bluuebunny/crossref_metadata_2025 huggingface dataset:
Low‐Temperature Crystallization of Forsterite and Orthoenstatite
Authors: Ban Takayuki , Ohya Yutaka , Takahashi Yasutaka
Published: July 2010

MgO–SiO2 precursor gels were prepared by mixing tetramethoxysilane (TMOS) or tetraethoxysilane (TEOS), H2O, and magnesium metal in methanol. Forsterite (Mg2SiO4) and orthoenstatite (MgSiO3) were crystallized from their precursors at temperatures as low as 500° and 700°C, respectively. The chemical compositions of the crystallized phases were richer in MgO content than those of the starting materials. Inductively coupled plasma analysis showed that an amorphous SiO2‐rich phase was present, together with crystalline phases. We speculate that the amorphous SiO2‐rich phase has an important role in the low‐temperature crystallizations of these magnesium silicates. Characterization of the preparation process via liquid‐state 29Si nuclear magnetic resonance (NMR) indicated that the breakage of the ≡Si–O–Si≡ bond was caused by the addition of magnesium metal. Solid‐state 29Si NMR showed that the Mg–O–Si bond might form in as‐prepared specimens.
Preparation and Characterization of Hydroxyapatite Coatings on Ti6Al4V Alloy by a Sol‐Gel Method
Authors: Weng Wenjian , Baptista Joao Lopes
Published: July 2010

Hydroxyapatite coatings on Ti6Al4V substrates were prepared by a sol–gel method, and characterized by X‐ray diffraction, scanning electron microscopy, and infrared reflection spectroscopy. The coatings obtained at 500°C in air had a hydroxyapatite phase, some of which was carbonated hydroxyapatite, and had a dense and smooth morphology. When the coatings were treated in a simulated body fluid, the coatings had an increase in large hydroxyapatite grains, and a rough and porous morphology. The adhesive strength of the coatings was more than 14 MPa.
Stress Relaxation of Polycrystalline Ceramics with Grain‐Boundary Sliding and Grain Interlocking
Authors: Sakai Mototsugu , Muto Hiroyuki , Haga Mikichika
Published: July 2010

The stress relaxation of two‐phase polycrystalline ceramics has been examined. A two‐dimensional array of elastic hexagonal grains embedded in a contiguous fluid has been used as a model for grain‐boundary sliding and grain interlocking. The viscoelastic constitutive equation, in a phenomenological sense, is of a nonlinear Maxwell type; the model is composed of a strain‐dependent dashpot and an elastic spring connected in series. The squeezing‐in/out processes and mechanisms of grain‐boundary fluid essentially result in the rheological nonlinearity. The experimental results in stress‐relaxation tests of a β‐spodumene glass‐ceramic under simple shear are characterized from the standpoint of the nonlinear constitutive equation. It is emphasized that the stress‐relaxation test is one of the important test techniques that enables one to study quantitatively the rheological behavior of polycrystalline ceramics with grain‐boundary sliding and grain interlocking without any of the difficulties and ambiguities that are accompanied by stress‐induced grain‐boundary cavities, which so often appear in conventional creep tests.
Indentation Fatigue in Random and Textured Alumina Composites
Authors: An Linan
Published: July 2010

The effect of grain orientation on contact fatigue behavior has been investigated by using alumina with elongated grains as a model system. Two kinds of composite microstructures, textured and random, were prepared by controlling the processing conditions. The textured material has the platelets aligned parallel to the surface, and the random material has the platelets randomly oriented. The Hertzian indentation results show that, although both materials exhibit damage accumulation with increasing number of cycles due to frictional degradation at the microstructural level, the damage evolution rate is much lower for the textured material. This suppression of fatigue damage in the textured material appears to result from the lower shear stress concentration along the textured weak interfaces between elongated alumina grains. The implication of the present results for structural design in improvement of contact‐fatigue resistance is also addressed.
A Source of the Immiscibility Controversy of Borate and Borosilicate Glass Systems
Authors: Tomozawa Minoru
Published: July 2010

Because phase separation affects glass properties such as chemical durability, it is important to clarify this phenomenon, especially the immiscibility boundaries. Despite extensive investigation, controversy persists in regard to the immiscibility boundary of borate and borosilicate systems. The controversy has been suggested to originate from a change in glass structure with heat‐treatment temperature or fictive temperature, which, in turn, causes a change in the immiscibility tendency.
Hot Isostatic Pressing of Reactive SnO2 Powder
Authors: Yoshinaka Masaru , Hirota Ken , Ito Masayuki , Takano Hiroshi , Yamaguchi Osamu
Published: July 2010

Tin(IV) oxide (SnO2) crystallizes at room temperature by adding hydrazine monohydrate ((NH2)2· H2O) to a hydrochloric acid solution of tin, followed by washing and drying. Well‐densified SnO2 ceramics (99.8% of theoretical) with an average grain size of 0.9 μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are 14.4 GPa and 200 MPa, respectively. They exhibit an electrical conductivity of 2 × 10−3−9 × 10−3 S·cm−1 at room temperature.
Preparation of Multiple‐Cation alpha‐SiAlON Ceramics Containing Lanthanum
Authors: Mandal Hasan , Hoffmann Michael J.
Published: July 2010

