bluuebunny/crossref_metadata_2025 huggingface dataset:
Near‐Surface Deformation in an Alumina–Silicon Carbide‐Whisker Composite due to Surface Machining
Authors: Odén Magnus , Ericsson Torsten
Published: September 2005

Deformation due to two different surface‐machining conditions—grinding (126 μm diamond) and polishing (3 μm diamond)—in an uniaxial hot‐pressed Al2O3–30%‐SiC‐whisker composite has been investigated. A Warren–Averbach analysis of grazing incidence X‐ray diffractometry data shows that the deformation is localized to the very top surface zone. The cell size and the root mean square of the strain show a gradient in the deformed layer. Transmission electron microscopy studies, in cross‐sectional view, also show a near‐surface deformation zone containing dislocations, twins, and cracks. This is seen for both machining procedures, but the depth of the zone and the degree of deformation, in terms of dislocation density and number of cracks, is much higher in the roughly ground specimen than in the polished one. For comparison, a monolithic Al2O3 sample also has been studied after grinding. The deformation zone is very similar to the Al2O3–SiC sample with the same grinding condition, but cracks and dislocations are present at a slightly larger depth. The deformation depth for the polished Al2O3–SiC sample is ∼50 nm. In the ground Al2O3–SiC sample, the deformation depth is 1–1.5 μm and corresponds to the grain size. The deformation zone in the ground monolithic Al2O3 sample is 1.5–2 μm deep. The observed grain‐boundary cracks are almost parallel to the surface and may originate from nonaccommodated plastic flow between grains.
Corrosion of Mullite by Molten Salts
Authors: Jacobson Nathan S. , Lee Kang N. , Yoshio Tetsuo
Published: September 2005

The interaction of molten salts of different Na2O activities and mullite is examined with furnace and burner tests. The more‐acidic molten salts form small amounts of Al2O3; the more‐basic molten salts form various Na2O–Al2O3–SiO2 compounds. The results are interpreted using the Na2O–Al2O3–SiO2 ternary phase diagram, and some possible diffusion paths are discussed. The generally higher melting points of Na2O–Al2O3–SiO2 compounds lead to better behavior of mullite in molten salts, as compared to SiO2‐protected ceramics such as SiC. Mullite‐coated SiC is discussed, and the corrosion behavior is evaluated.
Measurement of Small Concentrations of Vanadium in Rutile (TiO2) Using Electron Spin Resonance
Authors: de Biasi Ronaldo S. , Fernandes Antonio A. R. , Grillo Maria L. N.
Published: September 2005

Electron spin resonance (ESR) line widths of V4+ in rutile were measured in samples doped with small concentrations of V. The line width was found to change in a predictable way with V concentration. The experimental results show that the technique can be used to measure, rapidly and nondestructively, small concentrations of V in commercial TiO2.
Derivation of the Exponential Relation for the Effect of Ellipsoidal Porosity on Elastic Modulus
Authors: Andersson Clarence A.
Published: September 2005

An analytical basis for the exponential relationship between elastic modulus and fraction porosity is derived. The exponential constant in the equation is shown to be a function of the pore shape and the orientation of the pores with respect to the stress axis and to be independent of pore size. A similar exponential relationship between the modulus and the number of cracks per unit volume is crack‐size dependent.
Rutile Formation in Hydrothermally Crystallized Nanosized Titania
Authors: Bacsa Revathi R. , Grätzel Micheal
Published: September 2005

The present study shows that peptization aids in the anatase‐rutile transformation in hydrothermally processed (250°C, 4000 kPa) titania sols produced by the hydrolysis of alkoxide. HREM images show the presence of nanocrystals of 25–55 nm size. The anatase‐rutile phase transformation in peptized titania is critically dependent on the conditions of hydrolysis such as the water/alkoxide concentration ratio and the size of the alkoxide. Hydrolysis of the ethoxide gave rise to a predominantly rutile phase whereas the isopropoxide and butoxide resulted in a predominantly anatase powder, under the same conditions of treatment. BET surface areas decrease from 107.1 to 68 m2/g when the alkoxide is changed from tert‐butoxide to ethoxide for a given water/ alkoxide ratio.
Fabrication and Electrical Properties of Lead Zirconate Titanate Thick Films
Authors: Chen H. Daniel , Udayakumar K. R. , Gaskey Christopher J. , Cross L. Eric , Bernstein Jonathan J. , Niles Lance C.
Published: September 2005

Thick films of lead zirconate titanate of the morphotropic phase boundary composition, Pb(Zr0.52Ti0.48)O3, have been fabricated on platinum‐buffered silicon using a modified sol–gel spin‐coating technique. Crack‐free films of 12‐μm thickness can be uniformly deposited on 3‐in.‐diameter wafers with high yield and properties comparable to those of bulk ceramics. The thickness dependence of film structure and the dielectric, ferroelectric, and piezoelectric properties have been characterized over the thickness range of 1–12 μm. A strong (100) texture develops as film thickness increases above 5 μm; the films were marked by saturation values of longitudinal piezoelectric coefficient d33, 340 pC/N; remanent polarization, 27 μC/cm2; and dielectric permittivity, 1450. PZT films in this thickness range are extremely well‐suited to application as electromechanical transduction media in silicon‐based microelectromechanical systems (MEMS).
Thermoelectric Properties of Homologous Compounds in the ZnO–In2O3 System
Authors: Ohta Hiromichi , Seo Won‐Seon , Koumoto Kunihito
Published: September 2005

