bluuebunny/crossref_metadata_2025 huggingface dataset:
A quantitative and highly sensitive luciferase-based assay for bacterial toxins that inhibit protein synthesis
Authors: Zhao Luyi , Haslam David B
Published: September 2005

Inhibition of protein synthesis is a common mechanism by which bacterial and plant toxins injure human cells. Examples of toxins that inhibit protein synthesis include shiga toxins ofEscherichia coli, diphtheria toxin,Pseudomonasexotoxin A and the plant toxin ricin. In order to facilitate studies on toxin pathogenesis and to enable screening for inhibitors of toxin action, a quantitative and highly sensitive assay for the action of these toxins on mammalian cells was developed. The cDNA encoding destabilized luciferase was cloned into an adenoviral expression plasmid and a high-titre viral stock was prepared. Following transduction of Vero cells, luciferase expression was found to be linear with respect to viral multiplicity of infection. Luciferase expression by as few as 10 cells was readily detected. Treatment of transduced cells with either cycloheximide or shiga toxin resulted in a decrease in luciferase activity, with a half-life ranging from 1 to 2 h. Inhibition of luciferase expression was evident at toxin concentrations as low as 1 pg ml−1. The assay was adapted for use in 24-, 96- and 384-well plates, enabling rapid processing of large numbers of samples. Using this approach, susceptibility of Vero, Hep2, Chang, A549, COS-1 and HeLa cells to three different toxins was determined. These results demonstrate that the luciferase-based assay is applicable to the study of numerous cell types, is quantitative, highly sensitive and reproducible. These features will facilitate studies on pathophysiology of toxin-mediated diseases and allow high-throughput screening for inhibitors of cytotoxicity.
Metallo-β-lactamase IMP-1 in Providencia rettgeri from two different hospitals in Japan
Authors: Shiroto Katsuaki , Ishii Yoshikazu , Kimura Soichiro , Alba Jimena , Watanabe Kiwao , Matsushima Yoshiko , Yamaguchi Keizo
Published: September 2005

In 2002, 495 indole-positive proteae strains were isolated from patients at 60 hospitals in Japan. Nine indole-positive proteae strains had reduced susceptibility to imipenem (MIC ⩾ 8 μg ml−1) and were identified asProvidencia rettgeriby BD Phoenix. Eight of the nineProv. rettgeriisolates were confirmed as metallo-β-lactamase producers by the double-disc synergy test. All the metallo-β-lactamases were classified as IMP-1 by PCR and DNA sequence analysis. TheseblaIMP−1genes were encoded in the integron structure on conjugative plasmids. These plasmids could transfer fromProv. rettgericlinical isolates toEscherichia coliML4903 at a frequency between 1.5 × 10−5and 5.5 × 10−7. The eightblaIMP-positive strains were isolated from two hospitals, and showed two different PFGE patterns, two different integron structures and two different incompatibility groups, which corresponded to the two hospitals. These results strongly suggest the possibility of nosocomial infections byblaIMP−1-producingProv. rettgeriisolates.
Gene expression profiling in single cells from the pancreatic islets of Langerhans reveals lognormal distribution of mRNA levels
Authors: Bengtsson Martin , Ståhlberg Anders , Rorsman Patrik , Kubista Mikael
Published: October 2005

The transcriptional machinery in individual cells is controlled by a relatively small number of molecules, which may result in stochastic behavior in gene activity. Because of technical limitations in current collection and recording methods, most gene expression measurements are carried out on populations of cells and therefore reflect average mRNA levels. The variability of the transcript levels between different cells remains undefined, although it may have profound effects on cellular activities. Here we have measured gene expression levels of the five genes ActB, Ins1, Ins2, Abcc8, and Kcnj11 in individual cells from mouse pancreatic islets. Whereas Ins1 and Ins2 expression show a strong cell–cell correlation, this is not the case for the other genes. We further found that the transcript levels of the different genes are lognormally distributed. Hence, the geometric mean of expression levels provides a better estimate of gene activity of the typical cell than does the arithmetic mean measured on a cell population.
Modulation of retrieval processing reflects accuracy of emotional source memory
Authors: Smith Adam P.R. , Henson Richard N.A. , Rugg Michael D. , Dolan Raymond J.
Published: October 2005

There is considerable evidence that encoding and consolidation of memory
are modulated by emotion, but the retrieval of emotional memories is not well
characterized. Here we manipulated the emotional context with which
affectively neutral stimuli were associated during encoding, allowing us to
examine neural activity associated with retrieval of emotional memories
without confounding the emotional attributes of cue items and the retrieved
context. Using a source memory procedure we were also able to compare how
retrieval processing was modulated when the emotional encoding context was
recollected or not. An interaction between emotional encoding context and
accuracy of source memory revealed that successful retrieval of emotional
context was associated with activity in left amygdala, and a left
frontotemporal network including anterior insula, prefrontal cortex and
cingulate. In contrast, when contextual retrieval was unsuccessful, items
encoded in emotional contexts elicited enhanced activity in right amygdala and
a right-lateralized network that included extrastriate visual areas. These
findings indicate distinct effects of emotion on successful and unsuccessful
retrieval of source information, including lateralization of amygdala
responses.
Occupational protein contact dermatitis  from shiitake mushroom and demonstration of shiitake‐specific immunoglobulin E
Authors: Aalto‐Korte Kristiina , Susitaival Päivikki , Kaminska Renata , Mäkinen‐Kiljunen Soili
Published: September 2005

