bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics and Mechanism of Corrosion of SiC by Molten Salts
Authors: JACOBSON NATHAN S.
Published: March 2005

Corrosion of sintered α‐SiC under thin films of Na2CO3/CO2, Na2SO4/O2, and Na2SO4/SO3 was investigated at 1000°C. Chemical analysis was used to follow silicate and silica evolution as a function of time. This information couples with morphology observations leads to a detailed corrosion mechanism. In all cases the corrosion reactions occur primarily in the first few hours. In Na2CO3/CO2 case, rapid oxidation and dissolution lead to a thick layer of silicate melt in ∼0.25 h. After this, silica forms a protective layer on the carbide. In the Na2SO4/O2 case, a similar mechanism occurs. In the Na2SO4/SO3 case, a porous nonprotective layer of SiO2 grows directly on the carbidem and a silicate melt forms above this. In addition due to reaction of silicate with SO3 and SO2+O2. The reaction slows when the lower silica layer becomes nonporous.
Preparation and Sintering of Homogeneous Silicon Nitride Green Compacts
Authors: SHAW T.M. , PETHICA B.A.
Published: March 2005

Interactions between silicon nitride particles and hydroxide precipitates were investigated using electrophoresis measurements. Conditions under which stable suspensions of silicon nitride particles and flocculation and heteroflocculation of silicon nitride/hydroxide mixtures occur were Identified. On the basis of the observations, a method for producing uniform mixtures of silicon nitride powders and additive precipitates was formulated and used to produce green compacts of improved compositional homogeneity. The effect of the mixing process on the sintering of green silicon nitride compacts was investigated and compared to the sintering behavior of conventionally prepared green compacts. The results show that the improved homogeneity obtained using the precipitation mixing process leads to enhanced sintering of the green compacts.
Development of a West Valley Nuclear Waste Glass by Empirical Modeling
Authors: CHICK L. A. , LOKKEN R. O. , STRACHAN D. M. , BOWEN W. M.
Published: March 2005

The first full‐scale conversion of high‐level commercial U.S. nuclear wastes to a glass suitable for long‐term storage and disposal will be conducted at West Valley, Now York. The development of a nuclear waste glass for this demonstration project utilized a statistically designed study that led to empirical models of melt viscosity, electrical conductivity, crystallinity, and chemical durability as functions of glass composition. The method by which the candidate glass composition was chosen using these models is described, and the adjustments to the candidate composition in response to the evolving plant design are discussed.
Air Oxidation of UO2 Fuel Fragments at 175° to 400°C
Authors: Hastings Ian J. , Rose David H. , Kelm John R. , Irvine David A. , Novak J.
Published: March 2005

The air oxidation at 175° to 400°C Of unirradiated and irradiated UO2 fuel fragments was characterized by apparent activation energies of 140 ± 10 and 120 ± 10 kJ/mol, respectively. There was a small enhancement in the rate of weight gain for irradiated fragments compared with unirradiated fragments up to ∼300°C; from 300° to 400°C there was no significant difference in oxidation rate. Air availability had a strong effect on rate of weight change above 300°C.
Twin‐Related Tetragonal Variants in Yttria Partially Stabilized Zirconia
Authors: Ishizawa Nobuo , Saiki Atsushi , Yagi Takeshi , Mizutani Nobuyasu , Kato Masanori
Published: March 2005

Crystals of yttria partially stabilized zirconia were grown by the arc‐image floating‐zone technique and studied by transmission electron microscopy. Crystals annealed at 1700°C consist of tetragonal precipitates and a cubic matrix. The platelike domains in a precipitate are twin‐related tetragonal variants stacked alternately parallel to the (011) twin plane. The axial relations between the tetragonal precipitate and the cubic matrix are [100]tetragonal|[100]cubic, [011]tetragonal|[011]cubic.
Topotactic Growth of β‐Alumina on α‐Alumina
Authors: Susnitzky D. W. , Carter C. B.
Published: March 2005

Thin foils of polycrystalline α‐alumina were reacted with a potassium‐rich vapor at ≤900°C. Potassium β‐alumina formed along α‐alumina grain boundaries and protruded from holes in the foils. Conventional transmission electron microscopy was used to analyze the α‐alumina/β‐alumina phase boundary for possible orientation relations.
Phase Relations in the Pseudobinary System Na2TiSi4O11‐Na2Ti2Si2O9
Authors: Hollabaugh Curtis L. , Carr William H.
Published: March 2005

The quenching technique was used to study subliquidus and subsolidus phase relations in the pseudobinary system Na2 Ti2Si2 O11‐Na2 Ti2 Si2 O9. Both narsarukite (Na2TiSi4O11) and lorenzenite (Na2Ti2Si2O9) melt incongruently. Narsarsukite melts at 911°±°C to SiO2+liquid, with the liquidus at 1016°C. Lorenzenite melts at 910°±5°C to Na2 Ti6 O13+liquid; Na2 Ti6 O13 reacts with liquid to form TiO2 and is thus consumed by 985°±5°C. The liquidus occurs at 1252°C.
New Compound in the System SrO‐Al2O3
Authors: Yamaguchi Osamu , Narai Akira , Shimizu Kiyoshi
Published: March 2005

A new compound, 12SrO·7Al2O3, is formed from an amorphous material prepared by the simultaneous hydrolysis of strontium and aluminum alkoxides. It has a cubic unit cell with a =1.2325 nm. The structure contains tetrahedral AlO4 groups and octahedral AlO6 groups. This compound decomposes into 3SrO·Al2O3 and SrO·Al2O3 at higher temperatures.
Compositionally Dependent Si 2p Binding Energy Shifts in Silicon Oxynitride Thin Films
Authors: BROW RICHARD K. , PANTANO CARLO G.
Published: March 2005

