bluuebunny/crossref_metadata_2025 huggingface dataset:
Vibrational Technique for Stress Measurement in Films: I, Ideal Membrane Behavior
Authors: Maden Michele A. , Jagota Anand , Mazur Stephen , Farris Richard J.
Published: March 2005

A vibrational technique for the measurement of stress in films has been developed, based on the theory of membranes. Specimens for vibrational analysis are prepared by removing a circular or square piece of the substrate. It is shown that the error introduced due to substrate removal is negligible except for thin metallic films. The resulting specimen, a film stretched across a hole in the substrate, behaves as a membrane. Since its natural frequencies increase with the square root of in‐plane stress, these can be measured to compute the in‐plane stress. The only material parameter needed is the density of the film. Because a number of natural frequencies can be measured, each of which can be used to compute the stress, this method has a strong check for internal consistency. Two different techniques have been used to measure natural frequencies: (1) sinusoidal excitation and holographic imaging of the vibration modes, and (2) random excitation and Fourier analysis of measured vibrations. In this, the first part of the study, we discuss cases when ideal membrane behavior is obtained. Three applications of the method are presented: measurement of stress in a filled‐glass layer bonded to an aluminum substrate, a study of the effect of temperature and humidity on stress in a thermoset polymer coating, and stress in a silver film during heat treatment. The second part of the study1 deals with extensions of the technique when complicating effects, such as air loading, bending stiffness, and an aniso‐tropic state of stress, are important. In the third part of the study,2 the method is used to identify the orthotropic axes and all nine elasticity coefficients of a commercially made film.
Fracture Behavior of CVD SiC‐Coated Graphite: II, Conditions for the Onset of Multiple Cracking
Authors: Watkins Thomas R. , Green David J.
Published: March 2005

Crack arrest and multiple Cracking can be observed during the fracture of coated substrates even in the absence of coating delamination. Clearly, it would be useful to understand the mechanics and material parameters that control this process. The conditions for the arrest of the initial crack were modeled using an approximate stress intensity factor approach, and it was determined there is a critical coating thickness, below which the multiple cracking occurs. The critical thickness was determined to depend on the coating strength, substrate toughness, and the relative Young's moduli of the coating and the substrate. The effects of these parameters and residual stresses on the fracture behavior are discussed. The results of the model are compared to the experimental data on a SiC‐coated graphite (sandwich composite).
Stabilization of Ordered Zirconium Titanates through the Chemical Substitution of Ti4+by Al3+/Ta5+
Authors: Zhang Yan , Davies Peter K.
Published: March 2005

We have investigated the ZrO2–AITaO4 system to understand how selected chemical substitutions can be used to control cation‐ordering transformations in zirconium titanate based dielectric ceramics. The complete replacement of the Ti content of ZrxTi2–xO4 by a coupled Al3+/Ta5+ substitution permits the synthesis of a wide range of isostructural Zrx(Al0.5Ta0.5)2–xO4 solid solutions. At high temperatures a disordered α‐PbO2 type of structure is formed for 0.375 ≤x≤ 1.03. Samples with 0.67 ≤x≤ 1.03 undergo a cation‐ordering reaction to a structure in which the a and b axes of the parent disordered Cell are doubled. The stabilities of these cation‐ordered derivative structures are significantly greater than those of the ordered zirconium titanates. The ordering temperatures are composition dependent with a maximum of 1393°C occurring for Zr0.86(Al0.5TaO0.5)1.14O4. The higher transition temperatures also enhance the kinetics of the ordering transition; whereas the pure zirconium titanates require extended annealing to produce complete cation order, fully ordered Zrχ(Al0.5Ta0.5)2–χO4 solid solutions are produced during a normal furnace cool.
Colloid Mills: Theory and Experiment
Authors: King Alan G. , Keswani Santosh T.
Published: March 2005

In a colloid mill utilizing a rotating and a stationary plate, a high shear field exists. Particles rotate, generating a lift force moving them to the rotating plate. When particles collide, a substantial energy transfer occurs because their surface velocities are opposite. A mathematical model has been developed relating the particle rotational speed to the parameters of the colloid mill such as gap size, speed, slip viscosity, and particle size distribution. A slurry of the material being ground is forced into the gap. Grinding is autogenous as a result of collisions between rotating particles. All of the material in the process stream is ground finer than the gap setting and grinding can be optimized by adjusting mill operating parameters. However, the mill is not able to grind the incoming stream to submicrometer sizes and there is molecular contamination from the surface of theB4C cones.
Instability of Polycrystalline Bridges that Span Cracks in Powder Films Densified on a Substrate
Authors: Heintz Jean Marc , Sudre Olivier , Lange Fred F.
Published: March 2005

The opening of cracks within a powder film is described as the film densifies on a substrate that constrains biaxial shrinkage. Polycrystalline ligaments that bridge the crack fail by an instability mechanism known as “desintering.” This phenomenon is produced by one of two effects. At lower temperatures, where the porous material still has a high driving potential for densification, the polycrystalline bridges extend and deform with increasing crack‐opening displacement. Deformation occurs by combined grain rearrangement and desintering (separation of previously sintered grains) without coarsening. The bridge finally separates when the last, linking grain pair desinters. At higher temperatures, when the film is nearly dense and the grains within the remaining bridges near the crack tip have increased their size by coarsening, bridge failure occurs without extension. In this case coarsening of the grains promotes the instability, viz., desintering.
Development of Cell Structure Due to Bénard‐Marangoni‐Type Convection in RuO2‐Glass Thick Films
Authors: Yamaguchi Takashi , Kanai Ken
Published: March 2005

