CAS-Reg. No. 14807-96-6

Characteristics / Function:

Soapstone and talc are two different mineralic appearances of the chemically identical composition of magnesium silicate hydrate Mg₃ [(OH)₂(Si₄O₁₀)].

Structure:

There is a distinction between the coarse crystalline, flake like talc’s and the fine crystalline, grainy soapstone’s, depending on the size of the crystals and particle orientation. A strict separation does not exist. Fine crystalline, but texturated samples can have the same technical behavior as talc’s.

Chemical analysis:

Demands according to E. Alber-Schönberg:

MgO	30.00 %
SiO2	60.00 % - 61.00 %
Al2O3	1.50 %
Fe2O3	1.50 %
CaO	as low as possible
Loss at red heat	5.00 %

 

Mg0, Si0₂ and loss at red heat are the proof for the nearness of the actual sample and the demanded theoretic composition of the talc.

A stronger discrepancy between the loss at red heat and evaporated water during the heating, hints at carbonates in the materials. The exact value can be determined by a chemical analysis (calcite, dolomite, magnesite). Carbonates are mainly distributed inhomogeneous in their natural stocks; this causes a rather uneven quality.

The technology does rarely distinguish between talc, soapstone and steatite. The last name is often employed for fire products of soapstone gained by milling, forming with fluxes and plastifiers and burning at 1,400 °C. The name soapstone is derived from the greasy and soapy surface.

There also exist several mineral phases of soapstone, partly polluted with: chlorite, carbonate, quartz and amphiboles.

The four mentioned, main alien elements, disturb because they change the chemical compounds and therefore the sintering behavior of the material. Yet this is only interesting to the ceramics industry.

Application in the ceramics industry:

The minerals talc and soapstone serve as raw material for the production of steatite, which shows a high mechanical strength and low dielectric losses. Therefore it is an important substance in several branches of the electrotechnology for insulations and for condensers.

The high demands of high voltage and high frequency technology imply a careful selection of the raw materials. Whereas the chemical industry can produce synthetic substances, the ceramics industry relies on the natural qualities, although the structure, mineral percentage and purity differ from finding place to finding place. Even in the same mine there are some differences, depending on the amount of alien substances. Therefore, it is necessary to know the occurring accompanying materials for an even fabrication.

More applications:

Because of the technical qualities, caused by the chemical structure and the shape of the particles, micronised soapstone / talc is an important filling, especially for the varnish-, cellulose- and paper industry, for casting auxiliary substances and for the rubber- and plastics industry.

It is mainly a combination of several mineral powders, each having a special function depending on its specific qualities. Often, however, micronised talc is applied as a single extender, for instance as a metal-primer, based on polyvinyl butyral or in various thermoplastics.

Bibliography:

• Römpps Chemie-Lexikon
• H. Kittel; Lehrbuch der Lacke und Beschichtungen
• Geächter/Müller: Kunststoffadditive/3. Ausgabe

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