Lithium in Ceramics
Presented by Charles Merivale, Senior Vice President, Amalgamet Canada, Toronto,
at the CerMa/ACS Southeast Regional Joint Meeting Sept 11, 2002 in Asheville, N.C.
Ceramic usage of lithium in North America has historically been limited to special applications
where its imparted properties of extreme thermal stability, high fluxing capability or improved
viscosity made it the best choice however its potential exceeds these benefits. The following
summarizes what lithium does for ceramics including some information on North America’s only
lithium mineral producer, TANCO in Manitoba, Canada.
“There is no substitute for a genuine lack of preparation”
Most large energy users if pressed today would probably admit some concern about the
future of energy supplies and costs. There have already been some early warnings but
compared to the rest of the industrialized world, North American energy costs are still
quite low. So what actions are possible to prepare for the future and help companies
survive in a world where energy costs keep rising? Lithium’s characteristics and many
benefits make it an increasingly valuable raw material for today’s ceramicists. However,
lithia is not recognized for straight line performance and when combined in different
body formulations fired at different temperature, surprise is often the result of initial tests
suggesting there is room for further elaboration and expansion of known data and
experimentation is required to establish the optimum role for lithium which clearly has
many positive effects on ceramics in addition to the commonly voiced fluxing properties
and energy reduction.
Lithium 101
Lithium appears near the top of the periodic table with an atomic weight of 6.9, less than
one third of sodium at 22.9. Lithium is the lightest of all solid elements with a specific
gravity of only 0.5334; lithium metal floats on water or gasoline. Lithium has the
smallest ionic radius and the highest ionic potential of any alkali. It is highly reactive
and does not stay in its elemental form unless protected. Lithium is three times as
powerful as sodium in fluxing potential. It also differs from sodium in that it creates
favourable internal nucleation conditions whereas sodium tends towards external
nucleation. It raises the surface tension of glass and ceramics, whereas sodium and
potassium reduce it.
Relative Ionic Potential of Lithium, Sodium and Potassium
Element
Ionic Radius
Angstroms
Ionic Potential
Lithium
0.60
1.67
Sodium
0.95
1.05
Potassium
1.33
0.75
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The melting point of pure lithium is 180.5 C but of course pure lithium is only available in
metallic form which is highly reactive and must be packed in oil. Lithium carbonate has
a melting point of 720 C and spodumene’s melting point is 1420 C which means it must
be used in combination with other fluxes to achieve lower firing temperatures. Phase
diagrams available from the ACS demonstrate the eutectics achieved with spodumene.
The temperature composition projection of lithium and sodium oxides demonstrates how
the eutectic of lithium and sodium works to lower melting temperatures. It is important
to note that these diagrams do not indicate what form of lithium was used and this can
affect the result. In some cases, only lithium carbonate might be suitable due to limits
on alumina or iron for example.
Lithium makes up just 0.002% or 20 ppm of the earth’s crust but there are many viable
reserves identified by the US Geological Survey at almost 13 million tonnes contained
lithium in the world.
Lithium is currently extracted from both mineral and brine
resources. Many minerals contain traces of lithium but the primary ones used
commercially are amblygonite, spodumene, lepidolite, petalite, and montebrasite.
Lepidolite also contains fluorine. The lithia to alumina ratio in these minerals is
consistent and lower lithia levels are compensated by more silica.
At present,
spodumene is the dominant mineral supplied in North America supplemented by some
petalite from Zimbabwe and Brazil. Lithium brines have become the major source for
lithium carbonate production due to the lower conversion costs compared to hard rock.
In both glass and ceramic applications, it has been said that lithium carbonate can
cause outgassing problems as the CO2 is released. In glass this impacts fining, in
ceramics it may show up as pinholes in the glaze or body.
Comparative Analysis of Lithium Minerals
Mineral
Formula
Lithium Content
Spodumene LiAlSiO6
Petalite
LiAlSi4O10
Lepidolite
K(LiAl)3(SiAl)4O10(OHF)2
Amblygonite LiAlPO4(FOH)
Montebrasite LiAlPO4(F9)H)
4-8%
3.5 - 4.9%
3-6
8-10
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Figures for current demand for lithium in North America show about 50% is used in
glass, ceramics and aluminum smelting primarily for it’s fluxing capabilities. The
balance is made into downstream chemicals, metal or pharmaceutical uses. The US
Geological Survey estimated 2001 consumption in the USA at 1400 tons of contained
lithium, half of what it was in each of the previous four years, reflecting the economic
slowdown and particularly the drastic decline in aluminum production, where lithium
carbonate is used as a flux to improve throughput.
