bluuebunny/crossref_metadata_2025 huggingface dataset:
Study of Oxygen Vacancies in Ceramics by Perturbed Angular Correlation Spectroscopy
Authors: Su Han‐Tzong , Wang Ruiping , Fuchs Heinz , Gardner John A. , Evenson William E. , Sommers James A.
Published: March 2005

Perturbed angular correlation (PAC) measurements in tetragonal and cubic zirconia and in ceria are described. A physically reasonable and self‐consistent interpretation of these data implies that oxygen vacancies are trapped at a second‐neighbor position by Cd in tetragonal zirconia and by In in ceria. For Cd in tetragonal zirconia, the vacancy trap energy is found to be 0.44 eV, and the energy barrier between adjacent trap sites is approximately 0.8 eV. The activation energy of an oxygen vacancy hopping between trap sites around 111Cd in ceria is found to be 0.55 eV. The activation energy for oxygen vacancy hopping in cubic zirconia, as detected by 181Ta PAC, is about 1.0 eV and independent of the Y concentration.
Detection of Optically Excited States in Wide‐Band‐Gap Semiconductors with Tunneling Spectroscopy
Authors: Rohrer Gregory S. , Bonnell Dawn A. , French Roger H.
Published: March 2005

Tunneling spectroscopy has been used to detect the photoexcitation of charge carriers in the wide‐band‐gap semiconductors, ZnO and cubic SiC. Photoexcitation, which increases the charge carrier population and thus reduces the width of the depletion layer at the semiconductor surface, is detected as an enhancement in the tunnel current. Because the process is energy sensitive, valence‐to‐conduction band or defect charge transfer transitions may be selectively excited and detected by tunneling spectroscopy. Two types of transitions were detected which change the tunneling response; for cubic SiC valence‐to‐conduction band transitions were excited, while for Co2+ ‐ and Mn2+ ‐doped ZnO electron charge transfer transitions from the dopants to the conduction bands occur. The enhancement of the current was greater in air than under vacuum and more easily detected at small sample‐tip separations.
Thick Film Patterned Ceramics Using UV‐Curable Pastes
Authors: Haertling Carol L. , Yoshikawa Shoko , Newnham Robert E.
Published: March 2005

Screen‐printed layers of Al2O3, BaTiO3, 0.90Pb(Mg1/3Nb2/3)‐03–0.10PbTiO3, Pb(Zr,Ti)O3, ZnO, and glass alumina pastes have been patterned using photoprinting techniques. Curability of each paste by ultraviolet light and formation of holes with various diameters were studied for application as a production method for very small‐sized vias. The dependence of hole diameters on various experimental parameters is presented and discussed. Wall slopes were found to depend on the transmission of the powders used in the pastes.
Densification Behavior of Single‐Crystal and Polycrystalline Spherical Particles of Zirconia
Authors: Slamovich Elliott B. , Lange Frederick F.
Published: March 2005

Micrometer size polydispersed spheres of zirconia were produced via electrostatic atomization and pyrolysis of aqueous zirconium acetate‐yttrium acetate precursors. Varying the precursor composition in the ZrO2‐rich region of the ZrO2‐Y2O3 binary system resulted in the production of either single‐crystal (0 and 10 mol% Y2O3O or dense polycrystalline (3 mol% Y2O3) zirconia spheres of similar size distribution for densification studies. Powders of either the singlecrystal or the polycrystalline particles exhibited contrasting densification behavior; viz., powder compacts composed of polycrystalline particles obtained significantly higher endpoint densities than their single‐crystal counterparts. Microstructural observations showed that while necks between single‐crystal particles reached a stable size, necks between polycrystalline particles continued to grow.
Interfacial Segregation in Perovskites: IV, Internal Boundary Layer Devices
Authors: Desu Seshu B. , Payne David A.
Published: March 2005

A proposed model for interfacial segregation in perovskites, with induced heterogeneous defect distributions, is extended here to account for the formation of internal boundary layer devices, such as positive temperature coefficient of resistance (PTCR) thermistors and internal boundary layer capacitors (IBLC). Boundary layer effects in doped BaTiO3 are attributed to factors which contribute to the formation of highly resistive boundary layers by a segregation‐induced shift in donor incorporation and/or acceptor segregation, and the inhibiting action of segregated donors on boundary mobility and grain growth. The distribution of space charges, formed by electron transfer from conductive grains to resistive boundary layers, leads to the formation of impedance barriers in the grain‐boundary vicinity. Depending on the grain size, and on relative size and spatial distribution of the space charge layer and the resistive layer, a transition from semiconducting properties to insulating properties may take place. This model accounts for the observed PTCR and IBLC phenomena.
Semiconductor Passivation and Insulation Properties for Hydroxyl‐ and Fluoride‐Free ZnO‐SiO2‐B2O3‐Al2O3 Glasses Stabilized by Increased P2O5
Authors: Kobayashi Keiji
Published: March 2005

F−‐ and OH−‐free ZnO‐B2O3‐SiO2‐Al2O3‐P2O5 glasses used for semiconductor‐device passivation or insulation are investigated with regard to compositional dependencies for thermal expansion, viscosity points, and metal oxide semiconductor (MOS) capacitor properties. The experimental data show that thermal expansion increases, and flow points decrease, when P2O5 is substituted for B2O3. MOS capacitors passivated by OH−‐ and F−‐free ZnO‐based glasses exhibit normal capacitance‐voltage curves.
Lead Zirconate Titanate Fiber/Polymer Composites Prepared by a Replication Process
Authors: Waller David J. , Safari Ahmad , Card Roger J. , O'Toole Michael P.
Published: March 2005

