First Hour Of Exposure Research Articles

The diverse toxic effect of SiO2 and TiO2 nanoparticles toward the marine microalgae Dunaliella tertiolecta

Nanoparticles (NPs) are widely used in many industrial applications. NP fate and behavior in seawater are a very important issue for the assessment of their environmental impact and potential toxicity. In this study, the toxic effects of two nanomaterials, silicon dioxide (SiO2) and titanium dioxide (TiO2) NPs with similar primary size (~20 nm), on marine microalgae Dunaliella tertiolecta were investigated and compared. The dispersion behavior of SiO2 and TiO2 NPs in seawater matrix was investigated together with the relative trend of the exposed algal population growth. SiO2 aggregates rapidly reached a constant size (600 nm) irrespective of the concentration while TiO2 NP aggregates grew up to 4 ± 5 μm. The dose-response curve and population growth rate alteration of marine alga D. tertiolecta were evaluated showing that the algal population was clearly affected by the presence of TiO2 NPs. These particles showed effects on 50 % of the population at 24.10 [19.38-25.43] mg L(-1) (EC50) and a no observed effect concentration (NOEC) at 7.5 mg L(-1). The 1 % effect concentration (EC1) value was nearly above the actual estimated environmental concentration in the aquatic environment. SiO2 NPs were less toxic than TiO2 for D. tertiolecta, with EC50 and NOEC values one order of magnitude higher. The overall toxic action seemed due to the contact between aggregates and cell surfaces, but while for SiO2 a direct action upon membrane integrity could be observed after the third day of exposure, TiO2 seemed to exert its toxic action in the first hours of exposure, mostly via cell entrapment and agglomeration.

Glutathione metabolism in the HaCaT cell line as a model for the detoxification of the model sensitisers 2,4-dinitrohalobenzenes in human skin

Glutathione (GSH) is the most prominent antioxidant in cells and the co-factor of an important set of enzymes involved in the skin metabolic clearance system, glutathione S-transferases (GST). Here, we describe an LC–MS (liquid chromatography–mass spectroscopy) method to measure GSH and its disulfide form (GSSG) in HaCaT cells and a 3D Reconstructed Human Epidermis (RHE) model. In our assay, the basal level of GSH in both systems was in the low nmol/mg soluble protein range, while the level of GSSG was systematically below our limit of quantification (0.1μM). We found that 2,4-dinitrohalobenzenes deplete the GSH present in HaCaT cells within the first hour of exposure, in a dose dependent manner. The level of GSH in HaCaT cells treated with a single non-toxic dose of 10μM of dinitrohalobenzene was also shown to increase after two hours. While cells treated with 1-chloro-2,4-dinitrobenzene (DNCB) and 1-fluoro-2,4-dinitrobenzene (DNFB) repleted GSH to levels similar to untreated control cells within 24h, 1-bromo-2,4-dinitrobenzene (DNBB) seemed to prevent such a repletion and appeared to be the most toxic compound in all assays. A mathematical modelling of experimental results was performed to further rationalise the differences observed between test chemicals. For this purpose the biological phenomena observed were simplified into two sequential events: the initial depletion of the GSH stock after chemical treatment followed by the repletion of the GSH once the chemical was cleared. Activation of the nuclear factor E2-related factor 2 (Nrf2) pathway was observed with all compounds within two hours, and at concentrations less than 10μM. These data show that GSH depletion and repletion occur rapidly in skin cells and emphasize the importance of conducting kinetic studies when performing in vitro experiments exploring skin sensitization.