Homologous compounds of (ZnO)m In2O3 (m = integer) with layered structures were synthesized by reaction‐sintering a mixed powder of ZnO and In2O3 at 1823 K for 2 h in air, and their thermoelectric properties, i.e., electrical conductivity, Seebeck coefficient, and thermal conductivity, were measured at 500 to 1100 K. Their thermoelectric figure of merit depended on the composition, and an optimum value of m apparently existed giving the largest figure of merit.
Suppression of Grain Growth in Sol–Gel‐Derived Tin Dioxide Ultrathin Films
Authors: Yoo Do Joon , Tamaki Jun , Park Soon Ja , Miura Norio , Yamazoe Noboru
Published: September 2005

Tin dioxide thin films of various thicknesses up to 150 nm were prepared on quartz glass substrates from a sol solution of SnO2 (particle size 3 nm) by a spin‐coating method and subjected to calcination at different temperatures up to 800°C for 30 min. The grain size of SnO2 was found to be far smaller than those obtained from the SnO2 sol‐derived powder under the same calcination conditions. The suppression of grain growth of SnO2 was more conspicuous as the film thickness decreased so that in the thinnest film (20 nm thick) the SnO2 grain size remained as small as 6 nm after calcination at 800°C. It is suggested that the SnO2 grains in the ultrathin film deposited on the substrate are restrained from moving and coalescing with each other, resulting in the suppression of grain growth.
Crystallization of ZBLAN Glass
Authors: Aasland Siv , Grande Tor
Published: September 2005

The glass transition, onset crystallization, solidus, and liquidus temperatures of a ZBLAN glass have been measured by differential thermal analysis in a sealed Pt ampoule. The onset crystallization was observed at 335°C for a powdered glass, while for a monolithic glass, prepared by in situ quenching in the Pt capsule, the onset crystallization was observed at 395°C, 135°C higher than Tg. Surface‐induced heterogeneous nucleation is therefore proposed to be important for the crystallization of ZBLAN glasses. The solidus temperature was observed at 452°C, about 10°C lower than reported for the subsystem ZrF4–BaF2–NaF.
Sintering of Nanophase γ‐Al2O3 Powder
Authors: Wu Shun J. , De Jonghe Lutgard C. , Rahaman Mohamed N.
Published: September 2005

The sintering of ultrafine γ‐Al2O3 powder (particle size ∼10–20 nm) prepared by an inert gas condensation technique was investigated in air at a constant heating rate of 10°C/min. Qualitatively, the kinetics followed those of transition aluminas prepared by other methods. Measurable shrinkage commenced at ∼ 1000°C and showed a region of rapid sintering between ∼1125° and 1175°C followed by a transition to a much reduced sintering rate at higher temperatures. Starting from an initial density of ∼0.60 relative to the theoretical value, the powder compact reached a relative density of 0.82 after sintering to 1350°C. Compared to compacts prepared from the as‐received powder, dispersion of the powder in water prior to compaction produced a drastic change in the microstructural evolution and a significant reduction in the densification rate during sintering. The incorporation of a step involving the rapid heating of the loose powder to ∼1300°C prior to compaction (which resulted in the transformation to α‐Al2O3) provided a method for significantly increasing the density during sintering.
Synthesis of Spherical β‐Silicon Carbide Particles by Ultrasonic Spray Pyrolysis
Authors: Čerović Ljiljana S. , Milonjić Slobodan K. , Zivković Ljilana V. , Uskoković Dragan P.
Published: September 2005

Fine agglomerate‐free spherical β‐SiC powder was synthesized from a dispersion of colloidal silica, saccharose, and boric acid, by means of an ultrasonic spray pyrolysis method. Droplets of 2.2 μm were formed with an aerosol generator, operated at 2.5 MHz, and carried into a reaction furnace at 900°C with argon. Spherical X‐ray amorphous gel particles of 1.1 μm were obtained. β‐SiC particles with a mean diameter of 0.79 μm and spherical shape resulted when the SiC gel precursor particles were heated at 1500°C in argon.
Creep Deformation in an Alumina–Silicon Carbide Composite Produced via a Directed Metal Oxidation Process
Authors: Lin Hua‐Tay , Breder Kristin
Published: September 2005

Flexural creep studies were conducted in a commercially available alumina matrix composite reinforced with SiC particulates (SiCp) and aluminum metal at temperatures from 1200° to 1300°C under selected stress levels in air. The alumina composite (5 to 10 μm alumina grain size) containing 48 vol% SiC particulates and 13 vol% aluminum alloy was fabricated via a directed metal oxidation process (DIMOX(tm))† and had an external 15 μm oxide coating. Creep results indicated that the DIMOX Al2O3–SiCp composite exhibited creep rates that were comparable to alumina composites reinforced with 10 vol% (8 (μm grain size) and 50 vol% (1.5 μm grain size) SiC whiskers under the employed test conditions. The DIMOX Al2O3–SiCp composite exhibited a stress exponent of 2 at 1200°C and a higher exponent value (2.6) at ≥ 1260°C, which is associated with the enhanced creep cavitation. The creep mechanism in the DIMOX alumina composite was attributed to grain boundary sliding accommodated by diffusional processes. Creep damage observed in the DIMOX Al2O3‐SiCp composite resulted from the cavitation at alumina two‐grain facets and multiple‐grain junctions where aluminum alloy was present.
Mechanical Properties of Infiltrated Alumina‐Y‐TZP Composites
Authors: Glass S. Jill , Green David J.
Published: September 2005

