bluuebunny/crossref_metadata_2025 huggingface dataset:
Sol–Gel Synthesis of Nanophase Yttria‐Stabilized Tetragonal Zirconia and Densification Behavior below 1600 K
Authors: Bourell David L. , Parimal  , Kaysser Wolfgang
Published: March 2005

The hot‐pressing behavior of nanophase, 3‐mol%‐yttria‐stabilized, tetragonal zirconia (Y‐TZP) was studied in the temperature range 1290 to 1570 K. Powder was sol‐gel synthesized using zirconium tetrachloride and hydrated yttrium chloride precursors. After drying and calcination, the particle size was 40 nm, coarsening to 70 nm upon subsequent annealing at 1273 K. On compact heating at 23‐MPa applied stress, densification initiated near the calcination/annealing temperature. Theoretical density was obtained at densification temperature above 1490 K with particle coarsening consistent with classical coarsening kinetics. Microstructural change accompanying densification involved formation of dense regions 2 to 4 μm in size separated by irregularly shaped porous regions. The observed densification behavior complements calculated densification maps for fine‐particle Y‐TZP.
Preparation and ac Electrical Response Analysis for (Ba,Pb)TiO3 PTCR Ceramics
Authors: Lai Chun‐Hung , Tseng Tseung‐Yuen
Published: March 2005

For those PTCR materials with higher Pb content, the thermodynamic derivation of increasing values for “inversion temperature” and cation vacancy diffusion rate accounts for the increases in the calculated acceptor‐state densities Ns (cm−2). The influence of frequency‐dependent properties for the dielectric constant on the calculation of acceptor‐state densities is also presented. Applying the concept of suitable value for Ns to obtain a strong PTC effect, (Ba,Pb)TiO3 PTCR ceramics with Curie point Tc over 340°C up to 420°C have been successfully prepared by adopting higher cooling rates.
Model for the Formation of Silicon Carbide from the Pyrolysis of Dichlorodimethylsilane in Hydrogen: I, Silicon Formation from Chlorosilanes
Authors: Cagliostro Domenick E. , Riccitiello Salvatore R.
Published: March 2005

Silicon tetrachloride is a major product of the pyrolysis of dichlorodimethylsilane in hydrogen. A model is developed for the deposition of silicon from the reduction of silicon tetrachloride with hydrogen in a tubular reactor at temperatures from 700° to 1100°C and 1.013 × 105 Pa (1 atm) pressure. Concentrations of silicon tetrachloride varied from 1 to 9 vol%. Gas chromatography was used to determine the volatile products of reaction, and gravimetric analysis was used to determine the total silicon deposition on the tube. The model, based on the experimental data, assumes the following reversible chemical reactions:

image

The rate constants derived from a nonlinear regression analysis are reported.
Synchrotron Radiation Ti‐k XANES Study of TiO2─Y2O3‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Zschech Ehrenfried , Kountouros Paris N. , Petzow Günter , Behrens Peter , Lessmann Alex , Frahm Ronald
Published: March 2005

Valence state and site symmetry of Ti ions in TiO2–Y2O3–ZrO2 powders with 2 mol% Y2O3 and 5, 10, 15, and 20 mol% TiO2, respectively, are studied by X‐ray absorption near‐edge spectroscopy (XANES). Tetravalent Zr4+ ions are replaced predominantly by Ti4+ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO2 content in TiO2–Y2O3‐stabilized tetragonal ZrO2 polycrystals (Ti‐Y‐TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti4+ ions on Zr4+ lattice sites. On the contrary, this correlation between the TiO2 content in Ti‐Y‐TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO2 content, caused by a subsequent clustering of Ti ions.
Elevated‐Temperature Behavior of High‐Strength Silicon Carbide
Authors: Woodilla David , Buonomo Michael , Bar‐On Isa , Katz R. Nathan , Whalen Thomas
Published: March 2005

The room‐ and high‐temperature mechanical properties or a high‐strength, sintered silicon carbide were evaluated Room‐temperature strength was measured in four‐point bending. The room‐temperature fracture toughness was determined using a precracked single‐edge‐notched beam (SENB) bridge indentation technique. The high‐temperature behavior was evaluated using the stepped‐temperature stress rupture (STSR) procedure. Both the room‐ and the high‐temperature behavior are superior to those of previously tested commercial sintered α and β silicon carbides.
Preparation of Silicon Carbonitrides from an Organosilicon Polymer: I, Thermal Decomposition of the Cross‐linked Polysilazane
Authors: Bahloul Djamila , Pereira Mario , Goursat Paul , Yive N. S. Choong Kwet , Corriu Robert J. P.
Published: March 2005

The conversion of a solid copolymer (ViSiHNH)x─(MeSiHNH)y into a ceramic was studied in the 20–1450°C temperature range under different atmospheres (inert or oxidative). The ceramic yield, the ceramic composition, and the gaseous evolution directly depend on the heating rate, the pyrolysis atmosphere, and the duration of pyrolysis. The implications of these observations to the pyrolysis mechanism are discussed. The silicon carbonitride obtained after pyrolysis is amorphous up to 1400°C with high carbon content. It will be shown in Parts II and III that either SiC or Si3N4 could be selectively crystallized depending upon processing conditions.
Atomic Beam Modifications of Insulator Surfaces
Authors: Eipers‐Smith Ketti , Waters Kelley , Schultz J. Albert
Published: March 2005

