bluuebunny/crossref_metadata_2025 huggingface dataset:
Intramolecular hydrogen bonds in thiolato‐, sulfenato‐, and sulfinato‐Co(III) complexes
Authors: Aranyosiová Monika , Vollárová Ol'ga , Benko Ján , černušák Ivan
Published: October 2005

The formation of intramolecular hydrogen bonds is investigated for transition metal complexes in infrared (IR) spectroscopy experiments and B3LYP/LANL2DZ computational study. Three series of complexes are considered: [Co(en)2XCH2CH2NH2]2+, [Co(en)2XCH2CH(COO)NH2]+, and [Co(en)2XCH2COO]+ (en = NH2CH2CH2NH2, XS, SO, SOO). Both experimental and theoretical results confirm the formation of the intramolecular hydrogen bond between the NH2 group of the ethylene diamine ligand and the oxygen of the COO group, as well as between the NH2 and oxygen added to coordinated sulfur. In the second and third series, the interplay between SO (or SOO) and COO results in different patterns of red‐shifted bands in model IR spectra. The relationship between strength of the intramolecular hydrogen bond and some molecular parameters (H…O distance, IR red shift, size of the quasi‐ring) is discussed. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006
Evolution of the state of fish stocks in the Northeast Atlantic within a precautionary framework, 1970–2003: a synoptic evaluation
Authors: Garcia S.M. , De Leiva Moreno J.I.
Published: October 2005

The state and trajectory of some of the stocks assessed by ICES in the North Atlantic in the period 1970–2003 are synoptically represented on a single system of representation of fishing mortality and biomass with precautionary reference points used as limits and thresholds. The results indicate that for nearly 30 years, the status of the stocks in relation to the precautionary reference points has been degrading in terms of spawning biomass and excess fishing mortality, driving most resources down close to and often beyond those reference points. The situation seems to have improved during the past decade, with some exceptions, as shown by progressive shift of the mean position of the stocks away from excessive mortality (since the early 1990s) and, after a time-lag, away from low biomass (since the early 2000s). The proposed representation system sticks to the reference points and value judgements used in the ICES context, but could be used with any equivalent precautionary system of representation.
The Endoscopic Management of Cubital Tunnel Syndrome
Authors: HOFFMANN R. , SIEMIONOW M.
Published: October 2005

The overall success rate of surgical interventions for cubital tunnel syndrome is reported to be within 80% to 90% (Szabo, 1999). The discussion, however, whether to perform in situ nerve decompression or anterior transposition continues. In this paper, we present the results of our endoscopic approach to in situ cubital tunnel release, its rationale, clinical and anatomical indications and a detailed description of the technique.
The Unity of the Fact
Authors: Read Stephen
Published: October 2005

What binds the constituents of a state of affairs together and provides unity to the fact they constitute? I argue that the fact that they are related is basic and fundamental. This is the thesis of Factualism: the world is a world of facts. I draw three corollaries: first, that the Identity of truth is mistaken, in conflating what represents (the proposition) with what is represented (the fact). Secondly, a popular interpretation of Wittgenstein's Tractatus, due to Steinus, whereby false propositions are taken to picture non-existent state of affairs, cannot be right. For Wittgenstein, propositions had two poles, and a proposition and its negation picture the same fact. Finally, the metaphysics of modal realism must be wrong, for there are no non-actual states of affairs to constitute any world other than the actual world.
The diet and ecological role of giraffe (Giraffa camelopardalis) introduced to the Eastern Cape, South Africa
Authors: Parker D. M. , Bernard R. T. F.
Published: October 2005

With an increase in the popularity of wildlife ranching in southern Africa has come the introduction of non‐native (extralimital) mammalian herbivores. Financial gain has arguably been at the forefront of these introductions, with little or no assessment of the ecological consequences. The diet of three populations of introduced giraffe Giraffa camelopardalis was assessed by direct observation in the Eastern Cape Province, South Africa between January 2002 and October 2003, as the first step towards understanding the ecological role played by giraffe in the region. Similar to the diet of giraffe within their native range, a deciduous species from the genus Acacia (Acacia karroo) was the most important species in the diet. Giraffe in the Eastern Cape Province, however, consumed more evergreen species than those within their native range. The relative lack of deciduous species in the Eastern Cape Province provides a probable explanation for such a result. Seasonal variation in the consumption of the most important species in the diet was evident with members of the genus Rhus being more important in the winter months. This was attributed to the deciduous nature of A. karroo. The potential for giraffe to have a detrimental effect on the indigenous vegetation is discussed. We conclude that the study provides a much‐needed list of plant species threatened by giraffe browsing in a region where the vegetation is thought to have evolved in the absence of such a browser.
Body size and growth in tropical small mammals: examining variation using non‐linear mixed effects models
Authors: Griffiths A. D. , Brook B. W.
Published: October 2005

