bluuebunny/crossref_metadata_2025 huggingface dataset:
Wet Milling of Fe/Al/Al2O3and Fe2O3/Al/Al2O3Powder Mixtures
Authors: Schicker Silvia , García Daniel E. , Gorlov Igor , Janssen Rolf , Claussen Nils
Published: July 2010

Wet milling of Al2O3‐aluminide alloy (3A) precursor powders in acetone has been investigated by milling Fe/Al/Al2O3and Fe2O3/Al/Al2O3powder mixtures. The influence of the milling process on the physical and chemical properties of the milled powders has been studied. Particle refinement and homogenization were found not to play a dominant role, whereas plastic deformation of the metal particles leads to the formation of dislocations and a highly disarranged polycrystalline structure. Although no chemical reactions among the powder components in Fe2O3/Al/Al2O3powder mixtures were observed, the formation of a nanocrystalline, ordered intermetallic FeAl phase in Fe/Al/Al2O3powder mixtures caused by mechanical alloying was detected. Chemical reactions of Fe and Al particle surfaces with the atmosphere and the milling media lead to the formation of highly porous hydroxides on the particle surfaces. Hence the specific surface area of the powders increases, while the powder density decreases during milling. The fraction of Fe oxidized during milling was determined to be 0.13. The fraction of Al oxidized during milling strongly depends on the metal content of the powder mixture. It ranges between 0.4 and 0.8.
Dense Amorphous Zirconia–Alumina by Low‐Temperature Consolidation of Spray‐Pyrolyzed Powders
Authors: Gandhi Ashutosh S. , Jayaram Vikram , Chokshi Atul H.
Published: July 2010

Metastable amorphous ZrO2‐Al2O3 powders were hot‐pressed at low temperatures (873 and 923 K), under moderately high pressures (500 and 750 MPa), and amorphous pellets with 1%‐8% porosity were obtained. Crystallization of the amorphous pieces in the temperature range of 1173–1673 K produced a range of ultrafine microstructures, the finest of which had grains of tetragonal (ZrO2‐40‐mol%‐Al2O3) solid solution 6–8 nm in size that formed at 1173 K. Submicrometer grain sizes of the equilibrium monoclinic ZrO2 and alpha‐Al2O3 were stable against coarsening at 1673 K. The new technique was applied to produce a SiC‐reinforced composite with an amorphous ZrO2‐80‐mol%‐Al2O3 matrix; the high matrix sinterability overcame the reinforcement constraint. The results suggest a possible solution to the difficulties in the bulk processing of amorphous, nanocrystalline, and other novel ceramics.
Purification of Mullite by Reduction and Volatilization of Impurities
Authors: Souto Alejandro , Guitian Francisco , de Aza Salvador
Published: July 2010

Mullite materials usually contain a residual glassy phase rich in SiO2, which concentrates impurities as Na2O, K2O, Fe2O3, and other minority compounds. A suitable way to minimize this glassy phase is the reduction and volatilization of its components by calcination at high temperatures (1300–1450°C) in atmospheres with a very low partial pressure of O2. Over 95% of the Na2O, K2O, and Fe2O3 in mullite can be removed in this way, leaving concentrations lower than 0.02% by weight. To avoid the degradation of mullite that occurs when the partial pressure of O2 is too low, the material to be purified is covered with TiO2 plates.
Physical and Dielectric Properties of (1–x)PbZrO3·xBaTiO3 Thin Films Prepared by Chemical Solution Deposition
Authors: Park Jeong Hwan , Yoon Ki Hyun , Kang Dong Heon
Published: July 2010

Physical and dielectric properties of (1–x)PbZrO3·x BaTiO3 thin films prepared by a chemical coating process have been investigated as a function of BaTiO3 (x) content (0≤x≤0.2). Changing the molar ratio between propylene glycol and water prior to the deposition optimized the chemical precursors. (1–x)PbZrO3‐x BaTiO3 thin films that contained a majority of perovskite phase, but also contained large amounts of other phases, were fabricated. These films could withstand fields of 250 kV/cm at 1 kHz. The microstructure of the thin films was found to depend on the BaTiO3 content. The phase transition from antiferroelectric to ferroelectric was gradually induced as the BaTiO3 content increased. A maximum dielectric constant of ∼809 was obtained at the composition of x= 0.1. A maximum dielectric constant of ∼809 was obtained at the composition of x= 0.1. A thin film at the low‐field antiferroelectric‐ferroelectric phase boundary with x= 0.05 exhibited the highest Psat and Pr values. The maximum values of these were 45 and 31 μC/cm2, respectively.
Modeling the Dielectric Response and Relaxation Spectra of Relaxor Ferroelectrics
Authors: Lin Huh‐Tswen , Van Aken David C. , Huebner Wayne
Published: July 2010

A multi‐Debye relaxation model that is based upon the Boltzmann superposition principle has been used to determine the frequency‐dispersion behavior of Pb(Mg1/3‐Nb2/3)O3 (PMN) and Pb0.88La0.08(Zr0.65Ti0.35)O3 (PLZT 8/65/35) relaxor ferroelectrics. For PMN, relaxation times on the order of seconds contribute to the dispersive character of the dielectric properties. A defect‐relaxation mechanism that involves Mg cation hopping in a structure that is composed of interpenetrating 〈111〉 chains of ordered Pb(Mg1/2Nb1/2)O3 is proposed for PMN. Motion of the Mg cations results in destruction and reconstruction of these ordered chains, which contributes to the dispersive character of PMN.
Annealing Metamict Zircon: A Powder X‐ray Diffraction Study of a Highly Defective Phase
Authors: Colombo Monica , Chrosch Jutta , Salje Ekhard K. H.
Published: July 2010

