bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Shock Testing of Ceramics—A New Testing Method
Authors: Schneider Gerold A. , Petzow Günter
Published: March 2005

The thermal shock behavior of Si3N4 has been determined with a new type of computer‐controlled testing equipment. Thin circular disks are heated up to 1350°C with two tungsten halogen lamps yielding heating rates up to 1000°C/s. The sample temperature is measured in situ with an infrared pyrometer and used to calculate the transient thermal stresses. The simple geometry of radially orientated notches allows in situ observation of the crack growth behavior during thermal shock. Measured failure times are used to determine the fracture toughness of the material under thermal shock loading, KcTS, from room temperature (RT) up to 1000°C. Comparison of the results with KIcSENB values measured by the single‐edge notch beam method at RT shows excellent agreement.
Effect of Doping on the Strength and Infrared Transmittance of Hot‐Pressed Cesium Iodide
Authors: Kim Hyoun‐Ee , Moorhead A. J.
Published: March 2005

The effect of additions of other iodide materials on the mechanical strength and optical transmittance of polycrystalline CsI was investigated. Divalent or trivalent iodides were unsuitable as dopant materials because they tended to decrease transmittance in the extreme infrared region. However, significant increases in transmittance as well as in strength were observed when polycrystalline CsI was doped with small amounts of monovalent iodide materials, especially with AgI. In the case AgI, the increases in strength and transmittance were attributed to the pinning of grain boundaries and, therefore, the inhibition of grain growth during hot‐pressing, resulting in a material having much smaller grains. The maximum fracture strength obtained in this study (in CsI doped with 0.05 mol% of AgI, and pressed for 1 h at 150°C and a pressure of 103 MPa) was 40 MPa, which is about 4 times higher than that of an undoped sample and ∼10 times higher than that of pure single‐crystal CsI. The samples with maximum strength also exhibited the optimum optical transmittance.
Synergism of Toughening Mechanisms in Whisker‐Reinforced Ceramic‐Matrix Composites
Authors: Giannakopoulos Antonios E. , Breder Kristin
Published: March 2005

The improved fracture resistance of whisker‐reinforced ceramic‐matrix composites involves more than one energy‐absorbing mechanism. The possible mechanisms are reviewed and a micromechanical model evaluating the relative contributions to the overall toughness is presented. The mechanisms involve microcracking, load transfer, bridging, and crack deflection. The synergism of these mechanisms is examined using an energy release rate balance equation. The basic assumption of the proposed model is that the load transfer between the matrix and the whiskers is due to Coulomb friction. The model has been applied to an Al2O3/SiC whisker composite and shows reasonable agreement with reported experimental results. The role of the thermal residual stresses is also examined in light of the frictional load transfer assumption.
Preparation and Characterization of High‐Temperature Thermally Stable Alumina Composite Membrane
Authors: Lin Yue‐Sheng , Burggraaf Anthonie J.
Published: March 2005

A crack‐ and pinhole‐free composite membrane consisting of an α‐alumina support and a modified γ‐alumina top layer which is thermally stable up to 1100°C was prepared by the sol–gel method. The supported thermally stable top layer was made by dipcoating the support with a boehmite sol doped with lanthanum nitrate. The temperature effects on the microstructure of the (supported and unsupported) La‐doped top layers were compared with those of a common γ‐alumina membrane (without doping with lanthanum), using the gas permeability and nitrogen adsorption porosimetry data. After sintering at 1100°C for 30 h, the average pore diameter of the La‐doped alumina top layer was 17 nm, compared to 109 nm for the common alumina top layer. Addition of poly(vinyl alcohol) to the colloid boehmite precursor solution prevented formation of defects in the γ‐alumina top layer. After sintering at temperatures higher than 900°C, the common alumina top layer with addition of poly(vinyl alcohol) exhibits a bimodal pore distribution. The La‐doped alumina top layer (also with addition of poly(vinyl alcohol)) retains a monopore distribution after sintering at 1200°C.
Vapor‐Phase Growth of Transparent Zinc Oxide Ceramics with c‐Axis Orientation
Authors: Noritake Fumitomo , Yamamoto Nobuyuki , Horiguchi Yasunobu , Fujitsu Satoru , Koumoto Kunihito , Yanagida Hiroaki
Published: March 2005

Large transparent specimens of polycrystalline zinc oxide with c‐axis orientation have been prepared by the vapor transport method. Optical transmittance is 80% to 90% at 800 nm. X‐ray diffraction peaks from faces other than (001) are negligible.
Influence of Lead in the Processing of High‐Temperature 2223 Bi─Sr─Ca─Cu─O Superconductor
Authors: Tripathi Ramesh B. , Johnson David W.
Published: March 2005

Difficulty in reproducibility of results has often been encountered in the Pb‐doped 2223 Bi─Sr─Ca─Cu─O superconductor compound due to lead vaporization in samples prepared by standard ceramic methods. Various processing parameters such as quenching, slow cooling, or closed vs open sintering containers were found to affect the properties significantly in samples prepared by standard ceramic methods. In contrast, samples prepared by spray‐drying of nitrate solutions were very homogeneous and reproducible because of the rapid and uniform reaction of Pb with other constituents. The magnetic susceptibility and X‐ray diffraction data remained unchanged for spray‐dried samples processed with or without quenching and sintered in open or closed containers.
Interpenetrating Phase Composites
Authors: Clarke David R.
Published: March 2005

