A homogeneous and stable KSBN precursor solution was prepared by controlling the reaction of metallo‐organics. K0.4Sr0.4Ba0.4Nb2O6 (x= 0.4, K0.4SBN50) and K0.2Sr0.45Ba0.45Nb2O6 (x= 0.2, K0.2SBN50) powders and thin films directly crystallized to the tetragonal tungsten bronze phase above 600°C. The thin films were crystallized on MgO(100) and Pt(100)/MgO(100) with c‐axis preferred orientation. Two crystal lattice planes of K0.4SBN50 and K0.2SBN50 were intergrown at an orientation of 18.5° on MgO(100) and Pt(100)/MgO(100). K0.4SBN50 thin film on Pt(100)/MgO(100) showed the typical hysteresis loop (Pr= 22 µC/cm2, Ec= 99 kV/cm at −190°C). The change in remnant polarization with temperature is strongly related to the diffuse phase transition of the epsilon‐T curves.
Threshold Stress in Creep of Alumina‐Silicon Carbide Nanocomposites
Authors: Ohji Tatsuki , Kusunose Takafumi , Niihara Koichi
Published: July 2010

Tensile creep and the creep ruptures of an alumina‐17 vol% silicon carbide nanocomposite at 1200°C were investigated, with a particular interest in the behaviors at low applied stresses. At stresses of <50 MPa, the creep rates were remarkably decayed and the creep lives were substantially prolonged, which suggested the presence of a threshold stress, below which creep stopped, in the creep of the nanocomposite. The stress was estimated to be in the range of 20–35 MPa. This threshold stress was in agreement with that predicted from another model where the motion of grain‐boundary dislocations that were responsible for vacancy nucleation and annihilation was considered to be pinned by hard particles.
Effect of Poling Temperature on Optical Second‐Harmonic Intensity of Lithium Sodium Tellurite Glass
Authors: Narazaki Aiko , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2010

Second‐harmonic generation has been observed in poled 10Li2O10Na2O80TeO2 glass. The effect of poling temperature on the second‐harmonic intensity has been examined. The second‐harmonic intensity increases, attains a maximum, and then decreases as the poling temperature increases. In other words, an optimum poling temperature that results in a maximum second‐harmonic intensity exists. The optimum poling temperature linearly increases as the glass‐transition temperature increases for several types of tellurite glasses, including the present 10Li2O10Na2O80TeO2 glass. This fact suggests that the process to create a polarization that results in the second‐harmonic generation is affected by the structural relaxation at the glass‐transition range. The thermal stability of 10Li2O10Na2O80TeO2 glass is higher than that of 18Na2O82TeO2 (30NaO1/270TeO2) glass, as revealed via differential scanning calorimetry. As a result, the temperature range within which the poling is effective is wider for the former glass.
Synthesis of Tubes of a Magnesium‐Rich Carbonate and of Its Oxide Decomposition Products
Authors: Fukuhara Minoru , Fujii Nobumasa , Takada Jun , Kusano Yoshihiro
Published: July 2010

A new method to synthesize a hollow structure containing calcium and magnesium oxides is proposed. The method involves three processes: First, magnesium carbonate is formed around needlelike aragonite in an autoclave using urea. Second, the needlelike aragonite is removed with hydrochloric acid, and hollow magnesium carbonate is obtained. Third, the hollow magnesium carbonate is heated to form a product containing magnesium and calcium oxides without its shape being altered.
Influence of Electroless Nickel Plating on Multilayer Ceramic Capacitors and the Implications for Reliability in Multilayer Ceramic Capacitors
Authors: Chen Wanping , Li Longtu , Qi Jianquan , Wang Yu , Gui Zhilun
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.
Effects of Silver‐Paste Formulation on Camber Development during the Cofiring of a Silver‐Based, Low‐Temperature‐Cofired Ceramic Package
Authors: Chang Chia‐Ruey , Jean Jau‐Ho
Published: July 2010

