Mica Structure Research Articles

Influence of rheology modifiers and coating parameters on the color-changing effects of textile coatings with multi-layered mica pigments

In order to optimize the color-changing effects of textile knife-coatings containing multi-layered mica pigments (effect pigments; EPs), the properties and structure of the coating formulation/layer during and after application were investigated. Three pigment coating formulations were prepared by first mixing the EP dispersion into a water-based polyurethane binder. Different types of rheology modifiers (RMs), liquid dispersion of sodium polyacrylates (LDPSAP), hydrophobically alkali swellable emulsions (HASEs) and hydrophobically modified ethoxylated polyurethane, were then added to the dispersion. The rheological behavior of the coating formulations was characterized in terms of the shear rate dependence of the viscosity. The formulations were applied onto the same type of textile substrate using a knife-coating technique. The choice of RM as well as variations in gap height and coating speed increased the solids deposit. The increased amount of coating deposits (thicker coating layers) corresponded to more and better dispersed EPs within the coated layer as well as more horizontally oriented platelets as confirmed by scanning electron microscopy. Multi-angle spectrophotometer measurements showed that the CIE L*a*b* color coordinates varied strongly depending on detection angle. The variations of the absolute values of L* and a* were more pronounced between –15° and 15° detection angles, corresponding to angles with the greatest visual color changes. The slowly coated samples with higher solids deposit were measured to be lighter and of higher chroma compared to samples coated at a higher speed. Generally, the color-changing effects were governed by the choice of RM and coating parameters in terms of variations of the amount of coating deposited onto the samples.

A study of mica structure and strength properties of polymer materials based on it

The mica microstructure is studied, and its shape and particle sizes are found as dependent on coating technology. Using epoxy and organosilicon polymers, several lots of materials with different contents of mica are prepared and mechanical tests are performed. The optimal amounts of mica wherein the initial strength characteristics are preserved are found. The thicknesses of epoxy and organosilicon polymer wherein high optical decorative properties of mica are preserved are determined.

A single-crystal neutron and X-ray diffraction study of a Li, Be-bearing brittle mica

AbstractThe crystal chemistry of a meso-octahedral Li,Be-bearing mica from the Harding pegmatite (Dixon, Taos County, New Mexico, USA) has been investigated by constant-wavelength single-crystal neutron diffraction at 20 K, single-crystal X-ray diffraction at 100 K and inductively coupled plasma-atomic emission spectrometry (ICP-AES). The chemical composition based on ICP-AES analysis leads to the following chemical formula (calculated on the basis of 12 oxygen atoms):Ca(Na0.26K0.04Ca0.69)∑0.99M(Li0.29Mg0.03Fe0.023+Al1.78)∑2.12T(Al1.73Be0.16Si2.11)S4.00O12H2.53. The apparent excess of H is probably due to the fact that the fraction of H2O was assumed by difference to 100 wt.%, and slightly overestimated. On the basis of the previous experimental findings on Li,Be-bearing mica, X-ray (at 100 K) and neutron (at 20 K) structure refinements were performed in the space groupsCcandC2/c. The neutron structure refinement in the space groupCcoffers a view about the (Al,Be,Si)-tetrahedral ordering: the best fit of the refinement was reached with theT1 andT4 sites occupied by (Be + Al) andT2 andT3 fully occupied by Si. This leads to a final population ofT(Al1.88Be0.12Si2.00)∑4.00p.f.u., in reasonable agreement with the chemical analysis. The neutron refinement provides unambigous evidence of the occurrence of Li at theM1 site. The refined fraction of Li at theM1 site ranges between 0.27 and 0.29 a.p.f.u., in excellent agreement with the chemical analysis. The presence of Li, at least at a significant level, at theM2 (andM3) site can be ruled out, as a full site occupancy with the scattering length of Al was obtained. The location of the H sites and the complex hydrogen-bonding scheme are described. A comparison between the structure features of this Li,Be-mica and other brittle micas is carried out.

