Mica cost/availability

Thanks to their low cost and easy availability, many metal-exchanged clays have been patented as efficient solid catalysts in Friedel-Crafts acylation reactions. A great number of arylketones is prepared by electrophilic acylation of arenes with anhydrides in the presence of ion-exchanged clays at 150°C-250°C. Thus, for example, aluminum-enriched mica promotes the reaction of BAN with mcto-xylene at reflux for 4 h in 99% yield. 

Early band heaters used a resistance wire insulated with mica strips and encased in flexible sheet steel covers. These heaters are compact and low cost, but they are also fragile, not very reliable, and have limited power density. The maximum loading of these heaters is about 50 kW/m (30 W/in ) and maximum temperature about 500 °C. Newer types of mica heaters reportedly can handle power densities up to 165 kW/m (100 W/itf). The efficiency of the heater and its life are largely determined by how good the contact is between the heater and the barrel over the entire contact area. Improper contact will cause local overheating, and this will result in reduced heater life or even premature burnout of the heater element. Special pastes are commercially available to improve the heat transfer between heater and barrel. 

It must be mentioned, that there are several other industrial minerals being used directly or indirectly as paper fillers. These materials include barytes, barium sulfate, calcium sulfite, zinc oxide, zinc sulfide, diatomaceous earth, mica, bentonite and pyropholite. Synthetic organic fillers are, for example, based on polystyrene or urea-formaldehyde. Local availability, cost and the need for obtaining certain special properties are the deciding factors in the selection of these materials. However, the total volume is quite small in comparison to the major fillers and specialty pigments, as described above. 

The primary mineral fillers and reinforcements in plastics are calcium carbonate, kaolin, talc, mica, wollastonite and silica. Calcimn carbonate is by far the mineral most commonly used to fill plastics. This is mainly because it is low in cost, widely available and provides a good balance of properties. Calcium carbonate may be pure or in combination with magnesium carbonate as a dolomitic limestone. Dolomitic limestone is harder than pure calcium carbonate and is preferred when abrasion resistance is needed, as in floor tiles. 

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