bluuebunny/crossref_metadata_2025 huggingface dataset:
Origins of the Ductile Regime in Single‐Point Diamond Turning of Semiconductors
Authors: Morris Jonathan C. , Callahan Daniel L. , Kulik Joseph , Patten John A. , Scattergood Ronald O.
Published: July 2005

A germanium surface and the chips produced from a single‐point diamond turning process operated in the “ductile regime” have been analyzed by transmission electron microscopy and parallel electron‐energy‐loss spectroscopy. Lack of fracture damage on the finished surface and continuous chip formation are indicative of a ductile removal process. Periodic thickness variations perpendicular to the machining direction also are observed on these chips and are identified as ductile shear lamellae. The chips consist of an amorphous, elemental germanium matrix containing varying amounts of microcrystalline germanium fragments. The relative orientation of machining marks and crystallographic fragment texture are used to position individual chips with respect to the initial angular cutting zone on the wafer. Chips with high fragment content correlate directly to cutting zones subject to the highest resolved tensile stress on cleavage planes. These findings are explained in the context of a high‐pressure metallization (brittle‐to‐ductile) transformation with ductility limited by the onset of classical brittle fracture.
Characterization of Surface‐Oxidized Phase in Silicon Nitride and Silicon Oxynitride Powders by X‐ray Photoelectron Spectroscopy
Authors: Okada Kiyoshi , Fukuyama Koyo , Kameshima Yoshikazu
Published: July 2005

Surface‐oxidized phases on α‐silicon nitride, β‐silicon nitride, and silicon oxynitride powders were investigated by X‐ray photoelectron spectroscopy (XPS) and X‐ray Auger electron spectroscopy (XAES). The spectra of Si2p XPS and Si(KLL) XAES were measured precisely and were deconvoluted into some separate peaks, which correspond to each parent phase, a SiOxNy, oxidized phase, a nonstoichiometric SiNx. nitride phase, and a satellite peak of the parent phase, by the least‐squares method. The Auger parameter (AP) was calculated for each phase using the Si2p XPS and Si(KLL) XAES data, and the average chemical compositions of the oxidized phases in each sample were evaluated from the AP data. The chemical compositions of these phases were between those of silica and silicon oxynitride and varied among the samples, but were usually close to SiO2. Average thicknesses of the surface‐oxidized phases were estimated to be 0.1–0.8 nm from the peak area ratio of the oxidized phase against the parent phase of the XAES spectra, assuming a continuous surface layer model.
Angularly and Spectrally Resolved Light Scattering from Lead Zirconate Titanate Thin Films
Authors: Sinclair Michael B. , Dimos Duane , Potter Barrett G. , Schwartz Robert W.
Published: July 2005

The results of light‐scattering measurements of a series of Pb(Zr,Ti)O3 thin films prepared by a sol‐gel method are presented and analyzed. The films differed due to the addition of different concentrations of acetylacetone to the precursor solution immediately prior to film fabrication. Visual inspection of the films indicated improvements in optical quality with the addition of acetylacetone. To quantify these improvements, two types of light‐scattering measurements were performed: angularly resolved light scattering and spectrally resolved light scattering. Surprisingly, only slight differences between the films were observed using angularly resolved light scattering at 633 nm. In contrast, the spectrally resolved scattering revealed large differences between the films, with the films prepared using the largest concentrations of acetylacetone exhibiting the lowest scattering. The apparent contradiction between these findings is resolved using a theoretical model for light scattering due to fluctuations in the dielectric constant occurring within the volume of the thin film and by noting that slight thickness differences exist between the films in the series. Analysis of the light scattering from the best sample yields estimates for the amplitude (ζ0= 0.08) and the characteristic size (T0= 110 nm) of the dielectric constant fluctuations. These estimates are consistent with the variations of the dielectric constant expected due to the birefringent, polycrystalline nature of these films.
Microstructure, Orientation, and Properties of Sol‐Gel‐Derived KTiOPO4 Thin Films
Authors: Barbé Christophe J. , Harmer Mark A. , Scherer George W.
Published: July 2005

Dense and crack‐free thin films of potassium titanyl phosphate (KTP) were synthesized using a sol‐gel process. The decomposition of the organic precursors and the formation of the KTP were studied using thermal analysis, DRIFT, and XRD. Several processing parameters such as the nature of the precursors, the aging of the alkoxide solution, the firing atmosphere, time, and temperature were found to affect the final film microstructure. Thin films were deposited on single‐crystal KTP, LaGaO3, MgO, and sapphire substrates to promote crystallographic orientation. SEM and XRD studies reveal that films deposited on KTP and LaGaO3 single crystals are highly oriented. The films deposited on MgO or sapphire were found to detach or chemically degrade. The orientation as well as the degradation mechanisms were examined in detail.
Measurements of Excess Enthalpy in Ultrafine‐Grained Titanium Dioxide
Authors: Terwllliger Chrysanthe D. , Chiang Yet‐Ming
Published: July 2005

Differential scanning calorimetry has been used to make direct measurements of the excess enthalpy of TiO2 (rutile) with an initial grain size of 30–70 nm. When the heat released during grain growth is normalized to the change in grain boundary area, the specific excess enthalpy at low temperatures and fine grain sizes (600°–780°C, 30–200 nm) is found to be 0.5–1 J/m2, while values averaged over a larger temperature and size range (600°–1300°C, 30 nm‐ ∼2 μm) are 1.3–1.7 J/m2. After exclusion of extraneous contributions from other heat‐dissipating processes, origins of a specific grain boundary enthalpy that increases with grain size or temperature are considered, including solute segregation, changes in grain boundary structure, and contributions from grain boundary triple junctions. It is concluded that the most plausible explanation is a size‐dependent nonstoichiometry of TiO2 due to the impingement of space charge layers in the temperature and grain size range of the experiments.
Thermal Shock and Size Effects in Castable Refractories
Authors: Cotterell Brian , Ong Sze Woo , Qin Caidong
Published: July 2005