Until recently, it was accepted that Ce3+ cations, with an ionic radius (r) of 1.03 Å, were too large to form an α‐SiAlON structure. However, more‐recent studies have shown that cerium cations can be incorporated into α‐SiAlON via quenching at a rate of 600°C/min, after sintering at 1800°C. Thus far, no α‐SiAlON formation has been observed for La3+ cations with r= 1.06 Å. In the present work, the possibility of having the La3+ species as a dopant cation in α‐SiAlON has been investigated by using La2O3 alone or in equimolar mixtures with CaO or Yb2O3. The resulting materials have been heat‐treated at a temperature of 1450°C for up to 720 h to devitrify the grain‐boundary glass into crystalline phases and also to observe the α→β SiAlON transformation. X‐ray diffractometry on samples that were densified with single cations revealed that the La3+ cation alone does not form an α‐SiAlON; rather, it forms the N‐phase (La3Si8O4N11) with a ß‐SiAlON phase. In the case of multiple cations, α‐SiAlON was observed only as a matrix phase. Energy‐dispersive X‐ray measurements have proven that La3+ cations can be accommodated into the α‐SiAlON structure and this structure also does not transform to β‐SiAlON at lower temperatures.
Silicon Oxycarbide Ceramic Foams from a Preceramic Polymer
Authors: Colombo Paolo , Modesti Michele
Published: July 2010

Open‐cell ceramic foams were obtained from the pyrolysis, at 1000° to 1200°C under nitrogen, of a preceramic polymer (a silicone resin) and blown polyurethanes. The morphology of the expanded polyurethane was reproduced in the final architecture of the ceramic foam. The foams produced in this way consisted of an amorphous silicon oxycarbide ceramic (SiOC), having a bulk density ranging from 0.1 to 0.4 g/cm3 and variable cell size (300 to 600 µm). Young's modulus ranged from 20 to 170 MPa, and the compression strength from 1 to 5 MPa. The foams displayed excellent dimensional stability up to their pyrolysis temperature.
Effective Fiber Properties to Incorporate Coating Thermoelastic Effects in Fiber/Matrix Composite Models
Authors: Parthasarathy Triplicane A. , Kerans Ronald J. , Pagano Nicholas J.
Published: July 2010

A method to incorporate the thermoelastic effects of fiber coatings into models of fiber/matrix composites was deter‐mined. The coated fiber was replaced by an “effective” transversely isotropic fiber so that the properties of this effective fiber could be used in composite models. This ap‐proach was used to determine the magnitude of errors re‐sulting from neglect of the coatings in modeling fiber/matrix debonding and sliding and in reduction of data from real composites. The effects of carbon and BN coatings in the Nicalon/SiC system were found to be significant. It was found that significant errors could be expected from fitting models to experimental data if the compliance and coeffi‐cient of thermal expansion of the coatings were ignored, even when the coatings were thin. Wide use of the approach required revision of composite models to allow inclusion of a transversely isotropic fiber. Such a revision was de‐rived for a popular model of matrix cracking stress, and significant effects again were found to result from neglect of coatings.
Adsorption Behavior of Poly(ethylene glycol) at the Solid/Liquid Interface
Authors: Jr. Walker William J. , Reed James S. , Verma Surendra K. , Zirk Wayne E.
Published: July 2010

Adsorption behavior of two grades of poly(ethylene glycol) (PEG) was measured on silica and alumina in the presence of other organic and inorganic additives commonly used in ceramic processing. A fractional factorial designed experiment showed that the level of adsorption was significantly influenced by the powder or powder blend and the binder, but was not influenced significantly by small additions of auxiliary binder, surfactant, or the choice of deflocculant. Adsorption of PEG onto alumina was promoted by poly(acrylic acid) deflocculant due to formation of an association complex between the binder and adsorbed deflocculant molecules. A PEG compound containing an epoxide adsorbed at a higher level and the adsorption showed a larger pH dependence than did a lower molecular weight PEG homopolymer.
Polarization Switching of and Electron Emission from Lead Lanthanum Zirconate Titanate Ceramics
Authors: Zhang Weiming , Huebner Wayne , Sampayan Stephen E. , Krogh Mike L.
Published: July 2010

This paper focuses on understanding the influence of ma‐terial properties on the complicated ferroelectric (FE) emis‐sion process. Three different compositions in the lead lan‐thanum zirconate titanate (PLZT) system were chosen for study, based on their widely different dielectric and ferro‐electric properties: antiferroelectric (AFE) 2/95/5, “nor‐mal” ferroelectric 8/65/35, and nonferroelectric 15/65/35. Repeatable emission was obtained from the 2/95/5 compo‐sition, which could also be modulated at high frequency (200 kHz). The fast AFE ⇆ FE phase transition is respon‐sible for the FE emission properties of this material, which is supported by the relationship between the switching cur‐rent and the emission current. Comparatively, FE emission from the 8/65/35 composition degraded rapidly, which was attributed to decreases in the remanent polarization. No emission signal was detected from the 15/65/35 composi‐tion, because no switching activity occurs, which can be interpreted as additional evidence that electron emission from the previously mentioned two compositions was in‐deed a FE emission process.
Phosphorus‐Implanted Glass for Radiotherapy: Effect of Implantation Energy
Authors: Kawashita Masakazu , Miyaji Fumiaki , Kokubo Tadashi , Takaoka Gikan H. , Yamada Isao , Suzuki Yasuo , Kajiyama Kenji
Published: July 2010

