bluuebunny/crossref_metadata_2025 huggingface dataset:
A Century of Developments in Glassmelting Research
Authors: Cable Michael
Published: July 2010

This article reviews the progress in studies devoted to the understanding of glassmelting made since the foundation of The American Ceramic Society. After briefly considering some of the necessary preliminaries, the article briefly discusses studies in melting reactions, redox control, refining, homogenizing, volatilization, refractory corrosion, and flow in furnaces. Knowledge of all of these has advanced significantly in the period considered. However, although many aspects of glassmelting can be discussed on a reasonably sound theoretical foundation, the actual behavior of real, multicomponent systems can be predicted only rarely with confidence from the generally available data base. Computers now make it possible to store much more data than ever before and to analyze information in much more sophisticated ways. Nevertheless, there is often a need to continue carefully conducted basic work. The article concentrates on the older work not readily recovered by computer database searches.
Silicon Nitride/Silicon Carbide Nanocomposite Materials: I, Fabrication and Mechanical Properties at Room Temperature
Authors: Herrmann Mathias , Schuber Christian , Rendtel Andreas , Hübner Heinz
Published: July 2010

The fabrication of dense Si3N4/SiC nanocomposite materials that contained 2.5‐30 wt% SiC via gas‐pressure sintering and hot pressing was investigated. The SiC particles originated from admixed commercial SiC powders, SiCN powders produced by plasma synthesis, in situ reaction pyrolysis of carbon‐coated Si3N4 particles, and pyrolysis of a polycarbosilazane‐based SiCN precursor. Based on thermodynamic calculations, criteria for minimum liquid‐phase decomposition during sintering were developed. The best sintering results were obtained for sintering cycles that observed this criteria. Materials that contained plasma‐synthesized SiCN exhibited high strengths (835‐995 MPa) and fracture toughness values (7.4‐7.8 MPam1/2) at room temperature. Post‐sintering thermal treatments led to a strength reduction.
Crystallographic Data of a New Phase of Dicalcium Silicate
Authors: Miyazaki Makoto , Yamazaki Satoru , Sasaki Kaori , Ishida Hideki , Toraya Hideo
Published: July 2010

Unit‐cell parameters and the space group of a new phase of dicalcium silicate (Ca2SiO4) were determined by using powder X‐ray diffractometry and selected‐area electron diffraction techniques. This phase could be synthesized via the dissociation of hydrothermally synthesized alpha‐Ca2(SiO4H)OH at temperatures of ∼500°‐920°C. Crystallographic data for the sample synthesized at 600°C were as follows: Ca2SiO4, monoclinic; P21/c space group; lattice parameters of a= 0.82147(9) nm, b= 0.9808(1) nm, c= 0.9741(1) nm, and β= 94.642(7)°; cell volume (V) of 0.7857(1) nm3; Z= 8 (where Z is the number of chemical formula units in a unit cell); and a density of 2.91 g/cm3. The crystallographic data for samples synthesized at 800°C had slightly different unit‐cell parameters of a= 0.82124(6) nm, b= 0.97348(7) nm, c= 0.97935(7) nm, β= 94.831(5)°, and V= 0.7849(1) nm3. Structural relationships of the new phase with the other dicalcium silicates are discussed.
Hydrothermal Synthesis of Spherical Perovskite Oxide Powders Using Spherical Gel Powders
Authors: Choi Jae Young , Kim Chong Hee , Kim Do Kyung
Published: July 2010

Spherical perovskite oxide powders, composed of fine particulates, were prepared by using spherical gel powders under hydrothermal conditions. Spherical PbTiO3, BaTiO3, and SrTiO3 powders were synthesized from spherical TiO2 gel powders, and spherical PbZrO3 powder from spherical ZrO2 gel powder. Spherical Pb(Zr0.5, Ti0.5)O3 and Ba(Zr0.5,Ti0.5)O3 powders were prepared from spherical ZrTiO4 gel powders. Lead acetate trihydrate, barium hydroxide octahydrate, and strontium hydroxide octahydrate were used as the sources of A‐site ions in each perovskite oxide (ABO3). The spherical TiO2 and ZrO2 gel powders were prepared by thermal hydrolysis of titanium tetrachloride and zirconium oxychloride, respectively, and spherical ZrTiO4 gel powder by thermal hydrolysis of a mixture of them in alcohol‐water mixed solvent. During the hydrothermal treatment, the spherical gel powders retained their spherical shape to produce spherical perovskite oxide powders, composed of nanometer‐sized particulates.
Microstructure and Dielectric Properties of YMnO3 Thin Films Prepared by Dip‐Coating
Authors: Kitahata Hiroya , Tadanaga Kiyoharu , Minami Tsutomu , Fujimura Norifumi , Ito Taichiro
Published: July 2010

YMnO3 thin films with Y/Mn ratios from 1.00/1.05 to 1.00/0.90 were prepared by dip‐coating from solution, in which starting materials were refluxed, and the effects of the Y/Mn ratio on the structure and dielectric properties of YMnO3 thin films were investigated. XRD measurements indicated that the films with the Y/Mn ratios in this study were a single phase of polycrystalline YMnO3. The lattice constants along the a‐axis and c‐axis lengthened with an increase in the Y/Mn ratio. FE‐SEM micrographs of the films showed that the surface of the films became smoother and denser with an increase in the Y/Mn ratio. YMnO3 thin films with good dielectric properties were obtained with an Y/Mn ratio of 1.00/0.90, which gave the smoothest and densest microstructure and the smallest leakage current.
Effect of Post‐Precipitation Treatment on the Pore‐Structure Stability of Sol‐Gel‐Derived Lanthanum Zirconate
Authors: Nair Jalajakumari , Nair Padmakumar , Van Ommen Jan G. , Ross Julian R. H. , Burggraaf Anthonie J.
Published: July 2010

