Mica Layers Research Articles

Oxidation/cobalt ion-exchange method to improve biotite electrochemical properties

We prepared a hydrated mica mineral material with larger layer spacing by oxidized/cobalt ion exchange. The structural evolution during the modification and the electrochemical properties of the final obtained hydrated Co-mica were investigated. Results showed that the layer spacing of black mica increased, and the electrochemical properties were enhanced. In the oxidation environment, the divalent iron ions in the octahedral layer of black mica are oxidized. The potassium ions bound by Coulomb force in the black mica layer structure can be detached cobalt ions support the large layer spacing in the form of hydrated ions. Electrochemical performance tests showed that the electrochemical properties of hydrated Comica hydrate were significantly improved after the increase in layer spacing. The first discharge specific capacity of black mica raw ore was 1.769 F/g, and the first discharge-specific capacitance of hydrated Co-mica prepared by the oxide/cobalt ion-exchange method reached 4.305 F/g, which was significantly enhanced.

Effects of Nanofillers Based on Cetyltrimethylammonium-Modified Clays in a Polypropylene Nanocomposite.

Nanocomposites of hydrophobic organo-clay/polypropylene (organo-clay/PP) were efficiently developed through a solution-blending technique. For this, we utilized various smectite clays as host agents; namely, Na-montmorillonite (Mt, ~1000 nm), Na-fluorine mica (Mica, ~1500 nm), and Na-hectorite (Ht, ~60 nm) with varied sizes, layer charges, and aspect ratios. Such clays were functionalized with cetyltrimethylammonium (CTA) bromide via an intercalation technique to obtain hydrophobic organic clays. The as-made clay particles were further mixed with a PP/xylene solution; the latter was removed to obtain the final product of the CTA-clay/PP nanocomposite. An X-ray diffraction (XRD) analysis confirmed that there were no characteristic (001) diffraction peaks for CTA-Mica in the PP nanocomposites containing CTA-Mica, assuring the fact that the Mica layers could be completely exfoliated and thereby homogenously composited within the PP. On the other hand, the CTA-Mt and CTA-Ht incorporated composites had broader (001) peaks, which might have been due to the partial exfoliation of CTA-Mt and CTA-Ht in the composites. Among the three CTA-clay/PP nanocomposites, the CTA-Mica nanohybrid showed an enhanced thermal stability by ~42 °C compared to the intact host polymer matrix. We also noted that when the CTA-Mica content was ~9 mass % in the nanocomposites, the Young’s modulus was drastically maximized to 69%. Our preliminary results therefore validated that out of the three tested clay-PP nanocomposites, the CTA-Mica nanofiller served as the best one to improve both the thermal and mechanical properties of the PP nanocomposites.

Band gap engineering of the top layer of mica by organized defect formation

We report the narrowing of bandgap of the topmost layer of muscovite mica by low energy Ar+ ion beam induced defect formation. Variation of sputtering rate of the constituent elements of mica leads to organized defects creation. The first principle (DFT) calculation shows a bandgap of 4.63 eV for a single layer of muscovite mica, whereas the absence of specified atoms in that layer results in a reduction of bandgap to 1.3 eV. To examine the change of bandgap of a single mica layer, the top most layer of the muscovite mica is selected, and controlled atomic vacancies are created by low energy Ar+ ion sputtering at glancing angle. The bombarding ion energy and incidence angle are chosen by Monte Carlo Simulation (SRIM) to create the desired defects on the top most layer. Removal of the constituent atoms is probed by X-ray photoelectron spectroscopy and the change in bandgap is experimentally estimated by UV-Vis reflectance spectroscopy and conducting Atomic Force Microscopy (c-AFM). The experimental measurements of bandgap change are found to be consistent with the first principle calculation. The key features of bandgap alteration of the top layer of muscovite mica by ion induced sputtering are discussed.

