bluuebunny/crossref_metadata_2025 huggingface dataset:
Investigation of Glasses Using Surface Profiling by Spectrochemical Analysis of Sputter‐Induced Radiation: II, Field‐Driven Formation and Electrochemical Properties of Protonated Glasses Containing Various Proton Concentrations
Authors: BAUCKE FRIEDRICH G. K. , BACH HANS
Published: June 2006

The ion‐sputtering technique for measuring concentration profiles in glass surfaces provides a method for studying ionic transport in solids. Simultaneous field‐driven lithium ion and proton transfer from solutions into, and migration of these ions within, several lithium silicate glasses was investigated quantitatively. This work leads to the new field of protonated glasses which are distinguished by the availability of all sites to both cationic species. Conductivity and mobilities reported as a function of concentration (50°C) do not exhibit the typical features of the mixed‐alkali effect. Mechanisms are proposed for ionic transfer across solution‐glass interfaces and for migration of ions within protonated glasses. Small proton mobilities at low proton concentrations are explained in terms of specific sites which function as proton traps and are identified by infrared spectroscopy. The condition for stability of boundaries between migrating ions is discussed.
Radiation Damage in a Rare‐Earth Silicate With the Apatite Structure
Authors: WEBER W.J.
Published: June 2006

The effects of radiation on the rare‐earth silicate, Ca2Nd8 (SiO4)6O2, with the apatite structure was investigated using 244Cm doping and alpha, gamma, and electron irradiations. Amorphization of the initially crystalline material was observed to occur only in the Cm‐doped material. Alpha irradiation produced measurable lattice expansions, with no tendency toward amorphization. The gamma and electron irradiations produced no measurable effects. The results indicate that the thermal spikes produced by the recoil nuclei emitted in alpha decay are responsible for the observed amorphization; the alpha particles produce isolated defects which contribute little, if at all, to the amorphization process; and ionizing radiation has no measurable effect on this structure.
Properties and Structure of Lithium Borate and Strontium Borate Glasses
Authors: OHTA Y. , SHIMADA M. , KOIZUMI M.
Published: June 2006

Experimental results for some physical properties of Li2O‐B2O3 and SrO‐B2O3 glasses with high modifier content showed anomalies in the composition dependence of many properties such as thermal expansion coefficient, transformation temperature, softening temperature, density, and refractive index at 30 to 33 mol% modifier oxide in these glasses. These anomalies are attributed to the formation of nonbridging oxygens near this composition.
Diffusion of Alkali Ions in Vitreous Silica
Authors: ROTHMAN S.J. , MARCUSO T.L.M. , NOWICKI L.J. , BALDO P.M. , McCORMICK A. W.
Published: June 2006

The diffusion of Cs+, Rb+, and K+ ions was measured in three grades of vitreous SiO2 by the radiotracer‐sectioning technique or Rutherford, backscattering spectroscopy. The values of the diffusion coefficient, D, at 1000°C decrease strongly with increasing ionic radius, changing by about two and one‐half orders of magnitude per row of the periodic table. The difference between DCs and DRb is largely in the preexponential factor Do in the Arrhenius expression rather than in the activation enthalpy Q. The values of D are much smaller than the tracer D values for the alkali metal ion in homogeneous Rb or Cs silicate glasses. Residual metallic impurities in the SiO2 decrease both Q and Do for the diffusion of Rb. The results are analyzed in terms of the interstitial structure of vitreous SiO2.
Thermodynamics of Silicon Nitridation: Effect of Hydrogen
Authors: Shaw N.J. , Zeleznk F.J.
Published: June 2006

The effects of hydrogen on the equilibrium concentration of species formed during nitridation of silicon were studied using a computer program that calculates equilibrium compositions by minimizing the Gibbs free energy.
Stress‐Induced Transformation During Subcritical Crack Growth in Partially Stabilized Zirconia
Authors: Lenz L. K. , Heuer A. H.
Published: June 2006

Fracture surfaces of a commercial partially stabilized ZrO2 that had undergone subcritical crack growth in H20 were characterized by scanning and transmission electron microscopy. At high stress intensities (≥4.6 MPa·m−1/2), fracture was primarily trans granular, and coherent tetragonal ZrO2 precipitates had undergone a martensitic transformation to monoclinic symmetry. At lower stress intensities, where power‐law crack growth occurred, fracture suflaces were primarily inter‐granular, and the tetragonal ZrO2 had transformed to a new ZrO2 polymorph with orthorhombic symmetry.
Polymorphism and Hydration of Tricalcium Silicate Doped With ZnO
Authors: ODLER IVAN , ABDUL‐MAULA SAMIR
Published: June 2006

Up to 4.7% ZnO can be incorporated into the crystalline lattice of C3S. Five allotropic forms (i.e. TI, TII, MI, MII, and R) can be stabilized at room temperature, depending on the amount of ZnO. When heated to high temperature, the C3S‐ZnO solid solution decomposes and ZnO escapes from the crystalline lattice. The hydration and strength development of C3S are altered by ZnO doping.
Processing Ternary Sulfide Ceramics: Powder Preparation, Sintering, and Hot‐Pressing
Authors: CHESS DANIEL L. , CHESS CATHERINE A. , BIGGERS JAMES V. , WHITE WILLIAM B.
Published: June 2006

Ceramic processing of various AB2S4 sulfides with the Th3P4, CaFe2O4, and spinel structure types was investigated. These refractory sulfides show good sinterability when fired in flowing H2S. They can be densified by a combination of hot‐pressing and hot isostatic pressing into theoretically dense ceramics.
Double‐Cantilever‐Beam Testing of a Transversely Isotropic Fibrous Silica Material
Authors: GREEN DAVID J. , HAWKINS CHRISTOPHER A. , HIRLINGER MARGARET M.
Published: June 2006

