Size Effects in Thin Face-Centered Cubic Metals for Different Complex Forming Loadings

Influence of the size effects on the mechanical behavior of face-centered cubic metals was studied for complex loadings close to microforming ones. The effect of a reduction in thickness (t) over grain size (d) ratio on the mechanical behavior for high-purity nickel and copper is investigated for three different loadings by tensile and Nakazima tests (plane strain conditions and balanced biaxial expansion). Experimental results highlight a strong degradation of the mechanical properties of Cu and Ni when the t/d ratio is reduced below a critical value, independently of the strain path. However, this effect occurs if the equivalent plastic strain is larger than a critical level which is strain path dependent and related to the stress triaxiality. The current study reveals that plastic anisotropy is also affected by size effects. An excellent correlation is obtained between the t/d ratio and the thickness reduction, through the mean normal plastic anisotropy parameter which is widely used to estimate sheet formability. A size effect map based on forming limit diagrams is proposed to depict the optimal conditions of microforming.     

Determination of 3‐D Alumina Grain Orientation,Size, Shape,and Growth Kinetics from 2‐D Data in Nextel™ 610 Fibers

Nextel^? 610 alumina fibers were heat‐treated at 1100°C–1500°C for 1–100 h in air. Grain size distributions (GSDs) and grain orientation distributions (ODs) with respect to the fiber axis were characterized by analysis of TEM images from longitudinal fiber sections. The 2‐D GSDs and ODs were characterized as ellipses. 3‐D GSDs and ODs were calculated by fitting distributions of oriented oblate ellipsoids to 2‐D GSDs and ODs formed by ellipsoid–section‐plane intersections. The standard deviations (SDs) of log‐normal GSDs consistently increased with grain size, which is not diagnostic of normal grain growth. The grain aspect ratio (α) and the tendency of the short grain axis to orient perpendicular to the fiber axis also increased with grain size, resulting in more textured fibers at larger grain sizes. Average 3‐D grain sizes were larger than 2‐D sizes for GSDs with small SDs, but smaller for GSDs with large SDs because of under sampling of small grains. 3‐D grain growth kinetics had the same 815 kJ/mol activation energy as that found by 2‐D analysis, but the grain growth exponent m of 6.0 was larger and the pre‐exponential factor much smaller. Expressions for 3‐D log‐normal GSDs as a function of heat treatment temperature and time were determined. α‐distributions and ODs were determined as a function of grain size. Methods for determining 3‐D GSDs are discussed.     

Examination of radio‐opacity enhancing additives in shape memory polyurethane foams

Three microparticle additives, tungsten (W), zirconium oxide (ZrO₂) , and barium sulfate (BaSO₄) were selected to enhance the radio‐opacity in shape memory polymer (SMP) foam biomaterials. The addition of filler causes no significant alterations of glass transition temperatures, density of the materials increases, pore diameter decreases, and total volume recovery decreases from approximately 70 times in unfilled foams to 20 times (4% W and 10% ZrO₂). The addition of W increases time to recovery; ZrO₂ causes little variation in time to shape recovery; BaSO₄ increases the time to recovery. On a 2.00 mean X‐ray density (mean X.D.) scale, a GDC coil standard has a mean X.D. of 0.62 ; 4% W enhances the mean X.D. to 1.89, 10% ZrO₂ to 1.39 and 4% BaSO₄ to 0.74. Radio‐opacity enhancing additives could be used to produce SMP foams with controlled shape memory kinetics, low density , and enhanced X ‐ray opacity for medical materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42054.     

