1. Inorganic, non-metallic compounds formed by heat. Examples:
*See notes at bottom
Chapter 11 - Ceramics:
Inorganic, non-metallic compounds formed by heat. Examples:
Disk brake, silicone carbide
Ball Bearing: Silicone Nitride, Si3N4
or Alumina Oxide or Zirconia
Porcelain high voltage insulator
Ceramic Bearings: can be hybrid (rolling element only) or all ceramic (rolling element and races) – advantages include lighter, smoother, less vibration, stiffer, harder, corrosion resistant, electrically resistant, chemically resistant, higher loads and speeds, long life with minimum lubrication, higher temperature, more fuel efficient (since lighter). Ceramic balls can be used to replace steel in ball bearings. Their higher hardness means that they are much less susceptible to wear and can oftetn more than triple lifetime. Also deform less so less wear on race and retainer walls and can roll faster. In very high speed applications, heat from friction can cause problems for metal peratins. Ceramics also chemically resisitant, can be used in wet environments (where steel will rust). Finally electrically insulating! Major disadvantage = cost!!
See handout – holy grail of automotive design is the ceramic block. If perfected it would allow higher operating temperatures and therefore an increase in engine efficiency. In addition, it would lower sliding friction and permit the elimination of radiators, fan belts, cooling system pumps, coolant lines and coolant. The result would be a reduced weight and more compact engine. Fuel savings estimated at 30% or more!!
Work also being done developing ceramic parts for gas turbine engines (metal blades require cooling)
Rocket Nozzle: Silicone Nitride, Si3N4
Ceramic inserts, cutting tools, tungsten carbide
See HO for Common Types
Knife: Zirconium dioxide,
ZrO2
Dental implants

2. III. Types of Ceramics:

3. I. Overview of ceramics:
Characterized by:
Compounds between metallic and non-metallic elements (i.e. Si and O, Si and N, Al and O, etc..)
Frequently oxides, nitrides and carbides (i.e. silicon carbide – SpinWorks)
Can be crystalline or amorphous
Very strong covalent (sharing of electrons) or ionic (transfer of electrons) bonds.
Properties include:
Strong but brittle
Low fracture toughness
Good insulators of electricity BUT good conductor of heat (i.e. comparable to metals have reasonably high thermal conductivity, k) – this is unique to ceramics.
Excellent high temp properties
Low coef of thermal expansion

4. Example: Aluminum Oxide, Al2O3
I. Nature of ceramics:
Example: Aluminum Oxide, Al2O3
Covalent = strong
Electrons tied up
By sharing valeance electrons, each atom has eight electgrons in outer shell – called covalent bonding. Ionic bonding, valence electron form one atom transferred another.

5. II. Properties of Ceramics
Benefits:
High chemical resistance
High melting point and therefore high operating T.
Extremely hard and stiff (i.e. 180 E6 psi)
Good electrical insulator (electrons tied up). Exception = superconductors
Good thermal conductor (high K like metals)
But, low thermal expansion and good thermal stability
Good creep
High modulus
High compressive strength

6. II. Properties of Ceramics
Shortcomings:
Low tensile strength and BRITTLE. Sut = Suc/10. Do not readily slip like metals but fracture.
Catastrophic failure
The bond is ionic and covalent. A material held by either type of bond will tend to fracture before any plastic deformation can occur!
Low fracture toughness (1/10 to 1/100 KIC compared to metals)
Materials tend to be porous and microscopic imperfections act as stress concentration decreasing the toughness further.
Elongation = 0%
Low fatigue strength
Large statistical spread and less predictable than metals (size, shape and location of internal flaws is likely to differ from part to part)
Prone to thermal shock
Hard to machine and form
Cost 8X more than metals
See Table 8.2

