bluuebunny/crossref_metadata_2025 huggingface dataset:
Relationship between the Average Coordination Number and Properties of Chalconitride Glasses
Authors: Guorong Chen , Jijian Cheng
Published: July 2010

Chalconitride glasses obtained by doping Ge‐As‐Se and Ge‐S chalcogenide glass systems with Si3N4 (0.35 and 0.50 wt%) have been studied; these glasses have been doped with Si3N4 to improve their thermal and mechanical prop‐erties. The glasses have been melted under vacuum in sealed silica ampoules, quenched in air, and subsequently annealed. Measured properties include the transition temperature (Tg), microhardness (Hv), and thermal expansion coefficient (α). The effect of Si3N4 doping is system depen‐dent. The concept of average coordination number () is used to explain this dependence. For the glasses in the chal‐cogen‐rich region, a greater increase in thermal and mechanical properties with Si3N4 doping is assigned to the fact that both the introduction of silicon and the substitution of nitrogen for chalcogens enhance the degree of crosslinking within the substructures. However, for the glasses in the chalcogen‐deficient region, extra silicon atoms that are in‐troduced with Si3N4 doping are not helpful in further crosslinking the network, because of the deficiency in the bridging chalcogens. A slight increase in Tg with increasing , in the case of chalcogen deficiency, might result from the “wrong‐bond effect,” which provides some additional crosslinking in connections of the networked island sub‐structural units.
Modeling and Fabrication of Fine‐Grain Alumina‐Zirconia Composites Produced from Nanocrystalline Precursors
Authors: Freim John , McKittrick Joanna
Published: July 2010

Fully dense fine‐grained 32.6‐vol%‐zirconia‐toughened alumina composites have been fabricated from nanocrystalline rapidly solidified material. A model considering the thermodynamics of the constrained t‐ZrO2m‐ZrO2 phase transformation was developed for this percolated two‐phase material. This analysis indicated that the grain size at which this phase transformation is thermodynamically favorable was 1.26 µm in a composite that contained 32.6 vol% ZrO2 and was stabilized with 1.50 mol% Y2O3. These results of the model compared favorably with experimental results, showing that grains of this size could be retained after heating to temperatures of as high as 1600°C. The rapidly solidified precursor was ball‐milled into submicrometer powder and centrifugally cast into green specimens that were pressureless sintered to full density at temperatures as low as 1500°C. A composite containing nearly 100%t‐ZrO2 was produced by pressureless sintering at 1500°C and a composite containing 45 vol%t‐ZrO2/55 vol%m‐ZrO2 was obtained by sintering at 1600°C. The resulting two‐phase microstructures contained uniformly distributed, micrometer‐size grains whose sizes are consistent with the facilitation of transformation and microcrack toughening.
Mechanical Behavior and High‐Temperature Performance of a Woven Nicalon™/Si‐N‐C Ceramic‐Matrix Composite
Authors: Lee S. Steven , Zawada Larry P. , Staehler James M. , Folsom Craig A.
Published: July 2010

A modern ceramic‐matrix composite (CMC) has been extensively characterized for a high‐temperature aerospace turbine‐engine application. The CMC system has a silicon‐nitrogen‐carbon (Si‐N‐C) matrix reinforced with Nicalon fibers woven in a balanced eight‐harness satin weave fabric. Tensile tests have demonstrated that this CMC exhibits excellent strength retention up to 1100°C. The room‐temperature fatigue limit was 160 MPa, ∼80% of the room‐temperature tensile strength. The composite reached run‐out conditions under cyclic (105 cycles at 1 Hz) and sustained tension (100 h) conditions at a stress of 110 MPa, which was ∼35 MPa above the proportional limits at temperatures up to 1100°C in air. At stress levels >110 MPa, cyclic loading at 1000°C caused a more severe reduction in life, based on time, compared with sustained tension. Further life degradation was observed in the 1000°C fatigue specimens that were exposed to a salt‐fog environment. This degradation decreased the fatigue life ∼85% at the stress levels that were tested.
Melting Equilibria of the Bi‐Sr‐Ca‐Cu‐O (BSCCO) System in Air: The Primary Crystallization Phase Field of the 2212 Phase and the Effect of Silver Addition
Authors: Wong‐Ng Winnie Kwai , Cook Lawrence P. , Jiang Feng
Published: July 2010

The subsolidus and primary crystallization phase field of the “2212” (Bi:Sr:Ca:Cu) phase in the BSCCO system have been investigated. At 830°C, this phase was observed to be in equilibrium with ten phases. Sixteen four‐phase equilibrium regions that surround the 2212 phase have been identified at this temperature. The melting events as‐sociated with these four‐phase regions were studied with differential thermal analysis, quenching experiments, and wicking experiments, in which samples of the liquid for analysis were absorbed by capillary action. The melt com‐positions were obtained by using quantitative energy‐dis‐persive X‐ray spectrometry. The 2212 phase melts incon‐gruently, beginning at ∼825°C. Its primary crystallization field encompasses a compositional range of 24–42 mol% BiO1.5, 7–33 mol% SrO, 2–27 mol% CaO, and 19–43 mol% CuO. The compositions of melts in equilibrium with the 2212 phase were mostly on the calcium‐deficient side of the 2212 solid solution. An approximate polygonal model of the 2212 primary crystallization field has been presented. The addition of silver depresses the melting temperatures in the vicinity of the 2212 phase, from 4°C to 22°C. Silver entered the melt at a saturation level of 2–8 mol%. In the more copper‐rich liquids, silver replaced some of the copper, which resulted in a shift of the 2212 crystallization field away from the copper oxide corner.
Indentation of Ceramics with Spheres: A Century after Hertz
Authors: Lawn Brian R.
Published: July 2010

