In recent years, the branches of ceramics that have undergone the greatest
development in the world have been those of floor and wall tile manufacture. This
expansion has fostered the creation of companies dedicated to the manufacture of frits,
glazes and ceramic pigments, together with marked growth in other already existing
companies. On the other hand, the economic context in which the industrial activities
are being conducted have led manufacturers to seek more efficient production
technologies, among other processes including fast firing, single firing, etc. The focus
has been on reducing costs, mainly for fuels and this requires refractory bodies with
low dilatometric coefficients of expansion. For the manufacture of these refractories, as
well for that of the frits mentioned previously, spodumene offers numerous advantages
if it is included in their composition.
The thermal shock resistance of a ceramic body depends fundamentally on
the following properties: thermal conductivity, coefficient of expansion, mechanical
strength and modulus of elasticity. Of these properties, the one that can vary most
is thermal expansion. This is the cause of the great interest in Li2O·Al2O3·SiO2
systems, which include compounds with very low coefficients of expansion, which
allow making very thermally resistant pieces.
Spodumene is a lithium aluminosilicate LiAl(SiO3)2, which is found in the
natural state as α−spodumene, structurally a monoclinic ‘pyroxene’ that contains
7.9% Li2O and has a density of 3.2 g/cm3. At high temperatures, 900º-1000ºC, this
low temperature form undergoes an irreversible polymorphic transformation,
increasing its volume and converting to β−spodumene, which belongs to the
tetragonal crystalline system. In this form the mineral displays a density of 2.4
g/cm3, and is characterised by exhibiting a very low dilatometric expansion,
corresponding to values below 1.0·10-6 ºC-1.
On the other hand, spodumene has a very pronounced fluxing action, both
of its own and because of the eutectics it forms with other fluxes. This property
is used in the manufacture of frits for ceramic glazes and for earthenware.
It is also very important for reducing the vitrification temperature and the
final porosity of ceramic bodies. Beyond the applications of spodumene in the
ceramic industry, the high percentage of lithium present in the mineral opens up
numerous prospects for industrialisation; thus, lithium is considered worldwide
as a strategic material for its great variety of applications: glass manufacture,
lubricants, alloy obtainment, drug elaboration, operation of cooling systems, and
in the manufacture of batteries.
The spodumene deposits correspond in all the cases, to pegmatites with a
zoned structure, in which the mineral is located in the intermediate bands and the
core. In the Argentine Republic, the main deposits are in the provinces of San Luis
and Catamarca, and they are characterised by a great mineralogical variability. In
all of these, spodumene is associated with: quartz, potassium feldspar, plagioclasesoligoclases
and albite, muscovite and biotite, in addition to amblygonite and
sometimes beryl. In relation to other pegmatites, a little participation of muscovite
is observed and, in contrast, a greater one of albite.
For all these reasons, the objective of this work focuses on optimising the
business operation of spodumene by development of an appropriate infrastructure
and, in addition, to promoting knowledge in the mining field with respect to the
numerous applications that beneficiated spodumene can have.
2. Methedology
The purpose of this work is to transmit the experience developed in an
Argentine industry, in the mineral treatment of a spodumene-bearing pegmatite,
for use in the manufacture of ceramic materials. The beneficiation of the mineral
was done through a heat treatment and subsequent refining, producing the
irreversible the a-b polymorphic transformation of spodumene, which is why
its contribution to the microstructure of a ceramic body will increase its thermal
shock resistance. Comparative physical, chemical and mineralogical studies were
conducted with samples of natural lithium pegmatite from the El Alto area in the
Province of Catamarca and treated spodumene. Finally the effect of the spodumene
addition to an earthenware body has been compared.
5. CONCLUSIONS
ü The thermal transformation of a-b spodumene with a change of density from
3.2 g/cm3 to 2.4 g/cm3, facilitates its separation from quartz and feldspar
by selective sieving, since b-spodumene is concentrated in the finer sieving
fractions.
ü The coefficient of expansion of an earthenware body decreases strongly by
adding b-spodumene to its composition.
6. Acknowledgements
The author wishes to thank Mr. Alfredo Inocencio, Mrs. Gloria Brunetti, Mrs.
Ana Rodriguez Velo and Mr. Diego Pucciarelli, for their help in this work; thanks
also go to the Project for the ‘Improvement of the Efficiency and Competitiveness of
the Argentine Economy’, a Community (E.U.) cooperation project with the Argentine
Republic.
REFERENCES
[1] Botto, I., Baran, E., Cohen Arazi, S., Krenkel, T. Aspectos estructurales de la espodumena en relación con el
método de tratamiento ácido. Bol. Soc. Esp. Cer. y Vid., V15, Nº3, May/June 1976.
[2] Fishwick, J. Spodumene aids fast firing, improves bodies. Ceramic Industry Magazine p34, May 1967.
[3] González Peña, J.M. Materiales cerámicos de bajo coeficiente de dilatación a base de silicoaluminato de litio.
Bol. Soc. Esp. Cer. y Vid., V7, Nº3, 1968.
[4] Hummel, F.A review of thermal expansion data of ceramic materials. Especially ultra-low expansion
compositions. Interceram Nº6, p 27-30, 1984.
[5] Mc Cracken, D. Lithium minerals review 1993. Industrial minerals, p85-89, set/1994.
[6] Luis Sanchez-Muñoz, J.B. Carda Castelló. Enciclopedia cerámica: TOMOS 2.1 y 2.2. “Materias primas y
aditivos cerámicos”. 2002.
[7] Ginés F, Orenga A., Sheth A., Thiery D., “Ejemplo del espodumeno para fabricar pastas de gres porcelánico
técnico” QUALICER 2004, Pág. 233-236.
No comments:
Post a Comment