Interstitial Species Research Articles

Two new interstitial species of the genus Parapolycope (Crustacea: Ostracoda) from central Japan

Two new interstitial species of the genus Parapolycope (Crustacea: Ostracoda) from central Japan

Technetium Incorporation into Hematite (α-Fe2O3)

Quantum-mechanical methods were used to evaluate mechanisms for possible structural incorporation of Tc species into the model iron oxide, hematite (alpha-Fe2O3). Using periodic supercell models, energies for charge-neutral incorporation of Tc4+ or TcO4- ions were calculated using either a Tc4+/Fe2+ substitution scheme on the metal sublattice, or by insertion of TcO4- as an interstitial species within a hypothetical vacancy cluster. Although pertechnetate incorporation is found to be invariably unfavorable, incorporation of small amounts of Tc4+ (at least 2.6 wt %) is energetically feasible. Energy minimized bond distances around this impurity are provided to aid in future spectroscopic identification of these impurity species. The calculations also show that Fe2+ and Tc4+ prefer to cluster in the hematite lattice, attributed to less net Coulombic repulsion relative to that of Fe3+-Fe3+. These modeling predictions are generally consistent with observed selective association of Tc with iron oxide under reducing conditions, and in residual waste solids from underground storage tanks at the U.S. Department of Energy Hanford Site (Washington, U.S.). Here, even though relatively high pH and oxidizing conditions are dominant, Tc incorporation into iron oxides and (oxy)hydroxides is prospectively enabled by prior reduction of TcO4- to Tc4+ via interaction with radiolytic species.

Two new interstitial species of the genus Parapolycope (Crustacea: Ostracoda) from central Japan

Two new interstitial cladocopid ostracods are described from central Japan: Parapolycope oligohalina sp. nov, and Parapolycope spiralis sp. nov. These two species are the third and forth records of the genus Parapolycope Klie, 1936, respectively. Since P. oligohalina sp. nov. inhabits river mouth environments with low salinity at low tides, the wide tolerance to salinity in the species is shown. Myodocopan Ostracoda have so far been considered as a pure marine taxa. The occurrence of P. oligohalina sp. nov. indicates that a few myodocopan ostracods can live in oligohaline environments. The carapace surface covered with puncta of varying size is a unique character of P. oligohalina sp. nov. P. spiralis sp. nov. exhibits a spiral structure in both male copulatory duct and female spermatheca as specific characters. A key to the genera of the Polycopinae is presented.

Oxygen interstitial structures in close-packed metal oxides

We examine oxygen incorporation in alpha-Al 2O 3 using electronic structure techniques. We demonstrate that the ground-state configuration is a peroxide split interstitial, which is more than 2 eV lower in energy than the oxide closed-shell interstitial species in alumina, which proves to be only a transition state. Our results have general implications for the nature of oxygen interstitials in close-packed oxides.

Harpacticoida (Crustacea: Copepoda) of the South China Sea: faunistic and biogeographical analysis

Based on original and on published databases, a compendium of the Harpacticoida of the South China Sea is presented, and the distributional range of species is discussed. Up to now, a total of 77 harpacticoid species belonging to 57 genera and 19 families have been recorded in this region. Twenty of these species, collected in Nha-Trang Bay (Vietnam), have not hitherto been described. The most speciose families are the Miraciidae (20 species) and the Laophontidae (9 species). Thirteen families were represented by one to three species only and six families by four to seven species. A brief comparison is presented between the harpacticoid fauna of the South China Sea, the Philippine Islands, the inner Malayan Archipelago (Java, Flores, Banda, and Celebes Seas), New Guinea, the Yellow Sea, and the Andaman and Nicobar Islands. The overall similarity between the species lists of these areas was observed to be extremely low (average value of Simpson index is 0.15 ± 0.08). The lists of planktonic species from the different areas showed the highest similarity. The lowest similarity (highest endemism) was observed between the lists of interstitial species. It is likely that one of the factors determining the differences between the faunas is the poor knowledge about the composition and distribution of benthic harpacticoids in tropical latitudes.

