Spherical-Impact Damage and Strength Degradation in Silicon Nitrides for Automobile Turbocharger Rotors

Spherical-impact damage to two silicon nitrides is investigated. Gas-pressure-sintered silicon nitride exhibits an elastic response to impact by spherical partially stabilized zirconia particles, resulting in Hertzian cone-crack initiation in the sintered body. Pressureless-sintered silicon nitride, on the other hand, demonstrated an elastic/plastic response, with median/radical-crack initiation. These differences in behavior are due to their microstructural differences as well as to the different hardness values of the silicon nitrides in relation to those of the PSZ spheres. The postimpact bend strength of silicon nitrides is also degraded when crack length exceeds the inherent flaw size.     

Pervaporation separation of water/ethanol mixtures through polysaccharide membranes. II. The permselectivity of chitosan membrane

The separation of water/alcohol mixtures through chitosan membrane was investigated. The degree of the deacetylation of chitosan did not affect the selectivity of the membrane in the separation of the water/ethanol mixture. The selectivity of the chitosan membrane was affected by the specific salts such as CoSO₄, ZnSO₄, and MnSO₄ and it increased when the salts were present in the feed mixture or the membrane was pretreated with the salt solution. This behavior would be explained by the contraction of the “holes” produced by the thermal motion of polymer chains and this contraction would be correlated with the conformation change of chitosan molecule due to the formation of complexes with metal ions.     

High temperature water–gas shift reaction over hollow Ni–Fe–Al oxide nano-composite catalysts prepared by the solution-spray plasma technique

The effect of Fe content in Ni–Fe–Al oxide nano-composites prepared by the solution-spray plasma technique on their catalytic activity for the high temperature water–gas shift reaction was investigated. The composites showed a hollow sphere structure, with highly dispersed Fe–Ni particles supported on the outer surface of the spheres. When the water–gas shift reaction was performed over an Ni–Al oxide composite catalyst without Fe, undesired CO methanation took place predominantly compared to the water–gas shift reaction, and significant amounts of hydrogen were consumed. When appropriate amounts of Fe were added to the Ni–Al oxide composite catalyst during the plasma process, methanation was suppressed remarkably, without serious loss of activity for the water–gas shift reaction. The catalyst was characterized by STEM, XRD and H₂ chemisorption measurements.     

“Click Peptide“: pH‐Triggered in Situ Production and Aggregation of Monomer Aβ1–42

Into neutral : We demonstrate the unique features of a pH click peptide based on an O‐acyl isopeptide method. Under acidic conditions, the click peptide remains in a monomeric form. Upon increase of the pH to 7.4, the click peptide is quickly able to convert into Aβ1–42 through an O‐to‐N intramolecular acyl migration. Further study using this pH click peptide would elucidate the pathological role of Aβ1–42 in Alzheimer's disease.

     

Miscibility and Physical Properties of Poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate)/Poly(ethylene oxide) Binary Blends

In order to improve some inferior physical properties of bacterial poly(3‐hydroxybutyrate‐co‐3‐hydroxyhexanoate) [P(3HB‐co‐3HHx)] by blending with PEO, the miscibility, spherulite morphology, crystallization behavior and mechanical properties of P(3HB‐co‐3HHx)/PEO binary biodegradable polymer blends were investigated. A good miscibility between P(3HB‐co‐3HHx) with a 3HHx unit content of 11 mol‐% and PEO in the amorphous state was found when the PEO weight fraction was 10 wt.‐%, while the miscibility decreased dramatically when the PEO weight fraction exceeded 20 wt.‐%. Strongly depending on the blend composition, the mechanical properties of P(3HB‐co‐3HHx) was found to be significantly improved by blending with PEO with a weight fraction of ≈5–17.5 wt.‐%.

     

