bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of the Grain Boundary Thermal Expansion Coefficient on the Fracture Toughness in Silicon Nitride
Authors: Peterson Irene M. , Tien Tseng‐Ying
Published: July 2005

The effect of thermal expansion mismatch stress between silicon nitride and different grain boundary phases on the fracture toughness of silicon nitride was investigated. Different sintering aids in the Y‐Mg‐Si‐Al‐O‐N system produced silicon nitride specimens with very similar micro‐ structures but different grain boundary phase compositions and different values of fracture toughness. The fracture toughness of the silicon nitride increased as the thermal expansion coefficient of the grain boundary phase increased. The presence of tensile residual stress at the grain boundary caused by thermal expansion mismatch between the silicon nitride and the grain boundary phase enhanced crack deflection and grain bridging.
Surface Cracking in Layers Under Biaxial, Residual Compressive Stress
Authors: Ho S. , Hillman C. , Lange F. F. , Suo Z.
Published: July 2005

Thin two‐phase, Al2O3/t‐Zr(3Y)O2 layers bounded by much thicker Zr(3Y)O2 layers were fabricated by co‐sintering powders. After cooling, cracks were observed along the center of the two‐phase, Al2O3/t‐Zr(3Y)O2 layers. Although the Al2O3/t‐Zr(3Y)O2 layers are under residual, biaxial compression far from the surface, tensile stresses, normal to the center line, exist at and near the surface. These highly localized tensile stresses can cause cracks to extend parallel to the layer, to a depth proportional to the layer thickness. A tunneling/edge cracking energy release rate function is developed for these cracks. It shows that for a given residual stress, crack extension will take place only when the layer thickness is greater than a critical value. A value of the critical thickness is computed and compared with an available experimental datum point. In addition, the behavior of the energy release rate function due to elastic mismatch is calculated via the finite element method (FEM). It is also shown how this solution for crack extension can be applied to explain cracking associated with other phenomena, e.g., joining, reaction couples, etc.
Fugitive Diffusion Barrier for Integration of Sol‐Gel‐Derived Lead Titanate with Oxidized Silicon Substrates
Authors: Wright John S. , Schwartz Joseph M. , Schmidt Lanny D. , Francis Lorraine Falter
Published: July 2005

The crystalline phase development and microstructural changes with heating of sol‐gel‐derived lead titanate (PT) particles and films on silica with and without a fugitive (or removable) diffusion barrier layer were investigated. Amorphous gel‐derived PT particles were deposited on SiO2‐coated TEM grids with and without polyimide (PI) or carbon barrier layers between SiO2and PT. TEM analysis showed that PI or carbon barriers prevented reaction between the gel‐derived PT particles and SiO2. PT particles crystallize and then the PI or carbon film decomposes. Sol‐gel‐derived PT films were deposited on oxidized Si substrates (Si/SiO2) with and without a PI barrier layer. Perovskite PT films were prepared on Si/SiO2substrates with a PI barrier; however, some porosity remained in the films. Identically prepared films without the PI barrier formed a mixture of pyrochlore and perovskite. X‐ray photoelectron spectroscopy results indicate that the PI film pre‐ vents the diffusion of Si into the PT film.
Preventing Segregation during Centrifugal Consolidation of Particulate Suspensions: Particle Drafting
Authors: Roeder Ryan K. , Steinlage Greg A. , Trumble Kevin P. , Bowman Keith J.
Published: July 2005

Dilute, dispersed, multicomponent suspensions containing Ce‐ZrO2, Al2O3, and varying Al2O3‐platelet contents were centrifugally consolidated. Despite the favorable conditions for segregation, phase and size segregation did not occur in the highest Al2O3‐platelet content suspension. The suspension properties did not consist of agglomeration, high solids fractions, or high suspension viscosities typically attributed with segregation prevention. Thus, a new mechanism is suggested, considering the effects of hydrodynamic particle interactions (interference drag or “drafting”) on particle arrangement during consolidation. Particle drafting is proposed and supported as a mechanism for preventing segregation, and the importance of hydrodynamic particle interactions in ceramic processing is discussed.
Microcracking in B4C‐TiB2 Composites
Authors: Sigl Lorenz S. , Kleebe Hans‐Joachim
Published: July 2005

Boron carbide/titanium diboride composites with 20 and 40 vol% particulate TiB2 and various amounts of free carbon were investigated with respect to microcrack toughening. In agreement with previous work, the mere addition of TiB2 was found to raise the toughness from 2.2 MPa·m1/2 up to 3.0 and 3.5 MPa·m1/2, respectively. A further and very significant increase of composite toughness up to 6.0 MPa·m1/2 was discovered upon the incorporation of free carbon. SEM and TEM observations reveal that this toughening is associated with microcracking at B4C‐TiB2 phase boundaries. Microcracking is triggered by thin carbon interlayers, which are located at hetero interfaces and supply a weak fracture path.
Phase Transition of Rare‐Earth Aluminates (RE4Al2O9) and Rare‐Earth Gallates (RE4Ga2O9)
Authors: Yamane Hisanori , Ogawara Kazuhiro , Omori Mamoru , Hirai Toshio
Published: July 2005

Lattice parameters of RE4Al2O9(RE = Y, Sin, Eu, Gd, Tb, Dy, Ho, Er, Tm, and Yb) prepared at 1600–1800°C and those of RE4Ga2O9(RE = La, Pr, Nd, Sm, Eu, and Gd) prepared at 1400–1600°C were refined by Rietveld analysis for the X‐ray powder diffraction patterns. The parameters increased linearly with the ionic radius of the trivalent rare‐earth elements (rRE). High‐temperature differential calorimetry and dilatometry revealed that both RE4Al2O, and RE4Ga2O, have reversible phase transitions with volume shrinkages of 0.5–0.7% on heating and thermal hystereses. The transition temperatures (7tr) decreased from 1300°C (Yb) to 1044°C (Sm) for RE4A12O9, except for Y4Al2O9(Ttr= 1377°C), and from 1417°C (Gd) to 1271°C (La) for RE4Ga2O, with increasing ionic radius of the rare‐earth elements. These transition temperatures were plotted on a curve against the ionic radius ratio of Al3+or Gd3+and RE3+(rA1Ga/rRE) except for Y4Al2O9.
Effect of the Atomic Ratio of Ba to Ti on Optical Properties of Gold‐Dispersed BaTiO3 Thin Films
Authors: Mori Masami , Kineri Tohru , Kadono Kohei , Sakaguchi Toru , Miya Masaru , Wakabayashi Hajimu , Tsuchiya Toshio
Published: July 2005