Small Al2O3 additions (∼ 4 vol%) made to Y‐TZP using an infiltration technique increased the fracture toughness and strength by ∼15% and the amount of transgranular fracture. Ionic conductivity measurements showed decreased grain‐boundary conductivity, confirming a change in the grain‐boundary composition. The predominant failure origins for both the unmodified Y‐TZP and the Al2O3—Y‐TZP were surface flaws related to agglomerates in the original powder. Finishing reduced the severity of these flaws and substantially increased the strength of both materials (>50%). The infiltration approach introduced a new flaw population in some specimens; however, this problem was overcome by a simple processing modification.
Grain‐Boundary Relaxation in High‐Purity Silicon Nitride
Authors: Pezzotti Giuseppe , Ota Ken'ichi , Kleebe Hans‐Joachim
Published: September 2005

Internal friction, torsional creep, and shear modulus relaxation experiments were conducted on a model Si3N4 polycrystalline material, which contained a continuous amorphous film of pure SiO2 at the grain boundary. Internal friction experiments were performed in the frequency range between 3 and 13 Hz, in 5 Pa of nitrogen atmosphere. Very high temperatures (up to 2000°C) could be applied for the first time by using a newly developed torsional pendulum apparatus. This apparatus was also capable of precise torsional strain measurements under static‐load conditions. The internal friction curves at various frequencies were generally found to consist of a grain‐boundary peak super‐imposed on an exponential‐like background. The peak, of anelastic diffusive origin, was centered in the temperature range of 1612–1710°C depending on the frequency of the measurement, namely within an interval of about 100°C below the nominal melting point of the pure SiO2 phase (i.e., ∼ 1730°C). The background was instead found to be of viscoelastic nature. A common micromechanical origin between the creep plastic strain and the internal friction background curves was identified and the data could be fitted by the same Arrhenius plot. Structural and chemical characterization of internal grain boundaries was performed by high‐resolution electron microscopy (HREM) in addition to electron energy‐loss spectroscopy (EELS). A small amount of nitrogen was detected within the amorphous residue along grain boundaries. According to the above set of microstructural/chemical and mechanical data, the viscosity properties of the intergranular phase were assessed and the sliding mechanism between adjacent Si3N4 grains was modeled.
Temperature Effects on Structure and Dynamics in Borate and Borosilicate Liquids: High‐Resolution and High‐Temperature NMR Results
Authors: Stebbins Jonathan F. , Ellsworth Susan E.
Published: September 2005

The fictive temperature dependence of the relative abundances of three‐ and four‐coordinated boron was investigated in several sodium borate and borosilicate glasses using high‐resolution 11B nuclear magnetic resonance (NMR). In the compositions with low sodium/boron ratios, no effect was observed, but in the borosilicates, the fraction of the tetrahedral species decreased significantly as the fictive temperature increased because of the higher content of nonbridging oxygens. In situ, high‐temperature magic‐angle spinning NMR demonstrated the exchange of the two species at a rate comparable to the shear relaxation rate, indicating a close link between B‐O bond breaking and viscous flow.
Microstructure Development in In Situ Reinforced Reaction‐Bonded Aluminum Niobate‐Based Composites
Authors: Garciía Daniel E. , Janssen Rolf , Claussen Nils E.
Published: September 2005

Reaction‐bonded aluminum niobate‐based (AlNbO4‐based) composites with tailorable microstructures were fabricated through controlled nucleation and growth of needlelike AlNbO4 grains. Equiaxed to highly elongated grains were obtained by different heat treatments at 1340° and 1400°C in air. Scanning electron microscopy observations revealed that increasing the heating rate promoted the development of large, homogeneously distributed needlelike grains. Because of the elongated nature of the AlNbO4 grains and the high residual stresses at the interface, enhanced crack wake bridging occurred. This bridging accounted for the observed increase of fracture toughness.
Electromechanical Testing and Modeling of a Pb(Mg1/3Nb2/3)O3‐PbTiO3‐BaTiO3 Relaxor Ferroelectric
Authors: Brown Steve A. , Hom Craig L. , Massuda Mona , Prodey Jacqueline D. , Bridger Keith , Shankar Natarajan , Winzer Stephen R.
Published: September 2005

Compressive prestress effects on the electrical and mechanical properties of relaxor ferroelectric materials were studied as a function of temperature for several formulations of Pb(Mg1/3Nb2/3)O3‐PbTiO3‐BaTiO3 (PMN‐PT‐BT) ceramics. Experimentally measured polarization and strain, induced by an ac electric field, decreased as compressive stress increased. Effective Young's moduli also were measured under constant dc electric fields. A significant decrease in modulus was observed with increasing field. The prestress and modulus experiments were modeled analytically using a proposed relaxor ferroelectric constitutive law. In general, excellent agreement between the model and experiments was obtained, indicating that the model accurately predicted the coupled behavior of this relaxor ferroelectric material.
Synthesis of Strontium Barium Niobate Thin Films through Metal Alkoxide
Authors: Sakamoto Wataru , Yogo Toshinobu , Kikuta Koichi , Ogiso Ko‐ji , Kawase Akihiro , Hirano Shin‐ichi
Published: September 2005

