bluuebunny/crossref_metadata_2025 huggingface dataset:
Transformation Toughening in ZrO2‐Containing Ceramics
Authors: HEUER A. H.
Published: March 2005

Transformation toughening in ZrO2‐containing ceramics is discussed. Specifically, microstuctures of the three distinct types of ZrO2‐toughened ceramics are presented, after which microstructural evolution in MgO‐partially‐stabilized ZrO2 Mg‐PSZ) is reviewed. The mechanical properties of such transformation‐toughened ceramics are dominated by “resistance‐curve” (R‐curve) behavior, wherein the crack resistance increases during the course of crack propagation. Ceramics subject to R‐curve behavior require a more detailed failure criterion than those subject to the usual linear elastic fracture mechanics criterion involving a critical stress intensity factor, KIC.R‐curve‐controlled fracture in ceramics provides a degree of very desirable flaw insensitivity, but can lead to counterintuitive relationships concerning strength, toughness, and initial flaw size. Examples of R curves of Mg‐PSZ with different thermal histories are given.
Strength Improvement in Transformation‐Toughened Alumina by Selective Phase Transformation
Authors: CUTLER RAYMOND A. , BRIGHT JEFFREY D. , VITRKAR ANIL V. , SHETTY DINESH K.
Published: March 2005

A12O3‐15 vol% ZrO2 bar‐shaped ceramic specimens were fabricated in the green state in such a way that the near surface regions consisted of A12O3 and unstabilized ZrO2 while the bulk consisted of A12O3 and partially stabilized ZrO2. After sintering, specimens had macroscopic residual compressive surface stresses and balancing interior tensile stresses due to the tetragonal‐to‐monoclinic phase transformation in the outer layers which occurs during cooling. The depth of the surface region was controlled during green forming. Residual surface compressive stresses at room temperature varied between 100 and 400 MPa depending on the outer‐layer thickness. The increased strengths of the three‐layer specimens were obtained in the as‐fired unground condition, demonstrating that the stresses introduced are the result of transformation of tetragonal zirconia into monoclinic polymorph which occurred upon cooling from the sintering temperature. Specimens with residual surface compressive stresses were 200 MPa stronger at 750°C than monolithic specimens, demonstrating the viability of this approach for improving elevated‐temperature mechanical properties.
Characterization by Nuclear and Spectrophotometric Analysis of Near‐Surface Modifications of Glass Implanted with Heavy Ions
Authors: POLATO PIETRO , MAZZOLDI PAOLO , BOSCOLETTO ANGELO BOSCOLO
Published: March 2005

A soda‐lime‐silica glass was irradiated by different heavy ion (N, Ne, Ar, and Kr) with energies chosen in order to obtain the same penetration depth. The near‐surface sodium depletion layer, characterized by nuclear analysis and infrared reflectance spectrophotometry (IRRS), is deeper than the implanted‐ion range and grows with increasing incident‐ion mass at the same dose and current density. By using reflectance spectrophotometry in the solar range, the formation of a near‐surface perturbed layer having a modified refractive index as compared to the bulk and a thickness comparable to the sodium depletion layer was confirmed.
Densification and Microstructural Development of SrTiO3 Sintered with V2O5
Authors: Chen Jyh‐Shim , Young Ron‐Jong , Wu Tai‐Bor
Published: March 2005

Precipitation of TiO2 occurs during the sintering of SrTiO3 with V2O5 added as a liquid‐phase sintering agent. Satisfactory densification can be obtained at 1250°C when using a high content of V2O5 during sintering. However, a microstructure of fine grains and large pores results along with the precipitation of TiO2. The precipitation of TiO2 can be repressed by the addition of excess SrO. A well‐sintered microstructure with superior densification can thus be obtained at 125O°C from specimens sintered with a low content of V2O5 and an appropriate amount of excess SrO.
Devitrification and Delayed Crazing of SiO2 on Single‐Crystal Silicon and Chemically Vapor‐Deposited Silicon Nitride
Authors: Choi Doo Jin , Scott William D.
Published: March 2005

The linear growth rate of cristobalite was measured in thin SiO2 films on silicon and chemically vapor‐deposited silicon nitride. The presence of trace impurities from alumina furnace tubes greatly increased the crystal growth rate. Under clean conditions, the growth rate was still 1 order of magnitude greater than that for internally nucleated crystals in bulk silica. Crystallized films cracked and lifted from the surface after exposure to atmospheric water vapor. The crystallization and subsequent crazing and lifting of protective SiO2 films on silicon nitride should be considered in long‐term applications.
Sintering and Properties of Sialons without Externally Added Liquid Phase
Authors: Bandyopadhyay Siddhartha , Mckerji Joydhb
Published: March 2005

β′‐Sialon has the general formula Si6‐ZAlZOZN8‐Z The synthesis of pure β′‐sialon with three different Z values of 0.5, 1.0, and 2.0 in the system Si3N4‐AlN‐Al2O3‐SiO2 has been reported without the addition of a foreign sintering aid. A small shift in the composition toward the SiO2 corner has been made in each case. The Z=1.0 and 2.0 sialon can be sintered almost to full density while that with Z=0.5 sialon is difficult even with a higher amount of excess oxide addition. A packing bed of Si3N4 and SiO2 in a weight ratio of 7:3 was found to be most useful. The coefficient of linear thermal expansion of Z=1.0 sialon is 2.2°10‐6/°C (25° to 1000°C). The room‐temperature modulus of rupture value can be retained up to 90% of the value at 1400°C. A similar trend has also been observed in the KlC value with temperature. The steady‐state flexural creep rate varies from 0.5°10‐6 to 2.5°10‐6 h‐1 in the temperature and load ranges of 1200° to 1300°C and 100 to 250 MPa.
Fluid Flow Model for Ceramic Tape Casting
Authors: Chou Ye T. , Ko Ya T. , Yan Man F.
Published: March 2005