A deposition chamber is described comprising a unique broad‐beam, high‐flux (>2 mA/cm2), low‐energy (<100 eV) molecular and atomic nitrogen source suitable for growth and/or surface modification of ceramic thin films. Atom flux is generated by collisionally neutralizing and dissociating a diatomic nitrogen ion beam impinging a specially shaped surface interposed between the ion source and the substrate to be modified. The dissociation surface functions as a „funnel” to give the resulting neutral beam a tight geometric focus. In addition, our chamber possesses the unique capability of surface analysis at high pressures (mTorr) during thin‐film formation through the use of pulsed time‐of‐flight ion scattering techniques. This allows continuous monitoring (and control) of film stoichiometry during growth.
Transient Plastic Phase Processing of Titanium–Boron–Carbon Composites
Authors: Barsoum Michel W. , Houng Boen
Published: March 2005

Ceramic/ceramic composites in the Ti‐B‐C system were fabricated by a novel process referred to as transient plastic phase processing (TPPP). The basic concept is based on the following reaction:

“soft” transient plastic matrix

+ reactant phase → hard matrix

+ reinforcement phase

where the transient plastic phase is a phase with a wide range of stoichiometry and a yield point that is a strong function of that stoichiometry. The reactant phase is one that will react with the transient phase in such a way so as to shift the composition of the latter toward its harder and more refractory composition. The composite is formed in two stages: In the first, pressure is applied to shape and fully densify the reactants while the transient phase is soft, i.e., before reaction. Once the reactants are densified, the reaction is allowed to proceed, forming a new phase and rendering the matrix more refractory. If the volume change upon reaction is small, then the density of the final compact will remain near theoretical. Using this approach ceramic/ceramic composites in the Ti─B─C system were hotpressed to full density and complex shapes at temperatures as low as 1600°C.
Mechanism of Grain Growth of β‐SiAlON
Authors: Einarsrud Mari‐Ann , Mitomo Mamoru
Published: March 2005

The mechanism for grain growth of β‐SiAlON has been investigated by annealing high‐density β‐SiAlON–YAG materials at 1650°C. An observed decrease in grain growth with increasing weight fraction of liquid confirms a diffusion‐controlled growth mechanism in the system. The grain‐growth mechanism is further characterized by the development of large elongated grains in addition to smaller grains. After prolonged heating, an equilibrium maximum grain size is developed causing a homogenization of the microstructure.
Space Charge Segregation at Grain Boundaries in Titanium Dioxide: I, Relationship between Lattice Defect Chemistry and Space Charge Potential
Authors: Ikeda Jeri Ann S. , Chiang Yet‐Ming
Published: March 2005

The electrical potential difference between the interface and the bulk in TiO2 is obtained as a function of temperature, oxygen pressure, and acceptor or donor doping from a space charge model that explicitly includes the high‐temperature lattice defect chemistry. Using defect equilibrium constants for TiO2 from previous literature studies, it is shown that for a space charge determined by ionic defect equilibration with the interface, the potential is negative in undoped and acceptor‐doped TiO2 and positive at high donor concentrations. The isoelectric point lies in the donor‐doped regime at high temperatures due to the contribution of defects from reduction, even for fairly oxidizing ambients.
Linear and Nonlinear Optical Properties of TeO2 Glass
Authors: Kim Sae‐Hoon , Yoko Toshinobu , Sakka Sumio
Published: March 2005

A thin plate of TeO2 glass of 5.0 × 4.0 × 0.25 mm3 size, which was large enough for various optical measurements, was obtained by a rapid quenching method. The linear refractive index was measured as a function of wavelength from 486.1 to 1000 nm. The refractive index at 486.1 nm was as high as 2.239. The optical energy band gap was estimated as 3.37 eV from the optical absorption spectrum. The third‐order nonlinear optical susceptibility, χ(3), was determined by the third‐harmonic generation (THG) method. The χ(3) value was as high as 1.4 × 10−12 esu, about 50 times as large as that of SiO2 glass. The results are discussed based on Lines' model in which an influence of cationic empty d‐orbitals on the nonlinear properties was taken into account.
Cubic‐to‐Tetragonal Displacive Transformation in Gd2O3–Bi2O3 Ceramics
Authors: Su Pomin , Virkar Anil V. , Hubbard Camden R. , Cavin O. Burl , Porter Wallace D.
Published: March 2005

Gd2O3‐doped Bi2O3 polycrystalline ceramics containing between 2 and 7 mol% Gd2O3 were fabricated by pressureless sintering powder compacts. The as‐sintered samples were tetragonal at room temperature. Hightemperature X‐ray diffraction (XRD) traces showed that the samples were cubic at elevated temperatures and transformed into the tetragonal polymorph during cooling. On the basis of conductivity measurements as a function of temperature and differential scanning calorimetry (DSC), the cubic → tetragonal as well as tetragonal → cubic → teansition temperatures were determined as a function of Gd2O3 concentration. The cubic → tetragonal transformation appears to be a displacive transformation. It was observed that additions of ZrO2 as a dopant, which is known to suppress cation interdiffusion in rare‐earth oxide–Bi2O3 systems, did not suppress the transition, consistent with it being a displacive transition. Annealing of samples at temperatures 660°C for several hundred hours led to decomposition into a mixture of monoclinic and rhombohedral phases. This shows that the tetragonal polymorph is a metastable phase.
Effect of B2O3 and hBN Crystallinity on cBN Synthesis
Authors: Choi Jun‐Youp , Kang Suk‐Joong L. , Fukunaga O. , Park Jong‐Ku , Eun K. Y.
Published: March 2005

Four kinds of BN powders—amorphous BN with B2O3, partially crystallized BN without B2O3, well‐crystallized hBN with B2O3, and well‐crystallized hBN without B2O3—were prepared to determine the effect of B2O3 on the crystallization of amorphous BN and the effect of BN crystallinity on the formation of cBN under high pressure (4–5 GPa) and at high temperature (1350–1450°C). The amorphous BN with B2O3 easily crystallized and transformed to cBN in the presence of A1N catalyst, while the partially crystallized BN without B2O3 did not. The well‐crystallized hBN transformed very slowly to cBN without B2O3, in contrast to fast transformation with B2O3. It is thus found that the transformation from hBN to cBN in the presence of AIN catalyst is determined by the degree of BN crystallinity as well as the presence of B2O3. Cubic BN can be synthesized only from crystallized hBN under the experimental conditions used. The formation of cBN from amorphous BN is possible through its prior crystallization, which can occur in the presence of B2O3.
Structural Evolution of Colloidal Silica Gels to Glass
Authors: Ying Jackie Y. , Benziger Jay B. , Navrotsky Alexandra
Published: March 2005