A regular cell structure characteristic of Bénard–Maran‐goni convection has been observed in RuO2‐glass thick‐film resistors. It is shown that the viscosity of glass, among other parameters, plays an important role in the development of the cell structure.
Indentation Studies on Y2O2‐Stabilized ZrO2: I, Development of Indentation‐Induced Cracks
Authors: Kaliszewski Mary S. , Behrens Gesa , Heuer Arthur H. , Shaw Michael C. , Marshall David B. , Dransmanri Gerhard W. , Steinbrech Rolf W. , Pajares Antonia , Guiberteau Fernando , Cumbrera Francisco L. , Dominguez‐Rodriguez Arturo
Published: March 2005

The development of Vickers indent‐induced tracks with increasing indent load has been studied in two Y2O3‐stabilizel ZrO2 ceramics. Such cracks form as radial or Palmqvist cracks at low loads, assume “kidney” shapes at intermediate loads, and finally form median (half‐penny) cracks at high loads. The plastic zone directly beneath the indent is uncracked; a significant portion of the plasticity induced by indentation occurs by martensitic transformation.
Indentation Studies on Y2O3‐Stabilized ZrO2: II, Toughness Determination from Stable Growth of Indentation‐Induced Cracks
Authors: Dransmann Gerhard W. , Steinbrech Rolf W. , Pajares Antonia , Guiberteau Fernando , Dominguez‐Rodriguez Arturo , Heuer Arthur H.
Published: March 2005

Stable indentation cracks were grown in four‐point bend tests to study the fracture toughness of two Y2O3‐stabilized ZrO2 ceramics containing 3 and 4 mol% Y2O3. By combining microscopic in situ stable crack growth observations at discrete stresses with crack profile measurements, the dependence of toughness on crack extension was determined from crack extension plots, which graphically separate the crack driving residual stress intensity and applied stress intensity factors. Both materials exhibit steeply rising R‐curves, with a plateau toughness of 4.5 and 3.1 Mpa·m1/2 for the 3‐ and 4‐mol% materials, respectively. The magnitude of the plateau toughness reflects the fraction of tetragonal grains contributing to transformation toughening.
Extended Defects in ZnO Ceramics Containing Bi4Ti3O12 Additive
Authors: Makovec Darko , Trontelj Marija
Published: March 2005

Extended defects in ZnO ceramics containing, 6 wt% Bi4Ti3O12 were studied by analytical electron microscopy. Apart from basal plane condensation stacking faults, which are also present in as‐received ZnO, extended defects related to the presence of Bi4Ti3O12 were observed. In samples sintered at 900°C they lie in the basal or in the prismatic planes and they quite often form closed loops, whereas they form serpentine‐shaped boundaries in samples sintered at 1200°C. Evidence is given that they are inversion boundaries. Their TEM image characteristics, as well as the unambiguous presence of Ti at the boundaries, suggest that they are formed due to the presence of 2‐D coherent precipitates of Ti‐rich (possibly Zn2TiO4‐type spinel) phase.
Creep and Stress Rupture Behavior of an Advanced Silicon Nitride: Part I, Experimental Observations
Authors: Menon Mamballykalathil N. , Fang Ho T. , Wu David C. , Jenkins Michael G. , Ferber Mattison K. , More Karren L. , Hubbard Camden R. , Nolan Theodore A.
Published: March 2005

Cylindrical buttuohead specimens of an advanced silicon nitride were tested in uniaxial tension at temperatures between 1422 and 1673 K. In the range 1477 to 1673 K, creep deformation was reliably measured using high‐temperature contact probe extensometry. Extensive scanning and transmission electron microscopy has revealed the formation of lenticular cavities at two‐grain junctions at all temperatures (1422–1673 K) and extensive triple‐junction cavitation occurring at the higher temperatures (1644–1673 K). Cavitation is believed to be part of the net creep process. The stress rupture data show stratification of the Monkman–Grant lines with respect to temperature. Failure strain increased with increase in rupture time or temperature, or decrease in stress. Fractography showed that final failure occurred by subcritical crack growth in all specimens.
Creep and Stress Rupture Behavior of an Advanced Silicon Nitride: Part II, Creep Rate Behavior
Authors: Menon Mamballykalathil N. , Fang Ho T. , Wu David C. , Jenkins Michael G. , Ferber Mattison K.
Published: March 2005

In Part I of this paper, experimental observations on creep testing of 74 tensile specimens of an advanced silicon nitride were presented. In this part, equations are developed for predicting creep rates in the primary and secondary regimes in the temperature range 1477–1673 K. The resulting model predicts creep strain rates to within a factor of two. The underlying phenomenological basis, which employs an activation energy approach, is discussed. The mechanisms that are likely to be responsible for the transiency of the primary creep regime and for the unique stress and temperature dependencies of the creep rates are explored.
Effect of Dopants on Zirconia Stabilization—An X‐ray Absorption Study: II, Tetravalent Dopants
Authors: Li Ping , Chen I‐Wei , Penner‐Hahn James E.
Published: March 2005

X‐ray absorption spectra at Zr‐K, Ce‐L111 and Ge‐K edges in ZrO2–CeO2 and ZrO2–GeO2 solid solutions have been measured at 10 K. Both Ce and Ge substitute for Zr in the cation network, but CeO8 and GeO4 polyhedra are maintained around the dopants. The oversized CeO8 is compressed to a Ce–O distance of 2.30 Å, which is smaller than the 2.35 Å seen in fluorite‐type CeO2. Meanwhile, the distortion of the Zr‐cation network is increased and the tetragonality is reduced. The undersized Ge has a Ge–O distance of 1.80 Å, which is much shorter than the Zr–O, distance of 2.10 Å. A strong tendency for Ge–Zr ordering in tetragonal solid solutions into locally scheelite‐like clusters, even within the solubility limit, is observed. This results in an increase in the tetragonality and a decrease in the distortion of the cation network. Despite the opposite effects on tetragonality, both Ce and Ge doping can stabilize tetragonal zirconia albeit via different mechanisms. The structural origin of the cubic phase is also elucidated.
Characterization of C‐S‐H from Highly Reactive β‐Dicalcium Silicate Prepared from Hillebrandite
Authors: Okada Yoshihiko , Ishida Hideki , Sasaki Kaori , Young J. Francis , Mitsuda Takeshi
Published: March 2005

