MME391 Ceramic Materials Asst. Prof. Dr. Ayşe KALEMTAŞ Bursa Technical University, Metallurgical and Materials Engineering Department

Office Hours: Tuesday, 10:00-11:00 [email protected], [email protected]

Asst. Prof. Dr. Ayşe KALEMTAŞ

Traditional Ceramics Clay Products – Main Components Clay

Feldspar

Silica Asst. Prof. Dr. Ayşe KALEMTAŞ

Traditional Ceramics Clay 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

Clay products – Main Components Silica 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 temperatures required 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.

Feldspar 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. Asst. Prof. Dr. Ayşe KALEMTAŞ

Traditional Ceramics Fluxes are raw materials with high amount of alkaline oxides, mainly K2O and Na2O, whereby, in reaction with silica and alumina, promote liquid phase formation that facilitates the densification. The liquid phase surrounds the solid particles and by surface tension enables rearrangement of particles and decreasing the porosity. 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. The molten glass also reacts with the silica and clay particles.

Feldspar 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. Asst. Prof. Dr. Ayşe KALEMTAŞ

ORES AND MINERALS Earth’s Crust

Earth’s crust refers to the outher siliceous shell of the earth which is about 16 km thick. Metallic ores and mineral products are produced from this crust. Therefore, the original source of all metals is the earth’s crust. Ores are naturally occuring deposits in the earth’s crust. The ores are mined and treated by various • unit operations (mechanical processes) • unit processes (chemical metallurgical processes) to extract metals and to convert them into the metallic form.

Mine : It is a large area having an abundant quantity of mineral deposits that can be easily and economically extracted.

The mineral content of the ore must be in sufficient concentration to make its extraction commercially viable. Asst. Prof. Dr. Ayşe KALEMTAŞ

ORES AND MINERALS Minerals are the constituents of rocks, which make up the entire inorganic, solid portion of the earth. Rocks are usually not composed of a single mineral but, rather, an aggregate of two or more minerals. Broadly speaking, geologists divide rocks 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 of minerals. • Although over 2000 minerals have been discovered, only a few are abundantly found in most of the rocks. Asst. Prof. Dr. Ayşe KALEMTAŞ

ORES AND MINERALS Igneous rocks form when magma cools and solidifies. Magma is a complex molten 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.

Metamorphic rocks have undergone structural and/or chemical transitions (metamorphism or metamorphosis) from their original form as a result of high temperatures and pressures deep beneath the earth’s surface. These transitions occur in the solid state without melting and result in the formation of new minerals, such as kyanite, staurolite, sillimanite, andalusite, and some garnets. Other minerals, such as some of the igneous minerals, may be present in metamorphic rocks but are not necessarily the result of metamorphism. The word “metamorphic” has a Greek origin coming from meta, meaning “change,” and morpe, meaning “shape”. Asst. Prof. Dr. Ayşe KALEMTAŞ

ORES AND MINERALS Sedimentary rocks are formed when small particles or precipitated crystals become cemented together. Sedimentary rocks are classified as either clastic or chemical. Clastic sedimentary rocks form when rock particles produced by mechanical and chemical weathering are transported by water, ice, and wind 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 are dissolved in water and subsequently precipitate, forming layers in oceans 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 mineral component ▪ Distance traveled Asst. Prof. Dr. Ayşe KALEMTAŞ

ORES AND MINERALS Resistant minerals such as quartz are common constituents of sedimentary rocks, and some more rare minerals (e.g., garnet, rutile, zircon) have similar properties.

cooling and solidification of magma

Rocks that have undergone structural

and/or chemical transitions

Sedimentary

Rocks formed by

Metamorphic

Igneous

Feldspar is less resistant but is so common that it is a major constituent of many sedimentary rocks. Precipitated minerals include the carbonates (e.g., calcite, dolomite), the sulfates (e.g., gypsum, anhydrite), chlorides, and chalcedonic silica (e.g., chert, flint).

