bluuebunny/crossref_metadata_2025 huggingface dataset:
Mechanical Behavior of MoSi2 Reinforced–Si3N4Matrix Composites
Authors: Petrovic John J. , Pena Maria I. , Reimanis Ivar E. , Sandlin Michael S. , Conzone Samuel D. , Kung H. Harriet , Butt Darryl P.
Published: July 2010

The mechanical behavior of MoSi2 reinforced–Si3N4 matrix composites was investigated as a function of MoSi2 phase content, MoSi2 phase size, and amount of MgO densification aid for the Si3N4 phase. Coarse‐phase MoSi2‐Si3N4 composites exhibited higher room‐temperature fracture toughness than fine‐phase composites, reaching values >8 MP·am1/2. Composite fracture toughness levels increased at elevated temperature. Fine‐phase composites were stronger and more creep resistant than coarse phase composites. Room‐temperature strengths >1000 MPa and impression creep rates of ∼10−8 s−1 at 1200°C were observed. Increased MgO levels generally were deleterious to MoSi2‐Si3N4 mechanical properties. Internal stresses due to MoSi2 and Si3N4 thermal expansion coefficient mismatch appeared to contribute to fracture toughening in MoSi2‐Si3N4 composites.
Cofiring Kinetics and Mechanisms of an Ag‐Metallized Ceramic‐Filled Glass Electronic Package
Authors: Jean Jau‐Ho , Chang Chia‐Ruey
Published: July 2010

Cofiring kinetics and mechanisms of an Ag‐based ceramic‐filled glass packaging system have been investigated. Boundary diffusion controlled solid‐state sintering is identified as the controlling densification mechanism of the Ag film. For ceramic‐filled glass tape, which is a mixture of glass and ceramic powders, the sintering kinetics are controlled by the viscous flow of low‐softening‐point glass. With the densification results of Ag film and ceramic‐filled glass tape, the camber development during cofiring of a two‐layerd structure of Ag film/ceramic‐filled glass tape can be theoretically predicted by viscous analysis, which also agrees well with experimental observations.
Nanocrystalline Titanium Oxide Electrodes for Photovoltaic Applications
Authors: Barbé Christophe J. , Arendse Francine , Comte Pascal , Jirousek Marie , Lenzmann Frank , Shklover Valery , Grätzel Michael
Published: July 2010

During the past five years, we have developed in our laboratory a new type of solar cell that is based on a photoelectrochemical process. The light absorption is performed by a monolayer of dye (i.e., a Ruthenium complex) that is adsorbed chemically at the surface of a semiconductor (i.e., titanium oxide (TiO2)). When excited by a photon, the dye has the ability to transfer an electron to the semiconductor. The electric field that is inside the material allows extraction of the electron, and the positive charge is transferred from the dye to a redox mediator that is present in solution. A respectable photovoltaic efficiency (i.e., 10%) is obtained by the use of mesoporous, nanostructured films of anatase particles. We will show how the TiO2 electrode microstructure influences the photovoltaic response of the cell. More specifically, we will focus on how processing parameters such as precursor chemistry, temperature for hydrothermal growth, binder addition, and sintering conditions influence the film porosity, pore‐size distribution, light scattering, and electron percolation and consequently affect the solar‐cell efficiency.
Ceria–Yttria‐Stabilized Zirconia Composite Ceramic Systems for Applications as Low‐Temperature Electrolytes
Authors: Tompsett Geoffrey A. , Sammes Nigel M. , Yamamoto Osamu
Published: July 2010

Ceramic samples of Ce1−xGdxO2−y and yttria‐stabilized zirconia (YSZ) were prepared using solid‐state methods. Polished faces of disks of these materials were held in intimate contact in a reaction cell at temperatures ranging from 1000° to 1300°C for durations up to 72 h. XRD, SEM, and microprobe Raman techniques were used to analyze the resulting reactions and ion diffusion. No reaction was observed at 1000°C after 72 h between the 10‐mol%‐ and 20‐mol%‐Gd‐doped CeO2 and the YSZ. However, at 1300°C, a mixing region 25 μ m wide occurred, resulting in a cubic phase, where Zr4+ ions diffused into the CeO2.
Ab‐initio Calculation of Yttrium Substitutional Impurities in alpha‐Al2O3
Authors: Ching Wai‐Yim , Xu Yong‐Nain , Rühle Manfred
Published: July 2010

Yttrium has a very low solubility in bulk α‐Al2 O3 and a great propensity for segregation to the grain boundaries in polycrystalline Al2O3. The segregation of yttrium influ‐ences many properties of the material. To understand the nature of the chemical bonding of yttrium within Al2O3, we have, as a first step, conducted an ab‐initio self‐consistent calculation for a yttrium impurity atom replacing an aluminum atom in Al2O3. We have used the first‐principles orthogonalized linear combination of atomic orbitals (OLCAO) method and a supercell with 120 atoms in the hexagonal lattice. The relaxation of the nearby atoms, be‐cause of the presence of yttrium, is studied via total energy calculation within the local density approximation. The nearest‐neighbor oxygen atoms of yttrium move outward by 8% and the next‐nearest‐neighbor aluminum atoms move inward by 5% of the respective separations in the undistorted lattice. A substitutional energy of 4.79 eV is obtained. The yttrium impurity introduces three defect states in the gap near the conduction band edge, thus natu‐rally explaining the “donor effect.” Two of the defect states are degenerate, and all three are derived mainly from the Y4d orbitals with very different local symmetries. The effec‐tive‐charge and bond‐order calculations show a substantial covalent bonding character between yttrium and the re‐laxed oxygen and aluminum atoms in the host.
Novel Technology for X‐ray Mapping of Ceramic Microstructures
Authors: Friel John J. , Greenhut Victor A.
Published: July 2010