A diverse small mammal fauna inhabits the tropical savannas of Kakadu National Park in northern Australia. A detailed long‐term capture–mark–recapture study was conducted to estimate body growth parameters in relation to intrinsic and extrinsic factors that may influence them. Three non‐linear growth increment functions were compared to determine which one best represented the general growth patterns of nine small mammal species at Kapalga. The von Bertalanffy growth increment function provided the best fit to a pooled species dataset. Hierarchical mixed‐effects models were then used to examine variation in body size asymptote and growth and account for non‐independence of observations. Model selection was based on the Kullback–Leibler information theoretic approach. As expected, the body size growth constant was correlated to body mass at Kapalga, and body size sexual dimorphism was evident in most species. Difference in body growth constant was only evident in Isoodon macrourus, where females showed accelerated growth. Three of the four marsupial species exhibited either temporal (annual) and spatial (catchment level) variation in body size asymptote, whereas rodent species showed none. There was no clear influence of other extrinsic factors such as fire treatment, rainfall or habitat on body size asymptote or growth rate constant. Our results suggest that body growth is largely controlled by intrinsic factors for each species such as gender in small mammal species at Kapalga. Change in body size and growth caused by human‐induced changes to the landscape from factors such as altered fire regimes is unlikely to be substantial for tropical small mammals in northern Australia.
The Effects of Self-Image Threat on the Judgment of Out-Group Targets
Authors: Florack Arnd , Scarabis Martin , Gosejohann Stefanie
Published: October 2005

The authors argue that individuals may restore their self-esteem by derogating a member of an out-group, but only if they identify with the in-group and hold negative attitudes towards the out-group. In two experiments, the self-image of participants was either enhanced or threatened. Afterwards, participants evaluated an out-group target. The results provided broad support for the assumption that intergroup attitudes and in-group identification moderate the impact of self-image threat on the judgment of an out-group member. Self-image threat led to a more negative evaluation only in participants with negative out-group attitudes. It resulted in a more positive evaluation when participants held positive out-group attitudes and identified less with the in-group.
Integration of radiative transfer into satellite models of ocean primary production
Authors: Smyth T. J. , Tilstone G. H. , Groom S. B.
Published: October 2005

A major goal of ocean color observations from space is the determination of phytoplankton primary productivity (PP) and hence oceanic carbon uptake. Results of a PP model implemented to use satellite‐derived fields of chlorophyll, photosynthetically available radiation (PAR) and sea‐surface temperature (SST) are presented. The model gave a global estimate of PP of around 57 Gt C yr−1 and gives a low RMS (0.16) when compared with in situ data. However, as the model's in‐water light field parameterization only considers attenuation by pure water and chlorophyll, PP is overestimated in case II waters where other optically important constituents such as colored dissolved organic matter (CDOM) and suspended particulate matter (SPM) are also present. This paper develops a novel technique to determine PP by coupling a radiative transfer code, which allows the inclusion of CDOM and SPM, to the original photosynthesis model. For the global calculations, a look‐up table has been generated using chlorophyll, CDOM, SST, PAR and day length as inputs. The resultant 364,500 element look‐up table has been applied to data from the Sea‐viewing Wide Field‐of‐view Sensor (SeaWiFS) and Moderate‐Resolution Imaging Spectroradiometer (MODIS). PP retrievals are improved in case II waters and global estimates are reduced to between 52 and 55 Gt C yr−1.
Gravitational and tectonic forces controlling postcollisional deformation and the present‐day stress field of the Alps: Constraints from numerical modeling
Authors: Jiménez‐Munt I. , Garcia‐Castellanos D. , Negredo A. M. , Platt J. P.
Published: October 2005

We perform numerical modeling to investigate the mechanisms leading to the postcollisional tectonic evolution of the Alps. We model the lithospheric deformation as a viscous thin sheet with vertically averaged rheology and coupled with surface mass transport. The applied kinematic boundary conditions simulate the convergence between the Adria indenter and the European foreland during the last 35 Myr. Model predictions of elevation, lithospheric structure, erosion/sedimentation pattern and vertical axis rotation are compared with observations of the planform shape of the chain, topography, crustal thickness, distribution of rock exhumation and sediment thickness, and paleomagnetic rotations. Thickening of the lithosphere in the Alpine region is shown to be highly sensitive to the assumed viscosity law, to the strength contrasts between the different regions and to the surface mass transport. Modeling results indicate that the large‐scale deformation of the Alps during the postcollisional phase is mainly controlled by accommodation of convergence in a weak orogenic zone caught between a nearly rigid Adria plate and a strong European foreland. Modeling of the present‐day stress field shows that (1) the present rotation of Adria is responsible for the change of extension direction from strike‐perpendicular in the western Alps to strike‐parallel in the east and (2) the strike‐perpendicular extension observed in the western Alps is likely due to lateral variations of gravitational potential energy. The results suggest a NNE shift of about 700 km of the Euler pole of Adria relative to Europe from its mean position during postcollisional deformation to the present day.
Biomass burning as a source of dissolved iron to the open ocean?
Authors: Guieu Cécile , Bonnet Sophie , Wagener Thibaut , Loÿe‐Pilot Marie‐Dominique
Published: October 2005

While the Mediterranean region is typified by frequent summer fires, the 2003 heat wave that hit Europe, and France in particular, made this season longer causing devastating fires. Aerosol sampling performed in the French Riviera between August and September 2003 indicated that iron concentrations in 2003 were significantly higher than in previous years. Continuous pyrogenic emissions are suspected to be the cause of high Fe concentrations. When these particles were dissolved in seawater, 2% of the total iron content was found in solution. This amount could be significant for the water column on a regional scale. Indeed, these fires might explain the observed dissolved iron enrichment of the surface mixed layer (+0.4 nM) measured in the Ligurian Sea during August. In contrast to a locally significant effect, pyrogenic inputs have little impact on the global Fe budget since they represent at most 10% of desert dust inputs.
Changes in precipitation characteristics over North America for doubled CO2
Authors: Chen Ming , Mao Huiting , Talbot Robert , Pollard David
Published: October 2005