The gel‐to‐ceramic evolution of colloidal‐derived silica gels was examined by thermal analysis, infrared photoacoustic spectroscopy, physical characterization, and high‐temperature calorimetry. Oxygen in the firing atmosphere promoted sintering of colloidal gels relative to firing in a nitrogen or argon atmosphere. Water vapor in the atmosphere promoted consolidation and crystallization to cristobalite. Addition of PVA to the colloidal gel resulted in consolidation and crystallization of the gel at 1000°C, ∼150°C less than gels without the PVA binder. The enthalpy of consolidation of the gels to fused silica glass was approximately − 10 kJ/mol, primarily due to reduction of surface area.
Si‐Al‐O‐N Fibers from Polymeric Precursor: Synthesis, Structural, and Mechanical Characterization
Authors: Sorarù Gian Domenico , Mercadini Massimo , Maschio Roberto Dal , Taulelle Francis , Babonneau Florence
Published: March 2005

Polymeric fibers were produced from a polyaluminocarbosilane obtained by reacting polycarbosilane and an aluminum alkoxide modified with a β‐ceto ester. The pre‐ceramic fibers were converted into amorphous Si‐Al‐O‐N ceramic fibers after a pyrolysis process under flowing ammonia at 1000°C. 29Si and 27Al magic‐angle spinning nuclear magnetic resonance investigations were performed to characterize the conversion process of the polymeric precursor fibers into the ceramic product. However, because of the amount of matter required for the MAS‐NMR experiments, the heat treatment applied for fibers was done on powders assuming identical evolution for both materials. Tensile strength was measured at various stages of the pyrolysis process and related to the corresponding structural evolution.
Microstructure and Properties of Self‐Reinforced Silicon Nitride
Authors: Pyzik Aleksander J. , Beaman Donald R.
Published: March 2005

Problems associated with manufacturing Si3N4/SiC‐whisker composites have been overcome by developing selfreinforced Si3N4 with elongated β‐Si3N4 grains formed in situ from oxynitride glass. This Si3N4–Y2O3–MgO–SiO2–CaO‐based material has a flexure strength >1000 MPa and fracture toughness >8 MPa·m½. The optimum combination of mechanical properties has been obtained with Y2O3:MgO ratios ranging from 3:1 to 1:2, CaO contents ranging from 0.1 to 0.5 wt%, and Si3N4 contents between 90 and 96 wt%.
Influence of Iron Doping on the Microstructure of YBa2(Cu1−xFex)3O7−δ Ceramics
Authors: Diko Pavel , Duvigneaud Paul.‐H. , Lanckbeen Alain , Van Moer André , Naessens Georges , Deltour Robert
Published: March 2005

Porosity, grain growth, phase composition, and microstructural defects were studied in sintered YBa2 (Cu1−x)3O7−x ceramics for x values up to 0.3. The porosity of the samples, related to the sintering mechanism, was independent of iron concentration. A linear dependence of the grain size with the inverse of the iron concentration was found, strongly suggesting grain boundary segregation of iron. The solubility limit was estimated to be x= 0.18 at 950°C in O2. Beyond this limit, a new microstructural component was found consisting of YBa2(Cu1−xFex)3O7−δ, YBaCuFeO5 and Ba(Cu,Fe)O2. The transition from an orthorhombic twin to an orthorhombic tweed phase and a tetragonal phase was detected by polarized light microscopy.
Reaction Sintering of Cubic Boron Nitride Using Volatile Catalysts
Authors: Itoh Hideaki , Takao Hisaaki , Iwahara Hiroyasu
Published: March 2005

Reaction sintering behavior of cBN, which is accompanied by the transformation from hBN to cBN in the presence of 30 wt% diamond seed grains, was investigated under high pressure conditions (6.0–7.5 GPa, 1400–1700°C, 0–30 min) using volatile catalysts such as NH4NO3, NH4Cl, and NH2NH2. Fully dense sintered compacts having a Vickers microhardness of more than 5000 kg/mm2 were prepared with no residual catalytic solid components. The activation energy for the conversion from hBN to cBN was 200–230 kJ/mol. Adsorbed N2, H2, and/or NHx components which were formed by decomposition of these catalysts during high pressure and temperature treatments, would have a favorable kinetic effect on cBN formation from hBN and its simultaneous sintering.
Optically Translucent Mullite Ceramics
Authors: Schneider Hartmut , Schmücker Martin , Ikeda Ko , Kaysser Wolfgang A.
Published: March 2005

The optical transmittance of pressureless sintered and of hot isostatically pressed (HIPed) mullite ceramics was studied in the near infrared (NIR), visible light (VIS), and the ultraviolet (UV) spectrum ranges. Both processing methods provided fine‐grained microstructures (mean grain size of 5–10 μm) with equiaxed grains and a narrow grain‐size distribution. In pressureless sintered mullite, the porosity was 5.5% and transmittance was 20% in the VIS and NIR ranges. In the HIPed mullite, with porosity <1%, a transmittance of 40% was measured in the VIS range and up to 80% in NIR. UV transmittance of both pressureless sintered and HIPed mullite samples was low. The optically translucent mullite was found suitable for optical windows in the VIS and NIR ranges, particularly at elevated temperatures.
Highly Reactive β‐Dicalcium Silicate: V, Influence of Specific Surface Area on Hydration
Authors: Sasaki Kaori , Ishida Hideki , Okada Yoshihiko , Mitsuda Takeshi
Published: March 2005

