bluuebunny/crossref_metadata_2025 huggingface dataset:
Differential Effects of Acute and Chronic Ethanol Exposure on Orexin Expression in the Perifornical Lateral Hypothalamus
Authors: Morganstern Irene , Chang Guo‐Q , Barson Jessica R. , Ye Zhiyu , Karatayev Olga , Leibowitz Sarah F.
Published: March 2010

Background: Recent reports support the involvement of hypothalamic orexigenic peptides in stimulating ethanol intake. Our previous studies have examined the effects of ethanol on hypothalamic peptide systems of the paraventricular nucleus (PVN) and identified a positive feedback loop in which PVN peptides, such as enkephalin and galanin, stimulate ethanol intake and ethanol, in turn, stimulates the expression of these peptides. Recently, orexin (OX), a peptide produced mainly by cells in the perifornical lateral hypothalamus (PFLH), has been shown to play an important role in mediating the rewarding aspects of ethanol intake. However, there is little evidence showing the effects that ethanol itself may have on the OX peptide system. In order to understand the feedback relationship between ethanol and the OX system, the current investigation was designed to measure OX gene expression in the PFLH following acute as well as chronic ethanol intake.

Methods: In the first experiment, Sprague–Dawley rats were trained to voluntarily consume a 2 or 9% concentration of ethanol, and the expression of OX mRNA in the PFLH was measured using quantitative real‐time polymerase chain reaction (qRT‐PCR). The second set of experiments tested the impact of acute oral gavage of 0.75 and 2.5 g/kg ethanol solution on OX expression in the PFLH using qRT‐PCR, as well as radiolabeled in situ hybridization. Further tests using digoxigenin‐labeled in situ hybridization and immunofluorescence histochemistry allowed us to more clearly distinguish the effects of acute ethanol on OX cells in the lateral hypothalamic (LH) versus perifornical (PF) regions.

Results: The results showed chronic consumption of ethanol versus water to dose‐dependently reduce OX mRNA in the PFLH, with a larger effect observed in rats consuming 2.5 g/kg/d (−70%) or 1.0 g/kg/d (−50%) compared to animals consuming 0.75 g/kg/d (−40%). In contrast to chronic intake, acute oral ethanol compared to water significantly enhanced OX expression in the PFLH, and this effect occurred at the lower (0.75 g/kg) but not higher (2.5 g/kg) dose of ethanol. Additional analyses of the OX cells in the LH versus PF regions identified the former as the primary site of ethanol’s stimulatory effect on the OX system. In the LH but not the PF, acute ethanol increased the density of OX‐expressing and OX‐immunoreactive neurons. The increase in gene expression was detected only at the lower dose of ethanol (0.75 g/kg), whereas the increase in OX peptide was seen only at the higher dose of ethanol (2.5 g/kg).

Conclusion: These results lead us to propose that OX neurons, while responsive to negative feedback signals from chronic ethanol consumption, are stimulated by acute ethanol administration, most potently in the LH where OX may trigger central reward mechanisms that promote further ethanol consumption.
Adrenocortical and Pituitary Glucocorticoid Feedback in Abstinent Alcohol‐Dependent Women
Authors: Adinoff Bryon , Best Susan E. , Ye Wen , Williams Mark J. , Iranmenesh Ali
Published: March 2010

Background:  The long‐term ingestion of alcohol diminishes hypothalamic–pituitary–adrenal (HPA) axis reactivity in alcohol‐dependent men, potentially altering future relapse risk. Although sex differences in HPA axis functioning are apparent in healthy controls, disruptions in this system have received little attention in alcohol‐dependent women. In this study, we assessed the basal secretory profile of adrenocorticotropic hormone (ACTH) and cortisol, adrenocortical sensitivity in both the presence and absence of endogenous corticotropic pituitary activation, and feedback pituitary glucocorticoid sensitivity to dexamethasone.

Methods:  Seven women 4‐ to 8‐week abstinent alcohol‐only dependent subjects and 10 age‐matched female healthy controls were studied. All subjects were between 30 and 50 years old, not taking oral contraceptives, and were studied during the early follicular phase of their menstrual cycle. Circulating concentrations of ACTH and cortisol were measured in blood samples collected at frequent intervals from 2000 to 0800 hour. A submaximal dose of cosyntropin (0.01 μg/kg), a synthetic ACTH (1–24), was administered at 0800 hour to assess adrenocortical sensitivity. In a separate session, low‐dose cosyntropin was also administered following high‐dose dexamethasone (8 mg intravenous) to assess adrenocortical sensitivity in the relative absence of endogenous ACTH. In addition, the ACTH response to dexamethasone was measured to determine the pituitary glucocorticoid negative feedback. Sessions were 5 days apart, and blood draws were obtained every 5 to 10 minutes.

Results:  Mean concentrations and pulsatile characteristics of ACTH and cortisol over 12 hours were not statistically different between the 2 groups. Healthy controls had a somewhat higher (p < 0.08) net peak, but not net integrated, cortisol response to cosyntropin relative to the alcohol‐dependent women. There were no significant group differences in either the ACTH or cortisol response to dexamethasone nor in the net cortisol response to cosyntropin following dexamethasone.

Conclusion:  Significant differences in pituitary–adrenal function were not apparent between alcohol‐dependent women and matched controls. Despite the small n, it appears that alcohol‐dependent women do not show the same disruptions in HPA activity as alcohol‐dependent men. These findings may have relevance for gender‐specific treatment effectiveness.
Idiographically Determined Versus Standard Absorption Periods in Alcohol Administration Studies
Authors: Schacht Rebecca L. , Stoner Susan A. , George William H. , Norris Jeanette
Published: March 2010

Background:  Effects of alcohol vary depending on blood alcohol level and limb. Some researchers use standard absorption periods (SAPs) to determine when postdrinking experimental protocols should begin. Others use an idiographically determined absorption period (IDAP) based on criterion breath alcohol concentration (BrAC). We investigated and compared the characteristics of each method.