The Si 2p binding energies measured from a series of silicon oxynitride thin films are related to the nitrogen contents of the films using a simple Pauling charge distribution model. The linear relation found between the binding energy and the calculated charge is expected if Si–N bonds replace Si–O bonds as the nitrogen content of the films is increased.
Dynamic Compaction of Cubic Boron Nitride Powders
Authors: Akashi Tamotsu , Sawaoka Akira B.
Published: March 2005

Compacts of cubic boron nitride with 94% of theoretical density and a Vickers microhardness of 30.3 GPa were produced from coarse c‐BN powder by a shock compaction technique. The density and microhardness of these compacts depend strongly on the grain size of the starting powders.
Density of Molten Sodium Aluminosilicates
Authors: STEIN DANIEL J. , STEBBINS JONATHAN F. , CARMICHAEL IAN S.E.
Published: March 2005

In order to address controversial discrepancies among earlier measurements, the densities of eight sodium aluminosilicate melts were measured at 1100° to 1550°C. The double‐bob Archimedean method was used; it is the most accurate available technique and one not used in previous density measurements in this system. The results of a regression of molar volume with temperature and composition in terms of oxides are presented. The variation of molar volume with composition is linear within the range of the data. The standard error of the fit is < 0.2%.
Investigation of Foaming in Liquid‐Fed Melting of Simulated Nuclear Waste Glass
Authors: GOLDMAN D.S. , BRITE D.W. , RICHEY W.C.
Published: March 2005

Melt foaming in alkali‐iron borosilicate glasses considered for nuclear waste disposal was investigated to identify the causative reactions and stabilizing mechanisms. Foaming is attributed to the release of oxygen and water vapor from the melt. The oxygen is suggested to originate from oxidation‐reduction reactions of species other than iron. Foaming problems are largely solved under reducing conditions, which result in less stable foams. The results suggest that a greater proportion of water vapor is released into the foam under more reducing conditions. The water destabilizes the foam by viscosity or surface tension effects and causes the bubbles to rupture on the melt surface.
Zirconia Particle Coarsening and the Effects of Zirconia Additions on the Mechanical Properties of Certain Commercial Aluminas
Authors: WITEK S. R. , BUTLER E. P.
Published: March 2005

The effects of ZrO2 additions on the mechanical properties of four commercial aluminas have been studied, and the changes in intergranular and intragranular ZrO2 particle sizes during aging have been determined for one of the aluminas. In this ceramic, the intercranular and intragranular ZrO2 particles coarsen obeying t1/2 and t1/3 kinetics, respectively. Changes in strength of the aluminas with additions of ZrO2 are shown to be related to changes in the Al2O3 matrix microstructure. Differences in toughness of the resulting composites are explained in terms of the different size and morphology of the intergranular ZrO2 particles and the operation of several toughening mechanisms, with transformation toughening a relatively minor contributor.
Effects of Postsintering Hot Isostatic Pressing on the Strength of an Aluminosilicate Ceramic
Authors: Ohira H. , Bradt R. C.
Published: March 2005

Postsintering treatments of annealing and hot isostatic pressing were applied to an aluminosilicate ceramic body. The strength parameters and the structure were monitored, and their changes were related to the reduction of surface residual compressive stresses. It is concluded that property improvements to ceramic bodies through postsintering hot isostatic pressing treatments are material‐specific, depending on the availability of appropriate processes and mechanisms for improvement or change.
Humidity Sensitive Electrical Conduction of ZnO‐Ni1‐xLixO Heterocontacts
Authors: Marra Robert A. , Nakamura Yoshinobu , Fujitsu Satoru , Yanagida Hiroaki
Published: March 2005

Heterocontacts of p‐n semiconductors were produced by mechanically pressing together polished surfaces of ZnO and Ni1‐xLixO sintered pellets. The electrical conductivity of the heterocontacts was highly sensitive to humidity. The sensitivity to changes in humidity was dependent on the surface finish of the pellets, the lithium dopant level in the NiO ceramic, and the porosity of the ZnO ceramic.
Effect of Small Concentrations of Gallium Oxide on the Structure of Sodium Silicate Glasses
Authors: Lapp Josef C. , Shelby James E.
Published: March 2005

The glass transformation temperatures and de electrical conductivities of sodium silicate glasses with low‐level gallia additions have been measured. The composition/property relationships observed in these glasses are different from those observed with larger gallia additions. These trends are discussed in terms of structural models proposed for these glasses.
Magnetoplumbite‐Type Compounds: Further Discussion
Authors: Morgan Peter E. D. , Miles Jamie A.
Published: March 2005

Hexagonal magnetoplumbites are probably more common as minerals than has been appreciated. Over several years, we have synthesized a wide variety of these compounds to demonstrate their flexible cation substitution crystal chemistry, which is of importance for their consideration as potential ceramic radwaste hosts.
Microstructure and Evolution of a Barium Fluorozirconate Crystal in a ZrF4‐BaF2‐LaF3‐AlF3‐NaF Glass
Authors: LU GRANT , BRADLEY JOHN P.
Published: March 2005

The evolutionary growth of one type of crystal in our ZiF4‐BaF2‐LaF3‐AIF3‐NaF glasses is examined. The crystal was found to be a complex structure consisting of five coexisting barium fluorozirconate phases. In ihe initial very low bi‐refringent crystal, the principal phase was β‐ZrF4‐BaF2. Later crystal growth occurred on top of the initial crystal, and was identified as β‐2ZrF4·BaF2. A strong scattering center was found at the center of some of the crystals and this was identified as elemental platinum.
Crack Branching as a Mechanism of Crushing During Grinding
Authors: CONWAY JOSEPH C. , KIRCHNER HENRY P.
Published: March 2005