The woven replication process was used to fabricate lead zirconate titanate (PZT)/polymer composites with 1–3, 2–3, and 3–3 connectivities by starting with novoloid‐derived carbon fiber, woven fabric, and nonwoven felt templates, respectively. Activated carbon‐fiber template material was impregnated with PZT by soaking it in a solution containing stoichiometric amounts of dissolved lead, zirconium, titanium, and niobium ions. Heat treatment burned out the carbon, leaving a PZT replica with the same form as the template material. Replicas were sintered in a controlled atmosphere and backfilled with an epoxy polymer to form final composites. This method, which is believed to be adaptable for mass production, is capable of producing composites with extremely fine microstructures. Woven composite samples have fiber tow diameters of 200 to 250 μm and spacings between tows of about 150 to 250 μm. Average d33= 90 pC/N, g33= 211 mV · m/N, and dhgh hydrophone figure of merit of 2100 × 10−15 m2/N values are reported for woven PZT/polymer composites.
Formation of the Liquid Phase in the System Bi‐Pb‐Sr‐Ca‐Cu‐O
Authors: Huang Yao‐Tsung , Wang Wang‐Nan , Wu Sheng‐Feng , Shei Cheng‐Yei , Hurng Weir‐Mirn , Lee Wun‐Hsin , Wu Pieng‐Tien
Published: March 2005

Differential thermal analysis (DTA), powder X‐ray diffraction (XRD), and scanning electron microscopy (SEM) were carried out to investigate the origin of the partial melting which is closely related to the formation of the 110 K superconducting phase in the Bi‐Pb‐Sr‐Ca‐Cu‐O system. The occurrence of a liquid phase in the presence of the Bi2Sr2Ca‐Cu2Oy, Ca2PbO4, and CuO phases was demonstrated. Large grain growth and promotion of the 223 phase formation resulting from the reactive liquid‐phase‐aided sintering were also observed.
Properties of Calcium, Strontium, and Barium Galliosilicate Glasses
Authors: Balewick Laura Ann , Shelby James E.
Published: March 2005

Glasses in three alkaline‐earth (Ca, Sr, and Ba) galliosilicate systems were prepared, and the density, viscosity, thermal expansion coefficient, and glass transformation temperature were measured. All glasses contain 30 mol% alkaline‐earth oxide. It is suggested that alkaline‐earth ions can play a role in the glass structure which is similar to that of an intermediate ion.
Lanthanum‐Magnesium and Lanthanum‐Manganese Donor‐Acceptor‐Codoped Semiconducting Barium Titanate
Authors: Ting Ching‐Jui , Peng Cheng‐Jien , Lu Hong‐Yang , Wu Shinn‐Tyan
Published: March 2005

BaTiO3 powder doped with La donor and codoped with Mn or Mg acceptor was sintered at 1350°C/1 h in air. For Ladoped BaTiO3, the room‐temperature resistivity decreased to a minimum at [La3+] ∼ 0.15 mol%. For La‐Mn‐codoped BaTiO3, the minimum resistivity occurred at [La3+] ‐ 2[Mn2+] ∼ 0.15 mol%. When the ceramic was changed to a fine‐grained insulator by high donor doping ([La3+] >0.15 mol%), its semiconductivity was restored, and the relatively homogeneous, coarse‐grained microstructure recurred by codoping with either Mg or Mn acceptor, with the transition at [La3+] ‐ 2[Mg2+] = 0.15 mol% or [La3+] ‐ 2[Mn2+] = 0.15 mol%. The analogy of a compensation effect between La‐Mn‐ and La‐Mg‐codoped BaTiO3 suggested that Mn acceptor added to BaTiO3 exists as Mn2+ ion in the bulk grain region; its influence on the positive temperature coefficient of resistivity behavior is then discussed.
Effect of Dynamic Compaction on the Retention of Tetragonal Zirconia and Mechanical Properties of Alumina/Zirconia Composites
Authors: Bengisu Murat , Inal Osman T. , Hellmann John R.
Published: March 2005

Dynamic consolidation techniques were employed to investigate the retention of tetragonal zirconia and degree of consolidation in alumina/zirconia powder compacts. Heating the specimens prior to explosive shock compaction increased the tetragonal‐phase retention significantly. Low shock pressures yielded no macrocracking, although final densities were low (60% to 70% of the theoretical density). Heat treatment following dynamic consolidation enhanced the retention of the tetragonal zirconia polymorph regardless of the shock pressure employed. Compact densities were increased to over 90% of theoretical at relatively low sintering temperatures (1300°C). Hardness, toughness, and Young's modulus of the compacts were comparable to those achieved in composites that were synthesized using more conventional techniques. Dynamic compaction offers an alternative method for the fabrication of zirconia‐toughened alumina ceramics.
Viscosities of Porcelains Formulated from the Weinstein Patent
Authors: Twiggs S. Warren , Hashinger Delora T. , Fairhurst Carl W.
Published: March 2005

The viscosities of model porcelains based on the Weinstein patent on dental porcelain were determined using the bending beam method of Hagy. Two formulations (components one and three of the patent) were obtained from a production size sample and mixed to give blends of the two components in 10% increments by weight. The viscosity values were obtained over the range of 108 to 1012 Pa·s. The porcelains displayed Newtonian behavior with respect to load, and viscosity varied according to the rule of composition fractions between the viscosity values of components one and three.
Preparation of Mullite Cordierite Composite Powders by the Sol‐Gel Method: Its Characteristics and Sintering
Authors: Ismail Mohamed G.M.U. , Tsunatori Hideo , Nakai Zenjiro
Published: March 2005

