Off-Optimum Cure of Aerospace Epoxy Adhesives

Four epoxy film adhesives used in aircraft manufacture and repair have been examined to establish the effect of deviation from the cure cycle specified by the manufacturer. In addition to the variation of the cure cycle, two surface preparations of the aluminium adherends (chromic acid etch or grit blast followed by silane treatment) were evaluated. Thermal analysis was used to examine the cure envelope of the adhesive, and its extent of cure and glass transition temperature. The adhesive properties were assessed by shear strength (in both single lap joints and in Iosipescu configuration), durability (Boeing wedge test) and chemical resistance to selected aggressive fluids. The sensitivity of the performance of a particular adhesive to offoptimum cure conditions depends on its composition and needs to be determined, not predicted.     

A kinetic study on the structural and functional roles of lanthana in iron-based high temperature water–gas shift catalysts

The structural and functional roles of varying amounts of lanthana in co-precipitated high temperature Fe₂O₃/Cr₂O₃/CuO water–gas shift catalysts were studied at 1 atm and 350–425 °C temperature range.     

The effects of bimetallic Co–Ru nanoparticles on Co/RuO2/Al2O3 catalysts for the water gas shift and methanation

The effects of Co on RuO₂/Al₂O₃'s activities for water gas shift (WGS) and methanation were studied. Catalysts were characterized with BET, XRD, SEM/EDS, H₂-TPR and CO-TPR. The effects of various parameters, such as calcination temperature, Ru–Co loading, Ru/Co ratio, inlet CO concentration and H₂O/CO ratio on the activities of catalysts were investigated. There existed Co_I (strongly interact with RuO₂) and Co_II (weakly interact with RuO₂). For Co/RuO₂/Al₂O₃ (Ru/Co = 1, AT = 350), only Co_I existed as bimetallic Co–Ru nanoparticles. This unique structure led this catalyst to achieve the highest CO conversion of 98.6% exceeding WGS's theoretical thermodynamic equilibrium limit due to the co-occurrence of methanation. Co/RuO₂/Al₂O₃ was more favorable to catalyze CO methanation than CO₂ methanation. The apparent activation energies of forward and reverse WGS catalyzed by Co/RuO₂/Al₂O₃ were 37.8 and 74.6 kJ mol⁻¹, respectively. The difference was corresponding well to the enthalpy change (−41.1 kJ mol⁻¹) of WGS.     

FUEL INSTABILITY STUDIES: LIQUID PHASE OXIDATION OF TETRAHYDROTHIOPHENE BY TERT-BUTYL HYDROPEROXIDE

ABSTRACT

The reactions that lead to fuel instability are the subject of conflicting reports in the literature. Confusion results from the difficulty in relating differences in fuel composition, temperature, surface effects and dissolved oxygen content that comprise the multitude of reported studies. Model studies offer a means by which the mechanism of an individual reaction can be related to a simple system and then extended to the more complex fuel media. This paper reports a model oxidation study of a cyclic sulfide, tetrahydrothiophene, with an active oxygen species, t-butyl hydroperoxide under mild reaction conditions, 120°C, in a tetradecane model fuel. The major oxidation product was tetrahydrothiophene sulfoxide from the sulfide and t-butanol from the hydroperoxide. The complete suite of products is reported.     

Influence of milk proteins on the pasting behaviour and microstructural characteristics of waxy maize starch

Gelatinisation of 5 wt% waxy maize starch (WMS) under shear (16.8 s⁻¹), alone and in mixtures with 5 wt% α-lactalbumin (α-lac), β-lactoglobulin (β-lg), α-caseinate or β-caseinate, showed reinforcement of the starch granule structure by both caseinates, but not by the whey proteins (α-lac and β-lg). Reinforcement was evident from (i) later onset of increase in viscosity on heating; (ii) higher gelatinisation temperature by differential scanning calorimetry; (iii) micrographs showing reduced swelling during heating and in the final pastes obtained on cooling; and (iv) elimination of a characteristic “secondary swelling peak” observed for WMS immediately after completion of heating to 95 °C and attributed to fracture of a restricting layer of lipid and protein at the surface of the granules. A likely mechanism of reinforcement is binding of caseinate to the lipid–protein layer. Images from confocal laser scanning microscopy with fluorescent labelling of protein showed attachment of aggregated β-caseinate to the surface of WMS granules in mixtures that had been heated (under shear) to 70 °C. Corresponding images for mixtures with α-caseinate (which is less aggregated) showed penetration of protein to the interior of the granules, which would allow binding to occur on the inside of the surface layer as well as the outside. The inability of the more hydrophilic whey proteins to reinforce the WMS granules suggests that binding of caseinates to the lipid–protein layer occurs predominantly by hydrophobic association. The understanding that caseinates make gelatinised WMS granules smaller and tougher could be useful in product formulation.     

