bluuebunny/crossref_metadata_2025 huggingface dataset:
Nature of Alumina in Phosphate Glass: I, Properties of Sodium Aluminophosphate Glass
Authors: Brow Richard K.
Published: March 2005

Glasses along four compositional tie lines, I: xAl(PO3)3’(1 – x)NaPO3, II: xAlPO4′(1 – x)NaPO3, III: xAl2O3′(1 – x)NaPO3, and IV: xNaAlO2,(1 – x)NaPO3, have been prepared and a number of their properties evaluated. In general, Al2O3 additions increase the glass transition temperature, decrease thermal expansion, and improve aqueous durability. However, the composition/property relationships are strongly influenced by relative cation ratios and thus the overall O/P ratio. The nature of these glasses undergoes significant transformations at both the pyrophosphate (O/P = 3.5) and the orthophosphate (O/P = 4.0) compositions, producing significant changes in the property behavior. Spectroscopic analyses of glass structure, described in part II of this report, reveal that changes in Al coordination coincide with the breaks in the property behavior.
Electrical Conduction in Aluminum Nitride
Authors: Jang Se‐Aug , Choi Gyeong Man
Published: March 2005

Electrical conductivities of aluminum nitride (AIN) doped with various ions of different sizes and valences have been measured at elevated temperatures. Grain conductivities of samples doped with large cations, obtained from complex impedance patterns, were much higher than those doped with small cations. The temperature dependence of electrical conductivity showed two regions having different activation energies. It was proposed that the precipitated impurities play a decisive role in the electrical conduction of AIN.
Fabrication and Evaluation of Al2O3–AgCl–Agl Composites by Use of Electrochemical Deposition
Authors: Nagai Masayuki , Nishino Tadashi
Published: March 2005

Al2O3–AgCl–AgI composites were fabricated by an electrochemical deposition technique utilizing porous α–Al2O3 ceramics as a matrix. The growth process was presumed to be dominated by the diffusion rate of the Ag+ ion. The phases identified in the composites were α‐Al2O3, AgCl, and β‐AgI. The deposited AgCl and AgI showed enhanced conductivity compared with the reported bulk values. The deposited mixture exhibited enhanced conductivity compared with pressed polycrystalline AgCl or AgI. The enhancement was explained using a model that a deposit with a high conductivity grows much faster than that with a low conductivity.
Preparation of Zirconia Coatings by Hydrolysis of Zirconium Alkoxide with Hydrogen Peroxide
Authors: Sakurai Chihiro , Fukui Toshimi , Okuyama Masahiko
Published: March 2005

Coatings of 8.8‐mol%‐yttria‐doped zirconia were fabricated using a transparent and spinnable sol prepared by hydrolysis of zirconium alkoxide with hydrogen peroxide and nitric acid. The sol gave a crack‐free coating film consisting of fine grains. The crystalline phase was cubic after heating at 1000° and 1200°C and cubic and tetragonal at 1350°C, with the coating being highly oriented in the (111) plane, especially at 1000°C. Activation energy of the coating films was higher than that of the bulk. Transmittance through a film thickness of about 0.3 μm on each side was 75%.
29‐Si and 27‐Al Magic‐Angle Spinning Nuclear Magnetic Resonance Study of the Thermal Transformations of Pyrophyllite
Authors: Sánchez‐Soto Pedro J. , Sobrados Isabel , Sanz Jesús , Pérez‐Rodríguez José L.
Published: March 2005

The thermal transformation of pyrophyllite was analyzed using 27‐Al and 29‐Si MAS‐NMR spectroscopies, thermal analysis (DTA‐TG), dilatometry, and X‐ray diffraction techniques. Above 800°C, dehydroxylation of pyrophyllite is the origin of a broad component in the 27‐Al NMR spectra which is associated with a distorted pentahedral coordination of Al. At 1000°C, tetrahedral sheet breakdown takes place and a partial segregation of amorphous SiO2 is detected by NMR spectroscopy. This process permits rearrangements of aluminum ions and favors the formation of small disordered nuclei of mullite. The 27‐Al NMR signals observed at 59.5, 40.7, and 1 ppm have been assigned to 4‐ and 6‐coordinated Al in mullite, and the 29‐Si NMR signals observed at −110 and −88 ppm are assigned to well‐crystallized mullite and cristobalite, respectively, formed during thermal decomposition of pyrophyllite.
Microstructure of Epitaxial Ferroelectric YBa2Cu3O7−x/Pb0.9La0.1(Zr0.2Ti0.8)0.975O3/YBa2Cu3O7−x Heterostructures on LaAlO3
Authors: Ghonge Subodh G. , Goo Edward , Ramesh R. , Sands T. , Keramidas V. G.
Published: March 2005

The microstructure of an epitaxial YBa2Cu3O7−x/Pb0.9‐La0.1(Zr0.2Ti0.8)0.975O3/YBa2Cu3O7−x (YBCO/PLZT/YBCO) heterostructure on [001] LaAlO3 (LAO) has been investigated by X‐ray diffractometry and transmission electron microscopy. The ferroelectric film is c‐axis oriented and epitaxial with the underlying YBCO film. The YBCO film, which is b‐axis oriented, is epitaxial with the LAO substrate and shows two variants.
Effect of Y2O3 Additions on the Densification of an Al2O3–TiC Composite
Authors: Chae Ki‐Woong , Kim Doh‐Yeon , Kim Byung‐Chan , Kim Kyung‐Bae
Published: March 2005

