1. 1
Materials in a low-end hairdryer
Roland
Papp
Trinity
College,
rp496
Experiment
performed
in
the
IB
laboratory
of
the
Department
of
Materials
Science
and
Metallurgy
in
the
University
of
Cambridge.
Abstract
I
investigated
seven
parts
of
a
low-­‐end
hairdryer
in
a
Materials
Science
point
of
view.
The
heating
wire
was
made
of
Kanthal,
which
is
widely
used
for
heating
purposes.
The
back
part
of
the
case
was
made
of
ABS
by
injection
moulding.
The
wire
insulators
were
made
of
PVC,
which
is
an
environmentally
unfriendly,
however
rather
cheap
material.
There
is
also
a
bimetallic
strip,
which
acts
as
a
high
temperature
emergency
switch.
It
is
made
of
copper
and
steel
pieces
cut
out
from
rolled
metal
sheets.
There
are
two
magnets
and
two
carbon
brushes
in
the
electric
motor.
The
former
is
a
ceramic
magnet
made
of
Strontium
hexaferrite,
and
the
latter
is
simply
graphite.
1 Introduction
I
took
apart
a
low-­‐end
Argos
hairdryer
and
investigated
the
properties
of
the
materials
some
of
its
parts
were
made
of.
I
tried
to
work
out
what
materials
were
used,
how
they
were
manufactured
and
why
they
were
good
choices.
Photos
of
the
investigated
parts
are
shown
on
the
exploded
diagram
(Photo
1).
2 Method
I
used
various
techniques
such
as
measurement
of
density
by
achieving
critical
buoyancy,
Vickers
hardness
testing,
measurement
of
resistance
and
dimensions
(by
a
calliper),
chemical
tests
(MEK-­‐reaction,
chlorine
test),
optical
and
scanning
electron
microscopy,
and
infrared
spectroscopy.
Then
I
compared
the
measured
results
to
values
and
graphs
from
references
such
as
the
IB
Data
Book1
,
websites
of
materials
manufacturing
related
companies,
online
databases
and
the
Wikipedia.

2. 2
Photo
1
—
Exploded
diagram

3. 3
3 Experiments
1,
Heating
wire
I
cut
off
a
1
m
long
piece
from
the
heating
wire
(Photo
2),
straightened
it
by
pulling
and
measured
the
diameter,
length,
mass
and
resistance
to
obtain
its
density
and
conductivity:
𝜌 =
𝑚
𝑑! 𝜋
4
∙ 𝑙
= 7141 kg/m!
𝜎 =
𝑙
𝑅 ∙
𝑑! 𝜋
4
= 6.60 ∙ 10!
1/𝛺m
Photo
2
—
Heating
wire
I
found
it
to
be
ferromagnetic.
I
mounted,
grinded
and
polished
a
sample
for
hardness
(0.5
kg)
and
metallographic
examination.
𝐻! = 238.3
The
most
widely
used
materials
for
heating
elements
are
Nichrome
and
Kanthal.
Nichrome
is
not
ferromagnetic
and
its
density
is
8400 kg/m!
,
which
is
out
of
error
range.
Steel
has
double
the
conductivity,
which
is
also
out
of
error
range.
Kanthal,
which
is
ferromagnetic,
matches
the
values
above
very
well.
Official
data
of
Kanthal:2
𝜌 = 7150 kg/m!
𝜎 = 7.2 ∙ 10!
1/𝛺m
𝐻! = 230
After
the
hardness
measurement
I
etched
the
sample
with
Nital
but
it
did
not
react.
Then
I
performed
electrolytic
etching,
which
gave
rise
to
a
nice
microstructure
shown
on
Micrograph
1.

4. 4
Micrograph
1
—
Heating
wire
grains
Even
though
the
etching
did
not
reveal
elongated
grains,
the
wire
had
to
be
produced
by
stretching
a
thicker
wire
and
then
coiling
it
up.

5. 5
2,
Case
(black
part)
I
cut
the
black
part
of
the
case
into
pieces
and
did
different
experiments
on
them:
-­‐ Inspection:
It
was
clearly
injection-­‐moulded
(Photo
3).
-­‐ When
compressed
in
a
vice
it
first
deformed
elastically
but
then
a
fracture
propagated
in
a
brittle
manner.
-­‐ Using
the
golden
syrup
method
I
measured
the
density
to
be
𝜌 = 1070 kg/m!
.
-­‐ Thermoplastic
-­‐ Negative
chlorine
test
-­‐ Positive
MEK
test
⟹
Contains
aromatic
rings
-­‐ Hardness
with
1
kg:
𝐻! = 13.5
Photo
3
—
Case
showing
signs
of
injection
moulding
High
impact
polystyrene
(HIPS)
matches
these
data
very
well
(𝜌 = 1080 kg/m!
,
𝐻! = 13.2)3,4
and
is
widely
used
as
product
cases.
Acrylonitrile
butadiene
styrene
(ABS)
also
matches
these
data
very
well
( 𝜌 = 1060 −
1080 kg/m!
,
𝐻! = 5.6 − 15.3)5,6
and
it
is
also
frequently
used
in
everyday
products.
I
used
infrared
spectroscopy
to
distinguish
between
these
guesses.
Graph
1
shows
that
the
spectrum
is
exactly
similar
to
that
of
ABS7
over
2000
and
between
696
and
757
cm-­‐1
with
some

