Phase composition and morphology of nanostructured coatings deposited by laser dispersion of a mixture of polyethylene with iron oxalate

Peculiarities of forming of iron oxide coatings with reinforced carbon nanostructures from gas phase generated by laser dispersion of composite target were explored. Influence of technological modes of heat treatment on morphology and phase composition of nanostructured film layers was determined. It was found that on a substrate highly dispersed layers containing carbon nanostructures are formed. Using Raman spectroscopy it was shown that in oxide matrix carbon structures, which are mainly in the form of planar located nanotubes, appear. It was found that with a mass ratio of polyethylene and iron oxalate equal to 1:1, the distribution of the formed nanostructures in size is unimodal with a maximum near 20 nm. At dispersing of polyethylene and iron oxalate mixture with mass ratio 1:2 in deposited layers nanotubes have the least defectiveness. Patterns of influence on morphology and coatings phase composition of relative component abundance in being dispersed by laser radiation composite target were determined. It was shown that with the growing of iron oxalate concentration in the target coating structural heterogeneity increases, subroughness and average size of separate nanostructures in the deposited condensate grow. The obtained polymer matrix nanocomposite films can be used in sensors.

Do oscillating redox conditions affect long-term Si release from phytoliths?

<p>Phytoliths are a major source of plant-available Si in weathered soils, particularly for crops with high Si demand, such as rice. Yet, not much is known about the evolution of Si release from phytoliths under real soil conditions. The extraction of phytoliths from soil is difficult and usually leads to changes in phytolith surface chemistry. Paddy rice cultivation induces oscillations in redox potential by alternating submergence and drainage. These oscillations may have a major impact on the evolution of phytolith Si release. For instance, reduced Fe<sup>2+</sup>, abundantly in solution under low redox potential may sorb onto negatively charged phytolith surfaces and form iron oxide coatings when redox potential rises after drainage. We thus hypothesise that phytolith Si release decreases with time in soil as phytolith surfaces are increasingly coated with oxides and organic matter. To test the effect of oscillating redox potential on phytolith surface chemistry and implicit changes in Si release we conduct experiments with phytoliths extracted from rice straw by dry ashing. Extracted phytoliths are sequentially exposed to soil solutions with contrasting redox potentials (anoxic vs. oxic), using either alternating anoxic-oxic solutions or exclusively oxic solutions. Anoxic exposure is conducted in Ar atmosphere (< 1% O<sub>2</sub> partial pressure). After each exposure events the filtrate is analysed for pH and redox potential, Fe<sup>2+</sup> with the Ferrozine method, and total Fe, Al and Si with inductive-coupled plasma-optical emission spectrometry. Filter residues are sampled and analysed after 1, 2, 4, and 8 exposure steps (each lasting 2 hours), respectively. Surface chemical composition is analysed with X-ray photoelectron spectroscopy. Specific surface area is determined with N<sub>2</sub> gas adsorption at 77 K and surface charge is measured by determining electrophoretic mobility using dynamic light scattering. Batch dissolution experiments in mini-reactors are carried out for assessing the Si release of untreated and treated phytoliths. The experimental results will provide important information on the changes of phytolith surface chemistry and Si release from phytoliths in systems with alternating redox potentials such as rice paddies.</p>

Electrochemical Impedance Spectroscopy Investigation on the Corrosive Behaviour of Waterborne Silicate Micaceous Iron Oxide Coatings in Seawater

The anticorrosive composite coatings based on waterborne silicate were prepared to replace existing solvent-based coatings suitable for ships. A series of composite coatings were prepared by adding zinc powder and micaceous iron oxide to the waterborne silicate resin. The adhesion, pencil hardness and impact resistance of the coatings were investigated and corrosion performance in seawater is characterized by electrochemical impedance spectroscopy (EIS). The results show that coatings have excellent adhesion and impact resistance and their pencil hardness can reach up to 4H. During the immersion of composite coatings in seawater for 8 h, only one time constant appears in the Bode plot, coating capacitance (Qc) gradually increases but dispersion coefficient (n) and coating resistance (Rc) gradually decrease. The breakpoint frequency formula was deduced, considering the dispersion effect. With the increase of micaceous iron oxide, the fluctuation of breakpoint frequency with immersion time is weakened. It can be used to evaluate the corrosion resistance of inorganic anticorrosive coatings in seawater. In addition, different penetration models of corrosive media were proposed for the coatings with low or high content of micaceous iron oxide.