bluuebunny/crossref_metadata_2025 huggingface dataset:
Preparation Conditions and Morphology of Superconducting Fine Particles in the Bi‐Ca‐Sr‐Cu‐O System Prepared by Spray Pyrolysis
Authors: Tohge Noboru , Tatsumisago Masahiro , Minami Tsutomu , Adachi Motoaki , Kousaka Yasuo , Okuyama Kikuo
Published: July 2005

The morphology and crystalline phases of superconducting fine particles with a composition of Bi2Ca1Sr2Cu2Ox were studied in terms of preparation conditions, using an aerosol flow reactor with varying temperature profiles: constant, increasing, and humped temperature distributions. The temperature profile in the reactor was found to affect greatly the morphology of the superconducting particles produced. The humped distribution with maximum temperatures over 900°C provided solid particles consisting mainly of the 80 K phase, when other preparation conditions were optimized. This finding indicates the possibility of controlling the morphology, as well as the crystalline phases, of superconducting particles by spray pyrolysis.
Journal. Effects of Composition Changes on the Crystallization Behavior of MgO‐CaO‐SiO2‐P2O5 Glass‐Ceramics
Authors: Shyu Jiin‐Jyh , Wu Jenn‐Ming
Published: July 2005

The effects of composition changes on the crystallization behavior of apatite‐containing glass‐ceramics in the system MgO‐CaO–SiO2–P2O5 were studied. The eutectic composition of 40 wt% 3CaO‐P2O5–60 wt% CaO MgO 2SiO2 was selected as the base glass. Several parameters were quantitatively or qualitatively derived from thermal analysis, X‐ray diffraction, and microstructural observations. These parameters can be divided into two groups according to their variation with glass composition. The parameters in the first group depend mainly on the apatite nucleation rate, which increases with an increase in CaO or PiO5, and with a decrease in MgO or SiO2. The parameters in the second group are closely related to the extent of deviation of the glass composition from the eutectic. The classical theory for nucleation employed to explain the observed phenomena is discussed.
Preparation of Dispersed Phase Ceramic Boron Nitride and Aluminum Nitride Composite Coatings by Chemical Vapor Deposition
Authors: Lee Woo Y. , Lackey W. J. , Freeman Garth B. , Agrawal Pradeep K. , Twait D. J.
Published: July 2005

Dispersed phase ceramic composite coatings containing BN and AIN were prepared by chemical vapor deposition. The BN + AIN coatings were deposited on Al2O3 from the BCI3–AICI3‐NH3 reagent system in the temperature range of 700° to 1200°C. Also, single‐phase BN and AIN coatings were prepared for comparison purposes. The composite coatings consisted of very small BN and AIN regions which were either crystalline or amorphous, depending on deposition temperature and reagent concentrations. For example, a composite containing AlN whiskers of less than 100‐nm diameter in a matrix of turbostratic BN of 2‐nm grain size was deposited at 1100°C and 20 kPa.
Phase Equilibria in the Systems CaO–CuO and CaO‐Bi2O3
Authors: Roth Robert S. , Hwang Nong M. , Rawn Claudia J. , Burton Benjamin P. , Ritter Joseph J.
Published: July 2005

New data are presented on the phase equilibria of the binary systems CaO‐CuO and CaO‐Bi2O3. Corrected compositions are reported for Ca.Bi6O13 and Ca2Bi2O5 and a new metastable high‐temperature phase is reported for a composition near Ca6Bi7O16.5. The composition and decomposition temperatures for Ca1–x.CuO2 are given for both air and 1 atm of oxygen at 755 ± 5° and 835 ± 5°C, respectively.
Reaction of YBa2Cu3O7‐δ Powder with NOx Gas in an Aerosol Reactor
Authors: Hitchcock David C. , Rusin Richard P. , Lynn Johnson D.
Published: July 2005

Thermodynamic calculations predict, and experiments verify, that YBa2Cu3O7‐8 (123) powder is unstable in the presence of NOx‐containing aerosol reactor exhaust gases at temperatures below about 600°C. Powders collected above the stability temperature are single‐phase 123, while powders collected at lower temperature contain Ba(NO3)2 formed by reaction of the powder with NOx, after exit from the hot zone.
Effect of Forming Pressure on the Internal Structure of Alumina Green Bodies Examined with Immersion Liquid Technique
Authors: Uematsu Keizo , Miyashita Masayori , Kim Jin‐Young , Kato Zenji , Uchida Nozomu
Published: July 2005

Green bodies prepared by compaction of alumina granules were made transparent by an immersion liquid technique, and the internal structure was characterized with an optical microscope to study the effect of forming pressure on the internal structure. Clear images obtained by the technique provide more detailed information than other existing methods for structures ranging from one to tens of micrometers. Intergranular pores were present between unfractured granules. Their sizes and concentration tended to decrease with increasing forming pressure. However, pores were clearly present even in the green body prepared at 600 MPa. A rod‐ and needlelike feature was also found and was concluded to correspond to a high‐density region. The significance of large pores and high‐density regions on processing as well as the details of the technique is discussed.
Journal Effect of a Liquid Phase on the Sintering of Heterogeneous YBa2Cu3O6+x Compacts
Authors: Stearns Laura C. , Harmer Martin P. , Chan Helen M.
Published: July 2005

