bluuebunny/crossref_metadata_2025 huggingface dataset:
Temperature Oscillations of Alternating‐Current‐Heated Thin Filaments in Ceramic Fiber Production
Authors: Viljoen Hendrik J. , Hlavacek Vladimir
Published: March 2005

Resistively heated filaments are used to manufacture ceramic fibers. When an ac power source is used for heating, the temperature of the filament oscillates. These oscillations influence the deposition rate on the surface of the filament. An analysis of this problem is presented, and it is also shown that these oscillatory effects diminish as the filament gauge increases. The analysis can help to decide whether an ac or a dc power source should be used.
Microstructure and Electrical Properties of MgAl2O4 Thin Films for Humidity Sensing
Authors: Gusmano Gualtiero , Montesperelli Giampiero , Traversa Enrico , Mattogno Giulia
Published: March 2005

Active elements for humidity sensors based upon MgAl2O4 thin films or sintered pellets were investigated. Thin films were deposited on Si/SiO2 substrates by radiofrequency (rf) sputtering. Sintered MgAl2O4 pellets were prepared by traditional ceramic processing. Scanning electron microscopy (SEM) analysis showed that the thin films were rather dense and homogeneous, made up of clustered particles of about 20–30 nm, while the pellets showed a wide pore‐size distribution. X‐ray photoelectron spectroscopy (XPS) demonstrated that the thin films have a stoichiometry close to that of MgAl2O4. Sintered MgAl2O4 is crystalline, while it is disordered in thin‐film form. The presence of two different components of the Al 2p peaks was correlated with the structural difference between pellets and thin films. The relationship between good film–substrate adhesive properties and the chemical composition at the interface was studied. The electrical properties of the sensing elements were studied at 40°C in environments at different relative humidity (RH) values between 2% and 95%, using ac impedance spectroscopy. MgAl2O4 thin films showed interesting characteristics in terms of their use in humidity‐measurement devices. Resistance versus RH sensitivity values showed variations as high as 4 orders of magnitude in the RH range tested for thin films, and 5 orders of magnitude for pellets. The differences in the electrical behavior of MgAl2O4 pellets and thin films were correlated with their different microstructures.
Preparation of Spherical SnO2 Powders by Ultrasonic Spray Pyrolysis
Authors: Lee Jong‐Heun , Park Soon‐Ja
Published: March 2005

Spherical SnO2 powders were prepared from SnCl4 aqueous solution by ultrasonic spray pyrlysis. The particle size distributions normalized by mean diameters are almost identical in spite of the variation in the concentration of the source solution. The mean diameter of SnO2 particles increases with the concentration of the source solution and it is in the range of 0.2 to 0.8 μm. Each spherical particle is composed of many primary particles and has a solid, microporous structure.
Novel Niobium‐Doped Titania Varistor with Added Barium and Bismuth
Authors: Yang Seng‐Lu , Wu Jenn‐Ming
Published: March 2005

Characteristics of the sintered compacts and the microstructures and electrical properties of Nb‐doped TiO2 varistors with added Ba and Bi were studied at various sintering temperatures ranging from 1250° to 1400°C. Adding both Ba and Bi to Nb‐doped TiO2 ceramics resulted in a maximum intergranular phase and a minimum weight loss at 1350°C. In contrast, adding either Ba or Bi alone produced no such maxima and minima. The intergranular phases included mainly a Bi2Ti2O7 crystal phase, apt to occur at a triple junction, and a Ba‐rich amorphous phase that surrounded the grains, but discontinuously. The intergranular phases varied consistently with variation in electrical properties. The optimum conditions for the most efficient boundary barrier layer, with the lowest weight loss and the highest resistivity at low frequencies, were 1350°C with both Ba and Bi addition. The highest values for α (∼9.5), Vgb10 (∼0.8 V), and EB (∼0.42 e V) support that finding. The effective relative dielectric constant, Keff∼ 20 000, also was obtained under optimum conditions. The single addition of either Ba or Bi, however, produced nearly the opposite results, as discussed in this paper.
Low‐Cost Melt Formed Siliconized Silicon Carbide Radiant Tube Materials
Authors: Darroudi Taghi , Tressler Richard E. , Kasprzyk Martin R.
Published: March 2005

This paper describes a new low‐cost, melt infiltration method for manufacturing silicon carbide–silicon (SiC─Si) and graphite–silicon (G─Si) materials for radiant tube applications, and the physical and mechanical characteristics of these materials. Characterization of the microstructures and various physical and mechanical properties of three SiC─Si and one G─Si materials which were produced by this newly developed processing method are discussed in detail. The C‐ring and O‐ring specimens tested in compression showed that at all test temperatures (room to 1350°C), the SiC─Si materials are substantially stronger than the G─Si material, which actually contained 8.5 vol% SiC due to reaction of the graphite with the molten Si during processing. The strengths as determined by the C‐ring and O‐ring tests for each of the materials were similar, thus indicating that the inherent flaws on the inside and outside surfaces of the tubes are similar in severity. Since these materials showed significant deformation when tested at and above 1000°C, the strength of the G─Si material and one of the SiC─Si materials was also measured at room and at elevated temperatures, using a tensile test procedure. Results of the tensile tests illustrate that, due to stress redistribution at 1000°C and above, the C‐ring and O‐ring data overestimate the actual fracture strengths of these materials. The fracture toughness of the G─Si material measured at room temperature and 1000°C was much less than that of the SiC─Si materials. This behavior was explained by the presence of low‐strength graphite grains, which did not inhibit crack propagation as effectively as the SiC grains.
Thermochemical Evaluation of Combustion Synthesis of MoSi2─SiC Composites
Authors: Jandhyala Subrahmanyam
Published: March 2005