A crushing model, based on a crack‐branching mechanism of crushing, an elastic analysis of the stress distribution, and a critical stress, intensity factor criterion for the extent of crack propagation, was used to estimate the extent of crushing under a diamond point subjected to an inclined load. The depths of the crushed region were compared with the groove depths formed in several materials during single‐point grinding under similar loading conditions. Good agreement was observed between the absolute values of the groove depths and crushing depths, and the load dependence of these values for soda‐lime glass. In the case of silicon nitride and silicon carbide, there was good agreement between the calculated and the experimental load dependencies but the absolute values of the experimentally determined groove depths were somewhat smaller than the calculated crushing depths.
A Simple Model for the Deformation Behavior of Tantalum Carbide
Authors: HOFFMAN MARK , WILLIAMS WENDELL S.
Published: March 2005

The high‐temperature hardness of tantalum carbide is linked to the presence of extended stacking faults. Suzuki hardening limited by carbon diffusion is presented as the mechanism which distinguishes tantalum carbide from other carbides with the same structure. Softening is predicted to occur at temperatures near those observed experimentally.
Redistribution of Aluminum Ions During Processing of Sialon Ceramics
Authors: BONNELL D. A. , RÜHLE M. , TIEN T.‐Y.
Published: March 2005

Precise determinations of the variation in Al concentration in β‐sialon grains of the garnet and cordierite sialon systems were made by means of quantitative energy‐dispersive X‐ray analysis in an analytical electron microscope. Different signs of the concentration gradients in the grain indicate differences in secondary crystallization mechanisms, while Al distributions with respect to grain size indicate a changing glass‐silicon nitride compatability during crystallization. The technique was also applied to the glassy grain‐boundary phase allowing the determination of the glass‐forming region of the cor‐dierite‐sialon system. A detailed evaluation of errors in analytical transmission electron microscopy (AEM) is described.
Reliability of Brittle Materials in Thermal Shock
Authors: BROCKENBROUGH JOHN R. , FORSYTHE L. EDGAR , ROLF RICHARD L.
Published: March 2005

The fracture‐of alumina disks subjected to thermal shock is predicted from Weibull parameters derived from isothermal three‐point‐bend tests. Both the shear‐insensitive Batdorf model and the principle of independent action model are used to compare results from three‐point‐benr1 and isothermal biaxial strength tests to results from thermal fracture tests. It is found that the shear‐insensitive Batdorf model gives good agreement between mechanical tests and fracture of the thermally shocked disks.
High‐Pressure Hot Isostatic Pressing of Synthetic Mica
Authors: Hattori Takeo , Yoshimura Masahiro , Sōmiya Shigeyuki
Published: March 2005

Powder compacts of synthetic mica (fluorphlogopite) encapsulated in a boro‐silicate glass tube were isostatically hot‐pressed using high‐pressure‐high‐temperature hot isostatic pressing equipment with Ar gas and a Mo heater. Synthetic mica was isostatically hot‐pressed, while retaining the composition and structure of the starting material, to 96.8% of theoretical density without additives at 500 MPa and 700°C for 3 h.
Origin of Strength Increase of Abraded or Indented Glass upon Annealing
Authors: Tomozawa Mlnoru , Hirao Kazuyuki , Bean Paul E.
Published: March 2005

The mechanical strength of soda‐lime and boresilicate glass rods with an extended crack was found to increase upon annealing. Since the residual stress near the extended crack tip is small, this strength increase indicates that crack tip blunting is taking place.
Pore‐Grain Boundary Configurations in Lithium Fluoride
Authors: WANG ZHANYI Y. , HARMER MARTIN P. , CHOU YE T.
Published: March 2005

A high‐angle tilt boundary of LiF with attached pores was made to migrate under the influence of temperature and an imposed boundary curvature. The boundary was fractured along the boundary plane to observe its leading and trailing faces by stereo scanning electron microscopy. A detailed analysis of the attached pore shape and pore drag mechanism has been made. The quasi‐equilibrium pore shape developed by pores detached from the boundary was used to determine the orientation dependence of surface energy in LiF.
Experimental‐Statistical Method for Investigation of Multicomponent Yttrium Garnet Systems
Authors: KOJOUHAROFF V. , IONCHEV H.
Published: March 2005

In the present work, some problems are discussed arising in the construction and study of a mathematical model describing the synthesis of multicomponent yttrium garnets with predetermined microwave parameters. To construct the model, the following formula was used for Ca‐V YIG substituted with In and Cr: Y3–2xCa2xFe5–(x+y+z) Iny CrzVxO12. For this purpose, ferrogarnets were synthesized differing in x, y, and z with their values chosen so as to obtain real roots of a set of equations of the type Yk=ΣBiXi+Σ Bij XiXj+Σ BijkXiXjXk, where Yk are the ferrogarnet microwave properties. The graphical presentation of these solutions as triple diagrams is a very convenient way of obtaining ferrogarnets with predetermined microwave characteristics. On the other hand, the possibility is created of mathematically predicting and determining the influence of the different components on the yttrium ferrogarnet parameters as a function of their concentration.
Plastic Deformation and Solid‐Solution Hardening of Y2O3‐Stabilized ZrO2
Authors: DOMINGUEZ‐RODRIGUEZ A. , LAGERLöF K. P. D. , HEUER A. H.
Published: March 2005

Fully stabilized cubic ZrO2 single crystals containing various Y2O3 concentrations were deformed at 1400°C in air. The orientation chosen favored (001)(110) slip, which was confirmed by slip‐trace analysis and transmission electron microscopy; (111)(110) slip could also be activated. The yield and flow stresses increased with increasing Y2O3 concentration, and stress‐strain curves were dominated by a region of zero work hardening from very small strains for all compositions.
Characterization of Synthetic and Naturally Occurring Clays by 27Al and 29Si Magic‐Angle Spinning NMR Spectroscopy
Authors: Komarneni Sridhar , Fyfe Colin A. , Kennedy Gordon J. , Strobl Harold
Published: March 2005

