Ferroelastic and Plastic Deformation of t'-Zirconia Single Crystals

Polydomain tetragonal ( t' ) zirconia was deformed in compression along a 〈100〉 orientation at various temperatures between 500° and 1400°C. The stress-strain curves showed a plateau corresponding to ferroelastic deformation, followed by plastic deformation at a higher yield stress level. In both ranges, the strain-rate sensitivity of the stress was measured by stress-relaxation tests. The microstructure of the tetragonal domains after ferroelastic deformation and the dislocation substructure were studied by transmission electron microscopy in a high-voltage electron microscope. As expected, ferroelastic deformation suppressed the tetragonal variant with its c -axis parallel to the loading direction. The dislocation structure consisted of intersecting dislocations on different slip systems with strongly bowed-out segments. The microprocesses of deformation are discussed here by comparing the deformation data with those of cubic zirconia deformed in the same orientation and based on the observed microstructure. The particular microstructure of t' zirconia seems to prevent recovery, so that the high flow stress of ∼700 MPa is preserved up to 1400°C.     

Effectiveness of recycled P products as P fertilizers, as evaluated in pot experiments

World phosphorus (P) resources are limited and may be exhausted within 70?C175 years. Therefore recycling of P from waste materials by chemical or thermal processes is important. This study evaluated the effectiveness of recycled P products from sewage sludge and animal wastes as P fertilizer. Four products were obtained from chemical processes, three magnesium-ammonium-phosphates (MAP) of different sewage treatment plants and a Ca phosphate precipitated from wastewater (Ca-P) and four from thermal processes, an alkali sinter phosphate (Sinter-P), a heavy metal depleted sewage sludge ash (Sl-ash), a cupola furnace slag made from sewage sludge (Cupola slag) and a meat-and-bone meal ash (MB meal ash). The effectiveness of these products as P fertilizers compared with triple superphosphate (TSP) and phosphate rock (PR) was determined in a 2-year pot experiment with maize (Zea mays L., cv. Atletico) in two soils with contrasting pH (pH(CaCl₂) 4.7 and 6.6). The parameters used to evaluate the effectiveness were P uptake, P concentration in soil solution (C_Li) and isotopically exchangeable P (IEP). MAP products were as effective as TSP in both soils, while Ca-P was only effective in the acid soil. Sinter-P was as effective as TSP in the acid soil, while Cupola slag was in the neutral soil. The products Sl-ash and MB meal ash were of low effectiveness and were comparable to PR. The effect of the fertilizers on IEP, but not on C_Li, described their effectiveness. Recycled P products obtained by chemical processes, especially MAP, could be directly applied as P fertilizers, while products such as Sl-ash and MB meal ash are potential raw materials for P fertilizer production.     

Unexpected NADPH Hydratase Activity in the Nitrile Reductase QueF from Escherichia coli

The nitrile reductase QueF catalyzes NADPH-dependent reduction of the nitrile group of preQ₀ (7-cyano-7-deazaguanine) into the primary amine of preQ₁ (7-aminomethyl-7-deazaguanine), a biologically unique reaction important in bacterial nucleoside biosynthesis. Here we have discovered that the QueF from Escherichia coli—its D197A and E89L variants in particular (apparent k_cat≈10⁻² min⁻¹)—also catalyze the slow hydration of the C5=C6 double bond of the dihydronicotinamide moiety of NADPH. The enzymatically C6-hydrated NADPH is a 3.5:1 mixture of R and S forms and rearranges spontaneously through anomeric epimerization (β→α) and cyclization at the tetrahydronicotinamide C6 and the ribosyl O2. NADH and 1-methyl- or 1-benzyl-1,4-dihydronicotinamide are not substrates of the enzymatic hydration. Mutagenesis results support a QueF hydratase mechanism, in which Cys190—the essential catalytic nucleophile for nitrile reduction—acts as the general acid for protonation at the dihydronicotinamide C5 of NADPH. Thus, the NADPH hydration in the presence of QueF bears mechanistic resemblance to the C=C double bond hydration in natural hydratases.     

Flexibler Betrieb von Luftzerlegungsanlagen

As part of the Energiewende, the current research on energy-optimized, flexible operation of air separation units is described. A realistic, pressure-driven approach for dynamic simulation is presented, which is used to provide a detailed, transient simulation model, a digital twin, of an air separation unit. Extreme operation scenarios, such as start-up and shutdown of the main heat exchanger, the distillation columns or the entire air separation unit, are described. Since the main heat exchanger experiences repeated temperature changes, its lifetime is investigated in a test rig. The gathered data is used to derive and validate three dimensional simulation models.     

