Chapter 13 Flashcards
What are the different classifications of ceramics?
- Glasses (glass/glass-ceramics)
- Clay products (structural/whiteware)
- Refractories (clay/nonclay)
- Abrasives
- Cements
- Ceramic biomaterials
- Carbons (diamond/graphite/fibers)
- Advanced ceramics
What are some applications of glasses?
- Optical
- Composite/reinforcement
- Containers/household
What are some applications of clay products?
- Structural
- Whiteware
What are the applications of refractories?
- Bricks for high temperature furnaces
What are some applications of abrasives?
- Sandpaper
- Cutting
- Polishing
What are some applications of cements?
- Composites
- Structural
What are the applications of ceramic biomaterials?
- Implants
What are some applications of carbons?
- Composites
- Abrasives
What are some applications of advanced ceramics?
- Engine rotors, valves, bearings
- Sensors
Why are ceramics used in die blanks?
- They are used for their wear-resistant properties
- Polycrystalline diamond particles are sintered onto a cemented tungsten carbide substrate
- The diamond gives uniform/isotropic hardness
What tools are ceramics used in?
- To grind glass, tungsten carbide, and other ceramics
- For cutting silicon wafers
- For oil drilling
What is the structure of a ceramic cutting tool?
- Manufactured single crystal or polycrystalline diamonds in a metal or resin matrix
- Polycrystalline diamonds resharpen by microfracturing along cleavage planes
How are ceramics used in sensors?
Ceramic sensors convert physical inputs into electrical outputs. An example of this is ZrO2 as an oxygen sensor, where the diffusion of oxygen through the sensor creates a voltage difference.
What are refractories?
A metal or ceramic that may be exposed to extremely high temperatures without deteriorating rapidly or without melting.
How does porosity affect refractory bricks?
As porosity increases, the strength and chemical resistivity decreases, but thermal insulation increases.
What are the advantages of using advanced ceramics in engines?
- Can operate at high temperatures
- Low friction (high efficiency)
- Operate without a cooling system
- Lower weights than metal counterparts
What are the disadvantages of using advanced ceramics in engines?
- Ceramics are brittle
- Difficult to remove internal voids that weaken structure
- Ceramic parts are difficult to form and machine
How are advanced ceramics used in armor?
- Used to form facing plates and backing sheets
- Facing plates are hard and brittle and fracture high velocity projectiles
- Backing sheets are soft and ductile and deform, absorbing energy
What are the three types of nanocarbons?
- Fullerenes
- Carbon nanotubes
- Graphene
What are fullerenes?
Spherical clusters of 60 carbon atoms.
What are carbon nanotubes?
A sheet of graphite rolled into a tube and each end is capped with fullerene hemispheres.
What is graphene?
A single atomic layer of graphite composed of hexagonally bonded carbon atoms.
What are the three types of ceramic fabrication techniques?
- Glass forming
- Particulate forming
- Cementation
What are the four types of glass forming?
- Pressing (gob into parison mold -> pressed)
- Blowing (mold around suspended parison -> blown)
- Fiber Drawing (molten glass pulled into fibers)
- Sheet forming (sheets formed on pool of molten tin)
What is the melting point of glass?
Where the glass is fluid enough to be considered liquid
What is the working point of glass?
Where glass is easily deformed
What is the softening point of glass?
The maximum temperature at which a glass piece may be handled without permanent deformation
What is the annealing point of glass?
The temperature at which residual stresses in a glass are eliminated within about 15 min
What is the strain point of glass?
For temperatures below the strain point, fracture will occur before the onset of plastic deformation
What is the basic structure of glass?
- Noncrystalline/amorphous
- SiO2
- Common impurity atoms are Na, Ca, Al, B
What is quartz?
Crystalline SiO2 (not glass)
What is specific volume?
1/density
What are the properties of glasses?
- Do not crystalize
- Slope of specific volume curve changes at glass transition temperature
- Transparent because there are no grain boundaries to scatter light
What is the glass transition temperature?
The temperature at which, upon cooling, a noncrystalline ceramic or polymer transforms from a supercooled liquid into a rigid glass.
What is viscosity?
- Shear stress/velocity gradient
- Viscosity decreases as temperature decreases
What is annealing?
- Where glass is heated to its annealing point to remove internal stresses caused by uneven cooling
How does tempering affect glass?
- Puts surface layers in compression while the interior is in tension
- Suppresses growth of cracks on the surface
- Layers in compression cool faster
What are the four types of particulate-forming techniques?
- Hydroplastic
- Slip casting
- Powder pressing
- Tape casting
What is hydroplastic forming?
- Particles at a desired size are mixed with water
- Mass is extruded
- The formed piece is dried and fired
What is slip casting?
- Particles at a desired size are mixed with water (forms slip)
- Slip is poured into a porous mold
- Water absorbing into the mold forms a solid component
- Water poured out of the mold forms a hollow component
- Green ceramic remains (dried but not fired)
- Green ceramic is fired
What is a typical composition of porcelain?
- 50% Clay
- 25% Filler (finely ground, ex, quartz)
- 25% Fluxing agent (Feldspar)
What are Feldspars?
- Aluminosilicates with varying levels of potassium, sodium, and calcium
- When fired forms a low-melting-temperature glass
How does the addition of water affect dry clay?
Water molecules fit in between the layered clay sheets and reduce the degree of van de Walls bonding. When external forces are applied, the weakened bonds allow the clay to become malleable.
What is the drying process?
- Water is removed causing interparticle spacing decreases (shrinkage)
- Drying too fast can cause warping or cracking due to non-uniform shrinkage
What is the firing process?
- Heat treatment between 900-1400 deg C
What is vitrification?
During the firing of a ceramic body, a liquid phase forms from clay and flux. Upon cooling it becomes a glass-bonding matrix.
What is powder pressing?
- Used for both clay and non-clay compositions
- Powder and a binder is compacted by pressure in a mold
- Uniaxial compression, isostatic compression, hot pressing
What is uniaxial compression?
Compaction in a single direction/axis
What is isostatic (hydrostatic) compression?
Pressure applied by fluid, powder is contained in a rubber envelope
What is hot pressing?
Pressure and heat
What is sintering?
-The firing of a powder pressed piece
- Powder particles join together and pore/void size decreases
What is tape casting?
- Slip is formed into thin sheets by a blade and carried by a film
- Dried by warm air, resulting in a flexible tape of green ceramic
- Used for integrated circuits and capacitors
What is cementation?
- Hardening of cement/water paste
- Forms rigid structures having varied/complex shapes
What are the two primary constituents of clay?
Alumina and silica
What is Portland cement?
- Mix clay and lime-bearing minerals
- Calcine (heat to 1400°C)
- Grind into fine powder