The transition from highly defective (metamict) to crystalline zircon is characterized by short‐range structural order, which follows a different kinetic behavior than the corresponding long‐range order. Experimental results from in situ powder X‐ray diffraction experiments are analyzed using Rietveld refinement and direct Fourier analysis. The Rietveld refinement leads to a detailed assessment of the structural contraction of the crystalline portion of the same during thermal annealing. The Fourier analysis shows a highly heterogeneous distribution of interatomic bond distances. The main effect of structural annealing is a change of the distances between Si and O atoms and the average Si–Zr distance. The Zr–Zr distance seems to be less affected by this thermal treatment. Short‐range order is recovered at lower temperatures than that of long‐range order. Crystallinity is recovered anisotropically with slower annealing along the crystallographic c‐direction than along the a‐direction.
Permeability and Infiltration of Partially Sintered Ceramics
Authors: Glass S. Jill , Green David J.
Published: July 2010

For infiltration of a molten salt into porous zirconia (relative densities = 0.56 to 0.88), the infiltration depth was found to be a function of both infiltration time and initial compact density. The intrinsic liquid permeability of the porous Y‐TZP was determined by extrapolation of gas permeability data. Permeability values, which ranged from 0.5 × 10−18 to 25 × 10−18 m2 (∼0.5 to 25 microdarcy), could be used to predict the trend in infiltration depth with compact density, though they underestimated the absolute values. The Carman‐Kozeny relationship, which relates the permeability to measurable microstructural parameters, was also evaluated. There was good agreement at relative densities <0.75, but not at the higher densities, likely due to the increasing tortuosity of the flow path as pores shrink and close.
Spectroscopic Properties of and Energy Transfer in PbO–Bi2O3–Ga2O3 Glass Doped with Er2O3
Authors: Choi Yong Gyu , Kim Kyong Hon , Heo Jong
Published: July 2010

Er2O3‐doped PbO‐Bi2O3‐Ga2O3 glasses were prepared through the conventional melt‐quenching method, and the energy transfer mechanisms in Er3+ were investigated. The fluorescent emission at 2.73 μm, which is normally quenched in silicate glasses, became evident because of the low phonon energy of PbO‐Bi2O3‐Ga2O3 glasses. The measured lifetime of the upper level of 4I11/2 was 0.9 ms, and it decreased to ∼0.6 ms with increased Er3+ concentration. When the concentration of Er2O3 was 0.05 wt%, the coefficient of the cross‐relaxation rate for the 4I11/2 level was ∼18 times larger than that of the 4I13/2 level. On the other hand, the interaction parameter of energy migration was considerably larger for the 4I13/2 level (∼52 × 10−40 cm6·s−1) compared with the 4I11/2 level (∼3.1 × 10−40 cm6·s−1). Therefore, the major energy transfer mechanism associated with the 4I13/2 level was migration induced, whereas that for the 4I11/2 level was direct cross relaxation of 4I11/2:4I11/2→4F7/2:4I15/2.
Photoluminescence Behavior of Manganese‐Doped Zinc Silicate Phosphors
Authors: Sohn Kee‐Sun , Cho Bonghyun , Park Hee Dong
Published: July 2010

The purpose of the present study is to develop an understanding of the photoluminescence properties of Mn2+‐doped zinc silicate (Zn2SiO4:Mn) phosphors, which have served as a gree‐emitting phosphor in many industrial applications. Thus, several experimental techniques, such as time‐resolved emission spectra, decay curves, and time‐resolved photoluminescence excitation spectra, have been conducted on Zn2SiO4:Mn phosphors. The characterization has been performed in terms of dopant concentration. The decay curves, together with the characteristic decay time, in particular, are measured as a function of excitation‐light wavelength, in the range of 200–520 nm. The decay behavior is strongly dependent on the excitation‐light wavelength. The excitation range is categorized into three regimes: the manganese direct excitation range, below the absorption‐edge (ET) energy level; the manganese ionization range, from ET to the optical band‐gap energy (Eg) of Zn2SiO4; and the intergap transition range, above the Eg energy level.
Microscopic Mechanisms of Oxidation in SiC‐Whisker‐Reinforced Mullite/ZrO2 Matrix Composites
Authors: Lin Chien‐Cheng , Zangvil Avigdor , Ruh Robert
Published: July 2010

The oxidation of SiC whiskers, contained in alkoxide‐derived mullite‐based matrices and exposed in air at 1000–1350°C for up to 1000 h, has been studied by analytical TEM, high‐resolution SEM, and XRD. Silicon carbide whiskers were effectively protected from oxidation when embedded in a pure mullite matrix, but oxidized considerably when embedded in mullite/ZrO2 matrices. The oxidation mechanisms varied with matrix composition and exposure temperature. At 1350°C the amorphous layer first crystallized as cristobalite, then gradually incorporated alumina. At later times, the mullite portion of the mullite/ZrO2 matrix dissolved extensively into the layer. Also, the zirconia particles reacted with silica to form zircon. At 1200°C less extensive interdiffusion and chemical reaction occurred, and the silica layer devitrified into cristobalite and quartz. At 1000°C no interdiffusion or chemical reaction was seen, and the silica layer tended to devitrify into quartz. The thickness of the oxide layer around a SiC whisker in a particular matrix depended on the morphology and composition of grains abutting it or adjacent to it.
Phase Transformation Sequence from Kaolinite to Mullite Investigated by an Energy‐Filtering Transmission Electron Microscope
Authors: Lee Sujeong , Kim Youn Joong , Moon Hi‐Soo
Published: July 2010