Thermochemical calculations were carried out for the selfpropagating high‐temperature synthesis (SHS) of SiC‐particulate‐reinforced MoSi2 composites. These composites can be prepared using the elemental powders of Mo, Si, and C by SHS. Adiabatic temperatures were calculated at different initial temperatures for the reactions forming MoSi2, SiC, and their composites. Amounts of liquid phase of MoSi2 formed at various temperatures and mole ratios were computed.
Formation of Frozen α‐Agl in Twin‐Roller‐Quenched Agl─Ag2 O─MxOy (MxOy= WO3, V2O5) Glasses at Ambient Temperature
Authors: Tatsumisago Masahiro , Taniguchi Akihiro , Minami Tsutomu
Published: March 2005

Superionic conductor α‐AgI, which is stable only above 147°C, was successfully frozen at ambient temperature in AgI─Ag2O─MxOy (MxOy= WO3, V2O5) glass matrices by a twin‐roller‐quenching technique. The system with WO3, provided the larger composition regions where α‐AgI was frozen at ambient temperature, compared to the system with V2O5. The matrix glasses with higher glass‐transition temperatures had a stronger effect in depressing the α–β transformation of AgI. The α‐AgI‐frozen samples exhibited extremely large conductivities of 3 × 10−2‐5 × 10−2S.cm−1at 25°C.
Preparation of Barium Titanates from Oxalates
Authors: Stockenhuber Michael , Mayer Helmut , Lercher Johannes A.
Published: March 2005

The decomposition of mixed barium titanium oxalates was studied by means of various thermochemical as well as spectroscopic methods. Infrared (IR) spectra of the mixed oxalates indicate the existence of an octahedral complex with Ti chelated by oxalate groups. In general, the results of both IR and the thermochemical analyses suggest that the oxalates are first converted to unidentate carbonate, then to ionic carbonate, and finally to mixed oxides of perovskite structure. The decomposition processes were found to depend upon the atmosphere. In the presence of oxygen the stoichiometrically mixed oxalates decompose by forming TiO2 and BaCO3 as intermediates. Under vacuum, two routes of decomposition occur in parallel. In one route, TiO2 and BaCO3 are formed as intermediates; in the other, partially reduced TiOx(x < 2) is formed, which further reacts with BaCO3 to produce also BaTiO3, CO2 and CO.
Synthesis of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Using a Carbon Dioxide Laser
Authors: Suzuki Masaaki , Maniette Yves , Nakata Yoshinori , Okutani Takeshi
Published: March 2005

The synthesis and the structure of silicon carbide‐silicon nitride (SiC─Si3N4) composite ultrafine particles have been studied. SiC─Si3N4 composite ultrafine particles were prepared by irradiating a SiH4, C2H4, and NH3 gas mixture with a CO2 laser at atmospheric pressure. The composition of composite powders changed with the reactant gas flow rate. The carbon and nitrogen content of the powder could be controlled in a wide range from 0 to 30 wt%. The composite powder, which contained 25.3 wt%. carbon and 5.8 wt% nitrogen, had a (β‐SiC structure. As the nitrogen con‐ tent increased, SiC decreased and amorphous phase, Si3N4, Si appeared. The results of XPS and lattice constant measurements suggested that Si, C, and N atoms were intimately mixed in the composite particles.
Mass Transport in the Presence of Internal Defect Reactions—Concept of Conservative Ensembles: IV, Tracer Diffusion and Intercorrelation with Chemical Diffusion and Ion Conductivity
Authors: Maier Joachim
Published: March 2005

The tracer diffusion coefficient is analyzed for the case in which internal ionization equilibria have to be considered, using the concept of conservative ensembles. The relationships of the tracer diffusion coefficient with other phenome‐nological parameters, viz., the chemical diffusion coefficient and the diffusion coefficient derived from the ionic conductivity, as well as with the defect diffusivities are given. The importance of mobile partially ionized or neutral defects is highlighted. In this respect the formulation of the tracer diffusion as an ambipolar diffusion of the different isotopes is helpful.
Solid‐State Diffusion Bonding of Carbon–Carbon Composites with Borides and Carbides
Authors: Dadras Parviz , Mehrotra Gopal M.
Published: March 2005

Solid‐state diffusion bonding of carbon–carbon (C─C) composites by using boride and carbide interlayers has been investigated. The interlayer materials used in this study were single‐phase borides (TiB2 or ZrB2), eutectic mixtures of borides and carbides (ZrB2+ ZrC or TiB2+ B4C), and mixtures of TiB2+ SiC + B4C produced in situ by chemical reactions between B4C, Ti, and Si or between TiC, Si, and B. The double‐notch shear strengths of the joints produced by solid‐state reaction sintering of B4C + Ti + Si interlayers were much higher than those of joints produced with other interlayers. The maximum strength was achieved for C─C specimens bonded at 2000°C with a 2:1:1 mole ratio of Ti, Si, and B4C powders. The reaction products identified in the interlayers, after joining, were TiB2, SiC, and TiC. The joint shear strength increased with the test temperature, from 8.99 MPa at room temperature to an average value of 14.51 MPa at 2000°C.
Low‐Temperature Formation of Aluminum Orthophosphate
Authors: Bothe James V. , Brown Paul W.
Published: March 2005

