Synthesis of Novel Niobium Aluminide-Based Composites

A reactive sintering process has been used to produce almost fully dense composites with interpenetrating networks of NbAl₃ and Al₂O₃. The process involves the reaction synthesis of niobium aluminides and Al₂O₃ from compacts of intensively milled aluminum and Nb₂O₅ powder mixtures. During carefully controlled heating under an inert atmosphere, the oxide reduction by aluminum to form niobium aluminides and Al₂O₃ proceeds at temperatures below the melting point of aluminum. At temperatures of >1000°C, the reaction-formed niobium aluminides and Al₂O₃ sinter. The present paper discusses processing parameters, such as attrition milling, the heating cycle, and the metal:ceramic ratio in the starting mixture, that control microstructure development and mechanical properties.     

A Photographic Study of Flash-Boiling Atomization

To gain an insight into the mechanisms of flash-boiling atomization, heated water was injected from a single-hole orifice into heated air (steady injections, liquid pressure 697 kPa, air pressure ambient, test temperatures from 300 to 426 K, orifice diameter 0.34 mm, length 1.37 mm). The breakup regime of interest in the study was that where the spray divergence starts at the nozzle exit. Short-duration backlit photographs and laser diffraction dropsize measurements showed that these flashing jets comprise an inner intact core which is surrounded by the diverging fine spray. These details about the spray structure are not visible in conventional photographs of flashing sprays that use scattered light illumination. The present results cast doubt on a previously proposed theory of flash-boiling atomization that attributes the divergence of the spray cone to the expansion processes that occur in an underex-panded compressible flow, since that theory implies that the liquid is already atomized upon leaving the nozzle. Instead, the photographs show that drops are expelled from the unbroken liquid jet starting at the nozzle exit (presumably by rapid vapor bubble growth within the jet). The core region remains intact for some distance downstream of the nozzle exit, and its breakup eventually produces relatively large drops. As the liquid temperature approaches boiling, the intact length and the core drop size decrease. Thus operation close to boiling is desirable for effective atomization. However, the nozzle mass flow rate decreases and practical difficulties are found (owing to “vapor-lock”) as the liquid is heated near boiling.     

Hierarchically Structured Materials by Anodic Coagulation Casting of Fibrinogenic Alumina Suspensions

Anodic coagulation casting of fibrinogenic ceramic suspensions is a novel processing technology, which is based on the electrically induced transformation of the water soluble fibrinogen into the insoluble fibrin. Contrary to the direct coagulation casting (DCC) technology, green formation does not depend on a pH‐shift and as the fibrin coagulate forms on an anode, it can be combined with the electrophoretic deposition (EPD) technology. In this study, the conversion of fibrinogen into fibrin is activated via electron transfer processes at an electrode material and is combined with the green formation of alumina by embedding the ceramic particles in the protein matrix. The focus of this work was to establish a technology to shape thin hierarchically structured ceramic films and thick porous materials with a distinct pore structure. Film thickness and porosity were controlled by the applied voltage and the processing‐time. The range of the established green bodies included two‐dimensional and simple three‐dimensional shapes including multilayered deposition and fiber coatings. Overall the process of anodic coagulation casting can be reported to be successful for all established ceramic shapes except multilayers, where delamination was observed. The deposited alumina ceramics were characterized using light microscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and synchrotron micro computed tomography (μCT), while the coagulation mechanism was studied using high‐performance liquid chromatography (HPLC).     

Detection of Pinosylvins in Solid Wood of Scots Pine Using Fourier Transform Raman and Infrared Spectroscopy

Abstract

Diffuse reflectance Fourier transform infrared (DRIFT) and near infrared (NIR) FT-Raman spectroscopy were used to detect pinosylvins in the wood of Pinus sylvestris L. trees. NIR FT-Raman spectroscopy offered the possibility of revealing pinosylvins simply by visual inspection of Raman spectra whereas DRIFT spectra needed a more complicated evaluation. Pinosylvin and resin acids from Scots pine were examined as to the possibility of their being the cause of observed spectral differences between sapwood and heartwood. Since pinosylvins are important compounds for the decay resistance of Scots pine wood, the detection of pinosylvins with Raman spectroscopy might be used to assess durability of wood products.     