Highly oriented Sr0.5Ba0.5Nb2O6 (SBN50) thin films have been prepared using a sol‐gel method. A homogeneous and stable strontium barium niobate (Sr1‐xBaxNb2O6, SBN) precursor solution could be prepared via the reaction control of metal alkoxides. The SBN precursor was stabilized by the coordination of the 2‐ethoxyethoxy group to metals. SBN thin films on MgO(100) crystallized to a mixture of orthorhombic and tetragonal phase at 700°C and then transformed completely to the tetragonal phase of tungsten bronze at 1000°C. Two crystal lattice planes of SBN were intergrown at an orientation of 18.5° on MgO(100). SBN50 thin films on Pt(100)/MgO(100) substrates exhibited the P‐E hysteresis.
Orientation Control and Laser‐Beam‐Assisted Crystallization of Sol‐Gel‐Derived, Titanium‐Doped LiNbO3 Thin Films
Authors: Kikuta Koichi , Isobe Yasuhide , Yogo Toshinobu , Ono Satomi , Hirano Shin‐ichi
Published: September 2005

Two processes for the crystallization of titanium‐doped LiNbO3 (LNT) gel thin films were investigated in the present study. LNT gel thin films were prepared on platinized glass and platinized sapphire substrates, as the application of a platinum intermediate layer greatly affected the orientation of LNT films on these substrates. X‐ray pole figures revealed the well‐oriented growth for LiNbO3 both on the platinum (111)/sapphire C substrate and bare sapphire C. Another approach to crystallizing LNT gel film was attempted by developing a new technique to fabricate a LiNbO3 waveguide on the sapphire substrate using a Nd:YAG laser beam. The crystallization of LNT was achieved successfully with no cracking or peeling. The prepared crystalline LNT films also were characterized by Raman microspectroscopy. S. E. Trolier‐McKinstry—contributing editor
Fracture Process of Silicon Carbide Fiber‐Reinforced Glasses
Authors: Tsuda Hiroshi , Takahashi Jun , Kemmochi Kiyoshi , Hayashi Ryuichi
Published: September 2005

This paper evaluates the fracture process for fiber‐reinforced glasses under tensile loading. Two types of unidirectionally aligned Nicalon SiC‐fiber‐reinforced glass with different fiber coatings were examined. One channel acoustic emission (AE) measurement was employed during the tensile tests. Probabilistic fracture analysis as well as the replication technique were used to investigate the relation between the AE signals and fracture processes. The AE technique proved to be an effective method for observing fracture processes of the material systems studied. The fracture process could be distinguished in terms of the AE amplitude. AE signals with high amplitudes corresponded to fiber breaking; AE signals with low amplitudes corresponded to matrix cracking, interfacial debonding, and fiber pullout. In the well‐toughened material studied the reinforcing fibers would break extensively over 75% load of the ultimate strength.
Synthesis Routes and Characterization of High‐Purity, Single‐Phase Gallium Nitride Powders
Authors: Balkaş Cengiz M. , Davis Robert F.
Published: September 2005

Synthesis of high‐purity, single‐phase gallium nitride powder has been achieved in a hot‐wall tube furnace via (i) the reaction of gallium with ammonia (NH3) and (ii) the conversion of gallium oxide (Ga2O3). For complete reaction, the optimum temperatures, NH3 flow rates, and boat positions relative to the NH3 inlet were 975°C, 400 standard cubic centimeters per minute (sccm), and 50 cm, respectively, for the gallium‐NH3 reaction, and 1050°C, 500 sccm, and 50 cm, respectively, for the Ga2O3 conversion. Polyhedra of various shapes were obtained from both processes; some rod‐shaped crystals also were observed in the material derived from Ga2O3.
Phase Equilibria in the Quaternary System Ti‐Al‐C‐N
Authors: Pietzka Markus A. , Schuster Julius C.
Published: September 2005

The quaternary system Ti‐Al‐C‐N and its binary and ternary boundary systems are investigated using powder methods and XRD analysis. Phase equilibria at 1375°C are presented in an isothermal network for alloys up to 50 at.% Ti. In the vertical section Ti2AIC1‐x‐Ti2AlN1‐x a complete series of solid solutions exists at 1495°C, but a wide miscibility gap occurs at 1375°C. The vertical section Ti3AlC1‐x‐Ti3AlN1‐x is more complex because of the occurrence of the quaternary, tetragonally distorted phase Ti3Al(C,N)1‐x (a= 0.41135(4) nm, c= 0.41366(5) nm) and the transformation of perovskite‐type Ti3AlN1‐x into filled Re3B‐type Ti3AlN1‐x below 1200°C.
Effect of Heat Treatment on Grain Size, Phase Assemblage, and Mechanical Properties of 3 mol% Y‐TZP
Authors: Ruiz Laurence , Readey Michael J.
Published: September 2005

The effect of heat treatment on the grain size, phase assemblage, and mechanical properties of a 3 mol% Y‐TZP ceramic was investigated. Specimens were initially sintered for 2 h at 1450°C to near theoretical density; some specimens were then heat‐treated at 1550°, 1650°, 1750°, or 1850°C to coarsen the microstructure. The average grain size increased with heat treatment from <0.5 to ∼10 μ‐m. Phase analyses revealed predominantly tetragonal and cubic phases below 1750°C, with a significant decrease in tetragonal content and increase in monoclinic content for temperatures >1750°C. The maximum fraction of tetragonal phase that transformed during fracture corresponded with the largest tetragonal grain size of ∼5–6 μm. Strength was on the order of 1 GPa, and was surprisingly insensitive to heat‐treatment temperature and grain size, contrary to previous studies. The fracture toughness increased from 4 to 10 MPa.m1/2 with increasing grain size, owing to an increasing transformation zone size. Grain sizes larger than 5–6 μm spontaneously transformed to monoclinic phase during cooling. Such critical grain sizes are much larger than those found in past investigations, and may be due to the greater fraction of cubic phase present which decreases the strain energy arising from crystallographic thermal expansion anisotropy of the tetragonal phase.
Scanning Force Microscopy Study of Ceramic Fibers for Advanced Composites
Authors: Wang Hsin‐Fu
Published: September 2005

