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What is Talc?
The Industrial Minerals Association
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 Mg3Si4O10(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-crystallizes into different forms of enstatite (anhydrous magnesium
silicate).
Talc's
melting point is at 1500°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
lamellarity. 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 neighbors are very weak, the platelets slide apart 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).
Talc -
carbonate ores are processed to removed associated minerals and to produce pure
talc concentrate.
Talc's
properties (platyness, softness, hydro-phobicity, organophilicity, inertness
and mineralogical composition) provide specific functions in many industries.
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 also
is 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.
Ceramics: Talc is a phyllosilicate which imparts a wide range of functions to
floor and wall tiles and sanitaryware, 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.
In
refractory applications, chlorite-rich talc is 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.
Coatings: Talc confers 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, talc is used to improve corrosion resistance and paint
adhesion. Talc also brings benefits to inks, jointing compounds, putties and
adhesives.
Paper: Talc is used in both uncoated and coated rotogravure papers where it
improves printability as well as reducing surface friction, giving substantial
improvements in productivity at the paper mill and print house.
It also
improves mattness and reduce ink scuff in offset papers.
Used as
pitch control agents, talc "cleans" the paper making 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
specialty papers such as colored papers or labels, talc helps to improve
quality and productivity.
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.
Plastics: Talc imparts a variety of benefits to polypropylene, for instance
higher stiffness and improved dimensional stability.
In
automotive parts (under-the-hood, dashboard, bumper interiors and exterior
trim), household appliances and white goods.
It
requires advanced milling technology to obtain the finest talc without
diminishing the reinforcing power of its lamellar structure.
Talc also
is 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.
Rubber: Talc reduces the viscosity of rubber compounds, thereby facilitating
the processing of moulded parts.
It also
improves 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, while in
pharmaceutical stoppers, they create a barrier against liquids.
In
cables, talc functions as insulators and in tire manufacture it makes excellent
processing aids.
Wastewater
treatment: Specialty 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 fertilizing value of sewage sludge.
The Industrial Minerals Association - North America (IMA-NA) is the representative voice of companies which extract and process a vital and beneficial group of raw materials known as industrial minerals. Industrial minerals are the ingredients for many of the products used in everyday life, and our companies and the people they employ are proud of their industry and the socially responsible methods they use to deliver these beneficial resources.
IMA-NA represents ball clay, barite,
bentonite, borates, calcium carbonate, diatomite, feldspar, industrial sand,
kaolin, magnesia, soda ash, talc and wollastonite.
Industrial minerals . . . Your world is made
of them!
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