[0001] This invention relates to anodes for use in electrodeposition and more particularly
to composite anode materials for use in the electrodeposition of nickel-iron alloys.
[0002] Electrodeposition of nickel-iron alloys is carried out commercially both for decorative
purposes and for the manufacture of magnetizable components for use in the electronics
industry. The means by which such electrodeposition can be performed are well known.
Consumable anode materials which have been used commercially are of two types, firstly
alloy anode materials and secondly individual iron and nickel anode materials in the
form of small pieces, ie rounds, squares, pellets, etc, of nickel and iron contained
in separate baskets, for example those made of titanium, or in the form of separate
nickel and iron slabs. Both types of anode materials previously used suffer from some
disadvantages. The principal disadvantages of the separate iron and nickel anodes
are firstly the necessity for maintaining separate inventories of iron and nickel,
secondly the need in some instances for separate anode controls, thirdly the danger
of placing the wrong material in a basket and fourthly the possible effect of the
imbalance to the electroplating system if one anode loses current. Alloy anodes have
the disadvantage that they must be specially melted and cast and thus are more costly
than the basic metals.
[0003] It has now been found that such disadvantages can in general be avoided by use of
the composite anode material of the present invention.
[0004] According to the invention, a composite anode material for use in the electrodeposition
of nickel-iron alloys is characterized by the fact that it comprises a sheet of iron
or low alloy steel coated on both sides with nickel, the ratio of the exposed area
of nickel to the exposed area of iron being from 3 to 80.
[0005] The anode material is preferably of suitable size for use in conjunction with an
anode basket and therefore, can conveniently be square in shape and have sides measuring
from 1 to 10cm. Such square or other suitably shaped pieces of anode material are
usefully prepared from a large sheet of composite material of, for example, 1m square
which is cut or sheared to provide pieces of the desired shape.
[0006] The anode material is preferably prepared by electrodepositing the nickel coating
onto the iron or steel sheet although other methods of forming the coating may be
employed. For example, a sheet of nickel can be hot rolled onto the iron or steel
sheet or alternatively nickel in the form of a powder can be sintered and compacted
onto the surface of the iron sheet. Whichever method is employed, it is essential
that there is a relatively strong bond between the iron sheet and the nickel coating
to avoid possible delamination during shearing or during use of the anode material.
[0007] The nickel coating of the anode material can usefully contain, and preferably does
contain, an activator for controlling or increasing the dissolution characteristics
of the nickel during use of the anode material. Sulphur is an activator which can
readily be incorporated into the nickel, particularly when the nickel coating is prepared
by electrodeposition onto the iron sheet. A range of up to 5% sulphur can be present
in the nickel, suitably up to 0.2% sulphur. Generally, when the sulphur content of
the nickel is at the lower end of this range the ratio of exposed area of nickel to
exposed area of iron is at the higher end of its range whereas when the sulphur content
is high, the ratio of exposed areas is low.
[0008] Although sulphur is the preferred activator when the nickel coating of the anode
material is produced by electrodeposition, it will be apreciated that other activators
may be employed, especially when the nickel coating is prepared by means other than
electrodeposition. Examples of such other activating materials include silicon, oxygen
and carbon. It is well known that in general the relative activity of nickel under
electrocorroding conditions can be controlled by the amounts and type of activator
employed. Consequently, when a particular activator is present in the nickel coating,
it is evident that the activator content relative to the ratio of exposed area of
nickel to exposed area of iron can be adjusted in a manner similar to that disclosed
above with respect to sulphur as an activator.
[0009] The sheet bearing the nickel coating can be either iron or a low alloy steel. It
will be appreciated that what is desired for the iron portion of the anode material
of the invention is a relatively pure iron material. Steels which contain large amounts
of elements other than iron, for example, stainless steels are not useful. Likewise,
high alloyed carbon steels containing elements such as molybdenum, chromium, tungsten,
etc should not be used because of the possibility that these elements will be carried
into the electroplating bath and cause contamination. Steels suitable for use in manufacturing
the anode material of the present invention include, but are not limited to, the following
grades: 1010, 1020 and low carbon grade steels.
[0010] The weight ratio of nickel to iron (or steel) can be varied to suit a particular
nickel-iron alloy plating bath. Commercial decorative nickel-iron alloy plating baths
currently used normally utilise anode materials containing about 15 to about 50% iron
when considered as a whole. For example, as a practical matter, an anode containing
about 25% iron is suitable for use in most decorative nickel- iron alloy plating baths.
However, there is no specific limitation on the weight ratio of the anode material
that must be observed.