The flow behavior of a ceramic slurry during tape casting is analyzed based on the principles of fluid dynamics. The fluid model yields explicit expressions for tape thickness as a function of viscosity, the pressure gradient, and the speed and geometry of the casting head. The theoretical predictions are verified by experiments using a perovskite slurry as the testing material. The results show that within the range of normal operating conditions a uniform tape thickness can be attained. Furthermore, it is feasible to maintain a high‐speed casting operation without any deleterious effect on the tape quality.
Thermal Expansion of 12CaO°7Al2O3
Authors: Datta R. K.
Published: March 2005

Literature data for the 12CaO°7Al2O3 phase show certain discrepancies in the structure, thermal stability, and mean linear thermal expansion obtained by different techniques. Phase‐pure, cubic, polycrystallin I2CaO°7Al2O3 was synthesized by annealing a stoichiometric melt in air. Infrared spectrophotometry indicated stabilization by moisture. Differential thermal analysis and thermogravimetric analysis showed the cubic phase to be stable up to at least 1200° C. High‐temperature X‐ray diffraction analysis of a polycrystalline sample and dilatometric measurement of sintered pellets indicated a linear thermal expansion of 41 × 10‐7 to 43X10‐7/°C in the temperature range 200° to 800°C.
Cation Tracer Diffusion in Cr2O3 and Cr2O3‐0.09 wt% Y2O3
Authors: PARK JONG‐HEE , KING WAYNE E. , ROTHMAN STEVEN J.
Published: March 2005

The cation diffusivities in the lattice and along dislocations and grain boundaries have been measured on sintered polycrysals of Cr2O3; and Cr2Cr2O3‐0.09 wt% Y2O3 at1100°C and at the pO2 corresponding to that of Cr/Cr2O3 equilibrium at that temperature. Results for lattice and dislocation diffusivities in pure Cr2O3 are in good agreement with previous work. The present results indicate that yttrium additions have negligible effect on lattice and dislocation diffusion. However, grain‐boundary diffusion in pure Cr2O3 is significantly slower than grain‐boundary diffusion in Cr2O3‐0.09 wt% Y2O3. The results are discussed in terms of their implications for the reactive‐element effect in high‐temperature oxidation of chromium‐containing alloys.
A Colloidal Method to Ensure Phase Homogeneity in β‐Al2O3/ZrO2 Composite Systems
Authors: LANGE F. F. , MILLER K. T.
Published: March 2005

A colloidal processing method that ensures phase homogeneity has been developed for β″‐Al2O3/ZrO2 composites. High volume fractions (<55 vol%) of β″‐AI2O3 and limited volume fractions (5 vol%) of ZrO2 powders were dispersed in 2‐propanoI. It is suspected that ions associated with the powders (e.g., Na+) and, possibly, trace amounts of water produce the coulombic repulsive forces needed for dispersion in the alcohol. All particles larger than a predetermined size were eliminated by sedimentation. To concentrate the fine solids of the slurry and to prevent mass segregation during storage, the ZrO2 powder was flocced with small additions of nitric acid. The water in nitric acid, however, leaches Na+ from the β″‐Al2O3, creating large NaNO3 crystals in the slurry that volatilize upon firing, leaving voids in the composite material. The β″‐AI2O3 powder, therefore, was sedimented from a concentrated (35 vol%) dispersed 2‐propanol slurry and was not flocced. The two‐phase slurry, which exhibited the thixotropic rheology indicative of a flocced system, was mixed by passing through an ultrasonic mixing chamber. The viscosity and mixing uniformity, quantified by high spatial resolution phase analysis of sintered materials, increased with utrasonification time. These observations suggest that when the flocced ZrO2 globules were sheared apart, they recombined with the dispersed β″‐Al2O3 phase, causing two‐phase heteroflocculation. Viscosity measurements can therefore be used as a measure of phase homogeneity. The two‐phase slurries could be consolidated by slip casting or pressure filtration.
Technique for Measuring Stresses Which Occur During Sintering of a Fiber‐Reinforced Ceramic Composite
Authors: Ostertag Claudia P.
Published: March 2005

A new technique for monitoring stresses during sintering of a ceramic composite has been developed. The stress is measured by means of the heterogeneity stresses that build up in a sandwich compact, which consists of a layer, or plane, ofSiC fibers between two layers of ceramic powder of different thicknesses. Upon sintering, this configuration produces an asymmetric stress field across the thickness of the specimen, which results in the bending of the compact, as characterized by the curvature of the fibers. In situ observations of ihe process provide information about the temperature dependence of stress initiation.
Effect of Uniformity on the Electrical Resistivity of SiC‐ZrB2 Ceramic Composites
Authors: Takahashi Ken , Jimbou Ryutaro
Published: March 2005

Effect of uniformity on the resistivity was investigated for SiC‐ZrB2 ceramic composites. Dispersion of ZrB2 particles was numerically characterized by image analysis. Spatial fluctuation of composition greatly affected the resistivity of composites. The effective medium theory was extended to treat composites with composition spatial fluctuation. The extended theory successfully explained the effect of uniformity on the resistivity of composites in relatively uniform cases. In composites of low uniformity, enhancing the uniformity increased the resistivity by breaking chains of ZrB2 particles.
Further Consideration of Phases in the System Ba2SiO4–Ca2SiO4
Authors: Thompson John G. , Withers Ray L. , Hyde Bruce G.
Published: March 2005

The results of an investigation of the system Ba2SiO4–Ca2SiO4 by powder X‐ray and electron diffraction suggest a greater complexity than supposed hitherto. The previously recognized phases α, α′hα′l, X, T, and the newly reported Y have room‐temperature structures that are modulated distortions of hexagonal (or pseudohexagonal) parent structures. Each displays characteristic and distinctive modulations. The phases are more readily distinguished in this way than by their unit‐cell dimensions and compositions which, for a given phase, can vary with bulk starting composition and thermal history.
Plasma‐Induced Morphological Changes in α‐Silicon Carbide
Authors: Porter Richard L.
Published: March 2005

