3-D surface analysis of worn spherical roller thrust bearings

Wear of boundary lubricated spherical roller thrust bearings has been characterised with 3-D surface measurements and analysis. Due to the curved contact surface in a spherical roller thrust bearing, the rollers will undergo sliding in the contact. For an unskewed roller there will be two points along each contact where the sliding velocity is zero. At all other points along the contact, sliding is present. Previously presented results from measurements of the contacting surfaces show that outside the zero sliding points there is a significant change in the washer surface profile due to wear. In order to study how the wear depends on the number of revolutions ten tests were performed. After the tests, 3-D surface roughness measurements were performed. The results from these measurements show that there are different wear mechanisms involved. Initially, the surfaces are run in by possible plastic deformation and two-body abrasion. After running-in, the surfaces are subjected to mild wear probably caused by two-body abrasion and/or delanunation wear. For the long term tests, three-body abrasion clearly influences the amount of wear. A 3-D parameter set was used to characterise the different wear mechanisms. Three amplitude parameters (S_a, S_q S_z) and three of the functional Abbot curve parameters (S_pk, S_k, S_vk) were able to characterise all the wear mechanisms.     

Nanoscale Indentation and Scratch of Short Carbon Fiber Reinforced PEEK/PTFE Composite Blend by Atomic Force Microscope Lithography

The atomic force microscope (AFM) has become a popular tool for characterizing surfaces of different types of materials. In this paper a new technology of AFM–SPM lithography was used to conduct nanoscale scratch and indentation tests on a short carbon fiber reinforced PEEK/PTFE composite blend. In the scratch test, by moving the tip across the surface at constant velocity and fixed applied force, grooves with nanometer scale dimensions were fabricated on the PEEK matrix surfaces. The grooves consisted of a central trough with pile-ups on each side. These grooves provided information about deformation mechanisms and scratch resistance of the individual phases. In the nanoscale indentation and scratch of the polymeric phases, microploughing and microcutting are the dominant wear mechanisms. The harder phases, i.e., graphite and carbon fibers, get worn by microcracking events.     

Catalysis with Soluble Hybrids of Highly Branched Macromolecules with Palladium Nanoparticles in a Continuously Operated Membrane Reactor

The continuous recovery and recycling of soluble metal nanoparticles by means of ultrafiltration is described, employing hybrids of palladium nanoparticles with highly branched amphiphilic polyglycerol as a catalyst for cyclohexene hydrogenation as a model reaction. In a continuously operated membrane reactor a productivity of 29000 TO over 30 exchanged reactor volumes was observed for nanoparticles of 2.2 nm size, with a maximum rate of 1200 TO h⁻¹. Catalysis by soluble metal complexes can be excluded. After 30 hours of operation, some decrease in activity is observed which is due to deposition of palladium on the ultrafiltration membrane, however this material does not contribute to catalytic activity.     

The use of new blockcopolymeric dispersing agents for waterborne paints — theoretical and practical aspects

Newly developed blockcopolymeric dispersing agents are evaluated in their performance with a number of pigments in order to obtain a deeper understanding of the dispersing process and of the factors that affect the stability of waterborne binder free pigment concentrates. Special attention is paid to the variation of the amphiphilic ionic/non-ionic and hydrophobic/hydrophilic properties of these new dispersants. By measuring particle surface charges and particle size distributions of pigment pastes and by determining relevant properties of the films obtained after application the effect of a number of binders and other paint components on the stability of dispersions is also evaluated. Guidelines for efficient and economically optimum preparation of pigmented waterborne paints are given.     

In-line measurement of tempered cocoa butter and chocolate by means of near-infrared spectroscopy

In the present work cocoa butter and chocolate were precrystallized by means of a newly developed shear crystallizer. The shear crystallizer was integrated into a circular loop. The handling of precrystallized cocoa butter showed a high dependency on the timing of applied analysis. Differential scanning calorimetry, calorimetry, rheometry, and in-line near-infrared (NIR) were all directly influenced by the fat crystal structure. Nevertheless, for cocoa butter it was shown that mechanical energy input (rpm) had a significant influence on viscosity, melting enthalpy, and slope at the second point of inflection of a temper curve. Experiments with cocoa butter at constant exit temperature showed a linear increase of viscosity between 0.1 and 0.8 Pa·s in the range of 300 to 1300 rpm. Melting enthalpy increased in the same rpm interval from 0.02 to 2.5 J/g. Solidification time (from 4.5 to 0.5 min) and slope (from 0.82 to 0.15, second point of inflection of temper curve) consequently decreased (both with exponential approximation). For cocoa butter, slope and solidification time correlated linearly whereas solidification time and viscosity followed a power law fit. This proved that defined relationships exist between rheological data and data from temper curve measurements. Viscosity was linearly dependent on crystal content. By means of NIR spectroscopy good correlation models for cocoa butter viscosity, enthalpy (crystal content), and slope values were found. For precrystallized chocolate, analytical values such as viscosity and slope values were detected off-line and used for calibration of NIR spectroscopy.     