The importance of post‐precipitation treatments (pore‐fluid exchange and its removal) on the evolution of the texture of coprecipitated lanthanum zirconate has been investigated. The nature of the pore fluid and the type of fluid‐removal (drying) process have shown a profound effect on the aggregate structure (packing of primary particles within the aggregates of the gel). Exchanging the pore fluid with organic fluids such as ethanol or tetrahydrofuran resulted in higher specific surface area, larger pore volume, and, most frequently, larger pore radii. The effect has been attributed to the surface tension of the pore fluid rather than to the polycondensation effect. Freeze drying and microwave drying of ethanol‐washed lanthanum zirconate gel also resulted in higher surface area, compared to the oven‐dried gel. Freeze drying and microwave drying yielded a surface area of ∼30 m2/g, whereas oven drying yielded a surface area of 20 m2/g after heating at 800°C.
Fatigue Crack Growth Behavior in Mullite/Alumina Functionally Graded Ceramics
Authors: Bartolomé José F. , Moya José S. , Requena Joaquín , LLorca Javier , Anglada Marc
Published: July 2010

Mullite/Al2O3 functionally graded ceramics (FGCs) have been obtained by sequential slip casting and subsequently firing at 1650°C in air. Functionally graded layered dense (similar/congruent99% of the theoretical density) compacts, with five different layers with thickness ranging from 670 to 850 µm, were obtained. The layer composition was gradually changed from 100% mullite to 80% mullite/20% alumina. The elastic modulus, the flexure strength, and the fatigue life of the monolithic (80% mullite/20% alumina) and mullite/alumina FGCs were measured by means of four‐point bending tests. The mullite/alumina FGCs exhibited lower strength than the monolithic material but the fatigue resistance and reliability were improved in the high cycle fatigue regime. These results were rationalized in terms of the residual stress distribution in the FGCs, which was computed using a description of stresses and strains in the multilayer composite based on the simple beam analysis. The tensile residual stresses which developed in the surfaces were responsible for the lower strength, while the compressive residual stresses within the bulk arrested the fatigue crack and improved the fatigue life of the FGC material.
Novel Preparation Method of Hydroxyapatite Fibers
Authors: Ota Yoshio , Iwashita Tetsushi , Kasuga Toshihiro , Abe Yoshihiro
Published: July 2010

A novel method for preparing calcium hydroxyapatite (Ca10(PO4)6(OH)2: HAp) fibers has been developed. HAp fibers can be prepared successfully by heating a compact consisting of calcium metaphosphate (ß‐Ca(PO3)2) fibers with Ca(OH)2 particles in air at 1000°C and subsequently treating the resultant compact with dilute aqueous HCl solution. The ß‐Ca(PO3)2 fibers and the Ca(OH)2 in the compact were converted into fibrous HAp and CaO phases by the heating, and the CaO phase was removed by acid‐leaching. HAp fibers obtained in the present work were 40‐150 µm in length and 2‐10 µm in diameter. The fibers had almost the same dimensions as those of the ß‐Ca(PO3)2 fibers.
Combined Effects of Exposure to Salt (NaCl) Water and Oxidation on the Strength of Uncoated and BN‐Coated Nicalon™ Fibers
Authors: Parthasarathy Triplicane A. , Folsom Craig A. , Zawada Larry P.
Published: July 2010

The environmental stability of uncoated and boron nitride‐coated (BN‐coated) Nicalon fiber has been investigated by studying the effect of annealing in air at 1000°C (2 h) on the strength of the fibers. The results imply that uncoated and BN‐coated fibers both degrade in strength, with the BN‐coated fiber suffering a higher strength loss. The degradation is significantly enhanced if the fibers are exposed to salt (NaCl) water prior to the air anneal, if the concentration of salt is >0.5 wt%. The BN‐coated Nicalon fibers also have been studied at 800° and 900°C; the degradation in strength due to salt water exposure is greater at 800°C than that at 900° or 1000°C.
Viscosity of Amorphous Oxide Scales on SiSiC at Elevated Temperatures
Authors: Futakawa Masatoshi , Steinbrech Rolf W.
Published: July 2010

The high‐temperature corrosion resistance of non‐oxide Si‐containing ceramics is governed by the properties of the protecting silica scales, which develop in oxidizing atmospheres. Bilayered scales of about 8 µm total thickness with crystalline and amorphous layers were grown on reaction‐bonded SiC (SiSiC) to study viscosity aspects of the scale. As the amorphous layer formed at the free surface, specimens were scale bonded by means of high‐temperature compression and thereafter tested in symmetric shear relaxation experiments. With this novel technique the scale viscosity was determined in the range between 920° and 1020°C. The tests revealed a strong temperature dependence with viscosity values between those of pure silica and commercial aluminosilicate glass. The results are discussed in terms of impurities deliberately introduced into the oxidation atmosphere during the formation of the silica scale on SiSiC.
Mössbauer Spectroscopy of Borate Glasses Containing Divalent Europium Ions
Authors: Fujita Koji , Tanaka Katsuhisa , Hirao Kazuyuki , Soga Naohiro
Published: July 2010

Borate glasses containing 0.99–30.0 mol% EuO have been prepared under a reducing atmosphere and 151Eu Mössbauer effect measurements have been carried out at room temperature in order to examine the chemical state of Eu2+ ions in these glasses. Mössbauer spectra indicate that most of the europium ions are present as the divalent oxidation state. In dilute Eu2+‐containing borate glasses, spectra are split due to paramagnetic hyperfine interactions in the glasses with low and high sodium contents. In concentrated Eu2+‐containing borate glasses, line broadening results from the contribution of quadrupole splitting due to asymmetrical oxygen coordination around Eu2+ and the contribution of inhomogeneous broadening due to site‐to‐site variation. The compositional dependence of isomer shift and quadrupole interaction parameter can be related to the structural changes in the borate glass. The variation of the isomer shift has a good correlation with the optical basicity of glass, and the trend can be explained in terms of the covalent admixture with 6s character. The Eu‐O bond in the borate glasses is more ionic than that in EuTiO3 and EuZrO3, where the oxygen coordination number for Eu2+ is 12. The average coordination number for Eu2+ is found to be 12 in all of the present glasses.
Sol‐Gel Route to Ferroelectric Layer‐Structured Perovskite SrBi2Ta2O9 and SrBi2Nb2O9 Thin Films
Authors: Kato Kazumi , Zheng Can , Finder Jeffrey M. , Dey Sandwip K. , Torii Yasuyoshi
Published: July 2010