Shiitake are popular edible mushrooms all over the world, and eating raw shiitake may lead to relatively common ‘shiitake dermatitis’ or toxicodermia. Workers involved in shiitake cultivation and marketing have distinct occupational respiratory and skin diseases unrelated to ‘shiitake dermatitis’. There are no previous reports of protein contact dermatitis (PCD) from shiitake, and there is only 1 report of shiitake‐specific immunoglobulin (Ig) E. We report 2 shiitake growers who developed work‐related eczematous eruption on their hands. Both of the patients had small prick test reactions to fresh shiitake, and specific IgE to shiitake was detected in their sera by immunospot. One of the patients had a large prick test reaction to dry shiitake and also a positive wheal reaction to fresh shiitake in an open application test. Neither of the patients had noticed any symptoms of contact urticaria at work. Both of the patients had immediate IgE‐mediated allergy to shiitake, and the diagnosis of occupational PCD was made. There are no commercial in vitro tests for shiitake‐specific IgE. Tests for immediate allergy are important when shiitake contact dermatitis is investigated.
Nickel‐elicited systemic contact dermatitis from a peripheral intravenous catheter
Authors: Raison‐Peyron N. , Guillard O. , Khalil Z. , Guilhou J.‐J. , Guillot B.
Published: September 2005

Nickel‐elicited systemic contact dermatitis is a well‐known entity, although it is far less common than allergic contact dermatitis. In most of the cases, the main way of nickel administration is oral. Clinical manifestations are miscellaneous including pompholyx, diffuse exanthema, flexural dermatitis or baboon syndrome. Systemic nickel dermatitis induced by venous catheters is very uncommon, but it is probably underdiagnosed. We report here 2 patients with diffuse recurrent maculopapular rash corresponding to nickel‐elicited systemic contact dermatitis. They were both perfused during the last episode with the assistance of a peripheral polyurethane venous catheter during or just before the cutaneous eruption. At the base of the catheter, there was a small metallic eyelet on which dimethylglyoxime test was positive, indicating a release of nickel. Then, we measured nickel release in normal use conditions and found high nickel levels, although the manufacturer denied that nickel could be released. This diagnosis is important to know because such exanthema often occurred during postoperative or postpartum period. Its frequency is probably underestimated because it is often considered as a cutaneous drug reaction. To our knowledge, only 2 cases have been reported in the literature.
Patch testing with patients' own cosmetics and toiletries – results of the IVDK*, 1998–2002
Authors: Uter Wolfgang , Balzer Christina , Geier Johannes , Frosch Peter J. , Schnuch Axel
Published: September 2005

Patch test results with products brought in by the patients collected by the members of the Information Network of Departments of Dermatology (IVDK) between 1998 and 2002 were analysed. 5911 patients were patch tested with their own cosmetics and toiletries during this period. The 34 082 single test preparations applied to these 5911 patients were manually assigned to 1 of 26 categories, based on the EU Classification Annex I to 76/768/EEC, which had been further refined. The leave‐on product category most commonly tested was ‘creams, emulsions, lotions, gels and oils for the skin’ (n = 3621 tested, n = 312 positive). The rinse‐off product type most commonly tested was ‘bath and shower preparations’ (n = 1333 tested, n = 71 positive). In one‐third of patients tested positive to these products, no other positive test result was observed. In the remainder, positive reactions to the fragrance mix, Myroxylon pereirae resin, methyldibromo glutaronitrile, (chloro‐)methylisothiazolinone, 2‐bromo‐2‐nitropropane‐1,3‐diole and further ingredients of cosmetics and toiletries were more common than in product‐negative patients. However, in view of the potential for false‐positive reactions mainly to rinse‐off products, the results must be interpreted with caution. In conclusion, testing of patients' own products can be regarded as efficient and safe, if in accordance with current recommendations.
The relation between the localization of foot dermatitis and the causative allergens in shoes: a 13‐year retrospective study
Authors: Nardelli A. , Taveirne M. , Drieghe J. , Carbonez A. , Degreef H. , Goossens A.
Published: September 2005

The purpose of this retrospective study was to test whether the initial pattern of clinical presentation of shoe dermatitis could indicate the causative allergen(s) and to estimate the odds on foot dermatitis in patients with a positive patch test versus those with a negative patch‐test result. Between 1990 and 2002, 8543 patients were patch tested with the standard series (and additional allergens, if appropriate). Of them, 1168 (14%) had been referred because of foot dermatitis and 474 of these patients (5.5% of the total group) presented a positive reaction to one or more substances related to shoes. We found that 6 standard allergens in the male group and 8 standard allergens in the female group were statistically significant for the shoe dermatitis group. The data showed a relationship between the distribution pattern of the foot lesions and most of the allergens. These results have clinical applications since the gender of the patients and the localization of the foot eruptions can, indeed, indicate what allergen is involved.
Colourants in transferable picture tattoos for the skin
Authors: Rastogi Suresh Chandra , Johansen Jeanne Duus
Published: September 2005

Transferable picture tattoos for the skin are popular among children. There is however very little knowledge about the colourants that may be present in the picture tattoos and thus of the risk of contact allergic reactions. In the present investigation, 36 picture tattoos were analysed for the content of 129 organic colourants listed in the Cosmetic Directive, to which these products should comply as they are used on the skin. Only 11 of the cosmetic colourants could be identified in the analysed samples. Allergenic potential of 7 of these colourants (CI 15850, CI 11920, CI 45220, CI 75300, CI 13015, CI 45100 and CI 15525, maximum concentration 35–4479 p.p.m.) was evaluated on the basis of published scientific data. Only scarce information regarding contact allergy to these substances was found in the available literature. Most information in the literature regarding contact allergy has concerned CI 75300, curcumin, which is reported to have caused a few cases of contact allergy as a colourant in food or in disinfectants used prior to surgery. In no case, allergic reactions to any of the colourants have been verified from transferable picture tattoos. On the basis of this investigation, the risk of allergic reactions from the colourants in the transferable picture tattoos seems to be limited.
Generalized dermatitis due to codeine. Cross‐sensitization among opium alkaloids
Authors: Rodríguez Ángel , Barranco Ruth , Latasa Margarita , De Urbina Juan J. Ortiz , Estrada Juan Luis
Published: September 2005