On its own, spodumene converts to its beta phase when heated to 1080C at which point
it undergoes a volume expansion of about 30% and a decrease in specific gravity from
3.2 to 2.4 but reaches a stage of extreme thermal stability only compromised when it
melts at 1420C. This aspect of expansion during firing with high loadings of spodumene
to create a thermally stable ceramic was exploited by S.D. Stookey’s famous patents for
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Pyro Ceram products such as Corningware and Visions cookware and also enables the
open flame cooking pots used throughout Asia. Comments on the development of
these body formulas emphasize the critical nature of getting the correct addition ranges
of each component and proper firing cycle to assure the finished properties are as
desired which often is only reached after a long series of tests. Were he still alive, it
would be interesting to ask Mr. Stookey how many formulas and firing cycles he tried!
While the application list for lithium is growing longer and longer with much current
enthusiasm focused on the lithium ion battery, the important thing is lithium’s use in
ceramics which has been researched since before the 20th century. It is important to
maintain consumer confidentiality which means full exploitation of lithium’s potential
requires individual experimentation. One caution however, with lithium more may not be
better and instead the key is identifying the range where the maximum benefits can be
found depending on the desired characteristics. In all cases however the benefits go
beyond lower firing times and temperatures summarized as follows based on the
application starting with
Lithium’s Benefits To Glaze and Enamel:
As both glaze and enamel are glassy materials, they will be addressed under one
heading. Specifics of the application may limit alumina or iron in turn dictating use of
lithium carbonate instead of spodumene which may cause other issues. Some of the
benefits overlap and are extensions of the new body properties.
Viscosity – Lithia lowers the viscosity of glass giving better flow characteristics and
permitting a thinner and more even glaze or enamel coating which has benefits in
limiting thermal expansion and controlling crazing. A thinner coating will be less
affected by changes in temperature.
Lustre/Brilliance – Lithia increases the luster and brilliance of glass and in glaze will
enhance the colour significantly.
Lower Maturation Times/Temperatures – The high fluxing capability of lithium
enables glazes or enamels to mature faster or at lower temperatures or a combination
of the two.
Low expansion glazes – Fast fire low expansion ceramics require low expansion
glazes which can be produced with lithium additions. Some glaze formulas show lithia
contents from .5% to 25%.
Lower Thermal Expansion – Equal weights of lithium and other fluxes will provide
many more molecules of lithium so less can be used. Combined with lithium’s
inherently better thermal expansion characteristics means there is less potential for
thermal expansion in a lithia based glaze which contains a smaller total flux content.
Improved Thermal Shock Resistance – Similar to the comments on thermal
expansion, contraction and expansion rates are based on the oxide weights in a glaze.
Using lithium as the flux means the flux makes up a smaller proportion of the glaze
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compared to feldspar in this application, and therefore it allows a lower thermal
expansion and the overall thermal shock resistance improves and the potential for
crazing is reduced.
Lower Density – Lithium silicate glasses have a lower density than other alkali surface
glazes.
Surface Tension - In general terms, lithium has been shown to raise surface tensions
of enamels. The mechanism just described should also apply for glazes although there
are contradictory accounts of this dependant largely on the other components in the
glaze. However, reports of benefits from a stronger exterior, a more uniform and thinner
coating are consistent.
Acid and Chemical Attack Resistance – Because of lithium’s small atomic size, it
provides a stronger exterior and is better able to resist incursions providing improved
resistance to acids and alkalis.
Lithium’s Benefits in the Body
Fluxing – As the smallest solid element, lithia is the most active flux available providing
the most opportunity to reduce energy demand. Spodumene feldspar mixtures have
been shown to have fusion temperatures well below those for feldspar alone depending
on the quantity of lithium used which can be quite high to achieve other objectives.
General ranges quoted for lithia additions to realize fluxing benefits would be as low as
2% spodumene or from 0.15% up to 2.5% Li2O. As a flux lithia completely dissolves in
the glass phase and reduces expansion in addition to the firing temperature and/or time.