β‐dicalcium silicate synthesized by thermal dissociation of hydrothermally prepared hillebrandite (Ca2(SiO3)(OH)2) exhibits extremely high hydration activity. Characterization of the hydrates obtained and investigation of the hydration mechanism was carried out with the aid of trimethylsilylation analysis, 29Si magic angle spinning nuclear magnetic resonance, transmission electron microscopy selected area electron diffraction, and XRD. The silicate anion structure of C‐S‐H consisted mainly of a dimer and a single‐chain polymer. Polymerization advances with increasing curing temperature and curing time. The C‐S‐H has an oriented fibrous structure and exhibits a 0.73‐nm dreierketten in the longitudinal direction. On heating, the C‐S‐H dissociates to form β‐C2S. The temperature at which βC2S begins to form decreases with increasing chain length of the C‐S‐H or as the Ca/Si ratio becomes higher. The high activity of β‐C2S is due to its large specific surface area and the fact that the hydration is chemical‐reaction‐rate‐controlled until its completion. As a result, the hydration progresses in situ and C‐S‐H with a high Ca/Si ratio is formed.
Domain Structure in Excess‐WO3 Lead Complex Perovskite
Authors: Uchikoba Fumio , Sawamura Kentaro
Published: March 2005

Ferroelectric domain structures in the polycrystalline ternary system Pb(Mg1/3Nb2/3)O3–PbTiO3–Pb(Mg1/2W1/2)O3 were investigated with regard to excess‐WO3 addition. Core–shell domain structures were observed in the 2 wt% excess‐WO3 specimens. Above 3 wt% excess‐WO3 addition, the ferroelectric fringe pattern disappeared at the center of the grain, and ringlike domain structures were observed. This tendency became distinct in 5 wt% excess‐WO3 addition, and clear, ringlike domain structures were observed. The structures that consisted of fringe shell parts and non‐fringe core parts were reversals of normal core–shell structures.
Effect of Pressure on Plasma‐Assisted Chemical Vapor. Deposition of Silicon Oxide(s)
Authors: Banerjee Aditi , DebRoy Tarasankar
Published: March 2005

In most chemical vapor deposition processes, the film growth rate increases with the concentrations of the reactant gases. However, in the plasma‐assisted chemical vapor deposition of silicon oxide films, the deposition rate decreases when the concentrations of silane and nitrous oxide are increased by enhancing the reactor pressure from 0.5 to 2 torr (66 to 270 Pa). The deposition rate and the plasma properties have been examined for various reactor pressures to seek an improved understanding of the deposition process. Photo emissions from the plasma were monitored to determine the species present in the plasma and to calculate electron energy and density. With the increase in pressure, both the electron temperature and density decreased, and, consequently, the concentration of active species decreased. Although the concentrations of both silane and nitrous oxide increased with total pressure, the deposition rate decreased. The results emphasize the crucial importance of electron energy and density to generate sufficient concentration of active species responsible for film growth.
Viscosity and Yield Stress of Alumina Slurries Containing Large Concentrations of Electrolyte
Authors: Chang Jeanne C. , Lange Fred F. , Pearson Dale S.
Published: March 2005

Viscosity and yield stress measurements of A12O3 slurries containing high concentrations of electrolyte are reported. Contrary to what is expected from DLVO theory, the particles in coagulated slurries produced in this way are held together by weaker forces than particles in slurries brought to the isoelectric point by changing the pH. In both cases an attractive, connective particle network is present. However, the network at the isoelectric point is stronger, as indicated by its much higher yield stress and by its higher viscosity at stresses above the yield point. An additional short‐range repulsive force that appears at low pH and high electrolyte concentrations is believed to be responsible. This force prevents the particles from reaching the primary minimum associated with particle contact. The effects of solids loading, electrolyte concentration and type, and particle size have been investigated.
Preparation and Characterization of Tl‐Ba‐Ca‐Cu‐O Superconducting Films by Spray Pyrolysis and Tl‐Diffusion Technique
Authors: Koo Horng‐Show , Tu George C. , Tseng Tseung‐Yuen
Published: March 2005

The present work reports that highly c‐axis‐oriented Tl‐Ba‐Ca‐Cu‐O superconducting films with zero‐resistance temperature up to 112 K were successfully prepared using the spray pyrolysis technique with a subsequent Tl‐diffusion treatment. The insalating Ba‐Ca‐Cu‐O precursor films (Ba:Ca:Cu = 2:2:3) were made by spray deposition of the related metal nitrate solution on a preheated (300°–400°C) MgO(001) single‐crystal substrate. The presence of the superconducting phases of the resultant films depended strongly on the types of Tl sources used. The results showed that the formation of the super conducting phases could be achieved more readily by using the bulk Tl‐Ba‐Ca‐du‐O rather than Tl2O3 as a Tl source. In other words, the low Tl content in the TlBaCaCuO bulk source with a resulting low Tl‐vapor pressure is favorable for the formation of a higher Tc superconducting phase. The dominant phases in the prepared films were mainly TlBa2Ca2Cu3O/(1223 phase) and Tl2Ba2CaCu2Oy(2212 phase). The critical current density of a film with a nearly single‐phase(1223) structure was measured to be 1.2 × 104 A/cm2 at 77 K under zero magnetic field.
Crystallization of Precursors to Forsterite and Chromium‐Doped Forsterite
Authors: Park Dong Gon , Martin M. Hogan E. , Ober Christopher K. , Burlitch James M. , Cavin O. Burl , Porter Wallace D. , Hubbard Camden R.
Published: March 2005

