Post on 02-Jun-2018
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Ceramic Materials :
Structures and Properties
Application and Processing
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Outline
Ceramic structures and properties What is ceramic?
Ceramic Structures Silicate Ceramics
Ceramic properties Ceramic application and processing
Ceramic application
Ceramic processing
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What are ceramics?
Inorganic and non-metallic materials
Compounds between metallic and non metallic elements
Ceramic comes from the Greek word keramikos (burn stuff) Desirable properties of ceramics are normally achieved through a high
temperature treatment (firing)
Ceramic product
traditional ceramics New generation of ceramic products
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Ceramic products
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Why study structures and properties of
ceramics? Some of properties of ceramics may be
explained by their structures
The hydroplasticity of clays (upon the addition ofwater
The optical transparency of inorganic glass materials
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Struktur ikatan atom dalam
bahan1. Struktur molekuler
2. Struktur kristal
3. Struktur amorph
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Struktur kristal
Teratur
Berulang (periodik)
Jarak ikatan relatif panjang
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Sistem kristal dan model visualiasasi
Lattice parameters
(dimensi kisi) a, b, c, ,,
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Ceramic structures : crystal structures
Characteristics of component ions influence crystalstructures The magnitude of the electrical charge
The crystal must be neutrally charged The relative size of the ion electric
There is critical minimum ratio of cation radius and anion radius forwhich the contact can be established
The coordination number : the number of anion nearestneighbours for a cation Most common coordination number for ceramics : 4, 6, and 8.
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Figure 12.2 coordination number
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Ceramic structures : crystal structures
example of crystal structure
Sodium chloride (NaCl)
Coordination number : 6 Cation-anion radius ratio :
0.414-0.732
Two interpenetrating FCC
latticesMgO, FeO, MnS, memiliki
structure yang sama dengan
NaCl
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Ceramic structures : silicate ceramics
Silicates are materials composed primarily of silicon and oxygen
Silicon and oxygen are the most abundant elements in the earths
crust.
Various silica structure arise from the different ways in which the
SiO4 units can be combined into one-,two- and three dimensionalarragements
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Most Most simple silicates Every oxygen atom is shared by
adjacent tetrahedral
Electrically neutral
Crystalline and amorphous
Crystalline : quartz, cristobaliteand tridymite
Structures are relatively open and
not closely packed thus it has low
densities.
silicate ceramics : Silica
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Fused or vitreous silica :
Non crystalline having highdegree of randomness
Basic unit is the same as
silica but beyond thisstructure, considerabledisorder exists.
Inorganic glasses such asused for containers and
windows are silica glassesadded other oxides such asCaO and Na2O
Such oxides also lower themelting point and viscosity
of silica glasses
silicate ceramics : silica glasses
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Ceramic structures : silicate ceramics
Simple Silicates
Contoh : forsterite (Mg2SiO4), akermanite (Ca2MgSi2O7)
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Repeating unit formula :
(Si2O5)2-
Clays minerals such askaolinite Al2(Si2O5)(OH)4;
talc Mg3(Si2O5)2(OH)2
Whereas the bonding within this
two layered sheet is stomg andintermediate ionic-covalent;
adjacent sheets are only loosy
bund to one another by weak
van der waals force.
Ceramic structures : silicate ceramics
Layered Silicates
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Impercations in ceramics:
stoichiometry defect
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Impercations in ceramics:
un-stoichiometry defect
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Ceramic phase diagram
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Ceramic phase diagram
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Mechanical Properties of Ceramics :
brittle fracture of ceramics
Ceramic materials are somewhat limited in applicabilityby their mechanical properties, which in many respectsare inferior to those of metals.
The principal drawback is a disposition to catastrophicfracture in a brittle manner with very little energyabsorption.
At room temperature, both crystalline and non crystallineceramics almost always fracture before any plasticdeformation can occur in response to an applied tensileload.
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Figure 12.29 Cracks in brittle ceramics materials
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Ceramic Applications : Glasses
Glasses Non-crystalline silicates containing other oxides such as CaO, Na2O
and Al2O3 Containers, lenses,
Glass-ceramics Most inorganic glasses can be made to transform a non-crystalline
state to one that is crystalline by the proper high temperature heattreatment.
High mechanical strength, low coefficient of thermal expansion,relatively high temperature capabilities
Trade names such as pyroceram, corningware, etc are used forovenware, table ware, oven windows,...
