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Materials Science > Chapter 13 (Applications and Processing of Ceramics) > Flashcards

Chapter 13 (Applications and Processing of Ceramics) Flashcards

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1
Q

what are die blanks made of

A

polycrystalline diamond particles

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2
Q

why do is polycrystalline diamond used?

A

helps control fracture and gives a uniform hardness in all directions

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3
Q

list the advantages of using ceramics for automobile engines

A

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

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4
Q

list the disadvantages

A

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

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5
Q

what are bottles windows and lenses all made from?

A

silica based glass

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6
Q

what are the main properties of glass

A 
optical transparency
easy manufacturing and shaping of objects
hard
vaccum tight
chemically resistant
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7
Q

what is particular about glasses in comparison to crystalline materials

A
  • they don’t solidify at particular temperature
  • they increase in viscocity as temperature drops
  • they don’t show sudden change in volume upon solidifying.
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8
Q

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

A

they gradullly shrink

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9
Q

what is the basic structure of glass

A

(SiO4)4- tetrahedron

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10
Q

what do impurities do for glass

A

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

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11
Q

describe the behaviour of crystalline materials as they are cooled

A

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

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12
Q

describe the behaviour of glasses as they are cooled

A

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

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13
Q

what is the glass viscosity

A

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

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14
Q

what is the working point

A

the temp at which the glass is easily deformed

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15
Q

what is the softening point

A

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

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16
Q

what is the annealing point

A

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

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17
Q

what are the units of viscosity?

A

Pa-s

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18
Q

what is the relationship between viscosity and temperature

A

as temp increases, viscosity decreases

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19
Q

which is the most common type of glass

A

soda-lime

20
Q

what is sheet forming

A

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

21
Q

What can happen during annealing

A

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

22
Q

how can you avoid spontaneous fracture

A

slow cooling

23
Q

what is glass tempering

A

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

24
Q

what are the benefits of glass tempering

A

it suppresses the growth of cracks from surface scratches

25
Q

describe glass tempering

A
  • 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
26
Q

what is chemical toughening

A
  • 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
27
Q

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

A

by heat treatment to produce a crystalline material called glass ceramic

28
Q

what is hydroplastic forming

A

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

29
Q

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

A

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

30
Q

briefly explain the drying and firing process?

A

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

31
Q

what would drying the cermaic body too fast cause?

A

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

32
Q

what is sintering useful for?

A

both clay and non-clay compositions

33
Q

describe the sintering process?

A
  • grind to produce ceramic or glass particles
  • inject into the mold
  • press at elevated temp to reduce pore size
34
Q

list the types of powder pressing and describe them

A
  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
35
Q

what is tape casting, and name 2 of its applications

A

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

36
Q

describe the cementation process

A
  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
37
Q

what are refractories?

A

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

38
Q

what properties do refractories need to have? (3)

A
  1. high melting temps (withstand melting/deforming)
  2. must be inert
  3. thermal insulators
39
Q

what are the 4 types of refractories?

A
  1. silica/acidic
  2. basic
  3. neutral
  4. special
40
Q

how would one make diffusion of ions fast

A

add Ca impurity

41
Q

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

A

it will lower

42
Q

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

A

glass tempering

43
Q

what is the typical composition of porcelain

A

50% clay
25% filler
25% fluxing agent

44
Q

which process forms a neck

A

sintering process

45
Q

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

A
  1. Humidity
  2. Temperature
  3. Rate of Air flow
46
Q

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

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

Materials Science (13 decks)

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