The pyrolysis and crystallization of poly(methacrylate) precursors and xerogels of forsterite and chromium‐doped forsterite were studied by in situ high‐temperature, dynamic X‐ray diffraction and thermal analysis. For both types of precursor, crystallization of forsterite occurred at lower temperature when doped with chromium. Also, exotherms above 700°C occurred 50°C lower when chromium was present. When residual carbon in the xerogels was more than ∼1%, an unidentified crystalline intermediate phase formed at ∼800°C. Conversion of the intermediate phase to forsterite was faster than amorphous material. Thus, full crystallinity was attained at a lower temperature when the xerogels had some residual carbon.
Coating Additives for Improved Mechanical Reliability of Optical Fiber
Authors: Rondinella Vincenzo V. , Matthewson M. John , Kurkjian Charles R.
Published: March 2005

Fused silica glass is subject to delayed failure, i.e., failure occurring after a certain time under stress conditions far below the level required to have fast, catastrophic rupture. While the behavior at high applied stress may be described, at least empirically, by the subcritical crack growth model, it is well known that fused silica shows a transition, or “knee,” to a more severe delayed failure behavior, or “enhanced fatigue,” at low applied stress and long time to failure. This makes predictions of the expected lifetime unreliable. The addition of nanosized particles of fumed silica to the polymer coating of fused silica optical fiber is shown to improve long‐term mechanical properties of the fiber: it delays the onset of the fatigue transition and reduces the strength degradation due to zero stress aging. Atomic force microscopy analysis shows that the presence of the additive dramatically reduces the rate of development of surface roughness, thus indicating that the effect of the additive is to suppress surface dissolution processes. The additive has little effect on the fatigue behavior before the transition. These results indicate that dissolution is the cause of the transition but has less importance on the pre‐transition region.
Spray Drying of Metal Alkoxide Sol for Strontium Titanate Ceramics
Authors: Varma Hari Krishna , Pillai P. Krishna , Mani Themanam Veettil , Warrier Krishna Gopa Kumara , Damodaran Alathoor D.
Published: March 2005

Conditions for obtaining a stable sol in an isopropyl alcohol–water medium containing titanium isopropoxide and strontium nitrate, and acetic acid as a modifier, have been described. Spray drying of the sol results in submicrometer spherical agglomerates which on further thermal decomposition yield submicrometer particles of strontium titanate at temperatures as low as 500°C. The thermal decomposition characteristics of the spray‐dried precursor and the development of strontium titanate phase have been discussed. Calcined precursor powder possesses a specific surface area of 12m2/g, a comp action density of 57%, and a sintered density of > 98%. The optimum sintering temperature of such a powder was 1450°C, which resulted in a sintered grain size around 1.5 μm. Further, such a sintered sample had a dielectric constant of 260 and a loss factor of 0.008 at 1 kHz. This method appears to be very convenient with respect to handling of stable sols and thus avoids the usual difficulties regarding extended gelation as well as inhomogeneous precipitation.
Phase Relations in the System Cu─Ho─O and Stability of Cu2Ho2O5
Authors: Mathews Tom , Jacob K. Thomas
Published: March 2005

The phase relations in the system Cu─Ho─O have been determined at 1300 K using X‐ray diffraction, optical microscopy, and electron microprobe analysis of samples equilibrated in evacuated quartz ampules and in pure oxygen. Only one ternary compound, Cu2Ho2O5, was found to be stable. The Gibbs free energy of formation of this compound has been measurer using the solid‐state cell
Pt, Cu2O + Cu2Ho2O5+ Ho2O3/(Y2O3)ZrO2/CuO + Cu2O, Pt
in the temperature range of 973 to 1350 K. For the formation of Cu2Ho2O5 from its binary component oxides,
2CuO(s) + Ho2O3(s) → Cu2Ho2O5(s)
ΔG°= 11190 − 13.8T(±120)J·mol−1

Since the formation is endothermic, Cu2Ho2O5 becomes thermodynamically unstable with respect to CuO and Ho2O3 below 810 K. When the oxygen partial pressure over Cu2Ho2O5 is lowered, it decomposes according to the reaction
2Cu2Ho2O5(s) → 2Ho2O3(s) + 2Cu2O(s) + O2(g)
for which the equilibrium oxygen potential is given by
Δμo2=−238510 + 160.2T(±450) J·mol−1

The decomposition temperature at an oxygen partial pressure of 1.52 × 104 Pa was measured using a combined DTA–TGA apparatus. Based on these results, an oxygen potential diagram for the system Cu─Ho─O at 1300 K is presented.
CO2 Decomposition by Oxide Ceramics Intercalated in Layered Compound
Authors: Tsuji Masamichi , Tabata Masahiro , Tamaura Yutaka
Published: March 2005