The densification of Al2O3–30TiC (in weight percent) composite is investigated as a function of Y2O3 additions. It is observed that very small amounts of Y2O3 are effective in aiding the densification. The density was observed to pass through a maximum at 0.35 wt% of Y2O3. The gas‐generating reaction of Al2O3 with TiC is likely to be suppressed by the addition of Y2O3.
Role of Interfacial Gaseous Heat Transfer in the Transverse Thermal Conductivity of a Uniaxial Carbon Fiber‐Reinforced Aluminoborosilicate Glass
Authors: Donaldson Kimberly Y. , Bhatt Hemanshu D. , Hasselman D. P. H. , Chyung Kenneth , Taylor Mark P.
Published: March 2005

The transverse thermal conductivity of an aluminoborosilicate glass uniaxially reinforced with carbon fibers was found to be lower under near‐vacuum than in nitrogen, whereas no such difference was found for the longitudinal thermal conductivity. This effect was attributed to the existence of an interfacial gap resulting from the thermal expansion mismatch between the matrix and fibers. The presence of this gap permits the gaseous environment access to the fiber‐matrix interface and thereby contributes to the interfacial heat transfer. Its presence does not affect the longitudinal thermal conductivity, however, because the gap is aligned parallel to the fibers and, therefore, the direction of heat flow. Analysis of the experimental data indicates that, in nitrogen at atmospheric pressure, the gaseous conductance constitutes about one‐third of the total interfacial conductance.
Preparation by a Sol‐Gel Process of Borosilicate Glasses Containing Microcrystals of Tellurium and Zinc Telluride
Authors: Li Guangming , Nogami Masayuki , Abe Yoshihiro
Published: March 2005

Borosilicate glasses, 5B2O3· 95SiO2 (mol%), containing TeO2 and ZnO nominally equivalent to 10 wt% Te and ZnTe were prepared by a solgel method from Si(OC2H5)4, B(OCH3)3, H6TeO6, and Zn(NO3)2. A study by electron spectroscopy for chemical analysis (ESCA) showed that glasses heated at high temperature (450°C) in air contained both Te6+ and Te4+ ions on the surface layer, but that mainly Te4+ ions occurred inside the bulk glass. When solgel‐derived borosilicate glasses containing the TeO2 compound were reduced at elevated temperature in a hydrogen atmosphere, Te crystallites ranging in size from 4 to 15 nm were produced at a lower temperature, between 200° and 250°C. The absorption edge moved from the infrared to the visible wavelength region as the particle size decreased to about 4 nm. For glasses containing both TeO2 and ZnO, ZnTe crystallites formed at high temperature—over 300°C—and existed along with the Te phase.
Metal‐organic Surfactants as Sintering Aids for Silicon Nitride in an Aqueous Medium
Authors: Joshi Pankaj N. , McCauley Ronald A.
Published: March 2005

Interaction between two commercial silicon nitride powders and various metal‐organic surfactants was investigated in an aqueous medium to obtain a homogeneous distribution of sintering aid. Conditions under which the silicon nitride particles could be coated with metal oxide sintering aids were identified. Acoustophoresis, XPS, TEM, and FTIR were used to characterize the interaction between the metalorganic and the silicon nitride powder. From these data, the mechanism of attachment of the coatings was proposed. The surface area and surface chemistry of the powder, the pH of the solution, the structure of the surfactant, and the surface charge behavior of the powder and the coating were found to be the crucial parameters. The control of these parameters offered a simple and reproducible method to homogeneously distribute various metal oxides. Multicomponent coatings were also possible. The coated powders containing 0.5–4 wt% sintering aid could be compacted to 72% green density.
High‐Temperature Stability of Ca2ZrSi4O12
Authors: Jacob K. Thomas , Waseda Yoshio
Published: March 2005

The standard Gibbs free energy of formation of orthorhombic Ca2ZrSi4O12 from component oxides ZrO2 (monoclinic), CaO (rock salt), and SiO2 (quartz) has been determined in the temperature range 973 to 1273 K using a solid‐state cell incorporating single‐crystal CaF2 as the electrolyte:

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This is the only quantitative information now available on the stability Ca2ZrSi4O12.
Electrical Conductivity of Alumina/Aluminum Composites Synthesized by Directed Metal Oxidation
Authors: Venugopalan Hari , Tankala Kanishka , DebRoy Tarasankar
Published: March 2005

Electrical conductivities of Al2O3/A1 composite synthesized by directed oxidation of an aluminum alloy, and sintered Al2O3–4% MgO are measured. The high conductivity of the Al2O3/A1 composite compared to sintered Al2O3–4% MgO is shown as proof of the presence of continuous metal channels in the composite. Furthermore, the conductivity data are used to determine the activation energy for the diffusion of the dominant charge carrier in the oxide matrix.
Synthesis of Yttria Powders by Electrospray Pyrolysis
Authors: Rulison Aaron J. , Flagan Richard C.
Published: March 2005

Electrospray atomization of high‐concentration (∼400 g/L) chemical precursor solutions was applied to the synthesis of yttria powders. Conditions were found which led to high‐quality powders, composed of dense, spheroidal, submicrometer, and nanocrystalline oxide particles. The precursor solutions were hydrated yttrium nitrates dissolved in n‐propyl alcohol at concentrations ranging from 44.1 to 455 g/L. Electrospray atomization produced submicrometer precursor droplets which were dispersed in air and carried through an electric furnace for thermal decomposition at 500°C for several seconds residence time. X‐ray powder diffraction patterns indicated the expected cubic phase. Transmission electron micrographs showed that the particle structure varied with solution composition, ranging from hollow, inflated spheres for 6‐hydrated nitrates to dense spheroids for 5‐hydrated nitrates. The use of 6‐hydrated nitrates in the solutions appeared to form particle surfaces which were impermeable to alcohol vapor evolved during thermal decomposition, leading to hollow, inflated spheres.
Microstructure and Fracture Toughness of Hot‐Pressed Silicon Carbide Reinforced with Silicon Carbide Whisker
Authors: Lee Dong‐Han , Kim Hyoun‐Ee , Cho Seong‐Jai
Published: March 2005