Dense, polycrystalline YBa2Cu3O6+x inclusions were incorporated into YBa2Cu3O6+x: powder in order to investigate the effect of nondensifying inclusions on the sintering behavior of the matrix. The presence of these inclusions caused a significant reduction in the densification rate of the matrix, as well as some microstructural damage. However, when approximately 2.5 vol% of a liquid phase was present during sintering, there was some retardation of densification in the early stages, but this disappeared with time. Also, the final sintered microstructures were damage‐free and essentially identical to those of samples containing no inclusions. Possible roles for the liquid phase in correcting this microstructural damage are briefly discussed.
Journal. Pseudoelastic Behavior in Ce‐TZP Al2O3 Ceramics
Authors: Sun Qingping , Si Wenjie , Huang Yong , Jiang ZuoZhao
Published: July 2005

The pseudoelastic behaviour of 12 mol% Ce–TZP + 10 wt% Al2O3 ceramics in the loading–unloading cycles was found for the first time at room temperature, and corresponding reversible tm martensitic transformation mechanism was clearly identified the possibility of reversible ferroelastic domain switching at room temperature was also discussed.
Interface Structure and Bond Strength of Copper‐Bonded Alumina Substrates
Authors: Yoshino Yuichi , Ohtsu Hidehiko
Published: July 2005

Copper‐bonded alumina substrates with different interface structures were studied to elucidate their effect on the bond strength and the resistance to hydrogen embrittlement and thermal cracking. The substrates were made by bonding copper either directly to alumina using Cu‐O eutectic reaction or indirectly with an interlayer of cuprous aluminate between the metal and the ceramic. The substrate with the aluminate interlayer shows somewhat lower bond strength, still adequate for its use, than the directly bonded substrate. However, the substrate with the aluminate layer has greater resistance to hydrogen embrittlement and thermal cracking. The cause of such improvement is ascribed to the porosity of the aluminate layer and the compressive stress induced in alumina.
Effects of Organic Dispersants on the Dispersion, Packing, and Sintering of Alumina
Authors: Sumita Shigekazu , Rhine Wendell E. , Bowen H. Kent
Published: July 2005

The effects of water‐soluble polymers and benzoic acid derivatives on green and sintered Al203 compacts were studied for two types of alumina powder. The percent of theoretical density achieved by each Al203 sediment was dependent primarily on the concentration of water‐soluble polymeric dispersant rather than on the pH. Aromatic acids, such as 4‐hydroxy‐ and 4‐aminobenzoic acid, were also effective dispersants. The final density and grain size of sintered compacts depended on the green microstructure of the compacts and on differences in the concentration of trace elements in the two powders.
Combustion Synthesis of Si3N4–SiC Composite Powders
Authors: Zeng Jianren , Miyamoto Yoshinari , Yamada Osamu
Published: July 2005

Fine Si3N4‐SiC composite powders were synthesized in various SiC compositions to 46 vol% by nitriding combustion of silicon and carbon. The powders were composed of α‐Si3N4, β‐Si3N4, and β‐SiC. The reaction analysis suggested that the SiC formation is assisted by the high reaction heat of Si nitridation. The sintered bodies consisted of uniformly dispersed grains of β‐Si3N4, β‐SiC, and a few Si2N2O.
Centrifugal Consolidation of Al2O3 and AI2O3/ZrO2 Composite Slurries vs Interparticle Potentials: Particle Packing and Mass Segregation
Authors: Chang Jeanne C. , Velamakanni Bhaskar V. , Lange Fred F. , Pearson Dale S.
Published: July 2005

Dispersed ceramic slurries with high concentrations of indifferent electrolyte have been shown to effectively eliminate mass segregation effects in composite materials. Furthermore, high packing efficiencies have been achieved with these systems. It has been suggested that the addition of high concentrations of indifferent electrolytes to an otherwise dispersed ceramic slurry modifies the interaction potential so that the short‐range adhesive attraction is diminished by additional repulsive forces. This lower attractive force is still high enough to cause coagulation which raises the viscosity, but small enough to allow easy particle rearrangement during filtration or centrifugation. This rearrangement leads to high packing densities. The effectiveness of this behavior on the improvement of ceramic powder processing of composites is demonstrated with Al2O3 and ZrO2.
Effect of Ionic Substitution on the Thermal Expansion of ZrTiO4
Authors: Bayer Gerhard , Hofmann Martin , Gauckler Ludwig J.
Published: July 2005

New oxide compounds with α‐PbO2 structure have been synthesized by solid‐state reactions. These are derived from ZrTiO4 and HfTiO4 by a different kind of ionic substitution. The thermal expansion behavior of these phases was investigated by means of a dilatometer and an X‐ray heating diffractometer. These measurements revealed rather low expansion for some of the Zr(Me3+/Me5+)O4, solid solutions. This behavior is attributed to their high expansion anisotropy, which leads to extended formation of microcracks.
Activity–Composition Relations in the Nickel Oxide–Magnesium Oxide System at 1300 K by the Solid‐State Galvanic Cell Technique
Authors: Kale Girish M.
Published: July 2005

The activity of NiO in NiO‐MgO rock salt solid solution has been measured at 1300 K by employing a solid‐state galvanic cell: Pt,Ni+ NiO||(CaO)ZrO2||Ni + (Nix,Mgl‐x)O, Pt. A high‐density tube of Zr02‐15 mol% CaO has been used as the solid electrolyte for the emf measurements. The activities of the component oxides in the rock salt solid solution exhibit negative deviation from ideality at the temperature of investigation. The solid solution obeys regular solution behavior at 1300 K. The value of the regular solution parameter is found to be ‐12000 ((l000) J mol‐1. The composition dependence of ΔGEx obtained in this study agrees reasonably well with the calorimetric data reported in the literature for NiO‐MgO solid solution.
Microstructural Effects on the Thermal Conductivity of Polycrystalline Aluminum Nitride
Authors: Enloe Jack H. , Rice Roy W. , Lau John W. , Kumar R. , Lee S.Y.
Published: July 2005

