Carbon Intercalation Research Articles

The Karakorum Block in Central Asia, from Ordovician to Cretaceous

The Karakorum Block records a predominantly marine Ordovician to Cretaceous sedimentary history. Six major sedimentary cycles are recognised. The oldest sediments, Early Ordovician, transgress over a crystalline basement. The 1-km-thick Ordovician-Silurian mostly shaly succession contains rare carbonate intercalations. In the Early Devonian, a wide peritidal platform spread over the craton. Sedimentation rates were low, 10–20 m/Ma, and Upper Devonian-probable Lower Carboniferous carbonates and clastics rest unconformably on the Early Devonian carbonates. No evidence has been found for either Late Carboniferous or glaciogenic deposits. Sedimentation rates increased during the Permian up to 50 m/Ma, with thicknesses between 1 and 2.5 km. Three steps are identified. (1) A huge alluvial to marginal-marine terrigenous prism aggraded during the Asselian-Sakmarian. (2) The Artinskian-Murgabian is characterised by local emergence and erosion, linked to extension with block rotations. (3) Greater differentiation occurred from Late Permian to Middle Triassic, when a peritidal carbonate flat developed in the southwest, facing a deeper basin to the northeast. Carbonate sediments prevailed throughout the Carnian-Norian. The Permo-Triassic evolution is interpreted as the passive margin stage of the Karakorum Block, which previously belonged to the Perigondwanian fringe, when, like Mega Lhasa, it drifted northward on the Tethyan Transit Plate. Mega Lhasa is considered as a collage of blocks possibly separated by thinned crust or short-lived seas with ocean crust. Quartzo-lithic sandstones with grains of mafic volcanics and serpentinite, overlain with gentle unconformity by Pliensbachian-Toarcian red sandstones with sedimentary and metasedimentary clasts, record the Eo-Cimmerian deformation in the Karakorum. This orogenic episode was over by the Aalenian, when a shallow-water carbonate ramp aggraded onto the previously emergent area. The pre-Barremian, Upper Jurassic and Lower Cretaceous are poorly documented. In post-Barremian times the sedimentary succession of N Karakorum was severely deformed in huge thrust sheets, including slabs of crystalline basement. A coarse conglomerate of mid-Cretaceous age sealed the thrust sheet edifice. Finally, isolated Campanian pelagic mudstones are recorded. Anticlockwise rotation of Mega Lhasa followed the Late Triassic docking of the Iranian Spur, using the latter as pivot. The rotation was completed during the Middle Jurassic, when SE Pamir, Shaksgam and Karakorum joined the Qiangtang, more closely assembling Mega Lhasa as it approached the Asian margin.

Palaeoproterozoic rifting and formation of sulphide deposits along the southwestern margin of the Svecofennian Domain, southern Sweden

A mineralized Palaeoproterozoic volcanic sequence has been identified southwest of Vetlanda in southern Sweden. The sequence, which is defined as the Fröderyd Group, is surrounded by 1.78 Ga granitoids and may be considered as the southernmost segment of Svecofennian crust in Sweden. The Fröderyd Group has a bimodal geochemical character and is dominated by pillow basalts and associated gabbros but rhyolites, thin intercalations of marble and stratiform sulphide ores do also occur. The carbonate intercalations and the stratiform sulphide ores are interpreted as submarine exhalites formed syngenetically with the volcanic activity. The mafic rocks have a typical mid-ocean ridge basalt geochemistry with flat rare earth elements patterns. The lead isotopic compositions of the mafic rocks and the associated stratiform sulphide ores support such a close affinity to juvenile sources with mantle character. In contrast, the rhyolites display more evolved geochemical signatures and isotopic patterns and are interpreted to represent remelted products of slightly older sialic crust. A model for the formation of the Fröderyd Group is presented, suggesting rifting along a continental margin which may have occurred in the final stage of the Svecofennian crust-forming period.