Mica-based triboelectric nanogenerators for energy harvesting

Mica, an abundant raw clay mineral, has negatively charged silicate layers owing to the replacement of Si atoms with Al atoms; hence, it easily loses electrons during the friction contact with other materials. Mica is reported as the most positive inorganic non-metal triboelectric material. However, the triboelectric performance characteristics of mica and its influencing factors have not been sufficiently studied. Herein, a triboelectric nanogenerator (TENG) was fabricated using a raw mica layer and a polytetrafluoroethylene film as the positive and negative friction materials, respectively. The effects of the mica layer thickness, air-bubble defect in mica, applied force, and working frequency on the TENG performance were investigated. Mainly owing to the excellent positive triboelectric property and extremely flat and smooth surface of mica, the mica-based TENG achieved the maximum output power density of 62.82 mW/m2. A multi-layer sandwich mica-based TENG generated −147 V under the force of 1 N. Moreover, the mica layers attached to a shoe sole could harvest mechanical energy when walking on a plastic floor, thereby directly lighting four LEDs. This study reveals that mica exhibits excellent triboelectric performance and is a promising positive friction layer candidate for environmentally friendly TENGs.

Textural and genetic relationships between glauconite and celadonite at the nanoscale: two different structural-compositional fields

Abstract. Glauconite and celadonite coexist at the nanometre scale in Early Jurassic submarine volcanic rocks of the Betic Cordillera (southern Spain) as a result of microbial activity. Samples from the limit between the two micas, recognizable in scanning electron microscopy, have been extracted using the focussed ion beam technique and studied by high-resolution analytical electron microscopy. Both micas are present as randomly oriented differentiated small crystals in the boundary area. They define clearly distinct compositional fields with gaps affecting to Fe, Mg and K. At the lattice scale, celadonite shows a high degree of order, with homogeneous orientation of the visible lattice parameters being a difference from glauconite, formed by packets no more than 10-layers thick. Smectite layers were also detected alongside glauconite packets, in accordance with X-ray diffractograms which indicate that glauconite is a mica–smectite interstratification being more than 90 % mica layers. The compositional gap indicates that celadonite is not the endmember of the glauconitic series and the two micas represent two different structural tendencies of mica, with glauconite having more distorted octahedral sheets, indicated by systematically higher b parameters than celadonite.

What controls the width of ductile shear zones?

It is widely recognized that major brittle faults in the upper crust transition downwards into ductile shear zones that then widen with depth. However, the controls on shear zone width at any specific depth, and the mechanisms that may cause the width to change over time, are less well understood. This study therefore reconstructs the geometry and rheology of the crustal-scale, normal-sense Simplon Shear Zone between the depths of ~3 and ~ 26 km, by combining field- and microstructural mapping, quartz paleopiezometry, and published estimates for the pressure, temperature, and timing of deformation at different crustal levels. The geometry is complex, with multiple strands actively deforming at any one depth, although overall the cumulative width does increase downwards. A scaling law is developed relating shear zone width to rheology and displacement rate, assuming simple shear and neglecting stretching parallel to the shear plane, and rheological parameters for granitoids with a quartz, feldspar, or mica dominated microstructure are quantified. Localization during exhumation was primarily accompanied by hydrous retrogression of feldspar to white mica, and the associated formation of interconnected weak mica layers. This weakened the shear zone, allowing the degree of strain localization to increase (and the shear zone width to decrease) by a factor of ~4–9.

Mineralogical and Crystal-Chemical Constraints on the Glauconite-Forming Process in Neogene Sediments of the Lower Guadalquivir Basin (SW Spain)