Methods:  Sixty‐eight social drinkers (47% women) consumed a bolus dose of alcohol intended to raise BrAC to 0.08%. BrACs were recorded every 3 minutes until beginning to descend. Minutes to reach criterion BrAC (0.06%) and between‐subjects postdrinking BrAC variability were analyzed.

Results:  Mean time to reach 0.06% BrAC was 22.9 ± 14.6 minutes. Standard deviations in BrAC were 4 times greater using SAPs compared to IDAPs. Ten percent of participants’ BrAC readings were on the descending limb 30 minutes postdrinking, and 25% were descending at 45 minutes postdrinking.

Conclusions:  IDAPs result in less BrAC variability and may reduce experimental noise relative to SAPs. Experimental control in future alcohol administration studies may be enhanced by the use of IDAPs instead of SAPs.
Same‐Race and Same‐Gender Voting Preferences and the Role of Perceived Realistic Threat in the Democratic Primaries and Caucuses 2008
Authors: Böhm Robert , Funke Friedrich , Harth Nicole S.
Published: March 2010

Previous research has demonstrated the relevance of voters' and candidates' group memberships on voting behavior. We examined the impact of voters' race (Black vs. White) and gender (male vs. female) on voting preferences for either Barack Obama or Hillary Clinton in the Democratic primaries and caucuses of 2008. Study 1 investigated national exit poll data, representative for voters from various U.S. states. Analyses revealed a same‐race and same‐gender voting preference. Confirming the threat hypothesis (Blalock, 1967), same‐race preference among White voters (but not among Black voters) increased with the proportion of Blacks per state. In Study 2, we assessed voting preferences, racial identification, and perceived realistic threat by Blacks among White voters. High racial identification was associated with a stronger same‐race preference. This effect was mediated by perceived realistic threat. We discuss the results with regard to the intergroup threat versus contact hypothesis, and psychological differences between racial majority and minority members.
Inverse Probability of Censoring Weighted Estimates of Kendall's τ for Gap Time Analyses
Authors: Lakhal‐Chaieb Lajmi , Cook Richard J. , Lin Xihong
Published: March 2010

Summary In life history studies, interest often lies in the analysis of the interevent, or gap times and the association between event times. Gap time analyses are challenging however, even when the length of follow‐up is determined independently of the event process, because associations between gap times induce dependent censoring for second and subsequent gap times. This article discusses nonparametric estimation of the association between consecutive gap times based on Kendall's τ in the presence of this type of dependent censoring. A nonparametric estimator that uses inverse probability of censoring weights is provided. Estimates of conditional gap time distributions can be obtained following specification of a particular copula function. Simulation studies show the estimator performs well and compares favorably with an alternative estimator. Generalizations to a piecewise constant Clayton copula are given. Several simulation studies and illustrations with real data sets are also provided.
Alpha‐Tubulin and Small Subunit rRNA Phylogenies of Peritrichs Are Congruent and Do Not Support the Clustering of Mobilids and Sessilids (Ciliophora, Oligohymenophorea)
Authors: GONG YINGCHUN , XU KUIDONG , ZHAN ZIFENG , YU YUHE , LI XUEMEI , VILLALOBO EDUARDO , FENG WEISONG
Published: March 2010

ABSTRACT. Peritrich ciliates have been traditionally subdivided into two orders, Sessilida and Mobilida within the subclass Peritrichia. However, all the existing small subunit (SSU) rRNA phylogenetic trees showed that the sessilids and mobilids did not branch together. To shed some light on this disagreement, we tested whether or not the classic Peritrichia is a monophyletic group by assessing the reliability of the SSU rRNA phylogeny in terms of congruency with α‐tubulin phylogeny. For this purpose, we obtained 10 partial α‐tubulin sequences from peritrichs and built phylogenetic trees based on α‐tubulin nucleotide and amino acid data. A phylogenetic tree from the α‐tubulin and SSU rRNA genes in combination was also constructed and compared with that from the SSU rRNA gene using a similar species sampling. Our results show that the mobilids and sessilids are consistently separated in all trees, which reinforces the idea that the peritrichs do not constitute a monophyletic group. However, in all α‐tubulin gene trees, the urceolariids and trichodiniids do not group together, suggested mobilids may not be a monophyletic group.
A New Flagship Peritrich (Ciliophora, Peritrichida) from the River Rhine, Germany:Apocarchesium arndtin. sp.
Authors: NORF HELGE , FOISSNER WILHELM
Published: March 2010