A chemically durable glass that contains a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to be a β‐emitter with a half‐life of 14·3 d by using neutron bombardment. Microspheres of the activated glass that are injected to tumors can irradiate the tumors directly with β‐rays without irradiating neighboring normal tissues. In the present study, P+ ions in various doses have been implanted into a pure silica glass in a plate form at 200 keV. Almost all the implanted phosphorus is present in the inner region of the glass rather than in the surface region, taking the form of phosphorus colloids for all the doses in the range of 5 × 1016‐1 × 1018 cm‐2. A large number of amorphous phosphorus colloid particles with diameters of 10‐150 nm are formed in the silica glass that has been implanted with a dose of 1 × 1018 cm‐2; these colloid particles are distributed widely in a layer that is centered at a depth of 200‐250 nm. All the investigated glasses hardly release any phosphorus and silicon into water at a temperature of 95°C, even after 7 d. A silica glass that has been implanted with P+ ions at 200 keV with a dose of 1 × 1018 cm‐2 is believed to be useful as a radiotherapy glass with sufficient phosphorus content and high chemical durability.
Origin of the Red Color of Satsuma Copper‐Ruby Glass as Determined by EXAFS and Optical Absorption Spectroscopy
Authors: Nakai Izumi , Numako Chiya , Hosono Hideo , Yamasaki Kazuo
Published: July 2010

The origin of the ruby color of Satsuma glass, a famous copper‐ruby glass produced in Japan in the mid‐19th century, has been examined by electron microprobe analysis (EPMA), X‐ray absorption fine structure (XAFS), and optical absorption spectroscopy analyses. CuK XAFS analysis reveals that the major component of copper in the ruby glass consists of Cu(I) ions in the glass structure. This species is distinct from Cu2O (cuprite), which we conclude is not responsible for the ruby color. Optical absorption spectra measured at 300 and 77 K clearly distinguishes the absorptions due to the colloidal particles of metallic copper and Cu2O. It is concluded that the trace amount of copper in the ruby glass, which is below the detection limit of the EPMA and XAFS techniques, exists as metallic copper particles of nanometer size and is responsible for the ruby‐red appearance of the Satsuma glass.
Strength and Microstructure of Brazed Alumina‐Silicon Carbide Ceramic‐Matrix Composites
Authors: Zurbuchen Mark A. , Carim Altaf H.
Published: July 2010

Alumina‐silicon carbide whisker (Al2O3‐SiCw) composite pieces were brazed under high vacuum with Ag‐Cu‐based active braze alloys. Joined specimens exhibit mean fracture strengths of 480 MPa (4.5 wt% titanium in braze) and 591 MPa (2.0 wt% titanium in braze) in four‐point bend tests; these strengths are 78%−96% of the measured strength of the composite. The interfacial phases have been identified, by using transmission electron microscopy and electron probe microanalysis, as being Ti3(Cu,Al,Si)3O, Ti5Si3, TiC, and γ‐TiO, and the relative locations of the interfacial phases are described. The high strengths are believed to result from both good wetting behavior under high vacuum and the composite nature of the reaction product morphology.
Dehydration Sequence of Gibbsite by Electron‐Beam Irradiation in a TEM
Authors: Kogure Toshihiro
Published: July 2010

To understand the dehydration mechanisms of aluminum hydrates, the dehydration sequence of gibbsite (γ‐Al(OH)3) by electron‐beam irradiation has been investigated using transmission electron microscope (TEM). The electron diffraction pattern indicates the formation of chi‐alumina in the initial dehydration stage. The intensity distribution in the diffraction pattern of chi‐alumina is explained by the random close‐packed structure of oxygen/hydroxyl containing gibbsite layer structure. Further irradiation transforms χ‐alumina to η‐ or γ‐alumina and to a phase having a more ordered structure. The dehydrated product at this stage consists of crystallites and voids several nanometers in diameter.
Effects of Microstructure on the Deformation Mechanisms in Silicon Nitride
Authors: Schneider Judith A. , Mukherjee Amiya K.
Published: July 2010

Changes in phase composition and morphology were investigated in silicon nitride (Si3N4) both before and after compressive deformation testing. Different additive systems were used to prepare Si3N4 specimens, resulting in either an initial alpha‐phase or β‐phase microstructure. Constant‐strain‐rate compression tests were used to evaluate the differences in the strain‐rate dependency of the flow stress for the two phases. A flow‐stress dependency of n= 1 was observed in the β‐phase specimens, compared to an n value that approached 2 in the alpha‐phase specimens.
Thermal Expansion Behavior of Boron‐Doped Cordierite Glass‐Ceramics
Authors: Nandi Asok Kumar
Published: July 2010

The linear thermal expansion coefficients of cordierite glass‐ceramics that have been doped with a fixed amount of P2O5 and 1, 2, and 3 wt% of B2O3 show negative expansion in the temperature range of 100°‐300°C. The expansion of the undoped cordierite sample is positive. A relative decrease in the degree of negative expansion is observed as the B2O3 concentration increases. These negative expansion coefficients are similar to those of cordierite glass‐ceramics that have been doped with the potassium cation.
Ferroelectric Ceramics: History and Technology
Authors: Haertling Gene H.
Published: July 2010

Ferroelectric ceramics were born in the early 1940s with the discovery of the phenomenon of ferroelectricity as the source of the unusually high dielectric constant in ceramic barium titanate capacitors. Since that time, they have been the heart and soul of several multibillion dollar industries, ranging from high‐dielectric‐constant capacitors to later developments in piezoelectric transducers, positive temperature coefficient devices, and electrooptic light valves. Materials based on two compositional systems, barium titanate and lead zirconate titanate, have dominated the field throughout their history. The more recent developments in the field of ferroelectric ceramics, such as medical ultrasonic composites, high‐displacement piezoelectric actuators (Moonies, RAINBOWS), photostrictors, and thin and thick films for piezoelectric and integrated‐circuit applications have served to keep the industry young amidst its growing maturity. Various ceramic formulations, their form (bulk, films), fabrication, function (properties), and future are described in relation to their ferroelectric nature and specific areas of application.
Effect of Seeding and Water Vapor on the Nucleation and Growth of α‐Al2O3 from γ‐Al2O3
Authors: Bagwell Roger B. , Messing Gary L.
Published: July 2010