Low temperature diffusion and oxygen stoichiometry in lanthanum nickelate

The tracer diffusion ( D*) and surface exchange coefficients ( k*) of polycrystalline lanthanum nickelate, La 2NiO 4 + δ (LNO), were measured over the temperature range 350 °C–700 °C using isotopic exchange and Secondary Ion Mass Spectrometry (SIMS). Diffusion profiles were obtained at low temperatures after relatively short anneal times. The polycrystalline material exhibits low activation energies for oxygen diffusion and surface exchange, which were calculated to be 0.54 eV and 0.63 eV, respectively. Oxygen excess was determined by iodometric titration after oxygen isotopic exchange, allowing for the calculation of the oxygen interstitial concentration, [O i ″]. At temperatures below 450 °C, [O i ″] increases with decreasing temperature, resulting in the low activation energy for diffusion in this temperature regime and supporting the theory of diffusion via oxygen interstitial species. The oxygen interstitial diffusion coefficient ( D i ) is calculated and is found to have an activation energy of 0.63 eV over the temperature range 350 °C–550 °C and to be approximately an order of magnitude greater compared with D*. Values calculated for D i are of the same order of magnitude as values for vacancy diffusion coefficients ( D v ) in perovskites.

Metasideronatrite: Crystal structure and its relation with sideronatrite

Metasideronatrite was obtained as the first dehydration product of sideronatrite, Na 2 Fe(SO 4 ) 2 (OH)∙3H 2 O, from Sierra Gorda, Chile. The crystal structure of metasideronatrite was solved by direct methods and refined by full-matrix least-squares to R = 0.039, using 574 independent reflections with I > 3.0σ(I). It is orthorhombic, space group Pbnm, with a = 7.3959(8), b = 16.0979(15), c = 7.1607(8) Å, V = 852.5(2) Å 3 , Z = 4. The crystal-chemical formula derived from this structural study is Na2Fe(SO 4 ) 2 (OH)∙H 2 O. The backbone of the structure is the same as that in sideronatrite: infinite [Fe 3+ (SO 4 ) 2 (OH)] 2- chains of interconnected octahedra and tetrahedra parallel to the c axis. These chains are linked primarily by Na atoms to build a 3-dimensional network of strong (Fe-O-S) and weak (Na-O) bonds. Another prominent feature of the structure is the arrangement of distorted (NaO 5 H 2 O) octahedra, which alternately share one edge and one face to form columns parallel to the [Fe 3+ (SO 4 ) 2 (OH)] chains. Subsidiary intra-chain bonds are provided by H atoms belonging to OH- groups shared by adjacent Fe octahedra, and to the unique water molecule shared between two adjacent (NaO 5 H 2 O) octahedra. At normal conditions of relative humidity (RH) and temperature (i.e., RH > 60% and T < 40 °C), metasideronatrite rehydrates rapidly to sideronatrite. The structure solution has allowed us to: (1) investigate the strong relation between sideronatrite and metasideronitrite; (2) elucidate the mechanism involved in the transformation of metasideronatrite into the order/disorder (OD) structure of sideronatrite; and (3) get insight into the stability of this mineral from the valence-matching principle applied to the main structural unit [Fe 3+ (SO 4 ) 2 (OH)] 2 and Na + interstitial species. The weak hydrogen bonds and the particular arrangement of the face-sharing adjacent [NaO 5 (H 2 O)] octahedra are the main factors affecting the stability of metasideronatrite.

The Role of Interstitial Hydrogen Species in Ni/YSZ Patterned Anodes: A 2D Modeling Study

The mechanistic details of the hydrogen oxidation at Ni/YSZ anodes are subject of controversial discussion. In the light of potential accumulation of secondary phases at the three-phase boundary, a mechanism involving interstitial hydrogen species in the bulk phases and charge-transfer at the Ni/YSZ two-phase boundary has been proposed. We present a quantitative analysis of this mechanism based on a two-dimensional elementary kinetic model of electrochemistry and bulk diffusion. The use of literature diffusion coefficients yields diffusion-limited current densities that are below those observed in experiments. Assuming increased diffusivity allows to quantitatively reproduce published experimental pattern anode data, including their dependence on gas composition and temperature. This shows the feasibility of interstitial mechanisms when impurities are present and explains their decreased performance. For clean three-phase boundaries, surface spillover pathways are preferred.

Anchialine fauna of the Corona lava tube (Lanzarote, Canary Islands): diversity, endemism and distribution

A checklist of 77 taxa recorded from the anchialine sections of the Corona lava tube is provided, including information on habitats, faunal distribution within the cave, and main references. Of the nine major groups recorded, Crustacea shows the highest diversity with 31 species and the highest degree of endemism (90.0%). Twenty-five species of Annelida are reported, 16 of which also occur in offshore waters (36.0% endemic). Except for two species, all annelids are benthic or interstitial species, whereas most of the crustaceans are either nektonic or epibenthic. Additionally, 13 species of Mollusca, 2 Nematoda, 2 Cnidaria, and 1 species each of Priapula, Ctenophora, Echinodermata and Echiura, are known from the lava tube, of which only 1 mollusc is endemic to this cave system.

