bluuebunny/crossref_metadata_2025 huggingface dataset:
Load/Radial Crack Size Relations for Static Indentations in Zinc Sulfide
Authors: Klrchner H. P. , Larchuk T. J.
Published: June 2006

Contact damage was induced in zinc sulfide plates by pressing glass spheres into the surfaceshd The radial crack lengths (c) were measured and correlated with the applied load (P) using Pαd1f112, where di is the contact diameter. This yielded an excellent correlation and showed a load threshold and a transition region in the near field, as expected. Pαc3/2 yielded a poorer correlation.
Subsolidus Phase Relations Between 900° and 1700°C in the Systems BeO‐MgO‐CeO2, SrO‐MgO‐CeO2, BaO‐MgO‐CeO2, and BaO‐CaO‐CeO2
Authors: Longo V. , Meriani S. , Ricciardiello F.
Published: June 2006

Solid state phase relations in the systems BeO‐MgO‐CeOz, SrO‐MgO‐CeO2, BaO‐MgO‐CeOz, and BaO‐CaO‐CeO2 were investigated at 1700°, 1500°, 1300° 1200°, 1100°, 1000°, and 900°C by X‐ray diffractometry and reflected‐light microscopy. This study was conducted with quenched specimens. The most significant equilibrium isotherms are reported.
Thermally Stimulated Currents in Sodium Silicate Glasses
Authors: HONG CHI‐MING , DAY DELBERT E.
Published: June 2006

Sodium‐ion motion in three sodium silicate glasses and a sodium aluminosilicate glass was investigated by the thermally stimulated polarization (TSPC) and depolarization (TSDC) current techniques. The two TSDC peaks found in the sodium silicate glasses were attributed to localized sodium‐ion movement around a nonbridging oxygen ion, a type of dipolar orientational polarization, and to a longer‐range sodium motion leading to interfacial polarization at the immiscible phase boundaries. The high‐temperature background (HTB) current corresponded to the sodium motion for dc conductivity and diffusion. The commonly observed dc absorption current was found to be related to the two TSDC peaks.
Strength of a Ceramic at High Temperatures Under Biaxial and Uniaxial Tension
Authors: GIOVAN M. N. , SINES GEORGE
Published: June 2006

A design is presented for a fixture to test concentric‐ring loaded disks and four‐point loaded plates at high temperatures. In this fixture the loading plunger is guided by flexure plates to determine the load path with accuracy. The uniaxial and equibiaxial tensile strengths of a brittle material were measured at 982°C with this fixture. For lapped surfaces, the equibiaxial tensile strength of dense, isostatically pressed, sintered alumina was 16.0% lower than the uniaxial tensile strength. The uniaxial strength at 982°C was 42.3% lower than the previously reported value for comparable tests at room temperature. The effect of frictional forces and lateral constraint, of specimen and loading geometry, and of local stresses on the nominal stress are discussed.
Fracture Strength and Mirror Size in a Commercial Glass‐ Ceramic
Authors: LEWIS DAVID
Published: June 2006

Extensive observations on the strength‐fracture mirror size relation for a commercial cordierite‐based glass‐ceramic indicate a systematic deviation from the expected behavior at high strength/small mirror sizes. Calculations of internal stresses from phase properties suggest that the observations result from direct effects of internal stresses on fracture‐mirror formation or from indirect effects of internal stresses affecting the fracture toughness and hence fracture‐mirror size.
Effect of γ Radiation on Plastic Flow of NaCl
Authors: LERNER I. , KOHLSTEDT D. L.
Published: June 2006

Room‐temperature load‐relaxation tests were performed on γ‐irradiated and unirradiated NaCl single crystals. The σ‐ɛ reresults were analyzed in terms of Hart's constitutive equations for inelastic deformation. The log σ‐log ɛ curves for the unirradiated crystals were virtually flat, suggesting that both the high‐ and low‐temperature components of the flow stress were operating. The log σ‐log ɛ curves for the irradiated crystals were concave downward, indicating that the high‐temperature mechanism was dominating the flow stress.
Identification of a New Yttrium Oxycarbide, Y2OC
Authors: Holcombe C. E. , Carpenter D. A.
Published: June 2006

A new face‐centered‐cubic (fee) compound has been identified in the system yttrium‐oxygen‐carbon (Y‐O‐C). Several synthesis routes with reaction temperatures from 930° to 2000°C produce the phase. Quantitative X‐ray diffraction (XRD) phase analysis indicated the composition to be Y2OC. The powder XRD pattern and refined lattice parameter are reported.
Radiation‐Coloration‐Resistant Glasses With High‐Water Content
Authors: Acocella J. , Takata M. , Tomozawa M. , Watson E. B.
Published: June 2006

Radiation‐coloration‐resistant glasses were prepared by incorporating a larghd amount of water into dry glasses under hydrothermal conditions. After γ‐ray irradiation of 106 rad, the glasses remained transparent.
Morphology and Stability of the Glass Phase in Glass Ceramic Systems
Authors: RAJ RISHI
Published: June 2006

An explanation is given for the apparent stability of a minor phase in a two‐phase system, such as a glass in a glass ceramic, even though normally the glass would be expected to dissolve completely into the crystalline phase. It is shown that the glass would be stable only if it is segregated to the triple‐junction nodes and only if the dihedral angle is <π/3. The size and morphology of the glass pocket are obtained in terms of the interface energies, the undercooling below the solidus temperature, and the dihedral angle.
High‐Alumina Tailored Nuclear Waste Ceramics
Authors: MORGAN P. E. D. , CLARKE D. R. , JANTZEN C. M. , BARKER A. B.
Published: June 2006