Mullite/cordierite composite powders containing different proportions of cordierite were prepared by the sol‐gel method using boehmite, colloidal silica, and Mg(NO3)2·6H2O. Mullite and cordierite sols were prepared separately and mixed to form the composite sol. Mullitization temperature depends on the cordierite content in the composite. Also, α‐cordierite crystallizes at a lower temperature in a mullite‐rich (MC20) composite. The XRD patterns of the powders calcined at 1450°C for 12 h showed that mullite and cordierite exist as two different phases, and no additional phases were observed. The IR absorbance spectra of composites showed characteristic peak corresponding to both mullite and cordierite. The sintered density of the powders increases with temperature up to 1450°C and decreases beyound the melting point of cordierite (1455°C). The microstructure of MC30 sintered at 1440°C for 3 h consisted of acicular grains, whereas in MC40 and MC50 equiaxed grain morphology was observed under similar sintering conditions. The flexural strength and Vickers hardness decreases with the increase of cordierite content in the composite. Dielectric constant and thermal expansion showed a similar behavior.
Sintering of Particulate Composites under a Uniaxial Stress
Authors: Rahaman Mohamed N. , De Jonghe Lutgard C.
Published: March 2005

The sintering of particulate composites consisting of a finegrained zinc oxide matrix and <10 vol% of coarse silicon carbide inclusions was investigated at 725°C under a uniaxial stress of ⋍250 kPa. Data for the densification and creep rates of the composite were compared with those for the unreinforced matrix. The inclusions cause a drastic reduction in the measured densification and creep rates. They have a greater effect on the densification process, however; the ratio of the densification rate to the creep rate of the composite is approximately half that of the unreinforced compact. The factors that cause the reduction in this ratio are present from the very early stage of sintering.
Experimental Observations of Substrate Fracture Caused by Residually Stressed Films
Authors: Drory Michael D. , Evans Anthony G.
Published: March 2005

Model systems for studying thin‐film cracking consisting of thin plates of alumina and soda‐lime glass were diffusion bonded to silica substrates at high temperature. Upon slow cooling, substrate fracture was induced by residual stresses from the thermal and elastic mismatch of the film and substrate. In particular, multiple substrate cracks formed parallel to the interface. The observed crack paths closely followed predictions based on a zero mode II stress intensity. Crack depths were found to be strongly dependent on the relative substrate thickness and the Young's modulus ratio.
Properties of Taeniolite/Acriflavine Complex Film Before and After Carbonization: Effect of Acriflavine Content
Authors: Ōya Asao , Sato Akinori , Hanaoka Hirokazu , Ōtani Sugio
Published: March 2005

Taeniolite/acriflavine complexes (TAC) intercalated with various amounts of acriflavine were synthesized. The films derived from these complexes and raw taeniolite (TNL) as a reference were heated (carbonized) below 1273 K under a nitrogen atmosphere, followed by measurements of mechanical properties and electrical resistivity. Compared with TNL film, TAC films, especially with an amount of acriflavine equivalent to the cation exchange capacity of TNL, showed higher thermostability, higher flexibility, lower tensile strength, and larger modulus of toughness. Electrical resistivities of TAC films decreased remarkably after heating to 873 K or higher, in contrast to no change for TNL film. After heating to 1073 K, the electrical resistivities of TAC films clearly decreased with an increase of acriflavine content. This difference disappeared after heating to 1273 K. These behaviors are discussed on the basis of X‐ray diffraction, IR spectroscopy. SEM observation, and so on.
Stability Field of Cotunnite‐Type Zirconia
Authors: Ohtaka Osamu , Kume Shoichi , Ito Eiji
Published: March 2005

The stability field of cotunnite‐type ZrO2 was determined by both syntheses and measurements of electrical conductivity under pressure using a 6–8 anvil‐type device. The products synthesized below 1000°C were ortho II, whereas those above this temperature were monoclinic when quenched. Abrupt discontinuities in conductivity were observed around 1000°C at 16.5 GPa and around 1050°C at 18 GPa. It is concluded, therefore, that the phase boundary lies a little above about 1000°C at pressures from 15 to 20 GPa with slightly positive slope. The result is consistent with that obtained by synthesis experiment.
Superplastic Bulging of Fine‐Grained Zirconia
Authors: Wu Xin , Chen I‐Wei
Published: March 2005

A tetragonal zirconia containing 2 mol% Y2O3, with 0.3 mol% CuO addition as a grain‐boundary phase, was superplastically stretched at 1150°C using a hemispherical punch. Mechanical analyses were performed to establish that a biaxial tensile stress/strain state was achieved in the process with a maximal strain of 0.5 in the thinned hemispherical shell. The material was damage tolerant up to a critical strain rate, approximately 10−3 s−1.
Effect of α to β (β') Phase Transition on the Sintering of Silicon Nitride Ceramics
Authors: Lee Dong‐Duk , Kang Suk‐Joong L. , Petzow Gunter , Yoon Duk N.
Published: March 2005

By using α‐Si3N4 and β‐Si3N4 starting powders with similar particle size and distribution, the effect of α‐β (β') phase transition on densification and microstructure is investigated during the liquid‐phase sintering of 82Si3N4·9Al2O3·9Y2O3 (wt%) and 80Si3N4·13Al2O3·5AIN·5AIN·2Y2O3. When α‐Si3N4 powder is used, the grains become elongated, apparently hindering the densification process. Hence, the phase transition does not enhance the densification.
Acoustic Emission of Thermally Cycled Refractories
Authors: Konsztowicz Krzysztof J. , Fontaine Denise
Published: March 2005

