bluuebunny/crossref_metadata_2025 huggingface dataset:
Nucleation of Hydroxyapatite Crystal through Chemical Interaction with Collagen
Authors: Rhee Sang‐Hoon , Lee Jae Do , Tanaka Junzo
Published: July 2010

The nucleation of hydroxyapatite (HAp) crystal through chemical interaction with collagen was investigated. A collagen membrane was soaked in a supersaturated simulated body fluid (1.5 SBF) solution with ion concentrations at 1.5 times that of normal simulated body fluid (1.0 SBF). A few carbonate‐containing HAp crystals were formed mostly on the edge‐side of the collagen membrane after 4 weeks. In the Fourier‐transform infrared spectometry (FTIR) results, the carboxylate band of the collagen membrane showed red chemical shifts after the formation of HAp crystals, which coincided well with the decrease of the calculated bond orders of the carboxylate group when chelated with a calcium ion, which emulated the first‐step nucleation of HAp crystal on the carboxylate group of collagen. The result implies that the binding of a calcium ion to the carboxylate group of collagen is one of the key factors for the nucleation of HAp crystals in a 1.5 SBF solution.
Preparation of Dense Platinum‐Yttria Stabilized Zirconia and Yttria Stabilized Zirconia Films on Porous La0.9Sr0.1MnO3 (LSM) Substrates
Authors: Peng Zuoyan , Liu Meilin
Published: July 2010

A sol–gel process has been developed to prepare fine powder of La0.9Sr0.1MnO3 (LSM) with an average particle size ∼40 nm. The LSM powder is pressed to pellets, on which a uniform green yttria‐stabilized zirconia (YSZ) film is deposited using an electrophoretic deposition process. A green composite film of platinum and YSZ (Pt‐YSZ) is prepared on the top of the green YSZ film using a colloidal process, followed by filling the pores using a sol–gel process. The three‐layered structure, a green Pt‐YSZ film, and a green YSZ film on a green LSM substrate, is fired at 1250°C for 3 h, resulting in a dense Pt‐YSZ and YSZ film supported by a porous LSM substrate. Electrical measurements show that the sensors with the three‐layered structure display a well‐defined diffusion‐limited current in gases containing partial pressure of oxygen up to ∼9 vol%, implying that the quality of the Pt‐YSZ and YSZ film is adequate for the sensor application.
Molten Salt Synthesis of Calcium Hydroxyapatite Whiskers
Authors: Taş A. Cüneyt
Published: July 2010

Calcium hydroxyapatite (HA) whiskers and crystals were produced by the route of molten salt synthesis. The effects on whisker morphology of chosen flux, flux‐to‐HA ratio, synthesis temperature, and reaction time were investigated. The thermal stabilities of the produced whiskers were tested at 1300°C in an air atmosphere. A tentative X‐ray diffraction pattern was proposed for the HA whiskers. Molten salt synthesis with a K2SO4 flux was found to be a simple and sturdy technique for manufacturing short (≤60 μm) HA whiskers in the temperature range from 1080° to ∼1200°C. The alternative use of fluxes such as KCl, KBr, CaCl2, or Na2SO4, rather than K2SO4, over the temperature range 850°–1000°C resulted in the formation of large (∼25 μm) single crystals of HA.
Solid Freeforming of Silicon Carbide by Inkjet Printing Using a Polymeric Precursor
Authors: Mott Matthew , Evans Julian R. G.
Published: July 2010

Preceramic polymers can be dissolved in solvents to form low‐viscosity fluids. This makes them suitable for solid freeforming by direct inkjet printing. Two ways of using polycarbosilane (pcs) were investigated. In the first, it was dissolved in n‐heptane at up to 30 vol% and printed as a single‐phase material. In the second, it was used as an organic binder for silicon carbide powder suspended in an homologous series of hydrocarbon solvents ranging from n‐heptane to n‐decane. Polyisobutene succinimide was used as a surfactant. In both cases, components could be rendered successfully but pyrolysis of the unfilled pcs resulted in cracking. Components printed with powder suspensions did not crack on pyrolysis, retained overall near net shape, and underwent low shrinkage (8.2 vol%). The molecular weight of the n‐paraffin solvents influenced the viscosity and hence the maximum powder loading while the volatility, a property also related to molecular weight, influenced the quiescence time and the drying time needed between layers. Octane gave the best compromise between speed of printing, the quality and knitting of droplet relics, and the avoidance of nozzle blockage caused by too rapid drying.
Nepheline and Carnegieite Ceramics from A‐Type Zeolites by Microwave Heating
Authors: Ohgushi Tatsuo , Ishimaru Kazushi , Komarneni Sridhar
Published: July 2010

The thermal disintegration processes of A‐type zeolites and the properties of the materials that were formed after microwave heating (at 2.45 GHz) were studied. The thermal disintegration of 4A‐type zeolite proceeded as follows: disintegration at ∼880°C, followed by transformations to high‐carnegieite 1 at ∼920°C, nepheline (in nepheline(4A) form) at ∼990°C, and high‐carnegieite 2 at ∼1254°C (further heating led to melting at ∼1526°C). High‐carnegieite 1, nepheline(4A), and high‐carnegieite 2 efficiently absorbed microwaves. Cooling of the molten material yielded low‐carnegieite that contained some impurities. The change of 3A‐type zeolite proceeded as follows: disintegration at ∼910°C and transformation to nepheline (in nepheline(3A) form) at ∼1006°C. In 3A‐type zeolite, in contrast to 4A‐type zeolite, carnegieite did not form before the crystallization of nepheline(3A). Nepheline of high purity and carnegieite with some impurities were synthesized easily by heating 3A‐ and 4A‐type zeolites, respectively, using microwaves. These results suggest that the microwave heating of zeolites can be used to prepare some ceramic materials.
Energy Transfer Process for the Blue Up‐Conversion in Calcium Aluminate Glasses Doped with Tm3+ and Nd3+
Authors: Chung Woon Jin , Heo Jong
Published: July 2010