Significant alterations in the surface morphology of α‐silicon carbide powders have been observed after exposure to a low‐temperature Ar plasma. Surface alterations were observed in 3 min at 1900°C and 30 min at 1600°C. Powders heated with plasma exposure were characterized by contact development and particle rounding whereas without the plasma substantial faceting was observed at higher temperatures.
Exaggerated Grain Growth in Cemented Carbides Due to Inhomogeneous Milling
Authors: Seeker U. , Exner H. E.
Published: March 2005

Tungsten carbide powders mixed with cobalt in an attritor mill with low and high amounts of benzene show pronounced differences in particle size distribution. A significant portion of large crystals remains in the thicker slurry which leads to exaggerated grain growth during sintering.
An Oxygen‐Effervescent Aluminate Glass
Authors: Hosono Hideo , Abe Yoshihiro
Published: March 2005

A foaming‐agent‐free aluminate glass of the composition 59CaO·7MgO·27Al2O3·7SiO2 (mol%) exhibited marked effervescence on heating the as quenched glass to near its softening temperature. Numerous bubbles evolve over the entire glass. Their radii are nearly constant (50 μm) and depend on heat‐treatment conditions. Their maximum volume goes up to ∼ 10 vol%. The bubbles consist solely of oxygen gas and pressure is ∼ 130 kPa (1.3 atm) at the softening temperature.
Tensile Fracture Toughness Measurements in Ceramics
Authors: Tschegg Elmar K. , Suresh Subra
Published: March 2005

A novel procedure is outlined whereby fracture toughness values for ceramics can be measured under uniaxial tension (mode I) in specimens containing a fatigue crack. Circumferentially notched rods of rapolycrystalline aluminum oxide were precracked in cyclic compression to introduce a fatigue crack at room temperature, following the technique proposed by Suresh and co‐workers.7,10,11 Subsequently, the precracked rods were fractured in pure tension. Highly reproducible values of fracture toughness were obtained using this method.
Sodium Titanates: Stoichiometry and Raman Spectra
Authors: Bamberger Carlos E. , Begun George M.
Published: March 2005

The sodium titanates Na4TiO4, α, β‐, and γ‐Na2TiO3, Na8Ti5O14, Na2Ti3O7, and Na2Ti6O13, all of which can be synthesized in the temperature range 800° to 1200°C, have been characterized by X‐ray diffraction (XRD) and Raman spectroscopy. The existing XRD data have been critically reviewed and several inconsistencies and errors have been identified.
Determination of Phase Transformation Depth Profiles with Synchrotron Radiation
Authors: KEEFER KEITH D. , MICHALSKE TERRY A.
Published: March 2005

The transformation of tetragonal zirconia to monoclinic in a glass‐ceramic as a function of depth from a fracture surface was measured by X‐ray diffraction employing synchrotron radiation. The large number of photon energies which can be used in such an experiment permt rigorous testing of models of the transformation zone. A crack plane intersection model has been developed to interpret the observations for two phase‐transformation‐toughened glass‐ceramics of grossly different inicrostructures.
Aluminum Oxide Anomaly and Structure Model of Alkali Aluminosilicate Glasses
Authors: OSAKA AKIYOSHI , ONO MASAYUKI , TAKAHASHI KATSUAKI
Published: March 2005

The molar volume, Vickers hardness number, and optical basicity A(Pb2+/CaO = 1) were measured for alkali aluminosilicate glasses of composition (1 −χ)R2O ·χAl2O3·nSiO2 in the range 0.2 < χ < 0.7 (0.25 < Al/R < 2.33). On the basis of their composition dependences, the constitution of the glasses is discussed in terms of the formation of [RalO4/2] units in the range Al/R < 1 and that of triclusters of AlO4 and SiO4 units in the range Al/R > 1. The possibility of the presence of a small amount of the tricluster is proposed in the range Al/R < 1.
Grain‐Boundary and Surface Segregation of Ba‐Ti‐O Phases in Rutile
Authors: HAGEMANN HANS J. , O'BRYAN HENRY M.
Published: March 2005

The solubility of barium in rutile and the formation and morphology of second phase at external and internal surfaces of single‐crystal and polycrystalline rutile (TiO,2) have been studied for various heat treatments up to 1450°C and in several configurations of the barium source. It has been found that barium is not incorporated into the rutile lattice but instead forms an amorphous, quasi‐liquid film of Ba‐Ti‐O at high temperature (=1400°C) which covers the grain boundaries and the external surfaces. On cooling or annealing at lower temperature (=1100°C) the continuous film breaks up to form isolated segregation patterns. Transport of the second phase by surface and grain‐boundary diffusion is rapid and reversible by heat treatment.
Chemical Durability of Fluoride Glasses: II, Reaction of Barium‐Thorium‐Based Glasses with Water
Authors: SIMMONS CATHERINE J.
Published: March 2005

The aqueous leaching behavior of three Ba‐Th‐based fluoride glasses was studied. Results of solution analysis, SEM, and IR spectroscopy are reported and compared with earlier studies on fluorozirconate‐based glasses. Leaching appears to be by matrix dissolution dominated by component solubility. No hy‐drated leach layer was seen to form on the surface. Only a mild drift In solution pH, resulting from a limited hydrolysis of, dissolved thorium fluoride, was observed. The reduced pH drift away from neutral, coupled with lower component solubilities, is credited with the 100‐fold improvement in chemical durability of the Ba‐Th‐based fluoride glasses over the fluorozirconate‐based glasses reported previously.
Technique for the Static Fatigue Testing of Fibers
Authors: Cgwap Stephen F. , Brown Sherman D.
Published: March 2005

An easy‐to‐use, low‐cost method for static fatigue testing of fibers in harsh environments was developed. Stresses greater than 550 ksi (3791 MPa) are attainable yet the specimen is insensitive to external shock. The method gave good comparative results when used to test indium‐coated fused silica fibers under distilled water or 2M NaCl solution.
Effect of Sintering Temperature on the Densification of Al2O3
Authors: Kwon Sung‐Tae , Kim Doh‐Yeon , Kang Thae‐Khapp , Yoon Duk N.
Published: March 2005