Hybrid density functional based study on the band structure of trioctahedral mica and its dependence on the variation of Fe2+ content

A hybrid density functional based study of a phyllosilicate (PS) is presented here for the first time. Using all-electron electronic structure calculations with the B3LYP hybrid functional, we have investigated the electronic and structural properties of a series of trioctahedral 1M-polytype K-bearing micas starting from phlogopite (the Mg-end member), ending with the annite (the Fe-end member), and passing through the biotite (a solid solution of the end members). Electronic band gap is calculated for all the compositions and nature of the electronic transition is discussed with the aid of band structure and density of states plots. An excellent agreement with the available experimental data has been observed. An insulator to semiconductor transition is explained on the basis of orbital hybridization. A further comparison is made using the pure GGA functional. For the completeness of the study, the dielectric properties of phlogopite are calculated using the coupled perturbed Kohn–Sham scheme, as implemented within the CRYSTAL09 code.

Synthetic organofluoromica/poly(lactic acid) nanocomposites: Structure, rheological and thermal properties

Organically modified fluoromica/poly(lactic acid) (PLA) nanocomposites were prepared by melt processing at different compositions in an internal mixer at the same conditions. Gel permeation chromatography (GPC) was used to measure the molar masses of PLA alone, before and after processing. The results indicated that PLA presented some degradation during melt mixing. With the addition of the organically-modified fluoromica, higher reduction in the polymer molar masses was found. The structure of the synthetic mica and of the clay polymer nanocomposites (CPN) was studied by small-angle X-ray scattering (SAXS), which revealed the presence of nanometer-sized clay mineral aggregates. Dynamical rheological measurements were carried out in the linear viscoelastic region for both PLA and CPN molten samples. A predominantly viscous behavior was obtained for the polymer samples, whereas the CPN presented a pronounced elastic behavior. Addition of mica to PLA also had a significant effect on the complex viscosity of PLA, imparting an increasing shear thinning behavior with increasing mica composition. Below Tg, dynamical mechanical analysis results showed a substantial decrease of rigidity of the CPN in relation to PLA alone, attributed to the presence of high content of organic intercalant in the synthetic fluoromica. Lower cold crystallization rate was detected for the CPN in comparison with processed PLA alone.

Characterization of Preferred Crystal Nucleation Sites on Mica Surfaces

Rates of heterogeneous nucleation can be greatly increased not only through control of the chemistry of a surface, but also of its topography. Following previous work in which we showed that scratching a mica surface significantly enhances crystal nucleation from vapor, we here use a new experimental approach to understand better the effect of topography on crystal nucleation. The compounds carbon tetrabromide, camphor, norbornane, and hexachloroethane were deposited from vapor onto mica sheets containing various surface defects, and their nucleation was studied using optical microscopy. Following subsequent evaporation of the crystals, examination of the sites where these had nucleated with a scanning electron microscope enabled the nature of each material’s preferred nucleation sites to be determined, and all four compounds appeared to exhibit a strong preference for sites characterized by delamination of the layered mica structure. Indeed, comparison of the four compounds on the same mica substrates showed that they all favored the same nucleation sites. These observations are attributed to the presence of an acute wedge geometry at the delamination lines, which can provide a thermodynamic reduction in the free energy barrier to nucleation directly from vapor; alternatively, the results are also consistent with a two-step nucleation mechanism via a liquid capillary condensate.