Polycrystalline AIN bodies were made with a range of porosities from various AIN powders by sintering or hot‐pressing. Thermal conductivity data for material produced without sintering aids showed a gradual, yet definite, porosity dependence with scatter similar to other property‐porosity studies. The thermal conductivity‐porosity data for ALN with sintering aids showed the existence of two distinct regions: (1) a higher‐porosity region (greater than approximately 2%) which was similar to the data for material without sintering aids, and (2) a low‐porosity region where grain boundaries were seen to dominate thermal conductivity. Auger spectroscopy was used to investigate fracture surfaces for dense CaO‐doped materials. Thermal conductivity was observed to correlate to effective grain‐boundary thickness, which was calculated from quantitative analysis of the Auger data. A model consisting of cubic grains in a continuous grain‐boundary phase accurately describes these data.
Synthesis and Characterization of β’‐SiAlON Ceramics from Organosilicon Polymers
Authors: Soraru Gian Domenico , Ravagni Alberto , Campostrini Renzo , Babonneau Florence
Published: July 2005

A polycarbosilane has been modified with aluminum alkoxide to obtain a new preceramic compound. The pyrolysis in NH3 flow of this polyaluminocarbosilane leads to the formation of an amorphous Si‐Al‐O‐N phase. The nitridation process has been followed by IR and 29Si MAS‐NMR spectroscopies. A fine‐grained β‐SiAION ceramic is obtained by firing the amorphous phase at 1500°C. The crystallization process has been studied by XRD, 29Si MAS‐NMR, and TEM techniques.
Tribological Behavior of SiC‐Whisker/Al2O3 Composites against Carburized 8620 Steel in Lubricated Sliding
Authors: Liu Haiyan , Fine Morris E. , Cheng Herbert S.
Published: July 2005

Mineral oil lubricated sliding tests of Sic‐whisker (SiCw,)/A1203 composites and monolithic alumina against carburized 8620 steel were conducted on a cylinder‐on‐cylinder machine. The wear rate of the composites was one or two orders of magnitude less than that of pure alumina. Hot‐pressed 25 wt% SiCw,/A1203 composite had a lower wear rate than sintered and HIPed 7.5 wt% SiC/Al2O3 composite under the same conditions. The weight loss of the steel mating ring against the 25 wt% SiCw, composite was a factor of four lower than against the 7.5 wt% SiCw, composite, but the former was a factor of 50 to 60 less than that against pure alumina. The composites showed lower friction coefficients than alumina during the run‐in stage. The friction coefficients decreased with initial wear. The steady‐state friction coefficient decreased with increasing load up to 500 N for hot‐pressed 25 wt% SiC,/Al203 composite. Further, SEM observation showed much less microfracture in composites than in alumina. EDAX analysis revealed less Fe transfer from the steel ring to the composites than to pure alumina. Wear by microfracture and by adhesion in composites was suggested to be suppressed by SIC whiskers. This in turn reduced wear of the steel because of the generation of fewer hard particles.
Durability of High‐level Waste Glass in Groundwater
Authors: Kamizono Hiroshi
Published: July 2005

This paper reviews the leaching behavior of simulated high‐level‐waste glass in Japanese groundwater both on an in situ burial site and in our laboratory. During in situ burial leach tests, the glass is immersed in groundwater for up to 1 year and 7 months, retrieved, and analyzed. A leach rate obtained from the in situ burial tests is compared with other leach data under different conditions. Two factors, i.e., flow rate and composition of the groundwater, are extensively studied in the laboratory to supplement the in situ burial data. Effects of γ irradiation on the groundwater chemistry are also examined. Based on the results, mechanisms observed with the leaching of the glass in groundwater are discussed.
Development of High Thermal Conductivity Aluminum Nitride Ceramic
Authors: Lee Ran‐Rong
Published: July 2005

AIN ceramics with densities varying from 3.18 to 3.30 g/cm3 and room‐temperature thermal conductivities varying from 88 to 193 W/m K were produced. Different sintering conditions, packing powders, AIN powder sources, carbon additive, and sintering times were evaluated, and the key processing parameters which cause the differences in density and thermal conductivity were identified. SEM, TEM, and EDS were used to characterize the correlation between thermal conductivity, microstructure, and processing parameters. The important parameters which control the thermal conductivity of AIN ceramics are discussed.
Reaction of Uranium Hexafluoride Gas with Alumina and Zirconia at Elevated Temperatures
Authors: Wang Simon C. P. , Anghaie Samim , Collins Clayton
Published: July 2005

Alumina and zirconia are considered for potential use in uranium hexafluoride (UF6) based nuclear gaseous‐core reactors. The corrosion reactions of these oxide ceramics in high‐temperature UF6 environment were investigated. Chemical thermodynamic analysis of the reactions was performed by using a computer data base and code package, FACT, to identify stoichiometric products. An alumina reaction tube in a flowing loop test unit was used to expose alumina and calcia‐stabilized zirconia samples to UF, at temperatures from 873 to 1473 K and pressures of about 20.0 to 20.7 k Pa. Chemical reaction rates were measured by a discontinuous gravimetric method. X‐ray diffraction and EDS analyses and SEM microstructural examination identified corrosion products and the morphology of the exposed surfaces. Results indicate that reactions were not inhibited or slowed down for either oxide. At 1273 K and below, alumina samples formed stable AIF3 scales and showed acceptable compatibility with UF6. The rate of UF6 reaction with alumina and weight loss dramatically increased at 1473 K. Zirconia samples failed to resist degradation and reacted rapidly with UF6 at 1073 K. The maximum service temperatures for alumina and zirconia in UF6 environment do not seem to exceed 1273 and 973 K, respectively.
Deformation of Alumina/Titanium Carbide Composite at Elevated Temperatures
Authors: Nagano Takayuki , Kato Hidezumi , Wakai Fumihiro
Published: July 2005