The phase transformation from kaolinite to mullite was examined with new electron diffraction data obtained using an energy‐filtering transmission electron microscope. Kaolinite was finally transformed to mullite and cristobalite through several steps of endothermic and exothermic reactions, which resulted in metakaolinite, a microcrystalline spinel‐type phase and amorphous silica. Metakaolinite maintained its short‐range order even at 920°C. The spinel‐type phase resulted from a topotactic transformation of metakaolinite. Mullite first appeared at around 940°C, showing no clear crystallographic relationships to the parent metakaolinite structure. It coexisted with metakaolinite and the spinel‐type phase produced previously. The first strong exothermic peak on the DTA curve was mainly due to the extraction of amorphous silica from metakaolinite and the gradual nucleation of the mullite phase. The initially formed spinel‐type and mullite phases were suggested to be Al‐rich, but to progressively gain Si in their structures at higher temperatures. The spinel‐type phase decomposed completely through a second weak exothermic reaction, promoting the crystallization of cristobalite from amorphous silica, and the growth of mullite.
High Electrical Conductivity and High Fracture Strength of Sc2O3‐Doped Zirconia Ceramics with Submicrometer Grains
Authors: Hirano Masanori , Watanabe Shinzi , Kato Etsuro , Mizutani Yasunobu , Kawai Masayuki , Nakamura Yasuhisa
Published: July 2010

The microstructure, crystal phase, electrical conductivity, and mechanical strength of less than 7‐mol%‐Sc2O3‐doped zirconia ceramics fabricated by comparatively low‐temperature sintering at 1200–1300°C for 1 h were investigated. Zirconia ceramics having a uniform microstructure (grain size < 0.5 μm) stabilized with 6 mol% Sc2O3 showed high electrical conductivity (0.15 S/cm at 1000°C) and high fracture strength (660 MPa). With the increase of Sc2O3 content from 3.5 to 7 mol%, the grain size, fracture strength, and electrical conductivity at 1000°C changed from 0.2 to 0.5 μm, 970 to 440 MPa, and 0.07 to >0.2 S/cm, respectively. Sc2O3‐doped zirconia polycrystals with high fracture strength and high electrical conductivity are promising candidates for the electrolyte material of solid oxide fuel cells.
Atomistic Modeling of Native Point Defects in Yttrium Aluminum Garnet Crystals
Authors: Kuklja Maija M. , Pandey Ravindra
Published: July 2010

Native point defects in yttrium aluminum garnet (YAG) are studied in the framework of the pair‐potential approximation, coupled with the shell‐model description of the lattice ions. For the perfect lattice, a new set of potential parameters is obtained; these parameters reproduce the structure, elastic, and dielectric constants of YAG very well. The calculated formulation energies for native defects suggest that antisite disorder is preferred over Frenkel and Schottky‐like disorder in YAG. The calculated values of the distortion that is caused by the antisite Y atom that substitutes in the Al site in the lattice are in excellent agreement with the extended X‐ray absorption fine‐structure (EXAFS) measurements. In nonstoichiometric YAG, the calculated reaction energies indicate that excess Y2O3 or Al2O3 most likely is accommodated by the formation of antisites, rather than vacancies, in the lattice.
Superplasticity of Silicon Carbide
Authors: Shinoda Yutaka , Nagano Takayuki , Gu Hui , Wakai Fumihiro
Published: July 2010

Nanocrystalline silicon carbide that was doped with boron and carbon (B,C‐SiC) and contained 1 wt% boron additive and 3.5 wt% free carbon was fabricated using hot isostatic pressing under an ultrahigh pressure of 980 MPa and a temperature of 1600°C. The average grain size of the material was 200 nm. The tensile deformation behavior of this material at elevated temperature was investigated. The nanocrystalline B,C‐SiC exhibited superplastic elongation of >140% at a temperature of 1800°C. High‐resolution transmission electron microscopy observation and electron energy‐loss spectroscopy analysis revealed that this nanocrystalline SiC did not have a secondary glassy phase at the grain boundary and the grain boundary had a strong covalent nature, which means that an intergranular glassy phase was not necessary to obtain superplasticity of covalent materials.
A Novel Processing Route to Control Grain Growth in Submicrometer Alumina Compacts
Authors: Vernon Deborah M. , Rankin Janet , Caragianis‐Broadbridge Christine , Laube Bruce L.
Published: July 2010

A novel processing procedure for significantly suppressing grain growth in submicrometer alumina compacts has been developed and implemented with the intent of ultimately using the same processing route to control grain size in nanophase alumina compacts. In this study, partially sintered alumina pellets made from 0.5 µm starting powders are altered by the chemical infiltration of Si3N4. The control and infiltrated pellets are then heated to 1650°C for 4 h. The fully sintered pellets are approximately 97% dense. Suppressed grain growth is observed in the infiltrated pellets. The average grain size in the control pellets after densification is 4.2 and 1.2 µm in the infiltrated pellets. Depth of infiltration is measured using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). Depending on the specific infiltration conditions used, the outer 15‐50% of the infiltrated pellets exhibit a graded microstructure consisting of a region of abnormal grain growth and a region of suppressed grain growth. Abnormal grain growth is visible on the outer surfaces of the infiltrated pellets where a relatively high ratio of Si to N is present. Further into the pellet, after some depletion of the Si source gas has occurred, regions of suppressed grain growth are apparent. Based on these results, an infiltration profile is determined. A mathematical model is developed to describe the infiltration process and to determine optimal infiltration conditions. High‐resolution electron microscopy (HREM), energy dispersive spectroscopy (EDS), electron energy loss spectroscopy (EELS), and X‐ray photoelectron spectroscopy (XPS) are used to study the infiltrated samples.
Simulation of Microwave Sintering of Ceramic Bodies with Complex Geometry
Authors: Birnboim Amikam , Carmel Yuval
Published: July 2010