Opium alkaloids can cause immunological reactions. Cross‐sensitization among them must be considered in these situations.
Active‐Filler‐Controlled Pyrolysis of Preceramic Polymers
Authors: Greil Peter
Published: September 2005

Manufacturing of bulk ceramic components from materials in the system Si‐Me‐C‐N‐O (Me = Ti, Cr, V, Mo, Si, B, CrSi2, MoSi2, etc.) from preceramic organosilicon polymers ‐ such as poly(carbosilanes), poly(silazanes), or poly(siloxanes) ‐ has become possible by incorporating reactive filler particles into the liquid or solid polymer pre‐cursor. During pyrolytic decomposition of the polymer matrix, the filler particles react with carbon from the polymer precursor or nitrogen from the reaction gas atmosphere to form new (oxy)carbide or (oxy)nitride phases embedded in a nanocrystalline Si‐O‐C(‐N) matrix. The selective expansion encountered in the filler phase reaction can be used to compensate for the polymer shrinkage upon pyrolytic conversion. The formation of a transient pore net‐work between 400° and 1000°C is governed by the polymer decomposition as well as the filler particle reaction kinetics. Thus, the properties of the oxycarbonitride composite materials can be tailored by controlling the microstructures of the polymer‐derived matrix phase, the filler network, and the residual porosity. Near‐net‐shape forming of bulk ceramic components, even with complex geometry, is possible, making novel applications of polymer‐derived bulk materials in biomedical, electrical, and mechanical fields highly interesting.
New Approach to Selective Semiconductor Gas Sensors Using a de‐Biased pn Heterocontact
Authors: Hikita Kazuyasu , Miyayama Masaru , Yanagida Hiroaki
Published: September 2005

The complex impedance of a CuO/ZnO oxide semiconductor heterocontact was studied by applying a dc bias voltage in a mixture of CO or H2 (4000 ppm) in air between 250° and 400°C. The frequency dependence of reactance showed a minimum peak, and the absolute value of the reactance and the frequency giving the peak both changed in a different manner, depending on the presence of a reducing gas of either CO and H2, and also the dc bias. Sensing properties could be tuned to detect both CO and H2 gases in air or to detect only H2 gas in air, by selecting the measuring frequency and the applied dc bias at 400°C. Additional resistance and capacitance specific to the ambient gases were introduced to the interface impedance of the semiconductors, and then were estimated from impedance measurements. Tunable gas sensing was possible when the product of the resistance and the capacitance components in the interface had varying values, dependent on gas species and dc bias. This paper proposes this new method of tunable gas sensing that uses the complex impedance characteristics of a heterocontact. In addition, the mechanisms of the tuning function are discussed.
Effect of Silica on the Nonoxidative Thermal Degradation of an Acrylic Binder
Authors: Ai Jiu , Phegley Lisa L. , Christen Gert , White Robert L.
Published: September 2005

The nonoxidative thermal decomposition of a polymer binder containing methacrylate and acrylate functionalities is studied by using pyrolysis‐GC/MS, pyrolysis‐GC/FT‐IR, TGA‐MS, and variable‐temperature diffuse reflectance FT‐IR coupled with mass spectrometry (VT‐DRIFT‐MS). At temperatures ranging from 200° to 300°C, polymer pendant groups react with each other, releasing alcohols and water. At higher temperatures (ca. 350°C), the polymer decomposes, yielding ethylene glycol methacrylate and ethylene glycol dimethacrylate as major products. The presence of silica does not significantly alter the polymer degradation product distribution or the temperatures at which pendant group elimination reactions and thermolysis occur. However, silica that was previously heated to 1000°C catalyzes pendant group reactions. KBr exhibits an even greater catalytic effect on these reactions and also affects the temperature at which the major decomposition step occurs.
Effect of Grain Size on Scratch Interactions and Material Removal in Alumina
Authors: Xu Hockin H. K. , Jahanmir Said , Wang Yushu
Published: September 2005

Dramatic effects of scratch interactions on material removal are observed in alumina. A series of parallel scratches are made in aluminas with different grain sizes to investigate the influence of scratch interactions on the material removal process in abrasive machining. The separation distance between the two scratches and the normal load are varied and subsurface microfracture and damage modes are examined to assess the mechanisms of material removal. A very small amount of material is removed when the separation distance between the two parallel scratches is large or when the two scratches completely overlap. However, at intermediate distances the volume of material removed increases dramatically as a result of the interactions between the two scratches. The maximum amount of material removed and the corresponding distance between the two scratches are found to depend strongly on the grain size and the load. Observations of surface and subsurface damage reveal that grain dislodgement is the predominant mechanism of material removal, irrespective of the grain size. The relation between grain size, scratch interactions, and the material removal process in grinding and abrasive machining of ceramics is discussed in terms of the short‐crack toughness of ceramics.
Modification of αAI2O3 Platelet/ZrO2 Matrix Interface by Epitaxial Growth of β‐AI2O3 on the α‐AI2O3
Authors: Huang Xue‐Ning , Kuo Chu Kun , Nicholson Patrick S.
Published: September 2005