A dense high‐alumina ceramic has been developed for the immobilization of Savannah River Plant nuclear waste. The ceramic, fabricated by reactive hot‐pressing, consists of four compatible crystalline phases, alumina, spinel, magnetoplumbite, and uraninite. The magnetoplumbite phase can incorporate the elements Cs, Sr, Si, Na, Ca, Ba, La, Nd, Mn, Fe, Ce, K, and Ni in its crystal structure, whereas the uraninite phase hosts the elements U, Th, and Zr. The remaining phases in the ceramic provide microstructural isolation of both the uraninite and magnetoplumbite. The mineralogy of the system is modeled by phase‐compatibility investigations of the pseudoquaternary system Al2O3‐Nd2O,‐alkali + alkaline earth‐(Mg, Fe, Ni)O, enabling the extent of waste loading and the phase stability to be predicted.
Influence of Temperature and Humidity on Dynamic Fatigue of Optical Fibers
Authors: SAKAGUCHI SHIGEKI , KIMURA TAKAO
Published: June 2006

The influence of temperature and humidity on dynamic fatigue characteristics of silicone resin‐coated optical glass fibers is examined. Dynamic fatigue is shown to result from subcritical crack growth. Test results verify that subcritical crack growth during dynamic loading is a thermally activated process and that the effect of humidity on crack growth is a function of water vapor pressure.
Moessbauer Study of the Effect of Calcium Content on Iron Oxide Transformations in Fired Clays
Authors: MANIATIS Y. , SIMOPOULOS A. , KOSTIKAS A.
Published: June 2006

Sixteen clays were studied by Moessbauer measurements in their unfired and fired forms. Thirteen of these clays were collected near ancient Greek sites and the remaining three in England and the United States. They were fired at 700°, 900°, and 1080°C to investigate the physicochemical transformations of the clay components in this temperature range. The results show distinctly different responses of the clays, according to their CaO content. Firing of the calcareous clays (>5 % CaO content) at 700°C produces small oxide particles (mainly hematite). This phase remains stable on further firing up to 1080°C, where it decreases slightly. Contrary to this behavior, the noncalcareous clays display a continuous increase of the amount and size of the oxide particles when fired up to 1080°C. This difference is attributed to stable calcium aluminosilicate phases which are formed in the calcareous clays as opposed to the continuous vitrification which occurs for the noncalcareous clays by firing up to 1080°C. The variation of the quadrupole splitting of the central doublet with firing temperature also differs for the two types of clays. The quadrupole splitting values among the clays span a range of 1.1 to 1.6 mm/s for a firing temperature of 700°C. Above this temperature, a distinct separation of the two groups occurs with the quadrupole splitting of calcareous clays lying higher.
Ion Exchange of Soda‐Lime Glass with Univalent Cations
Authors: SHAISHA E. E. , COOPER A. R.
Published: June 2006

Fhdeld‐assisted and ordinary diffusion ion exchange of K+, Rb+hd Cs+, and Ag+ from nitrate salts with Na+ in soda‐lime glass tubes were investigated between 700 and 735 K by application of various currents between 0 and 20.0 mA. An analysis of the field‐assisted process with both a forward and a reverse field allowed calculation of the conductivity of the exchanged layer from the change of potential difference with time. Good agreement with experiment was found in both directions but anomalously high conductivities were observed in the Rb and Cs layers. Photoelastic measurements on rings sliced from the ion‐exchanged tubes were used to calculate the residual stress arising from the ion exchange with the different cations. These results showed that other factors in addition to the ion size influence the magnitude of residual stress after exchange. The voltage‐current relation during field‐assisted ion exchange, along with the Nernst‐Einstein equation, permitted calculation of the self‐discussion coefficient of the exchanged cation in the exchanged layer. The self‐diffusion coefficient was also estimated by applying the Nernst‐Planck equation to results from unassisted ion‐exchange experiments.
Effects of MoO3, on Phase Separation of Na2O‐B2O3‐SiO2 Glasses
Authors: KAWAMOTO Y. , CLEMENS K. , TOMOZAWA M.
Published: June 2006

Immiscibility temperatures of Na2O‐B2O3‐SiO glasses, with andwithout 1 mol% MoO3, additions, were determined and the effect of MoO3 additions on the 65O°C immiscibility isotherms was established. In addition, immiscibility temperature and phase‐separation morphology of an Na2O‐B2O3‐SiO2 glass with progressive additions of MoO3, were investigated. It was found that the addition of small amounts of MoO3 extends the immiscibility boundary of the system and raises the immiscibility temperature by ∼l8°C for each mol % MoO3, addition. Analysis of phase‐separation morphology suggests that the MoO3, additions do not significantly alter the tie lines of phase separation in the system, although such additions cause a lowering of the viscosities and the glass‐transition temperatures of these glasses.
Quantitative Studies of Thermal Shock in Ceramics Based on a Novel Test Technique
Authors: FABER K. T. , HUANG M. D. , EVANS A. G.
Published: June 2006

A thermal shock test was designed which permits the thermal fracture resistance and the mechanical strength of brittle materials to be quantitatively correlated. Thermal shock results for two materials, A12O3 and SiC, were accurately predicted from biaxial strength measurements and a transient thermal stress analysis (performed using a finite element method). General implications for the prediction of thermal shock resistance, with special reference to ceramic components, are discussed.
Mass‐Spectrometric and Electrochemical Studies of Thermodynamic Properties of Liquid and Solid Phases in the System CaO‐Al2O3
Authors: ALLIBERT MICHEL , CHATILLON CHRISTIAN , JACOB K. T. , LOURTAU ROGER
Published: June 2006

