bluuebunny/crossref_metadata_2025 huggingface dataset:
Crack Coalescence and Microscopic Crack Growth in the Delayed Fracture of Alumina
Authors: OKADA TATSUO , SINES GEORGE
Published: June 2006

Microscopic crack growth in the delayed fracture of alumina is studied. A model for the delayed fracture, based on microscopic cracks and their interaction and coalescence, is proposed as opposed to the conventional single‐worst‐crack model. The proposed analysis gives a more realistic prediction than the conventional one. It is found that an assembly of microscopic cracks, which may not be observable, may be worse than a single macroscopic crack in delayed fracture and that the coalescence of the microscopic cracks may occur in a very short time without being identified because the critical amount of slow crack growth from the individual inherent flaws can be very small. Applicability of proof‐testing concepts is reexamined. It is demonstrated that the existing concepts give nonconservative prediction in time‐to‐failure; but the nonconservative prediction is partially or sometimes excessively compensated by conservative estimation of the initial crack size.
Crack Resistance Behavior of Ceramic Materials
Authors: Wieninger Herbert , Pabst Reiner Friedrich
Published: June 2006

Notched three‐point bend specimens of two aluminas were precracked to form long sharp cracks of varied lengths in a displacement‐controlled experiment at room temperature. Critical stress intensity factors were then measured in a load‐controlled test at high loading rates as a function of sharp crack length. The crack resistance curves (KIc vs crack length) proved to be independent of crack length.
Phase Relations in the System Li2O‐ZrO2‐SiO2
Authors: Gardiner Clayton F. , Chang Luke L. Y.
Published: June 2006

Phase relations in the system Li2O‐ZrO2‐SiO2 are characterized by four invariant points. Two eutectics occur at 1016°C and 29:3:68 (mol% Li2O:ZrO2:SiO2) and at 1005°C and 32:5:53. One peritectic point was found at 1043°C and 31:113:56, whereas the other is inferred from the present and previous investigations. No ternary phases are stable in the system.
Uniformity of Al2O3‐ZrO2 Composites by Colloidal Filtration
Authors: Aksay I. A. , Lange F. F. , Davis B.I.
Published: June 2006

Dispersion states of aqueous composite Al2O3/ZrO2 colloidal suspensions were studied by measuring particle size distribution as a function of pH. Mutual dispersion was achieved at pH values of 2.0 to 3.5. Consolidated composites formed by colloidal filtration reflected the uniformity of the colloidal state. The mean flexural strength (896 MPa) of the sintered compacts was 1.6 times that of bodies consolidated by isostatic pressing.
Effect of Drop Height on Critical Temperature Difference (ΔTc) for Brittle Ceramics Subjected to Thermal Shock by Quenching into Water
Authors: Singh Jitendra P. , Hasselman D. P. H. , Ziegler Gunter
Published: June 2006

The critical quenching temperature differences required to initiate thermal stress failure of soda‐lime‐silica glass, polycrystalline Al2O3, mullite, and reaction‐sintered Si3N4 quenched into water were found to be independent of the height from which the specimens were dropped. These results suggest that, within the range of usual laboratory practice, drop height need not be closely controlled. The implications of these observations for the mechanism of heat transfer responsible for thermal stress failure in water quenching are discussed.
Stability of Ultrafine Tetragonal ZrO2 Coprecipitated with Al2O3 by the Spray‐ICP Technique
Authors: KAGAWA M. , KIKUCHI M. , SYONO Y. , NAGAE T.
Published: June 2006

The transformation of ultrafine powders (particle size, 0.01 to 0.04 μm) of the system ZrO2–Al2O3, prepared by spraying their corresponding nitrate solutions into an inductively coupled plasma (ICP) of ultrahigh temperature, was investigated. The powders were composed of metastable tetragonal ZrO2 (mt‐ZrO2) and γ‐Al2O3. On heating, the mt‐ZrO2 (or tetragonal ZrO2, t‐ZrO2) was retained up to 1200°C. At 1380°C the transformation to monoclinic ZrO2 (m‐ZrO2) occurred and the amount of the m‐ZrO2 decreased with the increase in Al2O3 content, thus indicating the stabilization of the t‐ZrO2 by the Al2O3, which seems to be explained in terms of the retardation of grain growth.
Oxynitride Glass Formation from Gels
Authors: BRINKER C. J. , HAALAND D.M.
Published: June 2006

Porous, multicomponent silicate gels were heated in flowing and pressurized ammonia. These treatments resulted in dense, homogeneous oxynitride (O‐N) glasses which were synthesized at low temperature (∼1000°C) without melting. The O‐N glasses exhibited increased microhardness and glass‐transition temperature and altered thermal expansion characteristics compared to the respective oxide glasses prepared by densi‐fying gels in air or by conventional melting of oxide powders. Spectroscopic evidence indicates that ammonia reacts with all of the network‐formers investigated, Si, Al, and B, hut from nitrogen content measurements, it appears that B and/or Al are required for significant nitridation below 1000°C.
Elastic Recovery at Static Loading and Impact Indentations in MgF2
Authors: KIRCHNER H.P. , TIRACORDA J.A. , LARCHUK T.J.
Published: June 2006

The extent of elastic recovery at spherical indentations in MgF2 indented by static and impact loads was analyzed. The fraction of the indentation depth that was recovered decreased with increasing static load. Similar results were observed for impact loads. The kinetic energy losses increased with a velocity exponent of 2.61 despite substantial variations in the contributions of various loss mechanisms over the range of velocities for which measurements were made. Apparently, the losses are partitioned among the various loss mechanisms that derive their energy from the elastic field.
Inverse Spinel Pigments
Authors: EPPLER RICHARD A.
Published: June 2006