To study accurately the effects of thermal shock on castable refractories, it is necessary to model the fracture process zone. The fictitious crack model, which is often used for the analysis of cementitious materials, is a suitable way to include the fracture process zone in thermal shock analysis. The analysis reinforces the importance of the thermal shock resistance parameter, R″″, which has the units of length and is very similar to the characteristic length, lch, used as a size scale in studies of the fracture of cementitious materials. Whether a cementitious bar behaves in a brittle or ductile fashion depends on the size of the bar relative to its characteristic length. Therefore, the behavior of refractories after they have been quenched is dependent on their size relative to R″″. It is also shown that the critical temperature to cause strength degradation by thermal shock is dependent on the relative size of the bar.
In‐Plane Mechanical Properties of Several Ceramic‐Matrix Composites
Authors: Cady Carl , Heredia Fernando E. , Evans Anthony G.
Published: July 2005

An attempt has been made to assess the generalized in‐plane inelastic deformation and rupture properties of typical laminated or woven ceramic‐matrix composites. The assessment is made by first identifying two principal classes of behavior. These classes are distinguished by the ratio of the elastic properties of the fibers to those of the matrix, which determines the mechanisms of deformation and rupture. These mechanisms, in turn, control the magnitude and orientation sensitivity of the stress/strain curves. Assessment of the inelastic deformations is achieved by first establishing the evolution of matrix cracks and their influence on the elastic moduli. Subsequent evaluation is made by using constituent properties, particularly the interface debonding and sliding resistances in the presence of matrix cracks. This is achieved by analyses of hysteresis loops, using a matrix cracking model. This model provides a representation of the influence of load direction on the interface responses and the inelastic strains. The ultimate strength is controlled by two mechanisms. It is fiber‐controlled in 0/90 tension but becomes matrix controlled in ±45° tension. A model characterizing this mechanism change has yet to be devised.
Dependence of Diamond Transition on Microtexture in Graphite Starting Materials under Shock Compression
Authors: Hirai Hisako , Kukino Satoru , Ohwada Takeshi , Kondo Ken‐ichi
Published: July 2005

The effect of microtexture on diamond transition was examined for graphite starting materials under shock compressions of 50 to 60 GPa and 80 to 90 GPa. Each of the starting materials used in the present study possessed a fully homogeneous microtexture. To distinguish the effect of microtexture from that of other experimental parameters, the shock conditions were standardized for all specimens tested. Three graphite materials—a glassy carbon, a carbon black, and a natural graphite—were selected and shock compressed using a quenching technique to generate conditions common to all samples. Detailed characterization by transmission electron microscopy and electron energy‐loss spectroscopy revealed a clear tendency: The lower the crystallinity and crystallite size of the starting graphite, the more easily the graphite transformed to diamond when the transition mechanism was reconstructive.
Cavitation Contributes Substantially to Tensile Creep in Silicon Nitride
Authors: Luecke William E. , Wiederhorn Sheldon M. , Hockey Bernard J. , Krause Ralph F. , Long Gabrielle G.
Published: July 2005

During tensile creep of a hot isostatically pressed (HIPed) silicon nitride, the volume fraction of cavities increases linearly with strain; these cavities produce nearly all of the measured strain. In contrast, compressive creep in the same stress and temperature range produces very little cavitation. A stress exponent that increases with stress (ε∞σn, 2 < n < 7) characterizes the tensile creep response, while the compressive creep response exhibits a stress dependence of unity. Furthermore, under the same stress and temperature, the material creeps nearly 100 times faster in tension than in compression. Transmission electron microscopy (TEM) indicates that the cavities formed during tensile creep occur in pockets of residual crystalline silicate phase located at silicon nitride multigrain junctions. Small‐angle X‐ray scattering (SAXS) from crept material quantifies the size distribution of cavities observed in TEM and demonstrates that cavity addition, rather than cavity growth, dominates the cavitation process. These observations are in accord with a model for creep based on the deformation of granular materials in which the microstructure must dilate for individual grains to slide past one another. During tensile creep the silicon nitride grains remain rigid; cavitation in the multigrain junctions allows the silicate to flow from cavities to surrounding silicate pockets, allowing the dilatation of the microstructure and deformation of the material. Silicon nitride grain boundary sliding accommodates this expansion and leads to extension of the specimen. In compression, where cavitation is suppressed, deformation occurs by solution—reprecipitation of silicon nitride.
Oxidation Embrittlement Probe for Ceramic‐Matrix Composites
Authors: Heredia Fernando E. , McNulty John C. , Zok Frank W. , Evans Anthony G.
Published: July 2005

A test method for probing oxidation embrittlement in ceramic‐matrix composites has been devised and demonstrated for three composites: SiC/magnesium aluminosilite, SiC/SiC, and SiC/Al2O3. The method identifies a “pest” temperature Tp. The growth of an embrittled region from the surface, at TP, has been illustrated. The embrittlement mechanism involves oxygen ingress through matrix cracks and silicate formation at the fibers, causing fiber failure.
Grain Growth, Microstructure, and Superconducting Properties of Pure and Y2BaCuO5‐Doped YBa2Cu3O7–x Ceramics
Authors: Gotor Francisco J. , Fert André R. , Odier Philippe , Pellerin Nadia
Published: July 2005