Isothermal transformation kinetics and coarsening rates were studied in unseeded and alpha‐Al2O3‐seeded γ‐Al2O3 powders heated in dry air and water vapor. Unseeded samples heated in dry air transformed to alpha‐Al2O3 with an activation energy of 567 kJ/mol. Seeding with alpha‐Al2O3 increased the transformation rates and reduced incubation times by providing low‐energy sites for nucleation/growth of the alpha‐Al2O3 transformation. The activation energy for the transformation was reduced to 350 kJ/mol in seeded samples heated in dry air. Seeded samples completely transformed to alpha‐Al2O3 after 1 h at 1050°C when heated in dry air compared to 1 h at 925°C when heated in saturated water vapor. The combined effects of a lower nucleation barrier due to seeding and the increased diffusion due to water vapor reduced the activation energy for the transformation by 390 kJ/mol and the transformation temperature by ∼225°C compared to the unseeded samples heated in dry air. The accelerated kinetics is believed to be due to increased surface diffusion.
Processing Aluminum Nitride‐Silicon Carbide Composites via Polymer Infiltration and Pyrolysis of Polymethylsilane, a Precursor to Stoichiometric Silicon Carbide
Authors: Chew Kean W. , Sellinger Alan , Laine Richard M.
Published: July 2010

AlN‐SiC‐particle‐reinforced composites have been prepared at lessthan equal to1400°C using submicrometer AlN, ‐325 mesh alpha‐SiC particles, and polymethylsilane (PMS; ‐(CH3SiH)n‐) via a polymer infiltration and pyrolysis (PIP) process. PMS is an organometallic SiC polymer precursor that can be modified with 16 wt% cross‐linking aid to provide mPMS. mPMS converts to nanocrystalline β‐SiC with >80% ceramic yield (1000°C in argon) with some excess (<5 wt%) graphitic carbon. mPMS has been used successfully as a nonfugitive binder for AlN‐SiC compacts. Densities of 2.5 versus 2.1 g/cm3 have been obtained after nine PIP cycles for disk‐shaped compacts formulated with and without mPMS binder, respectively. alpha‐SiC seeds crystallization of β‐SiC derived from mPMS at temperatures as low as 1000°C. Some evidence suggests that AlN‐SiC solid solutions form at particle/matrix interfaces.
Semiclosed‐Cell Mullite Foams: Preparation and Macro‐ and Micromechanical Characterization
Authors: Tulliani Jean‐Marc , Montanaro Laura , Bell Trevor J. , Swain Michael V.
Published: July 2010

The preparation and characterization of the properties of mullite ceramic foams suitable for diesel exhaust filtration systems are described. Two foams of different cell sizes, 32 and 61 ppi (pores per inch), were prepared from slurries by the replication process with polyurethane sponges as the templates. The microstructure and the dependence of the porosity and the mechanical properties on the preparation and resulting foam cell size and normalized density are discussed. In addition the micro‐ and macromechanical properties have been characterized using instrumented indentation techniques; with sharp (Berkovich) and small spherical‐tipped indenters the hardness and modulus of the dense strut materials have been measured. The macroproperties have been measured with a large sapphire indenter, ∼5 mm radius using a load partial‐unloading technique. The latter enables the modulus and the contact pressure versus penetration to be measured. These values are compared with traditional bulk measurements for crushing strength and elastic modulus. The results are discussed in terms of available theoretical treatments of the indentation of brittle porous materials.
In Vitro Behavior of Silica‐Based Xerogels Intended as Controlled Release Carriers
Authors: Falaize Sylvie , Radin Shulamit , Ducheyne Paul
Published: July 2010

We report on the in vitro behavior of room‐temperature‐prepared xerogels upon immersion in typical physiologic solutions. The effect of various parameters was studied: xerogel composition and particle size; solution composition; and immersion protocol. Three xerogel compositions were tested: a silica xerogel (S100); a Vancomycin–silica xerogel composite (S100V); and a calcium‐ and phosphorus‐containing silica xerogel (S70). The immersion was per‐formed integrally (i.e., without solution exchange) or dif‐ferentially (i.e., with solution exchange) to model the continuous flow of body fluids past implant surfaces. Four different solutions were used: tris(hydroxymethyl)amino‐methane hydrochloric acid buffer solution plus electrolytes (TE); TE supplemented with 3% H2O2; TE supplemented with 10% serum; and serum. Carbonated hydroxyapatite formed on all xerogels. The reaction was faster on S70 than on S100. The silica network fully dissolved for all xerogels in the differential experiment. S70 particles transformed to calcium‐ and phosphorus‐containing “shells” upon differ‐ential immersion. The presence of H2 O2 and serum proteins in the immersion solution slowed down the silicon dissolu‐tion of both xerogels. Xerogel dissolution was associated with decreased BET surface area and increased mean pore size. The data showed a linear relationship between the dissolution rate and the time‐dependent surface area. Re‐gardless of this relationship, our data also suggested that the rate‐limiting step of the dissolution during integral im‐mersion was the diffusion of the dissolved species to the bulk solution.
Chemical and Structural Properties of Nickel Hydroxide Xerogels Obtained by the Sol‐Gel Procedure in the Presence of Acetic Acid
Authors: Sharma Pramod K. , Fischer Hannes , Craievich Aldo F.
Published: July 2010