Magic‐angle spinning nuclear magnetic resonance (MASNMR) spectroscopy (27Al) detected the coordination of Al in clays containing as little as 0.26% Al2O3. The 29Si MASNMR of fluorphlogopite showed three distinct Si chemical environments which suggested short‐range ordering. Synthetic laponite and mica‐montmorillonite showed broad 29Si resonances indicative of short‐range disorder. A saponite showed four 29Si resonances. Considerable insight into the short‐range ordering of clays can be gained by 27Al and 29Si MASNMR.
Oxide Reduction in NiO‐Containing Solid‐Solution Systems During Transmission Electron Microscopy
Authors: Davies Peter K. , Mackinnon Ian D. R.
Published: March 2005

The effects of electron irradiation on NiO‐containing solid solution systems are described. Partially hydrated NiO solid solutions, e.g., NiO‐MgO, undergo surface reduction to Ni metal after examination by TEM. This surface layer results in the formation of moire interference patterns.
High‐Pressure Transformation Toughening: A Case Study on Zirconia
Authors: Block Stanley , Piermarini Gasper J. , Hockey Bernard J. , Lawn Brian R. , Munro Ronald G.
Published: March 2005

Transformation‐toughened zirconia compacts have been produced using a pressure‐induced phase of zirconia as the toughening agent. The high‐pressure phase is retained metastably after compaction at 8.6 GPa and sintering at temperatures as low as 250°C. High‐pressure processing offers potential for new transformation‐toughening phases in other ceramic materials.
Formation and Crystallization of Yttrium Aluminosilicate Glasses Containing Calcium Oxide
Authors: Makishima Akio , Kubo Hajime , Shimohira Takajjro
Published: March 2005

Formation of yttrium aluminosilicate glasses containing calcium oxide from batches melted at 1550°C was investigated. Densities and thermal expansion coeflcients were measured for some glasses. In a specific compositional region, crystals with a needlelike habit were observed in the glass matrix. A crystal in the form of a tubular hexagonal prism was identified as Ca4Y60(Si04)6.
Elastic‐Plastic Contact Damage in a Lead Lanthanum Zirconate Titanate
Authors: PRICE JAMES J. , VARNER JAMES R.
Published: March 2005

Spherical indenters were used to produce elastic‐plastic contact damage in a lead lanthanum zirconate titanate (PLZT) under conditions of quasi‐static and impact loading. The extent of radial cracking produced under both loading conditions showed good correlation with the response predicted by an earlier fracture mechanics analysis for quasi‐static conditions. Calculated radial crack lengths corresponding to conditions of impact loading exhibited excellent agreement with experimentally measured values. The dynamic hardness of the PLZT was determined to be ∼ 1.5 times the quasi‐static hardness. Differences in the radial crack lengths produced under the two loading conditions were attributed primarily to this difference in hardness response.
Occurrence and Distribution of Boron‐Conitaining Phases in Sintered ş‐Silicon Carbide
Authors: MORE K.L. , CARTER C.H. , BENTLEY J. , WADLIN W. H. , LaVANIER L. , DAVIS R. F.
Published: March 2005

A variety of optical and analytical instruments have been employed to observe and characterize the mlcrostructure and composition of the B‐containing phases which occur in sintered α‐SiC as a result of either their use as a nensification aid or that which evolves as a result of annealing well below the sintering temperatures. The former have been identified as B4C containing a small amount of Si. The latirr occur as ∼20‐nm precipitates which have also been tentatively identified as B4C and are believed to contain trace quantities of Si. No B phase was observed on the SiC grain boundaries; furthermore, the precipitate formation was not enhanced by the application of stress.
Strengthening of Alumina by Reactions with Silicon Film on the Surface and Effects of Ion Irradiation
Authors: Noda Shoji , Doi Haruo , Hioki Tatsumi , Kawamoto Jun—ichi , Kamigaito Osami
Published: March 2005

Deposition of Si film on sintered alumina, followed by annealing at 1673 K in air, increased the flexural strength by ∼28%. Mullite formation on the surface was confirmed by X–ray diffraction analysis. Ion irradiation of the Si/alumina interface, followed by annealing, produced anorthite but not mullite, and the flexural strength also increased by ∼35%. Thermal expansion mismatch between surface compounds and the alumina body may be responsible for the strengthening.
Superplastic Creep of Fine‐Grained BaTiO3 in a Reducing Environment
Authors: Carry Claude , Mocellin Alain
Published: March 2005

Commercially available BaTiO3 powders were hot‐pressed 15 min at 1250★C to yield dense (≥99.5% of theoretical), fine‐grained (∼0.45‐pun average) poly‐crystals. These were creep tested under compressive 5‐ to 60‐MPa applied stresses at 1150★ to 1250★C. True strains reaching ‐0.50 were achieved without significant damage or structural change in the material. The observed flow behavior and microstructures are consistent with siructural superplastit. ity being the dominant deformation mode under the present testing conditions.
Identification of α‐Alumina Surface Structures by Electron Diffraction
Authors: Susnitzky David W. , Carter C. B.
Published: March 2005

Single‐crystal thin foils of a‐alumina were annealed i:i air and examined by transmission electron microscopy. Weak reflections, which are kinematically forbidden for the a‐alumina unit cell, were obscrxed in selected‐area diffraction patterns obtained from foils prepared parallel to (0001), (1012), and (1120) planes. These reflections are interpreted as giving evidence for surface periodicities which differ from those expected for the simple termination of the bulk crystal.
Hydration Reactions in the System CaO‐SiO2‐CaF2
Authors: ODLER* IVAN , ABDUL‐MAULA SAMIR
Published: March 2005

