bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhancement of MgO Evaporation from MgO‐Stabilized ZrO2 by Grain‐Boundary Diffusion
Authors: SAKKA YOSHIO , OISHI YASUMICHI , ANDO KEN
Published: March 2005

Preferential evaporation of MgO from cubic 14MgO·86ZrO2 solid solution was determined for two polycrystals with different grain sizes at 1800° to 2100°C and 7 × 10–3 Pa. The time dependence of the evaporation rate and the concentration in the solid phase indicated that the evaporation kinetics is controlled by cationic interdiffusion in the solid phase and enhanced by the presence of grain boundaries. The temperature dependence of the lattice diffusion coefficient calculated from the concentration distributions agreed with that previously determined for Mg‐Zr interdiffusion in polycrystalline MgO‐ZrO2 solid solutions.
New Modification of Pb5GeO7
Authors: Yamaguchi Osamu , Ogiso Nobuyuki , Shimizu Kiyoshi
Published: March 2005

A new modification of'Pb5Ge07 was formed by the simultaneous hydrolysis of lead and germanium alkoxides, followed by washing and drying. It has a hexagonal unit cell with a =0.7589 nm and c = 1.2421 nm. The chemical structure is described by the formula Pb5(GeO4)O3. Hexagonal Pb5GeO7 transforms to the orthorhombic modification at 460° to 485°C.
Microstructural Study of Sintered Mullite Obtained from Premullite
Authors: Rincon JesúsMa. , Thomas Gareth , Moya José S.
Published: March 2005

The microstructural evolution of sintered mullite prepared from a premullite powder after thermal treatments at 1570°C was observwed by transmission electron microscopy and energy‐dispersive X‐ray microanalysis. The results show that there are grains with lower and higher contents of Al2O3 than that in stoichiometric mullite and small glassy‐phase areas with the same composition as mullite; α‐Al2O3 precipitates after samples are annealed.
Periodic Accumulation of Voids Observed in Calcium Phosphate Glass‐Ceramics
Authors: Watanabe Akira , Imada Yukio , Kihara Seiji
Published: March 2005

After the crystallization of calcium phosphate glass, a pattern of stripes like the rings of a tree is observed in the glass‐ceramic. The pattern of stripes, formed only from a particular glass composition and under specific crystallization conditions, is made up of voids resulting from a difference in density between the original glass and the resulting glass‐ceramic. The size and distribution pattern of these voids must be controlled to achieve maximum mechanical properties.
Grain‐Boundary Migration in LiF: II, Microstructural Characteristics
Authors: GLAESER A.M. , BOWEN H.K. , CANNON R.M.
Published: March 2005

Discontinuous recrystallization experiments were used to examine relationships between grain morphology, displacement uniformity, and mobility characteristics in LiF. Irregular migration behavior is attributed to alternate solute breakaway and reattachment occurring erratically around a grain. The results suggest (1) growth occurs such that morphology is continually or periodically smoothed, and (2) a relatively wide transition temperature range exists within which most boundaries migrate at both high‐ and low‐V extremes. Mechanisms based on substantial variations in Fmax and in the subboundary segregant account for the local breakaway and attachment. Variation in the interaction energy resulting from misorientation differences is suggested as an important source of variability.
Mechanism of Ni‐Zn Ferrite Formation in the Presence of Molten Li2SO4‐Na2SO4
Authors: HAYASHI YOSHIHIRO , KIMURA TOSHIO , YAMAGUCHI TAKASHI
Published: March 2005

Nickel‐zinc ferrite powder was prepared from the constituent oxides in the presence of molten Li2SO4‐Na2SO4. The effect of ZnO on the reactivity of NiO was studied. The process of Ni‐Zn ferrite formation was followed by X‐ray diffraction and thermomagnetic analyses. Particle size and shape of the product were determined by scanning electron microscopy. In the presence of molten salt, ZnO enhances the reactivity of NiO, and Ni‐Zn‐ferrite formation is completed at lower temperature than Ni ferrite formation. In the reaction for the formation of Ni‐Zn ferrite, Zn ferrite forms before NiO is incorporated into the ferrite phase. The reaction between the initially formed Zn ferrite and NiO leads to a rate of Ni‐Zn ferrite formation higher than that of Ni ferrite formation from NiO and Fe2O3.
Subsolidus Compatibility in the System NaCl‐KCl‐AlCl3‐NaF‐KF‐AlF3
Authors: SORRELL CHARLES A. , GROETSCH JOHN G.
Published: March 2005

The chemistry and properties of salts used as fluxes for recycling aluminum were studied. Many fluxing salts fall within the system NaCl‐KCl‐AlCl3‐NaF‐KF‐AlF3, which has been shown to be a reciprocal system, with NaF‐KCl, KC1‐AIF3, and NaCl‐AIF3 as the stable mixed‐halide binaries. Twelve subsolidus compatibility tetrahedra were determined by X‐ray analyses of samples heated in evacuated sealed tubes. X‐ray measurements of quenched and annealed samples indicate that elpasolite, nominally K2NaAlF6, has a compositional range between 60 mo% Na3AlF6, 40 mol% K3AlF6 and 25 mol% Na3AlF6, 75 mol% K3AIF6. Improved X‐ray powder data are given for KAIF4, showing a previously reported structure to be essentially correct.
Brittleness Dependence of Crack Branching in Ceramics
Authors: KIRCHNER HENRY P.
Published: March 2005

A linear correlation between the degree of overloading on the crack tip and brittleness was observed. The intercept, which was √2, is identified with a minimum condition of overloading where branching occurs at twice the fracture energy. The slope was identified with the degree of plastic deformation at the crack tip necessary to nucleate the branching crack. A total crack tip strain criterion for crack branching in ceramics was investigated. This criterion is supported by the fact that average total elastic strain at the boundary of the yield zone is approximately equal to the square of the slope of the curve.
Retardation of Cs+ and Cl− Diffusion Using Blended Cement Admixtures
Authors: KUMAR A. , ROY B. D. M.
Published: March 2005