Glaucony is a significant green marine facies in the northwestern passive margin of the Guadalquivir Basin (Spain), where glauconite formed authigenically on a sediment-starved continental shelf, with fecal pellets and benthic foraminiferal tests being the main glauconitized substrates. Results from a study using XRD, TGA-DSC, SEM-EDS, and EPMA have revealed that glauconite is remarkably heterogeneous in mineral composition and chemical maturity, even in a single grain, reflecting a complex interaction of micro-environmental factors, substrate influences and post-depositional alterations. In its early stage, the glauconitization process is consistent with the slow precipitation of a Fe-rich smectite phase, most likely intergrade between nontronite and Fe-montmorillonite end-members, which evolved to a regularly interstratified glauconite-smectite (Gl/S). The Fe-smectite-to-Gl/S transformation is interpreted as a diffusion-controlled reaction, involving sufficient Fe availability in pore water and the constant diffusive transport of seawater K+ and Mg2+ ions towards the substrate. The pelletal glauconite is actually a highly evolved Gl/S consisting almost totally of mica layers, with 0.74 ± 0.05 apfu of K+ in the interlayer, while the Gl/S occurring as replacements of foraminiferal tests contains a mean of 7% of expandable layers in the walls and 16% in the chamber fillings, due to rate-limited ion diffusion.

Modification of Spent Bleaching Earth with WO3 and the Application for Photocatalytic Degradation of Waste Dyestuff under Solar Light

Degradation of blue dye waste in Sarong Samarinda production using WO3-bleaching earth (BE) has been conducted. Structural and morphological characterization has conducted using X-ray diffraction (XRD), and Scanning electron microscopy-energy dispersive spectroscopy (SEM-EDX). The X-ray diffraction results show the mineral on bleaching earth is rectorite dioctahedral mica layer and dioctahedral smectite with a ratio 2:1. The WO3 pattern is appeared after the calcination. After calcination at 500°C, the WO3 is deposited homogeneously on the BE surface. The catalytic performance of WO3-BE for photodegradation of the blue dye waste under the solar light is 99.85 % within 1 h.

Structural and Crystal-Chemical Features and Rb–Sr Age of Globular Glauconite in the Ust-Il’ya Formation (Lower Riphean, Anabar Uplift)

For the first time, mineralogical, structural, crystal-chemical and isotope-geochronological data were obtained for a glauconite sample from the Lower Riphean Ust-Il’ya Formation on the Magan River (western slope of the Anabar Massif, northern Siberia). It has been established that glauconite from the lenticular layer of friable glauconitite (glauconite grains ≥80%) contains two populations of mixed-layer crystals, in which mica layers (93%) alternate with either smectite-type (7%) or vermiculite-type layers (7%) with the short-range order factor R = 3. The ratio KAl = (VIAl / (VIFe3+ + VIAl) equal to 0.45 allows identifying the micaceous mineral as glauconite with the unit-cell parameter b = 9.065 A and K2O content of 8.29%. Comparison of new data with the previously obtained mineralogical and crystal-chemical characteristics of Ust-Il’ya glauconites from the Kotuikan River section (2.5 km above the Il’ya River mouth), located 65 km south of the Magan River section, showed both similarities and differences. Analysis of the crystal-chemical heterogeneity of Kotuikan glauconite samples from rocks of different lithological types revealed peculiarities in the distribution of individual mica varieties composing the glauconite globules. Isotopic dating of glauconite from the Magan River section was performed in combination with simulation of the distribution of octahedral cations and comparison of the results obtained with Mossbauer and infrared (IR) spectroscopy data. Such an approach combined with the mineralogical and crystal-chemical analyses contributes to correct interpretation of the stratigraphic significance of isotope data. The results obtained provide grounds for the conclusion that isotopic dates of glauconite from the Magan section (1474 ± 21 Ma) coincides within the error limit with the earlier Rb–Sr and K–Ar dating of the Ust-Il’ya Formation (1485 ± 13 and 1459 ± 20 Ma, respectively) based on the glauconite in the Kotuikan section (Zaitseva et al., 2016). The former value marks the stage of early diagenesis of sediments and is suitable for estimating the age of this formation.

