bluuebunny/crossref_metadata_2025 huggingface dataset:
Density Measurements of Glasses in the Series xNa2S + (1 −x)B2S3
Authors: Martin Steve W. , Polewik Tamara
Published: March 2005

Measurements of the densities of glasses in the series xNa2S + (1 −x)B2S3 are reported for the first time. As has been found in the corresponding oxyborate series xNa2O + (1 −x)B2O3, the addition of Na2S to B2S3 causes the density to increase, from 1.80 g/mL for pure B2S3 to 1.99 g/mL at the limit of the low‐alkali sulfide glass‐forming range of x= 0.25. These data provide evidence for the formation of tetrahedral boron units (BS4−) as alkali is added. Volumes for the trigonal BS3 and tetrahedral BS4− groups of 57.55 and 51.79 Å3, respectively, were determined. As has also been found in the oxyborates, the tetrahedral boron group occupies a smaller volume than the trigonal boron group and causes the increase in density with added Na2S.
Grain Growth Kinetics in Liquid‐Phase‐Sintered Zinc Oxide–Barium Oxide Ceramics
Authors: Yang Sung‐Chul , German Randall M.
Published: March 2005

Grain growth of ZnO in the presence of a liquid phase of the ZnO–BaO system has been studied for temperatures from 1300° to 1400°C. The specimens were treated in boiling water and the grains were separated by dissolving the matrix phase in an ultrasonic bath. As a consequence three‐dimensional grain size measurements were possible. Microstructural examination shows some grain coalescence with a wide range of neck size ratios and corresponding dihedral angles, however, most grains are isolated. Lognormal grain size distributions show similar shapes, indicating that the growth mechanism is invariant over this time and temperature. All regressions between Gn and time for n= 2 and 3 proved statistically significant. The rate constants calculated with the growth exponent set to n= 3 are on the same order of magnitude as in metallic systems. The apparent activation energy for growth is estimated between 355 and 458 kJ/mol.
Tribological Characteristics of α‐Alumina at Elevated Temperatures
Authors: Dong X. , Jahanmir Said , Hsu Stephen M.
Published: March 2005

The tribological characteristics of a high‐purity α‐alumina sliding on a similar material under unlubricated conditions are divided into four distinct regimes. At low temperatures, T < 200°C, tribochemical reactions between the alumina surface and water vapor in the environment control the tribological performance. The coefficient of friction in this temperature range is approximately 0.40 and the wear coefficient is less than 10−6, independent of contact load. At intermediate temperatures, 200°C < T < 800°C, the wear behavior depends on the contact load. At low loads, wear occurs by plastic flow and plowing; the coefficient of friction is approximately 0.60 and the wear coefficient is less than 10−6. At loads larger than a threshold value, severe wear occurs by intergranular fracture. The coefficient of friction increases to 0.85 and the wear coefficient increases to a value greater than 10−4. At temperatures above 800°C, formation of a silicon‐rich layer on the wear track by diffusion and viscous flow of the grain‐boundary phase reduces the coefficient of friction to 0.40, and the wear coefficient is reduced to a value less than 10−6. The results of the wear tests and observations of the fundamental mechanisms controlling the tribological behavior of this material are consolidated in a simple wear transition diagram.
Preparation and Crystallization of Sol‐Gel Calcia–Alumina Compositions
Authors: Goktas A. Aydin , Weinberg Michael C.
Published: March 2005

The preparation of several amorphous calcium aluminate compositions by the sol‐gel procedure is reported. Although a broad composition range of amorphous gels could be prepared, they invariably crystallized when heated to sufficiently high temperatures. The crystallization behavior of bulk samples and thin gel films on SiO2 slides were studied with the aid of XRD. Also, IR spectra were obtained from room‐temperature and heated gels in order to evaluate the transformation which the gels underwent upon heating.
Mechanism for the Radiolytically Induced Decomposition of Soda–Silicate Glasses
Authors: Howitt David G. , Chan Hing W. , DeNatale Jeffrey F. , Heuer James P.
Published: March 2005

A mechanism is proposed for the radiolysis which occurs in soda‐silicate glasses when they are irradiated. The mechanism is consistent with the observations of the reaction products which are produced and the rates at which the decomposition proceeds.
Sol–Gel Kinetics Followed by Cylindrical Attenuated Total Reflectance Infrared Spectroscopy
Authors: Kline Andrew A. , Mullins Michael E. , Cornilsen Bahne C.
Published: March 2005

This paper describes a unique solution infrared technique, a cylindrical attenuated total reflectance cell, to monitor in situ kinetics of the sol‐gel process, especially at short times after mixing. The sol‐gel kinetics of acidic ethanol : TEOS : Al(III) solutions have been followed as a function of temperature and aluminum concentration. The hydrolysis rate and the condensation rate increase with temperature and Al/Si ratio. The Al(III) hydrolysis and concomitant increase in acidity increase the reaction rate. By controlling the initial pH, it is seen that a higher Al(III) concentration itself increases the reaction rate. The properties of a sol‐gel glass depend upon the kinetics, which are controlled by the processing conditions, including cation content.
Model of Transformation Toughening in Brittle Materials
Authors: Chen I‐Wei
Published: March 2005