Precursors for layer‐structured perovskite thin films of SrBi2Ta2O9 (SBT) and SrBi2Nb2O9 (SBN) were prepared by the reactions of a strontium‐bismuth double methoxyethoxide and tantalum or niobium methoxyethoxide in methoxyethanol, followed by partial hydrolysis. Several spectroscopic techniques, such as 1H‐, 13C‐, and 93Nb‐NMR (nuclear magnetic resonance), and Fourier‐transform infrared spectroscopy were used to analyze the arrangement of the metals and oxygen in the precursor molecules. The precursors contained Sr‐O‐M (where M is Ta or Nb) bonds (i.e., a strontium is connected to two MO6 octahedra) and Sr‐O‐Bi bonds with a bismuth atom bonded to the oxygens of the MO6 octahedron. The arrangement of metals and oxygens was considered to be similar to the layer‐structured perovskite crystal sublattice. As a result, the sol‐gel‐derived SBT thin films crystallized, by rapid thermal annealing in an oxygen atmosphere below 550°C, and they exhibited preferred (115) orientation. The crystallinity improved and the crystallite size increased with temperature up to 700°C. In the case of SBN thin films, a low heating rate (2°C/min) was necessary for the control of the crystallographic (115) orientation, whereas a rate of 200°C/s (rapid thermal annealing) produced films that exhibited c‐axis orientation. The (115) SBT thin film, heated to 700°C, exhibited improved ferroelectric properties.
Crystallization of Gallium Lanthanum Sulfide Glasses
Authors: Morgan S. P. , Reaney I. M. , Buckley R. , Furniss D. , Seddon A. B.
Published: July 2010

The crystallization of gallium lanthanum sulfide (GLS) glasses of composition (100 ‐ x)Ga2S3xLa2S3 (mol%) has been analyzed using X‐ray diffraction, and optical and transmission electron microscopy. The major crystalline phase, X, was found to be different from the La3.33Ga6S14 phase reported previously in similar compositions. X was the primary phase present and was observed in all samples, forming on quenching as well as on subsequent heat treatment. The phase occurred as spherulites composed of lamellae, approximately 1 µm wide and all of the same orientation. A small quantity of crystals of Ga2S3 (20 nm) were observed to grow discontinuously between the lamellae. Electron diffraction and energy dispersive X‐ray analysis suggested that phase X was monoclinic and had approximately a 2:1 Ga2S3:La2S3 ratio.
Point Defects and Chromium(IV) Formation Mechanism in Gallia‐ and Alumina‐Based Oxide Glasses
Authors: Murata Takahiro , Torisaka Masanori , Takebe Hiromichi , Morinaga Kenji
Published: July 2010

Point defects were found in as‐quenched GeO2, 65CaO35Al2O3, and 65SrO35Ga2O3 glasses on the basis of electron paramagnetic resonance (EPR) measurements. These defects were identified as Ge É centers in GeO2 glass and O‐2, O‐3, and M‐OHC (oxygen hole center) (where M = Al, Ga) in 65CaO35Al2O3 and 65SrO35Ga2O3 glasses. The formation of Ge É centers in as‐quenched GeO2 glass was due to the thermodynamic stability of GeO at the melting temperature. The latter oxygen‐excess defects are supposed to be formed by excess oxygen ions derived from the modifiers in the aluminate and gallate glasses during the formation of these glasses. To investigate some of the properties of the oxygen‐excess defects in the calcium aluminate and strontium gallate glasses, chromium ions were doped in these glasses as a probe and the relationship between the valency state of the chromium ion and the defects was determined. We conclude that the peroxy bonding (‐O‐O‐) oxidizes the Cr3+ species to Cr4+. Similar defects have been identified in host compounds that are used for Cr4+ tunable lasers. These results reveal that the point defects are necessary to stabilize the Cr4+ ions in glasses and crystals.
A New, Low‐Temperature Polymorph of Ó‐SiAlON
Authors: Bowden Mark E. , Barris Glen C. , Brown Ian W. M. , Jefferson David A.
Published: July 2010

A new phase in the Si‐Al‐O‐N system has been identified, following syntheses based on the nitridation of silicon/clay mixtures at low temperatures (<1350°C). The structure of the new phase was determined using a combination of diffraction and high‐resolution imaging techniques, and this new phase possessed the same sheet structure as Ó‐SiAlON (Si2−xAlxO1+xN2−x) but with a different stacking arrangement. It is considered to be a low‐temperature polymorph of Ó‐SiAlON and transforms to conventional Ó‐SiAlON at temperatures greater than ∼1350°C.
Electrical and Thermal Conductivities of Nickel‐Zirconia Cermets
Authors: Hu Wangyu , Guan Hengrong , Sun Xiaofeng , Li Shizhuo , Fukumoto Masahiro , Okane Isao
Published: July 2010

The microstructure, electrical resistivity, and thermal diffusivity of nickel‐zirconia cermets have been studied. Scanning electron microscopy of the fracture surfaces of samples shows that there are some small isolated nickel granules adhering to the surface of the zirconia particles. Considering such a microstructural feature of samples and the law of mixtures, an improved model for electrical and thermal conductivity is established. With this model, the experimental results‐that electrical conductivity and thermal diffusivity increase with increasing nickel content‐are interpreted. Moreover, the thermal diffusivity is observed to be almost linearly related to temperature.
Formation, Powder Characterization and Sintering of MgCr2O4 by the Hydrazine Method
Authors: Yoshida Noriyuki , Takano Yoshihiko , Yoshinaka Masaru , Hirota Ken , Yamaguchi Osamu
Published: July 2010