Thermal Expansion - Large lithium mineral loadings are used to create a very
thermally stable product able to withstand repeated thermal shocks in the freezer to
oven cycle. In this case, spodumene converts to its beta phase and forms a low
expansion lithium alumino silicate which significantly reduces the expansion co-efficient
of a body enabling a fast fire and creating a finished product suitable for heat shock
resistant applications.
Changes in the firing cycle or temperature have been shown to have a dramatic impact
on ceramics containing lithium as a result of its non-linear behavior. Some test bodies
which failed when fired at cone 10 were completely suitable when fired at cone 11 or 12,
the different results attributed to the different thermal expansion of the lithium.
Thermal Shock Resistance – Lower thermal expansion means better thermal shock
resistance in the finished body.
Shrinkage – To counter shrinkage, lithia is often added to whitewares as a low
expansion filler where it forms the low expansion lithium aluminosilicate, beta
spodumene, which can significantly reduce the thermal expansion coefficient of the final
whiteware body, enabling faster firing and also imparting some thermal shock
resistance while countering shrinkage.
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Vitrification – Minor levels of lithium additions, promote formation of a glassy phase in
ceramics at lower temperatures particularly in combination with other fluxes. The more
spodumene in the body, the lower the vitrification temperature, particularly when the
eutectic with soda is at work. Fully vitrified ceramics utilize lithium to achieve glassy
phase faster also increasing the body strength. Gres porcellanato uses lithia to provide
low porosity, good mechanical properties such as impact strength, hardness and
durability in addition to shape stability. Terra Tile in California tell me they are unique
in their 12 x 12 clay tiles which contain spodumene. They attribute their success in
getting their tiles to lay flat to spodumene in the body plus they fire at lower
temperatures. We have other customers who have literally experimented for years to
achieve the perfect body but having done so, are very happy and continue to use
spodumene as an important component of their formulas
Absorbtion – As lithia accelerates the glassy phase, it improves water resistance by
lowering absorbtion.
Apparent Porosity/Bulk Density – Spodumene impacts the porosity of a body and
depending on the amount and the other fluxes used it can be higher or lower. Bulk
density is also affected. Nepheline syenite and spodumene lower porosity and raise
the bulk density. Feldspar and spodumene raise porosity and lower the bulk density.
Mechanical Strength – Over the years many tests have shown that lithia increases the
mechanical strength of a body in some cases very significantly.
Free Silica – In his book, Applications of Lithium in Ceramics, John Fishwick suggests
spodumene can reduce the free silica in a whiteware body by assimilating it into the
beta spodumene structure during firing which results in an even lower thermal
expansion body than with beta spodumene alone. Fishwick also reported that petalite
cannot theoretically assimilate silica.
Extended refractory life/Lower emissions
The lower temperature firings made possible by the addition of lithium will extend
refractory life and reduce environmental emissions, two favourable benefits in
combination with the others outlined.
Summary of Advantages
There is increasing interest being shown in lithium by ceramic manufacturers. In the
past there has been something of a Dr. Feelgoode aura about lithium which is being
replaced by enthusiastic support as a result of lab and production trials which have
substantiated the claims of benefits leading to wider usage. In the past lithium has often
been ruled out as a batch ingredient purely based on the cost. Prices have come down
in recent years but apart from that, the benefits to the body and glaze or enamel just
outlined combined with energy savings and reduced kiln repair or reline costs and
reduced emissions need to be factored into any calculation instead of just trying to
offset the additional batch cost with energy bill reductions although this is certainly a key
part of the justification to management. Lithium in combination with traditional fluxes
like feldpar and nepheline syenite offers advantages for all.
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In summary, benefits in both glass and ceramic applications are quite similar and are
usually achieved with very low levels of lithium or spodumene additions. Replacement
of soda by lithium can be done on a mol or weight basis and while the debate on which
is correct is unresolved, although the mol basis may be better. 7% spodumene or
0.5% lithia added to a glaze has been shown to increase the brightness, gloss, stability,
wear and acid resistance while improving uniformity and fluidity allowing more even
coverage and reducing firing temperatures and maturing times. In glass containing
lithium increased tensile strength is reported and in ceramics another benefit may be
improved chip resistance although more work needs to be done to verify this.