The activities of CaO and Al2O3 in lime‐alumina melts were studied by Knudsen cell‐mass spectrometry at 2060 K. Emf of solid state cells, with CaF2 as the electrolyte, was measured from 923 to 1223 K to obtain the free energies of formation of the interoxide compounds. The results are critically evaluated in the light of data reported in the literature on phase equilibria, activities in melts, and stabilities of compounds. A coherent set of data is presented, including the previously unknown free energy of formation of CaO.6Al2O3 and the temperature dependence of activities in the liquid phase.
Toughening of Ceramics by Circumferential Microcracking
Authors: EVANS A. G. , FABER K. T.
Published: June 2006

An approximate analysis is presented of the toughening induced by the incorporation of second‐phase particles subject to microcrack‐ing. It is demonstrated that the toughening becomes appreciable for a narrow size distribution of particles of appropriate size. The magnitude of the toughening is determined by the mismatch strain (due to thermal contraction incompatibility) and the microfracture resistance of the particle/matrix interface. Implications for designing optimally tough ceramics are presented.
Role of Water Vapor and Sulfur Compounds in Sodium Vaporization During Glass Melting
Authors: SANDERS D. M. , WILKE M. E. , HURWITZ S. , HALLER W. K.
Published: June 2006

The influence of sulfur compounds on the vaporization of sodium from soda‐lime‐silica glass was investigated using the newly developed stirrable transpiration apparatus (STA). With increasing sulfur concentration in either the melt or the atmosphere above it, the sodium‐vapor density was found to increase until attaining the value found over pure sodium‐sulfate liquid. At that point, the sodium‐vapor density became independent of sulfur concentration, presumably due to separation of sodium‐sulfate liquid from the glass. Since the vaporization behavior of the glass containing sulfur was similar to that of molten Na2SO4, the thermodynamically predicted increase in sodium‐vapor density in the presence of water vapor was explored. Due to apparent kinetic limitations, however, no such increase was observed. The possible importance of these results in commercial glassmelting practice is discussed
Acoustic Emission in the Drying of Hardened Cement Paste and Mortar
Authors: NADEAU J. S. , BENNETT R. , MINDESS S.
Published: June 2006

Acoustic emission (AE) during the drying of cement and mortar was studied extensively; AE in direct fracture of notched beams was also measured. A new method for observing the hydration of cement by measuring acoustic conductivity was developed and used to aid in the interpretation of the drying experiments. Acoustic emission due to drying increased rapidly with the time of hydration. It reached a maximum value at ∼60 days for hardened cement paste and 240 days for a standard mortar. It is shown to be caused by fractures in structures that develop, at least in part, during the drying process.
Stability of Si3N4 and Liquid Phase(s) During Sintering
Authors: Greskovich C. , Prochazka S.
Published: June 2006

Advanced sintering techniques for consolidation of Si3N4 powders in the presence of an oxygen‐rich liquid phase(s) require high temperatures and usually high nitrogen pressures. A stability diagram is constructed for Si3N4 as a function of the partial pressures of nitrogen (PN2) and silicon (PSi). High PN2 (20 to 100 atm) increases the stability of Si3N4 and the oxygen‐rich liquid phase by reducing the PSi and PSi0, respectively. The region of high sinterability is outlined for submicrometer Si3N4 powders containing 7 wt% BeSiN2 and 7 wt% SiO2 as densification aids.
Verification of the Double‐Torsion Equation by Using Different Thickness Samples of a Machinable Glass‐Ceramic
Authors: Biswas D. R. , Pujari V. K.
Published: June 2006

The double‐torsion technique is commonly used to measure fracture toughness. A finite thickness of samples is used for the measurement; however, for samples of varying thickness, a correction factor is introduced in the double‐torsion equation. This was verified by using machinable glass ceramic samples differing in thickness.
Dielectric Breakdown of Porous MgAl2O4
Authors: Rupaal A. S. , Garnier J. E. , Bates J. L.
Published: June 2006

The effects of controlled porosity on the dielectric breakdown of sintered MgAl2O4 were measured using an acoustic emission technique. Results are compared to a statistical model relating dielectric strength to a random distribution of spherical pores and the probability of pores aligned in a vertical column. Data are in good agreement with the model when only maximum pore size is considered.
Interaction of BaCl2 and BaCO3 at Elevated Temperatures
Authors: Chandra Satish
Published: June 2006

The effect of adding BaCl2 to BaCO3 at elevated temperatures was studied. DTA and hot‐stage microscopy revealed that a eutectic occurs at 840°C and 14.0 mol% BaCO3. The microstructure in the reaction zone indicated that BaCO3 recrystallizes from the eutectic melt. Thus, BaCl2 additions can activate BaCO3 at a temperature as low as 840°C.
Effect of Surface Energy on the Mechanical Strength of a High‐Silica Glass
Authors: OKA Y. , WAHL J. M. , TOMOZAWA M.
Published: June 2006

The mechanical strength of high‐silica glass was measured in various organic liquids and in water. The extent of the surface‐energy reduction of glass was also estimated from the swelling or the expansion of porous glass, immersed in liquids, by measuring the stress in the core of a partially leached glass. The stress, normalized to the value in water, showed a good correlation with the heat of immersion, which is a measure of the surface‐energy reduction. Mechanical strength and the stress due to swelling showed a reasonable correlation, suggesting that the strength variation in various liquids is due to the surface‐energy variation and the accompanying force which caused the swelling.
The System CaO‐Al2O3‐P2O5‐H2O at 200°C
Authors: YUH SHANG JUNG , ROCKETT T. J.
Published: June 2006

The phase relations were established experimentally for the system CaO‐Al2O3‐P2O5‐H2O at 200°C and 1710 kPa. The quaternary compound, crandallite, CaAl3(PO4)2(OH)5· H2O, was found to be stable. Compatibility joins in the system were determined. The phase relations are presented on the isothermal‐isobaric 90 wt% water plane and by projecting the primary fields of the liquidus surface onto the same plane.
Post‐Indentation Slow Growth of Radial Cracks in Glasses
Authors: Gupta Prabhat K. , Jubb Nancy J.
Published: June 2006

