Michael addition of ethyl acrylate and acetone over solid bases

The catalytic behaviour of the superbases Na/NaOH/-Al₂O₃ and Cs_xO/-Al₂O₃ as well as of the basic zeolites Na/NaX and Cs_xO/CsX were investigated in the Michael addition of ethyl acrylate and acetone. The reactions were carried out in the liquid phase at catalyst loadings varying from 0.05 to 0.1 mol ester/g catalyst.     

Supported binary oxide monolayers as selective oxidation catalysts: Bi2Mo3O12/TiO2

Monolayers of bismuth molybdates supported on low-area TiO₂ (anatase) catalyse the oxidation/isomerisation of 1-butene to butadiene and 2-butenes with combined selectivities of 80–100% and show significantly lower specific rates of deep oxidation than does -Bi₂Mo₃O₁₂. As loadings are increased above 2 wt% (equivalent to one monolayer), selectivities remain high and, although the butadiene yields are generally only moderate, in some cases they exceed that shown by the unsupported -phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Arachidonic, eicosapentaenoic, and biosynthetically related fatty acids in the seed lipids from a primitive gymnosperm, Agathis robusta

The fatty acid composition of the seeds from Agathis robusta, an Australian gymnosperm (Araucariaceae), was determined by a combination of chromatographic and spectrometric techniques. These enabled the identification of small amounts of arachidonic (5,8,11,14–20∶4) and eicosapentaenoic (5,8,11,14,17–20∶5) acid for the first time in the seed oil of a higher plant. They were apparently derived from γ-linolenic (6,9,12–18∶3) and stearidonic (6,9,12,15–18∶4) acids, which were also present, via chain elongation and desaturation, together with other expected biosynthetic intermediates [bis-homo-γ-linolenic (8,11,14–20∶3) and bishomo-stearidonic (8,11,14,17–20∶4) acids]. Also present were a number of C₂₀ fatty acids, known to occur in most gymnosperm families, i.e., 5,11–20∶2, 11,14–20∶2 (bishomo-linoleic), 5,11,14–20∶3 (sciadonic), 11,14,17–20∶3 (bishomo-α-linolenic), and 5,11,14,17–20∶4 (juniperonic) acids. In contrast to most other gymnosperm seed lipids analyzed so far, A. robusta seed lipids did not contain C₁₈ Δ5-desaturated acids [i.e., 5,9–18∶2 (taxoleic), 5,9,12–18∶3 (pinolenic), or 5,9,12,15–18∶4 (coniferonic)]. These structures support the simultaneous existence of Δ6- and Δ5-desaturase activities in A. robusta seeds. The Δ6-ethylenic bond is apparently introduced into C₁₈ polyunsaturated acids, whereas the Δ5-ethylenic bond is introduced into C₂₀ polyunsaturated acids. A general metabolic pathway for the biosynthesis of unsaturated fatty acids in gymnosperm seeds is proposed. When compared to Bryophytes, Pteridophytes (known to contain arachidonic and eicosapentaenoic acids), and species from other gymnosperm families (without such acids), A. robusta appears as an “intermediate,” with the C₁₈ Δ6-desaturase/C₁₈→C₂₀ elongase/C₂₀ Δ5-desaturase system in common with the former subphyla, and the unsaturated C₁₈→C₂₀ elongase/C₂₀ Δ5-desaturase system specific to gymnosperms. The following hypothetical evolutionary sequence for the C₁₈ Δ6/Δ5-desaturase class in gymnosperm seeds is suggested: Δ6 (initial)→Δ6/Δ5 (intermediate)→Δ5 (final).     

Effects of morphology and surface treatment of inorganic pigments on waterborne coating properties

Inorganic pigments in aqueous coatings are investigated using atomic force microscopy and microprobe analysers. The first method characterises the topography at a very high resolution. The findings obtained using the second method reveal the distribution of the pigment in the paint film. Taking selected titanium dioxide and iron oxide pigments, the effects of particle morphology as well as inorganic and organic surface treatment on the dispersibility and flocculation stability are shown. These two phenomena are factors in gloss, hazing, hiding power, tinting strength and viscosity – key quality parameters in waterborne coatings.     

Electrochemical water disinfection. Part II: Hypochlorite production from potable water, chlorine consumption and the problem of calcareous deposits

The electrolytic production of hypochlorite from tap water in a flow-through reactor system is investigated using stacked platinum or iridium oxide coated titanium sheet or expanded metal electrodes. The influence of fast chlorine consumption and polarity reversal on the hypochlorite production rate was determined along with the dependence of the hypochlorite production rate on temperature, flow through velocity and current density. It was found that in most cases, the hypochlorite production rate was higher on iridium oxide compared to platinum electrodes. An increase in the flow-through velocity leads to an increased hypochlorite production rate while the hypochlorite production rate falls with increasing temperature.     