A key aspect to economic supply of any mineral is the transportation cost which nature
sometimes overlooked. For example there is a large lithium mineral deposit in
Canada’s far north which may be inexpensive to mine and concentrate but the transport
costs to market mean it can only be developed if consumers move north.
The TANCO Mine in Canada
While TANCO’s mine is in southeastern Manitoba, north of Minnesota, the economics
of transportation and production from this site are workable thanks in part to mother
nature which left a most interesting pegmatite orebody containing over 80 different
minerals, some of which were found there first, and which has been the subject of
numerous P.H.D. theses and lots of study since its first documented exploration in 1914
by a survey crew. During the late 1920’s a shaft still used for fresh air supply to today’s
mine was dug to extract tin. The pegmatite was explored further and in the late 1930’s
spodumene was mined but the records suggest little was shipped and the claim was
abandoned. In 1955 a 300 foot deep incline was put in with intent to capitalize on the
new demand for lithium grease. In 1967, the mine reopened as the Tantalum Mining
Corporation of Canada to recover tantalum from the pegmatite. In the 1970’s Corning
approached the mine’s owners about spodumene production to supply their Martinsburg
facility and helped establish the flow sheet and circuit controls leading to Manitoba
spodumene being a popular gift when transformed into Corningware.
Today the deposit is mined about 60 meters under Bernic Lake, accessed by both a 20
degree incline and a shaft for hoisting the ore to surface. Mining is done by the room
and pillar method and the rooms average 22 square meters with a 20 meter roof
although in some areas it is as high as 50 meters. Ore is moved by train from the mine
face to the hoist. TANCO’s geologists carefully study the ore underground to make sure
it is suitable before being moved for surface beneficiation. The mill has six levels which
crush, grind, float, concentrate, magnetically remove iron, dry and classify the ore
before it is packed or shipped in bulk. TANCO has a fully equipped lab on site to
analyze samples from each shipment by XRF, AA or UV spectrophotometry with
metallurgical balances computed on an IBM microcomputer system. Every shipment is
tested and a split is kept for future reference, and the lab results specific to each
shipment are supplied to the customer. The minesite also has fully equipped machine
and diesel repair shops and they keep a large inventory of spare parts. TANCO is
working towards ISO approval and follows the Total Quality Concepts reflected in their
mission statement, “better every day”. Today TANCO processes over 700 tons of ore
per day and the product list has expanded to include not only spodumene and tantalum
concentrates but also montebrasite and pollucite, a source of cesium. The pollucite is
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converted on site to cesium formate, a biodegradable high density solution used in oil
well drilling which allows extraction of reserves not otherwise recoverable. Cesium
formate is the next generation of drilling and completion fluids and the market is still
growing as users have found the performance substantially exceeded expectations.
TANCO’s pegmatite holds the world’s largest proven reserve of cesium and an
expansion of the chemical plant is now underway.
TANCO is a wholly owned
subsidiary of the Cabot Corporation who purchase all their tantalum concentrates and
through Cabot Specialty Fluids Division sell the cesium formate to the oil well drilling
industry.
Tanco Lithium Minerals
Li2O
Fe2O3
Al2O3
P2O5
Na2O
K2O
MnO2
Concentrate -
200 mesh
Montebrasite
7.25
0.07
26.0
0.30
0.30
0.20
0.04
7.1
0.12
25.0
0.35
0.30
0.35
0.06
7.0
0.13
26.5
8.0
0.3
0.6
0.3
TANCO will supply samples of spodumene for testing purposes.
Acknowledgements
• American Ceramic Society – “Phase Diagrams for
Ceramicists”; 1956 ACS
• Anonymous – 1980- present
• Fishwick, John H., “Applications of Lithium in
Ceramics”; 1974(?) Cahners Books, Boston, Mass
• Harben, Peter; “Mineral Handybook”, 1995,
Industrial Minerals Books
• Lawrence, W. G., “Ceramic Science for the Potter”,
1972, Chilton Book Company
• Stookey, S.D., Low Expansion Glass-Ceramic and
Method of Making It”, US Patent 3157522,
November 17, 1964
• U.S. Geological Survey, “Lithium 2001 Annual
Review”, USGS 2001
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