Field‐emission scanning electron microscopy (FESEM) was coupled with a technology called position‐tagged spectrometry (PTS) to characterize the microstructure of a ceramic‐matrix composite at the submicrometer level. Low‐voltage microscopy with an FESEM microscope achieves both high‐resolution imaging of uncoated ceramic specimens and submicrometer X‐ray resolution with minimal specimen charging. The PTS technology involves scanning the electron beam and collecting X‐rays, as in mapping; however, in this case, the X‐ray photons are tagged with position information. X‐ray maps and full spectra were reconstructed from discrete parts of the composite. The distribution of oxygen within the fibers was measured and found to decrease from the surface to the interior. The composition and phase distribution of the matrix were also revealed at high resolution, and the phase compositions were quantified.
Preparation and Magnetic Properties of Barium Hexaferrite Nanoparticles Produced by the Citrate Process
Authors: Zhong Wei , Ding Weiping , Jiang Yumei , Zhang Ning , Zhang Jianrong , Du Youwei , Yan Qijie
Published: July 2010

The sol‐gel synthesis technique has been used to produce barium ferrite particles. Several methods such as X‐ray diffractometry, transmission electron microscopy, and magnetism measurement (VSM) have been used to obtain detailed information on the crystallography and magnetic properties of the precursor and the calcined particles. The correlation of BaFe12O19 formation with the precursor properties and thermal treatment has been studied. The optimum conditions for preparing BaFe12O19 nanoparticles at a low calcining temperature are reported, and homogeneous ultrafine BaFe12O19 with almost‐ideal single‐domain behavior and coercive force (5950 Oe) and specific magnetization (70 emu/g) values that are similar to the theoretically predicted values is obtained.
Stress‐Rupture of Nicalon/SiC Continuous Fiber Ceramic Composites in Air at 950°C
Authors: Lara‐Curzio Edgar
Published: July 2010

The stress‐rupture behavior of plain‐weave CG‐Nicalon/enhanced SiC was studied in air at 950°C. It was found that this material exhibits delayed failure and that the lives of specimens subjected to constant stress levels of 80, 100, and 120 MPa were 21.6, 9.6, and 2.7 h, respectively. The strain histories of these tests revealed a continuous increase of the specimen compliance and accelerated deformation prior to failure. It is shown that both the shape of the strain vs time curves and the time dependence of the loss of strength can be explained using a simple model based on the oxidation‐induced stress‐rupture of the reinforcing fiber bundles.
Chemical and Morphological Changes of Vacuum‐Plasma‐Sprayed Hydroxyapatite Coatings during Immersion in Simulated Physiological Solutions
Authors: Ha Suk‐Woo , Reber Roland , Eckert Karl‐Ludwig , Petitmermet Marc , Mayer Jörg , Wintermantel Erich , Baerlocher Christian , Gruner Heiko
Published: July 2010

The purpose of this investigation was to study the behavior of vacuum‐plasma‐sprayed hydroxyapatite (VPS‐HA) coatings in a defined simulated physiological environment that mimics the conditions that the material experiences after implantation in the human body. Commercially available and clinically used HA coatings on titanium alloy substrates were immersed in an inorganic simulated body fluid (SBF) with ion concentrations that were almost equal to those of human blood plasma and in fetal calf serum (FCS) for time periods of 1, 3, 7, 14, and 28 days. At each time interval, the VPS‐HA coatings were analyzed using scanning electron microscopy, X‐ray diffractometry, Fourier transform infrared spectroscopy, and inductively coupled plasma‐atomic emission spectroscopy. The as‐received VPS coatings consisted of HA as the main phase component; in addition, small concentrations of tricalciumphosphate (TCP) were determined to be present. During immersion in SBF, transformation of the peripheral area of the VPS coating to a regular spherical shape was observed. Concentration measurements of the immersion solution indicated that dissolution of the more‐soluble TCP started within the first day. At the same time, precipitation of a carbonate‐containing, marginally crystalline calcium phosphate with very small coherently scattering domains was observed. In FCS, the dissolution of calcium and phosphorus was observed; however, the precipitation of the new calcium phosphate layer was retarded by the presence of proteins, which indicates their important role in the ion‐exchange mechanisms. In both solutions, the coating integrity was not adversely affected, which indicates the high stability of VPS‐HA coatings in a simulated physiological environment.
Texture Development, Microstructure Evolution, and Crystallization of Chemically Derived PZT Thin Films
Authors: Chen San‐Yuan , Chen I‐Wei
Published: July 2010

Two solution‐based methods, metallo‐organic decomposition and sol—gel processes, were used to study the effects of precursor solution type on the microstructure evolution and texture development of oriented PZT films. Microstructure development and perovskite content are strongly dependent on the heating rate. Fast heating rate forms a dense fine‐grained microstructure with (111) orientation. Intermediate‐temperature pyrolysis followed by a fast heating rate forms clustered or island structures of submicrometer grains with (100) orientation. Intermediate‐temperature pyrolysis followed by a very slow heating rate forms larger spherical rosettes with random orientations. Pt5–7Pb is a (111) textured transient intermetallic phase that nucleates PZT(111) texture. PbO is a (001) textured layer compound that nucleates PZT(100) texture. The texture selection of PZT films is independent of precursor systems but sensitive to the film thickness especially when sol—gel precursors and oxidizing atmosphere are used. Correlation and comparison of oriented sol—gel and MOD PZT films with electrical properties are also made.
Preparation of Novel Core‐Shell Nanocomposite Particles by Controlled Polymer Bridging
Authors: Chen Tsung‐yuan , Somasundaran P.
Published: July 2010