ABSTRACT.We discovered a free‐living peritrich ciliate with outstanding features in the River Rhine. Its morphology and 18S rRNA gene sequence were studied with standard methods.Apocarchesium arndtin. sp. has several peculiarities. (i) There are ordinary zooids, macrozooids, and microzooids, which form a hemispherical rosette on a discoidal base, the stalk dish, locking the ∼18 μm wide and up to 2 mm long, spirally contracting colony stalk. (ii) The stalk myoneme is connected only to the microzooids. (iii) A rosette contains up to 50 zooids not connected to each other but individually attached to the stalk dish with the scopula. (iv) The ordinary zooids are epistylidid, trumpet‐shaped (∼6:1 length:width), about 180 × 30 μm in size, and have an ellipsoidal macronucleus subapically between oral cavity and dorsal side. (v) The myoneme system of the zooids, which can contract individually, forms a tube‐like structure in the narrow posterior half of the cell. (vi) The silverline pattern belongs to the transverse‐striate type. (vii) The oral apparatus is of usual structure, with kinety 1 of peniculus 3 distinctly shortened proximally. (viii) The 18S rRNA placesA. arndtin. sp. as a distinct lineage nearVorticellaandCarchesium. These data are used to provide an improved diagnosis of the genusApocarchesium. Features (i)–(iii) and the molecular data indicate thatApocarchesiumcould be the type genus of a new peritrich family.
Mechanosynthesis and Thermal Stability of Piezoelectric Perovskite 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 Powders
Authors: Algueró Miguel , Ricote Jesús , Castro Alicia
Published: March 2010

The mechanosynthesis of piezoelectric perovskite 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 (PZN–PT) by direct mechanochemical activation of the constituent oxides has been studied by X‐ray diffraction (XRD) and transmission electron microscopy (TEM). This and the PbO flux method are the only two procedures that have succeeded in synthesizing this phase, which has recently been shown to present very high electromechanical response. The thermal stability of the single perovskite phase powders has been studied by differential thermal analysis/thermogravimetry and by high‐temperature XRD as a function of mechanical activation time and pressure. The phase was found to transform into a pyrochlore type structure at temperatures above 400°C. The transformation presented a significant time dependence, and it was slowed down by increasing mechanical activation time and by the application of pressures by hot pressing. Sintering experiments were accomplished and 85% density, 77% perovskite‐phase ceramics were obtained after heating at 1000°C for 1 h. Hot pressing at this temperature failed to increase the percentage of perovskite phase. Results are discussed, and procedures for obtaining dense single‐phase PZN–PT‐based ceramics with ultrahigh piezoelectricity are proposed.
Synthesis of Dense, High‐Defect‐Concentration B4C through Mechanical Activation and Field‐Assisted Combustion
Authors: Heian E. M. , Khalsa S. K. , Lee J. W. , Munir Z. A. , Yamamoto T. , Ohyanagi M.
Published: March 2010

Dense fine‐grained B4C was synthesized by the spark plasma sintering (SPS) method using mechanically activated elemental powders. Relative densities of up to 95% were achieved. When characterized by X‐ray line broadening methods, the grains of the resulting product were determined to be nanometric in scale. However, transmission electron microscopy (TEM) observations showed the product to be composed of a mixture of fine (nanometric) crystallites and grains in the micrometer range. The TEM images showed a highly defective structure containing a high density of twins. Their presence is the reason for the discrepancy between the X‐ray and TEM results.
Mullite (3Al2O3·2SiO2)–Aluminum Phosphate (AlPO4), Oxide, Fibrous Monolithic Composites
Authors: Kim Dong‐Kyu , Kriven Waltraud M.
Published: March 2010

Mullite–AlPO4 fibrous monolithic composites were fabricated by a co‐extrusion technique using ethylene vinyl acetate (EVA) as a binder. Processing routes such as mixing formulation, extrusion sequence, binder removal cycle, pressing, and sintering procedures are described. An effort to make tougher composites was conducted by modifying the microstructures of the composites. Different kinds of monolithic composites were fabricated by changing the number of filaments, and the composition and thickness of interphase layers, and their microstructural and mechanical properties were characterized. To make the interphase more porous and to facilitate debonding and fiber pullout in the composite, graphite was added as a fugitive “space filler” into the interphase material and then removed. A fibrous monolithic composite with a sintered interphase thickness of 5–10 μm and an interphase composition of 50 vol% graphite and 50 vol% AlPO4 had a three‐point bend strength and a work of fracture of 129 ± 2 MPa and 0.86 ± 0.05 kJ/m2, respectively. This corresponded to 42% of the strength but 162% of the work of fracture when compared with the values for a single‐phase mullite. Two‐layer, mixed 50% two‐layer:50% three‐layer, and three‐layer fibrous monoliths were fabricated and their microstructural and mechanical properties were studied. The difference in the sintering behaviors of the two‐layer and three‐layer composites is described.
Oxidation Resistance of Multiwalled Carbon Nanotubes Coated with Silicon Carbide
Authors: Morisada Yoshiaki , Maeda Masakatsu , Shibayanagi Toshiya , Miyamoto Yoshinari
Published: March 2010

Multiwalled carbon nanotubes (MWCNTs) were coated with a SiC layer using SiO vapor. The growth mechanism of SiC and the oxidation resistance of the SiC‐coated MWCNTs were studied. The growth of the SiC layer was controlled by adjusting the partial pressure of CO2 using carbon felt placed in a crucible. The nanometer‐sized SiC particles were deposited onto the tubes by the reaction between SiO(g) and CO(g). On the other hand, the thin surface of the MWCNTs was converted to the SiC layer when the carbon felt was not used. The oxidation durability of MWCNTs was improved by the SiC coating. MWCNTs were oxidized completely in air at 650°C for 60 min. However, about 90 mass% of the SiC‐coated MWCNTs remained after the same oxidation test.
Microwave‐Assisted Synthesis and Sintering of NZP Compounds
Authors: Vaidhyanathan Balasubramaniam , Agrawal Dinesh K. , Roy Rustum
Published: March 2010