Rocks formed when smaller particles become cemented

Asst. Prof. Dr. Ayşe KALEMTAŞ

Average Analysis of the Earth’s Crust It is clear that :  Oxygen  Silicon  Aluminum  Iron are the 4 most abundant elements

Most common elements in the crust

Since engineering metals Al, Fe, Mg and Ti are far more abundant than the other metals, there is never likely to be a shortage of those metals due to exhaustion of the ore deposits. The commonly known metals like Au, Pb, Sn are in so small quantities in the earth’s crust that their commercial recovery is impossible. Asst. Prof. Dr. Ayşe KALEMTAŞ

A group of aluminosilicates, tetrahedra form three-dimensional

frameworks with Ca, Na and K as the balancing cations.

Feldspars

Feldspars

Feldspars

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

Feldspars Feldspar Group

light silicates (K-Na-Ca, Al)

K-feldspar

Most common mineral group

Orthoclase Plagioclase

2-directions of cleavage (at 90 degrees)

Ca/Na-feldspar Asst. Prof. Dr. Ayşe KALEMTAŞ

hard

K-feldspar Most

Has

multiply colors

Feldspars

Is very

Feldspars

Feldspars

Feldspars common mineral group

orthoclase KAlSi3O8 ...

... weathers to kaolinite: Al2Si2O5(OH)4 ... which can weather further to bauxite: AlO(OH) Asst. Prof. Dr. Ayşe KALEMTAŞ

Feldspars of ceramic ware. Feldspar produces a glassy phase during firing increasing the strength and translucency of the

Feldspars are

alumino-silicate minerals found in nearly all igneous rocks.

Feldspars

a flux in the sintering

Feldspars

Feldspars

Feldspars are used as

The plagioclase feldspars are solid solutions of albite and anorthite. Na+ Si4+ is replaced by Ca2+ Al3+

body.

are solid solutions of albite and orthoclase.

Na is replaced by K

There is virtually no solid solution between anorhite and orthoclase.

Feldspars

The alkali feldspars

Feldspars

Feldspars

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

minerals are likely

to enter the composition of silicate ceramic pastes. They are:

Orthoclase, a mineral rich in potassium with the composition K2O.Al2O3.6SiO2

Feldspars

Four feldspathic

Feldspars

Feldspars

Feldspars Albite, a mineral rich in sodium with the

composition Na2O.Al2O3.6SiO2

rich in calcium with the composition CaO.Al2O3.2SiO2

Petalite, a mineral rich in lithium with the composition Li2O.Al2O3.8SiO2

Feldspars

Anorthite, a mineral

Feldspars

Feldspars

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

occur in nature as pure minerals.

Albite and anorthite form a complete solid solution series.

Feldspars

Feldspars rarely

Feldspars

Feldspars

Feldspars Even though orthoclase and albite

form only limited solid solutions, deposits of orthoclase always

contain some albite.

syenite is a mixture of orthoclase, albite and nepheline with minor impurities.

typically ground to a relatively coarse powder, on the order of 70 to 100 m, for use in

Feldspars

The rock nepheline

Feldspars

Feldspars

These materials are

The Republic of Korea is the largest producer of feldspar in the world.

ceramic (or glass) production. Asst. Prof. Dr. Ayşe KALEMTAŞ

albite, which form eutectics with silica, respectively,

at 990 and

Anorthite is rather regarded as a substitute to chalk.

1050°C, are

Natural feldspars used for the

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.

Feldspars

Feldspars

can contain between 2.5 and

especially owing to its negative expansion coefficient, is

Potassic feldspar is particularly

preparation of ceramics are

commercial potassium products

The use of petalite,

marginal.

widely used as flux.

mineral mixtures. Thus, the

Feldspars

Orthoclase and

Feldspars

Feldspars

Feldspars

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 of polymerized silicon-aluminum-oxygen tetrahedra in the liquid.

Despite lower melting points, the alkali feldspars produce much more viscous liquids than anorthite.



In the case of albite this is interpreted as evidence for a higher degree of polymerization 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 ceramic processing.

encountered in

Albite melts at the lower temperature than orthoclase, but the addition of anorthite increases the melting temperature of soda feldspar while decreasing that of the potash feldspar (down to a minimum at about 22% anorthite). Similarly a 50%: 50% mixture of albite and orthoclase melts at a lower temperature than either end member.



Often mixtures of fluxes are employed in order to take advantage of melting.



eutectic

Lithium

bearing minerals are often very effective fluxes when used in conjunction with feldspar since such combinations form deep eutectics.