The surface roughness and topography of three different Al2O3 fibers were evaluated using atomic force microscopy (AFM). The fibers used were as‐received, refractory‐metal coated, and Y2O3/refractory‐metal duplex‐layer coated. The refractory‐metal coating and Y2O3 coating on the Al2O3 fibers increased the average surface roughness from 13.3 to 17.1 and 18.8 nm, respectively. The topographic image of the fibers evaluated by AFM was compared to that obtained by scanning electron microscopy. Lateral force microscopy (LFM) was used to measure the distribution of the friction force on the refractory‐metal‐coated Al2O3 surfaces, with friction coefficients ranging from 0.2 to 0.8; the average friction coefficient was 0.38. Tailoring the mechanical properties at fiber/matrix interfaces by surface modification of Al2O3 fibers to improve the overall mechanical properties of the composites also was proposed.
Tensile Creep Behavior of a Vitreous‐Bonded Aluminum Oxide under Static and Cyclic Loading
Authors: Dey Nishit , Socie Darrell F. , Hsia K. Jimmy
Published: September 2005

Creep deformation and rupture behavior of a vitreousbonded aluminum oxide was investigated under uniaxial static and cyclic tensile loadings at 1000°, 1100°, and 1175°C. The material was more creep resistant, i.e., having lower creep strain rates, under cyclic loading compared to that under static loading. For the same maximum applied stress, the ratio of steady‐state creep rate under static loading to that under cyclic loading at 1100°C was approximately 100. However, the value of this ratio decreased to about 10 when the testing temperature was raised to 1175°C or lowered to 1000°C. Under static loading the material had more propensity to develop creep damage in the form of micro‐ and macrocracks, leading to early failure, whereas under cyclic loading the creep damage was more uniformly distributed in the form of cavities confined to the multigrain junctions. Viscous bridging by the grain boundary second phase may be the primary contributor to the lower creep deformation rate and improved lifetime under cyclic loading.
Oxidation Behavior of a Si‐C‐O‐Fiber‐Reinforced Magnesium Aluminosilicate
Authors: Kumar Atul , Knowles Kevin M.
Published: September 2005

The oxidation behavior of a Si‐C‐O‐fiber‐reinforced magnesium aluminosilicate has been investigated in the temperature range 1000°‐1200°C. Parabolic weight gain, together with other experimental observations, has suggested that the oxidation process was controlled by the outward diffusion of carbon monoxide gas. The matrix and fibers reacted to form enstatite and forsterite. During the initial stages of oxidation, an interlayer containing a mixture of silica and turbostratic carbon was formed. This interlayer was modified progressively over time to create interface morphologies near the surface and near the center of the oxidized samples that were different from one another. A mechanism explaining the morphological evolution of the fiber‐matrix interfaces has been proposed.
Microstructure and Crystal Phases of Praseodymium Oxides in Zinc Oxide Varistor Ceramics
Authors: Lee Yih‐Shing , Liao Kao‐Shiang , Tseng Tseung‐Yuen
Published: September 2005

The effect of sintering temperature on the microstructure and crystal phases of the intergranular praseodymium oxides in ZnO varistor ceramics was investigated using transmission electron microscopy and high‐resolution electron microscopy. The ZnO grains were three‐dimensionally separated from the intergranular praseodymium oxides. On the basis of microdiffraction analyses of the intergranular layer, the phase transformation from fcc‐Pr6O11 into hcp‐Pr2O3 was found when the sintering temperature increased from 1300° to 1350°C. The defect reaction equation and the decrease of donor concentration with increasing sintering temperature can verify the certainty of phase transition during the liquid‐phase sintering observed by transmission elecron microscopy. Additionally, on the basis of the small variations of the breakdown voltage per grain boundary, the number of active grain boundaries is not a dominant factor for the donor concentration dependence on the sintering temperature.
Machining‐Induced Surface Residual Stress Behavior in Al2O3–SiC Nanocomposites
Authors: Chou Irene A. , Chan Helen M. , Harmer Martin P.
Published: September 2005

The machining and subsequent annealing behavior of an Al2O3‐SiC nanocomposite (A12O3+ 5 vol% 0.2 μm SiC particles) was compared to that of single‐phase A12O3. The machining‐induced residual line force was determined by measuring the extent of elastic bending in thin disk specimens, and the surface roughness was evaluated by profilometry. The results showed that, when the two materials were subjected to the same grinding conditions, they developed compressive residual stresses and surface roughness values of similar magnitude. The maximum thickness of the residual stress layers was estimated to be ∼ 10 μm for the A12O3 and ∼12 μm for the nanocomposite. A direct linear correlation was observed between the residual force and the surface roughness for different machining treatments. Annealing of the machined samples produced complete relaxation of residual stresses in the single‐phase Al2O3, whereas only partial stress relaxation occurred for the nanocomposite.
Influence of Molybdenum Silicide Additions on High‐Temperature Oxidation Resistance of Silicon Nitride Materials
Authors: Klemm Hagen , Tangermann Katja , Schubert Christian , Hermel Waldemar
Published: September 2005