We conducted two 10‐year climate simulations for North America that correspond to present‐day CO2 (1991–1999) and future conditions with doubled CO2 (2090–2099). Our study focused on changes in precipitation characteristics using comparisons of model simulations with observations from recent decades exhibiting a predominance of cool and warm periods. The predicted trends were strikingly similar to observations and suggest that heavy precipitation events (>32 mm day−1) will become more prevalent in the U.S. under increased CO2. Moreover, precipitation in the future should become more episodic and convectively driven than at present with larger daily amounts. Our results point to an increased prevalence of drying and flooding conditions across the U.S. at the end of the 21st century.
Characteristics of the interplanetary coronal mass ejections in the heliosphere between 0.3 and 5.4 AU
Authors: Wang C. , Du D. , Richardson J. D.
Published: October 2005

We identify and characterize interplanetary coronal mass ejections (ICMEs) observed by spacecraft in the solar wind, namely Helios 1 and 2, PVO, ACE, and Ulysses, which together cover heliocentric distances from 0.3 to 5.4 AU. The primary identification signature used to look for ICMEs is abnormally low proton temperatures. About 600 probable ICMEs were identified from the solar wind plasma and magnetic field data from these spacecraft. We use these events to study the radial evolution of ICMEs between 0.3 and 5.4 AU, mainly in a statistical sense. The occurrence rate of ICME approximately follows the solar activity cycle. ICMEs expand as they move outward since the internal pressure is generally larger than the external pressure. The average radial width of ICMEs increases with distance. ICMEs expand by a factor of 2.7 in radial width between 1 and 5 AU. The radial expansion speed of ICMEs decreases with distance and is of the order of the Alfvén speed. The density and magnetic field magnitude decrease faster in ICMEs, which fall off with distance R as R−2.4 and R−1.5, respectively, than in the ambient solar wind; however, the temperature decreases as R−0.7, slightly less rapid than in the ambient solar wind. These results are consistent with previous findings with relatively limited data coverage. We also use a one‐dimensional MHD model to investigate the radial expansion of the ICMEs and find that the radial expansion speed is of the order of the Alfvén speed, consistent with the observations.
Teleportation schemes in infinite dimensional Hilbert spaces
Authors: Fichtner Karl-Heinz , Freudenberg Wolfgang , Ohya Masanori
Published: October 2005

The success of quantum mechanics is due to the discovery that nature is described in infinite dimension Hilbert spaces, so that it is desirable to demonstrate the quantum teleportation process in a certain infinite dimensional Hilbert space. We describe the teleportation process in an infinite dimensional Hilbert space by giving simple examples.
T
dependence of vibrational dynamics of water in ion-exchanged zeolites A: A detailed Fourier transform infrared attenuated total reflection study
Authors: Crupi Vincenza , Longo Francesca , Majolino Domenico , Venuti Valentina
Published: October 2005

In order to explore the influence of cation substitution on the vibrational dynamics of water molecules in zeolites, the evolution of structural properties of the O–H stretching band of water in fully hydrated Na–A and Mg-exchanged A zeolites has been studied, for different percentages of induced ion exchange, by Fourier transform infrared attenuated total reflection spectroscopy as a function of temperature. The differences revealed in the O–H stretching band shapes have been accounted by fitting the spectra as a sum of four components, corresponding to water molecules exhibiting different types of hydrogen bonding. The dependencies of the relative intensities, peak wave numbers, and bandwidths of the resolved components on temperature and Mg2+ content have been discussed. Evidence of the “structure-maker” role played by a zeolitic surface on physisorbed water, systematically enhanced by increasing the percentage of induced ion exchange, is given in the whole explored temperature range.
Hardness and softness reactivity kernels within the spin-polarized density-functional theory
Authors: Chamorro Eduardo , De Proft Frank , Geerlings Paul
Published: October 2005

Generalized hardness and softness reactivity kernels are defined within a spin-polarized density-functional theory (SP-DFT) conceptual framework. These quantities constitute the basis for the global, local (i.e., r-position dependent), and nonlocal (i.e., r and r′-position dependents) indices devoted to the treatment of both charge-transfer and spin-polarization processes in such a reactivity framework. The exact relationships between these descriptors within a SP-DFT framework are derived and the implications for chemical reactivity in such context are outlined.
Evolution of basal plane dislocations during 4H-silicon carbide homoepitaxy
Authors: Zhang Z. , Sudarshan T. S.
Published: October 2005

A method based on the combination of molten KOH etching and reactive ion etching was developed to track dislocations from 4H-silicon carbide homoepilayer to the substrate. The conversion of basal plane dislocations (BPDs) to threading edge dislocations (TEDs) was found to occur at the epilayer/substrate interface. The BPDs with dislocation lines parallel (or approximately parallel) to the off-cut direction may propagate as BPDs into the epilayer, while those with dislocation lines forming large angles (>10°) with the off-cut direction will get converted to TEDs. A model is proposed to explain the observations.
Temperature dependence of the mechanical properties of tetrahedrally coordinated amorphous carbon thin films
Authors: Czaplewski David A. , Sullivan J. P. , Friedmann T. A. , Wendt J. R.
Published: October 2005