Iron oxide polymers intercalated and/or loaded within täniolite have been studied as a CO2 decomposition medium. Fe2+ was exchanged for Li+ in täniolite, oxidized by air‐bubbling at 60°–70°C. The basic d‐spacing (13.75 Å in the Li+ form) was expanded to give 14.86 Å in the Fe2+ form. Oxidation by air in the form of suspension gave a 15.3‐Å phase, which was ascribed to formation of magnetite within the interlayer. The interlayer distance of the intercalated phase remained the same upon heating at 300°C. The magnetite–intercalated täniolite was heated to activate in a H2 and/or H2O steam. CO2 decomposition reactivity at 300°C has been evidenced by evolution of CO gas. The high reactivity for CO2 decomposition is ascribed to the highly dispersed iron oxide ceramics within the interlayer of täniolite Li[(Mg2Li)(Si4O10)]F2nH2O.
Lubricated Rolling Wear of SiC‐Whisker‐Reinforced Al2O3 Composites against M2 Tool Steel
Authors: Liu Haiyan , Fine Morris E. , Cheng H. S. , Geiger Alan L.
Published: March 2005

Lubricated rolling wear studies of SiC‐whisker (SiCw) reinforced A12O3 composites and monolithic A12O3 against M2 tool steel were conducted using a cylinder‐on‐cylinder apparatus. The composites wore considerably less than A12O3. The wear of the tool steel against the composites was also considerably less than against A12O3. Microfracture occurred on a smaller scale in the composites than in the Al2O3. This was attributed to the differences in microstruc‐ture and fracture toughness. The worn surfaces of the steel and the composites were polished, possibly due to fine, hard wear debris circulating with the lubricant to the contact area.
New Experimental Setup for Wettability Characterization under Monitored Oxygen Activity: II, Wettability of Sapphire by Silver‐Oxygen Melts
Authors: Chatain Dominique , Chabert Françoise , Ghetta Véronique , Fouletier Jacques
Published: March 2005

Wetting of silver on sapphire and surface tension of silver are both determined as a function of oxygen activity in a range corresponding to oxygen content in silver varying from 10−12 to 10−2. The contact angle is shown to decrease at high oxygen activity when simultaneous decreases in surface tension of silver and interfacial energy between silver and alumina occur. This double oxygen adsorption is ther‐modynamically analyzed and some relevant parameters inducing oxygen segregation at the silver interfaces are proposed.
Magnetoplumbite‐Corundum Phase Equilibria in the System Sr─Fe─Al─O at 1100°C
Authors: Takaoka Hidemitsu , Suito Hideaki
Published: March 2005

The phase relations in the region of the Fe2O3‐ and Al2O3‐rich sides of the quaternary system SrO─Fe2O3–Al2O3–B2O3 and the location of conjugation lines between magnetoplumbite solid solution SrO·(6 − x)Fe2O3·xAl2O3 and corundum (α‐Fe2O3, α‐Al2O3) phases were determined at 1100°C in air by using the flux‐growth method based on the Ostwald ripening mechanism. Activity–composition relations and the lattice parameters along the magnetoplumbite solid solutions were also obtained.
Effect of Preliminary Mechanical Treatment on the Microhomogenization during Heating of Hydrous Gels as Precursors for Lead Titanate
Authors: Komatsubara Satoru , Isobe Tetsuhiko , Senna Mamoru
Published: March 2005

Change in compositional microhomogeneity as a function of temperature was determined for various hydrous gels obtained from a component sol mixture as precursors for PbTiO3. The local molar ratio, Pb:Ti, was determined by energy dispersive spectroscopy with a 25‐nm electron beam. Homogenization during heating was accelerated by preliminary ball milling or pressing of the sol mixture. The mechanism of homogenization is discussed in the present paper with respect to mechanochemical effects.
Sigmoidal Indentation–Strength Characteristics of Polycrystalline Alumina
Authors: Cook Robert F. , Liniger Eric G. , Steinbrech Rolf W. , Deuerler Friederike
Published: March 2005

The fracture properties of a series of three polycrystailine aluminas are examined using indentationstrength and double cantilever beam techniques. The indentation‐strength response is shown to be sigmoidal with concave‐down behavior at small indentation loads and concave‐up behavior at large indentation loads. A model is developed for the general response, combining increasing toughening by ligamentary bridging at small crack lengths and increasing residual‐stress relief by lateral cracking at large indentation loads. The model is fit to the strength data and used to deconvolute the underlying toughness variation and predict the intrinsic strength of the materials. Direct measurements of toughness using the “long‐crack” double cantilever beam geometry are shown to overestimate the toughness variations effective during “short‐crack” strength tests.
Forces between Alumina Surfaces in Salt Solutions: Non‐DLVO Forces and the Implications for Colloidal Processing
Authors: Ducker William A. , Xu Z. , Clarke David R. , Israelachvili Jacob N.
Published: March 2005

Direct measurements of the forces between basal (0001) surfaces of sapphire in salt solutions are presented. The measurements reveal the presence of forces in addition to those described by classical DLVO theory. At pH 7.2 in 0.01M NaBr solution, we find an additional short‐range oscillatory force with periodicity approximately equal to twice the diameter of a water molecule. At pH 3 we find an additional strong, short‐range, monotonic, repulsive force and a long‐range attractive force over a range of NaBr concentrations from 0.001 M to 0.1 M. Both monotonic forces are approximately exponential, with decay lengths of 0.55 and 12 nm, respectively. The short‐range force is analogous to hydration forces previously measured on negatively charged surfaces. This force would provide plasticity to alumina slurries and is suggested to be the force responsible for the anomalous viscosity and consolidation behavior of alumina slurries at high salt concentrations.
Stability and Surface Energies of Wetted Grain Boundaries in Aluminum Oxide
Authors: Kim Doh‐Yeon , Wiederhorn Sheldon M. , Hockey Bernard J. , Handwerker Carol A. , Blendell John E.
Published: March 2005