The influence of additions of molybdenum disilicide (MoSi2) on the microstructure and the mechanical properties of a silicon nitride (Si3N4) material, with neodymium oxide (Nd2O3) and aluminum nitride (AIN) as sintering aids, was studied. The composites, containing 5, 10, and 17.6 wt% MoSi2, were fabricated by hot pressing. All materials exhibited a similar phase composition, detected by X‐ray diffractometry. Up to MoSi2 additions of 10 wt%, mechanical properties such as strength, fracture toughness, or creep at 1400°C were not affected significantly, in comparison to that of monolithic Si3N4. The oxidation resistance of the composites, in terms of weight gain, degraded. After 1000 h of oxidation at 1400° and 1450°C in air, a greater weight gain (by a factor of approximately three) was obtained, in comparison to that of the material without MoSi2. Nevertheless, after 1000 h of oxidation, the degradation in strength of the composites was considerably less severe than that of the material without MoSi2. An additional layer was formed, caused by processes at the surface of the Si3N4 material, preventing the formation of pores, cracks, or glassy‐phase‐rich areas, which are common features of oxidation damage in Si3N4 materials. This surface layer, containing Mo5Si3 and silicon oxynitride (Si2ON2), was the result of reactions between MoSi2, Si3N4, and the oxygen penetrating by diffusion into the material during the hightemperature treatment.
Stoichiometric Dependence of the Aging Phenomena in Lead Iron Tungstate Ceramics
Authors: Zhou Liqin , Vilarinho Paula M. , Baptista João L.
Published: September 2005

Lead iron tungstate, Pb(Fe2/3W1/3)O3, ceramics with different stoichiometries were used to study the isothermal aging of this relaxor ferroelectric. The tungsten‐deficient samples showed evident aging effects, more pronounced as the tungsten deficiency increased. The aging behavior showed a strong dependence on the frequency, a log‐linear function of the aging time, and a shift of the dielectric distortion with the aging temperature. Defect associations between tungsten and oxygen vacancies seemed to be responsible for this behavior. On the other hand, lead‐deficient samples showed no aging phenomena. The structural positions of point defects, tungsten, lead, and oxygen vacancies and the reorientation of defect dipole pairs have been discussed for the compositions and suggested to be responsible for the observed behavior.
Possible Explanations of Transient Neck Formation between Pairs of (100) Faceted Particles
Authors: Searcy Alan W. , Billiard Jeffrey W. , Carter W. Craig
Published: September 2005

Rankin and Boatner have observed that (100) faceted MgO particles in contact along either corners or edges developed, on heating, necks that initially grew, but then shrank and broke. General thermodynamic models are provided that predict this transient neck formation for any cubic particles that share only a small fraction of an edge and for particles that share an edge that is less than 0.6 times as long as the orthogonal edges. A third model, which assumes that reaction of MgO particles with their carbon substrate removes MgO from the MgO–carbon interface at a constant rate, explains the observation that the neck shrinkage rate greatly exceeds the neck growth rate. Application of the theory to explaining the seeming prevalence of rounded surfaces in sintering powders is described.
Fracture Behavior of Multilayer Silicon Nitride/Boron Nitride Ceramics
Authors: Liu Haiyan , Hsu Stephen M.
Published: September 2005

The fracture behavior of multilayer Si3N4/BN ceramics in bending has been studied. The materials were prepared by a process of tape casting, coating, laminating, and hot pressing. The Si3N4 layers were separated by thin, weak BN interlayers. Crack patterns in bending bars were examined with a scanning electron microscope. The weak layers deflected cracks in bending and thus prevented catastrophic failure. In one well‐aligned multilayer ceramic A, a main crack propagated through the specimen although along a zigzag path. A second multilayer ceramic B was made to simulate a wood grain structure. Its failure was dominated by shear cracking along the weak BN layers. Besides crack deflection, interlock bridging between toothlike layers in the wake of the main crack appeared also to contribute to toughening.
Formation of Reaction‐Bonded Silicon Nitride Using Microwave Heating
Authors: Thomas Jeffrey J. , Skamser Daniel J. , Jennings Hamlin M. , Johnson D. Lynn
Published: September 2005

Rod‐shaped silicon compacts were nitrided in a microwave applicator using a minimum of insulation in order to maximize the temperature gradients to effect an inside‐out reaction. These specimens exhibited very nonuniform conversion to Si3N4, and fully nitrided areas had poor microstructures consisting of alternating regions of high and low density. The key factor was found to be sintering of the silicon powder during initial heating which caused the specimens to be electrically conducting during the early stages of the reaction and led to large changes in the microwave heating behavior of the specimens as they nitrided. The temperature and composition profiles in the specimens were simulated using a numerical model. The results of the model indicated that the observed microstructures were caused by high temperatures and temperature gradients in the areas of maximum nitridation rate which caused silicon vapor to diffuse within the specimens. Some compacts were made from a mixture of silicon powder and silicon nitride powder to avoid sintering of the silicon particles. These specimens nitrided uniformly with inside‐out composition profiles, indicating that microwave heating would be beneficial for the nitridation of pure silicon powder compacts if sintering could be avoided.
Infrared Studies of Calcia‐Alumina Fibers
Authors: Fondeur Fernando , Mitchell Brian S.
Published: September 2005