An epitaxial β‐alumina crystal growth method was used to modify α‐AI2O3 platelet surfaces before inclusion as a reinforcing phase in partially stabilized zirconia (3Y‐TZP). The as‐grown surface phase was Na‐β″‐AI2O3. This was converted to Ca‐β″‐AI2O3 by ion exchange, as the latter is more temperature‐stable at composite sintering temperatures. The conditions of formation, thermal stability, and chemical compatibility of these interfacial phases were examined. α‐AI2O3 platelets with Ca‐β″‐AI2O3 film were incorporated into 3Y‐TZP. The β″‐AI2O3/ZrO2 interface was found to promote platelet debonding and pullout, thus enhancing the α‐AI2O3 platelet/crack interactions during the fracture process.
Preparation and Characterization of NTC Thermistors: Nickel Manganites Doped with Lithium
Authors: Sarrión Maria Luisa Martínez , Morales Manuel
Published: September 2005

Oxides of the form NixMn3‐x O4 present properties that make them useful as NTC thermistors. Nickel manganites doped with lithium were synthesized by two methods: insertion with n‐BuLi and reaction of nickel‐manganese formates with lithium formate. XPS and XRD studies showed that both procedures led to oxides with spinel structure, although with different cation distributions. Dilatometry established that a cationic reordering took place on manganites doped by insertion with n‐BuLi during sintering. SEM mapping studies showed that a segregation on grain boundaries took place, leading to an increase in Mn content and a decrease in nickel on the particle surface. Finally, electrical studies showed the nickel manganites doped with lithium, NixMn3‐x‐yLiyO4, had similar resistivities and sensitivity indexes to nickel manganites, NixMn3‐xO4, but higher electrical stability.
High‐Temperature Mixed Oxidation of Nitride‐Bonded Silicon Carbide in Oxidizing Gas Mixtures Containing 2% Cl2
Authors: Park Chan , McNallan Michael J.
Published: September 2005

Nitride‐bonded silicon carbide ceramics have lower processing costs than many other SiC‐based ceramics and adequate properties for use as high‐temperature heat exchangers in oxidizing environments. Silicon nitride has much better resistance to attack by chlorine at temperatures above 900°C than silicon carbide. When nitride‐bonded silicon carbide ceramics are exposed to gas mixtures containing 2% Cl2 and small amounts of oxygen in this temperature range, the SiC is selectively chlorinated, leaving behind a porous matrix of silicon nitride. The rate of corrosion is controlled by a combination of interfacial kinetics at the surfaces of the SiC grains and transport of volatile species through the silicon nitride skeleton. In more oxidizing environments, the rate of chlorination is suppressed by the formation of a protective SiO2 film. In highly oxidizing environments at temperatures in excess of 1200°C, the formation of volatile chloride reaction products at the interface between the SiC and the passivating SiO2 layer causes bubbles to form in the SiO2, which accelerates the oxidation.
Chemical Compatibility between Strontium‐Doped Lanthanum Manganite and Yttria‐Stabilized Zirconia
Authors: Stochniol Guido , Syskakis Emmanuel , Naoumidis Aristides
Published: September 2005

Equimolar powder mixtures and multilayer pellets of single‐phase Sr‐doped lanthanum manganite perovskite materials Lay‐xSrxMnO3 with La content y = 1 and 0.95 and Sr content 0 ≤ x ≤ 0.5 were annealed in air with 8 mol% Y2O3‐ZrO2 at 1470 K, up to 400 h and at 1670 K. up to 200 h. X‐ray diffraction and electron probe microanalysis confirmed the formation of La2Zr2O7 or SrZrO3 depending on the composition of the perovskites. No reaction products could be detected for La0.95‐xSr xMnO3 with 0.2 ≤ x ≤ 0.4 after annealing for 400 h at 1470 K, and for the perovskite La0.65Sr0.3MnO3 even after annealing for 200 h at 1670 K. The results demonstrate the improved chemical compatibility of La‐deficient perovskites against reaction with zirconia and can provide a basis for the selection of a sufficiently chemically stable material for the air electrode of solid oxide fuel cells.
Effect of Synthesis Techniques on Crystallite Size and Morphology of Lithium Aluminate
Authors: Carrera Luz María , Jimenez‐Becerril Jaime , Bosch Pedro , Bulbulian Silvia
Published: September 2005

γ‐LiAlO2 is considered as a candidate tritium breeder material for fusion reactors because of its thermophysical, chemical, and mechanical stability at high temperatures and its favorable neutron irradiation behavior. Crystallite size and shape could, however, alter these features. In this study the mean crystallite size, the crystallite size distribution, and the morphology of γ‐LiAlO2 are correlated to the synthesis procedure. The characterization techniques were powder X‐ray diffraction and scanning electron microscopy.
Aqueous Phase Equilibria in the System CaO‐Al2O3‐CaCl2‐H2O: The Significance and Stability of Friedel's Salt
Authors: Abate Christopher , Scheetz Barry E.
Published: September 2005

Friedel's Salt is a poorly understood phase in the CaO‐Al2O3‐CaCl2‐H2O system, which is critical in the function and stability of salt‐saturated portland cement‐based grouts. Such grouts are required to seal exploratory excavations in a radioactive waste repository sited in bedded salt. The phase equilibria of this system were investigated, and four quaternary invariant points were determined to allow construction of a phase diagram. The diagram is constructed using a plotting technique applicable to double‐decomposition systems or systems with a reciprocal salt pair. Statistical analysis of solution data was performed to assess the precision and accuracy of the invariant points.
Evaluation of the Bridging Relation from Crack‐Opening‐Displacement Measurements by Use of the Weight Function
Authors: Fett Theo
Published: September 2005