An approach to the genesis of palygorskite in a Neogene-Quaternary continental basin using principal factor analysis

AbstractThe Carrión lacustrine basin (≈10 km2), central Spain, is filled with Neogene-Quaternary sediments (20–25 m thick) rich in palygorskite. Two clay units of ∼15 m thick are of particular interest in the basin. The lower one contains over 75% phyllosilicates (palygorskite up to 90%, smectites and illite) in marginal areas (facies A), and it is laterally bound by a distal facies (B) also rich in clay minerals (smectites and illite, and some palygorskite) and gypsum, and includes dolomitic marl intercalations. The composition at the top is primarily marly, with some gypsum (C). The upper clay unit, mainly clay-size material, (D) is rich in smectites, palygorskite and sepiolite, and contains carbonate intercalations near the top. A statistical treatment of the mineralogical and chemical composition data from 120 samples, using principal factor analysis, suggests that: (a) illite and smectite are detrital in origin; (b) palygorskite was formed by transformation of illite and smectite involving reaction with Mg; and (c) sepiolite was a neoformation product favoured by evaporation of silica- and Mg-bearing waters.

The Correlation Between the Surface Chemistry and the Performance of Li‐Carbon Intercalation Anodes for Rechargeable ‘Rocking‐Chair’ Type Batteries

The correlation between the electrochemical properties of Li carbon intercalation electrodes and their surface chemistry in solutions was investigated. The carbons investigated were primarily graphite and petroleum coke, and the solvent systems included methyl formate (MF), propylene and ethylene carbonates, ethers and their mixtures. The surface chemistry of the electrodes was studied using mainly diffuse reflectance Fourier transform infrared spectroscopy. The following aspects were studied: (i) the effect of temperature on the buildup of the surface films; (ii) the effect of additives (e.g., , crown ethers), (iii) the behavior when the passive layer is built in one solution followed by cycling in another; and (iv) the effect of cosolvent in MF solutions. The results obtained further prove that the electrochemical behavior of these systems is surface film controlled. An understanding of the surface chemistry of these electrodes enables judicious optimization of carbon‐solution systems for use in rechargeable Li batteries.

Late Cretaceous benthic foraminiferal proliferation on the Arabian Platform: Taxonomic remarks on the genus Orbitoides d'Orbigny 1848

AbstractIn south‐eastern Turkey, a transgressive phase with a rich benthic foraminiferal association followed the Late Cretaceous emplacement of nappes onto the passive northern margin of the Arabian Platform. At the base, this transgressive sequence is represented by coarse clastics and local carbonate intercalations of the Antak Formation and the overlying, shallow water friable sands and carbonate facies of the Besni Formation, which is characterized by a sudden proliferation of benthic foraminifera, rudists and other macrofossil groups. Finally, below the unconformable Tertiary units, the more basinal marls and regressive sandstone‐carbonate lithologies of the Germav Formation complete the Mesozoic succession.In the light of the newly discovered benthic and planktonic foraminiferal associations, the age of this transgression has been assigned to the Late Campanian. Overlying levels yield more diversified foraminiferal assemblages including genera such as Orbitoides, Siderolites, Omphalocyclus, Loftusia, Lepidorbitoides, Sirtina and other benthic taxa suggesting a Maastrichtian age. However, biometric analysis of the embriyon size of the Orbitoides populations from these levels show that these specimens are more primitive than the type Maastrichtian forms.

La serie Triasica de Los Pastores (Algeciras)

Seven superimposed lithostratigraphic units have been distinguished in the Upper Trias of Los Pastores (Algeciras). The four lower units (1 to 4) show clayey-sandy-evaporitic Keuper facies. Pollen associations obtained from dark pelitic levels, and bivalves sampled from carbonate intercalations within these four lower units allow to date them as Carnian. These lower units can be correlated with the K1 to K3 units of the Keuper of the Subbetic and of other regions of the Iberian Peninsula. Concerning the three higher units, the unit 6 is pelitic-carbonatic and evaporitic and it also bears Carnian pollen associations. The units 5 and 7, however, are carbonatic and show clearly marine facies and organisms (Involutinidae and dasycladacean algae) of the same type than those shown by the Upper Triassic of Alpine Facies of the Internal Zones of the Chain (Alpujarrides and Rondaides). The Trias of Los Pastores belongs to an arid ecuatorial phytogeographical province, whose the vegetation was dominated by xerophytic elements. It was deposited in a wide coastal flat with marginal terrigenuos influence and close to a carbonate platform, in peritidal and shallow marine depositional environments, very sensitive to sea-level fluctuations. The marine carbonate intercalations bear low-diversity, dwarf and opportunistic marine faunal associations, typical of shallow, restricted, unstable and ecologicaUy inmature environments, as it has been confirmed independently by facies analysis.

