ALLOY FOR USE IN GALVANIC PROTECTION

ALLIAGE POUR UTILISATION EN PROTECTION GALVANIQUE

English Abstract

The invention relates to an aluminium alloy and anode made therefrom
containing
silicon, iron, copper, manganese, magnesium, chromium, zinc and titanium. The
anode is
used as a sacrificial anode in water vessels with non-metallic hulls.

Claims

CLAIMS
1. An alloy which comprises from 0.30 to 0.6 per cent silicon plus or minus 5
per
cent, 0.1 to 0.30 per cent iron plus or minus 5 per cent, 0.10 copper plus or
minus 5 per
cent, 0.10 per cent manganese plus or minus 5 per cent, 0.35 to 0,6 per cent
magnesium
plus or minus 5 per cent, 0.05 per cent chromium plus or minus 5 per cent,
0.15 per cent
zinc plus or minus 5 per cent, 0.10 per cent titanium plus or minus 5 per
cent, 0.05
maximum individual trace metals plus or minus 5 per cent, 0.15 per cent total
trace
metals plus or minus 5 per cent and the balance aluminium.
2. An anode formed of an alloy according to claim 1.
3. An anode as according to claim 2, wherein the electrochemical potential of
the
anode is more negative than that of the cathode.
4. An anode as according to claim 3, wherein the electrochemical potential of
the
anode is in the range of -500 to -1200 mV.
5. An anode as according to claim 4, wherein the electrochemical potential of
the
anode is in the range of -500 to -1100 mV.
6. An anode as according to any of the claims 2 to 5, wherein the capacity of
the
anode to protect the physical integrity of the cathode is in the range of 1000
to 2000
Ah/kg.
7. An alloy as according to claim 6, wherein the capacity of the anode to
protect the
physical integrity of the cathode is in the range of 1400 to 1700 Ah/kg.
9. An anode as according to any of the claims 2 to 7, for use in the galvanic
protection of water vessels with non-metallic hulls.
9. An anode as according to claim 8, wherein the vessel is designed for use in
seawater.
6

10. An anode as according to any of the claims 2 to 9, wherein the surface
area ratio
of the anode to the cathode in the electrochemical cell is in the range of 1:1
to 1:20.
11. An anode as according to claim 10, wherein the surface area ratio of the
anode to
the cathode is in the range of 1:2 to 1:20.
12. An anode as according to any of the claims 2 to 11, characterised in that
an excess
negative electrochemical potential is applied across the electrochemical cell.
7

Description

CA 02567681 2006-11-10
TITLE
"ALLOY FOR USE IN GALVANIC PROTECTION"
FIELD OF THE YNVENTION
The present invention relates to an alloy used in the galvanic protection of
non metallic
water vessels.
BACKGROUND TO THE INVEN'TION
In the marine industry the prevention of corrosion of components, such as
metal
fasteners, shaft and propeller components, constructed from stainless steel
and bronze
alloys is a primazy concern. In aerated marine environments these materials
are
susceptible to crevice and pitting corrosion. Sacrificial anodes are commonly
employed to
provide cathodic protection to these components. Application of these
sacrificial anodes
on wooden and fibreglass vessels can result in an over protection, which may
result in a
reduced life of coatings and an enhanced level of marine growth and wood rot.
The present invention seeks, therefore, among other things, to provide an
alloy which
overcomes some of the above mentioned disadvantages.
SiJMMARY OF THE INVENTION
An alloy which comprises from 0.30 to 0.6 per cent silicon plus or minus 5 per
cent, 0. l
to 0.30 per cent iron plus or minus 5 per cent, 0.10 copper plus or minus 5
per cent, 0,10
per cent manganese plus or minus 5 per cent, 0.35 to 0.6 per cent magnesium
plus or
minus 5 per cent, 0.05 per cent chromium plus or minus 5 per cent, 0.15 per
cent zinc
plus or minus 5 per cent, 0.10 per cent titanium plus or minus 5 per cent,
0.05 maximum
2