The deformation behavior of an Al2O3/30 wt% TIC composite in uniaxial tension was evaluated under vacuum over the temperature range of 1300° to 1550°C. The Al203/TiC composite exhibited the maximum elongation of 66% at an initial strain rate of 1.19 X l0‐4 s‐1 at 1550°C. The stress exponent calculated from peak stresses of true stress‐true strain curves at 1500OC was 3.8, which was in good agreement with that obtained by changing the crosshead speed during the tension test. The apparent activation energy at 20 MPa was 853 kJ/mol. In addition the deformation of the Al2O3/TiC composite in uniaxial tension at elevated temperature was accompanied by cavitation.
Preparation of Monodisperse, Spherical Alumina Powders from Alkoxides
Authors: Ogihara Takashi , Nakajima Hidenori , Yanagawa Teruaki , Ogata Nobuo , Yoshida Kokichi , Matsushita Noritaka
Published: July 2005

Monodisperse, spherical alumina powders were prepared by the controlled hydrolysis of aluminum alkoxide in a dilute solution consisting of octanoi and acetonitrile. The reagent concentration influenced the particle size, size distribution, morphology, and state of agglomeration. The addition of acetonitrile and octanol affected both particle shape and the state of agglomeration and prevented gelation during hydrolysis. Sub‐micrometer‐sized alumina particles grew to 10 μm with increased concentration of hydroxypropylcellulose dispersant. As‐prepared amorphous powders crystal‐lized to γ‐alumina at 1000°C and converted to α‐alumina at 1150°C without intermediate phases. The particle morphology was retained after crystallization to γ‐alumina.
Nucleation and Concurrent Anomalous Grain Growth of α‐Al2O3 During γ ‐ α Phase Transformation
Authors: Chou Ting C. , Nieh Tai G.
Published: July 2005

Nanocrystalline Al203 thin films (50 nm in thickness) have been synthesized by rf reactive sputtering deposition and subjected to annealing at temperatures ranging from 800° to 1200°C. TEM analysis indicated that the as‐deposited alumina films contained both amorphous phase and metastable γ phase. Structural texture evolved in the films annealed at 800°C for 24 h; the texture had a [00l] preferred orientation and occurred along the {400} and {440} planes of γ Al203, . In the films annealed a t 1200°C for 2h, nucleation and concurrent anomalous grain growth of α‐Al203took place in a fine‐grained, polycrystalline γ‐Al203 matrix. The anomalously grown γ‐AL2O3 grains were primarily [0001]‐oriented single crystals with grain sizes varying from 3 to 15 pm, while the γ‐Al2O3 matrix had an average grain size of 50 nm. The γ‐Al2O3 matrix was also strongly textured along the [001] axis and exhibited a heavily faulted, layered micro‐structure. Most of these layers were oriented along the {220} crystallographic planes. Periodic superstructure was identified in the layered γ‐ Al2O3. The formation of layered structure in γ‐ Al2O3 is attributable to the change of stacking sequence of atomic layers along the {220} orientations. An atomic model is presented to explain the formation of layered structure in γ‐ Al2O3. The nucleation of α‐ Al2O3 appears to occur along the {220} crystallographic planes of γ‐ Al2O3. The explosive grain growth of α‐ Al2O3 during the γαphase transformation is explained by a mechanism involving interface boundary migration and lattice epitaxy. The orientation relationships between γ‐ and α‐ Al2O3 are determined.
Elevated‐Temperature Toughening Mechanisms in a SiCw/Al2O3 Composite
Authors: White Kenneth W. , Guazzone Laurent
Published: July 2005

Crack growth resistance studies of a Sic‐whisker‐reinforced Al2O3‐matrix composite have been correlated with the composite microstructure to determine the active fracture toughening mechanism, at each of three test temperatures through 1400°C. Evidence of cumulative toughening at all temperatures, as reported in the literature, was validated by R‐curves; however, isolation of the following wake zone effects from that of the frontal process zone elicits a departure from published assumptions. A frontal zone mechanism, presumably microcrack toughening, dominates at room temperature, while a following wake zone mechanism of crack face whisker‐bridging controls at temperatures near 1200°C.
Elemental Concentration Profiles in an Oxidized Silicon Nitride Material
Authors: Falk Lena K. L. , Urban EngstrÖm E.
Published: July 2005

Secondary ion mass spectrometry (SIMS) has been used to characterize elemental concentration profiles which build up within and below the oxide scale on a Si3N4 material during oxidation. By in‐depth profiling it was shown that the oxide scale had a high concentration of cations originating from the intergranular regions of the material. The subscalar region contained a zone depleted in these elements, and the width of this zone was dependent upon the particular element. Prolonged oxidation at elevated temperatures appeared to level out the initially formed concentration profiles.
Noise Sensitivity of Fit Procedures for Weibull Parameter Extraction
Authors: Dortmans Leonardus J. M.G. , de With Gysbertus
Published: July 2005

The noise sensitivity of three fit methods frequently applied to determine the parameters of a Weibull distribution has been analyzed. Using the estimator P = (i ‐ 0.5)/N and a linear least‐squares fit procedure with no weight function, the least biased results are obtained, although the amount of bias strongly depends upon the Weibull modulus mand the amount of noise. From the results it can be concluded that the larger the value of the Weibull modulus m, the smaller the amount of noise should be (<1%, e.g.) to avoid systematic large underestimation of m. Therefore increasing experimental accuracy is required, to be able to discriminate the effects of material improvement (higher Weibull modulus).
Prediction of Glass Formation Regions by Calculation of Eutectics Using the Ideal‐Solution Model
Authors: Yong Ding , Zhonghong Jiang
Published: July 2005

