Natural Mica Research Articles

The Adsorption of Dodecyltrimethylammonium Bromide on Mica in Aqueous Solution Studied by X-Ray Diffraction and Atomic Force Microscopy

The adsorption of dodecyltrimethylammonium bromide (DTAB) onto natural muscovite mica and a synthetic expandable mica (EM) in aqueous solution has been investigated using both microscopic and macroscopic surface characterization techniques. The electrokinetic properties of the surfaces were monitored as a function of the concentration of DTAB using atomic force microscopy and microelectrophoresis. The adsorption isotherm of DTAB on EM was measured up to a solution concentration just below the critical micelle concentration of the surfactant. The thickness of the adsorbed layer on EM was determined using X-ray diffraction. Results indicate that the adsorbed layer consists of molecules lying quite flat on the mica surface at low concentrations and adsorbed in interleaved aggregate structures at concentrations approaching the critical micelle concentration of the surfactant in solution.

Effects of non‐isometric pigment particles in organic coatings for corrosion protection

Studies the effects of non‐isometric pigments on the anticorrosion properties of coating films. The optimum concentrations for using iron mica, muscovite, and graphite have been determined. The results obtained on using the natural iron mica are compared to those obtained with a synthetic product. As binders for the coatings epoxy resin, polyurethane and alkyd resins were used. The results allow the conclusion that on the pigmentation with iron mica the protection function of top coatings against the corrosive media can be considerably increased.

Measurements of Streaming Potential for Mica Covered by Colloid Particles

The zeta potentials of natural mica, bare and covered by positively charged latex particles of micrometer size range, were determined by the streaming potential method. Measurements were carried out using the parallel-plate channel formed by clamping together two mica sheets separated by a Teflon spacer. The dependence of streaming potential on surface coverage (ϑ) of adsorbed particles was determined for various ionic strengths and particle sizes. The coverage was determined directly by optical and electron microscope counting procedures. It was found that the negative streaming potential for bare mica Es was significantly increased by the presence of adsorbed particles. The dependence of the reduced streaming potential Esp/Es (where Esp is the zeta potential in the presence of particles) on ϑ exhibited an universal behavior being independent of particle size and ionic strength. These experimental data were interpreted in terms of a theoretical model postulating that the streaming potential change was due to flow damping over the interface and by charge transport from the double-layer surrounding adsorbed particles. In contrast with previous approaches no assumption of the slip (shear) plane shift upon particle adsorption was made. By exploiting the experimental results it was suggested that colloid and bioparticle adsorption kinetics can be studied in situ using the streaming potential method.

Characterization of mica crystals as reflectors for an ultracold neutron doppler converter

Natural mica crystals have been characterized for use as reflectors for an ultracold neutron source using Bragg scattering of cold (400 m/s) neutrons from a moving mica reflector, recently installed at the Los Alamos neutron science center (LANSCE). In particular, the triotahedral Mg-rich mica phlogopite has been obtained in large sheets. The structure factor for the first-order Bragg reflection is a factor of four larger than for muscovite, the first variety of mica examined. The observed peak reflectivity for a phlogopite of 0.25 mm thickness is about 8.2% at 1.9 Å, with a mosaic spread of about 0.3° FWHM, in good agreement with the ideally imperfect crystal model. This can be extrapolated to a reflectivity of about 63% at the 17.4 Å operating wavelength of the ultracold neutron source. Improvements are possible by obtaining Fe-rich mica, which should be almost as effective as the alternative approach of using synthetic perfluorinated mica.

Growth of YBa2Cu3O7-x Superconducting Thin Films on [111] Oriented Ag Films

YBa2Cu3O7-x (YBCO) superconducting thin film was prepared on a [111] oriented Ag film using off-axis rf magnetron-sputtering. The [111] oriented Ag film was prepared on the (001) single-crystal natural mica substrate at a substrate temperature of 200° C under argon atmosphere. The YBCO film grew with, not only a strong orientation for the c-axis, but also with the three-symmetrical orientation for a and b axes on the mica/Ag substrate without post-annealing. The full-width at half maximum (FWHM) intensity of the 003 ω-rocking curve of the YBCO film was 1.52°. The optimal substrate temperature was 620° C, when the partial pressure of oxygen was 1.0×10-2 Torr. T c (onset) and T c (zero) of the films were 84 K and 77 K, respectively, according to the AC magnetic susceptibility measurements. The J c of the film was measured by the conventional four-probe method, and the J c (J//ab) value was 1.4×104 A/cm2 at 77 K in a liquid nitrogen bath. The YBCO film showed the thickness dependence of T c to be due to the large lattice mismatch of Ag(111) to YBCO (001).

