Post on 14-Oct-2019
Asst. Prof. Dr. Ayşe KALEMTAŞ
MME391 CeramicMaterials
Asst. Prof. Dr. Ayşe KALEMTAŞ
Bursa Technical University, Metallurgical and Materials Engineering Department
Office Hours: Tuesday, 10:00-11:00ayse.kalemtas@btu.edu.tr, akalemtas@gmail.com
Asst. Prof. Dr. Ayşe KALEMTAŞ
Clay Products – Main Components
Clay
SilicaFeldspar
Traditional Ceramics
Asst. Prof. Dr. Ayşe KALEMTAŞ
Clay products – Main Components
When mixed with water the crystals can easily slide over each other (like a pack of cards),and this phenomenon
gives rise to the plasticity of clays.
Provides plasticity, when mixed with
water Hardens upon drying and firing
(without losing the shape)
Adding water to clay-- allows material to
shear easily along weak van der Waals bonds-- enables extrusion
-- enables slip casting
Silica, SiO2, is mixed with clay to reduce
shrinkage of the ware while it is being fired,
and thus prevent cracking, and to
increase the rigidity of the ware so that it will not collapse at
the high temperaturesrequired for firing.
Silica is useful for this purpose becasue it is
hard, chemically stable, has a high
melting point and can readily be obtained in a pure state in the
form of quartz.
Feldspars are used as a flux in the firing of
ceramic ware. When a body is fired, the
feldspar melts at a lower temperature
than clay or silica, due to the presence of Na+, K+ or Ca2+ ions, and forms a molten glass which causes solid particles of clay to
cling together: when the glass solidifies it gives strength and
hardness to the body.
Clay
SilicaFeldspar
Traditional Ceramics
Asst. Prof. Dr. Ayşe KALEMTAŞ
Feldspars are used as a flux in the firing of
ceramic ware. When a body is fired, the
feldspar melts at a lower temperature
than clay or silica, due to the presence of Na+, K+ or Ca2+ ions, and forms a molten glass which causes solid particles of clay to
cling together: when the glass solidifies it gives strength and
hardness to the body.
Feldspar
Traditional CeramicsFluxes are raw materials with high amountof alkaline oxides, mainly K2O and Na2O,whereby, in reaction with silica and alumina,promote liquid phase formation thatfacilitates the densification.
The liquid phase surrounds the solid particlesand by surface tension enablesrearrangement of particles and decreasingthe porosity.
Feldspars are used as a flux in the firing ofceramic ware. When a body is fired, thefeldspar melts at a lower temperature thanclay or silica, due to the presence of Na+ , K+or Ca2+ ions, and forms a molten glasswhich causes solid particles of clay to clingtogether: when the glass solidifies it givesstrength and hardness to the body. Themolten glass also reacts with the silica andclay particles.
Asst. Prof. Dr. Ayşe KALEMTAŞ
Earth’s CrustEarth’s crust refers to the outher siliceous shell ofthe earth which is about 16 km thick.
Metallic ores and mineral products are producedfrom this crust. Therefore, the original source ofall metals is the earth’s crust.
Ores are naturally occuring deposits in theearth’s crust. The ores are mined and treatedby various• unit operations (mechanical processes)• unit processes (chemical metallurgical
processes)to extract metals and to convert them intothe metallic form.
ORES AND MINERALS
The mineral content of the ore must be in sufficientconcentration to make its extraction commerciallyviable.
Mine : It is a large area having an abundant quantity of
mineral deposits that can be easily and economically
extracted.
Asst. Prof. Dr. Ayşe KALEMTAŞ
Minerals are the constituents of rocks, which make up theentire inorganic, solid portion of the earth. Rocks are usuallynot composed of a single mineral but, rather, an aggregate oftwo or more minerals. Broadly speaking, geologists dividerocks into three types:
igneous, metamorphic, and sedimentary.
Rocks: • They are a combination of minerals along with impurities.
A rock can contain either a single mineral or a number ofminerals.
• Although over 2000 minerals have been discovered, onlya few are abundantly found in most of the rocks.
ORES AND MINERALS
Asst. Prof. Dr. Ayşe KALEMTAŞ
Metamorphic rocks have undergone structural and/or chemical transitions(metamorphism or metamorphosis) from their original form as a result of hightemperatures and pressures deep beneath the earth’s surface. These transitionsoccur in the solid state without melting and result in the formation of newminerals, such as kyanite, staurolite, sillimanite, andalusite, and some garnets.