The sol‐gel route to glasses and ceramics has attracted an increasing amount of scientific and technological interest recently. In this process, sols with different concentrations are used as precursors for xerogels and to produce materials that consist of fine oxide particles. In the present work, nickel hydroxide gels have been obtained via the hydrolysis of a molecular precursor in the presence of acetic acid. The chemical aspects of the material transformation have been studied by using Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) for different acetic acid contents and several heat‐treatment temperatures. The carboxylic acid acts as a ligand at a molecular level in the precursor, therefore modifying the entire hydrolysis and condensation process. Small‐angle X‐ray scattering (SAXS) studies and density measurements have been performed for the structural characterization of the xerogels. A denser, final oxide material is obtained when a higher acetic acid concentration is used. The porosity of the dry gels coarsens when they are heat‐treated up to a temperature of ∼400°C and its density decreases. The material that has been heat‐treated up to a temperature of 800°C densifies and exhibits a finer porosity. The chemical properties at a molecular level satisfactorily explain and are well correlated with the structural characteristics of the studied material.
XPS Investigation of Si3N4/SiC Nanocomposites Prepared Using a Commercial Polymer
Authors: Oh Yoon‐Suk , Cho Woo‐Seok , Kim Chang‐Sam , Lim Dae Soon , Cheong Deock‐Soo
Published: July 2010

We have synthesized Si3N4/SiC nanocomposites using a commercial polymer. Formation behavior of SiC nanoparticles has been studied using X‐ray photoelectron spectroscopy (XPS). Based on the XPS results, we concluded that SiC nanoparticles were formed by a chemical reaction of Si provided from Si3N4 with free carbon obtained by pyrolysis of a polymer around 1300°C. The presence of CNx compounds in samples processed in an Ar atmosphere supported our explanation.
Combustion Synthesis of Hexaaluminate Phosphors
Authors: Ravichandran Duraiswamy , Roy Rustum , Ravindranathan Palaniappan , White William B.
Published: July 2010

Green phosphors of the composition Ce1‐xTbxMgAl11O19 (0.1 < x < 0.6) were prepared via self‐propagating (combustion) synthesis, using urea as a fuel. The phosphors that were produced via the combustion route were fine powders and produced a luminous intensity of 72%, compared to an optimized commercial phosphor. The excitation spectra were characteristic of the Ce3+ cation; however, no Ce3+ emission was observed. Energy transfer from the Ce3+ cation to the Tb3+ cation was complete, and only the 542 nm Tb3+ emission was observed. Concentration quenching occurred with x > 0.5. Scanning electron microscopy images showed a well‐crystallized, platelike morphology, with a particle size of 10‐20 µm.
Hydrothermal Synthesis of Manganese Zinc Ferrite Powders from Oxides
Authors: Makovec Darko , Drofenik Miha , Žnidaršič Andrej
Published: July 2010

Manganese zinc (MnZn) ferrite powders were prepared via the hydrothermal treatment of a homogeneous mixture of the raw oxides (i.e., Fe2O3, ZnO, and Mn3O4 or MnO) at temperatures of 220°‐320°C in air or an inert atmosphere. The final results of the hydrothermal reactions between the raw oxides were fine powders with a heterogeneous phase composition. In addition to lower concentrations of the residual reactants (Fe2O3, Mn3O4), two types of spinel‐structure‐based reaction products‐ferrite ((Mn2+,Zn)Fe2O4) and manganate ((Zn,Mn2+)Mn23+O4)‐were detected after the synthesis. The composition of the ferrite products, as well as the ratio of ferrite products to manganate products, were mainly functions of the oxidation state of the manganese that was present during treatment. The oxidation state of manganese during reaction was dependent on the valence of the manganese in the starting manganese oxide and on the atmosphere in the autoclave during reaction. When the hydrothermal reaction was conducted in air, almost‐pure zinc ferrite was identified, whereas during reaction in an inert atmosphere, MnZn ferrite was formed. The kinetics of the hydrothermal reactions also were dependent on the oxidation state of manganese, as well as the temperature and specific surface area of the starting Fe2O3.
Forces Measured between Zirconia Surfaces in Poly(acrylic acid) Solutions
Authors: Pedersen Henrik Guldberg , Bergström Lennart
Published: July 2010

We have studied the forces between a sphere and a plane surface of yttria‐partially‐stabilized tetragonal‐zirconia immersed in aqueous solutions of low‐molecular‐weight (Mw= 10 000) poly(acrylic acid) (PAA) using atomic force microscopy. The measurements are performed at high pH where the adsorbed, highly charged anionic polyelectrolyte extends far into the solution, resulting in a combination of polymeric (steric) and electrostatic interactions. Analysis of the experimental data using scaling theory shows that the polymeric contribution dominates and that the electrostatic contribution is small at relatively high ionic strength (0.01M NaCl). We find that the measured forces are highly dependent on time and interaction history of the absorbed PAA layer; consecutive compression‐decompression cycles result in an increase of the surface coverage and the range of the repulsive polymeric interaction. This buildup of PAA at the interface is strongly related to attractive bridging interactions manifested as strong adhesion during decompression at less than full surface coverage. The force results are compared to rheological observations of zirconia suspensions stabilized by the same dispersant; the poor colloidal stability and high viscosity at low surface coverage of PAA are related to the attractive bridging interactions.
Strength and Magnetic Properties of a Laminated Composite of Magnetic Metal Foil and Zirconia
Authors: Moorhead Arthur J. , Kim Hyoun‐Ee
Published: July 2010