An assessment of the processing and properties of interpenetrating phase composites is presented. Such materials, defined as multiphase composites in which each phase is topologically interconnected throughout the micro‐structure, were the subject of a DOE Basic Energy Sciences sponsored workshop on research needs and opportunities held in July 1989 in Snowmass, Colorado. In place of a report representing the proceeding of the workshop, this paper provides a review of the field in its present, nascent state and identifies some of the critical scientific and technological issues posed by development of this class of material. The emphasis is on processing approaches and properties of interpenetrating phase composites. A list of the participants contributing to the workshop is given.
Effect of Pore Distribution on Microstructure Development: III, Model Experiments
Authors: Zhao Junhong , Harmer Martin P.
Published: March 2005

Model experiments have been conducted on a series of alumina samples in which the microstructures have been tailored to conform to the classical configuratins depicted in the models of final‐stage sintering. Simultaneous measurements of sintered density, grain size, pore number density, and pore size distribution were made as a function of sintering time at constant temperature (1850°C). The data supported a model of grain‐boundary‐diffusion‐controlled densification and surface‐diffusion‐controlled grain growth. An atom flux equation for grain‐boundary diffusion transport was deduced from the data. The kinetics analysis highlights the importance of incorporating the number of pores per grain as an independent variable in mechanistic studies of final‐stage sintering. The number of pores per unit volume was identified as a critical factor influencing densification kinetics. The effect of pore distribution on microstructure development was simulated for comparison with the data obtained from the model experiments.
Failure Waves in Glass
Authors: Bless Stephan J. , Brar N. Singh , Kanel Gennady , Rosenberg Zvi
Published: March 2005

Failure waves have been recently observed in glass plates and rods struck by high‐speed projectiles. These waves propagate into material that has been prestressed by a compressive shock. The wave propagation speed exceeds the maximum crack speed and is not constant. Behind the failure wave there is a total loss of tensile strength and a substantial drop in shear strength. The failure is explosive, leading to radial expansion in unconfined targets and presurization in confined targets.
Liquidus–Solidus Phase Relations in the System CaO─CrO─Cr2O3─SiO2
Authors: de Villiers Johan P. R. , Muan Arnulf
Published: March 2005

Phase relations in the system CaO–chromium oxide–SiO2 were determined (a) in equilibrium with metallic chromium and (b) at various oxygen pressures in the range of ∼ 10−10 to 10−13 atm. Two ternary phases occur on the liquidus surface in equilibrium with metallic chromium, viz, the garnet Ca3Cr2Si3O12 (uvarovite), and CaCrSi4O10 of the gillespite‐type structure and in which essentially all the chromium is present in the divalent state (Cr2+). Furthermore, a previously reported binary calcium chromite phase “X” of approximate composition (Ca0.4Cr0.6)Cr2O4 is stable also on the liquidus surface of the present system. The lowest liquidus and solidus temperatures in the system under these conditions (contact with metallic chromium) are significantly lower (by 100° to 200°C, depending on CaO/SiO2 ratios of the melts) than those for the same system in air. Furthermore, there is considerable solid solution of chromium oxide in lime (CaO) and the various crystalline calcium silicates (pseudowollastonite, CaSiO3; rankinite, Ca3Si2O7; dicalcium silicate, Ca2SiO4; tricalcium silicate, Ca3SiO5), presumably by partial substitution of Cr2+ for Ca2+ toward hypothetical chromium analogs of each CaO‐containing phase, particularly in lime and Ca2SiO4. At the somewhat higher oxygen pressures imposed by the CO2─H2 gas mixtures of CO2/H2 ratios of 1/24 and 1/8.1, the phases containing most of the chromium in the divalent state (CaCrSi4O10 and (Ca0.4Cr0.6)Cr2O4) do not appear on the liquidus surface, the primary phase area of garnet (uvarovite) decreases, the lowest liquidus and solidus temperatures increase noticeably (−50° to 100°C), and the amounts of chromium substituting in lime and the various crystalline calcium silicate phases (CaSiO3, Ca3Si2O7, Ca2SiO4, and Ca3SiO5) decrease considerably from those observed for the system in equilibrium with metallic chromium. Combination of the data obtained under these reducing conditions with those previously reported for the system under more oxidizing conditions permits derivation of the general features of phase relations in the quaternary system CaO─CrO─Cr2O3─SiO2.
Floating Zone Crystal Growth and Phase Equilibria: A Review
Authors: Kimura Shigeyuki , Kitamura Kenji
Published: March 2005

The thermal‐imaging floating zone technique can be used to grow crystals of yttrium iron garnet (Y3Fe5O12), aluminum‐doped yttrium orthoferrite (YFe0.88Al0.12O12), and magnetite (Fe3O4), which represent peritectic compounds, solid‐solution crystals, and atmosphere‐sensitive materials, respectively. The reactions involved in floating zone crystal growth are explained on the basis of phase diagrams. A review of crystal growth reports, including unpublished findings by the present authors, demonstrates how the crystallization processes, the reaction with the ambient atmosphere, and the composition variation in the obtained crystals can be explained or controlled on the basis of phase equilibrium. The floating zone technique is applicable to a variety of materials and remains a handy tool for materials research; however, its industrial application may be limited.
Application of an Ion‐Packing Model Based on Defect Clusters to Zirconia Solid Solutions: I, Modeling and Local Structure of Solid Solutions
Authors: Yashima Masatomo , Ishizawa Nobuo , Yoshimura Masahiro
Published: March 2005