Characterization of forced oxidation of sardine oil: Physicochemical data and mathematical modeling

It is of major interest to the food industry to understand the mechanisms and kinetics underlying spontaneous oxidation of marine oils because these polyunsaturated fatty acid (PUFA)-rich oils, the object of several health claims, have been repeatedly recommended for dietary intake. The present study attempts to characterize forced oxidation and hydrolytic breakdown of glycerides and fatty acids in sardine oil. A simple, first-order mathematical model was postulated and successfully fitted to the experimental data. This model confirmed that the rate of decrease in concentration of intact fatty acid moieties is almost directly proportional to the number of double bonds present. Therefore, as expected, the rate of oxidative decay was virtually independent of chain length, with an overall activation energy of ca. 22 kJ mol⁻¹. Additionally, the rate of hydrolysis was correlated with the rate of oxidative decay. With the exception of fatty acids possessing more than four double bonds, PUFA proved to be relatively stable to oxidation for up to 10 h at 50–70°C, and the qualitatively richest pattern of volatiles was obtained when the reaction was performed at the highest temperature (80°C).     

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.     

Integration of algae-based biofuel production with an oil refinery: Energy and carbon footprint assessment

Biofuel production from algae feedstock has become a topic of interest in the recent decades since algae biomass cultivation is feasible in aquaculture and does therefore not compete with use of arable land. In the present work, hydrothermal liquefaction of both microalgae and macroalgae is evaluated for biofuel production and compared with transesterifying lipids extracted from microalgae as a benchmark process. The focus of the evaluation is on both the energy and carbon footprint performance of the processes. In addition, integration of the processes with an oil refinery has been assessed with regard to heat and material integration. It is shown that there are several potential benefits of co-locating an algae-based biorefinery at an oil refinery site and that the use of macroalgae as feedstock is more beneficial than the use of microalgae from a system energy performance perspective. Macroalgae-based hydrothermal liquefaction achieves the highest system energy efficiency of 38.6%, but has the lowest yield of liquid fuel (22.5 MJ per 100 MJ_algae) with a substantial amount of solid biochar produced (28.0 MJ per 100 MJ_algae). Microalgae-based hydrothermal liquefaction achieves the highest liquid biofuel yield (54.1 MJ per 100 MJ_algae), achieving a system efficiency of 30.6%. Macro-algae-based hydrothermal liquefaction achieves the highest CO₂ reduction potential, leading to savings of 24.5 resp 92 kt CO_2eq/year for the two future energy market scenarios considered, assuming a constant feedstock supply rate of 100 MW algae, generating 184.5, 177.1 and 229.6 GWh_biochar/year, respectively. Heat integration with the oil refinery is only possible to a limited extent for the hydrothermal liquefaction process routes, whereas the lipid extraction process can benefit to a larger extent from heat integration due to the lower temperature level of the process heat demand.     

Alpha‐Synuclein Binds to the Inner Membrane of Mitochondria in an α‐Helical Conformation

The human alpha‐Synuclein (αS) protein is of significant interest because of its association with Parkinson's disease and related neurodegenerative disorders. The intrinsically disordered protein (140 amino acids) is characterized by the absence of a well‐defined structure in solution. It displays remarkable conformational flexibility upon macromolecular interactions, and can associate with mitochondrial membranes. Site‐directed spin‐labeling in combination with electron paramagnetic resonance spectroscopy enabled us to study the local binding properties of αS on artificial membranes (mimicking the inner and outer mitochondrial membranes), and to evaluate the importance of cardiolipin in this interaction. With pulsed, twofrequency, double‐electron electron paramagnetic resonance (DEER) approaches, we examined, to the best of our knowledge for the first time, the conformation of αS bound to isolated mitochondria.