The double‐cantilever‐beam (DCB) geometry was used to study the fracture behavior of a transversely isotropic fibrous silica material that is used in the thermal protection system of the Space Shuttle. For this testing geometry, the evaluation of Kc requires measurement of the elastic constants of the material. Determination of the compliance behavior of the material allowed the various analytical beam models that have been put forward to describe the DCB geometry, to be distinguished. The Timoshenko beam on a generalized foundation was found to be the best model to describe the experimental compliance behavior and the Kc measurements. The measured Kc values were found to be higher than for previous work that had used the double edge‐notched tensile geometry. Crack propagation in the material was found to be characterized by variations in the crack‐resistance force, probably reflecting microstructural variations. The subcritical crack‐growth behavior was studied using the constant‐load‐mode DCB technique, and the results were in agreement with the predictions of an earlier study.
Effect of ΔT‐ and Spatially Varying Heat Transfer Coefficient on Thermal Stress Resistance of Brittle Ceramics Measured by the Quenching Method
Authors: OZYENER T. , SATYAMURTHY K. , KNIGHT CHARLES EUGENE , SINGH JITENDRA P. , HASSELMAN D. P. H. , ZIEGLER G.
Published: June 2006

A study was conducted of the effect of a spatial variation in heat transfer coefficient during forced convection and the effect of temperature dependence of the heat transfer coefficient during free convection on the magnitude of thermal stress encountered during the thermal shock testing of brittle ceramics by the quenching method. For specimens with circular geometry, the results obtained by the finite element method indicate that, depending on the value of the Biot number, a factor of three spatial variation in heat transfer coefficient changes the tensile thermal stresses on cooling by a maximum of about 17% over the value for spatially uniform heat transfer. On heating, the corresponding tensile thermal stresses are lower by a maximum of about 6%. In free convection for a heat transfer coefficient, h, proportional to ΔTi1/4, where ΔTi is the instantaneous temperature difference between the specimen and quenching medium, the stresses are appreciably less than those for ΔTi‐independent heat transfer for the same initial value of h at the onset of the thermal quench. The validity of the dependence of h on ΔTi was established experimentally. The relevance of this result to the interpretation of thermal quenching studies is discussed.
Ba2Ti9O20 Phase Equilibria
Authors: O'BRYAN HENRY M. , THOMSON JOHN
Published: June 2006

The heterogeneous phase distribution found in Ba2Ti9O20 ceramic resonators results from a temperature‐dependent phase boundary and slow reaction kinetics. When sintered at 1350°C or higher in oxygen the Ba2Ti9O20 phase becomes slightly reduced and barium‐rich. Thus a stoichiometric composition forms rutile and ″Ba2Ti9O20'phase. On slow cooling the excess barium diffuses to the oxygen‐rich surface where it reacts to form an envelope of rutile‐free material surrounding a core containing a small amount of rutile.
Neutron Scattering Studies of Vitrified Radioactive Waste
Authors: SINCLAIR ROGER N. , DESA J. A. ERWIN , WRIGHT ADRIAN C.
Published: June 2006

The structure of a borosilicate glass containing simulated nuclear waste on a distance scale up to several tens of nanometers was investigated using neutron scattering techniques. Comparison of samples with and without waste suggests that the nature of the basic network of SiO4 tetrahedra and BO3 triangles is largely unchanged by addition of the waste. The real‐space correlation function for the glass plus waste has clear features at distances below 0.5 nm, which can be attributed to the above network building units. Study of a partially devitrified sample shows diffraction effects due to polycrystalline and vitreous phases. Vitreous and partially devitrified glass containing waste produced a significant amount of small‐angle scattering corresponding to regions of inhomogeneity which are 10 nm and larger.
Glass Formation, a Contemporary View
Authors: UHLMANN D.R.
Published: June 2006

The process of glass formation is discussed from several perspectives. Particular attention is directed to kinetic treatments of glass formation and to the question of how fast a given liquid must be cooled in order to form a glass. Specific consideration is paid to the calculation of critical cooling rates for glass formation, to the effects of nucleating heterogeneities and transients in nucleation on the critical cooling rates, to crystallization on reheating a glass, to the experimental determination of nucleation rates and barriers to crystal nucleation, and to the characteristics of materials which are most conducive to glass formation.
Phase Relations and Ordering in the System Erbia‐Hafnia
Authors: DURAN PEDRO , PASCUAL CARMEN , COUTURES JEAN‐PIERRE , SKAGGS SAMUEL R.
Published: June 2006

The system erbia‐hafnia was investigated using thermal expansion measurements and room‐temperature X‐ray diffraction of quenched and annealed samples. The range of existence of the solid solutions based on HfO2 and Er2O3 was determined by the precision lattice parameter method. Three compounds with hexagonal structure are reported: the first is an ordered fluorite‐related phase with the ideal formula Er4Hf3O12 and decomposes with increasing temperature at ∼1500°C into a solid solution of the fluorite type; the second is formed at ∼55 mol% Er2O3, corresponding closely to the formula Er5Hf2O11.5, and undergoes a transformation at ∼1650°C into cubic solid solutions to fluorite and C type. The third compound is formed within the concentration range between 60 and 90 mol% Er2O3. This compound, Er6HfO11, decomposes at ∼1700°C into a cubic solid solution of the C type. A proposed phase diagram for the system erbia‐hafnia is presented.
Calcium Segregation to a Magnesium Oxide (100) Surface
Authors: McCUNE ROBERT C. , WYNBLATT PAUL
Published: June 2006