Ceramics that are composed of nanosized granules show enhanced properties in various applications. A layer‐by‐layer deposition process is developed in this study to prepare core—shell nanocomposite particles, using controlled polymer adsorption. Submicrometer‐sized alumina particles that have been chosen as the starting core particles are first dispersed by pH control and then modified by adsorption of anionic poly(acrylic acid) to facilitate the subsequent deposition of nanoparticles on them. A key step in the processing involves the removal of excess polymer in the supernatant after the adsorption by controlled washing, so that the added nanoparticles do not self‐flocculate among themselves. A coating of nanosized particles is indicated by the charge reversal of the micrometer‐sized composite particles. The isoelectric point of the composite particle is similar to that of nanosized particles under both low and high coverage conditions. Scanning electron microscopic observation of coated particles shows full monolayer coverage of the nanoparticles on core particles, which confirms the efficiency of the coating scheme that is discussed here. The present study reveals the feasibility of coating nanoparticles onto micrometer‐sized core particles, using controlled polymer bridging, for the preparation of the multilayer nanocomposite powders.
Morphological Effects of Grinding on Bismuth‐Based Cuprate Superconductors
Authors: Kusano Yoshihiro , Takada Jun , Fukuhara Minoru , Doi Akira , Ikeda Yasunori , Takano Mikio
Published: July 2010

Morphological changes of bismuth‐based cuprate superconductors, such as the 2223 phase, via a small mechanical force were studied mainly by means of high‐resolution transmission electron microscopy and atomic force microscopy. Even light mechanical grinding of the sintered 2223 samples led to the formation of superfine particles that had a width of ∼5 nm. Moreover, we found first that the superfine particles had a discrete thickness of odd numbers of a half unit length c/2 of the 2223 phase, e.g. 1.9 nm, 5.6 nm, and so on. The formation of the superfine particles was due to cleavage at Bi—O double layers that were bound weakly to each other in a unit cell.
Determination of Valence States of Chromium in Calcium Chromates by Using X‐ray Absorption Near‐Edge Structure (XANES) Spectroscopy
Authors: Arcon Iztok , Mirtic Breda , Kodre Alojz
Published: July 2010

Calcium chromates with the empirical formulas Ca10Cr6−O25, Ca3Cr2O8, and Ca5Cr3O12, which form at temperatures >900°C at CaO:Cr2O3 molar ratios of 3 in an oxidation atmosphere have been synthesized in the pure state. X‐ray absorption near‐edge structure (XANES) spectroscopy has been used to determine the average valence state of chromium in the samples. The presence of unusual chromium valence states, 4+ and 5+, which was proposed via X‐ray diffractometry studies, is strongly supported.
Orthophosphates and Diphosphates Containing Zinc and Copper and Zinc and Cobalt
Authors: Bamberger Carlos E. , Specht Eliot D.
Published: July 2010

Solid solutions of diphosphates of zinc and copper and of zinc and cobalt were synthesized from mixtures of pure diphosphates at temperatures up to 1000°C. Their X‐ray diffractometry patterns varied continuously from one end member to the other. Solid solutions of orthophosphates of composition Zn3−xCox(PO4)2, with x= 0.4–1.6, were formed at temperatures up to 950°C; all exhibited the structure of γ‐Zn3(PO4)2. Solid solutions of orthophosphates of composition Zn3−xCux(PO4)2 exhibited more‐complex behavior. At 1000°C and copper contents of 20–80 mol%, a phase that is related to Cu3(PO4)2, termed here the “ε‐phase,” predominated. At 850°–950°C and in the region from 20 mol% to ∼33 mol% of copper, the solid solutions (the “η‐phase”) adopted the structure of graftonite. At 800°–900°C and 10–15 mol% of copper, the solid solutions exhibited a new structure (the “δ‐phase”), which we found to be related to the mineral sarcopside. At temperatures 950°C, the solutions that contained 5–15 mol% of copper (the “β‐phase”) had the structure of β‐Zn3(PO4)2, whereas at 800°–850°C, solutions with 5 mol% of copper (the “‐phase”) exhibited the structure of γ‐Zn3(PO4)2. Attempts to synthesize Cu+ZnPO4 and Cu+Cu2+Zn3(PO4)3 were unsuccessful.
Oxidation‐Induced Microstructural Change of Si‐Ti‐C‐O Fibers
Authors: Kakimoto Ken‐ichi , Shimoo Toshio , Okamura Kiyohito
Published: July 2010

Two types of Si‐Ti‐C‐O fibers STC(6HS) and STC(6H), with different C/Si molar ratios of 0.99 and 1.65, respectively, have been subjected to oxidation tests at high temperatures between 1000° and 1500°C. Both fibers showed different mass gain during the oxidation tests. In the unoxidized region, there was no change in the chemical composition. For STC(6HS), coarse ß‐SiC grains were formed throughout the region, while the grain coarsening in STC(6H) was restricted to the vicinity of the film/fiber interface. In this paper, the influence of free carbon on the oxidation‐induced microstructural change of Si‐Ti‐C‐O fibers is discussed.
Highly Oriented (Zr0.7Sn0.3)TiO4 Thin Films Grown by rf Magnetron Sputtering
Authors: Wu Fang–Jy , Tseng Tseung‐Yuen
Published: July 2010

Thin films of (Zr0.7Sn0.3) TiO4 on Si(100) were prepared by rf magnetron sputtering in the present study. Films of a highly preferred [020] orientation, as demonstrated by X‐ray diffraction and transmission electron microscopic examinations, were grown successfully on a Si substrate with in situ postannealing at 700°C. The chemical composition of the films, measured by secondary ion mass spectroscopy, exhibited a uniform concentration distribution for all species. A study by X‐ray photoelectron spectroscopy further revealed some firm evidence of a molecular orbital that affected the chemical structure. The dielectric constants of 400‐nm‐thick (Zr0.7Sn0.3)TiO4 films in the present study were >18 for the films with a preferred orientation and ~11 for polycrystalline films.
Yttrium Aluminum Garnet Fibers from Metalloorganic Precursors
Authors: Liu Yin , Zhang Zhi‐Fan , Halloran John , Laine Richard M.
Published: July 2010