Diazoverbindungen. 72. (Diazoalkyl)phosphane – Synthese durch elektrophile Diazoalkansubstitution und oxidative Additionsreaktionen am Phosphor

Diazo Compounds. 72. Diazoalkylphosphanes – Synthesis by Electrophilic Diazoalkane Substitution and Oxidative Addition Reactions at Phosphorus Electrophilic diazoalkane substitution of the diazomethyl compounds 1a,b with the chloro phosphanes 2a-o in the presence of lithium diethylamide yields the diazoalkyl phosphanes 3a-z . Oxidative addition of oxygen, sulfur and selenium at phosphorus leads into the series of oxo, thioxo and selenoxo phosphanes having diazoalkyl substituents ( 4a-d, 5a-m and 7a-d ). The silyl group of 5n,o is cleaved by chromatography on aluminium oxide to yield the (diazomethyl)phosphane sulfides 6a,b .     

Spatial and temporal trends of perfluorinated compounds in Beluga Whales (Delphinapterus leucas) from Alaska

Wildlife from remote locations have been shown to bioaccumulate perfluorinated compounds (PFCs) in their tissues. Twelve PFCs, consisting of perfluorinated carboxylic (PFCA) and sulfonic (PFSA) acids as well as the perfluorooctane sulfonate (PFOS) precursor perfluorooctane sulfonamide (PFOSA), were measured in livers of 68 beluga whales (Delphinapterus leucas) collected from two subpopulations, Cook Inlet and eastern Chukchi Sea, in Alaska between 1989 and 2006. PFOS and PFOSA were the dominant compounds measured in both beluga stock populations, with overall median concentrations of 10.8 ng/g and 22.8 ng/g, respectively. Long-chain perfluorocarboxylates, PFCAs (9 to 14 carbons), were detected in more than 80% of the samples. Perfluoroundecanoic acid (PFUnA) and perfluorotridecanoic acid (PFTriA) made up a large percentage of the PFCAs measured with median concentrations of 8.49 ng/g and 4.38 ng/g, respectively. To compare differences in location, year, sex, and length, backward stepwise multiple regression models of the individual and total PFC concentrations were used. Spatially, the Cook Inlet belugas had higher concentrations of most PFCAs and PFOS (p < 0.05); however, these belugas had a lower median concentration of PFOSA when compared to belugas from the eastern Chukchi Sea (p < 0.05). Temporal trends indicated most PFCAs, PFHxS, PFOS, and PFOSA concentrations increased from 1989 to 2006 (p < 0.05). Males had significantly higher concentrations of PFTriA, ΣPFCA, and PFOS (p < 0.05). Perfluorononanic acid (PFNA) and PFOS showed a significant decrease in concentration with increasing animal length (p < 0.05). These observations suggest the accumulation of PFCs in belugas is influenced by year, location, sex, and length.     

Structure‐Based Mechanism of Oleate Hydratase from Elizabethkingia meningoseptica

Hydratases provide access to secondary and tertiary alcohols by regio‐ and/or stereospecifically adding water to carbon‐carbon double bonds. Thereby, hydroxy groups are introduced without the need for costly cofactor recycling, and that makes this approach highly interesting on an industrial scale. Here we present the first crystal structure of a recombinant oleate hydratase originating from Elizabethkingia meningoseptica in the presence of flavin adenine dinucleotide (FAD). A structure‐based mutagenesis study targeting active site residues identified E122 and Y241 as crucial for the activation of a water molecule and for protonation of the double bond, respectively. Moreover, we also observed that two‐electron reduction of FAD results in a sevenfold increase in the substrate hydration rate. We propose the first reaction mechanism for this enzyme class that explains the requirement for the flavin cofactor and the involvement of conserved amino acid residues in this regio‐ and stereoselective hydration.     