The stability of a calcium‐aluminum‐silicate liquid film between two near‐basal plane surfaces of sapphire at 1650°C was studied. Samples were prepared having an average basal misorientation across the interface of 6–7° about < 〈1010〉. The interfaces varied in orientation from 0° to ∼38° to the [0001] direction. Three types of interfaces were observed: faceted, solid‐liquid interfaces; low‐angle grain boundaries consisting of aligned arrays of dislocations; and boundaries consisting of alternating regions of dislocations and faceted solid‐liquid interfaces. The type of interface observed depended on the orientation of the interface and could be predicted by using a construction based on Wulff shapes. Because the type of interface depends on crystal alignment and interface angle, these results suggest an absolute method of determining the surface free energy of wetted boundaries.
Tribological Characteristics of Si3N4 Ceramic in High‐Temperature and High‐Pressure Water
Authors: Kitaoka Satoshi , Tsuji Toshihide , Katoh Toshio , Yamaguchi Yoshimi , Sato Kōji
Published: March 2005

The effects of sliding speed and dissolved oxygen on the tribological behavior of Si3N4 sliding on itself in water were investigated at room temperature and at 120°C saturated vapor pressure. The friction coefficients and specific wear rates at 120°C were much larger than those at room temperature and had a minimum at about 0.4 m/s, whereats ‐the specific wear rate of the disk increased with increasing the sliding speed. The wear rate at lower sliding speeds in water at 120°C is considered to be primarily controlled by the increase of the contact stress on the asperities which are formed by the dissolution of grain boundaries of the Si3N4 ceramic and the subsequent dissolution of the silica layer of the reaction product However, the wear rate at higher sliding speeds is governed by the direct oxidation and microfracture of the Si3N4 substrate. The tribochemical reaction to produce NH3 mainly occurred at all sliding conditions in water at room temperature and 120°C, and the reaction to produce H2 gas appeared slightly only at the sliding speeds above 0.4 m/s at 120°C. The tribological behavior was independent of dissolved oxygen concentration for all sliding conditions in water at room temperature and 120°C.
Features of Notch Preparation for Fracture Toughness Measurements in Partially Stabilized Zirconia
Authors: Krell Andreas
Published: March 2005

Fracture toughness measurements with the use of saw cut notches or indentation flaws often give overestimated KIc values when the flaws are introduced into sintered bodies which contain a metastable phase. Notching before sintering offers a way to eliminate the problem of residual stresses generated by flaw preparation, as has been demonstrated with yttria‐partially‐stabilized tetragonal zirconia. However, the response of each new material to the notching procedure in the unsintered stage has to be considered carefully to exclude possible effects of locally changed den‐sification and grain‐growth kinetics. Untransformable alumina microstructures show similar KIc values as determined by ISB and SENB methods with 0.1‐mm narrow notches introduced in the green state, and similar KIc values measured with notches of the same width introduced before and after sintering. Notches introduced before sintering generate the well‐known, rather strong notch width influence on KIc in the notch width range between 0.1 and 0.2 mm.
Ultrafine‐Grained Dense Monoclinic and Tetragonal Zirconia
Authors: Skandan Ganesh , Hahn Horst , Roddy Mike , Cannon W. Roger
Published: March 2005

Nanoparticles of ZrO2 with diameters ranging from 4 to 8 nm were synthesized by gas condensation. As‐prepared n‐ZrO2 particles have a monoclinic and a high‐pressure tetragonal structure depending on size. Pure ZrO2 was sintered to full density under vacuum at 04Tm within the monoclinic phase field. Final grain sizes in theoretically dense pellets are below 60 nm. By sintering below the monoclinic–tetragonal transition temperature, microcracking was completely avoided. Tetragonal ZrO2 stabilized with 3 mol% Y2O3 was prepared by interdiffusion of nanoparticles and sintered to near‐theoretical density.
Nucleation and Growth of α′‐SiAlON on α‐Si3N4
Authors: Hwang Shyh‐Lung , Chen I‐Wei
Published: March 2005

Morphology, composition, and growth defects of α′‐SiAION have been studied in a fine‐grained material with an overall composition Y0.33Si10Al2O1N15 prepared from α‐Si3N4, AlN, Al2O3, and Y2O3 powders. TEM analysis has shown that fully grown α′‐SiAloN grains always contain an α‐Si3N4 core, implicating heterogeneous nucleation operating in the present system. The growth mode is epitaxial, despite the composition and lattice parameter difference between α‐Si3N4 and α′‐SiAlON. The inversion boundary that separates two domains in the seed crystal is seen to continue in the grown α′‐SiAION. Lacking a special growth habit, the growth typically proceeds from more than one site on the seed crystal, and the different growth fronts impinge on each other to give an equiaxed appearance of α′‐SiAlON. Misfit dislocations on the α/α’interface are identified as [0001] type (b= 5.62 Å) and 1/3 [1210] type (b= 7.75 Å). These nucleation and growth characteristics dictate that microstructural control of α′‐SiAlON must rest on the size distribution of the starting α‐Si3N4 powder.
Alumina/Aluminum Composites Formed by the Directed Oxidation of Aluminum Using Magnesia as a Surface Dopant
Authors: Xiao Ping , Derby Brian
Published: March 2005

Al2O3/AI composites have been formed by the directed oxidation of pure Al doped with MgO powder. Thermal gravimetric analysis was used to characterize reaction kinetics. Optical and scanning electron microscopy and SEM coupled with microanalysis were used to characterize the microstructure of product. Directed oxidation is initiated without an incubation period. The particle size of the MgO powder determines the initial microstructure. Mg is retained in some form at the growth surface after the disappearance of the original MgO; however, there is a continuous loss of Mg from the system. The presence and distribution of the Mg compounds play a key role in the directed oxidation.
Electric‐Field‐Induced Fatigue Crack Growth in Piezoelectrics
Authors: Cao Hengchu , Evans Anthony G.
Published: March 2005