The system Zn2TiO4‐Co2TiO4‐Ni2TiO4 yields a bright green pigment with the orthotitanate spinel structure. Brick‐red, orange, and brown pigments are found in the system Zn2TiO4‐Co2TiO4‐Ni2TiO4.
Compressive Surface Strengthening of Brittle Materials by a Residual Stress Distribution
Authors: GREEN DAVID J.
Published: June 2006

A theoretical approach is presented for predicting the strengthening of brittle materials subjected to a residual stress distribution represented by a polynomial series. In the approach, the stress intensity factor for a surface crack is derived incorporating the effect of crack closure. The crack‐closure distance is then calculated using an approximate approach which allows the strengthening due to the residual stresses to be estimated. Illustrating the approach using residual stresses typical of tempering, it was found the approach agreed well with previous work. The influence of partial crack closure was found to give higher values of the stress intensity factor than would be calculated if the crack were assumed to be open. This effect decreases the amount of strengthening predicted and gives a wide range of conditions for which subcritical crack‐growth processes can occur. For the example of tempering it was also found that these are conditions when weakening or spontaneous failure of the body can occur.
Mechanism and Kinetics of Reactions in the System Ni‐Ti‐O
Authors: GOLDMAN DOV B.
Published: June 2006

Reactions at T=600° to 1250°C between nickel oxide and titanium dioxide, metallic nickel and titanium dioxide, and the oxidation of Ni‐TiO2 cermet were studied. The formation of compouuds was observed by temperature‐programmed reduction in hydrogen flow. At T > 600°C, NiTiO3 forms. During the initial stages of the reaction, a solid solution of TiO2 in NiO is formed. The reaction is influenced by anatase‐rutile transformation. The apparent activation energy of the formation of NiTiO3 is considerably lower during the reaction in the mixture of metallic nickel with titanium dioxide (218 kJ°mol‐1 for powder and 255 kJ.mo1‐1 for cermet oxidation) than it is for the reaction between NiO and rutile (385 kJ.mol‐1).
Particle Size Distribution and Its Relation to Sintering—A Case Study for UO2 Powders
Authors: BURK R. C. , ZAWIDZKI T. W. , APTE P. S.
Published: June 2006

It is generally recognized that the particle size distribution (PSD) of powders plays a very significant role in powder compaction and sintering. However, particle size distribution data are generally presented in the form of one number (mean diameter). In the case of PSD data obtained by sedimentation, analysis of the whole curve reveals some interesting information. The type of information obtained by such an analysis and its application to an analysis of compaction and sintering is discussed using the case of uranium dioxide powders as an example.
Plastic Deformation of Partially Stabilized Zirconia
Authors: Lankford James
Published: June 2006

The results of room‐temperature compression experiments conducted on poly‐crystalline Mg partially stabilized zirconia are described. It is shown that, in addition to prefuilure axial microfracture, the material exhibits significant plasticity. This plasticity arises from deformation bands formed by cooperative martensitic transformation of melastable tetragonal precipitates; the deformation bands lead to significant surface rumpling. It is suggested that both stress‐ and strain‐induced martensitic transformations may be involved in the deformation process.
PTCR Characteristics in Barium Titanate Ceramics with Curie Points Between 60° and 360°C
Authors: Kuwabara Makoto , Kumamoto Kenji
Published: June 2006

PTCR characteristics in porous semiconducting barium titanate ceramics with Curie points from 60° to 360°C were investigated. The magnitude of the PTCR effect in these cerumics decreases self‐onsistently with increasing Curie point within this temperature range. A PTCR efSect of more than 4 orders of magnitude was ahserved, for a Ba0.44Pb0.6TiO3ceramic with a Curie point of 360°C.
Revised Phase Diagram of the System ZrO2‐CeO2 Below 1400°C
Authors: TANI EIJI , YOSHIMURA MASAHIRO , SOMIYA SHIGEYUKI
Published: June 2006

The phase diagram of the system ZrO2‐CeO2 was rein‐vestigated using hydrothermal techniques. Cubic, tetragonal, and monoclinic solid solutions are present in this system. The tetragonal solid solution decomposes to monoclinic and cubic solid solutions by a eutectoid reaction at 1050°50°C. The solubility limits of the tetragonal and cubic solid solutions are about 18 and 70 mol% CeO2, respectively, at 1400°C, and about 16 and 80 mol% CeO2, respectively, at 1200°C. Solubility limits of the monoclinic and cubic solid solutions are about 1.5 and 88 mol% CeO2 at 1000°C, and 1.5 and 98 mol% CeO2 at 800°C, respectively. The compound Ce2Zr3O10 is not found in this system.
Relation Between Multiregion Crack Growth and Dynamic Fatigue of Glass Using Indentation Flaws
Authors: CHANTIKUL P. , LAWN BRIAN R. , RICHTER HERBERT , FREIMAN STEPHEN W.
Published: June 2006

The influence of transport‐limited kinetic crack growth on the fatigue properties of soda‐lime glass was examined. Dynamic fatigue data were taken on specimens with controlled indentation flaws and were compared with the predicted response from measured crack velocity characteristics. Heptane was used as the operational test environment because of its pronounced crack velocity plateau; control tests in water served to establish a baseline reference for comparing the results. Frac‐tographic observations using a stress wave marker technique showed a complex growth history for flaws broken in heptane compared to that for flaws broken in water. The magnitude of the predicted region II influence is too small to be detected in the dynamic fatigue results, even allowing for the relatively high degree of data reproducibility. The implications of this conclusion for lifetime predictions are discussed.
Solid Solubility of GeO2 in SnO2
Authors: Watanabe Akiteru , Kikuchi Takeshi , Tsutsumi Masayuki , Takenouchi Satoshi , Uchida Kenji
Published: June 2006