Alumina powder compacts sintered at various temperatures were isostatically hot‐pressed. The specimens sintered to the closed‐pore state can be densified further by hot isostatic pressing. If the open pores are eliminated during sintering, sintering at a low temperature is desirable to achieve a full densification after hot‐pressing. Sintering at high temperatures causes pores to be trapped inside the grains; these pores are difficult to eliminate by subsequent hot‐pressing.
Structure and Tensile Strength of LaS1.4
Authors: Whittenberger J. Daniel , Smoke Richard H.
Published: March 2005

The tensile strength of LaS1.4 has been estimated by diametral stress testing at room temperature, 800 and 1300 K. Brittle, tensile‐type failures were obtained at all temperatures when the crosshead speed was 2.1 × 10−3 mm/s; however, a 1300 K test at 8.5 × 10−4 mm/s produced plastic flow. The microstructure of LaS1.4 consisted of two phases with β‐La2S3 comprising about 15 vol% of the structure and γ‐La2S3 the remainder. Because of the limited amount of material available for testing, no correlation between microstructure and mechanical strength could be drawn.
Preparation of Cubic Perovskites A(B2/5W3/5)O3 (A=Ba or Sr, B=Na or Li)
Authors: Hikichi Yasuo , Suzuki Suguru
Published: March 2005

Pure cubic perovskites Ba(Na2/5W3/5)O3, Sr(Na2/5W3/5)l5)O3, and Sr(Li2/5W3/5)O3 were prepared by solid‐state reaction at 600° to 650°C in air, by starting with oxides or carbonates of the various elements. The cubic forms have an ordered arrangement of the B cations in the ABO3 structure, and the lattice constants are a =0.8324 nm [Ba(Na2/5W3/5)O3], 0.8136 nm Sr(Na2/5W3/5)O3], and 0.7958 nm [Sr(Li2/5W3/5)O3]
Thermal Stability and Acid Resistivity of Glasses Based on ZnO‐Al2O3‐SiO2
Authors: Shimbo Masaru
Published: March 2005

The glass‐forming region in the ZnO‐Al2O3‐SiO2 system was studied, and the acid resistivity of the glass stabilized by PbO addition was measured. Glass containing more than 50 at.% SiO2 had a markedly increased acid resistivity. At about 50 at.% SiO2, the crystallization of the glass caused its resistivity to decrease.
Introducing Compressive Surface Stresses into Brittle Materials
Authors: Troczynski Thomas B , Nicholson Patrick S.
Published: March 2005

Sodium β‐Al2O3 changes its molar volume upon ion exchange. This effect can be utilized to introduce surface compression into brittle matrices. Experiments are reported wherein spinel/20 vol% Na‐β‐Al2O3 and glass/20 vol% Na‐β‐Al2O3 composites containing constrained Na‐β‐Al2O3 particles underwent Na+ to K+ ion exchange in KNO3 melts and thereafter exhibited shorter Vickers microindentation cracks.
Grain Growth in Two‐Phase Ceramics: Al2O3 Inclusions in ZrO
Authors: LANGE FRED F. , HIRLINGER MARGARET M.
Published: March 2005

The effect of Al2O3 inclusions with a greater average size (0.6 μm) than the average particle size of the major phase powder (<0.1 μm) on grain gowth was examined by sintering ZrO2/Al2O3 composites (0,3,5,10, and 20 vol%) at 1400°C and then heat‐treating at temperatures up to 1700°C. Normal grain growth was observed for all conditions. The inclusions appeared to have no effect on grain growth until the ZrO2 grain size was ∼1.5 times the average inclusion size. Grain growth inhibition increased with volume fraction of the Al2O3 inclusion phase. At temperatures 1600°C, the inclusions were relatively immobile and most were located within the ZrO2 grains for volume fractions <0.20; at higher temperatures, the inclusions could move with the grain boundary to coalesce. Grain growth was less inhilited when the inclusions could move with the boundaries, resulting in a larger increase in grain size than observed at lower temperatures. Analogies between mobile voids, entrapped within grain at lower temperature due to abnormal grain growth during the last state of sintering, and the observations concerning the mobile inclusions are made suggesting that grain‐boundary movement can “sweep” voids to grain boundaries and eventually of four‐grain junctions, where they are more likely to disappear by mass transport.
Phase Equilibria in the Iron Oxide‐Cobalt Oxide‐Phosphorus Oxide System
Authors: DE GUIRE MARK R. , PRASANNA T. R. S. , KALONJI GRETCHEN , O'HANDLEY ROBERT C.
Published: March 2005

Solid‐state equilibria at 1000°C were determined in the Fe2O3‐FePO4‐Co3(PO4)2‐CoO area of the Fe‐Co‐P‐O system in air. Two new ternary compounds were observed: CoFe(PO4)O, an oxyphosphate which melts incongruently at 1130°C, and Co3Fe4(PO4)6, an orthophosphate which melts incongruently at 1080°C. The ramifications of the liquidus behavior for the formation of rapidly solidified cobalt ferrite from cobalt ferrite‐phosphate melts are discussed.
The System HfO2‐TiO2
Authors: COUTURES JEAN PIERRE , COUTURES JULIETTE
Published: March 2005