Diffusion of cesium chloride through thin plates of hardened cement pastes was studied. Blast‐furnace slag and condensed silica fume were used as blending admixtures in an attempt to retard the diffusion of cesium and chloride ions. The curing and diffusion temperatures were varied from 27° to 60°C, and the water/solid ratio was varied from 0.30 to 0.40. Results indicate that the cesium ion diffuses more slowly than the chloride ion in hardened cement paste systems. Blending admixtures caused a further reduction in diffusivity for both ions, which is important for preventing corrosion or restricting radionuclide transport.
Kinetics of Hydration of Monocaldum Aluminate
Authors: FUJII KINJIRO , KONDO WAKICHI , UENO HISAHIRO
Published: March 2005

Hydration of CaAl2O4 (CA) was studied by calorimetry, analysis of the liquid phase, measurement of the combined water, and electron microscopy. During the induction period, the solution remains almost unchanged and is equilibrated temporarily with both superficially intrusion‐hydrated CA particles and Al(OH)3 gel formed by dissociation of Al(OH)4– ions, the solubility of the Al(OH)3 gel being 10–4.24 molkg–1 at 25°C, while the intrusion‐hydrated layer on the CA particles grows following a nearly linear law to reach a critical thickness (∼3 nm at 10° to 20°C, or 12 nm at 30°C). At this point destruction of the layer occurs, nuclei of hydrous compounds are generated, and the induction period terminates. Subsequent reaction proceeds in accordance with the rate equation of Schiller based on the dissolution‐crystallization mechanism.
Thermodynamic Mixing Properties of Sodium‐Potassium β″‐ Aluminas
Authors: Davies Peter K. , Canfield Steven
Published: March 2005

Measurements of the activities of Na+ and K+ ions in β″‐alumina solid solutions revealed complicated nonideal behavior throughout the system. At sodium‐rich compositions, activity coefficients for Na are less than unity, suggesting either some degree of order between Na+ and K+ or increased local order between Na+ and vacancies. The system shows a change in thermodynamic behavior near XK=0.15. This composition corresponds closely to that showing the lowest ionic conductivity in the Na‐K β″‐gallate system.
Preparation of Ba(Mg1/3Ta2/3)O3 Using Oxine
Authors: Kakegawa Kazuyuki , Wakapayashi Tsuyoshi , Sasaki Yoshinori
Published: March 2005

A solution containing Mg2+ and Ta5+ was added to an aqueous ammonia solution of oxine, resulting in a precipitate. After the precipitate was thermally decomposed and fired, it was mixed with BaCO3 powder and fired again at high temperatures to obtain Ba(Mg1/3Ta2/3)O3 (BMT). This method resulted in BMT formation at temperatures lower than those used in the conventional mixed‐oxide method, and single‐phase BMT formed directly at 1300°C without intermediates.
Vacuum Centrifugal‐ Thermite Process for Producing Ceramic‐Lined Pipes
Authors: Odawara Osamu , Ikeuchi Jun
Published: March 2005

A vacuum centrifugal‐thermite process was used to prepare ceramic‐lined pipes rapidly. The ceramic layer was dense, and the grain size was smaller than that produced under atmospheric pressure, resulting in improved mechanical properties.
Kinetics of Precipitation of α‐Al2O3 in Polycrystalline Supersaturated MgO ‐ 2Al2O3 Spinel Solid Solution
Authors: PANDA P. C. , RAJ R.
Published: March 2005

Supersaturated polycrystals of solid‐solution spinel were heat‐treated below the solvus temperature. Precipitation of α‐alumina was examined by X‐ray diffraction, microprobe, and scanning transmission electron microscopy. Precipitation kinetics followed classical time‐temperature‐transformation behavior: the precipitation rate was growth controlled at large undercoolings and nucleation controlled at low undercoolings. Scanning transmission electron microscopy and microprobe analysis revealed that the growth of precipitates was limited by interface reaction. Nucleation occurred throughout the polycrystal and was probably promoted by the grain boundaries. Precipitation was accompanied by the growth of pores at interfaces, presumably to accommodate the change in volume required by the phase transformation. Our observations in polycrystals contrast sharply with single‐crystal work, where it has been reported that nucleation occurs at the free surface and that the formation of α‐alumina is preceded by metastable phases.
Cation Effects in NaPO3 Glasses Doped with Metal Nitrides and Oxides
Authors: RAJARAM MOHAN , DAY DELBERT E.
Published: March 2005

Oxynitride glasses were prepared by doping a NaPO3 melt with either AIN, Mg3N2, or Ca3N2 NaPO3 glasses doped with AI2O3, MgO, or CaO, so as to contain the same weight percent of each cation as in the oxynitride glasses were also prepared. The dissolution rate in water and the thermal expansion coefficient both decreased while the dilatometric softening point, glass transition temperature, and refractive index increased with increasing nitride or oxide dopant concentration. The properties of the corresponding oxide‐ or nitride‐doped glasses were essentially equal, which indicated that the cation was primarily responsible for the change in each property.
Preparation of Ultrafine Silica‐Germania Powders Using an Inductively Coupled Plasma Torch
Authors: Biswas Dipak R. , Oh Paul S.
Published: March 2005

Ultrafine silica‐germania powders (<1 ×10–7 m) were prepared by using an inductively coupled oxygen/argon plasma torch. The high‐temperature plasma was generated inside a quartz tube through which oxygen/argon carrier gas and the tetrachlorides of silicon and germanium were injected. The powders were collected on a substrate.
Origins of Planar, Concave, and Convex Boundaries During Exaggerated Grain Growth
Authors: Searcy Alan W.
Published: March 2005