Density functional simulations of noble-gas impurities in diamond

Noble-gas species are important impurities in the geological analysis of natural diamond and are also used in ion implantation on the basis of chemical inertness. We present the results of density functional simulations of noble-gas atoms in diamond. We show that interstitial species are relatively mobile under geological conditions but require annealing above $\ensuremath{\sim}700\text{ }\text{K}$ for laboratory-based experiments. In addition, with the exception of interstitial helium and neon, the noble-gas atoms are able to react chemically with the diamond due to the compact diamond lattice. This is of particular significance in terms of ion implanted material where noble-gas species trapped in lattice vacancies are electrically active and stable to high temperatures.

The Role of Interstitial Hydrogen Species in Ni/YSZ Patterned Anodes: A 2D Modeling Study

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The nitrogen photoactive centre in N-doped titanium dioxide formed via interaction of N atoms with the solid. Nature and energy level of the species

N-doped titanium dioxide has been prepared generating a nitrogen plasma in the atmosphere over a sample of pre-reduced TiO 2. This solid, investigated by EPR and XPS, is similar to materials prepared via sol–gel or different chemical methods. The cleaner preparation method, however, avoids complications in the assignments due to by-products of the chemical synthesis. The experiment unambiguously confirms previous theoretical forecast and indicates the formation of an interstitial paramagnetic nitrogen species already described in the case of sol–gel prepared materials. The energy of this species lies slightly over the valence band limit and well below the Ti 3+ states of reduced TiO 2.

Oxygen Exchange at the Internal Surface of AmorphousSiO2Studied by Photoluminescence of Isotopically Labeled Oxygen Molecules

The exchange between lattice and interstitial oxygen species in an oxide was studied by the 16O-18O isotope shift of the a1Deltag(v=0)-->X3Sigmag-(v=1) infrared photoluminescence band of the oxygen molecules (O2) incorporated into the interstitial voids of amorphous SiO2 (a-SiO2) by thermal annealing in 18O2 gas. A large site to site variation of the oxygen exchange rate, originating from structural disorder of a-SiO2, is found. The average exchange rate has an activation energy of approximately 2 eV, which is much larger than that for the diffusion of interstitial O2 (approximately 0.8-1.2 eV). The average exchange-free diffusion length of interstitial O2 exceeds approximately 1 microm below 900 degrees C, providing definite evidence that oxygen diffuses as interstitial molecules in a-SiO2.

Influence of Interstitials Content on the Diffusion of Niobium in Alloy 718

Many studies have emphasized the beneficial effect of niobium on the physical metallurgy of Ni-Cr-Fe alloy 718. Among the different strengthening actions of niobium, such as solid solution hardening and carbide precipitation, the precipitation of niobium with nickel in a strengthening phase γ” (Ni3Nb) during the aging heat treatment has the largest influence on the mechanical properties of alloy 718. The improvement of the niobium distribution and diffusion in the Ni-matrix may allow a more homogenized repartition of γ” precipitates and seems then to be an effective way to upgrade the mechanical properties. As γ” precipitates decompose to the stable δ phase at very long aging times, the study of the effect of carbon, nitrogen and oxygen concentrations on precipitation and dissolution of the δ phase may give information on γ” precipitation and on niobium distribution. It is the purpose of the present work to examine the role that the alloy content of interstitial species plays with the niobium-rich δ phase evolution in alloy 718. Alloy 718 samples were heat treated under hydrogenated argon at 980°C for 0 to 96 hours in order to gradually curb the content of interstitial species by reaction with the reducing atmosphere. Chemical analyses realized by glow discharge mass spectrometry (GDMS) confirmed the reduction of the concentration of these species. Specimens were solution-treated for 1h at 1050°C in an inert atmosphere and furnace cooled. Some of the samples were then aged at 920°C for times ranging from 10 min to 1 hour. The precipitation was measured quantitatively in terms of volume fraction and the morphology of the precipitates was appreciated using scanning electron microscopy (SEM). The differences in the precipitation kinetics and in the microstructure evolution for each interstitial concentration are then discussed.