Antioxidative response of the three macrophytes Ceratophyllum demersum, Egeria densa, and Hydrilla verticillata to a time dependent exposure of cell-free crude extracts containing three microcystins from cyanobacterial blooms of Lake Amatitlán, Guatemala

Microcystins (MCs) produced by cyanobacteria in natural environments are a potential risk to the integrity of ecosystems. In this study, the effects of cyanobacterial cell-free crude extracts from a Microcystis aeruginosa bloom containing three MC-congeners MC-LR, -RR, and -YR at environmental relevant concentrations of 49.3±2.9, 49.8±5.9, and 6.9±3.8μg/L, respectively, were evaluated on Ceratophyllum demersum (L.), Egeria densa (Planch.), and Hydrilla verticillata (L.f.). Effects on photosynthetic pigments (total chlorophyll (chl), chl a, chl b, and carotenoids), enzymatic defense led by catalase (CAT), peroxidase (POD) and glutathione reductase (GR), and biotransformation enzyme glutathione S-transferase (GST) were measured after 1, 4, and 8h and after 1, 3, 7, and 14 days of exposure. Results show that in all exposed macrophytes, photosynthetic pigments were negatively affected. While chl a and total chl decreased with increasing exposure time, a parallel increase in chl b was observed after 8h. Concomitant increase of ∼5, 16, and 34% of antioxidant carotenoid concentration in exposed C. demersum, E. densa, and H. verticillata, respectively, was also displayed. Enzymatic antioxidant defense systems in all exposed macrophytes were initiated within the first hour of exposure. In exposed E. densa, highest values of CAT and GR activities were observed after 4 and 8h, respectively, while in exposed H. verticillata highest value of POD activity was observed after 8h. An early induction with a significant increase of biotransformation enzyme GST was observed in E. densa after 4h and in C. demersum and H. verticillata after 8h. These results are the first to show rapid induction of stress and further possible MC biotransformation (based on the activation of GST enzymatic activity included in MC metabolization during the biotransformation mechanism) in macrophytes exposed to crude extract containing a mixture of MCs.

Early Transient Sarcoplasmic Reticulum Calcium Decrease Prior to Initiation of Unfolded Protein Response in Vascular Smooth Muscle Cells

This study investigates calcium dysregulation during the initial phase of the brefeldin A (BFA)-induced sarco/endoplasmic reticulum (SR/ER) stress response in vascular smooth muscle cells (VSMCs). BFA is most commonly cited as initiating this response through an accumulation of unfolded protein in the lumen due to blockage of protein transport from the ER to the Golgi apparatus. However, BFA's effect on calcium signals within the SR is poorly understood. Based on our observations, acute exposure to BFA causes a non-significant initial wave of SR calcium movement, which is minor compared to that induced by other popular ER stressors such as thapsigargin and tunicamycin. Time-course studies were conducted to observe the effects of BFA exposure on SR calcium over six time points (0, 1, 3, 6, 9, 12 hrs). We observed that BFA caused an approximate 50% decrease in SR calcium concentration within the first hour of exposure. Interestingly, the unfolded protein response (UPR) was detected after 6 hours of treatment, and was associated with slight recovery of SR calcium concentration. We have therefore concluded that the SR calcium drop characteristic of the cellular stress response occurs prior to the initiation of the UPR, rather than, as suggested before, being a result of its many corrective pathways. We reason that this calcium drop is potentially the trigger setting off the entire SR/ER stress process. This study was supported by a grant from the Canadian Institutes of Health Research [MOP-111266] to C.V.B. & M.E.

Oxidative damage and cell-programmed death induced in Zea mays L. by allelochemical stress.

The allelochemical stress on Zea mays was analyzed by using walnut husk washing waters (WHWW), a by-product of Juglans regia post-harvest process, which possesses strong allelopathic potential and phytotoxic effects. Oxidative damage and cell-programmed death were induced by WHWW in roots of maize seedlings. Treatment induced ROS burst, with excess of H2O2 content. Enzymatic activities of catalase were strongly increased during the first hours of exposure. The excess in malonildialdehyde following exposure to WHWW confirmed that oxidative stress severely damaged maize roots. Membrane alteration caused a decrease in NADPH oxidase activity along with DNA damage as confirmed by DNA laddering. The DNA instability was also assessed through sequence-related amplified polymorphism assay, thus suggesting the danger of walnut processing by-product and focusing the attention on the necessity of an efficient treatment of WHWW.

Time dependent wettability of graphite upon ambient exposure: the role of water adsorption.