A new surface thermodynamic theory is used to show that exaggerated grain growth is driven by reductions in grain boundary and dislocation free energies produced when a larger grain sweeps out a volume element formerly occupied by small grains. Whether the advancing boundary is planar, concave, or convex depends on the relative rates of ledge nucleation and growth, on the growth direction, and on whether growth occurs at screw dislocations.
The System TiO2‐Bi2Ti4O11
Authors: Bamberger C.E. , Begun G.M. , Dunn H.W.
Published: March 2005

The system TiO2‐Bi2Ti4O11 was examined by Raman spectroscopy and X‐ray diffraction to determine whether TiO2 is soluble in Bi2Ti4O11. The Raman spectral data obtained from preparations made at ∼ 1050°C and cooled to room temperature led us to conclude that TiO2 is not soluble in the “high‐temperature” form of Bi2Ti4O11. It was also found that extensive grinding of the phase identified as the “high‐temperature” form converts it to the “low‐temperature” form, stable below 250°C.
Synthesis of BN Using BPO4 as the Boron Source
Authors: Bamberger Carlos E. , Begun George M.
Published: March 2005

The reaction of BPO4 with different amounts of NaCN to yield BN and sodium phosphates was studied, mainly as a function of temperature and of the ratio NaCN/BPO4. Gravimetric data, together with analytical results, allowed us to postulate and confirm that the yield of reaction products is dependent on the initial ratio NaCN/BPO4. An additional reaction between NaCN, BPO4, and Na3PO4 yielding BN was also studied.
Estimating Tensile Creep Data from Flexure Data
Authors: Rosenfield A.R. , Shetty D.K. , Duckworth W.H.
Published: March 2005

Safety factors are derived for converting bend data to tensile data for creep. It is assumed that the ceramic being stressed is subject to preferential damage in tension. The analysis shows that the safety factors can be relaxed considerably when compression data are available to augment the bend data.
Silver‐Sodium Exchange in Sodium Galliosilicate Glasses
Authors: Lapp Josef C. , Shelby James E.
Published: March 2005

The silver‐sodium interdiffusion coefficients of several glasses in the sodium galliosilicate system were determined. The compositional dependence of the interdiffusion coefficient is compared to that observed in the self‐diffusion coefficients calculated from dc electrical conductivity data. The observed trends are discussed in terms of a structural model proposed for these glasses.
Dilatant Center‐Crack Tip Interaction Effects
Authors: HOAGLAND R. G. , HIRTH J. P.
Published: March 2005

In this paper we consider the toughening effects of a collection of discrete particles, acting as dilatant centers, in the vicinity of a crack tip. The results are compared with those of continuum treatments in which the material is treated as a homogeneous continuum with a constitutive relation that mimics the macroscopic constitutive behavior of the material containing discrete, transformable particles. In terms of the force on the crack tip, J, there is no difference between the predictions of the two approaches but, in terms of R, the energy dissipation rate, additional terms emerge in the discretized picture. The additional terms are associated with the supply of interaction energy between the crack tip and transformed particle as the crack tip and its attendant zone of transformed particles advance and due to far‐field contributions.
Effect of SrO Additions on the Grain‐Boundary Microstructure and Mechanical Properties of Magnesia‐Partially‐Stabilized Zirconia
Authors: DRENNAN J. , HANNINK R.H.J.
Published: March 2005

Improvements in the mechanical properties of magnesia‐partially‐stabilized zirconia are obtained by the addition of SrO. Evidence is presented which indicates that the added SrO effectively neutralizes the detrimental effects of SiO2 contaminant by forming a glass phase which is ejected from the bulk of the ceramic during sintering. This combined effect results in the retardation of the subeutectoid decomposition reaction while minimizing retention of glass phases at the grain boundaries.
Transmission Electron Microscopic Observation of the Martensitic Phase Transformation in Tetragonal ZrO2
Authors: WEN SHULIN , MA LITAI , GUO JINGKUN , YEN TUNGSHENG
Published: March 2005

The present work involves the observation of phase transformation in Y2O3‐containing tetragonal ZrO2 polycrystals (Y‐TZP) using electron microscopy. The observations indicate that the martensitic phase transformation ususally starts from grain boundaries. Transformation was also observed at the tip of a microcrack and its adjacent region. Our observations also indicate that the tetragonal ZrO2 grains do not all transform at the same time at the fracture surfaces.
Dilatation Behavior of Two Differently Heat‐Treated Commercial Magnesia‐Partially‐Stabilized Zirconias
Authors: DWORAK ULF , OLAPINSKI HANS , BURGER WOLFGANG
Published: March 2005

The dilatation behavior of two grades of partially stabilized zirconia (PSZ) was determined. ZN 40 is a material which contains 40% to 50%t‐ZrO2 particles, and has a reproducible dilatometric behavior up to 900°C. ZN 50 is a Mg‐PSZ containing 20% to 30% of the monoclinic phase. The cyclic dilatation curves show an unstable hysteresis effect which arises from the tetragonal‐monoclinic phase transformation.
Sensitivity of the Potential Drop Technique for Crack Length Measurement in a Chevron‐Notched Specimen
Authors: Troczynski Thomas B. , Nicholson Patrick S.
Published: March 2005

It is shown that the electrical potential drop technique applied to the study of fracture in chevron‐notched specimens is insensitive to errors in the potential and current interprobe distance measurements. It is concluded, therefore, that the method is useful whenever the contact area between the probe and material is difficult to define, i.e., for metal‐ceramic surface contacts.
Preparation of SiO2‐TiO2‐ZrO2 Glasses from Alkoxides
Authors: Beier Wolfram , Göktas A. Aydin , Frischat Günther H.
Published: March 2005