The system HfO2‐TiO2 was studied in the 0 to 50 mol% TiO2 region using X‐ray diffraction and thermal analysis. The monoclinic (M) ⇌ tetragonal (T) phase transition of HfO2 was found at 1750°± 20°C. The definite compound HfTiO4 melts incongruently at 1980°± 10°C, 53 mol% TiO2. A metatectic at 2300°± 20°C, 35 mol% TiO2 was observed. The eutectoid decomposition of HfO2,ss) (T) → HfO2,ss (M) + HfTiO34,ssss occurred at 1570°± 20°C and 22.5 mol% TiO2. The maximum solubility of TiO2 in HfO2,ss,(M) is 10 mol% at 1570°± 20°C and in HfO2,ss (T) is 30 mol% at 1980°± 10°C. On the HfO2‐rich side and in the 10 to 30 mol% TiO2 range a second monoclinic phase M of HfO2(M) type was observed for samples cooled after a melting or an annealing above 1600°C. The phase relations of the complete phase diagram are given, using the data of Schevchenko et al. for the 50% to 100% TiO2 region, which are based on thermal analysis techniques.
Phase Equilibria in the System Nd2O3‐P2O5
Authors: WONG MING‐SHIH , KREIDLER ERIC R.
Published: March 2005

The phase diagram for the system NdI2O3‐P2O5 was constructed. Six intermediate compounds, having molar Nd2O3: P2O5 ratios of 3:1, 7:3, 1:1, 1:2, 1:3, and 1:5, were identified. The 3:1, 7:3, and 1:1 compounds are stable to at least 1500°C. The 1:2 compound decomposes to 1:1 and 1:3 at 730 ± 5°C. The 1:3 and 1:5 compounds melt congruently at 1280 ± 5° and 1055 ± 5°C, respectively. None of the neodymium phosphates show lower temperature limits of stability.
Phase Stability of CdF2‐LiF‐AIF3‐PbF2 Glasses
Authors: EL‐BAYOUMI OSAMA H. , SIMMONS CATHERINE J. , CLAUSEN EDWARD M. , SUSCAVAGE MICHAEL J. , SIMMONS JOSEPH H.
Published: March 2005

The techniques of scanning electron microscopy, energy dispersive X‐ray microanalysis, and dark‐field transmission electron microscopy were combined to study the phase stability of CdF2‐LiF‐AlF3‐PbF2 glasses. The selected compositions, presumed to be exceptionally stable, exhibited a liquid‐liquid immiscibility phase transition; this led to the formation of two amorphous phases consisting of a matrix near the original glass composition and an isolated spherical phase which was richer in CdF2 and poorer in PbF2 than the matrix. Subsequent secondary‐phase separation and crystallization were observed following heat treatments near the glass transition temperature.
Negative Pressure Dependence of Viscosity
Authors: Gupta Prabhat K.
Published: March 2005

It is shown that according to the Adam‐Gibbs theory of viscosity the sign of the pressure dependence of viscosity is the same as the sign of the relaxational expansion coefficient. Existing data on systems where negative pressure dependence of viscosity has been observed and relaxational expansion coefficient values are available under the same temperature and pressure conditions appear to support this result. It is therefore suggested that the negative pressure dependence of viscosity and the negative relaxational expansion coefficient have a common mechanistic origin and that this result, in turn, supports the Adam‐Gibbs model of viscosity.
Structural Changes in Stressed As2S3 Glass Fibers Determined by Raman Spectroscopy
Authors: KNIGHT JIANE S. , MECHOLSKY J.J. , WHITE WILLIAM B.
Published: March 2005

Raman spectra were measured transverse to As2S3 glass fibers which were stressed to various levels up to their breaking strength of 200 MPa. The spectra consisted of a single intense band near 340 cm‐1, several weak bands, and a scattering tail at low wavenumbers. The intense band exhibited a decrease in intensity and a small wavenumber shift but retained the same half‐width in the stressed fibers. A new band appeared as a shoulder at 320 cm‐1 with an intensity that could be related to the stress level. The stress‐related band is postulated to arise from local broken‐bond defect centers containing nonbridging sulfur atoms.
Comparison of the Stress‐Intensity and Johnson‐and‐Holloway Criteria for Crack Branching in Rectangular Bars
Authors: KIRCHNER HENRY P. , CONWAY J.C.
Published: March 2005

The angular and radial dependencies of the mirror‐mist boundaries predicted by the stress‐intensity and Johnson‐and‐Holloway criteria were compared with experimentally determined shapes of the boundaries in rectangular specimens fractured in tension and flexure. The stress‐intensity criterion provided better predictions than the Johnson‐and‐Holloway criterion.
V2O3‐Polymer Composite Thermistors
Authors: HU K. A. , MOFFATT DAWNE , RUNT JAMES , SAFARI AHMAD , NEWNHAM ROBERT
Published: March 2005

V2O3 was incorporated into polymer matrices to produce composite materials with low room‐temperature resistivities and sizable positive temperature coefficient (PTC) resistance effects. In addition, a negative temperature coefficient effect, associated with the semiconductor‐to‐metal phase transition in V2O3, was also observed. The resistivity vs temperature curve for these composites resembles a square well with three temperature regimes in which the composite behaves like a semiconductor, a metal, and an insulator. The intensity of the PTC effect for these composites was found to be as large as 10 orders of magnitude.
Low‐Thermal‐Expansion Polycrystalline Zirconyl Phosphate Ceramic: Solid‐Solution and Microcracking‐Related Properties
Authors: YAMAI IWAO , OTA TOSHITAKA
Published: March 2005

The effects of the addition of Ta205 or Nb205 on the sintering and refractory properties of 2ZrO2·P2O5‐based ceramics have been investigated. The solid solution with Nb2O5 has a lower average thermal expansion coefficient than the pure phase. The strength of the polycrystalline ceramic is reduced when the grain size exceeds the transition grain size for microcracking. The thermal expansion of the ceramic is abruptly lowered when the grain size exceeds a value which should be termed the “second transition grain size” for additional wider microcracking. SiO2 was found most effective for inhibiting grain growth to prevent microcracking and for obtaining a strong ceramic.
Redox Chemistry in Candidate Glasses for Nuclear Waste Immobilization
Authors: SCHREIBER HENRY D. , HOCKMAN ANGELA L.
Published: March 2005