Gold‐dispersed BaTiO, thin films were prepared by the rf magnetron sputtering method. The atomic ratio of Ba to Ti in the films was varied and the effects on the linear and nonlinear optical properties were investigated. As the atomic ratio increased, the value of χ(3)/α532 for the gold‐dispersed BaTiO3 thin films slightly increased. It was found that the increase in the value of χ(3)/α532 is due mainly to a change in the crystalline state of the BaTiO3 matrix. However, it was also found that the atomic ratio had a smaller effect on the value of χ(3)/α532 than did the refractive index of the matrix.
Chemical Interaction between Silicon Nitride and Titanium Carbide Powder
Authors: Yeh Chih‐Hung , Hon Min‐Hsiung
Published: July 2005

Chemical interaction within the system Si3N4‐TiC was investigated in the present study by using thermodynamic calculations and kinetic analyses. The thermodynamic stabilities of such Si3N4‐TiC composites as Si3N4‐TiN‐C and Si3N4‐Ti(C,N)‐C, and SiC‐Ti(C,N) stability regions were defined and related to temperature and nitrogen partial pressures. Kinetic analyses were performed by constructing a relative weight‐loss analysis of various Si3N4:TiC molar ratios reacted at temperatures from 1300° to 1750°C in an argon atmosphere. The reaction rates increased with the decreases in the Si3N4:TiC ratio and with increases in temperature. The reaction products consisted mainly of SiC and Ti(C,N) phases. The overall chemical interaction observed in the present study is attributable to chemical reactions between Si3N4 and TiC and to the diffusion of carbon and nitrogen through the reaction layer after a dense reaction product layer had covered the titanium carbide.
Characterization of Optical Thin Films by Spectroscopic Ellipsometry
Authors: Trolier‐McKinstry Susan , Chindaudom Pong , Vedam Kuppuswami , Hiremath Basavaraj V.
Published: July 2005

Spectroscopic ellipsometry was used to rapidly and nonde‐ structively characterize ion‐plated SiO2 and Ta2O5 films on glass substrates as a function of temperature. The analysis provided the density (as a function of depth) and optical properties of the films. The SiO2 film had a higher refractive index than is typical for thermally grown SiO2. This was attributed to compaction of the film during the deposition process. Similarly, the ion‐plated Ta2O5 film had the high refractive index characteristic of a high‐density film. The films were not affected strongly by temperature during heating >100°C.
Microstructural Evolution during Pressureless Sintering of Lead Lanthanum Zirconate Titanate Ceramics with Excess Lead(II) Oxide
Authors: Akbas Mehmet A. , McCoy Michael A. , Lee William E.
Published: July 2005

The early stages of sintering of lead lanthanum zirconate titanate (PLZT) 9/65/35† ceramics prepared with 10 wt% excess PbO were monitored by quenching uniaxially pressed pellets after a variety of heat treatments. TEM revealed a PbO‐rich amorphous film covering the particle surfaces and interparticle porosity in pellets quenched after 5 min at 1125° to 1180°C. This amorphous phase is indicative of the presence of a high‐temperature liquid phase with composition approximately Pb0.87Zr0.15Ti0.04O1.19. The liquid composition moves toward the PbO‐TiO2 eutectic as sintering progresses. After 10 to 30 min at 1180°C, the liquid composition was approximately Pb0.9Zr0.04Yi0.06Ol.1 and crystallized on quenching. High densities of dislocations with b̄= 1/2〈110〉 and low‐angle boundaries were observed in samples quenched from 1180°C after 10 to 30 min. Mechanisms for the formation of these dislocations are suggested.
Processing of 1‐3 Piezoelectric Ceramic/Polymer Composites
Authors: Janas Victor F. , McNulty Thomas F. , Walker Francis R. , Schaeffer Robert E , Safari Ahmad
Published: July 2005

Several methods of forming fine‐scale 1–3 piezoelectric ceramic/polymer composites for possible transducer applications were demonstrated. These methods include tape casting, honeycomb dicing, and ceramic fiber weaving. In the tape casting technique, laminated structures were formed using thin PZT tapes. The tapes were stacked, with spacers separating the layers, and the stack embedded in polymer. Dicing the stack resulted in a composite with 1–3 connectivity. The thin tape technique can be used to develop composites with ceramic or polymer volume fraction gradients and multifunctional ceramics. Dicing of PZT honeycombs yields 1–3 composites with uniquely shaped rods. Shapes included +, T, and L. In the ceramic fiber weaving technique, green PZT fibers were woven through a PZT honeycomb support structure. The structure was fired to sinter the PZT fibers, and embedded with polymer to yield 1–3 composites. All 1–3 composites showed high and uniform piezoelectric coefficients across the electroded area.
Nucleation and Growth of Diamond Films on Ni‐Cemented Tungsten Carbide: II, Effects of Deposition Conditions
Authors: Polini Riccardo , Marcheselli Giancarlo , Mattei Giorgio , Traversa Enrico
Published: July 2005