We have identified the high microwave susceptibility of the sodium di‐hydrogen phosphate monohydrate (NHPM), NH2PO4·H2O. This acid phosphate of sodium can be heated to >900°C when exposed to 2.45 GHz microwave radiation. Using NHPM and microwave energy, a novel single‐step synthesis of many important crystalline NZP compounds has been accomplished in a very short time. Interestingly, the combination of microwaves and nonstoichiometric oxide precursors for the preparation of NZP materials is found to reduce the reaction temperatures and enhance the reaction kinetics further. The microwave synthesis method is found to be simple and fast, minimizing the loss of volatile chemical species from the reaction. A microwave‐assisted procedure for the rapid sintering of NZP compounds has also been demonstrated. Densification (>97%) has been achieved in <30 min at sintering temperature much lower than normally required in conventional processes. Finer microstructure and better densification are the main advantages of the microwave sintering in this study.
Fatigue Crack Growth in Ferroelectric Ceramics Driven by Alternating Electric Fields
Authors: Fang Daining , Liu Bin , Sun Chin Teh
Published: March 2010

Electric‐field‐induced fatigue crack growth in ferroelectric ceramic PZT‐5 with precracks was investigated. The experimental results showed that there were two distinct characteristics in the crack growth under electric loading. Under low electric loads, microcracks located ahead of the main crack emerged and grew and, as a result, impeded the growth of the main crack. On the other hand, under high electric loads, microcracks were absent, and the main crack was the only mode of fatigue cracking. The main crack grew macroscopically along the original path perpendicular to the electric field. Microscopically, the crack grew along the grain boundaries and grain breakaway was observed. The crack growth rate was nonlinearly related to the cyclic electric load. Similar to mechanical fatigue, there existed a crack growth threshold in the applied electric‐field amplitude below which the crack ceased to grow. A steady crack growth occurred when the applied electric field exceeded this threshold. An empirical model for crack growth was obtained. Domain‐switching effect and fracture‐mechanics concepts were used to explain the observed crack closure and crack growth under electric loads.
Microwave Dielectric Properties of Low‐Fired ZnNb2O6 Ceramics with BiVO4 Addition
Authors: Wee Sung‐Hun , Kim Dong‐Wan , Yoo Sang‐Im
Published: March 2010

The BiVO4 additive was found effective for low‐temperature firing of ZnNb2O6 polycrystalline ceramics below 950°C in air without a serious degradation in their microwave dielectric properties. Dense BiVO4‐doped ZnNb2O6 samples of a relative sintered density over 95% could be prepared even at 925°C. An optimally processed specimen exhibited excellent microwave dielectric properties of Q·f= 55000 GHz, ɛr= 26, and τf=−57 ppm/°C. With increasing BiVO4 addition up to 20 mol% relative to ZnNb2O6, while the quality factor Q·f was gradually decreased, the relative dielectric constant, ɛr, was linearly increased and the temperature coefficient of resonant frequency, τf, was slightly increased. The variations in Q·f and ɛr are surely attributable to the residual BiVO4 in the ZnNb2O6 matrix. An unexpected slight increase in τf is probably due to the formation of the Bi(V,Nb)O4‐type solid solution.
Delayed Failure at Intermediate Temperatures (600°–700°C) in Air in Silicon Carbide Multifilament Tows
Authors: Forio Philippe , Lavaire Fabien , Lamon Jacques
Published: March 2010

Unexpected failure of Nicalon/SiC composites is observed under low stresses at intermediate temperatures (600°–800°C) in air. This effect has been designated as a nuisance by a few authors. The lifetime of SiC (Nicalon) multifilament tows is investigated in static fatigue in air at temperatures in the range of 600°–700°C. The various features that have been identified suggest that delayed failure under low stresses results from a slow‐crack‐growth mechanism. Analysis of acoustic emission data allows the number of failures during the tests to be determined. Scanning electron microscopy examination of tow fracture surfaces allows typical crack patterns to be identified. A model of delayed failure is proposed. The model is based on the Paris law and on the well‐known model of subcritical crack growth devised by Davidge et al. for ceramics. The model takes into account the statistics of fiber failure. The slow‐crack‐growth constants have been determined from stress‐rupture data. Finally, the model allows satisfactory description of the lifetime of tows and prediction of the lifetime of Nicalon/SiC minicomposites.
Fabrication and Mechanical Properties of Si3N4/Carbon Fiber Composites with Aligned Microstructure Produced by a Seeding and Extrusion Method
Authors: Hyuga Hideki , Jones Mark I. , Hirao Kiyoshi , Yamauchi Yukihiko
Published: March 2010

Si3N4/carbon fiber composites have been produced with and without seeding by an extrusion and sintering process. In both cases the carbon fibers were aligned along the direction of extrusion, but the Si3N4 grains were only aligned in the seeded material. The mechanical properties of the specimens showed anisotropy with respect to the grain alignment, with both strength and toughness being highest in the direction parallel to the extruding direction. In this direction the seeded specimen, where both the Si3N4 grains and the carbon fibers were aligned, showed both higher fracture toughness and higher fracture strength than the nonseeded specimen where only the fibers were aligned.
Thermal Cyclic Fatigue Behavior of Porous Ceramics for Gas Cleaning
Authors: Kitaoka Satoshi , Matsushima Yasushi , Chen Chunhong , Awaji Hideo
Published: March 2010