An expression is developed for the slow growth of radial cracks after indentation using established notions of slow crack growth and residual stresses at the tip of radial cracks. This expression is substantiated by data gathered on indentation of microscope slides tested in air and water environments. The agreement is reasonable with the published values of the glass stress‐corrosion susceptibility coefficients. It is suggested that the present approach represents a simple and straightforward method of measuring the stress‐corrosion susceptibility of glasses.
High‐Temperature Strength of AIN Hot‐Pressed with A12O3 Additions
Authors: SAKAI TOSIKAZU
Published: June 2006

The flexural strength of hot‐pressed AIN with alumina was investigated at temperatures up to 1500°C. The strength depended on the crystal phases which formed from raw materials in the compact. The hot‐pressed specimens consisted of AIN and a pseudopolytype of AIN and showed considerable flexural strength up to 1500°C.
Stress‐Induced Microcracking at Second‐Phase Inclusions
Authors: GREEN D. J.
Published: June 2006

The critical inclusion size for microcracking due to an applied stress for an inclusion that has a residual stress field is estimated using fracture mechanics. In particular, an analysis is presented for both circumferential and radial crack formation at spherical inclusions that have a uniform misfit strain compared to the matrix. It is found that the critical size can be greatly reduced below that for spontaneous microcracking when the applied stress is of the order of the residual stress. It was predicted that the applied stress would cause extensive micro‐cracking when the local fracture toughness is low and when the size of the inclusions approaches the critical size for spontaneous microcracking.
A Mixed‐Mode Crack‐Growth and Fracture Model for Field‐Assisted Ion‐Exchanged Glass
Authors: ABOU‐EL‐LEIL MAHMOUD , COOPER A. R.
Published: June 2006

It is suggested that shear forces from the compression layer during field‐assisted ion exchange of glass cause stable growth of preexisting flaws when the advancing ion‐exchanged layer approaches the flaw tip. A quantitative model is presented which explains most of the previously puzzling experimental results, even though it ignores the change in crack direction required if the maximum tensile stress criterion is appropriate for fracture.
Molecular Dynamic Calculations of A Sodium Borosilicate Glass Structure
Authors: SOULES THOMAS F. , VARSHNEYA ARUN K.
Published: June 2006

The structure of seven sodium borosilicate glasses was calculated using molecular dynamics. Consistent with Zachariasen's rules of glass formation, silicon and boron were found to form a continuous near‐random network of SiO4, BO3, and BO4 polyhedra linked to each other at corners, whereas sodium ions occupied interstitial sites only. The most probable coordination of oxygen around sodium was five. There were roughly six oxygen atoms around an oxygen, nearly independent of the glass composition. The trigonal to tetrahedral conversion of boron with the addition of sodium agreed with the NMR results. The glasses studied showed no tendency to form boroxol groups.
Dehydroxylation of Porous Glass by Means of Chlorine
Authors: ELMER THOMAS H.
Published: June 2006

Water in reconstructed 96 % SiO2 glass is effectively removed by exposing porous glass to chlorine at high temperatures prior to final firing in vacuum. The annealing point of the final glass is markedly increased by such treatment, which results in elimination of the OH band due to replacement of OH− by Cl− ions.
Visible Spectroscopy of Irradiated High‐Alkali Borate and Mixed‐Alkali Phosphate Glasses
Authors: BARKATT A. , ANGELL C. A. , MILLER J. R.
Published: June 2006

Expectations of increased stability for trapped electrons in high‐alkali glasses, based on extrapolations from observations on low‐alkali borate glasses, are not borne out. In 69Na2O‐31B2O3 glass, electron centers have approximately the same thermal stability as in Na2O·2B2O3 glass. In Na2Oplus;P2O5 glasses the lifetimes, 3 · 0.5 μS, of transiently trapped electrons as well as their absorption spectra prove to be independent of increase of Na2O content from 50 to 60 mol%. The same composition change destabilizes “permanent” hole centers. Exchange of Na2O with K2O in the metaphosphate glass also has no effect on the trapped electron lifetime. Small linear shifts in the trapped‐hole absorption peak wavelengths are observed in the latter case. The most important positive finding in the phosphate glasses is a pronounced mixed‐alkali effect on the yield of transiently trapped electrons and holes and of permanently trapped holes. The yield is a minimum at Na:K=1:1, due either to the elimination of trap sites or to the reduction of alkali ion mobilities which play a role in trap formation.
Analysis of Thermal Stress Resistance of Partially Absorbing Ceramic Plate Subjected to Asymmetric Radiation, II: Convective Cooling at Front Surface
Authors: SINGH J. P. , SATYAMURTHY K. , THOMAS J. R. , HASSELMAN D. P. H.
Published: June 2006

Thermal stresses in a partially absorbing brittle ceramic plate asymmetrically heated by radiation and cooled by convection on the same surface with finite and infinite heat transfer coefficients are analyzed. Comparison of the results from this study with those obtained in Part I, where the plate is subjected to radiation heating in the front surface and cooled by convection at the rear surface, indicates that the magnitudes of the maximum steady‐state tensile thermal stresses are nearly identical. Significant differences are found in the transient thermal stresses and the temperature distribution. The relative temperature levels in the present case are found to be significantly lower than those obtained in Part I. Implications of these results to the design and operation of engineering structures such as concentrated solar receivers are discussed.
Residual Stress in Siliceous Glass Between Mullite Crystals
Authors: Yamana Kazuo , Tokonami Masayasu , Nobugai Kohji , Morimoto Nobuo , Koizumi Mitsue , Shindo Isamu
Published: June 2006