Pressure solution in sandstones: influence of clays and dependence on temperature and stress

The enhancement of dissolution of quartz under the influence of clays has been recognized in sandstones for many years. It is well known that a grain of quartz in contact with a clay flake dissolves faster than when in contact with another grain of quartz. This phenomenon promotes silica transfer during the diagenesis of sandstones and is responsible of deformation and porosity variations. Here we make an attempt to explain the process of this rock deformation using a pressure solution mechanism. The model of water film diffusion assumes that matter is dissolved inside the contact between two grains. The resulting solutes are transported to the pore fluid through diffusion along an adsorbed water film. Between two micas, this trapped film is thicker than between two grains of quartz. As a consequence diffusion is easier and the rate of pressure solution faster. Experiments on pressure solution show that diffusion controls the mechanism at great depth whereas a model based on natural mica indentation indicates that kinetics is the limiting process through the precipitation rate of quartz at low depth, thus temperature is a crucial parameter. There should be a transition between thermally controlled rate and diffusion limited evolution.

Reactivity of gypsum faces according to the relative humidity by scanning force microscopy

This article reports the experimental observation of the stability of the different faces of calcium sulphate dihydrate (gypsum CaSO 4.2H 2O) according to the relative humidity. Scanning Force Microscopy experiments were carried out with a view to discerning the topography of the surfaces, the chemical compositional domains, and in an attempt to evaluate the friction and viscoelastic properties of the surface. Our results indicate that the (010) face of gypsum is hydrophilic and very reactive contrary to the less hydrophilic (120) and (1̄01) faces which remain stable depending on the relative humidity. It is clear from our results that a precipitation like process can be induced by the SFM tip. The dissolution of this precipitate depends on the amount of water in the meniscus between the probe and the surface. For the purpose of comparison, the cleaved surfaces of natural anhydrite (CaSO 4), calcite (CaCO 3), and muscovite mica were also observed. The Lateral Force Microscopy images provided the undisputed evidence that the process of dehydration of the (010) face actually occurs with a change of the elastic constant of the crystal.

Unique Signature of Dark Matter in Ancient Mica

Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from WIMPs. Because a background from fission neutrons will eventually limit this technique, a unique signature for WIMPs in ancient mica is needed. Our motion around the center of the Galaxy causes WIMPs, unlike neutrons, to enter the mica from a preferred direction on the sky. Mica is a directional detector and despite the complex rotations that natural mica crystals make with respect to this WIMP ``wind,'' there is a substantial dependence of etch pit density on present day mica orientation.

Ordering and manipulation of MoS2 platelets on differently charged micas by atomic force microscopy

Atomic force microscopy (AFM) has been used to investigate how dispersed MoS2 platelets (from colloidal suspensions) deposit onto three natural (Muscovite) mica (001) surfaces. Different platelet arrangements are observed, which are attributed to defects and charging effects of the mica (as well as the concentration of starting colloid). The provenance of the mica influences the self-organisation of the platelets into long tape-like assemblies (South Dakota mica) or individual flakes (Alps mica). Atomic scale imaging of the tapes reveals a distorted octahedral (Oh)-based local structure, different from the trigonal prismatic structure found in the 2H-polytype of annealed MoS2, in agreement with previous structural results on water-dispersed MoS2 platelets. The buckling and susceptibility to stripping of the tapes is ascribed to the presence of a water layer between the substrate mica and MoS2, and after stripping by the tip, the platelets ultimately form small clusters. The ordering of these clusters depends not only on the defect and charge structure of the mica, but also on complex hydration reactions between the H2O layer associated with the MoS2 and K + ions of the mica. Relatively symmetrical squares may be lifted out of the tapes, supporting the presence of weak bonding between tape and mica. Conversely, Alps and Bihar micas give rise to separate platelets, which are resistent to tip manipulation, which is attributed to hydrophobic interaction between MoS2 platelets and the mica surface.

Substitution of [4]Al in layer silicates: Calculation of the Al-Si configurational entropy according to 29Si NMR Spectra

A new constructive statistical method was used to simulate the Al-Si distributions in tetrahedral layer of mica according to short range and long range order restrictions and to calculate values of configurational entropy which correspond to simulated distributions. The simulations and the calculated entropy values were constrained by the existing 29Si NMR data for natural and synthetic mica samples. The results of simulation confirm previous conclusions on the importance of short range order restrictions such as Al-avoidance and homogeneous dispersion of charges (HDC) in the tetrahedral layer. The results suggest, however, that the Al-Si distribution in mica closely follows the HDC restriction only for the samples with the Al/(Si+Al) ratios in the range of 0.11–0.3. At higher values of the ratio (0.3–0.37) the degree of the HDC-type ordering decreases towards pure Al-avoidance. In the range of 0.37–0.5 two alternative models namely the HDC model and the model with partial long range order can be used to explain the observed NMR intensities.

