ANODIZING
•
Eric Olander, Electrochemical Products, Inc.
Anodizing
Anodizing
History of Aluminum.

1821 P. Berthier (France) discovers a hard
reddish clay-like material containing 52%
aluminum oxide near the village of Les Baux
(Bauxite)

SO ALUMINUM IS A VERY YOUNG METAL
NOW DAYS!!!
History of Aluminum.

Aluminum is the third most abundant element
in the Earth’s crust.

In nature it only exists in very stable
combinations with other materials (particularly
as silicates and oxides).

It was not until 1808 that its existence was first
established by Sir Humphry Davy (Britain)
Aluminum production.
Characteristics of Aluminum.
 Second
most used metal in the world
(First iron, second Aluminum, third
copper).
 Aluminum has very good properties.
 So it is makes aluminum very
attractive for many possibilities.
Physical properties of
Aluminum.
 Density
of
 Melting Point
 EC* at 20ºC
* Electrical conductivity
2.7 (iron is 2,5 x heavier).
660ºC.
64.94%
What is Anodizing?
 Electrochemical
process that forms a
protective coating of Aluminum oxide
on the Aluminum surface.
The reaction in the
anodizing process.
The anode reaction:
2 Al (metal) + 3 H2O → Al2O3 (oxide coating) + 6H+ + 6e

There is an oxidation process taking place on the “anode” surface
(aluminum material).
The cathode reaction:
6H+ + 6e → 3H2 (gas)


There is a reduction process taking place on the cathode surface.
Hydrogen gas is evolved at the cathode and appears as bubbles during
the anodizing process.
The total reaction.
2 Al (metal) + 3 H2O → Al2O3 (oxide coating) + 3H2 (gas)↑

Aluminum metal is oxidized (anodized), and hydrogen gas is evolved
at the cathode.
Anodizing benefits.

Anodic coatings are highly abrasion-resistant an
durable.

Anodic coatings do not peel, chip etc.

Anodic coatings are translucent, resulting in a
deep, rich metallic appearance.

Anodic coatings are scarcely affected by
sunlight.
Anodizing benefits.

Anodic coatings are excellent finishes for areas
subject to filiform corrosion.

The anodizing process uses chemicals without
VOC’s and aluminum is recyclable.

Anodized aluminum can be colored in a full
spectrum of shades.
The anodic oxide coating.

Consists of two layers.
 The porous thick outer layer growing on an inner
layer which is thin and dense.
• Thin layer is the barrier layer which is very thin
(0.1 and 2.0% of the total film)
• The outer layer is porous due to the attack
from the electrolyte.
The structure of a typical cell.
Attack of the electrolyte.

Parameters.




Type and concentration electrolyte (Sulfuric acid)
Temperature and agitation of the electrolyte.
Time in the anodizing tank.
Current density (A/dm²)
Sulfuric acid electrolyte.

Parameters.



H2SO4 200 g/l ± 10 g/l
Aluminum content < 20 g/l (5-10 g/l)
Chloride content < 100 mg/l
The acid concentration is only critical at high
anodizing temperatures. High acid concentrations
lower the anodizing voltage required (about 0.04 V
per g/lH2SO4)
Temperature.

Parameters.



H2SO4 bath: not above 21ºC
H2SO4 bath + oxalic acid: not above 25ºC
H2SO4 bath + Hardcoat 93: not above 27ºC
Current density.

Parameters.



1.2 – 2.0 A/dm2 (5-10 µm)
1.4 – 2.0 A/dm2 (15 µm)
1.5 – 2.0 A/dm2 (20-25 µm)
Other important parameters to
have a good anodization bath

Cathodes surface (cathode-anode ratio must be
1:1.5 to 1:2.5).

The distance between the cathode and the anode
should not be less than 150 mm.

Jigs submerged in the electrolyte must have a cross
section representing more than 0.2 mm²/amp
Other important parameters to
have a good anodization bath

Contacts must be sufficient to conduct the current
evenly to all parts in the load and over the hole part.

The cooling capacity of the system used must be
capable of absorbing all heat generated during
anodizing.

Good agitation is essential to maintain constant
temperature of the bath.
Other steps prior to anodizing


















Alkaline Degreasing
Rinse
De-anodizing
Alkaline etch
Rinse
Rinse
Desmutting
Rinse
Anodization bath
Anodization bath
Rinse
Rinse
Electrocolor
Rinse
Rinse
D.I. water
Sealing
Sealing
AD-ANO CLEANER 219
AD-ANO ADDITION AL28
AD-ANO ADDITION Al 28
AD-ANO ADEOX 11
AD-ANO HARDCOAT 93
AD-ANO HARDCOAT 93
AD-ANO E-Color 200
AD-ANO FASTSEAL
AD-ANO FASTSEAL
Alkaline Degreasing

AD-ANO CLEANER 219
•
In the degreasing tank oil, grease, and other surface
contamination is removed from the profile surface.
•
Conditions:


Concentration
Time
Temperature
Agitation

pH


: 3 - 5 % (30 - 50 g/l)
: 5 - 15 minutes
: 60 – 70°C
: Air pressure or pumping the bath
solution is necessary
: 9.2 – 9.6 (to avoid degradation of
aluminum pH 9.2 – 9.3)
Rinse

•
Usually there is a rinsing step (or more)
after each process step. Counter flow of
the rinse water from the tank with the
cleanest water to the tank with the most
dirty water is normal.
Agitation of the water is an advantage to get a better rinsing.
De-anodizing / etching

AD-ANO ADDITION AL28
•
Aluminum has a thin natural oxide coating on the surface
which has to be removed before the anodizing could start.
•
Conditions:
Operating conditions decorative finishing
 Concentration caustic soda
: 50 - 70 g/l
 Concentration AD Addition AL 28
: 15 - 20 g/l
 Aluminum content
: 20 -150 g/l
 Temperature
: 60 - 65C.
 Time
: 6 - 15 minutes depending on
required finish
Operating conditions de-anodizing
 Concentration caustic soda
 Concentration AD Addition AL 28
 Temperature
 Time
: 90 - 120 g/l
: 10 - 15 g/l
: ambient
: 8-15 minutes
Desmutting
 AD-ANO ADEOX 11
•
During the etching operation a black smut layer may
be left on the aluminum surface. The smut is coming
from the alloys in the aluminum. It consist of
particles which are insoluble in the alkaline solution.
•
Conditions:

AD-ANO ADEOX 11
H2SO4
: 20 - 30 g/l
: 50 - 100 g/l
Combined with nitric acid
 AD-ANO ADEOX 11
 HNO3
: 25 - 30 g/l
: 40 - 50 g/l

Anodization

AD-ANO HARDCOAT 93
It is recommended to use higher current density because of shorter times and less
dissolving of aluminum. The obtained layers have a higher specific gravity.
The advantages of AD-ANO HARDCOAT 91.




•




Anodizing at temperatures up to 30°C. and saving energy for cooling.
Better conductivity caused by the higher temperature and saving energy for
anodizing.
Slower dissolution of aluminum, longer bath-life.
Lower sulfuric acid concentration, less drag-out and saving chemicals for
neutralizing.
Conditions:
Sulfuric acid concentration
AD-ANO HARDCOAT 93
Aluminum concentration
Temperature
Current density
: 140 - 160 g/l (150 g/l)
: 20 - 30 g/l (30 g/l )
: 5 - 25 g/l
: 25 - 30°C.
: 1.2 - 1.8 A/dm2
Electrocolor

AD-ANO E-COLOR 200
•
Is a two step color anodizing process. Dyeing with
metal salt and uses electric current.
•
Composition:


AD-ANO Stannad L40 stabilizer
Stannous sulphate
25 - 40 g/l
15 - 20 g/l

Sulfuric acid
20 g/l

Replenish with AD-ANO C200 ADII
DI water

De-ionized water is very important
as rinse before sealing. Also the
time of rinsing.
Agitation of the water is an advantage to get a better rinsing.
Sealing

AD-ANO FASTSEAL
•
Sealing is one of the most important steps in the anodizing
process. Sealing process influences wear and corrosion
resistance, chemical resistance and color stability.
•
Condition:


Concentrations AD-ANO Fastseal Start
pH range
Temperature
Dipping time per micron

Replenishing should be done with AD-ANO Fastseal Replenisher ME


: 2 - 3 ml/l
: 5.8 - 6.2
: 88 - 98 °C.
: 2 - 3 minutes
Save Energy
Anodize at high
temperature
HEA
H(high) E(ffinciency) A(nodizing)
This technique makes it possible to
produce an quality and perfect anodizing
layer. The technique reduce the
necessary working energy.
Technology HEA
New technology for anodizing systems.