A birefringence of siliceous glass, which is coexisting with mullite crystals, was studied by an optical polarizing microscope. The cause of the birefringence was assumed to be the residual stress induced by a large contraction difference between the mullite and glass on cooling. The stress has been evaluated to be as high as—0.3 GPa, and to correspond to the elastic one which began to develop at the glass transition point.
Internal Phase Changes in Dense Si3N4 Associated with High‐Temperature Oxidation
Authors: McDonough W. J. , Wu C. CM. , Morgan P. E. D.
Published: June 2006

The effects of oxidation at 1400°C for 100 h on both surface and internal composition of commercial and laboratory hot‐pressed Si3N4 with MgO or ZrO2 additives as well as chemically vapor deposited (CVD) Si3N4 were studied using X‐ray diffraction. Samples were also compared to the same temperature treatments in Ar. The results indicate the grain boundaries act as rapid diffusion paths for the transport of oxygen.
Concurrent Flaw Populations in SiC
Authors: Easler T. E. , Bradt R. C. , Tressler R. E.
Published: June 2006

Concurrent surface and edge flaw populations were identified on fracture surfaces of as‐machined specimens of sintered silicon carbide. The overall strength distribution and the individual concurrent distributions were estimated using Weibull statistics. Design implications of using a single flaw population and the difficulties associated with rigorously separating the concurrent distributions are discussed.
Grain‐Size Dependence of Strength
Authors: Sirkar A. V. , Shetty D. K. , Evans A. G.
Published: June 2006

The potential for stable crack growth preceding fracture in poly crystalline ceramics depends upon the functional relation between the local toughness and the crack length. The existence of a single crystal region of crack growth resistance is conducive to the occurrence of stable crack growth or crack arrest. If stable crack growth or crack arrest does occur, the strength will be independent of the initial crack size.
Chemical Durability of Sodium Silicate Glasses Containing AI2O3 and ZrO2
Authors: DAS C. R.
Published: June 2006

A sodium silicate glass and ternary glasses derived from it by substituting AI2O3 and ZrO2 for SiO2 were exposed to water and aqueous solutions of pH 1.4 to 12.7; the kinetics of the reactions were studied. Diffusion of alkali ions and leaching of alkali and SiO2 from the glasses were influenced by the occupancy of surface sites by alkali ions above a critical pH; however, the activation energies of the processes varied linearly with the logarithm of mole fraction of surface sites occupied by Hplus;. Identical slopes were obtained for all glasses for a given process. The results are explained on the basis that transport of alkali ions is retarded as a result of increased boundary concentration and that suitable sites for reaction are lacking.
Kinetics of Dissolution and Crystallization in a β‐Spodumene Glass‐Ceramic
Authors: DALAL K. H. , RAJ R.
Published: June 2006

The kinetics of partial melting in a β‐spodumene glass‐ceramic was measured by holding fully crystallized material above the solidus but below the liquidus temperature. The kinetics was apparently limited by the rate of diffusion of silica in the crystalline phase. The measured lattice diffusivity of silica was 8×10−10 exp(‐251 kJ mol−1/RT) m2 s−1 with a possible error of ±60 kJ mol−1 in the activation energy. The partially molten samples were heat‐treated below the solidus to obtain the kinetics of crystallization, which was found to be interface‐reaction‐controlled.
Dielectric and Electrostrictive Properties of Ferroelectric Relaxors in the System Pb(Mg1/3Nb2/3)O3:PbTiO3: Ba(Zn1/3Nb2/3)O3
Authors: JANG S. J. , CROSS L. E. , UCHINO K. , NOMURA S.
Published: June 2006

Ceramic dielectrics which have been fabricated in the Pb(Mg1/3 Nb2/3)O3:PbTiO3:Ba(Zn1/3Nb2/3)O3 composition system are shown to exhibit two distinct dielectric maxima, both of which show the characteristic loss spectra of ferroelectrics with diffuse phase transitions. The height of the individual maxima can be controlled by the Zn:Mg ratio in the starting material and, in suitably chosen compositions, a wide range of almost temperature‐independent high dielectric permittivity is possible. These dielectrics show strong electrostrictive deformations under high electric fields but the electrostrictive strain is much less temperature‐sensitive than in other relaxors.
Corrosion of AZS and Fireclay Refractories in Contact with Lead Glass
Authors: HILGER J. P. , BABEL D. , PRIOUL N. , FISSOLO A.
Published: June 2006

Corrosion processes of Al2O3‐ZrO2‐SiO2 and Al2O3‐SiO2 refractories were studied. Chemical, microscopic, and X‐ray diffraction investigations are reported. The results are interpreted using the SiO2A12O3‐K2O and SiO2‐Al2O3‐PbO phase diagrams. An explanation is put forward regarding the process of corrosion by K2O and PbO.
Defect Equilibria in Transition Metal Oxides
Authors: CATLOW C. R. A. , STONEHAM A. M.
Published: June 2006

This paper assesses the importance of vacancy aggregates in transition metal oxides. It presents the predictions of quantitative atomistic calculations and discusses them in relation to observed structural, diffusion, thermodynamic, and other data. The results indicate that vacancy complexes constitute the major defect species at high nonstoichiometry. The commonly discussed vacancy‐hole complexes appear to be unimportant except, perhaps, over a very limited composition range.
Reactions During Milling of Aluminum Oxide
Authors: Dynys F. W. , Halloran J. W.
Published: June 2006

Exothermic reactions are observed at ∼400°C in alumina powders ball‐milled in isopropanol. These are believed to be due to the oxidation of an Al2O3‐alcohol reaction product formed during milling.
Debye Temperature and Electrical Conduction of Fe2O3‐CaO‐SiO2 Glasses
Authors: Nasu H. , Hirao K. , Soga N.
Published: June 2006

