No abstract

No abstract

Exceptionally well-preserved three-dimensional insects with fine details and even labile tissues are ubiquitous in the Crato Member Konservat Lagerstätte (northeastern Brazil). Here we investigate the preservational pathways which yielded such specimens. We employed high resolution techniques (EDXRF, SR-SXS, SEM, EDS, micro Raman, and PIXE) to understand their fossilisation on mineralogical and geochemical grounds. Pseudomorphs of framboidal pyrite, the dominant fossil microfabric, display size variation when comparing cuticle with inner areas or soft tissues, which we interpret as the result of the balance between ion diffusion rates and nucleation rates of pyrite through the originally decaying carcasses. Furthermore, the mineral fabrics are associated with structures that can be the remains of extracellular polymeric substances (EPS). Geochemical data also point to a concentration of Fe, Zn, and Cu in the fossils in comparison to the embedding rock. Therefore, we consider that biofilms of sulphate reducing bacteria (SRB) had a central role in insect decay and mineralisation. Therefore, we shed light on exceptional preservation of fossils by pyritisation in a Cretaceous limestone lacustrine palaeoenvironment.

Films were produced on stainless-steel substrates by radiofrequency Plasma Enhanced Chemical Vapor Deposition (RF-PECVD) of mixtures containing 70% hexamethyldisiloxane, 20% oxygen and 10% argon. While the plasma excitation power was varied from 15 to 75 W, the deposition time and total gas pressure were kept constant at 1800 s and 8.0 Pa, respectively. The influences of the plasma power on the plasma kinetics and the ion bombardment of the growing film are discussed. Film composition and chemical structure were determined using X-ray photoelectron-and infrared reflectance-absorbance spectroscopy, respectively. Profilometry was used to measure the thicknesses of the resulting layers. The root mean square roughness was evaluated from surface topographic profiles acquired by atomic force microscopy. Scanning electron microscopy and energy dispersive spectroscopy were employed to evaluate the morphology and elemental composition of the coatings. Electrochemical impedance spectroscopy and potentiodynamic polarization tests were used to derive the corrosion resistance of the samples to a saline solution. Substantial changes in the material structure and progressive increases in film thickness were observed with increasing applied power. The resulting material was an organosilicon layer composed of Si\ \O backbones surrounded by methyl groups, very similar to conventional polydimethylsiloxane. Increases in the proportions of Si\ \O and methylsilyl groups in the structure were observed at greater plasma excitation powers, indicating densification of the structure owing to greater ion bombardment. The surface morphology and roughness were also dependent on the treatment power. Independently of the deposition conditions, application of the film increased the corrosion resistance of the stainless steel. A 10,000-fold elevation in the total system resistance under electrochemical testing was achieved for the film prepared with the greatest ion bombardment intensity. Film thickness was observed to be a key parameter but the coating structure had a major effect on this result.

Because of its excellent properties, carbon steel is a material widely used in several sectors. However, it is easily corroded when exposed to the environment. Seeking to remedy this problem, the possibility of coating carbon steel with SiO x /SiO x C y H z films generated by deposition and oxidation in low-pressure plasmas was investigated. Specifically, the effects of excitation power of the oxidation plasma on layer thickness, chemical structure, elemental composition, and barrier properties of the obtained coatings were investigated. The coating of the steel with the SiO x C y H z film, generated by plasma in an atmosphere of hexamethyldisiloxane (HMDSO), increased the total resistance to the passage of electric current, measured by electrochemical impedance spectroscopy. However, under the condition of moderate power oxidation (50 W), the results point to the creation of a bilayer system with high resistance to electrochemical attack compared to the SiO x C y H z film, even though its thickness is less than this.

No abstract

Recently, there has been growing interest in the incorporation of particles in plasma deposited thin films to creation of multifunctional surfaces. In this work a new hybrid methodology based on the plasma enhanced chemical vapor deposition (PECVD) of hexamethyldisiloxane combined to the reactive sputtering of TiO 2 is proposed for the preparation of SiO x C y H z -TiO 2 composite films. Specifically, the effect of the proportion of O 2 in the plasma environment on the morphology, chemical structure, elemental composition, wettability, thickness and surface roughness, of the films was studied. Agglomerates of TiO 2 (16-83 μm) were detected into the organosilicon matrix with the concentration of particulates growing with the percentage of oxygen in the feed. In general, there was elevation in the angle of contact of the surfaces as the oxygen supply increased. Interpretation is proposed in terms of the influence of the oxygen supply on the TiO 2 sputtering rate and in the oxidation of plasma species.

Alumina, or aluminum oxide, has several applications as Biomaterial in addition to being used in machining tools, grinding, thermal insulation, shielding, refractory for heating furnaces, electrical insulators, electronic components due to its high resistance to high temperatures, hardness, mechanical resistance and chemical resistance. Its achievement is due to intermediate processes in the manufacture of primary aluminum, as well as physical and chemical deposition processes. This work aims to obtain thin films of alumina through the Plasma Electrolytic Oxidation process, using the 5052 aluminum alloy as a substrate. This study serves as a basis for applications of thin films of alumina in Implantable Centrifugal Blood Pump rotors used as Ventricular Assist Devices developed by the Laboratory of Bioengineering and Biomaterials in the Federal Institute of São Paulo. The samples were prepared with same surface area of the rotor, in order to simulate the same behavior of the rotor film deposition, thus being able to observe the morphology at different oxidation times and energies, and how the influence of time and energy on the generation of plasma micro-arcs act in the formation of the alumina film. The film was characterized with Scanning Electron Microscopy, Dispersive Energy Spectroscopy and X-Ray Diffraction. The ceramic films in the PEO are created by the reaction of the electrolytic solution with the electrical discharges produced by a source, being deposited on the surface of the samples through micro arcs. In the future, the films will be tested for cell viability, and will also be evaluated as an internal coating of Implantable Centrifugal Blood Pump for use as Ventricular Assist Device.