IR depth profiling of propane‐stabilized calcia‐alumina fibers showed that carbon deposited on the fibers during melt‐spinning induced tetrahedral coordination of aluminum atoms near the fiber surface. It is proposed that this effect increases melt surface viscosity and stabilizes calcia‐alumina fibers. Ethers, esters, and carboxylates were also seen on the fiber surfaces and it is proposed that carbon monoxide reacts with carbon in the fiber to make these species.
Monoclinic Phase Measurement in Mg‐PSZ Using X‐ray Diffraction
Authors: Batchelor Warren J. , Finlayson Trevor R. , Kelly Georgina L.
Published: September 2005

This paper reports a systematic study in which both the surface preparation and the amount of orthorhombic phase in the samples were varied and the effect on the observed monoclinic peaks was examined. The monoclinic 111 peak is largely unaffected by the state of the surface and can be considered as representative of the bulk of the sample. This is used to derive a simple method for determining the bulk monoclinic phase content in Mg‐PSZ ceramics. Acceptable agreement was found between XRD and neutron diffraction measurements. It was also found that the presence of substantial amounts of orthorhombic phase in the sample had little effect on the measured monoclinic phase content.
High Thermal Conductivity in Silicon Nitride with Anisotropie Microstructure
Authors: Hirao Kiyoshi , Watari Koji , Brito Manuel E. , Toriyama Motohiro , Kanzaki Shuzo
Published: September 2005

Silicon nitride was fabricated by tape casting of α‐Si3N4 powder with 5 wt% Y2O3 and 5 vol% rodlike β‐Si3N4 seed particles, followed by tape stacking, hot pressing under 40 MPa, and annealing at 1850°C for 2‐66 h under a nitrogen pressure of 0.9 MPa. Silicon nitrides fabricated by this procedure exhibited a highly anisotropic microstructure with large elongated grains (developed from seed particles) uniaxially oriented parallel to the casting direction. Thermal conductivities parallel to the grain alignment were much higher than those measured in other directions and exhibited high values of up to 120 W/(m.K). The anisotropic thermal conductivity of the specimen could be explained by the rule of mixture, considering that large elongated grains developed from seeds have higher thermal conductivity than a small‐grained matrix.
Characterization of Si3N4 Coated with Chemically‐Vapor‐Deposited Mullite after Na2SO4‐lnduced Corrosion
Authors: Lee Woo Y. , More Karren L. , Stinton David P. , Bae Yong W.
Published: September 2005

Si3N4 substrates coated with chemically‐vapor‐deposited, crystalline mullite (3Al2O3.2SiO2) were subjected to a corrosive environment containing Na2SO4 and O2 at 1000°C for 100 h. The composition and microstructure of the as‐deposited and corroded specimens were examined and compared. The coating appeared to be effective in preserving and therefore protecting the surface microstructure of the underlying Si3N3 substrates. However, a small degree of Na penetration through mullite grain boundaries was observed to a coating depth of ∼1 μm.
Oriented Barium Titanate Thick Films by Reactive Coating on Rutile
Authors: Steier Hanns P , Moya José S.
Published: September 2005

A mechanically stable [110] oriented tetragonal barium titanate layer of ≤50 μm thickness on a rutile substrate has been obtained by reactive coating of screen printed barium titanate submicrometer powder on the substrate and following a two‐step firing cycle at 1400°C for 6 min and 1310°C for 60 min. The results have been explained taking into account the BaTiO3–TiO2 equilibrium phase diagram.
Near‐Net‐Shape Processing of Metal‐Ceramic Composites by Reactive Metal Penetration
Authors: Fahrenholtz William G. , Ewsuk Kevin G. , Ellerby Donald T. , Loehman Ronald E.
Published: September 2005

Metal‐ceramic composites were made to near‐net shape by reacting phase‐pure mullite and mullite‐glass preforms with molten Al using a reactive metal penetration process. Conversion of the two ceramic preforms to Al2O3/Al composites was accompanied by a 0.32% volume expansion and a 1.42% volume shrinkage, respectively. Molar volume and density calculations made assuming a net‐shape reaction estimate ∼17 and ∼27 vol% Al to be present in the two composites after reaction. Results from quantitative stereology measurements used to quantify the concentration of metal in the reactively formed composites validate the calculations.
Crystallization and Transformation of Aluminum Orthophosphates in Organic Solvent Containing a Small Amount of Water
Authors: Kominami Hiroshi , Matsuo Kentarou , Kera Yoshiya
Published: September 2005

Aluminum orthophosphate (AlPO4) samples were synthesized by high‐temperature (200‐300°C) hydrolysis of a mixture of aluminum triisopropoxide and triethyl phosphate with a small amount of water dissolved in an organic solvent from the gas phase. At 250°C, cristobalite‐type AlPO4, which is the metastable phase at that temperature, was first crystallized from the amorphous phase and then transformed to stable quartz‐type AlPO4 (berlinite) with a prolonged reaction time. When the amount of water charged into the system was increased, berlinite was formed immediately. The formation of the metastable phase could be attributed to the low solubility of AlPO4 in the organic solvent containing a small amount of water.
What is supportive when an adult next‐of‐kin is in critical care?
Authors: Johansson Ingrid , Fridlund Bengt , Hildingh Cathrine
Published: October 2005