Factors influencing the low‐temperature formation of AIPO4 and its precursor phases, AIPO4·xH2O (1 x 2), were investigated. AIPO4 formed by reaction between 33.3 wt% H3PO4 solution and alumina. Five aluminas (three anhydrous and two hydrated) were utilized. Each differed in particle size, surface area, and crystallinity. The reaction temperatures investigated were 113°, 123°, and 133°C. The high‐surface‐area aluminas were sufficiently reactive in the phosphoric acid solution at these temperatures to produce crystalline reaction products. However, only hydrated forms of AIPO4, AIPO4·xH2O (1 x 2), crystallized directly out of solution. x generally decreased as the curing temperature was increased. Upon dehydration of these hydrated reaction products, anhydrous AIPO4 was formed, primarily in the berlinite and/or cristobalite modifications. Both the temperature of reaction and the alumina used influence the hydrates that form. In turn, the hydrates which form, the macroscopic assemblages into which they may crystallize, and the morphologies of the crystallites all affect the polymorphic form and the crystallinity of the anhydrous AIPO4 phase ultimately produced on dehydration. Phase‐pure and highly crystalline AIPO4‐cristobalite (the high‐temperature modification) was formed by the dehydration of AIPO4·H2O at a temperature as low as 113°C.
Stress Measurement in Single‐Crystal and Polycrystalline Ceramics Using Their Optical Fluorescence
Authors: Ma Qing , Clarke David R.
Published: March 2005

A general methodology is developed for determining the state of stress and the numerical value of the stresses from observed shifts and broadening of optical fluorescence lines. The method is based on the piezospectroscopic properties of single crystals. We present general relationships between the measured fluorescence shifts and the stress state for a number of illustrative cases, pertinent to both polycrystalline and single‐crystal ceramics under stress. These include measuring the stresses applied to polycrystalline ceramics, the residual stress distribution due to crystallographically anisotropic thermal expansion, and the stresses applied to single crystals. Using the recently implemented technique of performing the fluorescence measurements in an optical microprobe, we also provide experimental tests of the relationships derived.
Synthesis of Lead Titanate: Thermodynamic Modeling and Experimental Verification
Authors: Łencka Małgorzata M. , Riman Richard E.
Published: March 2005

A comprehensive thermodynamic model has been developed to determine the reaction conditions favoring hydro‐thermal synthesis of lead titanate (PbTiO3). The model combines standard‐state thermodynamic data for solid and aqueous species and an excess Gibbs energy model to account for the nonideality of the solution. The method has been used to generate phase stability diagrams that indicate the ranges of pH and reagent concentrations for which various species predominate in the system at a given temperature and pressure. Also, yield diagrams have been constructed that indicate the concentration, pH, and temperature conditions for which different yields of crystalline PbTiO3 can be obtained. The stability and yield diagrams have been used to predict the optimum synthesis conditions (e.g., reagent concentrations, pH, and temperature). Subsequently, these predictions have been experimentally verified. As a result, phase‐pure perovskite PbTiO3 has been obtained at temperatures ranging from 413 to 433 K using lead acetate or lead nitrate and commercial TiO2 powder. Also, PbTiO3 has been synthesized at lower temperatures (353 T 363 K) by using lead acetate and hydrous (reactive) TiO2 and calcining the obtained amorphous product.
Role of Oxidation in the Time‐Dependent Failure Behavior of Hot Isostatically Pressed Silicon Nitride at 1370°C
Authors: Wereszczak Andrew A. , Breder Kristin , Ferber Mattison K.
Published: March 2005

Dynamic fatigue studies were conducted on a hot isostatically pressed silicon nitride in ambient air and inert (argon or nitrogen) environments using four‐point flexure at 1370°C. Specimens tested in ambient air exhibited a stressing rate dependence with decreased flexure strength with decreased stressing rates. All fracture surfaces of specimens tested in ambient air possessed a sweeping stress‐oxidation damage zone that originated at the tensile side of each bend bar. In addition to this stress‐oxidation damage, creep damage (e.g., cavitation) was concurrently observed in the specimens tested at the slower stressing rates, which appeared to further weaken the material. However, tests conducted in argon or nitrogen revealed flexure strength to be independent of the stressing rate. Creep damage was present at the slower stressing rates, but no stress‐oxidation damage was evident similar to that observed on the specimens tested in ambient air. By decoupling the effects of oxidation and creep, it was evident that the former contributed to the formation of a detrimental stress‐oxidation damage zone which significantly reduced the strength of this material at 1370°C.
Indentation Creep of Hydrated Soda–Lime Silicate Glass Determined by Nanoindentation
Authors: Keulen Nico M.
Published: March 2005

Time‐dependent deformation behavior was investigated for soda–lime silicate glass with various water contents, using a nanoindentation technique. The complete indentation curve, loading and unloading part, is analyzed. It is shown that this deformation behavior may be represented in terms of a simple mechanical model analogous to a viscoelastic system. Values for Young's modulus were derived, a retardation spectrum was deduced, and apparent viscosity values were calculated. Structural rearrangements of the glass appear to be responsible for the observed changes of the viscoelastic properties. Water in the glass reduces Young's modulus and yield stress and thus promotes viscous flow.
Tape Casting Slip Preparation by in Situ Polymerization
Authors: Grader Gideon S. , Zuri Limor
Published: March 2005

The present work describes the polymerization of methylmethacrylate monomer into polymethylmethacrylate (PMMA), in the presence of either coarse or ultrafine alumina powder. The flexibility of the material was modified by addition of either butylbenzyl phthalate (S‐160), or butylacrylate (BA) monomer as plasticizers. It was found that BA is more compatible than S‐160 in the PMMA system. A density of 97%–99% was reached with ultrafine alumina. The maximum tensile strength of the green and sintered tapes was 10 and 140 MPa, respectively. Due to improved homogeneity in the polymerized slip, the sintered tapes prepared by in situ polymerization were stronger and denser than those prepared by conventional blending of commercial PMMA.
Effect of Grain Growth of β‐Silicon Nitride on Strength, Weibull Modulus, and Fracture Toughness
Authors: Hirosaki Naoto , Akimune Yoshio , Mitomo Mamoru
Published: March 2005