Other minerals, such as some of the igneous minerals, may be present inmetamorphic rocks but are not necessarily the result of metamorphism. Theword “metamorphic” has a Greek origin coming from meta, meaning“change,” and morpe, meaning “shape”.
Igneous rocks form when magma cools and solidifies. Magma is a complexmolten material that originates deep within the earth.
The word igneous comes from the Latin word ignis, which means “fire”;igneous rocks then are “formed from fire.”
Magma is rich in the elements Si, O, Al, Na, K, Ca, Fe, and Mg.
Feldspars are alumino-silicate minerals found in nearly all igneous rocks.
ORES AND MINERALS
Asst. Prof. Dr. Ayşe KALEMTAŞ
Sedimentary rocks are formed when small particles or precipitatedcrystals become cemented together. Sedimentary rocks are classified aseither clastic or chemical.
Clastic sedimentary rocks form when rock particles produced bymechanical and chemical weathering are transported by water, ice, andwind to new locations where they become cemented together.
Chemical sedimentary rocks form when highly soluble ions, such as, Na+,K+, Ca2+, Mg2+, Cl-, F-, (SO4)2-, (CO3)2-, (PO4)3- from existing rocks aredissolved in water and subsequently precipitate, forming layers inoceans and lakes, where they become cemented together.
The composition of sedimentary rocks depends on:▪ Composition of original source rocks▪ Chemical and mechanical resistance of each mineralcomponent▪ Distance traveled
ORES AND MINERALS
Asst. Prof. Dr. Ayşe KALEMTAŞ
Resistant minerals such as quartz are common constituents ofsedimentary rocks, and some more rare minerals (e.g., garnet, rutile,zircon) have similar properties.
Feldspar is less resistant but is so common that it is a majorconstituent of many sedimentary rocks. Precipitated minerals includethe carbonates (e.g., calcite, dolomite), the sulfates (e.g., gypsum,anhydrite), chlorides, and chalcedonic silica (e.g., chert, flint).
Igneo
us
Rocks formed by
cooling and
solidification of
magma Met
am
orphic
Rocks that have
undergone
structural
and/or chemical
transitions Sed
imen
tary
Rocks formed
when smaller
particles become
cemented
ORES AND MINERALS
Asst. Prof. Dr. Ayşe KALEMTAŞ
Average Analysis of the Earth’s Crust
It is clear that :
Oxygen Silicon
Aluminum Iron
are the 4 mostabundant elements
Since engineering metals Al, Fe,Mg and Ti are far moreabundant than the othermetals, there is never likely tobe a shortage of those metalsdue to exhaustion of the oredeposits.
The commonly known metalslike Au, Pb, Sn are in so smallquantities in the earth’s crustthat their commercial recoveryis impossible.
Most commonelements in the crust
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
A group of alumino-
silicates, tetrahedra form
three-dimensional
frameworks with Ca, Na
and K as the balancing
cations.
Fel
dsp
ars
The very abundant
feldspar are subdivided in
K-Na bearing alkali
feldspars and the Ca-Na
solid-solution series called
the plagioclase feldspars.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFeldspar Group
light silicates (K-Na-Ca, Al)
2-directionsof cleavage
(at 90 degrees)
Orthoclase
Plagioclase
K-feldspar
Ca/Na-feldspar
Most common mineral group
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsK-feldspar
... which can weather further to bauxite: AlO(OH)
... weathers to kaolinite:Al2Si2O5(OH)4
orthoclase KAlSi3O8 ...
Fel
dsp
ars
Is very
hard Fel
dsp
ars Has
multiply
colors Fel
dsp
ars Most
common
mineral
group
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
Feldspars are used as
a flux in the sintering
of ceramic ware.
Feldspar produces a
glassy phase during
firing increasing the
strength and
translucency of the
body.
Fel
dsp
ars Feldspars are
alumino-silicate
minerals found in
nearly all igneous
rocks.
Fel
dsp
ars The plagioclase
feldspars are solid
solutions of albite
and anorthite.
Na+ Si4+ is replaced
by Ca2+ Al3+
Fel
dsp
ars The alkali feldspars
are solid solutions
of albite and
orthoclase.
Na is replaced by K
Fel
dsp
ars
There is virtually no
solid solution
between anorhite
and orthoclase.
