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What is talc?
Talc is the world’s softest mineral. Although all talc ores are
soft, platy, water repellent and chemically inert, no two
talcs are quite the same. Talc is a vital part of everyday life.
The magazines we read, the polymers in our cars and
houses, the paints we use and the tiles we walk on are just
some of the products that talc enhances.
Talc is a hydrated magnesium sheet silicate with the
chemical formula Mg3 Si4 O10 (OH)2. The elementary sheet
is composed of a layer of magnesium-oxygen/hydroxyl
octahedra, sandwiched between two layers of siliconoxygen
tetrahedra. The main or basal surfaces of this
elementary sheet do not contain hydroxyl groups or active
ions, which explains talc’s hydrophobicity and inertness.
Talc is practically insoluble in water and in weak acids and
alkalis. It is neither explosive nor flammable. Although it has
very little chemical reactivity, talc does have a marked
affinity for certain organic chemicals, i.e. it is organophilic.
Above 900°C, talc progressively loses its hydroxyl groups
and above 1050°C, it re-crystallises into different forms of
enstatite (anhydrous magnesium silicate). Talc’s melting
point is at 1500°C.
Talc is a hydrated
magnesium
silicate with the
chemical formula
Mg3 Si4 O10 (OH)2
Ta l c
Morphology
The size of an individual talc platelet (= a few thousand
elementary sheets) can vary from approximately 1 micron
to over 100 microns depending on the deposit. It is this
individual platelet size that determines a talc’s platyness or
l a m e l l a r i t y. A highly lamellar talc has large individual
platelets whereas a microcrystalline talc’s platelets are
much smaller.
The elementary sheets are
stacked on top of one another,
like flaky pastry, and, because
the binding forces (known as
Van der Waal’s forces) linking
one elementary sheet to its
neighbours are very weak, the
platelets slide apar t at the
slightest touch, giving talc its
characteristic softness.
Related minerals
Talc ores also differ according to their mineralogical
composition (i.e. the type and proportion of associated
minerals present). They can be divided into two main types
of deposits: talc-chlorite and talc-carbonate. Talc-chlorite
ore bodies consist mainly of talc (sometimes 100%) and
chlorite, which is hydrated magnesium and aluminium
silicate. Chlorite is lamellar, soft and organophilic like talc. It
is however more hydrophylic. Talc-carbonate ore bodies are
mainly composed of talc carbonate and traces of chlorite.
Carbonate is typically magnesite (magnesium carbonate) or
dolomite (magnesium and calcium carbonate). Ta l c -
carbonate ores are processed to removed associated
minerals and to produce pure talc concentrate.
Multiple properties – manifold uses
Talc’s properties (platyness, softness, hydro-phobicity,
organophilicity, inertness and mineralogical composition)
provide specific functions in many industries.
l Agriculture and Food: Talc is an effective anti-caking
agent, dispersing agent and die lubricant and therefore
helps animal feed and fertilizer plants to function more
efficiently. In premixes and agricultural chemicals, it
makes an ideal inert carrier.
Talc is also used as an anti-stick coating agent in a
number of popular foods including chewing gum, boiled
sweets, cured meats, and for rice polishing. In olive oil
production, as a processing aid, it increases yield and
improves the clarity of the oil.
l Ceramics: Talc is a phyllosilicate which imparts a wide
range of functions to floor and wall tiles and
s a n i t a ryware, tableware, refractories and technical
ceramics. In traditional building ceramics (tiles and
sanitaryware), it is used essentially as a flux, enabling
firing temperatures and cycles to be reduced.
Industrial minerals. Yo u r world is made of them
In refractory applications, chlorite-rich talcs are
transformed into cordierite to improve thermal shock
resistance. For steatite ceramics, talcs with a microcrystalline
are the most appropriate. During firing, the
talc is transformed into enstatite, which possesses
electro-insulating properties. As for very low iron
content talcs, they are particularly suitable for use in frit,
engobe and glaze compositions.
l Coatings: Talcs confer a whole range of benefits to
coatings. In interior and exterior decorative paints, they
act as extenders to improve hiding power and titanium
dioxide efficiency. Talc’s lamellar platelets make paint
easier to apply and improve cracking resistance and
sagging. They also enhance matting. In anti-corrosion
primers, talcs are used to improve corrosion resistance
and paint adhesion. They also bring benefits to inks,
jointing compounds, putties and adhesives.
l Paper: Talcs are used in both uncoated and coated
rotogravure papers where they improve printability as
well as reducing surface friction, giving substantial
improvements in productivity at the paper mill and print
house. They also improve mattness and reduce ink scuff
in offset papers. Used as pitch control agents, talcs
« clean » the papermaking process by adsorbing any
sticky resinous particles in the pulp onto their platy
surfaces, thereby preventing the agglomeration and
deposition of these on the felts and calenders. As
opposed to chemical pitch-control products that pollute
the process water, talc is removed together with the pulp,
enabling the papermaker to operate more easily in
closed-circuit. In speciality papers such as coloured
papers or labels, talcs help to improve quality and
productivity.
l Personal Care: As it is soft to the touch and inert, talc
has been valued for centuries as a body powder. Today
it also plays an important role in many cosmetic
products, providing the silkiness in blushes, powder
compacts and eye shadows, the transparency of
foundations and the sheen of beauty creams. In
pharmaceuticals, talc is an ideal excipient, used as a
glidant, lubricant and diluent. Soap manufacturers also
use talc to enhance skin care performance.
l P l a s t i c s : Talcs impart a variety of benefits to
polypropylene, for instance higher stiffness and
improved dimensional stability. In automotive part s
(under-the-hood/bonnet, dashboard, bumper interiors
and exterior trim), household appliances and white
goods. It requires advanced milling technology to obtain
the finest talcs without diminishing the reinforcing power
of their lamellar structure.
Talcs are also used for linear low density polyethylene
(LLDPE) antiblocking and as a nucleating agent in semicrystalline
polymers. In polypropylene food packaging
applications, talc is a highly effective reinforcing filler.
l Ru b b e r : Talcs reduce the viscosity of ru b b e r
compounds, thereby facilitating the processing of
moulded parts. They also improve extrudate qualities,
increasing production rates and enhancing UV radiation
resistance of exterior parts such as automotive profiles.
In sealants and gaskets, they provide good compression
resistance, whilst in pharmaceutical stoppers, they
create a barrier against liquids. In cables, talcs function
as insulators and in tyre manufacture they make
excellent processing aids.
l Wastewater treatment: Speciality talc can improve the
performance of biological wastewater treatment plants.
The talc particles ballast the flocs of bacteria and
accelerate their sedimentation. The addition of talc
results in top quality discharge and zero bacterial loss. It
can help to upgrade plants without resorting to costly
plant expansions. As opposed to most chemicals used
to clean wastewater, such as chlorine or aluminium
salts, talc is a natural, environmentally-friendly mineral
additive. And because it is inert, it preserves the
fertilising value of sewage sludge.[img][/img] |
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