[0011] A prefered method of making the anode material of the invention is to employ a piece
of sheet iron or steel of appropriate dimensions, for example, lm square and about
0.08cm thick as mandrel on which sulphur-containing nickel is electrodeposited during
a typical nickel electrowinning or electrorefining operation. It is convenient to
deposit approximately 0.32cm of nickel containing about 200 to 300 parts per million
(ppm) of sulphur on both sides of the iron mandrel. Following completion of electrodeposition
of the sulphur-bearing nickel, the plated mandrel is removed from the electrolytic
cell washed, dried, and sheared into appropriate sized pieces such as squares or rectangular
pieces. Alternatively, the iron mandrel bearing the electro deposited nickel can be
"blanked" to form round or oval pieces and the scrap sheared to produce irregular
pieces of anode material. It will also be appreciated that the cathode mandrel, eg
the iron sheet in an electrowinning operation, can be selectively masked to provide
lines of weakness where the mandrel can be sheared with less effort than required
with an unmasked mandrel. In general however, such masking is unnecessary and is somewhat
troublesome in that it dictates the size of the end product at a time when the size
required may not be readily determinable.
[0012] The nickel-iron anode material can be typically employed in a commercial nickel-iron
aqueous sulphate electrolyte containing about 30 to 120 g/1 of nickel, about 1 to
about 10 g/1 of iron, about 10 to about 75 g/1 of chloride ion, about 30 g/1 to about
saturation with boric acid, a bath stabilizer to prevent precipitation of iron hydrate
(iron hydroxide) and a stress reducer with the balance being water. The pH of the
electrolyte is maintained at about 2.3 to about 4.2. In this bath, a stabilizer can
be either a reducing agent such as ascorbic acid or an isomer of ascorbic acid to
maintain iron in the ferrous state or it can comprise a complexing agent such as sodium
gluconate or sodium oxalate which will complex ferric ions in solution. A typical
stress reducer used along with a bath stabilizer in commercial baths is sodium saccharin.
This bath can be operated at temperatures of about 50 to about 75°C and adjustments
of bath composition can be performed as necessary. The anode material of the invention
cap be employed in this bath at an anode current density of about 1.0 to about 7.5
A/dm
2. Other types of nickel-iron baths can be employed with other electroplating conditions
usual to those baths. Some examples will now be given.
EXAMPLE Ia
[0013] Anode material in accordance with the invention was prepared by electrodepositing
0.119cm of nickel containing about 200 to 300 ppm sulphur on both sides of a 0.079cm
thick iron sheet. The sheet was then sheared into square pieces having 2.54cm edges
to form anode material of the invention having a ratio of exposed area of nickel to
exposed area of iron of about 19. The material of this example contained about 75%
nickel, 25% iron.
EXAMPLE Ib
[0014] Anode material was made in the same way as in Example Ia except that type 1010 steel
sheet 0.094cm thick was used instead of iron sheet and the nickel was electrodeposited
to a thickness of 0.131cm to produce a ration of surface area of nickel to exposed
area of iron of about 16.3. The material of this example also contained about 75%
nickel, 25% iron.
EXAMPLE Ic
[0015] Anode material was made in the same way as in Example Ia except that the nickel was
essentially free of an activator, containing only 5 to 10 ppm sulphur.
EXAMPLE Id
[0016] Anode material was made in a similar manner to Example Ib except that the nickel
was electrodeposited to a thickness of 0.093cm to produce anode material containing
about 65% nickel, 35% iron. The ratio of exposed nickel to iron surface area of the
anode material of this example was about 15.5.
EXAMPLE Ie
[0017] Anode material is made in the same way as Example Ib except for the fact that the
sheet was sheared into square pieces having edges of 1.27 cm to form anode material
having a ratio of surface area of nickel to exposed area of iron of about 11.0.
EXAMPLE II
[0018] The anode material of Examples Ia and Ib were electro-dissolved separately in a titanium
basket in a plating bath having the following nominal composition at the start of
dissolution:
![](https://data.epo.org/publication-server/image?imagePath=1980/02/DOC/EPNWA1/EP79301254NWA1/imgb0001)
[0019] The bath was operated at a temperature of 60°C and pH was maintained at about 3.2.
The superficial anode current density was 2.7 A/dm2 and the cathode current density
was 2.7
A/dm
2. Over a period of 32 and 44 days the anode materials of Example Ia and Ib respectively
dissolved and after an initial equilibration period established the equilibrium composition
of the electrolyte with respect to ionic nickel/iron ratio and maintain this composition
substantially constant. The cathodic depositsproduced were of commercial quality.
EXAMPLE IIIa
[0020] The anode material of Example Ia was electro-dissolved in a titanium basket in a
proprietary decorative nickel-iron alloy plating bath having the following nominal
composition at the start dissolution as recommended by by the bath manufacturers:
![](https://data.epo.org/publication-server/image?imagePath=1980/02/DOC/EPNWA1/EP79301254NWA1/imgb0002)
plus proprietary additives as recommended the bath manufacturer.