Acoustic emission (AE) technique was applied to continuously monitor property degradation during standard thermal shock fatique testing of three distinct types of refractories. AE results were correlated with respective strength losses of analyzed materials after a defined number of heating and cooling cycles. The complex nature of the AE signals was revealed by AE amplitude and duration analysis indicating that not all of the signals that were registered during thermal shock tests could be correlated with strength changes. On this basis, it was postulated that simple counting of a number of AE events should not be used as a measure of the degree of damage in refractories under thermal shock.
Crack‐Wake Debonding and Toughness in Fiber‐ or Whisker‐Reinforced Brittle‐Matrix Composites
Authors: Nair Shanti V.
Published: March 2005

Solutions are obtained for the mechanics of debonding in the crack wake in fiber‐ or whisker‐reinforced composites for the case where a finite shear traction exists at the fiber/matrix interface in the debonded zone. These solutions are then applied to derive expressions for the steady‐state toughness increases obtained in bonded composites wherein the toughness contribution is provided by crack‐wake fiber/matrix debonding and crack bridging. The solutions for an unbonded composite containing a frictional fiber/matrix interface can be obtained from the derived equations in the limit of the fiber/matrix interface toughness equal to zero. In this limit, the debond crack length reduces to the slip length and the expressions for the crack opening and the predicted toughness increase reduce to previously derived expressions for unbonded composites. The steady‐state toughness is found to depend sensitively on the interface toughness, the fiber fracture strength, and the shear tractions in the debonded zone including other material parameters, such as fiber radius and volume fraction and the moduli of the constituent phases. It is shown that in order to obtain finite toughness increases, the fiber/matrix interface toughness must be less than a critical value dependent on the fiber fracture strength, fiber radius and volume fraction, and fiber and matrix moduli. The predictions of the model are applied to published experimental results from a detailed and complete study of toughness increases in a bonded whisker‐reinforced composite.
Steric Stabilization of Nonaqueous Silicon Slips: II, Pressure Casting of Powder Compacts
Authors: Kerkar Awdhoot V. , Henderson Robert J. M. , Feke Donald L.
Published: March 2005

The application of a steric stabilization strategy to the processing of nonaqueous silicon slips is investigated. With this method, unfavorable particle interactions within silicon slips processed in benzene and trichloroethylene can be effectively controlled. Use of specific polymers additives (poly(styrene), poly(methyl methacrylate), and their copolymer) results in a substantial improvement in the pressure casting performance of silicon slips. Control of particle agglomeration during processing yields green compacts with better packing as reflected by the measurements of cake permeability and casting resistance. Substantial improvement in green compacts density was seen. The polymer additives also acted as binders providing sufficient green strength to the compacts so as to render them handleable.
Synthesis of Gray Zirconium Silicate Pigments from Zircon Mineral
Authors: Trojan Miroslav
Published: March 2005

Zirconium silicate (zircon) pigments in new gray hues have been prepared from mineral zircon as a low‐cost raw material. In the first step this material was deocmposed with a waste mixture of NaOH‐KOH. In the second step the pigments were synthesized with addition of manganese, especially manganese(II) carbonate, as the chromophore. The optimum conditions for the syntheses of pigments have been estimated and the properties of products (hues, applicability to ceramic glazes) have been evaluated.
Control of Radioactive Waste Glass Melters: II, Residence Time and Melt Rate Limitations
Authors: Bickford Dennis F. , Hrma Pavel , Bowan Bradley W.
Published: March 2005

Slurries of simulated high‐level radioactive waste (HLW) and glass formers have been isothermally reacted and analyzed to identify the sequence of the major chemical reactions in waste vitrification, their effect on glass production rate, and the development of leach resistance. Melting rates of waste batches have been increased by the addition of reducing agents (formic acid, sucrose) and nitrates. The rate increases are attributable in part to exothermic reactions which occur at critical stages in the vitrification process. Nitrates must be balanced by adequate reducing agents to avoid the formation of persistent foam, which would destabilize the melting process. The effect of foaming on waste glass production rates is analyzed, and melt rate limitations are defined for waste glass melters, based upon measurable thermophysical properties. Minimum melter residence times required to homogenize glass and assure glass quality are much smaller than those used in current practice. Thus, melter size can be reduced without adversely affecting glass quality. Physical chemistry and localized heat transfer of the waste glass melting process are examined, to refine the available models for predicting and assuring glass production rate. It is concluded that the size of replacement melters and future waste processing facilities can be significantly decreased if minimum heat transfer requirements for effective melting are met by mechanical agitation. A new class of waste glass melters has been designed, and proof of concept tests completed on simulated HLW slurry. Melt rates have exceeded 155 kg · m−2· h−1 with slurry feeds (32 lb · ft−2· h−1), and 229 kg · m−2· h−1 with dry feed (47 lb · ft−2· h−1). This is about 8 times the melt rate possible in conventional waste glass melters of the same size.
Reaction‐Layer Interfaces in SiC‐Fiber‐Reinforced Glass‐Ceramics: A High‐Resolution Scanning Transmission Electron Microscopy Analysis
Authors: Bonney Laura A. , Cooper Reid F.
Published: March 2005