Tectonic evolution of the Nakasib suture, Red Sea Hills, Sudan: evidence for a late Precambrian Wilson Cycle

The Nakasib suture is a late Proterozoic (Pan-African) ophiolite-decorated structural belt in the central Red Sea Hills of the Sudan. It represents one of the sutures along which the island arc/back-arc terranes and continental microplates of the Arabian-Nubian Shield are welded together. The Nakasib suture separates the 900–850 Ma old Haya terrane in the south from the 830–720 Ma old Gebeit terrane to the north. Five thrust-bounded stratigraphical groups are identified across the suture. These are, from south to north, Arbaat volcanic group (c. 730 Ma rift-related volcanic rocks), Salatib group (early passive margin volcanic and sedimentary rocks), Meritri group (the lower part of which contains alluvial and submarine fans of an incipient ocean basin, while its upper part can be tentatively equated with a platform of clastic sedimentary and carbonate intercalations which mark the stage of mature ocean basin opening), Nakasib ophiolite, and Shalhout group (arc-related volcanic and sedimentary rocks). These are intruded by syn-tectonic and post-tectonic plutonic rocks. The tectonic setting of the above lithological groups suggests that the early stage of the Nakasib suture development was marked by rifting of older crust, probably the Haya terrane, which culminated in development of a passive margin on the south margin of an oceanic basin prior to collapse into an ophiolite-decorated suture. This indicates that the Nakasib suture evolved through a complete Wilson cycle orogeny from rifting, through passive margin formation, to closure of the basin and suturing.

HREM imaging of single unit cell carbide precipitates in Pt-C alloys

Dilute Pt-C alloys are prototypical for studying oversize carbide phase precipitation from interstitial solid solution. Earlier studies showed the essential function of quenched-in vacancies in the precipitation process. Vacancies play a dual, volume accommodation and structural, role in the transformation by modifying both the habit plane spacing and stacking sequence. It was also shown how the precipitation sequence in interstitial Pt-C alloys is analogous to that in substitutional Al-Cu alloys. Initially a “GP zone” consisting of a monolayer plate of carbon atoms and vacancies forms. Atomic resolution images of the socalled a precipitates have confirmed their structure. During subsequent coarsening of the precipitates, α’ platelets form. Schematic diagrams illustrating the α and α’ structures in <100> projection are given in Fig. 1. The single-layer a structure, or GP zone is identical to a ﹛100﹜ stacking fault stabilized by an intercalation of carbon. The two-layer α’ structure is the first true precipitate phase and has a crystal structure anti-isomorphous with calcium fluoride.

Problems of loess chronology

Loess as a typically subaerial, loess deposit has long been regarded a Pleistocene sediment and its date of formation has been put to ca 600 ka BP. Recently, the beginning of the Pleistocene is identified in the official concord reached — at 1.6 Ma BP, while not infrequently others propose 2.4 Ma BP. Until the fifties the whole loess (loess-paleosol-sand) sequence could be referred into the ‘shorter Pleistocene’ period, which —according to the climatic claendar by Milankovitch — consisted of nine cold and eight warm intervals. Some supporters of the ‘longer Pleistocene’ chronology hold that the beginning of loess formation can be put as far back as 1.6 – 2.4 Ma BP. Loess formation intervals are usually correlated with the cold stages (nos 2, 4, 6 etc.) of the Emiliani oxygen isotope timescale, while soil formation is believed to correspond to the warm stages (nos 1, 3, 5, 7 etc.). The typical loess, i. e. loess proper, are not older than stage no 23 (Jaramillo event — 0.96 Ma BP). Previous to this date climatic conditions had not generally favoured loess formation and paleosols formed one above the other with clay, loam or carbonate intercalations.

ChemInform Abstract: Chemical Chameleons. Organosulfones as Synthetic Building Blocks

An overview of the duality of function of organosulfones as nucleophiles in basic media and electrophiles in Lewis acidic media, a change of reactivity for which they have been dubbed “chemical chameleons,” is presented. In the first phase, transition metal catalysts activate allyl sulfones towards displacements. Use of palladium, molybdenum, and nickel catalysts allow stabilized anions to effect displacement; copper catalysts allow non-stabilized nucleophiles to be used. The use of the anion stabilizing and leaving group abilities of sulfones created a novel three carbon intercalation and a novel cyclocontraction-spiroannulation in which β-hydroxy sulfones participate in a Lewis acid catalyzed pinacol rearrangement. The lability of allyl and tertiary sulfones towards Lewis acids creates a wide array of electrophilic reactions such as Friedel–Crafts type cyclizations, intermolecular alkylations with organoalanes and enol silyl ethers, and ring expansions. The ability to design novel reagents for synthesis...