Microwave sintering, an emerging technology in which the energy is applied directly to the material, enabling rapid sintering, shows potential for the synthesis of advanced ceramic materials with superior properties. The process is complex, combining the propagation and absorption of electromagnetic waves in the ceramic material, heat transport within the geometric body, and densification. The densification changes both macroscopic shape and microstructural morphology. A dynamic balance between the rate of electromagnetic energy absorbed within the bulk of the sample and the rate of energy loss from its surface generally results in temperature gradients. These temperature gradients may be especially important during the microwave sintering of bodies with a complex geometry, because neither the diffusion distance nor the electromagnetic penetration depth scale with sample dimensions. The gradients generated in a ZnO green body of a complex geometry were studied theoretically using various microwave‐sintering approaches, and it was found that (1) dual‐frequency (2.45 and 30 GHz) microwave processing leads to a decrease in the duration of the temperature gradients, and (2) an increase in the heating rate from 5°C/min to 1400°C/min at 2.45 GHz decreases the total required microwave energy by a factor of 55, while at the same time the internal temperature gradients are maintained over a substantially shorter time.
Erosion and Damage by Hard Spherical Particles on Glass
Authors: Slikkerveer Peter J. , Verspui Mariëtte , Skerka Erik
Published: July 2010

Solid particle impact of hard spherical particles on glass is of fundamental interest because of the presence of a number of different impact regimes. Understanding the impact of spherical particles is also a step toward modeling the behavior of rounded particles. This paper verifies theoretical models for the transitions between the different impact regimes and process parameters like erosion rate and surface roughness. The work also includes rounded particles. The transitions plotted in a so‐called erosion map are validated with single‐impact experiments. Data from erosion experiments are used to test the relations for the erosion rate and resulting surface roughness following from the models. Although the theoretical transitions compare reasonably with experiments, the models for erosion rate and surface roughness do not describe the experimentally found behavior. The models not incorporating the interaction between an impact and the damage remaining from earlier impacts might cause this deviation.
Effect of Chemisorption and Physisorption of Water on the Surface Structure and Stability of alpha‐Alumina
Authors: de Leeuw Nora H. , Parker Stephen C.
Published: July 2010

Chemisorption and physisorption of water onto the {0001}, {1011}, {1120}, and {2243} surfaces of alpha‐alumina have been studied via atomistic simulation techniques, using potentials that have been verified against the structures of hydrated ß‐alumina and diaspore. Both physisorption and chemisorption of all surfaces are energetically favorable, especially the hydroxylation of dipolar oxygen‐terminated planes. The equilibrium morphology is calculated, as a way to assess the change in surface energies, and the equilibrium morphologies agree with the experimentally observed crystal morphologies. The calculated energies of both physisorption and chemisorption agree well with experimentally obtained hydration energies.
Hydrothermal Synthesis of Tetragonal Barium Titanate from Barium Hydroxide and Titanium Dioxide under Moderate Conditions
Authors: Wu Mingmei , Long Junbiao , Wang Guangguo , Huang Aihong , Luo Yuji , Feng Shouhua , Xu Ruren
Published: July 2010

Tetragonal BaTiO3 powders were prepared hydrothermally, using Ba(OH)2·8H2O and TiO2 (anatase), in the absence of anions such as chloride ions, at a temperature of 220°C for several days. Characterization via X‐ray diffractometry, scanning electron microscopy, and differential scanning calorimetry confirmed that increasing the Ba:Ti molar ratios (from 1:1 to 4:1) and alkaline concentrations (from 1.0M to 3.0M) promotes the formation of tetragonal BaTiO3.
Formulation and Multilayer Jet Printing of Ceramic Inks
Authors: Song Jin Hua , Edirisinghe Mohan J. , Evans Julian R. G.
Published: July 2010

This paper describes the preparation of ceramic inks for forming ceramic components by multilayer printing using a continuous‐ink‐jet printer. The selection of appropriate binders and dispersants combined with high shear and ultrasonic mixing has enabled zirconia‐containing inks to be printed successfully to produce 2.5 mm thick bars. Printing trials show that the method of dispersion of the ceramic powder in the ink is decisive for accurate ink droplet positioning. The quality of the vertical walls and the top surface of the bars are related closely to the rate of drying of each printed layer. Inks with higher ceramic volume loadings (up to 10%) were also studied and produced useful information for further investigations.
Low‐Fired (Zn,Mg)TiO3 Microwave Dielectrics
Authors: Kim Hyo Tae , Nahm Sahn , Byun Jae Dong , Kim Yoonho
Published: July 2010

A dielectric ceramic comprised of (Zn1‐xMgx)TiO3 (x= 0 to x= 0.5) with low sintering temperature and promising microwave properties was prepared by applying a semichemical synthesis route and a microbeads milling technique. X‐ray diffractometry and thermal analyses results indicated that the phase stability region of the hexagonal (Zn,Mg)TiO3 extended to higher temperatures as the amount of magnesium increased. The dielectric properties in this system exhibited a significant dependence on the sintering conditions, especially near the phase decomposition temperature. From 950°C, the temperature compensation characteristics occurred as the phase composition changed from hexagonal (Zn,Mg)TiO3 to two phases: (Zn,Mg)2TiO4 and rutile. The magnesium content for zero temperature coefficient (tauf) was ~3 mol% at 950°C; however, tauf increased with the sintering temperatures because of the shift of the decomposition temperature.
Thermal Stability of Low‐SiC Fiber (Hi‐Nicalon) Treated in a Hot Isostatic Press
Authors: Shimoo Toshio , Tsukada Ichiro , Seguchi Tadao , Okamura Kiyohito
Published: July 2010