The thermal shock fatigue resistance of cordierite and SiC filters with a mullite filtration layer was evaluated under simulated reverse cleaning conditions. O‐ring specimens were thermally shocked by cyclically blowing cold air outward through them while they were exposed to high‐temperature flue gas. The calculated values of the tangential tensile stresses induced by the temperature differences between the inner and outer surfaces were found to be largest at the inner surfaces. It was also found that the elastic modulus and the thermal expansion coefficient of the filters affect the magnitude of the thermal stresses more than the thermal diffusivity and thermal transfer area, which were directly related to the microstructure of the filters. Failure of both filters is believed to have initiated at the inner subsurfaces because of the effects of thermal shock. The thermal shock fatigue lifetimes increased as thermal stresses decreased. The fatigue parameters for the SiC and cordierite filters were found to be 41 and 22, respectively. These parameters probably vary over different operating temperature ranges, especially in the case of SiC filters, where changes in their composite microstructures affect their high‐temperature strength.
Notch Sensitivity of Ceramic Composites with Rising Fracture Resistance
Authors: Mattoni Michael A. , Zok Frank W.
Published: March 2010

A theoretical framework is developed for the notched strength of ceramic composites that exhibit rising fracture resistance. It is based on established concepts of crack stability under stress‐controlled loadings. On using a linear representation of the resistance curve (expressed in terms of an energy release rate), straightforward analytical solutions are obtained for the strength as well the amount of stable crack growth preceding fracture and the associated fracture resistance. Calculations are performed for several test configurations commonly used for material characterization, including single‐ and double‐edge‐notched tension, center‐notched tension, and single‐edge‐notched bending. The results reveal salient trends in strength with notch length and specimen geometry. An assessment of the theory is made through comparison with experimental measurements on an all‐oxide fiber composite. Transitions in the degree of notch sensitivity with notch length are identified and explored. The utility of the theoretical results both for rationalizing the trends in measured notched strength and for guiding experimental studies of notch sensitivity is demonstrated.
Creep Viscosity of Vitreous China
Authors: Porte Frédéric , Brydson Rik , Rand Brian , Riley Frank L.
Published: March 2010

Creep in four‐point bend of a set of vitreous china compositions containing different amounts of mullite and quartz has been measured over the stress range 1.5 to 4 MPa at temperatures between 1035°–1100°C. Creep deformation is treated as the flow under load of a viscous liquid‐particulate suspension, and creep rates are related to the measured mullite and quartz contents. Kaolinite relicts, containing the larger proportion of the mullite in the system, are expected to behave as rigid particles and to have a major influence on creep rate. The composition of the primarily feldspathic liquid phase has a lesser influence on creep rate.
Effect of Li2O and PbO Additions on Abnormal Grain Growth in the Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 System
Authors: Fisher John Gerard , Kim Min‐Soo , Lee Ho‐Yong , Kang Suk‐Joong L.
Published: March 2010

Abnormal grain growth in Pb(Mg1/3Nb2/3)O3–35 mol% PbTiO3 (PMN‐35PT) ceramics doped with Li2O and PbO has been investigated. Replacing the PbO dopant with up to 2 mol% Li2O caused an increase in the number of abnormal grains. For the composition containing 2 mol% Li2O and 6 mol% PbO, the amount of abnormal grain growth decreased with increasing sintering temperature. Single crystals of ∼6 mm × 6 mm × 2 mm thickness were grown from the 2 mol% Li2O, 6 mol% PbO‐containing composition via the templated grain growth method. Grain growth behavior with temperature is explained in terms of the effect of Li2O on interface‐reaction‐controlled grain growth and the critical driving force.
Determination of Lattice Parameters of Polytypes in Liquid‐Phase‐Sintered SiC Using the Rietveld Method
Authors: Hernández‐Jiménez Angel , Ortiz Angel L. , Sánchez‐Bajo Florentino , Guiberteau Fernando , Cumbrera Francisco L.
Published: March 2010

Accurate determination of lattice parameters of polytypes in liquid‐phase‐sintered (LPS) SiC by conventional X‐ray powder diffractometry is difficult due to the severe overlap between different Bragg reflections and to the presence of geometrical aberrations. For this reason, results obtained by traditional internal‐standard d‐spacing methods will be in general unrealistic. In this context, the Rietveld method, which is based on the refinement of a structural, profile, and instrumental model, is a more appropriate procedure to determine lattice constants of polytypes in these ceramics. Therefore, in this study we evaluated the accuracy of the results given by the Rietveld method for multiphase mixtures of SiC polytypes, when line broadening is dominated by the crystallite size. The accuracy was found to be remarkable, being sensitive to the number of polytypes but insensitive to the length of the lattice parameters and to the number of geometrical aberrations. In addition, an application to an LPS SiC specimen revealed the usefulness of the Rietveld method to better understand the microstructural evolution during sintering.
Nucleation and Growth of Anatase Crystallites on Cotton Fabrics at Low Temperatures
Authors: Daoud Walid A. , Xin John H.
Published: March 2010

Anatase nanocrystalline titania coatings were produced on cotton fabrics from alkoxide solutions using a low‐temperature sol–gel process under ambient pressure. Titania coatings of the anatase form were obtained via a classical hydrolysis and condensation reaction of titanium isopropoxide that was followed by a boiling water treatment for 180 min. Spectroscopic and microscopic characterizations of the titania thin films showed that the anatase form is predominant throughout the film after the boiling water treatment and that the size of the grains is about 20 nm. The titania coating on fabrics is a promising process for use as an antibacterial photocatalyst in the textile industry.
Method Used to Measure the Thermal Diffusivity of Ceramic Materials
Authors: Treviño‐Cardona Brenda , Gómez‐de‐la‐Fuente Idalia , Colás Rafael
Published: March 2010

A method used to determine the thermal diffusivity of ceramic materials is discussed. This technique uses the readings from at least three equally spaced thermocouples inserted in either powdered or bulk samples of the ceramic material. The method requires that a transient, one‐dimensional heat flow, either by heating or cooling, is established in the sample. The values of thermal diffusivity obtained by the present method yield reasonable results in bulk samples of insulating silica blankets and in samples of powdered magnesia.
Preparation of Anode/Electrolyte Ceramic Composites by Coextrusion of Pastes
Authors: Chen Zhongchun , Takeda Takenobu , Kikuchi Keisuke , Kikuchi Shin‐ichi , Ikeda Keisuke
Published: March 2010