The complete elastic properties of tetrahedrally coordinated amorphous carbon (ta-C) thin films have been measured in the temperature range of 300–873K. Flexural and torsional mechanical oscillators were fabricated from ta-C, and using the resonant frequency of the oscillators as a function of temperature, we calculated the temperature-dependent Young’s and shear moduli (658±24 and 271±6.6GPa, at 300K, respectively). From these values, we calculated the bulk modulus, Poisson’s ratio, and the elastic stiffness and compliance constants as a function of temperature. In addition, the temperature dependence of the coefficient of thermal expansion of ta-C was determined using a wafer curvature technique.
Barrierless self-assembly of Ge quantum dots on Si(001) substrates with high local vicinality
Authors: Sutter P. , Sutter E. , Vescan L.
Published: October 2005

In Ge heteroepitaxy on vicinal Si(001), miscut by 4.8° toward [100], pyramid-shaped faceted quantum dot islands (“huts”) form continuously from individual (105) facets on a wetting layer of coexisting (105) and (001) segments. Via this barrierless kinetic route the first three-dimensional islands rapidly form wherever there are substantial local gradients along ⟨100⟩ in-plane directions.
Controlled growth of well-faceted zigzag tin oxide mesostructures
Authors: Huang Lisheng , Pu Lin , Shi Yi , Zhang Rong , Gu Benxi , Du Youwei , Wright Stuart
Published: October 2005

Reproducibly high-yield growth of zigzag fibers and well-faceted nanobelts of SnO2 was achieved via tuning the reactant vapor. The investigation of the morphological evolution via scanning electron microscopy and transmission electron microscopy hints that the formation of the zigzag SnO2 fiber is based on the pregrowing SnO2 nanobelt. The elucidation of the growth mechanism should provide a fully controlled route for reproducibly high-yield growth of zigzag fibers of SnO2 and give some valuable hints to synthesis other zigzag mesostructures. Optical characterizations of these structures show very weak defect-related emissions.
Controlling secondary atomization during drop impact on hot surfaces by polymer additives
Authors: Bertola V. , Sefiane K.
Published: October 2005

The effect of small amounts of a polymer additive (200 parts per million polyethylene oxide) on the impact dynamics of liquid droplets on heated surfaces is studied experimentally for Weber numbers between 20 and 100, and wall temperatures ranging from 150 to 350 °C. The additive is found to oppose the scattering of secondary droplets from the free surface of the liquid, which can be observed if the wall temperature is not sufficiently high to sustain a continuous vapor layer between the impacting drop and the hot surface. Therefore, the critical temperature value for which secondary atomization disappears, also known as dynamic Leidenfrost temperature, is much lower for drops of a dilute polymer solution than for drops of pure solvent. However, the different behaviors of the two fluids suggest that for dilute polymer solutions the expression “dynamic Leidenfrost temperature” may not be appropriate, because the additive inhibits secondary atomization even if the vapor layer is unstable.
FOREIGN OWNERSHIP, WAGES, AND WAGE CHANGES IN U.S. INDUSTRIES, 1987–92
Authors: FELICIANO ZADIA M. , LIPSEY ROBERT E.
Published: October 2005

The authors construct a data set by industry by state by ownership for establishments in the United States using 1987 and 1992 U.S. Census and Bureau of Economic Analysis matched data to investigate the relationship between foreign ownership and wages. They find evidence that foreign‐owned establishments pay higher wages in manufacturing, retail trade, and other relatively low‐skill industries, but not in other higher‐skill industries. A growth in the fraction of employment in foreign establishments was not significantly associated with an increase in overall wages. There is no evidence of a wage spillover to domestic establishments. (JEL J3, F2)
Microstructure and Reactions of SiCw‐Reinforced Alumina with Ag‐Cu‐In‐Ti
Authors: Park Eun‐Sung , Lannutti John J. , Cawley James D.
Published: October 2005

Brazing experiments were performed at 750°C for 2 h between Ag–Cu–In–Ti alloy and SiCw/Al2O3. The first clearly nonbraze layer consists of an oxide layer of metallic composition 33Ti–31Al–22Cu–14Si. Areas adjacent to the SiC whiskers were of different composition. A thin, continuous layer on the alumina portion of the composite appears to be γ‐TiO. The SiC whiskers are preferentially consumed and undergo reductions in diameter of approximately 40%. Observed “knobby” whisker morphologies may be related to SiC stacking faults, η‐type phases detected near the Ag–Cu eutectic portion of the joint appear to consist of Ti‐Cu‐Al‐Si‐O and Ti3Cu3O.
Microstructure and Grain Boundary Structure of Na+‐Diffused (Sr,Ca)TiO3 Capacitor‐Varistor Ceramics
Authors: Zou Qing , Meng Zhongyan
Published: October 2005

The microstructure of (Sr,Ca)TiO3 capacitor‐varistor materials has been investigated by employing electron microscopy techniques (TEM, STEM, HREM, EDX, and EPA). The material is found to contain (Sr,Ca)TiO3 grains (∼30 μm) having perovskite crystal structure with domains, a Na+‐diffused layer at the grain boundaries which is dependent on thermal diffusion conditions, and multiple‐grain junctions in which the TinO2n–1 Magneli phase coexists with an amorphous intergranular phase. In addition, wider grain boundaries (10–30 nm), thin grain boundaries (∼1 nm), and clean grain boundaries which are free from intergranular phase were observed, and the effects of different grain boundaries on the diffusion of Na+are discussed.
Flaw‐Tolerance and R‐Curve Behavior of Liquid‐Phase‐Sintered Silicon Carbides with Different Microstructures
Authors: Lee Seung Kun , Kim Do Kyung , Kim Chong Hee
Published: October 2005