The phases existing in the system CaO‐SiO2‐CaF2 were synthesized and their hydraulicity was determined. Out of these only the phase which corresponds to the formula Ca6–0.5xSi2O10‐xFx exhibited distinct hydraulic properties. The hydration rate of tricalcium silicate doped with CaF2 declined with increasing degree of doping, while its compressive strength—found at a given degree of hydration—increased. The stoichiometry and specific surface area of the formed hydrates were altered because of the presence of fluorine in the crystalline lattice.
Sol‐Gel‐Derived Soda Lime‐High Silica Glass
Authors: Varshneya Arun K. , Suh Nungil
Published: March 2005

Sols containing well‐mixed tetraethyl orthosilicate, sodium methylate (CH3ONa), and Ca metal dissolved in HCIO4 were hydrolyzed at low pH. After gelation, controlled drying, and subsequent firing at 600°C, the mixture yielded clear glass chunks. Glasses containing 85% to <100% SiO2, which otherwise are difficult to make by conventional melting techniques, could be made using this technique.
Steric Effects in Stress Corrosion Fracture of Glass
Authors: MICHALSKE TERRY A. , BUNKER BRUCE C.
Published: March 2005

Previous studies show that stress corrosion crack growth in glass is controlled by chemically enhanced crack tip bond rupture reactions. The brittle nature of fracture in glass suggests that the region where bond rupture reactions occur must be on the order of the atomic spacings in the material. Crack growth kinetics and zeolite diffusion data were used to determine the relation between molecular size and reactivity at the crack tip. Crack growth rates in silica glass were measured in the presence of a series of chemical species that have comparable chemical features and systematically increasing molecular diameters. Results show that chemically active species with diameters greater than 0.5 nm are ineffective as stress corrosion agents. A comparison of crack growth results and zeolite diffusion measurements was used to conclude that the opening to the crack tip is less than or equal to 0.5 nm. This crack tip dimension is consistent with the concept of atomic scale brittle fracture in silica glass.
Influence of Fluorine on Thermal Properties of Fluorophosphate Glasses
Authors: Stević Smiljka , Aleksić Radoslav , Backovi Nevnka
Published: March 2005

Thermal properties of fluorinated and unfluorinated glasses based on the systems AlF3‐NaPO3 and AlF3‐CaF2‐NaPO3 were investigated. Crystallization is more distinct in glasses with a higher fluorine content. The increase in fluorine content in aluminofluorophosphate glasses increases the thermal dilatometry coefficient.
Crystal Growth of Rod‐Shaped β‐LiA1O2
Authors: Watanabe Akira , Takeuchi Yoshimitsu , Saeki Goji
Published: March 2005

LiAlO2crystals are obtained conventionally in the form of powder. In a few publications, crystal growth of rod‐shaped LiAlO2 has been described, but the fiber length was very short, <4 μm. In the present study, rod‐shaped β‐LiAIO2 crystals 10 to 15 μm long were grown using LiOH‐AI2O3NaOH as the raw material.
Interfacial Cracks in Ceramic‐to‐Metal Bonds under Transient Thermal Loads
Authors: KOKINI KLOD
Published: March 2005

The effect of a transient thermal load on an interfacial edge crack and center crack between a ceramic‐to‐metal bond was analyzed with the use of fracture mechanics. The deformations of the crack and the strain energy release rate were calculated for the case of a ceramic layer of equal thickness to the metal, one with one‐tenth the thickness of the metal, and one with 10 times the thickness of the metal. It was determined that for an edge crack, under slow cooling conditions, the steady‐state value of G is the largest, and G is largest for equal thicknesses of ceramic and metal. For a center crack, a maximum transient G occurs which is larger than the steady‐state value and the strain energy release rate is smallest for equal thicknesses of ceramic and metal.
Effects of Counterions on Crack Growth in Vitreous Silica
Authors: WHITE GRADY S. , FREIMAN STEPHEN W. , WIEDERHORN SHELDON M. , COYLE THOMAS D.
Published: March 2005

Crack‐growth studies on vitreous silica were conducted in aqueous solutions as a function of pH in‐ the range 1 to 14. Slopes of crack velocity‐KI curves were steeper in acidic and neutral solutions than in basic solutions. Of the four alkali‐metal hydroxide solutions studied, only lithium hydroxide behaved differently from the others and only in concentrated, ≥1M, solutions. At this concentration, the slope and position of the crack‐growth curves for LiOH were nearly identical to those obtained in acidic or neutral solutions. It is suggested that the influence of alkali‐metal hydroxides on crack growth is largely chemical in nature, involving short‐range forces associated with the breaking of bonds at the crack tip. Two mechanisms for chemical attack are considered: in basic solutions the siloxane bonds at the crack tip are believed to be attacked directly by the hydroxide ions in solution; in acidic or neutral solutions the siloxane bonds are believed to be attacked by water in the electrolyte. Lithium hydroxide behaves differently from the others because lithium ions associate with hydroxide ions, reducing the effective activity of the hydroxide ions at the crack tip.
Evaluation of Fracture Toughness Determination Methods as Applied to Ceria‐Stabilized Tetragonal Zirconia Polycrystal
Authors: Matsumoto Roger L. K.
Published: March 2005

A comparison of several fracture toughness determination methods based upon the use of cracks emanating from a Vickers hardness indent to the bulk techniques of double cantilever beam and single edge notch beam is made in a tough zirconia material which shows little evidence of transformation toughening based on the amount of monoclinic phase detected by XRD on ground surfaces. Results indicate that some indentation methods yield values close to those obtained by bulk methods, in contrast to results obtained on zirconia materials which show large effects of transformation toughening.
Alternating‐Current‐Assisted Poling of Lead Zirconate Titanate (PZT)
Authors: Gallo Christopher A. , Schulze Walter A.
Published: March 2005