Relatively large compact glass samples (∼5 mm in diameter) of 65SiO2·20TiO2·15ZrO2 and other binary and ternary compositions were prepared by the alkoxide gel method. Prolonged storage of the gels in water before they were dried reduced the residual carbon content of the resulting glasses considerably. Optimal preparation conditions are given, and the microstructure of the gels and glasses obtained is discussed.
Crystallization of Monoclinic 2TiO2·5Nb2O5
Authors: Yamaguchi Osamu , Tomihisa Daijo , Ogiso Nobuyuki , Shimizu Kiyoshi
Published: March 2005

Monoclinic 2TiO2·5Nb2O5 crystallizes at 810° to 835°C from an amorphous material prepared by the simultaneous hydrolysis of titanium and niobium alkoxides. Crystallization isotherms are described by the contracting cube equation 1 − (1 − f)113= k(t − t0); the activation energy is 315 kJ·mol−1. Monoclinic 2TiO2·5Nb2O5 transforms to the orthorhombic modification at ∼1200° to 1300°C.
Grain Growth in Dense Cadmium Oxide
Authors: Quadir Tariq , Readey Dennis W.
Published: March 2005

The grain size in dense cadmium oxide was found to increase with the one‐third power of time. The apparent activation energy was 134±17 kJ/mol and the grain size distributions were lognormal.
Weakening of Soda‐Lime Glass by Particle Impact During Hydrofluoric Acid Etching
Authors: Roach David H. , Cooper Alfred R.
Published: March 2005

During etching of soda‐lime glass in hydrofluoric acid solutions, insoluble reaction products can collect in the acid solution or deposit on the glass surface. In this study it is shown that impact of these insoluble reaction products on the etching surfaces can cause strength degradation. The insoluble reaction products are characterized by scanning electron microscopy, wet chemical, X‐ray diffraction, and surface area analyses.
Application of Compositionally Diphasic Xerogels for Enhanced Densification: The System Al2O3‐SiO2
Authors: Komarneni Sridhar , Suwa Yoshiko , Roy Rustum
Published: March 2005

Stoichiometric mullite (71.38 wt% Al2O3‐28.17 wt% SiO2) and 80 wt% Al2O3‐20 wt% SiO2 gels were prepared by the single‐phase and/or diphasic routes. Dense sintered bodies were prepared from both sets of gels in the Al2O3‐SiO2 system. Apparent densities of 96% and 97% of theoretical density were measured for the diphasic (using two sols) mullite samples sintered at 1200° and 1300°C for 100 min, respectively; this compared with 85% and 94% for the single‐phase xerogels under the same conditions, and to much lower values for mullite prepared from conventional mixed powders. The microstructure of the mullite pellets from diphasic xerogel precursors is also considerably finer.
Crystallization of Fluorite‐Type Solid Solution from Alkoxides in the System Y2O3‐TiO2
Authors: Yamaguchi Osamu , Narai Akira , Kudara Hideki , Shimizu Kiyoshi
Published: March 2005

Fluorite‐type solid solutions crystallize directly at lower temperatures from amorphous materials prepared by the simultaneous hydrolysis of yttrium and titanium alkoxides. The lattice constant of the solid solution changes continuously as a function of composition. The kinetics of crystallization of the fluorite phase have been studied by X‐ray measurements. The initial stage at each temperature proceeds rapidly in a short time. The final stage can be expressed in terms of the contracting cube equation 1—(1 —f)113= kt, the activation energy being 184 mol−1. A pyrochlore‐type solid solution corresponding to the composition Y2Ti2O7 crystallizes at 8l5° to 900°C.
Preparation of Dicalcium Siliciate at 950°C
Authors: Kralj D. , Matković B. , Trojko R. , Young J. F. , Chan C. J.
Published: March 2005

β‐Ca2Si04 can be obtained from a mixture ofCaC2O4‐H2O and amorphous silica by firing at 950°C as opposed to a normal sintering temperature around 1450°C. If CaCO3 is used instead of CaC2O4·H2O, four repeated firings under CO2 atmosphere are needed to obtain β‐Ca2SiO4. The role of CO2 atmosphere during firing and the influence of specific surface of reactanm on the rate of reaction are discussed.
Hot Forging Characteristics of Fine‐Grained ZrO2 and Al2O3/ZrO2 Ceramics
Authors: Kellett B. J. , Lange F. F.
Published: March 2005

Preliminary results indicate that large strains (∼80%) and strain rates (0.001 s−1) can be obtained without tearing (or cracking) in fine‐grain ZrO2 (0.3 μm) and Al2O3/ZrO2 (1 μm) ceramics. Alumina develops crystallographic and morphological texture as previously reported by Heuer et al.1
A New Phenomenon in Barium‐Lead Titanate Ceramics with Positive Temperature Coefficients of Resistivity
Authors: Kuwabara M. , Nagata H.
Published: March 2005

A curious resistivity anomaly in high‐Curie‐point barium‐lead titanate materials with positive temperature coefficients of resistivity (PTCR) has been observed just below the Curie point (∼420°C), besides the normal PTCR anomaly. The additional resistivity anomaly was observed in the resistivity‐temperature characteristics, especially on cooling, and shewed a significant dependence on the cooling rate.
Microstructure of Lead‐Magnesium Niobate Ceramics
Authors: Goo E. , Yamamoto T. , Okazaki K.
Published: March 2005

Lead‐magnesium niobate ceramics were processed with excess MgO and by precalcining MgO and Nb2O5. Transmission electron microscopy revealed sub‐micrometer MgO inclusions in the perovskite phase. The pyrochlore phase exists as submicrometer rectangular crystals in an amorphous PbO matrix. The composition of the pyrochlore phase was calculated to be Pb2.25Mg0.27Nb1.79O7.
Dopant Distribution in Nominally Yttrium‐Doped Sapphire
Authors: Cawley James D. , Halloran John W.
Published: March 2005