β‐SiC powder containing 6 wt% A12O3 and 4 wt% Y2O3 as sintering additives was pressureless sintered at 2000°C for 1 h (AYE‐SiC) and 3 h (AYP‐SiC). AYE‐SiC consisted of an equiaxed grain structure and AYP‐SiC exhibited a micro‐structure with platelike grains as a result of grain growth related to β→α phase transformation during sintering, R‐curve behavior and flaw tolerance for these silicon carbides were evaluated by the indentation‐strength technique. For comparison, the R‐curve behavior of conventional sintered, boron‐ and carbon‐doped SiC (SS‐SiC) was evaluated. AYE‐SiC and AYP‐SiC exhibited rising R‐curve behavior with toughening exponents of m= 0.042 and m= 0.135, respectively. AYP‐SiC exhibited better flaw tolerance and more sharply rising R‐curve behavior than AYE‐SiC. The more sharply rising R‐curve behavior and the better flaw tolerance of AYP‐SiC were attributed mainly to grain bridging of crack faces by platelike grains. Because of the high degree of transgranular fracture, SS‐SiC exhibited a flat R‐curve despite a microstructural feature with platelike grains.
Formation and Properties of Ln‐Si‐O‐N Glasses (Ln = Lanthanides or Y)
Authors: Ohashi Masayoshi , Nakamura Kazuo , Hirao Kiyoshi , Kanzaki Shuzo , Hampshire Stuart
Published: October 2005

Homogeneous Y‐Si‐O‐N glasses containing 15 or 20 eq% nitrogen (N) were prepared from compositions with Y/Si ratios in the vicinity of that of the lowest eutectic point on the Y2O3–SiO2 phase diagram. The liquidus on the phase diagram shifted toward lower temperatures by incorporation of N. The density, the elastic moduli, and the glass transition temperature of the Y‐Si‐O‐N glasses increased with incorporation of N. This is due to the closer packing of atoms in the glasses by the substitution of N, which is in three‐fold coordination with Si, for O which is in two‐fold coordination, and the stronger covalent nature of the Si–N bond compared with the Si–O bond. The coefficient of thermal expansion of the Y‐Si‐O‐N glasses increased with increasing Y content, because the discontinuity of the glass network developed with increasing nonbridging anions by the introduction of Y. In contrast, the glass transition temperature and the elastic moduli increased with Y content due to the high coordination of Y for O, and the relatively high cationic field strength of Y. Furthermore, the effect of cationic field strength on properties of Ln‐Si‐O‐N glasses (Ln = lanthanides or Y) is discussed.
Characterization of Silicon Carbide–Silicon Nitride Composite Ultrafine Particles Synthesized Using a CO2 Laser by Silicon‐29 Magic Angle Spinning NMR and ESR
Authors: Suzuki Masaaki , Hasegawa Yoshihisa , Aizawa Masayuki , Nakata Yoshinori , Okutani Takeshi , Uosaki Kohei
Published: October 2005

The structure of silicon carbide–silicon nitride (SiC–Si3N4) composite particles synthesized using a CO2 laser was studied by magic angle spinning nuclear magnetic resonance (MAS‐NMR) and electron spin resonance (ESR). The structure around Si atoms changed by introducing N. C atoms around Si were substituted by N atoms, and N‐rich configurations around Si atoms increased stepwise as the N content increased. The low N content composite particles consisted of mainly SiC phase containing dissolved N. N atoms were partly present in β‐SiC microcrystal and partly in the grain boundary layer in the particle. N atoms were tetrahedrally surrounded by four Si atoms in β‐SiC microcrystal and were trivalent state bonded to three Si atoms in the grain boundary layer. The high N content particles consisted of SiC, Si3N4, and amorphous phases, whose amount depended on N content.
Silicon Carbide Platelet/Silicon Carbide Composites
Authors: Mitchell Tyrone , De Jonghe Lutgard C. , MoberlyChan Warren J. , Ritchie Robert O.
Published: October 2005

α‐silicon carbide platelet/β‐silicon carbide composites have been produced in which the individual platelets were coated with an aluminum oxide layer. Hot‐pressed composites showed a fracture toughness as high as 7.2 MPa·m1/2. The experiments indicated that the significant increase in fracture toughness is mainly the result of crack deflection and accompanying platelet pullout. The coating on the platelets also served to prevent the platelets from acting as nucleation sites for the α‐ to β‐phase transformation, so that the advantageous microstructure remains preserved during high‐temperature processing.
Preparation of Silicon Nitride Whiskers from Diatomaceous Earth: I, Reaction Conditions
Authors: Mizuhara Yukako , Noguchi Masao , Ishihara Tatsumi , Takita Yusaku
Published: October 2005

Whiskers and powder of silicon nitride were prepared by the carbothermal reduction and nitridation of diatomaceous earth in the presence of flowing N2 and NH3. The optimum temperature for the formation of Si3N4 whiskers was 1350°C and the yield reached almost 20% after 24 h. The α‐Si3N4 content decreased with increasing nitridation temperature. Yields of the whiskers were dependent on NH3 concentration and the total gas feed rate. The maximum yield of inside whiskers was obtained for a 25 vol% NH3/N2 mixture, while the maximum quantity of outside whiskers was produced for 75 vol% NH3/N2. The sum of the yield of the inside and outside whiskers increased with decreasing total gas feed rate. However, no nitridation of SiO2 was observed at a feed gas rate below 0.18 mmol·min−1. The yield of the inside whiskers increased gradually with increasing reaction time up to 36 h, whereupon a constant value was attained. Although the amount of outside whiskers produced was relatively small, the quantity seemed to increase until 60 h.
low‐Temperature Sinter Forging of Nanostructured Y‐TZP and YCe‐TZP
Authors: Boutz Michel M. R. , Winnubst Louis , Burggraaf Antonie J. , Naue Marco , Carry Claude
Published: October 2005