A layered composite material composed of magnetic metal foil and ZrO2was fabricated by hot‐pressing. The interfacial strength between the metal and the ceramic increased with hot‐pressing temperature up to 1250°C, and decreased thereafter because of excessive reactions at the interface. The maximum interfacial fracture strength obtained was 420 MPa. Reasonably good magnetic properties, i.e., permeabilities greater than 2000 and ac core losses less than 100 W/kg, were obtained from these specimens. Magnetic core materials fabricated in this process can thus be used under severe conditions such as high temperature and high speed rotation with little dimensional tolerance.
Forming of Ceramics during Firing without the Application of External Pressure
Authors: Lombardo Stephen J. , Bianchi David , Bishop Bruce , Giannakopoulos Antonios , Goldsmith Robert , Higgins Richard , Pober Richard , Suresh Subra
Published: July 2010

A method to form thin ceramic bodies is described in which curvature in the component is introduced at high temperature without the application of an external stress. The internal stress that drives the deformation results as a consequence of cation penetration from a coating into a substrate material. This technique has been developed for alumina substrates that are coated with layers of chromia, magnesia, titania, calcia, silica, and iron oxide. Normalized deflections of segment height to sample thickness (A/t) of up to 10 were observed for samples with beam geometry and A/t values of 4 were obtained for disks. The magnitude of the deflection is dependent on the amount of dopant that is applied, as well as the soak temperature and time. An analytical model has been developed to describe the magnitude of the deflections. The best agreement with the experimental data is obtained when the deflections are treated as occurring at high temperature, where the resistance to bending from stiffness effects is reduced. This forming method is shown to be suitable to produce shapes of moderate complexity, such as ceramic wave springs.
Effects of Molar Ratio of Citric Acid to Cations and of pH Value on the Formation and Thermal‐Decomposition Behavior of Barium Titanium Citrate
Authors: Tsay Jenq‐dar , Fang Tsang‐tse
Published: July 2010

Several experiments were conducted to examine the effects of the molar ratio of citric acid to cations and of the pH value on the chemistry of a solution prepared by the Pechini method. Two types of precipitates, barium titanium citrate (BTC) and barium citrate, developed, depending on the experimental conditions. Characterization of BTC by FT‐IR spectroscopy and solid‐state 13C‐NMR spectroscopy indicated that barium and titanium ions were chelated simultaneously by the central deprotonated alcoholic ligands and by dissociated carboxylic acid groups with a unidentate type of three citric acid molecules. The possible coordinated structure of BTC was proposed. The thermal decomposition behavior of BTC was investigated by powder X‐ray diffractometry, FT‐IR spectroscopy, and solid‐state 13C‐NMR spectroscopy. During decomposition, the nature of bonding between carboxylate groups and cations changed in the order unidentate → bridging → ionic, and carbonate species were detected at 500°C. A small amount of BaCO3 and the intermediate oxycarbonate coexisted at 550°‐600°C.
Initiation of Self‐Propagating Combustion Waves in Dense Mo + 2Si Reactants through Field‐Activation
Authors: Xue H. , Vandersall K. , Carrillo‐Heian E. , Thadhani N. N. , Munir Z. A.
Published: July 2010

Because of kinetic limitations, self‐sustaining combustion synthesis reactions cannot be initiated in dense powder compacts. In compacts of Mo + 2Si, self‐propagating waves can be initiated in samples with less than 78% relative density. At this and higher densities, no waves could be initiated without field‐activation. In the presence of an electric field (at values of 7 and 13 V·cm‐1), reactant compacts with densities up to 95% could sustain a combustion wave to produce MoSi2. In the absence of a field (for lower‐density samples) the wave propagated in a non‐steady‐state (pulsating) mode, while under the influence of a field the wave propagated in a steady‐state mode. The dependences of wave velocity and combustion temperature on the relative density of the reactants were qualitatively similar, showing maxima at a relative density of about 65%. These observations are explained in terms of the contribution of a liquid phase in the MoSi2‐Mo5Si3 binary to the synthesis kinetics. Although not detected by X‐ray diffraction analysis, small amounts of Mo5Si3 were discerned at the grain boundaries of the MoSi2 product. The particle size of the silicide synthesized from 95% dense reactants was significantly smaller than those synthesized from reactants with lower densities, but the reason for this observation is not well understood at this time.
Theory of Cast Formation in Electrophoretic Deposition
Authors: Biesheuvel P. Maarten , Verweij Henk
Published: July 2010

The rate of cast formation in electrophoretic deposition is described by a combination of the equation of continuity for the suspension phase with expressions for the particle velocity and the movement of the cast‐suspension boundary. The assumptions necessary to arrive at the well‐known equations of Hamaker (1940) and Avgustinik (1962) are summarized, and it is shown that, in both equations, a factor is missing that tends to unity only for diluted suspensions. After incorporation of this factor, it is possible to understand better the more‐than‐linear increase of cast formation with increasing suspension concentration as reported by several authors.
Processing of Oriented K(Ta,Nb)O3 Films Using Chemical Solution Deposition
Authors: Suzuki Kazuyuki , Sakamoto Wataru , Yogo Toshinobu , Hirano Shin‐ichi
Published: July 2010

K(Ta,Nb)O3 (KTN) thin films have been prepared by the chemical solution deposition method. KTN precursors consisted of a uniform mixture of K[Ta(OC2H5)6] and K[Nb(OC2H5)6] with interaction at the molecular level. Perovskite KTN thin films with the desired composition (Ta/Nb = 65/35, 50/50, and 35/65) were synthesized from the precursor solutions by the dip coating method. KTN thin films with (100) preferred orientation were successfully synthesized on MgO(100) and Pt(100)/MgO(100) substrates. X‐ray pole figure measurements showed that grains of KTN films had a prominent three‐dimensional regularity on MgO(100) and Pt(100)/MgO(100) surfaces. The Curie temperatures of KTN films decreased with increasing Ta/Nb ratio. Typical P‐E hysteresis loops were observed for KTN thin films of three compositions on Pt(100)/MgO(100) substrates. The values of remanent polarization (Pr) of KTN films increased as the Ta/Nb ratio changed from 65/35 to 35/65.
High‐Temperature Oxidation of Boron Nitride: II, Boron Nitride Layers in Composites
Authors: Jacobson Nathan S. , Morscher Gregory N. , Bryant Darren R. , Tressler Richard E.
Published: July 2010