6. 6
differences
in
the
fingerprint
region
which
can
be
due
to
the
presence
of
additives
and
colorants.
Polystyrene
has
a
very
different
spectrum;8
therefore
I
conclude
that
the
case
is
most
probably
die-­‐casted
ABS
with
some
additives,
e.g.
colorants.
ABS
is
a
widely
used,
relatively
cheap
and
high
impact
resistance
polymer
capable
of
injection
moulding
with
heat
resistance
up
to
80℃.
These
make
it
a
very
sensible
choice
for
the
case.
Graph
1
—
IR-­‐spectrum
of
the
case
I
also
performed
a
density
measurement
on
the
front
(grey)
part
of
the
case.
𝜌!"#$% = 1122
kg
m!
This
means
that
it
is
a
clearly
different
material,
possibly
with
higher
heat
resistance.
The
experiment
could
be
improved
by
analysing
this
part
as
well.

7. 7
Photo
4
—
Wire
insulators
3,
Wire
insulators
I
cut
off
the
plastic
insulator
(Photo
4)
from
the
wires
running
in
the
hairdryer.
It
is
ductile
and
deformable
without
damage.
It
is
a
thermoplastic
with
positive
chlorine
but
negative
MEK
test.
According
to
these
measurements
PVC
is
the
only
reasonable
material
choice.
To
prove
it
I
also
performed
IR
spectroscopy
(Graph
2),
which
shows
very
similar
peaks
with
the
reference
spectrum9
.
70%
of
the
peaks
can
be
found
with
an
accuracy
of
±10
cm-­‐1
.
The
differences
all
come
in
the
fingerprint
region,
which
are
due
to
bending
vibrations
in
the
molecules.
These
differences
possibly
come
from
additives,
colorants
and
variations
of
manufacturing
methods.
PVC
is
a
very
cheap
—
though
environmentally
unfriendly
—
ductile
insulator,
optimal
for
use
in
low-­‐end
electrical
devices
such
as
this
hairdryer.
I
can
conclude
that
the
electric
wire
insulators
were
made
of
coloured
PVC,
which
is
the
polymerised
form
of
VCM.

8. 8
Graph
2
—
IR
spectrum
of
the
wire
insulator
sample
4
–
5,
Bimetallic
strip
There
is
a
bimetallic
strip
in
the
heated
area
of
the
hairdryer,
which
acts
as
a
high
temperature
emergency
switch.
It
consists
of
two
flat
metal
pieces
with
different
thermal
expansion
coefficients.
When
the
temperature
rises,
the
bottom
one
expands
more
than
the
top,
breaking
the
circuit
as
shown
on
Photo
5.
The
bottom
picture
was
taken
after
heating
it
up
on
a
cooking
plate,
which
proves
that
the
top
sheet
(b)
has
the
lower
thermal
expansion
coefficient.
According
to
Wikipedia10
the
two
metals
are
usually
copper
and
steel
or
brass
and
steel.

9. 9
Photo
5
—
Bimetallic
strip
Top
and
middle
photos
were
taken
at
room
temperature,
bottom
one
at
high
temperature.

