Overview: Structures, Chemistry, Properties and Applications of Advanced Ceramics Flashcards
What enabled the development of new ways of transport?
increasing the strength to density ratio
What is the first definition of ceramics?
What is the 2nd definition of ceramics?
what did increasing material maximum use temperature lead to?
new engine types that burn fuel at higher temps improving combustion efficiency
What are ceramics? Comprised of?
solid compounds that are formed by the application of heat, and sometimes heat and pressure, comprising at least:
- one metal and a nonmetallic elemental solid or a nonmetal
- a combination at least of two nonmetallic elemental solids
- or a combination of at least two nonmetallic elemental solids and a nonmetal
What are ceramics (types)?
Any of a large class of inorganics, nonmetallic products including, but not limited to,
metallic oxides, borides, carbides, nitrides, sulfides, and mixtures or compounds of such
materials.
What are general properties about ceramic processing?
With a few exceptions, high temperatures (>600°C) are required to fabricate useful
ceramic products. Composition and processing conditions can be varied considerably to yield
a wide range of products and properties.
What’s an example of the different types of ceramic combinations?
What are bonds like in ceramics?
ionic or covalent bonds and electrons are not free to move from atoms
what are the three different types of arrangements of atoms in solids?
- long-range order (crystalline)
- short-range order (amorpous)
- mixture
What are ceramics composed of (microstructure)?
they’re polycrystalline solids, or a collection of many single crystals called “grains”, which are separated by grain boundaries
Test questions “what are ceramics”?
either of the first 2 definitions
1) Solid compounds that are formed by the application of heat, and sometimes heat and
pressure, comprising at least:
‐ one metal and a nonmetallic elemental solid or a nonmetal,
‐ a combination at least of two nonmetallic elemental solids,
‐ or a combination of at least two nonmetallic elemental solids and a nonmetal.
2) Any of a large class of inorganics, nonmetallic products including, but not limited to, metallic oxides, borides, carbides, nitrides, sulfides, and mixtures or compounds of such materials. With a few exceptions, high temperatures (>600°C) are required to fabricate useful ceramic products. Composition and processing conditions can be varied considerably to yield a wide range of products and properties
What components describe the “microstructure”
- shape and size of the grains, porosity, second phases, etc.
- their distribution
What are features of glasses (images too)?
- high disorder atom structure & amorphous
- different properties
- solidified upon cooling from melt
- based on silica (SiO2)
what are features of glass-ceramics?
- combination of siliceous glass and oxide crystals in the same microstructure
- long and short range order in same compound
- different properties than glasses and ceramics
How does the stiffness (young’s modulus) of ceramics compare to metals, polymers, and composites?
How does the corrosion resistance of ceramics compare?
ceramics: high
metals: low/medium
polymers: low/medium
How does the high temp stability of ceramics compare?
ceramics: high
metal: low/medium
polymer: low
how does the compressive strength of ceramics compare?
ceramics: high
metals: medium
polymers: low
test question “what makes ceramics different than other classes?”
(look @ chart)
- high temp strength
- high elastic modulus
- high compressive strength
- high hardness
- high corrosion resistance
- high temp stability
- low CTE
- low ductility
How does the tensile strength of ceramics compare?
How does resistance of fracture of ceramics compare?
does dislocation and deformation happen in ceramic materials?
yes, just to a lesser extent than other materials
how does the electrical conductivity of ceramics compare?
How big is the ceramic industry?
$500 billion/ year
What are the large ceramic industries?
- glass and glass-ceramics
- cements
What are the medium-sized ceramic industries?
- structural clay products
- technical
- advanced
- whitewares
- refractories
what are the small-sized ceramic industries?
- porcelain enamels (coatings)
- abrasives
- art
- novelty/miscellaneous
Around how much money was the global advanced ceramics market valued at in 2015? What were the largest subcategories?
56.7 billion
electrical equipment and electronic devices
what’s the main market for ceramics?
electronics (equipment and devices)
also catalyst and bioceramics are big-ish
What are examples of common ceramics?
- clays
- sands
- feldspars
What are different applications of the common ceramics clays, sand, and feldspars?