The oxidation of BN composite interphases was examined with a series of model materials. Oxidation was examined in both low‐water‐vapor (∼20 ppm H2O/O2) environments at 900°C and high‐water‐vapor (1% and 10% H2O/O2) environments at 700° and 800°C. The low‐water‐vapor case was explored with layered BN/SiC materials. This case was dominated by borosilicate glass formation, and the 20 ppm water vapor gradually removed the boron from the glass, leaving a larger amount of SiO2 than would be expected from simple SiC oxidation. Layered SiC/BN/SiC materials were also used to study low‐water‐vapor oxidation effects within the composite. The high‐water‐vapor case was explored with SiC/BN/SiC minicomposites, and it was dominated by volatilization of BN as HBO2(g), H3BO3(g), and H3B3O6(g). A model for recession of the BN fiber coating was developed based on the gas‐phase diffusion of these species out of the annular region around the SiC fiber and concurrent sealing of this annular region by oxidation.
Effect of Grain Size on the Sliding Wear and Friction of Alumina at Elevated Temperatures
Authors: Senda Tetsuya , Yasuda Eiichi , Kaji Masaki , Bradt Richard C.
Published: July 2010

The sliding friction and wear of three different grain‐size aluminas were studied from room temperature through 1000°C. The coefficient of friction revealed two distinct regions of decrease with increased temperature, with a transition at ∼700°C. Below 700°C, the coefficient of friction decreased rapidly with increased temperature (∼10‐3/°C). However, above 700°C, the decrease was more gradual (∼10‐5/°C). This was believed to be related to a brittle‐to‐ductile transition at the wear surface. The coefficient of friction was only weakly dependent on grain size, because the largest grain sizes exhibited slightly higher friction coefficients. However, the specific wear loss of the aluminas increased with increased grain size at room temperature and at 600°C, both below the 700°C transition. The primary mechanism of wear was ascertained to be brittle microfracture along grain boundaries. At 1000°C, above the 700°C transition, the specific wear loss was significantly decreased and appeared to be independent of the alumina grain size. At 1000°C, the wear surfaces developed a thin layer of fine grains formed by dynamic recrystallization. The grain size within the thin layer was in agreement with the previously reported grain‐size/Zener‐Hollomon parameter relationship.
Multiple‐Quantum Magic‐Angle Spinning 17O NMR Studies of Borate, Borosilicate, and Boroaluminate Glasses
Authors: Wang Shuanhu , Stebbins Jonathan F.
Published: July 2010

Multiple‐quantum magic‐angle spinning (MQMAS) 17O NMR spectroscopy has been applied to study boron oxide, sodium borate, sodium potassium borosilicate, and sodium boroaluminate glasses. Up to eight distinct oxygen sites are identified, with the chemical shift and quadrupolar coupling parameters determined for each. Previous assignment of the B‐O‐B and Si‐O‐B resonances has been found to be incorrect. In contrast to standard models of glass structure, three‐coordinated boron mixes with the silicon oxide network to a great extent. Sodium borosilicate glasses with low‐sodium content are likely to be phase‐separated on the nanoscale. Those with intermediate sodium content form homogeneous glasses with boron atoms distributed evenly in the SiO2 network. A boron avoidance rule analogous to the aluminum avoidance rule may apply in this region, when BO4 groups are abundant. Adding excess sodium cations to the system may again lead to compositional heterogeneity. The existence of diborate group as the basic building unit in glasses with appropriate sodium content is not well supported. The network‐forming cations in sodium boroaluminate glasses are well mixed, with no Al‐O‐Al resonance observed by MQMAS. The effect of cation type and thermal history on glass structures is also discussed.
A Diffuse Interface Description of Intergranular Films in Polycrystalline Ceramics
Authors: Bobeth Manfred , Clarke David R. , Pompe Wolfgang
Published: July 2010

The thermodynamic equilibrium between a thin liquid phase and adjoining grains of a co‐existing solid phase is treated, using a diffuse interface formulation applied to a multilayer of liquid and solid phases. The analysis leads to spatial variation in composition, which minimizes the overall free energy. The overall energy includes a gradient‐energy contribution. For a fixed overall composition, the equilibrium concentration profile is dependent on the thicknesses of the two phases, relative to the interface width (a characteristic‐length scale in the analysis). When the thickness of the liquid phase approaches the characteristic length, its composition can deviate markedly from the bulk liquid‐phase composition. In the absence of any stabilizing interactions, such as repulsive structural and electrostatic forces, the analysis indicates that there is a driving force for thinning of the film and a minimum thickness exists at which it becomes favorable for the film to dissolve. Therefore, the observations of equilibrium film thicknesses in certain ceramics imply that, in those materials, additional stabilizing forces must exist between the grains.
Solution Mechanisms for Dopant Oxides in Yttria
Authors: Busker Gerdjan , Chroneos Alex , Grimes Robin W. , Chen I‐Wei
Published: July 2010

