ELECTRODEPOSITION OF PLATINUM PARTICLES ON GLASSY-CARBON MODIFIED WITH COBALT PORPHYRIN AND NAFION FILM AND THEIR ELECTROCATALYTIC REDUCTION OF DIOXYGEN

In this paper, five types of chemically modified electrode (CMEs) prepared with the deposition of platinum particles on various surfaces of glassy carbon (GC) modified with cobalt porphyrin and Nafion(R) solution are characterized using the electron scanning microscope (SEM). Their activities in the four-electron reduction of dioxygen to water on the basis of their electrochemical data from cyclic voltammetric and rotating ring-disk electrode (RRDE) experiments are examined and compared. Platinum particles dispersed on the GC surface adsorbed with the cobalt porphyrin exhibit the highest activity for the electrocatalytic reduction of dioxygen. However it is interesting that the cobalt ion is lost from the center of the porphyrin ring during the preparation of the cobalt porphyrin + Nafion mixture solution, while the porphyrin ring still remains in the Nafion film, as shown by EDX analysis. The incorporation of the porphyrin may change the structure of the Nafion film into a looser form, since the platinum particles dispersed in the film are more readily exposed, resulting in more favourable mass transfer and higher activity for the electrocatalytic reduction of dioxygen.

Electrochemical investigations of micro-droplets formed on metals during the deliquescence of salt particles in atmosphere

CORROSION; WATER; SPECTROSCOPY; CHLORIDE; ZINC; NUCLEATION; INTERFACE; ELECTRODE; SURFACES; GROWTH

Phenomenon of micro-droplets formation on metals during the deliquescence of salt particles in atmosphere

CORROSION; MECHANISM; WATER; ZINC

Effective nonlinear AC response to composite with spherical particles

An effective nonlinear alternative-current (AC) response to granular nonlinear-composite with spherical inclusions embedded in a host medium under the action of an external AC field is investigated by using a perturbation approach. The local potentials of composite at higher harmonics are derived both in a region of local inclusion particles and in a local host region under the action of a sinusoidal field E-1 sin ω t + E-3 sin 3ω t. An effective nonlinear-response to composite and the relationship between the effective nonlinear-responses at the fundamental frequency and the third harmonics are also studied for the spherical inclusions in a dilute limit.

Effective dielectric responses of graded composites of the particles with a general power-law gradation profile

The effective dielectric response of graded spherical composites having general power-law gradient inclusions is investigated under a uniform applied electric field, where the dielectric gradation profile of the spherical inclusions is modeled by the equation epsilon(i) (r) = c(b+r)(k). Analytical solutions of the local electrical potentials are derived in terms of hyper-geometric function and the effective dielectric response of the graded composites is predicted in the dilute limit. From our result, the local potentials of graded spherical composites having both simple power-law dielectric profile epsilon(i)(r) = cr(k) and linear dielectric profile epsilon(i) (r) = c(b+r) are derived exactly by taking the limits b --> 0 and k --> 1, respectively. In the dilute limit, our exact result is used to test the validity of differential effective dipole approximation (DEDA) for estimating the effective response of graded spherical composites, and it is shown that the DEDA is in excellent agreement with exact result. (C) 2005 Elsevier B.V. All rights reserved.

Dielectric response of composites with graded cylindrical particles

Effective dielectric responses of graded cylindrical composites are investigated when an external uniform field is applied to the composites. Considering linear random composites of cylindrical particles with a specific dielectric function, which varies along the radial direction of the particles, we have studied three cases of dielectric profiles: exponential function, linear and power-law profiles. For each case, the effective dielectric response of graded composites is given on the basis of exact solutions of the local potentials of composites in the dilute limit. For a larger volume fraction, we have proposed an effective medium approximation to estimate the effective dielectric response.

