Mica, flake

Since the early days of the development of phenolic molding compounds for electrical applications, mica has been extensively used as a filler of choice. It was not until the late 1960s/early 1970s that the realization of the importance of the aspect 

The multiple functions of mica have been outlined in Chapter 1 of this book, along with an example of its role in the search of multifunctional fillers for polypropylene compounds for automotive applications. Mica-reinforced thermoplastics such as polypropylene, polyethylene, nylon, and polyesters are now established in a variety of automotive applications and consumer products where mica supplements or replaces glass fibers and other mineral fillers. The wider use of mica in many applications has been limited by low impact strength and low weld-line strength in certain plastics. These issues are the focus of continuing R D efforts by materials suppliers and compounders/molders. 

In addition to its primary function as a high aspect ratio mechanical property enhancer, mica is also used as a modifier of electrical properties and as an important component of sound-deadening formulations it is also used for reducing permeability, improving dimensional stability, and as a modifier of optical properties. The multiple functions of mica are compared to those of other fillers in Table 1.4. 

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The hard rock deposits are mined mainly for feldspar with mica and quartz being accessory minerals. These deposits are extensive, often covering hundreds of square meters and are recognized by the light-colored, granite-like appearance with shiny mica flakes being a prominent feature. The mica content of these deposits ranges from approximately 6—10 wt %. 

Flake Mica. Flake mica is mined from weathered and hard rock pegmatites, granodiorite, and schist and gneiss by conventional open-pit methods. In soft, residual material, dozers, shovels, scrapers, and front-end loaders are used to mine the ore. Often kaolin, quartz, and feldspar are recovered along with the mica (see also Clays Silicon compounds). 

Sealers. Mica is used in all types of sealers for porous surfaces, such as waHboard masonry, and concrete blocks, to reduce penetration and improve holdout (see Sealants). It permits a thicker film to be appHed and at the same time reduces sagging. Cracking is reduced by the reinforcing action of the flakes, and gaps and holes in rough masonry are bridged by the mica flakes. 

Asphalt, crushed, 1/4 in and under 45 C26 Mica, flakes 17-22 B17WY... 

Although development work on shellac in blends with other synthetic resins has been carried out over a period of time, the only current use in the plastics industry is in the manufacture of electrical insulators. At one time electrical insulators and like equipment were fabricated from mica but with increase in both the size and quantity of such equipment shellac was introduced as a binder for mica flake. For commutator work the amount of shellac used is only 3-5% of the mica but in hot moulding Micanite for V-rings, transformer rings etc., more than 10% may be used. The structures after assembly are pressed and cured, typically for two hours at 150-160°C under pressure. 

Iron(III) oxide is the most important metal oxide for combination with titanium dioxide on mica flakes. Brilliant golden pigments result which can be applied for several purposes. Two routes are used to synthesize these pigments, and different structures are formed [5.190], [5.192]-[5.194]. In the first case, a thin layer of Fe203... 

As seen in the figure, the surfaces of mica flakes had 170 to 200 nm diameter objects on them. These objects are not layered (not montmorillonite), are likely to be amorphous, and are likely the particles that were weakly absorbed on the montmorillonite and transferred to the mica surfaces. However, AFM cannot provide analytical information on the samples only morphological information can be obtained. In order to have some analytical information, the prepared mica surfaces can be examined by SEM (Figure 2.29). 

Lead enrichments can be detected only when the system contains both lead ions and montmorillonite. However, they cannot be observed on mica flakes immersed... 

Thin slices were microtomed from the flat (5-50/a) strip (Figure 2) in the three mutually perpendicular directions. Fractured surface replicas were also made of the three different directions for samples precooled to liquid nitrogen temeprature. The specimens fractured most readily between the (010) planes (Figure 2), exhibiting layered cleavage somewhat akin to mica flakes. Traverse to this plane, fracture was less well defined and less facile. However no difficulty was experienced in microtoming the material in all three directions. 

Mica flakes can also be coated in CVD processes using the same technique as discussed for metal flakes. In addition, one can also use metal chlorides as precursors for oxide coating on mica. However, essentially the same products can be obtained more easily by precipitating the oxides from the liquid phase. 

For narrowly classified mica flakes and carbon fibers in the 1 to 100 pm size range it was found that partiele shape could be estimated from the ratio of median sizes by laser diffraetion and sedimentation [35]. Austin found that conversion between Sedigraph and sieve analyses depends not only on a mean shape factor, but also on size distribution. He generated an equation that applies for overall conversion when the sieve distribution followed a Schuman form (Equation 2.97) [36]... 

If fluorphlogopite is used as an internal standard, an alignment of the mica flakes parallel to the sample surface is preferred. This can be obtained if a small amount of the mixture sample/standard is suspended in acetone or isopropanol and is sedimented to a single crystal sample holder. 

Chemical composition variable composition silver coatings in Conduct-O-Fil solid glass spheres and fibers -4-16 wt%, 30% on hollow glass spheres, 65 wt% on mica flakes, 8-19 wt% on copper flakes, 24 wt% on nickel granules, 20 wt% on aluminum particles, nickel coating on Compmat carbon fiber is 24 wt%... 

Conduct-O-Fil S series - silver coated solid glass spheres. Twelve grades in particle sizes range of 12-92 pm. Materials for conductive adhesives, caulks, coatings, elastomers, greases, inks Conduct-O-Fil SH - silver coated hollow borosilicate glass spheres containing 30 wt% silver Conduct-O-Fil SM - silver coated mica flake... 

Mica flakes Bari saddles Raschig rings... 

Experience in the electrical industry has also shown that thorough impregnation of the groundwall" insulation materials (e.g., mica flake paper) becomes difficult if the viscosity of the resin increases above 1,000 cps (as measured at 25 C). The impregnation process, however, with more viscous resins, can be made more effective by using higher pressures and elevated temperatures, but this is not always desirable or possible in production. 

Siderite is most abundant (up to 14%) in finegrained sandstones rich in mica and clay pseudomatrix. It occurs as small subhedral or flattened rhombs (<3-15 pm) (Fig. lOF) that replaced the detrital clays, and expanded as well as replaced the mica flakes (Fig. 13A). In coarser-grained sand-... 

Ankerite occurs as disseminated intergranular rhombs in wells 30/6-7, 30/6-8 and 30/9-1. It was identified by XRD and EPMA (Table 1). Ankerite rhombs ate often precipitated within exfoliated mica flakes or on detrital surfaces of adjacent quartz grains (Fig. 6B). Ankerite abundance does not exceed a few percent, except in sample 30/9-1 2781.0, where it reaches 33% of the total rock volume. This is the only occurrence of abundant ankerite cement found in the samples investigated in this study. 

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