Picrochromite (MgCr2O4) crystallizes at 480° to 530°C from an amorphous material prepared by the hydrazine method. The MgCr2O4 powders were characterized for particle size and surface area. Individual particles tend toward a hexagonal morphology above 1000°C. Dense MgCr2O4 ceramics (99.5% of theoretical) with an average grain size of 2 μm have been fabricated by spark plasma sintering for 5 min at 1400°C and 30 MPa. Their fracture toughness and bending strength are 3.7 MPa·m1/2 and 310 MPa, respectively.
Crystallization Hierarchy of CaO‐P2O5‐SiO2‐Al2O3‐TiO2 Glass‐Ceramics
Authors: Jordery Sophie , Lee William E. , James Peter F.
Published: July 2010

Glasses in the tricalcium phosphate‐anorthite (Ca3(PO4)2‐CaAl2Si2O8 or TCP‐CAS2) system with additional TiO2 were melted. Crystallization was investigated using thermal analysis, X‐ray diffraction, and transmission optical and electron microscopies. During the heat treatment, as the growth temperature increases, successive crystalline phases separate from the glass matrix. The phases present in the fully heat‐treated glass‐ceramic are ß‐TCP, anor‐thite (CAS2), and rutile (TiO2). Apart from TiO2, these phases evolve from other polymorphs during the heat treatment. The metastable phases, pseudo‐orthorhombic CAS2 and alpha‐TCP, appear first around 880°C and transform into the stable phases, triclinic anorthite CAS2 and ß‐TCP, around 940° and 1000°C, respectively. The material crystallizes in stages. The first stage is the separation from the glass matrix of rutile and what is believed to be a calcium phosphate phase, with crystal sizes varying from 20 to 200 nm. This is followed by the appearance of larger crystals (1‐2 µm) of the metastable pseudo‐orthorhombic CAS2, surrounding the previously crystallized phases. Finally, this pseudo‐orthorhombic CAS2 phase transforms to anorthite (15‐20 µm) spherulites. TiO2 does not act as a direct nucleating agent in the glass composition studied: no sign of heterogeneous nucleation and growth from TiO2 crystals has been found, and moreover, TiO2‐free base glass crystallizes in a manner similar to that of the glass containing TiO2.
Synthesis of Calcium Hydroxyapatite‐Tricalcium Phosphate (HA‐TCP) Composite Bioceramic Powders and Their Sintering Behavior
Authors: Kivrak Nezahat , Taş A. Cuneyt
Published: July 2010

Composite (biphasic) mixtures of two of the most important inorganic phases of synthetic bone applications‐namely, calcium hydroxyapatite (Ca10(PO4)6(OH)2 (HA)) and tricalcium phosphate (Ca3(PO4)2 (TCP))‐were prepared as submicrometer‐sized, chemically homogeneous, and high‐purity ceramic powders by using a novel, one‐step chemical precipitation technique. Starting materials of calcium nitrate tetrahydrate and diammonium hydrogen phosphate salts that were dissolved in appropriate amounts in distilled water were used during powder precipitation runs. The composite bioceramic powders were prepared with compositions of 20%‐90% HA (the balance being the TCP phase) with increments of 10%. The pellets prepared from the composite powders were sintered to almost full density in a dry air atmosphere at a temperature of ~1200°C. Phase‐evolution characteristics of the composite powders were studied via X‐ray diffractometry as a function of temperature in the range of 1000°‐1300°C. The sintering behavior of the composite bioceramics were observed by using scanning electron microscopy. Chemical analysis of the composite samples was performed by using the inductively coupled plasma‐atomic emission spectroscopy technique.
Electron Paramagnetic Resonance Spectroscopy of gamma‐Radiation‐Induced Paramagnetic Centers in Titania‐Bearing Sodium Silicate Glasses
Authors: Pelikán Peter , Liska Marek , Mazúr Milan , Lukác Peter , Antalík Jozef , Lesn Juraj
Published: July 2010

The electron paramagnetic resonance (EPR) spectra of gamma‐irradiated titania‐bearing sodium silicate glasses were quantitatively analyzed by using the spectral decomposition of the EPR spectra and categorizing it into two types of randomly oriented paramagnetic centers: the orthorhombic (HC1) center and the axially symmetric (HC2) center. The orthorhombic HC1 center was assigned to the Q2 structural unit (the term Qi represents a SiO4 tetrahedron with i bridging oxygens), whereas the generation of the axially symmetric HC2 radical was expected in the case of the Q3 unit. The relative amounts x(HC1) and x(HC2) of HC1 and HC2 radicals were evaluated using the obtained data of the measured EPR spectra for five gamma‐irradiated glasses with titania contents in the range of 0‐10 mol%. The strong increase of the HC1 relative abundance, from a value of 26% (for titania‐free glass) to a value of 89% (obtained for glass with 1 mol% of titania) confirmed the preferred sensitivity of Q2 units at low titania contents. Thus, titanium, which has a great absorption cross section, preferably entered the positions in the neighborhood of the Q2 units. The semi‐empirical linear combination of atomic orbitals to form molecular orbitals by a self‐consistent field (LCAO‐MO‐SCF) quasi‐relativistic intermediate neglect of differential overlap (INDO) method was used to confirm this effect. For titania contents of >1 mol%, the above‐mentioned effect was overwhelmed by the structural changes induced by titania in the silicate network, namely the diminishing of the Q2 content. Only the axially symmetric HC2 centers were present in the glasses with titania contents of >5 mol%.
Mechanical Properties of Si3N4‐SiC Three‐Layer Composite Materials
Authors: Choi Byung‐Jin , Koh Young‐Hag , Kim Hyoun‐Ee
Published: July 2010