Assuming that the energy dissipation decreases inversely with distance from the crack tip, the increase in steady‐state toughness of a transformation‐toughened ceramic is estimated to be δJ= (δJ0/ω) In (1 +ω), where (i) δJ0 denotes the toughness increment which would be expected for a given zone height h0 assuming full transformation throughout the zone, and (ii) ω is a nondimensional parameter giving the ratio of the inelastic transformation strain (for full transformation) to the initial elastic strain at the onset of transformation. This estimate extends the earlier result of McMeeking and Evans (1982) in two significant respects: (i) the transformation strain may include a shear component, instead of being purely dilatational, and (ii) the range of ω is now unrestricted, whereas the McMeeking and Evans approach strictly applies only in the weak transformation limit, ω« 1. The height of the inner zone hi within which transformation has proceeded to completion (or saturation) is estimated to be hi=h0/(1 +ω). Experimental data of Mg‐PSZ and Ce‐TZP can be quantitatively accounted for using this approximate model, which is also in very good agreement with the rigorous finite‐element results of Budiansky, Hutchinson, and Lambropoulos in the special case of subcritical dilatational transformation.
Boron Nitride Coatings on Oxide Substrates: Role of Surface Modifications
Authors: Borek Theodore T. , Qiu Xiaomei , Rayfuse Leann M. , Datye Abhaya K. , Paine Robert T. , Allard Lawrence F.
Published: March 2005

Physical mixtures of a BN polymeric precursor with oxides such as MgO, Al2O3, and TiO2 have been found to yield crystalline, tightly adherent coatings of hexagonal BN on the oxide surface, after appropriate heat treatments. In every instance, the BN (0001) basal planes are parallel to the oxide surface. Generally, the coating conforms very well to the contours of the oxide surface. However, an exception was the silica surface where no coatings were observed. It appears that the surface silanols condense to form siloxanes at high temperatures, yielding a surface that is unreactive and unable to bind to the BN. Modification of the silica surface by incorporation of a monolayer of titania dramatically alters the ability of the silica to stabilize BN coatings. It was found that stable BN coatings could be obtained when the silica surfaces were thus modified.
Effect of Alkali Hydroxides on the Strength and Fatigue of Fused Silica Optical Fiber
Authors: Matthewson M. John , Rondinella Vincenzo V. , Lin Bochein , Keyes Scott W.
Published: March 2005

A two‐point bend technique is used to determine the strength of “pristine” bare fused silica optical fiber in aqueous solutions of the group I alkali metal hydroxides (Li through Cs) in the concentration range 10−4N to 1N (pH range 10 to 14). In the highest concentration solutions, a strong cation effect is exhibited with a minimum strength for KOH while fibers in LiOH and CsOH are typically 20% and 10% stronger, respectively. The cation effect decreases with decreasing concentration until at 10−4N no effect is apparent. Tetramethylammonium hydroxide gives intermediate strengths between CsOH and LiOH. The results correlate closely with published results for the dissolution rate of silica which exhibit a maximum rate for KOH. In contrast, the results do not correlated with published subcritical crack growth data which show no cation effect for Na through Cs. These results support the pit etching model for pristine fiber strength proposed by Kurkjian et al. and argue against the presence of cracks or cracklike objects in these materials.
Thermopower of YBa2Cu3O7‐δ–Ag Composites
Authors: Muralidharan Pottayil Uma Devi , Paulose Kannai V. , Koshy Jacob , Damodaran Alathoor D.
Published: March 2005

The percolation behavior of normal‐state thermopower, resistivity, and superconductivity have been studied in YBa2Cu3O7‐δ─Ag (YBCO─Ag) composite systems. The normal‐state resistivity and thermopower show a percolation threshold at a Ag volume fraction (VAg) of 20% to 30%, whereas the superconducting network shows a threshold at a VAg of ≅70% to 80%. The results obtained from this study show that the YBCO─Ag composite obtained from Ag2O and YBCO powders is uniformly distributed with Ag and YBCO remaining as separate phases without changing their characteristics. The measurements of thermopower indicate that the normal‐state thermopower and phonon‐drag thermopower are affected by the Ag addition. The stability of YBCO is increased when it is in composite form.
Degradation of Multilayer Ceramic Capacitors with Nickel Electrodes
Authors: Sumita Shigekazu , Ikeda Masaaki , Nakano Yukie , Nishiyama Kousuke , Nomura Takeshi
Published: March 2005

The mechanism of degradation, or IR drop, of BaTiO3‐based Ni‐electrode chip capacitors has been studied, with special attention to the microstructure. Degradation occurred mainly at the center of the capacitors. Longer‐life capacitors were obtained under conditions of low oxygen partial pressure, 10−12 atm, during sintering, and had larger grain sizes and smaller quantities of grain boundary phase. The existence of oxygen vacancies in the grain boundary phase was confirmed by cathode luminescence measurement. Double layers along the surfaces of the Ni electrodes were also related to the life of the capacitors.
Microstructural Design of Toughened Ceramics
Authors: Becher Paul F.
Published: March 2005

The fracture toughness of ceramics can be improved by the incorporation of a variety of discontinuous, elastic reinforcing phases that generate a crack‐bridging zone. Recent models of toughening by crack‐bridging processes are discussed and used to describe the behavior observed in whisker‐reinforced ceramics. The toughening response in ceramics reinforced with other types of discontinuous reinforcements is then considered (e.g., matrix and second‐phase platelike grains, elongated matrix grains, and grain‐size effects in noncubic matrices). It is shown that crack‐bridging toughening processes can be combined with other bridging mechanisms and with other toughening mechanisms (e.g., transformation toughening) to achieve synergistic effects. From these discussions, it is shown that the design of the toughened materials relies heavily on the control of the material properties and microstructural components influencing the toughening behavior to optimize the contributions of both the reinforcing phase and the matrix.
Reliability Analysis of Structural Ceramics Subjected to Biaxial Flexure
Authors: Chao Luen‐Yuan , Shetty Dinesh K.
Published: March 2005

