1. CERAMICS Duygu ALTINÖZ 20519517 Emine ÖZTAŞ 20519943
Melodi HASÇUHADAR
Merve ÇAY
Hacettepe University
KMU

2. Outline What are ceramics? Classification of ceramics
Thermal Properties of ceramics
Optical Properties
Mechanical Properties
Electrical Properties
Ceramic Processing

3. Spectrum of Ceramics Uses

4. What are ceramics?
Periodic table with ceramics compounds indicated by a combination of one or more metallic elements (in light color) with one or more nonmetallic elements (in dark color).

5. What are ceramics?
To be most frequently silicates, oxides, nitrides and carbides
Typically insulative to the passage of electricity and heat
More resistant to high temperatures and harsh environments than metals and polymers
Hard but very brittle

6. Ceramic Crystal Structures
ceramics that are predominantly ionic in nature
have crystal structures comprised of charged ions,
where positively-charged (metal) ions are called
cations, and negatively-charged (non-metal) ions
are called anions – the crystal structure for a given
ceramic depends upon two characteristics:

7. Ceramic Crystal Structures
1. the magnitude of electrical charge on eachcomponent ion, recognizing that the overallstructure must be electrically neutral 2. the relative size of the cation(s) and anion(s),which determines the type of interstitial site(s) for the cation(s) in an anion lattice

8. Example of Crystal Structure
Rock salt structure(AX)(NaCl )
Fluorite structure(AX2)(CaF2)
Perovskite structure(ABX3)(BaTiO3)
Spinel structure(AB2X4)(MgAl2O4)

9. Imperfections in Ceramics
Include point defects and impurities
Non-stoichiometry refers to a change in composition
the effect of non-stoichiometry is a redistribution of the atomic charges to minimize the energy
Charge neutral defects include the Frenkel defects(a vacancy- interstitial pair of cations) and Schottky defects (a pair of nearby cation and anion vacancies)
Defects will appear if the charge of the impurities is not balanced 

10. Properties of Ceramics
Extreme hardness
– High wear resistance
– Extreme hardness can reduce wear caused by friction
Corrosion resistance
Heat resistance
– Low electrical conductivity
– Low thermal conductivity
– Low thermal expansion
– Poor thermal shock resistance

11. Properties of Ceramics
Low ductility
– Very brittle
– High elastic modulus
Low toughness
– Low fracture toughness
– Indicates the ability of a crack or flaw to produce a catastrophic failure
Low density
– Porosity affects properties
High strength at elevated temperatures

12. General Comparison of Materials
Property              Ceramic     Metal    Polymer 
Hardness Very High Low Very Low
Elastic modulus Very High   High Low
Thermal expansion High  Low Very Low
Wear resistance  High  Low   Low
Corrosion resistance  High Low  Low 

13. General Comparison of Materials
Property             Ceramic          Metal     Polymer
Ductility Low High  High
Density  Low  High  Very Low 
Electrical conductivity  Depends   High   Low 
on material
Thermal conductivity  Depends   High  Low
  on material
Magnetic Depends High  Very Low 

14. Classification of ceramics

15. Classification of ceramics
Traditional Ceramics
the older and more generally known types (porcelain, brick, earthenware, etc.)
Based primarily on natural raw materials of clay and silicates
Applications;
building materials (brick, clay pipe, glass)
household goods (pottery, cooking ware)
manufacturing ( abbrasives, electrical devices, fibers)
Traditional Ceramics

16. Classifications of ceramics
Advanced Ceramics
have been developed over the past half century
Include artificial raw materials, exhibit specialized properties, require more sophisticated processing
Applied as thermal barrier coatings to protect metal structures, wearing surfaces,
Engine applications (silicon nitride (Si3N4), silicon carbide (SiC), Zirconia (ZrO2), Alumina (Al2O3))
bioceramic implants

17. Classification of ceramics
Oxides
Nonoxides
Composite
Oxides: Alumina, zirconia
Non-oxides: Carbides, borides, nitrides, silicides
Composites: Particulate reinforced, combinations of oxides and non-oxides

18. Classification of ceramics
Oxide Ceramics:
Oxidation resistant
chemically inert
electrically insulating
generally low thermal conductivity
slightly complex manufacturing
low cost for alumina
more complex manufacturing
higher cost for zirconia.
zirconia

19. Classification of ceramics
Non-Oxide Ceramics:
Low oxidation resistance
extreme hardness
chemically inert
high thermal conductivity
electrically conducting
difficult energy dependent manufacturing and high cost.
Silicon carbide cermic foam filter (CFS)

20. Classification of ceramics
Ceramic-Based Composites:
Toughness
low and high oxidation resistance (type related)
variable thermal and electrical conductivity
complex manufacturing processes
high cost.
Ceramic Matrix Composite (CMC) rotor