In this article we review the nature and mechanics of damage induced in ceramics by spherical indenters, from the classical studies of Hertz over a century ago to the present day. Basic descriptions of continuum elastic and elastic–plastic contact stress fields are first given. Two distinct modes of damage are then identified: Hertzian cone cracks, in relatively hard, homogeneous materials, such as glasses, single crystals, fine‐grain ceramics (tensile, “brittle” mode); and diffuse subsurface damage zones, in relatively tough ceramics with heterogeneous microstructures (shear, “quasi‐plastic” mode). Ceramographic evidence is presented for the two damage types in a broad range of materials, illustrating how an effective brittle–ductile transition can be engineered by coarsening and weakening the grain structure. Continuum analyses for cone fracture and quasi plasticity, using Griffith–Irwin fracture mechanics and yield theory, respectively, are surveyed. Recent micro‐mechanical models of the quasi‐plastic mode are also considered, in terms of grain‐localized “shear faults” with extensile “wing cracks.” The effect of contact‐induced damage on the ensuing strength properties of both brittle and quasi‐plastic ceramics is examined. Whereas cone cracking causes abrupt losses in strength, the effect of quasi‐plastic damage is more gradual—so that more heterogeneous ceramics are more damage tolerant. On the other hand, quasi‐plastic ceramics are subject to accelerated strength losses in extreme cyclic conditions (“contact fatigue”), because of coalescence of attendant microcracks, with implications concerning wear resistance and machinability. Extension of Hertzian contact testing to novel layer structures with hard, brittle outer layers and soft, tough underlayers, designed to impart high toughness while preserving wear resistance, is described.
Grain Growth of Silica‐Added Zirconia Annealed in the Cubic/Tetragonal Two‐Phase Region
Authors: Zhao Jian , Ikuhara Yuichi , Sakuma Taketo
Published: July 2010

The grain growth in silica‐doped 3‐mol%‐yttria‐stabilized tetragonal zirconia polycrystals (SiO2‐doped 3Y‐TZP) and undoped 3Y‐TZP has been examined in the temperature range of 1400°‐1800°C. The presence of a SiO2 phase inhibits rather than promotes the grain growth in 3Y‐TZP, particularly at high temperatures. During the grain growth in 3Y‐TZP, yttrium ions are partitioned between grains, and the grain growth mechanism can be understood from Ostwald ripening dominated by lattice diffusion of cations. In SiO2‐doped 3Y‐TZP, an amorphous SiO2‐rich phase exists only in the grain‐boundary corners or junctions, not in the grain‐boundary faces. The grain growth in SiO2‐doped 3Y‐TZP is controlled by using different mechanisms below and above the eutectic temperature of the zirconia‐silica (ZrO2‐SiO2) system. The glass phase does not have a major role in grain growth below the eutectic temperature, and the grain growth is dominated by a similar mechanism in undoped 3Y‐TZP. The grain growth is more effectively retarded by the presence of a SiO2 phase above the eutectic temperature and is likely to be controlled by a solution‐reprecipitation process in the amorphous phase at the grain‐boundary corners or junctions.
Chemisorption of Organofunctional Silanes on Silicon Nitride for Improved Aqueous Processing
Authors: Colic Miroslav , Franks George , Fisher Matthew , Lange Fred
Published: July 2010

Different chem‐adsorbed silane molecules have been used to produce weakly attractive silicon nitride particle networks for aqueous colloidal processing. Silanes with diamino and poly(ethylene glycol) hydrophilic heads yielded slurries with the lowest viscosity, longest sedimentation stability, and highest packing density. Chem‐adsorbed silane molecules protected silicon nitride and yttrium oxide, a common processing aid, from hydrolysis at pHs between 5.5 and 11. A novel approach was used to produce short‐range repulsive potentials necessary to yield the weakly attractive networks. Addition of salt to dispersed silicon nitride slurries with particles coated with poly(ethylene glycol)‐silane caused the collapse of the 22‐atom‐long chains and residual electrical double layer. This produced a weakly attractive network which persisted during consolidation to yield a plastic body with a flow stress that was dependent on the counterion size. When 0.5M tetramethylammonium chloride was used at pH 10, plastic bodies had a flow stress similar to clay, whereas lithium counterions produced bodies with a much higher flow stress.
Machinable Ceramics Containing Rare‐Earth Phosphates
Authors: Davis Janet B. , Marshall David B. , Housley Robert M. , Morgan Peter E. D.
Published: July 2010

Two‐phase composites consisting of LaPO4 or CePO4 and alumina, mullite, or zirconia were found to be machinable; i.e., they can be cut and drilled using conventional tungsten carbide metal‐working tools. Single‐phase LaPO4 was also machinable. Measurements of drilling rates, grinding rates, and normal forces are used to compare the ease of machining in these materials and in a conventional machinable glass‐ceramic material, and to provide preliminary information on the relation between microstructure and machining properties. In Hertzian contact experiments these materials showed extensive nonlinear behavior associated with a damage zone beneath the contact site, similar to other machinable ceramics. Mechanisms of material removal are discussed.
Low‐Temperature TiO2‐SnO2 Phase Diagram Using the Molten‐Salt Method
Authors: Naidu Hari Prasad , Virkar Anil V.
Published: July 2010

The molten‐salt method has been used for low‐temperature synthesis of ceramic compounds. It has been used in the present work to determine the phase diagram of the TiO2‐SnO2 system down to 400°C, which is not possible by the conventional solid‐state annealing method. LiCl‐KCl eutectic has been used as the molten salt. The experimental procedure consists of annealing powder of the TiO2‐SnO2 solid solution in the molten‐salt eutectic for a sufficient length of time at the temperature of interest. The a and c lattice parameters have been determined for the decomposed phases by X‐ray diffractometry. The phase diagram determined in the present work has been compared with that determined by conventional solid‐state annealing methods. The phase diagram determined in the present work exhibits a wider miscibility gap compared to the gap determined by the solid‐state annealing method. This is attributed to sluggish solid‐state kinetics at lower temperatures. The phase diagram determined in the present work agrees well with a regular solution model, except for a slight deviation in the SnO2‐rich portion of phase diagram above 1200°C. Scanning electron microscopy has been used to study the particle‐growth morphology. The solubility has been estimated from particle‐growth kinetics as well as from the direct‐current plasma technique. The results indicate that a modest solubility is sufficient to enhance the kinetics in the molten salt and, thereby, facilitate the determination of low‐temperature phase equilibria in ceramics.
Thermal, Mechanical, and Chemical Properties of Sintered Xenotime‐Type RPO4 (R = Y, Er, Yb, or Lu)
Authors: Hikichi Yasuo , Ota Toshitaka , Daimon Keiji , Hattori Tomotoshi , Mizuno Masatoshi
Published: July 2010