A modification of the conventional poling procedure for piezoelectric materials was investigated because of inconsistencies in the literature. Preliminary investigations appeared to support the theory of ac‐assisted poling. However, a temperature studyl limited duty cycle experiment seemed to indicate that the increase in piezoelectric response (d33 coefficient) was probably due to heat produced by the body in resonance.
Diffraction from a Natural Grain Boundary in a Magnetite Bicrystal
Authors: STOCK STUART R. , AHN SANG HO , COHEN JEROME B.
Published: March 2005

The structure of a natural small‐angle boundary in a magnetite bicrystal was investigated by X‐ray diffraction. This boundary was a “general” type with a mixed twist and tilt character. The grain‐boundary reflections observed around an 040 matrix reflection were in good agreement with those predicted by Boll‐mann's O‐lattice theory. These extra reflections appear to arise from a predominantly planar dislocation network. The structural width of the boundary, determined from the length of the relrods of the grain‐boundary reflections, was of the order of four unit cells, close to the average spacing of the expected dislocation network.
Creep Cavitation in Liquid‐Phase‐Sintered Alumina
Authors: PAGE RICHARD A. , LANKFORD JAMES , CHAN K. S. , HARDMAN‐RHYNE KAY , SPOONER S.
Published: March 2005

The early stages of cavitation during compressive creep of a liquid‐phase‐sintered alumina have been characterized using small‐angle neutron scattering. Grain‐boundary cavities were found to nucleate throughout creep, although at a steadily decreasing rate. The cavities were located on two‐grain junctions as well as triple points and were spaced approximately 100 to 200 nm apart. The cavity spacing corresponded to the spacings observed for grain‐boundary ledges, suggesting that the ledges were the cavity nucleation sites. Cavity nucleation was also found to be relatively independent of the applied stress. This behavior has been rationalized based on the decreasing ratio of ɛgbs/ɛt, where ɛgbs is the strain due to grain‐boundary sliding and ɛt is the total strain, at increasing stresses. Cavity growth, on the other hand, was highly stress dependent. Above a certain “threshold” stress cavity growth was observed. In all cases, however, the observed growth was transient; i.e., the cavity growth rate decreased with time. Lowering the stress below the “threshold” resulted in a condition in which cavities nucleated but continued growth of the cavities did not occur. In all cases the cavities nucleated and grew, when growth did occur, with relatively equiaxed shapes.
Microstructural Inhomogeneity in Sintered Pb(Mg1/3Nb2/3)O3‐PbTiO3 Based Dielectrics
Authors: Guha J. P. , Anderson H. U.
Published: March 2005

The sintering behavior and microstructural development of dielectric ceramics based on Pb(Mg1/3Nb2/3)O3‐PbTiO3 solid solutions are greatly affected by the formation of a liquid phase at ∼ 1290°C. Prolonged sintering at and above this temperature gives rise to an excessive PbO loss and the resultant variation in composition leads to an inhomogeneous microstructure. The inhomogeneity is characterized by the formation of a dense, localized region containing a PbO‐rich liquid near the surface with a porous interior region in the bulk of the sample.
Transmission Electron Microscopic Characterization of Ceramics Formed by Pyrolysis of Organometallic Polymer Precursors
Authors: Bender Barry A. , Rice Roy W. , Spann Joseph R.
Published: March 2005

Transmission lectron microscopy using bright‐field and darkfield imaging and selected area electron diffraction was used to study ceramics pyrolyzed from a variety of organometallic polymer precursors. Determination of whether the pyrolyzed products were truly amorphous or microcrystalline was made and correlated to previous scanning electron microscopy or powder X‐ray diffraction observations. Results indicated that most of the resultant as‐pyrolyzed microstructures were amorphous, and that polymer pyrolysis presents significant opportunities for fabricating unique amorphous materials.
Nitrogen Dissolution in Sodium Alkaline‐Earth Metaphosphate Melts
Authors: RAJARAM MOHAN , DAY DELBERT E.
Published: March 2005

Phosphorus oxynitride glasses were prepared by remelting (5O –X)Na2O ·XBaO · 50P2O5, X = 0, 10, 20, 25, and 30, and 30Na2O · 20MO · 50P2O5, M = Mg, Ca, Sr, and Ba‘, glasses in anhydrous ammonia. The nitrogen content depends upon the temperature and time of remelting in ammonia and the concentration and size of the alkaline‐earth ion. Nitriding the starting glass decreased the dissolution rate in deionized water and thermal expansion coefficient and increased the dilatometric softening temperature and refractive index. The dissolution rate of the base glass in deionized water depended upon the concentration and size of the alkaline‐earth ion, but for nitrided glasses, it was essentially independent of the alkaline‐earth cation. The thermal expansion coefficient for all the oxynitride glasses decreased with increasing alkaline‐earth concentration and cation field strength.
Asymmetric Polarization Behavior of Sodium β″‐Alumina Electrolyte
Authors: SINGH RAJ N.
Published: March 2005

The roles of electrolyte composition and surface treatments in the phenomenon of asymmetric polarization in sodium β″‐alumina ceramics are investigated. The results indicate that Asymmetric polarization is only displayed by electrolyte compositions containing 80 vol%β″‐alumina phase and that a chemical treatment utilizing phosphoric acid, or a water treatment, is effective in circumventing the asymmetric polarization via removal of the asymmetric‐polarization‐causing resistive surface film. The surface film is soda rich, 20 to 40 nm thick, and there is a considerable concentration gradient from the surface into the bulk of an as‐sintered sodium β″‐alumina electrolyte.
Factors Affecting Nitrogen Dissolution in Sodium Metaphosphate Glass
Authors: PENG YONGREN B. , DAY DELBERT E.
Published: March 2005