Hydrothermal alteration of sedimentary organic matter in the presence and absence of hydrogen to tar then oil

Hydrothermal alteration (hydrous pyrolysis) experiments, in the absence and presence of H₂ (reductive), were conducted on organic matter from marine and lacustrine sediments. The experiments were carried out at discrete temperatures from 150 °C to 350 °C to assess the yields and compositions of the bitumen (tar) formed and subsequently at higher temperatures the oil generated. The yield of bitumen was observed to increase with increasing temperatures. Under hydrous pyrolysis conditions with hydrogen, the yield increases by an order of magnitude and immature lacustrine organic matter shows the highest yield. Bitumen, the extractable organic matter at temperatures below 250-300 °C, contains mainly polar compounds, an unresolved complex mixture (UCM) of branched and cyclic compounds, with low amounts of saturated hydrocarbons. The polar compounds include n-alkanoic acids, n-alkanedioic acids, n-alkanols, isoprenoid ketones and methyl alkanoates. At temperatures above 300 °C, the bitumens transform into petroleum products with saturated hydrocarbons (n-alkanes and biomarkers) and UCM as the major components (>95% of total yield). The degree of maturation of the generated oil increases with increasing temperature under both pyrolysis conditions to full maturity at >350 °C. Although, the bitumen yield is much higher under conditions with added hydrogen, the maturity of the generated oil is lower than with just hydrous pyrolysis.     

Atomic force microscopy study on structure and properties of irradiation grafted silica particles in polypropylene‐based nanocomposites

Nanosilica particles treated by irradiation grafting polymerization can effectively improve the strength and toughness of a thermoplastic polymer at a rather low filler content. A detailed investigation on the modified nanoparticles in the absence and presence of a polypropylene matrix is carried out by using atomic force microscopy. The results indicate that the loosen agglomerates of the untreated SiO₂ became more compact due to the linkage between the nanoparticles offered by the grafting polymer. In addition, the molecules of the polypropylene matrix are able to diffuse into the modified nanoparticle agglomerates during the melt processing. Entanglement between the molecules of the grafting polymer and the matrix is thus available, which in turn facilitates a strong particle–matrix interfacial interaction. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 2218–2227, 2001     

NMR Spectroscopy: Determination of Peroxide Value in Vegetable and Krill Oil by Using Triphenylphosphine as Tagging Reagent

Hydroperoxides are formed as the primary product during lipid oxidation, being analyzed as the peroxide value to detect the degradation level of oils and fats. As an alternative to the classical titration method according to Wheeler, a ¹H‐{³¹P} decoupled NMR method is developed using triphenylphosphine (TPP) as a tagging agent. TPP reacts with peroxides to form TPP oxides. The quantification of the peroxide value is performed by comparing the amount of reacted TPP oxide and non‐reacted TPP. This approach eliminates the requirement for an additional internal standard. Low‐oxidized oils (peroxide value < 3 meq/kg) and high‐oxidized oils with peroxide values of 150 meq/kg are precisely quantified with an relative standard deviation (RSD) of 4.90% and 0.16%, respectively. A total number of 108 oil samples are examined using the newly‐developed ¹H‐{³¹P} decoupled NMR method, indicating the applicability for vegetable oils and krill oils. Practical Applications: The developed NMR method is applicable for the determination of the peroxide value in vegetable, marine and krill oils presenting a powerful alternative for the Wheeler titration method.     

Thermal exposure effects on the long‐term behavior of a mullite fiber at high temperature

The behavior of an oxide fiber at elevated temperatures was analyzed before and after thermal exposures. The material studied was a mullite fiber developed for high‐temperature applications, CeraFib 75. Heat treatments were performed at temperatures ranging from 1200°C to 1400°C for 25 hours. Quantitative high‐temperature X‐ray analysis and creep tests at 1200°C were carried out to analyze the effect of previous heat treatment on the thermal stability of the fibers. The as‐received fibers presented a metastable microstructure of mullite grains with traces of alumina. Starting at 1200°C, grain growth and phase transformations occurred, including the initial formation of mullite, followed by the dissociation of the previous alumina‐rich mullite phase. The observed transformations are continuous and occur until the mullite phase reaches a state near the stoichiometric 3/2 mullite. Only the fibers previously heat treated at 1400°C did not show further changes when exposed again to 1200°C. Overall, the heat treatments increased the fiber stability and creep resistance but reduced the tensile strength. Changes observed in the creep strain vs. time curves of the fibers were related to the observed microstructural transformations. Based on these results, the chemical composition of the stable mullite fiber is suggested.     

Modellierung der Einlaufstrecke und deren Auswirkungen auf die Verweilzeitverteilung in laminar durchströmten Rohren und Kanälen

A one‐range and a two‐range model for the laminar velocity distribution in the entrance region of tubes and ducts are presented. These allow the calculation of the residence time distribution under the impact of the flow development in the hydrodynamic entrance region. For the dispersion‐free case, an analytical solution is given. A cell model with place‐changing probability (ZEMP) is applied for the consideration of dispersion. This approach allows the fast quantification of the influence of different parameters on the residence time distribution for relatively short pipes and ducts. The numerical results are compared with earlier presented results of semi‐empirical models.     

Fluorine in medicinal chemistry

Fluorinated compounds are synthesized in pharmaceutical research on a routine basis and many marketed compounds contain fluorine. The present review summarizes some of the most frequently employed strategies for using fluorine substituents in medicinal chemistry. Quite often, fluorine is introduced to improve the metabolic stability by blocking metabolically labile sites. However, fluorine can also be used to modulate the physicochemical properties, such as lipophilicity or basicity. It may exert a substantial effect on the conformation of a molecule. Increasingly, fluorine is used to enhance the binding affinity to the target protein. Recent 3D-structure determinations of protein complexes with bound fluorinated ligands have led to an improved understanding of the nonbonding protein-ligand interactions that involve fluorine.