Xenotime‐type RPO4 (R = Y, Er, Yb, or Lu) powder was dry‐pressed into disks and bars. The disks and bars could be sintered to a relative density of greaterthan equal to98% in air without cracking at 1300° (R = Yb or Lu) or 1500°C (R = Y or Er), depending on the grain size. The linear thermal expansion coefficient (at 1000°C), thermal conductivity (at 20°C), and bending strength (at 20°C) of the xenotime‐type RPO4 ceramics were 6.2 10‐6/°C, 12.02 W(mK)‐1, and 95 ± 29 MPa for R = Y; 6.0 10‐6/°C, 12.01 W(mK)‐1, and 100 ± 21 MPa for R = Er; 6.0 10‐6/°C, 11.71 W(mK)‐1, and 135 ± 34 MPa for R = Yb; and 6.2 10‐6/°C, 11.97 W(mK)‐1, and 155 ± 25 MPa for R = Lu. The xenotime‐type RPO4 ceramics did not react with SiO2, TiO2, Al2O3, ZrO2, or ZrSiO4, even at 1600°C for 3 h in air, and were stable in aqueous solutions of HCl, H2SO4, HNO3, NaOH, and NH4OH at 20°C.
Fracture Toughness, Ionic Conductivity, and Low‐Temperature Phase Stability of Tetragonal Zirconia Codoped with Yttria and Niobium Oxide
Authors: Kim Dae‐Joon , Jung Hyung‐Jin , Jang Joo‐Wung , Lee Hong‐Lim
Published: July 2010

Tetragonal zirconia (t‐ZrO2) solid solutions were prepared with additions of up to 1.5 mol% of niobium oxide (Nb2O5) into 3‐mol%‐yttria‐stabilized t‐ZrO2 (3Y‐TZP). The influence of pentavalent cation doping on fracture toughness, ionic conductivity, and the tetragonal‐to‐monoclinic phase transformation in the temperature range of 120°‐210°C was investigated. Fracture toughness and ionic conductivity increased and decreased, respectively, as the Nb2O5 content increased, which indicated that the annihilation of oxygen vacancies in 3Y‐TZP was responsible for the instability of the t‐ZrO2 lattice. The activation enthalpy related to the conductivity was ~83 kJ/mol, regardless of the dopant content, which was consistent with that for the low‐temperature degradation of 3Y‐TZP doped with Nb2O5. Degradation under an applied electric field occurred only on the specimen surface that was in contact with the anode, which suggests that depletion of the oxygen vacancies led to the degradation. The identical activation enthalpies and the involvement of the vacancy migration in both processes fortified the belief that the low‐temperature degradation of yttria‐stabilized t‐ZrO2 is attributed to oxygen vacancy diffusion.
Structure of Duplex Multilayer Pb(Zr0.53Ti0.47)O3> Films Prepared by Sol‐Gel Processing
Authors: Miyazawa Kun'ichi , Ito Kunio , Mayer Joachim , Rühle Manfred
Published: July 2010

Multilayer PZT films were prepared by sol‐gel processing, and their structure and composition were investigated by cross‐sectional TEM and EDX analyses. The films made by firing at 600°C (as‐deposited films) are composed of alternating porous and dense layers, and the porosity increases by a factor of 2 through heating at 750°C. The pyrochlore phase observed in the as‐deposited films turns to the perovskite phase by the heat treatment at 750°C. The Ti/Zr ratio along the film stacking direction is shown to change with the elevation of heat treatment temperature. The porous soft layers are considered to reduce the thermal stress and prevent the introduction of cracks during the firing process.
Assessment of the Interfacial Properties of Ceramic‐Matrix Composites Using Strain Partition under Load
Authors: Morvan Jean‐Marie , Baste Stéphane
Published: July 2010

The interfacial sliding stress is a key parameter in the global behavior of ceramic‐matrix composites. An ultrasonic characterization, through the complete determination of the stiffness tensor along a tensile test, detects all the damage mechanisms: transverse matrix microcracking and the existence of longitudinal cracks at the fiber/matrix interface. It also allows a strain partition under load. A micromechanical model is established and gives access to the value of the interfacial sliding stress during the entire tensile test, whether the damage occurs at the mesostructural or at the microstructural level of the composite.
Preparation and Characterization of Barium Titanate Electrolytic Capacitors from Porous Titanium Anodes
Authors: Venigalla Sridhar , Chodelka Robert E. , Adair James H.
Published: July 2010

