Dr Chris J Wheatley

ovariesracialΠολεοδομικά Έργα

25 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

51 εμφανίσεις



Dr Chris J Wheatley

Palm Springs, August 2011



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


But soft and too active

in aggressive
environments





Why Aluminum ?

Excellent barrier

Low density

Not too reactive

Harder than zinc



Expensive and can it be

trusted to act
sacrificially?

Palm Springs, August 2011

Zinc


Now expensive
-

when

density is considered.


220 million tonnes at

11 million tonnes per

year = 20 years



Aluminum


New alloys



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


)

100 micron sprayed



0.5% NaCl 1000 hrs


)
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

-1.2
-1.1
-1
-0.9
-0.8
-0.7
-0.6
0
50
100
150
200
Potential (V vs SCE)

Elapsed Time (h)

Aluminum

AlZnIn

Palm Springs, August 2011



Palm Springs, August 2011

0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
8.E-05
0
20
40
60
80
100
120
140
160
180
Current (A)

Elapsed Time (h)

AlZnIn

Aluminum

-1.2
-1.1
-1
-0.9
-0.8
-0.7
-0.6
0
20
40
60
80
100
120
140
160
180
Potential (V vs SCE)

Elapsed Time (h)

Aluminum

AlZnIn

Palm Springs, August 2011

0.E+00
1.E-05
2.E-05
3.E-05
4.E-05
5.E-05
6.E-05
7.E-05
8.E-05
0
50
100
150
200
Current (A)

Elapsed Time (h)

AlZnIn

Palm Springs, August 2011

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
-




InCl
2+

+ 3e
-


2InCl
2+

+ 3Zn


3Zn
2+

+ 2Cl
-

+ 2In








Pitting

InCl
2+

+ Al



Al
3+

+ 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.
Increasing cost of zinc will mean that new
aluminum alloys will become more
important for thermal spraying.

2.
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.

3.
Al
-
Zn
-
In will be more effective than zinc in
conditions of high erosion.

4.
Al
-
Zn
-
In can only be used where
temperatures exceed 60
°
C (140
°
F)

Palm Springs, August 2011

Palm Springs, August 2011

1.
London & Scandinavian Metallurgical
Limited made the alloy wires.

2.
Metallisation Limited did the spraying

3.
Sheffield Hallam University did the corrosion
testing.

4.
BAC Corrosion Control Limited provided
information, especially on concrete.

Palm Springs, August 2011