The weight function method for the determination of bridging stresses in coarse‐grained Al2O3 from displacement data during crack extension is outlined in detail. A special strategy for the evaluation of the integral equation between stresses and displacements is discussed. The procedure is applied to displacement measurements available in the literature. A monotonically decreasing bridging stress is found with increasing crack opening displacement.
Evaluation of Bridging Parameters in Aluminas from R‐Curves by Use of the Fracture Mechanical Weight Function
Authors: Fett Theo , Munz Dietrich , Thun Gerhard , Bahr Hans‐Achim
Published: September 2005

Coarse‐grained Al2O3 shows an R‐curve behavior which is characterized by an increase in crack growth resistance with increasing crack extension. In case of alumina, this effect is caused by crack‐border interactions in the wake of the advancing crack. In the first part of the paper, the weight function method for the determination of bridging stresses from controlled fracture tests is described. In the second part, this procedure is applied for the evaluation of our own experimental results as well as results available in the literature.
29Si MAS‐NMR Study of the Short‐Range Order in Potassium Borosilicate Glasses
Authors: Martin Steve W. , Bhatnagar Ajay , Parameswar Chitra , Feller Steve , MacKenzie Joshua
Published: September 2005

Potassium borosilicate glasses were prepared in families having the general formula of RK2O·B2O3·NSiO2, where R is the ratio of potassium oxide to boron oxide and N is the ratio of silicon dioxide to boron oxide. The glasses were prepared for values of R ranging from 0 to 7.0 in the families N= 0.5, 1.0, 2.0, and 4.0. 29Si MAS‐NMR measurements were performed on these glasses to determine the short‐range order around the silicon atom. A model of proportional sharing of the added potassium oxide between the silicate and the borate groups was suggested. This model was tested against other suggested models where proportional sharing begins after a minimum amount of potassium oxide, R0, and was observed to provide a better fit to the 29Si chemical shifts obtained. As was observed in the 29Si MAS‐NMR studies of the RLi2O·B2O3·NSiO2 glasses, the proportional sharing model with R0= 0 is in stark disagreement with that proposed by the 11B NMR studies of the alkali borosilicate glasses. This problem is as yet not understood. Since K2CO3 was used as the starting material for K2O, it was observed that at large R values, R > RCO2, where RCO2= 2.3 for N= 1, RCO2= 4.0 for N= 2, and RCO2= 5.0 for N= 4, CO2 was retained in the melt in the fashion similar to that observed for other high‐alkali borate and silicate glasses. The N= 0.5 family did not exhibit retention at the compositions studied. 29Si MAS‐NMR could be used to determine where CO2 retention began in composition and the proportion of K2O/K2CO3 in the melt (glass).
Electron Paramagnetic Resonance of Titanium Impurities in Reduced Yttria‐Stabilized Zirconia
Authors: Swider Karen E. , Worrell Wayne L.
Published: September 2005

The electronic defects in single crystals of yttria‐stabilized zirconia (YSZ) have been examined using electron paramagnetic resonance (EPR). The EPR spectra of hydrogen‐reduced YSZ single crystals are almost identical to those of polycrystalline yttria (12 mol%)‐stabilized zirconia‐titania, indicating that the Ti3+ cation is the predominant electronic defect in both materials. The disparity between the discoloration of the polycrystals and single crystals (blue vs yellow) is attributed to the different crystalline environments of the Ti3+ cations in the grain boundaries and lattice. The concentration of titanium cations in the YSZ single crystals (ca. 600 ppm) is probably too dilute to contribute to the electronic conductivity.
Oxidation Kinetics of Graphite Phase in Magnesia‐Carbon Refractories
Authors: Li Xiangmin , Rigaud Michel , Palco Stefan
Published: September 2005

Decarbonization of resin‐bonded magnesia‐graphite refractories, as one of the most important parameters for brick lining performance in service, has been studied kinetically in the temperature range from 1000° to 1400°C in air, where carbon burnout by oxygen is the dominant decarbonizing mechanism. The rate of carbon burnout was followed by gas analysis, measuring the amount of CO converted into CO2 as a function of reaction time. The experimental results have been rationalized using a mathematical model proposed for the oxidation kinetics, wherein the rate of inward diffusion of oxygen from the exterior atmosphere is predominant.
Oxidation Kinetics of a Continuous Carbon Phase in a Nonreactive Matrix
Authors: Eckel Andrew J. , Cawley James D. , Parthasarathy Triplicane A.
Published: September 2005

Analytical solutions of and experimental results on the oxidation kinetics of carbon in a pore are presented. Reaction rate, reaction sequence, oxidant partial pressure, total system pressure, pore/crack dimensions, and temperature are analyzed with respect to the influence of each on an overall linear‐parabolic rate relationship. Direct measurement of carbon recession is performed using two microcomposite model systems oxidized in the temperature range of 700° to 1200°C, and for times to 35 h. Experimental results are evaluated using the derived analytical solutions. Implications on the oxidation resistance of continuous‐fiber‐reinforced ceramic‐matrix composites containing a carbon constituent are discussed.
Reaction of TiO2‐Al‐C in the Combustion Synthesis of TiC‐Al2O3 Composite
Authors: Choi Yoon , Rhee Shi‐Woo
Published: September 2005