Anode/electrolyte two‐layer ceramic composites for tubular solid oxide fuel cells were prepared through coextrusion of multiple pastes containing a water‐based binder (an aqueous solution of hydroxypropyl methylcellulose). The multibillet extrusion (MBE) technique was found to be effective in achieving the anode/electrolyte composite pipes. Furthermore, it is possible to reduce the wall thickness of both anode and electrolyte layers by raising the extrusion ratio of each layer. The extrusion pressure and binder content required to obtain sound extrudates decreased with an increase in the fraction of nickel oxide in an anode layer. It is feasible to decrease the difference in the sintering shrinkage between the anode and electrolyte layers by incorporating calcined coarse yttria‐stabilized zirconia (YSZ) powder in the electrolyte layer. The incorporation of coarse YSZ powder in an anode is effective in forming a continuous NiO network within the YSZ matrix.
Growth of Pb((Zn1/3Nb2/3)0.91Ti0.09)O3 Single Crystals Using an Allomeric Seed Crystal and Their Electrical Properties
Authors: Fang Bijun , Xu Haiqing , He Tianhou , Luo Haosu , Yin Zhiwen
Published: March 2010

Single crystals of Pb((Zn1/3Nb2/3)0.91Ti0.09)O3 (PZNT 91/9), 28 mm in diameter and 30 mm in length, have been successfully grown using a modified Bridgman technique with an allomeric seed crystal. X‐ray fluorescence analysis (XRFA) measurement confirms that the effect of segregation is not serious. The segregation coefficient k for PbTiO3 content during crystal growth is 0.99, which causes some fluctuation in the composition along the growth direction. The fluctuation of composition and the complicated domain structure cause a variation of electric properties. Dielectric measurement indicates that PZNT 91/9 crystals exhibit an almost normal ferroelectric phase transition at ∼183°C from the tetragonal phase to the cubic phase. In addition, a weak frequency‐dependent ferroelectric‐ferroelectric phase transition is observed at ∼85°C, which is attributed to partial conversion of the rhombohedral phase to a tetragonal phase. The dielectric thermal hysteresis behavior and the existence of polarization above the Curie temperature verify that the phase transitions at ∼85° and 183°C are first order with a slight diffuse character and first order, respectively. It is demonstrated that the effects of segregation can be decreased and the homogeneity of the obtained PZNT 91/9 single crystals can be improved by optimizing growth parameters.
Preparation of Silicon‐Titanium‐Carbon‐Oxygen Fabric/ Mullite Filler/Polytitanocarbosilane Laminates by Polymer Impregnation and Pyrolysis Method
Authors: Hirata Yoshihiro , Hayata Kazunori , Maeda Tomoyuki , Shibuya Masaki
Published: March 2010

A polytitanocarbosilane (PTC, 20–50 mass%)–xylene solution was infiltrated into a porous, laminated woven fabric of 21–33 vol% Si‐Ti‐C‐O fibers including 26–46 vol% mullite powder (filler) and decomposed at 1000°C in an argon atmosphere. This polymer impregnation and pyrolysis method (PIP) was repeated eight times to produce a laminated composite of 68%–85% of theoretical density. The effects of the polymer concentration and the fraction of mullite filler on the densification rate and microstructure of the layered composite were studied. The pseudoductility of the densified composite, as measured using four‐point flexural testing, was caused by buckling after the elastic deformation and was followed by delamination along the direction of the layered fabric. The strength and the energy of fracture were enhanced by controlling the incorporation of mullite filler in the filament yarn (formation of a narrow pore‐size distribution) and densification with a low‐viscosity PTC solution. The composite with a higher strength provided a higher energy of fracture. The maximum energy of fracture reached 22 kJ/m2 in the composite with 330 MPa of strength in four‐point flexure.
Role of Cinnabar in Luster Production
Authors: Pradell Trinitat , Molera Judit , Vendrell Màrius , Pérez‐Arantegui Josefina , Pantos Emmanuel , Roberts Mark. , DiMichiel Marco
Published: March 2010

Ancient documentation referring to the use of cinnabar in the production of luster decorations has recently been corroborated by archaeological findings. However, luster decorations do not show any trace of the use of cinnabar in their composition because the temperatures involved in luster firing (500°–600°C) result in the complete decomposition and volatilization of cinnabar. An in situ x‐ray diffraction experiment was designed to clarify the role of cinnabar in the production of luster decorations. The high‐energy, high‐flux radiation ID15B beamline at the European Synchrotron Radiation Facility was necessary to ensure good time/temperature resolution, penetration, and high‐quality data. Results show that cinnabar acts as a reducing agent for copper because it provides the formation of copper (Cu+) and silver (Ag+) sulfur‐containing phases, and it inhibits the crystallization of metallic silver in the temperature range of interest in luster production. The addition of elemental sulfur also produces these phases, but at temperatures <500°C, which are not adequate for the production of copper‐containing lusters.
Analysis of Ferroelectric Domain Switching in 0.7Pb(Mg1/3Nb2/3)O3·0.3PbTiO3: Heterogeneous Nucleation
Authors: Viehland Dwight D. , Li Jie‐Fan
Published: March 2010