Fel
dsp
ars
The glass industry uses
most of the feldspar
produced. Feldspar is a
source of Al2O3, which
improves the
mechanical properties
of glass such as its
scratch resistance and
its ability to withstand
thermal shock.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
Four feldspathic
minerals are likely
to enter the
composition of
silicate ceramic
pastes. They are:
Fel
dsp
ars Orthoclase, a
mineral rich in
potassium with the
composition
K2O.Al2O3.6SiO2
Fel
dsp
ars Albite, a mineral
rich in sodium
with the
composition
Na2O.Al2O3.6SiO2
Fel
dsp
ars
Anorthite, a mineral
rich in calcium with
the composition
CaO.Al2O3.2SiO2
Fel
dsp
ars
Petalite, a mineral
rich in lithium with
the composition
Li2O.Al2O3.8SiO2
Fel
dsp
ars
Feldspars constitute
an abundant mineral
group and make up
an estimated 60% of
the earth’s crust. They
are present in many
sedimentary deposits
and are found in
almost all igneous and
metamorphic rocks.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
Feldspars rarely
occur in nature as
pure minerals. Fel
dsp
ars
Albite and anorthite
form a complete
solid solution series. Fel
dsp
ars
Even though
orthoclase and albite
form only limited
solid solutions,
deposits of
orthoclase always
contain some albite.
Fel
dsp
ars The rock nepheline
syenite is a mixture
of orthoclase, albite
and nepheline with
minor impurities.
Fel
dsp
ars
These materials are
typically ground to
a relatively coarse
powder, on the
order of 70 to 100
m, for use in
ceramic (or glass)
production.Fel
dsp
ars
The Republic of
Korea is the largest
producer of feldspar
in the world.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
Orthoclase and
albite, which form
eutectics with
silica, respectively,
at 990 and
1050°C, are
widely used as flux.
Fel
dsp
ars
Anorthite is rather
regarded as a
substitute to chalk. Fel
dsp
ars The use of petalite,
especially owing to
its negative
expansion
coefficient, is
marginal.
Fel
dsp
ars
Natural feldspars used for the
preparation of ceramics are
mineral mixtures. Thus, the
commercial potassium products
can contain between 2.5 and
3.5% of albite mass, whereas
anorthite and a small quantity
of orthoclase, between 0.5 and
3.2%, are often present in the
available sodium feldspars.
Fel
dsp
ars
Potassic feldspar is particularly
appreciated by ceramists because its
reaction with silica leads to the
formation of a liquid whose
relatively high viscosity decreases
slightly when the temperature
increases. This behavior is
considered as a guarantee against
the excessive deformation of the
pieces during the heat treatment.
Asst. Prof. Dr. Ayşe KALEMTAŞ
Feldspars
Asst. Prof. Dr. Ayşe KALEMTAŞ
Feldspars
The tendency to form a glass is strongly correlated to the viscosity of a melt.
In general, molten feldspars are rather viscous which is ascribed to the existence ofpolymerized silicon-aluminum-oxygen tetrahedra in the liquid.
Despite lower melting points, the alkali feldspars produce much more viscous liquidsthan anorthite.
In the case of albite this is interpreted as evidence for a higher degree ofpolymerization in the melt.
In the case of orthoclase it is due to the formation of leucite, KAlSi2O6, crystals.
In all cases glasses are produced under the cooling rates normally encountered inceramic processing.
Albite melts at the lower temperature than orthoclase, but the addition of anorthiteincreases the melting temperature of soda feldspar while decreasing that of the potashfeldspar (down to a minimum at about 22% anorthite). Similarly a 50%: 50% mixtureof albite and orthoclase melts at a lower temperature than either end member.
Often mixtures of fluxes are employed in order to take advantage of eutecticmelting.
Lithium bearing minerals are often very effective fluxes when used in conjunction withfeldspar since such combinations form deep eutectics.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars The materials
treated at higher
temperatures or in
the presence of a
large quantity of
flux are generally
the least porous.
Fel
dsp
ars Whiteness is
primarily the result
of the use of raw
materials free from
iron and titanium or
containing only
small contents of
transition metals.
Fel
dsp
ars
Fine china represents the
opposite end of the
spectrum where aesthetics
take priority. China clays
are used in these
formulations, because they
are nearly phase pure and
do not occur as iron
bearing solid solutions (as
do the smectites and
illites).
Fel
dsp
ars
Increasing the relative amount of ball
clay generally improves the plasticity
as well as the green strength, but often
leads to discoloration as a result of
contamination by iron-bearing
accessory minerals. Therefore
applications where green strength is at
a premium, and color is of less
importance, employ larger amounts of
ball clay.