Excitation of Tm3+ to 3H4 using the 791 nm pump source showed the frequency up‐converted blue emission (∼480 nm) due to the Tm3+:1G4→3H6 transition in Tm3+/Nd3+ codoped CaO·Al2O3 glasses. Intensity and lifetime changes with rare‐earth concentrations suggested the efficient energy transfer of Tm3+:3H4→ Nd3+:4F5/2 and Nd3+:4F3/2→ Tm3+:1G4. The latter transfer enabled Tm3+ to reach its 1G4 level, and the blue emission became possible through the 1G4→3H6 transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm3+ and Nd3+. Calculated up‐conversion efficiency of the Tm3+/Nd3+ combination in CaO·Al2O3 glass was 6.6 × 10−3, and it was ∼4 orders of magnitude larger than those reported for other oxide glasses.
Neutron Diffraction Study of Ferroelasticity in a 3 mol% Y2O3–ZrO2
Authors: Ma Yuxiang , Kisi Erich H. , Kennedy Shane J.
Published: July 2010

In situ neutron diffraction patterns were recorded from a 3Y‐TZP sample during a complete loading–unloading cycle at compressive loads up to 2.3 GPa. The macroscopic stress–strain diagram shows elastic behavior to 1.7 GPa followed by volume conserving plastic strains of ∼1.6 × 10−3. There were no signs of t→m transformation in the neutron diffraction patterns, and intensity changes in the pattern show that the plasticity is due to ferroelastic switching of tetragonal zirconia crystals. Quantification of the degree of switching gives good agreement with the macroscopic strains. The ferroelastic switching is completely reversed by a process akin to creep relaxation on unloading. Lattice parameters, elastic constants, and structural changes as a function of load are also discussed.
Solubility of Magnesia in Polycrystalline Alumina at High Temperatures
Authors: Greskovich C. , Brewer J. Anthony
Published: July 2010

High‐purity Al2O3 compacts were doped with 0–350 ppm (by weight) of MgO using a liquid immersion technique and equilibrated at temperatures between 1700° and 2000°C under hydrogen. The solubility limits of MgO in Al2O3 at temperatures of 1720° and 1880°C were very low, ∼75 and 175 ppm, respectively. Variation of MgO solubility with temperature could be represented by the equation, ln Mg/Al = 3.80–2.63 × 104/T. The small MgO solubilities were understood by the high enthalpy (326 kJ/mol) of solution. The results of this study suggested that previous investigations on sintering and grain‐growth mechanisms in MgO‐doped Al2O3 were probably not done in single‐phase Al2O3 solid solutions. However, the conclusions on sintering and grain‐growth mechanisms in prior research work in MgO‐doped A2O3 may be correct. The effects of SiO2 impurity and grain size on MgO solubility are discussed. Previous grain‐growth experiments in MgO‐doped Al2O3 are described that demonstrate the clearest evidence for grain‐boundary mobility controlled by a solid‐solution mechanism.
Sodium Carbonate Flux Effects on the Luminescence Characteristics of (Y0.5Gd0.5)2O3:Eu Phosphor Particles Prepared by Spray Pyrolysis
Authors: Kang Yun Chan , Roh Hyun Sook , Park Seung Bin
Published: July 2010

Na2CO3 flux was introduced in the preparation of phosphor particles by spray pyrolysis to improve the photoluminescence (PL) characteristics of (Y0.5Gd0.5)2O3:Eu phosphor particles. The phosphor particles directly prepared by spray pyrolysis at 1300°C from solutions with 20 wt% Na2CO3 flux had the highest PL intensity, which corresponded to 130% of that of particles prepared from solution without flux. On the other hand, the maximum PL intensity of the annealed particles, which were as‐prepared at 900°C and posttreated at 1200°C for 3 h, was obtained from a solution with 5 wt% Na2CO3 flux. The maximum PL intensity of particles directly prepared by spray pyrolysis without posttreatment was 86% of that of posttreated phosphor particles. Na2CO3 flux was also important in control of morphology of (Y0.5Gd0.5)2O3:Eu phosphor particles.
Synthesis of Low‐Dielectric Silica Aerogel Films by Ambient Drying
Authors: Kim Gun S. , Hyun Sang H. , Park Hyung H.
Published: July 2010

A new ambient drying process that is simple, effective, and reproducible has been developed to synthesize low‐k SiO2 aerogel thin films for intermetal dielectric (IMD) materials. The SiO2 aerogel films having a thickness of 9500 Å, a high porosity of 79.5%, and a low dielectric constant of 2.0 were obtained by a new ambient drying process using n‐heptane as a drying solvent.
Mechanochemical Synthesis of Hydroxyapatite from Calcium Oxide and Brushite
Authors: Yeong Bernard , Junmin Xue , Wang John
Published: July 2010

Fine hydroxyapatite (HA) powders were prepared by mechanically activating a mixture of calcium oxide and brushite powders in a high‐energy shaker mill. A defective HA phase was formed when the starting powder mixture was activated for ≤20 h. When the mixture was calcined at 800°C, it was converted to β‐tricalcium phosphate. In contrast, a nanocrystalline HA phase was formed when the mechanical activation was extended to 30 h. The material was transformed to a HA compound (Ca10(PO4)6(OH)2) of high crystallinity when it was calcined at 800°C.
Preparation of Hydroxyapatite Lathlike Particles Using High‐Speed Dispersing Equipment
Authors: Koumoulidis George C. , Vaimakis Tiberius C. , Sdoukos Antonios T. , Boukos Nikos K. , Trapalis Christos C.
Published: July 2010