We report the temporal evolution of the wettability of highly ordered pyrolytic graphite (HOPG) exposed to environmental conditions. Macroscopic wettability is investigated by static and dynamic contact angles (SCA and DCA) obtaining values comparable to the ones presented in the literature. SCA increases from ∼68° to ∼90° during the first hour of exposure after cleaving, whereas DCA is characterized by longer-scale (24 h) time evolution. We interpret these results in light of Fourier transform infrared spectroscopy, which indicates that the evolution of the HOPG wettability is due to adsorption of molecules from the surrounding atmosphere. This hypothesis is further confirmed by nanoscopic observations obtained by atomic force microscope (AFM)-based force spectroscopy, which monitor the evolution of surface properties with a spatial resolution superior to macroscopic experiments. Moreover, we observe that the results of macro- and nanoscale measurements evolve in similar fashion with time and we propose a quantitative correlation between SCA and AFM measurements. Our results suggest that the cause of the transition in the wettability of HOPG is due to the adsorption of hydrocarbon contaminations and water molecules from the environment. This is corroborated by annealing the HOPG is vacuum conditions at 150°, allowing the desorption of molecules on the surface, and thus re-establishing the initial macro and nano surface properties. Our findings can be used in the interpretation of the wettability of more complicated systems derived from HOPG (i.e., graphene).

Super-resolution imaging of C-type lectin spatial rearrangement within the dendritic cell plasma membrane at fungal microbe contact sites.

Dendritic cells express DC-SIGN and CD206, C-type lectins (CTLs) that bind a variety of pathogens and may facilitate pathogen uptake for subsequent antigen presentation. Both proteins form punctate membrane nanodomains (∼80 nm) on naïve cells. We analyzed the spatiotemporal distribution of CTLs following host-fungal particle contact using confocal microscopy and three distinct methods of cluster identification and measurement of receptor clusters in super-resolution datasets: DBSCAN, Pair Correlation and a custom implementation of the Getis spatial statistic. Quantitative analysis of confocal and super-resolution images demonstrated that CTL nanodomains become concentrated in the contact site relative to non-contact membrane after the first hour of exposure and established that this recruitment is sustained out to 4 h. DC-SIGN nanodomains in fungal contact sites exhibit a 70% area increase and a 38% decrease in interdomain separation. Contact site CD206 nanodomains possess 90% greater area and 42% lower interdomain separation relative to non-contact regions. Contact site CTL clusters appear as disk-shaped domains of approximately 150-175 nm in diameter. The increase in length scale of CTL nanostructure in contact sites suggests that the smaller nanodomains on resting membranes may merge during fungal recognition, or that they become packed closely enough to achieve sub-resolution inter-domain edge separations of <30 nm. This study provides evidence of local receptor spatial rearrangements on the nanoscale that occur in the plasma membrane upon pathogen binding and may direct important signaling interactions required to recognize and respond to the presence of a relatively large pathogen.

ANALÝZA BARVY DŘEVA A JEJÍ ZMĚNY VLIVEM SIMULOVANÉHO SLUNEČNÍHO ZÁŘENÍ U TROPICKÝCH DŘEV

This study investigated the wood surface discolouration due to simulated sunlight of three tropical woods native in South America. These woods are commonly used in the Czech Republic. Wood of jatoba (Hymenea courbaril L.), massaranduba (Manilkara bidentata A. Chev.) and tigerwood (Astronium graveolens Jacq.) was exposed to treatment by light of xenon-arc lamp, which simulates outdoor sunlight, for 144 hours. Colour measurements of exposed and non-exposed areas of samples were performed by means of spectrophotometer measuring in CIEL*a*b* colour system. The resulting wood discolouration was evaluated according to value of the overall colour change ∆E*. Changes of particular parameters (L*, a* and b*) were also observed during exposure. The wood surface darkened rapidly during the first hours of exposure to simulated sunlight, then samples showed only a slight increase in lightness. After 144 hours of sunlight irradiation the values of chromaticity coordinates were lower compared with the original surface. The initial variations in the lightness of different wood decreased to the minimum after exposure. The most distinctive discolouration of wood was found in the initially brightest wood tigerwood, the darkest massaranduba was affected the least.