The effects of β‐SiC whisker addition on the microstructural evolution and fracture toughness (KIC) of hot‐pressed SiC were investigated. Most of the whiskers added disappeared during the densifcation process by transformation into the α‐phase. The remaining whiskers acted as nuclei for grain growth, resulting in the formation of large tabular grains around the whiskers. The tabular grains around the whiskers were believed to be formed because of the extreme anisotropy of the interfacial energy between α‐ and β‐SiC. The KIC of the material was improved significantly by the whisker addition. The increase in the KIC was attributed to crack bridging followed by grain pullout as a result of the formation of tabular grains in a fine matrix.
Frequency Dependence of Fatigue Life and Internal Heating of a Fiber‐Reinforced/Ceramic‐Matrix Composite
Authors: Holmes John W. , Wu Xin , Sørensen Bent F.
Published: March 2005

The influence of loading frequency on the fatigue life and internal (frictional) heating of unidirectional SiC‐fiber/ calcium aluminosilicate‐matrix composites was investigated at room temperature. Specimens were subjected to tension–tension fatigue at sinusoidal loading frequencies from 25 to 350 Hz and maximum fatigue stresses of 180 to 240 MPa. The key findings of the study were that (1) fatigue life decreased sharply as the loading frequency was increased, (2) for all loading frequencies, fatigue failures occurred at stress levels that were significantly below the monotonic proportional limit stress of ∼285 MPa, and (3) pronounced internal heating occurred during fatigue, with the surface temperature of the fatigue specimens increasing by 160 K during 350‐Hz fatigue at a peak stress of 240 MPa.
Effects of Silver and Lead on the Phase Stability of Bi2Sr2Ca1Cu2O8+x and Bi2Sr2Ca2Cu3O10+x above and below the Solidus Temperature
Authors: MacManus‐Driscoll Judith L. , Bravman John C. , Savoy Richard J. , Gorman Grace , Beyers Robert B.
Published: March 2005

A solid‐state ionic technique has been used to determine the effects of Ag on the phase stability of Bi2Sr2Ca1Cu2O8+x(Bi‐2212), and Ag and Pb on the phase stability of Bi2Sr2Ca2Cu3O10+x (Bi‐2223), over a temperature range of 600° to 910°C and oxygen partial pressure range of 10–6 to 10°atm (10–1 to 105 Pa). The addition of Ag to Bi‐2212 leads to a marginal decrease in the stability of the phase above 883°± 3°C and 7 × 10–2 atm (7 kPa) oxygen, resulting in a reduction in the incongruent melting point by 15°C in air. The substitution of Pb for Bi in the (Bi,Pb)‐2223 phase leads to an increase in phase stability below the solidus, but to only a minor change in stability above the solidus. For both phases, several incongruent melting reactions have been identified over the range of reduced oxygen partial pressures studied. In addition, the phase equilibria both above and below the stability line have been determined for certain regions of the stability diagrams. From the thermo‐dynamic information obtained in this study an improved melt‐processing route for Bi‐2212 has been found which minimizes unwanted phases. In addition, the optimum precursors for the formation of more phase‐pure (Bi,Pb)‐2223 during shorter time periods have been found by determining the initial decomposition products of (Bi,Pb)‐2223, both above and below the solidus.
29Si and 27Al MAS‐NMR of NaOH‐Activated Blast‐Furnace Slag
Authors: Schilling Paul J. , Butler Leslie G. , Roy Amitava , Eaton Harvill C.
Published: March 2005

b29Si and 27Al MAS‐NMR were performed on NaOH‐activated blast‐furnace slag to better characterize the amorphous and poorly crystalline phases which occur in this system. The unreacted glass has a mainly dimeric silicate structure represented by a broad 29Si peak (FWHM = 15 ppm) centered at –74.5 ppm [Q1], with aluminum present exclusively in tetrahedral coordination. Upon reaction with 5M NaOH (w/s= 0.4), three new 29Si peaks with widths of ca. 2 ppm are formed at ‐78.5 Q1, –81.4 [Q2(1Al)J, and ‐84.3 [Q2]. Relative peak areas indicate a mostly dimeric silicate structure for the tobermorite‐like C─S─H layers, with roughly a third of the bridging sites occupied by aluminum, and less than 10% by silicon. In addition to the tetrahedrally coordinated aluminum substituted in the C─S─H structure, 27Al MAS‐NMR reveals the presence of aluminum in octahedral sites, which is attributed to the aluminate phase (C,M)4AH13. 29Si results indicate rapid initial consumption of the glass, with roughly a third of the glass reacting within the first day and another third consumed over the following 27 days.
Effects of Glass Additions on (Zr,Sn)TiO4 for Microwave Applications
Authors: Takada Takahiro , Wang Sea Fue , Yoshikawa Shoko , Jang Sei‐Joo , Newnham Robert E.
Published: March 2005

The effects of glass additions on the properties of (Zr,Sn)TiO4 as a microwave dielectric material were investigated. The (Zr,Sn)TiO4 ceramics with no glass addition sintered at 1360°C gave Q= 4900 and K= 37 at 7.9 GHz. Several glasses, including SiO2, B2O3, 5ZnO–2B2O3, and nine commercial glasses, were tested during this study. Among these glasses, (Zr,Sn)TiO4 sintered with ZnO‐B2O3–SiO2 (Corning 7574) showed more than 20% higher density than that of pure (Zr,Sn)TiO4 sintered at the same temperature. A 5‐wt% addition of SiO2, to (Zr,Sn)TiO4, when sintered at 1200°C, gave the best Q: Q= 2700 at 9 GHz. Results of XRD analysis and scanning electron microscopy and the effect of glass content are also presented.
Effect‐of Processing Varcables on Interfacial Properties of an SiG‐Fiber‐Reinforced Reaction‐Bonded Si3N4 Matrix Composite
Authors: Singh Dileep , Singh Jitendra P. , Majumdar Saurin , Kupperman David S. , Cowdin Eric , Bhatt Ramakrishna T.
Published: March 2005