Sintered alumina and silicon nitride were tested in uniaxial (four‐point and three‐point bend) and biaxial (uniformpressure‐on‐disk) flexure tests in inert conditions. Fracture origins were identified to be surface flaws in alumina and subsurface pores in silicon nitride. Batdorf's statistical fracture theory and two different fracture criteria, the critical normal stress criterion and a noncoplanar strain energy release rate criterion, were used to examine size and stress‐state effects on fracture strengths of the two ceramics. Size effects assessed in four‐point and three‐point bend tests were in good agreement with the theoretical predictions for both ceramics. Measured biaxial strengths of alumina were in good agreement with the prediction when a noncoplanar strain energy release rate criterion and random surface flaw orientations were assumed. On the other hand, biaxial fracture strength of the silicon nitride was consistent with a prediction based on preferred flaw orientation (i.e., normal to the principal stress in the disks) and the normal stress fracture criterion. Orientation distributions of the fracture planes assessed from the fracture patterns of the disks supported the assumptions of random flaw orientations (alumina) and the preferred flaw orientations (silicon nitride), respectively, for the two ceramics. The preferred flaw orientation in silicon nitride is suggested to originate at subsurface pores as a result of crack nucleation in the plane of maximum tensile stress concentration, i.e., a diametral plane normal to the maximum principal stress.
Synthesis and Preparation of Lanthanum Aluminate Target for Radio‐Frequency Magnetron Sputtering
Authors: Sung Gun Yong , Kang Kwang Yong , Park Sin‐Chong
Published: March 2005

A polycrystalline LaAlO3 target for the radio‐frequency (rf) magnetron sputterings of LaAlO3 thin films has been prepared. These films serve as a buffer layer for high‐Tc YBa2Cu3O7–x superconducting thin films on Si. Synthesis of lanthanum aluminate powder from a mixture of La2O3 and Al2O3 powders was performed by calcining from 1000° to 1600°C in air. Characterization of the calcined powders by X‐ray diffraction indicates that full development of LaAlO3 phase was evident in the sample calcined for 3 h at 1600°C in air. A polycrystalline LaAlO3 target was prepared by heat treatment at 1500°C for 2 h in air after pressureless sintering at 1750°C for 3 h in Ar. Thin films of the LaAlO3 on Si (100) were obtained by rf magnetron sputtering using the target and oxygen‐annealing the as‐deposited films.
Phase Relations in the System Al2O3–B2O3–Nd2O3
Authors: Ji Yangyang , Liang Jingkui , Chen Zhan , Xie Sishen
Published: March 2005

The phase relations at a temperature below “subsolidus” in the system Al2O3–B2O3–Nd2O3 are reported. Specimens were prepared from various compositions of Al2O3, B2O3, and Nd2O3 of purity 99.5%, 99.99%, and 99.9%, respectively, and fired at 1100°C. There are six binary compounds and one ternary compound in this system. The ternary compound, NdAl3(BO3)4 (NAB), has a phase transition at 950°C ± 15°C. The high‐temperature form of NAB has a second harmonic generation (SHG) efficiency of KH2PO4 (KDP) of the order of magnitude of the form which has been used as a good self‐activated laser material, and the low‐temperature form of NAB has no SHG efficiency.
Processing and Characterization of Thin Films of the One‐Layer Phase in the Bi‐Sr‐Ca‐Cu‐O System: Ca Solubility
Authors: Golden Steve J. , Lange Fred F. , Vaidya Kaushik J. , Bloomer Tamara E.
Published: March 2005

Thin films in the Bi‐Sr‐Ca‐Cu‐O system have been synthesized from liquid ethyl hexanoate precursors by spin pyrolysis. The extension of the ternary one‐layer phase field into the quaternary system has been determined through the replacement of Sr by Ca in single‐phase, c‐axis oriented thin films. A significant Ca solubility in the one‐layer phase was found, the maximum being around 0.4 per 1 Cu. All onelayer compositions were excess in Bi and deficient in (Sr + Ca) relative to the ideal composition and showed over all cation deficiency. The c lattice parameter and solidus temperature were found to vary systematically with composition. The interpretation of the Ca solubility results in terms of Ca doping of the cation‐deficient “Sr”sites and implications regarding the high‐Tc Cu‐layer phases in the system are discussed.
Plasma Etching of α‐Sialon Ceramics
Authors: Mitomo Mamoru , Sato Yoh‐ichiro , Ayuzawa Nobuo , Yashima Isamu
Published: March 2005

Plasma etching of β‐Si3N4, α‐sialon/β‐Si3N4 and α‐sialon ceramics were performed with hydrogen glow plasma at 600°C for 10 h. The preferential etching of β‐Si3N4 grains was observed. The etching rate of α‐sialon grains and of the grain‐boundary glassy phase was distinctly lower than that of β‐Si3N4 grains. The size, shape, and distribution of β‐Si3N4 grains in the α‐sialon/β‐Si3N4 composite ceramics were revealed by the present method.
Preparation of Li2B4O7 Films with Preferential Orientation by Sol–Gel Method
Authors: Yamashita Hiroya , Yoko Toshinobu , Sakka Sumio
Published: March 2005

Li2B4O7 films, a promising material for surface acoustic wave devices, were prepared by the sol—gel method using metal alkoxide precursors as starting materials. The Li2B4O7 films on silicon (100) and (111) single crystals prepared from a coating solution to which acetic or hydrochloric acid was added were highly oriented along the (122) plane, whereas those without acid additive were randomly oriented. The results were interpreted based on the basic sol‐gel chemistry and the lattice matching between the film and substrate.
Contribution of t→m Phase Transformation to the Toughening of ZTA
Authors: Karihaloo Bhushan L.
Published: March 2005

The toughness increment resulting from the stress‐induced dilatational component of the t→m transformation is calculated for a zirconia‐toughened‐alumina (ZTA) composition containing a high proportion of tetragonal zirconia precipitates and is shown to agree very well with the experimental value. The good agreement is made possible by allowing for the mismatch in the elastic constants between the zirconia particles and alumina matrix, and for the observed variation in the size of the transformable tetragonal particles with the height of the transformation zone. The actual variation is estimated from known experimental data.
Humidity Effect on the High‐Tc (Pb,Bi)SrCaCuO Superconductor
Authors: Chen Ying‐Chung , Chong Kwok‐Keung , Meen Teen‐Hang , Wu Long , Houng Mau‐Phon
Published: March 2005