Oxygen vacancies can be introduced into zirconia solid solution ZrO2–MOu (u= 1 and 1.5) to maintain electroneutrality. Recently, the local structures around Zr4+ and M2u+ ions in ZrO2–MOu solid solutions have been studied through EXAFS spectroscopy, diffuse scattering analysis, and single‐crystal structure analysis. The present study constructs an ion‐packing model for zirconia solid solutions based on some defect cluster models. The decrease of cell volume with the occurrence of vacancies is assumed to be expressed by decreasing the coordination number (CN) of cations around the vacancy. The distribution of CNs in a solid solution was calculated from a certain defect cluster model. The average interatomic distances, the average CN, and the short‐range order parameters were calculated using this distribution of CNs. The local structures calculated from the model were compared with experimental data in the systems ZrO2–MO1.5 (M = Y, Gd, Yb, and Ca). In the ZrO2–YO1.5 system, the r(s–O) interatomic distance, where s represents Zr4+ or Y3+ and O represents O2−, decreased with Y content and therefore vacancy content. The probability of finding Y3+ around a vacancy increases with increasing yttria content from a comparison of the calculated results with the ones from recent EXAFS studies. The present model can qualitatively explain compositional and size dependences of the dopant on various local structures.
Thermal Healing of Laser‐Induced Internal Cracks in Lithium Fluoride Crystals
Authors: Wang Zhanyi , Li Yan Z. , Harmer Martin P. , Chou Ye T.
Published: March 2005

Laser‐induced internal cracks in LiF single crystals were annealed and healed at various temperatures in the absence of environmental contamination. The thermal healing process consists of three distinct stages: (a) pinching off of the crack into radially directed cylindrical pores within the rim of the crack front and within inner regions close to 〈110〉 directions, (b) ovulation of the 〈110〉 pores into rows of isolated, square‐shaped pores and, simultaneously, regression of the plate‐shaped subcracks situated near 〈100〉 directions, and (c) shrinkage of the isolated pores. A modified Arrhenius relationship between the rate of subcrack shrinkage and the annealing temperature was obtained. The apparent activation energy was found to be 2.0 eV (192.7 kJ/mol), suggesting that the healing process is controlled by volume diffusion.
Formation of a Protective Layer During the Hydration of Cement
Authors: Sujata K , Jennings Hamlin M.
Published: March 2005

The mechanism for the slow rate of reaction between portland cement and water during the early stage is not well understood, but it probably is controlled by either the rate that the reactants diffuse through a barrier that surrounds the unreacted cement grains or by the rate that nuclei of the stable product form and grow or by both rates. New evidence using environmental scanning electron microscopy is presented about the structure of a layer that forms around the particles of cement. Preliminary observations that relate mixing to the structure of the layer are also presented.
Preparation of Potassium Tantalate Niobate by Sol–Gel Method
Authors: Hirano Shin‐ichi , Yogo Toshinobu , Kikuta Ko‐ichi , Morishita Toshiyuki , Ito Yasuhiro
Published: March 2005

Perovskite potassium tantalate niobate (KTN) powders and thin films were synthesized from a metal alkoxide solution. Homogeneous KTN coating solutions were prepared from KOC2H5, Ta(OC2H5)5, and Nb(OC2H5)5 in absolute ethanol. The precursor crystallized to pyrochlore at ∼ 650°C, and then to perovskite at ∼ 750°C, depending upon Ta:Nb ratio. H2O vapor during calcination was found to play a prominent role in the direct and predominant crystallization of perovskite films with preferred orientation. Highly oriented KTN films of perovskite structure were successfully prepared on MgO (100) substrates at 675°C.
Effects of Sintering Temperature and Time on Grain Size and Dielectric Constant of Potassium Tantalum Niobate Films
Authors: Catalan Antonio B. , Mantese Joseph V. , Micheli Adolph L. , Schubring Norm W. , Wong Curtis A.
Published: March 2005

Thin films of potassium tantalum niobate (KTN) formed by metalorganic deposition were subjected to one‐ and two‐step sinterings in air and potassium atmosphere. These polycrystalline films were found to be mechanically robust and display electrical properties similar to single‐crystal KTN. This report shows that film grain size increased with sintering temperature and time. Scanning electron micrographs revealed grain sizes ranging from submicrometer to 5 μm in diameter. The maximum relative permittivity, its corresponding rate of change with temperature, and film grain size were measured as a function of sintering temperature and time.
Objective Evaluation of Short‐Crack Toughness Curves Using Indentation Flaws: Case Study on Alumina‐Based Ceramics
Authors: Braun Linda M. , Bennison Stephen J. , Lawn Brian R.
Published: March 2005

An objective methodology is developed for evaluating toughness curves (T‐curves) of ceramics using indentation flaws. Two experimental routes are considered: (i) conventional measurement of inert strength as a function of indentation load; (ii) in situ measurement of crack size as a function of applied stress. Central to the procedure is a proper calibration of the indentation coefficients that determine the K‐field of indentation cracks in combined residual‐contact and applied‐stress loading, using data on an appropriate base material with single‐valued toughness. Tests on a fine‐grain alumina serve to demonstrate the approach. A key constraint in the coefficient evaluation is an observed satisfaction of the classical indentation strength–(load)−1/3 relation for such materials, implying an essential geometrical similarity in the crack configurations at failure. T‐curves for any alumina‐based ceramic without single‐valued toughness can then be generated objectively from inert‐strength or in situ crack‐size data. The methodology thereby circumvents the need for any preconceived model of toughening, or for any prescribed analytical representation of the T‐curve function. Data on coarse‐grained aluminas and alumina‐matrix material with aluminum titanate second‐phase particles are used in an illustrative case study.
Effect of Bi2O3 on Impurity Ion Distribution and Electrical Resistivity of Li‐Zn Ferrites
Authors: Brooks Keith G. , Berta Yolande , Amarakoon Vasantha R. W.
Published: March 2005