The hydration of β‐C2S prepared from hillebrandite [Ca2(SiO3)(OH)2] and having specific surface areas of 6.8, 5.5, and 3.1 m2/g was investigated. Different specific areas were obtained by varying the dissociation temperature of hillebrandite. In addition, the hydration of β‐C2S synthesized from high‐temperature solid‐state reaction was also studied as a comparison. The specific surface area exerts a strong influence on the hydration rate, which increases as the surface area increases. The degree of influence changes with the reaction, becoming greater as hydration progresses. There is initially a linear relationship between specific area and the time required to complete a specific reaction. The specific surface area also affects the reaction mechanism. In the case of specific areas of 5.5 m2/g or less, the reaction changes from a chemical reaction to a diffusion‐controlled one, and the degree of reaction comes almost to a halt at 80% to 85%. The Ca/Si ratios of hydrate and the silicate anion structures were also investigated in this study.
Mechanisms and Kinetics of Reaction‐Bonded Aluminum Oxide Ceramics
Authors: Wu Suxing , Holz Dietmar , Claussen Nils
Published: March 2005

Reaction‐bonded Al2O3 (RBAO) ceramics were fabricated starting from mechanically alloyed Al2O3/Al, Al2O3/ Al/ZrO2, and Al2O3/Al/ZrO2/Zr mixtures. Isopressed compacts were heat‐treated in air up to 1550°C. Reaction‐bonding mechanisms, kinetics, and the influence of ZrO2 and Zr additions are investigated. Independent of additive, oxidation of Al proceeds both as solid/gas and liquid/gas reaction, and the reaction kinetics follow a parabolic rate law. The reaction rate depends strongly on the particle size of Al. The activation energy of the reaction depends essentially on green density. Below the melting temperature of Al, in samples containing 45 vol% Al and 55 vol% Al2O3, it is 112 and 152 kJ/mol at ∼64% and ∼74% TD, respectively, while above the melting temperature, it lies in the range ∼ 26–33 kJ/mol. Zr additions reduce the activation energy to some extent. Samples with only ZrO2 additions exhibit nearly the same activation energies as ZrO2‐free samples, though ZrO2 has a very positive effect on the microstructural development in RBAO ceramics. Microstructure evolution and some strength data of RBAO bodies are also reported.
Phase Composition of Hydrated DSP Cement Pastes
Authors: Lu Ping , Sun Guokuang , Young J. Francis
Published: March 2005

Cement pastes densified with small particles (DSP) containing up to 48% silica fume by weight of cement, and hydrated to up to 180 d at room temperature, have been analyzed using TMS‐GPC, TGA, and 29Si NMR to quantitatively estimate the amount of unreacted cement, Ca(OH)2, and residual silica fume, respectively. Using a mass balance approach, the CaO/SiO2 and H2O/SiO2 molar ratios of the C‐S‐H in the samples were calculated. For samples containing silica fume, the values of CaO/SiO2 lie between 0.9 and 1.3, depending on the degree of hydration and silica fume content, whereas for samples without silica fume they were 1.6. Silicate polymerization analysis using TMS‐GPC suggests that the molecular structure of the C‐S‐H is similar to that formed in conventional hydration. No cross‐linking species were found, but the fraction of higher polymers (above octamer) increases as the CaO/SiO2 ratio decreases.
Determination of Critical Concentrations of Silica and/or Calcia for Abnormal Grain Growth in Alumina
Authors: Bae So Ik , Baik Sunggi
Published: March 2005

Minimum amounts of SiO2 and CaO required for inducing abnormal grain growth in alumina were determined using ultrapure alumina (>99.999%) and sintering at 1900°C for 1 h in a contamination‐free condition. The critical concentrations of silicon in cationic mole fractions in alumina were 300 ppm without calcium, 200 ppm with 10 ppm calcium, and 150 ppm with 20 ppm calcium. The critical concentration of calcium alone was 30 ppm. These concentrations seemed to match approximately the solubility limits reported in the literature, which suggested that the abnormal grain growth in commercially pure alumina was indeed related with the formation of a small amount of liquid phase during sintering.
Coalescence of Two Viscous Cylinders by Capillarity: Part II, Shape Evolution
Authors: Hopper Robert W.
Published: March 2005

The theoretical geometry of the creeping plane‐flow coalescence of two viscous cylinders driven by surface tension is described. Normalized results are given for initial diameter ratios D= (1, 2, 5, 20, ∞) Typical shapes are displayed. Time‐dependencies of geometric features, and interrelationships between them, are presented graphically. The following features are noted: The relationships between reduced time and most dimensions depend rather weakly on D. There is no undercutting at the neck. Two‐dimensional Frenkel theory is seriously incorrect. The theory describes experiments accurately for small times, but differences eventually appear. Their sources are uncertain.
Correlation between Radiative Transition Probabilities of Nd3+ and Composition in Silicate, Borate, and Phosphate Glasses
Authors: Nageno Yoshikazu , Takebe Hiromichi , Morinaga Kenji
Published: March 2005

Compositional dependence of spontaneous emission probabilities between initial 4F3/2 and terminal 4IJJ= 9/2, 11/2, 13/2, 15/2) levels of Nd3+ were studied for about 90 samples of silicate, borate, and phosphate glasses using the Judd–Ofelt theory. The effect of the covalency of the Nd–O bond on the magnitude of intensity parameters was estimated from the variation of spectral profiles of the 4I9/2→4G5/2, 2G7/2 and 4F7/2, 4S3/2 transitions. Intensity parameters Ω4 and Ω6 and the spontaneous emission probabilities were strongly affected by the ionic packing ratio of the glass host. The results were discussed in terms of the site selectivity of Nd3+ ions in glasses.
Inner Stress Induced by Cu Metal Precipitation at Grain Boundaries in Low‐Temperature‐Fired Ni‐Zn‐Cu Ferrite
Authors: Fujimoto Masayuki
Published: March 2005