Hydroxyapatite lathlike monocrystalline particles were prepared using high‐energy dispersing equipment in combination with a pH shock‐wave method. The Ca/P atomic ratios were very close to theoretical, and the acidic group content was very small. The particles were nonporous, with anisotropic crystal growth and average grain size ∼140–1300 nm in length, ∼20–100 nm in width, and ∼10–40 nm in thickness. The high‐speed dispersing equipment created the proper hydrodynamic conditions for lathlike particle growth in the [001] direction. The hydroxyapatite particles formed aggregates of 1–5 μm average diameter.
Heterocoagulation in Ionically Stabilized Mixed‐Oxide Colloidal Dispersions in Ethanol
Authors: Wang Gonghou , Nicholson Patrick S.
Published: July 2010

The heterocoagulation behavior of oxide‐mixture/ethanol suspension systems has been examined using well‐characterized systems. All the dispersions consist of large, monodispersed, spherical silica and small alumina (or magnesia) particles. It is demonstrated that the design of heterocoagulates of controlled architecture can be achieved by the control of the colloidal stability of the constituent particles.
Investigation of Thermal Shock in a High‐Temperature Refractory Ceramic: A Fracture Mechanics Approach
Authors: Soboyejo Winston O. , Mercer Christopher , Schymanski Jason , van der Laan Sieger R.
Published: July 2010

The results of a study on the thermal shock behavior of a high‐temperature refractory ceramic that is used as a furnace liner in the melting of steels are presented in this paper. The experimental studies show that thermal shock damage initiates by edge cracking after the first shock cycle. Subsequent subcritical crack growth occurs by the incremental extension of dominant cracks until catastrophic failure occurs. The observations of the crack profiles also reveal the formation of viscoelastic bridges that promote crack‐tip shielding/toughening via crack bridging. Following a brief discussion of the respective mechanisms of fracture and thermal shock damage at different temperatures and temperature ranges, the implications of the results are discussed for refractory ceramics that are toughened by viscoelastic crack bridging.
Influence of Thermal Conductivity and Fracture Toughness on the Thermal Shock Resistance of Alumina—Silicon–Carbide–Whisker Composites
Authors: Collin Marianne I. K. , Rowcliffe David J.
Published: July 2010

The thermal shock resistance (indentation–quench method), fracture toughness, and thermal conductivity of three alumina–silicon–carbide–whisker composites and alumina have been investigated. A new procedure for the evaluation of thermal conductivity data is suggested, and higher room‐temperature thermal conductivity than that reported in the literature is determined for silicon carbide whiskers. The ranking of the materials according to thermal shock resistance is consistent with the ranking according to fracture toughness but disagrees with the ranking according to thermal conductivity. This finding supports the analytically obtained result that, in defining thermal shock resistance, fracture toughness is more important than thermal conductivity.
Habit Modifications of SnO2 Crystals in SnO2–Cu2O Flux System in the Presence of Trivalent Impurity Cations
Authors: Kawamura Fumio , Yasui Itaru , Kamei Masayuki , Sunagawa Ichiro
Published: July 2010

SnO2 single crystals have short prismatic habits bounded by well‐developed {110} and {111} faces in a pure SnO2–Cu2O flux system. When trivalent cations are added to the system, the habits drastically change to needle, acicular, or whisker forms with large aspect ratios. The addition of trivalent cations also greatly increases the nucleation rate and drastically decreases the crystal size. SEM observations and EPMA investigations reveal that the flat {111} faces transform to rounded or rough {hkl} faces by the addition of trivalent cations. This roughening transition of {111} faces, keeping {110} faces unchanged, is the cause of drastic habit modification that is attributed to the breaking of the periodic bond chain in {111} faces by impurity cations.
Structure and Chemistry of Yttria‐Stabilized Cubic‐Zirconia Symmetric Tilt Grain Boundaries
Authors: Dickey Elizabeth C. , Fan Xudong , Pennycook Stephen J.
Published: July 2010

The atomic structures of two symmetric [001] tilt grain boundaries in yttria‐stabilized cubic‐zirconia, Σ5 (310) and near‐Σ13 (510), are studied by Z‐contrast scanning transmission electron microscopy. Both boundaries are composed of periodic arrays of highly symmetric structural units, with a distinct unit for each boundary. Oxygen K‐edge electron energy‐loss spectra show that the oxygen coordination is similar between the bulk and grain boundary, indicating that oxygen ions within the grain boundary reside in distorted tetrahedral sites. Atomic models of the grain boundaries are proposed that are consistent with the experimental data. The core structures are different from previously studied metal or oxide grain boundaries and are unique to the fluorite structure. Yttrium segregation to the grain boundaries is also investigated by electron energy‐loss spectroscopy. Yttrium is found to segregate preferentially to the Σ5 grain boundary, and the spatial distribution of the segregation layer is confined to within 1 nm of the boundary plane.
Phase Relations and Volume Changes of Hafnia under High Pressure and High Temperature
Authors: Ohtaka Osamu , Fukui Hiroshi , Kunisada Taichi , Fujisawa Tomoyuki , Funakoshi Kenichi , Utsumi Wataru , Irifune Tetsuo , Kuroda Koji , Kikegawa Takumi
Published: July 2010

Using multi‐anvil high‐pressure devices and synchrotron radiation, X‐ray in situ observations of HfO2 under high pressure and high temperature have been performed to investigate its phase relations and compression behavior. An orthorhombic phase (orthoI) is stable from 4 to 14.5 GPa below 1250°–1400°C and transforms to a tetragonal phase, which is one of the high‐temperature forms of HfO2, above these temperatures. Another orthorhombic phase (orthoII) with a cotunnite‐type structure appears above 14.5 GPa. OrthoII is stable up to 1800°C at 21 GPa. OrthoII is quenchable to ambient conditions. The orthoI‐to‐orthoII transition is accompanied by ∼8 vol% decrease. The bulk moduli of orthoI and orthoII at room temperature are 220 and 312 GPa, respectively. This low compressibility of orthoII indicates that it is a potential candidate for very hard materials.
Fabrication of Textured Alumina by High‐Temperature Deformation
Authors: Yoshizawa Yu‐ichi , Toriyama Motohiro , Kanzaki Shuzo
Published: July 2010