Preventing the incorporation of impurities in Li‐Zn ferrite grains during sintering is essential for production of ceramics with reproducible magnetic and electrical properties. Li‐Zn ferrites of composition Li0.3Zn0.4Mn0.05Fe2.25O4 were prepared with Bi2O3 and borosilicate sintering additives. The distribution of impurity ions in the sintered ferrites was investigated using transmission electron microscopy (TEM) coupled with energy dispersive spectroscopy (EDS). Ceramics prepared with Bi2O3 contained Si, Ca, and S impurities, located at grain boundaries and triple point regions. The low viscosity and good wetting properties of the Bi2O3 and to a lesser extent the borosilicate liquid phase allowed impurities to be selectively removed from the growing ferrite phase during sintering, thus improving sample resistivities.
Effect of MgO and SO3 on the Impurity Concentration in Alite in Portland Cement Clinker
Authors: Maki Iwao , Fukuda Koichiro , Yoshida Hideto , Kumaki Junichi
Published: March 2005

MgO in clinker promotes the stable growth of alite in favor of the occurrence of M3. Mg ions go into solid solution in alite by simply replacing the Ca‐sites in the structure. While the concentration of Mg in alite increases in proportion to the amount of MgO in the clinker, the concentration of Al, Fe, and Ti in alite remains constant. It is thus the Mg ions occupying the Ca‐sites that give rise to the occurrence of M3 at ambient temperature. By contrast, SO3 encourages the growth instability of alite. The concentration of impurity elements in alite tends to increase with increasing amount of SO3 in clinker. This is most remarkable for Al and seems closely connected with the occurrence of M1 at ambient temperature. The presence of S was clearly recognized in alite.
Vapor‐Phase‐Deposited Diamond—Problems and Potential
Authors: Yarbrough Walter A.
Published: March 2005

Considerable progress has been made toward the goal of diamond synthesis by chemical vapor deposition (CVD). This progress consists of improved methods for synthesis and understanding how diamond is formed. The field has rapidly expanded with industrial consortia, international joint ventures, specialized journals, novel methods for synthesis and processing, and the introduction of new products. Despite this expansion, many issues remain unresolved, generating considerable debate within the research community. Among these debates is the question of how diamond is formed. Both thermodynamics and kinetics are frequently debated at the many world‐wide meetings on this technology. The resolution of these issues awaits further progress and, with improved understanding, may have implications for the synthesis of other ceramic materials. The diamond research community includes not only ceramists and other materials scientists, but specialists in subjects that range from chemistry and chemical engineering to solid‐state physics and electrical engineering. Crystals are grown using methods that range from the use of high‐power plasmas and the combustion of acetylene in oxygen to the thermal decomposition of fluorocarbons and various hydrocarbons in the presence of fluorine. Although some evidence exists for diamond heteroepitaxy, the goal of large‐area heteroepitaxial diamond has proved elusive.

Thick (> 100 μm), free‐standing, polycrystalline diamond layers are being grown, and their properties rival those of natural crystals. Methods have been developed for the cutting, polishing, and brazing of diamond, and products are being tested in the marketplace. Engineering of the diamond–substrate interface for acceptable adhesion and reliability has progressed, although much work remains to be done. The central issues for commercialization are less the question of whether diamond can be grown in sufficient amounts or with sufficiently attractive properties, but rather whether the fabrication methods can be made sufficiently cost‐effective for the markets envisioned.
Silicon Carbide Platelet/Alumina Composites: I, Effect of Forming Technique on Platelet Orientation
Authors: Chou Yeong‐Shyung , Green David J.
Published: March 2005

SiC‐platelet‐reinforced Al2O3‐matrix composites were made by three different forming techniques, i.e., slip casting, tape casting, and dry compaction of a granulated powder. All samples were densified with hot pressing at 1650°C and 25 MPa for 0.5 h. The orientation of SiC platelets in the composites was studied before and after hot pressing using optical microscopy and a pole figure X‐ray device. X‐ray diffraction of the (0006) plane of silicon carbide (6H) was used to analyze the degree of preferred orientation. It was found that both tape casting and die pressing could give rise to preferred orientation in green bodies with the faces of SiC platelets parallel to the tape faces or perpendicular to the pressing direction, respectively. The preferred orientation in die‐pressed samples also showed an increase with the increase of the compaction stress; however, this reached a saturation level at about 70 MPa in a similar way to the green density. Samples formed by slip casting gave a platelet orientation close to a random one in the green body. After hot pressing, preferred orientation was observed in both slip‐cast and tape‐cast samples with the faces of SiC platelets perpendicular to the direction of hot pressing. The effect of platelet size on the orientation was also investigated. The preferred orientation in platelet composites was found to yield higher toughness than the random state.
Reactive Laser Ablation Synthesis of Nanosize Aluminum Nitride
Authors: Johnston Gregory P. , Muenchausen Ross E. , Smith Douglas M. , Foltyn Steve R.
Published: March 2005

An aluminum (Al) target was laser ablated in a nitrogen (N2) atmosphere, producing aluminum nitride (AlN) powder. These powders were calcined at 900°C for 2 h. Powders were produced at various nitrogen pressures, and the calcined powders were tested for unreacted aluminum content, using differential thermal analysis (DTA). The AlN powder, produced at a laser fluence of 12 J/cm2 and a nitrogen pressure of 10.0 kPa (75 torr), showed no evidence of unreacted aluminum by DTA and was phase‐pure AlN by X‐ray diffraction (XRD). The surface area of this powder is 82 m2/g, corresponding to a particle size of ∼11 nm, which is in good agreement with TEM observations.
Strain‐Rate‐Dependent Transformation Behavior of a 9 mol% Ce‐TZP Ceramic
Authors: Liu Tianshun , Mai Yiu‐Wing
Published: March 2005