The effect of humidity on the bismuth superconductor is investigated under 90% humidity at 30°C for 250 h. Nearly none of the peaks of high‐Tc phase (2223) can be observed in the X‐ray pattern after the test. The silver contact resistance of the sample also increases prominently in the time interval from 60 h to 100 h. When the humidity‐tested sample is heated again under sintering conditions (845°C for 50 h in air), the high‐Tc phase appears again.
Synthesis of Fine‐Grained Polycrystalline Diamond Compact and Its Microstructure
Authors: Akaishi Minoru , Ohsawa Toshikazu , Yamaoka Shinobu
Published: March 2005

Sintering of a fine‐grained polycrystalline diamond compact with grains less than 1 μm in size was successfully carried out by making a laminate on a WC/Co powder compact under sintering conditions of 5.8 GPa and 1430° to 1480°C for 30 min, in which small amounts of poly(ethylene glycol) and fine powder of cubic boron nitride were added to the starting diamond powder. The former played the role of preventing agglomeration of the diamond powder and the latter of suppressing abnormal grain growth during sintering. Microstructural observation of the polycrystalline diamond showed that in the regions near the WC/Co layer a comparatively large amount of Co metal was present between diamond grains, but in other regions the amount of Co decreased, and the diamond grains were seen to be bonded strongly. The Vickers hardness of the polycrystalline diamond was 55 ± 5 GPa with 19.6 N load.
Formation of Lead Niobates in Molten Salt Systems
Authors: Li Chen C. , Chiu Chien C. , Desu Seshu B.
Published: March 2005

The formation mechanisms, phase stability, impurity incorporation, and morphological characteristics of lead niobates obtained by molten salt synthesis were studied by X‐ray diffraction analysis, scanning electron microscopy, and energy dispersive analysis. Results indicate that PbO is the fastdissolving component of the constituent oxides and that the formation of lead niobates initiates at the surface of Nb2O5 powders. Reaction rates were faster in molten salts when compared to those of solid‐state synthesis. Significant morphological differences were observed between the powders prepared by both solid‐state and molten salt synthesis. At low PbO/Nb2O5 molar ratios, reaction between starting powders and molten salts resulted in the formation of NaNbO3, along with potassium incorporation into lead niobates. Orthorhombic PbNb2O6, monoclinic Pb2Nb2O7, and fcc Pb3Nb3O8 phases were stabilized using molten salt synthesis, while only rhombohedral PbNb2O6 and Pb2Nb2O7, and tetragonal Pb3Nb2O8, were obtained by solid‐state synthesis. Molten salt compositions containing PbO/Nb2O5 ratios of 2 and 3 resulted in the stabilization of phases different from those obtained using solid‐state synthesis. For a PbO/Nb2O5 ratio equal to 3, Pb5Nb4O13 observed in solidstate synthesis was not found in the products of molten salt synthesis.
Influence of the Fracture Criterion on the Failure Prediction of Ceramics Loaded in Biaxial Flexure
Authors: Thiemeier Thomas , Brückner‐Foit Angelika , Kölker Helmut
Published: March 2005

The failure probability of ceramic components in multiaxial stress states can be predicted from the results of uniaxial tests, if a suitable fracture criterion for multiaxial loading is known. In the paper it is investigated how the selected failure criterion influences the predicted distribution of the fracture stress of a component. Several acceptable failure criteria are found by comparing the results of four‐point‐bend tests performed with aluminum nitride with the results of concentric ring‐on‐ring tests.
Hydrogen Dissolution in and Release from Nonmetals: III, Tetragonal Zirconia
Authors: Park Kwangheon , Olander Donald R.
Published: March 2005

The solubility and release kinetics of hydrogen in single‐crystal zirconia were investigated by the infusion–extraction method. Equilibration in hydrogen at pressures between 1.4 and 11 atm (0.14 and 1.1 MPa) and at temperatures from 1300° to 1600°C produced H/Zr ratios varying from 4 × 10−5 to 1.3 × 10−4. Dissolution was exothermic with an enthalpy of solution of 6.6 kcal/mol (28 kJ/mol). The solubility increased with the extent of substoichiometry of the oxide caused by exposure to hydrogen. The solubility behavior and the kinetics of release indicated that hydrogen in the solid forms defect clusters consisting of a hydrogen atom, two trivalent cations, and a doubly charged oxygen vacancy. The trivalent ions were either impurities or reduced zirconium ions. Rate constants for first‐order detrapping were determined. Diffusion was shown not to be a rate‐limiting process in hydrogen release.
Interfacial Sliding Friction in Silicon Carbide–Borosilicate Glass Composites: A Comparison of Pullout and Pushout Tests
Authors: Bright Jeffrey D. , Danchaivijit Sawai , Shetty Dinesh K.
Published: March 2005

Interfacial sliding friction stress (τf) was assessed using both pushout and pullout tests on SiC‐borosilicate glass composite specimens. Single‐filament composite specimens were fabricated by heating to 950°C in argon borosilicate glass rods with fine‐diameter (250‐μm) capillary in which SiC filaments were inserted. The composite specimens prepared in this manner showed only frictional bonding. The maximum frictional sliding loads for pushout and the initial frictional sliding loads in pullout were measured as functions of the embedded length of the filament in the glass rods. The nonlinear variations of the frictional loads were analyzed using shear‐lag models that include corrections for the effects of Poisson expansion or contraction on the sliding friction stress. It is shown that under identical conditions of composite fabrication the two tests give nearly identical properties for the interfaces. Pushout tests on hotpressed bulk composite specimens, however, showed both chemical bonding and a higher sliding friction stress relative to the single‐filament capillary specimens. The presence of compressive residual stress on the filaments was independently confirmed by evidence of stress‐induced birefringence.
Evaluation of Glassy Phase in Sintered Silicon Nitride by Low‐Temperature Specific Heat Measurements
Authors: Watari Koji , Ishizaki Kozo , Mori Katsunori
Published: March 2005