Texture formation via high‐temperature deformation in sintered alumina was investigated. Fine‐grained, normal‐purity‐alumina sintered bodies deformed under stresses up to 80 MPa in a temperature range of 1200°–1300°C. Fine, disklike grains formed in the equiaxial fine‐grained matrix during high‐temperature deformation and aligned unidirectionally via material flow during deformation. Highly textured sintered alumina bodies were obtained via high‐temperature deformation and further annealing.
Potassium Lithium Niobate Films Derived from Aqueous Precursor Solution
Authors: Ono Satomi , Yamada Noriaki , Hirano Shin‐ichi
Published: July 2010

Potassium lithium niobate (KLN) films, which were prepared using an aqueous precursor solution, were characterized in terms of crystallinity, morphology, and electrical properties; 1.0 μm thick KLN films free from cracks and pores could be prepared on MgO(100), Pt(100)/MgO(100), and Pt(111)/Ti/SiO2/Si substrates by multiple coating and heating at 700°C. The films were composed of compact grains and had sintered textures. The films crystallized with (310) and (540) preferred orientations on MgO(100) and Pt(100)/MgO(100) substrates. The KLN film prepared on Pt(100)/MgO(100) substrate had ɛ′= 136 and tan δ= 0.026 at 1 kHz.
Synthesis and Processing of Barium Hexaaluminogallates
Authors: Yamaguchi Toshiaki , Sakamoto Wataru , Yogo Toshinobu , Hirano Shin‐ichi
Published: July 2010

Barium hexaaluminogallate was synthesized by the mixed‐oxide method and the coprecipitation method. Barium hexaaluminate and barium hexagallate were found to form barium hexaaluminogallate, Ba(Al,Ga)12O19, at 1400°C. BaCo(Al,Ga)11O19 of magnetoplumbite structure was formed from a mixture of metal oxides at 1200°C for 6 h. Co was successfully introduced to barium hexaaluminogallate, although the synthesis of BaCoAl11O19 is quite difficult via solid‐state reaction of oxide powders. Anisotropic BaCo(Al,Ga)11O19 particles crystallized at 1100°C for 2 h through the coprecipitation method using metal nitrates and ammonium carbonate. BaCo(Al,Ga)11O19 supported on a cordierite honeycomb had the ability to reduce NOx with methane over 500°C in the presence of excess oxygen.
Freeze Casting of Aqueous Alumina Slurries with Glycerol
Authors: Sofie Stephen W. , Dogan Fatih
Published: July 2010

Freeze‐drying concepts were utilized in the shape forming of alumina parts by pressureless slip molding using aqueous slurries. A water solidification modifier, glycerol, was utilized to eliminate the defects associated with the expansion and ceramic particle rejection of water during freezing. Castable alumina slurries with solids loading up to 60 vol% were prepared and characterized using viscosity and zeta‐potential measurements with and without glycerol additions. Frozen parts were dried under vacuum by sublimation of ice to obtain net‐shape green bodies. The combined effects of high‐solids‐loading slurries, >57.5 vol%, and glycerol additions were essential for freeze casting to achieve highly dense alumina bodies with a uniform microstructure.
Electrical Properties of Boron Nitride Matrix Composites: II, Dielectric Relaxations in Boron Nitride–Silicon Carbide Composites
Authors: Runyan Julie , Gerhardt Rosario A. , Ruh Robert
Published: July 2010

A low‐frequency Maxwell–Wagner relaxation, resulting from space‐charge buildup, was observed when BN–SiC composites were subjected to an ac current. This paper discusses the Maxwell–Wagner relaxation and information that it reveals about the microstructure of the composite. A modified Maxwell–Wagner equation for the real part of the permittivity is used to model the data. SiC has a higher dielectric constant than that of BN. The microstructure of these composites is anisotropic, with BN platelets preferentially oriented perpendicular to the hot‐pressing direction. Samples measured in this direction exhibit a lower dielectric constant than those measured parallel to the hot‐pressing direction. In regard to frequency response, the permittivity of BN shows no dependence on frequency, whereas frequency dependence is seen with increasing SiC content.
Gas‐Sensing Properties of Nanocrystalline WO3 Films Made by Advanced Reactive Gas Deposition
Authors: Solis Jose L. , Hoel Anders , Kish Laszlo B. , Granqvist Claes G. , Saukko Sami , Lantto Vilho
Published: July 2010

Nanocrystalline WO3 films were produced by advanced reactive gas deposition onto alumina substrates. The as‐deposited films had a tetragonal crystal structure and a mean grain size of around 6 nm, as found by X‐ray diffraction and electron microscopy. Sintering at a temperature τs > 770 K yielded monoclinic films. We investigated the gas‐sensing properties of films sintered up to 870 K. After an initial “activation” at τs= 750 K, the nanocrystalline WO3 films showed excellent gas‐sensing properties, even at room temperature, on exposure to low concentrations of H2S in air. As little as 10 ppm of H2S made the conductance increase by a factor of about 103 within 10 min. The initial properties could be restored by heating the films to 530 K for 1 min.
Advanced Alumina Composites Reinforced with Titanium‐Based Alloys
Authors: Günther Robert , Klassen Thomas , Dickau Birte , Gärtner Frank , Bartels Arno , Bormann Rüdiger
Published: July 2010

New (inter)metallic‐ceramic composites for high‐temperature structural and functional applications are prepared via high‐energy ball milling. During compaction by pressureless sintering, dense Al2O3/Ti‐based alloy composites are formed that consist of inter‐connected networks of the ceramic and the (inter)metallic phases. Ti‐Al‐V/Al2O3 and Ti‐Al‐Nb/Al2O3 composites show enhanced damage tolerance over monolithic Al2O3, i.e., fracture toughnesses up to 5.6 MPa·m0.5 and bending strengths up to 527 MPa. The resistance against abrasive wear is almost doubled with respect to monolithic Al2O3 ceramic. Electrical resistivity scales with the ceramic volume fraction and ranges between 0.3 mΩ·cm and 55.1 mΩ·cm, with only a weak temperature dependence ≤700°C.
Crystallographic Texture and Thermal Conductivity of Zirconia Thermal Barrier Coatings Deposited on Different Substrates
Authors: Heydt Paul , Luo Chongyang , Clarke David R.
Published: July 2010