The effects of silver‐paste formulation on camber development during the cofiring of a two‐layered structure of a silver‐based, low‐temperature‐cofired ceramic (LTCC) system have been investigated. The densification kinetics and mechanism of the silver film become more similar to that of LTCC as the amount of LTCC powder in the silver paste increases, which results in a smaller camber during cofiring. By using the densification results of silver film and LTCC, camber development during cofiring can be mathematically described by using viscous analysis, which agrees well with the experimental observations.
Microstructural Design of Silicon Nitride with Improved Fracture Toughness: I, Effects of Grain Shape and Size
Authors: Becher Paul F. , Sun Ellen Y. , Plucknett Kevin P. , Alexander Kathleen B. , Hsueh Chun‐Hway , Lin Hua‐Tay , Waters Shirley B. , Westmoreland C. Gary , Kang Eul‐Son , Hirao Kiyoshi , Brito Manuel E.
Published: July 2010

The use of self‐reinforcement by larger elongated grains in silicon nitride ceramics requires judicious control of the microstructure to achieve high steady‐state toughness and high fracture strength. With a distinct bimodal distribution of grain diameters, such as that achieved by the addition of 2% rodlike seeds, the fracture resistance rapidly rises with crack extension to steady‐state values of up to 10 MPam1/2 and is accompanied by fracture strengths in excess of 1 GPa. When the generation of elongated reinforcing grains is not regulated, a broad grain diameter distribution is typically generated. While some toughening is achieved, both the plateau (steady‐state) toughness and the R‐curve response suffer, and the fracture strength undergoes a substantial reduction. Unreinforced equiaxed silicon nitride exhibits the least R‐curve response with a steady‐state toughness of only 3.5 MPam1/2 coupled with a reduced fracture strength.
Acid Attack on High‐Alkali Cement Paste: Another Cause for Delayed Ettringite Formation
Authors: Macías Angeles , Goñi Sara
Published: July 2010

Cement pastes were immersed in an acid solution of 0.87M HAc/NaAc (pH 4.5) and in distilled water for different periods of time up to 90 days. Changes in the solid phases were evaluated by scanning electron microscopy, X‐ray microanalysis, and X‐ray diffraction after the extraction of the specimens from the solutions. Results showed that acid attack could lead to delayed ettringite formation.
Microstructural Characterization of Superplastic SiO2‐doped TZP with a Small Amount of Oxide Addition
Authors: Thavorniti Parjaree , Ikuhara Yuichi , Sakuma Taketo
Published: July 2010

The microstructures of 5 wt% SiO2‐doped TZP, 5 wt% (SiO2+ 2 wt% MgO)‐doped TZP, and 5 wt% (SiO2+ 2 wt% Al2O3)‐doped TZP are characterized by high‐resolution electron microscopy, energy‐dispersive X‐ray spectroscopy, and electron energy loss spectroscopy. An amorphous phase is formed at multiple grain junctions but not along the grain‐boundary faces in these three materials. A small addition of MgO and Al2O3 into the SiO2 phase results in a marked reduction in tensile ductility of SiO2‐doped TZP. This reduction seems to correlate with segregation of magnesium or aluminum ions at grain boundaries and a resultant change in the chemical bonding state.
In‐Situ Formation of Ce‐TZP‐M‐Type Hexaferrite Composites
Authors: Kojima Takashi , Sakamoto Wataru , Yogo Toshinobu , Fujii Takashi , Hirano Shin‐ichi
Published: July 2010

Composites consisting of a Ce‐TZP matrix and in‐situ grown particles of La(Fe,Al)12O19 were prepared by the solid‐state reaction of Ce‐TZP, La(Fe,Al)O3, and Al2O3 powders. The in‐situ formation process of La(Fe,Al)12O19 in a Ce‐TZP matrix was investigated in relation to the microstructure evolution. The Ce‐TZP‐La(Fe,Al)12O19 composites had significant magnetic properties and improved mechanical properties. The maximum value of magnetization of the Ce‐TZP‐La(Fe,Al)12O19 composites was obtained at 90 mol% LaFe12O19 in La(Fe,Al)12O19. The value of the three‐point bending strength of Ce‐TZP‐20 wt% La(Fe,Al)12O19 (90 mol% LaFe12O19) sintered at 1350°C was 780 MPa, compared with 500 MPa of Ce‐TZP ceramics. The composite demonstrated crack sensing based upon the change in magnetic gradient.
Crystallinity Analysis of Glass‐Ceramics by the Rietveld Method
Authors: Yasukawa Katsumasa , Terashi Yoshitake , Nakayama Akira
Published: July 2010