Multilayer chip inductors were characterized using analytical electron microscopy. The chip inductors consist of silver internal electrode sandwiched between low‐temperature‐fired, Ni‐Zn‐Cu ferrite layers. It was found that the cooling rate affected the inductance of the chip inductor. Elastic strain fields were observed at the grain boundaries in the rapidly cooled samples, causing degradation of the inductance. The strain field causing a decrease in the effective permeability of the ferrite was found to be due to interstitial‐type Cu precipitates at the grain boundaries. The occurrence of Cu metal precipitates was dependent on the starting chemical composition, oxygen partial pressure, and thermal equilibrium during cooling after the sintering process.
Phase Relations in the System Ce2O3–Al2O3 in Inert and Reducing Atmospheres
Authors: Tas A. Cuneyt , Akinc Mufit
Published: March 2005

The 1:1 compound, CeA1O3, in the system Ce2O3–Al2O3 has been synthesized from the oxides and shown to have a perovskite‐like tetragonal unit cell with the lattice parameters a= 3.763 and c= 3.792 Å. A new XRD pattern is suggested for CeA1O3. This compound is shown to be stable up to 1950°C. The 1:11 compound, CeAl11O18, has also been synthesized and shown to possess a magnetoplumbite‐like hexagonal unit cell with the lattice parameters α= 5.558 and c= 22.012 å. An XRD pattern is suggested for CeAl11O18 for the first time. The evolution of eutectic‐like microstructures was observed and reported in the Ce2O3‐rich side of this binary system.
Mechanically Induced Zone Darkening of Alumina/Ceria‐Stabrlized Zirconia Composites
Authors: Sergo Valter , Schmid Chiara , Meriani Sergio , Evans Anthony G.
Published: March 2005

Alumina/ceria‐stabilized zirconia bars tested in four‐point bending exhibited deformation bands on the tensile side due to localized tetragonal‐to‐monoclinic transformation. These bands became increasingly darker and were fully visible some weeks after the bending experiment. XPS spectra revealed that the darker regions are characterized by a higher concentration of cerium in the + 3 oxidation state, as opposed to other undeformed regions, in which + 4 is the predominant oxidation state. A numerical calculation established that residual stresses exist in the deformation bands. It is suggested that these stresses facilitate the reduction of cerium with the gradient in stress motivating the diffusion of oxygen vacancies.
Control of Leakage Resistance in Pb(Zr,Ti)O3 Thin Films by Donor Doping
Authors: Dimos Dunne , Schwartz Robert W. , Lockwood Steven J.
Published: March 2005

Donor doping, with La and Nb, has been used successfully to improve the leakage resistance of Pb(Zr,Ti)O3 (PZT) films. Donor doping of Pb(Zr0.5Ti0.5)O3 films has led to an improvement in the leakage resistance of over 2 1/2 orders of magnitude at elevated temperatures (T 100°C). The effect on leakage resistance is the same for the A‐site (La) and B‐site (Nb) dopants. However, the improvement is only about 1 order of magnitude near room temperature. This temperature effect is due to an increase in the transition temperature from a low activation energy mechanism to a higher activation energy mechanism. Similar improvements in leakage resistance have also been obtained by increasing the Pb concentration in the starting solution, which implies that Pb vacancies are the dominant acceptor species in the undoped films. In addition, donor doping has been effective in improving the electrical breakdown strength at elevated temperatures. Consequently, donor‐doped PZT films have been shown to be superior to undoped films for applications requiring high leakage resistance, such as decoupling capacitors.
Preparation of Apatite Thin Films through rf‐Sputtering from Calcium Phosphate Glasses
Authors: Yamashita Kimihiro , Arashi Tomohiro , Kitagaki Kazuhisa , Yamada Shinji , Umegaki Takao , Ogawa Kenji
Published: March 2005

Apatite thin films of calcium phosphate were successfully prepared by rf‐magnetron sputtering, followed by postannealing, from calcium phosphate glass targets with Ca/P atomic ratios of 0.6 to 0.75, much lower than the stoichio‐metric value of 1.67 for hydroxyapatite. Using targets with low Ca/P ratios of 0.65 to 0.25, tricalcium and pyrocalcium phosphate thin films were obtained. The formation of these calcium phosphates phases was attributed to the phosphorus oxide losses during sputtering. H2O vapor was effective in the formation of the apatite phase at high temperatures; apatite was the exclusive phase in the ambient H2O, even when the target with the low Ca/P ratio of 0.4 was used. Based on phase stability at high temperatures, it was assumed that various kinds of apatites, such as stoichiometric and nonstoichiometric hydroxy‐ and Ca‐deficient hydroxy‐apatites were formed, depending on the composition of the glass targets.
Stability of PZT Piezoelectric Ceramics under Vibration Level Change
Authors: Takahashi Sadayuki , Hirose Seiji , Uchino Kenji
Published: March 2005

Stability of the piezoelectric properties with changing vibration level was studied in lead zirconate–titanate (PZT) ceramics by using the constant‐current/velocity driving method. The changes of Young's modulus YE0 and mechanical loss factor Q–1m are a function of the square of effective vibration velocity v0. The nonlinear proportional constants of the above functions indicate the degree of stability under vibration level change. The stability of PZT estimated by these constants coincides with the results obtained through the heat generation study.
Critical Concentration of MgO for the Prevention of Abnormal Grain Growth in Alumina
Authors: Bae So Ik , Baik Sunggi
Published: March 2005