Polarization reversal and domain dynamics were investigated in 0.7Pb(Mg1/3Nb2/3)O3·0.3PbTiO3 using a method of current transients. Investigations were performed as a function of applied electric field. The kinetics of the transients were modeled to a stretched exponential‐type function.
Dielectric Properties and Relaxation in (1−x)BiScO3–xBa(Mg1/3Nb2/3)O3 Solid Solutions
Authors: Kwon Do‐Kyun , Randall Clive A. , Shrout Thomas R. , Lanagan Michael T.
Published: March 2010

The dielectric properties and frequency dispersion associated with a dielectric relaxation were evaluated within the perovskite (1−x)BiScO3–xBa(Mg1/3Nb2/3)O3 solid solution systems (0.7 ≤x≤ 1). With increasing BiScO3, the room‐temperature dielectric permittivity at low frequency (100 Hz) increased up to 115 at x= 0.7, and a dielectric relaxation phenomenon was evident. Relaxation parameters were analyzed using several Arrhenius‐type equations, and the microwave dielectric property measurement using rectangular wave‐guide method enabled confirmation of the extrapolated value of the Arrhenius plot. The result of the microwave dielectric property measurement was also checked with J‐function fitting based on the frequency‐dependent Gaussian distribution of the associated dielectric loss data at low frequency.
Fracture Toughness and Flexural Strength of Chemically Vapor‐Deposited Silicon Carbide As Determined Using Chevron‐Notched and Surface Crack in Flexure Specimens
Authors: Cockeram B. V.
Published: March 2010

Two different techniques used to measure the fracture toughness of silicon carbide (SiC) produced by chemical vapor deposition (CVD) are compared, and the influence of the material growth direction on toughness and flexural strength are evaluated. Fracture toughness values for monolithic CVD SiC are found to be independent of the CVD growth direction and test temperature from ambient to 1100°C with values ranging from 2.8 to 5.5 MPa·m1/2. This isotropic nature is notably different from hot‐pressed α‐SiC and is likely a result of the cubic β‐SiC structure produced by the CVD process and the transgranular fracture mode. The range of fracture toughness results obtained using a chevron‐notched specimen (2.8–4.0 MPa·m1/2) was less than values obtained using a surface crack in flexure method (3.7–5.5 MPa·m1/2), and these differences are statistically significant. These differences can be attributed to difficulties in resolving the true precrack size for the surface crack in the flexure specimen. Flexural strength values for monolithic CVD SiC are found to be isotropic with respect to the CVD growth direction from room temperature to 1090°C, as observed for the fracture toughness values. Flexural strength values measured at 1090°C are significantly higher (69% to 10% higher) than those measured at room temperature, while the modulus measured at 1090°C is less (−25% to −10% lower) than that measured at room temperature. Since the fracture toughness values are independent of temperature between room temperature and 1090°C, the increased flexural strength at elevated temperature is difficult to explain on the basis of classical fracture mechanics and must be influenced by other factors. Surface machining flaws on flexure specimens are shown to produce a 35% to 50% decrease in the flexure strength of monolithic CVD SiC that was quantified using the fracture toughness and flaw‐size data.
Strain Softening and Hardening during Superplastic‐Like Flow in a Fine‐Grained MgAl2O4Spinel Polycrystal
Authors: Morita Koji , Hiraga Keijiro , Kim Byung‐Nam , Suzuki Tohru S. , Sakka Yoshio
Published: March 2010

Superplastic‐like flow in a fine‐grained MgAl2O4polycrystal exhibits strain softening and hardening, which cannot be ascribed to cavity damage and grain growth during deformation, respectively. The softening and hardening can be related to a change in the internal stress, which depends on a decrease and an increase in the density of the intragranular dislocations, respectively, whose motion contributes to the relaxation of stress concentrations exerted through the predominant deformation mechanism of grain‐boundary sliding. In these two regions, the rate of deformation is controlled by the continuous recovery of the dislocations limited by lattice diffusion of the oxygen ions.
Influence of Thermal History on Crystal Nucleation in Silicon Carbide Amorphized with Neon Irradiation
Authors: Aihara Jun , Ishihara Masahiro , Hojou Kiichi , Furuno Shigemi
Published: March 2010

Silicon carbide (SiC) specimens were amorphized with neon ions and annealed at 1273 K via transmission electron microscopy (TEM). Two types of annealing procedures were conducted: (i) continuous annealing for 60 min and (ii) annealing for 5 min, repeated 10 times. TEM observations revealed that crystal nucleation was more apt to occur in the SiC amorphized by repeated annealing than in the continuously annealed SiC.
Rapid Reactive Synthesis and Sintering of Submicron TiC/SiC Composites through Spark Plasma Sintering
Authors: Wang Lianjun , Jiang Wan , Chen Lidong , Bai Shengqiang
Published: March 2010

Submicrometer TiC/SiC composites were fabricated by a rapid reactive sintering process through spark plasma sintering (SPS) technique using the carbon, titanium, and nanosized‐SiC powders without any additive. It was found that the composite could be sintered in a relatively short time (8 min at 1480°C) to 97.9% of theoretical density. After sintering, the phase constituents and microstructures of the samples were analyzed by X‐ray diffraction techniques and observed by scanning electron microscopy. The effect of nanosized and microsized SiC additives on the microstructure of TiC/SiC composites was investigated.
High‐Strength Zirconium Diboride‐Based Ceramics
Authors: Chamberlain Adam L. , Fahrenholtz William G. , Hilmas Gregory E. , Ellerby Donald T.
Published: March 2010