Chemical Chameleons. Organosulfones as Synthetic Building Blocks

Abstract An overview of the duality of function of organosulfones as nucleophiles in basic media and electrophiles in Lewis acidic media, a change of reactivity for which they have been dubbed “chemical chameleons,” is presented. In the first phase, transition metal catalysts activate allyl sulfones towards displacements. Use of palladium, molybdenum, and nickel catalysts allow stabilized anions to effect displacement; copper catalysts allow non-stabilized nucleophiles to be used. The use of the anion stabilizing and leaving group abilities of sulfones created a novel three carbon intercalation and a novel cyclocontraction-spiroannulation in which β-hydroxy sulfones participate in a Lewis acid catalyzed pinacol rearrangement. The lability of allyl and tertiary sulfones towards Lewis acids creates a wide array of electrophilic reactions such as Friedel–Crafts type cyclizations, intermolecular alkylations with organoalanes and enol silyl ethers, and ring expansions. The ability to design novel reagents for synthesis based upon this dual reactivity of organosulfones is illustrated by the use of an alkoxy-bis(phenylsulfonyl)methane as a synthon for a carbonyl 1,1-dipole.

Carbon Anode Reaction and Intercalation Compounds in Fluoride Melt

Carbon Anode Reaction and Intercalation Compounds in Fluoride Melt

Synthetic studies toward taxanes. A sulfur based approach to the benzilic acid rearrangement

Based upon the notion of a three carbon intercalation as a synthetic approach to texanes, a trans -perhydroindanone was required. In order to ensure the stereochemistry of the perhydroindanone, an approach based upon the stereocontrolled synthesis of a decalin followed by a ring contraction was adopted. In the course of this phase a C-acylation based upon the use of copper anolates was employed. A ring-contraction sequence was devloped initiated by a regioselective sulfenylation of a ketone. Acetoxylation of the resultant β-ketosulfide generated a monoprotected 1,2-diketone. Base treatment created a ring contracted α-hydroxycarboxylic acid which was cleaved directly to the nor-ketone. In this way, a suitable intermediate for elaboration into the taxanes was synthesized.

The Lower Cambrian of SW-Sardinia: From a clastic tidal shelf to an isolated carbonate platform

Much of the Lower Cambrian sediments of SW-Sardinia were deposited on a clastic tidal shelf, which changed into an isolated carbonate platform. Terrigenous clastics with carbonate intercalations (Nebida Fm.) grade into the pure carbonates of the Gonnesa Fm. Algal-archaeocyathan carbonates of Atdabanian to Lenian age occur within the clastics of the Lower Cambrian Nebida Fm. Smaller algal-archaeocyathan mounds evolve with time into a more complex facies-association of stacked mounds. The last stage produces flat-topped algal-archaeocyathan biostromes, several hundred meters long and locally more than ten meters thick. They consist mainly of algal bindstones (Girvanella especially) and also contain (sometimes branched) archaeocyathans. These buildups are interfingered and interbedded with coated grains and are underlain and overlain by terrigenous clastics. This association is similar in age and facies to the Poleta Fm. of western Nevada and eastern California, from which ROWLAND (1984) has reported the first appearance in the history of the earth of a wave-resistant reef-framework. We cannot assume that the algal-archaeocyathan community had a considerable resistance to waves and that it was environmentally dominant in SW-Sardinia. This association of algal-archaeocyathan carbonates and coated grains is to be found in the W and N of Iglesiente-Sulcis, apparently marking the rim of a platform situated further to the E. In the westernmost part of Iglesiente this platform-margin facies of the Nebida Fm. is overlain by a slope facies of the Gonnesa Fm., unknown so far. The slope is the lateral equivalent of tidal and sabkha deposits of the Dolomia Rigata Member (laminated dolomite member) located further to the E. This slope facies is called the Planu Sartu Member, a new member of the Gonnesa Fm. The Planu Sartu consists especially of varve-like laminated limestones and dolomites and up to m-thick calcareous mudstones with cherts. Slumping features are common in this facies. The Planu Sartu also occurs E of the platform, in the eastern part of Sulcis, forming another slope characterized again by slumping features. Because of these two slopes the size of the platform in between can be estimated. It extended approximately 50–60 km in the present E-W direction (taking into account a shortening to half its original size). The slopes were formed by tensional tectonics, active throughout Gonnesa and lower Cabitza time. In contrast to the slope in the W, the eastern slope has no predecessor in Nebida time. Because of the newly developed basin in the E, the clastic supply to today's SW-Sardinia was interrupted. This lasted until the breakdown of the platform in Cabitza time, when clastic delivery was reinstated. At least during the lower Gonnesa time, the platform wasnot rimmed by a barrier which consisted of ooids and an algal-archaeocyathan community. Ooids occur only locally. This lack of a special marginal facies, together with the slope-facies mentioned above, indicates poor water circulation in the two basinal areas during Gonnesa time, and possibly an increase in salinity. The tensional tectonics in the Cambrian might have initiated the separation of northern parts of Gondwana, which subsequently drifted to the N. Microcontinental collision might have been responsible for compressional tectonics (“Sardic phase”), which was active most probably in the lower or middle Ordovician.