9. Optimized selection using charts2 3 1
Search
area
This frame show index-based selection on a real property chart. The selection can be done using a hard copy chart, as illustrated here. The EduPack software gives greater flexibility, allowing the selection line to be moved and additional constraints to be applied. It lists, in the Results window, the materials that meet all the constraints and makes records for them immediately accessible. The list can be ranked by the value of any property used as a constraint or by the value of the index.
Here it is interesting to point out an interesting fact brought out by the method. Many components of aircraft are stiffness-limited – the wing spar is an example – and the objective here is to minimize mass. Materials texts often assert that, for aerospace, material with high specific modulus E/ρ are the best choice when stiffness is important. But aluminum and steel have the same value of specific stiffness, and steel is much cheaper that aluminum – so why are wing spars not made of steel? The answer is that they are loaded in bending, and then the correct criterion of choice is not E/ρ but E1/2/ρ . By that criterion aluminum is much better than steel, as the chart shows.
Results
22 pass
Material
Material
Material
etc...
Ranked
by Index

10. Electrical Resistance:
Ceramics = good electrical insulators, but…

11. Selection: one-property indices
Good thermal conductors!
Good conductors:
metals and ceramics
Good insulators:
polymer foams, cork,
wood, cardboard….
A material index is a metric of excellence for the component. Frequently, the index for is a single property. Here are three examples.
The pressure vessel has a given radius R and wall thickness t, and must carry a pressure p. It is impossible to be sure it has no cracks. The safest pressure vessel is the one that can tolerate the longest crack, c, without failing. The equation shows that this is the one made of the material with the largest fracture toughness Kic. It is the index for the problem.
The heat sink must conduct heat from the chips to the cooling fins. The best material is the one that conducts the most heat for a given temperature difference, ΔT. The equation shows that this is the one with the largest thermal conductivity λ. It is the index for the problem.
The fridge insulation must minimize the heat flux into the fridge. The best material is the one that, for a given thickness t, leads to the smallest heat flux. The equation shows that this is the one with the smallest thermal conductivity λ (or largest thermal resistivity 1/ λ).

14. III. Types of Ceramics: (see HO 6 – 10):
Structural (clay) and whiteware: bricks, pipes, floor and roof tiles, dinner ware, chinca, etc…
Refractory ceramics: kiln lingings, high T capability most are based on silicates (sand)
Glass, amorphous ceramic, most based on silica, SiO2
Annealed glass
Tempered glass
Laminated glass
Annealed glass is not usually treated any further. Annealing is a process of slowly cooling glass to relieve internal stresses after it was formed. The process may be carried out in a temperature-controlled kiln known as a lehr. Glass which has not been annealed is liable to crack or shatter when subjected to a relatively small temperature change or mechanical shock. Annealing glass is critical to its durability. If glass is not annealed, it will retain many of the thermal stresses caused by quenching and significantly decrease the overall strength of the glass. This is generally done for windows, drinking glasses, bottles and containers.
Tempered glass conditions the glass so the surface is placed in compression (done with hot air blast and then rapid cool outer surface). Side and rear windows on cars are tempered glass so they do not shatter causing injury or driving hazard. They break in small pieces (not large sharp pcs). Tempering also increases strength and fracture resisitance.
Laminated glass is used in windshields or other areas where safety is a concern. The glass is composed of a polymer + glass laminated sandwich so the glass doesn’t shatter. The plastic sheet core will adhere the glass pieces to it so the windshield doesn’t shatter.
Laminated glass
Go to HO pg 6!!

15. III. Types of Ceramics: (see HO 6 – 10):
d) Technical or engineering ceramics – 3 categories:
Oxides (alumina, zirconia) semiconductors
Non-oxide (carbides, borides, nitrides) i.e. tungsten carbide cutting tools, silicone nitride ball bearings, silicone carbide furnace inserts.
Cermits or composites – combination of metals and ceramics (powder metallurgy), combines high strength and hardness, thermal characteristic of ceramics with toughness of metals)

16. V. How to Strengthen: (see HO 4,5):
Flame polishing to reduce surface cracks
Close surface cracks use in compression (or compress with metal band)
Atom gun to fill in surface cracks (fires ions into cracks)
Reduce crystal size
Laminate or anneal (glass)
Combine materials to increase toughness (cermits)

17. V. Manufacturing – see HO In situ – cement – mix powder with water
Sintering based methods
WATCH!!!!