Fiber/matrix interfacial debonding and frictional sliding stresses were evaluated by single‐fiber pushout tests on unidirectional continuous silicon‐carbide‐fiber‐reinforced, reaction‐bonded silicon nitride matrix composites. The debonding and maximum pushout loads required to overcome interfacial friction were obtained from load–displacement plots of pushout tests. Interfacial debonding and frictional sliding stresses were evaluated for composites with various fiber contents and fiber surface conditions (coated and uncoated), and after matrix densification by hot isostatic pressing (HIPing). For as‐fabricated composites, both debonding and frictional sliding stresses decreased with increasing fiber content. The HIPed composites, however, exhibited higher interfacial debonding and frictional sliding stresses than those of the as‐fabricated composites. These results were related to variations in axial and transverse residual stresses on fibers in the composites. A shear‐lag model developed for a partially debonded composite, including full residual stress field, was employed to analyze the nonlinear dependence of maximum pushout load on embedded fiber length for as‐fabricated and HIPed composites. Interfacial friction coefficients of 0.1–0.16 fitted the experimental data well. The extremely high debonding stress observed in uncoated fibers is believed to be due to strong chemical bonding between fiber and matrix.
Oxidation Kinetics of Chemically Vapor‐Deposited Silicon Carbide in Wet Oxygen
Authors: Opila Elizabeth J.
Published: March 2005

The oxidation kinetics of chemically vapor‐deposited SiC in dry oxygen and wet oxygen (PH2O= 0.1 atm) at temperatures between 1200° and 1400°C were monitored using thermogravimetric analysis. It was found that in a clean environment, 10% water vapor enhanced the oxidation kinetics of SiC only very slightly compared to rates found in dry oxygen. Oxidation kinetics were examined in terms of the Deal and Grove model for oxidation of silicon. It was found that in an environment containing even small amounts of impurities, such as high‐purity Al2O3 reaction tubes containing 200 ppm Na, water vapor enhanced the transport of these impurities to the oxidation sample. Oxidation rates increased under these conditions presumably because of the formation of less protective sodium alumino‐silicate scales.
SHS Combustion Characteristics of Several Ceramics and Intermetallic Compounds
Authors: Makino Atsushi , Law Chung K.
Published: March 2005

Extensive comparisons have been conducted between experimental and theoretical results for the SHS combustion characteristics of a number of solid‐solid systems. The heterogeneous flame propagation theory describes a premixed mode of bulk flame propagation supported by the nonpremixed reaction of dispersed nonmetal (or higher melting point metal) particles in the liquid metal, with finite‐rate reaction at the particle surface and temperature‐sensitive Arrhenius‐type condensed‐phase mass diffusivity. Systems examined are those of borides (TiB2, ZrB2, and HfB2) and intermetallic compounds (NiAl, TiCo, and TiNi). By using a consistent set of physico‐chemical parameters for these systems, satisfactorily quantitative agreement is demonstrated for the effects of mixture ratio, degree of dilution, and particle size on the burning velocity. Experimental flammability limits are also predicted by the theory.
Dense Al2O3/ZrO2 Particulate Composites by Free Sintering of Coated Powders
Authors: Hu Ching‐Li , Rahaman Mohamed N.
Published: March 2005

Composite powders, prepared by coating coarse ZrO2 particles with fine Al2O3 powder using a chemical precipitation technique, were compacted and sintered freely at a constant heating rate of 4°C/min to ∼1600°C. Composites containing up to ∼30 vol% inclusions were sintered to nearly full density under the same conditions used for the unreinforced matrix. Furthermore, the sintering kinetics were not influenced significantly by the inclusion volume fraction. The sinterability of the composites formed from the coated powders was significantly better than that for similar composites formed from mechanically mixed powders. The present data provide a further demonstration that the use of coated powders may have widespread applicability for the fabrication, by free sintering, of dense ceramic particulate composites.
Semiconducting Barium Titanate Ceramics Prepared by Boron‐Containing Liquid‐Phase Sintering
Authors: Ho In‐Chyuan
Published: March 2005

Semiconducting BaTiO3 ceramics have been prepared by adding BN as a sintering aid. Density as high as 93% of theoretical and grain size as large as 16 μm are obtained after sintering at 1160°C. Most significant is that the semiconducting BaTiO3 is obtained at sintering temperatures as low as 1100°C. The low‐temperature‐sintered BaTiO3 exhibits a positive temperature coefficient. (PTC) anomaly above 120°C with a resistivity maximum at a temperature as high as 400°C, which is much higher than that of the conventional BaTiO3. The incorporation of B into the perovskite structure is negligible. Also, the presence of B at a grain boundary after sintering is believed to enhance the PTC effect.
Fibrous Monolithic Ceramics: III, Mechanical Properties and Oxidation Behavior of the Silicon Carbide/Boron Nitride System
Authors: Baskaran Suresh , Halloran John W.
Published: March 2005

Fibrous monolithic ceramics were fabricated in the SiC/BN system. The microstructure consists of high‐aspect‐ratio polycrystalline cells of SiC separated by cell boundaries of BN. The fibrous monolith with aligned cells fails noncatastrophically in flexure, with delamination cracking along the BN cell boundaries. Indentations cause controlled damage on the surface, but no strength‐degrading flaws. The flexural strength is in the range 300–375 MPa, and the estimated shear strength is ∼14 MPa. The SiC/BN fibrous monoliths also show excellent resistance to high‐temperature oxidation in air. Noncatastrophic fracture behavior is observed at room temperature after heat treatments between 1200° and 1500°C. The SiC cells on the surface are oxidized to form a protective silicate scale, which prevent deterioration of the BN cell boundaries.
Fabrication and Microstructure of Al2O3–SiC–YAG Hybrid Composites Prepared by Particulate Dispersion
Authors: Jang Byung‐Koog , Kishi Teruo
Published: March 2005