Mixtures of yttrium acetate hydrate (Y(O2CCH3)34H2O) and aluminum formate hydrate (Al(O2CH)33H2O in H2O) or yttrium isobutyrate (Y[O2CCH(CH3)2]3) and aluminum isobutyrate (Al[O2CCH(CH3)2]3) in tetrahydrofuran were used as precursors to process yttrium aluminum garnet (YAG, Al5Y3O12) fibers. The pyrolytic decomposition patterns of Al(O2CH)33H2O, Y(O2CCH3)34H2O, and a [3Y(O2CCH3)34H2O/5Al(O2CH)33H2O] YAG stoichiometry mixture were assessed by heating samples to selected temperatures and characterizing the products by thermogravimetric analysis, differential thermal analysis, X‐ray diffractometry, and Fourier transform infrared spectroscopy. The YAG acetate/formate precursor decomposes to an amorphous intermediate at temperatures >400°C and crystallizes (at ∼800°C) to phase‐pure YAG with a ceramic yield of 40% at 1000°C. YAG isobutyrate precursor fibers were extruded or hand drawn. YAG acetate/formate precursor fibers were formed using a commercial extruder. The pyrolysis behavior of both precursor fibers was studied to identify the best pyrolysis conditions for producing dense, defect‐free ceramic fibers. Only thin (diameter of <30 μm) precursor fibers could be processed to dense, defect‐free, thin YAG fibers (diameter of <20 μm). For the YAG isobutyrate precursor, crack‐free crystalline YAG fibers (diameter of ∼7 μm) were obtained at 1000°C. For YAG acetate/formate precursor fibers, dwell times of 2 h at temperatures of 400° and 900°C were necessary to process fully dense, defect‐free ceramic fibers. Heating the resulting 900°C fibers (at a rate of 30°C/min) to 1570°‐1650°C gave dense fibers with grain sizes of 0.7‐3.2 μm and bend strengths of up to 1.7 ± 0.2 GPa (for fibers that had a diameter of ∼10 μm and had undergone sintering at 1600°C).
In Situ Study of Single Aqueous Droplet Solidification of Ceramic Precursors Used for Spray Pyrolysis
Authors: Chan Chak K. , Flagan Richard C. , Seinfeld John H.
Published: July 2010

The electrodynamic balance (EDB) is demonstrated to be useful for the in situ study of aqueous droplet solidification. We have used an EDB to study the solidification of solution droplets used for ceramic powder synthesis by spray pyrolysis. The mass change and the elastic light scattering of the drying 20 μm solution droplets were monitored. We found that aqueous MgCl2 droplets crystallize but Mg(COOCH3)2, MgSO4, ZrO(OH)Cl, and Zr(COOCH3)4 droplets appear to form gels at high concentrations. As a result of the gel formation, the rate of loss of water from the droplets can be reduced by approximately 150 times and drying is limited by solute diffusion in the gel.
A Direct Method of Measuring Bridging Stresses
Authors: Mori Kazuya , Hashimura Shinji
Published: July 2010

A direct method of measuring bridging stresses using a double‐notched plate (DNP) specimen is developed. Bridging stresses are measured via the stable fracture of the DNP specimen using the bridging stabilizer developed in this study. The opening displacement of the fracture surfaces can be evaluated from the deformation of the bridging stabilizer and the DNP specimen. As an example of the application, the bridging stresses of polycrystalline alumina are measured under monotonic load. The bridging characteristics that have been measured using the present method are compared with those obtained via the other methods.
Configuration of Carbonate Ions in Apatite Structure Determined by Polarized Infrared Spectroscopy
Authors: Suetsugu Yasushi , Shimoya Ichiro , Tanaka Junzo
Published: July 2010

Carbonate apatite single crystals were grown under 50 MPa of argon gas using CaCO3 flux. The crystals obtained were hexagonal prismatic, 1 mm in length and 200 μm in diameter. Carbonate ions occupied both A(OH)‐sites and B(PO4)‐sites; A‐sites were completely substituted by carbonate ions. The space group was determined using a four‐circle diffractometer to be P. From the angular dependence of polarized IR spectra for out‐of‐plane and in‐plane bending vibrations of CO3 ions, it was indicated that the triangular plane of the CO3 ion was parallel to the c‐axis for A‐site substitution and perpendicular to the c‐axis for B‐site substitution.
Tensile Strength of Silicon Nitride Whiskers Synthesized by Reacting Amorphous Silicon Nitride and Titanium Dioxide
Authors: Iwanaga Hiroshi , Kawai Chihiro
Published: July 2010

The tensile strength of α‐Si3N4 whiskers synthesized by reacting amorphous Si3N4 and TiO2 at 1490°C under a N2 pressure of 700 torr was measured using a microbalance, and the diameter dependence of the strength was investigated. The Si3N4 whiskers had diameters of 0.04 and 0.8 μm and dominant [1011] and [1010] growth directions. Chemical analysis showed that they contained Ti and O impurities. The tensile strength of six Si3N4 whiskers increased from 17 to 59 GPa with decreasing whisker diameter.
Phase Diagram and Oxygen‐Ion Conductivity in the Y2O3‐Nb2O5 System
Authors: Lee Jin‐Ho , Yashima Masatomo , Kakihana Masato , Yoshimura Masahiro
Published: July 2010