10. 10
a) Red-­‐pinkish
piece
on
the
bottom:
14 mm × 5.0 mm × 0.15 mm;
0.10 g
b) Greyish
piece
on
the
top:
9 mm × 5.6 mm × 0.10 mm;
0.03 g
Photo
6
—
The
two
metal
pieces
a)
on
the
left
and
b)
on
the
right
on
both
photos
Both
pieces
(Photo
6)
have
very
low
resistances
(0.0 𝛺 < 𝑅 < 0.05 𝛺),
which
give
conductivity
values
of
𝜎! > 2×10!
1/Ωm
and
𝜎! > 3×10!
1/Ωm.
The
densities
are
𝜌! ≈ 9.5 g/cm!
𝜌! ≈ 6 g/cm!
I
prepared
samples
for
metallographic
examination.
a)
As
sample
a)
had
the
same
copper-­‐like
colour
after
grinding,
I
supposed
it
to
be
copper
and
etched
with
ferric
chloride.
The
microstructure
is
shown
on
Micrograph
2.
It
looks
very
similar
to
Micrograph
39
in
the
DoITPoMS
library11
,
which
shows
a
nearly
pure
copper
alloy:
Description:
Cu
98,
Be
2
(wt%),
Solution
treated,
quenched
and
aged
-­‐
annealing
twins.
Neither
copper,
nor
sample
a)
are
ferromagnetic.
Copper
has
a
density
of
9 g/cm!
,
which
is
within
error
range
of
the
measured
value
and
its
conductivity
is
much
higher
than
the
measured
minimum.
Therefore
I
am
convinced
that
sample
a)
is
a
nearly
pure
copper
alloy
with
some
additives.
The
process
possibly
included
solution
treating,
quenching
and
aging,
which
gave
rise
to
annealing
twins
in
the
microstructure.

11. 11
Micrograph
2
—
Grains
of
sample
a)
from
the
bimetallic
strip
b)
Sample
b)
is
ferromagnetic
and
its
density
(~6 g/cm!
)
is
within
error
range
of
the
density
of
iron
and
steels
(~8 g/cm!
)
because
it
was
too
small
to
measure
the
weight
precisely
and
it
also
had
holes
on
itself,
which
imply
a
slightly
higher
density
than
the
measured
value.
The
grains
of
the
etched
sample
are
shown
on
Micrograph
3.
Conclusion
The
thermal
expansion
coefficients
of
copper
and
steel
are
𝛼!" = 17×10!!
K!!
𝛼!"##$ = 12×10!!
K!!
Sample
a)
has
the
higher
𝛼
and
the
difference
𝛥 𝛼 = 5×10!
K!!
is
sufficient
to
open
the
switch
at
a
too
high
temperature.

12. 12
Both
of
the
metals
used
are
very
cheap
and
easy
to
work
with.
As
both
are
flat
pieces,
I
assume
they
were
processed
by
continuous
casting
and
made
thin
by
rolling.
The
pieces
were
cut
out
from
metal
sheets
and
the
waste
was
recycled
back
into
the
mould.
Micrograph
3
—
Grains
of
sample
b)
from
the
bimetallic
strip

13. 13
6,
Magnet
in
DC-­‐motor
The
dark
grey
coloured
magnets
used
in
the
electric
motor
are
extremely
hard
(𝐻! = 701),
though
brittle.
They
are
electrically
non-­‐conductive
(𝜎 ≈ 10!!
1/Ωm)
and
have
a
density
of
𝜌 ≈ 5.1 g/cm!
,
measured
by
recording
its
weight
and
dimensions.
These
features
suggested
a
ceramic
material,
so
I
used
the
SEM
for
analysing
the
composition.
The
image
and
spectrum
are
shown
on
Micrograph
4.
The
atomic%
ratio
of
Oxygen
to
Iron
and
Oxygen
to
Strontium
are
𝑛 𝑂
𝑛 𝐹𝑒
= 1.60
𝑛 𝑂
𝑛 𝑆𝑟
= 19.8
This
suggests
large
Fe2O3
content
with
some
added
Sr-­‐compound.
Strontium
hexaferrite
(SrO-­‐
6(Fe2O3))
has
very
close
values
to
these
ratios,
1.58
and
19
respectively.
According
to
ferrite-­‐
info.com,12
the
density
and
hardness
of
Strontium
hexaferrite
is
4.9 − 5.1 g/cm!
and
𝐻! =
400 − 700.
The
measured
value
is
within
this
range.
Ferrite
magnets
are
ferrimagnetic.
It
has
very
high
intrinsic
coercivity
making
very
good
at
resisting
demagnetisation
from
an
external
field
or
at
high
temperature.
Ferrite
magnets
are
therefore
extremely
popular
in
electric
motor
and
generator
manufacturing.
The
version
with
the
strongest
magnetic
properties
is
Strontium
hexaferrite.
It
is
also
cheap
because
the
raw
materials
used
are
strontium
carbonate
and
iron
oxide
both
of
which
are
readily
available.
To
conclude,
Strontium
hexaferrite
is
the
far
most
likely
material
used
for
the
magnets
in
the
DC-­‐motor.
Manufacturing13
:
Ferrite
Magnets
(Ceramic
Magnets)
are
produced
by
calcining
(at
1000 − 1350℃)
a
mixture
of
iron
oxide
(Fe2O3)
and
strontium
carbonate
(SrCO3)
to
form
a
metallic
oxide.
This
metallic
oxide
is
then
milled
to
a
small
particle
size.
The
process
involves
the
following
reaction:
𝑆𝑟𝐶𝑂! + 𝐹𝑒! 𝑂! → 𝑆𝑟𝑂𝐹𝑒! 𝑂! + 𝐶𝑂!
𝑆𝑟𝑂𝐹𝑒! 𝑂! + 5𝐹𝑒! 𝑂! → 𝑆𝑟𝑂. 6(𝐹𝑒! 𝑂!)
Then
the
fine
powder
is
sintered,
which
results
in
a
slightly
porous
structure
that
can
be
observed
in
the
low-­‐mag
optical
micrograph
of
our
sample
(Micrograph
5).