β‐Si3N4 powder containing 1 mol% of equimolar Y2O3–Nd2O3 was gas‐pressure sintered at 2000°C for 2 h (SN2), 4 h (SN4), and 8 h (SN8) in 30‐MPa nitrogen gas. These materials had a microstructure of “in‐situ composites” as a result of exaggerated grain growth of some β Si3N4 grains during firing. Growth of elongated grains was controlled by the sintering time, so that the desired microstructures were obtained. SN2 had a Weibull modulus as high as 53 because of the uniform size and spatial distribution of its large grains. SN4 had a fracture toughness of 10.3 MPa‐m1/2 because of toughening provided by the bridging of elongated grains, whereas SN8 showed a lower fracture toughness, possibly caused by extensive microcracking resulting from excessively large grains. Gas‐pressure sintering of β‐Si3N4 powder was shown to be effective in fostering selective grain growth for obtaining the desired composite microstructure.
The Alkali‐Silica Reaction in a Monolithic Opal
Authors: Scrivener Karen L. , Monteiro Paulo J. M.
Published: March 2005

The alkali–silica reaction in opal was studied in the SEM with backscattered electrons, combined with quantitative image analysis, and also in an electron microprobe. A system of cracks was observed in the bands of gel in the opal, ahead of narrow fingers of gel into the unreacted opal and running across the aggregate–cement paste interface into the cement paste. There appeared to be good adhesion of the cement paste to the opal at the interface. Chemical analysis of the gel indicated the presence of calcium‐rich gel with various compositions (CaO:SiO2= 0.5–1.0) in the opal. There was considerable variation in the concentrations of K2O and Na2O in the gel. The analyses of the gel fell into three distinct composition ranges, with distinct boundaries between gels of different composition. Close to the interface there was depletion of calcium in the cement paste inner product.
Electrical Properties of Multilayer‐Chip ZnO Varistors in a Moist‐Air Environment
Authors: Yen Ann‐Jeng , Lee Yih‐Shing , Tsen Tseung‐Yuen
Published: March 2005

Multilayer‐chip varistors were prepared using the ZnO‐glass system by applying tape casting technology. The effect of processing conditions on the multilayer ceramic microstructure and electrical properties was studied. The location, size, and density of the pores within the multilayer structure were examined by scanning electron microscopy and the displacement method using distilled water. The experimental results showed that the electrical properties of a multiplayerchip varistor could be influenced substantially by the porosities associated with environmental moisture in the range ≅15%–95% relative humidity at 25°C. Such an effect can cause substantial current leakage as well as the separation of the I–V curves into four regions, i.e., pre‐breakdown, linear, breakdown, and upturn. A proposed pore model and equivalent circuit for the multilayer‐chip ZnO varistors. have been simulated with a commercial varistor and a serial resistance to demonstrate the observed I–V phenomena.
Brittle–Ductile Transition and Dislocation Mobility in Sapphire
Authors: Kim Hyung‐Sun , Roberts Steve
Published: March 2005

The brittle‐to‐ductile transition (BDT) of Precracked sapphire in four‐point bending was studied as a function of orientation and strain rate from room temperature to 1500°C. Plastic deformatiom of sapphire occurs via basal and prismatic slip during loading at high temperature (above 1030–1100°C, depending on orientation). The BDT temperature, Tc, varies with strain rate and crystallographic orientation of the fracture plane. The activation, derived from the strain rate variation of Tc, is approximately energy of the process controllingh the BDT in sapphire, derived from the strain rate variation of Tc is sapproximately 3.2 eV, close to that for dislocation glide. In one specimen orientation, “warm‐prestressing” increases the room‐temperature fracture stress.
Optical, Electron Microscopic, and X‐ray Topographic Studies of Ferroic Domains in Barium Titanate Crystals Grown from High‐Temperature Solution
Authors: Park Bong Mo , Chung Su Jin
Published: March 2005

BaTiO3 single crystals were grown by the top‐seeded solution growth (TSSG) technique and the spatial domain configurations in the tetragonal crystals were observed by using a polarizing microscope, SEM, TEM, and X‐ray topography. The 90° domain boundaries were stopped, forming wedge shapes, by another 90° boundary. All of the straight lamellar boundaries in the observed domain patterns, even in the herringbone structure, can be interpreted as head‐to‐tail 90° walls. The irregular overlapped boundary can be observed by using a polarizing microscope and X‐ray topography. It looks as if the lamellar domains are penetrating one another because the wedge‐shaped lamellar domains are spatially overlapped at those boundaries. After thinning and polishing {001} crystal plates, some 90°a–c boundaries disappear and a‐domains become predominant.
Ceramic Surface Reactions and Carbon Retention during Non‐Oxidative Binder Removal Al2O3/Poly(methyl methacrylate) at 20°–700°C
Authors: Higgins Richard J , Rhine Wendell E. , Cima Michael J. , Bowen H. Kent , Farneth William E.
Published: March 2005