Superconducting properties of YBa2Cu3O7–r ceramics have been investigated with the aim of avoiding the weak links that are the principal reasons for low critical current densities in this compound. An efficient grain growth process should be useful in this respect. Superconducting ceramics were prepared from a commercial precursor powder (Hoechst) with or without addition of Y2BaCuO5 and from a gel precursor powder. Grain growth kinetics and densification are first derived under such conditions that control the liquid‐phase contribution. Grain growth in the solid‐state regime is anisotropic, possibly due to anisotropic grain boundary energies. Grains in the fine powder (gel precursor) grow 10 times faster than in the commercial reference but grain size saturates because of steric hindrance. Addition of Y2BaCuO5 particles inhibits grain growth in the solid‐state regime. 211 particles are incorporated into grains when a transient liquid phase is present. Superconducting properties were characterized by 50‐Hz magnetization hysteresis cycles at 77 K under H= 0.2 to 12 mT to probe weak‐link behavior. Additional studies were performed at 5 K using higher fields. Weak‐link contribution is decreased when samples from the gel route are processed in the solid‐state regime (below the peritectic temperature). This may be attributed to the propensity of gel powder to develop, naturally, preferential grain boundaries due to its intrinsic structural anisotropy.
Determination of Subcritical Crack Growth Parameters by In Situ Observation of Indentation Cracks
Authors: Dwivedi Priya J. , Green David J.
Published: July 2005

A technique to determine stress intensity factor—crack velocity (K—v) relationships for subcritical crack growth from in situ observation of indentation cracks is described. To minimize the effect of residual contact stresses and lateral crack interaction, measurements were made only on cracks that had undergone significant subcritical crack growth. Crack shapes were determined fractographically from crack‐arrest markings, produced by temporary unloading during the crack extension process. The subcritical crack growth parameters obtained by this technique were in excellent agreement with those determined from dynamic fatigue and previous studies.
Evolution of Stress Failure Resulting from High‐Temperature Stress‐Corrosion Cracking in a Hot Isostatically Pressed Silicon Nitride
Authors: Wereszczak Andrew A. , Ferber Mattison K. , Kirkland Timothy P. , More Karren L. , Foley Michael R. , Yeckley Russell L.
Published: July 2005

Stress‐corrosion cracking in a commercially available, hot isostatically pressed (HIPed), yttria‐fluxed, silicon nitride was the prevalent mode of failure in specimens creepruptured at 1370°C. High‐temperature diffusional processes associated with oxygen were responsible for the creation of an advancing stress‐corrosion front that had formed at the specimen surface and advanced radially inward. The volume of material in the wake of the stress‐corrosion front possessed a high concentration of lenticular cavities at two‐grain boundaries, a high concentration of multigrain junction cavities, and large amorphous “pockets” in other multigrain junctions that were abnormally rich in oxygen and yttrium. The combination of tensile stress and the high concentration of cavities in the near‐surface volume of the material resulted in microcrack coalescence or the formation of a planar, stress‐corrosion crack. The concurrent growth of the stress‐corrosion front and crack during the tensile creep‐rupture tests ultimately led to stress‐induced failure.
Polycrystalline Yttrium Aluminum Garnet Fibers from Colloidal Sols
Authors: King Bruce H. , Halloran John W.
Published: July 2005

Polycrystalline yttrium aluminum garnet (YAG) fibers were prepared from commercially available colloidal sols of Y2O3 and AlOOH and water‐soluble polymers. The fibers were dry spun and all processing was performed in air. Transformation to YAG was complete by ≅1300°C, and the fibers were mostly dense by 1600°C with a final fired diameter of 120 μm. A bend test was used to characterize mechanical strength, and an average of 522 ± 186 MPa with a Weibull modulus of 3.5 was determined. The bend stress relaxation (BSR) test was used to characterize creep properties. The creep resistance was better than that of all commercially available oxide fibers with the exception of Saphikon single‐crystal alumina (c‐axis oriented). The creep strain of the YAG fibers compared well with that calculated for YAG monoliths with roughly the same grain size.
Discontinuous Dissolution of Iron Aluminate Spinel in the Al2O3–Fe2O3 System
Authors: Lee Ho‐Yong , Pack Yeong‐Kyeun , Lee Byoung‐Ki , Kang Suk‐Joong L.
Published: July 2005

When sintered 85Al2O3–15Fe2O3 (in wt%) specimens consisting of corundum grains and spinel particles were annealed at temperature where only a corundum phase was stable, phase transformation of spinel into metastable FeAIO3 and subsequently complete dissolution of the metastable phase occurred together with the migration of grain boundaries at the surface of the specimens. Since the grain boundary migration was induced by grain boundary diffusion of Fe2O3 from the transforming and dissolving particles, the boundary migration by temperature decrease corresponds to a discontinuous dissolution of the spinel particles and a chemically induced grain boundary migration by temperature change. Inside the specimens, however, the transformation—dissolution and the grain boundary migration were suppressed because of unavailable accommodation of the volume expansion due to the transformation.
Joining of Zirconia Ceramic to Stainless Steel and to Itself Using Ag57Cu38Ti5 Filler Metal
Authors: Hao Hongqi , Wang Yonglan , Jin Zhihao , Wang Xiaotian
Published: July 2005

