ceramic material part 1 by pak rahman

8/10/2019 Ceramic Material Part 1 by Pak Rahman

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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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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.


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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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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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

ceramic material part 1 by pak rahman

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