Diamond films were deposited by hot‐filament chemical vapor deposition (HFCVD) on substrates made of WC sintered with 6 wt% of Ni. The as‐ground substrates were scratched with diamond powder (S samples) or scratched and wet‐etched (SE samples). Diamond synthesis was carried out at substrate temperatures ranging between 600° and 1050°C, and using 1.0% or 2.0% CH4 in H2. The diamond nucleation density, as measured by scanning electron microscopy (SEM) and automatic image analysis (AIA), did not significantly change in the 600°‐900°C temperature range, while at substrate temperatures higher than 900°C a steep decrease of the density of nuclei was observed and attributed to the thermal annealing of nucleation sites. The activation energy of the growth process was measured and found to be 21 ± 2 kcal/mol. Neither nucleation density nor growth rate were affected by an increase of CH4 concentration in the feed gas, while a lack of crystallinity was observed at the higher methane concentration. Raman analysis showed that phase purity of the films was affected mainly by the substrate temperature: the lower the temperature, the better the film quality. The presence of Ni on the substrate surface did not induce the preferential formation of non‐diamond carbon phases, as confirmed by comparing the Raman spectra obtained from both S and SE substrates. As a comparison, continuous films were deposited on scratched WC‐5 wt% Co substrates under the same experimental conditions. The results indicated that the use of Ni as a binder is preferable to Co.
Effects of Postdeposition Treatments on the Mechanical Properties of a Chemical‐Vapor‐Deposited Silicon Carbide
Authors: Wang Hongyu , Singh Raj N. , Goela Jitendra S.
Published: July 2005

The influence of different postdeposition treatments such as water quench and thermal heating in air, nitrogen, and vacuum on mechanical properties of chemical‐vapor‐deposited (CVD) silicon carbide was investigated. The results showed that these postdeposition treatments increased the flexural strength by as much as 60% but did not significantly change other properties such as hardness and fracture toughness. The strength increase was achieved by treatments performed in both the oxidizing and nonoxidizing environments. Compressive residual stresses in CVD SiC increased because of these treatments, but this increase was not large enough to explain fully the observed increase in the flexural strength. It is proposed that these thermal treatments led to strength increase via healing of surface machining flaws. Thermal treatments in nonoxodizing environments reduced or blunted the flaws through the rearrangement of atoms and restoration of damaged crystal structure in SiC, while in oxidizing environments, passive oxidation may have served as an additional flaw healing mechanism.
Effect of Microstructure on Material‐Removal Mechanisms and Damage Tolerance in Abrasive Machining of Silicon Carbide
Authors: Xu Hockin H. K. , Padture Nitin P. , Jahanmir Said
Published: July 2005

Effects of microstructural heterogeneity on material‐removal mechanisms and damage‐formation processes in the abrasive machining of silicon carbide are investigated. It is shown that the process of material removal in a conventional silicon carbide material with equiaxed‐grain micro‐structure and strong grain boundaries consists of the formation and propagation of transgranular cracks which results in macroscopic chipping. However, in a silicon carbide material, containing 20 vol% yttrium aluminum garnet (YAG) second phase, with elongated‐grain micro‐structure and weak grain boundaries, intergranular micro‐cracks are formed at the interphase boundaries, leading to dislodgment of individual grains. These different mechanisms of material‐removal affect the nature of machining‐induced damage. While in the conventional silicon carbide material the machining damage consists of transgranular median/radial cracks, in the heterogeneous silicon carbide material, abrasive machining produces interfacial micro‐cracks distributed within a thin surface layer. These two distinct types of machining damage result in a different strength response in the two forms of silicon carbide materials. In the case of the conventional silicon carbide, grinding damage results in a dramatic decrease in strength relative to the as‐polished specimens. In contrast, the ground heterogeneous silicon carbide specimens show no strength loss at all.
Hydrothermal Synthesis of Manganese Zinc Ferrites
Authors: Rozman Marko , Drofenik Miha
Published: July 2005

Hydrothermal synthesis has been used to synthesize nano‐sized manganese zinc ferrite powder. The results show that the pH value of the starting suspension has a decisive influence on the composition of the hydrothermally prepared manganese zinc ferrite powder. At a pH value of ∼8.5, stoichiometric amounts of manganese and zinc can be incorporated in the manganese zinc ferrite. The grain size of the powder increases with the temperature and time of hydrothermal treatment. The nanosized manganese zinc ferrite produced is superparamagnetic and becomes ferri‐magnetic after the ferrite grains become larger than ∼100 nm. The nanosized ferrite grains are very prone to oxidation and disintegrate at 600°C in air. The surfaces of the synthesized ferrite grains are covered with a thin film of water.
Kinetics Model for the Growth of Silicon Carbide by the Reaction of Liquid Silicon with Carbon
Authors: Zhou Hong , Singh Raj N.
Published: July 2005

The kinetics and mechanism of reaction of glassy carbon with a pure silicon melt or a Si + Mo melt were investigated. The results showed that the growth of a continuous reaction‐formed SiC layer followed a fourth‐power rate law in the temperature range of 1430° to 1510°C. A model that could explain the fourth‐power rate law was developed. In this model, an internal electric field was assumed to be set up over the reaction‐formed SiC layer through a negative space charge, and then the diffusion of the carbon‐ion vacancies across this layer, driven predominately by this electric field, was considered as the rate‐limiting step for the SiC growth. Neither an increase in the processing temperature nor an addition of 10 wt% Mo into the silicon melt had a significant influence on the reaction kinetics. X‐ray diffraction analysis revealed that the reaction products were β‐SiC, and β‐SiC + MoSi2 for the Si‐C and Si‐C‐Mo reactions, respectively.
Effect of Texture on the Rate of Hydroxyapatite Formation on Gel‐Silica Surface
Authors: Pereira Marivalda M. , Clark Arthur E. , Hench Larry L.
Published: July 2005