Stable Al2O3–SiC–YAG hybrid composites were successfully fabricated by reaction of Al2O3 and Y2O3 and incorporation of SiC. The hot‐pressed bodies consisted of uniformly dispersed grains of microsized YAG particulates and nanosized SiC particulates in an Al2O3 matrix. Although the grain size of monolithic A12O3 increases markedly with increased temperature, the grain size of the Al2O3–SiC–YAG hybrid composites was effectively restrained due to grain‐boundary pinning by the particulates.
Ion‐Beam Mixing of Iron Oxide Marker Layers in Doped and Undoped Alumina Thin Films
Authors: Cooper Elizabeth A. , Nastasi Michael
Published: March 2005

Thin films of iron‐doped and pure amorphous alumina with embedded marker layers of iron oxide (Fe2O3) were ion‐beam mixed with 210‐keV argon in a temperature range of −164° to 750°C. The marker exhibited a strong temperature‐dependent spreading (T > 470°C) into the undoped alumina matrix, but the marker spreading into the iron‐doped matrix was inhibited by the presence of the dopant.
High‐Temperature Strength of Fluorine‐Doped Silicon Nitride
Authors: Tanaka Isao , Igashira Ken'ichiro , Kleebe Hans‐Joachim , Rühle Manfred
Published: March 2005

High‐purity Si3N4 (with 2.5 wt% glassy SiO2) doped with F was prepared by immersion of the starting powder into dilute HF and hot isostatic pressing without sintering additives, using a glass encapsulation method. Oxygen content and cation impurity content were almost the same for the F‐doped and undoped materials. However, X‐ray fluorescence analysis revealed the order of 100 ppm of F in the doped material, and a considerable amount of F was detected from the amorphous SiO2 phase at grain‐boundary triple points by analytical transmission electron microscopy. High‐resolution electron microscopy found that an amorphous intergranular film was omnipresent in both of the materials, with an equilibrium thickness of 10 ± 1 å. Subcritical crack‐growth resistance and creep resistance at 1400°C were degraded significantly by the presence of F. Internal friction of doped materials exhibited a dear grain‐boundary relaxation peak, which suggested that F was present in the intergranular film at the two‐grain junctions; this decreased the grain‐boundary viscosity considerably. The film thickness of the doped material showed no apparent chemical effects and was explained by taking into account competing repulsive forces acting normal to the film.
Solution of MgO, CaO, and TiO2 in α‐AI2O3
Authors: Grimes Robin W.
Published: March 2005

Atomistic simulation methods are used to predict the preferred solution mechanisms and their associated energies. Both full‐ and partial‐charge models are discussed. It was found that defect clustering always results in a significant lowering of the solution energies but does not change the preferred solution reaction of any of the oxides. The large size of the Ca2+ ion results not only in a higher solution energy (lower solubility) for CaO compared to MgO but also to a different preferred compensation mechanism. The predicted energy for the cosolution of MgO and TiO2 is dramatically smaller than for either oxide separately. Conversely, whereas solution of TiO2 aids the solution of CaO, additions of CaO do not support TiO2, Solution.
Interband Electronic Structure of α‐Alumina up to 2167 K
Authors: French Roger H. , Jones David J. , Loughin Stephen
Published: March 2005

The electronic structure and interband transitions of α‐Al2O3 have been studied using temperature‐dependent vacuum ultraviolet spectroscopy from 5 to 43 eV, at temperatures ranging from 293 up to 2167 K, which is approaching the melting point of 2327 K. The energy range of the spectra spans the full range of interband electronic transitions. Kramers–Krönig analysis has been employed to recover the phase information, and the interband transition strength (Jcv) of the valence to conduction band transitions. Critical point (CP) analysis of Jcv, a modeling technique based on band structure topology, is then applied to the study of temperature‐induced changes in the interband electronic structure. This approach offers newinsights into the nature of the electronic structure of α‐Al2O3—by allowing us to decompose the interband transitions into subsets associated with states of O 2p nonbonding and Al = O bonding character, and by allowing us to apply partial optical sum rules to these subsets to determine changes in their electron occupancy as a function of temperature. Up to 1700 K the temperature dependence of the electronic structure is linear, corresponding to the linear behavior of the thermal lattice expansion and the vibrational Debye–Waller factors. Below 1700 K the absorption edge shifts at −1.1 meV/K while the exciton and band gap, decomposed through CP modelling, shift at 0.93 and 0.85 meV/K with an exciton binding energy of 0.13 eV. The electron occupancy of the O 2p nonbonding CP set decreases and the occupancy of the Al = O bonding CP set increases. Above 1700 K the temperature dependence of the electronic structure is nonlinear, reflecting the interaction of electrons with phonons in the anharmonic regime, and related to the nonlinearity observed in the vibrational Debye–Waller factors. Also above 1700 K, the O 2p nonbonding and Al = O bonding CP sets merge and this is discussed in the context of temperature‐induced changes in the interatomic bonding.
Development of Textured Microstructures in Ceramics with Large Thermal Expansion Anisotropy
Authors: Paulik Steven W. , Faber K. T. , Fuller Edwin R.
Published: March 2005