Subsolidus equilibrium relations were reexamined in the SnO2‐rich portion of the system GeO2‐SnO2 (60 to 98 mol% SnO2). A limited solid solution based on SnO2 was confirmed; 4mol% GeO2 dissolved in SnO2 at 1250 C, and glass was formed on quenching over the compositional range above 4mol% GeO2. Phase relutions in the system are discussed with reference to the polymorphism of GeO2 and its glass‐forming ability, and a possible phase diagram is given.
Microstructure and Mineral Chemistry of Synroc‐D
Authors: RYERSON F.J.
Published: June 2006

Synroc‐D is a polyphase nuclear waste ceramic optimally consisting of zirconolite, perovskite, an ulvospinel‐rich solid solution, a hercynitic spinel solid solution, and nepheline. A continuous intergranular glass phase is also present, which may aid in densification, but decreases the waste form's durability in aqueous environments, as does the presence of nepheline. The major radionuclides are distributed in the following manner: (1) Uranium is immobilized in zirconolite and perovskite, (2) the lanthanides and strontium are immobilized in perovskite, (3) cesium is distributed between nepheline and glass. The partitioning of tetravalent uranium and trivalent actinides may prove useful as surrogates for tetravalent and trivalent actinides, respectively. The spinels are free of radionuclides and provide a degree of microencapsulation for the radio‐nuclide‐bearing phases. Values of mineral‐mineral partition coefficients are largely dependent on powder preparation; the choice of zirconia reagent is of particular importance.
Preparation, Characterization, and Melting Point of High‐Purity Lithium Oxide
Authors: ORTMAN MARK S. , LARSEN EDWIN M.
Published: June 2006

High‐purity lithium oxide was synthesized by thermal decomposition of the peroxide at temperatures up to 1070 K under dynamic vacuum. Analyses of typical preparations gave carbonate 0.01 to 0.02%, hydroxide 0.0 to 0.2%, sodium 0.002%, manganese 0.0004%, and lithium oxide 99.8 to 100.0%. The corrected melting point was measured as 1711±5 K based on the thermal arrest observed when molten specimens were cooled.
Solid Solution Range and Microstructures of Melt‐Grown Mullite
Authors: KRIVEN W. M. , PASK JOSEPH A.
Published: June 2006

The solid solution range of melt‐grown mullite was examined by crystal‐chemical methods. The maximum Al2O3 content as determined by EDX was ∼83.6 wt%, 75 mol%, or the nominal composition 3Al2O3.SiO2. For samples of overall composition 81 to 83 wt% Al2O3, extra lines indicating crystallographic superstructure appeared in Guinier X‐ray patterns. The corresponding TEM microstructure consisted of a mullite matrix finely twinned on (001), the twins being 0.02 to 0.10 μm wide, with oriented exsolution of α‐A12O3, often twinned, also being present. The analogy between mullite superstructure and that of plagioclase feldspars, as well as the relevance of these findings to the SiO2‐Al2O3 metastable phase equilibria are discussed.
Compaction of Aggregated Alumina Powder
Authors: DYNYS F. W. , HALLORAN J. W.
Published: June 2006

The behavior of aggregated powders during compaction was studied using powders differing only in their aggregate size distribution. The relations between aggregate size distribution, compaction pressure, and green density were determined. The crushing of aggregates during compaction was followed by determining the changes in the aggregate size distribution. The presence of aggregates retards the compaction at all stages in the compaction process.
Oxygen Diffusion in MgO and α‐Fe2O3
Authors: REDDY K.P.R. , COOPER A.R.
Published: June 2006

Oxygen‐diffusion coefficients were determined in single crystals of MgO and α‐Fe2O3 by exchanging the samples with 18O enriched gas at 1 atm and measuring 18O profiles using a proton activation technique. For MgO, in the temperature range 1580 to 1820 K, the diffusion coefficient is represented by:
Plasma Etching of Sialon
Authors: Chatfield Chris , Norström Hans
Published: June 2006

A new technique is presented for the etching of sialon and Si3N4 for microstructural control purposes. This technique, plasma etching, is rapid and delineates both β‐sialon and glassy phases.
Elastic Moduli of Porous Sintered Materials as Modeled by a Variable‐Aspect‐Ratio Self‐Consistent Oblate‐Spheroidal‐Inclusion Theory
Authors: DEAN E. A.
Published: June 2006

If the porosity of sintered materials is modeled by oblate spheroids, self‐consistent elastic moduli theory can be used to determine an effective aspect ratio for the spheroids from experimental data on elastic moduli vs porosity. The resultant effective aspect ratio serves as an additional parameter to describe observed elastic behavior. With the exception of one case in the seven investigated, this single parameter satisfactorily describes both Young's modulus and shear modulus vs porosity data. The fit to these data sets is tested by comparing theoretical and experimental values for bulk moduli and Poisson ratios. An effective aspect ratio is also shown to accurately describe a continuous distribution of aspect ratios varying between spheres and disks, implying that a continuous distribution of oblate spheroids may be a useful model for the elastic behavior of sintered materials.
Microwave Clinkering with a Grooved Resonant Applicator
Authors: QUÉMÉNEUR L. , CHOISNET J. , RAVEAU B. , THIEBAUT J. M. , ROUSSY G.
Published: June 2006

Clinkering of cement raw materials under a microwave field was studied with a grooved cavity using the TE113 mode. Clinker with characteristics similar to industrial clinker was prepared for the first time using only microwaves, avoiding the formation of a plasma. The characteristics of the microwave and the industrial clinker were compared. The evolution of the imaginary part of the permittivity ɛ and of the absorbed power was established and interpreted in terms of the three main steps which characterize the clinkering process: decar‐bonation, formation of aluminoferrite phases and their melting, and formation of alite.
Influence of Gamma Irradiation on Leaching of Simulated Nuclear Waste Glass: Temperature and Dose Rate Dependence in Deaerated Water
Authors: PEDERSON L. R. , McVAY G. L.
Published: June 2006