An apatite layer can be formed on pure gel‐silica soaked in simulated body fluid. The rate of formation depends on solution parameters and sintering temperature of the gelsilica. In this study, the effect of the texture of the gel‐silica on the rate of hydroxyapatite formation was investigated. The apatite formation was monitored by means of Fourier‐transform infrared reflection spectroscopy as well as by the measurement of changes in the ion concentration of the fluid. The induction time for apatite nucleation on the gel silica decreased as pore size and pore volume increased. The substrate parameters that affect nucleation are discussed and a mechanism that assumes pores as nucleation sites for hydroxyapatite is proposed.
Grain Growth of ZnO in ZnO‐Bl2O3 Ceramics with Ai2O3 Additions
Authors: Nunes Silvia Irene , Bradt Richard C.
Published: July 2005

Grain growth of ZnO during liquid‐phase sintering of a ZnO‐6 wt% Bi2O3 ceramic was investigated for A12O3 additions from 0.10 to 0.80 wt%. Sintering in air for 0.5 to 4 h at 900° to 1400°C was studied. The AI2O3 reacted with the ZnO to form ZnAl2O4 spinel, which reduced the rate of ZnO grain growth. The ZnO grain‐growth exponent was determined to be 4 and the activation energy for ZnO grain growth was estimated to be 400 kJ/mol. These values were compared with the activation parameters for ZnO grain growth in other ceramic systems. It was confirmed that the reduced ZnO grain growth was a result of ZnAl2O4 spinel particles pinning the ZnO grain boundaries and reducing their mobility, which explained the grain‐growth exponent of 4. It was concluded that the 400 kJ/mol activation energy was related to the transport of the ZnAl2O4 spinel particles, most probably controlled by the diffusion of O2‐ in the ZnAl2O4 spinel structure.
Processing of Laminated Barium Titanate Structures for Stress‐Sensing Applications
Authors: Capurso Joseph S. , Alles Aldo B. , Schulze Walter A.
Published: July 2005

High‐purity, chemically prepared barium titanate was doped with 0.3 at.% lanthanum and, in some cases, counterdoped with 0.04 at.% manganese by precipitation. Using standard techniques, tape‐cast sheets of the positive temperature coefficient of resistance (PTCR) compositions as well as the base insulating powder were made. A multilayer sensor was laminated and sintered, with upper and lower PTCR regions separated by an insulating BaTiO3 region. The sensor was loaded using a four‐point bend test configuration. The change in resistivity with increased load was observed to be linear, with positive and negative piezo‐resistive coefficients for the PTCR layers under compression and tension, respectively. These trends were in general agreement with a stress‐dependent permittivity and the Heywang model of grain‐boundary potential barriers. Piezoresistivity values were derived from the resistivity‐stress slope; these were examined as a function of temperature and sensor geometry.
Structural Studies of Ordering in the (Pb1‐xBax)(Mg1/3Nb2/3)O3 Crystalline Solution Series
Authors: Viehland Dwight , Kim Nam , Xu Z. , Payne David A.
Published: July 2005

The ordered structures of the (Pb1‐xBax)(Mg1/3Nb2/3)O3crystalline solution series were investigated by selected area electron diffraction (SAED) and high‐resolution electron microscopy (HREM). At low Ba contents (e.g., x <0.40), the ordered structure was found to be isostructural with Pb(Mg1/3Nb2/3)O3, with a doubled unit cell characterized by 1/3{111} superlattice reflections. At higher Ba contents (e.g., x >0.60), the ordered structure was characterized by 1/3{111} superlattice reflections. For intermediate Ba contents (e.g., x ‐0.60), diffuse scattering along the {111} between diffuse 1/2{111} and 1/3{111} reflections was observed. The ordering is attributed to the distribution of the B‐site cations between multiple sublattices. Strong fluctuations in the B‐site cation ratio between ordered and disordered regions are believed not to exist; however, the possibility of weak fluctuations is consistent with the observed lattice images.
Volatile Metal Oxide Evaporation during Aerosol Decomposition
Authors: Xiong Yun , Lyons Shirley W , Kodas Toivo T. , Pratsinis Sotiris E.
Published: July 2005

The role of particle evaporation during synthesis of volatile metal oxide powders (Bi2O3, MoO3, PbO, and V2O5) by aerosol decomposition (spray pyrolysis) in a heated flow reactor was investigated. Solid particles (0.1–0.6 (Am) of predominantly β‐Bi2O3 were formed with smooth spherical shape at all reactor temperatures (673–1173 K) employed. Solid MoO3 particles (0.1–1.2 μm) produced at low temperatures (673–773 K) had a roughly spherical or faceted morphology and at high temperatures (873 K) had a platelike or layered structure. Solid V2O5 particles produced at low temperatures (573–673 K) were spherical and at high temperatures (973–1073 K) were platelike. The PbO particles were solid and spherical for all temperatures studied (773°–1073°C). Evaporative losses of up to 100% to the reactor walls were observed for all the metal oxides, due to their substantial vapor pressures. The evaporative losses were modeled by considering simultaneous particle evaporation and mass transfer of the metal oxide vapor to the reactor walls. The calculations indicated that, for most of these volatile metal oxides, evaporative losses were limited by diffusional transport of the vapor to the reactor walls and that evaporative losses occur when the vapor pressure of the oxides in the reactor is above 10‐5‐10‐3 mm Hg.
Generalized Fluid Flow Model for Ceramic Tape Casting
Authors: Pitchumani Rangarajan , Karbhari Vistasp M.
Published: July 2005

The fluid mechanics associated with the flow of a ceramic slurry during the tape casting process is analyzed in this paper. The rheology of the slurry is described in generalized terms using the Ostwald‐de Waele power‐law equation, T = m|γ|′, where the yield constant, m, and the shear rate exponent, n, are empirical functions of the particle loading in the slurry, the particle shape and size distributions in the slurry, and the slurry temperature. The effects of an imposed pressure gradient due to the height of the slurry in the casting head, as well as those of the drag due to the moving substrate on the slurry flow, are accounted for by modeling the slurry discharge as a generalized planar Couette flow. The model yields an analytical expression for the tape thickness as a function of various slurry and process parameters. The influence of the physical parameters of the slurry and the geometrical dimensions of the casting head on the tape thickness are examined in the context of a commonly used BaTiO, system. It is shown that the various parametric effects may be represented concisely in the form of a nondimensional design plot employing (a) a flow parameter, α, (b) a shrinkage parameter, β, and (c) the rheology exponent, n.
Stability of Bi2Sr2Ca1Cu2O8 ±δ Thick Films at Elevated Oxygen Pressures and Temperatures
Authors: Chmielewski David H. , Sandhage Kenneth H.
Published: July 2005