The crystallinity of multicomponent glass‐ceramic mixtures has been analyzed via the Rietveld method, using powder X‐ray diffractometry data. The Rietveld technique uses an internal standard but requires no calibration data to determine the total amorphous phase content of a mixture. This method of analyzing the crystallinity of synthetic mixtures gives high‐precision results, with an error of generally less than ±3.0%, for several glass‐ceramics.
New Preparation Method of Low‐Temperature‐Sinterable Perovskite 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 Powder and Its Dielectric Properties
Authors: Han Kyoung R. , Kim Sojin , Koo Hee Jin
Published: July 2010

A relaxor ferroelectric material, 0.9Pb(Mg1/3Nb2/3)O3‐0.1PbTiO3 (0.9PMN‐0.1PT) with a pyrochlore‐free phase, was prepared by using one‐step calcination in the present study. The 0.9PMN‐0.1PT powder with the pure perovskite phase was prepared successfully from a mixture of the PMN precursor and the crystalline PT by heating for 2 h at temperatures greaterthan equal to750°C. The PMN precursor was synthesized by adding an aqueous Mg(NO3)2 solution, rather than MgO, to the alcoholic slurry of PbO and Nb2O5. The 0.9PMN‐0.1PT powder sintered to >96% relative density via heat treatment for 2 h at temperatures of 900°‐1200°C. The highest room‐temperature dielectric constant (epsilonrt) was 24700 at 1 kHz for the samples that were sintered at 1100°C; however, the samples that were sintered at 900°C still had epsilonrt values of 22600 at 1 kHz.
Preparation of Ti3SiC2 by Electron‐Beam‐Ignited Solid‐State Reaction
Authors: Goesmann Fred , Wenzel Roland , Schmid‐Fetzer Rainer
Published: July 2010

This paper describes a novel way to prepare the ternary phase Ti3SiC2 in a single‐step procedure that we call electron‐beam‐ignited solid‐state reaction (EBI‐SSR). The preparation route is discussed by means of an isothermal section of the Ti‐Si‐C phase diagram. Properties such as the Vickers hardness and the electrical resistivity of the resulting samples are presented. Our property data compare well to those that have been published. The main advantages of this preparation method are the controllability of process parameters such as heating rates, temperatures, and times, as well as the short duration of the overall sample preparation. However, a disadvantage is the presence of second phases (typically in amounts of <8%) that must be reduced via further optimization of the process.
Hydroxyapatite Coating on a Collagen Membrane by a Biomimetic Method
Authors: Rhee Sang‐Hoon , Tanaka Junzo
Published: July 2010

The coating of a carbonate‐containing hydroxyapatite (HAp) on a nonbioactive collagen membrane via a biomimetic method has been investigated. The collagen membranes were soaked in a simulated body fluid (SBF) solution with and without citric acid, and carbonate‐containing HAp formed only in the SBF solution that contained citric acid. The results were explained in terms of the strong chelation ability of citric acid with the calcium ion. Practical application may involve the inclusion of citric acid in the SBF solution to promote the formation of HAp on previously nonbioactive collagen membranes.
Quantitative Evaluation of Void Distributions within a Plasma‐Sprayed Ceramic
Authors: Leigh Sang‐Ha , Berndt Christopher C.
Published: July 2010

The size–shape distribution of voids, which includes cracks and pores, was determined using quantitative stereological analysis. The analysis was performed on a water‐stabilized plasma‐spray‐formed Al2O3–13 wt% TiO2. The individual voids were assumed to have an oblate spheroidal shape, which could simulate shapes ranging from spherical pores to cracks. The cracks were generally intralamellar or translamellar, and the pores were interlamellar. The information obtained from two‐dimensional plane sections was unfolded to three‐dimensional information using stereological analysis. The quantitative information of voids was acquired in terms of shape and size.