A thermodynamic estimation method using the ideal‐solution model has been used for calculating the eutectic regions in some oxide‐, halide‐, and metal‐glass formation systems. The calculated results are compared with the glass formation regions. It is shown that most calculated eutectic areas lie in the glass formation regions. Thus, the glass‐ forming compositions can be predicted by using our method of calculating the eutectic regions.
Electron Paramagnetic Resonance Spectroscopic Determination of Ti3+ in Several Titanium Phosphate Compounds
Authors: Abraham Marvin M. , Bamberger Carlos E.
Published: July 2005

Electron paramagnetic resonance (EPR) spectroscopy was used to test the presence of Ti3+ in several novel compounds also containing Ti4+. The results obtained confirmed the presence of Ti3+, and indicated that differences in the EPR spectral lines of Ti3+ can make differentiation easier between compounds which have X‐ray diffraction (XRD) patterns that are not markedly different.
In Situ Growth of Superconducting Yba2Cu3O7‐xThin Films
Authors: Haung Chorng‐Jye , Chang Chih‐Yu , Chen Mao‐Chieh , Tseng Tseung‐Yuen
Published: July 2005

Using single‐target on‐axis sputter deposition, Y Ba2Cu3O7‐x films, with flatness oriented in the c axis and a zero‐resistance temperature (Tco) of 89 K, were prepared by an in situ growth technique. This work examines the effect of the growth temperature on the properties of in situ films. The experimental results show that high‐quality YBa2Cu3O7‐x films can be obtained by controlling the substrate temperature in a range from 680oto 690oC. In addition, a new parallel‐circuit model is proposed and a simulation of the resistance versus temperature curve is presented.
Mössbauer Study of the Influence of Fe‐Si‐N Liquid in the Synthesis of β‐Si3N4 from Silica
Authors: Sanyal Amiya S. , Mukerji Joydeb , Bandyopadhyay Siddhartha
Published: July 2005

Mössbauer spectra of the products obtained by carbothermal reduction and distribution of silica in the presence of iron in the temperatures range 1200o to 1540o were studied. The preponderance of β‐Si3N4 over the α form at a higher reaction temperature were assumed to be related to the formation of an Fe‐Si‐N liquid. The liquid did not alter its composition with the variation of reduction‐temprature, Iron had no effect on the reaction mechanism below 1300oC.
Crystal Structures of Two Orthorhombic Zirconias
Authors: Howard Christopher J. , Kisi Erich H. , Ohtaka Osamu
Published: July 2005

The crystal structures of orthorhombic zirconias formed by cooling magnesia‐partially‐stabilized zirconia (Mg‐PSZ) (space group Pbc21) and by quenching zirconia powder from 600°C and 6 GPa (space group Pbca) are compared and contrasted. It is demonstrated that the two structures are easily distinguished by the neutron powder diffraction techniques used to establish them. The occurrence of two distinct phases is hence proved. Structural relationships between these two phases and also with the in situ high‐pressure structure proposed from X‐ray diffraction (XRD) are discussed. The three structures are virtually indistinguishable by XRD and so the structure of the high‐pressure form “in situ” is considered to remain unknown.
Temperature Dependence of the Raman Spectrum in Lithium Oxide Single Crystal
Authors: Lshii Yoshinobu , Nagasaki Takanori , Igawa Naoki , Watanabe Hitoshi , Ohno Hideo
Published: July 2005

Temperature dependence of the Raman spectrum of lithium oxide single crystal has been measured over a temperature range of 80 to 1073 K. The frequency shift and the line width of the Raman spectrum in lithium oxide were about 531 and 4.5 cm‐1 at 80 K, respectively. At 1073 K, the frequency shift and the line width attained the values of 464 and 112 cm‐1, respectively. The strong temperature dependence of the frequency shift and line width was compared with data from some crystals with a fluorite structure.
SiAION Ceramics
Authors: Ekström Thommy , Nygren Mats
Published: July 2005

The phase relations in and physical properties of SiAlON ceramics prepared by the hot isostatic pressing technique or by pressureless sintering with a sintering aid are reviewed. The sintering aid used is an AIN and Al2O3 mixture either pure or in combination with Y2O3 and/or various rare‐earth oxides. Special attention is paid to the amount and type of phase(s) formed and to how properties such as hardness (HV10), fracture toughness (KIC), and oxidation resistance vary with the sintering aid used for different types of SiAlON materials, i.e., O'‐, almost monophasic α‐, pure β‐, and mixed (α+β)‐SiAION Ceramics.
Spectroscopic Analysis of the Structure and Properties of Alkali Tellurite Glasses
Authors: Heo Jong , Lam David , Sigel George H. , Mendoza Edgar A. , Hensley David A.
Published: July 2005

Structural development of tellurite glasses with the addition of Li2O and Na2O has been studied using infrared, Raman, and X‐ray photoelectron spectroscopies. The increase in intensity of the peak at 755 cm−1 in the infrared spectra as compared to the peak at 620 cm −1 suggests the transformation of TeO4 building units to TeO3 pyramids with the addition of alkali oxide. Proposed structural change is further supported by the strong compositional dependence of the 755‐cm−1 peak in the Raman spectra as well as by the formation of a shoulder in the O 1s peak of X‐ray photoelectron spectra. In contrast to alkali silicate glasses, formation of nonbridging oxygens with the addition of alkali oxide is not observed.
Metallurgical Route to High‐Tc Superconducting Ceramics
Authors: Luo Jian Shu , Michel Daniel , Chevalier Jean‐Pierre
Published: July 2005