Synthesis and characterization of single- and few-layer mica nanosheets by the microwave-assisted solvothermal approach

We have successfully fabricated single- and few-layer mica nanosheets, by means of using a solvothermal method in conjunction with a microwave irradiated expansion process. In the solvothermal process, dissolved potassium ions were intercalated onto the interlayer space of the mica. Following this, microwave irradiation facilitates the exfoliation of individual nanosheets. The synthesized products were characterized by field emission scanning electron microscopy, transmission electron microscopy (TEM), atomic force microscopy (AFM), x-ray diffraction, x-ray photoelectron spectroscopy (XPS), and Raman spectroscopy measurements. AFM and TEM studies claimed the existence of single-layer mica. High-resolution TEM (HR-TEM) investigations revealed that the exfoliated product corresponded to a crystalline mica structure, being comprised of Si, Al, O, and K elements. XPS spectra exhibited the major constituent peaks, including O 1s, Si 2p, Al 2p, and K 2p. In addition, C atomic concentration has been slightly increased by the contamination during exfoliation, presumably due to the increase of the exposed mica surface. The C 1s XPS spectra revealed that the C–C bonding in organic surface contaminants was broken, whereas the Si–C bonding was enhanced, by the exfoliation process. The O 1s XPS spectra revealed that the Si–O bonding in mica was broken, generating the O–Si–C bonding. This study paves the way towards the fabrication of single- or few-layer inorganic nanosheets of desired materials, via a convenient and efficient route.

Cesium stability in a typical mica structure in dry and wet environments from first-principles

Cesium ion stability in a typical mica structure in various environments of solid salts (XCl; X=Cs, K, and Na), metals (X) and saltwaters (XCl aqueous liquids) was investigated using first-principles density-functional theory (DFT) with the Perdew–Burke–Ernzerhof (PBE) functional as well as a van der Waals (vdW) corrected functional (vdW-DFC09x). We specifically examined interlayer ion-exchange in bulk phlogopite-type mica, which is expected to produce a well-defined benchmark in a thermodynamic equilibrium state. In general, theoretical models have well reproduced the experimental and theoretical data found in the literature from the viewpoints of structure, heat capacity, and entropy. The vdW-DFC09x lattice parameters of the mica appear to be better reproducible than the PBE parameters are. However, the vdW correction calculations of the thermodynamic properties with the harmonic approximation using the phonon frequencies showed poor results in some cases, whereas the PBE calculations yielded robust and reasonable results in terms of structure and thermodynamic properties. The isotope effect of the 137Cs atom appears to be confined in thermodynamic properties such as entropy, heat capacity, and ion-exchange energy, although the theoretical infrared spectra showed a small redshift ca. 1cm−1 in the far-infrared region of 50–75cm−1. The calculated RDF and the coordination number for X–O (i.e., X–H2O) for the saltwater model indicated that the Cs, K, and Na ions with respective hydrated radii of 0.323, 0.284, and 0.238nm were surrounded, respectively, by 6.5, 4.5, and 4.0 of H2O molecules in a water solution. Ion-exchange energy values based on free-energy calculations around ambient temperatures derived using the PBE functional and a harmonic approximation suggest that the cesium ion in mica interlayer phlogopite is stable in an environment consisting of KCl, NaCl, K, and Na solids, and in NaCl saltwater as well. However, it can be exchanged competitively by potassium ion in the KCl saltwater environment. The theoretical ion-selectivity order of the mica interlayer site is Cs>K>Na (PBE, vdW-DFC09x) in the solid environment, whereas the order of K⩾Cs>Na (PBE) or K>Cs⩾Na (vdW-DFC09x) is suggested in the saltwater environment. This selectivity-order difference between Cs and K underscores the importance of investigating the physical and chemical states of the counterphase as well as the host materials, and suggests that catching and releasing of the Cs atom in micaceous soil is possible through solvent control from a thermodynamic perspective.

Characterization of MicA interactions suggests a potential novel means of gene regulation by small non-coding RNAs

MicA is a small non-coding RNA that regulates ompA mRNA translation in Escherichia coli. MicA has an inhibitory function, base pairing to the translation initiation region of target mRNAs through short sequences of complementarity, blocking their ribosome-binding sites. The MicA structure contains two stem loops, which impede its interaction with target mRNAs, and it is thought that the RNA chaperone protein Hfq, known to be involved in MicA regulation of ompA, may structurally remodel MicA to reveal the ompA-binding site for cognate pairing. To further characterize these interactions, we undertook biochemical and biophysical studies using native MicA and a ‘stabilized’ version, modified to mimic the conformational state of MicA where the ompA-binding site is exposed. Our data corroborate two proposed roles for Hfq: first, to bring both MicA and ompA into close proximity, and second, to restructure MicA to allow exposure of the ompA-binding site for pairing, thereby demonstrating the RNA chaperone function of Hfq. Additionally, at accumulated MicA levels, we identified a Mg2+-dependent self-association that occludes the ompA-recognition region. We discuss the potential contribution of an Mg2+-mediated conformational switch of MicA for the regulation of MicA function.