The low‐oxygen SiC fiber fabricated by the electron‐beam irradiation curing method, Hi‐Nicalon, was heated at 1773 to 2273 K in a hot isostatic press (800 MPa of argon) and was subsequently reheated at 1873 K at 1 atm (101 kPa) of argon. The hot isostatic press treatment delayed the onset of fiber deterioration to higher temperature. The fiber strength remained almost unchanged by subsequent reheating at 1873 K in 101 kPa of argon. The thermal stability of Hi‐Nicalon, as a consequence of the permanent change in surface structure, can be greatly improved by treating in the hot isostatic press.
Corrosion of Alumina in Aqueous Hydrofluoric Acid
Authors: Mikeska Kurt R. , Bennison Stephen J.
Published: July 2010

A variety of alumina‐based ceramics were evaluated for dissolution in an azeotropic aqueous hydrofluoric acid test protocol at temperatures up to 200°C. Weight change measurements and microstructure analysis showed that HF corrosion in polycrystalline aluminas generally occurred at grain boundaries by the dissolution of silicate‐based, glass grain boundary films that segregate to grain boundaries. These materials often have useful service lifetimes even though thermodynamic calculations indicate high solubilities. It is proposed that corrosion rates are controlled by chemical reactions at the solid/liquid interface, the physical structure of the solid, and microstructure. The addition of MgO to alumina greatly increased corrosion resistance by removing silicate‐based glassy grain boundary films.
Effects of Solids Loading, pH, and Polyelectrolyte Addition on the Stabilization of Concentrated Aqueous BaTiO3 Suspensions
Authors: Jean Jau‐Ho , Wang Hong‐Ren
Published: July 2010

Colloidal stability of concentrated aqueous BaTiO3 suspensions with ammonium salts of poly(acrylic acid) (PAA‐NH4) and poly(methacrylic acid) (PMAA‐NH4) as a function of pH and solids loading is investigated. For suspensions with solids loading less than 40 vol%, the required polyelectrolyte concentration to stabilize aqueous BaTiO3 suspensions decreases with increasing pH, but remains relatively unchanged with increasing solids loading. As the solids loading continuously increases (e.g., >50 vol%), the required amount of polyelectrolyte increases, but exhibits a minimum at pH ∼ 9.2. The critical amount of polyelectrolyte needed to achieve colloidal stability of aqueous BaTiO3 suspensions as a function of pH and solids loading is summarized in a three‐dimensional stability map.
Fugitive Interfacial Carbon Coatings for Oxide/Oxide Composites
Authors: Keller Kristin A. , Mah Tai‐Il , Parthasarathy Triplicane A. , Cooke Charles M.
Published: July 2010

The effectiveness of fugitive interfacial carbon coatings in Nextel™ 720‐based composites was investigated. Dense (>90%) matrix (calcium aluminosilicate, 0° and ±45°) composites and porous matrix (mullite/alumina, eight‐harness satin fabric) composites were fabricated and tensile tested in two control conditions (uncoated or carbon‐coated) and with the carbon removed (fugitive interface). Results indicated that carbon removal in dense matrix composites did not significantly change unidirectional composite strength, even after long‐term exposure at 1000°C. For porous matrix composites, composite strength was independent of the fiber/matrix interface, even after exposure at 1150°C for 500 h in air.
Crack Tip Morphology of Slowly Growing Cracks in Glass
Authors: Hénaux Stéphane , Creuzet François
Published: July 2010

We present atomic force microscopy (AFM) observations of crack tips in glass during subcritical propagation. These have been obtained by means of an AFM sample holder which has been specially designed to propagate indentation cracks in glass plates. Crack tips in soda–lime–silica glass are always preceded by a few nanometers deep deformation. In vitreous silica, no other surface deformation than the crack itself could be detected. For both materials, the crack opening is found to largely exceed the elastic solution.
Synthesis and Characterization of Low‐Dielectric Silica Aerogel Films
Authors: Hyun Sang H. , Kim Joong J. , Park Hyung H.
Published: July 2010

Thin films of silica aerogel on a silicon wafer have been synthesized via supercritical drying of wet gel films that were obtained by spin coating the polymeric silica sol, followed by aging in an isopropanol (IPA) or tetraethoxysilane/isopropanol (TEOS/IPA) solution. The viscosity of the sol and the spin rate required to form uniform coating layers were optimized. The film thickness and microstructures could be controlled by adjusting the concentration of the sol, the spin rate, and the aging conditions. The porosities and the dielectric constants of the thin films were in the range of 76%–90% (densities of 0.59–0.22 g/cm3) and 2.0–1.5, respectively. The degree of planarization in the aerogel thin film was ∼100%, and the gap‐filling capability on a 0.2 μm tungsten patterning wafer was excellent. In particular, aging the wet gel film in the TEOS/IPA solution was very effective in improving the properties of the aerogel films.
Chloride‐Ion Activities in Simplified Synthetic Concrete Pore Solutions: The Effect of the Accompanying Ions
Authors: de Vera Guillem , Hidalgo Ana , Climent Miguel Angel , Andrade Carmen , Alonso Cruz
Published: July 2010

Concrete pore solutions are concentrated electrolytes in which the activity of the chemical species must be calculated properly to determine the equilibrium state of such solutions. In this work, the chloride‐ion activity coefficients in synthetic concrete pore solutions have been obtained potentiometrically, using different calibrated Cl− ion‐selective electrodes (ISEs); also, a discussion about the performance of the different Cl− ISEs in alkaline media is presented. Experimental results are compared with the calculated results, using Pitzer's specific ionic‐interaction model, and good agreement is observed between them.
Electrical Conductivity of the High‐Temperature Proton Conductor BaZr0.9Y0.1O2.95
Authors: Bohn Hans G. , Schober Tilman
Published: July 2010