Fe2TiO5 exhibits a high degree of anisotropy in both thermal expansion and paramagnetic susceptibility. Anisotropy in paramagnetic susceptibility allows textured microstructures to be produced using magnetically‐assisted grain alignment during sample fabrication. The resulting solid‐state sintered aligned samples had a b‐axis orientation coefficient of 3.33 (vs 6.60 for an aligned powder–epoxy suspension) where an orientation coefficient of 1 represents a randomly‐oriented sample. This texturing reduced the residual stresses generated from the large thermal expansion anisotropy of the control samples, as evidenced by reduced microcracking and morphological texturing of the aligned microstructure.
Structure and Dynamics in Calcium Aluminate Liquids: High‐Temperature 27Al NMR and Raman Spectroscopy
Authors: Poe Brent T. , McMillan Paul F. , Coté Bertrand , Massiot Dominique , Coutures Jean‐Pierre
Published: March 2005

27Al NMR spectra of CaO–Al2O3 liquids at 2500 K have been obtained using a recently developed technique that involves CO2 laser heating and sample levitation inside the NMR magnet. The spectra consist of single, narrow lines (100 to 200 Hz FWHM), indicating that rapid chemical exchange among molecular species occurs in the liquids. Isotropic chemical shifts vary linearly with composition, becoming more shielded with increasing Al2O3content. This is most likely due to an increase in the average nearest‐neighbor coordination of Al, as the proportion of higher coordinate Al species (AlO5 and AlO6) has been observed to increase with alumina content in glasses along this join. This is also in agreement with ion dynamics simulations of liquids along the CaO–Al2O3 join, which show the average Al coordination to range from 4 at low alumina content to 5 for Al2O3liquid. Correlation times for 27Al spin–lattice relaxation estimated from the NMR line widths are in agreement with shear relaxation times determined from experimental viscosity measurements. This may indicate that oxygen exchange between neighboring aluminate polyhedra is a key component in the mechanism for viscous flow. Viscosities determined from oxygen ion diffusion coefficients via ion dynamics simulation agree well with extrapolation of experimental data, in further support of this. We have also obtained high‐temperature Raman spectra of CaAl2O4 and Ca12Al14O33 glasses and liquids up to 1928 K. The liquid spectra contain structure similar to those of glasses, indicating that the aluminate liquids consist of AlOn polyhedral units on the vibrational time scale, rather than simple ionic species.
Improving Stabilized Zirconia with Strontium Gallate
Authors: Feng Man , Goodenough John B.
Published: March 2005

Use of Sr2Ga2o5 as a sintering aid in the synthesis of polycrystalline yttria‐stabilized zirconia yields well‐sintered samples at 1350°C; it also essentially eliminates the grainboundary resistance. The overall oxide‐ion conductivity is improved by about 10% at 800°C at a lower manufacturing cost. However, aging of the bulk electrolyte remains a problem.
Cluster Size Determination in the Chemical Vapor Deposition of Aluminum Nitride
Authors: Egashira Yasuyuki , Kim Hee‐Joon , Komiyama Hiroshi
Published: March 2005

Aluminum nitride was prepared in a laminar‐flow, tubular reactor using an atmospheric pressure chemical vapor deposition (APCVD) method at a reaction temperature ranging from 700° to 1100°C and AlCl3 and NH3 concentrations of 0.4 and 8 mol%, respectively. Films grew on the reactor wall and particles formed in the gas phase. The production rates of films and particles were independently determined. A comprehensive model was constructed to estimate the molecular size of the growth species in the APCVD process to simultaneously form films and particles of AIN from AlCl3, and NH3. Transport equations of a dominant growth species used in growing films on the reactor wall and particles in the gas phase in a laminar‐flow, tubular reactor were formulated and solved. An assumption made in the model was to use the surface reaction rate constant measured for the film surface for the particle surface. Comparing the film and particle growth data measured experimentally with those obtained from model prediction allows us to conclude that the growth species are clusters ranging in size from 0.8 nm at 700°C, equivalent to 8 units of AIN, to 0.5 nm at 1100°C, equivalent to 1 unit of AIN.
Fabrication of Transparent γ‐Al2O3 from Nanosize Particles
Authors: Gallas Marcia R. , Hockey Bernard , Pechenik Alexander , Piermarini Gasper J.
Published: March 2005

The compaction and heat‐treatment behavior of nanosize γ‐Al2O3 powder (average diameter = 20 nm) was studied. A diamond anvil high‐pressure cell was used to compact the powder at pressures up to 3 GPa, both in air at room temperature and under liquid nitrogen, followed by pressureless heat treatment at 800°C. For all conditions studied, the fabricated compacts were optically transparent. X‐ray diffraction confirmed retention of the γ‐phase. The compacts were also characterized before and after heat treatment by microhardness measurements and by transmission electron microscopy. For both ambient and cryogenic compaction, sample hardness increased with pressure, and heat treatment resulted in about a 50% increase in hardness independent of the initial green‐state value. Samples compacted in LN2 were significantly harder (up to 9.6 GPa) than those compacted in air. TEM examination revealed a random‐dense‐packed particle structure and interconnected porosity; interstitial void dimensions, however, were always less than the average particle diameter (20 nm). Observed effects on the increase in hardness could not be explained by microstructural changes normally attributed to increased compaction pressure or heat treatment, most notably densification. Alternative explanations are proposed.
Molecular Orbital Study of an Environmentally Enhanced Crack Growth Process in Silica
Authors: Lindsay Curtis G. , White Grady S. , Freiman Stephen W. , Wong‐Ng Winnie
Published: March 2005