21. Classification of ceramics

22. Classifications of ceramics
amorphous
crystalline
Amorphous
the atoms exhibit only short-range order
no distinct melting temperature (Tm) for these materials as there is with the crystalline materials
Na20, Ca0, K2O, etc
Amorphous silicon and thin film PV cells

23. Classifications of ceramics
Crystalline
atoms (or ions) are arranged in a regularly repeating pattern in three dimensions (i.e., they have long-range order)
Crystalline ceramics are the “Engineering” ceramics
– High melting points
– Strong
– Hard
– Brittle
– Good corrosion resistance
a ceramic (crystalline) and a glass (non-crystalline)

24. Thermal properties
most important thermal properties of ceramic materials:
Heat capacity : amount of heat required to raise material temperature by one unit (ceramics > metals)
Thermal expansion coefficient: the ratio that a material expands in accordance with changes in temperature
Thermal conductivity : the property of a material that indicates its ability to conduct heat
Thermal shock resistance: the name given to cracking as a result of rapid temperature change

25. Thermal properties Thermal expansion
The coefficients of thermal expansion depend on the bond strength between the atoms that make up the materials.
Strong bonding (diamond, silicon carbide, silicon nitrite) → low thermal expansion coefficient
Weak bonding ( stainless steel) → higher thermal expansion coefficient in comparison with fine ceramics
Comparison of thermal expansion coefficient between metals and fine ceramics

26. Thermal properties Thermal conductivity
generally less than that of metals such as steel or copper
ceramic materials, in contrast, are used for thermal insulation due to their low thermal conductivity (except silicon carbide, aluminium nitride)

27. Thermal properties Thermal shock resistance
A large number of ceramic materials are sensitive to thermal shock
Some ceramic materials → very high resistance to thermal shock is despite of low ductility (e.g. fused silica, Aluminium titanate )
Result of rapid cooling → tensile stress (thermal stress)→cracks and consequent failure
The thermal stresses responsible for the response to temperature stress depend on:
-geometrical boundary conditions
-thermal boundary conditions
-physical parameters (modulus of elasticity, strength…)

28. OPTICAL PROPERTIES OF CERAMICS
REFRACTION
Light that is transmitted from one medium into another, undergoes refraction.
Refractive index, (n) of a material is the ratio of the speed of light in a vacuum (c = 3 x 108 m/s) to the speed of light in that material.
n = c/v

29. OPTICAL PROPERTIES OF CERAMICS

30. OPTICAL PROPERTIES OF CERAMICS
Callister, W., D., (2007), Materials Science And Engineering, 7th Edition,

31. OPTICAL PROPERTIES OF CERAMICS
ABSORPTION
Color in ceramics
Most dielectric ceramics and glasses are colorless.
By adding transition metals (TM)
Ti, V, Cr, Mn, Fe, Co, Ni
Carter, C., B., Norton, M., G., Ceramic Materials Science And Engineering,

32. MECHANICAL PROPERTIES OF CERAMICS
STRESS-STRAIN BEHAVIUR of selected materials
Al2O3 
thermoplastic

33. MECHANICAL PROPERTIES OF CERAMICS
Flexural Strength
The stress at fracture using this flexure test is known as the flexural strength.
Flexure test :which a rod specimen having either a circular or rectangular cross section is bent until fracture using a three- or four-point loading technique
Callister, W., D., (2007), Materials Science And Engineering, 7th Edition,

34. MECHANICAL PROPERTIES OF CERAMICS
Stress is computed from,
specimen thickness
the bending moment
the moment of inertia of the cross section
For a rectangular cross section, the flexural strength σfs is equal to,
L is the distance between support points
When the cross section is circular,
R is the specimen radius
Callister, W., D., (2007), Materials Science And Engineering, 7th Edition,

35. MECHANICAL PROPERTIES OF CERAMICS
Callister, W., D., (2007), Materials Science And Engineering, 7th Edition,

36. MECHANICAL PROPERTIES OF CERAMICS
Hardness
Hardness implies a high resistance to deformation and is associated with a large modulus of elasticity.
In metals, ceramics and most polymers, the deformation considered is plastic deformation of the surface. For elastomers and some polymers, hardness is defined at the resistance to elastic deformation of the surface.
Technical ceramic components are therefore characterised by their stiffness and dimensional stability.
Hardness is affected from porosity in the surface, the grain size of the microstructure and the effects of grain boundary phases.

