Initial Immersion Period Research Articles

Seasonal patterns of colonization and early succession on sublittoral rocky cliffs

Understanding the mechanisms of ecological succession is fundamental to predict recovery patterns and restore the increasingly disturbed marine habitats; the season in which disturbance occurs severely affects these processes but this factor has not been thoroughly studied in sublittoral cliffs. Thus, seasonal patterns of benthic colonization and succession were investigated on a temperate rocky cliff (Aegean Sea, eastern Mediterranean). Cement panels, seasonally installed on the rocky substratum at 25–30 m depth, were sampled every 3 months over a 1-year period each, yielding 40 floral and 158 animal species. Diversity, cover and abundance were very low at the initial immersion period and increased toward the late periods. The immersion period and the season of installation had a strong effect on diversity and abundance; decapods showed increased colonization on panels installed in spring, and polychaetes on hibernal panels. The vagile fauna responded to the increasing habitat complexity offered by the development of algal turfs and sessile species. Community structure remained highly dynamic up to the end of the experimental installation and quite different from that of the surrounding benthic community. Two stages of succession, considering vagile and sessile biota, either separately or altogether, were observed over immersion periods; the first was characterized by high variability that can be related to the presence of different colonizers in different seasons, whereas the second, exhibited higher species richness and abundance and showed increased endogenous similarity. Thus, regardless of the season colonization started the developed communities converged toward a common structure, after one year of immersion. An exception was hibernal installation, in which the 12-month immersion period was recognized as a third stage characterized by increased diversity also showing an increased similarity with the adjacent algal community; this suggests that benthic colonization in such environments is faster when succession starts in winter.

Electrochemical Corrosion Behaviors of Rusted Carbon Steel

Electrochemical methods including polarization curves, linear polarization resistance (LPR), and electrochemical impedance spectroscopy (EIS) were used to characterize and investigate the electrochemical behavior of rusted carbon steel immersed in seawater. Results indicate that the inner rust layer that forms on the surface of the carbon steel after long. term immersion greatly affects the electrode process. Polarization resistance (R(p)), determined by LPR and EIS, increases during the initial immersion period. After long. term immersion, it decreases. R(p) initially increases and then decreases gradually with immersion time. The electrochemical characteristics of the rusted carbon steel were studied by removing the outer and inner rust layers. The materials were analyzed by Fourier transform infrared (FTIR) spectroscopy and their cross. sectional morphologies were obtained to determine the cause. The results show that the beta-FeOOH, which exists in the inner rust layer, has high electrochemical activity. Its content increases with the growth of the inner rust layer. In the electrochemical tests, even a small amount of polarization allows beta-FeOOH to participate in the cathodic reduction reaction. Besides the anodic dissolution of iron and the cathodic reduction of oxygen, rust reduction is also possible. For this reason, the cathodic reaction rate is promoted and R(p) decreases.

Degradation kinetics of calcium polyphosphate bioceramic: an experimental and theoretical study

In this work, the degradation kinetics of calcium polyphosphate bioceramic was studied. Liquid state 31P nuclear magnetic resonance (NMR), X-ray diffraction (XRD) and scanning electron microscope (SEM) were used to characterize the product. The in vitro degradation test was carried out at 37 oC for up to 48 hours for both the simulation solution and the extreme solution. The ion concentrations were measured and analyzed by establishing a mathematical model referring to the chemical reaction kinetics. The results indicated that the degradability of calcium polyphosphate increased with the decrease of pH value, and the sample showed a rapid loss of ion concentration within the initial period of immersion followed by a slower loss ratio. The relationship between ion concentration and the degradation time coincided with Boxlucas model.

Studies of water transport behavior and impedance models of epoxy-coated metals in NaCl solution by EIS

Using electrochemical impedance spectroscopy (EIS) technique, the analyses of impedance models and the water uptake processes of epoxy-coated mild steels and LY12 aluminum alloys immersed in 3.5% (weight fraction) NaCl solution were studied. The fitting results using suitable electrical equivalent circuits (EEC) suggested that there were four kinds of impedance models in the course of immersion. In the initial period of immersion, an EEC containing the coating capacitance and the coating resistance was used to fit the EIS data. Along with the immersion time, the number of time-constant of impedance spectra for metal/coating systems increased, indicating that corrosion reaction took place. After a certain time's attacking of metal substrates, the diffusion process towards solution of corrosion products forming at the metal/coating interface might be restrained due to the presence of coating barrier, resulting in the appearance of diffusion elements. This diffusion did not act as an ideal Warburg behavior, leading to a deviation of dispersive number, n, from 0.5. After longer immersion times, the Cl − ions reached the surface of metal through the coating and participated in chemical reactions with corrosion products to form salt film on aluminum alloy surface. The formation of chloride ion-incorporation salt film resulted in the change of impedance spectrum characteristics. The studies revealed that the water transport in epoxy varnish coatings followed the Fickian diffusion law during the initial time of exposure to the testing solution. After immersion for a certain time, the water uptake reached saturation and the coating capacitance tended to a relatively steady value. According to the variation of coating capacitance with time, the water diffusion coefficient was deduced. The experimental results indicated that the water diffusion coefficients in epoxy coatings were slightly dependent on coating thickness and were to some extent influenced by substrate type. The similar surface chemical structures of epoxy coatings on different metals were found from the Fourier transform infrared spectroscopy (FT-IR)–attenuated total reflection (ATR) measurements. The glass transition temperature ( T g) of epoxy coatings prepared on different metal substrates before and after immersion was measured by using differential scanning calorimetry (DSC). Lower diffusion rate of water in Al alloy based epoxy films than that in steel based ones was interpreted by the higher absolute value and smaller decrease of T g of organic coatings painted on the former substrate.