Colonisation and speciation on seamounts, evidence from Draconematidae (Nematoda) of the Great Meteor Seamount

The coarse calcareous sediments covering the plateau of the Great Meteor Seamount harbour 15 species of Draconematidae. Representatives of three genera are reported for the first time from the Atlantic region. The majority of Draconematidae from the plateau belong to four interstitial Dracograllus species. Three new species of the genus Prochaetosoma seem to form an endemic group on the plateau. Together with different morphotypes of a Dracograllus species, these species indicate an isolation of the Great Meteor Seamount. Possible areas are identified from which Draconematidae may have colonised the Great Meteor Seamount, among others shallow water habitats of the North Atlantic and Mediterranean Sea, or surrounding deep—sea habitats, especially reefs of cold—water corals of the North Atlantic. This study shows that Draconematidae have a much wider distribution than assumed before occurring also in many oceanic habitats, inclusively seamounts, than in subtidal or sublittoral ones where they have mainly been collected so far.

XPS spectra of uranyl minerals and synthetic uranyl compounds. I: The U 4f spectrum

The occurrence and binding energies of the U 6+, U 5+ and U 4+ bands in the U 4f 7/2 peak of 19 uranyl minerals of different composition and structure were measured by XPS. The results suggest that these minerals can be divided into the following four groups: (1) Uranyl-hydroxy-hydrate compounds with no or monovalent interstitial cations; (2) Uranyl-hydroxy-hydrate minerals with divalent interstitial cations; (3) Uranyl-oxysalt minerals with ( TO n ) groups ( T = Si, P, and C) in which all equatorial O-atoms of the uranyl-polyhedra are shared with ( TO n ) groups; (4) Uranyl-oxysalt minerals with ( TO n ) groups ( T = S and Se), in which some equatorial O-atoms are shared only between uranyl polyhedra. The average binding energies of the U 6+and U 4+ bands shift to lower values with (1) incorporation of divalent cations and (2) increase in the Lewis basicity of the anion group bonded to U. The first observation is a consequence of an increase in the bond-valence transfer from the interstitial species (cations, H 2O) groups to the O-atoms of the uranyl-groups, which results in an electron transfer from O to U 6+. The second trend correlates with an increase in the covalency of the U O bonds with increase in Lewis basicity of the anion group, which results in a shift of the electron density from O to U. The presence of U 4+ on the surface of uranyl minerals can be detected by the shape of the U 4f 7/2 peak, and the occurrence of the U 5f peak and satellite peaks belonging to the U 4f 5/2 peak. The presence of U 4+ in some of the uranyl minerals and synthetics examined may be related to the conditions during their formation. A charge-balance mechanism is proposed for the incorporation of lower-valence U in the structure of uranyl minerals. Exposure of a Na-substituted metaschoepite crystal in air and to Ultra-High Vacuum results in dehydration of its surface structure associated with a shift of the U 6+ bands to higher binding energies. The latter observation indicates a shift in electron density from U to O, which must be related to structural changes inside the upper surface layers of Na-substituted metaschoepite.

Adaptive radiation of gobies in the interstitial habitats of gravel beaches accompanied by body elongation and excessive vertebral segmentation

BackgroundThe seacoasts of the Japanese Arc are fringed by many gravel beaches owing to active tectonic uplift and intense denudation caused by heavy rainfall. These gravel beaches are inhabited by gobies of the genus Luciogobius that burrow into the gravel sediment and live interstitially. Although their habitat and morphology (e. g., reduced fins, elongated, scale-less body, and highly segmented vertebral column) are highly unusual among fishes, little is known on how their morphological evolution has facilitated the colonization of interstitial habitats and promoted extensive diversification. We conducted thorough sampling of Luciogobius and related species throughout Japan, and performed molecular phylogenetic analysis to explore the patterns of morphological evolution associated with gravel beach colonization.ResultsAn analysis of the mitochondrial cytochrome b gene suggested a remarkable diversity of previously unrecognized species. The species-level phylogeny based on six protein-coding nuclear genes clearly indicated that interstitial species cluster into two distinct clades, and that transitions from benthic or demersal habits to interstitial habits are strongly correlated with an increase in vertebral number. Colonization of gravel beach habitats is estimated to have occurred ca. 10 Ma, which coincides with the period of active orogenesis of the Japanese landmass. Different species of interstitial Luciogobius inhabit sediments with different granulometric properties, suggesting that microhabitat partitioning has been an important mechanism facilitating speciation in these fishes.ConclusionThis is the first study to document the adaptation to interstitial habitats by a vertebrate. Body elongation and excessive vertebral segmentation had been the key aspects enhancing body flexibility and fishes' ability to burrow into the gravel sediment. The rich diversity of coastal gravel habitats of the Japanese Arc has likely promoted the adaptive radiation of these unique gravel-dwelling fishes.