The dopant distribution in nominally yttrium‐doped sapphire is characterized. The results indicate that virtually all of the intended dopant segregated to the surface of the crystal during growth. This implies that the solubility of yttrium in alumina is <10 ppm even at temperatures approaching the melting point of alumina.
Thermodynamic Model for Nonstoichiometric Ionic Phases — Application to CeO2–x
Authors: HILLERT MATS , JANSSON BO
Published: March 2005

A two‐sublattice model for reciprocal solid solutions is applied to an ionic phase with vacancies on the anion sublattice, assuming that there are some cations with a lower valency than normal. The model is applied to CeO2–x, where x can take values up to 0.3. Experimental data on Po2, as a function of temperature and composition can be well represented by this model, if interactions are described by two parameters, corresponding to a regular and a subregular solution parameter.
Creep Behavior of Single Crystals of Vanadium‐Doped Forsterite
Authors: RICOULT D. L. , KOHLSTEDT D. L.
Published: March 2005

Vanadium‐doped forsterite single crystals have been crept at atmospheric pressure, at temperatures ranging from 1571 to 1923 K under controlled oxygen partial pressure, po2. In the absence of an oxide buffer, the creep strength, the activation energy (550 ± 100 kJ/mol), the stress exponent (3.5 ± 0.5), and the po2 exponent (1/8 to 1/4) for this material are similar to those for unbuffered iron‐bearing olivine. At po2= 10‐11 MPa and T= 1773 K, the strength of vanadium‐doped forsterite is slightly larger than that of undoped forsterite.
Mechanical Failure Characteristics of Ceramic Multilayer Capacitors
Authors: McKinney K. R. , Rice R. W. , Wu C. Cm.
Published: March 2005

The results of both uniaxial and biaxial flexure as well as toughness testing on actual commercial ceramic capacitor samples are reported. Necessary procedural adjustments are outlined for miniaturizing the applied‐moment double‐cantilever‐beam test to accommodate these small samples. Strength and toughness testing showed that the metal electrodes lowered the fracture toughness and that the metal‐ceramic interface was a preferred fracture path for crack propagation parallel to the electrodes. However, toughness did not clearly depend on crack propagation parallel or perpendicular to the electrodes, nor with flexural strengths. Flexural strengths were 0 to 40% lower, with the electrodes perpendicular to the tensile surface vs. parallel to the tensile surface. Fractures initiated from machining (or impact) flaws, or voids of various sizes, shapes, and locations, thus explaining the poor correlation between strength and toughness. Biaxial flexure tests of dielectric specimens of various sizes indicate that such a test could be scaled down and “calibrated” for actual testing of capacitors; e.g., a decrease in strength with increasing specimen thickness to support diameter ratio is indicated.
Thermochemical Analysis of the Stability of Continuous “SiC” Fibers
Authors: Luthra Krishan L.
Published: March 2005

Continuous “SiC” fibers manufactured at present contain Si, C, O, and N, with an excess of free carbor. Thermodynamic calculations show that these fibers are inherently unstable when exposed to high temperatures. The fiber composition is expected to change, irrespective of the environment that it is exposed to, whether gaseous or condensed. The stability can be improved by replacing the free carbon with an excess of free silicon.
Subsolidus Phase Relationships in Si3N4–AlN–Rare‐Earth Oxide Systems
Authors: Huang Zehn‐Kun , Tien Tseng‐Ying , Yen Tung‐Sheng
Published: March 2005

The subsolidus phase relationships in Si3N4–AlN–rare‐earth oxide (Me2O3 where Me=Nd, Sm, Gd, Dy, Er, and Yb) systems were studied. Solid‐solution regions with the α‐Si3N4 structure were delineated along the Si3N4–“Me2O3:9AIN” joins for all of the rare‐earth oxide systems studied. The solubility limits of these solid solutions increased with decreasing size of the rare‐earth ions.
Elastic Moduli of Silica Gels Prepared with Tetraethoxysilane
Authors: MURTAGH MARTIN J. , GRAHAM EARL K. , PANTANO CARLO G.
Published: March 2005

The elastic moduli of several organometallic silica gels were measured using pulse‐superposition interferometry (PSP). A series of gels were prepared under acid‐catalyzed conditions where the molar ratio of water to tetraethoxysilane (TEOS) in the sol was varied (4:1, 12:1, 16:1, and 24:1). It was found that the elastic moduli varied systematically with the hydrolysis conditions used to prepare the gels, as well as with the relative humidity used to equilibrate the gels before and during the PSP measurement. The experimental PSP data for the gels were evaluated using a composite model (matrix plus pores) and then the elastic moduli of the gel matrix were determined by applying a correction for porosity based on a self‐consistent‐scheme (SCS) approximation. The results show that the elastic moduli of the gel matrix also exhibit a systematic dependence upon the preparation conditions, but they always fall below the corresponding values for fused silica. Even when excess water Was used to hydrolyze the TEOS, this did not lead to a fully polymerized silica matrix structure. It is suggested that the lowered matrix moduli values are due to the presence of residual hydroxy and ethoxy groups which are internal to a polymeric structure.
Investigations of NiO‐CuO Solid Solutions Using Transmission Electron Microscopy: I, Tweed Microstructure
Authors: DAVIES P. K.
Published: March 2005

Compositions in the apparent one‐phase rock salt solid solution region of the system (NixCu1–x)O have been investigated using transmission electron microscopy. Diffraction and imaging experiments were conducted on compositions ranging from ×= 0.65 up to ×= 0.95. All the samples showed strong “tweed” contrast characterized by striations parallel to the traces of (110) planes. Diffraction patterns also exhibited <110> diffuse streaking associated with the tweed effect. It is proposed that the tweed microstructure is due to strain contrast resulting from strain centers associated with the formation of a tetragonally distorted phase. The observation of this complex microstructure supports previous thermodynamic predictions of nonideal behavior in this system.
Structural Studies of Gels and Gel‐Glasses in the SiO2‐GeO2 System Using Vibrational Spectroscopy
Authors: MUKHERJEE SHYAMA P. , SHARMA SHIV K.
Published: March 2005