The brazing of ZrO2 ceramic to 1Cr18Ni9Ti stainless steel and to itself was performed using Ag57Cu38Ti5 filler metal under a vacuum of 7 × 10‐3 Pa. The effects of interlayer copper on the ceramic to stainless steel joint strength, and the brazing temperature (1073 to 1323 K) and holding time (0 to 60 min) on ceramic to ceramic joint strength were investigated. The joint strength was evaluated by shear testing. An interfacial reaction layer between the ceramic and the filler metal was found, and the reaction products were δ‐TiO and γ‐AgTi3. The joint strength of ZrO2 ceramic to stainless steel was improved by using a layer of copper of a suitable thickness. The brazing temperature and holding time had a strong influence on the joint strength of ceramic to ceramic, and the joint strength was mainly controlled by reaction layer thickness and the properties of the reaction products. The maximum shear strength was obtained for brazing at 1123 K for 30 min and an interfacial reaction layer thickness of ∼4.4 μm.
Sintering, Crystallization, and Properties of B2O3/P2O5‐Doped Li2O·Al2O3·4SiO2 Glass‐Ceramics
Authors: Shyu Jiin‐Jyh , Lee Hsin‐Hui
Published: July 2005

Sintering, crystallization, microstructure, and thermal expansion of Li2O·Al2O3·4SiO2 glass‐ceramics doped with B2O3, P2O5, or (B2O3+ P2O5) have been investigated. On heating the glass powder compacts, the glassy phase first crystallized into high‐quartz s.s., which transformed into β‐spodumene after the crystallization process was essentially complete. The effects of dopants on the crystallization of glass to high‐quartz s.s. and the subsequent transformation of high‐quartz s.s. to β‐spodumene were discussed. The major densification occurred only in the early stage of sintering time due to the rapid crystallization. All dopants were found to promote the densification of the glass powders. The effect of doping on the densification can fairly well be explained by the crystallization tendency. All samples heated to 950°C exhibited a negative coefficient of thermal expansion ranging from about −4.7 × 10‐6 to −0.1 × 10‐6 K‐1. Codoping of B2O3 and P2O5 resulted in the highest densification and an extremely low coefficient of thermal expansion.
Phase Transition and Ferroelectric Characteristics of Pb[(Mg1/3Nb2/3)1‐xTix]O3 Ceramics Modified with La(Mg2/3Nb1/3)O3
Authors: Wu Tai‐Bor , Shyu Ming‐Jyh , Chung Chia‐Chi , Lee Hsin‐Yi
Published: July 2005

The effects of 0–5 mol% addition of La(Mg2/3Nb1/3)O3 (LMN) on the phase transition and ferroelectric behaviors of Pb[(Mg1/3Nb2/3)1‐xTix]O3 (PMNT) ceramics with compositions near the morphotropic phase boundary (MPB) were studied. An evolution of structure from rhombohedral to tetragonal was found with increasing PbTiO3 (PT) content across the MPB (at ∼32.5 mol% PT), and a coexistence of both rhombohedral and tetragonal phases was also found at the MPB. The dual‐phase field extended toward the lower PT content side of the MPB, and, moreover, the rhombohedrality or tetragonality was reduced, especially for the compositions near the MPB, by the addition of La in PMNT. The ferroelectric transition was found to change from normal to diffuse as the La content increased and the compositions became more rhombohedral. In accordance with the structural evolution, the change of remanent polarization (Pr) and coercive field (Ec) also became gradually indistinct, and both Pr and Ec were reduced. For compositions near the MPB, both PMNT and La‐modified PMNT had a similar electromechanical factor (kp) in a range around 0.55–0.60, but the mechanical quality factor (Qm) was significantly reduced for the La‐modified PMNT. The piezoelectric coefficient (d33), however, was largely improved with increasing La content in PMNT of compositions at MPB. A high value of d33∼ 815 pC/N was obtained for the 5‐mol%‐La‐modified ceramics, but it was associated with a low value of Qm.
Synthesis of Highly Oriented K(Ta,Nb)O3 (Ta:Nb = 65:35) Film Using Metal Alkoxides
Authors: Yogo Toshinobu , Kikuta Koichi , Ito Yasuhiro , Hirano Shin‐ichi
Published: July 2005

Highly oriented K(Ta,Nb)O3 (Ta:Nb = 65:35) (KTN) thin films of perovskite structure were synthesized successfully on Pt(100)/MgO(100) substrates from a metal alkoxide solution through reaction control. Homogeneous KTN coating solutions prepared from KOC2H5, Ta(OC2H5)5, and Nb(OC2H5)5 in ethanol were analyzed by 1H, 13C, and 93Nb NMR spectroscopy. The KTN precursor included a molecular‐level mixture of K[M(OC2H5)6] (M = Ta, Nb) units interacting in ethanol solution. X‐ray pole figure measurement showed that perovskite KTN films crystallized on Pt(100)/MgO(100) substrates had not only a (100) orientation but also a three‐dimensional regularity of grains. The remanent polarization and coercive field of the KTN film (thickness, 1.0 μm) crystallized at 700°C were 1.5 μC/cm2 and 8.7 kV/cm, respectively, at 225 K.
Crystallization of Celsian (BaAl2Si2O8) Glass
Authors: Lee William E. , Chen Makan , James Peter F.
Published: July 2005

The fabrication and crystallization of stoichiometric and near‐stoichiometric celsian, BaAl2Si2O8 (BAS), glass made via melt and sol‐gel routes is reviewed. After considering celsian polymorphism and methods of stabilizing monoclinic celsian, some new experimental results are presented which show that melt glass crystallizes predominantly via surface nucleation, but sol‐gel glass via volume nucleation. Possible reasons for this behavior and the kinetics of the crystallization process are examined.
Fracture Toughness of TiB2 and B4C Using the Single‐Edge Precracked Beam, Indentation Strength, Chevron Notched Beam, and Indentation Strength Methods
Authors: Conzone Samuel D. , Blumenthal William R. , Vainer James R.
Published: July 2005