The crystallographic texture and thermal conductivity of zirconia coatings deposited by electron beam evaporation on a variety of substrates have been measured. It was found that the thermal conductivity of coatings deposited at the same temperature was independent of whether they were deposited on polycrystalline alumina, single‐crystal sapphire, single‐crystal zirconia, or fused silica. The room‐temperature thermal conductivity of the coatings deposited at 700°C was 0.32 W/(m·K), increasing to 1.36 W/(m·K) for coatings deposited at 1150°C. Similarly, the crystallographic texture was also independent of the substrate and had a (111) fiber texture at 700° and 900°C, switching to a (200) fiber texture by 1050°C. The exception was the coating deposited at 1150°C on (111) single‐crystal zirconia which was epitaxial and exhibited a thermal conductivity of 2.46 W/(m·K). It is concluded that the properties of zirconia thermal barrier coatings are determined by the growth conditions rather than those associated with nucleation on the underlying substrate.
Strength Degradation and Failure Mechanisms of Electron‐Beam Physical‐Vapor‐Deposited Thermal Barrier Coatings
Authors: Ruud James A. , Bartz Andi , Borom Marcus P. , Johnson Curtis A.
Published: July 2010

Failure mechanisms were determined for electron‐beam physical‐vapor‐deposited thermal barrier coating (TBC) systems from the degradation of mechanical properties and microstructural changes in a furnace cycle test. Bond strength degradation for TBCs resulted from the initiation and growth of interfacial delamination defects between the yttria‐stabilized zirconia topcoat and the thermally grown alumina (TGO). It is proposed that defects started from concave depressions in the bondcoat surface created by the grit‐blast‐cleaning process and that defect growth was driven by the reduction in compressive strain in the TGO as the alumina deformed into and displaced the bondcoat during the cooling cycles. Inclusion of yttrium in the substrate resulted in a doubling of the furnace cycle life of the TBCs because of enhanced fracture toughness of the TGO‐bondcoat interface.
Oxidation Behavior of Silicon‐Infiltrated Carbon/Carbon Composites in High‐Enthalpy Convective Environment
Authors: Ogasawara Toshio , Ishikawa Takashi
Published: July 2010

Thermal response and oxidation behavior of commercial metal‐silicon‐infiltrated carbon/carbon composites (MICMATTM; Si‐CC) were evaluated in a high‐enthalpy convective environment using an arc jet facility (an arc wind tunnel). Composite specimens were put into a supersonic plasma air stream having a gas enthalpy of 12.7–18.8 MJ/kg for 50–600 s. Cold‐wall heat fluxes measured by a Gardon‐type calorimeter ranged from 1.0 to 1.8 MW/m2, and the maximum surface temperature reached 1300°–1660°C. After the arc jet testing, no surface recession was observed in the samples, and the mass loss rate of the composites was far less than that of graphite. The excellent oxidation resistance was caused by formation of a porous SiC layer at the surface of the composite. Oxidation behavior of the composites is discussed based on a simplified airflow blocking model of the porous SiC layer. The composites exhibited excellent oxidation resistance for short‐term exposure in high‐enthalpy airflow.
Multiple Cracking and Tensile Behavior for an Orthogonal 3‐D Woven Si‐Ti‐C‐O Fiber/Si‐Ti‐C‐O Matrix Composite
Authors: Ogasawara Toshio , Ishikawa Takashi , Ito Hiroshi , Watanabe Naoyuki , Davies Ian J.
Published: July 2010

This paper presents experimental results for the multiple microcracking and tensile behavior of an orthogonal 3‐D woven Si‐Ti‐C‐O fiber (Tyranno™ Lox‐M)/Si‐Ti‐C‐O matrix composite with a nanoscale carbon fiber/matrix interphase and processed using a polymer impregnation and pyrolysis route. Based on microscopic observations and unidirectional tensile tests, it is revealed that the inelastic tensile stress/strain behavior is governed by matrix cracking in transverse (90°) fiber bundles between 65 and 180 MPa, matrix cracking in longitudinal (0°) fiber bundles between 180 and 300 MPa, and fiber fragmentation above 300 MPa. A methodology for estimation of unidirectional tensile behavior in orthogonal 3‐D composites has been established by the use and modification of existing theory. A good correlation was obtained between the predicted and measured composite strain using this procedure.
Synthesis of α‐SiAlON Seed Crystals
Authors: Zenotchkine Misha , Shuba Roman , Kim Joo Sun , Chen I‐Wei
Published: July 2010

Single‐phase seed crystals of Ca‐ and Y‐α‐SiAlONs have been synthesized for tailoring microstructure of α‐SiAlON ceramics. The influence of composition, sintering temperature, and nitrogen pressure on the size and morphology of seeds has been explored. Guidelines for α‐SiAlON seed preparation and morphology control are provided.
Dispersion and Slip Casting of Hydroxyapatite
Authors: Rao R. Ramachandra , Kannan Thandali S.
Published: July 2010