The preparation of sodium phosphate oxynitride (Na‐P‐O‐N) glasses was investigated in dry ammonia, forming gas and 90% N2+ 10% CO atmospheres. Significant nitrogen dissolution, up to 13 wt% in a NaPO3 melt, occurred only in ammonia. The kinetics of nitrogen dissolution was studied as a function of remelting time (1 to 96 h) and temperature (660° to 760°C). Higher temperature accelerates nitrogen dissolution, but the temperature should not exceed 760°C. Great improvement in chemical durability occurs with nitrogen dissolution in a NaPO3 melt. Other property changes reported include softening temperature, thermal expansion coefficient, refractive index, microhardness, etc. A double chain structure model is proposed for the Na‐P‐O‐N glass.
High‐Temperature Stress Corrosion Cracking in Ceramics
Authors: CAO HENG C. , DALGLEISH BRIAN J. , HSUEH CHUN‐HWAY , EVANS ANTHONY G.
Published: March 2005

Single‐phase ceramics are shown to be susceptible to stress corrosion cracking at elevated temperatures in the presence of a wetting amorphous deposit. Crack arrest occurs when the crack is depleted of amorphous material, provided that the stress intensity is below a “blunting” threshold. A preliminary model of such cracking has been developed. The model considers stress corrosion as a process wherein the corrosive medium, by virtue of its wetting characteristics, allows the crack to propagate along grain boundaries. A crack velocity that depends sensitively on the dihedral angle is predicted. Furthermore, since the corrosive medium acts as a conduit for rapid atom transport to the crack tip, the crack velocity also exhibits a strong dependence on the viscosity of the fluid medium. Implications for such stress corrosion processes on premature failure are discussed.
Acid Durability of Sodium and Potassium Galliosilicate Glasses
Authors: LAPP JOSEF C. , SHELBY JAMES E.
Published: March 2005

The relative chemical durability in nitric acid of three series of glasses in the (Na,K)2O‐Ga2O3‐SiO2 system have been studied. In these compositions, gallium is proposed to behave as either a network modifier or former depending on the gallium to alkali ion ratio of the glass. The mechanisms of acid attack as found in the present work are postulated to be a combination of ion exchange and network dissolution dependent upon the glass composition/structure. This results in complex trends in the acid dissolution of these glasses as functions of the gallium to alkali ion ratio, and silica content.
Effect of Antimony Oxide on the Anatase‐Rutile Transformation in Titanium Dioxide
Authors: Eppler Richard A.
Published: March 2005

For both pure and doped titanium dioxides, the addition of antimony oxide lowers the temperature at which the anatase‐to‐rutile transformation occurs.Its presence also affects the color obtained in doped systems.
Origin of ZnO Varistor
Authors: Fujitsu Satoru , Toyoda Hiroshi , Yanagida Hiroaki
Published: March 2005

The varistor properties were examined in porous ZnO. The sample used contained no dopants such as Bi2O3 or Pr6O11, which are usually considered to be useful in developing varistors. Comparison of I‐V curves for the oxidized and unoxidized samples indicated that oxygen, which had chemisorbed and diffused into the grain boundary, played a role in developing varistor characteristics.
Influence of Ionic Charge on Diffusion in the Surface Layer of Magnesia
Authors: Lin Chang‐Ming , Stubican Vladimir S.
Published: March 2005

The diffusion of 57Co isotope on the MgO (100) surface was investigated by the edge‐source method. The surface diffusion parameter, αDsδ, where α is the segregation factor, Ds the surface diffusion coefficient, and δ the thickness of the high‐diffusivity layer, was determined over the temperature region 750° to 1250°C. An Arrhenius plot shows a break at ∼1100°C. Below this temperature ionic or localized transport predominates and above it nonlocalized transport seems to predominate. The divalent Co ion diffuses faster than the trivalent Cr ion in the surface layer. The apparent activation energies for the localized surface diffusion of 57Co and 59Cr are 59±12 and 110±12 kj/mol, respectively.
Strength of Lead Silicate Glass After H2 Reduction
Authors: Swiler Daniel R. , VARSHNEYA ARUN K. , Carville Patricia
Published: March 2005

Hydrogen‐reduced lead silicate glass canes showed nearly a 70% increase in four‐point bending strength over like specimens of the unreduced parent glass. No difference was observed in the strength of the reduced and the unreduced glasses after abrasion. Fractographs showed the presence of a surface layer (∼5 μm) in the reduced glass where the fracture traveled slowly. Secondary ion mass spectroscopic analysis showed this surface layer had decreased oxygen but increased Si+ and SiOH+ species. Although the possibility of surface compression could not be ruled out because of a possibly anomalous stress optical coefficient, it was concluded that the reduction altered the glass network to retard the subcritical crack velocity intrinsic to the system.
Transmission Electron Microscopic Observations of α‐Cristobalite in Fused Silica
Authors: Castano Victor M. , Takamori Takeshi , Shafer Merrill W.
Published: March 2005

Distinct crystalline phases in some commercial fused silicas were shown by transmission electron microscopy. They were identified to be α‐cristobalite by selectedarea electron diffraction. Their origin and the effect on the glass matrix are discussed.
Knoop Microhardness Anisotropy of Single‐Crystal Stoichiometric MgAl2O4 Spinel
Authors: Akimune Y. , Bradt R. C.
Published: March 2005

Microhardness anisotropy profiles for the (100) and (111) planes of single‐crystal stoichiometric MgAl2O., spinel were determined at room temperaturé. The (100) microhardness profile has ahardness maximum in tiie [001] and a minimum in the [O11], which supports the previous suggestion that the primary slip system is the {111}〈11¯0〉. The microhardness of the (111) plane is independent of indenter orientation, also consistent, with a {111}〈11¯0〉 primary slip system. It is concluded that these microhardness profiles are in accord with other experimental observations that the {111}〈11¯0〉 is the primary slip system in stoichiometric MgAl2O4 spinel.
Fracture Initiation in the Directionally Solidified NiO‐CaO Eutectic
Authors: BRUMELS MARK D. , PLETKA BRUCE J.
Published: March 2005

