Materials Processing (Ceramics and Metals)

Which type of bonding do ceramics use?

Ionic and covalent

Ceramics must have an overall positive charge

False- they must be neutral

Cations in ceramics should be larger than the anions

False- the anion radii should be larger to maximize coordination numbers

Larger r_c:r_a ratios have higher coordination numbers

True

Meaning of A_mB_nX_p structures

m/n = number of A/B cations

p = number of X anions

Ceramic unit cells form tetrahedrals and octahedrals

False- tetrahedral and octahedral positions are noted in close-packed stacking (as basic units), but they are not unit cells

Silicate ceramics are ionic

False- they are primarily covalent

Silicates are arranged in SiO₄^4- tetrahedrals

True!

What are the carbon isotropes?

Diamond, Graphite (hexagonal plate structure)

Graphite has basal plates connected to each other with covalent bonds

False- the basal plates are covalently bonded, but they are connected to each other by Van der Waals forces

Diamond molecules use sp² hybrid orbitals

False- they use sp³ orbitals with 109.5 degree orientation

Graphite uses sp² hybrid orbitals

True- the covalent bonds form 2D plates

Silica is made of tetrahedral SiO₄^4- basic units

True- silica is made of SiO₂, and the corners of the tetrahedrals are shared to keep the 1:2 Si:O ratio

Silica glasses are crystalline solids

False- silica glasses are noncrystalline solids with high atomic randomness

Network formers form glassy structures and polyhedral oxide structures

True

Network modifiers form glassy structures and polyhedral oxide structures

False- modifiers like Na⁺ and Ca²⁺ sit in the network and modify it

Intermediates form glassy structures and polyhedral oxide structures

False- intermediates like TiO₂ and Al₂O₃ substitute for silicon to stabilize the network

Adding modifiers and intermediates makes manufacturing more difficult

False- they lower the melting point and viscosity, making deformation easier

Layered silicates form a 3D structure with the tetrahedra

False- they form a 2D layered structure by sharing 3 Os in the tetrahedra

Layered silicates have neutral base units

False- (Si₂O₅)^2- has an unshared oxygen atom that is balanced by a cation-rich planar sheet structure

Layered silicates use Van der Waals forces between every sheet

False- each pair of silica tetrahedral-cation sheets are bonded by ionic-covalent bonds (within the sheets), and they are bonded with VDW (between the sheets)

Types of defects in ceramics

Frenkel defect- cation vacancy + cation interstitial pair

Schottky defect- cation vacancy + anion vacancy

Stoichiometry is a state for ionic compounds with a constant ratio of cations to anions

True

Ceramics can have interstitial and substitutional impurities

True

Interstitial impurities in ceramics should be the same size as the anion

False- they should be relatively small compared to the anion

Substitutional impurities in ceramics always substitute for cations

False- they substitute for whichever host ion is most similar (electrically)

Increased porosity increases E and reduces strength

False- it reduces both E and strength

Organic glasses crystallize at high temperatures

False- most inorganic glasses do this

What is glass-ceramic?

Glass processed by heat treatment to produce a fine-grained polycrystalline structure

Glasses only crystallize above the critical cooling rate

False- they only crystallize below the critical cooling rate

Shifting transformation curves in glass crystallization affects how glasses crystallize with time

True

Transformation curves in glass crystallization are shifted by changes in viscosity

False- they are shifted by the use of nucleating agents

Glass-ceramics have high coefficients of thermal expansion

False- they have low coefficients to reduce cracks from cycling stress (and therefore avoid thermal shock)

All glass-ceramics are transparent

False

Transparency is determined by the uniformity of grains/grain boundaries

True- grain boundaries scatter light, so fine uniform grains (<wavelength) are transparent

Larger grains increase transparency

False- this will only work if it is a single crystal

Glass-ceramics are electrical and thermal insulators

True

Steps in manufacturing clay products:

1. Clay and water are mixed for shaping

2. Shaped piece is dried

3. Fired at a high temperature to improve mechanical strength

Structural clay products have very high structural integrity

True- used for bricks, tiles, and sewer pipes

Whiteware clays have very high structural integrity

False- become white after firing, are more decorative (porcelain, china, sanitary ware)

Refractory ceramics are more reactive than other ceramics

False- they don’t degrade (even in high temps) and they are inert in extreme environments

Refractory ceramics provide thermal insulation and support mechanical loads

True

Refractory ceramics are used for products that need to withstand high temperatures

True

Abrasives are used to cut harder materials

False- they can only be able to grind/cut softer materials

Abrasives need to be hard, wear resistant, and tough

True

Abrasive particles remove large chunks of material

False- they remove very small amounts of material

Structure of a grinding wheel depends on spacing of grits

True

Grade of a grinding wheel depends on spacing of grits

False- it depends on the amount of bonding agent holding grains

Removed material from grinding is called “swarf”