Synthesis and single crystal structure refinement of the one-layer hydrate of sodium brittle mica

A sodium brittle mica with the ideal composition [Na4]inter[Mg6]oct[Si4Al4]tetO20F4 was synthesized via melt synthesis in a gas tight crucible. This mica is unusual inasmuch as the known mica structure holds only room for two interlayer cations per unit cell and inasmuch as it readily hydrates despite the high layer charge while ordinary micas and brittle micas are non-swelling. The crystal structure of one-layer hydrate sodium brittle mica was determined and refined from single crystal X-ray data. Interlayer cations reside at the center of the distorted hexagonal cavities and are coordinated by the three inner basal oxygen atoms. The coordination of the interlayer cation is completed by three interlayer water molecules residing at the center of the interlayer region. The relative position of adjacent 2:1-layers thus is fixed by these octahedrally coordinated interlayer cations. Pseudo-symmetry leads to extensive twinning. In total five twin operations generate the same environment for the interlayer species and are energetically degenerate.

Effect of Operating Parameters on the Mechanical Activation Process of Mica Powder

Mechanical activation of mica is a great technological and technical problem because of their specific crystallochemical structure. This is dependent upon the type of equipment used and the type of disintegration process. The paper presents the investigations of kinetics of operational parameters, effect on properties and structure of powder mica, etc. The mica sample was subjected to mechanical activation in ultra-centrifugal mechanoactivator with a peripheral comminution path. During the investigation, some operating parameters, viz. number of rotor revolutions (rpm), sieve mesh size (µm) and current intensity (A), and some technological parameters, viz. time of mechanical activation, t (min), circumferential rotor speed, v (m.s−1), capacity of ultra-centrifugal mechanoactivator, Q (kg.h−1) and specific energy consumption, W e (kWh.t−1) were monitored. Analyzing the results it can be concluded that the rate of mechanical activation of mica was increased with the increasing load and rotor revolution of ultra-centrifugal mechanoactivator with peripheral comminution path. Under these conditions, the powder mica was transformed into amorphous state. It was confirmed by X-ray and thermal analyses.

GEOCHEMISTRY AND EVOLUTION OF MICAS IN THE BARROSO-ALVAO PEGMATITE FIELD, NORTHERN PORTUGAL

Abstract Micas from the granitic pegmatites found in the Barroso–Alvao pegmatite field and the Cabeceiras de Basto granite present variations in their composition, textural characteristics and paragenesis. This pegmatite field in northern Portugal has numerous and varied aplite–pegmatite intrusions as well as diverse granitic bodies. The pegmatite bodies vary from barren to Li-rich ones with spodumene, petalite and lepidolite, and intrude a variety of rock types including metasedimentary and granitic rocks. The most fractionated bodies are enriched in Li, Sn, Nb, Ta, and Rb. In this study, we present the petrography and geochemistry of micas for the different types of aplite–pegmatite bodies and the Cabeceiras de Basto granite, and use this information to evaluate the evolution and petrogenesis of the pegmatite bodies. Micas are present in all of the pegmatites; they belong to the muscovite–lepidolite series. Micas from the granite and intragranite pegmatites have high octahedral-site occupancy and a few present Li enrichment. For most of the barren pegmatites and the Li-bearing pegmatites (spodumene and petalite), the stoichiometry of muscovite is close to the end member. Lithium-rich micas are mainly found in the petalite-and lepidolite-bearing pegmatites. The incorporation of Li into the mica structure seems to be controlled by the vectors Si2LiAl−3, and Li3Al−1□−2 (where □ represents a vacancy). The highest enrichment in large-ion lithophile elements (particularly Rb and Cs), F, and Li is found in the Li-bearing pegmatites, especially in the lepidolite-bearing ones. This variety of pegmatite is considered the most evolved on the basis of its low K/Rb value and the abundance of F, Rb, Cs, Li, Ta and Mn.