Compacts of ultrafine Y‐TZP and YCe‐TZP powders have been sinter forged under constant load at low temperatures (1100°–1200°C). The application of a uniaxial load leads to a strong reduction in sintering time, which in combination with the virtual absence of dynamic grain growth makes it possible to effectively limit grain growth. Nanostructured (grain size 100 nm) TZP with high relative densities (90%‐93%) could thus be produced by sinter forging under 84 MPa at 1100°C. The contributions of both creep and densification to the dimensional changes of the sinter‐forging samples have been analyzed. A strong reduction of the flaw concentration was observed in sinter‐forged materials as compared to freely sintered ones.
The Evolutionary Process during Pyrolytic Transformation of Poly(N‐methylsilazane) from a Preceramic Polymer into an Amorphous Silicon Nitride/Carbon Composite
Authors: Laine Richard M. , Babonneau Florence , Blowhowiak Kay Y. , Kennish Richard A. , Rahn Jeffrey A. , Exarhos Gregory J. , Waldner Kurt
Published: October 2005

The pyrolytic evolution of poly(N‐methylsilazane), –[H2SiN‐Me]x–, from preceramic polymer to ceramic product is followed by heating samples of the partially cross‐linked polymer, in 200°C increments, from ambient temperature to 1400°C. The intermediate products are characterized by chemical analysis, diffuse reflectance Fourier transform IR spectroscopy (DRIFTS), Raman spectroscopy, and29Si and13C magic‐angle spinning (MAS) solid‐state NMR. Spectro‐scopic characterization indicates that the 1400°C pyrolysis products are amorphous silicon nitride mixed with amorphous and graphitic carbon (as determined by Raman spectroscopy), rather than silicon carbide nitride, as expected based on the presence of up to 20 mol% retained carbon. Efforts to crystallize the silicon nitride through heat treatments up to 1400°C do not lead to any crystalline phases, as established by transmission electron microscopy (TEM) and small‐area electron diffraction (SAD). It appears that the presence of free carbon, along with the absence of oxygen, strongly inhibits crystallization of amorphous silicon nitride. These results contrast with the isostructural poly‐(Si‐methylsilazane), –[MeHSiNH]x–, which is reported to form silicon carbide nitride on pyrolysis.
Raman Spectroscopic Studies on the Formation Mechanism of Hydrous‐Zirconia Fine Particles
Authors: Matsui Koji , Suzuki Hajime , Ohgai Michiharu , Arashi Haruo
Published: October 2005

The Raman spectra of hydrous‐zirconia fine particles produced by the hydrolysis of various ZrOCl2 solutions were investigated. The Raman spectra of hydrous zirconia synthesized at HCl concentrations below 1 mol/L were similar to those of monoclinic, crystalline ZrO2; those of hydrous zirconia synthesized at HCl concentrations greater than 1 mol/L showed a crystal structure change. The line width of the Raman bands increased with increasing H+ ion concentration. Analyzing the relationship between Raman band width and particle size revealed that the primary particle size of hydrous zirconia was controlled by the H+ and Cl− ions, because these ions interfered with the polymerization in a hydrolysis reaction. Based on the experimental results, the formation mechanism for primary particles of hydrous zirconia was determined.
Estimation of Bridging Interactions for Natural Cracks from Bending Strength of Coarse‐Grained Al2O3
Authors: Fett Theo , Munz Dietrich
Published: October 2005

Several ceramic materials show R‐curve effects which in the past were investigated mainly with specimens containing artificial macrocracks. This paper describes how the R‐curve effects caused by bridging interactions between the crack surfaces will influence the strength of specimens with natural crack populations. Calculations in terms of averaged stress intensity factors were performed to describe the development of surface cracks from the initial size up to the size at failure. As a consequence of bridging interactions, deviations from the expected straight line in the Weibull representation of strength will occur even under the assumption that the initial crack size is Weibull‐distributed. A least‐squares procedure allows the bridging stresses to be estimated from bending strength measurements.
Initial Failure Maps for Fibrous CMC Laminates
Authors: Dvorak George J. , Sejnoha Michal
Published: October 2005

A simple micromechanics‐based procedure is used to evaluate initial failure maps for brittle composite laminates under combined in‐plane loads and temperature changes. The maps are derived from local stresses in the fiber, matrix and at their interfaces, and from selected magnitudes of the respective strengths. In a particular loading plane or space, the maps indicate the damage‐free load range of the laminate, and the source of likely initial failure by fiber or matrix cracking, or by fiber debonding. An application to Al2O3/MoSi2 laminates with unidirectional and (0/±45)slayups is presented. In this system, the thermal stresses are very small in the 1200°–20°C range; hence laminate failure is dominated by mechanical loads. Propensity to fiber debonding appears to limit the load magnitudes that can be safely applied to the angle‐ply laminate.
Fine‐Grained Silicon Nitride Ceramics Prepared from β‐Powder
Authors: Mitomo Mamoru , Hirotsuru Hideki , Suematsu Hisayuki , Nishimura Toshiyuki
Published: October 2005