BaTiO3 is widely used as the dielectric in ceramic chip capacitors and multilayer capacitors, because of its high dielectric constant and ferroelectric properties. Multilayer capacitors provide fairly high capacitance per unit volume (volumetric efficiency); however, processing difficulties in the preparation of ultrathin layers limit further enhancement. Tantalum solid electrolytic capacitors, on the other hand, provide very high volumetric efficiencies, because of the large surface area of the sintered, porous tantalum anode on which the dielectric Ta2O5 is electrochemically deposited. Recent developments in electrochemical methods to deposit BaTiO3 on titanium substrates provide an opportunity to fabricate barium titanate electrolytic capacitors using sintered, porous titanium anodes. The high dielectric constant of BaTiO3 and the high surface area of the sintered, porous anode provide a good combination to achieve larger volumetric efficiencies. Current work involves the fabrication and characterization of barium titanate electrolytic capacitors. Effects of electrochemical processing parameters on the formation of BaTiO3 on the surface of sintered titanium anodes are described. Influence of the purity of titanium powder, the porosity of the sintered anode, and the post‐deposition heat treatment on the dielectric properties of the fabricated capacitors is discussed. Complete penetration of the electrolyte solution and a thin uniform coating of TaTiO3 over the entire titanium surface was achieved using high‐porosity (35%‐40% of theoretical density) sintered titanium anodes. Samples treated for 8 h in 0.5M Ba(OH)28H2O electrolyte solutions at 100°C with an applied cell voltage of 12 V show the formation of a dense, uniform BaTiO3 coating on the surface of the titanium anode. High‐purity, chloride‐free titanium powder provides smaller dissipation factors at low frequencies. Heat treatment at 400°C significantly increases the capacitance at all frequencies, whereas the heat treatment lowers the dissipation factors at low frequencies. Calculated volumetric efficiencies are comparable to those typically obtained for tantalum solid electrolytic capacitors but are not as high as expected for barium titanate electrolytic capacitors. Penetration of the colloidal‐carbon (external) electrode was limited to a depth of ~300 µm, which might have caused the lower volumetric efficiencies.
Nonuniform Densification during Gas Pressure Sintering of an alpha‐Sialon Ceramic
Authors: Cho Seong‐Jai , Yoon Kyung‐Jin
Published: July 2010

Densification of α‐sialon ceramics during gas pressure intering was investigated experimentally. The densification did not occur uniformly throughout specimen compacts. Instead, it started at the surface and progressed into the interior of the compacts. The kinetics of this unique nonuniform densification was strongly influenced by the applied N2 pressure. The nonuniform densification behavior was attributed to the slow diffusion‐out of N2 gas entrapped in pores.
Coherent Precipitation of Copper Metal in Low‐Temperature‐Fired Ni‐Zn‐Cu Ferrite
Authors: Fujimoto Masayuki , Nishi Yuji , Suzuki Toshimasa , Shigetani Hisashi , Sekiguchi Shoichi
Published: July 2010

Coherent copper‐metal precipitates at grains adjacent to the Σ= 5 coincident‐site lattice (CSL) boundary in a low‐temperature‐fired Ni‐Zn‐Cu ferrite have been observed and analyzed using analytical electron microscopy. This precipitation behavior is related to the copper solubility limits in the Ni‐Zn‐Cu ferrite during cooling after sintering, and preferential solute segregation may be dominant at stacking faults rather than at the Sigma = 5 CSL boundary. Copper‐metal precipitates have a 〈100〉 matrix ∥〈100〉 Cu coherent relationship to the ferrite matrix.
Influence of Deposition Parameters and Substrate on the Quality of Pulsed‐Laser‐Deposited Pb1‐xCaxTiO3 Ferroelectric Films
Authors: Martín María José , Mendiola Jesús , Zaldo Carlos
Published: July 2010

Pb1‐xCaxTiO3 (PCaT) thin films have been prepared by pulsed laser deposition (PLD) on Pt/TiO2/SiO2/(100)Si, (100)MgO, and Pt/(100)MgO substrates. A Pb deficiency with regard to the target composition occurs in films prepared on heated substrates, while the Ca concentration in the film remains congruent with the target composition. The onset temperature for the Pb loss changes from 250°C using nonsintered targets to 450°C if sintered targets are used; moreover, the sintered targets also produce a low particle density on the film surface (0.4 µm−2). Increasing the laser fluence to about 10 J/cm2 improves the crystalline quality of the films. PCaT (x= 0.24) films obtained by PLD on Si‐based substrates have a lattice tetragonality c/a= 1.014, lower than the value obtained in films prepared by other methods. The film tetragonality can be slightly increased to c/a= 1.022 by using MgO substrates and much more efficiently by reducing the Ca concentration, up to reach c/a= 1.048 in Ca free films. The increase of the film tetragonality induces an enhancement of the film orientation with the [001] axis perpendicular to the substrate surface; moreover, the typical values of the spontaneous and remanent polarizations increase up to Pr similar/congruent 34 µCcm−2.
Decomposition of Al2TiO5 and Al2(1‐x)MgxTi(1+x)O5 Ceramics
Authors: Buscaglia Vincenzo , Nanni Paolo
Published: July 2010

The decomposition of Al2(1‐x)MgxTi(1+x)O5 ceramics in air has been studied between 900° and 1175°C for 0 lessthan equal to x lessthan equal to 0.6. The decomposition temperature versus composition x predicted using a thermodynamic model based on the regular solution approach is in satisfactory agreement with the experimental results. The decomposition kinetics has been studied at 1100°C for x= 0, 0.1, and 0.2 and follows a nucleation and growth mechanism. Random nucleation of the reaction products is hindered by the high elastic stresses that result from the molar volume change related to decomposition because of the small chemical driving force available. Decomposition occurs only at a limited number of sites, probably associated with the presence of impurities and/or glassy phase. The decomposition products grow as nodules formed by an Al2O3 (+ MgAl2O4 for x > 0) core and a TiO2 shell. The growth is parabolic for x= 0 and linear for x= 0.1 and 0.2. The rate‐controlling step in the decomposition mechanism of pure Al2TiO5 (x= 0) is the transport of Al3+ ions through the TiO2‐rutile phase.
Elastic Anisotropy of ß‐Silicon Nitride Whiskers
Authors: Hay Jack C. , Sun Ellen Y. , Pharr George M. , Becher Paul F. , Alexander Kathleen B.
Published: July 2010