Elemental leaching rates from a simulated nuclear waste glass undergoing gamma irradiation in deaerated deionized water were evaluated as a function of temperature and gamma dose rate. Deaeration of the water eliminated nitric acid formation via air radiolysis, previously shown to substantially accelerate waste glass corrosion, and thus allowed the effects of water radiolysis alone to be measured. Water radiolysis resulted in enhanced reaction‐layer thicknesses on glass samples as well as an approximate factor of three increase in the leach rate at 50°C. At 90°C, leach rates were indistinguishable for irradiated and unirradiated glasses. Most of the increase in glass dissolution occurred up to a gamma dose rate of ∼1 × 105 rad/h. Above this value, only minor further increases were observed. It is concluded that the observed glass corrosion enhancement was due to reaction with short‐lived transient species generated by water radiolysis and that the effect is unlikely to significantly contribute to long‐term waste isolation.
Fabrication of Grain‐Oriented PbBi2Nb2O9
Authors: LIN SHENG‐HE , SWARTZ S.L. , SCHULZE W. A. , BIGGERS J. V.
Published: June 2006

This paper describes a process for the fabrication of grain‐oriented PbBi2Nb2O9 ceramics. A molten salt technique was used to synthesize crystallites of PbBi2Nb2O9 with a high degree of shape anisotropy. Tape casting and subsequent uniaxial hot‐pressing resulted in ceramics with grain orientation of >90% with densities >96% theoretical.
Structural Reliability of Yttria‐Doped Hot‐Pressed Silicon Nitride at Elevated Temperatures
Authors: WIEDERHORN S.M. , TIGHE N.J.
Published: June 2006

The strength of yttria‐doped hot‐pressed silicon nitride was investigated as a function of temperature, time, and applied load. Data collected at 1200°C are presented in the form of a strength‐degradation diagram for an applied stress of 350 MPa. At this temperature, the behavior of yttria‐doped hot‐pressed silicon nitride is found to be superior to that of magnesia‐doped hot‐pressed silicon nitride, in which creep results in the formation of microcracks that lead to strength degradation. By contrast, the yttria‐doped material does not suffer from microcrack formation or strength degradation at 1200°C. Strength degradation does occur at higher temperatures and, as a consequence, an upper limit of 1200°C is recommended for yttria‐doped hot‐pressed silicon nitride in structural applications.
Identification of α‐Al2O3 Precipitates in Rutile Single Crystals
Authors: Thong Ngo , Carry Claude , Moeckli Pedro
Published: June 2006

After high‐temperature reaction between Al2O3 and TiO2 crystals, precipitates found in rutile were characterized by electron microprobe and X‐ray diffraction methods and by optical and electron microscopy. The precipitates were identified as α‐Al2O4. Geometric and crystallographic orientation relations with the TiO2 matrix constitute a reverse case of rutile precipitation in star sapphire.
Reaction of High‐Silica Optical Fibers with Hydrofluoric Acid
Authors: Lee Mou‐Tion
Published: June 2006

Optical fibers are used to determine the etching rate and activation energy of silica and high‐silica glasses in hydrofluoric acid. The reaction is linearly dependent on time and transport controlled.
Elasticity and Damping of Porous Materials and Impregnated Materials
Authors: NIELSEN LAUGE FUGLSANG
Published: June 2006

Earlier, a method was developed by the present author which predicts the elastic moduli of isotropic two‐phase materials with arbitrary phase geometry. The primary scope of the present article is to demonstrate how this method works when used to predict elasticity (Young's modulus) and damping (loss tangent) of porous materials and impregnated materials made of elastic and/or viscoelastic Components. Simple equations are developed which are directly applicable to practical situations. Their qualities are tested successfully against a number of experimental data.
Kinetic Behavior of H and D Atoms in γ‐Irradiated SiO2 as Studied by ESR Spectroscopy
Authors: MIYAZAKI TETSUO , AZUMA NAOTO , FUEKI KENJI
Published: June 2006

The decay of hydrogen atoms, produced by γ irradiation of fused silica and quartz, was studied by ESR spectroscopy. The decay of H atoms in silica cannot be explained by a secondorder kinetics nor by a simple first‐order kinetics. Also, the decay is not composed of several first‐order processes with different activation energies. The data for the decay of H atoms can be described by a first‐order kinetic equation with a timedependent rate constant of the form k(t) =Btα−1, where B and α are constants. The decay kinetics of D atoms in deuterated fused silica and H atoms in a single crystal of quartz are also explained by use of the time‐dependent rate constant. The apparent activation energies for the decay of H and D atoms in the silica are 15 to 16 kJ/mol and 14 to 15 kJ/mol, respectively. The decay rates for D and H atoms in the silica are similar.
Hexagonal β‐SiC Particles
Authors: SATO HIROSHI , OTSUKA NOBUO , LIEDL G.L. , MANSOUR SAID
Published: June 2006

Among small β‐SiC particles (0.2 ∼ 0.4 μm in size) produced by chemical vapor reaction, hexagonal particles having diameters around 0.2 μm are sometimes found. When observed by TEM, they have image contrasts reminiscent of “multiply twinned particles”. Analysis of diffraction patterns and image contrasts observed indicates that these particles consist of multiple twins with twin planes parallel to the basal plane. The characteristics of growth processes of such particles are discussed.
Dielectric Characteristics of Na2O · 3SiO2 Glasses with High Water Contents
Authors: TAKATA MASASUKE , MOLINELLI JOYCE E. , TOMOZAWA MINORU , WATSON E. BRUCE
Published: June 2006

