Effects of Heat Treatment in a Wet Hydrogen Atmosphere on the Reliability of Sintered α-Silicon Carbide

Sintered α-SiC was exposed, for times up to 2 h, to a flowing wet H₂ atmosphere ( P _H2O= 1 × 10^-4 MPa) at temperatures of 1300°, 1400°, and 1500°C. The effect of such conditions on the reliability of the ceramic was estimated by comparing the Weibull modulus of the groups of specimens, tested in four-point flexure, before and after exposure. The Weibull modulus of as-polished specimens was 6.7, indicating a wide variation in room-temperature flexural strength. The Weibull modulus was increased to 14.2 by the heat treatment for 2 h in wet H₂ at 1400°C. The average strength was also improved from 347 to 446 MPa by such exposure. Heat treatment at 1300° and 1500°C also improved the reliability of the material, as indicated by increases in the Weibull modulus, but to less a degree than did exposure at 1400°C. The increases in reliability and average strength were attributed to the blunting of surface flaws by the formation of a thin SiO₂ layer on the sample surface.     

The application of reactive dyes to cotton by a wet-on-wet cold pad-batch method

Cotton ha been dyed with reactive dyes by both wet-on-wet (WOW) and wet-on-dry (WOD) cold pad-batch processes, and by conventional exhaust methods. The colour yields, in terms of the Kubelka-Munk values as a function of the amount of fixed dye, showed that the WOW method required less fixed dye to produce a given depth of shade than the other methods. It is proposed that the higher colour yields are a consequence of limited dye penetration into the cotton fibre. Compared with exhaust dyeings, WOW and WOD dyeings were clearly ring dyed but, unfortunately, no definitive difference in the degree of dye penetration into the cotton fibres was found despite their colour yield differences. Although ring dyeings often have inferior fastness properties, the WOW dyeings were of equal or slightly superior fastness to repeated washing and to normal daylight in comparison with the other dyeings     

Scaling Analysis for the Axial Displacement and Pressure of Flextensional Transducers

We have examined the axial displacement, Δ h , and maximum axial pressure, P _max, of flextensional transducers such as the moonies and the rainbows with both scaling and mechanical analyses. For a constant electric field E across the transducer, Δ h / t ∝ E / t ² where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and Δ h / t , the relative axial displacement. Thus, for a constant voltage V across the transducer, Δ h / t ∝ V / t ³. As for the maximum pressure, P _max t ² for the rainbows and P _max∝ wt for the moonies where t is the thickness of the rainbow or the thickness of the metal end cap of the moonie and w the thickness of the piezoelectric disk of the moonie. These predictions agree well with the experimental results found in the rainbows and the moonies. Our analysis showed that although the rainbows and the moonies differ in design and processing, the underlying physics for the enhancement in the axial displacement are essentially the same: The nonuniform distribution of d ₃₁ through the thickness of the transducer causes the transducer to arch or flatten with an applied electrical field, which leads to the enhancement in the axial displacement. The only difference is that, for the transducer to arch, the applied field is in the opposite direction to the polarization in the rainbows but in the same direction as the polarization in the moonies.     

Thermodynamic Modeling of the MgO–Al2O3–CrO–Cr2O3 System

A complete critical evaluation and thermodynamic modeling of the phase diagrams and thermodynamic properties of the MgO–Al₂O₃–CrO–Cr₂O₃ system at 1 bar total pressure are presented. Optimized equations for the thermodynamic properties of all phases are obtained which reproduce all available thermodynamic and phase equilibrium data within experimental error limits from 25°C to above the liquidus temperatures at all compositions and oxygen partial pressures. The optimized thermodynamic properties and phase diagrams are believed to be the best estimates presently available. The database of the model parameters can be used along with software for Gibbs energy minimization in order to calculate any type of phase diagram section.     