Asst. Prof. Dr. Ayşe KALEMTAŞ

temperatures or in the presence of a large quantity of

primarily the result of the use of raw materials free from iron and titanium or

flux are generally

Feldspars

the least porous.

containing only

as well as the green strength, but often leads to discoloration as a result of contamination by iron-bearing

opposite end of the spectrum where aesthetics take priority. China clays are used in these formulations, because they are nearly phase pure and bearing solid solutions (as

transition metals.

clay generally improves the plasticity

Fine china represents the

do not occur as iron

small contents of

Increasing the relative amount of ball

Feldspars

treated at higher

Whiteness is

Feldspars

The materials

Feldspars

Feldspars

Feldspars

do the smectites and illites).

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

accessory minerals. Therefore

tiles) the extent of glass formation is

applications where green strength is at

kept to a minimum. In contrast,

a premium, and color is of less

dental porcelains must fuse at low

importance, employ larger amounts of

temperatures to be compatible with

ball clay.

metal substructures and therefore may contain in excess of 80% feldspars. Asst. Prof. Dr. Ayşe KALEMTAŞ

Feldspars The greatest consumption of

ceramics industries because of their chemical composition, particularly for their alkali content. The consumption of feldspars within these two industries

Feldspar is also used in

fillers and abrasive industries but not as much as in the ceramic and glass industries.

Feldspars

used in the glass and

Feldspars

Feldspars

Feldspars are commercially

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

is estimated at 85–90 % of

raw material batch for

the market.

ceramic bodies.

The typical feldspar content

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.

In pottery, a high amount of 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.

Feldspars

10–55 wt.%, from 15–30

Feldspars

Feldspars

in floor and wall tiles is from

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 Beneficiation is the process that most minerals need to go through before they can be used in producing ceramics. Physical beneficiation includes crushing and grinding of coarse rocks. The particle size of the raw material may affect subsequent steps in the production process. An example that we use is producing alumina from bauxite, a process that involves a chemical reaction. Chemical beneficiation includes processes of separating the desired mineral from unwanted waste products—for example, by dissolution in a suitable solvent followed by filtration. The Bayer process for producing alumina is also a good example of chemical beneficiation. Bauxite contains many impurities. The purity of the raw materials is reflected in the composition of the final product. For many ceramics, careful control over purity is required. For these applications, the raw materials are synthesized.

Furthermore, several important ceramics do not occur naturally in mineral form and must be fabricated chemically. Synthesis of ceramic powders can have advantages not only in purity but also in allowing the generation of fine particle sized powders having a well-defined morphology. Asst. Prof. Dr. Ayşe KALEMTAŞ

Traditional Ceramics • Structural clay products : bricks, sewer pipe, roofing tile • Triaxial bodies: Whiteware, porcelain, chinaware, sanitary ware.

Asst. Prof. Dr. Ayşe KALEMTAŞ

Traditional Ceramics Triaxial whiteware chemical composition

Asst. Prof. Dr. Ayşe KALEMTAŞ

Feldspars most abundant

forming minerals in the nature. They are components of many rock types,

including: pegmatite, granite, syenite (especially nepheline syenite),

feldspathic sand and sandstone (arkose).

Feldspars

Feldspars

group of rock-

For example, in the

value of feldspars rests

production of ceramic

on their chemical

wares of high

composition, especially

whiteness (porcelain),

on the content of

the content of Fe2O3

alkalis, i.e. K2O (min. 10%) – preferred in

the production of whiteware, or Na2O (min. 7%) – in glass and ceramic tile

Feldspars

Feldspars are the

The major commercial

and TiO2 cannot

exceed 0.15% and

0.05% respectively, while in the case of high quality glass – max. 0.08% Fe2O3 is

manufacture. In the

acceptable. The term

majority of

‘feldspar raw material’

applications the lowest

or ‘feldspar’ refers to

possible content of

both K and Na

colouring oxides, in

feldspar-rich grades as

particular of Fe2O3

well as to feldspar-

and TiO2, is required.

quartz ones. Asst. Prof. Dr. Ayşe KALEMTAŞ

QUESTIONS

Asst. Prof. Dr. Ayşe KALEMTAŞ