Distribution of calcifying and silicifying phytoplankton in relation to environmental and biogeochemical parameters during the late stages of the 2005 North East Atlantic Spring Bloom

The late stage of the North East Atlantic (NEA) spring bloom was investigated during June 2005 along a transect section from 45 to 66 degrees N between 15 and 20 degrees W in order to characterize the contribution of siliceous and calcareous phytoplankton groups and describe their distribution in relation to environmental factors. We measured several biogeochemical parameters such as nutrients, surface trace metals, algal pigments, biogenic silica (BSi), particulate inorganic carbon (PIC) or calcium carbonate, particulate organic carbon, nitrogen and phosphorus (POC, PON and POP, respectively), as well as transparent exopolymer particles (TEP). Results were compared with other studies undertaken in this area since the JGOFS NABE program. Characteristics of the spring bloom generally agreed well with the accepted scenario for the development of the autotrophic community. The NEA seasonal diatom bloom was in the late stages when we sampled the area and diatoms were constrained to the northern part of our transect, over the Icelandic Basin (IB) and Icelandic Shelf (IS). Coccolithophores dominated the phytoplankton community, with a large distribution over the Rockall-Hatton Plateau (RHP) and IB. The Porcupine Abyssal Plain (PAP) region at the southern end of our transect was the region with the lowest biomass, as demonstrated by very low Chla concentrations and a community dominated by picophytoplankton. Early depletion of dissolved silicic acid (DSi) and increased stratification of the surface layer most likely triggered the end of the diatom bloom, leading to coccolithophore dominance. The chronic Si deficiency observed in the NEA could be linked to moderate Fe limitation, which increases the efficiency of the Si pump. TEP closely mirrored the distribution of both biogenic silica at depth and prymnesiophytes in the surface layer suggesting the sedimentation of the diatom bloom in the form of aggregates, but the relative contribution of diatoms and coccolithophores to carbon export in this area still needs to be resolved.

Main geochemical characteristics and key biogeochemical carbon processes in the East China Sea

Research related to carbon geochemistry and biogeochemistry in the East China Sea is reviewed in this paper. The East China Sea is an annual net sink for atmospheric CO, and a large net source of dissolved inorganic carbon to the ocean. The sea absorbs CO, from the atmosphere in spring and summer and releases it in autumn and winter. The East China Sea is a CO, sink in summer because Changjiang River freshwater flows into it. The net average sea-air interface carbon flux of the East China Sea is estimated to be about 4.3 X 10(6) t/y. Vertical carbon transport is mainly in the form of particulate organic carbon in spring; more than 98% of total carbon is transported in this form in surface water, and the number exceeds 68% in water near the bottom. In the southern East China Sea, the average particulate organic carbon inventory was about one-tenth that of the dissolved organic carbon. Research indicates that the southern Okinawa Trough is an important site for particulate organic carbon export from the shelf. The annual cross-shelf exports are estimated to be 414 and 106 Gmol/y for dissolved organic carbon and particulate organic carbon, respectively. Near-bottom transport could be the key process for shelf-to-deep sea export of biogenic and lithogenic particles.

Trace metal concentrations in suspended particles, sediments and clams (Ruditapes philippinarum) from Jiaozhou Bay of China

Suspended particulate matter (SPM), sediments and clams were collected at three sites in Jiaozhou Bay to assess the magnitude of trace metal pollution in the area. Metal concentrations in SPM (Cu: 40.11-203; Zn: 118-447; Pb: 50.1-132; Cd: 0.55-4.39; Cr: 147.6-288; Mn: 762-1670 mu g/g), sediments (Cu: 17.64-34.26; Zn: 80.79-110; Pb: 24.57-49.59; Cd: 0.099-0.324; Cr: 41.6-88.1; Mn: 343-520 mu g/g) and bivalves (Cu: 6.41-19.76; Zn: 35.5-85.5; Pb: 0.31-1.01; Cd: 0.51-0.67; Mn: 27.45-67.6 mu g/g) are comparable to those reported for other moderately polluted world environments. SPM showed a less clear pattern. Metal concentrations in sediments displayed a clear geographical trend with values increasing with proximity to major urban centers. The clams (on dry weight) showed a complex pattern due to the variability introduced by age-related factors. Cd showed an apparent reverse industrial trend with higher concentrations in clams collected at distant stations. Zn, Pb and Mn showed no clear geographical pattern, whereas Cu increased in the clams collected in the most industrialized area. In addition, the bioaccumulation factors (BAF) were calculated. The result indicated that the studied Ruditapes philippinarum in Jiaozhou Bay possessed different bioaccumulation capacities for Cd, Zn, Cu, Pb and Mn, and Cd, Zn had a relatively high assimilation of those metals from sediment particles. A significant relationship with clam age was observed for Zn (positive) and Cu (negative) suggesting different physiological requirements for both metals with age. Trace metal concentrations measured in the tissue of the investigated clam were in the range considered safe by the WHO for human use.