The impedance of the cubic perovskite BaZr0.9Y0.1O3‐δ has been systematically investigated in dry and wet atmospheres at high and low oxygen partial pressures. In the grain interior, conductivity contributions from oxygen ions, electron holes, and protons can be identified. Below 300°C, proton conduction dominates and increases linearly with the frozen‐in proton concentration. The proton mobility, with an activation energy of 0.44 ± 0.01 eV is among the highest ever reported for a perovskite‐type oxide proton conductor. For dry oxygen atmos‐pheres, electron hole conduction dominates with an activation energy of ∼0.9 eV. At temperatures <500°C, the grain‐boundary conductivity can be separated and increases upon incorporation of protons. The high electrical conductivity and chemical stability make acceptor‐doped barium zirconate a good choice for application as a high‐temperature proton conductor.
Numerical Evaluation of Toughening by Crack‐Face Grain Interlocking in Self‐Reinforced Ceramics
Authors: Kovalev Serguei , Miyajima Tatsuya , Yamauchi Yukihiko , Sakai Mototsugu
Published: July 2010

Crack bridging associated with the pull‐out process of interlocking grains in self‐reinforced ceramic materials is studied through a micromechanical simulation. The pullout of a single inclined grain is modeled via the numerical solution of a general contact problem. The bridging‐force versus crack‐opening‐distance curve indicates a nonlinear, springlike response for the pullout of interlocking grains. The sliding friction along the debonded interface, induced by highly localized contact stresses, dominates the total bridging force. The bridging force increases with grain inclination until eventual bridge failure. The pullout of misaligned grains mainly affects short‐crack toughening, with a rising R‐curve, whereas aligned grains contribute to long‐crack toughening. The residual stresses of the thermal expansion anisotropy play a minor role in the pull‐out process of grain interlocking and the resultant toughening. The proposed mechanism is operative in both single‐phase and composite ceramics in which pullout of elongated grains/reinforcements occurs.
Superplastic Behavior of Fine‐Grained β‐Silicon Nitride Material under Compression
Authors: Zhan Guo‐Dong , Mitomo Mamoru , Nishimura Toshiyuki , Xie Rong‐Jun , Sakuma Taketo , Ikuhara Yuichi
Published: July 2010

The deformation behavior of a hot‐pressed, fine‐grained β‐Si3N4 ceramic was investigated in the temperature range 1450°—1650°C, under compression, and the results for strain rate and temperature dependence of the flow stress are presented here. The present results show that the material is capable of high rates of deformation (∼10−4—10−3 s−1) within a wide range of deformation temperatures and under a pressure of 5—100 MPa; no strain hardening occurs in the material, even at slow deformation rates, because of its stable microstructure; Newtonian flow occurs, with a stress exponent of approximately unity; and the material has activation energy values for flow in the range 344—410 kJ·mol−1. Grain‐boundary sliding and grain rotation, accommodated by viscous flow, might be the mechanisms of superplasticity for the present material.
Room‐Temperature Solubility Behavior of Barium Titanate in Aqueous Media
Authors: Neubrand Achim , Lindner Reinhard , Hoffmann Peter
Published: July 2010

In the present study, the incongruent dissolution of barium from barium titanate (BaTiO3) has been studied as a function of dispersion pH and powder volume fraction for two different BaTiO3 powders. In alkaline dispersions, the barium solubility strongly increases as the pH increases, as suggested by thermodynamic considerations. At pH <7, the barium solubility reaches a plateau, the height of which is dependent on the surface area of the powder and the solids loading of the slip. The BaTiO3 surface is completely depleted of barium in this region.
Effect of Electric Field on the Migration of Grain Boundaries in Alumina
Authors: Jeong Jin‐Wook , Han Joo‐Hwan , Kim Doh‐Yeon
Published: July 2010

The effect of an external electric field on the grain‐boundary migration in Al2O3 ceramics has been investigated. The boundary migration is dependent on the direction and magnitude of the applied bias, and the observed boundary migration behavior is attributed to the presence of an electrostatic potential that inherently forms at the grain boundaries of Al2O3 ceramics. The results give experimental evidence that the boundary phenomena in oxide ceramics are related to the grain‐boundary potential.
Dip Coating of Calcium Hydroxyapatite on Ti‐6Al‐4V Substrates
Authors: Mavis Bora , Taş A. Cüneyt
Published: July 2010

Ti‐6Al‐4V alloy is the most commonly used metallic material in the manufacture of orthopedic implants. The main inorganic phase of human bone is calcium hydroxyapatite (Ca10(PO4)6(OH)2, HA). To achieve better biocompatibility with bone, metal implants made of Ti‐6Al‐4V are often coated with bioceramics. Dip‐coating techniques scarcely are used to apply HA onto metallic implants. New dipping‐solution recipes to be used for HA coatings are described in this work. Scanning electron microscopy and X‐ray diffractometry have been used for sample characterization.
Effects of Alkaline‐Earth‐Metal Addition on the Sinterability and Microwave Characteristics of (Zr,Sn)TiO4 Dielectrics
Authors: Kim Duk‐Jun , Hahn Jin‐Woo , Han Gee‐Pyeong , Lee Sang‐Seok , Choy Tae‐Goo
Published: July 2010

The sinterability and microwave dielectric properties of (Zr0.8Sn0.2)TiO4 with additions of 1 mol% of magnesium, calcium, strontium, or barium were examined. All the alkaline‐earth metals were effective for densification, and the order of effectiveness was as follows: Mg < Ca < Sr < Ba. The dielectric constant and the temperature coefficient of the resonant frequency were not influenced very much by the additives; however, a strong deterioration of the quality factor (Q) did occur when magnesium was added. The presence of grain‐boundary phases was confirmed via microstructural observation, using transmission electron microscopy. In addition, energy‐dispersive X‐ray analysis was performed to investigate the cause of the deterioration in the Q value.
Self‐Propagating High‐Temperature Synthesis of Aluminum Nitride under Lower Nitrogen Pressures
Authors: Shin Jason , Ahn Do‐Hwan , Shin Mee‐Shik , Kim Yong‐Seog
Published: July 2010