The reaction layers between silicon carbide continuous fibers (Nicalon) and a calcium aluminosilicate glass‐ceramic (anorthite composition) matrix in hot‐pressed composites have been characterized both structurally and chemically using high‐resolution, field‐emission scanning transmission electron microscopy. Chemical compositions at 10‐nm spacings, with a resolution of ∼5 nm, were collected across the fiber‐matrix interface zone. The reaction sequence in the material is silicon carbide (fiber)—carbon (in this case, graphite)—silica‐rich glass—anorthite. The composition of the carbon layer is constant across its width; the interfaces between the four phases are planar. This morphology and the chemical gradients observed are consistent with the simple, ‘carbon‐condensed’ oxidation displacemetn reaction, SiC + O2→ SiO2+ C, being responsible for interface phase formation in the composites. The planar interfaces indicate that the rate‐limiting process in the interface formation reaction is the diffusion of oxygen through the matrix and silica glass layer; a corollary of this conclusion is that the diffusion of silicon through the carbon layer is a relatively faster process.
Determination of Flaw‐Size Distribution by the Crack‐Off Process
Authors: Santhanam Sridhar , Shaw Milton C.
Published: March 2005

The crack‐off process is a new alternative to diamond sawing for the cutting of brittle materials. The process involves exposing brittle rods (or plates) to biaxial fluid pressure. Fluid penetration into surface flaws causes fracture at pressures strongly dependent on the severity of the flaws. A method for calculating the probability‐density distribution of surface flaws in a batch of brittle rods, using the crack‐off pressures for a random sample, is presented here. The scatter in the pressure data is a consequence of the statistical nature of surface flaws. Parameters defining the flawsize distribution can hence be deduced from the crack‐off pressure distribution. The method has been tested on two batches of glass rods that have undergone different treatments, with satisfactory results.
Fatigue Crack Propagation in Ceria‐Partially‐Stabilized Zirconia (Ce‐TZP)‐Alumina Composites
Authors: Tsai Jing‐Fong , Yu Cheng‐Sheng , Shetty Dinesh K.
Published: March 2005

Fatigue crack propagation rates in tension‐tension load cycling were measured in ZrO2‐12 mol% CeO2‐10 wt% Al2O3 ceramics using precracked and annealed compact tension specimens. The fatigue crack growth behavior was examined for Ce‐TZPs of different transformation yield stresses obtained by sintering for 2 h at temperatures of 1500°C (type A), 1475°C (type B), 1450°C (type C), and 1425°C (type D). The threshold stress‐intensity range, ΔKth, for initiation of fatigue crack propagation increased systematically with decreasing transformation yield stress obtained with increasing sintering temperature. However, the critical stress‐intensity range for fast fracture, ΔKc, as well as the stress‐intensity exponent in a power‐law correlation (log (da/dN) vs log ΔK) were relatively insensitive to the transformation yield stress. The fatigue crack growth behavior was also strongly influenced by the history of crack shielding via the development of the crack‐tip transformation zones. In particular, the threshold stess‐intensity range, ΔKth, increased with increasing size of the transformation zone formed in prior quasi‐static loading. Crack growth rates under sustained peak loads were also measured and found to be significantly lower and occurred at higher peak stress intensities as compared to the fatigue crack growth rates. Calculations of crack shielding from the transformation zones indicated that the enhanced crack growth susceptibility of Ce‐TZP ceramics in fatigue is not due to reduced zone shielding. Alternate mechanisms that can lead to reduced crack shielding in tension‐tension cyclic loading and result in higher crack‐growth rates are explored.
Impact Damage and Strength Degradation in a Silicon Carbide Reinforced Silicon Nitride Composite
Authors: Akimune Yoshio
Published: March 2005

Adding SiC particles to Si3N4 and subjecting the mixture to a sinter‐hot‐isostatic‐pressing process increases both the strength and elastic modulus. It also decreases the hardness but maintains the fracture toughness, which results in a higher resistance to crack initiation and propagation during spherical particle impact. Sinter‐hot‐isostatically‐pressed composites exhibit elastic response as their dominant behavior. They also display a high resistance to Hertzian cone crack initiation and extension. This is due to the increased degree of inelastic deformation of sinter‐hot‐isostatically‐pressed composites.
Dissolution of Polydisperse Silica Grains in Glass Melts–Analysis
Authors: Choudhary Manoj K.
Published: March 2005

By combining population balance with mass‐transfer‐controlled dissolution, a formulation is developed to analyze the dissolution of polydisperse silica grains in glass furnaces. For an initial lognormal distriution of particle sizes, the change in the distribution with respect to a modified time scale is expressed analytically. This paper shows how the formulation can be combined with time‐temperature data along various flow path lines in a glass melter to calculate the extent of dissolution in the melter. Calculated results are presented on the dissolution of polydisperse silica grains in a glass melter for which the information on path lines was obtained by using a three‐dimensional mathematical model for flow and heat transfer. The effects of maximum particle size of a truncated distribution and the standard deviation on the extent of dissolution are examined.
Technique for the R‐Curve Determination of Y‐TZP Using Indentation‐Produced Flaws
Authors: Anderson Richard M. , Braun Linda M.
Published: March 2005

A technique was developed to estimate the R‐curve behavior of Y‐TZP using indentation‐produced flaws. This technique allows crack‐growth resistance to be determined for short crack extensions (micrometers). For Y‐TZP samples sintered at 1600°C for 1 h (mean grain size, 0.7 μm), the crackgrowth resistance increases rapidly over the first 10 μm. Peak toughness values determined from this technique correlate with chevron‐notch fracture toughness if the ellipticity of the indentation‐produced flaw is considered.
Role of Grain‐Boundary Glass Phase on the Superplastic Deformation of Tetragonal Zirconia Polycrystal
Authors: Yoshizawa Yu‐ichi , Sakuma Taketo
Published: March 2005