The elastic anisotropy of ß‐silicon nitride was examined using nanoindentation techniques. A coarse‐grained polycrystalline sample composed of whiskers up to 15 µm in diameter and 100 µm in length allowed for the positioning of small indentations near the centers of grains, where neighboring grains minimally affect the property measurements. The crystallographic directions along which measurements were made were determined from the grain geometries in polished sections. The primary directions of interest were parallel to the c‐axis (indenter penetration parallel to the whisker axis) and in the basal plane (indenter penetration perpendicular to the whisker axis), for which the indentation moduli were found to be 450 and 310 GPa, respectively. An indentation mechanics model used to estimate the single‐crystal elastic constants from the nano‐indentation results shows that Young's moduli for ß‐silicon nitride, which are similar to but not exactly the same as the moduli measured by nanoindentation techniques, vary from 540 GPa parallel to the c‐axis to 280 GPa perpendicular to it. Hardness data, which also exhibit a strong anisotropy, are also presented.
Effect of Crystal Grain Size and Thermal Stress on Martensitic Transformation of Phosphorus‐Bearing Dicalcium Silicates
Authors: Fukuda Koichiro , Iizuka Emi , Taguchi Hiroyuki , Ito Suketoshi
Published: July 2010

A series of P2O5‐bearing Ca2SiO4 solid solutions, (Ca2‐x/2open squarex/2)(Si1‐xPx)O4 with x= 0.02 and 0.06 lessthan equal to 0.11, was prepared. The alpha´L <–> ß martensitic transformation temperatures were determined by high‐temperature XRD for powder specimens with x= 0.02. With decreasing particle size, both Ms and Mf decreased, while both As and Af were almost unchanged. Each transformation temperature was lower than that of pure Ca2SiO4. The phase composition at 25°C for the crystals with 0.075 lessthan equal to x lessthan equal to 0.10 was dependent not only on the x‐value but also on the particle size and the intensity of the thermal stress upon quenching. The effect of the latter two was most clearly recognized in the phase composition of the crystals with x = 0.09. The phase composition was changed between the two extremes; one was composed of 8% alpha´L‐phase and 92%ß‐phase and the other was 96% alpha´L‐phase and 4%ß‐phase. For the crystals with 0.06 lessthan equal to x lessthan equal to 0.065 (ß‐phase) and 0.105 lessthan equal to x lessthan equal to 0.11 (alpha´L‐phase), only the x‐value governed the phase composition.
Compounds and Solid Solutions of Cobalt, Copper Phosphates
Authors: Bamberger Carlos E. , Specht Eliot D. , Anovitz Lawrence M.
Published: July 2010

Cobalt phosphates have been synthesized and their thermal behavior examined. The formation of compounds and solid solutions among cobalt and copper phosphates is studied by X‐ray diffraction. Unlimited solubility exists between the pyrophosphates Co2P2O7 and Cu2P2O7, the orthophosphates Co3(PO4)2 and Cu3(PO4)2, and Co3(PO4)2 and Cu2P2O7. X‐ray diffraction indicates that the structures of cobalt and copper pyrophosphate solid solutions vary gradually from one end member to the other. The structures of orthophosphate solid solutions vary in a more complex manner: the change is gradual from Co3(PO4)2 to Co2Cu(PO4)2. At Co1.5Cu1.5(PO4)2, a new structure (L) occurs. At 950°C, CoCu2(PO4)2 also exhibits this structure, which is similar to that of graftonite, Fe3(PO4)2. CoCu2(PO4)2 is dimorphic, changing reversibly at 1000°C to a triclinic structure (H) related to that of Cu3(PO4)2. From CoCu2(PO4)2 (H) to Cu3(PO4)2, the structure appears to vary gradually. A new phosphate, Cu+Cu2+Co3(PO4)3, has also been synthesized.
Effect of Temperature and Alcohols in the Preparation of Titania Nanoparticles from Alkoxides
Authors: Vorkapic Danijela , Matsoukas Themis
Published: July 2010

We report on the formation of titania (TiO2) colloids via the hydrolysis and condensation of alkoxides under a large excess of water. This process is characterized by a rapid precipitation of large aggregates, followed by a slow peptization (deaggregation) induced by the presence of nitric acid. We find that the hydrolysis temperature and the length of the alkoxy group have a minor effect on the size of the peptized colloid. In contrast, the particle size is sensitive to the peptization temperature and exhibits a minimum at 50|SDC. The presence of alcohols inhibits peptization and results in both larger colloids and longer peptization treatments. The smallest size (~20 nm in diameter) is obtained when no alcohol is added to the reaction mixture. The results suggest that the formation of TiO2 nanoparticles is controlled by colloidal interactions, whereas chemical factors (the rate of hydrolysis and condensation) have a secondary role.
Fine Patterning and Characterization of Gel Films Derived from Methyltriethoxysilane and Tetraethoxysilane
Authors: Matsuda Atsunori , Matsuno Yoshihiro , Tatsumisago Masahiro , Minami Tsutomu
Published: July 2010

Pregrooves of 1.6 µm pitch for optical data storage have been embossed successfully by pressing a stamper against xCH3Si(OC2H5)3(100 ‐ x)Si(OC2H5)4‐derived gel films (60 ≤x≤ 100 mol%) on glass‐disk substrates of 130 mm diameter. When x is <40 mol%, the resultant films are too hard to emboss patterns uniformly. The shrinkage of the patterns is ∼4% for all the films when 60 lessthan equal to x lessthan equal to 100 mol%, even after heat treatment at 350°C, so that the nearly net negative shape of the stamper is preserved. The methyl groups in the films decompose at temperatures from 500° to 600°C.
Preparation of Strontium Titanate Thin Films by the Hydrothermal‐Electrochemical Method in a Solution Flow System
Authors: Suchanek Wojciech L. , Yoshimura Masahiro
Published: July 2010