The effects of MgO on sintering and grain growth of alumina in the absence of any other impurities as well as in the presence of various amounts of CaO were investigated using ultrapure (>99.999%) alumina and sintering at 1900°C for 1 h in a clean contamination‐free condition. Critical concentrations of MgO required for the prevention of abnormal grain growth were linearly dependent on the CaO concentration. For a given concentration of CaO, at least the same amount of MgO has to be added to prevent abnormal grain growth. MgO addition alone to the ultrapure alumina enhanced both grain growth and densification kinetics during pressureless sintering. The beneficial effect of MgO doping could not be explained based on the solute drag (or pinning) model. It was more likely to be understood in terms of either a glass modification model or a solid–liquid interface modification model.
Graded Casting of Materials with Continuous Gradients
Authors: Marple Basil R. , Boulanger Jean
Published: March 2005

A process is introduced for producing continuously graded materials by slip casting with a continuous flow of slip of changing composition. The approach has been tested using alumina and zirconia slips to produce alumina/zirconia composites with a graded composition. Observation of the microstructure has shown that the phases are relatively well dispersed. Compositional analysis revealed a relatively smooth transition in composition through the thickness of sintered bodies. Results have also indicated that for flow rates up to ∼ 60 cm/min, the highest linear flow rate tested, the casting rate of alumina slips containing 38.6 vol% solids was not affected.
Synthesis of Metastable Tetragonal (t′) Zirconia–Ceria Solid Solutions by the Polymerized Complex Method
Authors: Yashima Masatomo , Ohtake Katsuya , Kakihana Masato , Yoshimura Masahiro
Published: March 2005

Homogeneous metastable tetragonal (t′) solid solutions of ZrO2—x mol% CeO2 (x= 20 and 50) were successfully synthesized by the organic polymerized complex method. The citric acid‐ethylene glycol solution containing Zr and Ce ions was polymerized at about 140°C and then heat‐treated at about 350°C to obtain a precursor. The black precursor was heated at 450°C and then fired up to 1300° or 1590°C, resulting in the homogeneous solid solutions.
Mechanical Characterization of Si–C(O) Fiber/SiC (CVI) Matrix Composites witrTa BN–Interphase
Authors: Prouhet Stéphane , Camus Gérald , Labrugere Christine , Guette Alain , Martin Eric
Published: March 2005

The mechanical behavior of three CVT‐processed 2D woven SiC/BN/SiC composite materials with different initial BN interphase thicknesses has been investigated by means of tensile and impact tests. The results have established the efficiency of a BN interphase in promoting a nonlinear/non–catastrophic tensile behavior and high impact resistance. The effect of the initial BN interphase thickness on the resulting mechanical behavior has also been demonstrated. Characterization of the fiber/matrix interfacial zones by AES and TEM has revealed the presence of a SiO2/C double layer at the BN/fiber interface, which might result from a decomposition undergone by the Si–C(O) Nicalon fiber during processing. It has been suggested that the influence of the initial BN interphase thickness on the mechanical properties of the composites results from both changes occurring in the composition and morphology of the interfacial zones and modifications of the interfacial forces due to accommodation of the radial residual clamping stress.
Erosion Wear Properties of Tetragonal ZrO2(Y2O3)‐Toughened Al2O3 Composites
Authors: Kamiya Hidehiro , Sakakibara Masato , Sakurai Yukio , Jimbo Genji , Wada Shigetaka
Published: March 2005

Erosion wear properties of tetragonal zirconia (t‐ZrO2 with 3 mol% Y2O3)/Al2O3 composites with different volume fractions of t‐ZrO2 in the rang of O to 100 vol% (including Al2O3 or t‐ZrO2 ceramics), were measured by a collision test between Al2O3 or SiC particles accelerated in an air stream (240 m/s) and a stationary composite or ceramics target. In the case of Al2O3 erodent particles, the wear rate of composites decreased to one‐tenth of the wear rate of Al2O3 or t‐ZrO2 ceramics. The optimum volume fraction of the addi‐tive phase for increased wear resistance was in the range of 7 to 22 vol% of t‐ZrO2. However, the wear resistance of all composites in collision with SiC particles deteriorated. The maximum wear rate appeared at about 40 vol% of t‐ZrO2, and reached two times that of the Al2O3 or t‐ZrO2 ceramics. The mean fracture load of the SiC erodent particle in a diametral compression test under quasi‐static loading was 2.3 times the value of the Al2O3 particle, which broke after collision with the target. Therefore, the mean impact force produced by Al2O3 particles striking the target was much lower than that from SiC particles. Because the impact force acting from the Al2O3 particles did not reach the threshold force required for lateral crack propagation in the composites, the principal damage mechanism, the wear resistance of composites increased. However, the impact force from SiC particles was greater than the threshold force, and lateral or other damaging cracking was promoted at the wear surface of the composite materials. This discussion is in agreement with the analysis by the lateral crack model and the results for the median crack length of each ceramic measured by Vickers indentation tests with different loads. The slope of the logarithm of median crack length as a function of the logarithm of Vickers indent load was larger than the value of 2/3 obtained theoretically.
Use of Transmission Electron Microscopy for the Characterization of Rapid Thermally Annealed, Solution‐Gel, Lead Zirconate Titanate Films
Authors: Reaney Ian M. , Brooks Keith , Klissurska Radosveta , Pawlaczyk Czezlaw , Setter Nava
Published: March 2005

The microstructure and preferred orientations of rapid thermally annealed Pb(Zr0.53,Ti0.47)O3 films, deposited on Pt/Ti/SiO2/Si electrode/substrates by solution‐gel spinning, have been investigated using analytical and high‐resolution electron microscopy and X‐ray diffraction. The temperature of pyrolysis of the PZT films was found to influence the preferred orientation of the film: lower temperatures (350°C) favored a (111) orientation, whereas higher temperatures (420°C) favored a (100) orientation. Excess Pb was used to control the A‐site stoichiometry of the film particularly at the film surface where Pb‐deficient crystals could often be observed. The absence of these crystals was shown to be correlated with an improvement in the dielectric response.
Microstructure and Properties of Plasma Ceramics
Authors: Lutz Ekkehard H.
Published: March 2005