We have prepared various high‐Tc superconductors, of the LnBa2Cu3O7‐x (Ln = Y, Eu, Yb) and Bi‐Sr‐Ca‐Cu‐O families, by oxidation of rapidly quenched precursor alloys. In this metallurgical approach, appropriate metallic constituents are first combined into homogeneous alloys by rapid solidification processing. Subsequent oxidation of the as‐obtained precursors leads to formation of the desired superconducting phases. For EuBa2Cu3O7‐x, a notable increase in critical current density is observed, and we attribute this to both the uniform grain size and a more homogeneous composition. In the case of bismuth compounds, the Bi4Sr3Ca3Cu4O16+x (4334) and Bi2Sr2Ca2Cu3O10+x (2223) phases obtained have properties similar to those of their ceramic‐processed counterparts, and there is evidence for accelerated kinetics for the 2223 phase formation. We have also studied effects of additions and substitutions in the Bi‐Sr‐Ca‐Cu‐O system prepared by this method, where passage through the liquid state can ensure good chemical homogeneity for multicomponent alloys. By this means, the substitution limit of bismuth by lead in the 2223 phase is estimated to be about 30 at.%, and there is evidence that lead substitution both accelerates the formation of the 2223 phase and sharpens the superconducting transition. Finally, silver addition to Bi4Sr3Ca3Cu4 alloy leads to the production of flexible metallic ribbons, which, after oxidation, form Ag/4334 microcomposites. These superconducting ribbons remain relatively ductile because of the formation of a layered microstructure in which superconducting regions alternate with silver bands aligned along the ribbon direction.
Reformulation of an Aqueous Alumina Slip Based on Modification of Particle‐Size Distribution and Particle Packing
Authors: Smith Peter A. , Haber Richard A.
Published: July 2005

Six alumina casting slips with particle‐size distributions varying from 44 to 0.1 μm were examined. Particle packing was calculated using the approach of Andreasen. Viscosity, green density, and pore‐size distribution were measured. It was found that contouring the intermediate size distribution for particles finer than 15 μm provided the most desirable viscosity for slips composed of wide size distributions. For slips containing 50 vol% solids, the lowest viscosity obtained was 196 × 10−3 N · s/m2 (with a two‐component size distribution), and a green density of 2.52 g/cm3 (65% of theoretical) was achieved with a ternary system. These casts had bimodal pore‐size distributions centered around approximately 1 and 0.1μm.
Conduction Mechanism of Single‐Crystal Alumina
Authors: Will Fritz G. , DeLorenzi Horst G. , Janora Kevin H.
Published: July 2005

The electrical conductivity of high‐purity single‐crystal alumina is determined in a temperature range from 400° to 1300°C. By applying an advanced fully guarded threeterminal measurement technique, reliable conductivity measurements are performed to as low as 10−17Ω−1· cm−1. Gas and surface conduction are measured separately and shown to be negligible. High‐purity sapphire exhibits a conductivity of 10−16Ω−1· cm−1 at 400°C, two characteristic activation energies of 0.4 and 4.8 eV with increasing temperature, and a conductivity of 3 × 10−8Ω−1· cm−1 at 1300°C. The fraction of the current carried by ions is determined by electron probe analysis of the electrodes following a 640‐h transference test at 1200°C with 4 kV/cm field applied. Only 0.3% of the current at 1200°C is carried by ions. A mathematical model of electrical conduction in sapphire is developed which describes sapphire as a wide‐bandgap semiconductor, doped with one dominant donor and one dominant acceptor. The observed conductivity is well described by the model over the entire temperature range from 400° to 1300°C.
Crack‐Shape Effects for Indentation Fracture Toughness Measurements
Authors: Smith Stanley M. , Scattergood Ronald O.
Published: July 2005

Various methods to measure fracture toughness using in‐dentation precracks were compared using soda‐lime glass as a test material. In situ measurements of crack size as a function of applied stress allow both the toughness Kc and the residual‐stress factor χ to be independently determined. Analysis of the data showed that stress intensity factors based on classical half‐penny crack shapes overestimate toughness values and produce an apparent R‐curve effect. This is due to a constraint on crack shape imposed by primary lateral cracks in soda—lime glass. Models based on elliptical cracks were developed to account for the crack‐shape effects.
Distribution of Matrix Cracks in a Uniaxial Ceramic Composite
Authors: Cho Chongdu , Holmes John W. , Barber James R.
Published: July 2005

Conventional shear‐lag analyses of matrix cracking and debonding in uniaxial composites loaded in tension predict that the matrix stress varies only very slowly with position except near existing cracks. It therefore follows that the location of subsequent cracks is very sensitive to minor local variations in matrix strength, leading to significant statistical variation in crack spacing. This question is investigated using a discrete random process model of a composite and by direct experimental measurements of crack spacing. In the limit of a completely homogeneous composite, it is shown that the crack spacing distribution tends to an inverse square distribution between the theoretical maximum spacing and half that value. The random process model recovers this behavior in the limit and exhibits an approximately Weibull distribution of crack spacings when the matrix strength has significant variance. The theoretical predictions are compared with experimental results obtained for a unidirectional ceramic‐matrix composite (SiC fibers in a calcium aluminosilicate matrix). The experimental results exhibit features similar to those predicted by the model and are compatible with a matrix strength whose standard deviation is of the order of 40% of the mean strength. An important point is that, with this magnitude of strength variation, the material exhibits a significant size effect and it is essential to take this into account in estimating the mean crack spacing from the corresponding mean matrix properties.
Microstructure and Mechanical Properties of Hot‐Pressed Silicon Carbide‐Aluminum Nitride Compositions
Authors: Xu Youren , Zangvil Avigdor , Landon Martine , Thevenot François
Published: July 2005