The mode I fracture toughness (KIc) of boron carbide (B4C) and titanium diboride (TiB2) was determined using four competing techniques. The indentation strength (IS), chevron notched beam (CNB), and indentation fracture (IF) methods are common techniques that were compared to the recently standardized single‐edge precrack beam (SEPB) method. The SEPB method was more difficult to apply, but it represents the most rigorous method for KIc determination, because it uses few assumptions and requires a direct measurement of crack length. The IS method was an expeditious and economical alternative when low indentation loads were used. CNB KIc values were virtually rate‐independent when displacement rates less than or equal to 0.5 mm/min were used. The IF method was the least satisfactory technique, because of high variability in Kc values and because of the low differentiation between the two materials studied.
Defect Structure and Phase Relations of Highly Lanthanum‐Doped Barium Titanate
Authors: Makovec Darko , Samardžija Zoran , Delalut Uroš , Kolar Drago
Published: July 2005

Incorporation of La3+ into the BaTiO3 lattice was studied on samples of various composition, using quantitative WDS microanalysis (EPMA) in combination with scanning electron microscopy (SEM) and X‐ray powder diffractometry (XRPD). Direct determination of solid‐solution formulas by microanalysis supports the structure model of a solid solution with La3+ on Ba2+ sites and a deficient Ti4+ sublattice, independent of the starting composition. Solid solution extends on the tie line, which points from BaTiO3 to La4Ti3O12, to the composition of approximately Ba0.70‐ La0.38Ti0.925(V″″)0.075O3. On the basis of these results, the BaTiO3‐rich part of the BaO‐La2O3‐TiO2 phase diagram was constructed.
Infrared Evanescent Absorption Spectroscopy of Toxic Chemicals Using Chalcogenide Glass Fibers
Authors: Sanghera Jas S. , Kung Fred H. , Busse Lynda E. , Pureza Paul C. , Aggarwal Ishwar D.
Published: July 2005

We have detected hazardous and toxic chemicals such as chlorinated hydrocarbons and benzene and its derivatives using evanescent wave spectroscopy with in‐house drawn chalcogenide glass fibers. Although, these chemicals have been readily detected down to the volume percent level, we make appropriate recommendations to lower the detection limits to the part per million level. While the current fibers can be used in lengths of up to 30 m for detection and identification of these chemicals, our results indicate that the remote capabilities of these fibers can be significantly improved into the several hundreds of meters range with lower loss fibers, as they become available with improved processing.
Varied Atmosphere Compensation—Exploring the Roles of Barium and Bismuth in (Ba,Bi,Nb)‐Doped TiO2 Varistors
Authors: Yang Seng‐Lu , Wu Jenn‐Ming
Published: July 2005

A novel (Ba,Bi,Nb)‐doped TiO2 ceramic was previously proved to be potentially useful as a varistor material. The present work attempts to clarify the roles of the dopants, Ba and Bi. Varied atmosphere compensation is an effective method to achieve the goal. The results show that varied atmosphere compensation had only a little influence on grain growth and microstructures in the interior of the sintered samples, whereas the varistor properties were affected greatly. Samples compensating with Ba are more beneficial to the boundary barrier than samples compensating with Bi only. Furthermore, samples compensating with both Ba and Bi are better than those compensating with Ba only. This is induced by different degrees of Bi evaporation and Ba diffusion from sintered compacts when sintering proceeds at high temperature.
Residual Stresses in Alumina/Ceria‐Stabilized Zirconia Composites
Authors: Sergo Valter , Wang Xun‐Li , Clarke David R. , Becher Paul F.
Published: July 2005

Measurements of the residual stresses in Al2O3/Ce‐TZP (12 mol% CeO2) sintered composites, containing 10, 20, and 40 vol% zirconia, obtained by neutron diffraction and by piezospectroscopy using optical fluorescence and Raman are compared. The techniques give essentially the same values for the spatial average of the hydrostatic residual stresses in the two phases despite the difference in the parameters measured in the two techniques. The measured stresses are also in accord with those predicted from a stochastic stress analysis for materials cooling from a stressfree temperature of ∼1180°C. Over the range of volume fraction investigated the hydrostatic stress in the alumina phase varies linearly with zirconia content, corresponding most closely to the upper Hashin bound.
Relationship between Isomorphic Substitutions and the Thermal Degradation of Bentonites
Authors: Siguín Dionisio , Ferreira Serafin , Foufre Luis , García Fernando
Published: July 2005

Data obtained by differential thermal analysis (DTA) are related to the temperature at which the OH‐ radical of the smectite crystals is irreversibly lost. A relationship between the DTA behavior and the isomorphic substitution in the crystals is established.
Ferroelectric Domains and Incommensuration in the Intermediate Phase Region of Lead Zirconate
Authors: Xu Zhengkui , Dai Xunhu , Viehland Dwight , Payne David A. , Li Zhuang , Jiang Yendao
Published: July 2005

Electron microscopy of lead zirconate (PbZrO3) identified the presence of an intermediate region between the high‐temperature cubic state and the low‐temperature antiferro‐electric state. Ferroelectric domains were found to occur between 200° and 230°C on cooling. Convergent‐beam electron diffraction studies identified rhombohedral symmetry for the ferroelectric phase. Selected area electron diffraction patterns determined ½{110} superlattice reflections in the ferroelectric state. The reflections were associated with a softening of an M‐type oxygen octahedral rotation mode. In addition, 1/x{110} incommensurate superlattice reflections were detected within a narrow temperature range for PbZrO3 between the intermediate ferroelectric and low‐temperature antiferroelectric states.
Effect of Dopant Species on Tetragonal (t′)‐to‐Monoclinic Phase Transformation of Arc‐Melted ZrO2‐RO,1.5 (R = Sm, Y, Er, and Sc) in Water at 200°C and 100 MPa Pressure
Authors: Yashima Masatomo , Nagatome Tomoo , Noma Tatsuo , Ishizawa Nobuo , Suzuki Yasuo , Yoshimura Masahiro
Published: July 2005