Plasma spraying, originally a surfacing technology used for ceramic coating of metal and nonmetal substrates, is suitable for producing large, full ceramic bodies, such as plates and tubes, in situ to almost the desired dimensions; i.e., conventional methods of designing by molding and casting green bodies followed by sintering are not required. These “plasma ceramics” exhibit characteristic mechanical and thermomechanical properties. Their porous laminar grain structure results in low E‐modulus and strength, and in extreme thermal shock resistance, which is enhanced by the comparably high fracture resistance of the material. Because of these properties and their low hardness, plasma ceramics can be easily machined with almost conventional methods of metal processing.
Formation of Zirconia Solid Solutions Containing Alumina Prepared by New Preparation Method
Authors: Ishida Koji , Hirota Ken , Yamaguchi Osamu , Kume Hideki , Inamura Suguru , Miyamoto Hiroki
Published: March 2005

In the system ZrO2–Al2O3, a new method for preparing ZrO2 solid solutions from ZrCl4 and AlCl3 using hydrazine monohydrate is investigated. c‐ZrO2 solid solutions containing up to ∼40 mol% Al2O3 crystallize at low temperatures from amorphous materials. The formation mechanism is discussed from IR spectral data. The values of the lattice parameter α increase linearly from 0.5072 to 0.5105 nm with increasing Al2O3 content. At higher temperatures, transformation of the solid solutions proceeds as follows: c(SS) →t(ss) →t(ss) +α‐Al2O3→m+α‐Al2O3. m‐ZrO2–α‐Al2O3 composite ceramics are fabricated by hot isostatic pressing for 2 h at 1250°C and 196 MPa. Microstructures and mechanical properties are examined, in connection with increasing Al2O3 content.
Point Defect Modeling of La2CuO4‐Based Superconductors
Authors: Shen Li , Salvador Paul A. , Mason Thomas O.
Published: March 2005

A point defect modeling study of the oxygen nonstoichiometry and high‐temperature electrical properties of La2−xAExCuO4−y (AE = Ba, Sr, and Ca) systems indicates that, whereas oxygen excess (y < 0) due to oxygen interstitials predominates as x→ 0, oxygen deficit (y > 0) results primarily from dopant‐vacancy associates at large x; isolated oxygen vacancies are apparently minority defect species. The onset of oxygen deficiency due to dopant‐vacancy associates occurs at x∼ 0.15 in the AE = Ba and Sr systems but at x∼ 0.05 in the AE = Ca system. Ideal ionic point defect behavior persists to x∼ 0.4 in the AE = Ba and Ca systems and to x∼ 0.5 in the AE = Sr system. A premature flattening of the electrical properties above x∼ 0.2 occurs in the AE = Ba and Sr systems. Reasons for the extensive range of ideal ionic behavior and for the onset of degenerate electronic behavior are discussed, as are ramifications for high‐Tc superconductivity in these materials.
Ultrasonic Sol/Gel Processing of Aluminoborosilicate Glass and Its Composite with Carbon Fiber Reinforcement
Authors: Chiou Song , Hahn H. Thomas
Published: March 2005

An ultrasonic sol/gel technique has been used to process aluminoborosilicate glass and its composite with carbon fiber reinforcement. In this new technique, ultrasonic energy is used in place of alcohol solvent. Gel time is easily controlled by varying the amount of ultrasonic energy and the resulting gel also exhibits less shrinkage during the densification process. The sonogel‐based composite has lower flexural strengths than the alcogel and has close values between the measured moduli, while still retaining the same fracture toughness. Micromechanical analysis produces higher values; however, ill is suspected that the in situ modulus of matrix is lower than the value used in the analysis.
Reaction Hot Pressing of α′‐ and β′‐ SiAlON Ceramics
Authors: Hwang Shyh‐Lung , Chen I‐Wei
Published: March 2005

Hot pressing kinetics of α‐Si3N4, AIN, Al2O3, and Y2O3 powder mixtures forming α′‐ and β′‐SiAlONs have been studied. Densification proceeds in two steps, first by a small shrinkage upon ternary eutectic oxide melting (SiO2–Al2O3–Y2O3) at 1340°C, followed by a massive particle rearrangement and further shrinkage at higher temperature when nitride dissolution begins. With better wettability, AIN initially traps the oxide melt and delays densification. In addition, the preferential dissolution of AIN at 1450°C enriches the melt composition in AI, triggering transient precipitation of supersaturated β′‐SiAlON. Full densification is readily achieved at 1550°C without complete α‐Si3N4 conversion.
Numerical Flow Simulation of Viscoplastic Slurries and Design Criteria for a Tape Casting Unit
Authors: Loest Hagen , Lipp Roland , Mitsoulis Evan
Published: March 2005

Numerical simulations have been carried out using the finite element method (FEM) for the forming flow of ceramic tapes. The flow domain encompasses both the slurry reservoir and the doctor‐blade region with free surface and is fully two‐dimensional. The material of this study is an organic‐bonded alumina slurry used in a previous experimental investigation and is modeled as a viscoplastic Bing‐ham fluid with a yield stress. For different substrate speeds, the entire flow domain is analyzed and the extent and shape of yielded/unyielded regions are found. The computed free surface profiles are in close agreement with the experimental ones. Large vortices appear in the reservoir and their intensity is computed under different operating conditions. The lubrication approximation theory (LAT) is then used to deduce a new reservoir design with tapered walls avoiding recirculation. Subsequent FEM studies show the adequacy of the new design to achieve certain criteria such as elimination of vortices and an evenly distributed unyielded region. It is proposed that a combination of LAT and FEM techniques be used for design of ceramic tape casting equipment.
Homogeneity Effects on Feedstock Viscosity in Powder Injection Molding
Authors: German Randall M.
Published: March 2005