The dispersibility in deionized water of hydroxyapatite (HA) synthesized by a high‐temperature (1000°C) solid‐state reaction between tricalcium phosphate and calcium hydroxide was investigated as a function of the pH of the medium and the quantity of two dispersing agents (A = inorganic, B = organic) added to the slips. Although pH modification had a negligible effect on dispersibility, both of the dispersing agents produced a good dispersion at considerably higher concentrations (>2 wt% of HA). At optimum amounts (2–4 wt%) of the dispersing agents, the slips showed near‐Newtonian flow behavior up to 45 wt% solids loading and non‐Newtonian behavior at >50 wt%. By the optimal addition of dispersing agents and conditioning by ball milling, 60–67 wt% (32–39 vol%) solids‐loaded HA slips could be cast into plaster molds to produce 50%–58% dense green bodies, which, in turn, sintered to 90%–94% density in the temperature range 1300°–1400°C. The sintered HA exhibited a three‐point flexural strength of 40–60 MPa and a homogeneous microstructure, with interspersed microporosities.
Optical Spectra of Nickel‐Bearing Silicate Gels Prepared by the Geopolymer Technique, with Special Reference to the Low‐Temperature Formation of Liebenbergite (Ni2SiO4)
Authors: Ko Ikeda  , Onikura Kyoichi , Nakamura Yoshinori , Vedanand Swaroop
Published: July 2010

A nickel‐bearing silicate gel was prepared from sodium disilicate and nickel nitrate solutions at room temperature. Then, the gel was heat‐treated in air up to 800°C at intervals of 200°C. The products were completely amorphous after heating at ≤600°C. However, liebenbergite and cristobalite were identified as products of the crystallization of the gel after heating at 800°C. The polycondensation process of the gel was discussed based on X‐ray diffractometry, thermogravimetry‐differential thermal analysis, and optical spectroscopy, to clarify the easy crystallization of the gel to liebenbergite and cristobalite. The present technique is very useful for the low‐temperature preparation of liebenbergite, which has potential application in the decomposition catalysis of chlorofluorocarbons, in connection with the problem with the ozone layer.
Diffusion of 110mAg Tracer in Polycrystalline and Single‐Crystal Lead‐Containing Piezoelectric Ceramics
Authors: Lewis Daniel J. , Gupta Devendra , Notis Michael R. , Imanaka Yoshihiko
Published: July 2010

We have conducted diffusion measurements of radioactive 110mAg tracer in single‐crystal PbMgNbO3–PbTiO3 (PMN‐PT) and in polycrystalline 50Pb(Ni1/3Nb2/3)O3·35PbTiO3·15PbZrO3 (PNN‐PT‐PZ) piezoelectric ceramics. Both materials measured belong to the perovskite family. Diffusion in PMN‐PT is characterized by an activation energy of 277 kJ/mol and pre‐exponential factor of 0.0034 m2/s and compares well with cation diffusion in high‐temperature superconducting YBa2Cu3O7–δ. Diffusion in polycrystalline PNN‐PT‐PZ, on the other hand, is many orders of magnitude faster and is attributed to grain boundaries. PNN‐PT‐PZ has a lower activation energy, 168 kJ/mol, and a combined pre‐exponential factor (sδ(Db)o, where s is the segregation factor of silver, δ the thickness, and (Db)o the pre‐exponential factor for grain boundaries) of 3.7 × 10−9 m3/s. The unusually large combined pre‐exponential factor infers large segregation of silver at the grain boundaries and small solid solubility within the grains. It is possible, using a semiempirical model, to compute metal– (silver–) ceramic interface energies as a function of temperature, from which values of 90 kJ/mol and 0.9R are obtained for enthalpy and entropy, respectively, for grain‐boundary segregation.
Raman Microprobe Evaluation of Bridging Stresses in Highly Anisotropic Silicon Nitride
Authors: Pezzotti Giuseppe , Ichimaru Hiroyuki , Ferroni Luca Paolo , Hirao Kiyoshi , Sbaizero Orfeo
Published: July 2010

The microscopic bridging stress distribution developed behind the crack tip of a highly anisotropic silicon nitride has been measured along the crack profile using Raman microprobe spectroscopy with a micrometer spatial resolution. The near‐tip rising R‐curve behavior and the crack‐opening displacement (COD) profile of the material were also determined and discussed in comparison with the Raman microstress data. A comparison with the fracture behavior of a previously investigated silicon nitride material with a three‐dimensional random microstructure is also proposed. According to this set of micro/macroscopic fracture characterizations, a self‐consistent view of toughening behavior in silicon nitride ceramics is obtained, and the role on toughness of anisotropically oriented acicular grains clarified. In agreement with previous studies, it is confirmed that crack‐face bridging is the most effective mechanism for toughening silicon nitride ceramics.
State of Water in Hydrating Tricalcium Silicate and Portland Cement Pastes as Measured by Quasi‐Elastic Neutron Scattering
Authors: Thomas Jeffrey J. , FitzGerald Stephen A. , Neumann Dan A. , Livingston Richard A.
Published: July 2010

Quasi‐elastic neutron scattering (QENS) was used to monitor the state of water in portland cement and tricalcium silicate pastes during the first 2 days of hydration at three different temperatures. By applying a double‐Lorentzian rather than a single‐Lorentzian fitting function, the QENS signal from water at a given hydration time was divided into three separate populations arising from liquid water, chemically bound water, and constrained water. The constrained water population consisted of water adsorbed on surfaces and contained in very small (<10 nm) pores, and could be associated primarily with the calcium‐silicate‐hydrate (C‐S‐H) phase. The rate of increase in the chemically bound water population closely followed the exothermic heat output, while the constrained water population increased more rapidly during the first several hours of hydration and then leveled off.
Effect of Cation Doping on the Superplastic Flow in Yttria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Mimurada Junpei , Nakano Manabu , Sasaki Kazutaka , Ikuhara Yuichi , Sakuma Taketo
Published: July 2010

The superplastic characteristics of various cation‐doped yttria‐stabilized tetragonal zirconia polycrystals (Y‐TZP) were examined. For 1 mol% cation doping the true stress of Y‐TZP is very dependent on the ionic radii of the doped cations; for instance, smaller cation radii give rise to lower true stress when compared with the other compositions for the same grain size, strain rate, and testing temperature. The altered true stress level must be due to the change in diffusivity of the accommodation process for grain boundary sliding caused by the addition of cations in ZrO2. The strain to failure of the doped zirconia is affected by both ionic radius and valence of the dopant cations.
Effect of Oxidation State of Iron on Phase Separation in Sodium Silicate Glasses
Authors: Jeoung Jun‐Sik , Poisl W. Howard , Weinberg Michael C. , Smith Gary L. , Li Hong
Published: July 2010