Superplastic deformation of tetragonal zirconia polycrystal (TZP) was investigated by compression test in the temperature range of 1000° to 1500°C. Special attention was paid to the role of the grain‐boundary glass phase on hightemperature deformation behavior. A small addition of glass phase markedly improved the high‐temperature deformability of TZP. Lithium silicate glass was much superior to aluminosilicate or lithium aluminum silicate glasses for lowering the high‐temperature flow stress. The deformation mechanism was discussed on the basis of mechanical testing data and microstructural examinations.
Phase Composition and Compatibilities at 930° to 950°C in the System Europium(III) Oxide‐Barium Oxide‐Copper(II) Oxide in Air
Authors: Pleczulewski C. N. , McAdams J. E. , Mason T. O.
Published: March 2005

Phase composition and compatibilites at 930° to 950°C were determined for the system Eu2O3–BaO–CuO in air. The binary compound Eu2CuO4 dissolves Ba to the extent 0 x 0.02 in Eu2‐xBaxCuO4, whereas the other binary compounds, Eu2BaO4 and BaCuO2, do not exhibit solid solubility. Three ternary compounds were obtained, Eu2BaCuO5 and two solid solution phases. The first contains the 90 K ‘123’ superconductor and has solubility limits represented by Eu1+xBa2‐xCu3O7±y, where 0 x 0.5. The second has a solubility limit represented as Eu1+xBa8‐xCu4Oy, where 0 x 0.44. The limited solid solution range of this phase provides insight concerning the probable solid solution range of the analogous phase in the Y2O3‐BaO‐CuO system.
Effect of Al(OH)3 Addition on β‐LiAlO2 Crystal Growth
Authors: Watanabe Akira , Takeuchi Yoshimitsu , Saeki Goji
Published: March 2005

Crystal growth of rod‐shaped β‐LiAlO2 was previously reported by us, and the rod‐shaped β‐LiAlO2 crystals were 1.5 μ in diameter and 10 to 15 μm long. In the present study needle‐shaped β‐LiAlO2 crystals which were thinner and had larger aspect ratios (length/diameter) than the rodshaped β‐LiAlO2 crystals were grown by using LiOH–Al2O3–Al(OH)3–NaOH as the raw material. These crystals were 0.7 to 1 μm in diameter, 9 to 13 μm long, and had aspect ratios of about 10 to 13.
Ion‐Beam Analysis of Silica Sol‐Gel Films: Structural and Compositional Evolution
Authors: Keddie J. L. , Giannelis E. P.
Published: March 2005

Rutherford backscattering and forward recoil spectrometry have been used to determine the chemical composition and density of SiO2sol‐gel films. The as‐deposited films are relatively dense, because of considerable interpenetration of weakly branched silicate precursors, while they contain significant amounts of hydroxyl groups in their structure. Annealing in flowing Ar increases the density of the films with values approaching that of amorphous silica at temperatures as low as 450°C but it fails to completely remove all the hydroxyl groups from the structure.
Superconductive Properties of the YBa2Cu4O8 Superconductor
Authors: Sarkar Asok K. , Kozlowski Gregory , Maartense Iman
Published: March 2005

A bulk density of 85% of the theoretical density was achieved by sintering a powder compact of YBa2Cu4O8 (124) at 850°C in flowing oxygen at 1 atm (≅105 Pa). This value is very close to that obtained by the hot isostatic pressure technique (90%). The superconducting properties of the sample were characterized by magnetization and ac susceptibility techniques. The magnetization critical current density at 20 K in zero field was determined to be ∼5 × 104 A/cm2, and the superconducting transition temperatures were found to be 77 K for the bulk material and 82 K for the granular phase. The powder X‐ray diffraction and ac susceptibility studies revealed the sintered 124 material to be single phase.
Effects of Thermal Expansion Mismatch Stresses on th Room‐Temperature Fracture of Boron Carbid
Authors: Rice Roy W.
Published: March 2005

Calculation of apparent fracture energies (γa) using the applied failure stress and fractographically determined flaw sizes (C) in B4 C shows γa decreasing with C, once C < 100 μm. This is attributed to increasing contributions of microstructural stresses (σi) due to thermal expansion anisotropy ( 1 × 10−6°C−1). Extrapolation of this σi contribution to C∼G (the grain size) and calculation from maximum thermal expansion mismatch are in reasonable agreement. e.g., giving σ∼ 1000 MPa. Strength‐mirror size data also show deviations at higher strengths‐smaller mirror sizes consistent with both the occurrence and estimated level of such microstructural stress contributions to failure.
Crack Shielding in Ceria‐Partially‐Stabilized Zirconia
Authors: Marshall David B.
Published: March 2005

The crack tip shielding stress intensity factor has been calculated for several elongated transformation zone shapes observed in high‐toughness ceria‐zirconia ceramics. The results show that the measured increases in fracture toughness of these materials are consistent with the crack tip shielding mechanism, to which the toughening of other zirconia ceramics has been attributed. Moreover, the presence of a very elongated zone ahead of a steady‐state crack is shown to decrease the degree of shielding compared with that of a zone with semicircular frontal shape and equivalent width by a factor of about 2.
Particle Packing in Ceramic Injection Molding
Authors: Wright Jadith K. , Edirisinghe Mohan J. , Zhang Jian G. , Evans Julian R. G.
Published: March 2005