Development and Characterization of Continuous SiC Fiber‐Reinforced HfB2‐Based UHTC Matrix Composites Using Polymer Impregnation and Slurry Infiltration Techniques

This paper discusses the development of continuous SiC fiber‐reinforced HfB₂‐SiC composite laminates. A range of techniques, based on resin‐based precursors and slurries, for infiltrating porous SiC preforms with HfB₂ powder were developed. While resin‐based precursors proved to be ineffective due to low HfB₂ yield and poor adhesion, the slurry infiltration techniques were effective to varying degrees. The greatest pore filling and composite densities were achieved using pressure and vibration‐assisted pressure infiltration techniques. SiC_f/HfB₂‐SiC laminates were subsequently developed via lamination, cure and pyrolysis of fabrics using a HfB₂‐loaded polymeric SiC precursor, followed by HfB₂ slurry infiltration and preceramic polymer infiltration and pyrolysis (PIP). Repeated PIP processing, for 6–10 cycles, resulted in density increases, from the 3.03–3.22 g/cm³ range after HfB₂ slurry infiltration, to 3.97–4.03 g/cm³ after PIP processing. Correspondingly, there was a decrease in open porosity from approximately 52% to less than 11%. The matrix consisted of discreet, lightly sintered HfB₂ particles dispersed in SiC. The PIP SiC matrix was primarily nanocrystalline after 1300°C pyrolysis, but experienced grain growth with further heat treatment at 1600°C.     

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

Nextel? 610 alumina fibers and alumina‐YAG (yttrium‐aluminum garnet) matrices were used to make oxide‐oxide ceramic matrix composites (CMCs) with and without monazite (LaPO₄) fiber‐matrix interfaces. Twelve sequential aluminum oxychloride (AlOCl) infiltrations with 1 hour heat treatments at 1100°C and a final 1 hour heat treatment at 1200°C were used for matrix densification. This matrix processing sequence severely degraded CMC mechanical properties. CMC tensile strengths and interlaminar tensile (ILT) strengths were less than 10 MPa and 1 MPa, respectively. Axial fracture of Nextel? 610 fibers was observed after ILT testing, highlighting the extreme degradation of fiber strength. Extensive characterization was done to attempt to determine the responsible degradation mechanisms. Changes in Nextel? 610 fiber microstructure after CMC processing were characterized by optical microscopy, SEM, and extensively by TEM. In AlOCl degraded fibers, grain boundaries near the fiber surface were wetted with a glass that contained Y₂O₃/SiO₂ or Y₂O₃/La₂O₃/P₂O₅/SiO₂, and near‐surface pores were partially filled with Al₂O₃. This glass must also contain some Al₂O₃ and initially some chlorine. AlOCl decomposition products were predicted using the FactSage^® Thermochemical code, and were characterized by mass spectrometry. Effects of AlOCl precursors on monazite coated and uncoated Nextel? 610 fibers tow and filament strength were evaluated. A mechanism for the severe degradation of the oxide‐oxide CMCs and Nextel? 610 fibers that involves subcritical crack growth promoted by release of chlorine containing species during breakdown of intergranular glasses in an anhydrous environment is proposed.     

The effect of pH on the competition between polyphosphate-accumulating organisms and glycogen-accumulating organisms

In enhanced biological phosphorus removal (EBPR) processes, glycogen-accumulating organisms (GAOs) may compete with polyphosphate-accumulating organisms (PAOs) for the often-limited carbon substrates, potentially resulting in disturbances to phosphorus removal. A detailed investigation of the effect of pH on the competition between PAOs and GAOs is reported in this study. The results show that a high external pH ( approximately 8) provided PAOs with an advantage over GAOs in EBPR systems. The phosphorus removal performance improved due to a population shift favouring PAOs over GAOs, which was shown through both chemical and microbiological methods. Two lab-scale reactors fed with propionate as the carbon source were subjected to an increase in pH from 7 to 8. The phosphorus removal and PAO population (as measured by quantitative fluorescence in situ hybridisation analysis of "Candidatus Accumulibacter phosphatis") increased in each system, where the PAOs appeared to out-compete a group of Alphaproteobacteria GAOs. A considerable improvement in the P removal was also observed in an acetate fed reactor, where the GAO population (primarily "Candidatus Competibacter phosphatis") decreased substantially after a similar increase in the pH. The results from this study suggest that pH could be used as a control parameter to reduce the undesirable proliferation of GAOs and improve phosphorus removal in EBPR systems.