The specific heat of HIP sintered Si3N4 with 3 mol% Y2O3 and 3 mol% Al2O3 additives was measured at different temperatures ranging from 2 to 10 K, in order to confirm the presence of a glassy phase in the sintered body. The grainboundary glassy phase in the sintered Si3N4 was evaluated by specific heat measurements. The difference between the experimental value and the lattice specific heat calculated from the Debye theory confirmed the existence of a glassy phase in sintered Si3N4.
Structure Change of Ca2SiO4 Solid Solutions with Ba Concentration
Authors: Fukuda Koichiro , Maki Iwao , Adachi Keisuke
Published: March 2005

A series of Ba‐bearing Ca2SiO4 solid solutions (C2S(ss)), (BaxCa1−x)2SiO4 with 0.075 x 0.30, were prepared and examined by X‐ray and electron beam diffraction. They are all made up of orthorhombic domains 120° different in orientation around the common c axis of the former α phase. The C2S solid solution with x= 0.075 shows a superstructure incommensurate along the a axis with λ (modulation wavelength) = 3.5 and commensurate along the c axis with Δ= 3. With x= 0.15, modulation is observed only along the a axis and Δ= 3.4. No evidence of superstructure is found with x= 0.24; the space group and cell dimensions are comparable with those of pure α’H‐C2S. The C2S(ss) with x= 0.30 gives a superlattice with the cell‐edge length of 3b. All the C2S(ss), when reheated at 1000°C for 24 h, produced lamellae of the trigonal phase T nearly in parallel with (001) of the host α’L phase. The crystallographic orientation between the two phases is

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This indicates that the above Ba‐bearing C2S(ss) phases occur as precursors to the thermodynamically more stable two‐phase mixtures.
Small‐Angle X‐ray Scattering Study of Gelling Silica–Organic Polymer Solution: Systems Containing Poly(Sodium Styrenesulfonate)
Authors: Nakanishi Kazuki , Soga Naohiro , Matsuoka Hideki , Ise Norio
Published: March 2005

Phase separations which result in micrometer‐range interconnected porous morphologies in a silica sol–gel system have been investigated using tetraethoxysilane and poly(sodium styrenesulfonate) (NaPSS) as starting materials. The dependence of domain size of interconnected structure on several important reaction variables such as solution composition and temperature is reported. Small‐angle X‐ray scattering measurements were performed to detect the effect of coexisting NaPSS on the polymerization behavior of silica in situ. The amount of NaPSS was found to play a key role in determining the micrometer‐range gel morphology by affecting the aggregation process and phase separation behavior of hydrolyzed silica.
Metal–Ceramic Composite Actuators
Authors: Sugawara Yutaka , Onitsuka Katsuhiko , Yoshikawa Shoko , Xu Qichang , Newnham Robert E. , Uchino Kenji
Published: March 2005

A new type of actuator composed of metal (brass) end caps and piezoelectric ceramics has been developed as a displacement transducer. Shallow cavities positioned between the metal caps and the central ceramic disk convert and amplify the radial displacement of the piezoelectric ceramic into a large axial motion of the metal end caps. Large d33 coefficients exceeding 2500 pC/N are obtained with the composite actuators. The behavior of the electrically induced strain with geometric variables, such as the thickness of the metal end caps, and with pressing force and driving frequency has been evaluated. Sizeable strains are obtained with both PZT (piezoelectric lead zirconate titanate) and PMN (electrostrictive lead magnesium niobate) ceramics.
Evidence of Secondary‐Phase Separation in an Alkali Borosilicate Glass
Authors: Ruller Jacqueline A. , Friebele E. Joseph
Published: March 2005

Transmission electron micrographs of a borosilicate glass containing CuCl semiconducting microcrystals clearly show that secondary‐phase separation is present. There are two minor‐phase (droplet) size distributions which indicate that upon heat treatment the initial droplet phase oversaturates, thus causing secondary‐phase separation.
Performance of ZrC‐Coated Particle Fuel in Irradiation and Postirradiation Heating Tests
Authors: Ogawa Toru , Fukuda Kousaku , Kashimura Satoru , Tobita Tsutomu , Kobayashi F. , Kado Shigeo , Miyanishi Hideshi , Takahashi Ishio , Kikuchi Teruo
Published: March 2005

The ZrC‐coated UO2 particle is a promising fuel for high‐temperature gas‐cooled reactors. Particle fuels with multiple layers of pyrolytic carbon and ZrC have been irratiation‐tested to a maximum fast‐neutron fluence exceeding 2 × 1025/m2 (E < 29 fJ). In‐reactor fission‐gas release measured at a burnup of 1.5 at.% was minimal. The failure fraction by postirradiation examination was null for all samples. The ZrC‐coated particles at 4 at.% burnup were postirradiation heated to 2400°C/min without failure until after 6000 s at the maximum temperature. It was found that the ZrC layer could sustain a large strain at such high temperatures. The behavior is in strong contrast with that of SiC of standard Triso coating, which is brittle to very high temperatures.
Influence of Tribochemical Reaction Products on Friction and Wear of Silicon Nitride at Elevated Temperatures in Reactive Environments
Authors: Park Dong Soo , Danyluk Steven , McNallan Michael J.
Published: March 2005

