M. Starykevich

Sealing of tartaric sulfuric (TSA) anodized AA2024 with nanostructured LDH layers

In this work, a functional sealing of a TSA anodic layer on AA2024 is suggested based upon the formation of inhibitor-containing Zn–Al layered double hydroxides (LDH). The LDH structures are formed in the pores of the anodic layer and on top of it as a result of hydrothermal treatment in a Zn2+-containing bath as shown by the structure, morphology and composition analysis. The resulting LDHs were loaded with a well-known corrosion inhibitor (vanadate). Electrochemical impedance spectroscopy, salt spray tests and scanning vibrating electrode techniques have shown a remarkable improvement in corrosion resistance of the LDH-modified sample in comparison with conventional hot-water sealing. The vanadate-loaded LDHs rendered a significant long-term active protection for the covered aluminum alloy substrate.

Active corrosion protection coating for a ZE41 magnesium alloy created by combining PEO and sol–gel techniques

An active protective coating for ZE41 magnesium alloy was produced by sealing an anodic layer, loaded with 1,2,4-triazole, with a sol–gel film. An anodic oxide layer was formed using PEO in a silicate–fluoride alkaline solution. This thin (1.8 μm) porous PEO layer was impregnated with corrosion inhibitor 1,2,4-triazole and sealed with a silica-based sol–gel film modified with titanium oxide. For the first time it was demonstrated that this relatively thin PEO-based composite coating revealed high barrier properties and provided superior protection against corrosion attack during 1 month of continuous exposure to 3% NaCl. A scanning vibrating electrode technique showed a sharp decrease (100 times) of corrosion activity in micro defects formed in the 1,2,4-triazole doped composite coating, when compared to blank samples.

Photocatalytic Deposition of Hydroxyapatite onto a Titanium Dioxide Nanotubular Layer with Fine Tuning of Layer Nanoarchitecture

A new effective method of photocatalytic deposition of hydroxyapatite (HA) onto semiconductor substrates is proposed. A highly ordered nanotubular TiO2 (TNT) layer formed on titanium via its anodization is chosen as the photoactive substrate. The method is based on photodecomposition of the phosphate anion precursor, triethylphosphate (TEP), on the semiconductor surface with the following reaction of formed phosphate anions with calcium cations presented in the solution. HA can be deposited only on irradiated areas, providing the possibility of photoresist-free HA patterning. It is shown that HA deposition can be controlled via pH, light intensity, and duration of the process. Energy-dispersive X-ray spectroscopy profile analysis and glow discharge optical emission spectroscopy of HA-modified TNT prove that HA deposits over the entire TNT depth. High biocompatibility of the surfaces is proven by protein adsorption and pre-osteoblast cell growth.

Gold nanorods induce early embryonic developmental delay and lethality in zebrafish (Danio rerio)

ABSTRACT Due to their unique electronic and optical features, gold nanoparticles (AuNP) have received a great deal of attention for application in different fields such as catalysis, electronics, and biomedicine. The large-volume manufacturing predicted for future decades and the inevitable release of these substances into the environment necessitated an assessment of potential adverse human and ecological risks due to exposure to AuNP. Accordingly, this study aimed to examine the acute and developmental toxicity attributed to a commercial suspension of Au nanorods stabilized with cetyltrimethylammonium bromide (CTAB-AuNR) using early embryonic stages of zebrafish (Danio rerio), a well-established model in ecotoxicology. Zebrafish embryos were exposed to CTAB-AuNR (0–150 µg/L) to determine for developmental assessment until 96 hr post fertilization (hpf) and lethality. Uptake of CTAB-AuNR by embryos and nanoparticles potential to induce DNA damage was also measured at 48 and 96 hpf. Analysis of the concentration-response curves with cumulative mortality at 96 hpf revealed a median lethal concentration (LC50,96h) of 110.2 μg/L. At sublethal concentrations, CTAB-AuNR suspensions were found to produce developmental abnormalities such as tail deformities, pericardial edema, decreased body length, and delayed eye, head, and tail elongation development. Further, less than 1% of the initial concentration of CTAB-AuNR present in the exposure media was internalized by zebrafish embryos prior to (48 hpf) and after hatching (96 hpf). In addition, no marked DNA damage was detected in embryos after exposure to CTAB-AuNR. Overall, CTAB-AuNR suspensions produced lethal and sublethal effects on zebrafish embryos with possible repercussions in fitness of adult stages. However, these results foresee a low risk for fish since the observed effects occurred at concentrations above the levels expected to find in the aquatic environment.

Compromising between phase stability and electrical performance: SrVO3-SrTiO3 solid solutions as SOFC anode components

The applicability of perovskite-type SrVO3-δ in high-temperature electrochemical energy conversion technology is hampered by the limited stability domain of the perovskite phase. The aim of the present work was to find a compromise between the phase stability and electrical performance by designing solid solutions in the SrVO3 -SrTiO3 system. Increasing titanium content in SrV1-y Tiy O3-δ (y=0-0.9) perovskites is demonstrated to result in a gradual shift of the upper-p(O2 ) phase stability boundary toward oxidizing conditions: from ≈10-15  bar at 900 °C for undoped SrVO3-δ to ≈10-11 -10-5  bar for y=0.3-0.5. Although the improvement in the phase stability is accompanied by a decrease in electrical conductivity, the conductivities of SrV0.7 Ti0.3 O3-δ and SrV0.5 Ti0.5 O3-δ at 900 °C remain as high as 80 and 20 S cm-1 , respectively, and is essentially independent of p(O2 ) within the phase-stability domain. Combined XRD, thermogravimetric analysis, and electrical studies revealed very sluggish kinetics of oxidation of SrV0.5 Ti0.5 O3-δ ceramics under inert gas conditions and a nearly reversible behavior after exposure to an inert atmosphere at elevated temperatures. Substitution by titanium in the SrV1-y Tiy O3-δ system results also in a decrease of oxygen deficiency in perovskite lattice and a favorable suppression of thermochemical expansion. Variations of oxygen nonstoichiometry and electrical properties in the SrV1-y Tiy O3-δ series are discussed in combination with the simulated defect chemistry of solid solutions.

Metastable perovskite Bi1-xLaxFe0.5Sc0.5O3 phases in the range of the compositional crossover

ABSTRACT Perovskite ceramics of the Bi1-xLaxFe0.5Sc0.5O3 composition (0.30 ≤ x ≤ 0.35) that cannot be sintered in bulk form as a single phase using the conventional ceramic route were successfully prepared using the high-pressure/high-temperature technique. It has been shown that the room-temperature compositional crossover from the antipolar phase whose incommensurate modulation of displacements of Bi/La and oxygen is described by the Imma(00γ)s00 superspace group to the non-polar Pnma phase occurs in the narrow range between x = 0.33 and x = 0.34 with no phase coexistence. The features of this compositional crossover are discussed in comparison with that observed in the Bi1-xLaxFeO3 system.