The effects of microstructure and residual stress on the mechanical properties of Si3N4‐based three‐layer composite materials were investigated. The microstructure of each layer was controlled by the addition of two differently sized silicon carbides: fine SiC nanoparticles (∼200 nm) or relatively large SiC platelets (∼20 µm). When the SiC nanoparticles were added, the average grain size of Si3N4 was reduced because of the inhibition of grain growth by the particles. On the other hand, when the SiC platelets were added, the microstructure of Si3N4 was not much changed because of the large size of the platelets. Three‐layer composites were fabricated by placing the Si3N4/SiC‐nanoparticle layers on the surface of the Si3N4/SiC‐platelet layer. The residual stress was controlled by varying the amount of SiC added. The mechanical properties of three‐layer composites with various combinations of microstructure and residual stress level were investigated.
Hydrothermal Synthesis of Nanosize alpha‐Al2O3 from Seeded Aluminum Hydroxide
Authors: Sharma Pramod K. , Jilavi M. H. , Burgard D. , Nass R. , Schmidt H.
Published: July 2010

alpha‐Alumina and boehmite particles were synthesized by coprecipitation followed by a hydrothermal treatment. X‐ray diffraction (XRD) indicated that alpha‐Al2O3 was the major phase and coexisted with 4% of boehmite in the presence of the alpha‐Al2O3 seeds. On the other hand, a single boehmite phase was obtained in the absence of the alpha‐Al2O3 seed particles. The powder densified in the temperature range from 1050° to 1350°C. High‐resolution transmission electron microscopy (HRTEM) showed that the particle size of the synthesized alpha‐Al2O3 was 60 nm. The surface area was 245 m2/g.
Kinetics of Thin‐Film Reactions of Nickel Oxide with Alumina: II, {1100} and {1102} Reaction Couples
Authors: Kotula Paul G. , Carter C. Barry
Published: July 2010

The kinetics of the earliest stages of solid‐state reactions between epitactic thin films of nickel oxide (NiO) and {11# 00}‐ and {11# 02}‐oriented single crystals of alumina (Al2 O3) have been studied. The starting reaction geometry consisted of a nickel aluminate (NiAl2 O4) buffer layer 20 nm thick and a NiO overlayer that was 400 nm thick, both of which were grown via pulsed‐laser deposition and were epitactic with the substrate. When heated, the reaction lay‐ers thickened mainly as the square root of time (i.e., para‐bolic kinetics) increased, which was indicative of reaction‐controlled kinetics via diffusion through the product layer. The activation energy for the reaction was 461 kJ/mol for {11# 00} and 464 kJ/mol for the {11# 02}; both values are consistent with measurements made previously using thin‐film and bulk reaction geometries. A smaller linear component to the kinetics has also been identified. The results of microstructural characterization and “marker” experiments will also be discussed.
Two‐Dimensional Simulation of Cake Growth in Slip Casting
Authors: Banno Takumi , Sano Saburo , Oda Kiichi
Published: July 2010

A two‐dimensional computer simulation of cake growth was studied for the slip casting of alumina with a gypsum mold. Based on the Adcock and McDowall model, the method of finite differences was applied to the simulation, and numerical calculations were performed for the cake growth on the inside wall of a rectangular, box‐type mold by using the cake‐growth controlling parameters that were obtained experimentally. Good agreement was observed between the experimental and calculated cake growth in the vicinity of the boundary between the gypsum mold and the silicon rubber and at the rectangular corner of the gypsum mold. The present simulation method is expected to be useful for estimating cake growth on molds with complicated shapes in slip casting.
Decomposition‐Crystallization of Polymer‐Derived Si‐C‐N Ceramics
Authors: Kleebe Hans‐Joachim , Suttor Daniel , Müller Heike , Ziegler Günter
Published: July 2010

Monolithic polymer‐derived Si‐C‐N ceramics were processed by blending an oligomeric Si‐C‐N precursor (liquid polysilazane) with 70 vol% of crosslinked or pyrolyzed Si‐C‐N powder particles, which were obtained from the same liquid precursor preheated at 300° or 1000°C, respectively. Powder compacts subsequently were annealed at 300°C to crosslink the liquid precursor acting as a binder between the powder particles, thus yielding monolithic green bodies. Heat treatment at 1540°C was performed to initiate crystallization in the various samples. Microstructure development and, in particular, crystallization behavior were characterized by X‐ray diffractometry (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and preliminary nuclear magnetic resonance (NMR) spectroscopy. The material containing 300°C polymer powder (with oligomeric binder, also crosslinked at 300°C) revealed a homogeneous amorphous microstructure after exposure to temperatures of 1540°C. In contrast, the specimen containing powder particles preheated at 1000°C exhibited a high volume fraction of SiC crystallites within regions that were previously filled by the binder; however, the Si‐C‐N powder particles themselves remained amorphous. SEM observations as well as XRD studies showed the formation of idiomorphic SiC and Si3N4 crystallites on specimen surfaces as well as along internal crack walls. This finding suggested that vapor‐phase reactions at the surface were involved in the formation of crystalline phases at temperatures >1250°C. Moreover, NMR spectroscopy data indicated a phase separation process, implying structural rearrangement prior to crystallization.
Epitaxial Thin Film Growth of Lanthanum and Neodymium Aluminate Films on Roll‐Textured Nickel Using a Sol‐Gel Method
Authors: Shoup Shara S. , Paranthaman M. , Goyal Amit , Specht Eliot D. , Lee Dominic F. , Kroeger Donald M. , Beach David B.
Published: July 2010

As part of an effort to develop a new, non‐vacuum‐processed substrate for high current superconducting films, thin films of LaAlO3 and NdAlO3 were deposited on biaxially textured (100) nickel substrates using a solution deposition technique. On heating to 1150°C in Ar‐4% H2 for 1 h, epitaxial films were obtained. Out‐of‐plane alignment was confirmed by obtaining rocking curves of the (002) plane of the LaAlO3 (full width at half‐maximum (fwhm) = 7.2°) and the NdAlO3 (fwhm = 5.8°) films. In‐plane alignment was demonstrated by obtaining phi scans of the (110) plane of the LaAlO3 (fwhm = 13.4°) and the NdAlO3 (fwhm = 8.8°) films. Grain alignment in the films is approximately equivalent to the alignment of the Ni substrate. Analysis of pole figures indicated that in both films there are two in‐plane orientations present, the major being (001)[100] and the minor (001)[110].
Influence of Granule Character on Strength and Weibull Modulus of Sintered Alumina
Authors: Jr. Walker William J. , Reed James S. , Verma Surendra K.
Published: July 2010