- floor and wall tiles
- food and bev containers
- kitchen and bathroom ware
- construction materials
What are 3 applications glass ceramics?
- porcelain enamels
- bulbs and windows
- stove tops and cook wares
What are examples of the compounds that make glasses and glass ceramics? (still common)
- soda-lime-silica glass
- lithia-silicate glass
- borosilicate glass
What are two large categories of applications of common ceramics? examples?
- refractories (furnace liners, filters for metal production)
a. furnace bricks (Al2O3)
b. SiC filter
c. ZrO2 filter
d. fused SiO2 crucibles - abrasives (sandpaper, grinding and cut-off wheels)
a. SiC coated paper
b. Diamond coated wheel
c. WC cutting tools
What are 5 examples of technical ceramics?
- spark plug (Al2O3)
- oxygen sensor (ZrO2)
- varistors (ZnO)
- ceramic insulators (clay, kaolin, silica, alumina and feldspar)
- cordierite catalytic converter
What are some examples of advanced ceramics?
- Si3N4 rotor
- bioglass
- SiC ball bearings
- UHTC for leading edges
- SiO2 aerogel
What differences increase as we move from common, to technical, to advanced ceramics? what decreases?
increases
- purity of raw materials
- unit cost
- required reliability
- specificity
decreases
- raw material particle size
What do properties depend on?
composition and struture
What are the 8 different properties?
- chemical inertness
- photonics/optical
- electrical/dielectric
- magnetic
- thermal
- mechanical
- density
- high temp stability
CPEMTMDH
where do the most important advances in ceramic applications occur?
at the intersection of properties
Describe the chemical inertness of ceramics in regards to their stability, performance, and corrosion.
- good stability in neutral ph aqueous environments near room temp
- better chemical inertness than metals and polymers in high/low pH & temp environments, also better in chemical solutions
- a) they can corrode in extreme conditions
b) complex corrosion mechanisms
c) thermo and kinetics of the corrosion is dependent on comp. and structure
What are 4 applications of the chemical inertness
- containment of nuclear waste (borosilicate glass)
- Aluminum smelting cathodes (TiB2)
- bioglass to repair bone
- ceramic implants (ZrO2)
How are optical properties defined?
by how a material interacts with light
what is photonics?
a broad category that includes any phenomena and devices that deal with the generation, manipulation, and sensing of light
what are the 5 parameters of optical/photonics
- absorption
- refraction
- transmission
- reflection
- scattering
what are the 5 different types of behavior of optical/photonics
- translucency
- transparency and opacity
- glass
- birefringence
- color
what are 4 applications of the optical prop of ceramics?
- fiber optics (SiO2)
- LASERS
- Photochromics (glass)
- transparent ceramic armor
What are the electric/dielectric properties of ceramics controlled by?
- long range transport (conductivity) of mobile carriers (ie electrons, ions)
- or short range movement of electrical diploes (polarization) in specific domains
What are applications of the electrical/dielectric of ceramics
- capacitors
- insulators
- electronic packaging
- batteries
What are 3 different thermal properties or ceramics?
- thermal conductivity
- thermal expansion
- thermal shock resistance (TSR)
What are the main and secondary properties we’re looking for implants?
- corrosion resistance
- compressive strength (elastic modulus)
What are the main and secondary properties we’re looking for implants?
- transparency
- strength
What are the main and secondary properties we’re looking for with fiber optics?
- refractive index/photonics/optical properties
- electrical/mechanical/thermal
What is thermal conductivity (k)?
The ability of the material to conduct heat (W/m-K)
How is the thermal conductivity of most ceramics?
poor
What are three ceramics with high thermal conductivity?
AlN, TiB2, ZrB2
k>90 W/mK
What is the variable for thermal conductivity
k
What is one method you could use to lower k?
k = thermal conductivity
porosity addition
What is thermal expansion
the ability of the ceramic to expand/contract during heating and cooling (cm/cm)
how does the thermal expansion of ceramics compare to metals
ceramics have lower thermal expansion than metals
What is a ceramic with one of the lowest expansion coefficients?