When subjected to large alternating electric fields, ferroelectric ceramics may experience cracking and mechanical degradation. This article describes an experimental procedure for characterizing crack extension from preexisting flaws in such materials subject to high‐amplitude, alternating electric fields. A new mode of electric‐field‐induced fatigue crack growth is identified. Fracture mechanics concepts are applied to interpret the observed cracking.
Role of Grain Size in Strength Variability of Alumina
Authors: Kovar Desiderio , Readey Michael J.
Published: March 2005

Relationships between grain size and strength variability in alumina were investigated. Results are presented for an Ultra‐high‐purity alumina with a narrow grain size distribution and an equiaxed grain morphology at three grain sizes ranging from 5 to 27 μ.m. Vickers indentations are used to introduce controlled flaws into the specimens. It is found that increasing the grain size leads to enhanced flaw tolerance owing to a rising R‐curve. However, contrary to recent theoretical predictions, no reduction in strength variability is found with increasing grain size. It is proposed that increasing variability in local fracture toughness with grain size offsets any improvement in reliability. This suggests that an upper bound to the reliability of grain bridging materials may exist.
New Gas‐Sensing Method for Detecting Carbon Monoxide by Use of the Complex Impedance of a CuO/ZnO Heterocontact under a dc Bias Voltage
Authors: Hikita Kazuyasu , Miyayama Masaru , Yanagida Hiroaki
Published: March 2005

The impedance characteristics of a CuO/ZnO oxide semiconductor heterocontact were investigated to study a new method of gas identification. This was done by applying a dc bias voltage in atmospheres of air‐balanced, flammable CO or H2 gas (4000 ppm). The frequency dependence of the reactance component showed a characteristic behavior that varied according to the testing atmosphere under the applied negative dc voltage at 400°C. The discrimination of CO gas from H2 gas in air was demonstrated as feasible by either varying the bias voltage in negative values at constant frequency or sweeping the frequency on a negative bias voltage. The new method of gas identification suggested by the present study uses a ceramic‐semiconductor heterocontact, on which a combination of dc bias voltage and ac signal is applied.
Microstructural Observations on Constrained Densification of Alumina Powder Containing a Periodic Array of Sapphire Fibers
Authors: Lam David C. C. , Lange Fred F.
Published: March 2005

Alumina powder was packed within and around a square array of 16 sapphire fibers to study the density and microstructure of the matrix powder after different heat treatments. The matrix powder along the cell edges of the array (most closely spaced distance between fiber centers) was observed to become dense and support grain growth before the regions within the centers of the square unit cells. The denser, larger‐grained material between the fibers formed a continuous network of creep resistant material that constrained the densification of the porous regions.
Effect of Oxygen Partial Pressure during Sintering on the Microstructure of Mg‐PSZ with Strontia and Silica Additions
Authors: Drennan John , Clarke David R. , Hannink Richard H. J. , Shaw Thomas M.
Published: March 2005

The microstructure, average grain size, and density of Mg‐PSZ sintered with SrO and SiO2 additions are found to depend on the partial pressure of oxygen in the sintering atmosphere. Over the range of 10−1 to 10° atm, both the average grain size and the density increase with oxygen partial pressure, for a constant SrO/SiO2 ratio. The partial pressure of oxygen also affects the microstructural distribution of the remnant liquid phase. At high partial pressures the liquid phase is uniformly distributed, whereas at lower oxygen pressures it is preferentially located near the surface. It is proposed that the microstructure produced by sintering is the result of a competition between liquid‐phase‐enhanced densification and the migration of the liquid phase to the free surface. The migration is attributed to vaporization of MgO from the liquid phase which increases with decreasing partial pressure of oxygen.
Effect of Cleaning and Abrasion‐Induced Damage on the Weibull Strength Distribution of Sapphire Fiber
Authors: Trumbauer Eric R. , Hellmann John R. , Shelleman David L. , Koss Donald A.
Published: March 2005

Fractographic analysis revealed the presence of concurrent flaw populations in sapphire fibers which were tensile tested in the as‐received condition (sized and unsized) and after various cleaning procedures. The following flaw populations were identified: surface flaws attributed to handling and abrasion damage (type A), volume or internal flaws attributed to shrinkage voids which form during the manufacturing process (type B), localized fiber surface reaction flaws introduced during the flame‐cleaning procedure (type C), and self‐abrasion surface flaws intentionally introduced on unsized fibers (type D). The strength distribution associated with each flaw type was characterized using a censored data Weibull analysis for both the least‐squares and maximum‐likelihood estimation methods. The strength distribution for type C (flame‐cleaning) flaws exhibited an approximately 20% degradation in strength compared to the distribution for type A flaws. The strength distribution for type D (self‐abrasion) flaws exhibited an approximately 35% degradation in strength compared to the strength distribution for type A flaws. This result underscores the need for fiber sizings to prevent damage during shipping and handling. However, higher purity sizings and/or improved procedures for sizing removal are required to mitigate cleaning‐induced fiber strength degradation during composite fabrication.
Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: I, Tobermorite Formation and Reaction Behavior of Slag
Authors: Isu Norifumi , Sasaki Kaori , Ishida Hideki , Mitsuda Takeshi
Published: March 2005