SrTiO3 thin films have been prepared on titanium substrates using strontium acetate solutions in newly constructed flow‐system equipment by the hydrothermal‐electrochemical method. The synthesis parameters (temperature of 120°‐200°C and flow rate of 1‐40 mL/min) allow fabrication of dense, single‐phase films with grain sizes in the range of 80‐340 nm by controlling nucleation and/or growth rates. The flow can be closed, enabling easy recycling of the solutions used. This processing route may serve as an inexpensive and environmentally friendly way of fabrication of single‐phase SrTiO3 thin films as well as functionally graded ferroelectric materials.
Structural Changes of Scandia‐Doped Zirconia Solid Solutions: Rietveld Analysis and Raman Scattering
Authors: Fujimori Hirotaka , Yashima Masatomo , Kakihana Masato , Yoshimura Masahiro
Published: July 2010

Powder X‐ray diffractometry (XRD) and Raman scattering measurements were used to study the structural changes of compositionally homogeneous metastable ZrO2solid solutions induced by ScO1.5doping. The crystal structures of monoclinic, tetragonal, cubic, and rhombohedral (Sc2Zr7O17, ß‐phase) solid‐solution phases have been refined by using the Rietveld analysis of the XRD data at room temperature of arc‐melted ZrO2‐XScO1.5(X= 0, 2, …, 20, and 22 mol%) samples. The results can be interpreted as indicating that the structures of the monoclinic and tetragonal phases approach those of the tetragonal and cubic phases, respectively, by ScO1.5doping. Raman scattering, as well as XRD, was useful to investigate the phase assemblage. Moreover, we could obtain Raman spectra of the ß‐phase probably for the first time.
Microstructure and Nonlinear Properties of Microwave‐Sintered ZnO‐V2O5 Varistors: II, Effect of Mn3O4 Doping
Authors: Kuo Cheng‐Tzu , Chen Chang‐Shun , Lin I‐Nan
Published: July 2010

The microstructure and nonlinear current‐voltage characteristics of Mn3O4‐doped ZnO‐V2O5 ceramics, microwave‐sintered at 800°‐1200°C for 10 min, have been investigated. A high density (96% of the theoretical density) has been achieved. The incorporation of Mn3O4 additives does not significantly alter the densification behavior of the ZnO‐V2O5 materials, but rather pronouncedly increases the nonlinear coefficient (α= 23.5) and markedly suppresses their leakage current density (JL= 2.4 10‐6 A/cm2). On the other hand, the intrinsic properties of the materials, including the Schottky barrier height (Phib) and the donor density (Nd), are only moderately modified; that is, Phib= 1.16 eV and Nd= 5.4 1017/cm3. X‐ray diffractometry analyses and energy‐dispersive X‐ray microanalyses (via scanning electron microscopy) indicate that the V2O5 species facilitate the densification and the development of microstructure via the formation of a liquid phase (Zn3(VO4)2) along the grain boundaries, whereas the Mn3O4 species markedly enhance the nonohmic behavior of the ZnO‐V2O5 materials by forming the surface states along the grain boundaries.
Effect of CaO Content on the Hot Strength of Alumina‐Spinel Castables in the Temperature Range of 1000° to 1500°C
Authors: Chan Chen‐Feng , Ko Yung‐Chao
Published: July 2010

The modulus of rupture of Al2O3‐spinel castables containing 20 wt% Al2O3‐rich MgO‐Al2O3 spinel and 1.36‐2.04 wt% CaO generally increases with an increase in both CaO content and temperature from 1300° to 1500°C, but it remains virtually constant from 1000° to 1300°C. Microscopic observation of the castable fired at 1500°C for 3 h reveals the growth of some CA6 crystals out of the Al2O3‐rich spinel grains in the bonding matrix of the castable. The bond linkage between the CA6 and spinel grains in the matrix is believed to cause both the CaO content and temperature dependence of the hot strength of the Al2O3‐spinel castables as well as the hot strength enhancement of high‐Al2O3 castables with addition of Al2O3‐rich spinel.
Microwave Synthesis of Yttrium Iron Garnet Powder
Authors: Kimura Teiichi , Takizawa Hirotsugu , Uheda Kyota , Endo Tadashi , Shimada Masahiko
Published: July 2010

A 28 GHz microwave heating method was used to react an Fe2O3+ Y2O3 powder mixture to form yttrium iron garnet (YIG, Y3Fe5O12) powder. The minimum temperature to form YIG was lower than the conventional (external) heating method. YIG began to form after only 70 s of irradiation, which means that the solid‐state reaction proceeded very rapidly. The amounts of byproducts were controlled by the starting composition and by the Y2O3 particle size. The resultant YIG particle size also was controlled by the Y2O3 particle size.
Optical Absorption in Sol‐Gel‐Derived Crystalline Barium Titanium Fine Particles
Authors: Matsuda Hirofumi , Kuwabara Makoto , Yamada Ken‐ichi , Shimooka Hirokazu , Takahashi Seiji
Published: July 2010

Pure, translucent, and highly crystallized barium titanate (BaTiO3) monolithic gels were synthesized via a sol‐gel technique at temperatures down to 90°C by using a high‐concentration solution of barium alkoxide and titanium alkoxide. The gels consisted of fine particles with an average diameter of ~10 nm and showed the X‐ray diffraction patterns of a pseudo‐cubic BaTiO3 system at room temperature; however, in bulk crystal, the tetragonal structure was more stable. The optical transmission spectra of the polycrystalline gels were similar to those for single‐crystalline BaTiO3. From the excitation energy dependence of the absorption‐edge structures, the optical‐gap energies for the gels were estimated to have values that were ~0.1 eV higher than those for the single crystal; these higher optical‐gap energies may be attributed to size effects.
Calcium Hydroxide Crystal Evolution upon Aging of Lime Putty
Authors: Rodriguez‐Navarro Carlos , Hansen Eric , Ginell William S.
Published: July 2010