The shrinkage of ceramic injection molding suspensions caused by pyrolytic removal of the organic vehicle was measured for initial ceramic volume fractions from 0.48 to 0.64. Shrinkage was inversely related to initial ceramic volume fraction V, and maximum volume fraction after pyrolysis V*,max was 0.65. The factors which restrict shrinkage are discussed. The maximum volume fraction, obtained from semiempirical equations relating the viscosity of suspensions to volume fraction of powder (Vmax) was 0.73 to 0.76. Both the viscosity of the suspensions and the shrinkage on removal of the organic vehicle can be interpreted in terms of a free volume of fluid over and above that needed to fill interstices between contacting particles. Thermomechanical measurements also show that the free‐volume concept helps to interpret the transition from fluid to quasi‐solid properties as the organic vehicle is removed by pyrolysis from a molded body.
Strength and Stiffness of Porous Materials
Authors: Nielsen Lauge Fuglsang
Published: March 2005

A contribution is given to the theoretical research on nondestructive testing of porous materials like ceramics, for example. Relations (so‐called modulus of elasticity‐modulus of rupture relations) are developed between stiffness and strength considering the material‐specific pore geometry. The results presented on strength can be given a form similar to the well‐known empirical Ryshkewitch formula. This means that the “constant” in this expression can be related to porosity and pore geometry such that consistency is respected between strength and elasticity.
Diffusivities of Dialkyl Phthalates in Plasticized Poly(vinyl butyral): Impact on Binder Thermolysis
Authors: Lewis Jennifer A. , Cima Michael J.
Published: March 2005

Hot‐stage/Fourier transform infrared microspectroscopy (FTIR‐M) was used to determine the diffusivities of a series of dialkyl phthalates in poly(vinyl butyral) (PVB) spin‐coated films. The diffusivities ranged from 10−12 to 10−10 cm2/s for the isotherms investigated (60° to 150°C). In their respective temperature regimes, dimethyl phthalate and diethyl phthalate exhibited nonlinear diffusion behavior, while dibutyl phthalate (DBP) and dioctyl phthalate (DOP) exhibited Fickian behavior in PVB. The activation energies for DBP and DOP diffusion in the PVB‐based films were calculated to be 76.3 and 114.7 kJ/mol, respectively. The diffusitivity of DBP was used to compare the relative importance of diffusion and capillary migration in the thermolysis of PVB‐DBP binders from ceramic greenware. Comparison of the calculated DBP loss due to diffusion alone could not account for the observed removal rates. A characteristic diffusion length is calculated from the experimental observations.
Colloidal Filtration and (Simultaneous) Sedimentation of Alumina and Silica Suspensions: Influence of Aggregates
Authors: Philipse Albert P. , Bonekamp Ben C. , Veringa Hubert J.
Published: March 2005

Colloidal filtration and (simultaneous) sedimentation is studied for suspensions of alumina particles and monodisperse silica spheres. A comparison is made between stable suspensions and systems which are aggregated due to salt addition (silica) or absence of a deflocculant (alumina). From separate sedimentation experiments we conclude that the stable silica settles as an ordered particle array, that the unstable silica sediments as separate aggregates, and that aggregated aluina behaves as a densifying network. The filtration results show that settling of aggregates during filtration changes the filtration kinetics in accordance with our model for simultaneous filtration and sedimentation. Further, aggregates in suspension are shown to have little influence on the silica compact microstructure, whereas they clearly increase porosity and permeability of the alumina compact. We also find that for all suspensions porosities of compacts prepared by sedimentation are clearly larger then porosities of filter compacts.
Synthesis of Cubic Boron Nitride from Boron Nitride Synthesized by Pressure Pyrolysis of Borazine
Authors: Hirano Shin‐ichi , Fujii Akira , Yogo Toshinobu , Naka Shigeharu
Published: March 2005

Cubic BN was synthesized under high‐temperature and ‐pressure conditions from BN powder formed by pressure pyrolysis of borazine below 700°C and 100 MPa. The conversion of BN powder to cubic BN was strongly influenced by the residual hydrogen identified by the BH/BN ratio of IR absorption band. The activation energy for cubic BN synthesis from BN powder‐20 mol% AIN was 46 kJ/mol, when the starting BN was synthesized at 250°C. A mixture of BN powder and cubic BN particles was converted to cubic BN in a 100% yield by heat treatment at 1800°C and 6.5 GPa without any catalyst. The presence of cubic BN particles does enhance the conversion to cubic BN from BN powder. The energy required for the transformation of starting BN to cubic BN in the presence of cubic BN seed was 355 kJ/mol.
Characterization of Polyphasic Silicon Carbide Using Surface‐Enhanced Raman and Nuclear Magnetic Resonance Spectroscopy
Authors: Dando Neal R. , Tadayyoni M. Azar
Published: March 2005

The present report explores the use of cross‐polarization (CP) and single‐pulse magic angle spinning nuclear magnetic resonance (MAS‐NMR) as well as normal and surfaceenhanced Raman spectroscopy (SERS), in concert, for characterizing highly crystalline polymorphic silicon carbide ceramics. The combined use of these techniques provides a wealth of information regarding bulk, near‐surface, and surface speciation. Both Raman and SERS are promising techniques for fracture surface characterization of these systems. The application of CPMAS‐NMR and SERS to the study of ceramics is reported for the first time in this investigation.
Comparison of Strength Development in Waste Industrial Gypsum Produced by the Hemihydrate and Dihydrate Processes
Authors: Gadalla Ahmed M. , Saylak Donald , Lindner Angela I.
Published: March 2005