Rectorite as a Syngenetic Component of a Soddy-Podzolic Soil

Rectorite (allevardite) is a regularly interstratified mica–smectite, in which each mica (A) layer is “sandwiched” between smectite (B) layers creating ABABAB…. sequence with 50% contribution of each layer. Similar to other ordered minerals, rectorite is rare in nature. The paper provides the results of the study on properties and mineral composition of the soddy weakly podzolic soil (Umbric Albeluvisol) in the Komi Republic, Russian Federation. Rectorite is found in fine fractions of A1 and A2 horizons of this soil. The studied soil has been formed on the light-textured parent material. The soil profile is texturally differentiated by the eluvial type. In the mineral horizons, $${\text{p}}{{{\text{H}}}_{{{{{\text{H}}}_{2}}{\text{O}}}}}$$ varies within 5.1–5.3. The mineral composition of fractions <2, 2.0-0.5 and <0.5 μm was studied by X-ray diffractometry (XRD). In the parent material, smectite predominates and is represented by the high-charged beidellite. In addition, its clay fraction contains mica, vermiculite, kaolinite and chlorite, as well as fine quartz. Vermiculite structure is chloritized. The mineral composition of the clay fraction undergoes transformation within the upper 40 cm of the profile, which is maximally pronounced in the upper 20 cm. The content of smectite is lower there; and that of fine quartz is higher, fine fractions additionally contain rectorite. This mineral is identified on the base of the integer (00h) reflection series 24.54 and 12.27 A for air-dry samples. After saturation with ethylene glycol, the (001) peak shifts to 26.77 A. Calcination during 2 h at 550°C results in shifting of this peak to 10 A. Rectorite is believed to be a syngenetic component of this soils and is formed at the early stage of smectite transformation into illite, being a transitional product of this transformation.

New insights into the nature of glauconite

AbstractGlauconite must be assessed as mica-rich mica-smectite R3 interstratified mineral, with the pure end-member mica also having intrinsic K-deficient chemical characteristics (K+ ~ 0.8 apfu). This assertion is in accordance with our X-ray diffraction (XRD) and high-resolution tranmission electron microscopy (HRTEM) studies and chemical analyses by electron probe microanalysis (EPMA) of mature glauconites in Cenozoic Antarctic sediments that indicate that: (1) It consists of a glauconite-smectite (R3 ordered) mixed-layer silicate, composed mainly of mica-type layers (&amp;gt;90%), but displaying slightly different proportions of Fe(III)-smectite layers (&amp;lt;10%). (2) More mature glaucony grains are characterized by major K+ and VIFe2+ (mica layers) and minor VIFe3+ (smectite layers) content in the interstratified glauconite-smectite. (3) Potassium is stabilized at the interlayer site by the octahedrally coordinated Fe2+. (4) Microtexture of the glauconite crystals are comparable with those of other micas and illite minerals, with straight, defect-free lattice fringes of ~10 Å spacings glauconite packets characteristic of mica with minor interstratified poorly crystalline smectite layers. In addition, our new findings give insights into the glauconitization process and at the same time investigate the potassium-deficient character of the dioctahedral mica “glauconite.” These findings show that glauconite crystallizes by a layer-growth mechanism at the expense of a poorly crystalline smectite precursor and that smectiteto-glauconite transformations are accompanied by a gradually higher octahedral charge deficiency (Fe2+/Fe3+) stabilized by K+ uptake into the interlayer sheet.

Study and practical investigations of Nano Supercapacitors

Capacitors are basically defined as a two-terminal electric component which stores potential energy in an electric field. The effect of the capacitor is known as capacitance. Generally, there exists some capacitance exists between any two electrical conductors in proximity in a circuit, a capacitor is a component designed to add capacitance. The capacitor was originally known as a condenser. The physical form and construction of the practical capacitors vary widely. Most capacitors contain two electrical conductors often in the form of metallic plates or surfaces separated by a dielectric medium. A conductor is generally a foil, thin film, sintered bead of metal, or an electrolyte. The nonconducting dielectric acts in order to increase the capacitor's charge capacity. Materials commonly used as the dielectrics include glass, ceramic, paper, plastic film, mica, and oxide layers. In the common world Capacitors are widely used as parts of electrical circuits in many common electrical devices. Unlike normal a resistor, an ideal capacitor does not dissipate energy. But the energy density of the capacitor is very low due to this greater number of capacitors are required to maintain a particular circuit.so to rectify these kinds of problems, we need a device which is more capable to hold the potential energy