Neat poly(methyl methacrylate) (PMMA) thermally decomposes in oxygen‐free environments with negligible production of nonvolatile residue. Compacts of α‐alumina powder containing PMMA that are fired in a non‐oxidative ambient, however, retain appreciable amounts of char. Fourier transform infrared (FTIR) spectroscopy and evolved gas analysis utilizing mass spectral detection were employed to probe the chemical mechanism that initiates the production of organic residue from non‐oxidatively fired PMMA/alumina bodies. We find that binding of organic groups to alumina particles is caused by a sponification reaction between either the ester groups of PMMA or thermally evolved PMMA fragments (including MMA) and hydroxyl groups on alumina particle surfaces. Isolated alumina surface hydroxyl groups were found to be much more reactive than mutually hydrogen‐bonded alumina surface hydroxyl groups in producing surface‐bound organic groups. This surface‐carboxylate‐forming reaction anchors organic residue to the inorganic surfaces to temperatures above the unzipping temperature of the polymer and leads to retention of organic fragments in the compacts at temperatures where neat PMMA has completely volatilized. Subsequent transformations of these surface‐bound organic fragments at high temperatures produce the nonvolatile carbonaceous residues, which are retained in the fired alumina compacts. We demonstrate that unsaturation in the carboxylate side chain plays an important role in this stage of the process in increasing the char yield. We also show that the char yields are proportional to surface carboxylate coverage but that it is difficult to control surface carboxylate coverage by thermal pretreatments of the alumina powders.
Investigation of Resistivity and Permittivity for (Ba,Pb)TiO3 PTCR Ceramics
Authors: Lai Chun‐Hung , Tseng Tseung‐Yuen
Published: March 2005

A scheme to examine quantitatively the interdependence between the measured resistance and permittivity data for semiconducting (Ba,Pb)TiO3 samples having Curie points above 300°C was developed based on the Schottky‐type potential barrier model. Specifically, the nonvanishing spontaneous polarization in the ferroelectric state was considered in terms of a useful parameter to explain the low resistivity below the Curie point. The resistivity derived from the measured permittivity shows a consistent temperature dependence with the dc measured one, i.e., the positive temperature coefficient of resistance (PTCR) characteristics. It is also observed that more satisfactory agreement can be achieved when the acceptor states are assumed to be distributed over a certain energy interval. The values of acceptor‐state densities thus obtained are found to be in excellent agreement with those extracted from the slope in the Arrhenius plots of resistivity vs l/(Tεm), where T is the absolute temperature and εm the dielectric constant. The validity of the present methodology is justified by obedience to the Curie–Weiss law for the calculated bulk dielectric constant.
Active Brazing Alloy Containing Carbon Fibers for Metal–Ceramic Joining
Authors: Zhu Mingguang , Chung D. D. L.
Published: March 2005

The addition of 8.4 vol% short metal‐coated carbon fibers to an active brazing alloy increased the debonding strength of metal/ceramic joints by 18% to 28%. The carbon fibers helped to strengthen the brazing alloy and to decrease slightly the thermal stress at the brazing interface. The carbon fibers were either uniformly distributed in the brazing layer or concentrated near the ceramic side of the metal/ ceramic brazing interface. The latter resulted in a lower thermal expansion in the part of the brazing filler near the ceramic arid gave superior joints such that the debonding occurred in the part of the brazing filler without carbon fibers. The titanium in the active brazing alloy was segregated at the interfaces between the brazing filler and the ceramic, between the brazing filler and the metal (steel), and between the carbon fibers and the matrix of the brazing filler. The amount of titanium at the interface between the brazing filler and the ceramic was smaller when carbon fibers were present in the brazing filler. Titanium segregation at the fiber–matrix interface was also observed when bare carbon fibers instead of metal‐coated fibers were used. The bare carbon fibers gave joints comparable in quality to the metal‐coated carbon fibers. The carbon fibers also served to lower the cost of the brazing material.
Stabilization of Cubic Zirconia with Manganese Oxide
Authors: Dravid Vinayak P. , Ravikumar V. , Notis Michael R. , Lyman Charles E. , Dhalenne Guy , Revcolevschi Alexandre
Published: March 2005

A directionally solidified eutectic (DSE) of MnO‐ZrO2 has been investigated using a variety of electron optical techniques. It is found that considerable MnO goes into ZrO2 to form a substitutional solid solution. About 14 wt% of MnO is soluble in ZrO2 close to the eutectic temperature. The solubility of ZrO2 in MnO, however, is quite low, less than 0.50 wt%. Electron diffraction experiments indicate that ZrO2 (MnO) has the cubic fluorite structure. Diffuse scattering, similar to other cubic zirconias (e.g., CaO, MgO stabilized zirconia), is also observed in manganese‐stabilized zirconia. Diffuse scattering indicates the presence of oxygen vacancies and thus confirms the defect nature of the fluorite structure. Electron energy loss spectrometry (EELS) fine structure analysis of the Mn L23 edge provided clear evidence that Mn is present as Mn2+ in Mn‐stabilized cubic ZrO2.
Microstructure/Process Relations in Sol‐Gel‐Prepared KnbO3 Thin Films on (100) MgO
Authors: Derderian Garo J. , Barrie James D. , Aitchison Kenneth A. , Adams Paul M. , Mecartney Martha L.
Published: March 2005

Epitaxial (110) orthorhombic KNbO3 thin films were prepared using alkoxide solutions. Single‐phase films were produced with stoichiometric sols while slight variations in stoichiometry (52/48 Nb/K or 48/52 Nb/K) created residual second phases. Nucleation and growth of KNbO3, as a function of process conditions were monitored by observing the KNbO3 rosettes produced from niobium‐rich solutions. Methanolic solutions produced films with the highest rosette density and the highest amount of KNbO3. Hydrolysis of the sol aided the crystallization of the KNbO3 phase but also promoted the formation of second phases. Hydrolysis at 0°C reduced second‐phase formation.
Stability of Molybdenum Disilicide in Combustion Gak Environments
Authors: Lin Wen‐yi , Hsu Jen‐Yan , Speyer Robert F.
Published: March 2005