The strain rate dependence of the stress‐induced t–m transformation behavior of a Ce‐TZP ceramic with a grain size of 1.1 μm has been investigated both in four‐point bend and Charpy impact tests. The crosshead speed was varied from 8.3 × 10−8 m/s to 8.3 × 10−3 m/s in the four‐point bend tests. In the impact tests, the striking velocity was 2.5 m/s. Double notches (a/w= 0.5) were made on one side of the specimen to measure the stress‐induced t–m transformation zone size at the nonpropagated notch tip. It was found that a transition of the transformation zone size with crosshead speed occurred at about 10−6 to 10−5 m/s. Above this critical speed, the transformation zone was at least an order of magnitude larger in size. This new strain‐rate‐dependent transformation behavior has not been previously reported.
Calcium Phosphate Cements Prepared by Acid–Base Reaction
Authors: Sugama Toshifumi , Allan Marita , Hill Janet M.
Published: March 2005

We investigated the characteristics of calcium phosphate cements (CPC) prepared by an exothermic acid–base reaction between NH4H2PO4‐based fertilizer (Poly‐N) and calcium aluminate compounds (CAC), such as 3CaO · Al2O3 (C3A), CaO · Al2O3 (CA), and CaO · 2Al2O3 (CA2), in a series of integrated studies of reaction kinetics, interfacial reactions, in‐situ phase transformations, and microstructure development. Two groups were compared: untreated and hydrothermally treated CPC specimens. The extent of reactivity of CAC with Poly‐N at 25°C was in the following order: CA > C3A ≫ CA2. The formation of a NH4CaPO4·xH2O salt during this reaction was responsible for the development of strength in the CPC specimens. The in‐situ phase transformation of amorphous NH4CaPO4·xH2O into crystalline Ca5(PO4)3(OH) and the conversion of hydrous Al2O3 gel →γ‐AIOOH occur in cement bodies during exposure in an autoclave to temperatures up to 300°C. This phase transformation significantly improved mechanical strength.
Sintering and Characterization of Polycrystalline Monoclinic, Tetragonal, and Cubic Zirconia
Authors: Cutler Raymond A. , Reynolds James R. , Jones Aaron
Published: March 2005

Polycrystalline monoclinic (m), tetragonal (t), and cubic (c) ZrO2, sintered at 1500°C, were annealed in the cubic stability field and rapidly cooled to permit the displacive c→t′ transformation to occur in compositions containing 0–6 mol% Y2O3. The bulk fracture toughness of coarse‐grained (> 25 μm) m, t′, and c zirconias were compared with conventionally sintered, fine‐grained (typically less than 1 μm) materials. The ferroelastic monoclinic and tetragonal zirconias were more than twice as tough as paraelastic cubic zirconia.
Refractory Lining for Alumina Electrolytic Cells
Authors: Allaire Claude
Published: March 2005

This paper provides the specifications of a refractory lining for alumina electrolytic cells capable of ensuring good resistance to corrosion by the cell chemicals, while maintaining desirable thermal characteristics during service.

Several refractory materials were tested in the Alcan's standard electrolysis bath test. Also, using Alcan's standard procedures, different insulating refractory products were tested for their gain in thermal conductivity after compression.
Exaggerated Texture and Grain Growth in a Supperplastic SiAlON
Authors: Wu Xin , Chen I‐Wei
Published: March 2005

A fine‐grained superplastic β′‐silicon nitride solid solution (SiAlON) was found to develop elongated grains and a pronounced texture during tensile deformation at 1550°C. The texture development is well‐described by a geometrical model of grain rotation in accordance with the strain field. Once aligned, grains can then grow with little constraint due to impingement and often coalesce into each other. With the above microstructural development, the stressstrain curve displayed unusually strong strain hardening characteristics due to a fiber–reinforcement effect of the aligned silicon nitride grains on the glass–containing matrix. By extending the rheological model of Chen and Yoon and considering these microstructural evolutions, we are able to simulate the deformation behavior.
Effect of Indentation Interaction on Cracking
Authors: Buijs Maarten , Martens Liesan A. A. G.
Published: March 2005

Most theories on abrasive machining of brittle materials are based on indentation experiments. Little attention has been paid to the consequences of indentation interaction. In this study it is shown that the residual stress field of an adjacent indentation strongly influences the radial crack length. This effect is analyzed on the basis of the concept of the expanding cavity. The presence of an adjacent indentation leads to the formation of a large new lateral crack system. Crack–crack interaction is found to be of minor importance. Implications for the description of machining processes are discussed.
Densification and Sintering Kinetics in Sintered Silicon Nitride
Authors: Suttor Daniel , Fischman Gary S.
Published: March 2005

The sintering sequence of Y2O3‐Al2O3‐doped Si3N4 was investigated with respect to the relationship between densification, α→β transformation, and microstructural development. Quenching studies were performed to reveal these interactions during a complete sintering cycle. Isothermal studies were conducted to examine the sintering kinetics and compared to Kingery's liquid‐phase sintering model. The bulk density increased to ≥90% of theoretical density with only minor transformation taking place. Major transformation occurred in a late sintering stage and was accompanied by the development of elongated grains. The kinetic order of the densification process, taking into account an appropriate correction, was larger than any of the rate exponents predicted by the Kingery model, indicating that other single or mixed mechanisms were active.
Combined‐Stage Sintering Model
Authors: Hansen James D. , Rusin Richard P. , Teng Mao‐Hua , Johnson D. Lynn
Published: March 2005