The phase equilibria in the Y2O3‐Nb2O5 system have been studied at temperatures of 1500° and 1700°C in the compositional region of 0‐50 mol% Nb2O5. The solubility limits of the C‐type Y2O3 cubic phase and the YNbO4 monoclinic phase are 2.5 (±1.0) mol% Nb2O5 and 0.2 (±0.4) mol% Y2O3, respectively, at 1700°C. The fluorite (F) single phase exists in the region of 20.1‐27.7 mol% Nb2O5 at 1700°C, and in the region of 21.1‐27.0 mol% Nb2O5 at 1500°C, respectively. Conductivity of the Y2O3‐ x mol% Nb2O5 system increases as the value of x increases, to a maximum at x= 20 in the compositional region of 0 ≤x≤ 20, as a result of the increase in the fraction of F phase. In the F single‐phase region, the conductivity decreases in the region of 20‐25 mol% Nb2O5, because of the decrease in the content of oxygen vacancies, whereas the conductivity at x= 27 is larger than that at x= 25. The conductivity decreases as the value of x increases in the region of 27.5 ≤x≤ 50, because of the decrease in the fraction of F. The 20 mol% Nb2O5 sample exhibits the highest conductivity and a very wide range of ionic domain, at least up to log pO2=−20 (where pO2 is given in units of atm), which indicates practical usefulness as an ionic conductor.
Stress and Strain Evolution in Cast Refractory Blocks during Cooling
Authors: Lu Tian Jian , Evans Anthony G. , Hutchinson John W. , Srinivasan Gajawalli V. , Winder Stephen M.
Published: July 2010

A computational model has been developed to study the stress and strain histories experienced by zirconia‐containing cast refractory blocks when they are cooled from the casting temperature. Incorporated into the model are strong temperature dependencies of the following material properties: elastic modulus, flow strength, thermal conductivity, and thermal expansion. The pressure‐sensitive Drucker‐Prager plasticity model has been used to account for the substantial difference between the tensile and compressive stress‐strain behaviors found in these refractories. The temperature‐induced phase transformation in the zirconia, as well as the overall thermal contraction, are united by introducing a coefficient of total dilatation. A nonuniform radial distribution of the transforming phase is also incorporated. The parameters that control the time‐dependent stress and strain responses are identified by performing calculations that span the range of expected variables. Process strategies for manufacturing crack‐free blocks are suggested.
Synthesis and Thermal Expansion Properties of the Ca(1+x)/2Sr(1+x)/2Zr4P6−2xSi2xO24 System
Authors: Breval Else , McKinstry Herbert A. , Agrawal Dinesh K.
Published: July 2010

Ca(1+x)/2Sr(1+x)/2Zr4P6−2xSi2xO24(x≤ 0.37) compositions, which belong to the [NZP] family of low‐thermal‐expansion materials, were synthesized using the solid‐state reaction method. The lattice thermal expansion of members of this system was determined up to 1000°C by high‐temperature X‐ray diffractometry. The bulk thermal expansion and the microcracking during cooling also were investigated. These properties depended on the composition, on the synthesis method, and on the sintering conditions.
High‐Temperature Phase Relations in Selected MnO‐CrOx‐Containing Systems
Authors: Garbers‐Craig Andrie M. , Dippenaar Rian J.
Published: July 2010

Phase relations in the pseudobinary MnO‐CrOx system were studied by the reaction of the individual oxides in the temperature range 1400°‐1750°C under a reducing atmosphere with a CO:CO2 volume ratio of 4.8, yielding oxygen partial pressures in the range 10‐9.98‐10‐6.97 atm. In the pseudoternary MnO‐CrOx‐containing systems that constitute the pseudoquaternary MnO‐CrOx‐CaO‐SiO2 system, phase relations were determined only at 1500°C under an oxygen partial pressure of 10−8.99 atm. Characteristic of these MnO‐CrOx‐containing systems was the dominance of the (Mn,Cr)3O4 spinel phase.
Cation Ordering Transformations in the Ba(Zn1/3Nb2/3)O3‐La(Zn2/3Nb1/3)O3 System
Authors: Akbas Mehmet A. , Davies Peter K.
Published: July 2010

Single‐phase perovskites were formed in the (1−x)Ba(Zn1/3Nb2/3)O3‐(x)La(Zn2/3Nb1/3)O3 system for compositions with 0.0≤x≤0.6. Although the stability of the trigonal “1:2” ordered structure of the Ba(Zn1/3Nb2/3)O3 end member is very limited (0.0≤x≤0.05), low levels of lanthanum induce a transformation to a cubic, “1:1” ordered structure that has a broad range of homogeneity (0.05≤x≤0.6). Samples with x > 0.6 were comprised of La3NbO7, ZnO, and a perovskite with x = 0.6. The cubic 1:1 phases were fully ordered and no evidence was found for a compositionally segregated microstructure. These observations could not be reconciled in terms of a “space‐charge” model; rather, they supported a charge‐balanced, “random‐site” structure for the 1:1 cation‐ordered Ba(β1/2′β1/2″)O3 phases.
Configurational Observation of Titanium Oxide Pigment Particles
Authors: Akiyama Kazuhiro , Toyama Nosho , Muraoka Kazuyoshi , Tsunashima Makoto
Published: July 2010

The physical and chemical configuration of anatase‐form titanium dioxide pigment particles was investigated with a field‐emission gun using transmission electron microscopy and energy‐dispersive spectroscopy (EDX). The particle was ∼0.2 µm in average size and had an amorphous‐surface‐layer thickness of 1‐2 nm around the single‐crystallized matrix. Niobium that had segregated in the amorphous surface layer was detected via EDX analysis.
Local Electrical Behavior, Crystallography, and Chemistry of Grain Boundaries in Mn‐Zn Ferrites
Authors: Laval Jean‐Yves , Cabanel Cecil , Berger Marie‐Hélène , Girard Paul
Published: July 2010

