Hasell - Manufacturing materials

Question 1

thermoplastics vs thermosetting

Answer 1

thermoplastics: soft when heated, hard when cooled, poorer high temp mechanical performance, heat deformation, poor elongation,

thermoset: don’t soften when heated, good high temp mechanical performance, good elongation, less heat deformation, HARD TO RECYCLE

Question 2

what is elastic modulus?

Answer 2

material’s resistance to being deformed elastically (non-permanent)

Question 3

converting sulfur ring to chain

Answer 3

> 165 degreesC

Question 4

silicon v silica v silicone

Answer 4

silicon: hard, brittle, semiconductor,

silica: SiO2, highly abundant, aerogels, hard, high mpt

silicone: sythetic polymer, liquid/rubber like, sealant/adhesive/lubricant, unreactive, stable, temp resistant

Question 5

describe properties of PDMS/silicone

Answer 5

silicone, if short chain = lubricant liquid, if long chain=rubber, very flexible backbone due to O-Si-O chain

Question 6

explain the stability of the Si-R bonds

Answer 6

Si-H: very reactive and flammable in air

Si-X (halogen): liable to displacement reactions

Si-C: stable

Si-O: v strong, gives good temp stability in polymers

Question 7

what causes thermosetting?

Answer 7

cross-linking of chains

Question 8

role of Pt in PDMS

Answer 8

catalyst works between the hydride and vinyl functionalised siloxane

Question 9

what is curing

Answer 9

process of a polymer thermosetting, crosslinking, solidifying, hardening, aka vulcanisation

Question 10

what affects curing rate

Answer 10

temp, chemical additives, UV light

Question 11

amorphous v crystal structures

Answer 11

amorphous: scatter x-rays without crystal planes to direct a diffraction pattern, harder to structurally characterise

Question 12

function of Na in soda lime silica?

Answer 12

to lower the mpt

Question 13

how is sol formed from metal alkoxide solution?

Answer 13

hydrolysis polymerisation

Question 14

formation of aerogel

Answer 14

sol gelled into wet gel, then solvent removed withou shrinking the gel using supercritical CO2

Question 15

key differences between TEM and SEM

Answer 15

SEM has detector to detect the e- and can have 3D samples (doesnt need to be thin) to give 3D image

SEM only looks at the surface image, not through it

Question 16

distinguishing between light and electron microscopy

Answer 16

electron will not state the magnification on the image, electron will not have colour (beware staining),

Question 17

for SEM why do insulating samples need to be coated with a conductive material

Answer 17

to avoid static in image, due to charge

Question 18

how are electrons read from TEM?

Answer 18

fluorescence screen or detector

Question 19

describe EDX

Answer 19

energy dispersive x-ray spectroscopy, ejects inner e- using high E e-, movement of e- to fill hole and radiation released analysed (characteristic of each element),

Question 20

advantages of EDX

Answer 20

can provide ratios of elements but only quantitative with ideal samples (polished, flat, stable) - usually qualitative data

can make an elemental map of a sample

Question 21

describe SAED

Answer 21

selected area electron diffraction, usually for TEM, electrons interact with electron cloud of atoms in the material

similar data to XRD, less material needed, identify atomic coordination, crystal/amorphous

Question 22

how do crystal and amorphous present in SAED

Answer 22

crystal: sharp points/rings

amorphous: broad rings