mica mica

La description

 Luster
Dull to pearly, bronzy
Streak
Greenish white
Diaphaneity
Translucent
Specific gravity
2.**2.6
 
 
 
Pleochroism
X in paler shades than Y and
 

General

Mica are sheet silicates historically significant for their ability to be split into large, thin sheets that are uniquely useful for their electrical, thermal, and mechanical properties. They have high electrical and thermal insulating properties; they are resistant to chemical attack; they can be split into
transparent or optically flat films; and they can be cut or stamped to shape .

-it have several types :
*- Sheet mica Sheet mica consists of “books” of mica laminate and is classified according to the thickness, purity, and maximum usable area that can be cut or stamped.
*- Built-up mica Also known as micanite, built-up mica is a fabricated sheet of desired thickness made by overlapping irregularly shaped splittings and then binding them together with an organic or inorganic binder, heat, and pressure ,it is produced as an alternative to natural sheet mica for electrical insulation applications..
*- Mica paper Mica paper is a fabricated alternative to natural sheet and builtup mica products. Scrap mica is delaminated through a combination of thermal, chemical, and mechanical treatments , on a papermaking machine into a continuous, homogeneous sheet of uniform thickness..
*- Flake mica Flake mica is essentially nonfactory-generated scrap mica. It is recovered by flotation from mica ores, from which quartz and feldspar are also generally separated and recovered, or as a floated byproduct during the beneficiation of feldspar, kaolin, or lithium-bearing ores.

Uses :
*- Joint cements : muscovite is used in drywall joint compounds, where it contributes to consistency and workability, smooth surface finish,and resistance to shrinkage and cracking.
*- Coatings Fine-ground, ***5 mesh and micronized mica grades are used in paint as a pigment extender and for dry film reinforcement. The inert, platy mica improves suspensi
on stability, controls film checking, chalking, shrinkage, and blistering, improves resistance to weathering, chemicals, and water penetration, and improves adhesion to most surfaces. Coarser grinds are used in textured paints, and wet-ground mica is used in high quality exterior house paints. High aspect ratio grades are preferred for porous surface sealers
to seal pores, control penetration, and reduce sagging and film cracking.
*- Plastics Finely ground, ***5 mesh and micronized micas are used in plastics to improve electrical, thermal, and insulating properties. Mica is considered the most effective mineral for reducing warpage and increasing stiffness and heat deflection temperature in plastics. In general, mica reinforces crystalline better than amorphous polymers. Best results are obtained with nonpolar polymers when mica is pretreated with a coupling agent to improve wetting. Mica is used in both thermoplastics and thermosets. Its largest single use is in
polyolefins, even though it requires stabilizers to prevent degradation of polypropylene.
*- Drilling fluids Coarse, hammermilled (**0 mesh) mica is used in waterbased oilwell drilling fluids to prevent fluid loss into porous rock formations. The coarse mica flakes bridge openings and seal porous sections of the drill hole against loss of circulation. Mica’s platy nature also aids in the suspension of drilling fluid solids and cuttings.
*- Ground mica is used as an asbestos substitute in certain thermal boards, brake linings, gaskets, and cement pipes, as a filler and nonstick surface coating for roll roofing and asphalt shingles, as a mold lubricant and release agent in the manufacture of tires and other molded rubber goods, as a flux coating on welding rods, and as a pearlescent pigment in wallpapers.