Dielectric characteristics of Na2O·3SiO2 glasses with water contents up to ∼12 wt% were found to be drastically affected by incorporated water. The high‐frequency dielectric constant increased with water content, while both the static dielectric constant and the low‐frequency dielectric relaxation strength showed a pronounced minimum at a water content of ∼3 wt%.
Influence of As2O3 on the Optical Properties of Ultrapure Multicomponent Silicate Glasses and Optical Fibers
Authors: SPIERINGS G. A. C. M.
Published: June 2006

To obtain low transmission loss optical fibers from ultrapure multicomponent silicate glasses, it is necessary to add small quantities of As2O3 (or Sb2O3). In optical fibers prepared from glasses without these agents, a significant increase in loss is observed. To investigate this effect, the influence of As2O3 (added to the batch and present in the glass as As2O5) on the optical properties of ultrapure silicate glasses was studied. These properties are the Rayleigh scattering loss coefficient, transition metal absorption, and position of the uv absorption edge. This study showed that the increase in loss of As2O3‐free glass cannot be assigned to any of these contributions and was attributed to absorption by electrons, trapped in relatively shallow traps in the glass network. The As5+ ions serve as deep traps and therefore remove the additional absorption. The same phenomenon, although much more pronounced, was observed in optical fibers prepared from alkali borosilicate glasses.
Damage Penetration at Elongated Machining Grooves in Hot‐Pressed Si3N4
Authors: KIRCHNER HENRY P.
Published: June 2006

In hot‐pressed Si3N4 subjected to single‐point diamond grinding, the damage penetration (c) at low vertical loads (Pv) is approximately related by Pvαc, whereas at high loads the load dependence of the crack length is much greater. The results at low loads are discussed in terms of available analyses. An analysis, based on the combined effect of the residual stresses and contact loads, is presented to model the behavior at high loads.
Development of Porous Antireflective Films on Soda‐Lime‐Silica Glass
Authors: ROHE V. TENGZELIUS , DANFORTH S. C. , HAGGERTY J. S.
Published: June 2006

Glass compositions were surveyed to identify candidates that could be heat‐treated to produce an interconnected phase‐separated structure needed for porous antireflective films and which matched the viscosity‐temperature characteristics needed for the float glass process. A glass composition of 10% Na2O,10% CaO, and 80% SiO2 meets these criteria. Microstructural development and film‐formation kinetics were characterized to permit definition of appropriate heat‐treatment and selective dissolution processes. Broadband antireflective characteristics were developed on treated glass surfaces.
High‐Temperature Cation Distributions in Fe3‐FeAl2O4
Authors: Mason T. O.
Published: June 2006

Cation distribution at 1600 K in the system Fe3O4‐FeA12O4 was derived from Seebeck coefficient measurements assuming that the aluminum distribution behaved according to the thermodynamic model proposed by O'Neill and Navrotsky. Approximately 10% of the aluminum resides tetrahedrally. This system provides a good test of thermodynamic models.
Resistance of Titanium Diboride to High‐Temperature Plastic Yielding
Authors: Ramberg Jeffrey R. , Wolfe Cynthia F. , Williams Wendell S.
Published: June 2006

Polycrystalline TiB2 specimens of 3 μm average grain size but free of lamellar precipitates were compression‐tested to 1900°C and 500 MPa. No plastic yielding was detected. Under such conditions, most other structural ceramics do exhibit yield behavior. The results suggest the existence of a high Peierls stress, presumably related to Ti—B bonding. This finding contrasts with a report on ZrB2 in which resistance to yielding was attributed to lamellar precipitates.
Boron Coordination in Rapidly Cooled and in Annealed Aluminum Borosilicate Glass Fibers
Authors: Gupta Prabhat K. , Lur Ming L. , Bray Philip J.
Published: June 2006

The fraction of four‐coordinated boron was observed to increase from 10% in a rapidly cooled aluminum borosilicate glass fiber to 16% in the same fiber after it was annealed; the refractive index also increased. The index of the annealed fiber agreed with that of the bulk glass. Crystallization was not observed in the annealed fiber. It is concluded that boron coordination is temperature dependent and associated with structural relaxation.
Effect of Crystallites on Subcritical Crack Growth and Strain‐Rate Sensitivity of Strength of Cordierite Glass‐Ceramics
Authors: BASKARAN S. , BHADURI S.B. , HASSELMAN D.P.H.
Published: June 2006

A study was conducted of the subcritical crack growth in a series of cordierite glass‐ceramics, including the original glass, by means of the double‐torsion method and measurement of the strain‐rate sensitivity of the strength of specimens with controlled indentation cracks subjected to biaxial flexure. The double‐torsion data showed that the same rate of crack growth required a stress intensity factor for the fully crystallized glass‐ceramic about 3 times higher than for the original glass, accompanied by a simultaneous increase in the stress intensity exponent (N). The suppression in the rate of crack growth in the crystallized material at any value of stress intensity factor was attributed to enhanced crack deflection around the crystallites. Limited observations suggested that the increase inNon crystallite formation may be due to a greater degree of crack deflection at the lower crack velocities than at the higher velocities. For strength specimens of the as‐received and crystallized glass with large surface flaws, theNvalues obtained by the strain‐rate measurements and the double‐torsion test showed good agreement. However, for the fully crystallized material with surface flaws too small to interact significantly with the coarser crystallites, theNvalue for the strain‐rate data was well below the value for the double‐torsion method. Indentation‐fracture data of the double‐torsion specimens confirmed the existence of crack‐size dependent fracture toughness. Limited fracture toughness data coupled with SEM fractography indicated that with increasing crystallite size toughening occurs by crack deflection as well as by microcrack toughening counteracted by fracture through the crystallites.
Analytical Study of Pure and Extended Portland Cement Pastes: I, Pure Portland Cement Pastes
Authors: TAYLOR H. F. W. , MOHAN K. , MOIR G. K.
Published: June 2006