By focusing on the similarities between the three stages of sintering, a single equation is derived that quantifies sintering as a continuous process from beginning to end. The microstructure is characterized by two separate parameters representing geometry and scale. The dimensionless geometry parameter, denoted T, comprises five scaling factors that relate specific microstructural featuers (e.g., surface curvature) to the scale (grain diameter). Calculations of T from experimental data show (a) agreement with computer simulations of initial‐stage sintering, (b) the effect of surface diffusion on T, and (c) changes in T with microstructural evolution during sintering. Application of the model to the design of firing schedules and the study of microstructural geometry effects on sintering is discussed.
2223 Phase Formation in Bi(Pb)─Sr─C─a─Cu─O: II, The Role of Temperature—Reaction Mechanism
Authors: Chen Yan Ling , Stevens Ronald
Published: March 2005

The formation mechanism, the temperature range for the growth, and the thermal stability of the 2223 phase in Bi(Pb)─Sr─Ca─Cu─O have been investigated using DTA/TG, XRD, SEM/EDAX, TEM, EPMA, four‐probe resistance and acsusceptibility measurement. The formation of the 2223 phase was found to follow a dissolution–precipitation process. A 2212 phase first reacts with the liquid phase formed via an incongruent melting of the Ca2PbO4 phase, and a dissolution of CaO and CuO takes place. The 2201 phase, which has the largest negative free energy, is then precipitated from the melt; the nucleation and growth of the 2223 phase are subsequently developed by the reaction between the 2201 phase precipitates and ions of Ca2+ and Cu2+ present in the liquid phase. The 2223 phase is formed at temperatures in the range 827°C T < 856°C. The optimum temperature Tf for the formation of 2223 phase is 845°± 5°C. The 2223 phase is thermodynamically unstable at temperatures above 856°C.
Heavy‐Metal Oxide Glasses
Authors: Dumbaugh William H. , Lapp Josef C.
Published: March 2005

Heavy‐metal oxide glasses might arbitrarily be defined as those containing over 50 cation percent of bismuth and lead which participate in the glass structure as network formers. Glass systems based on these heavy‐metal oxides in silicates, borates, phosphates, germanates, and ferrites are surveyed. Gallate systems are emphasized since they have a unique ability to form stable glasses while maintaining key properties, such as the best infrared transmission and the highest nonlinear optical susceptibilities and diamagnetic Verdet constants for oxide glasses.
Phase Equilibria and Structural Species in NdCl3–NaCl, NdCl3–CaCl2, PrCl3–NaCl, and PrCl3–CaCl2 Systems
Authors: Sharma Ram A. , Rogers Robert A
Published: March 2005

Equilibrium phase diagrams for the systems NdCl3–CaCl2 and NdCl3–NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl2 and 600°± 2°C in the NdCl3–CaCl2 system. A compound NaCl.3NdCl3 which melts incongruently at 545°± 5°C to NdCl3 and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl3–NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl3–CaCl2 system and the literature data for the PrCl3–CaCl2 system, the melts in the former system consist of Nd3+, Ca2+, and Cl− ions and in the latter system of Pr3+, Ca2+, and Cl− ions. The above approach indicates the presence of Na+, Cl−, and NdCl2‐5 ions in the NaCl‐rich melts and Nd3+, Cl−, and NdCl−4 in the NdCl3‐rich melts in the NdCl3–NaCl system. Analogous ions were indicated in the melts of the PrCl3–NaCl system.
Kinetics of Carbothermal Reduction Synthesis of Boron Carbide
Authors: Weimer Alan W. , Moore William G. , Roach Raymond P. , Hitt James E. , Dixit Ravindra S. , Pratsinis Sotiris E.
Published: March 2005

Carbothermal reduction kinetics to synthesize boron carbide are studied under conditions of high carbon/boron oxide precursor heating rates (> 103K/s) and intermediate temperatures (1803 K < T < 2123 K). For these conditions, fractional carbon conversion, X, can be described by a nucleation–growth rate expression: In (1 –X) =– (kt)3, where Ko= 3.86 × 106 s−1 and Ea= 301 ± 55 kJ/mol for the temperature range (1803 < T < 1976 K) and ko= 2 × 1020 s−1 and Ea= 820 ± 89 kJ/mol for the temperature range (1976 < T < 2123 K), respectively. Boron carbide formation is highly dependent upon the phase change of reactant boron oxide from solid to liquid to gaseous boron suboxides and the effect of reaction environment (i.e., heating rate and ultimate temperature) on the rate at which the phase changes occur.
Preparation of β‐BaB2O4 Powders and Thin Films by Sol–Gel Method
Authors: Hirano Shin‐ichi , Yogo Toshinobu , Kikuta Kō‐ichi , Yamagiwa Katsuya
Published: March 2005

β‐BaB2O4 (β‐BBO) powders and films were successfully synthesized by the sol–gel method using metal alkoxides. A homogeneous and stable solution was prepared by the reaction of barium metal with boron triethoxide in ethanol by addition of diethanolamine. The drip‐coated precursor films began to crystallize to β‐BBO on Pt substrates at 500°C and converted to β‐BBO films with preferred orientation to the c‐axis at 700°C.
Kinetics of β‐Si3N4 Grain Growth in Si3N4 Ceramics Sintered under High Nitrogen Pressure
Authors: Lai Kou‐Rueh , Tien Tseng‐Ying
Published: March 2005