Friction coefficients and wear rates of hot‐pressed Si3N4 have been measured in a ball‐on‐flat linear‐sliding geometry at temperatures ranging from room temperature to 1273 K in Ar and air containing up to 63% H2O. In inert environments, the friction coefficients (ranging between 0.6 and 0.7) are independent of temperature, and wear rates increase with temperature. In oxidizing environments, the friction and wear are reduced by the presence of tribochemical reaction products. Friction coefficients and wear rates are lowered when the wear debris spontaneously forms into rolls, oriented perpendicular to the direction of relative motion, at high H2O levels in the temperature range of 873 to 1073 K.
Oxidation of Sintered Aluminum Nitride at Near‐Ambient Temperatures
Authors: Dutta I. , Mitra S. , Rabenberg L.
Published: March 2005

Oxidation of sintered aluminum nitride at low temperatures (20°–200°C) was studied using transmission electron microscopy (TEM). Particles of α‐Al2O3, about 20–30 Å in size, were found to form within minutes on freshly cleaned surfaces of AlN at room temperature. The oxide was found to grow nearly epitaxially on AlN when the {0001}AlN planes were exposed to the surface. Limited nonepitaxial oxidation was also observed when the basal planes were inclined to the TEM foil surface. After 10 h in air at 75°C, the particles coarsened to about 50 Å, while after 150 h at 200°C, an oxide film, about 500 Å thick, was observed on some grains.
Corrosion of SiC Mateials in N2–H2–CO Gaseous Environments: II, Durability and Mechanical Properties
Authors: Butt Darryl P. , Tressler Richard E. , Spear Karl E.
Published: March 2005

Three SiC materials were exposed to two gas compositions in the N2–H2–CO system at 1200° and 1300°C, 133 Pa and 98.7 kPa for 50–1000 h. The durability was evaluated by fracturing bend bars at room temperature and C‐rings at room temperature and 1300°C in argon. Fractography was used to correlate changes in strength with changes in flaw populations. In all three materials, surface pitting was the primary cause of degradation. Under some conditions it was found that flaw healing and new flaw formation occurred simultaneously. C‐rings cut from tubes did not lose strength, although pitting occurred; however, machined bend bars lost strength under identical conditions. In the case of bend bars, following an initial loss of strength (∼10%–50%) after 50–150 h, there was typically no further loss observed with increased exposure time. Due to its higher Pco, degradation in an endothermic gas was generally more severe than that in a nitrogen–based gas.
Oxidation Behavior of Silicon Yttrium Oxynitride
Authors: Veyret Jean‐Bernard , Van de Voorde Marcel , Billy Michel
Published: March 2005

The oxidation behavior of the silicon yttrium oxynitride Y10Si7O23N4, so‐called H‐phase, in the temperature range 700–1400°C has been investigated. A nitrogen retention phenomenon in the oxidation product Y4.67(SiO4)3O (O‐apatite) is discussed. The H‐phase is one of the four quaternary compounds identified in hot‐pressed Si3N4 materials fabricated within the Si3N4–SiO2–Y2O3 pseudoternary system.
Effect of the ac Field Level on the Aging of the Dielectric Response in Polycrystalline BaTiO3
Authors: Wu Kaiwen , Schulze Walter A.
Published: March 2005

BaTiO3 ceramics with grain sizes from 0.6 to 60 μm and relative densities of 89% to 92% were prepared by hot forging and conventional sintering from very pure‐oxalate‐derived powder. The aging of both the dielectric constant and the dielectric loss was examined at weak and strong fields with respect to grain size and frequency. It was concluded that the main aging mechanism is the aging of hysteretic domain wall motion for coarse‐grained ceramics. At grain size of less than 1 μm, the lack of frequency and EAC dependence, along with a lower aging rate, suggests that domain motions or hysteretic domain wall motions are restricted in finegrained ceramic BaTiO3 and contribute little to the aging.
Formation and Sintering Characteristics of Aluminum Borate Whiskers
Authors: Readey Michael J.
Published: March 2005

A boric acid‐stabilized aluminum acetate powder was decomposed to aluminum borate (Al18B4O33) by calcining at 1000°C. The powder was then ball‐milled, compacted, and fired to temperatures of 1500°, 1600°, and 1700°C for a period of 1 h. The resulting aluminum borate ceramic had a whiskerlike grain morphology, with the whisker length approaching 20 μm and a diameter of 2–3 μm. The sintered compact showed no shrinkage upon firing, had a porosity of ∼50%, a narrow pore size distribution, and an average pore size of 1–3 μm.
Microwave Thermal Etching of Stabilized Zirconia
Authors: Plovnick Ross H. , Kiggans James O.
Published: March 2005

A method is discussed for etching stabilized zirconia using microwave heating. Microstructural features of microwave‐sintered stabilized zirconia are revealed by this technique. This approach requires less time at temperature than conventional thermal etching to achieve comparable results.
Postdeposition Process for Improving Optical Properties of Chemical‐Vapor‐Deposited Silicon
Authors: Goela Jitendra S. , Taylor Raymond L.
Published: March 2005

A high‐temperature, postdeposition treatment was developed to significantly improve the near‐infrared transmission of chemical‐vapor‐deposited polycrystalline Si (CVD‐Si). This treatment did not significantly affect the hardness and flexural strength of CVD‐Si, reduced the elastic modulus by 12%, and made the microstructure more uniform and isotropic by modifying the columnar growth structure that is typical of CVD materials.
Synthesis of Chemically Stabilized Cristobalite
Authors: Saltzberg Michael A. , Bors Susan L. , Bergna Horacio , Winchester Steven C.
Published: March 2005