SiCp及Al2O3w增强铸态混杂金属基复合材料的疲劳裂纹扩展机理（英文）

研究了一种SiCp及Al2O3w增强铸态混杂金属基复合材料(MMC)的疲劳裂纹扩展(FCG)机理,同时对比研究了Al2O3w增强铸态金属基复合材料和铸态铝合金的疲劳裂纹扩展机理。在研究近临界和裂纹稳定扩展区域的疲劳裂纹扩展(FCG)机理时,发现混杂MMC的临界应力强度因子?Kth值高于其他两种材料的?Kth值,说明应力强度因子?K值较低时混杂MMC可以更好地抵抗裂纹扩展。随着?K值的降低,两种MMC在近临界区域显示出相似的FCG机理,即主要由增强相–基体界面的剥离控制,随后由铝基体中空隙的形核与合并控制;在裂纹稳定或中等扩展区域,?K值较高时FCG除了受界面上周期性裂纹扩展引起的增强相–基体界面剥离的影响之外,还显著受到铝基体中疲劳条带的影响。此外,在高?K值下,因为局部失稳断裂机制,可见铝基体中空隙的形核与合并以及SiCp和Al2O3w中的穿晶断裂。对于铸态铝合金,在低?K值下,FCG主要受空隙的形核与合并所控制;在高?K值下,FCG主要受铝晶粒的疲劳条带控制,随后受Si团簇中空隙的形核与合并控制。     

Synthesis and characterization of fullerene grafted poly(ε‐caprolactone)

The fullerene grafted poly(ε‐caprolactone) (PCL) was successfully synthesized with a graft efficiency of 80%. The fullerene moieties grafted onto the PCL chain aggregate into 1–2 μm particles so that a physical pseudo‐network is formed. Because of the existence of the network structure, the fullerene grafted PCL film can retain its shape at much higher temperatures than that of pure PCL film, as observed in dynamic mechanical tests. It shows a hydrophobic gelling behavior in chloroform solution. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Thermal and mechanical properties of a poly(ϵ‐caprolactone)/graphite oxide composite

The effect of graphite oxide (GO) as the enforcing filler on the properties of poly(?‐caprolactone) (PCL) was investigated in this study. Through the introduction of GO, the Young's modulus of PCL was increased from 340 to 1000 MPa, and the tensile strength of PCL was increased from 15 to 26 MPa. Furthermore, the interlayer distance of GO (0.6 nm) was found to expand to 1.1 nm in the PCL/GO composite, which indicated the intercalation of the PCL chain into the GO layers. Because of this intercalation structure of the PCL/GO composite, GO showed a higher reinforcing effect than graphite on the mechanical properties of PCL. The intercalation should have enabled much effective load transfer in the PCL/GO composites. Moreover, GO showed a nucleating effect toward the crystallization of PCL, as the nonisothermal crystallization peak temperature shifted from 25°C for pure PCL to about 34°C for the PCL/GO composites. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Conversion of vegetable oil to biodiesel using immobilized Candida antarctica lipase

Biodiesel derived from vegetable oils has drawn considerable attention with increasing environmental consciousness. We attempted continuous methanolysis of vegetable oil by an enzymatic process. Immobilized Candida antarctica lipase was found to be the most effective for the methanolysis among lipases tested. The enzyme was inactivated by shaking in a mixture containing more than 1.5 molar equivalents of methanol against the oil. To fully convert the oil to its corresponding methyl esters, at least 3 molar equivalents of methanol are needed. Thus, the reaction was conducted by adding methanol stepwise to avoid lipase inactivation. The first step of the reaction was conducted at 30°C for 10 h in a mixture of oil/methanol (1:1, mol/mol) and 4% immobilized lipase with shaking at 130 oscillations/min. After more than 95% methanol was consumed in ester formation, a second molar equivalent of methanol was added and the reaction continued for 14 h. The third molar equivalent of methanol was finally added and the reaction continued for 24 h (total reaction time, 48 h). This three-step process converted 98.4% of the oil to its corresponding methyl esters. To investigate the stability of the lipase, the three-step methanolysis process was repeated by transferring the immobilized lipase to a fresh substrate mixture. As a result, more than 95% of the ester conversion was maintained even after 50 cycles of the reaction (100 d).     

Effect of Polymer Dispersant Structure on Electrosteric Interaction and Dense Alumina Suspension Behavior

The present paper reports on research on the effect of molecular structure of polymer dispersants on the relationship between the electrosteric interaction of dispersants on solid surfaces and the viscosity of suspensions. Ammonium polyacrylate with different hydrophilic to hydrophobic ratios ( m:n ) was prepared and added to dense Al₂O₃ suspensions (40 vol%). The steric interactions and adsorbed structures of dispersants on Al₂O₃ powders were examined under an atomic force microscope (AFM). An optimum hydrophilic to hydrophobic group ratio, which was obtained from the maximum repulsive force and the minimum viscosity of suspension, was determined at m :n = 3:7. The changing mechanism of the adsorbed structure and the steric interaction of dispersants and the suspension viscosity by the hydrophilic to hydrophobic molecular ratio were discussed by comparing the experimental force curve and DLVO theory.