14. 14
Micrograph
4
—
SEM
image
of
the
ceramic
magnet

15. 15
Micrograph
5
—
Optical
micrograph
of
the
magnet
showing
porosity

16. 16
Photo
7
—
Top
of
the
motor
with
two
carbon
brushes
7,
Carbon
brush
The
DC-­‐motor
also
uses
tiny
carbon
brushes
(Photo
7).
These
transfer
current
onto
a
rotating
shaft.
They
leave
mark
on
paper,
and
are
particularly
soft
(𝐻! = 33).
I
measured
the
electrical
conductivity
to
be
𝜎 = 1×10!
1/Ωm
by
recording
its
dimensions
and
the
resistance
between
opposite
faces.
Graphite
has
a
conductivity
of
𝜎!"#$!!"# = 3.3×10!
− 3×10!
depending
on
the
angle
with
respect
to
the
basal
plane.
The
only
other
material
I
found
with
matching
conductivity
was
amorphous
carbon,
which
is
clearly
not
convenient
for
use.
The
hardness
of
graphite
is
𝐻! = 7 − 11,
which
is
three
times
lower
than
the
measured
value,
therefore
I
suppose
it
was
possibly
hardened
by
additives.
The
Micrograph
6
also
reveals
a
graphite-­‐like
structure
with
shiny,
reflecting
areas.
Graphite
is
a
cheap
and
environmentally
friendly
material,
ideal
for
use
as
a
carbon
brush.
It
is
made
from
petroleum
coke
after
it
is
mixed
with
coal
tar
pitch.
It
is
then

17. 17
extruded
and
shaped,
baked
to
carbonize
the
binder,
and
finally
graphitized
by
heating
it
to
temperatures
approaching
3000°C,
where
the
atoms
arrange
into
graphite.14
Micrograph
6
—
Low-­‐mag
micrograph
of
the
carbon
brush
4 Conclusion
In
every
case
I
could
find
out
what
kind
of
materials
the
parts
were
made
of,
which
were
cheap
used
in
simple
ways.
Sadly
the
manufacturer
did
not
pay
much
attention
on
making
it
environmentally
friendly.

18. 18
References
1
IB
Data
Book
by
the
DMSM,
Univeristy
of
Cambridge
2
Website
of
Kanthal
Corporation:
http://kanthal.com/en/products/material-­‐
datasheets/wire/resistance-­‐heating-­‐wire-­‐and-­‐resistance-­‐wire/kanthal-­‐af/
3
AZO
Materials
website:
http://www.azom.com/article.aspx?ArticleID=424
4
Robert
F.
Landel,
Lawrence
E.
Nielsen:
Mechanical
Properties
of
Polymers
and
Composites,
Second
Edition,
page
366
5http://engr.bd.psu.edu/rxm61/METBD470/Lectures/PolymerProperties%20from%20CE
S.pdf
6
http://www.matbase.com/material-­‐categories/natural-­‐and-­‐synthetic-­‐
polymers/commodity-­‐polymers/material-­‐properties-­‐of-­‐acrylonitrile-­‐butadiene-­‐styrene-­‐
general-­‐purpose-­‐gp-­‐abs.html#properties
7
DoITPoMS
Reference
IR
Spectra:
http://www.doitpoms.ac.uk/tlplib/artefact/flash/infrared.swf
8
http://www.chemanalytical.com/ft-­‐ir-­‐spectra
9
DoITPoMS
Reference
IR
Spectra:
http://www.doitpoms.ac.uk/tlplib/artefact/flash/infrared.swf
10
Wikipedia
page
for
bimetallic
strip:
http://en.wikipedia.org/wiki/Bimetallic_strip
11
DoITPoMS
Micrograph
library:
www.doitpoms.ac.uk
12
http://www.ferrite-­‐info.com/characteristics.aspx
13
http://www.ferrite-­‐info.com/ferrite_magnets_made.aspx
14
Wikipedia
page
of
graphite:
http://en.wikipedia.org/wiki/Graphite