A flexural strength of up to 1 GPa was achieved in SiC‐AIN materials and is attributed to a dense, equiaxial grain structure of the 2H(δ) SiC‐AIN solid solution, with a relatively uniform grain size of ∼ 1 μm. The strength was found to decrease with increasing grain size. While the β→α phase transformation and the formation of various metastable polytypes make microstructural control difficult in SiC materials, excellent control is facilitated in SiC‐AIN materials as a result of the stable 2H solid solution. Several mechanisms of grain refinement during the β→ 2H transition were observed, most notably the direct formation of several 2H grains from a single β grain. In addition, grain growth is limited by the diffusion‐controlled nature of the transition. These mechanisms could be utilized to achieve even higher strength values, with potentially higher reliability of the materials in structural applications.
Role of Interfacial Carbon layer in the Thermal Diffusivity/Conductivity of Silicon Carbide Fiber‐Reinforced Reaction‐Bonded Silicon Nitride Matrix Composites
Authors: Bhatt Hemanshu , Donaldson Kimberly Y. , Hasselman D. P. II. , Bhatt Ramakrishna T.
Published: July 2005

The role of an interfacial carbon coating in the heat conduction behavior of a uniaxial silicon carbide nitride was investigated. For such a composite without an interfacial carbon coating the values for the thermal conductivity transverse to the fiber direction agreed very well with the values calculated from composite theory using experimental data parallel to the fiber direction, regardless of the ambient atmosphere. However, for a composite made with carbon‐coated fibers the experimental values for the thermal conductivity transverse to the fiber direction under vacuum at room temperature were about a factor of 2 lower than those calculated from composite theory assuming perfect interfacial thermal contact. This discrepancy was attributed to the formation of an interfacial gap, resulting from the thermal expansion mismatch between the fibers and the matrix in combination with the low adhesive strength of the carbon coating. In nitrogen or helium the thermal conductivity was found to be higher because of the contribution of gaseous conduction across the interfacial gap. On switching from vacuum to nitrogen a transient effect in the thermal diffusivity was observed, attributed to the diffusion‐limited entry of the gas phase into the interfacial gap. These effects decreased with increasing temperature, due to gap closure, to be virtually absent at 1000°C.
Microwave Sintering of Solid Oxide Fuel Cell Materials: I, Zirconia‐8 mol% Yttria
Authors: Janney Mark A. , Calhoun Clyde L. , Kimrey Hal D.
Published: July 2005

The successful microwave sintering of zirconia demonstrates the necessity to understand both the materials and electromagnetic field aspects of microwave processing. It was difficult to produce crack‐free parts in the multimode microwave furnace employed in this investigation. Nonuniformities in the microwave field, and dielectric properties that increased rapidly with temperature, produced “hot spot” in the parts, which led to differential sintering and subsequent cracking. To produce crack‐free sintered parts, an indirect heating method was developed that eliminated the severe differential heating. Using this indirect heating method, it was demonstrated that the sintering temperature of zirconia could be lowered from 1375° to 1200°C by microwave processing and that the resulting grain size was finer.
Effect of Temperature on the Formation of Creep Substructure in Sodium Chloride Single Crystals
Authors: Raj Sai V. , Pharr George M.
Published: July 2005

The effect of temperature on the formation of creep substructure in sodium chloride single crystals was studied in the temperature range 573 to 873 K. Microstructural observations conducted on polished specimens deformed under a constant value of normalized stress, σ/G∼ 4 × 10−4, where σ is the applied stress and G is the shear modulus, showed different types of substructural features such as a high density of dislocation etch pits, cells, and subgrains. Detailed measurements of the sizes of the cells and subgrains revealed that the cell size was essentially independent of temperature while the subgrain size increased only by about a factor of 2 for a 300 K increase in temperature. Although the cell and subgrain sizes were not significantly dependent on temperature in comparison to the effect of stress, there was a qualitative change in the substructure morphology with a variation in temperature; i.e., the cells and subgrains were better defined at higher temperatures. The volume fraction of the cell boundaries decreased with increasing temperature, thereby indicating a refinement of the microstructure at the higher temperatures. These observations suggest that while temperature does not change the final dimensions of the substructure significantly, it appears to influence the kinetics of substructure formation by influencing the recovery rate. As a result, the stresses acting on the cell boundaries increase considerably with increasing temperature to values several times the applied stress.
Highly Reactive β‐Dicalcium Silicate: I, Hydration Behavior at Room Temperature
Authors: Ishida Hideki , Sasaki Kaori , Mitsuda Takeshi
Published: July 2005

The hydration behavior at 25°C of β‐dicalcium silicate synthesized from hillebrandite (Ca2,(SiO3)(OH)2) at 600°C was studied over a period of 224 d. The hydration rate of the β‐dicalcium silicate having fibrous crystals with specific surface area of 7 m2/g is extremely rapid. For water/solids ratios of 0.5 and 1.0, the hydration reaction is completed in 28 and 14 d, respectively. The hydrate contains almost no Ca(OH)2, and its Ca/Si ratio is close to 2. SEM observations indicate that the hydrate forms an outer shell on the surface of β‐dicalcium silicate and grows inwards. The silicate anion structure is considered to consist of dimers and single‐chain structures from 29Si MAS NMR. Variations of physical properties of press‐formed bodies have also been discussed.
Highly Reactive β‐Dicalcium Silicate: II, Hydration Behavior at 25°C Followed by 29Si Nuclear Magnetic Resonance
Authors: Ishida Hideki , Okada Yoshihiko , Mitsuda Takeshi
Published: July 2005