Alumina specimens were prepared by compacting well‐characterized spray‐dried alumina granules of excellent deformability, followed by sintering. The strength and Weibull modulus were measured and microstructure was evaluated for specimens prepared from granules with different density and morphology. Compacts of spheroidal granules with lower density and lower granule strength sintered to 98% relative density and had fewer microstructural defects than compacts prepared from spheroidal or hollow granules of higher density. Flexural strength of sintered material was found to depend on initial granule size but not density or morphology of the granules. Weibull moduli of 18–20 were independent of particular granule characteristics.
Effect of the Orientation of Boron Nitride Grains on the Physical Properties of Hot‐Pressed Ceramics
Authors: Hubácek Milan , Ueki Masanori
Published: July 2010

Mixtures of two grades of boron nitride (BN) powder differing in their crystallinity were hot‐pressed in the presence of copper vapor. Two phenomena contributing to the bulk orientation have been recognized: the copper‐activated growth of microcrystalline BN grains, and the mechanical aligning of crystalline BN grains. The orientation of boron nitride grains varied widely, and a nearly isotropic material was prepared from a mixture containing 90 wt% microcrystalline powder. The relative intensity of the (100) diffraction line in the isotropic material was 50% higher than that in the standard BN powder. The flexural strength of a ceramic hot‐pressed from a composition containing 60 wt% microcrystalline powder reached 160 MPa. The thermal conductivity and Young's modulus showed a strong dependence on the grain orientation, being substantially higher along the BN layers than across them; the modulus, in addition, was negatively influenced by grain boundaries.
Thermodynamic Analysis of the FR(LT)‐FR(HT) Phase Transition in the Pb(Zr,Ti)O3 System under a Hydrostatic Pressure
Authors: Oh S. Hoon , Jang Hyun M.
Published: July 2010

Effects of hydrostatic pressure on the ferroelectric phase transition between the two rhombohedral phases in the Zr‐rich Pb(Zr,Ti)O3 (PZT) system have been investigated using the Landau‐Devonshire phenomenological theory. For this purpose, the rotostrictive coefficients related to the coupling between the oxygen octahedron and the stress were evaluated first. It was shown that the transition temperature between the two rhombohedral phases FR(LT) and FR(HT) decreased with increasing tensile hydrostatic pressure. Contrary to this, an opposite trend was predicted under the condition of compressive hydrostatic pressure.
Carbothermal Synthesis of Nanocrystalline Aluminum Nitride Powders
Authors: Pathak Lokesh Chandra , Ray Ajoy Kumar , Das Samar , Sivaramakrishnan C. S. , Ramachandrarao P.
Published: July 2010

A new precursor technique for the carbothermal synthesis of nanocrystalline AlN powder has been developed. A precursor that contains an intimate mixture of nanocrystalline Al2O3 and carbon has been synthesized by using a chemical pyrophoric reaction. The formation of AlN starts at 1473 K, and complete conversion has been observed at temperatures >1673 K. The synthesized AlN particles are nanocrystalline (<100 nm) in size.
Polymerized Organic‐Inorganic Synthesis of Mixed Oxides
Authors: Gülgün Mehmet A. , Nguyen My H. , Kriven Waltraud M.
Published: July 2010

A new and simple chemical route has been used to synthesize mixed‐oxide powders. The method uses long‐chain polymers, such as poly(vinyl alcohol) and poly(ethylene glycol). The chemistry of the precursor solution differs from other solution‐polymerization techniques. The stabilization of the cations in the precursor is established not only through the chemical binding of cations with the functional groups, but also, in major part, through the physical entrapment of the metal ions in the network of the dried polymer carrier. Pure, single‐phase calcium aluminate, yttrium aluminate, and yttrium phosphate powders have been produced, while maintaining a 4:1 ratio of positively charged valences of the cations (Men+) to negatively charged hydroxyl (‐OH−) groups. The ceramic yield of the new method (the ratio of the weight of the ceramic powders to the weight of the organics that are used in the preparation) is ∼2.
Effects of Calcination on the Microstructures and Photocatalytic Properties of Nanosized Titanium Dioxide Powders Prepared by Vapor Hydrolysis
Authors: Chan Chak K. , Porter John F. , Li Yu‐Guang , Guo Wei , Chan Chi‐Ming
Published: July 2010

Ultrafine titanium dioxide powders are produced in an aerosol reactor using vapor hydrolysis of titanium tetraisopropoxide (TTIP) at 260°C and higher temperatures (600°, 700°, 800°, and 900°C). The effect of calcination on the microstructure characteristics and the photoactivity is studied. The powders are characterized using Brunauer‐Emmett‐Teller (BET) surface area, X‐ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The photocatalytic activity of the powders is also studied using degradation of phenol in water as a test reaction. The powder produced at 260°C is calcined at 500° to 900°C while those produced at higher temperatures are calcined at 600°C for 3 h. Raw powder produced at 260°C is amorphous but becomes crystalline after calcination. As the calcination temperature increases, the surface area decreases but the rutile‐to‐anatase ratio and the anatase and rutile crystallite sizes increase. The photoactivity increases as calcination temperature increases to 900°C, when the powder becomes densified and the surface area drops significantly because of sintering. Powders produced at higher temperatures are predominantly anatase and are generally more photoactive. Calcination of the powders at 600°C for 3 h results in little loss of surface areas and enhances the photoactivity. Among the factors examined, large surface area and good dispersion of the powders in the reaction mixture are favorable to photoactivity. Conversely, prolonged calcination at high temperatures is detrimental to photoactivity. However, surface area, crystallite size, anatase‐to‐rutile ratio, and dispersity of the powders alone cannot account for the observed trend of photoactivity. The role of crystallinity needs to be investigated.
Thermal Shock Resistance of Ceramic Foams
Authors: Vedula Venkata R. , Green David J. , Hellman John R.
Published: July 2010