The synthesis of aluminum nitride (AlN) via self‐propagating high‐temperature synthesis (SHS) was attempted, using aluminum powder that was mixed with AlN powder as a diluent. The AlN content in the reactant was varied over a range of 30%–70%, and the nitrogen pressure was varied over a range of 0.1–1.0 MPa. The SHS reaction that was performed using a reactant that contained 50% AlN diluent, under a nitrogen‐gas pressure of 0.8 MPa, yielded the highest conversion ratio of aluminum powder to AlN powder. A mechanism for the reaction of aluminum with nitrogen gas during the SHS process was discussed, based on observations of the microstructures of the reaction zone and products.
Effect of Slurry Rheological Properties on the Coating of Ceramic Honeycombs with Yttria‐Stabilized‐Zirconia Washcoats
Authors: Agrafiotis Christos , Tsetsekou Athena , Leon Ioanna
Published: July 2010

Recently, a novel automotive catalyst design, based on the use of palladium supported on yttria‐stabilized zirconia (YSZ), was proposed. In the present work, the coating of cordierite honeycomb samples with YSZ slurries for the preparation of such washcoats was investigated. The loading percentage, homogeneity, and reproducibility were found to depend strongly on the slurry viscosity. Parameters such as the slurry‐solids content, pH, type of powder used, and use and quantity of the dispersants were optimized for the preparation of stable, low‐viscosity YSZ slurries, adjustments that could lead to an efficient coating process for honeycomb structures.
Synthesis and Structural Characterization of Trimetallic Perovskite‐Type Rare‐Earth Orthoferrites, LaxSm1–xFeO3
Authors: Traversa Enrico , Nunziante Patrizia , Sangaletti Luigi , Allieri Brigida , Depero Laura E. , Aono Hiromichi , Sadaoka Yoshihiko
Published: July 2010

Ultrafine powders of trimetallic orthoferrites containing lanthanum and samarium in various ratios were synthesized by thermal decomposition at low temperatures of the corresponding hexacyano complexes to modulate the functional properties of these perovskite‐type oxides. The precursors and their decomposition products were analyzed by simultaneous thermogravimetric and differential thermal analyses, X‐ray diffractometry, and Raman spectroscopy. Single‐phase trimetallic precursors and oxides were obtained. The crystal structure of the perovskite‐type oxides was orthorhombic, and the lattice parameters were affected by the ionic size of the rare‐earth elements present in the oxides. Raman spectra showed a broadening of the vibrational bands with increased lanthanum content. This was ascribed to some disorder in the oxygen sublattice, related to distortions of the cation–oxygen coordination, and to a reduction of the orthorhombic distortion in the unit‐cell basal plane. Most of the Raman modes above 200 cm−1, associated with the vibration of oxygen ions, showed a frequency increase with effective cation mass, defined asmeff=xmLa+ (1 –x)mSm, i.e., with samarium content. This was explained by assuming that the force constants increased with decreased Ln–O and Fe–O interatomic distances observed for high samarium content.
Dielectric Properties of Pb(Fe2/3W1/3)O3–PbTiO3 Solid‐Solution Ceramics
Authors: Vilarinho Paula M. , Zhou Liqin , Pöckl Manfred , Marques Nelson , Baptista João L.
Published: July 2010

The dielectric properties of (1−x)Pb(Fe2/3W1/3)O3·xPbTiO3 solid solutions were investigated from 102 to 106 Hz in the temperature range 150–600 K. The phase transition of Pb(Fe2/3W1/3)O3 (PFW) was shifted by PbTiO3 (PT) additions to higher temperatures at a rate of 6.3 K/mol% of PT. The temperature dependence of dielectric permittivity showed a sharper transition as the PT content increased. Dielectric measurements in a wide temperature range showed the presence of a second set of dielectric peaks at higher temperatures (350–600 K), besides the ferroelectric–paraelectric phase transition. This second set of peaks vanished when the samples were annealed in nitrogen. The activation energy values for the second relaxation varied between 0.50 and 0.63 eV, in agreement with the conduction activation energy determined for each sample. This relaxation is apparently related to electron holes.
Mechanical Activation‐Assisted Synthesis of Pb(Fe2/3W1/3)O3
Authors: Ang Seok Khim , Wang John , Wan Dongmei , Xue Junmin , Li Longtu
Published: July 2010

Perovskite Pb(Fe2/3W1/3)O3 (PFW) was prepared via a mechanical activation‐assisted synthesis route from mixed oxides of PbO, Fe2O3, and WO3. The mechanically activated oxide mixture, which exhibited a specific area of >10 m2/g, underwent phase conversion from nanocrystalline lead tungstate (PbWO4) and pyrochlore (Pb2FeWO6.5) phases on sintering to yield perovskite PFW, although the formation of perovskite phase was not triggered by mechanical activation. When heated to 700°C, >98% perovskite phase was formed in the mechanically activated oxide mixture. The perovskite phase was sintered to a density of ∼99% of theoretical density at 870°C for 2 h. The sintered PFW exhibited a dielectric constant of 9800 at 10 kHz, which was ∼30% higher than that of the PFW derived from the oxide mixture that was not subjected to mechanical activation.
Sintering of Translucent Alumina in a Nitrogen–Hydrogen Gas Atmosphere
Authors: Wei George C. , Rhodes William H.
Published: July 2010

