Chapter 13 (Applications and Processing of Ceramics)

Question 1

what are die blanks made of

Answer 1

polycrystalline diamond particles

Question 2

why do is polycrystalline diamond used?

Answer 2

helps control fracture and gives a uniform hardness in all directions

Question 3

list the advantages of using ceramics for automobile engines

Answer 3

high operating temperatures
low frictional losses
operate without a cooling system
lower weights than current engines

Question 4

list the disadvantages

Answer 4

ceramics are brittle
difficult to remove internal voids
ceramic parts are difficult to form and machine

Question 5

what are bottles windows and lenses all made from?

Answer 5

silica based glass

Question 6

what are the main properties of glass

Answer 6

optical transparency
easy manufacturing and shaping of objects
hard
vaccum tight
chemically resistant

Question 7

what is particular about glasses in comparison to crystalline materials

Answer 7

• they don’t solidify at particular temperature
• they increase in viscocity as temperature drops
• they don’t show sudden change in volume upon solidifying.

Question 8

what can be said about the change in volume for glasses as temperature decreases

Answer 8

they gradullly shrink

Question 9

what is the basic structure of glass

Answer 9

(SiO4)4- tetrahedron

Question 10

what do impurities do for glass

Answer 10

they interfere with the formation of crystalline structure, which then causes non-crystlline strucutre (amorphous)

Question 11

describe the behaviour of crystalline materials as they are cooled

Answer 11

they crystallize at melting temperature an have and abrupt change in specific volume at melting temp.

Question 12

describe the behaviour of glasses as they are cooled

Answer 12

they don’t crystallize. And the specific volume varies smoothly with temperature

Question 13

what is the glass viscosity

Answer 13

the temp at which glass is fluid enough to be considered a liquid

Question 14

what is the working point

Answer 14

the temp at which the glass is easily deformed

Question 15

what is the softening point

Answer 15

the maximum temp at which a glass piece may be handled without causing significant dimensional alterations

Question 16

what is the annealing point

Answer 16

temp at which atomic diffusion is sufficiently rapid that any residual stresses may be removed within 15 mins

Question 17

what are the units of viscosity?

Answer 17

Pa-s

Question 18

what is the relationship between viscosity and temperature

Answer 18

as temp increases, viscosity decreases

Question 19

which is the most common type of glass

Answer 19

soda-lime

Question 20

what is sheet forming

Answer 20

continuous casting: sheets are formed by floating the molten glass on a pool of molten tin

Question 21

What can happen during annealing

Answer 21

internal stresses build up during the cooling phase, can cause spontaneous fracture

Question 22

how can you avoid spontaneous fracture

Answer 22

slow cooling

Question 23

what is glass tempering

Answer 23

deliberate introduction of residual stresses by rapid surface cooling of hot glass

Question 24

what are the benefits of glass tempering

Answer 24

it suppresses the growth of cracks from surface scratches

Question 25

describe glass tempering

Answer 25

- surface contracts and hardens - inside stays warm and soft - inside cools and shrinks to try and pull surface (which is already rigid) inwards - this puts the surface into compression and the interior into tension

Question 26

what is chemical toughening

Answer 26

- replacing surface Na+ ions in soda-lime glass with larger K+ ions by soaking in hot salt bath - when the glass is cooled, the larger k+ ions induce compressive stress at surface, and tensile stress at the centre

Question 27

how can we "devitrify" glass, and what material does this yield

Answer 27

by heat treatment to produce a crystalline material called glass ceramic

Question 28

what is hydroplastic forming

Answer 28

the process of milling and screening the constituents to obtain a desired particle size

Question 29

why is is impractical to melt and cast ceramics, and what is used to get around this?

Answer 29

because they have very high melting points, instead, we form compacts from powders

Question 30

briefly explain the drying and firing process?

Answer 30

drying: as water is removed the inter particle spacing decrease firing: a heat treatment, this causes vitrification: liquid glass forms from clay and flux.

Question 31

what would drying the cermaic body too fast cause?

Answer 31

it would cause the sample to warp or crack due to non-uniform shrinkage.

Question 32

what is sintering useful for?

Answer 32

both clay and non-clay compositions

Question 33

describe the sintering process?

Answer 33

- grind to produce ceramic or glass particles - inject into the mold - press at elevated temp to reduce pore size

Question 34

list the types of powder pressing and describe them

Answer 34

1. uniaxial compression: compacted in a single directed direction 2. isostatic compression- pressure applied by fluid-powder is in a rubber envelope 3. hot pressing: pressure+heat

Question 35

what is tape casting, and name 2 of its applications

Answer 35

thin sheets of green ceramic are cast as flexible tape. used for ICs and capacitors

Question 36

describe the cementation process

Answer 36

1. involves the hardening of a paste. the paste is formed by mixing cement material with water 2. Hardening process: hydration 3. production of cement powder 4. addition of water sand and stones->> cementation

Question 37

what are refractories?

Answer 37

the materials used for producing/refining metals and glasses and other high temperature applications

Question 38

what properties do refractories need to have? (3)

Answer 38

1. high melting temps (withstand melting/deforming) 2. must be inert 3. thermal insulators

Question 39

what are the 4 types of refractories?

Answer 39

1. silica/acidic 2. basic 3. neutral 4. special

Question 40

how would one make diffusion of ions fast

Answer 40

add Ca impurity

Question 41

If we add impurities to glass, what will happen to the deformation Temp

Answer 41

it will lower

Question 42

if we want to remove a surface crack or scratch, what process can we use

Answer 42

glass tempering

Question 43

what is the typical composition of porcelain

Answer 43

50% clay 25% filler 25% fluxing agent

Question 44

which process forms a neck

Answer 44

sintering process

Question 45

what are three factors what would affect the rate of DRYING?

Answer 45

1. Humidity 2. Temperature 3. Rate of Air flow

Question 46

What are 3 factors that would affect the rate of SHRINKAGE?

Answer 46

1. thickness of the body 2. clay particle size 3. water content