The segregation of calcium to a (100) cleavage surface of an MgO crystal, with bulk calcium concentration of 200 ppm was measured in situ at T=900° to 1450°C in ultrahigh vacuum, using Auger and low‐energy ion‐scattering spectroscopies. A measured heat of segregation of approximately ‐50.3 kJ/mol (‐12 kcal/mol) is in favorable agreement with a value of ‐58.7 kJ/mol (‐14 kcal/mol) determined using solute strain energy and surface free energy criteria. The equilibrium value for the calcium segregation between 950° and 1000°C is estimated to correspond to a 20% occupation of the surface cation sites.
Twin Boundaries in Monoclinic ZrO2 Particles Confined in a Mullite Matrix
Authors: BISCHOFF EWALD , RÜHLE MANFRED
Published: June 2006

Internal defects and twin structures exist in thermally transformed monoclinic (m)‐ZrO2 particles confined in a mullite matrix. The defects were analyzed by transmission electron microscopy. Twin boundaries on (100), (110), (001), and (011) were found. Frequently, (100) and (110) twins formed complicated mosaiclike structures. Some particles could be divided into two or more twinned sections with well‐defined mutual orientation relations. Domains of closure were observed at the particle‐matrix interface. The observations are discussed in terms of a simple model which considered (i) the anisotropic volume increase of ZrO2 during the t→m transformation, (ii) the anisotropic thermal expansion coefficient of ZrO2, and (iii) the rather isotropic thermal expansion coefficient of the mullite matrix.
Dynamic Fracture Toughnesses of Reaction‐Bonded Silicon Nitride
Authors: KOBAYASHI ALBERT S. , EMERY ASHLEY F. , LIAW BEEN MING
Published: June 2006

Dynamic fracture toughness specimens consisting of 5.1‐mm thick, modified wedge‐loaded, tapered double‐cantilever‐beam (WL‐MTDCB) specimens, which are side‐grooved on one side, were used to establish the room‐temperature dynamic fracture toughness, KID vs crack velocity, a, relations of two reaction‐bonded silicon nitrides. The measured dynamic crack extension histories were then used to drive a dynamic finite‐element code in its generation mode which computes the dynamic stress intensity factors for a given crack extension. Results indicate that the KID vs a relations of reaction‐bonded silicon nitrides do not follow the general trend in those relations of brittle polymer and steel. The slow initial crack velocity which was reported for glass was observed again in silicon nitride and resulted in a nonunique KID vs a relation, in contrast to the unique KID vs a material properties reported for brittle polymers and metals.
Determination of Residual Surface Stresses Caused by Grinding in Polycrystalline Al2O3
Authors: Lange Fred F. , James Michael R. , Green David J.
Published: June 2006

Residual surface stresses introduced into polycrystalline Al2O3 during diamond grinding (320 grit) were examined by an X‐ray direction technique commonly used for metals. Compressive stresses, estimated to be in the range 135 to 170 MPa and to extend 15 μm deep, were observed at the surface. It is believed that the compressive surface layer coincides with the plastic layer produced by the elastie/plastic interaction of the abrasive grains with the ceramic. The results are discussed with regard to the effect of the compressive layer on the extension of surface cracks.
Investigation of the Phase Transition in ZrTiO4 and ZrTiO4‐SnO2 Solid Solutions
Authors: McHale Anna E. , Roth Robert S.
Published: June 2006

Continuous phase transitions were found to occur in ZrTiO4 above and below a major discontinuity at 1125°±10°C. The space group of both forms of ZrTiO4 is Pcnb. For specimens quenched from high temperatures, the volume of the unit cell decreases linearly from ∼1450°C to the discontinuity, with the major change occurring in the c axis. The volume decreases considerably at this temperature and continues to decrease with lower‐temperature annealing. Substitutional tin in solid solution stabilizes the high‐temperature structure type.
Crack‐Propagation Rates in β″‐Alurnina
Authors: VISWANATHAN LAKSHMINARAYAN , VIRKAR ANIL V.
Published: June 2006

Specimens of sodium and silver β″‐alumina were electrolyLed for 3ariom times and subsequently broken in bending. Using the Griffith equation, the lengths of the cracks after electrolysis were estimated as a function of electroljsis time. It way obsened that the crack length vs time plots were bimodal. During the early Ytages of crack propagation, the crack velocity war found to he independent of crack length. The rate of crack propagation in Na‐β″‐alumina was about three times batter than that in Ag‐β″‐alumina. Furthermore, in Na‐β″‐alumina, the rate of crack propagation was found to increase with increasing temperature. The dependence of crack velocity on temperature, the difference in crack‐growth rates in Na‐β‐alumina and Ag‐β″‐alumina, and the fact that crack velocity is independent of crack length were rationalized in terms of a model that takes into account the transient nature of ionic flux to the growing crack.
Oxidation Equilibrium of Iron in Borosilicate Glass
Authors: GOLDMAN DON S.
Published: June 2006

Ferrous/ferric equilibria were determined in alkali‐alkaline‐earth borosilicate glass as a function of temperature, oxygen partial pressure, and glass composition. Expected linear relations are found between log(Fe2+/Fe3+) and log(pO2) or 1/T. The slopes of the correlation with 10g(pO2) are near the expected value of ‐0.25, but are found to decrease with increasing temperature. Reaction enthalpies determined from the correlation with 1/T of –100 to –116 kJ/mol are similar to those reported for other silicate glasses. The ferroudferric equilibrium is not dependent on total iron content in the range 0.5 to 0.09% Fe2O3. More reducing conditions are required at lower temperatures to stabilize the amber chromophore. The ferroudferric equilibria are correlated to the number of bridging and nonbridging oxygen ions in the glass. The results suggest that the oxidation‐reduction reaction can be written as: Fe2++ (1/4)O2+ (3/2)O2‐= FeO2−
Thermal Expansion of Alkali Borate Glasses
Authors: SHELBY J.E.
Published: June 2006