GeO2 gel and gels in the SiO2‐GeO2 system synthesized by the hydrolytic polycondensation of metal alkoxides have been studied by infrared and Raman spectroscoptic techniques. The molecular structures, hydroxyl contents, and crystallinity of gels and gel‐glasses in relation to the thermal history and GeO2 concentration were investigated. The binary compositions having up to 70 mol% GeO2 were examined.
Strength Measurement of Optical Fibers by Bending
Authors: MATTHEWSON M. JOHN , KURKJIAN CHARLES R. , GULATI SURESH T.
Published: March 2005

A bending technique for the strength measurement of glass fibers is described and an analysis is presented which determines the effective tested length as a function of the statistical parameters which describe the fracture properties of the fiber. The analysis is used to compare strength data determined in both tension and bending for various representative fibers. It is found that the tensile strength cannot be predicted from the strength in bending and vice versa because the tested lengths differ by at least 3 orders of magnitude. Thus, while bending does not replace tension as a measurement technique, it does provide additional valuable information about the flaw size distribution.
Nitrogen‐Nitride Equilibria in Molten Uranium‐Thorium‐Tin Alloys
Authors: SLIVINSKY SANDRA H. , PARLEE NORMAN A.D.
Published: March 2005

Work has been done on the molten ternary system U‐Th‐Sn to provide a selective nitriding separation scheme. The nitride formation reaction has been studied as a function of temperature (1490° to 1700°C) and weight percent of U/Th in Sn, using a Sievert's‐type apparatus. Nitride formation has been demonstrated in a U‐Th‐Gd system.
Observation of Coherent Perovskite Particles in Growing Chromia Films
Authors: Przybylski Kazimierz , Garratt‐Reed Anthony J. , Yurek Gregory J.
Published: March 2005

A Co–45 wt% Cr alloy that was implanted with 2×1016 yttrium ions/cm2 was oxidized at 1000°C in pure oxygen for 25 h. The chromia film that formed on the surface of the alloy had a grain size of 200 to 300 nm. Yttrium was segregated to the chromia grain boundaries, and both coherent and incoherent particles of YcrO3 (<2 vol% of the oxide film) were present in the chromia film.
Effect of Step Size in Incremental Loading Tests
Authors: Ullner Christian , Gehrke Eckhard
Published: March 2005

Using the crack‐growth model, the deviation of real fracture stress from the stressing level measured by stepwise incremental loading with three starting modes is calculated. For both static and dynamic fatigue, the relative error depends only on the relative increment size and the crack‐growth parameter, n. The usefulness of stepwise incremental loading for strength testing can be confirmed.
Fractal Dimensions of Model Particle Packings Having Multiple Generations of Agglomerates
Authors: Onoda George Y. , Toner John
Published: March 2005

We examine a simple model for a powder having multiple generations of agglomerates. Over the size range over which the generations span, this structure is shown to be fractal. An equation expressing the fractal dimension for any Euclidean dimension is derived.
Elevated‐Temperature Creep of Silicon Carbide‐Aluminum Nitride Ceramics: Role of Grain Size
Authors: Jou Zuei Chown , Kuo Shih‐Yee , Virkar Anil V.
Published: March 2005

Samples containing 50 mol% SiC and 50 mol% AIN were fabricated to neartheoretical density by hot‐pressing in graphite dies in N2 atmosphere. Grain size was varied by varying the hot‐pressing conditions. Bar‐shaped samples cut from the billets were subjected to creep deformation in four‐point bending. Creep was found to depend upon the grain size with coarse‐grained material exhibiting lower creep rate. The stress exponent was ∼2.0.
Effect of Microstructures on the Ionic Conductivity of Ceria‐Calcia Oxides
Authors: Eguchi Koichi , Kunishaki Toshiya , Arai Hiromichi
Published: March 2005

Ceria‐calcia, (CeO2)1‐x(CaO)x, at x<0.23 consisted of a homogeneous solid solution; however, the calcia phase precipitated at × >0.23. The ionic conductivity and transference number of oxygen for CeO2‐CaO solid solution were high at low temperature and were maintained even when calcia was added in amounts exceeding the solubility limit. Crystals of precipitated CaO exist as small granules which are dispersed in the continuous matrix of CeO2‐CaO solid solution.
Preparation of Perovskite Pb(Mg1/3Nb2/3)03 Using Pb3Nb208 and MgO
Authors: Guha J. P. , Anderson H. U.
Published: March 2005

The synthesis of perovskite Pb(Mg1/3Nb2/3)O3 from an equimolar mixture of Pb3Nb208 and MgO was studied by solid‐state reaction techniques. An addition of 1 wt% excess MgO to the stoichiometric composition enhances the formation of the cubic perovskite phase. The absence of free PbO in the initial starting materials minimizes the volatilization loss during firing, thereby reducing the possibility of any compositional change and resulting in a substantial improvement of the perovskite phase purity over the conventional mixed‐oxide processing.
Thermodynamic Assessment of the System CoO‐MnO
Authors: BERGMAN BILL , ÅGREN JOHN
Published: March 2005

The thermodynamic properties of pure CoO and CoO‐MnO solutions have been analyzed in terms of thermodynamic models applying various experimental data. Expressions for the Gibbs energy of the individual phases have been obtained and the phase diagram is calculated. It reveals a homogeneous solid solution at temperatures above room temperature but a miscibility gap at very low temperatures.
Viscous Flow vs Phase Separation During Calorimetric Analysis of Fluoride Glasses
Authors: Drehman Alvin J.
Published: March 2005