The hydration behavior at 25°C of highly reactive β‐dicalcium silicate synthesized from hillebrandite (Ca2(SiO3)(OH)2) was studied over a period of 7 to 224 d using 29Si magic‐angle spinning nuclear magnetic resonance (MAS NMR). The hydration product, C‐S‐H, contains Q2 and Q1 silicate tetrahedra, the chemical shifts of which are independent of the water/solid (w/s) ratio and curing time. Until the reaction is completed, the amounts of Q1 and Q2 formed are independent of the w/s ratio, being determined only by the degree of reaction. The ratio Q2/Q1 increases as the reaction progresses and as the curing time becomes longer. From the values of Q2/Q1, it appears that the hydrate is a mixture of dimers and short single‐chain polymers. The Ca/Si ratio of the hydrate is high, taking values close to 2.0, but the Ca/Si ratio does not influence the Q2/Q1 ratio. It was also found that the NMR peak intensities allow quantitative assessment similar to XRD.
Effect of Sodium Chloride Solutions on the Strength and Fatigue of Bare Silica Fibers
Authors: Inniss Daryl , Brownlow Darryl L. , Kurkjian Charles R.
Published: July 2005

The strength of bare silica fiber in sodium chloride solutions decreases as the NaCl concentration increases. Static fatigue measurements in deionized water (pH 6) are compared to those in a 2 mM solution of NaCl (pH 5.2), both at 90°C. The pretransition stress corrosion parameter, determined from the power law, is 33 in deionized water and 18 in the NaCl soution. The effect of BaCl on the reaction mechanism in the pretransition region is investigated. The failure rate is proportional to the surface charge of silica raised to the second power.
Oxygen Fugacity Control in Nonflowing Atmospheres: I, Experimental Observations in CO/CO2 and O2/N2 Mixtures
Authors: Marques Fernando M. B. , Wirtz Gerald P.
Published: July 2005

The performance of a stabilized zirconia sensor and electrochemical oxygen pump combination in the isothermal control of oxygen fugacity in a nonflowing atmosphere was studied in a closed furnace system in the temperature range of 800° to 1100°C. Under certain conditions, large differences in oxygen pressure were found between sensors at the same constant temperature in close proximity to each other. This result reflected the existence of a stable steplike oxygen fugacity “front” in the furnace, separating regions which differed by several orders of magnitude in oxygen fugacity. This oxygen pressure profile in the furnace resulted from the steady‐state transport of oxygen from oxygen leakage sources to the pump. The existence, magnitude, and position of the oxygen fugacity front were found to depend on the gas‐phase composition, the relative locations of the leakage sources and the pump, the oxygen fugacity of the reference electrode, and the magnitude of the oxygen flux in the gas phase.
Limits of the Thermodynamic Stability of Cobalt—Iron—Manganese Mixed Oxides at 1200°C
Authors: Subramanian Ramesh , Dieckmann Rüdiger
Published: July 2005

The thermodynamic stability of spinel and rock‐salt structure phases has been investigated for the quasi‐ternary mixed oxide system Co‐Fe‐Mn‐O at 1200°C and at total pressures of the order of 1 atm (∼1.01 × 105 Pa) using thermogravimetric and electrical conductivity measurements. The results reveal the stability limits of the spinel and rock‐salt structure phases with varying cationic composition and oxygen partial pressure at 1200°C. The oxygen partial pressure was varied over 12 orders of magnitude, from log10ao2= 0 to log10ao2= ‐12, by using CO/CO2 and N2/O2 gas mixtures and monitored by an electrochemical, stabilized zirconia‐based EMF cell. The maximum cobalt mole fraction used in the investigation was about 0.33.
Aging Effects on Curium‐Doped Titanate Ceramic Containing Sodium‐Bearing High‐Level Nuclear Waste
Authors: Mitamura Hisayoshi , Matsumoto Seiichiro , Hart Kaye P. , Miyazaki Takashi , Vance Eric R. , Tamura Yukito , Togashi Yoshihiro , White Timothy J.
Published: July 2005

Curium‐doped titanate ceramic containing sodium‐rich high‐level nuclear waste showed a gradual decrease in density up to a dose of 8.5 × 1017α decays ·g−1. After that, the rate of density change increased apparently because of crack formation. Optical microscopy showed cracks >0.1 mm long and > 1 μm wide after a dose of 7.9 × 1017α decays ·g−1. Leach tests suggested that the dissolution‐control phases for sodium and cesium changed from freudenbergite and hollandite, respectively, to intergranular phases after significant cracking. Aging also enhanced strontium losses, relative to calcium, indicating that strontium may also be partitioned to the intergranular phases. After the fresh surfaces produced by cracking were exposed to leachant, and the dissolution of soluble intergranular surfaces was complete, the leaching of nonradioactive elements from the samples having a dose of 12.3 × 1017α decays ·g−1 was limited by the following dissolution‐control phases: freudenbergite (Na), hollandite (Cs and Ba), perovskite and/or zirconolite (Sr and Ca), and alloys (Mo). The leaching behavior of the nonradioactive indicator elements revealed that chemical durability was reduced by two main factors: (1) increasing the effective surface area by crack formation and (2) decreasing the stability of the actinide‐host phases by α‐recoil damage. In combination these factors increased longer‐term (>7 days) leach rates of sodium and cesium, and strontium and calcium by 1 and 2 orders of magnitude, respectively. In spite of deterioration of the actinide‐host phases, the curium leach rate after a dose of 12.3 × 1017α decays x g−1 decreased by 2 orders of magnitude, possibly as a result of precipitation of curium hydrolysis products.