Bi2Sr2Ca2Cu2O8±δ‐type compound thick films were exposed to oxygen‐argon‐gas mixtures (1% to 20% oxygen gas) at elevated pressures (up to 207 MPa) and temperatures (500° to 940°C) for times ranging from 5 to 96 h. At a sufficiently high oxygen fugacity and temperature, Bi2Sr2Ca1Cu2O8±δ decomposed via a solid‐state reaction. Room‐temperature X‐ray diffractometry and electron probe microanalysis of decomposed films revealed the presence of Bi2(Sr,Ca)2‐Cu1O6±θ ro‐type compound, Bi2Sr2,Ca1O8±δ‐type compound, and CuO. Bi2Sr2Ca1Cu2O8±δ decomposition was accompanied by a modest weight gain, which was consistent with an oxidation reaction. The solid‐state decomposition reaction could be reversed by heat treatment of decomposed films at 860°C in pure, flowing oxygen at ambient pressure.
Effect of High‐Temperature, High‐Oxygen‐Fugacity Annealing on the Stability of the (Bi,Pb)2Sr2Ca2Cu3O10 ±δ‐type Compound
Authors: Allemeh Seyed M. , Sandhage Kenneth H.
Published: July 2005

The stability of the (Bi,Pb)2Sr2Ca2Cu3O10±δ‐type compound has been evaluated under conditions of elevated temperature (500°‐860°C) and elevated oxygen fugacity (i.e., in O2/Ar gas mixtures containing ≤120% O2, at total pressures of 5207 MPa). At sufficiently high oxygen fugacities and temperatures, the (Bi,Pb)2Sr2Ca2Cu3O10±δ‐type compound transformed into a mixture of a strontium‐rich (Bi,Pb)1‐(Sr,Ca,Cu)2Oy‐type compound, a calcium‐rich (Bi,Pb)2‐(Sr,Ca,Cu)2Oy‐type compound, CuO, and a small amount of (Sr,Ca)O. The decomposition of the (Bi,Pb)2Sr2Ca2‐Cu3O10±δ‐type compound was accompanied by a 2%‐3% weight gain, which was consistent with an oxidation reaction. The conditions of oxygen fugacity and temperature leading to decomposition, and the resulting decomposition products, are compared for the (Bi,Pb)2Sr2Ca2Cu2O10±δ‐type and Bi2Sr2Ca1Cu2O8±Ψ‐type compounds.
Crystallization and Seeding Effect in BaAl2Si2O8 Gels
Authors: Liu Chunling , Komarneni Sridhar , Roy Rustum
Published: July 2005

Two sol‐gel routes have been used to prepare celsian (BaAl2Si2O8) precursors. The crystallization behaviors of unseeded gels and the gels seeded with 5 wt% feldspar, rutile, LiAISi2O2, and ZrO2 crystals as well as SrAl2Si2O8 gel have been studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), and thermal gravimetric and differential thermal analyses (TGA and DTA). It was found that metastable hexacelsian, rather than the preferred monoclinic celsian, was the major crystallization product in the two unseeded gels. Seeding largely enhanced the crystallization of monoclinic celsian, but the mechanisms involved were different for seeding with different crystals. SrAl2Si2O8 gel and ZrO2 crystals acted as normal heterogeneous centers and had little catalytic effect on monoclinic celsian crystallization. Feldspar and rutile crystals worked as epitaxial substrates for monoclinic celsian and produced pure monoclinic celsian in some temperature regions. LiAISi3O8 seeds lowered the glass transition temperature of the immediately adjacent gel matrix and led to the crystallization of pure monoclinic celsian.
Dependence of Compaction Efficiency in Dry Pressing on the Particle Size Distribution
Authors: Zheng Jingmin , Carlson William B. , Reed James S.
Published: July 2005

The compact densification with pressing pressure (compaction efficiency) was determined to be sensitive to the particle size distribution. For the three types of alumina powders used in this research, the compaction efficiency increased with increasing particle size. It has been demonstrated that if the compact density versus log (pressure) has a linear relationship for any two types of powders, so do the blends of the two powders. A model is proposed which can predict the compaction efficiency of a binary particle system based on the Furnas particle packing model and consider the packing efficiency as a function of forming pressure. The composition of the binary mixture at which the highest density is obtained under high pressures is also the composition having the largest compaction efficiency. When coarse particles were added to this composition, the compaction efficiency slowly decreased, and when fine particles were added, the compaction efficiency rapidly decreased. For a continuous particle size distribution, the highest compaction efficiency is related to the average value of ‐log (porefraction).
Preparation of Zirconium Boride Powder
Authors: Zhao Hong , He Yu , Jin Zongzhe
Published: July 2005

An intermediate reaction in the synthesis of ZrB2 powder by the reduction of ZrO2 with B4C and carbon was confirmed through both thermodynamical calculation and experimental results. Because the intermediate product B2O3 was volatile, excess boron should be added to compensate for the boron loss in order to prepare high‐purity ZrB2 powder. The synthesis temperatures of the intermediate reaction and carbothermic reduction were, respectively, about 1400 and 1600°C, obtained by experiments. The influence of processing temperature and time on the purity and the particle size of ZrB2 powder was also investigated.
Shrinkage of Large Isolated Pores during Hot Isostatic Pressing of Presintered Alumina Ceramics
Authors: Oh Kyung‐Sik , Kim Doh‐Yeon , Cho Seong‐Jai
Published: July 2005