The sintering of alumina doped with magnesia‐based additives to translucency previously has been possible only in atmospheres of hydrogen or oxygen or under vacuum. This paper reports on the sintering of alumina in N2–H2 atmospheres that contain as little as 2% H2, where optical transparency that is equivalent to that of normal H2 sintering is achieved. In an effort to explain these results, experiments that vary the content of H2 and H2O, as well as the changes in the dynamic atmosphere, have been conducted. The evidence indicates that the final‐stage sintering involves a point‐defect pair mechanism that includes hydrogen interstitials and nitrogen solutes.
Effects of Dry Grinding on the Structural Changes of Kaolinite Powders
Authors: Sánchez‐Soto Pedro J. , del Carmen Jiménez de Haro María , Pérez‐Maqueda Luis A. , Varona Ignacio , Pérez‐Rodríguez José L.
Published: July 2010

The present study examined the effects of dry grinding, using ball‐milling, on the structure of reference well‐crystallized (KGa‐1) and poorly crystallized (KGa‐2) kaolinite powders from Georgia. Grinding produced a strong structural alteration, mainly along the c axis, resulting in disorder and total degradation of the crystal structure of the kaolinite and the formation of an amorphous product. The surface area increased with grinding time, mainly in KGa‐2 (maximum value 50.27 m2/g), a result associated with particle‐size reduction. These particles became more agglomerated with grinding, and the surface area decreased after 30 min, as confirmed by scanning electron microscopy and particle‐size‐distribution analysis. There was a limit to particle‐size reduction with grinding time. When grinding time was increased, the original endothermic differential thermal analysis (DTA) effects of dehydroxylation in both samples shifted to lower temperatures, decreased in intensity, then disappeared completely after 120 min of grinding. The temperature of the characteristic first exothermic effect shifted slightly to lower temperatures with grinding, although the DTA effects did not increase with grinding time in either kaolinite sample, at least up to 325 min. The amorphous, mechanically activated kaolinite converted into low‐crystalline mullite nuclei at a lower temperature than did the unground samples, as deduced by thermal and X‐ray observations. This effect was especially important for the KGa‐2 sample. Grinding did not seem to influence the formation of silicon‐aluminum spinel from kaolinite. The present results may explain why ground kaolinite samples prepared via different routes—e.g., with differences in grinding—behave differently during high‐temperature transformations, as reported in the related literature.
Effects of Solvent Mixtures on Dispersion of Lanthanum‐Modified Lead Zirconate Titanate Tape Casting Slurries
Authors: Feng Jian‐Huei , Dogan Fatih
Published: July 2010

The effects of xylenes/ethanol solvent mixtures on lanthanum‐modified lead zirconate titanate (PLZT) nonaqueous suspensions were investigated by measuring sediment height, viscosity, and adsorption of dispersant. Well‐dispersed colloidal suspensions were obtained in xylene‐rich solvents with a minimum amount of menhaden fish oil as a dispersant. It was also shown that adsorption of dispersant on particle surfaces strongly depends on selection of solvent(s). The ratio of solvent mixture affects PLZT solids content of unfired tapes, in which using insufficient as well as excess dispersant could decrease the packing density of particles. Solubility of other organic additives, such as binder, was also considered when selecting a xylene/ethanol ratio.
Behavior of MgFe2O4 Films on MgO in an Electric Field
Authors: Johnson Matthew T. , Carter C. Barry , Schmalzried Hermann
Published: July 2010

Thin films of MgFe2O4 spinel on a (001) substrate of MgO have been heated to elevated temperatures in an applied electric field. The externally applied electric field produces a large driving force that influences the kinetic behavior of the spinel film and results in the formation of an MgO layer at the cathode due to the higher mobility of the Mg2+ cations in the spinel. Through the use of both scanning and transmission electron microscopy, the evolution of this layer was followed through a series of heat treatments. Analysis of the decomposition process shows that initially isolated pockets of MgO form at the cathode surface. These pockets grow and eventually coalesce to form a continuous MgO layer. The two MgO/spinel heterojunctions behave differently since one is morphologically stable while the other is morphologically unstable. TEM analysis showed that during the decomposition process, dislocation loops are formed in the vicinity of the MgO pockets. It is proposed that these dislocation loops form to accommodate the lattice misfit at the interface between the precipitating MgO and spinel.
Reaction‐Bonded and Superplastically Sinter‐Forged Silicon Nitride–Silicon Carbide Nanocomposites
Authors: Kondo Naoki , Suzuki Yoshikazu , Ohji Tatsuki
Published: July 2010

Silicon nitride–silicon carbide (Si3N4–SiC) nanocomposites were fabricated by a process involving reaction bonding followed by superplastic sinter‐forging. The nanocomposites exhibited an anisotropic microstructure, in which rod‐shaped, micrometer‐sized Si3N4 grains tended to align with their long axes along the material‐flow direction. SiC particles, typically measuring several hundred nanometers, were located at the Si3N4 grain boundaries, and nanosized particles were dispersed inside the Si3N4 grains. A high bending strength of 1246 ± 119 MPa, as well as a high fracture toughness of 8.2 ± 0.9 MPa·m1/2, was achieved when a stress was applied along the grain‐alignment direction.
Low‐Temperature Chemical Synthesis of Nanocrystalline MgAl2O4 Spinel Powder
Authors: Pati Ranjan K. , Pramanik Panchanan
Published: July 2010

Nanocrystalline MgAl2O4 spinel powder was synthesized by pyrolysis of complex compounds of aluminum and magnesium with triethanolamine (TEA). The soluble metal ion–TEA complexes formed the precursor material on complete dehydration of the complexes of aluminum–TEA and magnesium–TEA. Single‐phase MgAl2O4 spinel powder resulted after heat treatment of the precursor material at 675°C. The precursor and the heat‐treated powders were characterized by X‐ray diffractometry (XRD), differential thermal and thermogravimetric analysis, and transmission electron microscopy (TEM). The average crystallite size as measured from the X‐ray line broadening was around 14 nm and the average particle size from TEM studies was around 20 nm.