An electrochemical series of redox couples, originally developed for Savannah River Laboratory glass frit 131 (SRL‐131) as a reference composition, has been extended to two other alkali borosilicate compositions that are candidate glasses for nuclear waste immobilization. Because no dramatic differences were ascertained in the redox chemistry of selected multivalent elements in SRL‐131 vs that in Savannah River Laboratory glass frit 165 (SRL‐165) and in West Valley glass frit 205 (WV‐205), the comprehensive electrochemical series can readily be applied to a range of nuclear waste glass compositions. In order to alleviate potential problems with foaming and precipitation of insolubles during the processing of the nuclear waste in these glass melts, the [Fe2+]/[Fe3+] ratio of the melt should be between 0.1 and 0.5.
Low‐Temperature Synthesis and Characterization of Mixed Sodium Cerium(III) Hexa‐Aluminate
Authors: Aka Gérard , Thery Jeanine , Vivien Daniel
Published: March 2005

Two forms of sodium cerium(III) mixed hexa‐aluminate were prepared at temperature as low as 1270°C, i.e., 300°C lower than those reported previously, and characterized by X‐ray diffraction techniques. These compounds are formed by thermal treatment, under argon, of an amorphous organometallic precursor obtained by the “citric acid method”. During the synthesis, the 3+ oxidation state of cerium is retained at all temperatures.
Formation of (111) Twins in BaTiO3 Ceramics
Authors: Eibl Oliver , Pongratz Peter , Skalicky Peter , Schmelz Helmut
Published: March 2005

(111) twins are found frequently in the microstructure of BaTiO3 ceramics prepared by the mixed‐oxide technique. The processing steps by which the (111) twins are formed are in question. A BaCO3‐TiO2 powder mixture is milled and then Calcined at 1100°C for 2 h, where BaTiO3 is formed by the release of CO2. After the powder is calcined, it is analyzed by TEM. Image and diffraction pattern data are combined to prove the presence of (111) twins in powder particles; the formation of (111) twins occurred frequently during calcination. The formation mechanism of such twins and their role during anomalous grain growth are discussed.
Influence of Process Variables on Microstructure and V‐I Characteristics of Multicomponent ZnO‐Based Nonlinear Resistors
Authors: ASOKAN T. , IYENGAR G. N. K. , NAGABHUSHANA G. R.
Published: March 2005

Studies have been made of the effect of process variables such as calcination, initial particle size, and postsinterin on density, microstructure, V‐I characteri stics, and energy ‐handling capability of a ZnO‐based composite: 87.325 wt% ZuO + 0.1% Nb2O5+ 3.5% Sb2O5+ 6% Bi2O3+ 0.55% CoO + 0.7% MnO2+ 0.9% Cr2O3+ 0.9% NiO + 0.025% Al(NO3)3. The nonlinear characteristics were found to be improved by the calcination of a ZnO + Nb2O5 mixture at 1200°C for 1h. The postsintering heat treatment was found to rejuvenate V‐I characteristics of the degraded sample to a greater extent. Further, the postsintered sample containing Nb2O5, prepared by using a calcined charge of particle size around 1 μm, was found to possess better V‐I characteristics and energy‐handling capability compared to the samples prepared without the calcination step.
In Situ Laser Raman Determination of Electrochemical Reactions of Y2O3‐Stabilized ZrO2 and Molten Na2SO4
Authors: Windisch Charles F. , Bates J. Lambert , Boget Delmar I.
Published: March 2005

When used as components of advanced energy conversion systems, oxide ion conductors and molten electrolytes may react or decompose according to various mechanisms. Understanding these mechanisms is important in improving system performance. In situ laser Raman spectroscopy was used successfully to study the reactions between an oxide ion conductor and a molten salt. Changes in the Raman spectrum of molten Na2SO4 were observed near Y2O3‐stabilized ZrO2 electrodes when they were polarized anodically in the molten salt. These changes were interpreted to indicate the formation of yttrium sulfate complexes.
Phase Transformation of Diphasic Aluminosilicate Gels
Authors: WEI WEN‐CHENG , HALLORAN JOHN W.
Published: March 2005

Aluminosilicate gels with compositions Al2O2/SiO2 and 2 were prepared by gelling a mixture of colloidal pseudo‐boehmite and a silica sol prepared from acid‐hydrolyzed Si(OC2H5)4. Upon heating the pseudo‐boehmite transforms to γ‐Al2O3 around 400°C, then to δ‐Al2O3 at 1050°C, and at 1200°C reacts with amorphous SiO2 to form mullite. Some twinned θ‐Al2O3 forms before mullite. Nonstoichiometric specimens have a similar transformation sequence, but form mullite grains with inclusions of either Al2O3 or cristobalite, often associated with dislocation networks or micropores. Mullite grains are formed by nucleation and growth and have equiaxed shape.
Investigations of Calcium Silicate Hydrate Structure Using Silicon‐29 Nuclear Magnetic Resonance Spectroscopy
Authors: Francis Young J.
Published: March 2005

Silicon‐29 nuclear magnetic resonance has been used to probe the effects of temperature and the addition of reactive silica on the silicate structure of amorphous calcium silicate hydrate (C‐S‐H), produced by the hydration of alite (Ca3SiO5). Both an increase in the temperature of formation and the addition of reactive silica increase the degree of silicate polymerization in the C‐S‐H. However, in all cases the data are consistent with the formation of linear chain silicates and the absence of any cross‐linking. The initial formation of a hydrated orthosilicate is observed, and it is suggested that this species may form during the adsorption of water onto the surface of alite during storage.
Inclusion Size and Sintering of Composite Powders
Authors: Weiser Martin W. , De Jonghe Lutgard C.
Published: March 2005

Ceramic powders containing dispersed inert particulates often exhibit dramatically lower densification rates than the pure powder. This decrease results from the shrinkage incompatibilities of the matrix and the inclusion during densification. The analyses of this phenomenon all predict that the shrinkage rate is only dependent on the overall volume fraction of the inert second phase, and not on the particle size. Experiments on ZnO containing dispersed SiC particles of different size showed that the retarding effect of the second phase increases significantly with decreasing particle size, at constant SiC volume fraction.
Measurement of Residual Stresses in Oxide–ZrO2 Three‐Layer Composites
Authors: Virkar Anil V. , Fong Jue Jan , Hansen James J. , Cutler Raymond A.
Published: March 2005