Studies of impedance models and water transport behaviors of polypropylene coated metals in NaCl solution

Using electrochemical impedance spectroscopy (EIS) technique, the water uptake process and the evolution of impedance models of polypropylene coated mild steels and LY12 Al alloys immersed in 3.5% (weight fraction) NaCl solution were studied. The equivalent electrical circuit (EEC) fitting results suggested that there was one single semi-circle in the impedance spectra of immersed samples in the initial period of immersion, which was corresponded to one time constant. Along with the immersion time, the number of time constant in EEC for metal/coating electrode system increased. The diffusion process towards solution of corrosion products forming on the metal/coating interface might be restrained due to the influence of coating barrier, resulting in the initiation of diffusion component in EEC. This diffusion did not act as a Warburg behavior, leading to a deviation of dispersive number, n, from 0.5. The studies revealed that the water transport in polypropylene clear varnish followed the Fickian diffusion during the initial time of exposure to the solution. After a certain time of immersion, the water uptake reached a saturation value. According to the variation of coating capacitance with time, the water diffusion coefficient was deduced. The experimental results indicated that the water diffusion coefficients in polypropylene coatings were independent of substrate materials used and coating thickness. Relative dielectric constant of dry coatings ( ε d) and water volume fraction of the coatings at saturation ( φ ∞) were also calculated. The similar results were found in time dependence of coating capacitance calculated from the impedance imaginary component at a fixed high frequency and that obtained from the fitting result by EEC, which indicated that the coating capacitance from the impedance imaginary component was reliable to evaluate barrier performance of coatings against water.

Gas Generation Behavior of Transuranic Waste Under Disposal Conditions

AbstractThe generation of hydrogen-gas from metallic waste is an important issue for the safety analysis of geological disposal facilities for transuranic (TRU) radioactive waste in Japan. The objective of this study is to clarify the gas-generation behavior of stainless steel and carbon steel in non-oxidizing alkaline synthetic groundwater (pH 12.8 and 10.5) at 30 °C simulating geological disposal environments. At pH 12.8, the observed gas-generation rate from stainless steel in the initial period of immersion was 1.0 × 102 Nml/m2/y and 1.0 × 10 Nml/m2/y after 200 days (N represents the standard state of gas at 0 °C and 1 atm). At pH 10.5, gas generation was not observed for 60 days in the initial period. At 60 days, the gasgeneration observed was 5.0 × 10 Nml/m2/y. After 250 days, the gas-generation rate approaches zero. At pH 12.8, the observed gas generation rate of carbon steel in the initial period of immersion was 1.5 × 102 Nml/m2/y and the gas generation rate began to decrease after 200 days. After 300 days, it was 25 Nml/m2/y. At pH 10.5, the gas generation rate in the initial period was 5.0 × 102 Nml/m2/y and was 1.0 × 10 Nml/m2/y after 200 days.

Chemical Reaction of Lithium Surface during Immersion in LiClO4 or LiPF6 / DEC Electrolyte

Chemical reactions of lithium with diethyl carbonate (DEC) containing or ( or ) were studied by using in situ Fourier transform infrared (FTIR) and x‐ray photoelectron spectroscopies. The in situ FTIR spectra for both electrolytes show a penetration of the DEC electrolyte into the native surface film on lithium foils at the initial period of immersion. In the case of , the DEC solvent contacts the lithium metal, and then reacts directly with lithium metal to form reductive decomposition products of DEC, such as lithium alkylcarbonate, lithium alkoxide, and . When was used as the electrolyte, the native surface film was gradually etched and then changed to a bilayer surface film. The in situ FTIR spectra showed no formation of decomposition products of DEC. This means that the surface film consisting of was highly effective in suppressing the direct chemical reactions of DEC with lithium metal.