[0021] The bath was operated at a temperature of 60°C and pH was maintained in the range
of'2.8 to 3.5. Brightener additions were made as recommended during plating. The superficial
anode current density was 3.6 A/dm
2 and the cathode current density was 5.4 A/dm . Over a period of 42 days the anode
material of Example Ia dissolved and after an initial equilibration period established
and maintained the equilibrium composition of the electrolyte as in Example II. The
cathodic deposit was bright and level and of decorative quality.
EXAMPLE IIIb
[0022] The anode material of Example Id was electro-dissolved in a titanium basket in a
proprietary decorative nickel-iron alloy plated bath which was different to that of
the previous Example. This bath had the following nominal composition at the start
of dissolution as recommended by the bath manufacturer:
![](https://data.epo.org/publication-server/image?imagePath=1980/02/DOC/EPNWA1/EP79301254NWA1/imgb0003)
[0023] The bath was operated at a temperature of 57°C and the pH was maintained in the range
of 3.5 to 4.0. Brightener additions were made as recommended during plating. Anode
and cathode current densities were the same as in Example IIIa. Over a period of 30
days the anode material of Example Ib dissolved and after an initial equilibration
period established and maintained the equilibrium composition of the electrolyte as
in Example II. The cathodic deposit was bright and level and of decorative quality.
EXAMPLE IIIc
[0024] The anode material of Example Ie was electro-dissolved as in Example IIIb in a third
proprietary decorative nickel-iron alloy plating bath. This bath had the following
nominal composition at the start of the dissolution as recommended by the bath manufacturer:
![](https://data.epo.org/publication-server/image?imagePath=1980/02/DOC/EPNWA1/EP79301254NWA1/imgb0004)
[0025] The bath was operated at a temperature of 57°C and the pH was maintained in the range
of 3.4 to 4.2. Brightener additions were made as recommended during plating. Anode
and cathode current densities were the same as in Example IIIb. Over a period of 31
days the anode material of Example Ie dissolved and after an initial equilibration
period established and maintained the equilibrium composition of the electrolyte as
in Example II. The cathode deposit was bright and level and of decorative quality.
EXAMPLE IV
[0026] The anode material of Example Ic was electro-dissolved in a titanium basket in the
plating bath of Example II and under the same operating conditions as Example II.
Over a period of 39 days the anode material of Example Ic dissolved and after an initial
equilibration period established the equilibrium composition of the electrolyte with
respect to ionic nickel/iron ratio and maintained this composition substantially constant.
The cathodic deposit was of commercial quality.
[0027] The equilibrium composition of this electrolyte was however not maintained constant
using the anode of Example Ic as was the equilibrium composition of the electrolyte
in Example II which used the anodes of Example Ia or Ib. Abrupt changes in iron content
relative to nickel about the equilibrium composition occurred as the anode material
of Example Ic dissolved and settled in the anode basket and as fresh anode material
was added to the basket. This behaviour indicates an excessive rate of iron dissolution
relative to nickel dissolution in the anode material of Example Ic. The fluctuation
of iron content of the electrolyte relative to nickel content in this Example was
not so great as to render the anode material of Example Ic inoperative because the
high ratio of exposed nickel to iron surface area permitted the anode material of
Example Ic to function adequately in this Example despite the fact that the nickel
contained essentially no activator.
[0028] Examples Ia, b, d, e, II and IIIa, b, c, demonstrate a preferred aspect of the anode
material of the invention when the nickel portion of the anode contains sulphur as
an activator. Examples Ic and IV show the action of anode material of the invention
when the nickel is essentially sulphur-free. These Examples taken together demonstrate
the importance of correlating the ratio of exposed nickel to iron surface area to
the amount of activator in the nickel.
1. A composite anode material for use in the electrodeposition of nickel-iron alloy,
characterised in that it comprises a sheet of iron or low alloy steel coated on both
sides with nickel, the ratio of the exposed area of nickel to the exposed area of
iron being from 3 to 80.
2. An anode material according to claim 1 characterised in that the iron sheet is
coated with the nickel by electrodeposition.
3. An anode material according to claim 1 or claim 2 characterised in that the nickel
contains an activator.
4. An anode material according to claim 3 characterised in that the activator is sulphur
in a range of up to 5% of the nickel.
5. An anode material according to claim 4 characterised in that the sulphur is present
in the nickel in an amount up to 0.2%
6. An anode material according to claim 4 or claim 5 characterised in that when the
sulphur is at the lower end of the range, the ratio of the exposed area of nickel
to the exposed area of iron is at the higher end of the range and when the sulphur
is at the higher end of its range, the ratio of the exposed area of nickel to the
exposed area of iron is at the lower end of its range.
7. An anode material according to any preceding claim characterised in that it comprises
a plurality of relatively small pieces cut or sheared from a larger size sheet.