The synthesis of chemically stabilized cristobalite (CSC) by a wet‐chemical route is described. CSC is a form of silica (containing small amounts of other oxides) which is similar in many ways to β‐cristobalite, but does not invert to α‐cristobalite upon cooling. The effects of changing the dopant levels and various synthetic parameters on the phases formed in the CaO‐Al2O3‐SiO2 system have been investigated. Stabilization of cristobalite with a number of different dopant combinations has been attempted, with mixed results. The use of wet‐chemical techniques has led to the synthesis of apparently phase‐pure CSC in a composition region where traditional solid‐state synthetic techniques yield a mixture of other phases.
Production of Fine, High‐Purity Beta Silicon Carbide Powders
Authors: Krstic Vladimir D.
Published: March 2005

Submicrometer SiC (β‐form) powders were synthesized by reacting silica and carbon black at temperatures between 1450° and 1800°C. Simultaneous application of vacuum and mixing provides the condition for full conversion of silica to SiC. It was shown that two different reaction mechanisms are possible, depending on the reaction temperature and the partial pressure of CO. At lower temperatures (below approximately 1400°C), the dominant mechanism for silicon carbide formation involves the solid‐state reaction of silica and carbon. At higher temperatures (above approximately 1400°C), the dominant mechanism is the reaction between gaseous SiO and C. Above 1400°C, the rate of SiC formation is controlled by the rate of SiO formation. In as‐synthesized form, the SiC powders typically contain < 0.2 wt% of unreacted silica and free carbon in the range between 6 and 15 wt%. Precise control of partial pressure of CO in the reaction chamber and continuous mixing of the reactants provide the conditions under which the rate of silicon carbide formation may be increased by one order of magnitude. The process is suitable for large‐scale commercial production of SiC, requiring no postfabrication acid leaching or major milling.
High‐Temperature Strength and Cavitation Threshold of Silicon Nitride–Silica Ceramics
Authors: Zeng Jianren , Tanaka Isao , Miyamoto Yoshinari , Yamada Osamu , Niihara Koichi
Published: March 2005

The role of high‐purity silica in the fracture of Si3N4 at high temperatures has been investigated. The flexural strength at 1400°C was found to be greater than that at room temperature. Little plastic deformation was observed even when 10 wt% SiO2 was added and the strain rate was decreased 2 orders of magnitude from that for a standard bend test. Microstructural observations revealed that the glassy phase was localized at intergranular pockets when SiO2 additions were ≤ 10 wt%. High strength at 1400°C despite the presence of a fairly large amount of glassy phase is attributed to a high cavitation threshold in such glassy pockets consisting of high‐purity SiO2. However, the deformation behavior changed abruptly for SiO2 additions of 10 and 20 wt%, which is explained by the morphological change of the glassy phase to thicker intergranular layers which allow macroscopic viscous flow.
Structure Refinement of Mullite by the Rietveld Method and a New Method for Estimation of Chemical Composition
Authors: Ban Takayuki , Okada Kiyoshi
Published: March 2005

The structure of mullite was refined by the Rietveld method, and a new method for the estimation of chemical composition of mullite was proposed. Mullites were synthesized by firing the starting materials prepared by sol–gel and spray pyrolysis methods at various temperatures. Linear correlations were recongnized between the chemical composition of mullite analyzed with the Rietveld method and the lengths of a and b axes, but a small anomaly was found in the variation of the c axis. It was found to be caused by a difference in the c axis of pseudotetragonal mullite and that of orthorhombic mullite. A good correlation was found between the chemical composition of mullite and the intensity ratio of (I220/I111). This is a much more convenient method for estimating the chemical composition of mullite than Cameron's method, which uses a lattice constant.
Effect of Aqueous Processing Conditions on the Microstructure and Transformation Behavior in Al2O3─ZrO2(CeO2) Composites
Authors: Bleier Alan , Becher Paul F. , Alexander Kathleen B. , Westmoreland C. Gary
Published: March 2005

Aqueous processing of Al2O3─ZrO2 (123 mol% CeO2) composites, combined with sintering conditions, was used to control the microstructure and its influence on the martensitic transformation temperature of t‐ZrO2 and the transformation‐toughening contribution at room temperature. The resultant ZrO2 grain sizes in the dense composites were related to the transformation‐toughening behavior of t‐ZrO2. The data show that (1) the best processing conditions exist when the electrophoretic mobilities of the two solids are positive, adequately high to ensure colloidal stability, efficient packing,and uniform ZrO2 distribution but differ greatly in magnitude, (2) the colloidal stability of ZrO2 controls the overall stability and the rheological and processing behavior of this mixture, (3) the grain size distribution in dense pieces sintered for 1 h at 1500°C is comparable to the particle size distribution of the powders, (4) the martensite start temperature for the tetragonal to‐monoclinic transformation in Al2O3 containing 20 and 40 vol% ZrO2 increases and can approach 0°C with increasing average ZrO2 grain size, and as a result, (5) the fracture toughness values at room temperature are raised from 4–5 MPa.m1/2 to 9–12 MPa.m1/2 for these two compositions.
Minimization of Parasitic Currents in High‐Temperature Conductivity Measurements on High‐Resistivity Insulators
Authors: Will Fritz G. , Janora Kevin H.
Published: March 2005

An experimental setup and novel measurement technique are described which allow reliable conductivity measurements to be made at conductivities as low as 10−17Ω−1.cm−1 and temperatures up to at least 1300°C. This capability is of particular interest for conductivity measurements on high‐resistivity insulators over a large range of temperatures. This technique has been used to measure the conductivity of single‐crystal alumina from 400° to 1300°C in a 10−7 torr (∼1.3 × 10−5 Pa) vacuum, equivalent to an oxygen partial pressure of about 10−8 torr (∼1.3 × 10−11 atm or ∼ 1.3 × 10−6 Pa). Surface and gas‐phase conductance are determined as a function of temperature, and the requirements for their minimization are described. A key requirement is a very low voltage between the volume guard and the guarded electrode. The effect of leakage currents due to the sample fixture, electrical feedthroughs, and electronic instrumentation are also evaluated, and proper design features to make these effects negligible are outlined.
Thermal Expansion Anisotropy of Ceria‐Stabilized Tetragonal Zirconia
Authors: Scardi Paolo , Maggio Rosa Di , Lutterotti Luca , Maistrelli Paul
Published: March 2005