Evolution of the Cinovec (zinnwald) Granite Cupola, Czech Republic: Composition of Feldspars and Micas, a Clue to the Origin of W, sn Mineralization

A 1596-m-deep borehole (CS–1) located in the central part of the Cinovec (Zinnwald) granite cupola mineralized in Sn and W intersected zinnwaldite granite (ZG) followed by lithian annite (“protolithionite”) granite (PG). These two types of granite are separated by a transition zone (TZ). We studied the chemical composition of major mineral phases (plagioclase, K-feldspar, micas) by EPMA and LA–ICP–MS analyses. The plagioclase composition corresponds to albite (Ab 99.6–91.1 ) containing 0.09 to 0.18 wt.% Rb 2 O. Albite crystallized from the magma. K-feldspar is perthitic and shows an increase in Rb concentration (up to 0.83 wt.% Rb 2 O) in the apical part of the cupola. The partition coefficient K D–Rb Mi–Kfs is constant throughout the cupola, indicating a systematic re-equilibration of these two minerals with fluid. Lithian annite occurs below –735 m. Its F content decreases with depth and from –940.5 m, OH exceeds F. Magnesium and Ti concentrations show a remarkable positive correlation with depth. The TZ and adjacent area are characterized by strong variations in the chemical composition of micas, reflecting the fluctuation of saturation–oversaturation of residual liquid by a F-rich fluid phase. The Rb concentration in zinnwaldite (up to 2 wt.% Rb 2 O) strongly increases in the apical part of the cupola owing to a significant transfer of volatiles. The chemical composition of mica evolves gradually from the TZ to the apical zone. The discovery of lithian annite included in quartz at –97 m indicates the formation of zinnwaldite by interaction of lithian annite with F-rich fluid. The octahedral site of lithian annite allows the incorporation of Sn, Nb, Ta and W, replacing Ti. Because of the lithian annite → zinnwaldite transformation, these elements with higher ionic charges are expelled from the mica structure, transferred to the fluid phase and concentrated in the apical part of the cupola. The LA–ICP–MS analyses of the micas confirm this process. We envisage the transport of Sn, Nb, Ta and W in the form of fluorides and the precipitation of cassiterite by hydrolysis of SnF 4 . Tungsten was probably transported as H 2 WO 4 , resulting from the reaction of WF 6 with H 2 O. A similar behavior of Nb and Ta is suggested. The hydrolysis of fluorides leads to a strong enrichment of fluid in HF, which induced albite instability and formation of greisens. Calculations show that the amounts of Sn and W released by the transformation lithian annite → zinnwaldite transformation are close to the estimated reserves of these metals within the Cinovec cupola, corroborating the proposed metallogenic model.

Virtual-crystal approach to aluminum-avoidance materials: A first-principles density-functional calculation of micas

First-principles thermodynamic calculation of typical micas having a fractional occupancy of Al at the tetrahedral site is presented within a picture of the density-functional (perturbation) theory. A total-energy comparison conducted among the full set calculations on the Al tetrahedral site configurations within a mica unit cell confirmed an ``aluminum-avoidance'' rule. The energy difference of these structures is within room temperature energy of atoms. Therefore, it is most likely that the Al sites cannot be ordered in an ambient condition. A virtual atom generated by an average of Si ($0.75$) and Al ($0.25$) yields reasonable averaged features from the perspectives of its atomic eigenenergy and the optimized mica structures. The calculated infrared vibrational spectra with partial phonon density of states exhibit a marked difference between the Al-site specific and virtual-crystal models. However, the calculated thermodynamic properties for both models such as entropy and heat capacity exhibit good agreement with experimental values. An example of the virtual-crystal approach to estimation of a Na-K ion exchange energy is also presented. Results show that the virtual-crystal model can work well for energetic properties of aluminum-avoidance materials.