The electrical conductivity of iron‐containing silica glasses was measured from 80 to 350 K. The conductivity data were analyzed based on the hopping conduction theory. The hopping binding energy (Wp) and disorder energy WD) were calculated from the activation energy at high and low temperatures. The disorder energy obtained was much lower than reported for FeO‐P2O5 glasses, but similar to that for vandium‐containing glasses.
Revised ThO2‐Nb2O5 Phase Diagram
Authors: Cava R. J. , Roth R. S. , Minor D. B.
Published: June 2006

The phase equilibrium diagram of the system ThO2‐Nb2O was redetermined near the composition Th2Nb2O9. This phase was found to melt incongruenlly at 1362°C, with a eutectic temperature at ∼1350°C. The peritectic and eutectic compositions must occur between 60 and ∼64 mol % ThO2. From single crystal and powder X‐ray diffraction data, Th2 Nb2O9 was found to have a primitive monoclinic unit cell with a = 6.711(1), b = 25.254(5), c=7.757(1)×10−1nm, β=90.46 (1)°.
Penetration of Surface Damage Resulting from Abrasion and Heating of MgO Crystals
Authors: Sonder E. , Spadaro J. V. , Weeks R. A.
Published: June 2006

Chemical polishing and dislocation etch pit observations have been applied to the study of the depth of penetration of dislocations produced by abrading (100) surfaces of MgO. From the results it has been concluded that such dislocations penetrate from 100 to 700 μm depending on the source of the material. Heating of the abraded samples for short times up to 1300°C has little influence on the depth of penetration.
Densification of Cr2O3‐ZrO2 Ceramics by Sintering
Authors: Yamaguchi Akira
Published: June 2006

Cr2O3 and ZrO2 were mixed in various ratios and pressed to form compacts, which were then sintered in carbon powder. Compacts with >30 wt% Cr2O3 were sintered to densities >98% of true density at 1500°C. This method of sintering in carbon powder can be used to prepare very dense Cr2O3‐ZrO2 ceramics at a relatively low temperature, (∼1500°C) without additives.
X‐Ray Determination of Transformation Depths in Ceramics Containing Tetragonal ZrO2
Authors: Kosmać Thomaź , Wagner Rudolf , Claussen Nils
Published: June 2006

An X‐ray method to determine the transformation zone size in ceramics containing tetragonal ZrO2 is described. Results obtained on plane fracture surfaces of various composites were correlated to mechanical property data and TEM observations and were found to be in good agreement. This indicates that the method presented is a useful tool for estimating stress‐induced transformation zone sizes and for checking the effectiveness of tetragonal particles introduced in a ceramic matrix.
Platinum Condensation on MgO Grain Boundaries
Authors: Mckenzie D. R. , Taylor R. W.
Published: June 2006

Exposed to Pt‐saturated air, the surface of MgO crystals becomes spotted with metallic Pt crystals. The Pt is found concentrated along the interfaces between MgO crystals.
Analytical Electron Microscopy of Cement Pastes: III, Pastes Hydrated for Long Times
Authors: LACHOWSKI E. E. , MOHAN K. , TAYLOR H. F. W. , LAWRENCE C. D. , MOORE A. E.
Published: June 2006

Analyses of 131 particles of C‐S‐H in several mature tricalcium silicate pastes hydrated for 1 to 30 years gave a mean Ca/Si ratio of 1.46 with a range of 1.2 to 1.8. Similar analyses of 152 particles in mature cement pastes hydrated for 2 to 3 years gave a mean Ca/ Si ratio of 1.53 with a range of 1.0 to 2.8. Taken together with similar, previously published data for younger pastes, these findings indicate that the mean Ca/Si ratio does not change significantly after 1 day in tricalcium silicate pastes but decreases significantly with time in cement pastes; after several years, the mean Ca/Si ratios are similar in the two cases, despite the presence of other components in the C‐S‐H formed from cement. For the C‐S‐H of cement pastes, the mean Al/(Ca plus; Mg) and Fe/(Caplus;Mg) ratios increase with time but the mean S/(Caplus;Mg) ratio decreases. The composition of the AFm phase does not change greatly after 28 days.
Micromechanics of Flaw Growth in Static Fatigue: Influence of Residual Contact Stresses
Authors: CHANTIKUL P. , LAWN B. R. , MARSHALL D. B.
Published: June 2006

Residual contact stresses about indentation flaws are demonstrated to have a strong deleterious effect on specimen lifetime in static fatigue. The underlying basis of conventional fatigue analysis is first examined critically and is argued to be deficient in the way the stress intensity factor for the flaws is related to the characteristic parameters of crack geometry and applied loading. In general, it is necessary to incorporate a residual term into the stress intensity formulation. A modified theory of static fatigue is accordingly developed, in which the residual contact stresses play a far from secondary role in the micromechanics of flaw evolution to failure. Strength tests on Vickers‐indented soda‐lime glass disks in water environment provide clear experimental confirmation of the major theoretical predictions. Implications of the residual stress effect concerning fracture mechanics predictions of lifetimes for “real” ceramic components under service conditions are discussed.
Electron Diffraction and Microscopy Techniques for Studying Grain‐Boundary Structure
Authors: CARTER C. B. , SASS S. L.
Published: June 2006

Electron microscopy and diffraction techniques for studying grain‐boundary structure are reviewed. The experimental conditions for applying strong‐beam, weak‐beam, and lattice imaging and electron diffraction are described and examples from recent studies in ceramics, semiconductors, and metals are used to illustrate the information that these techniques provide. It is demonstrated that electron diffraction can be used to study both the periodic nature of the boundary layer and its thickness. A particularly valuable feature of weak‐beam imaging is that it can provide information on the details of the dislocation structure of the boundary, whereas strong‐beam imaging can be used to determine the rigid‐body translation between neighboring grains across special boundaries; these translations can be significantly smaller than the resolution of the microscope. Finally, lattice imaging can provide information on the location of dislocations and steps in the boundary.
Grain‐Size Dependence of Fracture Energy in Ceramics: II, A Model for Noncubic Materials
Authors: RICE R. W. , FREIMAN S. W.
Published: June 2006