The kinetics of anisotropic β‐Si3N4 grain growth in silicon nitride ceramics were studied. Specimens were sintered at temperatures ranging from 1600° to 1900°C under 10 atm of nitrogen pressure for various lengths of time. The results demonstrate that the grain growth behavior of β‐Si3N4 grains follows the empirical growth law Dn– D0n=kt, with the exponents equaling 3 and 5 for length [001] and width [210] directions, respectively. Activation energies for grain growth were 686 kJ/mol for length and 772 kJ/mol for width. These differences in growth rate constants and exponents for length and width directions are responsible for the anisotropy of β‐Si3N4 growth during isothermal grain growth. The resultant aspect ratio of these elongated grains increases with sintering temperature and time.
Effects of Mechanical Treatment on X‐ray Diffraction Line Broadening in Pyrophyllite
Authors: Sánchez‐Soto Pedro J. , Macías Manuel , Pérez‐Rodríguez José L.
Published: March 2005

When pyrophyllite was subjected to mechanical treatment by dry grinding, the alteration was greater along the c axis of its structure because reflections from basal planes (00l) disappeared well before those from nonbasal planes, producing anisotropic X‐ray line broadening observed on grinding. X‐ray analysis showed that the mean lattice microstrains increase and crystallite size decreases along the 00l direction, as grinding time increases. An inverse relationship between both parameters was found, and interpreted assuming that the number of grain boundaries of the small crystallites increases substantially through mechanical treatment. The maximum surface area of ground samples was reached after 30 min of grinding, with marked line broadening, mean crystallite size of ∼15 nm, and lattice microstrains 0.68. Reactive ground material aggregates, becoming amorphous to X‐rays, and surface area decreases markedly.
Effects of Pore Morphology and Grain Size on the Dielectric Properties and Tetragonal–Cubic Phase Transition of High‐Purity Barium Titanate
Authors: Fang Tsang‐Tse , Hsieh Huey‐Lin , Shiau Fuh‐Shan
Published: March 2005

The effects of pore morphology and grain size on the dielectric behavior of high‐purity stoichiometric BaTiO3 have been intensively investigated. It was found that the dielectric constant was influenced not only by grain size but also by pore morphology. Dielectric constants below the Curie temperature could be evaluated by the Maxwell relationship for specimens with fractional density >90%ρt and be estimated by the modified Niesel's equation, but depolarization might be involved for specimens with fractional density <90%ρt. Dielectric Behavior above the Curie temperature followed the Curie–Weiss low. The Curie constants could be separated into two regions depending on the pore morphology, decreasing linearly with increasing porosity at different rates. The results suggest that the tetragonal–cubic phase transition temperature of specimens with fractional density <90%ρt is affected by depolarization due to the presence of continous channel pores. The dissipation factor was increased with increasing porosity due to the adsorption of water. In this study, a high‐density (<99%ρt), uniform, and fine‐grained (∼1.2 μm) microstructure of high‐purity stoichimetric barium titanate has been produced by using wet processing ad pressureless sintering, in which a high dielectric constant (>6100 at 25°C and 1 kHz) and a low dissipation factor (<0.025) could be achieved.
Origin of Orientation in Sol‐Gel‐Derived Lead Titanate Films
Authors: Kushida Keiko , Udayakumar K. R. , Krupanidhi S. B. , Cross L. Eric
Published: March 2005

The origin of orientation in sol‐gel‐derived PbTiO3films is investigated in detail. Aging of the solution is found to promote (100) orientation of the films. Characterizing the solution by viscometry indicates that the preferred orientation might be attributable to the change of molecular size in the solution. The substrate also influences the film orientation: more strongly (100)‐oriented film forms on Pt‐coated Si than on fused quartz. Highlyc‐axis‐oriented films with azimuthal orientation are grown on a (100) SrTiO3single‐crystal disk.
Calculation, Measurement, and Control of Interface Strength in Composites
Authors: Gupta Vijay , Yuan Jun , Martinez Doris
Published: March 2005

Strength and energy criteria for interface delamination are given for composite systems involving anisotropic fibers. The tensile strength of planar interfaces is measured with a modified laser spallation experiment involving a laser Doppler displacement interferometer. The technique for achieving desired interface properties is demonstrated on an Nb/Al2O3, interface. In the as‐deposited state, the strength is determined to be 0.28 GPa. The interface strength is controlled with sputter‐deposited Cr and Sb interlayers. The strength of Nb/Al2O3 interfaces varies from 0.28 to 0.35 GPa when the Cr layer thickness varies from 1 to 50 Å. The strength is reduced to 0.16 GPa with Sb thickness of 70 Å.
Grain Boundary Oxidation in PTCR Barium Titanate Thermistors
Authors: Alles Aldo B. , Burdick Vernon L.
Published: March 2005

The phenomenon of grain boundary oxidation in PTCR BaTiO3 thermistors is discussed. In particular, the energy spectra of the surface states were calculated for different samples, and these were related to the nominal composition, the impurity content of the base BaTiO3 powder used, and the prevalent atmospheric conditions during cooling and/or annealing. It is proposed that the interaction of manganese with oxygen creates deep‐lying traps, and, in general, some proof is offered that the majority of the surface states are due to different oxidizing chemisorbed gases. It is believed that the ability of a particular sample to adsorb such gases in adequate amounts, and thus exhibit an appreciable PTCR effect, is related to the presence of acceptor‐type dopants perferentially segregated onto the grain surfaces. Notably, the role of 3d transition metal cations in this process is discussed in some detail.
Quantitative Comparison of TEM Techniques for Determining Amorphous Intergranular Film Thickness
Authors: Cinibulk Michael K. , Kleebe Hans‐Joachim , Rühle Manfred
Published: March 2005