We have used molecular orbital calculations to investigate effects of environmental substances and strain on fracture of the Si─O bond in an H6Si2O7 molecule. We believe that the tendencies observed simulate crack growth in silica in the vicinity of a crack tip. This study is focused on the initial Stage of environmental enhancement, in which a molecule of a substance from the environment approaches a reaction site in silica. Five environmental substances—ammonia, water, formamide, nitrogen, and argon—were considered. The total energy of each H6Si2O7–environmental molecule system was calculated with H6Si2O7 in each of two strain conditions and with the environmental molecule at two different distances from the bridging O in H6Si2O7. This provides estimates of the average force required to move an environmental molecule toward the reaction site in silica. The energy difference due to environmental molecule position is relatively small for ammonia and water, and is relatively large for nitrogen and argon. Experimentally, ammonia and water have shown the greatest tendency to enhance crack growth in silica, whereas nitrogen has shown virtually no such tendency. The tendency for a substance to enhance crack growth therefore appears to be at least partly an inverse function of the energy required to move a molecule of that substance toward the reaction site on the silica surface. Electron population analyses indicate that oxygen atoms adjacent to the reaction site engage in antibonding interactions with certain environmental‐molecule atoms. These interactions are much smaller in magnitude when H6Si2O7 is strained than when it is unstrained. It therefore appears possible that in a crack in silica, where an environmental molecule would experience restricted mobility, strain reduces steric hindrances to the approach of environmental molecules to the reaction site. Straining H6Si2O7 also increases the magnitudes of the charges on Si and O at the reaction site, probably leading to increased electrostatic attractions of environmental molecules and H6Si2O7.
Quantitative Powder X‐ray Diffractometry Phase Analysis of Silicon Nitride Materials by a Multiline, Mean‐Normalized‐Intensity Method
Authors: Li Deyu Y. , O'Connor Brian H. , Chen Qitao T. , Zadnik Marjan G.
Published: March 2005

A general purpose multiline, mean‐normalized‐intensity (MNI) method, derived from a procedure proposed in the literature, was applied to puase‐composition analysis of powders containing α‐ and β‐silicon nitride and small amounts of free silicon. Results obtained using peak and integrated intensities to derive the MNI values for the phases were compared with values determined by Rietveld pattern fitting according to error assessments based on the MNI standard deviation estimates calculated by assuming that the MNI data for each phase follow Gaussian statistics, and Rietveld‐derived standard deviations. The MNI results for the integrated intensities agreed reasonably with the Rietveld determinations and were discernibly superior to results obtained with peak intensities. The study demonstrated the power of the MNI method as a general tool for materials analysis.
Simulation of the Viscous Sintering of Coated Particles
Authors: Jagota Anand
Published: March 2005

Problems associated with the sintering of mixtures of hard and soft particles can be obviated by coating the hard particles (e.g., alumina) with a soft phase (e.g., glass). An analysis of the sintering kinetics of such materials based on finite‐element simulations of the sintering of a pair of rigid spheres coated with a viscous material is presented. Until the contact radius is greater than the thickness of the coating, the sintering kinetics are very similar to those obtained if the rigid core is not present. The sintering rate decreases as the rigid cores approach each other and is limited by flow in the gap between the core particles. If the coating thickness is in excess of 20%, the simulations predict that a packing of such particles sinters to full density at a rate comparable to that of particles without a rigid core.
Calcium Concentration Dependence of the Intergranular Film Thickness in Silicon Nitride
Authors: Tanaka Isao , Kleebe Hans‐Joachim , Cinibulk Michael K. , Bruley John , Clarke David R. , Ruhle Manfred
Published: March 2005

High‐resolution electron microscopy and nano‐beam analytical electron microscopy have been used to characterize both the intergranular silicate film thickness and its local composition in a series of high‐purity Si3N4 ceramics doped with 0–450 at. ppm Ca. Calcium was detected at both two‐grain junctions and triple junctions, even in the 80‐ppm‐Ca‐doped specimen. The thickness of the intergranular film at two‐grain junctions was found to depend sensitively on Ca content. In undoped material, the thickness was 1.0 ± 0.1 nm. With increasing Ca content, the thickness decreased in the dilute region (80 ppm Ca), but then increased. The variation in film thickness can be qualitatively understood in terms of the balance of three long‐range forces acting normal to the film, namely the van der Waals dispersion force, a structural “steric” force, and an electrical‐double‐layer force. By comparing the measured thicknesses to those predicted, estimates for the structural correlation length and the inverse Debye length can be made. These estimates have values of ∼ 0.22 nm and approximately 0.3–0.5 nm, respectively, for the calcia‐free and 80 ppm calcia materials.
Crack‐Growth Resistance of in Situ‐Toughened Silicon Nitride
Authors: Choi Sung R. , Salem Jonathan A.
Published: March 2005

The fracture toughness of a commercial, hot‐pressed, in situ‐toughened silicon nitride with an elongated grain structure is determined by four different testing methods. The fracture toughness is found to be 5.76 ± 0.27, 8.48 ± 0.50, 10.16 ± 0.66, and 10.68 ± 0.39 Mpa.m1/2, respectively, by indentation crack size measurement, indentation strength, single‐edge‐precracked‐beam, and chevron‐notched‐beam methods. The discrepancy in fracture toughness between the testing methods is related to R‐curve behavior, as measured using the indentation strength technique. These results indicate that there is no unique fracture toughness value and that a fracture toughness testing method with appropriate qualifiers is needed for rising R‐curve materials. Therefore, care should be taken in interpreting and utilizing fracture toughness values evaluated from different testing methods if a material exhibits a rising R‐curve. Complete characterization of the R‐curve may be a prerequisite.
A Catalytic Process for Mullite Whiskers
Authors: Moyer John R. , Hughes Neal N.
Published: March 2005

Mixtures of alumina and silica react with SiF4 above 600°C to form fluorotopaz. Pyrolysis of fluorotopaz gives a stoichiometric yield of interlocked whiskers of mullite and SiF4, which is recovered for reuse. The diameter of whiskers (aspect ratio ∼15) can be controlled from a maximum of ∼100 μm to less than 1 μm.
Glass‐Ceramic Coatings for Titanium Aluminides
Authors: Skowronski Raymund P.
Published: March 2005