Preparation of hydrophobic poly(isobutylene) star polymers with hydrophilic poly(propylene imine) dendritic cores

Summary Poly(propylene imine) dendrimers with amino chain ends have been used for the preparation of hydrophobic star polymers with hydrophilic dendritic cores. The unsaturated end groups of polyisobutylene (PIB) were transformed into reactive anhydride end groups by an “ene” reaction with maleic anhydride, and the resulting functionalized PIB was then reacted with dendrimers to afford dendrimer-PIB star copolymers. Received: 20 May 1999/Accepted: 17 June 1999     

Transition metals supported on oxides: density functional cluster studies of palladium deposition on MgO(001)

The interaction of isolated Pd atoms and of a square Pd₄ cluster with the (001) surface of MgO is investigated by means of density functional (DF) calculations. The oxide surface is represented by various model clusters and the effect of the surrounding is taken into account by embedding the cluster in point charges and total ion model potentials. The calculations are performed at the relativistic level using the Becke–Perdew exchange-correlation functional. The adsorption properties determined with this computational scheme are compared with other DF results. The bonding of the Pd atoms and clusters with the surface is analyzed in terms of charge density difference plots. It is found that the polarization of the metal adsorbate due to the surface electric field provides an important contribution to the metal–oxide adhesion energy. This revised version was published online in June 2006 with corrections to the Cover Date.     

Cold Spray Deposition of Freestanding Inconel Samples and Comparative Analysis with Selective Laser Melting

Cold spray offers the possibility of obtaining almost zero-porosity buildups with no theoretical limit to the thickness. Moreover, cold spray can eliminate particle melting, evaporation, crystallization, grain growth, unwanted oxidation, undesirable phases and thermally induced tensile residual stresses. Such characteristics can boost its potential to be used as an additive manufacturing technique. Indeed, deposition via cold spray is recently finding its path toward fabrication of freeform components since it can address the common challenges of powder-bed additive manufacturing techniques including major size constraints, deposition rate limitations and high process temperature. Herein, we prepared nickel-based superalloy Inconel 718 samples with cold spray technique and compared them with similar samples fabricated by selective laser melting method. The samples fabricated using both methods were characterized in terms of mechanical strength, microstructural and porosity characteristics, Vickers microhardness and residual stresses distribution. Different heat treatment cycles were applied to the cold-sprayed samples in order to enhance their mechanical characteristics. The obtained data confirm that cold spray technique can be used as a complementary additive manufacturing method for fabrication of high-quality freestanding components where higher deposition rate, larger final size and lower fabrication temperatures are desired.     

Experimental Investigation of the Epsilon Phase in Pb–Bi System

The Pb–Bi (Lead–Bismuth) binary system has gained some prominence in recent years due to the possible use of eutectic alloys as primary-circuit coolant in generation IV nuclear reactors. Apart from the terminal solid solutions A1-Pb and A7-Bi, the system presents also one intermetallic phase with the hexagonal close-packed structure (A3), usually denoted ε phase. Due to the low temperatures involved in this system, attainment of equilibrium is difficult, and in addition, the proximity of x-ray scattering factors for both elements raises questions about a possible polymorphic transition. In the present work, three samples with compositions Pb–29 wt.%Bi, Pb–31 wt.%Bi and Pb–33 wt.%Bi were prepared and characterized by x-ray diffraction. The lattice parameters of ε are consistent with those reported in the literature, and their dependence on Bi content was determined as well. Only the hexagonal phase was identified in the 29 wt.%Bi sample, although the currently assessed Pb–Bi phase diagram predicts the presence of the Pb-rich A1 terminal solid solution in this composition. A 2-year annealing at room temperature was performed and the XRD characterization results for these samples are compared with the original data.     

Analysis and specification of the crash behaviour of plastics/metal-hybrid composites by experimental and numerical methods

Plastics materials are nowadays used in many structural applications for the substitution of metals with respect to weight reduction. In order to utilize the high freedom of design and the light-weight potential of plastics materials in crash-relevant structural parts, so-called hybrid composites which combine the high rigidity and strength of steel with the advantages of plastics materials are investigated in the outlined research. Thereby, the joining of both materials as well as the design by means of numerical methods such as the finite element analysis (FEA) are challenges which have to be met. A new approach in joining is based on the modified arc welding process where metal pin structures are formed in one working step and subsequently welded onto the surface. The pins are formed with ball-shaped, cylindrical or spiky ends and produced directly from the welding wire without requiring additional pre-fabricated components such as studs or similar. This allows the small-scale surface structuring of metal components that can be adapted optimally for a form fit on the respective plastics structure. Subsequently, injection molding is used for the application of the plastics material onto the pin-structured metal part in order to generate a positive fit between metal and plastics in an intrinsic joining process. An additional joining process, which is carried out after injection molding, is not required. Within the framework of the research presented, comprehensive mechanical tests are presented to illustrate the suitability of pin-structured metal-hybrid composites in crash applications. In comparison to structures which are in particular exposed to static loads and therefore designed to exhibit maximum component strength, crash applications are designed to fail in a continuous process to achieve maximum energy consumption. The outlined research illustrates the enhanced failure behavior of pin-structured plastics/metal-hybrid composites and the increased energy consumption under impact loading. Moreover, a comparison between pin structuring and laser structuring with regard to the obtainable mechanical properties under impact loading is given. Concluding, the current potential and weak points in the simulation of plastics/metal-hybrid structures using FEA is presented and discussed.