EXAFS determination of the change in the structure of rhodium in highly dispersed Rh/γ-Al 2O 3 catalysts after CO and/or H 2 adsorption at different temperatures

Extended X-ray absorption spectroscopy (EXAFS) has been applied to study the Rh K-edge of two ultradisperse Rh/Al 2O 3 catalysts containing 0.47 and 1.04 wt.% rhodium respectively. The structural properties of the Rh crystallites were determined after reduction with H 2, evacuation at elevated temperatures, CO admission at room temperature, CO desorption, CO admission at 523 K (at which temperature the Boudouard reaction takes place) and after hydrogenation of CO at 523 K. During reduction of the catalyst, metallic rhodium crystallites are formed which are attached to the support via Rh 0-O 2− bonds, implying zero-valent rhodium. The Rh-Rh nearest-neighbour distance in the particles is contracted to 2.63 Å in vacuum and relaxes to 2.68 Å (similar to the bulk value) upon hydrogen chemisorption. Adsorption of CO at room temperature onto the reduced catalysts results in a partial disruption of the small Rh crystallites, ultimately leading to rhodium geminal dicarbonyl species. A subsequent desorption of CO leads to rearrangement of the metal clusters. The oxidation state of rhodium alters from 0 to 1+ upon CO chemisorption, and becomes 0 again after CO desorption. After CO admission at 523 K, the rhodium particles break up completely, probably because of intercalation of carbon and/or oxygen atoms. The highly dispersed Rh/Al 2O 3 catalysts change to poorly dispersed systems after reaction between CO and H 2 at 523 K, due to sintering of the metallic crystallites.

A thermochemical study of the reactive intermediate in the alkali-catalyzed carbon gasification. I. X-ray diffraction results on the alkali-carbon interaction

Intercalation compounds of metallic potassium with graphite or activated carbon have been prepared and characterized by means of X-ray diffraction. The thermal stability of these compounds has been studied by quenching experiments and high-temperature X-ray diffraction (HTX). It is shown that potassium—carbon intercalation compounds are thermodynamically not stable at temperatures at which the alkali-catalyzed carbon gasification proceeds (950–1150 K). On the other hand, HTX-patterns exhibit a considerable interaction between K 2CO 3 and the activated carbon at the gasification temperatures. Interaction with Na 2CO 3 also takes place, but at much higher temperatures than with K 2CO 3. Increasing pretreatment temperatures of the activated carbon resulted in a decrease of the alkali—carbon interaction, whereas with graphite no interaction at all takes place. This indicates that surface groups on the carbon are the reactive sites for this interaction.

A three carbon intercalation of an enediol silyl ether; a short entry to the bicyclo[5.3.1]undecyl system of taxanes

A three step synthesis of 11-methylene-bicyclo[5.3.1]undecan-2,6-dione is described.

Intercalation properties of the carbon cathode of aluminum reduction cells

The intercalation of cathode carbon and associated disordered carbons by AlCl 3 has been measured by a technique that eliminates surface adsorption and pore condensation. Intercalation by this electron acceptor is greater for the more ordered carbons that have been reported to intercalate less sodium (an electron donor). Measurement of intercalation by AlCl 3 is therefore a useful way of characterizing carbon cathodes. It shows that an anthracite-pitch cathode does graphitize during exposure to the Hall liquid at 900–1000°C.