DXP Synthase‐Catalyzed C?N Bond Formation: Nitroso Substrate Specificity Studies Guide Selective Inhibitor Design

1‐Deoxy‐D ‐xylulose 5‐phosphate (DXP) synthase catalyzes the first step in the nonmammalian isoprenoid biosynthetic pathway to form DXP from pyruvate and D ‐glyceraldehyde 3‐phosphate (D ‐GAP) in a thiamin diphosphate‐dependent manner. Its unique structure and mechanism distinguish DXP synthase from its homologues and suggest that it should be pursued as an anti‐infective drug target. However, few reports describe any development of selective inhibitors of this enzyme. Here, we reveal that DXP synthase catalyzes C? N bond formation and exploit aromatic nitroso substrates as active site probes. Substrate specificity studies reveal a high affinity of DXP synthase for aromatic nitroso substrates compared to the related ThDP‐dependent enzyme pyruvate dehydrogenase (PDH). Results from inhibition and mutagenesis studies indicate that nitroso substrates bind to E. coli DXP synthase in a manner distinct from that of D ‐GAP. Our results suggest that the incorporation of aryl acceptor substrate mimics into unnatural bisubstrate analogues will impart selectivity to DXP synthase inhibitors. As a proof of concept, we show selective inhibition of DXP synthase by benzylacetylphosphonate (BnAP).     

Variations in Tantalum Carbide Microstructures with Changing Carbon Content

A wide variety of microstructures have been obtained by vacuum plasma spraying (VPS) 39Ta:61C atomic percent feedstock powders. During processing, the powder feed was fed through a high energy VPS plasma plume, where altering nozzle angle changed the overall retained carbon concentration in the deposited material. The samples were subsequently sintered and hot isostatic pressed to homogenize and consolidate the microstructure. The microstructures consisted of grains that were either equiaxed or acicular. In the samples with less carbon loss, the equiaxed grains were either the TaC phase or a TaC matrix that encased fine laths of Ta₄C₃. In the sample with the most carbon loss, acicular grains were found containing layered and parallel TaC, Ta₂C, and Ta₄C₃ laths along the major‐axis of the grains. The phases of the compounds have been determined by using complimentary X‐ray diffraction and electron diffraction techniques. Focused ion beam serial sectioning and transmission electron microscopy tilt series tomography were performed to generate three‐dimensional reconstructions of the microstructure morphologies. This article addresses how tantalum carbide microstructures are controlled by the overall concentration and phase fraction content in each of these samples.     

A model for the evaporation of water from large glass particles in pneumatic transport

A model is presented for the evaporation of water from large particles in pneumatic transport. The work is relevant for estimating the coating solution feed rate and the length of the draft tube in Wurster‐type particle coaters. Specifically, the rate of evaporation of water from 1 mm glass particles in a 28.45 mm tube was calculated from the model. The rate increased with solids mass flow rate, inlet air temperature and inlet particle temperature. The heat was more rapidly removed from the particle phase than from the air phase and high inlet air temperatures are tolerated. The model presupposes that the gas and particle velocities, and voidage are known and that the water film on a particle is thin and uniformly distributed. Hydrodynamic considerations that impact on the calculations are discussed.     

The microstructure of ultrafine eutectic Au-Sn solder joints on Cu

The present work studies the microstructure and microstructural evolution of small volumes of nominally eutectic Au-Sn solder on Cu. The study includes solder bumps 140–145 μm in diameter and 55–65 μm tall deposited on Cu-plated Si, and solder joints 60 μm in diameter and 25 μm in height that join Cu-plated ceramic and polymide substrates. The results show that the microstructure is strongly affected by the addition of Cu from the substrate during reflow, which produces a thick intermetallic layer along the interface. In the case of the joints, normal processing produces a coarse microstructure that includes only a few grains between thick intermetallic coatings. Aging at high temperature causes a further monotonic increase in Cu content, which alters the intermetallic structure at the interfaces and can lead to intermetallic bridging across the joint. Thermal fatigue tests suggest that cyclic deformation breaks up the intermetallic structure, increasing the rate of Cu addition to the joint, but refining the apparent grain size.     

Ocular parameters as an objective tool for the assessment of truck drivers fatigue

Ocular parameters are influenced by sleep derivation and the use of chemical substances which are two major causes for traffic accidents. We assessed the use of these parameters as an objective screening tool for a driver's fitness for duty. Pupillary diameter, pupil reaction to light and saccadic velocity were measured in 29 army truck drivers every morning for two months and compared to baseline measurements taken while the subjects were alert. An index which expressed the difference between study and baseline measurements was calculated, and drivers with significant deviation from baseline were disqualified and interviewed. Non-disqualified drivers served as controls. Twenty-nine percent of disqualified drivers reported sleeping less than the minimum of 7 h required by army regulations compared with 8% of control drivers (p = 0.01). Disqualified drivers had worse sleep quality the night before the test (Groningen Sleep Quality Scale, p = 0.03) and incurred more accidents per driving day during their service (0.023 vs. 0.015 accidents/day, p = 0.03). Two disqualified drivers admitted to using alcohol or sleeping pills. Thus, these ocular parameters may serve as a screening tool for drivers that are at high risk for driving. Drivers who were disqualified even once, tend to be involved in more motor vehicle accidents than their peers.