Fel
dsp
ars The extent of glass formation affects
properties such as dimensional stability
and degree of densification. In systems
which require high dimensional
stability such as structural clay
products (i.e., large ceramic pipes and
tiles) the extent of glass formation is
kept to a minimum. In contrast,
dental porcelains must fuse at low
temperatures to be compatible with
metal substructures and therefore may
contain in excess of 80% feldspars.
Asst. Prof. Dr. Ayşe KALEMTAŞ
FeldsparsFel
dsp
ars
Feldspars are commercially
used in the glass and
ceramics industries because
of their chemical
composition, particularly for
their alkali content. The
consumption of feldspars
within these two industries
is estimated at 85–90 % of
the market.
Fel
dsp
ars
Feldspar is also used in
fillers and abrasive
industries but not as
much as in the ceramic
and glass industries. Fel
dsp
ars
The greatest consumption of
feldspar raw materials is in
ceramic products. Ceramic
products comprise sanitary
ware, ceramic tiles,
dinnerware, ceramic glazes,
and electrical porcelain. In
ceramic industries feldspar
is a basic component in the
raw material batch for
ceramic bodies.
Fel
dsp
ars
The typical feldspar content
in floor and wall tiles is from
10–55 wt.%, from 15–30
wt.% in white ware, chemical
porcelain and hotel china,
25–35 wt.% in sanitary
ware and 30–50 wt.% in
electrical porcelain. Feldspar
is also used in ceramic glazing
in amounts ranging from
30–50 wt.%; by providing
alumina and alkali it also acts
as a flux in fine ceramics.
Fel
dsp
ars In addition, feldspar also has
various significant usages such
as for ceramic shields. The
NASA space programme has
used a ceramic thermal shield
to protect spacecraft during
the re-entry to the
atmosphere.
Fel
dsp
ars
In pottery, a high amount of
potash feldspar increases
their strength. Potash
feldspar is also involved in
the ceramic materials which
increase the efficiency of gas
turbines. A particular
application that consumes a
significant amount of feldspar
is porcelain industry, which
uses 60–80 %.
Asst. Prof. Dr. Ayşe KALEMTAŞ
Beneficiation is the process that most minerals need to go through beforethey can be used in producing ceramics.
Physical beneficiation includes crushing and grinding of coarse rocks. Theparticle size of the raw material may affect subsequent steps in theproduction process. An example that we use is producing alumina frombauxite, a process that involves a chemical reaction.
Chemical beneficiation includes processes of separating the desired mineralfrom unwanted waste products—for example, by dissolution in a suitablesolvent followed by filtration. The Bayer process for producing alumina isalso a good example of chemical beneficiation. Bauxite contains manyimpurities. The purity of the raw materials is reflected in the composition ofthe final product. For many ceramics, careful control over purity isrequired. For these applications, the raw materials are synthesized.
Furthermore, several important ceramics do not occur naturally in mineralform and must be fabricated chemically. Synthesis of ceramic powders canhave advantages not only in purity but also in allowing the generation offine particle sized powders having a well-defined morphology.
Beneficiation
Asst. Prof. Dr. Ayşe KALEMTAŞ
• Structural clay products : bricks, sewer pipe, roofing tile
• Triaxial bodies: Whiteware, porcelain, chinaware, sanitary ware.
Traditional Ceramics
Asst. Prof. Dr. Ayşe KALEMTAŞ
Triaxial whiteware chemical composition
Traditional Ceramics
Asst. Prof. Dr. Ayşe KALEMTAŞ
Fel
dsp
ars
Feldspars are the
most abundant
group of rock-
forming minerals in
the nature. They
are components of
many rock types,
including:
pegmatite, granite,
syenite (especially
nepheline syenite),
feldspathic sand
and sandstone
(arkose).
Feldsp
ars
The major commercial
value of feldspars rests
on their chemical
composition, especially
on the content of
alkalis, i.e. K2O (min.
10%) – preferred in
the production of
whiteware, or Na2O
(min. 7%) – in glass
and ceramic tile
manufacture. In the
majority of
applications the lowest
possible content of
colouring oxides, in
particular of Fe2O3
and TiO2, is required.
Feldsp
ars
For example, in the
production of ceramic
wares of high
whiteness (porcelain),
the content of Fe2O3
and TiO2 cannot
exceed 0.15% and
0.05% respectively,
while in the case of
high quality glass –
max. 0.08% Fe2O3 is
acceptable. The term
‘feldspar raw material’
or ‘feldspar’ refers to
both K and Na
feldspar-rich grades as
well as to feldspar-
quartz ones.
Feldspars
Asst. Prof. Dr. Ayşe KALEMTAŞ
QUESTIONS