Nematicidal and quantitative phytochemical analysis of the chromatographic fractions from the leaf and stem of &lt;i&gt;Allamanda cathartica (L)&lt;/i&gt;

The environmental pollution of synthetic nematicides is enormous, due to their residual effects and nondegradability. This study was conducted to investigate the possibility of a green alternative that will eventually replace the pollution problems of synthetic nematicides. The activity of plant secondary metabolites against plant parasitic nematodes was tested in-vitro using chromatographic isolates from the stem and leaves of Allamanda cathartica. Isolates from the extracted plant materials were tested at various concentrations (0 mg/mL, 0.06 mg/mL, 0.1 mg/mL and 0.2mg/mL) against Meloidogyne incognita juveniles and eggs. The effect was determined through testing the inhibition of egg hatch and larval mortality. The result showed that egg hatching was totally inhibited among all the isolates at different concentrations except in the control which had 48.39% on day 5. The isolates showed strong nematicidal effect, with percentage mortality of 16.87% at the first hour of exposure which compared well with the commercial nematicide (oxamyl). However the leaves of A. cathartica proved more effective than the stem. Preliminaryphytochemical screening revealed that the quantities of secondary metabolites are more in the leaves of A. carthatica than in the stems. Infra-red spectroscopic data of three of the isolates revealed the presence of alkanes (2930; 2923 and 1460 cm-1) aldehydes (2855; 2851 and 1733cm-1) and phenols at (3650; 1115cm-1). Aliphatic amines (3200; 1460 and 1600 cm-1) and non-cyclic ethers (1310; 1300; 1240 and 1000cm-1) are present in isolate four. This study showed that the leaves of A. cathartica could serve as a bio-pesticide to reduce environmental pollutionKey words: Extraction, n-hexane, Isolation, Oxamyl, Nematodes, Chromatography.

Rapid post-oral stimulation of intake and flavor conditioning in rats by glucose but not a non-metabolizable glucose analog

Mice adapted to drink a flavored saccharin solution (CS−) paired with intragastric (IG) self-infusions of water rapidly increase their intake of a new flavored solution (CS+) that is paired with IG glucose self-infusions. The present study extends this method to examine post-oral glucose appetition in rats. Food-restricted rats were trained to consume a CS− flavor (e.g., grape saccharin) paired with IG water in 5 daily 1-h tests. In the next 3 tests, they drank a CS+ (e.g., cherry saccharin) paired with IG glucose. Rats infused with 8% glucose increased intake significantly on CS+ Test 1, but those infused with 16% glucose showed only a small increase in intake, which may reflect a counteracting satiating effect. Both groups further increased CS+ intakes in Tests 2 and 3, and preferred (81%) the CS+ to the CS− in a two-bottle test without infusions. A second experiment investigated rats' responses to IG alpha-methyl-d-glucopyranoside (MDG), a non-metabolizable sugar analog which stimulates CS+ intake and preference in mice. The rats reduced their intake of the MDG-paired CS+ flavor over sessions, and preferred the CS− to the CS+ in the choice test. The glucose data show that rats, like mice, rapidly detect the sugar's positive post-oral effects that can stimulate intake within the first hour of exposure. The MDG avoidance may indicate a greater sensitivity to its post-oral inhibitory effects in rats than in mice, or perhaps slower clearance of MDG in rats. The test protocol described here can be used to investigate the peripheral and central processes involved in stimulation of intake by post-oral nutrients in rats.