The thermal expansion behavior of lithium, sodium, potassium, and rubidium borate glasses was measured. The results indicate that the “borate anomaly” in the thermal expansion coefficient occurs at ∼20 mol% alkali oxide. A maximum in the glass transformation and dilatometric softening temperatures also occurs at ∼27 mol% alkali oxide. No evidence for phase separation was observed in this study. These effects are related to the structural changes reported for these glasses by Bray and coworkers.
Electron Microscopy of Annealed (Ni,Zn,Co)Fe2O4
Authors: Harmer Martin P. , Mishra Raja K. , Thomas Gareth
Published: June 2006

(Ni,Zn)Fe2O4 samples containing small amounts of Co were characterized in a transmission electron microscope to ascertain the micro structural changes accompanying low‐temperature oxidation of the samples. Although no new features resulting from oxidation were observed, prominent surjace reduction occurred in the thin foil specimens. Formation and growth of Ni particles on the ferrite surface are explained using the heats of formation of the oxides.2
Transformation Strengthening of β″Al2O3 with Tetragonal ZrO2
Authors: Lange Fred F. , Davis Burt I. , Raleigh Douglas O.
Published: June 2006

The solid sodium electrolyte β″‐Al2O3 (Li‐stabilized) was strengthened with additions of tetragonal ZrO2 (15 vol%). The conductivity of this composite material, measured in an Na/Na cell, was 7.7 Ω· at 300°C. Average values of strength and the critical stress intensity factor were 350 MPa and 4.5 MPa·m1/2, respectively, for the sintered composite material.
Microhardness and Transparency of an La‐Si‐O‐N Oxynitride Glass
Authors: Makishima Akio , Mitomo Mamoru , Ii Nobuo , Tsutsumi Masayuki
Published: June 2006

An oxynitride glass containing 18 at.% N was prepared under high N2 pressure. The glass was transparent and very hard, with a Vickers hardness of 12.0 GPa.
Theory of Fatigue for Brittle Flaws Originating from Residual Stress Concentrations
Authors: FULLER EDWIN R. , LAWN BRIAN R. , COOK ROBERT F.
Published: June 2006

A theory is formulated for the general fatigue response of brittle flaws which experience residual stress concentrations. The indentation crack is taken as a model flaw system for the purpose of setting up the basic fracture mechanics equations, but the essential results are expected to have a wider range of applicability in the strength characterization of ceramics. A starting fatigue differential equation is first set up by combining an appropriate stress intensity factor for point‐ or line‐contact flaws with a power‐law crack velocity function. Analytical solutions are then obtained for the case of static fatigue. The resulting relation between lifetime and failure stress is shown to have exactly the same power‐law form as the conventional solution for Griffith (residual‐stress‐free) flaws. This “equivalence” is used as a basis for extending the results to dynamic fatigue. A comparison of these analytical solutions with numerical counterparts defines the limits of accuracy of the theoretical procedure. However, while the form of the lifetime relation remains invariant, the values of the exponent and coefficient differ significantly for flaws with and without residual stress. Accordingly, the application of conventional fatigue theory to evaluate crack velocity parameters, without due regard for the nature of the critical flaw, can lead to serious errors. Explicit conversion formulas are given for transforming “apparent” velocity parameters for indentation flaws directly into “true” parameters. The implications of these results concerning the use of the indentation method for materials evaluation are discussed.
Multicomponent Glasses of GeO2 and Sb2O3 with Bi2O3, T12O, andlor PbO
Authors: NASSAU KURT , CHADWICK DANA L.
Published: June 2006

Previous studies on glass formation involving GeO2 with Bi2O3, TI2O, and PbO were extended by the use of Sb2O3. Wide areas of glass formation occur in the systems GeO2‐PbO‐Sb2O3 and GeO2‐Bi2O3‐Sb2O3 at all but the lowest GeO2 contents; the region of single‐phase glasses in the system GeO2‐Tl2O‐Sb2O3 is severely restricted. Glasses were examined by powder X‐ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes’technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities; these properties are presented in diagrams for the GeO2‐Sb2O3 binary and for two ternary systems. Based on calculated values of Δo,the waveleneth for zero material dispersion. and dM/dΔ. the material disiersion slope at Δo, compositions in these systems may be useful for the construction of ultralow‐loss optical waveguides in the 3 to 4 μm region.
Determination of Threshold Stress Intensity for Crack Growth at High Temperature in Silicon Carbide Ceramics
Authors: MINFORD ERIC J. , TRESSLER RICHARD E.
Published: June 2006

A method for estimating the threshold stress intensity for crack growth is presented. The technique requires prior knowledge of the flaw population of a material and uses applied static loads followed by fast fracture to assess the effect of initial applied stress intensity on flaw behavior. The technique was applied to a hot‐pressed Sic at 1200° and 1400°C in a nonoxidizing atmosphere. At 1400°C with a static load time of 4 h, the threshold stress intensity was determined to be ∼ 1.75 MPa·m1/2 with a slight tendency toward higher fracture stress with increasing initial stress intensity below the threshold. At 1200°C for a static load time of 4 h, apparent strengthening was observed below a threshold stress intensity of ∼2.25 MPa·m1/2. This strengthening effect appears to result from stress relaxation in the crack‐tip region, probably by plastic deformation which involves the oxide grain‐boundary phase.
Chemistry of Uranium in Glass‐Forming Melts: Redox Interactions of Uranium with Chromium and Iron in Aluminosilicates
Authors: SCHREIBER HENRY D. , BALAZS G. BRYAN , KOZAK SAMUEL J.
Published: June 2006