Ceria‐stabilized tetragonal zirconia polycrystals were obtained by thermal treatment of amorphous powder prepared by the sol–gel method. Detailed XRD profile analysis was employed to study microstructural disorder and crystallite size and shape; in particular, no fluctuation of stoichiometry was found, the main cause of disorder being attributable to dislocations. Thermal expansion measurements were carried out by high‐temperature XRD at 294, 473, 673, 873, and 1073 K using silicon as an internal standard. Thermal expansion coefficients are anisotropic and changes in the stabilizer content have little effect on them. A mean value, αa= 10.6 × 10−6 (K−1) and αc= 13.5 × 10−6 (K−1), can be assumed for Zr1−xCexO2 with x in the range 0.12–0.18.
Phase Separation in 12 mol% Ceria‐Doped Zirconia Induced by Heat Treatment in H2 and Ar
Authors: Zhu Hai‐Yan , Hirata Toshiya , Muramatsu Yuji
Published: March 2005

The phase separation in 12 mol% CeO2─ZrO2 ceramic heattreated in a mixture of H2 and Ar was investigated by X‐ray diffractometry (XRD), X‐ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, and Raman scattering. After heat treatment at temperatures above 1200°C, the tetragonal solid‐solution phase separated into Zr2Ce2O7 and the monoclinic phase. Raman scattering measurements also provided supplementary evidence for the phase separation. XPS showed that the valence change from Ce4+ to Ce3+ predominantly occurred, whereas the reduction from Zr4+ to Zr3+ took place above 1200°C. It is concluded, that in the highly reduced sample, where the valence changes from Ce4+ (Zr4+) to Ce3+ (Zr3+), the phase separation is noticeably promoted. Below 1000°C the phase separation was suppressed because of no appreciable valence change to trigger the phase separation, and the single tetragonal phase was retained.
X‐ray Photoelectron Spectroscopy Studies of Metallic Diborides
Authors: Zdaniewski Wieslaw A. , Brungard Nancy L.
Published: March 2005

The binding energies of core electrons in d‐type stoichiometric diborides of several transition metals were measured by X‐ray photoelectron spectroscopy. Metal core lines in the diborides shifted either to higher or to lower binding energies compared with those appertaining to corresponding elemental states and varied with the metal. The shifts were < 0.6 eV. Carbides, oxides, and oxycarbides of variable stoichiometries were the major impurities detected in the diborides. The binding energy shifts showed a progressive change as the electronegativity difference between the and the metalloid (boron, carbon, nitrogen, oxygen) increased. This indicated that the bond in boro‐oxycarbides may be partially ionic.
Preparation of C70‐Doped Solid Silica Gel via Sol–Gel Process
Authors: Dai Sheng , Compton Robert N. , Young Jack P. , Mamantov Gleb
Published: March 2005

We reported the first preparation of C70‐doped solid gel. Its UV‐visible spectrum was recorded.
Microstructure of Silicon Carbide Whiskers Synthesized by Carbothermal Reduction of Silicon Nitride
Authors: Wang Hongyu , Berta Yolande , Fischman Gary S.
Published: March 2005

The microstructure of silicon carbide whiskers synthesized by carbothermal reduction of silicon nitride has been studied using transmission electron microscopy. All of the whiskers examined are single crystals, and grow in the (111) crystallographic direction. Two different forms of stacking faults and microtwins were observed; in one the planar defects are normal to the whisker growth direction, and the other has the defect planes at an angle of about 70° to the growth axis, while both forms of the defects are on the [111] closed‐packed planes. Without the addition of catalyst, droplets containing metallic impurities were not found at the tips of the whiskers synthesized by the present process. A core and outer regions were observed in the single‐crystal whiskers, which may be evidence that the whiskers were formed by a two‐stage mechanism.
Sol–Gel Fabrication of Epitaxial and Oriented TiO2 Thin Films
Authors: Selvaraj Ulagaraj , Prasadarao Alamanda V. , Komarneni Sridhar , Roy Rustum
Published: March 2005

Thin films of titania have been prepared by spin coating on fused silica, Si(100), and rutile(110), starting with a sol–gel process. The alkoxide solution was chelated with diisopropanolamine, and the resulting precursor solution was hydrolyzed prior to coating. Oriented rutile films were obtained on fused silica and Si(100), while epitaxially oriented film was formed on rutile (110). X‐ray diffraction results indicated that the as‐deposited films transformed to rutile via anatase with increasing temperature. The phase transformation temperature was found to be dependent on the substrate, and it was in general higher on the substrates than that observed for the gel powder. Microstructural studies revealed that these films consisted of finely dispersed grains of 0.05 to 0.15 μm in size.
Mechanical Strength of Hemispheric Domes of Yttria and Lanthana‐Doped Yttria
Authors: Harris Daniel C. , Hayes George A. , Jaeger Nancy A. , Sawyer Larry D. , Scheri Richard C. , Hills Marian E. , Hayes Kenneth R. , Homer Scot E. , Tsai Y. L. , Mecholsky J. J.
Published: March 2005

The strength of hemispheric ceramic domes was measured in a biaxial flexure test using disklike circular pieces removed with a core drill. Yttria and lanthana‐doped yttria dome cores exhibit approximately 60% of the strength predicted from similarly fabricated flat disks. Measured strengths agree with those predicted from observed fracture‐initiating defects.