A range of portland cement pastes were examined by X‐ray diffraction, analytical electron microscopy, thermogravimetry, and CO2 analyses. Quantitative estimates of the phase compositions of the pastes and of the chemical compositions of the individual phases within them were obtained, and mass balance calculations were done for each oxide component to test the mutual consistency of the results. As a further test, thermo‐gravimetric curves were calculated from the phase compositions and compared with those found experimentally. Volume percents of phases, porosities, and related quantities were also calculated. For a typical cement cured for 28 d in a sealed container at a water, cement ratio of 0.5 and equilibrated at 11% rh, the calculated volume percents are as follows: unreacted clinker phases, 11; C‐S‐H, 29; Ca(OH)2, 11; AFm phase, 9; CaCO3, 1; pores, 39.
Synthesis of Si3N4 with Emphasis on Si‐S‐N Chemistry
Authors: MORGAN PETER E. D. , PUGAR ELOISE A.
Published: June 2006

Industrial production of Si3N4 from SiCI4, is increasing. An element rivaling CI in abundance and cheapness with potentially suitable chemistry for this application is sulfur. Thus, Si–S–N chemistry was investigated to determine its usefulness in producing Si3N4. Bifunctionality in S, as opposed to mono‐functionality in CI, may allow special routes via polymers to become important.
Work of Fracture and Crack Healing in Glass
Authors: INAGAKI MICHIO , URASHIMA KAZUHIRO , TOYOMASU SHINSUKE , GOTO YASUO , SAKAI MOTOTSUGU
Published: June 2006

The work of fracture, γwoF, of a soda‐lime‐silica glass was determined as 5.5 J/m2 in an inert atmosphere and 4.4 J/m2 in air by using a short bar specimen with a chevron notch. The critical stress intensity factor KIC calculated from γwof obtained in an inert atmosphere agreed with the value, 0.88 MN/m3/2, determined by the indentation method. In unloading‐loading cycles during stable crack growth, crack healing was observed both on the diagram of load vs load‐point displacement and visually. Crack healing is more prevalent in an inert atmosphere, occurring only minimally in air. The energy for healing was measured as 0.65 J/m2 in an inert atmosphere and ∼0.21 J/m2 in air.
Shock Consolidation of Coarse Sic Powder
Authors: Akashi Tamotsu , Lotrich Victor , Sawaoka Akira , Beauchamp Edwin K.
Published: June 2006

Sic compacts with 98.6% of theoretical density were obtained from coarse powder by a shock compaction technique. Microhardness values for the compacts obtained at 8 and 13 GPa ranged from 15.7 to 22.5 GPa and from 21.6 to 28.2 GPa, respectively. Scanning electron microscopy suggested that small amounts of molten material participated in the shock consolidation process.
Fracture Toughness of Ceramics Measured by a Chevron‐Notch Diametral‐Compression Test
Authors: Sheity Dinesh K. , Rosenfield Alan R. , Duckworth Winston H.
Published: June 2006

A diametral‐compression test that features disk specimens with chevron notches was developed and applied to measure fracture toughness (Klc) of three ceramics. Fracture–toughness values calculated from the fracture loads and a compliance analysis were in good agreement with values measured by other fracture–mechanics techniques. Advantages of the proposed test include simple specimen geometry, minimal requirements for fixtures, and consequent potential for application at elevated temperatures.
Isothermal Sintering of Spheroidized Cordierite‐Type Glass Powders
Authors: Giess Edward A. , Guerci Carl F. , Walker George F. , Wen Sheree H.
Published: June 2006

Jagged (ball–milled) glass particles were spheroidized and pressed into compacts which were isothermally sintered in air. Both jagged‐ and spheroidized‐particle compacts showed about the same 0.7 anisotropy of the ratio of axial to diametral shrinkage, but spheroidizing reduced the shrinkage rate. Thus, shrinkage anisotropy is not a simple particle shape effect; it may relate to differences in the axial and radial distributions of particle sizes present in these compacts.
Segregation at Special Boundaries in MgO
Authors: Roshko A. , Kingery W. D.
Published: June 2006

Segregation of Ca to three high‐angle boundaries in MgO was analyzed using scanning transmission electron microscopy. Two boundaries were special [001] twist boundaries (Σ=5 (Σ=36.9°), Σ=17 (Σ=28.5°)) and one was nonspecial. The concentration of Ca at the special boundaries was approximately half that at the nonspecial boundary.
Evaluation of Reliability of Brittle Components by Thermal Stress Testing
Authors: JOHNSON‐WALLS D. , DRORY M. D. , EVANS A. G. , MARSHALL D. B. , FABER K. T.
Published: June 2006

A thermal stressing technique was applied to evaluate two distinct flaw populations (surface and corner) in BaTiO3 multilayer capacitors. The mechanical reliability of the capacitors was deduced by relating the thermal stress response to the mechanical strength of the material. The surface flaw population alone yields relatively high survival probabilities, whereas incorporation of the corner flaw population severely reduces the probability of survival.
Solubility of BaO in BaTiO3
Authors: HU Y. H. , HARMER M. P. , SMYTH D. M.
Published: June 2006

The solubility and mode of incorporation for BaO in BaTiO3 were studied by X‐ray powder diffraction, scanning and transmission electron microscopy, electron probe microanalysis, and equilibrium electrical conductivity measurements. The presence of barium orthotitanate, Ba2TiO4, as a second phase for samples containing >0.1 mol% excess BaO was confirmed by direct microscopic examination. There was no evidence to support the incorporation of excess BaO into BaTiO3 by a Ruddlesden‐Popper type of superlattice ordering mechanism. Measurement of the equilibrium electrical conductivity showed no detectable shift in the conductivity profile resulting from excess BaO, thus setting an upper limit of 100 ppm for the solubility of BaO in BaTiO3.
Controlled Microwave Heating and Melting of Gels
Authors: ROY RUSTUM , KOMARNENI S. , YANG L. J.
Published: June 2006