The effect of the oxidation state of iron on the phase separation of xNa2O·(100 –x)SiO2 glasses, x= 18.56 and 13, containing 0.5 mol% Fe2O3 was studied. The oxidation state of iron in the glasses was varied by changing the melting conditions, such as melting temperature and melting atmosphere. The oxidation states of the iron ion were determined using colorimetric and UV–VIS–NIR spectrophotometric methods, and a comparison was made between the results obtained using these two methods. Immiscibility temperatures of the glasses were determined using opalescence and clearing methods. The immiscibility temperature of the sodium silicate binary glasses decreased ∼25°C with the addition of 0.5 mol% Fe2O3. The immiscibility temperature of the doped glasses increased slightly with increased concentration of Fe2+ ion in the glass. The prediction of immiscibility tendency on the addition of a minor amount of third component was made using models proposed by Tomozawa and Obara and Nakagawa and Izumitani. The Tomozawa and Obara model showed good agreement with measured immiscibility values.
Microstructure in Silicon Nitride Containing β‐Phase Seeding: III, Grain Growth and Coalescence
Authors: Lu Horng‐Hwa , Huang Jow‐Lay
Published: July 2010

The mechanical properties of Si3N4 materials depend mainly on the microstructure, which originates during the densification process. The microscopic evidence indicates that β‐Si3N4 seeds incorporated in the starting powders play an important role in microstructural development, especially in the heterogeneous grain growth of β‐Si3N4 grains during sintering. The growth of β‐grains is initiated from the β‐seeds, resulting in a core/shell microstructure. The presence of Moiré fringes and dislocations is attributed to misfit strain and compositional differences between the core and the shell. Coalescence can occur at the final stage of sintering.
Influence of Diaspore Seeding and Chloride Concentration on the Transformation of “Diasporic” Precursors to Corundum
Authors: Smith Richard L. , Rohrer Gregory S. , Perrotta Anthony J.
Published: July 2010

“Diasporic” precursors derived from sols formed by the controlled hydrolysis of aluminum sec‐butoxide in the presence of HCl yielded mixtures of corundum and amorphous alumina when calcined between 500° and 800°C. The fraction of corundum in the calcined products depended on the HCl/alkoxide ratio used during hydrolysis and was maximized at 64 wt% when the molar ratio was 1. Precursors formed from sols hydrolyzed in the presence of HNO3 rather than HCl yielded only amorphous products or transition aluminas when treated below 900°C. The corundum yield of the precursors was enhanced when they were seeded with diaspore (α‐AlOOH) crystals. Precursors synthesized with an HCl/alkoxide ratio of 1 and seeded with 7.6 × 1016 diaspore seeds/(mol of Al2O3) were transformed to phase‐pure corundum within 12 h at 700°C. Based on studies of the phase evolution of the precursors during calcining, it was concluded that the diaspore seeds promoted conversion by acting as corundum nuclei once they decomposed at ∼450°C.
Grain Boundaries of Semiconducting SrTiO3 and BaTiO3 Ceramics Synthesized from Surface‐Coated Powders
Authors: Park Myung‐Beom , Cho Nam‐Hee
Published: July 2010

The chemical and electrical features of the grain boundaries in polycrystalline SrTi0.99Nb0.01O3 (ST) and BaTiO3 (BT) ceramics, which were synthesized by hot‐press sintering Na‐ and Mn‐coated semiconducting ST and BT powders, respectively, were investigated. Because of the excess negative electric charges formed near grain boundaries, electrostatic potential barriers were formed near the grain boundaries. The electrical features of the grain boundaries in ceramics are very sensitive to the amount of the coating material. When the amount of the coating material was increased from 0 to 5 wt%, the threshold voltage of the ST ceramics and the resistivity jump ratio of the BT ceramics increased from 0.7 to 81.0 V/cm and from 1.0 to 2.0 × 103, respectively. The electrical features of the grain boundaries are related to their chemical characteristics.
Modeling the Kinetics of Volatilization from Glass Melts
Authors: Beerkens Ruud G. C.
Published: July 2010

A model description for the evaporation kinetics from glass melts in direct contact with static atmospheres or flowing gas phases is presented. The derived models and equations are based on the solution of the second Ficks’ diffusion law and quasi‐steady‐state mass transfer relations, taking into account changing melt/gas‐phase boundary concentrations. Mass transfer relations for turbulent and laminar gas flows are given. In almost static humid atmospheres, the depletion of sodium oxide at the glass melt surface, during evaporation of sodium hydroxide from soda–lime silicate melts, appears to be moderate. Exposed to flowing gas phases, the increased mass transfer in the gaseous phase will enhance the evaporation from the melt. But at high temperatures, high gas flow rates, and reactive evaporation from a melt, exposed to high water vapor pressure levels, the diffusion processes in the melt will affect the sodium evaporation losses. Consequently sodium oxide surface concentrations of static melts may become increasingly deviating from the parent melt composition at such high evaporation rates. Measured sodium and lead evaporation rates for static soda–lime silicate and lead silicate melts are compared with the results of modeling of volatilization kinetics in gas streams. Most evaporation processes in glass furnaces can be described by the assumption of static glass melt volume elements, each exposed during a certain average time period to a furnace atmosphere with laminar or turbulent gas flow conditions.
X‐ray Tomography Study on Green State Joining of Silicon Carbide Using Polymer Precursors
Authors: Zheng Jing , Beckman Scott P. , Gray Joe N. , Akinc Mufit
Published: July 2010