SiO2
~0.5
What is thermal shock resistance (TSR)?
the ability of the ceramic to resist fracture when cooled/heated (change in T/ change in t)
What does high thermal shock resistance (TSR)
high k (thermal conductivity)
low CTE
What are four examples of ceramics that take advantage of thermal properties?
- Si3N4 rotor
- leading edges (UHTCs)
- shuttle tiles (ceramic oxides foams and fibers)
- SiO2 aerogel
What are three important mechanical properties of materials ?
- strength (σƒ)
- fracture toughness (KIC)
- hardness (Hv)
What is strength (unit)? What test can measure it? How do they compare to other materials?
resistance to fracture (MPa)
4-point bend rest
ceramics have theoretical strengths higher than most other materials but have a wider variation in values bc of flaws
What is hardness (unit)? How do you measure it? How do ceramics compare & why?
resistance to indentation (Kg/mm^2)
diamond pyramid method (Vickers)
ceramics usually have much higher hardness due to their ionic/covalent bonding than other materials
What are 3 applications of ceramics that take advantage of mechanical properties?
- protective armor (SiC)
- ceramic implants (ZrO2)
- SiC, AlON, or Si3N4 engines
What are the different structure levels, their scale, and what you see?
structure levels
1. macro >10^-3
2. micro 10^-6
3. nano 10^-9
4. crystal 10^-10
5. atomic 10^-10
6. subatomic <10^-10
What are the kinds of bonding that are important in ceramic materials? Their strengths?
- ionic - strong
- covalent - strong
- van der waals - weak (~1/10 strength of ionic/covalent)
What does the strength of ionic/covalent bonds indicate?
large bond energy
- large Tm
- large E
- small alpha (CTE)
what are two examples of van der waals bonding?
- forming/shaping of traditional ceramics
- porous desiccants (silica gels)
How are van der waals bonds relevant in forming/shaping traditional ceramics?
the bonds are weak enough to allow slip during forming but strong enough to ensure the shape was maintained after forming. the presence of water promotes particle slippage and facilitates forming
how are van der waals bonds relevant to porous desiccants (silica gels)
The surfaces of these particles have negatively charged oxygen, which attracts water molecules from the environment
the internal surface area of the gels is very high because of nanopores, so large quantities of water can be absorbed
Describe the crystal structure, packing, and ion size of ionic bonding.
- contains cations and anions
- each lattice point must have a cation and an anion for electrical neutrality
- large ions (anions) form close packed HCP, FCC, or SC structures
- smaller ions (cations) usually in interstitial spaces
describe covalent bonding
- directional bonding
- difficulty in forming close packed structures
what determines the extent to which a ceramic is ionic/covalent
the difference in electronegativity between the two atoms
the GREATER the DIFFERENCE in electronegativity the MORE IONIC it’ll be
What does %ionicity affect
the processing characteristics and properties of the ceramic
which properties does covalency/ionicity affect
more covalency (small %ionicity) means stronger, more brittle, harder, and smaller diffusion coefficients
What is the different in electroneg and %ionic for the following ceramics: CsF, Al2O3, SiC
CsF: large dif, 95%
Al2O3: moderate dif, 60%
SiC: low, 20%
Describe the dislocation motion of metals
- dislocation motion easiest
- non-directional bonding
- close-packed directions for slip
Describe the dislocation motion of covalent ceramics
- motion difficult
- directional (angular) bonding
Describe the dislocation motion of ionic ceramics
- motion difficult
- need to avoid nearest neighbors of like sign (- and +)
What is an example of an important application for ceramic bonding? What is used and why? What’s the crystal structure?
nuclear fission
UO2 (a ceramic) is used as the fuel instead of just U because
- the oxide is stable up to high temps
- the crystal structure can accommodate fission products: the ions remain when the U is split and energy released
FCC with U ions, and oxygen at the 8 tetrahedral positions
What kind of processing is ceramic processing? Why?
a powder processing
1. very high melting temp - so casting isn’t economical
2. ceramics are brittle - large flaws reduce strength. casting produces large grains (flaws)
3. fine grain microstructures can be produced by sintering submicron particles
What is the ceramic processing scheme?
powders – > shaping –> sintering
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