True

Loading should occur in grinding

False- loading occurs when cavities fill with chips

Dressing and Truing definitions

Dressing- making edges sharper on a grinding wheel

Truing- making the wheel more circular

Glass-forming examples

Pressing, blowing, drawing, fiber forming

Particulate-forming examples

casting (slip/tape), powder pressing

Ceramics are produced by these 3 methods:

• glass-forming

• particulate-forming

• cementation

Glass is always amorphous

True- glass is amorphous, but they can be heat treated to form semi-crystalline glass-ceramics

The melting point of glasses is determined by when they become liquids

False- they are determined by their value of viscosity

Increased temperature in glasses increases viscosity

False- increased temperatures decrease viscosity

The glass temperature is above the strain point

True- the temperature is slightly higher and the viscosity is slightly lower

The points in glass forming (from low to high viscosity) (high to low temp)

Melting, working, softening, annealing, strain

Glass-forming should be done between the working and softening points

True- this is called the working point

At the strain point, glass will plastically deform and then fracture

False- glass will fracture before plastic deformation

Heating glasses causes residual stresses

False- cooling glasses causes residual stresses because of varying rates of contraction within the glass form

Stresses from cooling can be fixed just above the annealing point

True- at this point, mobility is high enough to relieve internal stresses

What are the steps in the press and blow technique?

1. Put gob into parison mold

2. Press it to make a concave shape

3. Blow in compressed air to fit the mold

The float process makes hollow containers

False- the float process makes sheets

Glass tempering decreases strength

False- it increases strength by intentionally inducing compressive surface stresses

Glass tempering occurs above the softening point

False- it occurs below the softening point

How is glass cooled in glass tempering?

With air or oil

Powder processing compacts powder into a solid

False- it compacts powder, but it needs to be sintered to be a bonded solid

What is embodied energy?

Embodied energy is the amount of energy needed to produce a material

Contour lines on embodied energy lines account for yield loss

True- the axes do not account for yield loss, but the contour lines do

Steel has higher embodied energy than aluminum

False

Increased scrap use reduces embodied energy

True

What is the difference between ironmaking and steelmaking?

Ironmaking reduces iron from its ore to make pig iron, and steelmaking reduces the carbon content to make steel

Blast furnace inputs:

iron ore, coke (C), limestone

Blast furnace outputs:

pig iron, slag

Coke produces more heat than coal because it is less porous

False- it is more porous, so it has more surface area to react with air

Limestone captures impurities like SiO_2, sulfur, and Al₂O₃

True

Blast furnaces use pure oxygen

False- basic oxygen furnaces use pure oxygen, but blast furnaces use air to control the heat

The slag sits on top of the liquid iron in the blast furnace

True- slag is less dense than the iron

Slag’s main purpose is to control the temperature in the blast furnace

False- slag captures oxidized impurities. Added air is what controls the temperature.

Iron is considered pig iron if it contains over 2% carbon

False- it is pig iron if it contains over 4% carbon

Cupula furnaces transform pig iron into steel

False- cupula furnaces transform pig iron into gray cast iron

Gray cast iron contains 2—4% carbon

True

The primary chemical reaction in the basic oxygen furnace oxidizes Fe

False- coke (C) is oxidized, as well as impurities like Si, Mn, and P

Basic oxygen furnace steps:

1. Adding scrap

2. Adding molten pig iron

3. Blowing O₂

4. Tapping molten steel (and adding additives)

5. Pouring off slag

Alloying elements are added to molten steel after the basic oxygen furnace to prevent their oxidation

True

The basic oxygen furnace uses scrap to input additives

False- the scrap is used to control temperature and cool down the reaction

The electric arc furnace uses both scrap iron and scrap steel

True

The electric arc furnace works by using an electric arc between electrodes to melt the charge

True

Using the BOF or EAF is the final step in steel production

False- the steel needs to be refined until the oxygen content reaches its intended level

All steel is cast into ingots

False- steel is often continuously cast into slabs/blooms/billets

In AISI-SAE designations, 10XX has oxygen content of 0.XX%

False- it has carbon content of 0.XX%

Low carbon steel has less than 0.2% carbon and is used in sheet metal for cars, while high carbon steel has over 0.5% carbon and is used for crankshafts

False- medium carbon steel is used for crankshafts, and high carbon steel is used for cutting tools

Increased carbon content increases strength and ductility

False- it increases strength and reduces ductility

Pearlite is made of…

ferrite and cementite

Gray iron has dark saddle-shaped flakes of graphite and is easiest to manufacture

True- the shape of the graphite also has more stress concentration points, so gray iron is brittle

Nodular (ductile) iron has round pieces of graphite and has high stress concentration

False- the round pieces of graphite do not have many sharp corners, so there is less stress concentration than gray iron

White iron contains areas of light-colored cementite

True

Rosette shapes of graphite make iron more brittle

False- this makes malleable iron