A mathematical model of the grain‐size dependence of fracture energy of noncubic ceramics is developed and discussed. This model attributes the maxima in fracture energy of noncubic materials to countertrends of increasing numbers of microcracks and decreasing energy absorption per microcrack as grain size increases. The model predicts results similar to those experimentally observed. Agreement between calculated and measured fracture energy values is generally good, except for materials with extreme anisotropy. Sources of these differences and methods of improving calculations are discussed.
Temperature Dependence of Hertzian Indentation Fracture Surface Energy of ThO2
Authors: INOUE T. , MATZKE Hj.
Published: June 2006

The fracture surface energy, γ, of ThO2 was measured between room temperature and 400°C using the Hertzian indentation technique with cold or preheated steel and alumina indentors. The value of γdecreased strongly with temperature with a suggested saturation at 350°C. This may indicate the change from an unrelaxed fracture surface to a relaxed surface at temperatures where oxygen becomes mobile. The result obtained at 400°C is γ=1.4 J m−2.
Liquid Immiscibility in the System Na2O‐ZnO‐B2O3‐SiO2
Authors: TAYLOR PETER , OWEN DERREK G.
Published: June 2006

The limits of miscibility within a portion of the system Na2O‐ZnO‐B2O3‐SiO2 were determined at 650°, 800°, and 950°C. The miscibility gap at 800° and 950°C is a low dome, adjoining the zinc borosilicate miscibility gap. Below 755°C the dome intersects the Na2O‐B2O3‐SiO2 face of the phase diagram. The locus of this intersection is in agreement with literature data on the sodium borosilicate system. Estimated tie‐line placement in the ZnO‐B2O3‐SiO2 miscibility gap at 1300°C resembles those reported for the corresponding CaO and SrO systems. The microscopic morphology of glasses with the weight composition xNa2O‐18ZnO‐18B2O3‐64SiO2 with 0≤×≤12 is described in detail.
Dependency of Fatigue Predictions on the Form of the Crack Velocity Equation
Authors: JAKUS K. , RITTER J. E. , SULLIVAN J. M.
Published: June 2006

A computer search technique was developed to analyze fatigue strength data using both exponential and power law forms of the subcritical crack velocity equation. All crack velocity equations would fit a given set of fatigue data equally well in the data range but failure predictions based on the different crack velocity equations diverge from each other outside the data range. The exponential form of the crack velocity equation best fit both the static and dynamic fatigue data of hot‐pressed Si3N4 and optical glass fibers, whereas the power law form best fit the static and dynamic fatigue data of soda‐lime glass and A12O3. To determine the most appropriate crack velocity equation for a given material/environment system, it is recommended that fatigue data be obtained under different loading conditions and the data numerically regressed using the computer search technique with each of the possible crack velocity equations to find which best fits the data.
Synthesis of β‐Si3N4 by Chemical Vapor Deposition
Authors: HIRAI TOSHIO , HAYASHI SHINSUKE
Published: June 2006

Beta‐type CVD‐Si3N4 plates (up to 1.1 mm thick) have been prepared by adding TiCl4 vapor to the system SiCl4‐NH3‐H2 at deposition temperatures of 1350° to 1450°C, while α‐type or amorphous CVD‐Si3N4 was obtained without TiCl4 vapor at the same deposition temperature. Three to four wt % 777V was included in the β‐type CVD‐Si3N4 matrix. The density, preferred orientation, and lattice parameters of β‐type CVD‐Si3N4 were examined.
EPR of Vanadium(IV) in Lead Silicate Glass
Authors: Momo F. , Sotgiu A. , Baiocchi E. , Montenero A.
Published: June 2006

EPR spectra of lead silicate glasses doped with small amounts of V2O5 were studied at −150°C to room temperature. Only the glasses with the higher SiO2 contents produced EPR signals. The spin Hamiltonian parameters are characteristic of the V(IV) species in axial symmetry. The values of g, g ⊥, A, and B indicate that V(IV) is present as VO2plus; in a tetragonally distorted octahedral site. This ion probably does not enter the SiO2 network but rather behaves as a modifier cation.
Transmission Electron Microscopy of Pb(Zr0.52Ti0.48)O3
Authors: GOO EDWARD K. W. , MISHRA RAJA K. , THOMAS GARETH
Published: June 2006

Transmission electron microscopy of Pb(Zr0.52Ti0.48)O3 sintered with 3 wt% excess PbO indicates that there is an amorphous grain‐boundary phase 10 nm thick. The grain‐boundary phase has a higher Pb content than the bulk material. Influence of such a phase on sintering is discussed.
Thermopower Measurement of Cation Distribution in Magnetite
Authors: WU C. C. , MASON T. O.
Published: June 2006

The cation distribution in stoichiometric Fe3O4 was determined from thermopower measurements at 600° to 1500°C. The distribution varies from inverse at low temperature to random at ∼1450°C. The equilibrium constant for cation distribution can be expressed as In KCD=2770/T−1.61, indicating temperature‐independent enthalpy and nonconfigurational entropy terms of −23.0 and −13.4 J/mol‐K, respectively.
Kinetics of Iron‐Sodium Disilicate Reactions and Wetting
Authors: TOMSIA ANTONI P. , PASK JOSEPH A.
Published: June 2006