Aging of lime putty, by storing slaked lime under excess water for extended periods of time, has been recognized for centuries as a means to improve the quality of hydrated lime as a binder in lime‐based mortar and plasters. However, there is limited, and at times contradictory, evidence about the effect of the extended exposure of portlandite (Ca(OH)2) to water. Our data from X‐ray diffraction, nitrogen adsorption, and scanning electron microscopy studies indicate that portlandite crystals undergo both an important size reduction and a significant morphological change, developing submicrometer, platelike crystals upon aging. A model for portlandite evolution is proposed and discussed, based upon (a) differences in solubility between {0001} basal pinacoid faces, and {1010} prism faces, and (b) heterogeneous secondary nucleation of nanometer‐scale platelike portlandite crystals.
Novel Method for Synthesis of Well‐Crystallized Vanadyl(2+) Hydrogen Phosphate Hemihydrate: Crystallization in Organic Media Containing a Small Amount of Water
Authors: Kominami Hiroshi , Matsuo Kentarou , Kera Yoshiya
Published: July 2010

Vanadyl(2+) hydrogen phosphate hemihydrate (VOHPO40.5H2O, VHP) that had high crystallinity and showed a strong (001) peak in its X‐ray diffractometry (XRD) pattern was synthesized via thermal treatment of a mixture of vanadyl(2+) acetylacetonate and triethyl phosphate at 200°C in organic solvents that contained a small amount of water. Scanning electron microscopy observations revealed that the product consisted of thin plates (2‐4 µm wide and <0.5 µm thick). When the reaction was conducted at 250°C, a VHP sample was formed that exhibited stronger XRD peaks and had a plate width of >20 µm. The present VHP sample was topotactically transformed to divanadyl(2+) pyrophosphate, which showed a strong (020) XRD peak, via thermal treatment in a nitrogen atmosphere at 500°C.
Interaction of BiNbO4‐Based Low‐Firing Ceramics with Silver Electrodes
Authors: Cho Seo‐Yong , Youn Hyuk‐Joon , Kim Dong‐Wan , Kim Tae‐Gyun , Hong Kug Sun
Published: July 2010

Several commercial silver electrode pastes have been evaluated for use with BiNbO4‐based low‐firing ceramics. After electrode application and subsequent cofiring, the electrode pattern on the ceramic was no longer visible. A bismuth‐rich second phase was present at the electrode/BiNbO4 interface, and silver was detected in the second phase. Systematic X‐ray diffractometry analysis of the mixtures between different silver pastes and doped/undoped BiNbO4 revealed an interaction between the silver and the BiNbO4. This reaction was responsible for the disappearance of the silver electrode patterns.
Evolution in Structural and Optical Properties of Stannic Oxide Xerogel upon Heat Treatment
Authors: Wu Nae‐Lih , Wu Li‐Fu , Rusakova Irene A. , Hamed Alejandro , Litvinchuk Alexader P.
Published: July 2010

Upon consecutive heat treatments at increasing temperatures, the microstructure of solution–sol–gel‐derived stannic oxide (SnO2) xerogel evolves in three stages: (I) below 300°C, characterized by extensive dehydroxylation and gel shrinkage with little grain growth and surface loss; (II) between 300° and 500°C, by extensive crystallization, leading to dramatic surface loss (by 70%); and (III) above 500°C, by grain growth. Concurrently, the UV‐absorption edge shows red shifts during stages I and II and blue shifts during stage III, resulting in distinct color variations. The edge displacement bears a close correlation with a Raman “defect band” at ∼305–328 cm−1.
Effect of Initial Microstructure on Final Intergranular Phase Distribution in Liquid‐Phase‐Sintered Ceramics
Authors: Ackler Harold D. , Chiang Yet‐Ming
Published: July 2010

The glass‐melt penetration of dense TiO2 polycrystals (where the grains are initially in contact) and the sintering of SiO2‐coated TiO2 powders (where the grains are initially separated) have been used to investigate the influence of initial particle separation on final microstructures. Grains that were initially in sintered contact resisted penetration by the liquid and retained crystalline boundaries. However, grains that were initially separated by liquid had a tendency to form a final state where they were separated by a glass film ∼1 nm thick. The results imply that crystalline grain boundaries and those that contain a thin amorphous film represent two local thermodynamic minima that are separated by an energy barrier. These observations are in agreement with a thermodynamic model that predicted such a barrier for this system, and these observations show that the stable phase distribution in liquid‐phase‐sintered ceramics can be dependent on the path.
Phase Relations in the System NaF‐CaF2‐NaAlSiO4‐CaAl2Si2O8
Authors: Færøyvik Marianne , Grande Tor , Julsrud Stein , Seltveit Arne
Published: July 2010

The phase diagram of the pseudoternary reciprocal system NaF–CaF2–NaAlSiO4–CaAl2Si2O8 is reported in this paper. The phase relations in the system have been investigated by differential thermal analysis, quenching melts, X‐ray diffractometry, and optical and electron microscopies. The stable diagonal CaF2–NaAlSiO4 divides the system in two pseudoternary systems. The solidus temperatures in the two subsystems NaF–CaF2–NaAlSiO4 and CaF2–NaAlSiO4–CaAl2Si2O8 are 805°± 2°C and 1095°± 4°C, respectively. An extensive region of liquid–liquid immiscibility is evident in the NaF–CaF2–NaAlSiO4 subsystem. The compositions of the two liquids fall outside the compositional surface NaF–CaF2–NaAlSiO4–CaAl2Si2O8, but only a small deviation from the ternary behavior is observed.
Hydrothermal Processing of PbTiO3 and PbTiO3/Polymer Thin Films from Titanium Metallo‐organic Precursors
Authors: Peterson Chad R. , Slamovich Elliott B.
Published: July 2010

