Metals & Alloys

Question 1

what are metals like at an ambient temp

Answer 1

hard and lustrous
closely packed crystalline
opaque
conduct heat and electricity

Question 2

what si the except to the metal’s features at an ambient temp

Answer 2

Hg

Question 3

what is an alloy

Answer 3

mix of two or more metals (binary alloy = 2)

Question 4

what is the alloy system

Answer 4

all possible combinations of an alloy

Question 5

what do metals show in a molten state

Answer 5

display mutual solubility

Question 6

what si the common structure of metals

Answer 6

crystalline structure

many small crystals

Question 7

what is metals form when cooling

Answer 7

impurities enable metal atoms to deposit

nucleate crystal growth

Question 8

what are crystals called

Answer 8

grains

Question 9

when do grains grow until

Answer 9

until all melt metal consumed

Question 10

what is the area where crystals abut their neighbours

Answer 10

grain boundary

Question 11

what are the types of nucelation

Answer 11

heterogenous

homogeneous

Question 12

what is heterogenous nucelation

Answer 12

many sites

majority dental applications

Question 13

what is homogenous nucelation

Answer 13

single site
metal is pure need 4 metal atoms to come together
requires specialised equipment

Question 14

what does grain size influence

Answer 14

physical properties

Question 15

what is grain size controlled by

Answer 15

manufacturer
-rapid solidification
- extra nucleation sites
(both small grain size)

Question 16

what is the technique for casting dental gold alloy

Answer 16

lost wax technique

Question 17

how does temp affect grain size

Answer 17

if similar to melt, slow cooling and large grain size

if diff melt, rapid cool and small grain size

Question 18

how does he shape of the mould affect grain size

Answer 18

walls of mould initiate growth and therefore influence direction of crystal growth

Question 19

what can be used to visualise grain boundaries

Answer 19

light reflecting microscope

Question 20

who using light reflecting microscope what has to be done to see grain boundaries

Answer 20

polish metal surface see irregularities - scatter light

apply etch chem

Question 21

when using an acid etching material what does it do

Answer 21

preferential attack of areas under high stress such as grain boundaries

Question 22

are metals easy to shape

Answer 22

readily deformable, malleable and ductile metals/alloys

Question 23

what can metals/alloys be shaped by

Answer 23

hammering 
rolling 
pressing
drawing into a wire thro a die 
wrought/ cold working

Question 24

how’s metal drawn into wire

Answer 24

grains elongated in direction of drawing

laminar structure

Question 25

how is there a limit to working with cold metals

Answer 25

practical implications

work hardening

Question 26

what is casting

Answer 26

molten –> investment mould

Question 27

what is amalgamation

Answer 27

mix with mercury
plastic mass
hardening chemical reaction
crystallisation

Question 28

what is ductility

Answer 28

the max degree of extension in response to an applied tensile force

Question 29

what is malleability

Answer 29

the max degree of compression in response to an applied compressive force

Question 30

what are elemental metals uses

Answer 30

not much practical uses
severe limitations of their props
extended uses when mixd with alloys

Question 31

when alloys cool from molten they may….

Answer 31

remai soluble - solid solution
be complete;ly insole in eachther
be partially sol in each other
for intermettalic compounds in metals have affinity for each other

Question 32

what are the three types of solid solution

Answer 32

ordered solid solution
random solid solution
interstitial solid solution

Question 33

what is ordered solid solution

Answer 33

component metal atoms have sp sites in common lattice
atom radii similar
if radii diff = distortion

Question 34

what is random solid solution

Answer 34

random sites in common crystal lattice

Question 35

what is interstitial solid solution

Answer 35

atoms of one lie in the primary lattice sites of other

atomic radii dept

Question 36

in solid solutions pure metals are…..

Answer 36

harder
stronger
higher elastic limits

Question 37

what is the hardening effect

Answer 37

solution hardening

as atoms of differing radii from mechanical resistance to dislocations

Question 38

what sit he insolubility of metals

Answer 38

rare
consequences - areas of pure metal a and/or b
risks of corrosion

Question 39

what are the different phases of alloys

Answer 39

solid solution of metal b in metal a

solid solution of metal a in b

Question 40

what bond does metals form in affinity

Answer 40

intermettalic compounds

Question 41

what is precise chemical formulation

Answer 41

sp valence requirements satisfied 
few crystal imperfections means less potential forlsip plane movement 
hard 
brittle
low ductility

Question 42

what si the use of cooling curves

Answer 42

melt metals/alloy

record and plot temp versus time

Question 43

what is Tm

Answer 43

melting point

Question 44

what does the plateau indicate in melting point

Answer 44

temp constant during crystallition

Question 45

what are phase diagrams

Answer 45

series of cooling curves for alloys of diff composition
phase diagram results
use to make struct and coring predictions

Question 46

in phase diagrams for each composiiotn…..

Answer 46

determine t1 and t2

plot these ag percentage composition

Question 47

what can be predicted between liquidus and solidus

Answer 47

solid and liquid composoitons

Question 48

what does distance between solidus and liquids show

Answer 48

larger separation = greater coring

Question 49

what happens when alloy components insoluble to each other

Answer 49

sp point where crystallisation occurs at sp temp

Question 50

what is a eutectic alloy

Answer 50

behave like pure metal
narrow MP
application as solders