Al2O3–ZrO2 and MgO–ZrO2 layered composites were fabricated in such a way that the outer layers of bar‐shaped specimens consisted of the oxide (Al2O3 or MgO) and unstabilized ZrO2, while the bulk consisted of the oxide and partially stabilized ZrO2. During cool‐down from the sintering or the annealing temperature, the outer layers expanded because of the tetragonal → monoclinic transition in ZrO2, thereby creating compressive stresses in the outer layers and tensile stresses in the bulk. Residual stresses were determined using a strain gage technique in which a strain gage was mounted on one face while the opposing face was incrementally ground off. Measurement of the strain as a function of thickness permitted the evaluation of residual stresses using pertinent equations from simple beam theory.
Long‐Term Operation of Positive Temperature Coefficient Resistors
Authors: Smith James W.
Published: March 2005

The effect of various atmospheres on the long‐term operation of positive temperature coefficient resistors was studied. In most cases where degradation of properties occurred, the operable mechanism appeared to be volatilization of oxygen from grain boundaries due to reduction of the partial pressure of oxygen in the atmosphere around the sample. The effect of CCl2F2, however, was much more pronounced and was attributed to a chemical mechanism.
Low‐Temperature Synthesis Route to MgNb2O6
Authors: Horowitz Harold S.
Published: March 2005

A solution‐derived precursor may be calcined at temperatures >500°C to yield MgNb2O6. Calcining temperatures 800°C result in the familiar, cation‐ordered columbite structure type. Calcining temperatures <800°C result in a previously unobserved, cation‐disordered α‐PbO2 structure type. The low‐temperature form of MgNb2O6 is a more reactive material than is obtained by conventional solid‐state reaction as evidenced by its small particle size and its ability to react with PbO to form lead magnesium niobate at lower temperatures.
Microstructural Analysis in Processing of the High‐Tc Superconductor Ba2YCu3O7‐x in Air
Authors: Guha Jyoti P.
Published: March 2005

In the synthesis of the superconducting compound Ba2YCu3O7‐x from a stoichiometric mixture containing BaCO3, Y2O3, and CuO In air, a low‐melting liquid phase is formed at about 890°C. The liquid phase was identified as a ternary eutectic located within the compatibility triangle Ba2YCu3O7‐x–BaCuO2–CuO. The implication of this finding for the processing of Ba2YCu3O7‐x is discussed.
Porosity in Spinel Compacts Using Small‐Angle Neutron Scattering
Authors: FRASE KATHARINE G. , HARDMAN‐RHYNE KAY
Published: March 2005

Unfired spinel (MgAl2O4) compacts and sintered materials with small hard agglomerates (<5 μm) were studied using small‐angle neutron scattering (SANS) techniques. The SANS results were compared with those from mercury porosimetry and gas adsorption. The results from green‐state samples are consistent with interconnected “ink‐bottle”‐type porosity. In the latter stages of densification the average void size is significantly larger than that found in the unfired compact. The presence of the hard agglomerates affects the observed SANS scattering much more in the partially densified samples than in the unfired compacts. It was demonstrated that the use of multiple SANS techniques to study large voids (<0.1 μm) and large pore fractions (45%) is a useful, sensitive, nondestructive diagnostic probe for the evaluation of porosity during sintering.
Thermally Induced Fast Fracture in a Glass Double‐Cantilever‐Beam Specimen
Authors: DAVIS MICHAEL W. , POPELAR CARL H. , ADVANI SUNDER H.
Published: March 2005

Rapid crack propagation and arrest in a soda‐lime glass double‐cantilever‐beam specimen subjected to a thermal shock loading are investigated. The crack growth‐time history is measured and compared with that predicted by a one‐dimensional dynamic fracture model. Good correlations between predicted and measured crack speeds and crack lengths at arrest were obtained. Inertial effects can be sufficient to produce complete fracture of the specimen. The predicted initial crack driving force required to produce this failure agreed with the observed value. These results are contrasted with the predictions of a quasi‐static analysis that always predicts crack arrest and underestimates the arrested crack length.
Derivation of a Revised Model for Activity Calculation in Multisilicate Melts
Authors: SCHLESINGER MARK E. , LYNCH DAVID C.
Published: March 2005

Hollitt's model for prediction of thermodynamic properties in multicomponent silicate melts has been revised to better reflect network modifier depolymerization effectiveness as a function of basicity and melt composition. This model is based on the free energy changes in a melt caused by the breaking of silicate polyions by the addition of basic oxides; these free energy changes are in turn related to the change in the concentration of various oxyanion molarities caused by such additions. Application of the revised model to actual systems shows good agreement with experimental data; possible model improvements are discussed.
Evaporation of Antimony Trioxide from Glass Melts
Authors: Lindig Matthias , Frischat Güenther H.
Published: March 2005

The transpiration method was used to study the evaporation of Sb2O3 from a glass melt with the composition 70SiO2·15K2O·15CaO·MgO (in wt%) at 1200° to 1300°C. The glass contained about 0.9 wt% Sb2O3. Assuming the monomer Sb2O3 is the species of evaporation, the saturation vapor pressures could be calculated with ΔHV=218±20 kJ·mol−1 and ΔSV=128±10 J·mol−1·K−1.
Thermal Stresses During Quenching of Short Glass Cylinders
Authors: Lambropoulos John C.
Published: March 2005

The thermal stresses are calculated during quenching of short glass cylinders for materials used in solid‐state laser devices. The stresses are determined numerically, and they are parameterized by the Biot number which characterizes cooling by convection. The solution is compared to the stresses for flat, penny‐shaped and for long, rod‐shaped cylinders. The validity of the steady‐state thermal boundary conditions is discussed.
Atomically Sharp Crack in 15R‐Sialon
Authors: Tanaka Hidehiko , Bando Yoshio , Inomata Yoshizo , Mitomo Mamoru
Published: March 2005