The mutual interactions by internal redox reactions of uranium and chromium and uranium and iron in two aluminosilicate glass‐forming melts were studied by optical spectrophotometry. Cr(VI) was found to oxidize completely all available U(V) and U(IV) to U(VI), whereas Fe(III) was not a strong enough oxidizing agent to affect the uranium redox states. Cr(II) totally reduced all the U(V) and U(VI) in the system to U(IV); Fe(II) did not reduce any of the uranium redox species. Cr(III) coexisted with U(VI), U(V), and U(IV) in the melts. The degree of mutual interaction was governed not only by the difference in redox potentials between the respective redox couples, but also by the stability of molecular associations between the redox ions within the melt microstructure.
Influence of Thermal Decomposition on the Mechanical Properties of Magnesia‐Stabilized Cubic Zirconia
Authors: SWAIN MICHAEL V. , GARVIE RONALD C. , HANNINK RICHARD H. J.
Published: June 2006

Cubic magnesia‐stabilized zirconia was decomposed by isothermal heat treatment at 1100°C. The mechanical properties, including strength, fracture toughness, and hardness, were measured at various stages during the decomposition process. The strength initially decreased with aging but then recovered almost to its initial value. This strength decrease was associated with cracking of islands of the cubic phase in the matrix of monoclinic zirconia. The fracture toughness followed the strength although it was found that the monoclinic phase exhibited stable crack growth during notched beam fracture experiments or R‐curve behavior. Measurements of the hardness indicated that the cubic phase was much harder than the monoclinic phase. In addition, X‐ray diffraction, optical, and transmission electron microscopy studies were made of the decomposition process.
Dielectric, Electromechanical, Optical, and Mechanical Properties of Lanthanum‐Modified Lead Titanate Ceramics
Authors: YAMAMOTO T. , IGARASHI HIDEJI , OKAZAKI KIYOSHI
Published: June 2006

Lanthanum‐modified lead titanate ceramics with a tetragonality of c/a= 1.028 to 1.000 were hot‐pressed and the dielectric, electromechanical, optical, and mechanical properties were investigated. With decreasing c/a, the Curie point, remnant polarization, coercive field, and electromechanical coupling factors decrease and the transmittance increases. The internal stress was measured using a microindentation technique by changing the indent load. The internal stress increases with increasing c/a in the tetragonal region and the value for the c/a=1.028 sample was 150 MN/m2.
Numerical Fracture Analysis of Chevron‐Notched Specimens: I, Shear Correction Factor, k
Authors: SAKAI MOTOTSUGU , YAMASAKI KOUZOU
Published: June 2006

Numerical analyses are developed in both short bar and 4‐point bend bar cases to estimate the interlaminar shear correction factor k of chevron‐notched specimens with various kinds of geometry. The values of k were calculated by comparing the specimen compliances of Bluhm's slice models with those of finite element models. We elucidated the effect of surface boundary on k and modified the Bluhm's assumption. The modification has a slight influence on compliance, but is substantial when considering the stress intensity factor and elastic stored energy at fracture load. The present results give a basis for further consideration of the fracture behavior of chevron‐notched specimens. Part II is a discussion of the stability condition for crack growth of chevron‐notched specimens using the present results.
Synthesis of TiB2 by High‐Dose Implantation of Boron Ions in Titanium Films
Authors: Okamoto Shoichi , Kawai Akira , Kobayashi Kenkichiro , Takata Masasuke , Yamashita Tsutomu , Yamashita Shiro
Published: June 2006

Boron ions were implanted at room temperature in Ti films at a high dose (7.1 × 10I7 and 2.3 × 1018 ions/cm2), The formation of TiB2 films was confirmed by X‐ray diffraction. Boron concentration profiles in implanted films were studied by secondary‐ion mass spectrometry.
Fundamentals of Preparing Suspensions of Silicon and Related Ceramic Powders
Authors: Bleier Alan
Published: June 2006

A dispensability model previously developed for silicon powder is extended to theoretically predict the behavior of silicon nitride and silicon carbide powders, and their nonstoichiometric analogs, in a variety of potential dispersing media.
Effects of Microsilica (Silica Fume) on Pore‐Solution Chemistry of Cement Pastes
Authors: Diamond Sidney
Published: June 2006

Pore solutions expressed from hydrated Portland cement pastes containing up to 30% microsilica (silica fume) as replacement for cement were analyzed. The presence of microsilica enhances early concentrations of alkalies and hydroxyl ions, but after 1 day the effect is reversed, and the concentrations of these ions are progressively reduced to very low values. Alkali reduction seems more pronounced for pastes of higher water content, and low levels of microsilica replacement (5 or 10%) exert substantially greater than proportional effects.
Comparison of Diffusion Data and of Activation Energies
Authors: DOSDALE T. , BROOK R. J.
Published: June 2006

When the available diffusion data for any one material are plotted in terms of the observed preexponential factors, In D0, as a function of the observed activation energies, ΔH, a linear dependence is commonly observed. It is shown that, among other explanations, the contribution of a series or parallel combination of single activated processes to the observed process will provide this dependence. The form of plot (In Do vs ΔH) is of value in comparing the results of new measurements with literature data.
Processing‐Related Fracture Origins: II, Agglomerate Motion and Cracklike Internal Surfaces Caused by Differential Sintering
Authors: LANGE F. F. , METCALF M.
Published: June 2006