Fine β‐powder with an average particle size of 0.28 μm was prepared by grinding and centrifugal sedimentation of sub‐micrometer β‐powder. Fine‐ and uniform‐grained ceramics were fabricated from the powder by hot pressing. The average grain size of the ceramic was 0.21 μm. It was shown that this kind of microstructure was desirable for the matrix of in situ composite. It was also shown that the ceramics could be superplastically deformed at a temperature as low as 1500°C.
Zirconia Gels in Concentrated NaOH
Authors: Pavlik Robert S. , Klein Lisa C. , McCauley Ronald A.
Published: October 2005

The sol‐gel process was used to produce zirconia powders that were pressed into compacts. The powders were synthesized from zirconium n‐propoxide, diluted in propanol, and hydrolyzed with molar ratios of water either l‐to‐l or lo‐to‐l. Zirconia compacts produced in this manner were soaked in 1N NaOH to simulate a membrane cleaning process, and their weight loss was recorded. Zirconia samples with a higher weight fraction of tetragonal phase exhibited less weight loss than samples with more monoclinic phase. The weight fraction of the tetragonal phase was controlled by synthesis conditions and tiring temperature.
Structural Analysis of Orthorhombic Hafnia by Neutron Powder Diffraction
Authors: Ohtaka Osamu , Yamanaka Takamitsu , Kume Shoichi , Hara Naoki , Asano Hajime , Izumi Fujio
Published: October 2005

The crystal structure of orthorhombic HfO2 synthesized at 600°C and 6 GPa was investigated by a time‐of‐flight neutron powder diffraction experiment. Rietveld analysis of these data revealed that the space group of this phase is Pbca. The refined lattice parameters are a0= 1.00177, b0= 0.52276, and c0= 0.50599 nm. The structure is derived from a distorted fluorite (CaF2) structure by a b‐glide parallel to the a‐axis. The hafnium atom is in seven‐fold coordination. The structure of orthorhombic HfO2 is found to be the same as that of an orthorhombic ZrO2, which occurs under high pressure above 3 GPa.
Nucleation of Solid‐State Reactions between Nickel Oxide and Aluminium Oxide
Authors: Kotula Paul G. , Carter C. Barry
Published: October 2005

The initial stages of the solid‐state reaction between high‐quality thin films of nickel oxide and single‐crystal aluminum oxide have been investigated. Thin films were grown on specially cleaned and annealed basal‐plane (0001) alumina substrates by pulsed‐laser deposition. The thin‐film reaction couples were then heat‐treated in air at 1080° and 1100°C for different times in order to induce the formation of the nickel aluminate spinel. The reaction couples were characterized in cross section by high‐resolution scanning electron microscopy and conventional transmission electron microscopy. The films of nickel oxide consisted of two twin variants with a common {111} plane, parallel to the basal plane of alumina, but rotated by 60° or 180° about the 〈111〉 direction normal to that plane. The spinel nucleated where the twin boundaries in the nickel oxide film met the alumina substrate and contained the same twin variants as the original NiO film.
Effect of SiC Submicrometer Particle Size and Content on Fracture Toughness of Alumina–SiC “Nanocomposites”
Authors: Levin Igor , Kaplan Wayne D. , Brandon David G. , Layyous Albir A.
Published: October 2005

A simple model was developed which describes the effect of SiC submicrometer particles on the fracture toughness of alumina–SiC “nanocomposites.” This effect was attributed to the change in the fracture mode observed in alumina on adding SiC submicrometer particles, which was suggested to be a result of both matrix weakening and grain boundary strengthening. The model suggests that the increase in fracture toughness should be obtained only for small additions (less than 5 wt%) of SiC.
Sintering of Al2O3–TiC Composite in the Presence of Liquid Phase
Authors: Chae Ki‐Woong , Kim Doh‐Yeon , Niihara Koichi
Published: October 2005

The results obtained from the sintering of Al2O3–50TiC (in weight percent) composite in the temperature range from 1650° to 1800°C with addition of Y2O3 are presented. Densification is accelerated by the formation of liquid at temperatures above 1750°C, and 99% of theoretical density can be achieved by vacuum sintering at 1800°C for 15 min. The liquid presented at the sintering temperature is crystallized to YAG (Y3Al5O12) during cooling.
Effect of Temperature on Toughness Curves in Alumina
Authors: Xu Hockin H. K. , Ostertag Claudia P. , Krause Ralph F.
Published: October 2005

The effect of temperature on fracture strength and toughness curves (T‐curves) in the short‐crack region of a polycrystalline alumina was studied. The indentation‐strength technique was used to measure strength and T‐curve behavior in the temperature range of 25° to 1300°C. Grain‐localized crack bridging resulted in improved flaw tolerance and rising T‐curves in this alumina. Both strength and toughness were observed to decrease with increasing temperature. A theoretical grain‐bridging model was used to calculate the T‐curves and fit to the experimental data. This allowed the evaluation of the temperature dependence of important bridging parameters.
Some Effects of Eutectic Liquid under Reducing Conditions in the Alumina–Tin Dioxide–Tin Composite System
Authors: Morgan Peter E. D. , Housley Robert M.
Published: October 2005

