Differences in Wear and Material Integrity of NAO and Low-Steel Brake Pads under Severe Conditions.

In this study, through severe reduced-scale braking tests, we investigate the wear and integrity of organic matrix brake pads against gray cast iron (GCI) discs. Two prototype pad materials are designed with the aim of representing a typical non-metal NAO and a low-steel (LS) formulation. The worn surfaces are observed with SEM. The toughness of the pad materials is tested at the raw state and after a heat treatment. During braking, the LS-GCI disc configuration produces heavy wear. The friction parts both keep their macroscopic integrity and wear appears to be homogeneous. The LS pad is mostly covered by a layer of solid oxidized steel. The NAO-GCI disc configuration wears dramatically and cannot reach the end of the test program. The NAO pad suffers many deep cracks. Compacted third body plateaus are scarce and the corresponding disc surface appears to be very heterogeneous. The pad materials both show similar strength at the raw state and similar weakening after heat treatment. However, the NAO material is much more brittle than the LS material in both states, which seems to favor the growth of cracks. The observations of crack faces suggest that long steel fibers in the LS material palliate the brittleness of the matrix, even after heat damage.

Isolation of the large {actinide}38 poly-oxo cluster with uranium.

By controlling the water content, a new poly-oxo-metalate species containing 38 uranium centers has been solvothermally synthesized in the presence of benzoic acid in tetrahydrofuran (THF). The {U38} motif contains a distorted UO2 core of fluorite type, stabilized by benzoate and THF molecules. This compound is analogous to the {Pu38} motif and was characterized by X-ray photoelectron spectroscopy and magnetic analyses.

Three-dimensional MOF-type architectures with tetravalent uranium hexanuclear motifs (U6O8).

Four metal-organic frameworks (MOF) with tetravalent uranium have been solvothermally synthesized by treating UCl4 with rigid dicarboxylate linkers in N,N-dimethylfomamide (DMF). The use of the ditopic ligands 4,4'-biphenyldicarboxylate (1), 2,6-naphthalenedicarboxylate (2), terephthalate (3), and fumarate (4) resulted in the formation of three-dimensional networks based on the hexanuclear uranium-centered motif [U6O4(OH)4(H2O)6]. This motif corresponds to an octahedral configuration of uranium nodes and is also known for thorium in crystalline solids. The atomic arrangement of this specific building unit with organic linkers is similar to that found in the zirconium-based porous compounds of the UiO-66/67 series. The structure of [U6O4(OH)4(H2O)6(L)6]⋅X (L = dicarboxylate ligand; X = DMF) shows the inorganic hexamers connected in a face-centered cubic manner through the ditopic linkers to build up a three-dimensional framework that delimits octahedral (from 5.4 Šfor 4 up to 14.0 Šfor 1) and tetrahedral cavities. The four compounds have been characterized by using single-crystal X-ray diffraction analysis (or powder diffraction analysis for 4). The tetravalent state of uranium has been examined by using XPS and solid-state UV/Vis analyses. The measurement of the Brunauer-Emmett-Teller surface area indicated very low values (Langmuir <300 m(2) g(-1) for 1, <7 m(2) g(-1) for 2-4) and showed that the structures are quite unstable upon removal of the encapsulated DMF solvent.

Plasma surface modification of polylactic acid to promote interaction with fibroblasts.

In this work, medium pressure plasma treatment of polylactic acid (PLA) is investigated. PLA is a biocompatible aliphatic polymer, which can be used for bone fixation devices and tissue engineering scaffolds. Due to inadequate surface properties, cell adhesion and proliferation are far less than optimal and a surface modification is required for most biomedical applications. By using a dielectric barrier discharge (DBD) operating at medium pressure in different atmospheres, the surface properties of a PLA foil are modified. After plasma treatment, water contact angle measurements showed an increased hydrophilic character of the foil surface. X-ray photoelectron spectroscopy (XPS) revealed an increased oxygen content. Cell culture tests showed that plasma modification of PLA films increased the initial cell attachment both quantitatively and qualitatively. After 1 day, cells on plasma-treated PLA showed a superior cell morphology in comparison with unmodified PLA samples. However, after 7 days of culture, no significant differences were observed between untreated and plasma-modified PLA samples. While plasma treatment improves the initial cell attachment, it does not seem to influence cell proliferation. It has also been observed that the difference between the 3 discharge gases is negligible when looking at the improved cell-material interactions. From economical point of view, plasma treatments in air are thus the best choice.

Enhanced cell-material interactions on medium-pressure plasma-treated polyhydroxybutyrate/polyhydroxyvalerate.

In this article, a medium-pressure DBD plasma treatment is used to improve the cell-material interaction of a polyhydroxybutyrate/polyhydroxyvalerate (PHB/PHV) film. PHB/PHV is a biodegradable natural polyester, used for different biomedical applications, including sutures, repair devices, and bone marrow scaffolds. The cell adhesion onto PHB/PHV is far less than optimal due to inadequate surface properties, and a surface modification is usually necessary to be able to use the full potential. Medium-pressure plasma treatments, in different atmospheres, are used to change the surface properties of a PHB/PHV foil. The hydrophilic character could be increased, as shown by water contact angle measurements. X-ray photoelectron spectroscopy (XPS) revealed an increased oxygen and nitrogen content. Cell culture test with human foreskin fibroblasts showed that the plasma was able to improve cell adhesion (both quantitatively and qualitatively). Both an increase in the number of adherent cells and an improved morphology were obtained after plasma treatment. After 7 days, a confluent cell layer could be observed on plasma-treated samples. The differences between the three discharge gases are negligible when looking at the improved cell-material interactions. From economical point of view, treatments in air are thus the best choice.

Metal-organic-framework-type 1D-channel open network of a tetravalent uranium trimesate.

An uranium trimesate open framework is built up from trinuclear building blocks (µ(3)-OU(3)) connected to each other by tricarboxylate linkers to generate honeycomb-like 3D topology. This compound was solvothermally synthesized from low-valent uranium in an N,N-dimethylformamide solvent under an inert atmosphere, favoring stabilization of the tetravalent oxidation state, which is confirmed by X-ray photoelectron spectroscopy analysis.