X‐ray tomography has been used to investigate the density variations in SiC joints formed using polymer pastes. It has been demonstrated that X‐ray tomography provides accurate bulk density measurements and volumetric density gradients. The results suggest that the magnitude of the applied pressure after green state joining and the amount of polymer (polycarbosilane, PCS) in the joining pastes influence the green density of the joints. All joints are prepared and applied in air atmosphere and at room temperature. The green densities of the joints increase from 54% to 66% of theoretical with the increase of the applied pressure from ambient to 138 MPa. Highest joint density without applied pressure is achieved using paste containing 50 vol% PCS. Furthermore, allylhydridopopolycarbosilane‐ (AHPCS‐) containing pastes resulted in higher densities at the joint–matrix interface, indicating infiltration of polymer into the matrix.
Phase Separation in Sol–Gel Process of Alkoxide‐Derived Silica‐Zirconia in the Presence of Polyethylene Oxide
Authors: Takahashi Ryoji , Sato Satoshi , Sodesawa Toshiaki , Suzuki Kei , Tafu Masamoto , Nakanishi Kazuki , Soga Naohiro
Published: July 2010

Phase separation in a sol–gel process of SiO2–ZrO2 in the presence of polyethylene oxide is investigated. An amorphous gel with interconnected macroporous morphology is obtained when phase separation and sol–gel transition concur to fix a transitional structure of spinodal decomposition. Macropore size, together with connectivity of the pores and gel skeleton, can be controlled precisely by selecting an appropriate starting composition for preparation at a zirconium content ≤11.7 mol%. The macroporous gel retains additional mesopores <4 nm and exhibits typical bimodal pore size distribution. The addition of ZrO2 in SiO2 improves the thermal stability of both macroporous and mesoporous structures.
Roles of Ba/Ti Ratios in the Dielectric Properties of BaTiO3 Ceramics
Authors: Lee Jung‐Kun , Hong Kug‐Sun , Jang Jin‐Wook
Published: July 2010

The effect of the Ba/Ti ratio on microstructure, dielectric/ferroelectric properties, and domain width was studied using optical microscopy, ɛ(T) curves, D–E hysteresis, and transmission electron microscopy. Although Ti‐excess samples showed abnormal grain growth and a decrease of room‐temperature permittivity due to a liquid phase at grain boundaries, its ferroelectric properties were similar to those of stoichiometric BaTiO3 ceramics. However, in Ba‐excess samples, an increase of permittivity and ferroelectric properties different from those of stoichiometry were found. Changes in domain width and ferroelectric transition behavior indicated that the variation of dielectric properties was related to the internal stress. It is proposed that this internal stress originated from differences in the thermal expansion coefficient between the matrix and the second phase.
Flexural Creep of an in Situ‐Toughened Silicon Carbide
Authors: Sixta Mark E. , Feng Zhang Xiao , De Jonghe Lutgard C.
Published: July 2010

Flexural creep behavior is reported for an in situ‐toughened SiC between 1100° and 1500°C in four‐point bending. The flexural creep rate of this SiC, sintered with aluminum, boron, and carbon (ABC‐SiC), exhibits linear stress dependence, low apparent activation energy, and low incidence of cavitation and dislocation production. Most grain boundaries in this ceramic contain 1–5 nm intergranular films. The creep rate is consistent with a grain‐boundary transport mechanism involving diffusion along the grain‐boundary film‐SiC interfaces. The microstructure and grain boundaries have been examined using transmission electron microscopy to assess possible changes during creep, particularly in relation to the applied stress direction.
Processing and Mechanical Properties of Al2O3/Ni3Al Composites with Interpenetrating Network Microstructure
Authors: Skirl Siegfried , Krause Ralph , Wiederhorn Sheldon M. , Rödel Jürgen
Published: July 2010

Composites with microstructures of interpenetrating networks were manufactured by gas pressure infiltration of Ni3Al into porous preforms of aluminum oxide. Composites with Ni3Al contents of between 15% and 30% by volume were made and evaluated mechanically at temperatures between room temperature and 1000°C. The fracture strength, the fracture toughness, Young's modulus, and the thermal expansion coefficient were measured for each composite and test condition and were correlated with the microstructures of the composites. Composites with low Ni3Al contents had strengths below 400 MPa, presumably due to microcracking along the interface between the Ni3Al and the Al2O3. The composite with the highest content of Ni3Al, 30 vol%, had a mean fracture strength of 675 ± 16 MPa, a Weibull modulus of 23.9, and a room‐temperature toughness of 9.2 ± 0.5 MPa·m1/2.
Temperature Dependence of Tensile Strength for a Woven Boron‐Nitride‐Coated Hi‐Nicalon™ SiC Fiber‐Reinforced Silicon‐Carbide‐Matrix Composite
Authors: Guo Shuqi , Kagawa Yutaka
Published: July 2010

The temperature dependence of tensile fracture behavior and tensile strength of a two‐dimensional woven BN‐coated Hi‐Nicalon™ SiC fiber‐reinforced SiC matrix composite fabricated by polymer infiltration pyrolysis (PIP) were studied. A tensile test of the composite was conducted in air at temperatures of 298 (room temperature), 1200, 1400, and 1600 K. The composite showed a nonlinear behavior for all the test temperatures; however, a large decrease in tensile strength was observed above 1200 K. Young's modulus was estimated from the initial linear regime of the tensile stress–strain curves at room and elevated temperatures, and a decrease in Young’s modulus became significant above 1200 K. The multiple transverse cracking that occurred was independent of temperature, and the transverse crack density was measured from fractographic observations of the tested specimens at room and elevated temperatures. The temperature dependence of the effective interfacial shear stress was estimated from the measurements of the transverse crack density. The temperature dependence of in situ fiber strength properties was determined from fracture mirror size on the fracture surfaces of fibers. The decrease in the tensile strength of the composite up to 1400 K was attributed to the degradation in the strength properties of in situ fibers, and to the damage behavior exception of the fiber properties for 1600 K.