Thermal shock behavior of a variety of open‐cell ceramic foams was evaluated using infrared heating and forced air cooling. The extent of damage after thermal shock was determined by a nondestructive, dynamic resonance technique. The damage in foams was found to be strongly dependent on cell size and weakly dependent on density. In zirconia‐based foams, damage was found to increase with an increase in zirconia content. A thermal stress resistance parameter R′f was derived to predict the effect of cell size and density on the damage incurred in foams. The experimental results were found to corroborate the predictions fairly well but a better approach was to compare the maximum applied thermal strains with the degree of damage.
Study of the Hydration Process of Calcium Phosphate Cement by AC Impedance Spectroscopy
Authors: Liu Changsheng , Huang Yue , Zheng Haiyan
Published: July 2010

AC impedance spectroscopy was used to study the hydration process and behavior of calcium phosphate cement. The results indicated that this method based on the theory of electrochemistry had certain advantages in the analysis of continuous microstructural changes of cement during the hydration process. The changes revealed by AC impedance at different hydration times were in agreement with the variation of compressive strength. In addition, the influences of conditions such as the ratio of powder to water, the concentration of solution, and crystal seeding on the microstructural changes could also be conveniently inspected using this method.
Effects of Interface Roughness on Residual Stresses in Thermal Barrier Coatings
Authors: Hsueh Chun‐Hway , Haynes James A. , Lance Michael J. , Becher Paul F. , Ferber Mattison K. , Fuller Edwin R. , Langer Stephen A. , Carter W. Craig , Cannon W. Roger
Published: July 2010

Using a newly developed object‐oriented finite‐element analysis method, both an actual microstructure and model microstructures of a plasma‐sprayed thermal barrier coating system were numerically simulated to analyze the full‐field residual stresses of this coating system. Residual stresses in the actual microstructure were influenced by both the irregular top‐coat/bond‐coat interface and cracks in the top coat. By treating the microcracked top coat as a more‐compliant solid microstructure, the effects of the irregular interface on residual stresses were examined. These results then could be compared to results that have been obtained by analyzing a model microstructure with a sinusoidal interface, which has been considered by some earlier investigators.
Monopyroxenic Basalt‐Based Glass‐Ceramics
Authors: El‐Shennawi Ahmed Wagdi A. , Mandour Mohamed A. , Morsi Morsi M. , Abdel‐Hameed Salwa A. M.
Published: July 2010

Uniform, ultrafine, microcrystalline, hard, pyroxenic glass‐ceramic materials have been obtained successfully from basalt rock; instead of adding nucleation catalysts, the FeO:Fe2O3, CaO:Na2O, and CaO:MgO ratios have been rectified. This process has been accomplished by deliberately adding the smallest permissible amounts of oxidizers, limestone, dolomite, and soda ash (as additives) that are necessary to fulfill the monominerality requirements; these requirements affect the melting, workability, crystallization, and microstructure of the glass‐ceramics. The melting temperature decreases as the ratios decrease (beyond certain limits); in addition, the workability, crystallization, and microstructure also improve as the ratios decrease. An almost‐stable solid solution of augite or aegirine‐augite composition is the only crystalline phase that is formed. The minimal FeO:Fe2O3 ratio and the likelihood of a greater affinity of the Na+ cation for the Fe3+ cation, rather than the Al3+ cation, may be responsible for increasing the stability and widening of the crystallization field of the complex aluminum‐bearing pyroxene solid solution.
Effect of Preparation Conditions on Phase Formation, Densification, and Microstructure Evolution in La‐β‐Al2O3/Al2O3 Composites
Authors: Barrera‐Solano Carmen , Esquivias Luis , Messing Gary L.
Published: July 2010

In situdevelopment of La‐ß‐Al2O3(LBA) platelets in alpha‐Al2O3was studied as a function of the preparation method: a conventional solid‐state reaction of commercial Al2O3powder and La(NO3)3as well as a sol‐gel method starting with boehmite and the same La2O3precursor. In both cases, homogeneous distribution of the reinforcing phase was achieved, and a noteworthy inhibition of Al2O3grain growth resulted. However, samples prepared by solid‐state reaction densified more easily than those prepared via sol‐gel, but the formation of the LBA phase occurred at a lower temperature in samples prepared by the sol‐gel approach. Results on the correlation of the onset of LBA grain growth and densification to microstructure are discussed.
Space Group Determination of Ba6‐3xNd8+2xTi18O54
Authors: Ubic Rick , Reaney Ian M. , Lee William E.
Published: July 2010

The space group of the solid solution phase Ba6‐3x‐RE8+2xTi18O54(RE = rare‐earth cation) has been variously reported as Pba2 (No. 32), Pbn21(No. 33), Pbam (No. 55), or Pbnm (No. 62). New results are presented here which indicate that its correct space group assignment may be Pb21m (No. 26).
Novel Low‐Temperature Processing Route of Dense Mullite Ceramics by Reaction Sintering of Amorphous SiO2‐Coated γ‐Al2O3 Particle Nanocomposites
Authors: Bartsch Marion , Saruhan Bilge , Schmücker Martin , Schneider Hartmut
Published: July 2010

Dense mullite ceramics were successfully produced at temperatures below 1300°C from amorphous SiO2‐coated gamma‐Al2O3 particle nanocomposites (AS‐gammaA). This method reduces processing temperatures by similar/congruent300°C or more with respect to amorphous SiO2‐coated alpha‐Al2O3 particle microcomposites (AS‐alphaA) and to other Al2O3‐SiO2 reaction couples. The good densification behavior and the relatively low mullite formation temperature make AS‐gammaA nanocomposites an excellent matrix raw material for polycrystalline aluminosilicate fiber‐reinforced mullite composites.
Molten Salt Synthesis of Anisotropic Sr2Nb2O7 Particles
Authors: Brahmaroutu Bhaskar , Messing Gary L. , Trolier‐McKinstry Susan
Published: July 2010