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Table. Some common commercial glasses
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Structural clay products and whiteware Stuctural clay products : bricks, tiles and sewer pipes
Whiteware : porcelain, pottery, sanitary ware,...
Characteristic of clay Hydro-plasticity
Drying and firing : fusestrong and dense
Clay are aluminosilicates, being composed of aluminaand silica that contain chemically bound water
Composition Ingredients : plastic (clay) and non-plastic: filler such
as quartz and flux such as feldspar (it can low meltingpoint,)
Ceramics Applications : Clay products
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Properties of refractory ceramics include
The capacity to withstand high temperature without melting
The capacity to remain uncreative and inert when exposed to severeenvironments
The ability to provide thermal insulation
The performance of a refractory ceramic to large extend depends on itscomposition.
Consist of both large and small particles
Porosity is one micro structural variable that must be controlled toproduced suitable refractory bricks.
Strength and resistance to corrosion attack increase with porosityreduction
Thermal insulation decreases with porosity reduction
Ceramics Applications : refractory
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Table Common ceramic refractory materials
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Inorganic cements : cement, plaster of paris, andlime, are produced in extremely large quantities.
Portland cement : mixture between clay, lime-bearing minerals, gypsum, etc. The process takeplace in a rotary kiln.
The principal constituents in Portland cementsare tricalcium silicate and dicalcium silicate.
Ceramics Applications : cements
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Ceramic Processing
The tolerance of finished product to defects determinesthe raw materials selected and the control that must beexercised during the processing
Ceramic processing is complicated both by the number ofsteps required in manufacture and by requirements tooptimize the processing in different steps.
Raw materials for ceramic processing range from impureclay material mined from natural mineral deposits toultrahigh purity powders prepared by chemical synthesis.
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Flow diagram of the steps and processes involved in manufacturing a ceramic
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Raw materials in ceramic processing
Natural
Silica, silicates, aluminosilicates (clays, feldspars)
Low costChemical impurity
Chemically synthesized powders
Pure, well defined properties
Expensive
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Chemically synthesized powders
Solid state Through calcinations at an elevated temperature
Due to low solid state diffusion, fine and well mixed
powders are required. Purify of the product is limited by the purity of the
constituents raw material
Less pure and having larger size
Solution chemistry Sub micrometer particle size, high purity ceramic
powder
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Chemically synthesized powders
Solution
Precipitation and extraction
Sol-Gel technique
Vapour phase technique
Mainly for preparing non-oxide powders such as
nitrides and carbides Vapour-condensation, vapour-vapour reactions
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Particle size reduction
Crushing (down to cm or mm size)
Grinding/ milling (down to micrometer size)
Pufification
Washing using water or other solvent
Chemical leaching
Magnetic separation
Beneficiation (1)
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Sizing
Sieve sizing
Vibrating sieve
Classification
Elutriation
Sedimentation
Cyclone and centrifugation (bellow ~ m)
Beneficiation (2)
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Forming / Fabrication process
Dry forming
By pressing a rigid die or flexible mold
Plastic formingDeform in-elastically without rupture
Slurry forming
Slip casting
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Silica from Biomass Waste
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Bagasse Ash
bagasse fly ash (BFA)and bagasse bottom ash(BBA)
BBA BFA
Silica content 73% 50%
Loss of weight on ignition 7.69% 36.5%
Other impurities (oxides) Al2O3, CaO, K2O, P2O5,
Fe2O3, Na2O, MgO, etc
Al2O3, CaO, K2O,
P2O5, Fe2O3, Na2O,
MgO, etc
Amount Huge amount A lot
Form Amorphous and
crystalline
Amorphous and
crystalline
BBA is used in the present work as it contains much highersilica. Additionally, BBA is produced in much larger amountthan BFA.
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Position [2Theta]
10 20 30 40 50 60
Counts
0
100
400
4.0
4943[];Cristobalitelow,syn;Quartzlow
3.2
1057[];Quartzlow
3.0
1175[];Magne
tite
2.9
0221[];Ankerite
2.4
9204[];Cristobalitel
ow,syn
2.0
2723[];Cristobalitelow,syn;Quartzlow;Ankerite
1.7
9299[];Ankerite
1.4
9489[];Cristobalitelow,syn;M
agnetite;Ankerite
R-1
XRD analysis on bagasse bottom ash shows that silica present in BBA is inamorphous form. However, the analysis also indicates the presence ofcristobalite.
Combustion of bagasse at high temperature in the furnace of cane sugar