Effects of differential sintering kinetics due to differential green density were studied by fabricating agglomerate‐powder matrix specimens from two Al2O3/ZrO2 (30 vol%) powders and subjecting them to a cyclic sintering schedule to allow intermittent observations. Low‐green‐density compacts sintered faster than high‐density compacts, although high‐green‐density compacts reached end‐point densities first. Specimens containing low‐green‐density agglomerates produced circumferential cracklike voids at the agglomerate/matrix interface. Agglomerates with a higher green density than the matrix were subjected to compressive strains by the matrix to produce agglomerate motion when the resulting stress field was non‐symmetric. Such agglomerates also produced a variety of cracklike separations. Implications regarding sintering kinetics and end‐point densities are discussed. Implications regarding strength of sintered bodies are obvious, viz. strength can be proportional to the square root of the agglomerate size.
Processing‐Related Fracture Origins: III, Differential Sintering of ZrO2 Agglomerates in Al2O3/ZrO2 Composite
Authors: LANGE F.F. , DAVIS B.I. , AKSAY I. A.
Published: June 2006

Large, hard ZrO2 agglomerates remained in an Al2O3/ZrO2 composite suspension after inefficient ball‐milling. The ZrO2 agglomerates shrank away from the consolidated Al2O3/ZrO2 powder matrix during sintering, producing crack‐like voids which were responsible for strength degradation.
Effect of Silver Doping on the Physical and Electrical Properties of PLZT Ceramics
Authors: MAHER GALEB H.
Published: June 2006

Additions of small amounts of silver to a PLZT dielectric with emphasis on the 88/12/70/30, Pb/La/Zr/Ti, composition were investigated. It was found that a few mole percent of Ag1+ could be incorporated into the PLZT lattice as a large acceptor cation and that it tended to reduce the lead vacancies, which are normally generated by the substitution of La3+ in the PLZT dielectric. The addition, up to 2 mol% of silver, decreased the 25°C dielectric constant from 2300 to 1700. However, the temperature coefficient of capacitance was improved to ±5% between ‐55° and +125°C, and the dissipation factor was reduced from 1.5 to 0.5%. Although the gravimetrically measured lead loss appeared to depend on the relative vapor pressure of lead oxide during sintering, the compensation mechanism of Ag1+ was not affected.
Ba(Zn1/3Ta2/3)O3 Ceramics with Low Dielectric Loss at Microwave Frequencies
Authors: KAWASHIMA SYUNICHIRO , NISHIDA MASAMITSU , UEDA ICHIRO , OUCHI⋆ HIROMU
Published: June 2006

The dielectric properties at microwave frequencies of Ba(Zn1/3Ta2/3)O3 ceramics prepared by sintering were investigated. These ceramics had lower density but higher loss quality than ceramics hot‐pressed at 1400°C. Loss quality was greatly improved by prolonged sintering. The Q of the ceramics measured by the dielectric resonator method was 14 000 at 12 GHz. The ceramics were investigated by X‐ray diffraction analysis. It was found that Q improvement corresponds with increased Zn and Ta ordered structures in the ceramics.
Raman Spectral Characterization of Silicon Carbide Nuclear Fuel Coatings
Authors: KRAUTWASSER P. , BEGUN G. M. , ANGELINI PETER
Published: June 2006

Raman spectral observations were used to characterize the vapor‐deposited Sic coatings on the microspheres used for fuels in high‐temperature gas‐cooled reactors. Good correlation was found between this nondestructive optical method and other characterization data. The SIC coatings, derived from methyltrichlorosilane, contained excess silicon or excess carbon, depending on deposition temperature, coating rate, and carrier gas used. Heat treatment of nonstoichiometric Sic resulted in many cases in the development of an outer layer of carbon. Fast‐neutron irradiation produced marked effects on the spectral properties of the coatings. Recovery of materials properties on thermal annealing was studied.
Investigation of Twin Lamellae in BaTiO3 Ceramics
Authors: OPPOLZER H. , SCHMELZ H.
Published: June 2006

The microstructure of many electroceramic components based on barium titanate is dominated by anomalous grain growth. At firing temperatures below the eutectic temperature nearly all large crystallites were found to contain lamellae. The crys‐tallographic orientation of these lamellae was studied by TEM. By combining image and diffraction information it could be directly shown that the lamellae lie on (111) planes and represent twins, which are ∼0.5 μm thick. The relevance of twin formation for the mechanism of anomalous grain growth is briefly discussed.
Dissolution of a Nuclear Waste Ceramic: An Experimental and Modeling Study
Authors: RYERSON F. J. , BAZAN F. , CAMPBELL J. H.
Published: June 2006

The degree of alteration of a multiphase ceramic waste form (Synroc‐D) exposed to flowing water at 75°C is reported. After 117 days, a 25‐ to 30‐μm deep leach zone developed from which all silicate phases have congruently dissolved. The associated spinel and titanate phases appear unaltered, whereas an Al(OH)3 precipitate ∼ 5‐μm thick develops at the sample surface. The dissolution of silicates and deposition of the precipitate are simulated using a modification of the crackling‐core model. The model predictions closely match the observed behavior of the material. Implications of these results for long‐term stability of the waste form are discussed.
Hydrothermal Reaction and Dissolution Studies of CsAISi5Or12 in Water and Brines
Authors: KOMARNENI SRIDHAR , ROY RUSTUM
Published: June 2006

The alteration of CsAlSi5O12, a possible host for 137Cs in tailored nuclear waste ceramics, was studied under simulated nuclear waste repository conditions of 100°, 200°, and 300°C with a confining pressure of 30 MPa. The cesium radiophase was found to be quite stable in water or 3N CaCl2, or 3N MgCl2 but not in 3N NaCl or 3N KCI or a bittern brine. The acid resistance of CsAlSi5O12 can be deduced from its stability in hydrothermal MgCl2 brine. Possible reaction mechanisms include the formations of pollucite and quartz in deionized water and the formation of Na or K feldspars and quartz in the presence of NaCl or KCl brines, respectively. A comparison of the various cesium aluminosilicates indicates that pollucite (CsAlSi2O6) is the best candidate for cesium‐137 immobilization.
High‐Resolution Electron Microscopy of Chemically Vapor‐Deposited β‐Si3N4‐TiN Composites
Authors: HIRAGA K. , HIRABAYASHI M. , HAYASHI S. , HIRAI T.
Published: June 2006