Initiation of fracture in the directionally solidified, lamellar NiO‐CaO eutectic was examined using the indentation fracture technique. Fracture could not be induced along the interphase boundary on transverse sections of the directionally solidified eutectic. Instead, radial cracks evolved at angles of approximately 35° and 55° with respect to the lamellar interface and were consistent with median/radial crack formation on (TlO) and (001) planes, respectively. Indentation of single‐crystal NiO resulted in fracture only along {110} planes. Crack initiation on {110} planes in both materials was attributed to a dislocation coalescence model proposed by Keh et al. while crack formation on (001) planes in the eutectic was believed to be initiated by a Stroh‐type mechanism involving dislocation pile‐ups. Variations in the interlamellar spacing resulted in a Hall‐Petch‐type behavior for the hardness but had little effect on the fracture toughness of the eutectic.
Anomalous X‐ray Line Broadening Observed in γ‐Fe2O3 Derived from γ‐FeOOH
Authors: NAKAJIMA K. , HIROTSU Y. , OKAMOTO S.
Published: March 2005

Defect structure of fine‐grained γ‐Fe2O3 powder obtained by dehydroxylation of y‐FeOOH powder has been studied by X‐ray diffraction and high‐resolution electron micrographs. An anomalous X‐ray line broadening was observed in the γ‐Fe2O3 powder. It is found that the X‐ray line breadth is dependent on the crystal structure factors of each reflection line: the reflections from net planes consisting of only metal ions on tetrahedral sites and octahedral sites of spinel structure are much broader than those from net planes including oxygen ions. The anomalous X‐ray line broadening is explained on the basis of stacking faults in the spinel structure.
Creep‐Sintering and Microstructure Development of Heterogeneous MgO Compacts
Authors: LIN MARK , RAHAMAN MOHAMMED N. , DE JONGHE LUTGARD C.
Published: March 2005

Simultaneous creep and densification and the microstructure development of magnesium oxide powder compacts were studied at 125°C and for applied stresses of up to 0.25 MPa. Die‐pressing the powder into compacts with a relative green density of ∼0.40 led to an approximately bimodal distribution of pores, with one fraction having sizes of the order of 10 times the (initial) particle size and the other fraction having pore sizes of the order of the particle size. The presence of the large pores in turn gave rise to rather unusual sintering effects. After first decreasing with relative density (ρ), the densification rate (dρ/dt) and the creep rate (dɛ/dt) then increased dramatically for 0.6 < ρ < 0.75. This range of ρ corresponded to the stage of microstructure development when grain growth and coalescence of the smaller pores have created a more uniform pore distribution. Above ρ∼ 0.75, both dρ/dt and dɛ/dt again decreased with ρ. These trends in the densification behavior are discussed in terms of material parameters such as the equilibrium dihedral angle and the pore coordination number.
Formation and Transformation of ZnTiO3
Authors: Yamaguchi Osamu , Morimi Msami , Kawabata Hidenao , Shimizu Klyoshi
Published: March 2005

A compound tentatively denoted as Zn2Ti,3O8 is determined to be a low‐temperature form of ZnTiO3. At a heating rate of 10°C·min−1 the low‐temperature form crystallizes at 600° to 765° C from an amorphous material prepared by the simultaneous hydrolysis of zinc acetylacetonate and titanium isopropoxide. It has a cubic unit cell with a =0.8408 nm. The cubic‐to‐hexagonal transformation occurs slowly above 820°C; during transformation ZnTiO3 decomposes into Zn2TiO4 and TiO2 (rutile) at 965° to 1010°C. A single phase of the hexagonal form can be prepared by heating for 5 h at 900°C. The structure of both forms consists of octahedral TiO6 groups.
Computer Simulations of R‐Curve Behavior in Microcracking Materials
Authors: BOWLING GREGORY D. , FABER K. T. , HOAGLAND R. G.
Published: March 2005

A computer program has been developed which simulates the process of microcracking in two‐phase ceramic materials. This simulation provides a method of examining the complex interactions which occur between a propagating crack and the residually stressed particles around it. As the residual stresses near second‐phase inclusions are relieved by microcrack formation, a process zone forms around the main crack, partially shielding it. The resulting crack resistance curves, or R curves, associated with crack shielding mechanisms are generated by the program. Three variables— the microcrack density (fs), the dilatant strain associated with each microcracked particle (θ), and the orientation of the microcracks (Ψ)— were used to determine their influence on fracture toughness. The steady‐state toughness was found to increase with second‐phase particle additions, increased dilatant strain, and the formation of microcracks parallel to the direction of applied stress. However, the magnitude of toughening increase attained in these‐simulations was generally lower than that predicted by continuum models. This discrepancy is attributed to the fact that interactions between microcracks produce frontal zones which result in a positive Δk, and hence, a lower steady‐state toughness. This behavior is enhanced when microcracks link with the main crack to promote further extension.
Solubility of NiO in Al2O3
Authors: Ando Ken , Momoda Masataka , Azumi Takeshi , Kitajima Sadakichi
Published: March 2005

Solubility of NiO in Al2O3 was determined by electron probe microanalysisy A diffusion couple method was used by coupling an NiO‐doped Al2O3 polycrystal to a pure single crystal of Al2O3. The solubility of NiO in Al2O3 in air was 230 wt ppm (157 at. ppm of cations) and 170 wt ppm (116 at. ppm) at 2073 and 1973 K, respectively. The solubility of NiO in Al2O3 obtained in this work was compared with our previous work of the solubility of MgO in Al2o3.