Four glass‐ceramic coatings have been successfully developed to function as both hydrogen barriers and oxidation protection on super α‐2 titanium aluminide. The coefficients of thermal expansion (88 × 10–7/°C to 117 × 10–7/°C) of these coatings provide a good match with that of the alloy, and the coatings show excellent adherence in thermal cycling to 982°C. In addition, the four coatings have measured emittances from 0.67 to 0.80 at this temperature. Finally, the coatings display the desired low hydrogen and oxygen permeation characteristics.
Vincristine, doxorubicin and dexamethasone (VAD) administered as rapid intravenous infusion for first‐line treatment in untreated multiple myeloma
Authors: Segeren C. M. , Sonneveld P. , Van Der Holt B. , Baars J. W. , Biesma D. H. , Cornellissen J. J. , Croockewit A. J. , Dekker A. W. , Fibbe W. E. , Löwenberg B. , Van Marwijk Kooy M. , Van Oers M. H. J. , Richel D. J. , Schouten H. C. , Vellenga E. , Verhoef G. E. G. , Wijermans P. W. , Wittebol S. , Lokhorst H. M.
Published: March 2005

We examined the feasibility of achieving a rapid response in patients with previously untreated multiple myeloma by administering vincristine 0.4 mg and doxorubicin 9 mg/m2 as a rapid intravenous infusion for 4 d together with intermittent high‐dose dexamethasone 40 mg (VAD) for remission induction treatment in patients who were scheduled to receive high‐dose therapy. 139 patients (86 male, 53 female; median age 53 years, range 32–65 years; Durie & Salmon stage IIA: 42, IIB: one, IIIA: 89, IIIB: seven) were included in a prospective multicentre study in which VAD was administered as remission induction treatment and was followed by intensified treatment. The response was evaluated according to the criteria of the Eastern Cooperative Oncology Group (ECOG). The results of treatment were evaluable in 134 patients. Five patients died before evaluation. 86 patients (62%) achieved a partial response (PR) and seven patients (5%) achieved a complete response (CR), which equates to a response rate of 67%. The main side‐effect was mild neurotoxicity, which was observed in 18% of the patients. Fever or infections were reported in 27% of the patients. VAD administered as an outpatient regimen, based on rapid intravenous infusion, is an effective induction regimen for untreated myeloma with a 67% response rate and acceptable toxicity.
The RET receptor tyrosine kinase, but not its specific ligand, GDNF, is preferentially expressed by acute leukaemias of monocytic phenotype and is up‐regulated upon differentiation
Authors: Gattei Valter , Degan Massimo , Rossi Francesca Maria , De Iuliis Angela , Mazzocco Francesca Tassan , Cesa Emiliana , Aldinucci Donatella , Zagonel Vittorina , Pinto Antonio
Published: March 2005

The RET gene product represents the signal‐transducing molecule of a surface receptor complex for the glial cell line‐derived neurotrophic factor (GDNF), which includes GDNFR‐α as a ligand‐binding component. By a semi‐quantitative competitive RT‐PCR approach, we have analysed the relative abundances of RET transcripts in blasts purified from 40 acute myeloid leukaemia (AML) cases, revealing significant amounts of RET transcripts in 60% of AML cases (24/40). RT‐PCR data was confirmed by immunocytochemical detection of RET protein in leukaemic blasts. The highest RET mRNA levels, almost exclusively confined to FAB M4/M5 AMLs, directly correlated with the presence on leukaemic cells of adhesion molecules and surface structures typically expressed by blasts of monocytic lineage and were inversely associated with the expression of the stem cell antigen CD34. Consistently, differentiation of the monoblastic cell line U937 resulted in an up‐regulated expression of RET proto‐oncogene, which was maximal upon exposure to agents inducing a more complete monocytic differentiation. Finally, while transcripts specific for GDNF and GDNFR‐α were never found in leukaemic blasts, stromal cells of the haemopoietic microenvironment expressed, in the absence of RET, significant amounts of both GDNF and GDNFR‐α. Our results suggest a role for RET in the functional regulation of AMLs through interactions with GDNF‐ and GDNFR‐α‐producing stromal cells.
Expansion and differentiation of haemopoietic progenitor cells on endothelialized hydroxyapatite under static conditions
Authors: Conrad Véronique , Dupouy Maryse , Bordenave Laurence , Lacombe Francis , Baquey Charles , Reiffers Josy , Ripoche Jean
Published: March 2005

We have analysed the potential of an endothelialized hydroxyapatite matrix (HAP), a synthetic bone substitute, as a cellularized support for the expansion of haemopoietic progenitor cells. Scanning electron microscopy (SEM) showed that the endothelial cells (EC) tended to form a monolayer fitting closely to the matrix, and that the progenitors adhered to the EC layer. Endothelialized HAP supported the proliferation and differentiation of the progenitors with the addition of the exogenous cytokines IL‐1, and IL‐3. The expanded cell population essentially belonged to the myeloid and monocytic lineages, with a smaller percentage of the megakaryocyte lineage. In comparative experiments CD34+ progenitors were expanded on endothelialized tissue culture flasks, and a significant higher viability of the expanded cells was found with the endothelialized HAP. A high percentage (approx. 40%) of mature granulocytes was generated in accordance with the presence of differentiating cytokines such as G‐CSF and GM‐CSF at high concentrations in the coculture medium. Other cytokines that could be detected were IL‐6, M‐CSF, SCF, flt3‐ligand. More than 50% of the expanded cell population was able to phagocytose bacteria and to generate an oxydative burst. These data indicate that cellularized HAP may be a useful matrix for stromal cell‐based expansion systems.