The chemical reactions in the formation of autoclaved aerated concrete (AAC) block were investigated. The samples were prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. Autoclaving for 1 h yielded 1.1‐nm tobermorite with higher Al substitution and lower Ca/(Al + Si) ratio than that made without slag, due to the high solubility of the slag during the initial stage of reaction. This suggests that the utilization of slag has an advantage of reducing processing time. On further reaction, the crystallinity of the tobermorite increases and its Ca/(Al + Si) ratio decreases, becoming constant after 64 h. After a long period of autoclaving. thick reaction rims are formed around unreacted slag particles, interrupting the diffusion of Ca from slag to matrix.
Mechanical Property Evolution during Autoclaving Process of Aerated Concrete Using Slag: II, Fracture Toughness and Microstructure
Authors: Isu Norifumi , Teramura Satoshi , Ishida Hideki , Mitsuda Takeshi
Published: March 2005

The mechanical properties were investigated for autociaved aerated concrete (AAC) block samples, prepared using blast furnace slag at 180°C under saturated steam pressures for various times from 1 to 128 h. The mechanical properties of AAC made using slag are comparable to those made without slag. With increased autoclaving time, the compressive strength increases due to the binder effect of the 1.1‐nm tobermorite. In contrast, the fracture energy GF. and resistance to crack growth decrease with increase of autoclaving time. This dependency is caused by the formation of voids around unreacted slag particles.
Texture Measurement on Materials Containing Platelets Using Stereology
Authors: Sandlin Michael S. , Peterson Chad R. , Bowman Keith J.
Published: March 2005

A method for determining three‐dimensional (3‐D) orientation distributions of platelike grains or inclusions using stereology is described. The method involves relating an orientation distribution of platelet cross‐section normals taken from a plane of polish, with a corresponding orientation distribution of platelet normals in 3‐D. In this investigation, SiC platelet orientation distributions were measured in Al2O3–SiC, and Cu–SiC composites by both stereological analysis and X‐ray diffraction. The stereological measurements yielded two‐dimensional (2‐D) platelet cross‐section normal orientation distributions, and the X‐ray diffraction measurements yielded 3‐D platelet normal orientation distributions (in the form of pole figures). The calculation described in this paper correlates 2‐D and 3‐D platelet normal distributions. To experimentally substantiate the calculation, a comparison between measured and calculated distributions is presented. Good agreement between calculation and measurement is shown, thereby confirming this analysis as a viable technique for orientation measurements.
Phase Equilibria and Crystal Chemistry in Portions of the System SrO─CaO─½Bi2O3─CuO: V, The System SrO─CaO─½Bi2O3
Authors: Rawn Claudia J. , Roth Robert S. , Burton Benjamin P. , Hill Michael D.
Published: March 2005

Data are presented on the phase equilibria and crystal chemistry of the ternary system SrO─CaO─½Bi2O3. Symmetry data and unit‐cell dimensions based on single‐crystal and powder X‐ray diffraction measurements are reported for the two monoclinic phases. The monoclinic phase with a Sr:Ca:Bi ratio of 99:33:68 was shown to have both high‐and low‐temperature (black) oxidized forms.
Subsolidus Relations in the La2O3─CuO─CaO Phase Diagram and the La2O3─CuO Binary Join
Authors: Skakle J. M. S. , West Anthony R.
Published: March 2005

The phase diagram for the CuO‐rich part of the La2O3─CuO join was redetermined. La2Cu2O5 was found to have a lower limit of stability at 1002°± 5°C and an incongruent melting temperature of ∼1035°C. LagCu7O19 had both a lower (1012°± 5°C) and an upper (1027°± 5°C) limit of stability. Subsolidus phase relations were studied in the La2O3─CuO─CaO system at 1000°, 1020°, and 1050°C in air. Two ternary phases, La1.9Ca1.1Cu2O5.9 and LaCa2Cu3O8.6, were stable at these temperatures, with three binary phases, Ca2CuO3, CaCu2O3, and La2CuO4. La2Cu2O5 and La8Cu7O19 were stable only at 1020°C, and did not support solid‐solution formation.
Characterization of Three‐Dimensional Through‐Thickness Transformation Zone in 9‐mol%‐Ce–TZP Ceramics
Authors: Liu Tianshun
Published: March 2005

The through‐thickness t–m transformation zone was characterized in two 9‐mol%‐Ce–TZP ceramics with 1.6‐ and 2.2‐μm grain size. Short, double‐cantilever‐beam (sDCB) specimens were used to measure the crack‐resistance curves (R‐curves). After the R‐curve measurements were made, the sDCB specimens were cut through the thickness, and the t–m transformation zone was characterized. The stress‐induced t–m transformation zone remained nearly the same shape and size through the thickness, but the amounts of the t–m transformation at the two free surfaces were much higher than inside the specimens. The results are discussed based on fracture mechanics.
Electrical Properties of β‐LixV2O5 Thin Layers Prepared by the Sol—Gel Process
Authors: Bae Seung‐Young , Miyayama Masaru , Yanagida Hiroaki
Published: March 2005

The electrical properties of a highly oriented thin layer of lithium vanadium beta bronze, β‐LixV2O5, were investigated through dc and ac conductivity measurements. The ionic transference number was determined by a simplified polarization method employing ion‐blocking electrodes. The electronic conductivity was 10 –3to 10–2 S cm–1 in air or N2 at 300–400°C, which was lower than that of a randomly oriented sintered specimen. The ionic conductivity was l0–2–10–1s cm–1 at 350°C, resulting in a high ion transference number of 0.8–0.9; it was higher than that reported for a bulk specimen. The lower electronic conductivity and higher ionic conductivity were assumed to be due to (1) the oriented microstructure, i.e., alignment of the b‐axis along the substrate direction which enhanced Li+ conduction through tunnels along the b‐axis, and (2) an open crystallo‐graphic structure, which promoted ionic motion in an open channel between adjacent (a‐c) places and suppressed the electron hopping process in the b‐axis direction.