The stability of MoSi2 in combustion gas at 1370° and 1600°C was evaluated using SOLGASMIX‐PV thermodynamic modeling, periodic weight measurements, and characterization via XRD, SEM, EDS, and image analysis. Passive oxidation occurred at both temperatures. During an initial stage of exposure, specimen surfaces oxidized to form MoO3(g) and amorphous SiO2 via reduction of CO2 and H2O. After a short time (<6.5 min at 1370°C, <1 min at 1600°C), the oxidation mechanism switched; Mo5Si3 and amorphous SiO2 formed as oxidation products. The first mechanism esulted in the formation of 46.1 vol% at 1370°C and 42.6 vol% at 1600°C of the amorphous silica surface coating. The attainment of a near‐terminal weight gain implied silica formation was limited by H2O and CO2 diffusion through the silica coating.
Effect of Peptization on Densification and Phase‐Transformation Behavior of Sol–Gel‐Derived Nanostructured Titania
Authors: Kumar Krishnankutty‐Nair P. , Kumar Jalajakumari , Keizer Klaas
Published: March 2005

Porosity reduction, packing, pore‐size distribution, and anatase to rutile phase transformation behavior of nanostructured titania ceramics prepared from both peptized and unpeptized sols were studied and compared using XRD, DSC, and nitrogen‐gas physisorption techniques. Precursor gels prepared from the peptized sol had a green density of about 70% after drying at 40°C, whereas the samples prepared from the unpeptized sol had a green density of only 50%. Samples prepared from the peptized sol showed higher sintering and phase transformation rates compared to the unpeptized sols.
Characterization of TiO2‐Based Sensor Materials Using Immittafice Spectroscopy
Authors: Azad Abdul M. , Younkman Lora B. , Akbar Sheikh A. , Alim Mohammad A.
Published: March 2005

The ac electrical data, monitored in the frequency range 5 Hz f 13 MHz, are used to establish the microstructure–property response of titania‐based composite polycrystalline sensor materials. These electrical data, when analyzed utilizing the lumped parameter/complex plane analysis, reveal several contributions from simultaneously operating mechanisms to the terminal admittance of the grain boundary. The nature of the electrically conducting paths, consisting of the lumped series–parallel network in the microstructure, is suggested via an equivalent circuit representation incorporating the underlying mechanisms in a systematic manner.
Shock‐Compacted Si3N4 Nanocrystalline Ceramics: Mechanisms of Consolidation and of Transition from α‐ to β‐form
Authors: Hirai Hisako , Kondo Ken‐ichi
Published: March 2005

Ultrafine powder of α‐Si3N4 several tens of nanometers in size was successfully consolidated using a shock‐compaction technique under 40 GPa. The bulk density of the most dense portion attained 99% of the theoretical value, and the Vick‐ers microhardness was 2300 kg/mm. Consolidation was achieved through both densificarion by plastic deformation of constituent grains and interparticle bonding by surface melting. A transition process to β‐Si3N4 was observed by transmission electron microscopy: Surface melting of the individual grains propagated into the center as temperature increased, and a large mass formed. A precursor of β–Si3N4 then emerged from the mass and finally grew into a β‐Si3N4 crystal.
Grain Sizes of Ceramics by Automatic Image Analysis
Authors: Chinn Richard
Published: March 2005

Automatic image analysis measurement of grain size has been investigated as an alternative to the manual stereological methods that are well established and widely accepted. Image analysis compares favorably to the manual methods, in as much as a “true” value for grain size cannot be determined. Image analysis minimizes the tedium and human bias associated with the manual methods, and can provide far more stereological information.
Deposition of Indium Tin Oxide Films on Acrylic Substrates by Radiofrequency Magnetron Sputtering
Authors: Chiou Bi‐Shiou , Hsieh Shu‐Ta , Wu Wen‐Fa
Published: March 2005

Indium tin oxide (ITO) films were deposited onto acrylic substrates by rf magnetron sputtering. Low substrate temperature (<80°C) and low rf power (<28 W) were maintained during sputtering to prevent acrylic substrate deformation. The influence of sputtering parameters, such as rf power, target‐to‐substrate distance, and chamber pressure, on the film deposition rate, the electrical properties, as well as the optical properties of the deposited films was investigated. Both the refractive index and the extinction coefficient were derived. The high reflection at wavelengths greater than 3 μ made these sputtered ITO films applicable to infrared mirrors.
Plasticity‐Induced Fatigue Damage in Ceria‐Stabilized Tetragonal Zirconia Polycrystals
Authors: Liu Shih‐Yu , Chen I‐Wei
Published: March 2005

Current studies on the fatigue lifetime of ceramics are mostly focused on the relation between the stress amplitude (or maximum Stress) and cycles to failure. For a more compliant and plastic ceramic which has a pronounced nonlinear stress–strain relation, the role of plastic strain in the fatigue damage is investigated for the first time in this study using a 12 mol% Ce‐TZP. By testing at different temperatures, we were able to vary the amount of transformation plasticity with the same microstructure. The Coffin–Manson relationship, which suggests that fatigue lifetime in the low cycle fatigue regime is best correlated with the plastic strain range, was confirmed for the tough ceramic. Fatigue damage is found to be a bulk process which continuously degrades flaw tolerance by microcracking. Evidence for the latter mechanism was also provided by uniaxial cyclic tension–compression stress–strain response and by TEM examination. Despite such damage, the possibility of plasticity‐induced surface‐crack nucleation in fatiguing ceramics, unlike in metals, appears unimportant.
Composition Microheterogeneity of Uvarovite–Grossularite Garnets
Authors: Carda Juan , Monrós Guillermo , Tena Ma. Angeles , Escribano Purificación , Rincón Jesús Ma.
Published: March 2005