This investigation is devoted to grain boundaries, since, for high‐frequency applications, eddy‐current losses can be minimized by selectively increasing the resistivity of grain boundaries. Two specific commercial Mn‐Zn ferrites were considered. The first one, selected to be a reference sample, exhibited good permeability, whereas the second one was chosen to promote a strong segregation of calcium on the grain boundaries via the addition of CaO and SiO2. To explain the behavior of this material chemical, crystallographical and electrical properties were collated. Initially, maps of potential barriers were recorded on a scale representative of the bulk microstructure by voltage contrast via scanning electron microscopy at 1 keV. In addition to the potential maps, the local electrical potential was measured quantitatively via local probing. It was evidenced that there was no percolation path through weak barriers at the grain boundaries. To gain information on very small voltage drops, in particular within grains, the microelectrode technique was used on the same areas. It showed a very different behavior between the two samples for the intragranular resistivity, as well as for interfacial barriers. Then, the crystallochemistry of the grain boundaries was investigated via analytical conventional transmission electron microscopy and scanning transmission electron microscopy techniques, and the specific segregation of calcium and the depletion of Fe2+ versus Fe3+ ions at general grain boundaries (GBs) was evidenced. The chemistry and microstructure of the grain boundaries were related to their crystallography. By local electrical probing via transmission electron microscopy, the interfacial barriers were directly related to the type of grain boundary. It was shown that high electrical barriers correspond to high‐energy GBs, where there are no orientation relationships between adjacent grains; on the other hand, low‐energy GBs, which present orientation relationships and/or dense interfacial planes, are characterized by low barriers.
Synthesis of Rare‐Earth Gallium Garnets by the Glycothermal Method
Authors: Inoue Masashi , Nishikawa Toshihiro , Otsu Hiroyuki , Kominami Hiroshi , Inui Tomoyuki
Published: July 2010

Single‐phase rare‐earth gallium garnets were obtained by the reaction of stoichiometric mixtures of gallium acetylacetonate and rare‐earth (Nd‐Lu) acetates in 1,4‐butanediol at 300°C (glycothermal reaction). Particles of gadolinium gallium garnet (GGG) and other gallium garnets with rare‐earth elements larger than Gd were spherical with diameters of 0.5‐2 μm, while particles of garnets with smaller rare‐earth ions (Tb‐Lu and Y) were much smaller (100‐300 nm) with particle size distributed in a quite narrow range. TEM observation revealed that each particle was essentially a single crystal grown from one nucleus, but that defects frequently occurred during the crystal growth. Cerium and praseodymium gallium garnets were also formed when the reaction was carried out in the presence of GGG seed crystals. Hydrothermal reactions of the same starting materials under identical conditions yielded mixtures of gamma‐Ga2O3 and the garnet phase.
Formation and Characterization of Monodisperse, Spherical Organo‐Silica Powders from Organo‐Alkoxysilane‐Water System
Authors: Choi Jae Young , Kim Chong Hee , Kim Do Kyung
Published: July 2010

Monodisperse, spherical organo‐silica powders were synthesized from an immiscible mixture of an aqueous NH4OH solution and organo‐alkoxysilanes, such as phenyl‐trimethoxysilane (PTMS), methyltrimethoxysilane (MTMS), and methyltriethoxysilane (MTES). When the organo‐alkoxysilanes were added to the aqueous NH4OH solution with stirring, organo‐alkoxysilane/water macroemulsions were formed because of the immiscibility of the aqueous NH4OH solution and the organo‐alkoxysilane. In the emulsion, organo‐alkoxysilane droplets dissolved into the water phase through the droplet‐water interface, and the organo‐silica powder was formed by the hydrolysis and condensation of the organo‐alkoxysilane. The powders were obtained reproducibly under broad concentrations of organo‐alkoxysilanes; 0.3‐1.5 mol/L for PTMS, 0.3‐0.6 mol/L for MTMS, and MTES, with concentrations of ammonia between 0.0625 and 2.0 mol/L. According to the analysis of the solid‐state MAS 29Si NMR and the 13C NMR analysis, the organo‐silica powder did not contain any residual alkoxy groups, only carbon sources from nonhydrolyzable R groups: phenyl groups in PTMS, and methyl groups in MTMS and MTES.
Preparation of Lead Lanthanum Zirconate Titanate (PLZT, (Pb,La)(Zr,Ti)O3) Fibers by Sol‐Gel Method
Authors: Kitaoka Kenji , Kozuka Hiromitsu , Yoko Toshinobu
Published: July 2010

Lead lanthanum zirconate titanate (PLZT, (Pb,La)(Zr,‐Ti)O3) ceramic fibers were prepared by the sol‐gel method from a solution of lead acetate trihydrate, lanthanum isopropoxide, zirconium n‐propoxide, and titanium isopropoxide that contained 2‐methoxyethanol as the solvent. The sols obtained from the solution were concentrated at 156°‐174°C for 2 h. Concentration at higher temperatures resulted in more‐viscous sols of higher specific gravities. The concentration resulted in the formation of spinnable sols, which had viscosities >105 mPas and exhibited Newtonian flow properties. These spinnable sols were formed to be so stable that no change in viscosity and spinnability was observed for more than three months when stored in a sealed container at room temperature. Gel‐to‐ceramic fiber conversion was investigated by means of X‐ray diffractometry, infrared spectroscopy, and thermal analysis. Single‐phase perovskite PLZT ceramic fibers 5‐200 μm in diameter and >20 cm in length were obtained. Scanning electron microscopy (SEM) observation and Brunauer‐Emmett‐Teller (BET) measurement showed that heat treatment of the fibers at a lower rate resulted in the formation of fibers of denser microstructure. Although the SEM image of the cross section of the fibers revealed a relatively dense microstructure and a laser beam could be transmitted through a fiber 6 mm in length, BET measurement of the fibers indicated that the fibers had more than a few percent of open porosities, and scattering of light was observed in the laser‐beam guiding test.
Temperature Dependence of the High‐Frequency Viscoelastic Behavior of a Soda‐Lime‐Silica Glass
Authors: Duffrène Lucas , Gy René , Masnik John E. , Kieffer John , Bass Jay D.
Published: July 2010