Depleted brittle mica structure determination in Ba-phlogopite glass–ceramics

This study concerns the bulk mica phase of a barium phlogopite glass–ceramic, with potential applications in Computer Aided Design and Computer Aided Manufacturing in dentistry, which has been studied in detail and characterized for the first time. A number of analytical techniques including powder X-ray diffraction (XRD), scanning electron microscopy, energy dispersive spectroscopy, electron micro-probe analysis (EMPA), single crystal XRD and Monte-Carlo methods have been used to determine the mica phase composition and crystallographic structure. This has led to the identification of a new species of trioctahedral interlayer deficient brittle mica with an ideal formula of Ba2/3Mg3(Si8/3Al4/3)O10F2. Monte-Carlo simulations of Si/Al cation ordering indicate that the (Si8/3Al4/3) tetrahedral composition is unique and energetically favoured over that of the original assumed mica phase of Ba0.5Mg3(Si3AlO10)F2. The general mica composition X0.5Mg3(Si3Al)O10F2 where X is a divalent interlayer cation; therefore, does not precipitate in brittle mica glass–ceramics.

Structure, morphology and thermal stability of synthetic fluorine mica and its organic derivatives

The morphology and thermal stability of a completely inorganic synthetic fluoromica (Somasif ME-100) and four organophilic fluoromicas were investigated comparatively by using different techniques as FTIR, XRD, SAXS, GPC, SEM and TGA. These organophilic micas which were intercalated with oligoether-based (Somasif MEE and MPE) and alkyl-based (Somasif MAE and MTE) ammonium salts present, as typical morphology, families of mica domains with lateral dimension up to 4 μm, formed by the association of nanosized mica aggregates having different distances between platelets. Somasif micas containing alkyl-based ammonium salt presented the higher proportion of lamellae not successfully organically modified, whereas the modified fluoromicas containing oligoether-modifiers showed the highest volume fraction of aggregates with higher interlayer distances d (up to 6.1 nm). All organophilic fluoromicas have thermal degradation from 200 to 460 °C and Somasif MPE with PPG moieties has the best thermal stability among the organomicas.

Clay-Mediated Synthesis of Silver Nanoparticles Exhibiting Low-Temperature Melting

Nanohybrids of silver nanoparticles (AgNPs) supported on mica clay were synthesized by in situ reduction of silver nitrate in an aqueous solution. The required mica platelets of high aspect ratio were previously prepared by the exfoliation of mica clay stacks in a multilayered structure through an ionic exchange reaction with poly(oxypropylene)-amine-salt. The exfoliated nanoscale mica platelets (Mica) are polydispersed such that each platelet is 300-1000 nm in width and 1 nm in thickness. These platelets possess ionic charges in the form of ≡SiO(-)Na(+) at 120 mequiv/100 g and are suitable for supporting AgNPs in the process of in situ reduction of silver nitrate. Transmission electronic microscopy revealed the formation of AgNPs with a narrow size distribution of ca. 8 nm in diameter on the rim of individual Mica platelets. However, the pristine layered Mica structure without exfoliation failed to produce a fine AgNP distribution but instead generated particles larger than 30 nm and some precipitates. Characterization by differential scanning calorimetry and field emission scanning electron microscopy revealed that the fine AgNPs on Mica platelets exhibited a low melting temperature of 110 °C. The AgNP/Mica nanohybrid not containing an organic dispersant is considered to be a "naked" silver particle.