Vesiculovirus Neutralization by Natural IgM and Complement

Because of its very low human seroprevalence, vesicular stomatitis virus (VSV) has promise as a systemic oncolytic agent for human cancer therapy. However, as demonstrated in this report, the VSV infectious titer drops by 4 log units during the first hour of exposure to nonimmune human serum. This neutralization occurs relatively slowly and is mediated by the concerted actions of natural IgM and complement. Maraba virus, whose G protein is about 80% homologous to that of VSV, is relatively resistant to the neutralizing activity of nonimmune human serum. We therefore constructed and rescued a recombinant VSV whose G gene was replaced by the corresponding gene from Maraba virus. Comparison of the parental VSV and VSV with Maraba G substituted revealed nearly identical host range properties and replication kinetics on a panel of tumor cell lines. Moreover, in contrast to the parental VSV, the VSV with Maraba G substituted was resistant to nonimmune human serum. Overall, our data suggest that VSV with Maraba G substituted should be further investigated as a candidate for human systemic oncolytic virotherapy applications. Oncolytic virotherapy is a promising approach for the treatment of disseminated cancers, but antibody neutralization of circulating oncolytic virus particles remains a formidable barrier. In this work, we developed a pseudotyped vesicular stomatitis virus (VSV) with a glycoprotein of Maraba virus, a closely related but serologically distinct member of the family Rhabdoviridae, which demonstrated greatly diminished susceptibility to both nonimmune and VSV-immune serum neutralization. VSV with Maraba G substituted or lentiviral vectors should therefore be further investigated as candidates for human systemic oncolytic virotherapy and gene therapy applications.

Microstructural Investigation of the HCl-Induced Corrosion of the Austenitic Alloy 310S (52Fe26Cr19Ni) at 500 °C

This paper investigates the influence of 500 ppm HCl in a 5 %O2-95 %N2 atmosphere on the oxidation of the austenitic stainless steel AISI 310S at 500 °C. Laboratory exposures were made for one, 24, 72 and 168 h and the samples were analysed with XRD, SEM/EDX, FIB and TEM/EDX. When exposed in oxygen a thin and protective chromium-rich oxide scale forms. Addition of HCl causes significantly accelerated corrosion. Within the first hour of exposure, accumulations of FeCl2, CrCl2 and NiCl2 forms below the chromium-rich oxide, especially at steel grain boundaries. The chlorine-induced corrosion is suggested to occur through an electrochemical reaction, in which the dissociation of HCl to form chloride ions at the scale surface is coupled to the oxidation of the metal surface beneath the scale by an outwards electronic current and inwards diffusion of chloride ions along oxide grain boundaries

Impact of contaminated-sediment resuspension on phytoplankton in the Biguglia lagoon (Corsica, Mediterranean Sea)

In shallow human-impacted systems, sediment resuspension events can result in pulsed exposures of pelagic organisms to multiple contaminants. Here, we examined the impact of the resuspension of contaminated sediment on phytoplankton in the Biguglia lagoon (Corsica, Mediterranean Sea), by conducting an in situ microcosm experiment over a 96-h period. Natural phytoplankton was exposed to elutriates prepared from a contaminated-sediment resuspension simulating process, and its functional and structural responses were compared with those of non-exposed phytoplankton. The elutriates displayed moderate multiple contamination by trace metals and PAHs. Our results show that elutriate exposure induced both functional and structural phytoplankton changes. Elutriates strongly stimulated phytoplankton growth after 24 h of exposure. They also enhanced phytoplankton photosynthetic performance during the first hours of exposure (up to 48 h), before reducing it toward the end of the experiment. Elutriates were also found to slightly stimulate Bacillariophyceae and conversely to slightly inhibit Dinophyceae in the short term. Additionally, they were found to stimulate phycocyanin-rich picocyanobacteria in the short term (8–48 h) before inhibiting it in the longer term (72–96 h), and to inhibit eukaryotic nanophytoplankton in the short term (8–48 h) before stimulating it in the longer term (72–96 h). Sediment resuspensions are thus likely to have significant effects on the global dynamics and functions of phytoplankton in contaminated coastal environments.