The shrinkage process of large pores during hot isostatic pressing (HIP) of presintered Al2O3 and Al2O3‐ZrO2 ceramics has been investigated. Large pores were observed to collapse by grain‐boundary sliding, and then small pores resulting from the misfit of flowed grains disappeared, mainly by diffusion. Due to the high resistance to grain‐boundary sliding, the pores in the Al2O3‐ZrO2 ceramics were hard to eliminate.
Acoustic Emission and Microcracking in Sapphire, Sintered Al2O3, Al/Al2O3 Composite, and Aluminum
Authors: Breval Else , Srikanth Varanasi , Subbarao Eleswarapu C.
Published: July 2005

A range of materials with brittle to ductile behavior (single‐crystal and polycrystalline alumina, aluminum/alumina composite, and metallic aluminum) were investigated by acoustic emission (AE) methods for microcracking during hardness indentations or cooling from elevated temperatures (800°C). During indentation, the extent of crack formation (and the AE counts) decreased in the following order: sapphire, sintered alumina, aluminum/alumina composite with no microcracking in metallic aluminum. During cooling from 800°C, polycrystalline alumina exhibited more extensive microcracking than the aluminum/alumina composite, suggesting that the metallic phase in the aluminum/alumina composite absorbs stresses more than the glassy boundary phase in sintered alumina.
Synthesis of Nd3+,Cr3+‐codoped YAG Ceramics for High‐Efficiency Solid‐State Lasers
Authors: Ikesue Akio , Kamata Kiichiro , Yoshida Kunio
Published: July 2005

Nd,Cr‐codoped transparent YAG (Y3Al5O12) ceramics with excellent optical properties were fabricated by a solid‐state reaction method using Al2O3, Y2O3, Nd2O3, and Cr2O3 powders of 99.99 wt% purity. The mixed powder compacts were sintered at 1750°C for 20 h under vacuum and annealed at 1400°C for 20 h in an oxygen atmosphere. The Nd,Crcodoped YAG ceramics consisted of grain sizes ranging from 5 to 35 μm and exhibited a pore‐free structure. The optical transmittance of a 0.8 at.% Nd,0.4 at.% Cr: YAG ceramic at 1000 nm was nearly equivalent to that of a 0.8 at.% Nd: YAG single crystal. In addition, the fluorescence intensity of the 0.8 at.% Nd,0.4 at.% Cr: YAG ceramic excited by a xenon lamp was double that of the 0.8 at.% Nd:YAG single crystal.
Growth of Highly Oriented TlBa2Ca2Cu3O9—y Superconducting Films on Ag Substrates Using a Dip‐Coated Barium Calcium Copper Oxide Sol—Gel Precursor
Authors: Paranthaman Mariappan , Beach David B.
Published: July 2005

Thin films of BazCa2Cu3O7 a precursor of TIBa2, Ca2‐Cu3O9‐y, were prepared by sol‐gel synthesis from an all alkoxide solution. The barium and calcium precursors were the respective metals reacted with 2‐methoxyethanol, and the copper precursor was copper methoxide complexed by triethanolamine. Silver substrates were coated using the sol‐gel solution by dip‐coating. Subsequent processing included a low‐temperature drying step (600°C), repeated coating to provide the desired thickness, heat treatment at 850°C in oxygen to remove carbon, and reaction at 860°C in a two‐zone thallination furnace to produce a TIBa2Ca2‐Cu3O9‐y, superconducting film. These films were strongly c‐axis‐aligned, had a zero‐resistance temperature (T2) of 110 K, and a critical‐current density (Jc) of 1.9 × 104 A/cmZ at 77 K and zero magnetic field.
Computer Simulation of the Dynamics of 180° Ferroelectric Domains
Authors: Yang Wei , Chen Long‐Qing
Published: July 2005

A computer simulation technique based on the time‐ dependent Ginzburg‐Landau (TDGL) equations formulated in the reciprocal space was proposed for modeling the dynamics of ferroelectric domain formation and domainwall motion. The temporal evolution of domain structures with 180° domain walls in a quenched paraelectric phase was studied. Both the long‐range electric dipole‐dipole interaction energy and the total domain wall energy for any arbitrary distributions of ferroelectric domains were evaluated in the reciprocal space. The effect of free surfaces on the polarization and domain morphologies was discussed. The domain‐wall motion under an electric field was investigated.
Grain Boundary Diffusion of Oxygen in Alumina Ceramics
Authors: Sakaguchi Isao , Srikanth Varanasi , Ikegami Takayasu , Haneda Hajime
Published: July 2005

The volume and grain boundary diffusion coefficients (Dv and δDgb) of oxygen at 1673 K in pure and Mg‐doped alumina were studied by using a resistive anode encoder of SIMS. The effect of Mg‐doping on Dv, was observed clearly. The differences on δDgb in pure and Mg‐doped alumina were about 3 orders and 1 order of magnitude, respectively. The Mg‐doping in alumina is useful for homogenizing grain boundary diffusion.
Titanium Zirconate Thick Films on Rutile Substrates by Reactive Coating of Zircon
Authors: Steier Hanns P. , Pena Pilar , Moya Jose S.
Published: July 2005

A mechanically stable thick layer (∼SO pm) of ZrTiO4 on a rutile substrate has been obtained at 1600°C by reactive coating of zircon. This layer is constituted by ZrTiO, grains of ∼10 μm average size embedded in a silica‐rich glassy matrix. The results are discussed in terms of the ZrO2‐SOi2‐TiO2, equilibrium diagram.
Organic Acid Adsorption on Lead Titanate Surfaces
Authors: Hirakata Keigo , Rhine Wendell E. , Cima Michael J.
Published: July 2005