Magnetism of synthetic and natural annite mica: ground state and nature of excitations in an exchange-wise two-dimensional easy-plane ferromagnet with disorder

We have studied the magnetism of annite mica (the Fe-end-member layer silicate having ideal structural formula: {K +}[Fe 3 2+] <Al 3+Si 3 4+〉 O 10 2-(OH -) 2) using SQUID magnetometry, Mössbauer spectroscopy, and neutron d iffraction on well characterized samples of both a synthetic powder and a natural single crystal. In disagreement with previous predictions, we find T c > 10 K and as large as T c = 58 K in the true end member and a metamagnetic ground state spin structure (predominantly ferromagnetic layers with in-plane moments, stacked antiferromagnetically along the c ∗-axis) that is stable despite significant amounts of Fe 3+, diamagnetic octahedral ions, and Mn 2+ in the natural sample. We propose that the antiferromagnetic stacking is part of the intrinsic zero-field magnetic domain structure and that it is entirely due to dipole-dipole forces. The most striking features are that a paramagnetic Fe 2+ temperature dependent fraction persists far below T c and that the Fe 3+ moments abruptly disorder significantly below T c, with the tetrahedral Fe 3+ going first as temperature is increased. Plausible causes for the latter intrinsic features are discussed.

Study of Arsenic Evolution During RTA of Au-Based Ohmic Contacts to GaAs

ABSTRACTWe report on the formation of AuZn/p-GaAs ohmic contacts by short time annealing either in open or closed configuration with a dielectric or metallic capping layer. Quantitative determination of the amount of arsenic losses was of primary concern. This was studied using the Cr-collector method, applying three types of collectors all of them using 100 nm thick Cr film for seizing evaporative As losses. In the first type, the Cr film was deposited onto oxidized Si substrate. In the second type - quartz substrate was used for the deposition of chromium film while the third collector used natural mica as a substrate for the Cr film. The obtained results show that the loss of arsenic is reduced below 2×1014 atom/cm2 using thin 20 nm Au/10 nm Zn/60 nm Au metallization annealed with a capping layer at 440°C for 15 sec. Electrical measurements indicate that under these conditions good ohmic contacts are obtained.

A Comparison of Magnetic Properties of Thin Films of Fe/GaAs(100) and Ni/MICA

ABSTRACTA comparison between the morphology and magnetic properties has been made with thin films of Fe grown on GaAs(lOO) and of Ni grown on natural mica in the 10Å to 1000Å thickness range, in ultra high vacuum. The films are characterized in-situ by Auger spectroscopy and by an in-situ UHV M/H hysteresis loop tracer. If the films are thermally annealed, above 550°C for less than a few seconds, the film morphology changes. The Fe films form surface assembled clusters which are epitaxial with the GaAs substrate with diameters of order of the original average film thickness, while the Ni films grow large grains. The Auger signals show that the Fe clustering exposes the GaAs substrate while the Ni films are continuous and cover the mica substrate. In-situ adsorption studies of CO on the Ni films were consistent with the continuous nature of the Ni films. Hysteresis M/H curves are taken as a function of thickness and plots of coercivity versus film thickness or average cluster size shows a maximum near 100Å for both the Ni and the Fe films. The maximum is believed to be due to a trade-off between super-paramagnetism and magnetostatic forces, but with the grains in the Ni film playing the role of the clusters in the Fe film.

Fission track dating of muscovite mica for searching for magnetic monopoles

According to Grand Unified Theories ( GUT ), magnetic monopole exists in the universe and has gigantic mass ( ≳ 10 16 GeV/c 2 ) and low speed ( ∼0.001c ). It should pick up a nucleus of 27 Al or 55Mn and forms monopole-nucleus bound state when passing through the crust of earth. Such a bound system will create an etchable track in mica in case of passing through underground mica mine due to elastic collisions of the Al or Mn nucleus with atoms in mica. Counting monopole-nucleus tracks and determining the geological age of mica, one can derive the flux of magnetic monopoles near the surface of earth. For this purpose, very large pieces of high-quality natural muscovite mica have been collected from First Mica Mine in Xinjiang, China. By counting spontaneous fission tracks and determining uranium content in mica, we have determined fission track age of the mica, which is ( 1.29±0.08 ) × 108 yrs. This age should be from the time when the mica stared to retain fission tracks. It should be a close approximation of age for mica to record monopole-nucleus tracks.

