Hasell - Manufacturing materials Flashcards
thermoplastics vs thermosetting
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
what is elastic modulus?
material’s resistance to being deformed elastically (non-permanent)
converting sulfur ring to chain
> 165 degreesC
silicon v silica v silicone
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
describe properties of PDMS/silicone
silicone, if short chain = lubricant liquid, if long chain=rubber, very flexible backbone due to O-Si-O chain
explain the stability of the Si-R bonds
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
what causes thermosetting?
cross-linking of chains
role of Pt in PDMS
catalyst works between the hydride and vinyl functionalised siloxane
what is curing
process of a polymer thermosetting, crosslinking, solidifying, hardening, aka vulcanisation
what affects curing rate
temp, chemical additives, UV light
amorphous v crystal structures
amorphous: scatter x-rays without crystal planes to direct a diffraction pattern, harder to structurally characterise
function of Na in soda lime silica?
to lower the mpt
how is sol formed from metal alkoxide solution?
hydrolysis polymerisation
formation of aerogel
sol gelled into wet gel, then solvent removed withou shrinking the gel using supercritical CO2
key differences between TEM and SEM
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
distinguishing between light and electron microscopy
electron will not state the magnification on the image, electron will not have colour (beware staining),
for SEM why do insulating samples need to be coated with a conductive material
to avoid static in image, due to charge
how are electrons read from TEM?
fluorescence screen or detector
describe EDX
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),
advantages of EDX
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
describe SAED
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
how do crystal and amorphous present in SAED
crystal: sharp points/rings
amorphous: broad rings