Acrylamide/2-acrylamido-2-methylpropane sulfonic acid and associated sodium salt superabsorbent copolymer nanocomposites with mica as fire retardants

Acrylamide (AM) and 2-acrylamido-2-methylpropane sulfonic acid (AMPS-H +) or its sodium salt (AMPS-Na +) were copolymerised by free-radical crosslinking polymerization to obtain poly(AM- co-AMPS-H +) and poly(AM- co-AMPS-Na +) superabsorbent polymers (SAPs). A maximum water absorbency in deionised water of 1200 g g −1 was achieved for poly(AM- co-AMPS-Na +) at a 85% mol of AMPS-Na +. The inclusion of mica at 5–30% (w w −1) into the preparation of poly(AM- co-AMPS-Na +) SAP leads to an intercalated structure, as detected by XRD and TEM analyses. Poly(AM- co-AMPS-Na +)/30% (w w −1) mica SAP nanocomposite showed a tap water absorbency of 593 g g −1 with a better thermal stability, compared to the pure SAP. Cone calorimetric analyses revealed that the wood specimens coated with the prepared poly(AM- co-AMPS-Na +) SAP or its 30% (w w −1) mica nanocomposite provided excellent protection in delaying the ignition time after exposure to an open flame when compared to that observed with the uncoated specimen. The maximum reduction in the peak heat release rate and the greatest extension of time at peak heat release rate were observed with the nanocomposite-coated surface, but the total heat release rate was increased. The delayed burning mechanism is brought by the intercalating structure of mica in the SAP nanocomposites, which provided a better shielding effect against external heat sources, and the capability of the SAP nanocomposite in holding a large amount of water.

Significance of Impurity Mineral Identification in the Value Addition of Kaolin – A Case Study with Reference to an Acidic Kaolin from India

Kaolin or china clay is a versatile industrial mineral with wide technological applications and is abundantly available in India. The major mineral in kaolin is kaolinite (Al2O3.2SiO2.2H2O). The common ancillary / impurity minerals occurring with kaolin include parent rocks like feldspar and mica, quartz, ferruginous, titanoferrous and carbonaceous materials. The most deleterious impurities in kaolin are iron minerals which imparts colour to the white kaolin. Iron exists as oxides, hydroxides, oxy hydroxides, sulphides and carbonates along with iron stained quartz/anatase and mica in kaolin. Kaolin finds extensive applications in paper, paint, rubber, ceramics, plastics etc. One of the highest value additions for kaolin is as pigment in paper and paint industries. The optical properties are important for pigment applications and removal of the iron impurity is very important to improve this property. Extensive research has been carried out on the nature of iron impurities present in kaolin, which leads to the conclusion that iron is present as a part of the kaolinite or ancillary mineral (mica or titania) structure, which can be termed as “structural iron” or as independent iron minerals such as oxides, hydroxides, oxyhydroxides, sulphides and carbonates, which can be termed as “free iron” [1]. The present paper discusses the iron speciation studies carried out on a typical china clay sample collected from Koraput district of Orissa State in the Union of India. Studies have shown that the major impurity mineral species is in “pyritic” (Iron sulphide) form along with other hydroxides, oxyhydoxides and oxides of Iron. Presence of limonite is also observed in the sample. The identification/quantification of the impurity minerals have played a crucial role in the selection / modification and sequentialisation of beneficiation processes and subsequent processing studies have shown that the sample can be value added to ceramic grade.

Potential of Mean Force for K+in Thin Water Films on Cleaved Mica

The atomically smooth surface of cleaved K(+)-mica is a common substrate for investigations of various phenomena at the mineral-water interface. In this study, K(+) inner-sphere adsorption above tetrahedral substitutions in the mica structure is found to be more favorable than that in mica's ditrigonal cavities for both dehydrated and hydrated cleaved mica. The activation energy necessary to transfer K(+) from the inner-sphere adsorption state to the outer-sphere adsorption state, in which K(+) can presumably migrate parallel to the surface, is calculated to be 45-48 kJ/mol on hydrated cleaved mica. The K(+) desorption state is predicted to be >13 A above the mica surface.