A crack which propagated naturally in 15R‐sialon was observed by high‐resolution TEM. The crack was found to be atomically sharp and there was no evidence of microplasticity near the tip. The deformation of the lattice around the crack is discussed by considering a linear fracture mechanics model.
Infrared Absorption Due to H2O and D2O in a Fluorozirconate Glass
Authors: Loehr Susan R. , Chung Ki‐Ho , Moynihan Cornelius T.
Published: March 2005

A comparative study of infrared absorption due to H2O and D2O impurities in a fluorozirconate glass (53ZrF4·20BaF2·4LaF3·3AlF3·20NaF) was carried out. The H2O and D2O were introduced into the glass by reaction of the surface at 260°C with H2O and D2O vapor entrained in a stream of N2. Reaction with H2O produced IR absorption bands at 2.9 μm (O–H stretch) and 6.1 μm (H2O bend). Reaction with D2O produced bands at 3.9 μm (O–D stretch) and 8.3 μm (D2O bend). The ratios of the corresponding D2O/H2O peak frequencies are 0.74 for both the stretching and bending vibrations, in good agreement with the value of 0.727 predicted from the difference in the OH and OD reduced masses.
Effects of TiO2 Addition to LiNbO3 on the Cation Vacancy Content, Curie Temperature, and Lattice Constants
Authors: Gallagher P.K. , O'Bryan H.M.
Published: March 2005

The defect model of Abrahams and Marsh is expanded to consider the addition of TiO2 and other oxides to form solid solutions with both the stoichiometric and congruent compositions of LiNbO3. It is shown that the Curie temperature (Tc) and the limits of solubility are determined by the cation vacancy content regardless of whether these are formed by Li deficiency or the addition or substitution of aliovalent ions. X‐ray powder diffraction patterns indicate that the a‐axis parameter decreases markedly with additions of TiO2 while the c‐axis parameter remains essentially unchanged. These results are compared with prior investigations, and the technological implications of this work to lightguide devices are described.
Comparison of the Surface Charge Behavior of Commercial Silicon Nitride and Silicon Carbide Powders
Authors: WHITMAN PAMELA K. , FEKE DONALD L.
Published: March 2005

The adsorption and desorption of protons from aqueous solution onto the surfaces of a variety of commercial silicon carbide and silicon nitride powders has been examined using a surface titration methodology. This method provides information on some colloidal characteristics, such as the point of zero charge (pzc) and the variation of proton adsorption with dispersion pH, useful for the prediction of optimal ceramic‐processing conditions. Qualitatively, the magnitude of the proton adsorption from solution reveals small differences among all of the materials studied. However, the results show that the pzc for the various silicon nitride powders is affected by the powder synthesis route. Complementary investigations have shown that milling can also act to shift the pzc exhibited by silicon nitride powder. Also, studies of the role of the electrolyte in the development of surface charge have indicated no evidence of specific adsorption of ammonium ion on either silicon nitride or silicon carbide powders.
Pore Evolution During Glow Discharge Sintering of Alumina
Authors: PAGE RICHARD A. , SPOONER STEPHEN , SANDERSON WAYNE B. , JOHNSON D. LYNN
Published: March 2005

A series of experiments have been performed to demonstrate the applicability of small‐angle neutron scattering to the study of pore evolution during sintering. Samples of α‐Al2O3 which had been zone sintered in a hydrogen hollow cathode glow discharge to densities exceeding 94% of theoretical were employed in these preliminary measurements. The neutron scattering results indicate that densification during the final stages of glow discharge sintering occurs primarily through a reduction in the number of pores present with only a small change in the average pore size.
Strength Degradation in Polycrystalline Alumina Due to Sharp‐Particle Impact Damage
Authors: BREDER KRISTIN , RITTER JOHN E. , JAKUS KARL
Published: March 2005

Sharp‐particle impact damage in five aluminas, varying in purity, grain size, and porosity, was studied, and postimpact strengths were determined. Target specimens were subjected to single‐particle impacts using a gas gun and multiparticle impacts using a slinger‐type apparatus. For comparison, static indentation damage in the same aluminas was studied using a Vickers microhardness indenter. For the fine‐grained materials the impact damage morphology was characterized by severe radial cracking and lateral chipping; the coarse‐grained materials exhibited chipping and grain fall‐out and very irregular radial crack patterns. The postimpact and postindentation fracture strength was modeled by assuming that the materials exhibited crack resistance toughening. Based on these results, fracture resistance curves (R curves) for each of the five aluminas were predicted and compared. The large‐grained aluminas exhibited the strongest R‐curve behavior and the greatest impact resistance; i.e., strength degradation was least sensitive to impacting energy.
Microchemistry and Mechanisms of Adherence in Steel/Enamel Interfaces
Authors: Paparazzo Ernesto , Fierro Giuseppe , Ingo Gabriel M. , Sturlese Stefano
Published: March 2005

The microchemistry of steel/enamel interfaces was investigated, on a nearly atomic scale, by means of X‐ray photoelectron spectroscopy. Experimental evidence is given that good adherence is characterized by a fully reacted iron silicate phase, which produces a local chemical continuity between steel and enamel, whereas bad adherence is associated with a heterogeneous mixture of an iron silicate phase plus unreacted FeO.
Fabrication of Dense Lithium Fluoride for Neutron Shielding
Authors: Stewart Martin W.A. , Buykx William J.
Published: March 2005

Polycrystalline LiF suitable for use as a thermal neutron shielding material was fabricated by both hot‐pressing and pressureless sintering to greater than 99.5% theoretical density. To achieve this, the poorly sinterable as‐received LiF powder had to be (a) ball‐milled to reduce particle size, (b) calcined to substantially remove porosity from the cubic particles, and (c) ball‐milled again to break up agglomerates formed during calcination.