Preparation and properties of binary and ternary composite solids in the clay-mica-glass system

Abstract Binary and ternary composite solids in the clay-mica-glass system have been fabricated by combining both natural mica flakes of the phlogopite type and ground powders prepared from recycled waste glass, and clay grains and mixtures of clay-glass powders, employing a simple sintering process at temperatures in the range of 850–1050°C. Results of the study showed that these composites have very different physical appearance and material characteristics. In the glass-mica system, mixtures can be fabricated into composite solids which exhibit either a porous cellular structure or a densified ceramic structure. The mixtures can also be fabricated into multilayer structural products consisting of both the cellular structure layer and the densified structure layer. In the clay-mica binary system and in the clay-mica-glass ternary system, mixtures can be readily fabricated into composite solids with low density and low thermal conductivity. All coposite solids showed excellent insulation properties and would contribute to energy conservation when used for building envelope design applications.

Decomposition of ethylene on small Pd particles

New results have been obtained which contribute to the understanding of hydrocarbon reactions on the surface of highly dispersed metal systems. Small particles of Pd were grown by electron beam evaporation on cleavage planes of high purity natural mica under ultrahigh vacuum conditions. Samples were subsequently characterized by transmission electron microscopy. Average particle sizes ranged from about 1 to 10 nm diameter. The chemisorption and decomposition of C2H4 on the Pd particles was studied using Auger electron spectroscopy and flash thermal desorption. We show that (a) C2H4 decomposes on Pd particles at room temperature, (b) specific surface sites are causing decomposition, and (c) the proportion of such active sites is significantly greater for the smaller metal particles. This enhanced reactivity may be due to an increase in the density of step, corner, and edge sites with a decrease in particle size.

Preparation and properties of binary and ternary composite solids in the clay-mica-glass system

Binary and ternary composite solids in the clay-mica-glass system have been fabricated by combining both natural mica flakes of the phlogopite type and ground powders prepared from recycled waste glass, and clay grains and mixtures of clay-glass powders, employing a simple sintering process at temperatures in the range of 850–1050°C. Results of the study showed that these composites have very different physical appearance and material characteristics. In the glass-mica system, mixtures can be fabricated into composite solids which exhibit either a porous cellular structure or a densified ceramic structure. The mixtures can also be fabricated into multilayer structural products consisting of both the cellular structure layer and the densified structure layer. In the clay-mica binary system and in the clay-mica-glass ternary system, mixtures can be readily fabricated into composite solids with low density and low thermal conductivity. All coposite solids showed excellent insulation properties and would contribute to energy conservation when used for building envelope design applications.

Optical glass wave plates

Permanent birefringence in excess of 300 nm/cm can be thermomechanically induced in the borosilicate optical glass ARG-2, making it an attractive alternative to natural crystalline quartz and mica for large-aperture wave-plate requirements in laser systems investigating inertial confinement fusion. The technique for fabricating glass wave plates is presented, including a detailed optical characterization of the uniformity of birefringence induced in glass plates. A comparison with other natural and synthetic candidate materials is made, and production scale-up problems are discussed.

A New Structural Thermal Insulating Material

A homogeneous glass-mica composite solid with different physical structures has been developed from mixtures of natural mica powders of the phlogopite-type and ground glass powders prepared from recycled waste soda- lime-silica glass. The mixtures can be fabricated into com posite solid with a cellular structure which consists of both closed and open cells or into composite solid with a highly densified ceramic body which contains very low porosity. The two different structural solids can also be jointly fabricated together in the form of sandwich and multi-layer products providing both load-bearing and thermal insulation in a single unit. The glass-mica composite solids exhibit several basic qualities as a thermal insulator including insulation efficiency, safety, strength and durability. Laboratory test results show that these glass-mica composite solids have great potential as structural thermal insulating material for building construc tion and other applications because of their contribution to energy conservation. This paper discusses some of the material characteristics.

The effect of mica dehydration on the fabrication of cellular glass-mica composite solids

Investigations have been conducted to show that hydrated mica flakes are one of the essential starting components for the development of a cellular-structure glass mica composite solid by sintering mixtures of natural mica powders of the phlogopite type and ground glass powders prepared from recycled soda-lime waste glass. Studies show that if the water of crystallization is removed from the mica structure by heating prior to mixing and reaction with the glass grains, the development of the cellular structure in the sintered glass-mica composite solid is partially or totally suppressed depending on the extent of the thermal dehydration of the mica powders.