The high‐frequency viscoelastic behavior of a soda‐lime‐silica glass has been investigated using the Brillouin scattering technique. The temperature dependence of instantaneous elastic constants and very short‐time relaxation mechanisms have been measured in a temperature range between 100° and 1000°C. Variations in the elastic constants in the transition region are significant, and have to be taken into account for numerical computations of tempering and annealing of glasses. A complex thermorheological behavior is observed for very fast relaxation mechanisms in the transition range, whereas intermediate and slow relaxation mechanisms exhibit a simple thermorheological behavior. The viscoelastic behavior of this glass can be adequately represented by assuming a different thermorheological behavior in the alpha‐ and β‐relaxation regimes.
Classical and Differential Thermal Analysis Studies of the Glass‐Ceramic Transformation in a YSiAlON Glass
Authors: Ramesh Raghavendra , Nestor Elizabeth , Pomeroy Michael J. , Hampshire Stuart
Published: July 2010

Nucleation and crystallization studies were conducted on a YSiAlON glass that contained 17 equiv.% nitrogen (7.5 at.%) by using a two‐stage nucleation‐and‐growth treatment. Classical and differential thermal analysis (DTA) techniques were both used to study the crystallization process, to ensure that the optimum heat‐treatment schedule that yielded a fine microstructure and minimum residual glass was applied. The optimum nucleation and crystallization temperatures were determined from DTA traces that were recorded from isothermal heat treatments at different nucleating temperatures, ranging between Tg ‐ 40°C and Tg+ 100°C for 1 h and crystal‐growth temperatures in the range of 1170°‐1310°C for 0.5 h, respectively. The activation energy for the crystallization process was determined, based on the analysis of the variation of peak temperature at five different heating rates. Specimens heat treated in a tube furnace under nitrogen gas were subjected to microscopical investigation, and results showed variations in the volume fraction of crystalline phases and crystal size with nucleation temperature. The nucleation temperature, Tg+ 40°C (1025°C), which corresponded to the maximum volume fraction of crystalline phases and minimum crystal size, was consistent with the optimum nucleation temperature, Tg+ 35°C (1020°C), as determined from DTA. The time and temperature of nucleation and crystal growth dictated the nature and size of the crystalline phases. Properties such as hardness and density were assessed and correlated to the nucleation temperature. The influence of sample specific surface on the devitrification mechanisms was estimated, and bulk nucleation was observed to be the dominant nucleation mechanism.
Single and Double Deflections of Cracks at the Carbon‐Carbon/BN Coating Interfaces in Ceramic‐Matrix Composites
Authors: Kumar Susmit , Singh Raj N.
Published: July 2010

A finite element technique is used to study the effects of coating properties on the deflection and penetration of cracks which terminate perpendicular to the bimaterial interfaces in SCS6‐zircon composites having three coatings (two carbon coatings and one boron nitride) on the fibers. Although, the change in the thickness of coatings has a very small effect on the stress ratio (ratio of hoop stresses along a crack and at the interface) and the energy release rate ratio (ratio of energy release rates for crack penetration and crack deflection), the magnitudes of the stresses and energy release rates change substantially. The finite element results are compared with experimental observations of Kumaria et al. on the nature of crack propagation behavior in these composites. Our finite element results explained the evidence of the doubly deflected cracks at the carbon‐carbon interface as experimentally seen by Kumaria et al.
Analysis of Phase Distribution for Ceramic Coatings Formed by Microarc Oxidation on Aluminum Alloy
Authors: Xue Wenbin , Deng Zhiwei , Lai Yonchun , Chen Ruyi
Published: July 2010

The phase distribution for ceramic coatings formed by microarc oxidation (MAO) on 2024 aluminum alloy was investigated using X‐ray diffraction. The results showed that the ceramic coatings mainly consisted of α‐Al2O3 and γ‐Al2O3 phases. The percentage of α‐Al2O3 gradually increased from the external surface to the interface between the coating and the substrate of samples. The surface layer of coatings mainly contained the γ‐Al2O3 phase, and its fraction of the composition remained almost constant with oxidation time. It is believed that the difference in the amounts of α‐Al2O3 and γ‐Al2O3 phases in the different layers of coatings was caused by the various cooling rates of molten Al2O3, which temporarily existed in the microarc zone.
Enzyme‐Catalyzed Inorganic Precipitation of Aluminum Basic Sulfate
Authors: II Robert E. Simpson , Habeger Craig , Rabinovich A. , Adair James H.
Published: July 2010

Particles of aluminum basic sulfate were synthesized from homogeneous solutions of aluminum acetate, sodium sulfate, urea, and the enzyme urease at room temperature. The urease was used to decompose the urea. The decomposition provided a controlled increase in the pH of the solution, from 5 to 9.
Grain Boundary Sliding Measurements during Tensile Creep of a Single‐Phase Alumina
Authors: Blanchard Cheryl R. , Lin Hua‐Tay , Becher Paul F.
Published: July 2010