Arc‐melted specimens of rare‐earth‐doped zirconia (ZrO2‐X mol% RO1.5; X= 4–10 for R = Sm, Y, Er, and X= 4–18 for Sc) were hydrothermally treated at 200°C, 100 MPa to investigate the dependence of the tetragonal‐to‐monoclinic transformation on dopant species and its content. The volume fraction of monoclinic phase Vm(t) increased from Vm(0) to a certain saturated value Vm(ω), following [Vm(t) −Vm(0)]/[Vm(t) −Vm(ω)] = 1 − exp(−k·t), where t is the annealing time at 200°C, 100 MPa. The transform‐abilities, Vm(0), Vm(ω), and k decrease with increasing dopant content. The Vm(ω) decreased with an increase of ionic radius of dopants. The relation 0 < Vm(ω) < 1 suggests that apparent noncompositional inhomogeneity exists in the hydrothermally treated sample.
Determination of the R‐Curve from the Strength—Indentation Load Relation
Authors: Hsueh Chun‐Hway , Becher Paul F.
Published: July 2005

Strength as a function of indentation load has been measured to evaluate toughness versus crack size curves (i.e., R‐curves) of ceramics. In the past, this evaluation is achieved by generating a family of global stress intensity versus crack size curves (i.e., K‐curves) at each indentation load and its corresponding strength, and then fitting an envelope of tangency points to these curves. This envelope yields the R‐curve. A methodology is proposed in the present study to define the point in the K‐curve at which the R‐curve intersects. This methodology complements the conventional “tangency condition” approach in determining the R‐curve from the experimental strength‐indentation load relation.
Colloidal Processing of SiC Whisker Composites
Authors: Huang Zhengren , Jiang Dongliang , Tan Shouhong
Published: July 2005

In the present study, the dispersion processing and the characterization of the dispersity of SiC whiskers for reinforced ceramic‐based composites were studied. Two kinds of methods were used to determine the dispersity of SiC whiskers. First, the sedimentation density was employed to directly characterize the dispersity of the SiC whiskers. The other is an indirect characterization. The dispersity and the distribution of the SiC whisker in a ceramic matrix were analyzed and characterized indirectly with SEM observation and the determination of the relative density. By means of the colloidal processing of the whiskers in which electrostatic and steric interaction were used to counteract the attractive forces between whiskers, four dispersion processing routes were used to mix the SiC whisker into the Al2O3 powder. The sedimentation results indicated that, with aluminum alkoxide as a dispersant, SiC whiskers were completely deflocculated and the sedimentation density increased twofold from 8.5% to 24% of theoretical density, and both the homogeneous distribution of SiC whiskers and densification of the 30 vol% SiC whisker‐reinforced Al2O3 (AS) were achieved by hot pressing. The relative density of the AS composites was more than 99.7%. SEM observation showed no agglomeration of SiC whiskers.
Pillared Smectite Clay Coatings for Ceramic‐Matrix Composites
Authors: Jagota Sujata , Harmer Mark A. , Lemon Michael F. , Jagota Anand , McCarron Eugene M.
Published: July 2005

This paper describes a novel route for the low‐temperature formation of mullite, from pillared smectite clay precursors, for use as fiber coatings in ceramic‐matrix composites. In particular, alumina‐pillared bentonite converts in part to mullite at the unusually low temperature of about 800°C. The clay precursors display excellent film‐forming capability and have been coated onto silicon carbide fibers. Mechanical tests on composites of the coated fibers and a borosilicate glass demonstrate their success as debond coatings, suggesting that this approach is a viable and simple route to oxide coatings for fibers.
Striation‐Free, Spin‐Coated Sol‐Gel Optical Films
Authors: Du Min Xin , Orignac Xavier , Almeida Rui M.
Published: July 2005

A process for eliminating surface striations in optical films prepared by sol‐gel spin coating is described. The surface morphology of Nd‐doped SiO2‐TiO2 films, codoped with phosphorus, was investigated, using stylus profilometry, ellipsometry, and reflective optical microscopy. Compared to the conventional spin coating technique, the new process, where a saturated ethanol atmosphere is created over the spinning substrate, leads to a very low surface roughness, but to the same refractive index value. The thickness of uniform thin films prepared by this process is about half that of films made by the conventional method, at any spinning rate and for any given solution aging time.
Standard Enthalpy of Formation of Lanthanum Zirconate
Authors: Bolech Mark , Cordfunke Erik H. E , Janssen Frans J. J. G. , Navrotsky Alexandra
Published: July 2005

The enthalpy of formation of lanthanum zirconate, La2Zr2O7, which is shown to have a distorted pyrochlore structure, was determined. High‐temperature solution calorimetry in molten lead borate was used to determine the heat of formation from the constituent oxides as −135.8 ± 6.4 kJ/mol at 974 K. Using additional data on the enthalpies of formation of the oxides and heat contents, this value was converted to a standard enthalpy of formation from the elements: ΔfH°298.15=−4130.4 ± 6.8 kJ/mol.
Silicon Carbide from Laser Pyrolysis of Polycarbosilane
Authors: Jakubenas Kevin , Marcus H. L.
Published: July 2005