CA 02567681 2006-11-10
individual trace metals plus or minus 5 per cent, 0. 15 per cent total trace
metals plus or
minus 5 per cent and the balance aluminium.
BRIEF DESCRIPTION OF THE DRAWING
In the drawing there is shown Figure 1 which is a schematic side elevation of
an
anode formed of the alloy of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In, a preferred embodiment of the present invention the metallic components of
a water
vessel with a non-metallic hull are protected by connecting the alloy of the
present
invention and the metallic components of the water vessel to form an
electrochemical
cell. This electrochemical cell is created through the electrical connection
of an anode
formed of the alloy the present invention to a cathode which are the metallic
components
of a vessel. The cathode and the anode are both located in a bridging medium.
The
connection of the anode and the cathode in this way allows for the passage of
electrons
from the anode to the cathode. These electrons are generated through oxidation
of species
at the anode and reduction of species at the cathode.
In a galvanic protection system the physical integrity of the anode is
sacrificed in orderto
maintain the physical integrity of the cathode. The physical integrity of the
anode is
sacrificed through the dissolution of the anode into the bridging medium. The
suitability
of the anode for galvanic protection is determined by the electrochemical
potential ofthe
anode compared to the cathode and the capacity of the anode to protect the
oathode.
3

CA 02567681 2006-11-10
The alloy forming the anode has a chemical composition comprising 0.30 to 0.6
per cent
silicon plus or minus 5 per cent, 0.1 to 0.30 per cent iron plus or minus 5
per cent, 0.10
copper plus or minus 5 per cent, 0.10 per cent manganese plus or minus 5 per
cent, 0.35
to 0.6 per cent magnesium plus or minus 5 per cent, 0.05 per cent chromium
plus or
minus 5 per cent, 0.15 per cetnt zinc plus or minus 5 per cent, 0.10 per cent
titanium plus
or minus S per cent, 0.05 maximum in.dividual trace metals plus or minus 5 per
cent, 0.15
per cent total trace metals plus or minus 5 per cent with the balance being
aluminium.
The anode forrned of the alloy of the present invention has an electrochemical
potential
more negative than that of the cathode, preferably with an electrochemical
potential in the
range of -500 to -1200 mV, more preferably with an electrochemical potential
in the
range of -500 to -1100 mV.
The capacity of the anode to protect the cathode may be in the range of 1000
to 2000
At/kg, preferably in the range of 1400 to 1700 Ah/kg.
The surface area of the anode 10 shown in Figure 1 is increased through the
incorporation
of ridges 12 on the surface of the anode. The surface area ratio of the anode
to the
cathode may be in the range of 1:1 to 1:20, preferably in the range of 1;2 to
1:20.
The electrical connection provides a passage for the flow of electrons between
the
cathode and the anode. The electrical connection is preferably a metallic
wire, more
preferably a copper wire.
4

CA 02567681 2006-11-10
The bridging medium provides a passage for the flow of electrons between the
anode and
the cathode. The bridging medium is preferably an aqueous solution, more
preferably
saltwater, particularly sea water.
s By applying an excess negative electcochemical potential applied across the
cell the
accumulation of excess calcium deposits, wood rot and paint disbondment may be
prevented. This excess negative electrochemical potential is applied across
the cell due to
the differences in the electrochemical potential of the anode and the cathode.
In an alternative embodiment of the invention, seawater as a bridging medium
may be
replaced with another suitable aqueous liquid, preferably brackish water or
fresh water.
The anode may be connected to the metallic components of the vessel using
known
techniques such as connecting the anode to the shaft gland/ seal and, or shaft
support
bracket and, or the rudder and, or the trimtabs through a bonding buss bar/
system via
bonding wire,
The anode of the present invention is particularly envisaged for use with
water vessels
with fibreglass or wooden hulls.
Modifications or variations as would be apparent to a slcilled addressee are
deemed to be
within the scope of the present invention.
5

Representative Drawing