Several carboxylic acids were adsorbed on the surface of lead titanate. The total amount of adsorbed acid was determined and characterized by diffuse reflectance infrared Fourier transmission spectroscopy (DRIFTS). The acids were found to be chemisorbed on the lead titanate surface by a metal carboxylate bond. This bond forms by reaction between surface hydroxyls and the organic acid functional group. The amount of adsorbed species per unit surface area varied with each carboxylic acid studied and generally correlated with the size of the individual molecules. The experiments also demonstrate an application of a sensitive method for carbon analysis, oxygen‐based coulombic titration.
Alkali Magnesium/Zinc Silicate Glasses with Low Rayleigh Scattering
Authors: Todoroki Shin‐ichi , Sakaguchi Shigeki
Published: July 2005

The Rayleigh scattering of silicate glasses (M2O‐RO‐SiO2, M: Na and K, R: Mg, Ca, and Zn) was measured. Soda magnesium silicate (NMS) glasses exhibited the smallest scattering intensity. It is comparable with that of soda aluminosilicate (NAS) glass, one of the candidates for use in fabricating ultralow‐loss fibers. The scattering intensity decreased with decreasing SiO2 content, and NMS glasses with 60 mol% of SiO2 are still stable against crystallization. It is concluded that NMS is a new candidate for ultralowloss fiber use.
Dependence of the Intrinsic Conductivity Minimum of SrTiO3 Ceramics on the Sintering Atmosphere
Authors: Moos Ralf , Härdtl Karl Heinz
Published: July 2005

A shift of the intrinsic conductivity minimum of strontium titanate ceramics, which depends on the oxygen partial pressure of the sintering atmospheres, was observed. Different hydrogen partial pressures (at constant oxygen partial pressures) did not affect the minimum position. A comparison of the results with defect chemical calculations may explain this behavior as an oxygen partial pressure dependent formation of strontium vacancies showing acceptor character.
Consolidation of Combustion‐Synthesized Titanium Diboride‐Based Materials
Authors: Hoke Darren A. , Meyers Marc A.
Published: July 2005

The quasi‐static consolidation in uniaxial compression of combustion‐synthesized TiB2‐based materials was investigated. Consolidation was carried out in insulated containers upon completion of the combustion reaction, while the porous reaction products were ductile. Since the consolidation is not an isothermal process, the temperature change during consolidation was monitored and recorded. The effect of the addition of metallic elements to the elemental powders was established, and it was found that nickel and chromium provide the best compact integrity. The partial densification is sufficient to show significant differences between the effects of metallic additives. A phenomenological (not based on the micromechanisms of densification) constitutive model was applied to the hot and porous reaction products incorporating the temperature dependence of flow stress. The activation energy for the temperature dependence of the flow stress is established and indicates that, in addition to diffusion‐induced plastic deformation, other processes occur, such as fracturing of ligaments.
Thermal Stresses in Ceramic‐Metal Joints with an Interlayer
Authors: Munz Dietrich , Sckuhr Matthias A. , Yang Yingyuan
Published: July 2005

The stresses near the free edge of the interface in joints of dissimilar materials with an interlayer were analyzed after a change in temperature. The effects of the thickness of the interlayer and of the material properties (elastic constants, thermal expansion coefficients) on the singular stress field are discussed.
Mechanism of Formation of Perovskite Phase and Dielectric Properties of Pb(Zn,Mg)1/3Nb2/3O3 Ceramics Prepared by Columbite Precursor Routes
Authors: Jang Hyun M. , Cho Sung R. , Lee Kyu‐Mann
Published: July 2005

The mechanism of formation of the perovskite phase and the dielectric properties of Pb(Zn,Mg)1/3Nb2/3O3 (PZMN) ceramics were examined using two different types of columbite precursors, (Mg,Zn)Nb2O6 (MZN) and MgNb2O6+ ZnNb2O6 (MN + ZN). The formation of perovskite phase in the PbO + MN + ZN system is characterized by an initial rapid formation of Mg‐rich perovskite phase, followed by a sluggish formation of Zn‐rich perovskite phase. On the other hand, due to the formation of pyrochlore phase of mixed divalent cations Pb2–x(Zn,Mg)yNb2−yO7−x−3y/2, the pyrochlore/perovskite transformation in the PbO + MZN system proceeded uniformly with a spatial homogeneity. Further analysis suggested that the formation of perovskite phase is a diffusion‐controlled process. The degree of diffuseness of the rhombohedral/cubic phase transition (DPT) is higher in the PbO + MN + ZN system than in the PbO + MZN specimen for T > Tmax (temperature of the dielectric permittivity maximum), indicating a broadened compositional distribution of the B‐site cations in the PbO + MN + ZN system.
Al‐B‐C Phase Development and Effects on Mechanical Properties of B4C/Al‐Derived Composites
Authors: Pyzik Aleksander J. , Beaman Donald R.
Published: July 2005

B4C/A1 offers a family of engineering materials in which a range of properties can be developed by postdensiflcation heat treatment. In applications where hardness and high modulus are required, heat treatment above 600°C provides a multiphase ceramic material containing only a small amount of residual metal. Heat treatment between 600° and 700°C produces mainly A1B2; 700° and 900°C results in a mixture of A1B2 and A14BC; 900° and 980°C produces primarily A14BC; and 1000° to 1050°C results in A1B24C4 with small amounts of A14C3 if the heating does not exceed 5 h. Deleterious A14C3 is avoided by processing below 1000°C. All of these phases tend to form large clusters of grains and result in lower strength regardless of which phase forms. Toughness is also reduced; the least determinal phase is A1B2. The highest hardness (88 Rockwell A) and Young's modulus (310 GPa) are obtained in Al4BC‐rich samples. AlB2‐containing samples exhibit lower hardness and Young's modulus but higher fracture toughness. While the modulus, Poisson's ratio, and hardness of multiphase B4C/A1 composites containing 5–10 vol% free metal are comparable to ceramics, the unique advantage of this family of materials is low density (>2.7 g/cm3) and higher than 7 MPa‐m1/2 fracture toughness.
Solid‐state Reactions and Phase Relations in the Ti‐Si‐O System at 1373 K
Authors: Goldstein Joseph I. , Choi Seung K. , Van Loo Frans J. J. , Bastin Guillaume F. , Metselaar Rudi
Published: July 2005