Controlled microwave heating and melting of silica, alumina, and aluminosilicate gels were achieved in a 600‐W domestic‐type oven. The microwave absorption mechanism of these gels is not yet clear. However, parameters were defined whereby rapid heating (including melting) is achieved for these gels. Empirical results indicate that the heating behavior is dependent on the chemistry, structure, and mass of the gel.
Fracture of Yttria‐Doped, Sintered Reaction‐Bonded Silicon Nitride
Authors: GOVILA R. K. , MANGELS J. A. , BAER J. R.
Published: June 2006

Flexural strength of an yttria‐doped, slip‐cast, sintered reaction‐bonded silicon nitride was evaluated as a function of temperature (20° to 1400°C in air), applied stress, and time. Static oxidation at 700o to 1400°C was investigated in detail; in tests at 1000°C in air, the material showed anomalous weight gain. Flexural stress‐rupture testing a 800° to 1200°C in air indicated that the material is susceptible to stress‐enhanced oxidation and early failure. Fractographic evidence for time‐dependent and ‐independent failures is presented.
Oxidation of Silicon Nitride Sintered with Rare‐Earth Oxide Additions
Authors: Mieskowski Diane M. , Sanders William A.
Published: June 2006

The effects of rare‐earth oxide additions on the oxidation of sintered Si3N4 were examined. Insignificant oxidation occurred at 700o and 1000oC, with no evidence of phase instability. At 1372oC, the oxidation rate was lowest for Y203 and increased for additions of La2O3, Sm2O3, and CeO2, in that order. Data obtained from X‐ray diffraction, electron microprobe analysis, and scanning electron microscopy indicate that oxidation occurs via diffusion of cationic species from Si3N4 grain boundaries.
Gamma‐to‐Alpha Transformation in Spherical Aluminum Oxide Powders
Authors: TUCKER DENNIS S. , BLEIER A.
Published: June 2006

The transformation of spherical alumina powders precipitated from an aluminum sulfate solution was studied using a combination of X‐ray diffraction and transmission electron microscopy. Particles calcined at 900°C consisted of poly‐crystalline γ‐alumina which transformed to essentially single‐crystal a‐alumina on further calcination.
Crystallization of Hexagonal BaNb2O6
Authors: YAMAGUCHI OSAMU , MATSUI KAZUHIRO , SHIMIZU KIYOSHI
Published: June 2006

Pure hexagonal BaNb2O6 crystallizes at 640° to 700°C from an amorphous material prepared by simultaneous hydrolysis of barium and niobium alkoxides. The structure is characterized by layer networks of NbO6 octahedra. Crystallization isotherms are described by the Avrami equation In (1—f) = ‐ktn with n=2; the activation energy is 268 kJ‐mol‐'. Hexagonal BaNb2O6 transforms to the ortho‐rhombic modification one at 12.50° to 1310°C.
Characterization of Interfacial Reactions Between β‐Al2O3 and Y2O3‐Partially‐Stabilized ZrO2
Authors: GLASS S. JILL , NICHOLSON PATRICK S. , CLARK C. BURTON , HEUER A. H.
Published: June 2006

The interfacial reaction between Y2O3‐partially‐stabilized ZrO2 and α‐Al2O3 was studied. It was noted that α‐Al2O3 forms inside the periphery of the β‐Al2O3 grains; its formation suggests the loss of Na2O from the p‐Al2O3, either by evaporation or by dissolution in the ZrO2 matrix. The presence of Na2ZrO3 is suspected.
Theory for the Load Relaxation Technique in Fracture Studies Using Four‐Point‐Bend Chevron‐Notched Specimens
Authors: TROCZYNSKI THOMAS B. , NICHOLSON PATRICK S.
Published: June 2006

The load‐relaxation technique is reviewed using the energy approach for four‐point‐bend chevron‐notched samples. The influence of the sample and bending geometry and the stiffness of the testing system on the strain‐energy release rate is considered. Proper experimental design allows the study of fracture initiation, propagation, and arrest, Special attention is paid to the effect of overload at fracture initiation on crack propagation. It is concluded that the chevron–notched sample offers great flexibility for gaining information on the fracture properties of ceramic materials.
Effect of Interfacial Space‐Charge Polarization on the Ionic Conductivity of Composite Electrolytes
Authors: DUDNEY N.J.
Published: June 2006

An enhanced carrier concentration within the interfacial space‐charge layers has been proposed as one possible mechanism leading to the enhanced ionic conductivity observed for a variety of composite electrolytes containing a dispersed second phase of fine insulating particles such as A12O3. This study tests this proposal by estimating the maximum space‐charge polarization that might reasonably occur at interfaces of nominally pure AgCI, β‐AgI, and LiI. The resulting interface conductances are used in effective medium calculations of the total conductivity of a randomly distributed composite of these salts with A12O3 particles. Comparison of the results with published conductivities for the composites shows that the modest enhancement found for AgC1/A12O3 can be accounted for by the interfacial space‐charge polarization. However, the large (50‐ to 500‐fold) enhancements found for β‐AgI/A12O3 and LiI/A12O3 must be attributed to another mechanism.
Microwave Loss Quality of BaZn13Ta2/3O3 Ceramics
Authors: DESU S. B. , O'BRYAN H. M.
Published: June 2006

Loss of ZnO explains the improved microwave loss quality (Q) for Ba(Zn1/3Ta2/3)O3 ceramics which have been sintered at high temperatures or longer times. Ordering of Zn and Ta is complete in 60 h at 1400°C, but crystallographic distortion and Q continue to increase up to 120 h. As ZnO volatilizes from the sample, Ba replaces Zn on the B sites and permits additional crystallographic distortion; meanwhile, barium tantalate phases also appear. Crystallographic compositional data are presented to confirm this interpretation.
Properties of Lead Fluorosilicate Glasses
Authors: Shelby James E.
Published: June 2006