Benefits:
 Less energy consumption in anodizing
 Less energy consumption for cooling
systems
 Efficient use of the plant installation
Parameters that impacts
quality of the anodizing layer
Concentration and temperature of the Sulfuric acid
Additives
Residence time depends on the current density and
layer thickness
Efficient bath agitation and bath cooling
Concentration Sulfuric Acid
(standard = 150-220 g/l)
The anodizing layer become weaker if the
Sulfuric Acid concentration is to high.
The abrasive resistance will be lower if the
concentration Sulfuric Acid is to high.
 (Soft anodizing layer)
Impact temperature of the
electrolyte
Higher temperatures:
 Anodizing layers with a lower density
 Difficult to close the pores in the anodizing
layer because the layer is to soft.
 Easy to give the anodizing layer a color,
but difficult to reproduce the color fastness
 (especially organic color systems)
Low temperatures :
 Hard Anodizing layers
 Better abrasive resistance
IMPACT of the current density
Low current density:
 A longer residence time is necessary that
caused degradation of the formed anodizing
layer.
 Fast color procedure of the anodizing layer.
IMPACT of the current density
High current density:
 Fast layer structure
 More heat
 Perfect anodizing layer if there’s enough bath
agitation and cooling.
How can we impact the anodizing
layer on a positive way?
 By reducing the Sulfuric Acid content.
 Improve the conductivity by using additives.
 Reduce aggressive impacts of the chemicals by
using corrosion agents.
 Care a good bath agitation and bath cooling
Anodizing conditions during the
test
Sulfuric Acid :
Aluminium :
Additives:
Temperature:
Current density :
Layer thickness:
180 g/l
5 g/l
HEA or Hardcoat 93
as indicated
as indicated
20±1 micron
Table 1-Voltage-trend of current density and
temperature
T
A/dm2
16° C
19° C
22° C
25° C
30° C
1,0 A/dm2
17.7
15.6
14.5
13.2
11.1
1,5 A/dm2
19.6
18.0
16.8
15.5
13.7
2,0 A/dm2
21.1
19.0
18.4
17.4
15.5
3,0 A/dm2
22.1
21.0
20.3
19.3
18.1
4,0 A/dm2
23.0
21.9
21.2
20.0
18.8
6,0 A/dm2
23.9
22.9
22.6
21.6
20.3
Table 2- Anodizing at different current
densities
A/dm2
min./microns
1.0
Time (min.) for
20 microns
64
1.5
44
2.2
2.0
32
1.6
3.0
22
1.1
4.0
16
0.8
6.0
11
0.5
3.2
Table 3-Power consumption (kWh/m2)
Temperature and current density variations
T
A/dm2
1.0
A/dm2
1.5
A/dm2
2.0
A/dm2
3.0
A/dm2
4.0
A/dm2
6.0
A/dm2
16° C
19° C
22° C
25° C
30° C
1.89
1.67
1.55
1.41
1.19
2.16
1.98
1.85
1.70
1.51
2.26
2.03
1.97
1.86
1.66
2.43
2.31
2.23
2.12
1.99
2.45
2.34
2.27
2.14
2.01
2.63
2.52
2.49
2.37
2.23
Summary:
Current density A/dm2
Temperature
Consumption Kwh/m2
1.5
19 ºC
1.98
1.5
25 ºC
1.70
+6
-0.28
Difference
A production of 2000 m2/a day save 2000 x 0.28=
560 Kwh(= 14%) THAT’s 140000 Kwh a YEAR.
Cost savings in $
 Milwaukee
WE Energies 0.19$/Kwh
140,000 x 0.19= $26,600
Use electricity saving you energy costs
FOR EXAMPLE (practical experience)
Anodizing at different temperatures (19 - 30°C)
Temperature
19°C
25°C
30°C
Current density
Amp./m2
150
150
150
Voltage
18 volt
15.5 volt
13.7 volt
Procestime
45 min
45 min
45 min
Bath conditions:
H2SO4 (g/l)
Aluminium (g/l)
Additive (g/l)
180
5 – 15
None
160
5 – 20
20
Hardcoat 93
160
5 – 20
35
HEA
Energy anodizing at higher temperatures

U=IXA
 Consumption a hour =
• voltage x amperage x time.
 Consumption/m² =
 19°C
• 18 (V) x 150 (A) x 45/60 (time) = 2025 watt
 25°C
• 15.5 (V) x 150 (A) x 45/60 (time) = 1744 watt
 30°C
• 13.7 (V) x 150 (A) x 45/60 (time) = 1541 watt
The advantage obtained in watts per m².


At 25°C en 150 Amp:
 2025 - 1744 = 281 watt (14%) less consumption
required for the formation of the anodizing layer.
Bij 30°C en 150 Amp:
 2025 - 1541 = 484 watt (24%) less consumption
required for the formation of the anodizing layer.
• Note: also for bath cooling there will be a
significantly consumption benefit because the
delta Temperature is larger.
Increase production capacity by
producing larger charges.
- You can increase the production with 14%,
because the current density will be equal to
normal anodizing procedures.
Anodizing at higher temperature
(25 - 30°C) and higher current density.
Temperature
19°C
25°C
30°C
Current density
Amp./m2
150
180
180
Voltage
18 volt
16.6 volt
14.8 volt
36 min
36 min
160
5 – 20
20
Hardcoat 93
160
5 – 20
35
HEA
Time
Bath conditions
H2SO4 (g/l)
Aluminium (g/l)
Additive (g/l)
45 min
180
5 – 15
None
Consumption Energy at higher temperature
and higher current density.

Consumption/m² =
 19°C = 2025 watt
 25°C
• 16.6 (V) x 180 (A) x 36/60 (time) = 1793 watt
 30°C
• 14.8 (V) x 180 (A) x 36/60 (time) = 1598 watt
The advantage obtained in watts per m².

At 25°C and 180 Amp:
 2025 - 1793 = 232 watt (11,5%) less consumption
required for the formation of the anodizing layer.
 Bij 30°C en 180 Amp:
 2025 - 1598 = 427 watt (21%) less consumption
required for the formation of the anodizing layer
• Note: also for bath cooling there will be a
significantly consumption benefit because the
delta Temperature is larger.
Conclusion:
How to use this technology:
•If the rectifier capacity is already fully exploited:
Only consumption saving of cooling and production
If the rectifier capacity is not already fully
exploited:
• Consumption saving of cooling and production.
More production capacity is possible.
•
Eric Olander, Electrochemical Products, Inc.