Laser pyrolysis offers a means of extending solid free‐form fabrication to polymeric precursors. Laser pyrolysis of polycarbosilane (PCS) produces controlled β‐SiC shapes with nanometer grain size although properties are currently limited by high porosity. By the addition of filler powders, either inert or reactive, ceramic‐metal and ceramic‐ceramic composite shapes are possible. The results of laser pyrolysis of PCS alone and in mixtures with 3‐SiC, Al, Si, Ti, and Zr are presented showing that the technique has the potential to produce a range of materials and shapes customized to particular design requirements.
Hot Isostatic Pressing and Characterization of Sol‐Gel‐Derived Chromium(III) Oxide
Authors: Kawabata Akio , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2005

Chromium (III) oxide (Cr2O3) crystallizes at low temperatures from an amorphous material prepared by adding hydrazine monohydrate to an aqueous solution of Cr(NO3)3‐9H2O. Individual particles of Cr2O3 tend toward a hexagonal morphology above 800°C. Well‐densified Cr2O3 pellets (98.8% of theoretical density) have been fabricated by hot isostatic pressing for 2 h at 1100°C and 196 MPa. Their fracture toughness is 4.4 MPa.m1/2. The sample annealed in air for 12 h at 1300°C exhibits a high electrical conductivity of 3.6 Ω‐1.m‐1at 700°C.
Anodic Dissolution of Uranium Mononitride in Lithium Chloride‐Potassium Chloride Eutectic Melt
Authors: Kobayashi Fumiaki , Ogawa Toru , Akabori Mitsuo , Kato Yoshio
Published: July 2005

Uranium‐plutonium nitride is a candidate fuel for fast reactors, but its major drawback is 14C formation from natural nitrogen. One would probably have to use highly 15N‐enriched nitrogen. A pyrochemical process with molten‐salt electroreflning has been proposed as a means to increase the nuclear proliferation resistance of the fuel cycle. Molten‐salt electroreflning could also be applied to nitride fuels to make possible the recycling of 15N. The anodic dissolution behavior of UN in LiCI‐KCI melt was studied to provide the basis for a feasibility study of electroreflning of irradiated nitride fuels.
Fracture Characteristics of Czochralski‐Grown Y3Al5O12
Authors: Reimanis Ivar E. , Hawley M. E. , Mitchell T. E. , Zhou D. S.
Published: July 2005

The fracture surfaces of single‐crystal Y3A15O12 (YAG) have been examined in detail using differential interference microscopy and atomic force microscopy. In YAG crystals grown in 1977 by the Czochralski method strikingly regular undulations of microscopic and submicroscopic dimensions (4–20 nm in amplitude, 1–20 μm in wavelength) are observed on every fracture surface. The undulations do not exhibit typical characteristics of Wallner lines; furthermore, they are not observed in identical fracture tests for YAG crystals grown in 1990 by the Czochralski method. Transmission electron microscopy reveals that the crystals grown in 1977 exhibit a periodic fluctuation of the ratio of the concentrations of aluminum to yttrium, suggesting that the fracture surface features are caused by periodic astoichiometry.
Behavior of Cyclic Fatigue Cracks in Monolithic Silicon Nitride
Authors: Gilbert Christopher J. , Dauskardt Reinhold H. , Ritchie Robert O.
Published: July 2005

Cyclic fatigue‐crack propagation behavior in monolithic silicon nitride is characterized in light of current fatiguecrack growth models for ceramics toughened by grainbridging mechanisms, with specific emphasis on the role of load ratio. Such models are based on diminished cracktip shielding in the crack wake under cyclic loads due to frictional‐wear degradation of the grain‐bridging zone. The notion of cyclic crack growth promoted by diminished shielding is seen to be consistent with measured (long‐crack) growth rates, fractography, in situ crack‐profile analyses, and measurements of back‐face strain compliance. Growth rates are found to display a much larger dependence on the maximum applied stress intensity, Kmax than on the applied stress‐intensity range, ΔK, with behavior described by the relationship da/dN ∞ K29maxΔK1.3. Fatigue thresholds similarly exhibit a marked dependence on the load ratio, R=Kmin/Kmax; such effects are shown to be inconsistent with traditional models of fatigue‐crack closure. In particular, when characterized in terms of Kmax growth rates below ∼10−9 m/cycle exhibit an inverse dependence on load ratio, an observation which is consistent with the grain‐bridging phenomenon; specifically, with increasing R, the sliding disance between the grain bridges is decreased, leading to less frictional wear, and hence less degradation in shielding, per loading cycle. The microstructural origins of such behavior are discussed.
Zinc Oxide Varistor Gas Sensors: I, Effect of Bi2O3 Content on the H2‐Sensing Properties
Authors: Lin Feng‐Gang , Takao Yuji , Shimizu Yasuhiro , Egashira Makoto
Published: July 2005

Current (I)‐voltage (V) characteristics of porous ZnO varistors with different Bi2O3 content have been investigated in air as well as in H2‐air mixtures in the temperature range room temperature (RT)‐600°C. The I‐V characteristics measured at RT remained unchanged in the presence of H2, but the breakdown voltage clearly shifted to a lower electric field in the temperature range 400–600°C. The breakdown voltage decreased with increasing H2 concentration in air. The optimum amount of Bi2O3 for the largest decrease was found to be 1.0 mol%. Thus, ZnO varistors can be used as a new type of H2 sensor. The results presented in this study also suggest the important role of excess oxygen ions existing at the ZnO‐ZnO grain boundaries in developing the Schottky barrier as well as in the H2‐sensing mechanism of the varistors.
Rolling‐Contact Fatigue and Wear of CVD‐SiC with Residual Surface Compression
Authors: Chao Luen‐Yuan , Lakshminarayanan R. , Shetty Dinesh K. , Cutler Raymond A.
Published: July 2005