Lead fluorosilicate glasses containing up to 25 mol% PbF2 were prepared. The dc electrical conductivity, thermal expansion, and transformation‐range viscosity of these glasses indicate that they are anionic conductors and that fluorine significantly decreases the continuity of the vitreous network.
Effect of Milling on Slip Casting of Partially Stabilized Zirconia
Authors: Taguchi Hideki , Takahashi Yuzuru , Miyamoto Hiroki
Published: June 2006

Specimens of partially stabilized zirconia were slip cast from aqueous suspensions and sintered at 1500°C for 3 h. The relative density of the cast specimens and the firing shrinkage of the sintered specimens depend on the milling time for the suspension. Vickers hardness and KIC values of 11.46±s0.07 GN/m2 and 6.10 ±0.04 MN.m3/2, respectively, were obtained for all sintered specimens. The dispersion of the suspension is important in increasing the relative density of the cast specimens.
Alkali Oxide Rich Sodium Titanates
Authors: Antony Hill W. , Moon Anthony R. , Higginbotham Geoffrey
Published: June 2006

In the characterization of sodium titanates to be used in glass melts, several inconsistencies in the published literature were noted, especially in the alkali oxide rich phase region. Contrary to published data, there are three separate phases with stoichiometry Na2O.TiO2. One of these has previously been incorrectly reported us 3Nu2O.2TiO2. The lattice parameters of these three phases were established using a precision powder diffractometer.
Driving Force for Sintering of Particles with Anisotropic Surface Energies
Authors: Searcy Alan W.
Published: June 2006

Crystalline aggregates at constant temperature and pressure are unstable toward shape changes for which , where δG is a dzgerential change in the Gibbs free energy, σiAi is the free energy of surface or interface i, and γihi is the free energy of edge, ledge, or dislocation defect i. The expression reduces to the familiar expression for the driving force for early‐stage sintering. Line defects play central roles in driving the sintering of crystalline solids.
Resistance to Fracture of a Partially Stabilized Zirconia/β‐Alumina Composite
Authors: Troczynski Thomas B. , Nicholson Patrick S.
Published: June 2006

Partially stabilized zirconia (PSZ) /β‐alumina composites exhibit extensive non‐elastic deformation during fracture. Repeated loading/stable fracture/unloading experiments were performed on chevron‐notched four‐point‐bend specimens of the composite and pure PSZ. The energy consumption during the propagation of long cracks in the composite (∼500 J/m2) is 1 order of magnitude larger than for PSZ (∼50 J/m2). Breaking strengths of 127 MPa were obtained with a Weibull modulus of 43.
Indenter Flaw Geometry and Fracture Toughness Estimates for a Glass‐Ceramic
Authors: SHEITY D. K. , ROSENFIELD A. R. , DUCKWORTH W. H.
Published: June 2006

Shapes of cracks associated with Vickers indenter flaws in a glass‐ceramic were assessed by stepwise polishing and measuring surface traces as a function of depth. The cracks were of the Palmqvist type even at200‐N indentation load. The toad dependence of crack lengths and fracture toughness estimates were examined in terms of relations proposed for Palmqvist and half‐penny cracks. Estimates based on the half‐penny crack analogy were in closer agreement with bulk fracture toughness measurements despite the Palmqvist nature of the cracks.
Noncontact Ultrasonic Characterization of Ceramics
Authors: Jen Cheng‐Kuei , Cielo Paolo , Maldague Xavier , El‐Assal Kamal
Published: June 2006

A noncontact ultrasonic technique for the characterization of piezoelectric ceramics is described. The velocity of a laser‐generated surface‐acoustic‐wave pulse propagating at the surface of the ceramic material is measured by an optical probe. The laser beam has an annular section in order to produce a conveniently strong ultrasonic pulse without overheating the surface. Applications to the characterization of PZT samples are described.
Feasibility Study of the Welding of Sic
Authors: Moore Thomas J.
Published: June 2006

In a brief study of the feasibility of welding sintered a‐Sic, solid‐state welding and brazing were investigated. Joint quality was determined solely by microstructural examination. Hot‐pressure welding was shown to be feasible at 1950°C. Diffusion welding and brazing were also successful under hot isostatic pressure at 1950°C when boride, carbide, and silicide interlayers were used. Furnace brazing was accomplished at 1750°C when a TiSia interlayer was introduced.
Outstanding Problems in the Kaolinite‐Mullite Reaction Sequence Investigated by 29Si and 27Al Solid‐state Nuclear Magnetic Resonance: 11, High‐Temperature Transformations of Metakaolinite
Authors: BROWN I. W. M. , MacKENZIE K. J. D. , BOWDEN M. E. , MEINHOLD R. H.
Published: June 2006

Solid‐state 29Si and 27Al NMR spectra of kaolinite fired at 800° to 1450°C, interpreted in light of a newly proposed metakaolinite structure and complementary X‐ray diffraction results, lead to the following conclusions about the hightemperature reactions: (1) Removal of the final residual hydroxyl radicals of metakaolinite at ∼9707deg;C triggers the separation of a considerable amount of amorphous free silica and the formation of poorly crystalline mullite and a spinel phase. (2) Mullite and spinel form in tandem, the former originating in the vicinity of AI‐0 units of regular octahedral and tetrahedral symmetry randomly distributed throughout the metakaolinite structure. (3) The initially formed mullite is alumina‐rich but at higher temperatures progressively gains silica, approaching the conventional 3Al2O3· 2SiO2 composition. (4) The spinel phase contains insufficient Si to be detected by 29Si NMR but has a 27Al NMR spectrum consistent with γ‐Al2O3. On further heating, the spinel is converted to mullite by reaction with some of the amorpholls silica, the balance of which eventually becomes cristobalite.