The Kinetics of the Thermal Decomposition of Thermoplastic Polyurethane Elastomers under Thermoplastic Processing Conditions

A theoretical approach to the kinetics of the thermal decomposition of molten thermoplastic polyurethane elastomers, under conditions of thermoplastic processing, is described. On the basis of these considerations, the thermal decomposition in different instruments (melt index analyser and measuring extruder) can be described quantitatively and the various results can be compared. As a result, identical conditions of decomposition of the melt can be defined accurately, thus opening up the possibility of combining experimental values from different instruments. The fundamental kinetic equation obtained for the kinetics of the thermal decomposition of thermoplastic polyurethanes describes the decomposition reaction and the reverse reaction (formation reaction) – which is dependent on the system of measurement and processing – as a function of the molar mass (end‐group concentration) of the original product, determined from the velocity constants for the decomposition reaction and back reaction. The consideration of the limiting value for t → ∞ is in agreement with the equilibrium constant. Consequently, the development of physical characteristic functions of thermoplastic polyurethane elastomers – independent of the system of measurement – is possible.

Experimental values and calculated curves for the thermal decomposition of PUR‐Et in a melt index analyser.     

Polymer Ionomers for Rapid Prototyping and Rapid Manufacturing by Means of 3D Printing

Summary: The powder blend of poly(acrylic acid) (PAA) with zinc oxide or zinc oxide/magnesium oxide was applied successfully to produce zinc polycarboxylate during the 3D dispensing of an aqueous ink by means of 3D printers (Z402? from ZCorporation and Deskmodeler? from bmt Company). The layer‐by‐layer inkjet printing afforded zinc ionomer 3D objects with excellent water resistance, no inherent color formation and high mechanical and dimensional stabilities. In contrast to the 3D printing of conventional powders such as starch/cellulose/dextrose blends, poly(vinyl alcohol) (PVA) or plaster, no postprinting treatments were required. Excellent dimensional accuracy of the models, as evidenced by very small deviation of the dimensions from those of the corresponding CAD data, was achieved. The mechanical properties improved with increasing PAA content, ink amount (saturation value), decreasing particle size of the sintered zinc oxide ceramic. At high PAA content >7 wt.‐%, post‐treatment with aqueous zinc acetate solution improved the mechanical properties. The setting time of the zinc cements shows no significant effect on the mechanical properties, but on the water resistance of the models. The porosity of the 3D objects, measured by means of X‐ray microtomography (μ‐CT), had profound impact on the variations of the mechanical properties of the 3D objects prepared by 3D printing processes.

Comparison of three‐point‐bending tests of commercially available powders with selected zinc cements (ZC1, ZC2, ZC4, ZC19). Commercially available powders printed with recommended values of manufacturer. Zinc cements printed with saturation value 1.14 (Z402?).     

Tracking Protein S‐Fatty Acylation with Proteomics

Recently, Hang and co‐workers developed “acyl‐PEG exchange” (APE), which allows the investigation of protein S‐fatty acylation with mass‐tag labelling and gel electrophoresis, methods that are accessible to any biochemistry laboratory.     

Structure and Substrate Recognition of the Bottromycin Maturation Enzyme BotP

The bottromycins are a family of highly modified peptide natural products, which display potent antimicrobial activity against Gram‐positive bacteria, including methicillin‐resistant Staphylococcus aureus. Bottromycins have recently been shown to be ribosomally synthesized and post‐translationally modified peptides (RiPPs). Unique amongst RiPPs, the precursor peptide BotA contains a C‐terminal “follower” sequence, rather than the canonical N‐terminal “leader” sequence. We report herein the structural and biochemical characterization of BotP, a leucyl‐aminopeptidase‐like enzyme from the bottromycin pathway. We demonstrate that BotP is responsible for the removal of the N‐terminal methionine from the precursor peptide. Determining the crystal structures of both apo BotP and BotP in complex with Mn²⁺ allowed us to model a BotP/substrate complex and to rationalize substrate recognition. Our data represent the first step towards targeted compound modification to unlock the full antibiotic potential of bottro‐ mycin.