Reaction mechanisms and the thermal structure in the reaction zone during the combustion of TiO2, Al, and C to form TiC‐Al2O3 composite were studied. The reaction between each component was studied and the combustion wave structure and real‐time temperature profile were analyzed. Titanium aluminide species, present in the aluminothermic reduction of TiO2, did not occur in the presence of C, because of the high thermodynamic stability of TiC. The activation energies of the exothermic reaction in the 3TiO2‐4Al‐3C system were determined by DSC analysis. This suggests that the combustion reaction is mainly controlled by carbon diffusion through solid TiC. The combustion wave was observed to propagate in an unstable mode. The temperature profiles in the reaction zone were of the sawtooth type and the products were of layered structure.
Interdiffusion and Kirkcndall Effect in Doped Barium Titanate‐Strontium Titanate Diffusion Couples
Authors: Gopalan Srikanth , Virkar Anil V.
Published: September 2005

Interdiffusion in perovskites (ABO3‐A'BO3) has been investigated, theoretically and experimentally. A theoretical model along the lines of L. S. Darken's analysis has been developed. The model lays down the criteria for the occurrence of Kirkendall effect in perovskites. It has been demonstrated that the lattice velocity should display a maximum at some concentration of a dopant that increases the vacancy concentration on the A‐A′sublattice in ABO3‐A'BO3 diffusion couples. Interdiffusion coefficients in “La2/3TiO3” doped barium titanate‐strontium titanate couples have been measured at 1573 K. As judged on the basis of porosity formation, the lattice velocity in these couples seems to exhibit a maximum at some concentration of La2/3TiO3, in accord with theoretical predictions.
The Mechanical Properties of β‐SiAlON Ceramics Joined Using Composite β‐SiAlON‐Glass Adhesives
Authors: Walls Philip A. , Ueki Masanori
Published: September 2005

The mechanical properties of β‐SiAlON ceramics joined using β‐SiAlON‐glass‐forming adhesives consisting of mixed Si3N4, Y2O3, Al2O3, and SiO2 powders are described. Use of adhesives with a β‐SiAlON:glass ratio of 60:40 gave an optimum joint strength of 650 MPa in four‐point bending mode, i.e., 85% of that of unbonded material, when joining was carried out at 1600°C for 10 min, under an applied uniaxial pressure of 2 MPa. Bonding pressures in excess of 2 MPa caused excessive compressive creep distortion during the joining operation. The strengths of postjoined HIPed material and HIPed, unbonded material, differed by only 4%, i.e., 975 and 1010 MPa, respectively, which indicates that HIPing reduces the size of critical defects in the joint. Fracture toughness of the joint also improved upon HIPing.
Indentation‐Induced Contact Deformation and Damage of Glasslike Carbon
Authors: Sakai Mototsugu , Hanyu Hiroyuki , Inagaki Michio
Published: September 2005

Fracture mechanics are examined for the Vickers‐indentation‐induced contact deformation and damage of glassy carbons produced by different densification processes. The indentation load versus indentation depth relationship during the loading‐unloading cycle reveals that the contact deformation is purely elastic even under such a sharp indentation, which subsequently leads to an indentation‐induced ring/cone crack system instead of the median/radial crack system. The processes and mechanisms of such an anomalous surface crack system are related to the very open microstructure of glassy carbons. The ring/cone cracks induced by Vickers indentation are, however, significantly different in nature from the well‐known Hertzian cone crack which is induced by pressing a spherical indenter on a brittle surface. Demonstrated is the superiority of glassy carbons to ordinary brittle ceramic materials in resistance to strength degradation by contact with hard particles such as in ballistic situations.
Reaction Mechanisms of Silicon Carbide Fiber Synthesis by Heat Treatment of Polycarbosilane Fibers Cured by Radiation: I, Evolved Gas Analysis.
Authors: Sugimoto Masaki , Shimoo Toshio , Okamura Kiyohito , Seguchi Tadao
Published: September 2005

SiC fibers were synthesized from polycarbosilane (PCS) fibers by heat treatment after electron beam irradiation curing. The pyrolysis reaction mechanisms from the organic PCS to ceramic SiC were investigated by the analysis of gases evolved during heat treatment. There were two steps in the major reaction: the first step was at 800–1200 K where H2 and CH4 evolved by scission of Si‐CH3 and Si‐H and by rearrangement reactions, and the second step was at 1000–1700 K where H2 evolved by reactions related to C atoms in the PCS main chain. H2 evolution in the first step was reduced with increasing oxygen content in the cured PCS fibers.
Grain Boundary Phases and Wake Zone Characterization in Monolithic Alumina
Authors: Hay Jack C. , White Kenneth W.
Published: September 2005

The postfracture tensile (PFT) technique has been used to characterize the wake zones of two alumina microstructures over a temperature range of 20° to 1280°C. Differing primarily in purity and grain size distribution, the behaviors of a commercial 99.7% alumina and a nominally pure alumina, Lucalox (General Electric, Cleveland, OH), were evaluated. Previously, the authors have demonstrated the dominant role of thermal expansion anisotropy in control of the toughening processes through 600°C. In this paper we relate microstructural aspects to those toughening mechanisms causing the behavioral change near 800°C, typical of commercial aluminas. This temperature coincides closely with the softening point of a glassy phase reported for some commercial aluminas. Since Lucalox exhibits the same behavior, but contains no added glassy phases, two possibilities remain: (1) trace quantities of a grain boundary phase are sufficient to promote the observed behavior, or (2) changes in toughening mechanisms result from more subtle microstructural transitions. Based upon studies of strain rate and time‐dependent behavior, we propose that the topographic changes of the fracture surface near this temperature may explain the increase in toughening behavior at high temperatures.
Fabrication and Optical Properties of High‐Performance Polycrystalline Nd:YAG Ceramics for Solid‐State Lasers
Authors: Ikesue Akio , Kinoshita Toshiyuki , Kamata Kiichiro , Yoshida Kunio
Published: September 2005