Tin dioxide (SnO2, cassiterite) is one of the few simple oxides that do not react with alumina below a eutectic at 1620°C in air. Consequently it has been of interest for weak interfacial coatings on alumina for ceramic‐matrix composites (CMCs). However, at low oxygen potentials in the Al–Sn–O ternary system an oxidic eutectic liquid containing dissolved tin appears at 1045°C and readily attacks the alumina; this bears some resemblance to liquid phenomena encountered in the Ag‐HTSC (high‐temperature superconductor) systems.
Effect of Seeding on Phase Development, Densification Behavior, and Microstmcture Evolution in Mullite Fabricated from Microcomposite Particles
Authors: Sacks Michael D. , Lin Yung‐Jen , Scheiffele Gary W. , Wang Keyun , Bozkurt Nazim
Published: October 2005

An investigation was carried out concerning the effect of mullite seed particles on phase development, densification behavior, and microstructure evolution in powder compacts prepared with silica/alumina microcomposite particles. The incorporation of ∼2 wt% seed particles in the microcomposite powder compacts had relatively little effect on densification, but resulted in significant decreases in the temperature for mullite formation and the grain sizes in mullitized samples. Samples could be sintered to almost full density and subsequently converted to mullite with average grain sizes ≤0.4 μm at temperatures in the range of 1300°‐1400°C. The available evidence indicated that mullite formation occurred primarily by nucleaton and growth in the siliceous matrix phase.
Nonstoichiometry and Its Effect on the Magnetic Properties of a Manganese‐Zinc Ferrite
Authors: Inaba Hideaki
Published: October 2005

The effect of oxygen nonstoichometry on physical and magnetic properties of a Mn‐Zn ferrite has been studied by using annealed samples under various oxygen pressures and temperaure. The dependence of oxygen nonstoichiometry7 on disaccommodation and Fe2+ content changed at the stoichiometric composition, and the lattice parameter became maximum at the stoichiometric composition. These results suggest that Mn‐Zn ferrites have two different defect structures: cation vacancies in cation‐deficient regons and oxygen vacancies in anion‐deficient regions. Initial permeability was maximum and power loss was minimum at the stoichiometric composition, suggesting he importance of the number of point defects for the magnetic properties.
Synthesis of KTiOPO4 (KTP) Thin Films Using Metallo‐organics
Authors: Hirano Shin‐Ichi , Yogo Toshinobu , Kikuta Ko‐Ichi , Noda Ken‐Ichi , Ichida Masao , Nakamura Arao
Published: October 2005

Crack‐free and highly transparent KTiOPO4 (KTP) thin films were synthesized by the sol‐gel method using a homogeneous precursor solution prepared from (“BuO)2‐P(O)(OH), Ti(OEt)4, and KOEt in EtOH. Precipitated powders from the solution crystallized directly to KTP above 550°C. Polycrystalline KTP thin films were obtained at 600°C on various substrates. On NdAlO3(100) substrates, KTP films with (101) and (240) preferred orientations were formed at 600°C. KTP films on glass substrates showed a refractive index of 1.75 and an absorption edge of 350 nm. KTP films exhibited the second harmonic generation of the 532 nm light on irradiaton with 1064 nm light.
Sliding Wear of Oxide Ceramics at Elevated Temperatures
Authors: Senda Tetsuya , Drennan John , McPherson Reg
Published: October 2005

Sliding wear tests of sintered alumina and mullite consistently showed that the wear loss significantly decreased at 800°C and above by an order of magnitude. Microscopy of the room‐temperature wear surfaces revealed a feature suggesting material removal by brittle fracture. Microscopy of the wear surface at 1000°C revealed that the immediate vicinity of the wear surface consisted of a very fine grain size polycrystalline structure. The zone below this consisted of heavily deformed grains containing dense dislocation networks forming a cellular structure. The results suggest that, at high temperatures, dynamic recrystallization at the wear surface forms the fine grain size structure which suppresses further material removal.
Measurement of Elastic Moduli from the Impact Sound of Engineering Ceramics and Composites at Elevated Temperatures
Authors: Sakata Masaru , Kimura Koji , Mizunuma Akiko
Published: October 2005

A simple instrumentation system is developed for determining the elastic moduli of engineering ceramics and their composites from the sound produced by the impact of a sphere on a specimen which is suspended by thin wires or ceramic threads in a furnace. The natural frequencies of the flexural and torsional vibration modes are measured from the impact noise by using a fast Fourier transform analyzer. Elastic moduli are then computed from those frequencies by using Timoshenko's beam theory and also Saint‐Venant's torsion theory. The validity of the measurementmethod is demonstrated by room‐temperature tests on ceramic and metallic specimens of known elastic moduli. SiAION and Al‐Al2O3 composites are tested at elevated temperatures up to 900°C. It is shown that the Young's and shear moduli of the materials tested decrease with an increase in temperature, while Poisson's ratio remains almost constant.
Microstructure of Silicon Carbide/Carbon Composites and Relationships with Mechanical Properties
Authors: Bourrat Xavier , Turner Kristofer S. , Evans Anthony G.
Published: October 2005

Three different 2‐D SiC/C composites, analyzed by TEM, have mechanical performances directly controlled by the interfacial structure resulting from processing. Localized attachment of the fibers to a brittle matrix constituent is shown to be responsible for composite weakening by impeding interface debonding and sliding. Moreover, the particulate phase used in the matrix is found to have a strong influence. There is a consequent sensitivity of composite strength to the particulate properties. Finally, it is demonstrated that the hindrance of debonding and sliding caused by the brittle matrix phase can be suppressed by using a C fiber coating.