Download presentation
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 Thank You 57
Similar presentations
© 2025 SlidePlayer.com. Inc.
All rights reserved.