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 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 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 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.
For more information, please contact:
INDUSTRIAL MINERALS ASSOCIATION - NORTH AMERICA
2011 Pennsylvania Avenue, NW, Suite 301
Washington, DC 20006 USA
Tel: 202-457-0200 Fax: 202-457-0287
Web Site: www.ima-na.org