Computer-based 3D anatomical reconstruction and systematic placement of the mesopsammic gastropod Platyhedyle denudata Salvini-Plawen, 1973 (Opisthobranchia, Sacoglossa)

The small marine interstitial gastropod species Platyhedyle denudata Salvini-Plawen, 1973 has a dorsoventrally flattened, worm-like body without a shell and head tentacles; its systematic position was enigmatic. Wawra's [1979. Zur systematischen Stellung von Platyhedyle denudata Salvini-Plawen, 1973 (Opisthobranchia, Gastropoda). Z. Zool. Syst. Evolutionsforsch. 17, 221–225] anatomical redescriptions based on paraffin-embedded histology preparations indicated the original description of P. denudata to be erroneous in many essential features. The present study uses newly collected specimens from the Mediterranean type locality, Secche della Meloria, Italy, for serial semi-thin histological sectioning. All major organ systems of P. denudata are reconstructed three-dimensionally with AMIRA software. Platyhedyle denudata is a simultaneous hermaphrodite with an androdiaulic, complex genital system lacking a receptaculum seminis. A heart could not be detected; the nephric duct opens into the intestine. The central nervous system is postpharyngeal and the cerebropleural ganglia are completely fused. The visceral loop is short, showing three distinct ganglia which connect to an additional, presumably osphradial ganglion, and to a posteriorly situated genital ganglion. Aggregations of precerebral accessory ganglia are present. The originally described jaws could not be detected. An ascus for storage of worn radula teeth clearly indicates that P. denudata is a sacoglossan. The digestive gland of the mesopsammic P. denudata resembles that of the depressed, tentacle-less semi-terrestrial sacoglossan Gascoignella aprica Jensen, 1985 by forming two long branches that are connected at the rear end. In G. aprica, the digestive-gland rami are separated by a unique median septum, which is described here, too, as part of the muscle system in P. denudata. The shared, most likely synapomorphic presence of this septum strongly supports the monophyly of a Platyhedyle+ Gascoignella clade in a sacoglossan family Platyhedylidae.

Influence of Interstitials Content on the Sensitivity of Alloy 718 to Oxidation Assisted Intergranular Fracture

Alloy 718 is known to be sensitive to oxidation assisted intergranular cracking. It is also demonstrated that the occurrence of jerky flow (also called Portevin-Le Châtelier effect) stops the intergranular damaging mechanism. As dynamic strain ageing is known to be linked with the alloy content of interstitial species, the aim of the present work is to study the effect of carbon, nitrogen and oxygen concentrations on the mechanical behaviour of thin tensile specimens tested under oxidation conditions close to those encountered industrially for turbo machine disks. Thanks to heat treatments performed under reducing atmosphere, the content of interstitial species in tested alloy 718 samples is gradually curbed. Tensile specimens were then tested between 550 and 700°C for the strain rate range [10-5, 10-1] s-1. The key point of this work is that, for a given testing temperature, the tensile tests clearly demonstrated that the transition from an intergranular fragile fracture mode to a transgranular ductile one was always linked with the occurrence of Portevin-Le Châtelier phenomenon but for slower strain rates in comparison with what was observed on the as received aged material tested in the same conditions. This shift of the transition of fracture mode through the lower strain rates remained true until a threshold value of the heat treatment time under reducing atmosphere. Specimens heat treated over this value systematically exhibited a fully transgranular ductile fracture mode, whatever the plastic flow regime was. Implication of such a finding on the intergranular embrittlement of alloy 718 by high temperature oxidation is then discussed.

Effect of operating conditions on the electrochemical behavior of hydrogen-fed solid oxide fuel cells

A solid oxide fuel cell (SOFC) test unit was constructed with yttria-stabilized zirconia (YSZ) as the solid electrolyte, Ni–YSZ as the anode and Pt as the cathode. The SOFC unit was tested by varying hydrogen supply time, voltage, and temperature at 700–900 °C. The phenomena of electrochemical promotion of bulk lattice-oxygen extraction and fuel-free current have been observed. The amount of lattice oxygen additionally extracted by electrochemical promotion is limited. This limitation is more pronounced as the operating temperature increases. The interstitial hydrogen species are formed as either the interstitial hydrogen atoms in the bulk of Ni electrode or the interstitial protons in the bulk of YSZ. The amount of the interstitial hydrogen species is also limited. Oxygen transport in YSZ to the YSZ–Ni interface is rate limiting for H 2O formation over the anode. These new characteristics on the electrochemical behavior can optimize the operating conditions and the designing features of hydrogen-fed SOFCs.