Zirconium diboride (ZrB2) and ZrB2 ceramics containing 10, 20, and 30 vol% SiC particulates were prepared from commercially available powders by hot pressing. Four‐point bend strength, fracture toughness, elastic modulus, and hardness were measured. Modulus and hardness did not vary significantly with SiC content. In contrast, strength and toughness increased as SiC content increased. Strength increased from 565 MPa for ZrB2 to >1000 MPa for samples containing 20 or 30 vol% SiC. The increase in strength was attributed to a decrease in grain size and the presence of WC.
Preparation of Mesoporous Silicon Nitride via a Nonaqueous Sol–Gel Route
Authors: Cheng Fei , Clark Stephen , Kelly Stephen M. , Bradley John S. , Lefebvre Frédéric
Published: March 2010

A silicon diimide gel Si(NH)x(NH2)y(NMe2)z was prepared by an acid‐catalyzed ammonolysis of tris(dimethylamino)silylamine. Pyrolysis of the gel at 1000°C under NH3 flow led to the formation of an amorphous silicon nitride material without carbon contamination. All of the gel and pyrolyzed products exhibited a mesoporous structure with a high surface area and narrow pore‐size distribution. The effective surface area of the pyrolyzed silicon nitride residues decreases with increasing temperature, but the heating rate during pyrolysis has little influence on the surface area and pore‐size distribution of the final mesoporous ceramic Si3N4 products because of the highly cross‐linked structures of the precursor silicon diimide gel.
Nanostructured Dense ZrO2 Thin Films from Nanoparticles Obtained by Emulsion Precipitation
Authors: Woudenberg Fiona C. M. , Sager Wiebke F. C. , ten Elshof Johan E. , Verweij Henk
Published: March 2010

Nonagglomerated spherical ZrO2 particles of 5–8 nm size were made by emulsion precipitation. Their crystallization and film‐forming characteristics were investigated and compared with nanosized ZrO2 powders obtained by sol–gel precipitation. High‐temperature X‐ray diffraction indicated that the emulsion‐derived particles are amorphous and crystallize at 500°C into tetragonal zirconia, which is stable up to 1000°C. Crystallite growth from 5–20 nm occurred between 500°–900°C. Films of 6–75 nm thickness were made by spreading, spin coating, and controlled deposition techniques and annealed at 500°–600°C. The occurrence of t‐ZrO2 in the emulsion‐precipitated powder is explained by the low degree of agglomeration and the corresponding low coarsening on heating to 500°–800°C, whereas the agglomerated state of the sol–gel precipitate powder favors the occurrence of the monoclinic form of zirconia under similar conditions.
Consolidation of Nanostructured β‐SiC by Spark Plasma Sintering
Authors: Yamamoto Takeshi , Kitaura Hidetoshi , Kodera Yasuhiro , Ishii Takashi , Ohyanagi Manshi , Munir Zuhair A.
Published: March 2010

Nanostructured β‐SiC, with crystallite size in the range of 5–20 nm in agglomerates of 50–150 nm, was formed by reactive high‐energy ball milling and consolidated to a relative density of 98% by sintering at 1700°C without the use of additives. X‐ray line broadening analysis gave a crystallite size of 25 nm, while transmission electron microscopy observations showed the crystallite size to be in the range of 30–50 nm. Evidence demonstrating the role of a disorder–order transformation in the densification process is provided by changes in the diffraction peak patterns and in the integral width with temperature.
High Surface‐Area Ceria Aerogel
Authors: Thundathil Mary A. , Lai Wei , Noailles Liam , Dunn Bruce S. , Haile Sossina M.
Published: March 2010

Ceria (CeO2) aerogels with high surface area and high porosity have been prepared. Ce‐methoxyethoxide diluted in excess methoxyethanol was slowly hydrolyzed to yield a gel, which was then supercritically dried in CO2. Both as‐synthesized and annealed aerogels were examined by X‐ray powder diffraction, infrared spectroscopy, scanning electron microscopy, and BET surface area and pore‐size analyses. Thermal analysis of the as‐synthesized gel showed it to contain only ∼5 wt% residual organics, which were removed by 300°C under oxygen. The unheated ceria aerogel was crystalline and exhibited a specific surface area of 349 m2/g with average pore diameter of ∼21.2 nm and 90% porosity. Heat treatment led to a reduction of porosity and pore size, as would be expected, but the extremely narrow pore‐size distribution of the aerogel was retained.
In Situ Cube‐Corner Indentation of Soda–Lime Glass and Fused Silica
Authors: Morris Dylan J. , Cook Robert F.
Published: March 2010

Indentation fracture with a cube‐corner diamond pyramid on soda–lime silicate glass and fused silica is investigated during the entire indentation cycle in both silicone oil and ambient‐air environments. Radial cracks form immediately on loading in all cases. The two‐component, elastic‐contact + elastic‐plastic mismatch (residual) stress field model that has been used successfully to describe radial crack evolution at Vickers indentations fails to describe the fracture response with the cube‐corner. The amplitudes of both elastic‐contact and residual stress‐intensity factors as deduced from these cube‐corner experiments are up to a factor of 10 greater than have been previously observed.
Crack‐Tip Toughness Measurements on a Sintered Reaction‐Bonded Si3N4
Authors: Njiwa Alain B. Kounga , Fett Theo , Rödel Jürgen , Quinn George D.
Published: March 2010

An evaluation of measurements of crack opening displacements (CODs) on a commercial sintered reaction‐bonded silicon nitride (SRBSN) was performed. To determine the intrinsic fracture toughness of this material, a new evaluation method is presented, which takes into account not only the near tip CODs, but the CODs of the complete crack profile. The method is applied on through‐thickness cracks in bend bars and contrasted to CODs of Vickers radial cracks. A crack‐tip toughness of ∼1.7 MPa·m1/2 is obtained.