Transparent polycrystalline YAG with nearly the same optical characteristics as those of a single crystal were fabricated by a solid‐state reaction method using high‐purity powders (>99.99 wt% purity). The average grain size and relative density of the 1.1 at.% Nd:YAG ceramics obtained were about 50 μm and 99.98%, respectively. An oscillation experiment was performed on a cw laser by the diode laser excitation system using the fabricated ceramics. The experimental results indicated an oscillation threshold and a slope efficiency of 309 mW and 28%, respectively. These values were equivalent or superior to those of the 0.9 at.% Nd:YAG single crystal fabricated by the Czochralski method.
Thermal Stability of Ceramic Materials in Microwave Heating
Authors: Spotz Mark S. , Skamser Daniel J. , Johnson D. Lynn
Published: September 2005

Thermal stability was examined theoretically for various commercial grades of alumina heated by microwave energy. The critical temperature for thermal runaway was evaluated as a function of Biot number and ambient temperature, employing various functional forms of the dependence of dielectric loss with temperature. Field‐temperature relationships were derived for the limit of small temperature gradients in the specimen. Finite difference methods were used under conditions where significant temperature gradients were sustained in the specimen. The critical temperature approached limiting asymptotes for the extremes in Biot number, with smooth variation in the intermediate regime. Stability diagrams were constructed which denote regions of stability and their dependence on important system parameters. The effects of ambient temperature on critical temperature were determined analytically and compared with experimental observations on heating alumina fiber bundles by a hybrid configuration utilizing an external suseptor. The results have implications for temperature control near the critical temperature and the design of hybrid heating systems.
Point Defects in Electron‐Irradiated Oxide Single Crystals
Authors: Caulfield Kevin J. , Cooper Ronald , Boas John E
Published: September 2005

Point defects have been produced in CaO, MgO, and α‐Al2O3 single crystals by electron irradiation, and thresholds for atomic displacement have been measured using timeresolved luminescence spectroscopy. Oxygen displacement energies of approximately 50 eV have been determined; however, a temperature‐dependent threshold observed for an emission band in MgO may arise from a magnesium displacement. A 300‐nm emission in α‐Al2O3 may be due to an F‐center transition. Studies of radiative recombination kinetics are consistent with an electron‐detrapping model.
Fracture Toughness of Al2O3‐Particle‐Dispersed Y2O3‐Partially Stabilized Zirconia
Authors: Li Jing‐Feng , Watanabe Ryuzo
Published: September 2005

The fracture toughness of 3 mol% Y2O3‐ZrO2 (3Y‐PSZ) composites containing 10–30 vol% Al2O3 with different particle sizes was investigated. It was found that Al2O3 dispersion of up to 30 vol% increased the fracture toughness by 17% to 30%, and the toughness increase was more remarkable in the composite dispersed with Al2O3 particles of larger sizes. By combining the effects of the dispersion toughening and phase transformation toughening, the toughness change in the present materials was theoretically predicted, which was in good agreement with the experimental data.
Hertzian Contact Damage in Magnesia‐Partially‐Stabilized Zirconia
Authors: Pajares Antonia , Guiberteau Fernando , Lawn Brian R. , Lathabai Srinivasarao
Published: September 2005

Hertzian contact damage in magnesia‐partially‐stabilized zirconia is examined. Ceramographic techniques and acoustic emission reveal the damage patterns to be fundamentally different in the as‐fired, peak‐aged, and over‐aged states. Indentation stress‐strain curves show that the plasticity component of the contact deformation increases monotonically with aging time. Whereas the tetragonal‐monoclinic transformation plays an important role in the peak‐aged material, alternative deformation processes dominate in the other states: microcracking in as‐fired, and monoclinic twinning in over‐aged.
Improvement in Thermoelectric Characteristics of n‐type Iron Disilicide by Local Composition Modification
Authors: Tokiai Takeo , Uesugi Takashi , Koumoto Kunihito
Published: September 2005

High thermoelectric figure of merit semiconducting ceramics of n‐type iron disilicide with modified local compositions have been developed. Sintering and annealing of the composite powder composed of iron disilicide and precipitated cobalt (II) hydroxide resulted in the dissolution of excess Co and oxygen into the iron disilicide phase. Excess Co segregated to the grain boundary region, while interstitially incorporated oxygen was distributed homogeneously in the microstructure. The maximum figure of merit achieved was 5.2 × 10−4/K at 673 K.
Molecular Orbital Models of Silica Rings and Their Vibrational Spectra
Authors: West Jon K. , Hench Larry L.
Published: September 2005

Amorphous silica (a‐silica) has a distribution of various ring sizes. It is generally known that these rings vary in size from 2‐membered rings through 6‐membered (or possibly higher) rings of silica tetrahedra. These silica rings are modeled by a semiempirical quantum molecular orbital method named AMI. The calculations predict a range of Si‐O bond lengths to be from 1.69 to 1.74 Å and a range of Si‐O‐Si bond angles to be from 102° to 174°. These values compare well with previous ab initio and PM3 results. The predicted infrared spectra also agree well with previous models and experimental results.
Dielectric Dispersion of Ferroelectric Ceramics and Single Crystals by Sound Generation in Piezoelectric Domains
Authors: Arlt Gottfried , Böttger Ulrich , Witte Stefan
Published: September 2005