Microstructures of Si3N4‐TiN composites prepared by chemical vapor deposition (CVD) were investigated by the multibeam imaging technique using a 1 MV electron microscope. High‐resolution images showed a number of fibrous TIN crystallites dispersed in the matrix of CVD β‐Si3N4. Crystallographic orientation relations between β‐Si3N4 and TiN were determined directly from the observed images in the subcell scale. The fibrous axis of TiN is parallel to the (110) direction of the NaCl structure and lies along the c axis of the hexagonal β‐Si3N4 crystal. Domain boundaries, planar faults, nonplanar faults, and dislocations were found in the CVD β‐Si3N4 matrix near the TiN crystallites. The origin of the structure defects is briefly discussed in connection with the formation of TiN crystallites in the matrix.
Precipitation and Solid Solubility in the System NiO‐Cr2O3
Authors: CHEN CHING‐HWA , NOTIS MICHAEL R. , WILLIAMS DAVID B.
Published: June 2006

The precipitation of NiCr2O4 and the solid solubility of Cr3+ in NiO were investigated. Homogeneous precipitation occurs in this system, and the decomposition of NiO‐Cr2O3 solid solution involves only one stable equilibrium phase, NiCr2O4. The small lattice misfit between precipitate and matrix results in the formation of randomly distributed spherical precipitates about 3 to 10 nm in diameter in the initial stage of growth. Above that size, precipitates form as ellipsoidal plates lying on (100) with all directions of the precipitate and matrix mutually parallel. Strain‐energy effects provide a rational explanation for the observed precipitate morphology during nucleation and subsequent growth. The precipitates grow along 100 to a size at which coherency is no longer maintained. The loss of coherency is associated with the development of interfacial dislocations, and the critical size at which coherency is lost is ∼300 nm. Dissolution of coherent precipitates and growth of semicoherent precipitates was directly observed to occur si multaneously when both are present. The NiO‐NiCr2O4 two‐phase boundary (the NiO(Cr)(ss) solvus line) was experimentally determined between 950° and 1150°C. Concentration profiles measured at two‐phase interfaces indicate that the growth of the NiCr2O4 phase is controlled by volume diffusion. In the present study, interface concentrations obtained from coherent precipitates are indistinguishable from those obtained from semicoherent precipitates. The maximum solubility of Cr in NiO was found to be 0.98°0.10 at 950°, 1.80°0.15 at 1050°, and 3.60°0.31 at 1150°C.
Corrosion of a Borosilicate Glass by Orthophosphoric Acid
Authors: WALTERS HELEN V.
Published: June 2006

A borosilicate glass was resistant to orthophosphoric acid at 95°C, whereas considerable corrosion occurred at higher temperatures. Tenacious crystal formation provided a barrier against further attack, but also produced stress resulting in spontaneous glass breakage. The acid‐glass reaction is attributed to acid dehydration and consequent transformation to aggressive pyrophosphate.
A Model for Optimizing Glass Batch Compositions
Authors: WESTERLUND TAPIO , HATAKKA LEENA , KARLSSON KAJ H.
Published: June 2006

A model is presented for finding the cheapest and least‐sensitive batch composition that meets a set of specified physical properties of a glass. The model is tested on two glasses reported in the literature and is shown to be a useful tool for simulating the consequences of a change either in the desired properties of a glass or in the composition and/or set of batch materials.
Evaluation of the Fatigue Constant n in Optical Fibers with Surface Particle Damage
Authors: DONAGHY F. A. , NICOL D. R.
Published: June 2006

A method of controllably damaging the surface of silica‐based optical fibers is described, producing in short lengths the tensile strength typical of long proof‐tested lengths. The stress‐corrosion constant n is obtained relatively rapidly, by correlating the results of static and dynamic fatigue measurements. For damaged 125‐μm‐diameter fibers, with an average strength of 1.25 GPa, a value for n=20 was found, similar to that in pristine fibers.
Surface Crystallization of a Fluoride Glass
Authors: Bansal Narottam P. , Doremus Robert H.
Published: June 2006

Growth of crystals on the surface of a Zr‐Ba‐La fluoride glass was observed by optical and scanning electron microscopy. Small, dark crystals nucleated rapidly and grew to a size of ∼10 μm; then they stopped growing, and wrinkled regions emerged, covering the entire crystal surface.
Effect of Trace Impurity Levels on the Viscosity of Vitreous Silica
Authors: Bihuniak Peter P. , Calabrese Andrew , Erwin Emmett M.
Published: June 2006

The transformation‐range viscosity dependence of vitreous silica on Al2O3 (25 to 350 molar ppm) and alkali oxide (1.0 to 75 molar ppm) was investigated. Viscosity increased with the molar ratio Al2O3/alkali oxide up to ∼8 and was constant at higher ratios.
Preparation and Melting Point of Octalithium Zirconate
Authors: Ortman Mark S. , Larsen Edwin M.
Published: June 2006

Octalithium zirconate was prepared by heating a pelletized stoichiometric mixture of fused lithium oxide and zirconium dioxide under a dynamic vacuum to 863 K for 40 h. The melting point was determined to be 1568 ∼5 K. Chemical inertness and high lithium atom density, 5.93 ∼1022 atoms /cm3, make octalithium zirconate a candidate for a solid tritium breeder.
Determination of the Si Diffusing Unit in the System Na2O‐CaO‐SiO2 Using a Multiatomic Ion Model
Authors: NANBA M. , OISHI Y.
Published: June 2006