Differential scanning calorimeter traces of heavy‐metal fluoride glasses can display an endothermic feature between the glass transition and the onset of crystallization. It is shown that this feature can be the result of viscous flow occurring during heating and is not necessarily a second glass transition, attributable to the coexistence of two vitreous phases.
Grain‐Boundary Cavitation and Bloating of Isostatically Hot‐Pressed Magnesia‐Partially‐Stabilized Zirconia on Air Annealing
Authors: HOGG C. L. , STRINGER R. K. , SWAIN M. V.
Published: March 2005

Commercially sintered magnesia‐partially‐stabilized zirconia was densified to near theoretical density by isostatic hot‐pressing at 200 MPa and 1700°C in argon. Subsequent air annealing above 1100°C resulted in bloating of the material due to grain‐boundary cavitation. Mass spectrometry of crushed samples detected the evolution of CO2 and possibly CO on annealing; the hot‐pressed material showed a sudden gas evolution above 1400°C. Preliminary Auger and ESCA analysis identified the presence of carbon as graphite and an undefined carbide in both the sintered and the hot‐pressed material.
Alumina Microstructural Sample Preparation Using a Borate Glaze
Authors: Scott Curtis , Hill Susan , Hosmer Kevin
Published: March 2005

A method was developed for preparing alumina surfaces for microstructural analysis. Samples were polished using a sodium borate glaze, which produced a smooth surface with the grain boundaries accented.
Analysis of Sintering of a Composite with a Glass or Ceramic Matrix
Authors: Bordia Rajendra K. , Raj Rishi
Published: March 2005

A recently developed theory for sintering of bimodal powders is applied to a composite where the matrix is either a glass or a ceramic. The filler phase is assumed to be rigid and nonsintering. It is shown that glass‐matrix composites should have predictable sintering behavior which follows the rule of mixtures, but ceramic‐matrix composites are expected to be more difficult to sinter, and their sintering behavior may deviate considerably from the rule of mixtures, even at low concentrations of the filler phase.
Mixed‐Mode Fracture of Ceramics in Diametral Compression
Authors: SHETTY D.K. , ROSENFIELD A.R. , DUCKWORTH W.H.
Published: March 2005

Mixed‐mode fracture of a glass‐ceramic and an alumina ceramic from inclined Knoop indenter flaws was studied in diametral compression and four‐point‐bend tests. In annealed specimens the directions of extension of the cracks and mode I and mode II stress‐intensity factors at fracture were analyzed and compared to the predictions of a maximum crack‐tip hoop stress theory. Knoop flaws in all cases extended in directions normal to the principal maximum tension rather than in the direction of maximum hoop stress near the crack tip. Mixed‐mode fracture envelopes assessed in experiments, particularly with the diametral‐compression test, showed significant deviation to higher KII values relative to the fracture‐mechanics predictions. As a consequence, an apparent KIIc value assessed in the diametral‐compression test was approximately twice the value of KIc.
Raman and Fourier Transform Infrared Spiectroscopy of CnO‐PbO‐SiO2 Glasses
Authors: van ROODE M. , HUANG T.‐H. , HECHLER J.J. , COLE K.C.
Published: March 2005

The structures of glasses in the system CuO‐PbO‐SiO2 have been investigated by Raman and Fourier transform infrared (FTIR) spectroscopy. Glasses of compositions represented by 2xCuO.(1 – x) PbO.(l – x)SiO2 (x = 0 to 0.1) and 3xCuO.(l – x)PbO.2(l – x)SiO2(x=0 to 0.1) may contain up to 2 and 4 mol% CuO, respectively, without significant changes to the silicate network of the copper‐free glasses. The incorporation of 10 mol% CuO in these glasses alters the Raman and FTER spectra of the copper‐free glasses significantly. The observed changes were attributed to depoly‐merization of metasilicate and higher polymerized silicate groupings through the creation of nonbridging Si‐O− groups hi the silicate network.
Creep of Mn1‐δO
Authors: Routbort Jules L. , Castaing Jacques , Goretta Kenneth C.
Published: March 2005

Constant‐load creep tests have been performence nonstoichiometnc (100) oriented MnO single crystals between 900° and 1400°C. Tests were conducted under a controlled oxygen partial pressure to ensure that dislocation‐climb recovery was controlled by diffusion of either oxygen vacancies (low pO2) or oxygen interstitials (high po2). Within experimental error, the activation energies and the stress exponents are independent of oxygen partial pressure. The activation energy measured for T≤1000°C is about half of that measured for higher temperatures.
Fatigue Weakening of Optical Fiber
Authors: Duncan William J.
Published: March 2005

The weakening of optical fiber under static strain was measured in water and as a funetion of time in air. The weakening did not fit the crack‐growth model of fatigue nor did it follow the same path in air and water. However, the size of the H2O/D2O isotope effect suggested that fatigue could still result from a silica‐water reaction.
Chemical Durability of Fluoride Glasses: I, Reaction of Fluorozirconate Glasses with Water
Authors: SIMMONS CATHERINE J. , SIMMONS JOSEPH H.
Published: March 2005

The chemical durability of five flouarozirconate glass compositions was studied. Measurements of leachant composition and solution chemistry by plasma emission spettroscopy, pH, and fluoride analysis are reported. Changes in surface structure were monitored by scanning electron microscopy, electron‐probe X‐ray analysis, and X‐ray diffraction. The modifer additives with high aqueous solubility (A1F3, NaF, LiF, PbF2) exhibited the highest leach rates with ZrF4, BaFs2, and LaF3 exhibiting lower rates. The leaching order of Zr > Ba > La was maintained for all samples. The leaching process consists of the dissolution of the glass matrix, leaving a thick and porous layer containing Zr, Ba, La, and molecular water. Hydroxylation of the Zr species to form a hydroxyfluoride complex in solution dominated a decrease in pH to moderately acidic values. The resulting increase in component solubility (particularly zirconium fluoride) in the acidic solutions accelerated the glass dissolution rate and demonstrated that, if no buffer is present to avert the pH drift, the chemical durability of these glasses in aqueous environments is extremely poor, being roughly equivalent to that of Na2O 2SiO2.
Effect of Fluorine and Magnesium on the Polymorphism of Tricalcium Silicate: A New Fluorine‐Containing Tricalcium Silicate Superlattice
Authors: PÉREZ‐MÉNDEZ MERCEDES , GROVES G. W. , FAYOS JOSÉ
Published: March 2005