The viscosity change with solids loading in injection molding feedstock is analyzed for the effects of mixture inhomogeneities on overall viscosity. The analysis shows that the lowest possible feedstock viscosity corresponds to the highest homogeneity.
Slip and Twinning in Sapphire (α‐Al2O3)
Authors: Lagerlöf K. Peter D. , Heuer Arthur H. , Castaing Jacques , Rivière Jean P. , Mitchell Terence E.
Published: March 2005

The plastic deformation of sapphire (α‐Al2O3) has been studied under hydrostatic confining pressure at temperatures below the ambient pressure brittle‐to‐ductile transition temperature. Samples oriented for prism plane slip (Type I samples) were deformed via dislocation slip at temperatures as low as 200°C. Samples oriented for basal slip (Type II samples) could be plastically deformed at temperatures as low as 400°C but showed more complicated deformation behavior, inasmuch as the sample orientation also allowed for the activation of basal twinning and two of the three rhombohedral twin systems. The temperature dependence of the critical resolved shear stress (τcrss),
ln τcrss= ln τ0– M·T
for basal slip was significantly greater than that for prism plane slip (Bbasal > Bprism plane), causing the latter system to be the easy slip system below ∼600°C (basal slip is the easy slip system at elevated temperatures). Type II samples deformed primarily by basal twinning in preference to both rhombohedral twinning and basal slip. The different temperature dependence of τcrss for basal and prism plane slip is attributed to details of the dislocation core structure; prism plane dislocations, having a large Burgers vector (∣bPP∣= 0.822 nm), can dissociate into three collinear par‐tials (∣bP∣= 0.274 nm) separated by relatively low‐energy stacking faults, whereas the comparable dissociation of basal dislocations (∣bB∣= 0.476 nm) produces two ncncol‐linear partials separated by a relatively high energy stacking fault. Thus, dissociation of basal dislocations is most likely restricted to the dislocation core, which is manifested in a higher Peierls stress at low temperatures for basal slip compared to prism plane slip.
Internal Reduction of Chromium‐Doped α‐Alumina
Authors: Backhaus‐Ricoult Monika , Hagège Serge , Peyrot Aurélie , Moreau Patrick
Published: March 2005

(Al,Cr)2O3 single crystals and polycrystals were internally reduced at 1873 K in an Al/Al2O3 buffer for periods of time ranging from 1 to 100 h. The growth kinetics of the reduction scale were measured. The microstructure of the reduction scale was investigated by SEM and TEM. As a result of the reduction, two types of discrete chromium precipitates developed inside the alumina matrix (inside the single crystal or the polycrystalline grains), each one being characterized by a particular morphology (needle or spheroid) and a low‐energy orientation relationship with respect to the alumina matrix. In addition, larger precipitates without special orientation relationship developed along the grain boundaries and at the triple junctions of the polycrystais. In the first part of this paper, the precipitate morphology and size are described in terms of the crystallography of the interface between the two crystal structures in relation to the reduction mechanism. In the second part, the global reduction scale growth is analyzed in terms of point defect fluxes across the reduction scale.
Application of Selective 29Si Isotopic Enrichment to Studies of the Structure of Calcium Silicate Hydrate (C‐S‐H) Gels
Authors: Brough Adrian R. , Dobson Christopher M. , Richardson Ian G. , Groves Geoffrey W.
Published: March 2005

Selective isotopic enrichment of SiO2 with 29Si in a mixture with tricalcium silicate (C3S) has allowed the Si from this phase to be effectively labeled during the course of the hydration reaction, thus isolating its contribution to the reaction. A double Q2 signal has been observed in 29SI solid‐state MAS NMR spectroscopy of C‐S‐H gels of relatively low Ca/Si ratio, prepared by hydration or by carbonation of a C3S paste. The origin of the weaker, downfield peak is discussed and tentatively attributed to bridging tetrahedra of a dreierkette silicate chain structure.
Creep Anisotropy of a Continuous‐Fiber‐Reinforced Silicon Carbide/Calcium Aluminosilicate Composite
Authors: Weber Christian H. , Löfvander Jan P. A. , Evans Anthony G.
Published: March 2005

Creep studies conducted on a unidirectional silicon carbide calcium aluminosilicate composite indicate that the Nicalon fibers provide longitudinal creep strengthening at 1200°C. The deformation is transient in nature because grain growth in the fibers enhances their creep resistance. The‘ transverse creep strength is considerably smaller, being dominated by the matrix, resulting in appreciable creep anisotropy. This anisotropy leads to severe distortion when off‐axis loadings are imposed. Residual stresses develop upon unloading alter creep, and cause superficial matrix cracking.
Characteristics of Yttrium Iron Garnet Ultrafine Particles Prepared by the Alkoxide Method
Authors: Taketomi Susamu , Kawasaki Kenji , Ozaki Yoshiharu , Yuasa Sinji , Otani Yoshichika , Miyajima Hideki
Published: March 2005

Hydrolysis of a mixture of iron ethoxide and yttrium butoxide produced amorphous yttrium iron garnet (YIG) ultrafine particles with a mean diameter of 9 nm. The particles prepared by hot water vapor hydrolysis were less agglomerated than those prepared by plain hot water. DTA revealed that a broad phase transition temperature To from amorphous YIG to crystalline YIG ultrafine particles is 691°C with heat discharge of 118 kJ/mol which is attributed to the entropy decrease accompanying the crystallization, whereas magnetic experiments gave a value of To= 650°C. The particles calcined at 700°C were single‐crystalline ones while those calcined at higher temperatures (at least higher than 800°C) were multicrystalline ones.