37. MECHANICAL PROPERTIES OF CERAMICS
Test procedures for determining the hardness according to Vickers, Knoop and Rockwell.
Some typical hardness values for ceramic materials are provided below:
Material Class
 Vickers Hardness (HV) GPa
Glasses
 5 – 10
Zirconias, Aluminium Nitrides  
Aluminas, Silicon Nitrides  
Silicon Carbides, Boron Carbides  
Cubic Boron Nitride CBN  
Diamond
 60 – 70 >
The high hardness of technical ceramics results in favourable wear resistance. Ceramics are thus good for tribological applications.

38. MECHANICAL PROPERTIES OF CERAMICS
Elastic modulus
The elastic modulus E [GPa] of almost all oxide and non-oxide ceramics is consistently higher than that of steel.
This results in an elastic deformation of only about 50 to 70 % of what is found in steel components.
The high stiffness implies, however, that forces experienced by bonded ceramic/metal constructions must primarily be taken up by the ceramic material.

39. MECHANICAL PROPERTIES OF CERAMICS
Density
The density, ρ (g/cm³) of technical ceramics lies between 20 and 70% of the density of steel.
The relative density, d [%], has a significant effect on the properties of the ceramic.

40. MECHANICAL PROPERTIES OF CERAMICS
A comparison of typical mechanical characteristics of some ceramics with grey cast-iron and construction steel

41. MECHANICAL PROPERTIES OF CERAMICS
Change in elastic modulus with the amount of porosity in SiOC ceramic foams obtained from a preceramic polymer
Porosity
Technical ceramic materials have no open porosity.
Porosity can be generated through the appropriate selection of raw materials, the manufacturing process, and in some cases through the use of additives.
This allows closed and open pores to be created with sizes from a few nm up to a few µm.

42. MECHANICAL PROPERTIES OF CERAMICS
Strength
The figure for the strength of ceramic materials, [MPa] is statistically distributed depending on
the material composition
the grain size of the initial material and the additives
the production conditions
the manufacturing process
Strength distribution within batches

43. MECHANICAL PROPERTIES OF CERAMICS
Toughness
Ability of material to resist fracture
affected from,
temperature
strain rate
relationship between the strenght and ductility of the material and presence of stress concentration (notch) on the specimen surface

44. MECHANICAL PROPERTIES OF CERAMICS
Material
KIc (MPa-m1 / 2)
Metals
Aluminum alloy (7075) 24
Steel alloy (4340) 50
Titanium alloy
44-66
Aluminum
14-28
Ceramics
Aluminum oxide
3-5
Silicon carbide
Soda-lime-glass
Concrete
Polymers
Polystyrene
Composites
Mullite fiber reinforced-mullite composite
Some typical values of fracture toughness for various materials

45. Electrical properties of ceramic
Electrical conductivity of ceramics varies with
The Frequency of field applied effect
charge transport mechanisms are frequency dependent.
The temperature effect
The activation energy needed for charge migration is achieved through thermal energy and immobile charge career becomes mobile.

46. Electrical properties of ceramic
Most of ceramic materials are dielectric. (materials, having very low electric conductivity, but supporting electrostatic field).
Dielectric ceramics are used for manufacturing capacitors, insulators and resistors.

47. Superconducting properties
Despite of very low electrical conductivity of most of the ceramic materials, there are ceramics, possessing superconductivity properties (near-to-zero electric resistivity).
Lanthanum (yttrium)-barium-copper oxide ceramic may be superconducting at temperature as high as 138 K. This critical temperature is much higher, than superconductivity critical temperature of other superconductors (up to 30 K).
The critical temperature is also higher than boiling point of liquid Nitrogen (77.4 K), which is very important for practical application of superconducting ceramics, since liquid nitrogen is relatively low cost material.

49. Preparation of Raw Materials
Crushing & Grinding (to get ready ceramic powder for shaping)

50. Powder processing
Ceramic powder is converted into a useful shape at this step.
Processing techniques
Tape casting
Slip casting
Injection molding

51. Slip casting
A suspension of seramic powders in water , slip, is poured into a porous plaster mold
Water from the mix is absorbed into the plaster to form a firm layer of clay at the mold surface

52. Then injected into the molding die
Raw materials are mixed with resin to provide the necessary fluidity degree.
Then injected into the molding die
The mold is then cooled to harden the binder and produce a "green" compact part (also known as an unsintered powder compact).

53. Difference between casting and molding
Slip Casting
Mixed raw materials are combined with solvating media and a dispersant
Then fed into an absorbent die.
The materials are dehydrated and solidified
Injection molding
raw materials are mixed with resin.
Then fed injected into the molding die
The mold is then cooled to harden the binder.

54. Drying process Water must be removed from clay piece before firing
Shrinkage is a problem during drying. Because water contributes volume to the piece, and the volume is reduced when it is removed.

56. REFERENCES http://www.azom.com/details.asp?ArticleID=2123

57. Ceramics
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