There is evidence both by XRPD and by TEM electron diffraction of the presence of a new tricalcium silicate phase containing fluorine with triclinic cell parameters a= 2.32(7), b= 0.71(3), c= 1.28(3) nm, α= 106.5(3), β= 90(1), γ= 118(1)°. It is a superlattice of the rhombohedral C3S, whose structure is probably deformed by the fluorine/oxygen substitution plus some calcium vacancies, the deformation being nevertheless smaller than that found in the triclinic polymorph of pure C3S. Magnesium proves to have an effect additional to that observed for fluorine probably because it fixes the fluorine to the silicate lattice.
Shear, Uniaxial, and Biaxial Stress Relaxation Functions
Authors: REKHSON MICHAEL S. , REKHSON SIMON M.
Published: March 2005

Performance of approximate methods for computing uniaxial and biaxial stress relaxation functions is evaluated by comparison with the exact solutions. Equally good results are obtained by neglecting dilational relaxation and by assuming that the shear modulus is negligible compared to the bulk modulus.
Impact Fracture of Chemically Tempered Glass Helicopter Windshields
Authors: ABOU EL LEIL MAHMOUD M. , CAMARATTA FRANK A. , DIGENOVA ROCCO R.
Published: March 2005

Helicopter windshield glass with different degrees of chemical tempering was impact tested by firing spherical projectiles at velocities between 50 and 250 m/s. The residual tempering stresses were measured photoelastically and their values superimposed on the Hertzian impact stresses. Modified forms ol Auerbach's law1 were utilized to study the experimental results. Lower impact fracture strength and deviations from the modified relations were attributed to changes in surface Flaw distributions.
Activity‐Composition Relationships of the Solid Solution (Ti,Mo)O2 in the Temperature Range 1350 to 1600 K
Authors: PEJRYD LARS
Published: March 2005

The activities of MoO2 in the (Ti,Mo)O2 solid solution were measured at seven different compositions, using an emf method involving calcia‐stabilized zircoinih as solid electrolyte. In the temperature range studied, 1350 to 1600 K, the activities of MoO2 show a strong positive deviation from ideal behavior. In addition, the solvus of the TiO2‐MoO2 system was determined with the equilibration and quenching technique. The solvus maximum was found at T= 1420 ± 5 K and X(MoO2) = 0.85 ± 0.05.
Viscous Sintering under a Uniaxial Load
Authors: Scherer George W.
Published: March 2005

An analysis is presented for viscous sintering under a uniaxial load; numerical results are presented for compressive loads. The load increases the axial contraction rate, hut counteracts the radial contraction rate. When the load is similar in magnitude to the capillary stress driving sintering, the radius remains essentially constant as the body densifies. Following a suggestion by Bordia, the viscosity and sintering kinetics can be determined in one experiment by measuring the axial and radial shrinkages simultaneously.
Frictional Stress Evaluation along the Fiber‐Matrix Interface in Ceramic Matrix Composites
Authors: Fabera K.T. , Advani S. H. , Lee J. K. , Jinn J.‐T.
Published: March 2005

A finite element algorithm, developed for frictional comact problems, has been used to evaluate the shear stresses along the fiber‐matrix interface in a ceramic composite and the load point fiber displacements dining fiber compression. The induced peak shear stress and the shear stress gradient were found to increase with increasing coefficients of friction. Calculated fiber displacements asymptotically decayed to the perfectly bonded condition as the coefficient of friction was increased. The computed average interfacial shear stress showed remarkable agreement with recent experimental findings hi the SiC‐LAS system.
Thermomechanical Mismatch in Ceramic‐Fiber‐Reinforced Glass‐Ceramic Composites
Authors: BOROM MARCUS P. , JOHNSON CURTIS A.
Published: March 2005

The thermomechanical relationship between mullite and a lithium aluminosilicate (LAS) glass‐ceramic has been studied by a technique of bimaterial dilatometry. The viscoelastic behavior of LAS was found to result in a temperature Trvsl below the glass‐transformation temperature Tg at which the interfacial stresses between the materials undergo a reversal in sign. The effect of Trvsl on the high‐temperature mechanical properties of mullite or SiC fiber‐reinforced glass‐ceramic composites is discussed. It is suggested that fiber clamping by the matrix at temperatures between Trvsl and Tg contributes to the brittle, high‐temperature behavior of such composites.
Joining of Alumina Ceramic by Inducing Localized Reducing Conditions
Authors: Zdaniewski Wieslaw A. , Kirchner Henry P.
Published: March 2005

Alumina ceramics were joined by hot‐pressing with polystyrene or mica sheets at temperatures of 1250° or 1350°C. The polystyrene decomposed during hot‐pressing, creating reducing conditions in the joints which enhanced interfacial diffusion and bonding. Measured fracture toughness and flexural strength of such joints approached values for monolithic alumina. Joints prepared under similar conditions but without polystyrene showed much lower KIC and strength values.
Coating Films of 20B2O3·80SiO2 by the Sol‐Gel Method
Authors: Tohge Noboru , Matsuda Atsunori , Minami Tsutomu
Published: March 2005

Alkali‐free borosilicate films of 20B2O3. 80SiO2 (in mol%) have been prepared by the sol‐gel method. The transparency of these films was found to be very sensitive to the humidity of the atmosphere during the coating process. Transparent films were obtained only in a dry atmosphere. Measurements of IR spectra and load at scratch showed that these films were densified above 600°C.