The rolling‐contact fatigue life and wear of CVD‐SiC coatings with surface compression were studied using a three‐ ball‐on‐rod rolling‐contact fatigue (RCF) tester. Two levels of surface compression in the coatings, approximately 190 μm thick, were introduced by using substrates of a liquid‐phase sintered SiC and a SiC‐30 vol% TiC to obtain desired thermal‐expansion mismatches with the CVD‐SiC. Residual surface compressions of 250 and 680 MPa were measured in the CVD‐SiC coatings on SiC and SiC‐30 vol% TiC substrates, respectively, by a strain‐gage technique. In the RCF test, the fatigue life of the CVD‐SiC coating with the moderate surface compression was limited by severe wear by a brittle fracture mechanism at a Hertzian contact stress of 5.5 GPa. The CVD‐SiC coating on the SiC‐30 vol% TiC composite, on the other hand, did not show measurable wear. A majority of the tests (11 out of 16) were suspended at 100 h or stopped due to failure of the steel balls. Five tests stopped due to spalling of the CVD‐SiC coating at weak interfaces 10 to 15 μm below the contact surface. Examination of the microstructure of the CVD‐SiC coating in cross sections revealed that the weak interfaces that led to the spalling were related to discontinuous growth of the CVD‐SiC in the form of nodules or growth regions. Elimination of these defective structures is likely to enhance the tribological performance of surface‐toughened CVD‐SiC.
Kinetic Demixing of Solute Cations in Alumina Single Crystals during Cooling
Authors: Ervas Georgette Petot , Petot Claude , Monceau Daniel , Sproule G. Irwin , Graham Michael J.
Published: July 2005

In this work we have analyzed the conditions leading to a kinetic demixing of species in ceramics during cooling. Estimation of cation redistributions during cooling in a model material shows that a segregation maximum could be observed near surfaces at an intermediate cooling rate. This result is explained on the basis of two competing effects: the cation redistribution kinetics and the driving force of matter transport related to the cooling rate. Experimental results obtained with titanium and magnesium‐doped α‐alumina single crystals show that the segregation of titanium increases when the oxygen partial pressure increases and when the cooling rate and annealing temperature decrease. The opposite effect is generally observed for magnesium and other detected impurities. Complementary characterizations show that these kinetic reactions are also significantly influenced by the impurities present in the material.
Nonlinear Hertzian Indentation Fracture Mechanics
Authors: Burns S. J. , Chia K. Y
Published: July 2005

Indentation cracking under blunt indenters is analyzed using nonlinear fracture mechanics. The usual assumptions of linear elastic fracture mechanics have been replaced with a nonlinear load vs load‐point displacement curve while assuming the material is linear elastic. The load, the load‐point displacement, and a function of the crack area have been related to the crack driving force, J, while assuming a cone fracture under the Hertzian sphere. Experimentally, it was found that the load‐displacement curve during loading, cracking, and unloading is nonlinear. The crack length is empirically shown to be proportional to the load‐point displacement for several indenters. The experimentally measured relations between indenter load, load‐point displacement, and crack geometries are then analyzed with mechanical energy balances based on the similitude of crack lengths with load‐point displacements. The Hertz hardness that describes the nonlinear load vs load‐point displacement relation during cracking is derived on the constant J line in load‐displacement space. Finally, well‐known experimental expressions that relate load to crack length are shown to be indistinguishable from the load‐point displacement analysis reported.
Nonlinear Compliance Testing Applied to Indentation Cracking in Ceramics
Authors: Burns S. J. , Chia K. Y.
Published: July 2005

Indentation cracking under sharp‐pointed indenters is analyzed using compliance‐based, nonlinear, fracture mechanics. The stress intensity factor, K, in linear elastic fracture mechanics is well known to be proportional to the load, P; in this nonlinear analysis K is proportional to P3/4. The observed relation between indenter load‐point displacement and crack length is based on similitude of crack lengths with load‐point displacements as a strain‐controlled fracture. The equations that relate load and a function of the crack length to the crack driving force, J, have been found for Vickers indentations. Analysis of the nonlinear load vs displacement assumes an equilibrium crack in the elastic material surrounding the indent. The hardness that describes the load vs load‐point displacement during cracking is derived on a constant J line in load‐displacement space. The crack length is shown experimentally to be proportional to the load‐point displacement after crack initiation for several different indenters in ZnS. The measured loading curves are nonlinear and display crack initiation during loading. The KIc expressions found here are very similar to correlations that have been applied to indentation cracks.
Effect of Heat Treatment on the Microstructure and Properties of Dense AIN Sintered with Y2O3 Additions
Authors: Mitra Shantanu , Dutta Geeta , Dutta Indranath
Published: July 2005

The secondary phase constitution in two sintered AIN ceramics (1.8% and 4.2% Y2O3 additions) was studied as a function of heat treatment temperatures between 1750° and 1900°C under pure nitrogen atmosphere. The effect of the phase constitution on the physical properties, such as density, thermal conductivity (K), and lattice constants, and on the mechanical properties in three‐point bending, was also investigated. Y3Al5O12 was found to getter dissolved oxygen from the AIN lattice below 1850°C, but evaporated at 1850°C and above. Y4Al2O9 appeared to sublimate below 1850°C in the atmosphere used in this study. Depending on the secondary phase constitution, heat treatment affected thermal conductivity favorably or adversely. Occasionally, samples with similar lattice oxygen contents were found to have different thermal conductivities, suggesting that factors besides dissolved oxygen can also influence K. Lattice parameter measurements indicated that, within the small range of lattice oxygen concentrations in the AIN samples studied, the c‐axis was more sensitive than the a‐axis to oxygen content.