Anisotropy of quartz mica schist based on quantitative extraction of fabric information

In this study, comprehensive laboratory experiments, such as thin-section and optical section analyses and P wave velocity and uniaxial compression tests, are performed on three types of quartz mica schist samples. The thin-section analysis reveals that the schist predominately consists of flaky mica and granular minerals, including quartz, feldspar, and calcite. The two types of minerals, both presenting a certain degree of orientation, are arranged to form a quasi-bedded structure as a whole, which essentially leads to macroscopic physicomechanic anisotropy. By means of optical section observation, directional microfissures are found to mainly be distributed alongside the edge of the oriented mica layer, while defects in other parts exhibit irregular orientation. Moreover, quantitative information is extracted from gray images by Image-Pro Plus (IPP), and then, relevant indicators are proposed to quantitatively analyze the differences in the content, morphology, and distribution characteristics of minerals and defects among the three types of samples. P wave velocity measurements of dry cylindrical specimens with different schistosity angles α show that the minimum value lies in the direction of the transverse schistosity planes (α = 90°) and that the P wave velocity increases with the decrease of the schistosity angle. There is an obvious linear positive correlation between the orientation coefficient of mica, which is adopted to indirectly reflect the orientation degree of microfissure, and the 0.5 power of the velocity anisotropy coefficient. The uniaxial compression test of specimens reveals the anisotropic characteristics of the peak strength, failure mode, and crack initiation and propagation for the schist samples. In particular, with the change of the schistosity angle, the peak strength and crack initiation strength have a U shape, characterized by a minimum value at α = 30° and maximum value at α = 0° or 90°. Directional microfissures and irregular defects with a dominant angle control the crack initiation of the specimens with 0° ≤ α ≤ 45° and 45° < α ≤ 90°, respectively. The weak edge of the directional mica layers has a more or less guiding effect on crack propagation when compressive loading is applied obliquely to the schistosity planes, while crack propagation is independent of weak edges when perpendicular to the planes. Three failure modes occur in the specimens with the change of the schistosity angle: tension-splitting failure, shear-slip failure, and shear failure. It is found that the mechanical anisotropy properties of the schist samples are closely associated with the content, morphology, and distribution characteristics of minerals and defects based on the analyses of the macro- and microquantitative data.

Analysis of the critical stresses in high-voltage composite winding insulations under thermal loads

Stator bars are the critical components in generators with respect to their lifespan. The winding insulation may be susceptible to damage under excessive alternating temperature loads incurred by a high number of start–stop cycles and heavy overloads. The differences in thermal expansion between the different components in the multi-layered winding insulation lead to thermal stresses. This work deals with the thermo-mechanical characterisation of the individual constituents of the winding insulation and the finite element model of a stator bar, based on the material data obtained from the tests that enable the identification of the thermal stresses leading to delamination over thermal cycles. The out-of-plane and the interfacial shear stress are found to be in the critical range with respect to the relatively low cohesive strength of the included individual mica layers.

Design swelling micas: Insights on heavy metals cation exchange reaction

Heavy metal pollution has become one of the most serious environmental problems, demanding specialized remediation mechanisms. Among the studied treatments, ion-exchange processes have been widely used due to their high remediation capacity, efficiency and fast kinetic. Here, the potential use of a new family of design micas as cation exchanger has been analysed. Micas with a layer charge in the range of brittle micas have been synthesized and their heavy metals cation exchange capacity analysed as a function of the nature of the heavy metal cations (Pb2+, Cd2+ or Hg2+), the nature of the counterions (Cl− or NO3−), concentration of the solutions and the micas layer charge. A cation exchange ratio between 35% and 154% of their cation exchange capacity (CEC) was achieved, being more efficient when mica layer charge diminished. In general, the maximum adsorption capacity followed the trend: Hg2+ > Pb2+ > Cd2+. The efficiency of the cation exchange and adsorption mechanism of the synthetic micas depended on the experimental conditions and they were more efficient than raw and modified natural clay minerals.