Reactions between Ti and SiO2 were studied at 1373 K (1100°C) under vacuum conditions using planar diffusion couples. A method to correct for the presence of surface oxide was developed which led to improved oxygen measurements with the electron probe microanalyzer. An isothermal section through the Ti‐Si‐O phase diagram at 1373 K was determined using measured diffusion paths and phase compositions in equilibrated alloys. The experimentally determined isothermal section was compared to isothermal sections calculated using thermodynamic data. In addition the sequence of reaction layers formed in the diffusion couples is discussed in terms of thermodynamic activity diagrams.
Early Stages of Crystallite Growth of ZnO Obtained from an Oxalate Precursor
Authors: Auffrédic Jean‐Paul , Boultif All , Langford J. Ian , Louër Daniel
Published: July 2005

A detailed analysis of the microstructure of zinc oxide produced by thermal decomposition of zinc oxalate at temperatures in the range 328° to 650°C is described. Parameters describing the breadth and shape of X‐ray diffraction line profiles were obtained by means of pattern decomposition, and a method based on the Voigt function was used to obtain information on the temperature dependence of the microstructure. It was found that the crystallites are prismatic, the dimensions increasing significantly with formation temperature, and that each contains one stacking fault, on average. The results of size determinations are in broad agreement with TEM and SEM measurements. The specific surface area of the crystallites, obtained by the BET method, is compared with the results of X‐ray diffraction line‐profile analysis, leading to a determination of the variation of “packing factor” with temperature. Results suggest a homogeneous crystallite growth in the initial sintering of the loosely packed zinc oxide powder.
Deposition of Pb(Zr,Ti)O3 Thin Films by Metal‐Organic Chemical Vapor Deposition Using β‐diketonate Precursors at Low Temperatures
Authors: Hwang Cheol Seong , Kim Hyeong Joon
Published: July 2005

Lead zirconate titanate (PZT) thin films were deposited by metal‐organic chemical vapor deposition (MOCVD) using β‐diketonate precursors and 02 at temperatures below 500°C on variously passivated Si substrates. PZT thin films could not be deposited on bare Si substrates, owing to a serious diffusion of Pb into the Si substrate during deposition. Pt/SiO2/Si substrates could partially block the diffusion of Pb, but a direct deposition of PZT thin films on the Pt/SiO2/Si substrates resulted in a very inhomogeneous deposition. A TiO2 buffer layer deposited on Pt/SiO2/Si substrates could partially suppress the diffusion of Pb and produce homogeneous thin films. However, the crystallinity of PZT thin films deposited on the TiO2‐buffered Pt/SiO2/Si substrate was not good enough, and the films showed random growth direction. PZT thin films deposited on the PbTiO3‐buffered Pt/SiO2/Si substrates had good crystallinity and a‐ and c‐axis oriented growth direction. However, the PZT thin film deposited at 350°C showed fine amorphous phases at the grain boundaries, owing to the low chemical reactivities of the constituent elements at that temperature, but they could be crystallized by rapid thermal anneaiing (RTA) at 700°C. PZT thin film deposited on a 1000‐å PbTiO3,‐thin‐film‐buffered Pt/SiO2/Si substrate at 350°C and rapid thermally annealed at 700°C for 6 min showed a single‐phase perovskite structure with a composition near the morphotropic boundary composition.
Pb‐Diffusion Barrier Layers for PbTiO3 Thin Films Deposited on Si Substrates by Metal Organic Chemical Vapor Deposition
Authors: Hwang Cheol Seong , Kim Hyeong Joon
Published: July 2005

The interfaces between metal organic chemical vapor deposited PbTiO3 thin films and various diffusion barrier layers deposited on Si substrates were investigated by transmission electron microscopy. Several diffusion barrier thin films such as polycrystalline TiO2, amorphous TiO2, ZrO2, and TiN were deposited between the PbTiO3 thin film and Si substrate, because the deposition of PbTiO3 thin films on bare Si substrates produced Pb silicate layers at the interface irrespective of the deposition conditions. The TiO2 films were converted to PbTiO3 by their reaction with diffused Pb and O ions during PbTiO3 deposition at a gubstrate temperature of 410°C. Further diffusion of Pb and O induces formation of a Pb silicate layer at the interface. ZrO2 did not seem to react with Pb and O during PbTiO3 deposition at the same temperature, but the Pb and O ions that diffused through the ZrO2 layer formed a Pb silicate layer between the ZrO2 and Si substrate. The TiN films did not seem to react with Pb and O ions during the deposition of PbTiO3 at 410°C, but reacted with PbTiO3 to form a lead‐deficient pyrochlore during postdeposition rapid thermal annealing at 700°C. However, TiN could effectively block the diffusion of Pb and O ions into the Si substrate and the formation of Pb silicate at the interface.
Si MAS‐NMR Study of Hydrated Cement Paste and Mortar Made with and without Silica Fume
Authors: Al‐Dulaijan Salah U. , Al‐Tayyib Abdul‐Hamid J. , Al‐Zahrani Mesfer M. , Parry‐Jones Gwilym , Al‐Mana Abdulaziz I.
Published: July 2005

This paper presents 29Si MAS‐NMR measurements that trace the hydration process in both cement paste and mortar specimens made from ordinary portland cement, Type I, when the cement content is replaced by 0, 10, 15, and 20 wt% of silica fume. The specimens were moist‐cured for 3, 7, 14, 28, 90, and 180 days at a laboratory temperature of 21°C (69.8°F). Compressive strength for all tested specimens was also determined. The results show that the degree of hydration (Q1+ Q2)/(Q°+ Q1+ Q2) increased with increasing content of silica fume, especially at the early ages of 3 to 28 days. In the same manner, compressive strength results were markedly increased up to 14 days and were lowered at later ages, compared to the control mix (0 wt% silica fume).