Periodic domain configurations with alternating 180° and 90° domains are not completely mechanically clamped up to microwave frequencies. Above the acoustic resonance of the ferroelectric sample, therefore, the dielectric constant comprises contributions which can be attributed to the free dielectric constant. Up to microwave frequencies the domains are piezoelectrically active; they emit longitudinal and shear thickness waves into the surroundings which cause dielectric loss in the sample. The dielectric step from the free condition to the clamped condition at the relaxation frequency is on the order of Δε∼ 10–100. This step is much smaller than the step caused by the emission of shear waves from 90° domain walls.
Calculations of Liquidus Curve and Subliquidus Miscibility Gap in the LiTaO3‐SiO2 System
Authors: Kim Sung S.
Published: September 2005

The phase diagram of the LiTaO3‐SiO2 system has been reassessed by thermodynamic modeling with existing data from the literature. The Redlich‐Kister model was used to represent the Gibbs free energy of the liquid solution. The liquidus curves calculated from this model are in good agreement with experimental data. Also, the metastable subliquidus miscibility gap and spinodal were calculated.
Preparation of Monodisperse ZrO2 by the Microwave Heating of Zirconyl Chloride Solutions
Authors: Moon Young Tae , Kim Do Kyung , Kim Chong Hee
Published: September 2005

Based on the principle that the solubility of a salt decreases as the dielectric constant of the solvent decreases, zirconia powders were prepared by heating a zirconyl chloride solution with a 2‐PrOH‐water mixture as the solvent. The morphology, size, and size distribution of the resulting particles were highly sensitive to the heating method used on the starting solution. Particles formed under conventional heating methods were polydisperse, agglomerated spherical, or irregularly shaped because of inhomogeneous precipitation through the temperature gradient, the shear force induced by stirring, compositional nonuniformity, and the low heating rate. The present study demonstrated that microwaves provide an excellent means of heating uniformly and rapidly without stirring. The particles resulting from microwave treatment were monodisperse and spherical, with a mean diameter of 0.28 μm.
Influence of Alumina Reaction Tube Impurities on the Oxidation of Chemically‐Vapor‐Deposited Silicon Carbide
Authors: Opila Elizabeth
Published: September 2005

Pure coupons of chemically vapor deposited (CVD) SiC were oxidized for 100 h in dry flowing oxygen at 1300°C. The oxidation kinetics were monitored using thermogra‐vimetry (TGA). The experiments were first performed using high‐purity alumina reaction tubes. The experiments were then repeated using fused quartz reaction tubes. Differences in oxidation kinetics, scale composition, and scale morphology were observed. These differences were attributed to impurities in the alumina tubes. Investigators interested in high‐temperature oxidation of silica formers should be aware that high‐purity alumina can have significant effects on experimental results.
Formation Mechanism of MoO3‐Doped YSr2Cu3Oy Using the Citrate Process
Authors: Wu Ma‐Shine , Fang Tsang‐Tse
Published: September 2005

The formation mechanism of the synthesis of MoO3‐doped YSr2Cu3Oy powders using the citrate process was investigated. It was shown that the precursor phase (Sr1‐xYx)14Cu24O41 played a crucial role in forming the superconducting phase. It was found that the precursor phase (Sr1‐xYx)14Cu24O41 interacted with water and decomposed when it was heavily milled and heated.
Crystallization of a Lithium Silicate Glass‐Ceramic under Pressure
Authors: Johnson Sylvia M. , Lamoreau Robert H. , Loehman Ronald E.
Published: September 2005

A lithium silicate glass has been crystallized under increasing pressure using a constant thermal cycle in a hot isostatic press. As pressure increases, the amount of cristobalite that crystallizes decreases, the amount of quartz increases, and the total volume fraction of crystalline phases increases. Crystallization without added pressure gives a mixture of lithium metasilicate, lithium disilicate, cristobalite, and residual glass; quartz is not normally observed with atmospheric‐pressure crystallization. The threshold pressure for the appearance of quartz is about 50 MPa, which is in qualitative agreement with the value obtained from thermodynamic calculation. In this glass‐ceramic, quartz is favored over cristobalite at high pressures because it is more dense.
Grain Size Dependence of Hardness in Dense Submicrometer Alumina
Authors: Krell Andreas , Blank Paul
Published: September 2005

Pressureless sintered alumina compacts with a submicrometer microstructure exhibit a hardness that approaches or even exceeds the level of advanced hotpressed composites of Al2O3+ 35 vol% TiC, whereas the strength of both ceramics is approximately the same. The combination of reduced dislocation mobility (due to the small grain size), high density, and density homogeneity are the prerequisites for the surprisingly high hardness. Quasiconventional powder processing is used to produce these outstanding alumina bodies.
Determination of the Cerium Oxidation State in Cerium Vanadate
Authors: Reidy Richard F. , Swider Karen E.
Published: September 2005

Use of low‐quality fuels in gas turbines can lead to vana‐dium hot corrosion of stabilized‐zirconia turbine blade coatings. The stabilizing oxide reacts with V2O5 in the melt, forming a vanadate, thus removing the stabilizer from the zirconia. To better understand the vanadation reaction of one such oxide, CeO2, we have employed X‐ray absorption spectroscopy to determine the oxidation state of the resulting vanadate, CeVO4. A comparison of the cerium vanadate X‐ray absorption spectra with Ce4+ and Ce3+ standards has established that the cerium valence in this compound is 3+. This result indicates that cerium is reduced during CeVO4 formation and suggests that the vanadium reactant remains in the 5+ oxidation state.