Piezoelectric Flexible Energy Harvester Based on BaTiO3 Thin Film Enabled by Exfoliating the Mica Substrate

Flexible piezoelectric energy harvesters (f‐PEHs) have exhibited significant potential as long‐lasting self‐powered sources or sensor devices, as they can generate reliable and repeatable electricity under harsh and tiny mechanical bending cycles without restraints anywhere and anytime. Herein, a new approach for transferring piezoelectric ceramic thin films onto a single flexible substrate via piecemeal elimination of the sacrificial mica substrates is proposed. The crystallized piezoelectric BaTiO3 thin film on a rigid mica substrate with electrodes and passivation layers is peeled off by means of a physical delamination process using sticky tape as the remover. The film is then transferred onto a flexible polyimide substrate using a polymer elastomer as a support. The fabricated BaTiO3 thin‐film f‐PEH successfully converts an open‐circuit voltage of ≈0.5 V and a short‐circuit current of ≈30 nA from repeated mechanical bending deformations. The energy generation mechanism and performance of the perovskite BaTiO3 thin‐film f‐PEH is supported using finite‐element analysis (FEA) with multiphysics simulations. The novel transfer techniques adopting the removal of sacrificial mica layers opens the door to various high‐performance flexible and wearable applications based on all‐inorganic materials.

Geochemical and organic petrological study of bituminous sediments from Dahomey Basin, SW Nigeria

Abstract The Dahomey Basin, SW Nigeria, hosts a 3000-m-thick sedimentary succession of Cretaceous and Cenozoic age, of which the Turonian-Maastrichtian Afowo Formation includes sandstones, arkoses, shales, shelly limestones, unconsolidated sand, clay and most importantly, bituminous (tar) sand strata. Eighteen samples were picked up from outcrops exposed by streams and channels, and were examined applying sedimentological, mineralogical, petrographical, geochemical (inorganic and organic) and radiological techniques with the aim of assessing the origin and the thermal maturity of the organic facies. The samples represent mostly coarse-grained sands and subordinately shales, referred usually as ‘tar sands’; they consist of mainly quartz and kaolinite, with variable amounts of mixed clay layers of illite-montmorillonite, mica and pyrite, probably derived from weathering of the Migmatite Gneiss Complex exposed to the north of the basin; this can also explain the relative enrichment in the natural radionuclides 40K, 238U, 226Ra and 232Th for some samples, although the radioactivity falls within the range for world values for soils. The clastic material of Afowo Formation was deposited in a rather oxic shallow marine environment. The particulate organic matter of the bituminous sediments comprises solid hydrocarbons, coalified (huminite) and partially oxidized (inertinite) remnants of terrestrial plants, and minor amounts of both terrestrial and marine liptinite macerals. The random reflectance values of the indigenous huminite population ranges between 0.40 and 0.45% pointing to an immature stage for oil generation. The respective reflectance of the migrabitumens ranges from 0.49 to 0.59% corresponding to vitrinite equivalent reflectance values of 0.70–0.76% falling well within the oil window. This study concludes that the hydrocarbons contained in the Afowo Formation are upwards migrating from parts of the basin where Afowo Formation has subsided at depths corresponding well within the oil window; the source rock corresponds to the middle shale horizon, whereas the sandy horizons act as migration paths and/or reservoirs.