The question of which transmission electron microscopy technique can best be used to quantitatively determine the thickness of thin intergranular films is addressed. Measurement of the film thickness by diffuse dark‐field imaging resulted in values 50% to 100% larger than those determined by high‐resolution lattice imaging. Defocus Fresnel fringe imaging is an indirect method of obtaining intergranular film thickness; with this method thicknesses were overestimated by 20% to 35%, with the largest error caused by uncertainty in the exact location of fringe maxima. Although technically difficult to use, high‐resolution lattice imaging is a method capable of the resolution necessary to obtain detailed information of the boundary and the intergranular phase itself; it was found to be the most applicable to quantitative measurements of film thicknesses in Si3N4 materials, with an accuracy of ± 1 Å (±0.1 nm).
Crystallization of Copper Metaphosphate Glass
Authors: Bae Byeong‐Soo , Weinberg Michael C.
Published: March 2005

The effect of the valence state of copper in copper metaphosphate glass on the crystallization behavior and glass transition temperature has been investigated. The crystallization of copper metaphosphate is initiated from the surface and its main crystalline phase is copper metaphosphate (Cu(PO)3), independent of the [Cu2+]/[Cutotal] ratio in the glass. However, the crystal morphology, the relative crystallization rates, and their temperature dependences are affected by the [Cu2+]/[Cutotal] ratio in the glass. The crystal formed in the reduced glass is oriented and needleshaped and less aligned at higher crystallization temperature. On the other hand, the totally oxidized glass crystallizes from all over the surface. The relative crystallization rate of the reduced glass to the totally oxidized glass is large at low temperature, out small at high temperature. The glass transition temperature of the glass increases as the [Cu2+]/[Cutotal] ratio is raised. This dependence may be used to explain the relative crystallization rates. It is also found that the atmosphere used during heat treatment does not influence the crystallization of the reduced glass, except for the formation of a very thin CuO surface layer when heated in air.
Phase Transformations in Dicalcium Silicate: III, Effects of Barium on the Stability of Fine‐Grained α′L and β Phases
Authors: Nettleship Ian , Slavick Kurt G. , Kim Youn Joong , Kriven Waltraud M.
Published: March 2005

Fine‐grained materials containing both α′‐Ca2SiO4 and β‐Ca2SiO4 were fabricated as an analogue to tetragonal zir‐conia polycrystals (TZP) with the use of barium to stabilize the high‐temperature polymorphs of Ca2SiO4. The micro‐structure of dense α′L‐Ca2SiO4 exhibited none of the twinning or residual strain previously observed in fine‐grained β‐Ca2SiO4 and there was no evidence of barium‐rich grain boundary phases. Materials fired in the α region exhibited large grain sizes. Stress‐induced α′L→β transformation was observed on ground surfaces but not on fracture surfaces.
Properties of Silicon Nitride–Molybdenum Disilicide Particulate Ceramic Composites
Authors: Kao Ming‐yuan
Published: March 2005

The physical and mechanical properties of hot‐pressed Si3N4–MoSi2 particulate composites containing 15 and 30 vol% MoSi2 were studied. The average room‐temperature four‐point bend strength, fracture toughness, and electrical resistivity are 522 MPa, 3.6 MPa·√m, and 6.3 × 105Χ·cm for the 15 vol% MoSi2 composite, and 487 MPa, 5.3 MPa·√m, and 0.31 Ω·cm for the 30 vol% MoSi2 composite. The mechanical properties of the composites are very close to those of hot‐pressed Si3N4 ceramics. The high electrical conductivity of the 30 vol% MoSi2 composite was attributed to the percolation effect of MoSi2 particles. Parabolic oxidation behaviors were observed for the 30 vol% MoSi2 composite during the 1200°C long‐term oxidation experiments.
Microtextures Formed by the Remelting Reaction in Belite Crystals
Authors: Fukuda Koichiro , Maki Iwao , Ikeda Susumu , Ito Suketoshi
Published: March 2005

When they are cooled below the stable temperature region of the α phase, crystals of belite (Ca2SiO4 solid solutions) inverted to the α′H phase without a change in chemical composition and gave six sets of lamellae within the crystals. After this transition remelting reaction occurred within the inverted α′H‐phase grains, the liquid phase became nucleated and grew heterogeneously on the lamellae boundaries, resulting in a decrease in impurity concentration in the host α′H phase. When the exsolved liquid wetted the lamellae, complete dissolution of the parent crystals occurred during slow cooling. A variety of microtextures resulted, depending on both quenching temperature and cooling rate.
Nonlinear Optical Properties of TeO2‐Based Glasses: La2O3‐TeO2 Binary Glasses
Authors: Kim Sae‐Hoon , Yoko Toshinobu , Sakka Sumio
Published: March 2005

The third‐order nonlinear optical susceptibilities, X(3), of the xLaO1.5·(100 – x)TeO2 binary glasses have been measured by the third harmonic generation (THG) method. In order to investigate the origin of high‐intensity third harmonic generation, the various optical properties, such as nonlinear refractive index (n2), Abbe number (vd), dispersion energy (Ed), average excitation energy (E0), (energy gap (Eg), and polarizability (αm), have been estimated from the refractive index and UV‐visible absorption spectrum measurements. The linear refractive index, polarizability, and Ed/E02 increased, and Abbe number and energy gap decreased, with increasing LaO1.5 content. The nonlinear optical susceptibility X(3) is discussed in relation to these optical parameters.