Extracting words from the speech stream at first exposure

The earliest stages of adult language acquisition have received increased attention in recent years (cf. Carroll, introduction to this issue). The study reported here aims to contribute to this discussion by investigating the role of several variables in the development of word recognition strategies during the very first hours of exposure to a novel target language (TL). Eighteen native speakers of French with no previous exposure to Polish were tested at intervals throughout a 6.5-hour intensive Polish course on their ability to extract target words from Polish sentences. Following Rast and Dommergues’ (2003) first exposure study, stimuli were designed to investigate the effect of three factors: the lexical transparency of the target word with respect to the native language (L1); the frequency of the target word in the input; the target word’s position in the sentence.Results suggest that utterance position plays an essential role in learners’ ability to recognize words in the signal at first exposure, indicating acute sensitivity to the edges of prosodic domains. In addition, transparent words (e.g. professor ‘professor’) were recognized significantly better than non-transparent words (e.g. lekarz ‘doctor’), suggesting that first exposure learners are highly dependent on L1 phonological forms. Furthermore, the frequency of a target word in the input did not affect performance, suggesting that at the very beginning stages of learning, the amount of exposure to a lexical item alone does not play a significant role in recognition.

Effects of Copper and Cadmium Exposure on mRNA Expression of Catalase, Glutamine Synthetase, Cytochrome P450 and Heat Shock Protein 70 in Tambaqui Fish (Colossoma Macropomum)

In this work the authors evaluated the expression of cat, glu, cypP450, hsp70 and 18S RNA in Colossoma macropomum following exposure to copper and cadmium by semi-quantitative RT-PCR and quantitative qRT-PCR. In RT-PCR and qRT-PCR hsp70 expression was highest after exposure to copper for 3 hours (h). glu expression increased after exposure to cadmium, regardless of time. cat expression increased after the first hour of exposure to both metals, and decreased after 3 hs. cyp450 expression was higher when compared to controls in exposed fish regardless of metal and exposure time. cyp450 expression after exposure to copper for 3 h was twice that recorded after 1 h. In the presence of cadmium, cyp450 expression was higher in the animals exposed for 1 h and lower at 3 h. Therefore, toxicology tests and biomonitoring based on molecular markers should focus on a set of molecular and/or environmental parameters, rather than isolated markers.

Dynamics of uptake and elimination of 17α-ethinylestradiol in male goldfish (Carassius auratus)

We used male goldfish (Carassius auratus) as a model species to determine the uptake, elimination, and bioaccumulation of 17α-ethinylestradiol (EE2). Goldfish were exposed to EE2 via two different routes: water (135ng/L±12.8 standard deviation) for 72h, and food (231ng/g±42 SD) for 120h. We observed a rapid uptake of EE2 in goldfish, reaching 8.4ng/g±1.2 dry weight (dw) after the first hour of exposure with an uptake rate coefficient (k1) of 45h−1. The elimination rate coefficient (k2) was determined by a depuration experiment to be 0.0786h−1. In the feeding experiment, EE2 concentrations increased rapidly, reaching an average of 1.4ng/g after 3h following the first dietary exposure with an estimated absorption efficiency (α) of 0.106. An average of 2.66ng/g±0.87 (n=8) was determined in the 24–72h samples, whereas EE2 concentrations in fish fell below our method detection limits (0.67ng/g) for all samples after 72h, suggesting efficient elimination over time. The bioconcentration factor (BCF) for EE2 reached a maximum of 377, similar to BCFs measured for other pharmaceuticals like fluoxetine and sertraline. Our kinetic data were also used to model various scenarios of EE2 uptake in the aquatic environment. To our knowledge, this is the first report to describe aqueous and dietary EE2 uptake and elimination in fish, as well as providing important data to model EE2 kinetics in fish.