Thermogravimetric and sessile drop measurements were used to study kinetics of redox reactions between sodium disilicate glass and iron. Two redox reaction sequences were identified; both introduced ferrous oxide into the glass at the interface. One consists of formation of ferrous oxide at the interface by reduction of sodium ions in the glass; this is primarily dependent on the a(FeO) in the metal being less than one. The second consists of oxidation of ferrous ions in the glass by the reduction of sodium ions to form ferric ions which subsequently react with the iron to form ferrous oxide. The reaction rates were shown to be sensitive to temperature, time, total ambient pressure, partial pressure of sodium and oxygen in the atmosphere, and the a(FeO) in the iron. Decrease of contact angles and spreading occur with the redox reaction in which the metal plays an active role, i.e. whose a(FeO) is less than one and whose composition undergoes a change.
Melting‐Point Relations for Simple Halides and Oxides
Authors: VAN UITERT L. G.
Published: June 2006

For simple halides and oxides, melting point (Tf) is related to structure, bond length (d), ionization, and exchange. For many structurally related series, the parameter Tfd2 increases linearly with (ip·ea) −1, where ip is the first ionization potential of the metal and ea is the electron affinity of the anion‐forming atom. Deviations from this relation can be attributed to internal coupling, catenation exchange, and exchange between atoms that form anions.
Effect of Iron, Titanium, and Hafnium on Second‐Stage Nitriding of Silicon
Authors: MUKERJI J. , BISWAS S. K.
Published: June 2006

The kinetics of the reaction 35i(1)+2N2(g)=Si3N4(s) was studied by measuring the growth rate of Si3N4 crystals. Adding up to 1% Fe does not accelerate the reaction; 1% Ti and Hf enhance the reaction rate. The activation energies for the reaction for pure Si and for Si doped with 1% Ti and Hf are 460, 364, and 247 kJ/mol, respectively. It is suggested that solution of N2 in the molten Si, followed by its diffusion to the growing tip, is probably rate‐controlling.
Strength and Transmittance of Sapphire and Strengthened Sapphire
Authors: Gentilman R. L. , Maguire E. A. , Starrett H. S. , Hartnett T. M. , Kirchner H. P.
Published: June 2006

Ambient and elevated temperature biaxial flexural strength were measured for polished sapphire windows. Tested for comparison were windows given an SiO or glaze surface treatment. Infrared transmittance and visible imaging quality were unaffected by surface treatment while significant increases in strength and thermal‐shock resistance resulted.
Shape of Complex Resistivity Arcs for lonically Conducting Glasses
Authors: Syed R. , Gavin D.L. , Moynihan C.T. , Lesikar A.V.
Published: June 2006

It is shown experimentally and theoretically that the plot of the bulk glass complex resistivity, ρ★, must approach the origin at high frequencies and intersect the real axis at low frequencies, in both cases at a 90° angle. The ρ★ plot is not described accurately by an arc of a circle with its center below the real axis, although such circular arcs retain their usefulness in some cases for extrapolating the dc resistivity, ρ.
An Unusual Form of Belite in Portland Cement Clinker
Authors: Ghose A. , Barnes P.
Published: June 2006

Potassium‐rich structures around the edge of a fissure in a portland cement clinker have been found to have compositional and structural properties similar to those of dendritic bellies. However, the potassium levels surprisingly exceed the accepted solubility limit.
Analysis and Measurement of Glue‐Spall Stresses in Glass‐Epoxy Bonds
Authors: GULATI SURESH T. , HAGY HENRY E.
Published: June 2006

An approximate analysis is presented of the glue‐spall stresses introduced by an organic sealant in the glass substrate to which it adheres. The results given by this analysis are compared with those obtained by the finite element method, as well as with the photoelastic measurements in glass at T=25 to −78°C during cooling. Good agreement is found between theory and experiment, if proper account is taken of the stress release due to creep of the organic sealant. Methods for minimizing glue‐spall stresses are outlined.
Solid‐State Storage of Radioactive Krypton in a Silica‐Based Matrix
Authors: TINGEY G. L. , LYTLE J. M. , GRAY W. J. , WHEELER K. R.
Published: June 2006

A solid silica‐based matrix containing 30 cm3 of Kr (STP)/cm3 of glass was prepared by sintering 96% SiO2 with 28% porosity under 140 MPa krypton pressure. The glass was heated to 850° or 900°C and held at temperature until the glass density was ∼2 g/cm3. At 420°C, only 0.7% of the krypton would be released after one half‐life of 85Kr (10.7 years). At T>600°C, release of krypton is accompanied by crack development, comminution, and glass softening. Advantages and disadvantages of this technique for radioactive gas storage and diffusion data are presented.
Anisotropy of Second‐Phase Distribution in Phase‐Separated and Stretched Glasses
Authors: TAKAMORI TAKESHI , TOMOZAWA MINORU
Published: June 2006

Computer simulation of the change in the distribution of second‐phase particles, on stretching a phase‐separated glass with randomly dispersed second‐phase particles surrounded by a depleted region, indicated the development of a uniaxial anisotropy in distribution. The anisotropy, expressed by the ratio of the magnitude of directional components of nearest‐neighbor distances, indicated a maximum at an elongation ratio (final length/initial length) <2, decreasing at further elongation. This is qualitatively similar to the microstructural birefringence data by Thomas. The results further indicate that, the higher the particle density, the greater the maximum anisotropy appearing at the smaller elongation ratio.
Kinetic Reactions in Quenched MgO:Fe3+ Crystals
Authors: YAGER T. A. , KINGERY W. D.
Published: June 2006

Quenched single crystals of trivalent iron‐doped MgO were studied using etching and EPR spectroscopy. Quench‐rate measurements indicated that a liquid nitrogen quench from 1100°C is not rapid enough to prevent localized association and clustering. The distribution, size, and concentrations of precipitates, clusters, and associates in quenched crystals are critically dependent on both solute concentration and quench rate. At T<600°C, the mobility of iron is reduced as a result of cluster formation. Above 600°C, clusters dissociate, liberating mobile associates and vacancies.