The grain boundary sliding (GBS) behavior of a single‐phase (relatively coarse‐grained) alumina material was studied after tensile creep experiments were performed at 1500°C at stress levels of 20 and 35 MPa. Specimens tested at 35 MPa exhibited a number of modes of GBS, including Mode II (shear) displacements, Mode I (opening) displacements, out‐of‐plane sliding displacements, and in‐plane grain rotation. Strains in the grain boundaries due to Mode II GBS ranged from 940% to 4400%. Average Mode II GBS displacements ranged from 0.08 to 0.29 µm in samples tested for 120 and 480 min, respectively, at 35 MPa. The GBS displacements were shown to fit a Weibull distribution. Tensile creep under a 35 MPa stress yielded a GBS rate of 9.5 10‐6µm/s, while the 20 MPa stress resulted in a GBS rate of 2.2 10‐6µm/s. The average Mode II GBS displacements increased linearly with specimen strain, suggesting that GBS may play an important role in creep cavitation during tensile creep. The data also revealed that compatibility and constraint rules appear to govern GBS behavior during tensile creep. GBS behavior during compressive creep will be compared to the tensile creep GBS measurements presented.
Novel Synthesis of Mullite Powder with High Surface Area
Authors: Imose Masayuki , Takano Yoshihiko , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Boehmite (AlO(OH)) solid‐solution gel, which yields stoichiometric mullite (3Al2O32SiO2) at high temperatures, has been prepared by the hydrazine method. The formation process leading to 3Al2O32SiO2 is discussed. The as‐prepared powder and powders heated below 1200°C consist of very fine particles showing needlelike morphology, whereas the particles of mullite powder show thin prismatic morphology. The mullite powder after heating at 1300°C has a high surface area (87 m2/g).
Effect of Delamination on the Transverse Thermal Conductivity of a SiC‐Fiber‐Reinforced SiC‐Matrix Composite
Authors: Donaldson Kimberly Y. , Trandell Barbara D. , Lu Yangsheng , Hasselman D. P. H. , Maurer Norb
Published: July 2010

The effect of delamination on the transverse thermal conductivity of a biaxial multiweave SiC‐fiber‐reinforced chemical‐vapor‐infiltrated‐matrix composite was studied. The delamination process, induced by compressive loading, consisted of enlarging and widening pre‐existing interply cavities in the as‐received composite. Ultrasonic scanning suggested that the delamination process resulted in mechanical debonding between the plies. At room temperature, the delamination reduced the transverse thermal conductivity by a factor of ∼5. As a result of gaseous conduction in the interply cavities and/or delamination, the thermal conductivity was higher in air/nitrogen at atmospheric pressure than under vacuum, a difference that was especially pronounced in the delaminated sample. The thermal conductivity of the as‐received and delaminated samples exhibited a negative and positive temperature dependence, respectively, which resulted in almost‐equal values at temperatures >1000°C. Data analysis showed that the thermal conductivity of the delaminated composite was almost independent of the thermal conductivity of the plies themselves; instead, the thermal conductivity of the composite was controlled primarily by conduction across the delaminations at areas of direct contact, conduction through the gaseous phase within the delaminations, and radiation across the delaminations.
Sol‐Gel Preparation of Transparent and Conductive Aluminum‐Doped Zinc Oxide Films with Highly Preferential Crystal Orientation
Authors: Ohyama Masashi , Kozuka Hiromitsu , Yoko Toshinobu
Published: July 2010

Transparent aluminum‐doped zinc oxide (ZnO) films were prepared via the sol‐gel method on silica‐glass substrates from 2‐methoxyethanol solutions of zinc acetate and aluminum chloride that contained monoethanolamine. Dip coating was conducted at room temperature, with substrate withdrawal rates of 1.2‐7.0 cm/min. After each deposition, the films were heat‐treated in air at 200°‐450°C for 10 min (pre‐heat‐treatment). After six to fourteen layers had been deposited, the films were then subjected to annealing in air at 500°‐800°C for 1 h (the first post‐heat‐treatment), followed by annealing in nitrogen at 500°‐700°C for 15 min to 4 h (the second post‐heat‐treatment). All the films obtained were transparent and showed only an extremely sharp ZnO (002) peak in the X‐ray diffractometry (XRD) patterns. The effects of the aluminum content, the substrate withdrawal speed, and the heat‐treatment conditions on the electrical resistivity of the films were studied. All these factors strongly affected the resistivity. The lowest resistivity value (6.5 10‐3 Omegacm) was achieved in a film that contained 0.5 at.% aluminum, prepared with a low substrate withdrawal speed (1.2 cm/min), and a pre‐heat‐treatment of individual layer at 400°C in air and a post‐heat‐treatment of the entire film at 600°C in air, followed by a post‐heat‐treatment at 600°C in nitrogen. These preparation parameters also affected the degree of crystal orientation, which was revealed by the intensity of the ZnO (002) XRD peak. Higher crystal orientation was effective in reducing the film resistivity, whereas the higher grain‐packing density and possible aluminum segregation were thought to have positive and negative effects, respectively, in reducing the resistivity.
Tailored Porosity Gradients via Colloidal Infiltration of Compression‐Molded Sponges
Authors: Jr. Cichocki Frank R. , Trumble Kevin P. , Rödel Jürgen
Published: July 2010

A technique for producing ceramic preforms with graded porosity via colloidal infiltration of molded polymer sponges has been developed. Polymer sponges have been compression molded into various shapes with continuous and/or stepwise gradients in porosity. Infiltration of the graded sponge with ceramic slurry, followed by pyrolysis of the sponge and sintering of the ceramic, produces a ceramic component with graded porosity. A relationship between compressive strain and the volume fraction of porosity in the sponge has been derived and compared to measured values. The applicability of this technique to the manufacture of planar and axisymmetric composite shapes is demonstrated.
Synthesis and Morphology of Niobium Monocarbide Whiskers
Authors: Li Jian‐Bao , Xu Gui‐Ying , Sun Ellen Y. , Huang Yong , Becher Paul F.
Published: July 2010

Niobium monocarbide (NbC) whiskers were successfully synthesized by heating mixtures of niobium oxide (Nb2O5) powder and carbon black in an argon atmosphere to temperatures in excess of 1100°C. The whiskers were mainly cuboid or cycloid needles with a square‐pyramid‐shaped tip and were 0.1‐2.0 µm in width and 5‐100 µm in length. The particular shape of the whiskers and the very low impurity levels detected suggest that the NbC whiskers grew via a solid‐vapor growth process.