Transcript Aluminum * Zinc - Indium

Dr Chris J Wheatley
Palm Springs, August 2011
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Metalizing
Thermal Spraying
Arc Spraying
(HVOF Spraying)
Metal Spraying
Palm Springs, August 2011
Galvanizing
Zinc Spraying (TSZ)
Aluminum Spraying (TSA)
Palm Springs, August 2011
Why Zinc ?
Reactive and reliable
Cheap
Trusted (from
galvanizing)
Easy to work with
Why Aluminum ?
Excellent barrier
Low density
Not too reactive
Harder than zinc
But soft and too active
in aggressive
environments
Expensive and can it be
trusted to act
sacrificially?
Palm Springs, August 2011
Zinc
Aluminum
Now expensive - when
density is considered.
New alloys
220 million tonnes at
11 million tonnes per
year = 20 years
34 million tonnes per
year primary output.
50% recycled. Almost
limitless stock.
Palm Springs, August 2011
Palm Springs, August 2011
Palm Springs, August 2011

Salt fog (ASTM B117)
5% NaCl 1000 hrs
0.5% NaCl 1000 hrs

)
)
100 micron sprayed
5mm scratch
Zero Resistance Ammeter
5% and 0.5% NaCl
 Galvanic current
 Potential
Palm Springs, August 2011
Sprayed Aluminum
Sprayed Al-Zn-In
Palm Springs, August 2011
Sprayed Aluminum
Sprayed Al-Zn-In
Palm Springs, August 2011
Sprayed Aluminum
Sprayed Al-Zn-In
Palm Springs, August 2011
Palm Springs, August 2011
Palm Springs, August 2011
-0.6
Potential (V vs SCE)
-0.7
-0.8
-0.9
Aluminum
-1
AlZnIn
-1.1
-1.2
0
50
100
150
Elapsed Time (h)
Palm Springs, August 2011
200
8.E-05
7.E-05
6.E-05
Current (A)
5.E-05
4.E-05
3.E-05
AlZnIn
2.E-05
Aluminum
1.E-05
0.E+00
0
20
40
60
80
100
120
Elapsed Time (h)
Palm Springs, August 2011
140
160
180
-0.6
Potential (V vs SCE)
-0.7
-0.8
-0.9
Aluminum
-1
AlZnIn
-1.1
-1.2
0
20
40
60
80
100
120
140
Elapsed Time (h)
Palm Springs, August 2011
160
180
8.E-05
7.E-05
Current (A)
6.E-05
5.E-05
4.E-05
3.E-05
AlZnIn
2.E-05
1.E-05
0.E+00
0
50
100
150
Elapsed Time (h)
Palm Springs, August 2011
200
1.In 5% NaCl solution and in 0.5% NaCl the
potential of the AlZnIn anode is about
100mV more negative than that of pure
aluminum.
2. The corresponding galvanic couple between
the coating and the steel substrate is more
aggressive in the protection of the steel and
has more throwing power. |It can therefore
be trusted at very low chloride
concentrations.
Palm Springs, August 2011
(AlZn)In + Cl-
InCl2+ + 3e-
2InCl2+ + 3Zn
3Zn2+ + 2Cl- + 2In
Pitting
InCl2+ + Al
Al3+ + Cl- + In
Palm Springs, August 2011
This paper
3,000 – 30,000 ppm
Previous work on cast anodes:
(1)
> 2000ppm
(2)
> 1000ppm
Palm Springs, August 2011
Erosion / corrosion – zinc is simply too soft
compared to aluminum alloys.
Where ambient temperatures can be higher
than 60°C (140°F) where zinc goes into polarity
reversal and becomes cathodic to steel.
Palm Springs, August 2011
At halide concentrations < 1000ppm it will
only act like pure aluminum (TSA) and will be
suitable as a barrier to corrosion.
In high concentrations of sulfate or bicarbonate
Ions where it is less effective – the same is true for
zinc. A lot more work is required here.
In river waters containing large concentrations of
fertilizers – the same is true for zinc. Neither TSA nor TSZ
should be used in the presence of high concentrations of nitrates.
Palm Springs, August 2011
1.
2.
3.
4.
Increasing cost of zinc will mean that new
aluminum alloys will become more
important for thermal spraying.
Al-Zn-In can be arc-sprayed instead of zinc
in almost every normal environment and will
galvanically protect steel, even in very low
halide concentrations.
Al-Zn-In will be more effective than zinc in
conditions of high erosion.
Al-Zn-In can only be used where
temperatures exceed 60°C (140°F)
Palm Springs, August 2011
Palm Springs, August 2011
1.
2.
3.
4.
London & Scandinavian Metallurgical
Limited made the alloy wires.
Metallisation Limited did the spraying
Sheffield Hallam University did the corrosion
testing.
BAC Corrosion Control Limited provided
information, especially on concrete.
Palm Springs, August 2011