The composition of the diffusing unit for silicon was determined for the system Na2O‐CaO‐SiO2 at 1200°C from an analysis of the concentration distributions in interdiffusion using a multiatomic ion model described in terms of self‐diffusion coefficients of constituent elements. The results indicated that silicon diffuses in a 7‐membered ring form and that the number of Si atoms in the silicate ion is not less than 35.
Critical Grain Size/Preexisting Flaw Size Relations in Anisotropic Brittle Solids
Authors: KRSTIC VLADIMIR D.
Published: June 2006

A known solution for the critical condition of thermoelastic microcrack initiation is adopted to evaluate the extent of crack propagation after initiation and the arrest condition. It is shown that the critical temperature for crack initiation and the strength of thermoelastically anisotropic polycrystalline materials is not determined by the grain size only but also by the ratio of grain‐to‐flaw size. The variation of slopes in the strength‐grain size plot is interpreted in terms of preexisting annular flaw‐size change. The major implications of the analysis are discussed in relation to experimental results on a number of polycrystalline ceramics.
Characterization and Sintering of Lead Zirconate‐Titanate Powders
Authors: CHO S.H. , BIGGERS JAMES V.
Published: June 2006

Two techniques — conventional calcining of mixed oxides and molten salt synthesis—have been used to prepare lead zirconate‐titanate powders for subsequent sintering experiments. Several characterization methods, including SEM microscopy and pressing behavior, were used to evaluate the primary particle size and agglomerate state of the powders. In the powders produced by conventional calcining of mixed oxides, the primary particle size was strongly dependent on calcining temperature. These powders also contained a large proportion of very strong agglomerates. The powders produced using molten salt synthesis had a primary particle size nearly independent of processing temperature. The agglomerates formed appeared to be quite friable. Subsequent sintering experiments showed that grain growth was more pronounced with the conventionally calcined powders. The ceramics produced from molten synthesized powders had a more uniform grain size which was nearly independent of powder processing conditions. The densities of these ceramics were, however, always lower than those produced from conventionally calcined powders.
Identification of BaO. A12O3.5TiO2 in the Ternary System BaO. A12O3‐TiO2
Authors: Solomah Ahmed G. , Odoj Reinhard , Freiburg Christoph
Published: June 2006

A new identification and indexing for the phase BaAl2Ti5O14 were accomplished using an X‐ray diffraction technique. The new lattice parameters for the tetragonal lattice structure are: a0=9.990 × 10‐10 m and c0=12.264 × 10‐10 m, with a corresponding volume 1.224 × 10‐27 m3. The data provided by the Joint Committee on Powder Diffraction Standards are inconsistent both in lattice parameter values and Miller indices. The X‐ray powder diffraction pattern of BaAl2Ti5O14 was indexed using the LSUCR (least‐squares unit cell refinement) computer program.
Use of Weibull Statistics to Correlate MOR, Ball‐on‐Ring, and Rotational Fast Fracture Tests
Authors: WILLIAMS ROBERT M. , SWANK LEWIS R.
Published: June 2006

Fast fracture strength data on slip‐cast reaction‐bonded Si3N4 determined by uniaxial MOR, biaxial ball‐on‐ring tests, and speed of rotational failure measurements were correlated using Weibull statistics and finite‐element techniques. The agreement between predicted and observed values demonstrated the applicability of the Weibull equation.
Effect of Reducing Atmosphere on Minerals and Iron Oxides Developed in Fired Clays: The Role of Ca
Authors: MANIATIS Y. , SIMOPOULOS A. , KOSTIKAS A. , PERDIKATSIS V.
Published: June 2006

The transformations induced in two clays differing in Ca content, by firing under reduced conditions up to 1080°C, were studied by X‐ray diffraction, scanning electron microscopy, Mossbauer, and magnetization measurements. In the calcareous clay, gehlenite forms at lower temperatures (900°C) and, in addition, wollastonite forms at higher temperatures (1080°C). Ferric iron persists even under strongly reducing conditions and its presence is attributed to trapping in gehlenite. Extensive vitrification is observed in the non‐calcareous clays. Ferrous iron, produced by dissociation of iron oxides, is partly dissolved into the vitreous matrix and partly incorporated into the spinel mineral hercynite. The key role of Ca in controlling the above transformations was verified by studying the clays after removal or addition of calcite. The interaction of Ca with the clay constituents and its progressive attack on the quartz grains forming wollastonite zones was observed with the electron microscope. The bulk magnetic properties of the samples depended principally on the amount of iron oxides present, which in turn were strongly affected by firing temperature and type of clay. Metallic iron was detected in strongly reducing atmospheres.
Reaction Kinetics in the Hydrothermal Oxidation of Hf
Authors: TORAYA HIDEO , YOSHIMURA MASAHIRO , SMIYA SHIGEYUKI
Published: June 2006

The hydrothermal oxidation of Hf was studied using metal powders and chips to change the surface‐area effect. Fine monoclinic HfO2 powders (32 to 34 nm) were formed through two parallel reaction paths, one the oxidation of Hf with H2O and the other the consecutive reaction via formation of Hf hydride. Based on the experimental results at 500°C under 100 MPa, three reaction rate constants were determined for two kinds of starting materials. The relative widths of two paths were proved to be independent of the size of starting materials, and the pulverization and oxidation of both metal powders and chips could be explained by the same mechanism, where the formation of hydride was a driving force in pulverization.
A Modified Indentation Toughness Technique
Authors: Cook Robert F. , Lawn Brian R.
Published: June 2006

A modified indentation technique for measuring toughness is described. The method retains the elastic/plastic basis of previous contact fracture descriptions but eliminates explicit reference to residual stress parameters in the toughness formulation. Accordingly, improved correlations between indentation data and “conventional” Kc values are obtained, even for materials (e.g. anomalous glasses) with nonideal deformation responses.