A solid‐solution series with up to 50 mol% uvarovite (Ca3Cr2Si3O12) and grossularite (Ca3Al2Si3O12) was synthesized by the sol–gel method at 1543 K. Colloidal silica was used as the starting reagent, together with chloride salts of the remaining components. X‐ray diffraction analysis of the evolution of the systems showed the formation of uvarovite in a nominal composition of 100 mol% uvarovite; a garnet‐phase solid solution; and gehlenite (Ca2Al2SiO7), pseudowollastonite (α‐CaSiO3), and α‐cristobalite in a nominal composition of 100 mol% grossularite. In some samples, small amounts of impurity phases appeared along with the major phase. The general microstructure was observed by scanning electron and transmission electron microscopy, and an agglomeration of crystals with 2‐μm average size was revealed. The crystals were similar and rounded in shape for all compositions. Additional observations carried out by transmission electron microscopy (TEM) (using the powder replica method) showed that the end series consists of cubic crystals displaying some deformation. Quantitative and semiquantitative scanning electron microscopy/energy‐dispersive X‐ray (SEM/EDX) and transmission electron microscopy/scanning electron microscopy/energy‐dispersive X‐ray (TEM/STEM/EDX) microanalysis (by the Cliff‐Lorimer method, working at 200 kV) were also conducted in all compositional ranges of the solid solutions synthesized in the present study.
Effect of Alumina on Sintering Behavior and Electrical Conductivity of High‐Purity Yttria‐Stabilized Zirconia
Authors: Mori Masashi , Yoshikawa Masahiro , Itoh Hibiki , Abe Toshio
Published: March 2005

The sintering behavior and electrical conductivity of high‐purity 8‐mol% Y2O3‐stabilized ZrO2 (8YSZ) with Al2O3 additions were investigated. The addition of 1 wt% AI2O3 to 8YSZ provided dense, sintered samples with 9.1% relative density at 1400°C without a holding time. Addition of 1 wt% SiO2 enhanced the sinterability of 8YSZ. Na2O addition of 0.1 wt% remarkably lowered it. Electrical conductivity at 1000°C in air increased slightly with increased Ai2O3 content up to 1 wt% and then monotonously decreased. 8YSZ with 1 wt% AI2O3 showed the maximum conductivity of 0.16 S/cm at 1000°C.
Dissolution of MgO in CaO–“FeO”–CaF2–SiO2 Slags under Static Conditions
Authors: Zhang Ping , Seetharaman Seshadri
Published: March 2005

The dissolution of MgO in CaO–“FeO”–CaF2–SiO2 slags has been studied in the temperature range 1573°–1673° K under static conditions. The concentration profiles of Mg in the product Mg1‐xFexO solid‐solution layer as well as slag were determined by EDS analysis. From this, the diffusivities of MgO in the slag and the. interdiffusivities in solid solution were estimated. The dissolution of MgO in CaO–“FeO”–CaF2–SiO2 slags increased with CaF2 content.
Nanocomposite Si/C/N Powder Production by Laser–Aerosol Interaction
Authors: Cauchetier Michel , Croix Odette , Herlin Nathalie , Luce Michel
Published: March 2005

Ultrafine preceramic Si/C/N powders were obtained via ultrasonic injection of aerosol particles into a highpower CO2 laser beam, using hexamethyldisilazane, which strongly absorbs the CO2 laser radiation at 10.6 μm, as the precursor. Introduction of aerosol droplets via a flowing argon or argon–NH3 mixture into the laser beam yielded nanosized (30 to 60 nm), amorphous powders. Yield and particle composition were controlled by varying the synthesis conditions. Powder changes, such as crystallization during heat treatment under nitrogen or argon, were studied.
Serum levels of inflammatory cytokines at diagnosis correlate to the bcl‐6 and CD10 defined germinal centre (GC) phenotype and bcl‐2 expression in patients with diffuse large B‐cell lymphoma
Authors: Pedersen Lars M. , Jürgensen Gitte W. , Johnsen Hans E.
Published: March 2005

Circulating inflammatory cytokines have a prognostic impact independent of the information provided by the International Prognostic Index (IPI) in diffuse large B‐cell lymphoma (DLBCL). The present study characterized prognostic cytokines in relation to stage‐specific B‐cell differentiation antigens and bcl‐2 protein expression, assessed by immunohistochemistry in de novo DLBCL. Serum levels of interleukin 6 (IL‐6) and tumour necrosis factor alpha (TNF‐α) were found to be significantly lower in patients with a germinal centre (GC) phenotype (co‐expression of bcl‐6 and CD10) compared with the non‐GC phenotype. IL‐6 and TNF‐α levels were significantly elevated in patients expressing bcl‐2 protein. Serum levels of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) were not associated with the GC phenotype. On the contrary, both VEGF and bFGF were strongly correlated to bcl‐2 expression. In survival analysis, IPI score remained the most important independent prognostic factor. However, IL‐6 and VEGF, combined with non‐GC phenotype and bcl‐2 positivity, respectively, had a similar independent prognostic power as the IPI. In conclusion, our data suggest that inflammatory cytokines are differently distributed in the GC and non‐GC phenotypes and correlate to bcl‐2 expression. Combining these biomarkers may add to the prognostic information given by clinical variables in the IPI alone.
Temporal changes in European eel, Anguilla anguilla, stocks in a small catchment after installation of fish passes
Authors: LAFFAILLE P. , ACOU A. , GUILLOUËT J. , LEGAULT A.
Published: March 2005