Solution mechanisms in Y2O3 have been studied by using atomistic simulation. Various defect reactions for the solution of A2+, M3+, and B4+ ions, assuming either single isolated impurities or defect clusters, have been considered. Generally, the radius of the dopant cation is an important factor in determining the solution site and cluster geometry, and it can be critical in deciding the solution mechanism. Mechanisms that are associated with codoping A2+ and B4+ ions also have been considered. Surprisingly, this action does not always result in a reduction in the solution enthalpy.
Effect of Grain Contiguity on the Thermal Diffusivity of Aluminum Nitride
Authors: Tajika Masahiko , Matsubara Hideaki , Rafaniello William
Published: July 2010

Thermal diffusivity of AlN‐based ceramics was studied as a function of second‐phase amount and heat‐treatment time. The Y2O3·Al2O3 contents varied over the range of 13‐31 vol%. The thermal diffusivity decreased as the amount of second phase increased. After sintering at 1850°C, the AlN ceramics consisted of rounded, largely isolated grains. Heat treatment of these samples for 5‐50 h at 1800°C resulted in microstructures that consisted of largely contiguous AlN grains. There was a substantial increase in the thermal diffusivity after the heat‐treatment step, and the incremental improvement was essentially constant for the three compositions that have been studied. The amount of second phase was unchanged during heat treatment; therefore, the increase in thermal diffusivity is assumed to be a direct result of the enhanced contiguity of AlN grains.
Preparation of Lead Zirconate Titanate (Pb(Zr0.52Ti0.48)O3) by Homogeneous Precipitation and Calcination
Authors: Tas A. Cüneyt
Published: July 2010

Preparation of phase‐pure PZT (Pb(Zr0.52Ti0.48)O3) powders was achieved, in the presence of urea (CH4N2O), by homogeneous precipitation. Aqueous solutions of PbCl2, ZrOCl2·8H2O, and TiCl4 were used as the starting materials in the synthesis of phase‐pure PZT powders. Phase evolution behavior of precursor powders was studied by powder X‐ray diffraction (XRD) in air, over the temperature range of 90° to 750°C. The morphology of the formed powders was studied by scanning electron microscopy (SEM). Semiquantitative chemical analyses of the samples were performed by energy‐dispersive X‐ray spectroscopy (EDXS).
Mechanical Properties and Microstructure of Alumina‐Glass Composites
Authors: Tian Jie‐Mo , Zhang Yun‐Long , Zhang Shi‐Xin , Luo Xiao‐Ping
Published: July 2010

Alumina blanks were prepared via isostatic pressing and sintering at 1400°C for 2 h, whereas alumina‐glass composites were prepared by infiltrating the molten glass into the partially sintered alumina compacts. The samples had a high bending strength (340 MPa) and high fracture toughness (3.91 MPa·m1/2) and were free of shrinkage. Concurrently, zirconia (5 wt%) was used as an additive to alumina to improve the mechanical properties of both partially sintered alumina and alumina‐glass composites. Results show that zirconia notably improves the mechanical properties of the partially sintered alumina but increases that of the composites by no more than 10%.
Plastic Flow of Saturated, Consolidated Alumina Powder Compacts: Particle Size and Binary Mixtures
Authors: Franks George V. , Lange Fred F.
Published: July 2010

The flow stresses and relaxed yield stresses of saturated, alumina powder compacts that have been consolidated via pressure filtration were measured in unconstrained uniaxial compression. Two different sized powders, as well as binary mixtures of the two powders, were investigated. Bodies that were consolidated from slurries of larger particles had lower flow and relaxed yield stresses, relative to bodies that were made of small particles with the same relative density and solution conditions. This result is primarily due to the lower number of particle‐particle contacts per unit volume in the body that was made of the large particles. The flow stress of the body can be controlled by adjusting the fraction of large particles to small particles.
Hot‐Pressed Mica Glass‐Ceramics with High Strength and Toughness
Authors: Cheng Kangguo , Wan Julin , Liang Kaiming
Published: July 2010

A new type of mica glass‐ceramics has been prepared by hot pressing. X‐ray diffractometry (XRD) has confirmed that (001) planes of mica crystals are almost perpendicular to the direction of hot pressing. Flexural strength and fracture toughness of the materials increase with increasing hot‐pressing deformation. The orientation of the hot‐pressed materials is attributed to the combination of viscous flow of the residual glass phase and rotation of mica plates under pressure at high temperature.
Morphology and Sinterability of Thermally Treated Carbothermally Synthesized Silicon Nitride Powders
Authors: Weimer Alan W. , Carroll Daniel F. , Susnitzky David W. , Beaman Donald R.
Published: July 2010

Carbothermally produced alpha‐Si3N4 powder is thermally treated (1400°‐1500°C for 4‐12 h) in nitrogen‐gas to determine the impact of thermal treatment on powder composition, particle size, morphology, and sinterability. Thermal treatment reduces residual carbon and oxygen content and reduces internal porosity (lower surface area), which results in a rounding of the particles. The lower oxygen content of the heat‐treated, carbothermally produced alpha‐Si3N4 powder allows Y2O3‐Al2O3‐SiO2 sintering formulation to be adjusted so that an improvement in the early stage of densification can be achieved.
SEM Analysis of Oxide Thin Films and Reactions
Authors: Johnson Matthew T. , Carter C. Barry , Michael Joseph
Published: July 2010

The determination of orientation relationships between thin oxide films and the underlying single‐crystal oxide substrates using electron backscattered diffraction (EBSD) in scanning electron microscopy (SEM) is discussed. In these well‐defined systems, complementary information concerning the local chemistry can be obtained using high‐resolution backscattered electron (BSE) imaging. Recent studies have shown the value of using EBSD patterns (EBSPs) in SEM.