Large-scale strain localization induced by phase nucleation in mid-crustal granitoids of the south Armorican massif

The reduction of grain size is believed to play a critical role in strain localization to form shear zones. Although many mechanisms have been proposed, the source of grain size reduction remains debated. The South Armorican Shear Zone (SASZ) is a crustal-scale strike-slip fault that deforms granitoids at mid-crustal conditions. The SASZ records the transition from protolith to ultramylonite, representative of increasing ductile shear strain. To investigate the evolution of strain localization, the different states of deformation were studied using a combination of detailed microstructural, chemical and electron backscatter diffraction analyzes. Increasing strain from protolith to ultramylonite resulted in (1) grain size reduction, (2) the development of interconnected monophase layers of mica and incipient mixed-phase zones composed of phengite-quartz ± K-feldspar in protomylonite and low-strain mylonite, and (3) the formation of fine-grained mixed-phase zones composed of K-feldspar-quartz ± phengite in high-strain mylonite and ultramylonite. We propose that the causes for interconnection of mica are the formation of cracks in the protolith combined with fluid-assisted nucleation. The latter process also plays a major role in phase mixing, as attested by the precipitation of K-feldspar at triple junctions in quartz-rich layers and in fine-grained tails of inherited K-feldspar porphyroclasts in ultramylonite. The transition from quartz-rich layers and mixed-phase zones is accompanied by a strong dispersion of the quartz lattice preferred orientation. These microstructural and textural evidences suggest that phase nucleation is the major process behind phase mixing, possibly accompanied by the action of grain-boundary sliding to open cavities during deformation. Instead of a single process, we therefore highlight a succession of weakening processes in the evolution of the SASZ, starting with the crystallization of mica as a first weakening material, and then evolving with the formation of very fine-grained mixed-phase zones made principally of feldspar, quartz and phengite.

Breakdown and current-voltage characteristics of DC micro-slit discharges in carbon dioxide

The breakdown voltage and current–voltage characteristics are essential parameters for understanding microplasma discharges and for optimal design of microplasma reactors. A metal–dielectric–metal sandwich configuration, consisting of two molybdenum foils with slit openings of different lengths at the anode, separated by mica layers of different thicknesses d, was used in this study. The measurements were performed in carbon dioxide under pressures from 4 to 40 Torr. It was found that although breakdown curves in carbon dioxide generally follow the conventional Paschen’s law, significant deviations occurred for the different cases in this study. The deviations may be due to the non-uniformity of electric field and the loss of charge carriers by diffusion to the inner wall of the slit. Current–voltage characteristics of the micro-slit discharge for different slit lengths and different pressures are presented. For a single-slit discharge, current–voltage curves are characterized by a positive slope, and the slopes decrease with increasing slit length and operating pressure. For the micro-slit array discharge, the sawtooth shape of the increasing current branch of the current–voltage curve is shown to be due to the change in the number of individual discharges and redistribution of current in the ignited opening slits. The formation of a stable discharge for the micro-slit array without individual ballasting allows the construction of large area, thin plasma sources for dissociation of carbon dioxide.

Ammonium-bearing micas in very low-grade metapelites: micro- and nano-texture and composition

ABSTRACTThe present study examines the micro- and nano-texture and composition of ammonium-bearing and potassium micas in very-low grade metamorphic black Silurian shales from the SE Iberian Range (NE Spain). Two organic-rich shales were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), transmission electron microscopy (TEM), analytical electron microscopy (AEM) and electron energy loss spectroscopy (EELS). The XRD showed the presence of two populations of micas: pure K micas with d001 = 9.98 Å and ammonium-bearing micas with larger d001 values (10.08 Å and 10.05 Å). The latter values indicate NH4 contents between 13 and 29% in the interlayer, which was confirmed by IR. Interstratifications of smectite and mica layers in the mica packets were not detected by XRD and TEM. Mica packets with sizes ranging from 100 to 250 Å show disordered polytypes and (001) lattice fringes that reflect the presence of K- and NH4-bearing layers (9.9–10.2 Å).The combination of AEM and EELS analyses on powdered and lamellar samples indicates that micas have typical dioctahedral compositions with highly variable K contents. This variation in K is consistent with the presence of K and NH4 in the interlayers, even though the NH4 and K are not distributed homogeneously; rather they are segregated in nm-sized domains in the mica interlayer.