Abstract  Changes in the abundance of European eel, Anguilla anguilla L., in the River Frémur, France, were examined over an 8‐year period. Natural connectivity of the river was disturbed by three high dams that inhibited eel upstream migration and reduced recruitment by elvers and yellow eels. After eel passes were installed, fish became more abundant upstream (mean density 0.5 eel m−2). Moreover, except in the more upstream areas, no decline in eel numbers and biomass was found, in contrast to the general decline of eel throughout its distribution range. It was concluded that eel passes are important to conserve and/or to recover eel stocks.
The prevalence of escaped farmed salmon, Salmo salar L., in the River Ewe, western Scotland, with notes on their ages, weights and spawning distribution
Authors: BUTLER J. R. A. , CUNNINGHAM P. D. , STARR K.
Published: March 2005

Abstract  The prevalence of escaped farmed Atlantic salmon, Salmo salar L., in the River Ewe, western Scotland, was assessed. After the establishment of smolt cages in the catchment and marine cages near the river mouth during 1986–1987, approximately 425 000 parr and smolts, and 122 000 growers have escaped. Between 1987 and 2001, farmed salmon occurred in the rod fishery in 13 of the 15 years, contributing at least 5.8% of the total catch, with a maximum annual frequency of 27.1%. It was estimated that <1% of fish escaping from the marine cages entered the river, but contributed at least 27% of potential anadromous spawners in 1997. Radiotagged, farmed fish in 2001 probably spawned in three subcatchments also used by tagged wild fish. Despite the likelihood of hybridisation there was no change in the median weight or marine age of wild fish, but smolt age decreased significantly (P < 0.02). The Ewe has a depleted wild salmon population (≤900 anadromous adults), and further genetic introgression by escapees should be prevented.
Oral lichen planus in childhood: a report of three cases
Authors: PATEL S. , YEOMAN C. M. , MURPHY R.
Published: March 2005

Lichen planus is a common mucocutaneous condition in which the occurrence of oral lesions has been cited as between 0·5 and 1·9% of the adult population. It is rare in childhood. Here we report three cases of children with intra oral lesions of lichen planus. Lichen planus, although reportedly rare in childhood, should be considered in the diagnosis of hyperkeratotic or erosive lesions of the oral mucosa in children.
Late onset vitiligo: A study of 182 patients
Authors: Dogra Sunil , Parsad Davinder , Handa Sanjeev , Kanwar Amrinder Jit
Published: March 2005

The elderly constitute a large and rapidly growing segment of the population; however, there is complete lack of information about the epidemiology of vitiligo in this age group. To study the clinical and epidemiological profile of vitiligo in the elderly, we retrospectively analyzed the data of patients with vitiligo having onset of disease after 50 years of age attending the pigmentary clinic of our center. Of the 182 patients, 87 (47.8%) were males and 95 (52.2%) were females. The mean age of onset of disease was 55 ± 2.3 years. Vitiligo vulgaris was the most common (83.5%) followed by focal (5.5%), segmental (4.4%), acrofacial (3.8%), mucosal (2.2%), and universal (0.5%).

The most common site of onset was the head and neck (24.2%) followed by the upper limbs (23%), trunk (22%), lower limbs (17.6%), oral/genital mucosae (7.1%), and flexures (6%). Koebner's phenomenon was observed in 14.8% while leukotrichia was present in 47.3% of the patients. Halo nevi were observed in 3.8% of patients, and vitiligo was stable in 64.8%.

Twenty‐nine (15.9%) patients had family history of vitiligo. Associated autoimmune autoimmune/endocrine disorders were present in 39 (21.4%) of the patients. Differences in disease characteristics compared with vitiligo in children and young adults are discussed.
THE REAL EXCHANGE RATE AND THE BALASSA–SAMUELSON EFFECT: THE ROLE OF THE DISTRIBUTION SECTOR
Authors: MacDonald Ronald , Ricci Luca Antonio
Published: March 2005

Abstract.  This paper investigates the long‐run impact of the distribution sector on the real exchange rate. The main result is that an increase in the productivity and product market competition of the distribution sector with respect to foreign countries leads to an appreciation of the real exchange rate, similar to what a relative increase in the domestic productivity of tradables does. This contrasts with the result that one would expect by considering the distribution sector as belonging to the non‐tradable sector. One explanation may lie in the use of the services from the distribution sector in the tradable sector.
Annotation: PANDAS: a model for human autoimmune disease
Authors: Swedo Susan E. , Grant Paul J.
Published: March 2005

Background:  Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcus infections (PANDAS) is a recently recognized syndrome in which pre‐adolescent children have abrupt onsets of tics and/or obsessive‐compulsive symptoms, a recurring and remitting course of illness temporally related to streptococcal infections, and associated neurologic findings including adventitious movements, hyperactivity and emotional lability.

Methods:  Inspired by observations of similar symptoms in children with Sydenham's chorea, a search was undertaken for clinical and laboratory evidence in support of the new syndrome.

Results:  Consistent and predictable clinical findings have been described in a large case series. Magnetic resonance imaging has supported the postulated pathobiology of the syndrome with evidence of inflammatory changes in basal ganglia. Antibasal ganglia antibodies have been found in some acute cases, mimicking streptococcal antigen epitopes.

Conclusions:  While PANDAS remains a controversial diagnostic concept, it has stimulated new research endeavors into the possible links between bacterial pathogens, autoimmune reactions, and neuropsychiatric symptoms.