Low-temperature molten salt synthesis and characterization of CoWO4 nano-particles

CoWO4 nano-particles were successfully synthesized at a low temperature of 270 degrees C by a molten salt method, and effects of such processing parameters as holding time and salt quantity on the crystallization and development Of CoWO4 crystallites were initially studied. The products were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM). and photoluminescent spectra techniques (PL), respectively. Experimental results showed that the well-crystallized CoWO4 nano-particles with ca. 45 nm in diameter could be obtained at 270 degrees C for a holding time of 8 h with 6:1 mass ratio of the salt to CoWO4 precursor, and XRD analysis evidenced that the as-prepared sample was a pure monoclinic phase Of CoWO4 with wolframite structure. Their PL spectra revealed that the CoWO4 nano-particles displayed a very strong PL peak at 453 nm with the excitation wavelength of 230 nm, and PL properties of CoWO4 crystallites relied on their crystalline state, especially on their particle size. (C) 2009 Elsevier B.V. All rights reserved.

Synthesis of NiWO4 nano-particles in low-temperature molten salt medium

Nickel tungstate (NiWO4) nano-particles were successfully synthesized at low temperatures by a molten salt method, and characterized by Xray diffraction (XRD), transmission electron microscopy (TEM) and ultraviolet visible spectra techniques (UV-vis), respectively. The effects of calcining temperature and salt quantity on the crystallization and development of NiWO4 crystallites were studied. Experimental results showed that the well-crystallized NiWO4 nano-particles with about 30 nm in diameter could be prepared at 270 degrees C with 6:1 mass ratio of the salt to NiWO4 precursor. XRD analysis confirmed that the product was a pure monoclinic phase of NiWO4 with wolframite structure. UV-vis spectrum revealed that NiWO4 nano-particles had good light absorption properties in both ultraviolet and visible light region. (C) 2009 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

动物地磁导航磁受体的磁学探测及其矿化机理研究

This thesis focuses on the study of the geomagnetic orientation and navigation of homing pigeon and migrating bats. Magnetic minerals, possibly the base of the “magnetoreceptors”, which can perceive the magnetic information from geomagnetic field, are studied using advanced mineral magnetic methods in combination of non-magnetic techniques. In addition, the mechanism of magnetite biomineralization in organism has been probed through the formation of ferritin under laboratory-controlled conditions. A series of magnetic measurements of selected pigeon samples found the biogenic magnetite particles. a significant rapid decay of SIRM5K in the interval of 5–20 K on both zero-field cooled and field cooled warming curves suggests the dominance of superparamagnetic particles in the samples. Additionally, we noted that the content of magnetite particles in the male and the female are different. It is also found that bats contain magnetite. The results of room temperature magnetic measurements of Rhinolophus ferrumequinum and Chaerophon　plicatus samples indicates there are magnetite in the heads of bats. The concentration of magnetic materials in the brain is higher than that in the skull. The results of low temperature magnetic measurements in Nyctalus plancyi samples show that the head may contain a small quantity of magnetite particles. In order to study the magnetite biomineralizaiton, ferritin was reconstituted. The results of electron nanodiffraction patterns indicate that the dominant mineral phases in the reconstituted ferritin are ferrihydrite, which is similar to that in the native ferritin. The blocking temperature (TB) is near 20K. A series of magnetic hysteresis at low temperatures (3-21K) show the wasp-waisted hysteresis loop. This can be interpreted by either grain size effects (SP + SD) or different coercivities minerals.

Low temperature specific heat and thermal stability of Fe-B ultrafine amorphous alloy particles

Fe-B ultrafine amorphous alloy particles (UFAAP) were prepared by chemical reduction of Fe3+ with NaBHO4 and confirmed to be ultrafine amorphous particles by transmission electron microscopy and X-ray diffraction. The specific heat of the sample was measured by a high precision adiabatic calorimeter, and a differential scanning calorimeter was used for thermal stability analysis. A topological structure of Fe-B atoms is proposed to explain two crystallization peaks and a melting peak observed at T=600, 868 and 1645 K, respectively.