Macroinvertebrates and the Processing of Leaf Litter in a Tropical Stream

The processing of leaf litter in temperate streams has been the subject of numerous studies but equivalent tropical ecosystems have received little attention. The decomposition and macroinvertebrate colonisation of leaf litter was investigated using litter bags placed in a first-order rainforest stream over a 48 day period. Changes in leaf chemistry were also studied. Decay of the fresh, mixed-species litter was rapid (2.5 % day-') in comparison to that typically observed in temperate streams. The high water temperatures (21?C) at the study site are considered an important factor in the decay rate observed. Initially, average nitrogen content was high (3.5%). Content decreased to 3.1 percent after six days immersion and, thereafter, remained relatively constant. The consequent lack of evidence for microbial conditioning was attributed to species-specific differences in decay rate, giving rise to an overlapping sequence of conditioning and mineralisation of each leaf species within individual litter bags. Soluble polyphenols were largely leached from litter during the initial period of immersion. Constancy in remaining polyphenol content may be due to complexing with proteins and/or lignin compounds. The invertebrate community which colonised litter bags was dominated by insect groups and species richness was lower than that typical of many temperate streams. Colonisation dynamics differed among functional feeding groups: collector abundance increased on a linear basis whereas shredder and predator groups increased logarithmically. Despite differences in decay rate and taxonomic composition of the invertebrate community, the pattern of leaf litter utilisation and decay in the tropical stream studied was similar to that typically observed in temperate streams.

The Corrosion Behavior of Iron and Aluminum Under Waste Disposal Conditions

ABSTRACTThe generation of hydrogen gas from metallic waste in corrosive disposal environment is an important issue for the safety analysis of low-level radioactive waste disposal facilities in Japan. In particular iron and aluminum are the possibly important elements regarding the gas generation. However, the corrosion behavior of these metals has not been sufficiently investigated under the highly alkaline non-oxidizing disposal conditions yet.We studied the corrosion behavior of iron and aluminum under simulated disposal environments. The quantity of hydrogen gas generated from iron was measured in a closed cell under highly alkaline non-oxidizing conditions. The observed corrosion rate of iron in the initial period of immersion was 4 nm/year at 15 °C, 20 nm/year at 30 °C, and 200 nm/year at 45 °C. The activation energy was found to be 100 kJ/mol from Arrhenius plotting of the above corrosion rates.The corrosion behavior of aluminum was studied under an environment simulating conditions in which aluminum was solidified with mortar. In the initial period aluminum corroded rapidly with a corrosion rate of 20 mm/year. However, the corrosion rate decreased with time, and after 1,000 hours the rate reached 0.001 to 0.01 mm/year.Thus we obtained data on hydrogen gas generation from iron and aluminum under the disposal environment relevant to the safety analysis of low-level radioactive disposal facilities in Japan.

Effect of phosphorus on the passivation behavior of amorphous Fe8Cr13P7C alloy in 9M H 2SO 4 solution

The beneficial effect of phosphorus on the corrosion and passivation behavior of amorphous Fe8Cr13P7C alloy was studied in 9M H 2SO 4 solution at 30 °C. The corrosion loss of the amorphous Fe8Cr13P7C alloy in an initial period of immersion was relatively high but was scarcely changed afterwards. The corrosion potential was initially in the active region of this alloy but was shifted positively up to the passive region within 30 min. The air-formed film was enriched in chromium but was not protective and dissolved quickly in the initial stage of corrosion. The concentration of chromic ions in the surface film increased with the immersion time. Elemental phosphorus was accumulated on the alloy surface during the initial dissolution. The formation of the elemental phosphorus layer made the open circuit potential more positive as a result of the acceleration of the cathodic hydrogen evolution and by the suppression of the anodic dissolution current. This led to spontaneous passivation as a result of the formation of the chromium-enriched passive film.

二重塗装鋼板の交流インピーダンス

A new electrochemical method was proposed for an evaluation of the protective ability of the inner paint film of doubly coated metal specimen with two different types of paint. The method consisted of the measurement of A. C. impedance of the doubly coated specimen and that of singly coated specimens with the constituent paint film. The impedance of the imagined doubly coated specimen was calculated from the measurements of the singly coated specimens. A comparison was made between the calculated and the observed impedances of doubly coated specimen in order to elucidate the influence of direct contact with the salt solution upon the impedance of inner paint film.The method was applied to three typical paint systems immersed in 0.5M NaCl solution, that is, the primer-top coat paint system, the wash primer-primer system and the zinc rich paint-primer system. No actual difference was observed in the first system. Moreover, in the second system, the inner layer of wash primer was found to exist in a highly conductive state even when it was covered with a primer paint film.The most remarkable change was observed in the last system, since the zinc rich paint was highly conductive when it was directly in contact with salt solution and, in contrast, highly resistive when indirectly in contact. From this observation, it is expected that, from the initial period of immersion, zinc rich paint acts in accordance with the so-called resistant control mechanism for a reasonably long while until the beginning of the breakdown of primer or top coat paint film.