There is little documented knowledge about what is supportive from the perspective of relatives with a critically ill next‐of‐kin in the intensive care unit (ICU). The aim of the present study was to generate a theoretical understanding of what relatives experience as supportive when faced with the situation of having an adult next‐of‐kin admitted to critical care. The study was designed using a grounded theory methodology. Interviews were conducted with 29 adult relatives of adult ICU patients in southwest Sweden. Relatives described the need to be empowered and that support was needed to enable them to use both internal and external resources to cope with having a next‐of‐kin in critical care. To achieve empowerment, the relatives described the need to trust in oneself, to encounter charity and to encounter professionalism. The findings can contribute understanding and sensitivity to the situation of the relatives as well as indicating what form social support should take. It is essential that healthcare professionals understand how important it is for relatives to have control over their vulnerable situation and that they also reflect upon how they would like to be treated themselves in a similar situation. Recommendations for future practice are presented.
Development of comparable agro‐climatic zones for the international exchange of data on the efficacy and crop safety of plant protection products1
Authors: Bouma E.
Published: October 2005

Data on the efficacy and crop safety of plant protection products can be used for registration purposes in other countries, provided crop growth conditions are comparable. This article identifies the main conditions which are relevant in this respect, with particular emphasis on climatic conditions. Comparison of several systems of agro‐climatic classification developed for the EPPO region, particularly the climate diagrams of Walter & Lieth, the climate classification system of Köppen & Geiger, the agro‐climatic areas of Thran & Broekhuizen and natural vegetation maps, has led to a division of the EPPO region (Europe, Mediterranean area, Middle East) into four agro‐climatic zones (Mediterranean, Maritime, North‐east, Central) within which conditions can be considered comparable.
Impacts of irrigation on fisheries in rain‐fed rice‐farming landscapes
Authors: KHOA SOPHIE NGUYEN , LORENZEN KAI , GARAWAY CAROLINE , CHAMSINHG BOUNTHANOM , SIEBERT DARRELL , RANDONE MAURO
Published: September 2005

Expanding irrigation development threatens the productive and diverse fisheries of rain‐fed rice‐farming landscapes. Environmental management of irrigation can minimize negative impacts on fisheries, but its effectiveness is constrained by a lack of reliable information on the nature and magnitude of impacts.

To quantify the impacts of small‐ to medium‐scale irrigation schemes on aquatic habitat availability, fish catches, species richness and ecological composition of fish assemblages in these landscapes, we conducted a field study in Laos. The observational study was replicated at irrigation scheme level, covering 10 weir and 10 dam irrigation schemes paired with non‐impacted control sites.

Weir schemes had no significant impact on aquatic habitat, but caused a significant decline (−36%) in fish catches that was only partly explained by a reduction in fishing effort. Weirs had no effect on species richness, but were associated with a significant increase (+17%) in the relative abundance of omnivores.

Dam irrigation schemes significantly reduced riverine habitat area, and increased lacustrine and dry‐season rice‐field areas. Dams led to a marked redistribution of catch and fishing effort from non‐reservoir habitats into reservoirs, but no overall change in catch or effort occurred. The redistribution reflected a response to fishing opportunities in the reservoir, rather than a loss of productivity in non‐reservoir habitats. No significant impacts were detected on fish species richness or the relative abundance of functional feeding groups.

Overall impacts of irrigation on fisheries were related mostly to changes in fishing effort, rather than ecological effects on the resources. The unexpectedly moderate level of ecological impacts may reflect compensatory effects at the landscape level and the fact that rice fields, which dominated the wet‐season habitat, continued to be managed as rain‐fed deep‐water systems even where dry‐season irrigation had been developed.

Synthesis and applications. Small‐ to medium‐scale irrigation schemes in rain‐fed rice‐farming landscapes have only moderate impacts on fisheries, which remain productive and diverse. Changes in agricultural practices in the wet season are likely to have greater effects on fisheries than dry‐season irrigation.
Comparison of threat and exploitation status in North‐East Atlantic marine populations
Authors: DULVY NICHOLAS K. , JENNINGS SIMON , GOODWIN NICHOLAS B. , GRANT ALASTAIR , REYNOLDS JOHN D.
Published: September 2005

Threat listing of exploited marine species has been controversial because of the scientific uncertainty of extinction risk as well as the social, economic and political costs of management procedures that may be triggered by designation of species as threatened.

We applied three sets of threat criteria to 76 stocks (populations) of 21 exploited marine fish and invertebrate species. Two criteria sets were based on decline rates: World Conservation Union (IUCN A1) and the American Fisheries Society (AFS). The third set of criteria, based on population viability (IUCN E), was assessed using non‐parametric simulation and two diffusion approximation methods.

We compared extinction risk outcomes (threatened or not) against the exploitation status of each stock as reported in fish stock assessments (inside or outside safe biological limits). For each combination of threat and exploitation we assessed the rate of hits, misses and false alarms.

Our analyses suggest that decline rate criteria provide risk categorizations consistent with population viability analyses when applied to exploited marine stocks. Nearly a quarter of the fish and invertebrate populations (n = 18) considered met one or more of the threat criteria.

None of the threat metrics produced false alarms, where sustainably exploited stocks were categorized as threatened. The quantitative IUCN E metrics produced higher hit rates than the decline rate metrics (IUCN A1 and AFS) and all of the metrics produced similar miss rates. However, the IUCN E methods could be applied to fewer stocks (12–14) compared with IUCN A1 decline rate and AFS criteria, both of which could be applied all 76 stocks.

Synthesis and applications. Threat criteria provide warnings of population collapse that are consistent with those provided in fisheries stock assessments. Our results suggest that scientists with different backgrounds and objectives should usually be able to agree on the stocks for which the most urgent management action is needed. Moreover, IUCN A1 decline rate metrics may provide useful indicators of population status when the information needed for full fisheries stock assessment is not available.