Impedance spectroscopy studies of electroless Ni–P matrix, Ni–W–P, Ni–P–ZrO2, and Ni–W–P–ZrO2 coatings exposed to 3.5% NaCl solution

AbstractNi–P matrix, ternary Ni–W–P and Ni–P–ZrO2 coatings, and quaternary Ni–W–P–ZrO2 coatings were deposited using electroless method from a glycine bath. Their corrosion resistance was evaluated by electrochemical impedance spectroscopy (EIS) for various immersion times in a 3.5% NaCl solution. From among the investigated coatings, the ternary Ni–W–P coatings show the highest resistance to corrosion in the first hour of exposure to the 3.5% NaCl medium. An addition of ZrO2 adversely affects the performance of both the Ni–P coatings and the Ni–W–P coatings. For all the coatings, including the ones containing tungsten, a marked decrease in pore resistance (Rpor) over time is observed. This means that their corrosion resistance and capacity to protect the substrate decline. On the other hand, after 24 h immersion in the 3.5% NaCl solution the Ni–W–P coating shows the highest low‐frequency impedance modulus (|Z|f = 0.01 Hz). As regards corrosion resistance, the Ni–P coatings and the Ni–W–P coatings perform best.

Formation and magnetic manipulation of periodically aligned microchains in thin plastic membranes

We demonstrate the fabrication of polymeric membranes that incorporate a few layers of periodically aligned magnetic microchains formed upon the application of variable magnetic fields. A homogeneous solution containing an elastomeric polymer and a small amount of colloidal magnetic nanoparticles is spin coated on glass slides, thereby forming thin magnetic membranes of ca. 10 μm thickness. Subsequent application of a homogeneous magnetic field results in the orientation of the magnetic clusters and their further motion into the matrix along the field lines forming layers of aligned chains. The study of the kinetics of alignment demonstrates that the chains are formed in the first hour of exposure to the magnetic field. Above all, a detailed microscopy study reveals that the dimensions and the periodicity of the microchains are effectively controlled by the intensity of the magnetic field, in good agreement with the theoretical simulations. This ability to form and manipulate the size and the distribution of chains into the polymeric matrix gives the opportunity to develop multifunctional composite materials ready to be used in various applications such as electromagnetic shielding, or multifunctional magnetic membranes etc.

Deposition and Characteristics of Submicrometer-Structured Thermal Barrier Coatings by Suspension Plasma Spraying

In the field of thermal barrier coatings (TBCs) for gas turbines, suspension plasma sprayed (SPS) submicrometer-structured coatings often show unique mechanical, thermal, and optical properties compared to conventional atmospheric plasma sprayed ones. They have thus the potential of providing increased TBC performances under severe thermo-mechanical loading. Experimental results showed the capability of SPS to obtain yttria stabilized zirconia coatings with very fine porosity and high density of vertical segmentation cracks, yielding high strain tolerance, and low Young’s modulus. The evolution of the coating microstructure and properties during thermal cycling test at very high surface temperature (1400 °C) in our burner rigs and under isothermal annealing was investigated. Results showed that, while segmentation cracks survive, sintering occurs quickly during the first hours of exposure, leading to pore coarsening and stiffening of the coating. In-situ measurements at 1400 °C of the elastic modulus were performed to investigate in more detail the sintering-related stiffening.

Enhanced Protective Properties and Structural Order of Self-Assembled Monolayers of Aromatic Thiols on Copper in Contact with Acidic Aqueous Solution

In the present work we used different techniques to study self-assembled monolayers (SAMs) of two aromatic thiols, namely, benzenethiol (BT) and 2-naphthalenethiol (2-NT), and one alkylic thiol, 1-undecanethiol (1-UT), on polycrystalline copper, comparing their corrosion inhibition efficiency and their stability up to a week in H2SO4 0.5 M. Both electrochemical impedance spectroscopy (EIS) and linear polarization highlighted different aging trends for 1-UT on one side and aromatic thiols on the other. 1-UT was initially the best corrosion inhibitor among the three thiols, as expected from its larger thickness, but it degraded very rapidly. On the contrary, BT and 2-NT showed a noticeable increase of their protective properties during the first hours of exposure to the electrolyte leading to a superior performance over any 1-UT sample. Raman spectroscopy suggested this behavior to be related to an enhancement of the structural order of the aromatic layer. In addition, both XP spectroscopy and electrochemical measurements revealed BT and 2-NT layers to be stabler than 1-UT. In particular, BT layers exposed to H2SO4 0.5 M exhibited better protective properties, with respect to the freshly prepared samples, lasting for over 1 week of aging.