Effects of ion group content and polyol molecular weight on physical properties of HTPB‐based waterborne poly(urethane‐urea)s

A series of waterborne poly(urethane‐urea)s, WPUUs, based on using nonpolar hydroxyl‐terminated polybutadiene (HTPB) as the soft segment, were successfully synthesized in this article. The effects of the COOH group content and soft‐segment molecular weight (Mn_s) on the dispersion, morphology, and physical properties were investigated. Variations of the particle size, viscosity, and zeta potential were first governed by the hydrophilicity of the polymer chain, and then by the swelling derived from water. Fourier transfer infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) indicated that the degree of phase separation decreased as the COOH group content increased or as Mn_s decreased. However, the hydrogen bonding between the soft and hard segments and the two‐phase mixing could not occur in this nonpolar HTPB‐based WPUU system, indicating that the hard segments tended to form smaller domains and to pack more loosely. It was attributed to the fact that the presence of bulky ionic salt groups destroyed the ordered arrangement of the hard segments. In this case, the increases of the interface area between the soft and hard phases resulted in that the present behaviors were similar to the phase mixing. In tensile properties, HTPB‐based WPUUs exhibited higher tensile stress, elongation at break, and modulus as the COOH group content decreased or as Mn_s decreased. In thermal degradation, the introduction of HTPB polyol improved the thermal stability of WPUU. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Synthesis and properties of aminopropyl nucleic acids

Oligonucleotides that contain up to three aminopropyl nucleoside analogues have been synthesized. Dimers of aminopropyl adenine and thymidine were prepared and used as building blocks by applying phosphoramidite chemistry. Both R and S isomers of the aminopropyl nucleosides were used. This incorporation led to a reduction of thermal stability of double-stranded DNA. Furthermore, the (R)-adenine analogue, which yielded (S)-APNA, can be considered as a candidate for universal base pairing.     

The Calcia–Zirconia Phase Diagram Revisited: Stability of the Ordered Phases φ1 and φ2

Single crystals of CaO-stabilized ZrO₂ containing between 15.3 and 18.9 mol% CaO were heat-treated for 5000 h at 1200°C to study the stability of the ordered defect-fluorite phase, CaZr₄O₉ (φ₁). Subsequent TEM analysis of the equiaxed φ₁ domains in samples richer than approximately 18 mol% in CaO showed a random distribution of φ₁ variants, with no preferred interfacial habit planes. A critical review of the literature, combined with the new data, supports the Stubican-Hellmann-Hannon version of the phase diagram in the region 15 to 26 mol% CaO and 1000° to 1400°C and strongly suggests that φ₁ is a stable phase in the ZrO₂-CaO systems.     

Mössbauer studies of illites and heat-treated illite as related to coal-conversion processes

Mossbauer spectra of iron species in the following illites were studied: Grundite, Fithian, Minerva, and New Albany. Spectra of samples of Fithian illite heated at temperatures of 225, 700, and 1000 °C were also obtained. Analyses of these spectra provide Mössbauer parameter values of iron species in the illites and heat-transformed illite for comparison with similar species found in coals containing illites and in coal process residues derived from them. The illites contain both ferric and ferrous species. Mössbauer parameters for one of the ferric species, designated M(2), are virtually the same as those of pyrite. The two species are therefore difficult to distinguish from one another. Values of the concentration of pyrite in coals and shales may be inflated if the pyrite concentration is measured by Mössbauer spectroscopy. Mössbauer spectra of the heat-treated illite samples reveal changes in iron distribution, principally at the 700 and 1000 °C levels, where there are found three and six different iron species respectively. These changes are accompanied by reduction of ferric to ferrous iron. This process should be integrated into any assessment of the iron chemistry which accompanies coal-conversion processes.     

Ontology-based similarity for product information retrieval

Product development of today is becoming increasingly knowledge intensive. Specifically, design teams face considerable challenges in making effective use of increasing amounts of information. In order to support product information retrieval and reuse, one approach is to use case-based reasoning (CBR) in which problems are solved “by using or adapting solutions to old problems.” In CBR, a case includes both a representation of the problem and a solution to that problem. Case-based reasoning uses similarity measures to identify cases which are more relevant to the problem to be solved. However, most non-numeric similarity measures are based on syntactic grounds, which often fail to produce good matches when confronted with the meaning associated to the words they compare. To overcome this limitation, ontologies can be used to produce similarity measures that are based on semantics. This paper presents an ontology-based approach that can determine the similarity between two classes using feature-based similarity measures that replace features with attributes. The proposed approach is evaluated against other existing similarities. Finally, the effectiveness of the proposed approach is illustrated with a case study on product–service–system design problems.