Growth of Sr2Nb2O7 particle size in KCl melts occurs by reaction on insoluble Nb2O5 particles in the melt. Thus, Sr2Nb2O7 size is controlled by the initial size of the reactants. By altering the reactant composition to include larger Nb‐rich reactants such as SrNb2O6, 5‐30 µm, anisotropic Sr2Nb2O7 particles are formed.
Delamination of Urea‐Kaolinite Complex by Using Intercalation Procedures
Authors: Tsunematsu Kinue , Tateyama Hiroshi
Published: July 2010

Kaolinite was delaminated by using a urea‐kaolinite complex via grinding. Grinding for 5 h, using a mechanical mortar, markedly increased the specific surface area of the kaolinate complex, which was mixed with 30 wt% urea, from 18 m2/g to 116 m2/g. Scanning electron microscopy of this sample indicated that the kaolinite particles were delaminated into very thin kaolinite particles.
Carbon‐Fiber‐Reinforced Composites with Graded Carbon‐Silicon Carbide Matrix Composition
Authors: Deng Jingyi , Wei Yongliang , Liu Wenchuan
Published: July 2010

Carbon‐silicon carbide (C‐SiC) graded‐matrix composites were prepared via chemical vapor infiltration with carbon and SiC codeposition from methyltrichlorosilane (CH3SiCl3), acetylene (C2H2), argon, and hydrogen. The graded‐matrix composites were prepared by gradually varying the source gases, from C2H2 to CH3SiCl3, in a semicontinuous process. Oxidation resistance, wear, and mechanical tests were conducted, and the microstructure was observed via optical microscopy, electron probe microanalysis, transmission electron microscopy, and scanning electron microscopy. The results show that this material seems to be macroscopically homogeneous, as an integral part of the entire material; however, microscopic examination shows a gradient variation of the matrix sheaths around each fiber. The oxidation resistance of the material is significantly superior to that of a C/C material, which is a promising thermostructural material, because of its low density, good mechanical properties, and good resistance to oxidation.
Processing of β‐Silicon Nitride from Water‐Based alpha‐Silicon Nitride, Alumina, and Yttria Powder Suspensions
Authors: Hruschka Martin K. M. , Si Wenjie , Tosatti Samuele , Graule Thomas J. , Gauckler Ludwig J.
Published: July 2010

A water‐based route for processing ß‐Si3N4 from alpha‐Si3N4, Al2O3, and Y2O3 powder mixtures was established. The surface charges and isoelectric points of the three different powders were investigated within the pH range from pH 3 to pH 12. Citric acid diammonium salt was found to be an effective deflocculant for shifting the isoelectric points to pH 3.5 for Al2O3 and to pH 6 for Y2O3. Aluminum hydroxide (Al(OH)3) showed strong interaction with the Si3N4 powder, shifting the isoelectric point from pH 7 to pH 5.5. Low‐viscosity, high‐solids‐loading suspensions (60‐63 vol%) thus were possible at pH 9.7. The preparation of homogeneous and stable suspensions with a solids content of ≤61 vol% and a viscosity <1 Pa·s was limited to a pH regime between pH 9 and pH 10.5 because of the high solubility of yttria. The homogeneous suspensions were easily solidified by direct coagulation casting (DCC), using the urease‐catalyzed decomposition of urea at pH 9 to pH 10, by forming salt. No shrinkage cracking, sedimentation, or phase separation was observed during coagulation or drying. The green‐density distribution was homogeneous throughout all bodies, even for complex geometries.
Preparation of Porous Anatase Coating from Sol‐Gel‐Derived Titanium Dioxide and Titanium Dioxide‐Silica by Water‐Vapor Exposure
Authors: Imai Hiroaki , Hirashima Hiroshi
Published: July 2010

The effects of water vapor on the crystallization behavior of sol‐gel‐derived titanium dioxide (TiO2) thin films that contained 0‐50 mol% silica (SiO2) were investigated. Anatase formed on exposure to water vapor at 60°‐180°C, with a simultaneous decrease in the concentration of OH groups. An increase in the SiO2 content of the exposed films led to an increase in the average crystalline size. Because crystallization of the exposed films of the films was not accompanied by shrinkage, porous anatase coatings were obtained via exposure at a relatively low temperature. Phase separation of the immiscible TiO2‐SiO2 system was induced with water vapor, which resulted in acceleration of the crystallization of the sol‐gel films.
Interfacial Reaction between Nickel Oxide and Lanthanum Gallate during Sintering and its Effect on Conductivity
Authors: Huang Pengnian , Horky Alesh , Petric Anthony
Published: July 2010

The results of interdiffusion and reaction between NiO and strontium‐ and magnesium‐doped lanthanum gallate (LSGM) during sintering were investigated. Electron microprobe analysis showed that the NiO content of LSGM sintered 4 h at 1350°C was slightly >2 wt% within 5 µm of the interface, which is equivalent to 7 mol% nickel on B cation sites. This concentration decreased rapidly to <0.25% at a distance of 15 µm. The interfacial reaction between NiO and LSGM, however, led to the formation of a LaSrGa(Ni)O4‐delta‐type phase. A separate experiment involving conductivity measurements of nickel‐doped LSGM indicated that the oxygenion conductivity did not decrease significantly if the nickel content was <5%‐8%. At higher nickel contents, the conductivity increased in air because of hole conduction and markedly decreased under conditions of low oxygen pressure because of the formation of the LaSrGa(Ni)O4‐delta‐type phase. The nickel ions in the LSGM electrolyte and in the reaction product, LaSrGa(Ni)O4‐delta, were stable as Ni2+ at reduced oxygen pressures and, therefore, did not cause electronic shorting.