Phosphogypsum produced by the hemihydrate process was characterized and compared to that produced by the dihydrate process. Neutralization with NaOH and Ca(OH)2 was studied. Stabilization with Type I portland cement and fly ash was investigated to see if the phosphogypsum developed enough strength to be used in road construction. Increasing the amount of neutralizer to adjust the pH level above 7, increasing the curing period to 7 d, and/or increasing the cement content increased the strength of phosphogypsum. The effect of grinding on grading and strength development was also studied. After achieving the required strength, extended curing periods above 28 d caused strength reversal. Using 20% fly ash is beneficial and did not show strength reversal. Further studies on prolonged curing times and on using cements with low tricalcium aluminate are needed.
Investigation of Shale Brick Interface with Cement‐Lime and Polymer‐Modified Mortars
Authors: Marusin Stella L.
Published: March 2005

Bonds between cement‐lime mortar and shale brick, and between polymer‐modified mortar and shale brick, were studied using a scanning electron microscope (SEM). The results showed that the bond is greatly influenced by the microstructure and chemical composition of the mortar at the interface contact area and by the microstructure of the brick surfaces. For relatively porous bricks, cement‐lime mortars give a better bond, apparently due to better interpenetration of the fresh mortar into the open pores of the brick, creating a greater bond area. The presence of calcium contributes to good bonds, while large amounts of silicon were found in poorly bonded areas. Latex‐modified mortars are not able to penetrate brick surfaces and are able to create strong bonds only on limited locations and allow water to enter brick masonary.
Characterization of Textured Ceramics by Electron Paramagnetic Resonance Spectroscopy: I, Concepts and Theory
Authors: Boatner Lynn A. , Boldú O. José Luis , Abraham Marvin M.
Published: March 2005

Electron paramagnetic resonance (EPR) spectroscopy is shown to be a powerful and versatile technique for the detection and characterization of preferred orientation effects in insulating ceramics. While the technique is applicable to both cubic and noncubic ceramics, in this work the conceptual and theoretical basis for the analysis of textured cubic materials is established. The practical utility of the EPR technique is illustrated for the specific case of a paramagnetic impurity (Mn2+) in the cubic ceramic MgO. For this example, EPR methods show that texturing occurs in a cold pressed, sintered body and that the preferred orientation corresponds to 〈111〉 axes lying nearly parallel to the direction of the cold‐pressing force. The advantages of the EPR technique in characterizing preferred orientation effects in ceramic materials are discussed and compared with more traditional diffraction‐based and optical characterization methods.
Improved Analysis for Flexural Creep with Application to Sialon Ceramics
Authors: Chen Ching‐Fong , Chuang Tze‐jer
Published: March 2005

By using a statistical least‐squares method to minimize the differences between predicted and measured load‐point displacement rates from four‐point bend specimens, power‐law creep parameters for tension and compression were estimated. An alternative but simpler method of estimating power‐law creep parameters from flexural creep data is also proposed. This method entails the direct measurements of steady‐state creep strain rates at two stress levels by an indentation technique. Based on a closed‐form solution, the power‐law creep parameters could then be estimated from both the measured neutral axis locations and curvature rates. The results from these two methods compare favorably with one another, and with the simple compressive creep data. Both methods yield a high stress exponent of about 14 for tension and a stress exponent of about unity for compression. Cavitation‐enhanced creep in tension and diffusional creep in compression are responsible for this asymmetric behavior.
Role of Grain Size in the Strength and R‐Curve Properties of Alumina
Authors: Chantikul Prapaipan , Bennison Stephen J. , Lawn Brian R.
Published: March 2005

An investigation of the interrelationships between strength, crack‐resistance (R‐curve) characteristics, and grain size for alumina ceramics has been carried out. Results of identation‐strength measurements on high‐density aluminas with uniform grain structures in the size range 2 to 80 μm are presented. A theoretical fit to the data, obtained by adjusting parameters of a constitutive frictional‐pullout relation in a grain‐bridging model, allows determination of the critical microstructural parameters controlling the R‐curve behavior of these aluminas. The primary role of grain size in the toughness characteristic is to determine the scale of grain pullout at the bridged interface. It is shown that the strength properties are a complex function of the bridged microstructure, governed at all but the finest grain sizes by the stabilizing effect of the R‐curve. The analysis confirms the usual negative dependence of strength on grain size for natural flaws that are small relative to the grain size, but the dependence does not conform exactly to the −1/2 power predicted on the basis of classical “Griffith‐Orowan” flaws. The analysis provides a self‐consistent account of the well‐documented transition from “Orowan” to “Petch” behavior.
Grain Growth During Gas‐Pressure Sintering of β‐Silicon Nitride
Authors: Mitomo M. , Tsutsumi M. , Tanaka H. , Uenosono S. , Saito F.
Published: March 2005

The microstructures of gas‐pressure‐sintered materials from β‐Si3N4 powder were characterized in terms of the diameter and aspect ratio of the grains. The size distributions of diameters in materials fabricated by heating for 1 h at 1850° to 2000°C were nearly constant when they were normalized by average diameters because of normal grain growth. The rate‐determining step in the densification and grain growth was expected to be the diffusion of materials through the liquid phase. The activation energy for grain growth was 372 kJ/mol. The average aspect ratio of the grains was 3 to 4, whereas that of large grains was smaller because of shape accommodation. The fracture toughness was about the same as that of material from α‐Si3N4 powder despite the smaller aspect ratio of the grains
Chemical Vapor Deposition in the Boron‐Carbon‐Nitrogen System
Authors: Besmann Theodore M.
Published: March 2005

The preparation of a two‐phase coating of B4C‐BN was addressed as a potential wear coating because of its likelihood of having a high fracture toughness resulting from its composite nature and inherent lubrication due to the presence of BN. Equilibrium analysis identified appropriate deposition conditions; however, deposited coatings were found to be single‐phase BN with a high degree of substitution of carbon for nitrogen.