PbTiO3 and PbTiO3/polymer thin films were synthesized from metallo‐organic precursors on metallized quartz substrates. Titanium dimethoxy dineodecanoate (TDD) was spin‐cast onto the substrates and converted to polycrystalline TiO2 via hydrolysis in deionized water for 5 h at 80°C. Polycrystalline PbTiO3 films were then formed by reacting the TiO2 films for 4 h at 200°C in aqueous solutions of KOH and Pb(CH3COO)2·3H2O. Low KOH concentrations suppressed film coarsening, thereby facilitating the formation of fine‐grain continuous PbTiO3 films. PbTiO3/polymer thin films were processed as above after first dissolving TDD and a polystyrene/polybutadiene block copolymer in p‐xylene. PbTiO3 and PbTiO3/polymer films had relative permittivities of ≈56 and 34 and dielectric strengths of ≈250 and 850 kV/cm, respectively.
High‐Temperature Stability of Alumina in Argon and Argon/Water‐Vapor Environments
Authors: Tai Weon‐Pil , Watanabe Tadahiko , Jacobson Nathan S.
Published: July 2010

The high‐temperature stability of alumina (Al2O3) in argon and argon/water‐vapor (Ar/H2O) environments has been investigated. Samples were exposed at temperatures of 1300°C–1700°C for 10 h. The microstructure, flexural strength, and volume all showed significant changes in the Ar/H2O environment at 1700°C. Samples also became whiter, because of the oxidation of graphite impurities that had diffused from the hot‐processing dies. In the Ar/H2O environment at 1700°C, grain‐boundary etching occurred and was much more severe than in the pure‐argon environment, which was very likely caused by the enhanced formation of gaseous Al(OH)3 and Al(OH)2 along grain boundaries. In addition, in the Ar/H2O environment, substantial grain growth occurred in the surface vicinity. This grain growth, together with grain‐boundary etching, led to a decrease in flexural strength.
A Physical Model for the Drying of Gelcast Ceramics
Authors: Ghosal Sarbajit , Emami‐Naeini Abbas , Harn Ywh‐Pyng , Draskovich Barry S. , Pollinger John P.
Published: July 2010

Gelcasting is a promising new technology for manufactur‐ing advanced structural ceramic components. The process involves drying of the “green” gelcast part before densifi‐cation. The physical mechanisms that control this relatively long drying process are not well understood. In this study, several controlled experiments have been performed to elu‐cidate the key mechanisms. A one‐dimensional drying model has been formulated, based on evaporation and gas‐eous diffusion through the part. Experimental data have been used to obtain correlations for model parameters. This model predicts the instantaneous moisture content of a gelcast sample with an accuracy of better than 10% when the dryer humidity, dryer temperature, and sample thick‐ness are specified.
Lamination and Sintering Shrinkage Behavior in Multilayered Ceramics
Authors: Sung Jae Suk , Koo Ki Duk , Park Jeong Hyun
Published: July 2010

Variations in lamination conditions, such as pressure, temperature, and time, changed the laminated density of multilayered alumina but had no effect on the sintered density. The present results showed that sintering shrinkage values differ with lamination conditions and vary inversely with laminated density. When lamination was accomplished using a press die, the difference in shrinkage between the X‐Y and the Z directions was <1%. The effect of the press die could be explained by introducing a new factor, the SDF (shear deformation factor), which represents the ratio of area change in the X‐Y direction before and after lamination. The lamination of green sheets exhibited almost the same behavior as did the compression of granules. A linear relationship also was found between laminated density and the logarithm of lamination pressure. Results for sintering shrinkage in the overall range of measured laminated densities showed that sintering shrinkage behavior could be divided into three regions; that is, the laminates had three packing structures with different laminated densities. A new factor (k), related to packing structure values before and after sintering, was introduced to explain the sintering shrinkage behavior. Each k value was obtained from the relationship between laminated density and sintering shrinkage. Comparing k factors for the laminated densities (X‐Y and Z) under various lamination conditions made it possible to systematically analyze variations in the sintering shrinkage behavior of laminates with processing conditions. An estimation of sintering shrinkage was possible from that analysis.
Thermal Analysis of Nucleation and Growth of Crystalline Phases in Vitrified Industrial Wastes
Authors: Gao Zheng , III Charles H. Drummond
Published: July 2010

Devitrification behavior of vitrified industrial waste (electric arc furnace dust and foundry sand) was examined by differential thermal analysis (DTA), X‐ray diffractometry, and scanning electron microscopy (SEM). Crystalline phases identified were primarily solid solutions of spinel and augite. The temperature of maximum nucleation rate for spinel was determined by DTA to be 635°C. Variations in the quench temperature resulted in changes of both grain size and volume fraction of an equixed spinel. The evolution of morphological changes upon heat treatment was examined by SEM. TiO2 additions were ineffective as spinel nucleating agents, because additions of >5 wt% resulted in decreased spinel formation and the crystallization of titanium‐iron and titanium‐divalent‐metal oxides. Controlling process and heat‐treatment temperatures to optimize the amount of the spinel and to achieve a high‐grade abrasive product also are discussed.
Effects of Aluminum Concentration on the Oxidation Behaviors of Reactively Sputtered TiAlN Films
Authors: Huang Jow‐Lay , Shew Bor‐Yuan
Published: July 2010

Polycrystalline TiAlN films were deposited on a substrate of high‐speed steel via a radio‐frequency‐bias reactive‐sputtering process. The effects of aluminum concentration (0–60 at.%) on the high‐temperature oxidation behavior of TiAlN films were explored by using in situthermogravimetric analysis and high‐temperature X‐ray diffractometry. The composition and distribution of the oxidizing layers over TiAlN films were investigated. Results indicated that the oxidation resistance increased as the aluminum concentration increased. The type and location of oxidizing phases also were dependent on the aluminum concentration. Three major oxides‐i.e., Al2O3, TiO2, and TiO‐were observed. The thickness of the Al2O3 layer increased and the TiO2 gradually changed to TiO as the aluminum content increased. Thermodynamic calculations were compared to experimental observations, and they showed good agreement.